Some applications of fluid inclusion studies in structural geology

This presentation highlights the scope of fluid inclusion studies in structural geology with the help of three case studies. It shows how the fluid inclusion studies are useful in tracing the nature and the compositional evolution of syntectonic fluids and, the physico-chemical conditions during the evolution of the tectonic structures. The first study traces the evolution of syntectonic fluids by studying the fluid inclusions that were trapped at different stages of fault-bend folding in the Appalachian Valley and Ridge province (Srivastava and Engelder, 1990). Three successive phases of brittle tectonics, each represented by a syntectonic veining, are correlated with different stages of the fault-bend folding. The first phase resulted into development of the bedding parallel veins at the basal décollement, whereas the second and the third phases produced the strike veins and the cross-fold veins at the ramp and the flat, respectively. Thermo-barometric data, obtained from the fluid inclusions in the different generations of veins, show that the syntectonic fluids became progressively less saline, and the pressure and temperature gradually lowered with the progressive evolution of the fault-bend folding. The second study focuses on the mechanism of development of the meter-scale brittle-ductile shear zones that cut through the Coburn Formation, Valley and Ridge province (Srivastava and Engelder, 1991). The shear zones contain en-échelon extensional veins that are composed of quartz, saddle dolomite and calcite in paragenetic order. The results of thermo-barometric studies on the co-existing methane-rich and brine-rich fluid inclusions reveal tha