Rb-Sr whole-rock isochron ages of late Precambrian to Cambrian igneous rocks from southern Britain

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Abstract
Rb-Sr age data are reported for late Precambrian to Cambrian igneous and metamorphic rocks from the border region of England and Wales. A felsic intrusion from Stanner Hill defines a good whole-rock isochron of 702 ±8 Ma. Uriconian pyroclastic rocks from the Wrekin area give a whole-rock age of 558± 16 Ma, while the late- or post-Uriconian Ercall granophyre from the same area gives a good whole-rock isochron of 533 ±13 Ma. A biotite cooling age from the nearby pre-volcanic Rushton Schist is consistent with these dates and suggests that the region cooled after the close of Uriconian magmatism at 536 ±8 Ma. All these results relate to widespread igneous/metamorphic activity in latest Precambrian to Lower Cambrian time. The Ercall granophyre and Rushton schist are directly overlain by Lower Cambrian sediments and 533±13Ma is thus a maximum age for the deposition of these rocks.