3-D velocity images of the crust and upper mantle of the Tianshan area

D velocity images of the crust and upper mantle in the Tianshan are established by means of seismic tomograghy. From the results, some understanding can be achieved as follows: (1) The northern and central parts of the Tianshan are the uplifted areas with high velocities. The low velocity areas in front of the northern and southern flanks of the Tianshan are formed by the southern margin of the Junggar Basin, Turpan Basin, Kuqa depression, Kalpin fault block and Kaxgar depression. The Ili Basin and the western Kunlun appear as intracrustal stable high velocity blocks, while the Bachu uplift extends down to the crustal bottom. Along the main peaks of the Tianshan and Mt. Kongur of the western Kunlun, the Moho depresses on a great scale to form five large low velocity areas. (2) In the northern Tianshan snd western Junggar Basin, the lithosphere is thicker and features a high velocity probably with an asthenolith layer existing on the top of the upper mantle. In the southern Tianshan, the feature of the lithosphere is not very clear, and the existence of a comic low velocity block between 120-280 km depth in the Kaxgar area is presumably related with the upwelling of astenolith from the upper mantle. (3) Some relation does exist between velocity structures and seismic activities, especially those gradient belts between the low velocity zone in the upper crust and the low velocity zone in the lower crust may be the tectonic positions for the preparation of moderate-strong earthquakes. (4) Seismically active areas on the northern and southern flanks of the Tianshan are locations with most inhomogeneous crustal media and welldeveloped deep faults. Fractures or interlayer-gliding are very likely to occur under the action of tectonic forces and thus to induce earthquakes in these areas.

S wave inelastic attenuation and site effect in the northern Tianshan area

In this paper, according to the relationship of observation spectrum with source spectrum, travel-path attenuation factor and site effect, we use the digital seismic data of moderate-small earthquakes to invert the soft rock site effect and S wave inelastic attenuation under the constraint of site effect, and determine the parameters of path and site. The parameters obtained by this method exclude the topographic effect of seismic stations, and truly reflect the seismic effect of free soft rock sites and the S wave inelastic attenuation in the studied region. The average soft rock site effect is about 1.5 times in the frequency domain of 2-4 Hz and the S wave quality factor is obtained as Qs=278f0.346, which can be directly applied to the stochastic modeling of ground motions in the studied region.

Spatiotemporal characteristics and trend assessment of Ms≥5.6 earthquakes in the Tianshan area of China based on co-occurrence analysis and commensurability

Based on the complete seismic data of the Tianshan area in the past 118 years,the co-occurrence rate of earthquakes in different fault zones is calculated,the fault zone with the highest associative degree in the Tianshan area is determined as the research object,extracted the earthquake time series information of the strong associative fault zone and the commensurability method is used to obtain the commensurability expression,the year of strongest earthquake signal is calculated and predicted,then the butterfly structure diagram and commensurability structure system are drawn.Combined the butterfly structure diagram and commensurability structure system to analyze the seismic spatiotemporal structure characteristics of the Tianshan area,judge the trend of future earthquakes,and predict the time of future earthquakes.The results demonstrate that Ms≥5.6 earthquake signals are strong in 2020 and 2021.In order to determine the location of future earthquakes,the historical epicenter migration law of the strongly correlated fault zone in the Tianshan area is analyzed.It is revealed that the epicenter distribution is symmetric in both the longitude and latitude directions.Analyzing the spatial distribution of epicenters,the five successive earthquakes in the strong associative fault zone in the Tianshan area present a pentagonal symmetrical structure in space.It is judged that the next earthquake will migrate toward the northeast.Additionally,the sunspot has a strong seismic correlation with the strong associative fault zone in the Tianshan area.Specifi cally,on the 11-year cycle scale of sunspot activity,64.71% of earthquakes occurred in the fluctuation descending range;on the monthly scale of sunspot activity.Hence,it has been verified that the proposed disaster prediction method based on commensurability theory is scientifi c and has a broad application prospect.

Focal Mechanism Solutions and Stress Field Inversion of Moderately Strong Earthquakes in the Northern Tianshan Area

Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.

Tomography for Q of the Eastern Section of the Tianshan Area from High-frequency Attenuation of S-wave

Based on the waveform data of 5,076 local earthquakes recorded at 25 stations in Xinjiang during the period from 2009 to 2014 and the observation reports provided by the Xinjiang Digital Seismic Network,a data set of 19,140 attenuation factors t*is obtained by fitting the high-frequency attenuation of S-wave spectra with a genetic algorithm. The spatial distribution of Q_S is determined by inverting the t*data with seismic tomography. The results show that the average Q0 in eastern Tianshan is 520,and there is a significant correlation between the Q_S value distribution or attenuation characteristics it disclosed and the surface structure of the study area. The Q_S value is lower in the intersection area of the mountain basin which is located on the north and south sides of the Tianshan Mountains,and the high Q_S distribution is more concentrated inside the Tianshan orogenic belt. The M≥6. 0 earthquakes have been basically located in the Low-Q_S region since 1900. 24 high heat flow points in eastern Tianshan are located at the north and south of Tianshan Mountains where low Q_S exists,indicating a negative correlation. In addition,there is a positive correlation between the velocity structure and the attenuation structure in the study area,which reflects the consistency of the 2-D attenuation structure with the velocity structure and the two-dimensional density structure.

An analysis of oasis stability in arid areas:a case study in the northern slope areas of the Tianshan Mountains

This paper discusses oasis stability at regional scale with a case study in the northern slope areas of the Tianshan Mountains (NSTM). The results showed certain significant aspects. (1) As long as water resources in the oasis keep stable and their utilization efficiency can be maintained or gradually increased, the primary productivity could be continuously increased and the natural primary productivity keeped relatively stable. In this case, it is considered that the oasis is stable and its sustainable development can be achieved at regional scale. (2) Considering the availability of water resources in the oases, the oases on the alluvial-diluvial fans are highly stable. In the alluvial plain downstream of the groundwater overflowing zones the oases are moderately stable and in the lacustrine deltas or dry lacustrine deltas the oases are lowly stable. (3) Enlargement of oases and the increase of water resources and vegetation coverage in the oasis will certainly enhance the 'cold-island effect' of the oasis and increase the stability of oases.

Relocation of Earthquakes in the Northeastern Tianshan Mountains Area and Improvement of Local 1-D Crustal Velocity Model

We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40' N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further.

Ore-forming Fluid and Mineral Source of the Hongshi Copper Deposit in the Kalatage Area, East Tianshan, Xinjiang, NW China

The Hongshi copper deposit is located in the middle of the Kalatage ore district in the northern segment of the Dananhu-Tousuquan island-arc belt in East Tianshan, Xinjiang, NW China. This study analyses the fluid inclusions and H, O, and S stable isotopic compositions of the deposit. The fluid-inclusion data indicate that aqueous fluid inclusions were trapped in chalcopyrite-bearing quartz veins in the gangue minerals. The homogenization temperatures range from 108°C to 299°C, and the salinities range from 0.5% to 11.8%, indicating medium to low temperatures and salinities. The trapping pressures range from 34.5 MPa to 56.8 MPa. The δ^（18）O_（H_2O） values and δD values of the fluid range from -6.94‰ to -5.33‰ and from -95.31‰ to -48.20‰, respectively. The H and O isotopic data indicate that the ore-forming fluid derived from a mix of magmatic water and meteoric water and that meteoric water played a significant role. The S isotopic composition of pyrite ranges from 1.9‰ to 5.2‰, with an average value of 3.1‰, and the S isotopic composition of chalcopyrite ranges from -0.9‰ to 4‰, with an average value of 1.36‰, implying that the S in the ore-forming materials was derived from the mantle. The introduction of meteoric water decreased the temperature, volatile content, and pressure, resulting in immiscibility. These factors may have been the major causes of the mineralization of the Hongshi copper deposit. Based on all the geologic and fluid characteristics, we conclude that the Hongshi copper deposit is an epithermal deposit.

Discovery and Geological Significance of Early Carboniferous High-Mg Diorite in the Balikun Area, Eastern Tianshan

The granodiorites,monzogranites and diorites are widely developed in the Balikun area of Eastern Tianshan Orogen.Of which,LA–ICP–MS zircon U-Pb isotopic dating from the diorites revealed that they were emplaced at 327~333 Ma,representing an important period of magmatism in the Early Carboniferous.Geochemically,they are characterized by moderate SiO2(51.33–62.48 wt%),high but variable MgO(2.04–11.16 wt%,average 5.35),higher Mg#(40–73)and TiO2(0.67–1.29 wt%),Na2O/K2O(1.39–2.95)as well as variable Cr(2.49–675 ppm)and Ni(1.31–174 ppm),showing a geochemistry similar to those of high-Mg diorites or sanukitoids.In addition,they are enriched in the LILE,poor HFSE with an evident negative Nb anomalies and a REE pattern of moderate fractionator between LREE and HREE without or weak negative Eu anomalies.TheirεHf(t)are positive(+3.63–+15.65),suggesting a source from the depleted mantle.In addition,they have high TiO2 and Pb,and large quantity of amphibolite and biotite,indicating that they were most likely derived from the partial melting of depleted mantle metasomatized by the slabderived melt under a hydrous condition.Consequently,combined with the contemporary volcanics and granitoids formed in the island arc settings,we proposed that the subduction was continued till Early Carboniferous in the Bogda-Harlik tectonic belt.After that,wide occurrence of the post-collisional A-type granites and mafic-ultramafic intrusions indicate this tectonic belt entered the post-collisional environment from Late Carboniferous to Permian.

Analysis on Variations of the Temperature and Precipitation in North Slope Area of the Western Tianshan in Recent 50 Years

[Objective] The research aimed to analyze variation characteristics of the temperature and precipitation in north slope area of the Western Tianshan in recent 50 years.[Method] According to temperature and rainfall data from 1961 to 2010 at three meteorological stations in north slope area of the Western Tianshan,climate change in the zone in recent 50 years was analyzed by using linear trend analysis method and 5-year sliding average method.[Result] The temperature in north slope area of the Western Tianshan showed significant warming trend.The annual average temperature significantly increased at 0.3 ℃/10 a in recent 50 years.But rise rates of the temperature in different seasons were different:autumn> winter> spring> summer.The annual rainfall in north slope area of the Western Tianshan in recent 50 years overall presented relative increase trend.Seen from annual rainfall,it significantly increased at 16.9 mm/10 a.Seen from seasonal rainfall,except in autumn,rainfalls in other three seasons in the past 50 years all showed significant increase trends,with amplitude of 3.2-11.2 mm/10 a.The largest increase amplitude was in summer.After a small precipitation peak in the 1980s,autumn rainfall slightly declined in the past 20 years.[Conclusion] The climate in north slope area of the Western Tianshan become warm and wet.

THE MORPHOLOGICAL FEATURES AND ENVIRONMENTAL CONDITIONS OF ROCK GLACIERS IN TIANSHAN MOUNTAINS

-Rock glaciers are developed at permafrost areas of periglacial environment in Tianshan Mountains [7,17]. Based on field surveying andair-photo interprestation, the paper discusses the shape, characteristics of supply area, formation conditions and environmental differentiations of rockglaciers at head area of Urmqi River (43°05'-43°08' N, 86°48’-86°53E) inKalawuchen Range and the head areas of Toudao River and Danangou River (43°30’-43°50’N, 85°00-85°30’E) in Yilanhabierga Rangu at ShawanCounty. Formation conditions and morphological characteristics of rockglaciers are studies in terms of topographic conditions, climate, compositionand age.

天山地区均衡剩余地形特征及其地质意义

新生代印度板块持续碰撞和俯冲欧亚大陆的远端效应,波及整个天山地区,强烈改造了天山及相邻块体的岩石圈结构。为了更好地研究天山地区的岩石圈演化和形变过程,本文首先采用联合重力和地震数据反演方法,获得研究区岩石圈密度异常结构,然后考虑有效弹性厚度的横向变化计算研究区均衡剩余地形。结果表明,均衡剩余地形幅值在-1.6~0.9 km之间,且与各构造单元具有良好的对应性。天山各段的均衡剩余地形呈现不同的分布特征,中部为较高幅值的负值,指示剧烈增厚的下地壳;西部为较低幅值的负值,可能与软流圈上涌有关;东部为较低幅值的正值,表明岩石圈形变以地表抬升为主。

天山冰川退缩区土壤汞分布特征及累积

本文以新疆天山乌鲁木齐河源一号冰川退缩区为研究区域,通过^(210)Pbex、^(137)Cs放射性同位素测年和侵蚀性堆积地貌判定退缩区的年代演替序列,并据此设置了系列采样点,对土壤进行分层采样,测定样品总汞浓度等指标,计算各年代退缩区的汞累积速率,探究乌鲁木齐河源一号冰川退缩区土壤中汞的分布特征及其累积过程.结果表明:冰川退缩区土壤汞含量和汞储量随着退缩时间增长呈现出增加的趋势,各层土壤汞的平均含量由大到小依次为:0~5cm[(13.28±6.60)μg/kg]>5~10cm[(11.47±7.34)μg/kg]>10~15cm[(10.19±6.57)μg/kg]>基岩[(0.23±0.09)μg/kg];冰川退缩区植被生长促进了土壤汞的富集,退缩区内土壤汞浓度与土壤有机碳、氮含量呈显著正相关,而且由于植被生物量很小,退缩区土壤中汞的累积速率也较低(0.09~33.43μg/(m^(2)·a),平均值为16.92μg/(m^(2)·a));近250a来(1777年以来),天山一号冰川退缩区土壤汞累积速率呈加速增加趋势,由1777年的0.09μg/(m^(2)·a)增加至2017年的33.43μg/(m^(2)·a),这意味着自工业革命以来大气汞含量及沉积量在不断增加.

新疆南天山红柳沟辉长岩地球化学特征及地质意义

红柳沟辉长岩位于南天山北缘东段哈尔克-萨阿尔明晚古生代沟弧带东部,是南天山北缘-中天山南缘早古生代弧岩浆带内出露为数不多的基岩侵入岩体。辉长岩主要由斜长石(±48%)、普通辉石(±42%)、黑云母(±5%)、角闪石(±5%)组成。岩石化学成分显示辉长岩Na_(2)O含量为2.49%~3.08%,平均为2.83%;K_(2)O含量为1.6%~2.4%,平均为2.02%,里特曼指数为1.78~2.09,均小于3.3;分异指数为50.3~57.06,主、微量图解显示其为拉斑-钙碱性系列;辉长岩稀土元素球粒陨石标准化配分模式与E-MORB相似,轻稀土富集,重稀土亏损,未见明显的δEu异常,微量元素具有Rb、Ba、Th、U等大离子亲石元素富集和Ta、Nb、Ti等高场强元素亏损;锆石原位εHf(t)值为-1.27~8.75,反映辉长岩来源于亏损地幔,并上升的过程中受到地壳明显混染,基性岩的(Na_(2)O+K_(2)O)/TiO2判别图解显示红柳沟辉长岩源区碳酸盐化橄榄岩部分熔融。锆石U-Pb测年显示辉长岩形成年龄为为(410.4±2.3)Ma(MSWD=0.51,n=25)。本次研究补充了南天山构造带辉长岩年代学、地球化学证据,结合区域地质资料,笔者提出在早泥盆世,南天山洋存在洋陆俯冲作用,并伴随有基性岩侵入。

新疆东天山康古尔一带金矿地质特征及成矿机制

新疆康古尔一带的金矿床位于塔里木板块北缘的东天山秋格明塔什—黄山韧性剪切带南缘,是新疆的重要金成矿区。二叠纪早中期,在SN向推覆韧性剪切和右行走滑韧-脆性剪切基础上,地壳快速抬升在韧性变形构造上叠加脆性破裂,一系列张性断裂成为主要容矿构造;同构造期侵位的中酸性浅成斑岩体(如石英斑岩)提供了充足的成矿热源和部分水源及成矿物质来源;康古尔一带金矿矿化型式各不相同,既有产于构造破碎带中的蚀变岩型金矿、石英脉金矿,也有产于火山角砾岩筒中的脉状金矿,还有产于斑岩体边缘或产于岩体内部的斑岩型金矿;但成矿流体的物理化学特征均具中低温、低盐度、中低压力的特点;金矿的形成分为2个热液成矿阶段,其中晚期阶段是金的主要形成阶段。本文对该区金的成矿物理化学环境进行了讨论,并总结了成矿机制,认为康古尔一带金矿形成于统一的岩浆热液成矿系统,成矿作用与区域构造的脆性构造活动同步发生,金矿成矿时段大致在二叠纪晚期(263 Ma—243 Ma);下一步找矿工作应在有利的物化探异常中预测和寻找不同地质产状的中低温浅成热液型金矿。

东天山造山带黑尖山地区花岗闪长岩岩石成因及构造意义:来自岩石学、锆石U-Pb年代学、地球化学证据

黑尖山花岗闪长岩位于东天山造山带晚古生代弧盆系之小热泉子—大南湖古生代残留弧内,通过分析其野外地质特征、岩相学、岩石地球化学以及锆石U-Pb年代学特征,探讨了其岩石成因、构造背景,为东天山地区古洋盆闭合、碰撞造山时限等洋-陆构造格局及其演化研究提供新的基础信息。电感耦合等离子体质谱(inductively coupled plasma mass spectrometry,LA-ICP-MS)锆石U-Pb同位素定年结果显示黑尖山花岗闪长岩形成年龄为(373.0±3.0)Ma。岩石地球化学研究表明,花岗闪长岩具有高硅、准铝质、中-高钾钙碱性系列的I型花岗岩特征;稀土元素总量变化范围为112.82×10^(-6)~129.91×10^(-6),且轻/重稀土的比值变化范围为8.73~11.26(平均值为9.64),指示轻稀土相对重稀土富集,弱Eu负异常(δEu=0.77~0.85);样品富集大离子亲石元素(LILE,如Rb、Ba、K、U),亏损高场强元素(HFSE,如Ta、Nb和Ti)及P、Ta、Nb负异常明显;显示岛弧岩浆岩的特征,形成于板块俯冲的构造环境。综合区域地质特征、岩石地球化学和岩浆源区特征,黑尖山花岗闪长岩是东天山小热泉子—大南湖岛弧内晚古生代大规模中酸性岩浆侵入作用的同期产物,表明东天山黑尖山地区晚泥盆世花岗闪长岩是古大洋(古北天山洋)板片向北俯冲的岛弧背景产物;进一步说明东天山黑尖山地区泥盆纪晚期古大洋仍未闭合。

新疆东天山地区白山钼矿床的成因分析

白山钼矿床位于东天山觉罗塔格构造带的东部,赋矿围岩为下石炭统干墩组的黑云母长英质角岩,矿化石英网脉发育。文章测得含矿石英脉中的石英流体包裹体δ18OSMOW值为9.1‰~10.0‰,平均9.425‰,与石英相平衡的水δ18OH2O值为3.357‰~4.257‰,平均为3.682‰;δDSMOW值为-105‰^-69%,平均-89.25‰。氢氧同位素组成显示白山钼矿床的成矿流体是岩浆水与发生了水-岩作用的大气降水的混合热液,含矿流体以岩浆水为主,演化大气降水的加入是成矿物质沉淀的重要因素。测得辉钼矿的Re-Os等时线年龄为(227.7±4.3)Ma(MSWD=0.32),指示白山钼矿床形成于中三叠世。矿床地质特征和地球化学特征指示白山钼矿床是斑岩型矿床,推测成矿物质主要来自于矿体下部的矿化花岗(斑)岩体。此外,作者还探讨了白山钼矿床的成矿背景,认为矿床形成于挤压的构造环境,是受到同时代古特提斯洋闭合的陆内远程效应影响而产生的成岩成矿作用。

