Transmantle (intratelluric) fluid flows: a new model for plumes and plume magmatism

A fluid model for the formation of mantle plumes is proposed. During the emission of gas from the Earth’s core, it accumulates as lenses at the core-mantle boundary. Reaching a critical size, the lenses burst out into the mantle and migrate to the surface. A relatively stationary transmantle fluid flow from the core-mantle boundary arises, which heats the mantle and the layer interacting with it. The flow stops in the base of the hard lithosphere and spreads laterally, causing its melting accompanied by the formation of magma chambers, which, reaching critical sizes, massively intrude and flow out.     

Deep fluids in subduction zones

The fluid inclusions preserved in high and ultrahigh pressure rocks provide direct information on the compositions of fluid phases evolved during subduction zone metamorphism, and on fluid–rock interactions occurring in such deep environments. Recent experiments and petrologic studies of eclogite–facies rocks demonstrate that stability of a number of hydrous phases in all rock systems allows fluid transport into the mantle sources of arc magmas, as well as into much deeper levels of the Earth's mantle. In eclogite–facies rocks, the presence of large ion lithophile elements (LILE) and light rare earths (LREE)-bearing hydrous phases such as epidote and lawsonite, together with HFSE repositories as rutile and other Ti-rich minerals, controls the trace element budget of evolved fluids and fluid-mediated cycling of slab components into the overlying mantle.

Studies of fluid inclusions in eclogite–facies terrains suggest that subduction mainly evolves aqueous solutions, melts being produced only locally. Eclogite-facies rocks diffusely record processes of fluid–melt–rock interactions that exerted considerable control on the element and volatile budget of subduction fluids. Trace element fractionation during such interactions needs to be tested and quantified in more detail to achieve the ultimate compositions actually attained by fluids leaving off the slab. Variably saline inclusions with minor CO₂ and N₂ are trapped in rock-forming high pressure minerals; brines with up to 50% by weight dissolved solute are diffusely found in veins. The latter inclusions are residues after fluid–rock interactions and deposition of complex vein mineralogies: this evidence suggests increased mineral solubility into the fluid and formation, at a certain stage, of silicate-rich aqueous solutions whose geochemical behaviour and transport capacity can approach that of a melt phase. This is supported by experimental work showing high solubility of silicate components in fluids at high pressures. However, natural examples of inclusions trapping such a fluid and quantitative analyses of its major and trace element composition are not yet available.

Fluids in high and very high pressure rocks do not move over large scales and the channelways of fluid escape from the slab are not yet identified. This suggests that only part of the slab fluid is lost and returned to the surface via magmatism; the remaining trapped fraction being subducted into deeper levels of the upper mantle, to renew its budget of substances initially stored in the exosphere.     

Rock material from the Weddell Sea Floor of the South Ocean

This work is devoted to the results of the joint Russian-German geodynamic research carried out in the Weddell Sea and West Antarctica during cruise ANT-XXII/3 of the R/V Polarstern in 2005. The study of rock samples collected from the sea floor showed that a heterogeneous structure of the Weddell Sea was formed by spatiotemporal combination of the destruction of continental crust, progressive thalassogenesis (oceanization-taphrogenesis), and rifting, as opposed to a spreading origin. High postconsolidation mobility during the destruction stage led to the areal dismembering and high permeability of the continental crust, as well as to tectonomagmatic activation. The main mechanism of reworking of the continental crust is recognized to be the magmatic replacement by basic-ultrabasic mantle material with formation of a secondary oceanic crust and preservation of relics of the continental crust. The Earth’s endogenous activity was driven by transmagmatic fluid flows, which ascended from the melted core and caused transformation of the Earth’s crust and mantle.     

化学地球动力学中的铂族元素地球化学

对球粒陨石和地幔样品来讲,Ru,Rh,Pd,Os,Ir和Pt等贵金属元素的含量比值在一定程度上是相同的,但是在地幔样品中它们的含量实际上比球粒陨石低大约2个数量级,因此提出了核幔分离之后地球增生过程的“后增薄层”假说。数百公里尺度地幔橄榄岩的PEG分布的不均一性除被认为由于增生阶段的不均一造成外,更可能是由于地幔形成之后的地幔过程、核－幔及壳－幔相互作用造成。部分熔融、岩浆结晶分异（特别是硫化物、金属相析离）、流体（包括岩浆）／岩石相互作用等造成了大型俯冲带、造山带中地幔橄榄岩、蛇绿岩和杂岩体的PGE分异,也是形成铬铁矿,大型贵金属矿床的主要机制。     

Isotopic constraints on the age of the Earth’s core: Mutual consistency of the Hf-W and U-Pb systems

The estimation of the time of Earth??s core formation on the basis of isotopic systems with short-lived and long-lived parent nuclides gives significantly different results. Isotopic data for the ¹⁸²Hf-¹⁸²W system with a ¹⁸²Hf half-life of approximately 9 Myr can be interpreted in such a way that the core was formed 34 Myr after the origin of the solar system assuming complete core-mantle equilibrium. Similar estimates on the basis of the U-Pb isotopic system suggest a significantly longer mean time of core formation of approximately 120 Myr. If the Earth??s core were formed instantaneously, both isotopic systems would have shown identical values corresponding to the true age. The discrepancy between the U-Pb and Hf-W systems can be resolved assuming prolonged differentiation of prototerrestrial material into silicate and metallic phases, which occurred not simultaneously and uniformly in different parts of the mantle. This resulted in the isotopic heterogeneity of the mantle, and its subsequent isotopic homogenization occurred slowly. Under such conditions, the mean isotopic compositions of W and Pb in the mantle do not correspond to the mean time of the separation of silicate and metallic phases. This is related to the fact that the exponential function of radioactive decay is strongly nonlinear at high values of the argument, and its mean value does not correspond to the mean value of the function. There are compelling reasons to believe that the early mantle was heterogeneous with respect to W isotopic composition and was subsequently homogenized by convective mixing. This follows from the fact that the lifetime of isotopic heterogeneities in the mantle is close to 1.8 Gyr for various long-lived isotopic systems. There is also no equilibrium between the mantle and the core with respect to the contents of siderophile elements. Because of this, the mean isotopic ratios of W and Pb cannot be used for the direct computation of the time of metal-silicate differentiation in the Earth. Such estimation requires more sophisticated models accounting for the duration of the differentiation process using several isotope pairs. Given the prolonged core formation, which has probably continued up to now, the question about its age becomes ambiguous, and only the most probable growth rate of the core can be estimated. The combined use of the U-Pb and Hf-W systems constrains the time of formation of 90% of the core mass between 0.12 and 2.7 billion years. These model estimates could have been realistic under the condition of complete disequilibrium between the silicate and metallic phases, which is as improbable as the suggestion of complete equilibrium between them on the whole Earth scale.     

Polyphase strain caps

Strain caps are one of a series of microstructures that typically form during deformation of a softer matrix around hard objects. However??in contrast to other microstructures around porphyroblasts, for example pressure shadows??strain caps are rarely described in the literature. Here we describe strain caps with particular focus on strain caps associated with growth of a new phase, not elsewhere present in the paragenesis. Examples from foliated, amphibolite facies, metapelitic schists from Alaska, Sinai and Bhutan are discussed. All examples show chlorite growth exclusively in strain caps formed around porphyroblasts. Porphyroblasts around which the strain caps grow are muscovite, staurolite and garnet, respectively. In all of these examples strain caps formed synkinematically, but the chlorite grew statically at a later stage. Three mechanisms can explain the formation of new phases in the strain cap region: (a) the strain cap region may have experienced different P-T conditions from the matrix; (b) the strain cap region has a different effective bulk composition from the surrounding matrix; (c) fluid flow that is preferentially focused parallel to the foliation planes causing only local adjustment to retrograde metamorphism in the strain cap region. We show that the third hypothesis is the most preferable mechanism. Indeed, the absence of chlorite outside the strain cap region allows a quantification of the amount of fluid that infiltrated the rock. It is shown that for Bhutan sample about 8.5 mole% more water must have been added to the rock during fluid infiltration to cause the strain cap formation.     

