The Troodos ophiolite of Cyprus records a prolonged tectono-thermal evolution from crustal accretion at an oceanic spreading center to emplacement over continental margins, involving multiple stages of serpentinization, deformation, and exhumation. Previous thermochronological studies, based on zircon and apatite from the lower and middle crust, identified Late Cretaceous and Late Miocene cooling phases, providing important constraints on the exhumation of the oceanic crustal section. In contrast, the ultramafic mantle section - where serpentinization is extensive - remains poorly constrained due to scarcity of datable minerals.
To resolve this gap, we apply here two novel isotopic tools, which have never been utilized in Troodos and only rarely tried elsewhere. Unlike bulk rock measurements, in-situ SIMS oxygen isotope analysis of serpentine enables micron-scale targeting of specific textural domains and thus facilitates the reconstruction of conditions during distinct serpentinization episodes. Likewise, (U–Th)/He thermochronology of chromite (Cr-spinel) provides a novel methodology to directly constrain the cooling within the serpentinized mantle and to extend the thermochronological information to deeper structural levels.
Preliminary SIMS measurements (>70 spots on five samples) yield abundant δ¹⁸Oserp values of ~5 to 7‰ (SMOW) in all samples, interpreted as an oceanic alteration stage. Higher values (11–15‰) recorded only in two highly serpentinized samples indicate a later hydration stage at lower temperature by high δ¹⁸O fluids, possibly brines or metamorphic fluids. Thus, serpentinization in Troodos was not a single uniform event but occurred in multiple episodes that varied spatially with respect to a crustal-scale detachment fault. A preliminary chromite (U–Th)/He age of 78 ± 8 Ma provides the first cooling age from the ultramafic mantle section of Troodos, offering new insight into the timing of mantle exhumation in the Troodos ophiolite. Additional analyses are required to evaluate its significance.