Multidisciplinary study of Santa
Eulalia Plutonic Complex (Central
Portugal): Preliminary insight
H. SANT’OVAIA1*, J. CARRILHO LOPES2
AND P. NOGUEIRA2
1DGAOT, Centro de Geologia, FCUP, Portugal
(*correspondence: [email protected])
2Dep. Geo., Univ. Évora, Centro de Geologia UL, Portugal
The Santa Eulália Plutonic Complex (SEPC) is a late-
Variscan calcalkaline granitic body that occupies an area of
400 km2 and is located in the Variscan Iberian sector. The host
rocks of the complex are composed by metamorphic
formations from Proterozoic to Lower Paleozoic. The SEPC
has two main facies which present different compositions and
textures. From the rim to the core, there is a medium- to
coarse-grained pinkish granite (G0) involving large masses of
mafic to intermediate rocks and a central gray monzonitic
granite (G1). The central facies can be divided into a
porphyritic facies (G1A) and a central medium-grained facies
(G1B). Multidisciplinary studies that include petrography,
mineral and whole-rock chemistry, Anisotropy of Magnetic
Susceptibility (AMS) and microstructural analyses were
carried out. Besides petrographic and mineral chemistry data,
whole-rock analytical results reveal clear differences between
these two main granitic facies. G0 granites represent more
evolved liquids (>SiO2 wt.% and <MgO wt.%), plot closer to
metaluminous and A-type fields, and present negative Eu
anomalies, while G1 facies are typically monzonitic granites
with a strong peraluminous character. The AMS study was
based on 50 sampling sites. The magnetic susceptibility ranges
between 55.09 and 7343.67 x 10-6 SI. Two major groups can
be established: facies G0, with Km > 10-3 SI which supports
the presence of magnetite, and the central facies (G1A, G1B)
with Km< 10-4 SI. In the central facies the paramagnetic
behaviour is due to ferromagnesian minerals, such as biotite,
and ilmenite. Magnetic anisotropy ranges between 2.2 and
18.2% being in mean >5% in facies G0 and <4% in the central
facies. The high P% in G0 facies may be caused by the
magnetic bearer, magnetite. Nevertheless, microscope
observations show signs of a post-magmatic deformation in
G0. These preliminary data support that the facies G0 and the
central facies (G1) have a distinct magnetic behaviour which
may suggest different redox conditions in magma genesis.
This work has been financially supported by PTDC/CTEGIX/
099447/2008 (FCT-Portugal, COMPETE/FEDER)
