Sequential development of interfering metamorphic core complexes: Numerical experiments and comparison with the Cyclades, Greece
Published:January 01, 2009
C. Tirel, P. Gautier, D. J. J. Van Hinsbergen, M. J. R. Wortel, 2009. "Sequential development of interfering metamorphic core complexes: Numerical experiments and comparison with the Cyclades, Greece", Collision and Collapse at the Africa–Arabia–Eurasia Subduction Zone, D. J. J. Van Hinsbergen, M. A. Edwards, R. Govers
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The mechanics of metamorphic core complex (MCC) development and the associated process of lower crustal flow have been the topic of several modelling studies. The model setup usually includes a local heterogeneity forcing deformation to localize at a given site, enabling only one MCC to develop. This paper presents numerical lithospheric-scale experiments in which deformation is not a priori localized in a specific place, in order to examine whether multiple MCCs could develop during extension, at which conditions, and how. Configurations with either a single MCC or several far-distant MCCs aligned in the section parallel to extension are obtained for a relatively wide range of initial conditions, the only firm requirement being that the lower crust and the sub-Moho mantle both have very low strengths. In contrast, only a narrow range of conditions leads to the development of closely spaced MCCs. In this case, the MCCs interfere with one another (the domes are partly superimposed or/and share a shear zone in common) and develop in sequence. This configuration is compared with the Cyclades archipelago, where closely spaced chains of MCCs have been described in the literature. A review of available data on the islands documents a good agreement with the experiments in terms of final depth of the Moho, geometry and kinematic pattern of the MCCs, and timing of exhumation of the metamorphic rocks. Based on this agreement, we tentatively deduce from the numerical results some of the conditions that prevailed at the initiation of, and during, post-orogenic MCC-type extension in the Cyclades. The most likely initial thickness of the crust is between 40 and 44 km. A thermal lithospheric thickness of only c. 60 km is also likely, which might be a condition at the onset of extension or may have been obtained during early stages of extension while the lithosphere was warmed up. Either a backarc subduction setting or a process of mantle delamination may account for this situation. The numerical results also suggest a boundary velocity of 2.0–2.3 cm/a, which should basically reflect the rate at which the South Hellenic subduction zone retreated. Considering c. 500 km as an upper bound for the amount of retreat balanced by Aegean extension and assuming that this retreat mostly occurred during MCC-type extension in the Cyclades, we find that the boundary velocity could have been as high as 2.1 cm/a if MCC-type extension lasted 24 Ma, starting at c. 30 Ma and finishing at c. 6 Ma, as suggested by available geochronological data. A velocity of 2.1 cm/a agrees well with the numerical results.
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Collision and Collapse at the Africa–Arabia–Eurasia Subduction Zone
The Mediterranean and northern Arabian regions provide a unique natural laboratory to constrain geodynamics associated with arc–continent and continent–continent collision and subsequent orogenic collapse by analysing regional and temporal distributions of the various elements in the geological archive. This book combines thirteen new contributions that highlight timing and distribution of the Cretaceous to Recent evolution of the Calabrian, Carpathian, Aegean and Anatolian segments of the Africa–Arabia–Eurasia subduction zone. These are subdivided into five papers documenting the timing and kinematics of Cretaceous arc–continent collision, and Eocene and Miocene continent–continent collision in Anatolia, with westward extrusion of Anatolia as a result. Eight papers provide an overview and new data from stratigraphy, structure, metamorphism and magmatism, covering the geological consequences of the largely Neogene collapse that characterizes the segments of interest, in response to late stage reorganization of the subduction zone, and the roll-back and break-off of (segments of) the subducting slab.