The Limerick Igneous Suite (LIS) in Co. Limerick, SW Ireland, contains two distinct basaltic igneous units: the Knockroe and Knockseefin, which are expressed as hypabyssal intrusions, porphyritic dykes, diatremes, lava flows, agglomerates, and tuffs. These units make up two distinct evolutionary trends: the Knockroe igneous units which range from alkaline basalts to trachyandesites and the Knockseefin igneous units which range from alkaline basalts to basanites. Uranium‒Pb dating of apatite establishes a primary crystallisation age of c. 350 Ma for the Knockroe units. Strontium and Nd isotopes from the least altered Knockroe bulk rock samples range from 0.70301 – 0.70454 and 0.512457 – 0.512493, respectively. The Sr isotopes for the least altered Knockseefin samples are similar, ranging from 0.70325 – 0.70386, but the Nd values are slightly more radiogenic, ranging from 0.512431 – 0.512437. Altered samples are buffered against changes in Nd, but some show excursions towards radiogenic Sr, suggesting contamination from Carboniferous seawater and/or introduction of Rb. Rubidium–Sr calculations conducted on altered Knockroe samples, returned ages within uncertainty of the U‒Pb dates. The bulk rock isotope values, normalised trace element plots as well as Zr/Sm, Ce/Pb, and Nb/U values demonstrate the LIS is comparable to ocean island basalts (OIBs) and Ce/Y and Zr/Nb values suggest the units likely originated from low degrees of partial melting likely caused by extension related to the assembly of Laurentia and Gondwana.

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