Determination of Early Paleozoic metamorphic event in the Longshan Complex and its geological implicationSCIEI北大核心CSCD

长期以来,陇山杂岩的归属问题一直存在争议。本文对出露于秦岭-祁连山结合部位的陇山杂岩中石榴黑云斜长片麻岩和石榴斜长角闪岩进行了详细的岩石学、P-T温压计算、独居石和榍石U-Pb年代学研究。通过详细的岩相学观察,石榴黑云斜长片麻岩的变质峰期矿物组合为石榴子石+黑云母+斜长石+石英;石榴斜长角闪岩中则识别出了以石榴子石+单斜辉石+角闪石+斜长石+石英为峰期的变质矿物组合。通过传统温压计计算,石榴黑云斜长片麻岩(样品21LS40)和石榴斜长角闪岩样品(样品21LS42-1)的峰期变质P-T条件分别为700℃、0.72GPa和710℃、0.74GPa。激光剥蚀电感耦合等离子体质谱(LA-ICP-MS) U-Pb数据表明,石榴黑云斜长片麻岩中独居石的206Pb/238U的加权平均年龄为407~435Ma。石榴斜长角闪岩中榍石的下交点年龄分别为410±7Ma、409±5Ma和426±10Ma,榍石中Zr含量温度计的计算结果分别为750℃、751℃和748℃(假定压力为0.7GPa)。本文从变质作用的角度出发,将陇山杂岩与秦岭杂岩进行温压条件和变质时代对比研究,认为陇山杂岩与东秦岭杂岩高压-超高压岩石的最后一期退变质作用和西秦岭天水地区的秦岭杂岩麻粒岩相变质作用类似,可能为北秦岭造山带的西延。     

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。     

Discovery of scandium enrichment and its geological significance in the Dawanshan Neoproterozoic metamorphic basalts from the Mouding area in Central Yunnan Province,ChinaSCIEI北大核心CSCD

钪(Sc)是世界各国竞相争夺的关键金属矿产资源之一。滇中牟定大弯山变质玄武岩厚度>36.5m,出露面积0.5km^(2),形成时代为新元古代南华纪(781.3±1.9Ma)。本文对该变质玄武岩开展了全岩地球化学分析、全自动矿物分析(TESCAN TIMA)观测、NPPM薄片区域面扫和单矿物原位LA-ICPMS分析等研究,结果显示变质玄武岩全岩Sc含量为47.0×10^(-6)~97.9×10^(-6),平均含量为69.1×10^(-6),钪氧化物(Sc_(2)O_(3))平均含量为106×10^(-6),变质玄武岩空间Sc矿化特征稳定,具有形成钪矿资源的潜力。同时,变质玄武岩共伴生有钛和铁矿化,全岩TiO_(2)含量为2.57×10^(-2)~6.13×10^(-2),平均为4.25×10^(-2);TFe含量为13.3×10^(-2)~23.7×10^(-2),平均为17.7×10^(-2)。Sc可能存在类质同象和离子相两种赋存形式,类质同象形式Sc主要赋存于钛铁矿和金红石矿物中,钛铁矿中Sc含量为70.0×10^(-6)~168×10^(-6),平均值为108×10^(-6);金红石中Sc含量高达297×10^(-6);而磁铁矿、黑云母等矿物中Sc含量较低,均低于全岩Sc含量,对全岩Sc矿化贡献较小。牟定大弯山Sc矿化与以往报道侵入岩及其风化壳中Sc矿化在富集特征、赋存岩性和载体矿物等方面不同,是变质火山岩中新发现的Sc矿化信息,显示了较好的找矿潜力,对Sc资源勘查和研究具有重要指示意义。     

Late Cretaceous arc magma differentiation in southern Tibet: Evidence from zircon U-Pb chronology,mineralogy and geochemistrySCIEI北大核心CSCD

