Metamorphic evolution,protolith formation time and tectonic implications of garnet-plagioclase amphibolite in the Susong complex of the Dabie Orogenic Belt
The Dabie Orogenic Belt(DOB)was formed by the subduction-collision between the Yangtze Plate and the North China Plate,which contained the largest and most complete variety of ultrahigh-pressure rocks in the world,and comprehensively recorded the process of continental deep subduction.However,few studies involve in the subduction and exhumation process of the'shallow'level(at crust),and restricts overall understanding for the formation process of the DOB.In this study,the garnet-plagioclase amphibolite from the Susong complex in the southernmost of the DOB has been investigated by carrying out petrology,mineral chemistry,P-T estimates and chronology in detail.The result show that the garnet-plagioclase amphibolite contains three metamorphic stages of Ⅰ,Ⅱ and Ⅲ,in further stage Ⅱ can be divided into stage Ⅱ-a and Ⅱ-b.The P-T conditions for these stages correspond to ① Stage Ⅰ:T=562±12℃,P=1.03±0.05GPa;② Stage Ⅱ-a:T=663±8℃,P=1.09±0.04GPa;③Stage Ⅱ-b:T=508～584℃,P-setting=0.5～0.7GPa;④ Stage Ⅲ:T=396～472℃,P-setting=0.1～0.3GPa,respectively,and display a clockwise P-T path.The process from ① to ② shows a nearly isobaric heating,and reflects a subduction stagnation.This imply that the'shallow'subdution terminates at the Moho and is subject to a continuous heating by the supply of heat from the underlying lithospheric mantle.While the process from② to ③ and ④ exhibits a cooling and depression pattern,and reveals a slow exhumation.Obviously,the'shallow'subduction in the DOB belongs to the'warm'subduction and shows a slow metamorphic evolution process.On the contrary,the continental deep subduction of the DOB as a typical'cold'subduction has undergone a rapid evolution process.In zircon U-Pb dating,all zircons from garnet-plagioclase amphibolite develop oscillatory zoning.Thirty-seven spots have been analyzed with 207Pb/206Pb ages ranging from 1470±80Ma to 1258±101Ma,and yield a weighted mean of 207Pb/206 Pb age of 1381±25Ma with higher Th/U ratio＞0.4,representing the age of igneous protolith2.This age can be considered as the end time of breakup of the Columbia supercontinent.In addition,129±5Ma of quartz-rich granite,which intruded into the garnet-plagioclase amphibolite,reflects the Mesozoic extensional event in eastern China.Combined with previous age data,1.38～1.30Ga can be inferred as time note of the transition from the Columbia to the Rodinia supercontinents.Meanwhile,it is confirmed that the Susong complex is composed of different ages and type of rocks,and a key metamorphic unit to unravel the complex and endless evolution process for the Yangtze Plate from Neo-Archean to the Mesozoic.
万方数据
维普
