Basic Ordovician magmatism of the Spanish Central System: Constraints on the source and geodynamic setting

Abstract

New geochemical and geochronological data obtained from metabasites intrusive into pre-Floian metasedimentary and metaigneous rocks of the Spanish Central System (Revenga and El Caloco sectors) represent a complex pre-Variscan magmatic event. Analysed samples exhibit tholeiitic affinity but relatively high incompatible element contents. These rocks can be distinguished from similar tholeiitic SCS metabasites because they represent more primitive liquids with higher metal (Cr, Ni) and LILE contents and display a slightly enriched isotopic (Sr, Nd) composition. These data point to the involvement of several mantle sources including lithospheric sections with a crustal imprint. Two samples yield Ordovician U–Pb zircon intrusion ages of 473.1 (+3.8/−6.8) and 453.3±4.6Ma. This episode of basic magmatism is not coetaneous with the abundant Cambrian–Ordovician felsic orthogneisses of the Central Iberian Zone and likely represents a rifting context (Rheic Ocean opening) which started about 477Ma. A comparison with Lower to Middle Paleozoic magmatic rocks from other west European terranes implies a heterogeneous evolution from the Ediacaran to Middle Paleozoic in the northern margin of Gondwana. While western terranes (e.g., Armorican Massif, Saxo–Thuringian Zone, Ossa–Morena Zone) display monotonous shelf sedimentation and magmatic quiescence from the Upper Ordovician to Variscan collision, eastern terranes (e.g., Central Iberian Zone, Corsica–Sardinia, Alps, Pyrenees) exhibit magmatism of contrasting geochemical affinity, including basic alkaline and tholeiitic series, indicative of a more complex tectonic evolution.