|Dietl, C. and Koyi, H. A. 2002. Emplacement of nested diapirs: Results of centrifuge modelling. In: Schellart, W. P. and Passchier, C. 2002. Analogue modelling of large-scale tectonic processes. Journal of the Virtual Explorer, 7, 79 - 86..|
Emplacement of nested diapirs: Results of centrifuge modelling
The model was centrifuged for 930 at 700 g before a profile was cut for photographing. Two mushroom-shaped diapirs of the buoyant layer intruded the overburden and spread below the less-dense PDMS layer (Fig. 5). One diapir developed at the perturbation site and another one developed at the margin of the model. Moreover, two smaller diapirs reached the surface of the model (Figs. 5a-b). A fifth diapir, which formed close to the opposite margin ceased rising after only 1 cm, probably as a result of shortage in supply of the buoyant material (Figs. 5c-d). During their rise, the diapirs deformed the overburden units. A strain grid on top of the model deformed significantly due to emplacement of the diapirs underneath the PDMS layer (Fig. 5a). Peripheral skirts developed at the rims of the two spreading diapirs, whereas intense folding developed in the overburden between these two diapirs. Moreover, although being less dense than the other two materials, the PDMS overburden was dragged downward between the two diapirs (Figs. 5cd).
After photographing, the model was put together and welded by contact. A second buoyant layer of similar density and viscosity as the first buoyant layer, (differently stained RG2 layer) was attached to the bottom of the model. The model was then centrifuged for an additional 610 at 700g.
the centrifuging a second-stage intrusion of the second buoyant material
occurred. The intrusion of this buoyant material led to extensive spreading
and expansion of the first stage diapirs, whose surface area increased
by 25 to 50%. The two small diapirs unified to just one expanded diapir
(Figs. 6a-b). As a result of this ballooning the diapirs were overthrusted
upon each other and upon the overburden (Figs. 6c-d). Internal flow
within the diapirs led to peripheral skirts at the rims of the second
stage intrusions. The RG2 material rose along the stem of the pre-existing
diapirs, using them as mechanically weak pathways for its rise (Figs.
The results of the experiment can be summarized as follows. During the first stage of centrifuging two mushroom-shaped diapirs of the buoyant RG1 layer intruded the overburden to spread below the less-dense PDMS layer. During their rise, the diapirs deformed the overburden units and caused the formation of rim synclines around the diapirs (Figs. 5b and d). During a second stage of centrifuging a second intrusion occurred within the stem of the pre-existing diapirs. Once reaching the level of neutral buoyancy, the intrusive material spread laterally resulting in expansion of the overhang of the pre-existing diapirs. This lead to the formation of tabular intrusive bodies (Figs. 6b and d).