ABSTRACT The Scandinavian Caledonides formed during the continental collision between Baltica and Laurentia. During the collision, a complex nappe stack was thrust over the Baltican continental margin. The orogen can be subdivided into segments based on architectural differences within the Scandian nappes. The southern and central segments of the orogen link up in the Gudbrandsdalen area in south-central Norway. Alpine-type metaperidotite-bearing metasedimentary complexes occur in the southern and central segments and can be traced continuously along the strike of the orogen from one into the other segment. Traditionally, these units have been assigned to different tectono-stratigraphic levels, one below the Middle Allochthon and one above the Middle Allochthon. Here, we trace the Alpine-type metaperidotite-bearing units from Bergen to Esandsjøen and show that these units exhibit a common geologic and metamorphic history, consistent with the metaperidotite-bearing units representing a single tectonic unit. We suggest that the metaperidotite-bearing units can be used as a “marker level” to revise the tectono-stratigraphy of the Gudbrandsdalen and adjacent areas. The tectono-stratigraphic revisions imply that the Scandian nappe stack consists of seven tectono-stratigraphic levels that can be traced throughout the southern and central segments of the Scandinavian Caledonides. Moreover, the revision of the tectono-stratigraphy and new U-Pb geochronology data also suggest a revision of the timing of the succession of tectonic events leading up to the Scandian continental collision. The available evidence indicates that Baltica-derived tectonic units collided with the Iapetan/Laurentian subduction complexes as early as ca. 450 Ma. The initial collision was followed by in-sequence nappe formation of Baltican-derived units, which occurred contemporaneously with the opening of a marginal basin in the upper plate. After the arrival of thick, buoyant, unthinned Baltican crust at the trench, the main zone of convergence stepped outboard, the marginal basins closed, and those basins were thrust out-of-sequence over the previously assembled nappe stack.

Abstract Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 640°C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500–600°C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant (<50% as opposed to <10% elsewhere), and has two different habits: inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon. Tectonic–hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences. The increasing abundance of graphite towards the fault zone core may be a significant source of strain localization, allowing fault weakening. Supplementary material: Raman spectra of graphite from the Alpine Fault rocks is available at https://doi.org/10.6084/m9.figshare.c.3911797

Abstract Graphitic (sp 2 -bonded) carbons are widespread on Earth and throughout the Universe. They have a complex structural organization ranging from amorphous and turbostratic phases to perfectly crystallized graphite. Raman spectroscopy is used extensively to characterize graphitic carbon in the Earth Sciences. In this chapter, we first review the theoretical knowledge of the Raman spectrum of graphitic carbons with an emphasis on the defect-activated peaks. These peaks have unique specificities that are described and explained in terms of the double-resonance theory. More practically, we discuss in detail all the peaks, their attributions and spectral properties. A methodology section is dedicated to the review of all possible analytical artifacts when characterizing graphitic carbons by Raman spectroscopy. A reference protocol is proposed for proper analysis. The last section reviews the application of Raman spectroscopy in the study of graphitic carbons in the Earth Sciences along the following theme: graphitization during metamorphism, fluid–rock interactions, fossils and traces of life in the geological record, cosmochemistry and Earth-surface processes.