2022 Vol. 47, No. 4
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2022, 47(4): 1143-1161.
doi: 10.3799/dqkx.2021.072
Abstract:
Neogene is the key period for the establishment of geomorphology and pattern of climate changes in China, involving the significant uplift of Tibetan Plateau and final formation of modern plateau landform, the termination of seafloor spreading for the South China Sea, the final establishment of the present large river system in East Asia, the final establishment of the west-tilting topography of China, the formation and enhancement of East Asian monsoon system. Through the comprehensive study of Neogene tectonics, sedimentary basins (groups), volcanic rocks, uplifting belts and large deformation structures in China, 10 first-order tectonic-stratigraphic units (super-realms) and 27 second-order tectonic-stratigraphic units (realms) have been subdivided, including 94 basins. Through the research of the types of basins in each unit, sedimentary sequence, sedimentary age and stratigraphic contact, the Neogene lithostratigraphic correlation framework in China was established and the sedimentary-tectonic-climate history was summarized.
Neogene is the key period for the establishment of geomorphology and pattern of climate changes in China, involving the significant uplift of Tibetan Plateau and final formation of modern plateau landform, the termination of seafloor spreading for the South China Sea, the final establishment of the present large river system in East Asia, the final establishment of the west-tilting topography of China, the formation and enhancement of East Asian monsoon system. Through the comprehensive study of Neogene tectonics, sedimentary basins (groups), volcanic rocks, uplifting belts and large deformation structures in China, 10 first-order tectonic-stratigraphic units (super-realms) and 27 second-order tectonic-stratigraphic units (realms) have been subdivided, including 94 basins. Through the research of the types of basins in each unit, sedimentary sequence, sedimentary age and stratigraphic contact, the Neogene lithostratigraphic correlation framework in China was established and the sedimentary-tectonic-climate history was summarized.
2022, 47(4): 1162-1176.
doi: 10.3799/dqkx.2021.083
Abstract:
The Sulu orogenic belt, located between the North China and South China plates, is one of the most prominent intracontinental orogenic belt in eastern China. Therefore, the denudation history of Sulu orogenic belt provides significant insight into the basin-mountain evolution in eastern China and their dynamic mechanism. Due to the apatite (U-Th)/He system has low closure temperature (ca. 70 ℃), it can constrain the cooling processes of geological bodies more accurately in the upper crust. In this study, the apatite (U-Th)/He method was used to analyze the exhumation time of rocks on the Duofu and Juchi mountains located in the eastern parts of Sulu orogenic belt. The apatite (U-Th)/He age-elevation relationship and thermal history simulation results show that the exhumation occurred in the Early-Middle Eocene (54-43 Ma) and Oligocene (35-27 Ma) for the Duofu and Juchi mountains, respectively. These cooling episodes were synchronized with the exhumation time of the western part of the Sulu orogenic belt. Combined with the results reported in the region, it is shown that the eastern China was influenced by the Pacific and Indian plates subduction into Eurasia, and the extensive exhumation process occurred in the Early Cenozoic, which established the basin-mountain distribution pattern during this time.
The Sulu orogenic belt, located between the North China and South China plates, is one of the most prominent intracontinental orogenic belt in eastern China. Therefore, the denudation history of Sulu orogenic belt provides significant insight into the basin-mountain evolution in eastern China and their dynamic mechanism. Due to the apatite (U-Th)/He system has low closure temperature (ca. 70 ℃), it can constrain the cooling processes of geological bodies more accurately in the upper crust. In this study, the apatite (U-Th)/He method was used to analyze the exhumation time of rocks on the Duofu and Juchi mountains located in the eastern parts of Sulu orogenic belt. The apatite (U-Th)/He age-elevation relationship and thermal history simulation results show that the exhumation occurred in the Early-Middle Eocene (54-43 Ma) and Oligocene (35-27 Ma) for the Duofu and Juchi mountains, respectively. These cooling episodes were synchronized with the exhumation time of the western part of the Sulu orogenic belt. Combined with the results reported in the region, it is shown that the eastern China was influenced by the Pacific and Indian plates subduction into Eurasia, and the extensive exhumation process occurred in the Early Cenozoic, which established the basin-mountain distribution pattern during this time.
2022, 47(4): 1177-1193.
doi: 10.3799/dqkx.2021.082
Abstract:
Beishan Group is the main part of Mingshui-Hanshan block in the middle part of the southern margin of Central Asia orogenic belt, which is of great significance to the study of the tectonic evolution of Precambrian basement and the process of orogenic accretion. In this paper, it reports for the first time the rock association, metamorphic deformation, section characteristics and detrital zircon age of the Beishan Group in the original Permian strata in the Shaomushangde area, southern Yagan, and compares it with the Beishan Group in the Beishan area. Two detrital zircon ages were obtained by LA-ICP-MS in the quartzites. The ages range from 1 075.7 to 2 708.1 Ma, mostly from 1 100 to 1 900 Ma, and the maximum depositional age of Beishan Group in this area is 1 075.7 Ma. The provenance analyses show tectonic affinity among microcontinent of the Beishan orogenic belts and Mongolia block, and may originate from a unified block with Beishan area.The discovery confirms that the northern Alxa area and Beishan area have the same Precambrian folded basement, and indirectly proves that the Yagan tectonic belt and Hongshishan-Baiheshan ophiolite tectonic melange belt are comparable in the sense of tectonic differentiation.
Beishan Group is the main part of Mingshui-Hanshan block in the middle part of the southern margin of Central Asia orogenic belt, which is of great significance to the study of the tectonic evolution of Precambrian basement and the process of orogenic accretion. In this paper, it reports for the first time the rock association, metamorphic deformation, section characteristics and detrital zircon age of the Beishan Group in the original Permian strata in the Shaomushangde area, southern Yagan, and compares it with the Beishan Group in the Beishan area. Two detrital zircon ages were obtained by LA-ICP-MS in the quartzites. The ages range from 1 075.7 to 2 708.1 Ma, mostly from 1 100 to 1 900 Ma, and the maximum depositional age of Beishan Group in this area is 1 075.7 Ma. The provenance analyses show tectonic affinity among microcontinent of the Beishan orogenic belts and Mongolia block, and may originate from a unified block with Beishan area.The discovery confirms that the northern Alxa area and Beishan area have the same Precambrian folded basement, and indirectly proves that the Yagan tectonic belt and Hongshishan-Baiheshan ophiolite tectonic melange belt are comparable in the sense of tectonic differentiation.
2022, 47(4): 1194-1216.
doi: 10.3799/dqkx.2021.116
Abstract:
Late Triassic intermediate-acid volcanic rocks exposed in the Boluositai area, East Kunlun orogenic belt are of great significance for studying the closure of the Paleo-Tethys ocean and subsequent collision orogenic processes. It conducted detailed zircon U-Pb chronology, geochemistry and Hf isotopic studies of the volcanic rock to determine its formation age, petrogenesis and tectonic environment. The results show that the zircon weighted average ages of dacites are 233.4±1.3 Ma and 234.7±1.5 Ma respectively, suggesting the Late Triassic. The whole-rock geochemical results show that the SiO2 contents range from 64.57% to 71.27%, with the total alkali contents (ALK) from 7.53% to 8.07%, the Na2O/K2O ratios from 0.84 to 1.01, the Mg# values from 35.66 to 45.39, and the A/CNK from 1.0 to 1.1. These features show weak peraluminous, high-potassium calcium alkaline series. The light and heavy rare earth elements of the rocks are obviously fractionated, which is characterized by the enrichment of light rare earth elements and the depletion of heavy rare earth elements, with a weak negative Eu anomaly. The zircon εHf(t=235) of dacites ranges from -4.81 to +0.09, and the two-stage model age is 1 059-1 309 Ma. The petrogenesis research indicates that the dacites were derived from feldspar-rich sandstone and basalts in the continental crust. Based on regional geological data, it is suggested that the dacites were formed in a post-collision setting and that the Paleo-Tethys Ocean had been closed in the early Late Triassic and the East Kunlun orogen transformed into a post-collision stage.
Late Triassic intermediate-acid volcanic rocks exposed in the Boluositai area, East Kunlun orogenic belt are of great significance for studying the closure of the Paleo-Tethys ocean and subsequent collision orogenic processes. It conducted detailed zircon U-Pb chronology, geochemistry and Hf isotopic studies of the volcanic rock to determine its formation age, petrogenesis and tectonic environment. The results show that the zircon weighted average ages of dacites are 233.4±1.3 Ma and 234.7±1.5 Ma respectively, suggesting the Late Triassic. The whole-rock geochemical results show that the SiO2 contents range from 64.57% to 71.27%, with the total alkali contents (ALK) from 7.53% to 8.07%, the Na2O/K2O ratios from 0.84 to 1.01, the Mg# values from 35.66 to 45.39, and the A/CNK from 1.0 to 1.1. These features show weak peraluminous, high-potassium calcium alkaline series. The light and heavy rare earth elements of the rocks are obviously fractionated, which is characterized by the enrichment of light rare earth elements and the depletion of heavy rare earth elements, with a weak negative Eu anomaly. The zircon εHf(t=235) of dacites ranges from -4.81 to +0.09, and the two-stage model age is 1 059-1 309 Ma. The petrogenesis research indicates that the dacites were derived from feldspar-rich sandstone and basalts in the continental crust. Based on regional geological data, it is suggested that the dacites were formed in a post-collision setting and that the Paleo-Tethys Ocean had been closed in the early Late Triassic and the East Kunlun orogen transformed into a post-collision stage.
2022, 47(4): 1217-1233.
doi: 10.3799/dqkx.2021.100
Abstract:
Tajigang copper polymetallic ore is located in the south margin of southern Qiangtang terrane, providing an ideal window for understanding the tectonic-magmatic activities and mineralization of Bangong Co-Nujiang metallogenic belt. In this paper, it focuses on the granites in Tajigang mining area and reports their zircon U-Pb ages, geochemical and zircon Hf isotopic data. These granite rocks were dated as Early Cretaceous (120-118 Ma) and characterized by high SiO2, total alkali (Na2O+K2O), and low P2O5 contents, with aluminum saturation index (A/CNK) of 0.78-1.02, suggesting geochemical affinity to calc alkaline Ⅰ-type granite. Furthermore, the granites display positive εHf(t) values (+3.9-+7.2) with relatively young crustal model age (TDMC=717-926 Ma) and show similar Zr/Hf (26.88-38.65), Nb/Ta (7.01-13.61), Sm/Nd (0.17-0.21), and Nb/La (0.32-0.58) ratios to crust, indicating a magma source of juvenile igneous lower crust. Together with data from the recent literature, it proposes that the Tajigang granites formed in a collision setting of Lhasa and southern Qiangtang terranes. In addition, the Tajigang granites show similar geochemical and isotopic compositions with the regional simultaneous metallogenic related rocks which were derived by partial melting of juvenile lower crust. In general, the juvenile crust was enriched in Cu, Au and other elements. Thus, our research proposes that these widely exposed juvenile-crust derived granitic rocks of central Tibet have certain metallogenic conditions and are the key exploration direction for prospecting porphyry Cu-Au deposits in the future.
Tajigang copper polymetallic ore is located in the south margin of southern Qiangtang terrane, providing an ideal window for understanding the tectonic-magmatic activities and mineralization of Bangong Co-Nujiang metallogenic belt. In this paper, it focuses on the granites in Tajigang mining area and reports their zircon U-Pb ages, geochemical and zircon Hf isotopic data. These granite rocks were dated as Early Cretaceous (120-118 Ma) and characterized by high SiO2, total alkali (Na2O+K2O), and low P2O5 contents, with aluminum saturation index (A/CNK) of 0.78-1.02, suggesting geochemical affinity to calc alkaline Ⅰ-type granite. Furthermore, the granites display positive εHf(t) values (+3.9-+7.2) with relatively young crustal model age (TDMC=717-926 Ma) and show similar Zr/Hf (26.88-38.65), Nb/Ta (7.01-13.61), Sm/Nd (0.17-0.21), and Nb/La (0.32-0.58) ratios to crust, indicating a magma source of juvenile igneous lower crust. Together with data from the recent literature, it proposes that the Tajigang granites formed in a collision setting of Lhasa and southern Qiangtang terranes. In addition, the Tajigang granites show similar geochemical and isotopic compositions with the regional simultaneous metallogenic related rocks which were derived by partial melting of juvenile lower crust. In general, the juvenile crust was enriched in Cu, Au and other elements. Thus, our research proposes that these widely exposed juvenile-crust derived granitic rocks of central Tibet have certain metallogenic conditions and are the key exploration direction for prospecting porphyry Cu-Au deposits in the future.
2022, 47(4): 1234-1252.
doi: 10.3799/dqkx.2021.059
Abstract:
In order to examine the magma origin and tectonic setting of the Bayern Daba rock mass in Inner Mongolia and thereby limit the closure of the paleo-Asian Ocean, zircon LA-ICP-MS U-Pb geochronological, geochemical and Sr-Nd isotopic measurement and analysis are presented in this paper. Zircon U-Pb dating yields a weighted mean age of 327±2 Ma(MSWD=1.4), indicating an Early Carboniferous magmatic event. The Bayern Daba rock mass is characterized by the high Si, Na, Mg, Fe and metaluminous-peraluminous features. They are relatively enriched in Rb, Th, U and K, depleted in Ba, Sr, P, Nb, Ta and Ti, and enriched in LREE over HREE with negative Eu anormaly, showing the calc-alkaline Ⅰ-type granite in island arc. Their depleted isotopic compositions with (87Sr/86Sr)i from 0.705 8 to 0.709 6, negative εNd(t) values from -4.93 to 0.01, and TDM2 from 1.08 to 1.48 Ga, as well as the inherited zircon present in zircon, indicating that the magma source was derived from the partial melting of Mesoproterozoic mantle-derived basic materials. High Rb/Sr (0.70-2.63) and Zr/Hf (35.88-77.17) ratios and the positive correlation of ISr and εNd(t) isotopic data suggest contamination by a proportion of mantle material. Combined with regional tectonic evolution, the Bayern Daba rock mass was formed in the island-arc environment of an active continental margin in Carboniferous, which further suggests that the subduction of the paleo-Asian Ocean was still ongoing at that time. The same conclusion is also reported about the Early Permian intermediate-acidic rock masses in the southern part of the Xing-Meng orogenic belt, suggesting that the paleo-Asian Ocean had been subducting northward from Late Carboniferous up to Late Permian and did not fully close until the appearance of granitoids formed in a post-orogenic extensional environment in Middle to Late Triassic.
In order to examine the magma origin and tectonic setting of the Bayern Daba rock mass in Inner Mongolia and thereby limit the closure of the paleo-Asian Ocean, zircon LA-ICP-MS U-Pb geochronological, geochemical and Sr-Nd isotopic measurement and analysis are presented in this paper. Zircon U-Pb dating yields a weighted mean age of 327±2 Ma(MSWD=1.4), indicating an Early Carboniferous magmatic event. The Bayern Daba rock mass is characterized by the high Si, Na, Mg, Fe and metaluminous-peraluminous features. They are relatively enriched in Rb, Th, U and K, depleted in Ba, Sr, P, Nb, Ta and Ti, and enriched in LREE over HREE with negative Eu anormaly, showing the calc-alkaline Ⅰ-type granite in island arc. Their depleted isotopic compositions with (87Sr/86Sr)i from 0.705 8 to 0.709 6, negative εNd(t) values from -4.93 to 0.01, and TDM2 from 1.08 to 1.48 Ga, as well as the inherited zircon present in zircon, indicating that the magma source was derived from the partial melting of Mesoproterozoic mantle-derived basic materials. High Rb/Sr (0.70-2.63) and Zr/Hf (35.88-77.17) ratios and the positive correlation of ISr and εNd(t) isotopic data suggest contamination by a proportion of mantle material. Combined with regional tectonic evolution, the Bayern Daba rock mass was formed in the island-arc environment of an active continental margin in Carboniferous, which further suggests that the subduction of the paleo-Asian Ocean was still ongoing at that time. The same conclusion is also reported about the Early Permian intermediate-acidic rock masses in the southern part of the Xing-Meng orogenic belt, suggesting that the paleo-Asian Ocean had been subducting northward from Late Carboniferous up to Late Permian and did not fully close until the appearance of granitoids formed in a post-orogenic extensional environment in Middle to Late Triassic.
2022, 47(4): 1253-1270.
doi: 10.3799/dqkx.2021.094
Abstract:
The Bulhanbuda arc is located in the south of the central fault of East Kunlun orogen. Different from the Late Paleozoic-Mesozoic magmatic arc in the North Kunlun, Early Paleozoic magmatic rocks are widely exposed in the Bulhanbuda area and of great significance to the researches of subduction-accretion process of the Proto-Tethyan Ocean. In this study, it reports the petrology, geochemistry, zircon U-Pb ages, Lu-Hf and Sr-Nd isotopic compositions of the Early Paleozoic magmatic rocks from the Bulhanbuda area. This and previous studies indicate that the subduction-related magmatic activities can be divided into three stages: Cambrian (515-482 Ma), Middle Ordovician (465-463 Ma), and Late Ordovician-Early Silurian (454-438 Ma). The Cambrian magmatic rocks contain Nb-enriched mafic-ultramafic rocks and metaluminous high-K calc-alkaline diorite. The Ordovician magmatic rocks are weakly peraluminous high-K calc-alkaline monzogranites. The Late Ordovician magmatic rocks are dominated by weakly peraluminous medium- and high-K calc-alkaline diorite and monzogranite and contain some metaluminous calc-alkaline quartz diorite and tholeiitic dolerite. These three stage intrusive rocks show similar trace element compositions with those of continental arc andesite. The Sr/Y ratios of the Cambrian diorite are low (22.6-30.0), the Sr/Y ratios of the Middle Ordovician monzogranite are medium, and these of Late Ordovician granodiorite and monzogranite are high. All of these intrusive rocks are enriched in radiogenic Sr and Nd isotopes. The Cambrian diorites display high initial 87Sr/86Sr ratios of 0.715 1-0.715 7 and low εNd(t) values of -7.4 to -7.3. The Middle Ordovician monzogranite have initial 87Sr/86Sr ratios of 0.707 6-0.707 7 and εNd(t) values of -2.5 to -2.4. The Late Ordovician granodiorite and monzogranite have low initial 87Sr/86Sr ratios (0.705 9-0.706 5) and negative εNd(t) values (-3.3 to -1.7). However, the diorite shows relatively high initial 87Sr/86Sr ratios (0.706 9-0.708 5) and low εNd(t) values (-6.0 to -5.6). The three stage magmatic rocks show wide range of the zircon Hf isotopes. Cambrian diorites have negative εHf(t) values (-6.8 to -4.4). Middle Ordovician monzogranites display positive εHf(t) values (+0.13 to +2.90). Late Ordovician granidorite and monzogranite show wide range of εHf(t) values (-2.7 to +9.2). The diorites mainly yield negative εHf(t) values (-8.6 to -2.1). In conclusion, the Bulhanbuda arc is an Andean-type continental margin arc formed during the southward subduction of the Proto-Tethyan Ocean. It has undergone three significant evolutionary stages. In the early stage (515-482 Ma), partial melting of the mantle wedge generated the basic magma, which induced remelting of the Paleoproterozoic lower crust to form intermediate-acid magma. In the middle period (465-463 Ma), the mantle derived basic magma underpenetrated and the thickened lower crust was partially melted to form small-scale acid magma. In the late period (454-438 Ma), the mantle derived basic magma underpenetrated and the thickened lower crust was partially melted to form large-scale intermediate-acid magmatic rocks with adakitic geochemical composition.
The Bulhanbuda arc is located in the south of the central fault of East Kunlun orogen. Different from the Late Paleozoic-Mesozoic magmatic arc in the North Kunlun, Early Paleozoic magmatic rocks are widely exposed in the Bulhanbuda area and of great significance to the researches of subduction-accretion process of the Proto-Tethyan Ocean. In this study, it reports the petrology, geochemistry, zircon U-Pb ages, Lu-Hf and Sr-Nd isotopic compositions of the Early Paleozoic magmatic rocks from the Bulhanbuda area. This and previous studies indicate that the subduction-related magmatic activities can be divided into three stages: Cambrian (515-482 Ma), Middle Ordovician (465-463 Ma), and Late Ordovician-Early Silurian (454-438 Ma). The Cambrian magmatic rocks contain Nb-enriched mafic-ultramafic rocks and metaluminous high-K calc-alkaline diorite. The Ordovician magmatic rocks are weakly peraluminous high-K calc-alkaline monzogranites. The Late Ordovician magmatic rocks are dominated by weakly peraluminous medium- and high-K calc-alkaline diorite and monzogranite and contain some metaluminous calc-alkaline quartz diorite and tholeiitic dolerite. These three stage intrusive rocks show similar trace element compositions with those of continental arc andesite. The Sr/Y ratios of the Cambrian diorite are low (22.6-30.0), the Sr/Y ratios of the Middle Ordovician monzogranite are medium, and these of Late Ordovician granodiorite and monzogranite are high. All of these intrusive rocks are enriched in radiogenic Sr and Nd isotopes. The Cambrian diorites display high initial 87Sr/86Sr ratios of 0.715 1-0.715 7 and low εNd(t) values of -7.4 to -7.3. The Middle Ordovician monzogranite have initial 87Sr/86Sr ratios of 0.707 6-0.707 7 and εNd(t) values of -2.5 to -2.4. The Late Ordovician granodiorite and monzogranite have low initial 87Sr/86Sr ratios (0.705 9-0.706 5) and negative εNd(t) values (-3.3 to -1.7). However, the diorite shows relatively high initial 87Sr/86Sr ratios (0.706 9-0.708 5) and low εNd(t) values (-6.0 to -5.6). The three stage magmatic rocks show wide range of the zircon Hf isotopes. Cambrian diorites have negative εHf(t) values (-6.8 to -4.4). Middle Ordovician monzogranites display positive εHf(t) values (+0.13 to +2.90). Late Ordovician granidorite and monzogranite show wide range of εHf(t) values (-2.7 to +9.2). The diorites mainly yield negative εHf(t) values (-8.6 to -2.1). In conclusion, the Bulhanbuda arc is an Andean-type continental margin arc formed during the southward subduction of the Proto-Tethyan Ocean. It has undergone three significant evolutionary stages. In the early stage (515-482 Ma), partial melting of the mantle wedge generated the basic magma, which induced remelting of the Paleoproterozoic lower crust to form intermediate-acid magma. In the middle period (465-463 Ma), the mantle derived basic magma underpenetrated and the thickened lower crust was partially melted to form small-scale acid magma. In the late period (454-438 Ma), the mantle derived basic magma underpenetrated and the thickened lower crust was partially melted to form large-scale intermediate-acid magmatic rocks with adakitic geochemical composition.
2022, 47(4): 1271-1294.
doi: 10.3799/dqkx.2021.104
Abstract:
The mafic rocks originating from deep earth are probes for lithospheric mantle evolution. In this paper, it presents a synthesis study of zircon U-Pb chronology, whole-rock elemental and Sr-Nd isotopic geochemistry, and zircon Hf isotope of the mafic intrusive rocks in the Zhongtiao Mountain area. Two periods of magmatism during the Late Triassic (217±2 Ma) and the Early Cretaceous (121±2 Ma) are unraveled. The Late Triassic samples are characterized by low to intermediate SiO2 contents (46.03%-53.87%), high MgO (14.37%-18.61%), Ni (282×10-6-433×10-6) and Cr (619×10-6-1 847×10-6) concentrations, low magmatophile element abundances, and convex rare earth element distribution patterns, indicating a cumulate origin. The existence of a large number of original amphiboles indicates that the parental magma is highly water-rich. All samples have nearly parallel trace element distribution patterns, which implies that their mild LILE-HFSE (large ion lithophile element - high field strength element) differentiation reflects the inherent attributes of mantle source region, and their parental magma probably originated from partial melting of the mantle wedge metasomatized by subducted sediment melt/fluid. The SiO2 content of Early Cretaceous mafic intrusive rocks lies between 49.23%-54.99%, while the contents of MgO and Fe2O3T are 4.29%-7.17% and 9.70%-14.79%, respectively. Meanwhile, these rocks are enriched in LILEs and light rare earth elements (LREEs), and depleted in HFSEs and heavy rare earth elements (HREEs). Their formation is ascribed to partial melting of lithospheric mantle metasomatized by subducted continental crust-derived melt. The Late Triassic complex may be related to post-orogenic oceanic slab breakoff caused by collision between the Yangtze plate and the North China craton (NCC), while the Early Cretaceous intrusive rocks may be linked with back arc lithospheric extension triggered by the retreat of Paleo-Pacific plate during its westward subduction. In addition, the relative depletion of whole-rock Nd (εNd(t)=-18.56 to -12.64) and zircon Hf (εHf(t)=-20.2 to +10.4) isotopic compositions in samples compared with that of typical craton lithospheric mantle indicates that the lithospheric mantle nature of the central and southern part of the NCC have changed significantly since the Late Triassic, and the Early Cretaceous craton destruction extends to the central part of the NCC.
