Modelling Evolution of Parental Magma in the Siqueiros Transform for the East Pacific Rise
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Date
2018-12
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The Ohio State University
Abstract
The East Pacific Rise (EPR) is a fast-spreading divergent plate boundary situated between the Cocos Plate and the Pacific Plate that acts as one of the primary sites of the Earth’s oceanic lithosphere formation through anatexis of ultramafic mantle. To elucidate the geochemical processes, the melt petrology, and the magma plumbing system in this ridge pressures of crystallization were calculated for a subset of more than 4397 natural glass samples between 4N to 14N along the EPR. Samples evaluated were ones that best reflected parent melt compositions for modelling. Fractional crystallization modelling was performed to simulate melt evolution along the ridge with physical parameters, mineral-melt models, and initial pressures following the Kelley and Barton method. Melt composition during cooling was compared with the compositions of the natural glass samples to find the best modelled crystallization pathway by plotting weight percent (wt.%) of major oxides against wt.% MgO. Most high MgO samples were located proximal to the Siqueiros transform fault cutting the ridge at 8.3oN and reflected primitive melt. There, sample ALV2384-007A was considered the best parent candidate. Modelling fractional crystallization required estimations of, but not limited to: initial pressures, H2O content and oxygen buffers, the three aspects of crystallization that this study primarily focused on. The crystallization pathway of modelled liquid that best agreed with composition of natural glass samples along the study area was estimated at 0.06 wt.% H2O and oxygen buffer of log units +1 at 100 MPa initial pressure which agree with mid crustal depth approximation of magma crystallization in the East Pacific Rise. Level of oxygen buffer is greater than that is expected in the EPR from previous studies, and estimations of H2O content is categorically assumed from other samples in the vicinity.
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Keywords
modelling magma evolution East Pacific Rise, pressure of crystallization, East Pacific Rise EPR Siqueiros Transform, Mid Ocean Ridge magma evolution