WP4 Fossil Magmatic systems

1
WP4 Fossil Magmatic systems

• D. Gagnevin and J.S. Daly

Department of Geology, University College Dublin,
Belfield, Dublin 4, Ireland ERUPT partner 7
2
(No Transcript)
3
WP4 Fossil Magmatic systems
Monte Capanne monzogranite, Elba (7Ma) Crust,
mantle, wall-rock xenoliths Monitor magma
components using intra-grain variations in
chemistry, Sr, Pb, Nd and Hf isotopes
in K-feldspar, plagioclase, apatite, zircon,
biotite Petrography (SEM), electron microprobe,
LA-ICPMS, ion microprobe, Rb-Sr micro-drill
core IDTIMS, Pb LA-MC-ICPMS
4
Fossil magmatic systems in the Tuscan Magmatic
Province
5
7 Ma Monte Capanne monzogranite
6
Spectacular field evidence for coeval magmas and
magma mixing
7
Main facies monzogranite, MME, hybrids, very rare
gabbroic enclaves
8
(No Transcript)
9
(No Transcript)
10
whole-rock isotopic data
11
How many components? Crustal melt, mantle melt,
wall-rock xenoliths
12
and mixtures of these, each potentially
modified by crystallization
13
Can we use K-feldspar megacrysts to monitor
magmatic evolution ?
14

• Many K-feldspar
• megacrysts display
• resorption surfaces
• gt10 volume loss

15
Core
Resorption zone
16
Ba increases rimward of resorption surfaces
17
Sometimes the resorption surfaces appear to be
correlated
distance to core (mm)
18
so far we see this only at one locality
distance to core (mm)
19
Some K-feldspar megacrysts display multiple
resorption surfaces
20
but so far we have data mainly from samples
with single resorption surfaces
21
In situ major and trace elements, Sr isotopes
on micro-drill cores by IDTIMS
22
and in situ Pb isotopes.
23
must take care to avoid inclusions, fractures
and alteration
24
Ion microprobe analyses
25
Diffusive equilibration is limited to c. 200
mm coreward of the resorption zone.
26
Sr isotopic data on drilled microsamples
27
Not diffusion!
Distance from rim (mm)
28
(No Transcript)
29
Initial Sr isotopic ratios across K-feldspar
megacrysts
30
208Pb/206Pb
LA-ICP-MCMS Pb isotope profiles, K-feldspar
megacrysts
31
208Pb/206Pb
accuracy checked by double-spike TIMS analysis of
micro-drill cores
32
Intracrystalline diffusion cannot explain the Pb
isotopic zoning
33
instead the progressive increase in
208Pb/206Pb from core to rim reflects gradual
change in the magma composition due to input of
a mantle-derived component
34
Conclusions

• Growth interruptions, chemical, Sr Pb isotopic
  variations across K-feldspar megacrysts

? zoning effects are real, not diffusion
? powerful tool to understand petrogenesis
of complex plutonic magmatic
systems
? possibility of identifying the end-members
involved in magma mixing
? extent of fractionation and interaction with
crustal melts
? late contribution from a mantle magma
35
WP4 Fossil Magmatic systems
UCD partner 7. Publications Gagnevin, D.,
Daly, J.S. and Poli, G. 2004a. Petrographic,
geochemical and isotopic constraints on magma
dynamics and mixing in the Monte Capanne
monzogranite (Elba Island, Italy). Lithos. (in
press).   Gagnevin, D., Daly, J.S., Waight, T.E.,
Morgan, D. and Poli, G. 2004b. Pb isotopic
zoning of K-feldspar megacrysts determined by
laser ablation multiple-collector ICP-MS
insights into granite petrogenesis. Geochimica
et Cosmochimica Acta (in revision). Gagnevin,
D., Daly, J.S. and Poli, G. 2004c.
Microchemical and Sr isotopic investigation of
zoned K-feldspar megacrysts insights into the
petrogenesis of a young plutonic system. Journal
of Petrology (in review). Gagnevin, D., Daly,
J.S. and Poli, G. 2005. Petrogenetic
implications of resorption surfaces in K-feldspar
megacrysts from the Monte Capanne pluton (Elba
Island, Italy). Mineralogical Magazine. (in
preparation)