2017 Vol. 42, No. 1
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2017, 42(1): 1-23.
doi: 10.3799/dqkx.2017.001
Abstract:
As the most important part of Bangong Lake-Nujiang River metallogenic belt, the Duolong ore-concentrated area is characterized by the occurrence of huge mineralization scale, extended time span and complex forming process, resulting in controversial understanding of its petrogenesis and tectonics and those of related deposits. To address this problem, this study firstly presents new data of LA-ICP-MS zircon U-Pb age, whole-rock geochemistry, and in situ zircon Hf isotopes for the mineralization-associated granite porphyry in Naruo porphyry copper (gold) deposit, and secondly we make a detailed comparison with research results of other porphyry deposits in Duolong area to find out the tectonic setting, petrogenesis and geodynamic processes of the mineralization-associated porphyry in Duolong area. The test results show that the age of the Naruo Cu (Au) deposit formation is consistent with that of other deposits in Duolong area formed at Early Cretaceous about 120Ma. All the main intrusive rocks have similar lithogeochemical characteristics, for they all show the relative enrichment in light rare earth elements (LREE) and large-ion lithophile elements (LILE: Rb, Ba, K, etc.), relatively depleted in heavy rare earth elements (HREE ) and high field strength elements (HFSE: Nb, Ta, Zr, Hf, etc.). Moreover, the granite porphyry shows positive εHf(t) values between 1.38-7.37, and two-stage model ages of zircons are 707-1086Ma. The results suggest that the formation of porphyry-epithermal copper (gold) deposit in Duolong ore-concentrated area is dominated by northward subduction of the Bangongcuo Tethys plate beneath Qiangtang block at Early Cretaceous. When the subducted oceanic crust reached 50-70km underground and generated different degrees of phase transformation, which leads to melt produced by dehydration of amphibole minerals metasomatized mantle wedge and induced mantle partial melting produced magmatic arc. Those deposits occurred in a continental arc tectonic setting which is similar to the continental margin arc environment of the ocean-continent subduction setting of the Andes metallogenic belt in South America.
As the most important part of Bangong Lake-Nujiang River metallogenic belt, the Duolong ore-concentrated area is characterized by the occurrence of huge mineralization scale, extended time span and complex forming process, resulting in controversial understanding of its petrogenesis and tectonics and those of related deposits. To address this problem, this study firstly presents new data of LA-ICP-MS zircon U-Pb age, whole-rock geochemistry, and in situ zircon Hf isotopes for the mineralization-associated granite porphyry in Naruo porphyry copper (gold) deposit, and secondly we make a detailed comparison with research results of other porphyry deposits in Duolong area to find out the tectonic setting, petrogenesis and geodynamic processes of the mineralization-associated porphyry in Duolong area. The test results show that the age of the Naruo Cu (Au) deposit formation is consistent with that of other deposits in Duolong area formed at Early Cretaceous about 120Ma. All the main intrusive rocks have similar lithogeochemical characteristics, for they all show the relative enrichment in light rare earth elements (LREE) and large-ion lithophile elements (LILE: Rb, Ba, K, etc.), relatively depleted in heavy rare earth elements (HREE ) and high field strength elements (HFSE: Nb, Ta, Zr, Hf, etc.). Moreover, the granite porphyry shows positive εHf(t) values between 1.38-7.37, and two-stage model ages of zircons are 707-1086Ma. The results suggest that the formation of porphyry-epithermal copper (gold) deposit in Duolong ore-concentrated area is dominated by northward subduction of the Bangongcuo Tethys plate beneath Qiangtang block at Early Cretaceous. When the subducted oceanic crust reached 50-70km underground and generated different degrees of phase transformation, which leads to melt produced by dehydration of amphibole minerals metasomatized mantle wedge and induced mantle partial melting produced magmatic arc. Those deposits occurred in a continental arc tectonic setting which is similar to the continental margin arc environment of the ocean-continent subduction setting of the Andes metallogenic belt in South America.
2017, 42(1): 24-34.
doi: 10.3799/dqkx.2017.002
Abstract:
Babu mafic/ultramafic rocks in Southeast Yunnan Province are interpreted as remnant ocean crust, and together with the ophiolite in Song Hien tectonic zone of North Vietnam, constitute significant components of the Babu-Song Hien Paleo-Tethyan suture, a possible southern extension of the Ailaoshan suture. Around the Babu ophiolite is a widespread siliclastic rocks dominated sequence, with thin-bedded cherts observed in some locations. These clastic rocks have long been considered to be Triassic turbidity current deposits in spite of absence of reliable fossil and isotopic dating. West to Longlin village, there outcrop coarse sandstone and sandy conglomerate beds nearby the Babu mafic/lutramific rocks. These sandstones contain andesite and rhyolite fragments and display detrital zircon age spectra similar to those of the Late Permian sandstones in Song Hien tectonic zone and Permian sandstones in western Ailaoshan belt, but distinguished from those of the Permian-Triassic clastic rocks of Youjiang and Shiwandashan basins in southwestern South China. The youngest zircon group with ages of ~285Ma, has geochemical affinities of magmatic zircons crystallized from arc/orogenic settings, corresponding to the occurrence of volcanic rock fragments, indicating a maximum depositional age, and showing an adjacent Early Permian volcanic source. The new findings of chert deposits within a clastic rock section to the east of Babu Village, and the comparison of detrital zircon U-Pb age spectra suggest that the analyzed clastic rocks should be Early Permian rather than Middle Triassic in age and their Permian volcanic source might be related to the subduction of Babu-Song Hien Paleo-Tethyan ocean.
Babu mafic/ultramafic rocks in Southeast Yunnan Province are interpreted as remnant ocean crust, and together with the ophiolite in Song Hien tectonic zone of North Vietnam, constitute significant components of the Babu-Song Hien Paleo-Tethyan suture, a possible southern extension of the Ailaoshan suture. Around the Babu ophiolite is a widespread siliclastic rocks dominated sequence, with thin-bedded cherts observed in some locations. These clastic rocks have long been considered to be Triassic turbidity current deposits in spite of absence of reliable fossil and isotopic dating. West to Longlin village, there outcrop coarse sandstone and sandy conglomerate beds nearby the Babu mafic/lutramific rocks. These sandstones contain andesite and rhyolite fragments and display detrital zircon age spectra similar to those of the Late Permian sandstones in Song Hien tectonic zone and Permian sandstones in western Ailaoshan belt, but distinguished from those of the Permian-Triassic clastic rocks of Youjiang and Shiwandashan basins in southwestern South China. The youngest zircon group with ages of ~285Ma, has geochemical affinities of magmatic zircons crystallized from arc/orogenic settings, corresponding to the occurrence of volcanic rock fragments, indicating a maximum depositional age, and showing an adjacent Early Permian volcanic source. The new findings of chert deposits within a clastic rock section to the east of Babu Village, and the comparison of detrital zircon U-Pb age spectra suggest that the analyzed clastic rocks should be Early Permian rather than Middle Triassic in age and their Permian volcanic source might be related to the subduction of Babu-Song Hien Paleo-Tethyan ocean.
2017, 42(1): 35-52.
doi: 10.3799/dqkx.2017.003
Abstract:
o address the controversy of the Ershi'erzhan Formation sandstone formation ages in the Mohe basin of the northern Great Khingan Range, this study presents an accurate limit to its formation ages using the LA-ICP-MS detrital zircon U-Pb dating for the first time in this paper, and discusses its provenance and tectonic setting combined with the geochemistry of major and trace elements. The results show that the fragmental material in sandstone has poor psephicity and sorting, indicating that source region is relatively unstable with characteristics of rapid denudation, transportation and sedimentation. The grains of detrital zircons are big with clear oscillatory zoning, and Th/U values range from 0.35-1.07, which is indicative of a magmatic origin. Zircon U-Pb dating results show that 90 dating data are distributed in the following three periods, namely, 152-170Ma with the peak of 158Ma, standing for the lower limit of Ershi'erzhan Formation sedimentary rocks at Late Jurassic; 179-193Ma with the peak of 190Ma and 205-214Ma with the peak of 210Ma. The three peak ages are the evolution records of the Mongolia-Okhotsk ocean. The peak ages of 210Ma and 190Ma are consistent with the Late Triassic and Early Jurassic magmatic events of south margin of the basin in the Erguna massif, the peak age of 158Ma fits the Late Jurassic magmatic event of north margin of the basin. The geochemical diagrams of major and trace elements reveal that the provenance has the background of active continental margin. Meanwhile, the zircon dating shows that there is no Pre-Mesozoic clastics in the Ershi'erzhan Formation. It suggest that these were generated within an active continental margin setting at the north margin of the Erguna massif in Mesozoic, and provided the most clastics for the Ershi'erzhan Formation. Combining with the previous studies, it is concluded that the Ershi'erzhan Formation sandstone was formed in Late Jurassic under the environment of rapid denudation, transportation and sedimentation, controlled by the uplift of the Mongolia-Okhotsk orogenic belt, indicating that the eastern Mongolia-Okhotsk ocean has already closed in Late Jurassic.
