The Cretaceous alkaline magmatism in northeast Iberia. Igneous processes and geodynamic implications

Durante la apertura del océano Atlántico, responsable de la ruptura del supercontinente Pangea, la apertura del Golfo de Vizcaya provocó la rotación y separación de Iberia respecto de Europa. Este evento condicionó el desarrollo de un magmatismo alcalino, previo al inicio de la colisión alpina que desencadenó la elevación de la cadena pirenaica entre Iberia y Europa. Dicho magmatismo alcalino es de edad cretácica y hoy se reconoce en los Pirineos y en el margen septentrional de las Cadenas Costero Catalanas. Sin embargo, no existen, hasta la fecha, estudios completos ni comparativos de estas rocas. Esto contrasta con su enorme interés científico, pues suponen una preciada fuente de información acerca del controvertido contexto geodinámico, así como de los procesos ígneos relacionados con la generación de fundidos en el manto y su ascenso a través de la corteza. Así, la presente Tesis Doctoral comprende la petrología, mineralogía, geoquímica y geocronología del magmatismo cretácico en todo el noreste de Iberia, incluyendo afloramientos en los Pirineos y con especial énfasis, en el margen septentrional de las Cadenas Costero Catalanas, ya que este dominio ha sido menos estudiado. Se han obtenido nuevas edades 40Ar/39Ar que actualizan los datos previos y delimitan temporal y geográficamente la provincia ígnea. Además, la edad del magmatismo, asociado a un rifting continental, aporta nuevos argumentos a considerar para evaluar las teorías sobre la evolución geodinámica del límite Iberia-Europa, tanto respecto a la apertura del Golfo de Vizcaya como al inicio de la compresión alpina. El estudio de la composición de las rocas en elementos mayores, elementos traza y relaciones isotópicas de Sr-Nd-Pb revela una signatura heterogénea y enriquecida del manto en este dominio, que podría haber perdurado desde el final de la orogenia varisca hasta el cuaternario. La composición de los minerales en elementos mayores y traza, junto con las estimaciones barométricas realizadas, informan de manera muy detallada acerca del origen de las poblaciones de cristales, complejas, que se observan en las rocas, revelando procesos de recarga y mezcla de magmas en profundidad y la incorporación de cristales heredados en magmas ascendentes hacia la superficie terrestre. Estos datos permiten reconstruir la historia de los procesos que tuvieron lugar en el sistema de alimentación durante el ascenso de los magmas y su evolución en cámaras magmáticas. En este trabajo se realiza la primera cuantificación de la influencia de cristales heredados (tipo antecristal) en la composición global de las rocas en las que se encuentran. El modelo geoquímico desarrollado muestra que la acumulación de antecristales máficos provoca modificaciones significativas en las composiciones de roca total, y esto cuestiona la interpretación tradicional de las composiciones magmáticas "primitivas", así como las ideas sobre procesos de acumulación gravitatoria de cristales y zonación composicional en cuerpos ígneos. La aplicación, en esta tesis, de métodos matemáticos como la elaboración de modelos cuantitativos y el análisis estadístico de componentes principales al tratamiento de datos geoquímicos, es novedosa en este campo científico y abre el camino a una mejor evaluación de hipótesis petrológicas en base a datos geoquímicos completos, proporcionando una metodología de trabajo potencialmente aplicable al estudio de sistemas ígneos. Finalmente, es importante destacar que los datos geoquímicos cobran todo su significado únicamente cuando se comprende, en detalle, la petrología de las rocas y las condiciones de equilibrio entre los minerales y el fundido que los engloba. Esto, además, lleva al cálculo, por primera vez, de un conjunto internamente consistente de coeficientes de reparto de elementos traza para clinopiroxeno y anfíbol en fundidos de tipo lamprófido alcalino (camptonita)

Age of the Cretaceous alkaline magmatism in northeast Iberia: implications for the Alpine cycle in the Pyrenees

