A non-arc tectonic setting for the evolution of Archean gabbro anorthosite Complexes: Evidence from the Singhbhum Craton, eastern India

Understanding the petrogenetic evolution of Archean gabbroic cumulates provides a window to the mantle geodynamics operated in the early Earth. Gabbroic cumulates are associated with various tectonic settings including convergent plate boundaries, mantle plumes, mid-ocean ridges, anorogenic, post-orogenic, continental rift settings and oceanic plateaus. The Mesoarchean Mayurbhanj Gabbro Anorthosite Complex (GAC) is a well-preserved mafic body situated along the eastern margin of the craton along with concomitant anorogenic Mayurbhanj granite. These rocks are devoid of deformational structures and/or mineral recrystallization. Based on their mineralogical characteristics, GAC rocks are mainly grouped into gabbronorite, leucogabbronorite, leucogabbro and gabbro. The minimal abundance of magmatic amphibole and the variation in the anorthite content rules out the role of a hydrous mantle source in the evolution of these rocks. The studied samples display tholeiitic trend transitioning to calc-alkaline field, major and trace element data indicates the fractional crystallization of olivine and pyroxene. The trace element systematics of the Mayurbhanj GAC show LILE enrichment over HFSE depletion and the geochemical signatures suggest that parental magmas of the Mayurbhanj GAC originated from a heterogeneous depleted mantle source, which has undergone assimilation by a Paleoarchean felsic crust. We argue that the ‘arc-like’ geochemical signatures displayed by these rocks resulted from crustal contamination and may not be due to subduction origin.

(La/Sm)CN vs (Gd/Yb)CN diagram as a proxy for lithospheric contribution and/or degree of partial melting vs depth of melting.

Citation: K. Rasheed D. Srinivasa Sarma, Ajay Dev Asokan, J.K. Dash, Rajneesh Bhutani, 2021. Precambrian Research 363, 106250, https://doi.org/10.1016/j.precamres.2021.106250 external link