Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Abstract

AbstractSouth central Pyrenean foreland basin fill preserves the eroded remnants of the early stages of fold‐thrust belt evolution and topographic growth. Specifically, the Eocene Hecho Group in the Ainsa Basin contains a succession of turbiditic channels and levees deposited in the transition zone between the fluvial‐deltaic and deep marine depozones. Detailed isotopic provenance analyses allow for the reconstruction of sediment sources of the ancient sediment routing systems. This study presents 2332 new detrital zircon (DZ) U‐Pb ages and 246 new DZ double‐dated (U‐Th)/(He‐Pb) ages from 19 turbiditic and fluvio‐deltatic sandstones in the Ainsa Basin. These data indicate a progressive provenance shift from Cadomian/Caledonian plutonic and metamorphic rocks of the eastern Pyrenees to Variscan plutonic rocks in the central Pyrenees. Minor sediment contributions from sources located to the S and SE of the basin are seen throughout the section. New DZ (U‐Th)/He results identify four main cooling events: Pyrenean orogenesis (~56 Ma), initial basin inversion (~80 Ma), Cretaceous rifting (~100 Ma), and pre‐Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that high‐frequency fluctuations in sediment delivery processes and sediment routing introduce superimposed noise upon the basin‐scale long‐term provenance evolution during orogenesis.