大别造山带变质岩地层年龄及其构造意义

Isotopic Ages of the Metamorphic Rocks in the Dabie Orogen and Their Tectonic Significance

选择近期在大别山及苏鲁地区各类变质岩地层中采用不同测试方法所获得的较为精确的同位素年龄数据共４５个进行分析，得到以下几点主要认识：１）扬子板块被动陆缘形成于８００～７００ＭａＢ．Ｐ．之间；２）根据原岩及折返动力学机制分析，南大别与苏鲁超高压、高压变质岩石是扬子板块被动陆缘（大陆隆）物质残余，在２３２～２２１ＭａＢ．Ｐ．伴随扬子板块被动陆缘俯冲到华北板块之下最大限度时在１００ｋｍ上地幔软流圈深度发生超高压变质作用，同时在较浅的构造层次上发生高压及角闪岩相变质作用。这些超高压、高压变质岩石在２２０ＭａＢ．Ｐ．开始折返，然后于２０６～１７８ＭａＢ．Ｐ．快速完成角闪岩相退变质作用；３）北大别高温变质岛弧在１３３～１２２ＭａＢ．Ｐ．伴随白垩纪花岗岩侵入体活动快速抬升，平均冷却速率达３５°Ｃ·Ｍａ－１；４）北大别高温变质岛弧与南大别超高压变质陆隆在１２０～１１０ＭａＢ．Ｐ．停止相对运动，归并为一体。

Based on 45 isotopic ages which were analyzed by several methods in stratigraphy of metamorphic rocks of the Dabie and Su Lu regions in recent years, this paper gives some conclusions in the following: 1) Passive continental margin of the Yangtze Plate was developed during 800~700Ma B.P.; 2) Ultrahigh pressure and high pressure metamorphic rocks of the south Dabie and Su Lu regions are relic components of passive continental margin of the Yangtze Plate according to the analyses of protolith and geodynamic mechanism of ultrahigh pressure metamorphic rocks returning. Material of passive continental margin of the Yangtze Plate experienced the ultrahigh pressure metamorphism at 100km of subasthenospheric depth, when passive continental margin of the Yangtze Plate subducted under the North China Plate within maximum limitation of 232~221Ma B.P., and others experienced high pressure or amphibolitic facies metamorphism at shallow structural levels. These ultrahigh pressure and high pressure metamorphic rocks began returning in 220Ma B.P. and then completed amphibolitic facies retrograded metamorphism between 206 and 178Ma B.P.; 3) North Dabie high temperature metamorphic rocks are relic material of an island arc and uplifted rapidly during 133~122Ma B.P.,accompanied with granite intrusion in Cretaceous age, the average cooling speed is 35°C·Ma -1 ; 4) The north Dabie high temperature metamorphic rocks were combined with the south Dabie ultrahigh pressure metamorphic rocks in 120~110Ma B.P., then joined together.