The Cycladic Basement (CB) and the overlying Cycladic Blueschist Unit (CBU) are part of the Paleogene Cycladic subduction complex exposed in Miocene metamorphic core complexes in the distended back-arc of the retreating Hellenic subduction zone of the southern Aegean. While the Cenozoic tectono-metamorphic evolutions of the CB and the CBU have been the foci of numerous studies, this study presents new laser ablation inductively coupled plasma mass spectrometry bedrock and detrital zircon (DZ) U-Pb ages that place robust constraints on the presubduction tectonic, magmatic, and paleogeographic evolution of the CB. Zircon U-Pb ages of crystalline CB are $\sim$306-330 Ma, demonstrating local plutonism associated with regional voluminous, protracted Carboniferous magmatism related to Paleo-Tethys subduction. The plutons intruded the CB metasedimentary host-rock sequence, characterized by distinct Gondwanan DZ U-Pb provenance, Neoproterozoic to early Paleozoic maximum depositional ages, and synmagmatic, contact metamorphic zircon rims ($\sim$300-330 Ma). DZ U-Pb dating revealed postmagmatic Permian metasedimentary rocks ($\sim$270-295 Ma) that unconformably overlie the CB and have unimodal DZ spectra that indicate exhumation of the CB prior to Permian deposition within extensional basins, as well as mark the onset of CBU deposition prior to formation of the Pindos rift domain. These U-Pb results clarify the late Paleozoic-early Mesozoic evolution of the CB as a peri-Gondwanan terrane composed of Neoproterozoic and early Paleozoic metasedimentary rocks, intruded by voluminous Carboniferous arc magmatism, and exhumed in the Permian, prior to Triassic rifting and CBU deposition. Additionally, these data provide a chronostratigraphic framework and illuminate subduction-related juxtaposition within the CB metasedimentary sequence.

The Lavrion district of the Attica Peninsula, Greece, exposes the West Cycladic Detachment System (WCDS), a low-angle crustal-scale extensional fault system separating tectonostratigraphic units of the Cycladic Blueschist Unit. New multiple single-grain fusion and step-heated white mica 40Ar/39Ar ages integrated with existing (U–Th)/He ages and independent paleothermometry resolves a syn- to post-orogenic deformation history. A structurally higher unit records Oligocene greenschist facies deformation that evolved into brittle conditions by the middle Miocene, and shares a similar history to Serifos at the southern end of the detachment system. The structurally lowest unit remained ductile until the late Miocene, preserving pervasive post-orogenic structures, similar to along-strike structures at the centre, deepest part of the fault. The similarities of structural styles and the timing of deformation across > 150 km of strike length of the detachment system indicates tens of kilometers of offset and extraordinary potential for correlating observations along Cycladic-style detachment systems.

©2019. American Geophysical Union. All Rights Reserved. The Cycladic Basement (CB) and the overlying Cycladic Blueschist Unit (CBU) are part of the Paleogene Cycladic subduction complex exposed in Miocene metamorphic core complexes in the distended back-arc of the retreating Hellenic subduction zone of the southern Aegean. While the Cenozoic tectono-metamorphic evolutions of the CB and the CBU have been the foci of numerous studies, this study presents new laser ablation inductively coupled plasma mass spectrometry bedrock and detrital zircon (DZ) U-Pb ages that place robust constraints on the presubduction tectonic, magmatic, and paleogeographic evolution of the CB. Zircon U-Pb ages of crystalline CB are $\sim$306-330 Ma, demonstrating local plutonism associated with regional voluminous, protracted Carboniferous magmatism related to Paleo-Tethys subduction. The plutons intruded the CB metasedimentary host-rock sequence, characterized by distinct Gondwanan DZ U-Pb provenance, Neoproterozoic to early Paleozoic maximum depositional ages, and synmagmatic, contact metamorphic zircon rims ($\sim$300-330 Ma). DZ U-Pb dating revealed postmagmatic Permian metasedimentary rocks ($\sim$270-295 Ma) that unconformably overlie the CB and have unimodal DZ spectra that indicate exhumation of the CB prior to Permian deposition within extensional basins, as well as mark the onset of CBU deposition prior to formation of the Pindos rift domain. These U-Pb results clarify the late Paleozoic-early Mesozoic evolution of the CB as a peri-Gondwanan terrane composed of Neoproterozoic and early Paleozoic metasedimentary rocks, intruded by voluminous Carboniferous arc magmatism, and exhumed in the Permian, prior to Triassic rifting and CBU deposition. Additionally, these data provide a chronostratigraphic framework and illuminate subduction-related juxtaposition within the CB metasedimentary sequence.

©2019. American Geophysical Union. All Rights Reserved. Sikinos and Ios Islands, located in the Southern Cyclades, represent part of a Cenozoic metamorphic core complex system that exposes subduction-related metamorphic rocks in the highly extended back-arc region of the Hellenic subduction zone. These exhumed HP-LT metamorphic units are composed of Mesozoic metasedimentary rocks of the Cycladic Blueschist Unit (CBU) and the Paleozoic Cycladic Basement (CB). The magmatic and stratigraphic evolution of these units, as well as the nature of the contact between the CBU and CB, have remained poorly understood. We used zircon U-Pb dating to determine crystallization ages of the CB on Sikinos and the maximum deposition ages and detrital provenance of the metasedimentary units to reconstruct the Mesozoic to early Cenozoic stratigraphic and tectonic evolution of the CBU on both islands. The results reveal that the CB in Sikinos is composed of Cambrian-Silurian metasedimentary rocks intruded by Carboniferous granites and is overlain by metasedimentary rocks of the CBU with depositional ages spanning from Permo-Triassic to Late Cretaceous. The provenance data from the CBU records a long-lived tectonic evolution from Paleo-Tethys subduction and rifting, to passive margin formation, and to subduction of the Neo-Tethyan Pindos basin. The continuous stratigraphic record and provenance evolution from the CB into the CBU imply a para-autochthonous relationship. On NE Sikinos and Ios, stratigraphic constraints suggest older-over-younger relationships along cryptic-thrusts, supporting premetamorphic or synmetamorphic structural repetition of the CBU by imbrication, likely during subduction underplating.

© 2019 Elsevier B.V. Identification of silver-rich sulfide mineralization in the abandoned mines at northern Hymittos Mt (central Attica, Greece) district has made this region important due to its structural relation to the world-class Lavrion mining district (25 km SE of Hymittos Mt.). At Agios Ioannis Kynigos mine veins of oxidized Fe-Pb-Zn-Ag ore are hosted in mylonitic marbles that were predominantly affected by brittle-ductile deformation associated with the West Cycladic Detachment System. The major sulfides are galena and arsenian pyrite which develop as open-space filling (fractures and vugs), disseminations and veinlets. Galena contains abundant inclusions of Pb-As-Sb-Cu-Ag sulfosalts (tetrahedrite group minerals, bournonite, jalpaite). An unusual silver-rich galena ore i.e from 192 to 1500 ppm Ag, is recorded from the present study, with Ag hosted mainly in Ag-tetrahedrite, acanthite and jalpaite. Compositionally pyrite shows As enrichment and the highest As concentration i.e. up to 3.9 wt% is found in the core of the oscillatory zoned pyrites. Values of $δ$34S of galena are isotopically light (−11.2 to −12.2‰), which suggests a sedimentary component to the ore fluid, that is likely derived from leaching of the meta-sedimentary (calc-mica schists) wall rocks. Carbon and oxygen isotope compositions of ore-stage carbonates show values i.e $δ$13CV-PDB (‰) = −8.2 to −11.7‰ and $δ$18O = 24.3 to 25.9‰ and for the non-mineralized carbonates $δ$13CV-PDB (‰) = +0.33 to 2.52‰ and $δ$18O = 20.8 to 26.1‰. The C and O isotopic composition of the carbonate wall rock distal to the orebody is typical of marine carbonates, whereas hydrothermal carbonates (brown calcite and dolomite) are dominated by an external, light C source. The lowest $δ$13CV-PDB values are recorded from cerussite and correspond to the low temperature supergene alteration from meteoric waters. The homogenized values of $δ$18O in the mineralized carbonates indicate interaction of fluid with host carbonates under a low fluid/rock ratio. The Pb-Zn-Ag mineralization at Agios Ioannis Kynigos bears many similarities with the low-temperature carbonate replacement-style mineralization in Kamariza, Lavrion area. Ore deposition in the northern Hymittos detachment fault is focused in the structurally upper parts of the detachment fault where circulation of meteoric fluids is dominant in the hydrothermal system.

© 2019 John Wiley & Sons Ltd The Lavrion district of the Attica Peninsula, Greece, exposes the West Cycladic Detachment System (WCDS), a low-angle crustal-scale extensional fault system separating tectonostratigraphic units of the Cycladic Blueschist Unit. New multiple single-grain fusion and step-heated white mica 40 Ar/ 39 Ar ages integrated with existing (U–Th)/He ages and independent paleothermometry resolves a syn- to post-orogenic deformation history. A structurally higher unit records Oligocene greenschist facies deformation that evolved into brittle conditions by the middle Miocene, and shares a similar history to Serifos at the southern end of the detachment system. The structurally lowest unit remained ductile until the late Miocene, preserving pervasive post-orogenic structures, similar to along-strike structures at the centre, deepest part of the fault. The similarities of structural styles and the timing of deformation across > 150 km of strike length of the detachment system indicates tens of kilometers of offset and extraordinary potential for correlating observations along Cycladic-style detachment systems.

The Stypsi Cu-Mo-Au-Re prospect, Lesvos island, is a shallow porphyry-epithermal system hosted within a middle Miocene microgranite porphyry, which was emplaced along NNE-, NW- and NE-trending structures, within trachyandesites to trachydacites and felsic pyroclastics of the Stypsi caldera. The mineralization comprises three stages: Stage I is characterized by magnetite-actinolite ± quartz in transitional and banded quartz veins mostly developed within the microgranite and the surrounding lavas related to calcic-potassic and propylitic alteration of the host rocks. In the banded veins, quartz is botryoidal, suggesting crystallization from a gel. Abundant vapor-rich inclusions in the bands produce a dark grey to black color. Within the veins, magnetite, chalcopyrite, bornite and native gold were followed in time by pyrite, hematite, sphalerite and galena. Stage I mineralization was synchronous and also postdates quartz formation in the veins, since it crosscuts and/or fills vugs in the center of the veins. Sulfides are associated with various combinations of K-feldspar, actinolite, epidote, chlorite, and calcite gangue minerals. Pyrite-molybdenite-chalcopyrite (Stage II) and late intermediate sulfidation epithermal veins (Stage III) overprint earlier mineralization and alteration, and are associated with sericite-calcite and sericite-kaolinite alteration of the porphyry system and spatially associated lavas, respectively. Molybdenite is widespread in the first two mineralization stages, with Re content ranging from about 0.3 wt% in Stage I to 1.96 wt% in Stage II. A barren silicic and advanced argillic (alunite-kaolinite) lithocap, is exposed on top of the porphyry-style mineralization and is crosscut by non-mineralized high-sulfidation epithermal chalcedony-barite veins. Bulk ore analyses of surface samples from the Stypsi prospect yielded values of up to 276 ppm Mo, 978 ppm Cu, up to 0.5 g/t Au, up to 3 g/t Ag, and up to 70 ppb Pd and Re. Fluid inclusion data indicate that the Stage I transitional and banded quartz veins were deposited at 420 °C–530 °C and at pressures up to 450 bars, from boiling hydrothermal fluids. The fluid in the veins consists of a brine (40–61 wt% NaCl equiv) that coexists with a lower salinity (6–14 wt% NaCl equiv) liquid phase and a low-density vapor-rich fluid. Fluid inclusions in quartz of the Stage III intermediate-sulfidation epithermal veins are characterized by relatively low homogenization temperatures (231 °C–288 °C) and salinities (up to 1.9 wt% NaCl equiv), which was the result of subsequent dilution of the moderately saline fluids by circulating meteoric water. This study verifies earlier works suggesting that Au-enriched felsic magmas are able to crystallize Re-rich molybdenite, and that Re may also be redistributed and enriched in later stages during the deposition of porphyry-style mineralization. The Stypsi prospect ressembles in many respects (e.g., Au grades, Cu/Mo ratios, the Re content of molybdenite and the presence of ore-grade calcic-potassic alteration), other porphyry Cu-Mo-Re-Au systems hosted in calc-alkaline rocks in northeastern Aegean, Greece.