A. Mohamad Ghazi

Geochemistry of subalkaline and alkaline extrusives from the Kermanshah ophiolite, Zagros Suture Zone, Western Iran: implications for Tethyan plate tectonics

Abstract The Kermanshah ophiolite is a highly dismembered ophiolite complex that is located in western Iran and belongs to the Zagros orogenic system. The igneous rocks of this complex consist of both mantle and crustal suites and include peridotites (dunite and harzburgite), cumulate gabbros, diorites, and a volcanic sequence that exhibits a wide range in composition from subalkaline basalts to alkaline basalts to trachytes. The associated sedimentary rocks include a variety of Upper Triassic to Lower Cretaceous deep- and shallow-water sedimentary rocks (e.g., dolomite, limestone, and pelagic sediments, including umber). Also present are extensive units of radiolarian chert. The geochemical data clearly identifies some of the volcanic rocks to have formed from two distinct types of basaltic melts: (i) those of the subalkaline suite, which formed from an initial melt with a light rare earth elements (LREE) enriched signature and incompatible trace element patterns that suggest an island arc affinity; and (ii) those of the alkaline suite with LREE-enriched signature and incompatible trace element patterns that are virtually identical to typical oceanic island basalt (OIB) pattern. The data also suggests that the trachytes were derived from the alkaline source, with fractionation controlled by extensive removal of plagioclase and to a lesser extent clinopyroxene. The presence of compositionally diverse volcanics together with the occurrence of a variety of Triassic–Cretaceous sedimentary rocks and radiolarian chert indicate that the studied volcanic rocks from the Kermanshah ophiolite represent off-axis volcanic units that were formed in intraplate oceanic island and island arc environments in an oceanic basin. They were located on the eastern and northern flanks of one of the spreading centers of a ridge-transform fault system that connected Troodos to Oman prior to its subduction under the Eurasian plate.

Petrology, geochemistry and tectonic setting of the Khoy ophiolite, northwest Iran: implications for Tethyan tectonics

Abstract The Khoy ophiolite in northwestern Iran represents a remnant of oceanic lithosphere formed in the Mesozoic Neo-Tethys. This northwest–southeast trending ophiolite complex consists from bottom to top (east to west) of a well-defined basal metamorphic zone, peridotites (dunite, harzburgite) and serpentinized peridotite, gabbros, sheeted dikes, pillow and massive lava flows, and pelagic sedimentary rocks, including radiolarian chert. The rocks of the metamorphic zone have an inverse thermal gradient from amphibolite facies to greenschist facies. The high-grade metamorphic rocks are immediately adjacent to the peridotite and the gabbros and the low-grade rocks are in contact with the Precambrian Kahar Formation. Based on mantle-normalized incompatible trace element diagrams there are two distinct types of basalt flows present at the Khoy ophiolite: (1) massive basalts that have patterns virtually identical to E-MORB, and (2) pillow basalts that have more primitive chemical composition whose trace element patterns plot between E-MORB and N-MORB. The chondrite-normalized REE patterns for the pillow basalts are LREE-depleted [(LaN/SmN)ave=0.70], similar to patterns for the mean diabase composition for the Oman ophiolite and LREE-depleted basalts of the Band-e-Zeyarat ophiolite of southern Iran. The REE patterns for the massive basalts are similar in general REE abundances to the pillow basalt patterns, but they are slightly LREE-enriched [(LaN/SmN)ave=1.09] and their patterns cross those of the pillow basalts. The REE patterns for the gabbros and diorites indicates that the crustal-suite rocks were most likely derived by a process of fractional crystallization from a common basaltic melt. This basaltic melt was most likely generated by approx. 20–25% partial melting of a simple lherzolite source and had REE concentrations of roughly 10× chondrite. A comparison between the results from the Khoy ophiolite and the data from other Iranian ophiolites reveals geochemical evidence to suggest a tectonic link between the Khoy ophiolite and the rest of the Iranian ophiolites. Our results suggest that Khoy ophiolite is equivalent to the inner group of Iranian ophiolites (e.g. Nain, Shahr-Babak, Sabzevar, Tchehel Kureh and Band-e-Zeyarat) and was formed as a result of closure of the northwestern branch of a narrow Mesozoic seaway which once surrounded the Central Iranian microcontinent.

Quantitative concentration profiling of nickel in tissues around metal implants: a new biomedical application of laser ablation sector field ICP-MS

Laser-ablation sector-field (high resolution) inductively coupled plasma mass spectrometry (LA-HR-ICP-MS) has been used for in situ determination and spatial elemental profiling of nickel concentrations in tissues that have been exposed to nickel wire. Nickel has a number of adverse biological effects that have made the use of nickel (or any other metal) in biomedical implants controversial. Yet, information about the distribution of nickel in tissues around nickel-containing implants is scarce. This study examines the diffusion of nickel with time and the spatial distribution of nickel around nickel-containing implants in vivo. Pure nickel wires were implanted subcutaneously into rats for seven days and the tissues were analyzed for nickel content and degree of inflammation away from the implants using 24Mg and 60Ni isotopes. Data were obtained by ablation with Nd:YAG laser operating in the UV region (266 nm and 213 nm) and element analysis with a high resolution ICP-MS. A 50 ppm glass standard (NIST-612) was also analyzed for the same isotopes. Quantification was performed by assuming a uniform nominal magnesium concentration value of 97 µg g−1 in untreated tissue and using 24Mg intensity for internal calibration. The precision (RSD%) of measurements for 24Mg for the NIST-612 Glass standard was within 3.8% to 4.6% and for the tissue samples was within 3.2% to 4.5%. The precision of analysis for 60Ni for the NIST-612 Glass standard was 5.4%. There was a significant penetration of nickel ions into tissues exposed to nickel wire implants. The concentration of nickel reached values as high as 60 µg g−1 near the implants, falling exponentially to undetectable levels 3–4 mm from the implants. The study showed that the laser ablation technique was well suited for analysis of soft tissues for metal ion content. This technique also allowed metal concentration spatial profiling as a function of time.

New quantitative approach in trace elemental analysis of single fluid inclusions: applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Laser ablation inductively coupled plasma mass spectrometry has been used for the in situ elemental analysis of individual fluid inclusions with artificially prepared fluid inclusions as external standards. Artificial fluid inclusions standards were prepared by drawing a standard solution of known composition into microcapillary tubes. An ICP-MS equipped with an Nd:YAG laser operating in the UV region (266 nm) was used for data acquisition. The laser was focused and fired on 25–30 µm spots on the microcapillary tubes until the fluid was reached. The content of the microcapillary tube then emptied and was transported with argon to the torch. The average volume of fluid released, per pulse of laser, was approximately 100 pl. Calibration curves were created by plotting signal intensity versus concentration. The long-term precision (RSD%) of measurements for Sr were 1.1–3.1% for a 1000 ppm solution, 2.7–4.9% for a 500 ppm solution and 3.1% for a 250 ppm solution. Similar measurements on the same solutions for Rb gave values of 1.9–2.3% for a 1000 ppm solution, 5.1–6.3% for a 500 ppm solution and 1.7% for a 250 ppm solution. The technique was tested on fluid inclusions in halite from the Palo Duro Basin, Texas, USA. The results show that concentrations for Sr range from 90 to 153 ppm, and for Rb from 98 to 100 ppm. The precision of analysis for individual natural fluid inclusions ranges from 5 to 31% for both Sr and Rb. The concentration of Sr calculated by this method is in agreement with earlier work.

Environmental Forensic Application of Lead Isotope Ratio Determination: A Case Study Using Laser Ablation Sector ICP-MS

Laser-ablation sector field inductively coupled plasma mass spectrometry (ICP-MS) has been used for the in situ determination of concentrations and isotope compositions of Pb in an environmental sample in a form of layered paint chip. This study examines feasibility of using the powerful method of isotope ratio analysis in laser ablation sector ICP-MS as a routine and rapid, but very reliable, analytical instrument for fingerprinting sources of lead in environmental forensic investigations. Significant lead concentrations were found in four of the six layers of a paint chip sample. The layers were analyzed for isotopes of lead (i.e., 204Pb, 206Pb, 207Pb, 208Pb) and two isotopes of mercury (i.e., 202Hg and 204Hg). In this study, Hg isotopes were measured for the purpose of interference correction for 204Pb isotope. Elemental data were obtained by ablation with Nd:YAG laser operating in the UV region (wavelength of 213 nm) manufactured by New Wave-Merchantek and isotopic analysis with a Finnigan MAT sector ICP-MS. A multielement reference glass standard (NIST-612) was also analyzed for the same isotopes and gave stable and flat response for all isotopes of lead. Four of the paint layers (C, D, E, F) contained significant amounts of lead and were used for isotope ratio measurements. An appreciable amount of Hg was found only in layer C. For layers D, E, and F, which had copious amount of Pb, the standard deviations for isotope ratios were: 0.492–1.347 for 206Pb/204Pb, 0.494–1.653 for 207Pb/204Pb, and 1.214–3.643 for 208Pb/204Pb. The lead isotope ratios for the layer with the highest Pb concentration, layer F, had a radiogenic signature similar to that of Mississippi Valley-type Pb-Zn mines in eastern Missouri. The lead isotope ratios of layer E are less radiogenic and had a signature similar to that of Pb-Zn-Ag mines of Sierra Madre in east central Mexico. The lead isotope ratio of the third layer, layer D, had a nonradiogenic signature.

Gallium Diffusion in Human Root Dentin: Quantitative Measurements by Pulsed Nd:YAG Laser Ablation Combined with an Inductively Coupled Plasma Mass Spectrometer

OBJECTIVE The purpose of this work was to determine if gallium nitrate placed in human root canals would diffuse across root dentin and reach concentrations high enough to inhibit osteoclasts (approximately 10(-4) M). BACKGROUND DATA External root resorption by osteoclasts is a common sequela of dental trauma. If not detected and treated, it can lead to the loss of a tooth. Gallium has recently been reported to inhibit osteoclastic resorption in vitro. METHODS Roots were cleaned and shaped using standard endodontic procedures and the tips sealed with cyanoacrylate cement. The root canal space was filled with an aqueous solution of 1.0 M gallium nitrate chelated with 1.0 M sodium citrate buffer (pH 7.2). The roots were then sectioned longitudinally into two equal halves. Each half was fixed to a translation stage that moved at a constant rate beneath a frequency-quadrupled Nd-YAG laser (266 nm) laser that was used to sample the concentration of 43Ca, 69Ga, and 71Ga by laser ablation across the thickness of root dentin to the periodontal surface. The plume of ablated dentin was swept into an inductively heated plasma chamber by argon gas and hence into a mass spectrometer. RESULTS Quantitative analyses of the distribution of gallium showed it was highest adjacent to the root canal space and fell as more peripheral sites were sampled but then rose slightly at the external boundary of the root which is covered with a thin layer of atubular cementum. CONCLUSIONS Even the lowest concentrations of gallium found in peripheral root dentin exceeded the 10(-4) M concentration required to inhibit osteoclastic activity. This simple endodontic treatment should undergo clinical trials to determine its efficacy in vivo. The laser ablation, inductively coupled mass spectrometry method is a powerful analytic tool for measuring spatial distribution of materials in mineralized tissues.

Trace element determination of single fluid inclusions by laser ablation ICP-MS: applications for halites from sedimentary basins

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to determine Ca, Sr and Rb in individual natural fluid inclusions in halite. Artificial fluid inclusions made in glass microcapillary tubes were used to quantify the data. An Nd:YAG laser operating at 266 nm was focused and fired in Q-switched mode on 20–30 μm diameter spots on the microcapillary tubes until the fluid was reached. The standard fluid was ablated and transported with argon to the ICP-MS. Analytes in fluid inclusions in the halite were determined using calibration curves obtained from standard solutions in the microcapillaries. Uncertainties in the analysis of individual fluid inclusions ranged from 4% to 20% RSD for samples from the Palo Duro and Paradox Basins in Texas and Utah, respectively. Ca and Sr in halite from the Palo Duro Basin ranged from 95 to 1028 ppm and from 6.7 to 607 ppm, respectively. Halite from the Paradox Basin contained fluid inclusions with 124 to 178 ppm Ca and 14 to 108 ppm Sr. In all inclusions, Ca had the highest concentration, followed by Sr and Rb. Ca and Sr concentrations for fluid inclusions in halite from the Palo Duro Basin were generally greater than those from the Paradox Basin, and were greater with depth in the basin.

Nanoleakage at the dentin adhesive interface: a new application for laser ablation-sector field-ICPMS

Laser ablation-sector field-inductively coupled plasma mass spectrometry has been used for in situ determination of silver concentration in treated human teeth. Silver nitrate has long been used to trace the presence of micro sized gaps between the walls of dental restorations and teeth, and more recently, to trace the presence of nanometer sized voids within resin-bonded restorations. This study examines the diffusion of silver nitrate into submicron voids beneath resin-bonded composite restorations. The silver treated-teeth were analyzed for 43Ca, 107Ag, and 109Ag isotopes. Elemental data were obtained by ablation with Nd:YAG laser operating in the UV region 266 nm and 213 nm by New Wave-Merchantek and isotopic analysis with a sector field ICP MS by Finnigan MAT. A 50 ppm glass standard (NIST-612) was also analyzed for the same isotopes. Quantification was performed by assuming a uniform nominal calcium concentration value of 27 g per 100 g of dry dentin across the root and using the 43Ca signal for internal calibration. The precision (RSD%) of measurements for 43Ca for the NIST-612 glass standard was found to be within 1.8% to 2.5% and for the tooth samples within 2.8% to 7.1%. The precision of analysis for 107Ag for the NIST-612 glass standard was between 2.6% and 4.4%. The analysis revealed a significant penetration of resin-bonded dentin by silver, ranging from ∼35000 ppm at the very bottom of the resin-infiltrated demineralized dentin to only 10 s of ppm in the areas within the underlying mineralized dentin. The analysis revealed that a significant amount of silver penetrated through resin-dentin bonds, and that the amount of silver increased with increased acid-etching time. The results from this study suggest that current adhesive resin system do not create perfect bonds and that laser ablation sector field ICPMS can be used to quantify the amount of nanoleakage of bonded restorations.

