Open Session - SWISS GEOSCIENCE MEETINGs

Fig. 1. 87 Sr/ 86 Sr vs. 143 Nd/ 144 Nd variation of the magmatic rocks. Fields for Upper Crust (UC); Bulk Silicate Earth (BSE), This symbole use for
sample in this figure:Basaltic andesite Andesite , Dacite with xenocrysts , Dacite
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Emplacement of the Torres del Paine mafic complex (Patagonia, Chile):
A progress report
Leuthold J.*, Müntener O.*, Baumgartner L.*, Putlitz B.*, Michel J.*, Chiaradia M.**
* Institute of Mineralogy and Geochemistry, Anthropole - UNIL, CH-1015 Lausanne, Switzerland (julien.leuthold@unil.ch)
** Department of Mineralogy, Rue des Maraîchers 13 – UNIGE, CH-1205 Geneva, Switzerland
The Torres del Paine pluton (Patagonia, Southern Chile) is a composite, upper crustal mafic and granitic intrusion that was
emplaced in the Miocene (Michel et al. 2008). It consists of a ≈400m thick, basal mafic complex (Paine Mafic Complex – PMC,
Michael 1991) and a younger granite complex at the top (1500m thick), which have been separated into 3 units based on field
data and U-Pb ages (Michel et al. 2008).
We distinguish a ‘feeder zone’ with subvertical contacts in the Western part of the pluton and a saucer-shaped laccolith in
the central and Eastern part with predominantly subhorizontal contacts. Field observations show that three different gabbros
and two different diorites can be distinguished. The relative chronology of the mafic rocks is based on intrusive relationships.
The earliest intrusions are layered olivine gabbros that are exclusively exposed in the ‘feeder zone’, cut by biotitehornblende
(olivine-) melagabbros. The two latter ones form a large sill complex in the Central part of the PMC, where two
broadly similar and generally well-exposed sections of mafic rocks have been sampled (Castillo, and Aleta de Tiburon). The
lower one has brown hornblende crystallized prior to plagioclase and the upper one contains spectacular poikilitic hornblende.
These mineralogical variations are reflected in the whole rock chemistry. The lower zone is generally poorer in K 2 O and
richer in CaO, consistent with hornblende accumulation and a higher hornblende/biotite ratio. The presence of remobilized
crystals, hornblende-rich clots, and decimetre-thick boudinaged sills of hornblendite indicates remobilisation of ferro-magnesian
cumulates.
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Symposium 2: Mineralogy-Petrology-Geochemistry