Sedimentary Provenance of Neogene Strata From the Southwestern Portuguese Coast (Sines Cape): Detrital Zircon U-Pb Geochronology

In this preliminary study of provenance analysis, Neogene sandstones and conglomerates of the Alvalade Basin were sampled from sea cliffs in the vicinity of the Sines Cape (southwestern Portuguese coast). Detrital zircons were extracted by conventional methods of particle size separation including magnetism and heavy liquids. Detrital zircons were dated using the U-Pb method by laser ablation with inductively coupled plasma mass spectrometry (LA-ICP-MS). The U-Pb geochronology results indicate the following as potential sources for the samples: (1) Carboniferous greywackes of the Mira Formation (South Portuguese Zone) or the Upper Triassic sandstones of the Silves Formation (Alentejo Basin) for the zircons with pre-Permian ages; and (2) syenites from the Sines Massif for the zircons with Late Cretaceous ages. One sample includes a significant population of detrital zircons of Permian age whose source is unidentified as there are no source rocks of such age in the Alvalade Basin.