Magmatic Evidence for Carbonate Metasomatism in the Lithospheric Mantle underneath the Ohr ˇe (Eger) Rift Philipp A. Brandl 1,2 *, Felix S. Genske 1,3,4 , Christoph Beier 1 , Karsten M. Haase 1 , Peter Sprung 5 and Stefan H. Krumm 1 1 GeoZentrum Nordbayern, Friedrich-Alexander-Universita ¨ t Erlangen–Nu ¨ rnberg, Schloßgarten 5, 91054 Erlangen, Germany, 2 Research School of Earth Sciences, The Australian National University, 142 Mills Road, Acton, ACT 2601, Australia, 3 CCFS, GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia, 4 Institut fu ¨r Mineralogie, Westfa ¨ lische Wilhelms-Universita ¨t Mu ¨nster, Corrensstr. 24, 48149 Mu ¨nster, Germany and 5 Institut fu ¨ r Geologie und Mineralogie, Universita ¨t zu Ko ¨ln, Zu ¨ lpicher Strasse 49b, 50674 Ko ¨ ln, Germany *Corresponding author. Telephone: þ61 (0)2 6125 4301. Fax: þ61 (0)2 6125 8253. E-mail: [email protected]Received September 12, 2014; Accepted August 18, 2015 ABSTRACT Magmas erupted in intracontinental rifts typically form from melting of variable proportions of as- thenospheric or lithospheric mantle sources and ascend through thick continental lithosphere. This ascent of magma is accompanied by differentiation and assimilation processes. Understanding the composition of rift-related intracontinental volcanism is important, particularly in densely popu- lated active rift zones such as the Ohr ˇe (Eger) Rift in Central Europe. We have sampled and ana- lysed nephelinites from Z ˇ elezna ´ hu ˚ rka (Eisenbu ¨ hl), the youngest (<300 ka) Quaternary volcano related to the Ohr ˇe Rift where frequent earthquake swarms indicate continuing magmatic activity in the crust. This nephelinite volcano is part of a larger eruptive centre (My ´ tina Maar) representing a single locality of recurrent volcanism in the Ohr ˇe Rift. We present a detailed petrographic, min- eralogical and geochemical study (major and trace elements and Sr–Nd–Hf–O isotopes) of Z ˇ elezna ´ hu ˚ rka to further resolve the magmatic history and mantle source of the erupted melt. We find evi- dence for a highly complex evolution of the nephelinitic melts during their ascent to the surface. Most importantly, mixing of melts derived from different sources and of strong chemical contrast controls the composition of the erupted volcanic products. These diverse parental melts originate from a highly metasomatized subcontinental lithospheric mantle (SCLM) source. We use a com- bined approach based on mineral, glass and whole-rock compositions to show that the mantle underneath the western Ohr ˇe Rift is metasomatized dominantly by carbonatitic melts. The nephel- inites of Z ˇ elezna ´ hu ˚ rka formed by interaction between a carbonatitic melt and residual mantle peri- dotite, partial crystallization in the lithospheric mantle and minor assimilation of upper continental crust. Thermobarometric estimates indicate that the stagnation levels of the youngest volcanism in this part of the Ohr ˇe Rift were deeper than the focal depths of recent earthquake swarms, indicating that those are not directly linked to magma ascent. Furthermore, close mineralogical and geochemical similarities between the Z ˇ elezna ´ hu ˚ rka nephelinite and fresh kimberlites may point towards a genetic link between kimberlites, melilitites and nephelinites. Key words: continental rift; nephelinite; carbonated peridotite; mantle metasomatism; assimilation V C The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: [email protected]1743 J OURNAL OF P ETROLOGY Journal of Petrology, 2015, Vol. 56, No. 9, 1743–1774 doi: 10.1093/petrology/egv052 Advance Access Publication Date: 13 October 2015 Original Article at Erlangen Nuernberg University on August 15, 2016 http://petrology.oxfordjournals.org/ Downloaded from
32
Embed
Magmatic Evidence for Carbonate Metasomatism in the ... · Magmatic Evidence for Carbonate Metasomatism in the Lithospheric Mantle underneath the Ohrˇe (Eger) Rift Philipp A. Brandl1,2*,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Magmatic Evidence for Carbonate
Metasomatism in the Lithospheric Mantle
underneath the Ohre (Eger) Rift
Philipp A. Brandl1,2*, Felix S. Genske1,3,4, Christoph Beier1,
Karsten M. Haase1, Peter Sprung5 and Stefan H. Krumm1
Received September 12, 2014; Accepted August 18, 2015
ABSTRACT
Magmas erupted in intracontinental rifts typically form from melting of variable proportions of as-
thenospheric or lithospheric mantle sources and ascend through thick continental lithosphere. Thisascent of magma is accompanied by differentiation and assimilation processes. Understanding the
composition of rift-related intracontinental volcanism is important, particularly in densely popu-
lated active rift zones such as the Ohre (Eger) Rift in Central Europe. We have sampled and ana-
lysed nephelinites from Zelezna hurka (Eisenbuhl), the youngest (<300 ka) Quaternary volcano
related to the Ohre Rift where frequent earthquake swarms indicate continuing magmatic activity
in the crust. This nephelinite volcano is part of a larger eruptive centre (Mytina Maar) representing
a single locality of recurrent volcanism in the Ohre Rift. We present a detailed petrographic, min-eralogical and geochemical study (major and trace elements and Sr–Nd–Hf–O isotopes) of Zelezna
hurka to further resolve the magmatic history and mantle source of the erupted melt. We find evi-
dence for a highly complex evolution of the nephelinitic melts during their ascent to the surface.
Most importantly, mixing of melts derived from different sources and of strong chemical contrast
controls the composition of the erupted volcanic products. These diverse parental melts originate
from a highly metasomatized subcontinental lithospheric mantle (SCLM) source. We use a com-bined approach based on mineral, glass and whole-rock compositions to show that the mantle
underneath the western Ohre Rift is metasomatized dominantly by carbonatitic melts. The nephel-
inites of Zelezna hurka formed by interaction between a carbonatitic melt and residual mantle peri-
dotite, partial crystallization in the lithospheric mantle and minor assimilation of upper continental
crust. Thermobarometric estimates indicate that the stagnation levels of the youngest volcanism in
this part of the Ohre Rift were deeper than the focal depths of recent earthquake swarms, indicating
that those are not directly linked to magma ascent. Furthermore, close mineralogical andgeochemical similarities between the Zelezna hurka nephelinite and fresh kimberlites may point
towards a genetic link between kimberlites, melilitites and nephelinites.
30 km wide, that follows Variscan crustal lineaments be-
tween the Saxothuringian terrane in the NW, the
Moldanubian terrane in the SE and the Tepla-
Barrandian terrane between those two terranes(Malkovsky, 1987; Babuska & Plomerova, 2010).
In the region of the Cheb Basin, the crust is thinned to
25–28 km (e.g. Geissler, 2005; Heuer, 2006). The
main phase of rift-related volcanism is dated to about
30–15 Ma with episodic volcanism extending to 0�26 Ma
(Ulrych et al., 2011, and references therein). Quaternary
volcanic rocks are present at Komornı hurka(Kammerbuhl) and the volcanic system of the Mytina
Maar and Zelezna hurka (Fig. 1a), both located roughly
above the locus of crustal thinning (Babuska &
Plomerova, 2010).
Komornı hurka is a 726 6 59 kyr old volcano (Wagner
et al., 2002) that has erupted sodalite-bearing or nephel-ine–olivine-melilitite as scoria and a lava flow (Ulrych
et al., 2013). In contrast, Zelezna hurka is younger and
consists of three eruptive units: volcaniclastic material
formed by a phreatomagmatic eruptive phase at its
base, overlain by highly olivine-phyric lava in the vent,
and tephra layers at the top (Fig. 1b). Recent studies(e.g. Geissler et al., 2004, 2007; Mrlina et al., 2009) that
combined geophysical studies with geochemistry and
information from scientific drilling found the remnants
of a larger eruption diatreme, the Mytina Maar, just
north of Zelezna hurka, which was dated by the Ar–Ar
method at 288 6 17 ka (Mrlina et al., 2007). Additional
evidence for continuing magmatic activity close to the
volcano are active degassing of CO2, mantle-derived He(high 3He/4He) in numerous mofette fields (e.g. at Soos
or Bublak; Weinlich, 2013) and recurrent earthquake
swarms (e.g. Fischer & Horalek, 2003). These earth-
quake swarms have a focal depth of around 6–11 km
and are either linked to the ascent, accumulation or
stagnation of magma in the crust (e.g. Dahm et al.,
2008) or, alternatively, may be explained by fluids as-cending along pre-existing and reactivated fault planes
(e.g. Bankwitz et al., 2003). Interestingly, the 3He/4He in
the gas exhalations increased significantly from 1993 to
2005, reaching values of 6�3 Ra that are similar to the
average of the SCLM (Brauer et al., 2009). This increase
was interpreted as evidence for the ascent of mantle-derived melts into the lithosphere beneath the western
Ohre Rift, with deep dike intrusions in 2006–2008
(Brauer et al., 2005, 2009). Thus, both seismic data and
the active degassing in the western Ohre Rift suggest
continuing magmatic activity at depth.
METHODS
Samples L1 to L3 were collected from a basal, brownish
phreatomagmatic tephra unit (lower tephra; Fig. 1b)
and samples V1 to V4 along a traverse directly
above sample L1 towards the west of the outcrop (vent;
Fig. 1b). Samples U1, U2 (with a fine-grained variety
U2f), and U3 were collected from the base, the middleand upper layer of the upper tephra unit (Fig. 1b). An
additional sample (EG0661) had previously been col-
lected from the upper tephra. For geochemical analyses
of whole-rocks, xenolith- and crystal-poor samples
were selected. Weathered surfaces were removed prior
to crushing and the rocks were rinsed in de-ionized
water. Splits of the crushed materials were further pro-cessed for glass and mineral separation and representa-
tive whole-rock pieces were cut for thin sections. A split
of sample V1 (massive but highly olivine-phyric lava)
was crushed by high-voltage pulse power fragmenta-
tion in the laboratories of Selfrag AG, Kerzers
(Switzerland), to separate olivine crystals for major andtrace element and O isotope analyses.
Major elementsMajor element analyses of glasses and minerals were
performed on a JEOL JXA-8200 electron microprobe atthe GeoZentrum Nordbayern, Friedrich-Alexander-
Universitat Erlangen–Nurnberg. Glasses were analysed
using an acceleration voltage of 15 kV, a beam current
of 15 nA and a defocused beam of 10 mm diameter.
Further details of the analytical conditions have been
given by Brandl et al. (2012). Major element compos-itions of minerals (olivine, clinopyroxene, spinel,
phlogopite and minerals of crustal xenoliths) were
200 km 40
Ch
M
S
DHM
OPF
KH
ZHMLF
WBSZ
Eger Rift
FL
12°E 14°E 16°E
50°N
51°N
49°N
CZ
ATD
PL
CZ
D
Cenozoicvolcanicrocks
Cenozoicsediments
Lowertephra
Lava (vent) Upper tephraL3
L1L2
V1V2V3V4
U3 U2U2f
U1
(a)
(b)
N
appr. 5 m
Fig. 1. (a) Map of the western Ohre Rift at the structural bound-ary between the Variscan Saxothuringian and Moldanubianterranes in the Czech–German border region. OPF, Oberpfalz;KH, Komornı hurka; ZH, Zelezna hurka; DHM, Doupovske horyMountains; M, Mitterteich Basin; Ch, Cheb Basin; S, SokolovBasin. Major structural features: MLF, Marianske Lazne Fault;WBSZ, West Bohemian Shear Zone; FL, Franconian Line. (b)Schematic cross-section of the outcrop at Zelezna hurka, show-ing its lithological structure and sample locations. Lx samplesrepresent the lower tephra unit; Vx samples are from the vent;Ux samples are from the upper tephra unit.
Table 2: Representative major and trace element analyses of mineral phases and one interstitial glass from Zelezna hurka
Mineral: Olivine Olivine Olivine Cpx Cpx Phl Hauyne Spinel GlassSample: V4-17 V4-17 U1-Ol11 V1-12 I V1-12 VI V1-12 I V1 H5 V4-5 I V1 glassSpot size:* core rim 25 mm
The full data table is given in Supplementary Data Table S1. b.d.l., below detection limit. n.d., not determined.*If not indicated otherwise, size of LA-ICP-MS spot is 50mm.
ClinopyroxeneClinopyroxenes generally occur as microphenocrysts,
as glomerocrysts that show zonation (Fig. 3b) or around
olivine grains (Fig. 3e), or as crystal cumulates inter-
grown with phlogopite (e.g. in sample V1, Figs 2a–c and
3d) or olivine (e.g. sample U3, Fig. 3f). One cumulate ofclinopyroxene (size of single crystals about 2–3 mm)
and phlogopite found in sample V1 is about 7–8 mm in
diameter, but cumulates and megacrysts in volcanic
bombs of the nearby Mytina Maar can reach several
centimetres in size (Geissler, 2005; Geissler et al., 2007).
Spongy reaction textures are especially visible within
and around the rims of the Ti-augite rich clinopyrox-
enes (see spongy ‘fractures’ in Fig. 3d). Diopside occurs
as zones around Ti-augite and shows largely idiomor-
phic overgrowth textures (Fig. 3d).
(a) (b)
(c) (d)
(e) (f)
phl
ol
sp
qtz
Ti-aug
digl
ol
Ti-aug
cpxlaths
spongyreaction
zone
Fig. 3. Electron microprobe backscattered electron (BSE) images of key petrological features of the Zelezna hurka lavas. (a) Olivinecrystals with forsterite-rich cores (Fo�90) and slightly more Fe-rich margins (Fo�86). (b) Zoned glomerophyric clinopyroxene. (c)Upper crustal xenolith composed of quartz (dark grey), potassic feldspar (grey) and accessory muscovite. (d) Contact between asingle (disaggregated) quartz crystal and a cumulate composed of intergrown phlogopite (not shown) and clinopyroxene (Ti-augitewith diopsidic overgrowth). The presence of mingled interstitial glass (dotted area) and the spongy reaction zone in the clinopyrox-ene cumulate should be noted. (e) Rounded phlogopite hosted in olivine. The clinopyroxene laths oriented along the edge of theolivine crystal should be noted. (f) Cumulate of clinopyroxene (Ti-augite with diopsidic overgrowth rim) and olivine.
Cores of clinopyroxenes in cumulates are augitic andhave high Mg# (82–90), low TiO2 (<1�8 wt %) and Al con-
tents (<0�33 a.p.f.u.; Fig. 5a) but high Cr# (up to 18) and
high Na2O (>0�7 wt %; Fig. 5b). However, green-core
clinopyroxenes, as reported from the Eifel (Duda &
Schmincke, 1985) and basanites from Slovakia (Dobosi
& Fodor, 1992) have not been observed. Clinopyroxene
overgrowth rims as well as microphenocrysts in thematrix have a greater wollastonite and ferrosilite com-
ponent (Fig. 5c). Moreover, overgrowth rims and
phenocrysts form trends towards compositions con-
trasting with those of clinopyroxene cores in cumulates
(lower Na2O and Mg#, higher TiO2 and wollastonite
contents). Aluminium substitutes for Si, leading to anegative correlation of Al (a.p.f.u.) and Si contents. The
fine laths of clinopyroxene (of a few hundred
micrometres) show rhythmic zonation on backscatteredelectron images. However, a clear evolution towards a
defined mineral composition is not observed and the
mineral composition ranges from augite with variable
contents of Ti to diopside with up to 5�7 wt % TiO2. In
terms of trace elements, cores show normal convex
rare earth element (REE) patterns with the bulge cen-
tred at the middle REE (MREE; Supplementary Data(SD) Fig. S1a), similar to mantle clinopyroxenes in
xenoliths from the Oberpfalz (Ackerman et al., 2013).
Clinopyroxene grains in the clinopyroxene–phlogopite
cumulate of sample V1 show a simple zonation from
core (augite: Wo43En48Fs9) to rim (diopside:
Wo50En42Fs8) but diopside overgrowth rims and thespongy contact zones between clinopyroxene and
phlogopite show a less weak bulge mainly owing to
Fig. 4. (a) Forsterite vs Ni (ppm) content in olivine (grouped into analyses of cores, ‘intermediate’, rim and groundmass) analysed inthis study compared with (b) literature data [literature data also plotted in (a) as grey symbols]. The ‘intermediate’ group definesspot analyses between the clearly defined core and overgrowth rim to test for any hidden chemical zonation. (c) and (d) show for-sterite content vs CaO (wt %) concentration in olivines from this study and literature data, respectively. The inset in (c) shows ahistogram of olivine compositions analysed in this study. Blue lines indicate the evolution of olivine composition during fractionalcrystallization. We used partition coefficients from Beattie (1994) for Fe (0�51–1�55), Mg (1�96–4�40) and Ca (0�0192–0�0375), andfrom Seifert et al. (1988) for Ni (3�8–6�0). We chose the high end of the range for all partition coefficients except for Fe, for which weused a partition coefficient of 1�32 to match an Mg–Fe exchange coefficient of 0�3, typical for a wide range of basaltic liquids(Roeder & Emslie, 1970). We selected a mafic dyke from the Ohre Rift as the starting liquid composition (olivine melanephelinitefrom the Spojil Dyke; Vaneckova et al., 1993), adopted to fit the composition of early crystallizing olivine. We added 37 ppm Ni(þ9�2%) but halved the concentration of CaO (–50%) to match the starting composition with the composition of the most primitiveolivine crystallized. The contents of relevant elements or oxides in the starting liquid are 10�35 wt % FeOt, 16�78 wt % MgO, 5�04 wt% CaO and 440 ppm Ni. The composition of the first olivine crystallizing in our model is marked by a blue star. The evolutionarystages [1, 2 and 3 in (a) and (b)], as discussed in the text, should be noted. Literature data include OPF (Oberpfalz) peridotites fromAckerman et al. (2013) and various types of olivine recovered from the Mytina Maar and Zelezna hurka (Geissler, 2005). Greenshaded field indicates the range of mantle olivine.
enrichment of the light REE (LREE) relative to MREE and
heavy REE (HREE; SD Fig. S1b). Spongy reaction tex-tures between Ti-augite and diopside (e.g. Fig. 3d) show
a chemical composition intermediate between the two
end-members (SD Fig. S1).
Accessory phasesPhlogopite is the main accessory mineral with an over-
all volume of the order of 1–2%; single crystals reach
sizes of up to 10 mm. Phlogopite crystals intergrownwith clinopyroxene (cumulates) are less rounded than
those that occur as inclusions in olivines (samples V2
and U3; Fig. 3b). These latter phlogopites are relatively
small (less than 300–400mm) and slightly more magnes-
ian (Mg# 87–88) than the large phlogopites in cumulates
(Mg# 83–84). In terms of BaO and TiO2 concentrations,
phlogopites in the Zelezna hurka lavas are relativelyprimitive, similar to mantle phlogopites and intermedi-
ate between those found in lamproites and carbonatites
(SD Fig. S2; Dunworth & Wilson, 1998).
Additional accessory minerals include hauyne and
opaque crystals of the spinel group. These spinels
sensu lato are common and occur predominantly as in-
clusions in olivine or in direct contact with olivine. Theyare generally Fe- and Ti-poor and display variable Cr
and Al concentrations, resulting in variable Cr#, ranging
from 37 to 58. Only very few spinels (often in contact
with clinopyroxenes and lower in Mg#) have Fe- and Ti-
rich compositions and are solid solutions of Ti-magnet-
ite. However, the majority of spinels belong to thegroup of Mg–Al-chromites (solid solutions of spinel
sensu stricto, hercynite, chromite and Mg–Al-chromite).
Hauyne is present as small (<100mm), idomorphic crys-
tals, typically associated with clinopyroxene
phenocrysts.
Crustal xenolithsMicroscopically, we distinguish two xenolith groups: a
felsic variety containing quartz and feldspar and a
brownish, porous variety with an undefined mineral as-
semblage. In addition to quartz and potassic feldspar,
the felsic xenoliths (Fig. 3c) also contain albite and mus-covite. Modal mineral contents cover a broad range
from almost pure quartz to almost pure potassic feld-
spar. These felsic xenoliths are interpreted as frag-
mented parts of the regional host-rocks, which are
dominated by phyllites, quartzites and mica shists
(Geissler et al., 2007). Some of these xenolithic rockfragments seem to have disintegrated almost com-
pletely leading to isolated, subrounded quartz crystals
in the volcanic matrix. In sample V1, the assimilation–
melting reaction between a quartz crystal and a clino-
pyroxene–phlogopite cumulate has been preserved in
the form of an interstitial, mingled glass (Fig. 3d). The
mineral assemblage of the brownish xenoliths couldnot be resolved with certainty but probably includes
amphibole and may represent altered parts of the phyl-
litic host-rocks.
Geochemistry of volcanic rocks and glassesMajor element compositionThe compositions of the Zelezna hurka samples arerelatively uniform (Fig. 6). However, the major element
contents of glasses from the lower and the upper tephra
differ significantly from those of the whole-rock sam-
ples. In particular, the glasses have much lower MgO
contents at a given SiO2 compared with the whole-rock
samples. Furthermore, the FeOt (Fig. 6c) contents of theglasses are slightly lower, whereas the concentrations
of the other elements are higher than those of the
Enstatite
Ferrosillite
Wol
last
onite
Diopside
Hedenbergite
30
40
50
60
100
90 80 70 60
403020100
Augite
65 70 75 80 85 90 95
Mg#
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Al [
a.p
.f.u
.]
CoresZonationRimsMatrixCumulates
65 70 75 80 85 90 95
Mg#
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Na 2
O [
wt.
%]
(c)
(a)
(b)
cumulates(main group)
Fig. 5. (a) Aluminium (a.p.f.u.) and (b) Na2O (wt %) vs Mg# inclinopyroxene. A noteworthy feature is the difference betweencumulates (Ti-augite) and diopsidic phenocrysts and over-growth rims, also obvious in the proportional changes in min-eral components (c).
dle the boundary between basanites and foidites in a
volatile-free total alkalis (Na2OþK2O) versus silica(SiO2) diagram (Fig. 7a, TAS diagram; Le Bas &
Streckeisen, 1991). However, the volcanic glasses
show significantly higher concentrations of alkalis
(>8 wt %) than the whole-rock samples. Thus, glasses
from Zelezna hurka can be classified as strongly
SiO2-undersaturated foidites. Melilite or nepheline have
not been observed in thin section and based on a
SiO2þAl2O3 (�54–55 wt %) versus CaOþNa2OþK2O(23�0–23�5 wt %) discriminant diagram (Le Bas, 1989) we
conclude that the lavas are part of the nephelinite
rock series, even though glass samples plot on the
boundary between the nephelinite and melilitite rock
series (Fig. 7b). We further note that the glasses contain
Fig. 6. Variation of MgO vs (a) TiO2, (b) Al2O3, (c) FeOt, (d) CaO, (e) Na2O and (f) K2O (all in wt %) ZH, Zelezna hurka samples, fromthis study and Ulrych et al. (2013). Data sources: central Ohre Rift, rift shoulder, Oberpfalz and Komornı hurka from Ulrych et al.(2013) and Haase & Renno (2008) and references therein; Mytina Maar from Geissler et al. (2007); Ohre Rift melilitites from Ulrychet al. (2008).
high concentrations of volatile elements such as S andCl (Table 1). The Cl/Nb ratios of about 17–20 are higher
than in mid-ocean ridge basalt (MORB) and ocean is-
land basalt (OIB) but similar to those of other continen-
tal rift regions (e.g. Rowe et al., 2015).
Trace element geochemistryThe whole-rock samples show primitive mantle-normal-
ized (Lyubetskaya & Korenaga, 2007) incompatibleelement patterns that are enriched in highly incompat-
ible trace elements and the LREE relative to HREE [e.g.
(La/Yb)N¼ 28�5–33�5, (Gd/Yb)N¼ 4�0–4�1 and (La/
Sm)N¼ 4�2–5�0] (Fig. 8a)]. The most prominent anomaly
in the multi-element pattern is a negative Pb anomaly
and there are slightly negative K and Ti anomalies. TheHFSE Nb and Ta are slightly enriched (Fig. 8a) whereas
Zr and Hf are slightly depleted. Overall, the whole-rock
samples are well within the range reported for the Ohre
Rift (e.g. Haase & Renno, 2008; Ulrych et al., 2013) but
with relatively high Rb, Ba, Th, U, Nb and Ta and low
MREE to HREE resulting in an overall slightly steeper
slope in a multielement diagram (Fig. 8a) comparedwith most other samples from the Ohre Rift. In contrast,
the trace element compositions of glasses extend the
range of published Ohre Rift data (Fig. 8a). Slight but
significant differences in trace element composition
exist between the glasses and whole-rocks (e.g. more
pronounced negative anomalies of Zr and Hf), resulting
in a strong contrast in some trace element ratios, suchas Nb/Zr (Fig. 8b). Generally, the whole-rock and glass
samples from Zelezna hurka have highly enriched trace
element ratios relative to the primitive mantle of
Lyubetskaya & Korenaga (2007); for example, Nb/Zr is
6–13�, Ta/Hf is 8–18�, La/Yb is 29–36� (Fig. 8c) and Nb/
U is 1�5–2�0� higher relative to the respective ratios ofthe primitive mantle.
Isotope geochemistryIn general, samples from the Ohre Rift and the CEVPspan a large range in their Nd–Sr isotopic composition,
with the Ohre Rift samples showing higher 87Sr/86Sr
at a given 143Nd/144Nd relative to other CEVP samples
(Fig. 9a). Whole-rock samples from Zelezna hurka are
relatively homogeneous in their Sr–Nd–Hf isotope com-
positions but slight differences are evident in Sr–Nd iso-
tope space amongst glass samples from the lowertephra unit (Fig. 9a). Their compositions overlap in eNd–
eHf (Fig. 9b) and fall within the broader mantle array of
Vervoort et al. (1999), consistent with data from the
CEVP. Two glass samples have significantly lower143Nd/144Nd and higher 87Sr/86Sr compared with other
Quaternary volcanic rocks from the Ohre Rift (e.g.Haase & Renno, 2008; Ulrych et al., 2013).
The O isotope compositions of glasses are between
d18O þ5�4 and þ5�8% V-SMOW, with the exception of
sample L1, which has a value of þ6�2% (þ6�13 and
þ6�25%; one duplicate analysis). The high d18O of sam-
ple L1 is associated with higher MgO, CaO, Cl/K, Ce/Pb
and 87Sr/86Sr, but lower Nb/Zr, La/Sm, K/Ti and177Hf/176Hf values.
DISCUSSION
Insights from mineral phasesOlivine antecrystsThe compositions of olivine crystals reveal insights into
the plumbing system of Zelezna hurka. Cores of olivinecrystals show normal mineral zonation (i.e. decrease in
forsterite content towards the rim) and plot within the
field of olivines in equilibrium with melts from ‘ordin-
ary’ mantle peridotite rather than melts from pyroxe-
nitic lithologies (Straub et al., 2011). However, olivine
cores are distinct from primary mantle olivines found inmantle peridotite xenoliths of the same region (Fig. 4c;
lower Fo and Ni, higher CaO). Primary mantle olivines
Fig. 7. (a) Volatile-free total alkalis, Na2OþK2O (wt %) vs SiO2
(wt %) after Le Bas & Streckeisen (1991). Whole-rock samplesfrom Zelezna hurka overlap with the range of basanitic lavasreported from the Oberpfalz, but glasses are much higher intheir alkali content at a given SiO2 content. (b) Combined vola-tile-free oxide diagram, SiO2þAl2O3 (wt %) vsCaOþNa2OþK2O (wt %), for the discrimination between bas-anite, nephelinite and melilitite after Le Bas (1989). Data sour-ces as in Fig. 6.
usually have CaO contents of less than 0�1 wt % and
characteristic Ni concentrations of 2600–3200 ppm,whereas magmatic olivines have CaO concentrations
>0�18 wt % (Stamper et al., 2014). Olivines entrained in
the Zelezna hurka lavas are thus of magmatic origin.
However, they are in disequilibrium with the host lava,
which is evident both petrographically (common dissol-
ution textures) and chemically (Mg# of melt much lower
than expected if assuming olivine–melt equilibrium).These olivines are thus antecrysts and their evolu-
tion can be differentiated into three generations:
(re-)crystallization (stage 1) in equilibrium with mantle
peridotite (Fo> 89, Ni> 1700 ppm; Straub et al., 2011),
as demonstrated by the modelled crystallization trend
shown in Fig. 4 (see figure caption for model details)and SD Table S2. Minor differences between the calcu-
lated fractionation trend and observed mineral
compositions during stage 1 (Fig. 4a) may be explained
by minor changes in the olivine–melt partition coeffi-cient for Ni as a result of changes in liquid composition
(e.g. concomitant crystallization of magnetite), pressure
and temperature (e.g. Matzen et al., 2013). Further crys-
tallization of olivine along the predicted crystallization
path from forsterite contents of 89 to 84 (Stage 2 in
Fig. 4a) is accompanied by a drop in Ni content from
>2000 ppm to <1000 ppm (Fig. 4a) but a minor increasein CaO (Fig. 4c). In Stage 3, groundmass crystals and
rims of olivine crystals show a significant drop in Ni
at constant forsterite content (500 ppm Ni and below;
Fig. 4a) but a strong enrichment in CaO (up to >1�0 wt
%; Fig. 4c) and MnO. These low-Ni–high-CaO rims of
olivine antecrysts have not been reported from Zeleznahurka in previous studies (e.g. Geissler, 2005). A very
similar pattern in mineral evolution (although at a
Fig. 8. (a) Multi-element plot for whole-rock and glass samples normalized to the primitive mantle values of Lyubetskaya &Korenaga (2007). Red, glass data; orange, whole-rock data. The grey field corresponds to literature data with two typical patternsshown as grey lines. (b) Nb/Zr vs MgO (wt %) and (c) chondrite-normalized (Palme & O’Neill, 2003) (La/Sm)N vs La (ppm). Data sour-ces as in Fig. 6.
smaller magnitude and at overall more primitive com-
positions) is recorded in fresh olivines of the
Udachnaya East kimberlite in Yakutia (Kamenetsky
et al., 2008). Furthermore, the composition of the olivineantecrysts cannot be explained by crystallization from a
single parental liquid, but instead requires at least one
other liquid with a very different composition (e.g. high
Ca and Mn, low Ni).
Compositional profiles from the rim of olivine crys-
tals towards the core (SD Fig. S3) allow tracking of thedifferent steps of crystal evolution (e.g. composition of
parental melt, solid-state crystal diffusion, presence or
Fig. 9. (a) 87Sr/86Sr vs 143Nd/144Nd for volcanic rocks from the CEVP (Hocheifel: Jung et al., 2006; Rohn: Jung et al., 2013;Vogelsberg: Jung & Masberg, 1998) compared with data from the Ohre Rift region (Ohre Rift: Haase & Renno, 2008, and referencestherein; Ulrych et al., 2013; Ohre Rift melilitites: Ulrych et al., 2008; Oberpfalz mantle xenoliths: Ackerman et al., 2013; Komornıhurka: Haase & Renno, 2008; Zelezna hurka glasses and whole-rocks: this study). Also shown are the approximate positions ofmantle endmembers PREMA, DMM, EM1 and EM2 (Stracke, 2012), LVC (Hoernle et al., 1995) and EAR (Cebria & Wilson, 1995; asdefined by Lustrino & Wilson, 2007). (b) (eNd)i vs (eHf)i of volcanic rocks from the CEVP [Vogelsberg (17 Ma), Rhon (24 Ma),Hocheifel (40 Ma): Jung & Masberg, 1998; Jung et al., 2011; Pfander et al., 2012], Zelezna hurka glasses and whole-rocks (this study)and the Udachnaya East kimberlite (Kamenetsky et al., 2009b). Fields for MORB, HIMU, EM1 and EM2 (after Pfander et al., 2007) areshown for comparison. The mantle array is after Vervoort et al. (1999; eHf¼1�33 eNdþ3�19) and data for CHUR are from Bouvieret al. (2008). Decay constants for 147Sm and 176Lu are from Begemann et al. (2001) and Scherer et al. (2001), respectively.
(Table 1). With respect to the low solidus temperature of
quartz in the presence of phlogopite and H2O–CO2 va-pour (�700–800�C at crustal depths; e.g. Wones &
Dodge, 1977; Bohlen et al., 1983) and the presence of
numerous dispersed single quartz crystals (likely to rep-
resent disintegrated crustal xenoliths) in the lavas, as-
similation of crustal material may play an important role
in the petrogenesis of the Zelezna hurka lavas. However,
because sample V1 was taken from a blocky lava, in
which temperatures may remain at higher levels for alonger period of time relative to the explosively erupted
tephra, we need to further constrain the possible role of
crustal assimilation using geochemistry.
Assimilation of crustal material may effectively
change elemental concentrations and ratios as well as
isotope ratios [e.g. decreasing Ce/Pb or Nb/U in con-
junction with increasing SiO2, 87Sr/86Sr or d18O ofwhole-rock or glass (subsequently noted as d18OWR; e.g.
Taylor, 1980; Jung & Hoernes, 2000; Jung et al., 2013)]
and has been found to play a key role in the magmatic
evolution of several suites of the CEVP. Lavas from the
Rhon, for example, show a broad positive correlation
between d18OWR and SiO2 (Fig. 11a), interpreted as theresult of combined assimilation and fractional crystal-
lization processes (Jung et al., 2013). Similarly, one of
our new samples from Zelezna hurka shows higher
d18OWR, associated with higher 87Sr/86Sr (0�7039),
whereas all other samples show mantle-like d18OWR
[mantle range of Taylor (1980) and Eiler et al. (2000)].
Quantification of the influence of continental crustalassimilation in the petrogenesis of the Zelezna hurka
lavas is difficult, in particular with respect to their iso-
tope characteristics. Further insights can be obtained
from the major element compositions of the crustal
xenocrysts and the general trace element charac-
teristics of the continental crust. We identified quartz,K-feldspar, albite and muscovite as the main phases in
the crustal xenoliths; amphibole may also be present.
LuRb
BaTh
UNb
TaLa
CePb
PrSr
NdZr
HfSm
EuTi
GdTb
DyY
HoEr
TmYb
100
10
1
0.001
0.01
0.1
Cpx phenocr. & rims
Cpx
/ Pr
imiti
ve M
antle
Cpx cores
Kimberlite cpx inclusions(Udachnaya East)
Fig. 10. Primitive mantle-normalized [values of Lyubetskaya & Korenaga (2007)] trace element patterns of clinopyroxenes fromZelezna hurka (cores of cumulates, and phenocrysts and overgrowth rims) and inclusions hosted in fresh olivines of theUdachnaya East kimberlite (Kamenetsky et al., 2009a). The similarity in the trace element patterns should be noted. However, theUdachnaya East kimberlite shows a more pronounced difference between the light (more enriched) and heavy (depleted relative tothe primitive mantle) REE.
The first phase of melting in metapelitic crustal xeno-
liths (such as phyllite) involves albite-rich plagioclase
(oligoclase), controlled by the H2O and alkali releaseduring the breakdown of muscovite (Grapes, 1986).
This pattern is well reflected by the trend of the Ohre
Fig. 11. Stable oxygen isotope composition in per mil relative to V-SMOW. Grey shaded bands indicate the d18O range (in per milrelative to V-SMOW) of normal (N)-MORB glasses (Eiler et al., 2000) and the range of d18OWR for primitive melts containing 4–5 wt% Na2O (Eiler, 2001). (a) d18O of Zelezna hurka (ZH) glasses and whole-rocks (Rhon: Jung et al., 2013; Garrotxa, NE Spain: Cebriaet al., 2000) vs SiO2 (wt %). Most of the Zelezna hurka glasses (except for L1) plot in the d18OWR range of N-MORB (Eiler et al., 2000).Rhon samples have been affected by assimilation of crustal material and subsequent fractional crystallization (Jung et al., 2013);this is also visible in the broad correlation between d18OWR and SiO2 (trend encompassed by the dashed lines). (b) d18OWR vs CaO/Al2O3 of whole-rocks from the Rhon (Jung et al., 2013), Garrotxa (NE Spain; Cebria et al., 2000) and Zelezna hurka glasses. The aver-age compositions of upper (UCC) and lower continental crust (LCC) are shown for comparison (Rudnick & Gao, 2003). Rhon lavasare consistent with assimilation of continental crust whereas glasses from Zelezna hurka show a positive correlation between O iso-tope composition and CaO/Al2O3.
Fig. 12. Major oxide composition of Ohre Rift lavas (data sources as in Fig. 6; this study) compared with single magmatic andxenocrystic mineral phases and experimental melt compositions for KLB-1 [dry peridotite of Hirose & Kushiro (1993); run details inFig. 15], PERC-3 [carbonated peridotite of Dasgupta et al. (2007); run details in Fig. 15] and KC2 [carbonatite melt of Sweeney(1994)]. (a) CaO and (b) Na2O vs SiO2 and (c) K2O vs Al2O3 (all in wt %). The compositions of the Quaternary volcanic rocks of theOhre Rift are controlled by variable proportions of the primary magmatic minerals [Cpx, clinopyroxene; Hbl, hornblende (Geissleret al., 2007); Hy, hauyne; Phl, phlogopite; Ol, olivine] rather than by assimilation of crustal components (Ab, albite; Kfsp, K-feldsparMs, muscovite; Qz, quartz). It should be noted that fractional crystallization would result in trajectories away from the crystallizingmineral compositions, whereas assimilation trajectories (grey arrows) would point towards the assimilated mineral. Albite-richplagioclase and potassic feldspar exhibit a range of compositions (grey and brown crosses, respectively).
Rift lavas in Fig. 12, extending from a parental magmacomposition, probably similar to the PERC-3 compos-
ition of Dasgupta et al. (2007), towards variable mix-
tures of albite and muscovite (plus K-feldspar).
However, the composition of the Zelezna hurka lavas is
controlled by the accumulation of olivine (whole-rock)
and fractional crystallization of clinopyroxene (glasses)as evident from the trajectories between whole-rocks,
glasses, olivine antecrysts, clinopyroxene and other
magmatic phases [hauyne as phenocryst and phlogo-
pite (þ hornblende; Geissler et al., 2007) as cumulate
phases; Fig. 12]. All these samples consistently fall at
the low-silica end of the range of most Ohre Rift lavas,
with only melilitites (Ulrych et al., 2008) being moreundersaturated. The predominant crustal assimilation
of albite and mica (6 K-feldspar) could also explain the
presence of residual single quartz crystals. The trends
in Fig. 12 point to a parental melt composition of the
Zelezna hurka lavas with even lower SiO2 and Al2O3,
but higher CaO and total alkalis, if we assume that thehighly silica-undersaturated nephelinites of Zelezna
hurka have already assimilated significant amounts of
silica-rich crustal lithologies. To produce such parental
melt compositions from a peridotite source, significant
amounts of carbonate (i.e. CO2) must be involved (see
PERC-3 and KC2 in Fig. 12 and discussion below).
In contrast to major elements, where large amountsof assimilated material are necessary to significantly
change the whole-rock chemical composition, trace
elements (and their ratios) are more sensitive to assimi-
lation. Trace element ratios such as Nb/U or Ce/Pb have
proven to be powerful tracers, with respective values of
47 6 10 and 25 6 5 in oceanic basalts (Hofmann et al.,1986) and 4.4 and 3.7 in the continental crust (Rudnick &
Gao, 2003; Fig. 13). Zelezna hurka lavas have Nb/U
similar to the range observed in oceanic basalts but
with Ce/Pb one to four times higher (Fig. 13).
Furthermore, O isotopes show a narrow range between
5�4 and 6�3% V-SMOW and are positively correlated
with CaO/Al2O3 in the glasses (Fig. 11b), contrary towhat is expected for the assimilation of upper continen-
tal (granitoid) crustal material as observed in the Rhon
province [Fig. 11b; tephrites, phonolites and trachytes
of Jung et al. (2013)].
Precise information on the composition of the paren-
tal melt (which is likely to have higher Ce/Pb) remains
obscure and thus assimilation of crustal material can beneither excluded nor confirmed and quantified with cer-
tainty. However, the Zelezna hurka lavas have much
higher trace element abundances than average upper
continental crust (Rudnick & Gao, 2003). The assimila-
tion of crustal material would thus lead to a relative de-
pletion of trace elements in the melt. Assuming amaximum of 10 vol. % of upper continental crust being
assimilated in the lavas erupted would not change their
overall incompatible trace element patterns signifi-
cantly. It is not sufficient to explain the high enrichment
in Nb, Ta, LREE to MREE and Sr along with a relative de-
pletion in Pb, Zr and Hf (Fig. 8a). These trace elementcharacteristics are thus assumed to be of primary mag-
matic origin (melting and/or source). Before we further
constrain these, we will first try to reconstruct the
plumbing system of Zelezna hurka.
Constraints on the magma plumbing systemThermobarometryThe composition of clinopyroxene phenocrysts can be
used to determine the thermobarometric conditions of
crystallization using equations 32c, 33 and 34 of Putirka
(2008; Excel spreadheets are available for download
from the website of K. Putirka: http://www.fresnostate.
edu/csm/ees/faculty-staff/putirka.html). Successful P–Testimates were assumed if (1) the calculated Fe–Mg ex-
change coefficient is within the range of experimental
observations (0�28 6 0�08; Putirka, 2008) and (2) the
clinopyroxene components [diopside–hedenbergite
and enstatite–ferrosilite, calculated using the normative
procedure of Putirka et al. (2003)] from measured min-eral compositions are in agreement (6 0�01) with the ex-
pected clinopyroxene components calculated from the
host-rock composition. This resulted in 38 successful P–
T estimates (Fig. 14; SD Table S3) that fall into two
groups. The first group consists of Na- and Cr-rich aug-
ites that occur as cores of cumulate crystals (Fig. 3d)
and indicate pressures of around 1�0–1�3 GPa at tem-peratures of 1250–1300�C (Fig. 14). The second clinopyr-
oxene group (diopsidic rims) displays lower pressures
and temperatures at around 0�8 GPa and 1150–1200�C,
respectively. These two groups are distinct from each
other even given the method’s relatively large uncer-
tainty of 60�15 GPa and 650�C (Putirka, 2008). We con-clude that cumulates formed in the upper SCLM,
whereas phenocrysts and overgrowth rims crystallized
47±10
25±5
UCC
0 20 40 60 80 100 120
Nb/U
0
20
40
60
80
100
120C
e/P
b
Assimilation of upper continental crust
Oh e (Eger) RiftOh e (Eger) Rift: melilititesOberpfalzKomorní h rkaM tina MaarZH whole rocksZH matrix glassesSWG melilitites
Fig. 13. Nb/U vs Ce/Pb for Ohre Rift lavas (data sources as inFig. 6; this study) and the SW German (SWG) melilitites ofHegner et al. (1995) and Dunworth & Wilson (1998). All theQuaternary lavas studied here fall within the oceanic array forNb/U (47 6 10; Hofmann et al., 1986) but are more enriched inCe/Pb. The average upper continental crust (UCC) has Nb/Uand Ce/Pb of 4�4 and 3�7, respectively (Rudnick & Gao, 2003).Assimilation trajectories are indicated.
in the lower continental crust (Fig. 14; Moho <28 km;
Babuska & Plomerova, 2010).
The temperature estimates of Geissler et al. (2007)
yield lower values for their xenolith suite (including
hornblendite, pyroxenite, wehrlite) compared with our
cpx–melt temperatures at similar pressures (Fig. 14).Geissler et al. (2007), however, speculated also about
the possible intrusive origin of these rocks or existing
mineral disequilibria in these rocks. In contrast, a dis-
tinct suite of cumulates (e.g. ol–cpx–spl cumulates)
studied by Geissler et al. (2007) (red open diamonds in
Fig. 14) points towards the magmatic temperatures re-
corded in our samples. This could possibly indicatelater reheating of those cumulates after their entrain-
ment in the Zelezna hurka host nephelinite (our data);
further studies are required to resolve the complex ther-
mobarometric history.
Volcanism in the West-Eifel and Hocheifel regions of
Germany shows close similarities to the volcanismin the Ohre Rift region (e.g. SiO2-undersaturated, high-
alkali volcanic rocks such as foidites, basanites and
nephelinites; e.g. Duda & Schmincke, 1985; Jung et al.,
2006) and is controlled by a combination of intraplate
magmatic activity and lithospheric extension (propaga-
tion of pre-rift volcanism linked to the Upper Rhine
Graben; Fekiacova et al., 2007). Depths of crystallizationare similar to our estimates for the nephelinitic rocks of
Zelezna hurka with respect to crystallization below the
Moho and within the lower crust (e.g. Duda &
Schmincke, 1985). However, Sachs & Hansteen (2000)
calculated the depth of a possible magma chamber at
0�6–0�7 GPa, which is at the low end of the pressures
calculated for the crystallization of clinopyroxene in theZelezna hurka lavas. The range of pressures recorded
by clinopyroxene overgrowth rims and phenocrysts at
Zelezna hurka (0�7–1�0 GPa; Fig. 14) argues against the
presence of a lower crustal magma chamber under-
neath this volcano but instead for continuous crystal-
lization during melt ascent.
Constraints on the parental melt compositionSo far, we have demonstrated that there is strong min-
eralogical evidence (in terms of mineral assemblage,
composition and evolution) for a genetic link betweenthe Quaternary nephelinites of Zelezna hurka and other
silica-undersaturated magmas, such as melilitites and
even kimberlites. Olivine antecrysts show very similar
chemical evolution, clinopyroxenes have similar trace
element patterns, phlogopites are intermediate be-
tween those found in carbonatites and lamproites, andhauyne and titanomagnetite indicate a shallow depth of
oxidation of the melt (e.g. during magma ascent).
Further evidence for the major role of carbonate in the
genesis of the parental magmas comes from the major
element composition of these rocks, which makes them
less sensitive to secondary processes such as crustal
assimilation.We use a simple Rayleigh fractionation model
involving olivine and an olivineþ clinopyroxene assem-
blage (Fig. 15) and compiled literature data from melt-
ing experiments of various source lithologies (e.g. dry
peridotite versus carbonated peridotite) close to our
thermobarometric estimates. For dry peridotite we usedthe melt composition generated by melting KLB-1 at
1�5 GPa and 1350�C (Hirose & Kushiro, 1993).
Experiments on carbonated peridotite are generally per-
formed at much higher pressures than those on dry
peridotite; thus we selected the melt composition gen-
erated by melting a peridotite carbonated with 1�0 wt %
CO2 (PERC-3) at 3�0 GPa and 1350�C [run A509 ofDasgupta et al. (2007)]. For each of these starting pri-
mary magma compositions we then calculated fraction-
ation paths for two scenarios: (1) simultaneous
crystallization of clinopyroxene (composition of L3-12
clinopyroxene phenocrysts) and olivine (composition of
L3-12 antecryst) in the relative proportion 4:1; (2) a two-step model involving first 20 vol. % fractionation of oliv-
ine only, followed by simultaneous crystallization of a
1SD
Focal depthof recent
earthquakeswarms
MOHO
SCLM
CC
Eifelmagma
chamber
incipient melting
major m
eltingalkali basalt
geotherm
Xenolithre-equilibrium
Re-
heat
ing/
entr
ainm
ent?
800 1000 1200 1400
Temperature [°C]
0
0.5
1.0
1.5
2.0
Pre
ssu
re [
GP
a]
10
20
30
40
50
60
0
CoresZonationRimsMatrixCumulates
Geissler et al. (2007)
CumulatesXenoliths
Dep
th [km
]
Fig. 14. Thermobarometric estimates for clinopyroxene crystal-lization using the method of Putirka (2008). (For full details seethe main text and SD Table S2.) The onset of clinopyroxenecrystallization is at about 1�2 GPa in the SCLM. However, mostclinopyroxenes indicate pressures of crystallization between0�7 and 1�0 GPa, close to the Moho (Babuska & Plomerova,2010) or within the continental crust. Focal depths of recentearthquake swarms (e.g. Horalek et al., 2000; http://www.ig.-cas.cz/en/structure/observatories/west-bohemia-seismic-net-work-webnet) and the inferred depth of a crustal magmachamber beneath the Eifel (Sachs & Hansteen, 2000) areshown for comparison. Geotherms, melting paths and add-itional P–T data are from Geissler et al. (2007).
similar to the first scenario (cpx:ol¼ 4:1).Fractionation of plagioclase or an olivineþplagio-
clase assemblage would result in a slight decrease in
CaO/Al2O3 and is not evident from compositional or
petrographic observations. Exclusive fractionation of
olivine does not change CaO/Al2O3 significantly but is
effective in explaining the relative compositional differ-
ence between glasses and whole-rocks (involving about20 vol. % olivine accumulation). However, with the
onset of fractional crystallization of clinopyroxene, CaO/
Al2O3 changes dramatically. One of the major differ-
ences between melts of carbonate-bearing and carbon-
ate-free mineral assemblages is the large contrast in
CaO/Al2O3. In carbonate-free peridotite, CaO/Al2O3 in-creases with increasing degree of partial melting but is
always less than 1�0 owing to the excess of Al2O3 over
CaO (Fig. 15). However, during melting of carbonate-
bearing peridotite and in experiments performed at
constant pressure (PERC and PERC-3 at 3�0 GPa;
Dasgupta et al., 2007), CaO/Al2O3 values are controlled
by the changing CaO contents of the partial melts ratherthan by changes in Al2O3 concentrations. At low de-
grees of partial melting, CaO concentrations are very
high because of non-modal melting dominated by clino-
pyroxene (high CaO/Al2O3). Further melting at increas-
ing temperatures consumes clinopyroxene (‘cpx-out’)
with the result of decreasing CaO and increasing Al2O3
(melting of garnet) content in the melt (Dasgupta et al.,
2007). The experimental evidence for various factors
exerting control on CaO/Al2O3 values explored above is
thus consistent with production of the parental magmafor Zelezna hurka lavas as low-degree partial melts of
carbonated peridotite.
Mantle sources and meltingIsotopic constraintsA distinct mantle reservoir has been proposed as acommon source component of the Cenozoic mafic alka-
line magmatism in Europe [i.e. ‘component A’ of Wilson
& Downes (1992); ‘Low Velocity Component’ of Hoernle
et al. (1995); ‘European Asthenospheric Reservoir’ of
Cebria & Wilson (1995)]. However, an alternative view
explains this common reservoir by variable degrees ofmixing between at least three distinct mantle sources
(e.g. Haase & Renno, 2008). Notably, basalts from
Lower Silesia extend to more radiogenic 143Nd/144Nd
values (Blusztajn & Hart, 1989; Fig. 9a) than the pro-
posed European mantle reservoir, close to the prevalent
mantle (PREMA) composition of Stracke (2012), thus
putting into question whether there is a uniqueEuropean mantle reservoir (Fig. 9a). For Zelezna hurka,
Sr and Nd isotope compositions may also point to-
wards three-component mixing (e.g. PREMA, EM1,
EM2), as suggested by Haase & Renno (2008), but could
also be explained by variable amounts of crustal con-
tamination. Slightly elevated 87Sr/86Sr ratios would beconsistent with a limited amount of crustal assimilation,
as discussed above. However, the observed range in
0 5 10 15 20 25
MgO [wt.%]
0.0
0.5
1.0
1.5
2.0
CaO
/Al 2
O3
PERC@1350°CCaO/Al2O3
= 2.62PERC-3
50
20
10
52
20% Ol
Cpx:Ol (4
:1)
Cpx
:Ol (
4:1)
1 GPa, 1250°C
3 GPa, 1500°C
20% Ol
5050
50
increasing F
1
Oh e (Eger) Rift
OberpfalzKomorní h rkaM tina MaarZH whole rocksZH matrix glassesthis studyliterature data
KLB-1 1350°CHK-66Mix-1GPERC-3 1350°PERC-3PERC
OR melilitites
Fig. 15. Variation of MgO (wt %) vs CaO/Al2O3. Blue diamonds, melting experiments of a carbonated peridotite (PERC and PERC-3with 2�5 and 1�0 wt % CO2, respectively) performed by Dasgupta et al. (2007) at 3�0 GPa pressure and temperatures from 1300 to1600�C. Melting trends are indicated by blue arrows. Orange diamonds, experimental melt compositions (1�0–3�0 GPa, 1250–1500�C) from Hirose & Kushiro (1993) of a natural spinel peridotite (HK-66); green diamonds, results from melting experiments(1�0–2�5 GPa, 1375–1500�C) on a garnet pyroxenite (Mix-1 G) by Hirschman et al. (2003). Hexagons, starting melt compositions[blue, PERC-3 at 1350�C and 3�0 GPa; orange, KLB-1 spinel lherzolite at 1350�C and 1�5 GPa of Hirose & Kushiro (1993)] for a simpleRayleigh fractionation model involving olivine and an olivine–clinopyroxene assemblage. Mineral/liquid partition coefficients usedfor MgO, CaO and Al2O3 are mean values of the experimentally determined range for olivine (Beattie, 1994) and clinopyroxene(Adam & Green, 2006). Tick marks correspond to 1%, 2%, 5%, 10%, 20% and 50% crystallization. Data for the Ohre Rift andOberpfalz are shown for comparison (see Fig. 6 for references).
Eiler, 2001) and initial d18O would then be similar to the
range of CEVP lavas (up to þ7�5% V-SMOW) reported
by Mayer et al. (2014). In combination with CaO/Al2O3
we can further show that there is a positive correlation
between heavier O isotope compositions and Ca excess
and that this trend is contrary to crustal assimilation
trends (Fig. 11b).
Additional details on the nature of the metasomaticagent may be resolved by considering the distinct trace
element composition of the Zelezna hurka lavas
(a)
(b)
H-group meltsL-group melts
GrtSpl
10
5
3
2
10
5
2
1
0.7
1010
5
52
23
31
1 0.7 0.5
0.7 0.5
30
asthenospheric
melts
lithosphericmelts
1
1 2 3 4 5 6 7 8
Zr/Nb
12
14
16
18
20
22
24
Nb
/Ta
0.7%
30%10%
5%
1%
2%
0.7%
3%
3%
2%
1% 0.7%
1%
2%
0.5%
Spl-Peridotite
Grt-Peridotite
metasomatisedSpl-Peridotite
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Nb/La
0
10
20
30
40
50
60
70
80
90
La/
Yb
222
NephelinitesOther lavas
VogelsbergEifelRhönSWG melilititesOR melilitites
Komorní hůrkaZH whole rock
Mýtina Maar
this studyliterature data
Ohře Rift
ZH glasses
Fig. 16. (a) Nb/Ta vs Zr/Nb for Quaternary and older volcanic rocks of the Ohre Rift and the CEVP (data sources as in Fig. 6). Coloreddashed curves indicate melting trends for garnet peridotite and spinel peridotite and a metasomatized, refractory spinel peridotite.[For full details see Pfander et al. (2012).] (b) La/Yb vs Nb/La for the same samples as in Fig. 13 (data sources as in Fig. 6) with melt-ing trends for asthenospheric melts and lithospheric melts according to Pfander et al. (2012). L- and H-group melts (moderately andhighly trace element enriched melts, respectively) are derived from melting an amphibole- and phlogopite-bearing spinel peridotitewith an enriched composition that has been constrained from natural mantle xenoliths from the Hessian depression [see Pfanderet al. (2012) for details]. Numbers adjacent to the model curves indicate the per cent melting.
[especially the transitional composition of glasses be-
tween the nephelinite and melilitite rock series (Fig. 7b)]
compared with other CEVP volcanic rocks. Carbonatiticmelt metasomatism is an effective process by which to
fractionate certain trace element ratios such as Ba/Th,
K/La, Zr/Sm or Ti/Eu (e.g. Sweeney et al., 1995; Yaxley
et al., 1998). More specifically, large ion lithophile elem-
ents (LILE), LREE and HREE, and also Th, Nb, Ta and Sr
become moderately to highly enriched, and decoupled
from Ti abundances (e.g. Green & Wallace, 1988;Yaxley et al., 1991, 1998). These characteristic enrich-
ments are easily recognizable in multi-element patterns
(Fig. 8a) with high concentrations of the LILE, a positive
Nb and Ta anomaly, and slight negative anomalies of
Zr, Hf and Ti. As a result, the Quaternary volcanic rocks
from the Ohre Rift (along with lavas from the Oberpfalz)plot at the high end of the CEVP range in CaO/Al2O3 vs
(La/Yb)N (Fig. 18a). This range is even further extended
by the melilitites of the Ohre Rift and those from SW
Germany. For the latter, an origin by partial melting of a
carbonated peridotite source has been proposed by
Dunworth & Wilson (1998). It has to be noted, however,
that La can also be fractionated from Yb by melting inthe stability field of garnet, as HREE are retained as
compatible elements in residual garnet. More unambi-
gous is the fractionation of Zr from Sm, a process that
has been associated with carbonatitic melt metasoma-
tism (e.g. Pfander et al., 2012). Samples from the
Oberpfalz, the Massif Central, the SW German melili-tites and Quaternary volcanic rocks of the Ohre Rift
show the strongest fractionation of (Ti/Eu)N relative to
(Zr/Sm)N (Fig. 18b). Whereas the change in (Ti/Eu)N
could also be attributed to assimilation of material of
the continental crust (UCC and LCC in Fig. 18b), this pro-
cess is insufficient to explain the subchondritic Zr/Sm
ratios, which provides strong evidence for carbonatitemetasomatism in the SCLM (Pfander et al., 2012).
The genetic link between kimberlites, melilititesand nephelinitesForsterite-rich, high-Ni olivine cores may be interpreted
either as the earliest crystallization products of a meltthat infiltrates the lithospheric mantle (e.g. Dunworth &
Wilson, 1998) or as direct reaction products of carbona-
titic melt infiltration into the SCLM. This reaction of en-
statite and dolomite to forsterite, diopside and melt
(e.g. Yaxley et al., 1991; Dalton & Wood, 1993) would be
a plausible explanation for the close similarities in min-eralogy and chemical composition between the Zelezna
hurka nephelinites and kimberlites. Olivines entrained
in the lava show the same compositional trends as
fresh olivines in the Udachnaya East kimberlite
(Kamenetsky et al., 2008), clinopyroxenes have similar
trace element patterns, and accessory phases such as
phlogopite and spinel sensu lato suggest a genetic link.Further evidence for the major role of a carbonate
phase during the petrogenesis of the Zelezna hurka
magmas comes from radiogenic (enriched mantle sig-
natures) and stable isotopes (high d18O of olivines and
glasses) and major (e.g. high CaO/Al2O3, high Cl and S
concentrations) and trace elements (e.g. low Ti/Eu andZr/Sm, Fig. 18b). Shallow oxidation owing to pressure
release indicated by titanomagnetite and hauyne
phenocrysts in the Zelezna hurka lavas is also observed
in kimberlites (Yaxley et al., 2012).
However, there are also important differences be-
tween ‘high-carbonate’ lavas (such as kimberlites) and
the nephelinites of Zelezna hurka. First of all, there isevidence for much shallower depths of melting and
melt segregation for the nephelinites and a general dif-
ference in their eruption style. Kimberlites form major
diatremes that indicate explosive eruptions, whereas
the Quaternary nephelinites in the Ohre Rift may erupt
extrusively (Komornı Hurka, Zelezna hurka vent) or ex-plosively when the ascending melt comes into contact
with aquifers (Zelezna hurka tephra, Mytina Maar). The
elemental and isotopic characteristics of the nephelin-
ites are also less extreme than those of kimberlites,
which, at least in the case of the fresh Udachnaya East
kimberlite, show a HIMU-like isotope signature and a
much higher degree of silica-undersaturation (�32 wt %SiO2; Kamenetsky et al., 2009b). This is also reflected in
the abundance of clinopyroxene, which is a major
phase in nephelinites but rarely present in kimberlites
(e.g. hosted as inclusions in olivine; Kamenetsky et al.,
2009a).
However, our new data provide direct magmaticevidence for a genetic link between kimberlites, melili-
tites and nephelinites as suggested previously by
Fig. 17. d18O of olivine vs forsterite content for Zelezna hurkacompared with data from South African melilitites (Day et al.,2014) and the Azores (Genske et al., 2013), where the oxygenisotope composition of olivine is related to assimilation–frac-tional crystallization processes (AFC; assimilation of alteredoceanic crust; blue arrow). An assimilation trend expected forcontinental crustal material is shown in orange [bulk continen-tal crust Mg#¼55 (Rudnick & Gao, 2003), d18O�6�5%], assum-ing a melt–olivine fractionation of �0�5% and a d18O of 7–14%for granitoid crust (Eiler, 2001). It should be noted that the Fo-rich olivines with d18O higher than the mantle array (Matteyet al., 1994) extend into the field (dark grey) of fresh olivinesfrom the Udachnaya East kimberlite (Kamenetsky et al., 2008).
experimental studies (e.g. Lee & Wyllie, 1997). We sug-
gest that the dominant controls on the parental melt
composition are the amount of carbonate involved, the
depth of melting and melt segregation, and the amount
of melt–rock reaction (assimilation of peridotite wall-rock during melt ascent). Kimberlites would represent
one endmember with high amounts of carbonate, a
great depth of melt segregation (erupting in thick cra-
tonic lithosphere) and minor interaction with the re-
sidual peridotite mantle. Rifting and lithosphere
thinning may produce preferential pathways for alkali-
carbonate melts or fluids to migrate towards the sur-face, with the potential to infiltrate and metasomatically
enrich the SCLM (e.g. Dalton & Wood, 1993; Giuliani
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2
(Zr/Sm)N
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
(Ti/E
u) N
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2
CaO/Al2O3
0
10
20
30
40
50
60
70
80
(La/
Yb
) N
PM
UCC
LCC
(a)
(b)
Ohře Rift
ZH glasses
NephelinitesOther lavas
Oberpfalz
VogelsbergEifelRhönSWG melilitites
OR melilitites
Komorní hůrkaZH whole rocks
Mýtina Maar
Fig. 18. (a) Chondrite-normalized (Palme & O’Neill, 2003) La/Yb vs CaO/Al2O3. Quaternary rocks from the Ohre Rift and SW Germanmelilitites point towards a mantle source metasomatized by carbonatitic melts (e.g. characteristic trace element enrichment andhigh CaO/Al2O3). (b) (Ti/Eu)N vs (Zr/Sm)N [normalized to Cl-values of Palme & O’Neill (2003)]. Compositions of upper (UCC) andlower continental crust (LCC) according to Rudnick & Gao (2003) and the value for the Primitive Mantle (PM; Palme & O’Neill, 2003)are shown for comparison. Assimilation of continental crust or partial (batch) melting of peridotite may effectively lower (Ti/Eu)Nbut cannot explain the fractionation of (Zr/Sm)N. These trace element ratios point clearly towards a carbonated mantle source. Datasources as in Fig. 13.
mantle and depleted asthenospheric mantle. The neph-elinites of the Quaternary Zelezna hurka volcano in the
Ohre Rift provide strong mineralogical and chemical
evidence for the nature of this mantle metasomatism,
involving alkaline-carbonate melts or fluids, as follows.
1. Olivine antecrysts entrained in the nephelinite lava
show chemical evidence for crystallization in the
mantle, subsequent ‘normal’ crystallization and a
later overprint reflecting solid-state diffusion; this
evolutionary pattern is similar to that observed in
fresh olivines of the Udachnaya East kimberlite.2. The trace element patterns of clinopyroxenes also
resemble those of kimberlitic clinopyroxenes and
their crystallization conditions argue for a continu-
ous process in the upper SCLM and lower crust ra-
ther than a long period of melt stagnation at a
distinct level in the lithosphere.3. The compositions of accessory phlogopite are inter-
mediate between those in lamproites and carbona-
tites; the presence of spinels sensu lato and hauyne
argues for shallow oxidation of the melt, similar to
observations in carbonate-rich melts.
4. Elevated O isotope ratios (relative to mantle values)
and distinct trace element enrichment (e.g. LILE,LREE, Nb and Ta) and trace element ratios (e.g. Ti/
Eu, Zr/Sm) provide further evidence for a contribu-
tion of carbonatite to the final melt composition.
Radiogenic Sr–Nd–Hf isotope data support this view,
although their signatures may also be explained by
processes other than carbonate melt metasomatism.
Furthermore, we have shown that crustal assimila-
tion may play a role in the petrogenesis of the Zelezna
hurka nephelinite, but is insufficient to account for allthe mineralogical and chemical evidence we have
found for carbonate melt–peridotite interaction. The
genetic link between kimberlites, melilitites and nephel-
inites has been previously suggested based on experi-
mental and xenolith studies, but this study provides
direct magmatic evidence. The depth of alkali-carbonate
melt–fluid segregation, its total volume and the propor-tion of peridotite assimilation during melt ascent
through the mantle may control the final magma type.
ACKNOWLEDGEMENTS
We collected our samples without using mechanical
tools to avoid any damage on the protected outcrop ofZelezna hurka and we would like to encourage every
visitor to this location to help to preserve it in its current
condition. We thank H. Bratz and M. Hertel at
GeoZentrum Nordbayern and N. Pearson at GEMOC for
their analytical help. We also acknowledge the co-oper-
ation and support of A. Weh and the Selfrag AG(Kerzers, Switzerland) for their help with high-voltage
pulse power fragmentation of olivine-phyric rocks. L.
Ackerman, S. Jung, J. Pfander and editor M. Wilson are
acknowledged for comments that significantly im-
proved the quality and clarity of this paper. P.A.B.
thanks G. Yaxley and O. Nebel for constructive com-
ments on an earlier version of this paper.
FUNDING
This work was supported by a grant of the
‘Sonderfonds fur wissenschaftliche Arbeiten an der
Universitat Erlangen–Nurnberg’ to P.A.B. and F.S.G.and by funding through grant WI 3675/1-1 from the
Deutsche Forschungsgemeinschaft. P.A.B. benefited
from a Feodor Lynen Research Fellowship of the
Alexander von Humboldt Foundation.
SUPPLEMENTARY DATA
Supplementary data for this paper are available at
Journal of Petrology online.
REFERENCES
Ackerman, L., Spacek, P., Magna, T., Ulrych, J., Svojtka, M.,Hegner, E. & Balogh, K. (2013). Alkaline and carbonate-richmelt metasomatism and melting of subcontinental litho-spheric mantle: evidence from mantle xenoliths,NE Bavaria, Bohemian Massif. Journal of Petrology 54,2597–2633.
Ackerman, L., Medaris, G., Jr, Spacek, P. & Ulrych, J. (2014).Geochemical and petrological constraints on mantle com-position of the Ohre (Eger) rift, Bohemian Massif: peridotitexenoliths from the Ceske Stredohorı Volcanic complex andnorthern Bohemia. International Journal of Earth Sciencesdoi:10.1007/s005.31-014-1054-1.
Adam, J. & Green, T. (2006). Trace element partitioning be-tween mica- and amphibole-bearing garnet lherzolite andhydrous basanitic melt: 1. Experimental results and the in-vestigation of controls on partitioning behaviour.Contributions to Mineralogy and Petrology 152, 1–17.
Babuska, V. & Plomerova, J. (2010). Mantle lithosphere controlof crustal tectonics and magmatism of the western Ohre(Eger) Rift. Journal of GEOsciences 55, 171–186.
Bankwitz, P., Schneider, G., Kampf, H. & Bankwitz, E. (2003).Structural characteristics of epicentral areas in CentralEurope: study case Cheb Basin (Czech Republic). Journal ofGeodynamics 35, 5–32.
Beattie, P. (1994). Systematics and energetics of trace-elementpartitioning between olivine and silicate melts: implicationsfor the nature of mineral/melt partitioning. ChemicalGeology 117, 57–71.
Begemann, F., Ludwig, K. R., Lugmair, G. W., Min, K., Nyquist,L. E., Patchett, P. J., Renne, P. R., Shih, C. Y., Villa, I. M. &Walker, R. J. (2001). Call for an improved set of decay con-stants for geochronological use. Geochimica etCosmochimica Acta 65, 111–121.
Blusztajn, J. & Hart, S. R. (1989). Sr, Nd, and Pb isotopic charac-ter of Tertiary basalts from southwest Poland. Geochimicaet Cosmochimica Acta 53, 2689–2696.
Bohlen, S. R., Boettcher, A. L., Wall, V. J. & Clemens, J. D.(1983). Stability of phlogopite–quartz and sanidine–quartz: Amodel for melting in the lower crust. Contributions toMineralogy and Petrology 83, 270–277.
Bouvier, A., Vervoort, J. D. & Patchett, P. J. (2008). The Lu–Hfand Sm–Nd isotopic composition of CHUR: Constraintsfrom unequilibrated chondrites and implications for the bulkcomposition of terrestrial planets. Earth and PlanetaryScience Letters 273, 48–57.
Brandl, P. A., Beier, C., Regelous, M., Abouchami, W., Haase, K.M., Garbe-Schonberg, D. & Galer, S. J. G. (2012). Volcanismon the flanks of the East Pacific Rise: Quantitative con-straints on mantle heterogeneity and melting processes.Chemical Geology 298–299, 41–56.
Brauer, K., Kampf, H., Niedermann, S., & Strauch, G. (2005).Evidence for ascending upper mantle-derived melt beneaththe Cheb basin, central Europe. Geophysical ResearchLetters 32, L08303.
Brauer, K., Kampf, H. & Strauch, G. (2009). Earthquake swarmsin non-volcanic regions: What fluids have to say.Geophysical Research Letters 36, L17309.
Cebria, J. M. & Wilson, M. (1995). Cenozoic mafic magmatismin Western/Central Europe: a common European astheno-spheric reservoir. Terra Abstracts 7, 162.
Cebria, J. M., Lopez-Ruiz, J., Doblas, M., Oyarzun, R., Hertogen,J. & Benito, R. (2000). Geochemistry of the Quaternary alkalibasalts of Garrotxa (NE Volcanic Province, Spain): a case ofdouble enrichment of the mantle lithosphere. Journal ofVolcanology and Geothermal Research 102, 217–235.
Dahm, T., Fischer, T. & Hainzl, S. (2008). Mechanical intrusionmodels and their implications for the possibility of magma-driven swarms in NW Bohemia Region. Studia Geophysicaet Geodaetica 52, 529–548.
Dalton, J. A. & Wood, B. J. (1993). The compositions of primarycarbonate melts and their evolution through wallrock reac-tion in the mantle. Earth and Planetary Science Letters 119,511–525.
Dasgupta, R., Hischmann, M. & Smith, N. (2007). Partial meltingexperiments of peridotiteþCO2 at 3 GPa and genesis ofalkalic ocean island basalts. Journal of Petrology 48,2093–2124.
Day, J. M. D., Peters, B. J. & Janney, P. E. (2014). Oxygen isotopesystematics of South African olivine melilitites and implica-tions for HIMU mantle reservoirs. Lithos 202–203, 76–84.
Dobosi, G. & Fodor, R. V. (1992). Magma fractionation, replen-ishment, and mixing as inferred from green-core clinopyr-oxenes in Pliocene basanite, southern Slovakia. Lithos 28,133–150.
Downes, H. (1987). Tertiary and Quaternary volcanism in theMassif Central, France. In: Fitton, J. G. & Upton, B. G. J. (eds)Alkaline Igneous Rocks. Geological Society, London,Special Publications 30, 517–530.
Duda, A. & Schmincke, H.-U. (1985). Polybaric differentiation ofalkali basaltic magmas: evidence from green-core clinopyr-oxenes (Eifel, FRG). Contributions to Mineralogy andPetrology 91, 340–353.
Dunworth, E. A. & Wilson, M. (1998). Olivine melilitites of theSW German Tertiary Volcanic Province: mineralogy andpetrogenesis. Journal of Petrology 39, 1805–1836.
