2020 Vol. 45, No. 5
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2020, 45(5): 1481-1489.
doi: 10.3799/dqkx.2019.158
Abstract:
Crystal intergrowth (or crystal clustering) is an important phenomenon during crystal growth and textural development of igneous rocks,which can provide much information about magmatic processes. We used electron backscattered diffraction (EBSD) technique and pole figures to analyze the quartz orientation relationships in Meichuan granodiorite and Tiantangzai granite. Dauphiné twins and intergrowths (by overlapping the same plane) are very abundant in these two rocks. Beside Dauphiné twins and intergrowths,we found a special kind of symmetric intergrowths among quartz crystals in these two rocks. Considering quartz's Laue Group 3 2/m (except the point group 32),Dauphiné twin plane (0001) or (1010) overlaps the symmetry plane (1120) of the third crystal in some intergrowths of quartz. The intergrowths composed by these three crystals retain some symmetry of Dauphiné twins because of the overlapping. The overlapping between twin plane and the symmetry plane of the third crystal has also been found in the aggregation of NH4Cl crystallites and diopside dendritic crystals reported in our previous work. It is reflected that symmetry controls the intergrowth of crystals. Laue Group is related to lattice symmetry but not to crystal structure symmetry. The lattice,rather than the crystal structure,plays an important role in quartz intergrowth in rocks.
Crystal intergrowth (or crystal clustering) is an important phenomenon during crystal growth and textural development of igneous rocks,which can provide much information about magmatic processes. We used electron backscattered diffraction (EBSD) technique and pole figures to analyze the quartz orientation relationships in Meichuan granodiorite and Tiantangzai granite. Dauphiné twins and intergrowths (by overlapping the same plane) are very abundant in these two rocks. Beside Dauphiné twins and intergrowths,we found a special kind of symmetric intergrowths among quartz crystals in these two rocks. Considering quartz's Laue Group 3 2/m (except the point group 32),Dauphiné twin plane (0001) or (1010) overlaps the symmetry plane (1120) of the third crystal in some intergrowths of quartz. The intergrowths composed by these three crystals retain some symmetry of Dauphiné twins because of the overlapping. The overlapping between twin plane and the symmetry plane of the third crystal has also been found in the aggregation of NH4Cl crystallites and diopside dendritic crystals reported in our previous work. It is reflected that symmetry controls the intergrowth of crystals. Laue Group is related to lattice symmetry but not to crystal structure symmetry. The lattice,rather than the crystal structure,plays an important role in quartz intergrowth in rocks.
2020, 45(5): 1490-1502.
doi: 10.3799/dqkx.2019.163
Abstract:
Although large volume of Triassic magmatism has been identified in the central Tibetan Plateau,the petrogenesis and geodynamic setting of these igneous rocks are still poorly understood. In this paper,we carried out a detailed study of zircon U-Pb geochronology,petrology,and geochemisrty for the diorite porphyrite in North Qiangtang terrane,aiming to reveal its petrogenesis and constaint the exploration of the Triassic tectonic-magmatic evolution. The LA-ICP-MS zircon U-Pb dating for this magmatic rock yields a crystallization age of 227±2 Ma (MSWD=0.86). All the samples have high contents of silicon and aluminum and belong to calc-alkaline series in composition. Compared with the primitive mantle,they exhibit enrichment of LREE,Th,and U,with depletion of Nb,Ta and Ti. All the samples have relatively low εNd(t) values (-4.53 to -4.99),relatively concentrated ISr values (0.707 05 to 0.707 14),and positive εHf(t) values (+0.81 to +2.48),suggesting an enriched mantle. Geochemical and isotopic variations reveal that the diorite-porphyrite was derived from partial melting of an enriched mantle that was previously modified by subduction-related components(e.g.,sediments). In addition,combined with the existing multi-disciplinary research data in the region,it could be concluded that the subduction of the Paleo-Tethyan ocean in the North Qiangtang terrane lasted at least to 227 Ma.
Although large volume of Triassic magmatism has been identified in the central Tibetan Plateau,the petrogenesis and geodynamic setting of these igneous rocks are still poorly understood. In this paper,we carried out a detailed study of zircon U-Pb geochronology,petrology,and geochemisrty for the diorite porphyrite in North Qiangtang terrane,aiming to reveal its petrogenesis and constaint the exploration of the Triassic tectonic-magmatic evolution. The LA-ICP-MS zircon U-Pb dating for this magmatic rock yields a crystallization age of 227±2 Ma (MSWD=0.86). All the samples have high contents of silicon and aluminum and belong to calc-alkaline series in composition. Compared with the primitive mantle,they exhibit enrichment of LREE,Th,and U,with depletion of Nb,Ta and Ti. All the samples have relatively low εNd(t) values (-4.53 to -4.99),relatively concentrated ISr values (0.707 05 to 0.707 14),and positive εHf(t) values (+0.81 to +2.48),suggesting an enriched mantle. Geochemical and isotopic variations reveal that the diorite-porphyrite was derived from partial melting of an enriched mantle that was previously modified by subduction-related components(e.g.,sediments). In addition,combined with the existing multi-disciplinary research data in the region,it could be concluded that the subduction of the Paleo-Tethyan ocean in the North Qiangtang terrane lasted at least to 227 Ma.
2020, 45(5): 1503-1516.
doi: 10.3799/dqkx.2019.207
Abstract:
The Banxi antimony deposit is located in the Central Hunan Sb belt,which is a quartz vein type deposit that has been mined for more than 100 years. Like many hydrothermal deposits,the Banxi deposit has many ore-free quartz veins,which are parallel with the ore-bearing quartz veins at a relatively fixed distance. However,the genetic connection between ore-free and ore-bearing veins is not clear. Based on the comparison of the forming age and fluid components of the two types of quartz veins,the genetic relationship between the two types of quartz veins and the possible geological significance of the ore-free quartz veins are discussed. Field observations,examination of fluid inclusions and hydrogen,oxygen,and sulfur isotope analyses reveal that the two types of quartz veins has no interpenetrating relationship,but the ore-free and ore-bearing veins are physically connected. Integrated with regional geological data,it is concluded that the ore-free vein was formed in Yanshanian period,which was consistent with the ore-bearing vein. The ore-free quartz veins contain a small amount of stibnite and pyrite. Sericitization,silicification and other types of wall rock alteration are both developed on the side of the two types of veins. Micro thermometric analyses of fluid inclusion in ore-free quartz veins yield homogenization temperature ranges of 143-266 ℃ and salinities of 1.7%-8.5% NaCl eqv.. While ore-bearing quartz veins inclusions have ranges of 185-332 ℃ with salinities of 3.3%-7.7% NaCl eqv.,showing that both types of veins formed in medium-low temperature and low salinity fluid systems. Laser Raman analyses of a fluid inclusion from both types of veins show that the gas phase components of both fluids are H2O±CO2±CH4±N2. LA-ICP-MS test results confirm that both types of veins contain the same elements (Sb,Fe,As,etc.),and that their fluid components are very similar. The values of δD and δ18OH2O of the ore-free quartz veins vary from -69.7‰ to -74.4‰,and 2.6‰ to 3.4‰,while the values in ore-bearing quartz vein vary from -140‰ to -107‰,and 5.9‰ to 8.4‰. The values of δ34S of sulfide are 3.04‰-4.87‰ (ore-free quartz vein) and 3.46‰-6.12‰ (ore-bearing quartz vein). Previous geologic work and field observations during this study indicate that quartz porphyry veins in the mining area developed without significant magmatic activity. This suggests that the original fluid for both types of veins was metamorphic water,and that the nature of quartz veins changed with time,regional cooling and different levels of meteoric water participation. In both types of veins,sulfur found in sulfides was derived from the host formation. The spatial relationship between the two types of quartz veins and their similar components and sources of ore-forming materials indicate that the two types of quartz veins are close to the same age of formation and belong to the same metallogenic hydrothermal system. The slight difference in geological and geochemical characteristics between the two types of quartz veins is the result of the continuous evolution and differentiation of ore-forming fluids. The study of the genetic relationship between the two types of quartz veins provides an example for the study of the ore-forming fluid mixing of this type of deposit. The distribution characteristics of the two types of quartz veins parallel at a relatively fixed distance not only provide a new mark for prospecting for banxi antimony deposit,but also enlighten us to pay attention to the possible indicating role of ore-free quartz veins in some deposits of this type or in the new exploration area for the ore-bearing quartz veins.
The Banxi antimony deposit is located in the Central Hunan Sb belt,which is a quartz vein type deposit that has been mined for more than 100 years. Like many hydrothermal deposits,the Banxi deposit has many ore-free quartz veins,which are parallel with the ore-bearing quartz veins at a relatively fixed distance. However,the genetic connection between ore-free and ore-bearing veins is not clear. Based on the comparison of the forming age and fluid components of the two types of quartz veins,the genetic relationship between the two types of quartz veins and the possible geological significance of the ore-free quartz veins are discussed. Field observations,examination of fluid inclusions and hydrogen,oxygen,and sulfur isotope analyses reveal that the two types of quartz veins has no interpenetrating relationship,but the ore-free and ore-bearing veins are physically connected. Integrated with regional geological data,it is concluded that the ore-free vein was formed in Yanshanian period,which was consistent with the ore-bearing vein. The ore-free quartz veins contain a small amount of stibnite and pyrite. Sericitization,silicification and other types of wall rock alteration are both developed on the side of the two types of veins. Micro thermometric analyses of fluid inclusion in ore-free quartz veins yield homogenization temperature ranges of 143-266 ℃ and salinities of 1.7%-8.5% NaCl eqv.. While ore-bearing quartz veins inclusions have ranges of 185-332 ℃ with salinities of 3.3%-7.7% NaCl eqv.,showing that both types of veins formed in medium-low temperature and low salinity fluid systems. Laser Raman analyses of a fluid inclusion from both types of veins show that the gas phase components of both fluids are H2O±CO2±CH4±N2. LA-ICP-MS test results confirm that both types of veins contain the same elements (Sb,Fe,As,etc.),and that their fluid components are very similar. The values of δD and δ18OH2O of the ore-free quartz veins vary from -69.7‰ to -74.4‰,and 2.6‰ to 3.4‰,while the values in ore-bearing quartz vein vary from -140‰ to -107‰,and 5.9‰ to 8.4‰. The values of δ34S of sulfide are 3.04‰-4.87‰ (ore-free quartz vein) and 3.46‰-6.12‰ (ore-bearing quartz vein). Previous geologic work and field observations during this study indicate that quartz porphyry veins in the mining area developed without significant magmatic activity. This suggests that the original fluid for both types of veins was metamorphic water,and that the nature of quartz veins changed with time,regional cooling and different levels of meteoric water participation. In both types of veins,sulfur found in sulfides was derived from the host formation. The spatial relationship between the two types of quartz veins and their similar components and sources of ore-forming materials indicate that the two types of quartz veins are close to the same age of formation and belong to the same metallogenic hydrothermal system. The slight difference in geological and geochemical characteristics between the two types of quartz veins is the result of the continuous evolution and differentiation of ore-forming fluids. The study of the genetic relationship between the two types of quartz veins provides an example for the study of the ore-forming fluid mixing of this type of deposit. The distribution characteristics of the two types of quartz veins parallel at a relatively fixed distance not only provide a new mark for prospecting for banxi antimony deposit,but also enlighten us to pay attention to the possible indicating role of ore-free quartz veins in some deposits of this type or in the new exploration area for the ore-bearing quartz veins.