新疆天山地区壳幔S波速度结构特征及变形分析

天山地区地质构造复杂,地震活动频繁,其壳幔变形和深部结构一直受到学者们的高度关注.然而,由于天山地区地震台站资料较少,致使壳幔变形研究结果与解释存在诸多争议.本研究利用在天山地区(40°N—46°N,78°E—92°E)新布设的11个流动宽频带地震台站和该地区39个固定台站的观测资料,采用接收函数与面波联合反演方法,获得了研究区地壳厚度及壳幔S波速度结构.反演结果显示天山地区(41.5°N—44°N,78°E—88°E)平均地壳厚度为56km,塔里木盆地(40°N—41.5°N,79°E—90°E)、准噶尔盆地(44°N—46°N,82°E—90°E)和吐鲁番盆地(42°N—43°N,88°E—90°E)具有较厚的沉积层,地壳平均厚度为43.km、53.km和46km,整体表现为天山厚、盆地相对较薄的特征;在研究区南天山的最高峰(42°N,80.5°E)及北天山的最高峰(43.5°N,86°E)附近,中下地壳存在较厚的低速层,我们认为在强烈挤压作用下低速、低强度的中下地壳强烈变形可能是导致该区域快速隆升的主要原因.在研究区中部,位于塔里木盆地与准噶尔盆地之间的天山地区,中下地壳及上地幔均存在低速层,且盆地莫霍面向天山倾斜明显.结合前人的研究成果推测,在南北向构造挤压应力作用下,塔里木盆地与准噶尔盆地发生了向天山造山带方向的双向壳幔层间插入俯冲.在研究区东部,塔里木盆地东北缘与天山东部接触带的地壳内没有明显的低速层,推测应处在早期挤压变形状态,该区域的壳幔边界为缓变的速度梯度带,可能与上地幔热物质侵入或渗透有关.

新疆东天山铅锌矿成矿规律及区域预测

东天山是中国西部重要的成矿区带,具备极佳的成矿条件。东天山的铅锌(银)矿主要分布于塔里木古陆块,部分产于阿奇山早石炭世裂谷带,矿床类型可分为层控-热液改造型、矽卡岩型、热液型和火山岩型4种,以层控-热液改造型为主。通过对研究区彩霞山等典型矿床的研究,总结了该区铅锌矿的成矿规律,确定了预测要素。在此基础上运用证据权法划分了68个预测区,并对预测区进行了评述,认为东天山具有很好的寻找层控-热液型铅锌矿的前景。

近36年新疆天山山区气候暖湿变化及其特征分析

根据天山山区10个气象台站1971-2006年的历史气候资料,采用线性回归、最大熵谱、Mann-Kendall和自然正交分解(EOF)等方法,对近36年的年平均气温、降水量、最大可能蒸散量和下垫面湿润指数等气候要素的基本变化特征进行了分析,结果表明:(1)近36年天山山区年平均气温呈升高趋势,降水量呈增多趋势,年最大可能蒸散量呈减少趋势,下垫面湿润指数呈增大趋势。受其综合影响,近36年天山山区气候呈较明显的暖湿化变化趋势。(2)突变检测表明,天山山区年平均气温在1976年发生了突变性的升高,降水量和湿润指数在1986年发生了突变性的增大,而最大可能蒸散量在1986年发生了突变性的减小。(3)36年里,降水量和湿润指数的变化不存在<36年的显著周期,而温度变化具有>36年、9年、4年和2.4年的显著周期,最大可能蒸散量变化具有>36年、5.1年和2.4年的显著周期。(4)10站的年平均气温、降水量、最大可能蒸散量和湿润指数等四要素的最主要空间分布特征均是同向变化。