Chinese Altai Mountains Research Articles

Evolution of the hydrothermal ore-forming system of Ashele VMS-type Cu-Zn deposit in Xinjiang, NW China: Insights from mineralogy and geochemistry of sulfides

The Ashele Cu-Zn deposit is one of the largest and most typical VMS-type Cu-Zn deposits in the Chinese Altai Mountains, Central Asian Orogenic Belt. The ore-forming processes of the Ashele deposit remains elusive, with particular uncertainties surrounding the physicochemical conditions underpinning their formation. In this study, major and trace element concentrations of the two types of sphalerite and sulfide sulfur isotopic compositions have been analyzed to constrain the mineralization conditions and ore genesis. Two stages of sphalerite have been identified, i.e., euhedral sphalerite of the early Cu mineralization stage (Sp1) and anhedral sphalerite of the late Zn mineralization stage (Sp2). Results show that Sp1 has relatively higher contents of In, Cu, Sn, and Hg, but lower levels of Cd, Ga, Ge, As, and Ag compared to that of Sp2. Utilizing the sphalerite GGIMFis geothermometer, mineralization temperatures for Sp1 and Sp2 were estimated at 225-296°C (average 258°C) and 166-264°C (average 210°C), respectively. Additionally, the Ashele sphalerite geochemistry suggests a relatively high sulfur fugacity during ore formation (lgfS2 = −8.99 to −6.55 for Sp1 and −13.58 to −6.83 for Sp2). The findings suggest an evolutionary trend of ore-forming fluids, characterized by a decrease in both temperature and sulfur fugacity from the early Cu mineralization stage to the later Zn mineralization stage. In situ δ34S values of sulfides (sphalerite, chalcopyrite, and pyrite) range from 0.84 ‰ to 6.07 ‰, indicating a sulfur origin from the thermochemical reduction of seawater sulfate and leaching of the underlying volcanic rocks, with a minor contribution from direct gas release from shallow magma chambers. Overall, this work unravels the physicochemical transformation between the two identified mineralization stages, thereby enhancing the understanding of the ore-forming process of the Ashele deposit.

Impact of Ancient Tectonics on Intracontinental Deformation Partitioning: Insights From Crustal Structures of the East Junggar‐Altai Area

AbstractCompressive stress generated at collision fronts can propagate over long distances, inducing deformation within the continent's interior. Nevertheless, the factors governing the partitioning of intracontinental deformation remain enigmatic. The Altai Mountains serve as a type‐example of ongoing intracontinental deformation. Here, we investigate the crustal architecture of the Chinese Altai Mountains, using receiver functions obtained from newly deployed dense seismic nodal arrays. The new seismic results reveal distinct crustal features, including (a) a negative polarity discontinuity beneath Chinese Altai Mountains, suggesting a low‐velocity layer; (b) a north‐dipping mid‐crustal structure beneath the suture zone between East Junggar and Chinese Altai, indicating underthrusting of East Junggar's lower crust beneath the Chinese Altai Mountains; (c) a double Moho structure beneath East Junggar, revealing a high‐velocity lower crustal layer. In conjunction with constraints from previous multi‐disciplinary regional studies, the double Moho structures are interpreted as mafic restite from Late Paleozoic magma underplating. The addition of mafic materials can significantly enhance the rheological strength of East Junggar's crust, causing it to function as an indenter that thrust beneath the Chinese Altai Mountains during the subsequent convergence process. As a consequence, significant deformation occurs in the Chinese Altai region, resulting in the emergence of decollements, as evident by the negative polarity discontinuity. The presence of pre‐existing decollements makes the Altai Mountains region more susceptible to deformation, thereby facilitating the concentration of intracontinental deformation. These findings illuminate the evolution history of the Chinese Altai Mountains and highlight the great impacts of ancient tectonics on intracontinental deformation partitioning.

The Variability of Snow Cover and Its Contribution to Water Resources in the Chinese Altai Mountains from 2000 to 2022

As one of the major water supply systems for inland rivers, especially in arid and semi-arid regions, snow cover strongly affects hydrological cycles. In this study, remote sensing datasets combined with in-situ observation data from a route survey of snow cover were used to investigate the changes in snow cover parameters on the Chinese Altai Mountains from 2000 to 2022, and the responses of snow cover to climate and hydrology were also discussed. The annual snow cover frequency (SCF), snow cover area, snow depth (SD), and snow density were 45.03%, 2.27 × 104 km2, 23.4 cm, and ~0.21 g·cm−3, respectively. The snow water equivalent ranged from 0.58 km3 to 1.49 km3, with an average of 1.12 km3. Higher and lower SCF were mainly distributed at high elevations and on both sides of the Irtysh river. The maximum and minimum snow cover parameters occurred in the Burqin River Basin and the Lhaster River Basin. In years with high SCF, abnormal westerly airflow was favorable for water vapor transport to the Chinese Altai Mountains, resulting in strong snowfall, and vice versa in years with low SCF. There were significant seasonal differences in the impact of temperature and precipitation on regional SCF changes. The snowmelt runoff ratios were 11.2%, 25.30%, 8.04%, 30.22%, and 11.56% in the Irtysh, Kayit, Haba, Kelan, and Burqin River Basins. Snow meltwater has made a significant contribution to the hydrology of the Chinese Altai Mountains.

Cryosphere changes and their impacts on regional water resources in the Chinese Altai Mountains from 2000 to 2021

The cryosphere has an important impact on regional water resources and ecosystems in the Chinese Altai Mountains and its piedmont zone. Using the latest remote-sensing datasets of cryosphere changes and combining with in-situ observation data from glacier monitoring stations and snow cover surveys, the main cryosphere elements including glaciers, snow cover, and permafrost are investigated with emphasis on their changes since 2000 and the current situation. Their water resource effects are also discussed. The results indicate that although the glaciers in the region have experienced continuous and intensive melting, mass loss has slowed because both glacier area shrinkage and thickness reduction were larger during 2000–2010 than during 2010–2021. Snow-cover water equivalent (w.e.) has increased due to obvious increases in snow depth, although snow-cover area has decreased slightly. Permafrost has been degrading. Overall, cryosphere contributions to the regional water resource are approximately 40.9% since 2000, among which snow-cover melting is the largest, contributing 37.1% to water resources in the Irtysh River Basin and significantly more in the mountainous sub-basins with increased snowfall. Glacier melting contributes 2.9%∼3.4%, lower than earlier estimations of 3.4%∼3.6% for the late 20th century. Permafrost thaw caused by active layer thickening contributes approximately 0.59%. Meteorological data shows a warming and wetting trend, but summer temperature has a much lower increase rate and a slowing increase trend after 2013. Moreover, snowfall frequency has increased. In the future, glacier water resource contribution will continue to decrease, but the water resource effects of snow-cover melting and permafrost degradation would increase.

Hydrothermal alteration, not metamictization, is the main trigger for modifying zircon in highly evolved granites

The question of whether the high U and Th concentrations in zircon are primary or secondary is often difficult to resolve, and a clear understanding of the modification processes of secondary U- and Th-rich zircon is lacking. Zircon crystals from two well-studied, highly evolved granites, the Jiangjunshan muscovite granite in the Chinese Altai Mountains and the Cuonadong leucogranite in the Eastern Tethyan Himalaya, have been investigated and classified into two types. Type I exhibits typical igneous growth zoning, and type II has “diffuse” or “spongy” internal structures. These textures, along with compositional data, indicate that the type II zircon crystals formed through hydrothermal modification of magmatic zircon (type I) by infiltrating hydrothermal fluids. During hydrothermal modification, the U and Th concentrations increase from type I to type II in the Jiangjunshan muscovite granite but decrease from type I to type II in the Cuonadong leucogranite. The Raman spectra of type II zircon crystals from Jiangjunshan muscovite granite have broader peaks (i.e., measured as the full width at half maximum, FWHM) with decreased intensities than their type I counterparts, which indicates that the former are affected by significant accumulated radiation damage. However, the preserved radiation damage in both the type I and II zircon measured by Raman spectroscopy is less than that expected from the total dose of alpha particles calculated from the U and Th contents, which indicates variable degrees of annealing. We propose that late magmatic-hydrothermal alteration was responsible for the modification of magmatic zircon grains in highly evolved granites and resulted in the enrichment or redistribution of U and Th. The calculated radiation dose of the Cuonadong leucogranite zircon is far below that required for metamictization, which indicates that metamictization is not always responsible for diffuse and spongy textures.

Response of model-based cambium phenology and climatic factors to tree growth in the Altai Mountains, Central Asia

• The principal growth limiting factor shifts from temperature to soil moisture from RU to FY. • Cambial dynamic was bimodal pattern in AL, right-skewed unimodal in FY and unimodal in RU. • The length of growing seasons had a significant positive trends in two sites from Northwest China – Chinese Altai Mountains for the last six decades. • The intra-seasonal growth rate regulated tree growth rather than length of growing season. It is important to study the relationships between tree growth and phenology and climate factors in Central Asia for the sustainable development of forest ecology and the exploration of carbon sink potential in the region in a context of global change. Herein, the process-based Vaganov-Shashkin model was used to simulate tree-ring growth rates, to assess a cambial phenology (start and end of growing season) of larch trees ( Larix sibirica ) based on three sites located on three different latitudes in the Altai-Sayan Mountains in Central Asia over 1960–2018. It was shown that the principal factor limiting growth rates was temperature in RU (located in southern central Siberia), cambial dynamic was unimodal. In RU site, although the length of growing season did not change significantly over the past 59 years, it was correlated with tree radial growth. Moisture was the principal factor limiting the growth rates of AL and FY (located in Chinese Altai Mountains), and cambium dynamics were bimodal and unimodal, respectively. Temperature and precipitation before the start of the growing season lengthen the growing season, but this did not promote the tree radial growth. In conclusion, we determined that the climate-influenced intra-seasonal growth rate regulated tree growth rather than length of growing season in this area. In this study, the VS-simulation showed high potential develop a long-term reconstruction of cambial phenology in the Altai Mountains, which was conducive to a more comprehensive understanding of the exogenous-endogenous factors effects on tree-ring growth.

A 50 m.y. melting model for the rare metal−rich Koktokay pegmatite in the Chinese Altai: Implications from a newly identified Jurassic granite

The petrogenesis of the world famous Koktokay No. 3 pegmatite in the Chinese Altai Mountains is still enigmatic due to its superenrichment of rare metals and the apparent absence of a parental granite. We present results from a granite apophysis that was recently discovered in the No. 3 pegmatite open pit. Results show that it has low K/Rb (32.35−38.76), Zr/Hf (13.78−23.30), Nb/Ta (1.00−6.02), and extremely low K2O/Na2O (0.12−0.20) ratios, which, together with its mica composition and the occurrences of garnet, indicate that it is a highly evolved muscovite albite granite. Columbite and apatite from the granite apophysis yielded U-Pb ages of 182.3 ± 1.0 Ma and 184.9 ± 4.3 Ma, respectively, which are younger than the Triassic ages (ca. 210 Ma) of the main magmatic stage but fall into the age range of the No. 3 pegmatite series (220−175 Ma). Both the granite and the apatite grains within it share nearly identical rare earth element patterns with the magmatic stage of the No. 3 pegmatite. The whole-rock εHf(t) values (t = 183 Ma) range from −0.11 to +1.32, consistent with those of the No. 3 pegmatite and indicating a similar source. We propose that the Jurassic granite represents a late pulse of magma injected as apophyses from a deep-seated magma chamber (perhaps from the lower crust), which overlapped with the early pegmatite and promoted the rare metal mineralization. The No. 3 pegmatite and the Jurassic granite may represent a continuous magmatic system with a 50 m.y. melting process, generating this unusual giant pegmatite intrusion with abundant rare metals.

Seasonal Variations in Voluntary Intake and ApparentDigestibility of Forages by Goats in the Chinese Altai Mountains.

Simple SummaryGrazing animals have a major impact on rangelands through the consumption and trampling of vegetation along with excreta deposition. In turn, forage availability and quality, shaped by environmental and grazing impacts, affect animal performance and health. This study investigated the interaction between amount and nutritional quality of vegetation on offer and animal feed intake on alpine pastures in the Chinese Altai Mountains. To this end, daily grazing routes, vegetation on offer along the pathways, and forage consumption of goats were monitored during spring and the early and late summer season of two consecutive years. Grazing routes were longer in spring than in summer, leading to larger pasture areas utilised in spring. Despite marked differences in vegetation on offer between the two study years, quantitative feed intake did not exhibit seasonal or annual differences, indicating that the goats’ nutrient intake was not restricted on the mountain ranges.Forage availability and quality directly impact animal performance, ultimately affecting productivity and health. This study aimed to understand the interaction between qualitative and quantitative vegetation availability and feed intake of goats on alpine pastures in the Chinese Altai Mountains. The daily grazing routes of three goats from a local herding family were monitored with GPS devices set at a logging rate of 64 s during spring and the early and late summer season in 2013 and 2014. The quantity and quality of vegetation along their grazing routes was determined, and the amount of feces excreted was measured in a total of five goats per season for the indirect determination of the animals’ feed intake. The grazing routes were longer in spring than in summer, leading to larger grazing areas visited in spring. Vegetation on offer ranged from 980 to 2400 kg dry mass per hectare and was similar in the spring and summer seasons but higher in 2013 than in 2014. Feed consumption of forage and nutrients did not significantly differ between seasons and years, respectively, suggesting that the goats’ nutrient intake was not restricted by interannual variability of forage on offer. Regular monitoring of animal numbers and of vegetation quantity and quality on the mountain rangelands can help responsible government agencies to estimate forage offtake of small ruminants in order to timely adjust grazing pressure in the study region.

Early Carboniferous brachiopod fauna from the Altai Mountains, northern Xinjiang, Central Asia: Systematics, and palaeobiogeographic and palaeogeographical implications

A diverse brachiopod fauna, comprising 37 species in 35 genera, is described from the Hongshanzui Formation of the Chinese Altai Mountains area, northern Xinjiang, north‐western China. A new speciesXinjiangiproductus?junggarensissp. nov. is erected. Faunal correlation constrains the Altai brachiopod fauna and its bearing formation as Tournaisian (Early Carboniferous) in age. The Altai brachiopod fauna is dominated by the Siberian elements that are also very common in the Kuznetsk Basin, Siberia, implying the same palaeobiogeographic province. In contrast, it shares much fewer species with the coeval assemblages reported from the Junggar terranes, suggesting a different palaeobiogeographic province from the latter. Moreover, the Altai fauna appears with high similarities to the coeval faunas reported from the Baoshan Block of western Yunnan, south‐western China, and, to a lesser context, resembles coeval faunas documented from north‐eastern Japan, North American mid‐continent, and Australia. In contrast, it shares very few elements with those reported from the Qaidam Basin, Tarim Basin, and South China. The rather high faunal affinity between the Altai area and Kuznetsk Basin indicates that these two regions were likely apart closely to one another during the Tournaisian, implying that the Altai area may have accreted to the Siberian Craton prior to the Tournaisian. The low faunal affinity between the western Junggar and Altai areas reveals that they both did not belong to the same palaeobiogeographic province, and the western Junggar terrane did not accrete to the Altaids, at least in the Tournaisian.

Soil microbial properties of subalpine steppe soils at different grazing intensities in the Chinese Altai Mountains

Long-term provision of ecosystem services by grasslands is threatened by increasing stocking densities. The functions of grassland ecosystems depend on a mutual relationship between aboveground and belowground biota. While the effects of increasing stocking density on plant biomass are well studied, little is known about its impact on soil microbial properties. To fill this knowledge gap a grazing experiment was conducted on a summer pasture in the Chinese Altai Mountains during the summers of 2014 and 2015 using a randomized block design with stocking densities of 0, 8, 16, and 24 sheep ha−1 replicated four times. After two summer grazing periods (each 56 days), topsoil samples (1–7 cm) were taken in September 2015 and analyzed for major physical, chemical, and microbial soil properties. Except for the metabolic quotient (qCO2; p < 0.05), the examined soil properties remained unaffected by the increasing stocking densities, likely due to high spatial variability. The qCO2 declined from 13.5 mg CO2–C g−1 microbial biomass C d−1 at zero grazing to 12.2 mg CO2–C g−1 microbial biomass C d−1 at a stocking density of 24 sheep ha−1. Low values of qCO2 indicate an aged and dormant microbial community that diverts less soil organic carbon (SOC) to catabolic processes within their cells, characteristic for C limiting conditions. The aboveground biomass affected by grazing intensity correlated positively with SOC (rs = 0.60, p = 0.015) and ergosterol (rs = 0.76, p = 0.001) pointing indirectly to the effect of stocking density. Additionally to the relatively high values of qCO2, highest values of SOC (39.2 mg g−1 soil), ergosterol (6.01 µg g−1 soil), and basal respiration (10.7 µg g−1 soil d−1) were observed at a stocking density of 8 sheep ha−1 indicating that a low grazing intensity is recommendable to avoid soil degradation.

A mid-Cretaceous change from fast to slow exhumation of the western Chinese Altai mountains: A climate driven exhumation signal?

The Chinese Altai Mountains in western China are bound by Cenozoic transpressional strike-slip faults, many of which show Quaternary activity. To better understand how Mesozoic–Cenozoic deformation has affected the history of exhumation and uplift of the Chinese Altai Mountains, we collected Paleozoic granitoid samples for apatite fission track and apatite U-Th-Sm/He thermochronology. Central apatite fission track ages for N = 6 samples range from 68 to 104 Ma, whereas apatite U-Th-Sm/He ages range from 56 to 272 Ma for N = 23 samples (n = 80 individual analyses) across four transects in the western Chinese Altai. Our results indicate fast cooling during the late Early Cretaceous followed by slow cooling since. Thermal modeling results suggests < 2 km exhumation has occurred over most of the Chinese Altai since the Paleocene. If significant late Cenozoic surface uplift occurred in the Altai Mountains, as has been proposed, it must have been associated with minimal erosional exhumation. We suggest that the relief of the Chinese Altai largely developed during the late Mesozoic and denudation since has been minimal because of semi-arid climate conditions.

Dissolved organic carbon in snow cover of the Chinese Altai Mountains, Central Asia: Concentrations, sources and light-absorption properties

Dissolved organic carbon (DOC) in snow plays an important role in river ecosystems that are fed by snowmelt water. However, limited knowledge is available on the DOC content in snow of the Chinese Altai Mountains in Central Asia. In this study, DOC in the snow cover of the Kayiertesi river basin, southern slope of Altai Mountains, was investigated during November 2016 to April 2017. The results showed that average concentrations of DOC in the surface snow cover (1.01 ± 0.52 mg L−1) were only a little higher than those in glaciers of the Tibetan Plateau, European Alps, and Alaska, but much higher than in Greenland Ice Sheet. Depth variations of DOC concentrations from snowpack profiles indicated higher values in the surface layer. During the observation period, scavenging efficiency for DOC in snow cover is estimated to be 0.15 ± 0.10, suggesting that DOC in snow can be affected more by the meltwater during ablation season than during accumulation season. The average mass absorption cross section at 365 nm and the absorption Ångström exponent of DOC were 0.45 ± 0.35 m2 g−1 and 2.59 ± 1.03, respectively, with higher values in March and April 2017. Fraction of radiative forcing caused by DOC relative to black carbon accounted for about 10.5%, implying DOC is a non-ignorable light-absorber of solar radiation in snow of the Altai regions. Backward trajectories analysis and aerosol vertical distribution images from satellites showed that DOC in the snow of the Altai Mountains was mainly influenced by air masses from Central Asia, Western Siberia, the Middle East, and some even from Europe. Biomass burning and organic carbon mixed with mineral dust contributed significantly to the DOC concentration. This study highlights the effects of DOC in the snow cover for radiative forcing and the need to study carbon cycling for evaluation of quality of the downstreams ecosystems.

Response of snow hydrological processes to a changing climate during 1961 to 2016 in the headwater of Irtysh River Basin, Chinese Altai Mountains

With changing climatic conditions and snow cover regime, regional hydrological cycle for a snowy basin will change and further available surface water resources will be redistributed. Assessing snow meltwater effect on runoff is the key to water safety, under climate warming and fast social-economic developing status. In this study, stable isotopic technology was utilized to analyze the snow meltwater effect on regional hydrological processes, and to declare the response of snow hydrology to climate change and snow cover regime, together with longterm meteorological and hydrological observations, in the headwater of Irtysh River, Chinese Altai Mountains during 1961-2015. The average δ18O values of rainfall, snowfall, meltwater, groundwater and river water for 2014–2015 hydrological year were -10.9‰, -22.3‰, -21.7‰, -15.7‰ and -16.0‰, respectively. The results from stable isotopes, snow melting observation and remote sensing indicated that the meltwater effect on hydrological processes in Kayiertesi River Basin mainly occurred during snowmelt supplying period from April to June. The contribution of meltwater to runoff reached 58.1% during this period, but rainfall, meltwater and groundwater supplied 49.1%, 36.9% and 14.0% of water resource to annual runoff, respectively. With rising air temperature and increasing snowfall in cold season, the snow water equivalent (SWE) had an increasing trend but the snow cover duration declined by about one month including 13-day delay of the first day and 17-day advancement of the end day during 1961–2016. Increase in SWE provided more available water resource. However, variations in snow cover timing had resulted in redistribution of surface water resource, represented by an increase of discharge percentage in April and May, and a decline in June and July. This trend of snow hydrology will render a deficit of water resource in June and July when the water resource demand is high for agricultural irrigation and industrial manufacture.

Impacts of future climate and land cover changes on threatened mammals in the semi-arid Chinese Altai Mountains

Dryland biodiversity plays important roles in the fight against desertification and poverty, but is highly vulnerable to the impacts of environmental change. However, little research has been conducted on dual pressure from climate and land cover changes on biodiversity in arid and semi-arid environments. Concequntly, it is crutial to understand the potential impacts of future climate and land cover changes on dryland biodiversity. Here, using the Chinese Altai Mountains as a case study area, we predicted the future spatial distributions and local assemblages of nine threatened mammal species under projected climate and land cover change scenarios for the period 2010–2050. The results show that remarkable declines in mammal species richness as well as high rates of species turnover are seen to occur across large areas in the Chinese Altai Mountains, highlighting an urgent need for developing protection strategies for areas outside of current nature reserve network. The selected mammals are predicted to lose more than 50% of their current ranges on average, which is much higher than species' range gains (around 15%) under future climate and land cover changes. Most of the species are predicted to contract their ranges while moving eastwards and to higher altitudes, raising the need for establishing cross-border migration pathways for species. Furthermore, the inclusion of land cover changes had notable effects on projected range shifts of individual species under climate changes, demonstrating that land cover changes should be incorporated into the assessment of future climate impacts to facilitate biodiversity conservation in arid and semi-arid environments.

Investigations on physical properties and ablation processes of snow cover during the spring snowmelt period in the headwater region of the Irtysh River, Chinese Altai Mountains

To explore the effects of the underlying surface on snow properties and the “forest effects” on snow accumulation and ablation processes in the headwater area of the Irtysh River in the Chinese Altai Mountains, the physical properties of snow and certain snowmelt processes were investigated during the snowmelt period in 2014. Our observations showed that the diurnal and daily variations of air and snow temperatures, the liquid water contents (LWCs), and the densities of surface snow layers at 0–5 cm depths were in agreement, but differences in snow properties were obvious at the bottom snow layers. The LWCs were divided into three categories according to snow temperature (T s): LWC = 0, T s < −3 °C; LWC <1 %, −3 ≤ T s < −1 °C; LWC <7 %, T s ≥ −1 °C. The snow densities were greatest in the top layers above all underlying surfaces (grassland, concrete, and river ice) during the snowmelt period. The snowmelt experiment indicated that the mean air temperature was the highest on the grassland and lowest in the glade, but the diurnal temperature range was the lowest in the continuous forest and highest on the grassland. The canopy snow interception rate of Abies sibirica reached up to 70 % and the mean value of the continuous forest cover was about 30 %. The snowmelt duration periods were 20 days on the grassland, 35 days in the continuous forest, and 43 days in the forest glade, and the corresponding average snow melt rates (SMRs) were 2.1, 1.2, and 1.4 mm d−1. For one single A. sibirica tree, the SMR in the sub-canopy was only half that on the edge and outside of the forest canopy.

Five decades of changes in the glaciers on the Friendship Peak in the Altai Mountains, China: Changes in area and ice surface elevation

Mountain glaciers are indicators of climate change and of current water resources. They are important ecological systems and can be used to support sustainable development of industry and agriculture. However, due to climate warming, most glaciers are in a state of rapid retreat. Using topographic maps in 1959, ASTER remote sensing data in 2008 and ASTER digital elevation models (DEMs), area, ice surface elevation, and volume changes of glaciers on the Friendship Peak in the Chinese Altai Mountains were analyzed. Results showed that the collective area of all 201 glaciers investigated was reduced by 30.4% from 1959 to 2008. Fifty-five glaciers disappeared entirely. The average rates of reduction in area of glaciers with sizes <0.5, 0.5–1, 1–4, 4–10, and >10km2 were 25.9%, 30.8%, 30.9%, 35.9%, and 27.4%, respectively. From 1959 to 2008, the elevation of the glacier surface decreased by 20m at an average rate of 0.4ma−1. For the Kanas Glacier, the changes in ice surface elevation ranged from −101 to +38m. Results showed that glaciers at lower altitudes and smaller sizes experienced more extensive changes in elevation. The intensive glacier ablation over the Friendship Peak in the Altai Mountains was found to be caused by increases in the regional temperature, which occurred at an average rate of 0.52°C per decade.

Mass loss from glaciers in the Chinese Altai Mountains between 1959 and 2008 revealed based on historical maps, SRTM, and ASTER images

Mass loss of glaciers in the Chinese Altai was detected using geodetic methods based on topographical maps (1959), the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) (2000), and the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) stereo images (2008). The results indicate that a continued and accelerating shrinkage has occurred in the Chinese Altai Mountains during the last 50 years, with mass deficits of 0.43 ± 0.02 and 0.54 ± 0.13 m a−1 water equivalent (w.e.) during the periods 1959–1999 and 1999–2008, respectively. Overall, the Chinese Altai Mountains have lost 7.06 ± 0.44 km3 in ice volume (equivalent to −0.43 ± 0.03 m a−1 w.e.) from 1959–2008. The spatial heterogeneity in mass loss was potentially affected by comprehensive changes in temperature and precipitation, and had a substantial correlation with glacier size and topographic settings. Comparison shows that in the Chinese Altai Mountains glaciers have experienced a more rapid mass loss than those in the Tianshan and northwestern Tibetan Plateau (TP), and the mass balance of glaciers was slightly less negative relative to those in the Russian Altai, Himalaya, and southern TP.

Rare and endangered plant species of the Chinese Altai Mountains

Altai (also named Altay in China) Mountain Country (Mountain System) is a unique natural region, located on the border between different floristic regimes of the Boreal and ancient Mediterranean sub-kingdoms, where distribution of plant species is actually limited. It is known to have sufficient endemic floral biodiversity in the Northern Asia. Many plants of Altai Mountain System need effective care and proper conservation measures for their survival and longer-term protection. Important Plant Area identified as the IUCN (the International Union for Conservation of Nature), specified criteria attract global attention for protection of floral biodiversity across the world. The records of 71 plant species from the Chinese Altai Mountains attributed to the criterion A and the dark conifer forests of Chinese Altai Mountains satisfied the criterion C, which may help qualify to fulfill the national obligation of the Convention on Biological Diversity.

Zircon U–Pb and Hf isotopic study of gneissic rocks from the Chinese Altai: Progressive accretionary history in the early to middle Palaeozoic

Gneissic rocks in the Chinese Altai Mountains have been interpreted as either Paleozoic metasedimentary rocks or Precambrian basement. This study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a NE–SW traverse in the northwestern Chinese Altai. Petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from I-type granites formed in a subduction environment. Three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources. Zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 Ma, some give Neoproterozoic ages, and a few yield discordant Paleoproterozoic to Archean ages. Zircon Hf isotopic compositions indicate that both juvenile/mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived. In contrast, zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids, and define single populations for each sample with mean ages between 380 and 453 Ma. The general absence of Precambrian inheritance and positive zircon ɛHf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas. Our data can be interpreted in terms of a progressive accretionary history in early to middle Palaeozoic times, and the Chinese Altai may possibly represent a magmatic arc built on a continental margin dominated by Neoproterozoic rocks.

Timing, Petrogenesis, and Setting of Paleozoic Synorogenic Intrusions from the Altai Mountains, Northwest China: Implications for the Tectonic Evolution of an Accretionary Orogen

The Altai Mountains are a key area for understanding the development of the Altai Tectonic Collage and accretionary orogen. However, the orogenic processes, particularly their early stage, have not been well understood. In this work, we undertake zircon U‐Pb dating of six Paleozoic synorogenic plutons in order to better define the early magmatic and tectonic evolution of the Chinese Altai Mountains. The results revealed three Paleozoic granitic plutonic events at ca. 460, 408, and 375 Ma. These ages, along with the structural patterns of the plutons, suggest two periods of regional deformation, 460–410 Ma and 410–370 Ma. The granitoids mainly follow the tholeiitic and calc‐alkaline trends and are mostly I type. Sr‐Nd isotopic analyses indicate that the sources of the granitoids contain both old continental and younger (juvenile) mantle‐derived components. Chemical, isotopic, and structural features suggest that the plutons were formed mainly in continental arc settings and that the subduction and accretion processes began at ca. 460 Ma and culminated at ca. 408 Ma. Thus, the Altai orogen was mainly built up during early‐middle Paleozoic time, rather than during late Paleozoic time. Furthermore, the southern Altai terrane comprises not only Silurian to Devonian island arcs but also old continental fragments. With these new constraints, we present a new model to account for the tectonic evolution of the Altai orogen. This model proposes that early‐middle Paleozoic Altai orogenic processes could have experienced formation of an active continental margin, the splitting of this margin to form a back‐arc oceanic basin, and the final closing of the back‐arc basin. Consequently, the opening and closure of back‐arc basins along active margins is probably a common process in the central Asian accretionary orogen.