软流层部分熔融岩浆竖向迁移模型分析

针对地幔蠕动过程中，软流层部分熔融岩浆上升这一地质背景，从力学的基本原理出发，将软流层岩石抽象为一类充满液体的多孔介质，并假定其以均匀速度上升，对岩石中部分熔融岩浆的迁移机理进行了分析，得到了一组简化的公式，并进行了计算。结果表明在此简化模型下，可以得到一个临界速度值的表达式。当岩石上升的速度低于该临界数值时，部分熔融岩浆将在一定的界面上形成；若大于这个临界数值，部分熔融岩浆的形成将滞后到一段竖向区域内完成。同时简单的计算结果也说明部分熔融岩浆的迁移运动是实现热量及成矿物质元素向上迁移的重要原因。其结果和某些岩浆过程的地质分析是一致的，这对进一步研究地幔蠕动及其成矿动力学具有重要的意义。     

试论地球深部地热能传输机理

本文在对前人地热成因认识归纳检验的基础上,通过演绎推理的方法,从几条基本的物理定律和基本假设组成的第一性原理出发,推理“地球内部热能从深部向浅表传输”的动力学过程,探讨深层地热能热源机制。热源机制问题从物理学的角度看,本质上就是热能从地球内部向近地表传输的问题。可以根据第一性原理,通过演绎法推理其可能的传输过程。深层热能传输的第一性原理由“温度的定义、热胀冷缩原理、阿基米德原理、热力学第二定律以及辐射、传导和对流三种热量传输方式的效率对比”5条基本的概念和定理组成。结合地球已知的圈层结构,通过演绎推理可知,在固态内核偏移驱动下,液态外核开始流动,在局部聚集导致地幔中形成上升的地幔柱;地幔柱在另一个地球圈层界面发生顶托作用,使得界面上凸,并产生烘烤加热作用,被烘烤的上层物质流变性增强发生侧向流动,于是物质垂直运动转换为水平运动。水平流动的热物质聚集到一定程度又会上浮产生垂直运动。如此垂直运动和水平运动不断转换,最终将地球深部地核中的热能传输到了地壳浅层。地球深部热能向浅表传输的过程会导致海底增生扩张、板块运动、盆山耦合等,同时也形成不同级别的控热构造系统。地球尺度的控热构造系统为:地球内核为生热构造,液态外核为储热构造,各级地幔柱和流动的高温物质为导热构造,地表的火山、温泉、地震为释热构造子系统。大陆地壳准固态流变物质的侧向流动是干热岩形成的主控因子,对于干热岩地热能勘查具有重要意义。     

论地幔流体参与大水金矿成矿的可能性

通过对大水金矿时空分布及元素地球化学特征的分析研究,探讨了地幔流体参与大水金矿床成矿的可能性。大水金矿属于川甘陕＂金三角＂矿集区的一个组成部分,在时空分布上受深大断裂、壳幔混合源岩浆岩的控制,是西秦岭地区勘查发现的大型金矿床之一。研究表明,矿石及贯穿于整个成矿过程中的方解石脉的稀土配分模式总体具相对富集轻稀土的特征。流体包裹体显微测温显示矿床的成矿温度范围为105℃-400℃。包裹体（方解石）气相成分主要为CO2和H2O,液相成分中阳离子以K^＋为主,Na^＋次之;阴离子以SO4^2-为主,Cl^-次之。矿物黄铁矿的δ^34S为-1.8‰-＋4.1‰,平均值＋2.4‰,反映成矿流体中硫部分来源于地幔。热液方解石的碳、氢、氧同位素组成反映成矿流体既有来自地幔的流体,也有来自岩浆岩、地层的流体,还有明显大气降水的加入。硅化灰岩矿石及硅质岩矿石的硅同位素组成具深部或岩浆热液和热水来源的特点,其氧同位素组成具火成石英来源的特点。矿石铅与矿区岩石铅（灰岩和脉岩）的铅同位素组成比较相近,在铅同位素构造模式图及Δγ-Δβ成因分类图解中,铅属壳幔混合铅。综上可知,矿床在成矿作用过程中存在地幔流体活动。     

Chemical composition of the primary aqueous phase of the earth and origin of life

