The post-Carboniferous evolution of Ireland: evidence from Thermal HistoryReconstruction

Integration of Apatite Fission Track Analysis (AFTA((R))) and vitrinite ref lectance (VR) data from onshore Ireland reveals a complex thermal history, characterized by multiple cooling episodes of late Carboniferous, Jurassic, early Cretaceous, early Tertiary and late Tertiary age. Peak palaeotempera tures in each episode decrease through time to produce an overall long-term cooling trend since the late Carboniferous. Thermal history styles across the region are very similar, though the magnitude of peak palaeotemperature s in individual episodes shows some variation. Similar thermal histories ar t: also identified in the surrounding offshore regions. The regional nature of all these palaeo-thermal episodes, and their correlation with regionall y significant unconformities, suggests that heating was due primarily to gr eater depth of burial, with subsequent cooling representing the progressive unroofing of the present onshore region since late Carboniferous times. In Northern Ireland, explanations of early Cretaceous and early Tertiary pala eotemperatures in terms of greater depth of burial are more difficult to re concile with geological evidence, and heating due to hot fluid movement app ears more likely. This applies particularly to early Tertiary effects, for which the Tertiary Igneous Province provides a ready explanation. Over the entire onshore region, maximum maturity levels in Carboniferous and older u nits were reached at the end of the Carboniferous, and preservation of hydr ocarbons to the present day, through several tectono-thermal episodes, appe ars unlikely.