Geochemistry and petrogenesis of Late Mesozoic granitoids in southeastern Hubei Province and constrains on the timing of lithospheric thinning,Middle-Lower Reaches of the Yangtze River,eastern China

The granitoids in southeastern Hubei Province are an important component of the Middle-Lower Yangtze River igneous rock belt,but the genesis and tectonic setting are poorly constrained.Geochemical study was carried out for these granitoids in southeastern Hubei Province,eastern China,in order to constrain their petrogenesis and timing of lithospheric thinning.These granitoids dominantly exhibit high alkali and high K_2O contents,and are characterized by enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE),and relative depletion in Nb,Ta and Ti.Geochemical evidence indicated that intermediate-acid rocks during the earlier stage are similar to high-SiO_2 adakite,but acid-rocks during the later stage such as granite and granite porphyry are different from adakite,and these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent.Integration of geochronology with the changing compositional trends for these granitoids indicates that lithospheric thinning probably commenced in the Early Cretaceous(132 ～ 128 Ma) in the Middle-Lower Yangtze River,eastern China.