Early Archean tonalite gneiss in the upper peninsula of Michigan

Geochronological results on tonalite gneiss of northern Michigan that is 3.56 Ga or slightly older is presented. Tonalitic augen gneiss and structurally overlying biotite gneiss and schist are exposed in a dome near Watersmeet. They are part of an extensive gneiss terrane of southern Minnesota, Wisconsin and Michigan that includes rocks of early to late Archean ages and lies south of the Wawa volcanic subprovince. Two samples of the augen gneiss and one of the biotite gneiss show zircon grains of similar shape, zoning, color, and development of crystal faces. These zircons give Pb/U isotopic ratios that plot on a chord of 3,560 + or - 40 m.y. upper intersect and of 1,250 + or m.y. lower intersect. The 3,560 m.y. number is believed to be a minimum age because analysis of one of the least discordant zircon fractions by ion microprobe that gave a nearly concordant age of 3,650 m.y. The 1,250 m.y. lower intersect is without geological significance: it is interpreted to be a result of multiple lead loss at 2.7, 1.8, and 0.5 Ga by U/Pb in zircon. Archean rocks 10 to 25 km northwest of the Watersmeet dome give a 2.75 Ga age on zircons. Quartz monzonite here is dated at 2.65 Ga

A Geochronologic Study of a Granite Pluton from the Llano Uplift, Texas

Granite and related pegmatite and aplite from several localities within a pluton from the Llano uplift, Texas, are being studied geochronologically. Biotite, muscovite, hornblende, microcline, plagioclase, quartz, apatite, and fluorite have been analyzed by refined chemical and mass spectrometric methods in order to determine the consistency in ages between various minerals and between different localities within an individual pluton. Field and petrologic evidence suggests that this intrusive has had a simple history of emplacement and no later metamorphism. Quadruplicate analyses on a master biotite yield K-Ar and Rb-Sr ages reproducible to 1 per cent. In most cases K-Ar determinations on biotites, muscovites, and hornblendes and Rb-Sr determinations on biotites, muscovites, and microclines give ages which fall within a 5 per cent spread. A half-life of 1.307 X 10^9 years and a branching ratio of 0.124 are used to calculate the K-Ar ages, and Rb-Sr ages are calculated with a half-life of 50 X 10^9 years. The average age of the pluton thus determined is 1060 m.y. K-Ar determinations on microclines give ages which are 5 to 15 per cent lower. One plagioclase from the granite gives a K-Ar age of 920 m.y. Two suites of biotites, one from pegmatites and one from a border facies of the granite, give anomalously low Rb-Sr ages. The pegmatitic biotite also has a somewhat low K-Ar age; however, the biotite from the granite gives a normal age by this method, as do coexisting microclines from both these rocks by the Rb-Sr method. Geologic evidence suggests that meteoric or hydrothermal fluids may have been responsible for this age discrepancy. Ages determined on a gneiss, a pegmatite cutting the gneiss, and a granite porphyry all give results approximately equal to those of the granite. No evidence of a significantly older basement rock or a younger igneous or metamorphic event in the area has been obtained to date

Helium, argon, and carbon in some natural gases

Thirty-nine samples of natural gases representing varied chemical compositions and geological occurrences were analyzed for their helium, radiogenic argon, and atmospheric argon contents. The total range in the (He/A)_(rad) ratio was found to be 1.6 to 130 with most samples having values between 6 and 25. This range of values is essentially equal to the production ratio from the uranium, thorium, and potassium in average igneous rocks and a wide variety of sediments. This indicates that all of these natural gases have obtained their radiogenic gases from rather average rock types. This is true in spite of the fact that the gases range in helium content from 37 to 62,000 ppm. A theoretical discussion of the origin of helium and argon in natural gases is given. It can be shown from the ratio of nitrogen to atmospheric argon that most of the nitrogen in these gases cannot come from the entrapment of air. From a consideration of the concentration of atmospheric argon in natural gases it is possible to estimate the proportion of gaseous and aqueous phases assuming diffusive equilibrium. The isotopic composition of the carbon in the methane of these gases was found to be very light. It was shown that for coexisting CH_4-CO_2 pairs the carbon dioxide was always isotopically heavier

From domestic to regional: The civil war conundrum and the cases of Syria and Algeria

This paper seeks to answer a simple question: When do regional powers get involved in civil wars? Some civil wars see a significant involvement of regional actors, while others show a remarkable level of isolation. What explains this difference? This research answers this question by looking at two case studies: the Algerian civil war (1991–2002) and the Syrian civil war (2011–up to date). The paper identifies and develops five factors of regional involvement. These are: capabilities, regional dynamics, country’s relevance, regional security issues/containment and domestic–external links. civil wars are today one of the most prominent and deadly forms of conflict, and this paper contributes to understanding the important but understudied issue of regional involvement.N/

From ‘Unilateral’ to ‘Dialogical’: Determinants of EU–Azerbaijan Negotiations

The European Union (EU) and Azerbaijan have negotiated three different agreements for a new legal basis underpinning their relationship since 2010. Whereas the EU tries to adhere to a more unilateral approach, Azerbaijan wants cooperation to take place on a more inclusive, dialogical, basis. The essay will present a model of ‘bargaining power’ to analyse how the Azerbaijani government has tried to enforce this, and to what degree it has been successful. It finds that the bargaining power model can explain some of the changing power dynamics in EU–Azerbaijan relations, and that these might speak to the broader Eurasian region too

