煌斑岩—硫化物熔体液态不混溶作用的高温高压实验研究

本文以云南老王寨金矿区煌斑岩和黄铁矿为初始物,在1.5～3.0GPa、1162～1560℃条件下进行了煌斑岩—硫化物熔体液态不混溶作用实验。结果表明,煌斑岩硫化物熔体的液态不混溶作用可能发生于岩浆演化的早期（高压条件）,但如有硫存在,在岩浆演化的各个阶段（高压条件→低压条件）均可能出现煌斑岩硫化物熔体的液态不混溶作用;与煌斑岩熔体分离的硫化物熔体在温度场、压力场中作定向运移,逐渐聚集于相对低温、低压区;由于硫化物熔体的密度相对较大,因而与煌斑岩熔体之间出现明显的分层现象。     

昌乐方山新生代玄武岩中深源捕虏岩与熔体的相互作用

昌乐方山新生代玄武岩中携带有大量深源捕虏岩,其岩石类型以二辉辉石岩、二辉橄榄岩为主,方辉橄榄岩、单斜辉石岩、单辉橄榄岩少见,未见纯橄岩。二辉辉石岩、二辉橄榄岩、方辉橄榄岩的矿物岩石、地球化学特征和平衡温度压力计算显示为地幔来源,采用地质温度压力计进行计算,获取三者都源于岩石圈地幔,形成的深度范围为41~66.7 km。根据单辉橄榄岩和单斜辉石岩的矿物化学分析,单斜辉石岩和单辉橄榄岩形成深度要低于前三者,且与前三者有密切成因联系。"熔体—岩石"反应在各类深源捕虏岩中广泛存在,除方辉橄榄岩样品不存在明显的"熔体—岩石"反应外,二辉辉石岩、单斜辉石岩、二辉橄榄岩中不同的矿物边缘与玄武质熔体接触部位有着不同类型的反应边和反应矿物出现:橄榄石边部发生(Mg,Fe)_2SiO_4(镁橄榄石)+熔体(原始岩浆)=(Mg,Fe)_2SiO_4(贵橄榄石)+熔体(演化岩浆)反应,使得边部富铁贫镁;单斜辉石与玄武质熔体反应,多具有粉红色反应边,具有富Ti、Al、Fe,贫Si、Mg,较玄武岩基质中单斜辉石斑晶更低Mg~#的特征。斜方辉石与玄武质熔体反应生成复杂的反应带,存在斜方辉石+熔体=橄榄石+SiO_2(熔体)+单斜辉石的反应,反应带内新生成的矿物由内向外具有明显趋向玄武质熔体成分的变化;尖晶石与玄武质熔体反应边缘具有富Fe、Ti,贫Mg、Al,以及更高的Cr~#,趋向于形成钛铁矿的变化特征。二辉橄榄岩中熔体囊和单辉橄榄岩中筛状单斜辉石以及粉红色的反应边都暗示了二者至少经历了两个期次的熔体作用。随着岩石圈地幔的演化,熔体的再富集作用使得难熔的方辉橄榄岩逐渐转变为相对富集的二辉橄榄岩,后期二辉橄榄岩又与玄武质熔体反应,生成更加富集的单辉橄榄岩,而方山方辉橄榄岩也受到了熔体的轻度改造,已不具有难熔古老岩石圈地幔岩石的显著特征,鲁西新生代玄武岩中深源捕虏体与熔体的反应广泛存在,熔体成分以玄武质为主,这可能是华北克拉通岩石圈置换的重要方式之一,导致古老岩石圈地幔的消失。     

The Mineral Chemistry of Ultramafic Xenoliths of Eastern China: Implications for Upper Mantle Composition and the Paleogeotherms

