Beneath the basalt columns of Northern Ireland’s famous coastline, and spreading south across the border into the Republic, lies one of the most significant records of ancient volcanism in the entire North Atlantic. For decades, geologists working this ground have carried a nagging problem: the dates never quite added up. The volcanic rocks here seemed too old at one end and too young at the other, stretching across a timeline so long it refused to fit neatly into any accepted model of how this part of the world was torn apart by fire and geological force some 60 million years ago.
That problem has now been solved, and the solution rewrites the volcanic history of Ireland in ways that reach far beyond the island itself.
A new study published in March 2026 by the Geological Society of America, authored by Mark R. Cooper of the Geological Survey of Northern Ireland alongside Simon Tapster and Daniel J. Condon of the British Geological Survey, has used some of the most precise dating techniques available to science to build a corrected timeline for the Paleogene volcanic rocks of Northern Ireland and the north of Ireland. What they found strips up to eight million years from a record that was always regarded as anomalous, compressing the entire period of volcanic activity in this region into a window of just 5.5 million years, running from approximately 61.6 million years ago to 55.9 million years ago.
To understand why that matters, you need to understand what the North Atlantic Igneous Province actually is. It is one of the largest and longest-running episodes of volcanic activity ever recorded on this planet, a colossal outpouring of magma that stretched from Greenland across Iceland and down through Scotland and Ireland as the North Atlantic Ocean began tearing itself open. At its heart was the proto-Icelandic plume, a column of superheated material rising from deep within the Earth’s mantle, punching through the overlying crust and feeding surface eruptions on a continental scale. The floods of basalt it produced built the landscape that today forms the Giant’s Causeway, the Antrim Plateau, and the dramatic volcanic complexes of the Mourne Mountains and Slieve Gullion.
The question that has driven geological debate for years is whether this plume operated in pulses, sending waves of magmatic energy outward in bursts, or whether the rifting of the Atlantic itself did most of the work by thinning the crust and allowing magma to find its way upward independently of any plume.
Ireland’s volcanic record, sitting at the far southeastern margin of this entire system, should have been the key to answering that question. Instead, under the old dating framework, it looked like an outlier that undermined both models.
The old dates came primarily from a technique called argon-argon dating, and they painted a picture that confused more than it clarified. Some results suggested volcanic activity in this region began as early as 64 million years ago, making it among the oldest in the entire eastern corridor of the North Atlantic Igneous Province. Others pushed the youngest activity to around 50 million years ago, a full six million years after the North Atlantic had already broken open and seafloor spreading had begun. That combination, oldest at one end and youngest at the other, made the Irish and Northern Irish rocks look disconnected from everything happening elsewhere in the province. It suggested the region had its own independent volcanic story, driven perhaps by local crustal thinning as the Atlantic rift crept northeastward, rather than by the same plume pulses controlling activity in Scotland, Greenland, and the Faroe Islands.
The new study dismantles that picture almost entirely. Cooper, Tapster, and Condon applied a technique called CA-ID-TIMS zircon U-Pb dating, one of the highest precision geochronological methods currently available, targeting zircon crystals extracted from a carefully selected range of rock types across the region. The work was guided by airborne geophysical survey data from the Tellus Project, which provided magnetic intensity images of Northern Ireland and the border region at a resolution that revealed geological relationships invisible at ground level, particularly the dense networks of ancient dikes cutting through the basalt sequences.
What emerged from this combined approach was a sequence that is far more coherent than anyone had previously managed to demonstrate. The Lower Basalt Formation, the oldest of the flood basalt units that built the Antrim Plateau, is now dated to shortly after 61.57 million years ago. The Tardree Rhyolite Complex, which cuts through those older basalts and therefore sets a minimum age for them, dates to 61.109 million years ago. The Scrabo Sill, previously dated by argon methods to around 50 million years ago and long regarded as evidence for anomalously late activity, has been redated to 61.318 million years ago, collapsing what looked like a 14-million-year tail of activity into the main sequence.
The youngest rocks in the revised framework are the granites of the Mourne Mountains Complex, with the oldest of those granites dating to 56.465 million years ago and the youngest to 55.918 million years ago. The entire volcanic history of Northern Ireland and the north of Ireland, from first eruption to final intrusion, fits within 5.5 million years.
That compressed timeline changes everything about how this corner of Ireland fits into the broader story of North Atlantic volcanism. Rather than a region that started early and kept going long after everywhere else had gone quiet, Northern Ireland and the north of Ireland now show a volcanic history that tracks closely with the pulses recorded across Scotland, Greenland, and the wider province. The onset of flood basalt eruptions here aligns with the start of magmatism in Scotland at around 61.7 million years ago, and both align with a well-documented environmental transition at the Danian-Selandian boundary, a moment in deep geological time when the North Sea Basin saw its first influx of coarse clastic sediment after 40 million years of carbonate deposition. That sediment influx has long been interpreted as evidence of crustal uplift driven by a pulse of plume activity, and the new Irish dates now fall precisely into that window.
The evidence also addresses the question of what was driving the stress conditions in the crust during the earliest phase of volcanism. Between the eruption of the Lower Basalt Formation and the intrusion of the later dike swarms, the structural record shows that the dominant stress regime was one of far-field alpine compression, not Atlantic rifting. The North Atlantic was not yet pulling this region apart with enough force to generate magma independently. That points directly toward the plume as the active driver, sending pulses of thermal energy outward from its head beneath Greenland and reaching even this distal southeastern corner of the province.
The final pulse of activity, focused on the Mourne Mountains granites and the Fleetwood Dike Swarm cutting southward into the Irish Sea, ended at around 55.9 million years ago. That is almost exactly when seafloor spreading locked in across the North Atlantic and the proto-Icelandic plume settled into the configuration that feeds Iceland’s volcanoes today. The melt-generating thermal anomaly beneath Ireland was effectively switched off as the ocean opened and the plume’s energy found a new and permanent outlet to the northwest.
The Irish Sea portion of that final pulse also sits directly above what is now known to be a finger of hot mantle material extending from the present-day Icelandic plume, a detail that suggests the deep geological plumbing established 56 million years ago has never fully gone away.
Source:
ooper, M.R., Tapster, S., and Condon, D.J., 2026, Feeling the pulse? Paleogene chronostratigraphy of Northern Ireland and the north of Ireland temporally coupled to the North Atlantic Igneous Province: Geology, Geological Society of America. https://doi.org/10.1130/G54157.1
