Abstract:
We have identified an extinct E-W spreading center in the northern Natal Valley from seafloor spreading magnetic anomalies which was active from chron M11 (~133 Ma) to ~125.3 Ma, just before chron M2 (~124 Ma) in the Early Cretaceous. Seafloor spreading in the northern Natal Valley accounts for approximately 150 km of north-south motion between the Mozambique Ridge and Africa. This extension resolves the predicted overlap of the continental (central and southern) Mozambique Ridge and Antarctica in the chron M2 to M11 reconstructions from Mesozoic finite rotation parameters for Africa and Antarctica. In addition the magnetic data reveal that the Mozambique Ridge was an independent microplate from at least 133 to 125 Ma. The northern Natal Valley extinct spreading center connects to the spreading center separating the Mozambique Basin and the Riiser-Larsen Sea to the east. It follows that the northern Mozambique Ridge was either formed after the emplacement of the surrounding oceanic crust or it is the product of a very robust spreading center. To the west the extinct spreading center connects to the spreading center separating the southern Natal Valley and Georgia Basin via a transform fault. Prior to chron M11 there is still a problem with the overlap of Mozambique Ridge if it is assumed to be fixed with respect to either the African or Antarctic plates. Some of this overlap can be accounted for by Jurassic deformation of the Mozambique Ridge, Mozambique Basin, and Dronning Maud Land. It appears though that the Mozambique Ridge was an independent microplate from the breakup of Gondwana, ~160 Ma, until it became part of the African plate, ~125 Ma.