2007 Vol. 32, No. 1
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2007, 32(1): 1-6.
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Abstract:
The principle prerequisite for the formation of a volcano is the generation of a channel for magma transportation. There is little research on the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan Plateau.Based on the subcrustal mantle convection-generated stress field inversed by gravity anomalies, together with its relationship to the Cenozoic volcanism in the plateau, and the mechanism of crustal fracture formation, as well as the numerical results of the evolution of mantle convection beneath the plateau, this paper investigates the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan Plateau. There are two significant extensional convection-generated stress zones beneath the plateau, in which the volcanic rocks in the central and northern parts of the plateau are distributed. The Linzizong volcanism in southern Tibet correlates the upwelling mantle flow prior to the India-Asia collision or during the early stage of the collision. The magnitude of the stress is ~ 100 MPa, which is the same order of force that causes crustal fractures. The evidence implies that the mantle convection-generated stress is one of the principle causes of crustal fractures, and furthermore, the formation of the magma transportation channel in the Tibetan Plateau.
The principle prerequisite for the formation of a volcano is the generation of a channel for magma transportation. There is little research on the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan Plateau.Based on the subcrustal mantle convection-generated stress field inversed by gravity anomalies, together with its relationship to the Cenozoic volcanism in the plateau, and the mechanism of crustal fracture formation, as well as the numerical results of the evolution of mantle convection beneath the plateau, this paper investigates the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan Plateau. There are two significant extensional convection-generated stress zones beneath the plateau, in which the volcanic rocks in the central and northern parts of the plateau are distributed. The Linzizong volcanism in southern Tibet correlates the upwelling mantle flow prior to the India-Asia collision or during the early stage of the collision. The magnitude of the stress is ~ 100 MPa, which is the same order of force that causes crustal fractures. The evidence implies that the mantle convection-generated stress is one of the principle causes of crustal fractures, and furthermore, the formation of the magma transportation channel in the Tibetan Plateau.
2007, 32(1): 7-21.
Abstract:
The formation of major-and trace-elemental and Sr-Nd-Pb isotopic geochemistries in Early Paleoproterozoic Mohe pluton and Early Triassic Cahanno pluton of the Oulongbuluke micro-block and Neoproterozoic Shaliuhe pluton, Late-Permian to Early-Triaasic Xiangride pluton and Late-Triassic Keri pluton of the Qaidam Block of northwestern China, were investigated. The Shaliuhe pluton and Keri muscovite pluton are characterized by S-type and paraaluminium granite, the others are by Ⅰ-type granodiorite or granite. It is concluded from the comparsion of TDM and εNd(t) that the magma source area of the Shaliuhe granite belongs to the Ⅱ-type metabasement of the Oulongbuluke micro-block, and the magma of the rest of the plutons could not originate from the exposed supracurstal sequences. The TDM are clustered at ~1.5-2.3 Ga and 0.9-1.3 Ga, with peak value of ~ 1.2 Ga, ~1.6 Ga and ~2.05 Ga for both granitoids and meta-supracurstal rocks, ~2.5 Ga and 2.8 Ga are solely distributed in the Oulongbuluke micro-block. The two micro-blocks have ratios of (206Pb/204Pb)t, (207Pb/204Pb)t and (206Pb/204Pb)t generally higher than 18, 15.5 and 38, respectively. These data suggest that the basements of the Oulongbuluke micro-blocks and the Qaidam micro-blocks are geochemically akin to that of the Yangtze Block, and that the Yangtze Block Domain can be extended northwestwards to the micro blocks on both sides of the Altyn-Tagh fault, and that the UHP-HP tectonic belt along the northern margin of the Qaidam micro-block is only a convergent boundary among the earlier broken-up micro-blocks within the Yangtze Block.
The formation of major-and trace-elemental and Sr-Nd-Pb isotopic geochemistries in Early Paleoproterozoic Mohe pluton and Early Triassic Cahanno pluton of the Oulongbuluke micro-block and Neoproterozoic Shaliuhe pluton, Late-Permian to Early-Triaasic Xiangride pluton and Late-Triassic Keri pluton of the Qaidam Block of northwestern China, were investigated. The Shaliuhe pluton and Keri muscovite pluton are characterized by S-type and paraaluminium granite, the others are by Ⅰ-type granodiorite or granite. It is concluded from the comparsion of TDM and εNd(t) that the magma source area of the Shaliuhe granite belongs to the Ⅱ-type metabasement of the Oulongbuluke micro-block, and the magma of the rest of the plutons could not originate from the exposed supracurstal sequences. The TDM are clustered at ~1.5-2.3 Ga and 0.9-1.3 Ga, with peak value of ~ 1.2 Ga, ~1.6 Ga and ~2.05 Ga for both granitoids and meta-supracurstal rocks, ~2.5 Ga and 2.8 Ga are solely distributed in the Oulongbuluke micro-block. The two micro-blocks have ratios of (206Pb/204Pb)t, (207Pb/204Pb)t and (206Pb/204Pb)t generally higher than 18, 15.5 and 38, respectively. These data suggest that the basements of the Oulongbuluke micro-blocks and the Qaidam micro-blocks are geochemically akin to that of the Yangtze Block, and that the Yangtze Block Domain can be extended northwestwards to the micro blocks on both sides of the Altyn-Tagh fault, and that the UHP-HP tectonic belt along the northern margin of the Qaidam micro-block is only a convergent boundary among the earlier broken-up micro-blocks within the Yangtze Block.
2007, 32(1): 22-28.
Abstract:
Isotopic ratios of Sr, Nd and Pb were analyzed for the Permian volcanic rocks in the Zhiduo and Zaduo areas of southern Qinghai which is located at the Qamdo block. The analytical results of the sample rocks are as follows: ISr = 0.703 33 -0.704 17, εNd(t) =4.1-5.5, 206Pb/204Pb=17.547-17.986, 207Pb/204Pb=15.476-15.584, 208Pb/204Pb= 37.778-37.976. Combined with lithological and geochemical research findings, the above results indicate that the volcanic rock is of OIB type and came into formation in the stretching rift tectonic environment. It falls into the Late Palaeozoic rift system of the Qinghai-Tibet Plateau and its adjacent areas. The primitive magma might have originated from the deplected asthenosphere and the continental breakup is related to the activity of mantle plume. With the V1 and V2 of the lead isotopic ratios ranging from 31.39 to 46.78, 22.38 to 42.45 respectively, the lead isotope of the rock samples can be labeled the Yangtze lead isotopes, which indicates that the Qamdo block belonged to Tethyan realm during Late Palaeozoic and was a part of the Pan-Cathaysian continental group or Yangtze Plate.
Isotopic ratios of Sr, Nd and Pb were analyzed for the Permian volcanic rocks in the Zhiduo and Zaduo areas of southern Qinghai which is located at the Qamdo block. The analytical results of the sample rocks are as follows: ISr = 0.703 33 -0.704 17, εNd(t) =4.1-5.5, 206Pb/204Pb=17.547-17.986, 207Pb/204Pb=15.476-15.584, 208Pb/204Pb= 37.778-37.976. Combined with lithological and geochemical research findings, the above results indicate that the volcanic rock is of OIB type and came into formation in the stretching rift tectonic environment. It falls into the Late Palaeozoic rift system of the Qinghai-Tibet Plateau and its adjacent areas. The primitive magma might have originated from the deplected asthenosphere and the continental breakup is related to the activity of mantle plume. With the V1 and V2 of the lead isotopic ratios ranging from 31.39 to 46.78, 22.38 to 42.45 respectively, the lead isotope of the rock samples can be labeled the Yangtze lead isotopes, which indicates that the Qamdo block belonged to Tethyan realm during Late Palaeozoic and was a part of the Pan-Cathaysian continental group or Yangtze Plate.
2007, 32(1): 29-38.
Abstract:
This paper presents Sm-Nd and geochemical data on fine-grained sediments of the north margin from the Yangtze craton, China. Systematic research leads to the following conclusions: (1) Nd isotope composition of the clastic sedimentary rocks from the Middle-Upper Proterozoic has the εNd(t) values of +2.72 to +0.69, with the Nd model ages of 1.40 Ga and 1.57 Ga, which corresponds to that of the contemporaneous volcanic rocks from Xixiang Group. It indicates that the arc materials from the Proterozoic control the geochemical composition of main provenances of the Middle-Upper Proterozoic sedimentary rocks. (2) The probable provenances of the Paleozoic sedimentary rocks are dominantly the recycled products of Proterozoic crust as indicated by the decrease of the εNd(t) with the time. The sedimentary rocks from the Cambrian-Silurian were derived ultimately from a polycyclic mixture of the old continental crust materials from the Kongling strata and arc materials from the Proterozoic volcanic in the north margin of the Yangtze craton. The derivation is markedly of sources relatively more felsic extreme weathering. The geochemical and isotopic data indicate that the provenance of Devonian terrain has changed with the progressively increasing proportions of materials from the Qinling complex by erosion. (3) The more prominent increase in the εNd(t) values of the Upper Permian formation probably reflects the significant incorporation of the mantle-derived materials. The comparison between the data of trace element and the data of EMS indicates that the dust of volcano from EMS was related to the Late Permian strata during the Late Permian when the volcanism, represented by Emeishan flood basalts (251-258) in the south-western margin of the Yangtze block was extremely active.
This paper presents Sm-Nd and geochemical data on fine-grained sediments of the north margin from the Yangtze craton, China. Systematic research leads to the following conclusions: (1) Nd isotope composition of the clastic sedimentary rocks from the Middle-Upper Proterozoic has the εNd(t) values of +2.72 to +0.69, with the Nd model ages of 1.40 Ga and 1.57 Ga, which corresponds to that of the contemporaneous volcanic rocks from Xixiang Group. It indicates that the arc materials from the Proterozoic control the geochemical composition of main provenances of the Middle-Upper Proterozoic sedimentary rocks. (2) The probable provenances of the Paleozoic sedimentary rocks are dominantly the recycled products of Proterozoic crust as indicated by the decrease of the εNd(t) with the time. The sedimentary rocks from the Cambrian-Silurian were derived ultimately from a polycyclic mixture of the old continental crust materials from the Kongling strata and arc materials from the Proterozoic volcanic in the north margin of the Yangtze craton. The derivation is markedly of sources relatively more felsic extreme weathering. The geochemical and isotopic data indicate that the provenance of Devonian terrain has changed with the progressively increasing proportions of materials from the Qinling complex by erosion. (3) The more prominent increase in the εNd(t) values of the Upper Permian formation probably reflects the significant incorporation of the mantle-derived materials. The comparison between the data of trace element and the data of EMS indicates that the dust of volcano from EMS was related to the Late Permian strata during the Late Permian when the volcanism, represented by Emeishan flood basalts (251-258) in the south-western margin of the Yangtze block was extremely active.
2007, 32(1): 39-44.
Abstract:
The middle Qilian orogenic belt and Lajishan orogenic belt of the Caledonian strike NW-SE direction in the southeast Qilian and its basement consists of Pre-Caledonian metamorphic rock series. The lozenge-cancellate-shaped ductile shear zone occurs in the crystalline basement, and the included angle of shortening direction of conjugated ductile shear zones ranges from 104° to 114° and the max principal stress direction indicates approximate SW210°. The 40Ar-39Ar plateau ages of muscovite obtained from the mylonitilization rock in ductile shear zone of Jinshaxia within middle Qilian massif and Keque in Hualong massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data determine the ductile shear zones in Caledonian basement metamorphic rock formed through the Caledonian orogeny. Furthermore, the chronological study of basement rock determines precise forming period for the close of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin. This offers a new approach to the determination of ocean basin closing time in the process of structural evolution of orogenic belt.
