Dynamics of rheological heterogeneities in mantle plumes

Autor: Albrecht W. Hofmann, Angela Limare, Cinzia G. Farnetani, Thomas Duvernay
Přispěvatelé: Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA, Max Planck Inst Chem, Hahn Meitner Weg 1, D-55128 Mainz, Germany, ‎ Australian Natl Univ, Sch Earth Sci, Canberra, ACT 2601, Australia, Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), PNP-INSU program
Rok vydání: 2018
Předmět:
Zdroj: Earth and Planetary Science Letters
Earth and Planetary Science Letters, Elsevier, 2018, 499, pp.74-82. ⟨10.1016/j.epsl.2018.07.022⟩
ISSN: 0012-821X
Popis: The geochemical record of Hawaiian basalts has been interpreted to reflect vertically stretched, partly filament-like heterogeneities in the Hawaiian plume, but one alternative interpretation has been that this record reflects intra-conduit mixing, caused by rheological contrasts across the conduit. Here we present numerical simulations of a mantle plume carrying rheological heterogeneities λ times more viscous than the surrounding fluid. Our first objective is to quantify how the heterogeneity deforms during upwelling. We find a full spectrum of shapes, from stretched filaments to nearly undeformed blobs, and we map the respective stability domain as a function of the viscosity ratio λ and of the flow characteristics, including the plume buoyancy flux. Our second objective is to test the hypothesis that a rheological heterogeneity can cause intra-conduit mixing. Although horizontal velocities do appear across the plume conduit, we have not found any toroidal “doughnut-shaped swirl” mode. Instead we show that perturbations of the flow trajectories are a local phenomenon, unable to cause permanent mixing. Our third objective is to determine over which time-scales a rheological heterogeneity crosses the magma capture zone (MCZ) beneath a hotspot volcano. For a blob-like heterogeneity of radius 30–40 km and viscosity ratio 15–20, the crossing time-scale is less than 1 Myr. Contrary to a stretched filament, a blob can entirely fill the MCZ, thereby representing the unique source rock of partial melts feeding a volcano. If the heterogeneity has a distinct isotopic fingerprint (or a distinct fertility), surface lavas will then record an isotopic fluctuation (or a fluctuation in melt productivity) lasting 0.5–0.8 Myr. Our simulations predict that such fluctuations should occur preferentially in low buoyancy flux hotspots, where blob-like rheological heterogeneities are more easily preserved than in the vigorous Hawaiian plume.
Databáze: OpenAIRE
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