Characterization of vein sets and estimation of stress orientations and stress ratios: Insights from the Buxa dolomite, Main Boundary thrust sheet, Siang valley, Arunachal Lesser Himalaya

Behera, Swastik Suman (2022) Characterization of vein sets and estimation of stress orientations and stress ratios: Insights from the Buxa dolomite, Main Boundary thrust sheet, Siang valley, Arunachal Lesser Himalaya. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Swastik Suman Behera (17MS061)) 17MS061_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

We estimate paleostress orientations (σ1, σ and σ3), stress ratios (ϕ) and driving pressure ratios (R′) from the extnesion veins exposed within the Buxa dolomites of the frontal Main Boundary thrust (MBT) sheet in the Siang valley, Arunachal Lesser Himalaya. Based on the angular relationship with the bedding, the fractures and veins were divided into low-angle (< 30°), moderate-angle (∼ 30° - 60°) and high-angle (> 60°) sets. Observations at a microscopic level indicate that the low-angle veins formed first followed by the moderate-angle and then the high-angle veins. The high-angle veins are the most dominant set (∼ 49%; mean orientation: 23° → 141°) followed by the moderate-angle (∼ 31%; mean orientation: 70° → 176°) and the low-angle (∼ 20%; mean orientation: 58° → 224°) set. The poles to all 3 sets of veins define a clustered distribution in the stereoplot indicating that the pore fluid pressure (Pf ) was less than the intermediate principal stress (σ2) during the formation of these sets of veins. On applying the stress inversion method (Yamaji et al., 2010) to the veins, 5 different generations of veins are revealed. Microstructural study indicates that the quartz-rich veins are generally low-angle veins, whereas the calcite-rich veins are generally high-angle veins. The study also indicates the presence of crack-seal and blocky texture in the veins with the growth direction of the mineral grains at a high angle to the veins wall. Based on the stress ratio (ϕ), driving pressure ratio (R′) and the orientation of the stress axes assciated with each generation, the different generations of veins most likely formed under different stress conditions.

Actions (login required)

View Item