2003 Vol. 28, No. 2
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2003, 28(2): 111-120.
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Abstract:
Detailed study of the structures in the Dabie-Sulu UHP metamorphic belt, east-central China indicates that most of Triassic UHP rocks were reworked and reset under eclogite- and amphibolite-facies conditions, following the peak UHP metamorphism. However, some of fresh coesite- and microdiamond-bearing massive eclogite bodies which are enclosed by marbles, foliated eclogites and garnet-peridotites respectively, remained almost undeformed on the centimeter to hundred of meter scale. The massive eclogites consist of garnet, omphacite, rutile and coesite/quartz with medium to fine-grained massive features in appearance. Most of diamond-bearing eclogites come from the eclogite lenses enclosed by the marbles which are surrounded, in turn, by the amphibolite facies gneisses and orthogneisses. Based on the analyses of petrography, structure and metamorphism of the massive eclogites, it can be inferred that these eclogites may record p-T conditions for the deep continental subduction, collision and peak UHP metamorphism. The massive eclogites have been equilibrated in the range of > 800 ℃ and 32×108-40×108 Pa. Furthermore, 250-220 Ma is considered the best estimate for the age of the peak UHP metamorphism and deep continental subduction. A comparative study of deformation features in the massive eclogite lenses and the country rocks shows that metamorphism and deformation partitioning played an important role in the preservation of the fresh massive eclogites as record-keepers of the deep subduction within the Dabie-Sulu UHP metamorphic belt. The episodic or progressive metamorphism and deformation partitioning has resulted in lens-shaped domains of low strain separated by anastomosing domains of high strain. The massive eclogites which occur within the domains, at different scales, of low strain are likely to survive a retrogressive metamorphism and deformation resetting, and consequently to retain the near peak metamorphic signature. Therefore, only these eclogites preserve the record of early UHP metamorphic and deformational events. A possible tectonic model is also given for the Dabie-Sulu UHP metamorphic belt, showing the general geometry of the Dabie-Sulu lithosphere at the time of peak metamorphism during the Triassic continental subduction and collision.
Detailed study of the structures in the Dabie-Sulu UHP metamorphic belt, east-central China indicates that most of Triassic UHP rocks were reworked and reset under eclogite- and amphibolite-facies conditions, following the peak UHP metamorphism. However, some of fresh coesite- and microdiamond-bearing massive eclogite bodies which are enclosed by marbles, foliated eclogites and garnet-peridotites respectively, remained almost undeformed on the centimeter to hundred of meter scale. The massive eclogites consist of garnet, omphacite, rutile and coesite/quartz with medium to fine-grained massive features in appearance. Most of diamond-bearing eclogites come from the eclogite lenses enclosed by the marbles which are surrounded, in turn, by the amphibolite facies gneisses and orthogneisses. Based on the analyses of petrography, structure and metamorphism of the massive eclogites, it can be inferred that these eclogites may record p-T conditions for the deep continental subduction, collision and peak UHP metamorphism. The massive eclogites have been equilibrated in the range of > 800 ℃ and 32×108-40×108 Pa. Furthermore, 250-220 Ma is considered the best estimate for the age of the peak UHP metamorphism and deep continental subduction. A comparative study of deformation features in the massive eclogite lenses and the country rocks shows that metamorphism and deformation partitioning played an important role in the preservation of the fresh massive eclogites as record-keepers of the deep subduction within the Dabie-Sulu UHP metamorphic belt. The episodic or progressive metamorphism and deformation partitioning has resulted in lens-shaped domains of low strain separated by anastomosing domains of high strain. The massive eclogites which occur within the domains, at different scales, of low strain are likely to survive a retrogressive metamorphism and deformation resetting, and consequently to retain the near peak metamorphic signature. Therefore, only these eclogites preserve the record of early UHP metamorphic and deformational events. A possible tectonic model is also given for the Dabie-Sulu UHP metamorphic belt, showing the general geometry of the Dabie-Sulu lithosphere at the time of peak metamorphism during the Triassic continental subduction and collision.
2003, 28(2): 121-128.
Abstract:
Partial melting of subducted oceanic crust is one of the most important processes of continental growth. However, we see little direct evidence of partial melting of the continental during subduction. The difference in trace elements and Pb isotope between dehydration and partial melting of island arc basalt (IAB) is discussed based on the distribution coefficients of trace elements published. Although Pb was incompatible in both dehydration and partial melting, the activity of Pb was higher significantly than other incompatible elements (Rb, Ba, Sr, Th and U) in dehydration, and lower in partial melting. As a result, the evolution pathlous of dehydration and partial melting shows a large difference in the w (Rb) /w (Pb) -w (Rb), w (Ba) /w (Pb) - w (Ba), w (Th) /w (Pb) -w (Th), w (U) /w (Pb) -w (U) figure. Furthermore, the difference of incompatibility among Pb, Th and U leads to a significant distinction of single mineral isotope of garnet and omphacite between dehydration and partial melting. Moreover, the composition of trace elements and Pb isotope of actual measurements and that of analog calculation was compared. Most eclogites from Dabie-Sulu ultrahigh pressure belt might be residual after partial melting of IAB, however, the others were products of dehydration of IAB. Therefore, continental basaltic rocks could also be partially melted during subduction like the oceanic crust.
