新疆西南天山蓝片岩的变质作用pTDt轨迹及构造演化   总被引：31，自引：1，他引：31  

高俊  肖序常 《地质论评》1994,40(6):544-553

西南天山蓝片岩的变质作用ｐＴＤｔ轨迹显示进变质作用为快速升压过程，退变质作用为近等热降压过程。自俯冲杂岩进入俯冲带到形成蓝片岩后抬升出露于造山带，变质作用经历了浊沸石相（４１５Ｍａ？）→硬柱石－蓝闪片岩相（４０８Ｍａ？）→蓝闪绿片岩相（３４５Ｍａ）→０绿片岩相（３１４Ｍａ）连续渐变演化的过程。蓝片岩中现存主要蓝闪绿片岩相矿物组合并非峰期变质矿物组合。造山运动晚期的大规模韧性推覆作用促成蓝片岩快速抬  相似文献   

Metamorphism and tectonic evolution of the Lancang paired metamorphic belts, south-western China   总被引：10，自引：0，他引：10  

RUYUAN ZHANG  BOLIN CONG  SHIGE MARUYAMA†  J. G. LIOU‡ 《Journal of Metamorphic Geology》1993,11(4):605-619

Abstract The Lancang metamorphic terrane consists of an eastern low- P/T belt and a western high- P/T belt divided by a N–S-trending fault. Protoliths of both units are mid–late Proterozoic basement and its cover. The low- P/T belt includes the Permian Lincang batholith, related amphibolite facies rocks of the Damenglong and Chongshan groups, and Permo-Triassic volcanic and volcaniclastic rocks. Most whole-rock Rb–Sr isochron and U–Pb zircon ages of the Lincang batholith are in the range 290–279 and 254–212 Ma, respectively. Metamorphism of the low- P/T belt reaches upper amphibolite with local granulite facies (735°C at 5 kbar), subsequently retrogressed at 450–500°C during post-Triassic time. The high- P/T rocks grade from west to east from blueschist through transitional blueschist/greenschist to epidote amphibolite facies. Estimated P–T conditions follow the high- P intermediate facies series up to about 550–600°C, at which oligoclase is stable. The ⁴⁰Ar/³⁹Ar plateau age of sodic amphibole in blueschist is 279 Ma.
The paired metamorphic belts combined with the spatial and temporal distribution of other blueschist belts lead us to propose a tentative tectonic history of south-east Asia since the latest Precambrian. Tectonic juxtaposition of paired belts with contrasting P–T conditions, perhaps during collision of the Baoshan block with south-east Asia, suggests that an intervening oceanic zone existed that has been removed. The Baoshan block is a microcontinent rifted from the northern periphery of Gondwana. Successive collision and amalgamation of microcontinents from either Gondwana or the Panthalassan ocean resulted in rapid southward continental growth of c. 500 km during the last 200 Ma. Hence, the Lancang region in south-east Asia represents a suture zone between two contrasting microcontinents.  相似文献   

Polyphase and anticlockwise P-T evolution for Franciscan eclogites and blueschists from Jenner, California, USA   总被引：1，自引：0，他引：1  

E. J. KROGH  C. W. OH  J. C. LIOU 《Journal of Metamorphic Geology》1994,12(2):121-134

High-grade exotic blocks in the Franciscan Complex at Jenner, California, show evidence for polydeformation/metamorphism, with eight distinct stages. Two parallel sets of mineral assemblages [(E) eclogite, and (BS) laminated blueschist] representing different bulk chemistry were identified. Stage 1, recorded by parallel aligned inclusions (S1) of crossite + omphacite + epidote + ilmenite + titanite + quartz (E), and glaucophane + actinolite + epidote + titanite (BS) in the central parts of zoned garnets, represents the epidote blueschist facies. The onset of a second stage (stage 2) is represented by a weak crenulation of S1 and growth of garnet. This stage develops a well-defined S2 foliation of orientated barroisite + epidote + titanite (E), or subcalcic actinolite + epidote + titanite (BS) at c. 90d? to S1, with syntectonic growth of garnet, defining the (albite-)epidote-amphibolite facies. A third stage, with aligned inclusions of glaucophane + (subcalcic) actinolite + phengite parallel to S2 in the outermost rims of large garnet grains, is assigned to the transitional (albite-)epidote-amphibolite/(garnet-bearing) epidote blueschist facies. The fourth stage represents the peak metamorphism, and was identified by unorientated matrix minerals in the least retrograded samples. In this stage the mineral assemblages garnet + omphacite + glaucophane + phengite (E) and garnet + winchite + phengite + epidote (BS) both represent the eclogite facies. Stage 5 is represented by the retrogression of eclogite facies assemblages to the epidote blueschist facies assemblages crossite/glaucophane + garnet + omphacite + epidote + phengite (E), and glaucophane + actinolite + epidote + phengite (BS), with the development of an S5 foliation subparallel to S2. Stage 6 represents a crenulation of S5, with the development of a well-defined S6 crenulation cleavage wrapping around relics of the eclogite facies assemblages. This crenulation cleavage is further weakly crenulated during a D7 event. Post-D7 (stage 8) is recorded by the growth of lawsonite + chlorite ± actinolite replacing garnet, and by veins of lawsonite + pumpellyite + aragonite and phengite + apatite. The different, yet coeval, mineral parageneses observed in rock types (E) and (BS) are probably due to differences in bulk chemistry. The metamorphic evolution from stage 1 to stage 8 seems to have been broadly continuous, following an anticlockwise P-Tpath: (1) epidote blueschist (garnet-free) to (2) (albite-)epidote-amphibolite to (3) transitional epidote blueschist (garnet-bearing)/(albite-)epidote-amphibolite to (4) eclogite to (5) epidote blueschist (garnet-bearing) to (6-7) epidote blueschist (garnet-free) facies to (8) lawsonite + pumpellyite + aragonite-bearing assemblages. This anticlockwise P-T path may have resulted from a decreasing geothermal gradient with time in the Mesozoic subduction zone of California at early or pre-Franciscan metamorphism.  相似文献   

