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Non-ultrahigh-pressure unit bordering the Sulu ultrahigh-pressure terrane, eastern China: Transformation of Proterozoic granulite and gabbro to garnet amphibolite

By
Ru Y. Zhang
Ru Y. Zhang
1
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
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Juhn G. Liou
Juhn G. Liou
1
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
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Tatsuki Tsujimori
Tatsuki Tsujimori
1
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
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Shigenori Maruyama
Shigenori Maruyama
2
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
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Published:
January 01, 2006

The Haiyangsuo area of the NE Sulu ultrahigh-pressure terrane, eastern China, consists of gneisses with minor granulite and amphibolite layers, metagabbros, and granitic dikes. The peak-stage assemblages of the granulites (garnet + orthopyroxene + clinopyroxene + plagioclase ± pargasite ± biotite ± quartz) formed at >750 °C and 9–11 kbar and were overprinted by amphibolite-facies phases characterized by well-developed corona layers of | garnet | amphibolite + quartz | at contacts between plagioclase and clinopyroxene or orthopyroxene, as well as by the exsolution of (orthopyroxene + ilmenite + amphibole) from clinopyroxene. These textures indicate a near-isobaric cooling history of the granulite-bearing gneiss terrane. The metagabbro preserves a relict igneous assemblage (orthopyroxene + clinopyroxene + plagioclase + pargasite ± ilmenite ± quartz) in its core, but in its margins has a metamorphic corona texture similar to the granulite that formed at ∼600–700 °C and 7–10 kbar. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb dating of zircons indicates that the protolith age of the garnetbiotite gneiss is older than 2500 Ma, whereas the granulite-facies metamorphism (the first regional metamorphic event) occurred at 1846 ± 26 Ma. Gabbro intrusion took place at 1734 ± 5 Ma, and the formation of amphibolite assemblages in both metagabbro and granulite occurred at ca. 340–370 Ma. Both gneiss and metagabbro were intruded by granitic dikes, with one dated at 158 ± 3 Ma. These data, together with a lack of eclogitic assemblages, suggest that this granulite-amphibolite–facies complex is exotic relative to the Triassic Sulu high-pressure–ultrahigh-pressure terrane; juxtaposition took place in Jurassic time.

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GSA Special Papers

Ultrahigh-pressure metamorphism: Deep continental subduction

Bradley R. Hacker
Bradley R. Hacker
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William C. McClelland
William C. McClelland
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J.G. Liou
J.G. Liou
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Geological Society of America
Volume
403
ISBN print:
9780813724034
Publication date:
January 01, 2006

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