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, Available online , doi: 10.31035/cg2021073
Abstract:
Based on the comprehensive study of geology and geophysics in African continent, three types of lithosphere (craton-type, orogenic-type and rift-type) can be identified. Considering lithosphere discontinuities as the boundary, two first-order tectonic units (mainly cratonic-type in the West and rift-type in the East) are proposed. Different types of lithosphere can be divided into secondary-order and third-order structural units, and the blocks within lithosphere can be further divided into fourth-order structural units. The geological history, the formation process and significance of different types of lithosphere in African continent are briefly discussed.
Based on the comprehensive study of geology and geophysics in African continent, three types of lithosphere (craton-type, orogenic-type and rift-type) can be identified. Considering lithosphere discontinuities as the boundary, two first-order tectonic units (mainly cratonic-type in the West and rift-type in the East) are proposed. Different types of lithosphere can be divided into secondary-order and third-order structural units, and the blocks within lithosphere can be further divided into fourth-order structural units. The geological history, the formation process and significance of different types of lithosphere in African continent are briefly discussed.
, Available online , doi: 10.31035/cg2021079
Abstract:
The eastern Central Asian Orogenic Belt (CAOB) in NE China is a key area for investigating continental growth. However, the complexity of its Paleozoic geological history has meant that the tectonic development of this belt is not fully understood. NE China is composed of the Erguna and Jiamusi blocks in the northern and eastern parts and the Xing'an and Songliao–Xilinhot accretionary terranes in the central and southern parts. The Erguna and Jiamusi blocks have Precambrian basements with Siberia and Gondwana affinities, respectively. In contrast, the Xing'an and Songliao–Xilinhot accretionary terranes were formed via subduction and collision processes. These blocks and terranes were separated by the Xinlin–Xiguitu, Heilongjiang, Nenjiang, and Solonker oceans from north to south, and these oceans closed during the Cambrian (ca. 500 Ma), Late Silurian (ca. 420 Ma), early Late Carboniferous (ca. 320 Ma), and Late Permian to Middle Triassic (260–240 Ma), respectively, forming the Xinlin–Xiguitu, Mudanjiang–Yilan, Hegenshan–Heihe, Solonker–Linxi, and Changchun–Yanji suture zones. Two oceanic tectonic cycles took place in the eastern Paleo–Asian Ocean (PAO), namely, the Early Paleozoic cycle involving the Xinlin–Xiguitu and Heilongjiang oceans and the late Paleozoic cycle involving the Nenjiang–Solonker oceans. The Paleozoic tectonic pattern of the eastern CAOB generally shows structural features that trend east–west. The timing of accretion and collision events of the eastern CAOB during the Paleozoic youngs progressively from north to south. The branch ocean basins of the eastern PAO closed from west to east in a scissor-like manner. A bi-directional subduction regime dominated during the narrowing and closure process of the eastern PAO, which led to “soft collision” of tectonic units on each side, forming huge accretionary mountain belts in central Asia.
The eastern Central Asian Orogenic Belt (CAOB) in NE China is a key area for investigating continental growth. However, the complexity of its Paleozoic geological history has meant that the tectonic development of this belt is not fully understood. NE China is composed of the Erguna and Jiamusi blocks in the northern and eastern parts and the Xing'an and Songliao–Xilinhot accretionary terranes in the central and southern parts. The Erguna and Jiamusi blocks have Precambrian basements with Siberia and Gondwana affinities, respectively. In contrast, the Xing'an and Songliao–Xilinhot accretionary terranes were formed via subduction and collision processes. These blocks and terranes were separated by the Xinlin–Xiguitu, Heilongjiang, Nenjiang, and Solonker oceans from north to south, and these oceans closed during the Cambrian (ca. 500 Ma), Late Silurian (ca. 420 Ma), early Late Carboniferous (ca. 320 Ma), and Late Permian to Middle Triassic (260–240 Ma), respectively, forming the Xinlin–Xiguitu, Mudanjiang–Yilan, Hegenshan–Heihe, Solonker–Linxi, and Changchun–Yanji suture zones. Two oceanic tectonic cycles took place in the eastern Paleo–Asian Ocean (PAO), namely, the Early Paleozoic cycle involving the Xinlin–Xiguitu and Heilongjiang oceans and the late Paleozoic cycle involving the Nenjiang–Solonker oceans. The Paleozoic tectonic pattern of the eastern CAOB generally shows structural features that trend east–west. The timing of accretion and collision events of the eastern CAOB during the Paleozoic youngs progressively from north to south. The branch ocean basins of the eastern PAO closed from west to east in a scissor-like manner. A bi-directional subduction regime dominated during the narrowing and closure process of the eastern PAO, which led to “soft collision” of tectonic units on each side, forming huge accretionary mountain belts in central Asia.
, Available online , doi: 10.31035/cg2021067
Abstract:
The Neoproterozoic Sugetbrak Formation in the Aksu area, which is located at the northwest margin of Tarim Block, comprises mafic rocks and provides key records of the evolution of the Rodinia supercontinent. However, the genetic relationship among these mafic rocks exposed in different geographical sections are still unclear. In this study, the petrology, geochemistry, and Sr-Nd-Pb isotope geochemistry of the mafic rocks exposed in the Aksu-Wushi and Yuermeinark areas have been studied in some detail along three sections. The authors found that the mafic rocks in these three typical sections were mainly composed of pyroxene and plagioclase, containing a small amount of Fe-Ti oxides and with typical diabasic textures. All the mafic rocks in this region also showed similar geochemical compositions. They were characterised by high TiO2 contents (1.47%–3.59%) and low MgO (3.52%–7.88%), K2O (0.12%–1.21%). Large ionic lithophile elements (LILEs) (e.g., Rb, Sr, and Cs) were significantly depleted. Meanwhile, high field strength elements (HFSEs) were relatively enriched. In the samples, light rare earth elements (LREEs) were enriched, while heavy rare earth elements (HREEs) were depleted. Based on the Zr/Nb, Nb/Y, and Zr/TiO2 ratios, the Aksu mafic rocks belong to a series of sub-alkaline and alkaline transitional rocks. The mafic rocks along the three typical sections showed similar initial values of 87Sr/86Sr (ISr) (0.7052–0.7097) and εNd(t) (–0.70 to –5.35), while the Pb isotopic compositions with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 16.908–17.982, 15.487–15.721, 37.276–38.603, respectively. Most of the samples plot into the area near EM-Ⅰ, indicating that the magma of the mafic rocks might have derived from a relatively enriched mantle with some crustal materials involved. The geochemical element characteristics of most samples showed typical OIB-type geochemical characteristics indicating that the source region had received metasomatism of recycled materials. Combining with the regional geological background and geochemical data, we inferred that the mafic rocks of the Sugetbrak Formation in the Aksu area were formed in an intraplate rift environment. Summarily, based on our study, the mafic rocks of the Sugetbrak Formation in the Aksu area were derived from a common enriched mantle source, and they were product of a magmatic event during the rift development period caused by the breakup of the Rodinia supercontinent.
The Neoproterozoic Sugetbrak Formation in the Aksu area, which is located at the northwest margin of Tarim Block, comprises mafic rocks and provides key records of the evolution of the Rodinia supercontinent. However, the genetic relationship among these mafic rocks exposed in different geographical sections are still unclear. In this study, the petrology, geochemistry, and Sr-Nd-Pb isotope geochemistry of the mafic rocks exposed in the Aksu-Wushi and Yuermeinark areas have been studied in some detail along three sections. The authors found that the mafic rocks in these three typical sections were mainly composed of pyroxene and plagioclase, containing a small amount of Fe-Ti oxides and with typical diabasic textures. All the mafic rocks in this region also showed similar geochemical compositions. They were characterised by high TiO2 contents (1.47%–3.59%) and low MgO (3.52%–7.88%), K2O (0.12%–1.21%). Large ionic lithophile elements (LILEs) (e.g., Rb, Sr, and Cs) were significantly depleted. Meanwhile, high field strength elements (HFSEs) were relatively enriched. In the samples, light rare earth elements (LREEs) were enriched, while heavy rare earth elements (HREEs) were depleted. Based on the Zr/Nb, Nb/Y, and Zr/TiO2 ratios, the Aksu mafic rocks belong to a series of sub-alkaline and alkaline transitional rocks. The mafic rocks along the three typical sections showed similar initial values of 87Sr/86Sr (ISr) (0.7052–0.7097) and εNd(t) (–0.70 to –5.35), while the Pb isotopic compositions with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 16.908–17.982, 15.487–15.721, 37.276–38.603, respectively. Most of the samples plot into the area near EM-Ⅰ, indicating that the magma of the mafic rocks might have derived from a relatively enriched mantle with some crustal materials involved. The geochemical element characteristics of most samples showed typical OIB-type geochemical characteristics indicating that the source region had received metasomatism of recycled materials. Combining with the regional geological background and geochemical data, we inferred that the mafic rocks of the Sugetbrak Formation in the Aksu area were formed in an intraplate rift environment. Summarily, based on our study, the mafic rocks of the Sugetbrak Formation in the Aksu area were derived from a common enriched mantle source, and they were product of a magmatic event during the rift development period caused by the breakup of the Rodinia supercontinent.
, Available online , doi: 10.31035/cg2021069
Abstract:
The shale gas resources in China have great potential and they are distributed in 13 stratigraphic series from the Mesoproterozoic to the Cenozoic. Organic-rich shales can be divided into three types according to their sedimentary environments, namely marine, marine-continental transitional, and continental shales. The geological resources of shale gas in China is over 100 trillion m3, which includes 20 trillion m3 of recoverable resources. The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas, and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation - Lower Silurian Longmaxi Formation in these areas, with a shale gas production of up to 20 ×109 m3 in 2020. China has seen rapid shale gas exploration and development over the last five years, successively achieving breakthroughs and important findings in many areas and strata. The details are as follows. (1) Large-scale development of middle-shallow shale gas (burial depth: less than 3500 m) has been realized, with the productivity having rapidly increased; (2) Breakthroughs have been constantly made in the development of deep shale gas (burial depth: 3500‒4500 m), and the ultra-deep shale gas (burial depth: greater than 4500 m) is under testing; (3) Breakthroughs have been made in the development of normal-pressure shale gas, and the assessment of the shale gas in complex tectonic areas is being accelerated; (4) Shale gas has been frequently discovered in new areas and new strata, exhibiting a great prospect. Based on the exploration and development practice, three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China. (1) In terms of deep-water fine-grained sediments, organic-rich shales are the base for the formation of shale gas; (2) In terms of high-quality reservoirs, the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation; (3) In terms of preservation conditions, weak structural transformation, a moderate degree of thermal evolution, and a high pressure coefficient are the key to shale gas enrichment. As a type of important low-carbon fossil energy, shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality. Based on the in-depth study of shale gas geological conditions and current exploration progress, three important directions for shale gas exploration in China in the next five years are put forward.
The shale gas resources in China have great potential and they are distributed in 13 stratigraphic series from the Mesoproterozoic to the Cenozoic. Organic-rich shales can be divided into three types according to their sedimentary environments, namely marine, marine-continental transitional, and continental shales. The geological resources of shale gas in China is over 100 trillion m3, which includes 20 trillion m3 of recoverable resources. The Sichuan Basin and its surrounding areas have the highest geological resources of shale gas, and the commercial development of shale gas has been achieved in the Upper Ordovician Wufeng Formation - Lower Silurian Longmaxi Formation in these areas, with a shale gas production of up to 20 ×109 m3 in 2020. China has seen rapid shale gas exploration and development over the last five years, successively achieving breakthroughs and important findings in many areas and strata. The details are as follows. (1) Large-scale development of middle-shallow shale gas (burial depth: less than 3500 m) has been realized, with the productivity having rapidly increased; (2) Breakthroughs have been constantly made in the development of deep shale gas (burial depth: 3500‒4500 m), and the ultra-deep shale gas (burial depth: greater than 4500 m) is under testing; (3) Breakthroughs have been made in the development of normal-pressure shale gas, and the assessment of the shale gas in complex tectonic areas is being accelerated; (4) Shale gas has been frequently discovered in new areas and new strata, exhibiting a great prospect. Based on the exploration and development practice, three aspects of consensus have been gradually reached on the research progress in the geological theories of shale gas achieved in China. (1) In terms of deep-water fine-grained sediments, organic-rich shales are the base for the formation of shale gas; (2) In terms of high-quality reservoirs, the development of micro-nano organic matter-hosted pores serves as the core of shale gas accumulation; (3) In terms of preservation conditions, weak structural transformation, a moderate degree of thermal evolution, and a high pressure coefficient are the key to shale gas enrichment. As a type of important low-carbon fossil energy, shale gas will play an increasingly important role in achieving the strategic goals of peak carbon dioxide emissions and carbon neutrality. Based on the in-depth study of shale gas geological conditions and current exploration progress, three important directions for shale gas exploration in China in the next five years are put forward.
, Available online , doi: 10.31035/cg2021065
Abstract:
The Jiama porphyry copper deposit in Tibet is one of the proven ultra-large-scale copper deposits in the Qinghai-Tibet Plateau at present, with the reserves of geological resources equivalent to nearly 20×106 t. However, it features wavy and steep terrain, leading to extremely difficult field operation and heavy interference. This study attempts to determine the effects of the tensor controlled-source audio-magnetotellurics (CSAMT) with high-power orthogonal signal sources (also referred to as the high-power tensor CSAMT) when it is applied to the deep geophysical exploration in plateaus with complex terrain and mining areas with strong interference. The test results show that the high current provided by the high-power tensor CSAMT not only greatly improved the signal-to-noise ratio but also guaranteed that effective signals were received in the case of a long transmitter-receiver distance. Meanwhile, the tensor data better described the anisotropy of deep geologic bodies. In addition, the tests also show that when the transmitting current reaches 60 A, it is still guaranteed that strong enough signals can be received in the case of the transmitter-receiver distance of about 25 km, sounding curves show no near field effect, and effective exploration depth can reach 3 km. The 2D inversion results are roughly consistent with drilling results, indicating that the high-power tensor CSAMT can be used to achieve nearly actual characteristics of underground electrical structures. Therefore, this method has great potential for application in deep geophysical exploration in plateaus and mining areas with complex terrain and strong interference, respectively. This study not only serves as important guidance on the prospecting in the Qinghai-Tibet Plateau but also can be used as positive references for deep mineral exploration in other areas.
The Jiama porphyry copper deposit in Tibet is one of the proven ultra-large-scale copper deposits in the Qinghai-Tibet Plateau at present, with the reserves of geological resources equivalent to nearly 20×106 t. However, it features wavy and steep terrain, leading to extremely difficult field operation and heavy interference. This study attempts to determine the effects of the tensor controlled-source audio-magnetotellurics (CSAMT) with high-power orthogonal signal sources (also referred to as the high-power tensor CSAMT) when it is applied to the deep geophysical exploration in plateaus with complex terrain and mining areas with strong interference. The test results show that the high current provided by the high-power tensor CSAMT not only greatly improved the signal-to-noise ratio but also guaranteed that effective signals were received in the case of a long transmitter-receiver distance. Meanwhile, the tensor data better described the anisotropy of deep geologic bodies. In addition, the tests also show that when the transmitting current reaches 60 A, it is still guaranteed that strong enough signals can be received in the case of the transmitter-receiver distance of about 25 km, sounding curves show no near field effect, and effective exploration depth can reach 3 km. The 2D inversion results are roughly consistent with drilling results, indicating that the high-power tensor CSAMT can be used to achieve nearly actual characteristics of underground electrical structures. Therefore, this method has great potential for application in deep geophysical exploration in plateaus and mining areas with complex terrain and strong interference, respectively. This study not only serves as important guidance on the prospecting in the Qinghai-Tibet Plateau but also can be used as positive references for deep mineral exploration in other areas.
, Available online , doi: 10.31035/cg2021048
Abstract:
The Paleoproterozoic tectonic evolution of the Bangweulu Block has long been controversial. Paleoproterozoic granites consisting of the basement complex of the Bangweulu Block are widely exposed in northeastern Zambia, and they are the critical media for studying the tectonic evolution of the Bangweulu Block. This study systematically investigated the petrography, zircon U-Pb chronology, and petrogeochemistry of the granitoid extensively exposed in the Lunte area, northeastern Zambia. The results show that the granitoid in the area formed during 2051±13–2009±20 Ma as a result of Paleoproterozoic magmatic events. Geochemical data show that the granites in the area mainly include syenogranites and monzogranites of high-K calc-alkaline series and are characterized by high SiO2 content (72.68%‒73.78%) and K2O/Na2O ratio (1.82‒2.29). The presence of garnets, the high aluminum saturation index (A/CNK is 1.13‒1.21), and the 1.27%‒1.95% of corundum molecules jointly indicate that granites in the Lunte area are S-type granites. Rare earth elements in all samples show a rightward inclination and noticeably negative Eu-anomalies (δEu = 0.16‒0.40) and are relatively rich in light rare earth elements. Furthermore, the granites are rich in large ion lithophile elements such as Rb, Th, U, and K and are depleted in Ba, Sr, and high field strength elements such as Ta and Nb. In addition, they bear low contents of Cr (6.31×10−6‒10.8×10−6), Ni (2.87×10−6‒4.76×10−6), and Co (2.62×10−6‒3.96×10−6). These data lead to the conclusion that the source rocks are meta-sedimentary rocks. Combining the above results and the study of regional tectonic evolution, the authors suggest that granitoid in the Lunte area were formed in a tectonic environment corresponding to the collision between the Tanzania Craton and the Bangweulu Block. The magmatic activities in this period may be related to the assembly of the Columbia supercontinent.
The Paleoproterozoic tectonic evolution of the Bangweulu Block has long been controversial. Paleoproterozoic granites consisting of the basement complex of the Bangweulu Block are widely exposed in northeastern Zambia, and they are the critical media for studying the tectonic evolution of the Bangweulu Block. This study systematically investigated the petrography, zircon U-Pb chronology, and petrogeochemistry of the granitoid extensively exposed in the Lunte area, northeastern Zambia. The results show that the granitoid in the area formed during 2051±13–2009±20 Ma as a result of Paleoproterozoic magmatic events. Geochemical data show that the granites in the area mainly include syenogranites and monzogranites of high-K calc-alkaline series and are characterized by high SiO2 content (72.68%‒73.78%) and K2O/Na2O ratio (1.82‒2.29). The presence of garnets, the high aluminum saturation index (A/CNK is 1.13‒1.21), and the 1.27%‒1.95% of corundum molecules jointly indicate that granites in the Lunte area are S-type granites. Rare earth elements in all samples show a rightward inclination and noticeably negative Eu-anomalies (δEu = 0.16‒0.40) and are relatively rich in light rare earth elements. Furthermore, the granites are rich in large ion lithophile elements such as Rb, Th, U, and K and are depleted in Ba, Sr, and high field strength elements such as Ta and Nb. In addition, they bear low contents of Cr (6.31×10−6‒10.8×10−6), Ni (2.87×10−6‒4.76×10−6), and Co (2.62×10−6‒3.96×10−6). These data lead to the conclusion that the source rocks are meta-sedimentary rocks. Combining the above results and the study of regional tectonic evolution, the authors suggest that granitoid in the Lunte area were formed in a tectonic environment corresponding to the collision between the Tanzania Craton and the Bangweulu Block. The magmatic activities in this period may be related to the assembly of the Columbia supercontinent.
, Available online , doi: 10.31035/cg2021038
Abstract:
To illuminate the migration and transformation of selenium (Se) in the igneous rock-soil-rice system, 285 pairs of rhizosphere soil and rice samples were collected from the granitoid and basalt areas in Hainan Province, South China. The contents of Se in soils derived from granitoid and basalt are, respectively, 0.19±0.12 mg/kg and 0.34±0.39 mg/kg, which are much higher than Se contents in granitoid and basalt. Selenium shows remarkable enrichment from granitoid and basalt to soils. The mobile fraction of Se in soils derived from granitoid is 0.0100±0.0034 mg/kg, which is significantly higher than that of basalt (0.0058±0.0039 mg/kg). Although soil derived from basalt shows higher Se contents, Se contents in rice samples, mobile fractions of Se in soils, and biological concentration factor (BCF) is similar or even lower than that from granitoid. Basalt consist of calcic plagioclase and pyroxene, and are much richer in Fe, Al, and Ca than granitoid. Correspondingly, the basalt-derived soils have higher goethite, hematite, kaolinite, cation exchange capacity (CEC) content, and higher pH than the granitoid-derived soils, which result in higher adsorption capacity for Se and relatively lower Se bioavailability. Soils derived from granitoid and basalt in tropical regions are beneficial to produce Se-rich rice.
To illuminate the migration and transformation of selenium (Se) in the igneous rock-soil-rice system, 285 pairs of rhizosphere soil and rice samples were collected from the granitoid and basalt areas in Hainan Province, South China. The contents of Se in soils derived from granitoid and basalt are, respectively, 0.19±0.12 mg/kg and 0.34±0.39 mg/kg, which are much higher than Se contents in granitoid and basalt. Selenium shows remarkable enrichment from granitoid and basalt to soils. The mobile fraction of Se in soils derived from granitoid is 0.0100±0.0034 mg/kg, which is significantly higher than that of basalt (0.0058±0.0039 mg/kg). Although soil derived from basalt shows higher Se contents, Se contents in rice samples, mobile fractions of Se in soils, and biological concentration factor (BCF) is similar or even lower than that from granitoid. Basalt consist of calcic plagioclase and pyroxene, and are much richer in Fe, Al, and Ca than granitoid. Correspondingly, the basalt-derived soils have higher goethite, hematite, kaolinite, cation exchange capacity (CEC) content, and higher pH than the granitoid-derived soils, which result in higher adsorption capacity for Se and relatively lower Se bioavailability. Soils derived from granitoid and basalt in tropical regions are beneficial to produce Se-rich rice.
, Available online , doi: 10.31035/cg2021040
Abstract:
The estuary and coastal zone are the key areas for socio-economic development, and they are also the important channels for pollutants transported to the sea. The construction of the Jiaozhou Bay Bridge changed the hydrodynamic condition of the bay, which made the self-purification capacity of the bay weakened and the pollution in the estuary and adjacent coastal zone become more serious. In this study, 55 surface sediment samples were collected from the three seriously polluted estuaries and the adjacent coastal zone of Jiaozhou Bay to comprehensively study how the benthic foraminifera response to heavy metal pollution and human engineering, and to assess the ecological risks of the bay. A total of 80 species, belonging to 42 genera, were identified in this study. The results showed that Cu, Pb, Cr, Hg, Zn, and As had low to median ecological risks in the study area which would definitely affect the ecological system. The construction of the Jiaozhou Bay Bridge has resulted in pollutants accumulated at the river mouth of Loushan River, which has adverse effects on the survival and growth of benthic foraminifera. The lowest population density and diversity as well as the highest FAI (Foraminiferal Abnormality Index) and FMI (Foraminiferal Monitoring Index) occurred at Loushan River Estuary which indicated that the ecological environment of the northeastern part of Jiaozhou Bay (Loushan River Estuary) had been seriously damaged. Licun River and Haipo River estuaries and the adjacent coastal zone were slightly polluted and had low ecological risk. As a consequence, it suggested that the supervision of industrial and domestic waste discharge and the protection of the ecological environment in northeast Jiaozhou Bay should be paid more attention..
The estuary and coastal zone are the key areas for socio-economic development, and they are also the important channels for pollutants transported to the sea. The construction of the Jiaozhou Bay Bridge changed the hydrodynamic condition of the bay, which made the self-purification capacity of the bay weakened and the pollution in the estuary and adjacent coastal zone become more serious. In this study, 55 surface sediment samples were collected from the three seriously polluted estuaries and the adjacent coastal zone of Jiaozhou Bay to comprehensively study how the benthic foraminifera response to heavy metal pollution and human engineering, and to assess the ecological risks of the bay. A total of 80 species, belonging to 42 genera, were identified in this study. The results showed that Cu, Pb, Cr, Hg, Zn, and As had low to median ecological risks in the study area which would definitely affect the ecological system. The construction of the Jiaozhou Bay Bridge has resulted in pollutants accumulated at the river mouth of Loushan River, which has adverse effects on the survival and growth of benthic foraminifera. The lowest population density and diversity as well as the highest FAI (Foraminiferal Abnormality Index) and FMI (Foraminiferal Monitoring Index) occurred at Loushan River Estuary which indicated that the ecological environment of the northeastern part of Jiaozhou Bay (Loushan River Estuary) had been seriously damaged. Licun River and Haipo River estuaries and the adjacent coastal zone were slightly polluted and had low ecological risk. As a consequence, it suggested that the supervision of industrial and domestic waste discharge and the protection of the ecological environment in northeast Jiaozhou Bay should be paid more attention..
, Available online , doi: 10.31035/cg2021045
Abstract:
Bangong-Nujiang collisional zone (BNCZ) is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt, which plays an important role in evaluating the formation and uplift mechanism of plateau. The northern and central Lhasa Terrane composed the southern part of the BNCZ. Since ore deposits can be used as markers of geodynamic evolution, we carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization, and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane. We find Early Cretaceous magma mainly resulted in Cu, Mo mineralization, Late Cretaceous magma mainly resulted in Cu, Mo, and W mineralization in the studying area. The results suggest a southward subduction, slab rolling back and break-off, and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.
Bangong-Nujiang collisional zone (BNCZ) is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt, which plays an important role in evaluating the formation and uplift mechanism of plateau. The northern and central Lhasa Terrane composed the southern part of the BNCZ. Since ore deposits can be used as markers of geodynamic evolution, we carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization, and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane. We find Early Cretaceous magma mainly resulted in Cu, Mo mineralization, Late Cretaceous magma mainly resulted in Cu, Mo, and W mineralization in the studying area. The results suggest a southward subduction, slab rolling back and break-off, and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.
, Available online , doi: 10.31035/cg2021035
Abstract:
Source rock assessment is a key step in any petroleum exploration activity. The results of Rock-Eval analysis showed that Sarchahan Formation was in the late oil window, while the Faraghun and Zakeen Formations were just in the early stages of the oil window. Furthermore, Sarchahan, Zakeen and Faraghun Formations exhibited different kerogen types (types-Ⅱ, types-Ⅲ and type-Ⅲ, respectively). Refining the kinetic parameters using the OPTKIN software, the error function returned error values below 0.1, indicating accurate optimization of the kinetic parameters. Based on the obtained values of activation energy, it was clear that Sarchahan Formation contained type-Ⅱ kerogen with an activation energy of 48–52 kcal/mol, while Zakeen and Faraghun Formations contained type-III kerogen with activation energies of 70–80 kcal/mol and 44–56 kcal/mol, respectively. The geographical distribution of the samples studied in this work, it was found that the organic matter (OM) quantity and quality increased as one moved toward the Coastal Fars in Sarchahan Formation. The same trend was observed as one moved from the southern coasts of Iran toward the shaly and coaly portions of Faraghun Formation in the center of the Persian Gulf.
Source rock assessment is a key step in any petroleum exploration activity. The results of Rock-Eval analysis showed that Sarchahan Formation was in the late oil window, while the Faraghun and Zakeen Formations were just in the early stages of the oil window. Furthermore, Sarchahan, Zakeen and Faraghun Formations exhibited different kerogen types (types-Ⅱ, types-Ⅲ and type-Ⅲ, respectively). Refining the kinetic parameters using the OPTKIN software, the error function returned error values below 0.1, indicating accurate optimization of the kinetic parameters. Based on the obtained values of activation energy, it was clear that Sarchahan Formation contained type-Ⅱ kerogen with an activation energy of 48–52 kcal/mol, while Zakeen and Faraghun Formations contained type-III kerogen with activation energies of 70–80 kcal/mol and 44–56 kcal/mol, respectively. The geographical distribution of the samples studied in this work, it was found that the organic matter (OM) quantity and quality increased as one moved toward the Coastal Fars in Sarchahan Formation. The same trend was observed as one moved from the southern coasts of Iran toward the shaly and coaly portions of Faraghun Formation in the center of the Persian Gulf.
, Available online , doi: 10.31035/cg2021024
Abstract:
The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.
The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.
, Available online , doi: 10.31035/cg2021043
Abstract:
The Hekoulinchang Sn polymetallic deposit (20000 t Sn at 0.27%, 236 t Ag at 122.89 g/t, 15000 t Pb at 0.84%, and 38000 t Zn at 1.43%) is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt. The timing of Sn polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals. The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma, respectively, indicating that Sn mineralization and magmatism occurred during the Early Cretaceous. The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb, Ta, and Ti and enriched in Rb, Th, U, and Pb. The εHf(t) values of the granite porphyry range from 0.9 to 7.4, with an average of about 5.6 and two-stage model ages (TDM2) of 705–1116 Ma, with an average age of 819 Ma. The εNd(t) values of the apatites are –1.60–0.45, with an average of –0.9, and two-stage model ages (TDM2) of 872–1040 Ma, with an average age of 983 Ma. The Nd–Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.
The Hekoulinchang Sn polymetallic deposit (20000 t Sn at 0.27%, 236 t Ag at 122.89 g/t, 15000 t Pb at 0.84%, and 38000 t Zn at 1.43%) is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt. The timing of Sn polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals. The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma, respectively, indicating that Sn mineralization and magmatism occurred during the Early Cretaceous. The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb, Ta, and Ti and enriched in Rb, Th, U, and Pb. The εHf(t) values of the granite porphyry range from 0.9 to 7.4, with an average of about 5.6 and two-stage model ages (TDM2) of 705–1116 Ma, with an average age of 819 Ma. The εNd(t) values of the apatites are –1.60–0.45, with an average of –0.9, and two-stage model ages (TDM2) of 872–1040 Ma, with an average age of 983 Ma. The Nd–Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.
, Available online , doi: 10.31035/cg2021044
Abstract:
A method is proposed for the prospecting prediction of subsurface mineral deposits based on soil geochemistry data and a deep convolutional neural network model. This method uses three techniques (window offset, scaling, and rotation) to enhance the number of training data for the model. A window area is used to extract the spatial distribution characteristics of soil geochemistry and measure their correspondence with the occurrence of known subsurface deposits. Prospecting prediction is achieved by matching the characteristics of the window area of an unknown area with the relationships established in the known area. This method can efficiently predict ore prospective areas where there are few ore deposits used for generating the training dataset, meaning that the deep-learning method can be effectively used for deposit prospecting prediction. Using soil active geochemical measurement data, this method was applied in the Daqiao area, Gansu, for which seven favorable gold prospecting target areas were predicted. The new method should be applicable to prospecting prediction using conventional geochemical data in other areas.
A method is proposed for the prospecting prediction of subsurface mineral deposits based on soil geochemistry data and a deep convolutional neural network model. This method uses three techniques (window offset, scaling, and rotation) to enhance the number of training data for the model. A window area is used to extract the spatial distribution characteristics of soil geochemistry and measure their correspondence with the occurrence of known subsurface deposits. Prospecting prediction is achieved by matching the characteristics of the window area of an unknown area with the relationships established in the known area. This method can efficiently predict ore prospective areas where there are few ore deposits used for generating the training dataset, meaning that the deep-learning method can be effectively used for deposit prospecting prediction. Using soil active geochemical measurement data, this method was applied in the Daqiao area, Gansu, for which seven favorable gold prospecting target areas were predicted. The new method should be applicable to prospecting prediction using conventional geochemical data in other areas.
, Available online , doi: 10.31035/cg2021034
Abstract:
The 1∶1000000 geochemical mapping of Zambia provides catchment sediment geochemical data for 58 elements including Au from 746 sediment samples at 736 sampling sites, corresponding to a sampling density of about one site per 1000 km2. Under strict quality control using field duplicates, certified reference materials, and analytical replicate samples, the Au was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The detection limit of Au was 0.20 × 10−9. The 95% range (2.5%–97.5%) of Au concentrations was from 0.24 × 10−9 to 1.36 × 10−9, and the median value was 0.40 × 10−9. The most noticeable Au distribution patterns shown on the map are mainly located between Lusaka and Ndola (Lufilian Arc Belt). In addition, several high Au value areas occurred in Mansa, Muyombe, Chipata, and Livingstone. The spatial distribution patterns of Au in tectonic units, drainage basins, and geomorphological landscapes could be related to the Lufilian Arc Belt and Bangweulu Block. The Au concentrations show metallogenic belts between Muyombe and Mbala areas, between Mansa and Ndola areas, and between Lusaka and Kasempa areas.
The 1∶1000000 geochemical mapping of Zambia provides catchment sediment geochemical data for 58 elements including Au from 746 sediment samples at 736 sampling sites, corresponding to a sampling density of about one site per 1000 km2. Under strict quality control using field duplicates, certified reference materials, and analytical replicate samples, the Au was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The detection limit of Au was 0.20 × 10−9. The 95% range (2.5%–97.5%) of Au concentrations was from 0.24 × 10−9 to 1.36 × 10−9, and the median value was 0.40 × 10−9. The most noticeable Au distribution patterns shown on the map are mainly located between Lusaka and Ndola (Lufilian Arc Belt). In addition, several high Au value areas occurred in Mansa, Muyombe, Chipata, and Livingstone. The spatial distribution patterns of Au in tectonic units, drainage basins, and geomorphological landscapes could be related to the Lufilian Arc Belt and Bangweulu Block. The Au concentrations show metallogenic belts between Muyombe and Mbala areas, between Mansa and Ndola areas, and between Lusaka and Kasempa areas.
, Available online , doi: 10.31035/cg2020052
Abstract:
The Cenozoic basalts with OIB-affinity in northern marginal region of the North China Craton are thought to experience minor even no crustal contamination during the magma evolution. The whole-rock Sr-Nd-Pb-Hf isotopes are attributed to a two-component mixing between depleted and enriched mantle sources, while the major element variations are controlled by the fractional crystallization of olivine and clinopyroxene. However, in this study, our new Os isotopic data proposes an opposite model for the Cenozoic basalts in northern marginal region of the North China Craton. In this model, the Jining basalts were contaminated by the Archean mafic rocks during the magma storage and ascent. The crustal contamination process is supported by (1) the highly radiogenic Os isotopic compositions, and (2) the positive correlation between 187Os/188Os and 1/Os of the Jining basalts. By modeling the Os isotopic composition of the basalts, an incorporation of < 10% mafic granulites/amphibolites to the parental magma can successfully explain the initial values of highly radiogenic Os. In contrast, the unradiogenic and uniform Os isotopic compositions of the Chifeng basalts suggest negligible crustal contamination. Os isotopic data acts as an indicator of crustal contamination during magma evolution, providing us a novel insight into the evolution of the intra-continental OIB-like basalts worldwide.
The Cenozoic basalts with OIB-affinity in northern marginal region of the North China Craton are thought to experience minor even no crustal contamination during the magma evolution. The whole-rock Sr-Nd-Pb-Hf isotopes are attributed to a two-component mixing between depleted and enriched mantle sources, while the major element variations are controlled by the fractional crystallization of olivine and clinopyroxene. However, in this study, our new Os isotopic data proposes an opposite model for the Cenozoic basalts in northern marginal region of the North China Craton. In this model, the Jining basalts were contaminated by the Archean mafic rocks during the magma storage and ascent. The crustal contamination process is supported by (1) the highly radiogenic Os isotopic compositions, and (2) the positive correlation between 187Os/188Os and 1/Os of the Jining basalts. By modeling the Os isotopic composition of the basalts, an incorporation of < 10% mafic granulites/amphibolites to the parental magma can successfully explain the initial values of highly radiogenic Os. In contrast, the unradiogenic and uniform Os isotopic compositions of the Chifeng basalts suggest negligible crustal contamination. Os isotopic data acts as an indicator of crustal contamination during magma evolution, providing us a novel insight into the evolution of the intra-continental OIB-like basalts worldwide.
, Available online , doi: 10.31035/cg2021033
Abstract:
The A-type granites with highly positive εNd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic source, and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon εHf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (e.g., high SiO2 and K2O contents, enriched LILEs (except Sr), depleted Sr, Ta, and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (range: 315 Ma to 305 Ma) and moderate 18O enrichments (δ18Ozircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (range: 305 Ma to 301 Ma) with higher 18O enrichments (δ18Ozircon=+8.72‰–+9.89‰). The authors deduce that the elevated 18O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere's counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.
The A-type granites with highly positive εNd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic source, and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon εHf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (e.g., high SiO2 and K2O contents, enriched LILEs (except Sr), depleted Sr, Ta, and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (range: 315 Ma to 305 Ma) and moderate 18O enrichments (δ18Ozircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (range: 305 Ma to 301 Ma) with higher 18O enrichments (δ18Ozircon=+8.72‰–+9.89‰). The authors deduce that the elevated 18O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere's counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.
, Available online , doi: 10.31035/cg2021005
Abstract:
The Nan Suture and Sukhothai Arc Terrane are products of the eastward subduction of the Paleotethyan Ocean during the Late Carboniferous to Triassic. However, their footprints in northwestern Laos are poorly constrained. New geochronological and geochemical data presented in this study demonstrate a Late Permian origin for the andesitic rocks in the B.Xiengnou area rather than Late Triassic. The breccia-bearing andesitic tuff in the B.On ultramafic complex yield a zircon U-Pb age of 260 ± 1.4 Ma, geochemically displaying a MORB-like signature. The andesitic tuff in the B.Kiophoulan-B.Houayhak belt gave the U-Pb age of 254 ± 1.3 Ma, with arc-like geochemical affinity. By combining geochronological and geochemical data from the Nan Suture and Sukhothai Arc Terrane, the authors suggest that the andesitic rocks in the B.On ultramafic complex formed in a back-arc basin background, which connected the Jinghong and Nan back-arc basin during the Permian; while the andesitic tuff in the B.Kiophoulan-B.Houayhak belt erupted in the Sukhothai continental island arc setting.
The Nan Suture and Sukhothai Arc Terrane are products of the eastward subduction of the Paleotethyan Ocean during the Late Carboniferous to Triassic. However, their footprints in northwestern Laos are poorly constrained. New geochronological and geochemical data presented in this study demonstrate a Late Permian origin for the andesitic rocks in the B.Xiengnou area rather than Late Triassic. The breccia-bearing andesitic tuff in the B.On ultramafic complex yield a zircon U-Pb age of 260 ± 1.4 Ma, geochemically displaying a MORB-like signature. The andesitic tuff in the B.Kiophoulan-B.Houayhak belt gave the U-Pb age of 254 ± 1.3 Ma, with arc-like geochemical affinity. By combining geochronological and geochemical data from the Nan Suture and Sukhothai Arc Terrane, the authors suggest that the andesitic rocks in the B.On ultramafic complex formed in a back-arc basin background, which connected the Jinghong and Nan back-arc basin during the Permian; while the andesitic tuff in the B.Kiophoulan-B.Houayhak belt erupted in the Sukhothai continental island arc setting.
, Available online , doi: 10.31035/cg2021006
Abstract:
The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin. This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area. The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The source rocks originated from a continental island arc environment in terms of tectonic setting. U-Pb ages of detrital zircons obtained can be roughly divided into three groups: 170‒500 Ma, 1600‒2050 Ma, and 2100‒2650 Ma. Based on the characteristics of trace elements and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks (such as granodioritic intrusions) and metamorphic rocks (such as gneiss and granulite) in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block. Based on sedimentological and petrological results, it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction. The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area. Meanwhile, the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin. The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.
The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin. This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area. The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The source rocks originated from a continental island arc environment in terms of tectonic setting. U-Pb ages of detrital zircons obtained can be roughly divided into three groups: 170‒500 Ma, 1600‒2050 Ma, and 2100‒2650 Ma. Based on the characteristics of trace elements and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks (such as granodioritic intrusions) and metamorphic rocks (such as gneiss and granulite) in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block. Based on sedimentological and petrological results, it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction. The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area. Meanwhile, the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin. The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.
, Available online , doi: 10.31035/cg2021046
Abstract:
Due to the high heterogeneity and complexity of water flow movement for multiple karst water-bearing mediums, the evaluation, effective development, and utilization of karst water resources are significantly limited. Matrix flow is usually laminar, whereas conduit flow is usually turbulent. The driving mechanisms of water exchange that occur between the karst conduit and its adjacent matrix are not well understood. This paper investigates the hydrodynamic characteristics and the mechanism of flow exchange in dual water-bearing mediums (conduit and matrix) of karst aquifers through laboratory experimentation and numerical simulation. A karst aquifer consisting of a matrix network and a conduit was proposed, and the relationship between the water exchange flux and hydraulic head differences generated from the laboratory experiments was analyzed. Two modes of experimental tests were performed with different fixed water level boundaries in the laboratory karst aquifer. The results indicate that the water exchange capacity was proportional to the square root of hydraulic head differences. The linear exchange term in the conduit flow process (CFP) source program was modified according to experimental results. The modified CFP and the original CFP model experimental data results were compared, and it was found that the modified CFP model had better fitting effects. These results showed that the water exchange mechanism between conduit and matrix is very important for solid-liquid interface reaction, water resource evaluation, and understanding of karst hydrodynamic behavior.
Due to the high heterogeneity and complexity of water flow movement for multiple karst water-bearing mediums, the evaluation, effective development, and utilization of karst water resources are significantly limited. Matrix flow is usually laminar, whereas conduit flow is usually turbulent. The driving mechanisms of water exchange that occur between the karst conduit and its adjacent matrix are not well understood. This paper investigates the hydrodynamic characteristics and the mechanism of flow exchange in dual water-bearing mediums (conduit and matrix) of karst aquifers through laboratory experimentation and numerical simulation. A karst aquifer consisting of a matrix network and a conduit was proposed, and the relationship between the water exchange flux and hydraulic head differences generated from the laboratory experiments was analyzed. Two modes of experimental tests were performed with different fixed water level boundaries in the laboratory karst aquifer. The results indicate that the water exchange capacity was proportional to the square root of hydraulic head differences. The linear exchange term in the conduit flow process (CFP) source program was modified according to experimental results. The modified CFP and the original CFP model experimental data results were compared, and it was found that the modified CFP model had better fitting effects. These results showed that the water exchange mechanism between conduit and matrix is very important for solid-liquid interface reaction, water resource evaluation, and understanding of karst hydrodynamic behavior.
, Available online , doi: 10.31035/cg2021068
Abstract:
The widely-developed, mixed clastic-carbonate succession in the northern Qaidam Basin records the paleo-environment changes under the glacial activity during the Late Paleozoic icehouse period in the context of regional tectonic stability, however, the depositional environment and sequence stratigraphy characteristics of the mixed deposits is rarely reported and still not clear. Combined the latest drilling wells data, we analyzed the sedimentary and stratigraphic characterization of the mixed strata via detailed field outcrops and core observations and thin section microscopic observations and recognized three depositional systems, including progradational coastal system, incised valley system, and carbonate-dominated marine shelf system, and identified four third-order sequences, SQ1, SQ2, SQ3 and SQ4, consisting of LST, TST, and HST. The depositional environment is overall belonged to marine-continental transition context and shifted from marine to continental environment frequently, showing an evolutionary pattern from marine towards terrestrial-marine transition and then back into the marine environment again in the long-term, which was controlled by the regional tectonic subsidence and the high-frequency and large-amplitude sea-level changes due to the Late Paleozoic glacial activity. The result is of significance in understanding the evolution of the Qinghai-Tibet Plateau and the sedimentation-climate response.
The widely-developed, mixed clastic-carbonate succession in the northern Qaidam Basin records the paleo-environment changes under the glacial activity during the Late Paleozoic icehouse period in the context of regional tectonic stability, however, the depositional environment and sequence stratigraphy characteristics of the mixed deposits is rarely reported and still not clear. Combined the latest drilling wells data, we analyzed the sedimentary and stratigraphic characterization of the mixed strata via detailed field outcrops and core observations and thin section microscopic observations and recognized three depositional systems, including progradational coastal system, incised valley system, and carbonate-dominated marine shelf system, and identified four third-order sequences, SQ1, SQ2, SQ3 and SQ4, consisting of LST, TST, and HST. The depositional environment is overall belonged to marine-continental transition context and shifted from marine to continental environment frequently, showing an evolutionary pattern from marine towards terrestrial-marine transition and then back into the marine environment again in the long-term, which was controlled by the regional tectonic subsidence and the high-frequency and large-amplitude sea-level changes due to the Late Paleozoic glacial activity. The result is of significance in understanding the evolution of the Qinghai-Tibet Plateau and the sedimentation-climate response.
, Available online , doi: 10.31035/cg2021026
Abstract:
Archaeanthus is a famous Cretaceous angiosperm from the Albian-Cenomanian of Kansas, the USA documented by Dilcher and Crane in 1984. Its seeds/ovules were interpreted as arranged along the adaxial (ventral) suture of the fruits. This interpretation used to sound plausible, especially under the light of the then-dominating doctrine of angiosperm evolution. However, Dilcher and Crane’s interpretation of seed/ovule insertion was not fully supported even by their own evidence. Considering the early age, importance, and influence of Archaeanthus in palaeobotany and angiosperm systematics, it is necessary to ascertain the seed/ovule position in Archaeanthus. New observation on the type materials of Archaeanthus indicates that at least some ovules/seeds in Archaeanthus are attached to the abaxial (dorsal) margin of the fruit. This information undermines the former assumed Magnoliaceous affinity of Archaeanthus and falsifies its support to the then-dominating speculation of carpel homology and origin of angiosperms. Analysis of the common reason underlying the misinterpretations of early fossil angiosperms (including Archaeanthus, Archaefructus, and others) indicates that the speculation of Arber and Parkin deviated much from the botanical reality.
Archaeanthus is a famous Cretaceous angiosperm from the Albian-Cenomanian of Kansas, the USA documented by Dilcher and Crane in 1984. Its seeds/ovules were interpreted as arranged along the adaxial (ventral) suture of the fruits. This interpretation used to sound plausible, especially under the light of the then-dominating doctrine of angiosperm evolution. However, Dilcher and Crane’s interpretation of seed/ovule insertion was not fully supported even by their own evidence. Considering the early age, importance, and influence of Archaeanthus in palaeobotany and angiosperm systematics, it is necessary to ascertain the seed/ovule position in Archaeanthus. New observation on the type materials of Archaeanthus indicates that at least some ovules/seeds in Archaeanthus are attached to the abaxial (dorsal) margin of the fruit. This information undermines the former assumed Magnoliaceous affinity of Archaeanthus and falsifies its support to the then-dominating speculation of carpel homology and origin of angiosperms. Analysis of the common reason underlying the misinterpretations of early fossil angiosperms (including Archaeanthus, Archaefructus, and others) indicates that the speculation of Arber and Parkin deviated much from the botanical reality.
, Available online , doi: 10.31035/cg2021004
Abstract:
The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area, central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks, which are closely related to the early tectonic evolution of the Earth. However, its formation era, sedimentary filling sequence, and geotectonic characteristics have always been in dispute. In this study, several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone. This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village, Tongchang Township, Yimen County. LA-ICP-MS zircon dating was conducted, achieving the crystallization age of magma of 2491 ± 15 Ma (MSWD = 1.19, n = 31) and the metamorphic ages of about 2.3 Ga, 2.0 Ga, and 1.8 Ga for the first time. Meanwhile, according to in-situ Hf isotope analysis, the zircon εHf(t) values were determined to range from -3.0 to 7.6, with an average of 2.7. Furthermore, the first-stage Hf model age (TDM1) was determined to be 2513−2916 Ma, indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean. Therefore, it is believed that the strata of the slate were deposited in the Late Neoarchean, instead of the Mesoproterozoic as determined by previous researchers. Accordingly, it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group. Instead, they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information. Furthermore, the magma ages of 2491 ± 15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton, and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic. The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland. Meanwhile, the metamorphic ages of 2.3 Ga, 2.0 Ga, and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga, 1.95 Ga, and 1.85 Ga of the northern margin of the Yangtze Craton, indicating that the strata experienced Paleoproterozoic tectonic-thermal events. The study area is located on the eastern margin of Qinghai-Tibet Plateau, and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous. The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area, central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks, which are closely related to the early tectonic evolution of the Earth. However, its formation era, sedimentary filling sequence, and geotectonic characteristics have always been in dispute. In this study, several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone. This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village, Tongchang Township, Yimen County. LA-ICP-MS zircon dating was conducted, achieving the crystallization age of magma of 2491 ± 15 Ma (MSWD = 1.19, n = 31) and the metamorphic ages of about 2.3 Ga, 2.0 Ga, and 1.8 Ga for the first time. Meanwhile, according to in-situ Hf isotope analysis, the zircon εHf(t) values were determined to range from -3.0 to 7.6, with an average of 2.7. Furthermore, the first-stage Hf model age (TDM1) was determined to be 2513−2916 Ma, indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean. Therefore, it is believed that the strata of the slate were deposited in the Late Neoarchean, instead of the Mesoproterozoic as determined by previous researchers. Accordingly, it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group. Instead, they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information. Furthermore, the magma ages of 2491 ± 15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton, and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic. The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland. Meanwhile, the metamorphic ages of 2.3 Ga, 2.0 Ga, and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga, 1.95 Ga, and 1.85 Ga of the northern margin of the Yangtze Craton, indicating that the strata experienced Paleoproterozoic tectonic-thermal events. The study area is located on the eastern margin of Qinghai-Tibet Plateau, and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous. The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
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