Scientists, including Keele University’s Emeritus Professor Peter Styles, have digitized and reanalyzed forgotten high- resolution aeromagnetic survey data from the late 1960s (around 1968/69) over the Afar region of Ethiopia (and what is now Eritrea), integrating it with other “vintage” magnetic data from the Red Sea and Gulf of Aden.

The original survey, flown by Hunting Geology and Geophysics Ltd under the University of Newcastle upon Tyne in one of Earth’s most inhospitable climates, produced data that was largely overlooked after the 1970s.

The team (P.G. Purcell, R. De Ritis, and P. Styles) processed it with modern methods to create Total Magnetic Intensity and First Vertical Derivative maps.

The Afar region is a classic site for studying the early stages of continental breakup (rifting), where the African, Arabian, and Somali plates meet in a triple junction near the East African Rift, Red Sea, and Gulf of Aden. As basaltic rocks form and cool during seafloor spreading, they record Earth’s magnetic field polarity reversals as linear “stripes” (like barcodes or tree rings). A standard triple- junction model would predict a triangular pattern of these magnetic lineations radiating from the Afar Depression.

Instead, the reanalyzed data show magnetic anomalies trending roughly east-west in southern Afar (continuing the Gulf of Aden trend into the continent and nearly perpendicular to the younger NNE-trending Wonji Fault Belt of the Ethiopian Rift). North of the Tendaho- Goba’Ad discontinuity, anomalies trend approximately NW/SE (deviating ~30° from the Red Sea axis). There are little or no clear signature matching expectations for simultaneous, equal-rate rifting along all three arms of the East African Rift.

The researchers interpret the dominant magnetic signature as evidence of earlier (possibly Miocene) continental rifting as Africa and Arabia separated along a primary fracture following the Gulf of Aden- Red Sea path, later overprinted by younger magmatism and faulting. Cross- rift magnetic anomalies also appear in the East African Rift and Red Sea, though their origins remain unclear.

Professor Styles noted: “These findings give a unique perspective on how our planet is constantly changing and shifting right beneath our feet. It’s also a great example of the benefits of looking at all of the available data, even historical data, when testing new models and theories. Models come and go, but well- measured data lasts forever.”

The paper concludes that the 1968 Afar Survey data has been “resurrected from an undeserved obscurity” and can now contribute to studies of this complex region.

This work highlights the value of revisiting historical geophysical datasets with modern tools to refine models of how continents stretch, thin, and eventually form new ocean basins, processes ongoing today in East Africa and the Red Sea region.

Miocene rifting mechanisms in the Afar- Red Sea- Gulf of Aden region (roughly 23- 5 Ma) represent a critical phase in the transition from continental extension to seafloor spreading as Arabia separated from Africa. This period followed the Oligocene impingement of the Afar mantle plume (~30- 31 Ma) and the associated Ethiopian-Yemen flood basalt province. It is highly relevant to the 1968 Afar magnetic survey reinterpretation, which suggests that the prominent east- west magnetic anomalies in southern Afar may record earlier Miocene magmatic rifting aligned with the Gulf of Aden trend (later overprinted by younger structures).

Timing overview

Gulf of Aden: Rifting began in the early- mid Oligocene (~35- 30 Ma) in the east/central parts; climax of continental rifting ~20- 18 Ma; seafloor spreading initiated ~21- 17 Ma in the east and propagated westward.

Red Sea: Continental rifting initiated ~27- 23 Ma (late Oligocene- early Miocene) along much of its length, often linked to a major dike event ~24- 22 Ma. Significant Miocene extension occurred with limited early volcanism in places; seafloor spreading began later (~13 Ma or younger in the central/southern parts).

Afar and northern Main Ethiopian Rift (MER): Extension in Afar started ~29- 25 Ma shortly after the traps. A major reorganization occurred ~13- 8 Ma, with northward propagation of Afar rifting, rotation of the Danakil Block, and development of the triple junction configuration. The northern MER formed around ~11 Ma.

Geological events were strongly diachronous across the region.

Rifting mechanisms are debated and often involve a combination of processes rather than pure end-members. Common frameworks include:

