CRYSTALLIZATION PRESSURES ALONG THE EAST PACIFIC RISE BETWEEN 9.5° AND 14°N
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Date
2019-05
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The Ohio State University
Abstract
The East Pacific Rise (EPR) is one of the many mid-ocean ridges around the Earth. This research is part of a bigger project that is attempting to understand the magma plumbing systems causing crustal accretion at divergent plate boundaries. The research reported herein was specifically aimed at the northern side of the East Pacific Rise, between 9.5 and 14°N. Chemical composition data for basaltic glasses were collected and analyzed. Normalized chemical datum and pressures of partial crystallization were calculated to investigate the magma chemistry of the ridge. The data was split into 12 Segments based on sample distributions. The average calculated pressures among the Segments range from 100 to 250 MPa, giving depths of partial crystallization from 4.5 to 8 km. This datum suggests that partial crystallization on the EPR takes place close to the base of oceanic crust. However, the northern Segments, F through L, contain larger pressures than the southern Segments. Such high pressures most likely do not represent true partial crystallization, instead the anomalous pressures are likely the result of multiple processes influencing the magma crystallization. Correlations between Al2O3/CaO and MgO, pressure and MgO, and P2O5 and K2O indicate that multiple complex processes are contributing to the magma’s composition, rather than simple crystallization. The Segments encompassing 11 to 11.5°N also contained anomalously high calculated pressures that suggest additional processes are affecting the magma below. Modifications of magma compositions by mantle plumes may account for the variations from typical MORB values.
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Keywords
East Pacific Rise, magma crystallization, crystallization pressure, magma plumbing