Browsing by Subject "Zircon U-Pb"

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Pre-Cenozoic tectono-metamorphic evolution of the Cycladic Basement, Ios Island, Greece
(2018-08-08) Flansburg, Megan Elysia; Stockli, Daniel F.
The Cycladic Basement is a HP-LT unit exposed in the highly distended back-arc region of the retreating Hellenic subduction zone of the southern Aegean. The HP-LT Cycladic Blueschist Unit (CBU) and the Cycladic Basement are parts of the Paleogene Cycladic subduction complex and are exposed in Miocene metamorphic core complexes in the southern Cyclades, such as Ios, Naxos, and Paros islands. While the Paleogene tectono-metamorphic evolution of the Cycladic Basement and the CBU have been the foci of numerous studies, robust constraints of the Cycladic Basement’s pre-subduction magmatic, tectonic, and paleogeographic evolution have been largely lacking. This study presents new bedrock and detrital zircon U-Pb age data to elucidate the pre-subduction tectonic, magmatic, and paleogeographic evolution of the Cycladic Basement. Zircon U-Pb dating of granitoids from the crystalline core of Ios yielded an age of ~306-330 Ma, demonstrating voluminous and protracted Carboniferous magmatism related to Paleo-Tethys subduction and emplaced into Peri-Gondwanan crust. The plutons were emplaced into paragneisses and garnet mica schists of the Carapace metasedimentary host-rock sequence, characterized by distinct Gondwanan detrital zircon U-Pb (DZ) provenance, Neoproterozoic to lower Paleozoic maximum depositional ages, and syn-magmatic zircon rims (~300-330 Ma). DZ U-Pb dating also revealed a distinct sequence of post-plutonic Permian metasedimentary rocks (~270-295 Ma), previously lumped with the pre-plutonic Carapace or CBU, that disconformably overlies the Basement complex. These DZ ages, coupled with early Permian apatite U-Pb cooling ages, indicate rapid cooling and exhumation of the Cycladic Basement prior to the deposition of these Permian siliciclastic sediments within extensional basins. These Transitional Rocks mark the onset of deposition of the Permo-Triassic to Late Cretaceous CBU within the Pindos rift domain. In summary, these new U-Pb results illuminate the pre-Mesozoic evolution of the Cycladic Basement as a peri-Gondwanan terrane composed of Neoproterozoic and lower Paleozoic metasedimentary rocks, intruded by voluminous Carboniferous arc magmatism, and rapidly exhumed in the Permian, prior to Permo-Triassic rifting and CBU deposition. These data provide a critical puzzle piece in the pre-Mesozoic reconstruction of the Cyclades and for the understanding of early Mesozoic rifting and Paleogene subduction processes.