The mafic rocks originating from deep earth are probes for lithospheric mantle evolution. In this paper, it presents a synthesis study of zircon U-Pb chronology, whole-rock elemental and Sr-Nd isotopic geochemistry, and zircon Hf isotope of the mafic intrusive rocks in the Zhongtiao Mountain area. Two periods of magmatism during the Late Triassic (217±2 Ma) and the Early Cretaceous (121±2 Ma) are unraveled. The Late Triassic samples are characterized by low to intermediate SiO2 contents (46.03%-53.87%), high MgO (14.37%-18.61%), Ni (282×10-6-433×10-6) and Cr (619×10-6-1 847×10-6) concentrations, low magmatophile element abundances, and convex rare earth element distribution patterns, indicating a cumulate origin. The existence of a large number of original amphiboles indicates that the parental magma is highly water-rich. All samples have nearly parallel trace element distribution patterns, which implies that their mild LILE-HFSE (large ion lithophile element - high field strength element) differentiation reflects the inherent attributes of mantle source region, and their parental magma probably originated from partial melting of the mantle wedge metasomatized by subducted sediment melt/fluid. The SiO2 content of Early Cretaceous mafic intrusive rocks lies between 49.23%-54.99%, while the contents of MgO and Fe2O3T are 4.29%-7.17% and 9.70%-14.79%, respectively. Meanwhile, these rocks are enriched in LILEs and light rare earth elements (LREEs), and depleted in HFSEs and heavy rare earth elements (HREEs). Their formation is ascribed to partial melting of lithospheric mantle metasomatized by subducted continental crust-derived melt. The Late Triassic complex may be related to post-orogenic oceanic slab breakoff caused by collision between the Yangtze plate and the North China craton (NCC), while the Early Cretaceous intrusive rocks may be linked with back arc lithospheric extension triggered by the retreat of Paleo-Pacific plate during its westward subduction. In addition, the relative depletion of whole-rock Nd (εNd(t)=-18.56 to -12.64) and zircon Hf (εHf(t)=-20.2 to +10.4) isotopic compositions in samples compared with that of typical craton lithospheric mantle indicates that the lithospheric mantle nature of the central and southern part of the NCC have changed significantly since the Late Triassic, and the Early Cretaceous craton destruction extends to the central part of the NCC.
2022, 47(4): 1295-1315.
doi: 10.3799/dqkx.2021.081
Abstract:
The Late Carboniferous alkaline granite belt in Erlian-Dongquqi area indicates regional extention after the closure of Hegenshan ocean. In this paper, it presents recently discovered Late Carboniferous alkaline granites in these regions: Honger(302±1 Ma), Zuhengdeleng (~299 Ma), and Narenbaolige (301.7±1.4 Ma) plutons. These rocks show characteristics of high silica (73.15%-77.38%), alkali (K2O=4.28%-5.35%, Na2O=4.01%-4.79%) contents, low CaO, MgO and relatively enriched FeOt(FeOt/MgO ratios are between 8.2-46.1) contents, similar with typical alkaline granite. Trace element analysis display enrichment of Rb, Th, U, K, Zr, Hf, but strong depletion of Sr, Ba, P, Ti. There are "sea gull" REE patterns with strong negative Eu abnormity (δEu ranges from 0.03 to 0.50). Furthermore, these rocks have depleted Nd-Hf isotopic composition, with two stage Hf-Nd model ages of Neoproterozoic-Early Paleozoic, indicating that the sources are juvenile crust derived from mantle in this period. Geochemical and Nd-Hf isotopic signatures argue for derivation from partial melting of juvenile crust by depression and heating of upwelling asthenosphere in post-orogeny extensional setting, demonstrating that the Hegenshan basin had closed before 300 Ma.
The Late Carboniferous alkaline granite belt in Erlian-Dongquqi area indicates regional extention after the closure of Hegenshan ocean. In this paper, it presents recently discovered Late Carboniferous alkaline granites in these regions: Honger(302±1 Ma), Zuhengdeleng (~299 Ma), and Narenbaolige (301.7±1.4 Ma) plutons. These rocks show characteristics of high silica (73.15%-77.38%), alkali (K2O=4.28%-5.35%, Na2O=4.01%-4.79%) contents, low CaO, MgO and relatively enriched FeOt(FeOt/MgO ratios are between 8.2-46.1) contents, similar with typical alkaline granite. Trace element analysis display enrichment of Rb, Th, U, K, Zr, Hf, but strong depletion of Sr, Ba, P, Ti. There are "sea gull" REE patterns with strong negative Eu abnormity (δEu ranges from 0.03 to 0.50). Furthermore, these rocks have depleted Nd-Hf isotopic composition, with two stage Hf-Nd model ages of Neoproterozoic-Early Paleozoic, indicating that the sources are juvenile crust derived from mantle in this period. Geochemical and Nd-Hf isotopic signatures argue for derivation from partial melting of juvenile crust by depression and heating of upwelling asthenosphere in post-orogeny extensional setting, demonstrating that the Hegenshan basin had closed before 300 Ma.
2022, 47(4): 1316-1332.
doi: 10.3799/dqkx.2021.134
Abstract:
The Tianbao niobium deposit, located in the Wudang area of the South Qinling belt, is a typical alkaline volcanic-rock hosted Nb deposit in China. However, the research on the origin and evolution of alkaline magma as well as the enrichment mechanism of Nb is lacking. The alkaline volcanic rocks in Tianbao can be divided into trachyte series and alkaline basalt series, which are spatially associated. In this study, it presents detailed petrography observation combined with in-situ U-Pb dating of titanite by LA-ICP-MS, and in-situ element analyses of different types of titanite by EPMA, to reveal the magma evolution and the Nb enrichment processes. The trachyte rocks have titanite U-Pb age of 432.4±4.4 Ma(n=30, MSWD=2.4), which is consistent with the zircon U-Pb age of other trachytes, mafic dykes, and carbonatite-alkaline complexes in the South Qinling belt, indicating that the study area had large-scale alkaline magmatism activation in the Early Silurian. The titanite from both trachyte and alkaline basalt rock are of magmatic and detrital origins based on their occurrences and geochemical characteristics. Most magmatic titanite grains are euhedral and coarse, and have oscillating zoning, while some grains are present in the form of small particles around the titanite phenocrysts. They have lower Al contents and Al/Fe ratios compared to detrital titanites, which are typically fragmented. The magmatic titanites in the early basaltic rock have lower concentrations of Nb2O5 (< 0.47%), Na2O (< 0.05%) and REE2O3 (< 0.87%), but have a large variety of Al2O3+ Fe2O3 (0.80%-2.91%), indicating that the Nb content in the early basaltic magma is relatively low. The magmatic titanites in the trachyte are obviously enriched in Nb2O5 (0.19%-1.50%) and REE2O3 (0.02%-4.06%). Trachytes also contain fine-grained other Nb minerals such as pyrochlore, columbite, and aeschynite, indicating that the contents of Nb are significantly increased during magma fractionation from basalt to trachyte, and eventually lead to ore-grade mineralization in trachyte.
The Tianbao niobium deposit, located in the Wudang area of the South Qinling belt, is a typical alkaline volcanic-rock hosted Nb deposit in China. However, the research on the origin and evolution of alkaline magma as well as the enrichment mechanism of Nb is lacking. The alkaline volcanic rocks in Tianbao can be divided into trachyte series and alkaline basalt series, which are spatially associated. In this study, it presents detailed petrography observation combined with in-situ U-Pb dating of titanite by LA-ICP-MS, and in-situ element analyses of different types of titanite by EPMA, to reveal the magma evolution and the Nb enrichment processes. The trachyte rocks have titanite U-Pb age of 432.4±4.4 Ma(n=30, MSWD=2.4), which is consistent with the zircon U-Pb age of other trachytes, mafic dykes, and carbonatite-alkaline complexes in the South Qinling belt, indicating that the study area had large-scale alkaline magmatism activation in the Early Silurian. The titanite from both trachyte and alkaline basalt rock are of magmatic and detrital origins based on their occurrences and geochemical characteristics. Most magmatic titanite grains are euhedral and coarse, and have oscillating zoning, while some grains are present in the form of small particles around the titanite phenocrysts. They have lower Al contents and Al/Fe ratios compared to detrital titanites, which are typically fragmented. The magmatic titanites in the early basaltic rock have lower concentrations of Nb2O5 (< 0.47%), Na2O (< 0.05%) and REE2O3 (< 0.87%), but have a large variety of Al2O3+ Fe2O3 (0.80%-2.91%), indicating that the Nb content in the early basaltic magma is relatively low. The magmatic titanites in the trachyte are obviously enriched in Nb2O5 (0.19%-1.50%) and REE2O3 (0.02%-4.06%). Trachytes also contain fine-grained other Nb minerals such as pyrochlore, columbite, and aeschynite, indicating that the contents of Nb are significantly increased during magma fractionation from basalt to trachyte, and eventually lead to ore-grade mineralization in trachyte.
