Magmatic Processes at Subduction Zones

Transcription

1 Magmatic Processes at Subduction Zones Katherine A. Kelley Graduate School of Oceanography Univ. of Rhode Island Thanks to Terry Plank Erik Hauri GVP: Liz Cottrell Simon Carn Jennifer Jay Ed Venzke Subduction Zone Observatory Special Interest Group 2014 AGU Fall Meeting

2 Conduits to the Slab, Mantle, and Crust

3 Studies at the Interface of Petrology/Volcanology & Geophysics Geochemical sensors of slab fluids/conditions Wedge structure/melting and connections to volcanoes Links between crustal structure and magmatism Magma storage, eruption timescales and dynamics (Many of these are examples from work related to the successful MARGINS program)

4 Geochemistry G 3 Geosystems Geochemical Sensors of Slab Geophysics Fluids/Conditions RUSCITTO ET AL.: GLO Cooper et al., 2012 Ruscitto et al., 2012 Figure 8. H 2 O/Ce ratios of primitive arc-front magmas as a function of H2O/Ce slab thermal may parameter sense slab (F). Symbols as in Figure 1. Temperatures surface corresponding temp to the H 2 O/Ce geothermometer at GPa (equation (2) in text) are shown on the right-hand axis. The shaded region highlights the range in H 2 O/Ce ratios found in mid-ocean ridge basalts (MORB) and or ocean-island hydrous melts basalts (OIB). The thick black curve shows the Kendall-Thiel line and the corresponding equation is given in the upper left (along with the upper and lower confidence limits of the slope). Slab fluids are more like solute-rich fluids Hot slabs are associated with magmas with muted subduction signatures

5 Wedge structure/melting and connections to volcanoes 0 Mariana Trough Mariana Arc Depth, km MT S G P Red: 1000/Q S = Distance from Trench, km A Kelley et al., 2010 Melt thermobarometry of arc magmas reveals depths of melting Petrological constraints are consistent with seismic attenuation and velocity models Barklage et al., submitted

6 Wedge structure/melting and connections to volcanoes Arc volcanoes require a mechanism to concentrate melts at a single locus New models including compaction pressure effects provide ways to focus fluids and melts through the wedge Wilson et al., 2014

7 Wedge structure/melting and connections to volcanoes M a 0 England & Katz, 2010 b 50 Depth (km) Water-saturated solidus Horizontal distance (km) Horizontal distance (km) If hot melts can be focused in the wedge, they can thermally erode a pathway to the surface Such a process may control the position of the arc volcanic front

8 Links between Crustal Structure and Magmatism Annen et al., 2006 Continuous delivery of mafic magma into the lower arc crust may create hot zones Locations of both basalt crystallization and partial melting of pre-existing crustal rocks One mechanism to create intermediate to silicic magma compositions

9 Links between Crustal Structure and Magmatism Seismic structure of arc crust varies along strike (IBM) Kodaira et al., 2007 Volcano composition correlates with thickness of the middle crust Silicic volcanoes overlie thin middle crust; mafic volcanoes overlie thick middle crust

10 Magma Storage, Eruption Timescales and Dynamics EQ Olivine-melt inclusion vapor-sat. depths InSAR Inflation Source Coincidence in: geodetic inflation source depth of earthquakes melt inclusion trapping depths Zimmer et al (2010) JPet and Zimmer thesis (2009) InSAR Interferogram km Makushin Volcano, Aleutians Lu et al. (2002) JGR

11 Magma Storage, Eruption Timescales and Dynamics Ruprecht & Plank, 2013 RESEARCH LETTER a Probability density b Analysed olivines Time for T = 1,200 C (yr) Time for T = 1,100 C (yr) IZ1013-ol53 IZ1013-ol22 Time for T = 1,200 C (yr) IZ1013-ol17 IZ1013-ol26 IZ1011-ol15 IZ1011-ol4 IZ1011-ol16 2 IZ1013-ol20 1 IZ1011-ol5 IZ1011-ol Time for T = 1,100 C (yr) c ~35 km Months-to-year magma transport (55 80 m per day) MOHO Mixing of high-fo melts Avg 1100 : yr 0.6 Avg 1200 : yr 0.2 Avg 1100 : yr 1.3 Avg 1200 : yr 0.4 a Ni (p.p.m.) b 4,000 3,000 2,000 1,000 Ni (p.p.m.) IZ1012-ol4 500 μm Forsterite content (mol.%) Fractional crystallization on liquid line of descent with minor melt mixing Zonation profiles in phenocrysts can give magmatic ascent times from mantle to eruption Mix man Forsterite content (mol.%) Forste Study of Irazú (Costa Rica) shows Figure 2 Nickel and forsterite zoning in olivine from Irazú volcano. a,ni versus forsterite variations for olivine phenocrysts that follow a single liquid line of descent. Colour coding in the crystal traverse ties the Ni Fo data spatially to the image of the crystal. b, Conceptual evolution of olivines evolving along subparallel olivine fractionation trends. The two red curves show that crystals often diverge slightly from the calculated olivine-fractionation trend, suggesting minor melt mixing. The grey curves are the same fractionation c d IZ1011-ol4 78 curves for d crystallizati olivine phe content, sug d, Conceptu mantle mel ascent and recharge from the mantle on months/years time scale

12 Eastern Pacific Holocene Volcanoes GeoMapApp and GMRT synthesis basemap of Ryan et al. (2009) Global Volcanism Program - Volcanoes of the World N 40 N 453 active volcanoes 20 N 761 eruptions in last 100 yrs 0 20 S 40 S 180 E 160 W 140 W 120 W 100 W 80 W 60 W 40 W VEI Last 100 Years expected in next decade

13 Eastern Pacific Holocene Volcanoes GeoMapApp and GMRT synthesis basemap of Ryan et al. (2009) Global Volcanism Program - Volcanoes of the World &#$, )#$, Black = basalt Gray = Andesite Pink = Dacite Red = Rhyolite *#$, #$ *#$+ )#$+!"#$%!&#$'(!)#$'(!*#$'(!##$'( "#$'( &#$'( )#$'( E. Pacific volcanoes by primary rock composition

14 Eastern Pacific Holocene Volcanoes GeoMapApp and GMRT synthesis basemap of Ryan et al. (2009) Global Volcanism Program - Volcanoes of the World N N N 0 20 S 40 S 180 E 160 W 140 W 120 W 100 W 80 W 60 W 40 W Human population within 100 km of an active volcano

15 Eastern Pacific Holocene Volcanoes GeoMapApp and GMRT synthesis basemap of Ryan et al. (2009) Global Volcanism Program - Volcanoes of the World N Red = Satellite SO2 40 N 20 N 0 20 S 40 S 180 E 160 W 140 W 120 W 100 W 80 W 60 W 40 W 20 W E. Pacific volcanoes with recent (last 5-15 yr) satellite deformation and emissions observations Purple = InSAR

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17 DECADE - Deep Earth Carbon Degassing Network Scope Builds on existing NOVAC SO 2 network (24 volcanoes) C. & S. America Addition of MultiGas instruments (CO 2, H 2 S, CO, others) Promotes new instrumentation/method development, data processing Highly collaborative: universities, observatories, agencies International: 11 nations participating in science team Building a platform for global volcano network for the future Emissions database connected to existing volcanic activity/chemistry databases (GVP/IEDA/MAGA) Science Improve current global volcanic CO 2 flux estimates dramatically Constrain sources (gas, fluid, magma) of volcanic seismicity New methods to improve abilities to forecast volcanic eruptions Provide means for correlating volcanic unrest with tectonic earthquakes