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TitleMiocene magmatism in the Western Nyainqentanglha mountains of southern Tibet: an exhumed bright spot?
AuthorWeller, O M; St-Onge, M R; Rayner, N; Searle, M P; Waters, D J
SourceLithos vol. 245, 2016 p. 147-160,
Alt SeriesEarth Sciences Sector, Contribution Series 20150107
Mediapaper; on-line; digital
File formatpdf
AreaTibet; Nyainqentanglha mountains
Lat/Long WENS 90.1667 91.1667 30.6667 29.9167
Subjectsigneous and metamorphic petrology; geochronology; magmatism; magmatic rocks; magmatic deposits; partial melting; thermobarometry; uranium lead dates; uranium lead dating; radiometric dating; Tibetan Plateau; Lhasa composite terrane
Illustrationslocation maps; photomicrographs; plots; Concordia diagrams; phase diagrams; schematic cross-sections
ProgramBaffin Bedrock Mapping, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Western Nyainqentanglha (WNT) mountain range of south-central Tibet was exhumed from ~15 to 19 km depth in the footwall of the Yangbajain graben during the late Neogene. The WNT thus provides a rare exposure of deeper crustal levels of Tibet, which can be used to gain insight into processes that may be occurring at depth today beneath the plateau. Field, petrological, thermobarometric and U-Pb geochronological analysis are applied to determine the magmatic and metamorphic history of the WNT. The metasedimentary strata of the WNT are calculated to have experienced peak metamorphic conditions of 4.5 ± 0.5 kbar and 670 ± 25 °C at c. 203 Ma, prior to being intruded by a variety of granitoids with crystallisation ages that range from c. 126 to 8 Ma. Synthesis of these results with all published age data in the region reveals that the WNT has experienced three tectonothermal events: (1) 213-201 Ma metamorphism and magmatism associated with north-south Lhasa terrane accretion, (2) 140-52 Ma magmatism resulting from north-directed subduction of Neo-Tethys preceding India-Asia collision, and (3) 25-8 Ma magmatism that is suggested to have resulted from partial melting of the thickened Tibetan plateau crust. The latter is correlated with seismic bright spots imaged in the region at ~15-20 km depth, indicating that restricted partial melting at mid-crustal levels may have been ongoing since 25 Ma, in accordance with observations from xenolith data and predictions made by thermal modelling of thickened crust.
Summary(Plain Language Summary, not published)
The Western Nyainqentanglha (WNT) is a mountain range located in southern Tibet (China) that was exhumed from ~17 km depth by normal faulting of the crust since 8 Ma. The WNT thus provides access to deep parts of Tibet, which is important because there are few localities in Tibet where such crustal levels can be directly studied. Field, thermobarometric (the calculation of pressure and temperature conditions of rock formation) and geochronological (the calculation of the age of rock formation) techniques are applied to determine the history of the WNT. The results reveal that the WNT has experienced three magmatic and metamorphic events, at 213-201 Ma, 140-52 Ma and 25-8 Ma. The youngest event is suggested to have resulted from partial melting of the thickened Tibetan crust, which is informative about present-day processes that may be occurring beneath Tibet.