蔓箐沟一带石榴基性麻粒岩变质反应与矿物演化

蔓箐沟地区石榴基性麻岩发育多期变质反应结构,矿物组合演化可划分三个阶段;（１）峰期阶段（Ｍ１）,以包裹于石榴石中的Ｏｐｘ＋Ｃｐｘ±Ｈｂ＋Ｐｌ±Ｑｚ和由Ｇｔ＋Ｏｐｘ＋Ｃｐｘ±Ｈｂ＋Ｐｌ±Ｑｚ组成基质矿物组合为代表;（２）退变早期近等温减压阶段（Ｍ２）形成蠕虫状后成合晶Ｏｐｘ＋Ｈｂ＋Ｐｌ±Ｍｔ;（３）退变脆晚期阶段（Ｍ３）。则形成细粒,黄绿色Ｈｂ＋中酸性Ｐｌ的较低温组合,并揭示该区古榴基性麻粒岩从中下     

天山东部麻粒岩定年与地球化学研究

天山造山带的下地壳麻粒岩主要出露在哈密市尾亚和托克逊县榆树沟.尾亚麻粒岩种类多,有基性岩类和中酸性岩类麻粒岩等,以推覆岩片或花岗岩顶垂体的面貌出现;榆树沟的则属基性岩类麻粒岩,呈构造岩片散布在蛇绿混杂岩中.根据岩相学特征,尾亚麻粒岩中可分出3期变质矿物组合,即M1:PI+Q+Mus+Bi;M2:Cpx+Gt+Q+Antiper±Opx;M3:Gt+Cd+Ep+Amp;榆树沟麻粒岩中可识别出2期变质矿物组合,M1:Cpx+Gt+PI±Opx;M2:Px+Amp+PI+Q±Bi.岩石化学数据表明,尾亚麻粒岩种类较多,基、中、酸性岩类俱全.基性岩类麻粒岩富钙贫镁;中酸性岩类麻粒岩富钙碱.基性岩类麻粒岩稀土元素配分曲线呈左倾斜的重稀土轻度富集型,稀土总量低,中酸性岩类麻粒岩则呈明显右倾的轻稀土富集型,稀土总量高.榆树沟麻粒岩属基性岩类麻粒岩,以低硅贫碱高钙为特征,稀土总量低,配分曲线平坦型.笔者对尾亚麻粒岩作斜长石+辉石+全岩Sm-Nd等时线测年,获(541±11)Ma同位素年龄值,它代表麻粒岩相变质的峰期年龄;又对尾亚麻粒岩从辉石退变质形成的角闪石作40Ar-39Ar年龄测定,获主坪年龄值(432.0±0.72)Ma和等时线年龄值(434.67±2.45)Ma,它们代表麻粒岩形成的退变质年龄,反映加里东期构造热事件在研究区表现强烈.     

西藏基性麻粒岩中的流体和熔融包裹体

用TEM对西藏喜马拉雅变质核杂岩基性麻粒岩中亚微米级、纳米级(粒径在20～500 nm之间)矿物包裹体的超微构造特征研究发现,流体包裹体的的精细结构、分布状态及化学特点等对于研究与麻粒岩有关的下地壳韧性剪切带形成、构造演化及其大陆动力学具有重要的意义.     

Formation history and protolith characteristics of granulite facies metamorphic rock in Central Cathaysia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Tao＇xi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic （-736 Ma） granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval （Early Paleozoic） show large Hf isotope variations, and their ZHf（t） values increase from -13.2 to ＋2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.     

内蒙古四子王旗早白垩世深源捕虏体的发现及意义

内蒙古四子王旗地区地处华北板块北缘,与西伯利亚板块的接合部,其早白垩世橄榄玄武岩中发现大量下地壳麻粒岩捕虏体,并可见辉石、长石捕虏晶。寄主岩石K-Ar同位素年龄在108.6～128.4 Ma之间。四子王旗地区下地壳捕虏体的发现对研究华北板块北缘中生代构造格局转化过程中深部壳幔的相互作用及物质成分的演变具有重要意义,为华北板块中生代末岩石圈拆沉事件提供了证据。     

Sapphirine-bearing high pressure marie granulite and its implications in the south Altyn Tagh

Sapphirine-bearing high pressure mafic granulites are recognized in the Bashiwake area of the south Altyn Tagh. Mafic granulites and associated peridotites occur as lenses within kyanite-bearing high pressure felsic granulites.Sapphirine occurs as intergrowths with corundum, spine land Ca-rich plagioclase in symplectite in between garnet and clinopyroxene. Reaction textures and mineral compositions indicate that sapphirine-bearing symplectites formed by reactions cons, ruing kyanite, garnet and clinopyroxene.Therefore, both petrographic observations and the mineral compositions suggest that these quartz-free magic granulites had an eclogite origin with an assemblage of garnet clinopyroxene kyanite, which is estimated to be stable at T =1000℃ and P≥2.1 GPa. The sapphirine-bearing symplectites are resulted from isothermal decompression or decompress‘ion with slight cooling during exhumation of the hos trock.     

汉诺坝非橄榄岩类包体的化学同位素特征

汉诺坝非橄榄岩包体主要是指辉石岩，辉长岩和麻粒岩，基主要元素，微量元素有较大和系统的变化，Ｎｄ，Ｓｒ，Ｐｂ同位素从非常亏损的ＤＭＭ源特征变至县ＥＭＩ和ＥＭＩＩ源趋势的富化特征。它们与寄主玄武岩及共生的橄榄岩包体无直接成因联系，有不同的形成时代并在不同的空间位置居留。     

河南桐柏北部秦岭群中麻粒岩相变质作用及变质矿物温压条件的研究

本文提供了桐柏北部秦岭群麻粒岩中石榴石、辉石和黑云母的部分电子探针分析数据。根据岩石中矿物共生组合特征和4种地质温度计、地质压力计的计算,确定了麻粒岩相变质作用的温度、压力条件为790—850℃和0.8—1.OGPa。变质时的地热梯度为28—33℃/km,属中压麻粒岩相。     

湖南道县玄武岩中壳源麻粒岩包体初步研究

湖南道县玄武岩中的麻粒岩包体属辉石麻粒岩类,其稳定矿物组合为斜长石-单斜辉石-斜方辉石-尖晶石-角闪石。它们与前寒武纪庥粒岩地体不完全相同。它们代表的是晚燕山期较新的下地壳特征。     

Paleoproterozoic lower crust beneath Nushan in Anhui Province： Evidence from zircon SHRIMP U-Pb dating on granulite xenoliths in Cenozoic alkali basalt

Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915 27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.     

鲁苏榴辉岩套的特征及其动力学演化

鲁苏榴辉岩套以广泛分布各类榴辉岩,密切伴生石榴石橄榄岩,石榴石麻粒岩等高压岩石组合,普遍发育韧性变形带,大量出露燕山晚期碱性花岗岩及深源脉岩为特征,它已经历三迭纪早期华南陆块与华北陆块的碰撞事件,大陆逆掩推覆构造事件及后期白垩纪早期开始的大陆伸展构造事件,是我国华南陆块与华北陆块之间的重要过渡单元。     

全球麻粒岩相地体与大陆下地壳成分模型

在出露地表的中、高压相麻粒岩地体代表下陆壳的认识基础上，建成全球麻粒岩相地体地球化学成分数据库（共１６８５套分析数据）。利用ＩＢＭ４３８１大型计算机对全部数据进行了多元变量统计分析，成功地建立了迄今为止精度最高的太古代、后太古代和全球大陆下地壳化学成分模型。     

Electron microprobe monazite Th-Pb dating and its constraints on multi-stage metamorphism of low-pressure pelitic granulite from the Jingshan Group in the Jiaobei terrane

U-Th-Pb chemical dating of monazite with the electron microprobe is a new method developed in the last dec-ade[1,2]. It is attracting more and more attention for its ad-vantages of quickness, cheapness and relative high reli-ability[3]. Although its precision (±10?30 Ma)[4,5] is not as high as the ion-probe (SHRIMP), it has very high spatial resolution (1?2 μm), more superior than other in-situ techniques for analyzing compositions of zoned monazite crystals of less than 50 μm in size. …     

Discovery and implications of the high-pressure pelitic granulite from the Jiaobei massif

The high pressure pelitic granulite with peak assemblage of garnet kyanite ternary feldspar muscovite rutile was discovered in Qixia area in the Precambrian Jiaobei massif, where high pressure basic granulites are widely distributed. The metamorphic peak conditions for the pelitic granulite were calculated as T=800-840℃ and P=1.0-1.25 GPa on the basis of P-T pseudosection. The post peak P-T path is characterized first by an isothermal decompression (ITD) pattern and then by an isobaric cooling (IBC) pattern, indicating a geodynamic process related to thinning of thickened continental crust.     

麻粒岩中的水对大陆下地壳性质和演化的启示

大陆下地壳是地球深部最重要的层圈结构之一，是壳幔物质发生交换和相互作用的直接场所. 麻粒岩是大陆下地壳的主要组成物质，其成岩模式和组成特点对于更好地理解大陆下地壳的性质、形成和演化具有重要的意义. 流体是下地壳内非常活跃的一种介质，不仅会对下地壳内许多性质产生显著影响，还可能对麻粒岩的成因和下地壳的形成方式有重要制约. 麻粒岩在某种程度上可以看作是大陆下地壳的代名词，变质作用造成的麻粒岩组成上的许多特点，如亏损生热元素（HPE）和大离子亲石元素（LILE）等，被广泛地认为是影响下地壳化学成分的直接因素. 文中综述了近些年来对大陆下地壳、麻粒岩和流体作用的若干进展和三者之间日趋突出的争议和问题，结合对中国东部一些典型产地产出的麻粒岩捕虏体/地体麻粒岩中主要组成矿物（斜方辉石， 单斜辉石， 斜长石和石榴石）的Fourier变换红外光谱（FTIR）分析结果，指出这些矿物中的结构水可能构成了大陆下地壳内最重要的水储库. 这些水的存在和发现，可能为研究下地壳内的流体活动、麻粒岩相变质作用和大陆下地壳的一些典型的地球物理学特征（如地震活动和电导率异常现象）提供新的途径，同时也表明大陆下地壳内的许多地质作用过程和原先的一些认识都可能要重新评估.     

华北北缘早中生代岩浆底侵作用的年代学记录: 来自辽西晚中生代安山岩锆石U-Pb定年结果

通过对辽西晚中生代义县组顶部玻基方辉安山岩中锆石的阴极发光光谱和LA-ICP-MS定年,发现这些火山岩中锆石常具有环带结构．其中心为残留锆石,边缘部分为从寄主岩浆中结晶的锆石．边缘部分锆石的U-Pb年龄为116 Ma,与寄主火山岩的Ar-Ar年龄完全一致;而中心部分锆石的U-Pb年龄为254 Ma,与该区早中生代底侵麻粒岩中锆石的U-Pb年龄251 Ma一致．玻基方辉安山岩中单斜辉石捕虏晶与底侵麻粒岩中单斜辉石的组成类似．说明早中生代新增生下地壳的麻粒岩在晚中生代软流圈底辟上涌背景下遭到了改造和破坏,并且参与了晚中生代的玻基方辉安山岩的形成．     

SHRIMP U-Pb zircon geochronology of granulites at Rimana （Southern Tibet） in the central segment of Himalayan Orogen

TheCenozoicHimalayanorogenisimportantinun-derstandingcontinentaldynamicprocesses.Lowercrustal,high-grademetamorphicrockshaverecentlybeendiscov-eredinNamcheBarwaandParmir,i.e.therespectivere-gionsofeasternandwesternsyntaxisoftheorogen[1—4].Eclogitesthatunderwentgranulite-faciesmetamorphismhaverecentlybeenreportedintheCadaareatotheeastofMountEverestinthecentralsegmentoftheHimalayanorogen[5].WiththehelpofthegeologicalsurveyofDing-gyeCountyandChentangSheets(scale1︰250000),high-pressuremafic…     

内蒙乌拉山群岩石的稀土地球化学特征及其所反映的成岩环境

18个乌拉山群片麻岩和麻粒岩样品的REE含量分析显示,乌拉山群岩石形成于古大陆边缘岛弧环境。碎屑沉积岩和火山碎屑沉积岩的沉积物来自邻近的火山岛弧。其中,138号标本(石英二长片麻岩)的ΣREE=62.3ppm,(La/Yb)_N=87.5,δEu=3.26,代表了太古代高级区的特征岩类。麻粒岩的ΣREE较低,显示在麻粒岩相变质过程中有REE的亏损。     

Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.