Petrogenesis of Ordovician Magmatism in the Pyrenees (Albera and Canigó Massifs) Determined on the Basis of Zircon Minor and Trace Element Composition

Abstract

Zircon composition (U, Th, rare earth elements, and Hf) was tested as a tracer of petrogenetic processes in a set of metaigneous rocks from two pre-Ordovician massifs in the Pyrenees, Canigo´ and Albera. Two groups were differentiated after analyzing a number of elements in zircon: (1) Casemı´ gneiss and Marialles amphibolite and (2) subvolcanic metaporphyries and Cadı´ and Sureda orthogneisses. Casemı´ gneiss and Marialles amphibolite from the Canigo´ massif have high Th, Th/U, and Ce/Sm and low Yb/Gd and U/Ce that define linear trends in most of the plots used. The anomalous trend of the data in the Th/U-versus-Hf plot suggests mantle involvement in the origin of these rocks and the participation of fractional crystallization during their evolution. Zircon of the metaporphyries and the Cadı´ and Sureda orthogneisses exhibit similar characteristics despite a difference in age. Zircon has low Th, Th/U, Ce/ Sm, and and high Yb/Gd and U/Ce, suggesting that this mineral grew in a melt formed by anatexis of a ∗ Eu/Eu continental crust, with stable plagioclase. These petrogenetic data are consistent with the previously studied wholerock geochemistry and Sr-Nd isotopes and confirmthe use of zircon as a marker of petrogenetic processes in preference to a lithological tracer.