Times And Significance Of The Late Paleozoic Intrusive Rocks In Xiwuqi Baiyinguole Area,Inner Mongolia

The research area is located in Xiwuqi Baiyinguole area, Inner Mongolia,the tectonic position is in Xilinhot microcontinent which is between the North China plate and the Siberia plate. This paper is based on the 1: 50000 regional mineral geological survey projects in Xiwuzhumuqinqi Baiyinguole and other four, Inner Mongolia to research the geochronology、petrology and geochemistry of Late Paleozoic gabbro mass 、 diorite mass and syenite granite in this region, and discuss its tectonic significance:The rock above were carried out accurately LA-ICP-MS zircon U-Pb dating in this time, dating results show: gabbro mass formed in the late of Early Carboniferous(322-325Ma);diorite mass formed in the early of Late Carboniferous(317.0 ± 3.4Ma);but syenite granite was in the late of Early Permian(258.5 ± 6.8Ma).The result of petrology and geochemistry of these intrusive rocks are displaying that: among the late of Early Carboniferous quartz monzonite gabbro、the early of Late Carboniferous quartz monzonite gabbro diorite and dioritic porphyrite, the content of SiO2 are between 54.13-63.29%, poor mafic, belonging to neutral rock which are high k calc-alkaline series, having relatively enrichment of light rare earth, REE pattern are displayed as the right type, negative Eu anomalies, trace elements are enriched Rb, Th, U, loss of Ta, Nb, P, having the characteristics of island arc magmatic rocks. There are both the product of lithospheric mantle partial melting and the effect of fractional crystallization of magma, and on the tectonic discrimination diagram, the samples are within the CAB area, suggesting the active continental margin environment which are related to the subduction of oceanic crust- abatement.The late of Early Permian syenogranite has highly SiO2 content, which is between 77.15-83.61%, poor calcium and magnesium, A/CNK is more than 1 which is between 1.08-1.79, belonging to a peraluminous rock which has the high-K calc-alkaline series, having relatively enrichment of light rare earth, REE pattern is rightist Seagull, trace elements are enriched K, Rb,loss of Ba, Sr, P, Ti, negative Eu anomalies which related to the fractional crystallization of plagioclase, and it should be a typical A-type granites. The rock is the result of shell type magma source which is strongly influenced by fractional crystallization. On the tectonic setting diagram, falling into the post-orogenic granite area, indicating post-orogenic extensional tectonic setting.Combining region intrusive rocks of geochronology, geochemistry and the evolution of environmental characteristics Hegenshan ocean basin in Late Paleozoic thought that the research area was already in active continental margin tectonic environment about Hegenshan subduction-abatement in the late of Early Carboniferous to the early of Late Carboniferous, during the late of Early Permian showing the post-orogenic extensional tectonic setting, all of these indicating that Hegenshan ocean should be closed in between the early of Late Carboniferous and the late of Early Permian.