Grenvillian Metamorphism And Tectonic Implication Of The Larsemann Hills,Prydz Bay,East Antarctica

Previous studies have shown that Grenvillian and Pan-African two-stage tectonic thermal events have extensive effects on the Prydz Bay in East Antarctic.Therefore,the evolution process of the Prydz belt is of great significance for studying the formation and evolution of the Rodinia supercontinent and Gondwana supercontinent.The Prydz Bay has attracted much attention from scholars,but there is still controversy about the formation time and tectonic evolution of the Prydz Belt.The Larsemann Hills are located in the center of the Prydz belt,so research on it can well reflect the evolution of the Prydz Bay.The middle-high grade metamorphic rocks exposed in the Larsemann Hills are the main components of the Prydz rock series,ideal objects for studying the composition and evolution of the Prydz Bay.This study has been based on the premise of systematic field geological survey,and further selected representative metamorphic rock series of the Larsemann Hills for petrology,petrography,mineral geochemistry,pseudosection modelling,zircon U-Pb isotope chronology,zircon REE,Zircon Lu-Hf isotope study.This study mainly obtained the following conclusions:?1?The original rocks of the garnet-bearing felsic paragneisses in the Larsemann Hills were dehydrated during the Grenvillian period to form the Grt+Pl+Kfs+Ilm+Sil+Qtz+melt mineral assemblage.Their sedimentary age is constrained not older than 1064±18 Ma.The source is Mesoproterozoic magmatic rock,which belongs to S-type granite.The P-T conditions in the early Grenvillian period(M_1-1,?1000 Ma)were?9.6 kbar,?820°C.?2?The primary rocks of the felsic orthogneisses in the Larsemann Hills of Prydz Bay are granites with an emplacement age of 976±9 Ma.The main minerals are Grt+Bt+Pl+Kfs+Qtz+Mgt.The metamorphic P-T conditions in the late Grenville(M_1-2,?900 Ma)were?9.5 kbar,?870?.?3?The large-scale metamorphic process of the Grenvillian period in the Prydz Bay is divided into two scenes.The first scene(M_1-1)occurs at?1000 Ma.It is mainly a rapid return of near isothermal decompression,followed by the second scene M_1-2??900 Ma?.Subsequently,the second act(M_1-2,?900 Ma)was mainly a plate turning back slowly,and the temperature and pressure gradually decreased.The process of metamorphism in the Prydz Bay during the Pan-African period reflects to a significant intracontinental reworking.The Pan-African suture zone should be located somewhere else under the ice cap in the Prydz Bay.After the Pan-African event,the Prydz Bay was a continental margin basin.?4?During the formation of the paragneisses and the orthogneisses in the Larsemann Hills,the environment has not changed significantly.Their deformation and metamorphic characteristics are also basically the same,indicating that they are formed in the same tectonic environment.?5?The Larsemann Hills existed as stable landmasses in the arc-shaped basin outside the Indian-Antarctic craton coast in the Mesoproterozoic.