Partial melting of subducted oceanic crust is one of the most important processes of continental growth. However, we see little direct evidence of partial melting of the continental during subduction. The difference in trace elements and Pb isotope between dehydration and partial melting of island arc basalt (IAB) is discussed based on the distribution coefficients of trace elements published. Although Pb was incompatible in both dehydration and partial melting, the activity of Pb was higher significantly than other incompatible elements (Rb, Ba, Sr, Th and U) in dehydration, and lower in partial melting. As a result, the evolution pathlous of dehydration and partial melting shows a large difference in the w (Rb) /w (Pb) -w (Rb), w (Ba) /w (Pb) - w (Ba), w (Th) /w (Pb) -w (Th), w (U) /w (Pb) -w (U) figure. Furthermore, the difference of incompatibility among Pb, Th and U leads to a significant distinction of single mineral isotope of garnet and omphacite between dehydration and partial melting. Moreover, the composition of trace elements and Pb isotope of actual measurements and that of analog calculation was compared. Most eclogites from Dabie-Sulu ultrahigh pressure belt might be residual after partial melting of IAB, however, the others were products of dehydration of IAB. Therefore, continental basaltic rocks could also be partially melted during subduction like the oceanic crust.
2003, 28(2): 129-136.
Abstract:
UHP eclogite samples were collected from surface exposures around Chinese Continental Scientific Drilling (CCSD) drill-site in Donghai area have been measured on thermal conductivity to investigate the effect of mineral components and texture on thermal conductivity (TC) of eclogite. Measured thermal conductivities vary from 3.222 to 3.716 Wm-1·K-1 with average value 3.511 Wm-1·K-1, which depend on the volume ratio of garnet and omphacite (VGrt/VOmp) in the rocks. This correlation was fitted to the function K=3.767-0.18× (VGrt/VOmp), which shows the thermal conductivity of eclogite in this area decreased as increasing of VGrt/VOmp. Inhomogeneous distribution of minerals and the foliation texture in rocks also significantly affect the value of thermal conductivity and induce the anisotropy up to 10% in eclogite. For temperature dependence, according to calculations from the correlation between K-T, thermal conductivities under high temperature were also fitted to a function: K (T) =1/ (7.85×10-2+6.95×10-4×T), T is absolute temperature. Based on this function and the published geothermal data of this area, a depth dependence of thermal conductivity can be concluded. The K of eclogite decreased as the increasing depth of CCSD drill hole. The K values of eclogite in surface and in bottom of hole are 3.511 Wm-1·K-1 and 2.687 Wm-1·K-1, respectively. The K of eclogite will be predicted to be decreased about 24% from surface to the end of 5 000 m depth of CCSD. These research results are helpful to establish the geothermal model of this area and to interpret well logging results from CCSD.
UHP eclogite samples were collected from surface exposures around Chinese Continental Scientific Drilling (CCSD) drill-site in Donghai area have been measured on thermal conductivity to investigate the effect of mineral components and texture on thermal conductivity (TC) of eclogite. Measured thermal conductivities vary from 3.222 to 3.716 Wm-1·K-1 with average value 3.511 Wm-1·K-1, which depend on the volume ratio of garnet and omphacite (VGrt/VOmp) in the rocks. This correlation was fitted to the function K=3.767-0.18× (VGrt/VOmp), which shows the thermal conductivity of eclogite in this area decreased as increasing of VGrt/VOmp. Inhomogeneous distribution of minerals and the foliation texture in rocks also significantly affect the value of thermal conductivity and induce the anisotropy up to 10% in eclogite. For temperature dependence, according to calculations from the correlation between K-T, thermal conductivities under high temperature were also fitted to a function: K (T) =1/ (7.85×10-2+6.95×10-4×T), T is absolute temperature. Based on this function and the published geothermal data of this area, a depth dependence of thermal conductivity can be concluded. The K of eclogite decreased as the increasing depth of CCSD drill hole. The K values of eclogite in surface and in bottom of hole are 3.511 Wm-1·K-1 and 2.687 Wm-1·K-1, respectively. The K of eclogite will be predicted to be decreased about 24% from surface to the end of 5 000 m depth of CCSD. These research results are helpful to establish the geothermal model of this area and to interpret well logging results from CCSD.
2003, 28(2): 137-142.
Abstract:
Pb isotopes have been comprehensively applied to isotopic geochronology, geochemical tracing and division of tectonic zones. Due to the difficulty for calibration of Pb isotopic fractionation in thermal ionization mass spectrometry (TIMS) analysis, the accurate determination of Pb isotopic ratios, especially for low-Pb samples, is generally difficult. This paper reports the preparation of samples with low-Pb contents, process of TIMS analysis and confect of emission reagent for accurate Pb isotope analysis. The role of emission reagent and affect of interferential elements on the Pb isotope analysis are also discussed. Some typical eclogites from Dabie-Sulu ultrahigh-pressure metamorphic belt are analyzed with this method. During the whole analysis process, the interior precision and exterior precision for the standard sample NBS981 are better than 0.25×10-3 and 0.4×10-3 respectively, and the relative error is 0.1×10-3 to 0.9×10-3 compared with the recommended values. The precision for eclogite Pb isotopic analysis is better than 0.25×10-3.
Pb isotopes have been comprehensively applied to isotopic geochronology, geochemical tracing and division of tectonic zones. Due to the difficulty for calibration of Pb isotopic fractionation in thermal ionization mass spectrometry (TIMS) analysis, the accurate determination of Pb isotopic ratios, especially for low-Pb samples, is generally difficult. This paper reports the preparation of samples with low-Pb contents, process of TIMS analysis and confect of emission reagent for accurate Pb isotope analysis. The role of emission reagent and affect of interferential elements on the Pb isotope analysis are also discussed. Some typical eclogites from Dabie-Sulu ultrahigh-pressure metamorphic belt are analyzed with this method. During the whole analysis process, the interior precision and exterior precision for the standard sample NBS981 are better than 0.25×10-3 and 0.4×10-3 respectively, and the relative error is 0.1×10-3 to 0.9×10-3 compared with the recommended values. The precision for eclogite Pb isotopic analysis is better than 0.25×10-3.
2003, 28(2): 143-150.
Abstract:
The studies on ultra-microstructure characteristic of quartz exsolution in eclogite and coesite in UHP eclogite of several localities are done with the appliance of laser Raman spectroscopy and U-stage. Research results show that the phase transformation of coesite-quartz in garnet and/or omphacite is a continuous process. Topological relationships are present between quartz exsolution in omphacite and its host mineral which shows orientations of two long axes of quartz exsolution parallel to (100) and (-101) of omphacite. At present, some of scholars suggest that the quartz exsolution in omphacite of eclogite is the evidence of UHP metamorphism. However, temperature and pressure condition and the exsolution mechanism of oriented needlelike quartz in omphacite still remain unclear. Therefore further study should be enhanced on experimental study on exsolution mechanism of super-silicate clinopyroxene, which could provide experimental quantitative constraint on quartz exsolution as UHP indicator.
The studies on ultra-microstructure characteristic of quartz exsolution in eclogite and coesite in UHP eclogite of several localities are done with the appliance of laser Raman spectroscopy and U-stage. Research results show that the phase transformation of coesite-quartz in garnet and/or omphacite is a continuous process. Topological relationships are present between quartz exsolution in omphacite and its host mineral which shows orientations of two long axes of quartz exsolution parallel to (100) and (-101) of omphacite. At present, some of scholars suggest that the quartz exsolution in omphacite of eclogite is the evidence of UHP metamorphism. However, temperature and pressure condition and the exsolution mechanism of oriented needlelike quartz in omphacite still remain unclear. Therefore further study should be enhanced on experimental study on exsolution mechanism of super-silicate clinopyroxene, which could provide experimental quantitative constraint on quartz exsolution as UHP indicator.
2003, 28(2): 151-156.
Abstract:
This study indicates that to obtain the accurate contents of Zr and Hf in the high-grade metamorphic rocks (e.g., gneiss, granulite and eclogite) with ICP-MS, the rock-digesting time must be > 36 h at 190 ℃ in closed Teflon Bomb. Unlike Zr and Hf, the most important factor limiting the analytical precision and accuracy of Nb and Ta in ICP-MS analysis is their instability in the medium of diluted HNO3. Our technique of rock-digesting at 190 ℃ for 48 h in high-pressure sealed Teflon Bomb incorporating with "F- matrix" match effectively solve the problem of accurate analysis of Zr, Hf, Nb and Ta with ICP-MS.
This study indicates that to obtain the accurate contents of Zr and Hf in the high-grade metamorphic rocks (e.g., gneiss, granulite and eclogite) with ICP-MS, the rock-digesting time must be > 36 h at 190 ℃ in closed Teflon Bomb. Unlike Zr and Hf, the most important factor limiting the analytical precision and accuracy of Nb and Ta in ICP-MS analysis is their instability in the medium of diluted HNO3. Our technique of rock-digesting at 190 ℃ for 48 h in high-pressure sealed Teflon Bomb incorporating with "F- matrix" match effectively solve the problem of accurate analysis of Zr, Hf, Nb and Ta with ICP-MS.
2003, 28(2): 157-162.
