Structure of the Bushveld Complex from resistivity measurements
Knowledge of the deep structure of the arc-like bodies constituting the Bushveld Complex (South Africa) is essential not only to understand the emplacement history of this huge layered intrusion, but also for success in the exploration for the platiniferous Merensky Reef and chromitite layers occurring near its base. Despite many studies the structure of the complex has remained obscure. Here we describe new insights into the structure and additional geophysical boundary conditions, based on a geoelectrical study. This has provided a geoelectrical stratigraphy according to which a conductive layer below the granitic rocks, of both the eastern and western compartments of the Complex, is correlated with sedimentary rocks of the Transvaal Sequence over large areas, rather than with the mafic sequence as conventionally assumed. A new feature of this model is that the mafic sequence in both compartments occurs as segments of an inward-dipping sheet transgressing the layering of the sedimentary rocks into which it intruded. The geoelectrical model supports earlier gravity models in that mafic rocks are absent from the central part of the Complex, but shows that here the Bushveld granite directly overlies Archaean basement rather than Transvaal Sequence rocks as previously accepted.
V s structure of the crust containing the Bushveld Complex
The Bushveld Complex (BC) (Fig. 1, end of paper) was emplaced at ca. 2.06 Ga in the northern part of the Kaapvaal Craton, South Africa and is one of the largest mafic layered igneous intrusions in the world. It covers an area of ~66,000 km 2 within the craton (e.g., Walraven, 1997; Eglington and Armstrong, 2004; Webb et al., 2004). It has an abundance of platiniferous group metals, as well as large reserves of chromium, titanium, vanadium, nickel and gold (e.g., Cawthorn et al., 2006). It intruded into the intracratonic sedimentary sequences of the Transvaal Supergroup and is stratigraphically divided into the Rooiberg Group (RG), the Rashoop Granophyre Suite (RGS), the Lebowa Granite Suite (LGS) and the Rustenburg Layered Suite (RLS; e.g., South African Committee for Stratigraphy, 1980; Hatton and Schweitzer, 1995; Cawthorn and Webb, 2001; Cawthorn et al., 2006).
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.