Upper mantle P wave velocity structure and transition zone thickness beneath the Arabian Shield

Benoit, M. H.; Nyblade, A.; VanDecar, J. C.; Gurrola, H.

doi:10.1029/2002gl016436

Cited by 62 publications

(72 citation statements)

References 14 publications

(21 reference statements)

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“…Also, slower-than-average P and S velocities were found in the uppermost mantle beneath the western part of the shield [25,26], indicating the upper mantle is anomalously hot and is possibly associated with the uplift of the Arabian shield [26,27]. The low velocity anomaly was found to extend from the Red Sea eastward into the interior of the shield and to be confined to depths shallower than 410 km [26].…”

Section: Introductionmentioning

confidence: 88%

“…Surface waves as well as regional waveform modeling indicate that on average the Arabian shield crust is 40 -45 km thick, slightly thicker than the average crust for most shields on earth [22][23][24]. Also, slower-than-average P and S velocities were found in the uppermost mantle beneath the western part of the shield [25,26], indicating the upper mantle is anomalously hot and is possibly associated with the uplift of the Arabian shield [26,27]. The low velocity anomaly was found to extend from the Red Sea eastward into the interior of the shield and to be confined to depths shallower than 410 km [26].…”

Section: Introductionmentioning

confidence: 98%

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Crustal structure of the Arabian plate: new constraints from the analysis of teleseismic receiver functions

Aldamegh¹,

Sandvol²,

Barazangi³

2005

Earth and Planetary Science Letters

133

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We also employed a grid search waveform modeling technique to estimate the crustal velocity structure for seven stations. A jackknife re-sampling approach was used to estimate errors in the grid search results for three stations. In addition to our results, we have also included published receiver function results from two temporary networks in the Arabian shield and Oman as well as three permanent GSN stations in the region.The average crustal thickness of the late Proterozoic Arabian shield is 39 km. The crust thins to about 23 km along the Red Sea coast and to about 25 km along the margin of the Gulf of Aqaba. In the northern part of the Arabian platform, the crust varies from 33 -37 km thick.However, the crust is thicker (41 -53 km) in the southeastern part of the platform. There is a dramatic change in crustal thickness between the topographic escarpment of the Arabian shield and the shorelines of the Red Sea. We compared our results in the Arabian shield to nine other Proterozoic and Archean shields that include reasonably well-determined Moho depths, mostly based on receiver functions. The average crustal thickness for all shields is 39 km, while the average for Proterozoic shields is 40 km, and the average for Archean shields is 38 km. We found the crustal thickness of Proterozoic shields to vary between 33 and 44 km, while Archean shields vary between 32 and 47 km. Overall, we do not observe a significant difference between Proterozoic and Archean crustal thickness. 3We observed a dramatic change in crustal thickness along the Red Sea margin that occurs over a very short distance. We projected our results over a cross section extending from the Red Sea ridge to the shield escarpment and contrasted it with a typical Atlantic margin. The transition from oceanic to continental crust of the Red Sea margin occurs over a distance of about 250 km, while the transition along a typical portion of the western Atlantic margin occurs at a distance of about 450 km. This important new observation highlights the abruptness of the breakup of Arabia. We argue that a preexisting zone of weakness coupled with anomalously hot upper mantle could have initiated and expedited the breakup.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 98%

Crustal structure of the Arabian plate: new constraints from the analysis of teleseismic receiver functions

Aldamegh¹,

Sandvol²,

Barazangi³

2005

Earth and Planetary Science Letters

133

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“…Regional tomography shows a thin tabular lowvelocity zone to depths of over 250 km beneath the continental part of the Ethiopian rift . This anomaly broadens laterally in the more oceanic northeasterly region and appears to connect with the Afar plume (Benoit et al 2003;Debayle et al 2001). There are also numerous lines of evidence for a separate plume or upper-mantle instability under Tanzania or Uganda (Ebinger & Sleep 1998;Weeraratne et al 2003), but its depth extent is unclear.…”

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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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“…The low diffusivity is depicting a fractured medium generated due to past intrusions of dykes through which the pore pressure perturbation took place. The existence of mantle plume beneath the western part of the Arabian plate including Harrat Lunayyir has been recognized by several studies (Benoti et al 2003, Daradich et al 2003, Julia et al 2003, Al-Damegh et al 2005 with surface expression of the plume-related ocean-island basalt volcanism (Moufti and Hashad 2005). Pronounced degassing of the CO 2 dominate upper mantle is probably the source of the H 2 O plus CO 2 dominated fluid (cf.…”

Section: Pore Presssue Perturbationmentioning

confidence: 99%

Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia

Mukhopadhyay

Mogren

Mukhopadhyay

et al. 2013

Geomatics, Natural Hazards and Risk

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The 2009 earthquake-swarm in the Al-Ays volcanic zone in Harrat-Lunayyir in NW Saudi-Arabia is unique because of its intense character and focal-depth distribution at two depth bands (5-10 and 15-20 km) in upper crust without volcanic eruption. We investigate an anatomy of the dyke-intrusion model that supports the mechanism for the swarm itself with seismotectonics, pore pressure diffusion process and inference model. Inferred dyke-intrusion initially started at depth had a five-day peak period (15-20 May 2009) since inception of eventrecordings, following which the activity diminished. The process of pore pressure perturbation and resultant ''r-t plot'' with modelled diffusivity (D ¼ 0.01) relates the diffusion of pore pressure to seismic sequence in a fractured poro-elastic fluidsaturated medium. The spatio-temporal b-values show high b-values (41.3) along the zone of dyke intrusion (length 10 km and height 5 km) at *20km depth. The main-shock and other prominent earthquakes originated on a moderate b-value zone (*1.0). Temporal b-value analysis indicates an exceptionally low b-value (*0.4) during the main-shock occurrence. The AlAys lava-field is inferred to underlie a seismic volume trending NW-SE bounded on both sides by two NW-SE trending fault systems, dipping 40-508 opposite to each other within a proposed nascent rift setting.

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Upper mantle P wave velocity structure and transition zone thickness beneath the Arabian Shield

Cited by 62 publications

References 14 publications

Crustal structure of the Arabian plate: new constraints from the analysis of teleseismic receiver functions

Crustal structure of the Arabian plate: new constraints from the analysis of teleseismic receiver functions

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

Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia

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