Fracture network characterization of syntectonic younger granite, western dharwar craton (South India)

Abstract

The study of fracture network system in granite has great implications in understanding the regional tectonics and also help to apprehend how fractures develop in them. It is known that the study of branches and nodes of fracture network can be useful to define the geometrical features of any fracture system. In the present study, this approach is followed to analyze the fracture network from the 2.61 Ga Chitradurga granite (CDG) of Archaean lode-gold bearing Chitradurga Schist Belt (Dharwar Craton, south India). The CDG is known to have emplaced during regional deformation, and the fabric in Northern part of the granite is simple shear dominated, while Southern part of it is pure shear dominated. This granitic pluton is oriented NNW-SSE, so that the Northern portion is closer to the Chitradurga Shear Zone (CSZ) than Southern portion. It is also replete with crisscross fractures with various orientations. The present investigation is aimed at understanding how this fracture network occurs and varies from pure shear to simple shear dominated regions in CDG. From topological analysis, it is observed that the total dimensionless intensity of fractures in northern part of the CDG is twice as much as the southern part. It is also noted that the proportion of isolated (I), abutting (Y), and crosscutting (X) nodes in northern and southern parts of the CDG are found to be 8.17, 3.29 and 5.56 respectively. Further, the average numbers of connections per branch (CB) are calculated to be 1.78 and 1.88 for northern and southern parts of CDG respectively. Similar contrasting results of average number of connections per line (CL) were obtained; which points to the ability of network topology to successfully quantify the differences between fracture networks formed in the same sample space, under different stress conditions. So it is envisaged that the pre-existing fabric along with regional far-field stresses in the CDG played an important role in partitioning the strain and subsequently developing the fracture network in them and this study establishes the credibility of using topology as a reliable tool to quantify and analyze differences between disparate fracture networks.