Silicate melt inclusions in mantle xenolith

Significance of fluid, silicate and sulfide melt
inclusions in mantle xenoliths from the
Carpathian-Pannonian Region
Csaba Szabó
Lithosphere Fluid Research Laboratory (LRG), Eötvös University
(ELTE), Budapest, Hungary
with contribution of Márta Berkesi, Károly Hidas, Enikő Bali, Tibor
Guzmics, Kálmán Török, László Aradi, Bob Bodnar, Jean Dubessy
11 th Pan-American Current Research On Fluid Inclusions
(PACROFI XI)
Windsor, Canada
18-20 June, 2012
http://lrg.elte.hu

Carpathian-Pannonian region – upper mantle xenoliths

Silicate melt inclusion
- Nógrád-Gömör Volcanic Field
- Bakony – Balaton Highland Volcanic Field

Silicate melt inclusions in mantle xenolith - pyroxenite
Cpx
Opx
Incl
Opx
Cpx
0.25 cm
Quartz (Qz) and CO 2 -bearing silicate melt inclusions
(Smi) in pyroxenite xenolith
Opx-orthopyroxene, Cpx-clinopyroxene, Incl-silicate melt
inclusions (photomicrographs, 1N)
Smi petrography:
- primary and secondary
- glass and CO 2 bubble
Q
Qz
Opx
CO 2
Gl
Smi
250 m
200 m

Silicate melt inclusions in mantle xenolith - pyroxenite
Heating experiments of smi Raman spectroscopy spectroscopy
of CO 2
~960 °C melting temperature
Density=0.87-1.18 g/cm 3
Depth of the present day uppemost mantle
Entrapment pressure >1.1 GPa

Silicate glass composition - major elements

Silicate glass composition - major elements
qz-opx+cpx+amp(?)
fractionation from a
silicic hybrid melt
formed on peridotiteslab
melt interface

Silicate melt inclusion composition (bulk)- trace elements
rutile
plagioclase?
apatite?
garnet
Rutile+plagioclase(?)+garnet in the source subducted oceanic crust?
Ni-content in SMI 140-635 ppm; Cr-content in SMI 185-850 ppm
reaction with peridotite

cpx
ol
1 mm
1 mm
ol
ol
amp smp
opx
opx
amp
amp
cpx
cpx
amp
a
b
Silicate melt inclusions in mantle xenolith -
peridotite
Two equigranular, modally metasomatized
spinel lherzolites (Szg07, Szg08)
Ol-olivine, Opx-orthopyroxene, Cpx-clinopyroxene,
Spl-spinel, Amp-amphibole (photomicrographs, 1N)

Silicate melt inclusions in mantle xenolith - peridotite
SMI in Cpx SMI in Opx
Primary silicate melt inclusions (smi) in clinopyroxene (cpx) and secondary silicate melt
inclusions in orthopyroxene (opx) from the same lherzolite xenoliths)
Smi phases: products of post-entrainment crystallization, glass (gl), mica, fluid bubble

Silicate glass composition - major elements
The same evolved melt
(high volatile content)
The same process
fractionation

Silicate melt inclusion composition (bulk) - trace elements
Mantle/melt interaction occurred at mantle temperature resulted in melting of clinopyroxene.
This melting was induced by a reagent melt with hydrous mafic nature resembling
compositionally the host alkaline basalts, which mixed with melt of the partially fused
clinopyroxene. Rims of clinopyroxene crystallized from this mixture melt simultaneously
entrapping drops of melt as primary silicate melt inclusions.
Amphibole formation?

Fluid incluions
- Nógrád-Gömör Volcanic Field
- Bakony – Balaton Highland Volcanic Field
- Persany Mountains Volcanic Field

Carpathian-Pannonian region – upper mantle xenoliths

Fluid inclusions in mantle xenolith - peridotite
Two equigranular, modally metasomatized spinel
peridotites (Szigliget)
Five coarse-grained, orthopyroxene-rich spinel
peridotites. The peridotites were formed most
probably by a SiO 2 and MgO-rich melt/peridotite
wall rock interaction (Tihany).
Ol-olivine, Opx-orthopyroxene, Cpx-clinopyroxene, Spl-spinel,
Amp-amphibole (photomicrographs, 1N)

Fluid inclusions in mantle xenolith – peridotite (Szigliget)
FI in Cpx
FI in Opx)
Melt mixing -> cpx melting and crystallization -> fluid/melt immiscibility

Fluid inclusions in mantle xenolith – peridotite (Tihany)
FI in Opx FI in Opx
FI in Cpx
FI in Opx
Opx-orthopyroxene,
Cpx-clinopyroxene,
L-liquid phase,
Mgs-carbonate
(photomicrograph, 1N)
mostly in orthopyroxene, rarely in clinopyroxene; primary or pseudosecondary
negative crystal shape with size ranging from 3 to 100 μm;
dominantly one liquid phase at room temperature
rarely visible solid phases within the fluid inclusions

Fluid inclusions: high density CO 2 -rich fluids
- Microthermometry of FI and fluid bubble of SMI
Homogenization T in fluid bubble of SMI could not be observed
(probably low density vapor at room T)

– Raman spectroscopy of FI
High density CO 2 -rich fluid inclusions that show no evidence for H 2 O

– Raman spectroscopy of FI

– Raman spectroscopy of FI
Raman spectroscopy at low and/or high temperature is able to detect small
amounts of H 2 O

CO 2+H 2O±H 2S fluids (C-O-H-S system) in the
fluid inclusions regardless location
– Raman spectroscopy of FI

– Raman spectroscopy for determination of bulk composition of FI (Tihany)
Raman spectroscopy
at high temperature
(from 75 to 200 o C):
bulk composition:
- 89-98 mol % CO 2
- 2-11 mol % H 2 O
- 0.3-1.0 mol % H 2 S
Solid phases (detected by Raman):
carbonates, quartz step-daughter phases

Raman microspectroscopy – step-daughter phases (Tihany)
Orthopyroxene–hosted fluid inclusion:
• Magnesite, α-Quartz
MgSiO 3 (enstatite)+CO 2 =
MgCO 3 (magnesite)+SiO 2 (quartz)

Raman microspectroscopy – step-daughter phases (Tihany)
Clinopyroxene–hosted fluid
inclusion:
• Dolomite
CaMgSi 2 O 6 (diopside) + 2CO 2
= CaMg(CO 3 ) 2 (dolomite) +
2SiO 2 (quartz)

Carbonation post-entrapment reaction
Pl – plagioclase, Spl – spinel, Grt – garnet, Px – pyroxene, Qtz - quartz
Carbonation reaction at
around 400 – 600 o C
Trommsdorff and
Connolly (1990);
Holland and Powell
(1990); Koziol and
Newmann (1995)

Magnesite
Opx-orthopyroxene
Focused Ion Beam – Scanning Electron Microscopy (FIB-SEM)
Opx
Quartz
Thin glass film on
the wall

Opx – orthopyroxene, Mgs – magnesite, GCM – Gallium contaminated material
Focused Ion Beam – Scanning Electron Microscopy (FIB-SEM)
The glass, representing silicate
components that were formerly
dissolved in the fluid, started
to precipitate later or
simultaneously with the
magnesite and quartz daughter
phases.
The glass film seems to be
playing great role in preserving
the CO 2 fluid in mantle fluid
inclusions.

- IR hyperspectral images of FI+SMI (Szigliget)

SMI:
fluid bubble: CO 2
solid phases (glass) : H 2 O
FI: CO 2 +H 2 O
Silicate melt inclusion (SMI)
and fluid inclusion (FI)
in orthopyroxene
Opx: ~200 wt ppm H 2 O
- IR hyperspectral images of FI+SMI (Szigliget)

– Traces of fluid metasomatism (Tihany)
Cryptic metasomatism

- trace element distributions similar
to the silicate melt inclusions
- small amount of dissolved silicate
melt in the fluid inclusions
– Trace element composition of SMI and FI (Szigliget)

Opx – orthopyroxene, Mgs – magnesite, GCM – Gallium contaminated material
Focused Ion Beam – Scanning Electron Microscopy (FIB-SEM)
The glass, representing silicate
components that were formerly
dissolved in the fluid, started
to precipitate later or
simultaneously with the
magnesite and quartz daughter
phases.
The glass film seems to be
playing great role in preserving
the CO 2 fluid in mantle fluid
inclusions.

Carpathian-Pannonian region – upper mantle xenoliths

Classification of sulfides
• Inclusions (blebs, enclosed phases)
primary and/or secondary
• Interstitial phases
• One- or multiphase
Abundances: pyroxenites >< peridotites

Petrography of the sulfides: enclosed sulfide
Microscopy image:
(reflected & transmitted
light, 1N)
ol
100 m
po
+pn
sec
cpx
cp
po
cp
pr
pr
100 m
cpx
po po
200 m
d.
pr
- pentlandite (pn),
- chalcopyrite (cp),
- pyrrhotite (po),
- pyrite (py),
-MSS
pr r & sec
200 m
cpx
sulfide blebs
cpx

Petrography of the sulfides: Interstitial sulfide
Microscopy image:
(reflected light, 1N)
MSS
cp
- pentlandite (pn),
- chalcopyrite (cp),
- pyrrhotite (po),
- pyrite (py),
- monosulfide solide solution (MSS)
X-Ray mapping:
pn
SE image:
Microscopy image:
(reflected light, 1N)
cp
py
pn

Bulk major and minor element compositions of the sulfides
PMVF

Sulfide – silicate equilibrium in peridotites
Fe/Ni exchange between coexisting ol & sulfide
Kd 3 = X sulf NiS*X ol Fe 2 SiO 4 / X sulf FeS*X ol Ni 2 SiO 4
experimental values Kd 3 = 22 – 41
mantle xenoliths from the Carpathian-Pannonian region
(31 samples):
W-SBVF: 2 +, 5 <
C-BBHV: - +, 6 <
N-NGVF: 5 +, 6 <
E-PMVF: 3 +, 4

Bulk trace element compositions of the sulfides

Conclusions
The fluid inclusions are CO 2-rich, but also contain small amounts of H 2O
and silicate melt indicating that the presence of water and silicate melt in
deep-seated fluid inclusions is not a special feature, but rather reflects the
general component of any fluid inclusions from a sub-continental
lithospheric setting.
These fluids/melts trapped, as potential metasomatic agents, could be
responsible for mantle metasomatism and also resulted in post-entrapment
reaction with the mantle.
The PGE patterns show high and variable abundances of Os, Ir, Ru and Rh,
with decreasing abundances of Pd and a strong negative Pt anomaly. The
PGE abundance is explained by different degrees of melting and
metasomatism in the CPR mantle, however the texture is not necessarily
correlated with PGE patterns.

Thanks for your attention!
http://lrg.elte.hu
The European Union and the European Social Fund have provided
financial support to the project under the grant agreement no.
TÁMOP 4.2.1./B-09/KMR-2010-0003
This work has partly done in the framework of of the
REG_KM_INFRA_09 Gábor Baross Programme (contract nr.
OMFB-0038/2010).