2022 Vol. 47, No. 9
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2022, 47(9): 3073-3106.
doi: 10.3799/dqkx.2022.380
Abstract:
Subduction zone, known as the subduction factory, is the most remarkable characteristics of plate tectonics and is the largest material circulation system on the earth. Subduction behaves as an important engine for driving and maintaining plate movement. A typical subduction zone comprises trench, accretionary wedge, forearc basin, magmatic arc, back-arc basin (or retroarc foreland basin). In some special circumstances, such as ridge subduction, subduction of young oceanic slab and seamount subduction, some special structure such as flat-slab subduction and subduction erosion may occur, resulting in the absence of arc magmatism, accretionary complex or forearc basin. Subducted slab may get through the mantle transition zone into the lower mantle and even reach the core-mantle boundary, and bring the crustal rocks into the deep earth, which ascend to earth's surface in the form of mantle plume. Subduction zone is characterized by active deformation including strike-slip, compression, and extension and structural overprinting. Magmatic arc and accretionary complex may migrate oceanward or landward along with the trench, leading to cyclic compression and extension of the upper plate and the formation of complex paleogeographic patterns. The accretion of microcontinent, arc, seamount and oceanic plateau can chock the subduction zone and lead to subduction zone transference or subduction polarity reversal with the formation of new subduction zone outboard. The detailed deep structure of subduction zone, subduction initiation mechanism, and the interplay between subduction and mantle plume are the research fronts of subduction zone. Conducting geophysical deep exploration of subduction zones, comparative studies of suture zones and active subduction zones, and numerical simulation of subduction zone geodynamics are important ways to solve the above scientific problems.
Subduction zone, known as the subduction factory, is the most remarkable characteristics of plate tectonics and is the largest material circulation system on the earth. Subduction behaves as an important engine for driving and maintaining plate movement. A typical subduction zone comprises trench, accretionary wedge, forearc basin, magmatic arc, back-arc basin (or retroarc foreland basin). In some special circumstances, such as ridge subduction, subduction of young oceanic slab and seamount subduction, some special structure such as flat-slab subduction and subduction erosion may occur, resulting in the absence of arc magmatism, accretionary complex or forearc basin. Subducted slab may get through the mantle transition zone into the lower mantle and even reach the core-mantle boundary, and bring the crustal rocks into the deep earth, which ascend to earth's surface in the form of mantle plume. Subduction zone is characterized by active deformation including strike-slip, compression, and extension and structural overprinting. Magmatic arc and accretionary complex may migrate oceanward or landward along with the trench, leading to cyclic compression and extension of the upper plate and the formation of complex paleogeographic patterns. The accretion of microcontinent, arc, seamount and oceanic plateau can chock the subduction zone and lead to subduction zone transference or subduction polarity reversal with the formation of new subduction zone outboard. The detailed deep structure of subduction zone, subduction initiation mechanism, and the interplay between subduction and mantle plume are the research fronts of subduction zone. Conducting geophysical deep exploration of subduction zones, comparative studies of suture zones and active subduction zones, and numerical simulation of subduction zone geodynamics are important ways to solve the above scientific problems.
2022, 47(9): 3107-3126.
doi: 10.3799/dqkx.2022.321
Abstract:
Ophiolites and their fragments in accretionary wedges record the whole process of orogenesis such as the formation, subduction, and closure of the oceanic lithosphere. Ophiolites or ophiolitic complexes are an important research object for orogenesis. This paper focuses on the inheritance structures of ophiolites, which formed in the original stage of oceanic lithosphere including ocean-continental transition, mid-ocean ridge type (Penrose type of fast spreading ridge and ocean core complex of slow spreading type), and supra-subduction zone (SSZ type). This paper also reviews the structures and features during ophiolite emplacement including obduction and subduction off-scraped types. The characteristics, differences and geological significances between the origin and emplacement stages of ophiolites are highlighted. This paper argues that the superposition of subducting fluids during ophiolite emplacement plays an important role as the ophiolite inevitably experienced the affection of the subducting fluid/melt, making most ophiolites show SSZ-type features. Finally, combined with the characteristics of the main ophiolites in the southern Central Asian Orogenic Belt (CAOB), some thoughts and prospects are put forward for future research, paying attention to the relics of the former OCT and/or OCC in the southern CAOB and the potential oroclinal bending and strike-slip displacement, long-distance low angle over-thrusting, and rotation of blocks for orogenesis anatomy of ophiolites.
Ophiolites and their fragments in accretionary wedges record the whole process of orogenesis such as the formation, subduction, and closure of the oceanic lithosphere. Ophiolites or ophiolitic complexes are an important research object for orogenesis. This paper focuses on the inheritance structures of ophiolites, which formed in the original stage of oceanic lithosphere including ocean-continental transition, mid-ocean ridge type (Penrose type of fast spreading ridge and ocean core complex of slow spreading type), and supra-subduction zone (SSZ type). This paper also reviews the structures and features during ophiolite emplacement including obduction and subduction off-scraped types. The characteristics, differences and geological significances between the origin and emplacement stages of ophiolites are highlighted. This paper argues that the superposition of subducting fluids during ophiolite emplacement plays an important role as the ophiolite inevitably experienced the affection of the subducting fluid/melt, making most ophiolites show SSZ-type features. Finally, combined with the characteristics of the main ophiolites in the southern Central Asian Orogenic Belt (CAOB), some thoughts and prospects are put forward for future research, paying attention to the relics of the former OCT and/or OCC in the southern CAOB and the potential oroclinal bending and strike-slip displacement, long-distance low angle over-thrusting, and rotation of blocks for orogenesis anatomy of ophiolites.
2022, 47(9): 3127-3146.
doi: 10.3799/dqkx.2021.222
Abstract:
The West Tianshan is located in the southwest margin of the Central Asian accretionary orogenic belt. It is sandwiched between Junggar Block and Tarim Craton. Its tectonic evolution is closely related to subduction-closed processes of Tianshan ocean. The geological structure of the West Tianshan is complex and its mineralization is unique. Some ore concentration areas were developed in West Tianshan orogen, such as porphyry gold-copper deposit and volcanic-sedimentary type ferromanganese deposit related to active continental margin, and submarine hydrothermal sedimentary lead-zinc deposit and epithermal hydrothermal gold deposit related to extensional tectonics setting. The tectonic evolution and mineralization of the West Tianshan have always been the focus of geological research. In recent years, significant progress has been made in geological prospecting and basic research. However, there are still some major geological and ore-forming problems to be solved urgently. Based on comprehensive study of the regional geological background, sedimentary formation, magmatic evolution, metallogenic geological characteristics, ore-forming material sources and ore-controlling factors, it is shown that West Tianshan orogen has experienced some geodynamic processes, namely the formation of Precambrian continent, ocean-continent subduction accretion, continent-continent collision orogen. Some main metallogenic belts were formed in the West Tianshan from Precambrian to Late Paleozoic, such as (1) Haldaban Precambrian Pb-Zn metallogenic belt, (2) Borokonu Paleozoic gold⁃copper⁃lead-zinc polymetallic metallogenic belt, (3) Awulale Late Paleozoic iron manganese polymetallic metallogenic belt, (4) Nalati Paleozoic gold-copper polymetallic metallogenic belt. And on that basis, some the ore-forming models of the main metallogenic belts were established, the metallogenic sequences related to sedimentary formation-tectonic-magmatic activity were determined, the spatiotemporal structural models of the regional dominant resources such as iron, copper, lead, zinc and gold were summarized.
The West Tianshan is located in the southwest margin of the Central Asian accretionary orogenic belt. It is sandwiched between Junggar Block and Tarim Craton. Its tectonic evolution is closely related to subduction-closed processes of Tianshan ocean. The geological structure of the West Tianshan is complex and its mineralization is unique. Some ore concentration areas were developed in West Tianshan orogen, such as porphyry gold-copper deposit and volcanic-sedimentary type ferromanganese deposit related to active continental margin, and submarine hydrothermal sedimentary lead-zinc deposit and epithermal hydrothermal gold deposit related to extensional tectonics setting. The tectonic evolution and mineralization of the West Tianshan have always been the focus of geological research. In recent years, significant progress has been made in geological prospecting and basic research. However, there are still some major geological and ore-forming problems to be solved urgently. Based on comprehensive study of the regional geological background, sedimentary formation, magmatic evolution, metallogenic geological characteristics, ore-forming material sources and ore-controlling factors, it is shown that West Tianshan orogen has experienced some geodynamic processes, namely the formation of Precambrian continent, ocean-continent subduction accretion, continent-continent collision orogen. Some main metallogenic belts were formed in the West Tianshan from Precambrian to Late Paleozoic, such as (1) Haldaban Precambrian Pb-Zn metallogenic belt, (2) Borokonu Paleozoic gold⁃copper⁃lead-zinc polymetallic metallogenic belt, (3) Awulale Late Paleozoic iron manganese polymetallic metallogenic belt, (4) Nalati Paleozoic gold-copper polymetallic metallogenic belt. And on that basis, some the ore-forming models of the main metallogenic belts were established, the metallogenic sequences related to sedimentary formation-tectonic-magmatic activity were determined, the spatiotemporal structural models of the regional dominant resources such as iron, copper, lead, zinc and gold were summarized.
2022, 47(9): 3147-3173.
doi: 10.3799/dqkx.2021.118
Abstract:
Volcanogenic massive sulfide (VMS) is one of the most important deposit types in the Central Asian Orogenic Belt (CAOB). In the CAOB in Xinjiang (northern Xinjiang), VMS deposits are mainly distributed in the Ashele, Kelan, Maizi, and Kalatag ore dense districts of the Altay and the East Tianshan. The orebodies occurr in marine volcanic sedimentary rocks from the Lower-Middle Silurian Hongliuxia Formation, the Upper Silurian-Lower Devonian Kangbutiebao Formation, the Lower-Middle Devonian Ashele Formation, and the Lower Carboniferous Xiaorequanzi Formation. Exhalation rocks are developed in these ore districts, such iron-bearing jasper rock, barite, siliceous rock, ferromanganese marble, pyrite layer, and chlorite rock. There are many mineralization types developed in VMS metallogenic system, including the "two-layered structure" (layered/lenticular type and vein type from recharge zone), vein type related to volcanic hydrothermal fluids, and disseminated/vein type associated with sub-volcanic hydrothermal fluids. The VMS deposits in Xinjiang formed in three metallogenic periods: the Early-Middle Silurian (428-438 Ma), the Early-Middle Devonian (379-413 Ma), and Early Carboniferous (332-359 Ma). Sulfur of these deposits is derived from the underlying volcanic rock, inorganic sulfate reduction of seawater, and bacterial sulfate reduction. Ore-forming fluids are characterized by medium-low temperature (300-120 ℃) and low salinity (2%-10% NaCleq), and are deep-circulation seawater mixed with magmatic water in different proportions. The VMS metallogenic system is affected by volcanic structure, lithofacies, mineralization type, ore-forming fluids source, and physical-chemical condition, which results in a complex combination of mineralization elements.
Volcanogenic massive sulfide (VMS) is one of the most important deposit types in the Central Asian Orogenic Belt (CAOB). In the CAOB in Xinjiang (northern Xinjiang), VMS deposits are mainly distributed in the Ashele, Kelan, Maizi, and Kalatag ore dense districts of the Altay and the East Tianshan. The orebodies occurr in marine volcanic sedimentary rocks from the Lower-Middle Silurian Hongliuxia Formation, the Upper Silurian-Lower Devonian Kangbutiebao Formation, the Lower-Middle Devonian Ashele Formation, and the Lower Carboniferous Xiaorequanzi Formation. Exhalation rocks are developed in these ore districts, such iron-bearing jasper rock, barite, siliceous rock, ferromanganese marble, pyrite layer, and chlorite rock. There are many mineralization types developed in VMS metallogenic system, including the "two-layered structure" (layered/lenticular type and vein type from recharge zone), vein type related to volcanic hydrothermal fluids, and disseminated/vein type associated with sub-volcanic hydrothermal fluids. The VMS deposits in Xinjiang formed in three metallogenic periods: the Early-Middle Silurian (428-438 Ma), the Early-Middle Devonian (379-413 Ma), and Early Carboniferous (332-359 Ma). Sulfur of these deposits is derived from the underlying volcanic rock, inorganic sulfate reduction of seawater, and bacterial sulfate reduction. Ore-forming fluids are characterized by medium-low temperature (300-120 ℃) and low salinity (2%-10% NaCleq), and are deep-circulation seawater mixed with magmatic water in different proportions. The VMS metallogenic system is affected by volcanic structure, lithofacies, mineralization type, ore-forming fluids source, and physical-chemical condition, which results in a complex combination of mineralization elements.
2022, 47(9): 3174-3191.
doi: 10.3799/dqkx.2022.100
Abstract:
Uranium mineralization around Kuqa depression is very active. The ore-controlling factors, metallogenic mechanism and metallogenic law, especially the prospective selection, of sandstone⁃type uranium deposits in the lower member of Pliocene Kuqa Formation have become the focus of uranium geologists in recent years. Based on the regional geological data, field geological survey and exploration drilling data, through comprehensive analysis, the author attempts to analyze the key ore-controlling factors and spatial and temporal collocation relationship of the formation and development of sandstone⁃type uranium deposits in the context of basin⁃mountain coupling mechanism (tectonics & sediments & geomorphology), following the general metallogenic mechanism of sandstone⁃type uranium deposits and the research idea from source to sink. From the perspective of uranium metallogenic system analysis, the cooperative ore control mechanism of key ore⁃controlling elements of Kuqa Formation is revealed in order to provide strategic services for uranium exploration. It is found that large-scale intracontinental thrust nappe of the Cenozoic South Tianshan orogenic belt not only controls the filling evolution process of the uranium bearing rock series of the Kuqa Formation, but also restricts the basic pattern and metallogenic process of uranium mineralization in the lower member of the Kuqa Formation. The basin⁃mountain coupling mechanism is the original force driving the formation and development of sandstone⁃type uranium deposits. Although the distribution scale of magmatic rocks in the South Tianshan orogen is limited, U-rich granites exist in the Tomur peak area. The fully developed surface water drainage system, on the one hand, can carry the debris of the orogenic belt to accumulate in the Kuqa depression, thus forming a series of large provenance-sedimentary lobes in stages, creating potential uranium bearing rock series and high-quality uranium reservoir. On the other hand, the drainage system crossing the U-rich granites in the orogenic belt not only provides the accumulation of original trace uranium for the uranium reservoir through physical transportation, but also promotes the development of regional interlayer oxidation zone and dissolved uranium required for mineralization through the derived underground ore-bearing fluid system. In Kuqa depression, the near East-West structure limits the ore-bearing flow field and the development space of interlayer oxidation zone (Baicheng sag). Uranium mineralization is concentrated near the front line of regional interlayer oxidation zone (especially the "water blocking surface" side in the South).At the southern edge of Baicheng sag, with the continuous uplift of Qiulitage structural belt with synsedimentary growth property, the regional ore-bearing flow field and interlayer oxidation zone were forced to migrate northward and caused "left-lateral" movement, thus creating "new" and "old" uranium metallogenic systems including Ridarik uranium deposit.
Uranium mineralization around Kuqa depression is very active. The ore-controlling factors, metallogenic mechanism and metallogenic law, especially the prospective selection, of sandstone⁃type uranium deposits in the lower member of Pliocene Kuqa Formation have become the focus of uranium geologists in recent years. Based on the regional geological data, field geological survey and exploration drilling data, through comprehensive analysis, the author attempts to analyze the key ore-controlling factors and spatial and temporal collocation relationship of the formation and development of sandstone⁃type uranium deposits in the context of basin⁃mountain coupling mechanism (tectonics & sediments & geomorphology), following the general metallogenic mechanism of sandstone⁃type uranium deposits and the research idea from source to sink. From the perspective of uranium metallogenic system analysis, the cooperative ore control mechanism of key ore⁃controlling elements of Kuqa Formation is revealed in order to provide strategic services for uranium exploration. It is found that large-scale intracontinental thrust nappe of the Cenozoic South Tianshan orogenic belt not only controls the filling evolution process of the uranium bearing rock series of the Kuqa Formation, but also restricts the basic pattern and metallogenic process of uranium mineralization in the lower member of the Kuqa Formation. The basin⁃mountain coupling mechanism is the original force driving the formation and development of sandstone⁃type uranium deposits. Although the distribution scale of magmatic rocks in the South Tianshan orogen is limited, U-rich granites exist in the Tomur peak area. The fully developed surface water drainage system, on the one hand, can carry the debris of the orogenic belt to accumulate in the Kuqa depression, thus forming a series of large provenance-sedimentary lobes in stages, creating potential uranium bearing rock series and high-quality uranium reservoir. On the other hand, the drainage system crossing the U-rich granites in the orogenic belt not only provides the accumulation of original trace uranium for the uranium reservoir through physical transportation, but also promotes the development of regional interlayer oxidation zone and dissolved uranium required for mineralization through the derived underground ore-bearing fluid system. In Kuqa depression, the near East-West structure limits the ore-bearing flow field and the development space of interlayer oxidation zone (Baicheng sag). Uranium mineralization is concentrated near the front line of regional interlayer oxidation zone (especially the "water blocking surface" side in the South).At the southern edge of Baicheng sag, with the continuous uplift of Qiulitage structural belt with synsedimentary growth property, the regional ore-bearing flow field and interlayer oxidation zone were forced to migrate northward and caused "left-lateral" movement, thus creating "new" and "old" uranium metallogenic systems including Ridarik uranium deposit.
