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成果名称: Sapphirine-bearing granulites from the Tongbai orogen, China: Petrology, phase equilibria, zircon U-Pb geochronology and implications for Paleozoic ultrahigh temperature metamorphism
作者: Hua Xiang
Zeng-Qiu Zhong
Ye Li
Min Qi
Han-Wen Zhou
Li Zhang
Ze-Ming Zhang
M. Santosh
主题关键词: Sapphirine granulite Ultrahigh-temperature metamorphism U–Pb Geochronology Phase equilibrium modeling Tongbai orogen
首次发表日期: 2014-09
出版者: Institute of Geology Chinese Academy of Geological Sciences
摘要: We report here for the first time the occurrence of sapphirine-bearing granulites within the Qinling Group of the Qinling-Tongbai orogen and provide robust evidence for extreme crustal metamorphism at ultrahigh-temperature (UHT) conditions. We document the UHT indicator of sapphirine and spinel in a mafic granulite consisting of orthopyroxene, biotite, plagioclase, amphibole and rutile/ilmenite. The ferromagnesian minerals in the sapphirine- bearing granulitehavehigh X Mg [Mg/(Mg+ Fe)](orthopyroxeneX Mg = 0.84–0.95;biotiteX Mg = 0.81; amphibole X Mg = 0.87–0.96).Thephaseequilibriamodelingdemonstratesthattheearlyspinel-bearingassemblageisstableat 923–950 °Cand6.7–8.9 kbar,andthepeakassemblageofOpx+Pl+Spr/Spl+Amp+Bt+Ilm(+melt)defines a field at 922–947 °C and 8.4–10.2 kbar. Rutiles have variable Zr concentrations but mostly cluster at ca. 1,500 and 3400 ppm. Zr-in-rutile geothermometry yielded high temperatures of up to 890–940 °C. Zircon U–Pb dating of the granulite constrains the timing of the immediate post-peak and retrograde metamorphic stages as 429 ± 7 Ma and 412 ± 4 Ma, respectively. The UHT metamorphism, together with extensive occurrence of coeval magmatic suites suggests that the Tongbai orogen experienced a Paleozoic Andean-type orogeny probably derived from mid-oceanic ridge subduction of the Qinling Ocean.
引用地址: http://www.igeodata.org/handle/20.500.11758/222
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