Relations between surface faulting and granite intrusions in analogue models of strike-slip deformation

Abstract

Analogue models investigating the emplacement of granitic magmas at upper crustal levels during strike-slip deformation are presented in this paper. Variations in parameters such as ratio between horizontal displacement ( D v) and vertical magma upraising ( I v), and the number of feeding points were considered during the experiments. Model results show that a strong interaction between surface faulting and granite intrusions develops during deformation. On one side, magma intrusion influences the sequence of structures development and the final fault pattern. On the other side, magma emplacement is strongly influenced by the syn-intrusion lateral displacement ( D t), which in turn reflects variations in D v and I v. For high D t values (i.e. high displacement velocity or low injection rate), the importance of the horizontal displacement with respect to the vertical magma upraising results in asymmetric and drop-shaped plutons, with a sheared tail elongating in the sense of the strike-slip displacement. In this case, the intrusion long-axis tracks the long-axis of the strain ellipsoid. For low D t values (i.e. low displacement velocity or high injection rate), the strike-slip displacement is strongly subordinated to the vertical magma upraising and pluton emplacement is controlled by development of tensional shears at the surface. In these conditions, the long-axis of the magmatic bodies lies in the quadrants of compression of the strike-slip deformation and intrusions are apparently dragged in an opposite sense to that imposed by the transcurrent deformation.