Geological Society of America

T139 State-of-the-Art and Future Directions in Petrology and Petrochronology II: A Session in Honor of Chris Yakymchuk, University of Waterloo, GSA MGPV Early Geological Career Awardee for 2024

Monday, 23 September 2024
1:30 PM - 5:30 PM
206B

GEOCHRONOLOGY AND THERMAL HISTORY OF THE MOUNT EVEREST MASSIF

Paper number: T139-11
Program: Technical Sessions
Time: 4:10 PM – 4:25 PM

Authors

Kyle P. Larson Presenting Author
University of British Columbia, Okanagan, Kelowna, BC
John Cottle
University of California Santa Barbara, Santa Barbara, CA
Sudip Shrestha
University of British Columbia, Okanagan, Kelowna, BC
Mark Button
University of British Columbia, Okanagan, Kelowna, BC
Alfredo Camacho
University of Manitoba, Winnipeg, MB
Matthew Steele-Macinnis
University of Alberta, Edmonton, AB
David Lageson
Montana State University, Bozeman, MT
Steven Creighton
Advanced Microanalysis Centre, Saskatoon, SK

Abstract

From the earliest expeditions on Mount Everest, the geology of the massif has been the subject of scientific observation. While the existing geologic information from the massif, which includes the occurrence of the large-scale Qomolangma and Lhotse detachment faults, facilitates a basic assessment of the geological history of the rocks therein, there remain significant gaps in spatial and thermal representation of the available data. No data, for example, have been published from the massif between the Yellow Band (~ 8500 m), in the immediate footwall of the Qomolangma detachment, and the structural level of the Nuptse granite below the Lhotse detachment (~ 7000 m), limiting interpretations about the kinematics within the massif.

The present study re-examines specimens collected from across the Mount Everest massif as part of the 2012 National Geographic Legacy Expedition using in situ geochronometers including apatite U-Pb, white mica and biotite Rb-Sr, single crystal white mica and biotite ⁴⁰Ar/³⁹Ar and thermometry based on Raman spectroscopy of carbonaceous material (RCSM). New specimens from the South Col and the Lhotse face were also examined to extend spatial coverage farther across the massif. The apatite U-Pb data show mixing or partial resetting of early Paleozoic (detrital?) material during Himalayan orogenesis. Rb-Sr and ⁴⁰Ar/³⁹Ar data is entirely Himalayan (<55 Ma) and records a significant break in dates from early Eocene (ca. 40-48 Ma) at an elevation of ~ 8500 m in the Yellow Band to early Miocene (ca. 18 Ma) at lower (~7900 to 7500 m) elevations. At ~7500 m, apparent prograde biotite yield overlapping ca. 18 Ma Rb-Sr and ⁴⁰Ar/³⁹Ar dates, whereas later, alteration-related white mica yield distinctly younger ca. 16 Ma dates. A similar break in RCSM temperature is noted over the same interval where temperatures increase from ~ 430 ˚C (8840 m) to ~510 ˚C (8520 m) before dropping to ~440˚C (7520 m). The apparent temperature break is further consistent with a ~ 400 ˚C Ti-in-biotite temperature at an elevation of 7906 m.

These new data demonstrate the geological complexity within Mount Everest massif. The new dataset can be reconciled by early Miocene movement across a previously unrecognized thrust fault, here termed the Adrishya thrust.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405757

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