Ultrahigh Pressure Metamorphism of the Sulu Terrane, Eastern China: A Prospective View
R. Y. ZHANG and J. G. LIOU Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305
The Sulu terrane, the Qinling Dabie Sulu collisional zone between the Sino Korean and Yangtze cratons, eastern China, consists of fault bounded ultrahigh pressure (UHP) and high pressure (HP) metamorphic belts. UHP metamorphic rocks include coesite bearing eclogites, metasediments and garnet peridotites. Eclogites are enclosed in quartzofeldspathic gneiss, marble and ultramafic rocks; protoliths of most eclogites are continental basaltic rocks. Garnet peridotites exhibit dual origins: type A peridotites were derived from a mantle wedge that have been inserted into a subducted continental lithosphere, whereas type B crustal hosted peridotites are the portions of mafic ultramafic complexes emplaced into a continental crust prior to the subduction. The Sulu UHPM rocks are characterized by (1) the occurrence of many volatile bearing phases, (2) the world record of the lowest δ 18 O values ( 15 per mil) for eclogitic and layered metasedimentary minerals, and (3) well developed exsolution rods or lamellae in UHP minerals. Several lines of evidence indicate that fluids were involved, but rock/fluid interactions were limited during UHP metamorphism. The supracrustal rocks with the mantle derived ultramafic rocks have experienced multistage metamorphism. Ultrahigh P peak metamorphism took place at 700 890 ℃ and P 28 kbar at c. 210 230 Ma for eclogites and associated metasediments; 800 to 1000 ℃ and 35 60 kbar for ultramafic rocks. Many petrochemical and geochronological characteristics have been well documented since the first discovery of coesite in the Dabie Sulu terrane nearly 10 years. In the next decade, many unresolved geodynamic and petrochemical problems including the mantle crust interaction, the role of fluid and the extent of UHP metamorphism require continuous research in conjunction with the deep continental drilling project in Donghai of eastern China.
【CateGory Index】： P588.3