Mantle Plume (mantle + plume)

Distribution by Scientific Domains

Selected Abstracts

Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau

N. DS.
Abstract The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ,1400,m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early,Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre-sedimentation phase, include pre-rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic,Early Jurassic fluvial sedimentation (Lower Sandstone, ,300,m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ,30,m thick); (c) Early,Middle Jurassic deepening of the basin (Lower Limestone, ,450,m thick); (d) desiccation of the basin and deposition of Early,Middle Jurassic gypsum; (e) Middle,Late Jurassic marine transgression (Upper Limestone, ,400,m thick); (f) Late Jurassic,Early Cretaceous basin-uplift and marine regression (alluvial/fluvial Upper Sandstone, ,280,m thick); (3) the post-sedimentation phase, including Early,Late Oligocene eruption of 500,2000,m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ,300,m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic,Cretaceous NE,SW-directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW-trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW,SE-directed extension related to the Main Ethiopian Rift that formed NE-trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E,W and NNE,SSW-directed extensions related to oblique opening of the Main Ethiopian Rift and development of E-trending transverse faults, as well as NE,SW-directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E,W-directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N-, ESE- and NW-trending extensional structures within the Blue Nile Basin. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Mantle plumes: heat-flow near Iceland

Carol A Stein
No abstract is available for this article. [source]

Seismic evidence for a mantle plume oceanwards of the Kamchatka,Aleutian trench junction

A. Gorbatov
Summary A non-linear iterative P- wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km, rising across the 600 km discontinuity, and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate. Data from the Geophysical Survey of Russia (1955,1997) were inverted jointly with the catalogues of International Seismological Centre and USGS National Earthquake Information Centre (1964, 1998). The result shows a 300,500 km-wide cylindrical low-velocity anomaly (, , 2 per cent) that extends from a depth of greater than 900 km to shallower than 200 km. The anomaly is almost vertical at depths up to ,400 km and rises obliquely to the north up to ,200 km under the ocean floor near the northern end of Emperor seamounts. Above ,300 km depth a subsidiary anomaly extends subhorizontally to the NW in fair agreement with the direction of movement of the Pacific Plate. The overlying seafloor is characterized by anomalously high heat flow, which may be attributed to the thermal effect of the mantle plume. [source]

Analyses of the stress field in southeastern France from earthquake focal mechanisms

Emmanuel Baroux
Summary Owing to the apparent deformation field heterogeneity, the stress regimes around the Provence block, from the fronts of the Massif Central and Alpine range up to the Ligurian Sea, have not been well defined. To improve the understanding of the SE France stress field, we determine new earthquake focal mechanisms and compute the present-day stress states by inversion of the 89 available focal mechanisms around the Provence domain, including 17 new ones calculated in the current study. This study provides evidence of six distinct deformation domains around the Provence block, with different tectonic regimes. On a regional scale, we identify three zones characterized by significantly different stress regimes: a western one affected by an extensional stress (normal faulting) regime; a southeastern one characterized by a compressional stress (reverse to strike-slip faulting) regime with NNW- to WNW-trending ,1; and a northeastern one, namely the Digne nappe front, marked by a NE-trending compression. Note that the Digne nappe back domain is controlled by an extensional regime that is deforming the western Alpine core. This extensional regime could be a response to buoyancy forces related to the Alpine high topography. The stress regimes in the southeast of the Argentera Massif and around the Durance fault are consistent with a coherent NNW-trending ,1, implying a left-lateral component of the active reverse oblique slip of the Moyenne Durance Fault. In the Rhone Valley, an E-trending extension characterizes the tectonic regime, implying a normal component of the present-day N,^mes fault displacement. This study provides evidence for short-scale variation of the stress states, which arises from abrupt changes in the boundary force influences on upper crustal fragments (blocks). These spatial stress changes around the Provence block result from the coeval influence of forces applied at both its extremities, namely in the northeast the Alpine front push, and in the southeast the northward African plate drift. In addition to these boundary forces, the mantle plume under the Massif Central influences the western block boundary. [source]

Crustal structure of central and northern Iceland from analysis of teleseismic receiver functions

Fiona A. Darbyshire
We present results from a teleseismic receiver function study of central and northern Iceland, carried out during the period 1995,1998. Data from eight broad-band seismometers installed in the SIL network operated by the Icelandic Meteorological Office were used for analysis. Receiver functions for each station were generated from events for a wide range of backazimuths and a combination of inversion and forward modelling was used to infer the crustal structure below each station. The models generated show a considerable variation in the nature and thickness of the crust across Iceland. The thinnest crust (20,21 km) is found in the northern half of the Northern Volcanic Zone approximately 120 km north of the centre of the Iceland mantle plume. Thicker crust (24,30 km) is found elsewhere in northern and central Iceland and the thickest crust (37 km) is found close to the plume centre. Velocity,depth profiles show a distinct division of the crust into two main sections, an upper high-velocity-gradient section of thickness 2,8 km and a lower crustal section with small or zero overall velocity gradient. The thickness of the upper crust correlates with the tectonic structure of Iceland; the upper crust is thickest on the flanks of the northern and central volcanic rift zones and thinnest close to active or extinct central volcanoes. Below the Krafla central volcano in northeastern Iceland the receiver function models show a prominent low-velocity zone at 10,15 km depth with minimum shear wave velocities of 2.0,2.5 km s,1. We suggest that this feature results from the presence of partially molten sills in the lower crust. Less prominent low-velocity zones found in other regions of Iceland may arise from locally high temperatures in the crust or from acidic intrusive bodies at depth. A combination of the receiver function results and seismic refraction results constrains the crustal thickness across a large part of Iceland. Melting by passive decompression of the hot mantle below the rift zone in northern Iceland forms a crust of thickness ,20 km. In contrast, the larger crustal thickness below central Iceland probably arises from enhanced melt production due to active upwelling in the plume core. [source]