2022, 47(4): 1333-1348.
doi: 10.3799/dqkx.2021.096
Abstract:
The Dabie orogen is located in the north margin of the Yangtze block. Recent studies show that the Dabie orogen has Archean-Paleoproterozoic crystalline base, but it has been lack of Mesoproterozoic material information all the time. In this article, it reports a set of Mesoproterozoic sedimentary rocks mainly composed of "metasandstone-marble" in the Dabie orogen for the first time. It analyzes the detrital zircon U-Pb chronology and Lu-Hf isotopic characteristics of the three samples in this strata, and the results show that the youngest average ages of three samples are: 1 556±13 Ma, 1 541±20 Ma and 1 584.3±24 Ma. This three ages are basically same within the error-range, which shows that the age of this strata should be the Mesoproterozoic. The metamorphic rims of detrital zircon record a metamorphic event at the age of 124.1±2.3 Ma, the U-Pb age histograms and Lu-Hf isotopes shows that the provenance characteristics of this strata are consistent with the Shennongjia Group. The main peaks of detrital zircon U-Pb ages of 2 682 Ma and 2 461 Ma record two important growth events of Dabie crystalline basement, and the peaks of 2 043 Ma, 1 803 Ma, 1 572 Ma implicate that the "Dabie block" may have participated in the aggregate event of Columbia supercontinent and become a part of it, and the "Dabie block" separated from the Columbia supercontinent during the breaking up event, and collided with the "Huangling continental nucleus" and became an important part of the basement of the Yangtze block during the Early Neoproterozoic.
The Dabie orogen is located in the north margin of the Yangtze block. Recent studies show that the Dabie orogen has Archean-Paleoproterozoic crystalline base, but it has been lack of Mesoproterozoic material information all the time. In this article, it reports a set of Mesoproterozoic sedimentary rocks mainly composed of "metasandstone-marble" in the Dabie orogen for the first time. It analyzes the detrital zircon U-Pb chronology and Lu-Hf isotopic characteristics of the three samples in this strata, and the results show that the youngest average ages of three samples are: 1 556±13 Ma, 1 541±20 Ma and 1 584.3±24 Ma. This three ages are basically same within the error-range, which shows that the age of this strata should be the Mesoproterozoic. The metamorphic rims of detrital zircon record a metamorphic event at the age of 124.1±2.3 Ma, the U-Pb age histograms and Lu-Hf isotopes shows that the provenance characteristics of this strata are consistent with the Shennongjia Group. The main peaks of detrital zircon U-Pb ages of 2 682 Ma and 2 461 Ma record two important growth events of Dabie crystalline basement, and the peaks of 2 043 Ma, 1 803 Ma, 1 572 Ma implicate that the "Dabie block" may have participated in the aggregate event of Columbia supercontinent and become a part of it, and the "Dabie block" separated from the Columbia supercontinent during the breaking up event, and collided with the "Huangling continental nucleus" and became an important part of the basement of the Yangtze block during the Early Neoproterozoic.
2022, 47(4): 1349-1370.
doi: 10.3799/dqkx.2021.137
Abstract:
The slab breakoff of the Neo-Tethys Ocean after the initial India-Asia collisional has not been well constrained up to now. In this paper, zircon U-Pb dating, whole rock major and trace element and Sr-Nd isotopes analysis of the Early Eocene gabbros in the Rongma area on the southern margin of the Lhasa terrane have been carried out, the petrogenesis and geodynamical implication are discussed to further constrain the slab breakoff of the Neo-Tethyan oceanic slab.The results show that zircon U-Pb ages of 51±1 Ma have been obtained for Rongma gabbros, indicating they were formed in the Early Eocene.The Rongma gabbros are enriched in LILEs (such as Rb, Sr, Ba) and depleted in HFSEs (such as Nb, Ta, Ti) with initial 87Sr/86Sr=0.705 9-0.706 6 and εNd(t)=+3.1-+3.3. Compared with typical arc magmas, the Rongma gabbros have high contents of Zr (134.28×10-6-230.07×10-6), TiO2(1.04%-1.51%) and Nb (9.01×10-6-14.67×10-6), suggesting a geochemical intraplate-affinity. In addition, Rongma gabbros were derived from depleted lithospheric mantle which metasomatized by slab-derived fluids during Neo-Tethyan subduction, accompanied with significant contributions from deep asthenosphere mantle.Combined with the geochemical and geochronological data of the Cenozoic magmatic rocks from the southern Lhasa terrane, it further proposes that slab breakoff of the Neo-Tethys Ocean has occurred before 51 Ma.
The slab breakoff of the Neo-Tethys Ocean after the initial India-Asia collisional has not been well constrained up to now. In this paper, zircon U-Pb dating, whole rock major and trace element and Sr-Nd isotopes analysis of the Early Eocene gabbros in the Rongma area on the southern margin of the Lhasa terrane have been carried out, the petrogenesis and geodynamical implication are discussed to further constrain the slab breakoff of the Neo-Tethyan oceanic slab.The results show that zircon U-Pb ages of 51±1 Ma have been obtained for Rongma gabbros, indicating they were formed in the Early Eocene.The Rongma gabbros are enriched in LILEs (such as Rb, Sr, Ba) and depleted in HFSEs (such as Nb, Ta, Ti) with initial 87Sr/86Sr=0.705 9-0.706 6 and εNd(t)=+3.1-+3.3. Compared with typical arc magmas, the Rongma gabbros have high contents of Zr (134.28×10-6-230.07×10-6), TiO2(1.04%-1.51%) and Nb (9.01×10-6-14.67×10-6), suggesting a geochemical intraplate-affinity. In addition, Rongma gabbros were derived from depleted lithospheric mantle which metasomatized by slab-derived fluids during Neo-Tethyan subduction, accompanied with significant contributions from deep asthenosphere mantle.Combined with the geochemical and geochronological data of the Cenozoic magmatic rocks from the southern Lhasa terrane, it further proposes that slab breakoff of the Neo-Tethys Ocean has occurred before 51 Ma.
2022, 47(4): 1371-1382.
doi: 10.3799/dqkx.2021.138
Abstract:
Turquoise (CuAl6(PO4)4(OH)8·4(H2O)) is an important supergene gemstone mineral. The isotope of Cu, its major component, has been increasingly used to trace the origin of such gemstone. However, the tracing mechanism is not clear. Besides, it is still unclear whether Cu isotope composition changes significantly or not during the complex growth of turquoise, limiting the reliable application of trace ability via Cu isotope. In this work it used MC-ICP-MS instrument to measure the Cu isotopic compositions of banded turquoise, which were obtained from Zhushan County, the largest gem-grade deposit of turquoise in the world.The results show that the values of Cu isotopes are very high, however, they are remarkably identical in different bands of the turquoise sample (δ65Cu=10.99‰-11.54‰).The Cu isotope fractionation, in the precipitation of ore-bearing hydrothermal solution, thus has been limited (< 1‰). Instead, the significant fractionation of Cu isotope would occur mainly during the formation of ore-bearing hydrothermal solution. The Cu isotope composition of primary Cu sulfides lies usually within the range of 0±1‰, significantly lower than the value measured in this study, suggesting that the oxidation of the primary sulfide in the source area is the major factor for the significant fractionation of Cu isotope in the ore-bearing hydrothermal solution. The results are consistent with the data of typical turquoise deposits in the world, which confirms that the Cu isotopic composition of turquoise is mainly controlled by the source environment.Even though the turquoise has experienced periodic growth and produced banded structure, the Cu isotope of turquoises formed in the same mine hardly change. This work has explored the mechanism of tracing the origin of turquoise deposits via Cu isotope, and better understanded Cu isotope fractionation in low-temperature hydrothermal process.
Turquoise (CuAl6(PO4)4(OH)8·4(H2O)) is an important supergene gemstone mineral. The isotope of Cu, its major component, has been increasingly used to trace the origin of such gemstone. However, the tracing mechanism is not clear. Besides, it is still unclear whether Cu isotope composition changes significantly or not during the complex growth of turquoise, limiting the reliable application of trace ability via Cu isotope. In this work it used MC-ICP-MS instrument to measure the Cu isotopic compositions of banded turquoise, which were obtained from Zhushan County, the largest gem-grade deposit of turquoise in the world.The results show that the values of Cu isotopes are very high, however, they are remarkably identical in different bands of the turquoise sample (δ65Cu=10.99‰-11.54‰).The Cu isotope fractionation, in the precipitation of ore-bearing hydrothermal solution, thus has been limited (< 1‰). Instead, the significant fractionation of Cu isotope would occur mainly during the formation of ore-bearing hydrothermal solution. The Cu isotope composition of primary Cu sulfides lies usually within the range of 0±1‰, significantly lower than the value measured in this study, suggesting that the oxidation of the primary sulfide in the source area is the major factor for the significant fractionation of Cu isotope in the ore-bearing hydrothermal solution. The results are consistent with the data of typical turquoise deposits in the world, which confirms that the Cu isotopic composition of turquoise is mainly controlled by the source environment.Even though the turquoise has experienced periodic growth and produced banded structure, the Cu isotope of turquoises formed in the same mine hardly change. This work has explored the mechanism of tracing the origin of turquoise deposits via Cu isotope, and better understanded Cu isotope fractionation in low-temperature hydrothermal process.
