The Nuvvuagittuq Greenstone Belt (NGB) in Northern Quebec, Canada, is dominated by mafic and ultramafic rocks metamorphosed to at least upper amphibolite facies. Rare felsic intrusive rocks provide zircon ages of up to similar to 3.8 Ga (David et al., 2009; Cates and Mojzsis, 2007) establishing the minimum formation age of the NGB as Eoarchean. Primary U-rich minerals that may provide reliable formation ages for the dominant mafic lithology, called the Ujaraaluk unit, have yet to be found. Metamorphic zircons, rutiles and monazites are present in the unit and give variably discordant results with (207)pb/Pb-206 ages ranging from 2.8 Ga to 2.5 Ga. The younger ages overlap 2686 +/- 4 Ma zircon ages for intruding pegmatites (David et al., 2009) and Sm-Nd ages for garnet formation in the Ujaraaluk rocks suggesting this era as the time of peak metamorphism and metasomatism in the NGB, coeval with regional metamorphism of the Superior craton. Sm-Nd data for Ujaraaluk whole rocks scatter about a Sm/Nd vs. Nd-143/Nd-144 correlation (MSWD = 134) whose slope would correspond to 3.6 +/- 0.2 Ga if interpreted as an isochron. This "isochron" is seen to consist of a series of younger similar to 3.2-2.5 Ga slopes for the different geochemical groups within the Ujaraaluk, emanating from a baseline distribution older than 4 Ga. The Sm-146-Nd-142 chronometer is less affected by metamorphism at 2.7 Ga because of Sm-146 extinction prior to similar to 4 Ga. Expansion of the Nd-142 dataset for the Ujaraaluk and associated ultramafic rocks continues to show a good correlation between Sm/Nd ratio and Nd-142/Nd-144 that corresponds to an age of 4388 (+15)(-17) Ma. The dataset now includes samples with superchondritic Sm/Nd ratios that extend the correlation to Nd-142 excesses of up to 8 ppm compared to the terrestrial standard with a total range in Nd-142/Nd-144 of 26 ppm. The upper Sm/Nd ratio end of the Ujaraaluk correlation is defined by rocks that are interpreted to be cumulates to compositionally related extrusive rocks indicating that this crystal fractionation had to occur while Sm-146 decay was active, i.e. well before 4 Ga. Intruding gabbros give Nd-143 and Nd-142 isochron ages of respectively 4115 +/- 100 Ma and 4313(-69)(+41) Ma, also supporting an Hadean age for the gabbros and providing a minimum age for the intruded Ujaraaluk unit. 3.6 Ga tonalites surrounding the NGB, 3.8 Ga trondhjemitic intrusive veins, and a 2.7 Ga pegmatite show a deficit in Nd-142 compared to the terrestrial standard. These felsic rocks plot to the low Sm/Nd ratio side of the Ujaraaluk isochron and do not show a correlation between their Sm/Nd and Nd-142/Nd-144 ratios, which can be explained if they are melts of ancient LREE-enriched mafic rocks, such as the Ujaraaluk, with the melting occurring after Sm-146 was extinct. A subset of least disturbed Ujaraaluk samples has coherent isotopic compositions for both short-lived and long-lived Nd isotopic systems giving Nd-143 and Nd-142 isochron ages overlapping within error of 4321 +/- 160 Ma (MSWD = 6.3) and 4406(-17)(+14) Ma (MSWD = 1.0), respectively. This age represents our best age estimate for the Ujaraaluk unit. The NGB thus preserves over 1.6 billion years of early Earth history including an expanse of mafic crust formed in the Hadean.

The composition of iron formations in the >= 3.75 Ga yr old Nuvvuagittuq Supracrustal Belt in northern Quebec provides a proxy for seawater composition of the Eoarchean, and perhaps Hadean oceans, as well as constraints on the types of nutrients available to Earth's earliest life forms. Integrated petrologic and geochemical relationships, mapped between mineral phases in thin section and whole-rock chemistry, provide a framework for interpreting bulk and micro-scale variations in these chemical sedimentary precipitates. Results show that there are two distinct chemical sedimentary units in the Nuvvuagittuq belt: i) a banded iron formation (BIF) consisting of alternating micro-bands of magnetite, Ca-Mg-Fe-silicates and quartz, and ii) a more silicate-rich (Fe-poor) unit, the banded silicate-formation (BSF), of alternating micro-bands of quartz and Ca-Mg-Fe silicates. Precursor BIF and BSF deposits were likely layered amorphous silica and ferric-oxyhydroxides, fine-grained carbonate oozes and/or Ca-Mg-Fe rich silicate gels deposited in a marine setting. Low Al2O3, TiO2 and HFSE concentrations show that they are relatively detritus-free, with distinctively seawater-like REE + Y profiles and consistently positive Eu anomalies. These features suggest that the rocks preserved their seawater-like compositions despite metamorphic overprinting. The most significant trace elements in the sediments are Ni and Zn. Experimentally-derived partitioning coefficients show that Ni was enriched in Eoarchean seawater as compared to today (up to 300 nM), while Zn was fairly similar (up to 20 nM). Compositional resemblances between the Nuvvuagittuq sediments and those documented in the ca. 3.8 Ga Isua supracrustals (West Greenland) provide a plausible case that global ocean processes - in terms of trace metal abundances - had reached steady-state by the Eoarchean. (C) 2011 Elsevier B.V. All rights reserved.

The Nuvvuagittuq greenstone belt is dominated by mafic rocks, called the Ujaraaluk unit, that are mostly composed of cummingtonite-plagioclase-biotite with variable amounts of garnet. While the oldest zircons contained in thin intrusive trondhjemitic bands are similar to 3.8 Ga, Sm-146-Nd-142 systematics suggest that the Ujaraaluk unit is as old as 4.4 Ga. The Nuvvuagittuq greenstone belt is surrounded by Eoarchean ITGs that have geochemical and isotopic compositions consistent with their derivation by partial melting of a source similar in composition and age to the Ujaraaluk unit. New zircon dates reported here show the Nuvvuagittuq TTGs to consist at least of four distinct age units of 3.76 Ga, 3.66 Ga, 3.5-3.4 Ga and 3.35 Ga. The Hf isotopic compositions of zircons from the TTG are consistent with derivation from Hadean mafic crust. The 3.66 Ga to 3.35 Ga ITGs appear to have been formed primarily from melting of a source compositionally similar to the 4.4 Ga Ujaraaluk unit, whereas the more radiogenic Hf of the zircons from the 3.76 Ga TTGs may suggest derivation from melting of a source compositionally similar to 4.1 Ga intrusive gabbros. Alternatively, the distinct rare earth element patterns of the 3.76 Ga and 3.66 Ga TTGs suggest their derivation from sources with variable amounts of residual garnet and hence formation at different depths. The composition of the older TTGs is indicative of a deeper source that may have involved a greater interaction between the melt and the mantle to explain the more radiogenic Hf isotopic compositions of their zircons. Sources compositionally similar to the Ujaraaluk unit and intrusive gabbros appear to be the most likely candidates for the Hadean precursor of the Nuvvuagittuq TTGs. (C) 2013 Elsevier B.V. All rights reserved.

The Nuvvuagittuq Supracrustal belt in northern Quebec is a rare similar to 9 km(2) fragment of the Earth's early crust. The belt contains a metamorphosed volcano-sedimentary sequence that is at least Eoarchean in age, including amphibolites of the Ujaraaluk Unit that may have protoliths as ancient as 4400 million years old (Ma; O'Neil and others, 2012). Upper amphibolite facies metamorphism and high-strain deformation have obscured many primary field relationships and disturbed whole-rock isotope systematics, leading to debate over the interpretation of previous geochronological data. We report new SHRIMP U-Pb isotopic analyses of zircons from key meta-igneous and newly identified metasedimentary units of the belt. The analyzed samples fall into four categories: (a) felsic gneisses, including sheets interlayered with the supracrustal assemblage and a tonalitic orthogneiss at the margin of the belt; (b) a newly identified metasedimentary unit; (c) fuchsite-bearing quartz-rich layers; (d) mafic gneisses, including a garnet-biotite amphibolite from the Ujaraaluk Unit and a meta-gabbro. The felsic lithologies place constraints on the minimum age of the supracrustal assemblage; oscillatory-zoned zircons separated from a felsic orthogneiss sheet form a discordant array with an upper intercept age of 3774 +/- 32 Ma, and the tonalitic orthogneiss yielded oscillatory zoned zircons with an upper intercept age of 3781 +/- 11 Ma.

Geologic processing of Earth's surface has removed most of the evidence concerning the nature of Earth's first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these similar to 2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 (Nd-142), the decay product of short-lived samarium-146 (Sm-146). Combined Sm146-147-Nd142-143 data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis.

We characterize the response of a novel 250 mu m thick, fully-depleted Skipper Charged-Coupled Device (CCD) to visible/near-infrared light with a focus on potential applications for astronomical observations. We achieve stable, single-electron resolution with readout noise sigma similar to 0:18 e(-) rms/pix from 400 non-destructive measurements of the charge in each pixel. We verify that the gain derived from photon transfer curve measurements agrees with the gain calculated from the quantized charge of individual electrons to within < 1%. We also perform relative quantum efficiency measurements and demonstrate high relative quantum efficiency at optical/near-infrared wavelengths, as is expected for a thick, fully depleted detector. Finally, we demonstrate the ability to perform multiple non-destructive measurements and achieve sub-electron readout noise over configurable subregions of the detector. This work is the first step toward demonstrating the utility of Skipper CCDs for future astronomical and cosmological applications.

The composition and evolution of the silicate Earth during Hadean/Eoarchean times are widely debated and largely unknown due to the sparse geological record preserved from Earth's infancy. The short-lived Sm-146-Nd-142 chronometer applied to 3.8-3.7 Ga old mantle-derived amphibolites from the Isua Supracrustal Belt (ISB) in southwest Greenland has revealed ubiquitous Nd-142 excesses in these rocks compared to modern samples and terrestrial Nd standards. Because the parent isotope, Sm-146, was extant only during the first few hundred million years of Solar System history, this implies derivation of the Greenland samples from a source formed in the Hadean. This mantle source is the oldest yet identified on Earth and therefore provides key information about the nature and evolution of early-differentiated reservoirs. In contrast, modern mantle-derived rocks from around the world do not have Nd-142 anomalies, suggesting that the primordial heterogeneities detected in Earth's early mantle have been erased over time. In order to better constrain the rate at which early mantle heterogeneities have been re-homogenized, we produced new Sm-146-Nd-142 data for both 3.8 and 3.3 Ga old mafic rocks from different tectonic domains of the ISB, accompanied by their corresponding Sm-147-Nd-143 and Lu-176-Hf-176 systematics. The 3.8 Ga suite yields Nd-142 excesses comparable to those detected previously in 3.7 Ga old ISB amphibolites, indicating that Eoarchean mafic ISB Iavas originated from sources with similar differentiation histories despite being from different juxtaposed tectonic segments. Conversely, 3.3 Ga old amphibolites from the ISB do not show resolvable Nd-142 anomalies compared to terrestrial Nd standards. Since Rizo et al. (2012) reported Nd-142 anomalies in 3.4 Ga old ISB samples, the present data suggest that the primordial Nd-142 heterogeneities in the Isua mantle disappeared between 3.4 and 3.3 Ga. The present data set consists of samples from a unique location where 500 million years of history of the early terrestrial mantle have been preserved, hence offering an exceptional opportunity to gain new insight into the compositional evolution and dynamic workings of Earth's primordial mantle. (C) 2013 Elsevier B.V. All rights reserved.

We report new data for W concentrations, stable W isotopic compositions, high-precision W-182/W-184 ratios, highly siderophile element (HSE) abundances and Re-187-Os-187 systematics in a suite of 3.8-3.3 Ga mafic and ultramafic rocks from the Isua supracrustal belt, and the Paleoarchean terrane in the northwestern part of the belt. These data are compared with published data for Sm-146-Nd-142 systematics in the same samples. The samples from the Isua supracrustal belt show well resolved excesses of W-182/W-184 of up to similar to 21 ppm, consistent with previous W isotopic data reported by Willbold et al. (2011). While there is abundant evidence that W was mobilized in the crust accessed by the Isua supracrustal suite, the isotopic anomalies are interpreted to primarily reflect processes that affected the mantle precursors to these rocks. The origin of the 182 W excesses in these rocks remains uncertain. The Isua mantle source could represent a portion of the post-core-formation mantle that was isolated from late accretionary additions (e.g., Willbold et al., 2011). However, the combined W-182, Re-Os isotopic systematics and HSE abundances estimated for the source of the Isua basalts are difficult to reconcile with this interpretation. The W isotope variations were more likely produced as a result of fractionation of the Hf/W ratio in the mantle during the lifetime of Hf-182, i.e., during the first 50 Ma of Solar System history. This could have occurred as a result of differentiation in an early magma ocean. The Isua suite examined is also characterized by variable Nd-142/Nd-144, but the variations do not correlate with the variations in W-182/W-184. Further, samples with ages between 3.8 and 3.3 Ga show gradual diminution of Nd-142 anomalies until these are no longer resolved from the modern mantle isotopic composition. By contrast, there is no diminishment of W-182 variability with time, suggesting different mechanisms of origin and retention of isotopic variations for these two extinct-radionuclide isotope systems. The presence of W-182 isotopic anomalies in rocks as young as 3.3 Ga, implies that early-formed, high Hf/W domains survived for more than 1 Ga in the convective mantle. (C) 2015 Elsevier Ltd. All rights reserved.

How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first similar to 50 million years of solar system history, indicating that portions of the mantle that formed during Earth's primary accretionary period have survived to the present.