The Turkei anorthosite complex revisited |
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Authors: | A K Maji A Bhattacharya M Raith |
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Institution: | (1) Operations Kerala, Geological Survey of India, 695 014 Thiruvananthapuram, India;(2) Department of Geology and Geophysics, Indian Institute of Technology, 721 302 Kharagpur, India;(3) Mineralogisch-Petrologisches Institut der Universitat Bonn, Poppeisdorfer Schloss, 531 15 Bonn, Germany |
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Abstract: | Geological investigation in recent years reveals that the anorthosite-leuconorite massif (81 sq km) is much larger than known
from previous studies. The massif is bordered by a suite of garnetiferous felsic rocks comprising quartz monzonite gneiss,
granite gneiss and megacrystic K-feldspar-bearing granite. Ferrodiorites, hitherto unknown from this area, occur as veins
at the massif-felsic suite interface, and as rare apophyses within leuconorites at the massif margin. The massif and the bordering
felsic rocks were presumably emplaced during the earliest of the three phases of folding documented by the metasedimentary
gneisses that host the massif.
The petrographic and geochemical characteristics suggest that the low-K anorthosite-leuconoriteferrodiorite suite does not
share a common parentage with the bordering high-K felsic intrusives. The anorthosites and leuconorites were derived by polybaric
fractionation of mantle-derived melts. The ferrodiorites are anorthosite residual melts that were not entirely segregated
from the host solids. By contrast, the granite gneisses and granites originated by incongruent melting of crustal rocks. The
chemical differences between quartz monzonite and granite gneisses point to their derivation from different crustal precursors. |
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Keywords: | Turkei (Orissa) massif anorthosite field setting petrography geochemistry |
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