Oxygen and hydrogen isotope characteristics of different water bodies in the Burqin River Basin of the Altay Mountains,China

Characterization of the spatial and temporal variability of stable isotopes in surface water is essential for interpreting hydrological processes.In this study,we collected the water samples of river water,groundwater,and reservoir water in the Burqin River Basin of the Altay Mountains,China in 2021,and characterized the oxygen and hydrogen isotope variations in different water bodies via instrumental analytics and modeling.Results showed significant seasonal variations in stable isotope ratios of oxygen and hydrogen(δ18O andδ2H,respectively)and significant differences inδ18O andδ2H among different water bodies.Higherδ18O andδ2H values were mainly found in river water,while groundwater and reservoir water had lower isotope ratios.River water and groundwater showed differentδ18O-δ2H relationships with the local meteoric water line,implying that river water and groundwater are controlled by evaporative enrichment and multi-source recharge processes.The evaporative enrichment experienced by reservoir water was less significant and largely influenced by topography,recharge sources,local moisture cycling,and anthropogenic factors.Higher deuterium excess(d-excess)value of 14.34‰for river water probably represented the isotopic signature of combined contributions from direct precipitation,snow and glacial meltwater,and groundwater recharge.The average annual d-excess values of groundwater(10.60‰)and reservoir water(11.49‰)were similar to the value of global precipitation(10.00‰).The findings contribute to understanding the hydroclimatic information reflected in the month-by-month variations in stable isotopes in different water bodies and provide a reference for the study of hydrological processes and climate change in the Altay Mountains,China.

A system-integrated approach for the design of tourist areas at the local level under changing conditions:A case study in the Altay Mountains

The existing approaches for the design of tourist areas often lead to limited flexibility in project implementation.To realize a more flexible approach,in this study,we formulated a model for planning and designing tourist areas at the local level.Moreover,specific tools for analyzing tourist areas and ensuring sustainable development under changing conditions were developed.This study was conducted in two tourist regions,Biryuzovaya Katun tourist complex and Belokurikha destination(including Belokurikha City with Belokurikha 2 Gornaya tourist complex and surrounding areas),in the Altay Mountains.We employed the recreation opportunity spectrum and proposed a system-integrated programming approach for the design of tourist areas at the destination and site levels.The key of this approach was the collection and analysis of current spatial data,including the spatial distribution of attractions and visitor flows.We constructed heat maps using video recording and unmanned aerial vehicle(UAV)observation data.Moreover,we analyzed the video stream using an image-analyzing framework You Only Look Once(YOLO)v5 software.The heat map of visitor flows based on video recording data in the Andreevskaya Sloboda museum of Belokurikha 2 Gornaya tourist complex allowed us to highlight the most attractive sites in this area and classify them into one of three types:points of functional concentration,points of transitional concentration,and points of attractions.The heat maps in Biryuzovaya Katun tourist complex,created using UAV observation data,allowed us to determine the spatiotemporal patterns of visitor flows and tourists’preferences throughout the day within four time intervals:09:00-12:00,13:00-14:00,14:00-15:00,and 16:00-18:00(LST).The maximum visitor flow density occurred from 16:00 to 18:00 in the beach area of the artificial lake.A comparison between the visitor-concentrated sites and the current facilities provided insights into the demand for attractions and facilities and the lacking areas.Heat maps are useful in analyzing the land use at the site level,while zoning based on the recreation opportunity spectrum can be used to design tourist areas at the destination level.The proposed methods for analyzing the use of tourist areas contribute to the development of adaptive tourism design.

Geochemistry, Geochronology and Genesis of Gold Mineralization in Nurt of Northern Altay, Xinjiang: A Case Study on the Aketishikan Gold Deposit

Gold deposits such as the Aketishikan, Togetobie, Tasbig-Kokeydlas, Kums and Hongshanzui gold deposits in the Nurt area in Altay of Xinjiang were found in Member 3 rhyolite tufflava, fragmental lava and ignimbrite of the Carboniferous Hongshanzui Group. Trace and rare earth elements, sulfur, lead, oxygen and hydrogen isotopes, and geochronological studies indicate that the ore-forming material was mostly supplied by the Carboniferous volcanic rocks through water-rock interaction under a low-to-moderate temperature, and the hydrothermal ore-forming fluid came from meteoric water with some magmatic water input evolved from the granitic magmas. Gold deposits in the Nurt area as well as in the northern Altay might form in multiple stages, and the Yanshanian mineralization period should be paid more attention besides the Variscan mineralization period.

HYDROTHERMAL SEDIMENTATION,DIAGENESIS AND MINERALIZATION OF SOUTHERN ALTAY MARGIN IN THE DEVONIAN PERIOD

The Devonian hydrotyermal sedimentation and mineralization are widespread and typical in Maizi、Kelang and Chonghuer basins of southern Altay margin, and have their respective signs in occurrence, fabric and geochemistry.Hydr)thermal sedimentary rocks mainly occur in the intermittent period between volcanic sub(?)ycles. They are thin-midium-bedded, lenticular and basically uniform to the occurrences of the overlying and underlying strata. The classification of the hydrothermal sedimentary rocks is proposed based on the mineral compositions. The detailed descriptions are given to the five types of hydrothermal sedimentary rocks: silicates, feldspar-rich rocks,

Environmental significance and hydrochemical characteristics of rivers in the western region of the Altay Mountains,China

Analysis of environmental significance and hydrochemical characteristics of river water in mountainous regions is vital for ensuring water security.In this study,we collected a total of 164 water samples in the western region of the Altay Mountains,China,in 2021.We used principal component analysis and enrichment factor analysis to examine the chemical properties and spatiotemporal variations of major ions(including F-,Cl-,NO_(3)-,SO_(4)^(2-),Li+,Na+,NH4+,K+,Mg^(2+),and Ca^(2+))present in river water,as well as to identify the factors influencing these variations.Additionally,we assessed the suitability of river water for drinking and irrigation purposes based on the total dissolved solids,soluble sodium percentage,sodium adsorption ratio,and total hardness.Results revealed that river water had an alkaline aquatic environment with a mean pH value of 8.00.The mean ion concentration was ranked as follows:Ca^(2+)>SO_(4)^(2-)>Na+>NO_(3)->Mg^(2+)>K+>Cl->F->NH_(4)+>Li+.Ca^(2+),SO_(4)^(2-),Na+,and NO_(3)-occupied 83%of the total ion concentration.In addition,compared with other seasons,the spatial variation of the ion concentration in spring was obvious.An analysis of the sources of major ions revealed that these ions originated mainly from carbonate dissolution and silicate weathering.The recharge impact of precipitation and snowmelt merely influenced the concentration of Cl-,NO_(3)-,SO_(4)^(2-),Ca^(2+),and Na+.Overall,river water was in pristine condition in terms of quality and was suitable for both irrigation and drinking.This study provides a scientific basis for sustainable management of water quality in rivers of the Altay Mountains.

Viscoelastic stress change from the 1931 M_(w)7.8 Fuyun earthquake and its impacts on seismic activity around the Altai mountains

The 1931 M_(w)7.8 Fuyun earthquake occurred around the Altai mountains, an intracontinental deformation belt with limited active strain-rate accumulation. To explore whether seismic activity in this deformation belt was affected by stress interaction among different active faults, we calculate the Coulomb failure stress change(ΔCFS) induced by the Fuyun earthquake due to coseismic deformation of the elastic crust and postseismic viscoelastic relaxation of the lower crust and upper mantle. Numerical results show that the total ΔCFS at a 10-km depth produced by the Fuyun earthquake attains approximately 0.015-0.134 bar near the epicenter, and just before the occurrence of the 2003 M_(w)7.2 Chuya earthquake, which distances about 400 km away from the Fuyun earthquake. Among the increased ΔCFS,viscoelastic relaxation from 1931 to 2003 contributes to approximately 0.014-0.131 bar, accounting for>90% of the total ΔCFS. More importantly, we find that for the recorded seismicity in the region with a radius of about 270 km to the Fuyun earthquake from 1970 to 2018, the percentage of earthquakes that fall in positive lobes of ΔCFS resolved on the NNW-SSE Fuyun strike-slip fault, on the NWW-SEE Irtysh strike-slip fault, and on the NW-SE Kurti reverse fault is up to 67.22%-91.36%. Therefore, the predictedΔCFS suggests that the impact of the 1931 M_(w)7.8 Fuyun earthquake on seismic activity around the Altai mountains is still significant as to hasten occurrence of the 2003 M_(w)7.2 Chuya earthquake at a relatively far distance and to trigger its aftershocks in the near-field even after several decades of the mainshock.

Flooding(or breaching)of inter-connected proglacial lakes by cascading overflow in the arid region of Western Mongolia(Mt.Tsambagarav,Mongolian Altai)

This study investigates the glacial lake outburst flood(GLOF)hazards in the Tsambagarav mountain range in Western Mongolia,focusing on the Khukhnuruu Valley and its interconnected proglacial lakes.Over the last 30 years,significant glacier retreats,driven by rising temperatures and changing precipitation patterns,have led to the formation and expansion of several proglacial lakes.Fieldwork combined with satellite data and meteorological analysis was used to assess the dynamics of glacier and lake area changes,with particular focus on the flood events of July 2021.The research reveals a substantial reduction in glacier area,particularly in the Khukhnuruu E complex,where glacier area decreased by 19.3%.The study highlights the influence of increasing temperatures and summer precipitation,which have accelerated ice melt,contributing to the expansion and eventual breaching of lakes.Additionally,lake area changes were influenced by the steepness of the terrain,with steeper slopes exacerbating peak discharge during floods.Of the studied seven lakes(Lake 1 to Lake 7),Lake 1 experienced the most dramatic reduction,with a decrease in area by 73.51%and volume by 84.84%,followed by Lake 7.This study underscores the region's vulnerability to climate-induced hazards and stresses the need for a comprehensive early warning system and disaster preparedness measures to mitigate future risks.

Tectono-Metallogenic System in the Altay Orogenic Belt,China

The Altay orogenic belt of China is an important metallogenic belt of base metals, rare metals and gold. The main orogenic-metallogenic epoch is the Hercynian (Late Palaeozoic). Hercynian orogeny underwent two tectonic stages: the early volcano-passive continental margin extension (D1-D2) and late subduction-collision (D3-P). There correspondingly developed two different metallogenic systems. One is the stratabound massive sulphide and iron metallogenic system related to volcano-passive continental margin, and the other is the epigenetic gold and granite-associated rare metals system formed by collision. Very few mineralizations were formed during the subduction time.

Massive Sulphide Deposits Related to the Volcano-Passive Continental Margin in the Altay Region

The Devonian volcano-passive continental margin in southern Altay is a significant volcanogenic massive sulphide metallogenic belt. Acidic volcanism has been dominant on the inner side of the volcano-passive continental margin, i.e., near the old land, resulting in a Pb-Zn metallogenic sub-belt, in which the ore deposits are hosted by sedimentary rocks in volcanic series, as represented by the large Koktal Pb-Zn deposits. In the central part of the margin far away from the old land, bimodal volcanic formations are well developed, forming volcanics-hosted Cu-Zn metallogenic sub-belts, e.g., the large-scale Ashele Cu-Zn deposit. The Qiaoxiahala sub-belt on the outer side of the margin near the ocean ridge is located at the spreading central trough, where ophiolite suites are developed. This type of deposits is rich in gold and copper, similar to the Cyprus-type Fe-Cu-Au metallogenic sub-belt in metallogenic environment (represented by the Qiaoxiahala medium-scale Fe-Cu-Au deposit). From the old land to the ocean, the mineralizing age becomes younger, i.e., from Early Devonian→Early and Middle Devonian→Middle Devonian, forming a complete metallogenic zoning series on the volcano-passive continental margin. Comparative studies show that the massive sulphide deposits distributed on the volcano-passive continental margin are different from those formed under a plate subduction regime and oceanic ridge environment; the former have their unique features and wide distributions, representing a new type of volcanogenic massive sulphide deposits—the Altay type.

Ore-forming elements diffusion and distribution in the altered host rock surrounding the Koktokay No.3 pegmatite in the Chinese Altay

Petrography and geochemistry of the altered and unaltered host rocks surrounding the Koktokay No.3 pegmatite revealed that the unaltered amphibolite is mainly composed of hornblende, plagioclase, and ilmenite.Beyond these primary components, the altered host rocks contain a few newly formed minerals, including biotite,tourmaline, chlorine, and muscovite. The alteration zone surrounding the Koktokay No.3 pegmatite is limited to 2.0 m, characterized by biotitization, tourmalization, and chloritization. In the altered host rocks, the contents of SiO2, MgO, MnO, Na2O, and TiO2 did not vary greatly.However, Al2O3 showed a weak decreasing trend with the increasing distance from the pegmatite contact zone, while Fe2O3 and CaO showed an increasing trend. The contents of Li, Rb, and Cs in the altered host rocks were much higher than those in the unaltered host rocks, decreasing with distance from the contact. The chondrite-normalized rare earth element（REE） pattern of the altered and unaltered host rock was right-inclined from La to Lu, but enriched in light REEs over heavy REEs after hydrothermal alteration. An isocon plot shows that some oxides migrated in with an order of P2O5〉K2O 〉TiO2〉Al2O3〉SiO2〉MnO≥MgO, while others migrated out with an order of Na2O 〉CaO 〉Fe2O3. For REEs, the migration ratios are positive values withCs 〉Rb 〉Li 〉Nb 〉Ta 〉Be, signifying that all REEs migrated from the exsolved magmatic fluid into the altered host rocks. It was concluded that diffusion was the only mechanism for migration of ore-forming elements in the alteration zone. The effective diffusion coefficients（Deff）of LiF, RbF, and CsF were estimated under a fluid temperature of 500–550℃. Using a function of concentration（C（x,t）） and distance（x）, the order of migration distance was determined to be LiF 〉CsF 〉RbF, with diffusion times of （3.39 ± 0.35）× 10^6,（3.19 ± 0.28） × 10^5 and（6.33 ± 0.05） × 10^5 years, respectively.

Middle Devonian Picrites of the Southern Margin of Altay Orogenic Belt and Implications for the Tectonic Setting and Petrogenesis

The Altay orogenic belt of Xinjiang in NW China represents one of the important sites of juvenile crustal growth during the Phanerozoic. However, some important issues, e.g., tectonic evolution and petrogenesis, still remain controversial. The picrites in the south margin of the Altay orogenic belt were discovered in the lower part of marine volcanic-sedimentary sequences of the northwest-striking Middle Devonian Beitashan Formation (Fm.), which consists chiefly of intermediate-basic volcanic rocks intercalated minor carbonate, siltstone and siliceous rocks. The picrites are usually highly porphyritic, and contain abundant forsteritic olivine phenocrysts with minor clinopyroxene distributed in the groundmass, which consist of olivine, clinopyroxene and plagioclase with minor Fe-Ti oxides. The MgO contents of the picrites range from 14 wt% to 22 wt% with Mg# (atomic Mg/(Mg+Fe) ratio) of 0.75-0.80. They are characterized by slightly negative Ti anomalies, remarkably negative Nb and Ta anomalies and slightly positive P and Sm anomalies with the similar abundances of HFSE as MORB on the MORB-normalized trace element patterns, all of which characterize typical island arc magmas. In combing with the southwestward migration of the magmas of the Beitashan Fm., we propose that the magmas may result from the southwestward subduction of Junggar ocean plate. The Zr/Nb ratios (23-66) of both picrites and basalts resemble the MORB (10-66), suggesting that they were derived from the MORB-like sources. However, the basalts and picrites display some distinguishable element ratios and REE patterns, e.g., Ti/V (23-35) and Zr/Sm (18-23) ratios of basalts are higher than those of picrites (14-17 and 14-15 respectively), and the basalts display flat-type REE-chondrite patterns whereas the picrites are characterized by lower total REE concentrations ((26-34)×10^-6) and slight enrichment of light REE. These distinguished geochemical characteristics could be interpreted by different partial melting degrees and mantle sources, i.e., the basalts were generated by lower partial melting of amphibole-bearing spinel peridotite which was metasomatized by fluids released from subducted oceanic crust, and the picrites were resulted from the higher degree of partial melting of metasomatized garnet peridotite under high temperature. In contrast, the andesite with significant LREE and LILE enrichment may be resulted from the partial melting of eclogites.

Science Letters:Discovery of ultrahigh-T spinel-garnet granulite with pure CO_2 fluid inclusions from the Altay erogenic belt, NW China

We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the or-thopyroxenes have high XMg and A12O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around -56.7℃, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3-23.8℃ translating into CO2 densities of the order of 0.86-0.88 g/cm3. Based on preliminary mineral paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions.

New Zircon U-Pb Age of Granodiorite from the Shayikenbulake Be Deposit in Altay, Xinjiang and its Significance

Objective Intrusive rocks are widely distributed in Altay, Xinjiang, and appear in every structural belt. The rocks are mainly granite （Song Peng et al., 2017）, which formed from 523 Ma to 202 Ma and can be divided into five periods： 479-421 Ma, 410-370 Ma, 368-313 Ma, 300- 252 Ma and 247-202 Ma. However, intrusive rocks earlier than the Ordovician are rarely found. The small- scale low-grade metamorphic granite intruded in the Kanasi Group is the oldest intrusion reported up to now, which is the only one formed in the Early Cambrian （5234-19 Ma, Liu Yuan et al., 2013）. Few Cambrian intrusions limit the study of early magmatic-tectonic evolution in Altay. Medium-free-grained granodiorite is exposed widely in the Shayikenbulake deposit of Central Altay, and occurs as batholith. It formed in the Early Cambrian indicated by U-Pb dating, and is an ideal intrusion for studying Cambrian magmatic-tectonic events in Altay.

Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg+Fe2+), and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg+Fe2+), Al2O3 and depletion of U, Th and Rb contents. The AG has moderate ∑REE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750 °C?780 °C and 0.6?0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.

Discovery and Genetic Mechanism of Basic Granulite in the Altay Orogenic Belt, Xinjiang, NW China

Altay granulite (AG), which represents the product of high-grade metamorphism in the lower crust, was newly found in the Wuqiagou area, Fuyun County in the Altay orogenic belt, Northwest China. It is composed mainly of hypersthene, augite, basic plagioclase, amphibole and brown biotite. Its mineral compositions of amphibole and biotite are rich in Mg/(Mg+Fe2+) and Ti. Geochemically, the AG is enriched in Mg/(Mg+Fe2+) and A12O3, and poor in CaO, with depletion of U, Th, K and Rb contents. Furthermore, geochemical data reflect that the protolith of the AG is igneous-genetic calc-alkaline basalt formed under an island arc environment. The AG has ZREE of 92.38-96.58 ppm and enriched LREE model with weak positive Eu anomaly of 1.09-1.15. In the MORB normalized spider diagram, the AG shows tri-doming pattern with a strong negative Nb anomaly and medium negative P and Ti anomalies, reflecting that the AG has tectonic relation with subduction or subduction-related materials. The P-T conditions of peak metamorphism of the AG are 750-780℃ and >0.6-0.7 GPa. Retrograde metamorphism implies that the protolith of the Altay granulite might undergo a metamorphic process along a clockwise P-T trajectory. Therefore, the formation and evolution of the AG may have a genetic association with continental collision/orogeny and the AG was taken into the Late Paleozoic meta-strata by way of tectonic emplacement.

Compositions and Pressure-Temperature Conditions of Metamorphic Fluids Overprinting the Talate VMS Pb-Zn Deposit,Southern Altay,China

The Talate Pb-Zn deposit,located in the east of the NW-SE extending Devonian Kelan volcanic-sedimentary basin of the southern Altaides,occurs in the metamorphic rock series of the upper second lithological section of the lower Devonian lower Kangbutiebao Formation（D_1k_1~2）.The Pb-Zn orebodies are stratiform and overprinted by late sulfide—quartz veins.Two distinct mineralization periods were identified：a submarine volcanic sedimentary exhalation period and a metamorphic hydrothermal mineralization period.The metamorphic overprinting period can be further divided into two stages：an early stage characterized by bedding-parallel lentoid quartz veins developed in the chlorite schist and leptite of the ore-bearing horizon,and a late stage represented by pyritechalcopyrite-quartz veins crosscutting chlorite schist and leptite or the massive Pb-Zn ores.Fluid inclusions in the early metamorphic quartz veins are mainly CO_2-H_2O-NaCI and carbonic（CO_2±CH_4±N_2） inclusions with minor aqueous inclusions.The CO_2-H_2O-NaCl inclusions have homogenization temperatures of 294-368℃,T_（m,CO2） of-62.6 to-60.5℃,T_（h,CO2） of 7.7 to 29.6℃（homogenized into liquid）,and salinities of 5.5-7.4 wt%NaCl eqv.The carbonic inclusions have T_（m,CO2）of-60.1 to-58.5℃,and T_（h,Co2） of-4.2 to 20.6℃.Fluid inclusions in late sulfide quartz veins are also dominated by CO_2-H_2O-NaCl and CO_2±CH_4 inclusions.The CO_2-H_2O-NaCl inclusions have T_（b,tot） of142 to 360℃,T_（m,CO2）of-66.0 to-56.6℃,T_（h,CO2） of-6.0 to 29.4℃（homogenized into liquid） and salinities of 2.4-16.5 wt%NaCl eqv.The carbonic inclusions have T_（m,Co2）of-61.5 to-57.3℃,and T_（h,CO2） of-27.0to 28.7℃.The aqueous inclusions（L-V） have T_（m,ice） of-9.8 to-1.3℃ and T_（h,tot） of 205 to 412℃.The P-T trapping conditions of CO_2-rich fluid inclusions（100-370 MPa,250-368℃） are comparable with the late- to post-regional metamorphism conditions.The CO_2-rich fluids,possibly derived from regional metamorphism,were involved in the reworking and metal enrichment of the primary ores.Based on these results,the Talate Pb-Zn deposit is classified as a VMS deposit modified by metamorphic fluids.The massive Pb-Zn ores with banded and breccia structures were developed in the early period of submarine volcanic sedimentary exhalation associated with an extensional subduction-related back-arc basin,and the quartz veins bearing polymetallic sulfides were formed in the late period of metamorphic hydrothermal superimposition related to the Permian-Triassic continental collision.

Orogenic and Anorogenic Granitoids in the Altay Mountains of Xinjiang and Their Discrimination Criteria

On the basis of field geological studies of the granotoids in the region, mineralogical, petrological, geochemical(including stable isotope geochemical) and isotopic geochronological investigations were carried out on selected representative granitic bodies of various types. The authors have concluded that, apart from the bodies of the orogenic granitoid series, there also exist intrusions of the anorogenic granitoid series in the region. The intrusives of the two series were formed not only in different ages and tectonic environments, but also were derived from different sources of materials. Moreover, they are associated with different mineralizations, belonging to different minerologenetic series(Cheng et al., 1983). They show distinctly a series of discriminative criteria. The problems under discussion in the present paper are of important theoretical and practical significance in the studies of granites of the orogenic belt, particularly the studies of the genesis and related metallogeny of the granites of the region.

