南阿尔金地区早古生代中酸性侵入岩的岩石成因及其对构造演化的指示意义

南阿尔金造山带位于塔里木盆地和柴达木盆地之间,是中国西北地区重要的俯冲-碰撞杂岩带,其早古生代构造演化过程是近年来的研究热点之一,然而,洋壳俯冲的时限一直存在争议。本文对茫崖石英二长岩开展岩石学、地球化学、锆石U-Pb年代学和锆石Lu-Hf同位素地球化学研究,探讨其岩石成因及成岩时的构造环境。样品显示高碱、富钾、低钛、贫铁及Nd-Ta-Ti异常等与钾玄岩相似的地球化学特征,成岩年龄为511~495 Ma,ε_(Hf)(t)主要为-3.51~-0.08,少量介于0.04~1.69之间。我们认为俯冲洋壳到达角闪岩相边界时释放大量水并上升进入地幔楔,导致地幔楔橄榄岩发生角闪石化交代作用,由于地幔楔沿俯冲带向下拖曳而温度升高,角闪石化橄榄岩熔融形成的熔体在上升过程诱发上地壳物质部分熔融,壳源岩浆混合少量幔源岩浆形成了石英二长岩,该期花岗岩是对造山带从大洋岛弧环境向活动大陆边缘过渡的岩石学响应。因此,南阿尔金洋壳可能在约517 Ma前已经开始俯冲。

茫崖闪长岩的成因及对造山带构造演化的指示意义

南阿尔金造山带是中国西北地区重要的俯冲—碰撞杂岩带。笔者等对茫崖地区出露的闪长岩开展岩石学、地球化学、锆石U-Pb年代学和Lu—Hf同位素地球化学研究,探讨其岩石成因和成岩时的构造环境。研究表明,茫崖闪长岩亏损Nb、Ta、Ti、P、Th、U、HREEs、Ba、Sr等元素,富集Rb等大离子亲石元素及LREEs,显示与俯冲相关岛弧岩浆岩相似的地球化学特征。样品的锆石U-Pb年龄为494~461 Ma,ε_(Hf)(t)为0.01~3.90,t_(DM2)为1496~1447 Ma,少量ε_(Hf)(t)为负值(-2.22~-0.03),t_(DM2)为1453~1254 Ma,指示其物质来源以中元古代(1453~1254 Ma)新生地壳物质为主,混合少量中元古代(1496~1447 Ma)古老地壳物质。综上,该期岩浆活动是幔源岩浆的底侵作用导致下地壳熔融的产物,指示南阿尔金造山带在<494 Ma进入深俯冲陆壳断离—折返阶段,同时伴随着大规模幔源岩浆的底侵作用,茫崖闪长岩是深俯冲陆壳断离后折返作用的岩浆活动响应。

秦岭南召岩体中花岗岩脉的锆石U-Pb定年:对燕山期构造环境的约束

通常认为,花岗岩体中的花岗岩脉与岩体是同一次岩浆活动的产物,是深部演化的岩浆沿着岩体的裂缝侵入后冷凝形成的。南召岩体位于北秦岭东部,近年来在岩体中发现一条宽约5 m的花岗岩脉。岩脉呈紫红色,斑状结构,斑晶为石英。LA-MC-ICP-MS锆石U-Pb定年得出该岩脉的形成时间为(119.6±0.7)Ma,与岩体的年龄(452.3±6.2)Ma相差很大。锆石Hf同位素测试结果表明,岩脉的源岩可能主要是新生地壳,结合地球化学研究分析得出该岩脉呈现I型花岗岩的特性。该岩脉的年龄、Hf同位素和地球化学特征同邻近的伏牛山岩体相近,推测岩脉的源岩可能和伏牛山岩体的源岩相同。根据研究结果及区域地质构造分析,认为燕山期由于太平洋板块的俯冲作用和陆內拉张作用,导致扬子板块及华北板块沿秦岭造山带形成一系列断裂。岩浆沿着断裂上侵,大部分形成了伏牛山岩体,小部分沿着周围的裂隙侵入形成岩脉,并在侵位的过程中与寄主岩发生物质交换。

