苏-鲁超高压变质岩带从上地幔返回地表的证据

EVIDENCE FOR THE JIANGSU-SHANDONG ULTRA-HIGH- PRESSURE METAMORPHIC BELT RETURNS FROM THE UPPER MANTLE TO THE EARTH SURFACE IN THE MESOZOIC-CENOZOIC

印支期苏—鲁超高压榴辉岩带是初始欧亚板块东部大陆边缘在与古太平洋板块强烈挤压作用过程中,由黄海—苏东北地体A—型俯冲至上地幔形成的。其回返地表主要是在中—新生代由弧后扩张作用引起的地壳拉伸、增长、减薄过程中实现的。中—晚白垩世非造山的碱性花岗岩带与榴辉岩带的重叠、晚白垩世红色盆地、第三纪巨厚沉积岩系和新生代大陆裂谷带玄武岩等的形成和发育等种种地质证据表明俯冲至上地幔中的榴辉岩带后来被向上拉伸至地表的。

This paper deals with the characteristics of the Jiangsu-Shandong (Su-lu) Indosinian (250-190 Ma) ultra-high-pressure metamorphic belt, i.e. the coesite- and diamond-bearing e-clogite belt, and evidence of its exhumation. More than one thousand eclogite bodies of varying size are scattered in the Su-lu eclogite belt, which extends northeastly about 350 km and has an average width of about 10 km. The rock association includes A-, B- and C-type eclogites, garnet- and garnet-quartz pyroxenite, garnet-phengite gneiss, kyanite schist, kyanite quartzite, blueschist and calc-silicate (containing clinopyroxene with exsolution lamellae of alkali-feldspar) marble.From a view-point of plate and terrane tectonics, the Su-lu eclogite belt was a collisional melange belt formed as a result of A-type subduction induced by the intense collision between the initial Eurasian and Paleo-Pacific plates in the Triassic and then became a super-ductile shear belt. During the post-Indosinian collision, especially in the Middle-Late Yanshanian (130-70 Ma) and Cenozoic, the active continental margin of eastern China entered into the period of intense back-arc spreading, which led to the formation of alkali granite belts (130-70 Ma) along the eclogite belt and the subsidence of many extensional red basins (100-70 Ma) and Cenozoic depression. These lines of evidence demonstrate the elevation of the ultra-high-pressure metamorphic belt from the upper mantle to the earth surface.