宁芜地区中生代岩浆岩的成因——岩石学与Nd,Sr,Pb同位素证据

宁芜中生代火山盆地产出火山岩与侵入岩，火山岩以玄武粗安岩，粗安岩和粗面岩为主，安山岩和响岩少量，火山岩以高钾富碱为特征，已确定为橄榄安粗岩系。侵入岩以辉长闪长玢岩－一辉长闪长岩为主，以高钠低硅为特征，并有辉长岩和花岗岩产生，据地质学和Ｎｄ，Ｓｒ，Ｐｂ同位素资料，侵入岩与火山岩属同一个岩浆系列，是碱性玄武岩浆在下地壳经过轻度ＡＦＣ混合后，侵入上地壳，在轻度混染的情况下，经过以结晶分离为主的岩浆分异形     

Zoning and geochemical characterization of volcanic soils on Kamchatka

The paper presents the first data on the zoning of modern volcanic soils on the Kamchatka Peninsula according to the age and composition of volcanic ashes in which the surface organogenic horizons of the soils were formed. The following soil provinces are recognized: Northern, Central, Western, and Southeastern. Parameters of their regional geochemical background (concentrations of trace elements) are determined. The main factor controlling the background concentrations of trace elements in these soils is the composition of the ashes underlying the soils. The geochemical specifics of the surface organogenic horizons of volcanic soils on Kamchatka may be variably affected only by the concentrations of trace elements whose average contents in magmatic rocks are the highest: Cr, Cu, Mn, Sc, Zn, Co, V, and Ag. The maximum concentrations of excess elements were determined in the soils underlain by ashes of basic composition, and the minimum concentrations of these elements occur in the soils formed in silicic ashes. All soil provinces recognized on Kamchatka are characterized by pervasively elevated Cu concentrations. It is proposed to identify volcanic soils formed in the peninsula in ashes of various composition with the application of a multiplicative geochemical coefficient.     

宁芜地区中生代岩浆岩的成因──岩石学与Nd、Sr、Ph同位素证据

宁芜中生代火山盆地产出火山岩与侵入岩。火山岩以玄武粗安岩、粗安岩和粗面岩为主，安山岩和响岩少量，火山岩以高钾富碱为特征，已确定为橄揽安粗岩系。侵入岩以辉长间长珍岩－辉长闪长岩为主，以高钠低硅为特征，并有辉长岩和花岗岩产出。据地质学和Ｎｄ、Ｓｒ、Ｐｈ同位素资料，侵入岩与火山岩属同一个岩浆系列，是碱性玄武岩浆在下地壳经过轻度ＡＦＣ混合后，侵入上地壳，在轻度混染的情况下，经过以结晶分离为主的岩浆分异形成的。     

北秦岭基性火山岩地球化学特征与上地幔岩浆源区性质

元古代和早古生代是北秦岭两个主要的火山岩浆作用时期,地球化学研究表明,元古代基性火山岩具有相对低SiO_2、Al_2O_3和高TiO_2特征,基性火山岩TiO_2-P_2O_5、MgO/FeO-Y、的变化显示了正常的、稳定的岩浆作用过程,相容元素分配模型表明这一时期基性火山岩与华北区上地幔部分熔融岩浆作用相吻合,早古生代基性火山岩除普遍具有高、低特征外,突出地表现出地球化学成分的不均匀性,多源、混合岩浆作用的干扰使单源岩浆演变特征遭受破坏,相容元素分配模型表明:这一时期基性火山岩浆与引起秦岭区、华北区上地幔岩浆共同作用有关系,北秦岭基性火山岩浆作用的特征与这一地区从元古代到早古生代的构造发展是相适应的,反映了该区上地幔性质及岩石圈构成的重大改变。     