华北板块南缘伏牛山花岗岩锆石LA-MC-ICP-MS U-Pb定年、Lu-Hf同位素特征及岩石成因

伏牛山花岗岩体出露于华北板块南缘,南召县城以北,面积超过4200km^2。岩体的岩石组合为花岗岩+花岗闪长岩+石英闪长岩,具有I型花岗岩的特征。花岗岩锆石的LA-MC-ICP-MS U-Pb定年得到145.4±1.0Ma和118.5±0.6Ma,说明岩体形成于燕山期,并经历了至少两期岩浆活动。锆石Hf同位素分析表明,第一期花岗岩的ε_(Hf)(t)平均值为-16.53,二阶段模式年龄(t_(DM2))平均为2216Ma,表明其源岩以壳源物质为主;第二期花岗岩的源岩分为两个部分,一部分花岗岩的ε_(Hf)(t)平均值为-13.67,二阶段模式年龄(t_(DM2))平均为2044Ma,表明其源岩以壳源物质为主,另一部分花岗岩的ε_(Hf)(t)平均值为1.61,二阶段模式年龄(t_(DM2))平均为1073Ma,表明其源岩以新生地壳为主。根据研究结果及区域地质构造分析,认为第一期岩浆作用是由于太平洋板块俯冲导致秦岭造山带断裂构造再活动,发生部分熔融形成小规模的岩浆作用;而第二期岩浆作用是由于太平洋板块俯冲导致岩石圈拆沉,使地幔软流圈的物质上升,形成巨大的热场,引起大陆地壳大规模的部分熔融形成花岗岩浆。最终形成的花岗岩浆沿着华北板块与扬子板块之间的断裂上侵至地壳浅处,形成了伏牛山复式岩体。

安徽铜陵凤凰山岩体LA-ICP-MS锆石U-Pb年龄和地球化学特征

安徽铜陵是我国著名的铜—金多金属矿集区,区内广泛出露与成矿作用有着密切关系的中酸性侵入岩,其中,凤凰山岩体是区内出露面积最大的岩体,岩体周围分布着许多重要的铜、金、钼等金属矿床。为了探讨凤凰山岩体的成因及构造意义,本文对该岩体开展了岩石学、锆石U-Pb年代学、岩石地球化学等方面的研究。研究结果表明,该岩体主要由花岗闪长岩和石英二长闪长岩组成,锆石LA-ICP-MS U-Pb年龄分别为140.6～144.7 Ma和142.2～143.4 Ma,反映岩体侵位时代为140.6～144.7 Ma。岩石主要由斜长石、石英、碱性长石组成,其次含角闪石、黑云母,副矿物为磷灰石、锆石等,岩体内部常见闪长质微粒包体。岩石的铝饱和指数A/CNK<1.1,Na_2O>K_2O,具Ⅰ型花岗岩特征。岩石的轻稀土元素富集而重稀土元素亏损,Eu呈较弱的负异常,富集Rb、Ba、Th、U、K等大离子亲石元素,相对亏损Nb、Ta、P、Ti等高场强元素,反映其源岩可能主要为壳幔混合源,形成岩体的岩浆是由古老地壳部分熔融形成的长英质岩浆与起源于富集地幔的富碱玄武质岩浆混合后形成。

铜陵凤凰山矿田成矿时代及成矿物质来源

铜陵是长江中下游铁铜金等多金属成矿带上一个重要的矿集区,凤凰山矿田是铜陵矿集区七大矿田之一,位于铜陵市东南部,近东西向铜陵-戴家汇构造-岩浆-成矿带的中部。为了探讨凤凰山矿田的成矿时代、成矿流体特征及其成矿物质来源,文章对矿田内仙人冲铜矿、清水塘铜矿、铁山头铜矿、金山冲铜矿、龙潭肖铜矿、朱家山铜矿、药园山铜矿开展了Re-Os同位素定年以及碳、氧、硫、铅同位素分析。结果表明,凤凰山矿田成矿时代为140.9～142.2 Ma,方解石的碳、氧同位素分析显示凤凰山矿田成矿流体δ^(13)C_(V-PDB)值为-4.3‰～+2.9‰,暗示成矿流体中的碳具多来源特征,部分来自岩浆,部分来自沉积碳酸盐围岩;测试样品的δ^(18)O_(V-SMOW)值为+10.7‰～+13.2‰,反映成矿流体中的水以岩浆热液为主;矿田内主要矿床硫化物的δ^(34)S值为+0.2‰～+6.5‰,硫具有岩浆来源特征,且部分可能来自幔源,铅同位素也显示了相似的特征。辉钼矿样品中的w(Re)为47.1×10^(-6)～103.2×10^(-6),显示出壳幔混合源的特征。