Ultramafic xenoliths of garnet lherzolite (?rare spinel), spinellherzolites, spinel harzburgites, clinopyroxenites, and clinopyroxenemegacrysts were collected from Cenozoic basalts in all partsof eastern China. From their modal composition and mineral chemistryall the xenoliths may be placed into three types representing:a fertile or more primitive mantle (garnet lherzolite and spinellherzolite), a refractory or more depleted mantle (spinel harzburgiteand dunite), and inclusions cognate with the host alkali basaltsat mantle pressures (pyroxenite and megacrysts). There are systematicdifferences between the mineral compositions of each type. Spinelshows a wide compositional range and the spinel cr-number [100Cr/(Cr + Al)] is a significant indicator of the xenolithtype. Spinel cr-number and Al₂O₃ of coexisting minerals (spinel,clinopyroxene, and orthopyroxene) are useful as refractory indicatorsfor spinel peridotite in that the cr-number increases and thepercentage of Al₂O₃ decreases with increasing degrees of melting.In garnet peridotite, however, the same functions vary withpressure, not degree of melting. According to P–T estimates,the various xenoliths were derived from a large range of depthsin the upper mantle: spinel peridotite from approximately 11to 22 kb (37–66 km), spinel/garnet lherzolite from 19to 24 kb (62–80 km), and garnet lherzolite from 24 to25 kb (79–83 km). We conclude that the uppermost mantlebeneath eastern China is heterogeneous, with a north-northeastzone of more depleted mantle lying beneath the continental marginand a more primitive mantle occurring towards the continentalinterior.     

Experimental Study on Gold Dissolution from Hosting Minerals of the Hadamengou Gold Deposit and the Implications

The Hadamengou gold deposit is located in western part of the northern margin of the North China craton. It is a hydrothermal deposit related to alkaline magmatism. Dissolution of Au, Fe from pyrite and iron oxide （including magnetite and hematite） individual minerals in the three main types of ore shows： in iron oxides （magnetite and hematite）, Au and Fe were dissolved simultaneously and their solubilities are positively correlated, which means Au is mainly chemical-bonded （lattice gold） and/or colloidal-adsorbed in iron oxides; while in pyrite, on the contrary, Au dissolution obviously lags behind Fe and the solubility of Au shows negative relationship with that of Fe, which indicates Au is mainly hosted as grains of elemental gold （or native gold） within pyrite. Previous studies revealed that the Hadamengou gold deposit is characterized by intensive K-feldspathization and holds high content of iron oxides occasionally replaced by sulfides, which was caused by oxidizing K-enriched alkaline fluids under a stretching geodynamic setting. These geological features, together with the high Au-content in iron oxides, comparable with that of the Olympic Dam deposit in South Australia, suggest that this deposit is the first example of iron oxide-type gold deposits in China.     

辉长岩的高压部分熔融实验研究

利用天然含水辉长岩在１．５～３．０ＧＰａ,９００℃～１４４０℃条件下进行了高温高压部分熔融实验,系统地分析了辉长岩部分熔融后实验产物的岩石学、矿物学、地球化学特征。获得了１）辉长岩的高压熔融曲线,２）辉长岩在不同压力下熔融时,残留相矿物组合及期间矿物相转变与熔融液相成分（相当于安山岩浆）特征。认识了辉长岩与榴辉岩相间的相变关系;辉长岩－榴辉岩－安山岩之间的内在联系以及高温榴辉岩的可能成因。     

Petrochemical Study of Mantle Xenoliths in Alkali Basalts from South Korea: P/T Regime of the Upper Mantle

Mantle xenoliths in alkali basalt at three locations in South Korea—Boun, the Gansung area, and Baegryung Island—are spinel lherzolites composed of olivine, orthopyroxene, clinopyroxene, and spinel. The xenoliths generally display triple junctions between grains, kink-banding in olivine and pyroxenes, and protogranular and equigranular textures, with no preferred crystal orientation. Anhedral brown spinels occur interstitially. Minerals in lherzolites from each of the three localities are compositionally homogeneous. Olivine compositions have Fo_89.0 to Fo_90.2, low CaO (.03 to 0.12 wt%), and NiO of 0.34 to 0.40 wt%; the orthopyroxene is enstatite with En_89.0 to En_90.0 Al₂O₃ of 4 to 5 wt%; the clinopyroxene is diopside with En_47.2 to En_49.1 and Al₂O₃ of 7.42 to 7.64 wt% from Boun and 4.70 to 4.91 wt% from Baegryung. Spinel chemistry shows a distinct negative trend, with increasing Al corresponding with decreasing Cr, and Mg# and Cr# of 75.1 to 81.9 and 8.5 to 12.6, respectively.

