Early Miocene stratigraphy of central west Anatolia,Turkey: implications for the tectonic evolution of the eastern Aegean area

Small‐mammalian faunas enable the discrimination and correlation of uppermost Lower Miocene lacustrine sedimentary units in central western Anatolia. On the basis of sequential stratigraphic relationships, early Early Miocene and latest Early Miocene relative ages are suggested for the older lacustrine mass‐flow deposits and younger paper shale units, respectively, which are devoid of age‐diagnostic fossils. In central western Anatolia, the sequential differences between the uppermost Lower Miocene successions delineate a deformation zone of NE–SW‐trending fault blocks separated by vertical faults. This deformation zone, inherited from Late Oligocene tectonics, underwent an early Early Miocene sinistral transtension leading to pull‐aparts that were emplaced by granitoids. Limited extension caused the late Early Miocene repetitive up‐ and down‐wards motions of the fault blocks, with variable magnitudes. This led to contrasting subsidence histories in the relevant basinal system. During the latest Early Miocene, fault blocks coalesced into a regional body characterized by uniform slow subsidence and non‐extensional deformation facies. The general trend of the above tectonic events can be explained by lateral slab segmentation and progressive asthenospheric wedging, in response to NE‐directed and decelerated palaeosubduction in the Aegean. Copyright © 2007 John Wiley & Sons, Ltd.     

大比例尺地貌晕渲的几种制作方法及比较

针对大比例尺地貌晕渲生成存在的问题,介绍了基于Atlas3D、基于Arc/Info、基于3DSMax三种制作大比例尺地貌晕渲的方法,并进行了比较。     

Volcanic history and tectonics of the Southwest Japan Arc

Abstract Remarkable changes in volcanism and tectonism have occurred in a synchronous manner since 1.5–2 Ma at the junction of the Southwest Japan Arc and the Ryukyu Arc. Although extensive volcanism occurred in Kyushu before 2 Ma, the subduction-related volcanism started at ca 1.5 Ma, forming a NE–SW trend volcanic front, preceded by significant changes in whole-rock chemistry and mode of eruptions at ca 2 Ma. The Median Tectonic Line has intensified dextral motion since 2 Ma, with a northward shift of its active trace of as much as 10 km, accompanied by the formation of rhomboidal basins in Central Kyushu. Crustal rotation and incipient rifting has also occurred in South Kyushu and the northern Okinawa Trough over the past 2 million years. We emphasize that the commencement age of these events coincides with that of the transition to the westward convergence of the Philippine Sea plate, which we interpret as a primary cause of these synchronous episodes. We assume that the shift in subduction direction led to an increase of fluid component contamination from subducted oceanic slab, which then produced island-arc type volcanism along the volcanic front. Accelerated trench retreat along the Ryukyu Trench may have caused rifting and crustal rotation in the northern Ryukyu Arc.     

新疆西天山金矿成矿条件分析及找矿远景预测

本文通过对西天山研究区的遥感地质解译、野外实地验证和综合对比研究,认为西天山地区与邻区的穆龙套金矿、库姆托尔金矿同处一条巨型的构造带上,具有非常相似的大地构造环境、构造演化和赋金建造条件,尤其是分布于那拉提构造带南缘的弧形构造带和南北向贯穿那拉提构造带的横向断裂组是控矿的重要因素。区域上赋金层炭质岩系的存在和蚀变体的广泛发育,使金元素活化、富集成为可能。研究区内大量的金矿化、异常是金矿体存在的客观反映。据此,笔者预测出４处找矿有利地段。     

松潘-甘孜造山带义敦岛弧中段三叠纪火山-沉积盆地的演化

通过对三叠纪义敦岛弧中段83条剖面和沉积等厚线的综合分析研究,将其划分为义敦弧后前陆盆地、义敦火山弧、昌台-禾尼弧间盆地群、沙鲁里火山岩浆弧、雄龙西-金厂沟弧前盆地群5个次级的构造古地理单元。其中弧后盆地主要有上麻绒和义敦2个沉积中心,义敦火山弧可进一步细分出果德、根隆、郎格、哈逮4个次级火山穹隆,弧间盆地群有拿它盆地、曲登盆地、夏塞盆地、哈日盆地,沙鲁里火山岩浆弧可进一步细分为木合沟和口娘公玛2个次级火山穹隆,弧前盆地有雄龙西盆地、莫坝盆地、金厂沟盆地等8个次级火山-沉积盆地。认为义敦岛弧的演化主要受理塘缝合带演化的控制,也受金沙江缝合带演化的影响,总体上在三叠纪经历了夭折裂陷槽→不成熟岛弧→成熟岛弧→残余盆地的演化历程。     

皖南祁门三堡地区花岗闪长斑岩的成因:地球化学、年代学和Hf同位素特征制约

皖南祁门三堡地区位于江南造山带的北缘,华南地区的东北部,属长江中下游地区。本文对该区侵入的花岗闪长斑岩进行了全岩主微量元素分析、锆石U-Pb定年与Hf同位素测试。花岗闪长斑岩的REE球粒陨石标准化配分曲线呈右倾型,Eu负异常,在原始地幔标准化蛛网图中显示明显的Nb-Ta、Zr-Hf负异常。LA-ICP-MS锆石U-Pb定年结果为~142Ma,表明花岗闪长斑岩侵入时代为早白垩世早期。锆石的εHf(t)值为-4.3~-0.3,Hf模式年龄(tDMC)为1220~1470Ma。花岗闪长斑岩在Sr/Y-Y图解上落在经典岛弧岩浆岩区,其岩浆Zr饱和温度(670~760℃)与锆石Ti温度(600~750℃)均较低。锆石的Ce(IV)/Ce(III)为150~1530,平均值为550,指示岩浆具有较高的氧逸度。该岩体的地球化学特征、地壳模式年龄等证据指示其源区物质可能为中(新)元古代古华南洋壳俯冲于扬子板块产生的新生弧壳物质。祁门三堡地区花岗闪长斑岩可能是由于早白垩世早期太平洋板块南西向俯冲并后撤形成该区域的拉张环境,诱发地壳部分熔融而形成。     

云南格咱岛弧成矿带铜厂沟铜钼多金属矿床地球化学特征及地质意义

通过对铜厂沟矿区花岗闪长斑岩地球化学元素及矿区地质特征分析研究,区内的花岗闪长斑岩SiO2含量为66.32%~69.60%,Al2O3含量为14.05%~15.55%,MgO含量为1.19%~1.39%,铝饱和指数A/CNK值为0.88~1.05,属于准铝质-弱过铝质,全碱(K2O+Na2O)含量为6.97%~9.11%,相比中酸性岩石碱度较高。岩石中的轻稀土比较富集(LREE/HREE=13.56~16.94),轻重稀土分馏明显(LaN/YbN=25.97~36.73),δEu(0.87~1.01)、δCe(0.89~0.94)均无明显的异常。富集大离子亲石元素(LILE,Rb、K、La、Ba),相对亏损高场强元素(HFSE,Nb、Hf、Ti),指示岩石是与板块俯冲相关的造山花岗岩系列。矿床中斑岩型矿体与岩浆侵入成矿作用关系密切,而矽卡岩型-热液脉型矿体与岩浆热液上侵充填-接触交代作用相关,矿区深部工程已揭露出深部存在隐伏花岗闪长斑岩体,找矿潜力巨大。     

新疆东准噶尔克拉麦里蛇绿岩地球化学：洋脊俯冲的产物

新疆东准噶尔克拉麦里蛇绿岩中的镁铁质岩兼具有洋中脊玄武岩(MORB)和岛弧拉斑玄武岩(IAB)的特征,岩石地球化学特征表现为轻稀土(LREE)亏损、平坦或略微富集,不同程度地亏损高场强元素(HFSE)而富集大离子亲石元素(LILE),成分上非常相似于受洋脊俯冲影响的 Chile Ridge 和 Cocos Ridge 玄武岩。可以认为其可能形成于受洋脊俯冲影响的岛弧或弧前扩张环境。相对较高的ε_(Nd)(t)(7.2～9.8)、低 Nb/Zr、Ta/Yb 比值,说明在洋脊俯冲的影响下,其源区可能存在有至少三种组分:弧下地幔、来自消减板片流体和俯冲沉积物、MORB 地幔。     

新疆觉罗塔格地区却勒塔格一带小热泉子组火山岩地球化学特征及构造意义

却勒塔格一带下石炭统小热泉子组为一套滨浅海相火山岩夹少量正常沉积碎屑岩建造,上被上石炭统底格尔组不整合覆盖,火山岩组合以玄武岩-安山岩-英安岩-流纹岩最为发育.火山岩岩石化学、地球化学特征表明,小热泉子组火山岩主要属钙碱性系列,一般以富钠为特征,稀土元素和微量元素分布型式与火山岛弧钙碱性火山岩分布型式基本吻合.     

Ophiolites of the Central Asian Orogenic Belt:Geochemical and petrological characterization and tectonic settings

We present a compilation of published data(field,petrography,ages and geochemistry)from 73 ophiolitic complexes of the Central Asian Orogenic Belt.The ophiolitic complexes,ranging in age from Neoproterozoic to Triassic.have been geochemically classified as subduction-related and subductionunrelated categories applying recent,well-established discrimination diagrams.The subductionunrelated category is further subdivided into Mid-Ocean Ridge type(MOR),a common rift-drift stage and Plume type,and the subduction-related category is subdivided into Backarc(BA),Forearc(FA).Backarc to Forearc(BA-FA)and Volcanic Arc(VA)types.The four subduction-related types define highly different geochemical features,with the BA and FA types defining end members showing subduction influence of 10%-100%and 90%-100%subduction influence,respectively,and the two other types(BAFA and VA)define values between the two end members.The subduction-related category comprises79%of the examined ophiolites,of which the BA type ophiolites is by far the dominant group,followed by the BA-FA type,and with FA and VA types as subordinate groups.The Neoproterozoic and Ordovician complexes exhibit the highest,whereas those of Silurian age exhibit the lowest subduction-influence.Of the remaining 21%subduction-unrelated ophiolites,the MOR type dominates.Both the subductionrelated and subduction-unrelated types,in particular the latter,are commonly associated with alkaline basalts taken to represent ocean island magmatism.Harzburgite,dunite,gabbro and basalt are the common lithologies in all ophiolite types,whereas the BA-FA,FA and VA types generally contain intermediate to felsic rocks,and in the FA type boninites occur.The subduction-related ophiolites types generally show low metamorphic grade,whereas greenschist.amphibolite and blueschist grades occur in the subduction-unrelated and BA types.The highly different subduction contribution(from 0 to 100%in the MOR and FA,respectively),attest to variable dips of the subducting slab,as well as variable flux of subduction-related elements into the mantle above subducting slabs,from where the ophiolite magmas got their geochemical fingerprints.As most MOR ophiolites get subducted to the deep mantle,the subduction-related ophiolites have become a dominant ophiolitic type on Earth’s surface through all times supporting the idea about the early start of Plate Tectonics.