Quantifying the crystal cargo of the Cerro Bayo cryptodome, Argentina; A window into pre-emplacement magma processes and storage conditions

• Shallow plumbing systems with intermediate to evolved volcanic systems can show complex magma recycling and recharge systematics. Such evidence is often stored in the information looked within the crystal cargo found in shallow systems. The Cerro Bayo cryptodome provides a classic example of such processes and was emplaced in the upper kilometre of the Miocene, back-arc Chachahuén volcano. Cerro Bayo formed during an extensive dome-building (and collapse) stage of the Chachahuén volcano, and is composed of a porphyritic trachyandesite which contains numerous mafic enclaves. This contribution investigates the deeper magma plumbing system and magmatic processes preceding the emplacement of Cerro Bayo with petrography, mineral chemistry, crystal size distributions and thermobarometry. The main crystals found in Cerro Bayo are plagioclase and amphiboles, found as mixed phenocryst/antecryst and glomerocryts, constituting about 30 vol. % of the rock. Minor mineral phases include pyroxene, apatite and magnetite. Several crystal populations are identified within the Cerro Bayo, which indicate differences within the growth histories of the populations. Some plagioclase crystal display resorbed textures and show zones with sharp increases in An mol% (up to 25 %), indicative of recharge events with hot (more mafic) magma. Whereas other crystals record only small temperature shifts, likely induced by latent heat of crystallisation. Amphibole and clinopyroxene barometers yield average crystallisation pressure estimates that range from 740 to 1036 MPa, however, they overlap within error of the barometers, revealing a storage region prior to shallow emplacement at about 30 to 40 km depth in the lower crust. The voluminous crystal cargo, diverse zoning patterns, sieve-textured plagioclase and the abundant enclaves in Cerro Bayo suggest that the magma was derived from a crystal mush storage region that was mobilised and partly mixed by the recharge of mafic melt.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Laccolith

Cryptodome

Magma Plumbing System

Thermobarometry

Crystal size distribution

Chachahuén volcano

Geovetenskap med inriktning mot mineralogi, petrologi och tektonik

Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)