Partial melting of amphibole–clinozoisite eclogite at the pressure maximum (eclogite type locality, Eastern Alps, Austria)

Pristine amphibole–clinozoisite eclogite from within the eclogite type locality (Hohl, Koralpe) of the Eastern Alps in Austria preserves centimetre-thick, concordant, laterally continuous leucocratic segregations of coarse-grained (up to ∼ 1 cm grain diameter) euhedral amphibole–clinozoisite–quartz and disseminated garnet–omphacite–rutile. The segregations locally show selvedges dominated by coarse-grained amphibole at the interface with their host eclogite. Retrogression is limited to thin films of texturally late plagioclase ± amphibole and minor symplectites of diopside–plagioclase partially replacing omphacite. Mineral compositions are largely homogeneous except for clinozoisite, which is significantly enriched in Fe3+, rare-earth and high-field-strength elements in the rock matrix compared to that in segregations. Petrography, mineral chemical data and phase diagram modelling are interpreted in terms of limited melting under high-aH2O conditions, at or close to the well-established pressure maximum (21 ± 3 kbar and 680–740 ∘C), followed by melt crystallization near these conditions. Exsolution of melt-dissolved H2O led to the formation of the amphibole-rich selvedges at the leucosome–eclogite interface. Plagioclase ± amphibole/clinopyroxene films formed at lower pressure from final melt vestiges adhering to grain boundaries or from secondary fluid–rock interaction. Natural variability in rock composition and the bulk oxidation state leads to variable mineral modes and calculated high-pressure solidus temperatures for compositional end-members sampled at Hohl. Modelling suggests that oxidized conditions (XFe3+&lt;0.5) favour hydrated but refractory amphibole–clinozoisite-rich assemblages with a fluid-present solidus temperature of ∼ 740 ∘C at 20 kbar, whereas more reduced conditions (XFe3+∼0.2) yield “true” eclogites (&gt; 80 vol % garnet + omphacite) that commence melting at ∼ 720 ∘C at the same pressure. The interlayering of such eclogites potentially constitutes a fluid source–sink couple under appropriate pressure–temperature conditions, favouring fluid transfer from neighbouring dehydrating layers to melt-bearing ones down gradients in the chemical potential of H2O (μH2O). Phase diagram calculations show that for moderate degrees of fluid-fluxed melting (≤ 10 vol % melt) near the pressure maximum, the observed equilibrium assemblage is preserved, provided the melt is subsequently removed from the source rock. The resulting hydrous melts may be, in part, parents to similar eclogite-hosted pegmatitic segregations described in the eclogite type locality. We suggest that eclogites with a comparable composition and metamorphic history are however unlikely to produce voluminous melts.</p

Tectonics of the Isua Supracrustal Belt 1: P‐T‐X‐d Constraints of a Poly‐Metamorphic Terrane

The Eoarchean Isua supracrustal belt (ISB) has been interpreted as one of the earliest records of subduction processes, leading to the conclusion that a plate tectonic geodynamic system was likely operating since the early Archean. However, proposed tectonic models remain difficult to evaluate as our understanding of the metamorphic and structural evolution remains fragmentary. Here, we present a metamorphic study of the supracrustal rocks of the ISB. We used petrographic and microstructural observations, phase equilibria, isopleth geothermobarometry, and conventional thermometry to explore the prograde, peak, and retrograde metamorphic evolution of the northeastern ISB. Our results show that the ISB records a syn‐tectonic, amphibolite facies metamorphic event (M1) with peak conditions of 550°C–600°C and 0.5–0.7 GPa. M1 was followed by a static, lower amphibolite facies metamorphic event (M2; 3.5 Ga) and the Neoarchean (<2.9 Ga), respectively. These events are partially overprinted by late low temperature (<500°C) retrogression (M3) that is most intensely developed in the northeastern part of the belt; it typically overprints some peak mineral phases while preserving the peak fabric. Our findings are consistent with spatially homogeneous syn‐tectonic amphibolite facies metamorphism and macroscale folding. Such features are predicted by a heat‐pipe tectonic model. Therefore, our findings permit the interpretation of the ISB as a record of early nonuniformitarian tectonic processes

The role of tenascin-C in tissue injury and tumorigenesis

The extracellular matrix molecule tenascin-C is highly expressed during embryonic development, tissue repair and in pathological situations such as chronic inflammation and cancer. Tenascin-C interacts with several other extracellular matrix molecules and cell-surface receptors, thus affecting tissue architecture, tissue resilience and cell responses. Tenascin-C modulates cell migration, proliferation and cellular signaling through induction of pro-inflammatory cytokines and oncogenic signaling molecules amongst other mechanisms. Given the causal role of inflammation in cancer progression, common mechanisms might be controlled by tenascin-C during both events. Drugs targeting the expression or function of tenascin-C or the tenascin-C protein itself are currently being developed and some drugs have already reached advanced clinical trials. This generates hope that increased knowledge about tenascin-C will further improve management of diseases with high tenascin-C expression such as chronic inflammation, heart failure, artheriosclerosis and cancer

Matrix Metalloproteinases in Cytotoxic Lymphocytes Impact on Tumour Infiltration and Immunomodulation

To efficiently combat solid tumours, endogenously or adoptively transferred cytotoxic T cells and natural killer (NK) cells, need to leave the vasculature, traverse the interstitium and ultimately infiltrate the tumour mass. During this locomotion and migration in the three dimensional environment many obstacles need to be overcome, one of which is the possible impediment of the extracellular matrix. The first and obvious one is the sub-endothelial basement membrane but the infiltrating cells will also meet other, both loose and tight, matrix structures that need to be overridden. Matrix metalloproteinases (MMPs) are believed to be one of the most important endoprotease families, with more than 25 members, which together have function on all known matrix components. This review summarizes what is known on synthesis, expression patterns and regulation of MMPs in cytotoxic lymphocytes and their possible role in the process of tumour infiltration. We also discuss different functions of MMPs as well as the possible use of other lymphocyte proteases for matrix degradation