2020, 45(5): 1517-1530.
doi: 10.3799/dqkx.2019.192
Abstract:
The Fukeshan copper depositis one of the major prospecting breakthroughs recently made in Heilongjiang Province. After detailed field work and microscopic observation,we found that this deposit has typical porphyry style characteristics. Out study shows that the diorite porphyry is the mineralization-causative porphyry. The emplacement of the diorite porphyry caused the potassic alteration,phyllicalteration and latest age chlorite-pyrite alteration in and around this porphyry. Mineralization in the Fukeshan deposit is mainly associated with phyllic alteration. Mineralization is mostly confined within diorite porphyry and granodiorite. Distribution of alteration and the causative diorite porphyry indicate that there may be a large-scale causative porphyry at depth in the southwest of the deposit. Detailed SWIR study indicates that the Pos2200 of muscovite and Pos2250 of chlorite are controlled by the composition of the original altered minerals,thus not suitable to be used as a vector for exploration. The IC values of muscovite group and MnO concentration in chlorite are controlled by temperature and can be used to be a vector to find the hydrothermal center at Fukeshan.This research highlights that the combination of alteration mapping and SWIR analysis can be of great help in mineral exploration.
The Fukeshan copper depositis one of the major prospecting breakthroughs recently made in Heilongjiang Province. After detailed field work and microscopic observation,we found that this deposit has typical porphyry style characteristics. Out study shows that the diorite porphyry is the mineralization-causative porphyry. The emplacement of the diorite porphyry caused the potassic alteration,phyllicalteration and latest age chlorite-pyrite alteration in and around this porphyry. Mineralization in the Fukeshan deposit is mainly associated with phyllic alteration. Mineralization is mostly confined within diorite porphyry and granodiorite. Distribution of alteration and the causative diorite porphyry indicate that there may be a large-scale causative porphyry at depth in the southwest of the deposit. Detailed SWIR study indicates that the Pos2200 of muscovite and Pos2250 of chlorite are controlled by the composition of the original altered minerals,thus not suitable to be used as a vector for exploration. The IC values of muscovite group and MnO concentration in chlorite are controlled by temperature and can be used to be a vector to find the hydrothermal center at Fukeshan.This research highlights that the combination of alteration mapping and SWIR analysis can be of great help in mineral exploration.
2020, 45(5): 1531-1543.
doi: 10.3799/dqkx.2019.164
Abstract:
To gain new insights into metallogenic processes and especially into uranium ore minerals enrichment mechanism, occurrence of uranium ore minerals in uranium deposits of northern Ordos basin, has been analyzed using various analytical techniques including α track radiograph, scanning electron microscope (SEM) and electron microprobe (EMP). It is found that the uranium ore minerals mainly consist of coffinite, a small amount of pitchblende and uranium-bearing titanium mineral in the study area. Primary uranium ore minerals / detrital uranium minerals occur within the lithic fragment, adsorbed on anatase during the sedimentary / diagenetic stage, becoming the pre-enrichment uranium for the uranium reservoir. During the metallogenic stage, uranium ore minerals occur dominantly in the intergranular pores, associated with pyrite and carbonaceous fragments, related to quartz grains and calcite cementation closely, and a small part of which are adsorbed on montmorillonite film coating clastic particles. Besides, pitchblende - hematite - pyrite mineral assemblages, clausthalite (PbSe) and ferroselite (FeSe2) co-existing with uranium ore minerals with high concentration of REEs, are recognized. Comprehensive analyses indicate that pitchblende is formed at the transitional interface between oxidizing acid fluid and reducing alkaline fluid, favoring the oxidizing acid side during the early metallogenic stage, and coffinite is mainly formed in the reducing alkaline conditions during the late metallogenic stage. The supply of dual uranium sources, abundant reductant, coupling of multi-source fluids, and partial superimposed transformation by hydrothermal fluid have resulted in the formation of large and rich uranium deposits in northern Ordos basin.
To gain new insights into metallogenic processes and especially into uranium ore minerals enrichment mechanism, occurrence of uranium ore minerals in uranium deposits of northern Ordos basin, has been analyzed using various analytical techniques including α track radiograph, scanning electron microscope (SEM) and electron microprobe (EMP). It is found that the uranium ore minerals mainly consist of coffinite, a small amount of pitchblende and uranium-bearing titanium mineral in the study area. Primary uranium ore minerals / detrital uranium minerals occur within the lithic fragment, adsorbed on anatase during the sedimentary / diagenetic stage, becoming the pre-enrichment uranium for the uranium reservoir. During the metallogenic stage, uranium ore minerals occur dominantly in the intergranular pores, associated with pyrite and carbonaceous fragments, related to quartz grains and calcite cementation closely, and a small part of which are adsorbed on montmorillonite film coating clastic particles. Besides, pitchblende - hematite - pyrite mineral assemblages, clausthalite (PbSe) and ferroselite (FeSe2) co-existing with uranium ore minerals with high concentration of REEs, are recognized. Comprehensive analyses indicate that pitchblende is formed at the transitional interface between oxidizing acid fluid and reducing alkaline fluid, favoring the oxidizing acid side during the early metallogenic stage, and coffinite is mainly formed in the reducing alkaline conditions during the late metallogenic stage. The supply of dual uranium sources, abundant reductant, coupling of multi-source fluids, and partial superimposed transformation by hydrothermal fluid have resulted in the formation of large and rich uranium deposits in northern Ordos basin.
2020, 45(5): 1544-1555.
doi: 10.3799/dqkx.2019.173
Abstract:
The distribution of Jurassic granite in the eastern Jilin province is relatively limited, with little discriminant evidence for regional tectonic evolution. This paper presents a synthesis study of zircon U-Pb chronology and geochemistry and Hf isotopes of the quartz monzonite porphyry in this area. The rocks yield an average zircon LA-ICP-MS U-Pb age of 165±1 Ma, indicating the Middle Jurassic. They show high SiO2(61.01%-61.99%), ALK(5.78%-7.98%), belonging to calc-alkaline granites. In addition, they also display the characteristics of I-type granite with obvious enrichment in LREE, unconspicuous europium anomalies (0.92-1.01), low MgO, CaO, Fe2O3Tas well as A/CNK(1.02-1.39). The Eu/Eu* values vary from -15.46 to -17.04, and TDM2=2 189-2 289 Ma. These samples are enriched in LILE and depleted in HFSE, with Mg#=26.90-33.04, low Yb(0.43×10-6~0.48×10-6) and Y(6.63×10-6~7.12×10-6). Zircon Ti temperature averages 744 ℃, belonging to low temperature granite. The magma was originated from the partial melting of Paleo-Proterozoic lower crust. The middle Jurassic igneous rocks in the eastpartofnorthern margin of the North China Craton were formed in the subduction rather than the remote effect of Mongols-Okhotsk Ocean closure. From late Jurassic to early Cretaceous, the continental margin of northeast China maydisplay the structural features of strike-slip.
The distribution of Jurassic granite in the eastern Jilin province is relatively limited, with little discriminant evidence for regional tectonic evolution. This paper presents a synthesis study of zircon U-Pb chronology and geochemistry and Hf isotopes of the quartz monzonite porphyry in this area. The rocks yield an average zircon LA-ICP-MS U-Pb age of 165±1 Ma, indicating the Middle Jurassic. They show high SiO2(61.01%-61.99%), ALK(5.78%-7.98%), belonging to calc-alkaline granites. In addition, they also display the characteristics of I-type granite with obvious enrichment in LREE, unconspicuous europium anomalies (0.92-1.01), low MgO, CaO, Fe2O3Tas well as A/CNK(1.02-1.39). The Eu/Eu* values vary from -15.46 to -17.04, and TDM2=2 189-2 289 Ma. These samples are enriched in LILE and depleted in HFSE, with Mg#=26.90-33.04, low Yb(0.43×10-6~0.48×10-6) and Y(6.63×10-6~7.12×10-6). Zircon Ti temperature averages 744 ℃, belonging to low temperature granite. The magma was originated from the partial melting of Paleo-Proterozoic lower crust. The middle Jurassic igneous rocks in the eastpartofnorthern margin of the North China Craton were formed in the subduction rather than the remote effect of Mongols-Okhotsk Ocean closure. From late Jurassic to early Cretaceous, the continental margin of northeast China maydisplay the structural features of strike-slip.
2020, 45(5): 1556-1572.
doi: 10.3799/dqkx.2019.196
Abstract:
In order to explore the petrogenesis types and tectonic setting of the Late Triassic-Early Jurassic magmatic rocks in the southern Gangdese, we report detailed petrography, geochronology, and whole-rock geochemistry of the Songduo biotite monzogranite plutons in the Mozhugongka area.The zircon LA-ICP-MS U-Pb dating results show that the age of the Songduo biotite monzogranite plutons is 190.2±2.9 Ma, indicating that it was formed in the Early Jurassic.In terms of geochemical composition, the Songduo biotite monzogranite plutons have low TiO2 (0.68%-0.75%), high SiO2 (65.22%-66.13%), Al2O3 (16.26%-16.73%), Na2O (4.05%-4.29%), and K2O (3.96%-4.24%) contents, belonging to the shoshonite series and weakly-peraluminous (A/CNK=1.04-1.11);In the spidergram, the samples show enrichment in Rb, Th, K, Zr and Hf, and depletion in Ba, Nb, Ta, Sr, Ti and P. The whole-rock zircon saturation temperature varies from 805 to 835 ℃, with high FeOT/MgO ratios. The Songduo pluton has an affinity with A-type granite. In combination with pervious research results, it shows that the Late Triassic-Early Jurassic magmatic rocks in central and southern Gangdese were formed in magmatic arc related to the northward subduction of the Neo-Tethys oceanic slab. We suggest that the Songduo biotite monzogranite plutons generated in a back-arc extensional environment during the subduction of the Neo-Tethys oceanic slab, and the formation of granite is related to the partial melting of the lower crust caused by the intrusion of mantle-derived magma.
In order to explore the petrogenesis types and tectonic setting of the Late Triassic-Early Jurassic magmatic rocks in the southern Gangdese, we report detailed petrography, geochronology, and whole-rock geochemistry of the Songduo biotite monzogranite plutons in the Mozhugongka area.The zircon LA-ICP-MS U-Pb dating results show that the age of the Songduo biotite monzogranite plutons is 190.2±2.9 Ma, indicating that it was formed in the Early Jurassic.In terms of geochemical composition, the Songduo biotite monzogranite plutons have low TiO2 (0.68%-0.75%), high SiO2 (65.22%-66.13%), Al2O3 (16.26%-16.73%), Na2O (4.05%-4.29%), and K2O (3.96%-4.24%) contents, belonging to the shoshonite series and weakly-peraluminous (A/CNK=1.04-1.11);In the spidergram, the samples show enrichment in Rb, Th, K, Zr and Hf, and depletion in Ba, Nb, Ta, Sr, Ti and P. The whole-rock zircon saturation temperature varies from 805 to 835 ℃, with high FeOT/MgO ratios. The Songduo pluton has an affinity with A-type granite. In combination with pervious research results, it shows that the Late Triassic-Early Jurassic magmatic rocks in central and southern Gangdese were formed in magmatic arc related to the northward subduction of the Neo-Tethys oceanic slab. We suggest that the Songduo biotite monzogranite plutons generated in a back-arc extensional environment during the subduction of the Neo-Tethys oceanic slab, and the formation of granite is related to the partial melting of the lower crust caused by the intrusion of mantle-derived magma.
2020, 45(5): 1573-1592.
doi: 10.3799/dqkx.2019.161
Abstract:
Volcanic rocks of the Linzizong Group are widely distributed in the southern part of the Lhasa Block, and are considered to related with tectonic settings during the transition from the northward subduction of Neo-Tethys to continent-continent collision.In this paper, we present detailed chronology, elemental geochemistry and isotope geochemistry of volcanic rock samples from the Linzizong Group, Shiquanhe area. The results show that LA-ICP-MS U-Pb zircon ages from volcanic rock samples of the Dianzhong Formation are mostly between 67.1±1.7 Ma and 70.8±1.1 Ma, establishing a Late Cretaceous age.The Dianzhong Formation in the study area comprises basaltic andesite, andesite and rhyolite. Medium-basic volcanic rocks belong to the potassium calcium-alkaline series, with low TiO2 (average < 1%) and high Al2O3 (average > 15%) contents, and are enriched in large ion lithophile elements (LILE), such as K, Rb, Th, and U, and depleted in high field strength elements (HFSE) such as Nb, Ta, Zr and Ti, thereby showing obvious island-arc volcanic affinity.The isotope study yields (87Sr/86Sr)i ratios of 0.707 437, 0.707 672, and εNd(t) of -5.06 and -4.30. The acid volcanic rocks have high SiO2 (76.01%-76.77%), high K2O (4.93%-4.98%) and high K2O/Na2O (1.41%-1.45%), and belong to the high potassium calc-alkaline series, with a relatively high Mg# (average 45.38), enrichment of large ion lithophile elements (LILE) such as K, Rb, Th, U, depletion of high field strength elements (HFSE) such as Nb, Ta, Zr, Ti, and have significant negative Eu and Sr anomalies. The above characteristics suggest that the medium-basic volcanic rocks of the Dianzhong Formation were generated from partial melting of the overlying mantle wedge during northward subduction of Neo-Tethys, and were crustally contaminated during emplacement, whereas the acidic rocks may have been derived from partial melting of the overlying crust and the addition of a small amount of mantle material.In addition, both chronology and geochemical characteristics indicate that rock units sampled during this study are not part of the Zenong Group, as considered by the previous studies, but should be redefined as volcanic rocks of the Linzizong Group.
Volcanic rocks of the Linzizong Group are widely distributed in the southern part of the Lhasa Block, and are considered to related with tectonic settings during the transition from the northward subduction of Neo-Tethys to continent-continent collision.In this paper, we present detailed chronology, elemental geochemistry and isotope geochemistry of volcanic rock samples from the Linzizong Group, Shiquanhe area. The results show that LA-ICP-MS U-Pb zircon ages from volcanic rock samples of the Dianzhong Formation are mostly between 67.1±1.7 Ma and 70.8±1.1 Ma, establishing a Late Cretaceous age.The Dianzhong Formation in the study area comprises basaltic andesite, andesite and rhyolite. Medium-basic volcanic rocks belong to the potassium calcium-alkaline series, with low TiO2 (average < 1%) and high Al2O3 (average > 15%) contents, and are enriched in large ion lithophile elements (LILE), such as K, Rb, Th, and U, and depleted in high field strength elements (HFSE) such as Nb, Ta, Zr and Ti, thereby showing obvious island-arc volcanic affinity.The isotope study yields (87Sr/86Sr)i ratios of 0.707 437, 0.707 672, and εNd(t) of -5.06 and -4.30. The acid volcanic rocks have high SiO2 (76.01%-76.77%), high K2O (4.93%-4.98%) and high K2O/Na2O (1.41%-1.45%), and belong to the high potassium calc-alkaline series, with a relatively high Mg# (average 45.38), enrichment of large ion lithophile elements (LILE) such as K, Rb, Th, U, depletion of high field strength elements (HFSE) such as Nb, Ta, Zr, Ti, and have significant negative Eu and Sr anomalies. The above characteristics suggest that the medium-basic volcanic rocks of the Dianzhong Formation were generated from partial melting of the overlying mantle wedge during northward subduction of Neo-Tethys, and were crustally contaminated during emplacement, whereas the acidic rocks may have been derived from partial melting of the overlying crust and the addition of a small amount of mantle material.In addition, both chronology and geochemical characteristics indicate that rock units sampled during this study are not part of the Zenong Group, as considered by the previous studies, but should be redefined as volcanic rocks of the Linzizong Group.
2020, 45(5): 1593-1608.
doi: 10.3799/dqkx.2019.190
Abstract:
Two main types of igneous rocks are distributed in the Cuizhong Fe polymetallic deposit, including the coarse-grained alkali-feldspar granite in the shallow part and the fine-grained alkali-feldspar granite at depth, whose relationships with ore mineralization have long been debated. Whole rock geochemistry, zircon U-Pb geochronology and Hf isotopic analyses are carried out for these two types of granitoids. Pb isotopic analyses are performed on both the granitoids and the sulfides. The coarse-grained alkali-feldspar granite and fine-grained alkali-feldspar granite yield weighted mean 206Pb/238U age of 503±2.9 Ma and 201±6.4 Ma respectively, indicating that they were formed during middle Caledonian and late Indosinian-early Yanshanian respectively.The Re-Os model age of molybdenite is 202±2.9 Ma, which is consistent with the crystallization age of the fine-grained alkali-feldspar granite.Zircons in the coarse-grained alkali-feldspar granite display εHf(t) values of -8.31 to 0.57, indicating that it was derived from partial melting of Mesoproterozoic crustal rocks. Zircon crystals in the fine-grained alkali-feldspar granite have εHf(t) values of 2.84 to 4.78, indicating that it was generated by reworking of newly-growing juvenile crustal material which was originated from depleted mantle. In combination with the metallogenic and petrologic ages, trend surface analysis of ore-forming elements, and the comparison of Pb isotopes, we suggest that the mineralization in the Cuizhong Fe polymetallic deposit is genetically associated with the fine-grained alkali-feldspar granite. The polymetallic mineralization was generated in a compressional tectonic setting in response to the subduction of the Jiamusi Block towards the Songnen Block.
Two main types of igneous rocks are distributed in the Cuizhong Fe polymetallic deposit, including the coarse-grained alkali-feldspar granite in the shallow part and the fine-grained alkali-feldspar granite at depth, whose relationships with ore mineralization have long been debated. Whole rock geochemistry, zircon U-Pb geochronology and Hf isotopic analyses are carried out for these two types of granitoids. Pb isotopic analyses are performed on both the granitoids and the sulfides. The coarse-grained alkali-feldspar granite and fine-grained alkali-feldspar granite yield weighted mean 206Pb/238U age of 503±2.9 Ma and 201±6.4 Ma respectively, indicating that they were formed during middle Caledonian and late Indosinian-early Yanshanian respectively.The Re-Os model age of molybdenite is 202±2.9 Ma, which is consistent with the crystallization age of the fine-grained alkali-feldspar granite.Zircons in the coarse-grained alkali-feldspar granite display εHf(t) values of -8.31 to 0.57, indicating that it was derived from partial melting of Mesoproterozoic crustal rocks. Zircon crystals in the fine-grained alkali-feldspar granite have εHf(t) values of 2.84 to 4.78, indicating that it was generated by reworking of newly-growing juvenile crustal material which was originated from depleted mantle. In combination with the metallogenic and petrologic ages, trend surface analysis of ore-forming elements, and the comparison of Pb isotopes, we suggest that the mineralization in the Cuizhong Fe polymetallic deposit is genetically associated with the fine-grained alkali-feldspar granite. The polymetallic mineralization was generated in a compressional tectonic setting in response to the subduction of the Jiamusi Block towards the Songnen Block.
2020, 45(5): 1609-1621.
doi: 10.3799/dqkx.2019.155
Abstract:
Erlian basin is one of the most important energy mineral bases bearing coal, oil and uranium. Although both of coal and uranium deposits mainly occur in lower Cretaceous Saihantala Formation, previous data reveal that most of coal mines are distributed in the eastern Erlian basin; while major uranium deposits are found in the midwestern Erlian basin. In order to understand the tectono-sedimentary evolution progress and its constraints on mineralization of coal and uranium, we took Saihantala Formation sandstones in Engeriyin area of southern Manite depression for geochemical and detrital zircons geochronological analysis. Combined with previous seismic data in eastern and western Manite depression, we conclude that (1) the lower and upper subinterval of the lower Saihantala Formation in southern Manite depression have different provenances, and the lower subinterval is composed of terrigenous materials from Bayinbaolige rise, while the upper subinterval from Sunite rise, which may indicate the Sunite rise began to uplift in the late substage of the Early Saihantala period; (2) the water depth became shallow in Southern Manite depression during the middle period of Saihantala and it counted against the formation of coal; (3) the uplift of Sunite rise might provide beneficial tectonic condition for uranium mineralization in the lower Saihantala Formation in southern Manite depression. This is significant for us to understand the space allocation of coal and uranium in Erlian basin and evaluate the uranium metallogenic prospects in southern Manite depression.
Erlian basin is one of the most important energy mineral bases bearing coal, oil and uranium. Although both of coal and uranium deposits mainly occur in lower Cretaceous Saihantala Formation, previous data reveal that most of coal mines are distributed in the eastern Erlian basin; while major uranium deposits are found in the midwestern Erlian basin. In order to understand the tectono-sedimentary evolution progress and its constraints on mineralization of coal and uranium, we took Saihantala Formation sandstones in Engeriyin area of southern Manite depression for geochemical and detrital zircons geochronological analysis. Combined with previous seismic data in eastern and western Manite depression, we conclude that (1) the lower and upper subinterval of the lower Saihantala Formation in southern Manite depression have different provenances, and the lower subinterval is composed of terrigenous materials from Bayinbaolige rise, while the upper subinterval from Sunite rise, which may indicate the Sunite rise began to uplift in the late substage of the Early Saihantala period; (2) the water depth became shallow in Southern Manite depression during the middle period of Saihantala and it counted against the formation of coal; (3) the uplift of Sunite rise might provide beneficial tectonic condition for uranium mineralization in the lower Saihantala Formation in southern Manite depression. This is significant for us to understand the space allocation of coal and uranium in Erlian basin and evaluate the uranium metallogenic prospects in southern Manite depression.
2020, 45(5): 1622-1635.
doi: 10.3799/dqkx.2019.160
Abstract:
To understand the thinning process of the western margin of the Pearl River Mouth basin, structure analysis, quantitative calculation and comparison between fault growth rate and one-dimensional unloaded tectonic subsidence were carried out to study the structural deformation and migration characteristics. It is found that extensional structures controlled by listric and detachment faults are dominant and inherited. The fault activity and tectonic subsidence were concentrated in Kaiping sag in the first rifting stage, and the maximum rates reached 239 m/myr and 108.6 m/myr, respectively. The fault activity and tectonic subsidence migrated to the ocean basin in the second rifting stage, and the maximum rates reached 192 m/myr and 210.7 m/myr, respectively. In the first rifting stage, lithospheric thinning was dominated by brittle crust thinning. In the second rifting stage, lithospheric thinning center migrated oceanward, regional thinning and asthenosphere upwelling mitigated the subsidence in sagson shelf and slope, at the same time the lithosphere in the ocean basin area thinned rapidly till break-up happened. The upper crust thins faster than lower crust in the northern COT of the Southwest Sub sea basin, compared with the situation in its southern conjugate margin, where the upper crust is thick and the lower crust is thin or even absent, we suggest that the northwest sub-basin may have undergone asymmetric simple shear thinning before break-up happened.
To understand the thinning process of the western margin of the Pearl River Mouth basin, structure analysis, quantitative calculation and comparison between fault growth rate and one-dimensional unloaded tectonic subsidence were carried out to study the structural deformation and migration characteristics. It is found that extensional structures controlled by listric and detachment faults are dominant and inherited. The fault activity and tectonic subsidence were concentrated in Kaiping sag in the first rifting stage, and the maximum rates reached 239 m/myr and 108.6 m/myr, respectively. The fault activity and tectonic subsidence migrated to the ocean basin in the second rifting stage, and the maximum rates reached 192 m/myr and 210.7 m/myr, respectively. In the first rifting stage, lithospheric thinning was dominated by brittle crust thinning. In the second rifting stage, lithospheric thinning center migrated oceanward, regional thinning and asthenosphere upwelling mitigated the subsidence in sagson shelf and slope, at the same time the lithosphere in the ocean basin area thinned rapidly till break-up happened. The upper crust thins faster than lower crust in the northern COT of the Southwest Sub sea basin, compared with the situation in its southern conjugate margin, where the upper crust is thick and the lower crust is thin or even absent, we suggest that the northwest sub-basin may have undergone asymmetric simple shear thinning before break-up happened.
2020, 45(5): 1636-1652.
doi: 10.3799/dqkx.2019.195
Abstract:
A east-west trending ductile deformation zone was identified between the Kanggur fault and Yamansu fault within the Carboniferous sedimental-volcanic series in the eastern Tianshan mountains. The deformation zone exhibits different characteristics in its evolutionary process, namely, the early stage ductile compressional deformation, and the later right lateral shear deformation. In this paper, the macrostructure (foliation, lineation, symmetrical boudinage structure and asymmetric fold, etc.), and microstructure (pressure shadow, boudinage structure, dynamic recrystallization, different types of gravel deformation, etc.) of early ductile compressed deformation were studied in detail. Systematic measurement of the finite strains of quartz and triaxial strain rate in mylonites indicates that the strain type in general compression is L-S and LS tectonites. The quartz grains occur as subgrain rotation recrystallization and a small amount of grain boundary migration recrystallization, and the feldspar porphyroclasts are elongated and some are fully bulging recrystallized. Quartz C-axis fabrics (EBSD) reveal that quartz fabrics are mainly middle temperature prismatic slip and rhomb slip system, and the later superimposed low temperature is slip-based. It is suggested that the deformation temperature of the early ductile compressional ranges from 450 ℃ to 550 ℃. Combined with regional tectonic, the early ductile compressional of Kanggur ductile deformation zone was formed in 300-290 Ma, which was related to the intracon-tinental N-S compression environment after collision between the Tarim plate and the middle Tianshan plate.
A east-west trending ductile deformation zone was identified between the Kanggur fault and Yamansu fault within the Carboniferous sedimental-volcanic series in the eastern Tianshan mountains. The deformation zone exhibits different characteristics in its evolutionary process, namely, the early stage ductile compressional deformation, and the later right lateral shear deformation. In this paper, the macrostructure (foliation, lineation, symmetrical boudinage structure and asymmetric fold, etc.), and microstructure (pressure shadow, boudinage structure, dynamic recrystallization, different types of gravel deformation, etc.) of early ductile compressed deformation were studied in detail. Systematic measurement of the finite strains of quartz and triaxial strain rate in mylonites indicates that the strain type in general compression is L-S and LS tectonites. The quartz grains occur as subgrain rotation recrystallization and a small amount of grain boundary migration recrystallization, and the feldspar porphyroclasts are elongated and some are fully bulging recrystallized. Quartz C-axis fabrics (EBSD) reveal that quartz fabrics are mainly middle temperature prismatic slip and rhomb slip system, and the later superimposed low temperature is slip-based. It is suggested that the deformation temperature of the early ductile compressional ranges from 450 ℃ to 550 ℃. Combined with regional tectonic, the early ductile compressional of Kanggur ductile deformation zone was formed in 300-290 Ma, which was related to the intracon-tinental N-S compression environment after collision between the Tarim plate and the middle Tianshan plate.
2020, 45(5): 1653-1675.
doi: 10.3799/dqkx.2019.151
Abstract:
The Phanerozoic tectonic evolution of the Yunkai massif has long been one of the hot topics in the South China Block. LA-ICP-MS U-Pb dating was carried out on the monazite, apatite and zircon of two gneiss samples from the Yunkai massif, yielding two magmatic zircon ages of 434±6 Ma (MSWD=3.0) and 437±12 Ma (MSWD=6.0) respectively, which represent the crystallization age of gneiss protolith (granitic rocks) and are basically consistent with the ages of regional Caledonian tectonic-magmatic-metamorphic-anatexis events responding to the Wuyi-Yunkai Caledonian orogenesis. Apatite yields metamorphic ages of 241±13 Ma (MSWD=2.2) and 242±6 Ma (MSWD=1.4) respectively; and monazite also yields metamorphic ages of 236.2±0.8 Ma (MSWD=0.66) and 229.4±1.2 Ma (MSWD=2.4) respectively. These U-Pb ages are consistent with the biotite Ar-Ar ages of the tectonite in the Yunkai massif, indicating the Indosinian (230-240 Ma) tectono-thermal reworking in the Yunkai massif. EPMA data of biotite from the gneiss show high Al, Ti and Mg contents, but low Fe content, with XMg ratios ranging from 0.37 to 0.45, which indicates ferruginous biotite affinity. The Ti saturation temperature of biotite is 650-700 ℃ (±50 ℃), agreeing with the monazite estimated temperature of 580-640 ℃ (±25 ℃), which indicates that the temperature of Indosinian reworking maybe reached up to 700 ℃. In conclusion, the present tectonic pattern of the Yunkai massif is superimposed by Indosinian tectono-thermal events on the basis of Caledonian orogeny, and the superimposed temperature may reach 700 ℃. In addition, the effect of Indosinian tectono-thermal events on mineral composition should be taken into account when restoring Caledonian metamorphic P-T path with mineral thermometers and baresthesiometers.
The Phanerozoic tectonic evolution of the Yunkai massif has long been one of the hot topics in the South China Block. LA-ICP-MS U-Pb dating was carried out on the monazite, apatite and zircon of two gneiss samples from the Yunkai massif, yielding two magmatic zircon ages of 434±6 Ma (MSWD=3.0) and 437±12 Ma (MSWD=6.0) respectively, which represent the crystallization age of gneiss protolith (granitic rocks) and are basically consistent with the ages of regional Caledonian tectonic-magmatic-metamorphic-anatexis events responding to the Wuyi-Yunkai Caledonian orogenesis. Apatite yields metamorphic ages of 241±13 Ma (MSWD=2.2) and 242±6 Ma (MSWD=1.4) respectively; and monazite also yields metamorphic ages of 236.2±0.8 Ma (MSWD=0.66) and 229.4±1.2 Ma (MSWD=2.4) respectively. These U-Pb ages are consistent with the biotite Ar-Ar ages of the tectonite in the Yunkai massif, indicating the Indosinian (230-240 Ma) tectono-thermal reworking in the Yunkai massif. EPMA data of biotite from the gneiss show high Al, Ti and Mg contents, but low Fe content, with XMg ratios ranging from 0.37 to 0.45, which indicates ferruginous biotite affinity. The Ti saturation temperature of biotite is 650-700 ℃ (±50 ℃), agreeing with the monazite estimated temperature of 580-640 ℃ (±25 ℃), which indicates that the temperature of Indosinian reworking maybe reached up to 700 ℃. In conclusion, the present tectonic pattern of the Yunkai massif is superimposed by Indosinian tectono-thermal events on the basis of Caledonian orogeny, and the superimposed temperature may reach 700 ℃. In addition, the effect of Indosinian tectono-thermal events on mineral composition should be taken into account when restoring Caledonian metamorphic P-T path with mineral thermometers and baresthesiometers.
2020, 45(5): 1676-1705.
doi: 10.3799/dqkx.2020.010
Abstract:
With the increasing global energy consumption and deepening glutenite oil and gas reservoirs study, glutenite reservoirs have become a new field of oil and gas exploration, especially since the significant discoveries of conglomeratic reservoirs in the Mahu area, Junggar basin of Xinjiang, and integrated condensate gas field of BZ19-6 in the offshore Bohai Bay basin. At present, the research on the sedimentary response of glutenite is concentrated on the background of steep slope or orogenic belt, focusing on the analysis of the forms, structural styles, controlling factors, depositional modes and differences of alluvial fan, fan delta, nearshore subaqueous fan and sublacustrine fan systems, but there are multiple explanations for the genetic mechanism. Glutenites in the offshore Bohai Bay basin are mainly developed in Eocene steep slope background and early Miocene gentle slope background. Among them, Eocene glutenite presents a near-source accumulation along the fault steep slope belt, and the hotspots focus on its structure identification and period characterization, so as to accurately predict the spatial and temporal distribution of underground glutenite reservoirs. However, at the transition interface of the early Miocene, a set of glutenite is widely distributed and accompanied by magmatic activities. The difficulty lies in defining the response relationship between sedimentological and chronological information of glutenite and the evolution of tectonic plates, and determining the genetic mechanism and development mode of large-scale glutenite reservoirs distribution. Sedimentary response research direction of glutenite will be based on the principles and standard of lithofacies subdivision, to deepen its relationship with regional tectonic events, analyze the infilling processes quantitatively and depict its trap target of industrialization. These results would not only offer better understanding of the formation and evolution of Cenozoic Bohai Bay basin, but also facilitate the exploration of the middle and large-scale oil and gas fields with the type of glutenite in the offshore Bohai Bay basin.
With the increasing global energy consumption and deepening glutenite oil and gas reservoirs study, glutenite reservoirs have become a new field of oil and gas exploration, especially since the significant discoveries of conglomeratic reservoirs in the Mahu area, Junggar basin of Xinjiang, and integrated condensate gas field of BZ19-6 in the offshore Bohai Bay basin. At present, the research on the sedimentary response of glutenite is concentrated on the background of steep slope or orogenic belt, focusing on the analysis of the forms, structural styles, controlling factors, depositional modes and differences of alluvial fan, fan delta, nearshore subaqueous fan and sublacustrine fan systems, but there are multiple explanations for the genetic mechanism. Glutenites in the offshore Bohai Bay basin are mainly developed in Eocene steep slope background and early Miocene gentle slope background. Among them, Eocene glutenite presents a near-source accumulation along the fault steep slope belt, and the hotspots focus on its structure identification and period characterization, so as to accurately predict the spatial and temporal distribution of underground glutenite reservoirs. However, at the transition interface of the early Miocene, a set of glutenite is widely distributed and accompanied by magmatic activities. The difficulty lies in defining the response relationship between sedimentological and chronological information of glutenite and the evolution of tectonic plates, and determining the genetic mechanism and development mode of large-scale glutenite reservoirs distribution. Sedimentary response research direction of glutenite will be based on the principles and standard of lithofacies subdivision, to deepen its relationship with regional tectonic events, analyze the infilling processes quantitatively and depict its trap target of industrialization. These results would not only offer better understanding of the formation and evolution of Cenozoic Bohai Bay basin, but also facilitate the exploration of the middle and large-scale oil and gas fields with the type of glutenite in the offshore Bohai Bay basin.
2020, 45(5): 1706-1721.
doi: 10.3799/dqkx.2019.174
Abstract:
Based on core observation, thin section examination, scanning electron microscopy, X-ray diffraction analysis and other experimental means, the reservoir performance, diagenetic characteristics and main control factors of conglomerate reservoir quality are studied in the third member of Liushagang Formation of northwest steep slope zone in Weixinan depression, combined with physical properties, organic matter thermal evolution, burial history and logging data. The results show as follows: (1) The main rock type of study area is litharenite, and the main lithologies are glutenite, conglomeratic sandstone and other coarse grained sandstones, with varying reservoir space types such as intragranular dissolved pores, residual intergranular pores, and mold pores. The physical properties, characterized by low porosity-ultra low permeability, medium porosity-low permeability, medium porosity-permeability and high porosity-permeability, show strong heterogeneity. (2) Continuous compaction is the major reason for the deterioration of physical properties. Carbonate cementations and authigenic clay minerals filling result in the loss of some primary pores, and the sites with high argillaceous content are characterized by early strong compaction. The medium strong dissolution of coarse grained sandstone is conducive to the development of secondary pores, and micro-fracture is one of the most important flow passages in deep glutenite reservoirs. The fan-delta subaqueous distributary channel in the third member of Liushagang Formation of the northwest steep slope zone develops thick layers of glutenite and conglomeratic sandstone with low content of matrix and weak compaction. It is a high-quality reservoir development zone in the study area. The compaction of sublacustrine fan is strong, while the micro-fracture provides the flow passages for organic acidic fluid migration. The secondary dissolution of the conglomerate reservoir improves the reservoir performance and is relatively favorable reservoir for the deep sandstones.
Based on core observation, thin section examination, scanning electron microscopy, X-ray diffraction analysis and other experimental means, the reservoir performance, diagenetic characteristics and main control factors of conglomerate reservoir quality are studied in the third member of Liushagang Formation of northwest steep slope zone in Weixinan depression, combined with physical properties, organic matter thermal evolution, burial history and logging data. The results show as follows: (1) The main rock type of study area is litharenite, and the main lithologies are glutenite, conglomeratic sandstone and other coarse grained sandstones, with varying reservoir space types such as intragranular dissolved pores, residual intergranular pores, and mold pores. The physical properties, characterized by low porosity-ultra low permeability, medium porosity-low permeability, medium porosity-permeability and high porosity-permeability, show strong heterogeneity. (2) Continuous compaction is the major reason for the deterioration of physical properties. Carbonate cementations and authigenic clay minerals filling result in the loss of some primary pores, and the sites with high argillaceous content are characterized by early strong compaction. The medium strong dissolution of coarse grained sandstone is conducive to the development of secondary pores, and micro-fracture is one of the most important flow passages in deep glutenite reservoirs. The fan-delta subaqueous distributary channel in the third member of Liushagang Formation of the northwest steep slope zone develops thick layers of glutenite and conglomeratic sandstone with low content of matrix and weak compaction. It is a high-quality reservoir development zone in the study area. The compaction of sublacustrine fan is strong, while the micro-fracture provides the flow passages for organic acidic fluid migration. The secondary dissolution of the conglomerate reservoir improves the reservoir performance and is relatively favorable reservoir for the deep sandstones.
2020, 45(5): 1722-1736.
doi: 10.3799/dqkx.2019.188
Abstract:
The western slope of Xihu deprssion is the realistic choice and main field of current petroleum exploration in East China Sea basin. However, there is no consensus reached on the basic geological problems such as the formation conditions and distribution rule of source rock. Based on sedimentology, coal petrography and organic geochemistry, using the drilling data, organic geochemistry of source rock and paleontology, genetic types and formation conditions of source rock of Pinghu Formation in western slope of Xihu depression have been systematically analyzed in this study. In addition, the organic facies division method corresponding to sedimentary environment has been established, and distribution law has been summarized.It is found that the source rocks are mainly coal-bearing source rocks, and secondly marine mudstones. The north-central region of western slope mainly develops costal sedimentary system affected by tidal, while the south-central region of western slope develops tidal-flat and semi-enclosed gulf system. Different sedimentary environments determine different types of source rocks. The tidal-flat and lagoon have higher coal-bearing development degree and hydrocarbon generation capacity than delta. This research is significant for source rock evaluation, reservoir prediction and exploration deployment in western slope.
The western slope of Xihu deprssion is the realistic choice and main field of current petroleum exploration in East China Sea basin. However, there is no consensus reached on the basic geological problems such as the formation conditions and distribution rule of source rock. Based on sedimentology, coal petrography and organic geochemistry, using the drilling data, organic geochemistry of source rock and paleontology, genetic types and formation conditions of source rock of Pinghu Formation in western slope of Xihu depression have been systematically analyzed in this study. In addition, the organic facies division method corresponding to sedimentary environment has been established, and distribution law has been summarized.It is found that the source rocks are mainly coal-bearing source rocks, and secondly marine mudstones. The north-central region of western slope mainly develops costal sedimentary system affected by tidal, while the south-central region of western slope develops tidal-flat and semi-enclosed gulf system. Different sedimentary environments determine different types of source rocks. The tidal-flat and lagoon have higher coal-bearing development degree and hydrocarbon generation capacity than delta. This research is significant for source rock evaluation, reservoir prediction and exploration deployment in western slope.
2020, 45(5): 1737-1753.
doi: 10.3799/dqkx.2019.157
Abstract:
Volatile reservoir and light reservoir have been discovered in the ultra-deep Ordovician Yijianfang to Yingshan Formations with vertical depths ranging from 7 200 to 7 863.60 m from North Shuntuoguole area in the Tarim basin. The limit depth of oil phase occurring has been continuously challenging the traditional theory. This study focuses on geochemical characteristics and secondary alterations of reservoirs from different faults in North Shuntuoguole area. Most oils of different faults from North Shuntuoguole area are characterized by light carbon isotope, C23TT/C21TT > 1, lower C28 sterane content, relatively high abundance of dibenzothiophene, suggesting that the source rock of oil in the North Shuntuoguole area is similar to that of Tahe oilfield. Using (C21+C22) sterane/(C27~C29) sterane, C27 diasterane/C27 regular steane, MPI index, dibenthiophene series maturity, the oil maturity trend in the North Shuntuoguole area is No.1 fault (including splay fault) ≈No.3 fault > secondary fault > No.5 fault > No.7 fault. The oil maturity is controlled by the reservoir initial static temperature. The natural gas in North Shuntuoguole area is wet gas and has light methane carbon isotope, ranging from -50.7‰ to -44.7‰. The gas maturity trend in different faults is similar to that of the oil. The abundance of (4-+3-) methyldiamantane in the oils from different faults is in the range of 9.25-36.44 μg/g, indicating low degree of oil cracking. The lower thiadiamondoids can be detected in the oils, with content ranging from 0.76 to 18.88 μg/g, showing low degree of thermochemical sulfate reduction (TSR). The Ordovician reservoir has suffered little gas invasion from the natural gas characteristics. The formation temperature indicates the geothermal gradient in the North Shuntuoguole area is low, only about 2.12 ℃/100 m. The formation temperature of strata buried at 8 000 m depth at present is in the range of 160-170 ℃. The maximum paleo-geotemperature of Ordovician has never been higher than 170 ℃, without reaching the temperature threshold of great scale oil cracking. The long term of low geothermal environment combined with low degree secondary alteration is the key to the preservation of ultra-deep Ordovician volatile reservoir in the North Shuntuogule area.
Volatile reservoir and light reservoir have been discovered in the ultra-deep Ordovician Yijianfang to Yingshan Formations with vertical depths ranging from 7 200 to 7 863.60 m from North Shuntuoguole area in the Tarim basin. The limit depth of oil phase occurring has been continuously challenging the traditional theory. This study focuses on geochemical characteristics and secondary alterations of reservoirs from different faults in North Shuntuoguole area. Most oils of different faults from North Shuntuoguole area are characterized by light carbon isotope, C23TT/C21TT > 1, lower C28 sterane content, relatively high abundance of dibenzothiophene, suggesting that the source rock of oil in the North Shuntuoguole area is similar to that of Tahe oilfield. Using (C21+C22) sterane/(C27~C29) sterane, C27 diasterane/C27 regular steane, MPI index, dibenthiophene series maturity, the oil maturity trend in the North Shuntuoguole area is No.1 fault (including splay fault) ≈No.3 fault > secondary fault > No.5 fault > No.7 fault. The oil maturity is controlled by the reservoir initial static temperature. The natural gas in North Shuntuoguole area is wet gas and has light methane carbon isotope, ranging from -50.7‰ to -44.7‰. The gas maturity trend in different faults is similar to that of the oil. The abundance of (4-+3-) methyldiamantane in the oils from different faults is in the range of 9.25-36.44 μg/g, indicating low degree of oil cracking. The lower thiadiamondoids can be detected in the oils, with content ranging from 0.76 to 18.88 μg/g, showing low degree of thermochemical sulfate reduction (TSR). The Ordovician reservoir has suffered little gas invasion from the natural gas characteristics. The formation temperature indicates the geothermal gradient in the North Shuntuoguole area is low, only about 2.12 ℃/100 m. The formation temperature of strata buried at 8 000 m depth at present is in the range of 160-170 ℃. The maximum paleo-geotemperature of Ordovician has never been higher than 170 ℃, without reaching the temperature threshold of great scale oil cracking. The long term of low geothermal environment combined with low degree secondary alteration is the key to the preservation of ultra-deep Ordovician volatile reservoir in the North Shuntuogule area.
2020, 45(5): 1754-1768.
doi: 10.3799/dqkx.2019.175
Abstract:
Potential fault zone refers to the weak deformation fault trend zone reflected by the fracture development zone or a series of geological body alignment before the formation of the main section in the early stage of fault development. In order to study the formation mechanism of potential fault zones in Ordos basin and their control on hydrocarbon migration and accumulation, basin-level, depression-level, sag-level and trap-level potential fault zones were identified in Ordos basin by fully utilizing the data of oil and gas exploration and field investigation on the basis of gravity, magnetism and regional geology analysis. These potential fault zones can be divided into east-west, north-west and north-east directions according to their strike. According to the sequence from recessive to dominant, the evolution of the potential fault zone can be divided into five basic stages: the development period of dense caprock fractures, the linear distribution period of echelon faults, the intermittent formation period of fracture surface, the successive connection period of fracture surface and the connection of fracture surfaces period. It is concluded that the potential fault zone has important impact on hydrocarbon generation and accumulation, regulating the structural pattern of basin, dividing depressions and uplifts, accelerating the development of source rocks, controlling the distribution of sedimentary systems, and improving reservoir and transport system. The development area of potential fault zone is often the target area for hydrocarbon accumulation.
Potential fault zone refers to the weak deformation fault trend zone reflected by the fracture development zone or a series of geological body alignment before the formation of the main section in the early stage of fault development. In order to study the formation mechanism of potential fault zones in Ordos basin and their control on hydrocarbon migration and accumulation, basin-level, depression-level, sag-level and trap-level potential fault zones were identified in Ordos basin by fully utilizing the data of oil and gas exploration and field investigation on the basis of gravity, magnetism and regional geology analysis. These potential fault zones can be divided into east-west, north-west and north-east directions according to their strike. According to the sequence from recessive to dominant, the evolution of the potential fault zone can be divided into five basic stages: the development period of dense caprock fractures, the linear distribution period of echelon faults, the intermittent formation period of fracture surface, the successive connection period of fracture surface and the connection of fracture surfaces period. It is concluded that the potential fault zone has important impact on hydrocarbon generation and accumulation, regulating the structural pattern of basin, dividing depressions and uplifts, accelerating the development of source rocks, controlling the distribution of sedimentary systems, and improving reservoir and transport system. The development area of potential fault zone is often the target area for hydrocarbon accumulation.
2020, 45(5): 1769-1781.
doi: 10.3799/dqkx.2019.187
Abstract:
The deep area of Biyang depression contains considerable lithologic hydrocarbon reservoirs, and the present pressure is mostly shown as normal-weak overpressure system. In this study, the paleopressure evolution history of the deep depression has been revealed combining with the numerical simulation and thermodynamics of fluid inclusion. The hydrocarbon generation history shows that the Biyang depression reached the peak of hydrocarbon generation when it reached the maximum burial depth at the end of the sedimentation of the Liaozhuang Formation (about 23.03 Ma). After the formation uplift, the hydrocarbon generation weakened and approached to a stop. Two different oil inclusions were detected in the deep sandstone reservoir, which were the orange-yellow fluorescent oil inclusion with low maturity and the blue-green fluorescent oil inclusion with relatively high maturity. The homogenization temperature of the inclusion combined with the burial history chart shows that the hydrocarbon charging time is 35.4-30.3 Ma and 27.8-26.5 Ma respectively. The numerical simulation results show that the pressure in the deep continued to increase from 39.3 Ma, and reached an obviously overpressure at about 23.03 Ma at the deepest burial. The pressure coefficient reached to about 1.5, and then the overpressure weakened and evolved into the present normal-weak overpressure system. The paleo-pressure of the thermodynamic simulation of the inclusions also shows a similar evolutionary trend. In conclusion, the coupling of the hydrocarbon generation period, the charging event and the overpressure period indicate that the present lithologic reservoir in deep is attributed to two-stage hydrocarbon charging driven by overpressure caused by hydrocarbon generation.
The deep area of Biyang depression contains considerable lithologic hydrocarbon reservoirs, and the present pressure is mostly shown as normal-weak overpressure system. In this study, the paleopressure evolution history of the deep depression has been revealed combining with the numerical simulation and thermodynamics of fluid inclusion. The hydrocarbon generation history shows that the Biyang depression reached the peak of hydrocarbon generation when it reached the maximum burial depth at the end of the sedimentation of the Liaozhuang Formation (about 23.03 Ma). After the formation uplift, the hydrocarbon generation weakened and approached to a stop. Two different oil inclusions were detected in the deep sandstone reservoir, which were the orange-yellow fluorescent oil inclusion with low maturity and the blue-green fluorescent oil inclusion with relatively high maturity. The homogenization temperature of the inclusion combined with the burial history chart shows that the hydrocarbon charging time is 35.4-30.3 Ma and 27.8-26.5 Ma respectively. The numerical simulation results show that the pressure in the deep continued to increase from 39.3 Ma, and reached an obviously overpressure at about 23.03 Ma at the deepest burial. The pressure coefficient reached to about 1.5, and then the overpressure weakened and evolved into the present normal-weak overpressure system. The paleo-pressure of the thermodynamic simulation of the inclusions also shows a similar evolutionary trend. In conclusion, the coupling of the hydrocarbon generation period, the charging event and the overpressure period indicate that the present lithologic reservoir in deep is attributed to two-stage hydrocarbon charging driven by overpressure caused by hydrocarbon generation.
2020, 45(5): 1782-1790.
doi: 10.3799/dqkx.2019.194
Abstract:
The adsorption gas is one of the main occurrence states of the shale gas, so the accurate evaluation of the adsorption gas amount is important for exploration. The key for the applicability of the models lies in whether the adsorption model obeys the occurrence state and its micro mechanisms of shale gas on the pore walls, which is the critical factor influencing the accuracy of the evaluation of the adsorption gas amount. The occurrence state and its micro mechanisms of shale gas on the pore walls are investigated in this study, aiming at optimizing the adsorption model. By the Grand Canonical Monte Carlo (GCMC) method, the adsorption behavior of CH4 in both organic and illite pores was simulated, and the molecular dynamic (MD) was performed on the molecular structure at a certain temperature and pressure. Based on the simulations, the gas distribution, the interaction distribution and density field were investigated to document the occurrence state and its micro mechanisms of shale gas on pore walls. It is found that the adsorption of shale gas on pore walls is not the single layer adsorption, and the adsorption phase can be divided into the strong adsorption layer, the weak adsorption layer and the trough of adsorption layer. The strong adsorption layer is mainly adsorbed by the pore walls, while the weak adsorption layer and the trough of adsorption layer are not only adsorbed by pore walls, but also adsorbed by the adsorption layers. This is inconsistent with the hypothetical condition of the Langmiur model or the BET model, so the reasonability of the models and the accuracy of the evaluating results would be limited. The occurrence state and its micro mechanisms of shale gas on pore walls revealed in this study can provide theoretical basis for optimizing and establishing adsorption models.
The adsorption gas is one of the main occurrence states of the shale gas, so the accurate evaluation of the adsorption gas amount is important for exploration. The key for the applicability of the models lies in whether the adsorption model obeys the occurrence state and its micro mechanisms of shale gas on the pore walls, which is the critical factor influencing the accuracy of the evaluation of the adsorption gas amount. The occurrence state and its micro mechanisms of shale gas on the pore walls are investigated in this study, aiming at optimizing the adsorption model. By the Grand Canonical Monte Carlo (GCMC) method, the adsorption behavior of CH4 in both organic and illite pores was simulated, and the molecular dynamic (MD) was performed on the molecular structure at a certain temperature and pressure. Based on the simulations, the gas distribution, the interaction distribution and density field were investigated to document the occurrence state and its micro mechanisms of shale gas on pore walls. It is found that the adsorption of shale gas on pore walls is not the single layer adsorption, and the adsorption phase can be divided into the strong adsorption layer, the weak adsorption layer and the trough of adsorption layer. The strong adsorption layer is mainly adsorbed by the pore walls, while the weak adsorption layer and the trough of adsorption layer are not only adsorbed by pore walls, but also adsorbed by the adsorption layers. This is inconsistent with the hypothetical condition of the Langmiur model or the BET model, so the reasonability of the models and the accuracy of the evaluating results would be limited. The occurrence state and its micro mechanisms of shale gas on pore walls revealed in this study can provide theoretical basis for optimizing and establishing adsorption models.
2020, 45(5): 1791-1806.
doi: 10.3799/dqkx.2019.165
Abstract:
This study focuses on the sedimentary characteristics of Huangyangquan fan through field investigation and trench excavation combined with satellite image interpretation and Quaternary geological as well as historical geography analysis. The authors suggest that the Huangyangquan fan is a fluvial fan developed in the inland arid area of northwestern Junggar basin margin, which is a gourd in plan metric shape and can be divided into three parts, namely, upper fan, middle fan and fan margin. The fan is dominated by fluvial deposits but not debris flow deposits. The channel is most of ephemeral with minor intermittent channel. The effect of wind on the sediment of fluvial fan surface is obvious. The fan is terminated in 4 types as into Eric lake, to the marshes, to the shore of small lakes and to an terrain block, these are all different to either of normal alluvial fan or fan deltas.Research shows that the ancient Manas lake appeared six times high level in the Quaternary. Before 30 ka, the fan was surrounded by ancient Manas lake as a fluvial fan delta system, after that time it changed gradually to be an fluvial fan due to the lake level down. The depositional model has been built based the historical geography research results to interpret the evolution of the fan from fluvial fan delta to fluvial fan system, and it shows the present Huangyangquan fan is in the transition period from fan delta to fluvial fan system.
This study focuses on the sedimentary characteristics of Huangyangquan fan through field investigation and trench excavation combined with satellite image interpretation and Quaternary geological as well as historical geography analysis. The authors suggest that the Huangyangquan fan is a fluvial fan developed in the inland arid area of northwestern Junggar basin margin, which is a gourd in plan metric shape and can be divided into three parts, namely, upper fan, middle fan and fan margin. The fan is dominated by fluvial deposits but not debris flow deposits. The channel is most of ephemeral with minor intermittent channel. The effect of wind on the sediment of fluvial fan surface is obvious. The fan is terminated in 4 types as into Eric lake, to the marshes, to the shore of small lakes and to an terrain block, these are all different to either of normal alluvial fan or fan deltas.Research shows that the ancient Manas lake appeared six times high level in the Quaternary. Before 30 ka, the fan was surrounded by ancient Manas lake as a fluvial fan delta system, after that time it changed gradually to be an fluvial fan due to the lake level down. The depositional model has been built based the historical geography research results to interpret the evolution of the fan from fluvial fan delta to fluvial fan system, and it shows the present Huangyangquan fan is in the transition period from fan delta to fluvial fan system.
Hydrochemical and Isotopic Markers of Groundwater Flow Systems in the Kashgar Delta Area in Xinjiang
2020, 45(5): 1807-1817.
doi: 10.3799/dqkx.2019.177
Abstract:
The shortage of groundwater caused by poor water quality is more prominent in the Kashgar delta of Xinjiang, so it is practical significance to study groundwater flow system. Based on the divisions of groundwater aquifer system in Kashgar delta, the characteristics of the groundwater hydrochemistry and cycle regeneration were analyzed using hydrogeochemistry and environmental isotope age test methods. The research results show that the delta aquifer system consists of unconfined groundwater in piedmont sloping alluvial-diluvial plain, unconfined groundwater in river alluvial plain and confined groundwater in river alluvial plain. The evolution of groundwater hydrochemistry types is HCO3·SO4-Ca→SO4-Ca→SO4·Cl-Mg·Na→SO4·Cl-Na along the groundwater flow direction. With the increased TDS, the groundwater quality tends towards salinization. Piedmont sloping alluvial-diluvial plain is the main dissolution-runoff zone and the river alluvial plain is main runoff-accumulation salt zone. The groundwater renewal rate in the study area is 0.03%~16.35%·a-1, which is characterized by unconfined groundwater in piedmont sloping alluvial-diluvial plain > unconfined groundwater in river alluvial plain > confined groundwater in river alluvial plain. Estimated by 3H, the age of unconfined groundwater in piedmont sloping alluvial-diluvial plain is 8~49 a, with an average of 29 a.The age of unconfined groundwater in river alluvial plain is 14~ > 50 a, in which the average age of upper unconfined groundwater is 24 a, and the average age of lower unconfined groundwater is > 50 a. Estimated by 14C, the age of unconfined groundwater in river alluvial plain is 476~33 623 a, with an average of 8 106 a. The age of confined groundwater in river alluvial plain is 5 186~34 578 a, with an average of 30 043 a, being "older" than unconfined groundwater. Based on the above characteristics, the groundwater aquifer systems in Kashgar delta are divided into two local flow systems (Ⅰ1 and Ⅰ2) with faster renewal rate and a regional flow system (Ⅱ) with slow circulation.
The shortage of groundwater caused by poor water quality is more prominent in the Kashgar delta of Xinjiang, so it is practical significance to study groundwater flow system. Based on the divisions of groundwater aquifer system in Kashgar delta, the characteristics of the groundwater hydrochemistry and cycle regeneration were analyzed using hydrogeochemistry and environmental isotope age test methods. The research results show that the delta aquifer system consists of unconfined groundwater in piedmont sloping alluvial-diluvial plain, unconfined groundwater in river alluvial plain and confined groundwater in river alluvial plain. The evolution of groundwater hydrochemistry types is HCO3·SO4-Ca→SO4-Ca→SO4·Cl-Mg·Na→SO4·Cl-Na along the groundwater flow direction. With the increased TDS, the groundwater quality tends towards salinization. Piedmont sloping alluvial-diluvial plain is the main dissolution-runoff zone and the river alluvial plain is main runoff-accumulation salt zone. The groundwater renewal rate in the study area is 0.03%~16.35%·a-1, which is characterized by unconfined groundwater in piedmont sloping alluvial-diluvial plain > unconfined groundwater in river alluvial plain > confined groundwater in river alluvial plain. Estimated by 3H, the age of unconfined groundwater in piedmont sloping alluvial-diluvial plain is 8~49 a, with an average of 29 a.The age of unconfined groundwater in river alluvial plain is 14~ > 50 a, in which the average age of upper unconfined groundwater is 24 a, and the average age of lower unconfined groundwater is > 50 a. Estimated by 14C, the age of unconfined groundwater in river alluvial plain is 476~33 623 a, with an average of 8 106 a. The age of confined groundwater in river alluvial plain is 5 186~34 578 a, with an average of 30 043 a, being "older" than unconfined groundwater. Based on the above characteristics, the groundwater aquifer systems in Kashgar delta are divided into two local flow systems (Ⅰ1 and Ⅰ2) with faster renewal rate and a regional flow system (Ⅱ) with slow circulation.
2020, 45(5): 1818-1829.
doi: 10.3799/dqkx.2019.198
Abstract:
Planktonic bacteria is the key component of water ecosystem, playing an important role in processes of materials and energy cycle. In this study, we have collected 43 water samples from the surface water, middle water and bottom water in the summer Dali-nor lake, an inland closed lake in the Inner Mongolia Plateau. Based on 16S rRNA gene-based high throughput sequencing technology, the vertical variation characteristics and ecological function of planktonic bacterial community have been analyzed in detail. The results show that: in summer, the diversity of phytoplankton community in Dali lake is the highest in surface water, the lowest in middle water, and the richness is the highest in bottom water, and the lowest in middle water. In addition, the Actinobacteria is the most dominant class, which is 24.70% in the surface water, 21.06% in the middle water, and 24.77% in the bottom water respectively. Redundancy analysis results show that the dominant microbial acceptance indicators in different depths of water have different effects. The dominant microflora in surface water of Dali-nor lake is most affected by TDS and EC, which represent exogenous input. The dominant microflora in middle water is mainly affected by different forms of nutrient elements. In bottom water, the dominant microflora is most obviously affected by Chla and COD. And the change of water depth is also one of the key factors affecting the structure of dominant flora in middle and bottom water. On the whole, the vertical difference of the physical and chemical proxies caused by the change of water depth, has become one of the key factors affecting the structural characteristics of planktonic bacteria in summer Dali-nor lake.
Planktonic bacteria is the key component of water ecosystem, playing an important role in processes of materials and energy cycle. In this study, we have collected 43 water samples from the surface water, middle water and bottom water in the summer Dali-nor lake, an inland closed lake in the Inner Mongolia Plateau. Based on 16S rRNA gene-based high throughput sequencing technology, the vertical variation characteristics and ecological function of planktonic bacterial community have been analyzed in detail. The results show that: in summer, the diversity of phytoplankton community in Dali lake is the highest in surface water, the lowest in middle water, and the richness is the highest in bottom water, and the lowest in middle water. In addition, the Actinobacteria is the most dominant class, which is 24.70% in the surface water, 21.06% in the middle water, and 24.77% in the bottom water respectively. Redundancy analysis results show that the dominant microbial acceptance indicators in different depths of water have different effects. The dominant microflora in surface water of Dali-nor lake is most affected by TDS and EC, which represent exogenous input. The dominant microflora in middle water is mainly affected by different forms of nutrient elements. In bottom water, the dominant microflora is most obviously affected by Chla and COD. And the change of water depth is also one of the key factors affecting the structure of dominant flora in middle and bottom water. On the whole, the vertical difference of the physical and chemical proxies caused by the change of water depth, has become one of the key factors affecting the structural characteristics of planktonic bacteria in summer Dali-nor lake.
2020, 45(5): 1830-1843.
doi: 10.3799/dqkx.2019.206
Abstract:
The distribution characteristics and sources of DIC and nitrate in the Lijiang River basin are studied using isotope mass balance models, by which the hydrochemical composition of the surface and underground rivers in the Lijiang River basin, δ13CDIC, δ15N-NO3- and δ18O-NO3- are measured and analyzed. The results show that the concentration of DIC (HCO3-) and inorganic carbon stable isotopes (δ13CDIC) in Lijiang River basin range from 12.20 to 402.60 mg·L-1, and from -17.29‰ to -10.01‰ respectively, with the average value of 140.3 mg·L-1 and -13.06‰ respectively. The concentration of NO3- is between 2.37 and 35.38 mg·L-1, and δ15N-NO3- is between 0.99‰ and 11.09‰, both showing obvious spatial variation characteristics. It is concluded that organic manure and sewage have the most significant contribution to nitrate in the Lijiang River basin, with a contribution ratio of 57.00%, which is followed by NH4+ in fertilizer and precipitation, and soil N, with contribution ratios of 36.45% and 6.55% respectively. The source of DIC in the drainage basin is mainly due to the weathering of carbonate rocks and the dissolution of soil CO2, which is also affected by the corrosion of carbonate rocks by nitric acid and atmospheric CO2. The corrosion intensity of nitric acid on carbonate rocks is controlled not only by the degree of nitrogen pollution in water, but also by the source of nitrogen pollution. The results can provide a basis for customizing effective nitrate input channels and purifying water quality.
The distribution characteristics and sources of DIC and nitrate in the Lijiang River basin are studied using isotope mass balance models, by which the hydrochemical composition of the surface and underground rivers in the Lijiang River basin, δ13CDIC, δ15N-NO3- and δ18O-NO3- are measured and analyzed. The results show that the concentration of DIC (HCO3-) and inorganic carbon stable isotopes (δ13CDIC) in Lijiang River basin range from 12.20 to 402.60 mg·L-1, and from -17.29‰ to -10.01‰ respectively, with the average value of 140.3 mg·L-1 and -13.06‰ respectively. The concentration of NO3- is between 2.37 and 35.38 mg·L-1, and δ15N-NO3- is between 0.99‰ and 11.09‰, both showing obvious spatial variation characteristics. It is concluded that organic manure and sewage have the most significant contribution to nitrate in the Lijiang River basin, with a contribution ratio of 57.00%, which is followed by NH4+ in fertilizer and precipitation, and soil N, with contribution ratios of 36.45% and 6.55% respectively. The source of DIC in the drainage basin is mainly due to the weathering of carbonate rocks and the dissolution of soil CO2, which is also affected by the corrosion of carbonate rocks by nitric acid and atmospheric CO2. The corrosion intensity of nitric acid on carbonate rocks is controlled not only by the degree of nitrogen pollution in water, but also by the source of nitrogen pollution. The results can provide a basis for customizing effective nitrate input channels and purifying water quality.
Geological Units Classification with Texture-Spectral Synergy of Multi-Sourced Remote Sensing Images
2020, 45(5): 1844-1854.
doi: 10.3799/dqkx.2019.168
Abstract:
The structural pattern, differential weathering, and outcrop situation of different geological units can be described by the texture information of remote sensing imagery as graphical features. The geological units compositions of differential minerals are shown as spectral cues.With regard to geological units classification, the classification accuracy of most studies is limited since they have mainly utilized the spectral cues from multis-pectral or hyperspectral images to characterize their spectral features, and high resolution imagery to depict the texture information as a supplement. In this study, the texture-spectral indices are established with the multi-sourced remote sensing images of Worldview-2 and ASTER(Advanced Spaceborne Thermal Emission and Reflection Radiometer)and tested for geological units classification in the western section of Beishan Mountain, which are located at the junction of Gansu Province and Xinjiang Uygur Autonomous Region. Based on the panchromatic band of Worldview-2 imagery, the following graphical features that quantify the bedding structure, distribution morphology and micro-topography features of different rock units were extracted: 0° and 45°directional filtering, the textures of homogeneity, dissimilarity and entropy generated from gray level co-occurrence matrix. Based on multi-spectral bands of Worldview-2 imagery and the short-wave infrared bands of ASTER imagery, the spectral indices were established by the band-ratio and addition-difference methods, including RI (Ratio index)ASTER, SI(Spectral index) ASTER, and SIWorldview-2. First, based on the object-oriented approach and the texture-spectral indices, texture-spectral features were used to conduct multi-resolution segmentation to produce numerous geological units with different scales. Second, the geological units were classified at different scales using spectral indices. The results show that: (1) 17 types of geological units were classified with an overall accuracy of 83.62%, based on the proposed method; (2) and only 13 or 14 types of geological units were classified, by using the Worldview-2 or ASTER images, respectively. The outlined approach could provide the theoretical and remote sensing technical support for geological survey and prospecting work in the high altitude with deep-cut unpopulated areas of western China.
The structural pattern, differential weathering, and outcrop situation of different geological units can be described by the texture information of remote sensing imagery as graphical features. The geological units compositions of differential minerals are shown as spectral cues.With regard to geological units classification, the classification accuracy of most studies is limited since they have mainly utilized the spectral cues from multis-pectral or hyperspectral images to characterize their spectral features, and high resolution imagery to depict the texture information as a supplement. In this study, the texture-spectral indices are established with the multi-sourced remote sensing images of Worldview-2 and ASTER(Advanced Spaceborne Thermal Emission and Reflection Radiometer)and tested for geological units classification in the western section of Beishan Mountain, which are located at the junction of Gansu Province and Xinjiang Uygur Autonomous Region. Based on the panchromatic band of Worldview-2 imagery, the following graphical features that quantify the bedding structure, distribution morphology and micro-topography features of different rock units were extracted: 0° and 45°directional filtering, the textures of homogeneity, dissimilarity and entropy generated from gray level co-occurrence matrix. Based on multi-spectral bands of Worldview-2 imagery and the short-wave infrared bands of ASTER imagery, the spectral indices were established by the band-ratio and addition-difference methods, including RI (Ratio index)ASTER, SI(Spectral index) ASTER, and SIWorldview-2. First, based on the object-oriented approach and the texture-spectral indices, texture-spectral features were used to conduct multi-resolution segmentation to produce numerous geological units with different scales. Second, the geological units were classified at different scales using spectral indices. The results show that: (1) 17 types of geological units were classified with an overall accuracy of 83.62%, based on the proposed method; (2) and only 13 or 14 types of geological units were classified, by using the Worldview-2 or ASTER images, respectively. The outlined approach could provide the theoretical and remote sensing technical support for geological survey and prospecting work in the high altitude with deep-cut unpopulated areas of western China.
2020, 45(5): 1855-1864.
doi: 10.3799/dqkx.2019.162
Abstract:
It is significant to research the provenance of Beikang basin in the southern South China Sea, because oil and gas resources were influenced by the changes of dispersion systems resulted from tectonic-induced migration of provenance. In this paper, seismic reflection data were used in seismic attribute analysis, where stratigraphic slices of RMS (root mean square amplitude) were used to analyze dispersion systems, in order to inquire into provenance migration and its controlling factors. During the Later Oligocene to Middle Miocene, the provenance of the Beikang basin was from the south and the dispersion systems extended from south to north. Two depositional cycles were separated by the Early Miocene Uncomformity (EMU), which formed during seawater deepening. In each cycle, sedimentary supply increased gradually upward. During the Middle Miocene, the depositional provenance migrated northwestward gradually. Regional analysis show that the provenance of the Beikang basin mainly came from Zengmu Foreland basin and the provenance migration is caused by landfill and overthrust northward of the Zengmu Foreland basin.
It is significant to research the provenance of Beikang basin in the southern South China Sea, because oil and gas resources were influenced by the changes of dispersion systems resulted from tectonic-induced migration of provenance. In this paper, seismic reflection data were used in seismic attribute analysis, where stratigraphic slices of RMS (root mean square amplitude) were used to analyze dispersion systems, in order to inquire into provenance migration and its controlling factors. During the Later Oligocene to Middle Miocene, the provenance of the Beikang basin was from the south and the dispersion systems extended from south to north. Two depositional cycles were separated by the Early Miocene Uncomformity (EMU), which formed during seawater deepening. In each cycle, sedimentary supply increased gradually upward. During the Middle Miocene, the depositional provenance migrated northwestward gradually. Regional analysis show that the provenance of the Beikang basin mainly came from Zengmu Foreland basin and the provenance migration is caused by landfill and overthrust northward of the Zengmu Foreland basin.