2022, 47(4): 1383-1398.
doi: 10.3799/dqkx.2021.157
Abstract:
Monazite U-Pb geochronology plays an important role in dating magmatism, metamorphism and sedimentation. Because of its complex genesis, characterizing different types of monazite in terms of genetic mineralogy and chemistry is of great significance to interpret geochronology data. In this paper, it summarizes the occurrence (mineral paragenesis), crystal morphology and mineral geochemistry of different monazite in origins. The results show that magmatic monazite has straight edges, angular or embayment shape, showing oscillatory zoning, sector zoning and homogeneous internal structure, generally existing as inclusions that coexisting with feldspar and quartz. Metamorphic monazite is divided into high-grade and low-grade types. High-grade metamorphic monazite has straight edges, with concentric zoning, patchy zoning and intergrowth-like zoning or unzoned, generally associated with metamorphic porphyroblast (such as garnet). Low-grade metamorphic monazite occurs as discrete crystals with numerous inclusions, commonly exhibiting skeletal texture. Hydrothermal monazite has two types: the first type occurs as a cluster of multiple small monazite grain (< 50 μm) and the other type is grains showing oscillatory zoning and sector zoning. The rare earth element pattern of monazite is commonly right-leaning. Magmatic monazite has the strongest negative Eu anomalies with high Th, U, Pb, Y and HREE contents. High-grade metamorphic monazite has moderate negative Eu anomalies with high Th, U; HREE and Y are correlated with its coexisting minerals, whereas low-grade metamorphic monazite has insignificant negative Eu with low Th and U. Hydrothermal monazite has weak negative Eu, extremely low U and high Th/U ratio.
Monazite U-Pb geochronology plays an important role in dating magmatism, metamorphism and sedimentation. Because of its complex genesis, characterizing different types of monazite in terms of genetic mineralogy and chemistry is of great significance to interpret geochronology data. In this paper, it summarizes the occurrence (mineral paragenesis), crystal morphology and mineral geochemistry of different monazite in origins. The results show that magmatic monazite has straight edges, angular or embayment shape, showing oscillatory zoning, sector zoning and homogeneous internal structure, generally existing as inclusions that coexisting with feldspar and quartz. Metamorphic monazite is divided into high-grade and low-grade types. High-grade metamorphic monazite has straight edges, with concentric zoning, patchy zoning and intergrowth-like zoning or unzoned, generally associated with metamorphic porphyroblast (such as garnet). Low-grade metamorphic monazite occurs as discrete crystals with numerous inclusions, commonly exhibiting skeletal texture. Hydrothermal monazite has two types: the first type occurs as a cluster of multiple small monazite grain (< 50 μm) and the other type is grains showing oscillatory zoning and sector zoning. The rare earth element pattern of monazite is commonly right-leaning. Magmatic monazite has the strongest negative Eu anomalies with high Th, U, Pb, Y and HREE contents. High-grade metamorphic monazite has moderate negative Eu anomalies with high Th, U; HREE and Y are correlated with its coexisting minerals, whereas low-grade metamorphic monazite has insignificant negative Eu with low Th and U. Hydrothermal monazite has weak negative Eu, extremely low U and high Th/U ratio.
2022, 47(4): 1399-1414.
doi: 10.3799/dqkx.2021.150
Abstract:
Twins in plagioclase are very common, and the twin laws are of more than 10 types. However, these twin laws are difficultly distinguished under optic microscope. In this paper, it provides a method based on electron back-scatter diffraction (EBSD) technique to determine accurately twin laws of plagioclase in three kinds of rocks (granite, diorite and leptite), occurring in Dabie Mountain, China. It is found that albite-carlsbad compound twin (including Albite law, Carlsbad law and Albite-Carlsbad law) is the most common twin type in the plagioclase in these three rocks. However, this Albite-Carlsbad compound twin (including 3-4 individuals) under EBSD test is just a polysynthetic twin (only 2 individuals) under optic microscope, because there are 1-2 individuals appearing as small domains inside other individuals, which cannot be resolved under optic microscope. A small amount of Pericline law, Prism {110}, {130} and {130} laws are also found. A new compound twin among Carlsbad law, Prism{110} law and Prism{130} law is found. The Albite-Carlsbad law, Prism {130} law and Prism {130} law can co-exist together to form an intergrowth with three-six fold symmetry, but they cannot form a compound twin. Based on the limited amount of statistics in this paper, the probability of twin laws of plagioclase is unvaried among these three kinds of rocks, possibly reflecting that the twin laws of plagiocalse are not related closely to the formation condition of rocks. The method provided in this paper to analyze twin laws of plagioclase based on EBSD is effective and convenient, which will be helpful to statistic twin laws of plagioclase in rocks on a large scale, and find some new twin laws as well as new compound twins.
Twins in plagioclase are very common, and the twin laws are of more than 10 types. However, these twin laws are difficultly distinguished under optic microscope. In this paper, it provides a method based on electron back-scatter diffraction (EBSD) technique to determine accurately twin laws of plagioclase in three kinds of rocks (granite, diorite and leptite), occurring in Dabie Mountain, China. It is found that albite-carlsbad compound twin (including Albite law, Carlsbad law and Albite-Carlsbad law) is the most common twin type in the plagioclase in these three rocks. However, this Albite-Carlsbad compound twin (including 3-4 individuals) under EBSD test is just a polysynthetic twin (only 2 individuals) under optic microscope, because there are 1-2 individuals appearing as small domains inside other individuals, which cannot be resolved under optic microscope. A small amount of Pericline law, Prism {110}, {130} and {130} laws are also found. A new compound twin among Carlsbad law, Prism{110} law and Prism{130} law is found. The Albite-Carlsbad law, Prism {130} law and Prism {130} law can co-exist together to form an intergrowth with three-six fold symmetry, but they cannot form a compound twin. Based on the limited amount of statistics in this paper, the probability of twin laws of plagioclase is unvaried among these three kinds of rocks, possibly reflecting that the twin laws of plagiocalse are not related closely to the formation condition of rocks. The method provided in this paper to analyze twin laws of plagioclase based on EBSD is effective and convenient, which will be helpful to statistic twin laws of plagioclase in rocks on a large scale, and find some new twin laws as well as new compound twins.
2022, 47(4): 1415-1434.
doi: 10.3799/dqkx.2021.126
Abstract:
The Dazhuang deposit is a newly discovered medium-scale Nb-REE deposit which is located at the Fangcheng County of Henan Province on the southern margin of the North China craton. The Nb-REE orebodies are hosted in biotite syenite and hornblende nepheline syenite of Neoproterozoic Shuangshan alkaline pluton. In this paper, major and trace elements, U-Pb geochronology and in-situ Nd isotope studies were carried out on the titanite from the alkaline rocks by EPMA and LA-ICP-MS. The average contents of SiO2 (28.597%-31.169%), CaO (25.492%-28.949%) and TiO2 (34.126%-38.940%) in titanite are significantly lower than the theoretical values, whereas it contains relatively high contents of F (0.141%-1.086%), Al2O3 (1.573%-2.817%) and FeO (0.446%-2.147%). The titanite in Dazhuang deposit has a very high total amount of REE (∑REE=781.47×10-6-31 766.59×10-6). In the chondrite-normalized REE patterns, the rare earth distribution curve is obviously right-leaning, and the light and heavy rare earth fractionation is obvious. There are obvious negative δEu anomalies (0.27-0.86) and inconspicuous δCe anomalies (0.97-1.22), with Th/U values ranging from 1.40 to 11.86, suggesting that the titanite is magmatic origin. The formation temperature of Dazhuang alkaline rocks obtained by the titanite Zr thermometer is 667-964 ℃, with an average of 933 ℃. The titanite in Dazhuang deposit has very high Nb and REE contents, indicating that the titanite is an important ore-bearing mineral, and the Nb and REE are the result of the gradual enrichment of magma evolution. Formation ages of 848±35 Ma, 849±22 Ma, 843±30 Ma, 845±20 Ma, 845±24 Ma, and 849±40 Ma were obtained from the Nb-rich titanite samples, constraining that the mineralization age of Dazhuang Nb-REE deposit is Neoproterozoic, of which related to the breakup of the Rodinia supercontinent. Titanite has a relatively uniform Nd isotope (εNd(t)=-3.25 to -0.66) value, indicating that the original magma was derived from mantle where rich in phlogopite.
