Kinematic analysis of the eastern Pelagonian metamorphic core: a multidisciplinary insight

Schenker, Filippo and Burg, Jean-Pierre and Gerya, Taras (2009) Kinematic analysis of the eastern Pelagonian metamorphic core: a multidisciplinary insight. In: Abstract Volume, 7th Swiss Geoscience Meeting 7th Swiss Geoscience Meeting, Neuchâtel, Switzerland.

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Geological mapping revealed a migmatitic dome in the footwall of a low angle detachment in the eastern Pelagonian region, to the north and east of the Aliakmon River artificial lake, in Greece. The dome dimensions are about 20 x 15 km with the long axis striking NNW-SSE. All lithologies show a penetrative foliation striking mainly NW-SE and dipping NE or SW, according to the dome flank. On the foliation plane a NE-SW stretching lineation is associated with sense of shear indicators. Systematic measurements average as follows: i) Top-to-the-SW sense of shear: Direction: 254°±15; Plunge: 12°±9, ii) Top-to-the-NE sense of shear: Direction: 47°±17; Plunge: 15°±13. While the top-to-the-SW sense of shear is regional, top-to-the-NE shear refers to relatively narrow (20 to 100 m) shear zones. The most spectacular of these shear zones juxtaposes highly migmatitic orthogneisses against non migmatitic ones. In the migmatitic core both biotite orthogneisses and amphibolites (former basaltic dykes that have intruded into the crystalline basement) have undergone partial melting. Melting of the metagranite locally produced garnet + amphibole + melt, which would indicate Pressure-temperature conditions of 10-20 kb and <800-900°C respectively under water-saturated conditions. Zircon U-Pb dating from a migmatite on the northwestern flank of the dome suggests that melting took place at 137±1 Ma [Anders, 2007]. The results were the basis for numerical modelling of migmatite domes in extensional setting. We employed I2ELVIS, a numerical 2D computer code designed for visco-elasto-plastic rheology and using conservative finite differences method [Gerya, 2003a]. The model domain is 300 km wide and 160 km deep. It consists of four rheological layers representing upper crust, lower crust, lithospheric mantle and asthenospheric mantle. Changing parameters as extension rate, lithosphere thickness and geotherms points to the importance of partial melting in the lower crustal: (1) it maintains a flat Moho and (2) positive buoyancy of molten rocks enhances doming. PTt paths of model points are used to discriminate thermo-mechanical scenari of migmatitic core complexes.

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