造山带岩浆作用记录了从大洋俯冲消减到陆陆碰撞的一系列地质过程,同时也蕴含了关于大陆地壳生成、生长的重要信息,其中,与俯冲相关的弧岩浆作用被认为是大陆地壳生长的主要机制。本文通过对西藏南部拉萨地体曲水县至贡嘎县一带出露的黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩开展同位素年代学、矿物学和岩石地球化学研究,探讨了该岩石组合的成因和弧岩浆的分异演化过程。锆石U-Pb定年结果表明,这些岩石的形成时代为91~88Ma。其中,黑云母二长花岗岩属中钾钙碱性偏铝质岩石系列(A/CNK=0.77~0.99),具高SiO 2(68.90%~69.18%)和Al_(2)O_(3)(15.21%~15.48%),低MgO(1.15%~1.16%)和Mg#值(~44),高Sr/Y比值(60~82),其地球化学特征与埃达克质岩石相似;镁铁质微粒包体的SiO 2含量为54.75%~54.96%,具有较高MgO含量(3.92%~5.40%)和Mg#值(52~61),并具弱的负Eu异常(δEu=0.79~0.82)。石英闪长岩为中钾钙碱性偏铝质岩石(A/CNK=0.84~0.88),其SiO 2含量为58.55%~63.32%,具有较高的Mg#值(44~48)和弱的负Eu异常(δEu=0.68~0.81)。另外,所有黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩样品的Sr-Nd同位素和锆石εHf(t)值相近((87 Sr/86 Sr)i=0.703594~0.703939,εNd(t)=+4.6~+4.8,εHf(t)=+10.9~+15.6)。矿物成分分析表明,黑云母二长花岗岩和镁铁质微粒包体中发育环带的斜长石An值由中心向边部逐渐下降,未发育反环带结构;石英闪长岩中的辉石为单斜辉石,所分析角闪石均为钙质角闪石,黑云母为镁质黑云母。综合上述特征,本文认为黑云母二长花岗岩、镁铁质微粒包体以及同生石英闪长岩分别代表了源自亏损地幔的母岩浆通过分离结晶作用所派生的不同阶段的产物:其中,石英闪长岩最先由基性岩浆发生以辉石、Ti-Fe氧化物和磷灰石为主的分离结晶作用形成,继而作为母岩浆进一步分异演化;镁铁质微粒包体是岩浆早期结晶的堆晶产物;而黑云母二长花岗岩代表了包体形成后残余熔体的组分。本文的研究表明,冈底斯岩浆岩带晚白垩世发生了富水条件下的岩浆分离结晶和堆晶作用,俯冲带弧岩浆分异对于大陆地壳的形成和演化发挥着重要的作用。     

Geochemical characteristics and LA-ICP-MS zircon U-Pb age of the Lanhualing granite in Ningguo,Anhui ProvinceEI北大核心CSCD

The Lanhualing tungsten-molybdenum deposit is a skarn-type deposit located in Ningguo county, Anhui province. This deposit is mainly hosted in the Yinzhubu Formation and the Yanwashan Formation of Ordovician, and genetically related to the Lanhualing granite. The Lanhualing granite belongs to high-K calc-alkaline series with high alkali (Na2O+K2O=4.00%-7.03%), SiO2 (67.87%-74.92%) and MgO (0.62%-1.23%) contents. The granitic rocks show right-dipping chondrite normalized REE patterns with weak δEu anomalies. The granitic rocks are relatively enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). The ore-bearing granite was dated at 148.17±0.94 Ma by LA-ICP-MS zircon U-Pb method. The late Yanshanian is the main tungsten mineralization epoch in the South Anhui-north Jiangxi area; and indeed, the Dongyuan, Zhuxi, Yangchuling, Dahutang and other large and super-large tungsten deposits were formed in this period. Geochemical Characteristics of the Lanhualing granite indicate a crustal source but with mantle input under tectonic regime of compression thickening. ©, 2015, Science Press. All right reserved.     