The middle Qilian orogenic belt and Lajishan orogenic belt of the Caledonian strike NW-SE direction in the southeast Qilian and its basement consists of Pre-Caledonian metamorphic rock series. The lozenge-cancellate-shaped ductile shear zone occurs in the crystalline basement, and the included angle of shortening direction of conjugated ductile shear zones ranges from 104° to 114° and the max principal stress direction indicates approximate SW210°. The 40Ar-39Ar plateau ages of muscovite obtained from the mylonitilization rock in ductile shear zone of Jinshaxia within middle Qilian massif and Keque in Hualong massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data determine the ductile shear zones in Caledonian basement metamorphic rock formed through the Caledonian orogeny. Furthermore, the chronological study of basement rock determines precise forming period for the close of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin. This offers a new approach to the determination of ocean basin closing time in the process of structural evolution of orogenic belt.
2007, 32(1): 45-50.
Abstract:
Tongren area is located in the lower reaches of the Longwuhe River, east of Qinghai Province, which is between the West Qinling and South Qilian orogenic belts. Along the two sides of Longwuhe River broadly develops stratum in Permian and Triassic. Through the analysis of rock assemblages, this area is determined to be turbidite fan facies of hemipelagic from the end of Late Permian to the beginning of Early Triassic. Through the geological research, we found volcanic rocks in the Shiguan Formation of Upper Permian. The volcanic rock assemblage is mainly composed of basalts, basaltic andesites and andesites. According to the characteristics of the ordinary elements, the volcanic rocks can be divided into two parts. The lower part: SiO2 content is 49.04%-52.43%, with the average of 51.28%; the TiO2 content is 0.67%-1.11%, with the average of 0.9%; and the ALK value is 2.64%-3.6%.The rock type is mainly tholeiitic basalt series, with high titanium quantity. The upper part: SiO2 content is 56.25%-60.36%, the average being 58.76%; The TiO2 content is 0.52%-0.63%, the average being 0.58%; the ALK value is 5.26%-5.54%. The rock type is calc-alkaline series with low titanium quantity. REE distribution patterns of the volcanic rocks are different. The lower part has lower REE, with (La/Lu)N average being 3.07, and its distribution patterns are consistent with those of transitional mid-oceanic ridge basalt. REE is rich in the upper part, especially the LREE. And its distribution patterns are similar to those of island arc andesite. The trace elements have the same characteristics, the distribution type of which is something like that of island arc basalt rock. Tectonic setting distinction reveals that the volcanic rocks of this area were formed in transitional mid-oceanic ridge basalt to island arc tectonic setting.
Tongren area is located in the lower reaches of the Longwuhe River, east of Qinghai Province, which is between the West Qinling and South Qilian orogenic belts. Along the two sides of Longwuhe River broadly develops stratum in Permian and Triassic. Through the analysis of rock assemblages, this area is determined to be turbidite fan facies of hemipelagic from the end of Late Permian to the beginning of Early Triassic. Through the geological research, we found volcanic rocks in the Shiguan Formation of Upper Permian. The volcanic rock assemblage is mainly composed of basalts, basaltic andesites and andesites. According to the characteristics of the ordinary elements, the volcanic rocks can be divided into two parts. The lower part: SiO2 content is 49.04%-52.43%, with the average of 51.28%; the TiO2 content is 0.67%-1.11%, with the average of 0.9%; and the ALK value is 2.64%-3.6%.The rock type is mainly tholeiitic basalt series, with high titanium quantity. The upper part: SiO2 content is 56.25%-60.36%, the average being 58.76%; The TiO2 content is 0.52%-0.63%, the average being 0.58%; the ALK value is 5.26%-5.54%. The rock type is calc-alkaline series with low titanium quantity. REE distribution patterns of the volcanic rocks are different. The lower part has lower REE, with (La/Lu)N average being 3.07, and its distribution patterns are consistent with those of transitional mid-oceanic ridge basalt. REE is rich in the upper part, especially the LREE. And its distribution patterns are similar to those of island arc andesite. The trace elements have the same characteristics, the distribution type of which is something like that of island arc basalt rock. Tectonic setting distinction reveals that the volcanic rocks of this area were formed in transitional mid-oceanic ridge basalt to island arc tectonic setting.
2007, 32(1): 51-58.
Abstract:
Apatite fission track (AFT) thermochronology of seven samples from the Xiaonanchuan pluton in the Kunlun pass area was carried out to determine the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0.020-0.035 mm/a during the Late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows paroxysmally rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive mountain building processes since the Pliocene, which were driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in east-west orientation from the western Kunlun range to the eastern. The uplifting trend is also supported by geomorphic characteristics including the elevation and the relief differences as well as the distribution of the Late Cenozoic volcanism.
Apatite fission track (AFT) thermochronology of seven samples from the Xiaonanchuan pluton in the Kunlun pass area was carried out to determine the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0.020-0.035 mm/a during the Late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows paroxysmally rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive mountain building processes since the Pliocene, which were driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in east-west orientation from the western Kunlun range to the eastern. The uplifting trend is also supported by geomorphic characteristics including the elevation and the relief differences as well as the distribution of the Late Cenozoic volcanism.
2007, 32(1): 59-62.
