Zircon U-Pb ages in the Nuratau ophiolitic mélange in the southern Tianshan,Uzbekistan:Implication for the closure of Paleo-Asian Ocean

1.Objective The Central Asian Orogenic Belt(CAOB),which is located between the European craton,Siberian craton,and Tarim-North China craton(Fig.1a),is the largest phanerozoic accretionary orogen in the world.It resulted from the longterm subduction and accretion of the Paleo-Asian Ocean(PAO).The PAO has been in existence since at least the late Mesoproterozoic(about 1020 Ma).However,there has been debate about the closing time of the PAO.

Regulation of vegetation pattern on the hydrodynamic processes of erosion on hillslope in Loess Plateau,China

As vegetation are closely related to soil erosion,hydrodynamic parameter changes under various vegetation pattern conditions can be used as an important basis for the research of the soil erosion mechanism.Through upstream water inflow experiments conducted on a loess hillslope,how the vegetation pattern influences the hydrodynamic processes of sediment transport was analyzed.The results show that the placement of a grass strip on the lower upslope can effectively reduce runoff erosion by 69%,relying on the efficiency of regulated hydrodynamic process.The effective location of grass strip for hillslope alleviating erosion is on the lower part of the upslope,mainly due to the grass strip measure used to regulate the hydrodynamic system.As a result,the underlying surface runoff resistance is increased by 5 times,runoff shear stress is decreased by more than 90%,and runoff power decreased by over 92%.The measure greatly separates the scouring energy of surface runoff that acts on the slope soil.Therefore,the use of grass strips effectively decreases the energy of runoff flowing along the slope,eliminating soil erosion to a great extent and thereby achieving a better regulation of hydrodynamic processe.

Investigation of groundwater characteristics and its influence on Landslides in Heifangtai Plateau using comprehensive geophysical methods

The occurrence of landslides in Heifangtai plateau is primarily caused by the rise in water levels due to irrigation. To accurately understand the distribution of groundwater and its impact on the landslide hazard, a combination of Electrical Resistivity Tomography(ERT), Induced Polarization(IP) and Surface Nuclear Magnetic Resonance(SNMR) methods were used in this study. By conducting a comprehensive analysis, the characteristics of water-bearing structure in vertical and groundwater distribution in horizontal were detected;and the influence of the groundwater on plateau and landslides was also identified. The results indicate that the groundwater occurs in the loess aquifer with a three-layer structure in vertical.Horizontally, the aquifer has a unified water table over the plateau, with a low water level in the north and high one in the south. The high resistivity bedrock uplift belt in the middle of the plateau forms a watershed,with the north side of the uplift belt being a relatively stable slope area with stable water content and fewer geological disasters. In contrast, the south side of the uplift belt is a disaster-prone region with vertical fissures well developed in the loess aquifers. The southern landslides are characterized by the interphase distribution of high and low electrical resistivity. The infiltration and discharge of groundwater result in the formation of a collapse belt in the low resistivity water-bearing structure of landslide, which causes the entire block with high resistivity and stable bedrock to slide. There was a newly formed landslide in a larger range at the landslide' s trailing edge. This study provides a scientific basis for the study of landslides mechanisms and disaster prevention by identifying the distribution characteristics of groundwater and analyzing its influence from a geophysical perspective in Heifangtai.

Subduction channel fluid-rock interaction:Indications from rutile-quartz veins within eclogite from the Yuka terrane,North Qaidam orogen

High-pressure(HP)or ultrahigh-pressure(UHP)rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones.To explore the fluid flow and the associated element mobility during deep subduction and exhumation of the continental crust,we investigated the major and trace elements of Ti-rich minerals.Additionally,U–Pb dating,trace element contents,and Lu–Hf isotopic composition of zircon grains in the UHP eclogite and associated rutile-quartz veins were examined in the North Qaidam UHP metamorphic belt,Yuka terrane.The zircon grains in the rutile-quartz veins have unzoned or weak oscillatory zonings,and show low Th/U ratios,steep chondrite-normalized patterns of heavy rare earth elements(HREEs),and insignificant negative Eu anomalies,indicating their growth in metamorphic fluids.These zircon grains formed in 431
3 Ma,which is consistent with the 432
2 Ma age of the host eclogite.As for the zircons in the rutile-quartz veins,they showed steep HREE patterns on one hand,and were different from the zircons present in the host eclogite on the other.This demonstrates that their formation might have been related to the breakdown of the early stage of garnet,which corresponds to the abundance of fluids during the early exhumation stage.The core-rim profile analyses of rutile recorded a two-stage rutile growth across a large rutile grain;the rutile core has higher Nb,Ta,W,and Zr contents and lower Nb/Ta ratios than the rim,indicating that the rutile domains grew in different metamorphic fluids from the core towards the rim.The significant enrichment of high field strength elements(HFSEs)in the rutile core suggests that the peak fluids have high solubility and transportation capacity of these HFSEs.Furthermore,variations in the Nb vs.Cr trends in rutile indicate a connection of rutile to mafic protolith.The zircon grains from both the rutile-quartz veins and the host eclogite have similar Hf isotopic compositions,indicating that the vein-forming fluids are internally derived from the host eclogite.These fluids accumulated in the subduction channel and were triggered by local dehydration of the deeply subducted eclogite during the early exhumation conditions.

Soil water movement and deep drainage through thick vadose zones on the northern slope of the Tianshan Mountain: Croplands vs.natural lands

Regional aridity is increasing under global climate change,and therefore the sustainable use of water resources has drawn attention from scientists and the public.Land-use changes can have a significant impact on groundwater recharge in arid regions,and quantitative assessment of the impact is key to sustainable groundwater resources management.In this study,the changes of groundwater recharge after the conversion of natural lands to croplands were investigated and compared in inland and arid region,i.e.,the northern slope of the Tianshan Mountain.Stable isotopes suggest that soil water in topsoil(<2 m)has experienced stronger evaporation under natural lands than croplands,and then moves downward as a piston flow.Recharge was estimated by the tracer-based mass balance method,i.e.,chloride and sulfate.Recharge rates under natural conditions estimated by the chloride mass balance(CMB)method were estimated to be 0.07 mm/a in deserts and 0.4 mm/a in oases.In contrast,the estimated groundwater recharge ranged from 61.2 mm/a to 44.8 mm/a in croplands,indicating that groundwater recharge would increase significantly after land changes from natural lands to irrigated croplands in arid regions.Recharge estimated by the sulfate mass balance method is consistent with that from the CMB method,indicating that sulfate is also a good tracer capable of estimating groundwater recharge.

Provenance Variability of the Triassic Strata in the TurpanHami Basin: Detrital Zircon Record of Indosinian Tectonic Reactivation in the Eastern Tianshan

The Triassic strata in the Turpan-Hami Basin potentially chronicled the missing sedimentary record of Indosinian tectonic evolution in the Eastern Tianshan.In this study,we conducted detrital zircon U-Pb geochronological analyses on subsurface Triassic samples collected from the Turpan-Hami Basin to unravel sedimentary response of Indosinian tectonic reactivation and its geodynamics.The detrital zircon age spectra of the Triassic samples are quite different,reflecting significant provenance variability.The zircon grains in the Lower Triassic sample were mainly from the Central Tianshan,while the Jueluotag acted as a minor provenance.By contrast,the Late Paleozoic rocks in Jueluotag act as the main provenance for the Middle-Upper Triassic samples,while the Central Tianshan acted as a minor provenance.Furthermore,zircon grains in the Middle Triassic sample were mainly from the Permian rocks in Jueluotag,while Indosinian strike-slipdriven rapid exhumation brought deeper Carboniferous rocks of Jueluotag as an important age population for the Upper Triassic sample.The inter-sample variability of age spectra of the Triassic samples provides sedimentary evidence for Indosinian tectonic reactivation in the Eastern Tianshan and its periphery,which could be attributed to differential exhumation of different sources driven by coeval strike-slip tectonics along deep faults.The Indosinian tectonic behavior in the Eastern Tianshan,which is characterized by partial melting of the pre-thickened crust and strike-slip deformation,acted as a far-field respond to the coeval continental accretion occurring along the southern Eurasian margin.Additionally,our new detrital zircon data,together with previously published data in the Turpan-Hami Basin,demonstrate that there are significant changes in source-to-sink system from the Permian to the Triassic,suggesting that the Permian-Triassic unconformity in the Eastern Tianshan and its periphery was generated by Late Permian-Early Triassic tectonic contraction and inversion rather than an increasingly arid climate.

Effi cient modeling of the gravity anomaly caused by a sedimentary basin with lateral variable density contrast and its application in basement relief estimation

The forward calculation of gravity anomalies is a non-negligible aspect contributing to the time consumption of the entire process of basement relief estimation.In this study,we develop a fast hybrid computing scheme to compute the gravity anomaly of a basement.We use the vertical prism source equation in a given region R centered at a certain gravity observation point and the vertical line source equation outside R to derive the gravity anomaly.We observe that the computation with the vertical line source equation is much faster than that of the vertical prism source equation,but the former is slightly inaccurate.Therefore,our method is highly effi cient and able to avoid the errors caused by the low accuracy of the vertical line source equation near the observation point.We then derive the general principle of choosing the size of R via a series of prism model tests.Our tests on the gravity anomaly over the Los Angeles Basin confirm the correctness of our proposed forward strategy.We modify Bott’s method with an accelerating factor to expedite the inversion procedure and presume that the density contrast between the sediments and the basement in a sedimentary basin varies laterally and can be obtained using the equivalent equation.Synthetic data and real data applications in the Weihe Basin illustrate that our proposed method can accurately and effi ciently estimate the basement relief of sedimentary basins.

Geology and mineralization of the Songpan-Ganze-West Kunlun pegmatite-type rare-metal metallogenic belt in China:An overview and synthesis

The Songpan-Ganze orogenic belt on the northeastern margin of the Tibetan Plateau extends westward from the Songpan-Ganze terrain in western Sichuan to the Tianshuihai region in West Kunlun,Xinjiang.It hosts numerous giant spodumene pegmatite deposits and ore fields,including Jiajika and Ke’eryin in western Sichuan Province,Zhawulong on the border between the Sichuan and Qinghai Provinces,and Dahongliutan in Xinjiang Region.These form the Songpan-Ganze-West Kunlun(SP-GZ-WK) pegmatite-type rare-metal metallogenic belt.The pegmatite type rare-metal deposits in this belt are hosted in the metamorphic thermal domes in the metamorphosed flysh of the Triassic Xikang and Bayankalashan Groups.The mineralized pegmatites are intimately related to the Li-and volatile-rich two-mica granites that are peraluminous and have high(Li+Na+K)/(Mn+Fe+Mg+Ca+Ti) ratios.Pegmatites and granites in individual ore field throughout the belt typically form a cogenetic granite-pegmatite system,in which pegmatite dikes commonly surround granites.Spodumene is the predominant ore mineral in most pegmatites with limited hydrothermal alteration.In the granite-pegmatite systems,granitic magmas were emplaced under P-T conditions of 800–850°C and ~550 MPa,while spodumene crystallized in an alkaline environment.The granite-pegmatite systems share similar Sr-Nd-Hf-Li isotopic compositions to the metasediments of the Xikang and Bayankalashan Groups.The δ7Li values tend to increase from the granites to the Li-poor pegmatites,whereas the reverse is observed between the Li-poor and Li-rich pegmatites.These geochronological data suggest that the granite-pegmatite systems formed in the Late Triassic and tend to be progressively younger from the outer to the inner zones of the metallogenic belt.These characteristics show that the granitic-pegmatitic melts were derived from the anatexis of the Xikang and Bayankalashan Groups during the Paleo-Tethyan orogeny in the Late Triassic.The separation of pegmatitic melts from granitic magmas can be best explained using the Jiajika-style “melt-melt immiscibility” or the Ke’eryin-style “fractional crystallization+melt-melt immiscibility” model.High-maturity terrestrial sediments are of key importance for the anatexis that results in the granitepegmatite melts.The bidirectional tectonic stresses in the Songpan-Ganze orogenic belt may have caused the mineralization difference between the Jiajika deposit and the Ke’eryin ore field.These features indicate the controls of the combination of orogenic deformation,metapelites anatexis,and magmatic differentiation on the rare-metal mineralization of pegmatites.We suggest that pegmatites,pegmatite–parental granite,and their protoliths are important indicators for rare-metal mineralization in the SP-GZ-WK pegmatite type rare-metal metallogenic belt.Based on the widespread presence of fertile metasediments and well development of metamorphic thermal dome,highly differentiated granites,and regional zonation of pegmatites,the Zhawulong ore field is the most prospective area for rare metals and thus should be the priority for future exploration.

Research on hydrogen and oxygen isotopes of paleoclimate reconstruction in Nuomuhong

As a typical alluvial-proluvial fan area in the Qaidam Basin, Nuomuhong is important to the research on paleoclimate reconstruction in proluvial fan areas and basin climate change and ecological protection. This paper analyzes features of 2H, 3H, 18 O and 14 C isotopes in Nuomuhong and reconstructs paleoclimate in this area. According to the results: since 28 ka B.P., the ground average temperature decreases and then increases in the Qaidam watershed, reaching the lowest in 17.7 ka B.P. before increasing gradually. In the past 30 000 years, average temperature has changed ranged from 1 ℃ to 5 ℃ in this area; the lowest temperature was different from today’s temperature only by 3 ℃. This shows that climate conditions and natural environment in this area have been relatively stable in the past 30 000 years.

The invention of an automatic measurement and data recording method of a fluorescence spectrophotometer

1.Objectives The laboratory of Xi’an Center,China Geological Survey has long been engaged in the testing of oil and gas geochemical samples.Among the different indexes,the measurement of the polycyclic aromatic hydrocarbon needs to be completed by the fluorescence spectrophotometer which is made in PE Company.According to the standard method,the fluorescence intensity values of three emission wavelengths under a certain excitation wavelength should be provided.

A New Discovery of Mineralization as Subseafloor Hydrothermal Replacement in the Duddar Super-Large SEDEX Lead-Zinc Deposit in Pakistan

0 INTRODUCTION Sedimentary exhalative(SEDEX)lead-zinc deposit was traditionally considered as a result of submarine hydrothermal exhalation,including exhalative plume and brine pool models(Izanloo et al.,2022;Spinks et al.,2021;Maghfouri et al.,2020;Sangster,2020,2018;Huang et al.,2019;Rajabi et al.,2015;Goodfellow and Lydon,2007;Large et al.,2005,2001;Peng et al.,2000;Goodfellow et al.,1993;Figures 1a,1b).However,recognition of mineralization as subseafloor hydrothermal replacement in a few SEDEX deposits has challenged the traditional consideration(Magnall et al.,2023,2021,2020a,b;Hayward et al.,2021;Figure 1c).Researchers come to believe that subseafloor replacement rather than submarine exhalation is a dominant process for SEDEX mineralization,but this needs to be examined through more case studies.

Paleo-Earthquakes along the Zheduotang Fault,Xianshuihe Fault System,Eastern Tibet:Implications for Seismic Hazard Evaluation

The Kangding City in eastern Tibet is at high risk due to frequent strong earthquakes along the Xianshuihe sinistral strike-slip fault bounding the Chuandian Block to the northeast.The knowledge of paleo-seismicity recurrence along this fault system is key to the evaluation of earthquake hazards in this region;thus,more accurate paleoseismic information are required.We examined the paleo-seismicity along the Zheduotang fault in the central segment of the Xianshuihe fault system by applying the field investigation,trenching,and Quaternary dating methods(e.g.,OSL and ^(14)C).Field observations found~8.5 m offset of stream by sinistral slip along the Zheduotang fault.We trenched the central fault zone of the Zheduotang fault and found that the colluvial wedges and five buried,discontinuous,A-soil horizons progressively have been offset in the shallow graben on the SW-side of the main fault indicative of the paleo-earthquakes.The dating results of OSL and ^(14)C,in line with existing data,enable us to establish the paleo-seismic history of the Zheduotang fault.It shows at least eight surface ruptures in the last 7500 years identified from displaced buried soils,colluvial wedges and terraces.Our study reveals~100 years minimum paleo-earthquake recurrence,suggesting potential large earthquakes in the Kangding area in the future.

Mesozoic Tectonothermal Evolution of the Southern Central Asian Orogenic Belt: Evidence from Apatite Fission-Track Thermochronology in Shalazha Mountain, Inner Mongolia

Mesozoic intracontinental orogeny and deformation were widespread within the southern Central Asian Orogenic Belt(CAOB). Chronological constraints remain unclear when assessing the Mesozoic evolution of the central segment of this region. The tectonic belt of Shalazha Mountain located in the center of this region is an ideal place to decode the deformation process. Apatite fission-track(AFT) thermochronology in Shalazha Mountain is applied to constrain the Mesozoic tectonothermal evolution of the central segment of southern CAOB. The bedrock AFT ages range from 161.8 ± 6.9 to 137.0 ± 7.3 Ma, and the first reported detrital AFT obtained from Lower Cretaceous strata shows three age peaks: P1(ca. 178 Ma), P2(ca. 149 Ma) and P3(ca. 105.6 Ma). Bedrock thermal history modeling indicates that Shalazha Mountain have experienced three stages of differential cooling: Late Triassic–Early Jurassic(~230–174 Ma), Late Jurassic–Earliest Cretaceous(~174–135 Ma) and later(~135 Ma). The first two cooling stages are well preserved by the detrital AFT thermochronological result(P1, P2) from the adjacent Lower Cretaceous strata, while P3(ca. 105.6 Ma) records coeval volcanic activity. Furthermore, our data uncover that hanging wall samples cooled faster between the Late Triassic and the Early Cretaceous than those from the footwall of Shalazha thrust fault, which synchronizes with the cooling of the Shalazha Mountain and implies significant two-stage thrust fault activation between ca. 230 and 135 Ma. These new low-temperature thermochronological results from the Shalazha Mountain region and nearby reveal three main phases of differential tectonothermal events representing the Mesozoic reactivation of the central segment of the southern CAOB. In our interpretations, the initial rapid uplift in the Late Triassic was possibly associated with intracontinental orogenesis of the CAOB. Subsequent Middle Jurassic–Earliest Cretaceous cooling is highly consistent with the Mesozoic intense intraplate compression that occurred in the southern CAOB, and is interpreted as a record of closure of the Mongol-Okhotsk Ocean. Then widespread Cretaceous denudation and burial in the adjacent fault basin could be linked with the oblique subduction of the Izanagi Plate along the eastern Eurasian Plate, creating a northeast-trending normal fault and synchronous extension. However, our AFT thermochronometry detects no intense Cenozoic reactivation information of Shalazha Mountain region.

Petrogenesis of the Chagangnuoer deposit,NW China:a general model for submarine volcanic-hosted skarn iron deposits

The Chagangnuoer deposit is a typical submarine volcanic rock-hosted skarn iron deposit, where orebodies mainly occur in andesitic rocks of the Dahalajunshan Formation （DF） with skams well developed around orebodies. The volcanic rocks of the DF in the Chagangnuoer deposit display calc-alkaline characteristics. The ore-bearing andesitic rocks have high ^87Sr/^86Sr（i） （0.7058-0.7117） and low εNd（t） （-3.51 to 1.67）. They probably formed through mixing of basaltic melts and the induced crustal melts. LA-ICP-MS U-Pb zircon ages of 250 and 305 Ma are obtained for the granite and granodiorite in the Chagangnuoer deposit, respectively, which are signifi- cantly younger than the timing of the skarn formation （316 Ma）. These age data indicate that the granitoids have no contribution to the skarn and associated iron mineralization. This paper proposes a new genetic model for submarine volcanic rock-hosted skam iron deposits, in which the iron mineralization, skarn formation and volcanic magmatism are necessary aspects of the same system; the iron separates and concentrates from the silicate magma in the form of Fe（II） carbonate complex. While this conceptual model is largely based on observations on the Chagangnuoer deposit, it may have general significance for skam-type iron deposits associated with submarine volcanic rock sequences and warrants further testing and improvement.