Generation of crystal-poor rhyolites from a shallow plutonic reservoir in the Famatinian arc (Argentina)

ESCRIBANO, FACUNDO; CORNER, JULIEN; CAMILLETTI GIULIANO C.; OTAMENDI, JUAN E.; ARMAS, MARIA P; CRISTOFOLINI, EBER A; BACHMANN, OLIVIER

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2022

0377-0273

The Ordovician rocksof Sierra Las Planchadas are an exceptionally preserved natural example of aplutonic-volcanic connection. Located in northwestern Argentina, the Las PlanchadasFormation consists of a monzogranitic batholith that displays a window into thesource of large subvolcanic rhyolitic rocks, cryptodomes and volcanicfeeder-dykes. Mafic intrusions and felsic dykes occur cutting the plutonicrocks. Grain-scale relationships, whole-rock compositions and mineral chemistryindicate that monzogranites and rhyolites are two comagmatic members whichdifferentiated within upper crust magma reservoirs. Monzogranites accumulatedsome plagioclase and trapped a large volume of melt, denoted by a high modalpercentage (~64–71%) of near-solidus minerals, comprised of alkali feldspar, An<30-containingplagioclase, and late crystallized quartz. The formation of felsic dykes andrhyolitic cryptodomes is the result of a late melt extraction stage facilitatedby the injection of hot mafic magmas from deeper in the system. Themafic-induced thermal reactivation increased the amount of pore melt storedwithin a highly-crystallized monzogranite reservoir. The breakdown of thelow-temperature phases overpressurized the mush and opened a network ofmicrofractures into which residual melts, depleted in feldspar-compatible traceelements (Ba, Sr, and Eu), infiltrated. The draining system involved thininterconnected vein-like channels that merged into wider sheet-like conduits.Our results suggest that channelized segregation of late-stage melts in thesubvolcanic environment is a mechanism for triggering rhyolitic eruptions.