Recurrent Cenozoic volcanic activity in the Bohemian Massif (Czech Republic)

Cenozoic anorogenic volcanism of the Bohemian Massif is an integral part of the Central European Volcanic Province. The temporal and spatial distribution of volcanic rocks in the Bohemian Massif, their geochemistry and mineralogy as well as their tectonic setting and paleostress data are used to characterize and classify this volcanic activity. Three main volcanic periods can be distinguished based on K–Ar data and known paleostress fields: (i) pre-rift (79–49 Ma), (ii) syn-rift (42–16 Ma) and (iii) late-rift (16–0.3 Ma), with the youngest period further subdivided into three episodes. The dominant mafic rock types (> 7 wt.% MgO) of all periods are of nephelinite–basanite/tephrite composition. The exceptions are suites of melilitic ultramafic rocks of the pre-rift period in northern Bohemia and of the final episode of the late-rift period in western Bohemia. The most voluminous are volcanic rocks of the syn-rift period occurring in the Ohře Rift Graben.The initial 87Sr/86Sr (0.7032 to 0.7050) and 143Nd/144Nd (0.51264 to 0.51301) ratios of the mafic volcanic rocks of the Bohemian Massif are characteristic of magmas derived from a sub-lithospheric mantle source. The isotopic ratios resemble those of the HIMU mantle source (206Pb/204Pb ca. 19 to 20). These rocks have the most isotopically depleted compositions among the Central European Volcanic Province volcanics.

Research Highlights
► Timing and character of volcanic activity were controlled by regional stress.
► Magma ascent was aided by pre-existing Variscan weakness zones.
► Pre-, syn- and late-rift periods of volcanic activities were established.
► Lithospheric mantle is compositionally only slightly heterogeneous.
► Sr–Nd isotopic ratios are among the most depleted compositions in central Europe.