Lateral growth of the continental crust through deep level subduction-accretion: a re-evaluation of central Greek Rhodope

The Rhodope Massif of northern Greece and southern Bulgaria has been variab ly interpreted as a fragment of pre-Alpine (possibly Hercynian or Precambri an age) continental crust that was actively involved in European margin con vergent tectonics during the Mesozoic and Tertiary. Alternatively we propos e that, for central creek Rhodope, the lithological associations and tecton othermal history are consistent with progressive south-directed Mesozoic cr ustal growth through deep level subduction-accretion, a process which invol ved the near continuous transferral of material of oceanic and continental margin affinity, from footwall to hanging wall within a north-directed Pala eotethyan subduction system. Central Creek Rhodope comprises a sequence of schists, gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing. Extensive occurrences of marble are associated with amphibolites, variably retrogressed eclogites, meta-gabbro s and ultramafic rocks. Quartzo-feldspathic gneisses are abundant throughou t the area, and are associated with psammitic meta-greywacke sequences, pel ites and quartzites. The presence of intercalated marble slivers and thin m anganiferous and iron-rich siliceous bands is significant. The various comp onents exposed in the subduction-accretion complex were first underthrust n orthwards to deep crustal levels, subjected to high pressure, eclogite faci es metamorphism and underplated to the base of the overriding Eurasian plat e. This latter accretion event was characterised by intense southwest-direc ted ductile thrusting and pervasive amphibolite facies metamorphic overprin ting. It was accompanied by migmatisation and intracrustal melt generation, and followed by subduction related magmatism. Deep level subduction-accret ion leads to southward growth of the continental margin, which in turn lead s to subduction retreat allowing the encroachment of the magmatic are from the north. Subsequent extensional tectonic exhumation brought the complex u p to its present position within the southern margin of Eurasia. This new i nterpretation may have implications for other high grade terrains within co nvergent and collisional systems that have been assumed to represent ancien t or pre-existing continental crust. If so, then the importance of deep lev el subduction-accretion as a mechanism of continental crustal growth has hi therto been underestimated. (C) 1999 Elsevier Science B.V. All rights reser ved.