Page 376 - Caldera Volcanism Analysis, Modelling and Response

CHA P T E R 9

Facilitating Dike Intrusions into

Ring-Faults

Thomas R. Walter

Contents

1. Introduction 352
2. Modeling Method 355
3. Results 356
3.1. Deformation around a depressurized magma chamber 356
3.2. Predicting the location of ring-dike intrusions 359
3.3. How processes external to the caldera system may affect the
location of ring-dike intrusions 363
4. Discussion 367
5. Conclusion 371
Acknowledgements 371
References 371

Abstract
Most caldera volcanoes are associated with circular dike intrusions. Ring-dikes form
during complete or partial subsidence of the caldera floor and may be responsible
for eruption locations that surround a structural basin. Through a systematic set of
numerical models, this paper summarizes a variety of types, mechanisms, and patterns
of caldera ring-dikes that can be observed in nature. Caldera subsidence is simulated
by magma chamber depressurization; three main sets of models are distinguished.
First, local linear and circular faults are included in order to understand their effect on
caldera-related displacements. Second, passive opening at a ring-fault is studied in
order to understand where ring-dike intrusions may occur. Third, models are designed
to exemplify how processes external to the caldera, such as a tectonic earthquake or
an eccentric intrusion, may affect the location of a ring-dike intrusion. These models
suggest that ring-dikes commonly form ‘‘incompletely,’’ i.e. only part of a ring can
be intruded because of the nonuniform displacement field around the ring-fault.
As described in the discussion, these models help explain the locations of ring-dikes in
various volcanic regions.

Corresponding author. Tel.: +49 (0)331 288 1253; Fax: +49 (0)331 288 1204
E-mail address: twalter@gfz-potsdam.de
GFZ Potsdam, Telegrafenberg, 14473 Potsdam, Germany
Developments in Volcanology, Volume 10 r 2008 Elsevier B.V.
ISSN 1871-644X, DOI 10.1016/S1871-644X(07)00009-5 All rights reserved.
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