2023 Vol. 48, No. 12
Display Method:
2023, 48(12): 4349-4369.
doi: 10.3799/dqkx.2023.028
PDF 30039KB
Abstract:
The Langmuri Cu-Ni-Co polymetallic deposit, located in the eastern segment of the eastern Kunlun orogenic belt, has recently delineated an independent platinum group element orebody. Further study on the metallogenic characteristics of the deposit is helpful to guide the further exploration work. Based on the analysis of the geological characteristics of the deposit, combined the analysis of the major and trace elements, Sr-Nd isotopes of the ore-bearing olivine pyroxenolite and the electron-probe microanalysis of major elements in olivine and mica from the ore-bearing olivine pyroxenolite, as well as the zircon U-Pb chronology and geochemistry of the biotite granite, In this paper it discusses the metallogenic characteristics, metallogenic age and genesis of the Langmuri deposit. Olivine in ore-bearing olivine pyroxenolite belongs to chrysolite series (Fo value is 86.72-88.39), and mica is phlogopite, which are all products of mantle-derived magmatism. The geochemical characters of the ore-bearing olivine pyroxene show a right-dipping REE distribution patterns, enriched with LILE elements such as Cs, Rb, U, etc., and with positive εNd(t) values of 0.66-2.66, suggest that the parent magma of olivine pyroxene experienced crustal contamination during its formation. The age of biotite granite is 414.5 ± 8.8 Ma, which shows the geochemical characteristics of arc magma.(87Sr/86Sr)i(0.718 609-0.719 177) and εNd(t) values (1.28-5.36) show that the biotite granite is the product of crust- mantle magma mixing. In this paper it proposes that Langmuri copper-polymetallic deposit underwent multi-period of superimposed mineralization. The Cu-Ni-Co-Pt-Pd sulfide orebodies hosted in olivine pyroxenolite were formed at 450-439 Ma, and the hydrothermal vein-type copper mineralization related to biotite granite with 415 Ma was superimposed upon it. The deposit is dominated by early sulfide mineralization related to olivine pyroxene. Crustal contamination in the process of magmatic evolution and post-magmatic hydrothermal activities have important contributions to mineralization.The bottom and top of the basic-ultrabasic complex in Langmuri mining area and the contact zone between biotite granite and it are all favorable prospecting areas.
The Langmuri Cu-Ni-Co polymetallic deposit, located in the eastern segment of the eastern Kunlun orogenic belt, has recently delineated an independent platinum group element orebody. Further study on the metallogenic characteristics of the deposit is helpful to guide the further exploration work. Based on the analysis of the geological characteristics of the deposit, combined the analysis of the major and trace elements, Sr-Nd isotopes of the ore-bearing olivine pyroxenolite and the electron-probe microanalysis of major elements in olivine and mica from the ore-bearing olivine pyroxenolite, as well as the zircon U-Pb chronology and geochemistry of the biotite granite, In this paper it discusses the metallogenic characteristics, metallogenic age and genesis of the Langmuri deposit. Olivine in ore-bearing olivine pyroxenolite belongs to chrysolite series (Fo value is 86.72-88.39), and mica is phlogopite, which are all products of mantle-derived magmatism. The geochemical characters of the ore-bearing olivine pyroxene show a right-dipping REE distribution patterns, enriched with LILE elements such as Cs, Rb, U, etc., and with positive εNd(t) values of 0.66-2.66, suggest that the parent magma of olivine pyroxene experienced crustal contamination during its formation. The age of biotite granite is 414.5 ± 8.8 Ma, which shows the geochemical characteristics of arc magma.(87Sr/86Sr)i(0.718 609-0.719 177) and εNd(t) values (1.28-5.36) show that the biotite granite is the product of crust- mantle magma mixing. In this paper it proposes that Langmuri copper-polymetallic deposit underwent multi-period of superimposed mineralization. The Cu-Ni-Co-Pt-Pd sulfide orebodies hosted in olivine pyroxenolite were formed at 450-439 Ma, and the hydrothermal vein-type copper mineralization related to biotite granite with 415 Ma was superimposed upon it. The deposit is dominated by early sulfide mineralization related to olivine pyroxene. Crustal contamination in the process of magmatic evolution and post-magmatic hydrothermal activities have important contributions to mineralization.The bottom and top of the basic-ultrabasic complex in Langmuri mining area and the contact zone between biotite granite and it are all favorable prospecting areas.
2023, 48(12): 4370-4386.
doi: 10.3799/dqkx.2023.193
Abstract:
The Dagang lithium deposit is a giant granite-associated deposit in the West Jiangxi Province, central Jiangnan orogenic belt (JNOB). Lithium mineralization is closely associated with muscovite granites. However, the occurrence of lithium and geochronology of magmatism and mineralization are not well defined. In this study, it presents microtextural studies, electron probe microanalysis (EPMA) of micas, as well as laser ablation inductively coupled plasma (LA-ICPMS) zircon and cassiterite U-Pb dating results to further constrain the occurrence state, metallogenic mechanism, and geochronology. LA-ICPMS U-Pb dating of cassiterite core yielded a Tera-Wasserburg U-Pb lower intercept age of 125±3 Ma and cassiterite rim yielded a lower intercept age of 108±7 Ma. Type Ⅰ zircon, which shows lower content of U, has an LA-ICPMS Tera-Wasserburg U-Pb lower intercept age of 129±2 Ma, and Type Ⅱ zircon grains with higher U content yielded a lower intercept age of 100±4 Ma. Geochronological results reveal two episodic Li mineralization events during the Early Cretaceous in the Dagang deposit. In addition, the mineralization ages of the Dagang Li deposit are consistent with the large-scale magmatic and metallogenic events for rare metal deposits in the central JNOB. Zoned micas which are revealed by BSE images from the Dagang Li deposit are composed of Li-muscovite, zinnwaldite, as well as lepidolite. The Li-bearing micas are the principal ore minerals in the muscovite granites. A gradual increase in Li, Si, and F in all micas from core to rim is exhibited by electron probe microanalysis (EPMA). The occurrence and geochemical features indicate that the Dagang Li deposit formed through an early-stage magma fractional crystallization and a late-stage hydrothermal process. The temporal relationship between Early Cretaceous S-type granitic magmatism and Li mineralization in the central JNOB can be used as a guideline for mineral exploration of granite rare metal deposits.
The Dagang lithium deposit is a giant granite-associated deposit in the West Jiangxi Province, central Jiangnan orogenic belt (JNOB). Lithium mineralization is closely associated with muscovite granites. However, the occurrence of lithium and geochronology of magmatism and mineralization are not well defined. In this study, it presents microtextural studies, electron probe microanalysis (EPMA) of micas, as well as laser ablation inductively coupled plasma (LA-ICPMS) zircon and cassiterite U-Pb dating results to further constrain the occurrence state, metallogenic mechanism, and geochronology. LA-ICPMS U-Pb dating of cassiterite core yielded a Tera-Wasserburg U-Pb lower intercept age of 125±3 Ma and cassiterite rim yielded a lower intercept age of 108±7 Ma. Type Ⅰ zircon, which shows lower content of U, has an LA-ICPMS Tera-Wasserburg U-Pb lower intercept age of 129±2 Ma, and Type Ⅱ zircon grains with higher U content yielded a lower intercept age of 100±4 Ma. Geochronological results reveal two episodic Li mineralization events during the Early Cretaceous in the Dagang deposit. In addition, the mineralization ages of the Dagang Li deposit are consistent with the large-scale magmatic and metallogenic events for rare metal deposits in the central JNOB. Zoned micas which are revealed by BSE images from the Dagang Li deposit are composed of Li-muscovite, zinnwaldite, as well as lepidolite. The Li-bearing micas are the principal ore minerals in the muscovite granites. A gradual increase in Li, Si, and F in all micas from core to rim is exhibited by electron probe microanalysis (EPMA). The occurrence and geochemical features indicate that the Dagang Li deposit formed through an early-stage magma fractional crystallization and a late-stage hydrothermal process. The temporal relationship between Early Cretaceous S-type granitic magmatism and Li mineralization in the central JNOB can be used as a guideline for mineral exploration of granite rare metal deposits.
2023, 48(12): 4387-4403.
doi: 10.3799/dqkx.2023.061
Abstract:
With the development of chemical procedures and instrumental analyses, Re-Os isotopes in low-Re sulfides and oxides have been precisely analyzed, making it possible to date more types of deposits and reveal ore genesis. However, accumulating data and refinement research work have revealed many problems in the application of sulfides Re-Os dating. Processes including sample collection, Re and Os separation and purification and instrumental analysis, could affect the results of Re-Os isotopic compositions. In this article it reviews the characteristics of sulfides Re-Os isotope system, introduces separation and purification methods, and mass spectrometry analysis techniques, and systematically discusses possible influencing factors of sulfide Re-Os dating. A summary of precautions during the Re-Os dating works, to provide some help for future works.
With the development of chemical procedures and instrumental analyses, Re-Os isotopes in low-Re sulfides and oxides have been precisely analyzed, making it possible to date more types of deposits and reveal ore genesis. However, accumulating data and refinement research work have revealed many problems in the application of sulfides Re-Os dating. Processes including sample collection, Re and Os separation and purification and instrumental analysis, could affect the results of Re-Os isotopic compositions. In this article it reviews the characteristics of sulfides Re-Os isotope system, introduces separation and purification methods, and mass spectrometry analysis techniques, and systematically discusses possible influencing factors of sulfide Re-Os dating. A summary of precautions during the Re-Os dating works, to provide some help for future works.
2023, 48(12): 4404-4426.
doi: 10.3799/dqkx.2022.293
Abstract:
In order to restrict the age and mineralization of the Yuanjiacun iron deposit and reveal its implications for the paleomarine environment, it determined the detrital zircon U-Pb chronology, major and trace elements of whole rock and trace elements of hematite for BIFs samples which collected from the Yuanjiacun iron deposit. Its detrital zircon U-Pb age constrains the sedimentary age of Yuanjiacun iron ore between 2 200 and 2 235 Ma. The characteristics of major and trace elements indicate that it is a relatively pure sediment and formed by the mixing of seawater and high temperature hydrothermal fluid. And the river input may be one of iron sources during the deposition process. Yuanjiacun iron deposit was formed at the end of the GOE. There are obvious grouping of REE distribution pattern characteristics in Yuanjiacun iron deposit, as well as negative Ce anomaly and slight positive Ce anomaly. This agrees with a reductive and oxidative environment, indicating that the paleomarine environment at that time was characterized by redox stratification. These features suggest a dramatic change in the paleo-marine environment after the GOE, with some degree of oxidation occurring in seawater and shifting from the original single reducing environment to a redox stratified state.
In order to restrict the age and mineralization of the Yuanjiacun iron deposit and reveal its implications for the paleomarine environment, it determined the detrital zircon U-Pb chronology, major and trace elements of whole rock and trace elements of hematite for BIFs samples which collected from the Yuanjiacun iron deposit. Its detrital zircon U-Pb age constrains the sedimentary age of Yuanjiacun iron ore between 2 200 and 2 235 Ma. The characteristics of major and trace elements indicate that it is a relatively pure sediment and formed by the mixing of seawater and high temperature hydrothermal fluid. And the river input may be one of iron sources during the deposition process. Yuanjiacun iron deposit was formed at the end of the GOE. There are obvious grouping of REE distribution pattern characteristics in Yuanjiacun iron deposit, as well as negative Ce anomaly and slight positive Ce anomaly. This agrees with a reductive and oxidative environment, indicating that the paleomarine environment at that time was characterized by redox stratification. These features suggest a dramatic change in the paleo-marine environment after the GOE, with some degree of oxidation occurring in seawater and shifting from the original single reducing environment to a redox stratified state.
2023, 48(12): 4427-4440.
doi: 10.3799/dqkx.2022.006
Abstract:
The combination of geological data and machine learning provides a new direction for mineral exploration. The granitic pluton is widely developed in South China, which is an important producing area for granite-type uranium deposits. Therefore, whether the granitic pluton has the potential to produce uranium deposits is of great significance for guiding the exploration of granite-type uranium deposits in South China. In this paper, the geochemical data of granites in South China are systematically collected (excluding the Jiufeng, Hongshan and Chashan granite plutons to be evaluated in Zhuguangshan area) from previous published papers, and a total of 1 711 data pieces are obtained. They are further divided into training set and test set according to the ratio of 7∶3. Then, the random forest (RF) algorithm and K-nearest neighbor (KNN) algorithm classification models were established respectively, and the accuracy, recall rate and ROC (receiver operating characteristic curve) curve of the two classification models were evaluated, and the models with good generalization ability were selected. Finally, the metallogenic potential of the Jiufeng pluton, Hongshan pluton and Chashan pluton in the Zhuguangshan area were evaluated using the models with good generalization ability. The results show that the classification accuracy and reliability of prediction results of random forest classification model are higher than those of K-nearest neighbor classification model, and the classification accuracy of the random forest classification model on the test set reached 93%. The random forest classification model created above was used to evaluate the metallogenetic potential of the Jiufeng, Hongshan and Chashan plutons. The prediction results show that the probability of metallogenetic potentiality in the Hongshan and Chashan plutons is high, whereas the probability in the Jiufeng pluton is low. This study provides a reliable basis for further geological prospecting, and the model can be used as an auxiliary tool for geological prospecting.
The combination of geological data and machine learning provides a new direction for mineral exploration. The granitic pluton is widely developed in South China, which is an important producing area for granite-type uranium deposits. Therefore, whether the granitic pluton has the potential to produce uranium deposits is of great significance for guiding the exploration of granite-type uranium deposits in South China. In this paper, the geochemical data of granites in South China are systematically collected (excluding the Jiufeng, Hongshan and Chashan granite plutons to be evaluated in Zhuguangshan area) from previous published papers, and a total of 1 711 data pieces are obtained. They are further divided into training set and test set according to the ratio of 7∶3. Then, the random forest (RF) algorithm and K-nearest neighbor (KNN) algorithm classification models were established respectively, and the accuracy, recall rate and ROC (receiver operating characteristic curve) curve of the two classification models were evaluated, and the models with good generalization ability were selected. Finally, the metallogenic potential of the Jiufeng pluton, Hongshan pluton and Chashan pluton in the Zhuguangshan area were evaluated using the models with good generalization ability. The results show that the classification accuracy and reliability of prediction results of random forest classification model are higher than those of K-nearest neighbor classification model, and the classification accuracy of the random forest classification model on the test set reached 93%. The random forest classification model created above was used to evaluate the metallogenetic potential of the Jiufeng, Hongshan and Chashan plutons. The prediction results show that the probability of metallogenetic potentiality in the Hongshan and Chashan plutons is high, whereas the probability in the Jiufeng pluton is low. This study provides a reliable basis for further geological prospecting, and the model can be used as an auxiliary tool for geological prospecting.
2023, 48(12): 4441-4464.
doi: 10.3799/dqkx.2021.184
Abstract:
The synergistic diagenesis of the sand-mudstone from the Qingshankou Formation and their uranium metallogenic significance were systematically researched through investigating the petro-mineralogy, major and trace elements, carbon and oxygen isotopes of various rocks with different colors. Results show that both sandstone and mudstone have similar clastic mineral composition, clay mineral assemblage and the major and trace element contents, reflecting the unified provenance and the same tectonic-sedimentary environment. The maximum burial evolution of the target strata probably reached the early stage-A of the middle diagenesis. The sandstone has undergone the acid-alkaline alternating diagenetic evolution. During burial diagenesis stage, it has widely developed the calcitization, dolomitization, sideritization, semctite-illitization, pyritization, kaolinization and local limonitization, hematitization and uranium mineralization. Also, the alkaline hydrothermal fluid derived from the intrusion of deep basic magma in Paleogene period, led to the occurrence of high manganese ankerite, chloritization, silicification, mimetite and the superimposed reformation of the early uranium ores. Then, the sand body developed strong limonitization, hematitization and associated uranium mineralization in the epigenetic stage. Thus, these conclusions could be draw, i.e. the red sandstone mainly formed by epigenetic oxidation, and a few from primary syn-sedimentary. Present residual grey sandstone, characterized by intense reduced capability, was secondary reduced by the deep fluid. The mudstone is characterized by alkaline diagenesis with the respects of the much aboundance of smectite mixed layer and illite, and the extensive development of the limonitization, hematitization, calcitization, dolomitization and semctite-illitization. Moreover, little pyritization and uranium mineralization were locally occurred within grey mudstone. The similar changing rules in terms of clay minerals, the movable element of Ca, Mg, Fe, Mo, U and the carbon isotopic compositions exist both in the sandstone and adjacent mudstone from the same borehole, which indicates that aboundant materials and fluids migrated and exchanged between various rocks with different geochemical properties in sedimentary-burial diagenetic stage. The two-stage ore-forming process of the tabular-shaped uranium deposit was proposed for the target bed of the Qingshankou Formation, i.e. (1) synsedimentary-diagenetic preconcentration and phreatic oxidation uranium initial mineralization from the Qingshankou to the Nenjiang period, (2) main coupling interlayer oxidation uranium mineralization superimposed by deep fluid since the end of Nenjiang era.
