榴辉岩中石英出熔体的拉曼光谱学研究及其构造意义

利用拉曼光谱学和费氏台方法对若干地区超高压榴辉岩中柯石英和榴辉岩中石英出溶体的超显微构造特征进行了研究。研究结果表明，石榴石（或绿辉石）中柯石英向石英相变是一个连续变化过程。绿辉石中石英出溶体和主晶具有一定的晶体学拓扑关系，即石英出溶体长轴有两个展布方向：平行于绿辉石（100）裂理面和平行于绿辉石（－101）面。目前，部分学者推断榴辉岩绿辉石中石英出溶体可作为超高压变质作用的标志。笔者认为，棒状定向石英在绿辉石中出溶的温压条件和出溶机理尚未查明。因此，需加强过量二氧化硅单斜辉石出溶机理的超高压实验研究，从而为证实石英出溶体作为超高压标志提供实验定量约束。     

胶东荣成榴辉岩中含铜磁黄铁矿出溶结构的磷灰石的发现及其意义

在苏鲁超高压变质带东北部胶东荣成地区的退变金红石榴辉岩中,我们发现了具含铜磁黄铁矿出溶结构的磷灰石。磷灰石在该榴辉岩中含量较高(≈5%),多为不规则形状,颗粒大小不一,粗大者可达1．2mm×0．6mm。样品中几乎所有的磷灰石均发育出溶结构,出溶棒可能分为相互垂直的两组,各自分别沿同一方向分布,出溶棒密度大,形状规则,宽度相似,长度最长可达0．1mm。在扫描电子显微镜下,利用X射线能谱仪测定出溶棒主要由Fe、Cu和S三种元素组成。由于很难准确确定三者的比例,暂将其定为含铜磁黄铁矿((Fe_(1-x)Cu_x)S)。报道的磷灰石含铜磁黄铁矿出溶结构,与江苏赣榆地区磷灰石的磁黄铁矿出溶结构,同产于苏鲁超高压变质带中,具有可对比性；磷灰石中Cu、Fe的溶解度可能是温压条件的函数；因此进一步精确研究磷灰石中这些出溶结构的成分和成因,将为深入探讨苏鲁超高压变质带不同地体变质条件、成因的差异及俯冲折返机制等问题提供重要线索。     

河南大别山区榴辉岩及蓝晶石石英岩中柯石英的发现

团麻断裂以西的河南大别山区榴辉岩及其围岩蓝晶石石英岩中首次发现柯石英。含柯石英榴辉岩的矿物共生组合为石榴石+绿辉石+蓝晶石+多硅白云母+石英(柯石英)+金红石,其形成温压条件为T=610～740℃,P≥2.8 GPa。含柯石英榴辉岩及其围岩同时经历了超高压变质作用,可能由扬子板块向华北板块深俯冲作用形成,俯冲深度可迭90km以上。河南大别山区含柯石英榴辉岩的发现扩大了中国中东部含柯石英榴辉岩带的分布区。     

大别山区含柯石英榴辉岩的发现

大别山区的榴辉岩可划分为四种类型,目前已在第Ⅲ类和第Ⅰ类中分别发现了柯石英及其假像。柯石英除鉴定其光学特征外,还经显微拉曼光谱证实。含柯石英榴辉岩的形成条件为T600°—710℃,P>2.8GPa,表明其形成于上地幔。大别山区含柯石英榴辉岩是目前世界上发现的少数几处非金伯利岩型高压变质岩之一。它的形成可能与三叠纪中朝板块与扬子板块间发生的陆内俯冲作用有关。     

柴达木盆地北缘鱼卡河含柯石英榴辉岩的确定及其意义

在柴达木盆地北缘鱼卡河边达肯大坂杂岩之花岗质片麻岩中发现典型的含柯石英榴辉岩。榴辉岩主要由石榴石、绿辉石和少量（多硅）白云母、柯石英和石英、角闪石、金红石等矿物组成。石榴石中铁铝、镁铝和钙铝榴石分子含量分别为５１％～５９％、２６％～３１％和１３％～１９％;绿辉石中硬玉分子含量为４５％～４８％;岩石中残留有ｂ０值极大的高压矿物多硅白云母（ｂ０＝９０７５×１０－１ｎｍ）;角闪石亦为高压类型的冻蓝闪石;最为重要的是确定了柯石英的存在。榴辉岩原始特征保存完好,仅遭受轻微的退变质作用和叠加变质作用。组成矿物可分为３个世代：（１）峰期矿物组合：石榴石＋绿辉石＋（多硅）白云母＋（柯）石英＋金红石;（２）退变交生组合：冻蓝闪石＋蠕虫状石英;（３）后期叠加变质矿物白云母。榴辉岩相变质作用发生在压力大于２８ＧＰａ的超高压至大约７３０℃、１７０ＧＰａ的高压环境,表明柴达木盆地北缘是一条重要的古板块汇聚边界。     

北苏鲁超高压变质岩锆石中的矿物包体

北苏鲁莒南—岚山头—日照—桃行—仰口—荣成—威海一带榴辉岩的围岩经历了强烈角闪岩相退变质作用的改造,峰期超高压矿物组合已完全被后期退变矿物组合所取代。锆石微区阴极发光图像和矿物包体激光拉曼测试研究结果表明,132件不同类型岩石(包括榴辉岩、斜长角闪岩、正片麻岩、副片麻岩、大理岩、蓝晶石英岩、云母片岩和钙镁硅酸盐类变质岩等)锆石中,普遍隐藏以柯石英为代表的超高压矿物包体。此外,在南苏鲁东海及其邻区的地表露头和一系列钻孔岩心的锆石中,也普遍发现以柯石英为代表的超高压矿物包体。该项研究成果表明,在苏鲁地体由榴辉岩及其围岩的原岩所组成的陆壳岩石(约320km×20km×5km)曾发生过巨量物质深俯冲—超高压变质的壮观地质事件。     

南苏鲁超高压变质带东海地区富钛榴辉岩及金红石矿的成因

苏鲁超高压变质带南部的东海地区有富Fe—Ti的钛铁矿榴辉岩和富Ti的金红石榴辉岩。富Fe—Ti榴辉岩的次要矿物主要由钛铁矿和钛磁铁矿组成,可舍少量金红石,具有很低的Si02（38．0％-42．3％）、Na20＋K20（0．48％～2．13％）和Zr、Nb、Ta、Ba、1Kb、REE含量,很高的FeO（18．24％-25．33％）、V和Co含量,并具有不同程度的LREE亏损、明显的正Eu异常;富Ti金红石榴辉岩舍有丰富的金红石和磷灰石,SiO2含量范围（38．0％-54．8％）较宽,FeO含量较低,P2O5含量较高（可达4．1％）,而X-TiO2与P205含量具正相关性。相对于原始地慢岩．富Ti金红石榴辉岩具有Rb、Th、K、Nb、Pr、Nd、Eu、Ti、Lu的负异常和Ba、Sr、Zr的正异常．并具相对较高的IKEE含量,LREE富集和HREE亏损的1KEE分配型式。岩石学和地球化学特征揭示,Fe—Ti榴辉岩的原岩是变质的Fe—Ti辉长岩,是基性岩浆强烈分离结晶作用形成的超基性-基性-中酸性层状侵入体的特征组成部分。     

The Lanshantou Kyanite-bearing Eclogite with Coesite Inclusions in the Sulu Ultrahigh-Pressure Metamorphic Belt and Its PTt Path

Coesite inclusions are found in kyanite from the Lanshantou eclogite in the Sulu ultrahigh-pressure (UHP) metamorphic belt. This discovery extends the stable region of kyanite to over 2.4 GPa. As an important UHP metamorphic belt in China, the Sulu eclogite belt is the product of A-subduction induced by strong compression of the Yellow Sea terrane to the Jiaodong-northereastern Jiangsu terrane during the interaction of the Eurasian plate and Palaeo-Pacific plate in the Indosinian. It stretches about 350 km and contains over 1000 eclogite bodies. Most eclogites in this belt belong to Groups B and C in the classification of Coleman et al., and commonly contain kyanite, while the Lanshantou eclogite belongs to Group A and contains coesite. The MgO, CaO and FeO contents in garnet and pyroxene show regular variation from the core to the rim, which reveals the PTt paths of progressive metamorphism during the Early Mesozoic (240-200 Ma) and retrogressive metamorphism during the Late Mesozoic and Cenozoic exhum     

Raman Spectrum Study on Quartz Exsolution in Omphacite of Eclogite and Its Tectonic Significances

The studies on ultra-microstructue characteristics of quartz exsolution in eclogite and coesite in UHP eclogite of several localities are done with the appliance of laser Raman spectroscopy and Ustage. Research results show that the phase transformation of coesite-quartz in garnet and/or omphacite is a continuous process. Topological relationship is present between quartz exsolution in omphacite and its host mineral which shows orientations of two long axes of quartz exsolution parallel to (100) and (-101) of omphacite. At present, some scholars suggest that thequartz exsolution in omphacite of eclogite is the evidence of UHP metamorphism. However, temperature and pressure condition and the exsolution mechanism of oriented needlelike quartz in omphacite still remain undear. Tnerefore, further study should be enhanced on experimental research on exsolution mechanism of super-silicate clinopyroxene, which could provide experimental quantitative constraint on quartz exsolution as UHP indicator.     

大别山北部榴辉岩的退变质特征及其地质意义

研究了大别山北部榴辉岩的变质岩岩石学。结果表明，该区榴辉岩相变质作用可分为早期(超高压)和晚期(高压)两个阶段，并在折返过程中形成了一系列特征性的退变质显微构造。其中，退变质结构主要包括：(1)由于压力降低而出溶形成的一些定向针状或叶片状矿物包裹体，如钠质单斜辉石中石英及石榴子石中的金红石、单斜辉石和磷灰石等；(2)冠状体或后成合晶，特别是石榴子石外围发育两期(“双层”)后成合晶；(3)反应边或退变边，如绿辉石的透辉石退变边、透辉石的角闪石退变边和金红石的钛铁矿退变边等。这些退变质结构为本区榴辉岩高级变质岩的快速折返过程和抬升历史提供了强有力的岩石学依据；石榴子石中针状矿物出溶体进一步证明研究区榴辉岩早期经历了超高压变质作用，峰期变质压力应大干4．0GPa，甚至可能达到5～7GPa或更高。     

超高压变质岩中柯石英→石英相变研究的进展

柯石英是石英的高压同质多相变体，是超高压变质作用的产物，它是识别超高压变质作用的重要标志矿物。柯石英的发现表明了近地表的岩石随板块运动曾被俯冲至地下大于90km的深度并经受了超高压变质作用。研究柯石英→石英相变过程中的微结构变化，对进一步研究超高压变质作用的机理及超高压变质岩折返过程的动力学机制具有重要意义。本文简述了近年来有关超高压变质岩中柯石英→石英相变研究的一些进展。     

榴辉岩中石英出溶体的拉曼光谱学研究及其构造意义

利用拉曼光谱学和费氏台方法对若干地区超高压榴辉岩中柯石英和榴辉岩中石英出溶体的超显微构造特征进行了研究.研究结果表明, 石榴石(或绿辉石) 中柯石英向石英相变是一个连续变化过程.绿辉石中石英出溶体和主晶具有一定的晶体学拓扑关系, 即石英出溶体长轴有两个展布方向: 平行于绿辉石(10 0) 裂理面和平行于绿辉石(- 10 1) 面.目前, 部分学者推断榴辉岩绿辉石中石英出溶体可作为超高压变质作用的标志.笔者认为, 棒状定向石英在绿辉石中出溶的温压条件和出溶机理尚未查明.因此, 需加强过量二氧化硅单斜辉石出溶机理的超高压实验研究, 从而为证实石英出溶体作为超高压标志提供实验定量约束.      

中国境内可能存在一条新的高压/超高压(?)变质带——青藏高原拉萨地体中发现榴辉岩带

新发现榴辉岩带位于拉萨北东方向,产在青藏高原拉萨地体中东部。观察到的榴辉岩带宽度约500~600m,呈近东西向延伸,已知规模10km以上。榴辉岩为常见的金红石榴辉岩、石英榴辉岩和多硅白云母榴辉岩。榴辉岩的单斜辉石中含硬玉分子变化较大,Jd=16%~44%,但均落于绿辉石成分区间;石榴子石中镁铝榴石(Pyrope)端元组分16%~33%,铁铝榴石(Alm)40%~54%,钙铝榴石(Gross)22%~31%。利用Grt-Omp-Phe和Grt-Omp矿物组合对变质温-压初步估算,获得金红石榴辉岩样品06Y-334的变质p、t分别为2.58GPa、635℃和2.67GPa、730℃,样品06Y-345的t主要在680~780℃区间,样品06Y-336的t主要在640~740℃区间,3个样品获得的结果相近。显微镜观察表明多硅白云母可能为折返阶段的退变质矿物而不属变质峰期的矿物,推测峰期的压力值有可能高于2.67GPa而进入柯石英稳定区间(p>2.8GPa)。石榴子石和绿辉石中出现的一些类似柯石英假象的石英包裹体与这一推断相吻合。以上初步研究结果表明,拉萨地体的榴辉岩带可能是中国境内又一条高压/超高压(?)变质带。     

Subduction of Continental Crust in the Early Palaeozoic North Qaidam Ultrahigh-Pressure Metamorphic Belt, NW China:Evidence from the Discovery of Coesite in the Belt

Coesite was discovered as inclusions in zircon separates from pelitic gneiss associated with a large eclogite body in the North Qaidam ultrahigh-pressure (UHP) terrane. Some graphite inclusions were also found. This finding suggested the occurrence of in-situ UHP metamorphism and that the terrane was most likely recrystallized at pressures below the diamond stability field. It supported other previous indirect UHP evidence, such as polycrystalline quartz inclusions in eclogitic garnet, quartz lamellae in omphacite and P-T estimates for both eclogite and garnet peridotite. The U-Pb and Sm-Nd ages of the North Qaidam eclogite indicated that subduction of continental crust occurred in the Early Palaeozoic, which probably recorded a collision between the Sino-Korean and Yangtze plates.     

SHRIMP U–Pb dating of coesite-bearing zircon from the ultrahigh-pressure metamorphic rocks, Sulu terrane, east China

This paper provides further evidence for the ongoing discussion as to whether the Dabie UHPM belt formed in Triassic or Palaeozoic time, and whether the Sulu UHPM belt formed in Triassic or Neoproterozoic time. Combined use of laser Raman spectrometer (LR), cathodoluminescence imaging (CL), and ion probe U–Pb in‐situ dating (SHRIMP) provided accurate ages of UHPM from rocks collected from Weihai, NE Sulu UHPM belt. LR was used to identify coesite and other UHP minerals as inclusions in zircon separates from an amphibolized peridotite and an eclogite. CL was used to examine the zoning structure of these zircon, and SHRIMP dating was performed on specific spots on zircon to obtain ages of different geological events. An age of 221 ± 12 Ma was obtained for coesite‐bearing zircon from the amphibolized peridotite; an age of 228 ± 29 Ma for eclogite was obtained from the lower intercept of a concordia plot. These ages are interpreted as the time of UHPM in the Weihai region. Ultramafic rocks to the east of Weihai yield a magmatic age at 581 ± 44 Ma. The zircon in the ultramafic rocks possibly also records a thermal event at c. 400 Ma, but no independent geological evidence for this event has been found. The eclogite protolith formed in the Middle Proterozoic (1821 ± 19 Ma), which is similar to the age of country rock gneisses of 1847–1744 Ma. The new geochronological data confirm that UHPM occurred in the Triassic in the Sulu area when subduction took the ultramafic body and the eclogite protolith, together with the adjacent supracrustal rocks, to mantle depths.