Abstract:
Physical property of deep-sea sediment core is useful to make an efficient calculation of the percent carbonate, which has been successful in low resolution research rather than in high resolution research. Multiple regression equations are generated based on the comparing diffuse reflectance and magnetic susceptibility records from ODP Leg 184 with carbonate contents measured in our laboratory. It is found that percent carbonate estimated with diffuse reflectance is closer to the measured one than that estimated with magnetic susceptibility, and the multiple regression equation varies in different sites.
Physical property of deep-sea sediment core is useful to make an efficient calculation of the percent carbonate, which has been successful in low resolution research rather than in high resolution research. Multiple regression equations are generated based on the comparing diffuse reflectance and magnetic susceptibility records from ODP Leg 184 with carbonate contents measured in our laboratory. It is found that percent carbonate estimated with diffuse reflectance is closer to the measured one than that estimated with magnetic susceptibility, and the multiple regression equation varies in different sites.
2003, 28(2): 163-166.
Abstract:
Carbonate pillared Mg-Al-In hydrotalcites were synthesized by coprecipitation. Various preparative factors such as precipitation method, operation temperature, pH value, aging time and n (Mg): n (Al): n (In) molar ratio, which affect the purity and crystal form of Mg-Al-In hydrotalcite-like compound were studied. The results of product characterization by XRD and IR methods show that high supersaturation coprecipitation at constant pH, handing precepitation temperature and aging temperature at 65℃, washing temperature at room temperature, pH ranging from 10 to 11.5, aging for 8 h and n (In3+)/n (M3+) molar ratio ranging from 0.1 to 0.8, may give rise to high purity and better crystal form of Mg-Al-In hydrotalcite-like compounds.
Carbonate pillared Mg-Al-In hydrotalcites were synthesized by coprecipitation. Various preparative factors such as precipitation method, operation temperature, pH value, aging time and n (Mg): n (Al): n (In) molar ratio, which affect the purity and crystal form of Mg-Al-In hydrotalcite-like compound were studied. The results of product characterization by XRD and IR methods show that high supersaturation coprecipitation at constant pH, handing precepitation temperature and aging temperature at 65℃, washing temperature at room temperature, pH ranging from 10 to 11.5, aging for 8 h and n (In3+)/n (M3+) molar ratio ranging from 0.1 to 0.8, may give rise to high purity and better crystal form of Mg-Al-In hydrotalcite-like compounds.
2003, 28(2): 167-172.
Abstract:
Bikou Group, a metamorphic terrene with a series of slabs, and formed in the mid-late Proterozoic era, has undergone multi-periods of complex metamorphisms and deformation. The composition of its major and trace elements of volcanic rocks shows there are obvious differences in source and tectonic settings between Damaoping and Faziba slabs. Damaoping slab, with alkalic and non-alkalic meta-volcanic rocks, possesses compositions similar to those of OIB-type and MORB-type source respectively. The systemic variations of the ratios between high incompatibility immobile elements and geochemical twins such as Nb/Ta indicate that derived from relative enrichment mantle for former and depleted mantle, they developed within plate tectonics and similar ridge setting respectively. Also the development of the alkalic rocks involved the participation of the crust material, so Damaoping slab volcanics may have been formed in rift or oceanic setting. Faziba slab with meta-basalt and medium-acid lava shows "double mode" composition characteristics, in which the source composition of meta-basalt is similar to that of mid-ridge basalt. This may clarify that they were derived from relative depleted mantle. The medium-acid volcanic rocks, which are obviously different from meta-basalts, show typical crust source rock characteristics, so Faziba volcanic rocks are thought to have been formed in continental rift setting. According to what is discussed above, Bikou Group volcanics may have possibly developed in continental rift or limited ocean setting.
Bikou Group, a metamorphic terrene with a series of slabs, and formed in the mid-late Proterozoic era, has undergone multi-periods of complex metamorphisms and deformation. The composition of its major and trace elements of volcanic rocks shows there are obvious differences in source and tectonic settings between Damaoping and Faziba slabs. Damaoping slab, with alkalic and non-alkalic meta-volcanic rocks, possesses compositions similar to those of OIB-type and MORB-type source respectively. The systemic variations of the ratios between high incompatibility immobile elements and geochemical twins such as Nb/Ta indicate that derived from relative enrichment mantle for former and depleted mantle, they developed within plate tectonics and similar ridge setting respectively. Also the development of the alkalic rocks involved the participation of the crust material, so Damaoping slab volcanics may have been formed in rift or oceanic setting. Faziba slab with meta-basalt and medium-acid lava shows "double mode" composition characteristics, in which the source composition of meta-basalt is similar to that of mid-ridge basalt. This may clarify that they were derived from relative depleted mantle. The medium-acid volcanic rocks, which are obviously different from meta-basalts, show typical crust source rock characteristics, so Faziba volcanic rocks are thought to have been formed in continental rift setting. According to what is discussed above, Bikou Group volcanics may have possibly developed in continental rift or limited ocean setting.
2003, 28(2): 173-178.