2022, 47(9): 3192-3209.
doi: 10.3799/dqkx.2022.128
Abstract:
Northern Xinjiang is the second largest Cu-Ni metallogenic area in China as an important part of the Central Asian Orogenic Belt with many mafic-ultramafic intrusions containing Cu-Ni sulfide. Kulabiye Cu-Ni deposit located in Fuyun County, Xinjiang is a new breakthrough in Cu-Ni prospecting in the northern margin of East Junggar after the largest Cu-Ni deposit (Kalatongke) in northern Xinjiang. Although the geological and geophysical characteristics of the deposit have been summarized and the genesis and prospecting criteria of deposit have been put forward in the previous studies, some key problems such as the genesis and tectonic significance of the ore bearing rock mass have not been solved. In this paper, the petrology, geochronology, chemistry and Sr-Nd-Hf isotope of Kulabiye ore bearing rock mass are studied. The ore bearing rock mass of Kulabiye Cu-Ni deposit are mainly gabbro. They show the right dipping pattern of LREE enrichment and HREE loss, enriched in LILE Ba, U and K, and depleted in HFSE Nb, Ta, Ti and Lu. The (87Sr/86Sr)i of gabbro is 0.703 948-0.704 109, εNd(t) is between 5.28 and 5.74, 176Hf/177Hf and εHf(t) varies greatly, ranging from 0.282 851 to 0.283 034 and +8.6-+15.1. The average value of εHf(t) is 12.9. Trace elements and Sr-Nd-Hf isotopes also show the addition of shell source materials in the source area. The formation age of the Kulabiye complex (about 278 Ma) is consistent with the mineralization age of the regional Cu-Ni deposit (about 300-270 Ma). The Kulabiye complex has probably been formed in a post collisional extensional environment, which is related to the upwelling of asthenosphere magma and the partial melting and magma mixing of the metasomatic mantle wedge. The diagenetic and metallogenic age of Kulabiye also reveals that magmatic activities related to Cu-Ni mineralization in the Early Permian occurred widely in the eastern Junggar area, and the northern margin of the eastern Junggar has superior Cu-Ni prospecting potential.
Northern Xinjiang is the second largest Cu-Ni metallogenic area in China as an important part of the Central Asian Orogenic Belt with many mafic-ultramafic intrusions containing Cu-Ni sulfide. Kulabiye Cu-Ni deposit located in Fuyun County, Xinjiang is a new breakthrough in Cu-Ni prospecting in the northern margin of East Junggar after the largest Cu-Ni deposit (Kalatongke) in northern Xinjiang. Although the geological and geophysical characteristics of the deposit have been summarized and the genesis and prospecting criteria of deposit have been put forward in the previous studies, some key problems such as the genesis and tectonic significance of the ore bearing rock mass have not been solved. In this paper, the petrology, geochronology, chemistry and Sr-Nd-Hf isotope of Kulabiye ore bearing rock mass are studied. The ore bearing rock mass of Kulabiye Cu-Ni deposit are mainly gabbro. They show the right dipping pattern of LREE enrichment and HREE loss, enriched in LILE Ba, U and K, and depleted in HFSE Nb, Ta, Ti and Lu. The (87Sr/86Sr)i of gabbro is 0.703 948-0.704 109, εNd(t) is between 5.28 and 5.74, 176Hf/177Hf and εHf(t) varies greatly, ranging from 0.282 851 to 0.283 034 and +8.6-+15.1. The average value of εHf(t) is 12.9. Trace elements and Sr-Nd-Hf isotopes also show the addition of shell source materials in the source area. The formation age of the Kulabiye complex (about 278 Ma) is consistent with the mineralization age of the regional Cu-Ni deposit (about 300-270 Ma). The Kulabiye complex has probably been formed in a post collisional extensional environment, which is related to the upwelling of asthenosphere magma and the partial melting and magma mixing of the metasomatic mantle wedge. The diagenetic and metallogenic age of Kulabiye also reveals that magmatic activities related to Cu-Ni mineralization in the Early Permian occurred widely in the eastern Junggar area, and the northern margin of the eastern Junggar has superior Cu-Ni prospecting potential.
2022, 47(9): 3210-3228.
doi: 10.3799/dqkx.2021.213
Abstract:
Pingtaishan intrusion located in the Kalatag area of eastern Tianshan, is a compound massif composed of gabbro, diabase, hornblende gabbro and quartz diorite, and is an ideal object to understand the tectonic evolution of the eastern Tianshan during the Late Paleozoic. LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements are performed to unravel their petrogenesis. The gabbro, diabase and hornblende gabbro exhibit low SiO2 (44.17%-50.14%) and high Fe2O3T (7.63%-12.75%), and variable alkali content (K2O+Na2O=1.79%-6.36%), MgO content (2.79% to 16.80%) and Mg# (41-73). In addition, these rocks are enriched in Rb, Ba, Sr, U, and Pb and depleted in Nb, Ta, Zr, Hf, and Ti, which is consistent with the characteristics of island arc magmatism. The quartz diorites exhibit high SiO2 (61.15%-64.62%) and total alkali (K2O+Na2O=8.50%-9.34%) content, enriched in LILEs (Rb and Ba) and HFSEs (Zr, Hf and Y), high (Ga/Al)×104 ratios (3.55 to 3.68) and Y/Nb ratios (14.31 to 16.28), depleted in Eu, Sr and Ti. Quartz diorites features exhibit an affinity with A2-type granites. On the one hand, these gabbro, diabase, and hornblende gabbro belong to the Alaskan-type mafic complexes, and their parental magma is derived from a mixture of depleted mantle and metasomatized lithospheric mantle. On the other hand, the parental magma of quartz diorite originates from the mixing of the depleted mantle and the lower crust. Collectively, we suggest that the Pingtaishan compound massif results from the oblique subduction of the Kangguer Ocean ridge, implying that the Kangguer Ocean was not yet closed in the Early Permian.
Pingtaishan intrusion located in the Kalatag area of eastern Tianshan, is a compound massif composed of gabbro, diabase, hornblende gabbro and quartz diorite, and is an ideal object to understand the tectonic evolution of the eastern Tianshan during the Late Paleozoic. LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements are performed to unravel their petrogenesis. The gabbro, diabase and hornblende gabbro exhibit low SiO2 (44.17%-50.14%) and high Fe2O3T (7.63%-12.75%), and variable alkali content (K2O+Na2O=1.79%-6.36%), MgO content (2.79% to 16.80%) and Mg# (41-73). In addition, these rocks are enriched in Rb, Ba, Sr, U, and Pb and depleted in Nb, Ta, Zr, Hf, and Ti, which is consistent with the characteristics of island arc magmatism. The quartz diorites exhibit high SiO2 (61.15%-64.62%) and total alkali (K2O+Na2O=8.50%-9.34%) content, enriched in LILEs (Rb and Ba) and HFSEs (Zr, Hf and Y), high (Ga/Al)×104 ratios (3.55 to 3.68) and Y/Nb ratios (14.31 to 16.28), depleted in Eu, Sr and Ti. Quartz diorites features exhibit an affinity with A2-type granites. On the one hand, these gabbro, diabase, and hornblende gabbro belong to the Alaskan-type mafic complexes, and their parental magma is derived from a mixture of depleted mantle and metasomatized lithospheric mantle. On the other hand, the parental magma of quartz diorite originates from the mixing of the depleted mantle and the lower crust. Collectively, we suggest that the Pingtaishan compound massif results from the oblique subduction of the Kangguer Ocean ridge, implying that the Kangguer Ocean was not yet closed in the Early Permian.
2022, 47(9): 3229-3243.
doi: 10.3799/dqkx.2022.121
Abstract:
The Aqishan-Yamansu tectonic belt is an important part of the eastern Tianshan Orogenic Belt, while the tectonic setting and evolution of this region have long been a matter of debate. The Xiaodongshan volcanic rocks located in the west of the Aqishan-Yamansu belt, consist of mafic-intermediate-felsic volcanic association, which present an appropriate "rock probe" to further understand the Aqishan-Yamansu belt. Geochronology, element geochemistry and Sr-Nd-Hf isotope studies on the Xiaodongshan volcanic rocks have been carried out in this paper. It is found that the Xiaodongshan volcanic rocks comprise dacite porphyry, granite porphyry, andesite, basalt and olivine basalt. The correlativity of major elements indicates that this volcanic association was resulted from the comagmatic evolution. LA-ICP-MS U-Pb dating on zircons of the volcanic rocks obtained the ages of 318-308 Ma, indicating the formation of Late Carboniferous. The SiO2 contents range from 48.10% to 76.82%, whereas the Al2O3 contents are relatively low and only have a little variation. From the mafic to felsic rocks, the abundances of rare earth elements (REE) gradually increase, and the Eu/Eu* values gradually decrease. The large ion lithophile elements (LILEs) of Rb, K, Pb, Sr are relatively enriched, whereas the high field strength elements (HFSEs) of Nb, Ta, Ti, P, Th are depleted for the intermediate-acid volcanic rocks. The mafic volcanic rocks mainly show negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of K, Pb and P. All volcanic rocks are characterized by low (87Sr/86Sr)i (0.704 50-0.707 14), high εNd(t) (+3.16-+5.71) and εHf (+5.45-+12.18). The above evidence indicates that the Xiaodongshan volcanic rocks originated from partial melting of metasomatic mantle wedge and fractional crystallization. Based on our new data and previous studies on the regional tectonic-magmatic evolution, we propose that the Aqishan-Yamansu tectonic belt is an island arc formed during the southward subduction of the ancient Tianshan Ocean in the Late Carboniferous.
The Aqishan-Yamansu tectonic belt is an important part of the eastern Tianshan Orogenic Belt, while the tectonic setting and evolution of this region have long been a matter of debate. The Xiaodongshan volcanic rocks located in the west of the Aqishan-Yamansu belt, consist of mafic-intermediate-felsic volcanic association, which present an appropriate "rock probe" to further understand the Aqishan-Yamansu belt. Geochronology, element geochemistry and Sr-Nd-Hf isotope studies on the Xiaodongshan volcanic rocks have been carried out in this paper. It is found that the Xiaodongshan volcanic rocks comprise dacite porphyry, granite porphyry, andesite, basalt and olivine basalt. The correlativity of major elements indicates that this volcanic association was resulted from the comagmatic evolution. LA-ICP-MS U-Pb dating on zircons of the volcanic rocks obtained the ages of 318-308 Ma, indicating the formation of Late Carboniferous. The SiO2 contents range from 48.10% to 76.82%, whereas the Al2O3 contents are relatively low and only have a little variation. From the mafic to felsic rocks, the abundances of rare earth elements (REE) gradually increase, and the Eu/Eu* values gradually decrease. The large ion lithophile elements (LILEs) of Rb, K, Pb, Sr are relatively enriched, whereas the high field strength elements (HFSEs) of Nb, Ta, Ti, P, Th are depleted for the intermediate-acid volcanic rocks. The mafic volcanic rocks mainly show negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of K, Pb and P. All volcanic rocks are characterized by low (87Sr/86Sr)i (0.704 50-0.707 14), high εNd(t) (+3.16-+5.71) and εHf (+5.45-+12.18). The above evidence indicates that the Xiaodongshan volcanic rocks originated from partial melting of metasomatic mantle wedge and fractional crystallization. Based on our new data and previous studies on the regional tectonic-magmatic evolution, we propose that the Aqishan-Yamansu tectonic belt is an island arc formed during the southward subduction of the ancient Tianshan Ocean in the Late Carboniferous.
2022, 47(9): 3244-3257.
doi: 10.3799/dqkx.2022.136
Abstract:
The Huangshandong and Huangshanxi mafic-ultramafic intrusions in East Tianshan are products of regional large scale Early Permian mantle-derived magmatism, and host two large scale Ni-Cu sulfide deposits. Major ore reserves of the Huangshandong and Huangshanxi deposits are hosted in the ultramafic rocks. Therefore, petrogenesis of their ore-bearing ultramafic rocks plays key role in understanding the matallogenesis of the regional Ni-Cu sulfide deposits. This study uses back scattered electron (BSE) images to observe the ore-bearing ultramafic rocks from Huangshandong and Huangshanxi deposits, and find out that plagioclase phenocrysts show significant disequilibrium. EMPA was used to analyze the chemical compositions and chemical profiles of the plagioclase phenocrysts. The An value of plagioclase from Huangshandong and Huangshanxi ore-bearing ultramafic rocks varies from 48.6 to 75.6 and 44.9 to 79.2, respectively, suggesting that the parental magma of the ore-bearing ultramafic rocks had experienced significant composition change during emplacement. Combined with geology of these two deposits, it is proposed that addition of high differentiated mafic magma into low differentiated ultramafic magma significantly changed parental magma composition, leading to sulfide segregation and formation of the Huangshandong and Huangshanxi large scale Ni-Cu sulfide deposits.
The Huangshandong and Huangshanxi mafic-ultramafic intrusions in East Tianshan are products of regional large scale Early Permian mantle-derived magmatism, and host two large scale Ni-Cu sulfide deposits. Major ore reserves of the Huangshandong and Huangshanxi deposits are hosted in the ultramafic rocks. Therefore, petrogenesis of their ore-bearing ultramafic rocks plays key role in understanding the matallogenesis of the regional Ni-Cu sulfide deposits. This study uses back scattered electron (BSE) images to observe the ore-bearing ultramafic rocks from Huangshandong and Huangshanxi deposits, and find out that plagioclase phenocrysts show significant disequilibrium. EMPA was used to analyze the chemical compositions and chemical profiles of the plagioclase phenocrysts. The An value of plagioclase from Huangshandong and Huangshanxi ore-bearing ultramafic rocks varies from 48.6 to 75.6 and 44.9 to 79.2, respectively, suggesting that the parental magma of the ore-bearing ultramafic rocks had experienced significant composition change during emplacement. Combined with geology of these two deposits, it is proposed that addition of high differentiated mafic magma into low differentiated ultramafic magma significantly changed parental magma composition, leading to sulfide segregation and formation of the Huangshandong and Huangshanxi large scale Ni-Cu sulfide deposits.
2022, 47(9): 3258-3269.
doi: 10.3799/dqkx.2021.203
Abstract:
A suite of high-magnesium gabbro is located in the Qinghegou-Hongliuxia area in the southern part of the Baiheshan ophillite mélange belt in the northern Beishan orogenic belt. Based on LA-ICP-MS zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic analyses, the gabbro was intruded at 278.2±1.3 Ma and they show high magnesium geochemical characteristic, belonging to low-tholeiite to calc-alkaline series. They are enriched in large-ion lithophile elements of Rb, Ba, Sr and depleted in high field strength elements of Nb, Ta, Ti. The values of εNd(t) of the gabbro vary from 5.64 to 6.77, with high Sm/Yb, implying magma originates from depleted mantle. Relatively high Mg#, Cr, Ni and negative Zr and Hf indicate that the primary magma has undergone limited fractional crystallization and crustal contamination. Combined with regional geological material, it is suggested that the end of the accretionary orogeny is Early to Middle Permian in the northern Beishan orogenic belt. The Paleo-Asian Ocean in the Beishan orogenic belt may have been lasted until or after Middle Permian.
A suite of high-magnesium gabbro is located in the Qinghegou-Hongliuxia area in the southern part of the Baiheshan ophillite mélange belt in the northern Beishan orogenic belt. Based on LA-ICP-MS zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic analyses, the gabbro was intruded at 278.2±1.3 Ma and they show high magnesium geochemical characteristic, belonging to low-tholeiite to calc-alkaline series. They are enriched in large-ion lithophile elements of Rb, Ba, Sr and depleted in high field strength elements of Nb, Ta, Ti. The values of εNd(t) of the gabbro vary from 5.64 to 6.77, with high Sm/Yb, implying magma originates from depleted mantle. Relatively high Mg#, Cr, Ni and negative Zr and Hf indicate that the primary magma has undergone limited fractional crystallization and crustal contamination. Combined with regional geological material, it is suggested that the end of the accretionary orogeny is Early to Middle Permian in the northern Beishan orogenic belt. The Paleo-Asian Ocean in the Beishan orogenic belt may have been lasted until or after Middle Permian.
2022, 47(9): 3270-3284.
doi: 10.3799/dqkx.2021.191
Abstract:
The Beishan orogen occupies the southernmost part of the Central Asian Orogenic Belt (CAOB) and it is an important part of the CAOB. In this paper, we presents petrographical, zircon U-Pb, Hf isotopic, and trace element and whole rock geochemical studies on a late Paleozoic granite-diorite association from the Shibandun-Baidunzi area of the southern Beishan, in order to better constrain the late Paleozoic tectono-magmatic evolution of the Beishan orogen. LA-ICP-MS zircon U-Pb dating yields crystallization ages of ~304-302 Ma for the Shibandun granite, ~291 Ma for the Shibandun diorite, and ~270 Ma for the Baidunzi diorite. These rocks are characterized by variable radiogenic zircon Hf isotopic compositions with εHf(t) values of -2.0-+15.7. Furthermore, they show a more depleted trend with decreasing ages. The petrographical and geochemical features indicate that the Late Paleozoic magmatisms in the southern Beishan was dominated by depleted mantle-derived magmas, and the complex Late Paleozoic rock assemblages of southern Beishan were likely produced by mixing of different proportions of juvenile mantle-derived magma with the ancient crust-derived magma. We further suggest that the Late Carboniferous-Early Permian granite-diorite were formed in a back-arc extension setting related to the retreating accretionary orogeny.
The Beishan orogen occupies the southernmost part of the Central Asian Orogenic Belt (CAOB) and it is an important part of the CAOB. In this paper, we presents petrographical, zircon U-Pb, Hf isotopic, and trace element and whole rock geochemical studies on a late Paleozoic granite-diorite association from the Shibandun-Baidunzi area of the southern Beishan, in order to better constrain the late Paleozoic tectono-magmatic evolution of the Beishan orogen. LA-ICP-MS zircon U-Pb dating yields crystallization ages of ~304-302 Ma for the Shibandun granite, ~291 Ma for the Shibandun diorite, and ~270 Ma for the Baidunzi diorite. These rocks are characterized by variable radiogenic zircon Hf isotopic compositions with εHf(t) values of -2.0-+15.7. Furthermore, they show a more depleted trend with decreasing ages. The petrographical and geochemical features indicate that the Late Paleozoic magmatisms in the southern Beishan was dominated by depleted mantle-derived magmas, and the complex Late Paleozoic rock assemblages of southern Beishan were likely produced by mixing of different proportions of juvenile mantle-derived magma with the ancient crust-derived magma. We further suggest that the Late Carboniferous-Early Permian granite-diorite were formed in a back-arc extension setting related to the retreating accretionary orogeny.
2022, 47(9): 3285-3300.
doi: 10.3799/dqkx.2021.155
Abstract:
To reveal the tectonic dynamic setting and timing of the ocean-continent transform in the southern Central Asian Orogenic Belt (CAOB), the geochronological data, major and trace elements and Sr-Nd-Pb isotopes of Late Paleozoic Huanuishan diorite porphyrites in the Beishan area of southern CAOB are studied. The diorite porphyrites yield a magmatic crystallization of 287.6±7.5 Ma (LA-ICP-MS zircon U-Pb dating). The SiO2, K2O+Na2O contents are 53.92%-54.84%, 6.34%-6.82% respectively. The rocks have high Al2O3 (14.66%-15.23%), low MgO (3.20%-3.99%) with Mg# values of 40.26-46.50. The diorite porphyrites have high LREE enrichment ((La/Yb)N=20.07-21.33) with negative Eu anomalies (δEu=0.79-0.82), enriched in Cs, Rb, Ba, K, Th and Pb, weakly enriched in Zr and Hf, depleted in Nb, Ta, Ti, P and Sr. Their (87Sr/86Sr)i values range from 0.707 009 to 0.708 799, (143Nd/144Nd)i values 0.512 248 to 0.512 272, 206Pb/204Pb values 18.613 to 18.711 and εNd(t) values are -0.39-+0.09. These features suggest that diorite porphyrites were derived from the mantle material, with assimilation and contamination by curst. Combined with regional geological background, the diorite porphyrites were formed in an intraplate extensional tectonic stage after the northward subduction and closure of Huitongshan-Zhangfangshan Ocean. These results indicate that the southern Beishan area has completed the ocean-continent tectonic transform during the Early Permian.
To reveal the tectonic dynamic setting and timing of the ocean-continent transform in the southern Central Asian Orogenic Belt (CAOB), the geochronological data, major and trace elements and Sr-Nd-Pb isotopes of Late Paleozoic Huanuishan diorite porphyrites in the Beishan area of southern CAOB are studied. The diorite porphyrites yield a magmatic crystallization of 287.6±7.5 Ma (LA-ICP-MS zircon U-Pb dating). The SiO2, K2O+Na2O contents are 53.92%-54.84%, 6.34%-6.82% respectively. The rocks have high Al2O3 (14.66%-15.23%), low MgO (3.20%-3.99%) with Mg# values of 40.26-46.50. The diorite porphyrites have high LREE enrichment ((La/Yb)N=20.07-21.33) with negative Eu anomalies (δEu=0.79-0.82), enriched in Cs, Rb, Ba, K, Th and Pb, weakly enriched in Zr and Hf, depleted in Nb, Ta, Ti, P and Sr. Their (87Sr/86Sr)i values range from 0.707 009 to 0.708 799, (143Nd/144Nd)i values 0.512 248 to 0.512 272, 206Pb/204Pb values 18.613 to 18.711 and εNd(t) values are -0.39-+0.09. These features suggest that diorite porphyrites were derived from the mantle material, with assimilation and contamination by curst. Combined with regional geological background, the diorite porphyrites were formed in an intraplate extensional tectonic stage after the northward subduction and closure of Huitongshan-Zhangfangshan Ocean. These results indicate that the southern Beishan area has completed the ocean-continent tectonic transform during the Early Permian.
2022, 47(9): 3301-3315.
doi: 10.3799/dqkx.2021.199
Abstract:
The Triassic granites in the southeastern margin of the Central Asian Orogenic Belt are of diverse types and complex genesis. In order to study their provenance and formation setting, we selected monzogranite, gneissic porphyritic granite and diorite porphyrite in the different locations of the Jiefangyingzi pluton, and performed the whole-rock elemental and Sr-Nd-Li isotope analyses, and zircon geochronology. Zircon U-Pb geochronology results show that the different rock types of the Jiefangyingzi pluton were similarly formed in the Late Triassic (234-226 Ma). Geochemical characteristics show that all of them are I-type granites undergoing different degrees of fractionation crystallization. Slightly negative to positive ɛNd(t) values (-3.9-+1.5) indicate that they derived from juvenile materials with the addition of ancient crustal materials to varying degrees. The whole-rock Li isotopic characteristics of pluton in this region are reported for the first time. The range of δ7Li value is +1.1- +6.6‰ with an average value of +3.37‰, similar to the average value of upper mantle, indicating that there is a significant contribution of mantle-derived components. Combined with regional geology, the Jiefangyingzi pluton was formed in the post-orogenic extension stage after the closure of the Paleo-Asian Ocean. Decompression melting induced the partial melting of the juvenile mantle-derived components without obvious water-rock interaction related to the early subduction process.
The Triassic granites in the southeastern margin of the Central Asian Orogenic Belt are of diverse types and complex genesis. In order to study their provenance and formation setting, we selected monzogranite, gneissic porphyritic granite and diorite porphyrite in the different locations of the Jiefangyingzi pluton, and performed the whole-rock elemental and Sr-Nd-Li isotope analyses, and zircon geochronology. Zircon U-Pb geochronology results show that the different rock types of the Jiefangyingzi pluton were similarly formed in the Late Triassic (234-226 Ma). Geochemical characteristics show that all of them are I-type granites undergoing different degrees of fractionation crystallization. Slightly negative to positive ɛNd(t) values (-3.9-+1.5) indicate that they derived from juvenile materials with the addition of ancient crustal materials to varying degrees. The whole-rock Li isotopic characteristics of pluton in this region are reported for the first time. The range of δ7Li value is +1.1- +6.6‰ with an average value of +3.37‰, similar to the average value of upper mantle, indicating that there is a significant contribution of mantle-derived components. Combined with regional geology, the Jiefangyingzi pluton was formed in the post-orogenic extension stage after the closure of the Paleo-Asian Ocean. Decompression melting induced the partial melting of the juvenile mantle-derived components without obvious water-rock interaction related to the early subduction process.
2022, 47(9): 3316-3333.
doi: 10.3799/dqkx.2022.065
Abstract:
The Hanjiayuanzi-Fulin area in the eastern Erguna Massif, located adjacent to the Mongol-Okhotsk suture zone, is characterized by numerous Early Jurassic to Early Cretaceous igneous rocks, which is important to reconstruct the subduction and closure history of the Mongol-Okhotsk Ocean. In this study, we present new petrology, LA-ICP-MS zircon U-Pb ages and whole-rock geochemical data for the Mesozoic igneous rocks from the Hanjiayuanzi-Fulin area. Zircon U-Pb ages of Hanjiayuanzi K-feldspar granite and Fulin trachyandesite are 196±2 Ma and 122±2 Ma, corresponding to the Early Jurassic and Early Cretaceous, respectively. The K-feldspar granite belongs to metaluminous Ⅰ-type granite, with low Mg# value (36) and Nb/Ta ratios (16.55-17.05) close to the primitive mantle, which could be derived from partial melting of the juvenile lower crust. It is enriched in large ion lithophile elements (LILEs, e.g., Rb, Ba, K), and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, Ti), showing the geochemical characteristics of typical arc igneous rocks. Combined with the spatial distribution of contemporary metaluminous-weakly peraluminous Ⅰ-type granites, we propose that the Early Jurassic Hanjiayuanzi K-feldspar granite may be related to the southward subduction of the Mongol-Okhotsk Ocean beneath the Erguna massif. By contrast, the trachyandesite has lower SiO2 contents (59.67%-59.93%), higher Mg# values (42-43), and is also enriched in LILEs and depleted in HFSEs. Besides, it has an enrichment of Sr and depletion of Th, suggesting an origin from the enriched lithospheric mantle. Based on the regional distribution of Early Cretaceous calc-alkaline volcanic rocks, A-type granites and metamorphic core complexes, we suggest that the Early Cretaceous trachyandesite was formed in an extensional environment after the closure of the Mongol-Okhotsk Ocean. Combined with published data from igneous and sedimentary rocks, the closure time of the Mongol-Okhotsk Ocean in the northern Great Xing'an Range is suggested to be between latest Late Jurassic and earliest Early Cretaceous (~150-140 Ma).
The Hanjiayuanzi-Fulin area in the eastern Erguna Massif, located adjacent to the Mongol-Okhotsk suture zone, is characterized by numerous Early Jurassic to Early Cretaceous igneous rocks, which is important to reconstruct the subduction and closure history of the Mongol-Okhotsk Ocean. In this study, we present new petrology, LA-ICP-MS zircon U-Pb ages and whole-rock geochemical data for the Mesozoic igneous rocks from the Hanjiayuanzi-Fulin area. Zircon U-Pb ages of Hanjiayuanzi K-feldspar granite and Fulin trachyandesite are 196±2 Ma and 122±2 Ma, corresponding to the Early Jurassic and Early Cretaceous, respectively. The K-feldspar granite belongs to metaluminous Ⅰ-type granite, with low Mg# value (36) and Nb/Ta ratios (16.55-17.05) close to the primitive mantle, which could be derived from partial melting of the juvenile lower crust. It is enriched in large ion lithophile elements (LILEs, e.g., Rb, Ba, K), and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, Ti), showing the geochemical characteristics of typical arc igneous rocks. Combined with the spatial distribution of contemporary metaluminous-weakly peraluminous Ⅰ-type granites, we propose that the Early Jurassic Hanjiayuanzi K-feldspar granite may be related to the southward subduction of the Mongol-Okhotsk Ocean beneath the Erguna massif. By contrast, the trachyandesite has lower SiO2 contents (59.67%-59.93%), higher Mg# values (42-43), and is also enriched in LILEs and depleted in HFSEs. Besides, it has an enrichment of Sr and depletion of Th, suggesting an origin from the enriched lithospheric mantle. Based on the regional distribution of Early Cretaceous calc-alkaline volcanic rocks, A-type granites and metamorphic core complexes, we suggest that the Early Cretaceous trachyandesite was formed in an extensional environment after the closure of the Mongol-Okhotsk Ocean. Combined with published data from igneous and sedimentary rocks, the closure time of the Mongol-Okhotsk Ocean in the northern Great Xing'an Range is suggested to be between latest Late Jurassic and earliest Early Cretaceous (~150-140 Ma).
