安徽大别山北部榴辉岩的分布及主要特征   总被引：1，自引：0，他引：1  

周存亭  高天山  汤加富  沈荷生  胡云琴 《地质通报》2000,19(3)

安徽大别山北部新发现的榴辉岩主要产于花岗质片麻岩及基性—超基性岩中 ,与大别山南部的榴辉岩在产出围岩、矿物组成及地球化学特征等方面均十分相似。现今榴辉岩南多北少的分布 ,主要是在中生代热隆构造体制下剧烈差异抬升剥蚀 ,中生代花岗岩大面积侵位所致。  相似文献   

榴辉岩中石英出溶体的拉曼光谱学研究及其构造意义   总被引：2，自引：0，他引：2  

王璐  金振民  何谋春 《地球科学》2003,28(2):143-150

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.   相似文献   

Overview of the geology, petrology and tectonic framework of the high-pressure–ultrahigh-pressure metamorphic belt of the Kokchetav Massif, Kazakhstan     

S. Maruyama  C. D. Parkinson. 《Island Arc》2000,9(3):439-455

Abstract High‐ to ultrahigh‐pressure metamorphic (HP–UHPM) rocks crop out over 150 km along an east–west axis in the Kokchetav Massif of northern Kazakhstan. They are disposed within the Massif as a 2 km thick, subhorizontal pile of sheet‐like nappes, predominantly composed of interlayered pelitic and psammitic schists and gneisses, amphibolite and orthogneiss, with discontinuous boudins and lenses of eclogite, dolomitic marble, whiteschist and garnet pyroxenite. On the basis of predominating lithologies, we subdivided the nappe group into four north‐dipping, fault‐bounded orogen‐parallel units (I–IV, from base to top). Constituent metabasic rocks exhibit a systematic progression of metamorphic grades, from high‐pressure amphibolite through quartz–eclogite and coesite–eclogite to diamond–eclogite facies. Coesite, diamond and other mineral inclusions within zircon offer the best means by which to clarify the regional extent of UHPM, as they are effectively sequestered from the effects of fluids during retrogression. Inclusion distribution and conventional geothermobarometric determinations demonstrate that the highest grade metamorphic rocks (Unit II: T = 780–1000°C, P = 37–60 kbar) are restricted to a medial position within the nappe group, and metamorphic grade decreases towards both the top (Unit III: T = 730–750°C, P = 11–14 kbar; Unit IV: T = 530°C, P = 7.5–9 kbar) and bottom (Unit I: T = 570–680°C; P = 7–13.5 kbar). Metamorphic zonal boundaries and internal structural fabrics are subhorizontal, and the latter exhibit opposing senses of shear at the bottom (top‐to‐the‐north) and top (top‐to‐the‐south) of the pile. The orogen‐scale architecture of the massif is sandwich‐like, with the HP–UHPM nappe group juxtaposed across large‐scale subhorizontal faults, against underlying low P–T metapelites (Daulet Suite) at the base, and overlying feebly metamorphosed clastic and carbonate rocks (Unit V). The available structural and petrologic data strongly suggest that the HP–UHPM rocks were extruded as a sequence of thin sheets, from a root zone in the south toward the foreland in the north, and juxtaposed into the adjacent lower‐grade units at shallow crustal levels of around 10 km. The nappe pile suffered considerable differential internal displacements, as the 2 km thick sequence contains rocks exhumed from depths of up to 200 km in the core, and around 30–40 km at the margins. Consequently, wedge extrusion, perhaps triggered by slab‐breakoff, is the most likely tectonic mechanism to exhume the Kokchetav HP–UHPM rocks.  相似文献   

Thermobaric structure of the Kokchetav ultrahigh-pressure–high-pressure massif deduced from a north–south transect in the Kulet and Saldat–Kol regions, northern Kazakhstan     

Tsutomu Ota  Masaru Terabayashi  Christopher D. Parkinson and  Hideki Masago 《Island Arc》2000,9(3):328-357

