1. Marcello Campione Università degli Studi di Milano Bicocca, Italy
EGU – Vienna – April 9th 2018
Mantle mineral microcavities filled with aqueous fluids
HPHT reactors producing unexpected mineral assemblages
Marcello Campione Università degli Studi di Milano Bicocca, Italy

2. Orthopyroxenites – Maowu Ultramafic Complex
Amp + H2O
Grt OM
5 µm
SEM
Interaction of harzburgites and
slab-derived silica-rich liquids at the slab-mantle interface
Multiphase solid inclusions in garnet
P = 4 Gpa
T = 800 °C
Malaspina et al., EPSL, 2006
Chen et al., LITHOS, 2017
Marcello Campione
EGU – Vienna – April 9th 2018
1#9

3. Garnet (pyrope) stability … and Assemblage Stability
Isochemical section (Perple_X, Connolly 2005)
Chemography 1
Amp + H2O
Grt
3MgO + Al2O3 + 3SiO2 1 2 2 3 3
Marcello Campione
EGU – Vienna – April 9th 2018
2#9

4. Garnet (pyrope) stability … and Assemblage Stability
Isochemical section (Perple_X, Connolly 2005)
Chemography
Amp + H2O
Grt
3MgO + Al2O3 + 3SiO2
Py is stable e at T = 800 °C and p  1.7 GPa
Py-sp-clin is a stable assemblage (T=800 °C and p4 Gpa)
WHAT DIRVES THE SELECTION OF A PY-SP-CLIN ASSEMBLAGE WITHIN THE MICROCAVITY???
Marcello Campione
EGU – Vienna – April 9th 2018
3#9

5. Solid-Liquid Interaction – Equilibrated Fluids
Aqueous speciation-solubility code
EQ3+ Deep Earth Model
(Wolery 1992; Facq et al., 2014; Sverjensky et al., 2014)
 Fluid in equilibrium with K-free eclogite
(Kessel et al., 2005)
SLAB
INCLUSION
 Fluid in equilibrium with mantle peridotites
(Dvir et al., 2011)
 Fluid in equilibrium with py-clin-sp assemblage (Fockenberg et al., 2008)
MANTLE
SLAB FLUIDS ARE SILICA-RICH IF EQUILIBRATED
Marcello Campione
EGU – Vienna – April 9th 2018
4#9

6. Solid-liquid Interaction – Non-Equilibrated Fluids
A Model of Dissolution-Reprecipitation
Campione et al., GPL, 2017
Pyrope congruent dissolution
Py(s)  3MgO(aq) + Al2O3(aq) + 3SiO2(aq)
m = molality of MgO(aq)
a = molality of Al2O3(aq)
s = molality of SiO2(aq)
M = molality of MgO(aq)
A = molality of Al2O3(aq)
S = molality of SiO2(aq)
Spinel precipitation
MgO(aq) + Al2O3(aq)  MgAl2O4(epi)
Clinochlore precipitation
10MgO(aq) + 2Al2O3(aq) + 6SiO2(aq) + 8H2O  Mg10Al2[Al2Si6O20](OH)16(s)
Marcello Campione
EGU – Vienna – April 9th 2018
5#9

7. Solid-liquid Interaction – Non-Equilibrated Fluids
A Model of Dissolution-Reprecipitation
Campione et al., GPL, 2017
Pyrope congruent dissolution
Py(s)  3MgO(aq) + Al2O3(aq) + 3SiO2(aq)
Spinel precipitation
MgO(aq) + Al2O3(aq)  MgAl2O4(epi)
Clinochlore precipitation
10MgO(aq) + 2Al2O3(aq) + 6SiO2(aq) + 8H2O  Mg10Al2[Al2Si6O20](OH)16(s)
𝑀=𝑚+ 3𝑝 𝑦 − 𝑠 𝑝 −10 𝑐 𝑙
py = moles of dissolved py
sp = moles of precipitated sp
cl = moles of precipitated clin
1 kg H2O
𝐴=𝑎+ 𝑝 𝑦 − 𝑠 𝑝 −2 𝑐 𝑙
𝑆=𝑠+ 3𝑝 𝑦 −6 𝑐 𝑙
𝐻=56−8 𝑐 𝑙
Marcello Campione
EGU – Vienna – April 9th 2018
6#9

8. Solid-liquid Interaction – Non-Equilibrated Fluids
A Model of Dissolution-Reprecipitation
Campione et al., GPL, 2017
𝑀=𝑚+ 3𝑝 𝑦 − 𝑠 𝑝 −10 𝑐 𝑙
𝐴=𝑎+ 𝑝 𝑦 − 𝑠 𝑝 −2 𝑐 𝑙
𝑆=𝑠+ 3𝑝 𝑦 −6 𝑐 𝑙
𝐻=56−8 𝑐 𝑙
m = molality of MgO(aq)
a = molality of Al2O3(aq)
s = molality of SiO2(aq)
Solving for py, sp, cl  0
𝑝 𝑦 = 𝑝 𝑦0 − 𝑎 2 − 2𝑠 3 + 𝑚 2
𝑠 𝑝 = 𝑠 𝑝0 +𝑎− 𝑠 3
𝑐 𝑙 = 𝑐 𝑙0 − 𝑎 4 − 𝑠 6 + 𝑚 4
THERE IS NO UPPER LIMIT FOR m
Chl INCREASES WITH m WHILE Sp IS CONSTANT
A SILICA-RICH FLUID SUPPRESSES THIS DISSOLUTION-REPRECIPITATION MECHANISM!!!
Marcello Campione
EGU – Vienna – April 9th 2018
7#9

9. Model of Metasomatic Garnet Growth
MANTLE En+Fo+Py
MANTLE En+Fo+Py
Silica-poor fluid
“FILTER” En+Py
Silica-rich fluid
SLAB Coe+Py+Ky
SLAB Coe+Py+Ky
MANTLE En+Fo+Py
SLAB Coe+Py+Ky
Marcello Campione
EGU – Vienna – April 9th 2018
8#9

10. Model of Metasomatic Garnet Growth
Retrograde crystallization of hydrous phases
Dissolution-reprecipitation of spinel and chlorite in garnet at UHP
Aqueous fluid entrapment in garnet
Marcello Campione
EGU – Vienna – April 9th 2018
9#9