Geochemical and Os-Hf-Nd-Sr isotopic characterization of north patagonian mantle xenoliths: Implications for extensive melt extraction and percolation processes

Alkali basalt hosted mantle xenoliths were sampled at four locations within the North Patagonian Massif, Argentina. The subcontinental lithospheric mantle (SCLM) beneath Comallo, Puesto Diaz and Cerro Chenque is mostly represented by spinel-harzburgites, whereas at Prahuaniyeu, spinel-garnet- and garnet-peridotites occur next to spinel-peridotites. Partial melting estimates for the north Patagonian mantle xenoliths determined from clinopyroxene trace element abundances reveal up to 25% melt extraction. Whereas the SCLM beneath Puesto Diaz, Cerro Chenque and Comallo is exclusively represented by highly depleted mantle xenoliths, the Prahuaniyeu sample suite comprises both fertile lherzolites and depleted harzburgites. Elevated trace element contents in all the studied north Patagonian mantle samples indicate that melt-rock interaction took place after an initial melt depletion event. Variable primitive mantle normalized REE patterns of clinopyroxenes from within one sample locality suggest compositional changes attributed to melt percolation, which has not significantly affected the bulk-rock and mineral major element compositions. Melt percolation processes have also been detected in the isotopic compositions of the xenoliths, as well as in their highly siderophile element systematics. Hf isotopic compositions are decoupled from those of Nd and Sr and have been affected by variable degrees of enrichment. Platinum group element (PGE) abundances also reveal indications of melt-rock reaction. In some samples this is reflected in fractionation of the iridium-group PGE and/or enrichment in the palladium-group PGE and/or rhenium, which cannot result merely from partial melting processes. Rhenium depletion ages (TRD) determined from Os isotopic analyses reveal an at least late Paleoproterozoic (1·7 Ga) stabilization of the Prahuaniyeu SCLM. Mantle xenoliths sampled from beneath Comallo and Puesto Diaz-Cerro Chenque yield distinctly younger TRD of 1·3 Ga and 1·0 Ga, respectively. Distinct differences in the character of mantle xenoliths from Prahuaniyeu and from Puesto Diaz and Cerro Chenque (i.e. SCLM stabilization age and range of fertility) suggest that at least two SCLM domains exist below the North Patagonian Massif.Fil: Mundl, A.. University of Vienna. Department Lithospheric Research; AustriaFil: Ntaflos, T.. University of Vienna. Department Lithospheric Research; AustriaFil: Ackerman, L.. Academy of Sciences of the Czech Republic; República ChecaFil: Bizimis, M.. University of South Carolina,; Estados UnidosFil: Bjerg, Ernesto Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Wegner, W.. University of Vienna. Department Lithospheric Research; AustriaFil: Hauzenberger, C. A.. University of Graz; Austri

Metamorphic evolution of the Sierras de San Luis, Argentina: granulite facies metamorphism related to mafic intrusions

The Sierras de San Luis, which are part of the Sierras Pampeanas, are located in Central Argentina. The crystalline basement of the Sierras de San Luis is built up of three main blocks (western block, central block, and eastern block), which are separated by mylonite zones. The western and the eastern block are dominated by migmatites, whereas the central block is mostly lower in metamorphic grade ranging from greenschist facies to amphibolite facies, and locally to granulite facies in the vicinity of numerous mafic bodies. Most parts of the central block is built up of amphibolite facies rocks. These were formed during a first metamorphic event (M1-A) which is characterized by a mineral assemblage of staurolite-garnet-biotite-muscovite-plagioclase-quartz- ilmenite±fibrolite±chlorite. The PT conditions of M1-A are about 570°C to 600°C and 5 to 5.7 kbar. A mafic intrusion, now seen as numerous mafic lenses included in the basement rocks caused local granulite facies metamorphism. The observed mineral assemblage consists of garnet-cordierite-sillimanite-biotite-K-feldspar-plagioclase-quartz-rutile- ilmenite±orthopyroxene (M2-G). The PT estimates for granulite facies conditions are 740°C to 790°C and 5.7 to 6.4 kbar. During cooling a mylonite zone developed within the central block retrograding most of the granulite facies rocks to amphibolite facies conditions. The newly formed mineral assemblage consists of garnet-biotite-sillimanite-plagioclase-muscovite-quartz-rutile±K-feldspar (M3-A). The PT estimates of the locally overprinting second amphibolite facies event (M3-A) are about 590°C to 650°C and 5.4 to 6.0 kbar. The deduced PT path shows a near isobaric heating from M1-A to M2-G. The mylonite mineral assemblage M3-A equilibrated at pressures close to M2-G. The PT path can be explained best by heating of an amphibolite facies middle crust by a mafic intrusion. During near-isobaric cooling tectonic activity in discrete parts of the basement caused mylonitization at amphibolite facies conditions.Fil: Hauzenberger, C. A.. Karl-Franzens University Graz; AustriaFil: Mogessie, A.. Karl-Franzens University Graz; AustriaFil: Hoinkes, G.. Karl-Franzens University Graz; AustriaFil: Felfernig, A.. Karl-Franzens University Graz; AustriaFil: Bjerg, Ernesto Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Kostadinoff, Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Delpino, Sergio Hugo. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Dimieri, Luis Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentin