Abstract

Constraining the timing of brittle faulting is critical in understanding crustal deformation and fluid flow, but many regional-scale fault systems lack readily available techniques to provide absolute chronological information. Calcite mineralization occurs in crustal faults in many geological settings and can be suitable for U-Pb geochronology. This application has remained underutilized because traditional bulk dissolution techniques require uncommonly high U concentration. Because U and Pb are distributed heterogeneously throughout calcite crystals, high-spatial-resolution sampling techniques can target domains with high U and variable U/Pb ratios. Here we present a novel application of in-situ laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) to basaltic fault rock geochronology in the Faroe Islands, northeast Atlantic margin. Faults that are kinematically linked to deformation associated with continental break-up were targeted. Acquired ages for fault events range from mid-Eocene to mid-Miocene and are therefore consistently younger than the regional early Eocene onset of ocean spreading, highlighting protracted brittle deformation within the newly developed continental margin. Calcite geochronology from LA-ICP-MS U-Pb analysis represents an important and novel method to constrain the absolute timing of fault and fluid-flow events.

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