Abstract:
Petrology and mineralogy of spinel-clinopyroxenite xenolith in Early Jurassic intrusive complex from Xu-Huai region, central China indicate that Mg-Fe spinel and Al-clinopyroxene assemblage could be present as the cumulate of the underplating magma in the lower crust or the most upper mantle, which were formed under 0.90 GPa and 835 ℃; that the mineral assemblage (Ⅱ) represented by spinel-garnet transition and clinopyroxene (Cpx) +garnet (Grt) +corundum (Co) assemblage could reflect that the spinel-clinopyroxenite was subjected to high pressure metamorphism with 1.40-1.65 GPa and 900-1 000 ℃; and that the occurrence of retrogressive amphibole implies that the spinel-clinopyroxenite could undergo the amphibolite facies retrogressive metamorphism with 0.70 GPa and 670-740 ℃. The discovery of the xenolith is of important implication for us to recognize the deep subduction direction and the scale of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt.
Petrology and mineralogy of spinel-clinopyroxenite xenolith in Early Jurassic intrusive complex from Xu-Huai region, central China indicate that Mg-Fe spinel and Al-clinopyroxene assemblage could be present as the cumulate of the underplating magma in the lower crust or the most upper mantle, which were formed under 0.90 GPa and 835 ℃; that the mineral assemblage (Ⅱ) represented by spinel-garnet transition and clinopyroxene (Cpx) +garnet (Grt) +corundum (Co) assemblage could reflect that the spinel-clinopyroxenite was subjected to high pressure metamorphism with 1.40-1.65 GPa and 900-1 000 ℃; and that the occurrence of retrogressive amphibole implies that the spinel-clinopyroxenite could undergo the amphibolite facies retrogressive metamorphism with 0.70 GPa and 670-740 ℃. The discovery of the xenolith is of important implication for us to recognize the deep subduction direction and the scale of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt.
2003, 28(2): 179-184.
Abstract:
Tectonic stress can cause the deformation of rocks as well as the change of fluid pressure in the pore of rocks forming anomaly tectonic fluid pressure. Through analysis of the lithomechanical experiment results of Paterson etc, the authors find that the stress has a non-linear relationship to anomaly fluid pressure, while the volume strain has a linear relationship to anomaly fluid pressure. The anomaly pressures formed by other mechanisms all have the same characters - the relative changes of pore volume and fluid volume in the pore. So the general process of anomaly pressure formed by different mechanisms: when the rocks that have been saturated by fluid, the relative reduction of the pore volume causes the expelling of fluid; and the relative enlargement of the pore volume causes the inflow of fluid. If the permeability of the surrounding rocks is large enough, there would be no obvious anomaly fluid pressure formed. In contrast, if the permeability of surrounding rocks is small, the anomaly fluid pressure will be formed. The thickness and permeability of surrounding rocks and the strain rate of the pore are the main factors for forming anomaly pressure.
Tectonic stress can cause the deformation of rocks as well as the change of fluid pressure in the pore of rocks forming anomaly tectonic fluid pressure. Through analysis of the lithomechanical experiment results of Paterson etc, the authors find that the stress has a non-linear relationship to anomaly fluid pressure, while the volume strain has a linear relationship to anomaly fluid pressure. The anomaly pressures formed by other mechanisms all have the same characters - the relative changes of pore volume and fluid volume in the pore. So the general process of anomaly pressure formed by different mechanisms: when the rocks that have been saturated by fluid, the relative reduction of the pore volume causes the expelling of fluid; and the relative enlargement of the pore volume causes the inflow of fluid. If the permeability of the surrounding rocks is large enough, there would be no obvious anomaly fluid pressure formed. In contrast, if the permeability of surrounding rocks is small, the anomaly fluid pressure will be formed. The thickness and permeability of surrounding rocks and the strain rate of the pore are the main factors for forming anomaly pressure.
2003, 28(2): 185-190.
Abstract:
On the basis of the geological study of hydrocarbon migrating and accumulating into reservoir in Guantao Fm., Zhanhua depression, this experiment models the influence of opening fault on petroleum migration and accumulation in the formation with a 2-D model. The results are as follows: (1) The moving pattern and phase of fluids in fault zone have great influence on moving path and pattern of petroleum in Guantao Fm.. When continuously injected, petroleum could have occupied the fault zone firstly, then moved laterally down the top of its upper formation, and finally down the top of its lower formation. However, in impulsive (unsteady) injection, petroleum occupied lower part of fault and the lower Guantao Fm., firstly, then upper part of fault, and migrates laterally in the lower Guantao Fm.. Finally, the upper Guantao Fm. moved laterally. In addition, when petroleum and water injected together, they would separate because of hydrodynamics. (2) When injected continuously (steadily), petroleum migrated laterally in sand bed above the barrier, while in impulsive (unsteady) injection, it migrated in both upper and lower Guantao Fm., in which quantity of lateral migration in lower sand bed is bigger than that in the upper sand bed when petroleum is injected only, and the quantity of lateral migration in upper sand bed is slightly bigger than that in lower sand bed when petroleum and water are injected together. (3) Continuous (steady) injection is favorable for petroleum accumulation in upper Guantao Fm., sand bed, while impulsive (unsteady) injection is favorable for petroleum accumulation in lower Guantao Fm., sand bed. In addition, petroleum is apt to accumulate in upper of Guantao Fm., when it is injected together with water because of hydrodynamics.