The Amazon Epiphyte Network: A First Glimpse Into Continental-Scale Patterns of Amazonian Vascular Epiphyte Assemblages

Epiphytes are still an understudied plant group in Amazonia. The aim of this study was to identify distributional patterns and conservation priorities for vascular epiphyte assemblages (VEA) across Amazonia. We compiled the largest Amazonian epiphyte plot database to date, through a multinational collaborative effort of 22 researchers and 32 field sites located across four Amazonian countries – the Amazonian Epiphyte Network (AEN). We addressed the following continental-scale questions by utilizing the AEN database comprising 96,448 epiphyte individuals, belonging to 518 vascular taxa, and growing on 10,907 tree individuals (phorophytes). Our objectives here are, first, to present a qualitative evaluation of the geographic distribution of the study sites and highlight regional lacunae as priorities for future quantitative inventories. Second, to present the floristic patterns for Amazonia-wide VEA and third, to combine multivariate analyses and rank abundance curves, controlled by major Amazonian habitat types, to determine how VEA vary geographically and ecologically based on major Amazonian habitat types. Three of the most striking patterns found are that: (1) VEA are spatially structured as floristic similarity decays with geographic distance; (2) a core group of 22 oligarchic taxa account for more than a half of all individuals; and (3) extensive floristic sampling gaps still exist, mainly across the highly threatened southern Amazonian deforestation belt. This work represents a first step toward unveiling distributional pattern of Amazonian VEA, which is important to guide future questions on ecology and species distribution ranges of VEA once the collaborative database grows allowing a clearer view of patterns

Comprehensive phylogenomic time tree of bryophytes reveals deep relationships and uncovers gene incongruences in the last 500 million years of diversification

Premise: Bryophytes form a major component of terrestrial plant biomass, structuring ecological communities in all biomes. Our understanding of the evolutionary history of hornworts, liverworts, and mosses has been significantly reshaped by inferences from molecular data, which have highlighted extensive homoplasy in various traits and repeated bursts of diversification. However, the timing of key events in the phylogeny, patterns, and processes of diversification across bryophytes remain unclear. Methods: Using the GoFlag probe set, we sequenced 405 exons representing 228 nuclear genes for 531 species from 52 of the 54 orders of bryophytes. We inferred the species phylogeny from gene tree analyses using concatenated and coalescence approaches, assessed gene conflict, and estimated the timing of divergences based on 29 fossil calibrations. Results: The phylogeny resolves many relationships across the bryophytes, enabling us to resurrect five liverwort orders and recognize three more and propose 10 new orders of mosses. Most orders originated in the Jurassic and diversified in the Cretaceous or later. The phylogenomic data also highlight topological conflict in parts of the tree, suggesting complex processes of diversification that cannot be adequately captured in a single gene-tree topology. Conclusions: We sampled hundreds of loci across a broad phylogenetic spectrum spanning at least 450 Ma of evolution; these data resolved many of the critical nodes of the diversification of bryophytes. The data also highlight the need to explore the mechanisms underlying the phylogenetic ambiguity at specific nodes. The phylogenomic data provide an expandable framework toward reconstructing a comprehensive phylogeny of this important group of plantsFunding was provided by the NSF collaborative project “Building a Comprehensive Evolutionary History of Flagellate Plants” (DEB #1541506 to J.G. Burleigh, E.C. Davis, S.F. McDaniel, and E.B. Sessa, and #1541545 to M von Konrat). B.G. acknowledges DEB‐1753811. J.C.V.A. acknowledges the Canada Research Chair (950‐232698); the CRNSG‐RGPIN 05967–2016 and the Canadian Foundation for Innovation (projects 36781, 39135). The authors thank the two anonymous reviewers and the Associate Editor for their constructive comments on previous versions of the manuscrip

Local spatial structure of forest biomass and its consequences for remote sensing of carbon stocks

Advances in forest carbon mapping have the potential to greatly reduce uncertainties in the global carbon budget and to facilitate effective emissions mitigation strategies such as REDD+. Though broad scale mapping is based primarily on remote sensing data, the accuracy of resulting forest carbon stock estimates depends critically on the quality of field measurements and calibration procedures. The mismatch in spatial scales between field inventory plots and larger pixels of current and planned remote sensing products for forest biomass mapping is of particular concern, as it has the potential to introduce errors, especially if forest biomass shows strong local spatial variation. Here, we used 30 large (8–50 ha) globally distributed permanent forest plots to quantify the spatial variability in aboveground biomass (AGB) at spatial grains ranging from 5 to 250m (0.025–6.25 ha), and we evaluate the implications of this variability for calibrating remote sensing products using simulated remote sensing footprints. We found that the spatial sampling error in AGB is large for standard plot sizes, averaging 46.3% for 0.1 ha subplots and 16.6% for 1 ha subplots. Topographically heterogeneous sites showed positive spatial autocorrelation in AGB at scales of 100m and above; at smaller scales, most study sites showed negative or nonexistent spatial autocorrelation in AGB. We further show that when field calibration plots are smaller than the remote sensing pixels, the high local spatial variability in AGB leads to a substantial “dilution” bias in calibration parameters, a bias that cannot be removed with current statistical methods. Overall, our results suggest that topography should be explicitly accounted for in future sampling strategies and that much care must be taken in designing calibration schemes if remote sensing of forest carbon is to achieve its promise