Contrasting records from mantle to surface of Holocene lavas of two nearby arc volcanic complexes: Caburgua-Huelemolle Small Eruptive Centers and Villarrica Volcano, Southern Chile

• We compared pre- and syn-eruptive conditions of lavas from two nearby volcanic complexes: Caburgua-Huelemolle and Villarica.
• In both centers a deep reservoir at upper mantle–lower crust depth was recognized.
• A shallow reservoir beneath Villarrica volcano was recognized.
• Heating of the shallow Villarrica reservoir took place prior to the studied lava.
• Similar syn-eruptive conditions were obtained for the studied lavas.

Most of the small eruptive centers of the Andean Southern Volcanic Zone are built over the Liquiñe-Ofqui Fault Zone (LOFZ), a NS strike-slip (> 1000 km length) major structure, and close to large stratovolcanoes. This contribution compares textural features, compositional parameters, and pre- and syn-eruptive P,T conditions, between basaltic lavas of the Caburgua-Huelemolle Small Eruptive Centers (CHSEC) and the 1971 basaltic andesite lava of the Villarrica Volcano located 10 km south of the CHSEC. Olivines and clinopyroxenes occur as phenocrysts and forming crystal clots of the studied lavas. They do not markedly show compositional differences, except for the more scattered composition of the CHSEC clinopyroxenes. Plagioclase in CHSEC lavas mainly occur as phenocrysts or as microlites in a glass-free matrix. Two groups of plagioclase phenocrysts were identified in the 1971 Villarrica lava based on crystal size, disequilibrium features and zonation patterns. Most of the CHSEC samples exhibit higher LaN/YbN and more scattered Sr–Nd values than 1971 Villarrica lava samples, which are clustered at higher 143Nd/144Nd values. Pre-eruptive temperatures of the CHSEC-type reservoir between 1162 and 1165 ± 6 °C and pressures between 10.8 and 11.4 ± 1.7 kb consistent with a deep-seated reservoir were obtained from olivine–augite phenocrysts. Conversely, olivine–augite phenocrysts of 1971 Villarrica lava samples record pre-eruptive conditions of two stages or pauses in the magma ascent to the surface: 1208 ± 6 °C and 6.3–8.1 kb ± 1.7 kb (deep-seated reservoir) and 1164–1175 ± 6 °C and ≤ 1.4 kb (shallow reservoir). At shallow reservoir conditions a magma heating prior to the 1971 Villarrica eruption is recorded in plagioclase phenocrysts. Syn-eruptive temperatures of 1081–1133 ± 6 °C and 1123–1148 ± 6 °C were obtained in CHSEC and 1971 Villarrica lava, respectively using equilibrium olivine–augite microlite pairs. The LOFZ could facilitate a direct transport to the surface of the CHSEC magmas and explain the observed differences with the pre-eruptive conditions of the 1971 Villarrica lava.

a) Schematic representation of the main characteristics of the CHSEC and Villarrica reservoirs. Both studied volcanic complexes would have deep reservoirs at the mantle–crust boundary, but unlike the Villarrica volcano, CHSEC do not have a shallow reservoir probably by role of the LOFZ as an efficient conduit for the ascending magma. b) Villarrica volcano shallow reservoir during the arrival of hotter magma. c) Ascending plumes of heated magma in the shallow reservoir prior to eruption of 1971 lava.Figure optionsDownload as PowerPoint slide