Provenance study of Pliocene–Pleistocene sands based on ancient detrital zircons (Alvalade basin, SW Iberian Atlantic Coast)

Pliocene–Pleistocene sand of the Alvalade basinwas taken fromthe sea-cliffs of SWIberia coast for a provenance study using radiometric dating. The U–Pb ages obtained revealed a wide interval ranging from Cretaceous to Archean, with predominance of Paleozoic, Neoproterozoic and Cretaceous zircon ages. Cretaceous ages interpreted to indicate a Sines Massif provenance are dominant in sands close to Cape Sines but are absent in sand sampled 12 km north. Carboniferous ages younger than ca. 315 Ma suggesting a possible contribution from the Central-Iberian Zone originally; however, these zircons may be multi-cyclic, having been reworked from Eocene–Miocene siliciclastic deposits related to transport from central Iberia (Lower Tagus basin drainage evolution). These signatures provide important constraints on the location and extent of the Pliocene–Pleistocene topography and drainage system that were probably controlled by: i) Miocene to Pleistocene landscape rejuvenation driven by Alpine movements along major faults; and ii) residual reliefs related to inherited Variscan structure. The U–Pb ages obtained also trace the pre-Cenozoic paleotectonic evolution of SWIberia recorded in their sources: i) the North Gondwana accretion and breakup; ii) the Gondwana and Laurussia collision; and iii) the Pangea breakup and opening of the Atlantic Ocean

Tracing the geodymamic evolution of the North Gondwana

Pliocene–Pleistocene sand of the Alvalade basin was sampled from the sea-cliffs of SW Iberia close to Cape Sines for a provenance study using LA-ICPMS U-Pb dating of detrital zircons. The results are used to compare age distributions and to trace potential source areas based on existing knowledge of zircon-forming events in the pre-Cenozoic basement of SW Iberia. The 492 U-Pb ages obtained span a wide interval ranging from Cretaceous to Archean, with predominance of Paleozoic (31–71%; mainly Carboniferous), Neoproterozoic (19–20%; mainly Cryogenian–Ediacaran) and Cretaceous (21–39%). Two important features were noted: i) Carboniferous ages younger than ~ 315 Ma infrequent or absent in SW Iberia, and ii) Cretaceous ages are interpreted to indicate a Sines massif provenance. The data obtained confirm previous studies that indicate a sediment source in the Paleozoic basement of SW Iberia (Ossa-Morena and South Portuguese zones) but also suggest a more complex history of drainage than previously documented, involving other sources located to the north. The detrital zircons age populations also enable recognition of previously undocumented sources of Pliocene–Pleistocene sands and decipher their paleotectonic meaning: i) Neoproterozoic to Early Paleozoic meta-sedimentary and meta-igneous rocks of the Ossa-Morena and Central- Iberian zones formed in North Gondwana during the Cadomian orogeny and opening of the Rheic Ocean, and ii) Devonian to Carboniferous sedimentary and igneous rocks of the Ossa- Morena, Central Iberian, and South Portuguese zones formed when Gondwana and Laurussia collided (Variscan orogeny)

U-Pb geochronolgy of the deformed Juzbado Granite (Salamanca, NW Spain)

Este trabajo se centra en el estudio de la edad de cristalización del granito deformado de Juzbado mediante geocronología U-Pb a través de ablación láser. Se dataron 7 granos de circón, obteniéndose edades comprendidas entre 340 y 2500 Ma. Los datos obtenidos proporcionan una edad máxima de cristalización de 340 Ma y aportan datos sobre la naturaleza de los potenciales materiales fuente. Las edades de circones heredados existentes en el granito son coincidentes con las encontradas en las posibles rocas fuente. Dado que esta intrusión está deformada intensamente por la fábrica relacionada con la Zona de Cizalla de Juzbado-Penalva do Castelo, la edad mínima de este cuerpo es de 308 Ma. La comparación de las características petrológicas de este granito con las de otros en los alrededores (en el Domo del Tormes) permite asignarle una edad en torno a 320 Ma

Großflächige Abscheidung von Graphen - Ein wichtiger Schritt für neuartige Bauelemente

Das wachsende Interesse an Graphen beruht auf seiner unverwechselbaren Bandstruktur und seinen damit zusammenhängenden herausragenden physikalischen Eigenschaften. Es wird daher weltweit nach einem Verfahren gesucht, Graphen großflächig und mit hoher Qualität abzuscheiden. In einer an der TH Wildau [FH] speziell für diese Aufgabe konzipierten Reaktionskammer wurde die Herstellung mittels chemischer Gasphasenabscheidung auf katalytischen Metalloberflächen für verschiedene Parameter studiert und deren Verträglichkeit mit der CMOS -Technologie untersucht. Die ersten Tests erfolgten auf Nickel, da hier eine im Volumen stattfindende katalytische Reaktion einsetzt. In weiteren Schritten fiel die Wahl auf Kupfer, da hier die Reaktion an der Oberfläche stattfindet und daher ein stabilerer Prozess realisiert werden konnte. Die Qualitätsprüfung der erzeugten Schichten erfolgte mittels Ramanspektrometrie

. U-Pb detrital zircon ages from the Beiras Group: Implications for the Neoproterozoic evolution of the SW Iberia

U-Pb detrital zircon ages from the Beiras Group greywackes (SW Central Iberian Zone - CIZ) indicate a maximum depositional age of late Ediacaran (c. 560-578 Ma). Two salient features distinguish the Beiras Group from the Série Negra greywackes (age equivalent from the Ossa-Morena Zone - OMZ): i) The presence of Tonian and Mesoproterozoic (<8%) age clusters in the Beiras Group greywackes, that are almost absent in the OMZ, imply either a distinct or an additional source of detrital zircons from the West African Craton; and 2) The higher content of Cryogenian zircon ages of the Beiras Group greywackes (mainly at c. 840-750 Ma and c. 685-660 Ma), that contrast with the dominant Ediacaran zircon ages of the Série Negra greywackes (OMZ). The Cryogenian zircon forming events that are dominant in the SW CIZ basins are probably related to a different source with early Cadomian juvenile crust (c. 700-635 Ma) and with a possible contribution of the Pan-African suture (c. 850-700 Ma). The Nd isotopic signatures support the addition of a juvenile source to pre-existent older crust for the Beiras Group metasediments. Although the Beiras Group (SW CIZ) and Serie Negra (OMZ) late Ediacaran basins have evolved together in the active margin of Gondwana, they were sufficiently separated to account for the differences in their detrital zircon content and isotopic signatures

The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the

U–Pb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovician (Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of the southwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passive margin transition. The LA-ICP-MS U–Pb data set (375 detrital zircons with 90–110% concordant ages) is dominated by Neoproterozoic ages (75% for the greywakes and 60% for the quartzites), among which the main age cluster (more significant for Beiras Group greywackes) is Cryogenian (c.840–750 Ma), while a few Mesoproterozoic and Tonian ages are also present (percentages <8%). These two features, and the predominance of Cryogenian ages over Ediacaran ages, distinguish the Beiras Group greywackes (SW CIZ) from the time-equivalent Serie Negra (Ossa-Morena Zone – OMZ), with which they are in inferred contact. The age spectra of the Beiras Group greywackes also reveal three major episodes of zircon crystallisation in the source area during the Neoproterozoic that are probably associated with a long-lived system of magmatism that developed either along or in the vicinity of the northern Gondwana margin at: (1) c. 850–700 Ma – Pan-African suture (not well represented in OMZ); (2) c. 700–635 Ma – early Cadomian arc; and (3) c. 635–545 Ma – late Cadomian arc. Comparison of Neoproterozoic ages and those of the Paleoproterozoic (c. 2–1.8 Ga) and Archean (mainly Neoarchean – 2.8–2.6 Ga, but also older) in the Beiras Group greywackes with U–Pb ages of Cadomian correlatives shows that: (1) SW CIZ, OMZ, Saxo- Thuringian Zone, North Armorican Cadomian Belt and Anti-Atlas) evolved together during the formation of back-arc basins on the northern Gondwana active margin and (2) all recorded synorogenic basins that were filled during the Ediacaran by detritus resulting from erosion of the West African craton, the Pan- African suture and a long-lived Cadomian magmatic arc. Differences in detrital zircon age populations in the greywackes of the Beiras Group (SW CIZ Cadomian basement) and the Serie Negra (OMZ Cadomian basement) are also observed in their respective overlying Early Ordovician quartzites. Since both these SW Iberia Cadomian basements evolved together along the active margin of Gondwana (but sufficiently separated to account for the differences in their detrital zircon content), this continuation of differing zircon populations into the Early Ordovician suggests that the inferred contact presently juxtaposing the Beiras Group and the Serie Negra is not pre-Early Ordovician and so is unlikely to demonstrate a Cadomian suture

Provenance analysis of the Paleozoic sequences of the northern Gondwana margin in NW Iberia: Passive margin to Variscan collision and orocline development

The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges from Neoproterozoic to Early Permian in age. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana or (ii) an active continental margin or (iii) a drifting ribbon continent. In this paper we present detrital zircon U–Pb laser ablation age data from 13 samples taken in detrital rocks from the Cantabrian Zone sequence ranging from Early Silurian to Early Permian in depositional age. The obtained results, together with previously published detrital zircon ages from Ediacaran– Ordovician strata, allow a comprehensive analysis of changing provenance through time. Collectively, these data indicate that this portion of Iberia was part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Zircon populations in all samples show strong similarities with the Sahara Craton and with zircons found in Libya, suggesting that NW Iberia occupied a paleoposition close to those regions of present-day northern Africa during this time interval. Changes in provenance in the Late Devonian are attributed to the onset of the collision between Gondwana and Laurussia. Additionally, the Middle Carboniferous to Permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the Variscan orogeny. Late-Devonian to Permian samples yield zircon populations that reflect topographic changes produced during the Variscan orogeny and development of the lithospheric scale oroclinal buckling

Evidence formulti-cycle sedimentation and provenance constraints from

Laser ablation ICP-MS U–Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U–Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U–Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296Ma),which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa–Morena and Central Iberian zones that outcrop in and close to the Porto–Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian–Carboniferous ages (ca. 315Ma) found in detrital zircons provide evidence of the denudation of Variscan and Cimmerian granites during the infilling of continental rift basins in western Iberia. The zircon age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin,which probably acted as an intermediate sediment repository.U–Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived fromlocal source areas with features typical of Gondwana,with no sediment from external sources from Laurussia or southwestern Iberia

Episodic melting and magmatic recycling along 50 Ma in the Variscan belt linked to the orogenic evolution in NW Iberia

The advent of a large amount of more precise U-Pb age data on Variscan granitoids from NW Iberia in recent years has provided a more focused picture of the magmatic history of the Western European Variscan belt (WEVB). Based on these data, three main pulses of magmatic activity seem to be well established