Depths of Crystallization Along the Gorda Ridge Based on Olivine-hosted Melt Inclusion Compositions

Document Type

Student Presentation

Presentation Date

April 2017

Faculty Sponsor

Dorsey Wanless


The Gorda ridge is an intermediate spreading center off the coast of Oregon and California that consists of 5 segments: N. Gorda, Jackson, Central, Phoenix, and Escanaba. Spreading rate decreases from 55 to 23mm/yr from north to south. This decrease is reflected by a wider axial valley in the south. We examine how depths of crystallization vary along the Gorda Ridge using major element and volatile compositions of naturally glassy olivine-hosted melt inclusions. Olivine were hand-picked, polished, and mounted in indium for geochemical analysis. Volatiles were measured using the 1280 ion microprobe and major element contents were collected using an electron microprobe. Trace element contents were measured using the LA-ICP-MS. Samples containing the lowest MgO content have the highest variability in major element compositions. To model this variability, fractional crystallization models were run using MELTS. These models indicate that the melt inclusion compositions at each segment require multiple parent magmas. Depths of crystallization are determined using the volatile contents. Escanaba melt inclusions are best explained by crystallization at 2 kbars, while the other segments have a mean crystallization pressure of 1 kbar.

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