TY - JOUR

T1 - The petrology of a hazardous volcano

T2 - Calbuco (Central Southern Volcanic Zone, Chile)

AU - Vander Auwera, Jacqueline

AU - Montalbano, Salvatrice

AU - Namur, Olivier

AU - Bechon, Tonin

AU - Schiano, Pierre

AU - Devidal, Jean Luc

AU - Bolle, Olivier

N1 - Funding Information: Luis Lara is greatly thanked for his help in the organization of the fieldwork. Pia Plese participated to the 2016 fieldwork. This research was supported by FNRS Grants CDR J.00066.14, PDR T.0079.18 to JVDA. ON acknowledges support from the FWO through an Odysseus grant. We thank our reviewers for providing constructive comments that improved this work.

PY - 2021/6

Y1 - 2021/6

N2 - The recurrent explosive eruptions of Calbuco (Andean Southern Volcanic Zone (SVZ)) threat a rapidly expanding touristic and economic region of Chile. Providing tighter constraints on its magmatic system is therefore important for better monitoring its activity. Calbuco is also distinguished by hornblende-bearing assemblages that contrast with the anhydrous parageneses of most Central SVZ volcanoes. Here we build on previous work to propose a detailed petrological model of the magmatic system beneath Calbuco. Geochemical data acquired on a hundred samples collected in the four units of the volcano show no secular compositional change indicating a steady magmatic system since ~ 300 ka. A tholeiitic Al2O3-rich (20 wt. %) basalt (Mg# = 0.59) is the parent magma of a differentiation trend straddling the tholeiitic/calc-alkaline fields and displaying a narrow compositional Daly gap. Amphibole crystallization was enabled by the higher H2O content of the basalt (3–3.5 wt. % H2O at 50 wt. % SiO2) compared to neighboring volcanoes. This characteristic is inherited from the primary mantle melt and possibly results from a lower degree of partial melting induced by the mantle wedge thermal structure. Although macrocrysts are not all in chemical equilibrium with their host rocks and were thus presumably unlocked from the zoned crystal mush and transported in the carrier melt, the bulk-rock trend follows both experimental liquid lines of descent and the chemical trend of calculated melts in equilibrium with amphibole (AEMs). These contradictory observations can be reconciled if minerals are transported in near cotectic proportions. The AEMs overlap the Daly gap revealing that the missing liquid compositions were present in the storage region. Geothermobarometers all indicate that the chemical diversity from basalt to dacite was acquired at a shallow depth (210–460 MPa). We suggest that differentiation from the primary magma to the parental basalt took place either in the same storage region or at the MOHO.

AB - The recurrent explosive eruptions of Calbuco (Andean Southern Volcanic Zone (SVZ)) threat a rapidly expanding touristic and economic region of Chile. Providing tighter constraints on its magmatic system is therefore important for better monitoring its activity. Calbuco is also distinguished by hornblende-bearing assemblages that contrast with the anhydrous parageneses of most Central SVZ volcanoes. Here we build on previous work to propose a detailed petrological model of the magmatic system beneath Calbuco. Geochemical data acquired on a hundred samples collected in the four units of the volcano show no secular compositional change indicating a steady magmatic system since ~ 300 ka. A tholeiitic Al2O3-rich (20 wt. %) basalt (Mg# = 0.59) is the parent magma of a differentiation trend straddling the tholeiitic/calc-alkaline fields and displaying a narrow compositional Daly gap. Amphibole crystallization was enabled by the higher H2O content of the basalt (3–3.5 wt. % H2O at 50 wt. % SiO2) compared to neighboring volcanoes. This characteristic is inherited from the primary mantle melt and possibly results from a lower degree of partial melting induced by the mantle wedge thermal structure. Although macrocrysts are not all in chemical equilibrium with their host rocks and were thus presumably unlocked from the zoned crystal mush and transported in the carrier melt, the bulk-rock trend follows both experimental liquid lines of descent and the chemical trend of calculated melts in equilibrium with amphibole (AEMs). These contradictory observations can be reconciled if minerals are transported in near cotectic proportions. The AEMs overlap the Daly gap revealing that the missing liquid compositions were present in the storage region. Geothermobarometers all indicate that the chemical diversity from basalt to dacite was acquired at a shallow depth (210–460 MPa). We suggest that differentiation from the primary magma to the parental basalt took place either in the same storage region or at the MOHO.

KW - Amphibole

KW - Arc magmatism

KW - Calbuco

KW - Magmatic processes

KW - Storage depth

UR - http://www.scopus.com/inward/record.url?scp=85106869666&partnerID=8YFLogxK

U2 - 10.1007/s00410-021-01803-7

DO - 10.1007/s00410-021-01803-7

M3 - Article

AN - SCOPUS:85106869666

VL - 176

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 6

M1 - 46

ER -