Evaluation of subduction-accretion as an important crustal growth mechanism : Rhodope, Northern Greece

The Rhodope Massif of northern Greece and southern Bulgaria has been variably interpreted as a fragment of pre-Alpine, Hercynian or Precambrian continental crust, that was actively involved in European margin convergent tectonics during the Mesozoic and Tertiary. Alternatively it is proposed in this thesis that, for central Greek Rhodope, the lithological associations and tectonothermal history are consistent with progressive south-directed crustal growth through deep-level underplating, or subcretion, of material of oceanic and continental margin affinity, which was transferred from footwall to hanging wall within a north-directed Palaeotethyan subduction system.;Central Greek Rhodope comprises a sequence of schists, gneisses and migmatites of wide compositional variation which have undergone intense tectonic intermixing. Extensive marble units occur in association with amphibolites, retrogressed eclogites, meta-gabbros and ultramafic rocks. These are intercalated with meta-sedimentary sequences, including quartzo-feldspathic gneisses, garnet and/or kyanite bearing mica schists and quartzites. The presence of slivers of pink marble and rare manganiferous and iron rich siliceous units is of significance. These various lithological components were underthrust northwards to deep crustal levels, subjected to high pressure (eclogite facies metamorphism) and underplated or subcreted to the base of the overriding Eurasian plate. The accretion event was characterised by a single phase of intense southwest-directed ductile thrusting accompanied by pervasive upper amphibolite facies metamorphism, migmatisation and intracrustal melt generation. Subsequent volcanic and plutonic activity occurred, and extensional tectonic exhumation brought the metamorphic complex up to its present position within the southern margin of Eurasia.;This new interpretation may have interesting implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre-existing continental crust. If so, then the importance of deep level subduction-accretion as a mechanism of continental crustal growth has hitherto been underestimated.