| The mechanisms of formation and petrogenesis of an orogen are always hot points forgeologists. The granites as important substance records for each stage of an orogen, theresearch for its characteristics of magma-origin and their mechanism is of significance toreconstruct the deep dynamics and interaction of crust-mantle during orogenesis. The EastKunlun Orogen located in the hinterland of the Qinghai-Tibetan Plateau, has long evolutionalhistory and is a composite orogeny consisted of multiple and different types of orogeneses.Granitoids intruded in overwhelming volume with features of multiple and complicatedlithology, especially for Hercynian-Indosinian. So the eastern segment of East Kunlun Orogenis an ideal region for researching the formation and multiple orogenesis of the whole EastKunlun Orogen. The dissertation managed to study systematically on field geology,facieology, geochemistry and SHRIMP zircon U-Pb chronology of the Halagatu granties, andfocused on petrogenesis, origin of petrologic material, tectonic setting and their geologicalsignificance. After that, together with regional geo-settings and the advanced achievements ofpetrology, following cognitions are concluded.1.Halagatu granitoids are mainly of granodiorite, porphyritic-like monzonite granite,monzonite granite and K-feldspar granites, According to field geological characteristics,petrographic and mineralogical study. The amphibole (Ca+Na)=2.28~2.41, Na=0.33~0.48, Ca=1.84~1.96, Suggestive of Hala GA granite magma mixing characteristics with spit;Biotite in Al VI content ranged from0.15-2.29, an average value of0.21, a Mg value between1.02and1.18, were greater than1, MF ranged from0.38to0.45, indicating that the rock I typegranite.2.The rock geochemistry Index of differentiation form granodiorite to K-feldspar granitehas gradually increased,all show that the magma splitting degree gradually grows up whileevoluting from granodiorite to K-feldspar granites. The A/CNK ranging from0.94～1.05, as awhole, the Halagatu granitoids show the attributes of metaluminous－weak peraluminousI-type granite. The rocks are enriched in LREE and weakly fractionating in HREE, and theratios of (La/Yb)N, and (La/Sm)Nare3.25～12.44and2.66～6.25respectively, together withδEu ranging between0.47and1.02and low contents of Y and Yb. For trace elements, therocks are enriched in LILE like Rb, Th, Ba, U, La et al., and are depleted in HFSE intensely,such as Nb, P, Ta, Ti et al. Besides, the MME show apparent differences with their host rocksin lithologic geochemistry, the elements of MME comparing to that of host rocks have an lowamplitude of variation. Nb/Ta is10.96～16.05with12.63for average. Totally, the MME is greatly similar to its host rocks, maybe it’s the result of magmatic mixing.3. Resorted to method of SHRIMP zircon U-Pb chronology, the intruded ages of theHalagatu granitoids are257.7±2.9Ma, and the crystallized age of the MME is255.1±2.9Ma,formated simultaneously with its host rocks, showing that there were magmatic mixingprocess in the eastern segment of the East Kunlun region during Indosinian.4. The dissertation determined the Halagatu granitoids are Late Permian－Early Triassiccontinental marginal arc-type. And the reseach for its petrogenesis shows that it undergone thecrust-mantle mixing and then the fractional crystallization. The characteristics of major andtrace elements indicate the Halagatu granitoids formated in the tectonic setting of volcanic arcor continental arc.5. The chronology and tectonic attributes of the Halagatu granitoids show that, thepaleo-Tethys ocean got into an intensely subducting southward stage in Late Permian－EarlyTriassic. |
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