Hf isotopes in zircon from the western Superior province, Canada: Implications for Archean crustal development and evolution of the depleted mantle reservoir

U-Pb and Hf isotopic measurements on zircons from the western Superior province confirm that the area contains at least three distinct terrane types. Juvenile terranes that formed mostly within the time span 2.75-2.68 Ga occupy much of the western Wabigoon subprovince as well as granite-greenstone belts to the south. Juvenile 3.0 Ga terranes that were reworked over the time span 2.7-3.0 Ga occupy the south-central part of the Wabigoon subprovince and the North Caribou block in the Sachigo subprovince. Rocks with mantle extraction ages as old as 3.5 Ga and zircon U-Pb ages extending to 3.3 Ga characterize a third type of terrane represented by the Winnipeg River subprovince. This terrane was strongly reworked during the late Archean. Arc-related magmatism was ongoing at 2.71-2.75 Ga in the different terranes, which probably accreted over the time span 2.71-2.68 Ga. Enriched Hf and high O isotopic signatures in late sanukitoid-suite plutons appear to be correlated, which suggests that assimilation of Mesoarchean crust was an important factor in their magmatic evolution. Enriched Hf isotopic signatures in detrital and igneous zircon from parts of the north-central Wabigoon subprovince support previous suggestions that the Winnipeg River terrane extends eastward beyond the Winnipeg River subprovince. The Winnipeg River subprovince was probably being uplifted and eroded into the Quetico sedimentary basin shortly after 2700 Ma, as shown by detrital zircons with enriched Hf isotopic signatures and Meso- to Paleoarchean ages. The pattern of ages and isotopic signatures from the North Caribou block and the south-central Wabigoon subprovince are similar, suggesting that these terranes are correlative. If so, the south-central Wabigoon terrane may have been tectonically transported from the north. Hf isotopic compositions of zircon from juvenile Archean sources are remarkably consistent and define an average εHf value of +3.5 ± 0.2 for samples with an average age of 2724 Ma and a best estimate of +2.7 ± 0.4 at 3000 Ma. Thus, the Neaoarchean depleted mantle reservoir beneath the Superior province appears to have been isotopically well mixed. εHf values were calculated using a value of 1.865 × 10-5 Ma-1 [Scherer, E., Munker, C., Mezger, K., 2001. Calibration of the Lutetium-Hafnium clock. Science 293, 683-687] for the 176Lu decay constant, which is thus far the best reproduced estimate and the one most consistent with depleted mantle evolution results based on Nd isotopes and Nb/Th ratios. A linear Hf mantle growth curve defined by these values and recent MORB intersects the chondritic Hf growth curve during the early Archean (3.4-4.0 Ga). This could indicate that the earliest formation of significant amounts of enriched crust coincides with ages of the oldest preserved rocks, but such a conclusion is contradicted by evidence from 142Nd and 143Nd in early Archean rocks for significant mantle depletion during the Hadean eon (>4.0 Ga). Both lines of evidence might be reconciled if Hadean enriched crust were largely remixed with its depleted mantle source near the beginning of the Archean, leaving only fragmentary evidence of its existence in the oldest rocks

Mobility and connection among the Early Bronze Age Syrian elite

The archaeological site of Umm el-Marra (in the Jabbul plain, western Syria), is a large, fortified urban center. Excavations have uncovered ten tomb structures built during the Early Bronze Age (ca. 2600–2150 BCE) that possibly contain royalty as evidenced by lavish grave goods and paleopathological evidence suggesting sociocultural buffering from the harsh social and physical environments of agricultural urban centers in the Bronze Age Near East. Inside adjacent brick installations are animal (primarily equid) skeletons interpreted as interments, possibly sacrifices in some instances, as part of ceremonies honoring the entombed. The burial site was eventually re-used as evidenced by a monumental platform above the tombs, interpreted as use for ritual activities of ancestor veneration. This study analyzed 87Sr/86Sr and δ18O values from enamel of 13 individuals interred in these tombs, along with enamel and bone samples from animals found in and around the tomb structures. Six of 13 (43 %) individuals analyzed in these tombs are identified as non-locals. Although contemporaneous data in the northern Levant is scarce, we see much higher evidence of human movement at Umm el-Marra compared to others. Only elites are included in this study, but their relative mobility might imply that the ancient city established its position as a secondary center along major trade routes through intermarriage and connectivity. The concept of ‘social memory’ is evident, as the lives and deaths of these elites are integrated into this site where ancestor veneration is evidenced in centuries following interment

A Meeting In The Forest: Hunters And Farmers At The Coneybury ‘Anomaly’, Wiltshire

