Petrology and mineralogy of PP3 ultramafic rocks in Sulu UHP belt and its significance
大陆科学钻探CCSD-PP3钻孔超镁铁岩岩石学和矿物学特征及其意义

Ultramafic rocks about 480 metres sandwiching eclogite are revealed, which include garnet peridotite, dunite, serpentinite and few hargzburgite and amphibole phlogopite peridotite, contain olivine, chromium spinel, diopside, endiopside, or/and garnet, orthopyroxene, amphibole and phlogopite. Olivines have forsterite contents ranging from 88.7 to 93. 1, SiO2 ranging from 38. 8wt. % to 42. 4wt. % . All garnets ( Py65.945 Alml8.095 Uv7.518 Gr4.695 And3.605 Sp0.142 ) are pyropic, with CaO between 5.4 to 6.4 wt. % , and Cr2 O3 from 0. 3 to 3. 3 wt. % , represent early stage of mineral assemblage. Orthopyroxenes ( En91.8 Fs7. 9 Wo0.25 ) are unzoned, Cr2O3 ranges from 0 to 0. 32wt. % , and CaO ranges from near detection limit to 0. 20wt. %. Most of the Orthopyroxenes (the average is 0. 72wt. % ) have Al2O3 < 1. 1wt. %. Composition of clinopyroxenes in PP3 ultramafic rocks is attributed to two generations. the early generation is called diopside ( Wo45. 98 En47.89 Fs2.73 Ac3.39 ) and the later is endiopside(Wo27.61 En68.78 Fs2.27 Ac1.34) with higher MgO. Chromite in PP3 ultramafic rocks is compositionally variable, Cr#( molarlOOCr/( Cr Al) ) varies from 51 to 89, and TiO2 and MnO2 are lower than 0. 26wt. % and 0. 46wt. % respectively. Olivines, chromites, and clinopyroxenes show multistage, which were associated with partial melting, subduction and exhumation.