火成岩自组织结构成因研究新进展

本文在综合国内外有关文献的基础上，评述了火成岩自组织结构成因研究的新进展；指出了今后研究时应注意的问题。     

定量化火成岩结构分析与岩浆固结的动力学过程

定量化火成岩结构分析将传统的定性或半定量化的岩相学研究提高到了与岩石地球化学分析相比拟的定量化程度,实现了诸如晶体粒度分布、晶体空间分布、晶体定向程度分析和二面角测量等方面的定量化研究。集中介绍了以上4种国际上应用广泛的定量化火成岩结构分析方法,包括各种研究方法的基本理论公式、岩浆动力学意义和实现方式。详细介绍了定量化火成岩结构分析中处于核心地位的晶体粒度分布理论,概括了二维岩石薄片法、三维连续剖面法和X射线层析技术,在定量化火成岩结构分析中的应用原理和现状。对晶体粒度分布分析中数据的封闭性和有效性检验进行了简要论述。综合阐述了晶体成核生长,晶体的聚集、分离和分解,岩浆混合,压滤、压熔和岩浆流动,结构的调整和平衡等一些基本的岩浆动力学过程中晶体粒度分布特征的表现。结合一些已发表的晶体粒度分布和晶体空间分布数据,简要概括了重要的基本定量化火成岩结构参数所表达的封闭和开放岩浆体系的特征,以及参数间协变关系所反映的岩浆固结动力学过程。最后给出了二维岩石光薄片分析法的基本流程和注意事项,认为今后定量化火成岩结构分析和地球化学分析结合在一起的综合方法,将成为研究成岩成矿动力学过程的重要手段,也将会逐步扩展到岩浆相关矿床中成岩成矿机制分析和成矿预测的方向。     

红石金矿成因矿物学的研究

本文通过显微金及含金黄铁矿成因矿物的研究，得出红石金矿床严格受地层、断裂、岩浆活动等多种因素控制，成矿物质具有多源特点的认识。     

东升庙矿床黄铁矿成因矿物学的研究

东升庙矿床中,从原始沉积—区域变质作用都有黄铁矿的形成。根据黄铁矿的产状、共生组合及结构构造相互关系,可划分出微晶黄铁矿、结核状黄铁矿、同心环状胶黄铁矿、重晶粗粒黄铁矿和脉状黄铁矿等五种类型。对黄铁矿化学分析、微量元素分析、晶脆参数和反射率测定均显示了五类黄铁矿成因差异的标型特征。 黄铁矿成因矿物学研究表明,该区矿化经历了原始沉积—热卤水成矿—变质重结晶及受后期岩浆作用影响局部活化等四个阶段。成矿作用表现由原始沉积向热卤水沉积成矿过渡的矿床类型。区域变质作用和局部活化只是对矿床产生了不同程度的改造,使矿体进一步富集。     

石英脉型金矿的石英成因矿物学与找矿矿物学特征

对金矿区石英的形态、成分、热发光、包裹体、红外谱的研究，可推测成矿热液来源方向，矿区剥蚀程度，以及矿区深部是否有远景。白桦岭石英脉型金矿中的石英假六方晶形、杂质含量高、热发光积分强度大、并且多峰、包裹体的爆裂脉冲数大并具多峰、红外吸收谱向低频偏移大为富矿标志。     

桂东金矿床的成因矿物学研究

桂东金矿产于寒武系水口群浅变质砂页岩内，石英和黄铁矿是各类金矿中主要的载金矿物，成因矿物学标型特征表明，矿床可分为变质热液，岩浆热液和复合迭加型，以后者为主。据硫，铅，氢，氧同位素组成特征，结合石英的含金性，晶胞参数和热发光性及黄铁矿微量元素等成因信息，论证了成矿物来源，成矿流体性质与成矿的关系，金的富集是处于造山带构造环境，经历加里东运动及其以后构造－岩浆活动多次迭加的长期演化结果，据矿物的标型     

火成岩中的超临界流体晶及其研究意义

流行火成岩理论中,岩浆被默认为自然熔体,因而火成岩中的矿物晶体都形成于熔体的结晶作用,可称为熔体晶。许多证据表明,火成岩中也可以含有从超临界流体析出的晶体,被称为超临界流体晶(文中简称为流体晶)。根据三个典型实例分析,流体晶既可以从超临界流体直接析出,类似于从热液析出晶体的过程;也可以由超临界流体浓缩产生的熔体结晶形成。不管是哪一种晶出方式,流体晶产生的前提都是岩浆达到流体过饱和态;而满足这一前提的基本条件则是透岩浆流体过程和岩浆快速上升。结合前人关于熔体流体平衡条件的研究进展,以及熔体黏度对挥发分含量和岩浆上升速度对熔体黏度的依赖,发现透岩浆流体过程与岩浆上升过程之间具有耦合关系,这种关系可以用来阐明岩浆系统行为非线性变化的原因。流体晶的研究具有重要意义,可用于：(1)提供一种研究岩浆系统流体条件的新途径;(2)揭示岩浆系统偏离理想态的程度;(3)为反演岩浆系统动力学过程提供新的约束;(4)为识别致矿侵入体和评估侵入体的找矿潜力提供新的矿物学标志;(5)理解火成岩理论中一些长期得不到解决的问题,如岩浆中挥发分溶解度问题、冻结岩浆的活化问题、岩浆成矿专属性问题。     

冀东地区早侏罗世岩浆岩成因及其意义

冀东地区位于华北克拉通东部,区内中生代岩浆活动强烈,形成了大量不同时代的侵入岩,成为研究华北克拉通破坏过程的重要研究对象。本文在冀东青龙地区对蛇盘兔花岗岩和龙须门闪长岩进行了锆石离子探针定年,分别获得了1920±24Ma和1905±13Ma的年龄,结合前人在冀东其它地区获得的190～199Ma的不同岩体的锆石年龄,表明冀东地区早侏罗世是一重要的岩浆作用时期。青龙地区的早侏罗世岩浆岩由经历了不同程度结晶分异的中-酸性岩组成,它们的锆石ε_(Hf)(t)明显高于华北古老下地壳的范围,说明可能并不是完全由古老下地壳重熔产生。另一方面,蛇盘兔花岗岩和龙须门闪长岩的锆石ε_(Hf)(t)均具有较小的变化范围,结合它们极低的Cr、Ni含量,可以排除壳幔岩浆的直接混合。鉴于该地区在三叠纪岩浆岩中存在亏损地幔物质的加入,推测冀东青龙地区早侏罗世岩浆岩可能来源于三叠纪底侵作用形成的新生地壳与古老地壳的混合源区的部分熔融。     

Sector-zoned phlogopites in igneous rocks

Sector-zoned micas are described in three occurrences of igneous rocks. Basal sectors (001) and lateral sectors (010) are well defined. Analyses of probably isochronous growth points indicate that there are consistent chemical composition differences between the sectors, the (010) sector being richer in Si and poorer in Ti, Fe, Al and Ba relative to the (001) sector. Within each sector type Fe/ (Fe + Mg) increases from core to rim. These differences vary in amplitude from one occurrence to the other, but are systematic for micas with extremely different tetrahedral cations. Possible factors influencing this type of crystallization are briefly reviewed: growth rate, geometry of protosites and bulk composition of the liquid.     

歧口凹陷火成岩的地球化学特征、形成时代及构造意义

歧口凹陷侏罗系火成岩主要以中-酸性的流纹岩、粗面岩和粗面安山岩为主,白垩系主要为中-基性的粗面玄武岩和玄武质粗面安山岩,第三系火成岩以粗面玄武岩、碱性玄武岩及辉绿岩为主。同位素定年结果获得白垩系玄武岩的年龄为133±20 Ma,安山岩和粗安岩年龄分别为111.8±0.9 Ma和122.1±3.1 Ma,第三系辉绿岩年龄为16.57±0.23 Ma。地球化学特征显示,侏罗系火成岩相对低钛、高碱和钠、低铁镁,轻重稀土元素强烈分馏、微量元素相对富集LILE、贫化HFSE、亏损Nb和Ti、P,部分高Sr、低Yb,总体指示为挤压环境下加厚地壳物质的熔融产物,白垩系火成岩中等钛和碱的含量,高钠、铁和镁,稀土和微量元素显示其来自于伸展背景的富集地幔源,但受到陆壳物质的混染,第三系火成岩高钛含量、中等碱含量但变化大、高钠、富铁镁,轻重稀土元素分馏弱到中等、微量元素富集LILE和HFSE,同样来自板内伸展环境的富集地幔源的产物。表明歧口凹陷构造转换发生在晚侏罗世和早白垩世之间。     

大湖塘钨矿区岩浆岩黑云母的成分特征及其成矿指示意义

大湖塘钨矿床是赣北地区近年来发现的超大型钨-多金属矿床,矿区内岩浆岩十分发育,且均含黑云母。按照黑云母的产出特征,大湖塘矿区岩浆黑云母可分为晋宁期花岗闪长岩中黑云母(类型一)、燕山期似斑状花岗岩中黑云母(类型二)、燕山期细粒花岗岩中黑云母(类型三)3种类型。对3类黑云母的电子探针和LA-ICP-MS分析结果显示,3类黑云母属于铁云母到铁叶云母,富F贫Cl,富集大离子亲石元素Rb、Ba、K和高场强元素Ta、Nb、Ti等。综合对比显示,与钨成矿相关的燕山期似斑状花岗岩中的黑云母(类型二)具有较低的X_(Mg)值和Fe~(3+)/Fe~(2+)值、较高的Cl含量、∑REE浓度和LREE/HREE值,可作为含钨岩浆岩的成矿专属性指标。     

Extremely magnesian olivine in igneous rocks

Published data on extremely magnesian olivine (> 96 mol.% forsterite) in igneous rocks were generalized and compared with data of new high-precision electron probe microanalyses of olivine from oxidized lavas of the Tolbachik Volcano (Kamchatka), chromitites from the Ray-Iz deposit (Russia), alkaline ultrabasic lavas from San Venanzo volcanoes (Italy), and skarns from the Kuh-i-Lal deposit (Tajikistan). All the found olivines resulted from low-temperature processes, such as subsurface oxidation, interaction with carbonates, and subsolidus re-equilibration. Low-temperature formation of olivine is reflected in its structure (hematite lamellae and abundance of inclusions of ore minerals) and abnormal contents of minor components (Mn, Ni, and Ca). The Mg content of olivine increases under the influence of postmagmatic processes and can be manifested in different rocks. This gives grounds to refine the genesis of olivine of exotic composition (93-96 mol.% forsterite) in some kimberlites, komatiites, and peridotites.     

新疆北部的富镁火成岩

本文重点讨论的富镁安山岩(MAs)是指 SiO_2>53%,Mg~#≥55的安山岩,也包括富镁英安岩和富镁闪长岩。阿尔泰南的富锾安山岩形成于中泥盆世,东、西天山和阿拉套山的富镁安山岩形成于石炭纪。本区富镁安山岩 SiO_2 53%～65%,TiO_2含量低于1%(0.21%～1.08%),平均0.72%;MgO 平均5.90%,与国外玻安岩平均值相比,Mg 含量较低,Ti、K、Na 含量较高。稀土元素总合量低(<100×10~(-6),范围15～95×10~(-6)),相对富重稀土(La/Yb)_N0.98～6.4,多数在4±;Eu 弱亏损到无亏损(Eu/Eu~*0.65～1.15)。相容微量元素 Cr、Ni 含量高,分别为72×10~(-6)～790×10~(-6)和29×10~(-6)～276×10~(-6);高场强元素 Nb、Ta、Ti 明显亏损;相对富集流体中富集的大离子亲石元素 Rb、K、Pb;Y 含量较高(>15×10~(-6));Sr/Y 比值较低(4.4～6.2)。(~(143)Nd/~(144)Nd)_i 值变化范围较大0.51221～0.51255,ε_(Nd)(t) 0.28- 7.2,Nd 模式年龄 t_(DM)485～1220Ma;(~(87)Sr/~(86)Sr)_i 值变化范围较大0.7029～0.7065,在ε_(Nd)(t)-(~(87)Sr/~(86)Sr)_i 图解中位于第一象限。上述特点表明,本区富镁安山岩源区为复合源,包括有蚀变洋壳、弧前增生棱柱的不成熟、新生地壳物质及地幔楔橄榄岩。成岩作用具复合性,既有俯冲洋壳板片的部分熔融,又有俯冲板片熔体对地幔楔橄榄岩的熔体交代作用。形成于特殊构造环境:高地热梯度和富挥发分;导致弧前增生棱柱俯冲的俯冲剥蚀作用;由俯冲板片撕裂、断离所形成的软流圈窗或洋脊俯冲。     

Nephelines and analcimes in some alkaline igneous rocks

The paper presents electron microprobe analyses of nephelines and analcimes in alkaline igneous rocks ranging from theralite and basanite to mugearite and tinguaite. With few exceptions, the nephelines are Si-rich types whose Qz (quartz) components exceed those defining the limits of excess SiO₂ in solid solution in the Ne-Ks-Qz-H₂O system at 700°C and 1 kbarP _{H 2 O}. Unlike the nephelines in the basanites which show only limited grain-to-grain compositional variation, those in theralites and tinguaites from the differentiated Square Top intrusion, New South Wales, and in a New Zealand tinguaite vary significantly in Ne (nepheline), Ks (kalsilite) and Qz, even within individual samples, and they also may be strongly zoned. The rims of zoned nephelines are enriched in Si and Fe³⁺, relative to core compositions. These zoning trends contrast with the composional trend of successive bulk nepheline fractions in the Square Top sequence theralite tinguaite whereby Qz decreases. The nephelines coexist with high-temperature alkali feldspars. In the Ne-Ks-Qz system they plot on the Ne side of the Barth compositional join defined by the omission solid solution series with end-members K₂Na₆Al₈Si₈O₃₂ (the Buerger ideal composition; Ne₇₅Ks₂₅ mol%) and ₂Na₆Al₂Si₁₀O₃₂ (=cavity cation vacancy). The compositions of most natural nephelines are restricted to the field defined by Ne and the Barth join, compositions more K-rich than the ideal composition being relatively rare. The compositions of nephelines on the Ne side of the join are controlled by a number of factors which include the physical conditions attending nepheline crystallization and the compositions of the alkaline hosts. Interstitial analcimes from the Square Top intrusion display extensive NaAlSi substitution and their compositions extend from analcime of natrolite composition to compositions slightly more Si-rich than ideal NaAlSi₂O₆. Groundmass analcimes in the basanites, mugearite and New Zealand tinguaite have relatively constant compositions which approach stoichiometric NaAlSi₂O₆. An unusually Si-rich deuteric analcime (60.2% SiO₂) is also present in vugs in the New Zealand tinguaite. Experimental and other evidence, includingP/T data defining the coexistence of analcime and silica-undersaturated silicate melt in the NaAlSiO₄-KAlSiO₄-SiO₂-H₂O system, and inferred solidus temperatures of the various hosts (they would have exceeded the stability range of analcime) preclude a primary magmatic origin for the interstitial and groundmass analcimes. These are interpreted as subsolidus phases produced by nepheline interaction with deuteric and/or hydrothermal fluids. Analyses of nephelines and their derivative analcimes indicate that the latter may form from both Si-rich and more Si-poor nephelines.