The effect of magnetic resonance imaging on mercury release from dental amalgam at 3T and 7T

Objectives To measure mercury release from standardised hydroxyapatite/amalgam constructs during MRI scanning and investigate the impact of static field strength and radiofrequency (RF) power on mercury release. Methods Amalgam was placed into 140 hydroxyapatite disks and matured for 14-days in artificial saliva. The solution was replaced, and samples split into five groups of 28 immediately prior to MRI. One group had no exposure, and the remainder were exposed to either a 3T or 7T MRI scanner, each at high and low RF power. Mercury concentration was measured by inductively coupled plasma mass spectrometry. Groups were compared using one-way ANOVA, and two-way ANOVA for main effects/ interaction of field strength/ RF power. Results Mercury concentration was increased in the 7T groups (high/ low: 15.43/ 11.33 ng mL−1) and 3T high group (3.59) compared to control (2.44). MRI field strength significantly increased mercury release (p < .001) as did RF power (p = .030). At 3T, mercury release was 20.3 times lower than during maturation of dental amalgam, and for the average person an estimated 1.50 ng kg−1 of mercury might be released during one 3T investigation; this is substantially lower than the tolerable weekly intake of 4,000 ng kg−1. Conclusion Mercury release from amalgam shows a measurable increase following MRI, and the magnitude changes with magnetic field strength and RF power. The amount of mercury released is small compared to release during amalgam maturation. Amalgam mercury release during MRI is unlikely to be clinically meaningful and highly likely to remain below safe levels

At the world's edge: Reconstructing diet and geographic origins in medieval Iceland using isotope and trace element analyses

Objectives A multi‐isotope study was conducted on individuals buried at Skriðuklaustur monastery (AD 1493–1554) to investigate their geographic origins and dietary composition. Comparative material from individuals excavated from Skeljastaðir, an inland farm site was also analyzed. Materials and methods Bone collagen was extracted from 50 humans (Skriðuklaustur and Skeljastaðir) and 25 animals (Skriðuklaustur) and analyzed for δ13C, δ15N, and δ34S. Dental enamel samples from 31 individuals (Skriðuklaustur) were also analyzed for 87Sr/86Sr, δ18O, δ13C, and trace elements (Pb, Sr, Zn, Ba). Results The mean value determined from individuals from Skriðuklaustur (n = 36) was δ13C = −18.7 ± 0.8‰, δ15N = 12.8 ± 1.1‰, and δ34S = 9.0 ± 1.6‰, whereas at Skeljastaðir (n = 14), it was δ13C = −20.5 ± 0.8‰, δ15N = 7.8 ± 0.9‰, and δ34S = 9.4 ± 1.6‰. At Skriðuklaustur, human dental enamel samples (n = 31) provided a 87Sr/86Sr range of 0.7060–0.7088, δ18Ophosphate from 13.9 to 16.1‰ and δ13Ccarbonate from −16.6 to −12.9‰. Inferred drinking water (δ18Odw) values range from −12.3 to −8.9‰. Sr concentrations range from 25.8 to 156.7 ppm, Ba from 0.11 to 0.81 ppm, Zn from 43.8 to 145.8 ppm, and Pb from 0.13 to 9.40 ppm. Discussion A combination of results indicates that the people from Skriðuklaustur were born in Iceland, but some lived inland during childhood while others lived closer to the coast. Since Skriðuklaustur was a hospital, these individuals may have sought medical treatment at the monastery. The δ13C and δ15N values determined from bone collagen indicate that the people residing at Skriðuklaustur consumed a diet high in marine protein, while those residing at Skeljastaðir exhibit values more consistent with terrestrial resources.This research was financed by Fornminjasjóður (the Archaeology Fund), Háskólasjóður Eimskipafélags Íslands (the Eimskip University Fund), and the Stable Isotope Biogeochemistry Laboratory (SIBL).Peer Reviewe

Adakites without a slab: Remelting of hydrous basalt in the crust and shallow mantle of Borneo to produce the Miocene Sintang Suite and Bau Suite magmatism of West Sarawak

We present new geochronological and geochemical data for Neogene magmatism from West Sarawak. Zircon U-Pb geochronology divides Neogene magmatic rocks of West Sarawak into a Lower Miocene West Sarawak Sintang Suite with ages of c. 19 to 21 Ma, and a Middle Miocene Bau Suite with ages of c. 12 to 14 Ma. Magmatism occurred in multiple short-lived pulses from approximately 24 Ma and was coeval with magmatic activity in NW Kalimantan and East Kalimantan. The majority of, but not all, Bau Suite samples display adakitic chemistry, while the West Sarawak Sintang Suite is predominantly non-adakitic. There was no active subduction zone or subducted slab associated with this adakitic magmatism. Instead, the geochemical diversity is consistent with the Bau and West Sarawak Sintang suites representing mixtures of mafic, mantle-derived magma with felsic magma derived from remelting of hydrous, mafic rock that had been emplaced into the lithosphere of Borneo as arc basalt tens or hundreds of millions of years previously. This origin is most evident in the main Sintang Suite of central Borneo (Kalimantan) which has preserved less contaminated examples of the mafic endmember. This endmember resembles basaltic rocks from several locations across Borneo suggesting that intraplate, mantle-derived magmatism was responsible for remelting older, hydrated basaltic rocks in the crust

Arc-related harzburgite-dunite-chromitite complexes in the mantle section of the Sabzevar ophiolite, Iran : a model for formation of podiform chromitites

Podiform chromitites are common within the mantle section of the Late Cretaceous Sabzevar ophiolite in NE Iran. We studied chromitite pods and related ultramafic rocks from three Sabzevar massifs: Baghjar-Kuh Siah, Gaft Chromitite Mine and Forumad peridotite-chromitite. These represent an upper mantle sequence just below the Sabzevar Moho. The Baghjar-Kuh Siah mantle sequence contains plagioclase lherzolites, enriched in bulk REEs, with low Cr# spinels and MORB-like clinopyroxenes. These lherzolites formed due to the impregnation of MORB-like melts. The Gaft and Forumad harzburgites are depleted in trace and rare earth elements and thus are residues after high degree of partial melting (more than exhaustion of Cpx). The Gaft Chromitite Mine includes two types of podiform chromitites, high Cr# and low Cr#. The melt precipitating high Cr# spinel was boninitic whereas the melt forming the low Cr# chromitites was tholeiitic. Most Forumad massif chromitites have high Cr# spinels, although those rich in silicate inclusions are aluminous. Trace and REE element patterns of Forumad harzburgite clinopyroxene are similar to those in supra-subduction zone (SSZ) peridotites while those of Baghjar-Kuh Siah lherzolites are similar to MOR peridotite clinopyroxenes. These mineral data are also consistent with bulk rock trace and rare earth elements composition of their host peridotites. Field observations indicate that early tholeiitic magmas were followed by late boninites, as revealed in chromitite compositions as well as mantle rocks and dikes. We suggest a time-integrated model for the evolution of the Sabzevar mantle sequence during an early stage of subduction initiation associated with formation of an incipient arc. In this scenario, MORB-like melts (forearc basalts) formed first, causing low Cr# chromitites and plagioclase-clinopyroxene impregnations. Subsequent arc-like or boninitic melts with increasing contribution of slab-derived fluids were responsible for the formation of replacive dunites and high Cr# chromitites.19 page(s

Supra-subduction zone magmatism of the Neyriz ophiolite, Iran: constraints from geochemistry and Sr-Nd-Pb isotopes

The Neyriz ophiolite along the northeast flank of the Zagros fold-thrust belt in southern Iran is an excellent example of a Late Cretaceous supra-subduction zone (SSZ)-related ophiolite on the north side of the Neotethys. The ophiolite comprises a mantle sequence including lherzolite, harzburgite, diabasic dikes, and cumulate to mylonitic gabbro lenses, and a crustal sequence comprising a sheeted dike complex and pillow lavas associated with pelagic limestone and radiolarite. Mantle harzburgites contain less CaO and Al2O3, are depleted in rare earth elements, and contain spinels that are more Cr-rich than lherzolites. Mineral compositions of peridotites are similar to those of both abyssal and SSZ- peridotites. Neyriz gabbroic rocks show boninitic (SSZ-related) affinities, while crustal rocks are similar to early arc tholeiites. Mineral compositions of gabbroic rocks resemble those of SSZ-related cumulates such as high forsterite olivine, anorthite-rich plagioclase, and high- Mg# clinopyroxene. Initial εNd(t) values range from +7.9 to +9.3 for the Neyriz magmatic rocks. Samples with radiogenic Nd overlap with least radiogenic mid-ocean ridge basalts and with Semail and other Late Cretaceous Tethyan ophiolitic rocks. Initial 87Sr/86Sr ranges from 0.7033 to 0.7044, suggesting modification due to seafloor alteration. Most Neyriz magmatic rocks are characterized by less radiogenic 207Pb/204Pb (near the northern hemisphere reference line), suggesting less involvement of sediments in their mantle source. Our results for Neyriz ophiolite and the similarity to other Iranian Zagros ophiolites support a subduction initiation setting for its generation

Coexistence of abyssal and ultra-depleted SSZ type mantle peridotites in a Neo-Tethyan Ophiolite in SW Turkey: Constraints from mineral composition, whole-rock geochemistry (major–trace–REE–PGE), and Re–Os isotope systematic.

We present new, whole-rock major and trace element chemistry, including rare earth elements (REE), platinum-group elements (PGE), and Re-Os isotope data from the upper mantle peridotites of a Cretaceous Neo-Tethyan ophiolite in the Mu\u1e7la area in SW Turkey. We also report extensive mineral chemistry data for these peridotites in order to better constrain their petrogenesis and tectonic environment of formation. The Mu\u1e7la peridotites consist mainly of cpx-harzburgite, depleted harzburgite, and dunite. Cpx-harzburgites are characterized by their higher average CaO (2.27wt.%), Al 2O 3 (2.07wt.%), REE (53ppb), and 187Os/ 188Os (i) ratios varying between 0.12497 and 0.12858. They contain Al-rich pyroxene with lower Cr content of coexisting spinel (Cr#=13-22). In contrast, the depleted harzburgites and dunites are characterized by their lower average CaO (0.58wt.%), Al 2O 3 (0.42wt.%), and REE (1.24ppb) values. Their clinopyroxenes are Al-poor and coexist with high-Cr spinel (Cr#=33-83). The 187Os/ 188Os (i) ratios are in the range of 0.12078-0.12588 and are more unradiogenic compared to those of the cpx-harzburgites.Mineral chemistry and whole rock trace and PGE data indicate that formation of the Mu\u1e7la peridotites cannot be explained by a single stage melting event; at least two-stages of melting and refertilization processes are needed to explain their geochemical characteristics. Trace element compositions of the cpx-harzburgites can be modeled by up to ~. 10-16% closed-system dynamic melting of a primitive mantle source, whereas those of the depleted harzburgites and dunites can be reproduced by ~. 10-16% open-system melting of an already depleted (~. 16%) mantle. These models indicate that the cpx-harzburgites are the products of first-stage melting and low-degrees of melt-rock interaction that occurred in a mid-ocean ridge (MOR) environment. However, the depleted harzburgites and dunites are the product of second-stage melting and related refertilization which took place in a supra subduction zone (SSZ) environment. The Re-Os isotope systematics of the Mu\u1e7la peridotites gives model age clusters of ~. 250. Ma, ~. 400. Ma and ~. 750. Ma that may record major tectonic events associated with the geodynamic evolution of the Neo-Tethyan, Rheic, and Proto-Tethyan oceans, respectively. Furthermore, > 1000. Ma model ages can be interpreted as a result of an ancient melting event before the Proto-Tethys evolution

LAPITA MIGRANTS IN THE PACIFIC’S OLDEST CEMETERY:ISOTOPIC ANALYSIS AT TEOUMA, VANUATU

Teouma, an archaeological site on Efate Island, Vanuatu, features the earliest cemetery yet discovered of the colonizers of Remote Oceania, from the late second millennium B.C. In order to investigate potential migration of seventeen human individuals, we measured isotopes of strontium (87Sr/86Sr), oxygen (d18O), and carbon (d13C), as well as barium (Ba) and strontium (Sr) concentrations, in tooth enamel from skeletons excavated in the first two field seasons. The majority of individuals cluster with similar isotope and Ba/Sr ratios, consistent with a diet of marine resources supplemented with plants grown on the local basaltic soils. Four outliers, with distinctive 87Sr/86Sr and d18O, are probably immigrants, three of which were buried in a distinctive position (supine, with the head to the south) with higher Ba/Sr and d13C, consistent with a terrestrial, nonlocal diet. Among the probable immigrants was a male buried with the crania of three of the locally raised individuals on his chest

Lapita Migrants in the Pacific's oldest Cemetery: Isotopic Analysis at Teouma, Vanuatu

Teouma, an archaeological site on Efate Island, Vanuatu, features the earliest cemetery yet discovered of the colonizers of Remote Oceania, from the late second millennium B. C. In order to investigate potential migration of seventeen human individuals, we measured isotopes of strontium ( 87Sr/86Sr), oxygen (δ18O), and carbon (δ13C), as well as barium (Ba) and strontium (Sr) concentrations, in tooth enamel from skeletons excavated in the first two field seasons. The majority of individuals cluster with similar isotope and Ba/Sr ratios, consistent with a diet of marine resources supplemented with plants grown on the local basaltic soils. Four outliers, with distinctive 87Sr/86Sr and δ18O, are probably immigrants, three of which were buried in a distinctive position (supine, with the head to the south) with higher Ba/Sr and δ13C, consistent with a terrestrial, nonlocal diet. Among the probable immigrants was a male buried with the crania of three of the locally raised individuals on his chest

Geochronology and geochemistry of exotic blocks of Cadomian crust from the salt diapirs of SE Zagros: the Chah-Banu example

Cadomian calc-alkaline I-type and within-plate A-type igneous rocks are widespread in the crust of Iran where they are ascribed to a convergent margin associated with the southward subduction of Prototethyan oceanic lithosphere beneath N Gondwana. These rocks are found as unmetamorphosed magmatic rocks and their metamorphic equivalents (mafic to felsic gneisses) could have been generated in both Cadomian arcs and associated rear-arcs. Nearly all these exposures also contain metamorphosed metasediments, whereas Cadomian igneous rocks of central Iran are associated with thick sequences of unmetamorphosed terrigenous rocks. In the Zagros Fold-Thrust belt of S Iran, salt diapirs contain abundant xenoliths of Cadomian igneous and sedimentary rocks in association with evaporites, dolomites, carbonates, and banded iron-salt deposits. This paper presents new zircon U-Pb and geochemical-isotopic data from igneous clasts in the Chah-Banu salt diapir in SE Zagros. Petrographic and geochemical data indicate two different types of rock clasts; calc-alkaline, I-type dacites-rhyolites, and arc-related to E-MORB-OIB-like gabbros, basalts, and dolerites. New zircon U-Pb ages show that dacites formed at 538.2 ± 2.2 Ma, whereas gabbros show ages of 539.0 ± 1.8 Ma. Zircons from dacites have negative εHf(t) values of – 1.1 to – 8.3. In contrast, zircons from gabbros have higher εHf(t) values of +4.5 to +8.5, indicating crystallization from mantle-derived juvenile magmas. Bulk rock Nd-Sr isotopic data (e.g. ɛNd(t) = +0.3 to +4.0 and 87Sr/86Sr(i) = 0.7059 to 0.70848) for gabbros, dolerites, and basalts confirm that these rocks originated from a mantle source similar to enriched parts of the subcontinental lithospheric mantle, whereas dacites and rhyolites (with εNd(t) = −3.4 to −4.1 and 87Sr/86Sr(i) = 0.70806 to 0.70907) show strong interaction with, and/or re-melting of older continental crust. We suggest that the bimodal calc-alkaline and E-MORB-OIB-like magmatic rocks in salt diapirs as well as associated evaporites and sedimentary rocks formed in a retro-arc rifted basin behind the Cadomian magmatic arc

Temporal changes in subduction- to collision-related magmatism in the Neotethyan orogen: The Southeast Iran example

Continental-arc igneous rock compositions change in response to the transition from subduction to collision and these changes can reveal how the crust, lithosphere and magma sources evolved. Neotethys-related Late Cretaceous to Pleistocene subduction- and collision-related magmatic rocks from the ~350 km long southeast Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran provide an excellent natural laboratory to better understand these changes. These igneous rocks are well-exposed and moderately eroded to reveal a nearly complete record since subduction initiation at ~95 Ma. We analyzed new samples for major and trace elements (83 samples), Srsingle bondNd isotopic compositions (47 samples), and Usingle bondPb zircon ages (26 samples) and compiled geochemical and geochronological data on the southeast segment of the UDMB. The geochronological data reveal two magmatic pulses at ~80–70 Ma and ~50–0 Ma. Important changes in magmatic compositions reflect initial collision with Arabia at ~32 Ma, changing from normal calc-alkaline to increasingly adakitic immediately after collision began. Five stages can be identified: 1) normal continental-arc magmatism during the Late Cretaceous; 2) arc quiescence in Paleocene and Early Eocene time; 3) Middle-Late Eocene extensional arc magmatism related to slab rollback; 4) early collision and crustal thickening during the Early Oligocene; and 5) slab breakoff, asthenospheric upwelling, and associated adakitic magmatism from Middle Miocene onward. Temporal changes in UDMB magmas reflect the response of the overriding plate to changes in the geometry of the subducting Neotethyan lithosphere and to collision between Arabia and Iran. Crustal thickening and arc narrowing during Miocene to Pleistocene post-collisional magmatism caused adakitic magmatism and associated Cu mineralization. Zircon Osingle bondHf and apatite O isotopes as well as bulk-rock Nd isotopes of Cu-bearing adakitic rocks are similar to other barren rocks, but nearly all fertile rocks have higher Hf/Y, Eu/Eu⁎(n) in zircon and higher Sr/Y, V/Y, Eu/Eu⁎(n) in apatite than barren rocks