北祁连造山带东段老虎山石英闪长岩成因及其地质意义

以北祁连造山带东段老虎山石英闪长岩体为研究对象,进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定,据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明,石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征,碱铝指数（AKI值） 均低于0.85,铝饱和指数（A/NKC 值） 多小于1.0,属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上,岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U）,亏损高场强元素（如Nb和Ta）,显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成,初始Sr同 位素值为0.7058~0.7071,εNd(t)值为-1.06~-0.31。综合分析表明,老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融,并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析,表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响,弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。     

北祁连造山带东段老虎山石英闪长岩成因及其地质意义

以北祁连造山带东段老虎山石英闪长岩体为研究对象，进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定，据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明，石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征，碱铝指数（AKI值） 均低于0.85，铝饱和指数（A/NKC 值） 多小于1.0，属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上，岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U），亏损高场强元素（如Nb和Ta），显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成，初始Sr同 位素值为0.7058~0.7071，εNd(t)值为-1.06~-0.31。综合分析表明，老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融，并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析，表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响，弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。     

Tectonics of the North Qilian orogen,NW China

The Qilian Orogen at the northern margin of the Tibetan Plateau is a type suture zone that recorded a complete history from continental breakup to ocean basin evolution, and to the ultimate continental collision in the time period from the Neoproterozoic to the Paleozoic. The Qilian Ocean, often interpreted as representing the “Proto-Tethyan Ocean”, may actually be an eastern branch of the worldwide “Iapetus Ocean” between the two continents of Baltica and Laurentia, opened at ≥ 710 Ma as a consequence of breakup of supercontinent Rodinia.Initiation of the subduction in the Qilian Ocean probably occurred at ~ 520 Ma with the development of an Andean-type active continental margin represented by infant arc magmatism of ~ 517–490 Ma. In the beginning of Ordovician (~ 490 Ma), part of the active margin was split from the continental Alashan block and the Andean-type active margin had thus evolved to western Pacific-type trench–arc–back-arc system represented by the MORB-like crust (i.e., SSZ-type ophiolite belt) formed in a back-arc basin setting in the time period of ~ 490–445 Ma. During this time, the subducting oceanic lithosphere underwent LT-HP metamorphism along a cold geotherm of ~ 6–7 °C/km.The Qilian Ocean was closed at the end of the Ordovician (~ 445 Ma). Continental blocks started to collide and the northern edge of the Qilian–Qaidam block was underthrust/dragged beneath the Alashan block by the downgoing oceanic lithosphere to depths of ~ 100–200 km at about 435–420 Ma. Intensive orogenic activities occurred in the late Silurian and early Devonian in response to the exhumation of the subducted crustal materials.Briefly, the Qilian Orogen is conceptually a type example of the workings of plate tectonics from continental breakup to the development and evolution of an ocean basin, to the initiation of oceanic subduction and formation of arc and back-arc system, and to the final continental collision/subduction and exhumation.     

Iron Isotopic Compositions of Forearc Mantle Peridotites Constrained by Ophiolites from the North Qilian Orogen,Northern Tibet

Previous studies on iron isotope compositions of subduction zone magmas have revealed significant and complex variations that have great bearings on petrogenetic processes in the mantle wedge, e.g., partial melting, fluid metasomatism and redox state. However, interpretations for the fractionations are highly debatable and lack direct constraints from mantle wedge peridotites. This study presents iron isotope compositions for whole rocks and mineral separates in fresh forearc peridotites from the Yushigou ophiolite, North Qilian orogen in northern Tibet. Major and trace element compositions of whole rock and mineral indicate that the peridotites are highly depleted forearc peridotites overprinted by melt metasomatism, in contrast to the long‐holding opinion that the peridotites are derived from mid‐oceanic ridges. The minerals fall on a line with a slope of ～1 on the plot of δ⁵⁶Fe vs. δ⁵⁶Fe, indicating isotope equilibrium between minerals. δ⁵⁶Fe fractionation between olivine and orthopyroxene is within the range of 0～0.05, while fractionation between olivine and spinel is about 0.05～0.10. The fractionation trend between olivine and spinel is opposite to previous theoretical and experimental constraints, which may be due to substantial Cr substitution into the spinel. This indicates that negative correlations between spinel Cr#, fO₂ and spinel δ⁵⁶Fe in previous studies are probably a reflection of gradual Cr enrichment in spinel during melt extraction, and spinel δ⁵⁶Fe values are not a proxy for oxygen fugacity. Whole rock δ⁵⁶Fe values are well correlated with mineral δ⁵⁶Fe values, varying from overlapping with depleted mantle to slightly lower than depleted mantle. Therefore, variations in iron isotope compositions of subduction zone magmas are probably due to combined effect of source heterogeneity and partial melting fractionation.     

北秦岭西段早侏罗世A型花岗岩及其地质意义

本文通过岩相学、岩石地球化学、锆石U?Pb定年和Lu?Hf同位素组成分析等方法,对出露于北秦岭西段宝鸡岩体王家山一带的黑云母花岗岩和其中的包体进行了研究。结果表明,该花岗岩形成时代为187±2 Ma,属于高钾钙碱性—钾玄岩系列岩石,富集Rb、Th、U等大离子亲石元素以及Nb、Zr和Hf等高场强元素,亏损Ba、Sr和Eu,具有高的全岩锆石饱和温度(825℃~838℃),显示A型花岗岩特征,形成于造山后的板内环境,可能为秦岭岩群副变质岩与安山质岩石部分熔融的产物。暗色包体显示塑性流变特征,具有岩浆结构,发育针状磷灰石和具有复杂成分环带的更长环斑结构长石,是幔源岩浆注入酸性岩浆发生混合作用的产物,形成时代为191±2 Ma,其锆石Hf同位素组成变化范围较大,εHf(t)值介于-11.26~-2.51,主要为富集地幔部分熔融产物。综合本文及前人已有研究结果,认为~190 Ma的早侏罗世早期秦岭地区早中生代碰撞造山过程已经结束,区域开始逐渐进入板内伸展构造演化阶段。     

北祁连洋早古生代双向俯冲的花岗岩证据

笔者主要对北祁连山中段的牛心山岩体、民乐窑沟岩体进行了锆石SHRIMP定年研究。结果表明：牛心山花岗岩的年龄为476Ma，民乐窑沟花岗闪长岩的年龄为463Ma。岩石地球化学显示．两岩体均具有大陆活动边缘的岩浆作用特征，结合岩体产出的区域构造位置及区域地质资料，笔者认为早古生代北祁连洋板块分别发生了向南、向北俯冲，其中向南俯冲形成牛心山花岗岩（476Ma），向北俯冲，形成了民乐窑沟花岗岩侵入体（463Ma）。     

北祁连早古生代花岗质岩浆作用及构造演化

北祁连山中段花岗岩锆石SHRIMP定年结果表明,柯柯里岩体的斜长花岗岩和石英闪长岩的年龄分别为512Ma和501Ma,野马咀和金佛寺花岗岩的年龄分别为508Ma和424Ma。结合区内其它花岗岩体的定年资料,根据花岗岩的岩石地球化学特征及岩体产出的构造位置、区域地质资料等,我们认为,早古生代北祁连洋板块向南俯冲,至少引发了两期花岗质岩浆作用,第一次岩浆作用形成柯柯里斜长花岗岩(512Ma)、野马咀花岗岩(508Ma)和柯柯里石英闪长岩(501Ma),第二次花岗质岩浆作用形成牛心山花岗岩(477Ma)。由于往南俯冲的板块受到柴达木板块向北俯冲的影响,俯冲受阻,继而俯冲极性发生变化,转向北俯冲,形成了民乐窑沟(463Ma)等花岗岩侵入体。大约440Ma之后,洋盆闭合,柴达木陆块和阿拉善陆块对接碰撞,形成北祁连造山带。由于造山带根部岩石圈发生折沉作用,造山带上不同的块体伸展、滑塌,形成一系列碰撞后花岗岩如金佛寺花岗岩(424Ma)及牛心山岩体的石英闪长岩(435Ma)等。     

Characteristic elemental compositions of the Yangtze River and Yellow River surface sediments and their geological background

Significant differences are noticed in major and trace element compositions between the Yangtze River and the Yellow River surface sediments.The former sediments are rich in some major elements such as K,Fe,Mg,Al,and most of the trace elements which show wide variations in element concentrations,whereas the Yellow River sediments only have higher Ca,Na,Sr,Ba,Th,Ga,Zr,Hf contents and show slight variations in element contents.In the Yangtze River Basin are widely distributed intermediate-acid igneous rocks and complicated source rocks together with strong chemical weathering which determine the elemental compositions of the Yangtze River sediments,while the elemental compositions of the Yellow River sediments are decided by the chemical composition of loess from the Loess Plateau and intense physical weatering.Cu,Zn,Sc,Ti,Fe,V,Ni,Cr,Co,Li and Be can be used to distinguish the Yangtze River sediments from te Yellow River sediments and be treated as tracers for both the sediments to study the processes of their mixing and diffusion in the coastal zones of China.     

