Vers une Meilleure Connaissance du Problème des Spilites à Partir de Données Nouvelles sur le Cortège Spilito-Keratophyrique Hercynotype

Juteau, Th.; Rocci, G.

doi:10.1007/978-3-642-88230-2_15

Cited by 6 publications

(3 citation statements)

References 7 publications

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“…but traces are not given. R201 lies outside plotted fields for south-west England Carboniferous volcanics given in Floyd (1982, 235), and an acid tuff from Ilevon quoted by Juteau and Rocci (1974) is much higher in Ti02 than R201. The availade data, therefore.…”

Section: P~~~c R R L I R R E J H R R2oimentioning

confidence: 71%

Laser Argon Dating and Geological Provenancing of a Stone Axe From the Stonehenge Environs*

1994

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The recently‐developed laser microprobe 40argon‐39 argon technique has been used to give a geological date for a rhyolitic tuff stone axe fragment from the Stonehenge environs. The method requires only milligramme‐sized samples and gives dates of sufficient accuracy to aid in provenancing artefacts to sources, as well as information on the heating history of samples. The axe sample is of Lower Carboniferous date (341 ± 5 Ma) and this limits possible sources to outcrops within the Scottish Midland Valley and small altered exposures in Dartmoor. X‐ray fluorescence analysis of the axe suggests the Scottish Midland Valley as the more likely source. The laser argon analysis also shows that the implement had not been heated in antiquity. Laser argon‐argon dating can, therefore, be a useful tool in artefact study.

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Section: P~~~c R R L I R R E J H R R2oimentioning

confidence: 71%

Laser Argon Dating and Geological Provenancing of a Stone Axe From the Stonehenge Environs*

1994

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“…5A) are a pervasive feature of the west European middle Paleozoic formations (de La Roche et al, 1974;Juteau and Rocci, 1974). In contrast to the lower Carboniferous south Iberian pyrite belt, where the acid volcanic rocks are overwhelming, their silicic counterparts (keratophyres) are less common in general and are missing in the Almaden district proper.…”

Section: Submarine Mafic Volcanic Rocksmentioning

confidence: 96%

Geology of the Almaden mercury deposit, Province of Ciudad Real, Spain

Saupé¹

1990

Economic Geology

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Almadan is the largest known mercury deposit in the world. It is formed by three lenticular strata-bound cinnabar impregnations in the two quartzite members of the Criadero quartzite formation of Lower Silurian age, adjacent to a lens of a phreatomagmatic explosion breccia (Frailesca) filling a crater piercing this quartzite. Cinnabar is the dominant ore mineral, with some native mercury, pyrite, and subordinate, late metacinnabar. The underlying, the intercalated, and the overlying shales (positioned with respect to the quartzites) are not hydrothermally altered. Spilitization of the mafic volcanic rocks is a regional process and thus is unrelated to ore deposition, whereas the mafic volcanic rocks overlying the ore deposit are sericitized and strongly carbonatized. The C isotope data do not indicate whether the carbonate CO2 was derived from the mantle or from hydrolysis of organic matter. The most probable source of mercury is the Ordovician black shales rather than a positive mercury anomaly in the mantle. The source of sulfur could not be determined by means of the S isotopes. These data suggest that mercury may have been transported as a sulfide complex and/or as HgPaq/.The deposit and its host rocks were folded vertically and faulted during the Hercynian orogenesis. The regional metamorphism is of very low grade (210ø-270øC, 1 kbar).The following sequence of events accounts best for the various field observations and laboratory work: (1) lying abruptly on top of clays, sands were deposited near a submarine delta on a shallow epicontinental platform (shelf) periodically subjected to incipient rifting; (2) these sands (the lower quartzite member) were impregnated by cinnabar and (3) underwent diagenesis, possibly accelerated by hydrothermal fluids; (4) the detrital (sand and clays) sedimentation resumed, subsequently leading to barren quartzite, shales, and the quartzite of the upper quartzite member; (5) the upper quartzite member was laterally impregnated by cinnabar and two conformable ore lenses formed--the impregnation followed zones of greater permeability parallel to palcocurrent directions and was possibly controlled by hydraulic fracturing; (6) a phreatomagmatic breccia, the Frailesca, formed in shallow volcanic explosion centers situated in the footwall shales without visible roots and intersected the two quartzite members; and (7) this sequence ended by volcano-sedimentary alternations including mafic intrusions and flows. During events (2) and/or (5) muddy cinnabar was deposited at a sedimentwater interface and impregnated porous quartzites.Other mines and occurrences in the Almadan district have similar features, although much smaller tonnages. Altogether, five morphologic types of mercury mineralization exist in the district. Outside of the district no other mine is similar to Almad(•n.

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“…El volcanismo devónico estudiado por nosotros en el sinclinal de Almadén presenta una gran similitud con la asociación espilita-keratófido de tipo Hercínico del distrito de Lahn-Dill, en el Maciw Esquistoso Renano (Juteau y Rocci, 1974), en cuanto a edad, medio paleogeográfico y facies ígneas se refiere. Estos autores suponen la existencia de un magma basáltico que, en un momento dado de su ascenso, sufre un proceso de asimilación masiva de agua y CO 2 , en un medio de tipo geosinclinal pre-orogénico, y que ocasiona el enfriamiento del magma favoreciendo el desarrollo de una paragénesis espilítica, a la vez que se produciría una decantación total del olivino.…”

Section: Discusión Y Conclusionesunclassified

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Baranda¹,

Hernandez²

1989

Estud. geol.

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In the Almadén region an important volcanic activity of Devonian age took place. It began in the Emsian in the central part of the sync1ine, and was developed in several consecutive episodes along the Frasnian.Intense postmagmatic deuteric or hydrothermal processes have generated a low-temperature mineralogical assemblage resembling the spilite-keratophyre association. Hence, the volcanism in the Almadén region is characterized, using minor and trace elements considered to be inmovile (Ti, Zr, Y, Nb and partly, P and Ga).We conc1ude the existence of a mildly alkaline primitive magma, place below an oceanic or transitional crust in a within-plate setting; later differentiation may have taken place by fractional crystallization.Key words: pre-hercynian aJkali volcanism, Almadén sincline. RESUMENEn el área de Almadén tiene lugar una importante actividad volcánica en el Devónico, que comienza en el Emsiense en la parte central del sinclinal, y se desarrolla en varios cic10s consecutivos durante todo el Frasniense.Este volcanismo ha sido afectado por intensos procesos de aÜeración post-magmática, de tipo deutérico e hidrotermal, que han originado una paragénesis de baja temperatura, asimilable a la asociación espilita-keratófido. Por esta razón, para su caracterización, se han utilizado los elementos menores y traza considerados como inmóviles (Ti, Zr, Y, Nb y en parte, P y Ga).De este estudio se deduce la existencia de un magma original moderadamente alcalino, situado bajo una corteza oceánica o transicional, en una región intraplaca, que evoluciona mediante un proceso probable de diferenciación por cristalización fraccionada.Palabras clave: volcanismo alcalino pre-hercínico, sinclinal de Almadén.

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Vers une Meilleure Connaissance du Problème des Spilites à Partir de Données Nouvelles sur le Cortège Spilito-Keratophyrique Hercynotype

Cited by 6 publications

References 7 publications

Laser Argon Dating and Geological Provenancing of a Stone Axe From the Stonehenge Environs*

Laser Argon Dating and Geological Provenancing of a Stone Axe From the Stonehenge Environs*

Geology of the Almaden mercury deposit, Province of Ciudad Real, Spain

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