Title: Experimental constraints on subduction-related magmatism I: Hydrous Melting of upper mantle perdotites
1Experimental constraints on subduction-related
magmatism IHydrous Melting of upper mantle
perdotites Peter Ulmer
(Blumone, Adamello, Italy)
Garnet-peridotite in kimberlite
2Topics
- Mantle composition? How do we constrain them?
- Dry Melting of mantle peridotites
- Hydrous Melting Basic concepts
- Hydrous Mantle Melting P-T-f-x relationships
- Conclusion Arc primary mantle magmas are
- basaltic, representing relatively large melt
fractions - wet (hydrous)
- hot (gt1200C)
- oxidized (NNO NNO2)
3Arc-Genesis Model I
4P-T Lherzolite (Dry) Melting
5What is the composition of the (upper)
mantle?How do we obtain this information?
- Geophysics Seismology seismic tomography
Geodesy (density and density
distribution) Geomagnetics
(core dynamo) - Natural observation of high pressure rocks and
minerals originating from the Earths interior - Cosmochemistry, analogy with meteorites and solar
element abundances - Experimentation (at pressure and temperature
relevant for the Earths interior) need to fit
the geophysical constraints - Thermo-mechanical modeling of Earth materials
6Seismic Constraints on the Earths interior
Seismic data Preliminary Reference Earth Model
PREM (Dziewonski Anderson 1981)
7Mineral constituents and compositions of high
pressure rock samples
- Peridotite Massifs (mantle segments)
- Mantle xenoliths (in basalts, kimberlites)
- Diamonds and their inclusions
Garnet-peridotite in kimberlite
8Evidence for Mass transfer Metasomatic
Peridotites
Carbonatite-globule
phl
olivine
CO2-rich fluid inclusions
olivine
phl
Phlogopite-Peridotite in kimberlite
Mantle-cpx in basanite
9Cosmochemistry Formation of the Earth from
primitive solar nebula
Chondritic meteorites represent the primitive
solar nebula composition
10Bulk Earth chondritic
- We know the composition of the Earths crust
- We have a good idea about the composition of the
Earths mantle - We have no access to the core
- Bulk Earth 0.007 crust 0.65 mantle
0.32 core
Bulk Silicate Earth (BSE)
Metal Earth
11Estimates of various parts of the Earth based on
Cosmochemistry and Petrology
Oxide CI carb. BSE BSE undepleted Peridotite Lower Core
chondrite (CI) (Pyrolite) Upper M DM Mantle 15 LE
-volatiles MS 95 MS 95 PN 85 Anders. 89 estimate (Elements)
SiO2 34.20 49.90 45.00 46.20 44.10 49.80 -
TiO2 0.11 0.16 0.20 0.23 0.13 - -
Al2O3 2.44 3.65 4.45 4.75 1.57 3.60 -
FeO 35.80 8.00 8.05 7.70 8.31 9.70 78.00
MgO 23.70 35.15 37.80 35.50 43.90 34.10 -
CaO 1.89 2.90 3.55 4.36 1.40 2.80 -
Na2O 0.98 0.34 0.36 0.40 0.15 - -
K2O 0.10 0.02 0.03 - lt0.1 - -
Cr2O3 0.58 0.44 0.38 0.43 0.34 - 0.80
NiO 2.10 0.25 0.25 0.43 0.34 - 4.90
Mg 0.54 0.89 0.89 0.89 0.90 0.86 -
Ca/Al 0.70 0.72 0.73 0.83 0.81 0.71 -
12Dry Lherzolite Melting
- Fundamental Principles (Phase Equilibria)
- Pressure effects on melting and composition of
primary melts - Temperature effects on melting and compositions
of primary melts
13Fundamentals Forsterite SiO2
Pressure lt 1.4 kbar
14Fundamentals Forsterite SiO2
Peritectic
Cotectic (thermal max)
Pressure lt 1.4 kbar
Pressure gt 1.4 kbar
15Schematic Phase Diagram showing LOW Pressure
Lherzolite Melting
Schematic Phase Diagram showing HIGH Pressure
Lherzolite Melting
Plt7kbar (or PH2O High)
Pgt7kbar (dry) (gt12 kbar wet)
16The Tools Piston Cylinder Solid Media Presses
0.5 - 4 (5) GPa, 2000C
Pressure Force / Area
17P-T slopes of dry melting in simple systems
Albite and Diopside
18Anhydrous Peridotite Melting Experiments
for fertile lherzolite gt15-20 melting
Base of basalt tetrahedron projected from cpx
(Ulmer, 2001)
19Anhydrous Peridotite Melting Melt fraction as a
function of pressure and source composition
Ulmer (2001)
20Anhydrous Peridotite Melting Solidus
temperatures and melt compositions as a function
of source composition at 3 GPa
Hirschmann (2003)
21Hydrous Lherzolite Melting
- Fundamental principles (phase equilibria)
- Pressure H2O effects on melting and composition
of primary melts - Temperature effects on melting and compositions
of primary melts - Geochemical signatures of Arc magmas
22Diopside Peridotite H2O - Melting
23H2O solubility in basalt and albite liquids at
1100C
24Early hydrous (H2O-saturated) experiments
Green DH (1973)
Kushiro et al (1968)
25Peridotite H2O Melting ACMA Average Current
Mantle Adiabat
26Schematic diagram showing melting phase relations
for a system containing Anhydrous minerals
(A) Hydrous mineral (H) H2O (V) Important
(univariant) curves H2O-saturated solidus
(A) Dehydration solidus (V) Dry solidus (V) (low
right)
27Peridotite H2O Melting ACMA Average Current
Mantle Adiabat (diamond symbols multiply
saturated primary liquids extraction depth?)
28multiple saturation (olopxcpx)of primitive
arc magmas
29Inverse multiple saturation experiments on
primary arc basalts
30Picrobasalt (3 wt. H2O) phase diagram with
multiple saturation
31Hydrous Peridotite Melting Melt fraction as
function of MELT H2O-content
Ulmer (2001)
32Effects of small amounts of H2O (in source) on
melt-fractions
33T.L. Groves new Chlorite-Solidus
Grove et al. (09)
Grove et al. (06)
34Parameterization (mostly thermodynamically based,
including PMELTS)
Katz et al (2003)
35Hydrous Peridotite Melting Experiments Comparison
with anhydrous melting
Low percentage melts plot to the left of Plag-Ol
gt alkaline, SiO2-undersaturated, Ne-normative
unlike gt99 of all arc rocks (volcanics and
plutonics, LP thermal divide) (jadeite component
of cpx is preferentially entering the melt gt 1/F
relationship)
36(No Transcript)
37- Evidences for hydrous nature of arc magmas and
geochemical characteristics of supra-subduction
magmas - Violent, explosive, gas-rich (H2O) eruptions
typical for differentiated magmas (andesite
rhyolite) - Melt inclusions (up to gt10 wt. H2O in primitive
Olivine inclusions (e.g. Shasta, Hess, Grove,
Sisson and co-workers) - Early amphibole (and biotite) saturation
indicating gt 4 wt H2O at time of crystallization - Geochemical characteristics of supra-subduction
magmas (major and traces) gt Calc-alkaline and
arc trace element signature of magmas and their
(metasomatized) mantle sources - high fO2 probably related to oxidation by
slab-derived fluids (Fe-isotopes indicate reduced
arc mantle prior to fluid metasomatism)
38Spiderdiagram of Island Arc Basalts (IAB)
HFSE depletion, LILE and LREE enrichment, fluid
mobile elements, residual rutile and garnet to
retain HFSE and HREE in slab source during
dehydration
39Spiderdiagram of Philippine Mantle Xenoliths
40Major Element composition of MORB - IAB
Arcs Silica enrichment and FeO-suppression due
to late plag, early amph and mag
41Mantle melting trend to high-SiO2 - low FeO/MgO
is controlled by reaction relations during ascent
to the base of the crust
Opx Olivine Liquid (SiO2-component)
Grove et al. (03)
42Composition of primitive arc magmas
wt. Picro- Olivine- SiO2-rich High-Mg Boninite
Basalt Tholeiite Tholeiite Andesite
SiO2 46.8 48.5 51.5 56.6 55.0
TiO2 0.7 1.0 1.8 0.9 0.2
Al2O3 12.4 14.4 13.8 17.6 12.5
Fe2O3 2.0 1.0 2.2 1.9 6.6
FeO 7.5 11.9 8.9 5.0 6.5
MgO 17.0 12.4 9.4 6.0 12.0
CaO 10.3 12.9 8.9 8.1 6.5
Na2O 1.2 1.5 2.5 3.4 1.9
K2O 0.4 0.5 0.7 1.0 0.7
xMg 0.77 0.65 0.65 0.68 0.77
max. Press 30kb 18kb 12kb 7-10kb ca.10
43Oxygen Fugacity from Ol-Spinel oxybarometry
44Oxygen Fugacity from volcanic glasses
45Effect of Oxygen Fugacity crystallization sequenes
46Mature Island Arc (after Ringwood, 1974)
47- 4 points to remember
- Presence of H2O during melting leads to enormous
solidus depression (function of pressure gt
solubility) - However, geochemistry (major elements) and
experimental constraints indicate significant
melt fractions (10-20) generated at conditions
close to the mantle adiabat (gt1200C) - Arc magmas are more siliceous at a given pressure
compared to dry tholeiites (MORB, OIB) gt
calc-alkaline - Arc magmas carry particular signatures (trace
elements, fO2, fH2O) that can be linked to
slab-derived components - gt Primary mantle melts are basaltic, hot, wet,
oxidized