Geological appraisal of Ladakh and Tirit granitoids in the Indus- Shyok Suture Zones of northwest Himalaya,India |
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| Authors: | Santosh Kumar Sita Bora Umesh K Sharma |
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| Abstract: | New field observations on granitoids and associated lithounits in some parts of Indus-Shyok Suture Zones have been documented in order to re-establish the geological relationships between various volcano-plutonic magmatic lithounits. Careful examination of outcrops and contact relationships between the various lithounits have pin-pointed the sequence of geological events. Field features of granitoids exposed along Leh-Saboo-Khardung_La suggest multiple pulses of mafic-felsic magma interactions (mingling to mixing) with almost 25% of the mafic to hybrid magma input in the evolution of the eastern part of Ladakh batholith. Along Khardung_La-Shyok-Diskit, thick sequence of volcanic lithounits is exposed, which dominantly consist of massive basaltic andesite, porphyritic andesite, dacite and rhyolite forming Khardung Formation. On the other hand Shyok Formation, dipping opposite to the Khardung Formation, composed predominantly of meta-sedimentary lithounits and subordinate amount of volcanic materials at present exposed level. Spectacular intrusive contacts of Ladakh granitoids with metavolcanics and meta-sedimentary country rocks of Shyok Formation near Diskit can be observed, which are manifested by ubiquitous xenoliths near the marginal parts. Although the nature of granitoid melt invasion into country-rocks was relatively winty, granitoid melt has produced leucogranite-pegmatite system because of devolatization and decompression effects. Frequent xenoliths of porphyritic andesite and dacite roof pendants are being reported in Tirit granitoids, which strongly suggest sub-volcanic emplacement of granitoid melt, extensive assimilation and roof collapse of overlying volcanic materials. It is more likely that the xenoliths hosted in Tirit granitoids belong to Shyok volcanics. It is suggested that multiple pulses of coeval mafic and felsic magmatism occurred extensively and emplaced at differential crustal levels. |
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