o address the controversy of the Ershi'erzhan Formation sandstone formation ages in the Mohe basin of the northern Great Khingan Range, this study presents an accurate limit to its formation ages using the LA-ICP-MS detrital zircon U-Pb dating for the first time in this paper, and discusses its provenance and tectonic setting combined with the geochemistry of major and trace elements. The results show that the fragmental material in sandstone has poor psephicity and sorting, indicating that source region is relatively unstable with characteristics of rapid denudation, transportation and sedimentation. The grains of detrital zircons are big with clear oscillatory zoning, and Th/U values range from 0.35-1.07, which is indicative of a magmatic origin. Zircon U-Pb dating results show that 90 dating data are distributed in the following three periods, namely, 152-170Ma with the peak of 158Ma, standing for the lower limit of Ershi'erzhan Formation sedimentary rocks at Late Jurassic; 179-193Ma with the peak of 190Ma and 205-214Ma with the peak of 210Ma. The three peak ages are the evolution records of the Mongolia-Okhotsk ocean. The peak ages of 210Ma and 190Ma are consistent with the Late Triassic and Early Jurassic magmatic events of south margin of the basin in the Erguna massif, the peak age of 158Ma fits the Late Jurassic magmatic event of north margin of the basin. The geochemical diagrams of major and trace elements reveal that the provenance has the background of active continental margin. Meanwhile, the zircon dating shows that there is no Pre-Mesozoic clastics in the Ershi'erzhan Formation. It suggest that these were generated within an active continental margin setting at the north margin of the Erguna massif in Mesozoic, and provided the most clastics for the Ershi'erzhan Formation. Combining with the previous studies, it is concluded that the Ershi'erzhan Formation sandstone was formed in Late Jurassic under the environment of rapid denudation, transportation and sedimentation, controlled by the uplift of the Mongolia-Okhotsk orogenic belt, indicating that the eastern Mongolia-Okhotsk ocean has already closed in Late Jurassic.
2017, 42(1): 53-67.
doi: 10.3799/dqkx.2017.004
Abstract:
The sedimentary development of the Jiyuan basin was controlled by the Qinling orogenic belt during the Early Mesozoic. Therefore, mountain building and uplift of the Qinling orogenic belt can be evidenced by the sediments from the Jiyuan basin. The Mesozoic mudstones geochemistry has been investigated to determine the provenance of the Jiyuan basin. The average values of corrected CIA (chemical weathering index) from the Early-Middle Triassic, Late Triassic and Early-Middle Jurassic samples increase from 68.5 to 76.4, then to 86 successively, but decrease to 73.7 from the late Middle Jurassic samples. The variation of CIA might correspond to the changing paleoclimate during the Mesozoic. However, the much lower values of CIA from the Triassic samples may be restricted to the active tectonic setting. The values of ICV (compositional variation index) reflect that the first cycle sediments are mainly concentrated in the Triassic samples. These sediments may come from the uplifted basement of the North China craton, which should consist of the continental marginal arc and/or arc-continent collision zone. The Early-Middle Jurassic samples showing higher CIA may be related with the recycling clastics of the uplifting orogen, whereas first deposition might occur in the back-arc basin. In the tectonic discrimination diagrams, the sediments from Jiyuan basin mainly formed under the active continental margin and the passive continental margin, but contained much more continental island arc materials. Our data support that sediments from the uplifted basement of the North China craton to the denudation of the orogen is most likely related to the Qinling orogenesis during the Indosinian.
