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Li C.-L.,China University of Geosciences | Yu X.-Q.,China University of Geosciences | Liu J.-L.,China University of Geosciences | Wang B.-Y.,Shaanxi Geological Survey | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2012

The Dongjikou pyroxene sysnite, appearing as irregular ovoid, intruding into the Palaeoproterozoic high-grade metamorphic rocks of Taihua group, and developing gneissic schistosity in Huayangchuan region, Xiaoqinling, is the only known Caledonian rock body. Detailed petrography and field work studies on Dongjikou pyroxene sysnite indicate that inner parts of the rock body, according to the different structural characteristics, can be divided into the earlier-formed fine-grained pyroxene syenite, developing optalic boeder and a little later-formed medium-grained porphyritic pyroxene syenite, developing chilled border. The mineral association in both types of rocks is composed of plagioclase, potassium feldspar, pyroxene, amphibole, quartz, etc. The phenocrysts are mainly composed of pyroxene and plagioclase. Pyroxene and amphibole have experienced the retrogressive metamorphism. LA-ICP-MS zircon U-Pb ages of the fine-grained pyroxene syenite and medium-grained porphyritic pyroxene syenite are (214.8±3.1) Ma(MSWD=0.48) and (212.9±3.1) Ma(MSWD=5.6) respectively, which represents that the formation age of the rock is Late Triassic instead of the Caledonian period. The isotopic dating results show that the Caledonian magmatism event was extremely weak or inexistent in Xiaoqinling area. According to isotopic dating in this paper and a systematical summary of the previous research on the geological characteristics, it can be concluded that the age of the Dongjikou pyroxene sysnite is very close to that of the Indosinian magmatic and metallogenic event in Xiaoqinling area. It's concerned that the Indosinian magmatism is related to the transition regime from oceanic slab subduction to intercontinental collision. Moreover, intensive crust-mantle interactions caused upwelling of the deep material and triggered the gold enrichment. Source

Fan L.-M.,Shaanxi Geological Survey | Fan L.-M.,Shaanxi Institute of Geo Environment Monitoring | Ma X.-D.,Changan University | Ji R.-J.,China University of Mining and Technology
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

It is the unique geological environment conditions in northern Ordos Basin Jurassic coalfield that the issue “ water-preserved coal mining” is presented. After years of research, there have been some significant progresses in basic research and engineering practice. This paper summarized the latest achievements in the research of water-preserved coal mining. In the basic research phase: identified spatial distribution relation between coal bed with aquifers and impermeable layer; established the structure type of coal bed roof; divided the coal mining area into different partitions to protect aquifer; and specified the mining methods in different regions to protect groundwater. In the engineering practice phase: five kinds of aquifer-structure-preserved mining methods be employed to protect roof aquifer structure, including cut-and-fill mining, strip mining, slice mining, short-wall continuous mechanical mining and fast marching mining; reinforced bottom plate by grouting to protect Karst confined water in Weibei mining area; and transferred swallet into mined-out area to improve the utilization. ©, 2015, Meitan Xuebao/Journal of the China Coal Society. All right reserved. Source

Yang X.,Changan University | Han K.,Changan University | Wu X.,Changan University | Wang B.,Shaanxi Geological Survey | And 5 more authors.
Earth Science Frontiers | Year: 2016

Intra-continental orogeny has recorded a complex geological process. The research area, Ann Kang Shiquan-Hanyin-Xunyang belt, belongs to South Qinling orogen, and lies on the convergence parts of South Qinling intra-continental compound orogen and the northern Yangtze plate. And there develops the early Paleozoic deformed metamorphic rock sheets of the Silurian system, which mainly is overthrust structure and multi-level ductile slip overthrust rock sheet. There widely produces new multi-stage foliations that can be classified into 3 stages since the Indosinian period; the foliation replacement shows distinctly, and S2 foliations replacing S1 foliations appears dominantly in the covering stratum area. Considering the following facts that the multi-stage structural deformation, the granite invasion into cap rock, the magma diapir-stretch and heat dome rising of the basement, the thermal metamorphism with the late granite veins and high temperature mineral pairs that consist of secondary enlargement biotite porphyroblasts and garnet phenocrysts, the wide development of many types of hydrothermal alteration, the differences between the temperature and pressure characteristics of the fluid inclusions in quartz veins that exist in different stage foliations, that the Ar-Ar dating of biotites along the ductile shear deformation foliations is 161-169 Ma in Shiquan area, that the Ar-Ar dating of micas along the ductile shear deformation foliations is 178-163 Ma in the northern part of Fenghuangshan dome etc., it is suggested that the research area has undergone at least the Indosinian and the Yanshanian, the two tectonic deformation periods. Particularly, S2 foliation roughly corresponds to Yanshanian period, it is typically an intra-continental orogenic structural deformation. The characteristics of plastic flow in solid state and brittle-ductile shear deformation are significant. Through the structure-petrography mapping, we conclude that the S2 foliations are predominant in the area, their strike is mainly to the northwest; most of the new minerals and rocks are distributed along the S2 foliation, those suggest that Yanshanian period have a close relation to intra-continental orogeny. The brittle-ductile shear zones can emerge in the intense portion of structure deformation. The late Indosinian-Yanshanian period has been mainly presented by the combination of folds+S2+3 foliations+overthrust faults, the Cenozoic has been shown by the fault-blocks with different degree in strike-slip and uplift. The evolution of intra-continental orogeny can be divided into three sub-stages: (1)the collapse stage in the late Indosinian-early Yanshanian period (T3-J1+2); (2)the extrusion-overthrust stage in the mid-late Yanshanian period (J3-K2); (3)the block uplifting and transformation stage in the Himalayan period. Intra-continental tectonic convergence and strike-slip induced the condensation of tectonic thermal power in the upper crust, and formed the Fenghuangshan-Niushan magma-heat dome, leading to the partial melting of crust and the invasion of granite veins. The southern part, Annkang fault belt and the northern part, Ning Shann fault belt has undergone dextral strikne-slip deformation and sinistral strike-slip deformation respectively in Yanshanian period, which formed the more distinct east extrusion slip shear deformation in the study area, showing that the strike-slip of intra-continental orogeny cannot be neglected. © 2016, Editorial Office of Earth Science Frontiers. All right reserved. Source

Gao X.-F.,Research Center for Orogenic Geology | Xiao P.-X.,Research Center for Orogenic Geology | Kang L.,Research Center for Orogenic Geology | Zhu H.-P.,Shaanxi Geological Survey | And 3 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013

This paper presents petrological and geochemical features and zircon U-Pb age of a suite of bimodal volcanic rocks in the Bulunkuole Group from the Taishuihai Massif, NW China. The zircon U-Pb dating results yield a mean 238U/206Pb age of 521.3±3.3 Ma, representing the extrusion time of the dacites in the Middle Cambrian, which indicates that the previously defined Paleoproterozoic Bulunkuole Group also includes early Paleozoic volcanic rocks. The basalts and dacites belong to low-K affinities. The basalts show enrichment in Rb, Ba, K and LREE, and depletion in Nb-Ta and Th, suggesting that they were derived from a previously metasomatized depleted mantle. The dacites also show more enrichment in LILE and Th, and larger depletion in Nb-Ta, Sr and Ti in comparison with the basalts. Different REE patterns and trace element features between the two rock types, and the absence of differentiation trend from the basalts to dacites, argue against the origin for the dacites as the differentiates of the basalts. Combining the dacites geochemical features and the experimental data suggest that they are melts of lower crustal mafic protoliths heated by contemporaneous underplating basaltic magmas at relatively low pressure conditions. The occurrence of the bimodal volcanic rocks reflects that the region experienced an extensional tectonic-magmatic event during early Paleozoic. The new data suggests that the previously defined "Paleoproterozoic Bulunkuole Group" includes at least three components: (1) the Paleoproterozoic khondalite series; (2) the Indo-Sinian high-pressure metamorphic complexes and (3) the early Paleozoic volcano-sedimentary associations. Source

Fan L.-M.,Shaanxi Geological Survey | Zhang X.-T.,Shaanxi Geological Survey | Xiang M.-X.,Shaanxi Geological Environment Monitoring Station | Zhang H.-Q.,Shaanxi Geological Survey | And 2 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

The paper analyzed the damage situation caused by coal mining at Yushenfu coal mining area by field survey and remote sensing interpretation. The study results show: 1802 (group) fissures and 95 ground subsidence have been caused by coal mining since 1993 within a total area 94.47 km2; The distribution of ground fissures on the surface has significant zonation. Ground fissures are intensive, and seriously damage the topography at the loess donga region, however, due to their partial closure, the surface appearance is not obvious at the aeolian sand region; Mining intensity plays a decisive role in the development of fissures. Ground fissures mainly occur in the North of Shigetai-Daliuta, Dachanghan-Laogaochuan, Yujialiang, Jinjie, Ningtiaota and the area of Dabianyao-Mhuangliang where underwent high intensive coal mining activities. ©, 2015, China Coal Society. All right reserved. Source

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