Pan-African Cratonization and the Arabian Plate (800–550 Ma)

Pan-African Cratonization (800–680 Ma)

Nehlig et al. (2002) conducted a study to review the Pan-African evolution of the Arabian Shield, on the premise that new perspectives on the geologic history and structural evolution of the Arabian Shield had emerged. These new perspectives were brought by extensive fieldwork as well as the synthesis and review of structural, aeromagnetic, geochemical, geologic, and geochronological data. The geologic evolution of the Arabian Shield took place between 900 and 550 Ma. This period was also characterized by the "formation, amalgamation, and final Pan-African cratonization of several tectonostratigraphic terranes" (Nehlig et al., 2002, p. 103). These terranes were separated by key NW-trending faults and variously oriented suture zones covered by ophiolites — that is, serpentinized ultramafic rocks.

Pan-African cratonization between 800 and 680 Ma incorporated the final cratonization of the terranes. The final cratonization, which took place between 680 and 610 Ma, generated a network of strike-slip, anastomosing faults that comprised the N-trending Nabitah belt. In addition, the network comprised key NW-striking left-lateral transpressive faults covered by gneiss domes and linked to sedimentary basins. Another component of this subsequent fault network is the N- to NE-trending right-lateral transpressive faults.

Pan-African cratonization around 800 to 680 Ma relates to the Arabian Plate through its products. This cratonization resulted in extensive alkaline granitization, which was simultaneous with the deposition of Jibalah volcanic and sedimentary rocks in transtensional pull-apart basins. However, Nehlig et al. (2002) state that the N-trending Nabitah and NW-trending Najd fault zones form part of oblique transpressional accretion, rather than representing two distinct events as proposed in earlier studies.

Pan-African Plate Tectonics

An important component of Pan-African cratonization is its associated plate tectonics, which had significant impacts on continental crust and is directly linked to the Arabian Plate. Through these plate tectonics, Pan-African cratonization constitutes a critical component of the baseline tectonics of the Arabian Plate. Kroner (2000) conducted a study examining Pan-African plate tectonics and its implications for the crust of the African continent, particularly the crust of northeast Africa. This study was carried out on the premise that Pan-African belts of the African mainland and the Arabian-Nubian Shield share similar evolutionary characteristics. These attributes are compatible either with intracontinental ensialic development or with plate margin settings, and are also considered compatible with Wilson cycle tectonics between 1100 and 500 Ma.

The essential subcrustal forces that drive current lithospheric motion are regarded as the causes of both ensialic and plate margin developments. Consequently, Pan-African cratonization is representative of the shift from Precambrian ensialic plate tectonics to Wilson cycle tectonics. Pan-African cratonization, especially of the North African craton, comprises widespread Pan-African thermal activity. Such activity incorporates voluminous calc-alkaline granitoid intrusions as well as alkaline to peralkaline ring complexes. Moreover, the widespread Pan-African thermal activity is characterized by a general resetting of mineral isotopic systems in mature basement rocks.

Kroner (2000) contends that pre-Pan-African continental crust already existed in northeast Africa and was affected by the intraplate pressures arising from the closure of the Pharusian Ocean and collisional tectonics in the Arabian Shield. Therefore, Pan-African cratonization relates to the Arabian Plate on the premise that intraplate pressures from collisional tectonics in the Arabian Shield affected the Pan-African continental crust.

Spread of Pan-African Cratonization Across All Terranes

Heikal (2013) examined the tectonic evolution of the basement rocks in the Republic of Yemen in relation to lithostratigraphy and deformation history. This review was motivated by the fact that basement rocks of alleged Precambrian age are exposed in both the southeastern and northwestern parts of Yemen. These rocks are similar to those in southern Saudi Arabia and are nearly continuous, sharing a comparable lithostratigraphic succession. However, they differ slightly in terms of local structural framework and major tectonic events. These tectonic events shape differences between the rock assemblages by influencing the results of lithostratigraphic analyses. Recent analyses have also identified new lithostratigraphic names, relationships, and tectonic events.

Based on their analysis, Heikal (2013) contends that Pan-African cratonization around 800 to 680 Ma was characterized by tectonic events that had impacts on all terranes. Accordingly, Pan-African cratonization of various rock units during this period was widespread across all terranes, and the deformation history and major tectonic events were concentrated within this cratonization episode. Through this cratonization, the Arabian-Nubian Shield is regarded as part of the East African Orogen, created by plate tectonic accretionary events that took place during the closing of the Mozambique Ocean and the resultant collision that formed Gondwana (Heikal, 2013, p. 1).

These findings imply that the final Pan-African cratonization of several rock units played a critical role in the evolution of the Arabian Plate. Pan-African cratonization affected the tectonic events of the Arabian Plate through its widespread impacts on all terranes. These impacts in turn became the basis for viewing the Arabian-Nubian Shield as part of the East African Orogen, and they influenced the evolution of Precambrian rocks in Egypt, Saudi Arabia, and Yemen.