过铝花岗岩基底对成矿物质贡献的地球化学证据——以富城过铝花岗岩体及6722铀矿床为例

采用核诱发裂变径迹、活动性铀钍浸取、Pb同位素组成示踪及元素地球化学对比等方法, 对6722隐爆角砾岩型铀矿床主岩(橄榄玄粗岩)及富城过铝花岗岩基底岩石进行综合研究表明: 1)淡色造岩矿物(石英、长石)的铀含量(0.18~0.36 mg/g)低于全岩铀含量(4.6 mg/g), 黑云母及其中包裹的副矿物(锆石、独居石、晶质铀矿等)是富城花岗岩铀的主要载体矿物, 蚀变矿物(水云母、绿泥石等)中裂隙铀明显增多; 2)黑云母花岗岩的活动铀浸出率为10.4%, 而蚀变花岗岩的活动铀浸出率增高为31%; 3)根据铅同位素计算,花岗岩及蚀变花岗岩以铀迁移带出(DU = -37%~-65%)为特征, 而橄榄玄粗岩及近矿橄榄玄粗岩则以铀的带入(DU = +37%~+58%)为特征. 这表明6722矿床的成矿物质(铀)主要来自蚀变的富城过铝花岗岩基底, 也为基底岩石对成矿作用的重要贡献提供了多方面的地球化学证据.     

赣中盛源盆地及邻区橄榄玄粗岩系列火山岩中黑云母化学成分特征

本文利用电子探针技术对赣中盛源盆地及邻区橄榄玄粗岩系列火山岩中黑云母的类型、化学成分及结晶时的温度和氧逸度条件等进行了研究。黑云母为镁质黑云母;结晶时温度的大致范围为1060℃～1100℃,氧逸度大致范围为10^-7bar-10^9bar。本文研究表明,黑云母的化学成分研究是揭示岩石成因类型的一种有效途径,可为研究岩体成因类型以及成岩时的物理化学条件提供依据,并对成岩具有重要的指示意义。     

腾冲火山岩矿物化学研究

通过电子探针分析,系统研究了腾冲火山岩１０５个造岩矿物的化学成分。研究表明：本区熔岩中的橄榄石为贵橄榄石兼少量透铁橄榄石,斜方石为古铜辉石兼紫苏辉石,单斜辉石为普通辉石兼少量 质透石,斜长石为拉长石兼部分中长石和少量更长石,角闪石为低铁普通角闪石,黑云母为钛铁黑云母为钛铁黑云母为钛铁黑云母兼富铁黑云母。     

郯庐断裂带南段韧性剪切带糜棱岩化过程中长石成分和结构状态变化特征的研究

在对郯庐断裂带南段３条韧性剪切带中糜棱岩及围岩进行矿物组合、结构构造观察研究的基础上,对长石矿物进行了多项分析测试,发现长石成分及其结构状态参数的变化与构造应力场的构造作用存在明显的对应关系：随剪切变形作用的加强,长石矿物的结构状态参数呈增大趋势,矿物单位晶胞的体积和斜长石中Ｓｉ／Ａｌ比值随之减小;长石的变形指数（Ｉｓｓ）和斜长石中的钙长石分子（Ａｎ）与岩石的变形强度呈明显的正相关关系。这些研究结果为探讨构造变形场中矿物岩石的变形 变质作用提供了一种简捷有效的手段     

高黎贡剪切带变形花岗质岩石中的长石细粒化和岩石流动特性

以高黎贡剪切带中发育的变形花岗质岩石为研究对象,主要通过光学显微镜(OM)、扫描电镜(SEM)、阴极发光仪(CL)和电子背散射衍射(EBSD)对其显微构造、组构以及矿物成分进行了精细的测试分析,重点针对岩石中的长石细粒化和流体制约因素进行了深入讨论.研究结果表明:(1)高黎贡剪切带中的变形花岗质岩石随糜棱岩化程度的增强,呈现出两个明显的端元变形岩石类型,即Ⅰ型-条带状花岗质糜棱岩和Ⅱ型-条带状超糜棱岩.(2)在Ⅰ型和Ⅱ型岩石中,主要矿物组合均为钾长石、斜长石、石英、黑云母和(或)白云母.然而其中Ⅰ型岩中矿物的成分含量为:钾长石(残斑为主)斜长石石英±黑云母;Ⅱ型岩中矿物的成分含量为:细粒化的斜长石钾长石石英±黑云母.(3) EBSD组构结果显示无论是Ⅰ型-条带状花岗质糜棱岩,还是Ⅱ型-条带状超糜棱岩,条带状石英在Y轴方向形成最大c轴0001主极密的结晶学优选定向,表示以柱面a滑移系发育为主;而Ⅱ型-条带状超糜棱岩基质中的石英单颗粒在X轴方向形成最大c轴0001主极密的结晶学优选定向,指示了柱面c滑移系.(4)Ⅱ型-条带状超糜棱岩基质中分布的钾长石矿物变形是以(100)[010]滑移系的发育占主导地位的位错蠕变动态重结晶,斜长石矿物呈现较弱的EBSD组构,表现出颗粒边界为主的滑移超塑性流动特征.值得注意的是从Ⅰ型-条带状花岗质糜棱岩到Ⅱ型-条带状超糜棱岩中,变形长石残斑主要为钾长石.在角闪岩相剪切变形过程中钾长石呈现出明显细粒化以及矿物相、矿物成分和结构的转变,表现为钾长石矿物残斑被细粒化斜长石和石英颗粒取代并伴随着流体作用.钾长石残斑的强烈细粒化进一步形成高应变局部化的超糜棱岩和整个岩石的超塑性流动.     

西昆仑阿什火山机构及岩石学、矿物学特征

阿什库勒盆地位于NE向阿尔金断裂与NW向康西瓦断裂的"弧形"交会处,构造活动十分活跃,盆地内发育10余座火山,其中阿什火山为该火山群中最新活动的火山。文中从火山地质、熔岩和斑晶成分、显微结构特征及地质温压计4个方面对阿什火山进行了详细研究。结果表明,阿什火山由火山锥和熔岩流组成,锥体由早期的渣锥和晚期的溅落锥组成,熔岩流分布面积约33km2,可划分为4个流动单元。熔岩属于钾玄岩系列,岩性为粗安岩,显微镜下呈斑状结构。斑晶以长石(主要为中长石)和辉石(包括普通辉石、古铜辉石和紫苏辉石)为主;基质为玻璃质、隐晶质、微晶质,部分含有大量的长石和辉石。斑晶与岩浆的平衡温度为1 104~1 194℃,压力为570~980MPa,对应的岩浆房深度为18.92~32.29km。     

南岭及邻区中生代含锡花岗岩的多样性:显著的矿物特征差异

南岭及邻区分布一系列与中生代花岗岩有关的锡矿床,这些岩石可以是含角闪石黑云母花岗岩,或是(黄玉)钠长石-(铁)锂云母花岗岩,其岩石化学特征指示它们分别对应于准铝质和过铝质花岗岩.细致的矿物学研究表明它们具有完全不同的矿物学特征.准铝质含锡花岗岩的矿物学特征表现为:(1)角闪石、黑云母、条纹长石等组成特征性的造岩矿物组合:(2)标志性副矿物榍石、磁铁矿等显示其原始岩浆具有较高的氧逸度;(3)含锡矿物为锡石、黑云母、榍石等;(4)锡石的成分比较纯,微量元素含量低.过铝质含锡花岗岩的矿物学特征主要表现为:(1)铁锂云母-锂云母、钾长石、钠长石为典型造岩矿物;(2)富铝矿物黄玉是较常见的副矿物,与花岗岩铝过饱和特征相符;(3)锡石是重要的锡矿物,且富含Nb、Ta.造成两类含锡花岗岩显著矿物学差异的原因可能包括熔体的氧逸度、挥发组分和岩浆分异程度的差异.氧化型准铝质花岗岩熔体中锡以四价为主,这导致锡容易富集在含钛的造岩矿物或副矿物中,在岩浆结晶分异阶段形成富锡矿物;这些富锡矿物可成为含锡花岗岩的标志性矿物.相对还原的过铝质花岗岩熔体中锡以二价为主,不易进入造岩矿物和副矿物,常常在岩浆结晶分异阶段形成岩浆成因的锡石;因此,岩浆成因锡石成为这类花岗岩的重要成矿和找矿标志.岩浆性质和锡在两类花岗岩岩浆中地球化学行为的差异,导致形成的矿床类型有所不同.准铝质花岗岩主要形成岩体浸染型、绿泥石-石英脉型、云英岩型、矽卡岩型等矿床,而过铝质花岗岩除形成云英岩型、矽卡岩型、石英脉型等矿床外,更易形成岩体浸染型锡矿化.     

云南腾冲全新世火山源区性质及其岩浆演化

在对腾冲火山区进行野外考察的基础上,重点对区内3座全新世火山(黑空山、打莺山和马鞍山)的岩石学及地球化学特征、岩浆源区性质及其演化进行研究。对主量元素和微量元素研究表明,这套岩石属于高钾钙碱性系列,包括粗面玄武岩、玄武粗安岩、粗面安山岩和英安岩,从基性岩到酸性岩都有分布。这套火山岩富集大离子亲石元素和轻稀土元素,亏损Nb-Ta-Ti不相容元素,具有岛弧火山岩特征。通过微量数据模拟认为,腾冲全新世火山岩为石榴石相地幔橄榄岩在低压条件下大比例部分熔融的产物。源区富钾矿物为金云母,不含角闪石。腾冲及其邻区新生代以来的火山喷发主要受盆地内断裂控制,不受板块俯冲或者火山弧作用的控制。其活动产物为板内火山岩,表现出的岛弧火山岩特征是由于地幔源区受到古洋壳的俯冲板片的富集作用,富集作用发生在部分熔融作用之前。富集地幔部分熔融形成的富钾岩浆沿断裂上升进入地壳形成岩浆房,在岩浆房阶段经历了分离结晶作用和地壳混染作用,有钛铁氧化物、磷灰石、橄榄石、单斜辉石和斜长石的结晶分离。     

甜水海地块古元古代火山岩的发现及其地质意义

本文报道甜水海地块西段古元古界布伦阔勒岩群中片理化变流纹岩的单颗粒锆石LA-ICP-MS测年为（2481±14）Ma.这套流纹岩与玄武岩、玄武安山岩互层状产出,可能共同组成布伦阔勒岩群中的古元古界组分.其中玄武岩、玄武安山岩主体属于低铝拉斑玄武岩系列,流纹岩属于低铝钙碱性系列;岩石富集大离子亲石元素和轻稀土,亏损亲石元素P及高场强元素Nb,Ta和Ti等,铕异常不明显.εNd（t）值（3.14～4.88之间）及微量元素地球化学特征显示具有亏损地幔源区特征,并受到强烈的地壳混染.基性火山岩多元素原始地幔标准化分配曲线及Zr/Y-Zr图解表明其形成于大陆板内构造环境.综合喀喇昆仑区域地质资料,参考华北克拉通新太古代基性火山岩研究成果,推测布伦阔勒岩群火山岩与地幔岩浆底侵作用有关.     

汶川地震断裂带水岩相互作用及其对断裂带演化影响

汶川地震断层岩的矿物学和地球化学特征揭示出地震断层经历了漫长时间演化和复杂的水岩相互作用.间震期水岩相互作用导致断层岩中的破碎矿物蚀变,尤其是长石等矿物含量渐渐减少甚至消失,而黏土矿物（蒙脱石、伊利石、伊/蒙混层、绿泥石等）含量逐渐增高,以及如黄铁矿、石膏、重晶石、坡缕石等热液系统中常见的矿物大量出现;Mg、P、Ti、Mn、Fe等元素倾向富集在断层带中,而Si、K和Na等出现明显的亏损;元素的大量迁移导致断层带的体积巨量亏损.实验结果表明,黏土矿物的亲水性引起水渗透率比干燥气体渗透率明显偏低,并且二者偏差无法通过Klinkenberg校正消除.蒙脱石吸水膨胀和黏土矿物颗粒表面吸附孔隙流体造成孔隙度降低是导致水渗透率偏低的重要原因.断层岩碎屑结构使得其中的孔隙可能在600 MPa围压下得以保存,从而有助于流体沿断层带下渗,并在断层带深部形成高流体孔隙压.地震断层的主要矿物学及粒度分布特征并非在地震破裂过程中形成,因此利用断层岩粒度分布资料估算地震破裂能并不合适.     

Subophitic lithologies in KREEP-rich poikilitic impact melt rocks from Cayley Plains,Apollo 16 — remnants of a volcanic highland crust?

KREEP-rich poikilitic impact melt rocks 65777,11, 65015,88, and 62235,66 are the only mafic impact melt rocks from Cayley Plains stations, Apollo 16, from which areas of subophitic texture can be reported.The bulk chemistry of these unique subophitic areas and the surrounding poikilitic matrices, as well as mineral compositions (olivine, plagioclase, pyroxene, Fe-Ni metal) were determined by electron microprobe analysis. All subophitic areas could be undoubtedly identified as impact melt rockclasts. Inclusion 65777,11 II is of uniquely KREEP-rich composition, 62235,66 II can be classified as anorthositic. Therefore our attempt to identify pristine volcanic basement rocks of the Cayley regions among these inclusions of basaltic texture failed.However, the absence of pristine volcanic target rock fragments and the existence of KREEP-rich and anorthositic impact melt clasts in KREEP-rich impact melt rocks from Cayley Plains favors the theory that the Cayley Plains formation is part of the ejecta blanket from a large basin-type impact crater (Imbrium?), which is underlain by anorthositic material (Nectaris ejecta?), and has been reworked by local impacts in post-Imbrian times.     

Petrochemistry and tectonic setting of mafic volcanic rocks in the Chon Daen–Wang Pong area,Phetchabun, Thailand

The mafic volcanic rocks and hypabyssal rocks in the Chon Dean‐Wang Pong area are possibly the southern extension of the western Loei Volcanic Sub‐belt, Northeast Thailand. They are least‐altered, and might have been formed in Permian–Triassic times. The rocks are commonly porphyritic, with different amounts of plagioclase, clinopyroxene, orthopyroxene, amphibole, Fe–Ti oxide, unknown mafic mineral, and apatite phenocrysts or microphenocrysts, and are uncommonly seriate textured. The groundmass mainly shows an intergranular texture, with occasionally hyalophitic, intersertal and ophitic–subophitic textures. The groundmass constituents have the same minerals as the phenocrysts or microphenocrysts and may contain altered glass. The groundmass plagioclase laths may show a preferred orientation. Chemically, the studied rock samples can be separated into three magmatic groups: Group I, Group II, and Group III. These magmatic groups are different in values for Ti/Zr ratios. The averaged Ti/Zr values for Group I, Group II, and Group III rocks are 83 ± 6, 46 ± 12, and 29 ± 5, respectively. In addition, the Group I rocks have higher P/Zr, but lower Zr/Nb relative to Group II and Group III rocks. The Group I and Group II rocks comprise tholeiitic andesite–basalt and microdiorite–microgabbro, while the Group III rocks are calc‐alkalic andesite and microdiorite. According to the magmatic affinities and the negative Nb anomalies on normal mid‐oceanic ridge basalt (N‐MORB) normalized multi‐element plot, arc‐related lavas are persuasive. The similarity between the studied lavas and the Quaternary lavas from the northern Kyukyu Arc, in terms of chondrite‐normalized rare earth element (REE) patterns and N‐MORB normalized multi‐element patterns, leads to a conclusion that the mafic volcanic rocks and hypabyssal rocks in the Chon Daen–Wang Pong area have been formed in a volcanic arc environment.     

基于QAPM矿物模型遗传算法评价火成岩储层

在松辽盆地深层发现了含气火成岩储层。由于火成岩矿物组成复杂和含量的变化,使得选择用于测井评价的解释参数很困难。基于IUGS提出的QAPF分类方案,本文提出了采用遗传算法,利用测井数据确定火成岩矿物含量的方法。根据QAPF分类方案,将火成岩中的矿物分为五类:Q-石英;A-碱性长石;P-斜长石和方柱石;F-副长石(研究区未出现);M-铁镁矿物。本文提出用包括孔隙度在内的QAPM模型对储层进行分析。建立密度、视中子孔隙度、声波时差、自然伽玛和体积光电吸收截面指数的测井响应方程,各矿物参数从斯伦贝谢的矿物参数手册中得到。用遗传算法计算骨架中四种矿物的体积,根据四种矿物的体积含量,依据QAPF分类对火成岩命名。基于解释参数计算的孔隙度可与岩心分析的孔隙度相比,本文给出的火成岩命名与岩心化学分析的命名相一致。     

Genetic relations of shoshonitic and absarokitic magmas, Absaroka Mountains, Wyoming