Abstract To investigate the regional thermobaric structure of the diamondiferous Kokchetav ultrahigh‐pressure and high‐pressure (UHP–HP) massif and adjacent units, eclogite and other metabasites in the Kulet and Saldat–Kol regions, northern Kazakhstan, were examined. The UHP–HP massif is subdivided into four units, bounded by subhorizontal faults. Unit I is situated at the lowest level of the massif and consists of garnet–amphibolite and acidic gneiss with minor pelitic schist and orthogneiss. Unit II, which structurally overlies Unit I, is composed mainly of pelitic schist and gneiss, and whiteschist locally with abundant eclogite blocks. The primary minerals observed in Kulet and Saldat–Kol eclogites are omphacite, sodic augite, garnet, quartz, rutile and minor barroisite, hornblende, zoisite, clinozoisite and phengite. Rare kyanite occurs as inclusions in garnet. Coesite inclusions occur in garnet porphyroblasts in whiteschist from Kulet, which are closely associated with eclogite masses. Unit III consists of alternating orthogneiss and amphibolite with local eclogite masses. The structurally highest unit, Unit IV, is composed of quartzitic schist with minor pelitic, calcareous, and basic schist intercalations. Mineral assemblages and compositions, and occurrences of polymorphs of SiO₂ (quartz or coesite) in metabasites and associated rocks in the Kulet and Saldat–Kol regions indicate that the metamorphic grades correspond to epidote–amphibolite, through high‐pressure amphibolite and quartz–eclogite, to coesite–eclogite facies conditions. Based on estimations by several geothermobarometers, eclogite from Unit II yielded the highest peak pressure and temperature conditions in the UHP–HP massif, with metamorphic pressure and temperature decreasing towards the upper and lower structural units. The observed thermobaric structure is subhorizontal. The UHP–HP massif is overlain by a weakly metamorphosed unit to the north and is underlain by the low‐pressure Daulet Suite to the south; boundaries are subhorizontal faults. There is a distinct pressure gap across these boundaries. These suggest that the highest grade unit, Unit II, has been selectively extruded from the greatest depths within the UHP–HP unit during the exhumation process, and that all of the UHP–HP unit has been tectonically intruded and juxtaposed into the adjacent lower grade units at shallower depths of about 10 km.  相似文献   

NORTH QAIDAM ULTRAHIGH PRESSURE METAMORPHIC (UHPM) BELT ON THE NORTHEASTERN QINGHAI-TIBET PLATEAU AND ITS EASTWARD EXTENSION     

Yang Jingsui  Song Suguang  Wu Cailai  Shi Rendeng  Marc Jalivet 《地学前缘》2000,(Z1)

NORTH QAIDAM ULTRAHIGH PRESSURE METAMORPHIC (UHPM) BELT ON THE NORTHEASTERN QINGHAI-TIBET PLATEAU AND ITS EASTWARD EXTENSION1　YangJS ,XuZQ ,LiHB ,etal.DiscoveryofeclogiteatnorthernmarginofQaidambasin ,NWChina[J] .ChineseScienceBulletin,1998,4 3:1755～ 176 0 . 2　ZhangJX ,ZhangZM ,XuZQ ,etal.TheagesofU PbandSm NdforeclogitefromthewesternsegmentofAltynTaghtectonicbelt—theevidencesforexistenceofCaledonianorogenicroot[J] .ChineseScienc…  相似文献   

Petrographic and SHRIMP Studies of Zircons fromthe Caledonian Xiongdian Eclogite, NorthwesternDabie Mountains   总被引：2，自引：0，他引：2  

I.S.WILLIAMS 《《地质学报》英文版》2000,74(4):766-773

The Xiongdian eclogite occurring in the Sujiahe tectonic melange zone at Luoshan County, Henan Province, in the western Dabie Mountains, is typical high-pressure (HP)-ultrahigh-pressure (UHP) and medium-temperature eclogite. The occurrence, internal texture and surface characteristics of zircons in eclogite were studied rather systematically petrographically combined with the cathodoluminescence (CL) and scanning electron microscope (SEM) methods. Zircons are mainly hosted in garnet and other metamorphic minerals with sharp boundaries, have a multifaceted morphology and are homogeneous or exhibit a metamorphic growth texture in the interior, thus indicating that they are the product of metamorphism. SHRIMP analyses give zircon 206Pb/238U ages of 335 to 424 Ma and show a certain degree of radiogenic Pb loss; therefore it may be inferred that the age of 424? Ma represents the minimum age of a HP-UHP metamorphic age. From the above analyses coupled with previous Sm-Nd, 40Ar-39Ar, U-Pb and 207Pb/206Pb age d  相似文献   

Phase equilibria modelling constraints on P–T conditions during fluid catalysed conversion of granulite to eclogite in the Bergen Arcs,Norway          下载免费PDF全文

K. Bhowany  M. Hand  C. Clark  D. E. Kelsey  S. M. Reddy  M. A. Pearce  N. M. Tucker  L. J. Morrissey 《Journal of Metamorphic Geology》2018,36(3):315-342

Exhumed eclogitic crust is rare and exposures that preserve both protoliths and altered domains are limited around the world. Nominally anhydrous Neoproterozoic anorthositic granulites exposed on the island of Holsnøy, in the Bergen Arcs in western Norway, preserve different stages of progressive prograde deformation, together with the corresponding fluid‐assisted metamorphism, which record the conversion to eclogite during the Ordovician–Silurian Caledonian Orogeny. Four stages of deformation can be identified: (1) brittle deformation resulting in the formation of fractures and the generation of pseudotachylites in the granulite; (2) development of mesoscale shear zones associated with increased fluid–rock interaction; (3) the complete large‐scale replacement of granulite by hydrous eclogite with blocks of granulite sitting in an eclogitic “matrix”; and (4) the break‐up of completely eclogitized granulite by continued fluid influx, resulting in the formation of coarse‐grained phengite‐dominated mineral assemblages. P–T constraints derived from phase equilibria forward modelling of mineral assemblages of the early and later stages of the conversion to eclogite document burial and partial exhumation path with peak metamorphic conditions of ~21–22 kbar and 670–690°C. The P–T models, in combination with existing T–t constraints, imply that the Lindås Nappe underwent extremely rapid retrogressive pressure change. Fluid infiltration began on the prograde burial path and continued throughout the recorded P–T evolution, implying a fluid source that underwent progressive dehydration during subduction of the granulites. However, in places limited fluid availability on the prograde path resulted in assemblages largely consuming the available fluid, essentially freezing in snapshots of the prograde evolution. These were carried metastably deeper into the mantle with strain and metamorphic recrystallization partitioned into areas where ongoing fluid infiltration was concentrated.  相似文献   

Isotopic constraints on fluid infiltration from an eclogite facies shear zone, Holsenøy, Norway     

D. MATTEY  D. H. JACKSON  N. B. W. HARRIS  S. KELLEY 《Journal of Metamorphic Geology》1994,12(3):311-325

Granulite facies anorthosites on Holsenøy Island in the Bergen Arcs region of western Norway are transected by shear zones 0.1–100 m wide characterized by eclogite facies assemblages. Eclogite formation is related to influx of fluid along the shears at temperatures of c. 700d?C and pressures in excess of 1.7 GPa. Combined carbon and nitrogen stable isotope, ⁴⁰Ar/³⁶Ar, trace-element and petrological data have been used to determine the nature and distribution of fluids across the anorthosite-eclogite transition. A metre-wide drilled section traverses the eclogitic centre of the shear into undeformed granulite facies garnet-clinopyroxene anorthosite. Clinozoisite occurs along grain boundaries and microcracks in undeformed anorthosite up to 1 m from the centre of the shear and clinozoisite increases in abundance as the edge of the shear zone is approached. The eclogite-granulite transition, marked by the appearance of sodic pyroxene and loss of albite, occurs within the most highly sheared section of the traverse. The jadeite-in reaction coincides with increased paragonite activity in mica. The separation between paragonite and clinozoisite reaction fronts can be semiquantitatively modelled assuming advective fluid flow perpendicular to the shear zone. The inner section of the traverse (0.25 m wide) is marked by retrogressive replacement of omphacite by plagioclase + paragonite accompanied by veins of quartz-phengite-plagioclase. C-N-Ar characteristics of fluid inclusions in garnet show that fluids associated with precursor granulite, eclogite and retrogressed eclogite are isotopically distinct. The granulite-eclogite transition coincides with a marked change in CO₂ abundance and δ¹³C (<36ppm, δ¹³C=-2% in the granulite; <180 ppm, δ¹³C=-10% in the eclogite). The distribution of Ar indicates mixing between influxed fluid (⁴⁰Ar/³⁶Ar > 25 times 10³) and pre-existing Ar in the granulite (⁴⁰Ar/³⁶Ar < 8 times 10³). δ¹⁵N values decrease from +6% in the anorthosite to +3% within the eclogite shear. The central zone of retrogressed eclogite post-dates shearing and is characterised by substantial enrichment of Si, K, Ba and Rb. Fluids are CO₂-rich (δ¹³C ～ -5%) with variable N₂ and Ar abundances and isotopic compositions. Both Ar and H₂O have penetrated the underformed granulite fabric more than 0.5m beyond the granulite/eclogite transition during eclogite formation. Argon isotopes show a mixing profile consistent with diffusion through an interconnecting H₂O-rich fluid network. In contrast, a carbon-isotope front coincides with the deformation boundary layer, indicating that the underformed anorthosite was impervious to CO₂-rich fluids. This is consistent with the high dihedral angle of carbonic fluids, and may be interpreted in terms of evolving fluid compositions within the shear zone.  相似文献   

西藏拉萨地体榴辉岩的地球化学特征和Sm-Nd、Rb-Sr同位素组成及其地质意义   总被引：2，自引：0，他引：2  

李兆丽  杨经绥  罗立强  李天福  徐向珍  任玉峰 《地质学报》2008,82(7):941-2008-01-30

最近在青藏高原拉萨地体新发现了一条榴辉岩带,该榴辉岩带位于冈底斯岩浆岛弧带的北缘。对该带榴辉岩的岩石地球化学特征及SmNd、RbSr同位素组成研究表明： ① 该带榴辉岩的原岩主要是一套低钾的大洋拉斑系列玄武岩,其原岩类似于典型的NMORB,源于亏损地幔; ② 该带榴辉岩样品 （87Sr/86Sr）i＝0.70335~0.70457,变化范围较大,且与εNd（t）值及微量元素特征均没有好的对应关系,可能是由于该套岩石形成于大洋环境,形成后遭受了海水的蚀变作用;（3）该带榴辉岩全岩的SmNd等时线年龄为305.5±50Ma （2σ）,（143Nd/144Nd）i＝0.5126±0.00007 （2σ）,表明该带榴辉岩可能形成于早石炭－晚二叠世,在这一时期冈底斯北缘可能存在古特提斯洋盆及古特提斯洋盆深俯冲作用。  相似文献   

Partial transformation of gabbro to coesite-bearing eclogite from Yangkou, the Sulu terrane, eastern China   总被引：18，自引：2，他引：18  

R. Y. ZHANG  & J. G. LIOU 《Journal of Metamorphic Geology》1997,15(2):183-202

An ultra-high-pressure (UHP) metamorphic slab at Yangkou Beach near Qingdao in the Sulu region of China consists of blocks of eclogite facies metagabbro, metagranitoid, ultramafic rock and mylonitic orthogneisses enclosed in granitic gneiss. A gradational sequence from incipiently metamorphosed gabbro to completely recrystallized coesite eclogite formed at ultra-high-pressures was identified in a single 30 m block; metagabbro is preserved in the core whereas coesite eclogite occurs along the block margins. The metagabbro contains an igneous assemblage of Pl+Aug+Opx+Qtz+Bt+Ilm/Ti-Mag; it shows relict magmatic textures and reaction coronas. Fine-grained garnet developed along boundaries between plagioclase and other phases; primary plagioclase broke down to Ab+Ky+Ms+Zo±Grt±Amp. Augite is rimmed by sodic augite or omphacite, whereas orthopyroxene is rimmed by a corona of Cum±Act and Omp+Qtz layers or only Omp+Qtz. In transitional rocks, augite and orthopyroxene are totally replaced by omphacite, and the lower-pressure assemblage Ab+Ky+Phn+Zo+Grt coexists with domains of Omp (Jd_70–73)+Ky±Phn in pseudomorphs after plagioclase. Both massive and weakly deformed coesite-bearing eclogites contain Omp+Ky+Grt+Phn+Coe/Qtz+Rt, and preserve a faint gabbroic texture. Coesite inclusions in garnet and omphacite exhibit limited conversion to palisade quartz; some intergranular coesite and quartz pseudomorphs after coesite also occur. Assemblages of the coronal stage, transitional and UHP peak occurred at about 540±50 °C at c. 13 kbar, 600–800 °C at ≥15–25 kbar and 800–850 °C at >30 kbar, respectively. Garnet from the coronal- through the transitional- to the eclogite-stage rocks show a decrease in almandine and an increase in grossular±pyrope components; garnet in low-grade rocks contains higher MnO and lower pyrope components. The growth textures of garnet within pseudomorphs after plagioclase or along grain boundaries between plagioclase and other phases are complex; the application of garnet zoning to estimate P–T should be carried out with caution. Some garnet enclosing quartz aggregates as inclusions shows radial growth boundaries; these quartz aggregates, as well as other primary and low-P phases, persisted metastably at UHP conditions due to sluggish reactions resulting from the lack of fluid during prograde and retrograde P–T evolution.  相似文献