青藏东缘新生代高钾岩浆活动的热年代学制约

热年代学研究表明 ,青藏东缘存在两期新生代高钾岩浆活动 ,其活动时限分别为 40～ 2 8Ma和 16～ 0Ma。两期高钾岩石在地质背景、岩石类型和地球化学特征上明显不同 ,表明早期高钾岩石是在转换压缩过程中产生的 ,起源于富集地幔的部分熔融 ,而晚期高钾岩石则与东亚和青藏地区构造伸展有关 ,起源于新近交代富集的亏损地幔。     

安徽铜陵地区燕山期花岗岩类岩石中的岩浆混合结构

本文采用“结构组合”的概念探讨了铜陵地区花岗岩类岩石中的典型混合结构类型，提出了岩浆混合作用是铜陵地区花岗岩类岩石形成的主要作用，混合作用属于化学混合，且至少发生了两次岩浆混合作用。     

铜陵矿集区燕山期中酸性侵入岩地球化学特征及其地质意义

铜陵矿集区燕山期中酸性侵入岩由橄榄玄粗质系列和高钾钙碱性系列岩石组成,两者的岩石化学和地球化学特征存在差异,相互间不存在岩浆分异演化关系.稀土和微量元素以及O、Pb、Sr、Nd同位素研究表明,高钾钙碱性系列侵入岩的原始岩浆以下地壳深变质岩部分熔融岩浆为主,在有幔源玄武质岩浆注入的情况下先于橄榄玄粗质系列岩浆侵位形成;起源于富集地幔的碱性玄武岩与有限的地壳物质发生同化混染并通过结晶分异作用(AFC)形成了橄榄玄粗质系列侵入岩.下地壳或岩石圈地幔拆沉继而环流热幔上涌是本区侵入岩形成的直接起因;同时,侵入岩浆的强烈活动也是本区构造环境由挤压向伸展转换的标志.     

西藏查孜地区中新世正长岩的锆石U-Pb年代学、地球化学及岩石成因

查孜正长岩体是拉萨地块中段新发现的中新世钾质-超钾质侵入岩,岩性主要为中粗粒石英角闪正长岩和斑状石英正长岩,有暗色包体发育.对两种正长岩进行了岩石学、锆石U-Pb年代学和地球化学研究.结果显示,两种岩石的锆石U-Pb年龄分别为10.37±0.24 Ma、11.06±0.39 Ma,代表它们形成于中新世,是拉萨地块后碰撞岩浆作用的产物.查孜正长岩具有相对高钾（K₂O=6.75%~7.39%）、低镁（MgO=1.44%~2.97%）的特征,K₂O/Na₂O>1,属钾质岩;具有与超钾质岩石相似的微量元素特征,强烈富集Rb、Th、U、K等大离子亲石元素（LILE）和轻稀土元素（LREE）,相对亏损Nb、Ta、Zr、Hf、Ti、P等高场强元素（HFSE）和重稀土元素（HREE）,但Cr（22.7×10-6~64.6×10-6）、Ni（18.9×10-6~46.6×10-6）含量明显偏低.其中,斑状石英正长岩的SiO₂含量相对较高,但MgO、K₂O、Cr、Ni、REE和Y等元素含量比石英角闪正长岩的低.综合分析认为,查孜正长岩主要形成于岩浆混合作用,是富集岩石圈地幔部分熔融形成的超钾质岩浆与地壳物质部分熔融形成的酸性岩浆混合的结果,两种岩石的地球化学差异主要是岩浆混合的程度和比例不同导致的;它的形成可能与岩石圈地幔的减薄作用有关.      

扬子克拉通西缘新生代幔源钾质-超钾质岩岩浆氧逸度及其对陆内斑岩成矿作用的启示

陆内环境斑岩型矿床的成矿金属与硫等物质主要来源于富原生硫化物且呈相对还原状态的角闪岩相下地壳的部分熔融,岩浆的高氧逸度和富水是成矿的关键,但还原性下地壳的熔融产物如何变成高氧逸度岩浆尚不十分明确。为此,本文对哀牢山-红河富碱斑岩带内与陆内成矿斑岩同时代的莴莊粗面玄武岩与谷装箐云煌岩开展了成岩物理化学条件研究。结果显示,这类钾质-超钾质岩的岩浆具有较高的ΔFMQ值(+0.8～+4.3),这一特征很可能继承于经历古大洋俯冲改造的岩石圈地幔。幔源高氧逸度岩浆具备调节与改造下地壳熔融产物氧逸度的潜力。因此,源于古俯冲改造的岩石圈地幔且具有较高ΔFMQ(+2.7～+4.3)的钾质-超钾质岩浆,可能是导致陆内斑岩成矿系统中斑岩岩浆具较高氧逸度的原因,这类钾质-超钾质岩浆与富硫化物的新生的下地壳来源的熔体的混合,可能是导致陆内斑岩成矿的关键。     

华北板块南缘熊耳群火山岩岩石学及其形成环境讨论

熊耳群火山岩系以熔岩为主,其岩石学、岩石化学及地球化学特征表明为双模式火山岩套:下、上熊耳群的主要岩石类型为钾细碧岩及细碧岩、钾角斑岩及角斑岩,属碱性玄武岩浆系列,其源岩浆来自地幔,在上升过程中曾在中间岩浆房停顿并与壳层物质混染。中熊耳群的主要岩石类型为钾石英角斑岩,属拉斑玄武岩浆系列,岩浆来源于下地壳的熔融。火山岩系的岩石地球化学特征及区域分布特征表明熊耳群火山岩系产于活动大陆边缘裂谷带,豫西—陕西这一裂谷带从下熊耳群至上熊耳群火山活动从北向南移动,从东向西扩展,上熊耳群形成时裂谷深度最大,东西范围也最广。中熊耳群形成时期裂谷带为相对闭合阶段,壳层熔融物质上升喷发。     

安徽铜陵凤凰山燕山期中酸性侵入岩地球化学特征及其与金属成矿关系

安徽铜陵凤凰山铜矿是铜陵矿集区内最典型的矽卡岩型铜矿床之一,也是凤凰山矿田内规模最大的铜矿床。矿区内新屋里岩体属于高钾钙碱性系列,主要岩性为石英二长闪长岩和花岗闪长岩。岩石地球化学特征表明凤凰山中酸性侵入岩岩浆属于壳幔混合型,原始岩浆来源于上地幔碱性玄武岩区并有地壳物质混染,在岩浆不断演化过程中有外来物质的加入,成岩过程以混合作用为主。凤凰山铜矿体分布于岩体与大理岩的内矽卡岩带上,岩体中铜含量较高。铜矿体是岩浆期后热液交代碳酸盐地层形成的。矿体的空间分布受构造变形-岩浆侵入高温高压作用的双重控制。矿化经历了从高温矽卡岩阶段到中低温热液阶段的多期次复合成矿作用。     

华北板块南缘熊耳群火山岩岩石学及其形成环境讨论

熊耳群火山岩系以熔岩为主,其岩石学、岩石化学及地球化学特征表明为双模式火山岩套:下、上熊耳群的主要岩石类型为钾细碧岩及细碧岩、钾角斑岩及角斑岩,属碱性玄武岩浆系列,其源岩浆来自地幔,在上升过程中曾在中间岩浆房停顿并与壳层物质混染。中熊耳群的主要岩石类型为钾石英角斑岩,属拉斑玄武岩浆系列,岩浆来源于下地壳的熔融。火山岩系的岩石地球化学特征及区域分布特征表明熊耳群火山岩系产于活动大陆边缘裂谷带,豫西-陕西这一裂谷带从下熊耳群至上熊耳群火山活动从北向南移动,从东向西扩展,上熊耳群形成时裂谷深度最大,东西范围也最广。中熊耳群形成时期裂谷带为相对闭合阶段,壳层熔融物质上升喷发。     

西藏措勤地区发现第三纪富钾岩浆岩

西藏措勤地区发现了第三纪富钾火山岩及正长岩,其同位素年龄分别为15.8～15.9Ma和27.15Ma。火山岩主要岩石类型为粗安岩,少量粗面岩、玄武粗安岩、白榴石玄武粗安岩;正长岩主要岩性为中—中粗粒或似斑状霓辉正长岩。岩石学、岩石化学初步研究表明其属于钾玄质-超钾质火山岩和碱性正长岩。这一发现填补了冈底斯北部新生代富钾质岩浆活动的空白,为进一步研究青藏高原形成和演化提供了重要资料。     

