The Mozambique Ridge: a document of massive multistage magmatism

Abstract

S U M M A R YThe Mozambique Ridge, a prominent basement high in the southwestern Indian Ocean, consists of four major geomorphological segments associated with numerous phases of volcanic activity in the Lower Cretaceous. The nature and origin of the Mozambique Ridge have been intensely debated with one hypothesis suggesting a Large Igneous Province origin. High-resolution seismic reflection data reveal a large number of extrusion centres with a random distribution throughout the southern Mozambique Ridge and the nearby Transkei Rise. Intrabasement reflections emerge from the extrusion centres and are interpreted to represent massive lava flow sequences. Such lava flow sequences are characteristic of eruptions leading to the formation of continental and oceanic flood basalt provinces, hence supporting a Large Igneous Province origin of the Mozambique Ridge. We observe evidence for widespread post-sedimentary magmatic activity that we correlate with a southward propagation of the East African Rift System. Based on our volumetric analysis of the southern Mozambique Ridge we infer a rapid sequential emplacement between ∼131 and ∼125 Ma, which is similar to the short formation periods of other Large Igneous Provinces like the Agulhas Plateau.

Neogene Modifications of Circulation in the Northeastern African‐Southern Ocean Gateway

“…Correlation of seismic reflection characteristics between the lithological results and reflection seismic data of DSDP Site 249 (a) (Simpson et al, ), the seismic stratigraphic model by Uenzelmann‐Neben et al () (b), and the newly acquired multichannel seismic reflection data during SO 232 (Fischer et al, ; Fischer & Uenzelmann‐Neben, ) (c). The Cenozoic lithological unit is highlighted with pink borders.…”

“…Thick blue line = top of Pleistocene to Holocene unit S2b‐II (blue), thick red line = top of mid‐Miocene to early Pliocene unit S2b‐I (red), thick green line = top of Cretaceous unit (transparent white). Yellow hatched postsedimentary magmatic with dashed black lines = late Neogene post‐sedimentary magmatic structure (Fischer et al, ). Depositional/erosional features are color‐coded (red = S2b‐I, blue = S2b‐II), and arrow shows extent of depositional feature.…”

“…In several areas, high‐amplitude reflections alternate with sets of low‐amplitude reflections (Figure , CDPs 10,200–10,800 and 4,600–5,000 ms TWT). Fischer et al () identified the strong amplitude reflections as discontinuities such as erosional truncation and onlap termination typical for contourite drifts (Faugères et al, ; Rebesco & Stow, ; Stow et al, ). The subunit's top (red line in Figure ) is marked by a strong amplitude reflection that represents a strong impedance contrast to the rest of the subunit and is unconformably covered by younger strata.…”

“…Thick blue line = top of Pleistocene to Holocene unit S2b‐II (blue), thick red line = top of mid‐Miocene to early Pliocene unit S2b‐I (red), thick green line = top of Cretaceous unit (transparent white). Red hatched PSM = late Neogene postsedimentary magmatic structure (Fischer et al, ). Color‐coded circles indicate current direction and approximate location of current core during deposition of the respective units (red = S2b‐I, blue = S2b‐II, black = valid for both intervals).…”

The Southwest Indian Ocean Bathymetric Compilation (swIOBC)

“…Recent geophysical studies (Fischer et al, ; König & Jokat, ; Parsiegla et al, ) support the interpretation of these ridges as large igneous provinces of Cretaceous age associated with the opening of the southwest Indian Ocean. Late Miocene neo‐volcanism at the Mozambique Ridge is interpreted as an extension of the western branch of the East African Rift System (Fischer et al, ).…”