Proterozoic mobile belts compatible with the plate tectonic concept

Publisher Website
Google Scholar
Abstract
Proterozoic foldbelts older than about 1 Ga lack the distinctive signatures of the contemporary Wilson cycle although they frequently contain thick sedimentary assemblages that resemble those in Phanerozoic orogens. Mafic volcanic rocks are rare, however, and occur intestratified with sedimentary strata; they are not layered and contain no sheeted dikes and can therefore not be interpreted as ophiolites. These characteristics as well as paleomagnetic and isotopic constraints preclude an evolution of these belts during closure of extensive oceans and subduction of significant amounts of oceanic lithosphere. An alternative plate tectonic model is developed that invokes rifting, heating, and stretching of the crust as a result of lithospheric thinning over a mantle plume. This mechanism eventually leads to a “geosynclinal” basin entirely floored by continental crust. The rise of asthenosphere enhances gravitational instabilities in the old and dense subcrustal lithosphere that, on fracturing after crustal stretching, may delaminate spontaneously. Hot asthenospheric material rises to take the place of the detached and sinking lithospheric slab, thereby inducing A-subduction and inter-stacking of continental crust. The much thickenend crust is partially melted at depth, intruded by synorogenic and postorogenic granites, and finally uplifted and eroded to its present level of exposure. Episodic thermal anomalies during orogeny are caused by the rise of asthenospheric magmas to the base of the crust and by radioactive self-heating after crustal interstacking. The model is entirely compatible with the concept of horizontally moving plates but differs from the Wilson cycle in that no wet oceanic crust is generated during basin formation and none is consumed during orogeny. Instead, dry subcrustal lithosphere sinks down but does not cause calc-alkalic magmatism. Towards the end of the Proterozoic, Wilson cycle signatures become widespread in the global rock record and signify a worldwide change from predominantly intraplate orogeny to predominantly plate margin orogeny that characterizes the Phanerozoic geodynamic pattern. Plate tectonics, therefore, is a nonuniformitarian process.

This publication has 0 references indexed in Scilit: