high-t heating stage: application for igneous petrogenesis ...petrology.geology.elte.hu/smi as key...
TRANSCRIPT
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)
http://lrg.elte.hu
ANNO 1998ELTE
LRG
http://lrg.elte.hu/oktatas/
• 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.
High-T heating stage (Linkam)
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 andquartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate melts and melt inclusions as evidences for mantleenrichment, interaction, and immiscibility
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 andoccurring 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 regardlessof 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 thefocus of interest.
Mantle melts – in general
Examples for different melt inclusions
Primary silicate melt inclusion in orthopyroxene from spinel lherzolite xenolith in basalt (Hungary)
Primary silicate melt inclusion inorthopyroxene from pyroxenite xenolith inbasalt (Hungary)
Interstitial sulfide inclusion in spinel lherzolitexenolith in lamprophyre (Hungary)
opx
glass
bubble
pn
cp
MSS olcpx
opx
glass
bubble
Primary silicate melt inclusions in spinelfrom basalt (Albania)
30 m 30 m
10 m200 m
CO2 50 m
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 andquartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate melts and melt inclusions as evidences for mantleenrichment, interaction, and immiscibility
Method of melt inclusion study
Room temperature
Low temperature(freezing experiments)
Petrography (presence of glass, crystallized and/orvolatile phases, rations)
Image analysis
SEM
Major element chemical analysis (EPMA) on solidphases mass balance calculation (rough estimationof bulk composition)
Spectroscopic methods (e.g., Raman, IR): volatilecontent of glass, fluid phases, + solid precipitations
Microthermometry on fluid phases of melt inclusions
Spectroscopic methods (e.g., Raman) during phasetransitions
useful for:• silicate• carbonatite• (sulfide)
useful for:• silicate• carbonatite
Instrumental techniques
Heating experiments (homogenization): heat melt 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)]
High temperature(heating experiments)
Homogenization experiments at mantle temperatures
Problems:
volatile content (usually high-p is necessaryfor total homogenization)
post-entrapment crystallization (amount of wallcrystals, sulfide)
useful for:• silicate• carbonatite
• 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.
High-T heating stage (Linkam)
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 andquartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate melts and melt inclusions as evidences for mantleenrichment, interaction, and immiscibility
Significance of magma drops in ol, sp, cpx, plag, q, zrn, apPetrography
• primary or secondary silicate melt inclusions
• post-entrapment crystallization (not a closed system!)
on the wall
in the inclusion partially or totally recrystallized silicate melt inclusions
• reheating 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 phenocrystsOlivine phenocrysts in basalt (Hungary, Russia, Israel, Korea, etc.) contain silicate melt inclusions (Smi), spinel inclusions (Sp) ±CO2 fluid inclusions
Reflected light
Transmitted light
Phases of silicate melt inclusions (sequence of crystallization):olivine - on the wallsulfide (sulf)Al-spinel (sp)rhöniteclinopyroxene (cpx)apatite(±amphibole)glass (gl, Na- & K-rich )CO2(–rich) bubble
Trapping conditions:>1250 oC, >7 kbars
Mafic magma drops in spinel phenocrysts
Spinel as a host: • early crystallizing phase coexisting with olivine composition of the trapped melt• oxide no reaction with the enclosed silicate melt but post-entrapment crystallization
of Cr-spinel happened
Cr-spinel (micro)phenocrysts in alkali basalt (Albania, Korea, etc.) contain silicate melt inclusions
Trapping conditions: min. 1250 oC
Mafic magma drops in olivine (and spinel) phenocrysts
35 40 45 50 55 60 65 70 750
2
4
6
8
10
12
14
16
Na
2O
+K2O
SiO 2
Andesite
Dacite
Trachyte
Trachy-dacite
Trachy-andesite
Trachy-basalt
TephriteBasanite
Tephri-phonolite
Phonolite
Foidite
glass in unheated smi HTU
glass in unheated smi PK
homogenized smi HTUhost rock HTU
homogenized smi PKhost rock PK
Major element compositions (TAS diagram) of heated silicate melt inclusions (smi) and host basalts (Hungary)
Heating experiment crystallization in smi &fractionation of host basalt
Host basaltbulk rock
Mafic magma drops in olivine (and spinel) phenocrysts
Heated and exposed silicate melt inclusion in olivine for SIMS
0.1
1
10
Ba NbK LaCe Sr P Nd SmEuTiDy Y Yb
Roc
k/O
IB
Sun/McDonough. (1989)
heated smi HTU (1250 °C)
heated smi PK (1250 °C)host basalt HTU
host basalt PK
1
10
100
1000
La Ce Nd Sm Eu Dy Er Yb
Roc
k/C
hond
rite
s
REEs-Nakamura (1974)
heated smi HTU (1250 °C)
heated smi PK (1250 °C)host basalt HTU
host basalt PKTrace element compositions of heated silicate melt inclusions (smi) and host basalts (Hungary)
Trace element distributions of in smi and host basalt pairs:P (apatite), similarities <-> differences (magma mixing)
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 andquartz phenocrysts of volcanic rocks (+apatite, zircon)
PART-IV: Silicate melts and melt inclusions as evidences for mantleenrichment, interaction, and immiscibility
Significance of silicate melts and melt inclusions
Provide information on:
• enrichment of incompatible elements mantle metasomatism (cryptic and modal)
• mantle/melt interaction crystallization process, (modal metasomatism)
• formation of melt partial melting at source region depletion in incompatible
elements at source region (and enrichment of incompatible elements in melts)
• melt immiscibility partitioning of elements, crystallization process
• physical properties of mantle (lattice preferred orientation, elastic feature,
anisotropy
Silicate glasses in mantle rocksThe presence of silicate glasses in mantle rocks always indicate in-situ melting or migration of melts/fluids
Interstitial glass patches
Open-system
Interstitial silicate melt pockets
partial melting (depletion) or metasomatism (enrichment)?
”Closed”-system
Silicate melt inclusion enclosed in mantle minerals
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 re-equilibration and decompression during ascent/cooling (e.g. Schiano & Bourdon 1999)
lucky case
0.25 cm
OpxOpx
Cpx
CpxIncl
200 m
Q
CO2
Gl
250 mOpx
QzSmi
Petrography: - Smi primary and secondary- Smi: glass and CO2 bubble
Silicate melt inclusions in mantle rock - pyroxenite
Quartz (Qz) and CO2-bearing silicate melt inclusions (Smi) in pyroxenite xenolith, Hungary.
Heating experiments of smi Raman spectroscopy of CO2
Density=0.87-1.18 g/cm3
Entrapment pressure >1.1 GPa
Depth of the present day uppermost mantle
~960 °C melting temperature
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(?)+garnet in the source subducted oceanic crust?
rutileplagioclase?apatite?
garnet
Ni-content in SMI 139-635 ppm; Cr-content in SMI 187-851 ppm 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 fractionation (where?)
Raman spectroscopy of fluid bubble in silicate melt inclusion
Cooling experiment
Beside CO2, H2O in peridotite (microthermometry also indicates)