Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry Research Articles

In situ S isotopic analysis in apatite using laser ablation-multiple collector-inductively coupled plasma mass spectrometry

The S isotope composition (34S/32S) in apatite has been considered as a new powerful tool to trace S source reservoirs and to evaluate redox state and dynamic sulfur behavior in magmatic systems. This study presents the first in situ method to analyze S isotope compositions in apatite using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The sulfur isotope analysis of low-S apatite suffered the problem of high background interference, resulting in a low ratio of signal to noise (S/N). A detailed investigation found that ∼50% background of S isotopes originated from memory effect in the aerosol particles transformation system and can be removed through careful cleaning or replacement. A linear regression calculation method was proposed instead of the traditional data reduction method to improve the performance of correcting the S background signal. Femtosecond laser ablation system (fs-LA) was used to reduce the thermal effect and suppress the potential fractionation of S isotopes during the laser ablation process, significantly improving the stability of δ34SV-CDT values at different laser ablation parameters. Seven natural apatite samples with a large S concentration range were measured by the presented method. A good agreement of δ34SV-CDT values between fs-LA-MC-ICP-MS and IR-MS was obtained. The reproducibility of δ34SV-CDT obtained from fs-LA-MC-ICP-MS was similar to that in SIMS. These results confirm that the presented method can provide high-quality S isotopic compositions in natural apatites. Four apatite samples (Sly-1, Sly-2, MG, and OL-1) with various concentrations of SO3 (0.21% to 1.26%) show the homogeneous S isotope compositions based on the large amounts of repeated analyses using fs-LA-MC-ICP-MS. They are suggested as the high-quality external reference materials for in situ S isotope analysis for LA-MC-ICP-MS and SIMS.

In situ calcium isotopic ratio determination in calcium carbonate materials and calcium phosphate materials using laser ablation-multiple collector-inductively coupled plasma mass spectrometry

This study presents a highly precise and accurate Ca isotope analysis method using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) in calcium carbonates and calcium phosphates. High-sensitivity cones and nitrogen gas were used to improve the performance of the LA-MC-ICP-MS. The experiment results show that at the N2 mode, the signal intensity of 44Ca+ in the high-sensitivity cones (Jet + X cones) was 5-fold higher than that in the normal cones (S + H cones), while the polyatomic interferences of 40Ar1H1H+ and 40Ar16O+ in the high-sensitivity cones were suppressed by factors of 6.1 and 10.6, respectively, after the addition of 8 ml min−1 N2. The combination of high sensitivity cones and N2 addition did not increase the production of double charged ions. Additionally, the interference correction of doubly charged Sr ions was investigated in detail. The experiment results demonstrate that the concentration ratio of Sr to Ca (represented as I87Sr++/I44Ca+), the 87Sr/86Sr ratio and the mass fractionation factor of Sr (fSr) during the measurement process were key parameters for in situ Ca isotope ratios analysis. The threshold values of these key parameters were evaluated and are recommended to ensure an accurate correction of doubly charged Sr ions. Using the optimized instrumental conditions and correction strategies, an excellent within-run precision (<0.06‰, 2SE) and external reproducibility (<0.15‰, 2SD) for the microanalysis of δ44/42Ca915b were obtained in natural calcium carbonates and calcium phosphates. These precisions are better than the values previously reported in the literature regarding using LA-MC-ICP-MS. Matrix effects were observed during the in situ Ca isotope analysis among calcium carbonates, hydroxy calcium phosphates and igneous apatites. Using the matrix-matching standards, accurate δ44/42Ca915b values in natural materials with various matrices were achieved, confirming the availability of the proposed method to resolve the spatial variation of δ44/42Ca in natural materials.

Boron isotope variations of Franciscan serpentinites, northern California

Serpentinites and serpentinized mantle peridotites with various tectonic origins occur in the Franciscan Complex of the Northern California Cordillera, USA. Boron isotopes of serpentinites differentiate with fluid-mediated processes, and have great potential for key geologic markers in convergent margins. To understand boron isotope behavior within the Franciscan subduction zone system, we apply a newly developed ablation volume correction (AVC) method for in-situ isotope/elemental analyses using a laser-ablation multiple collector inductively-coupled-plasma mass spectrometry (LA-MC-ICPMS) on seventeen different Franciscan serpentinites (sensu lato) collected from eight separate areas. Boron abundances and isotope compositions of the studied serpentinites show large variations B = 1.6–239 μg·g−1, δ11B = −12.0 to +24.4‰, which allow to discriminate the serpentinites into two groups: (1) a lighter δ11B of −12.0 to +8.8‰ with a lesser B < ~56 μg·g−1 and (2) a heavier δ11B of +7.2 to +24.4% with a greater B ~34–239 μg·g−1. These groups lithologically correspond to the presence or absence of associated blueschist-facies metamorphic rocks, respectively. The blueschist-bearing and/or blueschist-associated serpentinites might have been affected by a deep forearc slab fluids in the depth of > ~2 GPa. Preferential partitioning of 11B into fluids released from the subducted slab at shallow leaves lighter δ11B in the slab resulting in lighter δ11B in the deep slab fluids. In contrast, the blueschist-absent serpentinites with heavier δ11B may have formed at a shallow environment where shallow slab or hydrothermal fluids with heavier 11B were present. Lesser versus greater amounts of B in the deep versus shallow serpentinites are also consistent with the dehydration profile of B from a slab. Our results show the versatility of boron isotopes and composition for identification of the origin of serpentinite in Pacific-type orogenic belts.

Sulfur isotope analysis of microcrystalline iron sulfides using secondary ion mass spectrometry imaging: Extracting local paleo-environmental information from modern and ancient sediments.

Sulfur isotope ratio measurements of bulk sulfide from marine sediments have often been used to reconstruct environmental conditions associated with their formation. In situ microscale spot analyses by secondary ion mass spectrometry (SIMS) and laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) have been utilized for the same purpose. However, these techniques are often not suitable for studying small (≤10 μm) grains or for detecting intra-grain variability. Here, we present a method for the physical extraction (using lithium polytungstate heavy liquid) and subsequent sulfur isotope analysis (using SIMS; CAMECA IMS 7f-GEO) of microcrystalline iron sulfides. SIMS sulfur isotope ratio measurements were made via Cs+ bombardment of raster squares with sides of 20-130 μm, using an electron multiplier (EM) detector to collect counts of 32 S- and 34 S- for each pixel (128 × 128 pixel grids) for between 20 and 960 cycles. The extraction procedure did not discernibly alter pyrite grain-size distributions. The apparent inter-grain variability in 34 S/32 S in 1-4 μm-sized pyrite and marcasite fragments from isotopically homogeneous hydrothermal crystals was ~ ±2‰ (1σ), comparable with the standard error of the mean for individual measurements (≤ ±2‰, 1σ). In contrast, grain-specific 34 S/32 S ratios in modern and ancient sedimentary pyrites and marcasites can have inter- and intra-grain variability >60‰. The distributions of intra-sample isotopic variability are consistent with bulk 34 S/32 S values. SIMS analyses of isolated iron sulfide grains yielded distributions that are isotopically representative of bulk 34 S/32 S values. Populations of iron sulfide grains from sedimentary samples record the evolution of the S-isotopic composition of pore water sulfide in their S-isotopic compositions. These data allow past local environmental conditions to be inferred.

U-Pb Ages and Hf Isotopes of Detrital Zircon Grains from the Mesoproterozoic Chuanlinggou Formation in North China Craton: Implications for the Geochronology of Sedimentary Iron Deposits and Crustal Evolution

The Chuanlinggou Formation is the lower formation of the Changchengian System, and hosts sedimentary iron deposits (marine oolitic ironstones) of the North China Craton (NCC). To determine the age of the iron deposits, and provide insight into the crustal growth of the craton, laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)U-Pb and in situ Hf isotope analysis were performed on detrital zircon grains. Samples were taken from the roof sand-shale of the sedimentary iron deposits at Jiangjiazhai and Pangjiapbu. Overall, 186 detrital zircon grain U-Pb ages yield three major age populations, with weighted average ages of 2450 Ma, 1848 Ma, and 1765 Ma, respectively. Four younger ages from magmatic zircon grains were obtained, ranging from 1694 to 1657 Ma. Combined with observations from published studies, the results define the lower limit for the age of the Chuanlinggou Formation, and constrain the age of the sedimentary iron deposits (marine oolitic ironstone) close to 1650 Ma. The peak ages of 1848 Ma and 2450 Ma define the major collisional events of the NCC. The age of 1765 Ma can be linked to the age range of the widespread mafic dyke swarms that represent the rifting of the NCC within the Columbia supercontinent. Detrital zircon grains from the Chuanlinggou Formation form two obvious groups, with different εHf (t) values ranging from −1 to −8 and from +1 to +8, which correspond to the U-Pb age ranges of 1.7–1.9 Ga and 2.3–2.6 Ga, respectively. They have a similar two-stage Hf model age peak at 2.65–2.85 Ga, suggesting that the source rocks for each of these events were derived from the recycling of ancient crust. The source rocks of the older group of zircon grains might be derived from juvenile crust with a short reworking period. The critical crust–mantle differentiation event might happen during the period of 2.65–2.85 Ga, marking the most significant stage of the crustal growth in the NCC.

A novel sample cell for reducing the “Position Effect” in laser ablation MC-ICP-MS isotopic measurements

A novel laser ablation cell geometry significantly reduces the so-called position effect on high precision and accuracy isotopic measurements by Laser Ablation-Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS).

Improved in situ Sr isotopic analysis by a 257 nm femtosecond laser in combination with the addition of nitrogen for geological minerals

In situ Sr isotope analysis of geological materials by laser ablation multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tracer technique for tracking magmatic source components and geological processes. However, the accuracy and precision of the 87Sr/86Sr ratio are limited in the analysis of natural minerals because of the low-Sr concentration, the isobaric interference or small grains with complex textural contexts, especially for transparent minerals such as feldspars. In this study, analytical results demonstrated that ablation rates in fs laser ablation were consistent for various samples (0.08–0.11μm per pulse), but those in ns laser ablation were obviously material properties-dependent, such as the rates of 0.026μm per pulse and 0.144μm per pulse for feldspar and pyrite, respectively. In addition, at similar energy fluences, the sensitivities of Sr in feldspars analyzed by the fs laser were 3.4 times higher than those analyzed by the ns laser due to the higher ablation efficiency of the fs pulse. These advantages of the fs laser not only offer the benefit of eliminating or weakening the matrix effect during the laser ablation processes but also help to improve the analytical precision for transparent minerals. We also demonstrated that the isobaric interferences of calcium dimers and argides (CaAr++CaCa+) and Kr+ were dramatically reduced by factors of 6.5–11.7 and 5–12.5 in the presence of 6–12mlmin−1N2, respectively. Furthermore, with the addition of N2 (12mlmin−1), the sensitivity of Rb was inhibited, resulting in a decrease of 1.47 times in Rb/Sr signal ratios. Due to the effect of suppressing interferences by adding N2, both the stability and accuracy of the 87Sr/86Sr and 84Sr/86Sr ratios show improvement, especially for the Rb-rich feldspars.Combining the advantages of the fs laser system with the addition of nitrogen, an improved in situ Sr isotope analytical method is then developed. The satisfactory accuracy and precision of the 87Sr/86Sr ratio from natural plagioclases, a K-feldspar with high Rb/Sr ratios (0.46) and a low-Sr clinopyroxene were obtained, demonstrating the reliability of the proposed method. Four feldspars, which have different contents of the major elements, Sr and Rb, showed homogeneous Sr isotope compositions and were recommended as potential suitable reference materials for in situ Sr isotope analysis. As an application, two plagioclases in mafic microgranular enclaves (MMEs) with small grain sizes (200–300μm) and wide ranges of Rb/Sr ratios were analyzed and showed obvious variations of the 87Sr/86Sr ratios from core to rim, which indicated that the proposed method in this study can provide high spatial resolution geochemical information for a single mineral.

Strontium isotope measurement of basaltic glasses by laser ablation multiple collector inductively coupled plasma mass spectrometry based on a linear relationship between analytical bias and Rb/Sr ratios.

In situ strontium (Sr) isotope analysis of geological samples by laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) provides useful information about magma mixing, crustal contamination and crystal residence time. Without chemical separation, during Sr isotope analysis with laser ablation, many kinds of interference ions (such as Rb+ and Kr+ ) are on the Sr isotope spectrum. Most previous in situ Sr isotope studies only focused on Sr-enriched minerals (e.g. plagioclase, calcite). Here we established a simple method for in situ Sr isotope analysis of basaltic glass with Rb/Sr ratio less than 0.14 by LA-MC-ICP-MS. Seven Faraday cups, on a Neptune Plus MC-ICP-MS instrument, were used to receive the signals on m/z 82, 83, 84, 85, 86, 87 and 88 simultaneously for the Sr isotope analysis of basaltic glass. The isobaric interference of 87 Rb was corrected by the peak stripping method. The instrumental mass fractionation of 87 Sr/86 Sr was corrected to 86 Sr/88 Sr=0.1194 with an exponential law. Finally, the residual analytical biases of 87 Sr/86 Sr were corrected with a relationship between the deviation of 87 Sr/86 Sr from the reference values and the measured 87 Rb/86 Sr. The validity of the protocol present here was demonstrated by measuring the Sr isotopes of four basaltic glasses, a plagioclase crystal and a piece of modern coral. The measured 87 Sr/86 Sr ratios of all these samples agree within 100ppm with the reference values. In addition, the Sr isotopes of olivine-hosted melt inclusions from the Emeishan large igneous province (LIP) were measured to show the application of our method to real geological samples. A simple but accurate approach for in situ Sr isotope measurement by LA-MC-ICP-MS has been established, which should greatly facilitate the wider application of in situ Sr isotope geochemistry, especially to volcanic rock studies.

Timing of formation of the Keketale Pb–Zn deposit, Xinjiang, Northwest China, Central Asian Orogenic Belt: Implications for the metallogeny of the South Altay Orogenic Belt

The Keketale is the largest Pb–Zn deposit in the volcano‐sedimentary Maizi Basin of the South Altay Orogenic Belt (AOB), Northwest China. The stratabound orebodies are hosted in a suite of meta‐sedimentary rocks intercalated with volcanic rocks of the Lower Devonian Kangbutiebao Formation. The massive and banded ores representing the main mineralization stage are relatively well‐preserved in the ore district. This paper reports systematic geochronological results including the zircon laser ablation–multiple collector–inductively coupled plasma–mass spectrometry (LA‐MC‐ICP‐MS) U–Pb analyses on two meta‐felsic volcanic rocks from the Kangbutiebao Formation and Rb–Sr isotope dating on seven sphalerite samples from the main mineralization stage, together with some sulphur isotopic data to constrain the mineralization age and the genesis of the deposit. Rb–Sr isotope dating yield an isochron age of 398.2 ± 3.3 Ma generally synchronous with the zircon (LA‐MC‐ICP‐MS) U–Pb analyses of a meta‐rhyolite and a meta‐dacite from the strata (410.5 ± 1.3 Ma and 394.8 ± 1.9 Ma, respectively). The δ34S values of seven pyrite samples in the main massive and banded ores vary from −12.4‰ to −6.2‰, indicating that the main ore‐forming sulphur of the deposit was derived from bacterial reduction of seawater sulphate. By integrating the field, chronological, and isotopic evidences, we conclude that the Keketale Pb–Zn deposit is a VMS‐type deposit. Combining our results with the isotopic geochronology in the South AOB, we argue that the South AOB has undergone three mineralization episodes: the syndepositional mineralization (412–387 Ma), the subvolcanic hydrothermal‐related mineralization (382–379 Ma), and the epigenetic mineralization that is genetically linked to regional metamorphism and deformation (260–204 Ma). The Keketale Pb–Zn deposit is a product of the Devonian seafloor hydrothermal exhalation system in the South AOB.

Sulfur isotope fractionation in pyrite during laser ablation: Implications for laser ablation multiple collector inductively coupled plasma mass spectrometry mapping

This study reports a detailed evaluation of how key parameters of operation influence the measurement of sulfur isotopes using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Sulfur isotopes are observed to display a fractionation up to 2‰ δ34S during analysis of pyrite with different laser parameters using a 193nm ArF excimer laser. In order to understand why the laser parameters affect S isotope fractionation when measuring S isotopes in pyrite, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to characterize debris formed during the ablation of pyrite, i.e., morphology and speciation of phases. The results show that pyrite decomposes to two phases: ball-like troilite (FeS) and a sulfur-rich floc-like agglomeration surrounding the troilite. The measured δ34S values vary due to the different proportions of troilite balls and the floc-like material generated under different laser parameters. The proportion of troilite and S was evaluated with a LA-(Quadrupole)-ICP-MS through direct comparison of the counts per second (CPS) ratio of 56Fe to 32S. In contrast to pyrite, natural pyrrhotite shows no decomposition process and the particle size of the debris from pyrrhotite is nearly 10 times larger than that of pyrite (~5μm for pyrrhotite compared to <1μm for pyrite). Therefore, a biased analysis of pyrite may happen using laser ablation although this problem can be minimized using high raster velocity. Last but not least, we provide a case study of S isotope mapping using high raster velocity, which extends the application of the in-situ S isotope analysis technique. The results here carry implications for the choice of settings needed to obtain accurate LA-MC-ICP-MS S-isotope maps of pyrite.

Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River

Research Article| September 01, 2016 Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River Zengjie Zhang; Zengjie Zhang 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Shane Tyrrell; Shane Tyrrell 3Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland Search for other works by this author on: GSW Google Scholar Chang’an Li; Chang’an Li † 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China †chanli_cug@sohu.com Search for other works by this author on: GSW Google Scholar J. Stephen Daly; J. Stephen Daly 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Xilin Sun; Xilin Sun 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China4Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar Aoife Blowick; Aoife Blowick 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Xu Lin Xu Lin 5Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Author and Article Information Zengjie Zhang 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Shane Tyrrell 3Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland Chang’an Li † 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China J. Stephen Daly 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Xilin Sun 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China4Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, Netherlands Aoife Blowick 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Xu Lin 5Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China †chanli_cug@sohu.com Publisher: Geological Society of America Received: 23 Oct 2015 Revision Received: 10 Feb 2016 Accepted: 31 Mar 2016 First Online: 02 Jun 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2016 Geological Society of America GSA Bulletin (2016) 128 (9-10): 1339–1351. https://doi.org/10.1130/B31445.1 Article history Received: 23 Oct 2015 Revision Received: 10 Feb 2016 Accepted: 31 Mar 2016 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Zengjie Zhang, Shane Tyrrell, Chang’an Li, J. Stephen Daly, Xilin Sun, Aoife Blowick, Xu Lin; Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River. GSA Bulletin 2016;; 128 (9-10): 1339–1351. doi: https://doi.org/10.1130/B31445.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Yangtze River is the largest fluvial system draining the Tibetan Plateau, yet its time of formation—pre-Miocene versus Pleistocene—has been debated for more than a century, with a particular focus on the incision of the Three Gorges. In this study, we used laser-ablation–multiple collector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) to measure Pb isotope compositions of detrital K-feldspars from Pliocene–Pleistocene sediments in the Jianghan Basin, located just downstream of the Three Gorges. Our new Pb results indicate that feldspars from the Songpan-Ganzi terrane were already being delivered to the Jianghan Basin by ca. 3.4 Ma. Therefore, we suggest that the Three Gorges was incised prior to the late Pliocene. Moreover, the Pb isotopic data also record the first delivery of detritus from the Hanjiang River, one of the Yangtze’s largest tributaries in the middle reaches, into the Jianghan Basin at ca. 1.8 Ma. Most K-feldspar grains from the mid-late Pleistocene samples have similar Pb isotopic compositions to those from the major tributaries in the upper reaches, i.e., Minjiang and Jialingjiang Rivers, indicating that the eastern Tibetan Plateau, as the major sediment supplier to the Jianghan Basin and mid-lower Yangtze River, has played a key role in the sediment source-to-sink transport of this river. This study sheds light on the factors that control the supply of detrital K-feldspar in large-scale drainage systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In situ determination of hafnium isotopes from rutile using LA-MC-ICP-MS

The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals (zircon/baddeleyite/calzirtite/eudialyte), however, little work has been reported on Hf-poor (<100 ppm) minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from rutile using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with 176Hf/177Hf=0.281795±0.000015 (2SD, n=33) and 176Lu/177Hf=0.000018±0.000004 (2SD, n=17) that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material (R10, Sugluk-4 and PCA-S207) and the 176Hf/177Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought.

A novel paleo-bleaching proxy using boron isotopes and high-resolution laser ablation to reconstruct coral bleaching events

Abstract. Coral reefs occupy only ~ 0.1 percent of the ocean's habitat, but are the most biologically diverse marine ecosystem. In recent decades, coral reefs have experienced a significant global decline due to a variety of causes, one of the major causes being widespread coral bleaching events. During bleaching, the coral expels its symbiotic algae, thereby losing its main source of nutrition generally obtained through photosynthesis. While recent coral bleaching events have been extensively investigated, there is no scientific data on historical coral bleaching prior to 1979. In this study, we employ high-resolution femtosecond Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) to demonstrate a distinct biologically induced decline of boron (B) isotopic composition (δ11B) as a result of coral bleaching. These findings and methodology offer a new use for a previously developed isotopic proxy to reconstruct paleo-coral bleaching events. Based on a literature review of published δ11B data and our recorded vital effect of coral bleaching on the δ11B signal, we also describe at least two possible coral bleaching events since the Last Glacial Maximum. The implementation of this bleaching proxy holds the potential of identifying occurrences of coral bleaching throughout the geological record. A deeper temporal view of coral bleaching will enable scientists to determine if it occurred in the past during times of environmental change and what outcome it may have had on coral population structure. Understanding the frequency of bleaching events is also critical for determining the relationship between natural and anthropogenic causes of these events.

Pb isotope compositions of detrital K‐feldspar grains in the upper‐middle Yangtze River system: Implications for sediment provenance and drainage evolution

AbstractThe upper‐middle Yangtze River drains the Qiangtang Block, the Songpan‐Ganzi, the Yangtze Craton, and the Qinling‐Dabie orogenic belt. These tectonic units have been shown to have heterogeneous Pb isotopic compositions, which allow this isotope system to be used as a sediment provenance tool. In this study we have employed laser ablation multiple collector inductively coupled plasma mass spectrometry (LA‐MC‐ICPMS) to measure Pb isotope compositions of sand‐sized K‐feldspar grains from the upper‐middle Yangtze River. Data are presented from four major tributaries: Yalongjiang, Minjiang, Jialingjiang, and Hanjiang, as well as from the main Yangtze River near Yichang. A portion of K‐feldspar grains in the Yalongjiang shows an ultraradiogenic character (206Pb/204Pb &gt; 20), which is unique in the upper‐middle Yangtze. Moreover, these ultraradiogenic grains were transported as far as Yichang, just downstream from the Three Gorges, suggesting that the Pb‐in‐K‐feldspar method could be applied to the sediments within the Jianghan Basin to date the formation of the Three Gorges. Pb isotopic data from Yichang indicate that erosion in the Longmen Shan and neighboring regions is more important than the Jinshajiang in supplying sediment. The grains in Hanoi Basin have little overlap with the Songpan‐Ganzi, but show a good match with the Yangtze Craton in its range of lower 206Pb/204Pb ratios. These observations support the idea that the “Middle Yangtze” used to be a tributary of the paleo‐Red River and that there has been no drainage linking the Songpan‐Ganzi and the Red River since the Eocene.

Lead isotope signatures of Kerguelen plume-derived olivine-hosted melt inclusions: Constraints on the ocean island basalt petrogenesis

The nature of magmatic sources reflected by isotopic composition of the ocean island basalt (OIB) remains an on-going question in igneous geochemistry. To constrain the magmatic sources for OIB related to the Kerguelen plume activity, we performed detailed microanalytical investigation of the 21.4 Ma picritic basalt (MD109-D6-87) dredged during the “Marion Dufresne” cruise on a seamount between Kerguelen Archipelago and Heard Island. Lead isotope compositions of olivine-hosted melt inclusions and matrix glasses were measured by Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) and Secondary Ion Mass Spectrometry (SIMS). We also performed major and trace element microanalyses and mapping of the inclusions and the host olivine phenocrysts by electron microprobe (wavelength-dispersive X-ray spectroscopy, WDS). The observed significant major element (K 2 O/P 2 O 5 , Al 2 O 3 /TiO 2 ) and Pb isotope ( 207 Pb/ 206 Pb and 208 Pb/ 206 Pb) heterogeneities of parental melts (MgO = 7–10 wt.%) during early high pressure crystallisation stage (200–300 MPa, Fo 82–86 mol%), and relative homogeneity at later lower-pressure crystallisation stage (< 100 MPa, Fo 75–80 mol%) are interpreted by mixing between “Plume” and “Assimilant” melts during magma residence and transport. Lead isotope composition of the parental basaltic melts was inherited from both heterogeneous mantle and the Kerguelen Plateau crust. High K 2 O/P 2 O 5 (> 4), Al 2 O 3 /TiO 2 (> 4) ratios are attributed to assimilation of the plateau basaltic crust (≥ 50 wt.%) by the melts in the magma chamber at palaeodepths from 6 to 9 km. The crustal assimilation may have happened through plagioclase dissolution. The large chemical and isotopic heterogeneity of the parental OIB melts found by in situ microanalyses in this study suggests that the bulk rock chemistry alone cannot provide enough information to constrain the nature of the magmatic sources. • The new data on the Kerguelen melts are important for understanding the OIB genesis. • The plume mantle composition cannot be known from the OIB bulk rock chemistry. • Heterogeneous sources affect composition of the OIB parental melts. • Crustal assimilation happens through plagioclase dissolution. • Magma mixing is a dominant and fast process in the evolution of the OIB.

Transgenerational marking of brown troutSalmo trutta f.f.,using an84Sr spike

The maternal transmission of a naturally occurring and non-toxic minor isotope of strontium (84Sr) to the central otolith region of the progeny of a typical European freshwater fish species, brown trout, Salmo trutta f.f. L. was accomplished. The focus was to apply minimum doses of a non-toxic solution at physiological salt concentration to minimise potential adverse effects on the fish. Female spawners were intraperitoneally injected with doses of 12.5 and 30.2 μg 84Sr kg−1 fish. Eggs were stripped and the resulting progeny were reared in a hatchery for about 1 year before sampling the otoliths. Strontium isotope ratios in the otoliths of the offspring were measured by cross-sectional line scans using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). Otolith cores of marked juveniles showed a significantly elevated 84Sr/86Sr ratio compared with control fish and to otolith regions created after hatching. Mass marking of cohorts of progeny from individually spiked brown trout with Sr isotopes is therefore possible for dispersal and migration studies without the necessity of handling eggs and applying other larval marking methods like immersion.

