A melilite-bearing high-temperature calcic skarn, Camasunary Bay,Isle of Skyea

摘要

The occurrence of high-temperature calcic skarns is relatively rare, with around 30 being reported worldwide. Here, we report on a newly discovered occurrence of a melilite-bearing high-temperature calcic skarn at Camasunary Bay, Isle of Skye. The contact metamorphism was caused by the intrusion of the Cuillin Hills gabbro and the later intrusion of the Coire Uaigneich granophyre. The calcic skarn consists of a high-temperature assemblage of wollastonite, kermanite-gehlenite, vesuvianite, tilleyite, spurrite, andradite-grossular garnet, monticellite and perovskite. It also includes the very rare Zr-rich garnet kimzeyite and baghdadite (Ca3(Zr,Ti)Si2O9), indicating transfer of Zr, Ti and other incompatible element-rich fluids derived from the hydrous Coire Uaigneich granophyre. The calcic skarn contains numerous cherty nodules and stringers, which bear a remarkable resemblance to the Cambrian-Ordovician dolostone exposures observed in other parts of Skye, suggesting that the protolith was originally an impure dolomite. The nature of the contact between the calcic skarn and surrounding Torridonian sedimentary rocks could not be directly observed, but elsewhere on Skye this contact is the Kishorn Thrust plane. This has implications for the simplified tectonic map accompanying the British Geological Survey map of Broadford (Sheet 71W), which now requires modification.