Palaeomagnetism of the Early to Mid-Ordovician Salala igneous ring complex, Red Sea Hills, Sudan

A R Y Palaeomagnetic samples were collected from the Early to Mid-Ordovician igneous ring complex at Salala, northern Red Sea Hills, Sudan.Detailed demagnetization experiments on 114 samples from 17 sites yield two distinct groups of characteristic directions of the natural remanent magnetization.Component 'A', predominant in samples from the quartz syenitic central part and minor ring dyke of the complex, displays rather high blocking temperatures, well above 600 "C and is presumably carried by haematite.The direction of this component (Dec/Inc = 1"/+37") is virtually identical with the direction of the present day Earth's magnetic field at the sampling locality (Dec/Inc = 0"/+37").Mixed polarities of 'A' magnetization strongly suggest a Recent/pre-Brunhes age of this component, and the effects of long-term weathering and low-temperature oxidation.Component 'B', pointing to the southeast and upward, has been identified in seven sites from the major ring dyke, composed of aegirine syenite.Maximum blocking temperatures of this component do not exceed 580 "C and, together with the results of rock magnetic and optical examinations, are indicative of primary magnetite as the carrier of the characteristic magnetization.The mean direction (Dec/Inc = 124"/-50", agS = 9.2, k = 44.1)differs significantly from component 'A' and is thought to be primary and representative for the direction of the Earth's magnetic field during emplacement and cooling of the ring complex in Mid-Ordovician times.The resulting palaeomagnetic pole (40"N, 30"W, dp = 8, dm = 12), situated off the coast of West Africa, plots very close to a cluster of Ordovician palaeomagnetic poles from Africa.These poles have not been integrated into the majority of the various apparent polar wander paths for Gondwana but this new result re-enforces their correctness.The application of recently revised rotation parameters for eastern Gondwana significantly reduces the longitudinal gap between the African data and that from eastern Gondwana (particularly Australia) for the Ordovician.