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Petrogenesis And Tectonic Setting Of Granite Porphyry In Keyouzhongqi Area, Inner Mongolia

Posted on:2015-01-02Degree:MasterType:Thesis
Country:ChinaCandidate:Q WuFull Text:PDF
GTID:2250330428998748Subject:Structural geology
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This paper summarizes the geochemistry, zircon U-Pb ages, the Hf isotope of thegranite porphyry and its petrogenesis and tectonic setting in Keyouzhongqi area, InnerMongolia. The studies of the granite porphyry in this area will be significant indiscussing the regional tectonic evolution in Great Xing’an Mts..The LA-ICP-MS zircon U-Pb dating results of the three samples are121.6±1.7Ma,125.1±1.5Ma and127.4±0.8Ma. Combining with the whole rock K-Ardating results, it can be concluded that the granite porphyry were formed in late EarlyCretaceous.The granite porphyry in srudied area is characterized by high-SiO2andalkali-rich, which belongs to high-K calc-alkaline series rocks (A/CNK=0.95%-1.25%). Among them, a few of the samples are characterized by relatively highcontent of REE with positive abnormality of Ce and strong depletion of Eu, andLREE and HREE fractionation is not that obvious. Trace elements data show that theyare enriched in Rb, Th, U, Ta, Hf, Gd and depleted in Ba, Sr, P and Ti. The zirconssaturation temperatures of these granites are very high, which shows the samecharacteristics with A-type granites. And the rest of the samples have characteristicsof enrichment in LREEs and most of LILE and HFSE, depletion in Ba, Sr, Nb, P, Ti,etc.. In Ree distribution pattern, most of the samples show a visible right-tend shapeand the negative abnormality of Eu is from slight to obvious. In104×Ga/Al- FeOT/MgO, Zr, Nb, etc. diagram, the former fall into A-type granite distribution areaand the rest fall into I-, S-and M-type granite distribution area, while inZr+Nb+Ce+Y-FeOT/MgO diagram those who fall into I-, S-and M-type granitedistribution area are located in fractionated felsic granites distribution area. Andconsidering with the relatively low zircons saturation temperatures, the rest samplesof granite porphyry belong to high-fractionated I-type granite.In Harker diagram, all the samples share a well linearity similar. And the ratiosbetween incompatible trace elements are also similar. Both of the facts indicate thatthese two kinds of granite porphyry have similar magma sources. The positive valuesof εHf(t) and TMD2are close to the large volumes of granites rocks in XingmengOregon in Phanerozoic, suggesting the primary magma were derived from partialmelting of middle and lower crustal rocks. Combining with discrimination diagramsand regional tectonic environment, the formation of the granite porphyry in thestudying area were related with the orogenic movement of Mongolia-Okhotskorogenic belt and extensional environment under the post-orogenic movement. Theorogeny causes lithosphere thickening and delamination, which makes mantleunderplating and heating the lower crust, and the partial melting of lower-crust rocksbecame the primary magma.
Keywords/Search Tags:granite prophyry, zircon U-Pb dating, A-type granite, I-type granite, petrogenesis, Keyouzhongqi area, Great Xing’an Mts., Inner Mongolia
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