Variation in NbTa during differentiation of phonolitic magma,Tenerife, Canary Islands

Variation in $\text{Nb}\text{Ta}$ ratio through a suite of phonolitic volcanics is reported. Sphene, a phenocryst mineral, shows preferential incorporation of Ta relative to Mb, consistent with the bulk rock variation, where $\text{Nb}\text{Ta}$ increases with fractionation. Nb in these magmas may be partly present in the Nb³⁺ state.     

Alterations in guano phosphates and mio-pliocene carbonates of table mountain Santa Barbara,Curacao

The Table Mountain Santa Barbara, consisting of the Mio-Pliocene Seroe Domi Limestone Formation, was probably covered with a guano layer in the Pleistocene (?). Solutions, carrying guano-derived phosphate, percolated downwards, resulting in partial phosphatization of the underlying limestones. Only two phosphate minerals are present in the Table Mountain: apatite, and whitlockite.Phosphatization includes both replacement of the original carbonate or (pre-phosphate) dolomite, and cementation in primary- as well as secondary porosity (cryptocrystalline, isotropic phosphate cement, (micro)crystalline apatite, isopachous apatite fringe cement, multiple-zoned apatite crusts, rhombic whitlockite cements). Two factors controlled the final distribution of the phosphate within the Table Mountain. Firstly, changing positions of the sea level (and, therefore, of the diagenetic environments) determined the overall distribution of the phosphatized interval, a horizontal layer (98–128 m above sea level) sandwiched between two non-phosphatized limestone units.Original carbonate facies and -mineralogy was the second controlling factor causing the final variations in degree of phosphatization. The limestones comprise two lithofacies: (a) coralliferous limestone lenses erratically distributed amidst; and (b) micritic limestones. These coralliferous limestones are phosphatized preferentially forming so-called “phosphate pockets”, sharply outlined within a non-phosphatized micritic limestone “host”. These pockets are characteristically organized into five zones which are described in detail. Higher original porosity/permeability of the coralliferous limestone lenses as compared to the micrites, additionally enhanced by a phase of pre-phosphate dolomitization, determined preferential phosphatization of this facies type.A second controlling factor was the original carbonate mineralogy and resulting dia-     

Formation of the Green Tuff,Pantelleria

The strongly peralkaline Green Tuff, Pantelleria, is an example of a thin, densely welded air-fall tuff which mantles an area of at least 85 km². Offshore the tuff is correlated with the Y-6 ash layer in the central Mediterranean Sea, and the total volume of the eruption is estimated at 7 km³ D.R.E. New petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler, more fractionated upper zone relative to be bulk of the magma. Analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian-type eruption. It is shown that, due to the low viscosity of pantelleritic ejecta, dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm/minute is suggested for the Green Tuff; this yields an estimate for the eruption duration of rather less than one day. It is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma, and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism.     

Tectonostratigraphic development of the Trondheim region Caledonides, Central Norway

The metamorphic allochthon of the central Norwegian Caledonides comprises a complex of discrete nappes of metasediments and igneous rocks ranging in age from probable Svecofennian through Vendian to Silurian. This southeastward-translated allochthon overlies a thin cover of autochthonous Vendian to Cambrian sediments deposited upon a crystalline Precambrian basement, and is superseded by late-orogenic, intermontanebasinal sediments of latest Silurian to Middle Devonian age. Stratigraphical sequences in higher allochthonous units are floored by oceanic tholeiitic basalts with rare, subjacent sheeted-dyke and gabbro units, considered as fragments of an ophiolite assemblage which suffered initial eastward transport in pre-Middle Arenig times, an important orogenic event which is well represented in northern and southwestern Norway. The overlying Ordovician—Silurian sequences, disturbed by episodic parorogenic events, embrace a variety of sedimentary facies from shallow-water carbonates to deep-marine terrigenous turbidites and include both island arc and marginal basin lavas and intrusives. Polyphase Middle Silurian metamorphism and deformation resulted in a complex telescoping and dissection of the Lower Palaeozoic rocks and their Precambrian substrate, with nappe translation in the order of several hundred kilometres. Folding and thrusting of Old Red Sandstone molasse sediments attests to continuing tectonism well into Devonian times.     

Improved collection of rooftop micrometeorites through optimized extraction methods: The Budel collection

The scientific value of micrometeorites collected from deep-sea sediments or glacial deposits can be limited by poorly constrained accumulation times or severe alteration, coupled with a complex infrastructure of sampling expeditions. Collecting micrometeorites from rooftops has recently become a feasible alternative, but extraction methods have not been optimized or standardized to date. Here, we show that existing methods for the recovery of melted cosmic spherules (CSs) can be strongly improved by using a sequence of mineral separation techniques, including shape separation with an asymmetric vibrator and heavy liquid density separation with overflow centrifuges. We retrieved 1006 micrometeorites from the gutter of a barn in Budel, the Netherlands. Particle diameters are 80–515 μm, with the major mode at 130 μm and a slope exponent of −4.88. Differences in size distributions among various types of CSs indicate a multi-source influx, with CS textures controlled by their parent body's mineralogy and orbital parameters. Repeated sampling of the rooftop after accumulation times of 959 and 333 days allows for a time-integrated global mass flux estimate of 472 t year⁻¹. This estimate is notably higher than previous rooftop-based estimates but is still severely affected by micrometeorite loss from the gutter through drainage. The mass flux peaks at an equivalent particle diameter of ~200 μm. The Budel collection is the first rooftop collection to contain abundant vitreous micrometeorites and include the coarse-grained S-type CS class. Unmelted and I-type micrometeorites remain difficult to extract from rooftop samples. Vitreous micrometeorites display various stages of weathering, showing that severe alteration of glass can progress at a faster rate in populated regions than previously assumed. This study demonstrates that methodological adjustments can drastically increase the scientific potential of rooftop micrometeorite collections.     

The Santa Filomena meteorite shower: Trajectory,classification, and opaque phases as indicators of metamorphic conditions

On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15^o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr⁻¹.     

Agricultural land partitioning model based on irrigation efficiency using a multi‐objective artificial bee colony algorithm

In the process of agricultural land consolidation, the land parcels are optimally redesigned and rearranged in such a way that the dimensions of the resulting parcels are proportional to agricultural criteria such as irrigation discharge, soil texture, and cropping pattern. Besides these criteria, spatial factors like slope, road accessibility, volume of earthwork, and geometrical factors such as size and shape of parcels are also included in the design process of agricultural land partitioning. In this study, a land partitioning model was proposed using a multi‐objective artificial bee colony algorithm (MOABC‐LP) taking into consideration the mentioned factors. Initially, a feasible dimension range of parcels in a block was calculated based on irrigation efficiency. Two partitioning layouts were defined according to the topography and geometry of blocks. The proposed method was applied to a real study area and the results suggest that the land partitioning plan obtained by the MOABC‐LP model, in comparison with a designer's plan, not only makes the shape and size of parcels more compatible with the topographical and agricultural conditions of each block, but also reduces their cut‐and‐fill ratio.     

Planktonic diatom communities in temperate South-Central Chilean lakes with a focus on Asterionella formosa and the genus Aulacoseira

Journal of Paleolimnology - Paleolimnological records from temperate South-Central Chilean lakes revealed a recent and marked increase in the relative abundances of the key-planktonic diatom...