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Inherited argon preserved in plagioclase antecrysts in the Lesser Antilles allow to unravel residence times between reservoir remobilization and eruption

Aurelie Germa1, Xavier Quidelleur2, Thomas Shea3, Julia Ricci4

  • Affiliations: 1: School of Geosciences, University of South Florida, Tampa, U.S.A.; 2: laboratoire Géosciences Paris-Saclay (GEOPS), Universite Paris Saclay, Orsay, France; 3: Department of Earth Sciences, University of Hawaii at Manoa, Honolulu, U.S.A.; 4: New Mexico Bureau of Geology & Mineral Resources, New Mexico Institute of Mining & Technology, Socorro, U.S.A.

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 68

  • Programme No: 1.2.13

  • Theme 1 > Session 2

Abstract

We study lava domes from the Lesser Antilles, in which the plagioclase cargo yields K-Ar ages 2 to 3 times older than the eruption ages. The textures and chemistry of plagioclase antecrysts reveal several events related to the injection of mafic magma and crystal mush remobilization. The age difference is explained by the fact that the antecrysts, remobilized by an incoming magma prior to eruption, contain inherited radiogenic argon that accumulated in the crystals by K radioactive decay while crystals were in cold storage. The timescales between intrusion and eruption were too short to heat up the antecrysts above their closure temperatures for argon, and therefore were not completely reset. We use this age difference to calculate timescales between magma mixing and eruption using an innovative approach that combines multi-grains total fusion K-Ar ages and step-heating 40Ar/39Ar dating of plagioclase, argon diffusion modelling, and finite element diffusion modeling of Mg, in samples for which eruption was dated independently. We have calculated that the age differences observed require residence times of 10 to 100 years between the injection of a new magma and its eruption. This can be related to changes in the volcano's morphology due to large scale flank collapse or explosive events having remobilized the plumbing system relatively quickly. Our approach provides constraints on the timing between magmatic intrusion or flank collapse and explosive eruptions. The rapid remobilization and eruption of upper-crustal magmas indicates that the onset of eruptions at Lesser Antilles volcanoes may occur with little warning.