The synergistic diagenesis of the sand-mudstone from the Qingshankou Formation and their uranium metallogenic significance were systematically researched through investigating the petro-mineralogy, major and trace elements, carbon and oxygen isotopes of various rocks with different colors. Results show that both sandstone and mudstone have similar clastic mineral composition, clay mineral assemblage and the major and trace element contents, reflecting the unified provenance and the same tectonic-sedimentary environment. The maximum burial evolution of the target strata probably reached the early stage-A of the middle diagenesis. The sandstone has undergone the acid-alkaline alternating diagenetic evolution. During burial diagenesis stage, it has widely developed the calcitization, dolomitization, sideritization, semctite-illitization, pyritization, kaolinization and local limonitization, hematitization and uranium mineralization. Also, the alkaline hydrothermal fluid derived from the intrusion of deep basic magma in Paleogene period, led to the occurrence of high manganese ankerite, chloritization, silicification, mimetite and the superimposed reformation of the early uranium ores. Then, the sand body developed strong limonitization, hematitization and associated uranium mineralization in the epigenetic stage. Thus, these conclusions could be draw, i.e. the red sandstone mainly formed by epigenetic oxidation, and a few from primary syn-sedimentary. Present residual grey sandstone, characterized by intense reduced capability, was secondary reduced by the deep fluid. The mudstone is characterized by alkaline diagenesis with the respects of the much aboundance of smectite mixed layer and illite, and the extensive development of the limonitization, hematitization, calcitization, dolomitization and semctite-illitization. Moreover, little pyritization and uranium mineralization were locally occurred within grey mudstone. The similar changing rules in terms of clay minerals, the movable element of Ca, Mg, Fe, Mo, U and the carbon isotopic compositions exist both in the sandstone and adjacent mudstone from the same borehole, which indicates that aboundant materials and fluids migrated and exchanged between various rocks with different geochemical properties in sedimentary-burial diagenetic stage. The two-stage ore-forming process of the tabular-shaped uranium deposit was proposed for the target bed of the Qingshankou Formation, i.e. (1) synsedimentary-diagenetic preconcentration and phreatic oxidation uranium initial mineralization from the Qingshankou to the Nenjiang period, (2) main coupling interlayer oxidation uranium mineralization superimposed by deep fluid since the end of Nenjiang era.
2023, 48(12): 4465-4480.
doi: 10.3799/dqkx.2022.067
Abstract:
The Heishishan copper polymetallic deposit is located in Wulonggou area, middle part of the East Kunlun orogen belt. The Middle Triassic intrusions in the mining area are very developed, and the diorite produced nearly parallel to the ore bodies provides a good research object for limiting the closure time of the paleo-Tethys ocean in the East Kunlun area. In this article, investigations in terms of zircon U-Pb dating, geochemistry, and Sr-Nd-Hf isotope data were carried out on the Heishishan diorite. Zircon U-Pb dating of the diorite yields magmatic crystallization ages of 241.6±1.0 Ma. The diorite samples contain SiO2=52.23%-56.19%, K2O+Na2O=3.99%-6.26%, Na2O=2.79%-3.63%, K2O=1.06%-2.71% and MgO=2.55%-4.84%. The diorites are rich in Al, Ca and Fe. Also, they are enriched in light rare earth elements and large ion lithophile elements (Rb, Ba, K), and depleted in heavy rare earth elements and high field strength elements (Nb, Ta, Ti, P). Most samples have obvious negative Eu abnormality (δEu=0.39-0.59). Hf isotopic analysis shows that the zircon εHf(t) values of the diorite are from -4.1 to +0.7. The samples have whole-rock (87Sr/86Sr)t ratios from 0.708 860 to 0.708 960, εNd(t) of -5.0 to -4.9. The comprehensive analysis shows that the Heishishan diorite is of crust-mantle mixing origin. Based on the regional tectonic evolution history, the diorites were formed in a subduction tectonic setting, indicating that the closure of the paleo-Tethys ocean in the East Kunlun area was later than 241.6 Ma.
The Heishishan copper polymetallic deposit is located in Wulonggou area, middle part of the East Kunlun orogen belt. The Middle Triassic intrusions in the mining area are very developed, and the diorite produced nearly parallel to the ore bodies provides a good research object for limiting the closure time of the paleo-Tethys ocean in the East Kunlun area. In this article, investigations in terms of zircon U-Pb dating, geochemistry, and Sr-Nd-Hf isotope data were carried out on the Heishishan diorite. Zircon U-Pb dating of the diorite yields magmatic crystallization ages of 241.6±1.0 Ma. The diorite samples contain SiO2=52.23%-56.19%, K2O+Na2O=3.99%-6.26%, Na2O=2.79%-3.63%, K2O=1.06%-2.71% and MgO=2.55%-4.84%. The diorites are rich in Al, Ca and Fe. Also, they are enriched in light rare earth elements and large ion lithophile elements (Rb, Ba, K), and depleted in heavy rare earth elements and high field strength elements (Nb, Ta, Ti, P). Most samples have obvious negative Eu abnormality (δEu=0.39-0.59). Hf isotopic analysis shows that the zircon εHf(t) values of the diorite are from -4.1 to +0.7. The samples have whole-rock (87Sr/86Sr)t ratios from 0.708 860 to 0.708 960, εNd(t) of -5.0 to -4.9. The comprehensive analysis shows that the Heishishan diorite is of crust-mantle mixing origin. Based on the regional tectonic evolution history, the diorites were formed in a subduction tectonic setting, indicating that the closure of the paleo-Tethys ocean in the East Kunlun area was later than 241.6 Ma.
2023, 48(12): 4481-4494.
doi: 10.3799/dqkx.2022.117
Abstract:
The post-collision magmatic activity is of great significance to understand the orogenic collapse, delamination and continental crust growth. In this paper it summarizes the geochronological and geochemical characteristics of post-collisional magmatism at 400-360 Ma in the North Qaidam ultrahigh-pressure metamorphic belt. The granite intrusions have I-type characteristics and were formed by the crust-mantle magmatic mixing. Mafic dykes can be divided into two groups: (1) Intermediate-basic dykes at 392-375 Ma; (2) Ultrabasic dykes about 360 Ma. The geochemical characteristics show that the trace elements and isotopes of mafic dyke are gradually depleted with time, and the mantle source changes from lithospheric mantle to asthenosphere mantle. The mafic magmatic activity is the key of post-collision magmatic activity and orogen collapse. Combining the feature of magmatism after the collision, it proposes a geodynamic model to explain the activities of lithosphere and asthenosphere mantle in post-collision stage about 35 million years (Ma), the unrooting process of orogeny began at slow lithospheric mantle erosion in 395-375 Ma, and ended up with lithosphere delamination and asthenosphere upwelling at 360 Ma. The addition of mantle magma indicates that the post-collision stage is an important period for continental growth in earth history.
The post-collision magmatic activity is of great significance to understand the orogenic collapse, delamination and continental crust growth. In this paper it summarizes the geochronological and geochemical characteristics of post-collisional magmatism at 400-360 Ma in the North Qaidam ultrahigh-pressure metamorphic belt. The granite intrusions have I-type characteristics and were formed by the crust-mantle magmatic mixing. Mafic dykes can be divided into two groups: (1) Intermediate-basic dykes at 392-375 Ma; (2) Ultrabasic dykes about 360 Ma. The geochemical characteristics show that the trace elements and isotopes of mafic dyke are gradually depleted with time, and the mantle source changes from lithospheric mantle to asthenosphere mantle. The mafic magmatic activity is the key of post-collision magmatic activity and orogen collapse. Combining the feature of magmatism after the collision, it proposes a geodynamic model to explain the activities of lithosphere and asthenosphere mantle in post-collision stage about 35 million years (Ma), the unrooting process of orogeny began at slow lithospheric mantle erosion in 395-375 Ma, and ended up with lithosphere delamination and asthenosphere upwelling at 360 Ma. The addition of mantle magma indicates that the post-collision stage is an important period for continental growth in earth history.
2023, 48(12): 4495-4507.
doi: 10.3799/dqkx.2022.048
Abstract:
Numerous Neoproterozoic igneous rocks were identified along the northwestern and southeastern Yangtze block, whereas the synchronous mafic rocks have been poorly reported along the southwestern Yangtze block so far. The Yaoshan Group, located at the southwestern Yangtze block, preserves small amounts of matabasic rocks and metagabbro which occurred as lens, layers and fragments. Their formation timing, petrogenesis and dynamic implication are still unclear. In this study, it presents zircon U-Pb geochronological, geochemical and petrological data for the metabasic rocks in the Yaoshan Group. The data show that the metabasic rocks have zircon U-Pb ages of 766±3 Ma and 771±4 Ma, for the first time to identify Neoproterozoic metabasic rocks in the Yaoshan Group. Geochemical data suggest that the metabasic rocks have SiO2 of 48.41%-49.00% and Fe2O3T, MgO range in 10.30%-10.48% and 10.05%-10.15%, respectively. They have relative high Mg-number (69.3-69.5). They are characterized by enrichment in LREE((La/Yb)N=1.97-2.19), no obvious Eu anomalies(δEu=0.90-0.94), negative Nb anomalies, and depletion in Ti-P on primitive mantle-normalized trace element diagrams. Such geochemical signatures are similar to those of arc volcanic rocks. Together with other geological observations, it is proposed that the tectonic setting of the metabasic rocks is island arc which is dynamically related to ocean subduction along the southwestern margin of the Yangtze block. These results provide new evidence to understand the Neoproterozoic tectonic evolution of the Ailaoshan tectonic belt and even the whole South China.