江西省冷水坑银铅锌矿床铁锰碳酸盐角砾岩成因研究

江西省冷水坑银铅锌矿床的铁锰碳酸盐角砾岩层与顶底板侏罗系火山杂岩呈整合接触关系,填隙物内存在清晰可辨的火山凝灰物质。铁锰碳酸盐角砾岩的稀土元素配分型式属于轻稀土富集的右倾型,稀土组成特征有类似于正常湖相碳酸盐岩低的稀土总量,又类似于正长质岩浆岩的正Eu异常特征。碳氧同位素显示其形成环境属于陆相火山湖泊,陆相沉积岩与岩浆岩均为成岩提供了物质来源。通过顶底板火山杂岩锆石U-Pb年龄的限定,指示在155Ma左右,铁锰碳酸盐角砾岩经历了陆相火山湖泊沉积-火山喷发使之角砾化-正长质岩浆物质混入的成岩过程。     

老挝班康姆铜金矿床成矿条件及成矿机理研究

班康姆铜金矿床是近年来发现的大型铜金矿床,矿体主要赋存于中基性火山岩之中,其微量元素特征、玄武岩类的Ti-Zr-Y、Ti-Zr判别图、花岗岩类在Nb-Y(A)、Rb-(Y+Ta)判别图均表明成矿构造环境为岛弧环境,火山岩属于中钾钙碱性系列.岩浆岩稀土总量较低,标准化模式曲线均为略富集轻稀土的平坦型,Eu几乎不存在异常,说明火山岩、侵入岩为同源不同期的产物,岩浆热液来源于地幔或下地壳,热液活动划分为火山喷发期、热液叠加期,其成矿物质来源于安山岩,矿(化)体受NNE断裂构造、岩浆岩控制,矿床类型为与岩浆岩密切相关的复合型热液矿床.     

Arc related Jurassic igneous and meta-igneous rocks in the Coastal Cordillera of northern Chile/Region Antofagasta

A deep section of the Jurassic, 200-150 Ma old magmatic arc is exposed in the Coastal Cordillera south of Antofagasta in northern Chile. The chemical compositions of metabasic and plutonic rocks from the deep level are compared with those of Jurassic volcanic rocks and ≈ 150 Ma old dykes. The metabasites, most of the plutonic rocks, and the dykes have calc-alkaline characteristics. However, small postmetamorphic gabbro plutons are tholeiitic. The composition of the volcanic rocks is not related to the plutonic rocks, metabasites and dykes. All igneous and meta-igneous rocks of the arc are derived from a similar source in the upper mantle and evolved without major crustal contamination.

The general tectonic setting was dominated by extension, and Pre-Jurassic crust is extremely thinned or absent in the area. Details of the tectonic, magmatic and metamorphic development remain still a matter of speculation.     

中祁连北缘奥陶纪岩浆弧地层

奥陶纪是祁连山加里东期构造带俯冲-碰撞格局奠定时期。通过区域填图和沉积环境分析及岩石地球化学研究,系统分析了沉积及岩浆作用过程, 认为在肃北县野牛台地区的晚奥陶世地层是中祁连地块西段北缘岩浆弧的组成部分。该地层为一套浅变质的基性-中性火山岩、碎屑岩及少量含化石灰岩组合,由下部海相安静深水还原环境向上部近岸水下河道-滨岸过渡,上部夹有冲积扇-河流相沉积,物源区为近源的岩浆弧和古老结晶基底,反映出自下向上水体变浅、盆地收缩的进积序列。其中的火山岩自下向上由基性向中性转变、由岛弧拉斑-钠质碱性玄武岩向钾质碱性玄武岩过渡,反映出与挤压构造环境相关的成熟岩浆弧火山岩组合特点。晚奥陶世岩浆弧地层、侵入岩与其北的同期构造蛇绿混杂岩带的相伴产出,暗示北祁连西段该时期洋壳在北部向北俯冲的同时,南部还向南俯冲并形成汇聚大陆边缘。     

西藏冈底斯西段狮多地区火山岩的地质地球化学特征

西藏冈底斯西段狮多地区火山岩为一套高钾钙碱性和钙碱性系列岩石,分为古新世(59 7Ma)和中新世(17 2Ma)两个活动时期,早期的时代和层位大致相当于冈底斯东段的林子宗群典中组。与典中组火山岩相比较,该期火山岩的稀土元素总量(w(∑REE)=58 83×10-6)低得多,轻、重稀土分馏程度(w(La)N/w(Yb)N=3 44)较弱,分布曲线更为平缓;N(143Nd)/N(144Nd)的现在值(0 512275～0 512420)和初始值εNd(t)(-6 7～-4 0)也明显偏低,这反映冈底斯东、西段同一时期的火山活动及演化各具特色。根据Pb、Nd、Sr同位素的组成特征和微量元素构造环境判别推断,狮多地区火山岩形成于陆缘弧—陆 陆碰撞造山的发展演化环境,是新特提斯洋壳向大陆下俯冲作用过渡到陆 陆碰撞造山作用的产物。狮多铁 铜矿与古新世火山岩有成因联系。     

