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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.
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 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 exh Thus, the high Sr / Y granite that appeared at ~ 135 Ma is the product of the tectonic transition from early shortening to late overall extension.