SOME GEOCHEMICAL CHARACTERISTICS OF ORDOVICIAN AND CALEDONIAN ACID INTRUSIONS OF LLEYN, NORTH WALES

Abstract
Summary: Using twenty-four intrusions for which there is field evidence of age, the geochemical characteristics of the Upper Ordovician acid intrusive rocks of Lleyn are compared with those of similar rocks emplaced during the late phases of the Caledonian orogeny (probably Lower Devonian in age). The two groups of rocks are found to be quite distinct in several geochemical characteristics whilst they are largely different, with only a limited area of overlap, in many others. Using these geochemical characteristics an age is suggested for each of seven intrusions which lack field evidence.