Geochronology and Tectonic Evolution of the West Section of the Jiangnan Orogenic Belt

As an important part of South China Old Land, the Jiangnan Orogenic Belt plays a significant role in explaining the assembly and the evolution of the Upper Yangtze Block and Cathaysia, as well as the structure and growth mechanism of continental lithosphere in South China.The Lengjiaxi and the Banxi groups are the base strata of the west section of the Jiangnan Orogenic Belt.Thus, the research of geochronology and tectonic evolution of the Lengjiaxi and the Banxi groups is significant.The maximum sedimentary age of the Lengjiaxi Group is ca.862 Ma, and the minimum is ca.822 Ma.The Zhangjiawan Formation, which is situated in the upper part of the Banxi Group is ca.802 Ma.The Lengjiaxi Group and equivalent strata should thus belong to the Neoproterozoic in age.The Jiangnan Orogenic Belt consisting of the Lengjiaxi and the Banxi groups as important constituents is not a Greenville Orogen Belt(1.3 Ga–1.0 Ga).The Jiangnan Orogenic Belt is a recyclic orogenic belt, and the prototype basin is a foreland basin with materials derived from the southwest and the sediments belong to the active continental sedimentation.By combining large amounts of dating data of the Lengjiaxi and the Banxi groups as well as equivalent strata, the evolutionary model of the western section of the Jiangnan Orogenic Belt is established as follows: Before 862 Ma, the South China Ocean was subducted beneath the Upper Yangtze Block, while a continental island arc was formed on the side near the Upper Yangtze Block.The South China Ocean was not closed in this period.From 862 Ma to 822 Ma, the Upper Yangtze Block was collided with Cathaysia; and sediments began to be deposited in the foreland basin between the two blocks.The Lengjiaxi Group and equivalent strata were thus formed and the materials might be derived from the recyclic orogenic belt.From 822 Ma to 802 Ma, Cathaysia continued pushing to the Upper Yangtze Block, experienced the Jinning-Sibao Movement(Wuling Movement); as result, the folded basement of the Jiangnan Orogenic Belt was formed.After 802 Ma, Cathaysia and the Upper Yangtze Block were separated from each other, the Nanhua rift basin was formed and began to receive the sediments of the Banxi Group and equivalent strata.These large amounts of dating data and research results also indicate that before the collision of the Upper Yangtze Block with Cathaysia, materials of the continental crust became less and less from the southwest to the east in the Jiangnan Orogeneic Belt; only island arc and neomagmatic arc were developed in the eastern section.Ocean-continent subduction or continent-continent subduction took place in the western and southern sections, while intra-oceanic subduction occurred in the eastern section.Comprehensive analyses on U-Pb ages and Hf model ages of zircons, the main provenance of the Lengjiaxi Group is Cathaysia.     

湘东北岳阳地区冷家溪群和板溪群凝灰岩 SHRIMP 锆石U-Pb年龄 ——对武陵运动的制约

对冷家溪群及其上覆板溪群斑脱岩中的锆石进行研究,测得冷家溪群小木平组斑脱岩SHRIMP锆石U-Pb年龄(822Ma±10Ma)和上覆板溪群张家湾组斑脱岩锆石U-Pb年龄(802.6Ma±7.6Ma),结合“江南造山带”东部变质基底双桥山群和西南地区四堡群、下江群的SHRIMP锆石U-Pb年龄,将冷家溪群与其相应的江南古陆变质地层明确定位于新元古界。该年龄对重新界定“武陵运动”的时限和进行同期地层的区域对比、构造演化研究都有重要意义。冷家溪群与双桥山群、梵净山群、四堡群、双溪坞群一样,均为低变质绿片岩系,构成了江南古陆地区的变质基底。多年来冷家溪群一直划归中元古界,并且视为“武陵运动”的主体,其时代的定位将影响整个江南古陆变质基底的地层划分和对比,也将制约江南造山带的地质背景和成矿条件解疑。上述锆石U-Pb年龄不仅标示了湘东地区新元古代地层的时代,也为江南古陆中部变质基底提供了新的、精确的年代学数据。     

庐山筲箕洼组与星子岩群年代地层关系及SHRIMP锆石U-Pb年龄的制约

本文报道在庐山筲箕洼组中获得细碧岩SHIRMP锆石U-Pb年龄(840±6) Ma,MSWD=1.3,流纹岩锆石U-Pb年龄(833±4) Ma,MSWD=1.4,和流纹岩锆石U-Pb年龄(831±3) Ma,对应的MSWD=1.47.而在星子群流纹岩中获得206pb/238U年龄为(825±5)Ma,对应的MSWD=0.46.笔者依据上述精确锆石年龄,首次提出将筲箕洼组明确定位于星子岩群之下.本文结合“江南造山带”锆石U-Pb年龄:东部变质基底的双桥山群,西部变质基底梵净山群和似盖层下江群以及中部变质基底冷家溪群和似盖层板溪群的锆石SHRIMP U-Pb年龄,将筲箕洼组定位于“武陵运动”之下的新元古代地层.依据星子岩群年龄数据,首次将星子岩群明确定位于筲箕洼组之上与双桥山群为同期的深变质岩.该年龄对限定区域地层对比和构造演化都有着重要意义.上述锆石U-Pb年龄标示了赣西北地区同样存在820 Ma界面上下的新元古代地层,为江南古陆变质地层的对比提供了新的年代学数据.     

Time constraints on the closure of the Paleo–South China Ocean and the Neoproterozoic assembly of the Yangtze and Cathaysia blocks: Insight from new detrital zircon analyses

The South China Block was built up by the assembly of the Yangtze and Cathaysia blocks along the Neoproterozoic Jiangnan Orogenic Belt. The timing of the Jiangnan Orogeny remains controversial. The widespread orogeny–related Neoproterozoic angular unconformity that separates the underlying folded Sibao (ca.1000–820 Ma) and overlying Danzhou (ca.800–720 Ma) Groups was investigated. Six sedimentary samples, below and above the unconformity in three distal localities (Fanjingshan, Madiyi, and Sibao) yield detrital zircon with UPb ages ranging from 779 ± 16 Ma to 3006 ± 36 Ma, with a prominent peak at ca. 852 Ma. The youngest ages of 832 ± 11 Ma and 779 ± 16 Ma are revealed for the underlying Sibao and overlying Danzhou Groups, respectively. The detrital zircon UPb age relative probability plot of the Jiangnan Orogen matches well with those of the Yangtze and Cathaysia blocks since ca. 865 Ma. Integrating geological, geochemical and geochronological results, we suggest that the Paleo–South China Ocean began to subduct under the Yangtze block at ca. 1000 Ma, and was partly closed at ca. 865 Ma. Afterwards, the Yangtze and Cathaysia blocks initially collide at 865 Ma, forming the Jiangnan Orogen. This collision resulted in not only the folding of the Sibao Group, but also sediment deposition in a syn-collisional setting, which makes the upper part of the Sibao Group. The youngest S-type granite dated at ca. 820 Ma that intruded in the Sibao Group marks the late stage of the Jiangnan Orogeny.     

Qingbaikouan and Crygenian in South China: Constraints by SHRIMP Zircon U-Pb dating

The Qingbaikouan System is the lowest unit of the Neoproterozoic Erathem in Chinese stratigraphic succession,and it now provides a precise geochronological framework and geological time scale for mapping and stratal correlation in China.However,a sensitive high-resolution ion microprobe （SHRIMP） U-Pb zircon age date （1368±12 Ma） obtained from a bentonite in the Qingbaikouan Xiamaling Formation indicates that it belongs to the Mesoproterozoic Erathem instead.This change is a milestone in understanding the Precambrian Stratigraphic Time Scale in China,and it has had great influence on Precambrian correlations in Asia.Otherwise,a large amount of geochronological work has been done in the ＂Jiangnan Orogen Belt＂ of South China,and new isotopic data have redefined the traditional recognition of metamorphosed Mesoproterozoic strata from the Sibao orogeny to the Neoproterozoic Erathem.Based on SHRIMP zircon U-Pb age data,the authors regard the Sibao orogeny （equal to the Wuling orogeny） as a movement at ca 820 Ma,meaning that the Sibao orogeny was not equivalent to the Grenvillian orogeny.Finally,we report here the first SHRIMP U-Pb age of the boundary between the top of the Qingbaikouan Gongdong Formation （786.8±5.6 Ma） and the bottom of the Chang＇an （diamictite） Formation （778.4±5.2 Ma）,which is the age of the lowest diamictite of the Nanhuan System in China.     

湘东北岳阳地区冷家溪群和板溪群凝灰岩SHRIMP锆石U-Pb年龄——对武陵运动的制约

对冷家溪群及其上覆板溪群斑脱岩中的锆石进行研究,测得冷家溪群小木平组斑脱岩SHRIMP锆石U-Pb年龄（822Ma±10Ma）和上覆板溪群张家湾组斑脱岩锆石U-Pb年龄（802.6Ma±7.6Ma）,结合＂江南造山带＂东部变质基底双桥山群和西南地区四堡群、下江群的SHRIMP锆石U-Pb年龄,将冷家溪群与其相应的江南古陆变质地层明确定位于新元古界。该年龄对重新界定＂武陵运动＂的时限和进行同期地层的区域对比、构造演化研究都有重要意义。冷家溪群与双桥山群、梵净山群、四堡群、双溪坞群一样,均为低变质绿片岩系,构成了江南古陆地区的变质基底。多年来冷家溪群一直划归中元古界,并且视为＂武陵运动＂的主体,其时代的定位将影响整个江南古陆变质基底的地层划分和对比,也将制约江南造山带的地质背景和成矿条件解疑。上述锆石U-Pb年龄不仅标示了湘东地区新元古代地层的时代,也为江南古陆中部变质基底提供了新的、精确的年代学数据。     

早古生代阿拉善地块与华北地块之间的关系:来自阿拉善东缘中奥陶统碎屑锆石的信息

阿拉善东缘奥陶纪地层位于鄂尔多斯(华北地块)与北祁连早古生代造山带之间的过渡地区,该区的构造背景一直是长期争论的问题,它涉及到阿拉善地块是否与华北地块相连、奥陶系的物源以及"贺兰拗拉槽"是否存在等问题。分布于阿拉善地块东缘的中奥陶统米钵山组的碎屑锆石LA-ICP-MSU-Pb年龄测试表明,样品中数量最多的锆石年龄为900～950Ma,Alxa-1的峰值年龄为916Ma,Alxa-2的峰值年龄为953Ma,次者在494～623Ma之间,这个区间内存在多个峰值,如Alxa-1存在505Ma和588Ma两个主要峰值,Alxa-2则存在494Ma、517Ma、623Ma等几个峰值。在2.5Ga左右两个样品都存在一个弱的峰值,Alxa-1峰值为2517Ma,而Alxa-2峰值为2552Ma和2670Ma。除此之外,两个样品都有个别大于3.0Ga的成分,Alxa-1样品中最年轻的锆石为451±8Ma,Alxa-2样品则为483±4Ma。这些年龄以及沉积特征表明:(1)传统认为的奥陶纪"贺兰拗拉槽"并不存在,鄂尔多斯西南缘地区以及阿拉善东部地区当时属于北祁连早古生代周缘前陆盆地系统;(2)早古生代主要物源来自北祁连造山带,新元古代物源来自阿拉善地块;(3)鄂尔多斯西缘整个米钵山组的锆石年龄分布及其变化,指示出北祁连造山带(岛弧)逐渐靠近阿拉善地块,其间洋盆逐渐消失的过程;(4)阿拉善地块基底与华北有明显差别,阿拉善地块明显受到新元古代和古生代构造热事件的影响,两者可能是在中奥陶世或之后才拼贴在一起。     

浙西地区新元古代骆家门组SHRIMP锆石U-Pb 年龄及其地质意义

对河上镇群底部骆家门组2个凝灰岩样品进行锆石测年,得到的2组SHRIMP 锆石U-Pb年龄分别为824±5Ma和832±6Ma、791±15Ma。同时,对骆家门组底部花岗岩砾石中的锆石进行了测试,获得的SHRIMP 锆石U-Pb年龄为901±9Ma。由此进一步约束了骆家门组的形成时代。骆家门组年龄的标定对于浙江地区神功运动界面上、下地层双溪坞群和河上镇群年龄的完善,进而确定江南造山带的地层格架和地层对比具有重要意义。这些地层年龄和已经获得的角度不整合于骆家门组之下双溪坞群的年龄数据,为神功运动时限的约束和对比提供了重要依据。     

黔东南—桂北地区四堡群凝灰岩锆石SHRIMP U-Pb年龄及其地层学意义

首次获得黔桂地区晚前寒武纪四堡群凝灰岩(斑脱岩)锆石SHRIMP U-Pb年龄,结合新获得的侵位于四堡群的花岗岩锆石SHRIMP U-Pb年龄,将四堡群明确定位于新元古界。"江南造山带"普遍发育的新元古代四堡群(梵净山群、冷家溪群、双桥山群)和上覆的丹州群(下江群、板溪群、河上镇群)均为低变质绿片岩系,构成了江南古陆的变质基底。多年来四堡群一直划归中元古界,并且构成"四堡运动"的主体,其时代的定位一直影响着整个江南古陆变质基底的地层划分和对比,也制约着中国地质学家对江南造山带的地质背景和成矿条件解疑。通过对四堡群及其上覆地层中斑脱岩锆石的研究,精确地测定并获得了四堡群斑脱岩锆石的年龄841.7Ma±5.9Ma和黔东南摩天岭地区侵入四堡群的花岗岩锆石的年龄826.8Ma±5.9Ma。     

Re–Os and U–Pb Geochronology of Porphyry and Skarn Types Copper Deposits in Jilin Province,NE China

Jilin Province in NE China lies on the eastern edge of the Xing–Meng Orogenic Belt. Mineral exploration in this area has resulted in the discovery of numerous large, medium, and small sized Cu, Mo, Au, and Co deposits. To better understand the formation and distribution of both the porphyry and skarn types Cu deposits of the region, we examined the geological characteristics of the deposits and applied zircon U–Pb and molybdenite Re–Os isotope dating to constrain the age of the mineralization. The Binghugou Cu deposit yields a zircon U–Pb age for quartz diorite of 128.1 ± 1.6 Ma; the Chang'anpu Cu deposit yields a zircon U–Pb age for granite porphyry of 117.0 ± 1.4 Ma; the Ermi Cu deposit yields a zircon U–Pb age for granite porphyry of 96.8 ± 1.1 Ma; the Tongshan Cu deposit yields molybdenite Re–Os model ages of 128.7 to 130.2 Ma, an isochron age of 129.0 ± 1.6 Ma, and a weighted mean model age of 129.2 ± 0.7 Ma; and the Tianhexing Cu deposit yields molybdenite Re–Os model ages of 113.9 to 115.2 Ma, an isochron age of 114.7 ± 1.2 Ma, and a weighted mean model age of 114.7 ± 0.7 Ma. The new ages, combined with existing geochronology data, show that intense porphyry and skarn types Cu mineralization was coeval with Cretaceous magmatism. The geotectonic processes responsible for the genesis of the Cu mineralization were probably related to lithospheric thinning. By analyzing the accumulated molybdenite Re–Os, zircon U–Pb, and Ar–Ar ages for NE China, it is concluded that the Cu deposits formed during multiple events coinciding with periods of magmatic activity. We have identified five phases of mineralization: early Paleozoic (~476 Ma), late Paleozoic (286.5–273.6 Ma), early Mesozoic (~228.7 Ma), Jurassic (194.8–137.1 Ma), and Cretaceous (131.2–96.8 Ma). Although Cu deposits formed during each phase, most of the Cu mineralization occurred during the Cretaceous.     

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.     

江南隆起带中段新元古代花岗岩锆石U-Pb年代学和Hf同位素组成研究

对江南隆起带中段湘东西园坑岩体和赣西九岭岩体的LA-ICPMS锆石U-Pb年代学测定和LA-MC-ICPMS锆石Hf同位素原位分析测试表明:西园坑岩体形成于(804±3)Ma,赣西九岭岩体的年龄为(813±4)Ma和(823±2)Ma,均为新元古代花岗岩.上述三个样品的εHf(t)的加权平均值分别为0.68±0.71,...     

Thermochronology of Mesozoic Sandstone from the Beipiao Basin and Its Implication to Meso-Cenozoic Tectonic Evolution of the Eastern Yan-Liao Orogenic Belt

1 IntroductionThe Yan-Liao orogenic belt lies in the northern segmentof the North China Block (NCB) (Fig. 1). During Mesozoicto Cenozoic time, it experienced intense tectono-magmaticactivation, accompanied by the formation ofintracontinental basins and widespread magmatism and is avery important area to study continental dynamics andMeso-Cenozoic tectonic evolution in eastern China. Mostof previous work in this area has focused on the formationof basement, structural style and volcano-se…     

滇中新元古代澄江组层型剖面锆石U-Pb年代学及其地质意义

澄江组是华南新元古代地层中的重要地层单元之一,其确切沉积时限对于建立和完善华南新元古代区域地层格架具有关键意义。对滇中澄江组层型剖面顶部的凝灰岩夹层进行高精度SHRIMP锆石U-Pb定年研究,获得3组有效的206Pb/238U加权平均年龄值,其分别为(819±14)Ma(MSWD=0.15)、(781±11)Ma(MSWD=0.24)和(725±11)Ma(MSWD=0.65)。其中,最年轻的一组年龄值(725±11)Ma被解释为澄江组顶部凝灰岩夹层的形成时间,可以代表滇中澄江组的顶界年龄,从而进一步确认澄江组的沉积时限为800～725 Ma。结合相关研究资料,证实澄江组与开建桥组、莲沱组的沉积时限基本相当,三者与下冰期长安组不存在对比关系,而应与冰期前板溪群的上部进行对比。此外,推测两组年龄值较老的锆石可能是与新元古代罗迪尼亚(Rodinia)超大陆裂解有关的幕式岩浆活动的记录。     

Attribution of the Langshan Tectonic Belt: Evidence from zircon U-Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.     

贵州梵净山白云母花岗岩锆石年代、铪同位素及对华南地壳生长的制约

贵州梵净山地区位于＂江南造山带＂西南段,出露地层为中新元古界梵净山群、青白口系板溪群、南华系及古生界地层。梵净山群已强烈褶皱,被青白口系板溪群角度不整合覆盖。浅色白云母花岗岩侵位于褶皱的梵净山群中;锆石原位LA-ICP-MS分析结果显示,其形成时代为（838.5±1.5）Ma。地球化学分析结果表明,其A/CNK值〉1....     

江山—绍兴断裂带陈蔡岩群片麻岩SHRIMP锆石U-Pb年龄及其地质意义

浙江诸暨陈蔡地区发育一套副变质岩层,由中深度变质的片麻岩、片岩和大理岩组成,与双溪坞群为断层接触,其地质时代多被视为与江山—绍兴断裂带南东侧的华夏地块古老变质基底相同。陈蔡岩群地处江绍断裂带北东端,变质和变形较深,前人将其划归为华夏古陆的小块体,地层时代曾与福建古元古代麻源岩群或浙江八都岩群和江西中元古代铁砂街组对比。在陈蔡岩群下吴宅组含榴夕线黑云斜长片麻岩及含榴黑云斜长片麻岩中获得大量的锆石,具有典型的核、幔、边结构,核部年龄集中在新元古代,206Pb/238U年龄加权平均值为848±10Ma和845±9Ma,锆石后期增生边部年龄多为加里东期的年龄,206Pb/238U年龄加权平均值为431.4±7.8Ma。陈蔡岩群斜长片麻岩获得的锆石核部较单一的U-Pb年龄,反映出陈蔡岩群下吴宅组夕线石所代表的泥质成分所含的锆石单一,其锆石核部年龄应代表陈蔡岩群下吴宅组的原岩年龄;同时,认为陈蔡岩群既不能与福建古元古代的麻源岩群对比,也不能与江西地区中元古代铁砂街组对比。其原岩为稍晚于双溪坞群(905~877Ma)的新元古代地层(848~845Ma),从年代上倾向于江南造山带范畴。该年龄对江山—绍兴断裂带变质地层的区域对比和构造演化有重要意义。     

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.     

Proterozoic geology and regional correlation of the Ghanzi-Makunda area,western Botswana

The Ghanzi-Makunda area exposes three main Proterozoic assemblages. The oldest rocks belong to the Palaeoproterozoic (Eburnian) Okwa Basement Complex, which consists of porphyritic rhyolitic felsite and granitoids emplaced at 2055±4 Ma. A volcanic sequence named the Kgwebe volcanic complex consists of metarhyolites and metabasalts with interbedded tuff and agglomerate. These metavolcanic rocks represent a bimodal suite of continental tholeiites and high K rhyolites linked to the evolution of the Mesoproterozoic Kibaran orogenic system. Siliciclastic and carbonate rock successions of the Neoproterozoic to early Palaeozoic Ghanzi-Chobe Belt unconformably overlie the Mesoproterozoic Kgwebe volcanic complex. The Ghanzi-Chobe Supergroup comprises the Ghanzi Group and the Okwa Group. In Namibia, felsic lavas with UPb zircon ages of ca 750 Ma occur at the top of lithological units correlated to the Ghanzi Group. The deposition of the Ghanzi Group occured after 1020 Ma and before 750 Ma. In the Okwa Group, detrital zircons extracted from Neoproterozoic sedimentary rocks of the Takatswaane Formation yielded the following dates: 1887±14 Ma, 1246±4 Ma, 1054±5 Ma, 627±6 Ma and 579±12 Ma. The age of 579 ± 12 Ma is considered to represent the maximum depositional age of the Okwa Group. Based on the data in this paper, as well as lithological similarities, the Ghanzi Group is correlated with the Nosib Group of the Damara Belt, while the Okwa Group is correlated with the Nama Group in Namibia.     

北山造山带花牛山岛弧东段钨矿床成矿时代和成矿动力学过程

北山造山带位于中亚造山带最南缘,为多期岛弧、蛇绿混杂岩拼贴而成的增生型造山带;晚古生代,北山造山带的构造活动引发强烈的花岗质岩浆活动,伴随有广泛的钨(钼)成矿作用;本文对北山南带花牛山岛弧三个典型含钨花岗岩体:盘陀山、鹰嘴红山及玉山岩体进行详细的锆石U-Pb年代学、全岩地球化学研究。SIMS锆石U-Pb定年结果表明该区成矿花岗岩分为两个侵入期次:(1)晚志留世月牙山-洗肠井蛇绿混杂岩南段出露花岗岩,其中,盘陀山二长花岗岩422.0±1.5Ma;盘陀山钾长花岗岩417.0±1.7Ma;鹰咀红山钾长花岗岩424.0±1.3Ma;(2)晚二叠世柳园蛇绿混杂带北侧玉山花岗岩体,定年结果为280.8±3.0Ma。岩石地球化学研究表明盘陀山-鹰嘴红山花岗岩带为过铝质S型花岗岩,玉山岩体为A型花岗岩。岩体稀土含量较高,具右倾型稀土配分模式,LREE分异强烈,HREE分异不明显,样品Eu亏损强烈。原始地幔标准化蛛网图中总体显示较为一致的分布模式,大离子亲石元素Ba、Sr呈现明显负异常,富集Th、U、Pb、Zr、Hf等元素而亏损高场强元素Ta、Nb、Ti、P。结合晚古生代北山构造演化过程,推断国庆-鹰嘴红山钨矿为公婆泉岛弧与花牛山岛弧碰撞阶段形成,而玉山钨矿床为晚华力西期弧后伸展构造背景的产物。