Analogue modeling of overlapping spreading centers: insights into their propagation and coalescence

Abstract

The propagation and segmentation of mid-ocean ridges is studied using centrifuged analogue models built with non-linear materials. The deformation of the brittle-ductile model is controlled by diapiric uprise of buoyant analogous asthenospheric material induced by a centrifugal body force. This linear upwelling laterally stretches the model mantle that, in turn, induces failure in the upper layer simulating the brittle crust. Arrays of fractures initiate within zones of high stress concentration above the diapir. Fractures propagate laterally in a direction perpendicular to the maximum tensile (the minimum principal) stress. Secondary tension cracks initiate in the vicinity of parent fracture tips. Through-going fractures that crosscut the model surface develop by short fractures propagating toward each other and coalescing in different types of patterns. The overlap, overstep and inclination of fractures developed at the initial stage of extension control their subsequent growth and coalescence. Non-overlapping sub-parallel fractures propagate along nearly straight paths and coalesce to produce a single planar fracture. If overlapping fractures are parallel, they propagate towards each other along curved paths that enclose an intervening elliptical core of intact material. Fracture curvature in this case results from crack–crack interaction and is similar to that of overlapping spreading centers (OSCs) observed along mid-ocean ridges. Overlapping non-parallel fractures tend to coalesce by one of their tips propagating sub-parallel to the spreading direction toward the other fracture. Such offsets can serve as models for the development of the orthogonal ridge-transform fault patterns common along mid-ocean ridges.