Nanocrystalline olivine-structured Mg2SiO4 and MgCoSiO4, with an average particle size of 27 nm and 31 nm, respectively, were successfully synthesized from oxide precursors via mechanochemical methods. The two nanocrystalline products were obtained after milling for 360 min and displayed high concentrations of Mg2SiO4 (>94%) and MgCoSiO4 (>95%), together with minor amounts of WC (~3%) contaminant originating as debris abraded off milling balls and chambers. The macroscopic temperature monitoring of the grinding jars during milling trials recorded a peak temperature of 75 °C. A combination of analytical techniques that included XRD, TEM, SAED, and EDS were employed for the characterization of the synthesized products.

The compositions of mantle-derived magmas indicate a substantial variety in the abundances of volatiles in the upper mantle. CO2 and H2O depress the melting point of mantle peridotites considerably, delineating a pressure temperature region of incipient melting where small degrees of melt exist over a large temperature range (similar to 300 degrees C) before major melting begins. However, the chemical characterization of these melts in high-pressure experiments is challenging at low melt fractions (melt pockets may occupy volumes of only 10-50 mu m(3)) because of analytical uncertainties related to the ubiquitous formation of metastable phases during quenching. This systematic partial melting study presents carefully determined compositions of incipient melts of a range of peridotites in the presence of CO2 + H2O mixtures at 2.5 to 7 GPa. Four different fertile and depleted peridotites were used: Hawaiian pyrolite, K2O-enriched pyrolite, MORB pyrolite and depleted lherzolite. To arrive at accurate melt compositions, we introduce the melt tomography method that integrates multiple area scans of melt pockets polished to several depths. Results confirm that incipient and low degree melts progress abruptly (within 25 degrees C) from carbonatitic towards melilititic-nephelinitic compositions at 2.5 GPa, whereas they progress gradually from carbonate-rich to carbonated silicate (aillikitic) compositions at 4-5 GPa. Melt compositions at near-solidus conditions are mainly controlled by the breakdown of carbonate, and hydrous phases such as pargasite and phlogopite, and become less siliceous and slightly more magnesian with increasing pressure at given melt fractions. Melts exhibit strong increases in SiO2 (2.75 to 44 wt%) with increasing temperature, whereas TiO2, Na2O and K2O decrease. The generally strongly potassic (K2O <= 6.63 wt%) and sodic (Na2O <= 3.06 wt%) character of the volatile-rich, incipient and low-degree melts indicate that these would act as reactive metasomatic agents that may transport large amounts of energy and induce chemical changes in large volumes of the upper mantle. (C) 2021 Published by Elsevier B.V.

Co2SiO4 is a ceramic pigment and promising battery material of significant technological interest, as well as a model end-member of one of the most important mineral families in the Earth's crust and upper mantle. All previously developed methods for synthesis of Co2SiO4 require high-temperature processing, which promotes grain growth, while the nanocrystalline form is required for some important technological applications. Here, we report a successful method for synthesizing nanocrystalline Co(2)SiO(4)via a simple and inexpensive high-energy ball milling mechanochemical process. Products of the synthesis were characterized by a combination of XRD and TEM, and their crystal structures and elemental compositions are reported.

