Permian rhyolitic volcanism, changing from subaqueous to subaerial in post-Variscan intra-continental Sirinia Basin (SW Romania-Eastern Europe)

摘要

The Sirinia Basin is a well-exposed, Upper Carboniferous-Lower Permian intra-continental extensional basin, containing 1-2 km of Permian interbedded terrigeneous sediments and primary volcanic and volcaniclastic rocks of rhyolitic composition. These are mostly the products of subaqueous volcanism passing into a subaerial volcanism. The intra-continental basin lies on the Danubian metamorphic units in the south westernmost part of the Carpathians (SW Romania) and is N-S oriented (18×8km), as result of Alpine tectonic evolution and deformation. The Sirinia Basin setting formed a dynamic closed intra-continental sedimentary system that experienced a successive subsidence; it started with lacustrine sediments and then with large volumes of rhyolitic volcanic and volcaniclastic material dominantly sited in the central part of the basin. Volcanism included (1) subaqueous extrusion of domes surrounded by hyaloclastite deposits closely associated with secondary sedimentation, (2) extrusive and explosive Surtseyan-type and subaerial eruptions from shallow water to emergent volcanoes on dome-cap and associated reworked deposits, towards the southern side of the basin, and (3) subaerial extrusive domes. Fluvial erosion and deposition completed the evolution of the emerged marginal part of the basin. Most of the erupted material of the first and second phase filling the central part of the basin along extensional normal faults was rapidly transported on sides of the basin by turbidite sedimentation, debris flows, slumping and sliding. While turbidites prevail toward the central part of the basin, the debris flow sedimentation predominated at the margin of the basin, infrequently interrupted by deposition of fallout ash from hydromagmatic explosive eruptions related to the dome-cap tuff and pumice cones.