Origin of submarine volcanism at the eastern margin of the central atlantic: Investigation of the alkaline volcanic rocks of the carter seamount (Grimaldi Seamounts)     

S. G. Skolotnev  V. V. Petrova  A. A. Peyve 《Petrology》2012,20(1):59-85

This paper addresses the composition, geochemistry, isotopic characteristics, and age of rocks from the Carter Seamount of the Grimaldi seamount group at the eastern margin of the Central Atlantic. The age of the seamount was estimated as 57–58 Ma. Together with other seamounts of the Grimaldi system and the Nadir Seamount, it forms a “hot line” related to the Guinea Fracture Zone, which was formed during the late Paleocene pulse of volcanism. The Carter Seamount is made up of olivine melilitites, ankaramites, and analcime-bearing nepheline tephrites, which are differentiated products of the fractional crystallization of melts similar to an alkaline ultramafic magma. The volcanics contain xenoliths entrained by melt at different depths from the mantle, layer 3 of the oceanic crust, which was formed at 113–115 Ma, and earlier magma chambers. The rocks were altered by low-temperature hydrothermal solutions. The parental melts of the volcanics of the Carter Seamount were derived at very low degrees of mantle melting in the stability field of garnet lherzolite at depths of no less than 105 km. Anomalously high Th, Nb, Ta, and La contents in the volcanics indicate that a metasomatized mantle reservoir contributed to the formation of their primary melts. The Sr, Pb, and Nd isotopic systematics of the rocks show that the composition of the mantle source lies on the mixing line between two mantle components. One of them is a mixture of prevailing HIMU and the depleted mantle, and the other is an enriched EM2-type mantle reservoir. These data suggest that the formation of the Carter Seamount volcanics was caused by extension-related decompression melting in the Guinea Fracture Zone of either (1) hot mantle plume material (HIMU component) affected by carbonate metasomatism or (2) carbonated basic enclaves (eclogites) ubiquitous in the asthenosphere, whose isotopic characteristics corresponded to the HIMU and EM2 components. In the former case, it is assumed that the melt assimilated during ascent the material of the metasomatized subcontinental mantle (EM2 component), which was incorporated into the oceanic lithospheric mantle during rifting and the breakup of Pangea.  相似文献   

Seamounts off the West Antarctic margin: A case for non-hotspot driven intraplate volcanism     

《Gondwana Research》2014,26(4):1660-1679

New radiometric age and geochemical data of volcanic rocks from the guyot-type Marie Byrd Seamounts (MBS) and the De Gerlache Seamounts and Peter I Island (Amundsen Sea) are presented. ⁴⁰Ar/³⁹Ar ages of the shield phase of three MBS are Early Cenozoic (65 to 56 Ma) and indicate formation well after creation of the Pacific–Antarctic Ridge. A Pliocene age (3.0 Ma) documents a younger phase of volcanism at one MBS and a Pleistocene age (1.8 Ma) for the submarine base of Peter I Island. Together with published data, the new age data imply that Cenozoic intraplate magmatism occurred at distinct time intervals in spatially confined areas of the Amundsen Sea, excluding an origin through a fixed mantle plume. Peter I Island appears strongly influenced by an EMII type mantle component that may reflect shallow mantle recycling of a continental raft during the final breakup of Gondwana. By contrast the Sr–Nd–Pb–Hf isotopic compositions of the MBS display a strong affinity to a HIMU-type mantle source. On a regional scale the isotopic signatures overlap with those from volcanics related to the West Antarctic Rift System, and Cretaceous intraplate volcanics in and off New Zealand. We propose reactivation of the HIMU material, initially accreted to the base of continental lithosphere during the pre-rifting stage of Marie Byrd Land/Zealandia to explain intraplate volcanism in the Amundsen Sea in the absence of a long-lived hotspot. We propose continental insulation flow as the most plausible mechanism to transfer the sub-continental accreted plume material into the shallow oceanic mantle. Crustal extension at the southern boundary of the Bellingshausen Plate from about 74 to 62 Ma may have triggered adiabatic rise of the HIMU material from the base of Marie Byrd Land to form the MBS. The De Gerlache Seamounts are most likely related to a preserved zone of lithospheric weakness underneath the De Gerlache Gravity Anomaly.  相似文献   

Composition,structure, origin,and evolution of off-axis linear volcanic structures of the Brazil Basin,South Atlantic     