新疆富蕴希力库都克地区岩浆混合作用及其成矿意义

新疆北部希力库都克地区为-斑岩型铜钼金矿区,含矿的花岗闪长岩体中广泛发育4种暗色岩微粒包体似隐晶状安山玄武岩、细粒闪长岩、少斑状安山(玢)岩和安山玢岩,矿区还产有安山玢岩、英安斑岩、正长岩等脉岩.花岗闪长岩及其包体的岩相学、矿物化学和岩石地球化学特征表明该区发生了岩浆混合作用,其中酸性的花岗闪长质与基性的闪长质岩浆混合,形成了过渡相岩石--安山玢岩质岩浆混合岩.本区矿化与暗色微粒包体有关矿化较好的地段暗色微粒包体较多,有些包体中磁铁矿微粒普遍发育,有时甚至含少量黄铁矿和黄铜矿等硫化物.研究发现,本区岩浆混合岩--安山玢岩,与蚀变矿化的花岗闪长岩虽然在野外产状和岩石结构上截然有别,但二者的化学成分相当接近在哈克图上二者的投影点靠近;稀土元素和微量元素上,标准化曲线型式相似(或相同),表明二者具有相似的成因,换言之,岩浆混合作用可能伴随了热液蚀变和矿化的发生.推测本区岩浆混合作用可能是幔源基性岩浆与陆壳花岗质岩浆的混合,由此产生的中酸性岩浆经过分异和流体作用造就了本区的铜钼金矿化.     

Stepwise accumulation and ascent of magmas

One of the currently popular theories on magma ascent is that it mainly occurs by propagating hydrofractures (dykes) and that magma viscosity is the primary rate‐controlling factor. This theory is based on mathematical models for single hydrofractures under idealised conditions. We simulated magma ascent with air ascending through gelatine and observed that the air ascended in batches, following paths made by their predecessors. Multiple batches accumulate at obstacles along the path. Although magma viscosity may control ascent rate during movement, obstacles ultimately control the size and average ascent velocity of ascending batches. We propose that step‐wise movement of magma batches is the mechanism of primary accumulation and ascent from the partially molten source rock of a magma to its first emplacement site and therefore the main ascent mechanism for granitic magmas. ‘Classical’ dyking is the mechanism for secondary ascent from a magma chamber.     

Remobilization of Highly Crystalline Felsic Magma by Injection of Mafic Magma: Constraints from the Middle Sixth Century Eruption at Haruna Volcano, Honshu, Japan

The latest eruption of Haruna volcano at Futatsudake took placein the middle of the sixth century, starting with a Plinianfall, followed by pyroclastic flows, and ending with lava domeformation. Gray pumices found in the first Plinian phase (lowerfall) and the dome lavas are the products of mixing betweenfelsic (andesitic) magma having 50 vol. % phenocrysts and maficmagma. The mafic magma was aphyric in the initial phase, whereasit was relatively phyric during the final phase. The aphyricmagma is chemically equivalent to the melt part of the phyricmafic magma and probably resulted from the separation of phenocrystsat their storage depth of 15 km. The major part of the felsicmagma erupted as white pumice, without mixing and heating priorto the eruption, after the mixed magma (gray pumice) and heatedfelsic magma (white pumice) of the lower fall deposit. Althoughthe mafic magma was injected into the felsic magma reservoir(at 7 km depth), part of the product (lower fall ejecta) precedederuption of the felsic reservoir magma, as a consequence ofupward dragging by the convecting reservoir of felsic magma.The mafic magma injection made the nearly rigid felsic magmaerupt, letting low-viscosity mixed and heated magmas open theconduit and vent. Indeed the lower fall white pumices preservea record of syneruptive slow ascent of magma to 2 km depth,probably associated with conduit formation. KEY WORDS: high-crystallinity felsic magma; magma plumbing system; multistage magma mixing; upward dragging of injected magma; vent opening by low-viscosity magma     

Episodic granite accumulation and extraction from the mid‐crust

The processes of long‐range granitic magma transfer from mid‐ and lower crustal anatectic zones to upper crustal pluton emplacement sites remain controversial in the literature. This is partly because feeder networks that could have accommodated this large‐scale magma transport remain elusive in the field. Existing granite ascent models are based largely on numerical and theoretical studies that seek to demonstrate the viability of fracture‐controlled magma transport through dykes or self‐propagating hydrofractures. In most cases, the models present very little supporting field evidence, such as sufficiently voluminous near‐ or within‐source magma accumulations, to support their basic premises. We document large (deca‐ to hectometre‐scale), steeply dipping and largely homogeneous granite lenses in suprasolidus (~5 kbar, ~750 °C) mid‐crustal rocks in the Damara Belt in Namibia. The lenses are surrounded by and connected to shallowly dipping networks of stromatic leucogranites in the well‐layered gneisses of the deeply incised Husab Gorge. The outcrops define a four‐stage process from (i) the initial formation and growth of large, subvertical magma‐filled lenses as extension fractures developed at high angles to the subhorizontal regional extension in relatively competent wall‐rock layers. This stage is followed by (ii) the simultaneous lateral inflation and (iii) subcritical vertical growth of the lenses to a critical length that (iv) promotes fracture destabilization, buoyancy‐driven upward fracture mobilization and, consequently, vertical magma transport. These field observations are compared with existing numerical models and are used to constrain, by referring to the dimensions of the largest preserved inflated leucogranite lens, an estimate of the minimum fracture length (~100 m) and volume (~2.4 × 10⁵ m³) required to initiate buoyancy‐driven brittle fracture propagation in this particular mid‐crustal section. The critical values and field relationships compare favourably with theoretical models of magma ascent along vertical self‐propagating hydrofractures which close at their tails during propagation. This process leaves behind subtle wake‐like structures and thin leucogranite trails that mark the path of magma ascent. Reutilization of such conduits by repeated inflation and drainage is consistent with the episodic accumulation and removal of magma from the mid‐crust and is reflected in the sheeted nature of many upper crustal granitoid plutons.     

Pervasive granitoid magma transfer through the lower–middle crust during non-coaxial compressional deformation

Granitic magmas migrated through Early Proterozoic middle–lower crust at Mt Hay, central Australia, via a diverse network of narrow structurally controlled channelways, during a period of progressive W–SW-directed thrusting (D1a–D1d). They utilized existing folds, boudins and shear zones, or created new channels by magmatic fracture either parallel to layering or, rarely, in irregular arrays. The magmas rose obliquely, parallel to the plunging (50–60°) regional elongation direction, which was defined by coaxial folds, boudin necks and a strong mineral-elongation lineation. Megacrystic charnockitic magmas migrated through metre-scale conduits during D1a–D1b, but leucosomes were generally restricted to smaller (centimetre-scale) structures that existed throughout the entire deformation history. Thus, D1a/D1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma, thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting. The upper–middle crust of the Anmatjira–Reynolds Range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at Mt Hay. They are considered to have formed as syntectonic intrusions emplaced during W–SW-directed thrusting, as at Mt Hay, suggesting that granitic magmas formed near the base of the continental crust passed through the mid-lower crustal level (25–30 km) exposed at Mt Hay and accumulated, in batholithic proportions, at shallower crustal levels (12–20 km) such as the Anmatjira–Reynolds Range area. The observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive, noncoaxial shear deformation. Localization of magmas by sequentially developed, narrow, compressive structures suggests that dilatancy followed successive foliation-forming events, a situation that can occur during steady-state deformation if the effective confining pressures are low, which would be a result of high and possibly variable rates of magma influx. The inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust.     

岩浆侵位机制研究综述

岩浆侵位机制是研究地球动力作用的重要依据,综合国内外资料,对岩浆侵位机制提出了按侵位深度,岩浆迁移距离,岩浆结晶程度的分类方案及其联合侵位类型。分别对各类侵位机制 岩浆侵位过程,特点,研究现状进行了综述,并讨论了岩浆定位空间问题和影响岩浆定位的因素。     

Pre-eruptive storage conditions of the Holocene dacite erupted from Kizimen Volcano,Kamchatka

This study describes an investigation of the pre-eruptive conditions (T, P and fO₂) of dacite magma erupted during the KZI cycle (12,000–8400 years ago) of Kizimen Volcano, Kamchatka, the earliest, most voluminous and most explosive eruption cycle in the Kizimen record. Hydrothermal, water-saturated experiments on KZI dacite pumice coupled with titanomagnetite-ilmenite geothermometry calculations require that the KZI dacite existed at a temperature of 823 ± 20°C and pressures of 125–150 MPa immediately prior to eruption. This estimate corresponds to a lithologic contact between Miocene volcaniclastic rocks and Pliocene-Pleistocene volcanic rocks located at a depth of 5–6 km beneath the Kizimen edifice, which may have facilitated the accumulation of atypically large volumes of gas-rich dacite during the KZI cycle.     

