GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGY Lecture 19 Anorthosites and the Anorthosite Problem March 11, 2009
Mar 18, 2016
GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGY
Lecture 19Anorthositesand the Anorthosite Problem
March 11, 2009
GLOBAL OCCURRENCES OF ANORTHOSITE
1. Archean anorthosite 2. Proterozoic “massif-type”
anorthosite plutons 3. Centimeter-to-100m thick
layers in layered mafic intrusions 4. Thin cumulate layers in
ophiolites/oceanic crust 5. Small inclusions in other rock
types (xenoliths and cognate inclusions)
6. Lunar highland anorthosites (after Ashwal, 1993)
Streikeisen (1991)
ARCHEAN ANORTHOSITES• Hi-Ca plagioclase (An >80)• Equant crystal habit• Pl megacrysts in a gabbroic matrix• Sill-like bodies• Associated with gabbroic intrusions in greenstone belts• Commonly metamorphosed and deformed
MASSIF-TYPE ANORTHOSITES Proterozoic age (1.7-0.9
Ga) Intermediate Pl
composition (An 65-40) Tabular crystal habit Pl-adcumulates common
(minor interstitial mafics) Large pluton-scale bodies Anorogenic setting Associated with K-/Fe-rich
gabbros (jonuites) and “dry” felsic rocks (charnokites)
Grenville Province
ANORTHOSITE LAYERS/INCLUSIONS IN MAFIC LAYERED INTRUSIONS
Skaergaard IntrusionBushveld Complex
Stillwater Complex
ANORTHOSITE INCLUSIONS OF THE BEAVER BAY COMPLEX
•90-100% Plagioclase•An 70-90•Mafic phases – Ol, Opx•Single grains to 500m block•Isotopes indicate older crustal
component•Enclosing diabase NOT chilled
against inclusions
BEAVER RIVER DIABASEHOST OF ANORTHOSITE INCLUSIONS
Carlton Peak
Lutsen
Tofte
SplitRock
Silver Bay
Leveaux Porphyry
troctolitic anorthosite
olivine leucogabbro
poikilitic olivine anorthosite
gabbroic anorthosite
olivine-oxide leucogabbro
ANORTHOSITIC SERIES OF THE DULUTH COMPLEX
mTA (mPpO)
TA (cPPOc)
An (mPP)
GA (cPpcf)
TA(PpO)
pOGA(PPocf)
““An Igneous Breccia”An Igneous Breccia”R. Taylor, 1964
Summary of Lithologic and Structural Relationships of Anorthositic Series rocks in the Snowbank Lake Quadrangle
Weiblen and Morey (1980) Model for the formation of the Weiblen and Morey (1980) Model for the formation of the Anorthositic and Layered (Troctolitic) SeriesAnorthositic and Layered (Troctolitic) Series