Late Jurassic granitoids in the Xilamulun Mo belt,Northeastern China: geochronology,geochemistry, and tectonic implications

ABSTRACT

The Xilamulun Mo belt of Northeastern China, located in the southeastern segment of the Central Asia Orogenic Belt (CAOB), is composed of large deposits of porphyry Mo and quartz-vein-type Mo, which are related to Mesozoic granitoids. Previous studies led to the conclusion that all granitoids in the region formed during the Cretaceous and Triassic, but our new laser ablation inductively coupled plasma mass spectrometry U–Pb zircon dating of magmatic zircons from five samples of four mineralized plutons (Nailingou, Longtoushan, and Hashitu granites and Erbadi and Hashitu granite porphyries) reveals that these range in age from 143.8 ± 1.2 to 149.5 ± 1.0 Ma. These granites show post-collisional (A-type) geochemical characteristics (e.g. enrichment in total alkali, LILE, and LREE and depletion in Eu, Ba, P, and Nb). The Erbadi, Longtoushan, Hashitu, and Longtoushan granitoids exhibit moderately positive Hf isotopic compositions (ε_Hf(t) = ?0.3 to 10.2), indicating that granitic magmas may reflect mixtures of mantle melts and continental crust. These mineralized granites were all emplaced along a major fault over a time span of ~6 million years during the Late Jurassic. We conclude that igneous activity and mineralization resulted from the rollback of the subducted Palaeo-Pacific plate beneath Eurasia. Confirming that the Late Jurassic granitic intrusives are related to the Mo mineralization is useful for understanding the Mesozoic tectonic evolution of the Xilamulun Mo belt and also has significant implications for the regional exploration of ores.     

中国东北地区西部~500Ma泛非期孔兹岩系地球化学特征及其地质意义

最近在兴安、额尔古纳地块均发现原岩为中基性-中酸性火山岩、陆源碎屑沉积岩及碳酸盐岩组合组成的孔兹岩系,岩石组合主要分为富铝片岩-片麻岩类和斜长角闪岩两类。岩石地球化学特征表明,富铝片岩-片麻岩类的原岩为泥岩和砂岩,主量和微量元素的分配形式接近澳大利亚后太古宙页岩(PAAS)和北美页岩(NASC),稀土元素的分布特征与NASC相似,显示轻稀土元素富集及Eu负异常,(La/Yb)N=4～17,δEu=0.32～0.79。其Cr/Ti(0.01～0.03)、Zr/Y(1.2～13.3)、Cr/Th(0.1～8.63)、Cr/Zr(0.02～0.47)、Th/U(1.5～7.7)、CIW(68～99)表明物源区以花岗岩类为主,并可能含有碎屑沉积岩。其Ceanom(-0.04～-0.01)、Ce/Ce#(0.90～1.30)表明富铝片岩-片麻岩类原岩沉积环境为亚稳定的大陆边缘沉积。斜长角闪岩原岩为玄武岩或安山质玄武岩,其富Fe2O3(1.83%～12.37%)、MgO(4.28%～7.29%)、贫SiO2(47.06%～56.13%),呈低碱性。轻稀土元素相对富集,MORB标准化的微量元素配分型式为大隆起型,Zr/Nb、Hf/Th值均类似于板内拉斑玄武岩的特征。因此,研究区孔兹岩系应形成于裂谷沉积背景。这与佳木斯地块麻山群孔兹岩系形成环境一致,表明东北地区各地块的变质基底均为孔兹岩系,其原岩均形成于裂谷沉积环境,并统一经历～500Ma泛非期变质事件,这为研究我国前寒武纪的大陆演化、再造我国东北地区的构造格局及其在Gondwana大陆重建中的位置都将具有重大的理论意义。     

Architecture and depositional development of the Eocene deep‐marine Morillo and Coscojuela Formations,Aínsa Basin,Spain

The Aínsa Basin of northern Spain contains a deep‐marine succession comprising up to 24 sandstone bodies separated by thick marl‐rich units. A detailed analysis of nine outcrops (>900 m of sediment profiles) from the Morillo Formation of the San Vicente Group, from the upper part of the basin succession, has enabled a reappraisal of the unit. Within the Morillo Formation, sediment transport was to the NW, and a range of environments are recognized including channels, lobes and pelagic deposits. The overlying Coscojuela Formation, which partly cuts into the Morillo Formation, shows W‐directed palaeocurrents in its proximal reaches, with flows being deflected to the N along an adjacent slope. Destabilization of the adjacent carbonate platform resulted in a significant input of carbonate material into the flow. The final phases of sedimentation within the Aínsa Basin were more complex than previously suspected, probably as a result of a combination of factors, including tectonic activity, resulting in basin narrowing due to anticlinal growth, as well as encroachment and/or destabilization of the adjacent regional carbonate platforms. Copyright © 2013 John Wiley & Sons, Ltd.     

东北地区晚古生代-中生代I型和A型花岗岩Nd同位素变化趋势及其构造意义

中国东北地区位于中亚造山带巨型增生陆缘的东段,分布着巨量的具有新生特征的显生宙花岗岩和火山岩。本文对东北地区晚古生代-中生代I和A型花岗岩年代学和Nd同位素组成开展了综合分析和研究。东北地区的I型花岗岩有两种Nd同位素变化趋势:一是以额尔古纳和兴安地块为代表,其εNd(t)随着年龄变新而增大,与造山带垮塌、软流圈上涌的幔源熔体或蒙古-鄂霍茨克洋的俯冲交代地幔楔熔体加入引起的地壳增生作用相关。二是以松嫩地块西南区和张广才岭为代表,εNd(t)随着年龄变新而下降,反映花岗岩的熔融源区有从早期的新生岛弧中、下地壳向晚期含更多再循环物质的中、上地壳迁移的趋势。A型花岗岩侵位时代主要有三期,总体上具有正的εNd(t)值,绝大部分tDM21.0Ga,反映了东北地区强烈的地壳增生作用。晚古生代A型花岗岩主要沿着贺根山-黑河断裂分布,可能与兴安和松嫩地块碰撞后伸展作用相关;早中生代A型花岗岩主体分布于张广才岭,与松嫩、佳木斯和兴凯地块的碰撞后伸展作用相关;早白垩世A型花岗岩遍布整个东北地区,可能与古太平洋板块俯冲、后撤导致的区域性伸展作用相关。晚古生代-中生代花岗岩的Nd二阶段模式年龄(tDM2)与侵位年龄(t)的对比展示了东北各构造单元地壳增生作用的差异。与华北北缘中生代花岗岩的特征相似,额尔古纳和佳木斯地块的花岗岩表现出tDM2t+1000Ma的特征,表明这两个地块具有古老的结晶基底。兴安地块、松嫩地块西南区和张广才岭花岗岩的tDM2和侵位年龄差值集中在300~1000Ma,反映不同属性(年轻vs.古老)的地壳物质对熔融源区的贡献。东北地区tDM2和侵位年龄差值小于300Ma的花岗岩岩体极少,仅有乌兰浩特的查干岩体一例,可能由新近增生的新生地壳熔融形成。由Nd同位素特征显示,晚古生代-中生代东北地区显著的地壳增生作用主要发生在缝合带和岩石圈规模的断裂带,幔源岩浆沿断裂带上升到地壳不同深度并形成高εNd(t)和低tDM2的中酸性火成岩。除几个特殊岩体表现出过于亏损或富集Nd同位素的特征,早白垩世东北地区酸性火成岩的Nd同位素组成相近,εNd(t)值集中在0~+3之间,可能暗示此时期东北地区的中、下地壳成分组成趋于一致并与同时期的古太平洋俯冲作用有关。我们的结果显示东北地区晚古生代-中生代花岗岩的起源与古亚洲洋、蒙古鄂霍茨克洋和古太平洋的构造演化相关。这三个古大洋的扩张和俯冲作用提供了大量新生地壳物质,而新生和再循环地壳物质的重熔形成了东北地区大规模的显生宙花岗岩及其对应成分的喷出岩。     

内蒙古自治区阿巴嘎旗必鲁甘干铜钼矿地质特征及成因探讨

必鲁甘干矿区位于天山—阴山内蒙地槽华力西晚期褶皱带阿巴嘎旗复向斜中段,查干敖包(必鲁甘干)倒转背斜核部。区内NE向断裂构造控制了印支期花岗斑岩体及特大型斑岩型铜钼矿床的分布。通过勘探查明主矿体延长2 300m,延深1 850m,平均厚度46.24m。铜钼矿赋存于花岗斑岩与硅质角岩内外接触带,赋矿岩石主要为花岗斑岩和硅质角岩。矿体形态以透镜状—似层状为主,属斑岩型铜钼矿。     

柴达木西部地区新生代主控断裂演化过程及其意义

基于主干地震剖面的解释结果,本文探讨了柴达木西部地区新生代主控性断裂的活动模式、活动时间及空间演化过程。结果表明,断裂演化明显存在两个大的旋回:路乐河组—下干柴沟组上段沉积期间(约54～31 Ma)和下油砂山组沉积至今(约22 Ma至今);其中第2个构造期断裂活动强烈,尤其是狮子沟组沉积以来(约8 Ma至今),中部及北部区域北西西向断裂开始大规模逆冲活动,反映了盆地晚期强烈变形过程。断层生长指数定量分析结果与其空间演化过程相吻合,共同记录了印度—欧亚板块碰撞远程效应控制下的柴达木盆地在新生代具有阶段性变形特征,从而为青藏高原东北部分阶段隆升模式提供了新的证据。     

Church–state relations in Spain: Variations on a National-Catholic theme?

Contrary to the absence of a uniform Spanish identity (a phenomenon that is often referred to as Spain being a ‘nation of nations’), Spain’s confessional map is remarkably homogeneous. From the beginning of its existence as a political conglomeration, Spain has been a mono-confessional Catholic territory. Even at present, Catholicism is an intrinsic feature of Spanish society and – though officially a secular state – of state policy. A closer look at Spain’s religious situation and its corresponding pattern of church–state relations reveals, however, some recent cracks in the century’s old bond between Spain and Catholicism. Particularly secularization and religious pluralism challenge Spain’s mono-confessional Catholic nature, a development that fits well into Spain’s post-Francoist focus on Europe and European (secular) values. This paper discusses Spanish church–state relations from the beginning of its political existence until present times. Special attention will be paid to more recent societal developments and their impact on religious Spain and church–state relations.

川中东北部须家河组与珍珠冲段地层划分

通过地震反射终端研究,认为上三叠统须家河组（J2x）与下侏罗统（J1z）的分界面为一层序界面（T3x被界面截削,J1z沿界面上超）;因此可依据LUNA法则予以确定。LUNA认为,层序边界不整合可依据可容空间生成速率突变的岩层几何形态来识别,表现在古河道规模和河道砂岩的叠置方式,而拼合砂岩体底面乃是层序界面（SB）之所在...     

Genesis of the Jurassic Carbonate‐Hosted Pb–Zn Deposits of Jebel Ressas (North‐Eastern Tunisia): Evidence from Mineralogy,Petrography and Trace Metal Contents and Isotope (O,C, S,Pb) Geochemistry

The Jebel Ressas Pb–Zn deposits in North‐Eastern Tunisia occur mainly as open‐space fillings (lodes, tectonic breccia cements) in bioclastic limestones of the Upper Jurassic Ressas Formation and along the contact of this formation with Triassic rocks. The galena–sphalerite association and their alteration products (cerussite, hemimorphite, hydrozincite) are set within a calcite gangue. The Triassic rocks exhibit enrichments in trace metals, namely Pb, Co and Cd enrichment in clays and Pb, Zn, Cd, Co and Cr enrichment in carbonates, suggesting that the Triassic rocks have interacted with the ore‐bearing fluids associated with the Jebel Ressas Pb–Zn deposits. The δ¹⁸O content of calcite associated with the Pb–Zn mineralization suggests that it is likely to have precipitated from a fluid that was in equilibrium with the Triassic dolostones. The δ³⁴S values in galenas from the Pb–Zn deposits range from ?1.5 to +11.4‰, with an average of 5.9‰ and standard deviation of 3.9‰. These data imply mixing of thermochemically‐reduced heavy sulfur carried in geothermal‐ and fault‐stress‐driven deep‐seated source fluid with bacterially‐reduced light sulfur carried in topography‐driven meteoric fluid. Lead isotope ratios in galenas from the Pb–Zn deposits are homogenous and indicate a single upper crustal source of base‐metals for these deposits. Synthesis of the geochemical data with geological data suggests that the base‐metal mineralization at Jebel Ressas was formed during the Serravallian–Tortonian (or Middle–Late Miocene) Alpine compressional tectonics.     

40Ar/39Ar dating,fluid inclusions and S–Pb isotope systematics of the Shabaosi gold deposit,Heilongjiang Province,China

The Shabaosi deposit is the only large lode gold deposit in the northern Great Xing'an Range. The gold ore bodies are hosted by sandstone and siltstone of the Middle Jurassic Ershi'erzhan Formation, and are controlled by three N–S‐trending altered fracture zones. The gold ore bodies are composed of auriferous quartz veinlets and altered rocks. Fluid inclusion studies indicate that the ore‐forming fluids belong to a H₂O–NaCl–CO₂–CH₄ system, with salinities between 0.83 and 8.28 wt% NaCl eq., and homogenization temperatures ranging from 180 to 320 °C. The δ³⁴S values of sulphides show a large variation from −16.9‰ to 8.5‰. The Pb isotope compositions of sulphides are characterized by a narrow range of ratios: 18.289 to 18.517 for ²⁰⁶Pb/²⁰⁴Pb, 15.548 to 15.625 for ²⁰⁷Pb/²⁰⁴Pb, and 38.149 to 38.509 for ²⁰⁸Pb/²⁰⁴Pb. The μ values range from 9.36 to 9.51. These results suggest that the ore‐forming fluids/materials were mainly of magmatic hydrothermal origin, derived from magmas produced by partial melting of the lower crust. The ⁴⁰Ar/³⁹Ar age of auriferous quartz veinlets from the Shabaosi gold deposit is about 130 Ma. The Shabaosi gold deposit has counterparts in similar orogenic gold deposits, and was formed during the post‐collisional setting of the Mongolia–Okhotsk Orogen. Copyright © 2014 John Wiley & Sons, Ltd.