Rhodope and Vardar: the metamorphic and the olistostromic paired belts related to the Cretaceous subduction under Europe
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- 作者：Ricou ; L.-E. ; Burg ; J.-P. ; Godfriaux ; I. ; Ivanov ; Z.
- 关键词：Alpine chains ; regional synthesis ; thrust and exhumation tectonics ; Chaî ; nes alpines ; synthè ; se ré ; gional ; tectonique de charriage et exhumation
- 刊名：Geodinamica Acta
- 出版年：1998
- 出版时间：December, 1998
- 年：1998
- 卷：11
- 期：6
- 页码：285-309
- 全文大小：2.57 M
文摘
The Rhodope massif of Bulgaria and Greece is a complex of Mesozoic synmetamorphic nappes stacked in an Alpine active margin environment. A new analysis of the Triassic to Eocene history of the Vardar suture zone in Greece discloses its Cretaceous setting as a subduction trench. We present a geological traverse that takes into account these new observations and runs from the Hellenides to the Balkans, i.e. from the African to the Eurasian sides of the Tethys ocean, respectively. The present review first defines the revisited limits of the Rhodope metamorphic complex. In particular, the lower part of the Serbo-Macedonian massif is an extension of the Rhodope units to the west of the Struma river. Its upper part is separated as the Frolosh greenschist unit, which underlies tectonic slivers of Carpathic-Balkanic type. Several greenschist units, which locally yield Mesozoic fossils, follow the outer limits of the Rhodope. Their former attribution to a stratigraphic cover of the Rhodope has been proven false. They are divided into roof greenschists, which partly represent an extension of the Strandza Jurassic black shales basin, and western greenschists, which mostly derive from the Vardar Cretaceous olistostromic assemblage. The Rhodope complex of synmetamorphic nappes includes Continental Units and Mixed Units. The Continental Units comprise quartzo-feldspathic gneisses in addition to thick marble layers. The Mixed Units comprise meta-ophiolites as large bodies or small knockers. They are imbricated, forming an open dome whose lower, Continental Unit constitutes the Drama window. The uppermost Mixed Unit is overlain by remnants of the European plate. The presentday structure results from combined large-scale thrust and exhumation tectonics. Regional inversions of synmetamorphic sense-of-shear indicate that intermediate parts of the wedge moved upward and forward with respect to both the lower and upper plates. A kinematic model is based on buoyancy-driven decoupling at depth between subducted continental crust and the subducting lithosphere. Continuing convergence allows coeval underthrusting of continental crust at the footwall, decoupling at depth, and upward-forward expulsion of a low-density metamorphic wedge above. The continental crust input and its upward return may have lasted for at least the whole of the Early Cretaceous, as indicated by isotopic ages and the deformation history of the upper plate. A Late Eocene marine transgression divides the ensuing structural and thermal evolution into a follow-up uplift stage and a renewed uplift stage. Revision of the limits of the Vardar belt in Greece first resulted in separating the Paikon mountain as a tectonic window below the Vardar nappes. It belongs to the western, Hellenic foreland into which a system of thrust developed downward between 60 and 40 Ma. The eastern limit is a dextral strike-slip fault zone that developed greenschist facies foliations locally dated at 50-40 Ma. Revision of the lithological components discloses the preponderance of Cretaceous volcano-detritic and olistostromic sequences that include metamorphite blocks of Rhodope origin. Rock units that belong to the Vardar proper (ophiolites, Triassic and Jurassic radiolarites, remnants of an eastern Triassic passive margin) attest for a purely oceanic basin. The Guevgueli arc documents the Jurassic change of the eastern Triassic passive margin into an active one. This arc magmatic activity ended in the Late Jurassic and plate convergence was transferred farther northeast to the subduction boundary along which the Rhodope metamorphic complex formed. We interpret the Rhodope and the Vardar as paired elements of a Cretaceous accretionary wedge. They document the tectonic process that exhumed metamorphic material from under the upper plate, and the tectonic-sedimentary process that fed the trench on the lower plate. The history of the Rhodope-Vardar pair is placed in the light of the history of the Tethys ocean between Africa and Europe. The Cretaceous subduction then appears as the forerunner of the present Hellenic subduction, accounting for several shifts at the expense of the lower plate. The Late Eocene shift, at the closure of the Pindos basin, is coeval with the initiation of new uplift and magmatism in the Rhodope, which probably document the final release of the low-density, continental root of the Rhodope from subduction drag.