From the geological structure of the columnar jointed rock mass, a visual model was established in software AUTOCAD by programming based on the algorithm of the Voronoi diagram. Furthermore, a program to convert the A...From the geological structure of the columnar jointed rock mass, a visual model was established in software AUTOCAD by programming based on the algorithm of the Voronoi diagram. Furthermore, a program to convert the AUTOCAD model into 3DEC (3-dimensional distinct element code) model was developed, and a numerical model was established in 3DEC. Moreover, the results of triaxial compression tests of columnar jointed rock masses were simulated numerically. The REV (representative element volume) scale was studied, and the result shows that the REV size is 3 m × 3 m. The proposed approach, the established model and the numerical simulation were applied to study the macro-mechanical properties and the equivalent strength parameters of the columnar jointed rock mass. The numerical simulation results are in good accordance with the in-situ test results.展开更多
The scale and characteristics of rock mass are important indexes of the rock mass structural plane classification. This paper firstly analyzes the spatial distribution characteristics, the structural plane types （ori...The scale and characteristics of rock mass are important indexes of the rock mass structural plane classification. This paper firstly analyzes the spatial distribution characteristics, the structural plane types （original structural plane, tectonic structural plane and hypergenic structural plane） and the associated features of the Emeishan basalts and then studies the classification schemes of the built hydropower structure planes of different rock areas （the east district, the central district and the west district） in the Emeishan basalt distribution area, Southwest China. Based on the analysis and comparison of the scale and the engineering geological characteristics of the typical structure planes in the basalt hydroelectric Stations, the types of structural planes are used in the first order classification. The secondary order classification is made by considering the impact factors of rock mass quality, e.g., the state of the structural planes, infilling, joint opening, extending length, the grade of weathering and strength. The engineering geological classification for Emeishan basalt is proposed. Because there are no evidences of a large structure presenting in study area, the first-order （Ⅰ） controlling structural planes do not appear in the classification, there only appear Ⅱ, Ⅲ, Ⅳ and Ⅴ grade structural planes influencing the rock-mass quality. According to the different rock-block types in bedding fault zone, the second-grade （Ⅱ） structural planes consisted of bedding fault zone is further classified into Ⅱ1, Ⅱ2 and Ⅱ3. The third-grade （Ⅲ） structural planes constructed by intraformational faulted zones are not subdivided. According to the different characteristics of intrusion, alteration and weathering unloading structural planes, the Ⅳ grade structure plane is divided into Ⅳ1, Ⅳ2 and Ⅳ3. According to the development characteristics of joints and fractures, the V grade structure plane is divided into fracture Ⅴ1 and columnar joint Ⅴ2. In all, the structural planes are classified into four groups with nine subsets. The research proposes the engineering geological classification of the structural plane for the hydropower project in the Emishan basalts, and the result of the study has a potential application in similar regions.展开更多
The material sources and control factors of rare earth elemems （REEs） for 25 borehole bulk samples from the Late Permian Longtan Formation in Mount Huaying （borehole number： ZK10-6）, Sichuan Province, South China...The material sources and control factors of rare earth elemems （REEs） for 25 borehole bulk samples from the Late Permian Longtan Formation in Mount Huaying （borehole number： ZK10-6）, Sichuan Province, South China, were investigated. All samples were determined by inductively coupled plasma mass spectrometry （ICP-MS）. The chondrite-normalized distribution patterns of mudstone samples are uniform. All samples belong to the light rare earth element （LREE）-rich type and are enriched in LREEs relative to heavy rare earth elements （HREEs）. The distribution curves of REEs in mudstone are highly similar to Mount Emei basalt and the three periods of REEs enrichment correspond to three Mount Emei basalt eruption cycles in Longtan period. The results indicate that REE patterns are not controlled by materials from the seawater or land plants. The predominant sources of REEs are from terrigenous material as indicated by negative Eu anomaly. So, the sources of REEs are controlled by terrigenous material, and the Mount Emei basalt is the predominant source of terrigenous material. Thus, transgression-regression is another control factor of REEs enrichment.展开更多
Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse...Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse＇ experiments） argue for no significant temperature differences between them. However, there are differences in major, minor and trace elements which characterise geochemical, not thermal, anomalies beneath ‘hot-spots＇. We suggest that diapiric upwelling from interfaces （redox contrasts） between old subducted slab and normal MOR basalt source mantle is the major reason for the observed characteristics of island chain or ‘hot-spot＇ volcanism. Intraplate basalts also include widely distributed volcanic centres containing lherzolite xenoliths, i.e. mantle-derived magmas. Inverse experiments on olivine basalt, alkali oli- vine basalt, olivine basanite, olivine nephelinite, olivine melilitite and olivine leucitite （lamproite） determined liquidus phases as a function of pressure, initially under anhydrous and CO2-absent conditions. Under C- and H-absent conditions, only tholeiites to alkali olivine basalts had O1 ＋ Opx 4-Cpx as high-pressure liquidus phases. Addition of H20 accessed olivine basanites at 2.5-3 GPa, ,- 1,200 ℃, but both CO2 and H20 were necessary to obtain saturation with O1, Opx, Cpx and Ga at 2.5-3.5 GPa for olivine nephelinite and olivine melilitite. The forward and inverse experimental studies are combined to formulate a petrogenetic grid for intraplate, ‘hot-spot＇ and MOR magmatism within the plate tectonics paradigm. The asthenosphere is geochemically zoned by slow upward migration of incipient melt. The solidus and phasestabilities of lherzolite with very small water contents （〈3,000 ppm） determine the thin plate behaviour of the oceanic lithosphere and thus the Earth＇s convection in the form of plate tectonics. There is no evidence from the parental magmas of MOR and ‘hot-spots＇ to support the ＇deep mantle thermal plume＇ hypothesis. The preferred alternative is the presence of old subducted slabs, relatively buoyant and oxidised with respect to MORB source mantle and suspended or upwelling in or below the lower asthenosphere （and thus detached from overlying plate movement）.展开更多
The water contents of minerals and whole-rock in mantle-derived xenoliths from eastern China exhibit large variations and are generally lower than those from other on- and off-craton lithotectonic units. Nevertheless,...The water contents of minerals and whole-rock in mantle-derived xenoliths from eastern China exhibit large variations and are generally lower than those from other on- and off-craton lithotectonic units. Nevertheless, the water contents of mineral and whole-rock in Junan peridotite xenoliths, which sourced from the juvenile lithospheric mantle, are generally higher than those elsewhere in eastern China. This suggests that the initial water content of juvenile lithospheric mantle is not low. There is no obvious correlation between the water contents and Mg~# values of minerals in the mantle xenoliths and no occurrence of diffusion profile in pyroxene, suggesting no relationship between the low water content of mantle xenolith and the diffusion loss of water during xenolith ascent with host basaltic magmas. If the subcontinental lithospheric mantle（SCLM） base is heated by the asthenospheric mantle, the diffusion loss of water is expected to occur. On the other hand, extraction of basaltic melts from the SCLM is a more efficient mechanism to reduce the water content of xenoliths. The primary melts of Mesozoic and Cenozoic basalts in eastern China have water contents, as calculated from the water contents of phenocrysts, higher than those of normal mid-ocean ridge basalts（MORB）. The Mesozoic basalts exhibit similar water contents to those of island arc basalts, whereas the Cenozoic basalts exhibit comparable water contents to oceanic island basalts and backarc basin basalts with some of them resembling island arc basalts. These observations suggest the water enrichment in the mantle source of continental basalts due to metasomatism by aqueous fluids and hydrous melts derived from dehydration and melting of deeply subducted crust. Mantle-derived megacrysts, minerals in xenoliths and phenocrysts in basalts from eastern China also exhibit largely variable hydrogen isotope compositions, indicating a large isotopic heterogeneity for the Cenozoic SCLM in eastern China. The water content that is higher than that of depleted MORB mantle and the hydrogen isotope composition that is deviated from that of depleted MORB mantle suggest that the Cenozoic continental lithospheric mantle suffered the metasomatism by hydrous melts derived from partial melting of the subducted Pacific slab below eastern China continent. The metasomatism would lead to the increase of water content in the SCLM base and then to the decrease of its viscosity. As a consequence, the SCLM base would be weakened and thus susceptible to tectonic erosion and delamination. As such, the crust-mantle interaction in oceanic subduction channel is the major cause for thinning of the craton lithosphere in North China.展开更多
基金Projects(50911130366, 50979030) supported by the National Natural Science Foundation of China
文摘From the geological structure of the columnar jointed rock mass, a visual model was established in software AUTOCAD by programming based on the algorithm of the Voronoi diagram. Furthermore, a program to convert the AUTOCAD model into 3DEC (3-dimensional distinct element code) model was developed, and a numerical model was established in 3DEC. Moreover, the results of triaxial compression tests of columnar jointed rock masses were simulated numerically. The REV (representative element volume) scale was studied, and the result shows that the REV size is 3 m × 3 m. The proposed approach, the established model and the numerical simulation were applied to study the macro-mechanical properties and the equivalent strength parameters of the columnar jointed rock mass. The numerical simulation results are in good accordance with the in-situ test results.
