Section 4. Phanerozoic anorogenic magmatism: Plate tectonic implications and mineralization

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 170 KB
• Volume: 22
• Category: Article
• ISSN: 0072-1050
• DOI: 10.1002/gj.3350220621

✦ Synopsis

Section 4 Phanerozoic anorogenic magmatism : plate tectonic implications and mineralization Phanerozoic alkaline magmatism on the African continent is considered in this part of the book. The scene is set by Kinnaird and Bowden who consider the implications of the Pan-African orogeny to Phanerozoic subvolcanic complexes for providing source materials for magmas and mineralization by assimilation and/ or melting, and assess the isotopic constraints on magma generation and the source of mineralizing fluids throughout the African plate.

The African continent consists of a number of terranes accreted during major orogenies. Phanerozoic fold belts in Africa are limited to the northwest and southwest fringes. Over the African shield as a whole therefore, the Phanerozoic plutonism is anorogenic in nature and dominated by the formation of alkaline ring complexes. Prior to 180 Ma ago, Africa formed part of Gondwanaland. It was the exploitation and reactivation of the Pan-African shear zones and transcurrent faults during the period leading up to and following the fragmentation of Gondwana, that controlled the locations of Phanerozoic intraplate magmatism in Africa. Many of these intersecting shear zones and transcurrent fault systems formed a network of NE-SW and NW-SE lineaments which transect Africa. These structures have been reactivated at different times throughout the Phanerozoic and dictate the location of the alkaline igneous complexes and their mineralization.

The earliest anorogenic activity which began at the end of the Pan-African orogeny, was confined to a relatively short period of geological time and shows no significant widespread mineralization throughout the African plate. Where reactivation occurred in the Palaeozoic the alkaline ring-complexes are more economically mineralized. It is within the group of alkaline ring-complexes of Mesozoic age that major mineralization is found. The initiation and location of these centres is related to the separation of South America and Africa. There is widespread anorogenic activity centred along major lineaments and reactivated shear zones throughout Africa. A group of late Mesozoic to Cainozoic volcanic and subvolcanic activity is mainly connected with re-exploitation of zones of faulting and rifting. Some of these subvolcanic centres are also mineralized. This magmatism is almost exclusively restricted to areas of the convection-generated 0 1987 by John Wiley & Sons, Ltd.