SIGNIFICANCE OF SUBDUCTION-RELATED METAMORPHIC ROCKS IN SW CYPRUS AND NW SYRIA

The Late Cretaceous ophiolites of Troodos in Cyprus and Baer-Bassit in Syria form a part of the Tethyan ophiolite belt. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic mélange zones, which contain blocks of metamorphic rocks.

Structural mapping reveals that the metamorphic rocks have undergone polyphase deformation. Trace element geochemistry suggests that they are derived from Triassic oceanic rocks associated with continental margin sequences rather than from the Cretaceous ophiolites. Precise laser probe ⁴⁰Ar/³⁹Ar incremental-heating measurements were performed on 4 amphibolite samples from SW Cyprus and 6 from NW Syria. Plateau ages fall into two groups: the first includes older ages of 88.9 ± 0.8 Ma (Cyprus) and 88.4 ± 0.4 Ma (Syria) which are interpreted as the age of peak metamorphism (formation); the second ranges from 75.7 ± 0.3 Ma to 80.5 ± 0.3 Ma in Cyprus and 71.7 ± 0.5 Ma to 81.6 ± 0.3 Ma in Syria which are interpreted as the age of exhumation.

The metamorphic rocks found in Cyprus and Syria both formed in Turonian time, during the inception of intra-oceanic subduction, by subcretion below the overriding Troodos and Baer-Bassit ophiolites, which were developed above the subduction zone. The metamorphic rocks were exhumed by extension and crustal thinning above the subduction zone associated with subduction roll-back, and by the buoyancy of associated serpentinite protrusion, until the cessation of subduction in the Maastrichtian. The obduction of the Baer-Bassit ophiolite onto the Arabian carbonate platform induced an anticlockwise rotation of the Troodos ophiolite, which was juxtaposed with the the passive continental margin sequences (Mamonia Complex), along an arcuate fault zone. The Baer-Bassit ophiolite was fragmented during obduction and is now essentially represented by serpentinite mélange.

Alkaline lamprophyric dykes intruding the Late Triassic oceanic rocks provide amphibole ⁴⁰Ar/³⁹Ar ages of 140 ± 0.4 Ma. Thus intra-plate alkaline volcanism was possibly taking place close to the Mamonia continental margin for a period of up to 90 Ma.

These data place time constraints on the development of the passive continental margin, its associated oceanic lithosphere, and the onset and cessation of intra-oceanic subduction.