S. G. Skolotnev  A. A. Peive 《Geotectonics》2017,51(1):53-73

The paper considers the conditions and mechanisms of the formation of linear volcanic structures in the Brazil Basin, South Atlantic. Among these objects, those related to the ascent of deep mantle plumes predominate. It is shown that the ascent of melts from plume sources leads to the formation of (a) hot spot tracks in the form of linear volcanic ridges and (b) active hot lines in the form of submarine mountain chains with trends differing from those of hot spot tracks and with a more variable character of the age distribution of volcanic rocks. Fault tectonics affects the character of plume activity. In addition, plume material from a hot spot area is dragged by a moving plate as a flow or a sublithospheric lens, which leads to the long-term existence of particular independent segments of linear structures and sometimes to late volcanism reactivation within their limits. Decompression melting of the asthenospheric mantle in zones where thin lithosphere undergoes tension causes the formation of passive hot lines. The main mantle source for the considered volcanic rocks was a mixture of DMM and HIMU mantle components, with the latter abruptly dominating. In marginal oceanic regions, the EM1 component is also present (the EM2 component is found more rarely) within fragments of tectonically delaminated continental mantle that was trapped by the oceanic mantle during the breakup of Gondwana.  相似文献   

New data on the composition and age of rocks from the Bathymetrists Seamounts (Eastern margin of the equatorial Atlantic)     

S. G. Skolotnev  A. A. Peyve  M. E. Bylinskaya  L. A. Golovina 《Doklady Earth Sciences》2017,472(1):20-25

The petrology, geochemistry, and isotope ratios of volcanics dredged during the 43rd cruise of R/V Academik Ioffe on the Bathymetrists Seamounts in the eastern equatorial Atlantic have been studied. These are alkaline volcanics of basic and ultramafic compositions. Spider diagrams of the trace elements of volcanic rocks demonstrate strong fractionation, indicating formation of their primary melts from an enriched mantle source at garnet depth facies. Considering the isotope ratio values of ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, and ⁸⁷Sr/⁸⁶Sr and the character of their variations, the volcanic mantle source was chemically heterogeneous: for various volcanic rocks it was a mixture of the mantle components HIMU with EM–1 or EM–2. Limestones dredged together with the volcanics yielded microfossils suggesting a Middle Eocene age of their formation in a carbonate platform environment.  相似文献   

Specific features of basalts from the western part of Andrew Bain Fault,Southwest Indian Ridge     

A. A. Peyve  S. G. Skolotnev 《Doklady Earth Sciences》2017,477(2):1384-1390

This paper reports original data on the composition of volcanic rocks in the western part of the Andrew Bain Fault of the South-West Indian Ridge obtained in the 23rd voyage of R/V Akademik Nikolai Strakhov. In accordance with high La/Th and low Nb/U ratios, the basalt compositions of stations S2317, S2318, and S2330 could result from melting of the DM-type source with HIMU traces. Meanwhile, the enriched samples of station S2326 correspond to a mantle source with a considerable contribution of recycled sediments (EM). Sample S2326/35, which is composed of a melt almost completely depleted in EM material, corresponds to the volcanic rocks of the Marion and Prince Edward islands. The obtained and available data on the SWIR segment from Bouvet Island to Andrew Bain Fault are indicative of small mantle heterogeneities in this region. Two possible variants of their origin are considered: either preservation of the enriched material fragments in the depleted mantle during the split of Gondwana or “contamination” of the mantle with plume material with the formation of vein irregularities before opening of the ocean in this region. In the latter case, the plume material could cover a huge area not constrained by the young plume magmatism regions on Bouvet, Marion, and Prince Edward islands.  相似文献   

Modeling of subduction components in the Genesis of the Meso-Cenozoic igneous rocks from the South Shetland Arc, Antarctica     

Adriane Machado  Farid Chemale Jr.  Rommulo V. Conceio  Koji Kawaskita  Diego Morata  Orlando Oteíza  William R. Van Schmus 《Lithos》2005,82(3-4):435-453

