亚洲内陆荒漠化和干旱化与中国西部人类生存环境和社会可持续发展密切相关。中国西部地区的气候自晚更新世以来经历了多次冷暖、干湿变化,研究其晚更新世古气候变化,有助于预测未来气候的变化趋势。文章分析了宁夏南部清水河盆地晚更新...亚洲内陆荒漠化和干旱化与中国西部人类生存环境和社会可持续发展密切相关。中国西部地区的气候自晚更新世以来经历了多次冷暖、干湿变化,研究其晚更新世古气候变化,有助于预测未来气候的变化趋势。文章分析了宁夏南部清水河盆地晚更新世中晚期的孢粉记录,结果显示孢粉序列可从下至上划分为4个组合带,反映了该地区晚更新世中晚期植被和气候变化规律。研究表明研究区晚更新世中期(75~50 ka B.P.)是植被以蒿属为主的干草原,气候温凉偏干;晚更新世晚期(25~15 ka B.P.)由荒漠草原-干草原和疏林草原交替出现逐渐过渡到荒漠草原,该时期冬季风呈现逐渐增强的趋势,致使气候逐渐变冷变干,气候类型由温凉偏湿过渡到冷干。宁夏南部清水河盆地晚更新世中晚期孢粉记录的深入研究对于正确认识黄土高原自然环境历史演变和黄土高原治理决策的制定具有重要指导意义。展开更多
The northeastern margin of the Tibetan Plateau is the youngest part of the Tibetan Plateau where tectonic activity is intense and climate change is complex.In this study,combined with field investigations,we explored ...The northeastern margin of the Tibetan Plateau is the youngest part of the Tibetan Plateau where tectonic activity is intense and climate change is complex.In this study,combined with field investigations,we explored accelerator mass spectrometry 14C and optically stimulated luminescence dating and palynological analysis of the sedimentary sequence in the Qingshuihe Basin to explain the origin of soft-sediment deformation layer.Dating and palynological results from the Sanchahe section in the basin revealed a detailed history of vegetation variation and associated climate change from~18 to~5 ka BP.The results indicate that the permafrost developed at~18–11.7 ka BP,and the soft-sediment deformation structures formed at~11.7–5 ka BP.Together with the characteristics of the deformation(meter-scale,continuous symmetrical wave)and paleoclimate,we suggest that the soft-sediment deformation layer in the late Pleistocene was cryoturbated under climatic conditions.The discovery of a series of cryoturbations in the Qingshuihe Basin has further enriched the regional distribution of periglacial phenomena in the west of the Ordos Plateau,expanded the distribution range of periglacial phenomena,and provided evidence for exploring the temporal and spatial changes in permafrost in northern China at the end of the late Pleistocene.展开更多
In order to understand the petrogenesis and tectonic setting of diorite and diabase units on Doumer Island, Antarctic Peninsula, this paper reports new laser ablation-inductively coupled plasma-mass spectrometry(LA-IC...In order to understand the petrogenesis and tectonic setting of diorite and diabase units on Doumer Island, Antarctic Peninsula, this paper reports new laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) zircon U-Pb, geochemical, and Lu-Hf isotopic data for the magmatism. The diorite and diabase samples yielded zircon U-Pb ages of 55.4 ± 0.3 and 52.8 ± 0.4 Ma, respectively. These samples are enriched in the large ion lithophile elements and the light rare earth elements, and are depleted in the high field strength elements. The zircons in these samples yield eHf(t) values from 9.03 to 11.87 and model ages(TDM2) of 342–524 Ma. The major, trace, rare earth element(REE), and Hf isotopic data for the diorites indicate that these units were formed by the mixing of magmas generated by(a) the partial melting of mantle wedge material that experienced fluid-metasomatism in a subduction zone setting, and(b) the melting of juvenile crustal material induced by the upwelling of mantle-derived magmas in a subduction–collision setting. The diabase units contain higher total REE concentrations than the diorite, indicating they were derived from a different source region. These samples also have higher Mg~# values and contain lower concentrations of Cr and Ni than the diorites, and have weakly negative Nb and Ta anomalies with Nb/Ta values of <3. The zircons in these samples yield eHf(t) values from 9.08 to 11.11 and model ages(TDM2) of 389–503 Ma. The major, trace, REE, and Hf isotopic compositions of the diabase units indicate that that they were derived from the mixing of depleted mantle-derived magmas with magmas generated by the melting of juvenile crustal material which was induced by the upwelling of the mantle into the crust. Overall the Cenozoic diorite and diabase on Doumer Island is related to subduction environment.展开更多
The Liuqu Conglomerates consist of a suit of terrestrial molasse deposits formed in a foreland basin of the Himalaya-Tibet orogenic belt before the collision of India and Eurasia.These deposits record considerable geo...The Liuqu Conglomerates consist of a suit of terrestrial molasse deposits formed in a foreland basin of the Himalaya-Tibet orogenic belt before the collision of India and Eurasia.These deposits record considerable geological information regarding the late tectonic evolution of the Neotethyan ocean.The palynological study of interlayers of mudstone and mud-sandstones indicates an Oligocene age.The palynological assemblage consists mainly of deciduous broad-leaved angiosperms,with some coniferous gymnosperms and evergreen broad-leaved angiosperms.The deposits reflect a broad-leaved deciduous forest or mixed with conifer-broad-leaved forest ecotypes,showing a warm-temperate or temperate zone climatic environment.This work provides significant new information about the tectonic evolution,paleogeography,and paleoenvironment of southern Tibet during the Cenozoic.展开更多
The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional ...The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith bodies.The Mesozoic sedimentary facies and its evolution in both north and south of the ophiolite zone are corresponding in time.The ophiolite zone has often been divided into parallel branches,separated by narrow flysch slats.There is also a similarity of the Paleozoic and the basement of the High Himalaya,Lhasa and Qiangtang Terranes,and they are distinctly different from those of the Indian continent.The geologic information does not warrant a postulate that the Himalaya and Tibet were once separated by a great ocean;it is therefore consistent with an alternative tectonic model by back-arc basin collapse with its juvenile narrow oceanic crust.The real plate tectonic suture,the Neotethys might be covered under the Miocene Siwalik molasse in the southern slope of the High Himalaya range.Based on the new model,the Neotethyan ocean floor was subducted beneath the Asia since the Late Triassic.The outer continental margin of Eurasia was split from the Lhasa Terrane so that a back-arc basin came into existence.Hemi-pelagic and deep sea sediments were deposited before the Late Cretaceous flysch sedimentation,with the linear juvenile oceanic crust when back-arc volcanism occurred in the Gandese region.The Yarlung Zangbo back-arc basin was eventually eliminated when the High Himalayas were sutured onto Eurasia.The ocean floor lightly underthrusted to north and south sides,sediments of the basin were deformed as fold-thrusting.The Neotethys was eliminated during the Tertiary when India collided with Himalaya arc from the Oligocene.The crust of southern Tibet suffered penetrative shortening,the ophiolite zone became exposed during regional uplifting,and the South Tibet Detachment System,doming in southern Tibet and rifting in a north-south direction since the Middle Miocene Epoch.展开更多
文摘亚洲内陆荒漠化和干旱化与中国西部人类生存环境和社会可持续发展密切相关。中国西部地区的气候自晚更新世以来经历了多次冷暖、干湿变化,研究其晚更新世古气候变化,有助于预测未来气候的变化趋势。文章分析了宁夏南部清水河盆地晚更新世中晚期的孢粉记录,结果显示孢粉序列可从下至上划分为4个组合带,反映了该地区晚更新世中晚期植被和气候变化规律。研究表明研究区晚更新世中期(75~50 ka B.P.)是植被以蒿属为主的干草原,气候温凉偏干;晚更新世晚期(25~15 ka B.P.)由荒漠草原-干草原和疏林草原交替出现逐渐过渡到荒漠草原,该时期冬季风呈现逐渐增强的趋势,致使气候逐渐变冷变干,气候类型由温凉偏湿过渡到冷干。宁夏南部清水河盆地晚更新世中晚期孢粉记录的深入研究对于正确认识黄土高原自然环境历史演变和黄土高原治理决策的制定具有重要指导意义。
基金supported by the National Natural Science Foundation of China(Grant No.41972119)the Geological Investigation Project of the China Geological Survey(Grant Nos.DD20190018 and DD20221644)。
文摘The northeastern margin of the Tibetan Plateau is the youngest part of the Tibetan Plateau where tectonic activity is intense and climate change is complex.In this study,combined with field investigations,we explored accelerator mass spectrometry 14C and optically stimulated luminescence dating and palynological analysis of the sedimentary sequence in the Qingshuihe Basin to explain the origin of soft-sediment deformation layer.Dating and palynological results from the Sanchahe section in the basin revealed a detailed history of vegetation variation and associated climate change from~18 to~5 ka BP.The results indicate that the permafrost developed at~18–11.7 ka BP,and the soft-sediment deformation structures formed at~11.7–5 ka BP.Together with the characteristics of the deformation(meter-scale,continuous symmetrical wave)and paleoclimate,we suggest that the soft-sediment deformation layer in the late Pleistocene was cryoturbated under climatic conditions.The discovery of a series of cryoturbations in the Qingshuihe Basin has further enriched the regional distribution of periglacial phenomena in the west of the Ordos Plateau,expanded the distribution range of periglacial phenomena,and provided evidence for exploring the temporal and spatial changes in permafrost in northern China at the end of the late Pleistocene.
基金financially supported by China Geological Survey (Grant no. DD20160060)the National Natural Science Foundation of China (Grant nos. 4153209, 41872135)
文摘In order to understand the petrogenesis and tectonic setting of diorite and diabase units on Doumer Island, Antarctic Peninsula, this paper reports new laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) zircon U-Pb, geochemical, and Lu-Hf isotopic data for the magmatism. The diorite and diabase samples yielded zircon U-Pb ages of 55.4 ± 0.3 and 52.8 ± 0.4 Ma, respectively. These samples are enriched in the large ion lithophile elements and the light rare earth elements, and are depleted in the high field strength elements. The zircons in these samples yield eHf(t) values from 9.03 to 11.87 and model ages(TDM2) of 342–524 Ma. The major, trace, rare earth element(REE), and Hf isotopic data for the diorites indicate that these units were formed by the mixing of magmas generated by(a) the partial melting of mantle wedge material that experienced fluid-metasomatism in a subduction zone setting, and(b) the melting of juvenile crustal material induced by the upwelling of mantle-derived magmas in a subduction–collision setting. The diabase units contain higher total REE concentrations than the diorite, indicating they were derived from a different source region. These samples also have higher Mg~# values and contain lower concentrations of Cr and Ni than the diorites, and have weakly negative Nb and Ta anomalies with Nb/Ta values of <3. The zircons in these samples yield eHf(t) values from 9.08 to 11.11 and model ages(TDM2) of 389–503 Ma. The major, trace, REE, and Hf isotopic compositions of the diabase units indicate that that they were derived from the mixing of depleted mantle-derived magmas with magmas generated by the melting of juvenile crustal material which was induced by the upwelling of the mantle into the crust. Overall the Cenozoic diorite and diabase on Doumer Island is related to subduction environment.
基金supported by National Natural Science Foundation of China (Grant No. 40631004)
文摘The Liuqu Conglomerates consist of a suit of terrestrial molasse deposits formed in a foreland basin of the Himalaya-Tibet orogenic belt before the collision of India and Eurasia.These deposits record considerable geological information regarding the late tectonic evolution of the Neotethyan ocean.The palynological study of interlayers of mudstone and mud-sandstones indicates an Oligocene age.The palynological assemblage consists mainly of deciduous broad-leaved angiosperms,with some coniferous gymnosperms and evergreen broad-leaved angiosperms.The deposits reflect a broad-leaved deciduous forest or mixed with conifer-broad-leaved forest ecotypes,showing a warm-temperate or temperate zone climatic environment.This work provides significant new information about the tectonic evolution,paleogeography,and paleoenvironment of southern Tibet during the Cenozoic.
基金supported by Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No.KZCX3-SW-143)National Natural Science Foundation of China (Grant No.40631004)
文摘The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith bodies.The Mesozoic sedimentary facies and its evolution in both north and south of the ophiolite zone are corresponding in time.The ophiolite zone has often been divided into parallel branches,separated by narrow flysch slats.There is also a similarity of the Paleozoic and the basement of the High Himalaya,Lhasa and Qiangtang Terranes,and they are distinctly different from those of the Indian continent.The geologic information does not warrant a postulate that the Himalaya and Tibet were once separated by a great ocean;it is therefore consistent with an alternative tectonic model by back-arc basin collapse with its juvenile narrow oceanic crust.The real plate tectonic suture,the Neotethys might be covered under the Miocene Siwalik molasse in the southern slope of the High Himalaya range.Based on the new model,the Neotethyan ocean floor was subducted beneath the Asia since the Late Triassic.The outer continental margin of Eurasia was split from the Lhasa Terrane so that a back-arc basin came into existence.Hemi-pelagic and deep sea sediments were deposited before the Late Cretaceous flysch sedimentation,with the linear juvenile oceanic crust when back-arc volcanism occurred in the Gandese region.The Yarlung Zangbo back-arc basin was eventually eliminated when the High Himalayas were sutured onto Eurasia.The ocean floor lightly underthrusted to north and south sides,sediments of the basin were deformed as fold-thrusting.The Neotethys was eliminated during the Tertiary when India collided with Himalaya arc from the Oligocene.The crust of southern Tibet suffered penetrative shortening,the ophiolite zone became exposed during regional uplifting,and the South Tibet Detachment System,doming in southern Tibet and rifting in a north-south direction since the Middle Miocene Epoch.
