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post in: News Date:22 Nov 2017, 19:27 views:649
Fractional asthma crystallization and replenishment of the magma chamber at the East Pacific Rise 950'. Petrological data collected from the eruptions provide a record of the. More, petrological data collected from the eruptions provide a record of the compositional evolution of erupted magmas over a 14-15 year period at the East Pacific Rise near 950'.
This data, when coupled with mathematical modeling of convection and replenishment, present a unique opportunity to understand coupled magmatic and hydrothermal processes at a fast-spreading oceanic ridge. We use the multicomponent geochemical modeling software melts (Ghiorso and Sack, 1995; Asimow and Ghiorso, 1998) to determine how the sub-axial magma lens has evolved as a result of cooling, crystal fractionation, and melt replenishment in the period between the 19 eruptions.
Following a spreading rate-dependent permeability barrier model for lateral melt transport and extraction (Hebert and Montesi, submitted and utilizing an initial depleted mantle source (DMM, Workman and Hart, 2005) under anhydrous conditions and with a potential temperature of 1375C, we obtain a starting composition for.
A liquid line of descent involving simple fractionation for this composition passes through the lava dataset. We then implemented isobaric fractionation calculations, using melts. We tested an array of scenarios including simple fractionation, replenishment with both more and less evolved magmas, the addition of water, and changes in oxygen fugacity.
Our initial temperature conditions were set by the results of a 2-D geodynamic ridge model, and replenishment timescales and cooling rates were guided by the modeling study of Liu and Lowell (2009). Simple fractionation can explain the evolution of the magmas for some of the major elements, but not all of them.
Therefore, we argue that some amount of replenishment must have occurred in the magma chamber between eruptions to explain the small change in composition as well as temperature. The results are independent of whether the replenishment is continuous or periodic. The observed changes cannot be explained by anhydrous replenishment using more evolved magmas.
The conditions that best match the evolution of the lavas to the lavas are hydrous replenishment of a more primitive composition with oxygen fugacity at the QFM buffer.
The petrological results are consistent with a mathematical model of a rapidly mixed convecting, cooling, replenished magma chamber, in which crystals are assumed to settle rapidly to the floor.
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