基金funded by the National Natural Science Foundation of China (Grant No.41072228)
文摘The scale and characteristics of rock mass are important indexes of the rock mass structural plane classification. This paper firstly analyzes the spatial distribution characteristics, the structural plane types （original structural plane, tectonic structural plane and hypergenic structural plane） and the associated features of the Emeishan basalts and then studies the classification schemes of the built hydropower structure planes of different rock areas （the east district, the central district and the west district） in the Emeishan basalt distribution area, Southwest China. Based on the analysis and comparison of the scale and the engineering geological characteristics of the typical structure planes in the basalt hydroelectric Stations, the types of structural planes are used in the first order classification. The secondary order classification is made by considering the impact factors of rock mass quality, e.g., the state of the structural planes, infilling, joint opening, extending length, the grade of weathering and strength. The engineering geological classification for Emeishan basalt is proposed. Because there are no evidences of a large structure presenting in study area, the first-order （Ⅰ） controlling structural planes do not appear in the classification, there only appear Ⅱ, Ⅲ, Ⅳ and Ⅴ grade structural planes influencing the rock-mass quality. According to the different rock-block types in bedding fault zone, the second-grade （Ⅱ） structural planes consisted of bedding fault zone is further classified into Ⅱ1, Ⅱ2 and Ⅱ3. The third-grade （Ⅲ） structural planes constructed by intraformational faulted zones are not subdivided. According to the different characteristics of intrusion, alteration and weathering unloading structural planes, the Ⅳ grade structure plane is divided into Ⅳ1, Ⅳ2 and Ⅳ3. According to the development characteristics of joints and fractures, the V grade structure plane is divided into fracture Ⅴ1 and columnar joint Ⅴ2. In all, the structural planes are classified into four groups with nine subsets. The research proposes the engineering geological classification of the structural plane for the hydropower project in the Emishan basalts, and the result of the study has a potential application in similar regions.
基金Project(40839910) supported by the National Natural Science Foundation of China
文摘The material sources and control factors of rare earth elemems （REEs） for 25 borehole bulk samples from the Late Permian Longtan Formation in Mount Huaying （borehole number： ZK10-6）, Sichuan Province, South China, were investigated. All samples were determined by inductively coupled plasma mass spectrometry （ICP-MS）. The chondrite-normalized distribution patterns of mudstone samples are uniform. All samples belong to the light rare earth element （LREE）-rich type and are enriched in LREEs relative to heavy rare earth elements （HREEs）. The distribution curves of REEs in mudstone are highly similar to Mount Emei basalt and the three periods of REEs enrichment correspond to three Mount Emei basalt eruption cycles in Longtan period. The results indicate that REE patterns are not controlled by materials from the seawater or land plants. The predominant sources of REEs are from terrigenous material as indicated by negative Eu anomaly. So, the sources of REEs are controlled by terrigenous material, and the Mount Emei basalt is the predominant source of terrigenous material. Thus, transgression-regression is another control factor of REEs enrichment.
