Petrographic observations, mineral-geochemical data and results of in situ U-Pb dating and Nd isotope analyses provide evidence not only for authigenic growth of zircon, xenotime, rutile and monazite in white-mica schist at ca. 530 Ma, but also for the preservation of detrital grains of zircon, rutile and monazite that crystallized between ~3100 and 1150 Ma. The authigenic character is indicated by zircon outgrowths closely intergrown with xenotime and rutile crystals, and by a U-Pb lower intercept age of 530 ± 5 Ma, estimated for xenotime and monazite rims. The zircon outgrowths occur where detrital zircon faces are dissolved in contact with Fe-Mg-rich phengitic muscovite, suggesting the involvement of an aqueous fluid enriched in K-Mg-Fe-Al-Ti-P near the thermal peak at 510 °C. In contrast, authigenic monazite rims overgrowing rounded cores were formed during the retrograde evolution, as indicated by their local occurrence in assemblage with kaolinite and extreme geochemical compositions. The monazite rims show very low U contents (4–14 ppm), extremely high Th/U ratios (up to 1670), and nearly identical ¹⁴³Nd/¹⁴⁴Nd_t (0.51184 ± 0.00006), values that markedly differ from the detrital cores (¹⁴³Nd/¹⁴⁴Nd_t=0.51000±0.00050; U=162-16418 ppm; Th/U=2.6-153). The high Th/U ratios point to the involvement of an oxidizing fluid, in line with late goethite formation. Monazite microstructures, results of geothermobarometry, and Nd isotope characteristics point to a chain of processes, from partial dissolution of detrital monazite, through REE transport and Nd isotope homogenization in an aqueous fluid, to monazite-rim growth at T = 280 °C and P <3 kbar.

Ten eclogites from the Caledonide orogen in western Norway, whose mineral chemistry records metamorphic conditions of up to 850 °C and 5.5 GPa, were investigated quantitatively for structural hydroxyl (OH). Each rock sample contains clinopyroxene with oriented inclusions of either quartz, albite or quartz + pargasite. Five orthopyroxene-bearing eclogites have relatively homogeneous amounts of structural OH in garnet (13–32 μg g⁻¹ H₂O equivalent), clinopyroxene (119–174 μg g⁻¹) and orthopyroxene (4–17 μg g⁻¹). In contrast, the other five orthopyroxene-free eclogites have variable amounts of OH and it ranges in garnet from 8 to 306 μg g⁻¹ and in clinopyroxene from 58 to 711 μg g⁻¹. Apart from extreme values, the OH content of clinopyroxene in these eclogites is significantly lower than in comparable ultra-high-pressure metamorphic samples, such as metasomatised and pristine eclogite xenoliths from the lithospheric mantle underneath several cratons and coesite- and quartz-eclogites from the Erzgebirge and the Kokchetav massifs. The low structural OH contents, the deficiency of molecular water and the evidence for the preservation of diffusion-sensitive mineral chemistry arising from metamorphism well beyond the stability field of amphibole suggest that oriented inclusions of quartz + pargasite were formed isochemically during eclogite-facies decompression.

Situated in the High Arctic, the island of Nordaustlandet is one of the least understood geological terranes on Earth regarding Precambrian and Paleozoic geodynamic processes. Such knowledge is, however, essential to reconstruct the geological evolution of the continental crust surrounding the Arctic Ocean. To elucidate the age of intrusion and tectono-metamorphic activity, the foliation-forming mineral phases, alkali feldspar and zircon grains from a total of 10 samples of meta-igneous rocks from northern Nordaustlandet were dated by ⁴⁰Ar/³⁹Ar and U-Pb geochronology. The geochronological study was complemented by a regional compilation of planar metamorphic fabrics and a microstructural analysis. The geochronological results reveal that the emplacement of metagranitoid rocks occurred during the Late Meso- to Early Neoproterozoic era (Stenian - Tonian), followed by Late Caledonian (Scandian) deformation and metamorphism during a Late Silurian to Early Devonian event. Neoproterozoic magmatic bodies intruded at mid-crustal level and were exhumed during the Caledonian orogeny between 420.1 ± 2.3 Ma and 399.9 ± 1.7 Ma. Structural observations allowed us to constrain the mechanisms, intensities and shortening directions of this deformation, which occurred under medium-grade metamorphism. This study indicates that Meso- to Neoproterozoic granitoid rocks, pervasively exposed at the northern coast of Nordaustlandet, were exhumed during Late Silurian to Early Devonian times and served as host to Late Caledonian felsic intrusions.

Karst-induced sinkholes in Pliocene strata, the youngest sequence of Tertiary rocks covering the 66 Ma Chicxulub meteorite impact crater, form a semicircle that is congruent with the underlying crater margin as imaged by gravity anomalies. The causal relationship between the crater margin and the formation of the sinkholes has remained elusive since the discovery of the Chicxulub crater more than 30 years ago. Ground water flow of the northwestern Yucatán aquifer calls for the presence of prominent structural discontinuities in Tertiary strata above the buried crater margin, which likely control sinkhole formation. Based on the analysis of high-resolution satellite scenes, we mapped the ellipticity and respective long axes of some 6500 sinkholes. Assuming that the long axes represent traces of subsurface dilation fractures and, thus, orientations of maximum principal stresses, the angular departures of these stresses from the uniform regional trend point to local stress perturbations above the crater margin. The patterns of these perturbations agree with experimentally produced ones observed in scaled numerical and physical models, in which model craters are embedded in elastic materials and subjected to uniaxial compression. Moreover, concentric fractures preferentially form at model crater margins in physical experiments simulating cratering-induced crustal relaxation on the order of hundreds of thousands of years. We conclude that the localization of sinkholes in Pliocene strata above the Chicxulub crater rim is the combined result of the concentration of ambient stresses at the crater rim and the consequent reactivation of concentric fractures and their propagation into the overlying Tertiary strata.

The theoretical root of structural geology is in continuum mechanics, founded by Euler (stress, 1776), Lagrange (strain, 1784), and Cauchy (1827). Compared with the principles of modern physics it is hopelessly obsolete. It completely ignores all the developments in physics after 1830, especially the rise of energetic thinking (starting 1840), physical work (Joule 1845), the First Law of thermodynamics (Mayer 1842), bonds in solids (Maxwell 1850), the mathematics of 3D space (Grassmann 1866), and others. It will be shown that Cauchy’s derivation of the stress tensor is invalid, and that strain is physically meaningless (Koenemann 2008, 2014). Continuum mechanics is as obsolete as a trilobite. It fails completely and systematically for simple shear in the elastic (Poynting 1909), viscous (Nikuradse 1933), and plastic field (Koenemann 2008). This is particularly relevant for geologists trying to understand mylonites. Any attempt to tackle simple shear with a theory that is older than the discovery of bonds is a waste of time. Mathematics and physics provided the full set of necessary conceptual tools (thermodynamics, vector algebra) starting in 1901. A realistic grasp of elastic and plastic deformation satisfying modern standards is plainly impossible without solid training in mathematics (differential equations, linear algebra, vector algebra, potential theory), physics (thermodynamics in scalar [P, V, T] and vector field form [f, r, T]), and material science.