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1.
在苏尼特左旗以南地区的中古生代造山带的混杂岩带内发现了以岩块形式出现的蓝片岩,其矿物组合为斜长石+阳起石+蓝闪石+绿帘石+榍石。蓝片岩化学成分说明由基性火山岩变质而成。矿物化学分析表明,蓝片岩中角闪石可分为钙质、钙钠质和钠质3类。钙质闪石均为阳起石,钙钠质闪石为蓝透闪石和冻蓝闪石,钠质闪石为蓝闪石和青铝闪石及少量镁钠闪石。利用Na(M4)和AlⅣ的含量推测本区钙质、钙钠质和钠质3类闪石的压力从0.3～0.7Gpa,表明蓝片岩相变质作用的压力约为0.7GPa。用化学反应限定蓝片岩的形成温度为200～375℃左右。40Ar39Ar同位素年代学测定蓝闪石的等时线年龄为383±13Ma(1δ)。这些结果进一步证实沿贺根山—苏尼特左旗南是一条中古生代的缝合线,其俯冲—碰撞的标志即为混杂岩带以及其中的蓝片岩。 相似文献
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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
3.
中国西部元古代蓝片岩带——世界上保存最好的前寒武纪蓝片岩 总被引：13，自引：0，他引：13
阿克苏附近所发现的元古界阿克苏群为一完整的蓝片岩-绿片岩系列,我们通过野外调查肯定了这一认识,并认为它是高压-温相的变质块体,长40km,宽约2.5km.该变质岩由强烈片理化的绿泥石-黑硬绿泥石石墨片岩、黑硬绿泥石-多硅白云母片岩、绿片岩、蓝片岩及少量石英岩、变铁质岩组成.原岩包活泥质岩、砂岩、基性玻屑凝灰岩、块状熔岩、枕状熔岩及少量深海沉积物.蓝片岩的矿物组合:青铝闪石-绿帘石-绿泥石-钠长石-石英-阳起石.阿克苏群为世界上真正的前震旦纪蓝片岩之一,其变质年龄至少有800Ma. 相似文献
4.
安徽张八岭蓝片岩带的矿物分带 总被引：5，自引：1，他引：5
皖中张八岭蓝片岩带含硬玉和石英组合，位于扬子地块北缘，是我国蓝片岩带压力最高的地区。以矿物共生组合为基础，将蓝片岩带划分为５个矿物带：黑硬绿泥石－白云母带；红帘石－白云母带；蓝闪石－青铝闪石带；阳起石带；白云母带。阐述了蓝片岩可能在板底垫托作用下抬升至地表的机制。 相似文献
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中国蓝闪石片岩带的一般特征及其分布 总被引：28，自引：4，他引：28
蓝闪石片岩相可依据其温度划分为蓝闪石-硬柱石和蓝闪石-绿片岩相区,并与一些变质相组成不同相系。中国蓝闪石片岩带根据其平均温度-压力梯度和构造地质环境可分为:(1)元古代克拉通内蓝闪石片岩带;(2)加里东期克拉通内裂谷型蓝闪石片岩带;(3)古生代中国陆台北缘蓝闪石片岩带;(4)中新生代与俯冲作用有关的蓝闪石片岩带。蓝闪石变质作用的形成和演化与构造地质环境有关。中国蓝闪石片岩带大部分形成于硅铝壳环境,从陆壳开始裂开,直至出现洋壳。这一演化与地壳内热流变化格局有关,形成机理不属于均变论的观点。 相似文献
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藏北羌塘中部绒玛地区蓝片岩岩石学、矿物学和40Ar/39Ar年代学 总被引：5，自引：4，他引：1
藏北羌塘中部沿龙木错-双湖-线出露一条低温高压变质带,目前已有多处蓝片岩的报道.然而,除冈玛错地区产有典型的蓝闪石外,多数地区并没有典型蓝闪石的报道.绒玛蓝片岩位于羌塘中部高压变质带的中段,是该带中规模最大、保存最好的蓝片岩,对蓝片岩进行了详细的岩石学和矿物学研究,钠质角闪石主要为蓝闪石、青铝闪石、钠闪石和镁钠闪石.对蓝片岩中蓝闪石和多硅白云母进行了40Ar/39Ar定年,获得了227.3±3.8Ma和215±1.5Ma的坪年龄,分别代表蓝片岩快速俯冲消减和俯冲作用结束开始折返抬升的时代.绒玛蓝片岩岩石学、矿物学和40Ar/39Ar年代学研究为羌塘中部高压变质带的研究提供了新的资料. 相似文献
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中国蓝闪片岩相的变质作用 总被引：7，自引：1，他引：7
本文论述了中国蓝闪片岩的分布、变质条件及其构造位置。中国的蓝闪片岩从中晚元古代开始,各变质期均有出现。根据矿物组合,可分为两类:第一类蓝闪片岩常含有高压矿物,如硬柱石、硬玉和文石以及蓝闪石、绿纤石、黑硬绿泥石、多硅白云母、红帘石等,属高压亚绿片岩相,称蓝闪—硬柱石片岩相,形成温度约250—350℃,压力大于500—800MPa,甚至可达1200MPa。此类蓝闪—硬柱石片岩相多代表海洋板块古消减带。第二类蓝闪片岩的常见矿物为蓝闪石、青铝闪石或镁钠闪石、黑硬绿泥石、红帘石和绿片岩相中的绿帘石、阳起石、绿泥石、白云母、有时还有黑云母、铁铝榴石和钠质辉石。形成温度约350—450℃,压力500—800MPa。此类蓝闪绿片岩相虽处于活动带,但与板块构造没有直接关系。我国西藏南部和内蒙温都尔庙属第一类,但大部分蓝闪片岩带属第二类。 相似文献
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Zr-in-rutile thermometry in blueschists from Sifnos, Greece 总被引：1，自引：0，他引：1
Frank S. Spear David A. Wark John T. Cheney John C. Schumacher E. Bruce Watson 《Contributions to Mineralogy and Petrology》2006,152(3):375-385
Zr-in-rutile thermometry on samples of blueschist from Sifnos, Greece, yields temperatures that reflect progressive crystallization of rutile from ca. 445 to 505°C with an analytical precision of + 18/−27 and ± 10°C using the electron microprobe and ± 1.5–3.5°C using the ion microprobe. Individual grains are generally homogeneous within analytical uncertainty. Different grains within a single sample record temperature differences as large 55°, although in most samples the range of temperatures is on the order of 25°. In several samples, Zr-in-rutile temperatures from grains within garnet are lower than temperatures from matrix grains, reflecting growth of rutile with increasing temperature of metamorphism. Although the specific rutile-producing reactions have not been identified, it is inferred that rutile grows from either continuous reaction involving the breakdown of lower grade phases (possibly ilmenite), or from pseudomorph reactions involving the breakdown of relic igneous precursors at blueschist-facies conditions. No systematic variation in rutile temperatures was observed across the blueschist belt of northern Sifnos, consistent with the belt having behaved as a coherent block during subduction. 相似文献
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ABSTRACT Blueschists occur along the Indus Suture Zone in Ladakh as tectonic thrust slices, as isolated blocks within mélange units and as pebbles within continental detrital series. In the Shergol-Baltikar section high-pressure rocks within the Mélange unit lie between the Dras-Naktul-Nindam nappes in the north and the Lamayuru units in the south. The blueschists are imbricated with mélange formation of probably upper Cretaceous age. They are overlain discordantly by the Shergol conglomerate of post Eocene (Oligo-Miocene ?) age. Blueschist lithologies are dominated by volcanoclastic rock sequences of basic material with subordinate interbedding of cherts and minor carbonates. Mineral assemblages in metabasic rocks are characterized by lawsonite-glaucophane/crossite-Na-pyroxene-chlorite-phengite-titanite ± albite ± stilpnomelane. In the quartz bearing assemblages garnet is present but omphacite absent. P-T estimates indicate temperatures of 350 to 420°c and pressures around 9–11 kbar. Geochemical investigations show the primary alkaline character of the blueschist, which suggests an oceanic island or a transitional MORB type primary geotectonic setting. K/Ar isotopic investigations yield middle Cretaceous ages for both whole rocks and minerals. Subduction related HP-metamorphism affecting the Mesozoic Tethyan oceanic crust developed contemporaneously with magmatism in the Dras volcanic are and the Ladakh batholith. Subsequent collision of India with Asia obducted relics of subduction zone material which later became involved in nappe emplacement during the Himalayan mountain building. 相似文献
13.
