Textures and magmatic evolution of intermediate-composition dome complexes; evidence from the northern Tatoosh Complex, southern Washington Cascades.
Murphy, Mark T; Marsh, Bruce D (1993) Textures and magmatic evolution of intermediate-composition dome complexes; evidence from the northern Tatoosh Complex, southern Washington Cascades. Journal of Volcanology and Geothermal Research. 54; 3-4, Pages 197-220. 1993.
| Authors | Murphy, Mark T; Marsh, Bruce D |
|---|---|
| Year | 1993 |
| Title | Textures and magmatic evolution of intermediate-composition dome complexes; evidence from the northern Tatoosh Complex, southern Washington Cascades. |
| Source | Journal of Volcanology and Geothermal Research. 54; 3-4, Pages 197-220. 1993. |
| Publisher | Elsevier. Amsterdam, Netherlands. 1993. |
| Document type | Serial |
| ISSN | 0377-0273 |
| GeoRef | 1993-000243 |
| Keywords | Cascade-Range; complexes-; cooling-; crystallization-; domes-; emplacement-; evolution-; folds-; igneous-rocks; intrusions-; magmas-; Mount-Fremont; Mount-Rainier-National-Park; petrology-; Pierce-County-Washington; plugs-; plutons-; pressure-; pyroclastics-; shield-volcanoes; Sourdough-Mountains; Sunrise-Ridge; Tatoosh-Complex; temperature-; textures-; United-States; volatiles-; volcanic-centers; volcanic-features; volcanic-rocks; volcanoes-; Washington-; water-; west-central-Washington |
| DOI | 10.1016/0377-0273(93)90064-X |
Abstract
The emplacement history of a magma, whether it becomes a pluton, dome, or lava, results from its path-dependent cooling during transport. Transport is coupled to the cooling rate through the production of solids (crystals) which greatly affects magma viscosity. Thus, the temperature/H (sub 2) O history of a magma, measured by its near-surface phase diagram, may strongly influence the style of emplacement or eruption. This idea has been tested against textural and stratigraphical data collected from the Tatoosh igneous complex, Mount Rainier National Park, WA. Detailed mapping suggests a system evolving from extrusive lavas, through dome-building plugs and flows to a shallow sill-like pluton. Explosive volcanism preceded emplacement of the pluton. Chemical and mineralogical data point to a magma that equilibrated at about 2 kbar pressure with a low (about 1.5 wt.%) water content, 10-15 vol.% crystallinity (plag, mag, opx, cpx+ or -ol, hrn). Continued crystallization built up a volatile-rich (about 4.5% H (sub 2) O) cap, which eventually erupted as a low-energy, ""over-spilling cloud"" pyroclastic flow. Maximum crystallinity in these rocks was about 27% in rocks containing a cryptocrystalline groundmass. Textural distinction can be drawn between dome-filling, cryptocrystalline, subvolcanic plugs and dome-centered, granophyric, shallow plutons. In all cases, water acts to buffer the mass of groundmass crystallinity, and this effect increases with increasing initial water content. Low water contents allow the melt to reach more easily the conditions necessary to produce granophyric and granitic textures. High water contents give rise to coarsening of pre-existing phenocrysts and cryptocrystalline groundmass as temperature is controlled by a dynamic, water-buffered liquidus. A simple mass balance model of these ideas suggests that faster cooling is favored by melts deficient in water. High crystallinities of dome rocks (> 25%) are probably attained through explosive, in situ degassing and textural coarsening of magma that was emplaced at a much lower crystallinities.