川西双江口地区花岗岩的岩石学、地球化学特征及其成因研究

双江口地区出露的花岗岩主要为二云二长花岗岩和似斑状黑云花岗岩,二者呈侵入接触关系,在岩体特征、岩石颜色、结构、矿物组成及后期改造等方面存在较为明显的差异。岩相学特征表明二云二长花岗岩形成晚于似斑状花岗岩,岩石地球化学特征表明二者成因为部分熔融,物源为壳源,形成环境为同碰撞-造山带环境,形成时间为印支晚期。     

西准噶尔巴尔雷克一带石炭系黑山头组火山岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及构造环境

内容提要：西准噶尔巴尔雷克山南部的石炭系黑山头组火山岩主要由灰-灰紫色（气孔）杏仁状安山岩、杏仁状玄武安山岩组成,属亚碱性系列。LA-ICP-MS锆石U-Pb年龄为349±8Ma,MSWD=0.14（95%置信度）,时代属早石炭世。Mg#介于23.82~50.45,全碱含量（Na2O+K2O=3.74%~8.02%）较高且相对富钠,轻稀土（LREE）相对富集（（La/Yb）N=2.87~13.41）且分馏较好（（La/Sm）N值均大于1（1.46~3.41）,重稀土分馏较差（（Gd/Yb）N=1.46~3.48）。仅部分样品有微弱的负铕异常（δEu=0.82~1.47）。大离子亲石元素（LILE）Ba、Th、K、Sr相对富集,其中Ba、K的富集尤为明显,高场强元素（HFSE）Nb、Ta相对亏损,Ti轻微亏损,Zr、Hf略富集。地球化学特征表明其为俯冲带流体交代岩石圈地幔的产物,综合分析认为其形成于活动大陆边缘环境。黑山头组火山岩时代的确定及构造环境信息为进一步认识西准噶尔巴尔雷克一带的构造演化提供了新的证据。     

大兴安岭敖包查干地区安山岩年代学、地球化学研究

在大兴安岭敖包查干地区首次识别出中三叠世安山质岩石,主要岩性为玄武质安山岩、粗面安山岩,应用锆石U—DbLA—ICPM—AS法定年,结果表明安山岩形成于234．8±3．2Ma～231．4±1．2Ma,属中三叠世。地球化学特征显示,研究区安山岩具高SiO2（54．19％～62．30％）、A12O3（15．78％～17．30％）、K20（1．77％～3．92％）、Na2O（2．95％～5．66％）、Na2O＋K20（5．4～8．99）的特征和低MgO（1．23％～3．66％,Mg^#=27．89～50．48）含量,并与SiO2含量呈负相关关系。岩石富Na20（Na2O／K2O=1．01～2．86）,铝指数A／CNK=0．81～1．21,属准铝质一弱过铝质钙碱性系列岩石。富集大离子亲石元素（LILE）K、Rb、Th和轻稀土元素,亏损高场强元素（HFSE）№、Ta、P、Ti,轻重稀土元素分馏明显[（LaMb）N=3．31～10．33]．无Eu异常（δEu=0．80～1．03）,显示弧火山岩的特征,但所研究样品的Zr、Hf呈弱正异常、Rb弱负异常却不同于正常岛弧安山岩,Zr／Y—Zr图解以及高钾特征显示出板内伸展构造环境的特征。综合研究表明敖包查干地区中三叠世钙碱性安山岩可能为古亚洲洋残余俯冲洋壳部分熔融的产物,与底侵作用有关,形成于大陆内部伸展构造环境。     

Geochemistry of Fe-Mn deposits of the Atlantic Ocean (Strakhov Basin,Elena Seamount,and Cape Verde Quadrangle)

Fe-Mn deposits for this research were sampled at the floor of the Atlantic Ocean in the Cape Verde Quadrangle, Elena Seamount, and Strakhov Basin. The samples were analyzed for major components and for Ni, Co, Cu, P, S, and other trace elements by ICP-AES. Common features in the distribution of REE (high positive Ce anomalies) were discovered, and trends in the distribution of elements with depths are revealed. As, Pb, Sr, Co, and Pt are prone to accumulate in shallower water areas, whereas Cu and Li are enriched at deeper water territories. The samples are analyzed in compliance with Andreev’s classification, and their noble metal composition is determined.     

