The Larne No. 2 Borehole: discovery of a new Permian volcanic centre

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Abstract
Synopsis: The Larne No. 2 Borehole is situated in an area where Mesozoic and Tertiary rocks cover the assumed westerly extension of the Midland Valley of Scotland. It penetrated 2880·36 m of New Red Sandstone sediments and volcanic rocks and is one of the deepest boreholes drilled in Ireland. Beneath thin Quaternary clays, a Triassic succession consisting of saliferous Mercia Mudstone Group (958·3 m), overlying Sherwood Sandstone Group (648·3 m) was encountered. Permian Upper Marls (185·4 m), including a thick (113·1 m) basal halite, and Magnesian Limestone (21·6 m) successively underlie the Triassic rocks and with the latter may be correlated with similar sequences in Northern Ireland, England and the Irish Sea. The Permian succession beneath the Magnesian Limestone resembles that of south-west Scotland and comprises 440·l7 m of sandstone and pebble conglomerate overlying a hitherto unsuspected 616·7 m proven thickness of intermediate to basic volcanic rocks. These altered lavas have yielded K/Ar ages of c . 245 ± 13 Ma and the balance of evidence suggests that they are of early Permian age.