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Wang Y.,Chengdu University of Technology | Zheng W.,Chinese Academy of Geological Sciences | Zheng W.,China University of Ceosciences | Chen Y.,Chinese Academy of Geological Sciences | And 5 more authors.
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2017

With the highest exploration and the first large-scale exploitation, Jiama copper polymetallic deposits is a supper-large skarn-porphyry deposit, located at the middle-eastern section of gangdise in Tibet. In this paper, taking the typical phenomenon "copper upside and molybdenum underside" of hornfels- and porphyry-orebodies from Jiama deposit as the starting point, the differences of ore forming fluids among physical and chemical conditions and the migrating behavior of trace elements in the copper and molybdenum mineralization stages have been discussed in virtue of microthermometry, laser Raman testing, synchrotron radiation X-ray fluorescence analysis (SR-XRF) and other researching methods. The results of fluid inclusions microthermometry show that the temperature of ore-forming fluid in the copper mineralization stage (roughly 235 ∼ 451 °C, mainly between 340 and 380°C) is overall greater than that in the molybdenum stage (roughly 213-500°C, mainly between 310 and 360°C), sharing the similar salinity that is less than 18% NaCleqv and more than 30% NaCleqv, and lack of the transition zone, which explained ore-forming fluids had experienced boiling. And the results of Raman microprobe show that the oxidizability of ore-forming fluids in the copper mineralization stage is a little stronger than that in the molybdenum mineralization stage, while the reducibility is reverse. Synchrotron radiation X-ray fluorescence analysis of single fluid inclusion indicates that Cu, Au, Fe, Mn, S, As and other elements are mainly and widely distributed in the gas phase, while the residual Mo is mainly concentrated in the liquid phase. Thus it can be concluded the main controlling factors leading to "copper earlier and molybdenum later and copper upside and molybdenum underside" of hornfels- and porphyry-orebodies in the Jiama deposit are the physical and chemical properties of copper and molybdenum, the natures of ore-bearing magma, and their emplacing sequence and depth, along with the different redox and the ulfur content of ore-forming fluids released after that.

Guan Q.,China University of Ceosciences | Guan Q.,Shijiazhuang University of Economics | Zhu D.C.,China University of Ceosciences | Zhao Z.D.,China University of Ceosciences | And 6 more authors.
Acta Petrologica Sinica | Year: 2010

Contrasting views remain exist so far for the nature and geodynamic mechanism of the Late Cretaceous magmatism in the southern Gangdese Belt, southern Tibet. To further constrain the tectonomagmatic evolution of southern Tibet during the Late Cretaceous, we present zircon LA-ICPMS U-Pb data, geochemical and Hf isotopic data for the granitoids from the eastern segment of the southern Gangdese Belt, southern Tibet. New age data indicate that the granitoids were emplaced at 84 -78Ma. These rocks are characterized by high Al2:O3 ( 15. 69% - 17. 65% ) , low MgO (0.47% - 1. 24% ) , very low abundances of compatible elements ( Cr = 1.34 × 10"h -3.27 × I0-6 ,Ni =0.69 × 10-6 -3.32× 10 -6) , high Sr (542 × I0-6 -774 × I0 -6) and high Sr/Y ratios (48 -397) , similar to those of adakite. The rocks are medinm-K calc-alkaline, metaliiminoiis ( A/CNK = 0. 95 - 1. 04) , and are enriched in LILE, depleted in HFSE, and are heterogeneous in zircon sw-(t) values ( + 0.2 ∼- +15. I). Some of they show distinct positive En anomalies (SEn = 1. 16 - 2. 26) and middle REE depletion. The Late Cretaceous adakites are interpreted as the products of partial melting of newly nnderplated mafic lower crust under hydrous amphibolite facies conditions. Compared with the zonal magmatic flare-up events at about IIOMa documented in the middle-northern Gangdese and at about 50Ma documented in the southern Gangdese, we argue that the Neo-Tethyan ridge subduction is the most probable mechanism to trigger the generation of the widespread zonal magmatism in the southern Gangdese during the Late Cretaceous.

Jiang X.,Peking University | Jiang X.,China University of Ceosciences | Zhao Z.D.,China University of Ceosciences | Zhu D.C.,China University of Ceosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2010

The study on the Mesozoic granitoids in the Western Gangdese belt is still limited. This paper presents the zircon SHRIMP U-Ph dating and Hf isotopic results on the Jiangba, Bangba, and Xiongba granitoids. The results are also applied to the discussion of the granitoids distribution as well as the nature of the crustal basement from which the granites originated. The ages of the Middle-Late Jurassic Jiangba granodiorite and Xiongba alkali granite are 170 ±3Ma and 149 ±3Ma, respectively. The ages of the Bangba orthogranite and its quartz monzodiorite enclaves are 144 ±3Ma and 133 ±3Ma, respectively, suggesting the Early Cretaceous magmatism. The Hf isotopes (εhi(t.) ) and Hf crustal model age of the Middle-Late Jurassic Jiangba ( -16.∼ 8 - -13.4 and 2. I ∼- 2. 3Ga) and Xiongba ( - 11. 3 ∼ -6. 2 and I. 6 -2. 0) granitoids are similar, which indicates an enriched, Paleoproterrozoic crustal basement under the study areas. The Early Cretaceous Bangba intrusive (suf(t.) = ∼4 - - 0. 8, model age = 1.2 - 1. 5Ga) and the dioritic enclave (εhi(t.) = - 2. 8 - +0. 6, model age = 1.2 - 1. 4Ga) have similar features, suggesting the magma mixing event during their forming processes. The result in this paper further implies that the Paleoproterrozoic crustal basement has involved in the reworking of the Mesozoic magmatism, although they have not been revealed on the surface.

Dong W.,China University of Ceosciences | Dong W.,Virginia Polytechnic Institute and State University | Lin C.,China University of Geosciences | Eriksson K.A.,Virginia Polytechnic Institute and State University | And 3 more authors.
AAPG Bulletin | Year: 2011

The sequence-stratigraphic framework and depositional sys-tems of an Oligocene lacustrine rift succession in the Liaozhong depression of Bohai Bay Basin in northeastern China were investigated using seismic profiles, complemented by well logs and cores. Seven sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center. Depositional systems are associated with systems tracts within sequences. Lowstand systems tracts are dominated by sublacustrine fans; transgressive systems tracts are mainly composed of beach-bar deposits; and highstand systems tracts are characterized by deep lacustrine fan or braid-delta deposits. Episodic tectonic movement was the principal factor that controlled the development of the sequences. Lake-level changes resulting from climatic oscillations may have controlled the development of these sequences. The balance between tectonic subsidence and sediment supply controlled the type of lake basin. The Bohai Bay Basin was a balanced-fill basin in the early and middle stages of the Dongying Formation and evolved into an overfilled basin at the end of deposition of the Dongying Formation. This study enhances the understanding of depositional system configuration and systems tracts in a typical rift basin and proposes that the most favorable sandstone reservoirs are developed in sublacustrine fan deposits. Relative lowstand sublacustrine fan deposits capped by relative highstand prodelta or deep lacustrine mudstone form the higest potential lithostratigraphic traps. © 2011 The American Association of Petroleum Geologists.

Zhou Z.,China University of Ceosciences | Wang G.,China University of Ceosciences | Zhang D.,China University of Ceosciences | Gu Y.,Tianjin Institute of Geology and Mineral Resources | And 4 more authors.
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2016

The Bayan Obo Group outcropped in the Dajingpo, Siziwangqi, Inner Mongolia, is the eastern extension of Bayan Obo ore deposit. Two gabbro plutons intruded into Bayan Obo Group were discovered through geological survey, whose zircon ages will provide new clues to constrain the controversial formation time of the Bayan Obo Group. The gabbro intruded into Dulahala Formation is named Jishengtai pluton, while the one intruded into Bilute Formation is termed Dajingpo pluton. LA-ICP-MS U-Pb dating yielded ages of 1670 ± 14Ma (MSWD = 1.6) for Jishengtai pluton and 1342 ±9Ma ( MSWD =0. 94) for Dajingpo pluton, respectively. Based on the new ages, together with published data of Proterozoic strata and magmatic events in Yanliao rift, we suggest that Dulahala and Jianshan formations should belong to Paleoproterzoic Changchengian System, equivalent to Statherian in International Clironostratigraphic Chart (ICC); Halahuogete Formation should be Mesoproterozoic Jixianian System, equivalent to Calymmian in ICC; Bilute Formation should be Mesoproterozoic lower part of an awaiting build System, the same to Ectasian in ICC, and the Baiyinbaolage Formation should be Neoproterozoic Qingbaikouian System, which referred as Tonian in ICC. The magmatic events in the North China Craton, Bayan Obo and Yanliao rifts are comparable, which probably related to the breakup of the Columbia supercontinent.

Gu F.,Chengdu University of Technology | Gu F.,China University of Ceosciences | Zhang Y.,China University of Ceosciences | Liu R.,China University of Ceosciences | And 2 more authors.
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2015

The Shadegai K-feldspar granite in the Wulashan area at the north margin of the North China craton contains abundant mafic microgranular enclaves (MMEs) consisting mainly of monzonite. The MMEs have either a sharp or a gradual contact zone with their host granite, indicating different rheological properties of the contrasting magmas. Petrographic observation shows that the MMEs contain various typical textures whose origin can be explained in terms of magma mixing and mingling, including quartz ocelli, rapakivi feldspars, mafic clots, resorption of K-feldspar megacrystals, acicular apatite morphology, inclusion zones in feldspars, and anorthite "spikes" in plagioclase. Microprobe analyses on the rock-forming minerals suggest that magma mixing and mingling played an important role during the formation the Shadegai granite. The host granite magma may be derived from the lower crust, while magma for the MMEs originated from the mantle. LA-ICP-MS U-Pb isotopic dating on zircons from the Shadegai granite and its MMEs obtained similar ages of 233. 4 ±2. 3 Ma and 229. 7 ± 1. 5 Ma, respectively, further indicating the existence of magma mixing and mingling during their genesis. It is thus suggested that the quench of mafic magama upon its incorporation into the relatively cooler felsic host magma resulted in the formation of MMEs with sharp contact zones, chiiled margins and more abundant mafic minerals. Subsequent interaction of mafic and felsic magmas caused the decrease in temperature diiference of magmas and the formation of MMEs that have gradual contact zone, more abundant felsic minerals and no evident chiiled margins.

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