Abstract

Pb isotopes in detrital K-feldspar grains provide a powerful provenance tracer for feldspathic sandstones. Common Pb isotopic compositions show broad (hundred-kilometer scale) regional variation, and this signature can survive weathering, transport, and diagenesis. The feldspar Pb signature can be measured rapidly using laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS), and careful targeting can avoid inclusions and altered regions within grains. Here, we combine a new Pb domain map for the circum–North Atlantic with detrital K-feldspar Pb isotopic data from Triassic and Jurassic sandstones from basins on the Irish Atlantic margin. The Pb isotopic compositions reveal otherwise cryptic feldspar populations that constrain the evolving drainage pattern. Triassic sandstones originated from distant Archean and Paleoproterozoic rocks, probably in Green-land, Labrador, and the Rockall Bank to the NW, implying long (>500 km) transport across a nascent rift system. Later, Jurassic sandstones had a composite Paleo- and Mesoproterozoic source in more proximal sources to the north (<150 km away). No recognizable feldspar was recycled from Triassic into Jurassic sandstones, and the change in provenance is consistent with distributed, low-relief Triassic extension in a wide rift, followed by narrower Jurassic rifting with more localized fault-controlled sediment sources and sinks.

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