AgeSpectraAnalyst: A MATLAB based package to model zircon age distributions in silicic magmatic systems.

In the last decade, improvements in the analytical precision achievable by zircon U-Pb geochronological techniques have allowed to resolve complexities of zircon crystallization histories in magmatic rocks to an unprecedented level. A number of studies have strived to link resolvable dispersion in zircon age spectra of samples from fossil magmatic systems to the physical parameters of their parent magma bodies. However, the methodologies developed have so far been limited to reproduce the effect of simple thermal histories on the final distribution of zircon ages. In this work we take a more nuanced approach, fine-tuning a thermodynamics-based zircon saturation model to predict the relative distribution of zircon ages in samples from silicic magma reservoirs experiencing open-system processes (e.g. heat/mass addition, mechanical mixing). Employing the MATLAB package (AgeSpectraAnalyst) presented in this contribution:•Users can forward model the effect that diverse thermal histories and mechanical mixing processes characteristic of silicic magma bodies have on zircon age distributions as measured by high-precision, chemical abrasion thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronology.•Zircon CA-ID-TIMS datasets from silicic magmatic systems can be easily compared with model output to gain semi-quantitative information on thermo-mechanical history of the system of interest.•We demonstrated (Tavazzani et al., in press) that distribution of high-precision zircon ages in crystallized remnants of shallow (∼ 250 MPa), silicic magma reservoirs can discriminate between systems that experienced catastrophic, caldera-forming eruptions and systems that underwent monotonic cooling histories.

Remote detection of a lunar granitic batholith at Compton-Belkovich.

Granites are nearly absent in the Solar System outside of Earth. Achieving granitic compositions in magmatic systems requires multi-stage melting and fractionation, which also increases the concentration of radiogenic elements1. Abundant water and plate tectonics facilitate these processes on Earth, aiding in remelting. Although these drivers are absent on the Moon, small granite samples have been found, but details of their origin and the scale of systems they represent are unknown2. Here we report microwave-wavelength measurements of an anomalously hot geothermal source that is best explained by the presence of an approximately 50-kilometre-diameter granitic system below the thorium-rich farside feature known as Compton-Belkovich. Passive microwave radiometry is sensitive to the integrated thermal gradient to several wavelengths depth. The 3-37-gigahertz antenna temperatures of the Chang'e-1 and Chang'e-2 microwave instruments allow us to measure a peak heat flux of about 180 milliwatts per square metre, which is about 20 times higher than that of the average lunar highlands3,4. The surprising magnitude and geographic extent of this feature imply an Earth-like, evolved granitic system larger than believed possible on the Moon, especially outside of the Procellarum region5. Furthermore, these methods are generalizable: similar uses of passive radiometric data could vastly expand our knowledge of geothermal processes on the Moon and other planetary bodies.

Degassing-induced fractionation of multiple sulphur isotopes unveils post-Archaean recycled oceanic crust signal in hotspot lava.

Mantle source regions feeding hotspot volcanoes likely contain recycled subducted material. Anomalous sulphur (S) isotope signatures in hotspot lavas have tied ancient surface S to this deep geological cycle, but their potential modification by shallow magmatic processes has generally been overlooked. Here we present S isotope measurements in magmatic sulphides, silicate melt inclusions and matrix glasses from the recent eruption of a hotspot volcano at El Hierro, Canary Islands, which show that degassing induces strongly negative δ34S fractionation in both silicate and sulphide melts. Our results reflect the complex interplay among redox conditions, S speciation and degassing. The isotopic fractionation is mass dependent (Δ33S = 0‰), thus lacking evidence for the recycled Archaean crust signal recently identified at other hotspot volcanoes. However, the source has an enriched signature (δ34S ~ + 3‰), which supports the presence of younger 34S-rich recycled oceanic material in the Canary Island mantle plume.

Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars.

The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear. This issue features prominently in efforts to understand whether the source of light rare-earth elements in enriched shergottites lies in crustal material incorporated into melts or in mixing between enriched and depleted mantle reservoirs. Sulphur isotope systematics offer insight into some aspects of crustal assimilation. The presence of igneous sulphides in Martian meteorites with sulphur isotope signatures indicative of mass-independent fractionation suggests the assimilation of sulphur both during passage of magmas through the crust of Mars and at sites of emplacement. Here we report isotopic analyses of 40 Martian meteorites that represent more than half of the distinct known Martian meteorites, including 30 shergottites (28 plus 2 pairs, where pairs are separate fragments of a single meteorite), 8 nakhlites (5 plus 3 pairs), Allan Hills 84001 and Chassigny. Our data provide strong evidence that assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet's history. The signature of mass-independent fractionation observed also indicates that the atmospheric imprint of photochemical processing preserved in Martian meteoritic sulphide and sulphate is distinct from that observed in terrestrial analogues, suggesting fundamental differences between the dominant sulphur chemistry in the atmosphere of Mars and that in the atmosphere of Earth.