Controls on caldera structure: Results from analogue sandbox modeling

Research Article| May 01, 2004 Controls on caldera structure: Results from analogue sandbox modeling Ben Kennedy; Ben Kennedy 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Search for other works by this author on: GSW Google Scholar John Stix; John Stix 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Search for other works by this author on: GSW Google Scholar James W. Vallance; James W. Vallance 2Department of Civil Engineering and Applied Mechanics, McGill University, 817 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada Search for other works by this author on: GSW Google Scholar Yan Lavallée; Yan Lavallée 3Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Search for other works by this author on: GSW Google Scholar Marc-Antoine Longpré Marc-Antoine Longpré 3Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Ben Kennedy 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada John Stix 1Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada James W. Vallance 2Department of Civil Engineering and Applied Mechanics, McGill University, 817 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada Yan Lavallée 3Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Marc-Antoine Longpré 3Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Publisher: Geological Society of America Received: 01 Aug 2002 Revision Received: 30 Jan 2003 Accepted: 20 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (5-6): 515–524. https://doi.org/10.1130/B25228.1 Article history Received: 01 Aug 2002 Revision Received: 30 Jan 2003 Accepted: 20 Jul 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Ben Kennedy, John Stix, James W. Vallance, Yan Lavallée, Marc-Antoine Longpré; Controls on caldera structure: Results from analogue sandbox modeling. GSA Bulletin 2004;; 116 (5-6): 515–524. doi: https://doi.org/10.1130/B25228.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We conducted scaled analogue sandbox models of caldera formation in order to understand the effects of chamber depth and orientation on the spatial and temporal development of calderas. Dry sand contained in a 1-m-diameter cylinder served as a crustal rock analogue, and a water-filled 0.6-m-diameter rubber bladder served as an analogue magma chamber. Scaling parameters included a length ratio (L*) of 2.5 × 10–5 and a stress ratio (σ*) of 1.8–2.4 × 10–5. In contrast to some previous analogue models, the viscosity of the fluid in the chamber and its withdrawal rate were properly scaled. Generally, deformation began with broad sagging, followed by an arcuate or linear outward-dipping fault that formed on one side of the caldera. This fault propagated laterally around the caldera in both directions, sometimes joining other faults, and typically forming an overall polygonal structure. As subsidence continued, the caldera grew incrementally outward and progressively formed a series of concentric outward-dipping faults. Lastly, a peripheral zone of extension and pronounced sagging, and commonly an inward- dipping outer fault related to extension, developed at the surface. As the depth of the chamber increased, (1) the area of faulting decreased, (2) the symmetry of the caldera was affected, and (3) the coherence of the subsiding block decreased. Tilting the chamber caused highly asymmetric subsidence to occur. In this case, faults formed first where the bladder was shallowest. Subsidence then shifted rapidly to where the bladder was deepest, producing an elongate trapdoor caldera that was deepest where the bladder was deepest. Our experiments highlight the roles of sagging and faulting during caldera subsidence. Surface fault patterns both in our experiments and at natural calderas are frequently not circular. The aspect ratio of the block above the magma chamber controls the shape of the caldera, which is frequently polygonal. The faults at natural calderas determine locations and migration of eruptive vents, the degree of subsidence, the style of postcal dera resurgent magmatism, and the extent of hydrothermal circulation. Our experiments reveal details of how calderas grow outward incrementally and demonstrate that asymmetric subsidence along linear and arcuate faults is common to many calderas. 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