In situ LA-ICPMS U–Pb dating of sulfates: applicability of carbonate reference materials as matrix-matched standards

Recent developments in analytical capabilities in the field of in situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U–Pb geochronometers in low-U minerals such as carbonates or garnets. The rapid evolution of the technique relies on well-characterized matrix-matched reference materials. In this article, we explore the suitability of using carbonate as an “almost-matrix-matched reference material” for in situ U–Pb dating of sulfates. For such purpose, we have used the astrochronologically dated gypsum and anhydrite samples deposited during the Messinian Salinity Crisis (5.97–5.33 Ma) and compared these dates with the U–Pb ages obtained by LA-ICPMS. Although the majority of the samples failed due to the elevated common Pb content and low 238U/204Pb ratios, five of the samples showed a higher dispersion on U/Pb ratios. The obtained dates in four of these samples are comparable with the expected ages, while another gave an unexpected younger age, each of them with 6 %–11 % of uncertainty. The pit depth of the spots showed that the sulfates ablate similar to carbonates, so the offset due to the crater geometry mismatch or downhole fractionation can be assumed to be negligible. To sum up, the bias between the U–Pb and expected cyclostratigraphic ages, if any, is included in the uncertainty, and thus the results obtained here suggest that carbonate reference material is currently the best option for standardization of in situ U–Pb sulfate analyses.</p

Two distinct age groups of melilitites, foidites, and basanites from the southern Central European Volcanic Province reflect lithospheric heterogeneity

Petrographic observations and in situ U–Pb ages of melilitites, foidites, basanites, phonolites, and trachytes from the southern part of the Central European Volcanic Province (CEVP) and related plutonic inclusions therein reveal two distinct age groups separated by a gap of ~ 20 Myr. A late Cretaceous to early Eocene group (~ 73–47 Ma; Taunus, Lower Main plain, Odenwald and Kraichgau area, Bonndorfer Graben and Freiburger Bucht area, Vosges and Pfälzerwald) is characterized by nephelinites and basanites mostly devoid of melilite and perovskite, and by rare haüynites, and trachytes. In contrast, a late Oligocene to late Miocene group (~ 27–9 Ma; Lorraine, southern Upper Rhine Graben, Urach, Hegau area) is dominated by melilitites, melilite-bearing nephelinites (both carrying perovskite), and phonolites. Both magmatic episodes are related to domal topographic uplift, erosion, and formation of major angular unconformities in the Upper Rhine Graben, suggesting an association with dynamic topography interrupted by phases of subsidence (or abatements of uplift). The investigated rocks in the southern CEVP (south of a line Eifel–Vogelsberg–Rhön–Heldburg), except for the Kaiserstuhl volcanic complex, mostly comprise small and isolated occurrences or monogenetic volcanic fields, whereas the northern CEVP is dominated by large volcanic complexes and dyke swarms, which are mostly SiO$_2$-saturated to weakly SiO$_2$-undersaturated. In the northern CEVP, evidence of spatially varying but recurrent volcanic activity exists since the Eocene, lacking the distinct 20 Myr gap as documented from the southern CEVP. While the temporal and spatial distribution of volcanism are a result of the Cretaceous to Miocene tectonic evolution in Central Europe, further studies are needed to explain the petrographic differences between the two age groups in the south

In situ garnet U-Pb dating of granulitized eclogites from NE Sardinia, Italy

A sample from the Punta de li Tulchi granulitized eclogite, cropping out within the Variscan migmatites of NE Sardinia, was investigated by LA-ICPMS garnet U–Pb age dating. The majority of U-Pb analyses define a regression line with a lower intercept date of 395.1 ± 9.8 / 12.4 Ma. In addition, nine data points define a second regression line with a lower intercept date of 355.0 ± 18.1 / 19.4 Ma. The ~395 Ma age is interpreted to represent initial garnet growth during eclogite facies metamorphism. This age is another indication for an extensive subduction event at 380-400 Ma during the Variscan orogeny, as reported from other areas of the European Variscides. The ~355 Ma age is interpreted to indicate partial Pb-loss or fluid-mediated recrystallization of the garnet during the amphibolite to granulite facies metamorphism. This work demonstrates that in situ garnet U-Pb dating by LA-ICPMS is a powerful tool for deciphering the evolution of metamorphic rocks and that this method can provide valuable information and context for the interpretation of geochronological U-Pb data obtained from other geochronometers such as zircon

Upper Ordovician magmatism in the Central Pyrenees: First U-Pb zircon age from the Pallaresa Massif

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)The Late Ordovician magmatism is well represented in all massifs of the Eastern Pyrenees and the Catalan Coastal Ranges, which contain Upper Ordovician rocks. Nevertheless, data about this magmatic episode in the Central Pyrenees are scarce. This work shows the first geochronological data for Upper Ordovician magmatism in the Pallaresa massif. This massif is a large E-W trend antiformal structure included in the metamorphic structural units of the Pyrenean Axial Zone, where Cambro-Ordovician and Upper Ordovician rocks crop out. The Cambro-Ordovician rocks consist of a low-grade monotonous alternation of quartzites and slates with some limestone and conglomerate intercalations, which show evidence of a pre-Variscan penetrative deformation. The Upper Ordovician succession lies unconformably on the older Cambro-Ordovician beds and is represented by a siliciclastic succession with an intermediate limestone level. Volcanic rock levels have been observed interbedded within what was considered a Cambro-Ordovician succession close to outcrops of Upper Ordovician rocks in the eastern part of Pallaresa massif. Both metasedimentary and volcanic rocks were deformed and metamorphosed during the Variscan Orogeny.The volcanic rocks are rhyodacitic to dacitic crystal-rich meta-tuffs with a pervasive foliation. Their mineralogical composition is mainly volcanic quartz, feldspar and biotite. The matrix consists of fine grained of biotite, muscovite, quartz and clinozoisite, the latter mainly developed in highly deformed bands. In addition to these mineral phases, idiomorphic crystals of zircon are recognized.Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Oviedo, EspañaPeer reviewe

