Provenance of quartz-rich metamorphic tectonite pebbles from the “Black Flysch” (W Pyrenees, N Spain): An EBSD and detrital zircon LA–ICP-MS study

Abstract

Metasandstone and quartz–tectonite conglomerate pebbles from the Albian Black Flysch encapsulate evidence of pre-Mesozoic igneous and metamorphic events. Quartz deformation microstructures and crystallographic fabrics characterize plastic flow under sub-greenschists (250–300°C) to high-grade metamorphic conditions (above 550–600°C). Detrital zircon grains from the pebbles provide concordant 206Pb/238U radiometric ages ranging from 473±26Ma to 2261±59Ma, with four major populations clustered in the intervals 1.96–1.80Ga (Paleoproterozoic), 1.11–0.93Ga (Stenian–Tonian), 765–571Ma (Neoproterozoic), and 500–475Ma (Cambro-Ordovician). The youngest zircons and the probability distribution of the studied population permit us to establish an Early Ordovician maximum depositional age for tectonite pebble protoliths and relate them with the Armorican Quartzite detrital zircon signature. We identify the currently submerged Landes Massif of the Armorican platform as the most likely candidate to being the source of Black Flysch metamorphic conglomerate pebbles.