Determining the Timing and Type of Subduction Initiation Along the Cycladic Subduction Complex: The High and Low Temperature Sole in Tinos Island, Greece.

The initiation of a subduction zone is commonly characterized by rapid dynamic refrigeration of the subduction channel, resulting in an inverted thermal gradient due to underthrusting of the cold oceanic slab. This rapid initial cooling after subduction initiation is recorded by metamorphic rocks, referred to as the metamorphic sole, that were progressively accreted along the base of the upper-plate mantle wedge. The metamorphic sole is often characterized by highly attenuated, discrete tectonic slivers of early underplated material commonly classified as an upper high-temperature granulite or amphibolite and a lower low-temperature greenschist. Determining the metamorphic ages of the different slivers of the metamorphic sole itself and the associated surrounding HP-LT schists provide critical insights into subduction initiation.

A high-temperature and low-temperature metamorphic sole has been proposed on in Tinos Island, Greece, above the Attic-Cycladic Crystalline Complex, allowing for the study of subduction initiation and early stages of the Cycladic Subduction Complex (CSC). This metamorphic sole lies beneath the metamorphosed late Jurassic Tsiknias Ophiolite suite (161.9 ± 2.8 Ma) and above the early Eocene HP-LT metamorphosed Cycladic Blueschist Unit (CBU). This proposed metamorphic sole was likely further sheared and attenuated during Miocene crustal-scale extension, accommodated along the North Cycladic Detachment system.

Samples from the Tinos metamorphic sole at the base of the Tsiknias Ophiolite are characterized by garnet amphiboles above greenschists. Petrochronological data from the metamorphic sole is scarce but provides important information. Previous work has dated a leucodioritic vein within the metamorphic sole as Late Cretaceous (74 ± 3.5 Ma). This study provides new U-Pb petrochronological data for both the high- and low-temperature metamorphic sole rocks that provide new insights into the early tectono-metamorphic evolution of the Cycladic subduction complex prior to early Eocene peak HP-LT metamorphism.