We discuss the assembly and tectonochronology of the Cycladic Blueschist Unit (CBU) in the central Aegean Sea region, Greece, as a composite, subduction-related, high-pressure (blueschist to eclogite facies) stack of nappes. Our work is based on a review of geochronologic data from the Cycladic islands of Tinos, Syros and Sifnos. In addition, we present a large set of 34 new, internally consistent Rb-Sr multimineral isochron age data from these islands that can be linked to distinct metamorphic stages and episodes of ductile deformation. The reviewed and new ages provide remarkably similar results indicating that the age data and their interpretation is robust. We find that three distinct, significantly diachronous, CBU high-pressure nappes were sequentially accreted between ~55 and ~30 Ma, with a fourth ~24-22 Ma old high-pressure belt, the Basal Unit, below the CBU. Each CBU nappe was exhumed soon after its high-pressure imprint and experienced greenschist-facies overprinting with partial metamorphic reworking ~10 Ma after high-pressure accretion. At the time the structurally higher high-pressure nappe was exhumed, an underlying nappe was accreted and metamorphosed at high-pressure conditions. Our work suggests that the high-pressure nappes were considerably exhumed as rather coherent units during sustained lithospheric shortening in a subduction channel by return flow. The early Oligocene underthrusting of the External Hellenides to the south of the Cyclades, and tectonically below the CBU, is interpreted to have reduced the taper of the Hellenic subduction wedge, which caused significant shortening across the Cyclades region and an important phase of out-of-sequence thrusting that emplaced the non-high-pressure upper units above the CBU. Our analysis shows that this shortening event also caused significant reimbrication within the CBU along the recently discovered Trans Cycladic Thrust.

我们讨论了希腊爱琴海中部地区基克拉迪蓝片岩单元 (CBU) 的组装和构造年代学，它是一个复合的、与俯冲相关的高压（蓝片岩到榴辉岩相）推覆岩堆。我们的工作基于对来自基克拉迪群岛蒂诺斯岛、锡罗斯岛和锡弗诺斯岛的地质年代学数据的审查。此外，我们提供了来自这些岛屿的 34 个新的、内部一致的 Rb-Sr 多矿物等时线年龄数据，这些数据可以与不同的变质阶段和韧性变形事件相关联。审查的和新的年龄提供了非常相似的结果，表明年龄数据及其解释是可靠的。我们发现三个不同的、显着历时的、CBU 高压推带在~55 到~30 Ma 之间依次增加，第四个~24-22 Ma 旧高压带，基础单元，位于 CBU 下方。每个 CBU 推覆在其高压压印后不久就被挖掘出来，并在高压吸积后经历了约 10 Ma 的部分变质再加工的绿片岩相叠印。在挖掘结构较高的高压推覆体时，下面的推覆体在高压条件下增生并变形。我们的工作表明，在俯冲通道中，由于回流，在持续的岩石圈缩短期间，高压推覆体作为相当连贯的单元被大量挖掘出来。基克拉泽斯以南的外部希腊化早期的渐新世下冲，在构造上低于 CBU，被解释为减少了希腊俯冲楔的锥度，这导致了整个基克拉泽斯地区的显着缩短和一个重要的无序推进阶段，将非高压上部单元置于 CBU 上方。我们的分析表明，这种缩短事件还沿着最近发现的跨基克拉迪逆冲断层在 CBU 内造成了显着的再利用。