Trace Elements of Zircon from Late Permian Granites in the Ailaoshan Tectonic Belt and Its Significance
The Ailaoshan tectonic belt is an excellent subject for studying the evolution of the Paleo-Tethys Ocean.However,this tectonic belt has undergone multi-stage tectonic deformations due to later geological processes,particularly the collision between the India-Eurasian plates during the Cenozoic,which has led to a controversial evolution history for the Ailaoshan tectonic belt.Most previous geochemical studies focused on the analyses of the whole-rock major and trace elements.While whole-rock compositions can be affected by later multiple geological alterations,these results are ambiguous.As a common accessory mineral in granitic rocks,zircon exhibits high resistance to both physical and chemical weathering;therefore,its chemical characteristics are well preserved.To address problems concerning the subduction in the Ailaoshan tectonic belt,three S-type granitoid samples(two from the east high-grade metamorphic belt and one from the west volcanic rock belt)were chosen for zircon trace element analyses.The previous zircon U-Pb dating results showed that all zircon grains were formed during the Late Permian.Their zircon trace elements show obvious characteristics of S-type granite.In the chondrite-normalized REE patterns of the zircon grains,light rare earth elements were relatively depleted,while heavy rare earth elements were are obviously enriched and are characterized by obvious positive Ce anomalies and negative Eu anomalies.The zircon LREE-HREE trace element characteristics of these three samples are similar to those of granitoids formed during subduction,which differ from previous understandings that S-type granites are the products of plate collision.Therefore,combined with the data from previous studies,we suggest that the Ailaoshan Ocean was still experiencing subduction during the Late Permian and that it was likely subducted eastward and westward simultaneously.
Late PermianAilaoshan Oceanzircon trace elementsubductioncollision
万方数据
维普