2022, 47(9): 3334-3353.
doi: 10.3799/dqkx.2021.159
Abstract:
The Mohe basin is located in the southern margin of the eastern Mongol-Okhotsk suture zone (MOSB), which is an excellent window for studying the evolution of the eastern Mongol-Okhotsk Ocean. In this paper, four sandstone samples from the Xiufeng Formation in the eastern margin of the Mohe basin were analyzed by petrography, chronology and geochemistry. The results show that the sandstone debris of the Xiufeng Formation has poor roundness and sorting, and shows the characteristics of near-source denudation. A total of 217 concordant ages were obtained from U-Pb zircon dating, divided into three age groups, and the peak ages of all concordant ages correspond identically to the regional magmatic activities on the Erguna Block. LA‐ICP‐MS U-Pb zircon dating yields the youngest concordant ages of 158±2 Ma (N=5) for the Xiufeng Formation. Based on the previous research results, we try to limit the evolution of the Mongol-Okhotsk Ocean and even the eastern part of the Central Asian Orogenic Belt. All samples are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), and have obvious negative Eu anomalies. The lithology of the source rocks is mainly felsic from the upper crust and is situated in active continental margins. The continental island arc provides the sediments in the Xiufeng Formation in the south of the Mohe basin, the Erguna block and the old basement of the basin. The provenance is located in the tectonic environment of the continental island arc, which is related to the southward subduction, collision and closure of the Mongol-Okhotsk Ocean in the Late Jurassic. Based on all the evidence above, we can infer that the Mongol-Okhotsk Ocean was still in the subduction stage and did not close during the sedimentation of the Xiufeng Formation (ca. 158 Ma). Combined with previous data, it is inferred that the final closure of the Mongol-Okhotsk Ocean may be limited between the Late Jurassic and Early Cretaceous.
The Mohe basin is located in the southern margin of the eastern Mongol-Okhotsk suture zone (MOSB), which is an excellent window for studying the evolution of the eastern Mongol-Okhotsk Ocean. In this paper, four sandstone samples from the Xiufeng Formation in the eastern margin of the Mohe basin were analyzed by petrography, chronology and geochemistry. The results show that the sandstone debris of the Xiufeng Formation has poor roundness and sorting, and shows the characteristics of near-source denudation. A total of 217 concordant ages were obtained from U-Pb zircon dating, divided into three age groups, and the peak ages of all concordant ages correspond identically to the regional magmatic activities on the Erguna Block. LA‐ICP‐MS U-Pb zircon dating yields the youngest concordant ages of 158±2 Ma (N=5) for the Xiufeng Formation. Based on the previous research results, we try to limit the evolution of the Mongol-Okhotsk Ocean and even the eastern part of the Central Asian Orogenic Belt. All samples are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), and have obvious negative Eu anomalies. The lithology of the source rocks is mainly felsic from the upper crust and is situated in active continental margins. The continental island arc provides the sediments in the Xiufeng Formation in the south of the Mohe basin, the Erguna block and the old basement of the basin. The provenance is located in the tectonic environment of the continental island arc, which is related to the southward subduction, collision and closure of the Mongol-Okhotsk Ocean in the Late Jurassic. Based on all the evidence above, we can infer that the Mongol-Okhotsk Ocean was still in the subduction stage and did not close during the sedimentation of the Xiufeng Formation (ca. 158 Ma). Combined with previous data, it is inferred that the final closure of the Mongol-Okhotsk Ocean may be limited between the Late Jurassic and Early Cretaceous.
2022, 47(9): 3354-3370.
doi: 10.3799/dqkx.2021.189
Abstract:
The southern of Zhalantun in the Great Xing'an Range is located between the Xing'an Block (XB) and Songnen Block (SB) in the eastern section of the Central Asian Orogenic Belt (CAOB), which is of great importance for the study on the collision and combination of blocks during the tectonic evolution process. The exposed granitic mylonites were analyzed by geological and geochemical analysis, and zircon U-Pb dating in this paper. LA-ICP-MS zircon U-Pb dating results show that the granitic mylonites are divided into two phases: Phase Ⅰ is the Early Devonian (-398.8 Ma), and Phase Ⅱ is the end of the Late Devonian to the beginning of the Early Carboniferous (351.6-365.7 Ma). The rocks of the two periods are characterized by high SiO2 (68.20%-77.90%), high alkali (K2O+Na2O=6.32%-9.67%) and low magnesium (MgO=0.22%-0.97%), belonging to the aluminous and high potassium calc-alkaline series. The REE distribution pattern is right-leaning [(La/Yb)N=4.33-10.77], with a slight negative Eu anomaly (δEu=0.03-0.13). All samples were enriched in LILE and depleted in HFSE, which have the characteristics of differentiating Ⅰ-type granites. The two phases of granitic mylonites may be Ⅰ-type-differentiated Ⅰ-type granites formed by island arc magmatism under the background of subduction. Combining regional tectonic evolution and petrochemical research, the early Late Paleozoic granitic magmatism in the northern section of the Great Xing'an Range is related to the collision and combination of the XB and SB. During the Early Devonian-Early Carboniferous, the Zhalantun area was under the subduction environment of the Paleo-Asian Ocean-oriented XB and SB, the collision and closure time of the two blocks here may be the Late Carboniferous.
The southern of Zhalantun in the Great Xing'an Range is located between the Xing'an Block (XB) and Songnen Block (SB) in the eastern section of the Central Asian Orogenic Belt (CAOB), which is of great importance for the study on the collision and combination of blocks during the tectonic evolution process. The exposed granitic mylonites were analyzed by geological and geochemical analysis, and zircon U-Pb dating in this paper. LA-ICP-MS zircon U-Pb dating results show that the granitic mylonites are divided into two phases: Phase Ⅰ is the Early Devonian (-398.8 Ma), and Phase Ⅱ is the end of the Late Devonian to the beginning of the Early Carboniferous (351.6-365.7 Ma). The rocks of the two periods are characterized by high SiO2 (68.20%-77.90%), high alkali (K2O+Na2O=6.32%-9.67%) and low magnesium (MgO=0.22%-0.97%), belonging to the aluminous and high potassium calc-alkaline series. The REE distribution pattern is right-leaning [(La/Yb)N=4.33-10.77], with a slight negative Eu anomaly (δEu=0.03-0.13). All samples were enriched in LILE and depleted in HFSE, which have the characteristics of differentiating Ⅰ-type granites. The two phases of granitic mylonites may be Ⅰ-type-differentiated Ⅰ-type granites formed by island arc magmatism under the background of subduction. Combining regional tectonic evolution and petrochemical research, the early Late Paleozoic granitic magmatism in the northern section of the Great Xing'an Range is related to the collision and combination of the XB and SB. During the Early Devonian-Early Carboniferous, the Zhalantun area was under the subduction environment of the Paleo-Asian Ocean-oriented XB and SB, the collision and closure time of the two blocks here may be the Late Carboniferous.
2022, 47(9): 3371-3388.
doi: 10.3799/dqkx.2021.235
Abstract:
Recently, many tin polymetallic deposits related to Cretaceous granite have been discovered in the southern part of the Great Xing'an Range. However, not all granites of this period are associated with tin deposits. To obtain a better understanding of the formation conditions of granite associated tin deposits, (Method) in this paper, the cassiterite U-Pb age, zircon U-Pb age, whole rock geochemistry and mineral chemistry analysis of the cassiterite-bearing granites (the Mopanshan area) and barren granites (the Kulongshan area) in the Beidashan pluton were carried out. The geochronology, geochemistry and physical-chemical conditions of magma evolution were compared. The U-Pb weighted average zircon ages of the Kulongshan porphyritic quartz syenite and the Mopanshan biotite granite are 140.2±0.7 Ma and 139.9±0.7 Ma, respectively, and the cassiterite U-Pb weighted average age of the Mopanshan area is 134.9±1.4 Ma. All of them are Early Cretaceous in age. The whole rock geochemical analysis results show that these rocks are rich in silicon (SiO2=64.96%-76.71%), alkali (Na2O+ K2O=8.28%-9.03%), and aluminum (Al2O3=12.42%-15.88%). For trace elements, they are relatively enriched in elements such as Th, Pb, and Hf, and deficient in elements such as Nb, Ta, Ti, Sr, and P. For rare earth elements, they show significant enriched HREEs than LREEs, and Eu negative anomaly is unusually obvious. As the content of SiO2 increases, the content of TiO2, FeOT, Al2O3, CaO, Na2O, and P2O5 gradually decreases, showing a good negative correlation, suggesting a homogeneous magmatic source. However, the DI value of the Kulongshan sample is 89 and the Sn content is 2×10-6; the Mopanshan samples have a higher DI value (96-98) and higher Sn content (15×10-6~36×10-6). Based on the physical- chemical conditions inverted from mineralogy, the Kulongshan granite has experienced a process of oxygen fugacity increase during cooling, while the oxygen fugacity of the Mopanshan granite has further decreased during the cooling process. In addition, in terms of fluid halogen content, the Ⅳ (F) and Ⅳ (Cl) of biotite indicate the Mopanshan granite (Ⅳ(F)=0.95-1.15; Ⅳ(Cl)=-3.66--3.54) compared to the Kulongshan porphyritic quartz syenite (Ⅳ(F)=1.24-1.28; Ⅳ(Cl)=-2.96--2.52) has a higher concentration of Cl and F. In summary, low oxygen fugacity, high degree of evolution, and high F and Cl abundance, are the main factors affecting enrichment of cassiterite in granite in the Beidashan area.
Recently, many tin polymetallic deposits related to Cretaceous granite have been discovered in the southern part of the Great Xing'an Range. However, not all granites of this period are associated with tin deposits. To obtain a better understanding of the formation conditions of granite associated tin deposits, (Method) in this paper, the cassiterite U-Pb age, zircon U-Pb age, whole rock geochemistry and mineral chemistry analysis of the cassiterite-bearing granites (the Mopanshan area) and barren granites (the Kulongshan area) in the Beidashan pluton were carried out. The geochronology, geochemistry and physical-chemical conditions of magma evolution were compared. The U-Pb weighted average zircon ages of the Kulongshan porphyritic quartz syenite and the Mopanshan biotite granite are 140.2±0.7 Ma and 139.9±0.7 Ma, respectively, and the cassiterite U-Pb weighted average age of the Mopanshan area is 134.9±1.4 Ma. All of them are Early Cretaceous in age. The whole rock geochemical analysis results show that these rocks are rich in silicon (SiO2=64.96%-76.71%), alkali (Na2O+ K2O=8.28%-9.03%), and aluminum (Al2O3=12.42%-15.88%). For trace elements, they are relatively enriched in elements such as Th, Pb, and Hf, and deficient in elements such as Nb, Ta, Ti, Sr, and P. For rare earth elements, they show significant enriched HREEs than LREEs, and Eu negative anomaly is unusually obvious. As the content of SiO2 increases, the content of TiO2, FeOT, Al2O3, CaO, Na2O, and P2O5 gradually decreases, showing a good negative correlation, suggesting a homogeneous magmatic source. However, the DI value of the Kulongshan sample is 89 and the Sn content is 2×10-6; the Mopanshan samples have a higher DI value (96-98) and higher Sn content (15×10-6~36×10-6). Based on the physical- chemical conditions inverted from mineralogy, the Kulongshan granite has experienced a process of oxygen fugacity increase during cooling, while the oxygen fugacity of the Mopanshan granite has further decreased during the cooling process. In addition, in terms of fluid halogen content, the Ⅳ (F) and Ⅳ (Cl) of biotite indicate the Mopanshan granite (Ⅳ(F)=0.95-1.15; Ⅳ(Cl)=-3.66--3.54) compared to the Kulongshan porphyritic quartz syenite (Ⅳ(F)=1.24-1.28; Ⅳ(Cl)=-2.96--2.52) has a higher concentration of Cl and F. In summary, low oxygen fugacity, high degree of evolution, and high F and Cl abundance, are the main factors affecting enrichment of cassiterite in granite in the Beidashan area.
2022, 47(9): 3389-3400.
doi: 10.3799/dqkx.2022.032
Abstract:
The strike-slip fault zone plays an important role in controlling the formation and distribution of large and medium oil and gas fields in the compressional superimposed basins in western China, which is also one of the difficult problems in the study. Based on the high-density 3D seismic data, a fine strike-slip fault zone interpretation and deformation pattern analysis of the Jurassic in the central Junggar basin using a variety of structural analysis techniques are conducted in this study. During the second episode of Yanshan tectonic movement, two types of strike-slip fault zones of NWW left-lateral compression-torsion and NE left-lateral tension-torsion were developed in the Jurassic. They were both composed of four groups of shear faults, which followed the simple left-lateral shear mode, but they were very different in their geometric characteristics and structural attributes. There is no conjugate shear relationship between NWW and NE strike-slip fault zones, but arc-shaped joint and merge in the blunt angle zone (about 135°). In the tectonic deformation, the arc-shaped joint action of two types of left-lateral strike-slip faults controlled torsion deformation and shear fracture in the deformation area, forming a large scale clockwise torsional structural system. The deformation pattern of torsional structure can be used as a reference for the study of intracontinental orogenic belts, and also provides a new idea for oil and gas exploration in compression-torsional basins.
The strike-slip fault zone plays an important role in controlling the formation and distribution of large and medium oil and gas fields in the compressional superimposed basins in western China, which is also one of the difficult problems in the study. Based on the high-density 3D seismic data, a fine strike-slip fault zone interpretation and deformation pattern analysis of the Jurassic in the central Junggar basin using a variety of structural analysis techniques are conducted in this study. During the second episode of Yanshan tectonic movement, two types of strike-slip fault zones of NWW left-lateral compression-torsion and NE left-lateral tension-torsion were developed in the Jurassic. They were both composed of four groups of shear faults, which followed the simple left-lateral shear mode, but they were very different in their geometric characteristics and structural attributes. There is no conjugate shear relationship between NWW and NE strike-slip fault zones, but arc-shaped joint and merge in the blunt angle zone (about 135°). In the tectonic deformation, the arc-shaped joint action of two types of left-lateral strike-slip faults controlled torsion deformation and shear fracture in the deformation area, forming a large scale clockwise torsional structural system. The deformation pattern of torsional structure can be used as a reference for the study of intracontinental orogenic belts, and also provides a new idea for oil and gas exploration in compression-torsional basins.
2022, 47(9): 3401-3416.
doi: 10.3799/dqkx.2022.131
Abstract:
Analysis and mining of high-precision aeromagnetic data is one of the important methods to reveal the spatial distribution of regional deep fault zones and lithospheric thermal structure. In order to reveal the relationship between the aeromagnetic anomaly and the regional fault zones and estimate the Curie-point depths and lithospheric thicknesses in Liaoning and its adjacent areas, the Curie-point depths are calculated by the power spectrum method, based on reduction to pole of aeromagnetic data. Meanwhile, the lithospheric thicknesses of the eastern segments of Liaoning are calculated by the 1D stable thermal conduction equations. Our new aeromagnetic data reveals that: (1) There are several NE/NNE striking aeromagnetic anomaly zones in the eastern and western parts of Liaoning and the Bohai Bay, which are interpreted as the products of the alternation of long-term extension and brief compression of the active continental margins under the background of the Pacific Plate subduction since the Late Mesozoic. The near NW/NWW striking aeromagnetic anomaly zones in the northern segments of Liaoning, which are interrupted by the NE/NNE striking magnetic anomaly zones, are interpreted as the tectonic traces which were extended and uplifted to the middle crust after the closure of the Paleo-Asian Ocean during the late collisional orogeny. (2) Our aeromagnetic anomalies also show that the estimated Curie-point depths of Liaoning and its adjacent areas ranges from 16 km to 40 km, with an average depth of 28 km. The heat flow values of the Fuxin and Panjin Curie uplifted are relatively higher. However, the heat flow values of the Shenyang and Liaoyuan Curie depression are relatively lower. (3) The estimated lithospheric thicknesses of the Liaoning and its adjacent areas show spatial heterogeneity, ranging from 70 km to 150 km with an average of 100 km. The estimated lithospheric thickness of the Yingkou-Anshan area near the Tan-Lu fault zone is the thinnest with a thickness of 60-80 km. The spatial heterogeneity of regional thermal lithospheric thicknesses in the eastern segments of Liaoning and Bohai Bay most likely results from the combined effects of the spatially heterogeneous distribution of wet upwellings triggered by the subducted Pacific slab and pre-existing weak zones in the cratonic lithosphere since the Late Mesozoic.
Analysis and mining of high-precision aeromagnetic data is one of the important methods to reveal the spatial distribution of regional deep fault zones and lithospheric thermal structure. In order to reveal the relationship between the aeromagnetic anomaly and the regional fault zones and estimate the Curie-point depths and lithospheric thicknesses in Liaoning and its adjacent areas, the Curie-point depths are calculated by the power spectrum method, based on reduction to pole of aeromagnetic data. Meanwhile, the lithospheric thicknesses of the eastern segments of Liaoning are calculated by the 1D stable thermal conduction equations. Our new aeromagnetic data reveals that: (1) There are several NE/NNE striking aeromagnetic anomaly zones in the eastern and western parts of Liaoning and the Bohai Bay, which are interpreted as the products of the alternation of long-term extension and brief compression of the active continental margins under the background of the Pacific Plate subduction since the Late Mesozoic. The near NW/NWW striking aeromagnetic anomaly zones in the northern segments of Liaoning, which are interrupted by the NE/NNE striking magnetic anomaly zones, are interpreted as the tectonic traces which were extended and uplifted to the middle crust after the closure of the Paleo-Asian Ocean during the late collisional orogeny. (2) Our aeromagnetic anomalies also show that the estimated Curie-point depths of Liaoning and its adjacent areas ranges from 16 km to 40 km, with an average depth of 28 km. The heat flow values of the Fuxin and Panjin Curie uplifted are relatively higher. However, the heat flow values of the Shenyang and Liaoyuan Curie depression are relatively lower. (3) The estimated lithospheric thicknesses of the Liaoning and its adjacent areas show spatial heterogeneity, ranging from 70 km to 150 km with an average of 100 km. The estimated lithospheric thickness of the Yingkou-Anshan area near the Tan-Lu fault zone is the thinnest with a thickness of 60-80 km. The spatial heterogeneity of regional thermal lithospheric thicknesses in the eastern segments of Liaoning and Bohai Bay most likely results from the combined effects of the spatially heterogeneous distribution of wet upwellings triggered by the subducted Pacific slab and pre-existing weak zones in the cratonic lithosphere since the Late Mesozoic.
