| The southern Anhui Province is located in the southeastern margin of the Yangtze Craton, with the eastern Jiangnan uplift. In this paper we select the Qingyang-Jiuhuashan complex plutons and the Taiping-Huangshan complex plutons for major elements, LA-ICPMS zircon U-Pb and Hf-O isotopic studies. LA-ICPMS zircon U-Pb dating results show that Qingyang-Jiuhuashan complex plutons and Taiping-Huangshan complex plutons can be divided into three different sub-period. Early intrusive rocks of granodiorite formed between 149.3±2.4 Ma to 138.3±1.4 Ma; Middle intrusive rocks of monzogranite formed between 145.1±1.7 Ma to 132.8±1.5 Ma; Later intrusive rocks of K-feldspar granite formed between 134.9±2.6 Ma to 128.4±1.4 Ma. Combined with other high-precision published chronology data, Yanshanian magmatism in the southern Anhui Province can be subdivided into three stages:the early stage of 136-153 Ma, the middle stage of 136-129 Ma, and the latest stage of 129-122 Ma. Granodiorite of the early stage have SiO2 contents ranging from 66%-68%, relatively lower MgO contents (1.2%-1.5%), total alkali contents ranging from 7.1% to 7.5%, K2O/Na20>1, A/CNK<1, A>NK, a geochemical signatures which belong to the high potassium calc-alkaline series and metaluminous Ⅰ-type granite. Monzogranite of the middle stage have relatively high SiO2 contents 68%-69%, other signatures of the major elements are similar, total alkali contents ranging from 7.7%-8.6%, K20/Na20>1, A/CNK>1, A>NK, belong to the high potassium calc-alkaline series and weakly peraluminous Ⅰ-type granite; K-feldspar granite of the latest stage is charactered by high SiO2 (73%-77%), lower CaO contents (0.2%-0.8%), A/CNK>1, A>NK, K2O/Na2O>1, also showing the high potassium calc-alkaline series affinities, but being A-type granite. The εHf(t) values of zircons in granodiorite from the Qingyang pluton and the Taiping pluton range from-9.54±4.86, with the zircon δ18O values are between 6.68‰-8.42‰; The εHf(t) values of zircons in monzogranite from the Qingyang pluton and the Taiping pluton range from -11.40±9.43, with the zircon δ18O values are between 7.16‰±8.04‰; Zircon Hf-O isotopic in K-feldspar granite from the Jiuhuashan pluton and the Huangshan pluton show different characteristics, the Jiuhuashan pluton have relatively high εHf(t) values range from -7.62±4.78, with the zircon ε18O values are between 7.03‰-8.84‰, the Huangshan pluton εHf(t) values range from -6.56±1.20, zircon δ18O values are between 6.27%o-8.34%o.Integrated studies of the major elements and zircon Hf-O isotopes indicate that, the granodiorite and monzogranite pluton of southern area of Anhui Province were formed by melt mixing which separately derived from partial melting of the lithospheric mantle which metasomatized by the fluid/melts from the subducted slab, and the late Archaean-early Proterozoic crust which were induced to partial melting by the underplating basaltic magma, under a tectonic setting of the Pacific plate low-angle subduction. Associated with increase of the subducted angle and roll-back of the subducted slab, the tectonic setting in the southern Anhui Province transformed into back arc extension, caused by slab tearing formed slab window ridge subduction, then the asthenospheric mantle upwelling along the fault. K-feldspar granites of the southern Anhui Province were formed by anatexis of the Mesoproterozoic basement under a condition of relatively low pressure and high temperature. |
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