Growth and Dispersal of a Southeast African Large Igneous Province

Abstract

The Mozambique Ridge (MOZR) and the Agulhas Plateau (AP) are prominent bathymetrically elevated rises off south-eastern Africa connected by a rise of less bathymetric expression. Intuitively, this observation would imply that the plateaus and rises underwent a related crustal formation. Deep crustal ocean-bottom seismometer data and a multichannel seismic reflection profile from the southern MOZR show evidence for its predominantly oceanic crustal origin with excessive volcanic eruption and magmatic accretion phases. The lower two-thirds of the crustal column exhibit P-wave velocities of more than 7.0 km/s, increasing to 7.5 to 7.6 km/s at the crustal base. These velocities suggest that the lower crust was accreted by large volumes of mantle-derived material to form an over-thickened equivalent of an oceanic layer 3. The velocity-depth model and the seismic reflection data of the MOZR resemble those of the AP, which suggests that a greater Southeast African Large Igneous Province (LIP) must have formed between 140 and 95 Ma in phases of highly varying magmatic and volcanic activities. The timing, size, and formation history of the Southeast African LIP is similar to those of the Kerguelen-Heard Plateau, which invites speculation about related processes of episodic magma generation at that time.

Palaeoceanographic Interpretation of a Seismic Profile From the Southern Mozambique Ridge, Southwestern Indian Ocean

“…A continental provenance is suggested by Tucholke et al (1981), Raillard and Mougenot (1990), Mougenot et al (1991), and Hartnady et al (1992). New seismic refraction data is interpreted as strong evidence for a LIP origin of the southern Mozambique Ridge (Gohl et al, 2011) and is supported by a recent magnetic survey (König and Jokat, 2010).…”

“…The older unit S1 fills the basement topography, which is strongly affected by faulting. Gohl et al (2011) suggest that the Mozambique Ridge was formed at the same magmatic province as the Astrid Ridge. Faulting then occurred during the separation of the Mozambique Ridge from the Astrid Ridge shortly after 120 Ma.…”

The Mozambique Ridge: a document of massive multistage magmatism

“…Seismic refraction and reflection data collected across the swMozR are interpreted as strong evidence for an oceanic LIP origin of the southern MozR (parallel to the purple line in Fig. 1; Gohl et al 2011). A LIP origin of the whole MozR could have had an immense influence on climate during the Early Cretaceous with the emission of gases and heat into atmosphere and ocean and in addition implications on the development of the South African gateway with the formation of obstacles for surface and deep circulation.…”

“…Chetty & Green (1977) concluded that the over-thickened crust lacks characteristic velocities of the continental basement and therefore a basement of continental crust was not strongly supported. The interpretation of 2-D seismic refraction data showed that the MozR is characterized by over-thickened (16-22 km), seismically homogeneous, lower crustal units making up between half to two-thirds of the crustal column with P-wave velocities of more than 7.0 km s −1 (Gohl et al 2011). According to them these velocities suggest that large volumes of mantle-derived material accreted in the lower crust and indicate a formation of MozR and Agulhas Plateau at the same magmatic province (Gohl & Uenzelmann-Neben 2001;Parsiegla et al 2008).…”

“…The first samples from the basement of the MozR were collected at DSDP Leg 25 Site 249 on the nMozR, where 3.1 m of tholeiitic basalt was recovered (Simpson et al 1974). Gohl et al (2011) is coincident with NNE-SSW striking MCS profile AWI-20050018 of SO 182 depicted in purple (Gohl et al 2011;Uenzelmann-Neben et al 2011). White numbers depict the segments of the Mozambique Ridge: 1 = northern Mozambique Ridge, 2 = central Mozambique Ridge, 3 = southwestern Mozambique Ridge, 4 = southeastern Mozambique Ridge.…”