Rebuttal The Case against the Null Hypothesis of Marsh Jim Miller Department of Geological Sciences Precambrian Research Center University of Minnesota.

RebuttalThe Case against the Null Hypothesis of

Marsh

Jim MillerDepartment of Geological Sciences

Precambrian Research CenterUniversity of Minnesota Duluth

Mineralogical Magazine(1996)

Elements(2006)

Bruce MarshJohns Hopkins U.

Contributions to Mineralogy and Petrology (2013)

Contributions to Mineralogy and Petrology (in press)

With Rais Latypov, 2005, Finland

Marsh’s Arguments against In Situ Crystallization Differentiation

1)Massive, undifferentiated mafic-ultramafic intrusions are common; indeed, they are the rule.

2)The abundance of homogeneous intrusions is due to crystallization from phenocryst –free basaltic magmas that are not able to differentiate in crustal chambers because evolved melts are trapped in solidificaton fronts. (Examples: Sudbury Complex and Ferrar Peneplain Sill).

3)Layered intrusions with pronounced phase and cryptic layering are attributed to the repeated emplacement of batches of magma with phenocrysts in different combinations and with varied chemical compositions (Examples – Hawaiian lava lakes, Ferrar Basement Sill, Palisade Sill)

Postulate 1Massive, undifferentiated mafic-ultramafic

intrusions are common• By Marsh’s definition, differentiated intrusion must have produce a grantitic distillate. Bowen showed that even perfect fractional crystallization will produce a high silica liquid fractionate – and even the, it will only comprise about 5% of the total magma volume.

• Marsh uses whole rock SiO2, MgO, and CaO and indicators of differentiation but ignores other important indicators - phase layering, cryptic layering of solid solution minerals, enrichment in incompatible trace elements and depletion of compatible elements.

• Marsh ignores or reinterprets units of the Sudbury Igneous Complex that clearly indicate internal differentiation - lower mafic norite and upper quartz gabbro, and considers only whole rock MgO rather than the mg# of pyroxene.

Marsh’s evidence of undifferentiated mafic intrusions with late small granite segregations filling delaminated chill in the roof zone

Marsh (1996)

Even the Sudbury Complex shows Cryptic Variation

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Postulate 2Phenocryst –free basaltic magmas are not able to differentiate in crustal chambers because evolved

melts are trapped in solidification fronts

• In mafic intrusions of all sizes, shapes and depths of emplacement, it is clear that these intrusion show systematic differentiation whether as shown dramatically in the closed systems of the Skaergaard and Sonju Lake, or in large thick sequences like Stillwater, Bushveld and the Layered Series at Duluth.

• Many MLI lack an upper border series as would be expected in Marsh’s model of collapsing solidification fronts. Sonju Lake in particular can be modeled by bottom up crystallization differentiation of single evolved tholeiitic magma.

SiO2 47.6TiO2 2.28Al2O3 14.0FeOt 14.7MnO 0.21MgO 8.3CaO 9.4Na2O 2.47K2O 0.55P2O5 0.30Volatiles 0.20Total 100.0mg# 50.2

Sc 34V 192Cr 111Co 75Ni 185Rb 20Sr 233Ba 171Y 20Zr 114Nb 17Hf 3.1La 14.7Ce 33.4Sm 4.1Eu 1.6Tb 0.8Yb 2.1 Lu .32

Bulk Intrusion CompositionBulk Intrusion Composition= Parent Magma= Parent Magma

= moderately evolved olivine tholeiitic basalt= moderately evolved olivine tholeiitic basalt

From Miller and Chandler (1998)and Miller and Ripley (1997)

Liquid Line of DescentLiquid Line of Descent

Calculated by summing composition of rock column above a specific horizon

Fractional Crystallization ModellingCHAOS 2 (NIELSEN, 1990)

Model Parameters : fO2 = -2 log QFM; trapped liquid = 20%

Postulate 3Layered intrusions with pronounced phase and cryptic

layering are attributed to the repeated emplacement of batches of magma with phenocrysts in different

combinations and with varied chemical compositions• How did these crystal slurries of varied composition acquired their variability if not by differentiation in some ficticous magma chamber at depth? It is paradoxical that even in the case of the largest known intrusion of largely basaltic composition, most of the fractional crystallization reflected in the cryptic compositional trends of the layered sequence has to be relegated to conjectural processes that took place in an underlying (and possibly even more voluminous) chamber• How can the random input of varied crystal slurry compositions create a systematic phase stratigraphy commonly observed in both closed and open system intrusions?•Why aren’t porphyritic basalts more common in LIPs hosting many differentiated layered intrusions – e.g. the MCR? And why are they typically dominated by only Pl phenocrysts?

From Latypov (2009)

“An attempt is made at the outset to provide a list of inviolate Magmatic First Principles that are relevant to analyzing most magmatic problems. These involve: initial conditions; critical crystallinity; solidification fronts; transport and emplacementfluxes; phenocrysts, xenocrysts, primocrysts; crystal size;layering and crystal sorting; thermal convection; magmaticprocesses are physical”.

