Publication Date

Summer 2024

Abstract

As a result of the Indo-Asia collision, the Main Central Thrust (MCT) is a ductile shear zone that extends across the Himalayas and marks the fault boundary between the Greater Himalayan Crystallines (GHC) and the Lesser Himalayan Sequence (LHS). Due to the nature of this thrust fault, the GHCs are being stacked on top of the LHS despite their older age and higher grade of metamorphism. However, previously published works show that the MCT is more active in certain regions of Nepal than others. The GHC in the Modi Khola region to the west is thicker than the Marsyangdi region to the east potentially due to more slip along the MCT as well as other possible high strain zones. Samples were collected from Manang (above the MCT) to Bhulbhule (below the MCT) and through mineral and textural observations, a KFMASH petrogenetic grid was utilized to estimate the pressure and temperature conditions of samples in the Marsyangdi region. Comparison between the data collected from the samples and research papers on the Modi Khola revealed different conditions along the MCT. Rocks in the Marsyangdi above the MCT equilibrated to an average 722 °C and 8.4 kbar whereas below the MCT the average was 650 °C and 7.5 kbar. Data presented here suggest higher pressure conditions under similar temperatures above the MCT in the Modi Khola, yet higher temperatures under similar pressures below the MCT in the Marsyangdi. Additionally, mineral assemblages collected from the samples pointed out a major difference between the two regions that could be the reason for the varying conditions. This may be due in part to the increased crustal thickening in the Modi Khola region or to an unrecognized high strain zone.

Disciplines

Life Sciences | Physical Sciences and Mathematics

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