1. Magma assisted shear-zone nucleation and transition from magmatic to solid-state deformation in large granitic provinces: A case of ~2.5 Ga old voluminous granitoids of southern Bundelkhand Craton, India.
- Author
-
Kumar, Abhinav, Bind, Geeta, and Hazra, Dipak
- Subjects
- *
DEFORMATIONS (Mechanics) , *MAGMAS , *RHEOLOGY , *GRANITE , *SHEAR zones , *URANIUM-lead dating , *HEMORHEOLOGY , *ROCK deformation - Abstract
The transition from magmatic to solid-state deformation in granitic rocks is observed either in cases of shear-zone-controlled magma emplacement or in cases of magma-assisted shear-zone nucleation. In the latter case, pre-emplaced granitoid magmas that are later subjected to a dynamic regime with decreasing temperature accommodate stress that causes strain localization. Shear zones in this case are generally restricted to the contact zone between wall rock and granitoid magma, as it represents large viscosity discontinuities. In large granitic provinces (LGPs), however, rheological properties are mainly driven by the changes in physical parameters of granitic magmas, and thus, shear-zone nucleation in magmatic or sub-magmatic conditions cannot be attributed to the viscosity discontinuities caused by the presence of wall rock. Rather, in LGPs, it is only dependent on the rheological discontinuities within the granitic magmas, and thus, a detailed knowledge of the transition from magmatic to solid-state deformation can give important insights into the dynamic history of granitoid magmas in LGPs. The ~2.5 Ga old, voluminous granitoids of Bundelkhand Craton have been affected by multiple shear systems. Among these, the NE–SW and E–W shear systems are major systems that affected the granitoid microstructures. The NE–SW shear system transects the craton as multiple small- and large-scale shear zones, while the E–W shear system is mainly present in the central part of the Bundelkhand Craton. A petrographic study of a ~25 km long, NE–SW trending Baldeogarh shear zone and granite microstructures in associated areas show important magmatic and solid-state deformation features. Overprinting of solid-state deformation over sub-magmatic deformation confirms the progression of deformation with decreasing temperature. Contrary to this, E–W trending microstructures are primarily magmatic to sub-magmatic with rare small-scale solid-state deformation. This indicates that the E–W shear system is older in southern Bundelkhand and was followed by the NE–SW shear system in magmatic conditions. Therefore, the presence of a transition from magmatic to solid-state deformation along the NE–SW trending shear zone indicates that bulk cooling of the granitoid took place while the NE–SW shear system was active. Research Highlights: Transition from magmatic to solid-state deformation in Large Granitic Provinces. Magmatic to solid-state deformation along NE-SW shear zone. Overprinting textures of transition from sub-magmatic to solid-state deformation. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF