The U–Pb LA-SF-ICP-MS Age of Zircon from Metaplagiogranite of the Kharbei Metamorphic Complex (Polar Urals)

Doklady Earth Sciences - For timing of endogenous events in the Kharbei metamorphic complex (Polar Urals), U–Pb isotopic dating of zircons from garnet–clinozoisite–twomica...     

Cambrian metamorphism of the Qaidam block:Constraints from phase equilibrium modeling and monazite U-Pb datingSCIEI北大核心CSCD

柴达木地块位于青藏高原东北缘的祁连-阿尔金-昆仑早古生代造山系之中,它的西段出露一套(超)高温变质岩组合:变泥质岩、长英质片麻岩、基性麻粒岩、钙硅酸盐岩、含橄榄石大理岩及少量Mg-Al麻粒岩。本文以相平衡模拟和独居石U-Pb年代学为主要手段,限定柴西缘变泥质岩的变质作用P-T-t轨迹。变泥质岩记录了顺时针P-T轨迹,其中,压力峰期条件约为0.89GPa和800℃,温度峰期条件约为0.64GPa和825℃,退变质条件为0.58GPa和800℃至0.37±0.05GPa和702±50℃。变泥质岩的独居石U-Pb年龄集中在517~496Ma之间,三个样品的加权平均年龄分别为508±2Ma(MSWD=2.0)、506±1Ma(MSWD=1.7)、506±1Ma(MSWD=1.3)。本文将其解释为独居石的形成年龄,并认为独居石主要形成于退变质过程中的残留熔体结晶阶段(0.58GPa和800℃左右)。结合已有的工作可以得出,柴达木地块西段麻粒岩相变质作用具有顺时针P-T轨迹和1000~1300℃/GPa的峰期T/P值,并且在高温变质条件(>800℃)持续了超过30Myr。该类高T/P型变质作用最有可能发生在大型碰撞造山带内,可以与冈瓦纳大陆内部的晚泛非期的高T/P型变质作用对比,很可能是与冈瓦纳大陆最终拼合有关的晚泛非期造山事件的体现。     

Metallogeny of the Huaaobaote Ag-polymetallic deposit in Inner Mongolia: Constraints from zircon and cassiterite U-Pb datingSCIEI北大核心CSCD

花敖包特超大型银多金属矿床位于大兴安岭南段,矿体主要呈脉状赋存于二叠系寿山沟组的断裂中,部分矿体呈囊状产于寿山沟组与华力西期蛇绿岩的接触带中。矿体主要包括银铅锌锑矿体、锡铜矿体、铜铅锌矿体、锡矿体和银矿体。花敖包特矿床可划分为4个成矿阶段,分别为石英-锡石-毒砂-黄铁矿阶段(Ⅰ阶段)、石英-绢云母-锡石-黄铜矿-毒砂-磁黄铁矿-闪锌矿-黝铜矿阶段(Ⅱ阶段)、石英-绢云母-萤石-方解石-闪锌矿-方铅矿-黄铁矿-辉锑矿-含银硫盐矿物阶段(Ⅲ阶段)和石英-方解石-黄铁矿-辉银矿-深红银矿阶段(Ⅳ阶段)。对花敖包特矿区2件次流纹岩样品开展了LA-ICP-MS锆石U-Pb定年,分别获得135.4±0.8Ma和134.8±0.8Ma的年龄。对成矿Ⅰ阶段锡矿石和Ⅱ阶段锡铜矿石进行了LA-ICP-MS锡石U-Pb定年,分别获得136.3±2.0Ma和134.3±1.7Ma的加权平均年龄。定年结果表明,花敖包特矿床次流纹岩、锡矿体和锡铜矿体均形成于早白垩世。尽管二者形成时间相近,但脉体穿切关系及矿化分带特征均表明次流纹岩并非成矿物质和成矿流体的主要来源。本文认为,花敖包特矿床真正的成矿地质体为隐伏于矿区深部的次火山岩钟,其矿床成因类型为与次火山岩相关的热液矿床。     

Constraints on the evolution of the Paleo.Tethys Ocean from the Elashan Formation andesites in Xiarihamu area,western segment of East Kunlun.SCIEI北大核心CSCD

东昆仑西段夏日哈木地区出露一套鄂拉山组火山岩,其成因对古特提斯洋演化过程具有重要的指示意义。通过对其进行锆石U-Pb年代学、Hf同位素和全岩主、微量元素、Sm-Nd同位素等研究确定其形成时代、岩石成因及其构造意义。安山岩中锆石的^(206)Pb/^(238)U加权平均年龄为223±2Ma,属于晚三叠世。岩石具有较低的SiO_(2)(59.45%~63.10%)和Mg^(#)值(28~51)、较高的Al_(2)O_(3)(16.19%~17.66%)和K_(2)O含量(1.42%~3.50%),表现为弱过铝高钾钙碱性系列。岩石具有富集轻稀土和大离子亲石元素,亏损高场强元素的特征,结合全岩ε_(Nd)(t)值(-4.3~-3.1)和锆石ε_(Hf)(t)值(-3.4~+1.1),表明其可能来源于受富集地幔熔体底侵的古老下地壳部分熔融。结合区域地质资料,认为这些安山岩形成于碰撞后伸展环境,而古特提斯洋在晚三叠世已关闭。本文研究结果也说明在造山带研究中需谨慎利用火成岩的岛弧性质来判断其俯冲环境这一构造属性。     

Genesis of the Dalingzi Pb-Zn Deposit in the Western Margin of Yangtze Plate: Constraints from Fluid Inclusions and Isotopic EvidenceEI北大核心CSCD

The Daliangzi Pb-Zn deposit is a large deposit hosted in the Sinian Dengying Formation dolostone, located in the Sichuan-Yunnan-Guizhou ore concentration area. Ore minerals are mianly sphalerite, galena, and gangue minerals consist of dolomite, quartz and calcite. The metallogenic stages may be divided into sphalerite-pyrite-carbon stage, sphalerite-galena stage and galena-chalcopyrite-carbonate stage. The ore-forming fluid is basin brine, which is characterized by medium-low temperature of 117.5 ℃ to 320.3 ℃ and medium salinity of 5.11% NaCleqv to 18.96% NaCleqv, moreover, the abundant CH4 and pitch in the fluid inclusions indicate that the participation of organic matter in the mineralization. The δ13CV-PDB and δ18OSMOW values of the Dengying Formation dolostone are similar to that of marine carbonate, revealing that the dolostone belongs to marine carbonate. Both the δ13CV-PDB and δ18OSMOW values of hydrothermal calcites are lower than that of the Dengying Formation dolostone, which may result from dissolution of the Dengying Formation dolostone. The δ34S values of ore minerals are mainly in the range of 9.8‰-20.8‰, indicating the sulfur may come from thermochemical reduction of marine sulfate in the Dengying Formation. The 207Pb/204Pb versus 206Pb/204Pb diagram manifests that Pb is crustal origin, and likely comes mainly from the wall rocks and less from the basement. (87Sr/86Sr)i ratios of sphalerites and hydrothermal calcite are higher than that of the Dengying Formation dolostone, indicating that the ore-forming fluid flew through the basement. In conclusion, the ore-forming fluid was basin brine, which extracted the metallogenic materials, Pb and Zn, from the basement and wall rocks. When the ore-forming fluid reached the "black fractured zones", carbonized tectonic breccia zone, S2- was produced by the thermochemical reduction reaction under the influence of the organic matter, and interaction between the S2- and Pb2+, Zn2+, resulted in the precipitation of ore metals. © 2018, Science Press. All right reserved.     

Superimposition of Fabrics in North Dabie Dome: Constraints of Numerical ModelingEI北大核心CSCD

Mineral stretching lineations and foliations are the basic kinematic factors of ductile deformation. However, the actual stretching lineations and foliations are usually inconsistent. Interpretation of these lineations and foliations is still controversial. In this paper we modeled numerically the lineations and foliations produced in two successive flowing fields. Our modeling demonstrates that the lineations defined by the softer minerals can only keep the kinematic information of the last structural deformation. Our modeling results indicate that the lineations and foliations of the North Dabie dome only recorded the post-orogenic extensional deformation. © 2018, Science Press. All right reserved.     

Subduction of the Proto-Tethyan Ocean: Evidence from the Huimin Formation of Lancang Group in southwestern Yunnan Province,SE Tibetan PlateauSCIEI北大核心CSCD

滇西南昌宁-孟连缝合带东侧出露的澜沧岩群是重建原特提斯构造演化的关键,但其物质组成、时代和属性长期存在争议。近期地质调查表明,惠民地区的澜沧岩群惠民岩组主要由玄武岩、玄武安山岩、凝灰岩、砂岩、泥岩及灰岩组成,普遍经历了强烈构造变形和绿片岩相变质作用。岩石地球化学特征显示,玄武安山岩属于钙碱性系列,富集轻稀土元素和大离子亲石元素,具Nb、Ta和Ti的负异常,具有与俯冲相关火山弧的地球化学属性。其玄武安山岩锆石LA-ICP-MS^(206)Pb/^(238)U加权平均年龄为461.8±5.5Ma(MSWD=1.19,n=25);3件变质碎屑岩夹层的最年轻碎屑锆石U-Pb年龄峰值分别为469Ma、470Ma和475Ma,且同时期火山岩锆石占主导,指示其形成于汇聚板块边缘环境。结合本区东侧兰坪-思茅盆地西缘发育的同时期裂谷型双峰式火山岩分析,澜沧岩群惠民岩组变质火山-沉积岩组合可能是原特提斯洋沿扬子地块西缘向东俯冲过程(现今地理方位)形成的产物。研究表明古特提斯与原特提斯构造演化是连续的。     

Neoproterozoic ana texts of the yunkai metamorphic Complex; Evidence from U-Pb geochronology of zircon in migniatite北大核心CSCD

In order to determine the migmatization time of the Preeambrian metamorphic basement(the Yunkai metamorphic complex) of the Yunkai terrain, a study of LA-MC-1CP-MS U-Pb dating of zircon in matrixes and felsic veins of mig-matites from the Tiantangshan Group. Results show that the inherited magmatic cores of zircon grains from the matrix of migmatite have oscillatory zoning and yield a U-Pb age of 1086 ±24 Ma, representing the pmtolith age, whereas the metamprohic rims of zircon grains from the felsic vein of migmatite yield an age of 852. 6±8. 8 Ma, representing the timing of the anatex is (migmatization). These results imply that there is a Mesoproterozoic metamorphic basement with a Neoproterozoic anatexis event in the Yunkai area. The timing of this anatexis event is consistent with that of the Sibao Movement. Therefore, we conclude that the timing of the anataxis could be an important geological record for the amalgamation of the Yangtze and Cathaysian blocks.     

Jurassic-Cretaceous Basin-range Pattern in the Southwestern Tian Shan Foreland Basin: Evidence from Detrital U-Pb Zircon GeochronologyEI北大核心CSCD

The Mesozoic basin-range pattern in the Tian Shan area is actively debated, especially on the southern flank of the Tian Shan. This important and contrasting hypothesis involves an intracontinental foreland basin, and a passive subsiding basin characterized by a wide source area, a weak basin-range differentiation, as well as a positive physiographic feature. This study focuses on the critical stage of basin-range relationship and reports detrital zircon U-Pb ages from the sandstones of Middle Jurassic Yangye Formation and Lower Cretaceous Group collected from the Kangsu section, aiming to constrain the Mesozoic provenance of the southwestern Tian Shan foreland basin. The U-Pb isotopic ages of zircons from these two units of clastic rocks were obtained by using in situ LA-ICP-MS. The U-Pb ages of detrital zircons from the Middle Jurassic series range from 369 Ma to 2687 Ma and can be divided into three main groups: (1) 369-404 Ma (accounting for 4%), (2) 418-501 Ma (accounting for 19%), (3) 544-2687 Ma (accounting for 77%), and the zircon ages from the Lower Cretaceous series range from 243 Ma to 2820 Ma and can be divided into three groups: (1) 253-414 Ma (accounting for 35%), (2) 423-489 Ma (accounting for 27%), (3) 668-2820 Ma (accounting for 37%). All age groups are prominent in the Middle Jurassic sample, suggesting a large-scale drainage system and wide source area characterized by established connection between the basin and main sources. The distribution of U-Pb ages of detrital zircons from the Lower Cretaceous sample has more groups and reflects a shrink age in coeval source area. The southern flank of southwestern Tian Shan and the Kuqa rejuvenated foreland basin have difference sediment provenance during the Middle Jurassic, whereas in the Early Cretaceous they have similar sedimentary provenance. The southwestern Tian Shan foreland basin, as well as the other areas of the south margin of the Tian Shan underwent a minor tectonic inversion and adjustment throughout the Early Cretaceous, which led to an intension in basin-range differentiation and corresponding uplift-exhumation, and a deconstruction of the link between sedimentary piedmont and older basements distributed in interior of the mountain. © 2017, Science Press. All right reserved.     

Constraints from phase equilibrium modeling and in -situ U-Pb dating of monazite.SCIEI北大核心CSCD

西秦岭天水北道地区位于西秦岭造山带北缘,地处秦岭造山带和祁连造山带的结合部位。近来,我们在该地区秦岭杂岩中识别出一套麻粒岩相岩石(石榴夕线黑云片麻岩),峰期矿物组合为石榴子石+钛铁矿+金红石+夕线石+钾长石+石英,相平衡模拟计算结果显示其峰期温压条件为P=1.02GPa,T=820℃,经历了进变质阶段以升温升压为特征,峰期之后以大致近等温降压为特征的顺时针P-T轨迹。独居石原位LA-ICP-MS U-Pb年代学结果显示石榴夕线黑云片麻岩经历了~421Ma、~388Ma和368~362Ma三期构造热事件。结合独居石的产出位置,我们推测421Ma代表了麻粒岩相变质作用的时代,这与天水花庙地区获得的麻粒岩峰期年龄一致;388Ma近似代表了峰期之后大致近等温降压至固相线附近的年龄;368~362Ma与区域韧性剪切作用的时代一致,可能记录了与新阳-元龙韧性剪切变形作用相关的热事件的时代。结合区域地质资料和本研究成果(矿物演化特征、顺时针的P-T演化轨迹和独居石原位定年结果),我们推测西秦岭造山带北缘天水北道地区的麻粒岩可能是早古生代陆-陆碰撞造山过程的产物。     

Characteristics and Formation Mechanism of Thrust Structures in the Eastern Margin of Pamir Salient: Insights from Analogue Modeling and DiscussionEI北大核心CSCD

Two models with different boundary conditions were carried out to simulate the structural evolution of the Kekeya-Hetian fold-and-thrust belt and Kashi-Yecheng strike-slip belt in the eastern margin of Pamir salient, respectively. The analogue modeling results show that: (1) Both of the Kekeya-Hetian fold-and-thrust belt and Kashi-Yecheng strike-slip belt in the eastern margin of Pamir salient were formed under compressive shearing. Strike-slip faults occurred within both of the belts, but the displacement of these strike-slip faults in the Kekeya-Hetian fold-and-thrust belt is less than that in the Kashi-Yecheng strike-slip belt; (2) The Kekeya-Hetian fold-and-thrust belt is mainly under the influence of compression stress with weaker shearing stress while the Kashi-Yecheng strike-slip belt is mainly under the influence of shearing stress with oblique compressive stress. The strike-slip faults are mainly located in the piedmont within these two belts. The effect of the strike-slip fault diminishes towards the front of the thrust belt (to the interior basin); (3) In the front of the boundary strike-slip faults (to the interior basin), the intersecting arc thrust faults occurred successively along the shortening direction. These structural features demonstrated that the structures evolved northwards in the eastern margin of Pamir salient; (4) The oblique compression does not necessarily result in high angle faults or vertical faults, whereas low-middle angle thrust faults with strike-slip displacement are also possible. Hence, more attention should be paid to such thrust faults during the structural analysis of seismic profiles in the eastern margin of Pamir salient (e.g. the structural belts in piedmont of western Tarim Basin). © 2017, Science Press. All right reserved.     

Forceful Emplacement of Granitic Plutons in an Extensional Tectonic Setting:Syn-kinematic Plutons in the Yagan-Onch Hayrhan Metamorphic Core Complex

It is generally considered that granitic plutons are forcefully emplaced in a compressional setting and permissively emplaced in an extensional setting. This paper, however, shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhan metamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by (1) concentric distribution of the rock units, (2) a strain pattern with strong strains on the margins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shortening of the host rocks within the aureole. The strain analysis for the host rocks shows that the host-rock ductile shortening, i.e. forceful emplacement, provides about 16-24% of the emplacement space for the present plutons. All these suggest that forceful emplacement occurs not only in a compressional tectonic setting, but also in an extensional setting. This study further demonstrates the significance of the multiple emplacement of granitic plutons and provi     

Crystallization conditions of magma from Longmen potassic pluton of the Trans-North China Orogen,North China Craton: Constraints from mineral chemistry and zircon trace elementSCIEI北大核心CSCD

华北克拉通中部造山带发育的早白垩世钾质岩是研究华北克拉通中部幔源岩浆成因的天然样品,然而其成岩物理化学条件仍不明确。本文选取了涞源县龙门岩体中闪长岩和二长岩开展了矿物原位地球化学和锆石微量元素分析,以探讨矿物形成的温压条件及氧逸度与矿化的关系。分析结果显示,二长岩和闪长岩的锆石Th/U比值较高(>0.1),轻稀土亏损、重稀土富集,具明显的Ce正异常和Eu负异常特征,并具有明显的震荡环带,为典型岩浆成因锆石。电子探针结果显示,龙门岩体中斜长石主要为中性斜长石,黑云母为原生镁质黑云母,角闪石主要为钙铁闪石。闪长岩中角闪石结晶温度为793~842℃,压力为0.50~0.75GPa,深度范围为19~28km,具有较低氧逸度(log f O 2为-12.21~-11.38)和高的含水量(8.5%~10.75%);二长岩中黑云母结晶温度为764~788℃,具有更低的氧逸度(log f O 2=-15.14~-14.54);闪长岩和二长岩中锆石结晶温度为770~978℃,具有较低的氧逸度(ΔFMQ=-0.37~+1.70)。矿物化学分析表明,角闪石和黑云母虽都在地壳开始结晶,但角闪石形成于比黑云母更深的岩浆房。龙门岩体中角闪石、黑云母和锆石的结晶主要受岩浆分异控制,其地球化学动力学机制主要为岩浆上侵时减压熔融,进而引起岩浆氧逸度随岩浆演化而变化。随着岩浆上涌,闪长岩中角闪石随着温度降低和压力减少逐渐结晶,地幔交代作用导致二长岩中的黑云母具有较高的X Mg值,进而形成镁质黑云母。结合区域地质背景,古太平洋板块(伊佐奈琦板块)俯冲-后撤释放的流体交代上覆岩石圈地幔对中部造山带钾质岩(~141Ma)的形成有一定贡献,该过程导致了岩浆具有较高的含水量,但龙门岩体低的氧逸度和区域上较厚的岩石圈制约了成矿金属物质(Fe-Au等)的迁移和富集,因而不利于亲硫、亲铁元素聚集以及铁、金矿化的形成。     

Late Permian to Early Triassic subduction and retreating of the Paleopacific slab: Constraints from continental arc magmatism in Hainan IslandSCIEI北大核心CSCD

海南岛大规模二叠-三叠纪侵入岩的形成是与古特提斯洋有关,还是与古太平洋俯冲闭合有关还存在巨大争议。本文对琼中金波两处辉绿岩脉及其围岩花岗岩的研究显示,露头1辉绿岩脉的锆石U-Pb年龄为245.4±3.8Ma,TiO_(2)含量(1.07%~1.18%)低,而MgO(8.60%~9.41%)和Mg^(#)值(62.31~65.02)较高,为钙碱性系列,球粒陨石和原始地幔标准化配分曲线中具有明显的Eu、Nb、Ta、Ti和Ba负异常,以及显著Th、U、Zr、Rb和Pb等正异常,(^(87)Sr/^(86)Sr)_(i)=0.707138~0.712797,(^(143) Nd/^(144)Nd)_(i)=0.511884~0.511965,ε_(Nd)(t)值为-7.01~-8.58,指示其形成于大陆岛弧环境。相比之下,露头2辉绿岩锆石U-Pb年龄为242.8±3.1Ma,但其TiO_(2)(2.65%~3.06%)含量较高,而MgO(4.24%~5.39%)和Mg^(#)值(40.09~45.86)较低,具有Eu、Rb、Pb、Nb、Ta和Ti弱正异常和Th负异常,(^(87)Sr/^(86)Sr)_(i)=0.690244~0.717031,(^(143) Nd/^(144)Nd)_(i)=0.512886~0.512915,ε_(Nd)(t)值为+6.41~+7.93,具有板内玄武岩的特征,指示其形成于板内裂解环境。辉绿岩脉围岩二长花岗岩的锆石U-Pb年龄为255.3±3.0Ma和255.7±3.2Ma,含少量角闪石和黑云母,具有较高的SiO_(2)(71.62%~73.72%)、Na_(2)O+K_(2)O(6.60%~9.17%)和Al_(2)O_(3)(平均14.88%)含量,A/CNK值(0.97~1.03)较低,亏损Nb、Ta、Ti、Sr和Ba,富集Rb、Th、U和Pb,为高分异I型岛弧花岗岩。总的来看,二长花岗岩和辉绿岩形成于大陆岛弧挤压向伸展过渡的构造环境。对比二叠-三叠纪侵入岩体的走向、碰撞前-同碰撞-碰撞后岩浆岩的时代以及榴辉岩的变质年龄等,发现海南岛侵入岩与哀牢山-松马造山带明显不同,而与日本和朝鲜半岛的岛弧岩浆岩类似,由此我们认为海南岛大规模晚二叠-早三叠世岩浆岩为古太平洋板片向欧亚板块俯冲后撤的产物,后撤过程受到古特提斯俯冲板片的影响。     

Two Phases of Mineralization in the Dabaoshan Polymetallic Deposit,Guangdong Province: Constraints from Re-Os Geochronology of Black Carbonaceous Mudstone and MolybdeniteEI北大核心CSCD

The Dabaoshan polymetallic deposit is a polygenetic composite ore deposit located at south of the Qinhang (Qinzhou-Hangzhou) Metallogenic Belt, which is composed mainly of SEDEX type Cu-Pb-Zn and porphyry-skarn type W-Mo orebodies. Systematic field study shows that the W-Mo mineralization exhibits as quartz-vein type and skarn type orebodies around the granodioritic porphyry, or superimposes on the SEDEX type Cu-Pb-Zn orebody, while the Cu-Pb-Zn mineralization occurs mainly in the Qiziqiao Formation as stratiform-substratiform type and breccia type orebodies with typical SEDEX-type characteristics. Re-Os dating of five molybdenite separates from porphyry-skarn type W-Mo orebodies yielded isochron ages of 163.6±1.0 Ma (MSWD=0.58), which represents the age of W-Mo mineralization. Re-Os dating of seven black carbonaceous mudstone samples from a Cu-Pb-Zn orebody yielded isochron age of 387.6±9.9 Ma (MSWD=56), which is interpreted to be the age of SEDEX-type Cu-Pb-Zn mineralization. These ages indicate that there are at least two stages of ore mineralization in the Dabaoshan polymetallic deposit. The W-Mo mineralization is related to the Yanshanian intermediated-acidic intrusions, while the stratiform-substratiform SEDEX-type Cu-Pb-Zn mineralization is associated with the Hercynian seafloor hydrothermal activities. © 2018, Science Press. All right reserved.     

Structural Analysis of Jianglang Metamorphic Core Complex in Western Margin of yangtze Crston,Sichuan Province

There is a belt of metamorphic core complexes in the western margin of the Yangtze craton . The geological setting of the belt is similar to that of the Cordilleran metamorphic core complexes . A typical one in this belt is the Jianglang metamorphic core complex , which has a configuration consisting of three layers :a core complex consisting of Mesoproterozoic schist sequence , a ductile middle slab consisting of Paleozoic meta-sedimentary-basalt characterized by the development of "folding layer" and an upper cover consisting of Xikang Group which has suffered both buckling and flattening . A detachment fault developed along the contact boundary between the cover and basement causes the omission of Upper Sinian and Cambrian at the base of cover . A lot of normal ductile shear zones developed in the cover causes the thinning of it . All the features show that the early extension results in the thinning of crust , but the formation of the dome and exposure of basement rocks may be the results of superimp     

Geochemical Constraints of the Ediacaran Volcano-Sedimentary Succession of the Sa’al Metamorphic Complex at Wadi Zaghra, South Sinai, Egypt

The volcano-sedimentary succession around Wadi Zaghra in Sinai, at the northernmost segment of the Arabian Nubian Shield, comprises volcanic rocks interbedded with rather immature sediments. The succession is dominated by intermediate to silicic volcanics of medium-to high-K calc-alkaline affinity. It is divided into two units, the lower unit includes intermediate rocks and dacites interbedded with graywackes, semi-pelites and pelites and topped by polymict conglomerates. This unit is subjected to folding and regional metamorphism(up to garnet zone) and is intruded by quartz diorite-granodiorite inducing, locally, low-pressure contact thermal metamorphism. The unmetamorphosed upper unit encompasses acid volcanics intercalated with litharenite, sublitharenite and minor arenite. The rhyolites of this unit pertain to the highly fractionated granites and are characterized by an agpaitic index(NK/A) ranging from 0.87 to 0.96. They may reflect either extensive interaction of subduction-related magmas with the continental crust or a change in the tectonic regime. The present lithological and geochemical characteristics of the studied sediments together with available zircon ages indicate rather distal provenance of their detritus. This detritus comprises fluvial-alluvial sediments accumulated in the intermontane basins, which are half-grabens or tilted fault blocks. The tectonic setting of the depositional basins is active continental margin and continental island arcs. Geochemical patterns of the Zaghra volcano-sedimentary succession indicate their correlation with the Dokhan Volcanics-Hammamat Clastics sequence of the Eastern Desert of Egypt. Also, the Zaghra volcanics display geochemical similarities with those exposed in Sinai, at the Rutig, Ferani and Iqna Shar'a areas. The Zaghra succession is dated as Ediacaran but is not related either to the ensimatic island arc assemblage or to the rift-related assemblage formed during the early stages of the break-up of Rodinia as previously thought.     

Petrogenesis of Late Ordovician intrusive rocks in the West Kunlun orogenic belt: Constraints on the subduction process of the Proto-Tethys OceanSCIEI北大核心CSCD

