14 research outputs found
Intraaortic counterpulsation in a second-level institution: indications, management and outcome
U–Pb isotopic ages and Hf isotope composition of zircons in Variscan gabbros from central Spain: evidence of variable crustal contamination
Ion microprobe U–Pb analyses of zircons from
three gabbroic intrusions from the Spanish Central System
(SCS) (Talavera, La Solanilla and Navahermosa) yield
Variscan ages (300 to 305 Ma) in agreement with recent
studies. Only two zircon crystals from La Solanilla massif
gave slightly discordant Paleoproterozoic ages (1,848 and
2,010 Ma). Hf isotope data show a relatively large variation
with the juvenile end-members showing ɛHfi values as high
as +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa and
Talavera gabbros, respectively. These positive ɛHfi values up
to +6.9 might represent the composition of the subcontinental
mantle which generates these SCS gabbros. This ɛHfi
range is clearly below depleted mantle values suggesting the
involvement of enriched mantle components on the origin of
these Variscan gabbros, and is consistent with previous
whole-rock studies. The presence of zircons with negative
ɛHfi values suggest variable, but significant, crustal contamination
of the gabbros, mainly by mixing with coeval granite
magmas. Inherited Paleoproterozoic zircons of La Solanilla
gabbros have similar trace element composition (e.g. Th/U
ratios), but more evolved Hf-isotope signatures than associated
Variscan zircons. Similar inherited ages have been
recorded in zircons from coeval Variscan granitoids from the
Central Iberian Zone. Granitic rocks have Nd model ages
(TDM) predominantly in the range of 1.4 to 1.6 Ga,
suggesting a juvenile addition during the Proterozoic.
However, Hf crustal model ages of xenocrystic Proterozoic
zircons in La Solanilla gabbro indicate the presence of
reworked Archean protoliths (TDM2 model ages of 3.0 to
3.2 Ga) incorporated into the hybridized mafic magma
S-type granite generation and emplacement during a regional switch from extensional to contractional deformation (Central Iberian Zone, Iberian autochthonous domain, Variscan Orogeny)
Tectonic setting and isotopic sources (Sm–Nd) of the SW Iberian Autochthon (Variscan Orogen)
U–Pb geochronology and zircon composition of late Variscan S- and I-type granitoids from the Spanish Central System batholith
Variscan Magmatism
This chapter aims to identify, characterize and locate the main facts/events related to orogenesis in the Iberian Peninsula. Its succession in space and time determines the geodynamic environment of the broader geological phenomenon corresponding to the Variscan cycle. In this sense, this section comprises two parts: I—The Iberian orogenic magmatism seen through a space-time approach of its westernmost region—focus on the enormous complexity of the inherited basement, its nature, age and distribution in space. Establishes a space-time sequence of geodynamic environments correlated with the obtained data and tries to identify the agents responsible for its genesis. Some case studies are presented to illustrated significant regional aspects of the magmatic process and II—An overview of the petrogenesis of the great batholiths and of the basic, intermediate and mantle-related rocks—identify and analyze a great amount of these rocks intruding and extruded from 400 to 280 Ma and to better understanding the large-scale process involving the whole lithosphere during Variscan cycle.publishe