Infiltration of meteoric water in the South Tibetan Detachment (Mount Everest, Himalaya): When and why?

The South Tibetan Detachment (STD) in the Himalayan orogen juxtaposes low‐grade Tethyan Himalayan sequence sedimentary rocks over high‐grade metamorphic rocks of the Himalayan crystalline core. We document infiltration of meteoric fluids into the STD footwall at ~17–15 Ma, when recrystallized hydrou...

Full description

Saved in:
Bibliographic Details
Published in:Tectonics (Washington, D.C.) D.C.), 2017-04, Vol.36 (4), p.690-713
Main Authors: Gébelin, Aude, Jessup, Micah J., Teyssier, Christian, Cosca, Michael A., Law, Richard D., Brunel, Maurice, Mulch, Andreas
Format: Article
Language:English
Subjects:
40Ar/39Ar geochronology
Biotite
Chlorite
Convection
Deformation
Earth
Earth surface
Fluid flow
Fluids
fluid‐rock interaction
Geological time
Heat flow
hydrogen isotope
Hydrothermal activity
Infiltration
Isotopes
Metamorphic rocks
meteoric fluids
Meteoric water
Migration
Minerals
Miocene
Mount Everest
Plate tectonics
Precipitation
Rock
Rocks
Sciences of the Universe
Sedimentary rocks
Seismology
South Tibetan Detachment
Tectonics
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The South Tibetan Detachment (STD) in the Himalayan orogen juxtaposes low‐grade Tethyan Himalayan sequence sedimentary rocks over high‐grade metamorphic rocks of the Himalayan crystalline core. We document infiltration of meteoric fluids into the STD footwall at ~17–15 Ma, when recrystallized hydrous minerals equilibrated with low‐δD (meteoric) water. Synkinematic biotite collected over 200 m of structural section in the STD mylonitic footwall (Rongbuk Valley, near Mount Everest) record high‐temperature isotopic exchange with D‐depleted water (δDwater = −150 ± 5‰) that infiltrated the ductile segment of the detachment most likely during mylonitic deformation, although later isotopic exchange cannot be definitively excluded. These minerals also reveal a uniform pattern of middle Miocene (15 Ma) 40Ar/39Ar plateau ages. The presence of low‐δD meteoric water in the STD mylonitic footwall is further supported by hornblende and chlorite with very low δD values of −183‰ and −162‰, respectively. The δD values in the STD footwall suggest that surface‐derived fluids were channeled down to the brittle‐ductile transition. Migration of fluids from the Earth's surface to the active mylonitic detachment footwall may have been achieved by fluid flow along steep normal faults that developed during synconvergent extension of the upper Tethyan Himalayan plate. High heat flow helped sustain buoyancy‐driven fluid convection over the timescale of detachment tectonics. Low δD values in synkinematic fluids are indicative of precipitation‐derived fluids sourced at high elevation and document that the ground surface above this section of the STD had already attained similar‐to‐modern topographic elevations in the middle Miocene. Key Points Low δD meteoric fluids permeated the South Tibetan Detachment footwall in the Mount Everest region during mylonitic deformation The South Tibetan Detachment system represents an important orogen‐scale structure for fault‐controlled hydrothermal activity Localized north‐south extension characterized the upper Tethyan Himalayan plate during the middle Miocene within a convergent setting
ISSN:0278-7407
1944-9194
DOI:10.1002/2016TC004399