Files and links (1)
CC BY-NC-SA V4.0, Open Access
Thesis
The timing of prograde metamorphism of Greater Himalayan rocks in south-central Bhutan: Insights from garnet and monazite geochronology
Washington State University
Master of Science (MS), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004339
Handle:
https://hdl.handle.net/2376/124759
Abstract
Within the Himalayan mountain belt, the timing of structural burial of high-grade Greater Himalayan rocks, as well as the timing of their southward translation by shearing on the underlying Main Central Thrust, are critically important parameters for understanding the kinematic evolution of the orogen. New garnet Lu-Hf and monazite U-Th-Pb ages from Greater Himalayan rocks in south-central Bhutan collected in this study contribute to the resolution of these problems. Garnet Lu-Hf ages indicate that burial-initiated prograde metamorphism of Greater Himalayan rocks was underway by ~37 Ma and continued until at least ~24 Ma. An upward younging of Lu-Hf garnet ages within the Greater Himalayan package was observed and is interpreted as the consequence of the burial of Greater Himalayan rocks as a coherent package, with the structurally deepest rocks attaining garnet-stable conditions prior to the structurally shallowest rocks. Garnet Lu-Hf ages from the underlying Jaishidanda Formation, which lies beneath the mapped position of the Main Central Thrust, define prograde burial between ~27-31 Ma, which is contemporaneous with the burial history of overlying Greater Himalayan rocks, and predates the ~23-15 Ma interpreted timing of shearing on the Main Central Thrust. This indicates that the Jaishidanda Formation likely represents the basal part of the Greater Himalayan package and is not a Lesser Himalayan-affinity rock unit as previously proposed. The Jaishidanda Formation delineates the spatial limit of inverted metamorphism and high-intensity quartz fabrics and is interpreted to demarcate a ~1 km-thick, high-strain ‘Main Central Thrust zone’. The ~24 Ma youngest Lu-Hf garnet age in Greater Himalayan rocks above the Main Central Thrust, when combined with the ~20 Ma youngest prograde monazite core ages within the Main Central Thrust zone, suggests that shearing on the Main Central Thrust was underway no earlier than ~24-20 Ma, which corroborates published estimates of the initiation of Main Central Thrust shearing between ~23-20 Ma in other parts of Bhutan.
Metrics
2 File views/ downloads
12 Record Views
Details
- Title
- The timing of prograde metamorphism of Greater Himalayan rocks in south-central Bhutan: Insights from garnet and monazite geochronology
- Creators
- Kei Hasegawa
- Contributors
- Sean P Long (Advisor)Johannes Haemmerli (Committee Member)Jeffery D Vervoort (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 55
- Identifiers
- 99900882928801842
- Language
- English
- Resource Type
- Thesis