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Leucogranites are an igneous granitic rock with very few dark minerals. They are a significant characteristic of the Himalayan mountains and located throughout, but their formation history and evolution in the Himalayan region are understudied and unclear. Himalayan leucogranites contain mineral geochronometers, which selectively incorporate radioactive isotopes during formation, and can be dated using the known half-life of their isotopes. Zircon is one mineral geochronometer that contains three unique decay series collectively known as the uranium/lead (U/Pb) system. These isotopes can be dated, then checked against one another to determine the accuracy and precision of resultant age dates. Similarly, the depletion or enrichment of light rare-earth elements (LREEs) and heavy rare-earth elements (HREEs) has geologic implications: they may indicate the mode of magma generation and/or determine a rock’s mineral assemblage.

The Himalayan leucogranites’ age dates will determine when the parent magma crystallized, give insight into local fault movement timing, and clarify the number of metamorphic phases the leucogranites underwent. Additionally, further implications include: broadening geologic literature regarding mountain evolution following continental collision, which can be used globally to understand other mountain-building events; explaining the process of deep subsurface magma generation; and ascertaining the probability of viable ore deposits associated with leucogranites. If the presence of ore and rare-metal mineral deposits are confirmed, they may stimulate the local economy by providing resources for metal-workers, miners, and artisans. This study aims to answer three questions regarding the Himalayan leucogranites’ formation and evolution:

1. What is the crystallization age of the Mt. Everest region leucogranites?
2. How many metamorphic phases did the leucogranites undergo?
3. Can the age dates and trace/rare-earth element (t/REE) geochemistry be used to:
   • Constrain local fault movement timing
   • Determine the probability of economic ore and rare-metal mineral deposits associated with Himalayan leucogranites?

Eight leucogranite samples were collected May-June 2018 along the Everest Base Camp trekking path. National Petrographic Laboratory made thin sections of six samples in December 2020. Petrographic analysis began in January 2021 to identify mineral assemblages and metamorphic features and will continue to October 2021. All eight samples have been crushed according to standard mineral separation practices and four were sent to the Arizona LaserChron Center (ALC) in February 2021 to finalize mineral separation. LA-ICP-MS and SHRIMP will be utilized to determine the t/REE composition and zircon age of the leucogranites. Plans have been made to travel directly to ALC in May 2021 to conduct instrument analyses. Expected results are Miocene-age zircon dates, 2-3 metamorphic phases, a range of timing for the South Tibetan Detachment's motion of about 20 Ma, and the presence of rare-metal minerals apparent in thin section.

Faculty Mentor: Dr. Kirsten Nicholson

Secondary Mentors: Dr. Jeff Grigsby and Dr. Klaus Neumann

Department of Environment, Geology, and Natural Resources 

Graduate Student