The timing of tectonic transition from compression to extension in Dabieshan: Evidence from Mesozoic granites  

作　　者：MA Changqian YANG Kunguang MING Houli LIN Guangchun 

机构地区：[1]Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China

出　　处：《Science China Earth Sciences》2004年第5期453-462,共10页中国科学（地球科学英文版）

基　　金：This work was supported by the National Natural Science Foundation of China (Grant No. 40334037);the Research Fund for the Doctoral Program of Higher Education (Grant No. 20010491018) ; the China Geological Survey (Grant No. 20011390018); The research is part of "211 Project" of the Earth Material Science in China University of Geosciences.

摘　　要：With the methods of single grain zircon U-Pb and hornblende-biotite Ar-Ar dating, a U-Pb zircon age (135.4(2.7) Ma of Liujiawa high Sr/Y granite and 40Ar-39Ar plateau ages (139.0(1.0) Ma and (125.3(0.2) Ma of hornblende and biotite respectively of Fenliupu high Sr/Y granite in the Dabieshan high- and ultrahigh-pressure metamorphic belt are yielded. Following the emplacement of the high Sr/Y granites, extension-related mafic intrusions and late granitoids with negative Sr and Eu anomalies and isotopic ages of 105-130 Ma were emplaced. Geochemical comparison between the two types of granitoids shows that, from early to late, the alkalinities, the K2O contents and the Sr/Y ratios as well as FeO/(FeO+MgO) ratios of the rocks increase, while the abundance of Sr reduces, suggesting that as time goes on the depth of crustal melting decreases. Rheological stratification of the crust due to early Cretaceous partial melting of crustal rocks resulted in crustal extension and deep-buried rock exhumation. Therefore, the high Sr/Y granite that appeared at ~135 Ma is the product of the tectonic transition from early shortening to late overall extension.With the methods of single grain zircon U-Pb and hornblende-biotite Ar-Ar dating, a U-Pb zircon age (135.42.7) Ma of Liujiawa high Sr/Y granite and 40Ar-39Ar plateau ages (139.01.0) Ma and (125.30.2) Ma of hornblende and biotite respectively of Fenliupu high Sr/Y granite in the Dabieshan high- and ultrahigh-pressure metamorphic belt are yielded. Following the emplacement of the high Sr/Y granites, extension-related mafic intrusions and late granitoids with negative Sr and Eu anomalies and isotopic ages of 105—130 Ma were emplaced. Geo-chemical comparison between the two types of granitoids shows that, from early to late, the al-kalinities, the K2O contents and the Sr/Y ratios as well as FeO/(FeO+MgO) ratios of the rocks increase, while the abundance of Sr reduces, suggesting that as time goes on the depth of crustal melting decreases. Rheological stratification of the crust due to early Cretaceous partial melting of crustal rocks resulted in crustal extension and deep-buried rock exhumation. Therefore, the high Sr/Y granite that appeared at ~135 Ma is the product of the tectonic transition from early shortening to late overall extension.

关 键 词：ZIRCON U-PB age  granite  EXTENSIONAL collapse  DABIESHAN Mountains. 

分 类 号：N[自然科学总论]