Adakites or Adakitic Rocks and Associated Metallogenesis in Eastern China
LI Yin1,2,LING Mingxing1,2,DING Xing1,2,LIU Jian1,2,HAN Feng1,2 and SUN Weidong1(1.Guangzhou Institute of Geochemistry,Chinese Academic of Sciences,Guangzhou 510640,Guangzhou,China;2.Graduate University of Chinese Academic of Sciences,Beijing 100049,China)
Adakites were proposed over a decade ago to be products of the melting of young subducted oceanic crust,belonging to the intermediate-acid volcanic and intrusive rock,which have distinct characteristics of high Al2O3,Sr contents and Sr /Y ratios,but low Y,Yb contents and K2O/Na2O ratios,without obvious Eu anomalies. Since discovered and named 30 years ago,adakite is universally acknowledged as one of the frontier topics in earth science. There are two main reasons why the study on adakites is not forwarding rapidly. One is their special geochemical nature,the other is metallogenesis. Eastern China is the most abundant adakites concentrated area,mostly distributed in the Lower Yangtze Region and Eastern Shandong and Shanxi-Beijing-Liaoning (subdivided into Beijing-Hebei and northeast region) three districts. Among them except Beijing-Hebei,other three regions are all important copper-gold metallogenic belts. Four genetic model proposed before by other geologists are as follows: ancient thickening lower continental crust melting,underplated basaltic lower crust melting,melting of delaminated lower continental crust and mid-ocean ridge subduction. However,the relationship between copper-gold metallogenesis and adakites is still controversial. Generally,adakitic magmas are thought to be enriched in fluid,with high oxygen fugacity and mafic source rock,which are favored by Cu,Au and other deeply-source metals to be extracted,enriched,and finally mineralized.