U-PB LA-ICPMS ZIRCON GEOCHRONOLOGY OF THE GRANITES OF THE CORNUBIAN BATHOLITH, SW ENGLAND

Available U–Pb age data for the Cornubian Batholith of SW England is based almost entirely on monazite and xenotime, and very little zircon U–Pb age data has been published. As a result, no zircon inheritance data is available for the batholith, by which the nature of the unexposed basement of the Rhenohercynian Zone in SW England might be constrained.

Zircon LA-ICPMS data for the Cornubian Batholith provides Concordia ages (Bodmin Moor granite: 316 ± 4 Ma, Carnmenellis granite: 313 ± 3 Ma, Dartmoor granite: ~310 Ma, St. Austell granite: 305 ± 5 Ma, and Land’s End granite: 300 ± 5 Ma) that are consistently 20-30 Ma older than previously published emplacement ages for the batholith and unrealistic in terms of geologic relative age relationships. Several of the batholith’s granite plutons contain a component of late-Devonian inheritance that may record rift-related, lower crustal melting or arc-related magmatism associated with subduction of the Rheic Ocean.

In addition, the older granites likely contain Mesoproterozoic inheritance, although the highly discordant nature of the Mesoproterozoic ages precludes their use in assigning an affinity to the Rhenohercynian basement in SW England.