西准噶尔蛇绿混杂岩中洋岛玄武岩研究新进展   总被引：2，自引：0，他引：2  

杨高学  李永军  佟丽莉  杨宝凯  张胜龙  沈锐  段丰浩 《地质学报》2015,89(2):392-405

洋岛玄武岩(OIB)起源研究是当代固体地球岩石学及地球化学最基本问题之一,通常被认为源于地幔柱。西准噶尔位于中亚造山带的西南缘,该地区发育多条蛇绿混杂岩带,主要包括唐巴勒、玛依勒、达尔布特及克拉玛依蛇绿混杂岩带,它们组成相似,主要为蛇纹岩、蛇纹石化方辉橄榄岩、二辉橄榄岩、纯橄岩、铬铁矿、辉石岩、辉长岩、辉绿岩、玄武岩(拉斑质和碱性)、硅质岩及斜长花岗岩。随着研究的不断深入,在西准噶尔蛇绿混杂岩带中不断有不同时代OIB被识别。这些玄武岩属于碱性玄武岩系列,具有高TiO2和FeOt,低MgO,强烈富集轻稀土元素特征,没有明显Nb、Ta负异常,与日喀则及夏威夷洋岛玄武岩地球化学特征极为相似,可能形成于大洋板内的海山或洋底高原,认为其成因与地幔柱相关,表明在西准噶尔(洋)的演化过程中,不仅是洋内俯冲系统,还伴有地幔柱活动。结合前人研究,认为中亚造山带可能是洋内俯冲+地幔柱复合的演化模型。同时,对中亚造山带中的OIB及OIB型玄武岩形成时代进行系统总结发现,它们不仅时代宽度大,并且具有连续发育的特点。对正确认识地幔柱活动在显生宙中亚造山带地壳增生过程中的贡献提供新的资料和证据。  相似文献   

Anatomy of a subduction complex: architecture of the Franciscan Complex,California, at multiple length and time scales   总被引：1，自引：0，他引：1  

John Wakabayashi 《International Geology Review》2015,57(5-8):669-746

The Franciscan Complex of California records over 150 million years of continuous E-dipping subduction that terminated with conversion to a dextral transform plate boundary. The Franciscan comprises mélange and coherent units forming a stack of thrust nappes, with significant along-strike variability, and downward-decreasing metamorphic grade and accretion ages. The Franciscan records progressive subduction, accretion, metamorphism, and exhumation, spanning the extended period of subduction, rather than events superimposed on pre-existing stratigraphy. High-pressure (HP) metamorphic rocks lack a thermal overprint, indicating continuity of subduction from subduction initiation at ca. 165 Ma to termination at ca. 25 Ma. Accretionary periods may have alternated with episodes of subduction erosion that removed some previously accreted material, but the complex collectively reflects a net addition of material to the upper plate. Mélanges (serpentinite and siliciclastic matrix) with exotic blocks have sedimentary origins as submarine mass transport deposits, whereas mélanges formed by tectonism comprise disrupted ocean plate stratigraphy and lack exotic blocks. The former are interbedded with and grade into coherent siliciclastic units. Palaeomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow zones of <100 m thickness. Exhumation of Franciscan units, both coherent and mélange, was accommodated by significant extension of the hanging wall and cross-sectional extrusion. The amount of total exhumation, as well as exhumation since subduction termination, needs to be considered when comparing Franciscan architecture to modern and ancient subduction complexes. Equal dextral separation of folded Franciscan nappes and late Cenozoic (post-subduction) units across strands of the (post-subduction) San Andreas fault system shows that the folding of nappes took place prior to subduction termination. Dextral separation of similar clastic sedimentary suites in the Franciscan and the coeval Great Valley Group forearc basin is approximately that of the San Andreas fault system, precluding major syn-subduction strike-slip displacement within the Franciscan.  相似文献   

The Central Bundelkhand Archaean greenstone complex,Bundelkhand craton,central India: geology,composition, and geochronology of supracrustal rocks     

Vinod K. Singh  Alexander Slabunov 《International Geology Review》2015,57(11-12):1349-1364

Analysis of 3.3 Ga tonalite–trondhjemite–granodiorite (TTG) series granitoids and greenstone belt assemblages from the Bundelkhand craton in central India reveal that it is a typical Archaean craton. At least two greenstone complexes can be recognized in the Bundelkhand craton, namely the (i) Central Bundelkhand (Babina, Mauranipur belts) and (ii) Southern Bundelkhand (Girar, Madaura belts). The Central Bundelkhand greenstone complex contains three tectonostratigraphic assemblages: (1) metamorphosed basic or metabasic, high-Mg rocks; (2) banded iron formations (BIFs); and (3) felsic volcanics. The first two assemblages are regarded as representing an earlier sequence, which is in tectonic contact with the felsic volcanics. However, the contact between the BIFs and mafic volcanics is also evidently tectonic. Metabasic high-Mg rocks are represented by amphibolites and tremolite-actinolite schists in the Babina greenstone belt and are comparable in composition to tholeiitic basalts-basaltic andesites and komatiites. They are very similar to the metabasic high-Mg rocks of the Mauranipur greenstone belt. Felsic volcanics occur as fine-grained schists with phenocrysts of quartz, albite, and microcline. Felsic volcanics are classified as calc-alkaline dacites, less commonly rhyolites. The chondrite-normalized rare earth element distribution pattern is poorly fractionated (La_N/Lu_N = 11–16) with a small negative Eu anomaly (Eu/Eu* = 0.68–0.85), being characteristic of volcanics formed in a subduction setting. On Rb – Y + Nb, Nb – Y, Rb – Ta + Yb and Ta – Yb discrimination diagrams, the compositions of the volcanics are also consistent with those of felsic rocks formed in subduction settings. SHRIMP-dating of zircon from the felsic volcanics of the Babina belt of the Central Bundelkhand greenstone complex, performed for the first time, has shown that they were erupted in Neoarchaean time (2542 ± 17 Ma). The early sequence of the Babina belt is correlatable with the rocks of the Mauranipur belt, whose age is tentatively estimated as Mesoarchaean. The Central Bundelkhand greenstone complex consists of two (Meso- and Neoarchaean) sequences, which were formed in subduction settings.  相似文献   

Geochemical constraints on the contribution of Louisville seamount materials to magmagenesis in the Lau back-arc basin,SW Pacific     

Zheng-Gang Li  Yan-Hui Dong  Ji-Qiang Liu  Ling Chen 《International Geology Review》2015,57(5-8):978-997

Seamounts are an integral part of element recycling in global subduction zones. The published trace element and Pb-Sr-Nd isotope data for basaltic lavas from three key segments (Central Lau Spreading Ridge (CLSR), Eastern Lau Spreading Ridge (ELSR), and Valu Fa Ridge (VFR)) of the Lau back-arc basin were compiled to evaluate the contribution of Louisville seamount materials to their magma genesis. Two geochemical transitions, separating three provinces with distinct geochemical characteristics independent of ridge segmentation, were identified based on abrupt geochemical shifts. The origin of the geochemical transitions was determined to be the result of drastic compositional changes of subduction components added into the mantle source, rather than the transition from Indian to Pacific mid-ocean ridge basalt (MORB) mantle, or due to variable mantle fertilities. The most likely explanation for the drastic shifts in subduction input is the superimposition of Louisville materials on ‘normal’ subduction components consisting predominantly of aqueous fluids liberated from the down-going altered oceanic crust and minor pelagic sediment melts. Quantitative estimation reveals that Louisville materials contributed 0–74% and 21–83% of the Th budget, respectively, to CLSR and VFR lavas, but had no definite contribution to the lavas from the ELSR, which lies farthest away from the subducted Louisville seamount chain (LSC). The spatial association of the subducted LSC with the Louisville-affected segments suggests that the Louisville signature is regionally but not locally available in the Tonga subduction zone. Besides, the preferential melting of subducted old Cretaceous LSC crust instead of the old normal Pacific oceanic crust at similar depths implies that elevated temperature across the subduction interface or seamount erosion and rupture were required to trigger melting. A wider implication of this study, thus, is that seamount subduction may promote efficiency of element recycling in subduction zones.  相似文献   

尼泊尔Ms8.1地震构造背景及对周边地区地震活动趋势的影响     

雷东宁  蔡永建  李恒  吴建超  乔岳强  余松  廉超 《大地测量与地球动力学》2015,35(5):738-741

分析印度板块与欧亚板块俯冲带、尼泊尔Ms8.1地震震中区地震构造及地震发震构造,讨论主震对余震触发及余震的时空强特征和地震对周边地区地震活动趋势的影响。初步分析认为,主边界断裂为本次地震的发震构造,属于低角度逆冲断层地震;余震分布范围与震源破裂面积和方式基本一致,具有向东迁移的时空特征;西藏定日Ms5.9、聂拉木Ms5.3地震不属于尼泊尔地震余震,是应力扰动的结果;沿俯冲带向东至喜马拉雅东构造结是大震发生的危险地段。  相似文献   

Migrating magmatism in a continental arc: Geodynamics of the Eastern Mediterranean revisited   总被引：1，自引：0，他引：1  

Yener Eyuboglu  M. Santosh  Francis O. Dudas  Sun-Lin Chung  Enver Akaryal&#x; 《Journal of Geodynamics》2011,52(1):2-15

  相似文献   

Eclogitization of the Monviso ophiolite (W. Alps) and implications on subduction dynamics     