Temperatures and pressures of equilibration for these mantle xenoliths were estimated using various pyroxene geothermometers (Wood and Banno, 1973; Wells, 1977; Mercier, 1980; Sachtleben and Seck, 1981; Bertrand and Mercier, 1985; Brey and Köhler, 1990) and the Al-solubility geobarometer (Mercier, 1980; Lane and Ganguly, 1980). Temperature estimates from the recipes of Mercier (1980) and Sachtleben and Seck (1981) are compatible. The equilibrium temperatures of these xenoliths, taken as the average obtained from these two methods, lie between 970 and 1020° C, and equilibrium pressures derived from Mercier (1980) fall within the range of 12 to 19 kbar (i.e., 42 to 63 km). These temperatures and pressures are reinforced by considerations of the Al-isopleths in the MAS system (Lane and Ganguly, 1980), as adjusted for the Fe effect on Al solubility in orthopyroxene (Lee and Ganguly, 1988).

The equilibrium temperatures and pressures of xenoliths, as considered in P/T space, belong to the oceanic geotherm, based upon the various mantle geotherms presented by Mercier (1980). This geotherm is completely different from continental geotherms, e.g., from South Africa (Lesotho) and southern India. Mineral compositions of spinel-lherzolites in South Korea and eastern China are primitive; paleogeotherms of both are quite similar, but degrees of depletion of the upper mantle could vary locally. This is demonstrated by eastern China, which has various depleted xenoliths caused by different degrees of partial melting.     

俯冲带壳-幔相互作用的高温高压实验:对地幔不均一性成因的启示

使用活塞-圆筒式高温高压装置进行一系列榴辉岩部分熔融熔体与橄榄岩反应实验,可以为深入了解俯冲带壳-幔相互作用的影响因素及地幔不均一性的成因提供重要信息.实验使用反应偶的方法,并在0.8~3.0 GPa和1 200~1 425℃条件下进行.实验结果表明,榴辉岩部分熔融熔体-橄榄岩反应的动力学和结果受控于熔体主量元素成分、熔体中的H₂O、温度、压力和橄榄岩的物理状态等因素.大陆俯冲带地幔岩石中斜方辉石的富集是再循环陆壳熔体与上覆地幔反应的结果,地幔岩石中斜方辉石岩脉的形成与含水熔体交代有关,地幔岩石中的石榴辉石岩和石榴石岩可能形成于高压、低温条件下的熔体-橄榄岩反应.      

角闪石高温高压实验研究进展及其地球物理意义

高温高压实验作为地球科学研究的重要方向之一,通过模拟地球深部的温度和压力条件,了解地球深部物质的物理化学性质、地球内部结构和动力学演化。角闪石属于双链硅酸盐矿物,为地幔岩石圈的重要组成,广泛分布在海洋地壳、俯冲板块、变质岩和火成岩中。作为俯冲带的重要含水矿物,角闪石的广泛分布和高温高压下的脱水对于理解俯冲带水含量以及水迁移具有重要作用,同时在俯冲带的地震活动、高电导率异常、地震波速异常和岩浆活动中扮演重要角色。在过去的近百年时间里,国内外学者对角闪石高温高压物理化学性质进行了大量的研究。角闪石具有非常复杂的元素组成和结构特征,由此也导致了不同角闪石物理化学性质存在显著不同,包括脱水与脱羟基反应中元素迁移的差异、角闪石形成与分解过程中碱性元素(K+Na)和H2O含量对热稳定的影响、不同空间群结构下的高压结构相变、原位条件下不同结晶方向的电导率异常、不同结晶学优选方位(CPO)下的波速异常等。已有的研究对于角闪石的物理化学性质以及其在俯冲带中发挥的作用有了比较清楚的认识,但仍然有许多问题需要进一步研究,如角闪石的高压脱水动力学、热物性和变形机制等。     

蛇纹石化碱性橄榄石玄武岩、水和氢氧化钠溶液的高温高压实验研究

蛇纹石化碱性橄榄石玄武岩、水和氢氧化钠溶液的高温高压实验研究宋茂双（中国科学院地球化学研究所，贵阳５５０００２）关键词高温高压碱性玄武岩Ｐ波速度熔融－结晶蛇纹石脱水温度作者测量了高温高压下蛇纹石化碱性橄榄玄武岩的Ｐ波速度、蛇纹石脱水温度和Ｈ２Ｏ及Ｎａ...     

