Anatomy of a dying spreading ridge: paleomagnetic evidence for horizontal axis rotations in the Troodos Ophiolite, Cyprus

The Troodos ophiolite of Cyprus hosts a fossil spreading ridge at the Solea graben, whose last magmatic activity has been previously dated to 94.3±0.5 Ma. To study the evolution of a dying ridge, we collected structural geologic data and oriented specimens from the mantle section (serpentinized peridotites, pegmatitic dykes, pyroxenite and wehrlite intrusions) and lower crust (layered gabbros and massive gabbros) for paleomagnetic and rock magnetic analyses. Our results revealed a systematic pattern of horizontal axis rotations (i.e., tilt) in the region to the west of the Solea spreading axis, involving upper crust, lower crust, and upper mantle. Horizontal axis rotations vary in magnitude between ~20° to ~90° within the studied area, with the largest tilts observed to the west of the exposed mantle section at Mt. Olympus, and the smallest tilts observed near the NNW-SSE trending Troodos Forest-Amiandos fault system. This rotation pattern conflicts with previous interpretations considering the Troodos Forest-Amiandos fault as an oceanic detachment, and rather indicates the existence of deep-rooted listric faults that dismembered the Solea spreading ridge after the final phase of spreading.

 

Paleomagnetic directions from serpentinized peridotites indicate that serpentinization occurred both before and during dismemberment of the ridge by listric faulting. As these directions also record a well-studied regional 90° counter-clock-wise rotation of the Troodos ophiolite, we constrained the timing of ridge dismemberment and associated serpentinization between ~94 Ma and the beginning of the regional microplate rotation in the Turonian, hence encompassing a relatively short period of time of 2-4 Myr that well coincides with hydrothermal alteration in nearby plagiogranites dated at ~92–90 Ma.