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Song J.,China University of Petroleum - East China | Zhou Y.-S.,China Earthquake Administration | Yang W.-H.,Central Geological Exploration Fund
Dizhen Dizhi | Year: 2014

The depth distribution of aftershocks of the 1996 Lijiang MS7.0 earthquake is strongly time-dependent. Events occurring shortly after the main shock had deeper focal depths, and as the time going on, the focal depth of the aftershocks became shallower and shallower, i.e. the cutoff depth of seismicity became shallower and shallower with time. As we know, the lowermost events occur around the depth of brittle-plastic transition, and this depth depends on strain rate. The postseismic deformation model inferred from GPS data show that the major contribution of postseismic strain release comes from the lower layer of the crust. These results suggest that significant afterslip is related to viscous relaxation of lower layer. We estimated the lower bound of the strain rate according to Marone's et al. (1991) afterslip model and the slip data observed at the surface of Xianshuihe Fault. The results show that the strain rate is high after the main shock, and decreases gradually with time. We calculated the strength profile of middle crust based on flow law of wet quartz, estimated strain rate, temperature profile determined using the heat flow data at Lijiang, as well as crustal structure based on P wave velocity. By comparing the cutoff depth of seismicity and the brittle-plastic transition depth of the middle crust, we found the two depths are consistent to each other. We suggest the temporary existence of deeper small events after main shock and the depth distribution of aftershock is due to the changing brittle-plastic transition of the middle crust corresponding to strain rate variation from high to lower values after the main shock, and this kind of change is the manifestation of rheology of the middle crust. Source


Feng C.-Y.,Chinese Academy of Geological Sciences | Zhang D.-Q.,Chinese Academy of Geological Sciences | Li D.-X.,Chinese Academy of Geological Sciences | Yan S.-H.,Central Geological Exploration Fund | And 2 more authors.
Northwestern Geology | Year: 2012

The area around Qaidam basin in the northeastern Qinghai-Tibetan Plateau, located within the intersection between paleo-Asia and Tethyan tectonic domains, is a multiple orogen which underwent a very complicated evolutionary process, and is also a very important and potential metallogenic belt in China. Based on comprehensive analyses, the metallogenic setting, tectonic evolution, major deposit types, regional metallogenic rules and series in this area are described briefly in this paper. This area underwent four tectonic cycles including Precambrian old land formation, early Paleozoic orogenic activity, late Paleozoic- early Mesozoic orogenic process and Cenozoic overlap orogenic process. Of these, early Paleozoic and late Paleozoic-early Mesozoic orogenic activities were related genetically to metallic mineralization. Six types of deposits are recongnized including VMS and SEDEX types belonging to sedimentary exhalative deposit assemblage, and porphyry, skarn, hydrothermal vein and orogenic gold deposit belonging to orogenic deposit assemblage. The metallic mineralization is characterized by multiperiod, multi-elements and multistyles. Five metallogenic series of metallic deposits in the area are concluded, i. e. Cu-polymetallic deposit metallogenic series related to late Proterozoic-Cambrian splitting, Cu-Co-Pb-Zn polymetallic deposit metallogenic series related to Ordovician-Silurian splitting, Au-polymetallic deposit metallogenic series related to late Caledonian collision, Cu-polymetallic deposit metallogenic series related to late Paleozoic splitting and Fe-Cu-Pb-Zn-Au polymetallic deposit metallogenic series related to late Variscan-Indosinian orogenic activity. Source


Song X.-X.,Sinomine Resource Exploration Co. | Xin D.,Sinomine Resource Exploration Co. | Wang T.-G.,Nanjing Center | Sui X.,Sinomine Resource Exploration Co. | And 2 more authors.
Geological Bulletin of China | Year: 2014

The Papua New Guinea region evolved within the obliquely and rapidly converging Australian and Pacific plate boundary zone. It is arguably one of the most tectonically complex regions in the world, and its geodynamic evolution involved subduction and formation of volcanic (magmatic) arcs, arc-continent collision and collisional orogenesis, exhumation of continental crust, magmatic intrusion and mineralization. The geochronology of New Guinea suggests the geodynamic sequence of (1) collision causing uplift and exhumation, then (2)intrusion during or shortly after exhumation, and finally (3)mineralizing event during the late stages of the intrusive system. In the geodynamic sequence, ages of Cu-Au mineralization are mainly concentrated in the range of 25~0Ma. Most of the world class deposits in PNG are much younger (6~0Ma). On the basis of ages of mineralization, the authors divide Cu-Au mineralization into the three boom periods: the first boom of mineralization (23~12Ma); the second boom of mineralization (7~1Ma); the third boom of mineralization (0.5~0Ma) (still continuous at present). The controlling factors of Cu-Au mineralization in Papua New Guinea include tectonics, intrusive complex, special host strata, transfer structure, folds, various faults, caldera or diatreme and so on. In summary, Papua New Guinea has a relatively young (Meso-Cenozoic) and complex history of tectonic and metallogenic evolution with plate convergence, collisional orogenesis, and strong and frequent magmatic-hydrothermal activities, including Cu-Au mineralization. Source


Wang T.-G.,Nanjing Center | Yao Z.-Y.,Nanjing Center | Wang C.-S.,East China Mineral Exploration and Development Bureau | Li A.-Y.,The First Institute of Geology and Mineral Exploration of Shandong Province | Dai K.-M.,Central Geological Exploration Fund
Geological Bulletin of China | Year: 2014

This paper deals with the natural background, the conditions and problems of mining development, and the present mining investment situation in Australia. On such a basis, the main risks of the mining development in Australia are analyzed, and some suggestions related to the investment in mining industry in Australia are put forward. The authors hold that the Chinese investors should understand the current situation, clarify investment ideas and optimize the investment strategy so as to gain advantages in the fierce international mining investment competition and establish a completely new image of Chinese enterprises at the world economic stage. Source

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