In situ Sr isotope analysis of mantle carbonates: Constraints on the evolution and sources of metasomatic carbon-bearing fluids in a paleo-collisional setting

Carbonate-bearing wedge peridotites attest the mobilization of carbon (C) by slab fluids/melts circulating in a subduction setting. In general, COH fluids are thought to derive from the dehydration/partial melting of the crustal portions of slabs, especially during the exhumation of crust-mantle m\ue9langes along continental subduction channels. In this study we combined textural observations with in-situ Sr isotope analyses of mantle carbonates occurring in different microstructural sites to test whether the fluids responsible for the carbonation of a mantle wedge are derived from the subducted continental crust or not. We focus on the Ulten Zone peridotites (Eastern Italian Alps) associated with high-grade felsic rocks, where carbonates occur mainly as dolomite and minor magnesite and calcite. In situ laser MC-ICP-MS analysis of peridotites representing different episodes of a complex metasomatic history, indicates that Sr isotopic variations can be linked to the different microstructural positions of carbonates. The C-metasomatism of the UZ peridotites is proposed to have occurred in two stages. The first stage is the HP\u2011carbonation at peak (eclogite-facies) conditions, with formation of interstitial matrix dolomite in textural equilibrium with hornblende to pargasite amphibole and Cl-apatite. This dolomite exhibits relatively unradiogenic 87Sr/86Sr present day values of 0.70487\ub10.00010, requiring different sources with respect to the associated migmatites and the overhanging mantle wedge. Carbonation continued during exhumation, with local injection of C-rich fluids forming a dolomite vein in association with tremolite and chlorite. The dolomite vein shows a wide range of 87Sr/86Sr (0.7036\u20130.7083), reflecting both the primary composition of carbonates and the consequent interaction with crustal fluids as expected in a crust-mantle m\ue9lange. The second stage is C-remobilization by dolomite dissolution and precipitation of brucite intergrowths with calcite during the final exhumation. This remobilization event has resulted in a similar Sr composition to the precursor dolomite. The mantle wedge is therefore capable of storing carbonates which have been shown to represent a complex metasomatic evolution from eclogite-facies conditions to very shallow structural levels. Therefore, fluids released from subducting slabs of continental lithosphere might be responsible for the crystallization of metasomatic minerals such as amphibole, phlogopite and zircon in the overlying ultramafic rocks. Conversely, the role of these metasomatic fluids on the carbonation of mantle wedge is likely overestimated. The combination of geochemical, isotopic and textural evidence suggests that dolomite inclusions and interstitial dolomite are derived in large part from a distinct source of C-bearing fluids that could be related to depleted mantle wedge sources and/or trondhjemitic igneous activity. In contrast, at the end of exhumation, residual COH-fluids released by the associated stromatic gneisses and orthogneisses resulted in late-stage dolomite veins having the highest Sr isotope values in the Ulten Zone peridotites

In situ Sr isotope analysis of mantle carbonates: Constraints on the evolution and sources of metasomatic carbon-bearing fluids in a paleo-collisional setting

