Presentation-1 (Time: 12:30 PM-1:00 PM)

Speaker: Mr. Joyjit Dey 

 Affiliation: School of Earth and Environment (SEE), Institute of Geophysics and Tectonics (IGT), University of Leeds, UK

 Title of the talk: Identifying porous melt flow in the crust

Abstract: Partial melt extraction from lower crustal rocks and its transport to higher crustal levels are fundamental processes responsible for the differentiation of the crust. The presence of melt weakens the rock and controls orogenic deformation-crustal exhumations. Hence, understanding melt pathways help to discern crustal differentiation processes and is crucial to evaluating their effects on the rheology and physicochemical responses of a melt-bearing system. However, ‘how melt transfers through the crust’ still needs to be properly understood as the mechanism of melt movement through the viscous mid-low crust is highly debated. We document a case study where two heterogeneous structural domains are distinguished in the lower crust diorite gneiss, Akia terrane, SW Greenland. Mineralogy, mineral chemistry, melt volume%, and microstructures are studied using field, image analysis, and microanalytical methods. Our observation implies that an external melt influx, aided by deformation and regulated by a permeable grain boundary network, induces syn-melt strain partitioning in the crust and forms repetitive low-strain-high strain zones. In order to identify the grain boundary melt network, we also utilize electron backscattered diffraction (EBSD) and weighted burgers vector (WBV) analysis and document the microstructural features observed within grains of quartz crystallized from a silicate melt in different geotectonic scenarios. 

Presentation-2 (Time: 1:00PM-1:30PM)

Speaker: Dr. Sreyashi Bhowmick

Affiliation: GSU, ISI Kolkata

Title of the talk: Quantifying fault-valve action from vein orientation data

 Abstract: Faults and fractures often behave as fluid-pressure-activated valves. Fault valve behaviour is accompanied by fluctuating fluid pressure and seismogenic activities along the fracture surface. Pre-existing fractures are often reactivated under a tectonic stress field and fluid pressure surpassing the normal stress on the fracture wall. Thus, fracture networks are formed and reactivated under multiple fluid pressure events. Essentially fractures at first undergo slip movement followed by dilation with gradual rise in fluid pressure. Determining the fluid pressure events are essential to understand the overall mechanism of fracture reactivation, vein emplacement and for targeting the mineralized zones. Multiple studies have been conducted to indirectly determine the fluid pressure events from vein data distribution. However, it is difficult to quantify the plausible number of such fluid pressure events directly from a heterogeneous data distribution pattern. We have adopted a statistical method, well known and extensively used for fuzzy clustering of fracture data. Using a probability density function, we try to approximate the optimal number of such fluid pressure events. In this study, we have adopted multiple methods to understand the formation and reactivation of faults and fractures in an apparently massive host rock. We have also combined the deterministic method for quantifying fluid pressure events with the traditional method of scaling 3D Mohr circles for absolute fluid pressure determination in the auriferous quartz veins of the Gadag-Chitradurga Schist belt, western Dharwar Craton, south India. We have combined some published data from this region to understand the mechanism behind shallow crustal vein emplacement within a transtensional stress regime. We provide field evidence of fracture reactivation and estimate the reactivation potential of fractures which play a significant role in the spatial variation of fluid pressure along the greenstone belt.