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Late Hercynian porphyritic biotite granites of the Viseu region (Central Portugal) develop a 2 km wide contact aureole on older Hercynian muscovite-biotite granites. Several textural, mineralogical and geochemical transformations were recognized in the two-mica granites of the aureole. The most relevant mineralogical transformation is the progressive breakdown of muscovite, decreasing the modal abundance on average from ca. 11% to less than 2% near the contact; muscovite is replaced by K-feldspar, which increases modally from ca. 17 to 33%. Other dehydration reactions involving the breakdown of muscovite occur within 500 m of the contact producing andalusite, sillimanite and corundum, suggesting that temperatures higher than 600 ºC were probably reached. K-feldspar is less ordered and dominantly monoclinic close to the contact. Geochemical data from the muscovite-biotite Salgueiral granite obtained along a traverse and corroborated with other regional data indicate an important decrease in the abundances of the following elements towards the contact: P2O5, H2O, Li, F, Rb, Cs, Sn, Nb and probably W. The loss of most of these elements can be explained by the breakdown of muscovite, which is an important reservoir of water and many trace elements in the two-mica granites. Mineral δ18O and δD results show that no significant interaction with meteoric water has occurred; some degree of homogenization recognized through the aureole suggests, however, that interaction with dehydration fluids of composition close to magmatic was developed. From the data, a model emerges in which the breakdown of muscovite provided the release of ore forming elements and part of the fluid necessary for the development of a closed hydrothermal system, which resulted in the generation of a large number of Sn-W ore deposits, in the form of small mineralized quartz veins spatially related to the contact aureole.

Classification systems for corundum deposits have evolved over time and are based on different mineralogical and geological features. An enhanced classification for ruby deposits based on the geological environment, degree of metamorphism, styles of mineralization and the pressure-temperature conditions of formation is proposed :Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) Tectonic magmatic-related, and (Type II) Tectonic metamorphic-related.Type I is characterized by two sub-types: Type IA where xenocrysts or xenoliths of gem ruby of metamorphic origin are hosted by alkali basalts (Madagascar and others); and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo).Type II has two sub-types hosted either in metamorphic deposits sensu stricto (Type IIA) formed in the amphibolite to granulite facies, or metamorphic-metasomatic deposits (Type IIB) formed via high fluid-rock interaction and metasomatism:- Sub-Type IIA1 includes ruby in metamorphosed mafic and ultramafic rocks (M-UMR) as found at Montepuez (Mozambique) and Aappaluttoq (Greenland);- Sub-Type IIA2 concerns rubies in marble such those from the Mogok Stone Track (Myanmar), and from central and eastern Asia;- Sub-Type IIB1 corresponds to desilicated pegmatites i.e., plumasite in M-UMR as in the Rockland mine (Kenya) or Polar Urals (Russia);- Sub-Type IIB2 is characterized by ruby in shear zone-related or fold hinge-controlled deposits in different substrata, mainly ruby-bearing Mg-Cr-biotite schist (metamorphosed M-UMR) and marble. It includes the ruby occurrences of Zazafotsy (Madagascar), Kerala (southern India), Mahenge (Tanzania), and the Hokitika deposit (New-Zealand). Secondary ruby deposits i.e., placers, are termed Tectonic sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, silt) that formed due to erosion, gravity, mechanical transport and sedimentation along slopes or basins related to neotectonic movements. These are divided in two main sub-types:- Sub-Type IIIA i.e., gem placers in alkali basalt or kimberlite environments as in eastern Australia, central Madagascar, and the Democratic Republic of Congo;- Sub-Type IIIB i.e., gem placers in metamorphic environments such as at Montepuez in Mozambique or the Mogok Stone Track in Myanmar.- Sub-Type IIIC i.e., gem placers with ruby originating from multiple and unknown sources such as at Ilakaka (Madagascar), Tunduru and Songea (Tanzania).

Existing radio-isotopic age constraints indicate that the global Palaeoproterozoic Lomagundi-Jatuli large, positive carbonate carbon isotopic excursion, with δ13C values >+5‰, occurred between 2.2 and 2.06 Ga. In the North Transfennoscandian Greenstone Belt of the Kola Peninsula, NW Russia, northern Norway and Finland, the Lomagundi-Jatuli Event is recorded in the carbonate rocks of the Umba and Kuetsjärvi Sedimentary Formations in the Imandra-Varzuga and Pechenga greenstone belts. In both areas, thick mafic volcanic units (Umba and Kuetsjärvi Volcanic Formations) overlie the carbon isotopic excursion-bearing sedimentary units. Overlying and younger sedimentary units contain carbonate rocks with δ13C values typically ranging between c. −1 and +3‰, signalling the termination of the Lomagundi-Jatuli excursion.Two new U–Pb ID-TIMS (isotope-dilution thermal ionisation mass spectrometry) zircon dates constrain this termination in both successions. The lower unit of the Il’mozero Sedimentary Formation is a cross- and parallel-bedded volcaniclastic greywacke derived largely from erosion of the underlying Umba Volcanic Formation. It has yielded detrital zircons with 207Pb/206Pb dates as young as 2055.5 ± 2.3 Ma, which is a maximum age for deposition and is inferred to date part of the underlying Umba volcanics. In Pechenga, the Kolosjoki Sedimentary Formation was intersected by a drill hole obtained by the ICDP (International Continental Scientific Drilling Program)-supported FAR-DEEP (Fennoscandian Arctic Russia-Drilling Early Earth Project) drilling programme. Zircons from a mafic fine tuff in this drill core have yielded a 207Pb/206Pb age of 2056.6 ± 0.8 Ma. This age is interpreted as an eruption age contemporaneous with sedimentation. The new age determinations overlap each other within uncertainty, and is within error of previously published detrital zircon ages of 2058 ± 2 Ma from the Kolosjoki Sedimentary Formation and 2049 ± 28 Ma from the Kuetsjärvi Volcanic Formation. Combined, these indicate that the Lomagundi-Jatuli excursion terminated across Fennoscandia by 2056.6 ± 0.8 Ma and may correlate with similar termination ages in Fennoscandia and the Transvaal, South Africa.

APM, DJC, ARP and AEF were supported by NERC grant NE/G00398X/1. Organic-rich rocks (averaging 2–5% total organic carbon) and positive carbonate-carbon isotope excursions (δ13C > 5‰ and locally much higher, i.e. the Lomagundi-Jatuli Event) are hallmark features of Palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c. 2.3 Ga Great Oxidation Event. Here we combine new and published geochronology that shows that the main Palaeoproterozoic carbon burial episodes (CBEs) preserved in Russia, Gabon and Australia were temporally discrete depositional events between c. 2.10 and 1.85 Ga. In northwest Russia we can also show that timing of the termination of the Lomagundi-Jatuli Event may have differed by up to 50 Ma between localities, and that Ni mineralisation occurred at c. 1920 Ma. Further, CBEs have traits in common with Mesozoic Oceanic Anoxic Events (OAEs); both are exceptionally organic-rich relative to encasing strata, associated with contemporaneous igneous activity and marked by organic carbon isotope profiles that exhibit a stepped decrease followed by a stabilisation period and recovery. Although CBE strata are thicker and of greater duration than OAEs (100 s of metres versus metres, ∼106 years versus ∼105 years), their shared characteristics hint at a commonality of cause(s) and feedbacks. This suggests that CBEs represent processes that can be either basin-specific or global in nature and a combination of circumstances that are not unique to the Palaeoproterozoic. Our findings urge circumspection and re-consideration of models that assume CBEs are a Deep Time singularity. Postprint

Nutrient supply, uptake and cycling underpin high primary productivity over the continental shelf of the west Antarctic Peninsula (WAP). Here we use a suite of biogeochemical and isotopic data collected over five years in northern Marguerite Bay to examine these macronutrient dynamics and their controlling biological and physical processes in the WAP coastal ocean. We show pronounced nutrient drawdown over the summer months by primary production which drives a net seasonal nitrate uptake of 1.83 mol N m-2 yr-1, equivalent to net carbon uptake of 146 g C m-2 yr-1. High primary production fuelled primarily by deep-sourced macronutrients is diatom-dominated, but non-siliceous phytoplankton also play a role. Strong nutrient drawdown in the uppermost surface ocean has the potential to cause transient nitrogen limitation before nutrient resupply and/or regeneration. Interannual variability in nutrient utilisation corresponds to winter sea ice duration and the degree of upper ocean mixing, implying susceptibility to physical climate change. The nitrogen isotope composition of nitrate (δ15NNO3) shows a utilisation signal during the growing seasons with a community-level net isotope effect of 4.19 ± 0.29‰. We also observe significant deviation of our data from modelled and observed utilisation trends, and argue that this is driven primarily by water column nitrification and meltwater dilution of surface nitrate. This study is important because it provides a detailed description of the nutrient biogeochemistry underlying high primary productivity at the WAP, and shows that surface ocean nutrient inventories in the Antarctic sea ice zone can be affected by intense recycling in the water column, meltwater dilution and sea ice processes, in addition to utilisation in the upper ocean.

Two Palaeoproterozoic events have particularly interested Earth scientists. These are the global Lomagundi–Jatuli Event, the greatest magnitude positive carbonate carbon isotope excursion in Earth history, and the Shunga Event, the world’s largest organic carbon burial event. Analysis of newly acquired high-resolution C–O isotope data and U–Pb zircon geochronology refine understanding of carbon isotope characteristics and timing of deposition of the Palaeoproterozoic Loch Maree Group of NW Scotland. Petrographic examination reveals a basal unconformity between the Loch Maree Group and Archaean basement, permitting a stratigraphy and younging direction to be assigned. Detrital zircon ages from immediately above the unconformity are dated at c. 2.3 Ga. δ13Ccarbonate data on two temporally discrete carbonate packages range from c. +15 to 2‰ in the older unit and c. 2 to −5‰ in the younger carbonate unit. Current age constraints indicate that the Loch Maree Group is too young to be fully coeval with the Lomagundi–Jatuli Event but is within the age range of the Shunga Event. This revives consideration of a straightforward mass-balance process involving burial of organic carbon as an explanation for at least some of the C-cycle perturbations of Palaeoproterozoic time.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration.

WOS: 000073374500006, The Ana Yatak massive sulfide deposit is located in the Ergani-Maden District of south-eastern Turkey and has been a major source of copper for more than 4,000 years. The mineralization is hosted by strongly chloritized serpentinite, gabbro, diabase, and mudstone. The ore body is similar to 600 x 250 m in maximum dimension, mainly consists of pyrite and chalcopyrite, and locally contains abundant magnetite, pyrrhotite, and chromite. The gangue contains predominantly chlorite, rarely quartz. This paper is mainly concerned with an investigation of the sulfur-isotope systematics of the Ana Yatak deposit. Pyrite and chalcopyrite from the ore and pyrite from the host; rocks were sampled and analyzed to determine their delta(34)S composition. delta(34)S values were found to vary within the range from +4.5 to +9.3 parts per thousand for pyrites (mean delta(34)S = +6.5 +/- 1.8) and from +4.5 to +10.0 for chalcopyrites (mean delta(34)S = +6.7 +/- 1.9) of the ore, and from -5.8 to +8.8 for pyrites (mean delta(34)S = +7.3 +/- 1.3) of the host reck. The delta(34)S compositions of all samples were found to vary from +4.5 to +10.0 parts per thousand. For the chalcopyrite-pyrite pairs, there is a clear relationship of approximately equal delta(34)S values at each sampling site. Frequency distribution of the delta(34)S values is not unimodal and exhibits two peaks. The range of sulfur-isotope systematics implies that the Ana Yatak mineralization was influenced to a greater extent by seawater than by hydrothermal fluids.