Tectonic setting, petrology and geochronology of jadeite + glaucophane and chloritoid + glaucophane schists from north-west Turkey   总被引：5，自引：0，他引：5  

A. I. OKAY  S. P. KELLEY 《Journal of Metamorphic Geology》1994,12(4):455-466

The north-west Turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble. The depositional age of the blueschist protoliths are probably Palaeozoic to Mesozoic, while the age of the high-pressure/low-temperature metamorphism is Late Cretaceous. Blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices. The metaclastic rocks with regional jadeite and glaucophane, which comprise the lower part of the blueschist unit, make up an over 1000-m-thick coherent sequence in the Kocasu region of north-west Turkey. Rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole + Iawsonite but no garnet indicate lawsonite blueschist facies metamorphism. The blueschist metaclastics in the Kocasu region are practically free of calcium and ferric iron and closely approximate the NFMASH system in bulk composition. Two low-variance mineral assemblages (with quartz and phengite) are jadeite + glaucophane + chlorite + paragonite and chloritoid + glaucophane + paragonite. The metaclastics comprise up to several-metres-thick layers of jadeite schist with quartz, phengite and nearly 100 mol% jadeite. Phase relations in the metaclastics show that the chloritoid + glaucophane assemblage, even in Fe²⁺-rich compositions, is stable in the jadeite stability field. In the NFASH system the above assemblage without the accompanying garnet has a narrow thermal stability field. Mineral equilibria in the metaclastics involving chloritoid, glaucophane, jadeite, paragonite and chlorite indicate metamorphic P-T conditions of 20 ± 2 kbar and 430 ± 30 d? C, yielding geothermal gradients close to 5d? C km^-1, one of the lowest geotherms recorded. Blueschists in the Kocasu region, which have been buried to 70 km depth, are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km. Phengites from two jadeite schists were dated by Ar/Ar laser probe; they give an age of 88.5 ± 0.5 Ma, interpreted as the age of metamorphism. Blueschists and the overlying peridotite bodies are intruded by 48-53-Ma-old granodiorite bodies that were emplaced at 10 km depth. This suggests that the exhumation of blueschists by underplating of cold continental crust, and normal faulting at the blueschist-peridotite, interface occurred during the Late Cretaceous to Palaeocene (88-53 Ma).  相似文献   

The youngest blueschist belt in SW Japan: implication for the exhumation of the Cretaceous Sanbagawa high-P/T metamorphic belt     

K. AOKI  T. ITAYA  T. SHIBUYA  H. MASAGO  Y. KON  M. TERABAYASHI  Y. KANEKO  T. KAWAI  S. MARUYAMA 《Journal of Metamorphic Geology》2008,26(5):583-602

The tectonic evolution of the Northern Shimanto belt, central Shikoku, Japan, was examined based on petrological and geochronological studies in the Oboke area, where mafic schists of the Kawaguchi Formation contain sodic amphibole (magnesioriebeckite). The peak P–T conditions of metamorphism are estimated as 4–4.5 kbar (15–17 km depth), and 240–270 °C based on available phase equilibria and sodic amphibole compositions. These metamorphic conditions are transitional between blueschist, greenschist and pumpellyite–actinolite facies. Phengite K–Ar ages of 64.8 ± 1.4 and 64.4 ± 1.4 Ma were determined for the mafic schists, and 65.0 ± 1.4, 61.4 ± 1.3 and 63.6 ± 1.4 Ma for the pelitic schists. The metamorphic temperatures in the Oboke area are below the closure temperature of the K–Ar phengite system, so the K–Ar ages date the metamorphic peak in the Northern Shimanto belt. In the broad sense of the definition of blueschist facies, the highest‐grade part of the Northern Shimanto belt belongs to the blueschist facies. Our study and those of others identify the following constraints on the possible mechanism that led to the exhumation of the overlying Sanbagawa belt: (i) the Sanbagawa belt is a thin tectonic slice with a structural thickness of 3–4 km; (ii) within the belt, metamorphic conditions varied from 5 to 25 kbar, and 300 to 800 °C, with the grade of metamorphism decreasing symmetrically upward and downward from a structurally intermediate position; and (iii) the Sanbagawa metamorphic rocks were exhumed from ～60 km depth and emplaced onto the Northern Shimanto metamorphic rocks at 15–17 km depth and 240–270 °C. Integration of these results with those of previous geological studies for the Sanbagawa belt suggests that the most probable exhumation mechanism is wedge extrusion.  相似文献   