Numerous Neoproterozoic igneous rocks were identified along the northwestern and southeastern Yangtze block, whereas the synchronous mafic rocks have been poorly reported along the southwestern Yangtze block so far. The Yaoshan Group, located at the southwestern Yangtze block, preserves small amounts of matabasic rocks and metagabbro which occurred as lens, layers and fragments. Their formation timing, petrogenesis and dynamic implication are still unclear. In this study, it presents zircon U-Pb geochronological, geochemical and petrological data for the metabasic rocks in the Yaoshan Group. The data show that the metabasic rocks have zircon U-Pb ages of 766±3 Ma and 771±4 Ma, for the first time to identify Neoproterozoic metabasic rocks in the Yaoshan Group. Geochemical data suggest that the metabasic rocks have SiO2 of 48.41%-49.00% and Fe2O3T, MgO range in 10.30%-10.48% and 10.05%-10.15%, respectively. They have relative high Mg-number (69.3-69.5). They are characterized by enrichment in LREE((La/Yb)N=1.97-2.19), no obvious Eu anomalies(δEu=0.90-0.94), negative Nb anomalies, and depletion in Ti-P on primitive mantle-normalized trace element diagrams. Such geochemical signatures are similar to those of arc volcanic rocks. Together with other geological observations, it is proposed that the tectonic setting of the metabasic rocks is island arc which is dynamically related to ocean subduction along the southwestern margin of the Yangtze block. These results provide new evidence to understand the Neoproterozoic tectonic evolution of the Ailaoshan tectonic belt and even the whole South China.
2023, 48(12): 4508-4526.
doi: 10.3799/dqkx.2022.077
Abstract:
The Neoproterozoic Yanbian volcanic rocks are extensively exposed in the western Yangtze block, providing an ideal opportunity to study the Precambrian tectonic evolution of the Yangtze block. LA-ICP-MS zircon U-Pb dating of Zhagu Formation, Xiaoping Formation, Yumen Formation and Huangtian Formation yielded zircon U-Pb ages of 934±5 Ma, 863±4 Ma, 843±7 Ma and 797±9 Ma, respectively. The N-MORB (normal mid-ocean ridge basalts) type basalts from the Huangtian Formation belong to calc-alkaline series, and display light rare earth element depleted patterns, with moderate negative Nb, Ta anomaly and minor negative Ti anomalies. In addition, these rocks have positive εNd(t) values (+3.8 to +4.9). They are suggested to be derived from 10%-20% partial melting of the MORB-like source in a fore-arc basin setting in the garnet+spinel stability field. Combined with previous studies, the data confirm the existence of an arc-trench system in the western Yangtze block in the Neoproterozoic. It proposes that the western Yangtze block was located in a convergent setting during the Neoproterozoic. The subduction of oceanic lithosphere beneath the western margin of the Yangtze block initiated no later than 934 Ma.
The Neoproterozoic Yanbian volcanic rocks are extensively exposed in the western Yangtze block, providing an ideal opportunity to study the Precambrian tectonic evolution of the Yangtze block. LA-ICP-MS zircon U-Pb dating of Zhagu Formation, Xiaoping Formation, Yumen Formation and Huangtian Formation yielded zircon U-Pb ages of 934±5 Ma, 863±4 Ma, 843±7 Ma and 797±9 Ma, respectively. The N-MORB (normal mid-ocean ridge basalts) type basalts from the Huangtian Formation belong to calc-alkaline series, and display light rare earth element depleted patterns, with moderate negative Nb, Ta anomaly and minor negative Ti anomalies. In addition, these rocks have positive εNd(t) values (+3.8 to +4.9). They are suggested to be derived from 10%-20% partial melting of the MORB-like source in a fore-arc basin setting in the garnet+spinel stability field. Combined with previous studies, the data confirm the existence of an arc-trench system in the western Yangtze block in the Neoproterozoic. It proposes that the western Yangtze block was located in a convergent setting during the Neoproterozoic. The subduction of oceanic lithosphere beneath the western margin of the Yangtze block initiated no later than 934 Ma.
2023, 48(12): 4527-4539.
doi: 10.3799/dqkx.2022.026
Abstract:
One garnet sample from an extensively retrogressed eclogite and a quartz vein located at the boundary between the host gneiss and the eclogite lens from the Xitieshan terrane, North Qaidam, western China, have been analyzed by joint 40Ar/39Ar in vacuo crushing and stepwise heating techniques. The results provide significant information to directly constrain the origin and timing of hydrothermal fluid flow activity, as well as the age of the vein-forming. The stepwise heating result could further be used to decipher the hydrothermal alteration history of the ultrahigh pressure (UHP) metamorphic rocks. Garnet sample analyzed by in vacuo crushing forms a falling-down age spectrum and yields a relatively flat age plateaus for the last 7 steps (19 to 25) with a plateau age of 226.3±3.9 Ma (2σ). These data points constitute the plateau age yielding an excellent isochron with an isochron age of 222.6±16.7 Ma and initial 40Ar/36Ar ratio of 297±6. The crushed powders of the garnet yields, with further stepwise heating, a flat age spectrum with plateau age of 212.0±9.0 Ma, which defined a good isochron with an age of 212.1±8.1 Ma and initial 40Ar/36Ar ratio of 296±1. These results illustrate that the Xitieshan eclogites and their retrogressed equivalents were intensively overprinted by hydrothermal event in the Late Triassic. Quartz samples dated by 40Ar/39Ar in vacuo crushing method yield monotonic declining release patterns: anomalously old apparent ages are obtained at the first steps and relative flat age plateaus of 222.8±1.2 Ma over the final several steps. The gases liberated in the final steps are most derived from radiogenic and trapped argon in small primary fluid inclusions and pseudo-secondary fluid inclusions and also atmospheric argon from the crusher. The plateau age is interpreted as the best estimate for the age of quartz veining formation, witnessing a significant aqueous fluid flow episode during the Late Indosinian Period. Microthermometry analyses and 40Ar/39Ar in vacuo crushing dating suggest that the secondary inclusions may be originated from the extraneous 40Ar rich post-hydrothermal fluid from the depth. In contrast, it hypothesizes that these fluids of primary fluid inclusions mainly derived from meteoric waters transported by regional ductile fault/shearing zones and permeable schistosity. The garnet and quartz vein crushing results also suggest that the structurally-controlled fluid-rock interaction and rock metasomatism, resulting in that eclogites are extensively retrogressed and UHP metamorphic indicator minerals (such as coesite and diamond) are rarely preserved in the Xitieshan terrane.
One garnet sample from an extensively retrogressed eclogite and a quartz vein located at the boundary between the host gneiss and the eclogite lens from the Xitieshan terrane, North Qaidam, western China, have been analyzed by joint 40Ar/39Ar in vacuo crushing and stepwise heating techniques. The results provide significant information to directly constrain the origin and timing of hydrothermal fluid flow activity, as well as the age of the vein-forming. The stepwise heating result could further be used to decipher the hydrothermal alteration history of the ultrahigh pressure (UHP) metamorphic rocks. Garnet sample analyzed by in vacuo crushing forms a falling-down age spectrum and yields a relatively flat age plateaus for the last 7 steps (19 to 25) with a plateau age of 226.3±3.9 Ma (2σ). These data points constitute the plateau age yielding an excellent isochron with an isochron age of 222.6±16.7 Ma and initial 40Ar/36Ar ratio of 297±6. The crushed powders of the garnet yields, with further stepwise heating, a flat age spectrum with plateau age of 212.0±9.0 Ma, which defined a good isochron with an age of 212.1±8.1 Ma and initial 40Ar/36Ar ratio of 296±1. These results illustrate that the Xitieshan eclogites and their retrogressed equivalents were intensively overprinted by hydrothermal event in the Late Triassic. Quartz samples dated by 40Ar/39Ar in vacuo crushing method yield monotonic declining release patterns: anomalously old apparent ages are obtained at the first steps and relative flat age plateaus of 222.8±1.2 Ma over the final several steps. The gases liberated in the final steps are most derived from radiogenic and trapped argon in small primary fluid inclusions and pseudo-secondary fluid inclusions and also atmospheric argon from the crusher. The plateau age is interpreted as the best estimate for the age of quartz veining formation, witnessing a significant aqueous fluid flow episode during the Late Indosinian Period. Microthermometry analyses and 40Ar/39Ar in vacuo crushing dating suggest that the secondary inclusions may be originated from the extraneous 40Ar rich post-hydrothermal fluid from the depth. In contrast, it hypothesizes that these fluids of primary fluid inclusions mainly derived from meteoric waters transported by regional ductile fault/shearing zones and permeable schistosity. The garnet and quartz vein crushing results also suggest that the structurally-controlled fluid-rock interaction and rock metasomatism, resulting in that eclogites are extensively retrogressed and UHP metamorphic indicator minerals (such as coesite and diamond) are rarely preserved in the Xitieshan terrane.
