Southern Altay Research Articles

Carbon sequestration in a typical mountain lake associated with earthquakes, floods, droughts, and human activities in southern Altay during the late Holocene

Lakes, being key regulators of atmospheric carbon dioxide (CO2), have not yet been intensively explored in the carbon cycle. This study provides an attempt to investigate how carbon sequestration in mountain lakes responds to seismic activities, extreme climate events and human disturbance. The new data of grain-size end members (EMs), TN contents, C/N, concentrations of algal spores, and P and Mn contents, in addition to previously published data of TOC and Ca contents, Zr/Rb, Rb/Sr, and land-pollen assemblages of a well-dated sediment core from Yileimu Lake, depicted a more detailed history of environmental evolution in the region. A great earthquake happened in southern Altay at ∼ 3500 cal yr BP that triggered extensive landslides around the lake, and then frequent floods eroded the catchment between ∼ 3500 and 2300 cal yr BP, subsequently severe drought events occurred within the period of 2300–1000 cal yr BP, finally agricultural and pastoral activities intensified within the last 1000 yrs. Organic carbon accumulation rate (OCAR) in Yileimu Lake was extremely high (an underestimated value of ∼ 370 g m–2 yr–1) during the earthquake event, in response to the rapid accumulation of landslide materials. Regional comparison revealed that summer temperature was unexpected to have determined the OCAR during both flood and drought events (average 4.07 and 3.64 g m–2 yr–1, respectively), because it dominated the production of land- and aquatic plants. Human activities increased the OCAR prominently (averages 6.26 g m–2 yr–1) via changing sediment production and vegetation planting, which decoupled the OCAR from climate factors. These data imply that carbon sequestration in lakes from mountain areas where temperature adversity stress dominated vegetation growth would have the potential to increase under anthropogenic warming. In addition, seismically induced carbon sequestration in lakes from tectonically active regions cannot be ignored.

Precipitation Variations in China’s Altay Mountains Detected from Tree Rings Dating Back to AD 1615

As the primary mountain range in Central Asia, the Altay Mountains receive water vapor carried by westerly circulation, resulting in relatively abundant local precipitation and lush pastures in all seasons. Consequently, it has become one of the important transportation routes between Asia and Europe. The exploration of long-term variations in precipitation is meaningful for understanding the ebb and flow of the Asia–Europe steppe trade routes. However, previous dendroclimatological studies of the Altay Mountains focused more on temperature changes than precipitations variations. We carried out a 404-year precipitation reconstruction based on the tree rings of Siberian larch growing on the south slopes of the Altay Mountains, which could explain 45.9% of the variance observed in the February–October precipitation. Our reconstruction demonstrated some severe drought events which could be found in the historical documents, such as the drought in the late Ming Dynasty (1640s) and the Ding-Wu Disaster (1870s). The spatial correlation analysis, cross-wavelet spectrum and wavelet coherency analysis indicated that the precipitation variations in the study area may be related to the ENSO and NAO. This study presents a robust precipitation reconstruction of the southern Altay Mountains, serving as a reference for future research on large-scale climatic forces acting on Altay precipitation.

Millennial‐ to centennial‐scale anti‐phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

AbstractIt is strongly debated whether the Westerlies and the East Asian summer monsoon (EASM) are in‐phase, anti‐phase or out‐of‐phase, and how hydroclimatic changes in the above two climate systems affected trans‐Eurasian cultural exchanges during the late Holocene. In this study, we establish a 3500‐a‐long paleoclimatic sequence based on high‐resolution analyses of sedimentological and geochemical data of a well‐dated sediment core from Yileimu Lake in southern Altay. High percentages of the >63‐µm fraction and high values of Zr/Rb and Rb/Sr ratios indicate strong transport of weakly weathered, coarse sediments into the depocenter of the lake caused by enhanced surface runoff and catchment erosion associated with a wet climate, and vice versa. High values of Ca and total inorganic carbon (TIC) contents imply increased precipitation of endogenic carbonates in the lake water under intense evaporation associated with a dry climate, and vice versa. This new record indicates two wet intervals at 3500–2300 and 600–100 cal a bp, interrupted by a severe and prolonged dry interval from 2300 to 1000 cal a bp, and a mild dry interval with occasionally wet conditions from 1000 to 600 cal a bp. These results are broadly consistent with other paleoclimatic records in Westerlies‐dominated Asia and are generally anti‐phase with those in the EASM region. We suggest that a strengthening/weakening and southward/northward migration of the Westerlies during a negative/positive phase of the North Atlantic Oscillation (NAO) transported more/less water vapor into arid Asia. Meanwhile, a decreasing/increasing El Niño‐Southern Oscillation (ENSO) superimposed on a southward/northward shift of the Intertropical Convergence Zone (ITCZ) triggered a weakening/strengthening and southward/northward movement of the West‐Pacific subtropical high (WPSH), resulting in decreasing/increasing EASM intensity. In addition, the wet climate from 3500 to 2300 cal a bp may have contributed to the development of nomadic herding in the eastern Eurasian Steppe and Altay region, and to the opening of the proto‐Silk Roads. Potentially, intense seismic activities in the Altay Mountains ~3500 cal a bp may have also promoted the opening of the proto‐Silk Roads by forcing the herdsmen to move to the inter‐mountainous basins. The strong EASM intensity from 2300 to 1000 cal a bp in eastern China may have contributed to the creation of the ancient Silk Roads by the Han Dynasty.

Ore‐forming mafic plutons emplaced at syn‐collisional compressive setting in Kalatongke Ni–Cu sulphide district, Southern Altay, CAOB: New evidence from the Late Carboniferous granitic porphyries

The Kalatongke deposit is the largest Ni–Cu sulphide deposit in the Central Asian Orogenic Belt (CAOB) in northern Xinjiang. The tectonic setting of the Kalatongke deposit and the collision period of the Altai and East Junggar terranes remain controversial. This study involves petrological, geochemical, and geochronological evaluations of granitic porphyries in the Kalatongke. The granitic porphyries are divided into three types according to the characteristics of petrology and geochemistry, dated at ~339, ~325, and ~310 Ma. Type‐1 granitic porphyry exhibits evident syn‐collisional characteristics, with plagioclase phenocrysts extending in one direction. This type is metaluminous (A/CNK <1.1), characterized by low SiO2 and K2O contents, and depleted in Nb, Ta, P, and Ti. Type‐2 granitic porphyry is strongly peraluminous (A/CNK >1.1) and characterized by high SiO2 and Al2O3 but low Sr contents. Type‐3 granitic porphyry is also metaluminous (A/CNK <1.1) and has high SiO2 and K2O contents. The estimated crustal thickness of the Kalatongke area increased from 40 to 55 km from 339 to 310 Ma, thereby indicating that its existence within the collisional orogeny period. According to the estimated emplacement depth of the granitic and mafic intrusions, the crust had been thickening since then. During the late collision period, lithospheric detachment caused by terrane collision resulted in asthenospheric mantle upwelling and formed regional mafic intrusions along the Irtysh fault.

A 450-year warming and wetting climate in southern Altay inferred from a Yileimu Lake sediment core

Numerous paleoclimatic records from lake sediment cores in arid central Asia (ACA) suggest a more humid climate in the Little Ice Age (LIA) cold period than that of the contemporary warm period (the last century). Our high-resolution study of a sediment core from Yileimu Lake presents end members (EMs) of grain-size distributions (~5-year resolution), and major and trace elements (~10-year resolution), including the Chemical Index of Alteration (CIA) and Rb/Sr ratio. In contrast to records from these other lakes in ACA, our study indicates a warming and wetting trend in the southern Altay regional climate over the last five centuries. We suggest that continuously increasing snow/ice meltwater from the surrounding high mountains related to an increasing trend in atmospheric temperature, and increasing winter snowfall triggered by a decreasing trend in winter North Atlantic Oscillation (NAO) index, have dominated the regional climate in the southern Altay Mountains during 1620–1835 AD. We also suggest that temperature dependent evaporative losses greatly exceeding the water input to the lake, and reduced summer precipitation, caused the drought events during 1586–1620 and 1835–1870 AD. Heavy summer precipitation associated with significant increases in the local moisture supply induced by intense evaporation of snow/ice meltwater in the alpine and gorge terrain of the Altay Mountains played a critical role in the summer floods around the 1900s AD.

Geochronology and trace elements of zircon in the Southern Chinese Altay: Implications for tectonic setting

Zircon (ZrSiO4) trace elements are commonly used to distinguish the tectonic settings of their host rocks. The Chinese Altay is a key area for deciphering the accretionary history of the Central Asian Orogenic Belt (CAOB), and its tectonic setting during the Devonian is debated. In this study, we describe the systematic investigations of the magmatic and metamorphic rocks from the Qiemuerqieke and Qinghe areas situated to the west and east of Southern Altay, respectively. In doing so, we present the first attempt to elucidate the Devonian tectonic setting of the Southern Altay based on zircon trace elements. Zircon U–Pb geochronological studies on the magmatic and metamorphic rocks in Southern Altay yielded ages of 395–360 Ma, which indicate that these metamorphic rocks formed in the Devonian rather than the Precambrian. Furthermore, most of the zircons from these rocks were concentrated in the arc‐related orogenic setting of the discrimination diagrams of Th/U versus Nb/Hf and Th/Nb versus Hf/Th, and in the continental field of the discrimination diagrams of Yb versus U, Hf versus U/Yb, Y versus U/Yb, and Nb/Yb versus U/Yb. These results are consistent with the geochronology and whole‐rock geochemistry of Devonian granitoids in Southern Altay. Therefore, we propose that the continental arc along the Southern Chinese Altay was triggered by the active continental margin of the Altay‐Mongolian Terrane during the Devonian.

Geology and geochemistry of the submarine volcanism-related Qiaxia Fe–Cu deposit in the southern Altay, Xinjiang, Central Asian Orogenic Belt

The Qiaxia Fe–Cu deposit is located on the southern Altay margin, Xinjiang, China, and is hosted in the submarine volcanic–sedimentary rocks of the Lower Devonian Kangbutiebao Formation. Ore genesis of the Qiaxia deposit plays an important role on understanding the metallogenesis of submarine volcanic-hosted Fe deposits. In the Qiaxia deposit, stratiform and podiform Fe orebodies are conformable with host sequence strike, whereas lenticular Cu mineralization is closely related to skarn. Wall-rock alteration is dominated by silicification with minor skarn (actinolite, chlorite, diopside, and tremolite). Based on field evidence and petrographic observations, the paragenesis of the Qiaxia deposit includes the following three periods: (1) a volcanic–sedimentary period characterized by the formation of barite and Fe orebodies; (2) a magmatic–hydrothermal period with the formation of skarn-type Cu mineralization; and (3) a regional metamorphism period. The volcanic–sedimentary period shows moderate temperature and moderate- to low-salinity fluids with compositions of predominantly K+, Cl−, and SO42− in the liquid phase and H2O, CO2, and N2 in the gaseous phase. By contrast, the regional metamorphism period reveals high- to moderate-temperature and high- to low-salinity fluids and compositions of predominantly Na+, K+, Cl−, and SO42− in the liquid phase and H2O, CO2, N2, CH4, and C2H6 in the gaseous phase. The H–O isotopic compositions suggest that the volcanic–sedimentary period involved both magmatic fluids and seawater, while the fluids of the regional metamorphism period were derived from a mixture of metamorphic water and deeply circulated meteoric water. Sulfur isotope analysis shows that sulfur of volcanic–sedimentary period is mainly formed from thermochemical sulfate reduction of seawater sulfate, while sulfur of the magmatic–hydrothermal period reveals a mantle-derived source. The metamorphic quartz diorite yields a zircon U–Pb age of 398.9 ± 6.2 Ma (MSWD = 0.31). Combining with the available data, we conclude that the Fe orebodies formed from 413 to 399 Ma. The geological and geochemical evidence presented in this paper suggest that the Qiaxia deposit was initially a volcanic–sedimentary Fe deposit, which was overprinted by a later skarn Cu mineralization, and finally underwent greenschist-facies metamorphism.

Gemstones of eastern Kazakhstan

Abstract An overview is presented of gemstones from eastern Kazakhstan in terms of their geographical distribution, geological provenance and genesis, gemmological characteristics, historical use and current applications. Locally occurring precious, semi-precious and decorative stones were extracted and traded along the northern part of the Silk Road that traversed the area in earlier historical times. Currently, non-metallic minerals, which largely originate from mafic igneous and metamorphic bodies of the Altay and Kalba Mountains of Kazakhstan, still are insufficiently known and exploited industrially only marginally. For the present study, selected depositories of coloured stones at the Mineralogy Museum of the East Kazakhstan State Technical University were used, supplemented by the newly collected material during personal fieldwork in the southern Altay between 2005 and 2015. Standard documentation of the gemstones selected is provided, alongside with their known occurrence sites and an evaluation of the perspective gemstone-bearing deposits with respect to regional morphostructural bedrock characteristics. The most precious gemstones include topaz, corundum (sapphire and ruby), beryl (emerald and aquamarine), coloured tourmalines, agates as well as diamonds. Despite the great variety, the majority of these traditionally most valued stones are currently commercially not viable, unlike high-quality decorative stones.

Drought reconstruction based on tree-ring earlywood of Picea obovata Ledeb. for the southern Altay Mountains

ABSTRACT In this study, a 177-year April–June Palmer Drought Severity Index (PDSI) for the southern slopes of the Altay Mountains (China) was reconstructed based on the earlywood width of 96 Siberian spruce (Picea obovata Ledeb.) samples located at eight different sites. The reconstructed PDSI tracked the observed data well (r = 0.723, p < .0001, n = 52). This PDSI reconstruction captures some drought years and periods noted in historical documents, and it agrees well with other hydroclimatic reconstructions for the surrounding area. The 22-, 11-, 2.3-, and 2.1-year cycles of the reconstruction and the spatial correlation with sea surface temperature revealed that the variability of the PDSI for the study area might be influenced by both the Schwabe cycle of solar activity and the interannual oscillation of land–atmosphere–ocean circulation systems. Spatial correlation also showed the reconstruction contained climatic signals, being representative of a larger area extending from northern Xinjiang to northeastern Kazakhstan and a part of southern Russia. Synoptic climatology analysis revealed a relationship between anomalous atmospheric circulation and wet/dry years on the southern slopes of the Altay Mountains in China and its surrounding area.

Reconstruction of hydrological changes based on tree-ring data of the Haba River, northwestern China

Reconstructing the hydrological change based on dendrohydrological data has important implications for understanding the dynamic distribution and evolution pattern of a given river. The widespread, long-living coniferous forests on the Altay Mountains provide a good example for carrying out the dendrohydrological studies. In this study, a regional composite tree-ring width chronology developed by Larix sibirica Ledeb. and Picea obovata Ledeb. was used to reconstruct a 301-year annual (from preceding July to succeeding June) streamflow for the Haba River, which originates in the southern Altay Mountains, Xinjiang, China. Results indicated that the reconstructed streamflow series and the observations were fitting well, and explained 47.5% of the variation in the observed streamflow of 1957–2008. Moreover, floods and droughts in 1949–2000 were precisely captured by the streamflow reconstruction. Based on the frequencies of the wettest/driest years and decades, we identified the 19th century as the century with the largest occurrence of hydrological fluctuations for the last 300 years. After applying a 21-year moving average, we found five wet (1724–1758, 1780–1810, 1822–1853, 1931–1967, and 1986–2004) and four dry (1759–1779, 1811–1821, 1854–1930, and 1968–1985) periods in the streamflow reconstruction. Furthermore, four periods (1770–1796, 1816–1836, 1884–1949, and 1973–1997) identified by the streamflow series had an obvious increasing trend. The increasing trend of streamflow since the 1970s was the biggest in the last 300 years and coincided with the recent warming-wetting trend in northwestern China. A significant correlation between streamflow and precipitation in the Altay Mountains indicated that the streamflow reconstruction contained not only local, but also broad-scale, hydro-climatic signals. The 24-year, 12-year, and 2.2–4.5-year cycles of the reconstruction revealed that the streamflow variability of the Haba River may be influenced by solar activity and the atmosphere–ocean system.

Temporal and spatial variations of precipitation in Northwest China during 1960–2013

Based on the precipitation data from 96 weather stations in Northwest China (NWC) during 1960–2013, the Continuous Wavelet Transform (CWT) and the Mann-Kendall (MK) test were applied to analyze the precipitation spatiotemporal variations at different time scales. The relationships between the original precipitation and different periodic components were investigated. The results indicated that the annual precipitation was significantly increasing (P<0.01) at the rate of 0.55mm/a in the NWC. In terms of seasonal precipitation, the summer original precipitation significantly increased (P<0.05) in the Southern Altay Mountain Basin (SAMB), Qaidam Basin (QB), Qiang Tang Plateau Basin (QTPB), Turpan-Hami Basin (THB), Tarim Desert Basin (TDB), Northern Tianshan Mountain Basin (NTMB) and NWC. For the winter original precipitation, except the Inner Mongolia Inland Rivers Basin and Northern Kunlun Mountain Basin, the significant increases (P<0.05) were detected in the other sub-basins. In terms of monthly precipitation, significant increases were detected in January in the SAMB, NTMB and NWC, and July in the QB, Headstreams of Tarim River Basin (HTRB) and N. Additionally, most of the increasing and decreasing trends began in the mid-1980s or mid-1990s. Moreover, the periodic components were not always similar to the original data with the significant trends. The dominant scale of the original data from the periodic components was different in spatiotemporal distribution. Meanwhile, the relationship between the precipitation and El Niño-Southern Oscillation (ENSO) was different from period to period and from time scale to time scale. This study will help to develop better management measures to account for climate change and the supply/demand of water.

The adder (Vipera berus) in Southern Altay Mountains: population characteristics, distribution, morphology and phylogenetic position.

As the most widely distributed snake in Eurasia, the adder (Vipera berus) has been extensively investigated in Europe but poorly understood in Asia. The Southern Altay Mountains represent the adder’s southern distribution limit in Central Asia, whereas its population status has never been assessed. We conducted, for the first time, field surveys for the adder at two areas of Southern Altay Mountains using a combination of line transects and random searches. We also described the morphological characteristics of the collected specimens and conducted analyses of external morphology and molecular phylogeny. The results showed that the adder distributed in both survey sites and we recorded a total of 34 sightings. In Kanas river valley, the estimated encounter rate over a total of 137 km transects was 0.15 ± 0.05 sightings/km. The occurrence of melanism was only 17%. The small size was typical for the adders in Southern Altay Mountains in contrast to other geographic populations of the nominate subspecies. A phylogenetic tree obtained by Bayesian Inference based on DNA sequences of the mitochondrial cytochrome b (1,023 bp) grouped them within the Northern clade of the species but failed to separate them from the subspecies V. b. sachalinensis. Our discovery extends the distribution range of V. berus and provides a basis for further researches. We discuss the hypothesis that the adder expands its distribution border to the southwest along the mountains’ elevation gradient, but the population abundance declines gradually due to a drying climate.

树轮宽度记录的额尔齐斯河上游地区过去291年的降水变化

PDF HTML阅读 XML下载 导出引用 引用提醒 树轮宽度记录的额尔齐斯河上游地区过去291年的降水变化 DOI: 10.5846/stxb201410202060 作者: 作者单位: 中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所,中国气象局乌鲁木齐沙漠气象研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41275120,40975056);科技部气象行业专项资助项目(GYHY201206014);科技支撑资助项目(2012BAC23B01);自治区重点实验室开放课题基金项目(XJDX0909-2012-04) A 291 year precipitation reconstruction in the Upper Irtysh river basin based on tree-ring width Author: Affiliation: Institute of Desert Meteorology,China Meteorological Administration,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi,Institute of Desert Meteorology,China Meteorological Administration,Key Laboratory of Tree-ring Physical and Chemical Research of China Meteorological Administration,Xinjiang Laboratory of Tree Ring Ecology,Urumqi Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用采自额尔齐斯河上游6个采点的西伯利亚云杉(Picea obovata Ledeb)树轮样本建立了区域树轮宽度年表。与气候要素的相关分析表明,该地区树木径向生长主要受降水制约,区域树轮宽度年表与富蕴气象站上年7月至当年6月的降水总量相关显著。在此基础上建立了转换方程,重建了额尔齐斯河上游地区1722-2012年上年7月至当年6月的降水总量,方差解释量高达55.1%(调整自由度后为54.2%)。重建结果显示,该地区过去291年间存在9个降水偏多的时期和8个降水偏少的时期。降水重建序列还存在2.1a和3.2a的显著周期及2.3、21.6、24.3a的较显著周期,并且在1876-1877年及1983年前后发生了降水突变。空间相关分析表明,重建的上年7月至当年6月降水量对额尔齐斯河上游阿勒泰地区的降水量具有很好的空间代表性。此外,重建结果还与周边地区其他基于树轮资料重建的降水序列的干湿变化有较好的一致性。 Abstract:Dendroclimatology is one of the most important methods for reconstructing past climate change. Owing to the characteristics of precise dating, annual resolution, and comparability with meteorological observational data, tree-ring data have been widely used as important archival material in paleoclimatic research. We selected Siberian spruce (Picea obovata Ledeb) trees with little or no apparent evidence of human or other disturbances for sampling. Tree-ring chronologies at six individual sites were developed for Siberian spruce from the Upper Irtysh River, and then a regional tree-ring chronology (RTC) was established based on all of the detrended data obtained from individual tree cores of the six sites. We analyzed the correlations between the RTC chronology and the meteorological data of the Fuyun weather station. The results showed that precipitation was the main factor limiting the radial growth of spruce trees in this region. The RTC chronology showed the highest correlation with precipitation from the previous July to June of the current year. Based on the results of correlation analysis, we reconstructed annual precipitation patterns (July-June) of the Upper Irtysh River basin from 1722 to 2012. The precipitation reconstruction explained 55.1% of the instrumental precipitation variance during the period of 1963-2012. During the past 291 years, there were nine wet periods and eight dry periods. The wettest period occurred from 1984 to 2008, and the driest period occurred from 1877 to 1891. The period 1829-1876 was the most extended wet period, while the period 1807-1828 was the most prolonged dry period. Power spectrum analysis indicated the existence of some decadal (21.6 and 24.3 year) and interannual (2.1, 2.3 and 3.2 year) cycles. A moving t-test indicated that an abrupt change of precipitation occurred in 1876-1877 and 1983 in this region. The results of spatial correlation analysis indicated that our precipitation reconstruction correlated well (r>0.6) with the July-June precipitation gridded data over a large area of the Altay region, with the highest correlations occurring in the Southern Altay Mountains. When compared with other tree ring based precipitation reconstructions from the surrounding area, our results showed a similar trend in the variation of drought and precipitation. 参考文献 相似文献 引证文献

Petrogenesis and tectonic settings of volcanic rocks of the Ashele Cu–Zn deposit in southern Altay, Xinjiang, Northwest China: Insights from zircon U–Pb geochronology, geochemistry and Sr–Nd isotopes

The Early–Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu–Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U–Pb geochronology, geochemistry, and Sr–Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U–Pb ages of 402±6Ma and 403±2Ma. The dacites are calc-alkaline, and characterized by high Na2O/K2O ratios (3.6–9.3), and high Mg# values (47–63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive εNd(t) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe–Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66–73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive εNd(t) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction.

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 (D1k12). 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 pyrite–chalcopyrite–quartz veins crosscutting chlorite schist and leptite or the massive Pb–Zn ores. Fluid inclusions in the early metamorphic quartz veins are mainly CO2–H2O–NaCl and carbonic (CO2±CH4±N2) inclusions with minor aqueous inclusions. The CO2–H2O–NaCl inclusions have homogenization temperatures of 294–368° C, Tm,CO2 of –62.6 to –60.5°C, Th,CO2 of 7.7 to 29.6°C (homogenized into liquid), and salinities of 5.5–7.4 wt% NaCl eqv. The carbonic inclusions have Tm,CO2 of –60.1 to –58.5°C, and Th, CO2 of –4.2 to 20.6°C. Fluid inclusions in late sulfide quartz veins are also dominated by CO2–H2O–NaCl and CO2±CH4 inclusions. The CO2–H2O–NaCl inclusions have Th,tot of 142 to 360°C, Tm,CO2 of –66.0 to –56.6°C, Th,CO2 of –6.0 to 29.4°C (homogenized into liquid) and salinities of 2.4–16.5 wt% NaCl eqv. The carbonic inclusions have Tm, CO2 of –61.5 to –57.3°C, and Th, CO2 of –27.0 to 28.7°C. The aqueous inclusions (L‐V) have Tm,ice of –9.8 to –1.3°C and Th,tot of 205 to 412°C. The P–T trapping conditions of CO2‐rich fluid inclusions (100–370 MPa, 250–368°C) are comparable with the late‐ to post‐regional metamorphism conditions. The CO2‐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.

Early Silurian (~440Ma) adakitic, andesitic and Nb-enriched basaltic lavas in the southern Altay Range, Northern Xinjiang (western China): Slab melting and implications for crustal growth in the Central Asian Orogenic Belt

As an important part of the Central Asian Orogenic Belt (CAOB), the Altay Range contains large-scale Paleozoic magmatic rocks. However, owing to the lack of precise age constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area have been controversial, which has led to the debate on Phanerozoic crustal growth mechanisms and accretionary orogenic processes in the CAOB. Herein, we report geochronological and geochemical data of the Suoerkuduke adakitic, andesitic and Nb-enriched basaltic (NEB) lavas in the southern margin of the southern Altay Range. LA-ICP-MS zircon U–Pb analyses for five adakitic, andesitic and NEB samples indicate that they were coevally generated in the Early Silurian (~ 440 Ma). The adakites and basaltic andesites are geochemically characterized by high Na2O/K2O, Sr/Y, Al2O3, Sr, εNd(t) and zircon εHf(t) values and relatively low (87Sr/86Sr)i ratios. The NEBs are sodium-rich and have higher TiO2, P2O5, Zr, Nb, and Nb/U values than those of typical arc basalts. They also have positive εNd(t) values and positive and variable zircon εHf(t) values. We suggest that the Suoerkuduke adakites were derived by a partial melting of the subducted oceanic crust with minor overlying sediments, and the continuous compositional variations between adakites and basaltic andesites confirm that the interaction between slab melts and mantle peridotite played an important role in the formation of basaltic andesites. The associated NEBs were possibly generated by a partial melting of mantle wedge peridotites metasomatized by slab-derived adakitic melts and minor fluids. In combination with the occurrence of voluminous Silurian–Devonian granitoids, coeval ophiolite mélanges, and a series of intra-arc basins, a slab window model triggered by slab tearing is proposed to account for the formation of the Suoerkuduke adakite–basaltic andesite–NEB suites. The upwelling of the asthenospheric mantle through the slab window probably caused significant extension in the overlying lithosphere; extensive melting of the subducted oceanic crust, mantle and juvenile lower crust; and intense interaction between slab-derived melts or fluids and the mantle wedge. Slab tearing and subsequent asthenospheric upwelling possibly played an important role in the crustal growth of the CAOB during the Phanerozoic.

Genesis of the Dadonggou Pb–Zn deposit in Kelan basin, Altay, NW China: Constraints from zircon U–Pb and biotite 40Ar/39Ar geochronological data

The genesis of polymetallic deposits in southern Altay, NW China has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic-type mineralization. The Dadonggou Pb–Zn deposit occurs as NW-trending veins in the Devonian Kangbutiebao Formation volcanic-sedimentary sequence in the Kelan basin, southern Altay. A set of integrated zircon U–Pb and biotite 40Ar/39Ar geochronological data were applied to constrain the forming ages of the ores and their country rocks. Three samples of host volcanic rocks yielded weighted mean 206Pb/238U ages of 397.1±4.5Ma, 391.7±3.6Ma and 391.1±4.2Ma, respectively, indicating that the Kangbutiebao Formation was deposited in a Devonian back-arc basin. Two biotite samples separated from the Pb–Zn-containing quartz veins yielded 40Ar/39Ar plateau ages of 205.9±2.1Ma and 204.3±2.2Ma, respectively, which represent the age of the Pb–Zn mineralization that is attributed to the closure of the Kelan back-arc basin and the Late Triassic orogeny. Combining the available geological and geochronological data, this contribution outlines the successive evolution from the development of a Devonian back-arc basin to the Late Triassic post-subduction orogeny, and proposes that the Dadonggou Pb–Zn deposit is an epigenetic orogenic-type deposit placed in the Late Triassic orogeny.

Peatland area change in the southern Altay Mountains over the last twenty years based on GIS and RS analysis

Analyses results of total peatland area changes in the southern Altay Mountain region over the past 20 years are discussed in this paper. These analyses were based on remote sensing (RS) and geographical information system (GIS) studies. Possible control methods are evaluated by comparing these results to other regional records and climate data. The area of the peatland zones was calculated by overlaying a peatland layer of Landsat TM (Thematic Map) image constructed by using supervised classification with a layer of slope based on a digital elevation model (DEM). The results show that slope layer is crucial to improving the accuracy of peatland extracted from TM images. The peatland area of the Altay Mountains increased from 931.5 km2 in 1990 to 977.7 km2 in 2010. This trend is consistent with the climate change in this region, due in part to increasing temperatures and precipitation, suggesting possible climate controls on peatland expansion. The increase in the peatland area in the Altay Mountains over the last 20 years has been influenced by the westerlies. Alternatively, changes in the largest highland peatland area of the Zoige Basin, located in the eastern Tibetan Plateau have been influenced by the intensity of the Asian summer monsoons. In addition to increased temperatures, decreased precipitation in the Zoige Basin and increased precipitation in the Altay Mountains, due to varied patterns of atmospheric circulation, are the probable causes for driving the change differences in these two peatland areas.

Precipitation reconstruction for the southern Altay Mountains (China) from tree rings of Siberian spruce, reveals recent wetting trend

We developed six tree-ring width chronologies of Siberian spruce (Picea obovata) from the low elevation forest of the southern Altay Mountains in northern Xinjiang, China. Although the six chronologies come from different sampling sites, significant correlations existed among the chronologies (r≥0.477), and the first principal component (PC1) accounted for 72.2% of total variance over their common period 1825–2010. Correlation response analysis revealed that radial growth of Siberian spruce is mainly limited by a 12-month precipitation starting from July of the previous year to June of the current year. We therefore developed a July–June precipitation reconstruction spanning 1825–2009, which explained 65.5% of the instrumental variance for the period 1962–2009. The information of our precipitation reconstruction suggested that dry conditions existed for the periods 1829–1838, 1852–1855, 1876–1888, 1898–1911, 1919–1923, 1932–1936, 1943–1955, 1963–1968, 1973–1984 and 2007–2009, and wet conditions for the periods AD 1825–1828, 1839–1851, 1856–1875, 1889–1897, 1912–1918, 1924–1931, 1937–1942, 1956–1962, 1969–1972 and 1985–2006. Spatial climate correlation analyses with gridded land surface data revealed that our precipitation reconstruction contains a strong precipitation signal for the Altay Mountain ranges. Our reconstruction agreed with the moisture-sensitive tree ring width series of Siberian larch from the Altay Mountains of Mongolia on a decadal timescale. In addition, in contrast to a drying trend in north central China, a clear wetting trend has occurred in the southern Altay Mountains since 1980s.

Swinging between Nomadism and Sedentarism: A Case Study of Social and Environmental Change in the Nomadic Society of the Altay Steppes, Xinjiang

Abstract The Altay Steppes are part of the vast Eurasian grasslands where nomadic peoples have lived for thousands of years. Mobile pastoral production is still practised in these steppes. In recent years, however, dramatic changes have occurred in the rangeland society and production system. These have mainly resulted from modernization policies at both state and Xinjiang Uyghur Autonomous Region level. Mobile pastoral production is shrinking and herders are switching between subsistence farming and other livelihood alternatives, at times managing to follow specialized livestock production strategies involving seasonal livestock migrations along transhumance routes. This paper uses original ethnographic data in the form of two case studies to describe this flux in a southern Altay Steppe community. Its Kazakh and Altay Uranghay Mongol herders alternate between sedentary subsistence farming and nomadic pastoralism. The paper looks first at the ways people negotiate these swings between different lifestyles and livelihood options. Second, it considers the environmental changes that result from this uncertainty, and particularly the changing patterns of grassland management in the area. Special attention is given to discussion of the complex impact of the national and regional development strategies and of the ways in which those strategies affect the economic and cultural responses of the local community. Study findings suggest a correlation between cultural fragmentation, which undermines grassland management institutions, and grassland fragmentation and pasture degradation.