geol 2312 igneous and metamorphic petrology

Download Geol 2312  Igneous and Metamorphic Petrology

Post on 18-Mar-2016

55 views

Category:

Documents

4 download

Embed Size (px)

DESCRIPTION

Geol 2312 Igneous and Metamorphic Petrology. Lecture 19 Anorthosites and 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 - PowerPoint PPT Presentation

TRANSCRIPT

  • GEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGYLecture 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 INTRUSIONSSkaergaard IntrusionBushveld ComplexStillwater Complex

  • ANORTHOSITIC ROCKS OF THE DULUTH COMPLEX AND RELATED ROCKS OF NE MNAnorthositic Rockbearing Units

  • ANORTHOSITE INCLUSIONS OF THE BEAVER BAY COMPLEX90-100% PlagioclaseAn 70-90Mafic phases Ol, OpxSingle grains to 500m blockIsotopes indicate older crustal componentEnclosing diabase NOT chilled against inclusions

  • Norwood (1852)Winchell (1899)Lawson (1893)LAKE SUPERIOR ANORTHOSITESA 150 YEAR PUZZLE

  • BEAVER RIVER DIABASEHOST OF ANORTHOSITE INCLUSIONSCarlton PeakLutsenTofteSplitRockSilver BayLeveaux Porphyry

  • PORPHYRITIC FE-DIORITE SILLSLEVEAUX PORPHYRY & CABIN CREEK PORPHYRITIC DIORITE

  • troctolitic anorthositeolivine leucogabbropoikilitic olivine anorthositegabbroic anorthositeolivine-oxide leucogabbro ANORTHOSITIC SERIES OF THE DULUTH COMPLEX

  • mTA (mPpO)TA (cPPOc)An (mPP)GA (cPpcf)TA(PpO)pOGA(PPocf)An Igneous BrecciaR. Taylor, 1964

  • Well developed, but erratic foliation

  • Summary of Lithologic and Structural Relationships of Anorthositic Series rocks in the Snowbank Lake Quadrangle

  • Fo-An Relationships

  • Plagioclase Zonation PatternsHi-PLo-PComplex Patterns

    Outer jump in An Decompression?

  • MODELS OF ANORTHOSITE PETROGENESIS

  • Weiblen and Morey (1980) Model for the formation of the Anorthositic and Layered (Troctolitic) Series

  • Major Problem:

    No Evidence for Significant Upper Crustal Ultramafic Rocks

  • AS Parent Magma =Plagioclase Crystal Mush

  • GEOCHRONOLOGY OF MCR INTRUSIONSANORTHOSITIC SERIES LAYERED SERIES

  • GENERAL MODEL OF ANORTHOSITE PETROGENESISASHWAL (1993)

    ************************

Recommended

View more >