GEO_FPI Project. South Portuguese Zone mapping (SPZ). Preliminary data of the geochronological U-Pb study

O volume 18 de Geo-Temas reúne os resumos das comunicações apresentadas no "X Congresso Geológico de España", que decorreu em Vitoria-Gasteiz entre 5 e 7 de Julho de 2021.RESUMEN: La ZSP es la unidad geotectónica más al suroeste del Orógeno Varisco y se consideran los siguientes dominios: Pulo do Lobo (Frasniense inferior y Fameniense superior), Faja Pirítica Ibérica (Givetiense-Viseense superior), Grupo Flysch Baixo Alen tejo (Viseense superior-Moscoviense superior) y Grupo Suroeste (Estruniense-Bashkiriense medio). En el proyecto GEO_FPI se ha prestado especial atención a la Faja Pirítica Ibérica, ya que es una de las provincias metalogenéticas más importantes del mundo, con depósitos de sulfuros masivos (VHMS) e importantes recursos de Cu, Zn, Pb, Ag, Au, Sn, In, Se, Ge. Se ha realizado un trabajo de campo en común en la región fronteriza de España y Portugal para permitir una mejor inte gración y correlación de los datos geológicos y cartográficos. Además, se han seleccionado 31 afloramientos donde se han recogido muestras para realizar un estudio de geocronología de U-Pb en circón. Los datos de edad obtenidos son importantes para restringir las estructuras geológicas de la Faja Pirítica Ibérica que albergan la mineralización masiva de sulfuros y, por otra parte, mejoran la visión geotectónica de toda la ZSPABSTRACT: The SPZ is the south westernmost geotectonic unit of the Variscan Orogeny and the following domains are considered: Pulo do Lobo (early Frasnian and late-Famennian), Iberian Pyrite Belt (Givetian-late Visean), Baixo Alentejo Flysch Group (late Visean-late Moscovian) and Southwest Group (late Strunian-mid Bashkirian). Special work was performed in the Iberian Pyrite Belt considered one of the most important metallogenetic massive sulfides deposit provinces (VHMS) with significant Cu, Zn, Pb, Ag, Au, Sn, In, Se, Ge, resources. A common fieldwork has been carried out in the Spanish/Portuguese border region to allow a better integration and corre lation of geological and mapping data. In addition, 31 outcrops have been selected where samples have been collected for a geochronology study of U-Pb in zircon. The age data obtained are important to restrict the geological structures of the Iberian Pyrite Belt that contain the massive sulphide mineralization. On the other hand, improve the geotectonic vision of the entire SPZ.info:eu-repo/semantics/publishedVersio

Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from UPb dating and structural, petrographic and geochemical constraints

This study integrates field structural data, petrographic and geochemical (δ18O, δ13C, Δ47, 87Sr/86Sr, and elemental composition) analyses and U-Pb dating of calcite veins cutting the Bóixols-Sant Corneli anticline (Southern Pyrenees) in order to date and to investigate the spatio-temporal relationships between fluid flow and fold evolution. This E-W trending anticline grew from Late Cretaceous to Paleocene at the front of the Bóixols thrust sheet deforming pre-growth and growth sedimentary sequences. U-Pb dating reveals Late Cretaceous to late Miocene deformation ages, which agree with the age of growth strata deposition and the sequence of deformation interpreted from field and microstructural data. Dates coeval (71.2 ± 6.4 to 56.9 ± 1.4 Ma) and postdating (55.5 ± 1.2 to 27.4 ± 0.9 Ma) Upper Cretaceous to Paleocene growth strata are interpreted to record: (i) the growth of the Bóixols-Sant Corneli anticline during the Bóixols thrust emplacement, and (ii) the tightening of the anticline during the southern tectonic transport of the South-Central Pyrenean Unit. Other ages (20.8 ± 1.2 to 9.0 ± 4.6 Ma) postdate the folding event and have been associated with the collapse of the Bóixols-Sant Corneli anticline. The geochemistry of calcite veins indicates that the fluid flow behavior varied across the Bóixols-Sant Corneli anticline through its growth, showing a compartmentalized fluid system. In the hinge of the anticline and in the upper Santonian to middle Campanian syn-orogenic sequence along the footwall of the Bóixols thrust, the similar petrographic and geochemical features between all calcite cements and host rocks point towards a locally-derived or well-equilibrated fluid system. Contrarily, along large faults such as the Bóixols thrust, and in the anticline limbs, the geochemistry of vein cements indicates a different scenario. Cements in large faults yielded the lightest δ18O values, from −8 to −14 VPDB, and variable enrichment in δ13C, 87Sr/86Sr, elemental composition and δ18Ofluid. This is interpreted as the migration of fluids, through fault zones, that evolved from distinct fluid origins. Cements in the fold limbs exhibit δ18O and δ13C between −8 and −6 VPDB and between −10 and + 2 VPDB, respectively, the lowest Sr contents and the lowest precipitation temperatures, suggesting that the anticline limbs recorded the infiltration and evolution of meteoric waters. The paleohydrological system in the Bóixols-Sant Corneli anticline was restricted to the Bóixols thrust sheet. The Upper Triassic evaporitic basal detachment likely acted as a lower fluid barrier, preventing the input of fluids from deeper parts of the Pyrenean crustal thrust system. This study provides a well-constrained absolute timing of fracturing and fluid flow during basin inversion and folding evolution and highlights the suitability of U-Pb geochronology to refine the age of fractures and veins and their sequential evolution in orogenic belts