Black locust (Robinia pseudoacacia) is widely planted throughout the semi-arid Loess Plateau of China. The spatial distribution of this species at different ages is highly heterogeneous due to restoration and manage...Black locust (Robinia pseudoacacia) is widely planted throughout the semi-arid Loess Plateau of China. The spatial distribution of this species at different ages is highly heterogeneous due to restoration and management practices. In this study, we aimed to compare the transpiration levels between different aged black locusts at the tree and stand scales, clarifying the physiological status of this species with different ages. Black locust trees with two representative age classes (12 and 28 years) were selected in the Yangjuangou catchment on the semi-arid Loess Plateau. Sap flux density (Fd) and environmental variables (solar radiation, air temperature, relative humidity and soil water content) were simultaneously monitored throughout the growing season of 2014. Tree transpiration (Et) was the product of Fd and sapwood area (As), and stand transpiration (Ec) was calculated basing on the stand sap flux density (Js) and stand total sapwood area (AsT). Stomatal conductance (gs) was measured in a controlled environment and hydraulic conductance was estimated using the relationship between transpiration rate and vapor pressure deficit (VPD). Our results showed that Et and Ec were higher in the 28-year-old stand than in the 12-year-old stand. The gs and hydraulic conductance of 28-year-old trees were also higher than those of 12-year-old trees, and the two parameters were thus the causes of variations in transpiration between different age classes. After rainfall, mean Fd increased by 9% in 28-year-old trees and by 5% in 12-year-old trees. This study thus suggests that stand age should be considered for estimating transpiration at the catchment and region scales in this area. These results provide ecophysiological evidences that the older black locust trees had more active physiological status than the younger ones in this area. These findings also provide basic information for the management of water resources and forests on the semi-arid Loess Plateau.展开更多
Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the...Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the dikes probably related to the activity of the nearly N-S faulting and micas from hydrothermal activity and the low- temperature thermochronology of plateau uplift. Previous research shows that there are at least three different ideas about the age of the rifts: (1) older than 16-12 Ma, (2) 14- 10 Ma, and (3) 8-4 Ma (Fig. la). For the old sedimentary strata represented the beginning of the rifting, the dating of the sediments helps to better define the initial rifting age.展开更多
Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite an...Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite and ophiolite are present in the Atbashi Range, Kyrgyzstan, which are believed to be the relics of the Southern Tianshan Ocean. New data obtained through Ar-Ar isotopic analysis in this research provide reliable chronological restrictions for this problem.展开更多
The fluctuation of lake levels in Tibetan area may be well reflected by the landformevidences, especially the last highest lake levels. This, in a certain degree, is more suitable fordetermning the climatic humidity a...The fluctuation of lake levels in Tibetan area may be well reflected by the landformevidences, especially the last highest lake levels. This, in a certain degree, is more suitable fordetermning the climatic humidity and aridity in macro scale compared with many other indicatorswhich are also sensitive to the sedimentary environmental change. According to the analyses of thelakes such as Tianshuihai Lake, Bangdag Co, Lungmu Co, Bangong Co, Serfing Co, Chabyer Caka,Qahan salt lake, Qinghai lake, the lake group in north-east Qiangtang and the lake group in southTibet. the authors thought that the lakes on the Tibetan Plateau generally appeared the high lakelevel during 40-25 ka BP. The plenty of water quantity may represent a special warm-humid stage inTibet area compared with the sub-warm-humid stage reflected by marine oxygen isotope records.Thus, there may existed different driving factors to climatic changes between the high latitUde areasand middle-low latitude mountains.展开更多
The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lodegold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has beenargued that it was formed in the Mesozoic...The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lodegold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has beenargued that it was formed in the Mesozoic, related isotopic age data have not been reported inprevious studies. Based on detailed geological study, the authors have carried out isotopic datingon various metallogenic generations. The ore-forming process of the Dongchuang gold deposit consistsof four stages: coarse-grained pyrite-bearing quartz veins (stage I), fine-grained pyrite-quartzveinlets (stage II), multi-sulfides (stage III) and carbonate-quartz veinlets (stage IV). Ar-Ardating on mineral separates of stages I, II and III yields plateau ages of 142.9 +- 2.9 Ma, 132.2 +-2.6 Ma and 128.3 +- 6.2 Ma, respectively. Sericite separates from stage II assemblage also yield anAr-Ar isochron age of 132.6 +- 2.7 Ma, similar to the Ar-Ar plateau age. These results suggest thatthe Dongchuang gold deposit was mainly formed during 143-128 Ma, coinciding with the authors'geological observations and previous hypothesis. This ore formation is coeval with theregional-tectonic transition from collisional compression to extension, strongly showing that thedecompression-geothermal increase regime during compression-to-extension transition is the mostconducive geodynamic environment to orogenic-type gold mineralization.展开更多
In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with veget...In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0-100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0-100 cm. Moreover, there was a time lag of about 15-30 years between biomass production and soil carbon sequestration in 0-100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.展开更多
Geochronology of continental flood basalts sampled from the Emei large igneous province (LIP) on the western margin of the Yangtze platform was investigated by the laser microprobe 40Ar/39Ar dating technique. These ba...Geochronology of continental flood basalts sampled from the Emei large igneous province (LIP) on the western margin of the Yangtze platform was investigated by the laser microprobe 40Ar/39Ar dating technique. These basalts yield a fairly wide range of 40Ar/39Ar ages, varying from 259 to 135 Ma. One basalt sample, at least altered, recorded the oldest 40Ar/39Ar age of about 259 Ma, corresponding to a peak eruption age of the Emei LIP continental flood basalts. Most of the samples yield much younger ages from 135 to 177 Ma, which are consistent with the K-Ar ages for the same samples (122.8-172.1 Ma). The dating data suggest that these Permian basalts had been widely affected by the regional tectonothermal event at 177-135 Ma. The event was probably caused by the convergence and collision among the Laurasia, Yangtze and Qiangtang-Qamdo continental blocks on the eastern margin of the Qinghai-Tibet plateau after the late Triassic. The age of the event reflects the timing of the peak collisional orogeny.展开更多
The dike swarm of lamprophyres at Pishan on the SW margin of the Tarimterrane is composed of ultra-potassic lamprophyres that have intruded into the Proterozoichornblende schists. ^(40)Ar/^(39)Ar dating data suggest t...The dike swarm of lamprophyres at Pishan on the SW margin of the Tarimterrane is composed of ultra-potassic lamprophyres that have intruded into the Proterozoichornblende schists. ^(40)Ar/^(39)Ar dating data suggest that the isochron ages for phlogopite andwhole rock separates of the lamprophyres are 231.7+-0.3 Ma and 228.5+-0.3 Ma, respectively.Geochemical data indicate that the dikes were derived from a subduction-related or metasomatizedmantle. During the Middle-Late Triassic the western Kunlun area entered the post-orogeny period, andthus the occurrence of the dike swarm in the study area may have been controlled by underplating.展开更多
The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related...The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related to the early tectonic evolution of the Earth.However,its formation era,sedimentary filling sequence,and geotectonic characteristics have always been in dispute.In this study,several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone.This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village,Tongchang Township,Yimen County.LA-ICP-MS zircon dating was conducted,achieving the crystallization age of magma of 2491±15 Ma and the metamorphic ages of about 2.3 Ga,2.0 Ga,and 1.8 Ga for the first time.Meanwhile,according to in-situ Hf isotope analysis,the zirconεHf(t)values were determined to range from−3.0 to 7.6,with an average of 2.7.Furthermore,the first-stage Hf model age(TDM1)was determined to be 2513−2916 Ma,indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean.Therefore,it is believed that the strata of the slate were deposited in the Late Neoarchean,instead of the Mesoproterozoic as determined by previous researchers.Accordingly,it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group.Instead,they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information.Furthermore,the magma ages of 2491±15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton,and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic.The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland.Meanwhile,the metamorphic ages of 2.3 Ga,2.0 Ga,and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga,1.95 Ga,and 1.85 Ga of the northern margin of the Yangtze Craton,indicating that the strata experienced Paleoproterozoic tectonic-thermal events.The study area is located on the eastern margin of Qinghai-Tibet Plateau,and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous.The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.展开更多
Delingha is located in the northeast margin of Qaidam Basin.Bayin River alluvial proluvial fan is the main aquifer of Delingha,in which groundwater generally flows from north to south.The hydrochemistry results showed...Delingha is located in the northeast margin of Qaidam Basin.Bayin River alluvial proluvial fan is the main aquifer of Delingha,in which groundwater generally flows from north to south.The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions,respectively.Cl-Na type groundwater was formed in front of Gahai Lake,and SO_(4)·HCO_(3)-Na·Ca type groundwater was formed in front of Keluke Lake.The results of deuterium(D)and 18O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions.In addition,results of ^(14)C indicated that the groundwater age was more than 1140 years,implying relatively poor renewal capability of regional groundwater.Moreover,our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.展开更多
Tibet is the largest and highest plateau on the Earth (having 82% of the world’s land surface area falling >4km above sea level) attributed to the India and Asian convergence tectonics. Recently, high\|resolution ...Tibet is the largest and highest plateau on the Earth (having 82% of the world’s land surface area falling >4km above sea level) attributed to the India and Asian convergence tectonics. Recently, high\|resolution digital topography data (Fielding et al., 1994) confirmed the earlier observations about flat erosional surfaces in the central part of the plateau (Jujin, et al., 1995) and suggested extraordinary flatness at a wide range of scales. Much of the Tibetan plateau across different accreted terranes has shallow slopes between 5°~10° and variation in relief of about 1 km, except in its marginal parts (Himalayan ranges; Kunlun mountains) where rough and high topography with intense fluvial dissections (variations in relief up to 7km) is quite frequent. However, in the southern and south\|central part of the plateau along the Pliocene\|Quaternary grabens, slopes generally steepen.展开更多
The impacts of vegetation restoration on the soil erosion have been widely elucidated in the semi-arid regions.However,the magnitude of soil erosion on abandoned sloping farmland still remained unclear and their respo...The impacts of vegetation restoration on the soil erosion have been widely elucidated in the semi-arid regions.However,the magnitude of soil erosion on abandoned sloping farmland still remained unclear and their responses to vegetation succession were rarely addressed.The main objective of this study is to determine the magnitude of soil erosion along vegetation succession and explore the impact of vegetation succession on soil erosion from abandoned sloping farmland.Field observations were employed to monitor the rainfall,runoff,and soil erosion of seven sloping farmland plots with different abandoned ages and bare land from 2015 to 2019.The results indicated that the annual runoff depth and soil erosion modulus of vegetation types were in the range of 0.46 to 5.49 mm·a^(-1)and 1.3 to 24.5 t·km^(-2)·a^(-1),respectively.The vegetation effectively reduced the annual surface runoff and soil erosion with reduction of 73.8% to 97.8%and 98.0% to 99.9% as opposed to bare land.However,there were no significant differences in runoff and soil erosion for different vegetation types along succession.The largest event of vegetation types contributed to 38.7%-44.1% of the annual runoff and 42.5%-66.3% of the annual soil erosion,respectively.Vegetation restoration considerably alleviated the contribution of largest erosive event to annual soil erosion.The relationships between soil erosion,runoff and rainfall factors could be fitted well by linear functions,and the performances of regression models in predicting runoff were more satisfactory compared to predicting soil erosion.The Artemisia gmelinii(Agm)+Stipa bungeana(Sb)optimized the trade-off between sediment reduction and runoff maintenance,which should be selected as the suitable vegetation types to achieve the sustainability of socio-ecological systems.展开更多
On the basis of the geomorphology, paleosol, paleoclimate and loess age, major changes of the Loess Plateau were studied. There are five major changes in the evolution of the Loess Plateau in China. Among them, the fi...On the basis of the geomorphology, paleosol, paleoclimate and loess age, major changes of the Loess Plateau were studied. There are five major changes in the evolution of the Loess Plateau in China. Among them, the first, second, third and fourth major changes have taken place since the formation of the Loess Plateau, and the fifth major change will happen in 100 years. The first major change, which occurred at about 2.50 Ma BP, was a transition from red earth plateau to the Loess Plateau, and reflects the climate from the warm-sub-humid to the alteration between cold-and-dry and warm-and-humid. The driving force of this first major change was climate. The second major change, which took place at about 1.60 Ma BP, was a vital transition of the main rivers in this area from non-existence to existence, and represented an important change on the Loess Plateau's neotectonic uplift from the slow rising to periodically accelerated rising, and making the river's erosion go from feeble to strong. The driving force of the second major change is tectonic uplift. The third major change which occurred at about 150 ka, was a great transition of the Yellow River's inpouring from a lake outlet to a sea outlet. At that time, the Yellow River cut the Sanmen Gorge. The transition led to the transformation of loess material from internal transportation to external transportation. The driving force of the third major change was running water erosion. The fourth one that occurred at about 1.1 ka was a change of the Loess Plateau from natural erosion to erosion accelerated by human influences. The driving force of the fourth major change is mainly human activities. The fifth major change, which is the opposite change to the fourth one, in which the motive power is human activity, too.展开更多
The Xianghualing Sn-polymetallic orefield in Hunan Province, southern China, is a largesize tin orefield. Although numerous studies have been undertaken on this orefield, its genesis, mineralization age, and tectonic ...The Xianghualing Sn-polymetallic orefield in Hunan Province, southern China, is a largesize tin orefield. Although numerous studies have been undertaken on this orefield, its genesis, mineralization age, and tectonic setting are still controversial, mainly because of the lack of reliable geochronological data on tin mineralization. The ^40Ar^39Ar stepwise heating dating method was first employed on muscovite from different deposits in this orefield. The muscovite sample from the Xianghualing Sn-polymetallic deposit defines a plateau age of 154.4±1.1 Ma and an isochron age of 151.9±3.0 Ma; muscovite from the Xianghuapu W-polymetallic deposit yields a plateau age of 161.3±1.1 Ma and an isochron age of 160.0±3.2 Ma; muscovite from the Jianfengling greisen-type Sn-polymetallic deposit gives a plateau age of 158.7±1.2 Ma and an isochron age of 160.3±3.2 Ma. The tungsten-tin mineralization ages in the Xianghualing area are therefore restricted within 150-160 Ma. The tungstentin mineralization in Xianghualing occurred at the same time as the regional tin-tungsten mineralization including the Furong tin orefield, Shizhuyuan tungsten-tin polymetallic deposit and Yaogangxian tungsten-polymetallic deposit. Thus, the large-scale tungsten-tin metallogenesis in South China occurring at 160-150 Ma, probably is closely related to asthenospheric upwelling and crustmantle interaction under a geodynamic setting of crustal extension and lithosphere thinning during the transformation of tectonic regimes during the Mid-Late Jurassic.展开更多
Furong, Hunan, is a large tin orefield discovered in China in recent years, which is mainly of the skarn-greisen-chlorite type. On the basis of the geological characteristics of the orefield, 40Ar-39Ar dating was perf...Furong, Hunan, is a large tin orefield discovered in China in recent years, which is mainly of the skarn-greisen-chlorite type. On the basis of the geological characteristics of the orefield, 40Ar-39Ar dating was performed on muscovite from greisen-type tin ore and biotite from related amphibole-biotite granite, which yielded three sets of age data, i.e., a plateau age of 157.5±0.3 Ma and an isochron age of 156.9±3 Ma for amphibole-biotite granite; a plateau age of 156.1±0.4 Ma and an isochron age of 155.7±1.7 Ma for the Sanmen greisen-type tin ore; and a plateau age of 160.1±0.9 Ma and an isochron age of 157.5±1.5 Ma for the Taoxiwo greisen-type tin ore. The three sets of age data coincide well with each other. They not only accurately reflect the timing of rock and ore formation but also indicate close relations between granite and tin deposits. In addition, the plateau ages of all three sets suggest that no subsequent thermal perturbation event occurred after the formation of granite and tin deposits. The Furong tin orefield is a component part of the southern Hunan large tungsten-tin polymetallic deposit concentration area and also a representative deposit formed in the time interval of 160-135 Ma in four peaks of Mesozoic tungsten-tin mineralization in the South China region. They might still correspond to the middle and late stages of the major geodynamic transition from a N-S- to an E-W-direction in eastern China.展开更多
The Gangdese porphyry copper belt consists of one large and five middle-small deposits in addition to dozens of ore-bearing porphyry bodies. The belt trends 350 km long along the EW-striking Gangdese batholith, and lo...The Gangdese porphyry copper belt consists of one large and five middle-small deposits in addition to dozens of ore-bearing porphyry bodies. The belt trends 350 km long along the EW-striking Gangdese batholith, and locally occurs as a string of beads extending about 50 km within the SN-trending rifting zones (grabens) on the Tibetan plateau. Monzonitic granite- porphyry and quartz monzonitic porphyry, as dominant host rocks, are shoshonitic and potassic calc-alkaline. Available dating data indicate that the ages of the shallow-level emplacement for these porphyries vary from 10 Ma to 18 Ma, which are identical to that of associated potassic calc-alkaline volcanic rocks (10—15 Ma) and mafic dykes (13—18 Ma). The timing and duration of Cu mineralization events are constrained by Re-Os ages for molybdenites from three porphyry copper deposits in the Gangdese porphyry copper belt. Five molybdenite samples from the Nanmu deposit yielded an 187Re-187Os isochron with a highly pre-cise age of (14.76?.22) Ma; six molybdenites from the Chongjiang deposit gave an isochron age of (14.04?.16) Ma. Re-Os model ages for two molybdenite samples from Lakang抏 deposit vary from 13.5 Ma to 13.6 Ma, which are basically identical to isochron ages mentioned above. All the thirteen samples from these three deposits yielded a linear array in the isochron diagram with a higher correlation coefficient of 0.99719 and an isochron age of (14.39?.22) Ma (1s error), suggesting an coeval event of the Cu mineralization and a shared source of ore materials for the Gangdese porphyry copper belt. Compared with the longer-lived felsic magmatic-hydrothermal system, the Cu mineralization is a relatively short event with duration of about 0.5 Ma, and usu-ally occurs in the later-stage of the complicate magmatic system. The emplacement age of the Gangdese porphyries indicates that they intruded after the rapid rising of the Gangdese Mountains at 21—23 Ma, and formed in a post-collision crustal ex-tension environment. Constraint of the NS-trending rifting zones (grabens) on localization of these porphyry bodies implies that the minor east-west stretching dates back to approximately 18 Ma. Highly precise Re-Os age of the Cu mineralization event indicates that a significant east-west extension has commenced at about (14?.5) Ma ago, which is identical to that of the normal faulting in central Tibet (13.5 Ma) and southern Tibet (14 Ma). The strong extension not only provided dilatant conduits for the migration and emplacement of the porphyry magmas pooling near the base of lithosphere, but also resulted in the rapid rising of a large volume of volatile, thus in turn constraining the temporal-spatial localization of the Gangdese porphyry Cu belt.展开更多
The accurately determining the lake ^14C reservoir age has a crucial significance for climatic reconstruction. In this study, the optically stimulated luminescence (OSL) dating method is employed to date samples fro...The accurately determining the lake ^14C reservoir age has a crucial significance for climatic reconstruction. In this study, the optically stimulated luminescence (OSL) dating method is employed to date samples from highstand lacustrine sediments, palaeoshoreline, fluvial terrace, and the alluvial fan of the Heihai Lake catchment. Accelerator mass spectrometry (AMS) 14C dating was also used to date fossil plants from highstand lacustrine sediments. Based on the calculations of linear regression with OSL against radiocarbon ages for same layers of two sections, the quantitative ^14C reservoir ages were estimated to lie between 3 353 and 3 464 yr during the 1.8 to 2.4 ka, which showed temporal variation. The sources of old carbon are the dissolution of carbonate bedrocks distributed along the Kunlun Mountain. The OSL ages of the different members of the hydatogen sedimentary system at Heihai Lake catchment indicate that a stronger hydrologic condition occurred from 3.0±0.2 to 1.8±0.2 ka, with a maximum lake level of 9 m higher than present. This humid stage was widely recorded in different sediments on the QTP and Chinese Loess Plateau (CLP), indicating its broad synchronicity across the Asian Summer Monsoon region. The enhanced East Asian Summer Monsoon (EASM) and the Indian Summer Monsoon (ISM) resulted in the increase of moisture availability for the Heihai Lake area during this stage.展开更多
The Nangqen Basin is one of the typical shearing-extensional basins situated in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been ...The Nangqen Basin is one of the typical shearing-extensional basins situated in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been reported in the note. The apparent ages of whole rock and separated biotite range from 32.04 to 36.50 Ma. The 40Ar-K (%) correlation isochronal line shows that there existed neither argon excessing , nor radiogenetic argon loosing, i.e. the age represents the true diagenetic time. Volcanic activity in this area occurred in the post-collision environment and is controlled by lithosphere substantial thickening and violent intercontinental shearing-strike slip faults. There is age difference of the magmatic activity in the east, the west and the north Tibet. The multi-periodic eruption-intrusion of the magmatic melt since Cenozoic is a tracer showing the pulsating uplift of the Tibetan Plateau.展开更多
基金supported by the National Natural Science Foundation of China(41390462,41201182,31300402)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry
文摘Black locust (Robinia pseudoacacia) is widely planted throughout the semi-arid Loess Plateau of China. The spatial distribution of this species at different ages is highly heterogeneous due to restoration and management practices. In this study, we aimed to compare the transpiration levels between different aged black locusts at the tree and stand scales, clarifying the physiological status of this species with different ages. Black locust trees with two representative age classes (12 and 28 years) were selected in the Yangjuangou catchment on the semi-arid Loess Plateau. Sap flux density (Fd) and environmental variables (solar radiation, air temperature, relative humidity and soil water content) were simultaneously monitored throughout the growing season of 2014. Tree transpiration (Et) was the product of Fd and sapwood area (As), and stand transpiration (Ec) was calculated basing on the stand sap flux density (Js) and stand total sapwood area (AsT). Stomatal conductance (gs) was measured in a controlled environment and hydraulic conductance was estimated using the relationship between transpiration rate and vapor pressure deficit (VPD). Our results showed that Et and Ec were higher in the 28-year-old stand than in the 12-year-old stand. The gs and hydraulic conductance of 28-year-old trees were also higher than those of 12-year-old trees, and the two parameters were thus the causes of variations in transpiration between different age classes. After rainfall, mean Fd increased by 9% in 28-year-old trees and by 5% in 12-year-old trees. This study thus suggests that stand age should be considered for estimating transpiration at the catchment and region scales in this area. These results provide ecophysiological evidences that the older black locust trees had more active physiological status than the younger ones in this area. These findings also provide basic information for the management of water resources and forests on the semi-arid Loess Plateau.
基金supported by the National Natural Science Foundation of China(grant No.41571013)Project of China Geological Survey(grant No.12120114002101)
文摘Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the dikes probably related to the activity of the nearly N-S faulting and micas from hydrothermal activity and the low- temperature thermochronology of plateau uplift. Previous research shows that there are at least three different ideas about the age of the rifts: (1) older than 16-12 Ma, (2) 14- 10 Ma, and (3) 8-4 Ma (Fig. la). For the old sedimentary strata represented the beginning of the rifting, the dating of the sediments helps to better define the initial rifting age.
基金sponsored by the China Geological Survey(grants No.1212011120335 and 12120114006201)
文摘Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite and ophiolite are present in the Atbashi Range, Kyrgyzstan, which are believed to be the relics of the Southern Tianshan Ocean. New data obtained through Ar-Ar isotopic analysis in this research provide reliable chronological restrictions for this problem.
文摘The fluctuation of lake levels in Tibetan area may be well reflected by the landformevidences, especially the last highest lake levels. This, in a certain degree, is more suitable fordetermning the climatic humidity and aridity in macro scale compared with many other indicatorswhich are also sensitive to the sedimentary environmental change. According to the analyses of thelakes such as Tianshuihai Lake, Bangdag Co, Lungmu Co, Bangong Co, Serfing Co, Chabyer Caka,Qahan salt lake, Qinghai lake, the lake group in north-east Qiangtang and the lake group in southTibet. the authors thought that the lakes on the Tibetan Plateau generally appeared the high lakelevel during 40-25 ka BP. The plenty of water quantity may represent a special warm-humid stage inTibet area compared with the sub-warm-humid stage reflected by marine oxygen isotope records.Thus, there may existed different driving factors to climatic changes between the high latitUde areasand middle-low latitude mountains.
基金This study was financially supported by the National Sciencc Foundation of China(No.49972035).
文摘The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lodegold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has beenargued that it was formed in the Mesozoic, related isotopic age data have not been reported inprevious studies. Based on detailed geological study, the authors have carried out isotopic datingon various metallogenic generations. The ore-forming process of the Dongchuang gold deposit consistsof four stages: coarse-grained pyrite-bearing quartz veins (stage I), fine-grained pyrite-quartzveinlets (stage II), multi-sulfides (stage III) and carbonate-quartz veinlets (stage IV). Ar-Ardating on mineral separates of stages I, II and III yields plateau ages of 142.9 +- 2.9 Ma, 132.2 +-2.6 Ma and 128.3 +- 6.2 Ma, respectively. Sericite separates from stage II assemblage also yield anAr-Ar isochron age of 132.6 +- 2.7 Ma, similar to the Ar-Ar plateau age. These results suggest thatthe Dongchuang gold deposit was mainly formed during 143-128 Ma, coinciding with the authors'geological observations and previous hypothesis. This ore formation is coeval with theregional-tectonic transition from collisional compression to extension, strongly showing that thedecompression-geothermal increase regime during compression-to-extension transition is the mostconducive geodynamic environment to orogenic-type gold mineralization.
基金funded by the National Natural Science Foundation of China(4130161041501094+3 种基金41330858)the Key Research Program of the Chinese Academy of Sciences(KZZD-EW-04)the Natural Science Basic Research Plan in Shaanxi Province of China(2014JQ5170)the open foundation of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau(A318009902-1510)
文摘In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0-100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0-100 cm. Moreover, there was a time lag of about 15-30 years between biomass production and soil carbon sequestration in 0-100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.
基金the Youth Foundation of the Ministry of Land and Resources and the National Natural Science Foundation of China(Grant 49973003).
文摘Geochronology of continental flood basalts sampled from the Emei large igneous province (LIP) on the western margin of the Yangtze platform was investigated by the laser microprobe 40Ar/39Ar dating technique. These basalts yield a fairly wide range of 40Ar/39Ar ages, varying from 259 to 135 Ma. One basalt sample, at least altered, recorded the oldest 40Ar/39Ar age of about 259 Ma, corresponding to a peak eruption age of the Emei LIP continental flood basalts. Most of the samples yield much younger ages from 135 to 177 Ma, which are consistent with the K-Ar ages for the same samples (122.8-172.1 Ma). The dating data suggest that these Permian basalts had been widely affected by the regional tectonothermal event at 177-135 Ma. The event was probably caused by the convergence and collision among the Laurasia, Yangtze and Qiangtang-Qamdo continental blocks on the eastern margin of the Qinghai-Tibet plateau after the late Triassic. The age of the event reflects the timing of the peak collisional orogeny.
文摘The dike swarm of lamprophyres at Pishan on the SW margin of the Tarimterrane is composed of ultra-potassic lamprophyres that have intruded into the Proterozoichornblende schists. ^(40)Ar/^(39)Ar dating data suggest that the isochron ages for phlogopite andwhole rock separates of the lamprophyres are 231.7+-0.3 Ma and 228.5+-0.3 Ma, respectively.Geochemical data indicate that the dikes were derived from a subduction-related or metasomatizedmantle. During the Middle-Late Triassic the western Kunlun area entered the post-orogeny period, andthus the occurrence of the dike swarm in the study area may have been controlled by underplating.
基金The work was financially supported by Project of 1∶50000 Regional Geological Survey of Samaki,Yinmin,Guicheng and Shugu Sheets in Yunnan Province by Land and Resources Department of Yunnan Province(D201905)Project of 1∶50000 Regional Geological Survey of Erjie,Yimen,Mingyihe and Shangpubei Sheets in Yunnan Province(DD20160017)Regional Geological Survey Area Summary and Service Product Development in Yunnan Province by China Geological Survey(121201102000150012-02).
文摘The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related to the early tectonic evolution of the Earth.However,its formation era,sedimentary filling sequence,and geotectonic characteristics have always been in dispute.In this study,several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone.This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village,Tongchang Township,Yimen County.LA-ICP-MS zircon dating was conducted,achieving the crystallization age of magma of 2491±15 Ma and the metamorphic ages of about 2.3 Ga,2.0 Ga,and 1.8 Ga for the first time.Meanwhile,according to in-situ Hf isotope analysis,the zirconεHf(t)values were determined to range from−3.0 to 7.6,with an average of 2.7.Furthermore,the first-stage Hf model age(TDM1)was determined to be 2513−2916 Ma,indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean.Therefore,it is believed that the strata of the slate were deposited in the Late Neoarchean,instead of the Mesoproterozoic as determined by previous researchers.Accordingly,it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group.Instead,they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information.Furthermore,the magma ages of 2491±15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton,and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic.The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland.Meanwhile,the metamorphic ages of 2.3 Ga,2.0 Ga,and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga,1.95 Ga,and 1.85 Ga of the northern margin of the Yangtze Craton,indicating that the strata experienced Paleoproterozoic tectonic-thermal events.The study area is located on the eastern margin of Qinghai-Tibet Plateau,and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous.The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.
基金This work was supported by the National Natural Science Foundation of China(41672243)the China Geological Survey Program(DD20160291,DD20189270).
文摘Delingha is located in the northeast margin of Qaidam Basin.Bayin River alluvial proluvial fan is the main aquifer of Delingha,in which groundwater generally flows from north to south.The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions,respectively.Cl-Na type groundwater was formed in front of Gahai Lake,and SO_(4)·HCO_(3)-Na·Ca type groundwater was formed in front of Keluke Lake.The results of deuterium(D)and 18O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions.In addition,results of ^(14)C indicated that the groundwater age was more than 1140 years,implying relatively poor renewal capability of regional groundwater.Moreover,our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.
文摘Tibet is the largest and highest plateau on the Earth (having 82% of the world’s land surface area falling >4km above sea level) attributed to the India and Asian convergence tectonics. Recently, high\|resolution digital topography data (Fielding et al., 1994) confirmed the earlier observations about flat erosional surfaces in the central part of the plateau (Jujin, et al., 1995) and suggested extraordinary flatness at a wide range of scales. Much of the Tibetan plateau across different accreted terranes has shallow slopes between 5°~10° and variation in relief of about 1 km, except in its marginal parts (Himalayan ranges; Kunlun mountains) where rough and high topography with intense fluvial dissections (variations in relief up to 7km) is quite frequent. However, in the southern and south\|central part of the plateau along the Pliocene\|Quaternary grabens, slopes generally steepen.
基金financially supported by the National Natural Science Foundation of China(U2243213,42077078)。
文摘The impacts of vegetation restoration on the soil erosion have been widely elucidated in the semi-arid regions.However,the magnitude of soil erosion on abandoned sloping farmland still remained unclear and their responses to vegetation succession were rarely addressed.The main objective of this study is to determine the magnitude of soil erosion along vegetation succession and explore the impact of vegetation succession on soil erosion from abandoned sloping farmland.Field observations were employed to monitor the rainfall,runoff,and soil erosion of seven sloping farmland plots with different abandoned ages and bare land from 2015 to 2019.The results indicated that the annual runoff depth and soil erosion modulus of vegetation types were in the range of 0.46 to 5.49 mm·a^(-1)and 1.3 to 24.5 t·km^(-2)·a^(-1),respectively.The vegetation effectively reduced the annual surface runoff and soil erosion with reduction of 73.8% to 97.8%and 98.0% to 99.9% as opposed to bare land.However,there were no significant differences in runoff and soil erosion for different vegetation types along succession.The largest event of vegetation types contributed to 38.7%-44.1% of the annual runoff and 42.5%-66.3% of the annual soil erosion,respectively.Vegetation restoration considerably alleviated the contribution of largest erosive event to annual soil erosion.The relationships between soil erosion,runoff and rainfall factors could be fitted well by linear functions,and the performances of regression models in predicting runoff were more satisfactory compared to predicting soil erosion.The Artemisia gmelinii(Agm)+Stipa bungeana(Sb)optimized the trade-off between sediment reduction and runoff maintenance,which should be selected as the suitable vegetation types to achieve the sustainability of socio-ecological systems.
文摘On the basis of the geomorphology, paleosol, paleoclimate and loess age, major changes of the Loess Plateau were studied. There are five major changes in the evolution of the Loess Plateau in China. Among them, the first, second, third and fourth major changes have taken place since the formation of the Loess Plateau, and the fifth major change will happen in 100 years. The first major change, which occurred at about 2.50 Ma BP, was a transition from red earth plateau to the Loess Plateau, and reflects the climate from the warm-sub-humid to the alteration between cold-and-dry and warm-and-humid. The driving force of this first major change was climate. The second major change, which took place at about 1.60 Ma BP, was a vital transition of the main rivers in this area from non-existence to existence, and represented an important change on the Loess Plateau's neotectonic uplift from the slow rising to periodically accelerated rising, and making the river's erosion go from feeble to strong. The driving force of the second major change is tectonic uplift. The third major change which occurred at about 150 ka, was a great transition of the Yellow River's inpouring from a lake outlet to a sea outlet. At that time, the Yellow River cut the Sanmen Gorge. The transition led to the transformation of loess material from internal transportation to external transportation. The driving force of the third major change was running water erosion. The fourth one that occurred at about 1.1 ka was a change of the Loess Plateau from natural erosion to erosion accelerated by human influences. The driving force of the fourth major change is mainly human activities. The fifth major change, which is the opposite change to the fourth one, in which the motive power is human activity, too.
基金the Innovative Project of the Chinese Academy of Sciences (Grant No. KZCX3-SW-125) National Natural Science Foundation of China (Grant No. 40472053 , No. 40673021).
文摘The Xianghualing Sn-polymetallic orefield in Hunan Province, southern China, is a largesize tin orefield. Although numerous studies have been undertaken on this orefield, its genesis, mineralization age, and tectonic setting are still controversial, mainly because of the lack of reliable geochronological data on tin mineralization. The ^40Ar^39Ar stepwise heating dating method was first employed on muscovite from different deposits in this orefield. The muscovite sample from the Xianghualing Sn-polymetallic deposit defines a plateau age of 154.4±1.1 Ma and an isochron age of 151.9±3.0 Ma; muscovite from the Xianghuapu W-polymetallic deposit yields a plateau age of 161.3±1.1 Ma and an isochron age of 160.0±3.2 Ma; muscovite from the Jianfengling greisen-type Sn-polymetallic deposit gives a plateau age of 158.7±1.2 Ma and an isochron age of 160.3±3.2 Ma. The tungsten-tin mineralization ages in the Xianghualing area are therefore restricted within 150-160 Ma. The tungstentin mineralization in Xianghualing occurred at the same time as the regional tin-tungsten mineralization including the Furong tin orefield, Shizhuyuan tungsten-tin polymetallic deposit and Yaogangxian tungsten-polymetallic deposit. Thus, the large-scale tungsten-tin metallogenesis in South China occurring at 160-150 Ma, probably is closely related to asthenospheric upwelling and crustmantle interaction under a geodynamic setting of crustal extension and lithosphere thinning during the transformation of tectonic regimes during the Mid-Late Jurassic.
文摘Furong, Hunan, is a large tin orefield discovered in China in recent years, which is mainly of the skarn-greisen-chlorite type. On the basis of the geological characteristics of the orefield, 40Ar-39Ar dating was performed on muscovite from greisen-type tin ore and biotite from related amphibole-biotite granite, which yielded three sets of age data, i.e., a plateau age of 157.5±0.3 Ma and an isochron age of 156.9±3 Ma for amphibole-biotite granite; a plateau age of 156.1±0.4 Ma and an isochron age of 155.7±1.7 Ma for the Sanmen greisen-type tin ore; and a plateau age of 160.1±0.9 Ma and an isochron age of 157.5±1.5 Ma for the Taoxiwo greisen-type tin ore. The three sets of age data coincide well with each other. They not only accurately reflect the timing of rock and ore formation but also indicate close relations between granite and tin deposits. In addition, the plateau ages of all three sets suggest that no subsequent thermal perturbation event occurred after the formation of granite and tin deposits. The Furong tin orefield is a component part of the southern Hunan large tungsten-tin polymetallic deposit concentration area and also a representative deposit formed in the time interval of 160-135 Ma in four peaks of Mesozoic tungsten-tin mineralization in the South China region. They might still correspond to the middle and late stages of the major geodynamic transition from a N-S- to an E-W-direction in eastern China.
文摘The Gangdese porphyry copper belt consists of one large and five middle-small deposits in addition to dozens of ore-bearing porphyry bodies. The belt trends 350 km long along the EW-striking Gangdese batholith, and locally occurs as a string of beads extending about 50 km within the SN-trending rifting zones (grabens) on the Tibetan plateau. Monzonitic granite- porphyry and quartz monzonitic porphyry, as dominant host rocks, are shoshonitic and potassic calc-alkaline. Available dating data indicate that the ages of the shallow-level emplacement for these porphyries vary from 10 Ma to 18 Ma, which are identical to that of associated potassic calc-alkaline volcanic rocks (10—15 Ma) and mafic dykes (13—18 Ma). The timing and duration of Cu mineralization events are constrained by Re-Os ages for molybdenites from three porphyry copper deposits in the Gangdese porphyry copper belt. Five molybdenite samples from the Nanmu deposit yielded an 187Re-187Os isochron with a highly pre-cise age of (14.76?.22) Ma; six molybdenites from the Chongjiang deposit gave an isochron age of (14.04?.16) Ma. Re-Os model ages for two molybdenite samples from Lakang抏 deposit vary from 13.5 Ma to 13.6 Ma, which are basically identical to isochron ages mentioned above. All the thirteen samples from these three deposits yielded a linear array in the isochron diagram with a higher correlation coefficient of 0.99719 and an isochron age of (14.39?.22) Ma (1s error), suggesting an coeval event of the Cu mineralization and a shared source of ore materials for the Gangdese porphyry copper belt. Compared with the longer-lived felsic magmatic-hydrothermal system, the Cu mineralization is a relatively short event with duration of about 0.5 Ma, and usu-ally occurs in the later-stage of the complicate magmatic system. The emplacement age of the Gangdese porphyries indicates that they intruded after the rapid rising of the Gangdese Mountains at 21—23 Ma, and formed in a post-collision crustal ex-tension environment. Constraint of the NS-trending rifting zones (grabens) on localization of these porphyry bodies implies that the minor east-west stretching dates back to approximately 18 Ma. Highly precise Re-Os age of the Cu mineralization event indicates that a significant east-west extension has commenced at about (14?.5) Ma ago, which is identical to that of the normal faulting in central Tibet (13.5 Ma) and southern Tibet (14 Ma). The strong extension not only provided dilatant conduits for the migration and emplacement of the porphyry magmas pooling near the base of lithosphere, but also resulted in the rapid rising of a large volume of volatile, thus in turn constraining the temporal-spatial localization of the Gangdese porphyry Cu belt.
基金supported by the National Natural Science Foundation of China(No.41401008)West Light Foundation of the Chinese Academy of Sciences(No.Y412021005)+1 种基金Natural Science Foundation of Qinghai Province(No.2016-ZJ-926Q)the instrument function development program of the Chinese Academy of Sciences(No.Y410041013)
文摘The accurately determining the lake ^14C reservoir age has a crucial significance for climatic reconstruction. In this study, the optically stimulated luminescence (OSL) dating method is employed to date samples from highstand lacustrine sediments, palaeoshoreline, fluvial terrace, and the alluvial fan of the Heihai Lake catchment. Accelerator mass spectrometry (AMS) 14C dating was also used to date fossil plants from highstand lacustrine sediments. Based on the calculations of linear regression with OSL against radiocarbon ages for same layers of two sections, the quantitative ^14C reservoir ages were estimated to lie between 3 353 and 3 464 yr during the 1.8 to 2.4 ka, which showed temporal variation. The sources of old carbon are the dissolution of carbonate bedrocks distributed along the Kunlun Mountain. The OSL ages of the different members of the hydatogen sedimentary system at Heihai Lake catchment indicate that a stronger hydrologic condition occurred from 3.0±0.2 to 1.8±0.2 ka, with a maximum lake level of 9 m higher than present. This humid stage was widely recorded in different sediments on the QTP and Chinese Loess Plateau (CLP), indicating its broad synchronicity across the Asian Summer Monsoon region. The enhanced East Asian Summer Monsoon (EASM) and the Indian Summer Monsoon (ISM) resulted in the increase of moisture availability for the Heihai Lake area during this stage.
文摘The Nangqen Basin is one of the typical shearing-extensional basins situated in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been reported in the note. The apparent ages of whole rock and separated biotite range from 32.04 to 36.50 Ma. The 40Ar-K (%) correlation isochronal line shows that there existed neither argon excessing , nor radiogenetic argon loosing, i.e. the age represents the true diagenetic time. Volcanic activity in this area occurred in the post-collision environment and is controlled by lithosphere substantial thickening and violent intercontinental shearing-strike slip faults. There is age difference of the magmatic activity in the east, the west and the north Tibet. The multi-periodic eruption-intrusion of the magmatic melt since Cenozoic is a tracer showing the pulsating uplift of the Tibetan Plateau.