One hundred and twenty‐five new lead isotopic analyses on galena, mainly from the Los Pedroches – Alcudia Valley area of southern Iberia, are presented. These data allow us to define four compositional groups in the 207Pb/206Pb versus 208Pb/206Pb and 207Pb/206Pb versus 206Pb/204Pb diagrams. Group I compositions are intermediate between those previously reported for southeastern and southwestern Iberian ore mineral locations. The compositions of Group II, the largest group, overlap with ore data from southwestern Spain. Groups III and IV have compositions that have never before been identified in this region and are comparable to those from the Sardinian Cu ores, which might explain the previously assumed exotic origin for local Bronze Age artefacts.
The Careón unit consists of imbricate tectonic sheets of serpentinite, metagabbro, and diabase dikes interpreted as a dismembered ophiolitic sequence. Zircons from leucogabbro intruding serpentinites point to an igneous crystallization at 395 ± ± 3 Ma, in accord with previous results. Combined with a reported 377 ± ± 1 Ma Ar/Ar cooling age, this date implies that ophiolite generation occurred shortly before its tectonic emplacement. Most samples are enriched in light rare earth elements (REE) relative to heavy REEs and show distinct fractionation of the heavy REEs. Enrichments in Th and La relative to Nb are ubiquitous, while negative anomalies of Zr and Ti occur in most samples. Initial ε ε Nd values (+ +6.4 to + +9.1), even for samples with high light REE/heavy REE ratios, point to a time-integrated mantle source strongly depleted in Nd relative to Sm, and preclude signiµcant contamination of maµc melts during their ascent through the crust. Combined trace element and Nd-isotope data favor an intraoceanic, suprasubduction-zone setting, where hydrous ×uids and silicate melts metasomatized a wedge of depleted mantle and triggered its partial melting. On the basis of magmatic afµnities, age constraints, and broad tectonometamorphic context, ophiolite generation is interpreted to re×ect oceanic spreading above a subduction zone dipping away from a passive continental margin. Suprasubduction extension might have been associated with subduction hinge retreat caused by instability of old, cold oceanic lithosphere entering the subduction zone. It is suggested that this occurred in the context of early stage arc collision documented at that epoch in the Variscan realm.
The first U-Pb geochronological results on the magmatic alignment of the Los Pedroches batholith are presented. The batholith is composed of a main granodioritic unit, several granite plutons and an important acid to basic dyke complex, all of them intrusive after the main Variscan regional deformation phase, D1, along the boundary between the Ossa-Morena and Central Iberian zones (SW Iberian Massif). Zircons from samples on both extremes of the granodiorite massif record nearly simultaneous magmatic crystallization at ca. 308 Ma, while the emplacement of granite plutons was diachronic between 314 and 304 Ma. The U-Pb results combined with new field and textural observations allow to better constrain the age of Variscan deformations D2 and D3 across the region, while the age of D1 remains imprecise. Transcurrent D2 shearing-tightening of D1 folds occurred around 314 Ma (lower Westphalian) in relation to the emplacement of the first granitic magmas. D3 faults and shear bands bearing a strong extensional component developed at ca. 308 Ma (upper Westphalian), associated to the intrusion of the main granodiorite pluton (granodiorite) of the batholith. Together with available geochemical and geophysical information, these results point to the Variscan reactivation of lithospheric fractures at the origin and subsequent emplacement of hybrid magmas within this sector of the Massif.
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