基金the support of the Department of Geology/School of Earth Sciences at University of Tasmaniathe Research School of Earth Sciences, Australian National UniversityAt University of Tasmania, ‘Earth Sciences’ and ‘Centre for Ore Deposits and Exploration Studies (CODES)’
文摘Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse＇ experiments） argue for no significant temperature differences between them. However, there are differences in major, minor and trace elements which characterise geochemical, not thermal, anomalies beneath ‘hot-spots＇. We suggest that diapiric upwelling from interfaces （redox contrasts） between old subducted slab and normal MOR basalt source mantle is the major reason for the observed characteristics of island chain or ‘hot-spot＇ volcanism. Intraplate basalts also include widely distributed volcanic centres containing lherzolite xenoliths, i.e. mantle-derived magmas. Inverse experiments on olivine basalt, alkali oli- vine basalt, olivine basanite, olivine nephelinite, olivine melilitite and olivine leucitite （lamproite） determined liquidus phases as a function of pressure, initially under anhydrous and CO2-absent conditions. Under C- and H-absent conditions, only tholeiites to alkali olivine basalts had O1 ＋ Opx 4-Cpx as high-pressure liquidus phases. Addition of H20 accessed olivine basanites at 2.5-3 GPa, ,- 1,200 ℃, but both CO2 and H20 were necessary to obtain saturation with O1, Opx, Cpx and Ga at 2.5-3.5 GPa for olivine nephelinite and olivine melilitite. The forward and inverse experimental studies are combined to formulate a petrogenetic grid for intraplate, ‘hot-spot＇ and MOR magmatism within the plate tectonics paradigm. The asthenosphere is geochemically zoned by slow upward migration of incipient melt. The solidus and phasestabilities of lherzolite with very small water contents （〈3,000 ppm） determine the thin plate behaviour of the oceanic lithosphere and thus the Earth＇s convection in the form of plate tectonics. There is no evidence from the parental magmas of MOR and ‘hot-spots＇ to support the ＇deep mantle thermal plume＇ hypothesis. The preferred alternative is the presence of old subducted slabs, relatively buoyant and oxidised with respect to MORB source mantle and suspended or upwelling in or below the lower asthenosphere （and thus detached from overlying plate movement）.
基金supported by funds from the Chinese Ministry of Science and Technology (Grant No. 2015CB856100)the National Natural Science Foundation of China (Grant Nos. 41303005 & 41590620)the Fundamental Research Funds for the Central Universities
文摘The water contents of minerals and whole-rock in mantle-derived xenoliths from eastern China exhibit large variations and are generally lower than those from other on- and off-craton lithotectonic units. Nevertheless, the water contents of mineral and whole-rock in Junan peridotite xenoliths, which sourced from the juvenile lithospheric mantle, are generally higher than those elsewhere in eastern China. This suggests that the initial water content of juvenile lithospheric mantle is not low. There is no obvious correlation between the water contents and Mg~# values of minerals in the mantle xenoliths and no occurrence of diffusion profile in pyroxene, suggesting no relationship between the low water content of mantle xenolith and the diffusion loss of water during xenolith ascent with host basaltic magmas. If the subcontinental lithospheric mantle（SCLM） base is heated by the asthenospheric mantle, the diffusion loss of water is expected to occur. On the other hand, extraction of basaltic melts from the SCLM is a more efficient mechanism to reduce the water content of xenoliths. The primary melts of Mesozoic and Cenozoic basalts in eastern China have water contents, as calculated from the water contents of phenocrysts, higher than those of normal mid-ocean ridge basalts（MORB）. The Mesozoic basalts exhibit similar water contents to those of island arc basalts, whereas the Cenozoic basalts exhibit comparable water contents to oceanic island basalts and backarc basin basalts with some of them resembling island arc basalts. These observations suggest the water enrichment in the mantle source of continental basalts due to metasomatism by aqueous fluids and hydrous melts derived from dehydration and melting of deeply subducted crust. Mantle-derived megacrysts, minerals in xenoliths and phenocrysts in basalts from eastern China also exhibit largely variable hydrogen isotope compositions, indicating a large isotopic heterogeneity for the Cenozoic SCLM in eastern China. The water content that is higher than that of depleted MORB mantle and the hydrogen isotope composition that is deviated from that of depleted MORB mantle suggest that the Cenozoic continental lithospheric mantle suffered the metasomatism by hydrous melts derived from partial melting of the subducted Pacific slab below eastern China continent. The metasomatism would lead to the increase of water content in the SCLM base and then to the decrease of its viscosity. As a consequence, the SCLM base would be weakened and thus susceptible to tectonic erosion and delamination. As such, the crust-mantle interaction in oceanic subduction channel is the major cause for thinning of the craton lithosphere in North China.