河北太行山南段符山杂岩体岩浆作用深部过程及其大地构造意义

华北克拉通中生代岩石圈减薄过程中,其深部复杂的壳-幔岩浆过程及深部岩浆房系统研究薄弱,岩石圈减薄过程的浅部响应也存在较大争议。本文以华北克拉通中部的邯邢地区符山杂岩体为研究对象,通过详细的野外地质调查、岩相学观察、岩石地球化学分析、锆石年代学和矿物电子探针分析等研究多重岩浆房系统、岩浆深部作用过程和浅部响应。锆石U-Pb测年结果显示,符山早期岩套中细粒二长岩的年龄为129 Ma,晚期似斑状岩套的斑状角闪二长岩的年龄为122 Ma。岩相学观察及背散射电子(back scatter electron,BSE)图像显示,符山杂岩体的角闪石和斜长石均具有复杂的环带结构,并通过对它们的晶体生长过程分析和环带成因讨论,表明其具有复杂的生长环境和过程。符山杂岩体的高镁、高钾、高Sr 等地球化学特征和角闪石、斜长石的环带成因证明了深部岩浆在幔源流体的活化作用下发生了强烈的岩浆混合作用和多重岩浆房过程。符山杂岩体早期岩套侵入岩定位深度为7 km,晚期岩套侵入岩定位深度为1.5 km,表明在7 Ma内地壳隆升了5.5 km。符山杂岩体中大部分侵入岩具高Sr、低Y及δEu正异常等地球化学特征,表明它们可能形成于加厚陆壳的部分熔融。这些特征表明晚中生代中国东部高原的存在。     

金川铜镍硫化物岩浆矿床前锋岩浆与岩浆通道

金川铜镍矿床是世界第三大镍、铜硫化物岩浆矿床,长期以来备受国内外矿床地质学家的关注.金川铜镍矿床Ⅳ矿区是金川矿床的有机组成部分,由于品位低(Ni 0.71％、Cu 0.48％)并且隐伏于地下140 m以下,生产与研究工作相对滞后.由于F23断裂构造的影响,金川矿床勘查以来,研究者均将其作为Ⅱ矿区2#岩体的东延部分.最近的详查钻探工程获得了较系统的样品测试,结果显示Ⅳ矿区含矿岩体是一个具有单独演化过程的独立含矿岩体,其Ni/Cu比值远高于其他矿区各个岩体,PGE强烈亏损,并且“R”因子数值低(30),微量、稀土元素配分也显示出独立的、复杂的演化过程,岩石结构与岩相变化显著,具有典型的岩浆通道前锋岩浆的特点.文章通过对比金川矿床几个主要含矿岩体的成矿元素与PGE特征,初步确定了金川铜镍硫化物成矿岩浆通道的空间位置,指出了金川深部资源勘查的关键问题与勘查方向.     

西昆仑阿卡阿孜山杂岩体的特征和成因

阿卡阿孜山杂岩体位于西昆仑昆南地体南侧,被新藏公路横切出一条南北长约2 km的剖面。在剖面范围内可见二长闪长岩、石英二长闪长岩、花岗闪长岩、二长花岗岩、正长花岗岩和碱长花岗岩等多种岩石类型出露。通过详细研究岩体的野外地质特征、地球化学和同位素地球化学特征发现：岩体中出现不平衡矿物组合;镁铁质微粒包体中可见石英和长石捕虏晶;各岩石样品的痕量元素配分型式呈现相似性;岩体的Sr、Nd、Pb同位素体系同时具有地幔和下地壳的贡献等,认为岩体形成于壳幔岩浆混合作用,幔源岩浆底侵作用可能是混合作用的直接原因。由此推测,幔源岩浆底侵作用是西昆仑地区印支晚期岩浆活动的重要诱发机制。     

铜、镍、铂族元素地球化学性质及其在幔源岩浆起源、演化和岩浆硫化物矿床研究中的意义

Ni、Cu和PGE具有不同于其他微量元素的特殊的地球化学性质,这些特殊的性质使得它们在幔源岩浆起源和演化以及岩浆硫化物矿床的成因研究中具有不可替代的作用。在S不饱和的条件下,Ni、Os、Ir和Ru具有相容元素的特性,而Cu和Pd是强不相容元素,因此,它们在玄武岩浆分离结晶过程中常常发生分异。一旦体系达到S饱和,这些元素则会强烈地进入硫化物熔浆,特别是PGE具有极高的硫化物熔浆/硅酸盐熔浆分配系数,极微量的硫化物熔离便可导致残余岩浆中PGE的显著亏损,因此,PGE是玄武岩浆硫化物熔离作用最敏感的示踪元素。硫化物熔离和成矿实质上是幔源岩浆特殊演化过程的结果,所以,Ni,Cu和PGE的特殊性质可用来探讨岩浆硫化物成矿的关键控制因素。Ni、Cu和PGE具有不同的单硫化物固溶体/硫化物熔浆分配系数,因此,它们也是硫化物熔浆结晶分异的重要示踪元素。本文试图从Ni、Cu和PGE地球化学性质和行为入手,并借助一些研究实例,对它们在幔源岩浆起源和演化以及岩浆硫化物矿床成因研究中的示踪意义进行系统介绍。