Mesoproterozoic emplacement and enriched mantle derivation of the Racherla alkali syenite, Palaeo-Mesoproterozoic Cuddapah Basin, southern India: insights from in situ Sr–Nd isotopic analysis on apatite

AbstractWe report anin situSm–Nd isochron age of 1326±73 Ma, determined by LA-MC-ICP-MS (laser ablation-multiple collector-inductively coupled plasma-mass spectrometry), on crystalline apatite grains from the Racherla alkali syenite occurring in the Palaeo-Mesoproterozoic Cuddapah Basin, southern India. The obtained Mesoproterozoic age necessitates the Racherla syenite to be an intrusive into the sedimentary rocks of the Cuddapah Basin contrary to some previous suggestion that it represents an inlier of the basement pluton. Age of the dated syenite, within its error limits, is also coeval with that of the nearby Chelima lamproite (1354±52 Ma) and other syenite complexes (c. 1352 Ma) located elsewhere within the Eastern Ghats Mobile Belt, southern India, thereby implying a common geotectonic control in all of their generation. Incompatible trace element signatures (high La/Nb, Zr/Nb and La/Yb),87Sr/86Sr (0.70432±10) and the lower Nd isotopic ratio (εNd(t) −8.9) of the apatite suggest derivation of the Racherla syenite parent magma from an enriched mantle source. Our findings provide compelling evidence for the existence of ancient (c. 2.6 Ga) metasomatized lithospheric mantle, at the Archaean–Palaeoproterozoic boundary, beneath the Cuddapah Basin. This enriched mantle appears to have had played a dominant role in the generation of co-spatial and coeval lamproites within and around the Cuddapah Basin and a plethora of alkaline and sub-alkaline syenites within the Eastern Ghats Mobile Belt. Implications of our study in the context of Indo-Antarctic collisional tectonics are also explored.

Precise and accurate determination of 147Sm/ 144Nd and 143Nd/ 144Nd in monazite using laser ablation-MC-ICPMS

The 147Sm– 143Nd radioactive decay system has been widely used in the Earth sciences as a geochronometer and isotopic tracer. Recent studies have shown that laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is capable of precise and rapid 143Nd/ 144Nd measurements with high spatial resolution, but its ability to measure 147Sm/ 144Nd accurately is still poorly constrained. A critical analytical issue is the fractionation effects between 147Sm and 144Nd in LA-MC-ICPMS, which must be carefully corrected to determine robust initial 143Nd/ 144Nd particularly for ancient geological samples. Here we show that LA-MC-ICPMS can produce substantial (> 5%) 147Sm/ 144Nd fractionation during analysis of monazite and that the fractionation can be corrected with uncertainty of ~ 1% by using an independently defined 147Sm– 143Nd isochron for an Archean monazite standard. In addition, we describe a method for improving the precision and accuracy of LA-MC-ICPMS isotopic measurements by calibration of Faraday amplifier response and isotopic ratio normalization using a synthetic standard. This method has been applied to one Neogene and two Archean monazites, which were also analyzed by isotope dilution-thermal ionization mass spectrometry (ID-TIMS). The LA-MC-ICPMS data were acquired from 16–37 μm single spots. The LA-MC-ICPMS determinations of the 145Nd/ 144Nd for all samples and 143Nd/ 144Nd for the Neogene monazite compare well with the ID-TIMS results, indicating the robustness of our method to measure Nd isotopic ratios. For the Archean monazites, the method yields initial 143Nd/ 144Nd values identical to the ID-TIMS values with reproducibilities (2 s.d.) of 39 and 58 ppm. Analytical precisions of individual spot analyses for initial 143Nd/ 144Nd were calculated by taking into account the uncertainty in (i) the Nd isotopic normalization to the synthetic monazite, (ii) the correction factor for 147Sm/ 144Nd fractionation and (iii) the age, which results in 2σ of 45–87 ppm. These results clearly demonstrate the capabilities of the LA-MC-ICPMS technique applied to monazite Sm–Nd isotope systematics for early crustal evolution studies.

LA-MC-ICPMS Pb–Pb dating of rutile from slowly cooled granulites: Confirmation of the high closure temperature for Pb diffusion in rutile

Rapid Pb–Pb dating of natural rutile crystals by laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is investigated as a tool for constraining geological temperature–time histories. LA-MC-ICPMS was used to analyse Pb isotopes in rutile from granulite-facies rocks from the Reynolds Range, Northern Territory, Australia. The resultant ages were compared with previous U–Pb zircon and monazite age determinations and new mica (muscovite, phlogopite, and biotite) Rb–Sr ages from the same metamorphic terrane. Rutile crystals ranging in size from 3.5 to 0.05 mm with ⩽20 ppm Pb were ablated with a 300–25 μm diameter laser beam. Crystals larger than 0.5 mm yielded sufficiently precise 206Pb/ 204Pb and 207Pb/ 204Pb ratios to correct for the presence of common Pb, and individual rutile crystals often exhibited sufficient Pb isotopic heterogeneity to allow isochron calculations to be performed on replicate analyses of a single crystal. The mean of 12 isochron ages is 1544 ± 8 Ma (2 SD), with isochron ages for single crystals having uncertainties as low as ±1.3 Myr (2 SD). The 207Pb– 206Pb ages calculated without correction for common Pb are typically <0.5% higher than the common-Pb-corrected isochron ages reflecting the very minor amounts of common Pb present in the rutile. The LA-MC-ICPMS method described samples only the outer 0.1–0.2 mm of the rutile crystals, resulting in a grain size-independent apparent closure temperature ( T c) for Pb diffusion in rutile that is less than the T c of monazite ⩽0.1 mm in diameter, but significantly higher than the Rb–Sr system in muscovite (550 °C), phlogopite (435 °C) and biotite (400 °C). Even small rutile crystals are extremely resistant to isotopic resetting. For the established slow cooling rate of ca. 3 °C/Myr, the T c for Pb diffusion in the analysed rutile is ca. 630 °C. This is in excellent agreement with recent experimental results that indicate that rutile has a higher T c than previously thought (ca. 600–640 °C for rutile 0.1–0.2 mm diameter cooled at 3 °C/Myr; near 600 °C [Cherniak D.J., 2000. Pb diffusion in rutile. Contrib. Mineral. Petrol. 139, 198-207], versus 400 °C [Mezger, K., Hanson G.N., Bohlen S.R., 1989a. High precision U–Pb ages of metamorphic rutile: applications to the cooling history of high-grade terranes. Earth Planet. Sci. Lett. 96, 106–118.] for 1 °C/Myr), and with current T c estimates for monazite and other high temperature geochronometers, which have been revised upwards in recent years. The new rutile ages, together with the other geochronological data from the region, support the interpretation that the Reynolds Range underwent prolonged slow cooling on a conductive geotherm, under nearly steady-state conditions. Slow cooling at ca. 3 °C/Myr persisted for at least 40 Myr followed the peak of high- T/low- P metamorphism to granulite-facies conditions, and probably continued at ca. 2–3 °C/Myr for ca. 200 Myr overall.

In situ determination of sulfur isotopes in sulfur-rich materials by laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)

A new method has been developed for the accurate and precise measurement of sulfur isotopes (32S, 33S, 34S) in solids on a scale down to 80–100 μm by laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The method was developed independently on two different sets of instrumentation, both of which give equivalent results with comparable accuracy and precision. The first instrumental set-up utilizes Xe gas in a hexapole collision and reaction cell for interference attenuation coupled with a mass discrimination correction by external normalization using a nebulised vapour of 37Cl/35Cl standard solution. The second employs high mass resolution by sector field mass spectrometry to avoid the interfering O2+ isobars with a 30Si/29Si standard aerosol for external normalization. The external isotope mass discrimination correction was applied using the exponential law and was further calibrated for both sets of instrumentation by linear interpolation in a sample–standard bracketing method. Mean δ34SV-CDT and δ33SV-CDT show excellent agreement (within analytical error, typically 0.6 and 1.5‰, respectively) with compiled data for IAEA-S series AgS standard reference materials. Results for NIST SRM 127 (sulfate) were less accurate when calibrated against the IAEA-S series sulfides, whilst significant and consistent deviations in accuracy of up to 3‰ were observed in both sets of instrumentation for Soufre de Lacq SRM sulfur. Such generic matrix effects may be widespread in LA-ICP-MS due to differential ablation rates, particle formation, particle transport efficiency and ionization efficiency in an argon plasma.