Cretaceous magmatism in northeast Iberia is related to the opening of the Bay of Biscay and counterclockwise rotation of Iberia with respect to Europe and predates the collision between Iberia and Europe that resulted in the formation of the Pyrenees. To better constrain the age of this magmatism, we have undertaken a Ar/Ar study on samples from the Pyrenees and the Catalonian Coastal Ranges. In the Basque-Cantabrian Basin and the North Pyrenean Basins, we have obtained Albian ages (ca. 102 Ma). In the northern Catalonian Coastal Ranges, we have obtained Campanian ages (ca. 79 Ma). We integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance. The Cretaceous magmatism in the Pyrenees is Albian-Santonian (mostly occurring between 105 to 85 Ma) and was emplaced in a tectonically unclear context after the opening of the Bay of Biscay and rotation of Iberia. The magmatism in the Catalonian Coastal Ranges is well constrained to ca. 79 Ma and could mark the onset of Alpine shortening in the Pyrenean realm in northeasternmost Iberia. Finally, we describe a Late Triassic (ca. 232 Ma)-Early Jurassic (ca. 180 Ma) phase of magmatism in the Central Pyrenees, previously considered to be Cretaceous, that widens temporally and geographically the extent of the rift-related alkaline magmatism in southwestern Europe at that time. Key Points New Ar/Ar data update the age of the Cretaceous magmatism in NE Iberia Magmatism in the Pyrenees postdates the rotation of Iberia Magmatism in the Catalonian Coastal Ranges could mark the onset of Alpine shortenin

Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

Sector-zoned clinopyroxene is common in igneous rocks, but has been overlooked in the study of magmatic processes. Whilst concentric zoning is commonly used as a record of physicochemical changes in the melt feeding crystal growth, clinopyroxene is also highly sensitive to crystallisation kinetics. In sector-zoned crystals, the fidelity of compositional changes as recorders of magma history is dubious and the interplay between thermodynamic and kinetic controls remains poorly understood. Here we combine electron probe and laser ablation micro-chemical maps of titanaugite crystals from Mt. Etna (Sicily, Italy) to explore the origin of sector zoning at the major and trace element levels, and its implications for the interpretation of magmatic histories. Elemental maps afford the possibility to revisit sector zoning from a spatially controlled perspective. The most striking observation is a clear decoupling of elements into sectors vs. concentric zones within single crystals. Most notably, Al-Ti enrichments and Si-Mg depletions in the prism sectors {1 0 0}, {1 1 0} and {0 1 0} relative to the hourglass (or basal) sectors {−1 1 1} correlate with enrichments in rare earth elements and highly charged high field strength elements due to cation exchanges driven by kinetic effects. In contrast, transition metals (Cr, Ni, Sc) show little partitioning into sectors and strong enrichments in concentric zones following resorbed surfaces, interpreted as evidence of mafic recharge and magma mixing. Our results document that kinetic partitioning has minor effects on the compositional variations of cations with low charge relative to the ideal charge/radius of the structural site they occupy in the clinopyroxene lattice. We suggest that this may be due to a lower efficiency in charge balance mechanisms compared to highly charged cations. It follows that compatible metals such as Cr can be considered trustworthy recorders of mafic intrusions and eruption triggers even in sector-zoned crystals. We also observe that in alkaline systems where clinopyroxene crystallisation takes place at near-equilibrium conditions, sector zoning should have little effect on Na-Ca partitioning and in turn, on the application of experimentally calibrated thermobarometers. Our data show that whilst non-sector-zoned crystals form under relatively stagnant conditions, sector zoning develops in response to low degrees of undercooling, such as during slow magma ascent. Thus, we propose that the chemistry of sector-zoned crystals can provide information on magma history, eruption triggers, and possibly ascent rates

El enjambre sub-vertical de diques de lamprófido de Aiguablava (Cadenas Costero-Catalanas): petrología y composición