Crustal stabilization:Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex,Singhbhum Craton,India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons.The understanding of how and where this process took place is significant to evaluate the architecture of continents.The Singhbhum Craton of eastern India has well preserved Precambrian volcanosedimentary sequences.The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/shales/phyllites.In the present study,we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton.The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix.Based on modal compositions and major element ratios,these quartzites are categorized as quartz arenite and sub-lithic arenites.Trace element abundances normalized to Archean Upper Continental Crust(AUCC)display positive anomalies at U,Zr,Hf and negative anomalies at Nb.REE patterns are characterized by negative Eu anomalies(Eu/Eu^*=0.47–0.97)and flat HREE suggesting felsic provenance.These quartzites show depletion of LILE,enrichment of HFSE and transition metals relative to AUCC.High weathering indices such as CIA,PIA,and ICV are suggestive of moderate to intense chemical weathering.Low trace element ratios such as Th/Cr,Th/Sc,La/Sc,La/Co and Th/Co indicate a predominantly felsic source for these rocks.The overall geochemical signatures indicate passive margin deposition for these quartzites.Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156±31 Ma suggesting Mesoarchean crustal heritage.The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton.These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite(SBG-III)provenance for these quartzites,thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.     

Zircon U-Pb geochronology of Early Jurassic-Late cretaceous volcanic rocks in North Yellow Sea BasinEI北大核心CSCD

The X-drilling cores of the North Yellow Sea basin reveal two sets of Mesozoic clastic rocks, which are the dark rocks in lower part and the red rocks in upper part, respectively. There are two layers of volcanic rocks at the bottom and the upper part of the dark rock unit. The volcanic rocks at the bottom part are trachytic dacite while rocks at the upper part are clastic dacite. The zircon grains from the upper and lower units of volcanic rocks are euhedral-subhedral columnar crystals and show oscillatory zoning on cathodoluminescence images. 22 tests of zircons in the trachytic dacite from the bottom part yield an age of 141-151 Ma, with weighted mean 206Pb/238U age of 145±2 Ma. Whereas 18 tests of zircons from the sample at the upper part give 206Pb/238U ages around 139-149 Ma with weighted mean 206Pb/238U age of 141±2 Ma, which implies that the X well volcanic rocks belong to Late Jurassic-Early Cretaceous. Comparing with the age and geochemical characteristics of the Mesozoic igneous rocks in Shandong peninsula, we suggest that the igneous rocks from both the North Yellow Sea basin and Jiaolai basin were formed under same dynamic setting, i.e., the subduction related volcano arc and back-arc extension. ©, 2015, Science Press. All right reserved.     

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.     

Evolution of the eastern segment of the northern margin of the North China Craton in the Triassic: Evidence from the geochronology and geochemistry of magmatic rocks in Kaiyuan area,North LiaoningSCIEI北大核心CSCD

To constrain the evolution of the eastern segment of the Paleo-Asian Ocean (PAO), petrography, geochemistry and zircon U-Pb dating analyses were conducted over the gabbro and rhyolite in the Kaiyuan area, North Liaoning, in the eastern segment of the northern margin of the North China Craton (NCC). Zircon dating results indicate that the gabbros and rhyolite were formed in the Trassic (246 +/- 2Ma, 241 +/- 2Ma, 226 +/- 3Ma and 241 +/- 2Ma). The three gabbros of Triassic have similar geochemical characteristics, originated from the mantle, and were contaminated by crust materials in the process of ascending and emplacement. The Early Triassic gabbro (246Ma) originated from the enriched mantle source metasomatized by fluid. It was formed by 1% partial melting of garnet spinel lherzolite in the extensional environment caused by breaking off slab. The Middle Triassic gabbro (241Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 1% to 2% partial melting of garnet spinel peridotite. The Late Triassic gabbro (226Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 3% similar to 4% partial melting of garnet spinel lherzolite in the post-orogenic extensional environment. The Middle Triassic rhyolite (241Ma) has the characteristic of post collisional I-type granite, that enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements, and negative Nb, Ti, P and Sr anomaly. The low content of Sr and Yb suggested a 30 similar to 40km depth source. The Middle Trassic "bimodal" igneous rocks implied an extensional environment caused by the remainder oceanic crust breaked away at the bottom of the crust. Based on the lithologic association, regional strata information and the chronological data in this paper and published by predecessors, the Triassic magmatism in the eastern segment of the northern margin of the NCC can be divided into five stages: 252 similar to 246Ma, 246 similar to 242Ma, 242 similar to 240Ma, 240 similar to 230Ma and 230 similar to 215Ma. These five magmatic events were the results of the southward subduction and extinction of the PAO: (1) The transformation from active continental margin to syn-collisional setting resulted in the final closure of the PAO (252 similar to 246 Ma); (2) Continuous pushing resulted in orogenic uplift (246 similar to 242Ma); (3) Extension caused by the detachment of the remainder subduction oceanic crust at the bottom of the crust (242 similar to 240Ma); (4) Rapid uplift and crustal thickening (240 similar to 230Ma); (5) Extension of post-orogenic(230 similar to 215Ma).     

Timing of high-pressure metamorphic events in the Bulgarian Rhodopes from Lu–Hf garnet geochronology

Within the Mediterranean realm, the Rhodopes represent a nappe stack of oceanic and continental fragments assembled along the Eurasian continental margin during the Alpine orogeny. The timing of the high-pressure (HP) metamorphism has long been ambiguous, lacking detailed geochronological and geochemical control on subduction-exhumation and nappe stacking processes. Here we apply the Lu–Hf and Sm–Nd chronometers to a suite of representative eclogite samples covering two different key units of the Rhodopean nappe stack: (1) the Kimi Complex (Upper Allochthon) and (2) the Middle Allochthon. In addition to geochronology, we also determined whole rock Hf and Nd isotope compositions as well as major and trace element concentrations in order to constrain the nature of the eclogite protoliths. Two HP metamorphic events were revealed by Lu–Hf geochronology: (1) a Lower Cretaceous event in the Upper Allochthon (126.0 ± 1.7 Ma) and (2) an Eocene event in the Middle Allochthon (44.6 ± 0.7 Ma; 43.5 ± 0.4 Ma; 42.8 ± 0.5 Ma), at conditions of ca. 700°C/20–25 kbar. Our new data provide direct evidence for multiple subduction events in the Rhodopes. Exhumation and subsequent thrusting of the Middle Allochthon on the Lower Allochthon can be narrowed down to the time span between 42 and 34 Ma. In a broader tectonic context, the Eocene ages for the HP metamorphism support the view that the Rhodopes represent a large-scale tectonic window, exposing the deepest nappe units of the Hellenides.     

Formation Time of the Kalaqin Metamorphic Core Complex: Constraints from Zircon DatingEI北大核心CSCD

The Kalaqin metamorphic core complex, located on the northern margin of the Yanshan Tectonic Belt, is an important structure to understand the Late Mesozoic destruction processes of the North China Craton. In this study, structural analysis and geochronological investigation were conducted for the Anjiayingzi pluton and associated granodiorite dikes that intruded the core complex. Field observations demonstrated that emplacement of the pluton and dikes took place after the early stage extensional deformation, and intrusions are products of syn-tectonic magmatism during the late stage extension deformation. LA-ICP-MS zircon U-Pb dating yielded ages of 133-131 Ma for the Anjiayingzi pluton and 135 Ma for the dike, which demonstrated that the early extensional deformation took place at 156-135 Ma, rather than the Early Cretaceous as proposed previously. By integrating with other dating results, the early extensional deformation occurred at 156-150 Ma (Late Jurassic) and led to the exhumation of the core complex. The core complex was overprinted by a late extension in the Early Cretaceous. The revision of formation time for the Kalaqin metamorphic core complex further confirms that the extensional deformation took place in the Late Jurassic in the Yanshan tectonic belt, and therefore, it is likely that the northern margin of the North China Craton might have destructed since the Late Jurassic. © 2018, Science Press. All right reserved.     

Magmatic and metamorphic history of the Deh-Salm metamorphic Complex, Eastern Lut block, (Eastern Iran), from U–Pb geochronology

The Deh-Salm metamorphic Complex (DMC) of the Lut block in East Iran consists of metapelites, amphibolites, marbles, and metasandstones intruded by granite and pegmatites. U–Pb dating of zircon, monazite, xenotime, and titanite by ID-TIMS show that the granitic rocks were emplaced at 166–163 Ma, confirming that the high temperature metamorphism was synchronous with the intrusive activity, and that the region cooled rapidly thereafter. Late- to post-magmatic hydrothermal activity was probably responsible for the late crystallization, at 159.5 Ma, of zircon and titanite in an amphibolite and of monazite in granite. Xenocrystic zircons yield indications for a Carboniferous component in the source, together with a variety of Precambrian ages, which indicate a provenance of the sedimentary protolith from mature continental crust. The timing and rapidity of the events are consistent with evolution of the DMC in a back-arc environment during the Jurassic subduction of the Neotethys Ocean.     

Contribution of SHRIMP U–Pb zircon geochronology to unravelling the evolution of Brazilian Neoproterozoic fold belts

The South-American continent is constituted of three major geologic–geotectonic entities: the homonym platform (consolidated at the end of the Cambrian), the Andean chain (essentially Meso-Cenozoic) and the Patagonian terrains, affected by tectonism and magmatism through almost all of the Phanerozoic. The platform is constituted by a series of cratonic nuclei (pre-Tonian, fragments of the Rodinia fission) surrounded by a complex fabric of Neoproterozoic structural provinces.     

Evidences from zircon U-Pb geochronology,whole -rock geochemistry and Hf isotope of Early Cretaceous magmatic rocks in Baishan area,southern Jilin Province: Constraints on destruction of the North China CratonSCIEI北大核心CSCD

This paper reports new geochemical data including zircon U-Pb ages with Hf isotopic data, whole -rock major and trace isotopic compositions for the Early Cretaceous magmatic rocks in the northeastern North China Craton ( NCC), with the purpose of constraining its petrogenesis and tectonic setting. It also provides a basis for further discussion on the formation and evolution of the lithosphere in the northeastern NCC during the Late Mesozoic. Zircons in the Xinglin granite porphyry, Hongtuya andesitic crystal tuff and Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff all show magmatic origin. Zircon U-Pb dating yield age are 130 +/- 1Ma, 128 +/- 1Ma and 120 +/- 1Ma, respectively. The Xinglin granite porphyry and the Hongtuya andesitic crystal tuff have high content of SiO2, Al2O3 Sr, high Na2O/K2O, Sr/Y and ( La/Yb)(N) ratios. In addition, they exhibit low Y and Yb. They are enriched in LILE ( e. g., Ba, Th and U), depleted in HFSE ( e. g., Nb, Ti and P) with weak negative Eu anomalies (delta Eu =0. 82 similar to 0. 94), showing they are typical of adakitic rocks. The Xinglin granite porphyry has high content of total -alkali, low content of TiO2, characterized by peraluminous-weakly peraluminous granite A/CNK = 1. 06 similar to 1. 14, the zircon saturated temperature values of 798 similar to 815 degrees C and a distribution pattern of LREE enrichment with incline to the right, which indicates it is I -type granite. The zircon ( t) values in the Xinglin granite porphyry ranged 17. 96 0. 19, and the two -stage model ages yield t(DM2) = 1197 similar to 2313Ma, which imply that the Xinglin granite porphyry is derived from partial melting of the thickened mafic lower crust of Paleoproterozoic to Mesoproterozoic. The zircon epsilon(Hf)( t) values in the Hongtuya andesitic crystal tuff ranged 3. 37 similar to 5. 47, and the two -stage model ages yield t(DM2) = 830 similar to 967Ma, indicating that the Hongtuya andesitic crystal tuff is a metasomatism product of the Neoproterozoic delaminated eclogite lower crust partial melting and mantle peridotite. Combined with the epsilon(Hf)( t) values in the Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff ranged 2. 69 1. 00, and the two -stage model ages yield t(DM2) = 1115 similar to 1349Ma, we conclude that the epsilon(Hf)( t) values of magmatic rocks are heterogeneous in the southern Jilin Province, and the magmatic source area is characterized by multi -component origin, including both ancient crust and juvenile crust. We supposed that there were two accretion evolution events in the continental crust of the northeastern NCC during Proterozoic. Comprehensive studies have shown that subduction and slab roll -back of the Paleo-Pacific plate ( Izanagi) led to the thickened the northeastern NCC being in an extensional tectonic setting during the Early Cretaceous, and the destruction of the northeastern NCC by delamination occurred spatially from west to east. The partial melting of delaminated lower continental crust resulted in a wide distribution of adakitic rocks.     

U-Pb geochronology of Paraná volcanics combined with trace element geochemistry of the zircon crystals and zircon Hf isotope data

The Paraná volcanic province is a window into mantle and crustal processes in the Cretaceous. The variability and complexity of this province can be determined through the study of minerals. An integrated study of zircon from Paraná lavas (one high-Ti basalt, one low-Ti andesite, one high-Ti rhyodacite and one high-Ti andesite sill) was achieved using backscattered electron imaging, sensitive high resolution ion microprobe (SHRIMP-IIe) for U-Pb geochronology, and laser ablation inductively coupled mass spectrometer (LA-ICPMS) to determine the Lu-Hf isotopes and the trace-element compositions. U-Pb-Hf and trace-element data indicate that zircon crystallized from the magma at approximately 134 Ma. This South American large igneous province originated from the mantle and was contaminated by crust either in the mantle or during ascent and crystallization of magma. Contaminant continental crust had Precambrian age. Trace elements point to a new compositional field for zircon, different from other types of provinces. Examination of volcanic zircon improves our understanding of age and contamination of the Paraná volcanics.     

U–Pb geochronology of two discrete Ordovician high-pressure metamorphic events in the Seve Nappe Complex, Scandinavian Caledonides

U–Pb geochronology for eclogites in two different areas of the Seve Nappe Complex (SNC) in Sweden confirms previous indications of discrete Ordovician high-pressure events affecting various parts of the complex. In Norrbotten, just north of the Arctic circle, eclogites from the Ts?kkok and Vaimok Lenses yield identical metamorphic zircon ages of 482 ± 1 Ma. Titanite in a metagabbro from the Vaimok Lens retains an older age of 607 ± 2 Ma, which may date a protolith coeval with mafic dikes in the overlying Sarek Lens; high-U zircon cores in one of the eclogites also indicate a similar age. Farther south, in J?mtland, the Tjeliken eclogite yields a significantly younger metamorphic age of 446 ± 1 Ma. Although they support the age discrepancy between the Norrbotten and J?mtland eclogites, the U–Pb ages of both eclogite suites are ca. 20 m.y. younger than previously reported Sm–Nd ages. The latter may either represent early prograde growth or be spuriously too old due to isotopic disequilibrium. The SNC has traditionally been taken to represent the outermost margin of Baltica, linking the Early Caledonian eclogite–forming events to subduction of Baltica below an offshore arc. Alternatively, the coincidence of these eclogite-forming events with orogenic phases recorded on the Laurentian margin may point to an origin from other regions of the Iapetus Ocean.     

Proto-Tethys ophiolitic mélange in SW Yunnan: Constraints from zircon U-Pb geochronology and geochemistry

An early Paleozoic Proto-Tethys ocean in western Yunnan has long been postulated although no robust geological evidence has been identified.Here we investigated the recently-identified Mayidui and Wanhe ophiolitic melanges in SW Yunnan,which occurs in a N-S trending belt east of the late Paleozoic Changning-Menglian suture zone.The ophiolites consist mainly of meta-basalts(amphibole schists),meta-(cumulate) gabbros and gabbroic diorites,and meta-chert-shale,representing ancient oceanic crust and pelagic and hemipelagic sediments,respectively.Six samples of gabbros and gabbroic diorites from 3 profiles(Mayidui,Kongjiao and Yinchanghe) yielded zircon U-Pb ages between 462±6 Ma and 447±9 Ma,constraining the formation of the Mayidui and Wanhe ophiolites to Middle Ordovician.Gabbros from the Mayidui and Kongjiao profiles share similar geochemical characteristics with affinities to tholeiitic series,and are characterized by depleted to slightly enriched LREEs relative to HREEs with(La/Sm)_N=0.69-1.87,(La/Yb)_N=0.66-4.72).These,along with their predominantly positive wholerock ε_(Nd)(t) and zircon ε_(Hf)(t) values,indicate a MORB-like magma source.By contrast,the meta-mafic rocks from the Yinchanghe profile show significantly enriched LREEs((La/Sm)_N=0.97-3.33,(La/Yb)N=1.19-14.93),as well as positive whole-rock ε_(Nd)(t) and positive to negative zircon ε_(Hf)(t) values,indicating an E-MORB-type mantle source.These geochemical features are consistent with an intra-oceanic setting for the formation of the Mayidui-Wanhe ophiolites.Our data,integrated with available geological evidence,provide robust constraints on the timing and nature of the Mayidui-Wanhe ophiolitic melange,and suggest that the ophiolites represent remnants of the Proto-Tethys Ocean,which opened through separation of the Indochina and Simao blocks from the northern margin of Gondwana before the Early Cambrian,and evolved through to the Silurian.     