Geochemistry of the volcanoplutonic association of the Shaw massif (East Antarctica): Composition,genesis, and geodynamic interpretation

This paper reports the first petrological and geochemical evidence for the Meso-Neoproterozoic metamorphic and metaintrusive rocks of the Shaw Mountain massif (Prince Charles Mountains, East Antarctica). It was shown that the orthogneisses (plagiogneisses) and metabasites of the massif were formed as constituents of a volcanoplutonic complex, which included a variety of igneous rocks of normal and subalkaline groups, from ultrabasic to silicic and was assigned to the volcanic tholeiite basalt-andesite-rhyolite, plutonic peridotite-gabbro, and late (?) calc-alkaline gabbro-diorite-plagiogranite associations. The distribution of major and compatible trace elements indicates the fractionation of the primary melts that produced the volcanoplutonic association of the Shaw massif. With respect to the distribution of REE and trace elements and some trace element ratios, the metabasic rocks of the Shaw massif correspond mainly to enriched and normal basalts of mid-ocean ridges, continental rifts, and ocean islands, which suggests a contribution from a plume mantle source. It was found that the region of the Shaw massif is a high-grade metamorphosed margin of the Fisher volcanoplutonic complex, a Mesoproterozoic structure of single geodynamic nature. This is supported by the spatial proximity of the Shaw and Fisher regions, the similar behaviors of most major elements and distribution patterns of trace elements and REE in comparable magmatic associations, and the similar ages of some plutonic associations. Based on the petrological and geochemical data, an alternative geotectonic model was proposed for this region. According to this model, the Fisher complex was formed in a setting of continental rifting coupled with the processes of mantle diapirism, which was subsequently changed by the compression stage. During rifting, the structure could experience significant opening accompanied by ultrabasic-basic tholeiitic magmatism with a significant contribution of mantle material. A subsequent inversion resulted in that the rift structure underwent considerable horizontal compression accompanied by calc-alkaline magmatism and the formation of narrow intracratonic fold zones. The cyclic character of rifting processes and superposition of young rift systems on older ones was also established in the Phanerozoic geotectonic history of the region of the Prince Charles Mountains.     

Geochemistry of the Onyx River (Wright Valley,Antarctica) and its role in the chemical evolution of Lake Vanda

The Onyx River (Wright Valley, Antarctica) is a dilute meltwater stream originating in the vicinity of the Wright Lower Glacier. It acquires a significant fraction of its salt content when glacial meltwaters contact Wright Valley soils at Lake Brownworth and the concentrations of all ions increase with distance along the 28-km channel down to Lake Vanda. Average millimolar concentrations of major ions at the Vanda weir during the 1980–1981 flow season were: Ca = 0.119; Mg = 0.061; Na = 0.212; K = 0.033; Q = 0.212; SO₄ = 0.045; HCO₃ = 0.295; and SiO₂ = 0.049. Based on the flow measurements of Chinn (1982), this amounts to an annual flux (in moles) to Lake Vanda of: Ca = 0.238 × 10⁶; Mg = 0.122 × 10⁶; Na = 0.424 × 10⁶; K = 0.066 × 10⁶; Cl = 0.424 × 10⁶; SO₄ = 0.09 × 10⁶; HCO₃ = 0.59 × 10⁶; SiO₂ = 0.098 × 10⁶.In spite of the large salt input from this source, equilibrium evaporation of Onyx River water would have resulted in early calcite deposition and in the formation of a Na-Mg-Cl-HCO₃ brine rather than in the Ca-Na-Mg-Cl waters observed in Lake Vanda. The river alone could not have produced a brine having the qualitative geochemical features of the lower saline waters of Lake Vanda.It is proposed that the Vanda brine is instead the result of past ( > 1200 yrs BP) mixing events between Onyx River inflows and calcium chloride-rich deep groundwaters derived from the Don Juan Basin. The mixing model presented here shows that the Onyx River is the major contributor of K, HCO₃, SO₄, and (possibly) Mg found in the lake and a significant contributor (approximately one half) of the observed Na. Calcium and Cl, on the other hand, came largely from deep groundwater sources in the Don Juan Basin. All concentrations except Mg are well predicted by this model. The chemical composition of the geologically recent upper lake is explained in terms of ionic diffusion from the pre-formed brine, coupled with Onyx River inflow. Ionic ratios calculated from this latter model are in very good agreement with those observed in the lake at 35 meters.     

新疆古伦沟地区古仍格萨拉东岩体的地球化学及锆石U-Pb年龄

古伦沟地区古仍格萨拉东花岗闪长斑岩体位于中天山构造带北缘。地球化学和锆石U-P年龄测定结果显示: 岩石高碱富Na、贫Fe和Mg、弱过铝质(ACNK=0.98~1.11), 稀土总量较低(∑REE=61.28×10-6~99.50×10-6)且分异明显(LaN/YbN=7.82~22.80)、铕弱负异常(δEu=0.72~0.97), 相对富集Rb、Ba、Th、U、K等, 亏损Nb、Ta、P、Ti等, 具火山弧花岗岩的特征。岩体具有较均一的Sr、Nd同位素组成: (87Sr/86Sr)i=0.70677~0.70685, εSr(t)=40.10~41.21, (143Nd/144Nd)i=0.51190~0.51191, εNd(t)= –2.62 ~ –2.30, tDM＝1.31~1.38 Ga。其锆石U-Pb年龄为(488.9±1.7)~(470.5±3.1) Ma。表明古仍格萨拉东岩体形成于早奥陶世陆缘弧环境, 可能是先存的中元古代幔源基性下地壳部分熔融的产物, 其形成与古准噶尔洋向伊犁—中天山板块下的俯冲作用有关, 标志着中天山北缘于早奥陶世时期已进入与俯冲消减有关的活动陆缘演化阶段。此次岩浆活动导致区内发生斑岩型铜矿化。     

The Geochemistry of Lake Joyce, McMurdo Dry Valleys, Antarctica

Lake Joyce is one of the least studied lakes of the McMurdo Dry Valleys. Similar to other lakes in this region, Lake Joyce is a closed-basin, permanently ice-covered, meromictic lake. We present here a detailed investigation of major ions, nutrients, and dissolved trace elements for Lake Joyce. Specifically, we investigate the role of iron and manganese oxides and hydrous oxides in trace metal cycling.Lake Joyce is characterized by fresh, oxic waters overlying an anoxic brine, primarily Na–Cl. Surface waters have a maximum nitrate concentration of 26M with a molar dissolved inorganic nitrogen to phosphorus ratio of 477. The supply of nitrogen is attributed to atmospheric deposition, possibly from polar stratospheric clouds. Dissolved phosphorus is scavenged by hydrous iron oxides. The pH is highest (10.15) just beneath the 7-m thick ice cover and decreases to a minimum of 7.29 in the redox transition zone. Dissolved Al exceeds 8M in surface waters, and appears to be controlled by equilibrium with gibbsite. In contrast, concentrations of other trace elements in surface waters are quite low (e.g., 5.4nM Cu, 0.19nM Co, <20pM La). Dissolved Fe, Mn, Ni and Cd were below our detection limits of 13 nM, 1. 8 nM, 4.7 nM and 15pM (respectively) in surface waters. There was a 6-m vertical separation in the onset of Mn and Fe reduction, with dissolved Mn appearing higher in the water column than Fe. Based on thermodynamic calculations, dissolved Mn appears to be controlled by equilibrium with hausmannite (Mn3O4). Co tracks the Mn profile closely, suggesting Co(III) is bound in the lattice of Mn oxides, whereas the Ce profile is similar, yet the Ce anomaly suggests oxidative scavenging of Ce. Release of Cu, Ni, Cd and trivalent REE appears to be controlled by pH-induced desorption from Fe and Mn oxides, although Cu (and perhaps Ni) may be scavenged by organic matter in surface waters.     