The sedimentary development of the Jiyuan basin was controlled by the Qinling orogenic belt during the Early Mesozoic. Therefore, mountain building and uplift of the Qinling orogenic belt can be evidenced by the sediments from the Jiyuan basin. The Mesozoic mudstones geochemistry has been investigated to determine the provenance of the Jiyuan basin. The average values of corrected CIA (chemical weathering index) from the Early-Middle Triassic, Late Triassic and Early-Middle Jurassic samples increase from 68.5 to 76.4, then to 86 successively, but decrease to 73.7 from the late Middle Jurassic samples. The variation of CIA might correspond to the changing paleoclimate during the Mesozoic. However, the much lower values of CIA from the Triassic samples may be restricted to the active tectonic setting. The values of ICV (compositional variation index) reflect that the first cycle sediments are mainly concentrated in the Triassic samples. These sediments may come from the uplifted basement of the North China craton, which should consist of the continental marginal arc and/or arc-continent collision zone. The Early-Middle Jurassic samples showing higher CIA may be related with the recycling clastics of the uplifting orogen, whereas first deposition might occur in the back-arc basin. In the tectonic discrimination diagrams, the sediments from Jiyuan basin mainly formed under the active continental margin and the passive continental margin, but contained much more continental island arc materials. Our data support that sediments from the uplifted basement of the North China craton to the denudation of the orogen is most likely related to the Qinling orogenesis during the Indosinian.
2017, 42(1): 68-77.
doi: 10.3799/dqkx.2017.005
Abstract:
Depositional processes, successions and models for various carbonate tempestites in different environments should be well documented in our country. The carbonate tempestites are frequently and widely developed in the Chaomidian Formation of the Upper Cambrian, central Shandong Province, providing an area favorable to comprehensively realize storm depositional processes. On the basis of outcrop observations in detail, typical storm sedimentary structures including scouring surface, gutter cast and hummocky cross-bedding, and tempestites including calcirudite, graded gravelly calcarenite, laminated calcisiltite and calcarenite were identified. Specially, according to petrologic features such as color, psephicity and arrangement mode of gravel and support fabric, the dominant calcirudites are classified as five sorts of lithofacies, including angular tightly-stacked calcirudite, matrix-supported calcirudite, sand-supported calcirudite, horizontal to imbricate calcirudite and radially-arranged calcirudite, which were attributed to autochthonous to near-sourced deposits at a fore-platform ramp, debris flow deposits, high-density to low-density turbidites, storm gravel beach deposits and storm vortex deposits respectively. Furthermore, storm depositional successes in the various environments of fore-platform ramp, platform margin and open platform were summarized, and an integrative depositional model for carbonate tempestites at the background of ramp platform was built up. Finally, the frequent tempestites were ascribed to warm climate, a sea-level rise and earthquakes. Significantly, many gutter casts occurred at the platform margin, and were commonly filled with radiate gravels indicative of storm vortex processes. Additionally, the integrative model is useful to illuminate various storm processes.
Depositional processes, successions and models for various carbonate tempestites in different environments should be well documented in our country. The carbonate tempestites are frequently and widely developed in the Chaomidian Formation of the Upper Cambrian, central Shandong Province, providing an area favorable to comprehensively realize storm depositional processes. On the basis of outcrop observations in detail, typical storm sedimentary structures including scouring surface, gutter cast and hummocky cross-bedding, and tempestites including calcirudite, graded gravelly calcarenite, laminated calcisiltite and calcarenite were identified. Specially, according to petrologic features such as color, psephicity and arrangement mode of gravel and support fabric, the dominant calcirudites are classified as five sorts of lithofacies, including angular tightly-stacked calcirudite, matrix-supported calcirudite, sand-supported calcirudite, horizontal to imbricate calcirudite and radially-arranged calcirudite, which were attributed to autochthonous to near-sourced deposits at a fore-platform ramp, debris flow deposits, high-density to low-density turbidites, storm gravel beach deposits and storm vortex deposits respectively. Furthermore, storm depositional successes in the various environments of fore-platform ramp, platform margin and open platform were summarized, and an integrative depositional model for carbonate tempestites at the background of ramp platform was built up. Finally, the frequent tempestites were ascribed to warm climate, a sea-level rise and earthquakes. Significantly, many gutter casts occurred at the platform margin, and were commonly filled with radiate gravels indicative of storm vortex processes. Additionally, the integrative model is useful to illuminate various storm processes.