On the basis of the geological study of hydrocarbon migrating and accumulating into reservoir in Guantao Fm., Zhanhua depression, this experiment models the influence of opening fault on petroleum migration and accumulation in the formation with a 2-D model. The results are as follows: (1) The moving pattern and phase of fluids in fault zone have great influence on moving path and pattern of petroleum in Guantao Fm.. When continuously injected, petroleum could have occupied the fault zone firstly, then moved laterally down the top of its upper formation, and finally down the top of its lower formation. However, in impulsive (unsteady) injection, petroleum occupied lower part of fault and the lower Guantao Fm., firstly, then upper part of fault, and migrates laterally in the lower Guantao Fm.. Finally, the upper Guantao Fm. moved laterally. In addition, when petroleum and water injected together, they would separate because of hydrodynamics. (2) When injected continuously (steadily), petroleum migrated laterally in sand bed above the barrier, while in impulsive (unsteady) injection, it migrated in both upper and lower Guantao Fm., in which quantity of lateral migration in lower sand bed is bigger than that in the upper sand bed when petroleum is injected only, and the quantity of lateral migration in upper sand bed is slightly bigger than that in lower sand bed when petroleum and water are injected together. (3) Continuous (steady) injection is favorable for petroleum accumulation in upper Guantao Fm., sand bed, while impulsive (unsteady) injection is favorable for petroleum accumulation in lower Guantao Fm., sand bed. In addition, petroleum is apt to accumulate in upper of Guantao Fm., when it is injected together with water because of hydrodynamics.
2003, 28(2): 191-195.
Abstract:
On the basis of lineament interpretation of DEM, TM, NOAA and ground magnetics, this study suggests that lineaments spatially coupled with gold deposits distribution. At regional scale, the first-order structural controls are NEE, NE and NW trending structures, particularly at their intersecting sites. At project scale, the first-order structural controls are WNW, NNW and NE structures, and the second-order structures are NNE and ring structures. At prospect scale, the NE, SN and ring structures are the most important structural controls. There is great potential of gold targets when the advantageous of lineament anomaly are higher than 40 at project scale.
On the basis of lineament interpretation of DEM, TM, NOAA and ground magnetics, this study suggests that lineaments spatially coupled with gold deposits distribution. At regional scale, the first-order structural controls are NEE, NE and NW trending structures, particularly at their intersecting sites. At project scale, the first-order structural controls are WNW, NNW and NE structures, and the second-order structures are NNE and ring structures. At prospect scale, the NE, SN and ring structures are the most important structural controls. There is great potential of gold targets when the advantageous of lineament anomaly are higher than 40 at project scale.
2003, 28(2): 196-200.
Abstract:
Based on capillary pressure theory, the accumulation and distribution of hydrocarbon in inhomogeneous sandstone reservoir with complicated pore structures were analyzed. It was concluded that the accumulation and distribution of hydrocarbon in inhomogeneous reservoir were predominated by the poor permeable layers (barrier beds). The analysis demonstrated that the transition intervals would be long in inhomogeneous reservoir with moderate to low porosity and permeability. The entrapment in this kind of reservoir requested larger closure height. In the situation of limited closure, the poor permeable layers resulted in sealing process and formed non-saturated, both hydrocarbon and free water-bearing stratum with broader distribution vertically. The production ability was much limited because of the low effective permeability in the porous media with two-phase liquid system. All those features bring about a contradiction between the gas logs, well logs and the well testing. The well log responses and characteristics of this reservoir were also discussed in this paper both theoretically and by the case study. Generally, the correlation in well logs between the hydrocarbon saturation and the porosity in this formation became obscure and difficult to distinguish due to the great changes in porosity and saturation of the reservoir vertically. A case study was also presented and proved a good evidence of the above theoretical deductions.
Based on capillary pressure theory, the accumulation and distribution of hydrocarbon in inhomogeneous sandstone reservoir with complicated pore structures were analyzed. It was concluded that the accumulation and distribution of hydrocarbon in inhomogeneous reservoir were predominated by the poor permeable layers (barrier beds). The analysis demonstrated that the transition intervals would be long in inhomogeneous reservoir with moderate to low porosity and permeability. The entrapment in this kind of reservoir requested larger closure height. In the situation of limited closure, the poor permeable layers resulted in sealing process and formed non-saturated, both hydrocarbon and free water-bearing stratum with broader distribution vertically. The production ability was much limited because of the low effective permeability in the porous media with two-phase liquid system. All those features bring about a contradiction between the gas logs, well logs and the well testing. The well log responses and characteristics of this reservoir were also discussed in this paper both theoretically and by the case study. Generally, the correlation in well logs between the hydrocarbon saturation and the porosity in this formation became obscure and difficult to distinguish due to the great changes in porosity and saturation of the reservoir vertically. A case study was also presented and proved a good evidence of the above theoretical deductions.