Isotope data and trace elements concentrations are presented for volcanic and plutonic rocks from the Livingston, Greenwich, Robert, King George and Ardley islands (South Shetland arc, Antarctica). These islands were formed during subduction of the Phoenix Plate under the Antarctica Plate from Cretaceous to Tertiary. Isotopically (⁸⁷Sr/⁸⁶Sr)_o ratios vary from 0.7033 to 0.7046 and (¹⁴³Nd/¹⁴⁴Nd)_o ratios from 0.5127 to 0.5129. εNd values vary from +2.71 to +7.30 that indicate asthenospheric mantle source for the analysed samples. ²⁰⁸Pb/²⁰⁴Pb ratios vary from 38.12 to 38.70, ²⁰⁷Pb/²⁰⁴Pb ratios are between 15.49 and 15.68, and ²⁰⁶Pb/²⁰⁴Pb from 18.28 to 18.81. The South Shetland rocks are thought to be derived from a depleted MORB mantle source (DMM) modified by mixtures of two enriched mantle components such as slab-derived melts and/or fluids and small fractions of oceanic sediment (EM I and EM II). The isotopic compositions of the subduction component can be explained by mixing between at least 4 wt.% of sediment and 96 wt.% of melts and/or fluids derived from altered MORB.  相似文献   

Geochemical evolution of Indian Ocean basaltic magmatism     

N. M. Sushchevskaya  V. S. Kamenetsky  B. V. Belyatsky  A. V. Artamonov 《Geochemistry International》2013,51(8):599-622

A comparison of new and published geochemical characteristics of magmatism in the western and eastern Indian Ocean at the initial and recent stages of its evolution revealed several important differences between the mantle sources of basaltic melts from this ocean.

1. The sources of basalts, from ancient rises and from flanks of the modern Central Indian Ridge within the western Indian Ocean contain an enriched component similar in composition to the source of the Réunion basalts (with radiogenic Pb and Sr and unradiogenic Nd), except for basalts from the Comores Islands, which exhibit a contribution from an enriched HIMU-like component.
2. The modern rift lavas of spreading ridges display generally similar geochemical compositions. Several local isotopic anomalies are characterized by the presence of an EM2-like component. However, two anomalous areas with distinctly different enriched mantle sources were recognized in the westernmost part of the Southwestern Indian Ridge (SWIR). The enriched mantle source of the western SWIR tholeiites in the vicinity of the Bouvet Triple Junction has the isotopic ratios indicating a mixture of HIMU + EM2 in the source. The rift anomaly distinguished at 40° E displays the EM1 signature in the mantle source, which is characterized by relatively low ²⁰⁶Pb/²⁰⁴Pb (up to 17.0) and high ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb and ⁸⁷Sr/⁸⁶Sr. This source may be due to mixing with material from the continental lithosphere of the ancient continent Gondwana. The material from this source can be distinguished in magmas related to the Mesozoic plume activity in Antarctica, as well as in basalts from the eastern Indian Ocean rises, which were formed by the Kerguelen plume at 100–90 Ma.
3. The geochemical heterogeneities identified in the ancient and present-day magmatic products from the western and eastern Indian Ocean are thought to reflect the geodynamic evolution of the region. In the eastern part of the ocean, the interaction of the evolving Kerguelen plume with the rift zones produced magmas with specific geochemical characteristics during the early opening of the ocean; such a dispersion of magma composition was not recognized in the western part of the ocean.

  相似文献   

Geochemical diversity in submarine HIMU basalts from Austral Islands, French Polynesia     

Takeshi Hanyu  Laure Dosso  Osamu Ishizuka  Kenichiro Tani  Barry B. Hanan  Claudia Adam  Shun’ichi Nakai  Ryoko Senda  Qing Chang  Yoshiyuki Tatsumi 《Contributions to Mineralogy and Petrology》2013,166(5):1285-1304

We present the first report of geochemical data for submarine basalts collected by a manned submersible from Rurutu, Tubuai, and Raivavae in the Austral Islands in the South Pacific, where subaerial basalts exhibit HIMU isotopic signatures with highly radiogenic Pb isotopic compositions. With the exception of one sample from Tubuai, the ⁴⁰Ar/³⁹Ar ages of the submarine basalts show no significant age gaps between the submarine and subaerial basalts, and the major element compositions are indistinguishable at each island. However, the variations in Pb, Sr, Nd, and Hf isotopic compositions in the submarine basalts are much larger than those previously reported in subaerial basalts. The submarine basalts with less-radiogenic Pb and radiogenic Nd and Hf isotopic compositions show systematically lower concentrations in highly incompatible elements than the typical HIMU basalts. These geochemical variations are best explained by a two-component mixing process in which the depleted asthenospheric mantle was entrained by the mantle plume from the HIMU reservoir during its upwelling, and the melts from the HIMU reservoir and depleted asthenospheric mantle were then mixed in various proportions. The present and compiled data demonstrate that the HIMU reservoir has a uniquely low ¹⁷⁶Hf/¹⁷⁷Hf decoupled from ¹⁴³Nd/¹⁴⁴Nd, suggesting that it was derived from an ancient subducted slab. Moreover, the Nd/Hf ratios of the HIMU basalts and curvilinear Nd–Hf isotopic mixing trend require higher Nd/Hf ratios for the melt from the HIMU reservoir than that from the depleted mantle component. Such elevated Nd/Hf ratios could reflect source enrichment by a subducted slab during reservoir formation.  相似文献   

Cenozoic Italian magmatism – Isotope constraints for possible plume-related activity     

《Journal of South American Earth Sciences》2013

Assessment of the isotope systematics and the magmatotectonic history of mainly Cenozoic igneous rocks from Italy shows them to be inconsistent with subduction-related magmatism. We attempt to fit these data into an alternative model involving long-term, recurrent plume activity that extended over a period of about 100 Ma, that involved mantle expansion and subsequent mixing between isotopically-distinct, mantle components. Sr, Nd and Pb isotopic compositions of Cenozoic Italian igneous rocks, rather than being random, reflect binary mixing involving a common end-member similar to FOZO. Most isotopic data from along the entire length of Italy, from the Aeolian Islands to the Alpine belt, define a Main Italian Radiogenic Trend (MIRT), characterized by mixing between FOZO and a highly radiogenic Sr, mantle end-member (ITEM, ITalian Enriched Mantle). Data from the Adria foreland, Sicily and the south-western Tyrrhenian Sea and Sardinia deviate from MIRT suggesting mixing with other components, perhaps HIMU and EM1. Both the absence of pure DMM, and the presence of isotopic end-members not recognized in present-day consuming-plate margins are incompatible with subduction-related models. Two models are discussed, one in which ITEM is attributed to melting of pre-Alpine sediments/upper continental crust entrained in a FOZO-like mantle and the other to widespread metasomatic activity involving deep-seated plume activity. In the latter, the widespread nature of FOZO is attributed to a late Triassic–early Jurassic plume that preceded the opening of the Alpine Tethys and led to modification of the lithosphere and/or asthenosphere. Late Jurassic–early Cretaceous plume activity produced mantle expansion and the opening of the Alpine Tethys. A new phase of plume activity started during the Oligocene with the opening of the western and central Mediterranean Basins. Stretching and large-scale extension of the Mediterranean lithosphere was caused by the progressive eastward growth and volume increase of a plume head trapped within the Transition Zone. Plume-generated fluids/melts enriched in K–Ca–CO₂–H₂O, produced mantle sources capable of generating widespread alkaline, mafic, and carbonatitic magmatism. Lithospheric unloading controlled the Tyrrhenian and peri-Tyrrhenian magmatic activity.  相似文献   

全球幔源岩Pb-Sr-Nd同位素体系   总被引：5，自引：0，他引：5  

朱炳泉 《地学前缘》2007,14(2):24-36

根据各种同位素数据库得到的3万多个晚古生代以来的幔源岩(包括洋中脊玄武岩、洋岛玄武岩、岛弧火山岩、大陆与大洋溢流玄武岩以及大陆板内玄武岩)Pb-Sr-Nd同位素资料和图解分析,对各类火山岩的源区以及地幔的垂向与横向不均一性问题作了进一步讨论。笔者认为不存在具有公共性质的EM1、EM2和HIMU地幔端员,它们的源区可能来自上、下地幔过渡带,只在局部地区出现,独一无二。PREMA(FOZO)则是洋岛玄武岩和溢流玄武岩公共端员。DUAPAL异常现象不只是在洋中脊玄武岩中出现,在洋岛玄武岩、岛弧火山岩和大洋溢流玄武岩中也存在同步的地球化学分区现象。溢流玄武岩的同位素体系特征表明它们的源区涉及再循环地幔的壳幔混合、岩石圈减压熔融、上—下地幔过渡带和似原始-略亏损的下地幔。Pb同位素体系为鉴别俯冲带的存在提供了更严格的证据,这种鉴别表明,安第斯弧火山作用不是洋陆俯冲带产生的。  相似文献   

The nephelinitic–phonolitic volcanism of the Trindade Island (South Atlantic Ocean): Review of the stratigraphy,and inferences on the volcanic styles and sources of nephelinites     

《Journal of South American Earth Sciences》2016

Trindade Island is located in the South Atlantic Ocean, 1170 km from the Brazilian coast, and represents the eastern end of the E–W Vitória–Trindade Chain. It shows the youngest plume-induced (ca. 3.7 to <0.17 Ma) subaerial volcanism on the South American plate, associated with the Trindade plume activity. Almeida (1961) recognized five volcanogenic successions at Trindade (in decreasing age): the Trindade Complex (TC, >2.4 Ma) and the Desejado (DF, ∼2.4 to 1.5 Ma), Morro Vermelho (MV, <0.17 Ma), Valado (VF, no age) and Paredão (PF, no age) formations, composed of effusive–pyroclastic deposits and subvolcanic intrusions associated with nephelinite–phonolite volcanic episodes. We revised the original Almeida's (1961) stratigraphy with additional field work and petrography to recognize eruptive styles and processes within the nephelinite–phonolite volcanism. Also, available geochemical databases were used to improve the stratigraphic correlation between nephelinites from different units and to characterize their mantle sources.The nephelinitic volcanism may represent Strombolian and Hawaiian–type activity of low viscosity and volatile–rich lavas interlayered with pyroclastic successions (fall–out deposits). Phonolitic deposits record explosive Vulcanian–style episodes of volatile–rich and higher–viscosity lavas interlayered with pyroclastic deposits (mostly pyroclastic flows). Geochemical data allowed the individualization of nephelinites as follows: (1) MV olivine–rich nephelinites and all olivine–free varieties are low K₂O/Na₂O, K₂O/TiO₂ and intermediate CaO/Al₂O₃ that may be derived from N–MORB and HIMU mantle components; (2) the VF olivine–rich nephelinites have high K₂O/Na₂O, K₂O/TiO₂ and CaO/Al₂O₃ that indicates both EM and HIMU mantle sources and; (3) the PF olivine–rich nephelinites show high K₂O/TiO₂ similar to those from VF, and intermediate CaO/Al₂O₃ as nephelinites from MV rocks, suggesting a mixed source with EM + HIMU > N–MORB components.We suggest that the HIMU and EM mantle types resulted from metasomatic episode(s) in the peridotitic mantle beneath the Trindade Island during the Brasiliano Orogeny and later, as previously pointed out by Marques et al. (1999). Thus, the major HIMU component would relate to recycled oceanic crust or lithospheric mantle (mostly CO₂–eclogites) whereas the less important EM component to recycled marine or continental sediments.  相似文献   

Petrogenesis of Tertiary Mafic Alkaline Magmas in the Hocheifel, Germany   总被引：5，自引：0，他引：5  

JUNG  CAROLINE; JUNG  STEFAN; HOFFER  EDGAR; BERNDT  JASPER 《Journal of Petrology》2006,47(8):1637-1671

Primitive nephelinites and basanites from the Tertiary Hocheifelarea of Germany (part of the Central European Volcanic Province;CEVP) have high Mg-number (>0·64), high Cr and Nicontents and strong light rare earth element enrichment butsystematic depletion in Rb, K and Ba relative to trace elementsof similar compatibility in anhydrous mantle. Alkali basaltsand more differentiated magmatic rocks have lower Mg-numberand lower abundances of Ni and Cr, and have undergone fractionationof mainly olivine, clinopyroxene, Fe–Ti oxide, amphiboleand plagioclase. Some nephelinites and basanites approach theSr–Nd–Pb isotope compositions inferred for the EAR(European Asthenospheric Reservoir) component. The Nd–Sr–Pbisotope composition of the differentiated rocks indicates thatassimilation of lower crustal material has modified the compositionof the primary mantle-derived magmas. Rare earth element meltingmodels can explain the petrogenesis of the most primitive maficmagmatic rocks in terms of mixing of melt fractions from anamphibole-bearing garnet peridotite source with melt fractionsfrom an amphibole-bearing spinel peridotite source, both sourcescontaining residual amphibole. It is inferred that amphibolewas precipitated in the asthenospheric mantle beneath the Hocheifel,close to the garnet peridotite–spinel peridotite boundary,by metasomatic fluids or melts from a rising mantle diapir orplume. Melt generation with amphibole present suggests relativelylow mantle potential temperatures (<1200°C); thus themantle plume is not thermally anomalous. A comparison of recentlypublished Ar/Ar ages for Hocheifel basanites with the geochemicaland isotopic composition of samples from this study collectedat the same sample sites indicates that eruption of earlierlavas with an EM signature was followed by the eruption of laterlavas derived from a source with EAR or HIMU characteristics,suggesting a contribution from the advancing plume. Thus, theHocheifel area represents an analogue for magmatism during continentalrift initiation, during which interaction of a mantle plumewith the overlying lithosphere may have led to the generationof partial melts from both the lower lithosphere and the asthenosphere. KEY WORDS: alkali basalts; continental volcanism; crustal contamination; partial melting; Eifel, Germany  相似文献   

碳酸岩Sr、Nd、Pb 同位素地球化学研究评述   总被引：3，自引：0，他引：3  

许成  黄智龙  穆肇南  漆亮  严再飞  管涛  申宝剑 《矿物岩石地球化学通报》2004,23(4):336-343

碳酸岩是出露相对较少的幔源岩石，其中Sr与Nd是研究地幔物质组成的主要对象之一。本文统计了世界上主要碳酸岩的锶、钕、铅同位素组成特征；研究显示，碳酸岩源区主要是洋岛玄武岩高U／Pb的HIMU端员和富集端员(EM1或EM2)的混合作用；此外大部分碳酸岩的锶、钕同位素落在大洋玄武岩范围内；这些均表明其成因与地慢柱有密切联系。碳酸岩及与之共生的硅酸岩的同源或独立源区模式部很难充分解释两者同位素组成特征，逭反映碳酸岩的演化模式涉及更复杂的过程。可能是俯冲作用使碳酸岩源区经历不同时间和程度的富集、亏损过程导致地幔源区成分不均一。  相似文献   

Aptian bimodal volcanic associations and granitoids in the northern margin of the Amur microcontinent: Age, sources of material, and geodynamic environments     

A. A. Sorokin  A. B. Kotov  V. A. Ponomarchuk  A. P. Sorokin  V. P. Kovach  V. M. Savatenkov 《Petrology》2013,21(1):66-84

Data on the composition, age, and source of material of Aptian rocks composing a bimodal volcanic complex and related granitoids in the northern margin of the Amur microcontinent indicate that the granodiorites of the Talalinskii Massif and subalkaline granites of the Dzhiktandiunskii Massif crystallized at 117 ± 2 and 119 ± 2 Ma, respectively (⁴⁰Ar/³⁹Ar method), and their crystallization ages coincide with the age of volcanic rocks of the Gal’kinskii bimodal complex. These data make it possible to combine the rocks within a single volcano-plutonic association. Geochemical and isotopic-geochemical features of trachybasaltic andesites of the Gal’kinskii bimodal complex suggest that the parental melts were derived from such sources as PREMA (or DM) and an enriched source of the EMII type at a subordinate contribution of a crustal source. The parental melts of rhyolites of the Gal’kinskii Complex and granitoids of the Talalinskii and Dzhiktandinskii massifs were derived from crustal material with minor amounts of juvenile material. The bimodal volcanic association and related granitoids dated at 119–115 Ma were most likely formed in geodynamic environments implying the ascent of the asthenospheric mantle.  相似文献   

Isotopic constraints on the Easter Seamount Chain source     

Q. C. Cheng  J. D. Macdougall  P. Zhu 《Contributions to Mineralogy and Petrology》1999,135(2-3):225-233

New isotopic data (Sr, Nd and Pb) for lavas from Easter and Salas y Gomez Islands, and nine seamounts along the length of the Easter Seamount Chain (ESC) to the east of these islands, exhibit a regular behavior that is consistent with two-component mixing between a MORB-like source and more enriched mantle (the Easter Plume source) characterized by relatively radiogenic Pb and unradiogenic Sr. Based on the linearity of mixing trends on the isotope diagrams, the plume source appears to have maintained approximately the same isotopic composition over the 20 to 30 Ma history of the Easter Plume sampled by the seamounts. In current nomenclature, the plume source resembles a mix of predominantly HIMU mantle with a small amount of EMI. The proportions of MORB and plume source mantle sampled by the lavas erupted along the ESC vary in a systematic way, with Easter Island and seamounts to the west containing larger fractions of the MORB component than Salas y Gomez Island and the older seamounts to the east. This variability is probably a reflection of the nearness to the spreading center, and therefore lithospheric thickness, at the time of volcanism Received: 27 April 1998 / Accepted: 11 December 1998  相似文献   

