Publication Date
Summer 2024
Abstract
Brittle-ductile transitions are key sites for analyzing metamorphism in a large-scale tectonic environment. Brittle zones are ruled by Coulomb’s Law, while ductile zones with plastic deformation are explained through the Flow law. The interaction of these two zones is not a finite point, but rather a transition that accounts for a large amount of tectonic activity. These transitions indicate areas of fault zones due to variations in rock strength. The Kali Gandaki valley has not been previously observed with these brittle-ductile transitions at the forefront of the research. Outcrops in the area provide evidence of both brittle and ductile deformation caused by the Main Himalayan Thrust from the collision of the Indian and Eurasian Plate 60 million years ago. While the MHT caused many fault zones in the Himalayas, the Main Central Thrust accounts for 90 km of shortening. The MCT is a key fault zone for brittle-ductile transition research. The data collected from field measurements plotted on a Stereonet, photographs, and samples will be necessary for drawing conclusions on the metamorphic environment of the area. Metamorphic minerals such as kyanite and garnets were observed at the outcrops, and indicated the pressure and temperature conditions that caused them to appear. The metamorphic structures observed were also crucial in describing the tectonic environment of the MCT in the Kali Gandaki. Brittle structures such as faults and fracturing were observed, along with ductile structures such as folds and deformed quartz veins. Metamorphic rocks like phyllites and schists contained these structures, further explaining depositional environment before the continental collision of the Indian and Eurasian plates and the metamorphism that occurred near the MCT. In analyzing the data collected in the field, it is evident that there is a brittle-ductile transition at the MCT in the Kali Gandaki. However, due to the presence of both brittle and ductile deformation outside the MCT, the brittle-ductile transition must extend beyond the MCT. From the field observations, the brittle-ductile transition begins with the Benighat Slate formation in the Lesser Himalayan sequence. This report will start with a discussion of the history of the Himalayas from the initial continental collision, with descriptions of the physics that explain both brittle and ductile deformation zones. The methods of the research will be detailed next, followed by the results of those methods and the interpretations made. Finally, the scope of this brittle-ductile transition will be overviewed in the conclusion with room for future research included at the end.
Disciplines
Life Sciences | Physical Sciences and Mathematics
Recommended Citation
Brubaker, Ashton, "Brittle-Ductile Transitions in the Kali Gandaki and their Tectonic Significance" (2024). Nepal: Geoscience in the Himalaya. 5.
https://digitalcollections.sit.edu/npg/5