Near-surface magma reservoir construction, prolonged cold storage, and defrosting as volcano feeder processes: A revealing case study in the Los Árboles pluton, NW Argentina

Abstract

Carboniferous plutonic activity in the Sierra Pampeanas region of NW Argentina resulted in the emplacement of several magma bodies at shallow levels, while contemporaneous volcanism was primarily recorded in the neighboring Puna region. One of these plutons, known as Los Árboles in the Sierra de Fiambalá, formed through two periods of significant felsic magma additions (326–322 Ma) and the subsequent development of tuffisites associated with subvolcanic dikes of predominantly mafic composition (315 ± 3 Ma). The presence of 2–5 -m wide tuffisite dikes, indicating subvolcanic depths (~ 1 km), provides an excellent opportunity to understand the connections between plutonic and volcanic processes. Our study reveals that for felsic magma batches to reach these subvolcanic depths, the input of synchronous mafic magmatism is a critical step. The Los Árboles pluton grew through alternating stages of accommodation by sheet intrusions, which subsequently merged during incubation into larger magma bodies with dominant lateral growth, forming a ductile halo. Both mildly alkaline mafic dike swarms and tuffisites intrude the pluton. The tuff-filled clastic dikes exhibit a variety of textural features and bulk rock compositions that indicate processes of late-stage heating and low-temperature remelting (~700 °C) of the host granite. Our findings document that magmatic plumbing systems, driven by mantle processes, can reach subvolcanic levels, induce brittle-ductile transitions in the host rock, and persist in a cold storage stage for millions of years, with temperatures below the granite solidus, and be potentially eruptive through defrosting.