Lithosphere thermal structure at the eastern margin of the Bohemian Massif: a case petrological and geophysical study of the Niedźwiedź amphibolite massif (SW Poland)

Abstract

The crustal section beneath amphibolite Niedźwiedź Massif (Fore-Sudetic Block in NE Bohemian Massif), modelled on the basis of geological and seismic data, is dominated by gneisses with subordinate granites (upper and middle crust) and melagabbros (lower crust). The geotherm was calculated based on the chemical analyses of the heat-producing elements in the rocks forming the crust and the measurements of their density and heat conductivity. The results were verified by heat flow calculations based on temperature measurements from 1,600 m deep well in the Niedźwiedź Massif and by temperaturedepth estimates in mantle xenoliths coming from the nearby ca. 4.5 My basanite plug in Lutynia. The paleoclimate-corrected heat flow in the Niedźwiedź Massif is 69.5 mW m -2 , and the mantle heat flow is 28 mW m -2 . The mantle beneath the Massif was located marginally relative to the areas of intense Cenozoic thermal rejuvenation connected with alkaline volcanism. This results in geotherm which is representative for lithosphere parts located at the margins of zones of continental alkaline volcanism and at its waning stages. The lithosphereasthenosphere boundary (LAB) beneath Niedźwiedź is located between 90 and 100 km depth and supposedly the rheological change at LAB is not related to the appearance of melt.

Subcontinental lithospheric mantle beneath Central Europe

“…The volume of moving magmas and/or the time of their migration was sufficient to rise temperature of SCLM beneath Księginki (on-rift location) to temperatures 1,060-1,120 °C at depth 35-50 km (Puziewicz et al 2011). The data from off-rift sites generally show temperatures varying between 910 and 1,000 °C (Wilcza Góra and some xenoliths from Krzeniów, Pilchowice, Winna Góra, irrespective of their chemical classification into A or B group), suggesting that temperatures increased during rifting, but were variable at the local Puziewicz et al (2012) speculated the 50 km depth of origin. These temperatures are similar to those characterising the off-rift SCLM at the time of syn-rift volcanism culmination.…”

“…The much younger xenolith suites from Kozákov in Czech Republic (ca. 4.0 Ma, Šibrava and Havlíček 1980;Ackerman et al 2007) and Lutynia (5.5-3.8 Ma, Birkenmajer et al 2002;Matusiak-Małek et al 2010) represent the cooled mantle lithologies, and conductive geotherms have been proposed for both sites (Christensen et al 2001;Puziewicz et al 2012).…”

Magmatic evolution of compositionally heterogeneous monogenetic Cenozoic Strzelin Volcanic Field (Fore-Sudetic Block, SW Poland)

“…According to Wood et al (2013), garnet is stable in fertile peridotites at solidus temperatures at depths greater than c. 85 km. The present-day lithosphere-asthenosphere boundary is located 90-100 km (Puziewicz et al 2012) or c. 100-105 km (Geisler et al 2012) below the SVF, but could have been at c. 70 km at the time when volcanic activity occurred (Puziewicz et al 2015). Considering the geochemical modelling and the geophysical constraints it is likely that the magmas under the SVF originated predominantly in the asthenospheric mantle, close to the base of lithosphere, or in the lowermost lithospheric mantle.…”

“…Amphibolites, locally over 3 km thick, occur in the near-surface part, and melagabbros are inferred to form the lower crust. The MOHO is located at a depth of c. 31 km and the lithosphere-asthenosphere boundary at c. 90 km (Puziewicz et al 2012) or 100-105 km (Geissler et al 2012). Recently, Puziewicz et al (2015) suggested that the transition from spinel to garnet peridotite, corresponding to the base of the lithospheric mantle, occurred at a depth of 50-70 km at the time of Cenozoic volcanism.…”

“…The structure and lithology of the lithosphere adjacent to the study area are constrained by drill core data, seismic profiles, heat flow modelling and data from mantle xenoliths (Awdankiewicz 2008;Geissler et al 2012;Puziewicz et al 2012, and references therein). According to these studies, the Earth's crust near the study area predominantly consists of various gneisses with minor granites.…”