Chloritoid-bearing rocks associated with blueschists and eclogites, northern New Caledonia 总被引：4，自引：0，他引：4
EDWARD D. GHENT MAVIS Z. STOUT P. M. BLACK R. N. BROTHERS 《Journal of Metamorphic Geology》1987,5(2):239-254
Abstract Chloritoid-bearing metasedimentary rocks occur in close proximity to blueschists and eclogites in the Tertiary high-pressure metamorphic belt of northern New Caledonia. The typical assemblage of chloritoid-bearing rocks in the epidote zone is quartzchlorite-muscovite-garnet-chloritoid. In the omphacite zone, epidote is an additional member of the chloritoid-bearing assemblage. Paragonite is rare, plagioclase was not detected, and rutile and ilmenite are the Fe-Ti oxide phases. Chloritoid-glaucophane is not a common assemblage. Chloritoid-bearing rocks have relatively low (Ca+K+Na)/Al ratios and the chloritoids are relatively Mg-rich with Mg/ (Mg+Fe) up to about 0.4. A comparison of the mineral assemblages and mineral chemistry with experimental and computed phase equilibria suggest an upper temperature limit near 560° C in the omphacite zone and a minimum temperature limit near 450° C at 10 kbar. An empirical garnet-chlorite Fe-Mg exchange thermometer does not yield consistent results for the higher-grade rocks, suggesting T s ranging from 390 to 535° C in the omphacite zone and 420–465° C in the epidote zone. The distribution coefficient K D = (Fe/Mg)ctd /(Fe/Mg)chl for chloritoid and chlorite ranges from 3.9 to 6.4, values which are lower than those (=10) from lower greenschist facies rocks, but are near those of upper greenschist facies and albite-epidote amphibolite facies. 相似文献
14.
新疆阿克苏地区前寒武纪蓝片岩构造—热演化史 总被引：4，自引：1，他引：3
阿克苏前寒武纪蓝片岩产于塔里木盆地西北缘的柯坪隆起区内。近二十年来,中外科学家对其展开了深入研究,并获得了许多新的同位素年龄资料,但是年龄测定大多偏重于确定蓝片岩的变质年龄,蓝片岩形成后的构造演化方面的研究尚显不足。为了讨论: 1.裂变径迹数据有没有记录到阿克苏蓝片岩形成后快速折返至地表的信息？2.阿克苏蓝片岩剥露以后是否经历过再次埋藏和剥露,再次埋藏的深度和剥露的时间？3.蓝片岩的构造热演化过程对大陆边缘不同构造事件的响应; 采集阿克苏地区前寒武纪蓝片岩带样品进行磷灰石裂变径迹测试,6个样品的年龄值介于107.5~62.5Ma之间,远小于高压变质年龄,径迹长度介于10.46~12.12μm。结合前人研究成果、本区地层序列和裂变径迹热史模拟结果,大致重建了蓝片岩的热史演化: 1.蓝片岩形成(872~862Ma)后快速折返至地表,可能在整个早震旦世一直遭受剥蚀,到晚震旦世才重新开始接受沉积埋藏; 2.晚震旦世地层基本保持连续,整个古生代也仅缺失中、上志留统,中、下石炭统。至古生代末,早震旦世和整个古生代地层厚度已近万米。蓝片岩完全退火,年龄被重置; 3.中生代晚期区内地层普遍开始隆升,裂变径迹时钟重新开始计时; 4.古新世开始有沉积作用发生,样品接受埋藏增温至部分退火带,随后可能由于印度-欧亚板块碰撞的远程效应,中新世地层重新开始隆升剥露。 相似文献
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Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction 总被引：1，自引：0，他引：1
Triassic eclogite and blueschist facies rocks occur as a thrust sheet, 25-km long and over 2-km thick, in an Eocene fold-and-thrust belt in northwest Turkey along the
zmir–Ankara suture. The thrust sheet consists mainly of metabasites with minor marble, phyllite and metachert, and rare lenses of serpentinite. The common blueschist facies mineral assemblage in the metabasites is sodic amphibole+epidote+albite+chlorite+phengite±garnet. Sodic amphibole commonly shows replacement by barroisite, and there is continuous petrographic transition from blueschist–metabasites to barroisite-bearing epidote–amphibolites. Eclogite with the mineral assemblage of garnet+sodic pyroxene+sodic–calcic amphibole+epidote is found only in one locality. P–T conditions of the epidote–blueschist facies metamorphism are estimated as 450±50 °C and 11±2 kbar. The blueschist formation was followed by a decrease in pressure and increase in temperature, leading to the development of barroisite-bearing epidote–amphibolites. Phengite, sodic amphibole and barroisite Ar/Ar ages from three metabasic rocks range between 215 and 205 Ma, and indicate Late Triassic high-pressure metamorphism. The Triassic blueschists in northwest Turkey constitute part of a much larger allochthonous tectonic unit of Triassic mafic volcanic rocks. They probably represent the upper layers of a Triassic oceanic plateau, which was accreted to the Laurasian margin during the latest Triassic. The close spatial association of the Triassic and Cretaceous blueschists along the
zmir–Ankara suture suggests that the suture represents a long-lived plate boundary of Late Palaeozoic to early Tertiary age. 相似文献
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High-pressure low-temperature (HP–LT) metamorphic rocks provide invaluable constraints on the evolution of convergent zones. Based on a worldwide compilation of key information pertaining to fossil subduction zones (shape of exhumation P–T–t paths, exhumation velocities, timing of exhumation with respect to the convergence process, convergence velocities, volume of exhumed rocks,…), this contribution reappraises the burial and exhumation of oceanic blueschists and eclogites, which have received much less attention than continental ones during the last two decades.Whereas the buoyancy-driven exhumation of continental rocks proceeds at relatively fast rates at mantle depths (≥ cm/yr), oceanic exhumation velocities for HP–LT oceanic rocks, whether sedimentary or crustal, are usually on the order of the mm/yr. For the sediments, characterized by the continuity of the P–T conditions and the importance of accretionary processes, the driving exhumation mechanisms are underthrusting, detachment faulting and erosion. In contrast, blueschist and eclogite mafic bodies are systematically associated with serpentinites and/or a mechanically weak matrix and crop out in an internal position in the orogen.Oceanic crust rarely records P conditions > 2.0–2.3 GPa, which suggests the existence of maximum depths for the sampling of slab-derived oceanic crust. On the basis of natural observations and calculations of the net buoyancy of the oceanic crust, we conclude that beyond depths around 70 km there are either not enough serpentinites and/or they are not light enough to compensate the negative buoyancy of the crust.Most importantly, this survey demonstrates that short-lived (< ～ 15 My), discontinuous exhumation is the rule for the oceanic crust and associated mantle rocks: exhumation takes place either early (group 1: Franciscan, Chile), late (group 2: New Caledonia, W. Alps) or incidentally (group 3: SE Zagros, Himalayas, Andes, N. Cuba) during the subduction history. This discontinuous exhumation is likely permitted by the specific thermal regime following the onset of a young, warm subduction (group 1), by continental subduction (group 2) or by a major, geodynamic modification of convergence across the subduction zone (group 3; change of kinematics, subduction of asperities, etc).Understanding what controls this short-lived exhumation and the detachment and migration of oceanic crustal slices along the subduction channel will provide useful insights into the interplate mechanical coupling in subduction zones. 相似文献
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The continental material of the Saih Hatat window has been affected by a Late Cretaceous, obduction-related, HP-LT metamorphism below the Oman ophiolite. A high-rate exhumation process is witnessed by the Maastrichtian-Palaeocene onlap onto the blueschist-facies rocks. Drastic metamorphic omissions are documented between the lowest, eclogitic units and the overlying, blueschist-facies ones. Widespread late-metamorphic shear structures point to a top-to-the-NNE detachment, in opposition to the sense of the Late Cretaceous obduction. The inversion of the shearing sense occurred under similar, low temperature conditions in both the blueschist and eclogite-facies units. Admitting that these HP-LT metamorphic rocks formed progressively at various depth in the subducting Arabian margin, a two-stage extensional mechanism of exhumation is suggested: (i) early uplift of the eclogitic rocks up to the blueschists depth by ductile thinning or squeezing of a 'blind extensional allochthon'; (ii) exhumation of the whole HP-LT metamorphic core complex by inversion of the obduction sole-thrust and isostatic rebound of the lower plate. 相似文献
18.
The transition between blueschists and lawsonite-bearing eclogites based on observations from Corsican metabasalts 总被引：2，自引：0，他引：2
Syntectonic eclogites, associated with blueschist parageneses, have recrystallized in metabasalts from eastern Corsica under very low temperatures (420°C). The evolution of these eclogites is recorded by the order of development of metamorphic minerals, as demonstrated by helicitic inclusions of lawsonite and actinolite in Fe-rich garnets, and the occurrence of fibrous Na-pyroxenes in the pressure shadows and cracks of boudinaged garnets, within a foliated matrix composed of glaucophane, Ca---Fe garnets and lawsonite.
