Full length articlePre-Himalayan tectono-magmatic imprints in the Darjeeling-Sikkim Himalaya (DSH) constrained by 40Ar/39Ar dating of muscovite

- 40Ar/39Ar age dates record pre-collisional tectonism in the Lesser Himalaya.
- Pre-Himalayan convergent belt is reconstructed along the northern Indian craton.
- Lesser Himalayan magmatism is used as a proxy to the ∼1850 Ma subduction system.
- The Daling mobile belt represents the active margin during Columbia supercontinent.

The Lower Lesser Himalayan Sequence (L-LHS) in Darjeeling-Sikkim Himalaya (DSH) displays intensely deformed, low-grade meta-sedimentary rocks, frequently intervened by granite intrusives of varied scales. The principal motivation of our present study is to constrain the timing of this granitic event. Using 40Ar/39Ar geochronology, we dated muscovite from pegmatites emplaced along the earliest fabric in the low grade Daling phyllite, and obtained ∼1850 Ma Ar-Ar muscovite cooling age, which is broadly coeval with crystallization ages of Lingtse granite protolith (e.g., 1800-1850 Ma U-Pb zircon ages) reported from the L-LHS. We present here field observations to show the imprints (tectonic fabrics) of multiple ductile deformation episodes in the LHS terrain. The earliest penetrative fabric, axial planar to N-S trending reclined folds, suggest a regional tectonic event in the DSH prior to the active phase of Indo-Asia collision. Based on the age of granitic bodies and their structural correlation with the earliest fabric, we propose that the L-LHS as a distinct convergent tectono-magmatic belt, delineating the northern margin of Indian craton in the framework of the ∼1850 Ma Columbia supercontinent assembly.

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