Early Cretaceous counterclockwise rotation of Northeast Africa within the equatorial zone: Paleomagnetic study on Mansouri ring complex, Southeastern Desert, Egypt

摘要

The Mansouri ring complex (132Ma) is, paleomagnetically, studied to shed light on the paleo-tectonic position of Northeast Africa during the Early Cretaceous. Progressive thermal demagnetization of all samples verified a general bi-vectorial decay of the natural remanence. After the removal of the present-day field overprint, the decaying anchored component was either:1.A dual-polarity, shallow NW–SE directed component residing in magnetite (400–585°C) of shiny fresh samples, or,2.A normal-polarity, medium-inclination, north-oriented component stored in haematite of few reddish ferruginous sites. This component was considered as chemical remagnetization carried by secondary haematite.Due to its steady stability, overwhelming existence in most sites, positive reversal test and its residence in fresh-samples’ magnetite, the first dual-polarity, shallow NW–SE component, was considered as the characteristic remanent magnetization [ChRM] representing the paleomagnetic field during cooling of the Mansouri ring complex. The mean paleomagnetic pole of the isolated ChRM was at 47°N/259°E, Dp/Dm=3.4°/6.6°.This Hauterivian pole from Egypt shows reasonable consistency with its coeval poles rotated from the main tectonic units to Northeast Africa. It reveals that in Early Cretaceous:1.Northeast Africa was equatorial, lying just south the Equator. Cairo, which is now at 30°N, was at ?1.5° paleo-latitude.2.The Azimuth of the African Plate was NE–SW, about 30° clockwise with respect to the present-dayN–S trend.Comparing this Hauterivian pole to that of the Wadi Natash basalts [107±4Ma], which was at [55°N/250°E] during the Albian, the African Plate seems to have rotated counter-clockwise about 10° with Northeast Africa moving northwards [Cairo was moving from 1.5°S to 1.5°N] within the equatorial zone, during the Early Cretaceous.