IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Dense welding caused by volatile resorption

Abstract: Welding of pyroclastic rocks is generally thought to occur by mechanical expulsion of interstitial gas from a deposit as it compacts under its own weight. We propose here that volatile resorption and compression can also be important factors in welding. We describe densely welded rocks which cannot be explained by loading and re-evaluate the welding process taking into account the effects of volatile resorption into the glassy fragments. Intra-caldera Oligocene ignimbrites from the Rhodope Mountains, Bulgaria, and intrusive tuffs of the Loch Ba ring dyke, Mull in Scotland are intensely welded but some samples lack foliation (eutaxitic texture). Fiamme and glass shards show no preferred orientation in thin section or on outcrop scale. Fiamme are sometimes complexy deformed into U or S shapes. We propose that these textures are the consequence of volatile dissolution in the glass and gas compression. Scaling analysis indicates that there are two regimes for gas behaviour following emplacement of hot pyroclastic deposits which depend on the relative characteristic time-scales of compaction, gas escape and gas resorption: a gas escape regime and a gas retention regime. During explosive eruption, glassy pyroclasts are decompressed to less than one atmosphere pressure and are outgassed. During deposition and subsequent burial in a thick hot deposit, volatiles will be retained and soluble gases (H 2 O) can be resorbed back into the glass, defining the gas retention regime. Poorly soluble gases (air) are compressed to small fractions of their original volume, resulting in destruction of pore spaces and vesicles in pumice. In some circumstances, such as volcanic vents, the volume changes involve isotropic strain and implosion of the tuff. Resorption of water greatly speeds up welding during compactional loading by reducing the viscosity of the glass. Welding is inhibited not only by lower temperatures but also by entrainment of insoluble atmospheric gases. The two regimes also can explain the common presence of post-emplacement gas escape pipes in non-welded ignimbrites and their rarity in densely welded ignimbrite. Factors that are likely to promote the gas retention regime include fine grain size, low collapsing columns, a large thickness of tuff and incorporation of external water.

High-precision analysis of chromium isotopes in terrestrial and meteorite samples by thermal ionization mass spectrometry

Abstract: We present a method for the chemical separation of Cr from meteorite and terrestrial samples for isotopic analysis by thermal ionization mass spectrometry (TIMS). After sample digestion, separation of Cr(III) is achieved by means of a two-column cation-exchange chromatography procedure using AG 50W-x8 resin. In a first column, Cr(III) is isolated from major elements and the majority of trace elements. In a second column, trace amounts of Fe, Al and Ti are further removed. Total procedural yields are > 80%. Cr isotopes are measured by TIMS in the static multicollection mode. Mn/Cr ratios are obtained by multi-collector inductively coupled plasma source mass spectrometry (MC-ICPMS). The accuracy of our protocol was tested by reference to terrestrial analogs and comparison of Cr isotopic data for samples that underwent Cr purification following the cation-exchange chromatography described here and an alternative separation method employing both a cationic and an anionic chromatography step. Using our technique, Mn/Cr ratios reproduce to <2% (2σ) and 53Cr/52Cr and 54Cr/52Cr to 6 ppm and 12 ppm, respectively (2σ). This highly precise procedure allows the variability of Cr isotopes in the inner solar system objects to be addressed. Our method enabled us to document an initial homogeneity for 50,52,53Cr isotopes within 10 ppm, while 20–70 ppm deficits in 54Cr abundances have been resolved for a number of meteorite samples.

From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin

Abstract: A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present-day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago.