Proterozoic Subduction-Related and Continental Rift-Zone Mafic Magmas from the Eastern Ghats Belt, SE India: Geochemical Characteristics and Mantle Sources

Understanding the origin and growth of continental crust is a fundamental problem in geological sciences. Two distinct ways in which the continental crust grows include horizontal (subduction) and vertical (plume/extension) accretions. As the mantle reservoirs in these two tectonic settings are generated and/or modified by contrasting processes, the erupted melts offer clues on the nature of these divergent mantle sources. Trace element geochemistry is a robust tool to quantitatively model the mantle sources, melting mechanisms and relative roles of mantle and crust in the petrogenesis of magmatic rocks, which ultimately lead us to unravel the origin of continental crust.

The present study portrays growth of the continental crust in the Proterozoic Eastern Ghats Belt, SE India. Mafic magmas within the Palaeoproterozoic Kondapalli-Kandra region illustrate subductionrelated island arc basalt-type geochemical signatures whereas alkali basaltic magmas in the Mesoproterozoic Prakasam continental rift-zone display ocean island basalt-type characteristics. Calculated mantle sources for subduction-zone and rift-related magmas display distinctly different geochemical traits. Mesoproterozoic gabbroic magmas in the Prakasam rift-zone exhibit geochemical signatures akin to the subduction-related mafic melts. This dichotomy of continental crust produced by intra-plate processes exhibiting plate-margin signatures advocates that we possibly have overestimated the proportion of continental crust generated above subduction zones.