岩浆补给作用对硅质火山岩浆系统演化的制约

硅质火山喷发作为大陆地壳岩浆活动的重要表现，在研究大陆地壳形成与演化、探讨岩浆过程与动力学机制等方面具有重要的价值，其通常所表现的强烈爆炸式喷发，甚至可以导致全球性的环境和气候变迁。硅质岩浆系统在开放体系中不同来源岩浆的贡献和相互作用是目前研究的热点问题。持续的岩浆补给可以延长岩浆存储的时间，促进岩浆房的对流、岩浆的分异演化以及晶体 熔体的分离和晶粥的再活化，同时也是触发火山喷发的重要机制之一。此外，岩浆补给以及硅质岩浆的晶体 熔体演化过程也是火山喷发产物多样性的原因，导致同一火山在其活动过程中喷发产物规律性的变化，如富晶体火山岩、贫晶体火山岩、火山岩成分分层、以及复活岩穹和中央侵入体等。因此，岩浆补给作用是制约硅质火山岩浆系统演化和火山岩成分多样性的重要因素，也是活动火山监测和灾害评估的重要依据。岩石学、岩石地球化学、矿物(长石、石英、石榴子石、锆石等)同位素及成分变化，以及模拟实验、地震层析成像等研究为揭示硅质岩浆系统中的岩浆补给作用和复杂岩浆过程提供了多种视角。     

Implications of Pb isotope signatures of rocks and iron oxide Cu-Au ores in the Candelaria-Punta del Cobre district,Chile

Lead isotope ratios of ores of the Candelaria-Punta del Cobre iron oxide Cu-Au deposits and associated Early Cretaceous volcanic and batholithic rocks have been determined. For the igneous rocks, a whole-rock acid attack technique based on the separate analyses of a leachate and the residual fraction of a sample was used. The lead isotope systematics of leachate–residue pairs are significantly different for unaltered and altered igneous rocks of the Candelaria-Punta del Cobre district. Residues of unaltered igneous rocks likely represent the common lead. In contrast, residues of all the altered igneous rocks except two samples have higher Pb isotope ratios than those of unaltered magmatic rocks and cannot represent common lead. We suggest that this is a result of the hydrothermal alteration suffered by these rocks and that the common lead composition of the altered igneous (volcanic and plutonic) rocks must have been similar to that of the unaltered batholith rocks. The conclusion that the altered volcanic rocks originally had a similar common lead isotope composition as the batholith is consistent with geological and geochemical arguments (e.g., setting, regional geologic evolution, ages and relative distribution of volcanic and intrusive rocks, magmatic affinities), which indicate that these rocks were derived from similar Early Cretaceous parent magmas. The modification of the leachate–residue pair lead isotope systematics of most altered igneous rocks is consistent with a selective removal of lead and uranium from these rocks by an oxidized hydrothermal fluid. The result of the hydrothermal leaching has been to alter magmatic rocks in a way that (1) their leachable fraction is presently a mix of common lead similar to that of the ore event and of radiogenic lead evolved from a source with a consistently high Th/U, and that (2) their residual fraction has less common lead than unaltered rocks. The outcrop area with altered volcanic rocks displaying anomalously high lead isotope ratios extends over 25 km along the eastern margin of the batholith. Since lead of the ores in the Candelaria-Punta del Cobre district has the same isotopic composition as the common lead of unaltered magmatic rocks of the area, the lead isotope data are consistent with a derivation of the ore lead (and by inference of other metals like Cu) both directly from a magmatic fluid exsolved during crystallization of the batholith and/or from hydrothermal leaching of the volcanic rocks originally having similar isotopic compositions as the batholith.Editorial handling: B. Lehmann     