The nature, origin, and tectonic significance of shoshonitic volcanism is currently the subject of widely differing views. In the type locality in the Absaroka Range, the rocks consist of a diverse group of lavas, all of Mid-Eocene age. High in the volcanic pile are subordinate volumes of absarokite and shoshonite flows, both of which contain calcic plagioclase and sanidine coexisting in the groundmass. Shoshonites contain plagioclase, olivine, and pyroxene phenocrysts; absarokites contain only olivine and pyroxene phenocrysts. A few absarokites contain modal leucite. A chemical study was made of six shoshonites and three absarokites from this area.Although resorption and zoning indicate disequilibrium in both types of rocks, there is no geochemical evidence of magmatic contamination. Calculated crystal/liquid distribution coefficients are in close agreement with previously determined values for basalts. Decrease in pressure during ascent is a likely cause for the observed disequilibrium.Mass balance calculations show that it would be possible to form a shoshonite by fractionation of olivine and pyroxene from an absarokitic magma. Trace element abundances are consistent with this relationship. Petrographic evidence suggests, however, that fractionation of plagioclase played a role in the formation of shoshonites.A high-pressure origin is consistent with rare earth compositions, and a high magmatic temperature is indicated by the composition of the plagioclase. A calculation of ln a_K^liquid2O for a reaction involving eclogite and a reaction involving a tested rock (Marsh and Carmichael, 1974) suggests a high-pressure origin for a latitude underlying the shoshonites and absarokites. This calculation is subject to large variances because of its sensitivity to estimated equilibrium temperatures.Comparison with lavas of similar composition indicates that shoshonites and absarokites of the Absaroka Range are influenced by their continental setting. There is little evidence for the generation of these magmas in a subduction environment.     

河北沽源—多伦地区中生代含铀火山岩地球化学

沽源和多伦地区是燕辽多金属成矿带的重要组成部分，中生界主要发育上侏罗统白旗组、张家口组，下白垩统大北沟组和花吉营组。张家口组火山岩分布广、厚度大，是铀（钼）矿床的主要含矿主岩。中生代火山岩属于钙碱性系列，化学成分富硅、偏碱，δ值1.17-7.60。稀土元素特征反映火山岩有壳幔混合和壳源改造两种成因。火山岩形成于弱造山环境，其年龄与库拉—太平洋板块向亚洲板块俯冲的时间吻合。张家口组酸性火山岩具有我国相山产铀火山杂岩富硅、富钾，铕极亏损的地球化学特征。     

Plagioclase picrites in the Kamchatsky Mys Peninsula,Eastern Kamchatka

The zone of serpentinite melange in the Kamchatsky Mys Peninsula was found to contain high-magnesium ultramafic volcanic rocks, viz., plagioclase picrite (oceanite) with a MgO concentration of 22.5–25.8%. We evaluated the petrochemical and geochemical characteristics of these rocks, as well as their mineral compositions. The olivine phenocrysts make up 50–60% of the rock volume; their composition (mostly 87–89 mol % Fo) and the composition of melt inclusions in them indicate their origin from a picritic melt with an additional cumulative enrichment in olivine. The geochemical parameters (Zr/Y = 3.1, Th/Yb = 0.14–0.18, Nb/Yb = 2.39–2.66, La_(N)/Sm_(N) = 1.0–1.1, La_(N)/Yb_(N) = 1.24–1.42) indicate an oceanic genesis of these rocks affected by a mantle plume.     

A combined rock magnetic and geochemical investigation of Upper Cretaceous volcanic rocks in the Pontides,Turkey

Upper Cretaceous volcanic rocks were collected at 24 sites along the Pontides, N-NE Turkey, for rock magnetic and geochemical studies. Rock magnetic and petrographic methods showed that the lavas are characterized predominantly by titanomagnetites with a mixture of pseudo-single and multi-domain grains, whereas in tephrite single domain titanohematite was dominant. Measurements of magnetic susceptibility and the geochemical properties on different volcanic rock types provide important knowledge about the magnetic stability of the rocks. The magnetic properties are interpreted in terms of the composition, concentration, magma generation. Tephrite and phonotephrites with the highest intensities (5200 mA/m) and high magnetic susceptibility values (2585 × 10⁻⁵), largest grain sizes and Fe/Ti values, showing minor or no alteration are the most magnetic stable samples in contrast to dacites with the lowest intensity-magnetic susceptibility (520 mA/m − 573 × 10⁻⁵) and high alteration degree. The basanite samples show very low NRM (48–165 mA/m) but very high magnetic susceptibility (2906–3100 × 10⁻⁵) values suggesting the alteration of Fe-Ti minerals. It is shown that the magnetic properties of the basic to acidic rocks show a systematic variation with magma differentiation and could be related to fractional crystallization. Major and trace elements revealed that the lavas are compatible with complex magma evolution, with mineral phases of olivine+magnetite+clinopyroxene in basic series, amphibole+ +clinopyroxene in intermediate rocks and plagioclase+clinopyroxene+biotite in acidic series.     

Adakitic lavas in the Central Luzon back‐arc region,Philippines: lower crust partial melting products?

Abstract Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc–trench gap region slab melts.