俯冲带温度条件下橄榄石中硅氧四面体的非谐振动:透射红外光谱研究

橄榄石既是上地幔的主要矿物,又是俯冲板块的主要矿物。在正常地幔温度条件下,橄榄石中原子之间的振动是非谐振动,这已成为学界共识;然而,对于俯冲带的较低温情况,橄榄石中原子之间的振动的非谐性是否重要,目前还没有比较一致的结论。本研究利用透射红外光谱的方法,系统研究了室温下不同厚度橄榄石中硅氧四面体的红外光谱特征,并着重对其在2100~1500cm-1区域形成的二倍频峰/合频峰进行了指认。在此基础上,本研究通过采集不同温度下的透射红外光谱数据(最高温度达约450℃),确立了橄榄石中硅氧四面体的相应基频峰及二倍频峰峰位对温度的依赖性,进而得出其相应红外振动的非谐系数(χ)随温度(T)的变化关系,具体为:χ838=6.37(2)×10-7×T+0.0014(1)及χ993=7.86(3)×10-7×T+0.0015(1),其中温度的单位为℃。外推到600℃时,有χ838=0.0018(1)及χ993=0.0020(2)。这些结果表明,在俯冲带的较低温条件下,橄榄石中硅氧四面体的内部振动的非谐性可能不重要。     

高温高压流体原位直测

水热金刚石压砧(Hydrothermd Dlamond Anvil Cell, HDAC)与显微机连接已用于研究水热系统相关系。作者把HDAC与傅里叶红外显微镜相连,实现高温高压条件下对液固反应,相变等原位波谱研究。已经研究850℃条件下高压(1GPa)NaCl H₂O体系,发现了两相不混溶区的新溶液结构。改进了HDAC窗口能够在红外显微镜上使用,使用高压指示矿物的红外谱特征标定压力。高温高压下直接观察、测定物质状态和同时确定温度压力条件,是超高压研究的新进展。还用同步辐射光源的高能X射线,红外研究超高压(10GPa)下卤水结构,有新发现。     

地球内部高温超高压流体的水热金刚石压砧原位观测

地球内部极端条件下流体原位观测实验研究有了巨大进展。使用金刚石压砧结合各种谱学方法及同步辐射光源技术,在高温超高压条件下原位直接测量水和水合物结构性质,已经获得关于地球内部流体的分子-原子尺度信息的新实验数据。本次研究通过金刚石压砧对高压(10GPa)和高温高压(800℃/3GPa)NaCl-H_2O和NaCl-D_2O-H_2O的红外谱原位直测,研究了高压和高温高压下水分子结构。发现高压高温水分子OH振动频率随温度升高向高波数变化,而且,在临界态区域时水分子间的氢键网络破坏。水分子OH振动频率随盐度升高向高波数变化。水分子的其它方式运动的频率也随温度改变。实验说明了水分子在极端条件下的结构和运动方式。地球内部由深到浅,不同深度上的流体性质不断变化,如水的密度、介电常数等物理参数随温度压力改变,水的性质在临界态会出现突变。这些变化可以用高压高温的水的各种谱学特征来表征。水的性质取决于水的分子结构(键态)、分子振动方式。在跨越临界区时的水性质异常涨落与水分子结构变化、分子振动形式变化和氢键网络破坏有关。高温超高压流体原位红外谱观测实验是从分子尺度认识地球内部流体性质。水分子尺度的信息有利于我们深入理解地球深部流体性质、活动及物质相互作用,有利于理解岩石圈和地球深内部过程。     

俯冲带硫的地球化学行为及硫循环SCIEI北大核心CSCD

俯冲带是全球最大的物质循环系统,控制着硫(S)在地球内部圈层及表层的循环,影响着大气圈、水圈、生物圈、岩石圈的稳定性以及地球的宜居性。厘清S在俯冲带中的地球化学行为和循环特征对理解地球各储库的氧化还原状态、岩浆作用与演化、成矿物质聚集、以及地球大气成分等具有重要意义。本文首先总结了进入俯冲带之前的大洋岩石圈的S结构模型,对S在大洋板片中的分布状态和地球化学特征进行了系统归纳。随后,系统阐述了俯冲带高压-超高压变质岩记录的板片变质及脱水过程中硫的地球化学行为。岩石学研究表明俯冲板片中的S多以硫化物相存在,硫酸盐矿物在弧前深度就已被释放或分解。相较于熔体,俯冲带流体中S的溶解度更高,是运移硫的更有效方式。DEW模型计算结果显示,流体中S含量总体较低,但在俯冲板片~90km处其含量有一个峰值(浓度0.5%~1.0%)。岩相学证据、地球化学测试结果、磷灰石S近边吸收结构(S-XANES)特征以及模拟结果都显示俯冲深部流体中S多以HS^(-)及H_(2)S形式存在,不含大量的SO_(4)^(2-)及硫酸盐;中f_(S_(2))流体有利于S迁移出俯冲板片,从而促进俯冲带大规模S循环,而高f_(S_(2))流体在流-岩交换过程沿流体通道发生S的锁固作用而不利于俯冲带S循环。质量平衡计算显示全球俯冲带S输入通量为4.65×10^(13)g/yr,弧下深度板片S输出通量为2.91×10^(12)g/yr,板片-岛弧S循环效率仅6.3%。俯冲板片在弧下深度可能存在一个短暂高效的S释放窗口,释放流体的δ^(34)S值为-2.1±3.0‰。基于高压-超高压变质岩中硫化物的研究,初步厘清了俯冲板片中S的地球化学行为,首次从板片角度全面、定量地限定了俯冲带的脱硫通量、效率、种型和同位素特征,提出俯冲带循环的S不是岛弧岩浆的氧化剂,与岛弧环境的正δ^(34)S值也无直接因果联系,对解析俯冲带S循环和理解地球长期的S循环具有重要意义。最后,本文还展望了俯冲带S循环的未来发展方向,应在俯冲带流体氧化还原性质(硫酸盐的命运)、俯冲沉积物对S循环的制约、俯冲带环境下多硫同位素的分馏效应、S循环与其它挥发分(如C等)循环之间的耦合关系、地球历史上深部S循环等方向做出探索,更深入地理解俯冲带及全球S循环过程。     

中红外光谱在月球探测中的应用

硅酸盐矿物的中红外光谱一般具有明显的CF特征和Reststrahlen吸收带,这些特征都与硅酸盐的组成密切相关,可以作为判别其组成的指示特征。月球表面的主要矿物有辉石、斜长石、钛铁矿和橄榄石,其中除了钛铁矿以外,都属于硅酸盐的范畴。如果充分利用月球表面硅酸盐的红外光谱特征,即CF特征和Reststrahlen吸收带,将可以用于探测VIS-NIR光谱无法完成的探测目标:钙长石、橄榄石、石英和碱性长石等。如果在嫦娥工程的后续探测器(如轨道器、月球车或者软着陆平台)上搭载中红外光谱仪对月表物质进行探测,将有利于成功实现对月球表面的矿物和岩石的精确探测,这也将是我国首次采用中红外光谱探测仪对月球进行系统的矿物与岩石探测。     

绿帘石记录俯冲带变质流体活动

俯冲带是连接地球表生圈层和深部圈层的关键纽带,深刻影响着地球内部的运行方式和人类宜居环境。俯冲板片脱水释放的高压-超高压变质流体控制着俯冲带诸多重要地质过程,如地幔楔交代和部分熔融、岛弧岩浆活动、中/深源地震以及地球内部的元素迁移和分异等等。深入了解这些流体的源区、运移、成分和物理化学条件是理解这些流体性质和行为的前提和关键。绿帘石是俯冲带变质岩中一个常见的含水造岩矿物,具有较宽广的稳定温压范围(绿片岩相-榴辉岩相)、较高的微量元素含量和缓慢的体扩散行为(如Sr、Pb、Th、U、Cr、V和LREE),能够指示俯冲带(多期)变质流体活动和地球化学效应。本文总结了近年来俯冲带变质绿帘石研究的主要进展及其在揭示俯冲带流体活动方面的重要应用,包括探究俯冲带流体的起源、成分特征、运移方式、氧逸度条件、交代效应和多期次结晶行为。这些研究表明绿帘石是一个极好的变质流体活动记录器,能够为理解俯冲带流体活动和深部元素迁移提供关键信息。     

超高压变质岩——造山带深部过程的见证

超高压变质岩是大陆碰撞过程中俯冲于地幔较深部位的地壳物质（包括早先从地幔就位于地壳的超基性岩）,记录了地球系统内部物质再循环的过程。了解折返至地壳的超高压岩石的峰变质深度,是讨论造山带深部变质作用、岩浆形成和流体活动的关键,也是讨论折返机制的基础。详细的岩相学和变质反应热力学分析通常还不足以对岩石峰变质物理条件作出判断。高压下矿物固溶体的稳定性、相转变及出溶机制是最终解决问题的前提知识。柯石英假象具有特征的结构。并非只有相变才能引起矿物包裹体周围的放射状裂开。柯石英在寄主矿物中的保存情况对岩石的ｐ Ｔ路径有指示意义。以构造过压为主导的超高压变质作用观点与现有地质观察和高压下岩石的力学状态分析不相一致。定量估计构造过压在岩石俯冲过程中的作用尚需更深入的理论分析和观察资料。准确的ｐ Ｔ路径对于理解俯冲、折返机制至关重要。流体和熔体是岩石俯冲至较深部位时与地幔围岩发生物质交换的主要介质。进变质过程中岩石多放出流体,但也有一些发生在超高压下的水化或碳化反应。退变质过程晚期围岩流体渗入折返的超高压变质岩,但在退变质过程早期,由于温度增高,一些超高压含水矿物可能发生脱水。典型的地壳岩石在俯冲带深部很容易发生部分熔融。高?     

红外光谱-拉曼光谱无损检测技术对透闪石和阳起石鉴定特征的研究

透闪石属于角闪石族矿物,与阳起石构成完全类质同象,有关透闪石和阳起石的红外光谱和拉曼光谱的特征差异还未见有报道。本文以外观特征相似的5件广西大化黑青色阳起石样品和2件新疆塔县青玉样品为研究对象,在前期矿物成分测试的基础下,采用红外光谱和拉曼光谱进行测试和对比分析。结果表明,阳起石的红外光谱和拉曼光谱都表现为闪石类矿物的特征峰,与透闪石的特征峰存在细微差异,漫反射红外光谱的差异特征是鉴别两者最准确、快速、无损的依据,并且适用于任意形状的样品,符合珠宝玉石饰品实验室检测领域的要求,可为和田玉的分类分级和产地鉴别等提供科学依据。按照GB/T 16552-2017与GB/T 16553-2017规定,广西大化黑青色阳起石可定名为和田玉。     

柴北缘野马滩超高压地体的成因:来自超高压榴辉岩中副片麻岩夹层年代学研究的启示

高压-超高压变质岩带是古板块汇聚边界的重要标志,若优俯冲环境和形成机制而言,可划分为大洋俯冲型和大陆俯冲型,前者与大洋岩石圈的消减和俯冲有关,常表现为高压-超高压榴辉岩和蓝片岩与具有洋壳性质的蛇绿岩和岛弧火山岩伴生,榴辉岩原岩为大洋火山岩;后者与陆壳的俯冲及陆-陆碰撞有关,常见高压-超高压榴辉岩呈透镜体状分布于长英质片麻岩、泥质片岩及大理岩等陆壳性质的变质岩石中,榴辉岩的原岩多为陆相火山岩.     

俯冲带变质作用与构造机制

形成在汇聚板块边缘的俯冲带由俯冲岩石圈板块和上部岩石圈板块组成,具有不对称的热结构。俯冲岩石圈板块具有冷的地温梯度,而上部岩石圈板块具有热的地温梯度。俯冲板块的变质作用发生在5~15℃/km地温梯度下,可进一步划分为冷俯冲板块型（5~10℃/km）和热俯冲板块型（10~15℃/km）,即西阿尔卑斯型和古巴型。俯冲带上板块的变质作用发生15~50℃/km地温梯度下,可进一步划为冷地壳型（15~25℃/km）和热地壳型（25~50℃/km）,统称为科迪勒拉型。冷俯冲板块的变质作用是以大洋和大陆地壳岩石深俯冲到地幔,发生低温/高压及超高压变质作用为特征。所形成的低温/高压和超高压变质岩具有顺时针型P-T轨迹,其折返过程是以近等温或升温降压和部分熔融为特征。热俯冲板块型变质作用发生在年轻板块的正常俯冲和古老板块的平缓俯冲过程中。从大洋岩石圈初始俯冲到成熟俯冲,俯冲板块的地温梯度由热到冷,从热俯冲型转变成冷俯冲型。热俯冲板块的变质岩可具有顺时针型,也可具有逆时针型P-T轨迹,可以发生高温和高压下的部分熔融,形成埃达克质岩浆岩。俯冲带上板块的冷地壳型变质作用发生在构造挤压导致的加厚地壳环境,加厚的下地壳发生高温、高压麻粒岩相和榴辉岩相变质作用,可具有顺时针和逆时针型P-T轨迹。加厚新生下地壳的部分熔融形成埃达克质岩浆和高密度的基性残留体（弧榴辉岩）。热地壳型变质作用发生在构造伸展导致的减薄地壳环境。由于强烈的幔源岩浆增生和软流圈上涌,下地壳发生高温或超高温麻粒岩相变质作用和部分熔融,所形成的变质岩可具有顺时针型或逆时针型P-T轨迹。在岩浆弧加厚地壳的伸展过程中,早先形成的高温和高压变质岩可以叠加超高温变质作用。俯冲带上板块的岩浆弧可能是超高温变质岩形成的最主要构造环境。上板块下地壳的部分熔融可以形成大体积的花岗岩,由此导致新生地壳组成和成分的分异,是大陆地壳生长和成熟的重要机制。大陆碰撞造山带的加厚下地壳具有冷的地温梯度,可以发生高压麻粒岩和榴辉岩相变质作用。这些高级变质岩具有顺时针型P-T轨迹,在其折返过程中叠加中压、高温,甚至超高温变质作用。碰撞造山带下地壳的长期部分熔融可以形成不同成分的壳源花岗岩。     

Prograde metamorphic evolution and development of chloritoid-bearing eclogitic assemblages in subcontinental metagabbro (Sesia–Lanzo zone, Italy)

In the coronitic metagabbroic rocks of the Corio and Monastero metagabbro bodies in the continental Sesia–Lanzo zone of the western Italian Alps, a variety of mineral reactions that testify to prograde conditions from greenschist to eclogite-facies can be recognised. A microstructural and microchemical study of a series of samples characterized by coronitic textures and pseudomorphic replacement of the original igneous minerals has allowed the prograde reactions undergone by the rocks to be established.

In completely eclogitized coronitic samples, paragonite, blue amphibole, garnet, epidote, fine grained jadeite and chloritoid occur in plagioclase microdomains (former igneous plagioclase). The mafic mineral microdomains consist of glaucophane and garnet. Complexly-zoned amphiboles constrain changing metamorphic conditions: cores of pre-Alpine brown hornblende and/or tremolite are preserved inside rims of a sodic–calcic amphibole that are in turn surrounded by a sodic amphibole. The main high-pressure mineral assemblage, as seen in mylonites, involves glaucophane, chloritoid, epidote, garnet ± phengite, ± paragonite. Some layers within the gabbro contain garnet, omphacite, ± glaucophane, and acid dykes crosscutting the gabbro body contain jadeite, quartz, garnet, epidote and paragonite.

The presence of chloritoid-bearing high-pressure assemblages reflects hydration of the gabbros during their pre-Alpine exhumation prior to subduction, as well as the composition of the microdomains operating during subduction. The pressure and temperature conditions of gabbro transformation during subduction are inferred to be 450–550 °C at up to 2 GPa on the basis of the chloritoid-bearing assemblages. The factors controlling the reaction pathway to form chloritoid-bearing high-pressure assemblages in mafic rocks are inferred from these observations.     

True metamorphic isograds or tectonically sliced metamorphic sequence? New high-spatial resolution petrological data for the New Caledonia case study

The metamorphic belt of northern New Caledonia represents one of the best-exposed example of fossil Pacific-type subduction zone and a worldwide reference for high-pressure (HP) metamorphism and metamorphic mineral isograds, marked by a gradual evolution from very low-grade lawsonite-bearing to high-grade epidote-bearing eclogite assemblages. Despite the general agreement on the progressive increase in metamorphism, open debates hinge on the tectonic meaning of such mineral isograds, either interpreted as fossilized continuous metamorphic gradients or as major tectonic discontinuities. We present a new and extensive metamorphic dataset acquired by means of Raman spectroscopy of carbonaceous material and pseudosection modeling. Additional PT estimates were also obtained via traditional thermobarometry. Our dataset indicates the occurrence of two tectonometamorphic domains characterized by distinct patterns and significantly modifies the past tectonic interpretation of the HP terranes. The first domain, rich in metasediments, shows a continuous metamorphic gradient starting at ~300 °C and ~0.8 GPa and reaching the blueschist-eclogite transition at 500–520 °C and ~1.8 GPa and is only locally cut by minor tectonic breaks. The second one, rich in metaophiolites, shows a rather constant metamorphism at 520–550 °C and ~2.4 GPa. The two terranes are separated by a conspicuous pressure gap (0.6 GPa, or ~20 km), but no temperature gap exists. We therefore interpret the metamorphic mineral isograds in the blueschist, metasediment-rich unit as a continuous prograde metamorphic gradient corresponding to ~35 km of accreted material (in a cold subduction zone favoring lawsonite stability) later affected by a factor of two decompressional thinning. Only the epidote isograd, which localized strain as a result of fluid release during decompression, reflects regional reequilibrations. Importantly, no significant tectonic break affects the regional distribution of the classical mineral isograds, and the most significant metamorphic break is best depicted by a lithological contrast (metasediment-rich vs. metamafic/ultramafic-rich domains). Comparable patterns are observed in Tethyan-type orogens like the Western Alps or Corsica. This contribution provides useful insights into the mechanisms of exhumation and stacking of HP terrains and mountain building of both Pacific and Tethyan orogenic belts.     

华北克拉通丰镇碳酸岩中榴辉岩捕虏体岩石学研究:现今板块体制古元古代开始启动证据

关于现今板块构造体制何时启动是目前地球科学研究的焦点问题。本文在原报道的古元古代丰镇火成碳酸岩中发现的榴辉岩捕虏体基础上,开展了详细的岩石学研究。该榴辉岩捕虏体分为两种类型:即相对富石榴石的Fz-2和贫石榴石的Fz-16,它们产于同一地点,且具有相同的矿物成分和结构构造特征。Xu et al.(2018)的研究表明该捕虏体具有1839±26Ma和1766±7Ma的独居石U-Th-Pb年龄且具有大洋辉长岩原岩的全岩成分特征。本文通过进一步的岩相学研究发现该榴辉岩至少经历了两期变质阶段:M1,角闪石/绿帘石-榴辉岩阶段;M2,硬柱石-榴辉岩阶段。具有放射状裂纹包裹特征的柯英石假象在石榴石变斑晶和基质绿辉石中以包体形式出现。以蓝晶石与黝帘石共存为特征的柱状硬柱石假象,也偶尔以包体形式存在于石榴石中。变斑晶石榴石分为富含包体的核部和比较干净的边部。石榴石从中心到边部具有明显的镁铝榴石含量增加和钙铝榴石含量降低的环带特征,通过相平衡模拟和等值线投图得到其温压范围为2.6~3.7GPa和655~670℃,记录了从M1到M2的近等温增压的进变质过程。通过石榴石边部-绿辉石-蓝晶石-石英的地质温压计计算得到温压条件为3.0GPa、734℃。金红石中的锆含量温度计也给出了相似的温度条件,即在2.6~3.7GPa压力时为601~685℃。石榴石边部的柯石英假象和硬柱石假象支持了M2硬柱石-榴辉岩阶段的存在,这表明丰镇古元古代榴辉岩可能是目前发现的世界上最古老的低温超高压变质岩。同时,我们得到该榴辉岩代表的进变质过程中的地温梯度为216±35℃/GPa,证明至少在~1.8Ga以来代表现今板块构造体制的板块冷俯冲作用就开始启动了。     

Prograde pressure–temperature paths in the pelitic schists of the Sambagawa metamorphic belt, SW Japan

Prograde P–T paths recorded by the chemistry of minerals of subduction‐related metamorphic rocks allow inference of tectonic processes at convergent margins. This paper elucidates the changing P–T conditions during garnet growth in pelitic schists of the Sambagawa metamorphic belt, which is a subduction related metamorphic belt in the south‐western part of Japan. Three types of chemical zoning patterns were observed in garnet: Ca‐rich normal zoning, Ca‐poor normal zoning and intrasectoral zoning. Petrological studies indicate that normally‐zoned garnet grains grew keeping surface chemical equilibrium with the matrix, in the stable mineral assemblage of garnet + muscovite + chlorite + plagioclase + paragonite + epidote + quartz ± biotite. Pressure and temperature histories were inversely calculated from the normally‐zoned garnet in this assemblage, applying the differential thermodynamic method (Gibbs' method) with the latest available thermodynamic data set for minerals. The deduced P–T paths indicate slight increase of temperature with increasing pressure throughout garnet growth, having an average dP/dT of 0.4–0.5 GPa/100 °C. Garnet started growing at around 470 °C and 0.6 GPa to achieve the thermal and baric peak condition near the rim (520 °C, 0.9 GPa). The high‐temperature condition at relatively low pressure (for subduction related metamorphism) suggests that heating occurred before or simultaneously with subduction.     

内蒙古黄岗梁不同色调鱼眼石的谱学特征及高压X射线衍射光谱研究

通过对内蒙古黄岗梁地区不同色调绿色鱼眼石样品的基础宝石学特征、 X射线荧光光谱(XRF)、 红外光谱、拉曼光谱等多方面综合分析,系统探讨了不同色调绿色鱼眼石的化学成分和谱学特征。通过高压X射线衍射(HPXRD)光谱测试,深入剖析了该矿物在高压环境下的晶体结构特征,为揭示鱼眼石在地质运动中再次俯冲进入地壳后的稳定存在深度提供了关键线索。研究结果表明,内蒙古黄岗梁地区的鱼眼石属于氟鱼眼石, Fe³⁺和结晶水的含量对绿色鱼眼石的色调深浅产生显著影响。在HPXRD实验中,随着压力的升高,鱼眼石的轴长和晶胞体积逐渐减小,特别是c轴的压缩率较a轴更高。在9.0 GPa和15.3 GPa两个压力节点上,观察到压缩率的突变,伴随着新衍射峰的出现以及旧衍射峰的分裂和消失。这一发现揭示了鱼眼石晶体在高压环境中发生的两次明显相变过程。本研究为鉴定鱼眼石、寻找矿物资源提供了有力的科学依据,同时为鱼眼石在地质学领域的进一步研究提供了新的视角和认识。     

Raman spectra of methane hydrate up to 86 GPa

High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν ₁ appeared at 17 GPa and that the splitting of vibration mode of ν ₃ occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition of the structure.     

豫南——鄂北大别山北部高压角闪石榴辉岩的研究

一个高压角闪石榴辉岩带出现在豫南——鄂北大别山高压超高压变质单元的最北部。榴辉岩的矿物组合为石榴石+绿辉石+角闪石+绿帘石+多硅白云母+石英+金红石。采用Powell等(1994)的Thermocalc估计的温压条件:压力为1.8-2.4GPa,温度为490-592℃。这个带的榴辉岩在矿物组合,矿物成分和温压条件上明显不同于该高压变质单元中其它带的榴辉岩。     

Petrology, Metamorphic Process and Genesis of The Dabie--Sulu Eclogite Belt, Eastern--Central China

The Qinling-Dabie-Sulu high-pressure and ultra-high pressure metamorphic belt wasformed by subduction and collision between the North China and Yangtze plates. The study ofthe eclogite belt is very important in understanding the evolution of the Qinling Dabie orogen. Inthe present paper the geology, petrology, minerology and chronology of the eclogites in the Dabieand Sulu areas are described. The principal conclusions of this work are as follows: (1) Based up-on the field occurrence and the P-T conditions of the eclogites, two types of eclogite can be dis-tinguished: Type 1—the low-temperature and high-pressure eclogite in the mid-late Proterozoicmetamorphic series, and Type 2—the ultra-high pressure eclogite in the late Archaean to earlyProterozoic metamorphic complex. In the Dabie area, the ultra-high-pressure eclogite,high-pressure eclogite and epidote-blueschist units are nearly parallel to each other and stretchintermittently from north to south. (2) The P-T conditions of the high-pressure eclogites and ul-tra-high pressure eclogites have been estimated. The former are formed at 450-550℃ and1.4-1.6 GPa; while the latter at 650-870℃ and >2.7-2.9 GPa in the Dabie area and at820-1000℃ and >2.8-3.1 GPa in the Sulu area. The metamorphic temperatures of the eclogitesincrease progressively from west to east. (3) The ultra-high pressure eclogites were subjected to 5stages of metamorphism: pre-eclogite epidote amphibolite facies, peak coesite eclogite facies,post-eclogite amphibolite facies, epidote-blueschist facies or epidote amphibolite facies andgreenschist facies. The general features of the PTt path of the ultra-high pressure eclogite are:clockwise pattern, progressive metamorphism being a process of slow increasing temperature andrapid increasing pressure, and the retrogressive section with nearly isothermal decompression atthe early stage, isobaric cooling at the middle stage and nearly isothermal decompression at thelate stage. (4) At least two stages of high-pressure metamorphism occurred in the orogenic belt:the high-pressure eclogite and ultra-high pressure eclogite were formed by the subduction of theoceanic crust northward beneath the North China plate or the Dabie block during theCaledonian; while the epidote-blueschist belt came into being by subdution and collision be-tween the two continental plates during the Indosinian. (5) Due to the continuous sequentialsubduction of the cold plate, the ultra high-presssure metamorphic rocks were uplifted to thecrust by the underplating processes. They can be preserved just because of the "frozen effect" re-sulting from the continuous subduction of the cold plate. (6) The carbonates, such as magnesite,breunnerite, aragonite and dolomite, and the H_2O-bearing minerals, such as phengite, epidoteand zoisite, were stable during the high-pressure and/or ultra-high pressure metamorphism.     

西藏羌塘中部绒马地区石榴蓝闪片岩变质演化过程的视剖面模拟及其意义

藏北羌塘地体中部产出一变质杂岩带,因其地貌突起,将羌塘地体一分为二,故常称其为羌中隆起带。虽然在该变质杂岩带中先后识别出蓝片岩、榴辉岩等变质岩,但对该变质杂岩带演化过程的认识却存在截然不同的观点,一种观点认为该变质杂岩带是原位的古特提斯板块缝合带的标志;另一观点则针锋相对,认为该变质杂岩带系外来的、底辟上升的杂岩带,不能作为古板块缝合带的证据。在该变质杂岩带中部的绒马乡,石榴蓝闪片岩呈大小不一的岩片和/或透镜体产出于石榴石多硅白云母石英片岩内,主要由石榴石变斑晶和由蓝闪石、绿泥石、白云母、绿帘石、石英、钠长石、金红石/钛铁矿、磷灰石、黑云母等矿物构成的基质组成。石榴石变斑晶粒径达2 mm,具典型的生长环带：核部富锰,锰铝榴石分子摩尔分数可达22%,至边部,铁铝榴石和镁铝榴石分子含量显著升高,而锰铝榴石分子含量则快速下降。石榴石变斑晶内部包体发育,可再细分为两类,一类包体产出于核部,包括被解释为硬柱石假象的细粒钠云母,绿帘石所构成的细粒板状集合体和细粒富铁蓝闪石、石英及金红石等包体;另一类包体则为数量较少的自形大颗粒绿帘石包体,产出于石榴石边部,在其内部还有细粒蓝闪石、金红石与石英等包体产出。基质中的角闪石可识别出3期：核部为富铁的蓝闪石,幔部为贫铁的蓝闪石,最外部为冻蓝闪石。基质中的绿帘石和绿泥石常为自形,绿帘石内常见细粒蓝闪石、石英、金红石等包体,而绿泥石边部常有黑云母的冠状体。在PEXPLE程序计算的p T视剖面图中,石榴石核部形成的p T条件为20 GPa、470 ℃,对应硬柱石榴辉岩相,而石榴石边部形成的p T条件为17~18 GPa、530~540 ℃,对应绿帘石榴辉岩相。岩相学观察与p T视剖面模拟研究充分反映了绒马地区石榴蓝闪片岩分别经历了硬柱石榴辉岩相、绿帘石榴辉岩相和近等温快速降压的退变质等变质过程,系冷洋壳快速俯冲与折返的产物,因此,文中支持该变质杂岩带为原位古特提斯板块缝合带的观点。硬柱石转变为绿帘石时,在俯冲通道中释放了大量的流体。T O视剖面研究进一步表明这种矿物相转变只发生于高氧逸度条件下,暗示所释放的流体可能也是高氧逸度流体。该高氧逸度流体可交代上覆地幔楔,并诱发后者发生部分熔融作用形成高氧逸度岩浆,如果这一推测是合理的,则羌塘地块内部应该存在斑岩型铜金矿床。 关键词：羌塘地体; 石榴蓝闪片岩; 视剖面模拟; 富氧流体     

北祁连山硬柱石蓝片岩p-T条件相平衡计算及其岩石学意义

北祁连硬柱石蓝片岩主要分布在甘肃省肃南县九个泉一带,是目前中国唯一报道的、确切地含有硬柱石的蓝片岩。文中在详细的岩石学和矿物学研究基础上,根据矿物共生组合的不同,将北祁连低温蓝片岩进一步划分为绿纤石蓝片岩、硬柱石蓝片岩和绿帘石蓝片岩。绿纤石蓝片岩的特征变质矿物组合为蓝闪石(>40%)+绿纤石(30%)+绿泥石(10%)+钠长石(8%)+石英(5%)+硬柱石(<3%)±方解石/文石(<1%)。硬柱石蓝片岩的矿物组合为蓝闪石(35%~40%)+硬柱石(35%~40%)+绿泥石(10%)+钠长石(10%)+石榴石(1%~2%)+黝帘石/斜黝帘石(<2%)+石英(<1%),副矿物有磷灰石和榍石,总含量小于2%。绿帘石蓝片岩的矿物组合为蓝闪石(30%~35%)+黝帘石/斜黝帘石/绿帘石(~30%)+绿泥石(15%)+钠长石(15%)+石榴石(2%)+石英(<2%),副矿物有金红石、磷灰石和磁铁矿,总含量小于2%。利用矿物内部一致性热力学数据和Domino/Theriak软件计算了这三种类型的蓝片岩形成的峰期温压条件,它们分别是绿纤石蓝片岩为320~350℃,0.75~0.85GPa;硬柱石蓝片岩为335~355℃,0.8~0.95GPa;绿帘石蓝片岩为345~375℃;0.75~0.85GPa。北祁连低温蓝片岩带由硬柱石蓝片岩相到绿帘石蓝片岩相的转化代表了俯冲变质过程中的递进变质过程。