伊通新生代玄武岩地球化学成分差异性研究

伊通火山群中的西尖山((21.0±0.65) Ma)和东小山玄武岩((5.46±0.32) Ma)的岩石学和地球化学研究表明,两处玄武岩均为OIB型,岩浆来源于软流圈地幔,地壳混染与结晶分异的程度微弱。西尖山火山岩为碱性橄榄玄武岩,不含地幔岩捕虏体,岩浆起源深度为70~100 km,SiO2、Al₂O₃、Na₂O含量较高,属钠质碱性岩;东小山火山岩为碧玄岩,含较多的地幔橄榄岩捕虏体,岩浆来源深度大于100 km,MgO、TiO₂、CaO、K2O含量较高,属钾质过碱性岩。岩浆来源深度的不同是造成两处玄武岩化学成分差异的主要原因。     

新疆和静县乔霍特铜矿地质地球化学特征

乔霍特铜矿是位于新疆西天山的一个中型铜矿床。似层状矿化体赋存于上志留统中基性火山岩及沉积岩中 ,矿化富集受地层、构造、侵入岩的多重控制。火山岩属于发育不成熟的裂谷环境中的中基性岩类 ,赋矿火山岩与无矿火山岩的稀土元素组成近似 ,而与后期叠加改造形成的脉状矿化体的稀土元素组成有较大差别。矿石矿物主要为辉铜矿、黄铜矿、斑铜矿等 ,呈粒状和浸染状分布。成矿温度为 130～ 140℃。矿化溶液含岩浆水和变质水 ,属于酸性的富含钾、氯和二氧化碳的流体。矿化过程经历晚志留世火山热液充填 交代作用和海西早期岩浆热液的叠加、改造作用。     

辽西义县盆地火山岩的基本特征及其成因探讨

通过对辽西义县盆地火山岩的岩石学、矿物学以及地球化学特征的研究，指出本区火山岩属于一套弱碱性、普通型的火山岩系列．通过热力学计算以及对岩石结构和动力学的分析，表明原始岩浆来自上地幔（约６７ｋｍ），并在约１７ｋｍ处（上下地壳附近）形成高位岩浆房．在高位岩浆房中，由于岩浆的双扩散对流作用，发生了伴随有分离结晶作用的液相分异作用，而同化混染作用则发生于岩浆演化的早期。喷出的岩浆成分受断裂切过高位岩浆房的相对位置的控制。     

胶东青山群基性火山岩的Ar-Ar年代学和地球化学特征: 对华北克拉通破坏过程的启示

青山群火山岩是华北克拉通破坏期间最具代表性的地幔或地壳熔融产物,记录了华北深部地质演化的重要信息。本文对胶东青山群基性火山岩进行了40Ar/39Ar定年和岩石地球化学分析,结合前人报道的胶东青山群酸性火山岩资料,发现:(1)基性火山岩喷发年龄为122～113Ma,早于青山群酸性火山岩(110～98Ma);(2)基性和酸性火山岩显示了不同的元素和同位素地球化学特征。岩石成因分析表明,基性火山岩为交代富集地幔部分熔融作用的产物,而酸性火山岩为古老下地壳和中生代底侵岩浆的熔融产物(Ling et al.,2009)。因此,胶东地区青山群火山岩记录了岩浆熔融源区从地幔向下地壳的转变。这与长时间尺度的岩石圈减薄过程中热能由地幔向地壳传递过程相吻合,而不同于地壳拆沉作用所预测的岩浆演化趋势。     

A Back-arc Palaeotectonic Setting for the Augaro Neoproterozoic Magmatic Rocks of Western Eritrea

The Augaro volcano-sedimentary assemblages of western Eritrea are part of the Neoproterozoic, N-S trending belt of low-grade volcano-sedimentary and associated plutonic rocks. In contrast to the volcanic-dominated oceanic-arc assemblages in central Eritrea, the predominant rock types in the west are supracrustal sequences of sedimentary origin with subordinate volcanic rocks. These Augaro supracrustal rocks are overlain, unconformably, by a basin-fill metasedimentary succession known as the Gulgula Group. The Augaro metavolcanic rocks are tholeiitic and range in composition from basalt to basaltic andesite. Comparison of trace element characteristics and N-MORB-normalised spidergrams of these rocks with those of modern volcanic environments and age-comparable metavolcanic rocks of known tectonic association from the Arabian-Nubian Shield suggest that the volcanic assemblages from western Eritrea were generated in a back-arc tectonic setting.

Single zircon Pb-Pb evaporation and vapour-transfer U-Pb analyses of magmatic zircons from pre/syn-tectonic granites yield a mean ²⁰⁷Pb/²⁰⁶Pb age of 849±20 Ma and an upper concordia intercept age of 849±26 Ma. These ages are interpreted to represent the time of major magmatism in western Eritrea and are comparable to ages of early arc magmatism in central and northern Eritrea and in the southern Nubian Shield. Initial eNd values and initial Sr isotope ratios of whole-rock samples of magmatic rocks calculated for an age of 850 Ma range from +4.0 to +7.1 and 0.7026 to 0.7037, respectively. Single zircon ²⁰⁷Pb/²⁰⁶Pb ages, initial eNd value and Sr isotope ratio for a granitic clast in the Gulgula metaconglomerate suggest that the source area for the Gulgula metasedimentary rocks is similar to the surrounding Neoproterozoic rocks of western Eritrea.     

幔源岩浆去气形成富二氧化碳含金流体——可能性与现实性

综合国内外研究资料并结合笔者的研究成果 ,评述了幔源岩浆去气形成富二氧化碳含金流体的可能性和现实性。笔者认为 ,在地幔熔融和富集交代过程中可以形成富金和二氧化碳的岩浆 ,进一步在岩浆去气过程中金可以气相形式随二氧化碳排出 ,而一个由深部稳定热源驱动、富含幔源岩浆去气带入的二氧化碳和金并与地壳浅部流体混合的热液环流系统是形成重要金矿化的必要条件。     

Volcanic ash layers in the Upper Cretaceous of the Central Apennines and a numerical age for the early Campanian

At Montagna della Maiella and at Gola del Furlo (central Apennines) two discrete layers of bentonic clay are intercalated within the pelagic (Furlo) and turbiditic/pelagic limestones (Maiella) of the Upper Cretaceous basinal succession of the Umbrian basin (Scaglia facies). The bentonite layers are dated by planktonic foraminifera to the Globotruncanita elevata zone, early Campanian, and by calcareous nannofossils to the Aspidolithus parcus zone (CC 18); they fall into the reversed interval of chron 33. Detailed correlation shows the layers to be of exactly the same age. The upper layer is dated by U/Pb on magmatic zircons to 81.67±0.21 Ma, an age compatible with the Cretaceous time-scale of Obradovich. The mineralogy of the bentonitic clays is almost pure montmorillonite and contrasts sharply with the clay mineral assemblage of the enclosing pelagic and turbiditic limestones, which is dominated by soil-derived smectite and illite in different proportions. The bentonite seams are interpreted as the submarine alteration products of wind-borne volcanic ashes. They can be followed with only minor changes in thickness over 200 km and must be derived from distant volcanic sources and related to extreme volcanic events. A possible source area is present in the Dinarides where Upper Cretaceous subduction-related magmatic rocks are widespread.     

Late Triassic siliceous-volcano-terrigenous deposits of the Chukchi Peninsula: composition of igneous rocks,U-Pb age of zircons,and geodynamic interpretations

Study of Late Triassic volcanic, subvolcanic, and volcanosedimentary rocks of the Chukchi Peninsula (Vel’may terrane) has shown their different geochemical types. Basalts, dolerites, and tuffs of the lower-middle strata of the Upper Triassic section bear evidence for their formation in suprasubductional geodynamic setting. Basalts and dolerites of the upper strata of this section correspond in composition to within-plate rocks and are similar to Middle-Late Triassic oceanic-plateau basalts and dolerites. U-Pb dating of magmatic zircons from tuffs of the lower-middle strata and from dolerites of the upper strata shows the almost synchronous magmatic activity in the suprasubductional (206 ± 5 Ma) and within-plate (212 ± 4 Ma) geodynamic settings.