Prokaryotes and cytoplasm of eukaryotes are dominated by K⁺, whereas the extracellular fluid of most species of multicellular organisms is dominated by Na⁺. It was substantiated that the K⁺/Na⁺ ratio in the salt constituent of the cells of modern organisms qualitatively reflects the proportions between these elements in the aqueous phase, in which the first forms of life and the protocell originated. The same conclusion is done by Armen Y. Mulkidjanian et al. (PNAS 13, 2012, E821-830). The chemical composition of primary aqueous phase of the Earth was reconstructed using thermodynamic numerical simulation of the equilibrium composition of the ??carbonaceous chondrite material-water??, ??primitive mantle material-water??, ??ultramafic rock-water??, ??mafic rocks-water?? systems that are open with respect to CO₂ and CH₄. It was shown that at 25°C, total pressure of 1 bar, and partial pressures of CO₂ and CH₄ 10^?5?C10^?8 and 10^?2?C10^?8 bar, respectively, the aqueous phase of the systems with carbonaceous chondrite and primitive mantle has K⁺/Na⁺ > 1, which corresponds to the proportions of these elements in the intracellular solution. The aqueous phase is characterized by pH = 8?C9, Eh = ?450 ± 50 mV, the presence of ammonium nitrogen, and concentrations of K, Na, and Mg close to those in the inferred intracellular fluid. The interaction of water with ultramafic and mafic rocks provides K⁺/Na⁺ < 1 in aqueous solution, which corresponds to the chemical composition of the modern natural waters of the Earth??s crust. Simulation results show that the protocell could arise in the primary aqueous phase of the Earth during differentiation of chondritic material into the Earth??s core and mantle, after the formation of the nitrogen atmosphere containing CH₄, CO₂, NH₃, H₂, H₂S, CO and other gases, but prior to the formation of the modern rocks of the Earth??s crust (first billion years of the planet??s lifetime).     

An oxygen isotope study of two contrasting orogenic vein gold systems in the Meguma Terrane, Nova Scotia, Canada, with implications for fluid sources and genetic models

Sampling of quartz vein material from two gold deposits of similar geological setting but different ages (The Ovens, 408?Ma; Dufferin, 380?Ma) in the Meguma Terrane of Nova Scotia has been done to compare and contrast their ??¹⁸O_quartz signatures. Despite different ages of formation, quartz from all vein types in each of the deposits (i.e. saddle-reef, bedding-concordant leg reefs, en echelon, discordant) shows limited intra-deposit variation with similar average ??¹⁸O values of +15.2?±?0.9?? (n?=?16) for The Ovens and +15.7?±?0.6?? (n?=?12) for Dufferin. Using an average ??¹⁸O value of +15.4?? for the two deposits, the corresponding ??¹⁸O_H2O values, calculated for 400°C and 350°C based on constraints from mineral assemblages and fluid inclusion studies, indicate averages of 11.4?±?0.2?? and +10.2?±?0.2??, respectively. The isotopic data indicate that: (1) the vein-forming fluids have a metamorphic signature, (2) all vein types in the two deposits represent formation from a single, isotopically homogeneous fluid, and (3) a fluid of similar isotopic signature was generated by two contrasting tectono-thermal events in the Meguma Terrane that were separated by 30?Ma. Integration of these results with previously published data for 14 Meguma gold deposits indicate a general stratigaphic dependence in ??¹⁸O_H2O values for deposits when arranged in their relative stratigraphic position such that ??¹⁸O_H2O values increase upwards in the stratigraphy. This apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein-forming fluids, but instead is modelled using fluid/rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy.     

