East side story of Gondwana: the last frontier of the Arabian Nubian shield at 720 Ma based on new high-quality paleomagnetic pole

Abstract

Unraveling the paleogeography is crucial to understand the changes in Earth Systems at the onset of the Cryogenian Period around ∼720 Ma. The Cryogenian Period is marked by widespread glaciations notably preserved in the Arabian Nubian Shield, and is a turning point in the supercontinent cycle between the dispersal of the Rodinia supercontinent and the assembly of Gondwana. Filling gaps from the paleomagnetic database remains an indispensable tool to solve the Proterozoic paleogeographic and paleogeodynamic puzzle, especially during challenging periods of continental dispersion. Through a detailed coupled paleomagnetic, structural and geochronologic study, the Shaat dyke swarm (∼720 Ma), intruding the Mirbat basement on the south-western coast of the Oman sultanate, has proven to be reliable witnesses of the evolution of the ancient Earth. A characteristic remanent magnetization (ChRM) was isolated in stable single to pseudo-single domain (SD/PSD) magnetite. Well constrained site mean directions obtained for 20 dykes lead to a mean direction for the Shaat dyke swarm of Dm = 249.9°, Im = −61.3° (N = 20, α95 = 5°, k = 43.1), yielding a paleomagnetic pole at 104.9°E, 25.9°N, (A95 = 7.2°, K = 21.3). The reliability of the paleomagnetic pole is assessed by 5 of the 7 Criteria of Meert et al. (2020). This new key paleomagnetic Mirbat pole represents the only reliable paleomagnetic pole for the Omani Neoproterozoic block/terrane at ∼720 Ma. It confirms the connection between the Omani terrane and the Indian Shield (already link to the Seychelles and Madagascar blocks) and defines a medium paleolatitude of ∼42.4° for the Omani block at ∼720 Ma. The confirmed connection also implies a moderate latitude (∼40°) for the Indian Shield at the beginning of the major Sturtian glaciation.