2019 Vol. 44, No. 1
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2019, 44(1): 1-22.
doi: 10.3799/dqkx.2018.259
Abstract:
The Early-Precambrian meta-supracrustal rocks in the Huai'an Complex of the North China Craton are characterized by high-grade metamorphism (granulite-facies), poor continuity, strong deformation and structural transposition, etc. Division of the stratigraphic units and their formation ages are still controversial. Through detailed geological survey, petrology and geochronological studies, four meta-supracrustal rock assemblages are newly defined, which are the Neoarchean Sanggan Group magnetite-quartzite Formation (MQF), garnet-biotite-plagiogneiss Formation (GBPF) and Paleoproterozoic Jining Group amphibolites marble Formation (AMF), graphite-sillimanite-garnet gneiss Formation (GSGF). Their corresponding petrological marks are also established. Field investigation reveals that the Neoarchean meta-supracrustal rocks usually appear as lenticular inclusions or banded sheet outcropped in the Neoarchean metamorphic plutonites, and the zircon age shows two peaks at ~2.5 Ga and ~1.8 Ga. The protolith of the MQF is a suite of basic volcanic rocks with magnetite quartzite, which produced Algoma-type BIF iron ore and formed at 2 489±19 Ma. The main rock type of GBPF is banded garnet-biotite-plagiogneiss and its protolith is greywacke, indicating that they originated from the Neoarchean TTG rocks. The protolith of the Paleoproterozoic AMF is a suite of basic volcanic rocks intercalated with marble, which formed earlier than~2.03 Ga. The GBPF, which is a suite of Khondalite, presents ribbon-like tectonic slices field outcrops and is characterized by good continuity and stratified but disordered structure. The detrital zircon age of the GBPF ranges from 2.30 to 1.99 Ga, which is regionally consistent with the age of the Khondalite, while its formation age is Late Paleoproterozoic (1.99-1.95 Ga). The Neoproterozoic and Paleoproterozoic meta-supracrustal rocks were all involved by the Late Paleoproterozoic orogeny (1.95-1.80 Ga) and underwent granulite-facies metamorphism and deformation. The Khondalites may be exotic tectonic slices during the Late Paleoproterozoic orogeny. This study clarifies that Neoarchean continental clastic rock and Paleoproterozoic oceanic crust exist at the border of Shanxi, Hebei, and Inner Mongolia provinces, which are different from the Khondalites. This may shed light on a new understanding of the geologic evolution of the Early Precambrian Huai'an Complex of the North China Craton.
The Early-Precambrian meta-supracrustal rocks in the Huai'an Complex of the North China Craton are characterized by high-grade metamorphism (granulite-facies), poor continuity, strong deformation and structural transposition, etc. Division of the stratigraphic units and their formation ages are still controversial. Through detailed geological survey, petrology and geochronological studies, four meta-supracrustal rock assemblages are newly defined, which are the Neoarchean Sanggan Group magnetite-quartzite Formation (MQF), garnet-biotite-plagiogneiss Formation (GBPF) and Paleoproterozoic Jining Group amphibolites marble Formation (AMF), graphite-sillimanite-garnet gneiss Formation (GSGF). Their corresponding petrological marks are also established. Field investigation reveals that the Neoarchean meta-supracrustal rocks usually appear as lenticular inclusions or banded sheet outcropped in the Neoarchean metamorphic plutonites, and the zircon age shows two peaks at ~2.5 Ga and ~1.8 Ga. The protolith of the MQF is a suite of basic volcanic rocks with magnetite quartzite, which produced Algoma-type BIF iron ore and formed at 2 489±19 Ma. The main rock type of GBPF is banded garnet-biotite-plagiogneiss and its protolith is greywacke, indicating that they originated from the Neoarchean TTG rocks. The protolith of the Paleoproterozoic AMF is a suite of basic volcanic rocks intercalated with marble, which formed earlier than~2.03 Ga. The GBPF, which is a suite of Khondalite, presents ribbon-like tectonic slices field outcrops and is characterized by good continuity and stratified but disordered structure. The detrital zircon age of the GBPF ranges from 2.30 to 1.99 Ga, which is regionally consistent with the age of the Khondalite, while its formation age is Late Paleoproterozoic (1.99-1.95 Ga). The Neoproterozoic and Paleoproterozoic meta-supracrustal rocks were all involved by the Late Paleoproterozoic orogeny (1.95-1.80 Ga) and underwent granulite-facies metamorphism and deformation. The Khondalites may be exotic tectonic slices during the Late Paleoproterozoic orogeny. This study clarifies that Neoarchean continental clastic rock and Paleoproterozoic oceanic crust exist at the border of Shanxi, Hebei, and Inner Mongolia provinces, which are different from the Khondalites. This may shed light on a new understanding of the geologic evolution of the Early Precambrian Huai'an Complex of the North China Craton.
2019, 44(1): 23-36.
doi: 10.3799/dqkx.2018.273
Abstract:
Eastern Hebei Province is located in the northern margin of the North China Craton, but magmatic genesis and tectonic setting of Neoarchean igneous rocks in the area still remain controversial. Systematic geochronologic and geochemical study of Neoarchean supracrustal and intrusive rocks in Qinglong-Shuangshanzi area, eastern Hebei are presented in this paper. Zircon LA-MC-ICP-MS U-Pb isotopic dating reveals that the meta-andesite erupted at 2 576 Ma, and the intrusive rocks (gabbro-diorites, tonalites and quartz diorites) emplaced in a range of 2 484 Ma to 2 535 Ma. Part of the early-formed meta-andesites shows high-Mg andesite geochemical characteristics, which indicates these rocks were generated from partial melting of mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab. The magnesian diorites show adakite characteristics, which suggests they have source characteristics of partial melting of mantle wedge peridotite metasomatised by felsic melts of the subducted slab. Both of the high-Mg meta-andesites and adakite like magnesian diorites belong to a suite of island arc assemblages. Combining previous regional studies, it is concluded that Qinglong-Shuangshanzi area was under a tectonic setting of active continental margin during Neoarchean era.
Eastern Hebei Province is located in the northern margin of the North China Craton, but magmatic genesis and tectonic setting of Neoarchean igneous rocks in the area still remain controversial. Systematic geochronologic and geochemical study of Neoarchean supracrustal and intrusive rocks in Qinglong-Shuangshanzi area, eastern Hebei are presented in this paper. Zircon LA-MC-ICP-MS U-Pb isotopic dating reveals that the meta-andesite erupted at 2 576 Ma, and the intrusive rocks (gabbro-diorites, tonalites and quartz diorites) emplaced in a range of 2 484 Ma to 2 535 Ma. Part of the early-formed meta-andesites shows high-Mg andesite geochemical characteristics, which indicates these rocks were generated from partial melting of mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab. The magnesian diorites show adakite characteristics, which suggests they have source characteristics of partial melting of mantle wedge peridotite metasomatised by felsic melts of the subducted slab. Both of the high-Mg meta-andesites and adakite like magnesian diorites belong to a suite of island arc assemblages. Combining previous regional studies, it is concluded that Qinglong-Shuangshanzi area was under a tectonic setting of active continental margin during Neoarchean era.
2019, 44(1): 37-51.
doi: 10.3799/dqkx.2018.301
Abstract:
Iron-bearing formations (BIFs) in lumpy, lenticular or stratified forms frequently occur in the Huai'an Complex, North China Craton. Compared with BIFs in greenstone belts on North China Craton, the iron-bearing formation with characteristics of small scale, complicated lithology, and high-grade metamorphism-deformation in the study area has rarely been studied. Petrology, geochronology and geochemical studies on the basis of field survey have been conducted, and it is concluded:(1) The iron-bearing formations in Tianzhen-Huai'an area are comprised of banded (perilla/amphibole) magnetic quartzite, metamorphic basic volcanic rock (two-pyroxene granulite/plagioclase amphibolites/high-pressure granulite), garnet-biotite-plagiogneiss, and a few garnet-quartzite strips or lumps, and these rocks are intercalated or symbiotic with each other. Characteristics of being small in scale, closely symbiotic with metamorphic volcanic rocks suggesting BIF ore in Tianzhen-Huai'an area belongs to Algoma type. (2) The age (2 489±19 Ma) of residual intermediate-basic igneous zircons in banded (perilla/amphibole) magnetic quartzite may represent the formation age of the BIFs in Tianzhen-Huai'an area, which afterwards underwent the 1 800-1 850 Ma metamorphism. (3) The geochemical characteristics of metamorphic volcanic rocks of iron-bearing formations show enrichment in elements Rb, Ba, U, Pb, and depletion in elements Nb and Ta. It is concluded the iron-bearing formations are closely related to seabed hydrothermal activity formed in back-arc basin according to the patterns of trace elements and rare earth distribution of metamorphic volcanic rocks and positive anomality of Eu in PAAS normalized rare earth elements distribution pattern of iron ore.
Iron-bearing formations (BIFs) in lumpy, lenticular or stratified forms frequently occur in the Huai'an Complex, North China Craton. Compared with BIFs in greenstone belts on North China Craton, the iron-bearing formation with characteristics of small scale, complicated lithology, and high-grade metamorphism-deformation in the study area has rarely been studied. Petrology, geochronology and geochemical studies on the basis of field survey have been conducted, and it is concluded:(1) The iron-bearing formations in Tianzhen-Huai'an area are comprised of banded (perilla/amphibole) magnetic quartzite, metamorphic basic volcanic rock (two-pyroxene granulite/plagioclase amphibolites/high-pressure granulite), garnet-biotite-plagiogneiss, and a few garnet-quartzite strips or lumps, and these rocks are intercalated or symbiotic with each other. Characteristics of being small in scale, closely symbiotic with metamorphic volcanic rocks suggesting BIF ore in Tianzhen-Huai'an area belongs to Algoma type. (2) The age (2 489±19 Ma) of residual intermediate-basic igneous zircons in banded (perilla/amphibole) magnetic quartzite may represent the formation age of the BIFs in Tianzhen-Huai'an area, which afterwards underwent the 1 800-1 850 Ma metamorphism. (3) The geochemical characteristics of metamorphic volcanic rocks of iron-bearing formations show enrichment in elements Rb, Ba, U, Pb, and depletion in elements Nb and Ta. It is concluded the iron-bearing formations are closely related to seabed hydrothermal activity formed in back-arc basin according to the patterns of trace elements and rare earth distribution of metamorphic volcanic rocks and positive anomality of Eu in PAAS normalized rare earth elements distribution pattern of iron ore.