Isotope-geochemical systematics of kimberlites and related rocks from the Siberian Platform

Using the ICP-MS method we have studied the isotope systematics of Sr and Nd as well as trace element composition of a representative collection of kimberlites and related rocks from the Siberian Platform. The summarized literature and our own data suggest that the kimberlites developed within the platform can be divided into several petrochemical and geochemical types, whose origin is related to different mantle sources. The petrochemical classification of kimberlites is based on persistent differences of their composition in mg# and in contents of indicator oxides such as FeO_tot, TiO₂, and K₂O. The recognized geochemical types of kimberlites differ from one another in the level of concentration of incompatible elements as well as in their ratios.Most of isotope characteristics of kimberlites and related rocks of the Siberian Platform correspond to the earlier studied Type 1 basaltoid kimberlites from different provinces of the world: Points of isotopic compositions are in the field of primitive and weakly depleted mantle. An exception is one sample of the rocks from veins of the Ingashi field (Sayan area), which is characterized by the Sr and Nd isotopic composition corresponding to Type 2 micaceous kimberlites (orangeites).The most important feature of distribution of isotopic and trace-element compositions (incompatible elements) is their independence of the chemical rock composition. It is shown that the kimberlite formation is connected with, at least, two independent sources, fluid and melt, responsible for the trace-element and chemical compositions of the rock. It is supposed that, when rising through the heterogeneous lithosphere of the mantle, a powerful flow of an asthenosphere-derived fluid provoked the formation of local kimberlite chambers there. Thus, the partial melting of the lithosphere mantle led to the formation of contrasting petrochemical types of kimberlites, while the geochemical specialization of kimberlites is due to the mantle fluid of asthenosphere origin, which drastically dominated in the rare-metal balance of a hybrid magma of the chamber.     

Carbon–oxygen isotope and trace element constraints on how fluids percolate faulted limestones from the San Andreas Fault system: partitioning of fluid sources and pathways

Understanding the way fluids flow in fault zones is of prime importance to develop correct models of earthquake mechanics, especially in the case of the abnormally weak San Andreas Fault (SAF) system. Because fluid flow can leave detectable signatures in rocks, geochemistry is essential to bring light on this topic. The present detailed study combines, for the first time, C–O isotope analyses with a comprehensive trace element data set to examine the geometry of fluid flow within a significant fault system hosted by a carbonate sequence, from a single locality across the Little Pine Fault–SAF system. Such a fault zone contains veins, deformation zones, and their host rocks. Stable isotope geochemistry is used to establish a relative scale of integrated fluid–rock ratios. Carbonate δ¹⁸O varies between 28‰ and 15‰ and δ¹³C between 5‰ and −7‰. From highest to lowest delta values, thus from least to most infiltrated, are the host rocks, the vein fillings, and the deformation zone fillings, respectively. Infiltration increases toward fault core. The fluids are H₂O–CO₂ mixtures. Two fluid sources, one internal and the other external, are found. The external fluid is inferred to come essentially from metamorphism of the Franciscan formation underneath. The internal (local) fluid is provided by a 30% volume reduction of the host limestones resulting from pressure solution and pore size reduction. Most trace elements, including the lanthanides, show enrichment at the 100-m scale in host carbonate rocks as fluid–rock ratios increase toward the fault core. In contrast, the same trace element concentrations are low, relative to host rocks, in veins and deformation zone carbonate fillings, and this difference in concentration increases as fluid–rock ratio increases toward the fault core. We suggest that the fluid trace elements are scavenged by complexation with organic matter in the host rocks. Elemental complexation is especially illustrated by large fractionation of Y–Ho and Nb–Ta geochemical pairs. Complexation associated with external fluid flow has a significant effect on trace element enrichment (up to 700% relative enrichment) while concentration by pressure solution associated with volume decrease of host rocks has a more limited effect (up to 40% relative enrichment). Our observations from the millimeter to the kilometer scale call for the partitioning of fluid sources and pathways, and for a mixed focused–pervasive fluid flow mechanism. The fluid mainly flows within veins and deformation zones and, simultaneously, within at least 10 cm from these channels, part of the fluid flows pervasively in the host rock, which controls the fluid composition. Scavenging of the fluid rare earth elements (REE) by host rocks is responsible for the formation of REE-depleted vein and deformation zone carbonate fillings. Fluid flow is not only restricted to veins or deformation zones as commonly believed. An important part of fluid flow takes place in host rocks near fault zones. Hence, the nature of the lithologies hosting fault zones must be considered in order to take into account the role of fluids in the seismic cycle.     

Reaction-induced fluid flow in synthetic quartz-bearing marbles

The reaction kinetics and fluid expulsion during the decarbonation reaction of calcite+quartz=wollastonite+CO₂ in water-absent conditions were experimentally investigated using a Paterson-type gas apparatus. Starting materials consisted of synthetic calcite/quartz rock powders with variable fractions of quartz (10, 20, and 30 wt%) and grain sizes of 10 µm (calcite) and 10 and 30 µm (quartz). Prior to reaction, samples were HIPed at 700 °C and 300 MPa confining pressure and varying pore pressures. Initial porosity was low at 2.7–6.3%, depending on pore pressure during HIP and the amount and grain size of quartz particles. Samples were annealed at reaction temperatures of 900 and 950 °C at 150 and 300 MPa confining pressures, well within the wollastonite stability field. Run durations were between 10 min and 20 h. SEM micrographs of quenched samples show growth of wollastonite rims on quartz grains and CO₂-filled pores between rims and calcite grains and along calcite grain boundaries. Measured widths of wollastonite rims vs. time indicate a parabolic growth law. The reaction is diffusion-controlled and reaction progress and CO₂ production are continuous. Porosity increases rapidly at initial stages of the reaction and attains about 10–12% after a few hours. Permeability at high reaction temperatures is below the detection limit of 10^–21 m² and not affected by increased porosity. This makes persistent pore connectivity improbable, in agreement with observed fluid inclusion trails in form of unconnected pores in SEM micrographs. Release of CO₂ from the sample was measured in a downstream reservoir. The most striking observation is that fluid release is not continuous but occurs episodic and in pulses. Ongoing continuous reaction produces increase in pore pressure, which is, once having attained a critical value (P_crit), spontaneously released. Connectivity of the pore space is short-lived and transient. The resulting cycle includes pore pressure build-up, formation of a local crack network, pore pressure release and crack closure. Using existing models for plastic stretching and decrepitation of pores along with critical stress intensity factors for the calcite matrix and measured pore widths, it results that P_crit is about 20 MPa. Patterns of fluid flow based on mineralogical and stable isotope evidence are commonly predicted using the simplifying assumption of a continuous and constant porosity and permeability during decarbonation of the rock. However, simple flow models, which assume constant pore pressure, constant fluid filled porosity, and constant permeability may not commonly apply. Properties are often transient and it is most likely that fluid flow in a specific reacting rock volume is a short-lived episodic process.Editorial responsibility: J. Hoefs     

深部过程中地幔流体现实微观踪迹的实验证据

伴随深部地质过程的地幔流体作用是引发地壳中成矿作用的重要物质源和动力源。由于地幔流体的超深源性及由此决定其性质和演化的复杂性,使人们很难具体捕捉其实际存在,或者多数情况下很难准确界定。通过岩相学、岩石化学、电子探针和扫描电镜及能谱分析的综合研究发现,地幔流体活动的现实微观踪迹和存在方式可以表现为富铁熔浆包体和富铁微晶玻璃,二者在透射偏光显微镜下无光性,呈黑色不透明状;反射偏光显微镜下不反光,但在电子显微镜下呈显微晶质结构,显示微晶金属和非金属矿物之间呈熔离交生,超微晶矿物组成以硅酸盐和石英为主,尤其是经过成分配比换算,得到碳硅石,含铬自然铁、钛铁矿、磷灰石和含钛镜铁矿等地幔标型矿物,反映了地幔流体的熔浆性质。捕捉和揭示深部地质过程中地幔流体作用的现实微观踪迹,对于深入分析和认识地壳地质作用的机制和成矿效应具有重要理论和现实意义。     

Analysis of the ore-controlling role of Guojiadian mantle branch structure, Northwest Shandong Peninsula, China

Metallogenesis in the gold ore-concentrated zone of Northwest Shandong Peninsula is closely related to deep processes.The region in the eastern part of North China entered into the stage of mantle plume evolution during the Yanshanian movement,following the long-time stage of stable platform evolution during Paleozoic time.At that time,the ore-concentrated zone of Northwest Shandong Peninsula just entered into the development-evolution stage of the Laiyang sub-mantle plume and the Guojiadian mantle branch structure in its periphery.The core-mantle-source gold was present in the gas-liquid form,and it migrated through mantle plume→sub-mantle plume→mantle branch structure→favorable tectonic expansion zone to the favorable loci of the mantle branch structure,where gold was deposited as ores,thereafter constituting a series of large-to medium-sized gold deposits distributed around the Guojiadian mantle branch structure.This study also dealt with the Jiaojia fault as the main detachment(fault altered rock) belt on the northwestern margin of the mantle branch structure and also presented a basic cognition about the fact that the Sanshandao fault as the listric fault on the hanging wall of the detachment belt.Furthermore,on this basis,this study also pointed out the orientation for further ore prospecting in this region.     

滇西富碱斑岩型矿床岩体和矿脉同位素地球化学研究

选取马厂箐铜钼金矿、金厂箐金矿、北衙铅金矿和姚安铅银金矿四个典型的富碱斑岩型多金属矿床，对岩体和矿脉的铅、硅、氢、氧、硫、碳及氦、氩同位素分析。结果表明，富碱岩浆和富硅成矿流体的最初和主要铅源均来自地幔，但混染了部分地壳或地层铅；富碱岩浆起源于地幔交代作用形成的富集地幔源区，而富硅成矿流体则具有原始地幔流体性质，前者的硅同位素组成表现为经历强烈动力分馏的高正值；后者则为几乎未经动力分馏的低负值。综合研究表明，该类矿床的成矿作用是在富碱岩浆的成岩过程中，伴随富硅成矿流体对岩体和地层围岩的(自)交代蚀变作用，并与岩石一定程度混染而实现的。因此，富硅成矿流体作用实质上是地幔流体交代作用在地壳内成矿作用中的延续。     

滇西地区富碱斑岩中地幔流体作用踪迹及其成矿作用意义

滇西地区大量产出的富碱斑岩及其包体岩石的形成和演化与该区新生代陆内变形、构造作用、幔源岩浆和深源流体活动,及其与此有关而广泛发育的内生多金属矿产存在必然的联系。本文通过岩相学、岩石化学、电子探针、扫描电镜和能谱分析,较为系统地分析论证了这一关联的内在统一制约和联系的纽带即深部地质过程和由此相伴的含矿地幔流体作用,初步揭示了这种深部过程和地幔流体作用的微观踪迹和方式可以直接表现为:(1)呈脉状和浸染状穿插于深源包体岩石中的富钠玻璃,透光镜下呈微晶和雏晶,颜色随成分差异而不均匀,化学成分以高硅、铝、钠、铁,低钾、钙、镁为特征,矿物成分以钠长石、角闪石、磁铁矿(镜铁矿)、钛铁矿组合为特征,是富碱岩浆携带包体岩石之前即已存在的上地幔流体;(2)呈脉状、团块状和浸染状穿插于主岩和各类包体岩石的富铁玻璃;(3)呈独立包体产出于霓辉正长斑岩中的富铁熔浆包体。后两者物质在透光镜下无光性,呈黑色不透明,反光镜下不反光,但在电子显微镜下呈显微晶质结构,化学成分以高硅、铝、铁,低钙、镁、钠、钾为特征,矿物组成上以硅酸盐和石英为主,含有碳硅石、含铬自然铁、钛铁矿、磷灰石等地幔标志矿物,其中微晶金属和非金属矿物之间呈熔离结构交生,反映了地幔流体的熔浆性质及其与富碱岩浆不混溶的特征;由地幔流体对岩石的交代浸染作用,引起主岩和包体岩石中普遍发育各种蚀变作用,如角闪石化、硅化和绿泥石化等,并导致矿物组合总体上表现为暗色矿物由辉石→角闪石→黑云母→绿泥石的退变序列。该地幔流体微观踪迹的三种表现形式与富碱岩浆共存,并共同运移,但两者由于组成和性质的差异而互不混溶;结合透岩浆流体成矿作用理论和本文论证的综合分析认为,当富碱岩浆和地幔流体系统封闭较好,地幔流体则伴随富碱岩浆的结晶过程对富碱斑岩进行同步自交代蚀变,在斑岩体或其深部形成矿床,构成正岩浆成矿体系,典型成矿实例如马厂箐斑岩钼矿床;若在此成岩成矿过程中发生构造作用扰动,则地幔流体进入岩体与围岩的接触带,或紧邻接触带的地层围岩中进行交代蚀变成矿,构成接触带成矿体系,典型成矿实例如马厂箐矿区中赋存于夕卡岩—大理岩带中的斑岩型铜矿和主要赋存于地层围岩中的斑岩型金矿,若金矿出现在斑岩体内,则一般受控于穿切斑岩体的成岩后断裂;若岩浆和流体运移通道的深大断裂体系发育,环境相对开放,则地幔流体伴随富碱岩浆的成岩过程而脱离岩浆沿分支断裂通道进入远离岩体的不同地层岩石中进行交代蚀变成矿,构成远程热液成矿系统,典型成矿实例如兰坪金顶超大型铅锌矿床;在这一成矿过程中,地幔流体可以随深度和环境变化引起的物理化学条件变化,其性质由熔浆→超临界流体→液相流体转化,并运载和沿途活化成矿物质至适宜容矿部位集中,促使幔壳物质叠加成矿;进而有利于深部成矿并形成大型和超大型矿床。     

