A seismic refraction investigation of the Archaean Kaapvaal Craton, South Africa, using mine tremors as the energy source

Durrheim, Raymond; Green, R. W. E.

doi:10.1111/j.1365-246x.1992.tb03472.x

Cited by 73 publications

(43 citation statements)

References 45 publications

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“…[19] The seismic structure of the crust and upper mantle beneath southern Africa has been investigated using refraction profiles [Baier et al, 1983;Stuart and Zengeni, 1987;Green and Durrhiem, 1990;Durrheim and Green, 1992] and teleseismic receiver functions [Nguuri et al, 2001;Stankiewicz et al, 2002]. Data for the receiver function analy-ses comes mainly from a large network of broadband seismic stations deployed across southern Africa between 1997 and 1999 as part of the Kaapvaal Project [Carlson et al, 1996].…”

Section: Geophysical and Geochemical Backgroundmentioning

confidence: 99%

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Nyblade

Sleep

2003

Geochem Geophys Geosyst

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We investigate under what conditions the present-day long wavelength anomalous elevation ($500 m) of the southern African Plateau can be attributed to Mesozoic plume events. The anomalous, long wavelength topography of the southern African Plateau cannot be easily explained by recent heating of the upper mantle, as opposed to other areas of the African Superswell, and geomorphological studies provide few hard constraints on the timing of the uplift. A Mesozoic origin for the plateau uplift is attractive in that southern Africa experienced several large magmatic events in the Mesozoic. We formulate numerical and scaling models to investigate if plume material ponded beneath cratonic lithosphere in the Mesozoic could produce 500 m of present-day elevation. We find that starting plume heads are ineffective at producing much long lasting uplift because the material spreads into a thin layer, tens of km thick. The ponded plume material also suppresses secondary convection by having a stable boundary at its base. Over time, heat continues to flow out of the top of the lithosphere, and a net imbalance of heat flow in the lithosphere develops, resulting in subsidence. Even after the plume material has cooled to the temperature of the mantle adiabat, secondary convection supplies less heat to the lithosphere than is lost upward by conduction. The cratonic lithosphere returns to its original thermal structure on a timescale of less than 200 m.y. Even two mantle starting plume heads, one at the time of Karoo volcanism (ca.183 Ma) and the other at the time of kimberlite eruption (ca. 80-90 Ma) in our models, cannot produce much (<200 m) of the present-day anomalous elevation. However, significant uplift can be generated by plume tails, provided they linger beneath the lithosphere for $25-30 m.y., and if the uplift effects of Mesozoic plume heads and tails are considered together, then it is possible to account for $500 m of present-day elevation. Consequently, a Mesozoic plume model for plateau uplift in southern Africa appears to be a viable model, if plume tails delivered heat to the southern African lithosphere over a period of 25 m.y. or more.Components: 15,106 words, 15 figures, 1 table.

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Section: Geophysical and Geochemical Backgroundmentioning

confidence: 99%

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Nyblade

Sleep

2003

Geochem Geophys Geosyst

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“…This value is also about 4 kilometres greater than the average thickness of the crust in the adjacent regions of the craton: a result that is expected for an intra-cratonic sedimentary basin. However, this thickness of 42 km is about 6-7 km greater than that inferred by Durrheim and Green (1992) and Durrheim (1998) from recordings of mine tremors along refraction lines deployed Fig. 10.…”

Section: Discussionmentioning

confidence: 49%

“…A feasibility study on the use of mine tremors in South Africa for determining crustal structure was pioneered more than fifty years ago by Gane et al (1946). P and S waves from these mining-induced events were subsequently used to determine the wavespeed structure of the crust and uppermost mantle around the Witwatersrand basin (Willmore et al, 1952;Hales and Sacks, 1959;Durrheim and Green, 1992;Durrheim, 1998). However, only recently have such events been used in conjunction with local and regional tectonic events to determine regional travel-time curves and earth structure from the surface to depths of 800 km Wright et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa

et al. 2014

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Estimates of crustal thicknesses using Pn times and receiver functions agree well for the southern part of the Kaapvaal craton, but not for the northern region. The average crustal thicknesses determined from Pn times for the northern and southern regions of the craton were 50.52 ± 0.88 km and 38.07 ± 0.85 km respectively, with corresponding estimates from receiver functions of 43.58 ± 0.57 km and 37.58 ± 0.70 km. The lower values of crustal thicknesses for receiver functions in the north are attributed to variations in composition and metamorphic grade in an underplated, mafic lower crust, resulting in a crust-mantle boundary that yields weak P-to-SV conversions. P and S wavespeeds in the uppermost mantle of the central regions of the Kaapvaal craton are high and uniform with average values of 8.35 and 4.81 km/s respectively, indicating the presence of depleted magnesium-rich peridotite. The presence of a low wavespeed zone for S waves in the upper mantle between depths of 210 and about 345 km that is not observed for P waves was inferred outside the Kaapvaal craton. The 410 km discontinuity shows similar characteristics to that in other continental regions, but occurs slightly deeper at 420 km. There is no evidence for a discontinuity near 520 km depth. The 660 km discontinuity also appears to be slightly deeper than average (668 km), and is poorly defined for P waves, but clear for S waves.

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“…These processes have long since erased the signature of the impact upon the rock's elastic physical properties. Other factors including the existence of thick melt sheets such as the Sudbury Igneous Complex (Therriault et al 2002) or of the central uplift of deeper and higher velocity materials as seen at Chicxulub (Morgan et al 2000) and Vredefort (Green and Chetty 1990;Durrheim and Green 1992) further complicates comparison of the larger structures to those at the scale of the Bosumtwi impact structure.…”

Section: Seismological Investigations Of Impact Structuresmentioning

confidence: 99%

In situ seismic measurements in borehole LB‐08A in the Bosumtwi impact structure, Ghana: Preliminary interpretation

Schmitt

Milkereit

Karp

et al. 2007

Meteorit & Planetary Scien

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Abstract-In order to assist in the interpretation of previous seismic refraction and reflection surveys, a vertical seismic profile was acquired in the Lake Bosumtwi (Ghana) hard-rock core hole LB-08A. No seismic reflections are seen in the up-going wave field obtained, and this observation is consistent with the lack of reflectivity observed in the corresponding 2-D surface seismic profile obtained in earlier studies. Direct down-going P-waves were found both in the cased sediment column from a depth of 73 m to 239 m below the lake surface and in the open-hole "hard rock" section from a depth of 239 m to 451 m of LB-08A. Analysis of the observed travel times indicates a nearly constant P-wave velocity of 1520 m/s through the soft lacustrine sediments. In the hard-rock, however, the P-wave velocity rapidly increases by nearly 30% from 2600 m/s to 3340 m/s. These values are in good agreement with the gross velocity structure obtained in the earlier joint inversion of seismic reflection and refraction data. These values are low relative to those expected for the metasedimentary protoliths, an observation that has been made at other young impact structures of similar size. The low velocities, together with the fact that they increase so rapidly, is suggestive of a decreasing density of fractures and microcracks with depth. Consequently, the seismic velocity trend may provide a proxy measure of damage, and hence, the decay of the shock pressure from the impact point. Validation of this requires additional detailed studies of the porosity structure in the core.

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A seismic refraction investigation of the Archaean Kaapvaal Craton, South Africa, using mine tremors as the energy source

Cited by 73 publications

References 45 publications

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa

In situ seismic measurements in borehole LB‐08A in the Bosumtwi impact structure, Ghana: Preliminary interpretation

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