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3 富集地幔人们曾经用大陆地壳拼凑和原始的下地幔柱解释所有非大洋中脊玄武岩(即富集玄武岩或来自所谓原生储层的玄武岩)。上地幔被看作是枯竭地幔和洋中脊玄武岩的储层,而仅是洋中脊玄武岩的储藏,它是 相似文献
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《中国科学:地球科学》2017,(10)
近20年来,塔里木早二叠世大火成岩省在各类火成岩的空间分布、时间序列、地球化学特征、地幔源区和岩浆演化等方面有了深入的认识,为揭示大火成岩省的成因模式和演化过程奠定了坚实的基础.本文将主要基于塔里木大火成岩省存在的两阶段岩浆产物,结合前期研究基础和前人研究成果,系统论证塔里木早二叠世大火成岩省成因的两阶段熔融模式.模式认为塔里木大火成岩省的形成与地幔柱活动有关,其地幔柱作用形式兼具"巴哈纳型"和"德干型"两种特点,即早期高热的地幔柱引起了岩石圈地幔的低程度部分熔融,后期地幔柱上升绝热减压引起地幔柱自身部分熔融.在早期熔融事件中,地幔柱主要表现为上部岩石圈熔融所需的热供给,后期熔融过程中地幔柱成为熔融发生的主要场所和物质供给源.第一阶段喷发的两类玄武岩具有高~(87)Sr/~(86)Sr、低~(143)Nd/~(144)Nd的同位素特征,富集大离子亲石元素和高场强元素,为富集的大陆岩石圈地幔部分熔融的产物,具有"巴哈纳型"特征;而第二阶段产出的基性-超基性侵入岩具有相对两类玄武岩较低的~(87)Sr/~(86)Sr,较高的~(143)Nd/~(144)Nd比值,为地幔热柱熔融的产物,具有"德干型"特征.其中第一阶段,可细分为Group1和Group2两类玄武岩,Group2玄武岩相对Group1玄武岩具有较低的~(87)Sr/~(86)Sr,较高的~(143)Nd/~(144)Nd比值.Group2玄武岩显示连接Group1玄武岩和第二阶段岩浆作用的过渡类型特征,表明塔里木早二叠世大火成岩省是地幔柱与岩石圈地幔持续相互作用的结果.关于塔里木大火成岩省成因模式的研究有助于增进对塔里木大火成岩省岩浆作用、深部地质过程和地球动力学过程的全面认识,有利于丰富大火成岩省的成因理论和地幔柱活动理论. 相似文献
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南海新生代碱性玄武岩主量、微量元素及Sr-Nd-Pb同位素研究 总被引：4，自引：0，他引：4
南海海盆玄武质岩石的全岩K-Ar年龄为7.9~3.8 Ma, 为南海扩张停止(15.5 Ma)后、晚中新世以来的板内火山作用的产物, 可与其周边地区(如雷琼半岛、南海北缘及中南半岛等)同期火山作用的岩石成因和源区性质进行对比研究. 在详细的岩相学研究基础上, 从中挑选出了新鲜的玄武质岩石, 并进行了主量、微量元素及Sr-Nd-Pb同位素分析研究. 结果表明, 该区玄武岩属于碱性玄武岩浆系列, 具有OIB型的稀土及微量元素特点, 形成岩浆的部分熔融作用程度较低, 岩浆在上升期间或在高位岩浆房中经历了结晶分异作用和堆晶作用. Sr-Nd-Pb同位素地球化学研究表明, 南海地幔存在不均一性, 岩浆源区性质为EM2与DMM的二端员混合模式, 其中EM2为来自地幔柱物质的富集端员, DMM端员为大洋软流圈或岩石圈亏损地幔; Pb同位素特征显示本区存在Dupal异常, 结合北冰洋Gakkel脊新发现的Dupal异常, 表明此异常并非只限于南半球. 从Sr-Nd-Pb同位素变异图解中可见, 南海与雷琼半岛、南海北缘以及中南半岛地区可能具有相似的地幔源区特征, 与中国华北及东北地区存在一定差异. 南海海盆晚中新世以来的玄武岩为海南地幔柱提供了地球化学制约. 相似文献
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川西新元古代基性岩墙群的SHRIMP锆石U-Pb年龄、元素和Nd-Hf同位素地球化学: 岩石成因与构造意义 总被引：7，自引：0，他引：7
扬子块体西缘新元古代岩浆活动非常强烈, 其成因对研究Rodinia超大陆的演化有重要意义. 目前对这些岩浆岩的成因和形成的构造背景存在地幔柱和岛弧两种截然不同的观点. 本文对川西康滇裂谷中康定-泸定-石棉地区广泛分布的基性岩墙群, 进行了SHRIMP锆石U-Pb年龄、元素和Nd-Hf同位素研究, 结果表明这些基性岩墙群形成于780 ~ 760 Ma, 与康定花岗质杂岩在时-空上密切共生. 岩浆起源于亏损的软流圈地幔, 虽然在上升侵位过程中受到年轻岛弧地壳物质不同程度的混染, 但元素和Nd-Hf同位素仍表现出板内玄武岩的特征, 很可能是高温地幔柱部分熔融的产物. 本文的研究结果支持华南位于澳大利亚和Laurentia大陆之间的Rodinia超大陆重建模式. 相似文献
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坐落在西北太平洋的沙茨基海隆为地球上第三大洋底高原,而其中的大塔穆火山被称为"地球上最大的单体火山".本文综述了国际科学团队近期对大塔穆火山进行的多次海洋地质与地球物理调查,阐述"地幔柱"与"洋中脊"两种端元成因假说各自的重要证据以及争论的焦点问题.沙茨基海隆自南西向北东年龄逐渐变年轻、火山规模变小,是支持"地幔柱"假说的直接证据.大塔穆火山上巨厚块状熔岩、低坡度盾状单体火山构造代表地幔柱头岩浆大规模快速喷发,而奥里火山和希尔绍夫火山枕状熔岩则反映从地幔柱头过渡到地幔柱尾的过程中岩浆作用减弱.另一方面,大塔穆火山水下喷发,岩石样品显示洋中脊玄武岩的特征,以及地壳厚度与平均速度负相关性(反映化学异常来源),这些证据与"地幔柱"假说的预测不符,因而更支持"洋中脊"假说.然而"洋中脊"假说不能解释大塔穆火山单个来源如何输出如此大量的岩浆.再一方面,由人工地震长剖面观测到的莫霍面与艾里重力均衡模型所预测的莫霍面基本吻合,但此观测本身并不能区别更符合哪一种端元模型.总之,大塔穆火山既有"地幔柱"的特征,又有"洋中脊"的特征,单靠一种端元模式无法解释所有的重要观测.因此,"地幔柱-洋中脊相互作用"可能是一种更合理的替代模型,但地幔柱与洋中脊相互作用的具体过程及机制等重要问题目前尚未解决,仍需进一步研究.获取高精度地磁异常等观测资料以及开展三维地球动力学模拟将实质性地推动对沙茨基海隆等洋底高原形成机制的研究. 相似文献
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华南大陆记录和保存了自太古代至今大陆生长层完整的历史过程.以杨子克拉通为核心，地壳不断向东南生长，古扬子块前寒武系以灰色片麻岩、古元古代科马提岩绿岩、新元古代蛇绿岩、绿岩为特征，为相对稳定高速高阻冷的残存地幔“残烃柱”；而沿海一带火成岩以中、新生代壳－幔混合源火山－侵入杂岩、碱性花岗岩和正长岩带以及不同类型的玄武岩类为特征，为相对活动低速高导热的超地幔柱．巨型裂解构造是物质热传输的主要形式，地幔柱迁移是华南大陆构造演化的原动力． 相似文献
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全球地震层析地幔密度横向不均匀及大陆动力学 总被引：4，自引：0，他引：4
地震层析为我们提供了研究全球及区域地幔横向不均匀的有力工具。本文使用Ｓ１２－ＷＭ１３［１］层析模型,假设地震波速度异常与密度异常之间呈线性关系［２］,以ＰＲＥＭ模型［３］为基础,计算了全球和部分区域的球谐展开１２×１２阶地幔密度异常分布;分析了一系列的结果,特别分析了大陆下部地幔密度异常的基本格局;讨论了其对大陆动力学研究的意义。应用于中国大陆发现,整个中国大陆下部７０ｋｍ－１５０ｋｍ深部范围内是地震剪切波的低速带或密度低的地区,而在１５０－４００ｋｍ范围中又处于密度高的异常地带。本文从地幔动力学的观念出发讨论了中国大陆岩石层构造运动的地幔动力学问题。 相似文献
10.
湘南中生代玄武岩类地球化学特征 总被引：108，自引：8，他引：100
湘南是有色、稀有及放射性矿产分布的密集区 ,区内玄武岩类在时间、空间和成矿元素含量上与矿床有密切关系 .该地区玄武岩类同位素年龄在 1 98～ 81Ma之间 ,属侏罗纪 白垩纪 ,主要岩石类型包括碱性玄武岩和拉斑玄武岩 ,它们形成于大陆板内构造环境 .微量元素和Sr,Nd ,Pb同位素组成研究表明其地幔源区经历了富集过程 ,这种富集地幔源区 3%～ 5 %的部分融熔形成本区的碱性玄武岩 ,1 0 %～1 5 %的部分融熔形成本区的拉斑玄武岩 .区域地幔的富集作用对湘南大 超大型矿床密集区的形成有重要的意义 . 相似文献
11.
《Journal of Geodynamics》2007,43(1):87-100
The petrology and geochemistry of Icelandic basalts have been studied for more than a century. The results reveal that the Holocene basalts belong to three magma series: two sub-alkaline series (tholeiitic and transitional alkaline) and an alkali one. The alkali and the transitional basalts, which occupy the off-rift volcanic zones, are enriched in incompatible trace elements compared to the tholeiites, and have more radiogenic Sr, Pb and He isotope compositions. Compared to the tholeiites, they are most likely formed by partial melting of a lithologically heterogeneous mantle with higher proportions of melts derived from recycled oceanic crust in the form of garnet pyroxenites compared to the tholeiites. The tholeiitic basalts characterise the mid-Atlantic rift zone that transects the island, and their most enriched compositions and highest primordial (least radiogenic) He isotope signature are observed close to the centre of the presumed mantle plume. High-MgO basalts are found scattered along the rift zone and probably represent partial melting of refractory mantle already depleted of initial water-rich melts. Higher mantle temperature in the centre of the Iceland mantle plume explains the combination of higher magma productivity and diluted signatures of garnet pyroxenites in basalts from Central Iceland. A crustal component, derived from altered basalts, is evident in evolved tholeiites and indeed in most basalts; however, distinguishing between contamination by the present hydrothermally altered crust, and melting of recycled oceanic crust, remains non-trivial. Constraints from radiogenic isotope ratios suggest the presence of three principal mantle components beneath Iceland: a depleted upper mantle source, enriched mantle plume, and recycled oceanic crust.The study of glass inclusions in primitive phenocrysts is still in its infancy but already shows results unattainable by other methods. Such studies reveal the existence of mantle melts with highly variable compositions, such as calcium-rich melts and a low-18O mantle component, probably recycled oceanic crust. Future high-resolution seismic studies may help to identify and reveal the relative proportions of different lithologies in the mantle. 相似文献
12.
《中国科学:地球科学(英文版)》2017,(10)
Over the last two decades great strides have been made in characterizing the spatial distribution, time sequence,geochemical characteristics, mantle sources, and magma evolution processes for various igneous rocks in the Early Permian Tarim Large Igneous Province(TLIP). This work has laid a solid foundation for revealing the evolutionary processes and genetic models of large igneous provinces(LIPs). This study systematically demonstrates the two-stage melting model for the TLIP based on our previous research work and predecessor achievements, and highlights the two types of magmatic rocks within the TLIP.The two-stage melting model suggests that the formation of the TLIP is mantle plume related. The early hot mantle plume caused the low-degree partial melting of the lithosphere mantle, while in the later stage, the plume partially melted due to adiabatic uplift and decompression. Therefore, this model carries signatures of both the "Parana" and "Deccan" models in terms of mantle plume activity. During the early stage, the mantle plume provided the heat required for partial melting of sub-continental lithosphere mantle(SCLM), similar to the "Parana Model", while later the plume acted as the main avenue for melting, as in the "Deccan Model". Basalts that erupted in the first stage have higher 87Sr/86 Sr, lower 143Nd/144 Nd ratios, and are enriched in large ion lithophile elements and high field strength elements, indicating a possible origin from the enriched continental lithosphere mantle,similar to the Parana type geochemical features. The basic-ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86 Sr,higher 143Nd/144 Nd ratios relative to the basalts, consistent with the involvement of a more depleted asthenospheric material,such as a mantle plume, similar to the Deccan type geochemical features. The first stage basalts can be further subdivided into two categories, i.e., Group 1 and Group 2 basalts. Group 2 basalts have lower 87Sr/86 Sr and higher 143Nd/144 Nd ratios than Group 1 basalts, and lie between compositions of the Group 1 basalts and second stage magmatism. Group 2 basalts may be the intermediate component of the TLIP, and the whole TLIP is the result of plume and lithosphere interaction. Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes. Furthermore, this work enriches the theories describing the origin of large igneous province and mantle plume activity. 相似文献
13.
D.W. Graham L.M. Larsen B.B. Hanan M. Storey A.K. Pedersen J.E. Lupton 《Earth and Planetary Science Letters》1998,160(3-4):241-255
Picrites from the 61 million year old Vaigat Formation of the Nuussuaq Peninsula in West Greenland have 3He/4He ratios trapped in olivine phenocrysts which range up to 30 times the atmospheric ratio. These high values, measured during gas extraction by crushing in vacuum, are similar to the highest magmatic 3He/4He ratios found in young terrestrial volcanic rocks. By analogy with young basalts, in which crushing selectively extracts magmatic helium, any significant cosmogenic 3He appears to be absent in these picrites. Additional evidence for the absence of cosmogenic helium is provided by fusion results on the crushed olivine powders and by a single stepwise crushing experiment, in which only magmatic and radiogenic helium components are resolvable. The West Greenland picrites have Pb, Nd and Sr isotope compositions which overlap those found in picrites from Iceland and in basalts from Loihi Seamount, localities which today also have high 3He/4He ratios. Isotopic variations in He, Pb, Nd and Sr for the West Greenland picrites are interpreted to largely result from interaction of the early Iceland mantle plume with the upper mantle during plume ascent and dispersion beneath the continental lithosphere. The presence of high 3He/4He ratios in West Greenland, and the onset of magmatism across the North Atlantic Volcanic Province near 62 Ma, supports the hypothesis for very rapid dispersion (>1 m/year) of mantle plume head material during the earliest stages of plume impact, as predicted in recent numerical simulations of plume behavior during thermal mantle convection with non-Newtonian rheology. 相似文献
14.
Geochemical characteristics of Carboniferous greenstones in the Inner Zone of Southwest Japan 总被引：3，自引：0，他引：3
Abstract Greenstones, representing remnants of paleo-oceanic crust, occur in Permian and Jurassic accretionary complexes of the Inner Zone in the Southwestern Japan arc. The formation age of most of the greenstones is early Carboniferous, based on fossil ages for overlying limestones and Sm-Nd isotope ages of the greenstones themselves. The geochemistry of such greenstones is similar to those of present-day oceanic islands. Greenstones of the Permian accretionary complex (Akiyoshi belt) are alkalic and tholeiitic in composition. Some alkali basalts show peculiar features from an EM-1 mantle source, such as the Gough Island and Tristan da Chunha basalts in the South Atlantic. Greenstones of the Jurassic accretionary complex (Tamba belt) are also alkali and tholeiitic basalts with both basalt types in the northern part of the Tamba belt coming from strongly depleted characters similar to a mid-ocean ridge basalt source mantle. The variable geochemistry of the oceanic basalts is explained by hypothesis on existence of a Carboniferous mantle plume below the spreading ridge which divides the Farallon and Izanagi plates. The Akiyoshi belt seamounts and/or oceanic islands of the Farallon plate and Tamba belt seamounts and/or oceanic islands of the Izanagi plate formed simultaneously by the upwelling of the thermal plume. Some part of the Akiyoshi belt basalts originated locally from an EM-1 mantle source, while basalts from the northern parts of the Tamba belt have a normal-type mid-ocean ridge basalt (N-MORB) source component. Existence of an N-MORB signature is consistent with the presence of a spreading center in a Carboniferous 'Pacific Ocean' that caused separation of the Farallon and Izanagi plates. Disparity in accretion ages of the basaltic rocks in the Permian and Jurassic may have been caused by differences in the relative motion of the two plates. 相似文献
15.
