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TitleAge and anatomy of the Gongga Shan batholith, eastern Tibetan Plateau, and its relationship to the active Xianshui-he fault
AuthorSearle, M P; Roberts, N; Chung, S L; Lee, Y H; Cook, K; Elliott, J; Weller, O M; St-Onge, M R; Xu, X; Tan, X; Li, K
SourceGeosphere vol. 12, no. 3, 2016 p. 948-970, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20150332
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
AreaTibet; China
Lat/Long WENS 96.0000 105.0000 34.0000 22.0000
Subjectsgeochemistry; geochronology; regional geology; structural geology; tectonics; igneous and metamorphic petrology; geophysics; batholiths; uranium lead dating; uranium lead dates; igneous petrology; whole rock geochemistry; isotope geochemistry; faulting; faults, thrust; crustal uplift; crustal thickness; crustal studies; crustal movements; crustal models; crustal structure; Gonga Shan batholith; Xianshui-he fault; Jurassic; Triassic; Cenozoic
Illustrationslocation maps; structural maps; photographs; photomicrographs; graphs; geochronological charts
ProgramGEM2: Geo-mapping for Energy and Minerals Baffin Bedrock Mapping
Released2016 05 05
AbstractThe Gongga Shan batholith of eastern Tibet, Sichuan, is a composite batholith composed dominantly of Triassic-Jurassic Indosinian biotite and hornblende-bearing granodiorites with dioritic enclaves and less common garnet-bearing leucogranites, with U-Pb zircon and allanite ages (from LA-ICPMS) crystallisation ages of ca 215-159 Ma. These rocks are related to Paleo-Tethyan subduction zone magmatism along the South China margin. A significant component of the batholith is made up of garnet, biotite and muscovite-bearing crustal melt granites with concordant Miocene U-Pb zircon ages ranging between 14 and 5 Ma. U-Pb ages of allanite show both older Indosinian ages, and young growth associated with <15 Ma migmatites. Zircon and allanite ages reflect multiple re-melting events, the youngest at ca. 5 Ma resulted in dissolution and crystallization of zircon and growth/resetting of allanite. In situ Hf isotope analyses indicate a typical crustal evolution trend from ca 800 Ma protolith to late Indosinian magmatism. The youngest ages reflect not only Pb-loss but reworking of older crust during Late Miocene-Pliocene time. At least seven stages of cross-cutting granites have been mapped in the Yanzigou valley east of Gongga Shan. The young S-type leucogranites occur mainly in the central part of the batholith and adjacent to the eastern margin of the batholith at Kangding where they are cut by the left-lateral Xianshui-he fault. These are amongst the youngest crustal melt granites exposed on the Tibetan Plateau, and may be related to localise partial melting of thickened Triassic flysch-type sediments in the Songpan-Ganze zone. The Xianshui-he fault is the most seismically active strike-slip fault in Tibet and thought to be responsible for the eastward extrusion of the central part of the Tibetan Plateau. The fault obliquely cuts all granites of the Gongga Shan massif as well as the Precambrian Kangding complex (ca 800 Ma), Palaeozoic metasediments, and Triassic Songpan-Ganze flysch. The course of the Jinsha River is offset by up to ~85 km along the Garze-Yushu fault, and the course of the Xianshui Jiang River along the Xianshui-he fault is offset by ~62 km. Thus, long-term average slip rate along the Xianshui-he fault assuming a maximum initiation age of 14 Ma is ~4.4 mm/yr. In the Kangding area, offsets of granites as young as ~5 Ma suggest slip rates more like 12.4 mm/yr. The Xianshui-he fault has a transpressional component in the Kangding Moxi sectors of the fault uplifting the batholith along its western flank.
Summary(Plain Language Summary, not published)
The Gongga Shan batholith is a large granite body present in eastern Tibet that reaches up to 200 km in length, and up to 7756 m in height. Previous studies have suggested that the batholith forms a relatively young component of the Tibetan plateau (c. 15 Ma). However, field observations indicate that the batholith 'anatomy' is relatively complex, and composed of several different types of granite. In this study, a variety of techniques are applied to date each of the granite phases present in the batholith. The results reveal that most of the batholith is in fact relatively old (c. 215-159 Ma), with only a small component of the batholith c. 15 Ma. This data help to improve tectonic models of the region, as they indicate that only localised parts of the plateau were recently molten.

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