Abstract:
Due to the lack of fossil evidence, the age of Amugang Group, previously referring to the large area of metamorphic formations developed along the south of Longmucuo-Shuanghu suture in southern Qiangtang area, northern Tibet, has been under heated debate. Some geologists were convinced that the age of metamorphic formations was of Pre-Devonian according to the emergence of nonmetamorphic fossil-bearing Devonian in Chasang area, north of the suture. Most geologists believed that its age was of Pre-Sinian. From 2003 to 2004, we collected a large amount of Nautiloid and Graptolite fossils in upper metamorphic formations of Mayigangri area and determined the age to be middle and Late Ordovician-Silurian. It is the first time to discover the Early Paleozoic strata based on reliable fossils, which not only provides evidence to its age ascription, classification of the strata and its correlation to adjacent areas but also offers data to lithofacies, palaeogeography and tectonic pattern of studied area.
Due to the lack of fossil evidence, the age of Amugang Group, previously referring to the large area of metamorphic formations developed along the south of Longmucuo-Shuanghu suture in southern Qiangtang area, northern Tibet, has been under heated debate. Some geologists were convinced that the age of metamorphic formations was of Pre-Devonian according to the emergence of nonmetamorphic fossil-bearing Devonian in Chasang area, north of the suture. Most geologists believed that its age was of Pre-Sinian. From 2003 to 2004, we collected a large amount of Nautiloid and Graptolite fossils in upper metamorphic formations of Mayigangri area and determined the age to be middle and Late Ordovician-Silurian. It is the first time to discover the Early Paleozoic strata based on reliable fossils, which not only provides evidence to its age ascription, classification of the strata and its correlation to adjacent areas but also offers data to lithofacies, palaeogeography and tectonic pattern of studied area.
2007, 32(1): 63-70.
Abstract:
The continental orogenesis is characterized with the following features, such as sudden start, global synchronicity and horizontal movement, occurring mainly in the upper part of the crust and weakening with depth, and SO on.It is difficult to explain these characteristics by the plate tectonic theory based on the heat convection in earth mantle.The geomechanics based on the change of rotating speed of the earth could answer a large part of the above mentioned questions, but the power which it depends on offered by the expansion or contract of the earth and tides et al is too weak to serve as the energy to change the rotating speed of the earth, SO it is also difficult to explain them quantitatively.This paper reveals the collision energy of a celestial body with the earth could induce a sufficient change of rotating speed of the earth to make the folding orogenesis, and briefly explains its mechanics, and therefore offers a brandnew perspective for researching continental orogenesis.
The continental orogenesis is characterized with the following features, such as sudden start, global synchronicity and horizontal movement, occurring mainly in the upper part of the crust and weakening with depth, and SO on.It is difficult to explain these characteristics by the plate tectonic theory based on the heat convection in earth mantle.The geomechanics based on the change of rotating speed of the earth could answer a large part of the above mentioned questions, but the power which it depends on offered by the expansion or contract of the earth and tides et al is too weak to serve as the energy to change the rotating speed of the earth, SO it is also difficult to explain them quantitatively.This paper reveals the collision energy of a celestial body with the earth could induce a sufficient change of rotating speed of the earth to make the folding orogenesis, and briefly explains its mechanics, and therefore offers a brandnew perspective for researching continental orogenesis.
2007, 32(1): 71-74.
Abstract:
To view earth sciences from the perspective of culture, or to see earth science as a phenomenon of culture, this paper suggests that earth science at least includes three aspects in that case: the first is research methodology or the logic thinking of earth science-so-called "truth"; the second is the relationship between human, the earth or values of earth sciences-so-called "goodness"; the third is the evolution balance of earth or harmony between human and the earth-so-called "beauty". Earth science from the perspective of culture is the integrated system of "truth", "goodness" and "beauty".
To view earth sciences from the perspective of culture, or to see earth science as a phenomenon of culture, this paper suggests that earth science at least includes three aspects in that case: the first is research methodology or the logic thinking of earth science-so-called "truth"; the second is the relationship between human, the earth or values of earth sciences-so-called "goodness"; the third is the evolution balance of earth or harmony between human and the earth-so-called "beauty". Earth science from the perspective of culture is the integrated system of "truth", "goodness" and "beauty".
2007, 32(1): 75-81.
Abstract:
Many kinds of gem-grade minerals such as beryl, scheelite, cassiterite and tourmaline, and sub-products such as K-feldspar, galenite, tabular quartz, tabular calcite and mica were found in beryl-scheelite vein deposit of Huya, Pingwu County, Sichuan Province. The major minerals like beryl, scheelite and cassiterite have relatively complicated chemical composition and remarkable isomorphism, which enables them to have typomorphic significance. Studies on the chemical composition, configuration and mineral assemblages of the typical minerals such as beryl, scheelite, cassiterite, feldspar and tourmaline of this area reveal the typomorphic significance of the mineral assemblage and it is determined that the deposit is a high temperature epithermal quartz vein deposit. So the appearance of the minerals tabular configuration is concerned with alkali-rich chemical composition, environment of the mineral and the direction of the mineralized hydrothermal liquid.
Many kinds of gem-grade minerals such as beryl, scheelite, cassiterite and tourmaline, and sub-products such as K-feldspar, galenite, tabular quartz, tabular calcite and mica were found in beryl-scheelite vein deposit of Huya, Pingwu County, Sichuan Province. The major minerals like beryl, scheelite and cassiterite have relatively complicated chemical composition and remarkable isomorphism, which enables them to have typomorphic significance. Studies on the chemical composition, configuration and mineral assemblages of the typical minerals such as beryl, scheelite, cassiterite, feldspar and tourmaline of this area reveal the typomorphic significance of the mineral assemblage and it is determined that the deposit is a high temperature epithermal quartz vein deposit. So the appearance of the minerals tabular configuration is concerned with alkali-rich chemical composition, environment of the mineral and the direction of the mineralized hydrothermal liquid.
2007, 32(1): 82-88.
