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TitleQuantifying Barrovian metamorphism in the Danba Structural Culmination of eastern Tibet
AuthorWeller, O M; St-Onge, M R; Waters, D J; Rayner, NORCID logo; Searle, M P; Chung, S L; Palin, R M; Lee, Y H; Xu, X
SourceJournal of Metamorphic Geology 2013, 27 pages,
LinksSupporting Information
Alt SeriesEarth Sciences Sector, Contribution Series 20130067
Mediaon-line; digital
File formatpdf
AreaTibet; Tibetan plateau; China
Lat/Long WENS101.5000 102.1667 31.3333 30.6667
Subjectstectonics; igneous and metamorphic petrology; geochronology; geochemistry; barrovian-type facies series; metamorphism; Upper Triassic; Lower Jurassic; pressure-temperature conditions; monazite; x-ray fluorescence analyses; staurolite; kyanite; sillimanite; petrographic analyses; garnet; thermobarometry; Danba Structural Culmination; Songpan-Garzê Fold Belt; Triassic; Jurassic
ProgramGEM: Geo-mapping for Energy and Minerals GEM Tri-Territorial Information Management & databases (Tri-Territorial Bedrock Framework)
Released2013 09 23
AbstractThe Danba Structural Culmination is a tectonic window into the late Triassic to early Jurassic Songpan-Garzê Fold Belt of eastern Tibet, which exposes an oblique section through a complete Barrovian-type metamorphic sequence. Systematic analysis of a suite of metapelites from this locality has enabled a general study of Barrovian metamorphism, and provided new insights into the early thermotectonic history of the Tibetan plateau. The suite was used to create a detailed petrographic framework, from which four samples ranging from staurolite to sillimanite grade were selected for thermobarometry and geochronology. Pseudosection analysis was applied to calculate P-T path segments and determine peak conditions between staurolite grade at ~5.2 kbar and 580 °C and sillimanite grade at ~6.0 kbar and 670 °C. In situ U-Pb monazite geochronology reveals that staurolite-grade conditions were reached at 191.5 ± 2.4 Ma, kyanite-grade conditions were attained at 184.2 ± 1.5 Ma, and sillimanite-grade conditions continued until 179.4 ± 1.6 Ma. Integration of the results has provided constraints on the evolution of metamorphism in the region, including a partial reconstruction of the regional metamorphic field gradient. Several key features of Barrovian metamorphism are documented, including nested P-T paths and a polychronic field gradient. In addition, several atypical features are noted, such as P-T path segments having similar slopes to the metamorphic field gradient, and Tmax and Pmax being reached simultaneously in some samples. These features are attributed to the effects of slow tectonic burial, which allows for thermal relaxation during compression. While nested, clockwise P-T-t loops provide a useful framework for Barrovian metamorphism, this study shows that the effects of slow burial can telescope this model in P-T space. Finally, the study demonstrates that eastern Tibet experienced a significant phase of crustal thickening during the Mesozoic, reinforcing the notion that the plateau may have a long history of uplift and growth.
Summary(Plain Language Summary, not published)
The Danba Structural Culmination provides a window to the base of the Tibetan plateau, the largest area of high-elevation on Earth and a result of India colliding with Asia starting c. 50 million years ago. A detailed field and laboratory study of the metamorphic (heated & deformed) rocks of the window enables part of the long-term history of the plateau to be constrained. A suite of four rock samples was selected for analysis to document paleotemperatures and paleopressures at different times. Results document changing conditions from c. 5.0 kbar and 570 C, 191.5 ± 2.4 million years ago, to c. 6.0 kbar and 670 C, 179.4 ± 1.6 million years ago. Heating and deformation at the base of the plateau therefore lasted at least 12 million years. The study demonstrates that eastern Tibet experienced a significant phase of crustal thickening prior to the India/Asia collision, indicative of a long history of uplift and growth. The geological evolution thus constrained is directly analogous to and can serve as a tectonic template for parts of east-central Nunavut in Canada.

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