Zircon U-Pb and trace element constraints on the evolution of the Tonian (829–831 Ma) alkaline plutons within the Mercara Shear Zone, south India

Abstract

The research sheds light on the age, origin, and tectonic environment of two significant alkaline plutons, Sullya and Angadimogar, located in the Mercara Shear Zone in the Southern Granulite Terrain of southern India. The zircon U-Pb dating indicates that the plutons crystallized at 829 ± 3.7 Ma and 831 ± 4.7 Ma, respectively. The zircon geochemistry suggests that Sullya and Angadimogar plutons underwent distinct crystallization processes, with zircons from Angadimogar samples crystallizing at varying temperatures over a prolonged period with limited fO₂ levels and zircons from Sullya samples crystallizing at stable temperatures and variable redox conditions. Most of the zircons from both plutons have trace element characteristics indicating formation in the continental crust. In contrast, some zircons from Sullya have trace elements similar to those found in the oceanic crust. The presence of two distinct types of zircons in Sullya samples indicates that the parental melt of the Sullya pluton consisted of magma from multiple sources. The average estimated temperature for zircon crystallization in Sullya was 691 °C, while the mean temperature in Angadimogar was 802 °C. The research implies that the plutons were emplaced parallel to the shear plane during an extensional regime, reactivating the paleo shears during the late Proterozoic era. The study highlights the importance of using multiple geochemical and geochronological techniques to gain a better understanding of the complex geological evolution of the Precambrian terrains.