Abstract:
In this paper, gas accumulation efficiency was defined and calculated in terms of gas reserves, gas-bearing areas and accumulation periods. The calculation of gas accumulation efficiencies for about 60 large and intermediate gas fields in China concludes three types of large and intermediate gas fields with high, middle and low gas accumulation efficiencies. The comprehensive study of gas accumulation efficiency and different pooling conditions reveals that the formation of large and intermediate gas fields with high gas accumulation efficiency in different types of basins in China was controlled by gas supply of source rocks, gas transportation and gas seal and preservation. The creation of high gas accumulation intensity of source rocks in the large and intermediate gas fields is indispensable to the foreland basin often greater than 80×108 m3/km2·Ma, to the cratonic basin often greater than 26×108 m3/km2·Ma, and to the rift basin often greater than 60×108 m3/km2·Ma. The gas transportation velocity of transporting layer in the foreland and rift basins should often be greater than 5×10-14 m/Pa·s, that in the cratonic basin greater than 6×10-12 m/Pa·s. The comprehensive caprock seal index in the foreland basin should often be greater than 1×1010 m/s, that in the cratonic basin greater than 5×109 m/s, and that in the rift basin greater than 3×1010 m/s. The gas accumulation period in the foreland basin should often be later than the Middle Eogene, and that in the cratonic and rift basins later than the Early Eogene.
In this paper, gas accumulation efficiency was defined and calculated in terms of gas reserves, gas-bearing areas and accumulation periods. The calculation of gas accumulation efficiencies for about 60 large and intermediate gas fields in China concludes three types of large and intermediate gas fields with high, middle and low gas accumulation efficiencies. The comprehensive study of gas accumulation efficiency and different pooling conditions reveals that the formation of large and intermediate gas fields with high gas accumulation efficiency in different types of basins in China was controlled by gas supply of source rocks, gas transportation and gas seal and preservation. The creation of high gas accumulation intensity of source rocks in the large and intermediate gas fields is indispensable to the foreland basin often greater than 80×108 m3/km2·Ma, to the cratonic basin often greater than 26×108 m3/km2·Ma, and to the rift basin often greater than 60×108 m3/km2·Ma. The gas transportation velocity of transporting layer in the foreland and rift basins should often be greater than 5×10-14 m/Pa·s, that in the cratonic basin greater than 6×10-12 m/Pa·s. The comprehensive caprock seal index in the foreland basin should often be greater than 1×1010 m/s, that in the cratonic basin greater than 5×109 m/s, and that in the rift basin greater than 3×1010 m/s. The gas accumulation period in the foreland basin should often be later than the Middle Eogene, and that in the cratonic and rift basins later than the Early Eogene.
2007, 32(1): 89-92.
Abstract:
On the basis of the Dacy Law and the formulae proposed byHubbert(1953) for the relationship between dips of oil-water and gas-water contacts in the oil and gas pools under hydrodynamic conditions and hydrodynamic heads, this paper proposes formulae of the relationship between dips of contacts and the waterflow seepage velocity. With the formulae, the paper discusses the possible relationship between the water seepage flow velocity and the slopes of oil(gas)equipotential surfaces. Based on the discussion, the paper concludes that the oil-water contacts in the hydrodynamic-anticline pools where hinge zones are not full of oil commonly are curve surfaces. For hydrodynamic-anticline pools where hinge zones of anticlines are full of oil, their oil-water contact lines in two limbs along cross sections of the cylinder anticlines are horizontal. Those along oblique sections of the cylinder anticlines are reverse; those along cross sections of the plunge anticlines might have the same dips but the two lines usually are not located in the same tilt straight line.
On the basis of the Dacy Law and the formulae proposed by
2007, 32(1): 93-98.
Abstract:
Reconstruction of paleo-fluid potential during each geological period after hydrocarbon generation may be helpful to clearly recognize the hydrocarbon reservoir distribution. In this research, the samples including reservoir fluid from Taiyuan and Shanxi formations of the Upper Paleozoic in Yi-Shaan slope, Ordos basin were obtained, and the systematic analysis of the sample was used to measure the homogenization temperature for all orders of fluid inclusions mainly in trails, salinity for aqueous inclusions and the fluorescence colors for hydrocarbon inclusions. The result indicates that there are six period times of hydrocarbon charging in the sandstone reservoirs, and the gas charging is statistically dominating. By integrating the average homogenization temperatures with burial historical curves, the six charging times are determined. By employing the fluid inclusion pVT thermodynamic modeling, the paleo-formation pressure of these six times of hydrocarbon charging is obtained, and the six periods of paleo-gas potential of No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope are calculated, and the paleo-gas potential distribution and evolution are depicted, and the evolution of regional tectonics and geothermal history are found out to be the main controlling factors. According to the regional geological conditions, the law of the nature gas migration and accumulation of No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope is discussed. From the middle Late Triassic to the late Middle Jurassic, the natural gas mainly migrated from southwest to north, northeast, because the paleo-gas potential in the southwest zone was higher than that in the north and northeast zones; from the late Middle Jurassic to the late Early Cretaceous, the paleo-gas potential in the west zone was higher than that in the east zone and the natural gas migrated eastward and then northeastward; after that, the natural gas accumulation is in equilibrium with dissipation, which results in today's distribution features. The Yulin zone and the southern zone of Yulin have the most important significance to the exploration of the No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope, and secondly to the Shenmu-Mizhi zone.
Reconstruction of paleo-fluid potential during each geological period after hydrocarbon generation may be helpful to clearly recognize the hydrocarbon reservoir distribution. In this research, the samples including reservoir fluid from Taiyuan and Shanxi formations of the Upper Paleozoic in Yi-Shaan slope, Ordos basin were obtained, and the systematic analysis of the sample was used to measure the homogenization temperature for all orders of fluid inclusions mainly in trails, salinity for aqueous inclusions and the fluorescence colors for hydrocarbon inclusions. The result indicates that there are six period times of hydrocarbon charging in the sandstone reservoirs, and the gas charging is statistically dominating. By integrating the average homogenization temperatures with burial historical curves, the six charging times are determined. By employing the fluid inclusion pVT thermodynamic modeling, the paleo-formation pressure of these six times of hydrocarbon charging is obtained, and the six periods of paleo-gas potential of No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope are calculated, and the paleo-gas potential distribution and evolution are depicted, and the evolution of regional tectonics and geothermal history are found out to be the main controlling factors. According to the regional geological conditions, the law of the nature gas migration and accumulation of No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope is discussed. From the middle Late Triassic to the late Middle Jurassic, the natural gas mainly migrated from southwest to north, northeast, because the paleo-gas potential in the southwest zone was higher than that in the north and northeast zones; from the late Middle Jurassic to the late Early Cretaceous, the paleo-gas potential in the west zone was higher than that in the east zone and the natural gas migrated eastward and then northeastward; after that, the natural gas accumulation is in equilibrium with dissipation, which results in today's distribution features. The Yulin zone and the southern zone of Yulin have the most important significance to the exploration of the No.2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope, and secondly to the Shenmu-Mizhi zone.
2007, 32(1): 99-104.
Abstract:
The Tertiary high quality reservoir was mainly developed in the fine, but not coarse granular detrital rocks of eastern Kuqa depression of the Tarim basin. The reservoir evolution is reconstructed in this paper, based on a deeper analysis of tectonic, sedimentary and diagenetic process of these two rocks combined with the paleo-climate of this area. A deep analysis of sedimentary and evolution of the fine and coarse granular detrital rocks suggests that the two rocks underwent multi superimposed diagenetic effects, including syn-sedimentary, local ground water in low depth, compaction in intermediate depth, structurally fracture and burial solution, and structurally extrusion. Therefore, the present reservoir features of the two rocks vary largely. The reconstructed model for the reservoir evolution enriches the study of forming mechanism research of detrital clastic rocks.
The Tertiary high quality reservoir was mainly developed in the fine, but not coarse granular detrital rocks of eastern Kuqa depression of the Tarim basin. The reservoir evolution is reconstructed in this paper, based on a deeper analysis of tectonic, sedimentary and diagenetic process of these two rocks combined with the paleo-climate of this area. A deep analysis of sedimentary and evolution of the fine and coarse granular detrital rocks suggests that the two rocks underwent multi superimposed diagenetic effects, including syn-sedimentary, local ground water in low depth, compaction in intermediate depth, structurally fracture and burial solution, and structurally extrusion. Therefore, the present reservoir features of the two rocks vary largely. The reconstructed model for the reservoir evolution enriches the study of forming mechanism research of detrital clastic rocks.
2007, 32(1): 105-110.
Abstract:
The effect of three different types of purification processes (roasting-magnetic dressing, acid pickling and calcining) on the sulfur content of rectorite clay (pyrite content 4.37%, sulfur content 2.32%) was investigated. By roasting-magnetic dressing, the sulfur content was reduced to 0.52% when roasting at 300 ℃ for 2 h and magnetic dressing twice; By acid pickling, the sulfur content remained 0.57% under the condition of 60 ℃ and acid pickling for 1 h with 60% nitric acid solution; By calcining, 0.78% of sulfur was left if calcined for 0.5 h at 550 ℃. The experimental results indicate there is no obvious inhibition effect (corresponding maximal sulfur content 0.78%) when rectorite/poly (sodium acrylate-Co-acrylamide) is synthesized by in-situ aqueous solution polymerization with the purified rectorite clay as material. At 65-70 ℃, the water absorbencies (WA) of superabsorbent composite (containing 20% purified rectorite clay, 15% acrylamide, 0.25% initiator and 0.08% cross linker, with the neutralization degree of acrylic acid being 80%) in distilled water, tap water and 0.9% NaCl (aq) are 870, 250 and 68 respectively. When the content of rectorite is between 0%-30%, WA of superabsorbent composite is higher than that of superabsorbent resin that contains no rectorite. When WA of superabsorbent composite in distilled water is reduced from 870 g/g to 84 g/g, its gel strength rises from 49 g/cm2 to 235 g/cm2.
The effect of three different types of purification processes (roasting-magnetic dressing, acid pickling and calcining) on the sulfur content of rectorite clay (pyrite content 4.37%, sulfur content 2.32%) was investigated. By roasting-magnetic dressing, the sulfur content was reduced to 0.52% when roasting at 300 ℃ for 2 h and magnetic dressing twice; By acid pickling, the sulfur content remained 0.57% under the condition of 60 ℃ and acid pickling for 1 h with 60% nitric acid solution; By calcining, 0.78% of sulfur was left if calcined for 0.5 h at 550 ℃. The experimental results indicate there is no obvious inhibition effect (corresponding maximal sulfur content 0.78%) when rectorite/poly (sodium acrylate-Co-acrylamide) is synthesized by in-situ aqueous solution polymerization with the purified rectorite clay as material. At 65-70 ℃, the water absorbencies (WA) of superabsorbent composite (containing 20% purified rectorite clay, 15% acrylamide, 0.25% initiator and 0.08% cross linker, with the neutralization degree of acrylic acid being 80%) in distilled water, tap water and 0.9% NaCl (aq) are 870, 250 and 68 respectively. When the content of rectorite is between 0%-30%, WA of superabsorbent composite is higher than that of superabsorbent resin that contains no rectorite. When WA of superabsorbent composite in distilled water is reduced from 870 g/g to 84 g/g, its gel strength rises from 49 g/cm2 to 235 g/cm2.
2007, 32(1): 111-118.
