Serpentinite Seamount Processes in the IBM system

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Serpentinite Seamount Processes in the IBM system
Patricia Fryer Synthesis of work by numerous
researchers S. Bloomer, M. Mottl, T. Ishii, H.
Maekawa, K. Saboda, J. Haggerty, G. Wheat, N.
Becker, J. Gharib, S. Hulme, C. Moyer, K. Takai,
F. Inagaki, L. Benton, J. Ryan, I. Savov D.
Wiens, B. Taylor, G. Moore, A. Oakley (Shipboard
Parties of ODP Legs 125 and 195)
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Active Serpentinite Mud Volcanism
Setting Past drilling and sampling Rocks,
fluids, biological communities, seismicity
models What we know we dont know Funded future
work
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Izu-Bonin-MarianaConvergent Plate Margin Setting
Izu-Bonin
Stretches 3000 km from Japan to Yap. Several
stages of rifting. The forearc preserves the
entire history of this convergent plate margin.
Mariana
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• Serpentinite Mud Volcano Characteristics
• Erupt serpentinite mud episodically
• and are long-lived (Eocene)
• Erupt slab fluids - compositions vary
• with distance from trench (depth to
• slab)
• Show forearc and slab metamorphism
• Associated with extensional tectonics
• Have seep communities (microbial
• populations are dominantly Archaea)
• Some have clusters of earthquakes

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Serpentinite Mud Volcano Sampling History 1981
Dredging 1989 ODP drilling, Leg 125, Sites
778-780 1995/96 Shinkai 6500 dives 1997 66
gravity/push cores on 10 smts. (red
serp) 2001 ODP drilling, Leg 195, Site
1200 2003 75 gravity/push cores on 12 smts.
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Serpentinite Mud Volcano Sampling History 1981
Dredging 1989 ODP drilling, Leg 125, Sites
778-780 1995/96 Shinkai 6500 dives 1997 66
gravity/push cores on 10 smts. (red
serp) 2001 ODP drilling, Leg 195, Site
1200 2003 75 gravity/push cores on 12
smts. 2009 IODP drilling on the schedule
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ODP Leg 125 Conical Seamount
Left - Perspective view with side-scan
backscatter imagery draped on bathymetry
Alvin bottom photo of unsedimented serpentinite
flow surface
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Successful ODP Borehole Observatory Site 1200C
South Chamorro Seamount
Site 1200
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2003 DSL-120 data for South Chamorro ODP Leg 195
Site 1200
2-km-diameter summit knoll (200 m high) - built
up of numerous small-volume, more fluid eruptions
(dashed red lines). (Red box area of drill
holes at Site 1200, shown in next slide)
DSL120 sidescan imagery
EM3000 bathymetry
Fryer and Salisbury, 2006
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Location of holes drilled at Site 1200
Wheat et al., in press
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Ocean Drilling Program, Leg 195, 2001
ODP Site 1200 - a cased, CORKed site on the
southern Mariana forearc.
JOIDES Resolution in Guam
The Jason2/Medea ROV was used to recover
down-hole instruments in 2003.
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Metabasites from the subducted slab included in
the serpentinite muds
Ca-Am Na-Am Sph Chl Na-Ca-Am
Na-Am Phg Chl
parageneses give 0.45 to 0.6 Gpa and 250
to 300C
Fryer et al., G3, 2006
Na-Ca-Am Na-Am Sph Chl Ep Na-Ca-Am Na-Am
Sph Chl Gar
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Compositional Variability in Mud Volcano Products
Fryer et al., Geology, 1999
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Anisotropy of forearc mantle
Olivine reorientation (from imposed stress
fields). Older mudflows may contain rocks with
different anisotropy. Statistical approach may
give information on changing mantle stress fields
through time.
S. Pozgay et al., JGI, 2007
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Peridotite studies of the forearc mantle
The rocks have varying degrees of alteration and
serpentinization, but many are relatively
fresh. Provide geochemical history of
fluid/mantle interaction over development of the
forearc.
Michibayashi et al., EPSL 2006
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Clues to anisotropy history of forearc mantle.
Michibayashi et al., EPSL 2006
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How Fluid Interacts with Forearc
Peridotite   Olivine to Serpentine (
Brucite)   2Mg2SiO4 3H2O Mg3Si2O5(OH)4
Mg(OH)2   Enstatite to Serpentine (
Talc)   6MgSiO3 3H2O Mg3Si2O5(OH)4
Mg3Si4O10(OH)2   Olivine Enstatite to
Serpentine   Mg2SiO4 MgSiO3 2H2O
Mg3Si2O5(OH)4
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How Fluid Interacts with Forearc
Peridotite Addition of 10 mol Fe produces
Magnetite and H2 Fayalite (Fe end-member
olivine)  3Fe2SiO4 2H2O
2Fe3O4 3SiO2(aq) 2H2 Hydrocarbon production
4H2 CO2 CH4 2H2O (at high pH
4H2 CO32- CH4 H2O 2OH-)
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Mariana Forearc, 2003 10 sites on 9 seamounts
With distance from the trench of 50-95
km100-300C (?) --alkalinity, sulfate, Na/Cl,
K, Rb, Cs, B increase --Ca, Sr decrease
(Mottl et al.,
G3, 2004)
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Summary of Effects of Pore Water Upwelling
through the Serpentinite Mud Volcanoes

• Pore waters fresher than seawater are upwelling
  at a few cm/yr.
• Freshened waters originate by dehydration of the
  subducting plate 15-25 km below the seafloor.
• Farther from the trench, dehydration is joined by
  decarbonation.
• Serpentinization generates H2, which reacts with
  carbonate dissolved from the subducting plate to
  produce methane (there is little or no organic C
  in the serpentinite muds).
• Methane concentrations are high enough to produce
  gas hydrates, but none have ever been observed,
  nor have brines that would be produced during gas
  hydrate formation.

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MCS data collected in 2002
Oakley et al., JGI, 2007
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Big Blue SeamountEM300 bathymetry with MCS
lineswhite crosses indicate drill sites
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Big Blue Seamount MCS Line 42-44 (N-S)
Line 42-44
Oakley et al., JGI, 2007
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Seismicity
Deepest events 700 km under the arc/backarc at
16-20N. Forearc events lt100 km, some trench
parallel bands, some clusters of
events. (Interesting temporal relationships.)
Data From Engdahl et al., 2003
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Recycling of serpentinized mantle to zone of arc
magma based on FME data (Savov et al., JGR in
press)
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Common Serpentine Phases Lizardite,
Chrysotile, and Antigorite Raman spectra
(Raman spectra from Rinaudo and Gastaldi (2003),
Can Min., 41, 883-890.)
Chrysotile
Lizardite
Antigorite
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Cautionary Notes Stability of Chrysotile
Bernard W. Evans (2004), The Serpentinite
Multisystem Revisited Chrysotile Is Metastable,
International Geology Review, Volume 46(6),
479-506. The two rock-forming polymorphs of
serpentine Mg3Si2O5(OH)4, lizardite and
chrysotile, occur in nature in virtually
identical ranges of temperature and pressure,
from surficial or near-surficial environments to
temperatures perhaps as high as 400C. Laboratory
evidence indicates that lizardite is the more
stable at low temperatures, but the difference in
their Gibbs free energies is not more than about
2 kJ in the 300-400C range. Above about 300C,
antigorite brucite is more stable than both in
other words, chrysotile is nowhere the most
stable.
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Behavior of Chrysotile
Moore D.E. et al., 2004, The Coefficient of
Friction of Chrysotile Gouge at Seismogenic
Depths, International Geology Review, Volume
46(6), 1 June 2004, pp. 385-398. The water is
progressively driven off the fiber surfaces with
increasing temperature and pressure, causing
chrysotile to approach its dry strength. Depth
profiles for a chrysotile-lined fault constructed
from these data would pass through a strength
minimum at 3 km depth, where sliding should be
stable. Below that depth, strength increases
rapidly as does the tendency for unstable
(seismic) slip. Such a trend would not have been
predicted from the room-temperature data.
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Funded Future Drilling
Scheduled new drilling on Mariana serpentinite
seamounts Summit sites will penetrate the mud
volcano conduit regions Fluid compositions and
flux Mineralogy and active alteration Microbiolo
gical activity CORK(s) would permit
monitoring Flank sites will provide muds and
clast information Mud rheology Slab-derived
clast paragenesis History of eruption History
of forearc mantle metamorphism Evolution of
mantle stress regimes