Petrological and Geochemical Variations within the Tal y Fan Intrusion: a Study of Element Mobility During Low-Grade Metamorphism with Implications for Petrotectonic Modelling

Merriman, R. J.; Bevins, R. E.; Ball, T. K.

doi:10.1093/petrology/27.6.1409

Cited by 44 publications

(26 citation statements)

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“…contents. Zr, Nb, Y, Th, Hf and REE are more immobile during secondary processes (Ludden et al, 1982;Merriman et al, 1986), and show a good negative correlation with magmatic differentiation. However, Zr and Y show more scattered patterns in the post- Triassic group than in the Triassic group.…”

Section: Petrography and Age Of The Ophitesmentioning

confidence: 92%

Untitled

Morata¹,

Puga²,

Demant³

et al. 1997

Estud. geol.

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Mesozoic basic magmatism in the External Zones of the Betic Cordilleras (S. Spain) is represented by small tectonic bodies (ophites) in Triassic formations, and submarine flows with abundant pillow-Iavas interbedded with Jurassic sediments. Both basic igneous manifestations suffered very low-to low-grade metamorphism, more intense in the case of the ophites.Two types of ophites are distinguished on the basis of their primary mineralogy. In the first type, orthopyroxene is present in the less differentiated products. Clinopyroxene and Ca-plagioclase are the main primary phases and quartz appears in the more evolved rocks. In the second type, olivine is present in the less differentiated products. Ti-rich augite and Ca-plagioclase are also important primary minerals, but quartz is absent.Whole-rock chemistry (major and trace elements, including REE) also allows us to discriminate between these two groups. The first group has higher SiO z and lower TiO z , PzOs and lower NazO/KzO ratios than the second. Normative quartz is almost invariably present in this first group, whereas normative nepheline (lower than 5%) is characteristic of the second group. Both groups are Sr, K, Ba, Rb, Th, Nb and Ce enriched with respect to normal MORB, but the first group has higher K, Rb, Ba, Th and lower Nb, Ce contents than the alkaline group. NblY and TiN ratios are also different and show a tholeiitic affinity for the first group and transitional to alkaline for the second. Chondrite-normalised REE patterns in both groups are similar and characterized by LREE enrichment with respect to HREE. LREE/HREE ratios are, however, slightly higher in the transitional to alkaline group.Various discriminant tectonic diagrams indicate a continental intraplate setting for both ophite groups. This magmatism is related to the first extensional period of the Betic Cordilleras, during the Triassic-Jurassic. Geochemical differences between the two groups could evidence different degrees of crustal contamination, and/or different mantle sources. Trace element ratios [(La/Ce)n> 1, La/Nb < 1.5] for both magmatism are indicative of an enriched mantle source. Differences in ThIYb, Zr/Nb, ZrIY and Ba/Zr ratios underline the greater influence of a lithospheric component in the case of the Triassic magmatism.Key wOl"ds: Ophites: Continental intraplate magmatism; Mesozoie; External Zones; Betie Cordilleras. RESUMENEl magmatismo basico mesozoico en las Zonas Externas de las Cordilleras Beticas (S. Espafia) esta representado por pequefios bloques tect6nicos (ofitas) en las formaciones triasicas, y coladas submarinas, con abundantes pillow-Iavas intercaladas en los sedimentos jurasicos. Ambos tipos de manifestaciones fgneas sufrieron transformaciones metam6rficas en condiciones de grado bajo a muy bajo, mas intensas en el caso de las ofitas.Sobre la base de la mineralogfa primaria se han distinguido dos tipos de ofitas. En el primer tipo, aparece ortopiroxeno en los terminos menos diferenciados, siendo los clino- piroxenos y plagioclasas calcicas las pr...

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Section: Petrography and Age Of The Ophitesmentioning

confidence: 92%

Untitled

Morata¹,

Puga²,

Demant³

et al. 1997

Estud. geol.

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show abstract

“…3a and b), which are generally considered to be relatively immobile during hydrothermal alteration and low-grade metamorphism (see Merriman et al, 1986 for a discussion), the five April 2008 excavation samples show a very tight clustering, reflecting a very limited range in contents of these elements. As Thorpe et al (1991) determined, these are elements which we identify as being key discriminators in the analysis of the Stonehenge and north Pembrokeshire datasets.…”

Section: April 2008 Stonehenge Excavationmentioning

confidence: 99%

Provenancing the rhyolitic and dacitic components of the Stonehenge landscape bluestone lithology: new petrographical and geochemical evidence

Bevins

Ixer

Webb

et al. 2012

Journal of Archaeological Science

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“…First, one must consider the possible eects on element mobility of the low-grade regional metamorphism which this area has suered. Merriman et al (1986) examined these eects in a thick (110 m) dolerite sill and found that mobility was mostly con®ned to the marginal 4±5 m, though the LIL elements showed some slight mobility throughout the intrusion. Howells et al (1991: 158) made the point that it is not clear whether chemical changes occurred during the cooling of the sill or the later regional metamorphism.…”

Section: Geochemical Variationmentioning

confidence: 99%

Geochemical variation in the Penmaenmawr intrusion (North Wales)

Tremlett

1997

Geol. J.

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To determine the pattern of geochemical variation within the Penmaenmawr intrusion, 41 rocks were analysed for major oxides and 15 minor elements. The results indicate pulsational emplacement of sheets of magma from a parental body at depth undergoing crystallization dierentiation. These sheets now strike NE±SW and dip southeastward. The resultant intrusion shows a range of SiO 2 contents from 57 . 3% to 65 . 6%

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Petrological and Geochemical Variations within the Tal y Fan Intrusion: a Study of Element Mobility During Low-Grade Metamorphism with Implications for Petrotectonic Modelling

Cited by 44 publications

References 0 publications

Untitled

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Provenancing the rhyolitic and dacitic components of the Stonehenge landscape bluestone lithology: new petrographical and geochemical evidence

Geochemical variation in the Penmaenmawr intrusion (North Wales)

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