Carbonate-bearing wedge peridotites attest the mobilization of carbon (C) by slab fluids/melts circulating in a subduction setting. In general, COH fluids are thought to derive from the dehydration/partial melting of the crustal portions of slabs, especially during the exhumation of crust-mantle mélanges along continental subduction channels. In this study we combined textural observations with in-situ Sr isotope analyses of mantle carbonates occurring in different microstructural sites to test whether the fluids responsible for the carbonation of a mantle wedge are derived from the subducted continental crust or not. We focus on the Ulten Zone peridotites (Eastern Italian Alps) associated with high-grade felsic rocks, where carbonates occur mainly as dolomite and minor magnesite and calcite. In situ laser MC-ICP-MS analysis of peridotites representing different episodes of a complex metasomatic history, indicates that Sr isotopic variations can be linked to the different microstructural positions of carbonates. The C-metasomatism of the UZ peridotites is proposed to have occurred in two stages. The first stage is the HP‑carbonation at peak (eclogite-facies) conditions, with formation of interstitial matrix dolomite in textural equilibrium with hornblende to pargasite amphibole and Cl-apatite. This dolomite exhibits relatively unradiogenic 87Sr/86Sr present day values of 0.70487±0.00010, requiring different sources with respect to the associated migmatites and the overhanging mantle wedge. Carbonation continued during exhumation, with local injection of C-rich fluids forming a dolomite vein in association with tremolite and chlorite. The dolomite vein shows a wide range of 87Sr/86Sr (0.7036–0.7083), reflecting both the primary composition of carbonates and the consequent interaction with crustal fluids as expected in a crust-mantle mélange. The second stage is C-remobilization by dolomite dissolution and precipitation of brucite intergrowths with calcite during the final exhumation. This remobilization event has resulted in a similar Sr composition to the precursor dolomite. The mantle wedge is therefore capable of storing carbonates which have been shown to represent a complex metasomatic evolution from eclogite-facies conditions to very shallow structural levels. Therefore, fluids released from subducting slabs of continental lithosphere might be responsible for the crystallization of metasomatic minerals such as amphibole, phlogopite and zircon in the overlying ultramafic rocks. Conversely, the role of these metasomatic fluids on the carbonation of mantle wedge is likely overestimated. The combination of geochemical, isotopic and textural evidence suggests that dolomite inclusions and interstitial dolomite are derived in large part from a distinct source of C-bearing fluids that could be related to depleted mantle wedge sources and/or trondhjemitic igneous activity. In contrast, at the end of exhumation, residual COH-fluids released by the associated stromatic gneisses and orthogneisses resulted in late-stage dolomite veins having the highest Sr isotope values in the Ulten Zone peridotites

Diode-pumped broadband vertical-external-cavity surface-emitting semiconductor lasers. Design and applications

Summary form only given. We report the demonstration of high output power (>1 W), single frequency and ultra-short pulse operation (50 nm) by simply changing the lasing spot position on the wafer. We also demonstrate, for the first time to our knowledge, high sensitivity Intra-Cavity Laser Absorption Spectroscopy (ICLAS) with a DP-VECSEL. A detection limit lower than 10/sup -10/ per cm of absorption path has been achieved given ~10/sup -11/ cmHz/sup 1/2/. For this application, the spectro-temporal dynamics of the DP-VECSEL has been studied in the time range from a few microseconds to about one second

A low threshold, room temperature 1.64µm Yb:Er:Y₃Al₅O₁₂ waveguide laser

Room temperature 1.64µm laser operation of Yb:Er:Y3Al5O12 has been achieved using a planar waveguide grown by liquid phase epitaxy. A comparatively low threshold of 17 mW was achieved for this transition indicating low waveguide propagation loss for this material and suggesting good prospects for low threshold 3µm and upconversion visible lasers based on this system

Active Terahertz Imaging for Security

Suicide bombers and anonymous mail attacks have become serious threats word wide. Since X-ray is difficult to apply for personnel scans due to radiation safety regulations, new technologies for remote detection of threats are required. Also fast and reliable technologies are needed to detect threats hidden in mail or similar. Due to their unique properties terahertz (THz) rays offer an alternative inspection method, which can cope with these new challenges. In response to the European Commissions first call for proposals in the frame of the Preparatoy Action in the Field of Security Research (PASR 2004) a proposal "Active Terahertz Imaging for Security (TeraSec)" was submitted by a consortium of 14 European research organizations, universities and industrial partners. The proposal was selected for funding in July 2004. The goal of this project is to improve security by developing technology, which will allow detecting threats, explosives, pathogens and chemicals hidden by a person or inside objects such as letters or luggage. The technology is based on THz radiation and advanced sensor concepts. In combiantion with existing sensors this may eventually lead to an increased level of security at public places for example airports. In this presentation an overview about the objectives of TeraSec, technological apporaches, and preliminary results will be given

High-power, single-mode picosecond fiber laser based on amplification of a passively mode-locked 1055-nm VECSEL

4.6 ps pulses at 910 MHz produced by a passively mode-locked VECSEL were amplified by ytterbium doped fiber amplifiers to average powers greater than 200 W and subsequently compressed to 430 fs duration.</p