U-Pb geochronology of detrital and igneous zircon grains from the Águilas Arc in the Internal Betics (SE Spain): Implications for Carboniferous-Permian paleogeography of Pangea

New U–Pb detrital zircon and U–Pb zircon ages of metaigneous rocks in the Águilas Arc (Betic Chain, SE Spain) allow us to determine the maximum depositional ages of the rocks. Within the Nevado-Filábride Complex, a Late Carboniferous depositional age for the Lomo de Bas schists and quartzites, and a Permian-Triassic maximum depositional age for the Tahal Fm are determined. Within the Alpujárride Complex, the maximum depositional age of the Micaschists and Quartzite Fm is Late Carboniferous and the Meta-detrital Fm was deposited in the Early Permian. Furthermore, the maximum depositional age of the Saladilla Fm in the Maláguide Complex is also Early Permian. The age distribution patterns for the Carboniferous rocks of the Nevado-Filábride and Alpujárride complexes are similar to those from the Cantabrian Zone of the Iberian Massif, suggesting deposition in Carboniferous foreland basins located eastwards of the Iberian Massif. However, age patterns in Maláguide and samples from the North-eastern Iberian Peninsula and South France show strong similarities suggesting that it can be located near those areas in the Late Carboniferous times. The samples with Early Permian maximum depositional ages from the three complexes contain more Paleozoic zircon grains relative to the older Carboniferous samples, but have similar age distribution patterns, suggesting that they were deposited in the same basin. Samples from unconformable Middle Miocene sediments have Early Permian youngest zircon populations and age distribution patterns corresponding to a mixing of detrital zircon grains from the Alpujárride and Maláguide complexes. Furthermore, there is no record of any major felsic rocks formation and/or exhumation event after the Early Permian in those two complexes

Olivine-rich veins in high-pressure serpentinites: A far-field paleo-stress snapshot during subduction

Field observations within the Atg-serpentinite domain of the subducted ultramafic massif from Cerro del Almirez (SE Spain) reveal the existence of two generations of abundant olivine-rich veins formed as open, mixed mode and shear fractures during prograde metamorphism. Type I veins were synchronous with the development of the serpentinite main foliation (S1) and shearing, whereas Type II veins post-date the S1 surfaces. These structural relationships indicate that, while the Atgserpentinites underwent ductile plastic deformation at temperatures of 450◦-600 ◦C and pressures of 0.7–1.7 GPa, they also experienced punctuated brittle behaviour events. The brittle fractures were most likely due to fluid overpressures formed by release of H2O during the brucite breakdown reaction for the case of Type I veins (2 vol % H2O) and due to a combination of minor dehydration reactions related to continuous compositional and structural changes in antigorite (0.3 vol % H2O) for Type II veins. Type II olivine-rich veins were formed by brittle failure in a well-defined paleo-stress field and were not significantly deformed after their formation. Comparison of the principal paleo-stress orientation inferred from Type II veins with those formed at peak metamorphic conditions in the ultramafic rocks at Cerro del Almirez shows a relative switch in the orientation of the maximum and minimum principal paleo-stress axes. These relative changes can be attributed to the cyclic evolution of shear stress, fluid pressure and fault-fracture permeability allowing for stress reversal.MICIN/AEI PID2019-105192GB-I00Junta de Andalucia RNM-208 RNM-141 RNM-145 RNM-131 RNM-374FEDER program "una manera de hacer Europa"Spanish Government RYC2018-024363-IUniversidad de Granada/ CBU

Systematics of detrital zircon U–Pb ages from Cambrian–Lower Devonian rocks of northern Morocco with implications for the northern Gondwanan passive margin

This study was found by the Ministerio de Economia y Competitividad (MINECO) of Spain through the project PANGEATOR (CGL2015-71692) and the Pre-Doctoral scholarship BES-2016-078168. We are indebted to Mike Hall and Brad McDonald for their assistance and technical support on sample preparation and the LA-ICPMS, respectively. The CL imaging was carried out on the Curtin University's Microscopy & Microanalysis Facility, whose instrumentation has been partially funded by the University, State and Commonwealth Governments, and the Scanning Electron Microscope (SEM) Facility at the University of Edinburgh. Analysis in the SHRIMP and GeoHistory Facilities, JdLC, Curtin University were enabled by AuScope (auscope.org.au) and the Australian Government via the National Collaborative Research Infrastructure Strategy (NCRIS) and an Australian Geophysical Observing System grant provided to AuScope Pty Ltd. by the AQ44 Australian Education Investment Fund program, respectively. The NPII multi-collector was obtained via funding from the Australian Research Council LIEF program (LE150100013). The SIMS analyses were performed at the NERC Ion Microprobe Facility of the University of Edinburgh (UK). Comments from two anonymous reviewers and editorial handling by Prof. Victoria Pease are acknowledged. Funding for open access charge: YUniversidad de Granada / CBUA.The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession.Ministerio de Economia y Competitividad (MINECO) of Spain through the project PANGEATOR CGL2015-71692Scanning Electron Microscope (SEM) Facility at the University of EdinburghAustralian Geophysical Observing System grant by AQ44 Australian Education Investment Fund programAustralian Research Council LE150100013Universidad de Granada / CBUA BES-2016-07816

Mountain age through low-temperature thermochronology. Contributions for Secondary Education

La formación de cadenas montañosas es uno de los procesos geológicos más importantes, y el establecer el momento (normalmente millones de años) en que se formó el relieve que vemos ha sido siempre un desafío para los investigadores en Ciencias de la Tierra. Existen numerosas técnicas que, en conjunto, permiten conocer la historia de formación de las cadenas de montañas. Una de las técnicas más usadas en los últimos tiempos es la termocronología de baja temperatura (huellas de fisión y U-Th/He en apatitos), ya que informa de la trayectoria tiempo-temperatura que sufre una roca durante su exhumación (el viaje hacia la superficie desde grandes profundidades). Estos métodos se aplican a determinados problemas en Geociencias, debido a su baja temperatura de cierre (120ºC huellas de fisión en apatitos y 60ºC en U-Th/He en apatitos). Esta baja temperatura de cierre permite conocer, por ejemplo, los últimos estadios de la formación de las cadenas de montañas. Sin embargo, por lo que se deduce de los manuales de texto de ciencias en bachillerato, la termocronología de baja temperatura es desconocida para los estudiantes de Educación obligatoria, y probablemente poco comprendida por sus docentes. Este trabajo pretende ofrecer una fundamentación básica de las técnicas de termocronología de baja temperatura y ejemplos de aplicación en la Península Ibérica. Así mismo, se presenta un análisis curricular y de libros de texto sobre estos tópicos.Mountain formation is one of the geological processes more important of the nature. Isotopic dating allows to know how and when mountains occur and their evolution through geological time. There are many techniques that, as a whole, let know the mountain history. One of most used in last times is low-temperature thermochronology (fission tracks and U-Th/He on apatite) because reveal the time-temperature history of the rocks during their surface exhumation, that is not possible to know with the noted and classic high-temperature geochronometers.. These methods present an extremely low closed temperature (120ºC for fission tracks on apatite and 60ºC for U-Th/He on apatite), which enable to be applied to resolve many problem on geosciences. For example, the low closed temperatures of these methods allow know the last step of the mountains evolution. However, as it is follows of the analysis of high school science textbooks, students from compulsory education ignore the use of these techniques. Even, maybe their teachers neither know very well. This paper aims to provide a basic foundation of these techniques of low-temperature thermochronology, as well as examples of application in Iberian Peninsula that may be useful for Secondary Education teachers. In addition, it is shown a curricular and textbooks analysis.Departamento de Didáctica de las Ciencias Experimentales (Universidad de Granada)Grupo de Investigación HUM613 (Didáctica de las Ciencias Experimentales y de la Sostenibilidad)Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR)Departamento de Geodinámica (Universidad de Granada

Mixed and recycled detrital zircons in the Paleozoic rocks of the Eastern Moroccan Meseta: Paleogeographic inferences

Ministerio de Economía y Competividad (MINECO) of Spain through the project CGL2015-71692-P and the Pre-Doctoral scholarship BES-2016-078168. Zircon analyses and imaging were carried out on the SHRIMP II, LA-ICPMS and SEM facilities at the John de Laeter Centre, Curtin University, with the financial support of the Australian Research Council (LE150100013) and Auscope NCRIS (AQ44 Australian Education Investment Fund program)The paleogeographic evolution of the Moroccan Variscides has been a matter of discussion for several decades, with current theoriesmostly based on classical geological correlations. In this regard, the scarce number of studies devoted to U-Pb geochronological analyses of detrital zircon populations is particularly limiting when trying to ascribe the different domains to a single continental piece either derived from the West African Craton or to different sources, with some located in the Nubian Shield or the SaharanMetacraton. In thiswork, detrital zircon grains from 10 samples of sandstones from the Paleozoic (Ordovician to Devonian) sequence of the Eastern Meseta andMiddle Atlaswere dated in order to identify possible sediment sources and elucidate the paleogeography of this easternmost portion of the Moroccan Variscides. The main detrital zircon populations have Ediacaran-Cryogenian ages (610–670 Ma, related to the Cadomian and/or Pan-African orogeny) and middle Paleoproterozoic ages (1980–2080 Ma, related to the Eburnean orogeny), which are in agreement with previous data from the Western Meseta, suggesting similarity between both Mesetas, and strong West African Craton affinity. Such an affinity verifies themost accepted paleogeographic interpretation considering that theMoroccan Mesetas remained attached to northern Gondwana during the entire Paleozoic period. The main differences between our samples and those from the Western Meseta concern the minor detrital zircon populations, such as the Cambro-Ordovician and the Tonian-Stenian ones. In particular, Eastern Meseta and Middle Atlas samples lack a Cambro-Ordovician detrital zircon population, usually interpreted as related to the rifting that opened the Rheic Ocean. This population is locally reported in the Western Meseta and widely described in southwestern Europe, where magmatism of this age is well known. Furthermore, the most northeastern samples are also characterized by a Tonian-Stenian detrital zircon population (up to 30% of the data), which might imply northeastern African sources (Saharan Metacraton and/or Arabian-Nubian Shield)Ministerio de Economía y Competividad (MINECO) of Spain CGL2015-71692-P, BES-2016-078168Australian Research Council (LE150100013)Auscope NCRIS (AQ44 Australian Education Investment Fund program

High-P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

The transition between antigorite-serpentinite and chlorite-harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite-metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the antigorite-serpentinite domain and has three generations of garnet. Grossular-rich Grt-1 formed during rodingitization at the seafloor (10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO ~HM buffer) released by brucite breakdown in the host antigorite-serpentinite. Type 2 Epidote-metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite-harzburgite. Type 2 formed by increasing μSiO (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high-P antigorite breakdown in serpentinite. The growth of Grt-4, with low-grandite and high-pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite-metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite-harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite-rich garnet (Grt-5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe/Fe ratios of antigorite-serpentinite and chlorite-harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle.“Ministerio de Economía, Industria y Competitividad” (MINECO), Grant/Award Number: CGL2012-32067, CGL201675224-R; Junta de Andalucía, Grant/ Award Number: RNM-145, P12-RNM3141; Ramón y Cajal, Grant/Award Number: RYC-2012-11314; MINECO, Grant/Award Number: CGL2016-81085-R, PCIN-2015-05