2024 Undergraduate Research Showcase

Moving Mountains: Determining Temperature Distribution in the Himalaya's Earliest Metamorphic Rocks

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Student Presentation

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Dr. Matt Kohn


The Himalayas of northern India expose a rare sheet of ultrahigh-pressure rocks, called the Tso Morari Complex, uplifted from at least one hundred kilometers depth. The widespread exposures of this rock complex provide an exceptional opportunity to examine the dynamics of how ultrahigh-pressure metamorphic rocks form and are exposed at the surface. These exposures have allowed us to sample geographically distributed rocks. In this project, I collected temperature data on four samples distributed along a 90-km long NW-SE transect across the entire complex. Additional thermometry from Thompson et al. (2024) is also available. I measured concentrations of temperature dependent zirconium in the mineral rutile using Laser Ablation - Inductively Coupled Plasma Mass Spectrometry. Using calibrated equations, we then estimated the maximum temperature experienced by these rocks at an assumed pressure of 25 kbar. Temperatures broadly increase from ~570 °C in the extreme northwest to ~625 °C ~45 km to the southeast, reaching ~770 °C in the extreme southeast. These are the first Zr-in-rutile data collected on geographically distributed samples across the Tso Morari complex. Although we have not yet calculated pressures, these data suggest possibly deeper origins of rocks to the southeast compared to the northwest, so that the sheet is tilted from its original orientation as it was exhumed. This implication is consistent with structural data that indicate NW-directed transport during exhumation (Long et al., 2020).

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