Eiler, J. M. (2001). Oxygen isotope variations of basaltic lavasand upper mantle rocks. In: Valley, J. W. & Cole, D. (eds)Stable Isotope Geochemistry. Mineralogical Society ofAmerica and Geochemical Society, Reviews in Mineralogyand Geochemistry 43, 319–364.
Eiler, J. M., Schiano, P., Kitchen, N. & Stolper, E. M. (2000).Oxygen isotope evidence for recycled crust in the sources ofmid ocean ridge basalts. Nature 403, 530–534.
Fekiacova, Z., Mertz, D. F. & Renne, P. R. (2007). Geodynamicsetting of the Tertiary Hocheifel volcanism (Germany), PartI: 40Ar/39Ar geochronology. In: Ritter, R.R., & Christensen,U.R. (eds) Mantle Plumes. Berlin: Springer, pp. 185–206.
Fischer, T. & Horalek, J. (2003). Space–time distribution ofearthquake swarms in the principal focal zone of the NWBohemia/Vogtland seismoactive region: period 1985–2001.Journal of Geodynamics 35, 125–144.
Foley, S. F. (1992). Petrological characterization of the sourcecomponents of potassic magmas: geochemical and experi-mental constraints. Lithos 28, 187–204.
Freund, S., Beier, C., Krumm, S. & Haase, K. M. (2013). Oxygenisotope evidence for the formation of andesitic–dacitic mag-mas from the fast-spreading Pacific–Antarctic Rise by as-similation–fractional crystallisation. Chemical Geology 347,271–283.
Geissler, W. (2005). Seismic and petrological investigations ofthe lithosphere in the swarm-earthquake and CO2-degass-ing region Vogtland/NW-Bohemia. GeoForschungsZentrumPotsdam, Scientific Technical Report STR05/06, 1–169.
Geissler, W., Kampf, H., Seifert, W. & Dulski, P. (2007).Petrological and seismic studies of the lithosphere in theearthquake swarm region Vogtland/NW Bohemia, centralEurope. Journal of Volcanology and Geothermal Research159, 33–69.
Geissler, W. H., Kampf, H., Bankwitz, P. & Bankwitz, E. (2004).Das quartare Tephra-Tuff-Vorkommen von Mytina (Sudranddes westlichen Eger-Grabens/Tschechische Republik):Indikationen fur die Ausbruchs- und Deformationsprozesse.Zeitschrift fur Geologische Wissenschaften 32, 31–54.
Genske, F. S., Turner, S. P., Beier, C. & Schaefer, B. F. (2012).The petrology and geochemistry of lavas from the westernAzores islands of Flores and Corvo. Journal of Petrology 53,1673–1708.
Genske, F. S., Beier, C., Haase, K. M., Turner, S. P., Krumm, S. &Brandl, P. A. (2013). Oxygen isotopes in the Azoresislands: Crustal assimilation recorded in olivine. Geology 41,491–494.
Giuliani, A., Kamenetsky, V. S., Phillips, D., Kendrick, M. A.,Wyatt, B. A. & Goemann, K. (2012). Nature of alkali-carbon-ate fluids in the sub-continental lithospheric mantle.Geology 40, 967–970.
Granet, M., Wilson, M. & Achauer, U. (1995). Imaging a mantleplume beneath the French Massif Central. Earth andPlanetary Science Letters 136, 281–296.
Grapes, R. H. (1986). Melting and thermal reconstitution of pel-itic xenoliths, Wehr Volcano, East Eifel, West Germany.Journal of Petrology 27, 343–396.
Green, D. H. & Wallace, M. E. (1988). Mantle metasomatism byephemeral carbonatite melts. Nature 336, 459–462.
Haase, K. & Renno, A. (2008). Variation of magma generationand mantle sources during continental rifting observed inCenozoic lavas from the Eger Rift, Central Europe. ChemicalGeology 257, 195–205.
Haase, K. M., Krumm, S., Regelous, M. & Joachimski, M. (2011).Oxygen isotope evidence for the formation of silicicKermadec island arc and Havre–Lau backarc magmas byfractional crystallisation. Earth and Planetary ScienceLetters 309, 348–355.
Hegner, E., Walter, H. J. & Satir, M. (1995). Pb–Sr–Nd isotopiccompositions and trace element geochemistry of mega-crysts and melilitites from the Tertiary Urach volcanic field:source composition of small volume melts under SWGermany. Contributions to Mineralogy and Petrology 122,322–335.
Hermann, J., O’Neill, H. S. C. & Berry, A. J. (2005). Titaniumsolubility in olivine in the system TiO2–MgO–SiO2: no evi-dence for an ultra-deep origin of Ti-bearing olivine.Contributions to Mineralogy and Petrology 148, 746–760.
Heuer, B. (2006). Lithospheric and upper mantle structure be-neath the Bohemian Massif obtained from teleseimsmic Pand S receiver functions. GeoForschungsZentrum Potsdam,Scientific Technical Report STR06/12, 1–161.
Hirose, K. & Kushiro, I. (1993). Partial melting of dry peridotitesat high pressures: Determination of compositions of meltssegregated from peridotite using aggregates of diamond.Earth and Planetary Science Letters 114, 477–489.
Hirschmann, M. M., Kogiso, T., Baker, M. B. & Stolper, E. M.(2003). Alkalic magmas generated by partial melting of gar-net pyroxenite. Geology 31, 481–484.
Hoernle, K., Zhang, Y.-S. & Graham, D. (1995). Seismic and geo-chemical evidence for large-scale mantle upwelling beneaththe eastern Atlantic and western and central Europe. Nature374, 34–39.
Hoernle, K., Tilton, G., Le Bas, M. J., Duggen, S. & Garbe-Schonberg, D. (2002). Geochemistry of oceanic carbonatitescompared with continental carbonatites: mantle recycling ofoceanic crustal carbonate. Contributions to Mineralogy andPetrology 142, 520–542.
Hofmann, A. W., Jochum, K. P., Seufert, M. & White, W. M.(1986). Nb and Pb in oceanic basalts: new constraints onmantle evolution. Earth and Planetary Science Letters 79,33–45.
Horalek, J., Sıleny, J., Fischer, T., Slancova, A. & Bouskova, A.(2000). Scenario of the January 1997 West BohemiaEarthquake Swarm. Studia Geophysica et Geodaetica 44,491–521.
Jackson, M. G. & Dasgupta, R. (2008). Compositions of HIMU,EM1, and EM2 from global trends between radiogenic iso-topes and major elements in ocean island basalts. Earth andPlanetary Science Letters 276, 175–186.
Jones, A. P. & Wyllie, P. J. (1985). Paragenetic trends of oxideminerals in carbonate-rich kimberlites, with new analysesfrom the Benfontein Sill, South Africa. Journal of Petrology26, 210–222.
Jung, C., Jung, S., Hoffer, E. & Berndt, J. (2006). Petrogenesis ofTertiary mafic alkaline magmas in the Hocheifel, Germany.Journal of Petrology 47, 1637–1671.
Jung, S. & Hoernes, S. (2000). The major- and trace-elementand isotope (Sr, Nd, O) geochemistry of Cenozoic alkalinerift-type volcanic rocks from the Rhon area (centralGermany): petrology, mantle source characteristics andimplications for asthenosphere–lithosphere interactions.Journal of Volcanology and Geothermal Research 99,27–53.
Jung, S. & Masberg, P. (1998). Major- and trace-element sys-tematics and isotope geochemistry of Cenozoic mafic vol-canic rocks from the Vogelsberg (central Germany). Journalof Volcanology and Geothermal Research 86, 151–177.
Jung, S., Pfander, J. A., Brauns, M. & Maas, R. (2011). Crustalcontamination and mantle source characteristics in contin-ental intra-plate volcanic rocks: Pb, Hf and Os isotopes fromcentral European volcanic province basalts. Geochimica etCosmochimica Acta 75, 2664–2683.
Jung, S., Mezger, K., Hauff, F., Pack, A. & Hoernes, S. (2013).Petrogenesis of rift-related tephrites, phonolites and trach-ytes (Central European Volcanic Province, Rhon, FRG):Constraints from Sr, Nd, Pb and O isotopes. ChemicalGeology 354, 203–215.
Jurewicz, A. J. G. & Watson, E. B. (1988). Cations in olivine, Part1: Calcium partitioning and calcium–magnesium distribu-tion between olivines and coexisting melts, with petrologicapplications. Contributions to Mineralogy and Petrology 99,176–185.
Kamenetsky, V. S., Kamenetsky, M. B., Sobolev, A. V., Golovin,A. V., Demouchy, S., Faure, K., Sharygin, V. V. & Kuzmin, D.V. (2008). Olivine in the Udachnaya-East kimberlite (Yakutia,Russia): types, compositions and origins. Journal ofPetrology 49, 823–839.
Kamenetsky, V. S., Kamenetsky, M. B., Sobolev, A. V., Golovin,A. V., Sharygin, V. V., Pokhilenko, N. P. & Sobolev, N. V.(2009a). Can pyroxenes be liquidus minerals in the kimber-lite magma? Lithos 112, 213–222.
Kamenetsky, V. S., Maas, R., Kamenetsky, M. B., Paton, C.,Phillips, D., Golovin, A. V. & Gornova, M. A. (2009b).Chlorine from the mantle: Magmatic halides in theUdachnaya-East kimberlite, Siberia. Earth and PlanetaryScience Letters 285, 96–104.
Kempton, P. D., Harmon, R. S., Stosch, H. G. & Hoefs, J. (1988).Open-system O-isotope behaviour and trace element en-richment in the sub-Eifel mantle. Earth and PlanetaryScience Letters 89, 273–287.
Le Bas, M. J. (1987). Nephelinites and carbonatites. In: Fitton, J.G. & Upton, B. G. J. (eds) Alkaline Igneous Rocks. GeologicalSociety, London, Special Publications 30, 53–83.
Le Bas, M. J. (1989). Nephelinitic and Basanitic Rocks. Journalof Petrology 30, 1299–1312.
Le Bas, M. J. & Streckeisen, A. L. (1991). The IUGS systematicsof igneous rocks. Journal of the Geological Society, London148, 825–833.
Lee, W.-J. & Wyllie, P. J. (1997). Liquid immiscibility betweennephelinite and carbonatite from 1�0 to 2�5 GPa comparedwith mantle melt compositions. Contributions toMineralogy and Petrology 127, 1–16.
Libourel, G. (1999). Systematics of calcium partitioning be-tween olivine and silicate melt: implications for melt struc-ture and calcium content of magmatic olivines.Contributions to Mineralogy and Petrology 136, 63–80.
Lustrino, M. & Wilson, M. (2007). The circum-Mediterraneananorogenic Cenozoic igneous province. Earth-ScienceReviews 81, 1–65.
Lyubetskaya, T. & Korenaga, J. (2007). Chemical compositionof Earth’s primitive mantle and its variance: 1. Method andresults. Journal of Geophysical Research 112, B03211.
Malkovsky, M. (1987). The Mesozoic and Tertiary basins of theBohemian Massif and their evolution. Tectonophysics 137,31–42.
Mattey, D., Lowry, D. & Macpherson, C. (1994). Oxygen isotopecomposition of mantle peridotite. Earth and PlanetaryScience Letters 128, 231–241.
Matzen, A. K., Baker, M. B., Beckett, J. R. & Stolper, E. M. (2013).The temperature and pressure dependence of nickel
partitioning between olivine and silicate melt. Journal ofPetrology 54, 2521–2545.
Mayer, B., Jung, S., Romer, R. L., Pfander, J. A., Klugel, A., Pack,A. & Groner, E. (2014). Amphibole in alkaline basalts fromintraplate settings: implications for the petrogenesis of alka-line lavas from the metasomatised lithospheric mantle.Contributions to Mineralogy and Petrology 167, 1–22.
Mrlina, J., Kampf, H., Geissler, W. & Van den Bogaard, P.(2007). Assumed Quaternary maar structure at the Czech/German border between Mytina and Neualbenreuth (west-ern Eger rift, Central Europe): geophysical, petrochemicaland geochronological indications. Zeitschrift furGeologische Wissenschaften 35, 213–230.
