0000000000505534
AUTHOR
Elena Druguet
Analysis of a complex high-strain zone at Cap de Creus, Spain
Abstract The structural analysis of a high-strain zone developed in medium- to high-grade metamorphic micaschists from the Cap de Creus area, Spain provides an example of the complex relationships between geometry, strain and kinematics to be found in deep crustal shear zones. This high-strain zone is composed of E-W trending structural domains characterized by different strain intensities and associated with syntectonic emplacement of pegmatite dykes. The main phase of deformation discussed here, D2, affects steeply dipping bedding, boudinaged quartz veins and S1 developed parallel to bedding. D2 deformation of these features and of syn-D2 pegmatite dykes gives rise to fold/boudin structur…
Geoethical education: A critical issue for geoconservation
Some geological outcrops have a special scientific or educational value, represent a geological type locality and/or have a considerable aesthetical/photographic value. Such important outcrops require appropriate management to safeguard them from potentially damaging and destructive activities. Damage done to such rock exposures can include drill sampling by geologist for scientific purposes. In this work, we show how outcrops important to structural geology and petrology can be damaged unnecessarily by drill coring. Unfortunately, regulation and protection mechanisms and codes of conduct can be ineffective. The many resources of geological information available to the geoscientist communit…
Numerical modelling of asymmetric boudinage
Abstract Asymmetric boudinage structures are commonly used as shear sense indicators but their development is incompletely understood. This paper describes the influence of initial shape and kinematic parameters on the evolution of boudin trains using a numerical approach based on the finite difference code FLAC. Boudin trains are simulated as a series of competent objects embedded in a soft matrix subjected to general monoclinic ductile flow. Deformation of boudin trains includes heterogeneous stretching, rotation of boudins and offset along the neck regions. The sense of relative boudin offset is mainly influenced by the initial orientation of the interboudin plane in the boudinaging laye…
Apparent boudinage in dykes
Intrusive rocks may be arranged in the form of strings of lenses or beads, as found on the Cap de Creus Peninsula, NE Spain, and in the South Finland Migmatite-Granite Belt. These structures first appear to be the result of stretching and boudinage of intrusive sheets or dykes. However, closer examination reveals that they are not boudins, but are instead primary intrusive structures. A detailed study was performed on a swarm of pegmatite intrusions at Cap de Creus. Layering is often continuous between beads, and, in some cases, individual beads exhibit a very irregular shape. These observations are shown to be incompatible with an origin by boudinage. Analogue experiments were used to test…