¿Bastan los datos geoquímicos para establecer el origen del circón? Aportaciones de los esquistos cloríticos en las peridotitas de Ronda

This study deals with the scarce chlorite schists scattered through the Ronda peridotites (Betic Cordilleras, Spain) related to the intrusion of granite dykes. Chlorite schists field data and the petrography, geochemistry and geothermometry of the extracted zircon crystals, point to late magmatic melts for the zircon origin. Moreover, LA-ICPMS analyses reveal that trace and rare earth elements alone could not be indicative for the magmatic or hydrothermal origin of zircon. Therefore, the combination of that information with zircon morphology, melt inclusions, geothermometry, and structural data, when possible, is crucial in the correct zircon origin identificationEste trabajo se centra en los escasos esquistos cloríticos, asociados a la intrusión de diques graníticos, que se encuentran en las peridotitas de Ronda (Cordilleras Béticas, España). A partir de los datos de campo de los esquistos y de la petrografía, geoquímica y geotermometría de circones extraídos, se concluye que su origen está ligado a fluidos magmáticos tardíos. Además, la información obtenida mediante LA-ICP-MS confirma que los elementos trazas y las tierras raras por sí solos no son determinantes acerca del origen magmático o hidrotermal del circón. Por tanto, la combinación de dicha información con la morfología de los circones, inclusiones de fundidos, geotermometría y el estudio estructural, en el caso de ser posible, es crucial para la correcta identificación del origen del circó

Chemical characterization of igneous sphene and application of the Zr-in-sphene thermometer to tardimagmatic processes

This preliminary work illustrates the chemical composition of sphene from Variscan tonalites with sphene-centered ocellar texture (Ribadelago pluton, NW Iberian Massif). The ocellar texture is linked with the percolation of a tardimagmatic melt, with trondhjemitic affinities, through an hyperdense crystal mush. Chemical zoning in sphene, revealed by BSE imaging, shows a heterogeneous distribution of heavy trace elements (Nb, Y, Ce and Zr) that depicts concentric, oscillatory, sector and patchy patterns. Application of the Zr-in-sphene thermometer yields a temperature range of 746 to 778 ºC for the crystallization of sphene in the tardimagmatic melt. It also constitutes a minimum temperature estimation for biotite partial destabilization in this litholog

Peri-Gondwanan Provenance and Geodynamic Evolution of The Guadaiza Nappe (Alpujarride Complex, Betic Cordilleras, Spain): Insights on The Paleotethyan Paleogeography

Based on the LA-ICP-MS U-Pb zircon ages of four metamorphic samples, we discuss the geochronology and provenance of the Guadaiza nappe, an allochthonous unit that underlies the Ronda peridotites (Betic Cordilleras, Spain). The Guadaiza nappe is composed of Triassic marbles overlying a metapelitic sequence with schists and migmatites. Zircons from a quartzite interlayered with the marbles yield a maximum depositional age of ca. 289 Ma that supports the Triassic age. The idiomorphic morphology of these Paleozoic zircon crystals and the lack of late-Variscan metamorphism (ca. 300 Ma) supports a proximal source area, and suggests that the marbles were discordantly deposited over the metapelitic sequence, along the northern margin of the Alboran microplate. The zircon patterns from the metapelitic sequence mainly yield Paleoproterozoic (ca. 1.6–2.5 Ga), Tonian–Stenian (ca. 1000 Ma), Ediacaran–Cryogenian (ca. 600 Ma) and Paleozoic (ca. 500 Ma) age clusters. These results suggest provenance from areas within the triangle bound by the West African Craton, the Metasaharan Craton and the Hun Superterrane during the Paleotethys opening (Silurian–Devonian). A Silurian–Carboniferous deposition age for the schist protoliths is constrained by the youngest detrital zircon population (ca. 443 Ma) and the Variscan age of their migmatization by an additional peak of around 299 Ma in the migmatites.This research was funded by Ministerio de Economía, Industria y Competitividad/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, European Union, grant number CGL2017-82976-P and Grupos de Investigación, University of the Basque Country, grant number GIU20/017

Provenance Analysis of the Ojén Nappe and Its Implication for the Geodynamic History (Alpujárride Complex, Betic Cordilleras, Spain)

The Ojén nappe, an allochthonous unit that underlies the Ronda peridotites (Betic Cordilleras), is composed of Triassic marbles overlying a metapelitic sequence. In order to carry out an LA-ICP-MS U-Pb age determination and provenance analysis, detrital zircon grains from two quartzites interlayered within marbles and metapelites were extracted. The obtained results yield the youngest zircon population of 254 ± 3 Ma (Late Permian) with a mean Th/U ratio of 0.34 that supports both the Permian–Triassic age of the marble member and the felsic magma nature for zircon-bearing protoliths. The Permian zircons exhibit tight age peaks in three main populations of 292 ± 2 Ma, 278 ± 3 Ma, and 254 ± 3 Ma, in agreement with the main age populations reported from rhyolites and shallow crustal basaltic–andesite subalkaline rocks emplaced in transtensional Permian basins of the Variscan Orogen during the break-up of Pangea. Moreover, the analyzed detrital zircon grains yield age distributions with clear Tonian–Stenian (ca. 950–975 Ma), Ediacaran–Cryogenian (ca. 560–615 Ma), Ordovician (ca. 460–465 Ma), and Cisuralian peaks (ca. 280–290 Ma) and smoothed Mesoproterozoic peaks that point to a weak and residual Cadomian peri-Gondwanan terrane inheritance. The identified Middle Ordovician detrital zircon populations (460–465 Ma) strengthen the hypothesis that the Alborán domain would be located along the southern passive margin of the European Hunic superterrane.This research was funded by Ministerio de Economía, Industria y Competitividad/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, European Union (grant number CGL2017-82976-P) and Grupos de Investigación, University of the Basque Country (grant number GIU20/017)

