The Geochemistry And Tectonic Significance Of The Volcanic Rocks In Tianbaoshan Formation Of The Huili Group In The Western Yangtze Block

The Tianbaoshan Formation volcanic rocks?¹.0Ga?of the Huili Group,NS-trending,located in the western margin of the Yangtze Block which are composed mainly of dacites,rhyolites.These volcanic rocks have the important significance to understanding the tectonic evolution of the basement of the Yangze Block and discussing the supercontinent Rodinia relationship?This article aims at analyzing the TianbaoshanFormationvolcanicrocks'petrological,zirconU-Pb chronology,geochemistry and isotopic geochemistry of the Hongchuanqiao and Tianbaoshan in Huili countryThe volcanic rocks we got from Tianbaoshan and Hongchuanqiao of Huili are dacites and rhyolites.They were dated at 1036±29Ma and 958±19Ma by the SHRIMP zircon U-Pb method,respectively.The rock geochemistry results indicate that dacites have SiO₂ contents ranging from 64.54 to 69.17 wt%,K₂O/Na₂O values from 0.45 to4.80,A/CNK>1.1,with the characteristics of“S”type granitic rocks.The dacites?Nd?t?=-5^-4,?Hf?t?=-35.8⁺4.8,T_2DM=1700²300Ma.show the source of dacites derive from partial melting of ancient continental crust,formed in the subduction-colision tectonic setting.Those Rhyolites have SiO₂ contents ranging from 73.67 to78.60 wt%,with high REE(254.39×10^-6489.1×10^-6),Zr+Nb+Ga+Y(586.41×10^-6726.80×10^-6)values,10000×Ga/Al>2.6,which have the characteristics of“A”typegranite.Thoserhyolites?Nd?t?=-1.1^-0.8,?Hf?t?=-2.2⁺9.4,T_2DM=1300¹500Ma he source rocks of felsic igneous rocks in the crust.In the Chondrite-normalized REE patterns.dacites and rhyolites have a obvious Eu anomaly.In the primitive mantle-normalized spidergrams show enrichment of Rb,Th,lower content of Nb,Ta,and have Ti,P,Sr.anomaly.Our results show the Mesoproteozoic magmatism activities in the western of the Yangtze block are according to the microplates movement.This studymay not support the existence of a Grenvillian orogenic belt in western Yangtze.