Palaeomagnetic insights into the evolution of Neotethyan oceanic crust in the eastern Mediterranean

Abstract

A synopsis of palaeomagnetic data from three Late Cretaceous eastern Mediterranean Tethyan ophiolites (Troodos, Hatay and Ba6r-Bassit) and their sedimentary cover sequences is presented. These data provide valuable insights into the role of regional-and local-scale tectonic rotations in the geodynamic evolution of Neotethyan oceanic crust. The geologically earliest phases of tectonic rotation are documented in the Troodos ophiolite, where rotations around both subvertical and subhorizontal axes are readily related to the development of the spreading fabrics and structures during crustal genesis. Subsequent c. 74 ~ anticlockwise intra-oceanic rotation of a 'Troodos microplate' has been quantified through analysis of the in situ sedimentary cover of the Troodos ophiolite. Results indicate that bulk anticlockwise rotation began soon after the cessation of spreading and ended by the end of the Eocene, with c. 50-60 ~ of microplate rotation being over by the Maastrichtian, the time at which ophiolite thrust sheets were emplaced onto the Arabian continental margin to the east of Troodos. Recent results from the emplaced, structurally dismembered Ba6r-Bassit ophiolite indicate extreme anticlockwise rotations of ophiolitic thrust sheets varying on a kilometre scale. New data from the post-emplacement sedimentary cover confirm that only a small component of these rotations is due to post-emplacement tectonism. Ba6r-Bassit represents the leading edge of the emplaced ophiolitic sheet. New data from the more coherent section preserved in the Hatay ophiolite to the north demonstrate significant anticlockwise rotation. This is equivalent to the rotation of the most northerly part of the Ba6r-Bassit units to the south, and is of the same sense and magnitude as the preMaastrichtian phase of microplate rotation documented in the Troodos. This suggests a common, intra-oceanic origin for the majority of the Troodos and Hatay rotations, and a significant component of the more variable rotations observed in Ba~Bassit. Overall, therefore, the data support a model involving: (1) intra-oceanic rotation of a coherent region of crust within the southern Neotethyan basin; this rotated unit is more areally extensive than has previously been inferred from consideration of data from the Troodos ophiolite alone; (2) emplacement of part of the rotated unit onto the Arabian platform; (3) subsequent localized post-emplacement modification, related to the development of the current plate configuration.

Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer–Bassit ophiolites: insights from 40Ar–39Ar geochronology

“…The age of the ophiolite can probably be further constrained by palaeomagnetic data, in that rocks of both normal and reverse polarities are found, implying that the ophiolite was formed in a magnetic transition period either prior to or after the long Cretaceous C34n interval (83.5-120 Ma: Gradstein et al 1994). The latter of these transition periods coincides with the radiometric ages mentioned above (Morris et al 2002(Morris et al , 2006. In these palaeomagnetic studies, the ophiolite blocks are inferred to have undergone anticlockwise rotation varying from 90 • to 200 • .…”

“…Palaeomagnetic studies show that the Troodos microplate underwent anticlockwise rotation soon after its formation (Moores & Vine, 1971;Clube, Creek & Robertson, 1985;Clube & Robertson, 1986;Morris et al 2006). Approximately 60 • of this rotation took place during the Late Campanian-Early Maastrichtian interval and the reorientation was completed by Early Eocene times.…”

“…The ∼ 74 • of reorientation involved two phases. The first was a regional intraoceanic rotation, associated with the Baer-Bassit and Hatay oceanic lithospheres during the G. H.-N. CHAN AND OTHERS Campanian-Maastrichtian, and the second, subsequent rotation was completed by Eocene times (Morris et al 2006).…”

“…The first was a regional scale, bulk intraoceanic rotation of the Troodos and Hatay oceanic lithosphere before the Baer-Bassit oceanic lithosphere was emplaced onto the Arabian passive margin. Subsequent rotation was probably induced by Late Tertiary deformation along the Dead Sea Fault Zone (Morris et al 2002(Morris et al , 2006.…”

The Ayyubid Orogen: An Ophiolite Obduction-Driven Orogen in the Late Cretaceous of the Neo-Tethyan South Margin

“…However, it has long been clear that the Eratosthenes seamount is a continental structure most likely torn from the AfroArabian margin as the eastern Mediterranean was opening (see Kempler 1998;Rybakov and Segev 2004 and the references therein). Here the Troodos was thrust for a very considerable distance and underwent an anticlockwise rotation for some 20° between the Turonian and the Campanian around a pole somewhere east of the present day Hatay, because it has recently turned out that the Hatay ophiolites have rotated in unison with the Troodos nappe (Morris et al 2006; Fig. 16).…”