Laser Ablation ICP-MS: A New Elemental and Isotopic Ratio Technique in Environmental Forensic Investigation

Environmental forensics is one the youngest and most rapidly growing scientific fields whose success is driven to a great extent by continuous developments in analytical instrumentation. During the last two decades, among high-end analytical instrumentation, inductively coupled plasma instruments (ICPs) arguably have received the largest share of attention in instrument development and application. This is particularly true since ICP has been coupled with mass spectrometry, and now ICP-MS has matured into one of the most sophisticated and successful methods in atomic spectrometry. This is due to a number of advantages this technique offers over all other atomic spectrometry methods, such as a superior sensitivity, lower detection limits, and the ability to make multielement and isotopic ratio measurements. However, perhaps the most important advantage of ICP-MS techniques is the versatility in sample introduction. Regardless of the type of introduction method (i.e., solution, solid, slurry) all samples are introduced at atmospheric condition. This gives ICP-MS the potential of being a true application-specific instrument with perhaps the widest range of inorganic analytical applications. The traditional ICP-MS instruments were based on using quadrolpole mass spectrometer (Q-ICP-MS) which provides a resolution of one atomic mass unit. The newer high resolution magnetic sector ICP mass spectrometers (HR-ICP-MS) offer yet greater advantages such as significantly greater resolving power, lower detection limits [routinely in parts per trillion (ppt) and under right conditions as low as parts per quadrillion (ppq)], and analysis of elements that are traditionally difficult to analyze by quadropole instruments such as phosphorous, sulfur and halogens. Nevertheless, in routine elemental and isotopic analysis, the Q-ICP-MS instruments are by far the most commonly used and the work horse for multielemental analysis in many analytical laboratories. The most recent development in ICP instrumentation has been the advent of multicollector high resolution magnetic sector ICP-mass spectrometers (MC-HR-ICP-MS) which has lead to significant improvement in detection limits and simultaneous measurement of isotope ratios. The development of the highresolution instrument with much lower detection limits and simultaneous isotope ratio analysis has been particularly advantageous in analysis of transuranium elements in biological and environmental samples with potential contamination of radioactive elements. Plasma spectrochemical methods (ICP-MS and ICP-AES) have always been performed as routine procedures for metal analysis in environmental samples, such as air monitoring, biota analysis, soil and sediment analysis, radionuclide determination and water and ecological monitoring. However, in environmental forensic applications, where more compoundspecific information is required, discrimination in relative isotopic abundances of metals is advantageous, particularly in studies of transport and ultimate fate of pollutants. Under special conditions, there is also a strong possibility for chemical fingerprinting and identification of the source of pollutant using variations in isotopic abundances (i.e., isotopic ratio analysis), or diagrams comparing variations in relative abundances of appropriate group of trace and ultra-trace metals. Furthermore, since trace metals play a critical role in biological activity and ecosystem, there is a clear potential to use ICP-MS as the ultimate analytical instrument to decipher the impact of the trace metals and to separately quantify the various specified ultratrace elements. Therefore, in more recent years, researchers in various areas have taken advantage of the extreme flexibility of the interface region (sample introduction) of ICP-MS and coupled the instrument with various pre-concentration methods such as ion-exchange columns, and on line separation techniques such as high performance liquid chromatography (HPLC), capillary electrophoresis (CE) or other species-selective sampling techniques for chemical speciation. The later technique has been particularly useful in working with multi-valance elements such as chromium and arsenic in biological and environmental samples. In terms of other sample introduction methods, laser ablation is perhaps the most exciting development for microsampling and analysis of samples that are commonly in solid form. However, there have been also numerous successful attempts in using laser ablation for analysis of metal contents in biota such as soft tissues, and plants that have been exposed to metal-bearing environmental contaminants. Similarly, there have been a number of successful attempts in direct analysis of samples in liquid form by laser ablation, such as enrapt liquid contents of microscopic void spaces in solid samples which