Rotational deformation during Palaeogene thrusting and basin closure in eastern central Greece: palaeomagnetic evidence from Mesozoic carbonates

Abstract

Palaeomagnetic studies in Greece have concentrated upon Neogene sequences, with Mesozoic rocks of mainland Greece receiving little attention. The Neogene data base is now sufficiently extensive, however, to allow meaningful interpretation of older units. This paper presents new palaeomagnetic data from Mesozoic and Tertiary sequences of eastern central Greece, which document a pre‐Neogene phase of rotational deformation. Mesozoic carbonates have been sampled within the classic Pelagonian Zone in the Argolis Peninsula, Beotia and Evvia. Pelagonian sequences record the development, drowning and subsequent re‐establishment of a carbonate platform separating two strands of the Neotethys Ocean (the Pindos and Vardar basins). Most platformal facies are too weakly magnetized for palaeomagnetic analysis. However, pelagic horizons consisting of pink condensed limestones have been deposited periodically in response to platform subsidence. These Middle‐Late Triassic, Jurassic and Upper Cretaceous sequences yield high‐quality palaeomagnetic data, which reveal a consistent clockwise rotation of about 94°. The constancy of rotation angle deduced from the Mesozoic rocks suggests that the total Tertiary rotation is uniform throughout the area studied. This implies that observed variations in declination within the Neogene sequences result from sampling of rocks of different ages deposited during a period of rapid overall rotation. Removal of the largest Neogene rotation (45°) from the Mesozoic data set reveals a pre‐Middle Miocene. post‐Late Cretaceous clockwise rotation of the southern Pelagonian Zone of 50°. The major tectonic event during this time period was the closure of the Pindos Ocean during the Eocene. A large carbonate platform within the Pindos basin, now preserved in the Parnassos Zone, presented a major obstacle to the advancing Pelagonian nappes during SW‐directed thrusting (present coordinates). Impingement of the nappes on to the Parnassos platform resulted in pinning and subsequent clockwise rotation of thrust units around the south‐eastern margin of the platform. The southernmost tip of the Pelagonian Zone (southern Argolis) was detached along a pre‐existing line of weakness along the present Migdhalitsa Graben, and experienced a different rotation history. Additional palaeomagnetic data from the Pindos nappes in the eastern Peloponnesos also provide evidence for significant rotation of thrust sheets during Eocene basin closure. The Pindos sequences formed by pelagic sedimentation within the Pindos Ocean. An overall anti‐clockwise rotation with respect to the underlying Gavrovo‐Tripolitza autochthon is implied by the data. This probably reflects oblique emplacement of the Pindos thrust sheets on to the adjacent platform. Variations in rotation angle probably result from variations in footwall topography. Copyright © 1995, Wiley Blackwell. All rights reserved