The Hanshan gold deposit in the Caledonian North Qilian orogenic belt, NW China

The recently discovered Hanshan gold deposit in northern Gansu Province, northwestern China, is hosted by a WNW-striking shear zone in Ordovician andesite and basalt. Mineralization consists of surface to near-surface oxidized ore (the yellow sandy gossan type) and three types of primary ore, i.e. early-stage quartz-sericite-pyrite ores in stockworks, early-stage disseminated ore, and the most important late-stage quartz ± calcite-sulfide veins. The ore system is characterized by variable degrees of potassic and silicic alteration. Late-stage gold-related fluid inclusions have homogenization temperatures between 170 to 310 °C, with a peak around 260 °C and low salinities. The ore fluids had high contents of CO₂, CH₄, and N₂. Sulfur isotope measurements of −1.9 to +1.7 per mil for hydrothermal pyrites could be consistent with a hydrothermal fluid source from the mantle, but the oxygen and carbon isotope data from calcite and quartz suggest mixing between mantle and crustal fluid sources. K-Ar ages for hydrothermal sericite from ore zones are 213.9 ± 3.1 and 224.4 ± 3.2 Ma. Due to the arid Cenozoic climate, a yellow gold-bearing gossan developed, which consists of jarosite, gypsum, and relict quartz. It could be a widespread and useful prospecting guide for gold in northwestern China. Received: 1 February 1999 / Accepted: 1 August 1999     

A Petrographic and Mineralogical Study of Volcanic Rocks from the Mayaxueshan Area, North Qilian Fold Belt, NW China

The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz, and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assemblages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. This indicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result of Caledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks should be re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age: prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpeilyite to lower greenschist facies for the lower part of the Middle Ordovician vol     

云南怒江河流沉积物碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素组成及其地质意义

采用LA-MC-ICP-MS测定技术,对怒江河流沉积物中的碎屑锆石进行了U-Pb和Lu-Hf同位素测定。结果显示,碎屑锆石U-Pb年龄可分为6个组段:50~74Ma、84~235Ma、275~413Ma、451~569Ma、657~1429Ma和1602~3436Ma,其中最主要的年龄组段为50~74Ma和84~235Ma。50~74Ma的年龄段为新特提斯洋从俯冲到碰撞闭合的阶段,约65Ma的年龄峰值可能是印度大陆与欧亚大陆主体碰撞的远程地质记录。84~235Ma年龄段代表了中特提斯洋演化阶段,年龄峰值约为110Ma,可能指示羌塘地块与拉萨地块的碰撞拼接此时已经完成,通过U-Pb年龄分布对比,羌塘地块几乎没有给怒江河流沉积物提供物质。怒江河流沉积物中碎屑锆石的εHf(t)值介于-18.7~+11.7之间,模式年龄分布于0.65~4.05Ga之间,其中中生代碎屑锆石的εHf(t)值分布于-16.4~+2.9之间,与中拉萨地块有密切的亲缘性,同时含有少量北拉萨地块的特征。因此,怒江河流沉积物代表了中拉萨地块与北拉萨地块的特征。     

云南怒江河流沉积物碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素组成及其地质意义

采用LA-MC-ICP-MS测定技术,对怒江河流沉积物中的碎屑锆石进行了U-Pb和Lu-Hf同位素测定。结果显示,碎屑锆石U-Pb年龄可分为6个组段：50~74Ma、84~235Ma、275~413Ma、451~569Ma、657~1429Ma和1602~3436Ma,其中最主要的年龄组段为50~74Ma 和84~235Ma。50~74Ma的年龄段为新特提斯洋从俯冲到碰撞闭合的阶段,约65Ma的年龄峰值可能是印度大陆与欧亚大陆主体碰撞的远程地质记录。84~235Ma年龄段代表了中特提斯洋演化阶段,年龄峰值约为110Ma,可能指示羌塘地块与拉萨地块的碰撞拼接此时已经完成,通过U-Pb年龄分布对比,羌塘地块几乎没有给怒江河流沉积物提供物质。怒江河流沉积物中碎屑锆石的εHf(t)值介于-18.7~+11.7之间,模式年龄分布于0.65~4.05Ga之间,其中中生代碎屑锆石的εHf(t)值分布于-16.4~+2.9之间,与中拉萨地块有密切的亲缘性,同时含有少量北拉萨地块的特征。因此,怒江河流沉积物代表了中拉萨地块与北拉萨地块的特征。     

太行山南段中生代杂岩体的岩石成因:元素和Nd-Sr-Pb同位素地球化学证据

通过太行山南段三个中生代杂岩体(西戌、武安和洪山)的元素和同位素地球化学特征的研究。讨论其成因和地球动力学环境。结果表明，西戌和武安杂岩体主要由从二长辉长岩到二长岩的一系列岩石组成，其地球化学性质相似(高Mg^s，具微弱至正Eu异常的REE模式等)。西戊杂岩体的εNd(135Ma)=-12．3～-16．9，Isε=0．7056～0．7071，与武安杂岩体稍有不同。西戌杂岩体的(^206Pb／^204Pb)i=16．92～17．3，(^207Pb／^204Pb)i=15．32～15．42，(^208Pb／^201Pb)i=37．16～37．63，较武安杂岩体的略高。西戊-武安杂岩体都起源于EM1型富集地幔，但被下地壳物质不同程度混染。洪山杂岩体(正长岩-花岗岩)也来自EM1型富集地幔的部分熔融，但属于不同的岩浆事件，并仅受轻微的下地壳混染。太行山岩浆作用的发生可能与古太平洋板块的水平俯冲消减而形成的弧后伸展环境有关。     

黑河出山径流的非线性特征分析

应用非线性动力学的理论和方法,对黑河出山径流的非线性特征进行了分析.结果表明,黑河月出山径流的年内分布、年平均流量的一次峰、谷变化符合单重或双重威布尔分布,并具有自相似性质.黑河出山径流多年变化在相空间中的运动轨迹收缩到一个约为4.32维的吸引子上,而描述流量的动力方程需要8个独立变量.黑河出山径流的非线性特征还表现在对内部结构为非线性函数的输入输出模型的良好应用上,如GRNN神经网络模型、非线性回归模型等.     

祁连山大通河河流阶地形成时代及地质意义

祁连山是研究青藏高原隆升与构造变形的关键部位,其中大通河河流阶地是祁连山地区早更新世以来构造隆升和气候变化的载体,厘定大通河河流阶地的形成时代及地质意义对于分析祁连山地区的区域构造和气候环境改变具有重要意义。通过ESR测年技术,并对大通河流域江仓区域的剖面样品实测,获取岩层形成时代数据,分别为(42±4) ka B.P.、(71±5) ka B.P.、(121±12) ka B.P.、(210±20) ka B.P.和(602±60) ka B.P.。根据测年结果,确认剖面为河流相沉积环境,形成时代对应中晚更新世酒泉砾岩和戈壁砾岩时期,表明大通河河流阶地在542~662 ka B.P.之前就已经形成,推测其可能是受到中新世白杨河组之后的盆山运动或早更新世祁连山的褶皱变形影响而形成的。利用测年数据计算抬升速率,从中更新世晚期到晚更新世中期,抬升速率加快,反映了大通河流域的构造运动和气候变化加强,祁连山江仓地区在此期间快速隆升,为青藏高原东北缘以面积和体积扩张的观点提供了新的依据。     

北祁连香子沟榴辉岩相变沉积岩的锆石U-Pb年代学、Hf同位素特征及其地质意义

榴辉岩相变沉积岩普遍分布在北祁连HP/LT变质带中,在HP/LT变质带的西段香子沟地区,变质沉积岩的矿物组合为石英+多硅白云母+石榴子石+绿帘石±蓝闪石±绿辉石(+金红石+锆石)。利用石榴子石-绿辉石-多硅白云母地质温压计获得变沉积岩的峰期变质温度为448~467℃,压力为2.0~2.2GPa。锆石SHRIMP和LA-ICPMS U-Pb测试结果显示,碎屑锆石核的年龄分布在532~2700Ma之间,大部分集中在中元古代和晚古元古代之间,显示原岩的碎屑物质主要来源于中-古元古代岩石。2个样品的变质锆石边获得的206Pb/238U加权平均年龄分别为495±7Ma(MSWD=0.63)和496±7Ma(MSWD=5.6),代表了榴辉岩相变质年龄。结合前人研究成果和锆石Hf同位素特征,表明榴辉岩相变沉积岩的原岩形成于以陆缘碎屑为主的活动大陆边缘或弧前环境,在早古生代洋壳俯冲过程中,通过俯冲剥蚀作用被卷入到俯冲带深部,与所包裹的基性岩(榴辉岩的原岩)一起发生榴辉岩相变质作用,并快速折返至浅部。     

北祁连水洞峡蛇绿岩形成时代与构造环境

蛇绿岩的时空关系与构造归属是深入认识俯冲带演化和重建古板块构造格局的关键地质依据之一.水洞峡蛇绿岩作为北祁连南带蛇绿岩东段的重要组成部分,其形成时代和构造环境一直缺乏准确的限定.采用LA-ICP-MS对水洞峡蛇绿岩中的辉长岩进行了锆石U-Pb测年,所获得的 206Pb/238U加权平均年龄为497.0±2.4 Ma(M...     

北祁连干沙鄂博矿区碱性岩锆石U- Pb年龄、Hf同位素及岩石地球化学特征

干沙鄂博稀土矿床位于北祁连造山带中段,是祁连成矿带内最大的稀土矿床。矿体产于早泥盆世碱性岩体及其围岩接触带内。为了查明含矿碱性岩体侵位时代、岩石成因和源区性质,本文开展了岩石学、锆石U- Pb定年、锆石Hf同位素及岩石地球化学研究。结果表明碱性岩体由霓辉正长岩、霓辉正长斑岩、石英正长斑岩和花岗斑岩组成,侵入于毛藏寺花岗闪长岩中。该岩体LA- ICPMS锆石U- Pb年龄为409.7±5.8Ma,εHf(t)值变化于-0.15~+2.34之间,平均1.03,tDM2(Hf)为1.2~1.1 Ga。岩石主量元素SiO2介于59.1%~68.5%之间,具高钾（Na2O/K2O =0.35~0.85）,富碱质（K2O+Na2O=7.91%~11.09%）、贫CaO（2.90%~8.17%）、MgO（0.21%~1.30%）的特征,属钾玄质系列碱性岩;岩石强烈富集轻稀土元素和大离子亲石元素（如Rb、Ba、Sr、U 和Pb等）,亏损重稀土元素和高场强元素（如Nb、Ta和Ti）,弱负Eu异常（δEu为0.7 ~ 0.8）,以及轻稀土富集的右倾型稀土元素配分模式,具A型花岗岩岩石地球化学特征。结合区域构造演化,认为干沙鄂博矿区碱性岩形成于造山后伸展环境,为晚奥陶世北祁连洋闭合后,于早泥盆世发生区域性拉张作用,诱发碱性岩浆侵入和与其共生稀土矿体的形成。     

西秦岭江里沟复式岩体LA-ICP-MS锆石U-Pb年龄、地球化学和Hf同位素特征及其地质意义

古特提斯洋在三叠纪时期沿现今勉略缝合带的闭合,标志着华北板块(NCB)和扬子板块(YZB)的最终拼贴完成。秦岭造山带西段发育印支期花岗岩浆活动,为该地区的成矿作用提供了有利的条件。对这些岩浆岩的形成时代、地化属性、演化、来源等的研究将有助于了解该时期的构造背景及动力学环境。本文以西秦岭北亚带的江里沟复式岩体作为研究对象,通过LA-ICP-MS锆石U-Pb测年、锆石Hf同位素测试和主微量元素分析,对该岩体进行了系统的研究。结果显示:江里沟复式岩体的三种主要岩性为斑状黑云母二长花岗岩、花岗斑岩和细粒花岗岩,加权平均年龄分别为:229.1±1.8Ma(MSWD=0.82)、222.5±1.4Ma(MSWD=0.41)和217.1±1.8Ma(MSWD=1.4),指示该岩体形成于晚三叠世。其地球化学性质具有高硅(SiO_2=72.67%~77.84%),富碱(K_2O+Na_2O=7.67%~8.75%),弱过铝质(A/CNK=1.01~1.06),高度分异(岩体由早至晚DI及Rb/Sr均升高,DI=88.9~95.36,Rb/Sr=1.76~12.19),富集Rb、Th、U、Ta、Zr、Hf和HREE元素特点,亏损Ba、Sr、P、Ti等元素;三个侵入体均发育明显负Eu异常(δEu=0.54~0.62、0.26~0.47、0.20~0.60);P_2O_5含量与SiO_2呈明显的负相关关系,而Y的含量反之,综合判定认为,岩体属高分异I型花岗岩。岩石形成温度从早至晚明显降低(平均由786℃至755℃)。εHf(t)值少数0外,绝大多数介于0.1~4.8之间,相应tDM2=0.95~1.25Ga。综合推断认为,江里沟岩体的原始岩浆是由部分熔融的岩石圈地幔与中新元古代的地壳混合,形成的混合岩浆,后经强烈的结晶分异作用形成江里沟复式岩体。