2003, 28(2): 201-208.
Abstract:
One of the most important ore fields in Qinling multi-metallic ore-forming belt is Xicheng Pb-Zn deposit which is controlled strictly in the Middle Devonian series. Viewing from organic geochemistry, the correlation between ore-forming elements and organic matter, organic molecules, the analysis of neutron activation for asphalt, ore, wall rock and the experiment simulation, this paper probes into the role of organic matter in the forming process of Xicheng Pb-Zn ore field. The analysis results for organic geochemistry of fresh rock and ore samples selected systematically show that the content of chloroform bitumen "A" from the cherts and the silicified limestones involved in mineralization is lower than that from the unmineralized rocks. While GC-MS-MS analysis of rocks and ores suggests that the dominant carbon is almost nC18 in all mineralization rocks (siliceous rocks and limestone rocks). Organic molecules of the rocks relevant to mineralization and limestones are mainly pentacyclic triterpene. Studies on the correlation analysis between organic matter and ore-forming elements show that the contents of Pb and Zn have striking negative correlations with aromatic hydrocarbon and chloroform asphalt "A" and positive correlation with non-hydrocarbon and organic sulfur/(organic carbon×1.22). The contents of Pb and Zn have positive correlations with the abundances of some organic molecules, whereas they have negative correlations with the ratios of some organic molecules. The analysis results of neutron activation for asphalt, ore, wall rock reveal that the asphalt has a close relationship with ores, and that the organic matter comes to the ore-forming site together with ore-forming elements at the reformed mineralization stage. The dissolution ability of Pb-Zn, the ability of the rock samples of releasing ore-forming elements have been increased because of the adding of organic water in hot water fluid. Therefore, it can be inferred that the organic matter played an important role in the formation of lead-zinc deposits in Xicheng ore field.
One of the most important ore fields in Qinling multi-metallic ore-forming belt is Xicheng Pb-Zn deposit which is controlled strictly in the Middle Devonian series. Viewing from organic geochemistry, the correlation between ore-forming elements and organic matter, organic molecules, the analysis of neutron activation for asphalt, ore, wall rock and the experiment simulation, this paper probes into the role of organic matter in the forming process of Xicheng Pb-Zn ore field. The analysis results for organic geochemistry of fresh rock and ore samples selected systematically show that the content of chloroform bitumen "A" from the cherts and the silicified limestones involved in mineralization is lower than that from the unmineralized rocks. While GC-MS-MS analysis of rocks and ores suggests that the dominant carbon is almost nC18 in all mineralization rocks (siliceous rocks and limestone rocks). Organic molecules of the rocks relevant to mineralization and limestones are mainly pentacyclic triterpene. Studies on the correlation analysis between organic matter and ore-forming elements show that the contents of Pb and Zn have striking negative correlations with aromatic hydrocarbon and chloroform asphalt "A" and positive correlation with non-hydrocarbon and organic sulfur/(organic carbon×1.22). The contents of Pb and Zn have positive correlations with the abundances of some organic molecules, whereas they have negative correlations with the ratios of some organic molecules. The analysis results of neutron activation for asphalt, ore, wall rock reveal that the asphalt has a close relationship with ores, and that the organic matter comes to the ore-forming site together with ore-forming elements at the reformed mineralization stage. The dissolution ability of Pb-Zn, the ability of the rock samples of releasing ore-forming elements have been increased because of the adding of organic water in hot water fluid. Therefore, it can be inferred that the organic matter played an important role in the formation of lead-zinc deposits in Xicheng ore field.
2003, 28(2): 209-213.
Abstract:
Based on a previous research, two typical high-As coal samples were conducted on subsequent leaching. Combining with instrument neutron active analyses (INAA), ICP-MS, ICP-AES, X-ray absorption fine structure (XAFS), low temperature ashing, and scanning electron microscopy with X-ray energy disperse analyzer, this paper discusses the occurrence mode of the arsenic in high-As coals from southwestern Guizhou Province. It is proved that more than 50% arsenic cannnot be leached out by NH 4Ac, HCl, HF and HNO3, and that arsenic mainly exists in the organic (Ⅴ) form.
Based on a previous research, two typical high-As coal samples were conducted on subsequent leaching. Combining with instrument neutron active analyses (INAA), ICP-MS, ICP-AES, X-ray absorption fine structure (XAFS), low temperature ashing, and scanning electron microscopy with X-ray energy disperse analyzer, this paper discusses the occurrence mode of the arsenic in high-As coals from southwestern Guizhou Province. It is proved that more than 50% arsenic cannnot be leached out by NH 4Ac, HCl, HF and HNO3, and that arsenic mainly exists in the organic (Ⅴ) form.
