6533b86efe1ef96bd12cbd45

RESEARCH PRODUCT

Structural analysis of a complex nappe sequence and late-orogenic basins from the Aegean Island of Samos, Greece

subject

description

The island of Samos in the Aegean Sea exposes high-pressure metamorphic rocks of the Cycladic blueschist unit which are sandwiched between the mildly blueschist-facies Kerketas nappe below and the overlying non-metamorphic Kallithea nappe. Structural and metamorphic analysis shows that deformation can generally be divided into four main stages: (1) Eocene and earliest Oligocene 0ESE‐WNW-oriented nappe stacking (D1 and D2) associated with blueschist- and transitional blueschist‐ greenschist-facies metamorphism (M1 and M2). D2 caused emplacement of the blueschist unit onto the Kerketas nappe indicating that thrusting occurred during decompression. (2) A subsequent history of Oligocene and Miocene horizontal crustal extension (D3) before and after greenschist-facies metamorphism (M3). Ductile flow during D3 was characterized by a high degree of coaxial deformation but in general caused displacement of upper units towards the ENE. Nonetheless, the late-stage D3 emplacement of the Kallithea nappe between 9 and 10 Ma had a top-to-the-NW/NNW sense of shear. (3) A short period of brittle E‐W crustal contraction (D4) occurred between <8.6 and 09 Ma. (4) A phase of N‐S-directed normal faulting (D5, <8.6 Ma to Recent). ESE‐WNW-directed tectonic transport during D1 through D3 is in contrast to uniform NNE‐SSWdirected tectonic transport in the adjacent Cyclades, Greece, as well as in the neighbouring Menderes Massif of western Turkey. Published paleomagnetic data reveal sinistral rotation between the Cyclades and western Turkey. We interpret this rotation as a consequence of diAerential extension between the severely extended Aegean and the moderately extended Menderes Massif during D3. The onset of D3 crustal extension is coeval with a marked change in the thermal structure. We propose that the thermal reorganization was associated with the retreat of the subduction zone towards the external Hellenides in the Early Oligocene and a subsequent increase in magmatic activity. # 1999 Elsevier Science Ltd. All rights reserved.