African Geological Atlas

Cenozoic Tectonic Maps of Africa

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Ypresian 50+-5Ma

Paleocene to Mid Eocene times represent a relatively stable and quiescent period in terms of tectonics, erosion, sedimentation and climate. Africa is now closing on various European platelets, but this does not seem to transmit to any significant tectonic activity on the African plate. Significant early post-rift subsidence characterises many of the Sirt (SI) rifts (Abdunaser and Mcafferty, 2014) . The offshore Gulf of Sirt may still be rifting (Fiduk, 2009). A further inversion phase occurs in Cyrenaica, though only of the Jebel El Akhbar rift (Martin et al, 2008, Geology of Eastern Libya) The NW-SE trending Central African rifts (TM, TN, ME, MU) are again in a syn-rift phase (Genik, 1993),, suggesting that the Central African lineament is still active, probably connected to Atlantic fracture systems. The Anza rift of Kenya (AN) also remains in a syn-rift phase, following a regional uplift of northern Kenya in the Latest Cretaceous to Paleocene (Morley et al, 1997).

Priabonian 35+-5Ma

The previously quiescent tectonics of the Mid Eocene are broken by the first period of compression in the Atlas (Frizon et al, 2011), the onset of volcanism in Ethiopia (Rooney, 2017) and possibly (dates uncertain) the first weak extensional movements of the East African system (Macgregor, 2015: Purcell, 2017). These mark changes in stress directions over earlier times. The Iberian plate collides with Europe, creating the ‘Pyrenean’ event (PY, causing the first period of inversion in the Atlas. The degree of compression seems to have been greater in Morocco than in Tunisia. Molassic deposits are less well developed or extensive in the Eo-Oligocene than they are in the Pliocene (Frizon et al, 2011): this suggests the phases of deformation at this time were less intense than in younger intervals. The Western Desert of Egypt (WD) suffers another inversion event (Bosworth and Tari, 2021).The first of a number of transpressional events are described along the Sabratah Fault (SA). The earliest Tertiary alkaline volcanics over north African swells are recorded on the Ahaggar (AH) Massif (Swezey, 2009).

Activity continues in the Central African Rift System, with continued extension of the Sudan rift, contemporaneous with inversion in the Doba (DO) Basin. The Melut (ME) rift appears more active than the Muglad (MU), with faulting now rotating from a previous NW-SE trend to NNW-SSE. A similar change occurs in the Tenere (TN) Basin of Niger (Ahmed et al, 2024). Some N-S trending small rifts in NW Kenya (Wescott et al 1999) and the Broadly Rifted Zone (BRZ) of Ethiopia may start to gently subside at this time, which could be considered as the first ‘EARS’ Rifts, though dating is uncertain. The first Ethiopian volcanics erupt between 45-34Ma (Rooney, 2017).

Sinistral strike slip movement recommences on the Seagap Fracture Zone (SG) offshore Tanzania (Iacopini et al, 2022) and possibly, by inference, also on the Davie Fracture Zone. This is likely related to rapid transform movement on the oceanic African-Indian plate boundary. Inversion occurs in the Anza (AN) Basin (Morley et al, 1999), which may be linked.

Rupelian 30+-5Ma

Compressional activity continues in Iberia and on the southern margin of the European plate but does not transmit into Africa. A backarc basin has now formed between Iberia and Alkapeca (at 32Ma, Carminati et al (2012)). This will spread at circa 21Ma to create the Western Mediterranean Ocean. The only Sirt rift still active is the Hon Graben (HON, Abunaser 2015).

CARS extensional movements now seem to be confined to the Sudanese rifts. Rifting trends here are moving towards a more N-S trend, with the Melut Basin (ME) more active than the Muglad (MU) Basin (Mchargue, 1992). It is speculated that an E-W transform trend across Central Africa may have been active at this time (Guiraud et al, 1995), and that this forms the sharp boundary in Niger between the Tenere (TN) rift, which is highly inverted and the dormant Termit (TM) Basin. The South Lokichar (SL) Basin forms the first clearly evidenced rift of the East African Rift System (Macgregor, 2015: Purcell, 2017) , being thought to be the earliest rift within a first cycle of rifting confined to Kenya and southern Ethiopia. A mild rifting and filling episode also occurs in the multi-phase Rukwa (RU) Basin (Morley et al, 1992). From now onwards, an ‘unzipping’ trend of rifting is observed from the Gulf of Aden (Purcell, 2017, GoA) to the Afar and subsequent to this period, north through what is now the Red Sea.

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Langhian 15+-3Ma

The Alkapeca set of plates detach from the Iberian Plate around 21Ma (Carminati et al (2012). Over a period of around 3Ma, this new ocean spreads, with the Kabylies then colliding with Africa to create the Tellian (TE) structural event and nappe, while the Alboran Plate is squeezed westwards between Iberia and Africa, creating the Rif (RI) mountain chain and a large olistostrome in the Rharb Basin (RH). Subduction of the Eastern Mediterranean commenced at around 20Ma, following the accretion of Turkish microplates (Menant, 2016) . An associated phase of folding and transform activity occurs in the Levantine Basin (LE) of Israel.

