Evidences Of Active Continental Arc Setting From Lesser And Higher Himalayan Granitoids, Bhutan Himalaya | 12145
Journal of Earth Science & Climatic Change
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here is a lot of hue and cry on the origin and provenance characteristics of Lesser Himalaya and Higher Himalayan rocks,
earlier it was assumed that they are passive margin sediments deposited on Indian oceanic front but in the last 3 decades,
geochemical and isotopic analysis had changed the scenario, which indicates active continental setting instead of passive margin
sediments means the geochemical study has great significance to work out recent active tectonic of Himalaya which is poorly
understood. Granitoids and granitic gneisses have been distinguished in relation to understand the heterogeneity of Himalayan
Orogenesis. My work is focused on geochemical and isotopic (Sm-Nd) analysis of Lesser Himalaya (Shumar Formation) and
Higher Himalayan granitoids of Bhutan Himalaya from the Kuru Chu and Mangde Chu catchments, these granitoids and
orthogneisses supports active continental setting theory.
On ASI plot both shows S-Type tectonic setting, and plots like TiO
vs. Zr, Rb/Sr vs. Sr, FeOT against TiO
versus Nb/Y represents that they have two different sources which are deposited on Indian oceanic front and are influenced by
metamorphism, deformation, thrusting and upliftment. On pearce tectonic plots these rocks fall within the range of volcanic arc
granite and orogenic granite, to discriminate the characteristics of Lesser Himalayan and Higher Himalayan granitoids Rb/Zr vs.
Nb and RB/Zr vs. Nb plots were made and they clearly represent that Lesser Himalayan sequences belongs to active continental
margin whereas Higher Himalayan sequences has some characteristics of active continental margin with some pre-arc and post-
arc sources. Sm-Nd isotopic data also suggest that kyanite rich paragneisses of HHC represents the characteristics of Indian
passive margin sediments and orthogneisses of Lesser and Higher Himalaya represents signatures of Active continental margin in
which the Lesser Himalaya gneisses has older arc source and HHC has younger sources. As a result of this work it has been seen
that geochemical and isotopic signature of Shumar orthogneisses of Lesser Himalaya has a definite range of T-Model age which
indicates that it has a single source, whereas granitoids of HHC shows a wide range in their geochemical and isotopic signature,
indicates that it has multiple sources during deposition and was tectonically consolidated with the northern margin of India,
placing it structurally above the Lesser Himalayan Sequence, and later on it has metamorphosed and intermixed with passive
margin sequences of northern margin of Indian Sub-continents and goes up to granulite facies of metamorphism.
Rajesh Pandey is a Ph.D. student in Indian Institute of Technology Roorkee, India.
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