Olivine-spinifex basalt from the Tamba Belt, southwest Japan: Evidence for Fe- and high field strength element-rich ultramafic volcanism in Permian Ocean

ISLAND ARC, Issue 3 2007
Yuji Ichiyama
Abstract Permian basalt showing typical spinifex texture with >10 cm-long olivine pseudomorphs was discovered from the Jurassic Tamba accretionary complex in southwest Japan. The spinifex basalt occurs as a river boulder accompanied by many ferropicritic boulders in a Permian chert-greenstone unit. Groundmass of this rock is holocrystalline, suggesting a thick lava or sill for its provenance. Minor kaersutite in the groundmass indicates a hydrous magma. The spinifex basalt, in common with the associated ferropicritic rocks, is characterized by high high field strength element (HFSE) contents (e.g. Nb = 62 ppm and Zr = 254 ppm) and high-HFSE ratios (Al2O3/TiO2 = 3.9, Nb/Zr = 0.24 and Zr/Y = 6.4) unlike typical komatiites. The spinifex basalt and ferropicrite might represent the upper fractionated melt and the lower olivine-rich cumulate, respectively, of a single ultramafic sill (or lava) as reported from the early Proterozoic Pechenga Series in Kola Peninsula. Their parental magma might have been produced by hydrous melting of a mantle plume that was dosed with Fe- and HFSE-rich garnet pyroxenite. The spinifex basalt is an evidence for the Pechenga-type ferropicritic volcanism taken place in a Permian oceanic plateau, which accreted to the Asian continental margin as greenstone slices in Jurassic time. [source]

Magmatic Event at the End of the Archean in Eastern Hebei Province and Its Geological Implication

GENG Yuansheng
Abstract: By using the SHRIMP U-Pb and single zircon stepwise evaporation methods, the authors have obtained some results for granitoids from eastern Hebei Province. The Yuhuzhai hyperthene tonalitic granite was formed 2550 Ma ago, the Qingyangshu gabbroic gneiss 2536 Ma, the Yinmahe granodioritic gneiss near Lücao, Lulong County, 2533 Ma, the gabbro-dioritic gneiss near Longwan, Qianxi County, 2518-2515 Ma, the Qiuhuayu trondjemitic gneiss at Zunhua 2515 Ma, the Xiaoguanzhuang tonalitic gneiss at Zunhua 2495 Ma, and the Cuizhangzi gneiss in Qianxi County 2492 Ma. These geochronilogical data demonstrate that, though diverse in composition, type and origin, the granitic gneisses in eastern Hebei Province were emplaced and crystallized in a rather short period of magmatic activity. The formation of such a great amount of gneisses in this small time gap suggests that it was a critical crust accretion stage at the end of Neoarchean. The fact that granitoids of various types occurred at the same time implies a large-scale underplating (mantle plume) activity, which was then responsible for the crust accretion. [source]

Controls of mantle plumes and lithospheric folding on modes of intraplate continental tectonics: differences and similarities

Evgueni Burov
SUMMARY Mantle plume activity and lithospheric folding by far-field stresses exerted from plate boundaries are two important end-members as mechanisms for continental intraplate deformation. The topographic expression of mantle plume impingement on continental lithosphere and lithospheric folding has some striking similarities. Observations from a number of areas in Europe's intraplate lithosphere demonstrate that these mechanisms commonly interact in space and time. We present the results of thermomechanical modelling addressing the role of factors such as the presence of a hot upper mantle, the spatial dimensions of the plume and the time constants involved in the temporal succession of plume activity and lithospheric folding by stress accumulation in intraplate continental lithosphere. The results demonstrate that both the processes, plume,lithosphere interactions and folding may interact resulting either in strong amplification, attenuation or modification of their surface expression. These inferences are compatible with a number of key observations on the nature and the temporal succession of topography evolution in the Alpine foreland, the Pannonian Basin, the Scandinavian continental margin and the Iberian Peninsula. [source]

Upwelling plumes, superswells and true polar wander

Marianne Greff-Lefftz
SUMMARY The geological evolution of the rotational axis of the Earth is most likely controlled by internal mass redistribution within the mantle. Palaeomagnetic observations suggest that it is episodic in nature, with periods of quasi-standstill alternating with periods of faster wander. Here, we investigate two models for the influence of mantle plumes that vary at different spatial wavelengths on the time variations of the rotational axis (true polar wander; TPW). In the first model, we represent an upwelling plume as a sphere whose radius varies as a function of the flux of material in the conduit and that traverses the mantle at the Stokes velocity. Such a plume produces very little wander of the rotational axis. We then study the effects of two superswells that mimic the ones observed with seismic tomography and conclude that a doming regime within the mantle involves significant polar wander. Some of the features of this TPW that are directly linked to the periodicity of doming are reminiscent of observed phases of slow and fast TPW, with similar peak velocities. [source]