内蒙古哈达门沟金矿床单矿物金浸出实验研究及其地质意义

哈达门沟金矿床产于华北克拉通北缘西段，形成于伸展构造背景中，成矿流体富钾高碱且氧化性强，矿石建造中铁氧化物含量高，并且可见铁氧化物被硫化物交代的现象。文章拟揭示金在铁氧化物中的含量和赋存状态，并探讨金矿床成因。对哈达门沟金矿3种类型矿石中的黄铁矿、铁氧化物(磁铁矿和赤铁矿)单矿物进行金、铁浸取实验，结果表明：铁氧化物含金较高；黄铁矿中的金和铁的浸出曲线不同步，金浸出率与铁浸出率呈负相关，表明黄铁矿中的金主要以颗粒金形式存在；铁氧化物中金、铁同步浸出，浸出率为正相关，表明铁氧化物中的金主要以品格金和(或)胶体吸附金形式存在。哈达门沟金矿床的上述特征均表明其具铁氧化物型金矿床的特点。     

Origin of Plagioclase Lherzolite from the Nikanbetsu Peridotite Complex, Hokkaido, Northern Japan: Implications for Incipient Melt Migration and Segregation in the Partially Molten Upper Mantle

The Nikanbetsu peridotite complex, Hokkaido, Japan, is composedof mainly fertile lherzolite, which shows several lines of evidencefor incipient partial melting in the spinel–plagioclasefacies. There are petrological, textural and mineral chemicalvariations in plagioclase-free and -bearing lherzolites fromthe base to the top of the complex within the total thicknessof 1400 m. Two-pyroxene and spinel symplectites occur only atthe base of the complex. Mass-balance calculations on theirbulk compositions suggest that they lost the Al component frompyropic garnet. The Wo content of orthopyroxene cores continuouslyincreases, whereas the Al content decreases from the base upward.Ca–Na zoning patterns of plagioclase in the plagioclaselherzolites characteristically change from W-shaped patternsat the base to oscillatory patterns in the upper part of thecomplex. These lines of petrological, textural and mineral chemicalevidence indicate that incipient partial melting occurred everywherein the complex, with an increase in the degree of melting fromthe base toward the top, in proportion to a monotonous riseof the equilibrium temperature from 1100°C to 1250°C.The systematics of plagioclase zoning provides evidence forsimultaneous incipient partial melting, melt migration, decompressionand melt crystallization in the ascending upper-mantle rocks. KEY WORDS: melt migration; oscillatory zoning; partial melting; plagioclase lherzolite; symplectite     

The Evolution of the Upper Mantle beneath the Canary Islands: Information from Trace Elements and Sr isotope Ratios in Minerals in Mantle Xenoliths

