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Basic data on the opening of backarc basin, South China Sea (abbreviated as SCS hereafter) basin, were obtained through a two-year Japan and China cooperative joint marine geophysical survey in 1993 and 1994. Some new gravity, mag...
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Basic data on the opening of backarc basin, South China Sea (abbreviated as SCS hereafter) basin, were obtained through a two-year Japan and China cooperative joint marine geophysical survey in 1993 and 1994. Some new gravity, magnetic and seismic structural data by reflection as well as refraction study of SCS were obtained and added to existing data. A systematic three component magnetic measurement was made for the first time in this basin. These data in addition to those of earlier studies are constraints for depicting a thinning of a continental crust and later followed by a backarc basin opening by ocean floor spreading. Gravimetric and magnetic anomalies, heat flow, and ages of drilled rocks from this area are referred to speculating on the opening scheme of SCS. Origin of disoriented and scattered magnetic anomaly lineations is suggested to be due to intermittent activities along opening ridge systems of SCS.
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Ocean tide was numerically calculated for various ocean continent configurations. The calculated tidal torque response for semidiurnal ocean tide is found to be bigger, when the continents are lined on the equator than when the co...
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Ocean tide was numerically calculated for various ocean continent configurations. The calculated tidal torque response for semidiurnal ocean tide is found to be bigger, when the continents are lined on the equator than when the continents are lined along the meridian. Since the ocean continent configuration significantly affects the tidal torque, variation of the Earth's spin rotation rate in the past should be associated with the continental drift. The present calculation suggests that the long and short term variation of l.o.d. (length of day) up to 600 Ma b.p. estimated From palaeontological studies is explained by temporal variation of the ocean continent configuration. Moreover it is highly probable from our result that the continents before Cambrian age were lined more or less on the meridian or of other configurations that gives smaller tidal torque than the Cambrian configuration.
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Over the past 20 years much work has gone into understanding the mechanisms of lithospheric extension, and producing models to explain the geometry and evolution of rift basins. These models have tended to simplify the deformation...
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Over the past 20 years much work has gone into understanding the mechanisms of lithospheric extension, and producing models to explain the geometry and evolution of rift basins. These models have tended to simplify the deformation occurring within the upper crust by assuming that extension occurs either by pure shear (such as the uniform extension model) or exclusively along a few large basin-bounding faults (such as the flexural cantilever model). However, the stratigraphic geometry of many basins cannot be explained by these simple models; for example, the common occurrence of thick sequences on the footwalls of basin-bounding faults. This requires the generation of accommodation space by subsidence. However, the flexural cantilever model predicts uplift, while the uniform stretching model cannot model the effects of faults at all. This paper looks at the St. George's Channel Basin, which has been mapped in detail using an extensive seismic dataset, and attempts to explain the structure and stratigraphic geometry of the basin by applying forward modelling techniques to four cross sections taken from different areas of the basin. This has allowed the determination of the detailed mechanisms by which extension has occurred within the upper crust, and of variations in these both spatially and through time. Results from the modelling indicate that a combination of extension on basin bounding faults and pure shear distributed across the basin is required to explain the geometry of the basin, although the pure shear component of extension probably represents extension on numerous sub-seismic scale faults across the basin. The relative influence of these different mechanisms of extension varies considerably across the basin, and throughout its history. During the Triassic, for example, up to 80 % of total extension in the brittle upper crust occurred by pure shear. During the Middle and Upper Jurassic, however, extension in the upper crust occurred mainly on a single fault (the St. George's Fault) in the basin centre, but on the edges of the basin, where the fault died out, pure shear extension was dominant.
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Discovery of lode gold deposits in many typical high grade metamorphic terranes of the world suggests a potential for further gold exploration in such terranes. Iron-rich lithologies in Archaean gneiss-granulite associations often...
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Discovery of lode gold deposits in many typical high grade metamorphic terranes of the world suggests a potential for further gold exploration in such terranes. Iron-rich lithologies in Archaean gneiss-granulite associations often provide the main source for gold mineralization which is either syn-metamorphic or post-metamorphic in most cases. High-temperature alterations which produce K-feldspar, biotite, garnet and pyroxene are closely associated with the gold mineralization. Both of the alteration and mineralization are controlled by ductile shear zones of different scales. Among the ore minerals, lollingite, pyrrhotite and arsenopyrite show a higher frequency of occurrence. Gold mineralization in Archaean high grade terranes occurs in a wider range of temperature than that in granite-greenstone belts, varying from 200-250 °C up to 700 °C. High grade regional metamorphism is not a destructive factor for the formation of lode gold deposits. High strain deformational zones, K-feldspar + biotite alteration and silicification as well as iron-rich lithologies are the key criteria for gold exploration in high grade terranes.
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Singliao Basin is a large nonmarine sedimentary basin, which can be divided into three supersequence sets, eight supersequences and forty-four third- order sequences corresponding to the rifting, depressing and shrinking stages, a...
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Singliao Basin is a large nonmarine sedimentary basin, which can be divided into three supersequence sets, eight supersequences and forty-four third- order sequences corresponding to the rifting, depressing and shrinking stages, according to space distribution and seismic reflection characters of the formations. The rifting stage's supersequence set, composed of three supersequences, is characterized by near source, quick subsidence and quick filling, with the reflecting characters of toplap, onlap and truncation for the top boundary of the set. Most source rocks are Type III, and reservoir rocks are mainly fan-delta sandstones. The depression stage's supersequence set develops into four sequences, characterized by flat ancient landform and far-source. Main source rocks are Type I/IU, and the reservoir rocks are dominantly large fluvial delta sandbodies, showing the parallel and continuous reflecting characters on the seismic profile, The shrinking stage's supersequence set is mainly composed of fluvial delta sediments. Organic matters are relatively underdeveloped, and the evolution level is low. Hydrocarbons are mainly contained in the two supersequence sets corresponding to the rifting and depressing stages within the basin, The rifting stage's supersequence set mainly generates gas, and the peripheral structural and stratigraphic overlap traps of the down-chasm hold annually distributed gas reservoirs. The large lacustrine delta complex deposited in-water transgressive and high-stand systems tracts matches the large placanticlinal structure, so forming a super-giant placanticlinal uplift in depression type oilfield in the central depression. Meanwhile, the lowstand systems tract, composed of extensively distributed distributary channel deposites constitutes large-area of staggered-stacking distribution of oil and gas reservoirs, "generating in upper layers and trapping in lower layers" type, sagging on both sides of the placanticline.
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The River Nile drainage basin collects heavy minerals from three petrologically and tectonically distinct source terranes. Amphibolite- and granulite-grade metamorphic rocks of the Central African Province feed the White Nile. Alk...
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The River Nile drainage basin collects heavy minerals from three petrologically and tectonically distinct source terranes. Amphibolite- and granulite-grade metamorphic rocks of the Central African Province feed the White Nile. Alkali and tholeiitic basalts of the Ethiopian Highlands are the sediment source for the Blue Nile and Atbara Rivers. Heterogeneous igneous and metamorphic rocks of the Red Sea Hills supply clastic sediments to currently dry river beds, termed wadis. Both detrital pyroxene and ilmenite from the three terranes are compositionally distinct. Therefore, detrital pyroxene and ilmenite grains from these source areas might be useful as provenance indicators of Nile delta sediments and paleoclimate indicators for northern Africa. Microprobe analyses of detrital ilmenite grains from a core through Nile delta sediments suggest periodic pulses of sediment input from the Red Sea Hills over the last 8,000 years.
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According to a large volume of data, a rapid crustal uplift began in the Oligocene over about one half of the continental areas after a period of relative stability, -150 Ma long. This Neotectonic uplift has produced most of the p...
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According to a large volume of data, a rapid crustal uplift began in the Oligocene over about one half of the continental areas after a period of relative stability, -150 Ma long. This Neotectonic uplift has produced most of the present high topographic features, e.g., the South African plateau and many mountain ranges in the Alpine belt and Central and North-eastern Asia. A wide occurrence of shallow-water fossils indicates, that the Tien Shan and Caucasus were below sea level 40 Ma and 10 Ma ago, respectively. A strong acceleration of the uplift took place during the last 3-5 Ma. 1.6 Ma ago the Tien Shan was at half the present-day elevation. Most of the Neotectonic uplift took place on Precambrian, Paleozoic and Mesozoic crust and occurred far from active plate boundaries, without significant horizontal deformation and disturbance of isostasy. High gradients of the uplift are observed in many areas. Under such circumstances, the uplift should be caused by a density decrease in the lithosphere. Geophysical data show that in some regions the Neotectonic uplift was associated with recent asthenospheric upwelling which resulted from a partial or complete erosion of mantle lithosphere. This collapse of mantle lithosphere occurred without significant horizontal deformations. It could probably be associated with infiltration of volatiles into this layer from a fluid-containing anomalous mantle which ascended from a deep mantle in some places and rapidly spread into the other areas along the base of the lithosphere. Asthenospheric upwelling can ensure up to 1.5-2.5 km of the uplift. Delamination of dense eclogite from the crust or transformation of garnet granulites in the lower crust into a less dense gabbro under a contact with the asthenosphere can increase the magnitude of the uplift up to 3-4 km.
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The interaction of an industrial river and the groundwater aquifer in Florida are modeled by time scries-, flow modeling- and particle (racking methods, The major piuposc of the mcxleling ellbil is to delineate (lie possible conta...
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The interaction of an industrial river and the groundwater aquifer in Florida are modeled by time scries-, flow modeling- and particle (racking methods, The major piuposc of the mcxleling ellbil is to delineate (lie possible contamination corridor in (lie aquifer as may be caused by llic infiltration cf polluted water from the industrial river. The interrelations of precipitation, river discharge and groundwater data series are first analyzed by methods of structural time series, in order to quantify the interdependence of the groundwater table and river gauge heights, and thus to statistically examine the hydraulic possibility of aquifer contamination. The interaction of the stream and the groundwater is simulated by tr?eUSGSMODFLOWmodel.For the calibration, simulated water tables are compared with the historical records of monitoring wells in the adjacent aquifer. Lateral 'stagnant' points of the water flow based on the transient simulation are connected to delineate the maximal contamination corridor along both sides of the stream. In addition, particle tracking simulations with varying water sources and forcing conditions are conducted to compute thedynamicmovementsofwatei'particlesoutandalongtheriver banks. The modeling results show that lateral migration of contaminants close to the industrial discharge point might be up to several thousands feet in cross-river direction during times when the normally gaining (effluent) stream becomes sectionally a losing (influent) stream. The last situation occurs especially during multiyear-long time spans with less-than-normal precipitation which, for Florida, happens during times between major El Niflo occurrences; i.e. during La Nina years.
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Palaeobiogeographic evolution of Permian brachiopods was investigated based on a quantitative analysis proceeded from the data base which collected 28,000 records of brachiopod taxa from 450 slratigraphic levels of 289 localities ...
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Palaeobiogeographic evolution of Permian brachiopods was investigated based on a quantitative analysis proceeded from the data base which collected 28,000 records of brachiopod taxa from 450 slratigraphic levels of 289 localities all over the world. The Otsuka coefficient was selected as the best quantitative indices in revealing faunal affiliation. The biogeographic affinities of coeval brachiopod faunas can be evidently revealed by the results of cluster analysis when the faunal analogs rooted in community relationship, bipolar distribution and low efficiency of collections have been identified. Changes in faunal affinity demonstrate that biogeographic evolution of Permian brachiopods had been profoundly influenced by the consolidation of the Pangea, which was finalized by the close of Ural seaway at the end of Artinskian Stage, and led to a sharp differentiation of a pro-Pangea faunas and the Tethyan faunas. The brachiopod faunas in peri-Pangea shelves are dominated by a group of such forms as Spiriferella, Neospirifer, the syringothyrids and the buxtoniids, which directly descended from Cisuralian faunas. These faunas are conservative as they extended upward to the Lopingian with little evolutionary changes. The faunas dwelt in off-shore islands of Tctliys and Panthalassa were characterized by newly developed endemic brachiopods but lacked pro-Pangea taxa. Between these two end-member faunas there were transitional faunas occurring in the peripheral islands of Pangea.
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The Jinchuan Cu-Ni Sulfide Deposit is the biggest magmatic Cu-Ni sulfide deposit in China. It occurs in the Jinchuan Ultramafic Massif which is located in central Gansu Province. The massif was formed through the intrusion of thre...
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The Jinchuan Cu-Ni Sulfide Deposit is the biggest magmatic Cu-Ni sulfide deposit in China. It occurs in the Jinchuan Ultramafic Massif which is located in central Gansu Province. The massif was formed through the intrusion of three stages. The lherzolite, plagioclase-lherzolite, olivine-websterite etc. were formed in the first and the second stages; and the sulfide dunite was formed in the third stage. The Cu-Ni orebodies of the Jinchuan Deposit mainly occur in the lherzolite and sulfide-dunite. The original magma of this massif is komatiitic. The main minerals of the massif and the orebodies are chrysolite, bronzite, endiopside, pargasite, plagioclase, Ti-bearing phlogopite, phlogopitc, clinochlore, pyrrhotite, pentlandite, chalcopyrite, cubanite, mackinawite, magnetite, chromite, etc. The chrysolite, pyroxenes was often replaced by serpentine, magnesiocummingtonite and tromolitc. The fabrics of the Tocks in the massif and ores in the orebodies are similar. Based on the mineral intergrowth relationships the authors get to the conclusion that the evolution history of each intrusive can be divided into two stages: The first stage is the main solidifying stage. During this stage, about 70-80% of the volume of the intrusive was solidified, and chrysolite, pyroxenes, plagioclase, euhedral pargasite, etc. formed. The second stage is the ore forming and autometamorphism stage. In this stage, pyrrhotite, pentlandite, chalcopyrite, chromite(Chr2), magnetite, etc. and some hydrosillcates such as Ti-bearing phlogopite, phlogopite, fibrous pargasite, tromolite, clinochlore, serpentine, etc. formed. There was a late stage liquation of Fe-Ni-Cu-Cr-S-O melt from silicate melt which was rich in water and alkalis in the residual magma after the main solidifying stage. The mineralization process of the Jinchuan Deposit is recognized as " crystallization differentiation + late stage liquation". The ore minerals of the Jinchuan deposit had a very special crystallization process. Simply, the process can be described as: chromite(Chri)→pyrrhotite→"pentlandite +magnetite solid solution (PMSS)"+iss; when PMSS exsolved, pentlandite and magnetite(Mt2) formed; and chalcopyrite and cubanite formed when iss exsolved.
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