Claude J. Allègre Bernard Dupré Bernard Lambret Pierre Richard 《Earth and Planetary Science Letters》1981,52(1):85-92
Pb, Nd and Sr isotopic compositions have been determined in lherzolite-xenolith-bearing alkali-basalts from the center of the African shield. The present data are very similar to those reported for ocean-island basalts and do not support the hypothesis of different mantle sources for alkali-basalts from continental and oceanic areas. From these observations and on the basis of data obtained for xenolith in kimberlite and for tholeiitic continental basalts one may infer the following terrestrial mantle structure: whereas oceanic tholeiites would originate in upper oceanic mantle, oceanic and continental alkali basalts would come from the lower mantle and tholeiitic continental basalts from the continental lithosphere. 相似文献
16.
Alan Zindler S.R. Hart F.A. Frey S.P. Jakobsson 《Earth and Planetary Science Letters》1979,45(2):249-262
Post-glacial tholeiitic basalts from the western Reykjanes Peninsula range from picrite basalts (oldest) to olivine tholeiites to tholeiites (youngest). In this sequence there are large systematic variations in rare earth element (REE) abundances (La/Sm normalized to chondrites ranges from 0.33 in the picrite basalts to 1.25 in the fissure tholeiites) and corresponding variations in 143Nd/144Nd (0.51317 in the picrite basalts to 0.51299 in the fissure tholeiites). The large viaration in 143Nd/144Nd, more than one-third the total range observed in most ocean islands and mid-ocean ridge basalts (MORB), is accompanied by only a small variation in 87Sr/86Sr (0.7031–0.7032). These 87Sr/86Sr ratios are within the range of other Icelandic tholeiites, and distinct from those of MORB.We conclude that the mantle beneath the Reykjanes Peninsula is heterogeneous with respect to relative REE abundances and 143Nd/144Nd ratios. On a time-averaged basis all parts of this mantle show evidence of relative depletion in light REE. Though parts of this mantle have REE abundances and Nd isotope ratios similar to the mantle source of “normal” MORB, 87Sr/86Sr is distinctly higher. Unlike previous studies we find no evidence for chondritic relative REE abundances in the mantle beneath the Reykjanes Peninsula; in fact, the data require significant chemical heterogeneity in the hypothesized mantle plume beneath Iceland, as well as lateral mantle heterogeneity from the Reykjanes Ridge to the Reykjanes Peninsula. The compositional range of the Reykjanes Peninsula basalts is consistent with mixing of magmas produced by different degrees of melting in different parts of the heterogeneous mantle source beneath the Reykjanes Peninsula. 相似文献
17.
A. F. Grachev 《Izvestiya Physics of the Solid Earth》2013,49(5):683-698
New data are presented on the chemical composition and helium isotopes for the mantle xenoliths and enclosed Cenozoic basalts of the Pannonian Basin and Bohemian Massif. New data on the helium isotopes in the basalts and mantle xenoliths of the Pannonian Basin and Bohemian Massif, which have been obtained for the first time, show very low R/Ra ratios close to or slightly above the typical values of the atmosphere. This indicates that the mantle beneath the considered areas is strongly degassed. The fact that, according to seismic tomography, the mantle plumes beneath the regions of recent volcanism in Central Europe are not traced below 200 km points to the extensive spreading of the plume material beneath the lithosphere of Europe, due to which the plume tail is too thin to be detectable by the existing methods. 相似文献
18.
Osmium-strontium-neodymium-lead isotopic covariations in mid-ocean ridge basalt glasses and the heterogeneity of the upper mantle 总被引：4，自引：0，他引：4
Pierre Schiano Jean-Louis Birck Claude J. Allgre 《Earth and Planetary Science Letters》1997,150(3-4):363-379
Osmium, strontium, neodymium, and lead isotopic data have been obtained for 30 hand picked samples of basaltic glass from the Pacific, Atlantic and Indian mid-oceanic ridges. Large variations in Os isotopic ratios exist in the glasses, from abyssal peridotite-like values to radiogenic compositions similar to oceanic island basalts (187Os/186Os and 187Os/188Os ratios range from 1.06 to 1.36 and from 0.128 to 0.163, respectively). Os isotopic and elemental data suggest the existence of mixing correlations. This relationship might be ascribed to secondary contamination processes; however, such a hypothesis cannot account for the negative correlation observed between Os and Nd isotopes and the existence of complementary covariations between Os and SrPb isotopes. In this case, OsSrNdPb isotopic variations are unrelated to late post-eruption or shallow level contamination. These relationships provide strong evidence that the Os isotopic composition of the samples are derived from the mantle and thus implies a global chemical heterogeneity of the oceanic upper mantle. The results are consistent with the presence of recycled oceanic crust in the mantle sources of mid-ocean ridge basalts, and indicate that the unique composition of the upper mantle below the Indian ocean results from its contamination by a mantle component characterized by radiogenic Os and particularly unradiogenic Nd and Pb isotopic compositions. 相似文献
19.
Asish R. Basu 《Earth and Planetary Science Letters》1975,28(2):261-274
The Wilson-Morgan hypothesis of hot-spots, characterized by high heat flow, positive gravity anomaly and alkalic volcanism, assumes that such hot-spots are surface expressions of mantle plumes rising by thermal convection. Possible evidence of this mantle upwelling is shown here from textural, structural and chemical aspects of ultramafic xenoliths in alkalic basalts. The xenolith-bearing basalts are constanly associated with Wilson-Morgan hot-spots in the ocean basins and with their continental counterparts in the rift valleys which show extensional tectonics. Most of the xenoliths are considered to be accidental fragments of the lithosphere in the host basalts. One remarkable aspect of xenoliths from all parts of the world is their ubiquitous tectonite fabric. The microstructures of these xenoliths are due to plastic deformation. Some of the xenoliths from Baja California show characteristic deformational features which are also found in the marginal parts of diapirically intruded high-temperature peridotite massifs. A model is proposed for the origin of xenoliths in alkalic basalts by mantle upwelling in which the plastic deformation of the xenoliths reflects this dynamic uprise. 相似文献
20.
Abstract Isotopic compositions of He, Ne and Ar were measured on Plio–Quaternary alkaline basalts of Marib–Sirwah and Shuqra volcanic fields in Yemen, south-western Arabian Peninsula. Very high 3 He/4 He isotope ratios were found in olivine phenocrysts of some Quaternary alkaline basalts in both volcanic fields, located on the margin of the dispersed Afar mantle plume, compared with the Afar–Ethiopian province in the center of the mantle plume. This suggests that the Afar mantle plume source may consist of common component (C or focal zone (FOZO)) with variable primordial 3 He/4 He ratio rather than high μ mantle (HIMU) component. The three component mixing C as the Afar mantle plume, depleted mantle (DM) as upper mantle and lithospheric mantle with a hybrid enriched mantle I–II (EM I–EM II) characteristics may be adequate to explain He–Sr–Nd–Pb isotope variation for the Afar–Arabian Cenozoic volcanics. The occurrence of high 3 He/4 He ratios in the Marib–Sirwah volcanic field appears to show that the primitive basaltic magma, derived from the margin of the dispersed trous-like Afar mantle plume during 15–0 Ma, was not by contamination of lithospheric and upper mantle materials in comparison with that from the center of the Afar mantle plume as a result of relatively low thermal anomaly. 相似文献