Using the traditional microscope for mineral grain orientation determination: A prototype image analysis pipeline for optic-axis mapping (POAM).

This paper reports on the development of an open-source image analysis software 'pipeline' dedicated to petrographic microscopy. Using conventional rock thin sections and images from a standard polarising microscope, the pipeline can classify minerals and subgrains into objects and obtain information about optic-axis orientation. Five metamorphic rocks were chosen to test and illustrate the method.

Deep, ultra-hot-melting residues as cradles of mantle diamond.

The ancient stable continents are up to 250 km deep, with roots extending into the diamond stability field. These cratons owe their mechanical strength to being cool and rigid, features inherited from extensive melt extraction. The most prominent model for craton formation anticipates dominant melting at relatively shallow depth (50-100 km) above diamond stability, followed by later imbrication to form the deeper roots.

Depth-dependent peridotite-melt interaction and the origin of variable silica in the cratonic mantle.

Peridotites from the thick roots of Archaean cratons are known for their compositional diversity, whose origin remains debated. We report thermodynamic modelling results for reactions between peridotite and ascending mantle melts. Reaction between highly magnesian melt (komatiite) and peridotite leads to orthopyroxene crystallisation, yielding silica-rich harzburgite.

Weathering, alteration and reconstructing Earth's oxygenation.

Deciphering the role-if any-that free oxygen levels played in controlling the timing and tempo of the radiation of complex life is one of the most fundamental questions in Earth and life sciences. Accurately reconstructing Earth's redox history is an essential part of tackling this question. Over the past few decades, there has been a proliferation of research employing geochemical redox proxies in an effort to tell the story of Earth's oxygenation.

Combined zinc-lead isotope and trace-metal assessment of recent atmospheric pollution sources recorded in Irish peatlands.

Atmospherically-fed Earth surface archives such as ombrotrophic peatlands, lake sediments, and ice consistently show an upward increase in Zn concentrations of hitherto unclear origin. Here, we present a combined stable Zn isotope and trace element (Zn, Cd, Ni, Cu, Cr, V, Ta, Pb) dataset for a historically polluted, near-urban bog (Liffey Head) from the east coast of Ireland. This peat record is compared to an archive from a rural site at the west coast of Ireland (Brackloon Wood).

Elemental and isotopic behaviour of Zn in Deccan basalt weathering profiles: Chemical weathering from bedrock to laterite and links to Zn deficiency in tropical soils.

Zinc (Zn) is a micronutrient for organisms and essential for plant growth, therefore knowledge of its elemental cycling in the surface environment is important regarding wider aspects of human nutrition and health. To explore the nature of Zn cycling, we compared its weathering behaviour in a sub-recent regolith versus an ancient laterite profile of the Deccan Traps, India - an area of known soil Zn deficiency. We demonstrate that progressive breakdown of primary minerals and the associated formation of phyllosilicates and iron oxides leads to a depletion in Zn, ultimately resulting in a loss of 80% in lateritic residues.

Volcanic crystals as time capsules of eruption history.

Crystals formed prior to a volcanic event can provide evidence of processes leading to and timing of eruptions. Clinopyroxene is common in basaltic to intermediate volcanoes, however, its ability as a recorder of pre-eruptive histories has remained comparatively underexplored. Here we show that novel high-resolution trace element images of clinopyroxene track eruption triggers and timescales at Mount Etna (Sicily, Italy).

Using trace elements in particulate matter to identify the sources of semivolatile organic contaminants in air at an alpine site.

An approach using trace elements in particulate matter (PM) to identify the geographic sources of atmospherically transported semivolatile organic contaminants (SOCs) was investigated. Daily samples of PM and SOCs were collected with high-volume air samplers from 16 January to 16 February 2009 at Temple Basin, a remote alpine site in New Zealand's Southern Alps. The most commonly detected pesticides were dieldrin, trans-chlordane, endosulfan I, and chlorpyrifos.

Atmospheric pollutants in alpine peat bogs record a detailed chronology of industrial and agricultural development on the Australian continent.

