两广交界地区花岗岩中包体的类型，特征与成因

据包体岩相学及矿物学研究，包体岩石为角闪岩相到麻粒岩相的副变质岩，岩石类型有麻粒岩，变粒岩，片麻岩和富云包体，角闪岩相包体形成的温度为633度，压力为460Mpa-550MPa，麻粒岩包体形成的温度为781－883度，压力为530MPa-710MPa，包体为部分熔融形成寄主花岗岩岩浆的源区岩石列余，其中大容－十万大山地区角闪岩相－ 麻粒岩相包体岩石为区域动热变质成因；云开大山地区麻粒岩包体岩石为热穹隆变质成因。     

麻粒岩相带变质作用

1 概述麻粒岩是前寒武纪麻粒岩相带的重要岩石组成。麻粒岩相带是地壳地质演化重大转变的一种标志。麻粒岩的研究对探索早期地球形成历史以及下地壳的特征具有重要意义。“麻粒岩”一词是变质岩名称;“麻粒岩相”指的是高级变质程度;而“麻粒岩区、麻粒岩相带、麻粒岩地体、高级区、麻粒岩—片麻岩区”等则是反映了大地构造特征的一些综合性术语。在阅读文献时,有时出于省略仅用麻粒岩一词表示,则要分辨是指岩石、变质相,还是大地构造单元,以免弄混。     

东喜马拉雅构造结高压麻粒岩特征、形成机制及折返过程

东喜马拉雅构造结一带断续分布的直白高压麻粒岩,是一套相当于下地壳根带深度形成的高压麻粒岩相岩石。该麻粒岩相地体归属印度大陆东北端,是世界上最年轻的麻粒岩相岩石之一,其变质作用与印度大陆与欧亚大陆之间碰撞过程中发生的陆内俯冲作用有关。对于高压麻粒岩的形成机制及折返过程一直是人们研究和观注的焦点。本文在1：25万墨脱幅区域地质调查项目的研究结果的基础上,依据高压麻粒岩相岩石出露的大地构造背景,讨论了与之有关的若干问题,并提出适合该区的高压麻粒岩的形成机制和折返过程的新认识。     

山东省沂水地区麻粒岩相变质作用演化及大地构造意义

山东沂水麻粒岩相岩石出露于断裂带中，它是断裂带中最古老的岩石。主要岩石类型有孔兹岩（石榴石－石英－条纹长石－夕线石片麻岩）、紫苏辉石麻粒岩（紫苏辉石－斜长石－厂长央片麻岩）以及紫苏花岗岩等。根据矿物共生组合、变质反应，温压条件得出本区麻粒岩相岩石经历了五个阶段的变质作用，前阶段为角闪岩相变质作用，温度条件为Ｔ＝５７５℃￣６００℃，Ｐ＝０．５９ＧＰａ；峰期他阶段经历了五个阶段的变质作用，峰前阶段为角     

麻粒岩相变质流体和流体岩石相互作用

麻粒岩作为下部地壳岩石的重要组成部分,是高温高压条件下的变质产物。变质流体是麻粒岩相变质过程的主要动力学因素之一。麻粒岩相变质流体成分以ＣＯ２为主,含有少量的Ｈ２Ｏ,ＣＨ４,Ｎ２和Ｈ２Ｓ等,具有高密度、低水活度、强还原弱氧化、低氧逸度和弱酸性的物理化学性质。麻粒岩的形成和大离子亲石元素的亏损均与流体岩石相互作用有关。稳定同位素的变化记录了麻粒岩相变质过程流体岩石相互作用的规模和范围。来源于地幔的富ＣＯ２流体的干化作用是麻粒岩形成的主要机制。角闪岩相到麻粒岩相的转变过程也是流体性质发生变化的过程。角闪岩相的流体成分以Ｈ２Ｏ为主,而麻粒岩相则以ＣＯ２为主。流体成分的变化也能导致变质相的转变。因此,流体是变质相转变的重要控制因素,直接影响和控制变质相的转变,应成为变质相划分的重要因素之一。     

变质成矿的理论基础(续完)