Abstract:
The potash slate of Bayan Obo REE-Nb-Fe deposit is characterized by potassium feldspar as major mineral phase enriched with potassium, from which potassium feldspar powder with purity up to 74% was prepared first. And then, with sodium carbonate as additives, the powder was calcinated at the temperature of 760 ℃ to 830 ℃, leading to thermal decomposition of potassium feldspar to form a mixture of sodium metesilicate and sodium (potassium) metaluminate. By injecting CO2 gas into the liquid coexisting with the calcinated materials and then filtrating it, the liquor became a solution of NaHCO3-KHCO3-H2O. By evaporating, crystallizing of NaHCO3, separating it from the liquid, and then purifying the residual liquor, evaporating, and crystallizing of KHCO3, owing to much lower solubility of the former, both of the precipitants were separated, and at last by calcinating the precipitants at 200 ℃ for 2 h, both sodium carbonate and potassium carbonate were prepared. The filtered aluminosilicate colloid was made into flyash-based mineral polymer with excellent mechanical properties and chemical stability. In this way, the components of K2O, Al2O3, and SiO2 in potassium feldspar of the ore are all made into industrial products, giving rise to nearly 100% output efficiency of the potassium feldspar resources, close to zero discharge of solid wastes, waste water, and exhaust gases. The technique is a "green process", characterized by energy conservation, and clean production. It is therefore feasible to be manufactured both for economic benefits and environmental friendliness.
The potash slate of Bayan Obo REE-Nb-Fe deposit is characterized by potassium feldspar as major mineral phase enriched with potassium, from which potassium feldspar powder with purity up to 74% was prepared first. And then, with sodium carbonate as additives, the powder was calcinated at the temperature of 760 ℃ to 830 ℃, leading to thermal decomposition of potassium feldspar to form a mixture of sodium metesilicate and sodium (potassium) metaluminate. By injecting CO2 gas into the liquid coexisting with the calcinated materials and then filtrating it, the liquor became a solution of NaHCO3-KHCO3-H2O. By evaporating, crystallizing of NaHCO3, separating it from the liquid, and then purifying the residual liquor, evaporating, and crystallizing of KHCO3, owing to much lower solubility of the former, both of the precipitants were separated, and at last by calcinating the precipitants at 200 ℃ for 2 h, both sodium carbonate and potassium carbonate were prepared. The filtered aluminosilicate colloid was made into flyash-based mineral polymer with excellent mechanical properties and chemical stability. In this way, the components of K2O, Al2O3, and SiO2 in potassium feldspar of the ore are all made into industrial products, giving rise to nearly 100% output efficiency of the potassium feldspar resources, close to zero discharge of solid wastes, waste water, and exhaust gases. The technique is a "green process", characterized by energy conservation, and clean production. It is therefore feasible to be manufactured both for economic benefits and environmental friendliness.
2007, 32(1): 119-122.
Abstract:
Immerse primary Mn ores in neutral solution, purify chemically, and manganese sulphate with high purity are obtained. Making use of the selective heating property of microwave, Mn3O4 powder can be prepared controllably. The best technology conditions were established through experiments. The samples are characterized by SEM, TEM, XRD and BET. The results show that using this method, high quality Mn3O4 can be prepared successfully from primary Mn ores with a high specific surface area of 28.27 m2/g.
Immerse primary Mn ores in neutral solution, purify chemically, and manganese sulphate with high purity are obtained. Making use of the selective heating property of microwave, Mn3O4 powder can be prepared controllably. The best technology conditions were established through experiments. The samples are characterized by SEM, TEM, XRD and BET. The results show that using this method, high quality Mn3O4 can be prepared successfully from primary Mn ores with a high specific surface area of 28.27 m2/g.
A Comparative Evaluation of Degree of Sustainable Development of Mineral Resources for a Mining City
2007, 32(1): 123-129.
Abstract:
In the perspective of development and circle economy, availability of mineral resources in a long term depends not only on their currently available amounts but also on future potential mineral resources (e.g., those undiscovered and low-grade ores) and substitutive renewable resources. Accordingly, a new concept of degree of sustainable development of mineral resources (DSDMR) is proposed to describe the ability of sustainable development of mineral resources to contribute to the development of human society. Its conceptual model, index system and regional six-factor judgment model are developed in the viewpoints of system science and sustainable development. They are used to evaluate the DSDMR of fifty representative Chinese mining cities in a quantitative way and their developing trends are indicated in the aspects of the type of mineral industry, age, location and size of the mining cities. The results show that the DSDMR of these Chinese mining cities decreases firstly in the type of mineral industry from petroleum to multi-resources to metallurgy to coal; secondly in city age from middle to young to old ages; thirdly in city location in China from eastern to western to central; and finally in city size from small to large and the above to middle. The results are expected to form a basis for decision-making in the exploration and the sustainable development of a mining city for a nation.
In the perspective of development and circle economy, availability of mineral resources in a long term depends not only on their currently available amounts but also on future potential mineral resources (e.g., those undiscovered and low-grade ores) and substitutive renewable resources. Accordingly, a new concept of degree of sustainable development of mineral resources (DSDMR) is proposed to describe the ability of sustainable development of mineral resources to contribute to the development of human society. Its conceptual model, index system and regional six-factor judgment model are developed in the viewpoints of system science and sustainable development. They are used to evaluate the DSDMR of fifty representative Chinese mining cities in a quantitative way and their developing trends are indicated in the aspects of the type of mineral industry, age, location and size of the mining cities. The results show that the DSDMR of these Chinese mining cities decreases firstly in the type of mineral industry from petroleum to multi-resources to metallurgy to coal; secondly in city age from middle to young to old ages; thirdly in city location in China from eastern to western to central; and finally in city size from small to large and the above to middle. The results are expected to form a basis for decision-making in the exploration and the sustainable development of a mining city for a nation.
2007, 32(1): 130-134.