Oxygen fugacity regime in the upper mantle as a reflection of the chemical differentiation of planetary materials

Oxygen fugacity (fO₂) in the Earth’s mantle has a bearing on the problems of the chemical differentiation of the Earth’s materials and formation of the chemical and phase state of its shells. This paper addresses some problems concerning changes in the redox state of the upper mantle over geologic time and through its depth and the possible influence of fO₂ stratification in the interiors on geochemical processes. Among these problems are the formation of fluids enriched in H₂O, CO₂, CH₄,and H₂; the possible influence of reduced fluid migration from mantle zones with low fO₂ values on reactions in the lithosphere; and the formation of films of silicate liquids with high H₂O and CO₂ contents, which could be responsible for metasomatic transformations in rocks. The formation of a metallic core and accompanying large-scale melting of the silicate part of the Earth are the early mechanisms of the chemical differentiation of the mantle that must have had an effect on the redox state and the composition of volatile components in planetary materials. The molten metallic and silicate phases were prone to gravitational migration, which affected the formation of the metallic core. Volatile components had to be simultaneously formed in the zones of large-scale melting of the early Earth. The composition of these volatiles was largely controlled by the interaction of hydrogen and carbon, the two major gas-forming elements in the mantle, with melt under low fO₂ values. A remarkable feature is that, despite fairly low fO₂ values imposed by the presence of a metallic phase, both reduced (CH₄ and H₂) and oxidized species of hydrogen and carbon (H₂O, OH^? and CO ₃ ^?2 ) are stable in the melt. This peculiarity of carbon and hydrogen dissolution in reduced melts may be crucial for the elucidation of mechanisms for the formation of initial amounts of CO₂ and H₂O connected with incipient melting in the reduced mantle.     

南海热幔柱构造与油气分布

南海处于欧亚、印度—澳大利亚和太平洋—菲律宾海三大板块的夹持地带,区内以NE向深海区-海盆为中心,周围有众多的含油气盆地。南海区具有"北断(裂)、南褶(皱)、东(俯)冲、西(碰)撞"的构造特征。南海及其周缘新生代玄武岩和花岗岩广为分布,故有潜在的大火成岩省之称。其中,火山岩以碱性玄武岩为主,多为OIB型成因,其成岩年龄自南海中心至外围呈由新逐渐变老的趋势。深部地幔流动呈现出涡旋式上涌的特点,上地幔明显具环带状结构,中心部位为上升流,外围为下降流,表现出热幔柱和冷幔柱活动"双模式"对流。从区域S波速度扰动异常来看,在670km间断面,对热流体上涌确有阻挡作用。通过层析成像研究,证实本区存在巨型复蘑菇云状地幔低速体,演化过程和相邻板块活动构成相辅相成关系。由于地幔热流体上涌,促使地壳-岩石圈上隆、熔融、减薄和断陷,形成南海从边缘向中心(海盆)热流温度逐步升高的轨迹,基本控制油气田"外油内气"环形有序分布的格局。