When a continent collides with an island arc or other continent, continental crust of the subducted continent may be buried to depths exceeding 100 km, and exposed to pressures that can cause formation of coesite and diamond. This process leads to substantial density increase in SiO₂-rich rocks and, in turn, to a reduction of the buoyancy of the subducted material, which should inhibit exhumation. Nevertheless, coesite- and diamond-bearing continental crustal rocks are known from several occurrences worldwide. We report on the discovery of microdiamond in kyanite-garnet gneiss from allochthonous metasediments of the Seve Nappe Complex in the Scandinavian Caledonides. Our discovery calls for general reconsideration of existing exhumation models of deeply subducted continental crust. We propose that the diamond-bearing rocks were subducted in an arc-continent collision setting, and their exhumation was facilitated by local pressure reduction resulting from extraction of the forearc lithospheric block.

Southwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic terranes with differing structural and metamorphic histories. The northern terrane experienced two Early Palaeozoic deformation events both accompanied by greenschist-facies metamorphism of similar grade. The southern terrane records a Neoproterozoic pervasive amphibolite-facies metamorphism and strong deformational fabric only locally retrogressed during a Caledonian greenschist-grade event. These terranes are separated by an important sinistral ductile shear zone defined as the Vimsodden–Kosibapasset zone, which comprises wrench- and contraction-dominated domains characteristic of strain partitioning in transpression zones; in this case apparently controlled by contrasting rheologies of the juxtaposed crustal domains. The northern terrane of Wedel Jarlsberg Land shares affinities with Pearya in northern Ellesmere Island of Arctic Canada whereas the southern one resembles the Timanide belt of NE Europe. A quantitative approach facilitated by a numerical plate model demonstrates that correlation with Pearya is feasible if sinistral displacement ofc. 600 km occurred during the Caledonian orogeny. The correlation with the Timanides is valid if the southern terrane represents an outlier of the Timanide belt separated from Baltica by the opening of the Iapetus Ocean.

Southwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic crustal blocks with differing metamorphic histories. Both blocks experienced Caledonian greenschist-facies metamorphism, but only the southern block records an earlier pervasive M1 amphibolite-facies metamorphism and strong deformational fabric. In situ EMPA total-Pb monazite geochronology from both matrix and porphyroblast inclusion results indicate that the older M1 metamorphism occurred at 643 ± 9 Ma, consistent with published cooling ages of c. 620 Ma (hornblende) and 580 Ma (mica) obtained from these same rocks. This region thus contains a lithostratigraphic profile and metamorphic history which are unique within the Svalbard Archipelago. Documentation of a pervasive late Neoproterozoic Barrovian metamorphism is difficult to reconcile with a quiescent non-tectonic regime typically inferred for this region, based on the occurrence of rift-drift sequences on the Baltic and Laurentian passive margins. Instead, our new metamorphic age implies an exotic origin of the pre-Devonian basement exposed in SW Spitsbergen and supports models of terrane assembly postulated for the Svalbard Archipelago.

Apatites provide a mechanism for in-situ remediation of Pb-contaminated sites, by supplying phosphate which combines with dissolved Pb to form highly insoluble pyromorphite. This study expanded upon previous research using hydroxylapatite (HAP), to focus on how the surface properties of natural chlorapatite (CAP) and fluorapatite (FAP) affect pyromorphite nucleation and growth, when aqueous Pb²⁺ ([Pb] < 50 mg/L as PbCl₂) is reacted with apatite at pH = 4.2, 22 ° C. A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), optical microscopy, energy dispersive X-ray fluorescence spectroscopy (EDS), infrared spectroscopy (FTIR), and X-ray diffraction (XRD) was used for in-situ and ex-situ examination of the interface and the reaction products. A variety of experiments were performed, and pyromorphite [PY = Pb₁₀(PO₄)₆Cl₂] was the only identified reaction product. PY nucleated both homogeneously (directly from solution) and heterogeneously on CAP and FAP; relationship between PY and HAP could not be determined definitively. The nucleation mechanism was sensitive to initial experimental conditions, which suggests that care should be taken to consider initial conditions in designing sorption and nucleation experiments. Heterogenous nucleation on FAP and CAP showed strong evidence for epitaxy. Epitaxial crystals of PY on CAP and FAP grew away from the substrate surface, which was the only source of phosphate available for crystal growth. Epitaxial crystals showed distinctly different morphologies from homogeneously nucleated crystals, and appeared to grow by a spiral growth mechanism.