Quality Challenges of the Chemical Analyses in Occupational Health

Much emphasis is put on the precision and accuracy of sampling and analytical procedures in the modern practice of occupation hygiene. This is due to its importance in risk management in various industries, in the occupation health care and in general consumer product safety. Typical examples of current practices include external quality control by analysis of unknown control samples, certification of control samples and materials, interlaboratory comparisons, and, finally, international standardization of sampling and analytical methods. The Institute of Occupational Health Sciences (IOHS) has participated for more than twenty years in several programs of the above-mentioned approaches, and its own methods have been validated by international quality control programs

Age of Izu-Bonin-Mariana arc basement

Documenting the early tectonic and magmatic evolution of the Izu–Bonin–Mariana (IBM) arc system in the Western Pacific is critical for understanding the process and cause of subduction initiation along the current convergent margin between the Pacific and Philippine Sea plates. Forearc igneous sections provide firm evidence for seafloor spreading at the time of subduction initiation (52 Ma) and production of “forearc basalt”. Ocean floor drilling (International Ocean Discovery Program Expedition 351) recovered basement-forming, low-Ti tholeiitic basalt crust formed shortly after subduction initiation but distal from the convergent margin (nominally reararc) of the future IBM arc (Amami Sankaku Basin: ASB). Radiometric dating of this basement gives an age range (49.3–46.8 Ma with a weighted average of 48.7 Ma) that overlaps that of basalt in the present-day IBM forearc, but up to 3.3 m.y. younger than the onset of forearc basalt activity. Similarity in age range and geochemical character between the reararc and forearc basalts implies that the ocean crust newly formed by seafloor spreading during subduction initiation extends from fore- to reararc of the present-day IBM arc. Given the age difference between the oldest forearc basalt and the ASB crust, asymmetric spreading caused by ridge migration might have taken place. This scenario for the formation of the ASB implies that the Mesozoic remnant arc terrane of the Daito Ridges comprised the overriding plate at subduction initiation. The juxtaposition of a relatively buoyant remnant arc terrane adjacent to an oceanic plate was more favourable for subduction initiation than would have been the case if both downgoing and overriding plates had been oceanic

Quality challenges of the chemical analyses in occupational health

Much emphasis is put on the precision and accuracy of sampling and analytical procedures in the modern practice of occupation hygiene. This is due to its importance in risk management in various industries, in the occupation health care and in general consumer product safety. Typical examples of current practices include external quality control by analysis of unknown control samples, certification of control samples and materials, interlaboratory comparisons, and, finally, international standardization of sampling and analytical methods. The Institute of Occupational Health Sciences (IOHS) has participated for more than twenty years in several programs of the above-mentioned approaches, and its own methods have been validated by international quality control programs

Fore-arc basalts and subduction initiation in the Izu-Bonin-Mariana system

International audienceRecent diving with the JAMSTEC Shinkai 6500 manned submersible in the Mariana fore arc southeast of Guam has discovered that MORB-like tholeiitic basalts crop out over large areas. These ''fore-arc basalts'' (FAB) underlie boninites and overlie diabasic and gabbroic rocks. Potential origins include eruption at a spreading center before subduction began or eruption during near-trench spreading after subduction began. FAB trace element patterns are similar to those of MORB and most Izu-Bonin-Mariana (IBM) back-arc lavas. However, Ti/V and Yb/V ratios are lower in FAB reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid-ocean ridges and back-arc basins. Some FAB also have higher concentrations of fluid-soluble elements than do spreading center lavas. Thus, the most likely origin of FAB is that they were the first lavas to erupt when the Pacific Plate began sinking beneath the Philippine Plate at about 51 Ma. The magmas were generated by mantle decompression during near-trench spreading with little or no mass transfer from the subducting plate. Boninites were generated later when the residual, highly depleted mantle melted at shallow levels after fluxing by a water-rich fluid derived from the sinking Pacific Plate. This magmatic stratigraphy of FAB overlain by transitional lavas and boninites is similar to that found in many ophiolites, suggesting that ophiolitic assemblages might commonly originate from near-trench volcanism caused by subduction initiation. Indeed, the widely dispersed Jurassic and Cretaceous Tethyan ophiolites could represent two such significant subduction initiation events