Evidence for upper cretaceous transform fault metamorphism in West Cyprus

Metamorphic rocks of low-pressure/medium-temperature facies occur in West Cyprus as blocks and slivers with mafic and ultramafic screens in high-angle, serpentinite-filled fault zones. A satisfactory explanation for the origin of the metamorphic rocks has previously remained a subject of controversy. The evidence presented here, based on a study of their bulk chemistry, mineralogy and⁴⁰Ar/³⁹Ar geochronology, indicates they were produced by greenschist to amphibolite facies dynamothermal metamorphism of alkalic and tholeiitic mafic rocks and associated sediments at between 83 and 90 m.y. Their field relations show similarities with present-day oceanic fracture zones suggesting that metamorphism occurred within strike-slip faults, some of which were probably extensions of the Arakapas transform. We propose that hot crust generated at an oceanic spreading centre provided the heat for metamorphism when juxtaposed against older, cooler rocks during ridge-ridge transform movements. In addition, shear heating may have been facilitated by the strike-slip faulting and contributed to the total heat available. These interpretations are compatible with many aspects of the broader regional geology of Cyprus, provide new constraints on the early evolution of the Troodos Complex and form the basis of a model for transform fault metamorphism.