A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be furt...A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.展开更多
Zircon grains of magmatic origin from tuffite layers in the Xiamaling Formation at Zhaojiashan Village, Xuanhua area, Hebei Province, were used for zircon dating with a Sensitive High-Resolution Ion Microprobe (SHRIMP...Zircon grains of magmatic origin from tuffite layers in the Xiamaling Formation at Zhaojiashan Village, Xuanhua area, Hebei Province, were used for zircon dating with a Sensitive High-Resolution Ion Microprobe (SHRIMP II), which gives a weighted mean 207Pb/206Pb age of 1366±9 Ma. It shows a very similar age (1368±12 Ma) as the zircon dating from the Xiamaling Formation in Western Hill, Beijing. This age proposes that the Xiamaling Formation in the North China plate should be of Mesoproterozoic, instead of Neoproterozoic based on K-Ar, Ar-Ar dating. The new zircon age also indicates the devel- opment of macrofossils algae from the Mesoproterozoic age.展开更多
Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphi...Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.展开更多
The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that ove...The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that overlie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 ( 12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Formation. This age is younger than previously reported values of 921-933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: (1) Lower Neoproterozoic strata (814-1000 Ma) are missing in the studied area; (2) the Nanhua rift system was initiated at about 820 Ma; and (3) an age of ~820 Ma may be taken as the lower boundary timing of the Nanhua System (even Neoproterozoic) in South China.展开更多
The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the ...The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec- trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685±5) (2 samples, MSWD=0.36) and (679±3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forma- tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830―780 Ma igne- ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.展开更多
In the last few decades, the Late Paleozoic-Early Mesozoic tectonic evolution of South China has been quite controversial. The focus of debate is on both the age of ophiolites and the Late Paleozoic-Early Mesozoic geo...In the last few decades, the Late Paleozoic-Early Mesozoic tectonic evolution of South China has been quite controversial. The focus of debate is on both the age of ophiolites and the Late Paleozoic-Early Mesozoic geological and geodynamic environment. The Huaiyu Domain is located in the NE part of South China and exposes numerous significant geological features that are keys to understand the tectonics of South China. In this paper, we present some new evidence on stratigraphy, petrology and SHRIMP zircon U-Pb geochronology, and together with other geological and geochemical data available in the literature, and the following conclusions are suggested： 1） The eastern Jiangnan ophiolites belt, dated at 858±11 Ma by SHRIMP zircon U-Pb method, was generated during the Neoproterozoic, but not the Late Paleozoic; 2） The sedimentary rocks associated with these oceanic rocks do not contain radiolarians but Neoproterozoic acritarchs; 3） During Permian-Early Triassic times, the Huaiyu Domain was dominantly characterized by a shallow sea depositional environment since deep sea sediments are absent; and 4） The pre-Devonian tectonics of South China has been reworked by late polyphase tectonism through the Triassic and the Cretaceous periods. A Late Paleozoic-Early Mesozoic deep marine domain floored by oceanic crust never existed in the study area. The geochronological and structural data do not comply with a Late Paleozoic-Early Mesozoic South China Ocean.展开更多
文摘A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.
文摘Zircon grains of magmatic origin from tuffite layers in the Xiamaling Formation at Zhaojiashan Village, Xuanhua area, Hebei Province, were used for zircon dating with a Sensitive High-Resolution Ion Microprobe (SHRIMP II), which gives a weighted mean 207Pb/206Pb age of 1366±9 Ma. It shows a very similar age (1368±12 Ma) as the zircon dating from the Xiamaling Formation in Western Hill, Beijing. This age proposes that the Xiamaling Formation in the North China plate should be of Mesoproterozoic, instead of Neoproterozoic based on K-Ar, Ar-Ar dating. The new zircon age also indicates the devel- opment of macrofossils algae from the Mesoproterozoic age.
基金Supported by the National Oil-Gas Special Project (Grant No. XQ-2004-07)SinoPetrol & Chemical Corporation (Grant No. P04031)the Key Laboratory of Continental Dynamics, Northwest University
文摘Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.
基金supported both by the National Natural Science Foundation of China(Grand Nos.40032010-B.40072083 and 49972046)“100 Young Geologists”grant from both Chinese Ministry of Geology and Minera1 Resources and Sichuan Province
文摘The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that overlie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 ( 12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Formation. This age is younger than previously reported values of 921-933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: (1) Lower Neoproterozoic strata (814-1000 Ma) are missing in the studied area; (2) the Nanhua rift system was initiated at about 820 Ma; and (3) an age of ~820 Ma may be taken as the lower boundary timing of the Nanhua System (even Neoproterozoic) in South China.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40373015, 40173016, 40472099 and 40521001)Program of Innovative Research Team of China University of Geosciences (Wuhan)
文摘The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas- tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec- trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685±5) (2 samples, MSWD=0.36) and (679±3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forma- tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830―780 Ma igne- ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.
基金This study is financially supported by grants from the National Natural Science Foundation of China （grant nos. 40221301, 40634022, and 40572118） and Ministry of Education in China （grant nos. 306007 and 20060284008）.
文摘In the last few decades, the Late Paleozoic-Early Mesozoic tectonic evolution of South China has been quite controversial. The focus of debate is on both the age of ophiolites and the Late Paleozoic-Early Mesozoic geological and geodynamic environment. The Huaiyu Domain is located in the NE part of South China and exposes numerous significant geological features that are keys to understand the tectonics of South China. In this paper, we present some new evidence on stratigraphy, petrology and SHRIMP zircon U-Pb geochronology, and together with other geological and geochemical data available in the literature, and the following conclusions are suggested： 1） The eastern Jiangnan ophiolites belt, dated at 858±11 Ma by SHRIMP zircon U-Pb method, was generated during the Neoproterozoic, but not the Late Paleozoic; 2） The sedimentary rocks associated with these oceanic rocks do not contain radiolarians but Neoproterozoic acritarchs; 3） During Permian-Early Triassic times, the Huaiyu Domain was dominantly characterized by a shallow sea depositional environment since deep sea sediments are absent; and 4） The pre-Devonian tectonics of South China has been reworked by late polyphase tectonism through the Triassic and the Cretaceous periods. A Late Paleozoic-Early Mesozoic deep marine domain floored by oceanic crust never existed in the study area. The geochronological and structural data do not comply with a Late Paleozoic-Early Mesozoic South China Ocean.
