It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continenta...It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continental rifting or展开更多
The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to c...The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to characterize crustal thicknesses.However,sometimes confusing results are obtained since there is no enough filtered data.Here,a state-of-the-art approach,based on a machine-learning algorithm,is proposed to predict crustal thickness using global major-and trace-element geochemical data of intermediate arc rocks and intraplate basalts,and their corresponding crustal thicknesses.After the validation processes,the root-mean-square error(RMSE)and the coefficient of determination(R2)score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase.The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods.The trained model predicts that the crustal thickness of the eastern North China Craton(ENCC)was-45 km from the Late Triassic to the Early Cretaceous,but-35 km from the Early Cretaceous,which corresponds to the paleo-elevation of 3.0±1.5 km at Early Mesozoic,and decease to the present-day elevation in the ENCC.The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC,which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.展开更多
Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures ...Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.展开更多
The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic...The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic igneous rocks including monzogranite,gabbro,and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC,which have LA-ICP-MS zircon U-Pb ages of 229.0±0.4 Ma,216.2±0.9 Ma,and 210.6±2.0 Ma,respectively.Monzogranite shows high-SiO_(2) adakite affinity,negative ε_(Hf)(t)values(-20.6 to-17.9),and old T_(DM2) ages(3.53-3.29 Ga),suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation.Gabbro is ultrapotassic,strongly enriched in LREEs and LILEs,depleted in HFSEs,and has evolved zircon Hf isotopes with negative ε_(Hf) of -10.04 to-5.85 and old T_(DM2) ages(2.59-2.22 Ga).These are diagnostic signatures of a crustal component,but their high contents of Mg O,Cr,Co,Ni indicate that the primary magma originated from enriched mantle.Diorite is enriched in LILEs and LREEs,depleted in HFSEs(with negative Nb,Ta,and Ti anomalies),and contains negative ε_(Hf)(t)values(-13.64 to-11.01).Compared with the gabbro,the diorite is relatively enriched in Nb,Ta and HREEs,and also contains younger T_(DM2) ages(2.11-1.94 Ga),suggesting that the diorite was formed by mixing between ancient lower crust-derived felsic magmas and asthenospheric mantle-derived magmas.Field observations,geochronology,geochemistry,and zircon Lu-Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area.This phase of tectonic activity was completed in the eastern NCC by the Late Triassic(216 Ma),and was subsequently followed by lithospheric thinning that began in the Late Triassic.展开更多
The pre-Cenozoic formation in the Cenozoic depositon centres in eastern North China reached its maximum temperature at present, and the earlier paleo-temperature, therefore, has been overprinted, but the record of pal...The pre-Cenozoic formation in the Cenozoic depositon centres in eastern North China reached its maximum temperature at present, and the earlier paleo-temperature, therefore, has been overprinted, but the record of paleo-temperature by the vitrinite reflectance (Ro) has not been overprinted by the later thermal events in the pre-Cenozoic formation located in the uplift or in the Paleozoic-Mesozoic residual basins out of the Cenozoic depositon centres. The reconstruction of paleo-temperature gradient and paleo-heat flow, based on the vitrinite reflectance in the Paleozoic and the Mesozoic structural layers in boreholes, indicated that the eastern North China was characterized by much higher paleo-temperature gradient (40-55℃/km) and heat flow (>80 mW/m2) during the Middle-Late Mesozoic than those in the Early Mesozoic and at present. The higher paleo-heat flow during the Middle-Late Mesozoic implies that the thickness of the 'thermal' lithosphere at that time was just 50-55 km, it had been much thinned relative to the thickness (135-148 km) at the Early Mesozoic. The transition of near-surface thermal regime in eastern North China occurred around 110 Ma, and the corresponding deep tectonothermal processes should take place at ~160 Ma.展开更多
Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient T...Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient Terranes. The Eastern Ancient Terrane is the best studied and understood of the three ancient terranes. It has a long geological history back to ca. 3.8 Ga ago and includes the areas of Anshan-Benxi, eastern Hebei, eastern Shandong and western Shandong. In Anshan-Benxi, several different types of 3.8 Ga rocks were discovered together with 3.1-3.7 Ga rocks, whereas 2.9-3.0 Ga K-rich granites and 2.5 Ga syenogranite occur on larger scales. In eastern Hebei, 3.0-3.4 Ga rocks and older detrital and xenocrystic zircons were identified. In eastern Shandong, there are a large volumes of 2.7 Ga and 2.9 Ga rocks. In western Shandong, early Neoarchean （2.6-2.7 Ga） intrusive and supracrustal rocks are widely distributed. Whole-rock Nd and zircon Hf isotope data suggest that both mantle additions and crustal recycling played important roles within the Eastern Ancient Terrane during almost every tectono-magmatic event. Most BIFs in the North China Craton are late Neoarchean in age and are distributed on continental crust along the western margin of the Eastern Ancient Terrane, probably suggesting that a stable environment was one of the key factors for the formation of large-scale BIFs.展开更多
In the eastern part of China there had occurred large\|scale gold mineralization during the Mesozoic, resulting in a large number of important gold ore\|concentrated areas. In this paper we have selected some isotope ...In the eastern part of China there had occurred large\|scale gold mineralization during the Mesozoic, resulting in a large number of important gold ore\|concentrated areas. In this paper we have selected some isotope data (including four gold deposits previously studied and two gold deposits in this work) of Au\|bearing quartz veins of the representative gold deposits in six important gold ore\|concentrated areas in the periphery of the North China Platform and calculated their metallogenic ages using the method of Ludwig (2.90 version). The results show that the representative gold deposits in the six gold ore\|concentrated areas were formed during the Mesozoic.展开更多
The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced...The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced westerly to the north of the EAJS＇s axis （type A）, while the second type is related to the weakened westerly within the EAJS＇s axis （type B）. In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A （B） jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast （North） China when the EAJS＇s axis jumps from 40~N to 55~N （50~N）. Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.展开更多
U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb ...U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.展开更多
The linkage between the Asian-Pacific oscillation （APO） and the precipitation over central eastern China in spring is preliminarily addressed by use of the observed data. Results show that they correlate very well, ...The linkage between the Asian-Pacific oscillation （APO） and the precipitation over central eastern China in spring is preliminarily addressed by use of the observed data. Results show that they correlate very well, with the positive （negative） phase of APO tending to increase （decrease） the precipitation over central eastern China. Such a relationship can be explained by the atmospheric circulation changes over Asia and the North Pacific in association with the anomalous APO. A positive phase of APO, characterized by a positive anomaly over Asia and a negative anomaly over the North Pacific in the upper-tropospheric temperature, corresponds to decreased low-level geopotential height （H） and increased high-level H over Asia, and these effects are concurrent with increased low-level H and decreased high-level H over the North Pacific. Meanwhile, an anticyclonic circulation anomaly in the upper troposphere and a cyclonic circulation anomaly in the lower troposphere are introduced in East Asia, and the low-level southerly wind is strengthened over central eastern China. These changes provide advantageous conditions for enhanced precipitation over central eastern China. The situation is reversed in the negative phase of APO, leading to reduced precipitation in this region.展开更多
ENSO＇s effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the E1 Nifio peak, the...ENSO＇s effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the E1 Nifio peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections： One is related to the western North Pacific （WNP） anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream （AJS） in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO＇s effect on the zonal flow in the whole Northern Hemisphere. After the E1 Nifio peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.展开更多
基金supported by 973 (2012CB416601) and NFSC (41322018) projects
文摘It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continental rifting or
基金co-funded by the National Natural Science Foundation of China(Grant Nos.42002089,41930428)the National Key R&D Program of China(Grant Nos.2016YFC0600401 and 2017YFC0602302)+1 种基金by Open Research Fund Program of Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University)Ministry of Education(Grant Nos.2020YSJS02,2020YSJS01).
文摘The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to characterize crustal thicknesses.However,sometimes confusing results are obtained since there is no enough filtered data.Here,a state-of-the-art approach,based on a machine-learning algorithm,is proposed to predict crustal thickness using global major-and trace-element geochemical data of intermediate arc rocks and intraplate basalts,and their corresponding crustal thicknesses.After the validation processes,the root-mean-square error(RMSE)and the coefficient of determination(R2)score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase.The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods.The trained model predicts that the crustal thickness of the eastern North China Craton(ENCC)was-45 km from the Late Triassic to the Early Cretaceous,but-35 km from the Early Cretaceous,which corresponds to the paleo-elevation of 3.0±1.5 km at Early Mesozoic,and decease to the present-day elevation in the ENCC.The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC,which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.
基金the National Natural Science Foundation of China(Grant Nos.41772043 and 41802043)the Chinese Academy of Sciences“Light of West China”Program(Dawei Fan,2017 and Jingui Xu,2019)+1 种基金the Youth Innovation Promotion Association CAS(Dawei Fan,2018434)the Innovation and Entrepreneurship Funding of High-Level Overseas Talents of Guizhou Province(Dawei Fan,[2019]10).
文摘Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.
基金supported by the project of China Geological Survey(Grant No.DD20190438)。
文摘The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic igneous rocks including monzogranite,gabbro,and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC,which have LA-ICP-MS zircon U-Pb ages of 229.0±0.4 Ma,216.2±0.9 Ma,and 210.6±2.0 Ma,respectively.Monzogranite shows high-SiO_(2) adakite affinity,negative ε_(Hf)(t)values(-20.6 to-17.9),and old T_(DM2) ages(3.53-3.29 Ga),suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation.Gabbro is ultrapotassic,strongly enriched in LREEs and LILEs,depleted in HFSEs,and has evolved zircon Hf isotopes with negative ε_(Hf) of -10.04 to-5.85 and old T_(DM2) ages(2.59-2.22 Ga).These are diagnostic signatures of a crustal component,but their high contents of Mg O,Cr,Co,Ni indicate that the primary magma originated from enriched mantle.Diorite is enriched in LILEs and LREEs,depleted in HFSEs(with negative Nb,Ta,and Ti anomalies),and contains negative ε_(Hf)(t)values(-13.64 to-11.01).Compared with the gabbro,the diorite is relatively enriched in Nb,Ta and HREEs,and also contains younger T_(DM2) ages(2.11-1.94 Ga),suggesting that the diorite was formed by mixing between ancient lower crust-derived felsic magmas and asthenospheric mantle-derived magmas.Field observations,geochronology,geochemistry,and zircon Lu-Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area.This phase of tectonic activity was completed in the eastern NCC by the Late Triassic(216 Ma),and was subsequently followed by lithospheric thinning that began in the Late Triassic.
基金the Chinese Academy of Sciences(Grant No.KZCX1-07) the National Basic Research Programme(973)(Grant No.G1999075504) the National Natural Science Foundation of China(Grant No.40172100).
文摘The pre-Cenozoic formation in the Cenozoic depositon centres in eastern North China reached its maximum temperature at present, and the earlier paleo-temperature, therefore, has been overprinted, but the record of paleo-temperature by the vitrinite reflectance (Ro) has not been overprinted by the later thermal events in the pre-Cenozoic formation located in the uplift or in the Paleozoic-Mesozoic residual basins out of the Cenozoic depositon centres. The reconstruction of paleo-temperature gradient and paleo-heat flow, based on the vitrinite reflectance in the Paleozoic and the Mesozoic structural layers in boreholes, indicated that the eastern North China was characterized by much higher paleo-temperature gradient (40-55℃/km) and heat flow (>80 mW/m2) during the Middle-Late Mesozoic than those in the Early Mesozoic and at present. The higher paleo-heat flow during the Middle-Late Mesozoic implies that the thickness of the 'thermal' lithosphere at that time was just 50-55 km, it had been much thinned relative to the thickness (135-148 km) at the Early Mesozoic. The transition of near-surface thermal regime in eastern North China occurred around 110 Ma, and the corresponding deep tectonothermal processes should take place at ~160 Ma.
基金financially supported by the Major State Basic Research Program of the People’s Republic of China(2012CB416600)the National Natural Science Foundation of China(41472169,41172127)the Key Program of the Ministry of Land and Resources of China(DD20160121-03,12120114021301,1212010811033,and 12120115070301)
文摘Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient Terranes. The Eastern Ancient Terrane is the best studied and understood of the three ancient terranes. It has a long geological history back to ca. 3.8 Ga ago and includes the areas of Anshan-Benxi, eastern Hebei, eastern Shandong and western Shandong. In Anshan-Benxi, several different types of 3.8 Ga rocks were discovered together with 3.1-3.7 Ga rocks, whereas 2.9-3.0 Ga K-rich granites and 2.5 Ga syenogranite occur on larger scales. In eastern Hebei, 3.0-3.4 Ga rocks and older detrital and xenocrystic zircons were identified. In eastern Shandong, there are a large volumes of 2.7 Ga and 2.9 Ga rocks. In western Shandong, early Neoarchean （2.6-2.7 Ga） intrusive and supracrustal rocks are widely distributed. Whole-rock Nd and zircon Hf isotope data suggest that both mantle additions and crustal recycling played important roles within the Eastern Ancient Terrane during almost every tectono-magmatic event. Most BIFs in the North China Craton are late Neoarchean in age and are distributed on continental crust along the western margin of the Eastern Ancient Terrane, probably suggesting that a stable environment was one of the key factors for the formation of large-scale BIFs.
基金This research project was granted jointly by the State Key Program (95pre39)sponsored by the China National Science and Tech nology Departmentthe State Out standing Young Scientists Foundation (GrantNo .4 96 2 5 3 0 4 ) and the Open Lab.of Ore Depo
文摘In the eastern part of China there had occurred large\|scale gold mineralization during the Mesozoic, resulting in a large number of important gold ore\|concentrated areas. In this paper we have selected some isotope data (including four gold deposits previously studied and two gold deposits in this work) of Au\|bearing quartz veins of the representative gold deposits in six important gold ore\|concentrated areas in the periphery of the North China Platform and calculated their metallogenic ages using the method of Ludwig (2.90 version). The results show that the representative gold deposits in the six gold ore\|concentrated areas were formed during the Mesozoic.
基金supported by the National Natural Science Foundation of China (Grant No. 40905025)GYHY201006019, and GYHY200906017
文摘The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced westerly to the north of the EAJS＇s axis （type A）, while the second type is related to the weakened westerly within the EAJS＇s axis （type B）. In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A （B） jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast （North） China when the EAJS＇s axis jumps from 40~N to 55~N （50~N）. Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.
基金supported by Opening Project(201206)of the State Key Laboratory of Ore deposit Geochemistry,Chinese Academia of Sciencesthe National Nature Science Foundation of China(40773020,40972071,90714010,and 40634020)
文摘U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.
基金supported by the National Basic Research Program of China (2009CB421407)the Special Fund for Public Welfare Industry(meteorology)(GYHY200906018)the National Natural Science Foundation of China(90711004 and 40921003)
文摘The linkage between the Asian-Pacific oscillation （APO） and the precipitation over central eastern China in spring is preliminarily addressed by use of the observed data. Results show that they correlate very well, with the positive （negative） phase of APO tending to increase （decrease） the precipitation over central eastern China. Such a relationship can be explained by the atmospheric circulation changes over Asia and the North Pacific in association with the anomalous APO. A positive phase of APO, characterized by a positive anomaly over Asia and a negative anomaly over the North Pacific in the upper-tropospheric temperature, corresponds to decreased low-level geopotential height （H） and increased high-level H over Asia, and these effects are concurrent with increased low-level H and decreased high-level H over the North Pacific. Meanwhile, an anticyclonic circulation anomaly in the upper troposphere and a cyclonic circulation anomaly in the lower troposphere are introduced in East Asia, and the low-level southerly wind is strengthened over central eastern China. These changes provide advantageous conditions for enhanced precipitation over central eastern China. The situation is reversed in the negative phase of APO, leading to reduced precipitation in this region.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40725016 and 40221503).
文摘ENSO＇s effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the E1 Nifio peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections： One is related to the western North Pacific （WNP） anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream （AJS） in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO＇s effect on the zonal flow in the whole Northern Hemisphere. After the E1 Nifio peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.
文摘2024年春季(3—5月)我国平均降水量为163 mm,为1961年以来历史同期第六多,4—5月东部地区旱涝灾害并重,华南和江南大部降水较常年同期偏多,尤其是华南大部降水偏多5成以上,多次暴雨过程造成部分地区发生洪涝;而黄淮、江淮北部降水显著偏少,春季后期干旱迅速发展。春季“华南涝、黄淮旱”的形成与东亚大气环流关键系统异常及其季节内阶段性变化密切相关。4月异常偏强、偏南的西北太平洋副热带高压和低层850 hPa偏强的西北太平洋反气旋为华南和江南提供了有利的水汽输送条件,导致南方地区发生多次强降水过程;而黄淮干旱主要受4—5月持续偏强的朝鲜半岛-日本海高压(小笠原高压)和偏南的西北太平洋副热带高压共同影响。此外,春季El Ni o衰减和热带印度洋海温异常偏暖有助于激发异常偏强的西北太平洋反气旋,是我国南方强降水发生的重要海洋外强迫背景。