Bruce Marsh, 2013

The High Priest of Magmatology

“It could be argued that regular, cryptically varying series of crystal mushes were successively injected, rather than liquids, which is equivalent to agreeing that layered intrusions existed, but with the unusual reservation that they always lay below the levels of present-day exposures. The regularity of the cryptic variation of many layered intrusions is particularly difficult to explain according to the idea of continuous tapping of a deeper magma reservoir, for it implies that the complete crystallization record of a deep-seated intrusion was transferred, stage by stage, to a higher level intrusion”.

Lawrence Wager and Malcolm Brown (1968, p. 546)

Wager and Brown actually considered the Sequential Slurry Model, but found it wanting because of chemical evidence and too much

coincidence.

Other Issues with Marsh’s (2013) ClaimsThe views of Wager and Brown (1968)

Marsh (2013, p. 669) attributes the improbable scenario of instantaneous emplacement of crystal-free magma for the origin of the Skaergaard, Stillwater and Bushveld intrusions to Wager and Brown.

Although they ascribed emplacement of the Skaergaard to be a geologically rapid event of one magma batch, in the case of the Bushveld intrusion, they state that it was “unlikely that the act of magma injection was a single incident” (p. 404) and they encompassed the idea of “stages when fresh supplies of basaltic magma entered the chamber from below”

Other Issues with Marsh’s (2013) ClaimsMineral-Melt Reactions

Marsh (2013) makes the curious statement (on p. 685) that “For magma to differentiate by fractional crystallization crystals must be available to react with the melt, the ultimate origin of the crystals is almost immaterial.”This is diametrically at odds with conventional wisdom: fractional crystallization is a consequence of the physical and/or kinetic isolation of crystals from their parent melt so that such a reaction is inhibited

Other Issues with Marsh’s (2013) ClaimsMisinterpretation of Bowen’s Reaction Series

Marsh’s view (on p. 666) that Bowen’s “reaction series became synonymous with fractional crystallization”. As Bowen (1928) was at pains to point out, the portrayal of “reaction series” incorporated into Figure 9 of Marsh (2013) principally expresses the relationship between mineral phases and generalized crystallization temperature. Mineral-melt reactions are in fact part and parcel of equilibrium crystallization whereas in perfect fractional crystallization they are prohibited.

Other Issues with Marsh’s (2013) ClaimsSize of Crystals in Sills and Layered Intrusions

Marsh (1996) points out that many mafic sills contain dense basal accumulations of large (2-10 mm) olivine or orthopyroxene phenocrysts and suggest that the size of these crystals alone preclude them from having grown in situ. In his new paper, Marsh (2013) makes the additional claim that “The crystals in Skaergaard…..are too large to have grown in a body of this size”. In particular, Marsh (2013) proposes a simple model of kinetic crystal growth that does not take into account the role of equilibration (coarsening) that is so important in the postcumulus textural development of most plutonic rocks (Higgins 2011).

Other Issues with Marsh’s (2013) ClaimsSize Distribution of Crystals in Sills and MLI

Skaergaard Intrusion and Palisades Sill both have upper border sequences that are compositionally mirror images of their extensively differentiated, and significantly thicker, lower sequences. In both the Skaergaard (Naslund 1984) and the Palisades (Hristov and Naslund 1994), rocks in the upper border sequences are 2 to 3 times coarser-grained than the time-equivalent lower sequences. If in situ crystallization is disallowed, then the formation of these two intrusions by multiple injections of crystal slurries must have involved sinking of the smaller crystals and floating of the larger crystals, which is exactly the opposite of what would be predicted by the crystallization front capture model of Marsh (2013).

Other Issues with Marsh’s (2013) ClaimsKilauea Lava Lake

Marsh (2013) presents the Kilauea Iki lava lake as an ‘end-member’ example of differentiation by simple accumulation of crystals transported in the lava. Recent research suggests, however, that filling and solidification of the lake may be complex (Vinet and Higgins 2011). Olivine CSDs are almost uniform throughout the lake and show no significant variation in slope that would indicate that settling has occurred. Furthermore, a detailed inventory of the zoning and deformation of olivine crystals suggests that the lake was partly filled from the base and that bulk compositional variations may be a relic of this process (Vinet and Higgins 2011).

Other Issues with Marsh’s (2013) ClaimsEvidence for In Situ Fractional Crystallization

Marsh (2013) presents the Kilauea Iki lava lake as an ‘end-member’ example of differentiation by simple accumulation of crystals transported in the lava. Recent research suggests, however, that filling and solidification of the lake may be complex (Vinet and Higgins 2011). Olivine CSDs are almost uniform throughout the lake and show no significant variation in slope that would indicate that settling has occurred. Furthermore, a detailed inventory of the zoning and deformation of olivine crystals suggests that the lake was partly filled from the base and that bulk compositional variations may be a relic of this process (Vinet and Higgins 2011).