玄武岩的 MnO-TiO2-P2O5判别图的修改与补充

近些年来,人们广泛地利用火山岩的主元素或微量元素的特征对火山岩进行地球化学、成因岩石学和构造岩石学的研究。Mullen(1983)利用玄武岩的 MnO、TiO₂和P₂O₅建立大洋型玄武岩的 MnO×10-TiO₂-P₂O₅×10的构造背景判别图(以下简称MTP图)和圈出了大陆拉斑玄武岩在 MTP 图中的分布范围。他选择了能反映玄武岩形成过程中的重要地球化学特征和成因机制的元素组作为该图的端元组分。     

由BaSO4直接热分解制备用于同位素分析的SO2

硫同位素地质研究工作中,经常遇到的研究对象是硫酸盐矿物。如何把这些硫酸盐矿物转化为适于质谱测定硫同位素组成的SO₂气体,是我国硫同位素地质研究中急待建立的实验手段之一。 经典的方法中,可溶于水的硫酸盐,通常是先把它沉淀为BaSO₄,然后通过一系列的化学反应转化为SO₂。 七十年代初期,B.D.Holt等人提出直接加热分解BaSO₄制备SO₂的方法。     

花岗岩—H2O—HF体系相关系及氟对花岗质熔体结构的影响

通过在0.1GPa压力下钠长花岗岩-H₂O-HF体系相关系实验获得,随体系F含量的增加,石英的温度稳定域上限升高,长石的温度稳定域上限降低;石英、碱性长石的晶-液平衡热力学计算表明,F导致花岗质熔体中组分SiO₂的活度增加,组分NaAlSi₃O₈和KAlSi₃O₈的活度减小,且NaAlSi₃O₈活度较KAlSi₃O₈活度减小幅度大。这些结果显示了F在花岗质熔体中与Si以外的阳离子Al、Na、K等产生了结合,且F与Na结合的优先性大于K,破坏了具有电荷平衡离子Na、K的AlO₂^-四面体,使熔体架状网格中Si/(Si+Al)和K/Na比值增大。通过F与H₂O对花岗岩体系相平衡的影响比较,作者认为F不与Si结合是它与OH^-在干扰熔体结构方面的最大区别。     

莱河矿(Fe0.52+Fe1.03+SiO4)的超结构

莱河矿于1976年在中国辽宁省的磁铁矿床中首次被发现,许多人对它进行过研究。该矿物为黑色、不透明,化学式为Fe_0.58²⁺Fe_1.0³⁺Mg_0.03Si_0.96O₄,虽然它的晶体结构近似于橄榄石,但已确定为单斜晶系,空间群为P2₁/b。本文作者利用X射线、电子探针、高分解能透过电子显微镜对该矿物进行了系统的研究,发现它具有假双晶、超结构和显微条纹结构。     

常用气体地热温度计的应用及效果评价

基于冰岛部分地热田的实际资料,选择有代表性的、不同温度的地热田,应用CO₂、H₂S、H₂、CO₂/H₂和H₂S/H₂气体地热温度计计算热储温度,深入探讨了影响温度计准确性的各种因素,提出CO₂和H₂S温度计具有良好的实用价值。在热储温度T<200℃时,CO₂温度计的预测温度略低;在200℃<T<300℃范围时,H₂S温度计标定不够准确。并对现有的其它气体地热温度计进行了简要评价。     

吉林陨石原始捕获的40Ar/36Ar比值及其地质意义

地球大气圈中⁴⁰Ar/³⁶Ar的现代比值被公认为295.5,在利用K-Ar法测定地球物质年龄时,它是校正大气氩混染量的重要参数。陨石中原始捕获(trapped)的(⁴⁰Ar/³⁶Ar)_t比值是否和地球大气圈中氩同位素丰度相一致,这个问题不但在地质年龄测定中具有现实意义,而且对探索太阳系的形成和演化也有重要理论价值。近十几年,随着质谱分析技术的提高以及登月计划的实施,国外出现了一批有关月岩中氩同位素原始组分的资料,但至今对陨石中原始氩同位素丰度的报道很少。笔者采用⁴⁰Ar/³⁹Ar快中子活化技术和约克方程^[3,4],对吉林陨石雨2号标本进行了原始捕获的(⁴⁰Ar/³⁶Ar)_t比值进行了测定,并探讨了它的地质意义。     

火山岩储层斜长石选择性溶蚀的岩石学特征和热力学条件

长石溶孔是火山岩中重要的孔隙类型之一,火山岩的主要孔隙类型中长石溶孔所占的比例在1.24%～60.61%之间,在储层中占有重要地位.从岩相学、岩石化学CIPW标准矿物成分、热力学等方面论证了斜长石的选择性溶蚀.岩相学特征表现出斜长石选择性溶蚀的特征,即钙长石溶蚀时钠长石没有溶蚀,同时出现斜长石选择性溶蚀时钠长石和钾长石生长的现象.斜长石选择性溶蚀得到了CIPW标准矿物成分的支持,在CIPW标准矿物成分中长石的端元组分主要为钠长石和钾长石,而钙长石绝大多数为0或接近0.热力学研究表明,在同样的温度、压力和地层水成分的条件下,在斜长石中优先溶解钙长石组分.当地层水中Na+和K+浓度达到饱和时发生钠长石和钾长石沉淀,出现斜长石选择性溶蚀的同时发生钠长石和钾长石生长的现象.     

白云鄂博的氟碳钡铈矿

氟碳钡铈矿(Cordylite)BaCe₂(CO₃)₃ F₂本世纪初首先发现于格陵兰纳尔萨尔苏克(Narssarssuk)的碱性正长伟晶岩脉中,与霓石、氟碳铈钙矿、柱星叶石和碳锶铈矿共生。1965年该矿物又发现于我国白云鄂博西矿区热液交代的元古代白云岩中。1975年,加拿大魁北克省圣赫莱山(Mont st. Hilaire,Quebec)的霞石正长岩中的伟晶岩脉中也发现了这一矿物,它与方沸石、霓石和钠闪石共生。     

根据汪清橄榄岩包体推导上地幔流变学状态初步研究

运用幔源橄榄岩包体的辉石地质温度计、地质压力计、橄榄石变形显微构造地质应力计以及橄榄石的高温流动律实验资料,计算上地幔的流变学参数是近年来探索上地幔流变学状态的一条新的途径,也是在地球物理手段之外研究上地幔状态的一个值得注意的进展^[1-4]。     

宝石采撷（6）

1 宝石矿物性质(表1)2 宝石中的包裹体2.1 拉长石中的铜 拉长石属于斜长石系列的长石矿物,它是含有数量不定的钠或钙的铝硅酸盐。此系列的钠终端成员是钠长石(NaAlSi_3O_8),而钙终端成员则是钙长石(CaAl_2Si_2O_8),拉长石则落在此系列中的钙长石一边,其中钠与钙之比约自50:50到30:70。     

Refinement of the Kudo-Weill plagioclase thermometer and its application to basaltic rocks

The Kudo-Weill plagioclase thermometer is applied to basaltic rocks. Comparison of measured and calculated crystallization temperatures shows that the latter are generally higher than measured values. The plagioclase thermometer predicts non-ideal behavoir of plagioclase solid solution and is in close agreement with experimental work at lower temperature. New equations are generated that relate plagioclase and melt chemistries to plagioclase crystallization temperatures; and these, combined with activity coefficient corrections, result in a refinement of the plagioclase thermometer.     

The Kudo-Weill plagioclase geothermometer and porphyritic acid glasses

The compositions of the cores and margins of the plagioclase phenocrysts in glassy acid rocks have been used to derive equilibration temperatures with their enclosing liquids using the Kudo-Weill geothermometer. The equilibration temperatures inferred from the compositions of the feldspar margins at 0.5 kilobars water pressure, or less, agree well with the temperatures obtained from the coexisting iron-titanium oxide microphenocrysts. These low water pressures are supported by the water fugacities deduced from the coexisting biotitemagnetite-sanidine assemblages. Acid magma represented by these rocks has a crystallization interval in excess of 100° C and liquidus temperatures above 900° C.     

Kaledonische Intrusivgesteine des Stavanger-Gebietes

An empirical approach has been taken to develop a geothermometer based on plagioclase-magmatic liquid equilibrium. Compositions of coexisting plagioclase and liquid (glass) obtained by electron microprobe analysis of quenched samples from equilibrium melting experiments of natural granitic rocks at water pressures of 0.5 and 1.0 kilobars have been used along with data from the equilibrium experiments of Bowen (1913, 1915), Prince (1943) and Yoder et al. (1957) to calibrate this geothermometer. Applications of this geothermometer to natural occurrences demonstrate that it can provide useful information on temperature of equilibration of coexisting plagioclase and liquid in rocks ranging in composition from basalt to rhyolite. The plagioclase geothermometer is in good general agreement with other geothermometers wherever these are applicable. Where temperatures are known from other sources it can be used to predict the equilibrium compositions of plagioclase in magmas as well as to provide a rough estimate of water pressure.     

Anorthositic Rocks of the Duluth Complex: Examples of Rocks Formed from Plagioclase Crystal Mush

Anorthositic rocks compose 35–40% of the Middle Proterozoic(Keweenawan; 1?1 Ga) Duluth Complex—a large, compositemafic body in northeastern Minnesota that was intruded beneatha comagmatic volcanic edifice during the formation of the Midcontinentrift system. Anorthositic rocks, of which six general lithologictypes occur in one area of the complex, are common in an earlyseries of intrusions. They are characterized on a local scale(meters to kilometers) by nonstratiform distribution of rocktypes, variably oriented plagioclase lamination, and compositeintrusive relationships. Variably zoned, subhedral plagioclaseof nearly constant average An (60) makes up 82–98% ofthe anorthositic rocks. Other phases include granular to poikiliticolivine (Fo_66–38), poikilitic clinopyrox-ene (En'_73–37),subpoikilitic Fe-Ti oxides, and various late-stage and secondaryminerals. Whole-rock compositions of anorthositic rocks are modelled bymass balance to consist of three components: cumulus plagioclase(70–95 wt.%), minor cumulus olivine (0–5%), anda gabbroic postcumulus assemblage (5–27%) representinga trapped liquid. The postcumulus assemblage has textural andcompositional characteristics which are consistent with crystallizationfrom basaltic magma ranging from moderately evolved olivinetholeiite to highly evolved tholeiite (mg=60–25). Sympatheticvariations of mg in plagioclase and in mafic minerals suggestthat cumulus plagioclase, though constant in An, was in approximateequilibrium with the variety of basaltic magma compositionswhich produced the postcumulus assemblages. Standard models of mafic cumulate formation by fractional crystallizationof basaltic magmas in Duluth Complex chambers, although ableto explain the petrogenesis of younger stratiform troctoliticto gabbroic intrusions, are inadequate to account for the field,petrographic, and geochemical characteristics of the anorthositicrocks. Rather, we suggest an origin by multiple intrusions ofplagioclase crystal mushes—basaltic magmas charged withas much as 60% intratelluric plagioclase. The high concentrationsof cumulus plagioclase (70–95%) estimated to compose theanorthositic rocks may reflect expulsion of some of the transportingmagma during emplacement or early postcumulus crystallizationof only plagioclase from evolved hyperfeldspathic magma. Althoughthe evolved compositions of anorthositic rocks require significantfractionation of mafic minerals, geophysical evidence indicatesthat ultramafic rocks are, as exposure implies, rare in theDuluth Complex and implies that plagioclase crystal mushes werederived from deeper staging chambers. This is consistent withinterpretations of olivine habit and plagioclase zoning. Moreover,plagioclase could have been segregated from coprecipitatingmafic phases in such lower crustal chambers because of the buoyancyof plagioclase in basaltic magmas at high pressure. The geochemicaleffects of plagioclase suspension in basaltic magmas are consistentwith observed compositions of cumulus plagioclase in the anorthositicrocks and with the geochemical characteristics of many comagmaticbasalts. The petrogenesis of the anorthositic rocks and theoverall evolution of Keweenawan magmas can be related to thedynamics of intracontinental rift formation.     

A precise olivine-augite Mg-Fe-exchange geothermometer

 Olivine and augite that were experimentally equilibrated in the temperature interval 1175–1080°C at 1 bar in natural basaltic and andesitic bulk compositions are used to calibrate an Mg-Fe²⁺ cation-exchange geothermometer. Within its temperature interval of experimental calibration, and over a broad range in olivine Mg/Fe ratio, the geothermometer has a standard error of ±6°C. In compositionally simpler synthetic systems, the same calibration retrieves appropriate experimental temperatures up to at least 1250°C. In application to intermediate and felsic volcanic rocks erupted at ∼1080 –800°C (below the range of experimental calibration), calculated olivine-augite temperatures are in good agreement with Fe-Ti oxide thermometry in the same samples. These results encourage confidence in the olivine-augite geothermometer over at least the 800–1250°C interval at low pressures. Sparse experimental data up to 1250°C at higher pressures for olivine + augite in the assemblage olivine + plagioclase + augite ± pigeonite or orthopyroxene suggest that the low-pressure calibration recovers experimental temperatures without systematic bias to pressures of 10 kbar. Examples illustrate applications to determining igneous equilibration temperatures in holocrystalline extrusive and intrusive rocks, and to estimating intratelluric H₂O content dissolved in magmas. Received: 24 February 1995 / Accepted: 1 March 1996     

Plagioclase buoyancy in oceanic basalts: Chemical effects

Certain petrological features of oceanic volcanic and plutonic rocks are not completely consistent with previously proposed models of crystal fractionation or magma mixing. For example, Sr is often higher in the differentiated basalts of a suite of aphyric rocks than in the relatively primitive basalts even though the differentiated basalts have apparently been produced by crystallization of large amounts of plagioclase with olivine and clinopyroxene. Additionally, oceanic basalts and gabbroic rocks often contain plagioclase crystals in excess of the appropriate cotectic proportions. Certain differentiated oceanic basaltic glasses and aphyric rocks crystallize plagioclase as the liquidus mineral, which would seem inconsistent with the strongly cotectic nature of the olivine + plagioclase + liquid surface.It is proposed here that plagioclase in mid-ocean ridge magma chambers separates from the basaltic liquid that it crystallizes in at a slower rate than does co-crystallizing olivine or pyroxene. Magma mixing in which a portion of the plagioclase remains suspended in the liquid during crystallization results in much more complex liquid lines of descent in mixed magmas and appears to resolve the apparent discrepancies noted above.     

不平衡条件下单斜辉石形成的一些探讨

辉石作为一种主要造岩矿物广泛出现于许多岩类中,在基性火成岩中它更占有重要的地位。平衡条件下辉石的产出条件及其有关的相平衡关系,前人已有大量实验研究。     

西南极菲尔德斯半岛第三纪钙碱性火山岩的生成与演化

西南极菲尔德斯半岛第三纪火山岩的岩石学和岩石化学特征表明,它们基本属于钙碱性火山岩系列,是岛弧火山作用的产物。该岩石组合中,随岩石中SiO_2含量的增加,斜长石斑晶数量减少,微量元素Cr、V丰度降低,Sr、Ba丰度下降,这些揭示了岩浆中斜长石和单斜辉石的分离结晶作用。稀土元素的系统变化也证明了这一点。主元素和微量元素的定量计算所验证了岩浆的分离结晶作用演化过程。     

Petrology and new data on the geochemistry of the Andahua volcanic group (Central Andes,southern Peru)

The Quaternary Andahua volcanic group is located within the Central Volcanic Zone in Southern Peru. The author presents new data on major and trace elements and ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios for Andahua rocks from all regions with volcanic centres. The TAS data identify the Andahua lavas as trachyandesites, basaltic trachyandesites and dacites. The phenocrysts are represented mainly by plagioclase, but olivine, clinopyroxene and hornblende are also present. In some cases the trachyandesites show Ca enrichment and their plagioclases have an andesine–bytownite composition. The plagioclase phenocrysts show a slight normal and occasionally reverse zonation. Their basaltic parental magmas were enriched in fluids derived from dehydration of the subducted oceanic crust. The chemical content of the Andahua volcanic rocks shows some similarity to both the slightly older and the contemporaneous and widespread Barroso Group rocks in this region.     

河南舞阳地区前寒武纪变质岩系中锆石特征及其对恢复原岩的应用

恢复变质岩原岩的性质是研究变质岩的重要课题。恢复变质岩原岩性质的方法很多,目前普遍采用的是岩石化学法和地球化学法。由于岩石的化学成分变化很大,有些沉积岩的成分与火成岩的成分很相似,变质产物也很相似,特别是那些经过非等化学的深变质的岩石,有的本来是副变质岩,却投影在正变质岩的区域内,或落在模稜两可的地区。目前,有人利用岩石中物理化学性质稳定的锆石区分正副变质岩。