Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints



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Villaseca González, Carlos and Barbero González, Luis C. (1998) Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints. Lithos (Oslo. Print) , 43 . pp. 55-79. ISSN 0024-4937

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In Central Spain, it is possible to distinguish two main types of peraluminous late-Hercynian granites: the PI types and
the PS types. The distinction between both types is made on the basis of differences in peraluminosity (PS types are more
peraluminous than PI types) and also on the appearance of some characteristic mafic minerals; PS types have biotite,
cordierite and monazite as the most typical accessory phase, whereas PI types have biotite, amphibole (in the less evolved
facies) and allanite as the accessory mineral. Both granite types have similar trace element ratios and initial Sr, Nd and Pb
isotopic signatures. Initial 87Sr/86Sr ratios of both types exhibit a large range from 0.7073 to 0.7193, whereas initial εNd
varies in a restricted range from -5.4 to -6.6. The scarce associated basic rocks do not play a significant role in the
chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite/monzogranite
parental magmas. Mixing and AFC modelling of Sr and Nd isotopic data reveal an unrealistically high
mantle contribution. Based on major and trace element and isotopic data, an orthogneissic protolith for both granitic series is
proposed. Nevertheless, none of the metamorphic country rocks of Central Spain has the appropriate Sr isotopic composition
to satisfy the origin of these granitic rocks, and so, it is argued that progressive isotopic re-equilibration of crustal material
during the granulization of the lower Hercynian crust, together with the possibility of isotopic disequilibrium during melting
as has been demonstrated in migmatitic terranes in nearby areas. may explain the isotopic differences between the granites
and the high level metamorphic country rocks

Item Type:Article
Uncontrolled Keywords:Igneous; Peraluminous granites; Iberian Hercynian Belt; Geochemistry; Sr–Nd isotopes; Central Spain
Subjects:Sciences > Geology > Petrology
ID Code:12328
Deposited On:02 Mar 2011 11:14
Last Modified:14 Mar 2014 13:05

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