查看更多>>摘要：The concept of fault junction is proposed to describe the relationship between the two faults by the authors. The junction relationship between Ganjiang and Tanlu faults is analyzed in this paper, and this has been elucidated through numerical simulation about the tectonic stress field analysis. Numerical simulation of the tectonic stress field conducted for the major mineralization stage of the Jiujiang-Ruichang junction area reveals that the stress field of the junction structure at the major mineralization stage shows a relatively close relationship with the formation of the ore deposits (occurrences).
查看更多>>摘要：We describe the earlier unknown, when applied to global tectonics, centrifugal inertial mechanism of lithosphere plate moving under the effect of forces appearing as a result of Earth's planetary rotation. The mechanism stated gives an insight into global tectonics of plates with the indirect participation of emanation streams which, in their turn, are the derivatives of centrifugal and inertial forces of planetary motion. The application of this mechanism provides a logical explanation for the regularities of global tectogenesis including the formation of mountain ridges mainly of submeridional and sublatitudinal strike,and also the drift of continental plates from the east to the west and from the south to the north. The mechanism clarifies the significance of the Arctic and the Antarctic Circles as geodynamic barriers.
查看更多>>摘要：The relation between earthquakes and active faults in Shanghai and its adjacent offshore region is quantitatively evaluated using GIS-based buffer and overlay analysis techniques. Statistics on the distance from the epicenter of an earthquake to its nearest active fault suggest that most earthquakes in the study area occurred within 10 to 20 km of major active faults. The strikes of active faults have significant influences on the occurrence of earthquakes. The NE-NNE-striked faults are less active than NW-NNW- or EW-striked faults.Along the NW-NNW- or EW-striked faults, the frequency of earthquakes is much higher than that along NE-NNE-striked faults. The time of fault activity has some degree of influence on the earthquakes. The newer the faults, the higher the frequency of earthquakes within the zone of the faults.
查看更多>>摘要：The early Cretaceous trachytes of Donglingtai Formation in Xishan, Beijing are characterized by slight Eu negative anomaly and significant enrichment in LREE, LILE (Ba, K and Sr) and depletion of Nb-Ta-Ti, Th-U. These trachytes have been highly enriched by Sr and Nd isotopic signatures (87Sr/86Sr(t)= 0.70638～ 0.70672, εNd(t) = -16.3～ -15.7), overlapping Sr-Nd isotopic range of late Mesozoic mafic igneous rocks in the region. Taking into account Nb-Ta fractionation and high Zr/Sm ratio for these trachytes, we consider that the trachytes of Donglingtai Formation are derived from the garnet-bearing amphibolite in the lower crust composed of garnet + plagioclase ± amphibole ± pyroxene residual phases. On the basis of the melting experimental results of crustal materials and regional extensional tectonics during late Mesozoic, it is concluded that the thermal input from underplating basaltic melt results in the partial melting of lower continental crust to generate the trachytes of Donglingtai Formation. And the characteristics of high Sr and Ba for these trachytes suggest that part of underplating basalts should take a share in partial melting at least.
查看更多>>摘要：The early Mesozoic granodiorites (ca. 165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O＞6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline series. They are characterized by LREE and LILEs enrichment, and HFSE depletion with slightly negative Eu anomalies (Eu/Eu*=0.62-0.90). The initial 87Sr/86Sr ratios are in range from 0.711458 to0.717461, and εNd values vary from -9.4 to -12.3, distinct from those of the contemporaneous granodiorites mantle-derived from the Southeastern Hunan Province (SEH) (87Sr/86Sr(i)=0.707962～0.710396, εNd(t)=-6.98～-2.30).By contrast, such signatures are roughly similar to those of the neighboring other Mesozoic granitic plutons (Eu/Eu*=0.30-0.70; 87Sr/86Sr ＞0.710; εNd = -12 to -16) in South China Block (SCB), which have been interpreted as the remelting products of Precambrian basement. The Proterozoic lower-middle crust is an important contributor to the petrogenesis of these early Mesozoic granodiorites in the NEH. An intracontinental extension setting is present in the northeastern Hunan Province at that time due to the demand of enough thermal transfer.
查看更多>>摘要：The Pengshan Sn-Pb-Zn polymetallic orefield is located in the Jiujiang-Ruichang region, which is a segment of the middle-lower Yangtze River metallogenic belt. The Pengshan late Yanshanian buried pluton with granitic composition is a calc-alkaline pluton, intrusion of which is responsible for the formation of the Sn-Pb-Zn polymetallic deposit through providing thermodynamic condition and ore-forming material.The long-active basement rifts initially formed in the Jinning period and the domal structure with induced secondary order faults formed by emplacement of the pluton, such as ring-detachment fault,top-detachment fault and joint fissure, act as the passage-way for magma and ore-forming fluid and impounding structure for ore deposit. The magma to form the pluton with DI＞90 is intensively differentiated. The variation of the ore-forming fluid in composition with falling in temperature caused by action of magmatic hydrothermal convection system combined with groundwater convection system attributes to mineralization of various types in the orefield. The mineralization process can be divided into six stages, i.e., greisenization, skarnization of early stage, fluorite-stanniferous silication stage, skarnization of advanced stage, quartz and cassiterite-sulfuration stage and carbonation stage. The mineral assemblages formed in different mineralization stages are different owing to temperature changing and may be overlapped in space. Malayaite is recognized from the mineral assemblage formed in the fluorite-stanniferous silication stage. The ores in the Pengshan Sn-Pb-Zn polymetallic deposit are spatially zoned with variation from As-Sn mineral assemblage of high temperature in the inner zone through Sn-Pb and Pb-Zn-Ag mineral assemblage of middle temperature in the middle zone to fluorite mineral assemblage of low temperature in the outer zone.The exchanging of Sn,Mg and Fe between biotite and hydrothermal fluid resulted from variation of physicochemical condition during evolution processes of the hydrothermal fluid and its role in mineralization are also disussed in this paper.
查看更多>>摘要：Anhua-Xupu fault belt plays a very important role in the formation of Xuefeng Mountains. The fault belt shows an arc-structure extruding towards NW. Fault rocks, microstructures and homogeneous temperature (concentrated around 160°C) of fluid inclusions in the quartz veins shows that the fault belt mainly underwent shallow brittle deformation and the highest-grade dynamic metamorphic rock is mylonitized sericite phyllite. The ESR (Electron Spin Resonance) dating from the quartz veins in the fault rocks shows that the fault belt underwent two intense fluid movement stages at Yanshanian (156.9～136.2Ma, 119.8～90.6Ma); moreover not only the occurrence and microstructures but also the homogeneous temperature of the quartz veins developed in that two stages show obvious diversity,which can prove that there exists the reversion period of Mesozoic extension and compression movement of Xuefeng mountains between these two stages.
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