2022, 47(9): 3417-3430.
doi: 10.3799/dqkx.2022.152
Abstract:
The rapid Mesozoic-Cenozoic exhumation of the Tianshan mountain range is of great significance for understanding its tectonic evolution process. However, the main exhumation time of the Mesozoic-Cenozoic remains controversial. In this study, we report new detrital apatite fission track data from the Mesozoic sedimentary succession on the northern margin of the Tarim basin (Kuqa river section) and the Early Permian rhyolite inverse thermal history modelling results. Thermochronologic age trends along the analyzed succession reveal two major age populations in 143.0-148.9 Ma and 35.7-38.1 Ma, of which the younger population has been completely reset, indicative of the exhumation information of the Kuqa depression. Inverse thermal history modelling results show a rapid cooling event occurred at 160-140 Ma. We infer that the compressive stress generated from collision between Lhasa and the southern margin of Eurasia transmitted to the Tianshan mountain range through the rigid Tarim, which caused that the Tianshan mountain range underwent strong uplift and denudation in the Late Jurassic-Early Cretaceous, generating widely distributed conglomerate in the Early Cretaceous Yageliemu Formation and angular unconformity developed in the Late Jurassic- Early Cretaceous strata. During the Eocene, the Tianshan was subjected to rapid uplift and intensified deformation in response to the continuous collision of several plates on the southern margin of Eurasia. And the compressive stress propagated southward, which caused that the Kuqa depression underwent uplift in the Late Eocene.
The rapid Mesozoic-Cenozoic exhumation of the Tianshan mountain range is of great significance for understanding its tectonic evolution process. However, the main exhumation time of the Mesozoic-Cenozoic remains controversial. In this study, we report new detrital apatite fission track data from the Mesozoic sedimentary succession on the northern margin of the Tarim basin (Kuqa river section) and the Early Permian rhyolite inverse thermal history modelling results. Thermochronologic age trends along the analyzed succession reveal two major age populations in 143.0-148.9 Ma and 35.7-38.1 Ma, of which the younger population has been completely reset, indicative of the exhumation information of the Kuqa depression. Inverse thermal history modelling results show a rapid cooling event occurred at 160-140 Ma. We infer that the compressive stress generated from collision between Lhasa and the southern margin of Eurasia transmitted to the Tianshan mountain range through the rigid Tarim, which caused that the Tianshan mountain range underwent strong uplift and denudation in the Late Jurassic-Early Cretaceous, generating widely distributed conglomerate in the Early Cretaceous Yageliemu Formation and angular unconformity developed in the Late Jurassic- Early Cretaceous strata. During the Eocene, the Tianshan was subjected to rapid uplift and intensified deformation in response to the continuous collision of several plates on the southern margin of Eurasia. And the compressive stress propagated southward, which caused that the Kuqa depression underwent uplift in the Late Eocene.
2022, 47(9): 3431-3446.
doi: 10.3799/dqkx.2021.261
Abstract:
The Jingshan Group, which has undergone high amphibolite to granulite facies metamorphism and ductile deformation, is one of the most widely distributed Paleoproterozoic meta-sedimentary rocks in the Jiaobei terrane of the Jiao-Liao-Ji Belt. Depositional timing and provenance of the Jingshan Group are vital for understanding the Paleoproterozoic tectonic evolution of the Jiao-Liao-Ji Belt. In this study, LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) was used to analyze the zircon U-Pb ages and rare earth element compositions of arkose-quartzites in the Lugezhuang Formation of the Jingshan Group. Based on the internal structure of zircons and U-Pb ages, the concordant 207Pb/206Pb age of 2 120 Ma in the youngest group of detrital zircons is chosen as the maximal depositional timing of the Lugezhuang Formation. Two metamorphic ages in the two samples are 1 886±12 Ma and 1 969±23 Ma, respectively. Combined with the above data and the geological relationship which the Lugezhuang Formation was intruded by the 2 103-2 085 Ma granitic gneisses in the Jingqishan area, it is speculated that the depositional timing of the Lugezhuang Formation is circa 2 100 Ma. Detrital zircon age patterns from samples are characterized by the major peak of 2 105 Ma and secondary peak of 2 185 Ma. The new detrital age data reveals that the Lugezhuang Formation in Jingqishan area is mainly derived from Paleoproterozoic intermediate-acidic magmatic rocks or recycled products of the Paleoproterozoic (2 200-2 100 Ma) rocks with a small amount of Archaean detrital material. Combined with other published data of the Jiao-Liao-Ji Belt, it is speculated that the bottom meta-sedimentary rocks in the southern part of the Jiao-Liao-Ji Belt, which is represented by the Lugezhuang Formation of the Jingshan Group, may be deposited on the side of the continental arc of the back-arc basin, and the bottom metasedimentary rocks in the northern part of the Belt, which is represented by the Xiaosong Formation of the Fenzishan Group, may be close to the side of the Archean continent of the back-arc basin.
The Jingshan Group, which has undergone high amphibolite to granulite facies metamorphism and ductile deformation, is one of the most widely distributed Paleoproterozoic meta-sedimentary rocks in the Jiaobei terrane of the Jiao-Liao-Ji Belt. Depositional timing and provenance of the Jingshan Group are vital for understanding the Paleoproterozoic tectonic evolution of the Jiao-Liao-Ji Belt. In this study, LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) was used to analyze the zircon U-Pb ages and rare earth element compositions of arkose-quartzites in the Lugezhuang Formation of the Jingshan Group. Based on the internal structure of zircons and U-Pb ages, the concordant 207Pb/206Pb age of 2 120 Ma in the youngest group of detrital zircons is chosen as the maximal depositional timing of the Lugezhuang Formation. Two metamorphic ages in the two samples are 1 886±12 Ma and 1 969±23 Ma, respectively. Combined with the above data and the geological relationship which the Lugezhuang Formation was intruded by the 2 103-2 085 Ma granitic gneisses in the Jingqishan area, it is speculated that the depositional timing of the Lugezhuang Formation is circa 2 100 Ma. Detrital zircon age patterns from samples are characterized by the major peak of 2 105 Ma and secondary peak of 2 185 Ma. The new detrital age data reveals that the Lugezhuang Formation in Jingqishan area is mainly derived from Paleoproterozoic intermediate-acidic magmatic rocks or recycled products of the Paleoproterozoic (2 200-2 100 Ma) rocks with a small amount of Archaean detrital material. Combined with other published data of the Jiao-Liao-Ji Belt, it is speculated that the bottom meta-sedimentary rocks in the southern part of the Jiao-Liao-Ji Belt, which is represented by the Lugezhuang Formation of the Jingshan Group, may be deposited on the side of the continental arc of the back-arc basin, and the bottom metasedimentary rocks in the northern part of the Belt, which is represented by the Xiaosong Formation of the Fenzishan Group, may be close to the side of the Archean continent of the back-arc basin.
2022, 47(9): 3463-3476.
doi: 10.3799/dqkx.2022.099
Abstract:
Identifying the three-dimensional distribution characteristics of rock mass fractures quickly and accurately is the key to the prevention and reduction of disasters on the railway in the mountainous area of southwest China. In this study, a new method for rock mass fracture visualization is proposed. The digital processing and dimension reduction of data are completed by the spherical coordinates and polar stereographic projection. K-Means++ clustering algorithm, Fisher distribution model and Monte Carlo simulation are used for automatic fracture occurrence data classification and simulation. Finally, the 3D visualization of fracture data is realized by Python and disc model. This research adopts coordinate transformation and triangular mesh surface, which is more conducive to nested analysis with other 3D modeling software. The advance application research of Hydropower Station project shows that the occurrence data correspond to Fisher distribution, and the model in this paper has certain advantages over the traditional rose chart and Schmidt chart. Therefore, the rock mass fracture model established in this paper describes the 3D distribution characteristics of regional fracture network intuitively and quickly. The research results can be directly applied to the fracture 3D visualization of tunnel face image and future disaster prevention and reduction of the railway in the mountain area of southwest China.
Identifying the three-dimensional distribution characteristics of rock mass fractures quickly and accurately is the key to the prevention and reduction of disasters on the railway in the mountainous area of southwest China. In this study, a new method for rock mass fracture visualization is proposed. The digital processing and dimension reduction of data are completed by the spherical coordinates and polar stereographic projection. K-Means++ clustering algorithm, Fisher distribution model and Monte Carlo simulation are used for automatic fracture occurrence data classification and simulation. Finally, the 3D visualization of fracture data is realized by Python and disc model. This research adopts coordinate transformation and triangular mesh surface, which is more conducive to nested analysis with other 3D modeling software. The advance application research of Hydropower Station project shows that the occurrence data correspond to Fisher distribution, and the model in this paper has certain advantages over the traditional rose chart and Schmidt chart. Therefore, the rock mass fracture model established in this paper describes the 3D distribution characteristics of regional fracture network intuitively and quickly. The research results can be directly applied to the fracture 3D visualization of tunnel face image and future disaster prevention and reduction of the railway in the mountain area of southwest China.
