LITHIC FINDS FROM THE ISLAND OF SUŠAC

Na pojedinim srednjodalmatinskim otočkim prapovijesnim nalazištima nađeni su litički artefakti za čiju je izradu korištena sirovina brana iz šljunka. Valutična okorina tih artefakata upućuje na porijeklo kamene sirovine s izdanaka šljunka ili drugih klastičnih sedimenata. Petrografi ja artefakata i specifi čni znakovi trošenja površine kamena, topografi ja regionalnih i izvanregionalnih izdanaka odnosnih stijena – u korelaciji s predmetnim arheološkim nalazištima – u materijalnoj analizi litičkih artefakata dopuštaju više načina interpretacije porijekla kamene sirovine kao regionalno primjenjivih modela. Na primjeru arheološkoga nalazišta na otoku Sušcu prikazujemo model interpretacije porijekla sirovine primjenjiv za nalaze s Gradine iz Visa, Divjenih doca kod Sućurja na Hvaru i Rata kod Ložišća na BračuPrehistoric stone artefacts made from gravel materials have been found at various sites on several islands in central Dalmatia. Th e pebble rind of these artefacts suggests that the raw material is derived from outcrops of gravel or other clastic sediments. Th e petrography of the artefacts, the specifi c signs of abrasion on the surface and the topography of regional and extra-regional outcrops of the relevant rock, in correlation with the pertinent archaeological sites, allow for several interpretations of the origin of the raw materials as regionally applicable models. Using the example of the archaeological sites on the island of Sušac, we use a model for interpretation of the origin of the raw materials applicable to fi nds from Gradina in Vis, Divjeni Doci at Sućuraj on the island of Hvar and Rat at Ložišće on the island of Bra

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Garnet-bearing and garnet-free pyroxenite xenoliths from Quaternary basanites of Marsabit, northern Kenya, were analysed for microstructures and mineral compositions (major and trace elements) to constrain the thermal and compositional evolution of the lithospheric mantle in this region. Garnet-bearing rocks are amphibole-bearing websterite with ~5-10 vol% orthopyroxene. Clinopyroxene is LREE-depleted and garnet has high HREE contents, in agreement with an origin as cumulates from basaltic mantle melts. Primary orthopyroxene inclusions in garnet suggest that the parental melts were orthopyroxene-saturated. Rock fabrics vary from weakly to strongly deformed. Thermobarometry indicates extensive decompression and cooling (~970-1,100°C at ~2.3-2.6GPa to ~700-800°C at ~0.5-1.0GPa) during deformation, best interpreted as pyroxenite intrusion into thick Paleozoic continental lithosphere subsequently followed by continental rifting (i.e., formation of the Mesozoic Anza Graben). During continental rifting, garnet websterites were decompressed (garnet-to-spinel transition) and experienced the same P-T evolution as their host peridotites. Strongly deformed samples show compositional overlaps with cpx-rich, initially garnet-bearing lherzolite, best explained by partial re-equilibration of peridotite and pyroxenite during deformation and mechanical mingling. In contrast, garnet-free pyroxenites include undeformed, cumulate-like samples, indicating that they are younger than the garnet websterites. Major and trace element compositions of clinopyroxene and calculated equilibrium melts suggest crystallisation from alkaline basaltic melt similar to the host basanite, which suggests formation in the context of alkaline magmatism during the development of the Kenya rif

Syros Metasomatic Tourmaline: Evidence for Very High-δ11B Fluids in Subduction Zones

High-pressure (HP) metamorphic blocks enclosed in a mafic to ultramafic matrix from a mélange on the island of Syros are rimmed by tourmaline-bearing reaction zones (blackwalls). The B isotopic composition of dravitic tourmaline within these blackwalls was investigated in situ by secondary ion mass spectrometry. Boron in these tourmalines is unusually heavy, with δ11B values exceeding +18‰ in all investigated samples and reaching an extreme value of +28·4‰ in one sample. Blackwalls formed during exhumation of the HP mélange at a depth of 20-25 km at temperatures of 400-430°C, by influx of external hydrous fluids. The compositions of the fluids are estimated to be in the range of 100-300 μg/g B with δ11B values of +18 to +28‰. The high δ11B values cannot be explained by tourmaline formation from unmodified slab-derived fluids. However, such fluids could interact with the material in the exhumation channel on their way from the dehydrating slab to the site of tourmaline formation in the blackwalls. This could produce exceptionally high δ11B values in the fluids, a case that is modelled in this study. The model demonstrates that subduction fluids may be effectively modified in both trace element and isotopic composition during their migration through the material overlying the subducting slab. Blackwall tourmaline from Syros has a large grain size (several centimetres), high abundance, and an exceptionally high δ11B value. The formation of tourmaline at the contact between mafic or felsic HP blocks and their ultramafic matrix involved fluids released during dehydration reactions in the subducting slab. It forms a heavy-boron reservoir in hybrid rocks overlying the subducting slab, and may, thus, have a significant impact on the geochemical cycle of B and its isotopes in subduction zone

Pleistocene-Holocene transition in the Vlakno Cave on the island of Dugi otok (Dalmatia, Croatia) – lithic perspective

