The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

Uenzelmann-Neben, Gabriele; Gohl, Karsten

doi:10.1007/s11001-005-1338-8

Cited by 16 publications

(14 citation statements)

References 30 publications

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“…These mounds with a size of <3 km in diameter and an elongated or amoeba‐type shape are associated with subhorizontal sills, intrusion of central vents and highly vesicular lava knolls. Intrusions at fractures zones in the North (Døssing et al 2008) and South Atlantic (Uenzelmann‐Neben & Gohl 2005) do not show sills either, so the lack of observed sills in our data does not rule out intrusions. On the other hand, strong variations in reflection amplitude of the sedimentary horizons above the basement highs point towards degassing as the result of magmatic intrusions (Lizarralde et al 2012).…”

Section: Discussioncontrasting

confidence: 61%

Intraplate volcanism off South Greenland: caused by glacial rebound?

Uenzelmann-Neben

Schmidt

Niessen

et al. 2012

Geophysical Journal International

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SUMMARY Plate tectonic mechanisms explain most of the dominant types of volcanism. Intraplate volcanism has been attributed to hotspots associated with mantle plumes, although alternative explanations have been proposed for settings not fed by plumes. We report young intraplate volcanism in an amagmatic margin south of Greenland in a 40‐Myr‐old plate. An elongated structure with a length of 110 km and a height of 2500 m above basement extends at an oblique angle to the Mid Atlantic ridge and the fracture zones. We propose that this structure is related to reactivation of a rudimentary fracture zone by edge‐driven convection across Minna Fracture Zone and partial melting caused by glacial rebound during the periodic melting of ice on Greenland in the last 3 Myr.

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Section: Discussioncontrasting

confidence: 61%

Intraplate volcanism off South Greenland: caused by glacial rebound?

Uenzelmann-Neben

Schmidt

Niessen

et al. 2012

Geophysical Journal International

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“…Their influence is therefore likely to be negligible. By contrast, the oceanic Agulhas Plateau (~100 to ~80 Ma), and its likely extensions preserved along the southern parts of the Mozambique Ridge, the Maud Rise, and the Maurice Ewing Bank adjacent to the Falkland Plateau (Gohl and Uenzelmann-Neben, 1999;Jokat et al, 2003;Uenzelmann-Neben and Gohl, 2004;Uenzelmann-Neben et al, 2004), closely flanked the sheared south-coast continental margin of southern Africa at the time of the first major uplift episode recorded here. This is also a time of distinct change in spreading direction in the South Atlantic (e.g.…”

Section: Large Igneous Provinces (Lips) and Basaltic Underplatingmentioning

confidence: 52%

“…This first event is followed by a period of quiescence for > 40 Ma before a second period of fast cooling occurred between ~110 and ~90 Ma, and during which up to 4 km denudation took place along the coastal plains and up to 2 km from the top of the plateau. This event overlaps with the second major cooling episode documented along the south coast (e.g.~100 to ~80 Ma), not associated with rifting but instead overlapping with oceanic flood basalt activity during the formation of the Agulhas Plateau (Figure 4; Uenzelmann-Neben et al, 1999;Uenzelmann-Neben and Gohl, 2004;Gohl and Uenzelmann-Neben 2001). (Hinz et al,1999), associated with large volumes of underplated basalts along both sides of the south Atlantic.…”

Section: Timing and Rates Of Uplift In Southern Africamentioning

confidence: 57%

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Wit

2007

South African Journal of Geology

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Southern Africa's high Kalahari plateau and its flanking mountain ranges formed over an extended period of ~200 million years through vertical tectonic processes different from those at convergent plate boundaries. We refer to this as the Kalahari epeirogeny. Episodic uplift and erosion during the Kalahari epeirogeny is inferred from thermo-chronology and from stratigraphy of sediment accumulated around its continental margin. A total thickness of 2 to 7 km of rock (of which basalt was a major component) was eroded from the subcontinent's surface during two punctuated episodes of exhumation, in the early-Cretaceous and in the mid-Cretaceous. Major exhumation was over by the end of the Cretaceous, and the rate of erosion decreased by more than an order of magnitude to remove less than 1 km thickness of rock during the Cenozoic. Cosmogenic dating shows that erosion rates today are almost an order of magnitude less still.The cause for the Kalahari epeirogeny remains elusive, but three striking observations stand out: (i) major exhumation occurred during the late Mesozoic break-up of Gondwana; (ii) large scale basaltic magmatism closely match two accelerated episodes of exhumation: first along the west coast (~132 Ma, Etendeka large igneous province [LIP], associated with vast amounts of underplating along this entire passive margin), and the second flanking the sheared south coast margin (~90 Ma, Agulhas oceanic LIP). Yet exhumation that might have accompanied the vast Karoo LIP (~180 Ma) is not readily detected; (iii) the two main regional episodes of accelerated exhumation and coastal sediment accumulation are near synchronous with two regional 'spikes' of kimberlite intrusions: >450 kimberlites at ~90 Ma, and >200 kimberlites at ~120 Ma. Southern Africa is underlain by an anomalous warm region in the lowermost ~1500 km of the mantle that is linked to core to mantle heat loss. This warm region was inherited from a large Cretaceous thermo-chemical anomaly in the mantle created during long-lived subduction beneath Gondwana. Associated Mesozoic kimberlite genesis and basaltic magmatism may have been sufficient to cause volatile/heat-induced density changes in the lithospheric mantle of southern Africa to sustain the Kalahari plateau. In addition, such changes may have been induced by tectonic uplift and decompressional melting resulting from far-field collision processes between Africa and Europe, and/or final continental lithosphere decoupling between the Falkland plateau and southern Africa. CO 2 released into the ocean-atmosphere system during the Kalahari epeirogeny contributed to the global mid-Cretaceous hot-house conditions. However, because the CO 2 -consumption rate associated with basalt weathering is about eight times that of granite, atmospheric CO 2 was also efficiently sequestrated during the rapid erosion of Karoo basalt. Thus, the Kalahari epeirogeny also may have catalysed the onset of long-term global Cenozoic cooling.

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“…This is also proposed for the similar cross-section geometry of the continental Algulhas Ridge (cf. Figure 5a) in the South Atlantic [Uenzelmann-Neben and Gohl, 2004]. The interpreted, segmented post-Chron A13 magnetic lineaments in the BB and the present, continuous outline of the Knipovich Ridge (Figure 18b) indicate recent changes in spreading direction, which could be responsible for this late tectonic activity over the EGR.…”

Section: The Greenland Fracture Zonementioning

confidence: 95%

“…A small channel is formed on the NE side of the high ( Figure 5). Notice the pronounced cross-sectional similarity between the EGR and the Agulhas Ridge ( Figure 5a); the latter has been interpreted as a continental sliver situated along the Agulhas-Falkland Fracture Zone in the South Atlantic [Uenzelmann-Neben and Gohl, 2004].…”

Section: Datamentioning

confidence: 99%

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

et al. 2008

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The combined Greenland‐Senja Fracture Zones (GSFZ) represent a first‐order plate tectonic feature in the North Atlantic Ocean. The GSFZ defines an abrupt change in the character of magnetic anomalies with well‐defined seafloor spreading anomalies in the Greenland and Norwegian basins to the south but ambiguous and weak magnetic anomalies in the Boreas Basin to the north. Substantial uncertainty exists concerning the plate tectonic evolution of the latter area, including the role of the East Greenland Ridge, which is situated along the Greenland Fracture Zone. In 2002, a combined ocean‐bottom seismometer and multichannel seismic (MCS) survey acquired two intersecting wide‐angle reflection and coincident MCS profiles across and along the East Greenland Ridge. We present the results of integrated reflection seismic interpretation, first‐arrival tomography, 2D kinematic raytracing, full‐wave amplitude modeling, and gravity modeling of the intersecting profiles. The results show that (1) the Greenland Basin is characterized by a normal oceanic crustal velocity structure, (2) the velocity structure of the East Greenland Ridge is of overall continental type, and (3) a major faulted basin province above highly extended continental crust exists to the NE of the ridge. The results further suggest that a zone of extremely thin and faulted continental crust above partially serpentinized mantle peridotite defines the NW edge of the East Greenland Ridge and the transition to the NE Greenland margin.

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The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

Cited by 16 publications

References 30 publications

Intraplate volcanism off South Greenland: caused by glacial rebound?

Intraplate volcanism off South Greenland: caused by glacial rebound?

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

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