volcanoes and the mantle in rifts -...
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Volcanoes and the Mantle in Rifts
Tobias Fischer University of New Mexico
Albuquerque, Rio Grande Rift
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Rio Grande Rift
Bastow et al., 2010
Northern East African Rift
Crossey et al., 2010 Sine et al., 2008
Hydrated lithosphere during earlier subduction (60 Ma)
Mantle Plume
Nature and Role of Mantle Fluids (melts, volatiles) Importance of integrated studies (cross-discipline and geography)
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Depiction of the Nyiragongo and Nyamuragira volcanoes, based on data from theShuttle Radar Topography Mission, Advanced Spaceborne Thermal Emissionand Reflection Radiometer, or Aster, and Landsat. Some lava flows (not all) fromthe 2002-01-17 eruption are shown in red.
Nyamuragira
Nyiragongo
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Around 10:00 p.m. local time on November 27, 2006, Mount Nyamulagiraerupted.
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1 Mt
Stratospheric SO2 emission during eruptions
TOMS group, NASA
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1 Mt
Stratospheric SO2 emission during eruptions
TOMS group, NASA
9 - 11 Mega tons of SO2 per km3 of erupted magma (Carn & Bluth, 2003) Iceland flood basalts: 5-9 Mega tons of SO2 per km3 of erupted magma (Thordarsson & Self, 2003)
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20 30 40 50 60 70 80 90
SiO2 (wt%)
Rio Grande RiftEast African RiftMid African RiftAntarctic RiftMORBglobal nephelinites
subalkaline
alkaline
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5
10
15
20
25
30
20 30 40 50 60 70 80 90
SiO2 (wt%)
Rio Grande RiftEast African RiftMid African RiftAntarctic RiftMORBglobal nephelinitesAleutian ArcCentral America
subalkaline
alkaline
Great Variety of Rock Compositions!
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Spectacularly Active Volcanoes!
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The East African Rift ~ 3000 km long Western and Eastern Branch Extensive volcanism (~20% rhyolites/ignimbrites) Earliest Volc. 45 Ma (S-Ethiopia) Huge Shield Volcanoes Ethiopia Flood basalts (30 - 1 Ma) Map of the East African Rift system (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
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Tertiary volcanic rocks plate trajectories from 50 m.y. to 10 m.y. S-Ethiopia was positioned over Kenya plume 50 m.y. ago Two Plumes Afar and Kenya (e.g. Ebinger et al., 1989)
George et al., 2010
Continental Flood Basalt Provinces are related to mantle plumes (e.g. White and McKenzie, 1995)
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Plume locations and eruption rates
Afar Plume
George et al., 2010
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Plume locations and eruption rates
Afar Plume
George et al., 2010
Average Iceland, Hawaii
RGR ~ 0.0002 km3/yr
Southern NM Calderas ~ 33 - 28 Ma Additional ~ 5000 km3
0.01 km3/yr
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The East African Rift
Chondrite-normalized REE variation diagram for examples of the four magmatic series of the East African Rift (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
MORB
OIB
Enrichment in LILE compared to MORB -> similar to OIB or Plume
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East African Rift System. a. Pre-rift stage,
asthenospheric mantle rises into the lithosphere. Decompression melting produces variably alkaline melts. Some partial melting of the metasomatized sub-continental lithospheric mantle (SCLM) may also occur.
b. Rift stage: development of continental rifting, eruption of alkaline magmas (red) mostly from a deep asthenospheric source.
c. Afar stage, in which asthenospheric ascent reaches crustal levels. This is transitional to the development of oceanic crust. After Kampunzu and Mohr (1991),
Winter (2001) An Introduction to Igneous and Metamorphic Petrology.
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Anisotropy: Large-scale mantle flow in astenosphere associated with the superplume
Bastow et al., 2010
astenosphere
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Plume location
Bastow et al., 2010
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Bastow et al., 2010
EAGLE
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Rooney et al., 2007
Geochemical/petrologic considerations
Wonjii Fault Belt
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Rooney et al., 2007
Geochemical/petrologic considerations
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Rooney et al., 2007
OIB-like REE
Geochemical/petrologic considerations
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Plume R/Ra > 9
Helium isotopes (phenocrysts, gas) Pik et al., 2006
Deep Plume “like Iceland”
Shallow mantle upwelling < 400 km
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0
20
40
60
80
100
20 30 40 50 60 70 80SiO2 (wt%)
East AfricaCentral AmericaRGR
Georoc database and Mike Carr’s data base
Aqueous Fluids from Slab in ARCS
FLUIDS??
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Melt inclusions: pre-eruptive melt volatile contents
Allow for assessment of pre-eruptive melt composition since they are assumed to be less susceptible to degassing and contamination than glasses
100µm
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1000
2000
3000
4000
5000
6000
0 1 2 3 4 5 6 7
H2O (wt%)
Volcanic Arcs
2 kbar
3 kbar
5 kbar
Etna
Fuego, Guatemala
Cerro Negro,Nicaragua
Open-systemdegassing
Georoc database and Roggensack et al., 2001
N-MORB
Melt inclusions: pre-eruptive melt volatile contents
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0
1000
2000
3000
4000
5000
6000
0 1 2 3 4 5 6 7
H2O (wt%)
Volcanic Arcs
2 kbar
3 kbar
5 kbar
Etna
Fuego, Guatemala
Cerro Negro,Nicaragua
Open-systemdegassing
Georoc database and Roggensack et al., 2001
Kilauea
N-MORB
E-MORB
‘fields’ from Wallace, 2005
Melt inclusions: pre-eruptive melt volatile contents
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Schmidt+Poli, 1998
Slab dehydration
In Arcs fluids come from the slab
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Trace amounts of H2O enhance melting….
