Intergranular basaltic melt is distributed in thin, elogated inclusions

Faul, U.; Toomey, D. R.; Waff, Harve S.

doi:10.1029/93gl03051

Cited by 146 publications

(158 citation statements)

References 10 publications

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“…Melilititic and nephelinitic rocks from the Natron lake area show degrees of partial melting consistent with melting zones as deep as 60-75 and 75-90 km (Mattsson et al 2013). A melt fraction of 3-6 per cent can reduce seismic velocity by 5-10 per cent in the upper mantle (Olugboji et al 2013), depending on melting body geometry (Faul et al 1994;Takei 2002). Moreover, accumulated melt at midlithosphere could feed the LVZ observed at low crustal depth and can be related to the intricate axial valley structure complexity observed in the RFs.…”

Section: Upper Mantle Structurementioning

confidence: 88%

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

Plasman¹,

Tiberi

Ebinger

et al. 2017

Geophysical Journal International

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Section: Upper Mantle Structurementioning

confidence: 88%

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

Plasman¹,

Tiberi

Ebinger

et al. 2017

Geophysical Journal International

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“…The main uncertainty is due to the strong dependence on melt geometry. Experiments on the distribution of basaltic melts [Faul et al, 1994] show most melt to be present in low aspect ratio inclusions, which would imply a relatively strong effect on seismic velocity. A further complication is that the presence of water strongly affects the melting temperature.…”

Section: Forward Modeling Of Seismic Velocitiesmentioning

confidence: 99%

Shallow mantle temperatures under Europe from P and S wave tomography

Goes¹,

Govers²,

Vacher³

2000

J. Geophys. Res.

537

640

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Abstract. Temperature is one of the key parameters controlling lithospheric and mantle dynamics and rheology. Using recent experimental data on elastic parameters and anelasticity, we obtain models of temperature at 50 to 200 km depth beneath Europe from the global P wave velocity model of Bijwaard et al. [ 1998] and the regional S wave velocity model of Marquering and Snieder [1996]. Forward modeling of seismic velocity allows us to assess the sensitivity of velocity to various parameters. In the depth range of interest, variations in temperature (when below the solidus) yield the largest effects. For a 100øC increase in temperature, a decrease of 0.5-2% in Vp and 0.7-4.5% in Vs is predicted, where the strongest decrease is due to the large effect of anelasticity at high temperature. The effect of composition is expected to give velocity anomalies <1% for the shallow mantle and would therefore be difficult to resolve. At depths >80 km the relative amplitudes of the European Vp and Vs anomalies are consistent with a thermal origin. At shallower depths, variations in crustal thickness and possibly the presence of partial melt appear to have an additional effect, mainly on S wave velocity. In regions where both P and S anomalies are well-resolved, Vp-and Vs-derived thermal models agree well with each other and with temperatures determined from surface heat flow observations. Furthermore, the thermal models are consistent with known tectonics. The inferred temperatures vary significantly, from around 400øC below an average mantle adiabat at 100 km depth under the Russian Platform and a 300øC increase from east to west across the Tornquist-Teisseyre zone to temperatures around the mantle adiabat in the depth range 50-200 km under areas with present surface volcanism. In spite of the uncertainties in the calculation of temperatures due to uncertainties in the experimental elastic parameters and anelasticity and uncertainties associated with tomographic imaging, we find that the tomographic models of the shallow mantle under Europe can yield useful estimates of the thermal structure.

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“…Spherical melt pockets are obviously the least-effective shapes for generating anisotropy. The shape and orientation of melt is controlled by wetting angles and strains in the medium (Schmeling 1985;Faul et al 1994). As strain and melt fraction increases, the melt will start to align along grain edges and then crystal faces.…”

Section: Mechanisms For Seismic Anisotropymentioning

confidence: 99%

Mantle upwellings, melt migration and the rifting of Africa: insights from seismic anisotropy

et al. 2006

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Abstract:The tiffing of continents and eventual formation of ocean basins is a fundamental component of plate tectonics, yet the mechanism for break-up is poorly understood. The East African Rift System (EARS) is an ideal place to study this process as it captures the initiation of a rift in the south through to incipient oceanic spreading in north-eastern Ethiopia. Measurements of seismic anisotropy can be used to test models of rifting. Here we summarize observations of anisotropy beneath the EARS from local and teleseismic body-waves and azimuthal variations in surfacewave velocities. Special attention is given to the Ethiopian part of the rift where the recent EAGLE project has provided a detailed image of anisotropy in the portion of the Ethiopian Rift that spans the transition from continental rifting to incipient oceanic spreading. Analyses of regional surface-waves show sub-lithospheric fast shear-waves coherently oriented in a northeastward direction from southern Kenya to the Red Sea. This parallels the trend of the deeper African superplume, which originates at the core-mantle boundary beneath southern Africa and rises towards the base of the lithosphere beneath Afar. The pattern of shear-wave anisotropy is more variable above depths of 150 km. Analyses of splitting in teleseismic phases (SKS) and local shear-waves within the rift valley consistently show rift-parallel orientations. The magnitude of the splitting correlates with the degree of magmatism and the polarizations of the shear-waves align with magmatic segmentation along the rift valley. Analysis of surface-wave propagation across the rift valley confirms that anisotropy in the uppermost 75 km is primarily due to melt alignment. Away from the rift valley, the anisotropy agrees reasonably well with the pre-existing Pan-African lithospheric fabric. An exception is the region beneath the Ethiopian plateau, where the anisotropy is variable and may correspond to pre-existing fabric and ongoing melt-migration processes. These observations support models of magma-assisted rifting, rather than those of simple mechanical stretching. Upwellings, which most probably originate from the larger superplume, thermally erode the lithosphere along sites of pre-existing weaknesses or topographic highs. Decompression leads to magmatism and dyke injection that weakens the lithosphere enough for rifting and the strain appears to be localized to plate boundaries, rather than wider zones of deformation.

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Intergranular basaltic melt is distributed in thin, elogated inclusions

Cited by 146 publications

References 10 publications

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

Shallow mantle temperatures under Europe from P and S wave tomography

Mantle upwellings, melt migration and the rifting of Africa: insights from seismic anisotropy

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