安徽铜陵沙滩脚矿田中酸性侵入岩成因及构造意义

安徽省铜陵地区是中国著名的以矽卡岩和斑岩型矿床为主的铜-金多金属矿集区,区内广泛产出的中酸性侵入岩与成矿关系十分密切。沙滩脚矿田位于该矿集区的东部,出露沙滩脚、桂花冲和姚家岭岩体及其不同规模、不同矿化类型的铜、金、锌等矿床,岩体对成矿起了重要的控制作用。本文在前人研究的基础上,对该矿田内的沙滩脚、姚家岭、桂花冲3个岩体进行了详细的岩石学、地球化学和锆石U-Pb年代学研究,以期查明沙滩脚矿田中酸性侵入岩的成因及成岩构造环境。岩石地球化学分析表明,3个岩体具有准铝质特征,均属于高钾钙碱性I型花岗岩类,轻稀土富集,重稀土亏损,具有弱的负Eu异常,富集Rb、Th等元素,亏损Nb、Ta等高场强元素。姚家岭岩体的锆石U-Pb年龄为140.4~140.9 Ma,沙滩脚岩体形成时代相对较早(141.4~144.1 Ma),桂花冲岩体形成相对较晚(138.3Ma)。结合区域地质背景,笔者认为沙滩脚矿田的这些岩体形成于早白垩世伸展环境,是由来自于富集地幔的分异的碱性玄武质岩浆与地壳易熔组分部分熔融形成的花岗质岩浆混合后分期侵位形成的。

阿尔金南缘阿克提山岩体锆石U-Pb定年、Hf同位素特征及构造意义

阿克提山花岗岩体位于阿尔金断裂南缘,其形成时代与区域内其他花岗岩体差异较大,该岩体走向明显地受阿尔金断裂带分支断裂控制。锆石LA-ICP-MS U-Pb年代学分析表明,该岩体结晶年龄约为262Ma,其形成可能与南阿尔金地区在华力西期-印支期发生的大规模线性构造运动有关。岩体的岩性主要为石英闪长岩、花岗闪长岩,其暗色矿物以角闪石、黑云母为主,岩石A/CNK值均小于1.1,显示准铝质—弱过铝质特征,属于高钾钙碱性系列;大离子亲石元素Rb、Th、K相对富集,高场强元素Nb、Ta、P、Sr、Ti明显呈负异常;稀土元素配分曲线具有中等负Eu异常,δEu的平均值为0.73,(La/Yb)_N平均值为14.57,说明该花岗岩体岩浆部分熔融程度较高。根据岩石学及地球化学特征可判断该岩体为I型花岗岩。锆石Lu-Hf同位素分析表明,锆石ε_(Hf)(t)值为+1.46～+9.14,均为正值,二阶段模式年龄的峰值平均为943Ma,表明其源岩主要为新元古代新生地壳物质的部分熔融。阿尔金断裂在印支期的走滑运动是从地壳深部的韧性变形开始的,随后在浅地表发生脆性断裂形成大规模走滑断裂带。阿克提山岩体的形成与地壳深部减压熔融有关。

北阿尔金西段正长花岗岩和闪长岩地球化学、锆石U-Pb定年及Hf同位素特征

北阿尔金西段出露大量中酸性侵入岩,为探讨西段地区花岗质岩石的成因、形成环境以及北阿尔金地区岩浆活动特点,本文选取北阿尔金西段的正长花岗岩体和闪长岩体作为研究对象,进行了岩石学、地球化学、锆石U-Pb年代学及Hf同位素等方面的研究。研究结果表明,正长花岗岩体形成时代为495.7～502.0Ma,铝饱和指数A/CNK为0.86～1.09小于1.1,P_2O_5与SiO_2含量呈负相关,具I型花岗岩特征。轻稀土富集而重稀土亏损,具有明显的负Eu异常,微量元素特征显示富集Rb、Ba、Th、U、K等元素,相对亏损Nb、Ta、P、Ti等元素。岩石地球化学及锆石Hf同位素特征暗示其源区物质成分不均一,源岩主要为0.95～1.4Ga的新生地壳(变中基性岩),并有1.42～1.83Ga的古老地壳物质的参与。闪长岩体的侵位时代为497.1±3Ma,轻稀土富集而重稀土亏损,较弱的负Eu异常,相对富集Rb、Ba、Th、U、K等元素,而亏损Nb、Ta、P、Ti。锆石ε_(Hf)(t)值为-1.61～+2.16,二阶段模式年龄t_(DM2)为1.34～1.56Ga,暗示其源岩可能主要为新生地壳,并有古老地壳物质参与成岩。北阿尔金西段正长花岗岩、闪长岩均形成于早古生代,具弧型花岗岩特点,结合区域构造背景,认为其形成可能与北阿尔金洋壳俯冲有关,产于陆弧环境。

北阿尔金喀孜萨依二长花岗岩成因及其构造意义

喀孜萨依二长花岗岩出露于北阿尔金蛇绿混杂岩带北缘,为探讨其成因、源区特征及构造环境,本文对其进行了岩石学、锆石U-Pb定年、Hf同位素及岩石地球化学等方面的研究。研究结果表明,喀孜萨依二长花岗岩主要由石英、斜长石、钾长石、角闪石、黑云母等矿物组成,岩体侵位时代为425~423Ma,铝饱和指数A/CNK为0.97~1.07,属弱过铝质钙碱性-高钾钙碱性岩石,P2O5与SiO2含量呈负相关,具I型花岗岩特征。轻稀土富集而重稀土亏损,Eu异常不明显,岩石富集Rb、Ba、Th、U、K等元素,相对亏损Nb、Ta、P、Ti等元素。锆石εHf(t)值为+2.65^+6.23,二阶段模式年龄tDM2为1015~1243Ma,其源岩主要来自新生地壳。结合区域构造背景,喀孜萨依二长花岗岩体可能形成于碰撞后伸展环境。

安徽铜陵焦冲矿田侵入岩锆石U-Pb定年、Hf同位素特征及成因

安徽铜陵矿集区出露的侵入岩可划分为高钾钙碱性和橄榄安粗岩系列,作为铜陵7大矿田之一的焦冲地区是否也存在两个系列侵入岩?它们的时代及成因与整个铜陵地区的侵入岩是否相同?这些问题目前仍不清楚。本文选择铜陵焦冲矿田的侵入岩开展了岩相学、岩石地球化学、LA-ICPMS锆石U-Pb定年及原位Hf同位素地球化学研究。结果表明,焦冲矿田也存在高钾钙碱性系列和橄榄安粗岩系列侵入岩,前者的主要岩石类型为石英二长闪长岩、花岗闪长岩,后者为辉石二长闪长岩。LA-ICPMS锆石U-Pb定年结果显示,高钾钙碱性系列侵入岩年代与铜陵地区其他矿区同类岩石年代相同,约为142 Ma;而橄榄安粗岩系列侵入岩年代比铜陵地区其他矿区同类岩石年轻,约为136 Ma。总体上看,铜陵地区两个系列侵入岩具有多期次侵位的特征。焦冲高钾钙碱性系列侵入岩含有较多的老的继承性锆石,说明本区古老地壳卷入了岩浆形成过程。结合铜陵地区侵入岩的特征和焦冲矿田侵入岩岩石地球化学研究结果,笔者认为,焦冲矿田两个系列侵入岩成因与铜陵地区侵入岩相似,即橄榄安粗岩系列侵入岩是来自莫霍面附近深部位岩浆房富碱基性岩浆结晶分异后的产物,而高钾钙碱性系列侵入岩是深位岩浆房分异后的岩浆与浅位岩浆房长英质岩浆混合后的产物。

