论文部分内容阅读
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4000km。柴北缘片麻岩中含柯石英锆石的SIMS离子探针原位微区U-Pb定年获得超高压变质年龄452±13.8Ma,锆石的退变质年龄419±6.7Ma。SHRIMPU-Pb定年获得秦岭含金刚石片麻岩中锆石的下交点年龄502±45Ma,上交点年龄1545±100Ma,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±82Ma和下交点493±170Ma,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441Ma±9Ma,449Ma±9Ma,和442±9Ma,平均444±9Ma,核部含斜长石+磷灰石锆石年龄为761±13Ma,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,如中央造山带中大量10亿年左右的花岗岩及基性超基性岩类;罗德尼亚大陆之后第一次裂解作用可能发生在800年左右;其后早古生代加里东期的洋盆裂开,蛇绿岩和超高压变质岩石的大量出现是一次十分强烈的板块构造事件,从东到西,沿中央造山带均有分布;加里东期造山事件之后印支期沿该造山带又有一次大的板块裂解和俯冲碰撞作用,表现在勉略蛇绿岩洋壳及大别-苏鲁印支期超高压变质带的存在。中央造山带保留和记录了多期裂解、会聚事件,通过对其解剖,不仅可以认识中国大地构造格局和演化,并由此理解全球的大陆漂移、一系列大裂解和大会聚等大的地质事件。
Along the central orogenic belt there is a huge UHP metamorphic belt, the west Altyn-Qilian, east Qinling, extending to Dabie - Sulu, the total length of more than 4000km. The U-Pb dating of SIMS ion probe with keshenite zircon in the gneiss of northern Qaidam resulted in ultrahigh-pressure metamorphism age of 452 ± 13.8Ma and degenerated age of zircon of 419 ± 6.7Ma. The SHRIMPU-Pb dating of the zircons in the diamond-bearing gneisses from Qinling Mountains is 502 ± 45Ma and the age of 1545 ± 100Ma at the turning-over point. The former indicates the age of ultrahigh-pressure metamorphism, and the latter is the magmatic zircon age of the original rocks. The upper zircon dating of 1381 ± 82Ma and the lower intersection of 493 ± 170Ma indicate that the upper intersection represents the eclogite protolith age and the lower intersection represents the ultrahigh-pressure metamorphism age. The Qinglongshan eclogite in Donghai County, Jiangsu Province contains ettringite and other ultra-high pressure The age of mineral zircons is 441Ma ± 9Ma, 449Ma ± 9Ma, and 442 ± 9Ma, with an average of 444 ± 9Ma. The zircons of plagioclase + apatite in the core are 761 ± 13Ma, indicating that the former represents the age of UHP metamorphism, The latter represents the original eclogite rock crystallization age. It is considered that there are two stages of UHP metamorphism along the central orogenic belt in central China. The first phase is the Caledonian phase and the second is the Indosinian phase. The UHP metamorphic events of the two phases are different in space-time distribution. High-pressure metamorphic events extend from the northern Arjin-Qaidam margin to the Dabie-Sulu, eastern Indosinian UHP metamorphic event was not found in the west of the Dabie. The central orogenic belt should be considered as a multi-period orogenic belt. The earlier formation of the Greenwell orogen in the mainland of Romania may have left about one billion tectonic magmatic events recorded in the Central Orogenic Belt. For example, The granites and mafic ultrabasic rocks in about years; the first cleavage after the mainland of Romania may occur about 800 years; later the Paleozoic Caledonian oceanic fissure, ophiolite and ultra-high pressure The massive occurrence of metamorphic rocks is a very intense tectonic event with distribution along the central orogenic belt from the east to the west. After the Caledonian orogeny, there was a major plate lump and subduction collision along the orogenic belt after the Caledonian orogeny It is manifested in the existence of the Miaoluo ophiolite oceanic crust and the Dabie-Sulu Indosinian UHP metamorphic belt. The Central Orogenic Belt retains and records multi-stage cracking and converging events. By dissecting it, not only the structure and evolution of the earth’s structure in China can be recognized, but also large geological events such as global continental drift, a series of major cracking and congress gatherings .