High‐temperature deformation of dry diabase with application to tectonics on Venus

Abstract

Abstract. We have performed an experimental study to quantify the high-temperature creep behavior of natural diabase rocks under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and plagioclase-to-pyroxene ratio on creep strength. Flow laws determined for creep of these diabases were characterized by an activation energy of Q = 485_+30 kJ/mol and a stress exponent of n = 4.7+0.6, indicative of deformation dominated by dislocation creep processes. Although n and Q are the same for the two rocks within experimental error, the Maryland diabase, which has the lower plagioclase content, is significantly stronger than the Columbia diabase. Thus the modal abundance of the various minerals plays an important role in defining rock strength. Within the sample-to-sample variation, no clear influence of oxygen fugacity on creep strength could be discerned for either rock. The dry creep strengths of both rocks are significantly greater than values previously measured on diabase under "as-received" or wet conditions [Shelton and Tullis, 1981; Caristan, 1982]. Application of these results to the present conditions in the lithosphere on Venus predicts a high viscosity crust with strong dynamic coupling between mantle convection and crustal deformation, consistent with measurements of topography and gravity for that planet.

The Alps 2: Controls on crustal subduction and (ultra)high‐pressure rock exhumation in Alpine‐type orogens

“…Each crustal unit (Figure 2 and Table 1) consists of an upper/middle crust with ϕ eff (hereafter simply ϕ) = 15-4°(except where noted) over ε = 0.5-1.5, and a scaled wet quartzite (WQ) flow law [Gleason and Tullis, 1995], overlying a lower crust with ϕ = 15-4°over ε = 0.5-1.5 (where ϕ = 4°is fully strain softened) and a dry Maryland diabase (DMD × 0.05) flow law, scaled to represent a lithology somewhat stronger than intermediate granulite [Mackwell et al, 1998]. The accretionary wedge comprises upper/middle crust (ϕ = 8-4°; WQ × 2).…”

“…We choose to base the power law flow calculations in the models on a reference set of well constrained laboratory experimental [Gleason and Tullis, 1995]; melt absent Black Hills quartzite), dry diabase (DMD [Mackwell et al, 1998]; dry Maryland diabase), and wet olivine (WOL) [Karato and Wu, 1993]. Laboratory-derived flow laws are subject to significant uncertainties associated with the measurements on individual samples, the variability of measured results among samples of similar rock types, the range of deformation mechanisms, the effects of water fugacity, the variability of results among different laboratories, and the known and unknown errors in extrapolating the laboratory results to natural conditions.…”

Dislocation and diffusion creep of synthetic anorthite aggregates

“…Independently, Meissner and Strehlau [1982] and Chen and Molnar [1983] suggested that reduced seismic activity of the lower crust indicates low ductile flow strength relative to the upper crust. However, mechanical data and flow law parameters on the rheology of rocks typical for the lower crust, i.e., gabbros, metabasites, etc., are still scarce [Caristan, 1982;Shelton and Tullis, 1981;Kirby, 1983;Carter and Tsenn, 1987;Mackwell et al, 1998]. The amount of stress transfer and partitioning of strain between crustal layers and the mantle has given rise to much controversy [e.g., Kirby, 1985; Ord and Hobbs, 1989].…”

Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal

“…Fig. 1(c) shows the predicted strength profiles for crust consisting of a felsic upper-mid crust and a mafic lower crust (Ranalli & Murphy 1987), using the rheological parameters of dry granite (Ranalli 1995) and dry Maryland diabase (Mackwell et al 1998), respectively. Fig.…”

“…(c) Effective viscosity profiles calculated for each geotherm [using same line colours as in (b)], assuming a felsic upper-mid crust and mafic lower crust. Rheology parameters for upper-mid crust are those of dry granite (Ranalli 1995), the lower crust uses dry Maryland diabase parameters (Mackwell et al 1998), and the mantle uses dry olivine parameters (Hirth & Kohlstedt 1996). The red rectangle shows the inferred depth and viscosity for a mid-crustal channel in southern Tibet (see the main text).…”