The Dazhuang deposit is a newly discovered medium-scale Nb-REE deposit which is located at the Fangcheng County of Henan Province on the southern margin of the North China craton. The Nb-REE orebodies are hosted in biotite syenite and hornblende nepheline syenite of Neoproterozoic Shuangshan alkaline pluton. In this paper, major and trace elements, U-Pb geochronology and in-situ Nd isotope studies were carried out on the titanite from the alkaline rocks by EPMA and LA-ICP-MS. The average contents of SiO2 (28.597%-31.169%), CaO (25.492%-28.949%) and TiO2 (34.126%-38.940%) in titanite are significantly lower than the theoretical values, whereas it contains relatively high contents of F (0.141%-1.086%), Al2O3 (1.573%-2.817%) and FeO (0.446%-2.147%). The titanite in Dazhuang deposit has a very high total amount of REE (∑REE=781.47×10-6-31 766.59×10-6). In the chondrite-normalized REE patterns, the rare earth distribution curve is obviously right-leaning, and the light and heavy rare earth fractionation is obvious. There are obvious negative δEu anomalies (0.27-0.86) and inconspicuous δCe anomalies (0.97-1.22), with Th/U values ranging from 1.40 to 11.86, suggesting that the titanite is magmatic origin. The formation temperature of Dazhuang alkaline rocks obtained by the titanite Zr thermometer is 667-964 ℃, with an average of 933 ℃. The titanite in Dazhuang deposit has very high Nb and REE contents, indicating that the titanite is an important ore-bearing mineral, and the Nb and REE are the result of the gradual enrichment of magma evolution. Formation ages of 848±35 Ma, 849±22 Ma, 843±30 Ma, 845±20 Ma, 845±24 Ma, and 849±40 Ma were obtained from the Nb-rich titanite samples, constraining that the mineralization age of Dazhuang Nb-REE deposit is Neoproterozoic, of which related to the breakup of the Rodinia supercontinent. Titanite has a relatively uniform Nd isotope (εNd(t)=-3.25 to -0.66) value, indicating that the original magma was derived from mantle where rich in phlogopite.
2022, 47(4): 1435-1458.
doi: 10.3799/dqkx.2021.079
Abstract:
Zhongdian Cu-Mo polymetallic ore-concentrated area is located in southern Yidun arc. The vast majority of deposits in this area are related to the two-stage magmatic activities of Late Triassic and Late Cretaceous. The research on the oxygen fugacity and differential mineralization of porphyry zircons in the two stages is currently weak.In this paper, LA-ICPMS trace element analysis was carried out on zircons from 5 types of rocks of 4 porphyry bodies, and the oxygen fugacity was estimated after the data were screened and tested.The calculated results of oxygen fugacity from high to low are: the Late Triassic quartz diorite porphyrite (Ce4+/Ce3+ value of 515) from the copper deposit in Disuga, the Late Triassic barren biotite granite (Ce4+/ Ce3+ value of 443) from Xiuwacu, the Late Cretaceous granodiorite porphyry (Ce4+/Ce3+ value of 368) from the molybdenum-copper deposit in Tongchanggou, the Late Cretaceous monzogranite (Ce4+/Ce3+ value of 237) from the molybdenum deposit in Relin, and the Late Cretaceous monzogranite (Ce4+/Ce3+ value of 104) from the tungsten-molybdenum deposit in Xiuwacu. Based on the previous research results, it is believed that Cu, either from a subduction-related porphyry copper deposit or a collision-related porphyry copper deposit, is mainly derived from the mantle, where high oxygen fugacity is necessary but insufficient in mineralization. The metallogenic elements of molybdenum and tungsten deposits related to collisional porphyry are predominantly derived from the ancient siliceous-alumina crust. Although the requirement in terms of oxygen fugacity is relatively low, oxygen fugacity is a major factor controlling the differential mineralization of molybdenum and tungsten. That is, the partially oxidized environment is favorable for the development of molybdenum deposits, while the partially reducing environment is favorable for the formation of tungsten deposits. When evaluating the mineral resources, more attention should be paid to the mantle source/crust source ratio and oxygen fugacity for porphyry copper deposits. The oxygen fugacity criteria in assessing the porphyry copper deposit should not be applied to the molybdenum and tungsten deposits, where a relatively lower oxygen fugacity or even partially reducing environment is still conducive to mineralization.
Zhongdian Cu-Mo polymetallic ore-concentrated area is located in southern Yidun arc. The vast majority of deposits in this area are related to the two-stage magmatic activities of Late Triassic and Late Cretaceous. The research on the oxygen fugacity and differential mineralization of porphyry zircons in the two stages is currently weak.In this paper, LA-ICPMS trace element analysis was carried out on zircons from 5 types of rocks of 4 porphyry bodies, and the oxygen fugacity was estimated after the data were screened and tested.The calculated results of oxygen fugacity from high to low are: the Late Triassic quartz diorite porphyrite (Ce4+/Ce3+ value of 515) from the copper deposit in Disuga, the Late Triassic barren biotite granite (Ce4+/ Ce3+ value of 443) from Xiuwacu, the Late Cretaceous granodiorite porphyry (Ce4+/Ce3+ value of 368) from the molybdenum-copper deposit in Tongchanggou, the Late Cretaceous monzogranite (Ce4+/Ce3+ value of 237) from the molybdenum deposit in Relin, and the Late Cretaceous monzogranite (Ce4+/Ce3+ value of 104) from the tungsten-molybdenum deposit in Xiuwacu. Based on the previous research results, it is believed that Cu, either from a subduction-related porphyry copper deposit or a collision-related porphyry copper deposit, is mainly derived from the mantle, where high oxygen fugacity is necessary but insufficient in mineralization. The metallogenic elements of molybdenum and tungsten deposits related to collisional porphyry are predominantly derived from the ancient siliceous-alumina crust. Although the requirement in terms of oxygen fugacity is relatively low, oxygen fugacity is a major factor controlling the differential mineralization of molybdenum and tungsten. That is, the partially oxidized environment is favorable for the development of molybdenum deposits, while the partially reducing environment is favorable for the formation of tungsten deposits. When evaluating the mineral resources, more attention should be paid to the mantle source/crust source ratio and oxygen fugacity for porphyry copper deposits. The oxygen fugacity criteria in assessing the porphyry copper deposit should not be applied to the molybdenum and tungsten deposits, where a relatively lower oxygen fugacity or even partially reducing environment is still conducive to mineralization.
2022, 47(4): 1459-1469.
doi: 10.3799/dqkx.2018.539
Abstract:
The oil discovery in the Paleogene of Palogue oilfield of the Melut basin is a milestone in the potentiality of new exploration play direction, it confirmed that the northern sag is hydrocarbon⁃rich sags. The Lower Cretaceous source rock is the major source rock of Melut basin, the Paleogene is its main seal reservoir assemblage.The formation mechanism and model of oil and gas accumulated were proposed based on the specific tectonic-stratigraphic assemblages and evolution history of the Melut basin. Oil and gas accumulation were influenced by mantle CO2. Analyzed characteristics of oil and hydrocarbon accumulation were investigated using a suite of burial history, fluid inclusions, CO2 and crude biomarker characteristics by taking Palogue oil reservoir as an example. The results show that the Palogue oil reservoir has experienced two episodes of hydrocarbon accumulations, the first episodes of the hydrocarbon accumulation happened in the Middle Paleogene, but the crude oil was strongly biodegraded.Since the Late Paleogene to Neogene, the second episodes of hydrocarbon accumulations accompany by mantle CO2.The oil and gas enter traps to form the anticlina reservoirs, CO2 under the gravity differentiation has carried on the intense gas washing effect to reservoir.
The oil discovery in the Paleogene of Palogue oilfield of the Melut basin is a milestone in the potentiality of new exploration play direction, it confirmed that the northern sag is hydrocarbon⁃rich sags. The Lower Cretaceous source rock is the major source rock of Melut basin, the Paleogene is its main seal reservoir assemblage.The formation mechanism and model of oil and gas accumulated were proposed based on the specific tectonic-stratigraphic assemblages and evolution history of the Melut basin. Oil and gas accumulation were influenced by mantle CO2. Analyzed characteristics of oil and hydrocarbon accumulation were investigated using a suite of burial history, fluid inclusions, CO2 and crude biomarker characteristics by taking Palogue oil reservoir as an example. The results show that the Palogue oil reservoir has experienced two episodes of hydrocarbon accumulations, the first episodes of the hydrocarbon accumulation happened in the Middle Paleogene, but the crude oil was strongly biodegraded.Since the Late Paleogene to Neogene, the second episodes of hydrocarbon accumulations accompany by mantle CO2.The oil and gas enter traps to form the anticlina reservoirs, CO2 under the gravity differentiation has carried on the intense gas washing effect to reservoir.