在麻粒岩相条件下的成矿作用.根据对矿物中气液包裹体的研究,成矿作用的温度可达700℃,压力在5000×10~5Pa以上.形成富矿的情况极为少见,这是由于在相当于麻粒岩相的高温高压条件下,Fe、Si和Al是活动的.其结果形成铁质辉石和数量极少的Fe的氧化物——磁铁矿.麻粒岩变质相的富矿体呈脉状、细脉状或其它形状,工业意义不大.麻粒岩相变质作用往往导致在岩石中形成粒粒磁铁矿,这对需要进行选矿的铁质岩石和贫矿石的技术评价,是一个有利的因素.铁矿床的分布.在岩石变质程度达到绿片岩相的地区,变质成矿作用发育最广泛.在角闪岩相地区,铁质岩石的矿化比较少见,而在岩石变质程度达到麻粒岩相的地区,富矿完全缺失.     

鞍山小岭子铁矿麻粒岩及麻粒岩相的发现

鞍山地区太古代鞍山群含铁岩系的变质程度,在以往的地质工作中曾认为属于绿片岩相至角闪岩相,未见有麻粒岩相的岩石,其地层层位一般认为属中、上鞍山群的大峪沟组至樱桃园组。我们于1979年野外工作中,在鞍山小岭子铁矿西段M_2磁异常(大屯附近)发现比较典型的麻粒岩及麻粒岩相,其地质产状、岩性和岩石组合、岩石化学特征如下:     

胶东海阳所,葛家集基性麻粒岩P—5演化及成因意义

胶东地体中麻粒岩相岩石主要分布于米山断裂以西，而榴辉岩等高压岩石组合主林分布于该断裂以东，通过对米山断裂以西的海阳所，葛家集两地基性麻岩岩石学，矿物学和岩石热力学研究后得出：海阳所麻粒岩主要经历了３期变质作用，其Ｐ－Ｔ演化趋势为顺时针方向。     

内蒙古乌拉山群麻粒岩相岩石中变质矿物的标型特征

晚太古宙乌拉山群高级变质岩系分布于内蒙古大青山地区,包括各种麻粒岩和片麻岩,构成了东西走向的大青山太古宙麻粒岩带。本文对这套岩石中的斜方辉石、单斜辉石、石榴子石、角闪石、黑云母的物性和成分标型特征进行了系统分析。结果表明,这些矿物均为麻粒岩相条件下变质而成,并反映在发生麻粒岩相变质时,大青山南麓乌拉山群岩石的变质温度和压力均高于北边的岩石。     

东南极格罗夫山泛非期麻粒岩相变质作用

东南极格罗夫山主要由麻粒岩相高级变质岩和花岗岩类组成，其中变质岩以浅色和暗色含斜方辉石长英质片麻岩占主导地位，夹有少量镁铁质麻粒岩、变沉积岩和含方柱石钙硅酸盐岩。这些岩石一般都展示了平衡的矿物共生结构，但在镁铁质麻粒岩的单斜辉石中普遍发育斜方辉石(易变辉石)的出溶片晶。根据出溶辉石的重组分析获得麻粒岩相变质作用的峰期温度约为850℃，而浅色片麻岩中的石榴子石—斜方辉石—斜长石—石英组合给出的变质压力为0．61～0．67GPa。镁铁质麻粒岩中火成亚钙质普通辉石斑晶的保存表明格罗夫山地区可能只发育单一的泛非期高温麻粒岩相变质事件，岩石在高温变质之后经历了缓慢冷却过程，这主要归因于花岗质岩浆的板底垫托作用。     

Uranium in metamorphic rocks

The distribution of U has been studied in two metamorphic rock-series with a gradient of regional metamorphism. One series ranges from the lowest greenschist to amphibolite facies and the other one shows increasing metamorphic grade from amphibolite to granulite facies. Several medium and high pressure granulitic inclusions from alkali basalts were also analyzed. The abundances of U in the rocks do not appear to be affected by metamorphism below the granulite facies grade. Granulites are depleted in U in comparison with equivalent rocks of amphibolite facies grade. There are also differences in their U distribution, as the bulk of U in amphibolite facies rocks is located along the fractures and cleavage planes of ferro-magnesian minerals and in U-rich accessories, while in granulites, most of the U resides in accessory minerals. It seems that the depletion of U in granulites is due to a loss of U which is not located in accessory minerals or in the crystal structure of rock-forming minerals and may also be related to a migration of hydrous fluids, perhaps during dehydration.     

