Zircon U-Pb Ages?geochemical Characteristics And Its Tectonic Setting Of Volcanic Rocks From Manitu Formation In Suolun Area,Central Great Xing'an Range

This thesis studies the well-developed Mannitu Formation volcanic rocks of Suolun area in the major ridge of the middle section of Great Xing'an Range.Based on previous studies,the rock assemblage,distribution rules and geochemistry of Mannitu Formation volcanic rocks will be described,and the nature of magma source,petrogenesis and tectonic settings will be discussed in this paper,which will provide new information to researches of the volcanism and tectonic evolution history in Late Jurassic to Early Cretaceous in mid-southern Great Xing'an Range area.1.Geological characteristics of Maitu Formation volcanic rocksPetrographically,the volcanic rocks in manitu formation from suolun are composed of andesite trachy-andesite and dacite,but they are mainly trachy-andesite with minor rhyolite or Basaltic andesite based on chemical composition.2.Chronology characteristic of Manitu Formation volcanic rocksThe results of LA-ICP-MS ziron U-Pb dating are 130±1Ma,132±1Ma and 130±2Ma,ircon U-Pb dating results show that they formed at early cretaceous from 130 to 132 Ma..3.Geochemistry characteristic of Manitu Formation volcanic rocksThese volcanic rocks are alkiline series in composition and rich in aikali and potassium;They are highly in total rare earth elements(? REE=95.19 ~ 198.38)×10-6,highly fractionated LREE From HREE(6.38 ~ 10.59)× 10-6and negative Euanomalies(?Eu=0.68~1.01).they contain LILE(K?Rb?Th)and LREE,but low HFSE(Nb?Ta?P?Ti).Trace element with high Sr(> 499×10-6)?low Yb(the maximum is2.83×10-6< 3.6×10-6)?low Y(majority < 29.9×10-6)and high Sr/Y as well as low Rb/Sr ratio,shows the characteristic of the arc volcanic rocks.4.Lu-Hf isotope Characteristics and evolution of magma source of Manitu Formation volcanic rocksManitu Formation volcanic rocks have positive values of ?Hf(t)(7.3~13.7),The initial176Hf/177 Hf ratios for magmatic zircons from these volcanic rocks vary in the range of0.282899-0.283077.The dates suggest that the magmas for these volcanic rocks derived from The upper mantle in major,and Affected by the subduction of fluid.5.The tectonic setting of Manitu Formation volcanic rocksThe volcanics belongs to high-K calc-alkaline series as well as a few and calc-alkaline rocks,which is Lower in Si O2 content.Volcanic Formed in the island arc environment,were related to the subduction of the palaeo-pacific plate.