An Early Cretaceous extinct spreading center in the northern Natal valley

We have identified an extinct E-W spreading center in the northern Natal valley on the basis of magnetic anomalies which was active from chron M11 ( similar to 133 Ma) to similar to 125.3 Ma, just before chron M2 ( similar to 124 Ma) in the Early Cretaceous. Seafloor spreading in the northern Natal valley accounts for approximately 170 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 M I I 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 RiiserLarsen 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 the 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, similar to 160 Ma, until it became part of the African plate, similar to 125 Ma. (C) 2002 Elsevier Science B.V. All rights reserved.