Chronology And Geochemistry Of The Early Cretaceous Intrusive Rocksin The Southern Of Tahe,Northern Great Xing'an Range

This thesis presents zircon U-Pb dating,in-situ Hf isotopic and geochemical data for intrusive rocks from the southern of Tahe,northern Great Xing'an Range,in order to constrain their petrogenesis and tectonic settings.Rock types involved are from the continuous series of basic to intermediate to acid?SiO₂=51.27%⁷4.90%?.Rock types include gabbro,monzodiorite,granite,etc.ZirconU-Pb dating indicate that the intrusive rockswere emplaced at 126.97±0.89 Ma,123.4±1.0Maand 123.6±0.6Ma,respectively?i.e.,in the Early Cretaceous?.The intrusive rocks in the Harker illustration,most of the major elements and trace elements have a good linear evolutionary trend with the increase of SiO₂ content?except K₂O and Rb?.Trace elements of the overall display are enriched Pb and LILE?K,Rb,Ba?,depletedinHFSE?Nb,Ta,Ti,P?,and have similar Sr and Nbisotope characteristics(⁸⁷Sr/⁸⁶Sri=0.705517⁰.706827,^?Nd?t?=-6.82⁰.79).These facts,indicate that the Early Cretaceous intrusive rocks in the southern of Tahe were derived froma mixed source of garnet lherzolite phase and spinellherzolite phasewhich were metasomatized by fluid or melt related to subduction,and the garnet lherzolite phasewaspredominant,in the process of the rapid rise of magma,it has experienced the process of fractional crystallization,finally,a broad spectrum of magma sequences is formed.The paper reviews the distribution of volcanic rocks in northeast China,paleomagnetic data,the time of the Mongolia-Okhotsk ocean closure and the subduction direction of the Paleo Pacific Plate.These data implythatthe Early Cretaceous intrusive rocks in the southern of Tahe,northern Great Xing'an Range was attributed to post-orogenic diffuse extension by the closure of the Mongolia-Okhotsk ocean.The magma activity of Transbaikalia,Mongolia and the northern Great Xing'an Rangewas mainly influenced by the closure of Mongolia-Okhotsk ocean,the magmatism in the eastern part of Jilin andHeilongjiang Province,the Liaodong Peninsula,the Jiaodong Peninsula and the Korean Peninsula is mainly influenced by the subduction of the Paleo Pacific Plate,the lesser Xing'an range-Zhangguangcai Ling range,the southern Great Xing'an Range and northern margin of North China may be the result of these two tectonic regimes.