Vadim S. Kamenetsky

The Amount of Recycled Crust in Sources of Mantle-Derived Melts

One proposed strategy for controlling the transmission of insect-borne pathogens uses a drive mechanism to ensure the rapid spread of transgenes conferring disease refractoriness throughout wild populations. Here, we report the creation of maternal-effect selfish genetic elements in Drosophila that drive population replacement and are resistant to recombination-mediated dissociation of drive and disease refractoriness functions. These selfish elements use microRNA-mediated silencing of a maternally expressed gene essential for embryogenesis, which is coupled with early zygotic expression of a rescuing transgene.The phosphoinositide phosphatase PTEN is mutated in many human cancers. Although the role of PTEN has been studied extensively, the relative contributions of its numerous potential downstream effectors to deregulated growth and tumorigenesis remain uncertain. We provide genetic evidence in Drosophila melanogaster for the paramount importance of the protein kinase Akt [also called protein kinase B (PKB)] in mediating the effects of increased phosphatidylinositol 3,4,5-trisphosphate (PIP3) concentrations that are caused by the loss of PTEN function. A mutation in the pleckstrin homology (PH) domain of Akt that reduces its affinity for PIP3 sufficed to rescue the lethality of flies devoid of PTEN activity. Thus, Akt appears to be the only critical target activated by increased PIP3 concentrations in Drosophila.Using genomic and mass spectrometry-based proteomic methods, we evaluated gene expression, identified key activities, and examined partitioning of metabolic functions in a natural acid mine drainage (AMD) microbial biofilm community. We detected 2033 proteins from the five most abundant species in the biofilm, including 48% of the predicted proteins from the dominant biofilm organism, Leptospirillum group II. Proteins involved in protein refolding and response to oxidative stress appeared to be highly expressed, which suggests that damage to biomolecules is a key challenge for survival. We validated and estimated the relative abundance and cellular localization of 357 unique and 215 conserved novel proteins and determined that one abundant novel protein is a cytochrome central to iron oxidation and AMD formation.

Kimberlite melts rich in alkali chlorides and carbonates: A potent metasomatic agent in the mantle

Kimberlite magmas, as the deepest probe into Earths mantle (>150 km), can supply unique information about volatile components (hydrogen, carbon, chlorine, sulfur) in mantle-derived melts and fluids. All known kimberlite rocks are not suitable for studies of mantle volatiles because of their pervasive postmagmatic alteration; however, this study discusses an exceptionally fresh group I kimberlites (<0.5 wt% H2O) from the Udachnaya-East diamondiferous pipe in Siberia. Kimberlite groundmass, in addition to euhedral olivine and calcite, is extremely enriched (at least 8 wt%) in water-soluble alkali chlorides, alkali carbonates, and sulfates (ratio 5:3:1), and often shows immiscibility textures. A primary magmatic origin of alkali chlorides and alkali carbonates is confirmed by the study of strontium isotopes in the water- and dilute acid-leachates of the groundmass (Sr-87/Sr-86 = 0.7069 and 0.7050) that contrast with much more radiogenic isotope composition of the Cambrian platform sedimentary rocks and the Udachnaya-East mine-site brines. Melt inclusions in groundmass olivine, composed of halite, sylvite, alkali-Ca carbonates, phlogopite, olivine, and CO2 fluid, were used to determine the composition and evolution of the kimberlite melt prior to emplacement. Melt inclusions show immiscibility between chloride and carbonate liquids at <600oC in heating stage experiments. The chloride and carbonate enrichment in the kimberlite parental magma suggests the presence of a powerful agent for chemical modifications (metasomatism) in the mantle and crust.

Release of gold-bearing fluids in convergent margin magmas prompted by magnetite crystallization

A relationship between convergent margin magmas and copper–gold ore mineralization has long been recognized. The nature of the genetic link is controversial, particularly whether the link is due to high-oxygen-fugacity (fO2) melts and fluids released from subducted slabs or to brine exsolution during magmatic evolution. For submarine, subduction-related volcanic glasses from the eastern Manus basin, Papua New Guinea, we here report abrupt decreases in gold and copper abundances, coupled with a switch in the behaviour of titanium and iron from concentration increases to decreases as SiO2 rises. We propose that the abrupt depletion in gold and copper results from concurrent sulphur reduction as a result of fO2 buffering, causing enhanced formation of copper–gold hydrosulphide complexes that become scavenged from crystallizing melts into cogenetic magmatic aqueous fluids. This process is particularly efficient in oxidized arc magmas with substantial sulphate. We infer that subsequent migration and cooling of exsolved aqueous fluids create links between copper–gold mineralization and arc magmatism in the Manus basin, and at convergent margins in general.

Metal saturation in the upper mantle.

The oxygen fugacity fO2of the Earth’s mantle is one of the fundamental variables in mantle petrology. Through ferric–ferrous iron and carbon–hydrogen–oxygen equilibria, fO2 influences the pressure–temperature positions of mantle solidi and compositions of small-degree mantle melts. Among other parameters, fO2 affects the water storage capacity and rheology of the mantle. The uppermost mantle, as represented by samples and partial melts, is sufficiently oxidized to sustain volatiles, such as H2O and CO2, as well as carbonatitic melts, but it is not known whether the shallow mantle is representative of the entire upper mantle. Using high-pressure experiments, we show here that large parts of the asthenosphere are likely to be metal-saturated. We found that pyroxene and garnet synthesized at >7 GPa in equilibrium with metallic Fe can incorporate sufficient ferric iron that the mantle at >250 km depth is so reduced that an (Fe,Ni)-metal phase may be stable. Our results indicate that the oxidized nature of the upper mantle can no longer be regarded as being representative for the Earth’s upper mantle as a whole and instead that oxidation is a shallow phenomenon restricted to an upper veneer only about 250 km in thickness.

Sr, Nd, and Pb isotope evidence for a mantle origin of alkali chlorides and carbonates in the Udachnaya kimberlite, Siberia

The kimberlite rocks of the Udachnaya-East pipe (Siberia) are uniquely fresh and contain very high abundances of primary volatiles (Cl, CO2, S). Alkali elements and chlorine are extremely abundant in the reconstructed kimberlite melt compositions, and this enrichment is very important for our understanding of deep-mantle melting and melt transport. Here we present new isotopic data that confirm a mantle origin for these kimberlitic chlorides and carbonates, and constrain the kimberlite emplacement age as ca. 347 Ma. The initial Nd and Ph isotope ratios in a large salt aggregate, in a CI-S-enriched water leachate of the groundmass, and in the silicate fraction of the groundmass are very similar (epsilon(Nd) = +3 to +4, Pb-206/Pb-204 = 18.6, Pb-207/Pb-204 = 15.53), implying a comagmatic origin of the chlorides and carbonates and the silicates. Combined Sr, Nd, and Ph isotope data are used to rule out any significant contributions to the kimberlite chlorine budget from crustal sources, such as the Cambrian evaporite sequences of the Siberian platform. Our data support the interpretation that exsolved Na-K chloride and Na-K-Ca carbonate formed directly from original uncontaminated kimberlite magma. High Cl abundances in kimberlites suggest the presence of a Cl-rich reservoir in the deep sublithospheric mantle

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same δ37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt–rock reaction=melting involving clinopyroxene-rich lithologies during MORB generation

Olivine-hosted homogenized melt inclusions in a primitive basalt AII32-12-7 from 43oN Mid-Atlantic Ridge have magnesian basalt compositions (10-12 wt% MgO) with high CaO (13.2-15.2 wt%), relatively low Al2O3 (12.8-15.5 wt%), and form a linear array that ranges to extremely high CaO/Al2O3 values (0.8-1.2). These melt compositions are unusual for MORB, as is the observed phenocryst assemblage, which comprises primitive olivine (Fo(87-92) with up to 0.45 wt% CaO), Cr-diopside (Mg# 90-92), and Cr-rich spinel (Cr# 50-70) and directly reflects these melt compositions. The melt compositional array extends from peridotite-saturated compositions formed near 1 GPa to lie well within the clinopyroxene phase volume, or possibly along a clinopyroxene + olivine phase boundary. We interpret the array as either the product of melt-wallrock reaction between a I GPa MORB melt and a clinopyroxene-rich lithology (wehrlite or clinopyroxenite), or of mixing between melt fractions derived separately from these distinct lithologies (i.e. peridotite and clinopyroxenite/wehrlite). Derivation of the melt array from a conventional mantle peridotite source, possibly involving fractional melting near or beyond the point of clinopyroxene exhaustion, is inconsistent with the melt compositions and the trend of the array. Trace element abundance patterns in the melt inclusions range from depleted to highly enriched (e.g. La-n/Yb-n 0.6-7.0), and indicate the generation of compositionally diverse melt fractions via fractional melting processes and/or melting of geochemically distinct source heterogeneities. Most melt inclusions, and the pillow-rim glass, are enriched in the more incompatible trace elements, and have high Nb and Ta contents relative to other highly incompatible elements. These characteristics and the Pb isotopic composition of the pillow-rim glass (Pb-206/Pb-204 = 19.654) indicate the presence of a HIMU mantle source component that can be linked to lateral dispersion of a geochemical signal commonly attributed to the Azores mantle plume.

Phenocryst and melt inclusion chemistry of near-axis seamounts, Valu Fa Ridge, Lau Basin: insight into mantle wedge melting and the addition of subduction components

Phenocryst assemblages, and mineral and melt inclusion compositions of magmas erupted at near-axis seamounts on either side of Valu Fa Ridge provide a hitherto unprecedented insight into the complexity of magma generation in this back-are basin tectonic setting, Two fundamentally different primitive primary melt compositions are identified based on melt inclusion compositions, olivine phenocryst chemistry, and the early co-crystallisation of either magnesian clinopyroxene (Mg# to 93) or magnesian orthopyroxene (Mg# to 93.5) with magnesian olivine (to Fo(94)) and Cr-rich spinel (Cr# = 0.78-0.87). One magma type is a H2O-rich (similar to 2.5 wt%), high-CaO (similar to 14 wt%), low-Al2O3 (similar to 8 wt%) magnesian basalt, variants of which occur in both the eastern and western seamounts, The other is a low-Ca boninite-like magma that only occurs as a component of the western seamount magmas.Large and systematic variations in incompatible trace-element compositions of melt inclusions trapped in primitive olivine phenocrysts, reflect an integration of diverse but geochemically related melt fractions to produce the magmas at each seamount. Trace-element systematics require the variable addition of a LILE-, Pb-, and Cl-rich component to the mantle wedge source with increased influence toward the Tofua are. This component, as invoked in most models of are magma genesis, is likely to be a supercritical aqueous fluid released by dehydrating subducting ocean crust beneath the volcanic are front.We propose that southward propagation of the back-are basin spreading center mantle provided heat necessary to generate both magmatic suites by decompression melting of refractory hydrated sub-are lithosphere, probably veined by clinopyroxene-rich dykes in the case of the high-CaO magma series, These near-ridge seamount lavas are very similar to those drilled at ODP Site 839 in the Lau Basin, and we suggest that the Site 839 basalts, as well as other Lau Basin seamount are-like magmas, were produced from sub-are lithosphere during southward propagation of the Eastern Lau Spreading Center similar to 2-3 Ma.

Enhanced mantle-to-crust rhenium transfer in undegassed arc magmas.

Variations in the 187Os/188Os isotopic signature of mantle and mantle-derived rocks have been thought to provide a powerful chemical tracer of deep Earth structure. Many studies have inferred from such data that a long-lived, high-rhenium component exists in the deep mantle (187Re is the parent isotope decaying to 187Os, with a half-life of ∼42 billion years), and that this reservoir probably consists of subducted oceanic crust. The interpretation of these isotopic signatures is, however, dependent on accurate estimates of rhenium and osmium concentrations in all of the main geochemical reservoirs, and the crust has generally been considered to be a minor contributor to such global budgets. In contrast, we here present observations of high rhenium concentrations and low Yb/Re ratios in arc-type melt inclusions. These results indicate strong enrichment of rhenium in undegassed arc rocks, and consequently the continental crust, which results in a crustal estimate of ∼2 p.p.b. rhenium, as compared to previous estimates of 0.4–0.2 p.p.b. (refs 4, 5). Previous determinations of rhenium in arc materials, which were largely measured on subaerially erupted samples, are likely to be in error owing to rhenium loss during degassing. High mantle-to-crust rhenium fluxes, as observed here, require a revaluation of geochemical models based on the 187Re-187Os decay system.

Survival times of anomalous melt inclusions from element diffusion in olivine and chromite

The chemical composition of basaltic magma erupted at the Earth’s surface is the end product of a complex series of processes, beginning with partial melting and melt extraction from a mantle source and ending with fractional crystallization and crustal assimilation at lower pressures. It has been proposed that studying inclusions of melt trapped in early crystallizing phenocrysts such as Mg-rich olivine and chromite may help petrologists to see beyond the later-stage processes and back to the origin of the partial melts in the mantle. Melt inclusion suites often span a much greater compositional range than associated erupted lavas, and a significant minority of inclusions carry distinct compositions that have been claimed to sample melts from earlier stages of melt production, preserving separate contributions from mantle heterogeneities. This hypothesis is underpinned by the assumption that melt inclusions, once trapped, remain chemically isolated from the external magma for all elements except those that are compatible in the host minerals. Here we show that the fluxes of rare-earth elements through olivine and chromite by lattice diffusion are sufficiently rapid at magmatic temperatures to re-equilibrate completely the rare-earth-element patterns of trapped melt inclusions in times that are short compared to those estimated for the production and ascent of mantle-derived magma or for magma residence in the crust. Phenocryst-hosted melt inclusions with anomalous trace-element signatures must therefore form shortly before magma eruption and cooling. We conclude that the assumption of chemical isolation of incompatible elements in olivine- and chromite-hosted melt inclusions is not valid, and we call for re-evaluation of the popular interpretation that anomalous melt inclusions represent preserved samples of unmodified mantle melts.