Abstract

The Shap Granite of northwest England is famous not only as the first rock that Cambridge Earth Sciences students see, but more widely as an ornamental stone with impressive K-feldspar megacrysts. The location of one prominent exposure of Shap Granite in Cambridge will be revealed.

The granite is one of the Trans-Suture suite, intruded either side of the recently closed Iapetus ocean in early Devonian time. The origin of this post-subduction suite is still uncertain, but melting was probably triggered by the heat pulse as the subducting slab broke off. The mechanism of upper crustal emplacement is also puzzling, overlapping as it does with the Acadian crustal shortening rather than with extension. Recent U-Pb zircon ages from the Shap Granite have clarified its emplacement age but have also revealed an unexpectedly long (20 Ma) magmatic history for the mid-crustal mush zone that fed the exposed plutons.

The Shap Granite is also famous in Quaternary studies. Its erratic boulders spread over northeast England were influential in persuading Victorian geologists that the superficial ‘Drift’ had been deposited by ice and not by Noah’s Flood. Disturbingly, the Flood theory is once more gaining favour.