秦岭—大别高压超高压变质带构造特征及构造演化

THE TECTONIC CHARACTERISTICS AND EVOLUTION OF THE QINLING-DABIE HIGH-PRESSURE AND ULTRAHIGHPRESSURE METAMORPHIC BELT,CENTRAL CHINA

秦岭—大别高压超高压变质带是地中海全球近纬向活动带的组成部分。地中海活动带具有长期活动历史，高压超高压变质岩发育在不同时代的褶皱带中。秦岭—大别高压超高压变质带以丹凤—商南—信阳—桐城对接带为界分为秦岭和鄂北—桐柏—大别两个高压超高压块体，前者分为南北两个高压变质带，后者进一步划分为蓝片岩带、高压低温榴辉岩带、超高压榴辉岩带、高压中温榴辉岩带和贫榴辉岩带。它们均具有准对称展布特征。不同地区高压超高压变质岩差别颇大，甚至是不同时期的产物，但概括起来它们共同经历了五个变形阶段：前高压超高压阶段（Ｄ＿１）、高压超高压变质形成阶段（Ｄ＿２）、区域性面理形成阶段（Ｄ＿３）、韧性剪切带形成阶段（Ｄ＿４）、隆升剥露阶段（Ｄ＿５）。它们组成一个完整的变形序列。通过构造年代学研究得出五组年龄值，分别代表不同地质意义，第一组２０００Ｍａ左右，可能为高压超高压变质岩原岩年龄，第二组晋宁期（７００～１０００Ｍａ），为高压变质岩形成时期，第三组加里东期（４００～５４０Ｍａ），是秦岭一大别高压超高压变质岩主要形成时期和变质峰期，第四组海西期（２１～３２６Ｍａ），代表榴辉岩退变质年龄，第五组印支期（２０５～２４３Ｍａ），是另一次高压变质?

The Qinling-Dabie high-pressure (HP) and ultrahigh-pressure (UHP) metamor-phic belt is one of the major constituents in the quasilatitudinal global mobile belt of Mediterraean, which has a long mobilization history. The HP-UHP rocks are developed in folded belts of various ages.In the Qinling-Dabie HP and UHP metamorphic belt the two HP and UHP metamorphic terranes, namely, the Qinling and North Hubei- Tongbai-Dabie, are subdivided by the delineation of the convergent suture of Dangfen g-Shangnan-Xinyang-Tongcheng fault. For the former, Qinling terrane, there are two HP belts in the south and north respectively. For the latter it is further subdivided into blueschist belt, HP/LT eclogite belt, UHP eclogite belt, HP/MT eclogite belt and eclogite-poor belt. All of them are roughly symmetric in spatial distribution.The HP and UHP metamorhpic rocks are greatly diversified in various regions. They were even formed in different ages. Generally speaking, there are five stages of deformation, namely,HP-UHP stage (D1 ), HP-UHP metamorphic stage (D,), the formation of regional foliation stage (D,), ductile shear deformation stage (D,), uplift and exhumation stage (D,), comprising a complete deformational sequence.Based on the study of tectono-isotope chronology, five age groups have been obtained. The first group about 2000Ma is probably the protolith age of HP and UHP metamorphic rocks; the 2nd group of Jiningian (700～1000Ma) is the formation stage of HP metamorphic rocks; the 3rd group of Caledonian (400-540Ma) represents the main period formation and metamorphic peak stage of HP-UHP metamorphic rocks; the 4th group of Hercynian (271～326Ma) represents the retrogressive metamorphism of eclogites; the sib group of Indosinian (205～243Ma) is another age of formation of HP metamorhpic rocks.Therefore, we can identify four tectonic evolution stages: Meso-Neoproterozoic stage, early Paleozoic stage, late Paleozoic to Middle Triassic, and the post-Triassic stage.