Mobilizing Salt: Magma-Salt Interactions

Salt sequences form an integral part of many sedimentary basins worldwide. Many of these basins have experienced igneous activity either syn- or post-deposition of the salt sequences. Despite this, little work has so far been undertaken to understand magma-salt interactions within the subsurface, and how aspects such as salt halokinesis may be influenced by igneous activity. Within this paper, we detail the first direct description of relationships and textures that are developed during intrusive igneous-salt interaction. We show that salt composition appears to play a dominant role in controlling where igneous intrusions invade laterally through salt sequences in a sedimentary basin. In particular, we illustrate that hydrous salts, such as carnallite, act as preferential horizons for lateral magma intrusion. This lithological control appears primarily related to the heating and subsequent dehydration reaction of carnallite, which causes the carnallite to behave as viscous fluidal horizons, resulting in the non-brittle emplacement of magma, and spectacular peperitic salt-magma mingling textures. We suggest that heating and transformation of carnallite and other hydrous salts into viscous fluidal horizons during igneous intrusion within a regional salt sequence may act as a possible trigger for contemporaneous halokinesis, by creating fluid-like viscous detachment layers. Over longer time scales, however, a solidified rigid boxwork of dikes and sills may create zones of increased mechanical strength that will locally inhibit further salt flow.