Geology of the Central Iberian and Galicia – Trás-Os-Montes zones in the Eastern part of the Morais Complex, Portugal/Spain

Texto principalmente en español, algunos capítulos en inglés.[EN] The Morais Allochthonous Complex (MAC) belonging to the Galicia Trás-os-Montes Zone, (GTMZ) is placed in the hinge zone of the Central Iberian Arc (CIA). Evidences of the pre- to syn-Variscan geological evolution of the NW Iberia are especially well exposed along the eastern rim of this first order structure, where this research work was achieved. Two major tectono-stratigraphic domains juxtaposed by a significant Variscan tectonic accident were redefined: the Schistose Domain of Galicia Trás-os-Montes (SDGTM) and Central Iberian Zone (CIZ). The first domain belongs to the lowermost tectonic slice of the different imbricated allochthonous units of the GTMZ. The SDGTM was settled over the CIZ during the Variscan C2 stage by the Main Trás-os-Montes Thrust (MTMT), and it is considered to be the least allochthonous unit (also called Parautochthonous or Peritransmontano Domain). Since the pre-variscan stratigraphic records of both domains are very similar, it is assumed that they must have been attached to the same continental margin but in different palaeogeographic locations, as their detrital zircon age populations point out. Both domains present a quite continuous and traceable Cambro-Silurian (?) stratigraphic sequence, although it underwent more Variscan deformation in the SDGTM than in its relative autochthonous (CIZ). In the CIZ the identification of two ichnofossil genera in the Desejosa Formation (Teichichnus rectus and Rosselia socialis) confirms that its upper part is at least uppermost-early Cambrian (Cambrian Stage 3), as previously proposed near the studied region with badly preserved trilobite remains (522Ma). A new stratigraphic unit (Montes Ermos formation, informal) was found concordantly overlaying the Desejosa Formation and lying below the Lower Ordovician unconformity (or Toledanic Unconformity) meaning that the uppermost record of the Slate and Greywacke Complex in Iberia could reach ages younger than Cambrian Stage 3. Over the Toledanic unconformity, a quite complete Lower-Middle Ordovician sequence was mapped, showing a laterally continuous and condensed Armorican Quartzite facies. At the base of the Upper Ordovician limestones of the Santo Adrião Formation another unconformity was identified, eroding the underlying units towards the Lower Ordovician formations, which locally eliminates the Middle Ordovician record (Moncorvo Formation). The youngest studied unit of the autochthonous domain recognized in this work is Silurian, but due to the strong C2 shearing that affects it no further assumptions on its age should be made. Although the pre-Variscan record of the SDGTM is intensely deformed under low metamorphic Barrovian conditions, it was possible to redefine its stratigraphy and the variscan structure based on field criteria and high resolution dating methods. With that purpose, two volcanic complexes were dated using U-Pb CA-ID-TIMS of magmatic zircon grains, proving the existence of two separated events in the same sedimentary sequence. The oldest, named Mora volcanics, is firstly described as a stratigraphic unit in this work. It presents a Furogian age (late Cambrian) and is characterized by a bimodal volcanic suite with sulphide mineralization. The youngest volcanic rocks dated in this thesis are Lower Ordovician. These are known as Saldanha Gneiss but the name Saldanha volcanics is preferably used. This unit is composed by porphyritic tuffs and rhyolites with calc-alkaline affinity. Since no important accident between these two volcanic complexes was identified, these ages add importance to the first order tectonic accident mapped at the base of the Upper Parautochthon, the MTMT, as Cambro-Ordovician rocks of the now proposed Mora-Saldanha Volcano-Sedimentary complex (MSVSc) are put over the Devono-Carboniferous synorogenic deposits of the Lower Parautochthon. The MSVSc is roofed by the white quartzite beds of the Algoso formation (informally proposed in this work) which is thought to be an equivalent to the Armorican Quartzite units of Iberia. Finally, the uppermost unit of the Upper Parautochthon studied in this work is composed by slates and basic to acid volcanic rocks with sulphide mineralization, known here as Peso formation (formerly as Vulcano- Siliceous Complex) and a possible correlation with the Middle Ordovician slaty units of Iberia is proposed. Along the boundary between the CIZ and the GTMZ, the two synorogenic deposits of the Lower Parautochthon Travanca and Vila Chã formations were detached over the autochthonous Silurian black slates and ampelites thus creating the Basal Lower Parautochthonous Detachment (BLPD) during the C2 Variscan phase. Because their zircon U-Pb age clusters are identical to the ones found in the pre-orogenic record of the SDGTM (and in the Basal Units) they were incorporated in the GTMZ. In this work it is proposed a new local tectono-stratigraphic sub-division of the SDGTM, where the synorogenic units define the Lower Parautochthon, whereas the pre-orogenic ones were included in the Upper Parautochthon. In this work it is also presented an integrated approach to the tectono-thermal evolution of the Variscan Orogeny in the eastern border of the MAC based on the regional study of macro and microscopic tectono-metamorphic fabrics. The first compressive event (C1) generated folding of both SDGTM and CIZ and marks the beginning of the prograde Barrovian evolution. Continuously the C2 event caused the thrusting of the Upper Parautochthon on top of the Lower creating the MTMT, and triggered the detachment of the synorogenic deposits over the CIZ along the BLPD. This event started the bending (CIA) of the previous C1 folds in both domains and it is thought to be related with the expansion of an extrusion wedge from the Variscan orogen axial zone. During this period the Barrovian metamorphism reached its peak. Following this initial compressional events, the instability of the thickened crust below the GTMZ, produced the synorogenic collapse and the formation of thermal domes (metamorphic core complexes) during the first extensional event (E1). This favoured the development of tectonic basins where the allochthonous complexes were preserved and the partial melt of the lower-middle crust while it was exhumed to upper crust conditions in the domes (following a Buchanian path). Immediately after the synorogenic extension a third compressive event (C3) generated disharmonic folding and lately fragile-ductile conjugate shear bands that led to the tightening of the CIA, and the formation of the Ibero-Armorican Arc. This event was accompanied by the intrusion of different granitic bodies. Finally, a late gravitational collapse (E2) followed by late-post Variscan compression (C4) produced gentle horizontal and vertical folding (respectively)[ES] El Morais alóctona Complex (MAC), perteneciente a la zona de Trás-os-Montes Galicia, (GTMZ) se coloca en la zona de articulación del Arco Centro-Ibérica (CIA). Evidencias de la pre-a sin-Varisco evolución geológica del NW de Iberia están especialmente expuestos a lo largo del borde oriental de esta primera estructura de orden, donde se logró este trabajo de investigación. Dos grandes dominios tectono-estratigráficas yuxtapuestas en un significativo accidente tectónico Varisco se redefinieron: el dominio esquistosa de Galicia Trás-os-Montes (SDGTM) y Zona Centro Ibérica (CIZ). El primer dominio pertenece a la rebanada tectónica más inferior de las diferentes unidades alóctonas imbricadas de la GTMZ. El SDGTM fue colocada sobre el CIZ durante la etapa C2 Varisco por el principal empuje Trás-os-Montes (MTMT), y es considerado como la unidad menos alóctona (también llamado parautóctonas o Peritransmontano Domain). Dado que los registros estratigráficos pre-Varisco de ambos dominios son muy similares, se supone se han adherido a la misma margen continental, pero en diferentes lugares paleogeográficas, como señalan sus poblaciones en edad de circón detrítico. Ambos dominios presentan una secuencia estratigráfica Cambro-Silúrico (?) Bastante continua y trazable, aunque sufrió una deformación más Varisco en el SDGTM que en su autóctona relativa (CIZ). En el CIZ la identificación de los dos géneros icnofósil en la Formación Desejosa (Teichichnus recto y Rosselia socialis) confirma que su parte superior es al menos superior-Cámbrico inferior (Cámbrico Etapa 3), tal como se propone anteriormente, cerca de la zona de estudio con mal conservado restos trilobite (522Ma). Se encontró una nueva unidad estratigráfica (formación Montes Ermos, informal) concordantemente superponer la Formación Desejosa y acostado debajo de la discordancia Ordovícico Inferior (o disconformidad Toledanic), que significa que el registro más alto de la pizarra y del Complejo Greywacke en Iberia podría llegar a edades más jóvenes que Cámbrico Stage 3. Durante la discordancia Toledánica, una bastante completa secuencia del Ordovícico Inferior-Medio se asignó, mostrando lateralmente continuas y condensadas facies cuarcita Armórica. En la base de las calizas del Ordovícico Superior de la Formación Santo Adrião otra discordancia fue identificada, erosionando las unidades subyacentes a las formaciones del Ordovícico inferior, lo que elimina localmente el registro Ordovícico Medio (Formación Moncorvo). La unidad más joven estudiada del dominio autóctona reconocida en este trabajo es Silúrico, pero debido a la fuerte cizalladura C2 que le afecta ninguna otra hipótesis sobre su edad debe hacerse. Aunque el registro de pre-Varisco del SDGTM es deformado intensamente en condiciones Barrovian bajo metamórficos, fue posible redefinir su estratigrafía y la estructura Varisca en base a criterios de campo y los métodos de datación de alta resolución. Con ese fin, dos complejos volcánicos fueron fechados con U-Pb CA-ID-mas de circones magmáticos, lo que demuestra la existencia de dos eventos separados en la misma secuencia sedimentaria. El más antiguo, llamado Mora volcánicos, se describe en primer lugar como una unidad estratigráfica en este trabajo. Presenta una edad Furogian (finales del Cámbrico) y se caracteriza por una serie volcánica bimodal con mineralización de sulfuro. Las rocas volcánicas más jóvenes de fechas en esta tesis son Ordovícico Inferior. Estos son conocidos como Saldanha gneis pero el nombre Saldanha volcánicas se utiliza preferentemente. Esta unidad está compuesta por tobas porfídicas y riolitas con afinidad calco-alcalina. Desde que se identificó ningún accidente importante entre estos dos complejos volcánicos, estas edades suman importancia a la primera orden accidente tectónico asignado en la base de la Parautochthon Superior, el MTMT, como Cambro-Ordovícico rocas de la Mora-Saldanha complejo Volcano-sedimentaria que ahora se propone (MSVSc) se colocan en los depósitos sinorogénicos Devono-Carbonífero del Parautochthon Baja. El MSVSc está cubierta por las camas blancas de la cuarcita de la formación Algoso (informalmente se propone en este trabajo), que se cree que es el equivalente a las unidades de cuarcita armoricanas de Iberia. Por último, la unidad superior de la Parautochthon superior estudiado en este trabajo está compuesto por pizarras y básicas a las rocas volcánicas ácidas con mineralización de sulfuro, conocida aquí como la formación de Peso (anteriormente como Complejo Vulcano-silícea) y una posible correlación con las unidades pizarrosas del Ordovícico Medio Se propone de Iberia. A lo largo de la frontera entre el CIZ y GTMZ, los dos depósitos sinorogénicos del Bajo Parautochthon Travanca y Vila Chã formaciones fueron separados en los autóctonos pizarras del Silúrico negros y ampelitas creando así el Basal Destacamento parautóctonas inferior (BLPD) durante la fase C2 Varisco. Debido a que sus grupos de edad U-Pb en circones son idénticos a los encontrados en el registro de pre-orogénica del SDGTM (y en las unidades basales) que se incorporaron en el GTMZ. En este trabajo se propone un nuevo tectono-estratigráfico sub-división local del SDGTM, donde las unidades sinorogénicos definen el Parautochthon inferior, mientras que los pre-orogénicos se incluyeron en el Parautochthon superior. En este trabajo también se presenta un enfoque integrado de la evolución tectono-térmica de la orogenia Hercínica en la frontera oriental de la MAC basado en el estudio regional de la macro y tejidos tectono-metamórficos microscópicas. El primer evento de compresión (C1) genera plegamiento tanto SDGTM y CIZ y marca el comienzo de la evolución Barrovian progrado. Continuamente el caso de C2 causó el empuje de la Parautochthon superior en la parte superior de la inferior de la creación de la MTMT, y provocó el desprendimiento de los depósitos sinorogénicos más de la CIZ lo largo de la BLPD. Este evento se inició la flexión (CIA) de los pliegues C1 anteriores en ambos dominios y que se cree que está relacionada con la expansión de una cuña de extrusión a partir de la zona axial orógeno Varisca. Durante este período, el metamorfismo Barrovian alcanzó su pico. A raíz de estos eventos iniciales de compresión, la inestabilidad de la corteza engrosado debajo de la GTMZ, produjo el colapso sinorogénicos y la formación de cúpulas térmicas (complejos de núcleo metamórficas) durante el primer evento de extensión (E1). Esto favoreció el desarrollo de las cuencas tectónicas donde se conservan los complejos alóctonos y la fusión parcial de la corteza media-baja, mientras que fue exhumado a las condiciones de la corteza superior de las cúpulas (siguiendo un camino Buchanian). Inmediatamente después de la extensión sinorogénicos un tercer evento de compresión (C3) generó plegamiento inarmónico y últimamente bandas de cizalla conjugadas frágil-dúctil que condujeron a la tensión de la CIA, y la formación del Arco Ibero-Armórica. Este evento estuvo acompañado por la intrusión de los diferentes cuerpos graníticos. Finalmente, un último colapso gravitacional (E2), seguida por la compresión tarde-post Varisco (C4) produjo plegado horizontal y vertical suave (respectivamente

