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Zhihui Cai, Key Laboratory for Continental Dynamics, Institute of Geology, CAGS (China)
Zhiqin Xu, Key Laboratory for Continental Dynamics, Institute of Geology, CAGS (China)
Tiannan Yang, Key Laboratory for Continental Dynamics, Institute of Geology, CAGS (China)
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Rongcheng County in Shandong province of China is located at northeast of Sulu UHP (ultrahigh-pressure) metamorphic terrane. It is composed of gneiss, paragneiss, eclogites, garnet pyroxenite, ultramafic rocks, granulites, quartzite, marble and amphibolites. Coesites as a reliable marker of ultra-high pressure environment are found in eclogites, quartzites, gneisses, marbles and amphibolites. The occurrence of mylonites extends NNE-SSW at the north part and NW-SE at south. Different parallel slices compositing the Rongcheng UHP metamorphic terranes are divided by some ductile shear zones. Based on field work, micro-structural analyses and EBSD studies of quartz, a conclution is arrived: These ductile shear zones are approximately SE trending normal faults.
Lattice-preferred orientation (LPO) of omphacite and garnet in several eclogite samples of Rongcheng were determined from electron backscatter diffraction (EBSD) technique shows that: LPO of Omphacite and rutile are characterized by high temperature type, where as garnet appears to be randomly oriented. From the original seismic reflection profile of Sulu UHP terrane an erosion antiform structure is shown. Rongcheng normal faults are situated in the lower part of this antiform, and southern Sulu thrusts are situated in the above part. Based on the petrologic, geochemical, strctual studies, the extrusion model of Sulu UHP terrane is verified further.
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