Large-ion lithophile element characteristics of an amphibolite facies to granulite facies transition at Gruinard Bay, North-west Scotland

Abstract Lewisian grey gneisses from Gruinard Bay, North-west Scotland retain mineralogical and geochemical evidence for Scourian horn-blende-granulite facies metamorphism, and they may be used to assess current models of elemental depletion at granulite grade. Their 'immobile'major and trace element geochemistry is indistinguishable from that of Lewisian amphibolite and pyroxene-granulite facies counterparts. The K, Rb, Th and U contents of the Gruinard Bay gneisses are depleted relative to amphibolite facies gneisses, but generally the abundances of these elements are above those of comparable pyroxene granulites. U and Th have reached an advanced stage of depletion, but allanite appears to be crucial in maintaining significantly higher U and Th abundances at Gruinard Bay than in pyroxene granulites. K and Rb loss is less extreme, and depends on the stability of the rock-forming minerals: K-feldspar; biotite; and, amphibole. Early removal of K and Rb has resulted in a small rise in K/Rb, but further preferential Rb loss would have been required to generate the characteristically high K/Rb ratios of Lewisian pyroxene granulites.
The residence of U and Th in the accessory minerals of granulite facies gneisses, which are often correlated with the residua of intracrustal partial melting, renders unlikely their extreme incompatibility required by such models. Even if such phases are ignored, high mineral-melt partition coefficients for silicic melts argue against partial fusion as an efficient depletion mechanism. On the other hand, the advanced stage of U and Th depletion reached in Gruinard Bay gneisses, which were still partly hydrous, severely restricts the role played by CO₂-dominated fluids and a hydrous medium is preferred.     

Multi-stage metamorphism by progressive accretion of continental blocks,example from the Western Hindu Kush

Basement rocks from the Western Hindu Kush preserve evidence of multiple metamorphic and magmatic events that occurred along the boundary between the Archean–Proterozoic Afghan Central and Afghan–Tajik Blocks. To verify the different metamorphic stages or events, mineral textures and phase equilibria in metamorphic basement rocks and their age relations to magmatic episodes have been investigated. Quartzofeldspathic gneiss and migmatite with lenses of amphibolite (with assumed Proterozoic age for their metamorphism) are intruded by the Triassic Hindu Kush granitoid batholith and small Cretaceous and Oligocene granite intrusions. The age of thermal overprint (210–170 Ma) by the Triassic batholith is confirmed by new monazite data. Both Triassic and Cretaceous granitoids and surrounding basement rocks underwent subsequent metamorphism up to epidote–amphibolite facies. The degree of this metamorphism increases southward at the contact to the Kabul Block, which under-plates the Western Hindu Kush from the south. An early Miocene age was obtained by Pb–Th analyses in thorite and huttonite, which are close or slightly younger than the Oligocene granite in this area. The Cretaceous meta-granodiorite near the border with the Kabul Block contains xenoliths of granulite facies rocks that could come from the Neoarchean granulite facies basement of the Kabul Block. The multi-stage metamorphic and magmatic evolution classifies the Hindu Kush mountain belt as a long-lived suture zone that was active since the early Palaeozoic. The results of this study support the interpretation about possible relations of the Afghan Central Blocks to the southern margin of Eurasia during the evolution of Para- and Neotethys.     

西藏班公湖岛弧带含硫化镍超基性岩的源区性质与基底背景

青藏高原班公湖一怒江成矿带上的超基性岩型硫化镍矿化是近年来在西藏地区发现的矿化新类型.文章根据成矿带西段班公湖地区含镍超基性岩体的岩石地球化学和Sr、Pb同位素分析结果,论述了含镍超基性岩浆的源区性质及生成条件,并根据锆石U-Pb LA-ICP-MS年龄测定结果,探讨了藏西北地区的基底背景.研究发现,班公湖地区的含镍超基性岩体以富集大离子不相容元素Rb、Th、U、Sr、Pb,亏损Ba、K为特点,高场强元素亏损Nb、Ti,富集Ta;稀士元素相对球粒陨石亏损强烈,但轻稀土元素相对富集.这些特点一致反映出含矿岩浆产生于受俯冲沉积物熔体交代的富集型岩石圈地幔源区.岩浆的生成深度较浅,为尖晶石二辉橄榄岩相,源区部分熔融程度较低,大体在10%左右.岩石中集中出现一批24.79亿年的残留锆石年龄,标志着当时班公湖中特斯洋盆沉积物的物源区较为单一,主要来自太古代末-元古代初的古老基底,并且推测太古代与元古代之交(25亿年)有可能是藏西北的一个古陆壳快速生长期.     

