西准噶尔晚古生代花岗岩类侵入体(40)~Ar/(39)~Ar热年代学

西准噶尔成矿带夹持在天山断裂与额尔齐斯断裂之间,是中亚成矿域西部的核心区域之一,广泛发育晚古生代深成岩浆活动、走滑断裂构造和斑岩铜矿、造山型金矿成矿作用。本文在西准噶尔成矿带包古图岩体、康德岩体、加曼岩体、库鲁木苏岩体、别鲁阿嘎希岩体、哈图岩体、阿克巴斯套岩体、庙尔沟岩体、克拉玛依岩体及红山岩体采集12个样品,通过黑云母和钾长石(40)~Ar/(39)~Ar阶段升温测年,给出了该地区(40)~Ar/(39)~Ar冷却年龄。其中,黑云母(40)~Ar/(39)~Ar年龄处在326~302 Ma范围内,钾长石(40)~Ar/(39)~Ar年龄为297~264 Ma,反映了西准噶尔地区晚石炭世-中二叠世的区域中温冷却历史。结合前人报道的锆石U-Pb、角闪石(40)~Ar/(39)~Ar、辉钼矿Re-Os、磷灰石裂变径迹等年龄数据,构建了西准噶尔成矿带晚古生代岩浆侵入,成矿作用与构造抬升,以及晚中生代剥露过程的整个热历史;并与区域左行走滑断裂活动的时间进行了对比,讨论了(40)~Ar/(39)~Ar冷却年龄的构造意义。     

新疆甘肃交界红柳河蛇绿岩中伸展构造与古洋盆演化过程

红柳河蛇绿岩中保存了大量伸展特征构造，如堆晶辉长岩层中发育丰富的辉长质糜棱面理、伸展褶劈理、小型韧性低角度正断层、韧-脆性共轭正断层和脆性正断层等伸展变形构造。蛇绿岩中伸展变形构造经历了完整的变形序列：从韧性变形、经韧脆性变形到脆性变形。构造几何学关系表明这些构造形成于红柳河古洋盆闭合之前洋壳扩张过程中。^40Ar／^39Ar年代学的研究确定了红柳河古洋盆演化的过程：洋盆扩张发育在462Ma之前，并在412Ma前闭合。     

北山中部增生造山过程:构造变形和~(40)Ar-~(39)Ar年代学制约

北山造山带是诠释中亚造山带南缘增生构造过程的关键区域之一。北山中部变质杂岩及相关侵入岩经历了复杂变质变形作用,是解剖北山增生构造演化过程的关键。本文在详细野外观察基础上,结合显微构造变形和黑云母~(40)Ar-~(39)Ar年代学研究,厘定北山中部相关岩石的变质变形时限。北山中部岩石普遍经历了韧性剪切变形。4个样品的黑云母~(40)Ar-~(39)Ar坪年龄分别为323.1±3.6Ma、296.0±3.7Ma、261.2±3.1Ma和209.2±4.0Ma,具有自北向南逐渐变年轻的特征。结合区域上岩石大地构造单元的展布特征,这些年龄反映了北山中部地区古生代至早中生代古洋壳(牛圈子洋盆)向北俯冲、造山带往南增生的过程。北山最晚的增生造山事件可能延续到三叠纪。     

中天山造山作用的同位素年代分期

我们把近年来所获得的一些年龄数据以及前人已有的年龄数据与区域地层接触关系作了对比,发现二者有意想不到的一致性,据此将中天山造山作用划分为5期,年龄分别大约为452—439Ma,412—402Ma,355—345Ma,334—327Ma和315—289Ma。中生代还可能有3期构造热事件,年龄大约为226—200Ma,165—160Ma和83Ma,代表了中天山的后期演化。上述年龄数据主要是从中天山南缘断裂带构造岩中获得的,它与区域年龄一致,这说明沿中天山两条边界断裂的逆冲推覆可能是导致中天山造山带变形的基本方式和原因。     

Detrital zircon ages and Hf isotopic compositions of metasedimentary rocks in the Wuqia area of Southwest Tianshan,NW China: implications for the early Paleozoic tectonic evolution of the Tianshan orogenic belt

ABSTRACT

The Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of ?22.0 to +11.3 and two-stage model ages (TDM₂) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (?15.0 to ?0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.     

中国阿尔泰造山带南缘额尔齐斯断裂带的构造变形及意义

额尔齐斯断裂是中亚造山带中的一条重要深大断裂,对于额尔齐斯断裂运动性质一直有着走滑断层、逆冲断层和压扭性断层等不同看法.本文在中国阿尔泰造山带南缘开展了详细的构造地质学工作,研究结果表明,额尔齐斯断裂及其次级断裂组成额尔齐斯断裂带.额尔齐斯断裂带在中国境内是一条宽约20 ～ 40km,长约400km,经受不同程度构造作用的强应变带,剪切作用影响范围遍布整个中国阿尔泰造山带南缘.额尔齐斯断裂带经历了左行走滑和右行走滑两个阶段.结合前人有关韧性剪切带成因型金矿、同构造岩体侵位与变形关系及对变质岩石40Ar/39Ar年代学研究,本文认为额尔齐斯断裂带的左行走滑构造形成于早二叠世(283～275Ma).早二叠世之后,额尔齐斯断裂带叠加了右行走滑事件,其活动时限可能为晚二叠世(260 ～ 245 Ma),其规模远远小于前期的左行走滑构造.额尔齐斯断裂带走滑活动性质的确定,为二叠纪北疆及整个中亚造山带造山后调整过程中不同的构造方式提供了佐证.     

Late Palaeozoic mineralization and tectonic evolution of the West Junggar metallogenic belt,Central Asia: constraints from Re–Os and 40Ar/39Ar geochronology

ABSTRACT

The West Junggar Metallogenic Belt (WJMB) is located between the Tianshan fault system and the Ertix fault system in the western part of the Central Asian Metallogenic Domain (CAMD). The belt features widespread late Palaeozoic granitic plutons, strike-slip faults, and porphyry copper and orogenic gold deposits. We collected nine molybdenite samples from the Baogutu III–IV Cu–Mo deposit and the Suyunhe Mo–W deposit, and 12 granitoid samples from the Jiaman, Kangde, Kulumusu, Bieluagaxi, Hatu, Akbastau, Miaoergou, Baogutu, Karamay, and Hongshan plutons in the WJMB. Molybdenite Re–Os dating gives metallogenesis ages of 312.7 and 299.7 Ma for the Baogutu III–IV and Suyunhe deposits, respectively. ⁴⁰Ar/³⁹Ar thermochronology yields biotite ages ranging from 326 to 302 Ma and K-feldspar ages from 297 to 264 Ma, indicating a regional medium-temperature cooling history in the WJMB during the late Carboniferous to middle Permian. By integrating these data with previous zircon U–Pb, amphibole ⁴⁰Ar/³⁹Ar, and zircon and apatite fission-track ages, we reconstruct the whole thermal history of the WJMB, which includes late Palaeozoic intrusive magmatism, porphyry Cu and W–Mo mineralization, and late Mesozoic tectonic uplift and exhumation of the WJMB. The regional ⁴⁰Ar/³⁹Ar cooling ages are consistent with the timing of regional sinistral strike-slip faulting, thereby indicating the tectonic significance of the cooling ages. We suggest that the biotite ⁴⁰Ar/³⁹Ar ages represent the static cooling of the granitic plutons after emplacement, since the ages are consistent with the U–Pb ages of the plutons. Thereafter, the oldest K-feldspar ⁴⁰Ar/³⁹Ar age may record the initiation of sinistral strike-slip movement on the Darabut, Mayile, and Baerluke faults. The regional faulting resulted in significant uplift of the WJMB during the early and middle Permian.     

Rapid cooling of the Yanshan Belt,northern China: Constraints from 40Ar/39Ar thermochronology and implications for cratonic lithospheric thinning

The Yanshan Orogenic Belt is located in the northern part of the North China Craton (NCC), which lost ∼120 km of lithospheric mantle during Phanerozoic tectonic reactivation. Mesozoic magmatism in the Yanshan fold-and-thrust belt began at 195–185 Ma (Early Jurassic), with most of the granitic plutons being Cretaceous in age (138–113 Ma). Along with this magmatism, multi-phase deformational structures, including multiple generations of folds, thrust and reverse faults, extensional faults, and strike-slip faults are present in this belt. Previous investigations have mostly focused on geochemical and isotopic studies of these magmatic rocks, but not on the thermal history of the Mesozoic plutons. We have applied ⁴⁰Ar/³⁹Ar thermochronology to biotites and K-feldspars from several Lower Cretaceous granitic plutons to decipher the cooling and uplift history of the Yanshan region. The biotite ⁴⁰Ar/³⁹Ar ages of these plutons range from 107 to 123 Ma, indicating that they cooled through about 350 °C at that time. All the K-feldspar step-heating results modeled using multiple diffusion domain theory yield similarly rapid cooling trends, although beginning at different times. Two rapid cooling phases have been identified at ca. 120–105 and 100–90 Ma. The first phase of rapid cooling occurred synchronously with widespread extensional deformation characterized by the formation of metamorphic core complexes, A-type magmatism, large-scale normal faults, and the development of half-graben basins. This suggests rapid exhumation took place in an extensional regime and was a shallow-crustal-level response to lithospheric thinning of the NCC. The second phase of rapid cooling was probably related to the regional uplift and unroofing of the Yanshan Belt, which is consistent with the lack of Upper Cretaceous sediments in most of the Yanshan region.     

西昆仑库地韧性剪切带的40Ar/39Ar年龄

西昆仑库地以南有一套变质变形较强的岩系,前人依照区域对比关系将其划为前寒武的古老基底。对西昆仑早期构造演化的论述均基于该观点,但没有提供确凿的同位素年代学证据。笔者通过野外观察、室内研究,确认库地以南的变质变形岩系是大型韧性推覆剪切作用的产物。通过对新生变质矿物角闪石和黑云母单矿物的⁴⁰Ar/³⁹Ar年龄分析,确定剪切变质年龄为426-451Ma,说明库地的变质变形岩系是形成于早古生代晚期的一条大型韧性剪切带,这对于解释西昆仑的早期构造演化具有重要意义。     

40Ar/39Ar Dating of Xuebaoding Granite in the Songpan-Garzê Orogenic Belt, Southwest China, and its Geological Significance

<正>Thus far,our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results.Therefore,in this study,the ~(40)Ar/~(39)Ar and sensitive high resolution ion micro-probe(SHRIMP) U-Pb dating methods were both used and the results compared,particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding,to establish ages that are close to the real emplacements.The results of SHRIMP U-Pb dating for zircon showed a high amount of U,but a very low value for Th/U.The high U amount,coupled with characteristics of inclusions in zircons,indicates that Xuebaoding granites are not suitable for U-Pb dating.Therefore,muscovite in the same granite samples was selected for ~(40)Ar/~(39)Ar dating.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding,gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ~(40)Ar/~(36)Ar intercept of 277.0±23.4(2σ) was very close to the air ratio,indicating that no apparent excess argon contamination was present.These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma,respectively.Through comparison of both dating methods and their results,we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ~(40)Ar/~(39)Ar dating without extra Ar.Based on this evidence,as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites,it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma.Moreover,compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt,the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze.Therefore,~(40)Ar/~(39)Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.     

哈萨克斯坦北东天山浅成低温热液型金矿床成矿时代及构造背景

哈萨克斯坦北东天山地区是中亚造山带重要的浅成低温热液型金矿床产出地区,但其成矿年代学研究非常薄弱。为确定成矿时代,作者运用高精度激光40Ar/39Ar定年法对阿尔哈尔雷金矿床和乌仁科布拉克金矿床的赋矿围岩进行了年龄测定。获得阿尔哈尔雷金矿床安山岩样品20个点40Ar/39Ar等时线年龄为304±7Ma(MSWD=6),乌仁科布拉克金矿床安山玄武岩样品21个点40Ar/39Ar等时线年龄为280±6Ma(MSWD=2.4),表明哈萨克斯坦北东天山地区浅成低温热液型金矿床主要形成于晚石炭世末期-早二叠世。初步的岩石学、地球化学研究表明,哈萨克斯坦北东天山地区晚石炭世末期-二叠纪火山岩主要为流纹岩、粗安岩、玄武粗安岩、玄武安山岩、粗面玄武岩和玄武岩,具双峰式特征,主体属于高钾钙碱性和橄榄玄粗岩系列。哈萨克斯坦北东天山地区晚石炭世末期浅成低温热液型金矿床形成于碰撞晚期向裂谷的转换阶段,而二叠纪浅成低温热液型金矿床产出于陆内裂谷环境。     

东天山造山带右行剪切变形及构造演化的40Ar-39Ar年代学证据

对新疆东天山觉罗格地区克孜尔塔格岩体（舌状岩体）角闪石、黑云母和钾长石进行了^40Ar/^39Ar年代学及热年代学研究，为确定该区右行走滑作用及NS向挤压作用结束的时间，提供了科学依据。研究表明，东天山造山带，NS向挤压作用结束于276Ma，右行走滑发生于276Ma至240－239Ma间，主要集中于276－253.9Ma。     

山西南部中条山古元古代花岗质片麻岩 白云母40Ar/39Ar测年及其地质意义

中条山前寒武纪岩石是洞悉华北克拉通前寒武纪基底构造演化的重要窗口之一,该区的前寒武纪岩系主要由涑水杂岩、绛县群、中条群、担山石群,以及西阳河群和汝阳群组成.本文以中条山地区涑水杂岩中古元古代花岗质片麻岩为研究对象,挑选其中的变形变质白云母进行激光40Ar/39Ar和常规40Ar/39Ar测年分析.激光40Ar/39Ar法获得的白云母等时年龄1830Ma±20Ma为白云母氩封闭温度年龄的最小估计,常规40Ar/39Ar法给出的白云母坪年龄1852Ma±11Ma为白云母氩封闭温度年龄的最佳估计.白云母1852Ma± 11Ma与先前获得的独居石电子探针U-Th-Pb主峰值年龄相近,并且与华北克拉通中部带的变质年龄一致,表明中条山地区涑水杂岩中古元古代花岗质片麻岩记录了古元古代晚期的一次变质作用事件.这一事件与华北克拉通中部怀安-吕梁-恒山-五台-赞皇等地的变质变形作用同时发生,揭示华北克拉通东、西部陆块沿中部带的碰撞拼合应发生在古元古代晚期,而非新太古代.     

福建紫金山矿田深部似斑状花岗闪长岩锆石SHRIMP U-Pb和单矿物~(40)Ar/~(39)Ar年龄及其地质意义

通过对福建紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩3组锆石SHRIMP U-Pb和2组角闪石、钾长石~(40)Ar/~(39)Ar测年,获得锆石~(206)Pb/~(238()U加权平均年龄为101.8±1.5 Ma(n=34,MSWD=1.0),代表紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩的成岩年龄;同时获得角闪石~(40)Ar/~(39)Ar冷却年龄为100±11 Ma、102.2 Ma,钾长石的~(40)Ar/~(39)Ar冷却年龄为96.3±1.7 Ma、98.5 Ma。依据矿物封闭温度理论,估算紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩由锆石结晶至角闪石40Ar/39Ar体系封闭、再到钾长石~(40)Ar/~(39)Ar体系封闭的岩石冷却速率分别是40.7~67.1℃/Ma、116.9~216.3℃/Ma,显示岩石的冷却速率较大;由古地温梯度推算主期似斑状花岗闪长岩结晶(101.8±1.5 Ma)至钾长石~(40)Ar/~(39)Ar体系封闭(96.3±1.7 Ma)期间岩体隆升剥露了约3 km,暗示地壳在这一时期发生了快速隆升剥蚀作用。紫金山矿田深部似斑状花岗闪长岩锆石206Pb/238U年龄佐证了紫金山矿田深部存在一个大岩基,并约束了紫金山矿田斑岩型矿床的成矿时代,单矿物的~(40)Ar/~(39)Ar年龄为矿区的隆升剥露研究提供新资料。     

Amphibole Ar/Ar Geochronology from the Okcheon Metamorphic Belt, South Korea and its Tectonic Implications

An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show ⁴⁰Ar/³⁹Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in ⁴⁰Ar/³⁹Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified ⁴⁰Ar/³⁹Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These ⁴⁰Ar/³⁹Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of ⁴⁰Ar/³⁹Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles.     

云南个旧锡铜多金属矿区云母~(40)Ar/~(39)Ar年龄及其地质意义

云南个旧是全球最大的锡铜多金属矿区,主要成矿作用是与燕山期花岗岩密切相关的岩浆-热液体系。矿区内铜矿的主要矿床类型为变玄武岩型层状铜矿和接触带型铜矿。赋存于花岗岩体的凹陷部位,接触带型铜矿体和氧化型矿体的精确年龄尚未有报道。以老厂矿田内与铜矿体同期的等粒花岗岩脉中的黑云母和与氧化矿同时形成的白云母作为研究对象,利用常规~(40)Ar/~(39)Ar同位素定年方法,获得了黑云母和白云母的~(40)Ar/~(39)Ar坪年龄分别为82.47±0.49Ma和76.17±0.42Ma,相应的正等时线年龄为82.38±0.48Ma和76.07±0.66Ma,反等时线年龄为82.38±0.49Ma和76.07±0.73Ma。结合野外地质接触关系和矿区内其他年代学结果认为,黑云母的~(40)Ar/~(39)Ar年龄82.38±0.48Ma可以代表接触带型铜矿体的形成年龄,也揭示了新山花岗岩体形成后的快速冷却作用过程;白云母的~(40)Ar/~(39)Ar年龄76.07±0.73Ma指示了氧化型矿体的形成年龄,也记录了矿区内与甲介山同期的南北向断裂的晚期活动时限。该年龄与个旧锡铜多金属矿床的成矿时代一致。     

Late Palaeozoic 40Ar/39Ar ages of the HP-LT metamorphic rocks from the Kekesu Valley,Chinese southwestern Tianshan: new constraints on exhumation tectonics

abstract

Although numerous ages have been obtained for the Chinese southwestern Tianshan high pressure/ultrahigh pressure-low temperature (HP/UHP-LT) metamorphic belt in the past two decades, its exhumation history is still controversial. The poor age constraint was related to the appealing low metamorphic temperatures and excess Ar commonly present under HP/UHP conditions. This study aims to provide new age constraints on the orogen’s exhumation by obtaining ⁴⁰Ar/³⁹Ar mica ages using the conventional step-heating technique, with emphasis on the avoidance of excess Ar contamination. From a cross section along the Kekesu Valley, four samples, three from the HP-LT metamorphic belt (TK050, TK051, and TK081) and one from the southern margin of the low pressure metamorphic belt (TK097), were selected for ⁴⁰Ar/³⁹Ar dating. Phengites from garnet glaucophane schist TK050 and the surrounding rock garnet phengite schist TK051 yield comparable plateau ages of 321.4 ± 1.6 and 318.6 ± 1.6 Ma, respectively, while epidote mica schist TK081 gives a younger plateau age of 293.3 ± 1.5 Ma. Considering the chemical compositions of phengites, mineral assemblages, and microstructures in the thin slices, we suppose that the former represents the time the HP rocks retrograded from the peak stage (eclogite facies) to the (epidote)-blueschist facies, whereas the latter reflects greenschist facies overprinting. Biotite and muscovite from two-mica quartzite TK097 give similar plateau ages of 253.0 ± 1.3 and 247.1 ± 1.2 Ma, interpreted to date movement on the post collisional transcrustal South Nalati ductile shear zone. By combining our new ages with published data, a two-stage exhumation model is suggested for the Chinese southwestern Tianshan HP/UHP-LT metamorphic belt: initial fast exhumation to a depth of about 30–35 km by ~320 Ma was followed by relatively slow (~1 mm year^–1) uplift to ~10 km by ~293 Ma.     

Thermo-tectonic history of the Junggar Alatau within the Central Asian Orogenic Belt(SE Kazakhstan,NW China):Insights from integrated apatite U/Pb,fission track and(U-Th)/He thermochronology

The Junggar Alatau forms the northern extent of the Tian Shan within the Central Asian Orogenic Belt(CAOB) at the border of SE Kazakhstan and NW China.This study presents the Palaeozoic-Mesozoic post-collisional thermo-tectonic history of this frontier locality using an integrated approach based on three apatite geo-/thermochronometers:apatite U-Pb,fission track and(U-Th)/He.The apatite U-Pb dates record Carboniferous-Permian post-magmatic cooling ages for the sampled granitoids,reflecting the progressive closure of the Palaeo-Asian Ocean.The apatite fission track(AFT) data record(partial)preservation of the late Palaeozoic cooling ages,supplemented by limited evidence for Late Triassic(~230-210 Ma) cooling and a more prominent record of(late) Early Cretaceous(~150-110 Ma) cooling.The apatite(U-Th)/He age results are consistent with the(late) Early Cretaceous AFT data,revealing a period of fast cooling at that time in resulting thermal history models.This Cretaceous rapid cooling signal is only observed for samples taken along the major NW-SE orientated shear zone that dissects the study area(the Central Kazakhstan Fault Zone),while Permian and Triassic cooling signals are preserved in low-relief areas,distal to this structure.This distinct geographical trend with respect to the shear zone,suggests that fault reactivation triggered the Cretaceous rapid cooling,which can be linked to a phase of slab-rollback and associated extension in the distant Tethys Ocean.Similar conclusions were drawn for thermochronology studies along other major NW-SE orientated shear zones in the Central Asian Orogenic Belt,suggesting a regional phase of Cretaceous exhumation in response to fault reactivation at that time.     

Provenance of latest Mesoproterozoic to early Neoproterozoic (meta)-sedimentary rocks and implications for paleographic reconstruction of the Yili Block

The Yili Block is one of the major Precambrian microcontinents of the Central Asian Orogenic Belt (CAOB). Detrital zircon U-Pb ages and Hf isotopic data of the Meso-Neoproterozoic (meta)-sedimentary units within the Yili Block constrain the tectonic affinity and early history of the block. Detrital zircon U-Pb ages, in combination with related magmatic age data, indicate that the Tekesi and Kusitai groups were deposited during the latest Mesoproterozoic-earliest Neoproterozoic (1040–960 Ma) and early Neoproterozoic (<926 Ma), respectively. Zircons from the Kusitai Group yield major age groups at 941–910 Ma and 1887–1122 Ma, whereas the Tekesi Group have a dominant age group at ca. 2.0–1.1 Ga with age peaks at ca. 1.9 Ga, 1.8 Ga, 1.75–1.70 Ga, 1.58 Ga, 1.5 Ga, 1.47–1.43 Ga and 1.27–1.20 Ga. A minor age peak of ca. 2.5 Ga is also recognized in the middle part of the Tekesi Group. Early Neoproterozoic detrital zircons with relatively uniform ε_Hf(t) values (+0.7 to +3.2) were mainly derived from contemporaneous magmatic rocks in the Yili Block. The Central Tianshan Block provides a likely source for detritus with ages of ca. 1.7–1.4 and 2.5 Ga. The predominant late Paleoproterozoic to latest Mesoproterozoic detrital zircons with positive ε_Hf(t) values (+0.5 to +12.0) in the Yili Block were probably derived primarily from regions exhumed during collisional assembly of Rodinia. These populations are consistent with those from the late Mesoproterozoic-early Neoproterozoic (meta)-sedimentary successions in the Central Tianshan, Kokchetav-North Tianshan and Erementau-Niyaz blocks, and Southeast Siberia and northeastern Laurentia cratons. The Yili Block, together with the Precambrian microcontinents in the southwestern Central Asian Orogenic Belt, was likely located at the margin of Rodinia supercontinent, between the southeast Siberia and northeast Laurentia during the early Neoproterozoic.     

星星峡石英闪长质片麻岩的锆石年代学:对天山造山带构造演化及基底归属的意义

天山造山带是中亚造山带(CAOB)的主要组成部分,对于其前寒武纪古老基底的起源、古生代构造单元划分和造山作用过程的认识还存在很大分歧。本文对分布在星星峡镇西的石英闪长质片麻岩开展了系统地岩相学观察和锆石U-Pb年龄、Hf同位素及全岩地球化学分析。根据矿物组成推测它们的原岩为石英闪长岩,两个样品中的锆石具有基本一致的内部结构特征,均发育黑色、均一的边部和具震荡环带的核部,部分保留有更早的继承锆石核。分析结果表明,它们的原岩形成于～425Ma,变质作用年龄为约320～360Ma,继承锆石的年龄为1381～1743Ma。原岩结晶锆石具有正的且变化较大的εHf(t)值(0.9～17.8),继承锆石的tDM2模式年龄变化于1.54～2.44Ga。在全岩地球化学组成上,石英闪长质片麻岩具有明显富集Rb、Ba、Th、K等大离子亲石元素和Pb、U元素,亏损Nb、Ta、Ti等高场强元素的特点。结合区域上已有的前寒武纪基底、高级变质岩、蛇绿混杂岩、岩浆岩的研究资料,获得以下认识:中天山地块的前寒武纪基底的起源与塔里木板块没有明显的相关性,可能是中元古代时期,由东欧板块边缘的弧增生造山作用形成;中天山地块东部在早古生代为大陆边缘弧的构造环境,可能形成于南天山洋向中天山板块的俯冲作用;南天山洋在天山造山带的东部和西部可能具有一致的闭合时间。