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<p>The Osorno and Calbuco stratovolcanoes are situated just 27&#xa0;km apart along the volcanic arc front of the Central Southern Volcanic Zone (Chile), yet they exhibit significantly different characteristics. Notably, Calbuco intermediate to andesitic lavas contain amphibole, which is absent in Osorno, and has a much higher explosivity (up to VEI = 4 to 5). Their olivine-hosted melt inclusions (MI) display similar major elements differentiation trends. Incompatible trace element ratios overlap in both volcanoes and therefore do not correlate with the H<sub>2</sub>O and Cl contents. Indeed, MIs data and petrological hygrometers indicate higher volatiles content at Calbuco (~ 3 wt% @ 51.3 wt% SiO<sub>2</sub>, 951–3232 ppm) compared to Osorno (~ 1 wt% @ 50.5 wt% SiO<sub>2</sub>, 521–1091 ppm). Because the Cpx-only geobarometers and geophysical data both place the Osorno and Calbuco main magma reservoirs at the same depth, their differing volatile contents are interpreted as inherited from the mantle melts. Their calculated primary magmas result from similar to identical partial melting fractions of mantle sources that differ only in their H<sub>2</sub>O content. The mantle source beneath Calbuco partially melted at a lower temperature, possibly because of the slightly more trench ward position of the volcano, which projects vertically into a cooler part of the mantle wedge “nose”. The lack of correlation between incompatible elements and H<sub>2</sub>O content is interpreted as resulting from evidence for a decoupling between H<sub>2</sub>O, transported mainly in a solute-poor fluid, and incompatible elements, which are delivered by melts derived from the subducting oceanic lithosphere. The variability of the mantle wedge H<sub>2</sub>O concentration and the uncorrelated content of slab tracers and H<sub>2</sub>O have also been observed at a global scale.</p>

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Calbuco and Osorno volcanoes (Chile) tap into mantle sources that only differ by their water content

  • 期刊论文

  • 发表日期：

    2026年1月20日

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  • Jacqueline Vander Auwera,
  • Tonin Bechon,
  • Salvatrice Montalbano,
  • Bernard Charlier,
  • Olivier Bolle,
  • Pierre Schiano,
  • Nicolas Cluzel,
  • Jean-Luc Devidal,
  • Luisa Ottolini,
  • Luis E. Lara,
  • Olivier Namur,
  • Thomas van Gerve

摘要

The Osorno and Calbuco stratovolcanoes are situated just 27 km apart along the volcanic arc front of the Central Southern Volcanic Zone (Chile), yet they exhibit significantly different characteristics. Notably, Calbuco intermediate to andesitic lavas contain amphibole, which is absent in Osorno, and has a much higher explosivity (up to VEI = 4 to 5). Their olivine-hosted melt inclusions (MI) display similar major elements differentiation trends. Incompatible trace element ratios overlap in both volcanoes and therefore do not correlate with the H2O and Cl contents. Indeed, MIs data and petrological hygrometers indicate higher volatiles content at Calbuco (~ 3 wt% @ 51.3 wt% SiO2, 951–3232 ppm) compared to Osorno (~ 1 wt% @ 50.5 wt% SiO2, 521–1091 ppm). Because the Cpx-only geobarometers and geophysical data both place the Osorno and Calbuco main magma reservoirs at the same depth, their differing volatile contents are interpreted as inherited from the mantle melts. Their calculated primary magmas result from similar to identical partial melting fractions of mantle sources that differ only in their H2O content. The mantle source beneath Calbuco partially melted at a lower temperature, possibly because of the slightly more trench ward position of the volcano, which projects vertically into a cooler part of the mantle wedge “nose”. The lack of correlation between incompatible elements and H2O content is interpreted as resulting from evidence for a decoupling between H2O, transported mainly in a solute-poor fluid, and incompatible elements, which are delivered by melts derived from the subducting oceanic lithosphere. The variability of the mantle wedge H2O concentration and the uncorrelated content of slab tracers and H2O have also been observed at a global scale.