R8: Metamorphic rocks and tectonics

[R8P-15] Unraveling the Link Between Deformation, Metamorphism, and Fluid Flow in the Archean Dharwar Craton, Southern India

*Sreehari LAKSHMANAN¹, Kiran Sasidharan², Satish-Kumar Madusoodhan², Tsuyoshi Toyoshima² (1. Shimane Uni., 2. Niigata Uni.)

Keywords:Dharwar Craton, Tectonics, Metamorphism, Deformation

The Dharwar Craton (DC) is the largest Archean(3500 to 2500 Ma) craton in the Indian Shield. The DC is divided into three main regions: the Western Dharwar Craton (WDC), the Central Dharwar Craton (CDC), and the Eastern Dharwar Craton (EDC). In this presentation, we aim to discuss the metamorphic history of the WDC and its interplay with deformation and fluid flow. We will present detailed petrological data from the eastern part of the WDC, specifically focusing on the southern section of the Chitradurga Schist Belt (CSB). The CSB consists of various rock formations, including the Sargur Group and Dharwar Supergroup. Through our detailed structural analysis, we have identified five major deformation events in the WDC. Among these, D2 (NNW-SSE trending reverse faults and upright folds) and D3 (strike-slip sinistral shear) are the regional-scale deformation events. Due to the limited availability of mineral assemblages suitable for geothermometry, we have employed carbonaceous material thermometry (CM) in metapelitic rocks from each formation. We have selected 15-samples containing CM from different Groups. Using Raman spectroscopy, we have identified differences in metamorphic temperatures among the Groups. The Bababudan and Chitradurga Groups exhibit metamorphic temperatures ranging from 500°–550°C, whereas the Hiriyur and Sargur Groups exhibit temperatures between 450°– 400°C. We interpret these differences in metamorphic temperatures as being associated with the spatial relation to the D₃ strike-slip shear zones within the study area. The fluid flow along these shear zones may have influenced the properties of the carbonaceous material, thereby affecting the observed temperatures. Additionally, based on the metamorphic mineral assemblage, the presence of Chlorite+Muscovite association is prominent in the D₃ shear zones, indicating fluid flow processes during the D₃ deformation. Moreover, microscopic observations reveal that Garnet-Biotite assemblages in the D2 shear zone are cross-cut by Fe-rich fluid veins, suggesting fluid flow processes following the D2 deformation. We interpret these fluid flow associated with the D3 deformation, which is directly connected to the regional-scale collision and associated strike-slip deformation processes that occurred throughout the entire DC.