2017, 42(1): 78-92.
doi: 10.3799/dqkx.2017.006
Abstract:
A large-scale braided delta is developed in the late stage of the Enping Formation in the Baiyun sag, but the sedimentary process, the internal development stages and the plane distribution of the delta remain unclear. Based on the nine wells which penetrated the third member of the Enping Formation, the detrital zircon U-Pb dating and the 2D and 3D seismic data analyses were carried out in this paper. The sediment supply patterns of the Enping Formation in different depositional periods were determined. During the first-second members of Enping Formation (SQ1-SQ2), sediments derived from the paleo-uplift were mainly composed of Mesozoic igneous rocks and are interpreted to have sourced via relatively short-distance transportation. During the third member of Enping Formation (SQ3), the sediments oriented from South China folded belt (SCFB) which mainly consists of Precambrian-Paleozoic metamorphic rocks. The sediments which are derived from SCFB and transported long-distance pathways through northwest-southeast orientation have deposited in Baiyun sag and the large-scale delta developed subsequently. Meanwhile, the sedimentary characteristics of large-scale delta of the SQ3 within Baiyun sag are described through typical seismic facies and the energy half-time seismic attribute analysis. The delta developed three stages of progradational wedges continuously to the southeast direction and with increasing scale initially, followed by decreasing scale until the rift basin disappeared. The results reveal that the deltaic coal-bearing and terrigenous-marine source rocks are mainly developed in the SQ3 and thus the large-scale delta has an excellent accumulation condition of source-reservoir-cap rock assemblages. And the delta front sand bodies tend to develop the updip pinch-out reservoir which will become an important target for oil and gas exploration in Paleogene of Baiyun deep-water region.
A large-scale braided delta is developed in the late stage of the Enping Formation in the Baiyun sag, but the sedimentary process, the internal development stages and the plane distribution of the delta remain unclear. Based on the nine wells which penetrated the third member of the Enping Formation, the detrital zircon U-Pb dating and the 2D and 3D seismic data analyses were carried out in this paper. The sediment supply patterns of the Enping Formation in different depositional periods were determined. During the first-second members of Enping Formation (SQ1-SQ2), sediments derived from the paleo-uplift were mainly composed of Mesozoic igneous rocks and are interpreted to have sourced via relatively short-distance transportation. During the third member of Enping Formation (SQ3), the sediments oriented from South China folded belt (SCFB) which mainly consists of Precambrian-Paleozoic metamorphic rocks. The sediments which are derived from SCFB and transported long-distance pathways through northwest-southeast orientation have deposited in Baiyun sag and the large-scale delta developed subsequently. Meanwhile, the sedimentary characteristics of large-scale delta of the SQ3 within Baiyun sag are described through typical seismic facies and the energy half-time seismic attribute analysis. The delta developed three stages of progradational wedges continuously to the southeast direction and with increasing scale initially, followed by decreasing scale until the rift basin disappeared. The results reveal that the deltaic coal-bearing and terrigenous-marine source rocks are mainly developed in the SQ3 and thus the large-scale delta has an excellent accumulation condition of source-reservoir-cap rock assemblages. And the delta front sand bodies tend to develop the updip pinch-out reservoir which will become an important target for oil and gas exploration in Paleogene of Baiyun deep-water region.
2017, 42(1): 93-104.
doi: 10.3799/dqkx.2017.007
Abstract:
The discovery of high yielding SN4 well of natural gas reveals great potential for oil and gas exploration of the deep-super deep reservoirs in Tarim basin, where the mechanism and distribution of reservoirs remain controversial due to the great burial-depth and low exploration maturity. This paper presents a study from both the macro and micro perspective on this issue. A 3-D seismic fine interpretation is employed to analyze the development of fault structures and the spatial distribution of carbonate reservoirs in Shunnan area of Tarim basin. Combined with the analysis of lithofacies and fluid inclusion, it is concluded that Shunnan area in Tarim basin experienced four major tectonic movements, which happened during early Caledonian, middle Caledonian, late Caledonian-early Hercynian and late Hercynian. The formation and transformation of the NE strike-slip faults were controlled by the tectonic movement of middle Caledonian and Caledonian-early Hercynian. The hypogenic karstification developed in Shunnan area on a large scale, which has a coupling relationship with the NE strike-slip faults. In the plane, the hypogenic karst mainly developed along the SN4 strike-slip faults zones with distinct segmentation. In the section, the hypogenic karstification is developed along the extensional strike-slip faults, and the migration in the transverse direction was mainly controlled by the pre-existing permeable zones which mostly comprised upper Yingshan calcarenite layer.
The discovery of high yielding SN4 well of natural gas reveals great potential for oil and gas exploration of the deep-super deep reservoirs in Tarim basin, where the mechanism and distribution of reservoirs remain controversial due to the great burial-depth and low exploration maturity. This paper presents a study from both the macro and micro perspective on this issue. A 3-D seismic fine interpretation is employed to analyze the development of fault structures and the spatial distribution of carbonate reservoirs in Shunnan area of Tarim basin. Combined with the analysis of lithofacies and fluid inclusion, it is concluded that Shunnan area in Tarim basin experienced four major tectonic movements, which happened during early Caledonian, middle Caledonian, late Caledonian-early Hercynian and late Hercynian. The formation and transformation of the NE strike-slip faults were controlled by the tectonic movement of middle Caledonian and Caledonian-early Hercynian. The hypogenic karstification developed in Shunnan area on a large scale, which has a coupling relationship with the NE strike-slip faults. In the plane, the hypogenic karst mainly developed along the SN4 strike-slip faults zones with distinct segmentation. In the section, the hypogenic karstification is developed along the extensional strike-slip faults, and the migration in the transverse direction was mainly controlled by the pre-existing permeable zones which mostly comprised upper Yingshan calcarenite layer.
2017, 42(1): 105-118.
doi: 10.3799/dqkx.2017.008
Abstract:
Post-rift fault plays an important role in hydrocarbon accumulation of the Neogene in Pearl River Mouth basin, but understanding of the features and dynamics evolution is to be enhanced in this paper, post-rift fault system in Zhu Ⅰ depression is studied by geometric and kinematic analysis methods using high quality 3D seismic reflection data. The analysis reveals two episodes of faulting in the post-rift stage, namely, Nanhai-phase faulting and Dongsha-phase faulting. Transition of fault geometry and kinematics from Nanhai-phase to Dongsha-phase indicates a change of dynamics. Both Nanhai-phase faulting and Dongsha-phase faulting have migration. The former migrates from south to north, and the latter migrates from east to west. The two periods of faulting are both extensional faults, with a slight component of shear in Dongsha-phase. Regional extensional direction transforms from NNE10°-15° in Nanhai-phase faulting to NNE20°-25° in Dongsha-phase faulting, with 5°-10° clockwise rotation. The Nanhai-phase faulting is related to the remaining extension in the northern margin of SCS. The Dongsha-phase faults formed after the cease of the sea-floor spreading of SCS. Coincidently, direction of the regional intermediate principal strain (σ2) during the Dongsha-phase faulting is consistent with the collision direction between the Luzon arc and the Eurasian plate. This feature of the Dongsha-phase faulting in Zhu Ⅰ depression confirms the conclusion that Dongsha movement is the result of the collision between the Luzon arc and the Eurasian plate since Middle Miocene. This study is significant for better understanding of Nanhai movement and Dongsha movement.
Post-rift fault plays an important role in hydrocarbon accumulation of the Neogene in Pearl River Mouth basin, but understanding of the features and dynamics evolution is to be enhanced in this paper, post-rift fault system in Zhu Ⅰ depression is studied by geometric and kinematic analysis methods using high quality 3D seismic reflection data. The analysis reveals two episodes of faulting in the post-rift stage, namely, Nanhai-phase faulting and Dongsha-phase faulting. Transition of fault geometry and kinematics from Nanhai-phase to Dongsha-phase indicates a change of dynamics. Both Nanhai-phase faulting and Dongsha-phase faulting have migration. The former migrates from south to north, and the latter migrates from east to west. The two periods of faulting are both extensional faults, with a slight component of shear in Dongsha-phase. Regional extensional direction transforms from NNE10°-15° in Nanhai-phase faulting to NNE20°-25° in Dongsha-phase faulting, with 5°-10° clockwise rotation. The Nanhai-phase faulting is related to the remaining extension in the northern margin of SCS. The Dongsha-phase faults formed after the cease of the sea-floor spreading of SCS. Coincidently, direction of the regional intermediate principal strain (σ2) during the Dongsha-phase faulting is consistent with the collision direction between the Luzon arc and the Eurasian plate. This feature of the Dongsha-phase faulting in Zhu Ⅰ depression confirms the conclusion that Dongsha movement is the result of the collision between the Luzon arc and the Eurasian plate since Middle Miocene. This study is significant for better understanding of Nanhai movement and Dongsha movement.
