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ΔT (K)
300 150 100 50
60 60
a Cleveland b Figure 5. Variation in volatile and trace
70 Seguam 70 element compositions of magmas with
slab depth (Rasmussen et al., 2018a).
(a) H O/Ce and H O/K O (agrees with
Okmok
Slab depth (km) 80 Akutan 80 H O/Ce, but not shown) are proxies for
2
2
2
2
slab temperature. Temperature relative
to the wet sediment solidus (ΔT) is
Makushin
calculated using the thermometer of
90
90
Westdahl Plank et al. (2009). (b) Increased Dy/
Yb may indicate an increased role of
100 Fisher 100 garnet.
Shishaldin
110 110
0 1 2 3 4 5 1.6 1.7 1.8 1.9 2.0 2.1 2.2
H O/Ce * 10 -3 Dy/Yb
2
For example, Shishaldin has the greatest slab depth, and its magmas project will focus on the missing link between the mantle melting
have the lowest H O/Ce and highest Dy/Yb. This relationship holds process that is driven by slab inputs and the water contents of magmas
2
overall, where H O/Ce (1000-4500) and H O/K O (2-9), both proxies that control magmatic plumbing systems.
2
2
2
for slab surface temperature (Plank et al., 2009), negatively correlate Our work is a prime example of the strength of the GeoPRISMS
with slab depth. This implies slab temperatures are just above the Program in facilitating multi-disciplinary research to understand
H O-saturated sediment solidus at 65 km depth and ~250 °C above dynamic processes occurring at plate boundaries. Additionally, this
2
the solidus at 100 km depth. Greater temperatures of the slab would work has been propelled forward by close partnerships with the Deep
predict melting deeper into the slab, which might explain the observed Carbon Observatory and Alaskan Volcano Observatory, which has led
increase in Dy/Yb with slab depth. Interestingly, the volcanoes are to several new active collaborations. Finally, our work has benefited
generally larger and closer together where the slab depth is greater, from additional funding provided by the Don Richter Memorial
possibly suggesting melt flux is greater in these locations. These results Scholarship awarded by the Alaska Geological Society and the Jack
indicate that slab depth has a strong influence on the generation of Kleinman Grant for Volcano Research awarded by the Community
arc magmas. Armed with this understanding, our final efforts on this Foundation for Southwest Washington and USGS. ■

References

Annen, C., J.D. Blundy, R.S.J. Sparks (2006). The genesis of intermediate Rasmussen, D.J., T. Plank, D. Roman, E. Hauri, H. Janiszewski, E. Lev, K.
and silicic magmas in deep crustal hot zones. Journal of Petrology, Nicolaysen, P. Izbekov (2018a). How slab depth is reflected in Aleutian
47(3), 505-539 Arc magmas. AGU Fall Meeting Abstracts
Chaussard, E., F. Amelung (2014). Regional controls on magma ascent and Rasmussen, D.J., T. Plank, D. Roman, M. Zimmer (2018b). Magmatic water
storage in volcanic arcs. Geochem. Geophys. Geosys. 15(4), 1407- content controls magma storage depth. AGU Fall Meeting Abstracts.
1418 Rasmussen, D.J., T.A. Plank, D.C. Roman, J.A. Power, R.J. Bodnar, E.H. Hauri
Hermann, J., C. Spandler, A. Hack, A.V. Korsakov, (2006). Aqueous fluids (2018c). When does eruption run-up begin? Multidisciplinary insight
and hydrous melts in high-pressure and ultra-high pressure rocks: from the 1999 eruption of Shishaldin volcano. Earth and Planetary
Implications for element transfer in subduction zones. Lithos, 92(3), Science Letters, 486, 1-14
399-417 Syracuse, E.M., G.A. Abers (2006). Global compilation of variations in slab
Larsen, J.F. (2016). Unraveling the diversity in arc volcanic eruption depth beneath arc volcanoes and implications. Geochem. Geophys.
styles: Examples from the Aleutian volcanic arc, Alaska. Journal of Geosys., 7(5), Q05017
Volcanology and Geothermal Research, 327, 643-668 van Keken, P.E., B.R. Hacker, E.M. Syracuse, G.A. Abers (2011). Subduction
Plank, T., L.B. Cooper, C.E. Manning (2009). Emerging geothermometers for factory: 4. Depth-dependent flux of H O from subducting slabs
2
estimating slab surface temperatures. Nature Geoscience, 2(9), 611 worldwide. 116(B1)

GeoPRISMS Postdoctoral Scholarship

Proposal Target Date: August 16, 2019
For details, visit the GeoPRISMS website:

http://geoprisms.org/education/geoprisms-postdoctoral-fellowship/

Spring 2019 Issue No. 42 GeoPRISMS Newsletter • 13