Formation and evolution of metapelitic-derived melts within anatectic complexes: Geochemical constraints and inferences on the protoliths and geodynamics of the Porto-Viseu Metamorphic Belt, Central Iberian Zone (central-north Portugal)

The Lusinde biotite granite constitutes a small late-post-tectonic Variscan massif, emplaced along the western termination of the Juzbado-Penalva Shear Zone (JPCSZ). The main objective of this work is to constrain the time of crystallisation of the Lusinde massif and to apply the technique of anisotropy of magnetic susceptibility to better understand pluton emplacement and internal structure. New LA–ICP–MS U–Pb zircon geochronological data for this intrusion yielded an emplacement age of 295 ± 1 Ma. The Lusinde granite shows relatively low values of magnetic susceptibility (Km = 152 × 10-6 to 271 × 10-6 SI), typical of granites of the ilmenite series in which biotite is the main carrier of magnetic signal. A pyroxene- and amphibole-bearing mafic microgranular enclave exhibits higher Km magnitudes (536 × 10-6 SI). Magnetic foliations are steeply plunging and strike subparallel to the pluton irregular margins. Magnetic lineations show rather variable directions and steep plunges, suggesting that the whole massif may correspond to a feeder zone. The studied pluton seems to belong to an E-W band of steep lineations traced along the northern border of the main mass of the Cota-Viseu late-post-tectonic granite and associated mafic and intermediate rocks, which has been interpreted as an alignment of feeder zones related to the extensional termination of the Juzbado-Penalva Shear Zone (JPCSZ). As a result, it is concluded that the emplacement of the Lusinde granite was tectonically controlled by the JPCSZ.

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Zircon U–Pb Dating and Lu–Hf Isotopic Composition of Some Granite Intrusions in Northern and Central Portugal: Constraints on the Emplacement Age and Nature of the Source Rocks

Gonçalves,

Teixeira,

Sant’Ovaia

et al. 2024

Minerals

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Freixo de Numão (FNG) and Capinha (CG) granites are prominent intrusions in the Douro Group (northern Central Iberian Zone, CIZ) and Beiras Supergroup (southern CIZ) metasediments, respectively. U-Pb dating revealed crystallization ages of 306 ± 2 Ma for FNG and 301 ± 3 Ma for CG, whereas Lu–Hf systematics has shown ɛHft values ranging from −4.5 to +0.6 and from −5.5 to +0.3 in FNG and CG autocrysts, respectively, suggesting that they originate from heterogeneous crustal anatectic melts, but a direct mantle-derived material contribution can also be considered. The isotopic data of inherited zircon cores of both granites, with ɛHft values ranging from −16.8 to +8.4 in FNG, and from −19.4 to +10.1 in CG, are compatible with a derivation from heterogeneous Neoproterozoic metasedimentary sources, consisting of juvenile and recycled crustal materials, comparable to those of the wall rocks. However, the less evolved initial 176Hf/177Hf signature of magmatic zircons of both granites requires more immature metasediments/juvenile materials as main sources for the parental magmas. In fact, for FNG, the high Sr and Ba whole-rock content, and the upper Cambrian inheritance highlight the involvement of a metaigneous protolith in its genesis.

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Formation and evolution of metapelitic-derived melts within anatectic complexes: Geochemical constraints and inferences on the protoliths and geodynamics of the Porto-Viseu Metamorphic Belt, Central Iberian Zone (central-north Portugal)

Cited by 3 publications

References 63 publications

The Lusinde late-post-tectonic Variscan granite (Central Iberian Zone): pluton emplacement at the termination of the Juzbado-Penalva do Castelo shear zone

The Lusinde late-post-tectonic Variscan granite (Central Iberian Zone): pluton emplacement at the termination of the Juzbado-Penalva do Castelo shear zone

The Lusinde late-post-tectonic Variscan granite (Central Iberian Zone): pluton emplacement at the termination of the Juzbado-Penalva shear zone

Zircon U–Pb Dating and Lu–Hf Isotopic Composition of Some Granite Intrusions in Northern and Central Portugal: Constraints on the Emplacement Age and Nature of the Source Rocks

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