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The Acasta Gneiss Complex (AGC) of the Northwest Territories, Canada, contains some of the oldest evolved terrestrial crust and has a sustained record of more than a billion years of magmatism (>4.0–2.9 Ga). These rocks provide an opportunity to investigate the nature of continental crust formation on the early Earth. Because complexities in zircons and bulk rocks are characteristic of the early Earth record—including the AGC—strategies are needed to extract accurate and meaningful age and isotopic information. In order to evaluate the accuracy of the early Earth Hf isotope record, we examined AGC zircons from a range of lithologies using paired chemical abrasion isotope dilution U-Pb age and solution Lu-Hf isotope analysis and compared these with previous results obtained using laser ablation split-stream (LASS) analysis. We describe an approach whereby LASS is used to identify rocks with the least complex zircons, and, when appropriate, solution methods are then used to refine the age and Hf isotopic composition to the highest precision. This two-pronged analytical approach results in a more robust determination of the age and Hf isotopic record of complex rocks and zircons and allows identification of complexity in the Hf isotopic record that would not be apparent by solution analysis alone, thereby refining the record of magmatic evolution on the early Earth. Despite the better precision, solution techniques are unsuitable for rocks with complexly zoned zircons. In particular, zircons from the two oldest AGC rocks in this study have positive initial eHf values when determined by solution analysis (+2.8 and +4.9 at 4.0 and 3.9 Ga, respectively) but have negative eHf values when determined by LASS (−3.4 and −4.7, respectively). This is attributable to the presence of later radiogenic overgrowths on the zircon grains which are incorporated in solution analyses but can be avoided using LASS. This provides important clarity to the AGC Hf isotope record. In total, all but one of the AGC rocks we analyzed, including the oldest samples, have negative eHf values and indicate derivation from an enriched reservoir; none of these samples—in contrast to whole rock Nd isotope compositions—have sufficiently positive eHf values to indicate their derivation from a depleted mantle reservoir. Despite the presence of ancient AGC crust, there is no record of corresponding mantle depletion. This implies that extraction of Hadean crust in this region did not happen in sufficient volume to result in widespread mantle depletion in the AGC source by the Eoarchean. Our results underscore the importance of identifying different components in ancient zircons—and the rocks that contain them—and accurately determining the age and isotopic composition of those components. This is critically important for clarifying the record of the formation of enriched crust and development of the depleted mantle in Earth’s early history.

The North Atlantic craton hosts extensive exposures of Eoarchean crust, spread through areas of Western Greenland and Northern Labrador (Canada). Of these two areas, the crust of the Saglek Block of Northern Labrador has received far less attention from the scrutiny of modern analytical methods than its better documented Western Greenland equivalent, the Itsaq Gneiss Complex. Here, we present the first coupled trace element and U–Pb/Hf/O isotope dataset for zircon from an early TTG component of the Saglek Block. The combination of textural, elemental and isotopic in-situ analyses enables selection of the least disturbed zircon domains. From these it is demonstrated that the oldest felsic remnants exposed in the Saglek Block were emplaced 3.86 ± 0.01 billion yr (Ga) ago through partial melting of basaltic protoliths. The Hf isotope signature of the oldest zircon domains from the Saglek Block TTG indicates derivation from sources that did not undergo substantial Lu/Hf fractionation, resulting in initial Hf isotope compositions that are chondritic within uncertainty. The oxygen isotope ratios of the least disturbed zircon portions vary from 5.38 ± 0.16‰ to 6.64 ± 0.19‰ and document the interaction of the TTG protoliths with Earth's early hydrosphere at low temperature (≤150–200 °C) prior partial melting in the Eoarchean. The results support TTG production in the Eoarchean from variably hydrated basaltic protoliths.

Southern West Greenland contains some of the best-studied and best-preserved magmatic Eoarchean rocks on Earth, and these provide an excellent vantage point from which to view long-standing questions regarding the growth of the earliest continental crust. In order to address the questions surrounding early crustal growth and complementary mantle depletion, we present Laser Ablation Split Stream (LASS) analyses of the U–Pb and Hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the Itsaq (Amitsoq) Gneisses of the Isukasia and Nuuk regions of southern West Greenland. This analytical technique allows a less ambiguous approach to determining the age and Hf isotope composition of complicated zircon. Results corroborate previous findings that Eoarchean zircon from the Itsaq Gneiss (∼3.85 Ga to ∼3.63 Ga) were derived from a broadly chondritic source. In contrast to the Sm–Nd whole rock isotope record for southern West Greenland, the zircon Lu–Hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 Ga in Greenland. Utilizing LASS U–Pb and Hf data from the Greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. We compare the Greenland Hf isotope data with other Eoarchean magmatic complexes such as the Acasta Gneiss Complex, Nuvvuagittuq greenstone belt, and the gneissic complexes of southern Africa, and all lack zircons with suprachondritic Hf isotope compositions. In total, these data suggest only a very modest volume of crust was produced during (or survived from) the Hadean and earliest Eoarchean. There remains no record of planet-scale early Earth mantle depletion in the Hf isotope record prior to 3.8 Ga.

Initial Hf and Nd isotope compositions of Earth's oldest rocks provide essential information on the differentiation of the Earth into enriched crustal and depleted mantle reservoirs in its early history. The majority of Eo-Paleoarchean rocks worldwide, however, have isotope compositions that appear to be decoupled: initial Hf isotope compositions, determined on zircon, are broadly chondritic with little variation; initial Nd isotopes on bulk rocks, in contrast are highly variable with both supra- and sub-chondritic compositions. Most of these studies are from polymetamorphic terranes where the potential for disturbance of the isotope system is high. This is particularly true for the Sm-Nd system where more easily altered REE-rich accessory phases are the major repositories for these elements. In order to better understand crust-mantle evolution during the Archean—and to address the issue of Hf and Nd isotope decoupling—we examine a suite of well-preserved Paleoarchean granites from the Pilbara Craton. Our approach integrates the initial Hf isotope composition and U-Pb ages of zircon, the initial Nd isotope compositions of titanite and apatite, and U-Pb ages of titanite by laser ablation split stream (LASS) analysis. The zircon and titanite U-Pb data yield crystallization ages of 3.47 to 3.28 Ga, in good agreement with the combined apatite-titanite-WR Sm-Nd isochron ages of each sample, demonstrating that both the U-Pb and Sm-Nd systems have not been modified since igneous crystallization. The initial Hf isotope compositions of zircon from all samples are broadly chondritic with eHf(i) values of −0.3 to +0.8, in agreement with the bulk-rock Hf. The initial Nd isotope compositions of the titanite and apatite are also broadly chondritic (eNd(i) titanite, −1.0 – +2.0; apatite, −0.6 – +0.9) and agree with the Nd isotope composition of the bulk-rock (eNd(i) = +0.2 to +1.2) and the initial 143Nd/144Nd ratios determined from the titanite-apatite-WR isochrons (eNd(i) −0.9 to +1.3). From these data, we make two fundamental observations. First, the granites in this study were derived from a source that was chondritic with respect to both Hf and Nd isotopes from 3.47 to 3.28 Ga; neither system supports the presence of either a strongly depleted mantle or enriched crustal source. Second, the Lu-Hf and Sm-Nd isotope systems in the Pilbara samples are in full agreement. This stands in stark contrast to the record of rocks from Eo-Paleoarchean terranes of higher metamorphic grade, where the Hf and Nd isotope compositions have been “decoupled”. This further underscores the importance of recognizing potential effects of high-grade metamorphism on the Sm-Nd bulk-rock record. The integrated age-isotope approach taken here illustrates a way to assess the integrity of bulk-rock Nd isotope data through examination of the Sm-Nd isotope systematics of the LREE-rich accessory minerals in rocks.

Rock clasts entrained in glacial deposits sourced from the continental interior of Antarctica provide an innovative means to determine the age and composition of ice-covered crust. Zircon U-Pb ages from a suite of granitoid clasts collected in glacial catchments draining central East Antarctica through the Transantarctic Mountains show that crust in this region was formed by a series of magmatic events at ∼2.01, 1.88–1.85, ∼1.79, ∼1.57, 1.50–1.41, and 1.20–1.06 Ga. The dominant granitoid populations are ca. 1.85, 1.45 and 1.20–1.06 Ga. None of these igneous ages are known from limited outcrop in the region. In addition to defining a previously unrecognized geologic history, zircon O and Hf isotopic compositions from this suite have: (1) mantle-like δ18O signatures (4.0–4.5‰) and near-chondritic Hf-isotope compositions (eHf ∼ +1.5) for granitoids of ∼2.0 Ga age; (2) mostly crustal δ18O (6.0–8.5‰) and variable Hf-isotope compositions (eHf = −6 to +5) in rocks with ages of ∼1.88–1.85, ∼1.79 and ∼1.57 Ga, in which the ∼1.88–1.79 Ga granitoids require involvement of older crust; (3) mostly juvenile isotopic signatures with low, mantle-like δ18O (∼4–5‰) and radiogenic Hf-isotope signatures (eHf = +6 to +10) in rocks of 1.50–1.41 Ga age, with some showing crustal sources or evidence of alteration; and (4) mixed crustal and mantle δ18O signatures (6.0–7.5‰) and radiogenic Hf isotopes (eHf = +3 to +4) in rocks of ∼1.2 Ga age. Together, these age and isotopic data indicate the presence in cratonic East Antarctica of a large, composite igneous province that formed through a punctuated sequence of relatively juvenile Proterozoic magmatic events. Further, they provide direct support for geological correlation of crust in East Antarctica with both the Gawler Craton of present-day Australia and Proterozoic provinces in western Laurentia. Prominent clast ages of ∼2.0, 1.85, 1.57 and 1.45 Ga, together with sediment source linkages, provide evidence for the temporal and spatial association of these cratonic elements in the Columbia supercontinent. Abundant ∼1.2–1.1 Ga igneous and metamorphic clasts may sample crust underlying the Gamburtsev Subglacial Mountains, indicating the presence of a Mesoproterozoic orogenic belt in the interior of East Antarctica that formed during final assembly of Rodinia.

The Acasta Gneiss Complex of the Northwest Territories, Canada, contains some of the earliest terrestrial continental crust and thus provides a critical sample set for characterization of crust-forming processes on the early Earth. Here we report the results of a combined Lu–Hf and U–Pb isotopic study of zircons from predominantly felsic orthogneisses from the Acasta Gneiss Complex that crystallized between ∼4.0 and 2.9 Ga, many of which contain complex zoning and therefore require an analytical treatment suited to distinguish amongst compositionally distinct age and Hf isotopic domains. To ensure the reliability of the analyses and of subsequent geologic interpretations, we employed the laser ablation split-stream (LASS) technique to concurrently measure the Lu–Hf and U–Pb isotopic systems in zircon. Our results confirm prior findings of precursor Hadean crust (>4.0 Ga) in the source of these rocks and the continued involvement of this reservoir until ∼3.6 Ga. We present evidence for the input of relatively more juvenile material at ∼3.6 Ga, which we suggest corresponds to a fundamental change in the source of the magmas. This study extends the lower bound of the published Acasta Hf isotopic record from 3.6 Ga to 2.9 Ga and demonstrates that the ∼3.6 Ga–2.9 Ga interval is largely represented by reworking of relatively juvenile ∼3.6 Ga crust and the diminution of the >4.0 Ga crustal signal. Significantly, there is no evidence that rocks within the Acasta Gneiss Complex were derived from a strongly depleted mantle.

Zircon and monazite U–Pb geochronology and zircon Hf isotopes place constraints on the temporal and source relationships between crustal anatexis, magmatism, and exhumation of the Priest River metamorphic core complex, northern Idaho. Granitoids that intruded the migmatitic, pelitic Hauser Lake gneiss include the

Monazite is a powerful U-Th-Pb geochronometer commonly used to determine the tempo of orogenic processes. As a light rare earth element (LREE)-enriched mineral, monazite also records key information for understanding the behavior of Sm-Nd isotope systematics during tectonothermal events. However, Sm-Nd isotope studies of monazite have received far less attention than its use as a U-Pb geochronometer. Here we investigate coupled U-Pb ages and Sm-Nd isotopic compositions of monazite from partially melted metasedimentary rocks in the Jiao-Liao-Ji orogenic belt (JLJB), North China craton, to provide insight into Sm-Nd isotope behavior during high-temperature metamorphism and crustal melting. We utilize several complementary dating systems in the same sample, including garnet Lu-Hf and Sm-Nd, zircon U-Pb, and monazite U-Pb geochronology, to gain precise time constraints on the P-T evolution of the JLJB. Garnet Lu-Hf isochron dates of 1.97–1.94 Ga are interpreted to represent prograde garnet growth, consistent with the prograde metamorphic zircon dates of 1.96–1.90 Ga; garnet Sm-Nd dates agree with retrograde metamorphic zircon dates, and all monazite U-Pb dates define a relatively narrow age range of 1.86–1.83 Ga, interpreted to represent retrograde cooling. The lack of older monazite grains matching zircon or garnet dates suggests the dissolution of pre-existing monazites into partial melt. Monazite in all samples, irrespective of occurring as garnet inclusions or in the matrix, yields homogenous Nd isotope compositions (eNd ~ −5) at ~1.85 Ga, which are consistent with the garnet and bulk-rock values. Thus, Nd isotope re-equilibration between bulk-rock and minerals occurs synchronously across the orogenic belt during high-T metamorphism (~750 °C) where melting was involved, with no evidence of a pre-metamorphic isotope signature. This suggests mobility in the Sm-Nd isotope system during high-grade metamorphism and melting, where the Nd isotope signature of monazite likely represents the most recent tectonothermal event.

Late- to post-collisional volcanism in the southern portion of the West African Craton (sWAC) has been described along the paleo-craton margin between the Paleoproterozoic Baoule-Mossi domain and Archean Kenema-Man nucleus. New lithostratigraphic and isotopic data for central Cote d'Ivoire, as well as revised regional stratigraphic correlations across the western sWAC, indicate that this volcanic resurgence is not only restricted to the paleo-craton margin, but extends to most greenstone belts of the western half of the sWAC. This late volcanic event, historically referred to as the ca. 2117–2080 Ma Bandamian Volcanic Cycle, has received little attention since its identification in 1996. Detailed geological investigation of the Bouafle granite-greenstone belt in Cote d'Ivoire, located 150 km east of paleo-craton margin, along with newly acquired U-Pb geochronological data indicate a peak in igneous activity showing evidence for bimodal magmatism affiliated to the Bandamian Volcanic Cycle in central Cote d'Ivoire between 2108 ± 5 Ma and 2105 ± 4 Ma. Whole-rock geochemistry and Lu-Hf isotopic measurements on magmatic zircons from the Bouafle region show that these Bandamian rocks are marked by a juvenile signature with little degree of crustal contamination. Collectively, the data collected in this study show that the Bandamian Volcanic Cycle represents an important thermal event that affected the sWAC during the late stages of the Eburnean orogeny, spanning the incremental change from folding and thrusting to dominantly transcurrent tectonics along major faults and shear zones. This paper discusses the possible geodynamic settings that may account for such a peak in thermal activity during the late stages of the Eburnean orogeny.

Continued improvements in both ICPMS (inductively-coupled plasma mass spectrometry) and laser ablation technologies are fueling advancements in accessory mineral investigations and their related isotope systems of interest, and are now being applied to a wide range of geological applications. In this contribution we present an updated methodology for laser ablation split-stream (LASS) analysis of the light rare earth element (LREE) enriched minerals monazite, titanite, and apatite for simultaneous analysis of the U-Th-Pb age (or trace element content) and the Sm-Nd isotope system. The data were collected with the current generation of high-sensitivity ICPMS and laser systems (ThermoFinnigan NeptunePlus MC-ICPMS and Element XR SF-ICPMS- coupled to a RESOlution 193 nm ArF excimer laser system). The increased sensitivity of these ICPMS instruments allows for improved spatial resolution and the ability to target minerals which previously contained insufficient concentrations of elements of interest (e.g., Sm-Nd in apatite), making their analysis difficult, if not impossible, using less sensitive instruments. Furthermore, the higher sensitivity allows less aggressive ablation parameters that facilitate thin section sampling and reduces inter-element and isotopic fractionation. To assess and improve the accuracy, precision, and efficiency of the technique, three new potential LASS reference materials (RMs) are evaluated for dual U-Pb and Sm-Nd analysis (Tory Hill apatite, Tory Hill titanite, and Steenskralkamp monazite). The homogeneity of these materials was first assessed using reconnaissance laser ablation analyses, with final characterization of U-Pb age and Sm-Nd isotope composition using isotope-dilution thermal ionization mass spectrometry (ID-TIMS). The precision and accuracy of the LASS method is explored using secondary mineral reference materials of known age and Sm-Nd isotope composition. The utility of the technique is evaluated with a case study of monazite and apatite from the Eoarchean Uivak Gneiss complex of Labrador, Canada. Finally, we suggest that there is a wide variety of geological applications for this methodology, such as multi-mineral detrital provenance, crustal growth, and petrogenic studies.

The whole rock 143Nd isotope record of the Acasta Gneiss Complex (AGC) has been used to argue for the development of both depleted mantle and enriched crustal reservoirs during the Hadean. The 147Sm–143Nd isotope compositions of rocks from AGC, however, fall on an array with an errorchron date of ∼3.3 Ga, despite the majority of samples yielding substantially older zircon U–Pb ages. This has led to the suggestion of a major Sm–Nd “resetting” event at this time in the AGC. To better understand the Sm–Nd bulk-rock systematics of the AGC, we investigate the U–Pb age and Sm–Nd isotope compositions of apatite and titanite from the AGC, using the laser ablation split stream (LASS) method. Apatite from all samples yield broadly similar U–Pb dates of ∼1.89 to 1.83 Ga, in agreement with resetting during the 1.9 Ga Wopmay orogen. The Sm–Nd isotope compositions of the apatite, however, lie off the WR errorchron and show a high degree of initial Nd isotope heterogeneity. Conversely, titanite Sm–Nd systematics are consistent with the ∼3.3 Ga whole rock errorchron further supporting Sm–Nd modification at ∼3.3 Ga. Taken together, these show that the oldest rocks in the AGC underwent at least two post-crystallization events (at 3.3 and 1.9 Ga) that modified the Sm–Nd isotope system. These results also demonstrate the relative mobility of the Sm–Nd isotope system during orogenic events, which may compromise the ability to determine robust bulk-rock 143Nd isotope signatures.

article i nfo We present compelling isotopic evidence from ~15 Ma rhyolites that erupted coeval with the Columbia River Ba- salts insouthwestIdaho'sJ-PDesertandthe JarbidgeMountainsofnorthern Nevada atthatsuggeststhatthe Yel- lowstone mantle plume caused hydrothermal alteration and remelting of diverse compositions of shallow crust in the area where they erupted. These rhyolites also constitute the earliest known Miocene volcanism in the vi- cinity of the Bruneau-Jarbidge and Twin Falls (BJTF) volcanic complexes, a major center of voluminous (10 3 - 10 4 km 3 )l ow-δ 18 O rhyolitic volcanism that was previously defined as being active from 13 to 6 Ma. The Jarbidge Rhyolite has above-mantle δ 18 O( δ 18 Oo f +7.9‰ SMOW) and extremely unradiogenic eHf (−34.7) and eNd (−24.0). By contrast, the J-P Desert units are lower in δ 18

Invited Technical Paper High quality analytical data are essential for the development of sound scientific interpretations. To ensure the quality of the data published in Chemical Geology, a new type of contribution has been introduced - the "Invited Technical Paper". When a particular technical issue needing discussion or clarification is identified, specialists in the technique will be invited to share their expertise. As is true for all articles published in the journal, these contributions will be subject to peer review before publication. The first topic to be treated concerns in situ Hf isotopic measurements in zircon by laser ablation inductively coupled plasma mass spectrometry. This is an extremely powerful and promising technique that has been adopted by many laboratories throughout the world. However, if insufficient care is taken during analysis and data processing, inaccurate results can be obtained, notably because of the existence of very large isobaric interferences on the isotope of interest. To address this issue, we have asked Christopher Fisher, Jeffery Vervoort and John Hanchar to provide a set of guidelines that can be adopted to assure that reliable Hf isotopic data are obtained by this technique. Abstract Over the past decade, the Hf isotope composition of zircon, as determined in situ by laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS), has been applied increasingly to a wide range of geological problems and has proven to be a valuable analytical tool. There has been no uniformity, however, in the reporting of in situ Hf isotopic data and, quite often, reviewers and readers of papers are not provided with sufficient information to assess data quality. The goal of this invited contribution is to provide the non-specialist with a brief outline and explanation of what is required for proper presentation and documentation of in situ Hf isotopic data from zircon, including details of how the challenging large isobaric interference corrections have been made. In addition, we discuss a number of potential pitfalls vis-a-vis the assignment of the incorrect age to the measured Hf isotope composition. Non-specialists should be aware of these important issues when doing their own analyses and evaluating the analyses done by others.

Zircon morphology, internal texture, U/Pb age distributions and Th/U ratios are used to characterize aluminous gneisses in the Canyon domain (Manicouagan area, central Grenville Province) from two contrasting supracrustal sequences, metamorphosed at granulite-facies: one, a package of paragneiss and the other, a dominantly bimodal felsic–mafic volcanic sequence. The aluminous paragneisses yielded zircon with fragmental igneous cores, overgrown by metamorphic rims. These cores show a spread in ages between 1500 Ma and 2700 Ma, consistent with a supply of detritus from the adjacent Canadian Shield. In contrast, a felsic gneiss with aluminous nodules inferred to represent a hydrothermally-altered felsic volcanic rock of the bimodal sequence yielded well-preserved igneous zircon dated at 1238 ± 13 Ma, an age that integrated with previously published data links this volcanic sequence to a major episode of crustal extension in the central Grenville Province. Metamorphic zircon grains and rims from the paragneisses gave two groups of pre-Grenvillian ages that demonstrate the effect of major magmatic events on the country rocks in the Canyon domain: (a) 1391–1408 Ma, coeval with the emplacement of an older layered mafic to intermediate volcanic suite and (b) 1217–1260 Ma, coeval with the development of the 1238 Ma bimodal felsic–mafic volcanic sequence. In addition, metamorphic zircon from all the investigated aluminous gneisses records the high-grade Grenvillian metamorphism (∼1080–1040 Ma).

An improved method for precise and accurate in situ determination of Sm–Nd isotopes, with high spatial resolution, and high sample throughput, in light rare earth element enriched accessory minerals by laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is discussed. The accuracy of the method is demonstrated by comparison of LA-MC-ICPMS analyses of several natural minerals (Durango apatite, Hondo Canyon titanite, Daibosatsu allanite, Mae Klang monazite, and Trebilcock monazite) to isotope dilution-thermal ionization mass spectrometry (ID-TIMS) analyses of the same minerals. The TIMS analyses demonstrate that each of these minerals, with the possible exception of Durango apatite, is more homogeneous in Nd isotopic composition than can be measured based upon the internal precision of the LA-MC-ICPMS analyses in this study. Thus, these natural minerals may be considered as isotopically homogeneous reference materials for Nd isotopic determinations. In addition two synthetic glasses produced specifically for in situ Sm–Nd isotopic determination and external calibration are presented here. The three main obstacles in obtaining accurate and precise Sm–Nd isotopic measurements by LA-MC-ICPMS are the isobaric interference correction of 144Sm on 144Nd, determination of the Sm mass bias, and accurately measuring the 147Sm/144Nd which is imperative for producing robust initial Nd isotopic compositions. The 144Sm interference correction was calculated using the measured 149Sm and recently published Sm isotopic abundances. The Sm mass bias was determined using an exponential law and the 147Sm/149Sm measured in the sample. Determination of 147Sm/144Nd was done by calibration to an external glass reference material synthesized specifically for this purpose. This approach produced 147Sm/144Nd that is in agreement with ID-TIMS analysis. The MC-ICPMS instrument configuration used in this study also allows for the determination of Eu and Gd, thereby permitting simultaneous determination of Eu anomalies along with Sm–Nd isotopic composition. The high spatial resolution and sample throughput at a geologically useful level of accuracy and precision possible with LA-MC-ICPMS offers numerous potential geochemical applications including provenance tracing, terrane reconstruction, crustal growth studies, fluid composition and evolution, metamorphic reaction pathways, and silicic magma generation and evolution.

The synthesis of 1-(4-nitrobenzyl)-2-chloromethyl benzimidazole, which undergoes a nucleophilic substitution with pyridine in the absence of additional base, is reported. The key steps are the reaction of 1,2-phenylenediamine to give exclusively the mono-substituted product and the avoidance of minor by-products via the use of glycolic acid for the cyclisation step. The X-ray structures of 1-(4-nitrobenzyl)-2-chloromethyl benzimidazolium chloride and 1-[1-(4-nitrobenzyl)benzimidazol-2-ylmethyl]pyridinium chloride are presented.

In situ analyses of hafnium isotopes in zircon combined with U–Pb zircon ages, and trace element data, provide new information on the characterization and evolution of magnetite–apatite (“Kiruna-type”) deposits and the tectonic environments in which they occur. The Lyon Mountain granite in the Adirondack Mountains of New York is the host to numerous zircon-bearing magnetite–apatite deposits. Hafnium isotopic compositions and rare earth element contents in individual zircon crystals were measured in situ in both the host granites and the ore bodies by laser ablation inductively coupled plasma-mass spectrometry. Hafnium isotopic compositions in the ore zircon can be divided into two groups: those that have initial eHf ( t ) values that are indistinguishable from those of the host granites (e.g., eHf ( t ) less than + 7) and are typical of relatively juvenile Proterozoic crust, and those that have extremely radiogenic eHf ( t ) values (as high + 40). Two models are proposed to explain the observed eHf ( t ) values in the zircon crystals: 1) early-formed ore bodies containing magnetite, apatite, and clinopyroxene were remobilized by secondary fluid alteration, releasing Zr and Hf for the crystallization of new zircon; or alternatively, 2) fluids responsible for ore formation have interacted with garnet-bearing rocks during retrograde metamorphism, scavenging rare earth elements and radiogenic Hf. Previous work done to determine the U–Pb ages from the same zircon crystals, which were analyzed for the Hf isotopic composition in this study, revealed that ore bodies record a mineralizing event that is 20 to 60 m.y. younger than the age of granite emplacement. This age discrepancy, plus the highly radiogenic eHf ( t ) values in the ore zircon crystals, suggests that the fluids responsible for this younger event could not have been derived from the granite hosts. These data argue that magnetite–apatite deposits in the LMG have multiple mineralizing events superimposed upon one another and that early-formed deposits may be reworked, modified and redeposited by fluids subsequent to magma crystallization.

Mutations in the gene encoding presenilin 1 (PS-1) account for 50% of early-onset familial Alzheimer’s disease (EOFAD) cases. In this study, we identified two missense mutations in the coding sequence of the presenilin (PS-1) gene in two EOFAD pedigrees. AD was confirmed in one pedigree by autopsy. Mutation analysis of PCR products amplified from genomic DNA templates showed two novel PS-1 mutations resulting in Gln222His and Tyr256Ser. The two novel mutations are located within predicted transmembrane domains five (TM-5) and six (TM-6), respectively, and are associated with very early ages of onset. The Tyr256Ser is associated with one of the youngest age of AD onset, 25 years, which is consistent with a drastic change in function of the altered PS-1 protein. A morphometric analysis of the cortical degenerative changes of the Tyr256Ser case, showed severe involvement of the primary motor cortex, which correlated well with the pyramidal changes, including tetraspasticity. Immunoblot analysis showed the Tyr256Ser case had the greatest expression of Aβ1–40 and Aβ1–42, which was confirmed by ELISA, compared to other PS-1 mutant FAD cases and age-matched controls and, thus, contributes to the severity of the disease pathology.