南阿尔金玉苏普阿勒克塔格花岗岩体成因及其对区域早古生代构造演化的启示

【研究目的】玉苏普阿勒克塔格花岗岩体位于阿尔金造山带南部茫崖蛇绿混杂岩带内,主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成。玉苏普阿勒克塔格岩体的形成时代、成因类型和岩浆物质来源尚不明确,制约了我们进一步认识该岩体形成的地球动力学背景以及南阿尔金造山带早古生代构造演化过程。【研究方法】因此,本文对玉苏普阿勒克塔格岩体进行了岩石学、锆石U-Pb年代学、全岩地球化学、黑云母矿物化学及Hf同位素组成等方面的研究。【研究结果】锆石U-Pb年代学研究结果表明该岩体中粗粒似斑状黑云二长花岗岩的锆石U-Pb加权平均年龄为451~447 Ma。结合前期工作获得该岩体中细粒含斑黑云二长花岗岩的年龄(430~423 Ma),笔者认为玉苏普阿勒克塔格花岗岩体属于早古生代岩浆活动的产物。黑云母矿物化学研究结果表明,玉苏普阿勒克塔格岩体形成于温度较低压力较高环境。根据玉苏普阿勒克塔格岩体两期花岗岩的矿物组成、全岩地球化学特征及形成的物理化学环境,认为该岩体属于I型花岗岩。Hf同位素组成研究结果表明,玉苏普阿勒克塔格岩体两期花岗岩具有相似的Hf同位素组成,暗示它们具有相似的物质来源:源岩以新生地壳的部分熔融为主,在侵位过程中经历了部分古老地壳物质的混染。【结论】综合玉苏普阿勒克塔格花岗岩体的形成时代、成因类型、物质来源,结合区域构造演化资料,本文认为玉苏普阿勒克塔格岩体形成于与南阿尔金洋北向俯冲有关的活动大陆边缘环境。

南阿尔金茫崖A型花岗岩的成因及构造意义

南阿尔金造山带位于柴达木盆地和祁连-昆仑造山带之间,是一条重要的大陆俯冲-碰撞造山带,带中分布的大量早古生代花岗岩蕴含着造山带构造演化的重要信息。茫崖A型碱长花岗岩对限定南阿尔金进入造山后伸展环境的时限以及壳幔相互作用具有指示意义,然而该岩体的成因类型、物质来源和形成的构造环境缺乏详细研究。因此,本文利用岩相学、岩石地球化学、LA-ICP-MS U-Pb年代学和Lu-Hf同位素分析对碱长花岗岩进行系统的研究,并探讨岩浆活动对造山带构造演化的响应。碱长花岗岩显示高硅、富铁、富碱、贫钙和镁的特点,并强烈亏损Ba、Sr、P、Eu和Ti,属于A2型花岗岩;岩体的结晶年龄为403~424Ma,是中-新元古代新生地壳(新生长英质物质或钙碱性花岗岩类)部分熔融的产物,岩浆源区可能存在少量富Ca斜长石残留相;南阿尔金造山带在424Ma之后进入造山后的伸展环境,不同块体之间的均衡调整导致深部幔源物质持续上涌,造成地壳的部分熔融,形成了这一期A型花岗岩。

Types of Enclaves and Their Features and Origins in Intermediate-Acid Intrusive Rocks from the Tongling District, Anhui Province, China

Abstract: Enclaves in intermediate-acid plutons from Tongling can be divided into three types: xenoliths, relics and magmatogenic enclaves. The magmatogenic enclaves consist of cumulates, micrograined dioritite mixtite and dioritic chilled border enclaves. Petrologically, relics with eyed and meta-poikilitic texture are characterized by high content of biotite (>80%) and low content of cordierite and grossular. The cumulates with accumulate texture consist of a great amount of pyroxene, hornblende and minor spinel and phlogopite. The micrograined dioritic mixtite is composed of more hornblendes and feldspar and less needle apatites and an ellipsoid basic core included in plagioclase. The chilled border enclaves have the same mineral association, but more dark minerals than the host rocks consisting of plagioclase, quartz, alkaline feldspar, hornblende and biotite. Geochemically, the relics exhibit high REE content (455.8×10?6) and high ratio of LREE/HREE, more obvious Eu negative anomaly and are rich in Cr and Ni, poor in Ba, Nb and Sr. All kinds of magmatogenic enclaves have the same REE pattern without Eu anomaly, and the total REE is 74.9×10?6 for spinel pyroxene cumulate, 179.7×10?6 for hornblende cumulate, 226.9 × 10?6 for hornblende cumulate crystal, 289.9×10?6 for micrograined dioritic mixtite and 131.2×10?6 for chilled border enclaves. Calculation with the thermometer and barometer for minerals shows that the temperature and pressure of formation are 1126 °C and 8.44 kbar (7.15–9.04 kbar) for the spinel pyroxene cumulate, 1065 °C-1029 °C and 8.23 kbar (7.13–9.50 kbar) for the hornblende pyroxene cumulate, 959 °C and 3.40 kbar (2.86–4.09 kbar) for the micrograined dioritic mixtite enclaves, and 951 °C and 0.59 kbar for the dioritic chilled border enclaves, respectively. Thus, the following conclusions can be drawn. Relic enclaves were derived from the crustal partial melting and all cumulate enclaves originated from deep magma chambers near the Moho in the lower crust, which are cumulate fragments formed by fractional crystallization of basic magma; mixtite came from shallow magma chambers in the middle-upper crust, formed by the mixture of mantle-derived magma and acid magma derived from the crustal partial melting; and the chilled border enclaves came from the border fragments of early intrusive bodies.

The Geochemical and Zircon Trace Elements Characteristics of A-type Granitoids in Boziguoer, Baicheng County, Xinjiang

The Boziguoer A-type granitoids in Baicheng County,Xinjiang,belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks.The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite,an aegirine or arfvedsonite alkali feldspar granite,and a biotite alkali feldspar syenite.The major rock-forming minerals are albite,K-feldspar,quartz,arfvedsonite,aegirine,and siderophyllite.The accessory minerals are mainly zircon,pyrochlore,thorite,fluorite,monazite,bastnaesite,xenotime,and astrophyllite.The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55％ to 72.29％ with a mean value of 67.32％,Na2O＋K2O is high （9.85％-11.87％） with a mean of 11.14％,K2O is 2.39％-5.47％ （mean =4.73％）,the K2O/Na2O ratios are 0.31-0.96,Al2O3 ranges from 12.58％ to 15.44％,and total FeOT is between 2.35％ and 5.65％.CaO,MgO,MnO,and TiO2 are low.The REE content is high and the total SREE is （263-1219） ppm （mean =776 ppm）,showing LREE enrichment and HREE depletion with strong negative Eu anomalies.In addition,the chondrite-normalized REE patterns of the alkaline granitoids belong to the ＂seagull＂ pattern of the right-type.The Zr content is （113-1246） ppm （mean =594 ppm）,Zr＋Nb＋Ce＋Y is between （478-2203） ppm with a mean of 1362 ppm.Furthermore,the alkaline granitoids have high HFSE （Ga,Nb,Ta,Zr,and Hf） content and low LILE （Ba,K,and Sr） content.The Nb/Ta ratio varies from 7.23 to 32.59 （mean =16.59） and the Zr/Hf ratio is 16.69-58.04 （mean =36.80）.The zircons are depleted in LREE and enriched in HREE.The chondrite-normalized REE patterns of the zircons are of the ＂seagull＂ pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly.The Boziguoer A-type granitoids share similar features with A1-type granites.The average temperature of the granitic magma was estimated at 832-839℃.The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature,anhydrous,and low oxygen fugacity conditions.