2017, 42(1): 119-129.
doi: 10.3799/dqkx.2017.009
Abstract:
Overpressure is widely developed in Xihu depression, which has complicated formation mechanism. However, there is no in-depth study on this topic at present. In this paper, starting from the main factors that produce overpressure, we use both the micro analysis and macro evidence to comprehensively analyze the mudstone overpressure formation mechanism in the Xihu depression of the East China sea shelf basin, based on the logging response characteristics of overpressure formation, as well as the relationship between speed and vertical effective stress, the relationship between the evolution history of deposition and porosity, the coupling of pressure evolution history and that of hydrocarbon-generated rate. It is concluded that overpressure formation in Baochu slope belt is mainly attributed to under-compaction, and its hydrocarbon generation contribution rate is estimated at 23%-57% with an average of 41%. In the central anticlinal belt, overpressure formation mainly has the following two models: one is the model of hydrocarbon generation with a contribution rate of 51%-78%, and the other is the model of under-compaction interaction. Both the hydrocarbon generation and under-compaction have played an important role in the overpressure formation in Santan sag and the average contribution rate of hydrocarbon generation is about 60%.
Overpressure is widely developed in Xihu depression, which has complicated formation mechanism. However, there is no in-depth study on this topic at present. In this paper, starting from the main factors that produce overpressure, we use both the micro analysis and macro evidence to comprehensively analyze the mudstone overpressure formation mechanism in the Xihu depression of the East China sea shelf basin, based on the logging response characteristics of overpressure formation, as well as the relationship between speed and vertical effective stress, the relationship between the evolution history of deposition and porosity, the coupling of pressure evolution history and that of hydrocarbon-generated rate. It is concluded that overpressure formation in Baochu slope belt is mainly attributed to under-compaction, and its hydrocarbon generation contribution rate is estimated at 23%-57% with an average of 41%. In the central anticlinal belt, overpressure formation mainly has the following two models: one is the model of hydrocarbon generation with a contribution rate of 51%-78%, and the other is the model of under-compaction interaction. Both the hydrocarbon generation and under-compaction have played an important role in the overpressure formation in Santan sag and the average contribution rate of hydrocarbon generation is about 60%.
2017, 42(1): 130-141.
doi: 10.3799/dqkx.2017.010
Abstract:
The submarine channel is one of the important targets for deep water hydrocarbon exploration as well as the key point for the investigation into source and sink. Based on the newly acquired 3D seismic data and 3 boreholes in the Ledong area of the Yinggehai basin, the sequence stratigraphic framework for the first member of the Yinggehai Formation is set up. The development of every fourth-order sequence is derived by the enough sediment supply and high frequency sea-level changes under stable tectonic setting. The submarine channels occur in lowstand systems of every fourth-order sequence, which can be classified into slope channel and axial channel. Furthermore, the evolution of submarine channels is described, such as flowing through the lower topography with a convergent system, being reworked by mass-transport deposits (MTDs) and diapirs. Controlled by the sediment supply, high-frequency sea-level fluctuation and regional tectonic activities, the number and scale of submarine channels gradually decrease. The recorded high-frequency sea-level fluctuation by high sedimentary rate in Ledong area makes it possible to better understand the evolution and controlling factors of submarine channels, which facilitates future hydrocarbon exploration.
The submarine channel is one of the important targets for deep water hydrocarbon exploration as well as the key point for the investigation into source and sink. Based on the newly acquired 3D seismic data and 3 boreholes in the Ledong area of the Yinggehai basin, the sequence stratigraphic framework for the first member of the Yinggehai Formation is set up. The development of every fourth-order sequence is derived by the enough sediment supply and high frequency sea-level changes under stable tectonic setting. The submarine channels occur in lowstand systems of every fourth-order sequence, which can be classified into slope channel and axial channel. Furthermore, the evolution of submarine channels is described, such as flowing through the lower topography with a convergent system, being reworked by mass-transport deposits (MTDs) and diapirs. Controlled by the sediment supply, high-frequency sea-level fluctuation and regional tectonic activities, the number and scale of submarine channels gradually decrease. The recorded high-frequency sea-level fluctuation by high sedimentary rate in Ledong area makes it possible to better understand the evolution and controlling factors of submarine channels, which facilitates future hydrocarbon exploration.
2017, 42(1): 142-154.
doi: 10.3799/dqkx.2017.011
Abstract:
Traditional geochemical geothermometers have limitations when used to estimate the temperature of shallow reservoirs(100-200 ℃)in high-temperature geothermal systems, and it remains unclear about the cause of the error due to the widely used geothermometers of Na-K and K-Mg. In this study, the hydrogeochemical data of 201 water samples from geothermal wells in the typical hydrothermal areas across the world were collected, based on which the corresponding geochemical compositions of reservoir fluids are calculated using the code WATCH. An evaluation of Na-K and K-Mg geothermometers was further made. The results show that K-feldspar and common dioctahedral potassium-rich clay minerals are likely to control the content of potassium in geothermal fluid from shallow reservoirs and dioctahedral magnesium-rich clay minerals can be equilibrated with geothermal fluid as well, whereas the content of sodium in geothermal fluid is little affected by water-rock interactions. Hence, the Na-K ratio of shallow geothermal fluid doesn't match well with reservoir temperature. K-Mg geothermometer is capable of indicating shallow reservoir temperature to some degree, but still not accurate enough.
Traditional geochemical geothermometers have limitations when used to estimate the temperature of shallow reservoirs(100-200 ℃)in high-temperature geothermal systems, and it remains unclear about the cause of the error due to the widely used geothermometers of Na-K and K-Mg. In this study, the hydrogeochemical data of 201 water samples from geothermal wells in the typical hydrothermal areas across the world were collected, based on which the corresponding geochemical compositions of reservoir fluids are calculated using the code WATCH. An evaluation of Na-K and K-Mg geothermometers was further made. The results show that K-feldspar and common dioctahedral potassium-rich clay minerals are likely to control the content of potassium in geothermal fluid from shallow reservoirs and dioctahedral magnesium-rich clay minerals can be equilibrated with geothermal fluid as well, whereas the content of sodium in geothermal fluid is little affected by water-rock interactions. Hence, the Na-K ratio of shallow geothermal fluid doesn't match well with reservoir temperature. K-Mg geothermometer is capable of indicating shallow reservoir temperature to some degree, but still not accurate enough.
2017, 42(1): 155-160.
doi: 10.3799/dqkx.2017.012
Abstract:
Studies on the groundwater tidal effect in unconfined aquifer and the method of calculating unconfined aquifer hydrogeological parameters are relatively inefficient. In this study, spectral analysis is used to obtain an analytical formula for tidal level description by firstly observing groundwater table in a well of a coastal unconfined aquifer and tidal level in Gulei peninsula. Then the formula is used as the boundary condition of groundwater flow to deduce the solution of groundwater table in the unconfined aquifer. At last the least square method is used to calculate the hydrogeological parameters in the unconfined aquifer, which provides a reference to similar areas and gives basic information for the study on the groundwater solute transport in this area.
Studies on the groundwater tidal effect in unconfined aquifer and the method of calculating unconfined aquifer hydrogeological parameters are relatively inefficient. In this study, spectral analysis is used to obtain an analytical formula for tidal level description by firstly observing groundwater table in a well of a coastal unconfined aquifer and tidal level in Gulei peninsula. Then the formula is used as the boundary condition of groundwater flow to deduce the solution of groundwater table in the unconfined aquifer. At last the least square method is used to calculate the hydrogeological parameters in the unconfined aquifer, which provides a reference to similar areas and gives basic information for the study on the groundwater solute transport in this area.