1. Active vs. passive rifting
   • Active (plume-driven): The Afar plume causes uplift, lithospheric thinning, and decompression melting, driving extension. Evidence includes the spatial association with flood basalts and long-lived dynamic topography. However, pure active models struggle to explain the diachronous onset of rifting arms (Gulf of Aden earlier than Red Sea/MER) and the fact that oceanic spreading often initiated far from the plume center.
   • Passive (far-field driven): Extension results from plate- boundary forces, primarily slab pull from Neotethys subduction beneath Eurasia to the north, or changes in plate motion after collision locking in the Mediterranean region ~25 Ma. This better explains the relatively low volume of rift- related volcanism during the main Miocene phase in parts of the Red Sea/Gulf of Suez.
   • Hybrid models: Many researchers favor combinations. One recent proposal is plume- induced plate rotation: the Afar plume head generates horizontal asthenospheric flow and a “push” force that promotes rotation of the Arabian plate around a nearby pole, facilitating rifting along the Red Sea and Gulf of Aden. This integrates active and passive elements and accounts for progressive development of the system.
2. Modes of lithospheric extension
   • Pure shear (symmetric stretching): Uniform thinning of the lithosphere (classic McKenzie model). Common in earlier or less magmatic stages and parts of the southern MER.
   • Simple shear (asymmetric, detachment faults): Large- scale low- angle faults lead to asymmetric margins. Suggested for some Western Afar Margin structures and possibly parts of central Afar during later stages.
   • Magma- assisted/magma- controlled rifting: Magma intrusion and underplating accommodate much of the extension, weaken the lithosphere, and allow strain localization into narrow magmatic segments. This is dominant in magma- rich settings like central Afar and the modern northern MER. During the Miocene in the southern Red Sea/Afar, extension and volcanism migrated inland from border faults into narrow zones of intrusion, similar to present-day axial magmatic segments. Magma-compensated thinning can maintain relatively thick crust despite significant extension. flore.unifi.it
3. Strain localization and propagation
   Early Miocene extension was often distributed (“wide rift” style in central Afar during the Mio-Pliocene). Over time, strain localized into narrower zones. Rifts propagated (e.g., Gulf of Aden westward toward Afar; Afar northward as a relay with the Red Sea). Pre- existing structures (Precambrian fabrics, earlier faults) strongly influenced geometry. The Danakil Block began independent rotation in the mid- to- late Miocene, contributing to the complex triple- junction
4. Role of magmatism
   Miocene magmatism in Afar included dykes, plutons, and volcanic series (e.g., Mabla, Dahla). In southern Afar, linear magnetic anomalies (high- amplitude, E- W trending) may reflect intrusive bodies or early oceanic/transitional crust formed during this phase of Gulf of Aden, aligned rifting. Magmatism helped accommodate extension early, with a later shift toward more mechanical stretching or focused extrusive activity in some models. Cross- rift magnetic anomalies elsewhere in the system remain enigmatic.

The 1968 survey data show E- W magnetic lineations in southern Afar that continue the Gulf of Aden trend and sit nearly perpendicular to younger NNE- trending Ethiopian Rift faults (e.g., Wonji Fault Belt).

This supports the interpretation of an earlier Miocene magmatic rifting episode aligned with the Gulf of Aden, subsequently obscured by Plio-Pleistocene faulting and volcanism. Good correlation between magnetic anomalies and structures near the Gulf of Tadjura (Djibouti) contrasts with the mismatch farther west, highlighting the complex, multiphase history.

Miocene processes in this region illustrate how continental breakup can involve sequential phases of distributed then localized extension, strong magmatic influence in plume-affected areas, and reorganization driven by plate rotations and propagating rifts.

Analog and numerical models emphasize the roles of rotational extension, pre- existing weaknesses, and varying degrees of magmatism in producing the observed geometries. The system ultimately transitioned toward focused seafloor spreading, providing a natural laboratory for the early stages of ocean basin formation.

Ongoing research continues to refine these models using geophysics, geochronology, and structural data. The “resurrected” magnetic datasets add valuable constraints on the subsurface architecture of these early rifting phases.

A review of the 1968 Afar Magnetic Survey data and integration with vintage Red Sea and Gulf of Aden data

Miocene rifting mechanisms in the Afar- Red Sea- Gulf of Aden region (roughly 23- 5 Ma) represent a critical phase in the transition from continental extension to seafloor spreading as Arabia separated from Africa.

This period followed the Oligocene impingement of the Afar mantle plume (~30- 31 Ma) and the associated Ethiopian-Yemen flood basalt province. It is highly relevant to the 1968 Afar magnetic survey reinterpretation, which suggests that the prominent east–west magnetic anomalies in southern Afar may record earlier Miocene magmatic rifting aligned with the Gulf of Aden trend (later overprinted by younger structures).

Highlights

• Vintage magnetic data in Afar show variable correlations with rift structure.
• Integrated regional magnetic data provide insight into tectonic framework.
• Magnetic anomalies align with some rift structures near the Gulf of Tadjura.
• Magnetic anomalies in southern Afar are perpendicular to rift faulting.
• Southern Afar magnetic anomalies might relate to Miocene rifting.

An extensive aeromagnetic survey of the Afar region of Ethiopia (and present- day Eritrea) was flown in 1968 to study this key site of embryonic continental breakup. The data received little attention after the 1970s.

The authors digitized and processed it, then integrated it with vintage magnetic data from the adjacent Red Sea and western Gulf of Aden. They produced Total Magnetic Intensity (TMI) and First Vertical Derivative (FVD) maps.

Key observations:

• In southern Afar, magnetic anomalies trend roughly east- west, nearly perpendicular to the NNE-trending Plio- Pleistocene Wonji Fault Belt of the Ethiopian Rift and continue the Gulf of Aden trend into the African continent.
• This contrasts with the fair- to-good correlation between magnetic anomalies and rift structures in the hinterland of the Gulf of Tadjura (Djibouti area).
• North of the Tendaho- Goba’Ad discontinuity, anomalies trend approximately NW- SE, offset by ~30° from the Red Sea axial spreading trend (as seen onshore in the Erta Ale magmatic complex).

The authors suggest the enigmatic east- west magnetic trends in southern Afar may record earlier (Miocene) magmatic rifting aligned with the Gulf of Aden, later obscured by younger magmatism and faulting. Cross- rift magnetic anomalies also occur in the East African Rift and Red Sea; their origin remains unclear.

They conclude that the 1968 Afar Survey data has been “resurrected from an undeserved obscurity” and can again contribute to understanding this complex region.

The Afar Triangle, Red Sea, and Gulf of Aden form a classic plate-tectonic triple- junction setting. Early models treated much of Afar as oceanic or “pseudo- oceanic” crust.

The 1968 survey (flown by Hunting Geology and Geophysics Ltd under the University of Newcastle upon Tyne as part of the Upper Mantle Project) revealed long (often >100 km), high-amplitude (up to ~1000 nT) linear magnetic anomalies trending roughly east- west in southern and central Afar, similar to those in the western Gulf of Aden.

Contemporary workers (e.g., Girdler, Barberi & Varet) interpreted these as evidence of oceanic spreading or mini- spreading centres. Later analysis by Mohr (1976) highlighted the lack of consistent alignment between magnetic anomalies and surface rift structures, especially the near- perpendicular relationship in southern Afar, and suggested a possible earlier rifting episode.

The present study:

• Digitized the original 1:500,000- scale TMI contour maps.
• Compared the Afar data with overlapping modern/higher- resolution surveys (Djibouti and Adigala) to validate navigation accuracy and anomaly trends (good correspondence was found).
• Upward- continued and merged selected public- domain vintage marine data from the Gulf of Aden (Whitmarsh, 1969) and Red Sea (Hall & Andreasen, 1977) to the Afar survey elevation (~1830 m).
• Incorporated higher-level Yemen data for regional context but did not fully merge it.

The primary aims were to evaluate the quality and reliability of the 1968 data, compare the magnetic patterns with surface tectonic features, and briefly consider implications for regional tectonic history.

The work demonstrates the enduring value of carefully collected historical geophysical datasets. When reprocessed with modern techniques and integrated with neighbouring data, the 1968 Afar survey provides new constraints on the timing, geometry, and evolution of continental rifting and the transition toward seafloor spreading in one of Earth’s best natural laboratories for these processes.

Title: A review of the 1968 Afar Magnetic Survey data and integration with vintage Red Sea and Gulf of Aden data

Published: Journal of African Earth Sciences, Volume 233, January 2026, Article 105881

DOI: 10.1016/j.jafrearsci.2025.105881

Provided: Keele University 

Authors: P.G. Purcell, R. De Ritis, P. Styles

Abstract

An extensive aeromagnetic survey of the Afar region of Ethiopia and (now) Eritrea was conducted in 1968 to investigate this complex tectonic province, long seen as a site of embryonic continental break-up. This vintage magnetic data, which has received little attention since the 1970s, has been digitized, processed, and integrated with vintage data from the adjacent Red Sea and western Gulf of Aden to produce Total Magnetic Intensity and First Vertical Derivative maps for the region. In southern Afar, the magnetic anomalies trend approximately east/west, almost perpendicular to the NNE-trending Plio-Pleistocene Wonji Fault Belt of the Ethiopia Rift segment, continuing the Gulf of Aden trend into the African continent. This is sharp contract with the fair to good correlation of magnetic anomaly and rift structures in the hinterland of the Gulf of Tadjura. North of the Tendaho-Goba’Ad discontinuity, the magnetic anomalies trend approximately NW/SE, deviating approximately 30^o from the Red Sea axial spreading trend, as manifest onshore in the Erta Ale magmatic complex. The enigmatic near east-west trend of the magnetic anomalies in southern Afar may be related to Miocene magmatic rifting aligned with the Gulf of Aden but now obscured by younger magmatism and rifting. Cross-rift trending magnetic anomalies are also present in the East African Rift and the Red Sea, but their origin is not clear. With this publication, the magnetic data from the 1968 Afar Survey has been resurrected from an undeserved obscurity and can now begin to contribute anew to the study of this complex and fascinating region.