Geochemistry and geodynamic frame of the Ojen Nappe´s eclogites and amphibolites, Alpujarride Complex, Betic Cordilleras

Amphibolite bodies with eclogite relics are found interlayered between the Ojen nappe´s crustal rocks, below the Ronda peridotites of the Betic Cordilleras (southern Spain). We present a geochemical study of such amphibolites and retrogressed eclogites, from which it is possible to deduce a gabbroic origin for their protoliths. We propose that their intrusion in the continental crust took place in a rift setting of Jurassic to Lower Cretaceous age. The recognition of this rifting event in the Alpujarride Complex places an additional constraint for Mesozoic reconstructions of the Western Mediterranea

Structural zoning in a serpentinite-bearing shear zone (Peña Parda Fault, Ronda peridotites)

We study deformation structures in a serpentinite-bearing normal shear zone in the Ronda peridotites, southern Spain. The fault zone displays a structural zoning composed by four domains showing similar strain gradients. Deformation is partitioned into distributed deformation expressed by foliated serpentinites and S-C structures and localized deformation expressed by R and P shear planes at lower and upper portions, respectively, of each domain. Such a structural zoning suggests that stable shear creep alternates with intermittent seismogenic events during the fault activit

Mantle diapirism induced by delamination in the Ronda peridotites (Betic Cordillera)

The contribution of asthenosphere diapirs to the exhumation of Orogenic Lherzolites from the mantle to the Earth’s surface stands as a major issue in the evolution of orogenic belts. Structural and textural data from the Carratraca massifs of the Ronda peridotites, in the Betic Cordillera of southern Spain, provide evidence for a narrow mantle diapir that was formed in Early Miocene times. Its development spent 1.1 Ma at an ascent rate of less than 4.5 mm/y. When set in its geological and petrological context, this diapir documents the injection of hot asthenosphere into older and cooler lithospheric mantle, in response to the delamination of the thickened lithosphere keel formed during the Mesozoic and Cenozoic convergence of the African and Iberian plates from Cretaceous times onward

Posets pluton: a geochronological piece in the puzzle of the Axial Zone of the Pyrenees

[EN]A detailed geochronological study was conducted on zircons from a diorite sample of the Posets pluton (Axial Zone, Pyrenees). The extracted igneous zircons constrain the emplacement of the pluton to 302 +/- 2 Ma and 301 +/- 3 Ma, by means of U-Pb sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, respectively. Considering the syn- to late-tectonic emplacement of the Posets pluton during the main Variscan deformation event (D-2), the obtained ages constrain the long-lasting D-2, associated with the dextral transpression registered through the Axial Zone of the Pyrenees.This work was supported by grants EHUA13/03 and GIU20/017 from the University of the Basque Country (UPV/EHU) and CGL2017-82976 from the Ministerio de Economia, Industria y Competitividad / Agencia Estatal de Investigacion / Fondo Europeo de Desarrollo Regional, European Union. E. Druguet, Y. Denele, an anonymous reviewer and the editor Olivier Lacombe are thanked for reviews and discussions that improved the final manuscript

Strain partition in synkinematic granitoids intruded in a transpressive setting (Sanabria, Central Iberian-Zone, Iberian Massif)

The Sanabria Lake plutons, located in the Central Iberian Zone of the Iberian Massif, intruded in a dextral strike-slip fault bridge under transpressive conditions. The deformed zone underwent a strain partitioning process, so that large folded domains and narrow shear zones were developed coevally. The microstructural study of the granitoids shows that the shear zones concentrate a variable degree of solid state deformation at high and medium temperatures, whereas the folded areas preserve microstructural evidences of magmatic and submagmatic flow at high temperatures, too. The most common fabric in these folded areas is defined by two sets of conjugate planes, composed by aligned crystals of plagioclase and biotite, which are bisected by the flow foliation. These conjugate bands represent an incipient phase of the strain localization process that involves strain weakening, migration of the late-magmatic melts and enhancement of the shear zone

Metamorphism and geothermobarometry of the Yunquera Unit in Casarabonela (Alpujárride Complex, Málaga)

The rocks of the Yunquera Unit (Alpujárride Complex) record two stages, at least, of recrystallization at different P-T conditions defined by the mineral associations: a) Grt + Pl + Ms + St + Ky + Qtz, and b) Grt + Pl + Sill + Qtz ± Bt. The metamorphic peak for the first stage has been estimated at ca. 1200-1300 MPa and 560-695 ºC through conventional thermobarometry. The second mineral association was equilibrated at 600 MPa and 700 ºC. These data support the existence of an initial high-pressure metamorphic stage followed by a pressure drop and final cooling during the Alpine exhumation of the Uni