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Petrology And Geochemistry Of Early Cretaceous Intrusive Rocks In Ulanhot, Inner Mongolia, And Its Geological Significance

Posted on:2015-02-14Degree:MasterType:Thesis
Country:ChinaCandidate:Y J TangFull Text:PDF
GTID:2250330428469324Subject:Geological Engineering
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The study area lies in Ulanhot, Inner Mongolia, bewteen Wunuer-Elunchun faultand Erenhot-Hegenshan-Hehe fault, the converging area between North China plateand Siberian plate and the intersection of Paleoasian tectonic domain and Pacificdomain. Study on petrology,oetogechemistry and chronology of early Cretaceousintrusive rocks was conducted based on regional geological survey.LA-ICP-MS U-Pb dating result revealed that the formation time of intrusiverock is144.05±0.6Ma、132.24±0.54Ma、130.8±0.95Ma、129.6±1.1Ma、125.9±1.1Ma、126.27±0.61Ma and125.9±1.4Ma. On basis of the chronology characteristics,three-phase early Cretaceous intrusive rocks can be identified, and the early stage isrepresented by quartzmonzodiorite from Xinglongtun pluton, while the middle stage isconsist of granite prohyry from Bagexincang pluton, and syenogranite,granite fromXinglongtun pluton and granite from Wubulinzhage pluton, and the late one isdominated by gabbro from Xieertala pluton.The trace elements and Hf isotopic characteristics indicate the granite probablyderived from the partial remelting of lithosphere. However,geochemical characteristicssuggest the gabbro might derive from lithospheric mantle. Compared with intrusiverocks in the study area and its adjacent areas, the early Cretaceous intrusive rocks inUlanhot area probably formed under an extensional setting related to the delaminationof lithsphere and the extension, to some extent, was different. In early Cretaceous, thepressure declined because of the transform of tectonic regime or the primarydelamination of lithsphere that magma upwelled and intruded to formed the early Cretaceous. And then in middle Cretaceous, large-scale delamination happened in crustand lithspheric mantle and started to melt due to the baking of asthenosphere matter.The magma upwelled to form the widely exposed igneous rocks with crustal-sourcecharacteristics. The delamination of lethsphere declined in late Cretaceous, andmantle-source magma upwelled along the tectonic weal belt to form the lateCretaceous intermidiate igneous rocks.
Keywords/Search Tags:Ulanhot, Early Cretaceous, intrusive rocks, Zircon U-Pb dating
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