Geochemical and isotopic disequilibrium in crustal melting: An insight from the anatectic granitoids from Toledo, Spain

Barbero, L.; Villaseca, Carlos; Rogers, G.; Brown, P. E.

doi:10.1029/95jb00036

Cited by 107 publications

(63 citation statements)

References 62 publications

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“…However, different melt batches, from different parts of the source, could have very different Sr contents (controlled only by Sr solubility in the melts). In addition, there is a growing body of evidence that disequilibrium processes control the contents of many trace-elements and isotopes in melts, especially during partial melting of crustal rocks (e.g., Sawyer, 1991;Watt and Harley, 1993;Barbero et al, 1995;Bea, 1996;Davies and Tommasini, 2000;Janák et al, 2001). Melt batches withdrawn from a source more rapidly could inherit much lower trace-element concentrations than batches that remained longer in the source, in contact and progressively equilibrating with the minerals that host these elements.…”

Section: Variation Diagramsmentioning

confidence: 99%

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Clemens

Darbyshire

Flinders

2009

Lithos

113

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The 425 Ma Arrochar and Garabal Hill-Glen Fyne complexes of highland Scotland are examples of post-orogenic magmatism accompanying extensional collapse of an orogen, in this case the Caledonian. The rocks are dominantly high-K series, but range from medium-K to shoshonitic. Mantle upwelling, melting and the intrusion of large volumes of mafic magma into the crust are inferred to have accompanied lithospheric thinning, and to have provided the heat source for melting of young arc crust accreted during the preceding subduction epoch.Fluids evolved from the subducting slab are inferred to have caused high degrees of enrichment in the overlying mantle wedge. Deep in the crust, the mantle-derived, K-rich mafic to intermediate magmas mixed with felsic crustal melts to form the spectrum of magmas intruded in the two complexes. Microgranular enclaves in the granitic rocks represent mafic magmas derived from the enriched mantle and hybridised by reaction, diffusion and mechanical mixing with their host felsic magmas, but they do not form part of the evolutionary series that produced the host magmas. Rather than inheriting its LILEenriched character directly from crustal melts, or from crustal assimilation by mafic magmas, the high-K series may commonly owe at least part of its potassic character to the involvement of mantle (highly metasomatised by slab-derived fluids) as a major magma source. Enclave suites, though prominent in some granitic rocks should not be assumed to represent magmas that played a significant role in the production of the chemical variations in their host magmas.

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Section: Variation Diagramsmentioning

confidence: 99%

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Clemens

Darbyshire

Flinders

2009

Lithos

113

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“…Peak metamorphic thermal conditions in different areas range from 800 50(C and 4-6 kbar (Barbero et al 1995) to 700-740(C and 2·5-3·5 kbar (Carnicero 1982;Escuder Viruete et al 2000;Gil Ibarguchi & Martínez 1982;Ugidos 1987). In the study region, low-P metamorphism changed muscovite+biotite-and biotite+sillimanite-rich mineral assemblages into cordierite-rich ( andalusite sillimanite) parageneses in the high-grade metamorphic and anatectic rocks.…”

Section: Geological Settingmentioning

confidence: 99%

“…The cordieritites show relatively high P 2 O 5 , MnO, Cs and Be and low TiO 2 , but they share, together with samples SSA-7 (sandstone) and SSA-8 (shale), some important chemical features, such as low contents of V, Cr, Ni, Cu, and low Eu/Eu* ratios. Barbero & Villaseca (1992) and Barbero et al (1995). Table 3 Analyses of nebulites and associated leucogranites S of Salamanca (Central Iberian Zone).…”

Section: Cordieritites and Related Rocksmentioning

confidence: 99%

“…A subset of samples were spiked with 87 Rb, 84 Sr, 145 Nd and 149 Sm and individual elements separated using methods similar to those described in Barbero et al (1995). Sr samples were analysed on either a VG54E single collector thermal ionisation mass spectrometer or a VG Sector 54-30 multiple collector mass spectrometer operated in multi-dynamic mode.…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…Cordierite in this granite 'usually occurs as euhedral or subhedral grains with frequent inclusions of acicular sillimanite, biotite and quartz'. Enclaves of metamorphic country rocks (orthogneisses, amphibolites, quartzitic conglomerates, calcsilicate rocks and marbles) are the most abundant, followed by cordierite-rich and sillimanite-rich enclaves and mafic igneous enclaves (amphibole-biotite-bearing quartz diorites and gabbros) (Barbero & Villaseca 1992;Barbero et al 1995). Nebulites have higher CaO contents (>0·5%) than shales and sandstones and Eu/Eu* ranges from 0·52 to 0·96.…”

mentioning

confidence: 99%

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A reactive assimilation model for regional-scale cordierite-bearing granitoids: geochemical evidence from the Late Variscan granites of the Central Iberian Zone, Spain

Ugidos¹,

Stephens

Carnicero³

et al. 2008

Earth and Environmental Science Transactions of the Royal Socie

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Regional scale biotite and cordierite-bearing granites (s.l.) in the Variscan of the Central Iberian Zone (CIZ) are spatially closely associated with cordierite-rich nebulites and cordierite-bearing two-mica granites, and with cordierite-rich high grade hornfelses and cordieritites (>60% cordierite) that are relatively common in the aureoles of these granites. Building on published field evidence, petrological data are presented which, combined with new chemical and isotopic (Sr-Nd) modelling, indicate that the cordierite-bearing granites cannot be derived by simple anatexis of regional sedimentary protoliths; but the data are consistent with a process of reactive assimilation that involves the interaction of biotite granite magma with high-grade host rocks ranging from cordierite nebulites to andalusite-bearing cordieritites. The contribution of the postulated cordieriterich contaminants to the diversity of cordierite granite compositions is modelled using the compositions of regional Lower Cambrian-Upper Neoproterozoic metasedimentary rocks that are generally chemically mature (CaO very rarely exceeds 1·4%). These rocks include specific horizons in which extreme chemical alteration is attributable to sediment reworking during eustatic falls in sea level. Such compositions may account for the presence of the high concentrations in Al that later produced cordieritites. Fractional crystallisation is also important, particularly in generating the more evolved cordierite granite and cordierite biotite muscovite granite compositions. Although assimilation in situ is normally regarded as a minor contributor volumetrically to evolving plutons, in this instance the emplacement of large volumes of granite magma into a high-T-low-P environment significantly increased the potential for reactive assimilation.

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Numerical modeling of geochemical variations caused by crustal relamination

Vogt

Castro

Gerya

2013

Geochem Geophys Geosyst

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[1] Geochemical consequences of composite diapirs formed in subduction zones have been studied using a thermomechanical numerical model of an ocean-continent subduction zone. This model includes dehydration of subducted crust, aqueous fluid transport, partial melting, and melt emplacement. Subduction of crustal material to sublithospheric depth results in the formation of a tectonic rock mélange composed of basalt, sediment, and hydrated /serpentinized mantle. At asthenospheric depth, this rock mélange may evolve into partially molten diapirs and rise through the mantle prior to emplacement (relamination) at crustal levels. We have investigated the composition and the geochemical evolution of liquids derived from such composite diapirs by analyzing the differing proportions of the crustal end-members in the source, i.e., basalt and sediment. Our results show that the proportions of the components (in the diapiric mélange) are limited to short-range variations within an interval of X b [=volume fraction of basalt/(basalt + sediment)] = 0.4 À 0.8, yielding melt with a relatively stable granodioritic major element composition. Hence, granodioritic melt is transported by rising composite diapirs to crustal levels, contributing to the growth of the continental crust. In addition to this, we have calculated Sr and Nd isotopic initial ratios of the diapiric mélange as a function of time, based on the fraction of the components in the mélange. Liquids derived from composite diapirs inherit the geochemical characteristics of the composite source and show distinct temporal variations of radiogenic isotopes depending on the changing values of X b . Partial melting of composite diapirs is therefore expected to produce melt with a constant major element composition but substantial changes in terms of radiogenic isotopes.

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Geochemical and isotopic disequilibrium in crustal melting: An insight from the anatectic granitoids from Toledo, Spain

Cited by 107 publications

References 62 publications

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

A reactive assimilation model for regional-scale cordierite-bearing granitoids: geochemical evidence from the Late Variscan granites of the Central Iberian Zone, Spain

Numerical modeling of geochemical variations caused by crustal relamination

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