新疆西天山高压变质带的变质矿物与变质作用演化

新疆西天山高压变质带主要由石榴石，角闪石，绿辉石，多硅白云母，钠云母，绿帘石，绿泥石，钠长石，石英，榍石和金红石等组成，石榴石主要含铁铝榴石组份，角闪石有蓝闪石，亚铁蓝闪石，青铝闪石，冻蓝闪石等类型，变质矿物组合显示高压变质带经历了由硬柱石蓝片岩相，榴辉岩相，绿帘蓝片岩相至绿片岩相的变质作用演化进程。     

高压变质作用中的稀土元素行为

研究高压变质作用中稀土元素(REE)行为估计可能用于确定榴辉岩母岩的地球动力学环境。本文研究了乌拉尔—蒙古褶皱带(哈萨克北部的科克切塔夫地块和苏联境内的天山中部的Atbashi地区)变质杂岩中显示各种程度的闪石化榴辉岩,同时还调查了奥地利阿尔卑斯山脉Koralpe的榴辉岩化变质辉长岩和科克切塔夫地块的由辉长岩转变的石榴石角闪岩。分析资料表明,榴辉岩中轻稀土元素约30～60％是存在于粒间的孔隙中。调查结果证明,在榴辉岩形成过程中REE实际上是不活动的。它们的低活动性既解释了变质杂岩缺少流体相,又解释了低流体/岩石比值。     

高压变质作用与金矿化——以东西伯利亚,远东高压杂岩体为例

综合东西伯利亚和远东高压岩石杂岩体分布地区地质资料表明,上述地区多为地动力高度活化地块区,并具专属性特点,应用地质构造、物质组分－矿物学特征,详细地划分了７种类型高压变质岩石组合,并根据化学特性,划分了３种岩石化学类型,即辉长－玄武岩,橄长岩,橄榄岩（二辉橄榄岩）类型。此外,论述了取决于原岩基质组成的变质反应特征,其规模直接与原岩基质的组成,特别是与Ａｌ２Ｏ３,Ｎａ２Ｏ,ＳｉＯ２的组成密切相关,即     

高压超高压变质作用中的流体

文章强调了高压和超高压变质岩中流体包裹体的研究意义，重点论述了几个问题：（１）高压和超高压变质岩中流体包裹体的成分以含Ｎ２量高为特点，在大别山含柯石英榴辉岩中找到的高压榴辉岩阶段捕获的原生包裹体，其中气相组分含ＣＯ（摩尔分数）为１４％，表明流体来源于深部。原生流体包裹体的保存，要求在ｐ－Ｔ区间内的抬升轨迹与等容线近于平行。（２）在大别山高压和超高压榴辉岩中首次确认熔融包裹体的存在，由硅酸盐玻相和以ＣＯ２为主要成分的气相组成，并发现熔融包裹体中的玻相成分与主矿物相近。（３）高压和超高压变质期间的局部流体迁移可由榴辉岩中流体包裹体和矿物同位素成分（Ｈ－Ｃ－Ｏ）来显示。（４）高压和超高压变质中流体－熔体－岩石（矿物）相互作用是一个非常复杂的过程，并证实在榴辉岩相ｐ－Ｔ条件下岩石的部分熔融。（５）变质流体的成分与变质级之间存在着相关关系。     

苏北高压-超高压变质变形作用与成矿

苏北榴辉岩经历了5期以上变质变形作用,其中至少有两期高压或超高压变质变形作用。其pTt轨迹呈顺时针方向旋转。榴辉岩形成后,随着地体的反弹、推覆,于印支期末迅速回返到中地壳,再经燕山期-喜山期区域隆升和拉伸折返,最终剥露于现代侵蚀面。苏胶造山带至少经历了晋宁期、印支期和燕山期三次造陆或造山运动。苏北榴辉岩等的成矿组合为金红石、蓝晶石、金刚石、石榴红宝石及水晶等。     

超高压变质作用压力模型的思考

该文在研究地球内部压力的计算过程和超高压变质作用过程的基础上,指出超高压变质作用的压力不仅包括静岩载荷压力,还应包括构造超压和体系内部的相变增压,并给出了超高压变质岩区的初步压力模型,得出了超高压变质作用中压力与深度是非线性关系的认识。     

中国中东部的双高压变质带

在我国中东部,华北板块和扬子板块之间,存在着两条紧密共生而变质作用类型不同的高压变质带。一条是以蓝片岩为代表的低温高压变质带、分布于东南一侧,主要由中一晚元古代双模式火山沉积变质岩系组成;另一条是以榴辉岩为代表的高温高压变质带,分布于西北一侧,主要由晚太古-早元古代结晶基底构成。两条高压带的变质年代基本一致,彼此以深断裂相接触。二者之间存在较明显的变质间断.其形成条件分别为0.7—1.4GPa,350—560℃和≥2.8GPa,680—840℃。双高压变质带的形成与晚元古代华北-扬子板块之间发生的陆内俯冲作用有关,俯冲的方向由扬子板块向华北板块进行。高温高压带俯冲的深度超过90km,并在连续俯冲-仰冲作用过程中快速向上抬升;低温高压带的俯冲深度约为25—50km,在俯冲速度降低或停止后,由于均衡作用使其逐渐抬升至地表。双高压变质带的确立对解决华北-扬子板块边界地球动力学演化问题具有重要意义。     

苏北高压变质带及其与北侧超高压变质带的关系

在苏北超高压变质带以南存在一条与之平行的高压变质带。带内由东南向西北可进一步划分出蓝闪石-黑硬绿泥石带,石榴石-绿帘石带和蓝晶石-黄玉带三个变质亚带。从蓝门石-黑硬绿泥石带到蓝晶石-黄玉带变质温压逐渐升高,其峰期地热梯度为15±3℃/km,属于高压变质相系。北侧超高压变质带的典型矿物组合是石榴石+绿辉石+柯石英+金红石,地热梯度为9±2℃/km。高压变质带峰期变质与北侧超高压带峰期变质的地热梯度明显不同,而与超高压变质体的退变质地热梯度相吻合。结合同位素年代学资料,本文指出本区的高压变质作用与北侧的超高压变质作用不是同时发生,而是与超高压变质体的退变质作用同时发生于中生代的印支期。含柯石英榴辉岩的超高压峰期变质早于印支期,并经两次抬升出露于地表。     

青藏高原东南缘哀牢山构造带泥质高压麻粒岩的发现及其构造意义

哀牢山构造带泥质高压麻粒岩主要由石榴石、夕线石、钾长石和斜长石变斑晶及尖晶石、铁假蓝宝石、蓝晶石、石英、金红石和钛铁矿包裹体组成,为确定印支地块和华南地块的边界提供了关键性标志。石榴石-黑云母-斜长石-石英地质温压计(GBPQ)计算结果及标志性高温矿物组合(Spl+Qz)表明泥质高压麻粒岩的形成和演化经历了高压/高温进变质到中温/低压退变质的顺时针P-T演化过程。其中:1)高压/高温进变质阶段的矿物组合为Ky+Sil+Grt1+Kf1+Pl1+Spr+Ter(Kf+Pl)+Bt1+Spl+Qtz+Ilm1+Rut1,形成于850～919℃,≥10.4kbar;2)中温/低压退变质阶段的矿物组合为Grt2+Bt2+Pl2+Ms+Qtz+Ilm2+Rut2,早期和晚期的温压条件分别为664～754℃,4.9～6.5kbar和572～576℃,3.5～3.9kbar。反映陆壳物质在碰撞过程中俯冲到地下深处(≥30km)经高压高温变质后快速折返到中上地壳的动力学演变轨迹。     

南天山榆树沟高压麻粒岩地体多期变质定年研究

通过详细的矿物学及岩石学研究,特别是对角闪石的系统研究,确定榆树沟麻粒岩地体至少经历过高压麻粒岩相、中压麻粒岩相、角闪岩相和绿片岩相四期变质作用的改造。总结了各期变质作用的期次和特点。在此基础上,采用~(40)Ar-~(39)Ar同位素定年获得368.2±4.8Ma坪年龄和360±10Ma等时线年龄。采用Sm-Nd同位素矿物等时线定年获得Gra+Pl+Ⅰlm+全岩的等时线年龄为310±5Ma。结合已发表的定年结果综合分析认为,前者可代表榆树沟地体峰期变质-高压麻粒岩相变质作用年龄;后者为峰期后经受中压麻粒岩相变质变形的叠加改造年龄。讨论了多期变质作用中同位素的均一化和封闭温度问题。     

青藏高原拉萨地块早中生代高压变质作用及大地构造意义

在西藏拉萨地块的东部,从松多到加兴,在晚古生代石英岩和碳酸岩地层中分布着一条近东西走向的榴辉岩带。尽管受到不同程度的海水蚀变和后期流体/岩浆渗滤的影响,多数松多榴辉岩保存了类似于N-MORB的微量元素地球化学特征,这也与榴辉岩的Sr-Nd同位素系统特征一致。这些榴辉岩经历了压力约为2.6GPa、温度约为650℃的高压变质作用。石榴石-绿辉石-全岩Sm-Nd等时线给出(239±3.5)Ma的等时线年龄,表明在早中生代,拉萨地块内部至少发生过一期洋壳俯冲事件。以松多榴辉岩为代表的洋壳俯冲事件同时表明带状基墨里大陆的形成有可能是一系列微陆块碰撞拼贴而成。     

五台山早元古代高压变质作用研究

根据对原五台群北金刚库组变质作用的深入研究,表明它们经历了三期变质作用,即经历了弧陆碰撞导致的初始的构造埋藏变质作用（M1）以及随后深埋到42km深度的峰期高压变质作用（M2）,压力可达0．8－1．4GPa,随后经历了快速抬升所导致的近等温的降压过程（M3）到0．5－0．7GPa,整个过程为顺时针方向演化的P－T轨迹,与造山带型P－T－t轨迹型式相同。     

Chronology of the high-pressure metamorphism of Norwegian garnet peridotites/pyroxenites

Eclogite facies mineral assemblages are variably preserved in mafic and ultramafic rocks within the Western Gneiss Region (WGR) of Norway. Mineralogical and microstructural data indicate that some Mg–Cr-rich, Alpine-type peridotites have had a complex metamorphic history. The metamorphic evolution of these rocks has been described in terms of a seven-stage evolutionary model; each stage is characterized by a specific mineral assemblage. Stages II and III both comprise garnet-bearing mineral assemblages. Garnet-bearing assemblages are also present in Fe–Ti-rich peridotites which commonly occur as layers in mafic complexes. Sm–Nd isotopic results are reported for mineral and whole rock samples from both of these types of peridotites and related rocks. The partitioning of Sm and Nd between coexisting garnet and clinopyroxene is used to assess chemical equilibrium. One sample of Mg–Cr-type peridotite shows non-disturbed partitioning of Sm and Nd between Stage II garnet and clinopyroxene pairs and yields a garnet–clinopyroxene–whole-rock date of 1703 ± 29 Ma (I= 0.51069, MSWD = 0.04). This is the best estimate for the age of the Stage II high-P assemblage. Other Stage II garnet–clinopyroxene pairs reflect later disturbance of the Sm–Nd system and yield dates in the range 1303 to 1040 Ma. These dates may not have any geological significance. Stage III garnet–clinopyroxene pairs typically have equilibrated Sm–Nd partitioning and two samples yield dates of 437 ± 58 and 511 ± 18 Ma. This suggests that equilibration of the Stage III high-P assemblage is related to the Caledonian orogeny and is more or less contemporaneous with high-P metamorphism of ‘country-rock’eclogites in the surrounding gneisses. The Sm–Nd mineral data for the Fe–Ti-rich garnet peridotites and for a superferrian eclogite, which occurs as a dyke within the Gurskebotn Mg–Cr-type peridotite, are consistent with a Palaeozoic high-P metamorphism. Finally a synoptic P–T–t path is proposed for the Mg–Cr-type peridotites which is consistent with the petrological and geochronological data.     

Regional progressive high-pressure metamorphism, Seward Peninsula, Alaska

Abstract Blueschist-facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high-pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Protolith sediments (Nome Group) are of intracontinental basin or continental margin type, and of lower Palaeozoic and possibly late Precambrian age, thus predating the high pressure metamorphism by more than 200 m.y. Blueschist-facies mineral assemblages were developed in almost all lithologies of the Nome Group, and are best preserved in FeTi-rich metabasites (glaucophane + almandine + epidote) and pelites (glaucophane + chloritoid + phengite). A lawsonite–crossite subfacies was developed in possible Nome Group rocks on the east flank of the Darby Mountains. Albite–epidote–amphibolite facies assemblages characterize Nome Group rocks in the southwestern part of the Peninsula. Metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote–almandine–glaucophane schist subfacies with the local development (east of the Nome River) of eclogitic assemblages. The high pressure metamorphic minerals were synkinematic with the development of mesoscopic-scale intrafolial isoclinal folds and a flattening foliation of consistent orientation. Initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles, and partial post-kinematic greenschist facies replacements record later stages of decompression. Ophiolites and melange are not associated with the Seward Peninsula blueschists. The high-pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin. The PT conditions of high pressure metamorphism were approximately 9–11 kbar, 400–450°C, thus falling between the PT paths of the Shuksan and Franciscan terranes.     

Low T heat capacity measurements and new entropy data for titanite (sphene): implications for thermobarometry of high-pressure rocks

The accepted standard state entropy of titanite (sphene) has been questioned in several recent studies, which suggested a revision from the literature value 129.3 ± 0.8 J/mol K to values in the range of 110–120 J/mol K. The heat capacity of titanite was therefore re-measured with a PPMS in the range 5 to 300 K and the standard entropy of titanite was calculated as 127.2 ± 0.2 J/mol K, much closer to the original data than the suggested revisions. Volume parameters for a modified Murgnahan equation of state: V _P,T  = V ₂₉₈° × [1 + a°(T − 298) − 20a°(T − 298)] × [1 – 4P/(K ₂₉₈ × (1 – 1.5 × 10⁻⁴ [T − 298]) + 4P)]^1/4 were fit to recent unit cell determinations at elevated pressures and temperatures, yielding the constants V ₂₉₈° = 5.568 J/bar, a° = 3.1 × 10⁻⁵ K⁻¹, and K = 1,100 kbar. The standard Gibbs free energy of formation of titanite, −2456.2 kJ/mol (∆H°_f = −2598.4 kJ/mol) was calculated from the new entropy and volume data combined with data from experimental reversals on the reaction, titanite + kyanite = anorthite + rutile. This value is 4–11 kJ/mol less negative than that obtained from experimental determinations of the enthalpy of formation, and it is slightly more negative than values given in internally consistent databases. The displacement of most calculated phase equilibria involving titanite is not large except for reactions with small ∆S. Re-calculated baric estimates for several metamorphic suites yield pressure differences on the order of 2 kbar in eclogites and 10 kbar for ultra-high pressure titanite-bearing assemblages.     

Hercynian blueschist metamorphism in North Portugal: tectonothermal implications

Abstract Aegirine–jadeite clinopyroxene (>60 mol% jadeite) locally occurs within blueschists of the 'Lower Allochthon'exposed in the Trás-os-Montes region of northern Portugal. Peak conditions attained during blueschist facies metamorphism are estimated to have been c. 420° C and >11 kbar. Porphyroblastic white mica (paragonite/phengite) within the blueschist assemblage records a ³⁶Ar/⁴⁰Ar versus ³⁹Ar/⁴⁰Ar isotope correlation age of 329.4 ± 1.6 Ma. In view of the relatively low- T nature of the metamorphism, the c. 330-Ma age is interpreted to date closely the high- P recrystallization. This tectonothermal activity is interpreted to have resulted from structural emplacement of a previously assembled crystalline nappe complex ('Upper Allochthon/Ophiolite Nappe') onto Iberian protoliths of the Lower Allochthon during terminal stages of the Hercynian orogeny.     

Prograde eclogite in the Gföhl Nappe, Czech Republic: new evidence on Variscan high-pressure metamorphism

A layer of relict, high-temperature, prograde eclogite has been discovered within felsic granulite of the Gföhl Nappe, which is the uppermost tectonic unit in the Moldanubian Zone of the Bohemian Massif, the easternmost of the European Variscan massifs. Pressure-temperature conditions for eclogite (≥890  °C, 18.0  kbar) and felsic granulite ( c . 1000  °C, 16  kbar) place early metamorphism of the polymetamorphic Gföhl crustal rocks within the eclogite facies, and preservation of prograde compositional zoning in small garnet grains in high-temperature eclogite requires very rapid heating, as well as cooling. Mantle-derived garnet and spinel–garnet peridotites are associated with the high temperature-high pressure crustal rocks in the Gföhl Nappe, and this distinctive lithological suite appears to be unique among European Phanerozoic orogenic belts, implying that tectonic processes during the late stages in evolution of the Variscan belt were different from those in the Caledonian and Alpine belts. The unusually high temperatures and pressures in Gföhl crustal rocks, mineralogical evidence for rapid heating and cooling, juxtaposition of lithospheric and asthenospheric mantle with crustal rocks, and widespread production of late-stage granites indicate that culmination of the Variscan Orogeny may have been driven by lithospheric delamination and asthenospheric upwelling.     

煤岩构造变形与动力变质作用

煤岩是一种对温度、压力等地质环境因素十分敏感的有机岩,地质演化过程中的各种构造-热事件必然导致煤岩发生一系列物理与化学结构的变化,并形成不同类型的构造煤。在构造应力作用下,煤岩不仅发生脆性和韧性变形,而且还产生不同程度的动力变质作用。因而,关于煤岩构造变形与动力变质作用的研究不仅具有重要的科学意义,而且在煤层气资源评价以及煤与瓦斯突出危险性预测方面也具有重要的实际意义。文中在已有研究成果基础上,通过对构造煤系列Ro,max、XRD和NMR(CP/MAS+TOSS)等测试和实验方法的对比研究,深入分析了煤岩不同构造变形和动力变质特征,进一步探讨了构造应力下煤岩动力变质作用的机理。研究成果表明,在构造应力作用下,煤岩脆性变形主要是通过破裂面上快速机械摩擦转化为热能而引起煤岩化学结构与其成分的改变;而韧性变形煤主要是通过局部区域应变能的积累而引起煤岩化学结构的破坏,从而发生不同机制的动力变质作用。