Abstract:
A numerical method is put forward in this paper, using the boundary element method (BEM) to model 3D terrain effects on magnetotelluric (MT) surveys. Using vector integral theory and electromagnetic field boundary conditions, the boundary problem of two electromagnetic fields in the upper half space (air) and lower half space (earth medium) was transformed into two vector integral equations just related to the topography: one magnetic equation for computing the magnetic field and the other electrical equation for computing the electrical field. The topography integral is decomposed into a series of integrals in a triangle element. For the integral in a triangle element, we suppose that the electromagnetic field in it is the stack of the electromagnetic field in the homogeneous earth and the topography response which is a constant; so the computation becomes simple, convenient and highly accurate. By decomposition and computation, each vector integral equation can be calculated by solving three linear equations that are related to the three Cartesian directions. The matrix of these linear equations is diagonally dominant and can be solved using the Symmetric Successive Over-Relaxation (SSOR) method. The apparent resistivity curve of MT on two 3D terrains calculated by BEM is shown in this paper.
A numerical method is put forward in this paper, using the boundary element method (BEM) to model 3D terrain effects on magnetotelluric (MT) surveys. Using vector integral theory and electromagnetic field boundary conditions, the boundary problem of two electromagnetic fields in the upper half space (air) and lower half space (earth medium) was transformed into two vector integral equations just related to the topography: one magnetic equation for computing the magnetic field and the other electrical equation for computing the electrical field. The topography integral is decomposed into a series of integrals in a triangle element. For the integral in a triangle element, we suppose that the electromagnetic field in it is the stack of the electromagnetic field in the homogeneous earth and the topography response which is a constant; so the computation becomes simple, convenient and highly accurate. By decomposition and computation, each vector integral equation can be calculated by solving three linear equations that are related to the three Cartesian directions. The matrix of these linear equations is diagonally dominant and can be solved using the Symmetric Successive Over-Relaxation (SSOR) method. The apparent resistivity curve of MT on two 3D terrains calculated by BEM is shown in this paper.
2007, 32(1): 135-140.
Abstract:
The shallow iron ores of Daye mines are exhausted after years of exploration and mining. In order to search for deep-buried ores, the wavelet multi-scale analysis method was employed to decompose the magnetic anomaly into different scales and further explain the deep-buried unknown ore body through the combination of spectrum analysis. Theoretical modeling indicates that this method is superior to ordinary approaches such as analytical continuation, higher order derivatives, matched filter and so on. Magnetic data processing and interpretation of the Daye iron mines show that there is no large-scale iron ore below the depth of 1 000 m at its western part (Jianlinshan, Longdong and Tiemenkan), for the residual magnetic anomaly is not present in its five order wavelet approximation map. On the contrary, the residual anomaly still exists in the five order wavelet approximation map of the eastern mines (Jianshan, Litoushan), indicating the possible existence of iron ores at the depth of 1 000 m, which needs to be further researched.
The shallow iron ores of Daye mines are exhausted after years of exploration and mining. In order to search for deep-buried ores, the wavelet multi-scale analysis method was employed to decompose the magnetic anomaly into different scales and further explain the deep-buried unknown ore body through the combination of spectrum analysis. Theoretical modeling indicates that this method is superior to ordinary approaches such as analytical continuation, higher order derivatives, matched filter and so on. Magnetic data processing and interpretation of the Daye iron mines show that there is no large-scale iron ore below the depth of 1 000 m at its western part (Jianlinshan, Longdong and Tiemenkan), for the residual magnetic anomaly is not present in its five order wavelet approximation map. On the contrary, the residual anomaly still exists in the five order wavelet approximation map of the eastern mines (Jianshan, Litoushan), indicating the possible existence of iron ores at the depth of 1 000 m, which needs to be further researched.
2007, 32(1): 141-146.
Abstract:
Changes in the thermohaline circulation (THC) arising from the increase in the CO2 concentration in the atmosphere will dominate the future climate regimes. In this paper, a new climate model developed at Max-Planck Institute for Meteorology is targeted at the variation of THC strength, the changes in North Atlantic deep water (NADW) formation and the regional responses of the THC in the North Atlantic to the increasing atmospheric CO2. From 2000 to 2100, the increase in CO2 (B1, A1B and A2) will have decreased the strength of THC by 4 Sv, 5.1 Sv and 5.2 Sv, respectively, or equivalently, reduced by 20%, 25% and 25.1% of the present THC strength. This research indicates that oceanic deep convective activity is significantly strengthened in the Greenland-Iceland-Norway (GIN) Seas owing to saltier (denser) upper oceans, but is weakened both in the Labrador Sea and in the south of the Denmark Strait region (SDSR) because of surface warming and freshening derived from global warming. The saltiness of the GIN Seas is mainly initiated by the increase in the saline North Atlantic inflow through Faro-Bank (FB) Channel. Under the scenario A1B, the deep water formation rate in the North Atlantic decreases from 16.2 Sv to 12.9 Sv with a corresponding increase in CO2.
Changes in the thermohaline circulation (THC) arising from the increase in the CO2 concentration in the atmosphere will dominate the future climate regimes. In this paper, a new climate model developed at Max-Planck Institute for Meteorology is targeted at the variation of THC strength, the changes in North Atlantic deep water (NADW) formation and the regional responses of the THC in the North Atlantic to the increasing atmospheric CO2. From 2000 to 2100, the increase in CO2 (B1, A1B and A2) will have decreased the strength of THC by 4 Sv, 5.1 Sv and 5.2 Sv, respectively, or equivalently, reduced by 20%, 25% and 25.1% of the present THC strength. This research indicates that oceanic deep convective activity is significantly strengthened in the Greenland-Iceland-Norway (GIN) Seas owing to saltier (denser) upper oceans, but is weakened both in the Labrador Sea and in the south of the Denmark Strait region (SDSR) because of surface warming and freshening derived from global warming. The saltiness of the GIN Seas is mainly initiated by the increase in the saline North Atlantic inflow through Faro-Bank (FB) Channel. Under the scenario A1B, the deep water formation rate in the North Atlantic decreases from 16.2 Sv to 12.9 Sv with a corresponding increase in CO2.