Lower Paleozoic detrital zircon U-Pb geochronological characteristics of the Baoshan Block in western Yunnan and its constraints on the Proto-Tethys tectonic evolutionSCIEI北大核心CSCD

滇西保山地块是东特提斯构造域的主要微陆块之一,但对其物源和古地理位置仍存在较大争议。本文通过对保山地块西缘早古生代地层进行碎屑锆石U-Pb定年来约束其物源及古地理位置,并进一步探讨原特提斯洋早古生代构造演化模式。保山地块西缘早古生代地层具有相似的年龄分布模式,主年龄峰期为-0.95Ga、次级年龄峰期为-1.2Ga和-2.5Ga。寒武系公养河群最小锆石年龄为526Ma,结合其上部年龄为499.2Ma的火山岩夹层,约束其沉积时代为早寒武世早期。对比保山地块不同区域早古生代地层的碎屑锆石年龄数据,它们都具有相似的锆石年龄分布模式和年龄峰值。-0.95Ga主年龄峰期和-2.5Ga的次级年龄峰期指示保山地块早古生代的沉积物主要来自于印度大陆,而-1.2Ga的次级年龄峰期表明有部分沉积物来自于西澳大利亚,其早古生代古地理位置位于印度和西澳大利亚之间。结合沉积学证据及滇西地区广泛发育的早古生代岩浆作用,本文认为早古生代冈瓦纳大陆北缘为活动大陆边缘。     

Late Paleozoic subduction–accretion along the southern margin of the North Qinling terrane,central China: Evidence from zircon U-Pb dating and geochemistry of the Wuguan Complex

The Qinling Orogen separating the North China plate from the Yangtze plate is a key area for understanding the timing and process of aggregation between the two plates. Two competing and highly contrasting tectonic models currently exist to explain the timing and nature of collision; one advocates a Devonian continental collision while the other favors a Triassic collision. The Wuguan Complex, between the early Paleozoic North Qinling and the Mesozoic South Qinling terranes, can provide important constraints on the late Paleozoic evolutionary processes of the Qinling Orogen. Metamorphosed sedimentary rock of the Wuguan Complex have a detrital zircon age spectrum with two major peaks at 453 Ma and 800 Ma, several minor age populations of 350–430 Ma and 1000–2868 Ma, and a youngest weighted mean age of 358 ± 3 Ma, indicating a mixed source from the North Qinling terrane. The recrystallized zircons yield a weighted mean age of 333 ± 2 Ma, representing the metamorphic age. Geochemical analyses imply that the sedimentary rocks were originally deposited in an active continental margin dominated by an acidic-arc source with a subordinate mafic-ultramafic source. The youngest population of detrital zircons (358 Ma) suggests that the Wuguan Complex developed as forearc basin along the southern accreted margin of the North Qinling terrane during the early Carboniferous, whereas the ca. 520–460 Ma mafic rocks with E-MORB, N-MORB, OIB or island arc basalt signatures probably derived from the Danfeng Group. In combination with regional data, we suggest that the depositional age of the Wuguan Complex is ca. 389–330 Ma, but it was subsequently incorporated into tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. A long-lived southward-facing subduction-accretionary system in front of the North Qinling terrane probably lasted until at least the early Carboniferous.