Permian komatiites and associated basalts from the marine sediments of Chhongtash Formation, southeast Karakoram, Ladakh, India |
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| Authors: | D Rameshwar Rao Hakim Rai |
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| Institution: | (1) Wadia Institute of Himalayan Geology, Dehradun, Uttaranchal, India |
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| Abstract: | Summary The Karakoram micro-plate is the southern most sector of the Central Asian micro-plate mosaic which was separated by a narrow
rift basin. A major rifting phase started during Permian time, which lead to drift of not only Karakoram but of the entire
Eurasian (Asian) Plate from Gondwana land. This was at a time when a prominent sequence of black argillites occupied most
part of the Karakoram Tethys basin. The geodynamic setting for this sequence may be interpreted as the evolution of a passive
margin affected by extensional tectonics. The extensional activity is evident from the extrusion of basalts and komatiitic
rocks in the region.
In this paper the geochemical relations between komatiites and basalts of the Chhongtash, southeast Karakoram are investigated.
The basaltic and komatiitic (ultrabasic) flows are petrologically and geochemically distinct, yet they display a close spatial
and temporal association, and they are related to each other through olivine and clinopyroxene fractionation. The chemical
characteristics of the ultrabasic to basic magmatism in the region is consistent with formation above a mantle plume that
impinged on the continental lithosphere. Hence, a model of partial melting in a mantle plume and fractional crystallization
in a deep-seated magma chamber is envisaged to explain the evolution of these volcanic rocks. The komatiite melts are interpreted
to have been derived by high degree partial melting of mantle plumes in the tail region, while the basalts were interpreted
to be the result of interaction of source plume with cool mantle through which the plume head passed. This study is the first
of its kind, to suggest a rift related nature in the Chhongtash, southeast Karakoram, that represent the initial stage of
Mesozoic rifting along the southern margin of Eurasia when Gondwana started to drift away from Eurasia. |
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