新疆西准噶尔白布谢河花岗斑岩锆石U-Pb年龄、地球化学特征及其构造意义

西准噶尔中部广泛发育晚石炭世—晚二叠世侵入岩,其产出构造背景对于揭示该区晚古生代构造演化具有重要意义.文章以巴尔鲁克山北侧侵入于上石炭统莫老坝组中的白布谢河花岗斑岩为研究对象,通过岩相学、锆石U-Pb年代学、全岩主—微量元素和Sr-Nd同位素分析,据此探讨其岩石成因和构造背景,以期为进一步深入研究西准噶尔中部构造演化提...     

Age,Mineralogical and Geochemical Features,and Tectonic Position of Gabbroids of the Dzhigdinskii Massif,Southeastern Environ of the North Asian Craton

Complex mineralogical, geochemical, and geochronological studies of the gabbroids from the Dzhigdinskii Massif located in the western part of the Dzhugdzhur–Stanovoy Superterrane are performed. It is established that the age of the rocks from the Dzhigdinskii Massif is Middle Triassic (244 ± 5 Ma), rather than Early Archean, as was previously assumed. The age of the Dzhigdinskii Massif is close to the age of the formation of the other Triassic gabbroid massifs, such as the Amnunaktinskii (~240 Ma), Lukindinskii (~250 Ma), and Luchinskii (~248 Ma) in the southeastern environ of the North Asian Craton. One of the stages in the formation of the Selenga–Vitim volcanoplutonic belt falls in this period as well. This indicates that the Selenga–Vitim volcanoplutonic belt, along with the granitoids and volcanic rocks, is composed of ultrabasic–basic and basic massifs and that this belt is superposed on the structures of the Selenga–Stanovoy Superterrane, as well as on the western part of the Dzhugdzhur–Stanovoy Superterrane. The gabbro, gabbro–diorite, and series of gabbro and gabbro–diorite with high sodic alkalinity from the Dzhigdinskii Massif show obvious geochemical features of duality, including combination of intraplate and super-subduction origin. In this relation, we can assume that the origin of the gabbroids of the Dzhigdinskii Massif is related to the detachment of the oceanic lithosphere and its subduction into the mantle with the formation of an “asthenospheric window.”     

The First Find of Fluorcalciobritholite and Fluorbritholite-(Ce) Minerals in Gabbroids

Doklady Earth Sciences - Fluorcalciobritholite and fluorbritholite-(Ce)—rare-earth minerals from the apatite supergroup—have been found in the course of the study in monzogabbro from...     

西昆仑黑伞顶新近纪次火山岩地球化学特征及成因

黑伞顶次火山岩分布于西昆仑东段华北板块与华南板块的结合部位, 主要由花岗斑岩体组成, 侵入于石炭系托库孜达坂群、二叠系树维门科组及古近系阿克塔什组地层中。花岗斑岩黑云母K-Ar同位素年龄值13.2 Ma, 为新近纪中新世的产物。黑伞顶次火山岩具有低硅镁、高铝钾的特点, SiO2含量介于65.19%~67.21%之间, MgO含量为0.83%~1.47%, Al2O3在14.53%~16.5%之间变化, K2O含量为4.44%~4.93%。K2O/Na2O为1.49~1.52, A/CNK为1.08~1.14, 里特曼指数σ为2.22~3.03, 为过铝质高钾钙碱性岩石。富集大离子亲石元素K、Rb、Th、U, 高场强元素Nb、Ta、Ti明显亏损。高Sr(528×10?6~707×10?6)及Sr/Y(38.2~63), 低Y(8.38×10?6~18.24×10?6)和Yb(0.73×10?6~1.64×10?6)。稀土元素总量较高, 介于307.87×10?6~458.20×10?6之间, 稀土元素配分曲线为右倾斜型。LREE/HREE为24.19~34.47, 属轻稀土元素富集型。具有弱至中等的负铕异常。地球化学特征表明, 黑伞顶次火山岩为高钾钙碱性C型埃达克质岩, 形成于青藏高原隆升和板内地壳加厚的背景下, 是青藏高原北部在中新世因陆壳加厚引起下地壳部分熔融的产物。     

Geochemistry of soils of King George Island, South Shetland Islands, West Antarctica: Implications for pedogenesis in cold polar regions

Fine fractions of soils on the Barton Peninsula, King George Island, West Antarctica have been forming during the last 6000 yr since the last deglaciation. Texturally, they are mostly composed of mineral and rock fragments with some volcanic ashes, which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration. No significant changes are observed in major- and trace element abundances. Such geochemical characteristics suggest that chemical weathering of bedrocks on the Barton Peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and Patagonian dusts. Chondrite-normalized rare earth element (REE) distribution patterns of the Barton Peninsula soils are slightly different from those of bedrocks, indicating that the REE abundances and characteristics were influenced by eolian additions. Mixing calculations, which mass-balance the REEs, suggest that volcanic ashes blown from Deception Island were the major eolian contributor, followed by atmospheric dusts sourced from Patagonia, South America. Even in the warmer and humid climatic conditions in the maritime Antarctic region, the chemical weathering of bedrocks appears to be insignificant, probably due to the relatively short duration of weathering since the last deglaciation.     

Geochemistry and petrology of ultramafic lamprophyres from Schirmacher Oasis, East Antarctica

Summary Petrographic and geochemical data are presented for some ouachitites from the Schirmacher Oasis. The studied dike intruded into the metamorphic basement of the East Antarctic craton. The ouachitite samples contain substantial amounts of zoned phlogopite and diopsidic to salitic pyroxene as phenocrysts. K-rich nepheline is the predominant phase of the matrix. The rocks are characterized by low SiO₂ concentrations (up to 36.5 wt.%), low mg# and high abundances of Al²O³, alkalis and volatiles. Trace element compositions of the Schirmacher ouachitites differ from those of ultramafic lamprophyres from other regions in that they contain significantly lower Cr and Ni concentrations and relatively low enrichments in LILE and LREE. The studied rocks have low¹⁴³Nd/¹⁴⁴Nd and enhanced⁸⁷Sr/⁸⁶Sr ratios. Pb isotope compositions of the ouachitites closely resemble those of MORB. The ¹⁸O values range between 4.1 and 4.7⁰/₀₀ which may be due to interactions with meteoric water. Because the Schirmacher ouachitites are only represented by a few samples it is impossible to discuss the petrogenesis of this magma. However, according to trace element and isotopic characteristics, it can be ruled out that Schirmacher ouachitites and associated minettes (documented inHoch, 1997;Hoch andTobschall, 1998) were derived from the same mantle reservoir.

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Geochemie und Petrologie von Ouachititen aus der Schirmacher Oase, Ostantarktika

Zusammenfassung In dieser Arbeit werden petrologische und geochemische Daten von Ouachititen aus der Schirmacher Oase vorgestellt. Der beprobte Gang intrudierte in das metamorphe Basement des ostantarktischen Kratons. Zonierte Phlogopite und diopsidische bis salitische Pyroxene sind die häufigsten mafischen Einsprenglinge. K-reiche Nepheline bilden die Hauptmineralphase der Grundmasse. Charakteristisch für die Ouachititproben sind niedrige SiO₂-Konzentrationen (bis 36.5 Gew.%) und mg#, aber hohe Gehalte an Al₂O₃ Alkalien und volatilen Bestandteilen. Die Spurenelementzusammensetzung der Schirmacher Ouachitite unterscheidet sich von UML-Proben aus anderen Regionen durch ihre extrem geringen Cr- und Ni-Konzentrationen und die vergleichsweise niedrigen Anreicherungen an LILE und LREE. Die bearbeiteten Gesteine zeigen niedrige¹⁴³Nd/¹⁴⁴Nd- und erhöhte⁸⁷Sr/⁸⁶Sr-Verhältnisse. Die Pb-Isotopie der Ouachitite entspricht der von MORB. 6180-Werte variieren zwischen 4.1 und 4.7⁰/₀₀, was auf eine eventuelle Beeinflussung durch meteorische Wässer hindeutet. Da von den Schirmacher Ouachititen nur wenige Proben für eine Bearbeitung zur Verfügung standen, ist es nicht möglich, die Petrogenese des Magmas zu diskutieren. Aber aufgrund der Spurenelement- und Isotopensignaturen kann ein gemeinsames Mantelreservoir der Schirmacher Ouachitite und Minette (beschrieben inHoch, 1997;Hoch undTobschall, 1998) ausgeschlossen werden.

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With 6 Figures     

滇西腾冲-梁河地区花岗岩锆石稀土元素组成和U-Pb同位素年龄

在详细的区域地质调查基础上,对滇西腾冲-梁河地区花岗岩的锆石进行了阴极发光观察,并通过LA-ICP-MS分析了其稀土元素组成和U-Pb同位素年龄。花岗岩中大部分锆石具有振荡环带,锆石稀土元素表现为亏损轻稀土、阶梯式富集重稀土、强烈正Ce异常及强烈负Eu异常,表明锆石为典型的岩浆锆石。花岗岩（D0053）锆石的²⁰⁶Pb/²³⁸U加权平均年龄为（127.9±1.0） Ma (MSWD=2.9,27个点),花岗岩（D4310）锆石的²⁰⁶Pb/²³⁸U加权平均年龄为（58.3±0.5） Ma (MSWD=1.8,21个点),表明腾冲-梁河地区存在大量早白垩世和早第三纪花岗岩浆活动,它们是特提斯演化过程的岩浆响应。     

Geochemistry of mafic igneous rocks of the northern Prince Charles Mountains,Antarctica

Rare mafic dykes, which intrude 1000 Ma high‐grade metamorphic rocks of the northern Prince Charles Mountains‐Mawson Coast area, are compositionally distinct from abundant early to middle Proterozoic tholeiite dykes, which are confined to Archaean or early Proterozoic terrains in the southern Prince Charles Mountains and elsewhere in East Antarctica, and which have therefore proved useful as stratigraphic markers. The younger dykes (and extrusive rocks) are a composition‐ally heterogeneous group with a wide range of ages (at least Cambrian to Eocene), although most are of K‐rich alkaline composition or have alkaline affinites. Their strong enrichment in highly incompatible elements (Rb, Ba, Th, Nb, K, Pb, Th and U) relative to less incompatible elements (La, Ce and P) suggests derivation by partial melting of more enriched mantle source regions than those of most of the Proterozoic tholeiite suites. However, unlike the latter, many incompatible element ratios have been significantly affected by fractional crystallisation and possibly also by the presence of residual minor phases during low degrees of melting.     

Geochemistry of Mercury Mineralization,Catian,West Hunan

The Tongfeng mercury zone is an important producer of mercury in China.The underlying Lower Cambrian black rock series is strongly depleted in mercury and is thought to be the major source bed for mercury mineralization .The Catian deposit ,as the representative of the zone, was formed at low temperature,which is characterized by a meteoric chlorine-rich and sulfur-poor ore-forming solution of high salinity.A geochemical genetic model of buried hydrothermal explosion is proposed.