Exhumation Kinetics Of Northern Sulu Ultrahigh-pressure Metamorphic Belt, Rongcheng Area

Rongcheng of Shandong province is located at northeast of Sulu UHP (high-pressure-ultrahigh-pressure) metamorphic terrane. It is composed of 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, 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 terrane, and these slices are divided by some ductile shear zones (about 2 km).These ductile shear zones are composed of high srain rock and mylonites. obvious lineation of penetration, foliation, S-C fabrics,"σ","δ"type porphyroclasts, A-type folds and asymmetric folds are common in the ductile shear zone. The mylonites fall into 3 types: Initial mylonite, mylonite and altramylonite. Based on field work microstructural analyse 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 8 eclogite samples of Rongcheng were determined from electron backscatter diffraction (EBSD) technique shows that: LPO of Omphacite is characterized by the (100) [001] type, where as garnet appears to be randomly oriented.From th original seismic reflection profile of Sulu UHP terrane shows an erode antiform structure. 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.