Shape evolution and finite deformation pattern in analog experiments of lithosphere necking

Abstract

[1] Lithosphere necking evolution determines the 3-D architecture of crustal and upper mantle thinning and related basins, and the heat flow distribution in rifted regions. Despite a large number of studies, lithosphere necking evolution is still a matter of debate. We present the result from lithospheric-scale analog models designed for investigating the necking shape during extension and the vertical distribution of finite deformation in the mechanical lithosphere. In our experiments, lithosphere necking is asymmetric and, in particular, the 3-D distribution of thinning is cylindrical in the crust and very heterogeneous in the mantle. Overall, the evolution of rifting and necking progresses from delocalized to localized deformation.

Strain rate‐dependent lithosphere rifting and necking architectures in analog experiments

“…Brittle-ductile parameter Γ computed for the crust (Γ C ), the lithospheric mantle (Γ M ), and the whole lithosphere (Γ L ) according to Schueller and Davy [2008]. For comparative purposes, Γ values are computed also for experiment NECK-10 described in Nestola et al [2013]. See text for details.…”

“…The evolution of the H/L aspect ratio during necking well illustrates such differences (Figure 5c). When the intermediate velocity case [Nestola et al, 2013] is also considered, H/L trends suggest that differences in necking shape can be imprinted in the very early evolutionary stages. Nevertheless, diagnostic first-order signatures of plate divergence rate on neck geometry may be hidden in natural rifts, particularly when trying to reconstruct rift architectures from conjugate passive margins separated by long-living drift histories.…”

“…In particular, in this paper we describe results from models extended at 5 mm/h (NECK-05) and 50 mm/h (NECK-50). Experimental rifting produced at 10 mm/h of side divergence rate, with the same model configuration, is described in Nestola et al [2013]. According to equation (3) These values are appropriate for narrow rifting [Buck, 1991].…”

“…The experimental evolution is quantitatively analyzed using the 3-D distribution of the thinning factor (TF = 1 À 1/β [Reston, 2009]), calculated according to Nestola et al [2013]. The crustal pattern of this parameter …”

“…We performed further research on this subject by exploiting the improved monitoring capability provided by coupled top and basal laser scanning of models implemented in our apparatus (Figure 1a). Such a device allows the evolution of lithosphere necking to be quantitatively analyzed through time [Nestola et al, 2013].…”