From Explosive Vent Opening to Effusive Outpouring: Mineral Constraints on Magma Dynamics and Timescales at Paricutin Monogenetic Volcano
Por:
Larrea, Patricia, Albert, Helena, Ubide, Teresa, Costa, Fidel, Colas, Vanessa, Widom, Elisabeth, SIEBE, CLAUS
Publicada:
1 abr 2021
Resumen:
Paricutin volcano is the youngest monogenetic cone of the
Michoacan-Guanajuato volcanic field (Mexico), with an excellent
historical eruption record from February 1943 to March 1952. The magma
emitted during the 9years of activity was compositionally zoned from
basaltic andesite to andesite. This eruption has been considered a
classic example of magma differentiation controlled by crustal
assimilation combined with fractional crystallization. However, a recent
geochemical study of the eruption products points to mantle source
heterogeneity and fractional crystallization as the key processes
involved in the compositional variability of the magmas. Here we present
a detailed petrological characterization of the minerals [olivine,
plagioclase, pyroxene, Cr-spinel, and (Ti-)magnetite] to shed light on
the processes that led to the chemical evolution of the eruptive
products. Our sample set includes the early tephra from the first weeks
or months of eruption and the whole sequence of lava flows that
followed. The mineral assemblage, their texture, and chemical
composition show a systematic evolution between the products from the
opening of the explosive vent to the effusive stage. The early tephra
are basaltic andesites with oscillatory-zoned olivine and plagioclase,
zoned Cr-spinel, and rare pyroxene xenocrysts. In contrast, later
erupted tephra and post-January 1944 lavas are basaltic andesites and
andesites with normally zoned olivine, Cr-spinel inclusions in
equilibrium with the host olivine, and frequent orthopyroxene (after
December 1947) with minor chemical zoning. Mineral chemistry data and
olivine diffusion timescales, together with whole-rock geochemistry,
suggest a convective magma regime with large temperature and oxygen
fugacity gradients characterized by short timescales (few days) during
the opening stage, followed by a steadier magma regime with longer
timescales (few months) and including periodic magma recharge, mixing,
and fractional crystallization. In addition, the mineralogical evidence
we have gathered does not support considerable crustal assimilation at
Paricutin. This study shows that monogenetic eruptions are far from
being geochemically simple, and instead involve multiple magma batches
with complex storage and mixing stages before eruption.
Filiaciones:
Larrea, Patricia:
Larrea, P (Corresponding Author), Univ Chile, Fac Ciencias Fis & Matemat, Dept Geol, Santiago, Chile. Larrea, P (Corresponding Author), Univ Chile, Fac Ciencias Fis & Matemat, Ctr Excelencia Geotermia Los Andes CEGA, Santiago, Chile. Larrea, P (Corresponding Author), Miami Univ, Dept Geol & Environm Earth Sci, Oxford, OH 45056 USA. Larrea, Patricia, Univ Chile, Fac Ciencias Fis & Matemat, Dept Geol, Santiago, Chile. Larrea, Patricia, Univ Chile, Fac Ciencias Fis & Matemat, Ctr Excelencia Geoterm
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