Backbone of the Americas—Patagonia to Alaska, (3–7 April 2006)
Paper No. 2-27
Presentation Time: 10:35 AM-7:45 PM

VILAMA CALDERA: ONSET OF LARGE ERUPTIONS DURING IGNIMBRITE FLARE-UP IN PUNA-REGION, AND ITS INDICATIONS OF STRESS FIELD ORIENTATION

SOLER, Miguel M., Instituto de Geología y Minería, Universidad Nacional de Jujuy, San Salvador de Jujuy / Jujuy, AL 4600, Argentina, msoler@idgym.unju.edu.ar, COIRA, Beatriz, Instituto de Geología y Mineria, Universidad Nacional de Jujuy, Av. Bolivia 1661, San Salvador de Jujuy, 4600, Argentina, KAY, Suzanne Mahlburg, Dept. Geological Sciences, Cornell Univ, Snee Hall, Ithaca, NY 14853, and CAFFE, Pablo J., Instituto de Geología y Minería, Universidad Nacional de Jujuy, San Salvador de Jujuy / Jujuy, 4600, Argentina

The central Andean plateau hosts an extensive back-arc ignimbritic province, erupted from several collapse calderas during 10-2 Ma, immediately after its main stage of uplift. The Vilama ignimbrite marks the onset of large ignimbrite eruptions in the Puna at ~8.4 Ma. The eruption, one of the largest of the world, involved the discharge of 2100 km3 (~1680 km3 DRE) of dacite magma. The related caldera is a subeliptical NW-SE structure (~ azimuth of 290°) of ~35 x 15 km, with central coordinates of 22°24'S - 66°57'W. Caldera collapse is thought to have been symmetric, during which ignimbrites with varying grades of welding were erupted. Resurgence caused bending of part of the intracaldera deposits, building a central dome. Late (postcaldera) eruptions channelled mainly through inferred structural borders. The high magma viscosity (crystal-rich, high-K dacites), and the large erupted volume require an external driving force to initiate and sustain the eruption. That “external force” was the mechanical failure of the roof of the pre-eruptive magma chamber. If we accept that the configuration of the Vilama caldera in map view reflects the shape of the underlying magma chamber, its elongation may be due to: a) stretching of the reservoir under regional WNW extension, or b) control by pre-existing WNW-ESE structures. The location of the Vilama caldera in the ~NW Lípez lineament suggests that the control of distensive WNW-ESE structures, related to a counterclockwise strike-slip movement of faults belonging to the former, would be the most likely explanation for the elongated shape of the Vilama magma chamber.

Backbone of the Americas—Patagonia to Alaska, (3–7 April 2006)
General Information for this Meeting
Session No. 2
T2. Plateau and Cordillera Uplift I
Congress & Exhibition Center: Foyer and Auditorio Bustelo
10:35 AM-7:45 PM, Monday, 3 April 2006

Geological Society of America Abstracts with Programs, Speciality Meeting No. 2, p. 32

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