Sequential development of interfering metamorphic core complexes: numerical experiments and comparison with the Cyclades, Greece
| Autor: | D.J.J. van Hinsbergen, M. J. R. Wortel, P. Gautier, Céline Tirel |
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| Rok vydání: | 2009 |
| Předmět: | |
| Zdroj: | Geological Society, London, Special Publications. 311:257-292 |
| ISSN: | 2041-4927 0305-8719 |
| DOI: | 10.1144/sp311.10 |
| Popis: | 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 whichdeformationis not a priorilocalizedinaspecificplace,inordertoexaminewhethermultiple MCCs could develop during extension, at which conditions, and how. Configurations with either a singleMCCorseveralfar-distantMCCsalignedinthesectionparalleltoextensionare obtainedfor arelativelywiderangeofinitialconditions,theonlyfirmrequirementbeingthatthelowercrustand 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 islandsdocumentsa goodagreement with the experiments intermsoffinal depthofthe Moho,geo- metry 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. Themostlikely initial thicknessofthecrust is between40 and44 km.A thermallithospheric thick- ness 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 situ- ation. The numerical results also suggest a boundary velocity of 2.0-2.3 cm/a, which should basi- cally 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. |
| Databáze: | OpenAIRE |
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