Pegmatites in the Mesoproterozoic Karagwe-Ankole belt of Central Africa are associated with large granitic complexes that were emplaced around 1 Ga. This study analyzes drill core samples of fresh albite-spodumene pegmatites from the Musha-Ntunga area (East Rwanda), spatially associated with the Lake Muhazi granitic pluton. We combine petrographic and cathodoluminescence microscopy with Raman spectroscopy and elemental geochemistry to study the paragenetic sequence, microtextural variations, and lithium distribution, from the magmatic and magmatic-hydrothermal stages to the hydrothermal stage and during deformation processes. Five textural types of spodumene are distinguished. Coarse-grained spodumene type 1 and symplectitic type 2 are interpreted to have formed during primary magmatic crystallization, whereas spodumene types 3 and 4 formed during magmatic-hydrothermal alteration. Deformation locally affected the pegmatite intrusions. Spodumene type 1 crystals deformed in a brittle and ductile manner, displaying sigma-clast-shaped porphyroclasts (“spodumene fish”) and boudinage textures. The large strained spodumene crystals were also partially recrystallized to fine-grained elongated crystals (type 5), which occur in bands along with mica, quartz, and apatite and define the main orientation of foliation. Montebrasite occurs both as a late primary magmatic phase with spodumene and as a secondary phase that recrystallized during magmatic-hydrothermal alteration and deformation. Eucryptite, lithiophilite, and cookeite occur as late-stage hydrothermal phases, replacing primary lithium assemblages. Associated phases muscovite, apatite, microcline, albite, quartz, and columbite-tantalite further demonstrate the transition from a magmatic to a (magmatic-)hydrothermal and deformational regime. Elevated lithium contents in tourmaline within the metasedimentary host rock indicate dispersion of lithium into the host rock during pegmatite emplacement, subsequent crystallization, and alteration. The results of this multimethod approach demonstrate that different generations of lithium-bearing minerals and associated textures not only record the full transition from a magmatic to hydrothermal regime but also document deformation-related processes that can impact the distribution of metals within pegmatites.
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RBINS Staff Publications 2025
Reconstructing dietary strategies in past urban environments is challenging because of the complexity of anthropogenic impacts on food webs, in which diverse local and imported resources with variable isotopic compositions limit the interpretive power of conventional bulk-collagen stable isotope analysis. We address this problem using domestic cats as dietary proxies, exploiting their opportunistic foraging behavior to track resource partitioning within a medieval urban landscape. We present an integrated multi-isotope study of cat bone collagen from medieval Gdańsk (northern Poland) and six regional comparative sites, combining bulk collagen δ13C, δ15N, and δ34S analysis with compound-specific δ13C and δ15N analysis of amino acids. Despite apparent isotopic homogeneity in the Gdańsk assemblage within the conventional bulk collagen dual-isotope space, the expanded isotopic framework reveals substantial individual-level dietary variability. Sulfur isotopes indicate diverse food provenances, including baseline values of the marine ecosystem and grain imported from inland regions. Amino acid-based fingerprinting identifies diets spanning terrestrial C3 and C4, freshwater, and marine ecosystem baselines, while amino acid-based trophic position proxies reveal highly variable individual trophic levels uncorrelated with bulk collagen δ15N values. These findings demonstrate that isotopic homogeneity in the conventional dual-isotope space can mask substantial dietary heterogeneity. Our study highlights the potential of integrating amino acid analysis with sulfur isotope analysis to reconstruct individual-level food choices in complex past environments.
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RBINS Staff Publications 2026
