The ammonium content of Caledonian granites

The Caledonian granites of the British Isles have NH + 4 contents in the range of 0–167 parts per million. High contents (>60 ppm) are confined to muscovite-rich granites, occurring principally in a restricted area, namely SE Ireland and the Isle of Man. Their magmas are inferred to have formed by the partial melting of a sedimentary protolith rich in organic matter. There is no apparent correlation between NH + 4 content and initial 87 Sr/ 86 Sr ratios.