2016), whereas whitelight interferometry, laser scanning, and image analysis are used in the laboratory or in the field to create digital shape models of the surfaces of shatter cones and allow the morphometric analysis of the macroscopic shapes or of the surface striations ( Baratoux et al. Such new developments include the application of the nondestructive microcomputer tomography technique to visualize the interior fracture pattern of a sample ( Zaag et al.
(2016) has elaborated and examined the value of a phenomenological model to reconstruct the geometry of a shatter cone, and in particular of the horse-tailing effect. 2016) are systemically confronted with the predictions of the various hypotheses of formation, whereas Kenkmann et al. 2016 Wilk and Kenkmann 2016), observations of vesicular films in experimentally produced shatter cones (Wilk and Kenkmann 2016) and relationships between shatter cones and pre-existing joints ( Hasch et al. Morphometric observations of natural or experimental shatter cones ( Baratoux et al. A first notable aspect of the special issue is the recent development of analytical techniques and innovative applications of existing techniques to characterize the structure of these objects, their 3dimensional geometry, or the internal distributions of fractures. Measurements of these quantities on four shatter cones from different impact structures and lithologies agree well with model predictions. The model predicts possible triples of enveloping cone angle, bifurcation angle, and subcone angle. Increasing subcone convexity leads to a stronger horse-tailing effect and the bifurcation angles increase with increasing distance from the enveloping cone apex.
Straight cones of various apical angles, constant slope, and constant bifurcation angles form if the subcone convexity is low (30°). The overall cone geometry including apex angle of the enveloping cone and the degree of concavity (horse-tailing) is largely governed by the convexity of the subcone ridges. We present a phenomenological model that fully constructs the shatter cone geometry to any order.
#HELICON REMOTE MODEL CRACK#
Multiple symmetric crack branching is the result of rapid fracture propagation that may approach the Raleigh wave speed. The characteristic diverging striations are interpreted as the intersection lineations delimiting each subcone. We propose that subcone ridges represent convex-curved fracture surfaces and their intersection corresponds to the bifurcation axis. This pattern is repeated to form new branches.
Tracing a single subcone ridge from its apex downward reveals that each ridge branches after some distance into two symmetrically equivalent subcone ridges. Here, we use the hierarchical arrangement of subcone ridges of shatter cone surfaces as key for understanding their formation. While these models are capable of explaining the overall conical shape of shatter cones, they are not capable of explaining the subcone structure and the diverging and branching striations that characterize the surface of shatter cones and lead to the so-called horse-tailing effect. This heterogeneity is the source of spherically expanding waves that interact with the planar shock front or the following release wave. Several models of shatter cone formation require a heterogeneity at the cone apex of high impedance mismatch to the surrounding bulk rock.
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