Volatiles in basaltic glasses from the East Pacific Rise at 21°N: implications for MORB sources and submarine lava flow morphology

Details Volatiles in basaltic glasses from the East Pacific Rise at 21°N: implications for MORB sources and submarine lava flow morphology Volatiles in basaltic glasses from the East Pacific Rise at 21°N: implications for MORB sources and submarine lava flow morphology

Aug 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986e%26psl..79....9b&link_type=abstract

Earth and Planetary Science Letters, Volume 79, Issue 1-2, p. 9-20.

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Scientific paper

Pillow-rim glasses from a suite of moderately evolved lavas erupted along the axis of the East Pacific Rise (EPR) at 21°N were analyzed by high-temperature mass spectrometry for volatile content. Concentrations of H2O, F and Cl in the 21°N glasses are low and correlate inversely with Mg# yielding well-defined trends. These and other geochemical data indicate derivation of the 21°N glasses from similar parental magmas produced from a highly depleted, nearly homogeneous source [1]. Total volatile, H2O, F and S contents are lower and CO2 content is somewhat higher in these samples than in previously analyzed Mid-Atlantic Ridge (MAR) glasses. 21°N glasses are similar in volatile content to glasses from the Galapagos Spreading Center (GSC) at 95°W except in Cl (lower) and CO2 (higher). Unlike most MAR and GSC glasses, CO2 is the dominant volatile in all of the 21°N glasses with Mg# > 62. All of the EPR and GSC glasses contain reduced carbon species (CO and CH4), unlike most previously analyzed MAR samples. These data indicate that sources for mid-ocean ridge basalts are extremely volatile-poor (< 0.10 wt.%) and are probably dominantly reduced (below quartz-fayalite-magnetite buffer).
Sheet flow and pillow basalts contain identical volatile contents. Thus, volatile abundance is not a factor controlling flow morphology. Extrusion rate and/or surface topography are probably the most important factors influencing flow morphology in submarine basalts. H2O-release patterns are however related to flow morphology. Mass pyrograms for sheet flow and pillow basalt glasses both show bimodal H2O-release behavior at the same temperatures (800°C and 1000°C +/- 50°C). However, the dominant H2O-release peak for sheet flow glasses is at the lower temperature; for pillow-rim glasses it is at the higher temperature. Infrared spectroscopic studies indicate that H2O in these glasses is present only as hydroxyl groups. Thus, the cause of differences in the bimodal H2O-release and how it is related to flow morphology is unclear.

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