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Supervisor:China Geological Survey

Sponsored by:XI'an Center of China Geological Survey
Geological Society of China

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1
Abstract:
Five metamorphic intermediate-acid intrusive rock bodies in Proterozoic have beenidentified in the central Qimantage by the 1∶50000 mineral prospect survey. The intermediate-acid intrusive rock bodies located in amphibolite facies the volcanic-sedimentary rocks are gray-pale flesh red two-feldspar gneiss with eye-shaped. The two-feldspar granites are their original rocks. Zircon U-Pb age is of 832±12 Ma on average,which are known the oldest intermediate-acid intrusive magma products. Geochemistry of rocks is as follows:high K2O(4.92—5.76 ×102), poor FeO, MgO, and CaO. Rocks with high-K are calc-alkaline S-type high-evolution granites that were formed about 34.7 km in crustal thickness. Tectonic setting is shown sys-collision by R1-R2 discriminant diagrams. Rodinia continent closed at about 830 Ma in the East Kunlun. Intermediate-acid magma action reproduced in early Paleozoic. In this process Rodiniabreakup and plates in low latitudes moved to high-latitude.The discovery is important to know the structure evolution of early Paleozoic in East Kunlun.
2
Abstract:
The intrusive magmatism of the midlater Hercynian granitoids is very strong in the Eastern Tian shan region,where the distribution of the Caledonian,the earlier Hercynian and the Indo-China granitoids arera rerelatively. The granitoids in the Eastern Tian shan region are divided in to two belts including Kangurtag-Harlik is land arc granite belt(the northern belt)and Aqishan-Yaman suisland arc belt(the southern belt). Except the Harlik Mounta in having several alka line granite plutons,the granitoids in the Eastern Tianshan region belong to the calc-alka line series. From the Caledonian period to the Indo-China period,the in trusive magma tism had undergone the six evolutional stages:preplate collision,volcanic arc,syn-collision,exten sion with in plate,orogenesis with in continent and anorogenesis. The genetic types of the Eastern Tian shan granitoids can bedivided in to M,CM,C and A types. The collision and the closing of the Southern is land a rc and the Northern island arc present prog ressive evolution from the northeast to the southwest.The copper,molybdenum and goldo redeposits such as Tuwu,Yandong,Chihu,Shiying tan,Weiquan,Baishan et al are bound up with the CM type of the a luminium supersatu rated calc-alka line granitoids.
3
Abstract:
Supercontinents are assemblies of all or nearly all (> 90%) of the earth's continental blocks. The oldest supercontinent speculated is the one at 3.0 Ga termed as Ur. It is difficult to test the existence of this supercontinent due to its old age. There appear to have been twice in earth history when all of the continents were fused into one supercontinent. The first truly coherent supercontinent in earth history was probably Columbia, which formed between 1.85 and 1.90 Ga, began to fragment at ~1.6 Ga, and finally broke up at ~1.3-1.2 Ga. Columbia was followed by the second supercontinent Rodinia, which lasted from ~1100 Ma to 540 Ma. The Pangea (0.25 Ga) was not a true supercontinent, but an unusually large assembly of continents making a semi-supercontinent. The southern half (Gondwanaland) of this semi-supercontinent has a dispersion history, and the northern half (Laurasia, i.e. Paleo-Asia) has an amalgamation history. At present, the third supercontinent has not formed yet, and our planet is in midway to make a true supercontinent (Amasia) in the future. The mechanisms of formation and disruption of supercontinents have been two controversial topics. A synthesis of some of the recent conceptual models suggests that mantle dynamics exerted a significant control on the assembly and breakup of supercontinents through the history of the Earth. The formation process of supercontinents is controlled by super downwelling that develops through double-sided subduction zones as seen in present-day western Pacific, and also endorsed by both geologic history and P-wave whole mantle tomography. The super downwelling swallows all material like a black hole in the outer space, pulling together continents into a tight assembly. The fate of supercontinents is managed by superplumes (super-upwelling) which break apart the continental assemblies. With the advancement in numerical modeling techniques as well as the enhancement in computational power and resource, the numerical studies of mantle dynamics have markedly progressed toward the realization of seismic tomography images of mantle structure and a better understanding of geodynamic mechanisms. The solid Earth can be considered to comprise a plate tectonics domain with broadly horizontal motion in the upper mantle, plume tectonics dominated by vertical movements in the lower mantle region and an "anti-plate tectonics" zone characterized by horizontal movements at the bottom of the mantle. Although mantle tomography opens windows into the deep Earth, the imbricated remnants of "ocean plate stratigraphy" preserved in accretionary orogens still constitute useful geological tools to study subduction-accretion-collision history, particularly in relation to the assembly of older supercontinents on the surface of the globe. The dynamics of supercontinents also impact the origin and extinction of life, surface environmental changes as well as magmatism and metallogeny. Massive flow of material and energy was induced by mantle downwelling and upwelling accompanied by supercontinent assembly and breakup, which would also lead to large-scale magmatism and metallogeny, catastrophic environmental changes, sometimes even triggering mass extinction. When a rising mantle plume impinges the base of a supercontinent, the consequent continental rifting, formation of large igneous provinces, large scale metallogeny and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to carry out the resource assessment, to understand the history of life, and to trace the major surface environmental changes of our planet.
4
Abstract:
The formation of ore deposits is, nevertheless, related to much the same sort of processes that gave rise to the formation of normal igneous, sedimentary, and metamorphic rocks in the Earth′s crust.The fact that close relationship exists between rock-forming and ore-forming processes means that metallogeny must be relevant to understanding the nature of crustal evolution through geological time. There are essentially two ways to do this. One is to empirically describe ore deposits in the tectonic environment and host rocks in which they occur. The other is to chart continental evolution and place ore deposits into a secular and tectonic framework. The former has been covered in considerable detail,and the latter is a more difficult undertaking and requires a thorough knowledge of the evolution of continents with time. It is difficult,particularly,that understanding ore-forming processes in amalgamation and dispersal of active continent by limitation in conventional undertaking. In this paper,it is applied that the point of view of active global tectonics, from rates of continental growth,evolution of the hydrosphere and atmosphere, secular evolution in global heat production into historic records of sea-level changes,to groping summary ore-forming processes in a setting of active global evolution in order to energizing more thorough research in this specialty.
5
Abstract:
Kuzigan alkaline complex is one of the major parts of the Taxkorgan alkaline complexterrane. It is mainly composed of aegirine-augite syenite, quartz aegirine-augite syenite, and alkali granite. There is great difference among the three rocks in the content of SiO2, 50.26%-54.11%, 59.74%-60.43% and 69.59%-72.13% for aegirine-augite syenite, quartz aegirine-augite syenite and alkali granite, respectively. Aegirine-augite syenite and quartz aegirine-augite syenite has similar Rittman index, namely 7.83-10.97 and 8.51-9.05, distinctly differing from 2.49-3.71 of alkali granite. These three rocks are strongly enriched in light rare earth elements (LREE) as well as some large ion lithophile element (LILE), such as Rb, Ba, Sr, and depleted in High Field Strength Element (HFSE) such as Nb, Ta and Ti. Abnormal high Sr, Ba and ∑ REE content may imply the mixing of enriched mantle materials. LA-ICP-MS in-situ zircon U-Pb dating obtain the ages of 10.9±0.1 Ma and 11.9±0.4Ma for the quartz aegirine-augite syenite and alkali granite respectively, representing the crystallization ages of the two rocks. The εHf(t) values of the quartz aegirine-augite syenite and alkali granite are of -9.78-3.24 and -13.54-5.78, showing the crust-mantle mixing in magma source area. According to the comprehensive analysis and combined with regional geological data, we preliminarily hypothesized that the Kuzigan alkaline complex is a product of the crust-mantle mixing, which is caused by the asthenosphere flowing northward due to the delamination of the Tibetan plateau at ~25Ma, and the asthenosphere upwelling as a result of the obstruction of the root of the Tarim craton lithosphere. Therefore, the formation of the complex is a fernwirkung of the magmation after Tibetan plateau large-scale delamination, and it signifies that during ~11 Ma the study area was in extensional tectonic setting.
6
Abstract:
The homology of the rock mass is analyzed according to the geology, petro-graphic andgeochemical along the rock group of adamellite in the western Qinling(commonly called as“Five golden flowers”).It shows that the invasion sequence is clear. The rock mass includes diorite in earlyphase,biotite adamellite in the metaphase,two-mica monzonitic granites in the late stage.The intrusion has an evolution trend from acidic to alkali with rock forming episode. In the space,the longitudinal lithology is consistent overall, and the structure become thinner from east to west;the transverse structure is similar and the composition is more partial acid to the south.The rock group from the old to the new,they are from the potassium and sodium transition area to potassium,belonging to shoshonitic series and high-K calc-alkaline series. They have similar geochemical features. The REE diagram of the Chondrite-normalized show that they are rich in LREE,and evidently depleted in Eu. The adamellite is formed at 181-232.9Ma (by Rb-Sr) and 178-248.8Ma (by K-Ar). Meanwhile, the value of the ANKC is lower than 1.1, with peraluminous granite. They are Himalayan-type granite. Research shows that the rock group of adamellite has homology.
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