西昆仑造山带发育有大量的早古生代岩浆岩,它们的形成与原特提斯洋俯冲-碰撞密切相关,然而,对于这些岩浆岩的岩石成因和形成的构造背景仍然存在较大的争议。本文对西昆仑造山带早古生代阿喀孜二长岩和赛图拉石英闪长岩岩体开展了详细的矿物学、锆石U-Pb年代学、全岩地球化学和Sr-Nd-Hf-O同位素研究,以探讨这些侵入岩的岩浆源区与成因,揭示原特提斯洋在这一时期的构造演化过程。这两个岩体的LA-ICP-MS锆石U-Pb年龄分别为456±2Ma和452±2Ma,指示它们形成于晚奥陶世。阿喀孜二长岩具有富碱(K_(2)O+Na_(2)O=10.5%~11.8%)、富钾(K_(2)O/Na_(2)O=1.20~1.44)特征,相对低MgO(0.89%~0.97%)、TiO_(2)(0.42%~0.45%)含量,富集Rb、Th、U等大离子亲石元素,且具有较高的全岩锆饱和温度(T_(Zr)=814~862℃),属于钾质碱性岩石。该岩体具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.72057~0.72186),负的全岩ε_(Nd)(t)值(-5.1~-4.5)和负的锆石ε_(Hf)(t)值(-7.6~-3.4),以及较高的锆石δ^(18) O值(5.39‰~7.94‰),表明其源区可能为伸展环境下古老基性下地壳部分熔融。赛图拉石英闪长岩SiO_(2)含量为56.8%~58.6%,全碱(Na_(2)O+K_(2)O)含量为5.75%~6.39%,具有较低的铝饱和指数(A/CNK=0.85~0.89),相对高的MgO含量(2.93%~3.41%)以及Mg^(#)值(~45),为高钾钙碱性系列岩石。它们富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Nb、Ta、Ti),且具有微弱的Eu异常(δEu=0.72~0.77),类似于俯冲带岩浆岩地球化学特征。这些石英闪长岩具有相对高的(^(87)Sr/^(86)Sr)_(i)比值(0.71317~0.71322),负的全岩ε_(Nd)(t)值(-5.6~-5.1)和负的锆石ε_(Hf)(t)值(-7.8~-2.9),与同时期来源于富集地幔的基性岩同位素特征相似,表明赛图拉石英闪长岩岩浆可能是由俯冲板片流体交代的富集地幔楔部分熔融形成,并在岩浆演化的过程中经历了橄榄石、辉石、角闪石、磷灰石和Fe-Ti氧化物等矿物的分离结晶作用。结合同位素和数字模拟计算(Rhyolite-MELTS)结果表明,赛图拉石英闪长岩可能由塔里木克拉通南缘玄武质岩浆的分离结晶而成。综合前人研究,本文提出晚奥陶世阿喀孜二长岩和赛图拉石英闪长岩形成于原特提斯洋向北俯冲相关的活动大陆边缘环境,该时期原特提斯洋板片回撤,诱发软流圈地幔的上涌,从而产生了大量的弧岩浆岩。     

Discussion of the genetic relations between W and Sb-Au mineralization of Xiangzhong ore district: Constraints from Sr-Nd-H-O isotopic compositions of the Caojiaba W and Longshan Sb-Au depositsSCIEI北大核心CSCD

湘中是全球最大的锑金矿集区,近年来又陆续探明了一批钨矿床,但这些钨矿和锑金矿之间的关系目前尚不明确。曹家坝钨矿床是目前该矿集区内规模最大的钨矿床(19.03Mt@0.37%WO3),矿体与矽卡岩密切共生,成矿作用划分为矽卡岩阶段、退化蚀变阶段和石英-白钨矿-硫化物阶段。不同阶段白钨矿δ18OV-SMOW变化范围为6.0‰-7.9‰,δDV-SMOW变化范围为-79.1‰--68.9‰,对应的δ18OH2O变化范围为3.3‰-5.2‰。白钨矿(87Sr/86Sr)t变化范围为0.72215-0.73049,εNd(t)变化范围为-12.8--10.6。龙山锑金矿床是矿集区内发育的大型脉状锑金矿床(4.2Mt@3.4%Sb和3.7g/t Au),矿体赋存在震旦系江口组板岩中,发育两个世代的白钨矿与辉锑矿共生。白钨矿δ18OV-SMOW变化范围为5.4‰-9.0‰,δDV-SMOW变化范围为-72.9‰--60.2‰,对应的δ18OH2O变化范围为3.1‰-6.7‰。Sr-Nd-H-O多元同位素特征显示,曹家坝钨矿床的成矿物质和成矿流体以岩浆来源为主,龙山锑金矿床有岩浆流体参与成矿,两者均有少量板溪群基底地层和大气降水的加入。综合本次及前人研究成果,曹家坝钨矿床和龙山锑金矿床具有成因联系,二者均是湘中矿集区晚三叠世岩浆热液W-Sb-Au成矿系统的重要组成部分。     

Extension of the Louzidian Metamorphic Core Complex and Development of Supradetachment Basins in Southern Chifeng, Inner Mongolia, China

The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the