Diapiric initiation and formation mechanism of diapir’s downbuilding—Insights from analogue modeling

The diapir structure is closely related to the distribution of oil and gas resources and has received extensive attention. In this regard, previous works have conducted much research on it. So far, many important achievements and understandings have been obtained on the formation environment and deformation styles of diapir structures, but there are few studies on the formation mechanism of salt or mud diapir initiation and its downbuilding. This study uses analog modeling to establish four sets of combined models of the basal silicon layer and overlying quartz sand, including the differences in initial geomorphology, the thickness of the covering layer above the ductile layer, sedimentary rate, and basal and lateral friction. Results show that the difference in geomorphology is the initial necessary condition for the formation of salt dome or mud dome structure, i.e., the extension, compression environment, and weak zone formed by tectonic activity are all conducive to the rapid start of the diapir structure. The formation of diapir downbuilding, rapid deposition loading, thick initial covering layer above the ductile layer, and significant basal and lateral friction will inhibit the development of early diapirs. In contrast, slow deposition rate, thin initial covering layer above the ductile layer, and reduced basal and lateral friction will promote the growth of early diapirs. Simultaneously, in the middle and late stages of diapir downbuilding, diapirs will grow and deform rapidly with the loading of the deposition rate. Based on the physical modeling results and natural deformation of the diapiric structure, comprehensive analysis shows that diapir downbuilding results from the combined effects of geomorphology, deposition rate, formation temperature and pressure, and diapir fluid depth. It is found that the salt diapir downbuilding in the North Sea Basin and mud diapir downbuilding in the Andaman back-arc basin are similar to the formation mechanism of analog modeling downbuilding in this paper.

 

Keywords: Diapir Structure; Downbuilding; Initial Geomorphology; Sedimentary Rate; Covering Thickness; Basal and Lateral Friction; Analogue Modeling