The multi-scale control of crustal structures on the exhumation of the British-Irish Isles, revealed by 40 years of AFT studies

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of the tectonic blocks between them, as is observed in the compilation of AFT data from northern Scotland and this could explain the dispersion in the timing of exhumation seen on the North Porcupine High, offshore Ireland.Finally, the Paleogene exhumation visible in the Central Irish Sea, and attributed in recent years to igneous underplating, has not been detected in the Malin Sea-Outer Hebrides, despite the area being underlain by a high-velocity body also interpreted as igneous underplating.
In conclusion, a detailed analysis of a large dataset of low-temperature thermochronological has revealed the possible influence of major crustal structure on the Mesozoic exhumation of this part of the NE Atlantic Margin, with large-scale decoupling occurring at a transfer zone and medium-scale decoupling occurring along regional-scale faults.The dataset also shed some doubts on the generic nature of exhumation caused by igneous underplating which has been much discussed in recent years.
The multi-scale control of crustal structures on the exhumation of the British-Irish Isles, revealed by 40 years of AFT studies

Irish-British Isles Database of Apatite Thermochronology (IBIDAT) -1977-2021
New insights from a synthesis of old and new apatite fission track and (U-Th-Sm)/He (AtT) data 1 Irish Sea and bordering highs (Lake District and eastern Ireland): Long-debated and still mysterious Irish Sea thermal anomaly.Small-scale variability showing that the cause of the thermal anomaly had complex shortwavelength thermal effects 2 English Midlands: stable craton with old AFT ages (young age is from an intrusion from the Lower Tertiary dyke swarm) 3 Scottish Highlands: First AFT ages published in the Irish British Isles (Hurford, 1977).Mixed ages showing a complex pattern of denudation.Old helium ages demonstrating limited amount of burial of summits and highs.
4 Hebrides Tertiary Igneous Province: all young AFT and AHe ages are related to the emplacement of the igneous centres rather than burial.Some old FT ages spread around the igneous centres (so the Irish Sea anomalous area does not extend to the Hebrides region)  The absence of significant exhumation despite the presence of these bodies reveal the non-systematic exhumation response to igneous underplating and therefore the large uncertainty present when using them as a prediction tool for exhumation.

Conclusions
• Compilation of a large AFT/Ahe database for the British-Irish Isles and offshore shelves + new offshore AFT/AHe ages.

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The database reveal for the first time the control of certain crustal structures (transfer zone and orogenic faults) on the Mesozoic exhumation of the area.

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The Anton Dohrn Transfer Zone might extends onshore to the SE and might have acted as a zone of decoupling during Mesozoic exhumation, with the zone to the SW being more uplifted than the zone to t he NE.

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Caledonian faults delineate tectonic blocks that seem to have responded differently to Mesozoic exhumation.

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The previously discovered mechanism of igneous underplating is shown to be ambiguous as it does explain the Greater Irish Sea Anomaly but is in contradiction with the old AFT ages found in the Donegal Basin and Outer Hebrides.

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After data filtering: older AFT ages in Scotland and Northern Ireland in comparison to Ireland.• Discrete rather than gradual boundary.Spatial correlation with 1) a possible extension of the offshore Anton Dohrn Transfer Zone (ADTZ) to the NW; 2) the southern edge of the locus of the Paleogene igneous dyke swarm.• Hypothesis: The Anton Dohrn transfer zone extends onshore to the SE and acted as a zone of weakness during Mesozoic rifting = greater amount of exhumation to the SW than to the NE.• Caledonian faults = orogenic regional-scale faults, correlated to faults in NE Canada.• Caledonian faults delinate tectonic blocks and basement terranes.• Younger AFT ages in the Northern Highlands terrane vs older ages in the surrounding Central Highlands and Hebrides terranes.• Hypothesis: Difference in ages = Differential response to Mesozoic exhumation controlled by Caledonian faults • Offshore Ireland, on the North Porcupine High, dredge and cored basement samples revealed thermal histories with significantly different timings of the main Mesozoic exhumation event.• Major Caledonian faults in the area based on magnetic anomaly and basement samples • Hypothesis: Discrepancies in age of main phase of exhumation due to differential exhumation across inferred Caledonian faults (similar to Northern Scotland example).• Greater Irish Sea Anomaly, GISA = Anomalously young (Paleogene) AFT ages in and around the central Irish Sea.Main focus of thermochronological studies in the British-Irish Isles over the last few decades.• Recent studies: correlated exhumation to the presence of a high velocity body at the base of the crust, interpreted as igneous underplating (emplaced during the Paleogene and derived from the Icelandic plume).• Igneous underplating can lead to significant localized exhumation due to isostatic compensation and subsequent erosion-led isostatic compensation.• New studies offshore Ireland: No Paleogene exhumation despite the presence of a thick high-velocity body at the base of the crust such as in the Donegal Basin and further north in the Outer Hebrides.•

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Ewan Pelleter and Thierry Dalle Mulle from Ifremer for facilitating the sampling at their core store in Brest • Andy Carter and Pieter Vermeesch from UCL for their help on the (U-Th)/He analyses • Oonagh O'Loughlin, Michael Hanrahan and the core store crew (Petroleum Affairs Directorate -PAD) for facilitating the sampling at the PAD core store • Alice Mitchinson and Martin Davies from the Irish Petroleum Infrastructure Programme (PIP) for providing industry reports (including thermal history studies) • PAD for the use of the seismic and well data