2022, 47(4): 1470-1482.
doi: 10.3799/dqkx.2021.056
Abstract:
The scanline mapping is a widely-used 1D field technique for fracture geometry observation. However, the 1D orientation observations from this technique poorly represent the 3D probability distribution. In this work, a numerical method for solving the 3D probability distribution of orientations is presented. It makes the assumption of observed dip direction-angle independence and adopts a mathematical relationship between the 1D observations and the 3D distribution. This method follows a two-step procedure that first using the relationship to solve the 3D cumulative, and then estimating the distribution type and parameters over the probabilities by employing the Kolmogorov-Smirnov approximation. Two cases of fractures (bedding planes and joints) illustrate that the presented method provides a smaller-error solution in comparison with the Fouché method. The minimum solution error of the presented method can be attained when the sample size is closely 150; if the sample size exceeds this value, the solution error will not decrease significantly as sample size increases. Moreover, the effectiveness of the presented method is investigated. The results show that the presented method performs effectively when applied to non-parallel fracture individuals, e.g. joints, whereas with low effectiveness when applied to sub-parallel fracture individuals, e.g. bedding planes.
The scanline mapping is a widely-used 1D field technique for fracture geometry observation. However, the 1D orientation observations from this technique poorly represent the 3D probability distribution. In this work, a numerical method for solving the 3D probability distribution of orientations is presented. It makes the assumption of observed dip direction-angle independence and adopts a mathematical relationship between the 1D observations and the 3D distribution. This method follows a two-step procedure that first using the relationship to solve the 3D cumulative, and then estimating the distribution type and parameters over the probabilities by employing the Kolmogorov-Smirnov approximation. Two cases of fractures (bedding planes and joints) illustrate that the presented method provides a smaller-error solution in comparison with the Fouché method. The minimum solution error of the presented method can be attained when the sample size is closely 150; if the sample size exceeds this value, the solution error will not decrease significantly as sample size increases. Moreover, the effectiveness of the presented method is investigated. The results show that the presented method performs effectively when applied to non-parallel fracture individuals, e.g. joints, whereas with low effectiveness when applied to sub-parallel fracture individuals, e.g. bedding planes.
2022, 47(4): 1483-1491.
doi: 10.3799/dqkx.2020.326
Abstract:
In this paper, based on the background of the earth pressure shield tunneling through the existing buildings in the extremely soft rock formation at a short distance, using the method of combining ABAQUS finite element numerical simulation and on-site monitoring, from the perspective of surface and building vertical displacement changes and their control, the impact of existing buildings on shield construction is studied. The actual measurement results show that the ground surface and buildings will show a trend of uplift first and then subsidence during the underpass of the shield. Among them, the surface and buildings will settle at a relatively large rate during the shield tail exit stage. Numerical simulation results show that the building changes the original stress field of the stratum, and the final settlement peak of the ground surface shifts and increases toward the direction of the building, and the width of the settlement trough is also increased in a smaller range. The research in this paper has a strong theoretical guiding significance for the earth pressure shield to penetrate the sensitive area of the formation. At the same time, in terms of engineering practice, a specific guidance plan for the use of construction parameter adjustment and reinforcement grouting for settlement control of the earth pressure shield is also proposed.
In this paper, based on the background of the earth pressure shield tunneling through the existing buildings in the extremely soft rock formation at a short distance, using the method of combining ABAQUS finite element numerical simulation and on-site monitoring, from the perspective of surface and building vertical displacement changes and their control, the impact of existing buildings on shield construction is studied. The actual measurement results show that the ground surface and buildings will show a trend of uplift first and then subsidence during the underpass of the shield. Among them, the surface and buildings will settle at a relatively large rate during the shield tail exit stage. Numerical simulation results show that the building changes the original stress field of the stratum, and the final settlement peak of the ground surface shifts and increases toward the direction of the building, and the width of the settlement trough is also increased in a smaller range. The research in this paper has a strong theoretical guiding significance for the earth pressure shield to penetrate the sensitive area of the formation. At the same time, in terms of engineering practice, a specific guidance plan for the use of construction parameter adjustment and reinforcement grouting for settlement control of the earth pressure shield is also proposed.
2022, 47(4): 1492-1506.
doi: 10.3799/dqkx.2021.070
Abstract:
In recent years, the rising of deep learning has significantly boosted the application of artificial intelligence techniques in fields such as seismic data processing, inversion, and interpretation. As a key technology for seismic exploration in the petroleum industry, the precision of seismic wave impedance inversion is essential to characterize hydrocarbon reservoir. A new algorithm is proposed for derivations of wave impedance model from seismic record data using data-driven temporal convolution network (TCN). The proposed algorithm takes the seismic amplitude data as input without relying on the initial inversion model and outputs the impedance information of the subsurface model by utilizing a few well log tag data from the work area and transforming the wave impedance inversion into a time series modeling task. In this paper, the TCN wave impedance inversion model is trained, validated, and tested using the Marmousi2 dataset. The results show high Pearson correlation coefficient (97.92%) and coefficient of determination (95.95%), respectively, on the test set, and also suggest well generalization for predicting wave impedance information far from the training area, and the proposed model significantly out performs previous related work in terms of prediction time and precision. The above results show case the excellent performance of TCN time series model in wave impedance inversion of complex stratigraphic and provide a new idea for seismic wave impedance inversion.
In recent years, the rising of deep learning has significantly boosted the application of artificial intelligence techniques in fields such as seismic data processing, inversion, and interpretation. As a key technology for seismic exploration in the petroleum industry, the precision of seismic wave impedance inversion is essential to characterize hydrocarbon reservoir. A new algorithm is proposed for derivations of wave impedance model from seismic record data using data-driven temporal convolution network (TCN). The proposed algorithm takes the seismic amplitude data as input without relying on the initial inversion model and outputs the impedance information of the subsurface model by utilizing a few well log tag data from the work area and transforming the wave impedance inversion into a time series modeling task. In this paper, the TCN wave impedance inversion model is trained, validated, and tested using the Marmousi2 dataset. The results show high Pearson correlation coefficient (97.92%) and coefficient of determination (95.95%), respectively, on the test set, and also suggest well generalization for predicting wave impedance information far from the training area, and the proposed model significantly out performs previous related work in terms of prediction time and precision. The above results show case the excellent performance of TCN time series model in wave impedance inversion of complex stratigraphic and provide a new idea for seismic wave impedance inversion.
2022, 47(4): 1507-1516.
doi: 10.3799/dqkx.2021.025
Abstract:
Guangxi is located in the convergent region among South China block, Indo-Chinese block and West Pacific plate. Due to its special tectonic position, there have been disputed on several basic geological problems in Guangxi region, such as the ascription and boundaries of tectonic units. Because the lithosphere has been reconstructed by the plate tectonic movements since the Cenozoic, the crust and upper mantle beneath Guangxi area have obvious differences in seismic wave velocity and temperature structures. It employs satellite gravity and magnetic data as well as regional gravity and aeromagnetic survey data to investigate the relationship between lithospheric density and magnetic susceptibility structure and upper crust structure in Guangxi area. Results suggest that the crustal density and upper-crust susceptibility structures coincide with the surface geological structures, and the density structures of the lower crust and the upper mantle are discontinuous beneath Guangxi area. Susceptibility structure implies that different extents of mid-lower crust decoupling had caused in different parts in Guangxi area. As a result, the scale and scope of mantle-derived materials into the upper crust were limited under the background of large-scale lithospheric reconstruction since Mesozoic. It may be the main reason why the upper mantle structure in Guangxi area is not corresponding to that of the crust. The mid-lower crust decoupling results in that the magmatic activity in Guangxi area is obviously weaker than that in the surrounding area since Cretaceous, especially in the northern region of the Pingxiang-Dali fault zone.
Guangxi is located in the convergent region among South China block, Indo-Chinese block and West Pacific plate. Due to its special tectonic position, there have been disputed on several basic geological problems in Guangxi region, such as the ascription and boundaries of tectonic units. Because the lithosphere has been reconstructed by the plate tectonic movements since the Cenozoic, the crust and upper mantle beneath Guangxi area have obvious differences in seismic wave velocity and temperature structures. It employs satellite gravity and magnetic data as well as regional gravity and aeromagnetic survey data to investigate the relationship between lithospheric density and magnetic susceptibility structure and upper crust structure in Guangxi area. Results suggest that the crustal density and upper-crust susceptibility structures coincide with the surface geological structures, and the density structures of the lower crust and the upper mantle are discontinuous beneath Guangxi area. Susceptibility structure implies that different extents of mid-lower crust decoupling had caused in different parts in Guangxi area. As a result, the scale and scope of mantle-derived materials into the upper crust were limited under the background of large-scale lithospheric reconstruction since Mesozoic. It may be the main reason why the upper mantle structure in Guangxi area is not corresponding to that of the crust. The mid-lower crust decoupling results in that the magmatic activity in Guangxi area is obviously weaker than that in the surrounding area since Cretaceous, especially in the northern region of the Pingxiang-Dali fault zone.
