Meta-analysis from different tracers of the small Local Arm around the Sun—extent,shape, pitch,origin

The Sun in not located in a major spiral arm, and sits in a small ‘Local Arm’ (variously called arm, armlet, blob, branch, bridge, feather, finger, segment, spur, sub-arm, swath, etc.). The diversity of names for the ‘Local Arm’ near the Sun indicates an uncertainty about its shape or pitch or its extent from the Sun in each galactic quadrant, as well as an uncertainty about its origin.Here we extract data about the small ‘Local Arm’ near the Sun, from the recent observational literature, over many arm tracers, and we use statistics in order to find the local arm’s mean extent from the Sun, its possible shape and pitch angle from the direction of galactic longitude \(90^{\circ}\). Employing all tracers, the Local Arm is about 4 kpc long by 2 kpc large. The Sun is within 1 kpc of the center of the local arm. Proposed ‘bridges’ and ‘fingers’ are assessed. These bridges to nearby spiral arms and fingers across spiral arms may not reach the nearest spiral arms, owing to kinematic and photometric distance effects.We then compare these statistical results with some predictions from recent models proposed to explain the local arm (perturbations, resonances, density wave, halo supercloud, debris trail from a dwarf galaxy).The least controversial models involve importing materials from elsewhere (halo supercloud, debris trail) as a first step, and to be later deformed in a second step (by the Galaxy’s differential rotation into become roughly parallel to spiral arms) and then subjected to ongoing forces (global density waves, local perturbations).     

Estimation of aboveground biomass and carbon in a tropical rain forest in Gabon using remote sensing and GPS data

The knowledge of biomass stocks in tropical forests is critical for climate change and ecosystem services studies. This research was conducted in a tropical rain forest located near the city of Libreville (the capital of Gabon), in the Akanda Peninsula. The forest cover was stratified in terms of mature, secondary and mangrove forests using Landsat-ETM data. A field inventory was conducted to measure the required basic forest parameters and estimate the aboveground biomass (AGB) and carbon over the different forest classes. The Shuttle Radar Topography Mission (SRTM) data were used in combination with ground-based GPS measurements to derive forest heights. Finally, the relationships between the estimated heights and AGB were established and validated. Highest biomass stocks were found in the mature stands (223 ± 37 MgC/ha), followed by the secondary forests (116 ± 17 MgC/ha) and finally the mangrove forests (36 ± 19 MgC/ha). Strong relationships were found between AGB and forest heights (R² > 0.85).     

地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演化──Ⅰ．实验研究

在温度为ｌｌ３０─ｌ４５０℃，压力为０．４─２．０ＧＰａ条件下，实验研究了地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演变。在部分熔融中，随熔融度的增大，橄榄石的Ｍｇ／（Ｍｇ＋Ｆｅ）尖晶石和斜方辉石的Ｍｇ／（Ｍｇ＋Ｆｅ）及Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；而橄榄石中的Ｃａ含量增至单斜辉石消失后逐渐降低；尖晶石中的Ｔｉ以较低的含量（ＴｉＯ２＜０．１５％）保持不变或稍有降低；斜方辉石中的Ｔｉ含量及单斜辉石的Ｎａ和Ｔｉ含量逐渐降低，直至非常小的值。在从尖晶石橄榄岩向斜长石橄榄岩的相转变过程中，尖晶石强烈富Ｔｉ，且其Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；斜方辉石中的Ｔｉ含量和Ｃｒ／（Ｃｒ＋Ａｌ）同时逐渐增大；单斜辉石中的Ｎａ含量降低而Ｔｉ含量升高或保持不变。当斜长石橄榄岩经受了部分熔融（即使很微弱），其在相转变过程中引起的各矿物相的化学成分特征要全部消失，而表现部分熔融作用的特征。这可作为判别橄榄岩在斜长石相域内是否经历了部分熔融的标志。关键词     

Cooling kinetics of garnet websterites from the Freychinède orogenic lherzolite massif,French Pyrenees

Clinopyroxene and orthopyroxene megacrysts with lamellar intergrowths of pyroxenes and garnet rarely survive in pyroxenite layers from the exposed spinel-lherzolite massifs because of the emplacement history into the crust. Such features are remarkably preserved in some thick bands (up to 1 m) from the Freychinède ultramafic body (Ariège, French Pyrenees). These bands display a symmetrical zoning from the edges to the centre due to the concurrent decrease of orthopyroxene/clinopyroxene and spinel/garnet modal ratios. Textural and chemical data suggest that the present pyroxenite parageneses resulted from subsolidus recrystallization of magmatic assemblages composed of Al-rich orthopyroxene and clinopyroxene with minor spinel. These primary assemblages were changed by subsolidus recrystallization connected with an isobaric cooling at upper-mantle depth (45–50 km) from solidus temperature (1250°C) down to steady equilibrium temperature (950° C). The primary Al-rich ortho-and clinopyroxenes behaved differently on cooling. In a first stage, orthopyroxene exsolved concomitant Al-rich clinopyroxene and garnet, whereas clinopyroxene exsolved only Al-rich orthopyroxene. The garnet exsolution in clinopyroxene host is delayed to lower temperatures. This multistage process could account for the contrasting shapes of diffusion gradients adjacent to exsolved garnet, which tend to be flat in host-orthopyroxene and steep in host-clinopyroxene. An independent thermal modelling, together with available Al-diffusion data in clinopyroxene, allows us to define a fast magmatic cooling followed by a two-stage subsolidus cooling (35° C/year^-6 from 1250° C to 1050° C and 9° C/year^-6 to 900° C). This matches the contrasted exsolution sequences observed in the pyroxene megacrysts.     