S. ANGIBOUST  R. LANGDON  P. AGARD  D. WATERS  C. CHOPIN 《Journal of Metamorphic Geology》2012,30(1):37-61

To constrain deep (40–100 km) subduction dynamics, extensive P–T data are provided on the eclogitic Monviso ophiolite derived from the subducted Liguro‐Piemontese oceanic lithosphere (which was exhumed, together with associated continental units, before the Alpine collision). The Monviso ophiolite has so far been interpreted either as a fossilized subduction channel, with tectonic blocks detached from the slab at different depths and gathered in a weak serpentinized matrix, or as a more or less continuous portion of oceanic lithosphere. To evaluate potential heterogeneities within and between the various subunits, extensive sampling was undertaken on metasedimentary rocks and Fe–Ti metagabbros. The results indicate that the Monviso ophiolite comprises two main coherent tectonic subunits (the Monviso and Lago Superiore Units) detached during subduction at different depths and later juxtaposed at epidote–blueschist facies during exhumation along the subduction interface. Raman spectroscopy of carbonaceous material suggests (i) a difference in peak temperature of ～50 °C between these two subunits and (ii) a good temperature homogeneity within each subunit. Pseudosections and average P–T estimates using thermocalc in the Lago Superiore Unit suggest for the first time homogeneous HP to UHP conditions (～550 °C, 26–27 kbar). Parageneses, peak conditions and tectonic setting are very similar to those of the Zermatt‐Saas ophiolite, 200 km northwards, thus suggesting a common detachment mechanism for the whole Western Alpine belt.  相似文献   

Metamorphic evolution of the Naga Hills eclogite and blueschist, Northeast India: implications for early subduction of the Indian plate under the Burma microplate     

N. CHATTERJEE  N. C. GHOSE 《Journal of Metamorphic Geology》2010,28(2):209-225

Tectonic slices and lenses of eclogite within mafic and ultramafic rocks of the Early Cretaceous–Eocene Naga Hills ophiolite were studied to constrain the physical conditions of eastward subduction of the Indian plate under the Burma microplate and convergence rate prior to the India–Eurasia collision. Some of the lenses are composed of eclogite, garnet-blueschist, glaucophanite and greenschist from core to margin, representing a retrograde hydrothermal alteration sequence. Barroisite, garnet, omphacite and epidote with minor chlorite, phengite, rutile and quartz constitute the peak metamorphic assemblage. In eclogite and garnet-blueschist, garnet shows an increase in Mg and Fe and decrease in Mn from core to rim. In chlorite in eclogite, Mg increases from core to rim. Inclusions of epidote, glaucophane, omphacite and quartz in garnet represent the pre-peak assemblage. Glaucophane also occurs profusely at the rims of barroisite. The matrix glaucophane and epidote represent the post-peak assemblage. The Fe³⁺ content of garnet-hosted omphacite is higher than that of matrix omphacite, and Fe³⁺ increases from core to rim in matrix glaucophane. Albite occurs in late stage veins. P – T pseudosection analysis indicates that the Naga Hills eclogites followed a clockwise P – T path with prograde metamorphism beginning at ∼1.3 GPa/525 °C and peaking at 1.7–2.0 GPa/580–610 °C, and subsequent retrogression to ∼1.1 GPa/540 °C. A comparison of these P – T conditions with numerical thermal models of plate subduction indicates that the Naga Hills eclogites probably formed near the top of the subducting crust with convergence rates of ∼ 55–100 km Myr⁻¹, consistent with high pre-collision convergence rates between India and Eurasia.  相似文献   

俯冲带板内地震竖向位移谱阻尼修正系数模型研究          下载免费PDF全文

王本三  靳羽阳  刘名吉 《世界地震工程》2022,38(1):175-189

基于日本K-NET和KiK-net台网中4695条俯冲板内地震记录的竖向分量,建立了位移谱阻尼修正系数(DMF)模型.采用基于场地周期的场地分类方法,并通过固定效应法推导出模型系数.该DMF模型考虑了谱周期、阻尼比和场地条件的影响,可以用来调整与震源和距离无关的设计反应谱.利用阻尼比对数的二次方程式对原数据进行拟合回归...  相似文献   

Cenozoic geodynamic evolution of the Andaman–Sumatra subduction margin: Current understanding     

Partha P.  Chakraborty  Prosanta K.  Khan 《Island Arc》2009,18(1):184-200

The Andaman–Sumatra margin displays a unique set‐up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner‐arc volcanoes, and an extensional back‐arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction‐related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right‐lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer‐arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction‐related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south‐trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench‐slope sediments, were uplifted and emplaced by a series of east‐dipping thrusts to shape the outer‐arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back‐arc occurred in two phases: an early (～11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner‐arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.  相似文献