An Overview of Geochemical Significance of Cretaceous Mafic Dykes in and around Nongchram Fault Zone of Shillong Plateau, NE India: Implications for Genetic Link to Kerguelen Plume

Abstract

The present study highlights the geochemical and petrological signatures of a group of Early Cretaceous mafic dykes from Shillong plateau of NE India. These medium to fine grained, melanocratic dykes are emplaced in the Precambrian Gneissic Basement Complex in the western part of the Shillong plateau and are directionally parallel to the N-S trending deep-seated Nongchram fault. The whole rock geochemistry suggests that these dykes are genetically related to each other and probably derived from the same parental magma. The wide range of major and trace element composition represented by these mid to high Ti basalts suggest a number of differentiation process involving partial melting, fractional crystallization and crustal contamination probably by the lower continental crust. Thegeochemical scenario in terms of enrichment in LREE relative to HREE and high field strength element (HFSE), systematic Nb anomalies, moderate MREE to HREE fractionation suggests different depths of melting of slightly enriched mantle source that point to a mantle plume source showing EM1 signature. The very good correlation of REE behaviour and other trace element behaviour of the studied dykes with Kerguelen plume derived Rajmahal Group II basalt, Sylhet volcanics and some ODP (Ocean Drilling project) sites from Kerguelen basalts implicate a genetic link between the studied dykes and the Kerguelen mantle plume.