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   总被引：3，自引：0，他引：3       下载免费PDF全文

刘焰  吕永增 《地学前缘》2011,18(2):100-115

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  相似文献   

中国东北黑龙江杂岩体蓝闪石片岩岩石学研究(英文)   总被引：1，自引：0，他引：1  

N I Volkova  李有柱 《地球科学与环境学报》2010,32(2):111-119

黑龙江杂岩主要由蓝闪石片岩构成,蓝闪石片岩主要包括绿帘石、绿泥石、钠长石、钠质角闪石、多硅白云母和石英以及为数不多的榍石、钛铁矿和黑硬绿泥石。其中,钠质角闪石包括蓝闪石和镁质钠闪石。变质条件的压力(P)温度(T)评价条件为400~425℃和0.69~0.86 MPa,对应岩相为绿帘蓝闪石片岩相。黑龙江杂岩蓝闪石片岩的地球化学研究表明,其原岩是可与洋岛型(OIB)玄武岩和一些洋中脊型(E-MORB)玄武岩相对比的大洋玄武岩,这说明黑龙江杂岩蓝闪石片岩的玄武岩原岩是在海底山或者在大洋隆起条件下由富集源形成的;具有洋岛型玄武岩地球化学特征的变质玄武岩以及富锰的变质燧石、大理石、变质硬砂岩和蛇绿岩鳞片的加入证明黑龙江杂岩是消减—增生杂岩,它含有变形洋壳的碎块和在被改造的前震旦纪佳木斯岩体西边缘上形成于侏罗纪的增生楔岩石;黑龙江杂岩在原岩成分上可与活动大陆边缘许多增生的杂岩相当。  相似文献   

The occurrence of deerite in highly oxidizing conditions within the 'schistes lustrés'of eastern Corsica     

P. VERNIÉ  J. R. KIENAST  C. MÉVEL 《Journal of Metamorphic Geology》1986,4(4):385-399

Abstract A deerite-bearing rock occurs at the boundary between quartzite and metabasites within the 'schistes lustrés'of eastern Corsica. It contains the typomorphic assemblage pyroxene, blue amphibole, hematite and magnetite. Pyroxene shows homogeneous composition close to the aegirine end-member and blue amphibole is zoned from crossite core to riebeckite rim. The bulk chemical analysis of the rock is remarkable by its very high iron content and the presence of an unusually large amount of Zn which is concentrated in both deerite and amphibole. Electron microprobe analyses of the Corsican deerite are compared with those published in the literature; as shown by deerite from the Fransciscan iron formation, the principal substitution for Fe²⁺ is Mn whereas the amount of substitution for Fe³⁺ is low. In the system SiO₂-FeO-Fe₂O₃-Al₂O₃-Na₂O-MgO-H₂O the typomorphic paragenesis can be described by an univariant reaction interpreted as the result of a pressure decrease. P-T conditions of metamorphism, previously estimated to be 8 kbar and 300°C, are in good agreement with present knowledge of the deerite stability field. The occurrence of hematite and magnetite in equilibrium permits an estimation of the oxygen fugacity (log f o₂= -29.41 bar). Oxidation conditions are higher than those previously mentioned in the literature for similar assemblages.  相似文献   

The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling   总被引：8，自引：0，他引：8  

G. L. CLARKE  R. POWELL  J. A. FITZHERBERT 《Journal of Metamorphic Geology》2006,24(8):715-725

Lawsonite equilibria are predicted to occur over a broad P–T spectrum developed during subduction, yet lawsonite‐bearing assemblages are rare. In the context of mafic mineral equilibria modelled for the range of common crustal metamorphism (4–23 kbar, 400–750 °C) using the system Na₂O‐CaO‐K₂O‐FeO‐MgO‐Al₂O₃‐SiO₂‐H₂O and the software thermocalc , unusually high water contents are demanded by lawsonite assemblages. As a consequence, lawsonite assemblages are predicted to have difficulty forming and lawsonite equilibria to be uncommon. Metabasalt undergoing cooler subduction may experience substantial periods involving the metastable persistence of mineral assemblages because of water under‐saturation with non‐occurrence of recrystallization. If formed, lawsonite‐bearing assemblages are observed to be highly unstable; their preservation requires that exhumation be accompanied by substantial cooling. The amount of structurally bound H₂O in minerals plays a critical role in the formation and preservation of mineral assemblages, controlling key changes in rocks undergoing subduction.  相似文献   

Regional progressive high-pressure metamorphism, Seward Peninsula, Alaska   总被引：1，自引：0，他引：1  

R. B. FORBES  B. W. EVANS  S. P. THURSTON 《Journal of Metamorphic Geology》1984,2(1):43-54

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.  相似文献