IL-1 Beta-Induced Inhibition of Beta-Cell Function is Mediated through Nitric oxide

Subduction-accretion complexes occur widely in the Central Asian Orogenic Belt (CAOB). Due to the scarcity of fossils, the depositional timing of the Habahe flysch sequence of the subduction-accretion complex in the Chinese Altai is poorly constrained, which gave rise to much controversy in understanding the time of the basement and the tectonic evolution of the Chinese Altai. U-Pb dating of detrital zircons from the Habahe sequence in the northwestern Chinese Altai reveals a young zircon population with a mean 206Pb/ 238U age around 438 Ma which, together with a mean 206Pb/ 238U age of 411 ± 5 Ma for the overlying rhyolite of the Dongxileke Formation, brackets the time of deposition of the sequence between early Silurian and early Devonian. The age of the Dongxileke rhyolite also indicates that the overlying Baihaba Formation possibly began to be deposited in the early Devonian, though U-Pb dating of detrital zircons from this formation gave a maximum depositional age of ∼ 438 Ma. The youngest detrital zircons and metamorphic grains of the Habahe sequence reveal different provenance to the sequence in the east. The youngest and metamorphic zircon grains, with early Paleozoic, Neoproterozoic and pre-Neoproterozoic populations, suggest a multi-source for the Habahe sequence. The predominantly early Paleozoic zircons, characterized by concentric zoning, high Th/U ratios and euhedral shapes, imply that the sediments of the sequence were mostly derived from a proximal magmatic source. Based on the age patterns of the Neoproterozoic and pre-Neoproterozoic populations, the Tuva-Mongol Massif, along with adjacent island arcs and metamorphic belts, may be an alternative source region for the Habahe sequence. In view of new geochemical and chronological data for granitoids and advancement in the study of regional metamorphism in the Chinese Altai, we suggest a tectonic model of subduction beneath a huge subduction-accretion complex for the evolution of the Chinese Altai in the early Paleozoic. © 2009 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Characterization of the potential reference material SA02 for micro-beam U–Pb geochronology and Hf–O isotopic composition analysis of zircon

In the present work, a natural zircon megacryst SA02 (the exact provenance unknown) is investigated as a new potential reference material for U–Pb geochronology and Hf–O isotopic composition analysis via micro-beam methods. The precise and accurate U–Pb age is determined by the chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method. The resultant mean 206Pb/238U date is 535.10 ± 0.24 Ma (2s, n = 2), interpreted as the crystallization age of the zircon megacryst. The mean ID-TIMS 206Pb/238U date of 533.7 ± 3.7 Ma (2s, n = 8) is recommended as the working value for micro-beam analyses when using untreated SA02 zircon grains as the primary reference material. 206Pb/238U dates of 533.0 ± 6.2 Ma (2s, n = 57) and 534 ± 8 Ma (2s, n = 101) obtained by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively are reproducible and in agreement with the results of ID-TIMS within < 0.3% relative analytical errors. Solution data of Hf isotope compositions measured by multi-collector ICP-MS (MC-ICP-MS) from SA02 zircon yield a mean 176Hf/177Hf of 0.282287 ± 0.000016 (2s, n = 31), which is recommended as a reference value for microbeam analysis. Hf isotope analyses by LA-MC-ICP-MS yield homogeneous Hf isotopic compositions with a mean 176Hf/177Hf of 0.282289 ± 0.000033 (2s, n = 142) identical to the solution value. The mean δ18O value measured by laser fluorination is 6.03 ± 0.28‰ (2s, n = 13), which is consistent with the result of SIMS analysis

In situ calcite U−Pb geochronology by high-sensitivity single-collector LA-SF-ICP-MS

U−Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method, with potential applications to a vast array of geological problems. Due to the low levels of U and Pb in calcite, measurement using higher-sensitivity instruments, such as sector field (SF) ICP-MS, have advantages over more commonly used quadrupole (Q) ICP-MS instruments. Using a Thermo Element XR ICP-MS, we demonstrate that the Jet+X cone combination with the N2 enhancement technique provides the best sensitivity for measuring U and Pb isotopes. This higher sensitivity improves the precision of calcite U−Pb isotope measurements, and permits dating at high spatial resolutions (<110 µm) and for samples containing low contents of 238U (<1 µg g−1) and/or 207Pb (i.e., young samples <10 Ma). Using a spot size of 85 µm with a low fluence (∼2.0 J cm−2), the laser-induced elemental fractionation of 206Pb/238U in the NIST SRM 614, ARM-3 and WC-1 reference materials are insignificant (<2.2%). Adopting the optimized instrument parameters, we analysed four commonly-used calcite U−Pb reference materials (WC-1, Duff Brown Tank, JT, and ASH-15). The results match well with published isotope dilution data, demonstrating the reliability of our technique. ARM-3, an andesitic glass, is shown to be an appropriate reference material for both 207Pb/206Pb calibration and instrument optimization because of its moderate contents of U (∼3.75 µg g−1) and Pb (∼12.7 µg g−1). We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages

Magnesium and oxygen isotopes in Roberts Victor eclogites

Magnesium and oxygen are critical elements in the solid Earth and hydrosphere. A better understanding of the combined behavior of Mg and O isotopes will refine their use as a tracer of geochemical processes and Earth evolution. In this study, the Mg-isotope compositions of garnet and omphacite separated from well-characterized xenolithic eclogites from the Roberts Victor kimberlite pipe (South Africa) have been measured by solution multi-collector ICP-MS. The reconstructed whole-rock δ²⁶Mg values of Type I (metasomatized) eclogites range from -0.61‰ to -0.20‰ (Type IA) and from -0.60‰ to -0.30‰ (Type IB) (mean -0.43‰ ± 0.12‰), while δ²⁶Mg of Type IIA (fresh, least metasomatized) eclogites ranges from -1.09‰ to -0.17‰ (mean -0.69‰ ± 0.41‰); a Type IIB (fresh, least metasomatized) has δ²⁶Mg of -0.37‰. Oxygen-isotope compositions of garnet were analyzed in situ by SIMS (CAMECA 1280) and cross-checked by laser fluorination. Garnets have δ¹⁸O of 6.53‰ to 9.08‰ in Type IA, 6.14‰ to 6.65‰ in Type IB, and 2.34‰ to 2.91‰ in Type IIB. The variation of δ²⁶Mg and δ¹⁸O in Type IA and IB eclogites is consistent with the previously proposed model for the evolution of these samples, based on major and trace elements and radiogenic isotopes. In this model, the protoliths (Type II eclogites) were metasomatized by carbonatitic to kimberlitic melts/fluids to produce first Type IA eclogites and then Type IB. Metasomatism has changed the O-isotope compositions, but the Mg-isotope compositions of Type IA are mainly controlled by the protoliths; those of Type IB eclogites reflect mixing between the protoliths and the kimberlitic melt/fluid. The combination of a large range of δ²⁶Mg and low δ¹⁸O in Type II eclogites cannot be explained easily by seawater alteration of oceanic crust, interaction of carbonate/silicate sediments with oceanic crust, or partial melting of mafic rocks.11 page(s