The Coneybury ‘Anomaly’ is an Early Neolithic pit located just south-east of Stonehenge, Wiltshire. Excavations recovered a faunal assemblage unique in its composition, consisting of both wild and domestic species, as well as large quantities of ceramics and stone tools, including a substantial proportion of blades/bladelets. We present a suite of new isotope analyses of the faunal material, together with ancient DNA sex determination, and reconsider the published faunal data to ask: What took place at Coneybury, and who was involved? We argue on the basis of multiple lines of evidence that Coneybury represents the material remains of a gathering organised by a regional community, with participants coming from different areas. One group of attendees provided deer instead of, or in addition to, cattle. We conclude that the most likely scenario is that this group comprised local hunter-gatherers who survived alongside local farmers

Early Eocene Arctic volcanism from carbonate-metasomatized mantle

Melilitite, nephelinite, basanite, and alkali basalt, along with phonolite differentiates, form the Freemans Cove Complex (FCC) in the south-eastern extremity of Bathurst Island (Nunavut, Canada). New 40Ar/39Ar chronology indicates their emplacement between ~ 56 and ~ 54 million years ago within a localized extensional structure. Melilitites and nephelinites, along with phonolite differentiates, likely relate to the beginning and end phases of extension, whereas alkali basalts were emplaced during a main extensional episode at ~ 55 Ma. The melilitites, nephelinites, and alkali basalts show no strong evidence for significant assimilation of crust, in contrast to some phonolites. Partial melting occurred within both the garnet- and spinel-facies mantle and sampled sources with He, O, Nd, Hf, and Os isotope characteristics indicative of peridotite with two distinct components. The first, expressed in higher degree partial melts, represents a relatively depleted component (“A”; 3He/4He ~ 8 RA, εNdi ~ + 3 εHfi ~ + 7, γOsi ~ 0). The second was an enriched component (“B” 3He/4He + 70) sampled by the lowest degree partial melts and represents carbonate-metasomatized peridotite. Magmatism in the FCC shows that rifting extended from the Labrador Sea to Bathurst Island and reached a zenith at ~ 55 Ma, during the Eurekan orogeny. The incompatible trace-element abundances and isotopic signatures of FCC rocks indicate melt generation occurred at the base of relatively thin lithosphere at the margin of a thick craton, with no mantle plume influence. FCC melt compositions are distinct from other continental rift magmatic provinces worldwide, and their metasomatized mantle source was plausibly formed synchronously with emplacement of Cretaceous kimberlites. The FCC illustrates that the range of isotopic compositions preserved in continental rift magmas are likely to be dominated by temporal changes in the extent of partial melting, as well as by the timing and degree of metasomatism recorded in the underlying continental lithosphere

Extensive crustal extraction in Earth’s early history inferred from molybdenum isotopes

Estimates of the volume of the earliest crust based on zircon ages and radiogenic isotopes remain equivocal. Stable isotope systems, such as molybdenum, have the potential to provide further constraints but remain underused due to the lack of complementarity between mantle and crustal reservoirs. Here we present molybdenum isotope data for Archaean komatiites and Phanerozoic komatiites and picrites and demonstrate that their mantle sources all possess subchondritic signatures complementary to the superchondritic continental crust. These results confirm that the present-day degree of mantle depletion was achieved by 3.5 billion years ago and that Earth has been in a steady state with respect to molybdenum recycling. Mass balance modelling shows that this early mantle depletion requires the extraction of a far greater volume of mafic-dominated protocrust than previously thought, more than twice the volume of the continental crust today, implying rapid crustal growth and destruction in the first billion years of Earth’s history

The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine ophiolites

Arc lavas display elevated Fe3+/ΣFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidized or oxidizing components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride, and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex, and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S-bearing and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilized from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in proximity to metasediments display a significant Fe isotope fractionation. The covariation of δ56Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction

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

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

Sublithospheric diamond ages and the supercontinent cycle.

Subduction related to the ancient supercontinent cycle is poorly constrained by mantle samples. Sublithospheric diamond crystallization records the release of melts from subducting oceanic lithosphere at 300-700 km depths1,2 and is especially suited to tracking the timing and effects of deep mantle processes on supercontinents. Here we show that four isotope systems (Rb-Sr, Sm-Nd, U-Pb and Re-Os) applied to Fe-sulfide and CaSiO3 inclusions within 13 sublithospheric diamonds from Juína (Brazil) and Kankan (Guinea) give broadly overlapping crystallization ages from around 450 to 650 million years ago. The intracratonic location of the diamond deposits on Gondwana and the ages, initial isotopic ratios, and trace element content of the inclusions indicate formation from a peri-Gondwanan subduction system. Preservation of these Neoproterozoic-Palaeozoic sublithospheric diamonds beneath Gondwana until its Cretaceous breakup, coupled with majorite geobarometry3,4, suggests that they accreted to and were retained in the lithospheric keel for more than 300 Myr during supercontinent migration. We propose that this process of lithosphere growth-with diamonds attached to the supercontinent keel by the diapiric uprise of depleted buoyant material and pieces of slab crust-could have enhanced supercontinent stability