TSK 11 Göttingen 2006 Burchardt et al.
 Dyke emplacement in Tener-
 ife (Canary Islands): Field
 studies and numerical models
 Poster
 Steffi Burchardt1
 Agust Gudmundsson1
 Sonja L. Philipp1
 Dykes are magma-driven extension frac-
 tures and the main conduits for magma
 in volcanic eruptions. To understand
 the mechanics of dyke emplacement is
 thus essential to assess volcanic hazards.
 To improve the understanding of the
 processes of dyke initiation from shal-
 low magma chambers and dyke propa-
 gation through a mechanically-layered
 crust, field measurements and obser-
 vations from Tenerife (Canary Islands)
 are used and compared with the results
 from numerical models.
 Careful studies of 550 dykes in three
 profiles in the Anaga massif (Tenerife)
 include measurements of dyke geometry
 and orientation. The results of these
 measurements show that dykes have
 been injected from a deep-seated reser-
 voir during the shield-building phase.
 Furthermore, the dyke attitudes agree
 with the main axial trends of Tenerife
 that are preserved in the old massifs of
 Teno, Anaga, and Roque del Conde. In
 addition, it has been observed that most
 studied dykes did not reach the surface
 to feed volcanic eruptions but became
 arrested.
 Using data from field studies in Tener-
 ife, numerical models on the effects of a
 mechanically layered crust on the stress
 fields around magma chambers of differ-
 ent geometries and around a propagat-
 1 Geowissenschaftliches Zentrum der
 Georg-August-Universität Göttingen,
 Abteilung Strukturgeologie und Geodynamik,
 Goldschmidtstr. 3, 37077 Göttingen
 ing dyke were made. These models use
 the finite element program ANSYS and
 the boundary element program BEASY.
 The numerical models of the stress
 field around circular and sill-like magma
 chambers show that a mechanically lay-
 ered crust is likely to arrest many dykes
 injected from a magma chamber. The
 numerical models indicate that, for the
 given loading conditions, most dykes ei-
 ther turn into sills at contacts between
 layers of contrasting mechanical prop-
 erties or, more likely, become arrested.
 Stress-field homogenisation is presum-
 ably a necessary condition for a dyke to
 be able to reach the surface to feed a
 volcanic eruption.
 The field studies and numerical models
 also indicate that the geometry of the
 tip of an arrested dyke depends much
 on the mechanical properties of the ar-
 resting layer. When a dyke is arrested
 on meeting a soft layer the dyke tip
 will be blunt. By contrast, a dyke ar-
 rested on meeting a stiff layer will have
 a rather sharp tip. The numerical mod-
 els on dyke propagation also show that
 the main tensile stress concentration can
 be expected around the dyke tip. Only
 if the tensile stresses at the dip of a dyke
 exceeds the tensile strength of the host-
 rock, has the dyke a chance of propagat-
 ing to shallower crustal levels or, even-
 tually, to the surface.
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