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1.
《Russian Geology and Geophysics》2014,55(5-6):649-667
Consolidated crust in the North Barents basin with sediments 16–18 km thick is attenuated approximately by two times. The normal faults in the basin basement ensure only 10-15% stretching, which caused the deposition of 2–3 km sediments during the early evolution of the basin. The overlying 16 km of sediments have accumulated since the Late Devonian. Judging by the undisturbed reflectors to a depth of 8 s, crustal subsidence was not accompanied by any significant stretching throughout that time. Dramatic subsidence under such conditions required considerable contraction of lithospheric rocks. The contraction was mainly due to high-grade metamorphism in mafic rocks in the lower crust. The metamorphism was favored by increasing pressure and temperature in the lower crust with the accumulation of a thick layer of sediments. According to gravity data, the Moho in the basin is underlain by large masses of high-velocity eclogites, which are denser than mantle peridotites. The same is typical of some other ultradeep basins: North Caspian, South Caspian, North Chukchi, and Gulf of Mexico basins. From Late Devonian to Late Jurassic, several episodes of rapid crustal subsidence took place in the North Barents basin, which is typical of large petroleum basins. The subsidence was due to metamorphism in the lower crust, when it was infiltrated by mantle-source fluids in several episodes. The metamorphic contraction in the lower crust gave rise to deep-water basins with sediments with a high content of unoxidized organic matter. Along with numerous structural and nonstructural traps in the cover of the North Barents basin, this is strong evidence that the North Barents basin is a large hydrocarbon basin. 相似文献
2.
榴辉岩的弹性波速评述 总被引：2，自引：0，他引：2
文中评述了榴辉岩的密度和高温高压下的纵波速度、速度各向异性、泊松比以及榴辉岩声软化现象的成因 ,着重介绍了榴辉岩的密度和波速对探讨岩石圈物质组成、莫霍界面性质、超高压岩石对实现壳幔物质交换的重要意义。榴辉岩的密度为 3 2～ 3 6 5g·cm-3 ,其中超高压榴辉岩具有更高的密度 (3 4～ 3 6 5g·cm-3 )。榴辉岩的纵波速度 (vp)在 1GPa时为 7 3～8 9km·s-1,其裂隙闭合压力可能高于 1GPa。榴辉岩的压力系数为 0 3～ 0 4km·s-1·GPa-1,温度系数为 - 3 4× 10 -4 km·s-1·℃ -1。它具有最弱的vP 各向异性 (<3% )。超高压榴辉岩的泊松比为 0 2 54～ 0 2 75。大别山榴辉岩的密度和波速研究表明 ,现今的大别山深部地壳可能依然存在榴辉岩 ,但数量应很少 ;大别山上地幔具有同超高压榴辉岩类似的弹性特征 ;拆沉作用是解释超高压榴辉岩折返机制的重要模式之一 ;榴辉岩的形成过程包含了壳幔物质循环作用 ,一部分榴辉岩已拆沉进入深部地幔 ,另一部分则快速折返至地壳内或通过其他构造作用进一步抬升、暴露地表。 相似文献
3.
"罗田穹隆"中的下地壳俯冲成因榴辉岩及其地质意义 总被引：12，自引：0，他引：12
在“罗田穹隆”中发现了下地壳俯冲成因榴辉岩．榴辉岩呈透镜状或板状产于含石榴子石条带状片麻岩中．新鲜的榴辉岩主要由石榴子石、绿辉石、金红石等组成．含少量退变质的角闪石、斜长石、紫苏辉石、透辉石、(钛)磁铁矿和石英等．研究区榴辉岩以保留早期麻粒岩相变质矿物残留体以及经受晚期麻粒岩相和角闪岩相退变为特征．指示它们由扬子镁铁质下地壳麻粒岩相岩石俯冲到深部发生变质并形成榴辉岩．然后折返至下地壳发生麻粒岩相退变，由于麻粒岩相退变质阶段仅以后成合晶形式出现．因而它们可能在下地壳停留时间不长．就又进一步被构造抬升至中上地壳而发生角闪岩相退变．大别山造山带乃至扬子板块北缘现今缺乏厚层镁铁质下地壳．它们也很少出露地表．推测这些俯冲的镁铁质下地壳可能已拆离再循环进人地幔．从而为“罗田穹隆”的形成和演化以及大别山高压-超高压岩石的形成与折返机制等研究提供了关键性的岩石学证据。 相似文献
4.
苏北榴辉岩成因类型及其形成条件 总被引：5，自引：0，他引：5
苏北榴辉岩至少存在高压壳源型（Ｈ型）、超高压壳源型（Ｕ型）和幔源型（Ｍ型）三类。其中Ｈ型榴辉岩的石榴石为铁铝榴石,具正环带结构,单斜辉石属低硬玉绿辉石,主要形成于晋宁期低温高压变质条件下的下地壳;Ｕ型榴辉岩含微粒金刚石（？）、柯石英及其假象等,发育放射状胀裂结构和正、反环带结构,石榴石为钙铝榴石,单斜辉石属高硬玉绿辉石,主要形成于印支期高温超高压变质条件下的上地幔;Ｍ型榴辉岩的石榴石属镁铝榴石,形成于晋宁期高温超高压条件下的岩石圈与软流圈交界附近。 相似文献
5.
苏北榴辉岩成因型及其形成条件 总被引：4，自引：0，他引：4
苏北榴辉岩至少存在高度压壳源型（Ｈ型）、超高压壳源型（Ｕ型）和幔源型（Ｍ型）三类。其中Ｈ型榴辉岩的石榴石为铁铝榴石,具正环带结构,单斜辉石属低硬玉绿辉石,主要形成于晋宁期低温度高压变质条件下的下地壳;Ｕ型榴辉岩含微粒金刚石（？）、柯石英及其假象等,发育放射状胀裂结构和正、反环带结构、石榴石为钙铝榴石、单斜辉石属高硬玉绿辉石,主要形成于印支期高温超高压变质条件下的上地幔;Ｍ型榴辉岩的石榴石属镁铝榴石 相似文献
6.
A crustal origin for eclogites and a mantle origin for garnet peridotites: Strontium isotopic evidence from clinopyroxenes 总被引：1，自引：0，他引：1
Hannes K. Brueckner 《Contributions to Mineralogy and Petrology》1977,60(1):1-15
Strontium isotopic data suggest that the classic eclogite-facies rocks of western south Norway described by Eskola (1921) formed from several parental materials in a variety of environments. Mineral separates from essentially basic, bi-minerallic (clinopyroxene and garnet) eclogites that occur as lens-shaped masses within high grade gneisses (country rock eclogites) have Sr87/Sr86 values that range from 0.704 for fine-grained varieties to 0.716 for coarse-grained, orthopyroxene-bearing varieties. These high, varied ratios contrast with the very low, restricted ratios (0.701 to 0.704) of similar minerals from ultrabasic, garnet-clinopyroxene-orthopyroxene-olivine assemblages (garnet peridotites) that occur as lenses within large peridotite bodies. The eclogite-facies metamorphism that generated the garnet peridotites may have occurred in the mantle. However, the metamorphism that generated at least the more radiogenic country-rock eclogites must have occurred in the crust. The high Sr87/Sr86 ratios of these eclogites could be generated either by forming them from crustal parental rocks or by contaminating mantle-derived parental rocks with radiogenic strontium from the country rocks. If this contamination occurred after intrusion and before eclogite-facies metamorphism, a rather contrived history must be postulated that involves intrusion, contamination accompanied by hydration, subsequent dehydration, and finally eclogite-facies metamorphism. These processes could have occurred within the long, complicated history of the enclosing country rocks. Alternatively, if the contamination occurred during eclogite-facies metamorphism, the presence of some hydrous fluid appears to be required to transport the radiogenic strontium from the enclosing country rocks. The eclogites with the highest Sr87/Sr86 ratios are also the most coarse-grained and it is possible that the presence of some intergranular fluid enabled these eclogites to recrystallize to a much larger grain size than would have been possible in a totally anhydrous environment. The garnet peridotites and fine-grained country rock eclogites may have formed from mantle material in the crust but escaped contamination by radiogenic strontium as a result of their position in a dry environment in the crust.Lamont-Doherty Geological Observatory Contribution No. 2443 相似文献
7.
大别山南部的超高压变质岩在其形成及折返过程中经过5期变形。D1变形为榴辉岩相前变形,形成于扬子板块北缘陆壳基底的俯冲过程中;D2变形形成于折返初期(220-210Ma)即超高压变质岩在浮力驱动下折返至下地壳底部的过程中,变形以块状榴辉岩的糜棱岩化及层状榴辉岩和基质的紧密-同斜褶皱为特征;D3变形发生在折返中期(200-180Ma)即超高压变质岩在南北陆块持续碰撞作用下被挤出并向北逆冲折返至中地壳的过程中,变形以榴辉岩的布丁化和基质的强烈韧性剪切变形为特征;D4变形是折返晚期(130-110Ma)超高压变质岩在地壳浅部伸展体制下向南滑脱所致;在折返至近地表时,超高压变质岩受到NE向断层(D5)的切割。 相似文献
8.
E.V. Artyushkov 《Russian Geology and Geophysics》2010,51(1):48-57
The large North Chukchi Basin in the northeastern Eurasian shelf is filled with up to 22 km of sediments, which is far thicker than filling a basin upon oceanic crust would require. The basin sedimentation began 380 Myr ago, and about 16 km of sediments have been deposited for the past 125 Myr, long after the oceanic crust would have completed its subsidence. This fact is in favor of the continental instead of oceanic crust origin. Rapid basin subsidence appears to be driven by a mechanism other than crustal stretching as the latter has no evidence over the greatest part of the basin area. The suggested basin formation model implies a transformation of gabbro into denser eclogite in the lower crust and related contraction of mafic rocks. To sustain consolidated crust beneath 22 km thick sediments, the layer of dense eclogites under the granitic layer must be at least ～25 km thick. The presence of basement flexures formed at several stages of the basin evolution indicates a considerable loss of lithospheric rigidity under the effect of fluid infiltration from small mantle plumes. The fluids catalyzed the eclogitization and thus increased the subsidence rate. Rapid subsidence apparently occurred in Barremian-Albian time when the basin had accumulated up to 11.5 km of sediments. Besides the Early Cretaceous event, there were, possibly several older events of rapid subsidence. This basin subsidence history, along with the evidence of steep lithospheric flexure, is a known feature of large petroleum basins. Therefore, the North Chukchi Basin may be expected to be an oil and gas producer. 相似文献
9.
1NTRoDUCTIONSincecoesiteandmicro-diamondinclusionswerefoundinDabieshaninl98Os,someimportantresultsofgeology,geo-chemistryandgeophysicsoftheDabieultrahighpressuremetamorphicbelthavebeenachieved(seethereviewofCongandWang,l994;Wangetal.,l997).Butthereisverylittleexperimentalstudyofphysicalpropertiesofthemetamorphicrockstillnow(HarleyandCarswell,l995).Elasticwaveve-locityisoneofthemostimportantparametersofrocks,whichisabridgeconnectinggeochemistryandgeophysics.Itwillbehelpfulindiscussingthe… 相似文献
10.
Eugene V. Artyushkov Michael A. Baer Peter A. Chekhovich Nils-Axel Mrner 《Tectonophysics》2000,320(3-4):271-310
An analysis is presented of the mechanisms of tectonic evolution of the southern part of the Urals between 48N and 60N in the Carboniferous–Triassic. A low tectonic activity was typical of the area in the Early Carboniferous — after closure of the Uralian ocean in the Late Devonian. A nappe, ≥10–15 km thick, overrode a shallow-water shelf on the margin of the East European platform in the early Late Carboniferous. It is commonly supposed that strong shortening and thickening of continental crust result in mountain building. However, no high mountains were formed, and the nappe surface reached the altitude of only ≤0.5 km. No high topography was formed after another collisional events at the end of the Late Carboniferous, in the second half of the Early Permian, and at the start of the Middle Triassic. A low magnitude of the crustal uplift in the regions of collision indicates a synchronous density increase from rapid metamorphism in mafic rocks in the lower crust. This required infiltration of volatiles from the asthenosphere as a catalyst. A layer of dense mafic rocks, 20 km thick, still exists at the base of the Uralian crust. It maintains the crust, up to 60 km thick, at a mean altitude 0.5 km. The mountains, 1.5 km high, were formed in the Late Permian and Early Triassic when there was no collision. Their moderate height precluded asthenospheric upwelling to the base of the crust, which at that time was 65–70 km thick. The mountains could be formed due to delamination of the lower part of mantle root with blocks of dense eclogite and/or retrogression in a presence of fluids of eclogites in the lower crust into less dense facies.
The formation of foreland basins is commonly attributed to deflection of the elastic lithosphere under surface and subsurface loads in thrust belts. Most of tectonic subsidence on the Uralian foreland occurred in a form of short impulses, a few million years long each. They took place at the beginning and at the end of the Late Carboniferous, and in the Late Permian. Rapid crustal subsidence occurred when there was no collision in the Urals. Furthermore, the basin deepened away from thrust belt. These features preclude deflection of the elastic lithosphere as a subsidence mechanism. To ensure the subsidence, a rapid density increase was necessary. It took place due to metamorphism in the lower crust under infiltration of volatiles.
The absence of flexural reaction on the Uralian foreland on collision in thrust belt together with narrow-wavelength basement deformations under the nappe indicate a high degree of weakening of the lithosphere. Such deformations took also place on the Uralian foreland at the epochs of rapid subsidences when there was no collision in thrust belt. Weakening of the lithosphere can be explained by infiltration of volatiles into this layer from the asthenosphere and rapid metamorphism in the mafic lower crust. Lithospheric weakening allowed the formation of the Uralian thrust belt under convergent motions of the plates which were separated by weak areas. 相似文献
11.
盆地形成及成矿与地幔流体间的成因联系 总被引：11，自引：0，他引：11
文中共讨论以下5个问题:(1)盆地起源于幔壳溃变和膨隆,后者是地幔流体(超临界态(>375℃)HACONS流体,简称幔汁)上涌、渗入、交代、富化、致熔的产物。地幔流体造成油气盆地深部的高热流、异常超高压、伊利水云母化、硅化和地层有机碳的加氢成油作用。(2)盆地成矿可分两大阶段,先是沉积时的同生成矿;地层沉积后还有众多的后生成矿。两者组成“盆地矿套”(杜乐天,2002)。成矿无论同生还是后生,其分布均受断裂控制,都和地幔流体活动有关。(3)黑色页岩的实质是碳-硅-泥三元岩系,和热液成矿中的碳酸盐-硅质-泥质蚀变三元完全相当。此类岩系中总是有几十种亲壳亲幔亲气元素的特殊富集。奇异的是,石油、油页岩、沥青及砂岩型铀矿彼此有完全类似的继承性元素特殊富集。此等元素群不可能都是来自盆地之外蚀源区岩体的风化。研究证明,相当多的元素是地幔流体携带上来的。(4)盆地地层中广泛发育由地幔流体衍生的热液作用。(5)盆地实质上是气盆,全盆地排气。许多气田是地幔流体排气形成的。沙漠(原地型)和天然气田的共生很值得注意,两者皆源于地球强烈排气,导致地下和大气增温,过度蒸发,不易降雨,长期干旱而形成沙漠。 相似文献
12.
Guochun ZHAO LIU Shuwen Min SUN LI Sanzhong Simon WILDE Xiaoping XIA Jian ZHANG Yanhong HE 《《地质学报》英文版》2006,80(6):790-806
The Trans-North China Orogen （TNCO） was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton （NCC）. Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greeustone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages. Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic （TTG） magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, -2250 Ma 2110-21760 Ma and -2050 Ma granites in the orogen. Contemporary volcano-sedimentary rocks developed in the back-arc or intra-are basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge, leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and the dosing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and transported some of the rocks into the lower crustal levels or upper mantle to form granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of asymmetric folds and symplectic textures in the rocks. 相似文献
13.
大别山榴辉岩的密度和波速及其对壳—幔循环的启示 总被引：7，自引：0，他引：7
测定了大别山地区榴辉岩和麻粒岩的密度和高温高压 (至 5 .0GPa和 130 0℃ )的纵波速度 (Vp)。超高压榴辉岩具有较高的密度和Vp 及较弱的各向异性。榴辉岩的压力系数为 0 .2 2～ 0 .33km/s·GPa ,超高压榴辉岩的温度系数为 - 3.41× 10 -4 km/s·℃。榴辉岩的密度和波速的分析表明 ,地幔深部的超高压榴辉岩形成后可能包含了两个过程 ,即一部分榴辉岩通过拆沉作用进入深部地幔 ,另一部分快速折返至地壳内或地表 ,榴辉岩的形成过程代表了壳幔物质循环。现今的大别山深部可能只存在少量榴辉岩。 相似文献
14.
变质流体研究新进展 总被引：7，自引：2，他引：7
变质流体是变质过程的主要动力学因素之一。目前变质流体研究主要集中在下部地壳麻粒岩相变质流体，俯冲带高压－超高压变质流体和接触变质流体等方面。研究的主要问题是流体流动机制和元素迁移，流体－岩石相互作用和流体来源。下部地壳麻粒岩相变质流体以ＣＯ２为主，具有较低的ａＨ２Ｏ。δ１３Ｃ研究表明大约２／３ＣＯ２是深成的。富ＣＯ２流体流动是紫苏花岗岩形成和热扰动的原因之一，也是麻粒岩形成和大离子亲石元素亏损的主要因素。俯冲带是高压、超高压变质作用发生和流体活动最活跃的场所。流体富含Ｈ２Ｏ、ＣＨ４和ＣＯ２，可以诱导部分熔融反应和岛弧岩浆作用。高压变质条件下的矿物稳定性也与流体有关。同位素研究表明，在超高压变质期间没有化学上完全相同的流体大规模循环。流体－熔体系统模式能更有效地解释下插板片的元素再循环。接触变质流体研究主要集中在含有易于发生流体－岩石反应的不纯碳酸盐岩地区。硅灰石带中流体／岩石比率高达４０∶１，表明接触变质岩石中有大量流体存在。接触变质过程流体成分有较大差异，主要取决于流体来源、原岩性质和侵入体特征。流体流动和循环模式受控于构造变形，岩浆作用和变质过程的动力学条件及流体成分。 相似文献
15.
下地壳拆沉作用及大陆地壳演化 总被引：13，自引：0，他引：13
讨论了下地壳拆沉作用的地球化学示踪方法,并以近来对秦岭－大别造山带和美国西部内华达岩基地区的研究成果为例,说明了下地壳拆沉在两地区壳－幔演化方面可能起的重要作用。 相似文献
16.
It has been suggested that eclogites in the Dabie orogenic belt are exhumation prod-ucts, which had subducted into the deep-seated mantle and undergone ultra-high pressure meta-morphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometem. The Late Cretaceous basalts studied in the pres-ent paper, however, have provided some geochemical evidence for crust-mantle interaction in the area. These basalts are distributed in Mesozoic faulted basins in central and southern Dabieorogenic belt. Since little obvious contamination from continental crust and differentiation-crys-tallization were observed, it is suggested, based on a study of trace elements, that the basaltsare alkaline and resultant from batch partial melting of the regional mantle rocks, and share thesame or similar geochemical features with respect to their magma source. In the spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrated in the continental crust, such as Pb, K,Rb and Ba, and slightly depleted in some HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic com-positions further suggest the mantle is the mixture of depleted mantle (DM) and enriched one(EMI EMII). This interaction can .explain the trace element characteristics of basaltic mag-mas, i.e.,the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpre-ted by the blending of the eclogites in DOB (enriched in Pb and depleted in Hf, P and Nd)with the East China depleted mantle (As compared to the primitive mantle, it is neither en-riched in Pb nor depleted in Hf, P and Nb). It is also indicated that the eclogites in the Dahieorogenic belt were surely derived from the exhumation materials, which had delaminated into thedeep-seated mantle. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes) , as revealed by the late mantle-derivedbasalts in the Dabie orogenic belt. 相似文献
17.
《Russian Geology and Geophysics》2016,57(5):713-722
Despite the violent eruption of the Siberian Traps at ~ 250 Ma, the Siberian craton has an extremely low heat flow (18–25 mW/m2) and a very thick lithosphere (300–350 km), which makes it an ideal place to study the influence of mantle plumes on the long-term stability of cratons. Compared with seismic velocities of rocks, the lower crust of the Siberian craton is composed mainly of mafic granulites and could be rather heterogeneous in composition. The very high Vp (> 7.2 km/s) in the lowermost crust can be fit by a mixture of garnet granulites, two-pyroxene granulites, and garnet gabbro due to magma underplating. The high-velocity anomaly in the upper mantle (Vp = 8.3-8.6 km/s) can be interpreted by a mixture of eclogites and garnet peridotites. Combined with the study of lower crustal and mantle xenoliths, we recognized multistage magma underplating at the crust-mantle boundary beneath the Siberian craton, including the Neoarchean growth and Paleoproterozoic assembly of the Siberian craton beneath the Markha terrane, the Proterozoic collision along the Sayan-Taimyr suture zone, and the Triassic Siberian Trap event beneath the central Tunguska basin. The Moho becomes a metamorphism boundary of mafic rocks between granulite facies and eclogite facies rather than a chemical boundary that separates the mafic lower crust from the ultramafic upper mantle. Therefore, multistage magma underplating since the Neoarchean will result in a seismic Moho shallower than the petrologic Moho. Such magmatism-induced compositional change and dehydration will increase viscosity of the lithospheric mantle, and finally trigger lithospheric thickening after mantle plume activity. Hence, mantle plumes are not the key factor for craton destruction. 相似文献
18.
The superdeep North Caspian, South Caspian, and Barents basins have their sedimentary fill much thicker and the Moho, correspondingly, much deeper than it is required for crustal subsidence by lithospheric stretching. In the absence of large gravity anomalies, this crustal structure indicates the presence under the Moho of a thick layer of eclogite which is denser than mantle peridotite. Crustal subsidence in the basins can be explained by high-grade metamorphism of mafic lower crust. The basins produced by lithospheric stretching normally subside for the first ～100 myr of their history, while at least half of the subsidence in the three basins occurred after that period, which is another evidence against the stretching formation mechanism. According to the seismic reflection profiling data, stretching can be responsible for only a minor part of the subsidence in the Caspian and Barents basins. As for the South Caspian basin, there has been a large recent subsidence event in a setting of compression. Therefore, eclogitization appears to be a realistic mechanism of crustal subsidence in superdeep basins. 相似文献
19.
苏鲁超高压带内石桥浅变质岩的地质成因及其研究意义 总被引：1，自引：1，他引：0
苏鲁造山带超高压变质带内部出露仅经过绿片岩相变质作用的浅变质岩系,地质调查显示,石桥浅变质岩与周边超高压变质岩呈构造接触(构造片岩);地球化学研究证实,该浅变质岩形成于扬子板块北缘大陆边缘厚地壳上裂陷或沉积盆地的构造背景;单矿物电子探针分析结果显示,其部分浅变质岩发育多硅白云母,形成于中-高压相变质环境,说明这些浅变质岩曾经历大陆板块俯冲的动力变质作用过程。在此基础上,进一步讨论浅变质岩的成因机制及其与超高压变质岩和扬子板块俯冲之间的关系。 相似文献
20.
对四道河地区超高压变质岩剖面的研究分析显示,该剖面有3种岩石类型:榴辉岩类、片麻岩和面理化含榴花岗岩。榴辉岩具不同程度的退变质现象,呈透镜体状产出于斜长角闪岩、片麻岩和面理化含榴花岗岩中,原生矿物组合为石榴石、绿辉石、柯石英和金红石。榴辉岩退变为斜长角闪岩近于等化学系列;片麻岩在主量成分上与榴辉岩及其退变产物(斜长角闪岩)存在突变关系,但微量元素与榴辉岩有一定的相似性;面理化含榴花岗岩主量元素和微量元素地球化学特点为:富SiO2 、K2 O Na2 O和高价阳离子Ga、Y以及REE ,K2 O/Na2 O值低,贫Al、Ca、Mg、Ti、P ,结合构造环境、同位素及年代学资料分析,其应属于后碰撞造山A型花岗岩。基于以上认识推断:大陆板片俯冲至上地幔经历了超高压变质作用,表壳岩变质形成榴辉岩;当超高压变质岩石折返至中下地壳时发生了强烈的减压退变质作用形成斜长角闪岩,随后,与片麻岩及面理化含榴花岗岩一道从中下地壳向地表进一步折返,并一同经历了后期的变质变形作用。 相似文献