Zircon U-Pb ages and causes of the Early-Middle Jurassic granites in the Da-Xiao Xinganling Copula

Da-xiao xinganling copula large areas of intrusive rocks on the traditional understanding for the Variscan. In view of these intrusive rock, we anatomy for three typical intrusive body, and access to the latest zircon SHRIMP U-Pb age, granodiorite age 169Ma±2Ma and 177.4Ma±1.7Ma, diorite enclaves age 179Ma±2Ma. Combined with characteristics of the main elements and microelement, it showed that they formed in early-middle Jurassic-high potassium calc-alkaline series I type granite. The three of intrusive bodies host rock and diorite enclaves have low ISr(an average of 0.704668) and positive εNd(t) (1.3837～3.10652) value characteristics, diorite enclaves development needle cylindrical hornblende and hollow apatite, the characteristics of the intrusive rocks reflect granite genesis and mantle has the close relation. Geology, petrology and geochemistry of the detailed research shows that the intrusive bodies has the crust-mantle mixed origin, granitic magma source is mainly from the mantle of separation of a newborn crust, and its and the original ancient partial melting of crust of magma and produce from depleted mantle magmatic mutual mix formation. Through the regional dynamics analysis, this paper puts forward the continental crust growth may experience two continuous process, the first is late Paleozoic post-orogenic lithosphere delamination effect, causing asthenosphere mantle uplift and mantle-derived magma mattresses effect; Secondly, a wide range of areas lack Triassic sedimentary records, explain at this time should be the northern orogenic belt strong orogenic period, this mechanism may be closely related with the Mongolia-okhotsk closed orogenic, after the lithosphere plate delamination, and lead to the pre-existing new crust and the original ancient crust partial melting, thus forming granitic magma. This may be is the important mechanism of continental crustal growth in Da-xiao xinganling copula.