Syenitic and mafic rocks in Mindif Complex (Far North of Cameroon) were surveyed and characterized to classify them, understand their formation history, and assess their economic interest. Syenitic bodies (hololeucocr...Syenitic and mafic rocks in Mindif Complex (Far North of Cameroon) were surveyed and characterized to classify them, understand their formation history, and assess their economic interest. Syenitic bodies (hololeucocratic microsyenites;mesocratic aplitic quartz-syenite;leucocratic porphyritic quartz-biotite syenite, and leucocratic porphyritic biotite-syenite) are silica-oversaturated to silica-saturated, alkaline, and metaluminous. Hololeucocratic microsyenites are structural oriented rocks, cooled in shallow depth from low trace and REE dry residual alkaline melts. Mesocratic aplitic quartz-syenite also crystallized in shallow depth from a much Ba-rich less dry residual melt. Leucocratic porphyritic quartz-biotite and biotite syenitic stocks represent two different rock types cooled from hydrous-rich melts in deep seated environments. The Mindif syenites probably crystallized in crustal source magmas (with important alkali feldspar accumulation) from partial melting of pre-existing igneous protoliths. Medium to coarse-grained-peraluminous granite found at the edge of pink microsyenitic dykes (in contact with granite host), is probably a crystallized product from magmatic mixture between the intrusive syenitic melt and a melt from partial fusion of the granite host rock. Mafic igneous rocks in Mindif are peridotgabbro and gabbro with different characteristics. Peridotgabbro, alkaline, holomelanocratic, medium-grained and ultrabasic, is an REE and incompatible elements depleted rock crystallized in shallow depth from a more evolved mantle source magma with plagioclase accumulation. Tholeiitic gabbro, melanocratic, and also medium-grained, was cooled in shallow depth, from a low-K and slightly LILE-enrichment magma probably originated from partial melting ultradepleted mantle source in sub-duction environment. Syenites and peridotgabbro with their high aluminum content (up to 18.5 wt%) greater than that of many parent rocks of lateritic bauxite in Cameroon, can be good parent rocks for bauxite-rich soils if found in a plateau topography and hot-humid tropical climate. The geochemical features of Mindif syenites are close to that of some syenites mined and used as raw materials in ceramic and glass industries. This similarity shows that these syenites are good for glass and ceramic manufacture.展开更多
The methods combined by test, field monitoring and theoretical analysis were adopted to do the systemic research on the rock mass from micro-structure to macro-deformation, and rheological model of Jinchuan rock mass ...The methods combined by test, field monitoring and theoretical analysis were adopted to do the systemic research on the rock mass from micro-structure to macro-deformation, and rheological model of Jinchuan rock mass was established to discuss the reasonable supporting time. Results show that supporting after suitable stress and displacement release can benefit for the long-term stability of surrounding rock.展开更多
Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton r...Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,展开更多
This paper is concerned with the geochemical features of major elements, transitionmetal elements, large ion lithophile elements, rare-earth elements and Sr isotopes in alkaline-ul-trabasic rocks in the Jijie complex ...This paper is concerned with the geochemical features of major elements, transitionmetal elements, large ion lithophile elements, rare-earth elements and Sr isotopes in alkaline-ul-trabasic rocks in the Jijie complex of Lufeng, Yunnan Province, which is located in southernSichuan-Yunnan rift zone, one of Luoci alkaline-ultrabasic complexes in central Ynnnan.Moreover, its origin pertaining primary magma, magma soure region, fractional crystallization,etc. are also discussed in the present paper.展开更多
Fault is a complex dynamic system controlled by the coupling of rock texture, reaction, fluid flow,stress, and rock deformation mechanism. A coupled reaction-transport- mechanical dynamic model for fault system is est...Fault is a complex dynamic system controlled by the coupling of rock texture, reaction, fluid flow,stress, and rock deformation mechanism. A coupled reaction-transport- mechanical dynamic model for fault system is established and described in this paper. An example is presented for the Shuikoushan deposit, Hunan. The results of dynamic simulation indicate that the evolution and magnitude of fracture permeability of different rocks are different, and that faulting can enhance the spatial heterogeneity of rock permeability and facilitate fluid flow and mineralization in local fault zone. The pressure for a fault usually shows a variation mode of aperiodic oscillation with time, which reflects the chaotic behavior of the evolution of a fault.展开更多
Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite norm...Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns （Lan/Ybn=0.86-1.3）, the lowest total REEs （29-52 ppm）, and weak negative to positive Eu anomalies （Eun/Eun=0.84-1.02）, nearly flat primitive mantle normalized patterns and strong negative Zr（Hf） anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs （34-116 ppm）, LREE-enriched （Lan/Ybn=1.76-4.34） chondrite normalized REE patterns with weak Eu anomalies （Eun/Eun=0.76-1.16）, and negative Nb, Ta, Zr（Hf）, Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slab-derived fluids. Rocks in Group #3 are characterized by the highest total REEs （61-192 ppm）, the strongest LREEs enrichment （Lan/Ybn=7.12-16） with slightly negative Eu anomalies （Eun/Eun=0.81-0.95） in the chondrite normalized diagram. In the primitive mantle normalized diagram, these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies. They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts. The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.展开更多
A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/s...A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory(UST) were used to simulate both the consolidated-undrained(CU) triaxial and the consolidated-drained(CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30% when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.展开更多
The Molopo Farms Complex(MFC)is a 13000 km2layered,mafic-ultramafic intrusion straddling the southern border of Botswana with South Africa.It does not outcrop due to Cenozoic cover,but is believed to intrude the
Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse ef...Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse effects on the final location results.To achieve a high-accuracy location in a complex cavern-containing structure,this study develops an MS location method using the fast marching method(FMM)with a second-order difference approach(FMM2).Based on the established velocity model with three-dimensional(3D)discrete grids,the realization of the MS location can be achieved by searching the minimum residual between the theoretical and actual first arrival times.Moreover,based on the calculation results of FMM2,the propagation paths from the MS sources to MS sensors can be obtained using the linear interpolation approach and the Runge–Kutta method.These methods were validated through a series of numerical experiments.In addition,our proposed method was applied to locate the recorded blasting and MS events that occurred during the excavation period of the underground caverns at the Houziyan hydropower station.The location results of the blasting activities show that our method can effectively reduce the location error compared with the results based on the uniform velocity model.Furthermore,the obtained MS location was verified through the occurrence of shotcrete fractures and spalling,and the monitoring results of the in-situ multipoint extensometer.Our proposed method can offer a more accurate rock fracture location and facilitate the delineation of damage zones inside the surrounding rock mass.展开更多
文摘Syenitic and mafic rocks in Mindif Complex (Far North of Cameroon) were surveyed and characterized to classify them, understand their formation history, and assess their economic interest. Syenitic bodies (hololeucocratic microsyenites;mesocratic aplitic quartz-syenite;leucocratic porphyritic quartz-biotite syenite, and leucocratic porphyritic biotite-syenite) are silica-oversaturated to silica-saturated, alkaline, and metaluminous. Hololeucocratic microsyenites are structural oriented rocks, cooled in shallow depth from low trace and REE dry residual alkaline melts. Mesocratic aplitic quartz-syenite also crystallized in shallow depth from a much Ba-rich less dry residual melt. Leucocratic porphyritic quartz-biotite and biotite syenitic stocks represent two different rock types cooled from hydrous-rich melts in deep seated environments. The Mindif syenites probably crystallized in crustal source magmas (with important alkali feldspar accumulation) from partial melting of pre-existing igneous protoliths. Medium to coarse-grained-peraluminous granite found at the edge of pink microsyenitic dykes (in contact with granite host), is probably a crystallized product from magmatic mixture between the intrusive syenitic melt and a melt from partial fusion of the granite host rock. Mafic igneous rocks in Mindif are peridotgabbro and gabbro with different characteristics. Peridotgabbro, alkaline, holomelanocratic, medium-grained and ultrabasic, is an REE and incompatible elements depleted rock crystallized in shallow depth from a more evolved mantle source magma with plagioclase accumulation. Tholeiitic gabbro, melanocratic, and also medium-grained, was cooled in shallow depth, from a low-K and slightly LILE-enrichment magma probably originated from partial melting ultradepleted mantle source in sub-duction environment. Syenites and peridotgabbro with their high aluminum content (up to 18.5 wt%) greater than that of many parent rocks of lateritic bauxite in Cameroon, can be good parent rocks for bauxite-rich soils if found in a plateau topography and hot-humid tropical climate. The geochemical features of Mindif syenites are close to that of some syenites mined and used as raw materials in ceramic and glass industries. This similarity shows that these syenites are good for glass and ceramic manufacture.
文摘The methods combined by test, field monitoring and theoretical analysis were adopted to do the systemic research on the rock mass from micro-structure to macro-deformation, and rheological model of Jinchuan rock mass was established to discuss the reasonable supporting time. Results show that supporting after suitable stress and displacement release can benefit for the long-term stability of surrounding rock.
基金financially supported by National Science Foundation of China(grant No.41303026)the funded project of the China Geological Survey(grants No.DD20160030,DD20160351 and DD20160029)
文摘Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,
文摘This paper is concerned with the geochemical features of major elements, transitionmetal elements, large ion lithophile elements, rare-earth elements and Sr isotopes in alkaline-ul-trabasic rocks in the Jijie complex of Lufeng, Yunnan Province, which is located in southernSichuan-Yunnan rift zone, one of Luoci alkaline-ultrabasic complexes in central Ynnnan.Moreover, its origin pertaining primary magma, magma soure region, fractional crystallization,etc. are also discussed in the present paper.
基金supported by the National Natural Science Foundation of China(Gramt No.70171057 and No.49702024)a Key Project of the Ninth Five-Year Plan of the Chinese Academof Sciences(Grant No.KZ952-S1-402).
文摘Fault is a complex dynamic system controlled by the coupling of rock texture, reaction, fluid flow,stress, and rock deformation mechanism. A coupled reaction-transport- mechanical dynamic model for fault system is established and described in this paper. An example is presented for the Shuikoushan deposit, Hunan. The results of dynamic simulation indicate that the evolution and magnitude of fracture permeability of different rocks are different, and that faulting can enhance the spatial heterogeneity of rock permeability and facilitate fluid flow and mineralization in local fault zone. The pressure for a fault usually shows a variation mode of aperiodic oscillation with time, which reflects the chaotic behavior of the evolution of a fault.
基金The National Natural Science Foundation of. China （Grant No.40420120135 and 40472096） are thankefl for the fthancial support.
文摘Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns （Lan/Ybn=0.86-1.3）, the lowest total REEs （29-52 ppm）, and weak negative to positive Eu anomalies （Eun/Eun=0.84-1.02）, nearly flat primitive mantle normalized patterns and strong negative Zr（Hf） anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs （34-116 ppm）, LREE-enriched （Lan/Ybn=1.76-4.34） chondrite normalized REE patterns with weak Eu anomalies （Eun/Eun=0.76-1.16）, and negative Nb, Ta, Zr（Hf）, Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slab-derived fluids. Rocks in Group #3 are characterized by the highest total REEs （61-192 ppm）, the strongest LREEs enrichment （Lan/Ybn=7.12-16） with slightly negative Eu anomalies （Eun/Eun=0.81-0.95） in the chondrite normalized diagram. In the primitive mantle normalized diagram, these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies. They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts. The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.
基金Projects(41172276,51279155)supported by the National Natural Science Foundation of ChinaProjects(106-00X101,106-5X1205)supported by the Central Financial Funds for the Development of Characteristic Key Disciplines in Local University,China
文摘A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory(UST) were used to simulate both the consolidated-undrained(CU) triaxial and the consolidated-drained(CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30% when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.
文摘The Molopo Farms Complex(MFC)is a 13000 km2layered,mafic-ultramafic intrusion straddling the southern border of Botswana with South Africa.It does not outcrop due to Cenozoic cover,but is believed to intrude the
基金the Key Program of National Natural Science Foundation of China(52039007)for providing financial support.
文摘Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse effects on the final location results.To achieve a high-accuracy location in a complex cavern-containing structure,this study develops an MS location method using the fast marching method(FMM)with a second-order difference approach(FMM2).Based on the established velocity model with three-dimensional(3D)discrete grids,the realization of the MS location can be achieved by searching the minimum residual between the theoretical and actual first arrival times.Moreover,based on the calculation results of FMM2,the propagation paths from the MS sources to MS sensors can be obtained using the linear interpolation approach and the Runge–Kutta method.These methods were validated through a series of numerical experiments.In addition,our proposed method was applied to locate the recorded blasting and MS events that occurred during the excavation period of the underground caverns at the Houziyan hydropower station.The location results of the blasting activities show that our method can effectively reduce the location error compared with the results based on the uniform velocity model.Furthermore,the obtained MS location was verified through the occurrence of shotcrete fractures and spalling,and the monitoring results of the in-situ multipoint extensometer.Our proposed method can offer a more accurate rock fracture location and facilitate the delineation of damage zones inside the surrounding rock mass.
