Geochemical Genesis Of Four Nearly EW Early Cretaceous Granitic Belts In The Eastern Yangtze Block

Four nearly EW-trending granite belts are distributed in the adjacent areas of Zhejiang,Jiangxi and Anhui in the eastern part of the Yangtze Block.From north to south,they include the Huayuangong-Yaocun Belt,the Guniujiang-Heqiao Belt,the Ehu-Duanshen Belt and the Damaoshan-Sanqingshan Belt.The predecessors have done detailed work on one or several of the granite intrusions,but have not carried out systematic analysis on the whole.In this paper,petrology,petrogeochemistry and chronology of four granite belts with characteristic nearly East-West distribution are systematically studied and comparatively analyzed.Results show that the four granite belts all belong to the high-k calc-alkaline series with high SiO₂ and total alkali.The earlier Ehu-Duanshen belt is strongly peraluminous and depleted of heavy rare earth elements.The REE patterns of this belt is a right-ward oblique curve with weak Eu negative anomalies and relatively obvious Nb-Ta anomaly;the later three belts are metaluminous to wake peraluminous,and are similar to the Late Yanshanian in geochemical characteristics,such as strong Eu negative anomaly,"V"type of rare earth element spider diagram,and the strong deplation of Ba,Sr,P,Ti,weak Nb-Ta abnormality,which is consistent with the characteristics of late Yanshanian A-type granite.The rocks of four belts are all A-type granites,indicating the extensional environment.The forming age of four belt granites are oncentrated in 135–120 Ma,the early Cretaceous,among which,the age 135–130 Ma of Ehu-Duanshen granite belt in northeast Jiangxi is slightly earlier than the other three granite belts,and the South China is in the extension stage during this period,therefore,it is presumed that the four belts are extensional A-type granites formed by two magmatic activities in late Yanshanian.The petrogenetic discriminative indicators reveals the formation environment of the Ehu-Duanshen belt is syn-collision,while the other three belts emplaced in the intraplate,suggesting that the diagenetic geological background has transited from the tectonic regime transition period to the later stage,reflecting the gradual evolution of the extensional environment of the Paleo-Pacific plate retreating from the subduction and compression environment in South China during this period.In addition,it is considered that the formation of the four EW-trending granite belts is jointly controlled by shallow response and the the extension caused by the roll-back.