Keywords: Gabbroic rocks Crustal recycling Variscan orogeny Uthospheric mantle Spanish Central SystemThe gabbroic intrusions that crop out along the Spanish Central System (SCS) are geochemically heterogeneous, including primitive and evolved rocks. Differentiation is mainly related to fractionation of Cr-spinel and olivine, but mixing with coeval granitic magmas or crustal assimilation may have also played a role in the evolution of the most differentiated rocks. The most primitive uncontaminated gabbros show arc like trace element chondrite and primitive-mantle normalised patterns, characterised by large ion Iithophile elements (ULE)-Iigh t rare earth elements (tREE) enrichment, Sr and Pb positive and Nb-Ta-Ti negative anomalies. However, paleogeographic constraints suggest that the SCS was located far from subduction zones, so these geochemical signatures could be better explained by a recycling of continental crustal components within the mantle. The most primitive SCS gabbros expand the Sr-Nd isotopic compositional range of the Variscan basic magmatism in the Central Iberian Zone to more depleted values. This reflects a heterogeneous sub-continental Iithospheric mantle under central Spain ranging from a depleted mantle (ENd = +3.1. 87Sr/86Sr= 0.704) towards an isotopically enriched component (ENd = -1.6, 87Sr/ 86Sr = 0.706). Geochemical modelling suggests that mantle enrichment could be explained by minor lower crustal metapelitic granulite contamination (-2%). Additionally. the Sr-Nd-Pb isotopic ratios of the most primitive gabbros match the composition of the European subcontinental lithospheric mantle recorded in ultramafic xenoliths from western and central Europe.

The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt'%, is assigned to the analysis of altered, porous minerals, With the example of three zircon populations we show that low totals are related to textural features (i,e" numerous pores of tens to hundreds of nanometers size) as well as to the chemical com position (i,e., water content well within the wt% range, which may affect partial sample degradation under the electron beam).The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volume expanded material in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non vol ume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incor poration of water. The alteration has also resulted in uptake of non-formula elements such as AI, P, Ca, Fe, Y, and REEs whereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because por ous, low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a sec ondary alteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatter intensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity) and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range.

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Basic and intermediate meta-igneous xenoliths are very scarce within the granulite population transported by the Per mian alkaline lamprophyric dyke swarm of the Spanish Central System (SCS). These xenoliths are metalurninous pyroxene-bearing chamockites (sensu lato). They show LREE-poor plagioclase and orthopyroxene-clinopyroxene. Crystallization conditions were estimated at about 850 to 1000 °C and 9 to 11 kbar, a slightly higher range than that estimated for the associated peralurninous granulites, but indicating derivation from the lowerrnost crust.\¥hole-rock geochemistry suggests that the chamockite samples are not a cogenetic suite. The more basic varieties have affinities with cumulates from previous calc-alkaline underplated protoliths, whereas intermediate charnockites have a restitic origin. The similarity in Sr-Nd-Pb isotopic signatures between these restitic chamockites and some SCS I-type granites suggests a genetic relationship. This study, including Pb isotopic data from the whole granulite xenolith suite, reinforces the lower-crustal derivation of the SCS Hercynian granitic batholith.

A post-tectonic plutonic array of felsic I-type granites crops out in the western Hercynian Iberian Belt. Isotope (Sr, N d, Pb) data favour the absence of an important input of juvenile magmas in late-to post-tectonic Hercynian felsic magmatism in western Iberia, but suggest a reworking of different crustal protoliths, including oceanic metabasic rocks accreted to mid-to-Iower crustal levels during the early stages of the collision. I-type granites were derived from different meta-igneous protoliths ranging from metabasic to felsic compositions depending on their geographical position from the external (e.g. Galicia-N Portugal, GNP) to the innermost continental areas (Spanish Central System and Los Pedroches Batholiths). The GNP 1-type pIu tons related to eo-Hercynian accretional terranes have lower initial 87 Sr/ 86 Sr ratios, lower negative ENd values, and higher 2 06 Pb P 04 Pb ratios than other I-type

We have investigated the zircon from granites of the Spanish Central System (SCS) batholith. This batholith is composed of plutons of both I-and S-type granite, with different degrees of fractionation. The association provides a natural laboratory for the study of compositional evolution of zircon. We recognize two types of magmatic zircon. Type-1 zircon consists of euhedral and elongate crystals showing an oscillatory zoning, usually hosted in the early major minerals, being more abundant in granodiorite and monzogranite plutons. Type-2 zircon is characterized by smaller and more equant crystals, unzoned, or irregularly zoned, and usually interstitial to the rock-forming minerals, and forming clusters with other accessory minerals. This second type is more abundant in leucogranites, aplites and pegmatites. Type-2 zircon shows the highest concentrations of Hf (16.58 wt.% HfO 2 ), U (4.83% UO 2 ), Th (4.87% ThO 2 ), Y (8.51% Y 2 O 3 ), and HREE (3.78% HREE 2 O 3 ), and the lowest analytical totals (down to 91.2%). The replacement of Zr by tetravalent cations (Th, U and Hf) is favored in the most evolved granites. Micro-areas of zircon with low analytical totals (91-98 wt.%) have a high level of cation substitution. Moreover, their high Th-U contents induce elevated levels of radiation damage. Disturbances in the original structure, combined with severe metamictization of U-Th-rich micro-areas, may have caused an enhanced susceptibility to secondary alteration. This process, in turn, is believed to have formed the observed strongly damaged and cation-defi cient zircon. The range of Zr/Hf values in zircon crystals of the granites studied and those of related metamorphic rocks (as possible crustal sources) are similar. The composition of zircon from SCS granulite xenoliths overlaps with the compositional fi eld of zircon from granite, supporting previous models of crustal recycling for the origin of the SCS batholith.

Ion microprobe U-Pb analyses of zircons from three gabbroic intrusions from the Spanish Central System (SCS) (Talavera, La Solanilla and Navahermosa) yield Variscan ages (300 to 305 Ma) in agreement with recent studies. Only two zircon crystals from La Solanilla massif gave slightly discordant Paleoproterozoic ages (1,848 and 2,010 Ma). Hf isotope data show a relatively large variation with the juvenile end-members showing rHfj values as high as +3.6 to +6.9 and + 1.5 to +2.9 in the Navahermosa and

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