En este trabajo presentamos un estudio petrológico detallado de algunos de los diques de lamprófido sub-verticales de edad Pérmica del complejo intrusivo de Aiguablava (Cadenas Costero Catalanas). Aportamos nuevos datos composicionales, tanto en minerales (elementos mayores) como en roca total (elementos mayores y traza), de algunos de los diques más inalterados. Del estudio realizado se deduce que todos los magmas lamprofídicos estudiados tienen un origen común, si bien presentan un pequeño rango de fraccionamiento, en el que diferenciamos tres etapas relacionadas con tres pulsos magmáticos. Según nuestros datos, algunos de los diques considerados anteriormente como espesartitas de afinidad calco-alcalina podrían tener una afinidad transicional (de subalcalina a alcalina

Megacristales de kaersutita en los diques máficos alcalinos del plutón de Panticosa (Zona Axial Pirenaica): xenocristales de origen profundo

Megacrysts of kaersutite have been identified in several alkaline mafic dikes from the Panticosa pluton. They show strongly anhedral habits and resorption features, including Krs overgrowths and/or Cpx-Opq coronae. Chemically, the liquid in equilibrium with the megacryst cores is clearly different from the host alkaline dikes. In contrast, the liquid in equilibrium with Krs overgrowths and Cpx from the coronae agrees with the composition of some of the host alkaline dikes. According to the obtained results, Krs megacrysts must be considered xenocrysts. Therefore, their Middle Permian age (268 Ma) predates the emplacement of the alkaline dikes. The xenocrysts crystallised at about 30 km depth and were afterwards reequilibrated at lower depthsEn los diques máficos alcalinos del plutón de Panticosa se han identificado megacristales de kaersutita.Muestran hábitos anhedrales y características típicas de reabsorción, así como recrecimientos de Krs y de una corona de Cpx y Opq. Los fundidos en equilibrio con los núcleos de Krs son muy distintos de los diques alcalinos que los contienen, mientras que los fundidos en equilibrio con los recrecimientos de Krs y los Cpx de las coronas son similares a algunos de los diques. Por lo tanto, los megacristales de Krs son xenocristales y su edad, Pérmico Medio (268 Ma), es previa a la edad de emplazamiento de los diques. Los xenocristales se formaron a unos 30 km de profundidad y se reequilibraron a menor profundida

The lamprophyre dikes in the Panticosa Pluton (Pyrenean Axial Zone): syn-emplacement with later-hercynian extension

El Plutón de Panticosa muestra dos grupos de diques de lamprófido con afinidades calcoalcalina y alcalina, emplazados en el intervalo Pérmico inferior y medio. Para estos diques, no se observa una clara relación entre sus orientaciones, dimensiones y composición. El análisis cinemático de los diques permite obtener una dirección de extensión próxima a N-S, compatible con la orientación del vector desplazamiento medido en campo. Los datos estructurales relacionados con la geometría de los diques y su cinemática y el patrón de fracturación del granito encajante permite proponer un modelo de emplazamiento para ambos litotipos dentro de un contexto extensional. Este modelo contempla tanto el emplazamiento del magma calcoalcalino (Pérmico inferior) asociado a fusión cortical, como el del magma alcalino (Pérmico medio), de carácter astenosférico. Este régimen extensional es posterior al régimen transpresivo de edad Carbonífero superior responsable del emplazamiento y fracturación del plutón graníticoThe Panticosa Pluton shows two groups of lamprophyre dykes with calcalkaline and alkaline affinities, which are emplaced during the Lower-Middle Permian interval. A clear relationship between their orientations, dimensions and composition does not occur. The kinematic analysis of the dykes gives a near N-S extension direction compatible with the orientation of the displacement vector measured in the field. The structural data related to the dyke geometry and kinematics and the fracturing pattern of the granitic pluton allow to propose an emplacement model for both lithotypes within a common extensional framework; this model includes both the former Lower Permian calc-alkaline magma, affected by crustal contamination and the Middle Permian mantle alkaline magma. This extensional regime post-dates the Upper Carboniferous transpressive regime responsible for the emplacement and fracturing of the granitic pluto

Olivine major and trace element compositions coupled with spinel chemistry to unravel the magmatic systems feeding monogenetic basaltic volcanoes

Monogenetic basaltic volcanic systems, despite their considerable smaller size and shorter lifetime compared to polygenetic volcanoes, can have complex pre-eruptive histories and composite volcanic facies architectures. Their source-to-surface investigation is essential for our better understanding of monogenetic volcanism and requires high-resolution mineral-scale analyses. In this study, we focus on diversely zoned olivine crystals and their spinel inclusions from alkaline basaltic volcanics that are the result of mixing of numerous magmas, crystals and fragments of various origins. The Fekete-hegy volcanic complex is one of the largest and most composite eruptive centers in the intracontinental monogenetic Bakony–Balaton Highland Volcanic Field (western Pannonian Basin, Eastern Central Europe). It is a compound multi-vent system built up by multiple eruption episodes: initial maar-forming phreatomagmatic eruptions were followed by massive lava flows and magmatic explosive activity. We performed stratigraphically controlled sampling in order to reveal the history of the successively erupted magma batches represented by the distinct eruptive units, as well as to discover the petrogenetic processes that controlled the evolution of the magmatic system. The juvenile pyroclasts of the phreatomagmatic eruption products (unit 1) contain a remarkably diverse mineral assemblage including five different olivine types and three distinct spinel groups. In addition, they comprise various xenoliths. Based on detailed textural investigations combined with in situ electron microprobe analyses, high-resolution laser ablation ICP-MS trace element mapping and single spot measurements on the variably zoned olivines of unit 1 samples, eight distinct environments are inferred to have been involved in their formation. Four of these environments account for the significant compositional variation of the olivine-hosted spinel inclusions. A complex set of open- and closed-system petrogenetic processes operated during the evolution of the magmatic system: magma stalling, accumulation, storage, fractionation, mixing, replenishments, cumulate remobilization, incorporation of foreign fragments and crystals from the wall rocks. All these diverse environments and processes resulted in the mixed character of the erupted magmas during the initial phreatomagmatic eruptive phase. In contrast, the uniform petrological features and the small variations shown by the olivines and spinels from unit 2‐–3 indicate that the later magmatic explosive – effusive phase was preceded by a considerable change in the magmatic system; it experienced a simple evolution through olivine + spinel fractional crystallization without any of the complexities seen during the initial phase. The present study emphasizes the importance of high-resolution mineral-scale textural and chemical investigations to unravel the complexity of the sub-volcanic magmatic systems feeding monogenetic basaltic volcanoes. Compared to the application of whole-rock geochemistry alone, this approach enables a direct and more detailed insight into the architecture and evolution of these systems

Stratigraphy and petrology of the Baix Ebre volcanic region (Tarragona, Spain): magmatic stages and age

El estudio estratigráfico y petrológico del conjunto de afloramientos basálticos de la región del Baix Ebre (Tarragona), permite confirmar un vulcanismo alcalino pluriepisódico acontecido durante el Triásico Superior. Pueden distinguirse dos etapas principales en función del estilo eruptivo predominante: una inicial hidromagmática, emplazada en el Keuper basal, y otra estromboliana que llega al techo del Keuper, por debajo de la Fm. Dolomías de Imón (Retiense). En esta última etapa los materiales masivos, emplazados en forma de sills, transportan xenolitos mantélicos, más abundantes en el sector occidental. En Prat de Compte es donde se da la mayor abundancia modal de xenolitos, y con diámetro máximo, siendo tal vez el lugar más próximo al foco magmático principalThe stratigraphic and petrological study of basaltic outcrops in the Baix Ebre volcanic region (Tarragona, Spain) indicates the development of a pluriepisodic alkaline volcanism during the Late Triassic. Two magmatic stages can be recognised based on the main eruptive style: an initial hidromagmatic stage emplaced within the basal Keuper and a strombolian stage emplaced into the upper Keuper, always below the Imón Fm. (Rhaetian). In this last stage massive igneous bodies (sills) carried xenoliths, which are more abundant in the western part of the studied sector.We thimk that the magmatic centre was probably situated close to Prat de Compte, given that in this area there is a greater modal abundance of xenoliths, showing the maximum diamete

Volcanic crystals as time capsules of eruption history

Crystals formed prior to a volcanic event can provide evidence of processes leading to and timing of eruptions. Clinopyroxene is common in basaltic to intermediate volcanoes, however, its ability as a recorder of pre-eruptive histories has remained comparatively underexplored. Here we show that novel high-resolution trace element images of clinopyroxene track eruption triggers and timescales at Mount Etna (Sicily, Italy). Chromium (Cr) distribution in clinopyroxene from 1974 to 2014 eruptions reveals punctuated episodes of intrusion of primitive magma at depth. Magma mixing efficiently triggered volcanism (success rate up to 90%), within only 2 weeks of arrival of mafic intrusions. Clinopyroxene zonations distinguish between injections of mafic magma and regular recharges with more evolved magma, which often fail to tip the system to erupt. High Cr zonations can therefore be used to reconstruct past eruptions and inform responses to geophysical signals of volcano unrest, potentially offering an additional approach to volcano hazard monitoring

Days to weeks of syn-eruptive magma interaction : High-resolution geochemistry of the 2002-03 branched eruption at Mount Etna

Eruption onset, style and duration are governed, in part, by the movement and interaction of distinct magma bodies at depth. High-resolution investigation of erupted products can retrospectively inform our understanding of such processes and improve future interpretation of real-time monitoring signals. In 2002-03, Mount Etna (Italy) erupted two elementally and isotopically distinct magmas simultaneously, providing a unique opportunity to explore magma transport and evolution through complex, well-documented and monitored volcanic activity. In this study, melt chemistry (groundmass fraction as opposed to whole-rock) and mineral zoning (X-ray fluorescence mapping and electron microprobe) are treated as separate recorders of magma history tracking syn- and pre-eruptive processes, respectively. Elemental mapping of entire thin sections revealed a largely antecrystic, hybrid crystal cargo hosting reverse-zoned clinopyroxene and olivine, supporting extensive magma mixing in southern flank conduits. Antecryst-free groundmass chemo-stratigraphies reveal melt compositional variations on timescales of days to weeks. In agreement with previous whole-rock studies, we find that during the early-middle stages of activity, melt erupted on the southern flank was rich in MgO, CaO, Cr, Ni, and radiogenic-Sr, and depleted in Al2O3, Na2O, La, Zr, relative to its north-eastern counterpart. In addition, high resolution tracking of melt composition reveals a progressive shift to increasingly evolved compositions over the course of the S-rift eruption. A corresponding shift in 87Sr/86Sr isotope ratios (0.70366 to 0.70358) across the same period implies progressive mixing of isotopically distinct magmas as the main driver of the observed compositional change. In contrast, NE-rift products lack evidence of mixing in both melt and mineral records, in agreement with previous work suggesting geodynamically controlled draining of shallow, isolated magma pockets. Comparing recharge-to-eruption timescales derived from mineral zonation with real-time monitoring data and groundmass compositional data, we show that the onset of magma mixing in the S-rift coincided with a deep seismic event (8-18 km) and was followed by the ascent of undegassed magma approximately 2 months before eruption onset. Finally, we demonstrate that high-resolution temporal changes in melt composition, approached through melt geochemistry, are closely linked to eruption intensity and SO2 emission. We suggest that composition and explosivity on the southern rift fluctuated in response to multiple phases of recharge-mixing-hybridisation between undegassed ‘eccentric’ magma and a degassed resident magma at 3-5 km depth. Our results highlight that high-resolution geochemistry can improve our understanding of deep magmatic processes driving eruption onset, duration and intensity. Rapid analysis of melt composition integrated with traditional monitoring approaches could improve future hazard response at Mount Etna and active volcanoes globally.</p