2023, 48(12): 4540-4557.
doi: 10.3799/dqkx.2022.085
Abstract:
The Indosinian Luzhou-Kaijiang paleo-uplift is located in the eastern part of Sichuan basin. It has been paid more attention due to the petroleum geological significance of the karst unconformity on the paleo-uplift. However, there is a debate to the evolution process and dynamic mechanism of Luzhou-Kaijiang paleo-uplift, which has affected both the understanding on the Indosinian tectonic evolution of Upper Yangtze block and the exploration of oil and gas in Sichuan basin. The unconformity on the Luzhou-Kaijiang paleo-uplift will be analyzed in detail, based on the seismic, drilling and field outcrop data. Combined with regional tectonic events and global sea level change, the evolution process and dynamic mechanism of the paleo-uplift will be studied systematically using the evolution model of foreland basin system. It is considered that the Luzhou-Kaijiang paleo-uplift was formed and developed in the Late Triassic Carnian to Norian, and died in the Rhaetian. The Luzhou-Kaijiang paleo-uplift is a component unit (forebulge) of the Late Triassic Longmenshan foreland basin system. Its formation was driven by the tectonic load of the Longmenshan orogenic wedge and the sedimentary load in the foreland basin. The evolution process of the paleo-uplift was mainly controlled by the thrust and nappe of the Longmenshan orogenic wedge toward the Yangtze block, which was probably resulted from southeastward shortening of the western margin of the Yangtze block in response to the Late Triassic convergence among Qiangtang, Yangtze and North China blocks.
The Indosinian Luzhou-Kaijiang paleo-uplift is located in the eastern part of Sichuan basin. It has been paid more attention due to the petroleum geological significance of the karst unconformity on the paleo-uplift. However, there is a debate to the evolution process and dynamic mechanism of Luzhou-Kaijiang paleo-uplift, which has affected both the understanding on the Indosinian tectonic evolution of Upper Yangtze block and the exploration of oil and gas in Sichuan basin. The unconformity on the Luzhou-Kaijiang paleo-uplift will be analyzed in detail, based on the seismic, drilling and field outcrop data. Combined with regional tectonic events and global sea level change, the evolution process and dynamic mechanism of the paleo-uplift will be studied systematically using the evolution model of foreland basin system. It is considered that the Luzhou-Kaijiang paleo-uplift was formed and developed in the Late Triassic Carnian to Norian, and died in the Rhaetian. The Luzhou-Kaijiang paleo-uplift is a component unit (forebulge) of the Late Triassic Longmenshan foreland basin system. Its formation was driven by the tectonic load of the Longmenshan orogenic wedge and the sedimentary load in the foreland basin. The evolution process of the paleo-uplift was mainly controlled by the thrust and nappe of the Longmenshan orogenic wedge toward the Yangtze block, which was probably resulted from southeastward shortening of the western margin of the Yangtze block in response to the Late Triassic convergence among Qiangtang, Yangtze and North China blocks.
2023, 48(12): 4558-4574.
doi: 10.3799/dqkx.2022.492
Abstract:
The Upper Sinian-Lower Paleozoic dolostones is widely developed in the Yangtze platform, which is one of the most important carbonate reservoirs. There has been few studies on the dolostone in the Lower Yangtze region, restraining our recognition to the properties of dolostone reservoir. In this paper it systematically investigates the geochemical characteristics and formation mechanisms of dolostone in the Lower Yangtze area based on an integrated petrological, major and trace element, rare earth element, and carbon oxygen isotope analyses. The results show that the studied dolostone can be divided into four types, namely, micrite dolostone, powder-fine dolostone, fine crystal dolostone, and medium crystal dolostone. The Upper Sinian micritic dolostone has high Mg content and low Fe, Mn, Sr contents, high δ18O value, forming temperature close to surface temperature, higher salinity index compared with sea water, low ΣREE value, negative Ce and Eu anomalies, and REE distribution pattern which are similar to marine limestone, indicating the dolostone belongs to penecontemporaneous dolomitization in an environment of concentrated seawater fluid with strong evaporation near the surface. The Middle Cambrian powder-fine dolostone is characterized by fog-core bright edge structure, similar contents of Mg, Fe, Mn and REE characteristics compared with micritic dolomite, high salinity index, and relatively medium δ18O value ranging from -2.5‰ to -6.5‰. The genesis of this dolomite is percolation reflux dolomitization in shallow burial environment. Marked by higher Fe content and ∑REE values, low δ18O value (-6.5‰ to -10‰), higher formation temperature, the Upper Cambrian fine-grained dolostone is attributed to buried dolomitization genetic. The Lower Ordovician medium crystal dolomite is characterized by high contents of Fe, Mn, Al, Si, Sr and ∑REE value, low δ18O value less than -10‰, lower salinity index compared with sea water, positive Eu anomaly, and high diagenetic temperature with thermal alteration characteristics, suggesting the dolomite is of hydrothermal dolomitization origin.
The Upper Sinian-Lower Paleozoic dolostones is widely developed in the Yangtze platform, which is one of the most important carbonate reservoirs. There has been few studies on the dolostone in the Lower Yangtze region, restraining our recognition to the properties of dolostone reservoir. In this paper it systematically investigates the geochemical characteristics and formation mechanisms of dolostone in the Lower Yangtze area based on an integrated petrological, major and trace element, rare earth element, and carbon oxygen isotope analyses. The results show that the studied dolostone can be divided into four types, namely, micrite dolostone, powder-fine dolostone, fine crystal dolostone, and medium crystal dolostone. The Upper Sinian micritic dolostone has high Mg content and low Fe, Mn, Sr contents, high δ18O value, forming temperature close to surface temperature, higher salinity index compared with sea water, low ΣREE value, negative Ce and Eu anomalies, and REE distribution pattern which are similar to marine limestone, indicating the dolostone belongs to penecontemporaneous dolomitization in an environment of concentrated seawater fluid with strong evaporation near the surface. The Middle Cambrian powder-fine dolostone is characterized by fog-core bright edge structure, similar contents of Mg, Fe, Mn and REE characteristics compared with micritic dolomite, high salinity index, and relatively medium δ18O value ranging from -2.5‰ to -6.5‰. The genesis of this dolomite is percolation reflux dolomitization in shallow burial environment. Marked by higher Fe content and ∑REE values, low δ18O value (-6.5‰ to -10‰), higher formation temperature, the Upper Cambrian fine-grained dolostone is attributed to buried dolomitization genetic. The Lower Ordovician medium crystal dolomite is characterized by high contents of Fe, Mn, Al, Si, Sr and ∑REE value, low δ18O value less than -10‰, lower salinity index compared with sea water, positive Eu anomaly, and high diagenetic temperature with thermal alteration characteristics, suggesting the dolomite is of hydrothermal dolomitization origin.
2023, 48(12): 4575-4585.
doi: 10.3799/dqkx.2023.118
Abstract:
In order to clarify the segmentation of the Cenozoic development and evolution and reveal the dynamical genetic mechanism of the southern fault zone in Zhu-3 depression, we analyze the geometric and kinematic features of the southern fault zone, and discuss the response of the segmental evolution of the southern fault zone to the regional tectonic background in conjunction with the results of previous research. The results show that there are obvious segmentation in the southern fault zone, and there are differences in the geometry, combination with secondary faults, and sedimentary stratigraphy of the descending plate in different segments, which can be divided into two branches and six segments. The Cenozoic tectonic evolution of the southern fault zone can be divided into three stages: reactivation in segment and grew in isolation with relatively weak activity during Paleocene-Middle Eocene; the fault activity increased and gradually connected, and the Wenchang C sag segment stopped activation and the Wenchang B sag northern segment underwent tectonic inversion during the Late Eocene-Oligocene; the fault activity decreased significantly and the segmentation reappeared and gradually died out from the Miocene to present. The complex tectonic movement such as the subduction direction and rate change of the Pacific plate, the collision of the Indian-Eurasian plate, the wedge of the Philippine Sea plate, the subduction and extinction of the ancient South China Sea and the expansion of the new South China Sea led to the change of the Cenozoic regional extension direction of the northern continental margin of the South China Sea. The segmentation of the Cenozoic development and evolution characteristics of the southern fault zone reflects the joint control of the pre-existing fault system in the Late Mesozoic and the change of the Cenozoic regional extension direction.