Iron‐dominant metallic phases are likely the primary hosts for nitrogen in the reduced deep Earth, hence the storage of nitrogen in the lower mantle and the core is governed by the behavior of the Fe‐N‐C system at high temperatures and pressures. In this study, phase transitions and thermoelastic properties of iron carbonitrides were investigated at high pressure‐temperature conditions by diamond anvil cell experiments and first‐principles calculations. Experimental data revealed no phase transition in ε ‐type Fe 4 (N 0.6 C 0.4 ) or Fe 7 (N 0.75 C 0.25 ) 3 up to 60 GPa at room temperature. At high temperature, Fe 7 (N 0.75 C 0.25 ) 3 transforms into the Fe 3 C‐type phase at ∼27 GPa, and then into the Fe 7 C 3 ‐type phase at ∼45 GPa, which is also corroborated by our theoretical calculations. We found that the phase stability of iron carbonitrides mainly depends on the N/C ratio, and the elastic properties of iron carbonitrides are dominantly affected by the Fe/(N+C) ratio. Iron carbonitrides with diverse structures may be the main host for nitrogen in the deep mantle. Some iron carbonitride inclusions in lower mantle diamonds could be the residue of the primordial mantle or originate from subducted nitrogen‐bearing materials, rather than iron‐enriched phases of the outer core. In addition, our experiments confirmed the existence of Fe 7 C 3 ‐type Fe 7 C 3 ‐Fe 7 N 3 solid solutions above 40 GPa. Fe 7 C 3 ‐type Fe 7 (C, N) 3 has comparable density and thermoelastic properties to its isostructural endmembers and may be a promising candidate constituent of the Earth's inner core.

Understanding the genetic relationship between the Narich TTG (tonalite-trondhjemite-granodiorite) suite of granitoids comprising the earliest continental masses, and their deep roots or “keels” in the underlying mantle is crucial to the development of models for the origin and growth of the continents and the chemical evolution of the cratonic lithosphere. Archean TTG granitoids are thought to originate by partial melting of primitive (basaltic) oceanic crust in unison with some sort of recycling (subduction?) mechanism. Partial melting experiments on hydrous basalt at pressures of 1-4 GPa produce liquids that closely resemble Archean TTG, as well as certain modern-day arc magmas, known as adakites, which are relatively rare and occur in association with “hot” subduction zones (e.g., ridge subduction, or subduction of very young oceanic lithosphere). As such, the composition of early Archean granitoids may provide clues to the tectonic setting and magmatic processes that governed continent growth and craton evolution. In assimilation experiments in which these same TTG liquids are allowed to infiltrate and react with a layer of depleted or fertile peridotite, “hybridized” granitoid melts (Mg-diorite), compositionally comparable to late-Archean sanukitoids, form in equilibrium with garnet websteritic (garnet + orthopyroxene ± clinopyroxene) reaction residues (Rapp et al., 1999). These experiments simulate melt-rock reaction across the slab-mantle wedge interface in a subduction zone setting, or, more generally, across the crust-mantle interface at the base of an evoloving Archean craton. Considered together, the experimental results from both basalt melting and peridotite assimilation experiments reveal a full compositional spectrum of granitoid liquids, ranging from pristine (low-Mg#) TTG melts in equilibrium with eclogite residues, to hybridized high-Mg# monzodiorite (sanukitoid) melts in equilibrium with garnet websterite residues. Both groups of granitoids have a common ‘eclogite melting’ origin, and a corresponding spectrum of crystalline residues of melting and melt-rock reaction, from eclogite to garnet websterite, are formed as well. We have used the ion microprobe to geochemically fingerprint, in terms of an array of trace elements (Ba, Rb,Th, U, Nb, Sr, Zr, Y, Cr, REEs), coexisting granitoid liquids, and crystalline residues of melting (eclogite) or melt-rock reaction (peridotite) in these experiments, generating mineral-melt partition coefficients relevant to partial melting and melt-rock reaction in the process. Because these measurements have been made at natural abundance levels, direct comparisons can be made between the experimental melts and Archean granitoids, including both TTG and sanukitoid compositions. Such comparisons give an indication of the extent to which the mantle was involved in the petrogenesis of Earth’s early continental crust. Similarly, direct comparisons can also be made between the crystalline residues of melting (eclogites) and TTG melt-peridotite interaction (garnet websterite), and the corresponding xenoliths and diamond inclusion parageneses from the subcratonic mantle. These comparisons help establish a genetic link between the granitoids that comprise the cratons, and their roots in the underlying lithospheric mantle, complementing isotopic (e.g., Pearson et al., 1995) and seismic studies that indicate an intimate, long-term coupling between these two domains.

Introduction Eclogite xenoliths in kimberlites, although representing only a small proportion of the total xenolith population, may contain important information on the petrologic processes responsible for the initial stabilization and growth of the continents (cratonization) in the Archean, and the nature and chemical evolution of the sub¬ continental lithospheric mantle (continental roots) . The fact that some mantle eclogites possess oxygen isotope ratios similar to hydrothermally-altered oceanic crust supports the idea that these samples may represent metamorphosed remnants of subducted basaltic crust, possibly modified by melting (MacGregor and Manton, 1986; Jacob et al., 1994). Low-degree partial melts of hydrated metabasalt (i.e., "wet eclogite") are virtually identical geochemically to the tonalite-trondhjemitegranodiorite (TTG) suite of granitoids that are the dominant felsic component of Archean high-grade gneiss and granite-greenstone terrains (Rapp and Watson, 1995). These observations suggest a genetic link between eclogite xenoliths in the lithospheric mantle beneath the Archean cratons, and the granite magmatism responsible for their stabilization. In order to evaluate this relationship, melting experiments were conducted at 2-11 GPa on a number of natural olivine tholeiite metabasalt compositions (amphibolites), and the major, minor and trace element characteristics of the melt products and crystalline residues were determined by a combination of electron and ion microprobe analysis. These measurements form the basis for comparisons between the eclogitic residues produced in the melting experiments with eclogite xenoliths from beneath the South African and Siberian cratons. What are the distinctive geochemical features of eclogites that are residues of basalt melting?

Despite evidence for the presence of continental crust on Earth at ~4.2-4.4Ga ago (Harrison et al., 2005), no rocks older than ~4.0 Ga survive, and consequently, the question of when and how Earth's first continents formed (as opposed to its earliest granitic crust) remains highly debatable.The physical and temporal juxtaposition of the oldest preserved granitoid rocks with old, cold roots extending deep into the underlying cratonic lithospheric mantle suggests a linked evolutionary history.Understanding the genetic relationship between Archean continental crust and cratonic lithosphere is therefore crucial to understanding how physically and chemically stable continental nuclei (cratons) formed.

Wang et al. (Contrib Mineral Petrol 171:62, 2016a) present data on composition of xenolith from Southern Tibet and conclude that ulrapotassic melts from the region formed by melting mantle, and complex interaction with a crustal component. In this discussion we demonstrate that numerous observations presented by Wang et al. (2016a) can be explained by partial melting of crust followed by interaction between that melt and the mantle. We show that this model can explain the variability of magmas in such suits without evoking occurrence of coincidental, unrelated events. Moreover we demonstrate that our model of a crustal origin of the proto-shoshonite melts is now supported by independent lines of evidence such as geochemistry of restites after high- and ultrahigh- pressure melting and melt inclusion studies.