U ovom radu predstavljamo rezultate analize litičke industrije iz pećine Vlakno otkrivene u iskopavanjima 2004. i 2007. godine. Radiokarbonski datumi smještaju analiziranu litičku industriju u vrijeme prijelaza iz pleistocena u holocen. Tehnološka i tipološka obilježja litičke industrije pokazuju kontinuitet tijekom navedenog prijelaza. Vrlo jasan kontinuitet može se pratiti i u nabavi sirovine uz određene razlike između kasnoga gornjeg paleolitika i mezolitika koje su mogle biti uvjetovane promjenama u okolišu. Određene prilagodbe lovaca skupljača iz Vlakna na nove okolišne uvjete mogu se pratiti kroz značajniju ulogu morskih izvora prehrane i kopnene malakofaune u strategijama preživljavanja tijekom mezolitika. Pećina Vlakno korištena je kao bazni logor manje grupe lovaca skupljača u vremenu prijelaza iz pleistocena u holocen.In this paper we present the results of the analysis of lithic industry from Vlakno Cave, which was discovered during excavations in 2004 and 2007. Radiocarbon dating positions the analysed lithic industry at the time of Pleistocene-Holocene transition. The technological and typological features of the lithic production show continuity during the abovementioned transition. Very clear continuity may also be observed in terms of the procurement of raw material, albeit with certain differences between the Late Upper Palaeolithic and Mesolithic, which could be the result of environmental changes. Certain adaptations of the hunter-gatherers from Vlakno to new environmental circumstances can also be traced through the more significant role of marine food sources and continental malacofauna in subsistence strategies during the Mesolithic. Vlakno cave was used as a residential base of a smaller group of hunter-gatherers at the time of the Pleistocene-Holocene transition

Petrological studies of Middle Neolithic stone artefacts from the Salenhof archaeological site near Trillfingen (SW Germany) give evidence for an early diversified long-distance exchange system

The Salenhof (N 48.384071/E 8.822974) archaeological site near Trillfingen contains fragmentary shards of ornamented pottery of the Hinkelstein, Großgartach, Planig-Friedberg and Rössen cultures/groups. In total, 1209 retouched silex artefacts could be recovered at the Middle Neolithic settlement. The high fractions of silex borers (40.9 % of the artefacts) and arrowheads (5.4 %) suggest that jewelry production and hunting activities played a substantial role in addition to ordinary farming activities. Various archaeological objects of imported materials were petrologically studied with standard high resolution research methods. The artefacts consist of material derived from eight remote localities: fine-grained metabasic rocks (amhibolites) from Jistebsko in Northern Bohemia (1), arrowheads and silex artefacts from Lengfeld (2) and Abensberg-Arnhoven (3) in Bavaria, fine-grained eclogites from Monviso (4) in the Western Alps, semi-transparent arrowheads of Cretaceous flint from Rijckholt near Maastricht in the Netherlands (5) and from the Paris Basin (6), siliceous red iron ores from the Lahn-Dill region (7), and a large arrowhead of silex material from Auggen/Schliengen in the Markgräflerland in SW Germany (8). All these artefacts are evidence of far-reaching contacts and the transfer of goods within a Middle Neolithic population at Salenhof. The climax of an early, diversified long-distance exchange system in Central Europe may have occurred during the period of the Rössen Culture ca. 6700 years ago

Metabasic rocks from the Variscan Schwarzwald (SW Germany): metamorphic evolution and igneous protoliths

In the Variscan Schwarzwald metabasic rocks form small bodies included within anatectic plagioclase-biotite gneisses. Many metabasites first underwent an eclogite-facies metamorphism at about 2.0 GPa and 670–700 °C, resulting in the assemblage garnet + omphacite + rutile + quartz ± epidote ± amphibole ± kyanite. Since these eclogites are nearly free of an OH-bearing phase, they underwent almost complete dehydration during subduction, suggesting formation along an average to warm top-of-the-slab geotherm of 10–13 °C/km. The age of the Variscan high-P/high-T metamorphism is > 333 Ma. After partial exhumation from ~ 65 to ~ 15 km depth, the eclogites were overprinted under increasing activity of H2O by a number of retrograde reactions. The degree of this overprint under amphibolite-facies conditions (0.4–0.5 GPa/675–690 °C) was very different. Up to now, only retrograde eclogites have been found, but some samples still contain omphacite. Kyanite is at least partially transformed to aggregates of plagioclase + spinel ± corundum ± sapphirine. On the other hand, there are amphibolites that are extensively recrystallized and show the assemblage amphibole + plagioclase + ilmenite/titanite ± biotite ± quartz ± sulphides. The last relic phase that can be found in such otherwise completely recrystallized amphibolites is rutile. After the amphibolite-facies metamorphism at ~ 333 Ma, the metabasites underwent a number of low-temperature transformations, such as sericitization of plagioclase, chloritization of amphibole, and formation of prehnite. The intimate association of metabasite bodies with gneisses of dominantly meta-greywacke compositions suggests derivation from an active plate margin. This view is corroborated by bulk-rock geochemical data. Excluding elements that were mobile during metamorphism (Cs, Rb, Ba, K, Pb, Sr, U), the concentrations of the remaining elements in most of the metabasites are compatible with a derivation from island-arc tholeiites, back-arc basin basalts or calc-alkaline basalts. Only some samples have MORB precursor rocks.Ruprecht-Karls-Universität Heidelberg (1026