A Schreinemakers analysis has been completed on the lawsonite-ferroglaucophane-actinolite-almandine-grossular-ferro-omphacite-chlorite system in a (T,P,μH2O)-space. The resulting three-dimensional relationships are applied to the studied samples. They are consistent with a prograde increase in temperature at low μH2O, producing eclogites from blueschists, and with a subsequent retrogressive decrease in pressure. 相似文献
19.
Hadi Omrani Mohssen Moazzen Roland Oberhänsli Uwe Altenberger Manuela Lange 《International Journal of Earth Sciences》2013,102(5):1491-1512
The Sabzevar ophiolites mark the Neotethys suture in east-north-central Iran. The Sabzevar metamorphic rocks, as part of the Cretaceous Sabzevar ophiolitic complex, consist of blueschist, amphibolite and greenschist. The Sabzevar blueschists contain sodic amphibole, epidote, phengite, calcite ± omphacite ± quartz. The epidote amphibolite is composed of sodic-calcic amphibole, epidote, albite, phengite, quartz ± omphacite, ilmenite and titanite. The greenschist contains chlorite, plagioclase and pyrite, as main minerals. Thermobarometry of a blueschist yields a pressure of 13–15.5 kbar at temperatures of 420–500 °C. Peak metamorphic temperature/depth ratios were low (~12 °C/km), consistent with metamorphism in a subduction zone. The presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field. Amphibole schist samples experienced pressures of 5–7 kbar and temperatures between 450 and 550 °C. The presence of chlorite, actinolite, biotite and titanite indicate greenschist facies metamorphism. Chlorite, albite and biotite replacing garnet or glaucophane suggests temperatures of >300 °C for greenschist facies. The formation of high-pressure metamorphic rocks is related to north-east-dipping subduction of the Neotethys oceanic crust and subsequent closure during lower Eocene between the Central Iranian Micro-continent and Eurasia (North Iran). 相似文献
20.
Giles T. R. Droop Muazzez . Karakaya Yaar Eren Necati Karakaya 《Geological Journal》2005,40(2):127-153
The Altınekin Complex in south central Turkey forms part of the south‐easterly extension of the Tavşanlı Zone, a Cretaceous subduction complex formed during the closure of the Neo‐Tethys ocean. The protoliths of metamorphic rocks within the Altınekin Complex include peridotites, chromitites, basalts, ferruginous cherts and flysch‐facies impure carbonate sediments. Structurally, the complex consists of a stack of thrust slices, with massive ophiolite tectonically overlying a Cretaceous sediment‐hosted ophiolitic mélange, in turn overlying a sequence of Mesozoic sediments. Rocks within the two lower structural units have undergone blueschist–facies metamorphism. Petrographic, mineral–chemical and thermobarometric studies were undertaken on selected samples of metasedimentary and metabasic rock in order to establish the time relations of deformation and metamorphism and to constrain metamorphic conditions. Microstructures record two phases of plastic deformation, one predating the metamorphic peak, and one postdating it. Estimated peak metamorphic pressures mostly fall in the range 9–11 kbar, corresponding to burial depths of 31–38 km, equivalent to the base of a continental crust of normal thickness. Best‐fit peak metamorphic temperatures range from 375 to 450°C. Metamorphic fluids had high H2O:CO2 ratios. Peak metamorphic temperature/depth ratios (T/d values) were low (c. 10–14°C/km), consistent with metamorphism in a subduction zone. Lawsonite‐bearing rocks in the southern part of the ophiolitic mélange record lower peak temperatures and T/d values than epidote blueschists elsewhere in the unit, hinting that the latter may consist of two or more thrust slices with different metamorphic histories. Differences in peak metamorphic conditions also exist between the ophiolitic mélange and the underlying metasediments. Rocks of the Altınekin Complex were subducted to much shallower depths, and experienced higher geothermal gradients, than those of the NW Tavşanlı Zone, possibly indicating dramatic lateral variation in subduction style. Retrograde P–T paths in the Altınekin Complex were strongly decompressive, resulting in localized overprinting of epidote blueschists by greenschist–facies assemblages, and of lawsonite blueschists by pumpellyite–facies assemblages. The observation that the second deformation was associated with decompression is consistent with, but not proof of, exhumation by a process that involved deformation of the hanging‐wall wedge, such as gravitational spreading, corner flow or buoyancy‐driven shallowing of the subduction zone. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献