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The Polish Basin : relationship between the crystalline consolidated and sedimentary crust

Dadlez R.

Geological Quarterly

2006

Vol. 50, No. 1

43-58

In the area of the Polish Basin five deep seismic sounding profiles, recorded during 1991–1997, were used to compare the structure of the crystalline and consolidated crusts with that of the sedimentary cover. Repeated reactivation of deep crustal fractures controlled the thickness distribution and development of faults in Palaeozoic andMesozoic sequences.NW–SE toWNW–ESE basin-parallel and transverse N–S to NE–SW striking fracture systems are evident. The former includes the isseyre–Tornquist Zone that marks the profound crustal boundary between the East European Craton and the typical Trans-European Suture Zone (TESZ) crust that is characterized by a variably thick consolidated upper crustal layer, composed of Caledonian-deformed Early Palaeozoic and possibly Vendian sediments, and defines the NE boundary of the Permian and Mesozoic Mid-Polish Trough (MPT). Its northwestern TTZ segment was intermittently active throughout the whole geological history of the area. The SW boundary of the TESZ, marked by the Dolsk Fault across which the consolidated crustal layer is replaced by a crystalline Variscan upper crust, is only evident on profiles LT-7 and P4. The deformation front of the Variscan Externides is located some 100 km to the NE of the Dolsk Fault within the confines of the TESZ crust. On profiles TTZ-PL and P2, significant lateral changes in the thickness of the consolidated and crystalline crust of the Pomeranian, Kuiavian and Holy Cross Mts. segments of the MPT are noted that coincide with the transverse Bydgoszcz-Poznań-Toruń and Grójec fault zones. These crustal changes are associated with substantial changes in the composition and thickness of supracrustal sedimentary sequences and the degree of inversion of the MPT.