Petrogenesis of the Limerick Igneous Suite: insights into the causes of post-eruptive alteration and the magmatic sources underlying the Iapetus Suture in SW Ireland

The Limerick Igneous Suite (LIS) in County 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 tuffs. These units make up evolutionary trends: range from alkaline basalts to trachyandesites, Knockseefin basanites. U‒Pb dating of apatite establishes a primary crystallization age c. 350 Ma for units. Strontium Nd isotopes least-altered bulk rock samples over 0.70301–0.70454 0.512457–0.512493, respectively. Sr similar, ranging 0.70325–0.70386, but values slightly more radiogenic, spanning 0.512431–0.512437. Altered buffered against changes Nd, some show excursions towards radiogenic Sr, suggesting contamination Carboniferous seawater and/or introduction Rb. Rb–Sr calculations conducted on altered returned ages within uncertainty dates. isotope values, normalized trace element plots well Zr/Sm, Ce/Pb Nb/U demonstrate LIS is comparable ocean island Ce/Y Zr/Nb suggest likely originated low degrees partial melting caused by extension related amalgamation Laurussia Gondwana. Supplementary material: ESM 1, whole geochemistry data; 2, chemistry geochronology 3, supplementary figures available at https://doi.org/10.6084/m9.figshare.c.6297395