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In the Central Iberian Zone there are several large thermal domes in which small bodies of ultramafic, mafic and intermediate rocks appear intimately associated with crustal granites and migmatites. The closest spatial association between the ultramafic, mafic and intermediate rocks and migmatites is in the Toledo Anatectic Complex, where field relationships suggest that these rocks are coeval and have an age close to 340 Ma. This, and the recent discovery in the neighbouring Ossa Morena Zone of a large mid-crustal seismic reflector interpreted as a 335-350 Ma mafic sill, reinforce the hypothesis that heat for crustal melting was supplied from early Variscan mantle magmas emplaced in the middle crust. However, precise ionmicroprobe U-Pb zircon dating and Ti-in-zircon thermometry in Toledo do not support this idea. Whereas the mean age of four mafic bodies is 307 AE 2 Ma, the migmatites are c. 25 Ma older. The migmatites hosting ultramafic, mafic and intermediate bodies have the same age and Ti-in-zircon temperatures as migmatites far from any mafic intrusion. These data reveal that ultramafic, mafic and intermediate magmas are late Variscan; they were emplaced in already cooling anatectic zones once the extensional collapse was initiated, and their thermal impact on the mid-crustal Variscan anatexis of Central Iberia was negligible.

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Single-zircon evaporation and ion-microprobe dating of migmatites and anatectic granites in the Peña Negra Complex of Central Iberia reveal that the Variscan anatexis occurred continuously from 352 to 297 Ma, with a maximum at 335–305 Ma. Anatexis began coeval with the main collision of continental masses. A limited melting event, probably related to syncollision crustal-scale shear zones, produced a population of zircons with ages of c . 350 Ma. The production of new zircons decreased to a minimum at c . 343 Ma but then increased swiftly as the internal thermal evolution of the thickened Central Iberian crust led to widespread anatexis in the Peña Negra region at 332 Ma. Shortly after this, the melt resident in the migmatites was locally segregated into small bodies that crystallized as cordierite leucogranites at 321 Ma. Simultaneously, extensional subhorizontal shear zones were preferentially developed over layers of the migmatite series that, owing to their elevated heat production and fertility, had the highest melt fraction. Shearing provoked further anatexis and contributed significantly to the in situ production of high melt-fraction granodiorites and adamellites from the migmatites. This process occurred from 325 to 305 Ma, with a maximum at 309 Ma marking the peak of the Variscan extensional collapse in Central Iberia. After c . 305 Ma the melt fraction decreased quickly, so that the production of new zircons was insignificant at 300 Ma and had stopped completely by 297 Ma.

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