Oceanic crust is now being established in the Gulf of Aden (Purcell, 2017). The unzipping trend of rifting in the Red Sea has advanced northwards substantially, with a peak of activity around 20Ma (Bosworth, 2015). The Dead Sea Transform first forms in the south around 19Ma and then propagates northwards, marking the end of syn-rift conditions in the Gulf of Suez (GoS). This time marks the end of the first phase of EARS rifting, which are confined to southern Ethiopia and northern Kenya, and the start of a second more extensive phase (Macgregor, 2015: Purcell, 2017) . Rifting in the Lokichar (SL)area jumps eastwards to Lake Turkana (TU). In addition to a spread southwards into the Gregory (GR) area of Kenya, the Aswa transform is created and rifting commences in the northernmost rifts of the Western Branch. The first rift fill of the Albertine (AL) Rift of Uganda was deposited at around 17Ma.

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Zanclean 5+-2Ma

The main phase of compressional tectonics in the Maghreb and Atlas (AT) likely commences in the Tortonian and peaks in the Pliocene (e.g., Said et al, 2011). An accretionary prism forms along the southern edge of the Algerian (AL) ocean (Strzwezynski et al, 2021). A new northern boundary to the African plate has been created through the island of Sicily as the Tyrrhenian Sea (TY) opens and Calabria moves eastwards. Maltese rifts (MA) form in the foreland to the Sicily Fold Belt. Folding, often associated with wrench movements, also affects the Nile Delta.

Spreading commences in the southern part of the Red Sea (RS), though the northern part is thought to remain in a magma-poor hyperextended state (Stockli and Bosworth, 2018). EARS rifting has now propagated considerably southwards. All rift basins between the Albertine Basin (AL) and Lake Malawi (LM) are now active, the latter forming at ca. 7Ma. (Macgregor, 2015). A northwards propagation is also interpreted in Ethiopia, to complete a continuous rift system through the Eastern Branch. A new offshore branch was also created in the Late Miocene, typified by the Kerimbas (KE) and Lacerda (LA) Basins offshore Mozambique (Franke et al, 2015). These East African (EARS) rifts show varying degrees of associated volcanism, differing associations with mantle S wave velocities and contrasts in the geometry and height of rift shoulders. The magma-rich Eastern Branch rifts have been taken to be the archetypal ‘active‘ rifts. Michon et al (2022) however believes that a plume-related (i.e. active) phase evolves around this time into a ‘plate-scale rifting’ phase, inferred to have a greater passive element. Our current view is that a purely ‘passive’ model for the Western Branch cannot explain the clear regional uplifts that are defined by the rift shoulders, indicated that active or intermediate models must apply. The offshore rifts could be transtensional in origin (i.e. transform-related passive rifts), evidencing continued sinistral movements on the Seagap and Davie Fracture Zones (Iacopini et al, 2022).

Uplift occurs over large parts of Central and Southern Africa from 11-3Ma (Guillocheau, et al, 2015). There is considerable debate over the magnitude of Neogene uplift of the South African Plateau (SAP), with researchers falling into two camps, one considering that uplift is minimal at this time and the other that there a second phase of kilometre scale uplift. The latter model is favoured by the immature nature of the drainage in the region (Roberts and White, 2010) and by significant sediment volumes off the wetter eastern coast (Baby et al, 2020). Stanley et al (2021) shows that both models remain possible with the available evidence: we choose to illustrate her ‘Hybrid Late’ model based on the evidence summarised above.

Holocene

Collision between Cyprus and the Eratosthenes Plateau (EP) hasnow occurred, and the remaining sections of the eastern Mediterranean are subducting rapidly. A new subduction zone is possibly being established below northern Algeria, evidence by earthquake epicentre depths (Strzwezynski, 2021) .

Pre-existing EARS rifts remain in syn-rift conditions. The EARS is still expanding, with a new southwestern branch now established through Kariba (KA) to the Etosha (ET) , with others through Lakes Mweru (LMW) and Upemba (LU) (Macgregor, 2015). Significant crustal thinning is interpreted over parts of this trend (Daly et al, 2020). Some authors now believe the ‘Somali Plate’ and the ‘San’ Plate, (containing South Africa), are in the process of rifting off the African Plate (Daly et al, 2020).

Most surrounding oceans are spreading in parallel with the Africa plate (as has been the case since the Late Cretaceous), which would therefore be expected to be under compression : this is clearly not the case, indicating that there are other active forces below the plate itself. A mantle convection cell has been interpreted from S wave velocities that rises from the lower mantle below the South African Plateau to an eruption in the southern Red Sea (Adams and Nyblade, 2011). Some regions are still actively uplifting, e.g. the margins of the Kwanza (KW) Basin.

Active faults on this map are mapped from earthquakes. The main source used is Meghraoui et al, 2016.The map shows active volcanoes as purple triangles, those with mild activity in pink and recently extinct ones in orange.