2008 Vol. 14, No. 4

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STUDY ON LATE CENOZOIC CRUSTAL TECTONISM
GAO Ming-xiu
2008, 14(4): 295-319.
Abstract (155) HTML (90) PDF (826KB)(18)
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This paper deals with late Cenozoic crustal tectonism by studying morphostructure and associated water system in a global scope.As young mountain belt is caused by deep dissection at the edge of a plateau, the keynote of complex morphostructure on Earth surface is actually made up of sequentially fixing arrangement of plateau-mountain-basin (P-M-B), with horst-like assemblage of B-M-P =P-M-B and step-like assemblage of P-M-B =P-M-B =P-M-B in different scales.It is found that the late Miocene planation surface preserved on the plateaus is comparable in age with the unconformity at the base of the Pliocene-early Pleistocene basins.Both imply the existence of a unified peneplain on the Earth surface until the latest Miocene.So the late Miocene peneplain substantially constrains the framework of the late Cenozoic crustal tectonism, and it is the late Cenozoic crustal tectonism that led to the breaking-up of the unified peneplain and brought about today' s morphostructure.From sedimentation, unconformity, and evolution of the water system, two evolutionary stages can be recognized for the late Cenozoic crustal tectonism, namely the Pliocene-early Pleistocene and middle Pleistocene-present.The paper also demonstrated the Asian mega-dividing.It extends from the mountain area of East Siberia in the northeast, passing through the Mongolian and Tibetan Plateaus, to the Aravalli Range in northwestern India to the southwest, and that divides water systems into the Pacific and Indian Oceans and the Arctic Ocean, respectively.It has emerged since middle Pleistocene (0.78 Ma), indicating the forming time of the global morphostructure.Geological records related to deformation of broken peneplain fragments indicate that vertical arching movement with block faulting at differential elevation and subsidence is predominant.It is debated that extensional and compressive crustal tectonism can be induced only from vertical movements at some specific areas.Except local compression deformation, no any geological records show that the Pleistocene sediments experienced any processes related with regionally horizontal compression on a global scope.Recent crustal tectonism follows the same keynote.
METHODS TO CALCULATE THE FAULT-RELATED STRAIN
XU Shun-shan, Nieto-Samaniego AF, Alaniz-Álvarez SA
2008, 14(4): 320-327.
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This paper presents some methods for calculation of fault strain. The faulting can produce continuous and discontinuous strain. The continuous strain has positive relationship with the ratio of fault displacement vs fault length and with the effective stress on the fault plane. When calculating the discontinuous fault strain, we should consider three factors that affect the establishment of equations: fault geometry, fault rotation, and fault size or fault displacement. There have been three mechanisms of fault rotation: rigid-body, vertical shear, and oblique shear. For these models, the calculation equations are established, respectively. These equations are related to the rotation angle and displacement of fault. For the rigid-body model, the fault has no internal deformation, thus the bed remain its length after rotation. The discontinuous strain due to this mechanism is smallest. The vertical shear produces bed deformation, whereas the horizontal length of bed does not change.The established equation indicates that, using the same data, the discontinuous fault strain is larger than that for the rigid-body model. Similarly, the oblique shear also causes bed deformation, but the horizontal length of bed remains constant. The obtained equation implies that the discontinuous fault strain is larger than that for the vertical shear model in the same condition.
DISTRIBUTION, ORIGIN AND MINERALIZATION OF TWO TYPES OF CENOZOIC ADAKITE AND ADAKITE-LIKE ROCKS IN SOUTHEASTERN ASIA
ZHU Zhang-xian, YANG Zhen-qiang
2008, 14(4): 328-338.
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The Sunda Islands of southeastern Asia is an area where Cenozoic adakite and adakite-like rocks are well developed.These intermediate-acid magmatic rocks are widespread in Guinea Island, Sulawesi (Indonesia), Papua New Guinea, and scattered in Sumatra western Java, Banda island arc and Central Kalimantan.The adakite and adakite-like rocks of the area belong respectively to island-arc tholeiitic /calc-alkaline series and high-potassium calc-alkaline series and are characterized by low HREE contents such as Y and Yb (Y ≤19 ×10-6 and Yb ≤1.8 ×10-6 respectively)and high Sr content (> 355 ×10-6).The spider diagrams show strongly positive anomalies of Ba, K and Sr and relatively negative anomalies of Th and Nb.The adakite and adakite-like rocks show enrichments in large-ion lithophitic element (LILE)and high-field strength elements (HFSE).The adakite and adakite-like rocks of Sunda Islands are tectonically distributed near the Cenozoic sutures, and can be divided into two types of origin.The first one, called oceanic type (O-type)of adakites, belongs to tholeiitic calcalk aline series with REE pattern of oceanic island arcs, and is seen at the oceanic island.The second type, named continental type (C-type)of adakites, belongs to high-potassium calc-alkaline series with REE patterns of continental type, often occurs in continental margin orogenic zone of continental plate and is originally related to arc-continent collision zone or post-collision.Our result reveals that the our research works reveals that the continental-type (C-type)adakite and adakite-like rocks have a similar distribution to the world-class porphyry copper-gold deposits, whereas the oceanic island arc type (Otyp e)adakite and adakite-like rocks are related in origin with epithermal hot-spring gold zones and ehalation ore deposits.
TYPICAL TECTONIC STYLES AND THEIR GEOLOGIC SIGNIFICANCE IN EASTERN GUIZHOU PROVINCE
DAI Chuan-gu, ZHANG Hui, HUANG Qing-hua
2008, 14(4): 339-345.
Abstract (131) HTML (108) PDF (335KB)(14)
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The Mesoproterozoic-Neoproterozoic to Cenozoic strata, including many types of magmatite and metamorphite, are developed in eastern Guizhou Province.Multi-periods of tectonic movements happening in the study region have been divided into Wuling structural cycle, Caledonian tectonic cycle, Yanshan tectonic cycle and Himalayan tectonic cycle.Typical structural styles are Alpine fold, Jura-type fold, thrust-nappe structure, ductile shear zone, metamorphic core complexes, extension-stripped fault system, strike-slip fault system, horst-graben structure, respectively.Difference of tectonic styles in different tectonic periods reflects the difference of structural positions.Therefore, in the plane, the Jiangnan orogenic belt is a composite orogenic belt composed of different orogenic sub-belts with evolution history of eastward migration.
SUPERPOSITION AND RECONSTRUCTION OF MARINE MESO-PALEOZOIC STRATA BY MESO-CENOZOIC BASINS IN SOUTHERN CHINA
ZHOU Xiao-jin, YANG Fan
2008, 14(4): 346-361.
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This paper focuses on the main basin prototypes developed in four tectonic evolution periods and their superposition in southern China during the Meso-Cenozoic.According to the superposition and tectonic reconstruction of basin prototype, five types of late reconstruction could be recognized for marine Meso-Paleozoic in southern China, namely the persistent foredeep superposition, foredeep-slide-faultdepression superposition, foredeep-slide or fault superposition, nappe structure and shadow basin, and relict reconstruction.Moreover we discuss their main tectonic characteristics and difference in the condition for oil-gas preservation.The study indicates that the persistent foreland basin superposition, represented by the Sichuan Basin, is most favorable for preservation of marine Meso-Cenozoic natural gas.The second favorable type is the foredeep-slide-fault-depression superposition, with its examples in Jiangsu Basin and Wannan-Subei Basin in middle-lower Yangtze.Under the early foreland basin superposition (Late Triassic to Middle Jurassic)and the late fault depression-depression superposition (since Middle Cretaceous), it successively constituted a regional enclosed condition for marine Meso-Paleozoic, and offered a condition for preservation of the second oil-gas formation of marine Meso-Paleozoic although it had been deformed by the strong Yanshanian compression-strike-slip during Late Jurassic to Early Cretaceous.The foredeepslide or fault superposition, represented by the Chuxiong Basin and Shiwan Mountain Basin, set up a regional enclosed condition for marine Meso-Paleozoic in the early stage (Late Triassic to Middle Jurassic), but then imposed an effect upon preservation of marine oil-gas, because it led the basins as a whole to form block structures under the effect of strike-slip and thrust since the second structure stage. In addition, it is pointed out that much attention should be drawn to the "shadow basin" in nappe structure, especially to oil-gas preservation condition below the regional decollement layer as well as the relict reconstructed weak deformation belt such as Nanpanjiang depression.
STRUCTURAL EVOLUTION AND HYDROCARBON ACCUMULATION IN THE XINDONG AREA OF DONGYING SAG, BOHAI BAY BASIN
HAN Qing-hua, YAN Peng, YU Zhao-hua, WU Shi-guo
2008, 14(4): 362-373345.
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The Xindong area is located at the conjunction of several structural belts, among which the Xinzhen structure constitutes the principal structural belt of the research area.The faults of the area display obvious growth and succession, and reached the acme in their development during the deposition of Es3-Es2 and Ed.Based on the analysis on balanced cross-section evolution of 4116 survey line, the Cenozoic tectonic evolution of this research area could be divided into three stages :pre-Es3 embryonic stage, Es3-Ed shaping stage, and Ng-present decline stage.The oil resource of this area mainly came from the nearby Minfeng and Niuzhuang sags.Ed and Ng-Nm are two oil and gas reservoir forming phases, and the latter is the main one.The generated oil and gas migrated laterally in the vicinity and accumulated in deep trap consisting of Es4 and Es11-2x-Es2; then, the oil and gas continued to migrate through large-scale accumulation body and active faults to the research area and concentrated in the Paleogene fault blocks involved in wing and core parts of structures near sags.Long-term development of active faults led to the change in condition for formation of oil and gas, so part of the generated oil and gas migrated upward along the active faults and formed secondary hydrocarbon reservoir in the Neogene beds.
EXPERIMENTAL STUDY OF EFFECT OF TEMPERATURE ON COAL GAS PERMEABILITY UNDER GAS-SOLID COUPLING
YANG Xin-le, ZHANG Yong-li
2008, 14(4): 374-380.
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To observe the effect of temperature on coal gas permeability, an experiment of coal gas permeability was carried out at different temperatures through a three-axial penetration instrument.The results show that, at different temperatures, the permeability of coals assumes a trend of quadric parabola, that is, the permeability first decreases and then increases as the effective stress decreases. In the early unloading, the degressive gradient of coal gas permeability is greater at lower temperature than at high temperature.In the late unloading, coal gas permeability ascending gradient is greater at high temperature than at low temperature.The results show that, in the process of coal bed gas mining, the change of coal gas permeability demonstrate three master phases of typical coal bed methane mining at different temperatures.The effective stress, gas heating and coal solid heating are the important factors influencing coal body permeability.In the early unloading, coal solid heating, expansion and effective stress play a leading role in permeability; in the later unloading, gas sliding and gas absorbing heat play a leading role in permeability.After experimental analysis, adopting the exploitation way of coal bed methane fracturing after injection will help to improve production of coal bed methane.
SENSITIVITY ANALYSIS ON FACTORS INFLUENCING LANDSLIDE STABILITY AND DISCUSSION ON ITS TREATMENT DESIGN
MA Xian-chun, WANG Lei, ZHAO Fa-suo
2008, 14(4): 381-388.
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The factors influencing landslide stability coefficients include cohesion of soil in the slide zone, internal friction angle, unit weight of the slide and the pore water pressure, etc.They affect the lan dslide stability coefficients in different degrees, so that one imposing the greatest influence on the lan dslide stability coefficients needs to be recognized by quantitative criteria, and studied more closely, to improve treatment effect.In this paper, all the factors are analyzed by using orthogonal analysis method, and various landslide stability coefficients calculated, which is thought helpful to reaching a reasonable and economic treatment.