Himalayan Geology, Vol. 43 (1B), 2022, pp. 262-280, Printed in India
Geochemistry and 40Ar-39Ar age of mafic dykes of Sor Valley in Pithoragarh, Kumaun Lesser Himalaya, India: Evidence for late Neoproterozoic continental rifting during Rodinia breakup
LAXMAN SINGH1, GAJENDER KUMAR1, RAJEEV UPADHYAY1*, HARSHITA JOSHI2, DEEPAK PANT2
1Department of Geology, Kumaun University, Nainital - 263002, India
2LSMGPG College, Kumaun University, Pithoragarh - 242502, India
*Email (Corresponding author): rajeev_up@yahoo.com
Abstract: The Pithoragarh Mafic Dykes (PMDs) are intruded into the Proterozoic formations of Sor Valley of Kumaun Lesser Himalaya are characterized by sub alkaline nature, positive anomalies for HFSEs, and negative anomalies for LILEs, high Ti contents (up to 2.54 wt.%), and inclined REEs patterns, showing oceanic island basaltic nature. The La/Sm (1.78-2.34) and Sm/Yb (2.09-3.26) ratios coupled with high TiO2 wt.% for PMDs possess a high degree of partial melting of garnet-lherzolite at a deeper level. The 40Ar-39Ar plateau age indicates that PMDs were emplaced at 644.7±2.4 Ma (MSWD=0.14). Petrological and geochemical characteristics suggest that the studied mafic dykes were formed noticeably in different tectonomagmatic environments than other western Lesser Himalayan mafic dykes. Conversely, the La/Ba, La/Nb, and Nb/Yb ratios suggest the geochemical signature of an extensional regime similar to Neoproterozoic (~650 Ma) mafic dykes of Ygntze block, South China. This study suggests that the PMDs were formed in a rift-related tectonic setting and magmatism related to the breakup of the Rodinia supercontinent feeded the northern margin of the Indian subcontinent up to ~650 Ma during the Neoproterozoic Period.
Keywords: Mafic Dykes, western Lesser Himalaya, Neoproterozoic, Rodinia breakup