The Middle-Upper Miocene Las Burras-Almagro-El Toro (BAT) magmatic complex within the Eastern Cordillera of the central Andes (~24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma; Mazzuoli et al. submitted) comprises magma-water contact facies related to: i) andesite flowing in a subaqueous setting and generating pillows enveloped by in-situ hyaloclastite and quenched flow breccia; and ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water that develops pillow-like lava lobes, perlitic and glassy textures, hyaloclastic breccia, and quenched glassy rims on juvenile clasts. The Lampazar member (7.8 Ma; Mazzuoli et al. submitted) is represented by a syn-volcanic andesite sheet intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. Due to rapid quenching and mixing with the host sediment, the andesite sheet became finger-shaped and graded into a pillowed intrusion. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment  50 m from the parent intrusion, probably as a result of efficient fluidization processes. The Almagro A member (7.2 Ma; Mazzuoli et al. submitted) shows evidence of mixing between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tube shapes and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and separated in lobes, which acquired sharp contacts and fluidal shapes, without quench fragmentation and formation of a hyaloclastic envelope. The presence of peperite and magma-water contact facies in the BAT volcanic sequence indicates the ready availability of water in the system between 11-7 Ma. These volcanological observations, coupled with other structural, paleoclimatological, and paleogeographic evidence (Starck and Anzótegui 2001; Hernandez et al. 2005; Hilley and Strecker 2005), suggest a depositional setting in this part of the foreland basin of the central Andes during the Late Miocene in which volcanism occurred in an overall topographically low coastal floodplain that included extensive wetlands.

Vezzoli, L., Matteini, M., Hauser, N., Omarini, R., Mazzuoli, R., Acocella, V. (2009). Non-explosive magma-water interaction in a continental setting: examples from the Miocene magmatism of the Eastern Cordillera (central Andes). BULLETIN OF VOLCANOLOGY [10.1007/s00445-008-0239-5].

Non-explosive magma-water interaction in a continental setting: examples from the Miocene magmatism of the Eastern Cordillera (central Andes)

ACOCELLA, Valerio
2009-01-01

Abstract

The Middle-Upper Miocene Las Burras-Almagro-El Toro (BAT) magmatic complex within the Eastern Cordillera of the central Andes (~24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma; Mazzuoli et al. submitted) comprises magma-water contact facies related to: i) andesite flowing in a subaqueous setting and generating pillows enveloped by in-situ hyaloclastite and quenched flow breccia; and ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water that develops pillow-like lava lobes, perlitic and glassy textures, hyaloclastic breccia, and quenched glassy rims on juvenile clasts. The Lampazar member (7.8 Ma; Mazzuoli et al. submitted) is represented by a syn-volcanic andesite sheet intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. Due to rapid quenching and mixing with the host sediment, the andesite sheet became finger-shaped and graded into a pillowed intrusion. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment  50 m from the parent intrusion, probably as a result of efficient fluidization processes. The Almagro A member (7.2 Ma; Mazzuoli et al. submitted) shows evidence of mixing between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tube shapes and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and separated in lobes, which acquired sharp contacts and fluidal shapes, without quench fragmentation and formation of a hyaloclastic envelope. The presence of peperite and magma-water contact facies in the BAT volcanic sequence indicates the ready availability of water in the system between 11-7 Ma. These volcanological observations, coupled with other structural, paleoclimatological, and paleogeographic evidence (Starck and Anzótegui 2001; Hernandez et al. 2005; Hilley and Strecker 2005), suggest a depositional setting in this part of the foreland basin of the central Andes during the Late Miocene in which volcanism occurred in an overall topographically low coastal floodplain that included extensive wetlands.
Vezzoli, L., Matteini, M., Hauser, N., Omarini, R., Mazzuoli, R., Acocella, V. (2009). Non-explosive magma-water interaction in a continental setting: examples from the Miocene magmatism of the Eastern Cordillera (central Andes). BULLETIN OF VOLCANOLOGY [10.1007/s00445-008-0239-5].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/147588
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