2008 Vol. 33, No. 6
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2008, 33(6): 723-742.
Abstract:
The Qinghai-Tibet plateau has trichotomy of temporal-spatial structure and three scales of dynamic system.The plateau includes northern, eastern and southern basin-mountain systems adjusted by three (northern, eastern and western) syntaxes that are separately controlled by Siberia plate, Pacific plate and India ocean plate, which underwent three tectonic stages including Precambrian supercontinent-superocean coupling, southward ocean-continent coupling of Proto-Tethys, Pa-leo-Tethys, Meso-Tethys, and Neo-Tethys that separately took place in the Caleodonian period, Indosinian period, Yans-hanian period and Early Himalayan period and intraplate basin-mountain coupling separately driven by laminar flow in core (core dynamics or global dynamics), laminar layer in mantle (mantle dynamics or lithospheric dynamics) and laminar flow in crust (crustal dynamics or dynamic dynamics), composing an earth system dynamics system.The Qinghai-Tibetan plateau is not the result of collision between the Indian plate and the Eurasia plate, but intraplate basin-mountain coupling driven by lower crust lateral flow from basin to plateau, which can be subdivided into two stages: intraplate orogeny characteristized by tectonic uplift, horizontal movement, geological process and metallogenesis during 180-7 Ma southward migration from Qilian-Kunlun to Himalaya and isostatic mountain building characteristized by pulsative integral quick uplift, vertical move-ment, geographical process and environmental change since 3.6 Ma.Tectonic pedigree determines mineralizing pedigree.Multistage regional tectonic evolution causes the increase of crustal maturity and enhancement of mineral deposit density.Three stages of tectonic and metallogenic evolution in the Qinghai-Tibet plateau include six main mineralizing phases inclu ding 1, 8-1.4 Ga, 500-420 Ma, 300-260 Ma, 180-120 Ma.65-30 Ma, and 23-7 Ma, constituting a metallogenic dy namics evolutional system, in which 1.8-1.4 Ga rifting event of supercontinent resulted in formation for Dahongshan-type reworked marine volcanic sedimentary iron-copper deposit, Jinchuan-type copper and nickel sulfide deposits associated with mafic and ultramafic rocks; 500-420 Ma rifting of Proto-Tethys, 300-260 Ma rifting of Paleo-Tethys, and 180-120 Ma rifting of Meso-Tethys and Neo-Tethys controlled Luobusha-type mantle shear and reworking vein (podiform) chromite de posits, Gacun-type volcanics-hosted massive sulfide (VHMS) deposits; 180-120Ma intraplate extension in the northern plateau, 65-30 Ma intraplate extension in the central plateau and 23-7 Ma intraplate extension in the southern plateau formed the Qulong-type porphyry Cu deposits, Ailaoshan-type shear zone Au deposits, and Jinding-type continental sedi mentary rock-hosted Pb-Zn deposits.
The Qinghai-Tibet plateau has trichotomy of temporal-spatial structure and three scales of dynamic system.The plateau includes northern, eastern and southern basin-mountain systems adjusted by three (northern, eastern and western) syntaxes that are separately controlled by Siberia plate, Pacific plate and India ocean plate, which underwent three tectonic stages including Precambrian supercontinent-superocean coupling, southward ocean-continent coupling of Proto-Tethys, Pa-leo-Tethys, Meso-Tethys, and Neo-Tethys that separately took place in the Caleodonian period, Indosinian period, Yans-hanian period and Early Himalayan period and intraplate basin-mountain coupling separately driven by laminar flow in core (core dynamics or global dynamics), laminar layer in mantle (mantle dynamics or lithospheric dynamics) and laminar flow in crust (crustal dynamics or dynamic dynamics), composing an earth system dynamics system.The Qinghai-Tibetan plateau is not the result of collision between the Indian plate and the Eurasia plate, but intraplate basin-mountain coupling driven by lower crust lateral flow from basin to plateau, which can be subdivided into two stages: intraplate orogeny characteristized by tectonic uplift, horizontal movement, geological process and metallogenesis during 180-7 Ma southward migration from Qilian-Kunlun to Himalaya and isostatic mountain building characteristized by pulsative integral quick uplift, vertical move-ment, geographical process and environmental change since 3.6 Ma.Tectonic pedigree determines mineralizing pedigree.Multistage regional tectonic evolution causes the increase of crustal maturity and enhancement of mineral deposit density.Three stages of tectonic and metallogenic evolution in the Qinghai-Tibet plateau include six main mineralizing phases inclu ding 1, 8-1.4 Ga, 500-420 Ma, 300-260 Ma, 180-120 Ma.65-30 Ma, and 23-7 Ma, constituting a metallogenic dy namics evolutional system, in which 1.8-1.4 Ga rifting event of supercontinent resulted in formation for Dahongshan-type reworked marine volcanic sedimentary iron-copper deposit, Jinchuan-type copper and nickel sulfide deposits associated with mafic and ultramafic rocks; 500-420 Ma rifting of Proto-Tethys, 300-260 Ma rifting of Paleo-Tethys, and 180-120 Ma rifting of Meso-Tethys and Neo-Tethys controlled Luobusha-type mantle shear and reworking vein (podiform) chromite de posits, Gacun-type volcanics-hosted massive sulfide (VHMS) deposits; 180-120Ma intraplate extension in the northern plateau, 65-30 Ma intraplate extension in the central plateau and 23-7 Ma intraplate extension in the southern plateau formed the Qulong-type porphyry Cu deposits, Ailaoshan-type shear zone Au deposits, and Jinding-type continental sedi mentary rock-hosted Pb-Zn deposits.
2008, 33(6): 743-754.
Abstract:
Kunlunguan pluton, located in the southwest part of the Nandan-Kunlunguan granite belt, Guangxi, is mainly composed of biotite granite. Petrography and chemical compositions show that it belongs to high-K calc-alkaline series characterized by high silicon, is enriched in alkali and aluminum but depleted in phosphorus and titanium. Its SiO2 contents range from 68. 13% to 72. 61%, while K2O/Na2O ratios and A/CNK values vary from 1.28 to 1.69 and 0. 72 to 1.28 respectively, ascribed to a suite of met aluminous to intensively peraluminous rock. Ga, Rb, Th, U and Pb elements are enriched in the intrusion while Ba, Nb, Sr, P and Ti depleted. REE is characterized by obvious negative anomalies with Eu/Eu* 0. 53-0. 73 and exhibits right-dipping "V" patterns with LREE enrichment. LA-ICP-MS zircon U-Pb dating yields a weighted mean 206pb/238U age of 93±1 Ma (MSDW=1. 7) for the Gumin unit of the pluton, implying its Late Cretaceous intrusion time. Mineralogy and geochemistry confirm that the Nandan-Kuntunguan granite belt is an important aluminous A-type granite belt in the South China, controlled by northwestward Nandan-Kunlunguan deep fault. Petrology, major and trace el- ement features display that the pluton intruded in a post-collisional extensive tectonic setting. These results, combined with Late Cretaceous tectonic environment and regional stress field matching relationship in the studied area, indicate the A-type granite action is due to back-arc extension related to high angle subduction of the ancient Pacific plate which is caused by Indian plate northward movement. This granite belt and those granite or alkaline rocks in the coastal areas of Zhejiang-Fujian provinces represent the two A-type granite belts under a matching tectonic system.
Kunlunguan pluton, located in the southwest part of the Nandan-Kunlunguan granite belt, Guangxi, is mainly composed of biotite granite. Petrography and chemical compositions show that it belongs to high-K calc-alkaline series characterized by high silicon, is enriched in alkali and aluminum but depleted in phosphorus and titanium. Its SiO2 contents range from 68. 13% to 72. 61%, while K2O/Na2O ratios and A/CNK values vary from 1.28 to 1.69 and 0. 72 to 1.28 respectively, ascribed to a suite of met aluminous to intensively peraluminous rock. Ga, Rb, Th, U and Pb elements are enriched in the intrusion while Ba, Nb, Sr, P and Ti depleted. REE is characterized by obvious negative anomalies with Eu/Eu* 0. 53-0. 73 and exhibits right-dipping "V" patterns with LREE enrichment. LA-ICP-MS zircon U-Pb dating yields a weighted mean 206pb/238U age of 93±1 Ma (MSDW=1. 7) for the Gumin unit of the pluton, implying its Late Cretaceous intrusion time. Mineralogy and geochemistry confirm that the Nandan-Kuntunguan granite belt is an important aluminous A-type granite belt in the South China, controlled by northwestward Nandan-Kunlunguan deep fault. Petrology, major and trace el- ement features display that the pluton intruded in a post-collisional extensive tectonic setting. These results, combined with Late Cretaceous tectonic environment and regional stress field matching relationship in the studied area, indicate the A-type granite action is due to back-arc extension related to high angle subduction of the ancient Pacific plate which is caused by Indian plate northward movement. This granite belt and those granite or alkaline rocks in the coastal areas of Zhejiang-Fujian provinces represent the two A-type granite belts under a matching tectonic system.
2008, 33(6): 755-763.
Abstract:
Xiyingzi granite-body in Guyang area, Inner Mongolia, belongs to calc-alkaline series, bearing the characteristics of island arc affinity.Its petrological geochemistry characteristics are almost similar to those of adakite: SiO2 content > 56% on average (57.28%-66.63%); Al2O3 > 15% (15.93%-18.04%); MgO=1.14%-3.47%, enriched in Na and depleted in K; Na2O/K2O=1.16-1.97;Sr content (446-582 μg/g) > 400 μg/g on average and Sr/Y ratio =31.32-103.74, > 20-40;low Y content (5.61-17.4 μg/g, less than 18 μg/g); low Yb (0.42-2.06 μg/g, only one sample's Yb content > 1.9 μg/g); with small positive Eu anomaly and without significantly negative Eu anomaly; REE has a strong differentiation, which belongs to the strong LREE enrichment type; Sr has obvious positive anomaly, while Nb has significant negative anomaly.The laser-plasma mass spectrometry (LA-ICP-MS) was used for the zircon U-Pb dating of adakitic granite in Guyang area and the isotope age was obtained to be 281.9±3.1 Ma (MSWD=3.3), indicating an Early Permian activity.The discovery of adakite in this region provides new clues on the closure time of Paleo-Asian Ocean, and is of great significance to the study of Central Asia Late Paleozoic orogenic belt's tectonic evolution and geodynamics characteristics.It also provides geological and geochemical constraints on resolving the long-term debates on the Inner Mongolia and Paleo-Asian Ocean.
Xiyingzi granite-body in Guyang area, Inner Mongolia, belongs to calc-alkaline series, bearing the characteristics of island arc affinity.Its petrological geochemistry characteristics are almost similar to those of adakite: SiO2 content > 56% on average (57.28%-66.63%); Al2O3 > 15% (15.93%-18.04%); MgO=1.14%-3.47%, enriched in Na and depleted in K; Na2O/K2O=1.16-1.97;Sr content (446-582 μg/g) > 400 μg/g on average and Sr/Y ratio =31.32-103.74, > 20-40;low Y content (5.61-17.4 μg/g, less than 18 μg/g); low Yb (0.42-2.06 μg/g, only one sample's Yb content > 1.9 μg/g); with small positive Eu anomaly and without significantly negative Eu anomaly; REE has a strong differentiation, which belongs to the strong LREE enrichment type; Sr has obvious positive anomaly, while Nb has significant negative anomaly.The laser-plasma mass spectrometry (LA-ICP-MS) was used for the zircon U-Pb dating of adakitic granite in Guyang area and the isotope age was obtained to be 281.9±3.1 Ma (MSWD=3.3), indicating an Early Permian activity.The discovery of adakite in this region provides new clues on the closure time of Paleo-Asian Ocean, and is of great significance to the study of Central Asia Late Paleozoic orogenic belt's tectonic evolution and geodynamics characteristics.It also provides geological and geochemical constraints on resolving the long-term debates on the Inner Mongolia and Paleo-Asian Ocean.
2008, 33(6): 764-774.
Abstract:
The upper basement of the Cathaysia block in Zhejiang and Fujian provinces consists mainly of the Neoproterozoic Longquan Group, Mamiansban Group, and Wanquan Group. These three groups exhibit similarity in rock assemblage as well as major and trace elements geochemistry. They are the main components of the uniform upper basement of the Cathaysia block, consisting mainly of schists, leptynites, quaterizes and marbles. Schists and the leptynites have variable composi-tions, with SiO2 contents ranging from 52.89% to 75.03%, TiO2 from 0.48% to 1.05%, Al2O3 from 9.19% to 20.3%, ∑REE between 149×10-6 and 323×10-6, δEu values between 0.34 and 0.80, and (La/Yb)N values between 7.96 and 15.6. The REE patterns display medium to high negative Eu anomaly with obvious fractionation between LREE and HREE. The quartzites have different compositions, with SiO2 contents varying from 95.49% to 97.44%, and relatively low ∑REE contents (8.89× 10-6 to 15.1 × 10-6). It is proposed that protoliths of the schists and the leptynites are wackes and clay rocks, whereas protoliths of the quartzites are ferruginous silica rocks, mainly quartz-feldspathic; and some protoliths show geochemical characteristics of ancient allochthonous sediments. The meta-sedimentary rocks of the Longquan Group, Mamianshan Group, and Wanquan Group were probably formed in an environment of arc-active continental margin. The lower maturity implies that they are near field sediments, similar to the metamorphic rock system of the lower basement in this area (Paleoproterozoic Tianjingping Formation, Badu Group, Chencai Group and Mayuan Group), analogous to the upper crustal rocks.
The upper basement of the Cathaysia block in Zhejiang and Fujian provinces consists mainly of the Neoproterozoic Longquan Group, Mamiansban Group, and Wanquan Group. These three groups exhibit similarity in rock assemblage as well as major and trace elements geochemistry. They are the main components of the uniform upper basement of the Cathaysia block, consisting mainly of schists, leptynites, quaterizes and marbles. Schists and the leptynites have variable composi-tions, with SiO2 contents ranging from 52.89% to 75.03%, TiO2 from 0.48% to 1.05%, Al2O3 from 9.19% to 20.3%, ∑REE between 149×10-6 and 323×10-6, δEu values between 0.34 and 0.80, and (La/Yb)N values between 7.96 and 15.6. The REE patterns display medium to high negative Eu anomaly with obvious fractionation between LREE and HREE. The quartzites have different compositions, with SiO2 contents varying from 95.49% to 97.44%, and relatively low ∑REE contents (8.89× 10-6 to 15.1 × 10-6). It is proposed that protoliths of the schists and the leptynites are wackes and clay rocks, whereas protoliths of the quartzites are ferruginous silica rocks, mainly quartz-feldspathic; and some protoliths show geochemical characteristics of ancient allochthonous sediments. The meta-sedimentary rocks of the Longquan Group, Mamianshan Group, and Wanquan Group were probably formed in an environment of arc-active continental margin. The lower maturity implies that they are near field sediments, similar to the metamorphic rock system of the lower basement in this area (Paleoproterozoic Tianjingping Formation, Badu Group, Chencai Group and Mayuan Group), analogous to the upper crustal rocks.
2008, 33(6): 775-782.
Abstract:
The South China Sea (SCS) features relatively complete physiographical units and ecologic environments of marginal sea, where there are a lot of radiolarian species and specimens preserved in the sediments.Methodsof quantitative statistics and clustering were used in this paper to analyze the radiolarian assemblages in surface sediments of the SCS so as to obtain their characteristics of compositions and distributions.Result of clustering analysis shows that the radiolarian assemblage in the surface sediments may be mainly divided into five groups, namely, assemblages of shallow shelf, coral slope, central basin, southern rich nutrition and summer upwelling, corresponding to different special marine environments respectively and consisting of certain radiolarian communities of dominant species.It is also indicated that the northern, central and southern SCS take on as three different ecologic costal areas respectively, such as the north affected mostly by terrigenous input, the central area controlled mainly by the central basin waters, submarine volcanic and summer upwelling activities, and the south generally belonging to a typical coral environment where there is a better ecologic and sedimental environment for radiolarian than in the northern SCS.The radiolarian assemblages and distributions in the SCS surface sediments are well responding to and reveal the marine ecologic conditions and sedimental environments, which may be important evidences for paleoceanographic exploration.
The South China Sea (SCS) features relatively complete physiographical units and ecologic environments of marginal sea, where there are a lot of radiolarian species and specimens preserved in the sediments.Methodsof quantitative statistics and clustering were used in this paper to analyze the radiolarian assemblages in surface sediments of the SCS so as to obtain their characteristics of compositions and distributions.Result of clustering analysis shows that the radiolarian assemblage in the surface sediments may be mainly divided into five groups, namely, assemblages of shallow shelf, coral slope, central basin, southern rich nutrition and summer upwelling, corresponding to different special marine environments respectively and consisting of certain radiolarian communities of dominant species.It is also indicated that the northern, central and southern SCS take on as three different ecologic costal areas respectively, such as the north affected mostly by terrigenous input, the central area controlled mainly by the central basin waters, submarine volcanic and summer upwelling activities, and the south generally belonging to a typical coral environment where there is a better ecologic and sedimental environment for radiolarian than in the northern SCS.The radiolarian assemblages and distributions in the SCS surface sediments are well responding to and reveal the marine ecologic conditions and sedimental environments, which may be important evidences for paleoceanographic exploration.
2008, 33(6): 783-792.
Abstract:
Nineteen specimens of Oryctocephalus indicus (Reed, 1910) from the middle-upper part of Kaili Formation of Middle Cambrian in Jianhe County, southeastern Guizhou, South China, which are interpreted as exuvial configurations, are described.Most of them are missing cranidium, remains of the articulated exoskeleton are in original relation.The series of events which may have resulted in the production of these configurations are as follows: (1) The trilobite flexed the cephalon downward throuth a certain angle less than ninety degrees.During this flexing downward, the cephalon splited from the thorax as well as the facial suture opened, so that the free cheeks disarticulated from the cranidium. (2) The animal regained its planar orientation and resulted in the old cranidium rotated. (3) The trilobite crawled forward with the old exoskeleton and overturned the cranidium to inverted in front of the cephalon. (4) The inverted cranidium was pushed aside by the crawled forward animal. (5) The animal continued to crawl forward, kept shaking and withdrew from the old exoskeleton.Finally, the old exoskeleton was shed.On the exuviae, the thorax joined up with pygidium, the rostral-hypostomal plate and free cheeks located at their original site.It is different from the "Phacopid mode of ecdysis"or "Salterian embedding".
Nineteen specimens of Oryctocephalus indicus (Reed, 1910) from the middle-upper part of Kaili Formation of Middle Cambrian in Jianhe County, southeastern Guizhou, South China, which are interpreted as exuvial configurations, are described.Most of them are missing cranidium, remains of the articulated exoskeleton are in original relation.The series of events which may have resulted in the production of these configurations are as follows: (1) The trilobite flexed the cephalon downward throuth a certain angle less than ninety degrees.During this flexing downward, the cephalon splited from the thorax as well as the facial suture opened, so that the free cheeks disarticulated from the cranidium. (2) The animal regained its planar orientation and resulted in the old cranidium rotated. (3) The trilobite crawled forward with the old exoskeleton and overturned the cranidium to inverted in front of the cephalon. (4) The inverted cranidium was pushed aside by the crawled forward animal. (5) The animal continued to crawl forward, kept shaking and withdrew from the old exoskeleton.Finally, the old exoskeleton was shed.On the exuviae, the thorax joined up with pygidium, the rostral-hypostomal plate and free cheeks located at their original site.It is different from the "Phacopid mode of ecdysis"or "Salterian embedding".
2008, 33(6): 793-799.
Abstract:
Molecular organic geochemical analysis of Core 17937 in the northern South China Sea has provided useful information on the paleoenvironmental change in the 40 ka and revealed that the average surface temperature of U37k'-SSTs in glacial and interglacial is 27 ℃ and 24 ℃ respectively, resulting in a difference of 4.5 ℃ between Holocene and LGM.The terrestrial input, mainly consisting of high molecular weight alkanes and marine primary productivity, constituting long chain alkenones, both exhibited a high value in glacial and low value in interglacial, which suggests the supply of organic matter from the land is enhanced and the productivity in the ocean during glacial is increased.Alkane ratio of C31/C27 indicated that the predominant plants in South China changed from grass during glacial to tree during interglacial.All the results show the instability of climate since the last glacial in the SCS, and the significant role played by marine and terrestrial ecosystems in climate changes, as well as the potential of molecular organic geochemistry in paleoenvironment and paleoclimate studies.
Molecular organic geochemical analysis of Core 17937 in the northern South China Sea has provided useful information on the paleoenvironmental change in the 40 ka and revealed that the average surface temperature of U37k'-SSTs in glacial and interglacial is 27 ℃ and 24 ℃ respectively, resulting in a difference of 4.5 ℃ between Holocene and LGM.The terrestrial input, mainly consisting of high molecular weight alkanes and marine primary productivity, constituting long chain alkenones, both exhibited a high value in glacial and low value in interglacial, which suggests the supply of organic matter from the land is enhanced and the productivity in the ocean during glacial is increased.Alkane ratio of C31/C27 indicated that the predominant plants in South China changed from grass during glacial to tree during interglacial.All the results show the instability of climate since the last glacial in the SCS, and the significant role played by marine and terrestrial ecosystems in climate changes, as well as the potential of molecular organic geochemistry in paleoenvironment and paleoclimate studies.
2008, 33(6): 800-806.
Abstract:
Superimposed basins in China are characterized by multiple-stage superposition of tectonic,multiple-stage charging and late-stage orientation.The formerly accumulated native reservoirs usually have undergone adjustment to a certain extent due to the neotectonics movements at Xishan epoch in the hinterland of Junggar basin.For being impersonally cognizant of the adjustment models and re-accumulation rules of oil/gas reservoirs,data analyzing,logging/testing outcome contrasting,reservoir physical property relationship studying and numerical experiment simulating are applied.Resultsshow the adjustment of formerly accumulated subtle reservoirs would lead to the occurrence of a series of genetically-related oil layers with complicated oil/water or gas/water contacts and physical property relationship.Three models of adjusted preservation,adjusted residue/remnant and adjusted dissipation subtle oil/gas reservoirs have been identified.The main adjusting track are simulated.The re-accumulation mechanism and distribution rules of adjusted reservoirs in the hinterland of Junggar basin are discussed.
Superimposed basins in China are characterized by multiple-stage superposition of tectonic,multiple-stage charging and late-stage orientation.The formerly accumulated native reservoirs usually have undergone adjustment to a certain extent due to the neotectonics movements at Xishan epoch in the hinterland of Junggar basin.For being impersonally cognizant of the adjustment models and re-accumulation rules of oil/gas reservoirs,data analyzing,logging/testing outcome contrasting,reservoir physical property relationship studying and numerical experiment simulating are applied.Resultsshow the adjustment of formerly accumulated subtle reservoirs would lead to the occurrence of a series of genetically-related oil layers with complicated oil/water or gas/water contacts and physical property relationship.Three models of adjusted preservation,adjusted residue/remnant and adjusted dissipation subtle oil/gas reservoirs have been identified.The main adjusting track are simulated.The re-accumulation mechanism and distribution rules of adjusted reservoirs in the hinterland of Junggar basin are discussed.
2008, 33(6): 807-812.
Abstract:
With the aim of studying reservoir-forming mechanism of coalbed methane (CBM) in the area of Jincheng, through the continuous development of coalbed methane in Jincheng, the dissection of fracturing coalbed methane wells, the extraction of underground coal seam gas, the study of tectonic stress field, the "CT"-dissection of the fracture system of coal reservoir and the sutdy of closed preservation conditions on coalbed methane, we found that there are a lot of CBM packages in 3 coal reservoir and these CBM packages merge together because of micro-structural breakdown. As a result, the heterogeneity of reservoir in CBM packages becomes weak; the permeability increases; the proportion of free gas increases in CBM package and the fluid pressure system gradually clears. Eventually, the above factors jointly contribute to the formation of the border of coalbed methane reservoir. The study on the accumulation mechanism of coalbed methane and the characteristics of the internal details of coalbed methane reservoir promotes the development of coalbed methane exploiting technology and improves the efficiency of extracting the underground coal seam gas.
With the aim of studying reservoir-forming mechanism of coalbed methane (CBM) in the area of Jincheng, through the continuous development of coalbed methane in Jincheng, the dissection of fracturing coalbed methane wells, the extraction of underground coal seam gas, the study of tectonic stress field, the "CT"-dissection of the fracture system of coal reservoir and the sutdy of closed preservation conditions on coalbed methane, we found that there are a lot of CBM packages in 3 coal reservoir and these CBM packages merge together because of micro-structural breakdown. As a result, the heterogeneity of reservoir in CBM packages becomes weak; the permeability increases; the proportion of free gas increases in CBM package and the fluid pressure system gradually clears. Eventually, the above factors jointly contribute to the formation of the border of coalbed methane reservoir. The study on the accumulation mechanism of coalbed methane and the characteristics of the internal details of coalbed methane reservoir promotes the development of coalbed methane exploiting technology and improves the efficiency of extracting the underground coal seam gas.
2008, 33(6): 813-824.
Abstract:
In order to figure out the genesis and the model of eastern Liaoning borate deposits, the four main controlling factors including boron-bearing rock system, magnesian host rocks, regional metamorphism and migmatitization, and tectonism are studied. It reveals that the boron-bearing rock system is rich in boron, the host rocks of the borate deposits in magnesium and is the precipitator for boron; besides, the boron of the boron-bearing rock system has gotten more active and a lot of boron-bearing fluid formed in the course of the regional metamorphism and migmatitization of the boron-bearing rock sys tem; while the magnesium borate deposits have formed in the metasomatism of the boron-bearing fluid with magnesian hosting rocks in favorable structural space. Thus, the boron-bearing rock system and the magnesian rocks are the foundation of the borate deposits, whereas regional metamorphism and migmatitization and tectonism are the necessary conditions. Oreforming model of eastern Liaoning borate deposits is the primary enrichment of the eovolcanic sediment and the metamorphic hydrothermal replacement between some boron-bearing fluid and the magnesian rocks during the process of regional metamorphism and migmatitization and tectonism.
In order to figure out the genesis and the model of eastern Liaoning borate deposits, the four main controlling factors including boron-bearing rock system, magnesian host rocks, regional metamorphism and migmatitization, and tectonism are studied. It reveals that the boron-bearing rock system is rich in boron, the host rocks of the borate deposits in magnesium and is the precipitator for boron; besides, the boron of the boron-bearing rock system has gotten more active and a lot of boron-bearing fluid formed in the course of the regional metamorphism and migmatitization of the boron-bearing rock sys tem; while the magnesium borate deposits have formed in the metasomatism of the boron-bearing fluid with magnesian hosting rocks in favorable structural space. Thus, the boron-bearing rock system and the magnesian rocks are the foundation of the borate deposits, whereas regional metamorphism and migmatitization and tectonism are the necessary conditions. Oreforming model of eastern Liaoning borate deposits is the primary enrichment of the eovolcanic sediment and the metamorphic hydrothermal replacement between some boron-bearing fluid and the magnesian rocks during the process of regional metamorphism and migmatitization and tectonism.
2008, 33(6): 825-833.
Abstract:
This paper mainly presents the definition and forming process of deepwater sediment,as well as the characteristics of deepwater sequence stratigraphy and sedimentary elements. The deepwater sediment is deposited in deepwater environment by the gravity flow,forms during the drop and earlier rise of relative water level,and mainly distributes in lowstand systems tract.The deepwater sequence is bounded by condensed section.Mass transport deposits form the beginning of a sequence formation and sit on the sequence boundary.Then they are overlaid by channel-levee deposits.The typical deepwater sedimentary elements include channel,levee and overbank,sheet sand,and mass transport deposits.These elements are systematically deposited in time and space.Channel is the main sediment conduit and deposition area.From updip to downdip area,the sinuosity of channel increases and the flow energy decreases.The channel migrates laterally and evolves from lower low sinuous sand-rich to upper high sinuous mud-rich channel.Levee and overbank are dominated by muddy deposits,and levee distributes along the channel and exhibits wedge shape.The proximal levee is characterized by high content of sandstone,thicker deposit and big dip angle,while the distal levee is characterized by low content of sandstone,thinner deposit,small dip angle,good lateral continuity and poor vertical communication.Sheet sand is the distal unconfined deposits of the deepwater fan and can be divided into conglomerate and layered types,and conglomerate sheet sand has a good lateral continuity and vertical communication.The layered sheet sand has a good lateral continuity and poor vertical communication.Mass transport deposits are the slumps,slides and debris flow due to the slope failure during lowstand period.It can erode the underlying strata,and the deformation structure is very common in mass transport deposit,and it can also serve as a good seal for oil and gas.
This paper mainly presents the definition and forming process of deepwater sediment,as well as the characteristics of deepwater sequence stratigraphy and sedimentary elements. The deepwater sediment is deposited in deepwater environment by the gravity flow,forms during the drop and earlier rise of relative water level,and mainly distributes in lowstand systems tract.The deepwater sequence is bounded by condensed section.Mass transport deposits form the beginning of a sequence formation and sit on the sequence boundary.Then they are overlaid by channel-levee deposits.The typical deepwater sedimentary elements include channel,levee and overbank,sheet sand,and mass transport deposits.These elements are systematically deposited in time and space.Channel is the main sediment conduit and deposition area.From updip to downdip area,the sinuosity of channel increases and the flow energy decreases.The channel migrates laterally and evolves from lower low sinuous sand-rich to upper high sinuous mud-rich channel.Levee and overbank are dominated by muddy deposits,and levee distributes along the channel and exhibits wedge shape.The proximal levee is characterized by high content of sandstone,thicker deposit and big dip angle,while the distal levee is characterized by low content of sandstone,thinner deposit,small dip angle,good lateral continuity and poor vertical communication.Sheet sand is the distal unconfined deposits of the deepwater fan and can be divided into conglomerate and layered types,and conglomerate sheet sand has a good lateral continuity and vertical communication.The layered sheet sand has a good lateral continuity and poor vertical communication.Mass transport deposits are the slumps,slides and debris flow due to the slope failure during lowstand period.It can erode the underlying strata,and the deformation structure is very common in mass transport deposit,and it can also serve as a good seal for oil and gas.
2008, 33(6): 834-842.
Abstract:
To ascertain the period of shaping and filling of the incised valley,and the incised valley filling architecture in the western Clinoform of Songliao basin,we made use of the data of core and of more than 300 boreholes,and adopted the theories and methods of sequence stratigraphy and sedimentology to make an in-depth study on the incised valley filled by Cretaceous Yaojia Formation in the western Clinoform of Songliao basin. The incised valley in the western Clinoform of Songliao basin formed during the end of the deposition period of Qingshankou Formation and the early deposition period of Yaojia Formation in Cretaceous. It was about 70 km long and 20 km wide,extending NW-SE,and was filled gradually in the time of the transgressive system tract of SQy23 sequence (TSTy23).The filling succession of the incised valley is characterized by its multi-cycle.The bottom boundary of a perfect short-term filling cycle is the erosion surface,above which successively develop gompholite,medium-fine sandstone contained terrigenous gravels and mud pebble with the cross bedding,silty mudstone with ripple stratification and mudstone.The architecture of sand bodies with different short-term cycles that filled the incised valley presents imbricate arrangement in space.In the dip-profile,the sand body overlaps bed by bed along the bottom surface of the valley,splits toward the basin and pinches out into mudstone,reflecting the joint influence of stream and lake.In the strike profile,the sand bodies present lenticular staggered arrangement.The early sand body was developed at the relatively deeper place of the valley,while the higher place of the valley was dominated by the mudstone.The later sand body was not limited by the former deep valley.In the period when the lake-level of SQy23 reached maximum,the incised valley was filled mainly by the muddy sediment.
To ascertain the period of shaping and filling of the incised valley,and the incised valley filling architecture in the western Clinoform of Songliao basin,we made use of the data of core and of more than 300 boreholes,and adopted the theories and methods of sequence stratigraphy and sedimentology to make an in-depth study on the incised valley filled by Cretaceous Yaojia Formation in the western Clinoform of Songliao basin. The incised valley in the western Clinoform of Songliao basin formed during the end of the deposition period of Qingshankou Formation and the early deposition period of Yaojia Formation in Cretaceous. It was about 70 km long and 20 km wide,extending NW-SE,and was filled gradually in the time of the transgressive system tract of SQy23 sequence (TSTy23).The filling succession of the incised valley is characterized by its multi-cycle.The bottom boundary of a perfect short-term filling cycle is the erosion surface,above which successively develop gompholite,medium-fine sandstone contained terrigenous gravels and mud pebble with the cross bedding,silty mudstone with ripple stratification and mudstone.The architecture of sand bodies with different short-term cycles that filled the incised valley presents imbricate arrangement in space.In the dip-profile,the sand body overlaps bed by bed along the bottom surface of the valley,splits toward the basin and pinches out into mudstone,reflecting the joint influence of stream and lake.In the strike profile,the sand bodies present lenticular staggered arrangement.The early sand body was developed at the relatively deeper place of the valley,while the higher place of the valley was dominated by the mudstone.The later sand body was not limited by the former deep valley.In the period when the lake-level of SQy23 reached maximum,the incised valley was filled mainly by the muddy sediment.
2008, 33(6): 843-851.
Abstract:
A new method and steps of setting up a finite fault source model of a scenario earthquake on an active fault for predicting near-fault strong ground motion are proposed here. Firstly,spatial orientation and slip type of the active fault are deduced from data of seismic geology,seismicity,and geophysics exploration and so on.Secondly,macro-source parameters of the active fault are inferred from seismic scaling laws.Thirdly,the hybrid slip model on the fault plane is generated by combining the asperity model with k square slip model.On the basis of the above mentioned,the finite fault source model of a scenario earthquake(its fault type and moment magnitude the same as 1994 Northridge earthquake's,i.e.,the reverse fault and Mw6.7) is predicted consequently.Lastly,combining the finite fault source model predicted by mentioned-above with stochastic method of synthesizing ground motion using dynamic corner frequency based on seismology,we predict acceleration time histories of the 12 stations during 1994 Northridge earthquake.And comparison between predicted and recorded acceleration time histories shows that the above-mentioned method and the steps of modeling finite fault source model are feasible and practicable.
A new method and steps of setting up a finite fault source model of a scenario earthquake on an active fault for predicting near-fault strong ground motion are proposed here. Firstly,spatial orientation and slip type of the active fault are deduced from data of seismic geology,seismicity,and geophysics exploration and so on.Secondly,macro-source parameters of the active fault are inferred from seismic scaling laws.Thirdly,the hybrid slip model on the fault plane is generated by combining the asperity model with k square slip model.On the basis of the above mentioned,the finite fault source model of a scenario earthquake(its fault type and moment magnitude the same as 1994 Northridge earthquake's,i.e.,the reverse fault and Mw6.7) is predicted consequently.Lastly,combining the finite fault source model predicted by mentioned-above with stochastic method of synthesizing ground motion using dynamic corner frequency based on seismology,we predict acceleration time histories of the 12 stations during 1994 Northridge earthquake.And comparison between predicted and recorded acceleration time histories shows that the above-mentioned method and the steps of modeling finite fault source model are feasible and practicable.
2008, 33(6): 852-860.
Abstract:
ETM data reveal that the Yuanmou fault is mainly characterized by horizontal left-lateral and shear strike-slip, including ringent shear and pressed shear in part.Taking the advantage of the level moving and offset of the gullies and ridges in 1∶50000 landform and ETM image, we estimated the activity of Yuanmou fault of Yipinglang-Jiangbian segment in the Late Quaternary, and later the results from field exploration, including the analysis of the profiles of landform offsets such as gullies and fluvial landforms, the sections of the active structures in the studied area and activity and active intensity in the Yuanmou fault is the same as what we presumed before.The result shows that the latest active time of the Yuanmou fault of Yipinglang-Jiangbian segment is from the mid-late of Late Pleistocene to Holocene.During these ages, the level moving velocity of left-lateral strike-slip of Yipinglang-Dalongtan segment is approximately 2.0 mm/a, the velocity of uprightness strike-slip approximately 0.07 mm/a.While the respective velocity of left-lateral strike-slip and uprightness strike-slip is approximately 0.53 mm/a and approximately 0.06 mm/a from Yangtianjing to Mulianjiu, the respective velocity of left-lateral strike-slip and uprightness strike-slip approximately 1.32 mm/a and 0.03 mm/a from Leshenggu to Jiangbian.Comprehensive analysis indicates that the level moving velocity since the Late Quaternary in the studied phase is 1~2.0 mm/a, with a major left-lateral shear strike-slip.
ETM data reveal that the Yuanmou fault is mainly characterized by horizontal left-lateral and shear strike-slip, including ringent shear and pressed shear in part.Taking the advantage of the level moving and offset of the gullies and ridges in 1∶50000 landform and ETM image, we estimated the activity of Yuanmou fault of Yipinglang-Jiangbian segment in the Late Quaternary, and later the results from field exploration, including the analysis of the profiles of landform offsets such as gullies and fluvial landforms, the sections of the active structures in the studied area and activity and active intensity in the Yuanmou fault is the same as what we presumed before.The result shows that the latest active time of the Yuanmou fault of Yipinglang-Jiangbian segment is from the mid-late of Late Pleistocene to Holocene.During these ages, the level moving velocity of left-lateral strike-slip of Yipinglang-Dalongtan segment is approximately 2.0 mm/a, the velocity of uprightness strike-slip approximately 0.07 mm/a.While the respective velocity of left-lateral strike-slip and uprightness strike-slip is approximately 0.53 mm/a and approximately 0.06 mm/a from Yangtianjing to Mulianjiu, the respective velocity of left-lateral strike-slip and uprightness strike-slip approximately 1.32 mm/a and 0.03 mm/a from Leshenggu to Jiangbian.Comprehensive analysis indicates that the level moving velocity since the Late Quaternary in the studied phase is 1~2.0 mm/a, with a major left-lateral shear strike-slip.
2008, 33(6): 861-866.
Abstract:
To improve the accuracy and the efficiency of seismic wave simulation and to couple the local and global information better, this paper develops a novel modeling approach referring to the convolutional differentiator based on generalized Forsyte orthogonal polynomial, which applies optimal convolutional operators for spatial differentiation in wave equation. The numerical experiment of complex heterogeneous model demonstrates that the algorithm can bring reliable results with high precision and can be extended to seismic wave simulation in anisotropic media. This method is highly precise in generalized orthogonal polynomial convolutional differentiator and also highly efficient in finite difference short operator method. The local and global information can be considered at the same time by optimizing the coefficients of the operator and adjusting the operator length.
To improve the accuracy and the efficiency of seismic wave simulation and to couple the local and global information better, this paper develops a novel modeling approach referring to the convolutional differentiator based on generalized Forsyte orthogonal polynomial, which applies optimal convolutional operators for spatial differentiation in wave equation. The numerical experiment of complex heterogeneous model demonstrates that the algorithm can bring reliable results with high precision and can be extended to seismic wave simulation in anisotropic media. This method is highly precise in generalized orthogonal polynomial convolutional differentiator and also highly efficient in finite difference short operator method. The local and global information can be considered at the same time by optimizing the coefficients of the operator and adjusting the operator length.