2019, 44(1): 52-68.
doi: 10.3799/dqkx.2018.372
Abstract:
The southern margin of the North China Craton has a large-scale ore-forming event during the Mesozoic, and includes three major deposit types of lode gold (as either quartz veins or disseminated ores), porphyry Mo, and quartz vein-type Ag-Pb-Zn deposits. Ore genesis and geodynamic setting for these deposits, however, are still in a matter of debate. Geochronological studies in recent years have revealed that all of these deposits were formed during the Early Cretaceous, and show close spatial-temporal relationship with regional large-scale magmatism. In this study, we make a summary of geological features and regionally spatial-temporal distributioin of the major deposit types, and discuss their probable metal sources and possible genetic links between different deposit types. We suggest that these different types of deposits formed a giant regional magmatic-hydrothermal metallogenic system. Moreover, the mineralization event at the southern margin of the North China Craton has ages and geological features consistent with those deposits in the neighboring eastern Qinling-Dabie metallogenic belt. They were formed in the same geodynamic setting, which was controlled by the Early Cretaceous large-scale extensional events of the East China. In combination with geophysical data, such an extensional and magmatic event at a lithospheric scale was mostly likely related to the subduction of the Paleo-Pacific Plate underneath the East Asia continent. Upwelling of the magmas and the related hydrothermal fluids were extensively interacted with upper crustal rocks and shallow-derived fluids, and formed a regional scale magmatic-hydrothermal matallogenic system at the priority structures of upper crustal level.
The southern margin of the North China Craton has a large-scale ore-forming event during the Mesozoic, and includes three major deposit types of lode gold (as either quartz veins or disseminated ores), porphyry Mo, and quartz vein-type Ag-Pb-Zn deposits. Ore genesis and geodynamic setting for these deposits, however, are still in a matter of debate. Geochronological studies in recent years have revealed that all of these deposits were formed during the Early Cretaceous, and show close spatial-temporal relationship with regional large-scale magmatism. In this study, we make a summary of geological features and regionally spatial-temporal distributioin of the major deposit types, and discuss their probable metal sources and possible genetic links between different deposit types. We suggest that these different types of deposits formed a giant regional magmatic-hydrothermal metallogenic system. Moreover, the mineralization event at the southern margin of the North China Craton has ages and geological features consistent with those deposits in the neighboring eastern Qinling-Dabie metallogenic belt. They were formed in the same geodynamic setting, which was controlled by the Early Cretaceous large-scale extensional events of the East China. In combination with geophysical data, such an extensional and magmatic event at a lithospheric scale was mostly likely related to the subduction of the Paleo-Pacific Plate underneath the East Asia continent. Upwelling of the magmas and the related hydrothermal fluids were extensively interacted with upper crustal rocks and shallow-derived fluids, and formed a regional scale magmatic-hydrothermal matallogenic system at the priority structures of upper crustal level.
2019, 44(1): 69-87.
doi: 10.3799/dqkx.2018.147
Abstract:
The newly discovered Laoliwan large Ag-Pb-Zn deposit is located in the Xiaoshan district, southern margin of North China Craton, which is different from other types of Ag-Pb-Zn deposit in the area since the ore bodies are mainly hosted in the Laoliwan granite porphyry and controlled by the regional faults. The mineralization could be subdivided into two periods:the hydrothermal period and the supergene period. The hydrothermal period consists of four stages:the quartz-siderite stage, the quartz-pyrite stage, the quartz-polymetallic sulfide stage, and the quartz-carbonate stage. LA-ICP-MS zircon U-Pb dating results of two samples from the Laoliwan granite porphyry are 129.0±1.7 Ma and 129.0±1.1 Ma, respectively, indicating the granite porphyry intruded during Early Cretaceous. Based on the rock geochemical analysis, the granite porphyry is characterized by high silicon, high alkali, and weak peraluminous. The REE and trace elements characteristics display enrichment of large ion lithophile elements (LREE, Rb, Ba, Sr, Pb) and depletion of high-field elements (HREE, Nb, Ta, Ti, P) and moderately negative anomaly of Eu. These features are similar with other Early Cretaceous granites in the area, indicating the magmatic activities are probably related to contemporaneous tectonic transition and lithosphere thinning in eastern China. Based on mineralization characteristics and regional geochronological data, it is supposed that the Ag-Pb-Zn mineralization formed later than the granite porphyry and they have no direct genetic relationships. However, they may be the products of activities of the same deep magma chamber. This study of the Laoliwan Ag-Pb-Zn deposit suggests that the superposition of faults and granite rocks could be the prospective places for exploring Ag-Pb-Zn deposits in the Xiaoshan disctrit, which is confirmed by the recent prospecting work at Zhonghe which is in north of Laoliwan. Compared with Xiaoqinling and Xiong'ershan area, the exhumation of the Xiaoshan area is quite shallower. It is potential to find porphyry molybdenum deposit under the Ag-Pb-Zn ore bodies of Laoliwan.
The newly discovered Laoliwan large Ag-Pb-Zn deposit is located in the Xiaoshan district, southern margin of North China Craton, which is different from other types of Ag-Pb-Zn deposit in the area since the ore bodies are mainly hosted in the Laoliwan granite porphyry and controlled by the regional faults. The mineralization could be subdivided into two periods:the hydrothermal period and the supergene period. The hydrothermal period consists of four stages:the quartz-siderite stage, the quartz-pyrite stage, the quartz-polymetallic sulfide stage, and the quartz-carbonate stage. LA-ICP-MS zircon U-Pb dating results of two samples from the Laoliwan granite porphyry are 129.0±1.7 Ma and 129.0±1.1 Ma, respectively, indicating the granite porphyry intruded during Early Cretaceous. Based on the rock geochemical analysis, the granite porphyry is characterized by high silicon, high alkali, and weak peraluminous. The REE and trace elements characteristics display enrichment of large ion lithophile elements (LREE, Rb, Ba, Sr, Pb) and depletion of high-field elements (HREE, Nb, Ta, Ti, P) and moderately negative anomaly of Eu. These features are similar with other Early Cretaceous granites in the area, indicating the magmatic activities are probably related to contemporaneous tectonic transition and lithosphere thinning in eastern China. Based on mineralization characteristics and regional geochronological data, it is supposed that the Ag-Pb-Zn mineralization formed later than the granite porphyry and they have no direct genetic relationships. However, they may be the products of activities of the same deep magma chamber. This study of the Laoliwan Ag-Pb-Zn deposit suggests that the superposition of faults and granite rocks could be the prospective places for exploring Ag-Pb-Zn deposits in the Xiaoshan disctrit, which is confirmed by the recent prospecting work at Zhonghe which is in north of Laoliwan. Compared with Xiaoqinling and Xiong'ershan area, the exhumation of the Xiaoshan area is quite shallower. It is potential to find porphyry molybdenum deposit under the Ag-Pb-Zn ore bodies of Laoliwan.
2019, 44(1): 88-108.
doi: 10.3799/dqkx.2018.281
Abstract:
As the volcanic-magmatic-metamorphic events related to the Caledonian subduction-collision are widely distributed in northern Qinling orogenic belt, Caledonian orogeny was believed to be limited there, and there is no response to Caledonian orogeny in southern-central Qinling orogenic belt, owing to the continuous/parallel unconformable "soft collision" between the Devonian and underlying strata. In this paper, deformation differences and discontinuous loss features of contact relationship between the Devonian and underlying strata of 22 outcrop sections in southern-central Qinling orogenic belt are investegated. In addition, the SHRIMP U-Pb geochronology and sedimentary environment on the "Silurian red strata" in unconformities are analyzed. It is indicated that the contact relationship between the Devonian and underlying folded basement strata (Pt3-S1) is a regional angular unconformity (regional micro-angular unconformity) in general, and the stratigraphic hiatus shows pronounced differences from north to south in eastern Qinling orogenic belt. What's more, different tectonic deformation features are presented in upper and lower strata. It is believed that the age of "Silurian red strata" in unconformities is the Middle-Later Silurian (S2-3, < 435 Ma) along Guanfang-Gongguan in Xunyang County. It should be front sedimentary response with the foreland basin formed by eastern Qinling Caledonian orogeny. It is confirmed that Caledonian orogeny induced strong folding orogeny in all Qinling orogenic belt, which will help us to get a better understanding for Caledonian orogenic-sedimentary evolution process in eastern Qinling mountains.
As the volcanic-magmatic-metamorphic events related to the Caledonian subduction-collision are widely distributed in northern Qinling orogenic belt, Caledonian orogeny was believed to be limited there, and there is no response to Caledonian orogeny in southern-central Qinling orogenic belt, owing to the continuous/parallel unconformable "soft collision" between the Devonian and underlying strata. In this paper, deformation differences and discontinuous loss features of contact relationship between the Devonian and underlying strata of 22 outcrop sections in southern-central Qinling orogenic belt are investegated. In addition, the SHRIMP U-Pb geochronology and sedimentary environment on the "Silurian red strata" in unconformities are analyzed. It is indicated that the contact relationship between the Devonian and underlying folded basement strata (Pt3-S1) is a regional angular unconformity (regional micro-angular unconformity) in general, and the stratigraphic hiatus shows pronounced differences from north to south in eastern Qinling orogenic belt. What's more, different tectonic deformation features are presented in upper and lower strata. It is believed that the age of "Silurian red strata" in unconformities is the Middle-Later Silurian (S2-3, < 435 Ma) along Guanfang-Gongguan in Xunyang County. It should be front sedimentary response with the foreland basin formed by eastern Qinling Caledonian orogeny. It is confirmed that Caledonian orogeny induced strong folding orogeny in all Qinling orogenic belt, which will help us to get a better understanding for Caledonian orogenic-sedimentary evolution process in eastern Qinling mountains.
2019, 44(1): 109-122.
doi: 10.3799/dqkx.2018.294
Abstract:
A great breakthrough has been achieved in prospecting in Banchang copper polymetallic deposit, East Qinling orogenic belt in recent years, which is characterized by obvious mineralization zoning in the mining area. The Cu, Pb, Zn and Ag mineralizations are developed in the upper part, and the Cu and Mo mineralizations are located in the lower part of the mining area. With Re-Os isotopic dating of molybdenite, LA-ICP-MS zircon U-Pb dating of granite rocks, sulfur and lead isotopic tracing of metal sulfide, the metallogenic time, ore genesis and metallogenic dynamic setting of the deposit are discussed in this study. Re-Os model ages of six molybdenite samples are 149.8±2.4 Ma to 151.5±2.3 Ma, with the weighted average age of 150.7±1.9 Ma and isochron age of 151.0±4.6 Ma, indicating that the metallogenic epoch was Late Jurassic. The zircon U-Pb age of Zhifanggou granite porphyry which is located to the south of Banchang deposit is 148±1 Ma, indicating that magmatic activities occurred during the metallogenic period. Eleven δ34SV-CDT values for sulfides range from -1.2‰ to +1.2‰, and the values are interpreted to reflect a deep magmatic source of the sulfur. In addition, the results show that 206Pb/204Pb values range from 17.178 to 17.709, 207Pb/204Pb values range from 15.430 to 15.528 and 208Pb/204Pb values range from 37.476 to 37.847, which are similar to lead isotope values of Yanshan Period granites in North Qinling and the crustal basement of South Qinling but very different from lead isotope values of the North Qinling strata. It is concluded that Banchang copper polymetallic deposit belongs to skarn-like type-hydrothermal vein type deposit which is related to Yanshannian magmatic activity, and it formed in the lithospheric thinning setting of East Qinling.
A great breakthrough has been achieved in prospecting in Banchang copper polymetallic deposit, East Qinling orogenic belt in recent years, which is characterized by obvious mineralization zoning in the mining area. The Cu, Pb, Zn and Ag mineralizations are developed in the upper part, and the Cu and Mo mineralizations are located in the lower part of the mining area. With Re-Os isotopic dating of molybdenite, LA-ICP-MS zircon U-Pb dating of granite rocks, sulfur and lead isotopic tracing of metal sulfide, the metallogenic time, ore genesis and metallogenic dynamic setting of the deposit are discussed in this study. Re-Os model ages of six molybdenite samples are 149.8±2.4 Ma to 151.5±2.3 Ma, with the weighted average age of 150.7±1.9 Ma and isochron age of 151.0±4.6 Ma, indicating that the metallogenic epoch was Late Jurassic. The zircon U-Pb age of Zhifanggou granite porphyry which is located to the south of Banchang deposit is 148±1 Ma, indicating that magmatic activities occurred during the metallogenic period. Eleven δ34SV-CDT values for sulfides range from -1.2‰ to +1.2‰, and the values are interpreted to reflect a deep magmatic source of the sulfur. In addition, the results show that 206Pb/204Pb values range from 17.178 to 17.709, 207Pb/204Pb values range from 15.430 to 15.528 and 208Pb/204Pb values range from 37.476 to 37.847, which are similar to lead isotope values of Yanshan Period granites in North Qinling and the crustal basement of South Qinling but very different from lead isotope values of the North Qinling strata. It is concluded that Banchang copper polymetallic deposit belongs to skarn-like type-hydrothermal vein type deposit which is related to Yanshannian magmatic activity, and it formed in the lithospheric thinning setting of East Qinling.
2019, 44(1): 123-134.
doi: 10.3799/dqkx.2018.306
Abstract:
The Qinling orogenic belt, located in the suture zone of the North China Plate and the Yangtze Plate, has undergone a complicated tectonic evolution process however, its plate combination mechanism and collision time limit have been controversial. In this study, petrogeochemistry analyses and LA-ICP-MS zircon U-Pb dating are undertaken for the two-mica granites from Wuduoshan in Nanzhao County, eastern Qinling mountains. Results show that the two-mica granites have SiO2=69.32%-74.28%, Al2O3=14.14%-17.28%, Na2O+K2O=7.68%-9.03%, and belong chemically to peraluminous series of S type. Meanwhile, the two-mica granites have a moderate amount of rare earth elements, with medium fractionation characteristics between light rare earth elements and heavy rare earth elements and medium negative Eu anomalies. The trace elements diagram shows enrichment of large ion lithophile elements (LILEs) and depletion of Ba, Nb, Sr, P and Ti, indicating that the two-mica granites may have been formed in the thickened crust caused by the collision between continents. Zircons from the two-mica granites in this study display fine-scale oscillatory growth and high ratios of Th/U (> 0.4), indicating a magmatic origin. The dating of the two-mica granites yields a LA-ICP-MS zircon U-Pb age of 433±2 Ma. Combined with constructional environment, it is concluded that it was transformed from plate subduction to continental collision in the Nanzhao County at late of Early Silurian.
The Qinling orogenic belt, located in the suture zone of the North China Plate and the Yangtze Plate, has undergone a complicated tectonic evolution process however, its plate combination mechanism and collision time limit have been controversial. In this study, petrogeochemistry analyses and LA-ICP-MS zircon U-Pb dating are undertaken for the two-mica granites from Wuduoshan in Nanzhao County, eastern Qinling mountains. Results show that the two-mica granites have SiO2=69.32%-74.28%, Al2O3=14.14%-17.28%, Na2O+K2O=7.68%-9.03%, and belong chemically to peraluminous series of S type. Meanwhile, the two-mica granites have a moderate amount of rare earth elements, with medium fractionation characteristics between light rare earth elements and heavy rare earth elements and medium negative Eu anomalies. The trace elements diagram shows enrichment of large ion lithophile elements (LILEs) and depletion of Ba, Nb, Sr, P and Ti, indicating that the two-mica granites may have been formed in the thickened crust caused by the collision between continents. Zircons from the two-mica granites in this study display fine-scale oscillatory growth and high ratios of Th/U (> 0.4), indicating a magmatic origin. The dating of the two-mica granites yields a LA-ICP-MS zircon U-Pb age of 433±2 Ma. Combined with constructional environment, it is concluded that it was transformed from plate subduction to continental collision in the Nanzhao County at late of Early Silurian.
2019, 44(1): 135-144.
doi: 10.3799/dqkx.2018.340
Abstract:
Nb-enriched gabbros are often associated with high-Mg diorite and adakite, which is considered to be a petrotectonic association of facies significance. However, this kind of magmatic activity has seldom been found in the southern side of the North Qinling orogenic belt in western Henan. Based on the method of petrology, geochemistry, isotope geochemistry and chronology for amphibolites from the Qinling Group in Zhaigen area, the Nb-enriched gabbros were separated from the deep plutonic complex in this study. The results show that the U-Pb age of metamorphic zircons from Nb-enriched gabbros is 484.3±1.8 Ma, which is similar to the peak of metamorphic ages of the UHP eclogites in this area. Nb-enriched gabbros are characterized by enrichment of Rb, Th and other heavy ion lithophilic elements and depletion of Nb, Ta, P and other high field strength elements. εNd(t) values range from -1.61 to +0.49, and (87Sr/86Sr)i values range from 0.714 273 to 0.723 936. We speculated that their formation was related to the remelting of mantle wedge peridotite by partially melted plate melts during the deep subduction of the Qinling paleocontinental crust. And a large amount of continental crust was added to the deep subduction. The discovery of Nb-enriched gabbros provides evidence for the existence of multiple small continental blocks in the Early Paleozoic of the Qinling orogen.
Nb-enriched gabbros are often associated with high-Mg diorite and adakite, which is considered to be a petrotectonic association of facies significance. However, this kind of magmatic activity has seldom been found in the southern side of the North Qinling orogenic belt in western Henan. Based on the method of petrology, geochemistry, isotope geochemistry and chronology for amphibolites from the Qinling Group in Zhaigen area, the Nb-enriched gabbros were separated from the deep plutonic complex in this study. The results show that the U-Pb age of metamorphic zircons from Nb-enriched gabbros is 484.3±1.8 Ma, which is similar to the peak of metamorphic ages of the UHP eclogites in this area. Nb-enriched gabbros are characterized by enrichment of Rb, Th and other heavy ion lithophilic elements and depletion of Nb, Ta, P and other high field strength elements. εNd(t) values range from -1.61 to +0.49, and (87Sr/86Sr)i values range from 0.714 273 to 0.723 936. We speculated that their formation was related to the remelting of mantle wedge peridotite by partially melted plate melts during the deep subduction of the Qinling paleocontinental crust. And a large amount of continental crust was added to the deep subduction. The discovery of Nb-enriched gabbros provides evidence for the existence of multiple small continental blocks in the Early Paleozoic of the Qinling orogen.
2019, 44(1): 145-160.
doi: 10.3799/dqkx.2018.350
Abstract:
Xing-Meng orogeny is the accretionary orogeny between Siberia and North China plates with complex multi-stage subduction and accretion, and its tectonic evolution. has remained controversial for a long time. To reveal the arc-continent collision in the end of Early Paleozoic, this paper presents a study on Chaoyangdi Middle Devonian high Sr/Y granite in southern part of Xing-Meng orogeny zircon U-Pb dating results yield a formation age of 386.8±2.9 Ma, with the corresponding age of Middle Devonian (D2). Geochemical data shows that these rocks have high SiO2, Al2O3 and Na2O, moderate CaO and K2O, but low FeOt and MgO contents with the Na2O/K2O>1 and calc-alkaline series signature. The A/CNK ratios range from 1.02 to 1.08, indicating these samples are weak peraluminous series. Trace element analysis results display enrichment of LILEs, such as Rb, Ba, K and Sr, but depletion of HFSE, i.e., Nb, Ta, P and Ti, with high Sr/Y ratios (103-146), similar with adakitic-affinity. These rocks have strong fractionation between LREE and HREE ((La/Yb)N=9.9-14.6), no obvious HREE fractionation ((Gd/Yb)N=1.45-1.97) and weak positive Eu anomalies (δEu=1.31-1.80). All these geochemical characteristics suggest that high Sr/Y signature is inherited from magma source. Sr-Nd-Hf analyses show enriched isotopic signatures-both εHf(t) and εNd(t) are negative(-38.30 to -23.59 and -18.6 to -17.9) with old two-stage model age (2 825 to 3 745 Ma for Hf, 2 584 to 2 642 Ma for Nd), indicating an old enriched crustal source. Based on petrology, geochemistry and Hf-Sr-Nd isotopic characteristics, we conclude that the Chaoyangdi Middle Devonian intrusive rocks were formed by partial melting of ancient basic lower crust with high Sr/Y ratios and formed by post-collisional extension and heating of asthenosphere upwelling, indicating the regional extension after collision between the Bainaimiao arc and the North China Block.
Xing-Meng orogeny is the accretionary orogeny between Siberia and North China plates with complex multi-stage subduction and accretion, and its tectonic evolution. has remained controversial for a long time. To reveal the arc-continent collision in the end of Early Paleozoic, this paper presents a study on Chaoyangdi Middle Devonian high Sr/Y granite in southern part of Xing-Meng orogeny zircon U-Pb dating results yield a formation age of 386.8±2.9 Ma, with the corresponding age of Middle Devonian (D2). Geochemical data shows that these rocks have high SiO2, Al2O3 and Na2O, moderate CaO and K2O, but low FeOt and MgO contents with the Na2O/K2O>1 and calc-alkaline series signature. The A/CNK ratios range from 1.02 to 1.08, indicating these samples are weak peraluminous series. Trace element analysis results display enrichment of LILEs, such as Rb, Ba, K and Sr, but depletion of HFSE, i.e., Nb, Ta, P and Ti, with high Sr/Y ratios (103-146), similar with adakitic-affinity. These rocks have strong fractionation between LREE and HREE ((La/Yb)N=9.9-14.6), no obvious HREE fractionation ((Gd/Yb)N=1.45-1.97) and weak positive Eu anomalies (δEu=1.31-1.80). All these geochemical characteristics suggest that high Sr/Y signature is inherited from magma source. Sr-Nd-Hf analyses show enriched isotopic signatures-both εHf(t) and εNd(t) are negative(-38.30 to -23.59 and -18.6 to -17.9) with old two-stage model age (2 825 to 3 745 Ma for Hf, 2 584 to 2 642 Ma for Nd), indicating an old enriched crustal source. Based on petrology, geochemistry and Hf-Sr-Nd isotopic characteristics, we conclude that the Chaoyangdi Middle Devonian intrusive rocks were formed by partial melting of ancient basic lower crust with high Sr/Y ratios and formed by post-collisional extension and heating of asthenosphere upwelling, indicating the regional extension after collision between the Bainaimiao arc and the North China Block.
2019, 44(1): 161-178.
doi: 10.3799/dqkx.2018.240
Abstract:
The tectonic affinity of the Baoyintu uplift is still controversial. Some researchers believe that the Baoyintu uplift is a microblock in CAOB, but others suggested that it's a part of the North China Craton (NCC). The formation age and tectonic affinity of the Baoyintu Group is important to solve this problem. LA-MC-ICP-MS zircon U-Pb ages of three quartzite samples in the Baoyintu Group are analyzed in this study. The minimum age of the zircons in the first, second and third formation, respectively, is 1 284 Ma, 1 319 Ma, and 1 395 Ma, representing the upper limit of the sedimentary.The zircon U-Pb age of the metamorphic mafic sill is 895.5±6.8 Ma, so the sedimentary age of the first to third formation of Baoyintu Group in the study area is limited to 895.5-1 284.0 Ma. It can be compared with the upper Alashan Group, the upper Bayan Obo and upper Huade Group. Geochemical characteristics of amphibolite from the Baoyintu Group infer that it is located in the rift of continental margin, and might be associated with the breackup of Rodinia. The age spectra of the detrital zircons in these sedimentary are similar, and the geological events defined by the main peaks correspond to those of the NCC, indicating that detrital of the Baoyintu Group is from NCC. And the Baoyintu Group is the sediment on north margin of the NCC, the Baoyintu uplift should be a part of NCC.
The tectonic affinity of the Baoyintu uplift is still controversial. Some researchers believe that the Baoyintu uplift is a microblock in CAOB, but others suggested that it's a part of the North China Craton (NCC). The formation age and tectonic affinity of the Baoyintu Group is important to solve this problem. LA-MC-ICP-MS zircon U-Pb ages of three quartzite samples in the Baoyintu Group are analyzed in this study. The minimum age of the zircons in the first, second and third formation, respectively, is 1 284 Ma, 1 319 Ma, and 1 395 Ma, representing the upper limit of the sedimentary.The zircon U-Pb age of the metamorphic mafic sill is 895.5±6.8 Ma, so the sedimentary age of the first to third formation of Baoyintu Group in the study area is limited to 895.5-1 284.0 Ma. It can be compared with the upper Alashan Group, the upper Bayan Obo and upper Huade Group. Geochemical characteristics of amphibolite from the Baoyintu Group infer that it is located in the rift of continental margin, and might be associated with the breackup of Rodinia. The age spectra of the detrital zircons in these sedimentary are similar, and the geological events defined by the main peaks correspond to those of the NCC, indicating that detrital of the Baoyintu Group is from NCC. And the Baoyintu Group is the sediment on north margin of the NCC, the Baoyintu uplift should be a part of NCC.
2019, 44(1): 179-192.
doi: 10.3799/dqkx.2018.305
Abstract:
The Langshan area in Inner Mongolia is a paramount transitional zone located between the North China Craton (NCC) and the Xingmeng orogenic belt (XOB), and structurally belongs to the Early Paleozoic marginal accretionary belt in the northern margin of the NCC. The Early Paleozoic magmatic rocks distributed in the Bayinhanggai area, the northern Langshan, have important implications for the reconstruction of regional Paleozoic tectonic setting and orogenic evolution. The dioritic batholith consists mainly of diorite and quartz-diorite, with the zircon 206Pb/238U ages of 435.8±2.2 Ma-437.7±2.2 Ma, which represent the crystallization age of the Early Silurian. The rocks are calc-alkaline series, enriched in LREE with the (La/Yb)N ratios 4.30~11.59, depleted in HFSE (especially Nb, Ta and Ti) and enriched in LILE (like Rb, Th, K, Ba and Sr), and weakly negative Eu anomalies (δEu=0.80~0.96), indicating that they are formed in island arcs or in active continents margin setting. The Early Silurian diorite batholith shows depleted isotopic compositions, εHf(t)=+5.2-+12.6, (87Sr/86Sr)i=0.704 665-0.706 174, εNd(t)=+1.84-+2.00. Integrated geochronology, geochemical, Sr-Nd-Hf isotopic data and regional geological data suggest that the Early Silurian diorite batholith in northern Langshan was generated in Early Paleozoic and resulted from the southward subduction of Wenduermiao ocean along Wenduermiao-Wude-northern Suolun. The diorites were formed by partial melting of juvenile crust which was modified by subduction slab fluids. The determination of the Silurian arc magmatic rocks makes it clear that the northern Langshan area belongs to the Early Paleozoic active continental margin of the northern NCC, and it is the westward extended part of the Bainaimiao island arc belt. At the same time, it also provides important materials for the Early Paleozoic "trench-arc-basin" system in the west section of the northern NCC.
The Langshan area in Inner Mongolia is a paramount transitional zone located between the North China Craton (NCC) and the Xingmeng orogenic belt (XOB), and structurally belongs to the Early Paleozoic marginal accretionary belt in the northern margin of the NCC. The Early Paleozoic magmatic rocks distributed in the Bayinhanggai area, the northern Langshan, have important implications for the reconstruction of regional Paleozoic tectonic setting and orogenic evolution. The dioritic batholith consists mainly of diorite and quartz-diorite, with the zircon 206Pb/238U ages of 435.8±2.2 Ma-437.7±2.2 Ma, which represent the crystallization age of the Early Silurian. The rocks are calc-alkaline series, enriched in LREE with the (La/Yb)N ratios 4.30~11.59, depleted in HFSE (especially Nb, Ta and Ti) and enriched in LILE (like Rb, Th, K, Ba and Sr), and weakly negative Eu anomalies (δEu=0.80~0.96), indicating that they are formed in island arcs or in active continents margin setting. The Early Silurian diorite batholith shows depleted isotopic compositions, εHf(t)=+5.2-+12.6, (87Sr/86Sr)i=0.704 665-0.706 174, εNd(t)=+1.84-+2.00. Integrated geochronology, geochemical, Sr-Nd-Hf isotopic data and regional geological data suggest that the Early Silurian diorite batholith in northern Langshan was generated in Early Paleozoic and resulted from the southward subduction of Wenduermiao ocean along Wenduermiao-Wude-northern Suolun. The diorites were formed by partial melting of juvenile crust which was modified by subduction slab fluids. The determination of the Silurian arc magmatic rocks makes it clear that the northern Langshan area belongs to the Early Paleozoic active continental margin of the northern NCC, and it is the westward extended part of the Bainaimiao island arc belt. At the same time, it also provides important materials for the Early Paleozoic "trench-arc-basin" system in the west section of the northern NCC.
2019, 44(1): 193-205.
doi: 10.3799/dqkx.2018.243
Abstract:
The study of sedimentary basins is important for understanding the tectonic evolution of orogenic belts. The Langshan region of Inner Mongolia is located in the middle central Asian orogenic belt and has a complicated structural evolutionary history. The tectonic setting of Late Paleozoic sedimentary basin is still in controversy. Based on the study of the lithology, sedimentary structure and sedimentary environment of Amushan Formation in Wulanaobao area in the northwestern of Langshan, we divide the Formation into three members. The first member is mainly composed of coarse clastic rocks with cross-bedding developed, and the sedimentary environment is braided river delta. The bottom of the second member is mainly composed of coarse clastic rocks with increasingly finer grain-size in the upper sediments and the bioclastic limestone at the top of second member, and the depositional environment is from braided river delta to littoral circumstances. At the same time, we firstly discovered plant fossils such as Calamites sp., Alethopteris sp., Cordaites principalis Gein from the lithic quartz sandstone of the second member. The third member consists of crystalline limestone and bioclastic limestone, and the sedimentary facies type is littoral-neritic facies. The detrital zircon ages of sandstone from the first and second members of Amushan Formation are divided into five groups of about~2.5 Ga, ~1.8-1.2 Ga, ~826 Ma, 461-440 Ma and 313-273 Ma, respectively. The youngest age of Amushan Formation is 273 Ma. Combining the results of plant fossils and the age of overlying volcanic rocks, the age of "Amushan Formation" is limited between 265 Ma and 273 Ma. The contemporaneous magmatic rocks in the study area were formed in the continental marginal arc. With the research of sedimentary characteristics, sedimentary age and tectonic position of Amushan Formation, we propose the method of stratigraphical divisions and correlation.
The study of sedimentary basins is important for understanding the tectonic evolution of orogenic belts. The Langshan region of Inner Mongolia is located in the middle central Asian orogenic belt and has a complicated structural evolutionary history. The tectonic setting of Late Paleozoic sedimentary basin is still in controversy. Based on the study of the lithology, sedimentary structure and sedimentary environment of Amushan Formation in Wulanaobao area in the northwestern of Langshan, we divide the Formation into three members. The first member is mainly composed of coarse clastic rocks with cross-bedding developed, and the sedimentary environment is braided river delta. The bottom of the second member is mainly composed of coarse clastic rocks with increasingly finer grain-size in the upper sediments and the bioclastic limestone at the top of second member, and the depositional environment is from braided river delta to littoral circumstances. At the same time, we firstly discovered plant fossils such as Calamites sp., Alethopteris sp., Cordaites principalis Gein from the lithic quartz sandstone of the second member. The third member consists of crystalline limestone and bioclastic limestone, and the sedimentary facies type is littoral-neritic facies. The detrital zircon ages of sandstone from the first and second members of Amushan Formation are divided into five groups of about~2.5 Ga, ~1.8-1.2 Ga, ~826 Ma, 461-440 Ma and 313-273 Ma, respectively. The youngest age of Amushan Formation is 273 Ma. Combining the results of plant fossils and the age of overlying volcanic rocks, the age of "Amushan Formation" is limited between 265 Ma and 273 Ma. The contemporaneous magmatic rocks in the study area were formed in the continental marginal arc. With the research of sedimentary characteristics, sedimentary age and tectonic position of Amushan Formation, we propose the method of stratigraphical divisions and correlation.
2019, 44(1): 206-219.
doi: 10.3799/dqkx.2018.315
Abstract:
The Carboniferous-Triassic magmatites are widely developed in the northern margin of the North China Block. It is an effective way to study subduction and accretion of the Paleo-Asian Ocean via magmatic rocks. However, the existing research focuses on the middle-eastern part of the northern margin of the North China Block, and the westward extension of magmatic activity needs further study. Through comprehensive analysis for the Late Paleozoic-Early Mesozoic magmatic rocks, we propose the Langshan area has experienced the obvious tectonic magmatism of the Early Carboniferous-Late Permian and Middle-Late Triassic. The Early Carboniferous-Late Permian magmatism was in 338-251 Ma, resulting in large scale regional exposure of gabbro+hornblende gabbro+diorite+quartz diorite+granodiorite+monzonitic granite rock assemblage.The trace elements and REEs characteristics of the gabbrides display affinity to arc signature, and the granitoids show characteristics of high Sr (>250×10-6, average 425×10-6), and low Y (6.89×10-6-24.30×10-6). The Middle-Late Triassic magmatism was in 245-228 Ma, resulting in large scale regional exposure of monzonitic granite+Syenite, whole rock geochemical data reveal that the granitoids are characterized by high K2O/Na2O (1.48-1.58), low Sr (154×10-6-49×10-6), low Yb (1.01×10-6-1.38×10-6) and the approximate seagull type of chondrite-normalized REE patterns, which reflects the geochemical characteristics of post-orogenic extension. Combining discrimination diagrams and regional geological data, the Langshan area was under the tectonic setting of continental margin arc during Early Carboniferous-Late Permian and post-orogenic during Middle-Late Triassic. The tectonic magmatism of Late Paleozoic-Early Mesozoic magmatic is similar between Langshan area and middle-eastern part of northern margin of NCC. Thus, the southern subduction of the Paleo-Asian Ocean formed the Late Paleozoic magmatic belt extending from east to west, and the collaged time for NCC and accretion orogenic belt was restricted to Latest Permian-Earliest Triassic.
The Carboniferous-Triassic magmatites are widely developed in the northern margin of the North China Block. It is an effective way to study subduction and accretion of the Paleo-Asian Ocean via magmatic rocks. However, the existing research focuses on the middle-eastern part of the northern margin of the North China Block, and the westward extension of magmatic activity needs further study. Through comprehensive analysis for the Late Paleozoic-Early Mesozoic magmatic rocks, we propose the Langshan area has experienced the obvious tectonic magmatism of the Early Carboniferous-Late Permian and Middle-Late Triassic. The Early Carboniferous-Late Permian magmatism was in 338-251 Ma, resulting in large scale regional exposure of gabbro+hornblende gabbro+diorite+quartz diorite+granodiorite+monzonitic granite rock assemblage.The trace elements and REEs characteristics of the gabbrides display affinity to arc signature, and the granitoids show characteristics of high Sr (>250×10-6, average 425×10-6), and low Y (6.89×10-6-24.30×10-6). The Middle-Late Triassic magmatism was in 245-228 Ma, resulting in large scale regional exposure of monzonitic granite+Syenite, whole rock geochemical data reveal that the granitoids are characterized by high K2O/Na2O (1.48-1.58), low Sr (154×10-6-49×10-6), low Yb (1.01×10-6-1.38×10-6) and the approximate seagull type of chondrite-normalized REE patterns, which reflects the geochemical characteristics of post-orogenic extension. Combining discrimination diagrams and regional geological data, the Langshan area was under the tectonic setting of continental margin arc during Early Carboniferous-Late Permian and post-orogenic during Middle-Late Triassic. The tectonic magmatism of Late Paleozoic-Early Mesozoic magmatic is similar between Langshan area and middle-eastern part of northern margin of NCC. Thus, the southern subduction of the Paleo-Asian Ocean formed the Late Paleozoic magmatic belt extending from east to west, and the collaged time for NCC and accretion orogenic belt was restricted to Latest Permian-Earliest Triassic.
2019, 44(1): 220-233.
doi: 10.3799/dqkx.2018.275
Abstract:
The Langshan structural belt is located in southwest of the Solonker suture zone and as well as the junction between the northern margin of the North China Craton and southern of Central Asian orogenic belt, which is an ideal workplace to study on tectonic-magmatic evolution and geodynamics background from Late Paleozoic to Early Mesozoic. An earliest Middle Triassic pluton with Adakite characteristics was discovered in this study and was called as Zhalashan pluton. The main rock types of Zhalashan Pluton are granodiorite and monzogranite. LA-ICP-MS zircon U-Pb ages yield the formation time of Zhalashan pluton between 244.9±1.2 Ma and 244.1±2.3 Ma. Geochemical characteristics show that the Zhalashan granites are typical C-type adakite with high SiO2(68.77%-72.58%), Al2O3(14.48%-16.28%), Sr(287×10-6-455×10-6, 413×10-6 on average) content and high Sr/Y ratio (46.07-95.50), low Y(4.07×10-6-8.01×10-6), Yb(0.43×10-6-0.78×10-6), Cr(5.18×10-6-8.92×10-6), Ni(1.34×10-6-7.71×10-6) content and low Mg#(35.54-41.64), Na2O/K2O ratio between 0.86 and 1.19. In addition, it exhibits significant fractionation between LREE and HREE[26.45 < (La/Yb)N < 56.13] and is depleted in HREE with slight Eu anomaly (0.82 < δEu < 1.02). Zircon Hf isotopic data displays that εHf(t) values vary from 2.5~8.9, Hf model ages TDM2 vary from 707-1 115 Ma, indicating a juvenile crustal material. Together with regional geological background, the authors hold that the Zhalashan pluton resulted from collision between Siberia Craton and North China Craton after the closure of the Paleo-Asian Ocean which is the product of partial melting of the thickened lower crust.
The Langshan structural belt is located in southwest of the Solonker suture zone and as well as the junction between the northern margin of the North China Craton and southern of Central Asian orogenic belt, which is an ideal workplace to study on tectonic-magmatic evolution and geodynamics background from Late Paleozoic to Early Mesozoic. An earliest Middle Triassic pluton with Adakite characteristics was discovered in this study and was called as Zhalashan pluton. The main rock types of Zhalashan Pluton are granodiorite and monzogranite. LA-ICP-MS zircon U-Pb ages yield the formation time of Zhalashan pluton between 244.9±1.2 Ma and 244.1±2.3 Ma. Geochemical characteristics show that the Zhalashan granites are typical C-type adakite with high SiO2(68.77%-72.58%), Al2O3(14.48%-16.28%), Sr(287×10-6-455×10-6, 413×10-6 on average) content and high Sr/Y ratio (46.07-95.50), low Y(4.07×10-6-8.01×10-6), Yb(0.43×10-6-0.78×10-6), Cr(5.18×10-6-8.92×10-6), Ni(1.34×10-6-7.71×10-6) content and low Mg#(35.54-41.64), Na2O/K2O ratio between 0.86 and 1.19. In addition, it exhibits significant fractionation between LREE and HREE[26.45 < (La/Yb)N < 56.13] and is depleted in HREE with slight Eu anomaly (0.82 < δEu < 1.02). Zircon Hf isotopic data displays that εHf(t) values vary from 2.5~8.9, Hf model ages TDM2 vary from 707-1 115 Ma, indicating a juvenile crustal material. Together with regional geological background, the authors hold that the Zhalashan pluton resulted from collision between Siberia Craton and North China Craton after the closure of the Paleo-Asian Ocean which is the product of partial melting of the thickened lower crust.
2019, 44(1): 234-247.
doi: 10.3799/dqkx.2018.100
Abstract:
The Zhaojinggou Nb-Ta deposit is a newly explored large-scale deposit in Wuchuan County, Inner Mongolia. The Nb-Ta orebody is mainly hosted in the amazonite-bearing albite granite, and partly hosted in the granite aplite, greisen and amazonite granite pegmatite. In this paper, we use monazite and zircon LA-MC-ICP-MS U-Pb and biotite 40Ar-39Ar dating methods to constrain the mineralization age. Monazite LA-MC-ICP-MS U-Pb geochronological dating of four samples from granites yields ages of 124±2 Ma (MSWD=2.9, n=27), 124±3 Ma (MSWD=2.0, n=46), 121±1 Ma (MSWD=3.3, n=43) and 124±2 Ma (MSWD=3.2, n=12). One zircon sample from albite granite yields age of 125±1 Ma (MSWD=1.6, n=18). Meanwhile, biotite 40Ar-39Ar dating obtains the plateau age of 133.84±0.79 Ma (MSWD=3.31), isochron age of 134.55±0.79 Ma (MSWD=1.93) and reverse isochron age of 134.58±0.80 Ma (MSWD=1.99). Therefore, all these ages constrain that the ore-forming period of Zhaojinggou Nb-Ta deposit is Early Cretaceous. In conclusion, the Zhaojinggou deposit resulted from the tectonic-magmatic activities of extensional setting, and the Yanshanian Period is the main Nb-Ta metallogenic age in Inner Mongolia.
The Zhaojinggou Nb-Ta deposit is a newly explored large-scale deposit in Wuchuan County, Inner Mongolia. The Nb-Ta orebody is mainly hosted in the amazonite-bearing albite granite, and partly hosted in the granite aplite, greisen and amazonite granite pegmatite. In this paper, we use monazite and zircon LA-MC-ICP-MS U-Pb and biotite 40Ar-39Ar dating methods to constrain the mineralization age. Monazite LA-MC-ICP-MS U-Pb geochronological dating of four samples from granites yields ages of 124±2 Ma (MSWD=2.9, n=27), 124±3 Ma (MSWD=2.0, n=46), 121±1 Ma (MSWD=3.3, n=43) and 124±2 Ma (MSWD=3.2, n=12). One zircon sample from albite granite yields age of 125±1 Ma (MSWD=1.6, n=18). Meanwhile, biotite 40Ar-39Ar dating obtains the plateau age of 133.84±0.79 Ma (MSWD=3.31), isochron age of 134.55±0.79 Ma (MSWD=1.93) and reverse isochron age of 134.58±0.80 Ma (MSWD=1.99). Therefore, all these ages constrain that the ore-forming period of Zhaojinggou Nb-Ta deposit is Early Cretaceous. In conclusion, the Zhaojinggou deposit resulted from the tectonic-magmatic activities of extensional setting, and the Yanshanian Period is the main Nb-Ta metallogenic age in Inner Mongolia.
2019, 44(1): 248-267.
doi: 10.3799/dqkx.2018.246
Abstract:
In recent years, great breakthroughs have been made in the deep Sn-Li prospecting in the Weilasituo area of the southern of Great Xing'an Range. However, the genesis and evolution of deep hidden rock mass closely related to the mineralization has not been studied in depth. In this paper, this cancealed granite was selected as example for a detailed geochronological, geochemical and Sr-Nd-Hf isotopic composition study in order to elucidate their petrogenesis. LA-ICP-MS U-Pb zircon age for Weilasituo pluton was 130.7±0.5 Ma (MSWD=0.53), indicating that it was generated in Early Cretaceous. Chemically, Weilasituo granite is metaluminous-(weakly) peraluminous (A/CNK concentrated in the range of 1.02-1.08), which shows high contents of silica, alkalis and natrium, low abundances of calcium, magnesium, iron and extremely low P2O5(< 0.01%), with high Rb/Sr, Nb/Ta and low Zr/Hf ratios. They are also enriched in Cs, Rb, Th, U, Nb, Ta, Li, F and depleted in Ba, Sr, Ti, REE elements with low LREE/HREE ratios and obviously negative Eu abnormality (δEu=0.02-0.15). Zircon saturation temperatures (691-727℃) and Zr+Nb+Ce+Y contents of Weilasituo pluton are less than those of the low-limit values of the A-type granite. Integrated geological and geochemical data suggest that the pluton was highly fractionated I-type granite. The granite has positive εNd(t)(+1.10-+3.75) and relatively high εHf(t)(+4.2-+8.7) and young two-stage Nd and Hf model ages (T(Nd)DMC=607-829 Ma; T(Hf)DMC=627-914 Ma), suggesting that the rock was dominantly derived from the partial melting of a juvenile lower crust with a mass of mantle magma mixed into the crust, followed by fractional crystallization during magma ascent. The Sn-(rare-metal) mineralization of the pluton was controlled jointly both by high fractionation of the magma and fluid-melt interaction during the late stage. A complete magmatic-hydrothermal system was revealed by the Sn-(rare-metal) mineralization granite with the surrounding vein ore bodies.
In recent years, great breakthroughs have been made in the deep Sn-Li prospecting in the Weilasituo area of the southern of Great Xing'an Range. However, the genesis and evolution of deep hidden rock mass closely related to the mineralization has not been studied in depth. In this paper, this cancealed granite was selected as example for a detailed geochronological, geochemical and Sr-Nd-Hf isotopic composition study in order to elucidate their petrogenesis. LA-ICP-MS U-Pb zircon age for Weilasituo pluton was 130.7±0.5 Ma (MSWD=0.53), indicating that it was generated in Early Cretaceous. Chemically, Weilasituo granite is metaluminous-(weakly) peraluminous (A/CNK concentrated in the range of 1.02-1.08), which shows high contents of silica, alkalis and natrium, low abundances of calcium, magnesium, iron and extremely low P2O5(< 0.01%), with high Rb/Sr, Nb/Ta and low Zr/Hf ratios. They are also enriched in Cs, Rb, Th, U, Nb, Ta, Li, F and depleted in Ba, Sr, Ti, REE elements with low LREE/HREE ratios and obviously negative Eu abnormality (δEu=0.02-0.15). Zircon saturation temperatures (691-727℃) and Zr+Nb+Ce+Y contents of Weilasituo pluton are less than those of the low-limit values of the A-type granite. Integrated geological and geochemical data suggest that the pluton was highly fractionated I-type granite. The granite has positive εNd(t)(+1.10-+3.75) and relatively high εHf(t)(+4.2-+8.7) and young two-stage Nd and Hf model ages (T(Nd)DMC=607-829 Ma; T(Hf)DMC=627-914 Ma), suggesting that the rock was dominantly derived from the partial melting of a juvenile lower crust with a mass of mantle magma mixed into the crust, followed by fractional crystallization during magma ascent. The Sn-(rare-metal) mineralization of the pluton was controlled jointly both by high fractionation of the magma and fluid-melt interaction during the late stage. A complete magmatic-hydrothermal system was revealed by the Sn-(rare-metal) mineralization granite with the surrounding vein ore bodies.
2019, 44(1): 268-283.
doi: 10.3799/dqkx.2018.260
Abstract:
The Dalaimiao pluton crops out in the northern of Suzuoqi, near the border areas between China and Mongolia, which is referred as an important component of the Erenhot-East Ujimqin Late Paleozoic arc magmatic belt and its petrogenesis can provide insights into the tectonic evolution of the northern margins of Xing'an-Mongolian orogenic belt. Based on field investigation, geochronology and geochemistry, it is found that the pluton lithologically consists of medium-fine grained biotite granites in the center and medium-grained granites on the margin. Zircon U-Pb dating yields a weighted mean age of 301.2±2.1 Ma (MSWD=1.2, 2σ), indicating these granites were generated during a Late Carboniferous magmatic event. All of these granites are highly siliceous, Fe-poor, slightly peraluminous, and show enrichments in Rb, Th, U, Pb and depletions in Ba, Sr, P, Nb and Ta. The medium-fine grained biotite granites are Na-rich, and have high concentrations of heavy rare earth elements (REE), whereas the medium-grained granites show higher K2O contents, more significant elemental differentiation and negative europium anomalies. Dalaimiao pluton shows depleted isotopic compositions with (87Sr/86Sr)i=0.703 6-0.707 5, εNd(t)=0.08-2.77, and positive εHf(t) values of 4.70-11.50. Integrated geochronology and geochemical data suggest the Dalaimiao pluton is genetically classified as I-type granites, with some geochemical features of A-type granites. The Dalaimiao granites derived from partial melting of juvenile crust which were generated by the underplating of mantle material, and were formed in a tectonic transitional stage from compression uplift to intracontinental extension. Emplacement of Dalaimiao pluton provides more detailed constraints on the specific timing of tectonic variation in the northern margins of Xing'an-Mongolian orogenic belt during the Late Carboniferous.
The Dalaimiao pluton crops out in the northern of Suzuoqi, near the border areas between China and Mongolia, which is referred as an important component of the Erenhot-East Ujimqin Late Paleozoic arc magmatic belt and its petrogenesis can provide insights into the tectonic evolution of the northern margins of Xing'an-Mongolian orogenic belt. Based on field investigation, geochronology and geochemistry, it is found that the pluton lithologically consists of medium-fine grained biotite granites in the center and medium-grained granites on the margin. Zircon U-Pb dating yields a weighted mean age of 301.2±2.1 Ma (MSWD=1.2, 2σ), indicating these granites were generated during a Late Carboniferous magmatic event. All of these granites are highly siliceous, Fe-poor, slightly peraluminous, and show enrichments in Rb, Th, U, Pb and depletions in Ba, Sr, P, Nb and Ta. The medium-fine grained biotite granites are Na-rich, and have high concentrations of heavy rare earth elements (REE), whereas the medium-grained granites show higher K2O contents, more significant elemental differentiation and negative europium anomalies. Dalaimiao pluton shows depleted isotopic compositions with (87Sr/86Sr)i=0.703 6-0.707 5, εNd(t)=0.08-2.77, and positive εHf(t) values of 4.70-11.50. Integrated geochronology and geochemical data suggest the Dalaimiao pluton is genetically classified as I-type granites, with some geochemical features of A-type granites. The Dalaimiao granites derived from partial melting of juvenile crust which were generated by the underplating of mantle material, and were formed in a tectonic transitional stage from compression uplift to intracontinental extension. Emplacement of Dalaimiao pluton provides more detailed constraints on the specific timing of tectonic variation in the northern margins of Xing'an-Mongolian orogenic belt during the Late Carboniferous.
2019, 44(1): 284-297.
doi: 10.3799/dqkx.2018.365
Abstract:
The Beishan orogenic belt is located in the middle of the Central Asian orogenic belt (CAOB) and the tectonic history of its Precambrian basement rocks is the key to understand the formation and evolution of the Beishan orogenic belt. In this study, we select the gneissic granites in the North Beishan orogenic belt (NBOB) for zircon U-Pb chronology and geochemical analysis. The results show that the gneissic granites formed in the 885±4 Ma, which reveals the Neoproterozoic magmatic events in the NBOB for the first time. The gneissic granites belong to the peraluminous, high-K, calc-alkaline series and are characterized by high SiO2 and K2O+Na2O, low CaO. The gneissic granites show an enrichment of light rare earth elements (LREE) with Europium negative anomaly and are characterized by enrichment of large ion lithophile elements (LILE) such as Rb, K, Th, U, but depletion in high field strength elements (HFSE) such as Nb, Sr, P, Ti. The petrography and geochemical signatures reveal a possible S-type granite affinity and are derived from the partial melting of metamorphic complex sandstone of source area with initial melt temperature (777-798℃). The gneissic granites were likely generated in a continental collision tectonic setting. By comparing our new data with previous results from the Precambrian basement in the South Beishan orogenic belt and the Tianshan block (microcontinent in the Chinese Tianshan), we suggest that the Precambrian microcontinents in the northern Beishan have similar crustal evolutionary history to the South Beishan orogenic belt (SBOB) and Central Tianshan block. They participated in the Rodinia supercontinent aggregation together and formed a part of Rodinia during the Neoproterozoic period. The Neoproterozoic magmatic events in the Beishan area are the response of the Rodinia supercontinent aggregation.
The Beishan orogenic belt is located in the middle of the Central Asian orogenic belt (CAOB) and the tectonic history of its Precambrian basement rocks is the key to understand the formation and evolution of the Beishan orogenic belt. In this study, we select the gneissic granites in the North Beishan orogenic belt (NBOB) for zircon U-Pb chronology and geochemical analysis. The results show that the gneissic granites formed in the 885±4 Ma, which reveals the Neoproterozoic magmatic events in the NBOB for the first time. The gneissic granites belong to the peraluminous, high-K, calc-alkaline series and are characterized by high SiO2 and K2O+Na2O, low CaO. The gneissic granites show an enrichment of light rare earth elements (LREE) with Europium negative anomaly and are characterized by enrichment of large ion lithophile elements (LILE) such as Rb, K, Th, U, but depletion in high field strength elements (HFSE) such as Nb, Sr, P, Ti. The petrography and geochemical signatures reveal a possible S-type granite affinity and are derived from the partial melting of metamorphic complex sandstone of source area with initial melt temperature (777-798℃). The gneissic granites were likely generated in a continental collision tectonic setting. By comparing our new data with previous results from the Precambrian basement in the South Beishan orogenic belt and the Tianshan block (microcontinent in the Chinese Tianshan), we suggest that the Precambrian microcontinents in the northern Beishan have similar crustal evolutionary history to the South Beishan orogenic belt (SBOB) and Central Tianshan block. They participated in the Rodinia supercontinent aggregation together and formed a part of Rodinia during the Neoproterozoic period. The Neoproterozoic magmatic events in the Beishan area are the response of the Rodinia supercontinent aggregation.
2019, 44(1): 298-311.
doi: 10.3799/dqkx.2018.356
Abstract:
The Beishan orogenic belt has always been one of study hotspots on the time of closure of the Paleoasian Ocean. Previous studies on the Hongshishan-Baiheshan-Pengboshan ophiolite mélange belt are more focused on a direct constraint on the time of the oceanic subduction, subduction polarity, and the origin and structural attributes of Carboniferous volcanic rocks, resulting in a lack of understanding of the tectonic setting and magmatic evolution of the Devonian volcanic rocks. In this paper, we present new detailed petrologic, geochemical, U-Pb ages and Hf isotope analyses on the Devonian volcanic rocks from the Hazhu formation of the Queershan Group in the Hazhudongshan area of Beishan. Combining with the previous works in this region, our study reveals that the volcanic rocks from the Hazhu Formation of the Queershan Group from Hazhudongshan formed in the Middle Devonian (386.9±1.7 Ma), which is characterized by enriched Na and low K of the low potassium tholeiite to calc-alkaline series. In the aspect of trace elements, these rocks are depleted in high field strength elements of Nb, Ta, P and Ti. These rocks were probably formed in the island arc environment, representing products of the southward subduction of the Paleoasian Ocean. The εHf(t) values of the rhyolite sample are uniform, ranging from 4.4 to 15, with the two-stage Hf model ages between 424 Ma and 1 109 Ma. Thus, the rhyolite of Queershan Group should be derived from partial melting of Early Paleozoic and Meso-Neoproterozoic juvenile crust. However, the magma of andesite of Queershan Group is derived from depleted mantel wedge metasomatized by fluid from subducted plate. Meanwhile the product created by the rising magma has experienced a certain fractional crystallization and assimilation and contamination of upper crustal material. According to previous regional geological studies, the Hongshishan-Baiheshan-Pengboshan ocean should be formed in the extension setting of a Queershan back-arc basin after the Late Devonian.
The Beishan orogenic belt has always been one of study hotspots on the time of closure of the Paleoasian Ocean. Previous studies on the Hongshishan-Baiheshan-Pengboshan ophiolite mélange belt are more focused on a direct constraint on the time of the oceanic subduction, subduction polarity, and the origin and structural attributes of Carboniferous volcanic rocks, resulting in a lack of understanding of the tectonic setting and magmatic evolution of the Devonian volcanic rocks. In this paper, we present new detailed petrologic, geochemical, U-Pb ages and Hf isotope analyses on the Devonian volcanic rocks from the Hazhu formation of the Queershan Group in the Hazhudongshan area of Beishan. Combining with the previous works in this region, our study reveals that the volcanic rocks from the Hazhu Formation of the Queershan Group from Hazhudongshan formed in the Middle Devonian (386.9±1.7 Ma), which is characterized by enriched Na and low K of the low potassium tholeiite to calc-alkaline series. In the aspect of trace elements, these rocks are depleted in high field strength elements of Nb, Ta, P and Ti. These rocks were probably formed in the island arc environment, representing products of the southward subduction of the Paleoasian Ocean. The εHf(t) values of the rhyolite sample are uniform, ranging from 4.4 to 15, with the two-stage Hf model ages between 424 Ma and 1 109 Ma. Thus, the rhyolite of Queershan Group should be derived from partial melting of Early Paleozoic and Meso-Neoproterozoic juvenile crust. However, the magma of andesite of Queershan Group is derived from depleted mantel wedge metasomatized by fluid from subducted plate. Meanwhile the product created by the rising magma has experienced a certain fractional crystallization and assimilation and contamination of upper crustal material. According to previous regional geological studies, the Hongshishan-Baiheshan-Pengboshan ocean should be formed in the extension setting of a Queershan back-arc basin after the Late Devonian.
2019, 44(1): 312-327.
doi: 10.3799/dqkx.2018.261
Abstract:
The character of Late Paleozoic magmatic events has great significance for the study of tectonic evolution in the northern Beishan. A systematic study of geochemistry, geochronology and Lu-Hf isotopes is made on Baishan Formation volcanic rocks in the Beishan Hazhu area of Inner Mongolia. The results show that Baishan Formation volcanic rocks are composed of basaltic andesite, andesite, dacitic and rhyolitic volcanic rocks. The diagenetic ages of andesite, dacite and rhyolite from the LA-ICP-MS zircon U-Pb dating are 325.6±1.4 Ma, 313.5±3.4 Ma and 314.7±1.7 Ma respectively, all which belong to the later period of Early Carboniferous epoch-medium period of Late Carboniferous epoch. Geochemical studies show that the Baishan Formation volcanic rocks are characterized by apparent "component polarity feature" in spatial distribution, displaying regional north-to-south evolution from intermediate volcanic rocks (calc-alkaline series) to acid volcanic rocks (high-K calc-alkaline series), with the increased content of K2O and ratio of K2O/Na2O, in which basaltic andesite and andesite belong to higher content of Al2O3, lower content of TiO2 and lower content of Ni and Cr. Additionally, microelements of all volcanic samples generally show depletion of high field strength elements such as Nb, Ta, P, Ti and apparent right-leaning distribution patterns of the REE with depletion in LREE and enrichment in HREE. The above characteristics suggest that the Baishan Formation volcanic rocks are formed from active continental margin arc in the process of southern subduction oceanic crust. Additionally, andesite in the Baishan Formation is characterized by higher value of εHf(t) (7.0-14.1)and the young average crustal model age TDMC (437-891 Ma), Rb/Sr ratio (0.01-0.15) near the upper mantle and Nb/Ta ration (12.59-18.80) between mean values of crust and mantle; rhyolite is characterized by later value of εHf(t) (4.3-8.2) and the older average crustal model age TDMC (804-1 054 Ma), Rb/Sr ratio (0.80-1.73) that is much larger than the mean values of crust and Nb/Ta ration (10.66-13.08) near the mean values of crust, which all indicate that magma source region was mainly new crust and mantle material near the ocean side and it was evolved gradually into the increasing of more continental crust (older crust) material close to the inland side. Based on the above analysis and combined with the previous data, it is concluded that Beishan Hazhu area Late Paleozoic Carboniferous Baishan Formation volcanic rocks were formed in the subduction process of Hong Shishan Ocean into the south side of micro plot of Mazong Mountain-Han Mountain, and it had been resulted from magmatism of the active continental margin.
The character of Late Paleozoic magmatic events has great significance for the study of tectonic evolution in the northern Beishan. A systematic study of geochemistry, geochronology and Lu-Hf isotopes is made on Baishan Formation volcanic rocks in the Beishan Hazhu area of Inner Mongolia. The results show that Baishan Formation volcanic rocks are composed of basaltic andesite, andesite, dacitic and rhyolitic volcanic rocks. The diagenetic ages of andesite, dacite and rhyolite from the LA-ICP-MS zircon U-Pb dating are 325.6±1.4 Ma, 313.5±3.4 Ma and 314.7±1.7 Ma respectively, all which belong to the later period of Early Carboniferous epoch-medium period of Late Carboniferous epoch. Geochemical studies show that the Baishan Formation volcanic rocks are characterized by apparent "component polarity feature" in spatial distribution, displaying regional north-to-south evolution from intermediate volcanic rocks (calc-alkaline series) to acid volcanic rocks (high-K calc-alkaline series), with the increased content of K2O and ratio of K2O/Na2O, in which basaltic andesite and andesite belong to higher content of Al2O3, lower content of TiO2 and lower content of Ni and Cr. Additionally, microelements of all volcanic samples generally show depletion of high field strength elements such as Nb, Ta, P, Ti and apparent right-leaning distribution patterns of the REE with depletion in LREE and enrichment in HREE. The above characteristics suggest that the Baishan Formation volcanic rocks are formed from active continental margin arc in the process of southern subduction oceanic crust. Additionally, andesite in the Baishan Formation is characterized by higher value of εHf(t) (7.0-14.1)and the young average crustal model age TDMC (437-891 Ma), Rb/Sr ratio (0.01-0.15) near the upper mantle and Nb/Ta ration (12.59-18.80) between mean values of crust and mantle; rhyolite is characterized by later value of εHf(t) (4.3-8.2) and the older average crustal model age TDMC (804-1 054 Ma), Rb/Sr ratio (0.80-1.73) that is much larger than the mean values of crust and Nb/Ta ration (10.66-13.08) near the mean values of crust, which all indicate that magma source region was mainly new crust and mantle material near the ocean side and it was evolved gradually into the increasing of more continental crust (older crust) material close to the inland side. Based on the above analysis and combined with the previous data, it is concluded that Beishan Hazhu area Late Paleozoic Carboniferous Baishan Formation volcanic rocks were formed in the subduction process of Hong Shishan Ocean into the south side of micro plot of Mazong Mountain-Han Mountain, and it had been resulted from magmatism of the active continental margin.
2019, 44(1): 328-343.
doi: 10.3799/dqkx.2018.238
Abstract:
The chronology, geochemistry and zircon Hf isotopes of granitoids in Hazhu area of the northern Beishan belt are systematically studied, and the genesis of the plutons and their restrictions on the tectonic magma evolution in Late Paleozoic are discussed. The zircon LA-MC-ICP-MS U-Pb dating results show that the granodiorites and monzogranites formed during the late Late Carboniferous in 298.6±1.7 Ma and 306.0±1.3 Ma, and the alkali-feldspar granites formed in Early Permian 289.3±1.3 Ma. Chemically, the granodiorites and monzogranites are characterized by middle potassium calc alkaline, low Mg# value and middle degree of differentiation (D.I.=79.2-86.9), metaluminum and enriched-magnesium. And alkali-feldspar granites show high contents of silica and alkalis, metaluminum, low abundances of calcium, magnesium and iron, and high degree of differentiation (D.I.=94.4-96.5). All of them are enriched in Rb, Ba, Th, U, La, Ce, and so on, and depleted in high field strength elements, Nb, Ta, P, Ti, Sr, and so on. The εHf(t) values in this paper are all positive. The Hf isotopic crustal model age TDMC is mainly concentrated from 800 Ma to 450 Ma. According to the data obtained in this paper and other regional geological data acquired recently, the subduction plate dehydrated, after then, the subduction fluid entered into the juvenile crust, and induced partial melting of the juvenile crust, forming the granitoids in Late Carboniferous. The extension resulted in the thinning and stretching of the lithosphere due to the post collisional extension in Early Permian, which caused the partial melting of the new crust, and then the alkali-spar granites were formed by a high degree of differentiation and evolution.
The chronology, geochemistry and zircon Hf isotopes of granitoids in Hazhu area of the northern Beishan belt are systematically studied, and the genesis of the plutons and their restrictions on the tectonic magma evolution in Late Paleozoic are discussed. The zircon LA-MC-ICP-MS U-Pb dating results show that the granodiorites and monzogranites formed during the late Late Carboniferous in 298.6±1.7 Ma and 306.0±1.3 Ma, and the alkali-feldspar granites formed in Early Permian 289.3±1.3 Ma. Chemically, the granodiorites and monzogranites are characterized by middle potassium calc alkaline, low Mg# value and middle degree of differentiation (D.I.=79.2-86.9), metaluminum and enriched-magnesium. And alkali-feldspar granites show high contents of silica and alkalis, metaluminum, low abundances of calcium, magnesium and iron, and high degree of differentiation (D.I.=94.4-96.5). All of them are enriched in Rb, Ba, Th, U, La, Ce, and so on, and depleted in high field strength elements, Nb, Ta, P, Ti, Sr, and so on. The εHf(t) values in this paper are all positive. The Hf isotopic crustal model age TDMC is mainly concentrated from 800 Ma to 450 Ma. According to the data obtained in this paper and other regional geological data acquired recently, the subduction plate dehydrated, after then, the subduction fluid entered into the juvenile crust, and induced partial melting of the juvenile crust, forming the granitoids in Late Carboniferous. The extension resulted in the thinning and stretching of the lithosphere due to the post collisional extension in Early Permian, which caused the partial melting of the new crust, and then the alkali-spar granites were formed by a high degree of differentiation and evolution.
Zircon U-Pb Geochronology of the Mesozoic Volcanic Rocks from Qingshan Group in the Eastern Shandong
2019, 44(1): 344-354.
doi: 10.3799/dqkx.2018.337
Abstract:
The mesozoic volcanic rocks from the Qingshan Group are the most representative in the Shandong Province, and investigation of its genesis and forming time is very important to reveal the evolution history of the eastern North China Craton. LA-ICP-MS zircon U-Pb ages of meta-basic volcanic rocks and meta-acid volcanic rocks from the Qingshan Group in the eastern Shandong are reported in this paper. The dating results show that the ages of the meta-basic and meta-acidic volcanic rocks are 117±2 Ma (MSWD=3.2) and 116±4 (MSWD=3.5) respectively, which represent the formation time of the volcanic rocks from the Qingshan Group. Based on the synthesis of geochronology, the start and the end age of the volcanic rocks from the Qingshan Group in the eastern Shandong are younger than those in the western Shandong. The meta-basic volcanic rocks might have undergone multiple events induced by continental crustal materials both from the North China Craton and the deep subduction of the Yangtze Craton.
The mesozoic volcanic rocks from the Qingshan Group are the most representative in the Shandong Province, and investigation of its genesis and forming time is very important to reveal the evolution history of the eastern North China Craton. LA-ICP-MS zircon U-Pb ages of meta-basic volcanic rocks and meta-acid volcanic rocks from the Qingshan Group in the eastern Shandong are reported in this paper. The dating results show that the ages of the meta-basic and meta-acidic volcanic rocks are 117±2 Ma (MSWD=3.2) and 116±4 (MSWD=3.5) respectively, which represent the formation time of the volcanic rocks from the Qingshan Group. Based on the synthesis of geochronology, the start and the end age of the volcanic rocks from the Qingshan Group in the eastern Shandong are younger than those in the western Shandong. The meta-basic volcanic rocks might have undergone multiple events induced by continental crustal materials both from the North China Craton and the deep subduction of the Yangtze Craton.
