Origin of oceanic plagiogranite in the Nidar ophiolitic sequence of eastern Ladakh, India

Occurrence of high-SiO2, low K2O leucocratic rocks, the 'oceanic plagiogranite' of Coleman and Peterman, within the basic and ultrabasic rocks of the ophiolites and modern oceanic settings, is of particular interest because of their extreme composition and controversial origin. Ophiolitic...

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Bibliographic Details
Published in:Current science (Bangalore) 2004-10, Vol.87 (7), p.999-1005
Main Authors: Rao, D. Rameshwar, Rai, Hakim, Kumar, J. Senthil
Format: Article
Language:English
Subjects:
Crystallization
Gabbro
Geochemistry
Geology
Liquids
Magma
Minerals
Ocean currents
Plagioclase
RESEARCH COMMUNICATIONS
Rocks
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Summary:Occurrence of high-SiO2, low K2O leucocratic rocks, the 'oceanic plagiogranite' of Coleman and Peterman, within the basic and ultrabasic rocks of the ophiolites and modern oceanic settings, is of particular interest because of their extreme composition and controversial origin. Ophiolitic sequences are considered incomplete without these rocks. However, these rocks are not present in all the known ophiolite sequences in the world. The present study reports the occurrence of plagiogranite to the north of Kyun Tso, within the Nidar ophiolitic sequence of eastern Ladakh. Plagiogranites occur as intrusives within the gabbro, in the northern part of the ophiolitic sequence. Chemically, they are classified into tonalite and trondhjemite. They show nearly flat REE pattern and fractionation relation that are comparable with the host gabbro. The origin of these rocks is explained by fractional crystallization aided by filter-pressing processes of sub-alkaline tholeiitic magmas.
ISSN:0011-3891