Boundaries of mantle–lithosphere domains in the Bohemian Massif as extinct exhumation channels for high-pressure rocks

Five domains (microplates) have been recognized by seismic anisotropy in the mantle lithosphere of the Bohemian Massif. The mantle domains correspond to major crustal units and each of the domains bears a consistent fossil olivine fabric formed before their Variscan assembly. The present-day mantle fabric indicates that this process consisted of at least three oceanic subductions, each followed by an underthrusting of the continental lithosphere. The seismic anisotropy does not detect remnants of the oceanic subductions, but it can trace boundaries of the preserved continental domains subsequently underthrust along the paths of previous oceanic subductions. The most robust continent–continent collision was followed by westward underthrusting of the Brunovistulian mantle lithosphere, still detectable by seismic anisotropy more than 100 km beneath the Moldanubian mantle lithosphere. Major occurrences of the high-pressure/ultra high-pressure (HP–UHP) rocks follow the ENE and NNE oriented sutures and boundaries of the mantle–lithosphere domains mapped from three-dimensional modeling of body-wave anisotropy. The HP–UHP rocks are products of oceanic subductions and the following underthrusting of the continental crust and mantle lithosphere exhumed along the mantle boundaries. The close relation of the mantle sutures and occurrences of the HP–UHP rocks near the paleosubductions testifies for models interpreting the granulite–garnet peridotite association by oceanic/continental subduction/underthrusting followed by the exhumation of deep-seated rocks. Our findings support the bivergent subduction model of tectonic development of the central part of the Bohemian Massif. The inferences from seismic anisotropy image the Bohemian Massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric. The collisional mantle boundaries, blurred by tectonometamorphic processes in easily deformed overlying crust, served as major exhumation channels of the HP–UHP rocks.     

Seismic model and geological interpretation of the basement beneath the Doupovské Hory Volcanic Complex (NW Czech Republic)

The Doupovské Hory Volcanic Complex (DHVC) is the best-preserved large volcanic suite of the Cenozoic intraplate volcanism in the Bohemian Massif. However, many uncertainties remain in the geological setting of its basement. In summer 2008, two seismic refraction profiles ran across this area to reveal the depth of the volcanic rocks and the underlying geological structure.     

Thermal behavior of ferric selenite hydrates (Fe2(SeO3)3·3H2O,Fe2(SeO3)3·5H2O) and the water content in the natural ferric selenite mandarinoite

Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe₂(SeO₃)₃·(6-x)H₂O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.     

Gradient-based Pareto optimal history matching for noisy data of multiple types

The advantages of the simultaneous integration of production and time-lapse seismic data for history matching have been demonstrated in a number of previous studies. Production data provide accurate observations at particular spatial locations (wells), while seismic data enable global, though filtered/noisy, estimates of state variables. In this work, we present an efficient computational tool for bi-objective history matching, in which data misfits for both production and seismic measurements are minimized using an adjoint-gradient approach. This enables us to obtain a set of Pareto optimal solutions defining the optimal trade-off between production and seismic data misfits (which are, to some extent, conflicting). The impact of noise structure and noise level on Pareto optimal solutions is investigated in detail. We discuss the existence of the “best” trade-off solution, or least-conflicting posterior model, which corresponds to the history-matched model that is expected to provide the least-conflicting forecast of future reservoir performance. The overall framework is successfully applied in 2D and 3D compositional simulation problems to provide a single least-conflicting posterior model and, for the 2D case, multiple samples from the posterior distribution using the randomized maximum likelihood method.