RT Journal Article
T1 Nature and Composition of the LowerContinental Crust in Central Spain and theGranulite–Granite Linkage: Inferences fromGranulitic Xenoliths
A1 Villaseca González, Carlos
A1 Downes, Hilary
A1 Pin, Christian
A1 Barbero González, Luis C.
AB Xenolith-bearing alkaline ultrabasic dykes were intruded into the of the Hercynian basement of the Spanish Central System in early Mesozoic times. The suite of lower-crustal xenoliths in the dykes divided into three groups: felsic peraluminous granulites, metapelitic granulites and charnockitic granulites. The felsic granulites form ~95% of the total volume of the xenoliths, whereas the charnockitic and metapelitic granulites are much less abundant (~0·01 5%, respectively). Thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around850–950°C, 7–11 kbar; thus the xenoliths represent lower continentalcrustal material. Superimposed on this high-T high-Passemblage is a high-T low-P paragenesis represented mainly bykelyphitic coronas, reflecting re-equilibration during transport in the clearly restitic mineral assemblages, with up to 50% garnet and37% sillimanite. Major and trace element modelling supports theidea that the late-Hercynian peraluminous granites of central Spainrepresent liquids in equilibrium with restitic material of similar composition to the studied lower-crustal xenoliths. 87Sr/86Sr and eNd of the felsic xenoliths, calculated at an average Hercynian age of 300 Ma, are in the range 0·706–0·712, and –1·4 to –8·2, respectively. These values match the isotopic composition of the outcropping late Hercynian granites. The Sr isotopic composition of the xenoliths is lower than that of the outcropping mid-crustal lithologies (orthogneisses, pelites). A major contribution from the lower crust to the source of Hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis. The felsic nature of the lower continental crust in central Spain contrasts with the more mafic lower-crustal composition estimated in other European Hercynian areas, suggesting a non underplated crust in this region of the Hercynian orogenic belt.
PB Oxford University Press
SN 0022-3530
YR 1999
FD 1999
LK https://hdl.handle.net/20.500.14352/57020
UL https://hdl.handle.net/20.500.14352/57020
LA eng
DS Docta Complutense
RD 7 abr 2025