2003, 28(2): 214-218.
Abstract:
The Dongting Lake has experienced several change processes since last glaciation. From later Pleistocene to early Holocene, the Dongting Lake area was a plain cutting by deep channel. Then the anthropologic has been to the Dongting Lake area frequently since the globe change warmer in Neolithic time. The Zaoshi civilization shows the human activity almost in the periphery of the Dongting Lake area and the Daxi civilization indicated the advance to the center of the lake area for fishing and hunting. It was warm and flooding in the Qujialing civilization time, and human being retreat from the lake area. Since the Longshan civilization time, it was cool and precipitation reduced, and human activity moved to the center of the lake area. The lake's delta developed and lake surface decreased. Since the last thousands years, the Dongting Lake experiences the expand and shrink periods several times.
The Dongting Lake has experienced several change processes since last glaciation. From later Pleistocene to early Holocene, the Dongting Lake area was a plain cutting by deep channel. Then the anthropologic has been to the Dongting Lake area frequently since the globe change warmer in Neolithic time. The Zaoshi civilization shows the human activity almost in the periphery of the Dongting Lake area and the Daxi civilization indicated the advance to the center of the lake area for fishing and hunting. It was warm and flooding in the Qujialing civilization time, and human being retreat from the lake area. Since the Longshan civilization time, it was cool and precipitation reduced, and human activity moved to the center of the lake area. The lake's delta developed and lake surface decreased. Since the last thousands years, the Dongting Lake experiences the expand and shrink periods several times.
2003, 28(2): 219-224.
Abstract:
During the last 40 years, nitrate has become one of the most common groundwater contaminants. In this paper, the nitrogen isotope rations in NO3- have been analyzed by a new sealed-tube combustion technique using CaO for quantitative removal of CO2 and water. Oxygen isotope analysis in NO3- was conducted by using new sealed-tube combustion technique of AgNO3+C. Extensive NO3--N contamination of drinking water in Lin and Anyang district to a level above drinking water limits is a major problem. It is found that the rate of death of esophagus cancer is proportional to the excessive content of NO3-, NO2-, NH4+ and nitrosamine in drinking water. The study data of δ(15N) and δ(18O) show that NO3- in drinking water was predominantly derived from manure and fertilizer in this region. The δ(18O) of groundwater NO3- indicated conclusively that no significant denitrification was found in this area. Conversely, the aerobic nitrification pathway from NH4+ to NO3- results in one third of the oxygen in the NO3- derived from air and two thirds derived from water.
During the last 40 years, nitrate has become one of the most common groundwater contaminants. In this paper, the nitrogen isotope rations in NO3- have been analyzed by a new sealed-tube combustion technique using CaO for quantitative removal of CO2 and water. Oxygen isotope analysis in NO3- was conducted by using new sealed-tube combustion technique of AgNO3+C. Extensive NO3--N contamination of drinking water in Lin and Anyang district to a level above drinking water limits is a major problem. It is found that the rate of death of esophagus cancer is proportional to the excessive content of NO3-, NO2-, NH4+ and nitrosamine in drinking water. The study data of δ(15N) and δ(18O) show that NO3- in drinking water was predominantly derived from manure and fertilizer in this region. The δ(18O) of groundwater NO3- indicated conclusively that no significant denitrification was found in this area. Conversely, the aerobic nitrification pathway from NH4+ to NO3- results in one third of the oxygen in the NO3- derived from air and two thirds derived from water.
2003, 28(2): 225-231.
Abstract:
One of the main tasks in studying saltwater intrusion into coastal aquifer system is to determine the position of the saltwater-freshwater interface. For a natural confined aquifer, this position is related to the roof length of the aquifer extending under the sea. This information can be obtained from fluctuations of confined groundwater level caused by tidal effect of the sea. In the paper, taking account to the density difference between freshwater and seawater, a three-dimensional density-dependent tidal-effect model is developed in the Jiahe River basin, Shandong Province, China. The position of the aquifer roof extending under the sea, which is called the equivalent boundary toward sea, is determined by converging hydraulic head fluctuations data observed in the tidal-effect observation experiment. The aquifer parameters near the sea side are also estimated according to tidal fluctuation information.
One of the main tasks in studying saltwater intrusion into coastal aquifer system is to determine the position of the saltwater-freshwater interface. For a natural confined aquifer, this position is related to the roof length of the aquifer extending under the sea. This information can be obtained from fluctuations of confined groundwater level caused by tidal effect of the sea. In the paper, taking account to the density difference between freshwater and seawater, a three-dimensional density-dependent tidal-effect model is developed in the Jiahe River basin, Shandong Province, China. The position of the aquifer roof extending under the sea, which is called the equivalent boundary toward sea, is determined by converging hydraulic head fluctuations data observed in the tidal-effect observation experiment. The aquifer parameters near the sea side are also estimated according to tidal fluctuation information.