Extreme Flood Events over the Past 300 Years Inferred from Lake Sedimentary Grain Sizes in the Altay Mountains,Northwestern China

Understanding the temporal variations of extreme floods that occur in response to climate change is essential to anticipate the trends in flood magnitude and frequency in the context of global warming. However, long-term records of paleofloods in arid regions are scarce, thus preventing a thorough understanding of such events. In this study, a reconstruction of paleofloods over the past 300 years was conducted through an analysis of grain sizes from the sediments of Kanas Lake in the Altay Mountains of northwestern China. Results showed that grain parameters and frequency distributions can be used to infer possible abrupt environmental events within the lake sedimentary sequence, and two extreme flood events corresponding to ca. 1736–1765 AD and ca. 1890 AD were further identified based on canonical discriminant analysis(CDA) and coarse percentile versus median grain size(C-M) pattern analysis, both of which occurred during warmer and wetter climate conditions by referring to tree-ring records. These two flood events are also evidenced by lake sedimentary records in the Altay and Tianshan mountains. Furthermore, through a comparison with other records, the flood event from ca. 1736–1765 AD in the study region seems to have occurred in both the arid central Asia and the Alps in Europe, and thus may have been associated with changes in the North Atlantic Oscillation(NAO) index.

Responses to climate warming of hydrological processes in the upper Kelan River in the Altay Mountains, Xinjiang, China

Kelan River is a branch of the Ertix River, originating in the Altay Mountains in Xinjiang, northwestern China. The upper streams of the Kelan River are located on the southern slope of the Altay Mountains; they arise from small glacial lakes at an elevation of more than 2,500 m. The total water-collection area of the studied basin, from 988 to 3,480 m, is about 1,655 km2. Almost 95 percent of the basin area is covered with snow in winter. The westerly air masses deplete nearly all the moisture that comes in the form of snow during the winter months in the upper and middle reaches of the basin. That annual flow from the basin is about 382 mm, about 45 percent of which is contributed by snowmelt. The mean annual precipitation in the basin is about 620 mm, which is primarily concentrated in the upper and middle basin. The Kelan River system could be vulnerable to climate change because of substantial contribution from snowmelt runoff. The hydrological system could be altered significantly because of a warming of the climate. The impact of climate change on the hydrological cycle and events would pose an additional threat to the Altay region. The Kelan River, a typical snow-dominated watershed, has more area at higher elevations and accumulates snow during the winter. The peak flow occurs as a result of snow-melting during the late spring or early summer. Stream flow varies strongly throughout the year because of seasonal cycles of precipitation, snowpack, temperature, and groundwater. Changes in the temperature and precipitation affect the timing and volume of stream-flow. The stream-flow consists of contributions from meltwater of snow and ice and from runoff of rainfall. Therefore, it has low flow in winter, high flow during the spring and early summer as the snowpack melts, and less flows during the late summer. Because of the warming of the current climate change, hydrology processes of the Kelan River have undergone marked changes, as evidenced by the shift of the maximum flood peak discharge from May to June; the largest monthly runoffs also have an increment of about 15 percent related to before 1980; April-June runoff increased from the 60 percent of the annual runoff before 1980 to nearly 70 percent after 1990. The long-term trend shows temperature and precipitation increased mainly in the winter, but the rainfall declined in summer; hydrological process is manifested by the rising runoff in May and decreasing in June. Warming and the increase of winter and spring snowcover would lead to increased snowmelt, increasing the spring-flood hazards and the maximum flood discharge with disastrous consequences. The changed hydrological patterns caused by climate change have already impacted the urban water supply and agricultural and livestock production along the river.

Dating and Fluid Geochemistry of the Sarkobu Gold Deposit in Altay, Xinjiang, China

The dating of fluid inclusions of quartz yields an Ar-Ar isochrone age of 320.4±6 Ma. Three types of fluid inclusions have been identified with the homogenization temperature ranging from 157℃ to 362℃. The homogenization temperature consists of two groups. The first group varies from 157℃ to 166℃, and the second from 232℃ to 362℃. Their chemical composition is dominated by Na+-Ca2+-Mg2+ and Cl-. The relative concentration of ions is characteristic by Na+>Ca2+>K+>Mg2+ and C1->SO42-> F-. The δD and δ18O values indicate that the ore-forming fluid originates from mixing of multi-source water. The Sarkobu gold deposit has experienced two mineralization stages: gold was enriched during the volcanic-exhalative-sedimentary process in the early stage, while the gold deposit was finally formed under compression-shearing during the orogenic period.