In order to clarify the segmentation of the Cenozoic development and evolution and reveal the dynamical genetic mechanism of the southern fault zone in Zhu-3 depression, we analyze the geometric and kinematic features of the southern fault zone, and discuss the response of the segmental evolution of the southern fault zone to the regional tectonic background in conjunction with the results of previous research. The results show that there are obvious segmentation in the southern fault zone, and there are differences in the geometry, combination with secondary faults, and sedimentary stratigraphy of the descending plate in different segments, which can be divided into two branches and six segments. The Cenozoic tectonic evolution of the southern fault zone can be divided into three stages: reactivation in segment and grew in isolation with relatively weak activity during Paleocene-Middle Eocene; the fault activity increased and gradually connected, and the Wenchang C sag segment stopped activation and the Wenchang B sag northern segment underwent tectonic inversion during the Late Eocene-Oligocene; the fault activity decreased significantly and the segmentation reappeared and gradually died out from the Miocene to present. The complex tectonic movement such as the subduction direction and rate change of the Pacific plate, the collision of the Indian-Eurasian plate, the wedge of the Philippine Sea plate, the subduction and extinction of the ancient South China Sea and the expansion of the new South China Sea led to the change of the Cenozoic regional extension direction of the northern continental margin of the South China Sea. The segmentation of the Cenozoic development and evolution characteristics of the southern fault zone reflects the joint control of the pre-existing fault system in the Late Mesozoic and the change of the Cenozoic regional extension direction.
2023, 48(12): 4586-4612.
doi: 10.3799/dqkx.2023.194
Abstract:
The deep-time source-to-sink system in continental rift basins is a cutting-edge research topic in sedimentology and has been attempted by building on the research experience on the Quaternary ocean-land margins. Four key geological issues are raised, namely the research scale or level of the source-to-sink system, geomorphologic evolution and sediment output in the catchment, signal propagation and modification through the sediment routing system, and multifactorial joint control of sedimentary-stratigraphic development in the basin. In light of these issues, it proposes that the potential innovations might emerge from the research fields of volcanism-modified sedimentary sequences, palaeoclimate-vegetation community-regulated weathering efficacy, the relationship between catchment geomorphology and sediment supply, prediction of sediment routing system interaction models, paleo water depth-hydrodynamics constraints on sandstone dispersal, forward modeling to restore source-to-sink processes, and source-to-sink response of carbonate dissolved matter. By doing so, it hopes that the problems of sediment-flux pickup and balance restoration under the influence of multiple driving factors and interacting media in the continental deep-time rift basins can be effectively solved. In addition, it suggests that multi-disciplinary cross-integration and multi-element construction of deep-time big data system are two key directions for expanding the research connotation of continental deep-time source-to-sink system with Chinese characteristic and serving the exploration and prediction of energy minerals.
The deep-time source-to-sink system in continental rift basins is a cutting-edge research topic in sedimentology and has been attempted by building on the research experience on the Quaternary ocean-land margins. Four key geological issues are raised, namely the research scale or level of the source-to-sink system, geomorphologic evolution and sediment output in the catchment, signal propagation and modification through the sediment routing system, and multifactorial joint control of sedimentary-stratigraphic development in the basin. In light of these issues, it proposes that the potential innovations might emerge from the research fields of volcanism-modified sedimentary sequences, palaeoclimate-vegetation community-regulated weathering efficacy, the relationship between catchment geomorphology and sediment supply, prediction of sediment routing system interaction models, paleo water depth-hydrodynamics constraints on sandstone dispersal, forward modeling to restore source-to-sink processes, and source-to-sink response of carbonate dissolved matter. By doing so, it hopes that the problems of sediment-flux pickup and balance restoration under the influence of multiple driving factors and interacting media in the continental deep-time rift basins can be effectively solved. In addition, it suggests that multi-disciplinary cross-integration and multi-element construction of deep-time big data system are two key directions for expanding the research connotation of continental deep-time source-to-sink system with Chinese characteristic and serving the exploration and prediction of energy minerals.
2023, 48(12): 4613-4627.
doi: 10.3799/dqkx.2022.041
Abstract:
With the development of petroleum exploration in new areas and new strata, the extensive distribution of Neoproterozoic-Cambrian marine fine-grained clastic rocks along the western-southwestern-southern margins of North China craton(NCC) has been attracted more and more attention as the high-quality source rocks of hydrocarbon. The related resource evaluation has been carried out along the southern margin of NCC and made significant progress, but little attention has been paid for the equivalent horizons along the western-southwestern margins of NCC. Because of lacking accurate biostratigraphic and chronostratigraphic data, the age and spatiotemporal correlation of those rocks as mentioned above have been poorly documented. The new finding of the typical late Ediacaran fossil Shaanxilithes from the Dongpo Formation along the southwestern margin of the NCC(Luonan and Longxian areas, Shaanxi Province), greatly extends its paleogeographic distribution and provides the convincing evidence for determining the age of the Dongpo Formation. Based on the new biostratigraphic evidence, it evaluates the tectonic depositional setting and spatiotemporal correlation of the late Ediacaran Dongpo Formation, which also has the great potential to be the important target horizons for the "new series" shale gas.
With the development of petroleum exploration in new areas and new strata, the extensive distribution of Neoproterozoic-Cambrian marine fine-grained clastic rocks along the western-southwestern-southern margins of North China craton(NCC) has been attracted more and more attention as the high-quality source rocks of hydrocarbon. The related resource evaluation has been carried out along the southern margin of NCC and made significant progress, but little attention has been paid for the equivalent horizons along the western-southwestern margins of NCC. Because of lacking accurate biostratigraphic and chronostratigraphic data, the age and spatiotemporal correlation of those rocks as mentioned above have been poorly documented. The new finding of the typical late Ediacaran fossil Shaanxilithes from the Dongpo Formation along the southwestern margin of the NCC(Luonan and Longxian areas, Shaanxi Province), greatly extends its paleogeographic distribution and provides the convincing evidence for determining the age of the Dongpo Formation. Based on the new biostratigraphic evidence, it evaluates the tectonic depositional setting and spatiotemporal correlation of the late Ediacaran Dongpo Formation, which also has the great potential to be the important target horizons for the "new series" shale gas.
2023, 48(12): 4628-4640.
doi: 10.3799/dqkx.2022.072
Abstract:
High saturation gas hydrate-bearing layers is the favorable target for gas hydrate exploration and development. To identify and estimate gas hydrate-bearing layers, it uses 3D seismic data which is reprocessed by broadband wave impedance inversion, attribute analysis and the calculation of base gas hydrate stability zone to study the characteristics of the bottom simulating reflector (BSR) and gas hydrate occurrence and accumulation in the Zhongjian basin. (1) The characteristics of BSR in this area is slightly different from that found in the gas hydrate drilling area, northern South China Sea. The BSRs identified in this basin are widely distributed with continuous reflections occurred in the fine-grain sediments. The BSR amplitude is particularly strong and continuous where the fault reaches the gas hydrate stability zone. (2) The saturation of gas hydrate-bearing layers is about 30%-40% of the pore space with regional high value. The gas hydrate layer has the same polarity with the seabed reflection and is characterized by continuous and strong amplitude reflections. (3) The gas hydrate-bearing layers are occurred above different depths of the BSR which is controlled by local faults and is affected by sedimentation and tectonic movements.
High saturation gas hydrate-bearing layers is the favorable target for gas hydrate exploration and development. To identify and estimate gas hydrate-bearing layers, it uses 3D seismic data which is reprocessed by broadband wave impedance inversion, attribute analysis and the calculation of base gas hydrate stability zone to study the characteristics of the bottom simulating reflector (BSR) and gas hydrate occurrence and accumulation in the Zhongjian basin. (1) The characteristics of BSR in this area is slightly different from that found in the gas hydrate drilling area, northern South China Sea. The BSRs identified in this basin are widely distributed with continuous reflections occurred in the fine-grain sediments. The BSR amplitude is particularly strong and continuous where the fault reaches the gas hydrate stability zone. (2) The saturation of gas hydrate-bearing layers is about 30%-40% of the pore space with regional high value. The gas hydrate layer has the same polarity with the seabed reflection and is characterized by continuous and strong amplitude reflections. (3) The gas hydrate-bearing layers are occurred above different depths of the BSR which is controlled by local faults and is affected by sedimentation and tectonic movements.
2023, 48(12): 4641-4657.
doi: 10.3799/dqkx.2022.130
Abstract:
Organic matter (OM) in mudstones/shales is the source of oil and gas, the organic petrographic classification of which has not reached a consensus. Traditional coal petrological methods do not fully apply to dispersed organic matter (DOM) in shales. OM-hosted pores are important constituents of the pore system in shale reservoirs, and they, to a large degree, control the gas content and porosity of shales. However, the origin of organic pores and their relationships with OM type and thermal maturity remain controversial. This study systematically summarized the types of DOM in shales, thermal evolution of different types of OM, and factors controlling the formation and preservation of organic pores, and proposed the issues related to DOM study and future research directions. DOM in shales can classified into five maceral groups: vitrinite, inertinite, liptinite, zooclasts, and secondary organic matter, with each group consisting of multiple macerals. Different macerals have different origins, and varying potential of hydrocarbon generation and development of organic pores. Organic pores in shales can be primary or secondary, the latter of which is the dominant type. Secondary organic pores occur in solid bitumen or pyrobitumen, and their development is related to thermal maturation of oil-prone macerals. The development of secondary organic pores is controlled by OM type and thermal maturity, and their preservation depends on thermal maturity, OM content, mineralogical composition of shales, and pore pressure. When conducting source rock evaluation, the hydrocarbon generation potential of OM should be studied based on a good understanding of maceral types, composition, and their hydrocarbon generation potential. In order to accurately assess the contribution of organic pores to the pore system of shale reservoirs, the influence of OM type, content, and thermal maturity should be taken into consideration.