Fractal Characteristics of Fault Structures and Their Use for Mapping Ore-prospecting Potential in the Qitianling Area, Southern Hunan Province, China

Quantitative analyses of the spatial distribution of fault structures can provide a theoretical basis for forecasting prospective ore deposits. Characteristics and complexity of fault structure distribution in the Qitianling area, Southern Hunan Province, China, were quantitatively calculated and appraised by fractal and multifractal methods to evaluate the relation between fault structures and ore-prospecting potential. The results show that the lengths of faults can be modeled as multifractals. Multifractal spectra evidently reflect the characteristics of the scaling of fault structures. The box- counting dimension value （D） of fault structures is equal to 1.656, as indicates complexity of the spatial distribution of faults and favorable structural conditions for the formation of ore deposits. Moreover, the D values of sub-regions were calculated and isopleths of their fractal dimension values were plotted accordingly. Overlay analyses of isopleths of fractal dimension values and distributions of known ore deposits show that areas with the larger fractal dimension values of fault structures have more ore deposits. This spatial coupling relationship between D values and ore deposits can be used to forecast and explore other ore deposits. On the basis of complexity theory for ore-forming systems, three exploration targets with high D values were delineated as prospective ore deposits.

Zircon U-Pb age, Lu-Hf Isotopic Characteristics and Origin of the Banshanping Granitoid Rocks in East Qinling Orogenic Belt

The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt.It is a diorite-quartz diorite-granodiorite-granite series,spreading in a NW-SE direction,and intrudes into the Erlangping Group.The SiO2 content ranges from 57.04% to 76.56%,Na2O from 2.05% to 4.65%,K2O from 0.84% to 3.40%.Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids.SREE ranges from 36.51 ppm to 473.25 ppm,and LREE/ HREE ratios lie between 3.95 and 22.18.Negative Eu anomalies are not obvious in most samples,though there are obvious Nb,P and Ti positive anomalies.The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma-486.9±9.3 Ma.Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876,εHf（t） values from 8.5 to 14,all positive,and corresponding modal ages （TDM2） range from 559 Ma to 908 Ma.Based on Hf isotope characteristics and existing SmNd and Rb-Sr isotope data,we consider that the Banshanping granitoid rocks originate from mantlederived material,i.e.the igneous rocks that formed in Neoproterozoic,and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.

SHRIMP U-Pb Zircon Dating of the Tula Granite Pluton on the South Side of the Altun Fault and Its Geological Implications

The Tula A2-subtype granite pluton is located between the Altun fault and its branching fault. According to the geological, geochemical, REE and trace elements characteristics, it belongs to the A2 （PA） subtype granite. The SHRIMP U-Pb zircon dating gives a result of 385.2±8.1 Ma, which is located between the Middle and Late Devonian in the international stratigraphic chart, and can be regarded as the crystallization age of the Tula granite. The study indicates that the Tula area was in a local extensional environment in the end of the Middle Devonian, and that environment was probably related to the synchronized strike-slip activity of the Altun fault.

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang-Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U-Pb chronology, and Hf isotope approaches. We obtained the following conclusions： （1） Yaganbuyang granitoids mainly consist of two-mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc-alkaline or high-K calc-alkaline granite types. Zircon U-Pb data yielded ages of 939~7.1 Ma for granodiorite and ~954 Ma for granitoids, respectively. （2） The ~Hf（t） values of two--mica granite and granodiorite are in the range of-3.93 to ＋5.30 and -8.64 to ＋5.19, respectively. The Hf model ages （TDM2） of two-mica granite and granodiorite range from 1.59-.05 Ga and 1.62-2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenUe crust. （3） Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.

Geochronology and Petrogenesis of the Late Paleozoic Yulinhe Granodiorite in the Dunhuang Block, Western China

The Dunhuang Block is located in the conjunction area of the Tarim Craton,Central Asian Orogenic Belt.North China Craton.and Tethyan tectonic domain,and is traditionally regarded as a Precambrian crystalline basement block.However,recent research concluded that the Dunhuang Block represents a Paleozoic orogenic belt.The granitoids that outcrop in the Dunhuang Block recorded tectonic-thermal events in both the Early and Late Paleozoic,which are crucial to understand the tectonic evolutionary history of the Dunhuang Block.In this study,we carried out new petrographic,zircon U-Pb geochronological,and geochemical analyses on the Late Paleozoic Yunlinhe granodiorite,and evaluated its petrogenesis,especially in terms of genesis type and the residual rock.