U–Pb zircon (TIMS and SIMS) and Sm–Nd whole-rock geochronology of the Gour Oumelalen granulitic basement, Hoggar massif, Tuareg shield, Algeria

Two major granulitic units are recognized in the Gour Oumelalen area. One of the units is composed partially of Archean gneisses (Red Gneiss complex) with U–Pb zircon SIMS and TIMS ages of approximately 2.7 Ga. Although they were formed from 3.0- to 3.2-Ga-old precursors, as indicated by Nd model ages, we find no evidence of any older history (≈3.5 Ga) as suggested by previous Pb–Pb ages. The other formation (Gour Oumelalen supergroup) is a metasedimentary sequence at least partly of Paleoproterozoic age, as indicated by zircon dates of a metavolcanic rock at approximately 2.2 Ga. A later magmatic event is recorded at approximately 1.9 Ga in both units and related to coeval granulite-facies metamorphism that affected both units. Nd model ages at approximately 2.0 Ga suggest an accretion of juvenile crust formation at that time. The existence of T_DM Nd model ages intermediate between 2.5 and 2.9 Ga could result from the mixing of 3.2 and 2.0-Ga-old material or may reflect separate events.     

Populism or Petrostate?: The Afterlives of Ecuador’s Yasuní-ITT Initiative

In 2007, the Government of Ecuador announced the Yasuní-ITT Initiative: a proposal to forego exploiting 20% of its oil reserves located in the Yasuní National Park – home to one of the earth’s most biodiverse places and several indigenous groups living in voluntary isolation. In exchange, Ecuador asked the international community for $3.6 billion, roughly half the projected revenues of conventional oil extraction. Five years later, Ecuador received less than 10% of the required pledges and the initiative was canceled. Many accounts emphasized the then President Rafael Correa’s perceived untrustworthiness as key in explaining the initiative’s failure. This article instead examines the role of entrenched institutions of the petrostate, emphasizing how the initiative defied expectations by offering a post-extractivist path for Ecuador. Despite its failure, this horizon continues to orient debates on development and extractivism, forming “afterlives” of a call to mitigate climate change by leaving oil in the ground.     

On the Accuracy of the Calibration of Superconducting Gravimeters Using Absolute and Spring Sensors: a Critical Comparison

Over the past two decades, superconducting gravimeters (SGs) have been a key tool to investigate a number of geophysical processes leading to time-variable gravity changes. As SGs are relative meters, even though they are the most sensitive and stable devices currently available, they need to be accurately calibrated. Each branch of Earth sciences that benefits from high-precision gravity monitoring demands calibration of gravity sensors to accuracy of better than 0.1%. This research deals with a calibration experiment performed at the Strasbourg (France) SG site by means of two FG5 (#206 and #211) absolute gravimeters (AGs) and new-generation spring meters (Scintrex Ltd. Autograv CG-3M and CG5 and Microg-LaCoste gPhone). Our goal is to try to use the newest generation of spring mechanical gravimeters (MGs) for calibrating SGs. We discuss the results in terms of precision and accuracy of the SG calibration by means of different metrological and methodological approaches. With the FG5 #211 we derive scale factors for the SG-GWR C026 located in Strasbourg in agreement with those routinely obtained since 1997 by means of the FG5 #206. This confirms that the estimation of the scale factors is independent of the AG sensor. From a moving-window regression analysis between the synthetic body tides and both the SG and MG gravity records we detect significant fluctuations of the SG scale factors over time due to the instability of the instrumental sensitivity of the MGs. Our main results demonstrate that, owing to the time variability of their sensitivity, the used spring meters, even if well calibrated, cannot be used as a stable reference for SGs. As a result, MGs are not suitable to replace AGs for SG calibration, and we conclude that currently the method using parallel recording with absolute gravity meters is still the most feasible calibration approach for SGs.     

Timing of initiation of extension in the Tianshan,based on structural,geochemical and geochronological analyses of bimodal volcanism and olistostrome in the Bogda Shan (NW China)

This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit. The turbidite unit is mainly composed of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and diabase dykes intrude these three units. Geochemically, rhyolites are characterized by high ACNK value of >1.1, depletion of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in K₂O, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) zircon U–Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked to an extensional setting that developed in the south of the Bogda Shan. Several lines of evidence, e.g. occurrence of large-scale strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data, demonstrate a significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous–Permian boundary times, and the peak period of intra-plate magmatism occurred in the interval of 300–250 Ma.     

The Wasatch Environmental Observatory: A mountain to urban research network in the semi-arid western US

The 2085 km² Jordan River Basin, and its seven sub-catchments draining the Central Wasatch Range immediately east of Salt Lake City, UT, are home to an array of hydrologic, atmospheric, climatic and chemical research infrastructure that collectively forms the Wasatch Environmental Observatory (WEO). WEO is geographically nested within a wildland to urban land-use gradient and built upon a strong foundation of over a century of discharge and climate records. A 2200 m gradient in elevation results in variable precipitation, temperature and vegetation patterns. Soil and subsurface structure reflect systematic variation in geology from granitic, intrusive to mixed sedimentary clastic across headwater catchments, all draining to the alluvial or colluvial sediments of the former Lake Bonneville. Winter snowfall and spring snowmelt control annual hydroclimate, rapid population growth dominates geographic change in lower elevations and urban gas and particle emissions contribute to episodes of severe air pollution in this closed-basin. Long-term hydroclimate observations across this diverse landscape provide the foundation for an expanding network of infrastructure in both montane and urban landscapes. Current infrastructure supports both basic and applied research in atmospheric chemistry, biogeochemistry, climate, ecology, hydrology, meteorology, resource management and urban redesign that is augmented through strong partnerships with cooperating agencies. These features allow WEO to serve as a unique natural laboratory for addressing research questions facing seasonally snow-covered, semi-arid regions in a rapidly changing world and an excellent facility for providing student education and research training.