大别山北大别杂岩的大地构造属性

北大别杂岩主要由花岗质片麻岩及斜长角闪岩组成 ,含有不同类型、大小不等的麻粒岩岩块和变质超镁铁质岩块 ,侵入有大量白垩纪花岗岩和辉石 -辉长岩类。其中的花岗质片麻岩、斜长角闪岩具有岛弧环境的岩石地球化学特征 ,代表拼贴于扬子陆块北缘的新元古代古岛弧。北大别杂岩北可与庐镇关群相连 ,南俯于超高压变质岩之下 ,在三叠纪扬子陆块与华北陆块的碰撞过程中 ,曾与超高压变质岩一起俯冲到地幔深度并经受榴辉岩相变质作用 ,然后在折返过程中叠加了麻粒岩相及角闪岩相变质作用 ,是扬子陆块北缘陆壳俯冲基底的一部分     

P–T conditions for the Arendal granulites, southern Norway: implications for the roles of P, T and CO2 in deep crustal LILE-depletion

Abstract The orthopyroxene-clinopyroxene, garnet-orthopyroxene and garnet-clinopyroxene geothermometers, and the garnet-orthopyroxene-plagioclase, garnet-clinopyroxene-plagioclase and anorthite-ferrosilite-grossular-almandine-quartz geobarometers are applied to metabasites and the garnetplagioclase-sillimanite-quartz geobarometer is applied to a metapelite from the Proterozoic Arendal granulite terrain, Bamble sector, Norway. P–T conditions of metamorphism were 7.3 ± 0.5 kbar and 800 ± 60°C.
This terrain shows a regional gradation from the amphibolite facies, into normal LILE content granulite facies rocks and finally strongly LILE deficient granulite facies gneisses. Neither P nor T vary significantly across the entire transition zone. The change in 'grade'parallels the increasing dominance of CO₂ over H₂O in the fluid phase.
LILE-depletion is not a pre-condition of granulite facies metamorphism: granulites may have either 'depleted'or 'normal'chemistries. The results presented herein show that LILE-deficiency in granulite facies orthogneisses is not necessarily related to variations in either P or T . The important mechanisms in the Arendal terrain were (a) direct synmetamorphic crystallization from magma, with primary LILE-poor mineralogies imposed by the prevailing fluid regime, and (b) metamorphic depletion, involving scavenging of LILEs during flushing by mantle-derived CO₂-rich fluids. The latter process is constrained by U–Pb and Rb–Sr isotopic work to have occurred no later than 50 Ma after intrusion of the acid-intermediate gneisses, and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin.     

The geochemistry of Precambrian granulite facies rocks from the Lewisian complex of Tiree,Inner Hebrides,Scotland

The metamorphism and geochemistry of the major components of a small area of granulite facies rock are described and discussed, and a chemical model for the evolution of anomalous trace element distributions in such materials is suggested. The local complex was subjected to medium to high pressure granulite facies metamorphism between 2,900 and 2,600 m.y. All the analysed granulite facies rocks from Tiree; acid to intermediate gneisses, basic metamorphic rocks, and granitic rocks, have anomalous chemistries, being depleted in K, Rb, Nb, Y and Th, and have high K/Rb, Ba/Rb and Ca/Y ratios, and very low K/Ba and Rb/Sr ratios relative to normal portions of the upper continental crust. The gneisses seem to have been enriched in Ba and Sr.The chemical features of the rocks are considered to reflect their stable mineral assemblages in the granulite facies, and to be representative of deep-level crustal materials. The geochemical peculiarities of the complex may have been largely controlled by an upward intergranular diffusion, or “degassing” caused by high-grade metamorphism. It is suggested that such diffusion may have been active at the crust/upper mantle interface, some diffused material of mantle origin accounting for certain chemical oddities typical of Lewisian and some other Precambrian granulite facies rocks.     