Two peat bogs from remote alpine sites in Australia were found to contain detailed and coherent histories of atmospheric metal pollution for Pb, Zn, Cu, Mo, Ag, As, Cd, Sb, Zn, In, Cr, Ni, Tl and V. Dramatic increases in metal deposition in the post-1850 AD portion of the cores coincide with the onset of mining in Australia. Using both Pb isotopes and metals, pollutants were ascribed to the main atmospheric pollution emitting sources in Australia, namely mining and smelting, coal combustion and agriculture.

Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event.

It has been suggested that a decrease in atmospheric methane levels triggered the progressive rise of atmospheric oxygen, the so-called Great Oxidation Event, about 2.4 Gyr ago. Oxidative weathering of terrestrial sulphides, increased oceanic sulphate, and the ecological success of sulphate-reducing microorganisms over methanogens has been proposed as a possible cause for the methane collapse, but this explanation is difficult to reconcile with the rock record.

Geochemistry: how well can Pb isotopes date core formation?

Timescale and the physics of planetary core formation are essential constraints for models of Earth's accretion and early differentiation. Wood and Halliday use the apparent mismatch in core-formation dates determined from tungsten (W) and lead (Pb) chrono-meters to argue for a two-stage core formation, involving an early phase of metal segregation followed by a protracted episode of sulphide melt addition. However, we show here that crust-;mantle Pb isotope systematics do not require diachronous core formation.

Stromatolite reef from the Early Archaean era of Australia.

The 3,430-million-year-old Strelley Pool Chert (SPC) (Pilbara Craton, Australia) is a sedimentary rock formation containing laminated structures of probable biological origin (stromatolites). Determining the biogenicity of such ancient fossils is the subject of ongoing debate. However, many obstacles to interpretation of the fossils are overcome in the SPC because of the broad extent, excellent preservation and morphological variety of its stromatolitic outcrops--which provide comprehensive palaeontological information on a scale exceeding other rocks of such age.

Geological constraints on detecting the earliest life on Earth: a perspective from the Early Archaean (older than 3.7 Gyr) of southwest Greenland.

At greater than 3.7 Gyr, Earth's oldest known supracrustal rocks, comprised dominantly of mafic igneous with less common sedimentary units including banded iron formation (BIF), are exposed in southwest Greenland. Regionally, they were intruded by younger tonalites, and then both were intensely dynamothermally metamorphosed to granulite facies (the highest pressures and temperatures generally encountered in the Earth's crust during metamorphism) in the Archaean and subsequently at lower grades until about 1500 Myr ago.

Simultaneous determination of delta33S(V-CDT) and delta34S(V-CDT) using masses 48, 49 and 50 on a continuous flow isotope ratio mass spectrometer.

A new, fast, continuous flow technique is described for the simultaneous determination of delta33S and delta34S using SO masses 48, 49 and 50. Analysis time is approximately 5 min/sample with measurement precision and accuracy better than +/-0.3 per thousand.

Tungsten isotope evidence from approximately 3.8-Gyr metamorphosed sediments for early meteorite bombardment of the Earth.

The 'Late Heavy Bombardment' was a phase in the impact history of the Moon that occurred 3.8 4.0 Gyr ago, when the lunar basins with known dates were formed.

Combined chemical separation of Lu, Hf, Sm, Nd, and Rees from a single rock digest: precise and accurate isotope determinations of Lu-Hf and Sm-Nd using multicollector-ICPMS.

A combined procedure for separating Lu, Hf, Sm, Nd, and rare earth elements (REEs) from a single sample digest is presented. The procedure consists of the following five steps: (1) sample dissolution via sodium peroxide sintering; (2) separation of the high field strength elements from the REEs and other matrix elements by a HF-free anion-exchange column procedure; (3) purification of Hf on a cation-exchange resin; (4) separation of REEs from other matrix elements by cation exchange; (5) Lu, Sm, and Nd separation from the other REEs by reversed-phase ion chromatography. Analytical reproducibilities of Sm-Nd and Lu-Hf isotope systematics are demonstrated for standard solutions and international rock reference materials.