Tectonic evolution of the West Kunlun Orogenic Belt along the northern margin of the Tibetan Plateau:Implications for the assembly of the Tarim terrane to Gondwana

The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the "Precambrian basement" of the South Kunlun terrane(SKT) and the Tianshuihai terrane(TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcanosedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian(600-500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term lowangle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolitefacies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the HongshihuQiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.

Intra-continental deformation and tectonic evolution of the West Junggar Orogenic Belt,Central Asia:Evidence from remote sensing and structural geological analyses

The West Junggar Orogenic Belt(WJOB)in northwestern Xinjiang,China,is located in the core of the western part of the Central Asian Orogenic Belt(CAOB).It has suffered two stage tectonic evolutions in Phanerozoic,before and after the ocean–continental conversion in Late Paleozoic.The later on intracontinental deformation,characterized by the development of the NE-trending West Junggar sinistral strike-slip fault system(WJFS)since Late Carboniferous and Early Permian,and the NW-trending Chingiz-Junggar dextral strike-slip fault(CJF)in Mesozoic and Cenozoic,has an important significance for the tectonic evolution of the WJOB and the CAOB.In this paper,we conduct geometric and kinematic analyses of the WJOB,based on field geological survey and structural interpretation of remote sensing image data.Using some piercing points such as truncated plutons and anticlines,an average magnitude of^73 km for the left-lateral strike-slip is calculated for the Darabut Fault,a major fault of the WJFS.Some partial of the displacement should be accommodated by strike-slip fault-related folds developed during the strike-slip faulting.Circular and curved faults,asymmetrical folds,and irregular contribution of ultramafic bodies,implies potential opposite vertical rotation of the Miao’ergou and the Akebasitao batholiths,resulted from the sinistral strike-slipping along the Darabut Fault.Due to conjugate shearing set of the sinistral WJFS and the dextral CJF since Early Mesozoic,superimposed folds formed with N–S convergence in southwestern part of the WJOB.

Isotope Geochronologic and Geochemical Constraints on the Magmatic Associations of the Collisional Orogenic Zone in the West Kunlun Orogen, China

The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision-related intrusive rock series, i.e., a gabbro-quartz diorite-granodiorite series that formed at 224±2.0 Ma and a monzonitic granite-syenogranite series that formed at 222±2.0 Ma. The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin （material source and thermal source）, tectonic setting, genesis and geotectonic implications of these rocks. The results of this analysis indicate that the parent magma of the first series, representing a transition from I-type to S-type granites, formed from thermally triggered partial melting of deep crustal components in an early island-arc-type igneous complex, similar to an I-type granite, during the continental collision orogenic stage. The parent magma of the second series, corresponding to an S-type granite, formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic-Triassic. During continued collision, the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region, forming an immiscible puncture-type complex. The deep tectonothermal events associated with the continent-continent collision during the orogenic cycle are constrained by the compositions and origins of the two series. The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.

Source and possible tectonic driver for Jurassic-Cretaceous gold deposits in the West Qinling Orogen, China

The West Qinling Orogen(WQO) in Central China Orogenic Belt contains numerous metasedimentary rock-hosted gold deposits(>2000 t Au), which mainly formed during two pulses: one previously recognized in the Late Triassic to Early Jurassic(T3 - J1) and one only recently identified in the Late Jurassic to Early Cretaceous(J3 - K1). Few studies have focused on the origin and geotectonic setting of the J3 - K1 gold deposits.Textural relationships, LA-ICP-MS trace element and sulfur isotope compositions of pyrites in hydrothermally altered T3 dykes within the J3 - K1 Daqiao deposit were used to constrain relative timing relationships between mineralization and pyrite growth in the dykes, and to characterize the source of ore fluid. These results are integrated with an overview of the regional geodynamic setting, to advance understanding of the tectonic driver for J3 - K1 hydrothermal gold systems. Pyrite in breccia-and dykehosted gold ores at Daqiao have similar chemical and isotopic compositions and are considered to be representative of J3 - K1 gold deposits in WQO. Co/Ni and sulfur isotope ratios suggest that ore fluids were derived from underlying Paleozoic Ni-and Se-rich carbonaceous sedimentary rocks. The geochemical data do not support the involvement of magmatic fluids. However, in the EQO(East Qinling Orogen), J3 - K1 deposits are genetically related to magmatism. Gold mineralization in WQO is contemporaneous with magmatic deposits in the EQO and both are mainly controlled by NE-and EWtrending structures produced by changes in plate motion of the Paleo-Pacific plate as it was subducted beneath the Eurasian continent. We therefore infer that the J3 - K1 structural regime facilitated the ascent of magma in the EQO and metamorphic fluids in the WQO with consequent differences in the character of contemporaneous ore deposits. If this is correct, then the far-field effects of subduction along the eastern margin of NE Asia extended 1000's of km into the continental interior.

Geology, Pb Isotope Geochemistry and Ore Genesis of the Liziyuan Gold Deposit, West Qinling Orogen, Central China

The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman’s plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ34S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.

Late Paleozoic Element Migration and Accumulation under Intracontinental Sinistral Strike-slip Faulting in the West Junggar Orogenic Belt, NW China

The migration,accumulation and dispersion of elements caused by tectonic dynamics have always been a focus of attention,and become the basis of tectono-geochemistry.However,the effects of faulting,especially strike-slip faulting,on the adjustment of geochemical element distribution,are still not clear.In this paper,we select the West Junggar Orogenic Belt(WJOB),NW China,as a case study to test the migration behavior of elements under tectonic dynamics.The WJOB is dominated by NE-trending large-scale sinistral strike-slip faults such as the Darabut Fault,the Mayile Fault,and the Baerluke Fault,which formed during the intracontinental adjustment under N-S compression during ocean-continental conversion in the Late Paleozoic.Geochemical maps of 13 elements,Al,W,Sn,Mo,Cu,Pb,Zn,As,Sb,Hg,Fe,Ni,and Au,are analyzed for the effects of faulting and folding on element distribution at the regional scale.The results show that the element distribution in the WJOB is controlled mainly by two mechanisms during tectonic deformation:first is the material transporting mechanism,where the movement of geological units is consistent with the direction of tectonic movement;second is the diffusion mechanism,especially by tectonic pressure dissolution driven by tectonic dynamics,where the migration of elements is approximately perpendicular or opposite to the direction of tectonic movement.We conclude that the adjustment of element distributions has been determined by the combined actions of transporting and diffusion mechanisms,and that the diffusion mechanism plays an important role in the formation of geochemical Au blocks in the WJOB.

GRANITOIDS AND TETONIC EVOLUTION OF THE WEST KUNLUN OROGENIC BELT

The West Kunlun orogenic belt, one of the least studied areas in China, is located at the junction between the Qinghai—Tibetan Plateau and Tarim Basin and has undergone intense tectonic action and frequent magmatism.The West Kunlun orogenic belt can be divided into five tectonic\|magmatic evolution stages according to the character of the igneous rocks, metamorphic rocks, sedimentation mode, tectonic phases and isotopic ages(Fig 1).Active stages have dominated with only short intervening stable stages. This kind of evolution is not simply repeated but that a later stage is elevation and development of its former stage.Space\|time distribution of granitoids varies with each different tectonic\| magmatic stage as well as within different periods of the same tectonic\| magmatism stage. Take time into condition , It is an important turning movement of tectonics\|magmatism evolution during the Indo\|Sinian movement, as space the middle fault (Jiang Chunfa 1982) of the West Kunlun orogenic belt is a significant border o f tectonics\|magmatism evolution. Granitoids formed before Indo\|Sinian movement are mainly distributed to the north of the middle fault of West Kunlun. These granitoids are mostly granites of early and middle Proterozoic, Caledonian and Hercynian ages. A unique control on the granitoid evolution is that they become younger from NE to SW, crossing the regional structure line. Granitoids formed after Indo\|Sinian movement are mainly distributed to the south of the middle fault. But distribution of granitoids of early Yanshan cycle cut across the middle fault of West Kunlun Mountain. Their age distribution shows a bidirectional control with the granitoids becoming younger across the regional structural lines from NE and SW boundary fault to the interior of the fracture belts.

新疆大红柳滩伟晶岩型锂矿深部结构与区域成矿模型解释

为揭示花岗岩-伟晶岩型锂等稀有金属矿成矿系统的深部结构,对西昆仑造山带大红柳滩伟晶岩型锂矿集区开展了大地电磁测深法(MT)探测。通过MT三维反演电阻率模型,探测到两个0~20 km深度范围的高阻体,反映了出露于地表的大红柳滩复式花岗岩基和半隐伏的大红柳滩东花岗岩基;20~80 km深度范围内发现的大范围高导异常,则反映了深达上地幔的地壳重熔形成的大规模长英质岩浆储库。可见,成矿母岩大红柳滩花岗岩基是有根的,而且是规模巨大深达上地幔的岩浆储库,它们为超大型大红柳滩伟晶岩型锂矿的形成提供了物源和热源。与松潘-甘孜甲基卡超大型伟晶岩型锂矿集区对比,尽管川西甲基卡地区地表出露的花岗岩有限,但MT三维反演电阻率模型显示,其也存在深达上地幔的大范围高导异常,同样反映了大规模长英质岩浆储库的存在,只是剥蚀深度浅,上侵的花岗岩未被剥蚀出来而已。从而,深剥蚀的大红柳滩地区表现为大面积花岗岩出露的“热隆”特征,而浅剥蚀的甲基卡地区则表现为花岗岩围岩“片麻岩穹隆”热变质构造特征。西昆仑-松潘-甘孜伟晶岩型锂等稀有金属巨型成矿带两端的晚三叠世超大型矿床是大规模地壳重熔长英质岩浆作用中心的产物,由于锂等稀有金属的喜水性,H2O的饱和度是造就伟晶岩型锂超常富集的关键,并在长英质岩浆储库、上侵花岗岩和伟晶岩不同分异演化阶段,锂的“预富集”为大规模伟晶岩型锂矿成矿奠定了重要基础。

西昆仑-喀喇昆仑造山带锂矿成矿特征与成矿规律初探

西昆仑-喀喇昆仑造山带中生代花岗伟晶岩相当发育,主要分布于麻扎-康西瓦缝合带以南的喀喇昆仑造山带,构成了西自木吉—塔什库尔干,东到大红柳滩长达600 km的喀喇昆仑稀有金属成矿带。通过多年的研究,本文对西昆仑-喀喇昆仑造山带37处稀有金属矿床(点)进行了全面系统的梳理,认为喀喇昆仑-喀喇昆仑造山带表现为“西铍东锂”的格局,稀有金属成矿年龄集中213~206 Ma。将喀喇昆仑造山带稀有金属成矿带划分为木吉-塔什库尔干稀有金属成矿亚带、赛图拉-大红柳滩稀有金属成矿亚带,从西向东可划定4个矿化集中区:木吉-布伦口稀有金属集中区、塔什库尔干-塔吐鲁沟稀有金属矿化集中区、康西瓦稀有金属矿化集中区、大红柳滩-白龙山稀有金属矿化集中区。同时,认为西昆仑-喀喇昆仑造山带西段下一阶段的找矿可放在西合休南锂铍找矿远景区、阿然保泰铍找矿远景区、木吉西锂铍找矿远景区。

新疆西准噶尔造山带北部晚石炭世I型花岗岩的岩石地球化学和锆石Hf- O同位素特征:对其岩石成因与构造过程的启示

新疆西准噶尔造山带发育大量的晚古生代侵入岩,但它们的岩浆源区和形成的构造背景仍然存在较大争议。本文对西准噶尔造山带北部阿尔加提山石英二长岩进行了详细的岩石学、地球化学、锆石Hf-O同位素研究,旨在揭示其岩石成因和构造背景,探讨其与地壳生长的关系。两件样品的锆石U-Pb定年结果分别为301.8±1.4 Ma和303.7±3.1 Ma,形成于晚石炭世。阿尔加提山石英二长岩样品含有角闪石,高硅(SiO_(2)=67.8%~68.9%)、富碱(K_(2)O+Na_(2)O=9.36%~9.89%)、具有低的铝饱和指数(A/CNK=0.96~1.00),伴有低的Ga/Al值(2.27~2.34),Rb/Sr值(0.35~0.50),显示出I型花岗岩的特征。同时,这些样品均富集大离子亲石元素和轻稀土,亏损高场强元素(如Nb、Ta和Ti等),和负的Eu异常(δEu=0.72~0.85),类似于典型俯冲相关的岛弧岩浆特征。这些I型花岗岩具有高的、正的锆石ε_(Hf)(t)值(+11.2~+14.5)和年轻的二阶段Hf模式年龄(t_(DM2)=604~392 Ma),以及比地幔值略高的锆石δ^(18)O值(5.73‰~6.51‰)和高的锆石饱和封闭温度(T_(zr)=854~895℃),可能是新生下地壳在高温背景下部分熔融的产物。结合前人在西准噶尔造山带北部发现的晚石炭世早二叠世A1和A2型花岗岩和埃达克质岩墙,本文认为这些高温岩石组合的形成可能与晚石炭世的洋中脊俯冲及其相关板片窗作用有关。在洋脊俯冲背景下,软流圈地幔上涌加热新生下地壳,促使其发生部分熔融形成I和A_(1)和A_(2)型花岗岩。西准噶尔造山带大多数下地壳主要形成于早古生代,表明该地区在显生宙发生了显著的地壳增长。

西昆仑三十里岩体黑云母二长花岗岩和暗色包体锆石U-Pb年代学、地球化学特征、Sr-Nd同位素组成及其地质意义

三十里岩体位于西昆仑造山带东段甜水海地体北缘,本文对三十里岩体黑云母二长花岗岩及其暗色包体进行了锆石U-Pb年代学和全岩地球化学、同位素地球化学研究。结果表明:黑云母二长花岗岩SiO_(2)含量为67.84%~68.95%,Al_(2)O_(3)含量为14.77%~15.28%,铝饱和指数A/CNK为1.02~1.06,属于弱过铝质岩石;强烈富集LREE,具有轻微Eu负异常;富集Rb、Th、K、La、Ce等大离子亲石元素,亏损Nb、Ta、Ti和P等高场强元素。锆石U-Pb测年结果显示,黑云母二长花岗岩及其暗色包体均形成于约216 Ma,二者有相似的Sr-Nd同位素特征及二阶段模式年龄。暗色包体为岩浆混合作用的产物。Sr-Nd同位素数据表明,黑云母二长花岗岩可能由前寒武纪变质火成岩和变质沉积岩的混合物部分熔融形成。结合区域地质和本次研究成果,三十里岩体应属于碰撞后阶段的产物。

Early Ordovician-Middle Silurian Subduction-Closure of the Proto-Tethys Ocean:Evidence from the Qiaerlong Pluton at the Northwestern Margin of the West Kunlun Orogenic Belt,NW China

Early Paleozoic magmatism in the West Kunlun Orogenic Belt(WKOB)preserves important information about the tectonic evolution of the Proto-Tethys Ocean.This paper reports whole-rock compositions,zircon and apatite U-Pb dating,and zircon Hf isotopes for the Qiaerlong Pluton(QEL)at the northwestern margin of WKOB,with the aim of elucidating the petrogenesis of the pluton and shedding insights into the subduction-collision process of this oceanic slab.The QEL is mainly composed of Ordovician quartz monzodiorite(479±3 Ma),quartz monzonite(467–472 Ma),and syenogranite(463±4 Ma),and is intruded by Middle Silurian peraluminous granite(429±20 Ma)and diabase(421±4 Ma).Zirconε_(Hf)(t)values reveal that quartz monzodiorites(+2.1 to+9.9)and quartz monzonites(+0.6 to+6.8)were derived from a mixed source of juvenile crust and older lower crust,and syenogranites(−5.6 to+4.5)and peraluminous granites(−2.9 to+2.0)were generated from a mixed source of lower crust and upper crust;diabases had zirconε_(Hf)(t)values ranging from−0.3 to+4.1,and contained 463±5 Ma captured zircon and 1048±39 Ma inherited zircon,indicating they originated from enriched lithospheric mantle and were contaminated by crustal materials.The Ordovician granitoids are enriched in LILEs and light rare-earth elements,and depleted in HFSEs with negative Nb,Ta,P,and Ti anomalies,suggesting that they formed in a subduction environment.Middle Silurian peraluminous granites have the characteristics of leucogranites with high SiO_(2)contents(74.92 wt.%–75.88 wt.%)and distinctly negative Eu anomalies(δEu=0.03–0.14),indicating that they belong to highly fractionated granite and were formed in a post-collision extension setting.Comparative analysis of these results with other Early Paleozoic magmas reveals that the Proto-Tethys ocean closed before the Middle Silurian and its southward subduction resulted in the formation of QEL.

西秦岭三叠纪大河坝组砂岩构造背景与物质来源

大河坝组是西秦岭夏河–碌曲地区出露最晚的一套海相地层,记录了印支期海退事件。笔者基于大河坝组层序特征、砂岩主微量元素成分和碎屑锆石U-Pb年龄基础上,探索其物质来源特征和构造背景指示意义。大河坝组主体为砂板岩复理石建造,包括长石砂岩、岩屑长石砂岩、含砾岩屑长石砂岩等。其中,砂岩具有中等SiO_(2)(64.11%~68.27%,平均为65.45%),较高Al_(2)O_(3)(13.61%~15.19%,平均为14.51%),较低Fe2O_(3)(0.82%~1.72%,平均为1.25%)、CaO(2.39%~3.32%,平均为3.06%)、MgO(0.06%~0.10%,平均为0.08%)特征。稀土元素总量较高,ΣREE值为184×10^(-6)~434×10^(-6),平均为252×10^(-6)。球粒陨石标准化图解中显示Eu负异常,具有与活动大陆边缘环境相似的Th、Zr、Ti、Co、Ni等微量元素含量。砂岩中碎屑锆石U-Pb年龄主要为2204~2520 Ma、1536~2067Ma、253.3~448.7Ma等3个阶段,在2445Ma、1986.4Ma、1757.6Ma、448.5Ma、278.2Ma等5个年龄段出现峰值,锆石最小年龄为253.3 Ma。砂岩主微量元素分析和碎屑锆石U-Pb年代学谱系显示,大河坝组源区构造环境为活动大陆边缘,碎屑物质来自上地壳中性火成岩,主要物源区为研究区北部北秦岭构造带、祁连造山带东段和华北板块南缘基底,少部分碎屑来自西秦岭同期岩浆岩和多旋回沉积物。

西昆仑南屏雪山地区奥陶纪弧型辉长岩的发现及其地质意义

西昆仑造山带早古生代岩浆岩记录了区内原特提斯构造演化的关键信息。近来,笔者所在课题组在西昆仑造山带南部南屏雪山地区新发现一套奥陶纪辉长岩。LA-MC-ICPMS锆石U-Pb定年结果显示辉长岩形成于476~471 Ma,为早奥陶世岩浆活动的产物。岩石化学特征显示,辉长岩具有高Al_(2)O_(3)(14.32%~16.91%)和TiO_(2)(1.20%~2.53%),贫P_(2)O_(5)(0.22%~0.55%)和低碱(Na_(2)O+K_(2)O=4.03%~5.84%)特征,SiO_(2)(52.27%~56.65%)与MgO(2.98%~7.59%)变化较大;其中部分样品表现出富Nb特征,相对高SiO_(2)(53.08%~56.86%),低MgO(2.98%~6.05%),高TiO_(2)(1.48%~2.54%)和Nb(7.64×10^(-6)~14.08×10^(-6))。南屏雪山辉长岩富集大离子亲石元素(Rb、Th、U、K)和轻稀土元素,明显亏损Nb、Ta、Sr等元素,表现出典型岛弧型岩浆岩特征。Sr-Nd同位素方面,南屏雪山辉长岩显示出亏损的ε_(Nd)(t)值(2.84~4.04)。综合研究表明,南屏雪山奥陶纪弧型辉长岩形成于受俯冲板片熔体交代的亏损地幔发生不同程度的部分熔融过程。结合区域地质特征,我们认为麻扎尔—甜水海地体内大陆弧辉长岩(约530 Ma)、富Nb弧型辉长岩(476~471 Ma)和OIB型枕状玄武岩(约465 Ma)的特殊岩石组合记录了原特提斯洋南向俯冲过程中,俯冲板片后撤诱发的弧后伸展过程。

Ore-forming Conditions and Prospecting in the West Kunlun Area,Xinjiang, China

The West Kunlun ore-forming belt is located between the northwestern Qinghai-Tibet Plateau and southwestern Tarim Basin. It situated between the Paleo-Asian Tectonic Domain and Tethyan Tectonic Domain. It is an important component of the giant tectonic belt in central China (the Kunlun-Qilian-Qinling Tectonic Belt or the Central Orogenic Belt). Many known ore-forming belts such as the Kunlun-Qilian Qinling ore-forming zone, Sanjiang (or Three river) ore-forming zone, Central Asian ore-forming zone, etc. pass through the West Kunlun area. Three ore-forming zones and seven ore-forming subzones were classified, and eighteen mineralization areas were marked. It is indicated that the West Kunlun area is one of the most favorable region for finding out large and superlarge ore deposits.

Direct Re–Os dating of pyrite from the Jianchaling Au deposit,West Qinling,China

The West Qingling Orogen is endowed with more than 1100 t gold resources and with 50 gold deposits,ranking it the third-largest gold province in China.The Jianchaling giant gold deposit with 52 t gold reserve is a typical orogenic gold deposit in West Qinling Orogen.The deposit lacks accurate and direct metallogenic age.Five pyrite samples collected from the quartz-polymetallic veins yielded Re–Os isochron age of 206.3±2.7 Ma and an initial187 Os/188 Os ratio of 0.1154±0.0016(MSWD=0.54).The pyrites were analyzed by the electron microprobe(EMPA),and the results show that the iron content ranges from 45.1 to 47.8 wt.%,the sulfur content ranges from 52.0 to 53.5 wt.%,and the gold content varies from0.022 to 0.035%.The higher gold content means that gold is closely related to pyrite,which is a gold-bearing mineral.Moreover,the age is very close to the previous fuchsite40 Ar/39 Ar isotopic ages of 199–194 Ma,which indicates that the gold mineralization at Jianchaling has begun in the Late Triassic(206 Ma),and continued into the Early Jurassic.Through summary and comparison,it is found that the gold metallogenic age of the southern ore belt of the Mian-Lue Suture belt in the West Qinling is younger than that of the northern ore belt,suggesting that the gold deposits in the southern ore belt such as Jianchaling were formed in the transitional period from oceanic subduction to continental collision.

Geochronology, geochemistry, and Sr-Nd isotopes of Early Carboniferous magmatism in southern West Junggar, northwestern China: Implications for Junggar oceanic plate subduction

West Junggar is a key area for understanding intra-oceanic plate subduction and the final closure of the Junggar Ocean.Knowledge of the Carboniferous tectonic evolution of the Junggar Ocean region is required for understanding the tectonic framework and accretionary processes in West Junggar,Central Asian Orogenic Belt.A series of Early Carboniferous volcanic and intrusive rocks,namely,basaltic andesite,andesite,dacite,and diorite,occur in the Mayile area of southern West Junggar,northwestern China.Our new LA-ICPMS zircon U-Pb geochronological data reveal that diorite intruded at 334(±1)Ma,and that basaltic andesite was erupted at 334(±4)Ma.These intrusive and volcanic rocks are calc-alkaline,display moderate MgO(1.62%-4.18%)contents and Mg#values(40-59),and low Cr(14.5×10-6-47.2×10-6)and Ni(7.5×10-6-34.6×10-6)contents,and are characterized by enrichment in light rare-earth elements and large-ion lithophile elements and depletion in heavy rare-earth elements and high-field-strength elements,meaning that they belong to typical subduction-zone island-arc magma.The samples show low initial 87Sr/86Sr ratios(range of 0.703649-0.705008),positiveεNd(t)values(range of 4.8-6.2 and mean of 5.4),and young TDM Nd model ages ranging from 1016 to 616 Ma,indicating a magmatic origin from depleted mantle involving partial melting of 10%-25%garnet and spinel lherzolite.Combining our results with those of previous studies,we suggest that these rocks were formed as a result of northwestward subduction of the Junggar oceanic plate,which caused partial melting of sub-arc mantle.We conclude that intra-oceanic arc magmatism was extensive in West Junggar during the Early Carboniferous.

A-type granites induced by a breaking-off and delamination of the subducted Junggar oceanic plate,West Junggar,Northwest China

The A-type granites with highly positiveε_(Nd)(t)values in the West Junggar,Central Asian Orogenic Belt(CAOB),have long been perceived as a group formed under the same tectonic and geodynamic setting,magmatic sourceq and petrogenetic model.Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate:the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc;whereas the Akebasitao and Miaoergou granites formed in the accretionary prism.Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes,zircon U-Pb ages and Hf-O isotopes data on these granites.The granites in the Baogutu continental arc and accretionary prism contain similar zirconε_(Hf)(t)values(+10.9 to+16.2)and bulk-rock geochemical characteristics(high SiO_(2)and K_(2)O contents,enriched LILEs(except Sr),depleted Sr,Ta and Ti,and negative anomalies in Ce and Eu).The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages(315-305 Ma)and moderate^(18)O enrichments(δ^(18)_(O_(zircon))=+6.41‰-+7.96‰);whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages(305-301 Ma)with higher^(18)O enrichments(δ^(18)_(O_(zircon))=+8.72‰-+9.89‰).The authors deduce that the elevated^(18)O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts.The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism.The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt(induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc).On the other hand,the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism,consisting of the low-temperature altered oceanic crust,juvenile oceanic sediments,and mantle basaltic melt.These granites could be related to the asthenosphere's counterflow and upwelling,caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.

Isotopic and geochemical constraints for a Paleoproterozoic accretionary orogen in the Borborema Province,NE Brazil:Implications for reconstructing Nuna/Columbia

The Alto MoxotóTerrane of the Borborema Province presents a wide exposure of Paleoproterozoic crust,but unlike other continental blocks of South America,its orogenic history is strongly obliterated by late Neoproterozoic deformation.New isotopic and geochemical studies were conducted in mafic-ultramafic(Fazenda Carmo Suite)and granitic-gneissic rocks(Riacho do Navio Suite)within the terrane.The former present zircon U-Pb crystallization ages at ca.2.13 Ga,whereas Sm-Nd data suggests a juvenile origin via melting of early Paleoproterozoic to Archean peridotitic sources.Geochemical data for these rocks are compatible with tholeiitic magmas with some degree of crustal contamination and trace element distribution points to a continental-arc related setting interpreted as remnants of the early stages of subduction.In contrast,the Riacho do Navio Suite was emplaced at ca.2.08 Ga and has highly negativeεNd(t)values indicating crustal reworking.The suite displays calc-alkali to alkali-calcic and ferroan geochemical signatures compatible with Cordilleran magmas.In addition,trace-element distribution as well as discriminant diagrams suggest that the precursor magmas were generated during the later stages of a continental arc or in a syn-collisional setting.Based on our results,we suggest that the studied units might represent missing pieces of a Paleoproterozoic accretionary orogen that formed the crustal framework of the Alto MoxotóTerrane,and that this represents a block associated with assembly of the Nuna/Columbia supercontinent,which is now largely hidden within the Neoproterozoic orogenic belts of West Gondwana.

阿尔金西段卡尔恰尔—库木塔什超大型萤石矿带矿床地质、控矿花岗岩特征及找矿远景

【研究目的】阿尔金西段近年来萤石找矿取得重大突破,新发现卡尔恰尔、库木塔什、小白河沟、布拉克北等矿床(点),已达超大型规模,初步形成西部重要的萤石大型资源基地。有关萤石成矿机制的研究非常薄弱,本文选择区内的典型矿床开展研究,以期揭示阿尔金西段超大型萤石成矿带矿床地质、控矿因素与找矿远景,深化矿床成因研究并指导区域找矿。【研究方法】本文在详尽野外调查的基础上,利用LA-ICP-MS锆石定年、岩石地球化学和Hf同位素分析,探讨成岩成矿时代、控矿碱长花岗岩成因及萤石成矿机制,总结区内控矿要素和找矿标志,通过地质、地球化学和遥感等数据进行成矿预测,分析区域找矿远景。【研究结果】研究发现,区内萤石成矿与碱长花岗岩密切相关,矿体明显受控于北东向及次级北东东、东西向断裂构造,赋矿地层主要为阿尔金岩群斜长片麻岩和大理岩,矿石类型主要有块状、脉状、角砾状矿石,矿物组成主要为萤石、方解石、少量石英及磷灰石,早期萤石呈白色,晚期萤石呈紫色,伴生含锂的带云母,属于岩浆热液充填型脉状萤石矿床。库木塔什萤石矿区控矿碱长花岗岩锆石U-Pb年龄为(450.0±2.7)Ma,εHf(t)为-5.33~+6.45,二阶段模式年龄(TDM2)为1020~1767 Ma,具有钾玄质、准铝质、高分异特点,具有富F、高ΣREE特征,明显富集大离子亲石元素Rb、Th、U、La、Ce、Nd、Zr、Hf等,强烈亏损Ta、Nb、Sr、P、Ti等,属于A型花岗岩,与奥陶纪造山后伸展背景下壳幔岩浆混合作用密切相关。【结论】区域广泛分布的高氟碱长花岗岩对于萤石-锡-稀有-稀土成矿十分有利。矿带萤石控矿要素主要为碱长花岗岩+北东向断裂及次级构造系+阿尔金岩群富钙地层,叠加“F化探异常+碳酸根离子异常”等重要找矿标志,成矿预测显示具有巨大的萤石找矿潜力,北东向与东西向构造系、碳酸根离子异常、F化探异常等套合区域具有较大找矿远景。