中央碰撞造山带中两期超高压变质作用来自含柯石英锆石的定年证据  

Two Ultrahigh Pressure Metamorphic Events Recognized in the Central Orogenic Belt of China: Evidence from the U-Pb Dating of Coesite-bearing Zircons

作　　者：杨经绥[1] 刘福来[1] 吴才来[1] 万渝生[1] 张建新[1] 史仁灯[1] 陈松永[1] 

机构地区：[1]中国地质科学院地质研究所大陆动力学实验室,北京100037

出　　处：《地质学报》2003年第4期463-477,共15页Acta Geologica Sinica

基　　金：国土资源部"十五"重点科技项目(编号 20010201);中国大陆科学钻探科学研究项目(编号 2001CCB00900);国家自然科学基金(编号 49732070)

摘　　要：沿中央造山带存在一条巨大的超高压变质带,其西起阿尔金—祁连,往东经秦岭,延至大别—苏鲁,全长超过4000 km。柴北缘片麻岩中含柯石英锫石的SIMS离子探针原位微区U-Pb定年获得超高压变质年龄452±13.8 Ma。锆石的退变质年龄419±6.7 Ma。SHRIMP U-Pb定年获得秦岭含金刚石片麻岩中锆石的下交点年龄502±45 Ma,上交点年龄1545±100 Ma,认为前者代表超高压变质年龄,后者为原岩岩浆锆石年龄;获得榴辉岩锆石的上交点年龄1381±82 Ma和下交点493±170 Ma,认为上交点代表榴辉岩原岩年龄,下交点代表超高压变质年龄;获得江苏东海县青龙山榴辉岩含柯石英等超高压矿物锆石的年龄为441±9 Ma,449±9 Ma,和442±9Ma,平均444±9 Ma,核部含斜长石+磷灰石锆石年龄为761±13 Ma,认为前者代表超高压变质年龄,后者代表榴辉岩原岩结晶年龄。认为中国中部沿中央造山带中存在两期超高压变质作用,第一期为加里东期,第二期为印支期,两期超高压变质事件在时空分布方面是不同的,加里东期超高压变质事件由西部阿尔金—柴北缘延至东部大别—苏鲁,印支期超高压变质事件没有在大别以西发现。认为中央造山带应是一个多期活动的造山带,较早形成罗德尼亚大陆的格林威尔造山运动可能留下了10亿年左右的构造岩浆事件记录。A^4000 km long ultrahigh pressure metamorphic (UHPM) belt has been set up based on the discovery of the coesite-bearing Altun-North Qaidam UHPM terrane in the west of the Central Orogenic Belt of China (COB), the finding of metamorphic diamond in Qinling in the middle, and the Dabie-Sulu UHPM terrane in the east. SIMS and SHRIMP U-Pb dating of zircons from coesite-bearing UHPM rocks indicate two UHPM events in the belt; one is occurred during the Early Paleozoic and the other during the Triassic. Coesite-bearing zircons from gneiss of North Qaidam yielded an UHP metamorphic age of 452±13. 8 Ma and a retrograde age of 419±6. 7 Ma. A diamond-bearing gneiss sample of Qinling gave a lower intercept age of 502±45 Ma,and an upper intercept age of 1545±100 Ma, while a Qinling eclogite sample gave a lower intercept age of 493±170 Ma and an upper intercept age of 1381±82 Ma. In both samples the lower and upper intercept ages are interpreted as UHPM ages and protolith ages of the rocks, respectively. Coesite-bearing zircons from the Qinglongshan eclogite in south Sulu yielded Early Paleozoic UHPM ages, 441±9 Ma,449±9 Ma and 442±9 Ma, whereas the core of zircon with plagioclase and apatite inclusion in it gave a protolith age of 761±13 Ma. The age data suggest that the Early Paleozoic UHPM rocks extend from west to east for about 4000 km across the COB and the Triassic UHPM belt extends within the Dabie-Sulu region for about 1000 km. Based on the available geochronological and geochemical data, we suggest the following tectonic model for the evolution of the COB. At about 1000 Ma the area was amalgamated to form the Rodinian continent, which contained some oceanic volcanic rocks, possibly as ophiolitic fragments. This part of Rodinia was then rifted at about 800~750 Ma to form an oceanic basin with a variety of MORB and ocean island basalts. Closure of this ocean basin produced the Neoproterozoic ophiolites and granitic gneisses. The UHPM rocks along with subduction related island arc volcanic rocks and granites o

关 键 词：中央碰撞造山带 超高压变质作用 柯石英锆石 定年证据 

分 类 号：P542.2[天文地球—构造地质学] P533[天文地球—地质学]