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The Yushugou Granulite-Peridotite Terrane as a Paleozoic Continental Crust-Mantle Transition Zone Exposed at the Northern Margin of the Southern Tianshan (Xinjiang)
Author(s): JI Shaocheng, WANG Qian, SHAO Tongbin, SUN Shengsi, LI Awei, MICHIBAYASHI Katsuyoshi, KONDO Yosuke, LI Jianfeng
Pages: 473-
494
Year: 2014
Issue:
3
Journal: Geotectonica et Metallogenia
Keyword: exposed continental Moho; window on crust-mantle transition zone; compressional uplift; granulite-peridotite terrain; Yushugou; Tianshan;
Abstract: The Yushugou massif in the Kumishi region at the nouthern margin of the southern Tianshan (Xinjiang) consists of extensively deformed peridotites (lherzolite, harzburgite and wehrlite) associated with foliated and lineated mafic composition-dominated granulites, together carried up and emplaced into greenschist-lower amphibolitefacies metasediments at 380-420 Ma. The granulite-peridotite units are interpreted as tectonic slices of continental mantle and lower crustal materials immediately adjacent the Moho. The high pressure metamorphic slices were extruded by tectonic compression from a detachment in the crust-mantle boundary up into the greenschist-lower amphibolite-facies midde crust along intracontinental thrust shear zones. Such compressional uplifts of the crust-mantle transition zone were similar to the Ivrea-Verbano zone in the southern Alps of Italy and the Jijal-Patan-Chilas seuqence in the Kohistan arc of Pakistan. The boundary between mafic granulites and peridotites, which represents an exposed example of the Moho, is a high strain zone: in the mantle rocks olivine defomed by diffusion-accommodated grain bounadry sliding while pyroxenes deformed by disloaction creep, and in the lower crustal mafic granulites both pyroxenes and plagioclase deformed by dislocation creep. Thus, the Yushugou massif provides important clues to the nature and seismic reflecitivity of the continental Moho.
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