Palynology, stratigraphy and geometry of the Pennsylvanian continental Santa Susana Basin (SW Portugal)

The continental Pennsylvanian Santa Susana Basin (SSB) is located along an important N-S strike shear zone (Santa Susana Shear Zone - SSSZ) that separates the Ossa-Morena and South Portuguese Zones (SW Portugal). This shear zone controlled the sedimentation of the basin and probably its post-sedimentary evolution. The lower (basal) unit is mostly conglomeratic and is known essentially from drill-hole data while the upper unit, that covers most of the current surface area, is composed by sandstones, shales and some coal beds. Fluvial sedimentary rocks seem to prevail, but evidences of lacustrine sedimentation can be found in restricted areas within the upper unit. Palynological data indicate that at least part of the sedimentation took place during the Early Kasimovian (Cantabrian) but the sporomorph content of different localities suggest that significantly older sediments (Late Moscovian-Early Bashkirian) may be present. Geometrical, structural, and cartographical evidences indicate that the SSB formed as a pull-apart basin along the SSSZ and was later partially uplifted during latest Varsican and Alpine orogeniesGalp Energia E&P, PortugalCentro de Geologia da Universidade de Lisboa, PortugalUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaCentro de Geofísica de Évora, Universidade de Évora, PortugalLaboratorio de Investigação em Rochas Industriais e Ornamentais, Universidade de Évora, Portuga

An overview on the Ordovician volcanic rocks and unconformities in the Central Iberian and Galicia-Trás-os-Montes Zones of the Iberian Variscan Massif

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)New detailed continuous digitalized maps (1:50.000 scale Geode program of the Spanish Geological Survey: IGME) facilitate an innovative regional approach to the Ordovician unconformities and volcanic rocks interbedded in the sequence (Clariana García et al., online; Villar Alonso et al., online). For this work, these maps have been actualized by up to date references from Spain and Portugal. At the selected areas of the Variscan Massif, two main Ordovician unconformities are generally described: (known ad the Toledanic and Sardic) but the regional approach unveils different stratigraphic positions at the diverse sectors. Besides, a new picture on the vulcanite abundance and variety arises. The general advances in geochronology and geochemistry of the interbedded volcanic bodies have been very useful to correlate the effusive events all over the vast area covered by this review (Coke et al., 2011; Dias da Silva et al., 2014, 2015; Díez Montes, 2007; Talavera et al., 2013).Unidad de Salamanca, Instituto Geológico y Minero de España, EspañaInstituto Dom Luis, Universidade de Lisboa, PortugalInstituto Geológico y Minero de España, EspañaPeer reviewe

U/Pb age of a large dacitic block locked in an Early Carboniferous synorogenic mélange in the Parautochthon of NW Iberia: New insights on the structure/sedimentation Variscan interplay

At the NW of the Iberian Variscan Massif the Parautochthon is envisaged as an intervening structural unit located between the far-traveled allochthonous stacked units and the autochthon. It has been recently divided in two structural slices; the Upper constitutes a repetition of the upper Cambrian to Silurian sequence of the Central Iberian Zone autochthon, while the Lower has been proposed as a thick Variscan synorogenic deposit. A large volcanic block embedded in the uppermost Devonian–lower Carboniferous Lower Parautochthon yields an U/Pb age of 497 ± 2 Ma (upper Cambrian). This age, joined to the petrographic features and the chemical composition, supports the provenance area for the large glided block in the Upper Parautochthon, where a magmatic event of similar age and characteristics has been identified. This source area for the slid block reinforces the idea of a mélange developed in the synorogenic trough at the front of a main thrust structure, which over thrusts the Upper Parautochthon on top of the Lower Parautochthon.Unidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Salamanca, EspañaInstituto Dom Luiz, Universidade de Lisboa, PortugalGeology and Geography Department, Tomsk State University, Rusi

Tangled up in folds: tectonic significance of superimposed folding at the core of the Central Iberian curve (West Iberia)

<p>The amalgamation of Pangea during the Carboniferous produced a winding mountain belt: the Variscan orogen of West Europe. In the Iberian Peninsula, this tortuous geometry is dominated by two major structures: the Cantabrian Orocline, to the north, and the Central Iberian curve (CIC) to the south. Here, we perform a detailed structural analysis of an area within the core of the CIC. This core was intensively deformed resulting in a corrugated superimposed folding pattern. We have identified three different phases of deformation that can be linked to regional Variscan deformation phases. The main collisional event produced upright to moderately inclined cylindrical folds with an associated axial planar cleavage. These folds were subsequently folded during extensional collapse, in which a second fold system with subhorizontal axes and an intense subhorizontal cleavage formed. Finally, during the formation of the Cantabrian Orocline, a third folding event refolded the two previous fold systems. This later phase formed upright open folds with fold axis trending 100° to 130°, a crenulation cleavage and brittle–ductile transcurrent conjugated shearing. Our results show that the first and last deformation phases are close to coaxial, which does not allow the CIC to be formed as a product of vertical axis rotations, i.e. an orocline. The origin of the curvature in Central Iberia, if a single process, had to be coeval or previous to the first deformation phase.</p

Furongian-Late Ordovician volcanism in the Upper Parautochthon of the Galicia-Trás-os-Montes Zone (NE Portugal): Paleogeographic meaning and geodynamic se

Ordovician geodynamics: The Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs International Meeting (2017. Figueras, España)In NE Portugal, the Upper Parautochthon (UP) of the Galicia‐Trás‐os‐Montes Zone (GTMZ) displays one of the best exposures of the Furongian‐Late Ordovician magmatic record, with a voluminous and temporally continuous volcanism, which is interbedded in a sedimentary sequence equivalent to the nearby autochthon, the Central Iberian Zone (CIZ) (Dias da Silva et al., 2014, 2015, 2016). This unit is structurally below the Morais Complex (Pereira et al., 2006); a thin‐skinned tectonic pile composed, from bottom to top, by three units: the Lower, Middle (ophiolitic) and Upper Allochthons (Ballèvre et al., 2014). The UP structurally overlies an intervening Variscan synorogenic unit (the Lower Parautochthon, LP), which separates the GTMZ from the CIZ (Fig. 1).Instituto Dom Luiz, Universidade de Lisboa, PortugalUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaUniversidad de Salamanca, EspañaPeer reviewe

Thrust geometry and the location of gneiss domes: implications of thermal models of the Central Iberian crustal domain during the Variscan

England and Thompson (1984) and Peacock (1989) developed a method to produce thermal models of the pressuretemperature-time (P-T-t) paths of regional metamorphism in thickened continental crust. Their models place the physical conditions undergone by rocks initially at different depths in a temporal frame and permit a better understanding of the orogenic processes involved. One common response to thickening that is observed in orogenic belts is the formation of gneiss domes (Whitney et al., 2004). Gneiss domes are an important feature of the Iberian crust affected by the Variscan orogeny and are abundant in the core of the Central Iberian arc (Martínez Catalán, 2011). Recent investigations (Rubio Pascua,l 2012) in the Central Iberian zone (CIZ) provide data that can be used to constrain thermal models and to evaluate the model response to changes in basic parameters and in the geometry of structural evolutionDepartment of Geosciences, Penn State, Estados UnidosInstituto Geológico y Minero de España, EspañaDepartamento de Geología, Universidad de Salamanca, EspañaUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartamento de Petrología y Geoquímica, Universidad Complutense de Madrid, EspañaInstituto de Geociencias, Consejo Superior de Investigaciones Científicas, EspañaInstituto de Geociencias, Universidad Complutense de Madrid, Españ

The late Variscan HT/LP metamorphic event in the Iberian branch of the Variscides: Relationships with crustal thickening, nappe emplacement, orocline development, and crustal evolution

Late Variscan metamorphism in the Iberian Massif is characterized by high-T and low-P associations overprinting a Barrovian zonation developed during -and partly following- crustal thickening related to the Variscan collision. The highgrade rocks, commonly reaching sillimanite-K feldsparmuscovite out parageneses and locally even granulitic (biotite out) conditions, crop out at the core of gneiss domes where partial melting, migmatite development and syn-kinematic granitoids are abundant. Gneiss domes are often bounded on top by ductile detachments that, like the domes, formed during an extensional phase of deformation reflecting thermal relaxation and the subsequent collapse of the thickened continental crustDepartamento de Geología, Universidad de Salamanca, EspañaInstituto Geológico y Minero de España, EspañaUnidad de Salamanca, Instituto Geológico y Minero de España, EspañaDepartment of Geosciences, Penn State, Estados Unido