Simultaneously ascending diapirs from different depths and different positions: a centrifuge study
Forien, Mélanie;Dietl, Carlo
In this study, we investigate the diapiric ascent of buoyant material from two source layers at different depths, rising from protrusions at different positions within a model made from different silicone putties in order to explain the origin of concentrically zoned, inflated plutons. Through these models, we wanted to test, if a rising diapir ascends straight upward or, if it might be deviated by a similar buoyant layer which is located within the overburden strata to follow the diapir stems developing from this layer. A centrifuge was used to model the kinematics and dynamics of the buoyant material during ascent and emplacement of the diapirs. Five experiments were carried out: each model consisted of two buoyant PDMS layers and two layers of overburden of greater density above each PDMS layer. Throughout the experimental runs, the effects of different overburden viscosities and perturbation positions on the number of the diapirs were observed, including the diapir pathways and the deformation patterns of the overburden layers. With higher overburden viscosity, the number of diapirs decreased. Model 1 - with no perturbation on top both the buoyant PDMS layers - resulted in diapirs growing close to the margins of the experiment, while in other the experiments with perturbations the diapir positions were controlled by those perturbations. The modeling results also show that two diapirs rising from offset perturbations (models 2-4) do not take the same pathway through the overburden layer when rising. Rather, each diapir takes a different pathway, with the deeper diapir piercing through its overburden while rising, regardless if it was a PDMS layer or denser overburden layers. However, when the two perturbations were situated directly above each other in the different PDMS layers (model 5), this resulted in the formation of one big diapir rather than several smaller ones. A similar spatial distribution of diapiric structures in natural salt diapirs as observed in our models 2-4 occurs within the Great Kavir Basin (Iran). The resulting structure of model 5 (two perturbations situated directly above each other) is close to what is observed in natural examples of composite batholiths such as the Bergsträßer Odenwald Crystalline Complex (Germany).