Chronology of granite magmatism and associated mineralization, SW England

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Abstract
An Rb-Sr study of Hercynian magmatism in SW England has established that the major granites were emplaced c. 290–280 Ma and that the inferred sequence of intrusion shows no geographic pattern. High initial 87 Sr/ 86 Sr ratios (0.710–0.716) are compatible with the ‘S–type’ and peraluminous mineralogical characteristics of the granites. REE distributions are consistent with those for normal leucogranites, in that they have a high LREE/HREE ratio and negative europium anomaly. However, the REE profiles for Bodmin and Carnmenellis contrast markedly with those of Land’s End and Dartmoor, implying differences both in the chemistry of the source region and in conditions of crystallization. Ages obtained for the Brannel and Wherry elvans (quartz porphyry dykes) suggest more than one episode of injection during the interval c. 280–270 Ma. An independent fluid inclusion Rb-Sr age for the South Crofty Sn–W deposit (269 ± 4 Ma) has shown that in the Camborne-Redruth area, the main stage Polymetallic mineralization is significantly younger than the Carnmenellis host granite. There is little evidence to support the idea of an older Westphalian event, and thus in the broader European Hercynian context the granites show greatest affinity with the younger Sn–W granites of Portugal.

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