A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP ^207Pb/^206Pb we...A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP ^207Pb/^206Pb weighted mean ages of 2180 ± 5 Ma and 2087 ± 9 Ma, respectively. The older date is within error of the age of the Dawaliang Granite in Wutaishan and is considered to be derived from a similar crustal magmatic source. The younger date is within error of reported ages from metasediments and meta-volcanics of the Wanzi supracrustal rocks and the Nanying granitic gneisses in the adjacent Fuping Complex and is interpreted to be the age of volcanism in the Hutuo Group. These data establish that: (1) the Hutuo Group is Paleoproterozoic and not Archean in age and (2) the volcanism and sedimentation were coeval in the Wutai and Fuping complexes. Sedimentation was therefore widespread at this time and possibly reflects deposition along an evolving continental margin, most likely the western margin of the Eastern Block of the North China Craton. The age of 2087±9 Ma for volcanism in the Hutuo Group means that it must have been deformed and metamorphosed after this time.This further supports the evidence, obtained from other recent studies, that the main tectonism in the Wutaishan areaoccurred at ～1.8 Ga during the Lüliang orogeny. This orogeny resulted in the collision of the Eastern and Western blocks of the North China Craton and formed part of a global supercontinental amalgamation event.展开更多
Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological s...Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological surveying confirms that these volcanic rocks are conformable within the neighboring sedimentary rocks. The SHRIMP results on basaltic andesite are divided into two groups. In one group the 207Pb/206Pb ages are from 2433 to 2558 Ma, which is consistent with the basement crustal age in Fuping and Wutai areas. In the other group, 13 grains yielded a weighted mean 207Pb/206Pb age of 2140±14 Ma. The latter is interpreted as the eruption age of the basaltic andesite, and gives the age of the base of the Hutuo Group. This result further suggests that the Hutuo Group formed in the middle Paleoproterozoic, not the early Palaeoproterozoic or late Archaean, as thought before, and is related to a 2.2-2.1 Ga rifting event in the Central North China Craton.展开更多
The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and dassical cross-section in the middle segment of the Trans-North China Orogen, generally divided into Eastern and Wes...The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and dassical cross-section in the middle segment of the Trans-North China Orogen, generally divided into Eastern and Western Blocks. Unconformably overlying the Wutai and Fuping Complexes is the Hutuo Group considered as the youngest lithostratigraphic unit in the region and important both for interpreting Precambrian history as well as the overall evolution of the Trans-North China Orogen. Lack of knowledge about provenance of the sedimentary rocks in this group has hindered understanding of the depositional environments and tectonic significance. LA-ICP-MS was applied to obtain U-Pb zircon ages for the granitic pebbles, the lowest lithostratigraphic rock of the Hutuo Group, which, combined with previous lithostratigraphic, geochronological, structural and metamorphic data, provides new constraints on the sedimentary provenance and tectonic evolution of the region. The sequence of the Hutuo Group ranges upward from lower basal conglomerates and volcaniclastic rocks （Doucun Subgroup）, through clastic sediments, slates, dolomites and marbles （Dongye Subgroup）, to sandstones and conglomerates at the top （Guojiazhai Subgroup）. Zircons from granitic pebbles preserved in the Doucun Subgroup basal conglomerates give weighted mean ^207pb/^206pb ages between 2517 Ma and 2566 Ma, which are the same as those for the late Archean Wutai Granitoids, indicating that the pebbles were derived from the Wutai granitic intrusions （2566-2515 Ma）. Based on the new data and previous studies, combined with an igneous zircon crystallization age of 2087±9 Ma obtained for volcanics in the Hutuo Group, the Hutuo Group was deposited in a subduction-related retro-arc foreland basin environment that developed behind the Wutai arc during the eastward-directed subduction of the Western Block beneath the western margin of the Eastern Block. This basin underwent long-lived sedimentation and finally closed during the -1850 Ma collision展开更多
The Lomagundi-Jatuli Event（LJE） is one of the largest and earliest positive carbon isotope excursions preserving δ^（13）C_（carb） values between ＋5 and ＋16‰ in Paleoproterozoic carbonates worldwide. However, t...The Lomagundi-Jatuli Event（LJE） is one of the largest and earliest positive carbon isotope excursions preserving δ^（13）C_（carb） values between ＋5 and ＋16‰ in Paleoproterozoic carbonates worldwide. However, the duration, amplitude and patterns of these excursions remain poorly constrained. The 2.14-1.83 Ga Hutuo Group in the North China Craton is a 〉10 km thick volcano-sedimentary sequence, including 〉5 km thick well-preserved carbonates that were deposited in supra-tidal to sub-tidal environments. C-O isotopic and elemental analyses of 152 least altered samples of the carbonates revealed a three-stage δ^（13）C evolution. It began with an exclusively positive δ^（13）C_（carb）（＋1.3 to ＋ 3.4‰） stage in the ~2.1 Ga carbonate in the Dashiling and Qingshicun Formations, followed by a transition from positive values to oscillating positive and negative values in ~3 000 m thick carbonates of the Wenshan, Hebiancun, Jianancun, and Daguandong Formations, and end with exclusively negative δ^（13）C_（carb） values preserved in 〉 500 m thick dolostones of the Huaiyincun and Beidaxing Formations. It appears that much of the LJE, particularly those extremely positive δ^（13）C_（carb） signals, was not recorded in the Hutuo carbonates. The exclusively positive δ^（13）C_（carb） values（＋1.3 to ＋ 3.4‰） preserved in the lower formations likely correspond to the end of the LJE, whereas the subsequent two stages reflect the aftermath of the LJE and the onset of Shunga-Francevillian event（SFE）. The present data point to an increased influence of oxygen on the carbon cycle from the Doucun to the Dongye Subgroups and demonstrate that the termination of the LJE in the North China Craton is nearly simultaneous with those in Fennoscandia and South Africa.展开更多
Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai...Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai Mountains area in the North China Craton.These two granite pebbles give zircon 207 Pb/206 Pb ages of 2513±8 Ma and 2527±8 Ma respectively,which are consistent with the emplacement ages of the Wangjiahui grey granite and Guangmingsi or Shifo granite in the Wutai Mountains.Detrital zircons from those two quartzite pebbles are mostly 2550-2490 Ma old with lesser number of 2800-2550 Ma grains,which is similar to the ages of detrital zircons from quartzites in the Gaofan Subgroup of the Neoarchean Wutai Group.Thus,the pebbles in the Hutuo Group basal conglomerates were derived locally from Wutai Mountains Neoarchean sources.Zircons from the Sijizhuang Formation conglomerate granite and quartzite pebbles mostly have positive ε Hf(t) values,a minority with ε Hf(t) values like model depleted mantle(DM) of the same age,but with most showing DM model ages 200-100 Ma.This indicates that most of the source materials were derived from the mantle within the previous 200 million years,whereas some are derived from 2550-2510 Ma juvenile crustal additions.This additional evidence suggests that in the North China Craton there was important initial polycyclic crustal formation and cratonization in the late Neoarchaean,prior to superimposed Palaeoproterozoic orogenic cycles.展开更多
文摘A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP ^207Pb/^206Pb weighted mean ages of 2180 ± 5 Ma and 2087 ± 9 Ma, respectively. The older date is within error of the age of the Dawaliang Granite in Wutaishan and is considered to be derived from a similar crustal magmatic source. The younger date is within error of reported ages from metasediments and meta-volcanics of the Wanzi supracrustal rocks and the Nanying granitic gneisses in the adjacent Fuping Complex and is interpreted to be the age of volcanism in the Hutuo Group. These data establish that: (1) the Hutuo Group is Paleoproterozoic and not Archean in age and (2) the volcanism and sedimentation were coeval in the Wutai and Fuping complexes. Sedimentation was therefore widespread at this time and possibly reflects deposition along an evolving continental margin, most likely the western margin of the Eastern Block of the North China Craton. The age of 2087±9 Ma for volcanism in the Hutuo Group means that it must have been deformed and metamorphosed after this time.This further supports the evidence, obtained from other recent studies, that the main tectonism in the Wutaishan areaoccurred at ～1.8 Ga during the Lüliang orogeny. This orogeny resulted in the collision of the Eastern and Western blocks of the North China Craton and formed part of a global supercontinental amalgamation event.
基金supported by the Basic Foundation of Scientific Research Work from Ministry of Science and Technology of China (J0721 and J0907)National Commission on Stratigraphy of China (1212010511702-01)China Geological Survey (1212010611801)
文摘Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological surveying confirms that these volcanic rocks are conformable within the neighboring sedimentary rocks. The SHRIMP results on basaltic andesite are divided into two groups. In one group the 207Pb/206Pb ages are from 2433 to 2558 Ma, which is consistent with the basement crustal age in Fuping and Wutai areas. In the other group, 13 grains yielded a weighted mean 207Pb/206Pb age of 2140±14 Ma. The latter is interpreted as the eruption age of the basaltic andesite, and gives the age of the base of the Hutuo Group. This result further suggests that the Hutuo Group formed in the middle Paleoproterozoic, not the early Palaeoproterozoic or late Archaean, as thought before, and is related to a 2.2-2.1 Ga rifting event in the Central North China Craton.
基金supported by the Ministry of Land and Re-sources of the Peoples’ Republic of China (Grant Nos. 1212010811033, 1212010711815) and the Beijing SHRIMP Center
基金This research was financially supported by the National Natural Science Foundation of China （Grants 40429001, 40420120135 and 40472098）Hong Kong RGC （Grants 7055/05P, 7058/04P, 7055/03P and 7048/03P）.
文摘The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and dassical cross-section in the middle segment of the Trans-North China Orogen, generally divided into Eastern and Western Blocks. Unconformably overlying the Wutai and Fuping Complexes is the Hutuo Group considered as the youngest lithostratigraphic unit in the region and important both for interpreting Precambrian history as well as the overall evolution of the Trans-North China Orogen. Lack of knowledge about provenance of the sedimentary rocks in this group has hindered understanding of the depositional environments and tectonic significance. LA-ICP-MS was applied to obtain U-Pb zircon ages for the granitic pebbles, the lowest lithostratigraphic rock of the Hutuo Group, which, combined with previous lithostratigraphic, geochronological, structural and metamorphic data, provides new constraints on the sedimentary provenance and tectonic evolution of the region. The sequence of the Hutuo Group ranges upward from lower basal conglomerates and volcaniclastic rocks （Doucun Subgroup）, through clastic sediments, slates, dolomites and marbles （Dongye Subgroup）, to sandstones and conglomerates at the top （Guojiazhai Subgroup）. Zircons from granitic pebbles preserved in the Doucun Subgroup basal conglomerates give weighted mean ^207pb/^206pb ages between 2517 Ma and 2566 Ma, which are the same as those for the late Archean Wutai Granitoids, indicating that the pebbles were derived from the Wutai granitic intrusions （2566-2515 Ma）. Based on the new data and previous studies, combined with an igneous zircon crystallization age of 2087±9 Ma obtained for volcanics in the Hutuo Group, the Hutuo Group was deposited in a subduction-related retro-arc foreland basin environment that developed behind the Wutai arc during the eastward-directed subduction of the Western Block beneath the western margin of the Eastern Block. This basin underwent long-lived sedimentation and finally closed during the -1850 Ma collision
基金National Natural Science Foundation of China (No. 41272038)National Universities, China University of Geosciences (Wuhan), State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences (No. GKZ14Y660)+1 种基金the 111 Program for the Ministry of Education of Chinathe State Administration of Foreign Expert Affairs of China (No. B07039)
文摘The Lomagundi-Jatuli Event（LJE） is one of the largest and earliest positive carbon isotope excursions preserving δ^（13）C_（carb） values between ＋5 and ＋16‰ in Paleoproterozoic carbonates worldwide. However, the duration, amplitude and patterns of these excursions remain poorly constrained. The 2.14-1.83 Ga Hutuo Group in the North China Craton is a 〉10 km thick volcano-sedimentary sequence, including 〉5 km thick well-preserved carbonates that were deposited in supra-tidal to sub-tidal environments. C-O isotopic and elemental analyses of 152 least altered samples of the carbonates revealed a three-stage δ^（13）C evolution. It began with an exclusively positive δ^（13）C_（carb）（＋1.3 to ＋ 3.4‰） stage in the ~2.1 Ga carbonate in the Dashiling and Qingshicun Formations, followed by a transition from positive values to oscillating positive and negative values in ~3 000 m thick carbonates of the Wenshan, Hebiancun, Jianancun, and Daguandong Formations, and end with exclusively negative δ^（13）C_（carb） values preserved in 〉 500 m thick dolostones of the Huaiyincun and Beidaxing Formations. It appears that much of the LJE, particularly those extremely positive δ^（13）C_（carb） signals, was not recorded in the Hutuo carbonates. The exclusively positive δ^（13）C_（carb） values（＋1.3 to ＋ 3.4‰） preserved in the lower formations likely correspond to the end of the LJE, whereas the subsequent two stages reflect the aftermath of the LJE and the onset of Shunga-Francevillian event（SFE）. The present data point to an increased influence of oxygen on the carbon cycle from the Doucun to the Dongye Subgroups and demonstrate that the termination of the LJE in the North China Craton is nearly simultaneous with those in Fennoscandia and South Africa.
基金supported by China Geological Survey (Grant Nos. 1212010611802,1212010711815 and 1212011120152)National Natural Science Foundation of China (Grant No. 41172171)+1 种基金Basic Foundation of Scientific Research Work from Ministry of Science and Technology of China (GrantNos. J0721 and J0907)National Commission on Stratigraphy of China(Grant Nos. 1212010511702-01 and 1212011120142)
文摘Zircon U-Pb ages(SHRIMP and LA-ICPMS) and Lu-Hf isotope data(LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai Mountains area in the North China Craton.These two granite pebbles give zircon 207 Pb/206 Pb ages of 2513±8 Ma and 2527±8 Ma respectively,which are consistent with the emplacement ages of the Wangjiahui grey granite and Guangmingsi or Shifo granite in the Wutai Mountains.Detrital zircons from those two quartzite pebbles are mostly 2550-2490 Ma old with lesser number of 2800-2550 Ma grains,which is similar to the ages of detrital zircons from quartzites in the Gaofan Subgroup of the Neoarchean Wutai Group.Thus,the pebbles in the Hutuo Group basal conglomerates were derived locally from Wutai Mountains Neoarchean sources.Zircons from the Sijizhuang Formation conglomerate granite and quartzite pebbles mostly have positive ε Hf(t) values,a minority with ε Hf(t) values like model depleted mantle(DM) of the same age,but with most showing DM model ages 200-100 Ma.This indicates that most of the source materials were derived from the mantle within the previous 200 million years,whereas some are derived from 2550-2510 Ma juvenile crustal additions.This additional evidence suggests that in the North China Craton there was important initial polycyclic crustal formation and cratonization in the late Neoarchaean,prior to superimposed Palaeoproterozoic orogenic cycles.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-153)the National Natural Science Foundation of China (40625006)the Fundamental Research Funds for the Central Universities (2011QNA04)