Chemical and Thermal Evolution of Archaean Sialic Crust, Southern West Greenland

The Archaean rocks of West Greenland are predominantly bandedquartzofeldspathic gneisses enclosing thin migmatized sheetsof older metabasic and metasedimentary lithologies. Isotopicdating (Moorbath & Pankhurst, 1976) indicates that muchof the Archaean crust presently exposed in southern West Greenlandwas generated from predominantly upper mantle sources 3000-2800m.y. ago. Parts of this crust crystallized under prograde granulitefacies conditions 2950-2750 m.y. ago. The granulite gneisseswere severely depleted in some of the lithophile and heat producingelements, Si, Na, Sr, Rb, U and Th, during the granulite metamorphism.These elements appear to have been transferred to higher crustallevels by the migration of a dispersed vapour phase. The pressureand temperature recorded by amphibolite and granulite faciesassemblages have been estimated using thermometers and barometerscalibrated against the results of phase equilibrium experiments.These estimates (800 °C, 10.5 kb and 630 °C, 7.3 kbfor granulite and amphibolite facies respectively) indicatethat the Archaean continental crust in southern West Greenlandwas at least 30–40 km thick 2800 m.y. ago. Water vapourpressures in the granulites were extremely low, 0.3 to 0.1 P_total.The thermal evolution of the Archaean crust during the period3000-2700 m.y. was controlled by the emplacement of large volumesof acid-intermediate melts into a relatively thin metabasiccrust. The thermal perturbations generated by this convectivetransfer of heat from the upper mantle to the crust relaxedduring the period immediately following crustal accretion. Progradegranulite facies assemblages could have developed under stronglydehydrating conditions and progressively falling temperatures,or during a phase of rising temperature in the lower crust.     

华北地台部分麻粒岩地体及包体的地球化学特征对比

华北地台麻粒岩包体（汉诺坝）与麻粒岩地体（西望山、蔓菁沟）存在明显的岩石地球化学特征差异，麻粒岩包体总体成分偏基性，麻粒岩地体总体成分偏长英质。形成时间、空间及构造背景的不同是造成成分差异的重要因素。汉诺坝麻粒岩包体是在拉线环境下玄武质岩浆底侵下地壳后结晶分异过程中堆晶作用的结果，其主、微量元素成分受控于辉石和斜长石堆晶的相对比例；下地壳物质的混染作用不是造成麻粒岩包体Nb、Ta、Th、U亏损的惟一因素，底侵的玄武质岩浆可能发生了含钛矿物相的结晶分离，造成了汉诺坝麻粒岩包体Nb、Ta亏损，而下地壳的麻粒岩相变质作用则使Th、U发生亏损。麻粒岩地体存在两种不同性质的微量元素组成，反映了两种不同构造环境的并置，是构造挤压抬升的结晶。     

An example of structural and metamorphic relationships in the Musgrave orogenic belt,central Australia

The western Musgrave Ranges are broadly divided into three groups of metamorphic rocks. A central granulite‐facies core is bounded on the north by rocks of amphibolite grade and on the south by rocks transitional between the granulite and amphibolite facies. Faults trending east‐west separate the three groups of rocks.

The detailed structural relationships between the granulites and the lower grade rocks are described and discussed. The granulites are structurally relatively simple and are characterised by the presence of a strong southwesterly‐plunging, mineral‐streaking lineation. In marked contrast, the transitional rocks are more complexly folded on a macroscopic scale and they also have a well‐developed mineral lineation plunging to the southeast. These two lineation orientations are considered to be directions of maximum elongation. The amphibolite‐facies rocks are also complexly folded and at least two lineations related to different phases of deformation have been recognized.

A suite of foliated and lineated dolerite dykes which occurs throughout the area inherited their fabric during a period of intense deformation and recrystallization, which resulted in the development of numerous mylonite zones.

It is suggested that the granulite‐facies rocks may represent a suite of cover rocks which have been thrust in a northerly direction over a pre‐existing amphibolite‐facies basement.