2019 Vol. 44, No. 10
Display Method:
PDF 294KB
2019, 44(10): 3157-3177.
doi: 10.3799/dqkx.2019.980
Abstract:
Whether the Paleozoic tectonic units of the Northeast China region north to North China craton are continental blocks or orogenic belts is a hot-debated tectonic issue in the China geological field. In this paper, based on the comprehensive study of available geological data, it briefly summarizes and discusses geological features of those so-called continental blocks, and points out that the Ergun of them was a ancient block from the Late Neoproterozoic to the beginning of Paleozoic and changed into Paleozoic orogenic belt in the Cambrian, and that all the others are Paleozoic accretionary or island arc orogenic belts which are composed of Paleozoic ophilolites, magmatic complexes in the active continental margins, accretionary complexes, and minor PreNanhua rocks. And then, several problems, such as the relationship between the ancient metamorphic rocks and continental blocks, Jia-Meng block, and evolution and change of tectonic units in their tectonic features with time, are discussed.
Whether the Paleozoic tectonic units of the Northeast China region north to North China craton are continental blocks or orogenic belts is a hot-debated tectonic issue in the China geological field. In this paper, based on the comprehensive study of available geological data, it briefly summarizes and discusses geological features of those so-called continental blocks, and points out that the Ergun of them was a ancient block from the Late Neoproterozoic to the beginning of Paleozoic and changed into Paleozoic orogenic belt in the Cambrian, and that all the others are Paleozoic accretionary or island arc orogenic belts which are composed of Paleozoic ophilolites, magmatic complexes in the active continental margins, accretionary complexes, and minor PreNanhua rocks. And then, several problems, such as the relationship between the ancient metamorphic rocks and continental blocks, Jia-Meng block, and evolution and change of tectonic units in their tectonic features with time, are discussed.
2019, 44(10): 3178-3192.
doi: 10.3799/dqkx.2019.239
Abstract:
The study area is located in the key part between the North China and the Siberia plates, which may represent the final closure of the Paleo-Asian Ocean. Granodiorites were recognized in the Gashun area for the first time. According to petrogeochemistry, zircon U-Pb geochronology and Lu-Hf isotope analysis, the granodiorites yield an LA-MC-ICP-MS zircon UPb age of 294.8±2.7 Ma, suggesting that they were formed in the Early Permian. The rocks have SiO2=64.69%-67.64%, Al2O3=15.00%-15.52%, MgO=1.14%-1.77%, Na2O=1.41%-3.61%, and K2O=3.25%-3.98%. The content of ∑ REE varies from 157.89×10-6 to 174.43×10-6, the content of LREE varies from 147.86×10-6 to 149.55×10-6, and the content of HREE vary from 9.34×10-6 to 11.8×10-6. The rocks display rightly-inclined REE distribution curves, slightly negative Eu anomalies, highly fractionated LREE/HREE, and more enriched LREE relative to HREE. In the rocks, Rb and K were obviously enriched, and Ba and Sr (LILE) were depleted; Th was enriched and Nb, Ta and Ti etc. (HFSE) were depleted. Zircon 176Hf/177Hf changes from 0.282 673 to 0.282 791, and εHf(t) varies from 2.7 to 7.0. The two-stage model ages (TDM2) vary from 861 Ma to 1 129 Ma, and 176Lu/177Hf ranges from 0.000 486 to 0.000 734. Combined with petrogeochemical characteristics, this set of granodiorites is considered to be formed by island-arc magmatism, confirming that the Paleo-Asian Ocean was still open in the Early Permian.
The study area is located in the key part between the North China and the Siberia plates, which may represent the final closure of the Paleo-Asian Ocean. Granodiorites were recognized in the Gashun area for the first time. According to petrogeochemistry, zircon U-Pb geochronology and Lu-Hf isotope analysis, the granodiorites yield an LA-MC-ICP-MS zircon UPb age of 294.8±2.7 Ma, suggesting that they were formed in the Early Permian. The rocks have SiO2=64.69%-67.64%, Al2O3=15.00%-15.52%, MgO=1.14%-1.77%, Na2O=1.41%-3.61%, and K2O=3.25%-3.98%. The content of ∑ REE varies from 157.89×10-6 to 174.43×10-6, the content of LREE varies from 147.86×10-6 to 149.55×10-6, and the content of HREE vary from 9.34×10-6 to 11.8×10-6. The rocks display rightly-inclined REE distribution curves, slightly negative Eu anomalies, highly fractionated LREE/HREE, and more enriched LREE relative to HREE. In the rocks, Rb and K were obviously enriched, and Ba and Sr (LILE) were depleted; Th was enriched and Nb, Ta and Ti etc. (HFSE) were depleted. Zircon 176Hf/177Hf changes from 0.282 673 to 0.282 791, and εHf(t) varies from 2.7 to 7.0. The two-stage model ages (TDM2) vary from 861 Ma to 1 129 Ma, and 176Lu/177Hf ranges from 0.000 486 to 0.000 734. Combined with petrogeochemical characteristics, this set of granodiorites is considered to be formed by island-arc magmatism, confirming that the Paleo-Asian Ocean was still open in the Early Permian.
2019, 44(10): 3193-3208.
doi: 10.3799/dqkx.2019.027
Abstract:
The Late Paleozoic magmatic rocks with ductile deformation occurred in the Zhalantun region located in the middle of the Hegenshan-Heihe tectonic belt, which well record the tectonic evolution history of the Late Paleozoic, but the research degree is low. Through the field investigation, the geochronology and geochemistry of amphibolite lenticles from granitic mylonite in the Toudaogou, southern Zhalantun, are systematically studied, and the petrogenesis and tectonic setting of the amphibolite are discussed. It is found that the protolith of amphibolite is basaltic andesite, yielding an average zircon U-Pb age of 373.0±2.6 Ma which is equivalent to the volcanic rocks of Daminshan Group. The rocks belong to sodium series, which are enriched in light rare earth elements, large ion lithophile elements, but are depleted in high field strength elements. The zircon εHf(t) values of the amphibolite range from +5.39 to +10.06, similar to the features of the Xing'an island arc, suggesting that the protolith of amphibolite may be derived from the melting of a juvenile lower crust originating from depleted mantle which were modified by fluids stemmed from altered ocean crust, and supposedly formed in an fore arc basin above the subduction zone. In the Late Devonian, back-arc basin, inter-arc basin and fore-arc basin ocurred in the southeast region of Erguan-Xing'an block. The amphibolite and its surrounding granitic mylonite experienced multistage metamorphic deformation. The amphibolite yielded a metamorphic age of about 241.5±9.6 Ma, which may be related to the extension of the late evolution of the Tianshan-Xingmeng orogenic belt.
The Late Paleozoic magmatic rocks with ductile deformation occurred in the Zhalantun region located in the middle of the Hegenshan-Heihe tectonic belt, which well record the tectonic evolution history of the Late Paleozoic, but the research degree is low. Through the field investigation, the geochronology and geochemistry of amphibolite lenticles from granitic mylonite in the Toudaogou, southern Zhalantun, are systematically studied, and the petrogenesis and tectonic setting of the amphibolite are discussed. It is found that the protolith of amphibolite is basaltic andesite, yielding an average zircon U-Pb age of 373.0±2.6 Ma which is equivalent to the volcanic rocks of Daminshan Group. The rocks belong to sodium series, which are enriched in light rare earth elements, large ion lithophile elements, but are depleted in high field strength elements. The zircon εHf(t) values of the amphibolite range from +5.39 to +10.06, similar to the features of the Xing'an island arc, suggesting that the protolith of amphibolite may be derived from the melting of a juvenile lower crust originating from depleted mantle which were modified by fluids stemmed from altered ocean crust, and supposedly formed in an fore arc basin above the subduction zone. In the Late Devonian, back-arc basin, inter-arc basin and fore-arc basin ocurred in the southeast region of Erguan-Xing'an block. The amphibolite and its surrounding granitic mylonite experienced multistage metamorphic deformation. The amphibolite yielded a metamorphic age of about 241.5±9.6 Ma, which may be related to the extension of the late evolution of the Tianshan-Xingmeng orogenic belt.
2019, 44(10): 3209-3222.
doi: 10.3799/dqkx.2019.204
Abstract:
The Mesozoic granitoids exposed in Jinchanggouliang area of Chifeng are of great significance to the Mesozoic tectonic framework and evolution in the middle part of the north margin of North China. In this study, geochemical analysis, zircon U-Pb (LA-ICP-MS) dating and Hf isotopic compositions were carried out for the Xitaizi, Jinchanggouliang, Xiaoxigou and Xiduimiangou rock bodies. U-Pb dating of zircons from Xitaizi and Jinchanggouliang rock bodies are 220.5±2.1 Ma, 225.5±1.7 Ma, respectively, which are Late Triassic. The two rock bodies have similar right-leaning chondrite-normalized distribution curves and show a certain weak positive Eu anomaly. The εHf(t) values of the two rock bodies range from -8.0 to -3.0, and -5.7 to -2.3. U-Pb dating of zircons from Xiaoxigou rock body is 162.5±1.6 Ma, which is Late Jurassic. The (La/Yb)N ratios of the rock body are 0.14 to 0.51 and have a slightly left-leaning "V" shape chondrite-normalized distribution curve and a weak negative Eu anomaly. The εHf(t) value is -7.3 to -4.4. U-Pb dating of zircons from Xiduimiangou rock body is 128.2±1.1 Ma and has right-leaning chondrite-normalized distribution curve and shows a certain weak positive Eu anomaly. The εHf(t) value is -11.4 to -10.4. Analyses of the above chronology, rock geochemistry and Hf isotope data, combined with regional geological data, show that Xitaizi and Jinchanggouliang rock bodies are I-type granites, Xiaoxigou rock body is A1-type granite and Xiduimiangou rock body is C-type adakite rocks. The source regions are all from the partial melting of the lower crustal materials in the North China craton. Xitaizi rock body and Jinchanggouliang rock body may have formed under the extensional dynamic background of the ancient Asian Ocean closure. Xiaoxigou rock body was formed in the extensional tectonic background after the closure of the Mongol-Okhotsk Ocean. The Xiduimiangou rock body was formed under the tectonic background of local thickening in the process of crust thinning.
The Mesozoic granitoids exposed in Jinchanggouliang area of Chifeng are of great significance to the Mesozoic tectonic framework and evolution in the middle part of the north margin of North China. In this study, geochemical analysis, zircon U-Pb (LA-ICP-MS) dating and Hf isotopic compositions were carried out for the Xitaizi, Jinchanggouliang, Xiaoxigou and Xiduimiangou rock bodies. U-Pb dating of zircons from Xitaizi and Jinchanggouliang rock bodies are 220.5±2.1 Ma, 225.5±1.7 Ma, respectively, which are Late Triassic. The two rock bodies have similar right-leaning chondrite-normalized distribution curves and show a certain weak positive Eu anomaly. The εHf(t) values of the two rock bodies range from -8.0 to -3.0, and -5.7 to -2.3. U-Pb dating of zircons from Xiaoxigou rock body is 162.5±1.6 Ma, which is Late Jurassic. The (La/Yb)N ratios of the rock body are 0.14 to 0.51 and have a slightly left-leaning "V" shape chondrite-normalized distribution curve and a weak negative Eu anomaly. The εHf(t) value is -7.3 to -4.4. U-Pb dating of zircons from Xiduimiangou rock body is 128.2±1.1 Ma and has right-leaning chondrite-normalized distribution curve and shows a certain weak positive Eu anomaly. The εHf(t) value is -11.4 to -10.4. Analyses of the above chronology, rock geochemistry and Hf isotope data, combined with regional geological data, show that Xitaizi and Jinchanggouliang rock bodies are I-type granites, Xiaoxigou rock body is A1-type granite and Xiduimiangou rock body is C-type adakite rocks. The source regions are all from the partial melting of the lower crustal materials in the North China craton. Xitaizi rock body and Jinchanggouliang rock body may have formed under the extensional dynamic background of the ancient Asian Ocean closure. Xiaoxigou rock body was formed in the extensional tectonic background after the closure of the Mongol-Okhotsk Ocean. The Xiduimiangou rock body was formed under the tectonic background of local thickening in the process of crust thinning.
2019, 44(10): 3223-3236.
doi: 10.3799/dqkx.2019.145
Abstract:
Previous studies on the Fuxingtun Formation in Zhangguangcai Range are relatively inadequate, which has limited the understanding of regional Paleozoic tectonic evolution. The weighted average age of zircons from tuff of 30 test points in the Fuxingtun Formation is 392±3 Ma, and the minimum age of detrital zircons from arkose is 393 Ma, indicating that the Fuxingtun Formation was formed in the Middle Devonian. Al2O3/TiO2 average value is 19.58, and chondrite-normalized REE patterns have the characteristics of enrichment in light rare earth, stability in heavy rare earth and negative Eu anomaly, which, combined with detrital zircons age populations, indicates that the provenance of the Fuxingtun Formation was mainly derived from the Late Paleozoic intermediate-acid igneous rocks and the Early Paleozoic granitic rocks. The geochemical and regional volcanic characteristics reveal that the Fuxingtun Formation was formed in extensional environment. 489-551 Ma detrital zircons are widely distributed in the Late Paleozoic early strata in Songnen-Zhangguangcai Range massif and Jiamusi massif, suggesting that the two blocks had been combined before the deposition of the Fuxingtun Formation, which provides a new evidence for the combination of the two blocks in the late Early Paleozoic.
Previous studies on the Fuxingtun Formation in Zhangguangcai Range are relatively inadequate, which has limited the understanding of regional Paleozoic tectonic evolution. The weighted average age of zircons from tuff of 30 test points in the Fuxingtun Formation is 392±3 Ma, and the minimum age of detrital zircons from arkose is 393 Ma, indicating that the Fuxingtun Formation was formed in the Middle Devonian. Al2O3/TiO2 average value is 19.58, and chondrite-normalized REE patterns have the characteristics of enrichment in light rare earth, stability in heavy rare earth and negative Eu anomaly, which, combined with detrital zircons age populations, indicates that the provenance of the Fuxingtun Formation was mainly derived from the Late Paleozoic intermediate-acid igneous rocks and the Early Paleozoic granitic rocks. The geochemical and regional volcanic characteristics reveal that the Fuxingtun Formation was formed in extensional environment. 489-551 Ma detrital zircons are widely distributed in the Late Paleozoic early strata in Songnen-Zhangguangcai Range massif and Jiamusi massif, suggesting that the two blocks had been combined before the deposition of the Fuxingtun Formation, which provides a new evidence for the combination of the two blocks in the late Early Paleozoic.
2019, 44(10): 3237-3251.
doi: 10.3799/dqkx.2019.080
Abstract:
In order to further understand the relationship between the Mesozoic volcanic rocks and the Paleo-Pacific tectonics in the Great Xing'an Range area, in this study, it redetermines the Mesozoic volcanic strata in the Great Xing'an Range area through the regional 1:1 000 000 scale geological mapping work. A large number of Early Cretaceous volcanic rocks were identified from previous Late Jurassic volcanic units according to the rock association, paleontology, contact relationships and regional comparison, combining with geochronology files (including zircon U-Pb, 40Ar/39Ar and paleontology information). The relationship between the Early Cretaceous volcanic rocks formed within 145-100 Ma in the Great Xing'an Range area and Paleo-Pacific Tectonics is discussed by rock association and spatial-temporal distribution characteristics. It is found that both Early Cretaceous volcanic rocks of the early stage(145-130 Ma) and the later stage(130-100 Ma) are distributed in NNE direction, and with close special spatial co-existence relationship. The geochronology trend of the volcanic rocks becomes increasingly younger from northwest to southeast, which is in accordance with the backward subduction process of the Paleo-Pacific plate beneath the East Asian continent since the Early Cretaceous, recording the subduction event of Izanagi plate to the East Asian continent as well, indicating that the Early Cretaceous volcanic rocks (145-100 Ma) in the Great Xing'an Range area formed under the subduction setting dominated by the Izanagi plate beneath the East Asian continent.
In order to further understand the relationship between the Mesozoic volcanic rocks and the Paleo-Pacific tectonics in the Great Xing'an Range area, in this study, it redetermines the Mesozoic volcanic strata in the Great Xing'an Range area through the regional 1:1 000 000 scale geological mapping work. A large number of Early Cretaceous volcanic rocks were identified from previous Late Jurassic volcanic units according to the rock association, paleontology, contact relationships and regional comparison, combining with geochronology files (including zircon U-Pb, 40Ar/39Ar and paleontology information). The relationship between the Early Cretaceous volcanic rocks formed within 145-100 Ma in the Great Xing'an Range area and Paleo-Pacific Tectonics is discussed by rock association and spatial-temporal distribution characteristics. It is found that both Early Cretaceous volcanic rocks of the early stage(145-130 Ma) and the later stage(130-100 Ma) are distributed in NNE direction, and with close special spatial co-existence relationship. The geochronology trend of the volcanic rocks becomes increasingly younger from northwest to southeast, which is in accordance with the backward subduction process of the Paleo-Pacific plate beneath the East Asian continent since the Early Cretaceous, recording the subduction event of Izanagi plate to the East Asian continent as well, indicating that the Early Cretaceous volcanic rocks (145-100 Ma) in the Great Xing'an Range area formed under the subduction setting dominated by the Izanagi plate beneath the East Asian continent.
2019, 44(10): 3252-3264.
doi: 10.3799/dqkx.2019.086
Abstract:
The Gudonghe ductile shear zone, located in southern section of eastern Xing-Meng orogenic belt, is a key to understanding the Late Paleozoic-Early Mesozoic tectonic evolution in Yanbian area. In this paper, zircon U-Pb dating and microstructure analysis were done for constraining the deformation time and features of Gudonghe ductile shear zone. The results show that Gudonghe ductile shear zone represents a multi-phase suite of mylonites with dextral shear thrust characteristics and W gneissosity and SW lineation. Systematic measurement of finite strains of Quartz in later mylonites indicates that the K value is 0.19 to 0.31. And Kruhl thermometer shows that the deformation temperatures of ductile shear zone range from 450 to 550℃. Fractal analysis shows that the numbers of fractal dimension vary from 1.159 to 1.214. The paleo-stress values from dynamically recrystallized grain sizes of quartz are 16.83 to 20.09 MPa, while estimated strain rates are on the order of 10-12 to 10-14 s-1. The zircon U-Pb dating of granitic mylonite is 192±2 Ma, indicating that the deformation time of Gudonghe ductile shear zone is not earlier than Early Jurassic and the deformation features show the ductile shear zone thrust from southwest to northeast. However, the tectonic setting of Gudonghe ductile shear zone is mostly related to the subduction of paleo-Pacific beneath the Eurasian continent.
The Gudonghe ductile shear zone, located in southern section of eastern Xing-Meng orogenic belt, is a key to understanding the Late Paleozoic-Early Mesozoic tectonic evolution in Yanbian area. In this paper, zircon U-Pb dating and microstructure analysis were done for constraining the deformation time and features of Gudonghe ductile shear zone. The results show that Gudonghe ductile shear zone represents a multi-phase suite of mylonites with dextral shear thrust characteristics and W gneissosity and SW lineation. Systematic measurement of finite strains of Quartz in later mylonites indicates that the K value is 0.19 to 0.31. And Kruhl thermometer shows that the deformation temperatures of ductile shear zone range from 450 to 550℃. Fractal analysis shows that the numbers of fractal dimension vary from 1.159 to 1.214. The paleo-stress values from dynamically recrystallized grain sizes of quartz are 16.83 to 20.09 MPa, while estimated strain rates are on the order of 10-12 to 10-14 s-1. The zircon U-Pb dating of granitic mylonite is 192±2 Ma, indicating that the deformation time of Gudonghe ductile shear zone is not earlier than Early Jurassic and the deformation features show the ductile shear zone thrust from southwest to northeast. However, the tectonic setting of Gudonghe ductile shear zone is mostly related to the subduction of paleo-Pacific beneath the Eurasian continent.
2019, 44(10): 3265-3278.
doi: 10.3799/dqkx.2019.083
Abstract:
Due to the lack of chronological data to constrain the material composition and protolithic age of the Keluo complex, and the lack of chronological date matching the knowledge of the industry scholars, in this study, based on the systematic analysis of different genesis zircon characteristics, genesis and isotopic chronologic results of metamorphic rocks from Keluo complex in northwestern Lesser Xing'an Range, the protolith and metamorphic period of Keluo complex was studied. The LA-ICP-MS magmatic zircon U-Pb ages of three metamorphic rocks (including weak gneissic amphibolite, biotite plagioclase gneiss and biotite amphibole plagioclase gneiss) show that the youngest clastic zircons ages are 286.3±3.6 Ma, 284.3±3.1 Ma and 345.3±4.8 Ma, respectively, which means they formed in Early Permian and Early Carboniferous instead of the Precambrian. Age data also show that the source of clastic sedimentary rocks in Keluo complex is regional basement debris with widely developed two-stage magmatic rocks. Meanwhile, the LA-ICP-MS U-Pb ages of metamorphic zircons indicate that the protolith of Keluo complex underwent at least two-stage metamorphism after diagenesis, the Early-Middle Triassic(peak age 248.5 Ma) and the Early-Middle Jurassic (peak age 173.1 Ma) respectively. The early metamorphism may be a long-range effect of the southward subduction of the Mongolia-Okhotsk plate, while the late metamorphism was controlled by the superposition of the southward subduction of the Mongolia-Okhotsk Ocean and the westward subduction of the paleo-Pacific Ocean.
Due to the lack of chronological data to constrain the material composition and protolithic age of the Keluo complex, and the lack of chronological date matching the knowledge of the industry scholars, in this study, based on the systematic analysis of different genesis zircon characteristics, genesis and isotopic chronologic results of metamorphic rocks from Keluo complex in northwestern Lesser Xing'an Range, the protolith and metamorphic period of Keluo complex was studied. The LA-ICP-MS magmatic zircon U-Pb ages of three metamorphic rocks (including weak gneissic amphibolite, biotite plagioclase gneiss and biotite amphibole plagioclase gneiss) show that the youngest clastic zircons ages are 286.3±3.6 Ma, 284.3±3.1 Ma and 345.3±4.8 Ma, respectively, which means they formed in Early Permian and Early Carboniferous instead of the Precambrian. Age data also show that the source of clastic sedimentary rocks in Keluo complex is regional basement debris with widely developed two-stage magmatic rocks. Meanwhile, the LA-ICP-MS U-Pb ages of metamorphic zircons indicate that the protolith of Keluo complex underwent at least two-stage metamorphism after diagenesis, the Early-Middle Triassic(peak age 248.5 Ma) and the Early-Middle Jurassic (peak age 173.1 Ma) respectively. The early metamorphism may be a long-range effect of the southward subduction of the Mongolia-Okhotsk plate, while the late metamorphism was controlled by the superposition of the southward subduction of the Mongolia-Okhotsk Ocean and the westward subduction of the paleo-Pacific Ocean.
2019, 44(10): 3279-3296.
doi: 10.3799/dqkx.2019.200
Abstract:
The Hellestein subduction accretive mélange occurs in the middle part of the Hegen Mountain-Heihe suture zone, and its structural style is left thrust shear as a whole. The accretive mélange consists of matrix and rock complex. The main matrix is composed of mylonite, phyllonite, ultramylonite and a small amount of tuff, siltstone and fine sandstone. The tectonic environment is a pre-arc basin and the age is mainly Middle Cambrian. The rock complex includes oceanic island seamount rock block, back-arc oceanic basin oceanic crust fragment, volcanic arc block and rift continental block. The age of the complexes ranges mainly from Middle Cambrian to Middle Ordovician. Based on the deformation degree and contact relationship of subduction accretion complex, and combined with the age of matrix, rock complex and TTG rock series, the age of formation of Hellestein subduction accretion complex is determined as Middle-Late Ordovician. The subduction of this area began in the Early Cambrian and formed a volcanic island arc on the continental margin, then the back-arc basin developed in the Early Ordovician, and the oceanic crust appeared in the back-arc basin of the Middle Ordovician. At the same time, the Middle Cambrian matrix returned to rise in the Middle Ordovician after subduction. In the end, the back-arc oceanic basin soon died due to the continuous regional convergence and compression of plate in the Late Ordovician. The arc land began to collide, leading to bidirectional subduction. During the process of arc-continent collision, the new blocks of the back-arc basin formed in the late stage were mixed into the matrix formed in the early stage.
The Hellestein subduction accretive mélange occurs in the middle part of the Hegen Mountain-Heihe suture zone, and its structural style is left thrust shear as a whole. The accretive mélange consists of matrix and rock complex. The main matrix is composed of mylonite, phyllonite, ultramylonite and a small amount of tuff, siltstone and fine sandstone. The tectonic environment is a pre-arc basin and the age is mainly Middle Cambrian. The rock complex includes oceanic island seamount rock block, back-arc oceanic basin oceanic crust fragment, volcanic arc block and rift continental block. The age of the complexes ranges mainly from Middle Cambrian to Middle Ordovician. Based on the deformation degree and contact relationship of subduction accretion complex, and combined with the age of matrix, rock complex and TTG rock series, the age of formation of Hellestein subduction accretion complex is determined as Middle-Late Ordovician. The subduction of this area began in the Early Cambrian and formed a volcanic island arc on the continental margin, then the back-arc basin developed in the Early Ordovician, and the oceanic crust appeared in the back-arc basin of the Middle Ordovician. At the same time, the Middle Cambrian matrix returned to rise in the Middle Ordovician after subduction. In the end, the back-arc oceanic basin soon died due to the continuous regional convergence and compression of plate in the Late Ordovician. The arc land began to collide, leading to bidirectional subduction. During the process of arc-continent collision, the new blocks of the back-arc basin formed in the late stage were mixed into the matrix formed in the early stage.
2019, 44(10): 3297-3313.
doi: 10.3799/dqkx.2019.129
Abstract:
In order to determine the rock types, petrogenic age and tectonic setting of the Mesozoic granites from the Dandong area in Liaodong peninsula, the lithology identification, zircon LA-ICP-MS U-Pb dating, major and trace elements, and Hf isotope data for the Sanguliu, Wulongbei and Dingqishan granites are presented in this paper. The LA-ICP-MS U-Pb ages of the Sanguliu pluton of the porphyritic biotite monzogranite and the medium-coarse grained biotite monzogranite are 137.2±1.2 Ma and 123.2±1.3 Ma. The LA-ICP-MS U-Pb geochronology of the Wulongbei medium-fine grained biotite monzogranite and Dinqishan alkali feldspar granite are 146.8±0.8 Ma and 121.1±1.5 Ma.The results of elemental and isotope geochemistry show that the Sanguliu granodiorite belong to shoshonite series, while the porphyritic biotite monzogranite and the medium-coarse grained biotite monzogranite, the Wulongbei medium-fine grained biotite monzogranite and Dinqishan alkali feldspar granite belong to high potassium Ca-alkaline series. Their aluminum indexes (A/CNK ratios) are all less than 1.1, showing the special feature of I-type granite. The samples of the Sanguliu, Wulongbei and Dingqishan granites are enriched in LREE and LILE, but depleted in HREE and HFSE with minor negative Eu anomalies. The zircon εHf(t) values of the three pluton are from -22.40 to -9.77, TDM2 are between 2 999 and 1 915 Ma, suggesting that the Sanguliu, Wulongbei and Dingqishan granites were mainly derived from the partial melting of the Paleoproterozoic crustal material. Combined with regional tectonic evolution, it is proposed that the Sanguliu, Wulongbei and Dinqishan rock plutonic diagenetic tectonic environment is the active continental margin, the Wulongbei rock may be formed in the compression tectonic environment and the Sanguliu rock and Dinqishan rock may be formed in the extension tectonic environment, which is closely associated with the subduction of the Paleo-Pacific plate.
In order to determine the rock types, petrogenic age and tectonic setting of the Mesozoic granites from the Dandong area in Liaodong peninsula, the lithology identification, zircon LA-ICP-MS U-Pb dating, major and trace elements, and Hf isotope data for the Sanguliu, Wulongbei and Dingqishan granites are presented in this paper. The LA-ICP-MS U-Pb ages of the Sanguliu pluton of the porphyritic biotite monzogranite and the medium-coarse grained biotite monzogranite are 137.2±1.2 Ma and 123.2±1.3 Ma. The LA-ICP-MS U-Pb geochronology of the Wulongbei medium-fine grained biotite monzogranite and Dinqishan alkali feldspar granite are 146.8±0.8 Ma and 121.1±1.5 Ma.The results of elemental and isotope geochemistry show that the Sanguliu granodiorite belong to shoshonite series, while the porphyritic biotite monzogranite and the medium-coarse grained biotite monzogranite, the Wulongbei medium-fine grained biotite monzogranite and Dinqishan alkali feldspar granite belong to high potassium Ca-alkaline series. Their aluminum indexes (A/CNK ratios) are all less than 1.1, showing the special feature of I-type granite. The samples of the Sanguliu, Wulongbei and Dingqishan granites are enriched in LREE and LILE, but depleted in HREE and HFSE with minor negative Eu anomalies. The zircon εHf(t) values of the three pluton are from -22.40 to -9.77, TDM2 are between 2 999 and 1 915 Ma, suggesting that the Sanguliu, Wulongbei and Dingqishan granites were mainly derived from the partial melting of the Paleoproterozoic crustal material. Combined with regional tectonic evolution, it is proposed that the Sanguliu, Wulongbei and Dinqishan rock plutonic diagenetic tectonic environment is the active continental margin, the Wulongbei rock may be formed in the compression tectonic environment and the Sanguliu rock and Dinqishan rock may be formed in the extension tectonic environment, which is closely associated with the subduction of the Paleo-Pacific plate.
2019, 44(10): 3314-3332.
doi: 10.3799/dqkx.2019.111
Abstract:
The identification and comparation of terrestrial Permian-Triassic have great significance to the understanding of coeval major global biological and environmental events. In this paper, it focuses on the newly discovered Lower Triassic Laolongtou Formation in Kundu area of Arkhorqin Banner, southern Great Xing'an Range. The contact relationship of Permian-Triassic stratigraphy was studied in particular, plant fossils and palynological fossils above and below the boundary were collected, and the zircon isotopic U-Pb analysis from the volcanic interlayer in the Laolongtou Formation were also analyzed. It is confirmed that there is a parallel unconformity contact relationship between the Laolongtou Formation and the underlying Linxi Formation, and there is a short sedimentary gap between them. The biostratigraphic records show that the Linxi Formation was formed in the Late Permian, however, the Laolongtou Formation was lack of fossil evidence, which may be related to the extinction event at the intersection of the Permian and Triassic. Three isotopes ages from Laolongtou Formation were 251.5±2.2 Ma, 249.7±2.5 Ma and 249.5±1.8 Ma, indicating that they formed at Early Triassic. However, the exact location of the Permian-Triassic boundary needs further study. The Early Triassic magmatic events which widely outcropped at southern Great Xing'an Range area probably related with the closure of Paleo-Asian Ocean. The Paleo-Asian Ocean finally closed along the Xilamulun River suture zone at least until the Early Triassic, and the sedimentary of Laolongtou Formation is the product of collision at its both sides.
The identification and comparation of terrestrial Permian-Triassic have great significance to the understanding of coeval major global biological and environmental events. In this paper, it focuses on the newly discovered Lower Triassic Laolongtou Formation in Kundu area of Arkhorqin Banner, southern Great Xing'an Range. The contact relationship of Permian-Triassic stratigraphy was studied in particular, plant fossils and palynological fossils above and below the boundary were collected, and the zircon isotopic U-Pb analysis from the volcanic interlayer in the Laolongtou Formation were also analyzed. It is confirmed that there is a parallel unconformity contact relationship between the Laolongtou Formation and the underlying Linxi Formation, and there is a short sedimentary gap between them. The biostratigraphic records show that the Linxi Formation was formed in the Late Permian, however, the Laolongtou Formation was lack of fossil evidence, which may be related to the extinction event at the intersection of the Permian and Triassic. Three isotopes ages from Laolongtou Formation were 251.5±2.2 Ma, 249.7±2.5 Ma and 249.5±1.8 Ma, indicating that they formed at Early Triassic. However, the exact location of the Permian-Triassic boundary needs further study. The Early Triassic magmatic events which widely outcropped at southern Great Xing'an Range area probably related with the closure of Paleo-Asian Ocean. The Paleo-Asian Ocean finally closed along the Xilamulun River suture zone at least until the Early Triassic, and the sedimentary of Laolongtou Formation is the product of collision at its both sides.
2019, 44(10): 3333-3345.
doi: 10.3799/dqkx.2019.185
Abstract:
The meta-gabbro, distributed in the Longchang area, eastern part of the North China craton, yields a zircon U-Pb age of 2 113±15 Ma by LA-ICP-MS. Detailed geochemistry analyses, whole rock Nd isotope and zircon U-Pb and in-situ Hf isotope analyses were made to confine tectonic settings of the Jiao-Liao-Ji orogenic belt and other crucial problems. The gabbro samples studied show calc-alkaline to high potassic alkaline series features with weak alteration and also low content of TiO2(< 1.31%), moderate content of MgO (6.88%-7.62%), FeOT(11.91%-14.25%) and K2O (0.85%-1.23%). The studied samples are characterized with low REE content and show weak REE fractionation and depletion in high field strength elements like P and Hf. The samples also show enrichment in large ion lithophile elements like Rb, Ba and K, and enrichment in Nd isotope content, with εNd(t) values of -1.6 to 2.6. (176Hf/177Hf)i of zircon from the meta-gabbro samples ranging from 0.281 497 to 0.281 612, and the calculated εHf(t) values ranging from 2.2 to 6.3. The calculated Hf modal ages are 2.25 to 2.33 Ga. Several crucial diagrams from meta-gabbro sample analysis results show far distance from MORB or OIB both of which are typical basalts distributed in a rift geological setting. E-MORB with continental crust component mixed in may be the exact origin of the meta-basalts in the Longchang area. It can be concluded that there was ocean crust subduction in~2.1 Ga within the Jiao-Liao-Ji orogenic belt, with possible paleo-arc and the evolution model of the Jiao-Liao-Ji orogenic belt is more like an arc-continental collision model.
The meta-gabbro, distributed in the Longchang area, eastern part of the North China craton, yields a zircon U-Pb age of 2 113±15 Ma by LA-ICP-MS. Detailed geochemistry analyses, whole rock Nd isotope and zircon U-Pb and in-situ Hf isotope analyses were made to confine tectonic settings of the Jiao-Liao-Ji orogenic belt and other crucial problems. The gabbro samples studied show calc-alkaline to high potassic alkaline series features with weak alteration and also low content of TiO2(< 1.31%), moderate content of MgO (6.88%-7.62%), FeOT(11.91%-14.25%) and K2O (0.85%-1.23%). The studied samples are characterized with low REE content and show weak REE fractionation and depletion in high field strength elements like P and Hf. The samples also show enrichment in large ion lithophile elements like Rb, Ba and K, and enrichment in Nd isotope content, with εNd(t) values of -1.6 to 2.6. (176Hf/177Hf)i of zircon from the meta-gabbro samples ranging from 0.281 497 to 0.281 612, and the calculated εHf(t) values ranging from 2.2 to 6.3. The calculated Hf modal ages are 2.25 to 2.33 Ga. Several crucial diagrams from meta-gabbro sample analysis results show far distance from MORB or OIB both of which are typical basalts distributed in a rift geological setting. E-MORB with continental crust component mixed in may be the exact origin of the meta-basalts in the Longchang area. It can be concluded that there was ocean crust subduction in~2.1 Ga within the Jiao-Liao-Ji orogenic belt, with possible paleo-arc and the evolution model of the Jiao-Liao-Ji orogenic belt is more like an arc-continental collision model.
2019, 44(10): 3346-3360.
doi: 10.3799/dqkx.2019.209
Abstract:
The Xinglong area in the northern Da-Hinggan Mountains is located in the north of the Xinlin-Xiguitu suture zone and the southern margin of the Erguna block and belongs to the northern Xingmeng orogenic belt. However, the tectonic settings for the Cambrian plutons have been still in debate due to the absence of available data, which hampers our understanding of the early tectonic evolution of Xinlin-Xiguitu Ocean. In this study, it carries out a detailed investigation on the Neihe pluton from the Xinglong area using zircon U-Pb dating and whole-rock geochemistry to constrain the age and petrogenesis, and provides new evidence for solving the problems. The LA-ICP-MS zircon U-Pb ages for the quartz monzonite and pyroxene diorite are 508±3 Ma and 507±5 Ma, respectively, indicating that they were formed during the Middle Cambrian. Geochemically, the quartz monzonite and pyroxene diorite are high-K calc-alkaline and calc-alkaline series, and both are enriched in light rare earth elements and show variable degrees of negative anomalies of Nb, Ta and Ti. The Nb/Ta ratios for the quartz monzonite and pyroxene diorite are 22.41 and 17.12, respectively, and they are low in the contents of the MgO(< 8%) and Mg# values (42-70). These geochemical features are typical of subduction-related rocks, suggesting that the studied rocks may be generated by partial melting of a primitive mantle source modified by subduction-related fluids. Combined with available data from coeval plutons, ophiolitic mélanges, and blueschists, the Neihe pluton should be generated in an active continental margin setting related to the Cambrian northward subduction of the northern Xinlin-Xiguitu Ocean. New findings provide important evidence for the early subductionrelated tectonic evolution of the Xingmeng orogenic belt.
The Xinglong area in the northern Da-Hinggan Mountains is located in the north of the Xinlin-Xiguitu suture zone and the southern margin of the Erguna block and belongs to the northern Xingmeng orogenic belt. However, the tectonic settings for the Cambrian plutons have been still in debate due to the absence of available data, which hampers our understanding of the early tectonic evolution of Xinlin-Xiguitu Ocean. In this study, it carries out a detailed investigation on the Neihe pluton from the Xinglong area using zircon U-Pb dating and whole-rock geochemistry to constrain the age and petrogenesis, and provides new evidence for solving the problems. The LA-ICP-MS zircon U-Pb ages for the quartz monzonite and pyroxene diorite are 508±3 Ma and 507±5 Ma, respectively, indicating that they were formed during the Middle Cambrian. Geochemically, the quartz monzonite and pyroxene diorite are high-K calc-alkaline and calc-alkaline series, and both are enriched in light rare earth elements and show variable degrees of negative anomalies of Nb, Ta and Ti. The Nb/Ta ratios for the quartz monzonite and pyroxene diorite are 22.41 and 17.12, respectively, and they are low in the contents of the MgO(< 8%) and Mg# values (42-70). These geochemical features are typical of subduction-related rocks, suggesting that the studied rocks may be generated by partial melting of a primitive mantle source modified by subduction-related fluids. Combined with available data from coeval plutons, ophiolitic mélanges, and blueschists, the Neihe pluton should be generated in an active continental margin setting related to the Cambrian northward subduction of the northern Xinlin-Xiguitu Ocean. New findings provide important evidence for the early subductionrelated tectonic evolution of the Xingmeng orogenic belt.
2019, 44(10): 3361-3377.
doi: 10.3799/dqkx.2019.215
Abstract:
It is a highly controversial topic about the closure of the Paleo-Asian Ocean. Based on the geochemistry, zircon U-Pb dating and Lu-Hf isotope studies of Bayanchagan pluton in Balinyouqi, in this paper, it discusses its formation age, petrogenesis and the regional tectonic setting. Bayanchagan pluton is two-mica monzogranites. LA-ICP-MS zircon U-Pb dating indicates the two-mica monzogranite formed in the Middle-Late Triassic(232.0-241.7 Ma). The two-mica monzogranite is high in SiO2, Al2O3 and low in MgO, Fe2O3, belonging to strongly peraluminous series(A/CNK=1.10-1.25), enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements(Nb, Ta), showing that it is S-type granite. Hf isotopic analysis results show εHf(t) values of -1.8 to +4.01, two-stage model ages ranging from 1 006 Ma to 1 380 Ma, respectively, indicating that the primary magma was derived from the partial melting of a thickened crust. Combined with the studies of the ophiolitic melange, magmatic belt and sedimentary environment of Late Paleozoic, collision related granites, and so on, it is suggested that the eastern segment of the Paleo-Asian Ocean closed in the Late Permian-Early Triassic, and was at the period of continental collision during Triassic.
It is a highly controversial topic about the closure of the Paleo-Asian Ocean. Based on the geochemistry, zircon U-Pb dating and Lu-Hf isotope studies of Bayanchagan pluton in Balinyouqi, in this paper, it discusses its formation age, petrogenesis and the regional tectonic setting. Bayanchagan pluton is two-mica monzogranites. LA-ICP-MS zircon U-Pb dating indicates the two-mica monzogranite formed in the Middle-Late Triassic(232.0-241.7 Ma). The two-mica monzogranite is high in SiO2, Al2O3 and low in MgO, Fe2O3, belonging to strongly peraluminous series(A/CNK=1.10-1.25), enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements(Nb, Ta), showing that it is S-type granite. Hf isotopic analysis results show εHf(t) values of -1.8 to +4.01, two-stage model ages ranging from 1 006 Ma to 1 380 Ma, respectively, indicating that the primary magma was derived from the partial melting of a thickened crust. Combined with the studies of the ophiolitic melange, magmatic belt and sedimentary environment of Late Paleozoic, collision related granites, and so on, it is suggested that the eastern segment of the Paleo-Asian Ocean closed in the Late Permian-Early Triassic, and was at the period of continental collision during Triassic.
2019, 44(10): 3378-3392.
doi: 10.3799/dqkx.2019.226
Abstract:
Zircon U-Pb dating and geochemical analysis were carried out to classify and compare the acidic volcanic rocks in Aohan, Inner Mongolia. Zircon U-Pb ages of rhyolite and rhyolitic crystal tuff are 122.8±2.3 Ma and 122.1±1.9 Ma, belonging to the Yixian Formation of Early Cretaceous. Late Jurassic rhyolite contains of high SiO2 and alkali (Na2O+ K2O), low Al2O3 and low total REE, with negative Eu anomaly, indicating REE "tetrad effect". It is enriched in large ion lithophile elements Rb, Th, U, K and and depleted in high field strength elements Ba, Sr, P and Ti. Early Cretaceous rhyolite has high contents of SiO2, alkali (Na2O+K2O) and Al2O3; it is characterized by high total REE, enrichment of LREE, clear fractionation of light and heavy rare earth, weak negative Eu anomaly; enrichment of large ion lithophile elements K, Rb, Ba, Th, U, and depletion of Nb, Ta, Sr, P and Ti. In this paper, the Late Jurassic acid volcanic rocks in Aohan area are disintegrated and most of them are classified as Early Cretaceous Yixian Formation for the first time. Late Jurassic rhyolite may be highly differentiated rhyolite. Geochemical characteristics show that it was formed under relatively low pressure environment and may have been originated from partial melting of upper and middle crustal materials. Early Cretaceous rhyolite shows the geochemical characteristics of adakitic rocks, which may formed in the thicker lower crustal environment.
Zircon U-Pb dating and geochemical analysis were carried out to classify and compare the acidic volcanic rocks in Aohan, Inner Mongolia. Zircon U-Pb ages of rhyolite and rhyolitic crystal tuff are 122.8±2.3 Ma and 122.1±1.9 Ma, belonging to the Yixian Formation of Early Cretaceous. Late Jurassic rhyolite contains of high SiO2 and alkali (Na2O+ K2O), low Al2O3 and low total REE, with negative Eu anomaly, indicating REE "tetrad effect". It is enriched in large ion lithophile elements Rb, Th, U, K and and depleted in high field strength elements Ba, Sr, P and Ti. Early Cretaceous rhyolite has high contents of SiO2, alkali (Na2O+K2O) and Al2O3; it is characterized by high total REE, enrichment of LREE, clear fractionation of light and heavy rare earth, weak negative Eu anomaly; enrichment of large ion lithophile elements K, Rb, Ba, Th, U, and depletion of Nb, Ta, Sr, P and Ti. In this paper, the Late Jurassic acid volcanic rocks in Aohan area are disintegrated and most of them are classified as Early Cretaceous Yixian Formation for the first time. Late Jurassic rhyolite may be highly differentiated rhyolite. Geochemical characteristics show that it was formed under relatively low pressure environment and may have been originated from partial melting of upper and middle crustal materials. Early Cretaceous rhyolite shows the geochemical characteristics of adakitic rocks, which may formed in the thicker lower crustal environment.
2019, 44(10): 3393-3408.
doi: 10.3799/dqkx.2019.152
Abstract:
The Beipiao Formation within the Jinyang basin at West Liaoning is an important coal-bearing and hydrocarbongenerating potential bed, the determination of its formation age and paleoclimatic environment is very important for its research. At present study, 20 palynological samples were collected from the section of Beipiao Formation at Kuntouyingzi area, and the zircon U-Pb ages of granite porphyry which intruded in the Beipiao Formation and andesite that from the lower strata of Xinglonggou Formation were analyzed. 3 sporo-pollen assemblages which represented by Monosulcites-Chasmatosporites-Polycingulatisporites of lower part, Protopinus-Paleoconiferus-Alisporites of middle part and Monosulcites-Protopinus-Paleoconiferus of upper part were identified from Beipiao Formation after systematical analysis, identification and research. The U-Pb dating results of zircon are 172.6 Ma and 189 Ma, respectively. The formation age of Beipiao Formation is determined as middle and late Early Jurassic and the bottom-up reflects the characteristics of the transition from a subhumid north subtropical climate to a humid temperate climate.
The Beipiao Formation within the Jinyang basin at West Liaoning is an important coal-bearing and hydrocarbongenerating potential bed, the determination of its formation age and paleoclimatic environment is very important for its research. At present study, 20 palynological samples were collected from the section of Beipiao Formation at Kuntouyingzi area, and the zircon U-Pb ages of granite porphyry which intruded in the Beipiao Formation and andesite that from the lower strata of Xinglonggou Formation were analyzed. 3 sporo-pollen assemblages which represented by Monosulcites-Chasmatosporites-Polycingulatisporites of lower part, Protopinus-Paleoconiferus-Alisporites of middle part and Monosulcites-Protopinus-Paleoconiferus of upper part were identified from Beipiao Formation after systematical analysis, identification and research. The U-Pb dating results of zircon are 172.6 Ma and 189 Ma, respectively. The formation age of Beipiao Formation is determined as middle and late Early Jurassic and the bottom-up reflects the characteristics of the transition from a subhumid north subtropical climate to a humid temperate climate.
2019, 44(10): 3409-3453.
doi: 10.3799/dqkx.2018.392
Abstract:
Due to the unique physicochemical characteristics, diamonds are of great significance in economic production and scientific research. Diamonds record valuable information about the physicochemical conditions and compositions of Earth's deep mantle and even the core-mantle boundary. Diamond mainly consists of carbon, with minor impurities such as nitrogen, boron and hydrogen. Of these impurities, nitrogen and boron play important roles in the classification of diamonds. Carbon and nitrogen are vital elements for life, the cycles of which are closely related to the environment that humans live in. Diamonds can provide clues for the deep carbon and nitrogen cycle on the Earth. Studies on the mineral inclusions show that diamonds mainly form between a depth window of 150-200 km, with 1% of the diamond population forming in the asthenosphere (>200 km), the mantle transition zone, the lower mantle or even the core-mantle boundary. China hosts different types of diamonds, however, diamonds of economic significance only exist in the Shandong Province and Liaoning Province. The discovery of ophiolite-hosted diamonds (also called ophiolitic diamonds) is an important progress in the study of diamonds. Ophiolite-hosted diamonds in China have been discovered in ophiolitic peridotites and chromitites in different orogenic belts, and have been accepted as a new occurrence for diamonds. Diamond research in China is very limited, which has hampered the understanding of diamond genesis and diamond exploration. New analytical methods need to be applied on diamond and country rock research to provide new constraints on diamond formation and theoretical basis for diamond explorations.
Due to the unique physicochemical characteristics, diamonds are of great significance in economic production and scientific research. Diamonds record valuable information about the physicochemical conditions and compositions of Earth's deep mantle and even the core-mantle boundary. Diamond mainly consists of carbon, with minor impurities such as nitrogen, boron and hydrogen. Of these impurities, nitrogen and boron play important roles in the classification of diamonds. Carbon and nitrogen are vital elements for life, the cycles of which are closely related to the environment that humans live in. Diamonds can provide clues for the deep carbon and nitrogen cycle on the Earth. Studies on the mineral inclusions show that diamonds mainly form between a depth window of 150-200 km, with 1% of the diamond population forming in the asthenosphere (>200 km), the mantle transition zone, the lower mantle or even the core-mantle boundary. China hosts different types of diamonds, however, diamonds of economic significance only exist in the Shandong Province and Liaoning Province. The discovery of ophiolite-hosted diamonds (also called ophiolitic diamonds) is an important progress in the study of diamonds. Ophiolite-hosted diamonds in China have been discovered in ophiolitic peridotites and chromitites in different orogenic belts, and have been accepted as a new occurrence for diamonds. Diamond research in China is very limited, which has hampered the understanding of diamond genesis and diamond exploration. New analytical methods need to be applied on diamond and country rock research to provide new constraints on diamond formation and theoretical basis for diamond explorations.
2019, 44(10): 3454-3468.
doi: 10.3799/dqkx.2019.085
Abstract:
The discovery of petrological evidence for the ocean-continent conversion (intra-oceanic arc) makes it possible to identify, reconstruct and study the ocean-continent conversion. In this paper, the ophiolite in the Diyanmiao subduction accretion complex belt in the eastern margin of the Central Asian orogenic belt was studied in terms of petrogeochemistry, Sr-Nd isotope and zircon U-Pb geochronology, and a set of igneous assemblages in the intra-oceanic arc were identified. The zircon U-Pb concordant age of MORB-like basalt is 286.1±6.1 Ma, representing the period of initial subduction in the ocean. The zircon U-Pb concordant age of HMA is 283.7±4.7 Ma, which represents the age of magmatism when subduction deepened after the first magmatic action. The zircon U-Pb concordant age of IAT is 241±5 Ma, indicating that the paleo-Asian Ocean developed towards continental transition of normal island arc magmatism in the Early Triassic. The sequence of rock assemblages from MORB-like to HMA to IAT represents the progressive evolution of intra-oceanic subduction from shallow to deep and the gradual evolution of ocean basin to the island arc of the continental marginal.
The discovery of petrological evidence for the ocean-continent conversion (intra-oceanic arc) makes it possible to identify, reconstruct and study the ocean-continent conversion. In this paper, the ophiolite in the Diyanmiao subduction accretion complex belt in the eastern margin of the Central Asian orogenic belt was studied in terms of petrogeochemistry, Sr-Nd isotope and zircon U-Pb geochronology, and a set of igneous assemblages in the intra-oceanic arc were identified. The zircon U-Pb concordant age of MORB-like basalt is 286.1±6.1 Ma, representing the period of initial subduction in the ocean. The zircon U-Pb concordant age of HMA is 283.7±4.7 Ma, which represents the age of magmatism when subduction deepened after the first magmatic action. The zircon U-Pb concordant age of IAT is 241±5 Ma, indicating that the paleo-Asian Ocean developed towards continental transition of normal island arc magmatism in the Early Triassic. The sequence of rock assemblages from MORB-like to HMA to IAT represents the progressive evolution of intra-oceanic subduction from shallow to deep and the gradual evolution of ocean basin to the island arc of the continental marginal.
2019, 44(10): 3469-3483.
doi: 10.3799/dqkx.2018.272
Abstract:
The basic vein is a "window" for studying mantle and its evolution, and has important relationship with gold, uranium, diamond deposits and the others. The most typical alaskite type uranium deposit in China occurs in Hongshiquan area of Gansu Province among which there are a number of basic veins. The fresh surface of the basic rocks in the study area is gray-green, with typical lamprophyre structure, and massive structure. The porphyry minerals are mainly hornblende, the matrix mainly is composed of plagioclase and biotite, and accessory minerals are mainly magnetite, apatite, zircon etc.. Based on this characteristics, it is determined that the basic rock is diorite lamprophyre. The characteristics of elemental geochemistry ascertain that the lamprophyres are rich in alkali, high in potassium, poor in iron, and enriched in LREE and LILE, indicating that they belong to potash calc-alkaline lamprophyres. The whole-rock 40Ar-39Ar dating yields a lamprophyre diagenetic age of 237.2±2.6 Ma. The magma of the lamprophyre originated from EMII-enriched mantle and formed in the intraplate extensional environment. The magma was contaminated with crustal materials during the process of rising emplacement, which was the product of the extension following closure of the Late Asian Paleozoic Paleo-Asian Ocean and continental collision. There is no direct genetic relationship between the uranium metallogenesis of the Hongshiquan lamprophyre and the uranium deposit, but only late-stage transformation of uranium deposits.
The basic vein is a "window" for studying mantle and its evolution, and has important relationship with gold, uranium, diamond deposits and the others. The most typical alaskite type uranium deposit in China occurs in Hongshiquan area of Gansu Province among which there are a number of basic veins. The fresh surface of the basic rocks in the study area is gray-green, with typical lamprophyre structure, and massive structure. The porphyry minerals are mainly hornblende, the matrix mainly is composed of plagioclase and biotite, and accessory minerals are mainly magnetite, apatite, zircon etc.. Based on this characteristics, it is determined that the basic rock is diorite lamprophyre. The characteristics of elemental geochemistry ascertain that the lamprophyres are rich in alkali, high in potassium, poor in iron, and enriched in LREE and LILE, indicating that they belong to potash calc-alkaline lamprophyres. The whole-rock 40Ar-39Ar dating yields a lamprophyre diagenetic age of 237.2±2.6 Ma. The magma of the lamprophyre originated from EMII-enriched mantle and formed in the intraplate extensional environment. The magma was contaminated with crustal materials during the process of rising emplacement, which was the product of the extension following closure of the Late Asian Paleozoic Paleo-Asian Ocean and continental collision. There is no direct genetic relationship between the uranium metallogenesis of the Hongshiquan lamprophyre and the uranium deposit, but only late-stage transformation of uranium deposits.
2019, 44(10): 3484-3494.
doi: 10.3799/dqkx.2019.075
Abstract:
In order to analyze sedimentary environment of Zhaodong manganese ore deposits located in the Southwestern Hunan Province from Datangpo Formation in Neoproterozoic Nanhua System (Cryogenian), the petrology and geochemistry of the manganese ore deposits were studied, considering that the Zhaodong manganese ore deposits are mainly hosted in manganous carbonate layer that includes two types of manganese-containing minerals, namely, striped rhodochrosite and massive rhodochrosite at the bottom of the Datangpo Formation. The major elements of Zhaodong manganese ore deposits in Datangpo Formation in Southwestern Hunan Province show positive correlation between the TiO2, SiO2, K2O, Fe2O3, S and Al2O3 and negative correlation between CaO, MgO, MnO, P2O5 and Al2O3, which is consistent with those of typical manganese ore deposits in eastern of Guizhou and western of Hunan Province. It reflects that these manganese ore deposits may have similar mineralization background. Zhaodong manganese ore deposits are characterized by the low Fe/Mn ratios. The ratios of redox sensitive trace elements which can be regarded as marker of sedimentary environment and paleo-oxygenation facies such as Th/U, Ni/Co, V/Cr and V/(V+Ni) indicate that the manganese ore deposits were formed in sub-oxidation to oxidation water condition in Zhaodong manganese ore deposits of the Southwestern Hunan Province. The Zhaodong manganese ore deposits of the Southwestern Hunan Province are characterized geochemically by high ∑ REE contents, PAAS-normalized REE patterns similar to that of ferromanganese nodules in modern ocean bottom, and positive Ce anomaly.
In order to analyze sedimentary environment of Zhaodong manganese ore deposits located in the Southwestern Hunan Province from Datangpo Formation in Neoproterozoic Nanhua System (Cryogenian), the petrology and geochemistry of the manganese ore deposits were studied, considering that the Zhaodong manganese ore deposits are mainly hosted in manganous carbonate layer that includes two types of manganese-containing minerals, namely, striped rhodochrosite and massive rhodochrosite at the bottom of the Datangpo Formation. The major elements of Zhaodong manganese ore deposits in Datangpo Formation in Southwestern Hunan Province show positive correlation between the TiO2, SiO2, K2O, Fe2O3, S and Al2O3 and negative correlation between CaO, MgO, MnO, P2O5 and Al2O3, which is consistent with those of typical manganese ore deposits in eastern of Guizhou and western of Hunan Province. It reflects that these manganese ore deposits may have similar mineralization background. Zhaodong manganese ore deposits are characterized by the low Fe/Mn ratios. The ratios of redox sensitive trace elements which can be regarded as marker of sedimentary environment and paleo-oxygenation facies such as Th/U, Ni/Co, V/Cr and V/(V+Ni) indicate that the manganese ore deposits were formed in sub-oxidation to oxidation water condition in Zhaodong manganese ore deposits of the Southwestern Hunan Province. The Zhaodong manganese ore deposits of the Southwestern Hunan Province are characterized geochemically by high ∑ REE contents, PAAS-normalized REE patterns similar to that of ferromanganese nodules in modern ocean bottom, and positive Ce anomaly.
2019, 44(10): 3495-3511.
doi: 10.3799/dqkx.2018.320
Abstract:
Tulasu pluton in Chinese West Tianshan is located in the northeastern of Tulasu basin, composed of three lithofacies, i. e. quartzdiorite, pyroxene diorite and granite. The granites are composed of granodiorite porphyrite and granite porphyry, characterized by high silicon, high aluminum, enrichment of alkali, Rittman index(σ)=1.61-3.18, A/CNK=1.00-1.09, A/NK=1.07-1.68, belonging to metaluminous-weakly peraluminous high-K calc-alkaline granite. They are relatively enriched in LILEs (Rb, Th, U), extremely poor in Nb, Ta, Sr, P, Ti, etc., obviously fractionated in LREE and HREE, (La/Yb)N=7.48-12.12, showing a medium negative Eu anomaly and no Ce anomaly, δEu=0.47-0.62. But granite porphyry has higher alkali content, more close to shoshonite series and Sr, P, Ti strongly negative, indicating increased involvement of crustal materials. Zircon LA-ICP-MS U-Pb dating for the granite yields an age of 305.9±5.9 Ma. Analyses on zircon Hf isotopic compositions yield positive εHf(t) values varying from +0.4 to +8.7, implying that the involvement of mantle-derived magmatic materials during the formation of granite; TDM2 varies from 766 to 1 294 Ma, showing that magma was derived from Proterozoic-Neoproterozoic crust. By comparison, it is concluded that fractional crystallization enhanced, involvement of crustal materials increased from granodiorite to granite porphyry. The granite was formed in post-collisional setting.
Tulasu pluton in Chinese West Tianshan is located in the northeastern of Tulasu basin, composed of three lithofacies, i. e. quartzdiorite, pyroxene diorite and granite. The granites are composed of granodiorite porphyrite and granite porphyry, characterized by high silicon, high aluminum, enrichment of alkali, Rittman index(σ)=1.61-3.18, A/CNK=1.00-1.09, A/NK=1.07-1.68, belonging to metaluminous-weakly peraluminous high-K calc-alkaline granite. They are relatively enriched in LILEs (Rb, Th, U), extremely poor in Nb, Ta, Sr, P, Ti, etc., obviously fractionated in LREE and HREE, (La/Yb)N=7.48-12.12, showing a medium negative Eu anomaly and no Ce anomaly, δEu=0.47-0.62. But granite porphyry has higher alkali content, more close to shoshonite series and Sr, P, Ti strongly negative, indicating increased involvement of crustal materials. Zircon LA-ICP-MS U-Pb dating for the granite yields an age of 305.9±5.9 Ma. Analyses on zircon Hf isotopic compositions yield positive εHf(t) values varying from +0.4 to +8.7, implying that the involvement of mantle-derived magmatic materials during the formation of granite; TDM2 varies from 766 to 1 294 Ma, showing that magma was derived from Proterozoic-Neoproterozoic crust. By comparison, it is concluded that fractional crystallization enhanced, involvement of crustal materials increased from granodiorite to granite porphyry. The granite was formed in post-collisional setting.
2019, 44(10): 3512-3528.
doi: 10.3799/dqkx.2019.956
Abstract:
The Lower Cambrian Niutitang Formation shale at the edge of Xuefeng ancient uplift is favorable for hydrocarbon generation and accumulation, and it is an important shale gas exploration target bed. But the preservation conditions of shale gas are very complex due to multistage tectonic activities, and no breakthrough has been made in shale gas exploration. Based on field geological survey and drilling data, combined with organic geochemistry analysis and test, it made a comprehensive evaluation of shale gas geological conditions and exploration prospect of the Lower Cambrian Niutitang Formation at the edge of the Xuefeng ancient uplift, namely the Yuanma basin. Results show that the Niutitang Formation is mainly composed of deep-shelf deposits, the organic carbon content is generally more than 2.0% and between 3.0% and 5.0%, and the organic matter type is type Ⅰ. The maturity of organic matter is 2.17% to 3.38%, with an average of 2.79%. The average content of shale debris minerals is 77.25%, and the average clay mineral content is 22.71%. Due to the high silicon content and brittleness, the reservoir reformation is easy. Based on comprehensive evaluation indexes such as geochemistry, reservoir property and preservation conditions, it is proposed that the Caotang sag and Fenghuang-Jishou-Zhangjiajie belt at the northwestern edge of the ancient uplift are favorable for Niutitang Formation shale gas exploration.
The Lower Cambrian Niutitang Formation shale at the edge of Xuefeng ancient uplift is favorable for hydrocarbon generation and accumulation, and it is an important shale gas exploration target bed. But the preservation conditions of shale gas are very complex due to multistage tectonic activities, and no breakthrough has been made in shale gas exploration. Based on field geological survey and drilling data, combined with organic geochemistry analysis and test, it made a comprehensive evaluation of shale gas geological conditions and exploration prospect of the Lower Cambrian Niutitang Formation at the edge of the Xuefeng ancient uplift, namely the Yuanma basin. Results show that the Niutitang Formation is mainly composed of deep-shelf deposits, the organic carbon content is generally more than 2.0% and between 3.0% and 5.0%, and the organic matter type is type Ⅰ. The maturity of organic matter is 2.17% to 3.38%, with an average of 2.79%. The average content of shale debris minerals is 77.25%, and the average clay mineral content is 22.71%. Due to the high silicon content and brittleness, the reservoir reformation is easy. Based on comprehensive evaluation indexes such as geochemistry, reservoir property and preservation conditions, it is proposed that the Caotang sag and Fenghuang-Jishou-Zhangjiajie belt at the northwestern edge of the ancient uplift are favorable for Niutitang Formation shale gas exploration.
2019, 44(10): 3529-3540.
doi: 10.3799/dqkx.2018.258
Abstract:
The contents of rare earth elements and yttrium (REY) are determined using ICP-MS spectrometry in 34 seawater samples obtained from various depths from Caiwei Guyot and Weijia Guyot in western Pacific. Based on the data, the vertical profile of ∑REY content of seawater column are established in cobalt-rich ferromanganese crust exploration contract area of China. The contents of rare earth element in seawater increase gradually with the water depth. The ∑ REY contents range from 14.0×10-12 to 65.5×10-12, with an average of 31.94×10-12. Both the absolute content and relative content of Y are high, ranging from 6.0×10-12 to 24.1×10-12, with mean (Y/Ho)N value of 1.98, followed by La, with content ranging from 1.8×10-12 to 11.6×10-12. Ce is relatively low, with contents ranging from 2.4×10-12 to 8.8×10-12. And the δCe is from 0.33 to 1.03, with mean value of 0.66. The NASC-normalized REY patterns show left mode, with mean (La/Yb)N value of 0.71, obvious negative Ce anomalies, positive Y anomaly and no obvious Eu anomaly. Aqueous cobalt-rich ferromanganese crust is widely distributed in the study area, whose rare earth elements and other components are derived from seawater. The rare earth content of cobalt-rich crusts is 6-7 orders of magnitude higher than that of seawater, while NASC-normalized REY patterns of cobalt-rich ferromanganese crust show remarkable positive Ce and negative Y anomaly. This coupling relationship indicates that cobalt-rich ferromanganese crust components are selective for the cleaning rare earth elements of sea water, causing seawater rare earth anomaly. Both the phosphate rock developed on the seamounts and the phosphate components in the deep mud of the surrounding basin have high rare earth contents and a rare earth pattern similar to that of seawater. These phenomena indicate that the marine phosphate is not fractionated but inherited the REE patterns of seawater. The unique characteristics of REE patterns of seawater are the result of the balance between supply and consumption. Ferromanganese oxide and marine phosphate are two typical marine autogenic components, which are essential for the formation of REE patterns of seawater.
The contents of rare earth elements and yttrium (REY) are determined using ICP-MS spectrometry in 34 seawater samples obtained from various depths from Caiwei Guyot and Weijia Guyot in western Pacific. Based on the data, the vertical profile of ∑REY content of seawater column are established in cobalt-rich ferromanganese crust exploration contract area of China. The contents of rare earth element in seawater increase gradually with the water depth. The ∑ REY contents range from 14.0×10-12 to 65.5×10-12, with an average of 31.94×10-12. Both the absolute content and relative content of Y are high, ranging from 6.0×10-12 to 24.1×10-12, with mean (Y/Ho)N value of 1.98, followed by La, with content ranging from 1.8×10-12 to 11.6×10-12. Ce is relatively low, with contents ranging from 2.4×10-12 to 8.8×10-12. And the δCe is from 0.33 to 1.03, with mean value of 0.66. The NASC-normalized REY patterns show left mode, with mean (La/Yb)N value of 0.71, obvious negative Ce anomalies, positive Y anomaly and no obvious Eu anomaly. Aqueous cobalt-rich ferromanganese crust is widely distributed in the study area, whose rare earth elements and other components are derived from seawater. The rare earth content of cobalt-rich crusts is 6-7 orders of magnitude higher than that of seawater, while NASC-normalized REY patterns of cobalt-rich ferromanganese crust show remarkable positive Ce and negative Y anomaly. This coupling relationship indicates that cobalt-rich ferromanganese crust components are selective for the cleaning rare earth elements of sea water, causing seawater rare earth anomaly. Both the phosphate rock developed on the seamounts and the phosphate components in the deep mud of the surrounding basin have high rare earth contents and a rare earth pattern similar to that of seawater. These phenomena indicate that the marine phosphate is not fractionated but inherited the REE patterns of seawater. The unique characteristics of REE patterns of seawater are the result of the balance between supply and consumption. Ferromanganese oxide and marine phosphate are two typical marine autogenic components, which are essential for the formation of REE patterns of seawater.
2019, 44(10): 3541-3550.
doi: 10.3799/dqkx.2018.396
Abstract:
North Wusunshan fault zone lies on southern margin of Yining basin, Xinjiang, which is a boundary fault between Yining basin and Wusunshan. The fault zone is composed of a suit of secondary parallel or en echelon faults. The faults strike in east-west direction, and dip to the south generally, the main fault next to Wusunshan is characterized by steep reverse fault plane with dip angle of 50°-80°, the frontal fault close to Yining basin shows gentler fault plane. The Carboniferous and Permian strata consist of hanging wall, and the Quaternary and Jurassic strata make up the footwall. ESR dating of sediments for hanging wall and footwall indicates that the Mid-Upper Pleistocene is truncated by the faults in specific places. Based on stratigraphic contact and regional tectonic analysis, North Wusunshan faults thrust intensively toward the north during the latest Mid-Pleistocene, in the meanwhile, North Yining faults thrust intensively toward the south, and the two groups of fault belts control basin-mountain geomorphic framework. This tectonic event is equivalent with the Gonghe Movement in the Tibet plateau, which is attributed to compression from the North and South Tianshan, which thrust toward Yili basin, regional tectonic mechanism stemmed from outward growth and expansion of the Tibetan plateau.
North Wusunshan fault zone lies on southern margin of Yining basin, Xinjiang, which is a boundary fault between Yining basin and Wusunshan. The fault zone is composed of a suit of secondary parallel or en echelon faults. The faults strike in east-west direction, and dip to the south generally, the main fault next to Wusunshan is characterized by steep reverse fault plane with dip angle of 50°-80°, the frontal fault close to Yining basin shows gentler fault plane. The Carboniferous and Permian strata consist of hanging wall, and the Quaternary and Jurassic strata make up the footwall. ESR dating of sediments for hanging wall and footwall indicates that the Mid-Upper Pleistocene is truncated by the faults in specific places. Based on stratigraphic contact and regional tectonic analysis, North Wusunshan faults thrust intensively toward the north during the latest Mid-Pleistocene, in the meanwhile, North Yining faults thrust intensively toward the south, and the two groups of fault belts control basin-mountain geomorphic framework. This tectonic event is equivalent with the Gonghe Movement in the Tibet plateau, which is attributed to compression from the North and South Tianshan, which thrust toward Yili basin, regional tectonic mechanism stemmed from outward growth and expansion of the Tibetan plateau.
2019, 44(10): 3551-3564.
doi: 10.3799/dqkx.2018.299
Abstract:
The Gongchangling granite is the part of Nanfen metamorphic core complex and is also an important part of the Precambrian basement of Anshan-Benxi area. In order to investigate the tectonic significance of North China craton in Neoproterozoic to Paleoproterozoic, the Gongchangling granite in the Nanfen metamorphic core complex was selected as the research object. LA-ICP-MS U-Pb analyses of 2 zircon samples yield the upper intercept ages of 2 505±14 Ma (MSWD=1.30, n=70) and 2 507±11 Ma (MSWD=1.16, n=80), which represents the crystallization time of the magma. The studied samples have high SiO2 of 70.14% to 75.36%, K2O of 3.12% to 6.84%, Al2O3 of 11.78% to 13.75% and total alkali (Na2O+K2O) of 7.8% to 9.64%.The samples show Rittmann index(δ) from 1.98 to 2.94, and AR from 3.6 to 9.1, which suggests that the granite is enriched in silicon and alkali. A/CNK=0.95-1.23, with the majority of more than 1.11, indicate that it is peraluminous rock. Results show ∑REE=177.15×10-6-505.64×10-6, LaN/YbN=8.14-29.92, obvious fractionation of LREE to HREE, enriched LILE, such as Rb, Th, Zr, Hf, depleted of Nb, Ti and other elements. The geochemical characteristics of rocks indicate that the Gongchangling granite was formed by partial melting of the crustal argillite in the collision tectonic setting of the continental block through differentiation and crystallization. It is indicated that the Anshan-Benxi area was in the transition period in 2.50 Ga from post-collision to stable stage after assemblage of the continental blocks.
The Gongchangling granite is the part of Nanfen metamorphic core complex and is also an important part of the Precambrian basement of Anshan-Benxi area. In order to investigate the tectonic significance of North China craton in Neoproterozoic to Paleoproterozoic, the Gongchangling granite in the Nanfen metamorphic core complex was selected as the research object. LA-ICP-MS U-Pb analyses of 2 zircon samples yield the upper intercept ages of 2 505±14 Ma (MSWD=1.30, n=70) and 2 507±11 Ma (MSWD=1.16, n=80), which represents the crystallization time of the magma. The studied samples have high SiO2 of 70.14% to 75.36%, K2O of 3.12% to 6.84%, Al2O3 of 11.78% to 13.75% and total alkali (Na2O+K2O) of 7.8% to 9.64%.The samples show Rittmann index(δ) from 1.98 to 2.94, and AR from 3.6 to 9.1, which suggests that the granite is enriched in silicon and alkali. A/CNK=0.95-1.23, with the majority of more than 1.11, indicate that it is peraluminous rock. Results show ∑REE=177.15×10-6-505.64×10-6, LaN/YbN=8.14-29.92, obvious fractionation of LREE to HREE, enriched LILE, such as Rb, Th, Zr, Hf, depleted of Nb, Ti and other elements. The geochemical characteristics of rocks indicate that the Gongchangling granite was formed by partial melting of the crustal argillite in the collision tectonic setting of the continental block through differentiation and crystallization. It is indicated that the Anshan-Benxi area was in the transition period in 2.50 Ga from post-collision to stable stage after assemblage of the continental blocks.
2019, 44(10): 3565-3582.
doi: 10.3799/dqkx.2019.079
Abstract:
The Late Carboniferous-Early Permian granitic intrusions extensively occur in the southern Tianshan block, whereas the petrogenesis of these granites and their tectonic setting remain controversial. In this paper, it reports new zircon U-Pb age, and geochemical and Sr-Nd compositions and zircon Hf isotopic compositions of the biotite monzonitic granites in the southern Tianshan block. Based on LA-ICP-MS U-Pb zircon dating, the biotite monzonitic granites were emplaced at 295.8±1.7 Ma. They are characterized by slightly peraluminous (A/CNK=1.02-1.04), rich alkali (K2O+Na2O=7.49%-8.78%) and potassium-rich (K2O/Na2O=1.05-1.53), belonging to high potassium calc-alkaline affinity, consistent with the geochemical features of Ⅰ-type granites. They are enriched in LILEs and LREEs, depleted in HFSEs (e.g., Nb, Ta, Ti), medium-negative Eu anomalies (δEu=0.38-0.57), and predominately negative Sr, Ba anomalies. In addition, most of the biotite monzonitic granites show high initial (87Sr/86Sr)i ratios, negative εNd(t) and εHf(t) values and few samples with low and positive εNd(t) and εHf(t) values, suggesting that they were produced by mixing of mafic melt-derived mantle and felsic melt derived ancient (Paleo-Mesoproterozoic) crust, with minor involvement of the Neoproterozoic crustal material, and that the crystal fractionation of plagioclase could have occurred before the parental magma emplaced. In association with previous analysis, it is proposed that the Late Carboniferous-Early Permian magmatism in the southern Tianshan block might be related to mixing of melt-derived Precambrian basement and melt-derived mantle induced by the slab roll-back of the subducted southern Tianshan oceanic lithosphere and asthenosphere upwelling. The Phanerozoic magmatic source of the southern Tianshan block is mainly characterized by the reworking of ancient crust. Compared to other regions of CAOB, there is no excessive juvenile crustal growth in the southern Tianshan.
The Late Carboniferous-Early Permian granitic intrusions extensively occur in the southern Tianshan block, whereas the petrogenesis of these granites and their tectonic setting remain controversial. In this paper, it reports new zircon U-Pb age, and geochemical and Sr-Nd compositions and zircon Hf isotopic compositions of the biotite monzonitic granites in the southern Tianshan block. Based on LA-ICP-MS U-Pb zircon dating, the biotite monzonitic granites were emplaced at 295.8±1.7 Ma. They are characterized by slightly peraluminous (A/CNK=1.02-1.04), rich alkali (K2O+Na2O=7.49%-8.78%) and potassium-rich (K2O/Na2O=1.05-1.53), belonging to high potassium calc-alkaline affinity, consistent with the geochemical features of Ⅰ-type granites. They are enriched in LILEs and LREEs, depleted in HFSEs (e.g., Nb, Ta, Ti), medium-negative Eu anomalies (δEu=0.38-0.57), and predominately negative Sr, Ba anomalies. In addition, most of the biotite monzonitic granites show high initial (87Sr/86Sr)i ratios, negative εNd(t) and εHf(t) values and few samples with low and positive εNd(t) and εHf(t) values, suggesting that they were produced by mixing of mafic melt-derived mantle and felsic melt derived ancient (Paleo-Mesoproterozoic) crust, with minor involvement of the Neoproterozoic crustal material, and that the crystal fractionation of plagioclase could have occurred before the parental magma emplaced. In association with previous analysis, it is proposed that the Late Carboniferous-Early Permian magmatism in the southern Tianshan block might be related to mixing of melt-derived Precambrian basement and melt-derived mantle induced by the slab roll-back of the subducted southern Tianshan oceanic lithosphere and asthenosphere upwelling. The Phanerozoic magmatic source of the southern Tianshan block is mainly characterized by the reworking of ancient crust. Compared to other regions of CAOB, there is no excessive juvenile crustal growth in the southern Tianshan.