Mrlina, J., Kampf, H., Kroner, C., Mingram, J., Stebich, M.,Brauer, A., Geissler, W. H., Kallmeyer, J., Matthes, H. &Seidl, M. (2009). Discovery of the first Quaternary maar inthe Bohemian Massif, Central Europe, based on combinedgeophysical and geological surveys. Journal of Volcanologyand Geothermal Research 182, 97–112.
Munker, C., Weyer, S., Scherer, E. & Mezger, K. (2001).Separation of high field strength elements (Nb, Ta, Zr, Hf)and Lu from rock samples for MC-ICPMS measurements.Geochemistry, Geophysics, Geosystems 2, doi:10.1029/2001GC000183.
Mysen, B. O. & Virgo, D. (1980). Solubility mechanisms of CO2
in silicate melts: a Raman spectroscopic study. AmericanMineralogist 65, 885–899.
Nowell, D. A. G., Jones, M. C. & Pyle, D. M. (2006). EpisodicQuaternary volcanism in France and Germany. Journal ofQuaternary Science 21, 645–675.
Palme, H. & O’Neill, H. (2003). Cosmochemical estimates ofmantle composition. In: Carlson, R.W. The Mantle and Core2, Amsterdam: Elsevier, pp. 1–38.
Pearce, N. J. G., Perkins, W. T., Westgate, J. A., Gorton, M. P.,Jackson, S. E., Neal, C. R. & Chenery, S. P. (1997). A compil-ation of new and published major and trace element data forNIST SRM 610 and NIST SRM 612 glass reference materials.Geostandards and Geoanalytical Research 21, 115–144.
Petry, C., Chakraborty, S. & Palme, H. (2004). Experimental de-termination of Ni diffusion coefficients in olivine and theirdependence on temperature, composition, oxygen fugacity,and crystallographic orientation. Geochimica etCosmochimica Acta 68, 4179–4188.
Pfander, J., Munker, C., Stracke, A. & Mezger, K. (2007). Nb/Taand Zr/Hf in ocean island basalts—Implications for crust–mantle differentiation and the fate of niobium. Earth andPlanetary Science Letters 254, 158–172.
Pfander, J. A., Jung, S., Munker, C., Stracke, A. & Mezger, K.(2012). A possible high Nb/Ta reservoir in the continentallithospheric mantle and consequences on the global Nbbudget—Evidence from continental basalts from CentralGermany. Geochimica et Cosmochimica Acta 77, 232–251.
Phipps Morgan, J. & Morgan, W. (1999). Two-stage melting andthe geochemical evolution of the mantle: a recipe for mantleplum-pudding. Earth and Planetary Science Letters 170,215–239.
Putirka, K. D. (2008). Thermometers and barometers for vol-canic systems. In: Putirka, K. D. & Tepley, F. J., III (eds)Minerals, Inclusions and Volcanic Processes. MineralogicalSociety of America and Geochemical Society, Reviews inMineralogy and Geochemistry 69, 61–120.
Putirka, K., Mikaelian, H., Ryerson, F. & Shaw, H. (2003). Newclinopyroxene–liquid thermobarometers for mafic, evolvedand volatile-bearing lava compositions, with applications tolavas from Tibet and the Snake River Plain, Idaho. AmericanMineralogist 10, 1542–1554.
Puziewicz, J., Koepke, J., Gregoire, M., Ntaflos, T. & Matusiak-Malek, M. (2011). Lithospheric mantle modification duringCenozoic rifting in Central Europe: evidence from theKsieginki nephelinite (SW Poland) xenolith suite. Journal ofPetrology 52, 2107–2145.
Roeder, P. & Emslie, R. (1970). Olivine–liquid equilibrium.Contributions to Mineralogy and Petrology 29, 275–289.
Rowe, M. C., Lassiter, J. C. & Goff, K. (2015). Basalt volatile fluc-tuations during continental rifting: An example from the RioGrande Rift, USA. Geochemistry, Geophysics, Geosystems16, doi:10.1002/2014GC005649.
Rudnick, R. L. & Gao, S. (2003). Composition of the continentalcrust. In: Rudnick, R.L. The Crust 3, Amsterdam: Elsevier,pp. 1–64.
Russell, W. A., Papanastassiou, D. A. & Tombrello, T. A. (1978).Ca isotope fractionation on the Earth and other solar systemmaterials. Geochimica et Cosmochimica Acta 42, 1075–1090.
Sachs, P. M. & Hansteen, T. H. (2000). Pleistocene underplatingand metasomatism of the lower continental crust: a xenolithstudy. Journal of Petrology 41, 331–356.
Scherer, E., Munker, C. & Mezger, K. (2001). Calibration of theLutetium–Hafnium Clock. Science 293, 683–687.
Scherer, E. E., Cameron, K. L. & Blichert-Toft, J. (2000). Lu–Hfgarnet geochronology: closure temperature relative to theSm–Nd system and the effects of trace mineral inclusions.Geochimica et Cosmochimica Acta 64, 3413–3432.
Schulmann, K., Lexa, O., Janousek, V. & Lardeaux, J. M. (2014).Anatomy of a diffuse cryptic suture zone: An example fromthe Bohemian Massif, European Variscides. Geology 42,275–278.
Seifert, S., O’Neill, H. S. C. & Brey, G. (1988). The partitioning ofFe, Ni and Co between olivine, metal, and basaltic liquid: Anexperimental and thermodynamic investigation, with appli-cation to the composition of the lunar core. Geochimica etCosmochimica Acta 52, 603–616.
Seifert, W. & Kampf, H. (1994). Ba-enrichment in phlogopite of anephelinite from Bohemia. European Journal of Mineralogy6, 497–502.
Spacek, P., Ackerman, L., Habler, G., Abart, R. & Ulrych, J.(2013). Garnet breakdown, symplectite formation and melt-ing in basanite-hosted peridotite xenoliths from Zinst(Bavaria, Bohemian Massif). Journal of Petrology 54, 1691–1723.
Spicak, A. & Horalek, J. (2001). Possible role of fluids in theprocess of earthquake swarm generation in the WestBohemia/Vogtland seismoactive region. Tectonophysics336, 151–161.
Sprung, P., Scherer, E. E., Upadhyay, D., Leya, I. & Mezger, K.(2010). Non-nucleosynthetic heterogeneity in non-radio-genic stable Hf isotopes: Implications for early solarsystem chronology. Earth and Planetary Science Letters295, 1–11.
Sprung, P., Kleine, T. & Scherer, E. E. (2013). Isotopic evidencefor chondritic Lu/Hf and Sm/Nd of the Moon. Earth andPlanetary Science Letters 380, 77–87.
Stamper, C. C., Blundy, J. D., Arculus, R. J. & Melekhova, E.(2014). Petrology of plutonic xenoliths and volcanic rocksfrom Grenada, Lesser Antilles. Journal of Petrology 55,1353–1387.
Stracke, A. (2012). Earth’s heterogeneous mantle: A product ofconvection-driven interaction between crust and mantle.Earth and Planetary Science Letters 330–331, 274–299.
Straub, S. M., Homez-Tuena, A., Stuart, F. M., Zellmer, G. F.,Espinasa-Perena, R., Cai, Y. & Iizuka, Y. (2011). Formation ofhybrid arc andesites beneath thick continental crust. Earthand Planetary Science Letters 303, 337–347.
Sweeney, R. J. (1994). Carbonatite melt compositions in theEarth’s mantle. Earth and Planetary Science Letters 128,259–270.
Sweeney, R. J., Prozesky, V. & Przybylowicz, W. (1995).Selected trace and minor element partitioning between peri-dotite minerals and carbonatite melts at 18–46 kb pressure.Geochimica et Cosmochimica Acta 59, 3671–3683.
Taylor, H. P., Jr. (1980). The effects of assimilation of countryrocks by magmas on 18O/16O and 87Sr/86Sr systematics in ig-neous rocks. Earth and Planetary Science Letters 47, 243–254.
Ulrych, J., Dostal, J., Hegner, E., Balogh, K. & Ackerman, L. (2008).Late Cretaceous to Paleocene melilitic rocks of the Ohre/EgerRift in northern Bohemia, Czech Republic: Insights into the ini-tial stages of continental rifting. Lithos 101, 141–161.
Ulrych, J., Dostal, J., Adamovic, J., Jelınek, E., Spacek, P.,Hegner, E. & Balogh, K. (2011). Recurrent Cenozoic volcanicactivity in the Bohemian Massif (Czech Republic). Lithos123, 133–144.
Ulrych, J., Ackerman, L., Balogh, K., Hegner, E., Jelınek, E.,Pecskay, Z., Prichystal, A., Upton, B. G. J., Zimak, J. &Foltynova, R. (2013). Plio-Pleistocene basanitic and melilititicseries of the Bohemian Massif: K–Ar ages, major/trace elem-ent and Sr–Nd isotopic data. Chemie der Erde 73, 429–450.
van den Bogaard, P. (1995). 40Ar/39Ar ages of sanidinephenocrysts from Laacher See Tephra (12,900 yr BP):Chronostratigraphic and petrological significance. Earth andPlanetary Science Letters 133, 163–174.
Vaneckova, M., Holub, F. V., Soucek, J. & Bowes, D. R. (1993).Geochemistry and petrogenesis of the Tertiary alkaline vol-canic suite of the Labe tectonovolcanic zone, CzechRepublic. Mineralogy and Petrology 48, 17–34.
Vervoort, J. D., Patchett, P. J., Blichert-Toft, J. & Albarede, F.(1999). Relationships between Lu–Hf and Sm–Nd isotopicsystems in the global sedimentary system. Earth andPlanetary Science Letters 168, 79–99.
Wagner, G. A., Gogen, K., Jonckheere, R., Wagner, I. & Woda,C. (2002). Dating of Quaternary volcanoes Komorni Hurka(Kammerbuhl) and Zelezna Hurka (Eisenbuhl), CzechRepublic, by TL, ESR, alpha recoil and fission track
Weinlich, F. H. (2013). Carbon dioxide controlled earthquake dis-tribution pattern in the NW Bohemian swarm earthquake re-gion, western Eger Rift, Czech Republic—gas migration in thecrystalline basement. Geofluids 1–17, doi:10.1111/gfl.12058.
Weinlich, F. H., Brauer, K., Kampf, H., Strauch, G., Tesar, J. &Weise, S. M. (1999). An active subcontinental mantle volatilesystem in the western Eger rift, Central Europe: Gas flux, iso-topic (He, C, and N) and compositional fingerprints.Geochimica et Cosmochimica Acta 63, 3653–3671.
Wilson, M. & Downes, H. (1991). Tertiary–Quaternary exten-sion-related alkaline magmatism in western and centralEurope. Journal of Petrology 32, 811–849.
Wilson, M. & Downes, H. (1992). Mafic alkaline magmatismassociated with the European Cenozoic rift system.Tectonophysics 208, 173–182.
Wones, D. R. & Dodge, F. C. W. (1977). The stability of phlogopitein the presence of quartz and diopside. In: Fraser, D.G.Thermodynamics in Geology. Dordrecht: Springer, pp. 229–247.
Yaxley, G. M., Crawford, A. J. & Green, D. H. (1991). Evidencefor carbonatite metasomatism in spinel peridotite xenolithsfrom western Victoria, Australia. Earth and PlanetaryScience Letters 107, 305–317.
Yaxley, G. M., Green, D. H. & Kamenetsky, V. (1998).Carbonatite metasomatism in the southeastern Australianlithosphere. Journal of Petrology 39, 1917–1930.
Yaxley, G. M., Berry, A. J., Kamenetsky, V. S., Woodland, A. B.& Golovin, A. V. (2012). An oxygen fugacity profile throughthe Siberian Craton—Fe K-edge XANES determinations ofFe3þ/
PFe in garnets in peridotite xenoliths from the
Udachnaya East kimberlite. Lithos 140–141, 142–151.Ziegler, P. A., Schumacher, M. E., Dezes, P., Van Wees, J.-D. &
Cloetingh, S. (2006). Post-Variscan evolution of the litho-sphere in the area of the European Cenozoic Rift System. In:Gee, D. G. & Stephenson, R. A. (eds) European LithosphereDynamics. Geological Society, London, Memoirs 32,97–112.