Does tectonic deformation control episodic continental arc magmatism? Evidence from granitic magnetic fabrics (AMS)

This paper applies magnetic fabric analyses to plutons of the East Pacific continental arc. Continental arc magmatism is strongly episodic, with voluminous granitic magma addition occurring during discrete high-flux events ('flare-ups'). The cause of these flare-ups is debated, variously invoking tectonic, mantle, or crustal controls. To understand how the syn-magmatic strain history changes during a flare-up, we compare granitic magnetic fabric (Anisotropy of Magnetic Susceptibility, AMS) and geochronological data from the Antarctic Peninsula (Lassiter Coast), Sierra Nevada, and Chile. This comparison indicates a common pattern in orientation and magnitude of syn-magmatic deformation, showing flare-up events occur during increased tectonic compression driven by enhanced interplate coupling and fast subduction. Flare-ups terminate as tectonic compression reduces or the regime becomes extensional, even if convergence rates remain high. As with enhanced seismicity, magmatic flare-ups result from high tectonic compression, during discrete periods of enhanced interplate coupling within broader periods of increased subduction rates. The enhanced magmatic flux results either from crustal thickening leading to partial melting of a newly accreted, hydrous mafic underplate, enhanced melt segregation in the source, or in response to high tectonic compression rendering lithostatic compression the weakest compressive force, enhancing magma extraction and ascent from the mantle. (c) 2022 The Authors. Published by Elsevier B.V. on behalf of International Association for Gondwana Research. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/ 4.0/).

Automated summary

This paper applies magnetic fabric analyses to plutons of the East Pacific continental arc. The study reveals that continental arc magmatism exhibits strong episodic characteristics and is associated with enhanced interplate coupling and fast subduction. Magmatic flare-ups typically occur during periods of increased tectonic compression and cease when the compression reduces or becomes extensional. The enhanced magmatic flux can be attributed to crustal thickening leading to partial melting of a newly accreted, hydrous mafic underplate, enhanced melt segregation in the source, or the lithostatic compression becoming the weakest compressive force, facilitating magma extraction and ascent from the mantle.