The Archean rock record contains seventeen asteroid impact ejecta units that represent the terrestrial vestiges of an extended late heavy bombardment (LHB). Correlated impact ejecta units include 3472-3470 Ma impact spherule layers in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa, and the Pilbara Craton, Western Australia, and several ejecta units dated between 3250 and 3220 Ma and between 2630 and 2480 Ma (Lowe and Byerly, 2010; Lowe et al., 2003, 2014). This paper reports the discovery and investigation of a new impact ejecta unit within the Marble Bar Chert Member (MBCM) of the felsic volcanic Duffer Formation, east Pilbara Craton, Western Australia. The age of the MBCM is constrained by a 3459 +/- 2 Ma U-Pb zircon date from the uppermost volcanic unit of the Duffer Formation and by a 3449 +/- 3 Ma U-Pb zircon date from the overlying felsic volcanic Panorama Formation, stratigraphically above the intervening un-dated Apex Basalt. The ejecta unit, observed in a drill core (ABDP 1) similar to 4 km south-southwest of Marble Bar, consists of multiple lenses and bands of almost totally silicified impact spherules 1-2 mm in diameter. All internal primary textures of the spherules have been destroyed. Nonetheless, Fe-rich spherule rims, largely composed of secondary siderite, are well preserved. Chemical analyses of the rims reveal iron-magnesium carbonate displaying high Fe, Mg, Ni, Co and Zn. Whole-rock and in-situ analyses (X-ray fluorescence, Inductively Coupled Plasma Mass Spectrometry (ICPMS), electron-microprobe (EMP) and EMP-calibrated laser ICPMS) reveal that the rims contain high Ni abundances and high Ni/Cr ratios (<50). The spherules are separated by an arenite matrix and spherule lenses also occur within bedded chert. The spherules are particularly visible over some similar to 14 m of true stratigraphic thickness in which chert breccia is interpreted to represent a tsunami generated diamictite affected by hydrothermal fragmentation and veining. Despite the almost total silicification of the MBCM whole-rock analysis by NIS Fire Assay and ICPMS indicates high Ir (2 ppb) and a low Pd/Ir ratio (2.0), consistent with geochemical features of impact ejecta units. Dense concentrations of spherules at the 57-58 m level and the 77 m level of the core, separated by banded chert, raise the possibility of two distinct impact events. Stratigraphic and isotopic age data distinguish between the 3459 and 3449 Ma age of the MBCM ejecta unit and similar to 3470.1 +/- 1.9 Ma impact ejecta units in the Antarctic Creek Member, Mount Ada Basalt, about 40 km to the west of Marble Bar. In combination with a 3472 +/- 2.3 Ma impact unit in the Barberton greenstone belt, these impact ejecta units record large Paleoarchean asteroid impacts, significant for understanding early bombardment rates on Earth and early crustal evolution. (C) 2016 Elsevier B.V. All rights reserved.

Meso-Archean sedimentary sequences at Mt. Narryer and the Jack Hills of the Narryer Terrane in Western Australia's Yilgarn Craton contain detrital zircon grains with ages as old as 4.37Ga, the oldest preserved terrestrial matter. These grains are rare remnants of Hadean (4.5–4.0Ga) terrestrial crust and their survival stems from the crystallographic properties of zircon during crustal reworking: they are resistant to physical and chemical weathering. Zircons are further suitable for single grain, precise age determinations making them a unique archive of the crustal past. Only a small proportion of all detrital zircons from the Narryer Terrane show Hadean age spectra and younger overgrowth rims on all ‘Hadean’ grains indicate multiple recycling events. Numerous studies that applied a spectacular range of analytical tools and proxies have been undertaken to decipher the geochemical nature of these zircons' host rocks, in order to place constraints on Hadean geodynamics and the processes responsible for creating the earliest terrestrial crust. Their elemental and isotope budget and mineral inclusions have helped to develop an emerging picture of a water-rich, evolved Hadean crust. However, subsequent studies have challenged this view and it seems that each piece of new evidence indicative of an early, evolved continental crust has non-unique interpretations also permissive of mafic to ultra-mafic crust. In this review we examine these disparate interpretations and their possible implications and conclude that at least parts of the earliest terrestrial crust were hydrated. However, to date there is no conclusive evidence for preserved granitic, continental crust. The protoliths of the Hadean detrital zircons were likely acidic in nature, yet the composition of the greater terrane from which these melts were derived was probably mafic. It remains unclear if the zircons formed in a geodynamic environment that includes Hadean subduction. We suspect that the Hadean crust was an initially homogeneous, thin, mafic layer. It was spiked with minor, low-degree, anatectic melts of granitoid composition formed from material that formerly resided at the surface and was subsequently buried. The process responsible for this was likely sag-subduction triggered by repeated volcanic resurfacing, possibly fed by early mantle plumes. Regional scale granitoid plutonism of the tonalite–trondhjemite–granodiorite suite (TTG) predominates granitoid-generating processes in the Eo-Archean, along with the first appearance of low-Ca (s-type) granites at around 3.9Ga, evidenced by the first occurrence of detrital monazite in the Narryer Terrane. This coincides with the first addition of juvenile crust as documented by the global detrital zircon record and temperature signatures of the late heavy bombardment in Narryer Terrane zircons. This age probably marks the onset of Archean-style tectonics, likely associated with subduction activity, which lasted until ~3Ga, when modern style plate tectonics emerged.

Layered mafic intrusions (LMI) are large, stratified igneous bodies of great economic significance. The constitutive crustal magma chamber(s) supplied by mantle-derived magma pulses exhibit complex mineralogical and chemical layering. Current magma chamber models invoke mineral density separation, liquid density inversion, and small-scale convection, superimposed on possible magma recharge and crustal assimilation, but petrogenetic interpretation is difficult. Four new drill cores from the Upper Zone and uppermost Middle Zone of the Windimurra Igneous Complex, the largest layered mafic intrusion in Australia, sample a continuous section of similar to 1300 m including several magnetitite horizons. The Upper Zone is free of primary hydrous minerals and exhibits ore-grade Fe-enrichment up to 62.7 wt% FeOT in some sections. Relatively high Cr in magnetite at the base and sustainedly lower Cr in the remainder of the Upper Zone is consistent with injection of a single magmatic pulse at the commencement of the zone. Major and trace element analyses of representative samples from macroscopically layered horizons from throughout the Upper Zone sequence define three magmatic trends that reflect physical separation of phases within a single magma chamber. Magnetite accumulated at the base of the Upper Zone and geochemical trends in major and trace elements indicate an early formation of magnetite with a subtle effect on oxygen fugacity in the magma chamber. Bulk Nb/Ta < 14 indicate that Fe enrichment was not the result of large-scale liquid immiscibility, but is interpreted here as the normal result of an advanced tholeiitic fractionation trend. Accumulation in magnetitite horizons close to the base of the Upper Zone is interpreted to result from density separation of magnetite crystals. Field evidence indicates a density inversion in the course of magma differentiation, probably caused by ongoing crystallisation that resulted in late-stage mass movement of magnetitites and anorthositic blocks. Strontium isotope data point to a mantle-derived origin with 87Sr/86Sr[2.8Ga]similar to 0.701, indicating little, if any crustal contamination. The Windimurra Upper Zone sequence is an ideal example to study closed system magma chamber processes in an evolving, dry mafic system in the absence of or with only very limited crustal interaction.

We report the results of monazite/melt partitioning experiments conducted in the piston-cylinder apparatus at 10-50 kbar and 750-1200 degrees C. using a synthetic granite mix with approximately 10 wt.% H2O and doped with trace-elements in proportions corresponding to the composition of monazite. Monazite was produced in all experiments, generally in the form of small grains. Electron microprobe and laser ablation-ICP-MS analyses were carried out on the resulting "monazite-melt" mixes from these experiments, and the composition of the crystallized monazite calculated using regression analysis. The concentrations of LREE and Th in the melts coexisting with monazite increase sharply with increasing temperature. Monazite solubility decreases by 35-40% as pressure increase from 10 to 30 kbar. Monazite solubility in granitic melts with an Alumina Saturation Index above 0.85 and FeO + CaO + MgO < 3 wt.% can be described by the following equation:In Sigma LREE = 16.16(+/- 0.3) + 0.23(+/- 0.07) root H2O-11494(+/- 410)/T-19.4(+/- 4)P/T + InXmnzLREEWhere H2O is in weight percent, T is in Kelvin, P in kbar and Sigma LREE is the sum of La-Sm in ppm; X-mnz(LREE) is the molar ratio of LREE to the sum of all cations (REE, Th, U) in monazite. REE, Th, U. V. V and As partition into monazite, whereas other trace elements (Li, Be, B. Sc, Ti, Mn, Sr, Zr, Nb, Ba, Hf, Ta and Pb) have monazite/melt partition coefficients less than unity. Monazite shows the greatest preference for LREE from La to Nd, with a progressive decrease in partition coefficients for Sm and the HREE. The partition coefficients for Th are 30% higher than those for the LREE, and Th/LREE ratios are independent of pressure and temperature. Partition coefficients for U are 4-23 times lower than for the LREE. The new experimental data provide a numerical basis for modeling the behavior of LREE, Th and U during fractional crystallization of granitic magmas, as well as the melting in the presence of monazite, both within the continental crust, and in subduction zones. (C) 2012 Elsevier B.V. All rights reserved.

EPMA chemical U-Th-Pb uraninite analysis has been used to constrain the age of the granite-related, Rössing South uranium prospect in Namibia and the Kintyre unconformity-related uranium deposit in Western Australia. Uraninite from the Rössing South prospect has an age of 496.1 ± 4.1 Ma, which is similar to the age of other uranium deposits in the region at Rössing and Goanikontes. Uraninite grains analysed from the Kintyre deposit have an age of 837 +35/-31 Ma suggesting that the uranium mineralisation occurred during or after the latest period of sedimentation in the Yeneena Basin during the ca 850 to ca 800 Ma Miles Orogeny.

Increased terrestrial phosphorus runoff is a major environmental problem that has been linked to deteriorating reef health. Unfortunately, long-term records of phosphorus are limited. Whilst phosphorus captured in coral skeletons could provide us with an archive of phosphorus variability, the mode of incorporation is poorly understood. In order to document phosphorus levels, we used laser ablation inductively coupled plasma mass spectrometry, followed by X-ray mapping of phosphorus in the skeleton at micron scale (~3–5 microns) using Electronprobe microanalysis. We recorded high phosphorus (≤8,700 ppm) in the living tissue zone associated with phosphorus-rich residues lining the internal pore network surfaces. The skeleton in the tissue zone had low, uniform levels of phosphorus, similar to older sections of the core (<50 ppm). Below the organic tissue layer, P was incorporated homogenously in the skeleton for extended periods (e.g., 5 mm growth bands). However, sections of the core (~1 cm down-core) displayed fine-scale elevated phosphorus concentrations associated with the presence of phosphorus-rich, often elongate (10–100 μm long), heterogeneities within the skeleton, the origin of these phosphorus-rich heterogeneities and their mode of incorporation requires further attention. In conclusion, these results support the continued development of this promising potential nutrient proxy.

ABSTRACTA specific type of granitoid, referred to as sanukitoid (Shirey & Hanson 1984), was emplaced mainly across the Archaean–Proterozoic transition. The major and trace element composition of sanukitoids is intermediate between typical Archaean TTG and modern arc granitoids. However, among sanukitoids, two groups can be distinguished on the basis of the Ti content of the less differentiated rocks of the suite: high- and low-Ti sanukitoids. Melting experiments and petrogenetic modelling show that they may have formed by either (1) melting of mantle peridotite previously metasomatised by felsic melts of TTG composition, or (2) by reaction between TTG melts and mantle peridotite (assimilation). Rocks of the sanukitoid suite were emplaced at the Archaean–Proterozoic boundary, possibly marking the time when TTG-dominated granitoid magmatism changed to a more modern-style, arc-dominated magmatism. Consequently, the intermediate character of sanukitoids is not only compositional but chronological. The succession of granitoid magmatism with time is integrated in a plate tectonic model where it is linked to the thermal evolution of subduction zones, reflecting the progressive cooling of Earth: (1) the Archaean Earth’s heat production was high enough to allow the production of large amounts of TTG granitoids formed by partial melting of recycled basaltic crust (‘slab melting’); (2) at the end of the Archaean, due to the progressive cooling of the Earth, the extent of slab melting was reduced, resulting in lower melt:rock ratios. In such conditions the slab melts can be strongly contaminated by assimilation of mantle peridotite, thus giving rise to low-Ti sanukitoids. It is also possible that the slab melts were totally consumed in reactions with mantle peridotite, subsequent melting of this ‘melt-metasomatised mantle’ producing the high-Ti sanukitoid magmas; (3) after 2·5 Ga, Earth heat production was too low to allow slab melting, except in relatively rare geodynamic circumstances, and most modern arc magmas are produced by melting of the mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab. Of course, such changes did not take place exactly at the same time all over the world. The Archaean mechanisms coexisted with new processes over a relatively long time period, even if they were subordinate to the more modern processes.