Mafic dykes of the Vestfold Hills, East Antarctica. An analysis of the emplacement mechanism of tholeiitic dyke swarms and of the role of dyke emplacement during crustal extension

Abstract

Mafic dyke swarms are common in Proterozoic continental crustal terrains. Although it is generally recognized that parallel mafic dyke swarms are formed in extensional tectonic settings and that they accommodate in the order of 10% of extensional strain, the tectonics and geodynamics of dyke swarm emplacement are poorly understood. Since observations suggest that the level of tectonic extensional stress required for dyke emplacement is less than that required for brittle failure or plastic flow, it is proposed that dyke swarm emplacement must be regarded as a crustal extensional deformation mechanism, rather than as a passive response to a tectonic event. In order to analyse the role of mafic dyke emplacement during continental crustal extension, it is necessary to understand the conditions that lead to dyke propagation under conditions representative for the crust. Exposed Proterozoic dyke swarms from the Vestfold Hills, East Antarctica, that were emplaced at intermediate crustal levels into granulite facies felsic crust, are studied with the objective to understand: [1] the specific conditions that led to arrest of exposed dyke tips; [2] the general conditions that are required for dyke propagation, and hence for the emplacement of a dyke swarm; and [3] the tectonic and geodynamic significance of mafic dyke swarm emplacement during continental crustal extension.