TY - JOUR
T1 - Volatiles contents, degassing and crystallisation of intermediate magmas at Volcan de Colima, Mexico, inferred from melt inclusions
AU - Reubi, Olivier
AU - Blundy, Jonathan
AU - Varley, Nicholas R.
AU - Blundy, Jon D
PY - 2013/6/1
Y1 - 2013/6/1
N2 - In volatile-saturated magmas, degassing and crystallisation are interrelated processes which influence the eruption style. Melt inclusions provide critical information on volatile and melt evolution, but this information can be compromised significantly by post-entrapment modification of the inclusions. We assess the reliability and significance of pyroxene-hosted melt inclusion analyses to document the volatile contents (particularly H2O) and evolution of intermediate arc magmas at Volcán de Colima, Mexico. The melt inclusions have maximal H2O contents (≤4 wt%) consistent with petrological estimates and the constraint that the magmas crystallised outside the amphibole stability field, demonstrating that pyroxene-hosted melt inclusions can preserve H2O contents close to their entrapment values even in effusive eruptions with low effusion rates (0.6 m3 s-1). The absence of noticeable H2O loss in some of the inclusions requires post-entrapment diffusion coefficients (≤1 × 10-13 m2 s-1) at least several order of magnitude smaller than experimentally determined H+ diffusion coefficient in pyroxenes. The H2O content distribution is, however, not uniform, and several peaks in the data, interpreted to result from diffusive H2O reequilibration, are observed around 1 and 0.2 wt%. H2O diffusive loss is also consistent with the manifest lack of correlations between H2O and CO2 or S contents. The absence of textural evidence supporting post-entrapment H2O loss suggests that diffusion most likely occurred via melt channels prior to sealing of the inclusions, rather than through the host crystals. Good correlation between the melt inclusion sealing and volcano-tectonic seismic swarm depths further indicate that, taken as a whole, the melt inclusion population accurately records the pre-eruptive conditions of the magmatic system. Our data demonstrate that H2O diffusive loss is a second-order process and that pyroxene-hosted melt inclusions can effectively record the volatile contents and decompression-induced crystallisation paths of vapour-saturated magmas.
AB - In volatile-saturated magmas, degassing and crystallisation are interrelated processes which influence the eruption style. Melt inclusions provide critical information on volatile and melt evolution, but this information can be compromised significantly by post-entrapment modification of the inclusions. We assess the reliability and significance of pyroxene-hosted melt inclusion analyses to document the volatile contents (particularly H2O) and evolution of intermediate arc magmas at Volcán de Colima, Mexico. The melt inclusions have maximal H2O contents (≤4 wt%) consistent with petrological estimates and the constraint that the magmas crystallised outside the amphibole stability field, demonstrating that pyroxene-hosted melt inclusions can preserve H2O contents close to their entrapment values even in effusive eruptions with low effusion rates (0.6 m3 s-1). The absence of noticeable H2O loss in some of the inclusions requires post-entrapment diffusion coefficients (≤1 × 10-13 m2 s-1) at least several order of magnitude smaller than experimentally determined H+ diffusion coefficient in pyroxenes. The H2O content distribution is, however, not uniform, and several peaks in the data, interpreted to result from diffusive H2O reequilibration, are observed around 1 and 0.2 wt%. H2O diffusive loss is also consistent with the manifest lack of correlations between H2O and CO2 or S contents. The absence of textural evidence supporting post-entrapment H2O loss suggests that diffusion most likely occurred via melt channels prior to sealing of the inclusions, rather than through the host crystals. Good correlation between the melt inclusion sealing and volcano-tectonic seismic swarm depths further indicate that, taken as a whole, the melt inclusion population accurately records the pre-eruptive conditions of the magmatic system. Our data demonstrate that H2O diffusive loss is a second-order process and that pyroxene-hosted melt inclusions can effectively record the volatile contents and decompression-induced crystallisation paths of vapour-saturated magmas.
KW - Arc magmas
KW - CO
KW - Crystallisation
KW - Degassing
KW - Diffusion
KW - HO
KW - Volcan de Colima
UR - http://www.scopus.com/inward/record.url?scp=84877819485&partnerID=8YFLogxK
U2 - 10.1007/s00410-013-0849-6
DO - 10.1007/s00410-013-0849-6
M3 - Article (Academic Journal)
AN - SCOPUS:84877819485
SN - 0010-7999
VL - 165
SP - 1087
EP - 1106
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 6
ER -