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1.
Based on laboratory and theoretical modeling results, we present the thermal and hydrodynamical structure of the plume conduit during plume ascent and eruption on the Earth’s surface. The modeling results show that a mushroom-shaped plume head forms after melt eruption on the surface for 1.9 < Ka < 10. Such plumes can be responsible for the formation of large intrusive bodies, including batholiths. The results of laboratory modeling of plumes with mushroom-shaped heads are presented for Ka = 8.7 for a constant viscosity and uniform melt composition. Images of flow patterns are obtained, as well as flow velocity profiles in the melt of the conduit and the head of the model plume. Based on the laboratory modeling data, we present a scheme of a thermochemical plume with a mushroom-shaped head responsible for the formation of a large intrusive body (batholith). After plume eruption to the surface, melting occurs along the base of the massif above the plume head, resulting in a mushroom-shaped plume head. A possible mechanism for the formation of localized surface manifestations of batholiths is presented. The parameters of some plumes with mushroom-shaped heads (plumes of the Altay-Sayan and Barguzin-Vitim large-igneous provinces, and Khangai and Khentei plumes) are estimated using geological data, including age intervals and volumes of magma melts. 相似文献
2.
The geologic structure and distribution of geophysical fields in the area of the Shatsky and Hess rises are considered. The ages of the Shatsky and Hess rises estimated at ～140 and ～100 Ma, respectively, from heat-flow parameters are consistent with the ages determined from magnetic measurements. The calculated thickness of the lithosphere beneath the rises (80–90 km) is close to that of the adjacent plates of the oceanic framework. This indicates that the rises were formed near the spreading axis. It is suggested that the rises evolved as autonomous structural features and their evolution followed the crystallization model of the oceanic-bottom formation. The tectonic analysis of the North Pacific has been carried out, and a geodynamic model of the growth of the Shatsky and Hess rises 140–83.5 Ma ago has been proposed. According to this model, the rises originated at the triple junction. This result is supported by the parameters of heat flow. The geothermal and geodynamic data and results of numerical modeling suggest that the origin of the Shatsky and Hess rises is related to plume tectonics. 相似文献
3.
Magmatic systems of large continental igneous provinces 总被引：1，自引：1，他引：0
Large igneous provinces (LIPs) formed by mantle superplume events have irreversibly changed their composition in the geological evolution of the Earth from high-Mg melts (during Archean and early Paleoproterozoic) to Phanerozoic-type geochemically enriched Fe-Ti basalts and picrites at 2.3 Ga. We propose that this upheaval could be related to the change in the source and nature of the mantle superplumes of different generations. The first generation plumes were derived from the depleted mantle, whereas the second generation (thermochemical) originated from the core-mantle boundary (CMB). This study mainly focuses on the second (Phanerozoic) type of LIPs, as exemplified by the mid-Paleoproterozoic Jatulian–Ludicovian LIP in the Fennoscandian Shield, the Permian–Triassic Siberian LIP, and the late Cenozoic flood basalts of Syria. The latter LIP contains mantle xenoliths represented by green and black series. These xenoliths are fragments of cooled upper margins of the mantle plume heads, above zones of adiabatic melting, and provide information about composition of the plume material and processes in the plume head. Based on the previous studies on the composition of the mantle xenoliths in within-plate basalts around the world, it is inferred that the heads of the mantle (thermochemical) plumes are made up of moderately depleted spinel peridotites (mainly lherzolites) and geochemically-enriched intergranular fluid/melt. Further, it is presumed that the plume heads intrude the mafic lower crust and reach up to the bottom of the upper crust at depths ～20 km. The generation of two major types of mantle-derived magmas (alkali and tholeiitic basalts) was previously attributed to the processes related to different PT-parameters in the adiabatic melting zone whereas this study relates to the fluid regime in the plume heads. It is also suggested that a newly-formed melt can occur on different sides of a critical plane of silica undersaturation and can acquire either alkalic or tholeiitic composition depending on the concentration and composition of the fluids. The presence of melt-pockets in the peridotite matrix indicates fluid migration to the rocks of cooled upper margin of the plume head from the lower portion. This process causes secondary melting in this zone and the generation of melts of the black series and differentiated trachytic magmas. 相似文献
4.
大火成岩省由一个体积巨大的、连续的、以富镁铁岩石占优势的喷出岩及其伴生的侵入岩组成，是一个全球现象。它包括大陆溢流玄武岩和伴生的侵入岩，火山被动边缘玄武岩，大洋高原、海岭、海山群和洋盆溢流玄武岩。Ontong Java和Kerguelen-Broken Ridge大洋高原、北大西洋火山被动边缘、德干和哥伦比亚河大陆溢流玄武岩是3个主要大火成岩省的典型代表。各种不同的大火成岩省在时空分布及组成上都具有相似性，它们具有非常大的体积、高的喷发速率，岩石类型以拉斑玄武岩为主。大火成岩省代表了地球上已知的最大的火山岩浆活动，记录了物质和能量从地球内部向外的大量转换。大火成岩省难以用板块构造来解释，可用热柱模式来解释，通常被认为是与来自下地幔的热柱“头”有关。大火成岩省是地球动力学过程在地壳的表现，因此大火成岩省参数可作为边界条件去反演地幔动力学过程。 相似文献
5.
Ming Zhang Suzanne Y. O’Reilly Kuo-Lung Wang Jon Hronsky William L. Griffin 《Earth》2008,86(1-4):145-174
Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”).Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages.Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential.The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al2O3 and Na2O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥ 0.03 to 10 ppb) and low Re/Os (< 10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models.Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤ 0.02 ppb) with high Re/Os (10–≥ 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots. 相似文献
6.
《Russian Geology and Geophysics》2016,57(6):858-867
Laboratory and numerical experiments simulating the heat transfer and flow structure of thermochemical mantle plumes provide insights into the mechanisms of plume eruption onto the surface depending on the relative thermal power of plumes Ka = N/N1, where N and N1 are the heat transferred from the plume base to the plume conduit and the heat transferred from the plume conduit to the surrounding mantle, respectively, under steady thermal conduction. There are three main types of plumes according to the Ka criterion: (i) plumes with low thermal power (Ka < 1.15), which fail to reach the surface, (ii) plumes with intermediate thermal power (1.15 < Ka < 1.9), which occur beneath cratons and transport melts from depths below 150 km, where diamond is stable (diamondiferous plumes), and (iii) plumes with a mushroom-shaped head (1.9 < Ka < 10), which are responsible for large intrusive bodies, including batholiths. The volume of erupted melt and the depth from which the melt is transported to the surface are estimated for plumes of types (ii) and (iii). The relationship between the plume head area (along with the plume head diameter) and the relative thermal power is obtained. The relationship between the thickness of the block above the plume head and the relative thermal power is derived. On the basis of the results obtained, the geodynamic-regime diagram of thermochemical mantle plumes, including the plumes with Ka > 10, has been constructed. 相似文献
7.
《地学前缘(英文版)》2021,12(4)
Massive gas emissions(e.g.,CO_2,CH_4 and SO_2) during the formation of large igneous provinces(LIPs) have been suggested as the primary cause of dramatic climatic change and the consequent ecological collapses and biotic crises.Thermogenic carbon of crustal sediments induced by intrusive magmatism throughout the LIPs is considered as the primary trigger for environmental catastrophe including mass extinction,as illustrated in the case of the Emeishan LIP in Southwest China.Here we evaluate the Emeishan LIP to address the causal link between carbon degassing and environmental crises during the end-Guadalupian of Middle Permian.An assessment of the carbon flux degassed from recycled oceanic crust in the Emeishan plume shows that recycled oceanic crust contributed significantly to the carbon flux.Using evidence from carbonate carbon isotopic records at the GualupianLopingian(G-L) boundary stratotype at Penglaitan of South China,our study suggests that carbon degassed from massive recycled components in the Emeishan plume served as a major end-Guadalupian(Middle Permian) carbon isotope excursion.The model based on the Emeishan LIP also offers new insights into the important role of recycled carbon released from other LIPs in climatic change and mass extinctions,as in the cases of the endPermian Siberian and end-Cretaceous Deccan Traps.Our work highlights that carbon released from subducted slabs is returned to the atmosphere via upwelling mantle plumes,which could drive global climatic change and mass extinction. 相似文献
8.
Frontiers in large igneous province research 总被引：33，自引：0，他引：33
Earth history is punctuated by events during which large volumes of mafic magmas were generated and emplaced by processes distinct from “normal” seafloor spreading and subduction-related magmatism. Large Igneous Provinces (LIPs) of Mesozoic and Cenozoic age are the best preserved, and comprise continental flood basalts, volcanic rifted margins, oceanic plateaus, ocean basin flood basalts, submarine ridges, ocean islands and seamount chains. Paleozoic and Proterozoic LIPs are typically more deeply eroded and are recognized by their exposed plumbing system of giant dyke swarms, sill provinces and layered intrusions. The most promising Archean LIP candidates (apart from the Fortescue and Ventersdorp platformal flood basalts) are those greenstone belts containing tholeiites with minor komatiites. Some LIPs have a substantial component of felsic rocks. Many LIPs can be linked to regional-scale uplift, continental rifting and breakup, climatic shifts that may result in extinction events, and Ni–Cu–PGE (platinum group element) ore deposits.
Some current frontiers in LIP research include:
- (1) Testing various mantle plume and alternative hypotheses for the origin for LIPs.
(2) Characterizing individual LIPs in terms of (a) original volume and areal extent of their combined extrusive and intrusive components, (b) melt production rates, (c) plumbing system geometry, (d) nature of the mantle source region, and (e) links with ore deposits.
(3) Determining the distribution of LIPs in time (from Archean to Present) and in space (after continental reconstruction). This will allow assessment of proposed links between LIPs and supercontinent breakup, juvenile crust production, climatic excursions, and mass extinctions. It will also allow an evaluation of periodicity in the LIP record, the identification of clusters of LIPs, and postulated links with the reversal frequency of the Earth's magnetic field.
(4) Comparing the characteristics, origin and distribution of LIPs on Earth with planets lacking plate tectonics, such as Venus and Mars. Interplanetary comparison may also provide a better understanding of convective processes in the mantles of the inner planets.
In order to achieve rapid progress in these frontier areas, a global campaign is proposed, which would focus on high-precision geochronology, integrated with paleomagnetism and geochemistry. Most fundamentally, such a campaign could help hasten the determination of continental configurations in the Precambrian back to 2.5 Ga or greater. Such reconstructions are vital for the proper assessment of the LIP record, as well as providing first-order information related to all geodynamic processes. 相似文献
9.
We present a thermophysical model for interaction between the conduit of a thermochemical plume and horizontal free convection flows in the mantle: The mantle flow incident on the plume conduit melts at the conduit boundary (front part) and crystallizes at its back. Geological data on the intensity of plume magmatism over the last 150 Myr are used to estimate the total thermal power of mantle plumes. A possible scenario for plume-related mantle recrystallization is proposed. Over the lifespan of a thermochemical plume, mantle melts and recrystallizes owing to the motion of the plume source and interaction between the plume conduit and horizontal free convection flows. The plume conduits can melt and recrystallize the entire mantle over a certain period of time. The model for the interaction of drifting plume conduits with mantle flows and the estimated total thermal power of mantle plumes are used to estimate the duration of plume-related melting and recrystallization of the entire mantle. The influence of mantle plumes on the convective structure of the mantle through melting is judged from the model for plume interaction with horizontal mantle flows. 相似文献
10.
Nickolay L. Dobretsov Alexey A. Kirdyashkin Anatoliy G. Kirdyashkin Valery A. Vernikovsky Igor N. Gladkov 《Lithos》2008,100(1-4):66-92
Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t1 between plume formation and eruption. These relationships are used to determine thermal power and time t1 for the Tunguska syneclise and the Siberian traps as a whole.
The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts. 相似文献
11.
The paper considers Cretaceous magmatism at the continental margin of the Arctic Region. It is shown that Cretaceous igneous rocks of this region are rather heterogeneous in age, composition, and geodynamic formation setting. This differentiates them from rocks of typical large igneous provinces (LIPs). Local areas of magmatic activity, their substantial remoteness them from one another, and significant distinctions in age, composition of rocks, and formation conditions prevent us from unreservedly combining all occurrences of Cretaceous magmatism at the continental margin of the Arctic Region into a common igneous province. The stage of tholeiitic magmatism in the Svalbard Archipelago, Franz Josef Land, Arctic Canada, and the Alpha–Mendeleev Rise, which can be considered an LIP, began in the Early Cretaceous and continued for a long time, at least until the Campanian. The magmatism apparently had a plume source and was caused by extension during opening of the Canada Basin. Tholeiitic magmatism gave way to the alkaline magmatism stage from the Campanian to the onset of the Paleocene, related to continental rifting at the initial stage of formation of Eurasian Basin in the Arctic Region. No convincing evidence for a genetic link between Early Cretaceous tholeiitic and Late Cretaceous alkaline magmatism is known at present, nor for the alkaline magmatism belonging to a plume source. 相似文献
12.
A.N. Distanova 《Russian Geology and Geophysics》2013,54(6):606-612
Global manifestations of Early Paleozoic granite formation in the Central Asian Mobile Belt and some other orogenic areas worldwide are considered. The work is based on the author’s studies of Early Paleozoic granitoids from the Altai–Sayan and West Transbaikalian orogenic areas as well as abundant literature data on other world provinces. Special attention is paid to the scales of granitoid magmatism in the Early Paleozoic, its geodynamic settings, periods, and stages, compositional evolution over time, lateral variability in structures of different types, relationship with LIPs, and, correspondingly, connection with mantle plumes and superplumes.. 相似文献
13.
N. L. Dobretsov A. A. Kirdyashkin A. G. Kirdyashkin I. N. Gladkov N. V. Surkov 《Petrology》2006,14(5):477-491
Thermochemical plumes develop at the core-mantle boundary in the presence of a heat flow from the outer core and at local chemical doping that decreases the melting temperature near the bottom of the lower mantle (this dope triggers the melting of the mantle material and the ascent of the plume). The paper presents evaluations for the heat power of the Hawaiian and Iceland plumes and the results of the experimental modeling of a thermochemical plume. The diameter of a plume conduit was determined to remain virtually unchanging in the course of plume ascent. When the top of a plume reaches a “refractory” layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped head of the plume develops beneath the bottom of this layer. The analysis of geological and geophysical data and the results of experimental modeling are used to develop a thermal physical model for a thermochemical plume. The balance relations for the mass and thermal energy and systematic tendencies in the heat and mass transfer during free convection were utilized to derive a system of equations for the heat and mass transfer of a thermochemical plume. Parameters were determined for a thermochemical plume ascending from the core-mantle boundary. Geodynamic processes are considered that occur during the ascent of a plume before it reaches the surface. The effect of the P-T conditions on the shape and size of a plume roof is analyzed, and a model is proposed for mass transfer between a thermochemical plume and the lithosphere, when the plume reaches the bottom of a “refractory” layer in the lithosphere. 相似文献
14.
大火成岩省是地幔柱作用引起的吗? 总被引：3，自引：0，他引：3
自Morgan在1971年提出地幔柱假说来解释大洋岛链的火山迁移规律以来,对于地幔柱是否存在一直存在着争论。大火成岩省以短时间内的巨量喷发为特征,这种特殊现象一般被认为是地幔柱作用的结果,原因是它可以解释大火成岩省中的许多现象:(1)短时间内的巨量幔源岩浆;(2)喷发前>500 m的隆起;(3)高温苦橄岩和科马提岩的存在;(4)热点轨迹;(5)在没有挥发分和压力降低的条件下地幔发生熔融;(6)高的3He/4He比值。但是并不是所有大火成岩省都具有上述特征,而且上述现象有的也可以用其他机制来解释,如边缘对流、大规模岩石圈拆沉、裂谷减压和陨石撞击等。但是目前还没有一个模式可以解释所有大火成岩省的所有现象,而总体上大火成岩省的许多地质现象与地幔柱模式较为吻合。 相似文献
15.
《地学前缘(英文版)》2020,11(5):1635-1649
A compilation of 178 more precise ages on 10 potential Large Igneous Provinces(LIPs) across southern Africa,is compared to Earth's supercontinental cycles,where 5 more prominent LIP-events all formed during the assembly of supercontinents,rather than during breakup.This temporal bias is confirmed by a focused review of field relationships,where these syn-assembly LIPs formed behind active continental arcs;whereas,the remaining postassembly-and likely breakup-related-LIPs never share such associations.Exploring the possibility of two radically different LIP-types,only the two younger breakup events(the Karoo LIP and Gannakouriep Suite) produced basalts with more enriched asthenospheric OIB-signatures;whereas,all assembly LIPs produced basalts with stronger lithospheric,as well as more or less primitive asthenospheric,signatures.A counterintuitive observation of Precambrian breakup LIPs outcropping as smaller fragments that are more peripherally located along craton margins,compared to assembly LIPs as well as the Phanerozoic Karoo breakup LIP,is explained by different preservation potentials during subsequent supercontinental cycles.Thus,further accentuating radical differences between(1) breakup LIPs,preferentially intruding along what evolves to become volcanic rifted margins that are more susceptible to deformation within subsequent orogens,and(2) assembly LIPs,typically emplaced along backarc rifts within more protected cratonic interiors.A conditioned duality is proposed,where assembly LIPs are primarily sustained by thermal blanketing(as well as local arc hydration and rifting) below assembling supercontinents and breakup LIPs more typically form above impinging mantle plumes.Such a duality is further related to an overall dynamic Earth model whereby predominantly supercontinent-orientated ocean lithospheric subduction establishes/revitalizes large low shear velocity provinces(LLSVPs) during assembly LIP-activity,and heating of such LLSVPs by the Earth's core subsequently leads to a derivation of mantle plumes during supercontinental breakup. 相似文献
16.
On thermochemical mantle plumes with an intermediate thermal power that erupt on the Earth’s surface
The relative plume thermal power Ka = N/N1 is used (N is the thermal power transferred from the plume base to its conduit and N1 is the thermal power transferred from the plume conduit into the surrounding mantle in the steady-state heat conduction regime). Thermochemical mantle plumes with small (Ka < 1.15) and intermediate (1.15 < Ka < 1.9) thermal powers are formed at the core–mantle boundary beneath cratons in the absence of horizontal free-convection mantle flows beneath them, or in the presence of weak horizontal mantle flows. Thermochemical plumes reach the Earth’s surface when their relative thermal power is Ka > 1.15. The thermal and hydrodynamical structure of the plume conduit ascending from the core–mantle interface to the level from which the magmatic melt erupts on the Earth’s surface is presented. The model of two-stage eruption of the melt from the plume conduit to the surface is considered. The critical height of the massif above the plume roof, at which the eruption conduit supplying magmatic melt to the surface forms, is determined. The volume of melt erupting through the eruption conduit to the surface is estimated. The dependence of depth Δx from which the melt is transported to the surface on the plume diameter for a kinematic viscosity of ν = 0.5–2 m2/s is presented. In the case when the value Δx is larger than the depth starting from which diamond is stable (150 km), the melt from the plume conduit can transport diamonds to the Earth’s surface. The melt flow in the eruption conduit is considered as a turbulent flow in a cylindrical duct. The velocity of the melt flow in the eruption conduit and the time for the melt to be transported to the surface from a depth of Δx = 150 km for a kinematic viscosity of the melt in the eruption conduit νv = 0.01–1 m2/s are determined. Tangential stress on the eruption conduit sidewall is estimated in cases of melt flow both in smooth and rough conduits. 相似文献
17.
N. P. Romanovskii Yu. F. Malyshev M. V. Goroshko 《Russian Journal of Pacific Geology》2008,2(2):137-149
Evidence on the Paleozoic granitoids of the eastern part of the Central Asian Fold Belt (CAFB) was analyzed. A tectonic chart of orogenic belts was compiled. Sketch maps were constructed for the geodynamic settings of the formation of Paleozoic granitoids and the extensiveness of their occurrence. Two types of deep controlling structures were distinguished: zones of lithospheric faults and plumes, including the newly recognized Jiamusi-Bureya plume. It was sown that the distribution of large and superlarge Paleozoic ore deposits is related to these structures, primarily to plumes. Sites promising for large and superlarge deposits related to the Paleozoic granitoid magmatism were determined in the Russian Far East. 相似文献
18.
Roberto Ventura Santos Carlos Eduardo Ganade Christian M. Lacasse Iago S. L. Costa Ivo Pessanha Eugenio P. Frazo Elton L. Dantas Jos A. Cavalcante 《地学学报》2019,31(5):424-429
Crystalline continental rocks and associated crust‐contaminated basaltic rocks were unexpectedly dredged on the crest and at seamounts of the Rio Grande Rise, South Atlantic. Zircon U–Pb ages of one gabbro (ca. 2,200 Ma) and four granitoids (between ca. 1,430–480 Ma) indicate that the breakup of SW Gondwana left behind continental fragments of dominantly African age. These rocks may have been incorporated into the oceanic lithosphere by complex processes including rifting and interaction of the Tristan‐Gough mantle plume with hyperextended continental margins. Until ca. 80–70 Ma, the Rio Grande Rise and an old portion of the Walvis Ridge formed a conjugate pair of aseismic ridges, and the Tristan‐Gough plume was positioned at the Mid‐Atlantic Ridge. The finding of continental rock fragments in one of these conjugate pairs opens new perspectives on the mechanisms of continental break‐up, the nature of this conjugate pair, and the geodynamic evolution of rifted Gondwana margins in the South Atlantic. 相似文献
19.
20.
A. D. Smith 《Australian Journal of Earth Sciences》2013,60(6-7):675-680
Source models for intraplate volcanism (IPV) include vertical introduction of material from deep in the mantle (plume model), contamination of the shallow mantle (perisphere and continental mantle delamination models) and derivation by selective partial melting of oceanic crust recycled into the depleted mantle (SUMA/streaky mantle models). The plume hypothesis became the ruling model after a flawed interpretation of helium isotope data in the mid 1980s that led to plumes being imposed on models for crustal recycling into the depleted mantle. This incorporation of otherwise competing concepts, is the cause of unnecessary complexity in modern geodynamic models. The plume model cannot explain all manifestations of IPV and a comprehensive explanation can only be found by invoking the alternative options, combined with their tapping by plate tectonic processes. 相似文献