EXHUMATION AND DOMING OF THE THASOS METAMORPHIC CORE COMPLEX (S-RHODOPE, GREECE) - STRUCTURAL AND GEOCHRONOLOGICAL CONSTRAINTS

The Thasos Island metamorphic core complex (S Rhodope, N Aegean Sea) w as generated between similar to 26 and 13 Ma, Progressive extensional tectonics was associated with upwarping of the deeper parts of this co re complex to a narrow gneiss dome and with formation of a steep topog raphic high. We present a combined structural, microstructural and geo chronological study that constrains the deformation-time path of progr essive extension and exhumation. Thasos Island consists of three super imposed, more or less flat-lying metamorphic units with downward-decre asing geochronologic ages which are separated by two systems of low-an gle normal detachment surfaces, trending NW-SE. The upper unit stayed in supracrustal level since 50 Ma, representing the upper plate. Durin g an early phase of extension, not later than 26-23 Ma, upper levels o f the core complex (intermediate unit) underwent pervasive mylonitizat ion with top-to-the-SW shear. From about 21 Ma onward, the intermediat e unit was rigid and top-to-the-SW slip continued at least until 13 (8 ?) Ma on the discrete detachment surface that separates the core compl ex from the upper plate. Yet, in the 21-15 Ma period, deeper levels (l ower unit) still deformed plastically, and deformation successively co ncentrated in zones of high strain and in discrete detachment surfaces that caused decoupling of the lower from the intermediate unit. These indicate downdip movements in opposite sense associated with doming o f the lower unit at that stage. Simultaneously, the intermediate unit was fragmented on high-angle normal faults that sole into the dome-bou nding detachment surface and roof into the core complex-bounding detac hment surface. These faults confine tilt blocks that are arranged arou nd the lower unit gneiss dome. Doming of the core complex occurred sim ultaneously with subsidence of basins located on the upper plate. (C) 1998 Elsevier Science B.V. All rights reserved.