Compositional Diversity and Degassing of Trachybasalts from the 1993 Submarine Eruption near Socorro Island, Mexico
Abstract
The petrogenesis and volatile degassing of magma erupted as buoyant basaltic scoria from the 1993 Socorro 'Nautilian' [1] eruption were investigated by electron microprobe for major elements, LA-ICP-MS for trace elements, and FTIR for volatiles. Similar to the alkaline basalts from nearby Socorro and San Benedicto Islands, recently collected seafloor samples from the 1993 Socorro submarine eruption contain 48.5-48.7 wt.% SiO2 and 5.1-5.5 wt.% Na2O+K2O. Seafloor Socorro samples are thus classified as trachybasalts, matching the buoyant clasts (collected in the first 6 months of the eruption). Buoyant scoria from early in the eruption are more evolved (e.g., lower MgO) than late-stage scoria collected from the seafloor. Mineral-melt evolution models indicate that fractional crystallization of a common parent magma explains shifts in major and trace elements from evolved early stage (buoyant) samples to the more primitive late stage (seafloor) clasts. Trace element patterns of the most primitive basalts have features in common with petit spots (e.g. positive Sr and Zr anomalies [2]), suggestive of commonalities between these different intra-plate magmatic systems. After accounting for post-entrapment crystallization and the presence of a vapor bubble, olivine-hosted melt inclusions reveal extreme CO2-oversaturation in the melt with highs of 3929 ppm CO2 and 0.73 wt.% H2O. Volatile modelling from seafloor samples provide tentative evidence that the magma sourcing the 1993 eruption likely shifted from an open system degassing regime to a closed system once the magma entered a staging zone at a pressure of about 3 kbar (9 km). Volatiles in buoyant clasts [3] suggest a similar shift in degassing regimes but at an approximate pressure of 1.2 kbar (5 km). This indicates that there was likely a change in conduit geometry from the beginning to the end of the eruption. The 1993 Socorro eruptive material was sourced from a fairly homogenous parental melt with a possible shift in magma staging depths from 5 km to 9 km throughout this year-long submarine eruption.
[1] Carey et al., 2019, Abstract to be presented at 2019 Fall Meeting, AGU, San Francisco, 9-13 Dec. [2] Hirano et al., 2006, Science, Vol. 313, 1426. [3] Balcanoff, J. 2016, MS Thesis, URI, 2752-71.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.U13C..16L
- Keywords:
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- 0810 Post-secondary education;
- EDUCATION;
- 0815 Informal education;
- EDUCATION