Tectono-Magmatic Evolution of the South Atlantic Continental Margins with Respect to Opening of the Ocean     

E.?N.?MelankholinaEmail author  N.?M.?Sushchevskaya 《Geotectonics》2018,52(2):173-193

The history of the opening of the South Atlantic in Early Cretaceous time is considered. It is shown that the determining role for continental breakup preparation has been played by tectono-magmatic events within the limits of the distal margins that developed above the plume head. The formation of the Rio Grande Rise–Walvis Ridge volcanic system along the trace of the hot spot is considered. The magmatism in the South Atlantic margins, its sources, and changes in composition during the evolution are described. On the basis of petrogeochemical data, the peculiarities of rocks with a continental signature are shown. Based on Pb–Sr–Nd isotopic studies, it is found that the manifestations of magmatism in the proximal margins had features of enriched components related to the EM I and EM II sources, sometimes with certain participation of the HIMU source. Within the limits of the Walvis Ridge, as magmatism expanded to the newly formed oceanic crust, the participation of depleted asthenospheric mantle became larger in the composition of magmas. The role played by the Tristan plume in magma generation is discussed: it is the most considered as the heat source that determined the melting of the ancient enriched lithosphere. The specifics of the tectono-magmatic evolution of the South Atlantic is pointed out: the origination during spreading of a number of hot spots above the periphery of the African superplume. The diachronous character of the opening of the ocean is considered in the context of northward progradation of the breakup line and its connection with the northern branch of the Atlantic Ocean in the Mid-Cretaceous.  相似文献   

Magmatic sources of dikes and veins in the Moncha Tundra Massif,Baltic Shield: Isotopic-geochronologic and geochemical evidence     

L. I. Nerovich  T. B. Bayanova  P. A. Serov  D. V. Elizarov 《Geochemistry International》2014,52(7):548-566

The dike-vein complex of the Moncha Tundra Massif comprises dolerites, gabbro-pegmatites, and aplites. The dolerite dikes are classified into three groups: high-Ti ferrodolerites, ferrodolerites, low-Ti and low-Fe gabbro-dolerites. The U-Pb age of the ferrodolerites is 2505 ± 8 Ma, and the amphibole-plagioclase metagabbroids hosting a ferrodolerite dike are dated at 2516 ± 12 Ma. Data on the U-Pb isotopic system of zircon from the gabbro-pegmatites and titanite from the aplites indicate that the late magmatic evolution of the Moncha Tundra Massif proceeded at 2445 ± 1.7 Ma, and the youngest magmatic events in the massif related to the Svecofennian orogeny occurred at 1900 ± 9 Ma. The data obtained on the Sm-Nd and Rb-Sr isotopic systems and the distribution of trace elements and REE in rocks of the dike-vein complex of the massifs provide insight into the composition of the sources from which the parental magmas were derived. The high-Ti ferrodolerites were melted out of a deep-sitting plume source that contained an asthenospheric component. The ferrodolerites were derived from a mantle MORB-type source that contained a crustal component. The parental melts of the gabbro-dolerites were melted out of the lithospheric mantle depleted in incompatible elements after Archean crust-forming processes above an ascending mantle plume, with the participation of a crustal component. The gabbro-dolerites and the rocks of the layered complex of the Moncha Tundra Massif exhibit similar geochemical characteristics, which suggest that their parental melts could be derived from similar sources but with more clearly pronounced crustal contamination of the parental melts of the rocks of the massif itself. The geochemical traits of the gabbro-pegmatites are thought to be explained not only by the enrichment of the residual magmas in trace elements and a contribution of a crustal component but also by the uneven effect of sublithospheric mantle sources. The aplites were derived from a sialic crustal source.  相似文献   

Intraplate volcanism in New Zealand: the role of fossil plume material and variable lithospheric properties     

Peter Sprung  Stephan Schuth  Carsten Münker  Leonore Hoke 《Contributions to Mineralogy and Petrology》2007,153(6):669-687

The geologic evolution of the New Zealand microcontinent was characterised by intermittent Cretaceous to Quaternary episodes of intraplate volcanism. To evaluate the corresponding mantle evolution beneath New Zealand with a specific focus on the tectonic evolution, we performed a combined major and trace element and Hf, Nd, Pb, Sr isotope investigation on a suite of representative intraplate volcanic rocks from both main islands and the Chatham Islands. Isotopically, the data set covers a range between “HIMU-like” end member compositions (²⁰⁶Pb/²⁰⁴Pb: 20.57, ²⁰⁷Pb/²⁰⁴Pb: 15.77, ⁸⁷Sr/⁸⁶Sr: 0.7030, εHf: + 3.8, εNd: + 4.2), compositions tending towards MORB (²⁰⁶Pb/²⁰⁴Pb: 19.01, ²⁰⁷Pb/²⁰⁴Pb: 15.62, ⁸⁷Sr/⁸⁶Sr: 0.7028, εHf: + 9.9, εNd: + 7.0) and compositions reflecting the influence of subducted sediments (²⁰⁶Pb/²⁰⁴Pb: 18.99, ²⁰⁷Pb/²⁰⁴Pb: 15.67, ⁸⁷Sr/⁸⁶Sr: 0.7037, εHf: + 4.4, εNd: + 3.9). Whereas volcanism on the Chatham Islands constitutes the HIMU end member of our data set, intraplate volcanic rocks from the North Island are dominated by MORB-like compositions with relatively radiogenic ²⁰⁶Pb/²⁰⁴Pb signatures. Volcanic rocks from the South Island form a trend between the three end members. Assuming a polybaric melting column model, the primary melt compositions reflect variations in the degree of melting, coupled to variable average melting depths. As the three isotope and trace element end members occur throughout the volcanic episodes, the “HIMU-like” and the sediment influenced signatures most likely originate from a heterogeneous subcontinental lithospheric mantle, whereas an asthenospheric origin is inferred for the MORB-like component. For the South Island, affinities to HIMU wane with decreasing average melting depths whereas MORB and sediment-like signatures become more distinct. We therefore propose a polybaric melting model involving upper asthenospheric mantle and a lithospheric mantle source that has been modified by subduction components and veins of fossil “HIMU-like” asthenospheric melts. The proportion of asthenospheric versus lithospheric source components is controlled by variations in lithospheric thickness and heat flow, reflecting the different tectonic settings and rates of extension. Generally, low degree melts preferentially tap enriched vein material with HIMU signatures. The widespread occurrence of old Gondwana-derived lithospheric mantle beneath intraplate volcanic fields in East Gondwana is suggested by overall similarities between New Zealand intraplate volcanic rocks and volcanic rocks in East Australia and Antarctica. The petrogenetic model proposed here may therefore serve as a general model for the petrogenesis of Cretaceous to Recent intraplate volcanic rocks in former East Gondwana. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

北祁连山元古宙末－寒武纪主动大陆裂谷火山作用   总被引：13，自引：2，他引：13  

夏祖春  夏林圻  徐学义 《地球学报》1996,17(3):282-291

北祁连山元古宙末－寒武纪大陆裂谷火山岩系为双峰式火山岩套，主要由基性与酸性火山岩组成。基性火山岩有磁性玄武岩与拉斑玄武岩两个岩浆系列，且富集ＬＲＥＥ与ＬＩＬ，其岩浆源区为与洋岛玄武岩源相似的富集地幔柱源。软流圈地幔柱上涌导致岩石圈地慢部分熔融，其熔体与地幔柱衍生熔浆混合，形成本区具有中等钕，锶同位素比值特点的基性岩浆。基性岩浆上侵至陆壳，引起下部陆壳深熔，产生长英质岩浆。地幔柱上隆促使大陆扩张，及至形成北祁连山元古宙末－寒武纪大陆裂谷。  相似文献   

HIMU型洋岛玄武岩的地球化学特征          下载免费PDF全文

王小均  刘建强  陈立辉 《高校地质学报》2014,20(3):353

    洋岛玄武岩的元素和同位素地球化学特征可以示踪深部地幔的化学结构和化学演化过程。HIMU(Highμ,μ=238U/204Pbt=0) 型玄武岩是一类元素和同位素组成特殊的洋岛玄武岩,被认为与地幔柱中再循环的洋壳物质直接相关,因此,HIMU型玄 武岩的成因是地幔柱（热点） 研究中长期关注的话题。本文概述了HIMU型玄武岩的地球化学定义,对HIMU洋岛的分布、 火山演化阶段以及岩性变化做了综合阐述,并在对比经典HIMU型玄武岩与其他板内玄武岩元素地球化学特征、放射成因 同位素组成以及惰性气体同位素组成特征的基础上,简要探讨其源区组成和成因上的不同。  相似文献