Welcome to Petroleum Geology Forums

Hi all,

I am doing a petroleum geology program and am currently learning about structural geology in ancient deep structural regions. My lecture notes tell me that deformation in ancient mountain belts and basins may have worked using different stress regimes and principles than apply now. Sandbox models seem to have supplied this info, but what are they and why was ductile and brittle deformation different then?

thanks in advance.

I think this is about the following article:

Deformation of the continental lithosphere insights from brittle-ductile models, 2002; Jean-Pierre Brun

Basically what mr Brun suggests is that by using a sandbox comprised of layers with different strength in extensional and compressional settings insight in the rheology and coupling of the lithosphere and mantle can be obtained. The morphology and structure of the sandbox after deformation can then be compared to actual geological settings. Results of this research show that a high strength sub-Moho will localize deformation in an extensional setting, while it will cause subduction of an underthrusted unit in an compressional setting. A ductile mantle will distribute the deformed areas more homogeneous throughout the entire system. By comparing the sandbox to ancient mountain belts and rift systems, it can be said that a 4 layered system with a strong sub-Moho was probably present in phanerozoic times, while two or three layered models with a ductile mantle can be observed in more specific tectonic settings of the phanerozoic (wide rifts, core complexes) and to the Archean and Early Proterozoic. Coupling between brittle and ductile layers is mainly important in 4 layer models. Also strain rate has influence on coupling, and thus the structures, as a low strain rate causes a decollement surface to form between the crust and mantle.

Hope this what you were looking for!

O_stevens,

Thank you clearing this up. I don't know if my prof is pointing towards this article by Brun, but it sure comes close. I am having a hard time finding it though. Can't seem to access it from the university journal license. I'll try trough other services later so I can have a detailed read.
Anyways, those sandbox models sound interesting. Must also be pretty fun to set up...

thanks!