Download melts and melt inclusions

High-T heating stage: application for igneous
petrogenesis and mantle processes
- melt inclusions as key tools SZABÓ, Csaba
Lithosphere Fluid Research Lab (LRG),
Department of Petrology and Geochemistry,
Institute of Geography and Earth Sciences,
Eötvös University (ELTE), Budapest
H-1117 Budapest (HUNGARY)
LR
G
ANNO 1998
ELTE
http://lrg.elte.hu
High-T heating stage (Linkam)
•
Stage + controller:
•
Small ceramic furnace with a hole at the
bottom, covered by sapphire, to provide
transmitted light for observation during
experiment.
•
Quartz lid window for observation.
•
Gas valves to purge the sample
chamber with inert gas.
•
Water valves hooked up with a sealed
circulating water tank to keep the stage
at low T during heating experiment.
Purpose of use of the stage:
- to study melt inclusions,
- to obtain (partially) homogenized melt,
- to record melting sequence (crystallization,
identification of phases).
PART-I: Forewords on melts and melt inclusions
PART-II: Method of melt inclusion study, instrumental/analytical techniques
PART-III: Magma drops in olivine, spinel, clinopyroxene, plagioclase and
quartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate and carbonatite (and sulfide) melts and melt inclusions as
evidences for mantle enrichment, interaction, and immiscibility
Mantle melts – in general
Melt inclusions, in general, are small droplets of any kind of melts enclosed
in a host mineral, which were trapped accidentally at lithospheric mantle and
crustal temperatures and pressures, and subsequently quenched or partially
or totally crystallized.
Why do we study melt inclusions trapped under lithosphere conditions and
occurring in any kind of rocks?
To figure out physical conditions of trapping and compositions of the trapped melt
(behind these, evolution, interaction, crystallization/solidification, immiscibility, etc.)
Possible melts trapped under lithospheric mantle and crustal conditions regardless
of primary or secondary entrapment:
• Silicate melt (ultramafic, mafic, neutral and acidic rocks)
• Carbonatite melt (alkali and ultramafic rocks)
• [Sulfide melt (ultramafic and mafic rocks)]
In the lithosperic environments silicate melt inclusions are the most abundant,
however carbonatite [and sulfide] melt inclusions also occur and are relevant to the
focus of interest.
Examples for different melt inclusions
bubble
glass
glass
30 μm
opx
Primary silicate melt inclusion in
orthopyroxene from spinel lherzolite
xenolith in basalt (Hungary)
bubble
30 μm
opx
Primary silicate melt inclusion in
orthopyroxene from pyroxenite xenolith in
basalt (Hungary)
cpx
MSS
10 μm
pn
ol
cp
Interstitial sulfide inclusion in spinel lherzolite
xenolith in lamprophyre (Hungary)
CO2
50 μm
200 μm
Primary silicate melt inclusions in spinel
from basalt (Albania)
PART-I: Forewords on melts and melt inclusions
PART-II: Method of melt inclusion study, instrumental/analytical techniques
PART-III: Magma drops in olivine, spinel, clinopyroxene, plagioclase and
quartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate and carbonatite (and sulfide) melts and melt inclusions as
evidences for mantle enrichment, interaction, and immiscibility
Method of melt inclusion study
Room temperature
useful for:
• silicate
• carbonatite
• (sulfide)
Petrography (presence of glass, crystallized and/or
volatile phases, rations)
Image analysis
SEM
Major element chemical analysis (EPMA) on solid
phases Æ mass balance calculation (rough estimation
of bulk composition)
Spectroscopic methods (e.g., Raman, IR): volatile
content of glass, fluid phases, + solid precipitations
Microthermometry on fluid phases of melt inclusions
Low temperature
(freezing experiments)
Spectroscopic methods (e.g., Raman) during phase
transitions
useful for:
• silicate
• carbonatite
Instrumental techniques
High temperature
(heating experiments)
useful for:
• silicate
• carbonatite
Homogenization experiments at mantle temperatures
Problems:
volatile content (usually high-p is necessary
for total homogenization)
post-entrapment crystallization (amount of wall
crystals, sulfide)
Heating experiments (homogenization): heat Æ melt Æ quench
•
high-T stages mounted on petrographic microscopes (direct info on changes)
•
furnace technique (no direct observation)
Chemical analysis:
•
EMPA (major elements): heated inclusions (solid phases of inclusions)
•
SIMS (trace elements): heated inclusions (solid phases of inclusions)
[LA-ICP-MS: unhomogenized inclusions (whole inclusion is ablated)]
[LA-MC-ICP-MS: unhomogenized inclusions (especially on sulfides)]
PART-I: Forewords on melts and melt inclusions
PART-II: Method of melt inclusion study, instrumental/analytical techniques
PART-III: Magma drops in olivine, spinel, clinopyroxene, plagioclase and
quartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate and carbonatite (and sulfide) melts and melt inclusions as
evidences for mantle enrichment, interaction, and immiscibility
Significance of magma drops in ol, sp, cpx, plag, q, zrn, ap
Petrography
• primary or secondary silicate melt inclusions
• post-entrapment crystallization (not a closed system!)
on the wall
in the inclusion Æ partially or totally recrystallized silicate melt inclusions
• reheating Æ to have trapped melt
Composition of the trapped (primary? primitive?) melt
right composition (should be compared to relevant phase diagram, Frezzotti, 2001)
•
volatile
bubble (CO2, H2S, CH4, N2)
glass (H2O, Cl, F, S)
Provide information on
• change in composition (fractionation, magma mixing)
• degassing/partitioning process during crystallization/solidification
• immiscibility
• post entrapment crystallization
Mafic magma drops in olivine phenocrysts
Olivine phenocrysts in basalt (Hungary, Russia, Israel, Korea, etc.)
contain silicate melt inclusions (Smi), spinel inclusions (Sp) ±CO2 fluid
inclusions
Transmitted light
Reflected light
Trapping conditions:
>1250 oC, >7 kbars
Phases of silicate melt
inclusions (sequence of
crystallization):
olivine - on the wall
sulfide (sulf)
Al-spinel (sp)
rhönite
clinopyroxene (cpx)
apatite
(±amphibole)
glass (gl, Na- & K-rich )
CO2(–rich) bubble
Mafic magma drops in spinel phenocrysts
Cr-spinel (micro)phenocrysts in alkali basalt (Albania, Korea, etc.) contain silicate
melt inclusions
Spinel as a host:
• early crystallizing phase coexisting with olivine Æ composition of the trapped melt
• oxide Æ no reaction with the enclosed silicate melt but post-entrapment crystallization
of Cr-spinel happened
Trapping conditions: min. 1250 oC
Mafic magma drops in olivine (and spinel) phenocrysts
Major element compositions (TAS diagram) of heated
silicate melt inclusions (smi) and host basalts
(Hungary)
glass in unheated smi HTU
homogenized smi HTU
host rock HTU
glass in unheated smi PK
homogenized smi PK
host rock PK
16
14
Tephriphonolite
Phonolite
Na 2 O+K 2 O
12
10
Trachyte
Trachyandesite
Foidite
8
Tephrite
Basanite
6
Heating experiment Æ
crystallization in smi &
fractionation of host
basalt
Trachydacite
Dacite
Trachybasalt
4
Andesite
Host basalt
bulk rock
2
0
35
40
45
50
55
60
SiO 2
65
70
75
Mafic magma drops in olivine (and spinel) phenocrysts
REEs-Nakamura (1974)
1000
Sun/McDonough. (1989)
10
Rock/Chondrites
Trace element compositions of heated silicate melt
inclusions (smi) and host basalts (Hungary)
heated smi HTU (1250 °C)
host basalt HTU
heated smi PK (1250 °C)
host basalt PK
Rock/OIB
heated smi HTU (1250 °C)
host basalt HTU
heated smi PK (1250 °C)
host basalt PK
100
10
1
La Ce
Nd
Sm Eu
Dy
Er
Yb
1
Trace element distributions of in smi and host basalt pairs:
P (apatite), similarities <-> differences (magma mixing)
Heated and exposed silicate melt
inclusion in olivine for SIMS
0.1
Ba
Nb K LaCe
Sr P Nd SmEuTiDy Y Yb
PART-I: Forewords on melts and melt inclusions
PART-II: Method of melt inclusion study, instrumental/analytical techniques
PART-III: Magma drops in olivine, spinel, clinopyroxene, plagioclase and
quartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate and carbonatite (and sulfide) melts and melt inclusions as
evidences for mantle enrichment, interaction, and immiscibility
Significance of silicate and carbonatite (and sulfide) melts
and melt inclusions
Provide information on:
• enrichment of incompatible elements Æ mantle metasomatism (cryptic and modal)
• mantle/melt interaction Æ crystallization process, (modal metasomatism)
• formation of melt Æ partial melting at source region Æ depletion in incompatible
elements at source region (and enrichment of incompatible elements in melts)
• melt immiscibility Æ partitioning of elements, crystallization process
• physical properties of mantle (lattice preferred orientation, elastic feature,
anisotropy
Silicate glasses in mantle rocks
The presence of silicate glasses in mantle rocks always indicate in-situ melting or
partial melting (depletion) or metasomatism (enrichment)?
migration of melts/fluids
Open-system
Interstitial glass patches
Interstitial silicate melt pockets
Mantle minerals may trap and preserve the
composition of high-pressure-temperature melts,
since the large elastic modulus of their host phase
prevents them from low-pressure chemical reequilibration and decompression during
ascent/cooling (e.g. Schiano & Bourdon 1999)
Æ lucky case
Silicate melt inclusion enclosed in mantle minerals
”Closed”-system
Silicate melt inclusions in mantle rock - pyroxenite
Cpx
Qz
Smi
Opx
Opx
Opx
Incl
Cpx
250 μm
0.25 cm
Quartz (Qz) and CO2-bearing silicate melt
inclusions (Smi) in pyroxenite xenolith, Hungary.
Petrography:
- Smi primary and secondary
- Smi: glass and CO2 bubble
Q
Gl
CO2
200 μm
Heating experiments of smi
Raman spectroscopy of CO2
Density=0.87-1.18 g/cm3
~960 °C melting temperature
Entrapment pressure >1.1 GPa
Depth of the present day uppermost mantle
Glass composition - major elements:
Glass composition - major elements:
Opx+qz+cpx+amp(?)
fractionation from a
hybrid melt formed on
peridotite-slab-melt
interface
Silicate melt inclusion composition (LA-ICP-MS) - trace elements:
rutile
plagioclase?
apatite?
garnet
Rutile+plagioclase(?)+garnet in the source Æ subducted oceanic crust?
Ni-content in SMI 139-635 ppm; Cr-content in SMI 187-851 ppm
Æ reaction with peridotite
Silicate melt inclusions in mantle rocks - peridotite
Primary silicate melt inclusions (smi) in clinopyroxene (cpx) and secondary silicate melt
inclusions in orthopyroxene (opx) from lherzolite xenolith (Hungary)
Smi phases: products of post-entrainment crystallization, glass (gl), mica, fluid bubble
The same evolved melt
(high volatile content)
The same process Æ
fractionation (where?)
Raman spectroscopy of fluid bubble in silicate melt inclusion
Cooling experiment
Beside CO2, H2O in peridotite (microthermometry also indicates)
Primary carbonatite melt inclusions in mantle xenoliths
Carbonatite melts are found very rarely because they are
• the product of very low degree partial melting,
• reactive melts,
• and prefer to interact with the chemically different mantle very fast.
Therefore, the carbonatite melt itself is usually missing, whereas its strong fingerprint
can be observed in mantle rocks
Primary Carbonatites
Have extremely low viscositiy, therefore they can move along the grain boundaries,
Have great role in carrying of incompatible trace and major element in the mantle,
Cause significant cryptic metasomatism when they infiltrate into the ultramafic mantle,
Can precipitate unusual phases (apatite and K feldspar) in the mantle in rock.
Primary carbonatite melt inclusions in mantle xenoliths
Clinopyroxene (Cpx),
apatite (Ap), K feldspar (Kfs)
and phlogopite (Phl)
xenolith from lamprophyre
dikes (Hungary)
Large number of randomly
distributed apatite- and K
feldspar-hosted primary
carbonatite melt inclusions
(CMI)
Primary carbonatite melt inclusions in mantle xenoliths
• Trace element content of the
near solidus melts (e.g., primary
carbonatites) are uncertain.
•CMI shows that their initial melt
was formed by very low degree
partial melting of a carbonated
and subducted slab.
Primitive mantle normalized REE (A) and trace element (B) distribution of average composition of
apatite- and K feldspar hosted carbonatite melt inclusion from clinopyroxene-rich xenoliths
Primary Carbonatites
Have extremely low viscositiy therefore they can move along
the grain boundaries→
Have great role in carrying of incompatible trace and major
element in the mantle →
Cause significant metasomatism when they infiltrate into the
ultramafic mantle →
Can precipitate unique phases (apatite and K feldspar) in
the mantle in rock forming amount
LR
G
ANNO 1998
ELTE
Thanks for your attention
http://lrg.elte.hu