Laser ablation microprobe data are presented for olivine, orthopyroxeneand clinopyroxene in spinel harzburgite and lherzolite xenolithsfrom La Palma, Hierro, and Lanzarote, and new whole-rock trace-elementdata for xenoliths from Hierro and Lanzarote. The xenolithsshow evidence of strong major, trace element and Sr isotopedepletion (⁸⁷Sr/⁸⁶Sr 0·7027 in clinopyroxene in themost refractory harzburgites) overprinted by metasomatism. Thelow Sr isotope ratios are not compatible with the former suggestionof a mantle plume in the area during opening of the AtlanticOcean. Estimates suggest that the composition of the originaloceanic lithospheric mantle beneath the Canary Islands correspondsto the residues after 25–30% fractional melting of primordialmantle material; it is thus significantly more refractory than‘normal’ mid-ocean ridge basalt (MORB) mantle. Thetrace element compositions and Sr isotopic ratios of the mineralsleast affected by metasomatization indicate that the upper mantlebeneath the Canary Islands originally formed as highly refractoryoceanic lithosphere during the opening of the Atlantic Oceanin the area. During the Canarian intraplate event the uppermantle was metasomatized; the metasomatic processes includecryptic metasomatism, resetting of the Sr–Nd isotopicratios to values within the range of Canary Islands basalts,formation of minor amounts of phlogopite, and melt–wall-rockreactions. The upper mantle beneath Tenerife and La Palma isstrongly metasomatized by carbonatitic or carbonaceous meltshighly enriched in light rare earth elements (REE) relativeto heavy REE, and depleted in Zr–Hf and Ti relative toREE. In the lithospheric mantle beneath Hierro and Lanzarote,metasomatism has been relatively weak, and appears to be causedby high-Si melts producing concave-upwards trace element patternsin clinopyroxene with weak negative Zr and Ti anomalies. Ti–Al–Fe-richharzburgites/lherzolites, dunites, wehrlites and clinopyroxenitesformed from mildly alkaline basaltic melts (similar to thosethat dominate the exposed parts of the islands), and appearto be mainly restricted to magma conduits; the alkali basaltmelts have caused only local metasomatism in the mantle wall-rocksof such conduits. The various metasomatic fluids formed as theresults of immiscible separations, melt–wall-rock reactionsand chromatographic fractionation either from a CO₂-rich basalticprimary melt, or, alternatively, from a basaltic and a siliceouscarbonatite or carbonaceous silicate melt. KEY WORDS: mantle xenoliths; mantle minerals; trace elements; depletion; carbonatite metasomatism     

Origin of Basalt Magmas: An Experimental Study of Natural and Synthetic Rock Systems

Natural basalts and eclogites were investigated experimentallyat a series of temperatures in the pressure range 1 atm to 40kb and with water pressures 1 to 10 kb. Some runs were alsomade on related synthetic systems at 10 and 33 kb. The two principal magma types recognized by field investigators—tholeiiteand alkali basalt types-appear to be separated by equilibriumthermal divides at 1 atm. The principal divides were found byexperiment at elevated pressures to give way to a new set ofequilibrium thermal divides resulting from a new mineralogy.The change of the equilibrium thermal divides with pressureleads to the derivation of the two principal magma trends fromthe same bulk composition. The melting behavior of basalts and eclogites indicates thatboth are the partial melting products of a more primitive rock(e.g. garnet peridotite). In the region of magma generation(below 60 km) the parental material, presumed to be garnet peridotite,yields an eclogitic magma and its fractionation depends on thegarnet and omphacite of the eclogite, not on plagioclase andclinopyroxene of a basaltic magma. Increase of the garnet constituentsin the magma at high pressure by effective removal of omphaciteor shift of the garnet-omphacite boundary ‘surface’will give rise to a tholeiite-type magma at low pressure. Similarly,increase of the omphacite constituents in the magma at highpressure by physical or physicochemical means will give riseto an alkali basalt-type magma at low pressure. In general,alkali basalt-type magmas are to be expected to be generatedat greater depths than tholeiite-type magmas from the same primarysource rock. Establishment of the two major basalt series takes place inthe region of generation; additional minor diversification ofeach series may come about after emplacement in or on the crustby crystal settling, oxidation or reduction, gas fluxing, contamination,and other processes. The derivative magmas are greatly restrictedby the course of liquid thermal descent imposed at generation. Pressure-temperature limits established experimentally suggestthat the basalt-eclogite transformation may be responsible forthe Mohorovii discontinuity under the continents, but not underthe oceans. The field of stability of basalt is drastically reduced in thepresence of water, and amphibolite is produced. The meltingof amphibolite takes place over a much greater range of temperaturethan basalt. At 10 kb water pressure the beginning of meltingof amphibolite closely approaches that of granite. Partial meltingof amphibolite may yield anorthositic liquids having a relativelylow anorthite content at exceptionally low temperatures. Eclogiteitself is not stable in the presence of water and gives placeto amphibolite or pyroxene hornblendite. Magmas which crystallizeto basalt, gabbro, or eclogite must have had a low water-contentat the time of crystallization. Fifteen rock and twenty-three mineral analyses as well as numerouspartial chemical analyses of experimental products were madeby J. H. Scoon in the course of the investigation. These chemicalanalyses bear on many mineralogical and petrological problems.     

Transport and Storage of Potassium in the Earths Upper Mantle and Transition Zone: an Experimental Study to 23 GPa in Simplified and Natural Bulk Compositions

We have investigated the stability and composition of potassiumamphibole and its high-pressure breakdown product phase X insynthetic peralkaline and subalkaline KNCMASH (K₂O–Na₂O–CaO–MgO–Al₂O₃–SiO₂–H₂O)and natural KLB-1 peridotite bulk compositions between 10 and23 GPa at 800–1800°C. In the KNCMASH system, potassiumamphibole reaches its upper pressure stability limit at 13–15GPa at     

秦岭造山带若干岩石高温高压脱水熔融的特征及其意义

对秦岭造山带和邻区块状岩石样品进行了高温（1 100~1 300 ℃）和高压（1.2~1.8 GPa）脱水熔融实验。通过对实验产物综合分析发现许多样品中出现了熔融玻璃和雏晶。玻璃代表的熔体成分为基性和中性,部分接近于超基性范围,熔体与原来岩石全岩成分比较,更偏基性。熔体出现的空间和成分都显示了局部熔融体系的特征,即含水矿物（角闪石或黑云母）和浅色矿物（石英或斜长石）控制了熔融的发生并且决定了熔体的成分。脱水熔融产生了比原岩更偏基性的熔体,这意味着熔融后残留部分将愈偏酸性。如果这种机制存在于大陆中-下地壳,将对探讨大陆地壳的结构和物质组成,解释某些地区的长英质中下地壳的成因等具有重要的意义。     

Assimilation and Fractional Crystallization Controlled by Transport Process of Crustal Melt: Implications from an Alkali Basalt-Dacite Suite from Rishiri Volcano, Japan

Mechanisms of fractional crystallization with simultaneous crustalassimilation (AFC) are examined for the Kutsugata and Tanetomilavas, an alkali basalt–dacite suite erupted sequentiallyfrom Rishiri Volcano, northern Japan. The major element variationswithin the suite can be explained by boundary layer fractionation;that is, mixing of a magma in the main part of the magma bodywith a fractionated interstitial melt transported from the mushyboundary layer at the floor. Systematic variations in SiO₂ correlatewith variations in the Pb, Sr and Nd isotopic compositions ofthe lavas. The geochemical variations of the lavas are explainedby a constant and relatively low ratio of assimilated mass tocrystallized mass (‘r value’). In the magma chamberin which the Kutsugata and Tanetomi magmas evolved, a strongthermal gradient was present and it is suggested that the marginalpart of the reservoir was completely solidified. The assimilantwas transported by crack flow from the partially fused floorcrust to the partially crystallized floor mush zone throughfractures in the solidified margin, formed mainly by thermalstresses resulting from cooling of the solidified margin andheating of the crust. The crustal melt was then mixed with thefractionated interstitial melt in the mushy zone, and the mixedmelt was further transported by compositional convection tothe main magma, causing its geochemical evolution to be characteristicof AFC. The volume flux of the assimilant from the crust tothe magma chamber is suggested to have decreased progressivelywith time (proportional to t^–1/2), and was about 3 x 10^–2m/year at t = 10 years and 1 x 10^–2 m/year at t = 100years. It has been commonly considered that the heat balancebetween magmas and the surrounding crust controls the couplingof assimilation and fractional crystallization processes (i.e.absolute value of r). However, it is inferred from this studythat the ratio of assimilated mass to crystallized mass canbe controlled by the transport process of the assimilant fromthe crust to magma chambers. KEY WORDS: assimilation and fractional crystallization; mass balance model; magma chamber; melt transport; Pb isotope