Organic matter (OM) in mudstones/shales is the source of oil and gas, the organic petrographic classification of which has not reached a consensus. Traditional coal petrological methods do not fully apply to dispersed organic matter (DOM) in shales. OM-hosted pores are important constituents of the pore system in shale reservoirs, and they, to a large degree, control the gas content and porosity of shales. However, the origin of organic pores and their relationships with OM type and thermal maturity remain controversial. This study systematically summarized the types of DOM in shales, thermal evolution of different types of OM, and factors controlling the formation and preservation of organic pores, and proposed the issues related to DOM study and future research directions. DOM in shales can classified into five maceral groups: vitrinite, inertinite, liptinite, zooclasts, and secondary organic matter, with each group consisting of multiple macerals. Different macerals have different origins, and varying potential of hydrocarbon generation and development of organic pores. Organic pores in shales can be primary or secondary, the latter of which is the dominant type. Secondary organic pores occur in solid bitumen or pyrobitumen, and their development is related to thermal maturation of oil-prone macerals. The development of secondary organic pores is controlled by OM type and thermal maturity, and their preservation depends on thermal maturity, OM content, mineralogical composition of shales, and pore pressure. When conducting source rock evaluation, the hydrocarbon generation potential of OM should be studied based on a good understanding of maceral types, composition, and their hydrocarbon generation potential. In order to accurately assess the contribution of organic pores to the pore system of shale reservoirs, the influence of OM type, content, and thermal maturity should be taken into consideration.
2023, 48(12): 4658-4667.
doi: 10.3799/dqkx.2022.486
Abstract:
It is of great significance to elucidate the multi-scale evolution mechanism of rock structures under the action of wetting and drying cycles in the field of engineering geology. However, due to the randomness and disorder of complex structural systems, it is extremely challenging to elucidate the relationship between microstructure and macroscopic mechanical structural properties. Taking the sandstone near the dam site of the Baihetan Hydropower Station as the research object, various fine testing techniques (including NMR, μCT and SEM) were adopted to explore the evolution characteristics of the mechanical properties, pore fracture characteristics and mineral structure of sandstone in different stages of wetting and drying cycles. When water molecules were absorbed by hydrophilic minerals, the surface hydration film thickened, and the swelling pressure led to the destruction of aggregates. With the increase in the number of wetting and drying cycles, the number of small pores and pore size increased, while the number of large pore size did not show a monotonically increasing trend. The pore-fracture connectivity was significantly improved during wetting and drying cycles, resulting in an exponential decline in the uniaxial compressive strength of sandstone, and the fracture surfaces tended to be complicated. Finally, the multiscale evolution mechanism of the sandstone structure was revealed based on detailed microstructure evolution observations and mineral-water molecular simulation results. The research results are of great significance to the study of geological hazards induced by rock structure deterioration.
It is of great significance to elucidate the multi-scale evolution mechanism of rock structures under the action of wetting and drying cycles in the field of engineering geology. However, due to the randomness and disorder of complex structural systems, it is extremely challenging to elucidate the relationship between microstructure and macroscopic mechanical structural properties. Taking the sandstone near the dam site of the Baihetan Hydropower Station as the research object, various fine testing techniques (including NMR, μCT and SEM) were adopted to explore the evolution characteristics of the mechanical properties, pore fracture characteristics and mineral structure of sandstone in different stages of wetting and drying cycles. When water molecules were absorbed by hydrophilic minerals, the surface hydration film thickened, and the swelling pressure led to the destruction of aggregates. With the increase in the number of wetting and drying cycles, the number of small pores and pore size increased, while the number of large pore size did not show a monotonically increasing trend. The pore-fracture connectivity was significantly improved during wetting and drying cycles, resulting in an exponential decline in the uniaxial compressive strength of sandstone, and the fracture surfaces tended to be complicated. Finally, the multiscale evolution mechanism of the sandstone structure was revealed based on detailed microstructure evolution observations and mineral-water molecular simulation results. The research results are of great significance to the study of geological hazards induced by rock structure deterioration.
2023, 48(12): 4668-4679.
doi: 10.3799/dqkx.2023.017
Abstract:
The Duolasi landslide is a super-large scale ancient landslide located in the Nu River tectonic mélange belt, which is characterized by the combination control of typical geological structure and special lithology. In this paper, several technical means, such as field investigation, geophysical exploration, unmanned aerial vehicle mapping, geo-mechanics and chronological testing, were applied to reveal the prone sliding geological structure, multi-stage development characteristics and high-position initiating mechanism of the Duolasi landslide. The results show follows: (1) The thick-bedded marble and ophiolite are stacked alternately and the corresponding clay-altered zone is an important prone-sliding geological structure of the Duolasi landslide. The altered clay is an important factor to the high-speed and long run-out of the landslide. (2) The Duolasi landslide has the characteristics of multi-stage activity, and can be divided into the main sliding body area, the secondary sliding body area and the modern colluvial area. The formation age of the main sliding body is 19.4±2.8 ka, and that of the secondary sliding bodies is 4.24±0.35 ka. (3) The high-position initiating process of the main landslide is closely related to factors such as steep slope landform, multi-permeable karst structure, weak base effect of altered clay, and seismic dynamic triggering. (4) The main landslide presents a pseudo-stratigraphic pattern of layered accumulation, i.e., coarse boulders in the upper part and fine-grained materials in the lower part, indicating that the overall landslide is mainly shear motion, and the material in the upper part of the landslide moves faster than the material in the lower part. The above understanding can provide a reference for the formation mechanism research and risk control of large scale landslides in the tectonic mélange belt on the east Tibetan plateau.
The Duolasi landslide is a super-large scale ancient landslide located in the Nu River tectonic mélange belt, which is characterized by the combination control of typical geological structure and special lithology. In this paper, several technical means, such as field investigation, geophysical exploration, unmanned aerial vehicle mapping, geo-mechanics and chronological testing, were applied to reveal the prone sliding geological structure, multi-stage development characteristics and high-position initiating mechanism of the Duolasi landslide. The results show follows: (1) The thick-bedded marble and ophiolite are stacked alternately and the corresponding clay-altered zone is an important prone-sliding geological structure of the Duolasi landslide. The altered clay is an important factor to the high-speed and long run-out of the landslide. (2) The Duolasi landslide has the characteristics of multi-stage activity, and can be divided into the main sliding body area, the secondary sliding body area and the modern colluvial area. The formation age of the main sliding body is 19.4±2.8 ka, and that of the secondary sliding bodies is 4.24±0.35 ka. (3) The high-position initiating process of the main landslide is closely related to factors such as steep slope landform, multi-permeable karst structure, weak base effect of altered clay, and seismic dynamic triggering. (4) The main landslide presents a pseudo-stratigraphic pattern of layered accumulation, i.e., coarse boulders in the upper part and fine-grained materials in the lower part, indicating that the overall landslide is mainly shear motion, and the material in the upper part of the landslide moves faster than the material in the lower part. The above understanding can provide a reference for the formation mechanism research and risk control of large scale landslides in the tectonic mélange belt on the east Tibetan plateau.
2023, 48(12): 4680-4688.
doi: 10.3799/dqkx.2023.102
Abstract:
Ordinary mortar often produces thermal deformation and cracks when it is applied. However, the low thermal conductivity of the existing phase change mortar easily leads to insufficient phase change and low energy storage efficiency, resulting in low thermal adaptability. Thus, it cannot effectively control the development of deformation, stress and fracture induced by temperature change. In this paper, paraffin-based phase change materials are used to prepare energy storage mortar, and by optimizing the three-dimensional microscopic parameters such as the specific surface area and thickness of the thermal conductivity enhancer, the focus is on improving the thermal conductivity of the phase change matrix and the energy storage rate of the phase change mortar, thereby improving its thermal adaptability. A thermal test platform was built to test its thermal performance including the energy storage and the thermal strain development with time. It is concluded that when the phase change matrix material was mixed with 30%, the surface temperature of the mortar block was lower by 9.7 ℃ than that of the ordinary mortar block, and the thermal strain was reduced by 27.54%, indicating that the phase change material improved the heat storage efficiency and significantly improved its thermal properties of self-controlled temperature.
Ordinary mortar often produces thermal deformation and cracks when it is applied. However, the low thermal conductivity of the existing phase change mortar easily leads to insufficient phase change and low energy storage efficiency, resulting in low thermal adaptability. Thus, it cannot effectively control the development of deformation, stress and fracture induced by temperature change. In this paper, paraffin-based phase change materials are used to prepare energy storage mortar, and by optimizing the three-dimensional microscopic parameters such as the specific surface area and thickness of the thermal conductivity enhancer, the focus is on improving the thermal conductivity of the phase change matrix and the energy storage rate of the phase change mortar, thereby improving its thermal adaptability. A thermal test platform was built to test its thermal performance including the energy storage and the thermal strain development with time. It is concluded that when the phase change matrix material was mixed with 30%, the surface temperature of the mortar block was lower by 9.7 ℃ than that of the ordinary mortar block, and the thermal strain was reduced by 27.54%, indicating that the phase change material improved the heat storage efficiency and significantly improved its thermal properties of self-controlled temperature.
2023, 48(12): 4689-4698.
doi: 10.3799/dqkx.2022.083
Abstract:
Global warming will lead to the thaw of permafrost degradation. The permafrost degradation can cause serious damage to engineering and infrastructure in permafrost regions, it can also change water, energy and carbon cycle between the land and the atmosphere and further create a feedback to climate change. Most permafrost is the ground below the earth's surface and thus is difficult to be detected. There are many literatures used the terms of permafrost region and permafrost area ambiguously, and the incorrectly use of the two terms can lead serious mistakes in permafrost change and carbon budget calculation. Recently, there are many advances in remote sensing and modelling of permafrost. Here it systematically reviews the literatures to clarify the area of permafrost regions and the actual permafrost area in the world as well as in China. The most recent studies show that the permafrost region in the northern hemisphere is about 21×106 km2, and the actual permafrost area is about 14×106 km2. For the Qinghai-Tibetan plateau in China, the permafrost region occupies an area of about 1.50×106 km2, and the actual permafrost area is about 1.06×106 km2. More data are required to quantify the actual permafrost area in other permafrost regions in China.
Global warming will lead to the thaw of permafrost degradation. The permafrost degradation can cause serious damage to engineering and infrastructure in permafrost regions, it can also change water, energy and carbon cycle between the land and the atmosphere and further create a feedback to climate change. Most permafrost is the ground below the earth's surface and thus is difficult to be detected. There are many literatures used the terms of permafrost region and permafrost area ambiguously, and the incorrectly use of the two terms can lead serious mistakes in permafrost change and carbon budget calculation. Recently, there are many advances in remote sensing and modelling of permafrost. Here it systematically reviews the literatures to clarify the area of permafrost regions and the actual permafrost area in the world as well as in China. The most recent studies show that the permafrost region in the northern hemisphere is about 21×106 km2, and the actual permafrost area is about 14×106 km2. For the Qinghai-Tibetan plateau in China, the permafrost region occupies an area of about 1.50×106 km2, and the actual permafrost area is about 1.06×106 km2. More data are required to quantify the actual permafrost area in other permafrost regions in China.
2023, 48(12): 4699-4710.
doi: 10.3799/dqkx.2022.009
Abstract:
Organic matter plays an important role in the mobilization of iodine in groundwater system. In this study, the high iodine groundwater from shallow and middle aquifers in Datong basin in China was collected to perform the effect of dissolved organic matter (DOM) on iodine mobilization in groundwater. The structure of dissolved organic matter (DOM) in groundwater was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The results show that the range of total iodine concentration in groundwater is 1.97-926.10 μg/L. Iodide is the main species of iodine in groundwater. The total iodine concentration has a positive correlation with DOM (r=0.84) and a negative correlation with biodegradable organic matter (r=-0.71), indicating that the organic matter in high iodine groundwater experience more intensive biodegradation. The differences of DOM molecular composition between high and low iodine groundwater further show that microorganisms preferentially use small molecular biodegradable compounds such as CHO, CHON1 and CHON2 to promote the release of bound iodine into groundwater during degradation. The hydrochemical fate of groundwater iodine under the reducing environment is mainly related to the reductive dissolution of iron (hydrogen) oxides and the biodegradation of organic matter, during which iodine species changed, while under oxidizing environment, it could be related to the transformation of natural organic matter.
Organic matter plays an important role in the mobilization of iodine in groundwater system. In this study, the high iodine groundwater from shallow and middle aquifers in Datong basin in China was collected to perform the effect of dissolved organic matter (DOM) on iodine mobilization in groundwater. The structure of dissolved organic matter (DOM) in groundwater was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The results show that the range of total iodine concentration in groundwater is 1.97-926.10 μg/L. Iodide is the main species of iodine in groundwater. The total iodine concentration has a positive correlation with DOM (r=0.84) and a negative correlation with biodegradable organic matter (r=-0.71), indicating that the organic matter in high iodine groundwater experience more intensive biodegradation. The differences of DOM molecular composition between high and low iodine groundwater further show that microorganisms preferentially use small molecular biodegradable compounds such as CHO, CHON1 and CHON2 to promote the release of bound iodine into groundwater during degradation. The hydrochemical fate of groundwater iodine under the reducing environment is mainly related to the reductive dissolution of iron (hydrogen) oxides and the biodegradation of organic matter, during which iodine species changed, while under oxidizing environment, it could be related to the transformation of natural organic matter.
2023, 48(12): 4711-4726.
doi: 10.3799/dqkx.2022.068
Abstract:
Karst caves serve as the natural laboratories to study subsurface biosphere, which provide ideal places to investigate microbial diversity and their interactions between microbes and environments. Guilin is one of the typical areas with developed karst landscape. Deep investigation of cave microbes in different niches and their response to environmental variables will provide valuable information on subsurface biosphere in terms of microbial diversity, function and interaction with environments. To this end, Samples were collected from overlying soils, sediments, cave wall, weathered crusted on cave walls, microbial biofilm on stalagmite surface and dripping water in the Panlong Cave in Guiling City to study microbial communities and their correlation with environmental variables via high throughput sequencing of 16S rRNA. Results show that bacterial communities show high specificity to niches and were dominated by Actinomycete and Proteobacteria. Each niche has its own specific indicator group. For example, Paemibacillus was the indicator for microbial biofilm on the dry surface of stalagmite, whilst Acidobacteriaceae and Pseudomonas were the indicator groups in microbial biofilm on the wet surface of stalagmite. Pseudomonadales and Branhamella were the indicator groups in dripping water, whereas indicator groups in overlying soils included Mycobacterium and Nocardioides. Bacillus and Gp-7 were indicators in sediments, whilst Chromatiales, Soilrubrobacteraceae and Rubrobcter were indicators in cave wall and Methylobacterium in weathered crust. Temperature was demonstrated to be the main variable impacting bacterial communities in the Panlong Cave as indicated by redundancy analysis. Tax4fun2 analysis shows that microbes participated in carbon and nitrogen cycles also varied with niches. Microbes in dripping water, microbial biofilm on dry/wet surface of stalagmite were closely related to nitrogen cycle. On the contrast, those in weathered crust, sediments and cave wall were more involved in carbon fixation. Co-occurrence network analysis inferred that corporation was the main strategy for microbial groups to survive in the oligotrophic karst caves.
Karst caves serve as the natural laboratories to study subsurface biosphere, which provide ideal places to investigate microbial diversity and their interactions between microbes and environments. Guilin is one of the typical areas with developed karst landscape. Deep investigation of cave microbes in different niches and their response to environmental variables will provide valuable information on subsurface biosphere in terms of microbial diversity, function and interaction with environments. To this end, Samples were collected from overlying soils, sediments, cave wall, weathered crusted on cave walls, microbial biofilm on stalagmite surface and dripping water in the Panlong Cave in Guiling City to study microbial communities and their correlation with environmental variables via high throughput sequencing of 16S rRNA. Results show that bacterial communities show high specificity to niches and were dominated by Actinomycete and Proteobacteria. Each niche has its own specific indicator group. For example, Paemibacillus was the indicator for microbial biofilm on the dry surface of stalagmite, whilst Acidobacteriaceae and Pseudomonas were the indicator groups in microbial biofilm on the wet surface of stalagmite. Pseudomonadales and Branhamella were the indicator groups in dripping water, whereas indicator groups in overlying soils included Mycobacterium and Nocardioides. Bacillus and Gp-7 were indicators in sediments, whilst Chromatiales, Soilrubrobacteraceae and Rubrobcter were indicators in cave wall and Methylobacterium in weathered crust. Temperature was demonstrated to be the main variable impacting bacterial communities in the Panlong Cave as indicated by redundancy analysis. Tax4fun2 analysis shows that microbes participated in carbon and nitrogen cycles also varied with niches. Microbes in dripping water, microbial biofilm on dry/wet surface of stalagmite were closely related to nitrogen cycle. On the contrast, those in weathered crust, sediments and cave wall were more involved in carbon fixation. Co-occurrence network analysis inferred that corporation was the main strategy for microbial groups to survive in the oligotrophic karst caves.
