Along-arc variations in magma chamber depth of large explosive eruptions in Central America: constraints from fluid inclusions and mineralogy.

Burkert, Cosima, Hansteen, Thor , Freundt, Armin and Kutterolf, Steffen (2012) Along-arc variations in magma chamber depth of large explosive eruptions in Central America: constraints from fluid inclusions and mineralogy. [Poster] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters. , 23.05-25.05.2012, Lübeck, Germany . The Lübeck Retreat - final colloquium of SFB 574, May 23-25, 2012: program & abstracts. ; p. 4 .

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We have applied a combination of fluid inclusion and amphibole thermobarometry to felsic tephras from highly explosive volcanic eruptions along the Central American volcanic arc (CAVA) from Guatemala through Nicaragua in order to constrain pre-eruptive magma ascent and storage conditions. We note that this is the first time a combination of pressure estimates from fluid inclusions and amphibole chemistry have been used to quantify multi-stage magma chamber processes and magma ascent velocities of large eruptions. Our data document a stepwise ascent of magmas through the crust, typically involving at least two levels of stagnation. Amphibole and fluid inclusion thermobarometry both indicate a shallow preeruptive magma storage level at 80 to 200 MPa (3-8 km depth) along the entire arc. The deeper levels of magma storage vary along-arc, with a tendency to greater maximum depths of up to 25 km in Guatemala and El Salvador, compared to maximum depths of 15 km in Nicaragua. We assume that the continental crust of about 45 km thickness in Guatemala, compared to the 30km thickness of the largely oceanic crust of Nicaragua, allowed for deeper positions of the magma chambers. Thus the
observed along-arc changes in mid-crustal magma storage depths indicate a dependence between
magma chamber formation and the composition and probably density of the local crust. The average composition of the pre-eruptive fluid phase for highly explosive eruptions in Central
America amounts to 90% water, 5% CO2 and 5% NaCl equivalents, and show no systematic alongarc variations. The pressures obtained from the earliest fluid inclusions were taken as the pressures of fluid oversaturation and thus for the beginning of degassing. They range between 150 and 400 MPa, and do not show systematic along-arc variations. Such fluid oversaturation pressures correspond to water contents between 4-8 wt% in the felsic melts. Our results show that the depths of fluid saturation are mostly independent of crustal properties. Degassing typically started at pressures 150 to 300 MPa higher that those corresponding to the last stagnation level, providing evidence for the pre-eruptive criticality of the systems.

Document Type: Conference or Workshop Item (Poster)
Keywords: Geodynamics
Research affiliation: OceanRep > SFB 574 > C4
OceanRep > SFB 574
OceanRep > SFB 754 > B5
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Projects: SFB754
Date Deposited: 28 Aug 2012 10:06
Last Modified: 28 Aug 2012 10:06

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