HR: 0800h
AN: V11A-0366    [Abstracts]
TI: How Deep Can be a Dyke? II: Common Misconceptions.
AU: * Cañón-Tapia, E
EM: ecanon@cicese.mx
AF: CICESE - Geology Department, PO Box 434843, San Diego, CA 92143, United States
AB: The choice of a conceptual model of a dyke either as a continuous conduit joining the region of magma storage and the surface during an eruptive event or, alternatively, as isolated batches of ascending magma, depends on a number of hypothesis that might not be explicitly stated. For instance, it is often assumed 1) that the internal pressure of a dyke equals the pressure exerted by the outer rock at the middle of the dyke, 2) that laboratory measured tensile strengths or fracture toughness of rocks control fracture initiation regardless of confining pressure, or 3) that the mantle behaves as an elastic solid during dyke events. These, and other hypothesis, are justified if fracture conditions are those of linear elastic fracture mechanics (LEFM). Geological and physical evidence, however, suggest that a) mantle rocks are a viscoelastic material with a relaxation time of ca. 34 yrs, b) confining pressure can invalidate the conditions behind LEFM, and c) the strong rheological contrast between magma and the surrounding rock influences the form in which stresses are transmitted in both materials. When these observations are accounted for, not only it becomes evident that LEFM might not be appropriate to describe the formation of dykes, but also it is shown that the continuous conduit model of a dyke is favored. Consequently, the existence of dykes extending to depths of 250 km beneath the surface is a physical reality. These observations also are important in controlling the ultimate 3D aspect of an intrusive, and might play an important role in the development of saucer shaped intrusions.
DE: 8434 Magma migration and fragmentation
DE: 8439 Physics and chemistry of magma bodies
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting