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.

The Isua supracrustal belt (ISB) and the Nuvvuagittuq greenstone belt (NGB) are among the oldest suites of mafic volcanic rocks preserved on Earth and are the best candidates for representing its early crust. Despite the possible 500 Ma age difference between the belts, these mantle -derived rocks show compositional similarities, with features resembling rocks formed in subduction initiation environments. With the addition of new Nd-142 data for the Garbenschiefer unit of the ISB reported here, high precision Nd-142 data are now available for all the mafic lithologies from both belts. Mantle -derived rocks from both the ISB and NGB belts exhibit a range of Nd-142/Nd-144 ratios. The datasets for the two belts, however, are significantly different, suggesting a different origin for their Nd-142 anomalies. Nearly all ISB samples have excesses in Nd-142, including the newly analyzed Garbenschiefer boninitic amphibolites (mean of +12 ppm). Excesses in Nd-142/Nd-144 compared to the Nd standard for all the ISB rocks range between +8 and +20 ppm, with a near Gaussian distribution around +12 ppm. This distribution could simply reflect the analytical error ( 5 ppm) around a single Nd-142/Nd-144 ratio indicating that the samples formed after the extinction of Sm-146 from a source with a nearly uniform Nd-142/Nd-144 ratio. In contrast, the NGB shows a range of Nd-142/Nd-144 ratios from +8 to 18 ppm relative to the modern Nd standard and displays a flat distribution of Nd-142/Nd-144 ratios, The ISB samples show no significant correlation between their Nd-142/144Nd and Sm/Nd ratios, consistent with their formation in the Eoarchean via melting of a Hadean depleted mantle. In contrast, all NGB samples display a Nd-142/144Nd vs. Sm/Nd correlation, consistent with their crystallization in the Hadean. The mantle sources for both the ISB and NGB mantle derived rocks have a similar Nd-142/144Nd ratio at the possible age of formation of the NGB (similar to 43 Ga) suggesting the derivation of ISB and NGB rocks from a common early-formed depleted mantle source formed between 4.47 and 4.42 Ga with a Sm-147/Nd-144 ratio similar to 0.218. This mantle appears to have been an important source component involved in the formation of the primitive crust during most of the Hadean and Eoarchean eons. (C )2016 Elsevier B.V. All rights reserved.

Several first order features of Earth owe their origin to processes occurring before, during, and within a few hundred million years of Earth formation. Arguably the most significant expression of these early events is the bulk composition of Earth. Earth's depletion in some volatile elements likely was inherited from the materials from which it formed. This is most easily attributed to Earth's accumulation from planetesimals formed in the inner Solar System where the temperatures were hot enough, for long enough, to keep many volatile elements in the gas phase until after the solids had accumulated into at least planetesimal-sized objects. Improved understanding of the processes of planetary accretion makes it increasingly clear that the main fraction of Earth's mass was accumulated through violent collisions with large planetesimals, not by gentle accumulation of primitive bodies. The accreted planetesimals likely had already experienced global differentiation to separate core from mantle and crust, and suffered additional volatile loss by gravitational escape of any atmosphere formed through this early differentiation on the small planetesimal. The short-lived Hf-182-W-182 system indicates that the metal-silicate separation associated with core formation began on planetesimals within a million years or less and on Earth within tens of millions of years of the start of Solar System formation. Metal-silicate separation left Earth's mantle deficient in siderophile elements relative to their abundances in bulk chondrites. Mantle abundances of moderately siderophile elements suggest high-pressure and temperature equilibrium between metal and silicate, consistent with metal-silicate segregation occurring during largely or entirely molten stages of early Earth history. By contrast, the mantle abundances of highly siderophile elements are most easily reconciled with addition of approximately half a percent of Earth's mass of material with chondritic composition after chemical exchange between mantle and core had stopped. Evidence for early differentiation of the silicate Earth, as would be expected for a terrestrial magma ocean, is remarkably subdued, but is now being extracted from information provided by short-lived radioactive systems such as I-129-Xe-129, Sm-146-Nd-142, and Hf-182-W-182. For example, Xe-129 and Nd-142 heterogeneities in the mantle point to a major terrestrial differentiation event occurring between circa 4.4 and 4.45 Ga, which is most easily attributed to the time of the Moon-forming giant impact. What little evidence remains for the nature of Earth's crust that formed immediately after the resulting magma ocean suggests the presence of a primitive mafic crust that did not become reworked into substantial felsic continental crust until 3.8 to 4.0 Ga.