Description: Accessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (Tzr) and titanium-in-zircon thermometry (T(Ti–zr)) estimate magma temperatures of ~ 795 ± 41 °C (Tzr) and ~ 845 ± 46 °C (T(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (Tzr) and ~ 785 ± 30 °C (T(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (Tzr) and ~ 850 ± 40 °C (T(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (Tzr) within the magma chamber, whereas the higher T(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H2O, whereas deeper melts contained 7 wt% H2O. Using these H2O contents, monazite saturation temperature (Tmz) estimates agree with Tzr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO2) melts. At inferred emplacement P–T conditions of 5 kbar and 730 °C, additional H2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.

Description: Centre of Excellence for Core to Crust Fluid Systems, Australian Research Council http://dx.doi.org/10.13039/100012537

Description: Ruhr-Universität Bochum (1007)

Description: The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of 2 years (2008–2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC or rBC and sulfate concentrations quite well, compared to previous comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January–March underestimated by 59 and 37% for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44% for July–September), but with overestimates as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is 3 times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modeling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anticorrelation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution.

Description: Accessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (Tzr) and titanium-in-zircon thermometry (T(Ti–zr)) estimate magma temperatures of ~ 795 ± 41 °C (Tzr) and ~ 845 ± 46 °C (T(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (Tzr) and ~ 785 ± 30 °C (T(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (Tzr) and ~ 850 ± 40 °C (T(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (Tzr) within the magma chamber, whereas the higher T(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H2O, whereas deeper melts contained 7 wt% H2O. Using these H2O contents, monazite saturation temperature (Tmz) estimates agree with Tzr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO2) melts. At inferred emplacement P–T conditions of 5 kbar and 730 °C, additional H2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.

Description: The tectonic regimes that drove the 1560–1490 Ma granitic magmatism c. 50 m.yr. after the final assembly of the Proterozoic supercontinent Nuna in NE Australia remain elusive. Collision between NE Australia (Mount Isa Inlier—MTI) and NW Laurentia (Georgetown Inlier—GTI) occurred at c. 1600 Ma and was associated with a west-dipping subduction zone, with the MTI as the upper plate and the GTI as the lower plate. Structural studies in the GTI showed that the collisional event involved 1600 Ma WNW-ESE shortening, followed by 1550 Ma WNW-ESE directed extension. During this later stage, a crustal-scale, west-dipping detachment fault-system juxtaposed middle- to lower-crustal levels, associated with voluminous, 1550 Ma S-type granites against greenschist facies upper crustal rocks. Regionally, post-collisional magmatism defines a westward, chemical, and temporal trend from 1560 to 1550 Ma, dominantly S-type confined to the lower plate (GTI) through c. 1545–1540 Ma I-/A-type (below the Carpenteria Basin) to 1540–1490 Ma A-type granites that intruded further west the Australian upper plate (eastern MTI). This transition from hydrous (S-type) granites in the east to drier (A-type) granites in the west is also supported by increasing zircon saturation temperatures and geochemical discriminators. Recent zircon Lu–Hf and new in-situ monazite Sm–Nd analyses in granites show increasingly radiogenic initial (at the time of crystallization) isotopic ratios from the GTI to the MTI, reflecting a concomitant westward increase in mantle input. Combined, these features suggest a spatio–temporal evolution of hotter and drier crustal conditions westward associated with progressive lithospheric extension. Classical Phanerozoic upper-plate delamination, slab break-off, and slab rollback and/or tearing tectonic models do not account for all the features of this post-collisional magmatic record. Alternatively, a hybrid tectonic scenario between fast–hard Indian and slow–soft Aegean collision better explains the attributes of Mesoproterozoic NE Australia during Nuna assembly.

Description: In this study, we examine whether the interhemispheric symmetry observed in broadband shortwave albedos also applies to the hemispheric-mean visible and near-infrared albedos. While several recent exploratory studies have examined this question using climate models, we explore this question using direct observations of the visible and near-infrared albedos collected by Nimbus-7, the last satellite with a near-infrared broadband radiometer. We find that the hemispheric-mean spectral partitioning of albedo is consistently and statistically significantly different between the two hemispheres. Consistent with prior studies, the origin of these differences is due to interhemispheric differences in cloud cover. Over oceans, the regional daily-mean differences between visible and near-IR albedos are closely correlated with cloud amount. The relative differences are maximized for clear-sky conditions and minimized for overcast conditions. Background: The shortwave albedo is a weighted sum of visible and near-infrared albedos. Under condensate-free conditions, the interactions of solar insolation in these bands with the atmosphere and surface are quite different. To an excellent approximation, the condensate-free atmosphere is a conservative Rayleigh-scattering medium in the visible. Solar radiation not reflected back to space is, to leading order, transmitted to the surface. In the near-infrared, the interactions of sunlight with the atmosphere are dominated by absorption. The solar radiation reaching the surface has therefore been reduced both by reflection to space and by absorption in the atmosphere. Hence, the relative partitioning of net TOA insolation between the visible and near-infrared bands will affect the relative partitioning between atmospheric absorption and transmission to the surface.