Crustal structure of the East African Limpopo margin, a strike-slip rifted corridor along the continental Mozambique Coastal Plain and North Natal Valley

Abstract

Abstract. Coincident wide-angle and multi-channel seismic data acquired within the scope of the PAMELA Moz3-5 project allow us to reconsider the formation mechanism of East African margins offshore of southern Mozambique. This study specifically focuses on the sedimentary and deep-crustal architecture of the Limpopo margin (LM) that fringes the eastern edge of the Mozambique’s Coastal Plain (MCP) and its offshore southern prolongation the North Natal Valley (NNV). It relies primarily on the MZ3 profile that runs obliquely from the northeastern NNV towards the Mozambique basin (MB) with additional inputs from a tectonostratigraphy analysis of industrial onshore–offshore seismic lines and nearby or crossing velocity models from companion studies. Over its entire N–S extension the LM appears segmented into (1) a western domain that shows the progressive eastward crustal thinning and termination of the MCP/NNV continental crust and its overlying pre-Neocomian volcano-sedimentary basement and (2) a central corridor of anomalous crust bounded to the east by the Mozambique fracture zone (MFZ) and the oceanic crust of the MB. A prominent basement high marks the boundary between these two domains. Its development was most probably controlled by a steep and deeply rooted fault, i.e., the Limpopo fault. We infer that strike-slip or slightly transtensional rifting occurred along the LM and was accommodated along this Limpopo fault. At depth we propose that ductile shearing was responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level during the rifting period and a shallow marine environment dominated the pre-Neocomian period during the early phase of continent–ocean interaction. It is only some time after break-up in the MB and the initiation of the MFZ that decoupling occurred between the MCP/NNV and the corridor, allowing for the latter to subside and become covered by deep marine sediments. A scenario for the early evolution and formation of the LM is proposed taking into account both recent kinematic and geological constraints. It implies that no or little change in extensional direction occurred between the intra-continental rifting and subsequent phase of continent–ocean interaction.

Contourite on the Limpopo Corridor, Mozambique margin: Long‐term evolution, facies distribution and Plio‐Quaternary processes

“…Initially subject to a dexterous movement, the Mozambique Channel finally opened by oceanic expansion from the Middle Jurassic, as the Antarctic and Australian continents moved south and eastward away from Africa. South of the Mozambique Coastal Plain, the Natal Valley is a sedimentary basin above a 30 km thick continental crust, 1000 m below sea‐level, probably resulting from a subsidence induced by probable intrusions of mantle‐derived melts in the lower crust (Moulin et al ., 2020; Evain et al ., 2021; Leprêtre et al ., 2021).…”

“…The Limpopo Corridor was supposed to be floored by oceanic crust, with emplacement during the opening of the Mozambique Basin as a northern extension of the magmatic Mozambique Ridge, south of the Naude ridge (Leinweber & Jokat, 2012; Mueller & Jokat, 2019). Combined wide‐angle and multi‐channel seismic studies and geodynamic studies have shown that the Limpopo Corridor is a strike‐slip margin with thin continental crust (Thompson et al ., 2019; Moulin et al ., 2020; Evain et al ., 2021; Li et al ., 2021; Watremez et al ., 2021). The positive gravity anomalies correspond to a series of bathymetric highs between 2000 m and 3000 m of water depth (Evain et al ., 2021), which were recognized as contourite drifts in seismic surveys (Wiles et al ., 2014; Thiéblemont et al ., 2019; Gao et al ., 2020; Li et al ., 2021) overlying mass transport deposits (MTD; Evain et al ., 2021).…”

“…Combined wide‐angle and multi‐channel seismic studies and geodynamic studies have shown that the Limpopo Corridor is a strike‐slip margin with thin continental crust (Thompson et al ., 2019; Moulin et al ., 2020; Evain et al ., 2021; Li et al ., 2021; Watremez et al ., 2021). The positive gravity anomalies correspond to a series of bathymetric highs between 2000 m and 3000 m of water depth (Evain et al ., 2021), which were recognized as contourite drifts in seismic surveys (Wiles et al ., 2014; Thiéblemont et al ., 2019; Gao et al ., 2020; Li et al ., 2021) overlying mass transport deposits (MTD; Evain et al ., 2021). These MTDs may be related to the emplacement of the first bathymetric step, during the passive margin formation.…”

The Limpopo Magma‐Rich Transform Margin, South Mozambique: 1. Insights From Deep‐Structure Seismic Imaging

“…Several plate kinematic models based upon geological studies, potential field data, and seismic data propose reconstructed initial positions of Africa and Antarctica (Evain et al, 2021;Gaina et al, 2013;Klimke et al, 2018;Leinweber & Jokat, 2012;Reeves et al, 2016;Sahabi, 1993;Thompson et al, 2019). These plate kinematic models show that Africa and Antarctica were joined along what is now the Mozambique margin, before the break-up of Gondwana.…”

Crustal Structure and Stratigraphy of the South Mozambique Margin to South Mozambique Ridge From Combined Wide‐Angle and Reflection Seismic and Drill Hole Data

“…The source was composed of an array of 15 airguns, synchronized on the first peak and providing a total volume of 6,500‐in 3 , with shot interval every 60 s. The 2,974 air‐gun shots along MZ6 start slightly south of MZ6OBS01 (296 km model distance) extending 185 km south of MZ6OBS25 and were recorded by all instruments and a marine 720‐channel streamer 4.5 km in length. This profile runs parallel to the MZ7 profile (Leprêtre et al., 2021) about 80 km eastward and crosses the MZ1, MZ2, and MZ3 (Evain et al., 2021) profiles at the positions of the MZ6OBS18, MZ6OBS08, and MZ6OBS15, respectively. It presents therefore three crossing points that constrain our model.…”