2:30 PM - 2:45 PM
[SMP25-09] Tectonometamorphic evolution of shear zones in the Western Dharwar craton, southern India and their regional-scale implications
Keywords:Dharwar Craton, Western Dharwar Craton, Tectonics, Shear Zone, Shear localization
The Dharwar Craton (DC, ~3500–2500 Ma) is one of the oldest cratons in the world and largest preserved craton in the Indian peninsula. The DC is traditionally divided into Western and Eastern subdivisions and respectively coined the names as the Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC). The EDC in recent literatures has another subdivision, the Central Dharwar Craton (CDC). A strike-slip sinistral shear zone, Gadag-Mandya Shear Zones (GMSZ) separates WDC and CDC and considered as a terrane boundary or suture zone in multiple literatures. But the details of this deformation zone are poorly explored. This study will be examining the structural evolution and associated metamorphic imprints of deformed rocks, especially in the eastern margin of the WDC.
Our detailed field and structural observation point out that the shear zones developed in the study area are part of three deformation stages: D2, D3, and D4. Shear zones associated with D2 deformations are reverse faults especially visible in the contacts of stratigraphic units. These reverse faults are showing east-to-the top motion sense.
Shear zones associated with D3 is the prominent deformation phase and overprinted most of the D2 structures and shows a strike-slip sinistral sense of motion. The GMSZ, one of the major D3 shear zone is examined detail. Most of the previous literatures considered GMSZ as a single, wide, N–S to NW–SE striking sinistral shear zone. But detailed examinations between Mandya in the south to Chitradurga in the north (160*30km) reveals some key information about the nature of the deformation in the GMSZ. Our direct field evidence shows that the GMSZ has multiple narrow shear zones rather than a single wide shear zones. Most of these shear zones have maximum width of ~10m. Width reaches a kilometer scale in the southern part near Mandya, and most of these shear zones are localized near the lithological contacts. Moreover, the associated plutonic (granitic) intrusions show syn-plutonic deformational structure. It is important to note the kinematic indicators from few locations shows sinistral transpression indicators also. Our study provides some important clues about the nature of GMSZ, based on the field evidence GMSZ cannot be considered as a single terrane boundary, in fact shear zones in the so called GMSZ is similar to numerous other shear zones observable throughout the WDC. So, the entire WDC should be consider as a deformation zone with many narrow shear zones and folded rock units. D4 deformation overprinting is dextral strike-slip movements are also preserved in some locations.
Metamorphic relations from the study area generally shows upper greenschist facies to low-grade amphibolite facies deformation condition. Garnet-biotite quartzite from the GMSZ also shows same deformation condition. Probably this deformation condition can be seen in the entire WDC. Based on the structural and metamorphic relations the determination of a clear cut terrane boundary in the WDC is difficult, the entire WDC is a wide deformation zone with some important regional-scale implications.
Our detailed field and structural observation point out that the shear zones developed in the study area are part of three deformation stages: D2, D3, and D4. Shear zones associated with D2 deformations are reverse faults especially visible in the contacts of stratigraphic units. These reverse faults are showing east-to-the top motion sense.
Shear zones associated with D3 is the prominent deformation phase and overprinted most of the D2 structures and shows a strike-slip sinistral sense of motion. The GMSZ, one of the major D3 shear zone is examined detail. Most of the previous literatures considered GMSZ as a single, wide, N–S to NW–SE striking sinistral shear zone. But detailed examinations between Mandya in the south to Chitradurga in the north (160*30km) reveals some key information about the nature of the deformation in the GMSZ. Our direct field evidence shows that the GMSZ has multiple narrow shear zones rather than a single wide shear zones. Most of these shear zones have maximum width of ~10m. Width reaches a kilometer scale in the southern part near Mandya, and most of these shear zones are localized near the lithological contacts. Moreover, the associated plutonic (granitic) intrusions show syn-plutonic deformational structure. It is important to note the kinematic indicators from few locations shows sinistral transpression indicators also. Our study provides some important clues about the nature of GMSZ, based on the field evidence GMSZ cannot be considered as a single terrane boundary, in fact shear zones in the so called GMSZ is similar to numerous other shear zones observable throughout the WDC. So, the entire WDC should be consider as a deformation zone with many narrow shear zones and folded rock units. D4 deformation overprinting is dextral strike-slip movements are also preserved in some locations.
Metamorphic relations from the study area generally shows upper greenschist facies to low-grade amphibolite facies deformation condition. Garnet-biotite quartzite from the GMSZ also shows same deformation condition. Probably this deformation condition can be seen in the entire WDC. Based on the structural and metamorphic relations the determination of a clear cut terrane boundary in the WDC is difficult, the entire WDC is a wide deformation zone with some important regional-scale implications.