Exhumation And Anatexis Of Subducted Continental Crust And Magnesium Isotopic Behavior During Subduction Process

The fate of subducting slab is one of the most important topics in the study oforogenic geodynamics. In order to better understand the fate of subducting slabs,present doctoral dissertation has carried out the following investigations:(1) theexhumation history and mechanism of subducting slabs;(2) the anatexis process andmechanism of subducting or exhumed slabs;(3) magnesium (Mg) isotopic behaviorduring subduction related metamorphic dehydration process. Collectively, the mainstudy contents and achievements can be summarized as follows:(1) Granulite in northDabie ultra-high pressure metamorphic terrane (NDT) has indicated a three-stageexhumation history of NDT and rare earth element behavior during retrogression;(2)Migmatites in NDT have recorded the anatexis process and mechanism of Dabieorogen and revealed the important role of middle orogenic crustal melting in themountain root removal process;(3) Bengbu leucogranite demonstrated the origin oflow-δ18O granite and its tectonic implications to the orogenic evolution.;(4) Mgisotopic study on the metamorphic rocks with various metamorphic grades rangingfrom deep diagenetic to lower greenschist-facies to greenschist-facies toamphibolite-facies to granulite-facies to eclogite-facies, has revealed that Mg isotopefractionation during metamorphic dehydration is limited;(5) cratonic eclogites fromKaapvaal craton in South Africa have light δ26Mg values, recording ancient oceaniccrustal stacking beneath lithospheric mantle;(6) oceanic eclogites from WesternTianshan in NW China have heavier δ26Mg values, recording ancient seawateralteration.(7) eclogites from Maowu in Dabie orogen, which represent pieces ofmetasomatized mantle wedge, have lighter δ26Mg values recording ancient mantlematasomatism;(8) carbonated eclogites from Rongcheng in Sulu orogne haveextremely light δ26Mg values making Mg isotopes potenital tracer for deep carbonrecycling.