Hirth & Kohlstedt, 1996; Asimow & Langmuir, 2003
From: Hirschman’s MARGINS talk WHOI 2006
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Dasgupta & Hirschmann (2006) - Nature From: Hirschman’s MARGINS talk WHOI 2006
CO2 also enhances melting….
~wt% CO2
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0
1000
2000
3000
4000
5000
6000
0 0.5 1 1.5 2
H2O (wt%)
African Rifts
Suh, 2008 Georoc MI data-base (last update 2010)
Kilauea
E-MORB
N-MORB
Melt inclusions (Lavas-olivines) -not much data! (yet)
Degassing?
‘fields’ from Wallace, 2005
Mt. Cameroon
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Gas sampling (fumaroles; springs;cold, pure CO2 vents)
Rungwe-region, Southern Tanzania
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1.0E+07
1.0E+08
1.0E+09
1.0E+10
1.0E+11
1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 1.0E+11 1.0E+12 1.0E+13
N2/3He
CO2/3He
2005 gases2009 gasesArc Central America2006 gasesRungwe Region
AIR
CO2 and N2 richSediments
Mantle w/ CO2 100 -300ppm
Mantle w/ 1% CO2
CO2 (and Nitrogen) in Gas Emissions (Lengai and Rungwe)
0.01% Non-mantle CO2 N2
Fischer et al. 2009 and Barry, Hilton et al., 2009 AGU
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1.0E+07
1.0E+08
1.0E+09
1.0E+10
1.0E+11
1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 1.0E+11 1.0E+12 1.0E+13
N2/3He
CO2/3He
2005 gases2009 gasesArc Central America2006 gasesRungwe Region
AIR
CO2 and N2 richSediments
Mantle w/ CO2 100 -300ppm
Mantle w/ 1% CO2
CO2 (and Nitrogen) in Gas Emissions (Lengai and Rungwe)
0.01% Non-mantle CO2 N2
Fischer et al. 2009 and Barry, Hilton et al., 2009 AGU
RGR (Crossey et al., )
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Rio Grande Rift
Crossey et al., 2010
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Suh, 2008; Wilding, 1993; Lowenstern, 1997 DUNBAR N. W.(1992)
0
1000
2000
3000
4000
5000
6000
0 1 2 3 4 5 6
H2O (wt%)
African RiftsRio Grande Rift
Melt inclusions (Lavas) -not much data! (yet)
Kilauea N-MORB
Max solubility 4 kbar (NNO+4)
sulfide solubility 4 kbar (NNO-2)
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Suh, 2008; Wilding, 1993; Lowenstern, 1997 DUNBAR N. W. (1992)
0
1000
2000
3000
4000
5000
6000
0 1 2 3 4 5 6
H2O (wt%)
African RiftsRio Grande Rift
Melt inclusions (Lavas) -not much data! (yet)
Kilauea N-MORB
Max solubility 4 kbar (NNO+4)
sulfide solubility 4 kbar (NNO-2)
Cerro Negro
Fuego
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OLD 1 OLD 2H2O 85.35 76.84CO2 14.13 22.80
Stotal 0.128 0.104SO2 0.060 0.039H2S 0.068 0.066HCl 0.068 0.044HF n.m. n.m.
He 0.0004 0.0001H2 0.2299 0.1633Ar 0.0014 0.0003O2 0.0009 n.d.N2 0.0687 0.0276
CH4 0.0002 0.0001CO 0.0242 0.0169
in mol % total gas
Oldoinyo Lengai Gas
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Volatiles analyzed by SIMS (DTM) July 4 2005 Carbonatite Lava flow
N- MORB
MORB glasses and arc melt inclusions from Wallace, 2005
Arcs
wt% H2O CO2 (wt%) S (ppm) Cl (ppm) F (ppm)0.022376 9.69 8376 9909 44950.103099 11.75 2242 5647 6400.016047 10.34 2255 5791 664
0.1-0.5 0.01-0.03 800-1500 <100
3.1-6.1 0 - 0.21 to 6000 to 4100
OLD.
OLD Nephelinite 2009: up to 0.8 wt% in glass and MI
Oldoinyo Lengai Rocks
Fischer et al., 2006 de Moor et al., AGU 2009
> > >
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de Moor et al. 2010 for Anatahan, Marianas
Seawater sulffate
Sulfur Degassing Model -> estimate S content and δ34S in source
2005 & 2009
Mantle volatiles
Lengai
Fischer et al., AGU 2009 de Moor et al., AGU 2009
Nepheline glass/MI 0.8 wt% S δ34S -0.7 ‰
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Some Issues related to Volcanoes and the Mantle
• Connection between mantle volatiles (H2O, CO2, S) and melt production/composition/location in rifts
• Volatile fluxes into and out of rifts not constrained • Is ‘big mantle plume’ below Afar expressed in
volatile/fluid composition at surface (beyond Helium)? • Role of mantle CO2 (experiments vs. observations) • Role of mantle sulfur in melt generation • Nature and role of metasomatism in melt
generation