Ordovician volcanic rocks record rifting, Variscan metamorphism and gold mineralization processes, Truchas Syncline, NW Iberia, Spain

  1. L. González Menéndez
  2. F. Gómez Fernández 1
  3. J. K. Cunningham 2
  4. S. Menéndez
  5. P. Caldevilla
  6. G. Gallastegui
  7. A. Cuesta 3
  1. 1 Universidad de León

    Universidad de León

    León, España

    ROR https://ror.org/02tzt0b78

  2. 2 University of London

    University of London

    Londres, Reino Unido

    ROR https://ror.org/04cw6st05

  3. 3 Universidad de Oviedo

    Universidad de Oviedo

    Oviedo, España

    ROR https://ror.org/006gksa02

Journal of iberian geology: an international publication of earth sciences

ISSN: 1886-7995 1698-6180

Year of publication: 2021

Issue Title: New developments in Geochemistry. A tribute to Carmen Galindo

Volume: 47

Issue: 1-2

Pages: 387-409

Type: Article

DOI: 10.1007/S41513-020-00147-8 DIALNET GOOGLE SCHOLAR lock_openOpen access editor

More publications in: Journal of iberian geology: an international publication of earth sciences


Ordovician volcanic rocks outcrop in several locations of the NW Iberian Variscan belt. Their composition is mainly basaltic (with less acid types) and occur as volcanic-volcanoclastic layers within a shale-slate succession. This work focuses on volcanic and related rocks within a prominent Variscan structure, the Truchas Syncline. We studied field relations, petrography, mineralogy, geochemistry and conducted thermodynamic modelling to review the petrogenesis and establish the evolution of these volcanic rocks classified as within-plate alkaline basalts (high Ti/Y, Nb/Y and Nb/Yb). Crustal contamination is absent given the elevated Nb/La ratio (1–1.5). These features indicate low melting degrees of the upper mantle and a continental rifting environment. The finding of Ordovician orthid brachiopods in some of the volcanoclastic rocks suggests a shallow marine environment for the volcanic deposition. Variscan metamorphism occurred at lower greenschist conditions with chlorite-temperatures of 374 ± 6 °C. Quartz + carbonate veins indicate that H2O– CO2 metamorphic fluids traversed some volcanic rocks, reacting with Ca–Fe–Mg phases to produce carbonates (Mg-calcite–Fe-dolomite). For this event, T-XCO2 modelling indicates temperatures below 350–360 °C and fluid XCO2 between 0.10 and 0.45. Such fluids can be important carriers of Au and might explain gold deposits in adjacent quartzites. Metasomatic shales (Fe-chlorite + quartz) outcrop nearby and were derived from a mixed protholith of shales and minor volcanic components. Its geochemistry shows Fe enrichment and high peraluminosity. Variscan deformation further modified its geochemistry causing Si-depletions and relative increases of other elements (K, Na, Ti, Al, Rb, Sr, Ba and LREE) in shear zones domains.

Bibliographic References

  • Anovitz, L. M., & Essene, E. J. (1987). Phase equilibria in the system CaCO3-MgCO3-FeCO3. Journal of Petrology 2, 389–414.
  • Babin, C., & Gutiérrez-Marco, J. C. (1991). Middle Ordovician bivalves from Spain and their phyletic and palaeogeographic significance. Palaeontology, 34, 109–147.
  • Brendan Murphy, J., Gutiérrez-Alonso, G., Fernández-Suárez, J., & Braid, J. A. (2008). Probing crustal and mantle lithosphere origin through Ordovician volcanic rocks along the Iberian passive margin of Gondwana. Tectonophysics, 461, 166–180.
  • Boynton, W. V. (1984). Geochemistry of rare earth elements: meteorite studies. In P. Henderson (Ed.), Rare earth element geochemistry (pp. 63–114). New York: Elsevier.
  • Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. New York: Springer.
  • Coggon, R., & Holland, T. J. B. (2002). Mixing properties of phengitic micas and revised garnet-phengite thermobarometers. Journal of Metamorphic Geology, 20, 683–696.
  • Diener, J. F. A., Powell, R., White, R. W., & Holland, T. J. B. (2007). A new thermodynamic model for clino- and orthoamphiboles in the system Na2O– CaO–FeO–MgO–Al2O3–SiO2–H2O–O2. Journal of Metamorphic Geology, 25, 631–656.
  • Díez Montes, A. (2007). La geología del dominio "Ollo de Sapo" en las comarcas de Sanabria y Terra do Bolo. Serie Nova Terra, nº34, 494 pp.
  • De Capitani, C., & Petrakakis, K. (2010). The computation of equilibrium assemblage diagrams with Theriak/Domino software. American Mineralogist, 95, 1006–1016.
  • Elmer, F. L., Powell, R., White, R. W., & Phillips, G. N. (2007). Timing of gold mineralization relative to the peak of metamorphism at Bronzewing, Western Australia. Economic Geology, 102, 379–392.
  • Emig, C. C., & Gutiérrez-Marco, J. C. (1997). Niveaux à lingulidés à la limite supérieure du Grès Armoricain (Ordovicien: Arenig) dans le SW de l’Europe: analyse des facteurs responsables et signification paléoécologique. Geobios, 30, 481–495.
  • Fernández-Lozano, J. (2012). Estudio geológico preliminar de un sector del cierre periclinal del Sinclinorio de Truchas (León): El anticlinal de Manzaneda. Geogaceta, 52, 17–20.
  • Gallastegui, G., Aramburu, C., Barba, P., Fernández, L.P., & Cuesta, A. (1992). El vulcanismo del Paleozoico Inferior de la Zona Cantábrica (NO de España). In J. C. Gutiérrez Marco, J. Saavedra, & I. Rábano (Eds.), El Paleozoico Inferior de Ibero-América (pp. 435–452). Gráficas Topacio, S.A., Madrid.
  • Gallastegui, G., & Cuesta, A. (2005). Mineralogía y geoquímica de manifestaciones filonianas post-variscas en el NO de la Península Ibérica (Provincias de Lugo y León). Macla, 3, 85–87.
  • García de Madinabeitia, S., Sánchez Lorda, M. E., & Gil Ibarguchi, J. I. (2008). Simultaneous determination of major to ultra trace elements in geological samples by fusion-dissolution and inductively coupled plasma mass spectrometry techniques. Analytica Chimica Acta, 625(2), 117–130.
  • Gómez-Fernández, F., Castaño, M. A., Bauluz, B., & Ward, C. R. (2009). Optical microscope and SEM evaluation of roofing slate fissility and durability. Materiales de Construcción, 59(296), 91–104.
  • Gómez-Fernández, F., Vindel, E., Martín-Crespo, T., Sánchez, V., González Clavijo, E., & Matías, R. (2012). The Llamas de Cabrera gold district, a new discovery in the Variscan basement of northwest Spain: a fluid inclusion and stable isotope study. Ore Geology Reviews, 46, 68–82.
  • Gómez-Fernández, F., Cunningham, J. K., Caldevilla, P., Herrero- Hernández, A., & Beard, A. D. (2019). The source of Au and S of the orogenic gold deposits in the Llamas de Cabrera district (Iberian Variscan Massif). Life with Ore Deposits on Earth – 15th SGA Biennial Meeting 2019, Glasgow, 2, 842–845.
  • González Menéndez, L., & Suárez, O. (2004). Caracterización petrológica y geoquímica de los diques basálticos de Cadavedo (Valdés, Asturias). Trabajos de Geología, Univ. Oviedo, 24, 81–89.
  • González-Menéndez, L., Gómez-Fernández, F., Cunningham, J. K., Caldevilla, P., Gallastegui, G., & Menéndez, S. (2019). Rifting, deformation, metamorphism, hydrothermalism and gold precipitation recorded in volcanic rocks (The Truchas Syncline, Variscan Belt, NW Spain). Geophysical Research Abstracts, 21, 9984–9994.
  • Grant, J. A. (1986). The isocon diagram: A simple solution to Gressens equation for metasomatic alteration. Economic Geology, 81, 1976–1982.
  • Grant, J. A. (2005). Isocon analysis: A brief review of the method and applications. Physics and Chemistry of the Earth, 30, 997–1004.
  • Groves, D. I., Golding, S. D., Rock, N. M. S., Barley, M. E., & McNaughton, N. J. (1988). Archean carbon reservoirs and their relevance to the fluid source for gold deposits. Nature, 331, 254–257.
  • Gromet, L. P., Dimek, R. F., Haskin, L. A., & Korotev, L. R. (1984). The “North American Shale Composite”: Its compilation, major and trace element characteristics. Geochimica et Cosmochimica Acta, 48, 2469–2482.
  • Gutiérrez-Marco, J. C. (1997). Tolmachovia babini nov. sp., nuevo ribeirioide (Mollusca, Rostroconchia) del Ordovícico Medio de la Zona Centroibérica Española. Geobios-Mémoire Spécial, 20, 291–298.
  • Gutiérrez-Marco, J. C., Aramburu, C., Arbizu, M., Bernárdez, E., Hacar Rodríguez, M. P., Méndez-Bedia, I., et al. (1999). Revisión bioestratigráfica de las pizarras del Ordovícico Medio en el noroeste de España (Zonas Cantábrica, Asturoccidental-Leonesa y Centroibérica septentrional). Acta Geológica Hispánica, 34(1), 3–87.
  • Gutiérrez-Marco, J., Robardet, M., Rábano, I., Sarmiento, G. N., de San José, M., Herranz Araújo, P., & Pieren, A. (2002). Ordovician. In W. Gibbons & T. Moreno (Eds.), The geology of Spain (pp. 31–49). London: Geological Society of London.
  • Herron, M. (1988). Geochemical classification of Terrigenous sands and Shales from core or log data. Journal of Sedimentary Research, 58(5), 820–829.
  • Holland, T. J. B., & Powell, R. (1998). An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology, 16(3), 309–343.
  • Holland, T. J. B., Baker, J. M., & Powell, R. (1998). Mixing properties and activity-composition relationships of chlorites in the system MgO-FeO-Al2O3-SiO2-H2O. European Journal of Mineralogy, 10, 395–406.
  • Holland, T. J. B., & Powell, R. (2003). Activity-composition relations for phases in petrological calculations: an asymmetric multicomponent formulation. Contributions to Mineralogy and Petrology, 145, 492–501.
  • Jowett, E.C. (1991). Fitting iron and magnesium into the hydrothermal chlorite geothermometer. In: GAC/MAC/SEG Joint Annual Meeting. Program and Abstracts, 16, A62.
  • Kesler, S. (2005). Ore forming fluids. Elements, 1, 13–18.
  • King, P. L., & White, A. R. J. (2003). Granites, volatile solubility and tracking the formation of magmatic fluids. In P. Blevin, M. Jones, & B. Chappel (Eds.), Magmas to Mineralisation: The Ishihara Symposium, Geoscience Australia, Record 2003/14, pp. 85–88.
  • Kleine, B. I., Skelton, A. D. L., Huet, B., & Pitcairn, I. K. (2014). Preservation of blueschists-facies minerals along a shear zone by coupled metasomatism and fast-flowing CO2- bearing fluids. Journal of Petrology, 55(10), 1905–1939.
  • Kleine, B. I., Pitcairn, I. K., & Skelton, A. D. L. (2015). The mechanism of infiltration of metamorphic fluids recorded by hydration and carbonation of epidote-amphibolite facies metabasaltic sills in the SW Scottish Highlands. American Mineralogist, 100, 2702–2717.
  • Kleine, B. I., Pitcairn, I. K., & Skelton, A. D. L. (2016). Mineralogical controls on metamorphic fluid flow in metabasaltic sills from Islay, Scotland. Lithos, 248–251, 22–39.
  • Liu, J.-Q., Chen, L.-H., Zeng, G., Wang, X.-J., Zhong, Y., & Yu, X. (2016). Lithospheric thickness controlled compositional variations in potassic basalts of Northeast China by melt-rock interactions. Geophysical Research Letters, 43, 2582–2589.
  • Marcos, A., Pérez-Estaún, A., Pulgar, J. A., Bastida, F., & Vargas, I. (1980). Memoria explicativa del Mapa Geológico de España E: 1:50.000 nº 99 (Becerreá). 2ª serie MAGNA, Primera edición. IGME. 32 pp.
  • Matas, J., & Velando, F. (1982). Memoria explicativa del Mapa Geológico de España E: 1:50.000 nº 230 (Castrocontrigo). Información complementaria: Análisis Paleontológico. 2ª serie MAGNA, Primera edición. IGME. 27 pp.
  • Montero, P., Talavera, C., & Bea, F. (2017). Geochemical, isotopic, and zircon (U-Pb, O, Hf isotopes) evidence for the magmatic sources of the volcano-plutonic Ollo de Sapo Formation Central Iberia. Geologica Acta, 15(4), 245–260.
  • Orejana, D., Villaseca, C., Billström, K., & Paterson, B. A. (2008). Petrogenesis of Permian alkaline lamprophyres and diabases from the Spanish central system and their geodynamic context within Europe. Contributions to Mineralogy and Petrology, 156, 477–500.
  • Pearce, J. A. (1982). Trace element characteristics of lavas from destructive plate boundaries. In R. S. Thorpe (Ed.), Andesites (pp. 525–548). New York: Wiley.
  • Pérez-Estaún, A. (1974). Algunas precisiones sobre la sucesión ordovícica y silúrica de la región de Truchas. Breviora Geológica Astúrica, 18, 23–25.
  • Pérez-Estaún, A. (1978). Estratigrafía y estructura de la Rama S. de la Zona Asturoccidental-leonesa. Memorias del Instituto Geológico y Minero de España, 92, 1–151.
  • Phillips, G. N., & Evans, K. A. (2004). Role of CO2 in the formation of gold deposits. Nature, 429, 860–863.
  • Phillips, G. N., & Powell, R. (2010). Formation of gold deposits: a metamorphic devolatilization model. Journal of Metamorphic geology, 28, 689–718.
  • Pitzer, K. S., & Sterner, S. M. (1994). Equations of state valid continuously from zero to extreme pressures for H2O and CO2. Journal of Chemical Physics, 101(4), 3111–3116.
  • Polechová, M. (2016). The bivalve fauna from the Fezouata Formation (Lower Ordovician) of Morocco and its significance for palaeobiogeography, palaeoecology and early diversification of bivalves. Palaeogeography, Palaeoclimatology, Palaeoecology, 460, 155–169.
  • Rollingson, H. (1993). Using geochemical data: evaluation, presentation, interpretation. Logman Group UK. 352 p.
  • Rodríguez Fernández, L. R., Pedrera, A., Pous, J., Ayala, C., González-Menéndez, L., Ibarra, P., et al. (2015). Crustal structure of the south-western termination of the Alpine Pyrenean- Cantabrian Orogen (NW Iberian Peninsula). Tectonophysics, 663, 322–338.
  • Rosenberg, P. E. (1967). Subsolidus relations in the system CaCO3- MgCO3-FeCO3. American Journal of Science, 52(5–6), 787–796.
  • Sparks, R.S.J. (2003). Dynamics of magma degassing. In Oppenheimer, C., Pyle, D.M. & Barclay, J. (eds), Volcanic Degassing. Geological Society of London Special Publication, 213, pp. 5–22
  • Suárez, A., Barba, P., Heredia, N., & Rodríguez Fernández, L. R. (1994). Mapa Geológico de la Provincia de León Escala 1:200.000. Instituto Tecnológico Geominero de España (ITGE).
  • Suárez, O., Gallastegui, G., Cuesta, A., Corretgé, L. G., & Tarrío, L. (1993). Geoquímica de las rocas basálticas del Cabo Peñas (Zona Cantábrica). In V Congreso de Geoquímica de España (pp. 42–47). Serv. De. CEDEX. ISBN: 84–7790–156–2.
  • Sun, S. S., & MacDonough, W. F. (1989). Chemical and isotopic systematics of oceanic basalts: implication for mantle composition and processes. In A. D. Saunders, & M. J. Norry (Eds.), Magmatism in Ocean Basins (Vol. 42, pp. 313–345). Geological Society of London Special Publication.
  • Taylor, S. R., & McLennan, S. H. (1985). The Continental crust: Its composition and evolution (p. 312). Oxford: Blackwell.
  • Valverde-Vaquero, P. (1992). Permo-Carboniferous magmatic activity in the Cantabrian Zone (NE Iberian Massif, NW Spain). Master of Science Boston College, 291 pp.
  • Valverde-Vaquero, P., & Dunning, G. R. (2000). New U-Pb ages for early Ordovician Magmatism in central Spain. Journal of the Geological Society, 157, 15–26.
  • Valverde-Vaquero, P., Hepburn, C. J., & Martínez García, E. (2016). Geochemistry of the Upper Ordovician alkaline basalts of the Castro Fm: (Cantabrian Zone): break-up along the Ibero-Armorican margin of the Rheic Ocean? Geo-Temas, 16(2), 207–210.
  • Villa, L., Corretgé, L. G., Arias, D., & Suárez, O. (2004). Los depósitos volcanoclásticos sineruptivos del paleozoico inferior del área de lago-Fontarón (Lugo, España). Trabajos de Geología, Univ. Oviedo, 24, 185–205.
  • Villar Alonso, P., Portero Urroz, G., González Cuadra, P., García Crespo, J., Nieto García, A. B., Rubio Pascual, F. J., Gómez- Fernández, F., & Giménez Benayas, S. (2019). Mapa Geológico Digital Continuo E. 1:50.000, Zona Centroibérica. Dominio Ollo de Sapo (Zona 1300). GEODE. Mapa Geológico Digital Continuo de España. Disponible en: https ://info.igme.es/carto grafíadigi tal/ geolo gica/geode zona.aspx?id=Z1300 .
  • Villas, E., Gisbert, J., & Montesinos, R. (1989). Brachiopods from volcanoclastic Middle and Upper Ordovician of Asturias (Northern Spain). Journal of Paleontology, 63(5), 554–565.
  • Villaseca, C., Merino Martínez, E., Orejana, D., Andersen, T., & Belousova, E. (2016). Zircon Hf signatures from granitic orthogneisses of the Spanish Central System: Significance and sources of the Cambro-Ordovician magmatism in the Iberian Variscan Belt. Gondwana Research, 34, 60–83.
  • Yardley, B. W. D., & Bodnar, R. I. (2014). Fluids in the continental crust. Geochemical Perspectives, 3, n°1.
  • Ward, C. R., & Gómez-Fernández, F. (2003). Quantitative mineralogical analysis of Spanish roofing slates using the Rietveld method and X-ray powder diffraction data. European Journal of Mineralogy, 15, 1051–1062.
  • White, R. W., Powell, R., & Holland, T. J. B. (2007). Progress relating to calculation of partial melting equilibria for metapelites. Journal of Metamorphic Geology, 25(5), 511–527.
  • Zane, A., & Weiss, Z. (1998). A procedure for classifying rock-forming chlorites based on microprobe data. Rendiconti Lincei Scienze Fisiche e Naturali Serie, 9(1), 51–56.