Elucidation of Provenance, Palaeoclimate and Tectonic Setting of the Gondwana Sandstones of Arunachal Himalayas: A Petrographic Approach
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The Permian Gondwana sequence of Arunachal Lesser Himalayas provides an excellent setup to study the provenance and associated tectonics during deposition due to its typical positioning at the margin of the Gondwanic Indian continent. Petrographic character of these Gondwana sandstones exposed in parts of East Siang and West Siang districts of Arunachal Pradesh and inferences on source rocks and tectonic setting are presented in this paper.
The modal analysis of the sandstones reveals that quartz is the dominant detrital framework grain with 58.1–78.30%, feldspar percentage varies between 0.5 to 4.7%, the percentage of rock fragments ranges from 1.0 to 12.6%, mica content varies between 1.3–14.0%, matrix percentage varies between 6.8–15% and cement constitutes 3.1–23.5%. The sandstones are classified as sublithic arenite and quartz arenite. The study suggests quartzose recycled orogen as well as transitional recycled source and indicates towards a low grade metamorphic source for the sediments. It is inferred that these recycled sandstones were originally having its source in the cratonic blocks and sedimentation in this Gondwana basin evolved through multiferous interplay of deformation due to thrust loading, changes in sea level resulting in progressive compaction and a humid climate.
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