Volcanic Plateau Research Articles

Comparing morphological investigation with χ index and gilbert metrics for analysis of drainage rearrangement and divide migration in inland plateaus

Drainage rearrangements and consequently divide migration are important processes in the dynamic evolution of landscapes. Two approaches have been used to identify, analyze, and describe these processes: traditional studies based on morphological and sedimentary evidence; and topographic metrics analysis, highlighting the χ index and Gilbert's three metrics (gradient, relief, and elevation). However, the two approaches have not been tested together for catchments located in areas of tectonic stability and low relief (i.e., inland plateaus). The present study uses traditional methods (morphological evidence) and topographic metrics to analyze drainage rearrangements and divide migration in an inland volcanic plateau: the high drainage divide between the Uruguai and Paraná rivers (two of the largest basins in South America). The results indicate that drainage divides in low reliefs with symmetrical characteristics on both sides have different behaviour of divide migration than asymmetrical ones. For symmetrical divides, past, present and future trends of mobility may occur in different directions, resulting in a back-and-forth movement. Because of similarities on both sides of the divide, local factors such as structural lineaments can be the lead causes of the imbalance that induces bidirectional migration. In this sense, current/future migration trends predicted by topographic metrics may not relate to the way the divide moved in the past. On the other hand, traditional analysis of evidence of stream capture does not guarantee that the drainage divide behaves the same in the present and/or in the future. Therefore, the combination of the two approaches can be helpful to better understand drainage divide migration dynamics through time, especially in areas of low relief such as inland plateaus.

Identification and Geomorphometric Characterization of Volcanic Cones in the Marius Hills, the Moon

AbstractInvestigation of the detailed geological characteristics of lunar volcanic cones can peer into their formation and emplacement processes, thus deepening our understanding of pyroclastic eruptions on the Moon. In this work, we focus on the Marius Hills region (centered at 13°N, 55°W), a volcanic plateau in south Oceanus Procellarum, which hosts the most abundant volcanic cones on the Moon, along with other volcanic features. The range of volcanic features indicates various eruption styles and complicated sequences of regional magmatic activities. Based on the SLDEM2015 topography data, with assistance from other multisource topography and image data sets, we identified 360 known and suspected volcanic cones and 22 volcanic domes in the Marius Hills. Following detailed morphological characterizations, the volcanic cones show various morphology types, including C‐shaped, elliptical‐shaped, elongated‐shaped, irregular‐shaped, and rounded‐shaped. The cones (median basal width ∼2.7 km, height ∼115 m, and volume 0.25 km3) contain summit pit craters (15%; median width ∼358 m), exhibiting smaller basal widths and summit pit crater widths compared with lunar mare domes. The mean slope (3.5°–15.6°) and rock abundance (0.3%–3.8%) of volcanic cones in Marius Hills are larger than those of the mare dome, suggesting different eruption mechanisms. Marius Hills cones also show larger basal widths and smaller height/width ratios than terrestrial volcanic cones, which are attributed to multiple factors, including subaerial environment, volatile content of the magma, eruption rate, and lava viscosity.

Multimodal Remote Sensing Applications in the Etruscan-Roman City of Vulci

ABSTRACT Vulci (Viterbo Province, Italy) was one of the most important Etruscan city-states in the 1st millennium b.c. and became a Roman city in 280 b.c. The habitation site had over 1500 years of continuous life and a very large funerary area around the volcanic plateau. An international research cooperation investigated the site in 2014–2019 using remote sensing technologies and conducting archaeological excavations in the urban area. This paper presents the integrated application of remote sensing methods, which include multispectral unmanned aerial vehicles, aerial photography, and high-resolution georadar measurements. The multimodal application of active and passive sensors permitted a multilayered identification of archaeological features and led to substantial new interpretations of the rich archaeological landscape, which calls for a reconsideration of traditional scholarly narratives of Vulci’s history.

Nature and sources of anomalous contamination of basalt magmas (Shufan plateau, Russian Far East)

When the primary mantle melts, the crustal contamination of basaltic magmas distorts the source composition of the melting substrate and the degree of its trace element and isotopic enrichments. Such contamination is also important in understanding the interactions of contrasting structures of melts with mafic and felsic compositions or solid-phase systems (xenoliths) and the capacity of basaltic magmas in relation to the volumes of assimilation of incoherent highly polymerized crustal matter. First, the mechanism of diffusive interaction with crustal matter in nonsuperheated magmas is of interest when elements coherent to the melt or structural groups near the emerging cluster groups of the melt are extracted from xenoliths. Second, the selectivity of the contamination is of interest. The features of interactions between contrasting magmatic melts and melt-solid phase systems (melt-xenolith) are considered by analyzing the reaction products of such interactions, i.e., basalts contaminated with acid aluminosilicate matter and buchites (crustal xenoliths subjected to chemical modification and melting). For the largest late Miocene Shufan basalt plateau in southern Primorye (Russia), a process that involves the contamination of tholeiitic basalts with crustal aluminosilicate matter, which is unique in scale, has been recognized. As a result, large volumes of andesite–trachyandesite formed, which compose the upper horizons of the volcanic plateau. They are represented by massive “nonvesicular” lavas with banded texture caused by oriented layers of silicic potassium granophyre immiscible felsic selective melts from xenoliths. Two associated processes are clearly traced: mingling and mixing. Contaminated varieties with SiO2 contents of 57–60 wt% abnormal are enriched with xenocrysts of quartz and sieve-like melted plagioclase evenly distributed throughout the volume, which suggests an unusual mechanism of convective homogenization of xenogenic crustal substances. Among the xenoliths, buсhites are found to be chemically modified and remelted rocks of primary pelitic composition. They are represented by glassy varieties with different and unusual chemical compositions (SiO2 = 37–45 wt%, Al2O3 = 29–36 wt%, and FeO + Fe2O3 = 17–23 wt%) and are depleted in Mg, Ca, Na, and K. The mineral associations of buchites are represented by ultraferrous sekaninaites (f = 85–95%), hercynites (f up to 100%), whose compositions have no analogs in metamorphogenic rocks, sillimanite, mullite, tridymite, bytownite, baddeleyite, zirconium and high‑aluminum armalcolite rich in pseudobrookite molecules, mono‑lanthanum monazite, scandium‑aluminum zircon and aluminosilicate‑barium-phosphate matrix. The melting of pelitic xenoliths and diffusion interactions with basaltic magma formed iron‑titanium rhyolitic liquids and anorthosite-like reaction coatings. The formation of buchites reflects a complementary relationship with contaminated basalt varieties due to the selective thermal and diffusive extraction of silicic-alkaline granitoid melts and a selective group of cations from pelitic xenoliths into the basaltic melt with the corresponding accumulation of refractory cations (Al, Fe, Ti, and Zr) in the restitic material. In the process of remelting xenoliths, the phenomenon of destruction and dispersion of the crystalline substance of xenoliths into fractal fragments and clusters (up to micro - to nanosizes), which are grouped into immiscible liquid-like suspensions of quartz, feldspar, and hercynite-ilmenite composition, is identified.

Metallogenic implications of volcanic quiescence during continental flood basalt eruption – The case of sediment hosted Mn-Fe mineralization in the Ethiopian volcanic plateau

The north-western volcanic province of Ethiopia is constituted by Continental Flood Basalt and Shield Volcanoes. A paucity in volcanism allowed the deposition of immature continental sediments in fluviolacustrine environment. A recent geologic expedition in the north-western volcanic plateau discovered an Mn-Fe mineralization hosted in nearly 100 m thick mudrock and volcaniclastic sandstone at two localities called Kulfamba and Wogeltena. This research was conducted to investigate the Mn-Fe mineralization hosted in the inter-trappean sediments. Geologic mapping, mineralogic and geochemical methods were employed to investigate the orebodies and host sediments. Mineralogical investigation was carried out using X-ray Diffraction, thin and polished section analysis under petrographic and ore microscopy. Major and trace element analyses was also conducted using ICP-MS. The Mn-Fe orebodies are dominantly layered occupying the transition zone between the mudrock and the sandstone. The orebody is about 1.6 m thick occupying the upper part of the mudrock (the Fe orebody) and the lower part of the sandstone (the Mn orebody). Mn ore is dominated by pyrolusite followed by manganite. Fe is in the form of hematite and goethite. Average ore grade is 34% MnO and 38% Fe2O3. Gangue minerals are quartz, alkali feldspar and clays. The dominantly layered nature of the orebody, absence of typical hydrothermal Mn ore minerals like todorokite and birnessite, high concentration of ∑REE, and other geochemical data support dominantly hydrogenous origin. The presence of distinct orebodies of Mn and Fe suggests the presence of redox-stratified water in the depositional environment. Sporadic occurrences of vein type, concretionary, and botryoidal textures of ores signify later hydrothermal and weathering remobilization and overprinting on the previously formed hydrogenous deposit. The geographic distribution of exposed sediments, their thickness and facies variations throughout the plateau suggests existence of a large shallow lake fed by streams flowing towards northern/north-eastern part of the plateau.

Ecological and Geochemical Features of Soils of the Tolbachik Dol Volcanic Plateau

Ecological and Geochemical Features of Soils of the Tolbachik Dol Volcanic Plateau

Inferring the biogeography of New Zealand’s only endemic holoparasitic plant, the threatened Dactylanthus taylorii (Mystropetalaceae)

ABSTRACT Despite a rich history of botanical research, little is known about the distribution of genetic variation within New Zealand plant species. With a native vascular flora that consists of ∼80% endemics, nearly one-half of which are threatened, there is a dire need for a better understanding of intraspecific diversity for individual plant species and of biogeographic patterns for the wider New Zealand flora. To these ends, we have investigated population genetic structure in the endemic root holoparasite, Dactylanthus taylorii (pua o te Rēinga, Mystropetalaceae). A total of 235 individuals from 31 locations across the North Island of New Zealand (Te Ika-a-Māui, Aotearoa) were genotyped for a suite of nuclear microsatellite loci. Genotype data were analysed at the individual and population levels to assess genetic diversity within and among populations and to investigate the geographic distribution of genetic variation within the species. Population structure was assessed using Bayesian clustering, discriminant analysis of principal components, and a Neighbor-Net analysis. A hierarchical pattern of genetic diversity was revealed, with evidence for three broad geographic regional groupings (West, East, and Central Volcanic Plateau (CVP)). Upon further analysis, each of the three geographic groups further subdivide hierarchically into two or three genetic subgroups. Genetic diversity was found to be relatively high in this endangered species but varies considerably across populations. The distribution of genetic groups appears to have been influenced by past volcanic activity as the CVP group is largely coincident with a distinct tephra isopach from the 1.8 ka Taupō eruption and the West and East groups may have diverged due to recurring volcanic activity in the Central Volcanic Zone. The genetic structure resolved here provides important information for the management of D. taylorii specifically and for our understanding of New Zealand biogeography generally.

Terrain analysis, erosion simulations, and sediment fingerprinting: a case study assessing the erosion sensitivity of agricultural catchments in the border of the volcanic plateau of Southern Brazil

PurposeErosion and its spatial distribution in three agricultural headwater catchments were assessed in the border of the volcanic plateau in Southern Brazil. We analyzed terrain, hydrological processes, and land use influence to provide a comprehensive assessment of the catchments’ sensitivity to erosion.MethodsTopographic attributes were acquired from a digital elevation map, WaterSed model was parameterized to simulate runoff, diffuse erosion, and sediment yield, and sediment source contributions were estimated using sediment fingerprinting based on near-infrared spectroscopy.ResultsAccording to the modeled results, areas covered by crop fields, grasslands, and those adjacent to the drainage network are the most sensitive to erosion. Short distances from the source to the river network and the occurrence of high magnitude rainfall events (80 mm) promoted increases in connectivity for runoff/sediment transfer. Erosion simulations show that areas of low infiltration, such as unpaved roads, were important runoff generators during lower volume rainfall events (25 mm). Sediment fingerprinting provided satisfactory results to quantify the contributions of unpaved roads to sediment (~ 39%). Topsoil and stream channels were also significant sediment sources for the set of analyzed samples, corresponding to average contributions of 38 and 23%, respectively.ConclusionAreas sharing geomorphological similarities did not lead to similar sediment contributions. Vegetation cover controlled erosion in topographically sensitive areas. Unpaved roads provide a significant sediment source, followed by topsoil and stream channels. The complementary results provide useful insights to better coordinate planning environmental conservation strategies in these fragile landscapes.

Taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis; Boraginaceae) based on morphological, population genetic and climate-edaphic niche modelling data

A taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis L.; Boraginaceae) is presented here. Climate-edaphic niches are modelled and compared for five species in the pygmy group, namely, M. antarctica Hook.f., M. brevis de Lange & Barkla, M. drucei (L.B.Moore) de Lange & Barkla, M. pygmaea Colenso and M. glauca (G.Simpson & J.S.Thomson) de Lange & Barkla, and one unnamed putative taxon, M. “Volcanic Plateau”. In this case, niche-modelling data mostly do not aid species delimitation, but morphological and genetic data provide evidence for recognising the following three species within the group: M. brevis and M. glauca (both endemic to New Zealand), and an enlarged M. antarctica (native to New Zealand, Campbell Island and Chile). Myosotis antarctica is here circumscribed to include M. antarctica sens. strict., M. drucei and M. pygmaea. The following two allopatric subspecies of M. antarctica are recognised on the basis of minor morphological differences: subsp. antarctica (formerly M. antarctica from Campbell Island and Chile, M. drucei and M. “Volcanic Plateau”) and subsp. traillii Kirk (formerly known by New Zealand botanists as M. pygmaea Colenso, an illegitimate name). For all three species, which are considered Threatened or At Risk, most of their genetic variation is partitioned between rather than within populations, meaning that conserving as many populations as possible should be the priority to minimise risk of extinction.

АКТИВНАЯ РАЗЛОМНАЯ ТЕКТОНИКА СРЕДИННОГО ХРЕБТА, П-ОВ КАМЧАТКА

The paper presents the results of remote sensing interpretation of active faults of the Sredinny Range of Kamchatka. The use of remote sensing data allowed us to identify fault scarps and magma-conducting fractures, expressed in the topography by chains of eruption centers. Most of the detected faults are located on volcanic plateaus, what indicates the relation of faulting with thinning of the brittle crust under the volcanic belt, similar to the faults of the Eastern Volcanic Belt. The geometrical characteristics of the most preserved scarps provide an estimate of the magnitude of paleoearthquakes Mw = 5.8±0.2, which significantly exceeds the historical seismicity. The identified faults are located above the northern edge of the subducted portion of the Pacific plate and form a zone oblique to the axis of the Kuril-Kamchatka island-arc system. The strike and normal sense of the faults are consistent with the transverse extension in Kamchatka. These new data provide the northern and western boundaries of the above-subduction extensional setting in Kamchatka.

Tracking magmatism and oceanic change through the early Aptian Anoxic Event (OAE 1a) to the late Aptian: Insights from osmium isotopes from the westernmost Tethys (SE Spain) Cau Core

Some of the major Carbon cycle perturbations of the Phanerozoic occurred during the Aptian, in relation to magmatism. The highest temperatures reconstructed for the Cretaceous Period correspond to the Oceanic Anoxic Event of the early Aptian (OAE 1a), an episode of accelerated global change. Here we present a chemostratigraphic study based on osmium isotopes integrated with high-resolution Carbon-Oxygen stable isotope data from the Cau Core (Western Tethys, SE Spain), including a 6.4 Ma record from the early to the late Aptian. This high-resolution study of the continuous and expanded Cau section permits a thorough understanding of the duration of the Aptian events, as well as an evaluation of the mechanisms triggering the abrupt changes of the global carbon and osmium cycles and their interdependence. Here we show that the Large Igneous Province (LIP) Aptian magmatism initiated 550–750 kyr prior to the OAE 1a, and persisted for 1.4 Myr after the event, influencing the composition of seawater for 2.8 Myr. We show a continuous Os isotope record encompassing the OAE 1a and the late Aptian for the first time, and demonstrate that the recovery from the exceptionally unradiogenic composition of seawater Os produced by the dominance of the Ontong Java Plateau volcanism, was slow. Our results demonstrate the different time duration of some events, and the asynchronous relationship between the carbon and osmium cycles

Directions Old and New: Palaeomagnetism and Fisher (1953) Meet Modern Statistics

SummaryMost modern articles in the palaeomagnetism literature are based on statistics developed by Fisher's 1953 paper ‘Dispersion on a sphere’, which assumes independent and identically distributed (iid) spherical data. However, palaeomagnetic sample designs are usually hierarchical, where specimens are collected within sites and the data are then combined across sites to calculate an overall mean direction for a geological formation. The specimens within sites are typically more similar than specimens between different sites, and so the iid assumptions fail. This article has three principal goals. The first is to review, contrast and compare both the statistics and geophysics literature on the topic of analysis methods for clustered data on spheres. The second is to present a new hierarchical parametric model, which avoids the unrealistic assumption of rotational symmetry in Fisher's 1953 paper ‘Dispersion on a sphere’ and may be broadly useful in the analysis of many palaeomagnetic datasets. To help develop the model, we use publicly available data as a case study collected from the Golan Heights volcanic plateau. The third goal is to explore different methods for constructing confidence regions for the overall mean direction based on clustered data. Two bootstrap confidence regions that we propose perform well and will be especially useful to geophysics practitioners.

Quantifying Non‐Thermal Silicate Weathering Using Ge/Si and Si Isotopes in Rivers Draining the Yellowstone Plateau Volcanic Field, USA

AbstractIn active volcanic regions, high‐temperature chemical reactions in the hydrothermal system consume CO2 sourced from magma or from the deep crust, whereas reactions with silicates at shallow depths mainly consume atmospheric CO2. Numerous studies have quantified the load of dissolved solids in rivers that drain volcanic regions to determine chemical weathering rates and atmospheric CO2 consumption rates. However, the balance between thermal and non‐thermal components to riverine fluxes in these areas remains poorly constrained, hindering accurate estimates of atmospheric CO2 consumption rates. Here we use the Ge/Si ratio and the stable silicon isotopes (δ30Si) as tracers for quantifying non‐thermal silicon contributions in rivers draining the Yellowstone Plateau Volcanic Field, USA. The Ge/Si ratio (µmol.mol−1) was determined for seven thermal water samples (183 ± 22), eight rivers (35 ± 23) and six creeks flowing into Yellowstone Lake (5 ± 3) during base flow and during peak water discharge following snowmelt. The δ30Si value (‰) was determined for thermal waters (−0.09 ± 0.04), Yellowstone River at Yellowstone Lake outlet (1.91 ± 0.23) and creek samples (0.82 ± 0.29). The calculated atmospheric CO2 consumption associated with non‐thermal waters flowing through Yellowstone's rivers during peak discharge is ∼3.03 ton.km−2.yr−1, which is ∼2% of the annual mean atmospheric CO2 consumption in other volcanic regions. This study highlights the significance of quantifying seasonal variations in chemical weathering rates for improving estimates of atmospheric CO2 consumption rates in active volcanic regions.

السمات الجيومورفولوجية والمورفومترية للأودية الموسمية في منطقة السبلوقة - شمال الخرطوم السودان

Research done on Sabaloka area (latitudes 160 12/, and 160 24/ N., and longitudes 330 and 330 36/ E) focused more on its geology rather than on its geomorphology, and particularly the seasonal wadis in the area. The authors consider that, understanding the geomorphological and morphometrical characteristics of these seasonal wadis is important for better understanding of its geomorphology, the influence of paleoclimate and for future utilization. The objective of this research is to identify the geomorphological and morphometrical characteristics of the seasonal wadis of Sabaloka area and to discuss the influence of major physical factors, particularly paleoclimate, on determining the nature and origin of these wadis. Methods of data collection included field works during 1996 and 1997, field trips between 2010 and 2014, and analysis of satellite images for the years 1983 and 2014, to determine the in particular the morphometric and topographic characteristics.. اًاThe main analysis revealed that seasonal wadis of the study area can be divided geographically into eastern wadis and western wadis based on the area’s topography, water divides and slope towards the River Nile. The Eastern wadis exhibit differences in depth, type,, shape, and size of deposits whereas in the western wadis,differences are confined to the shape and size of the deposits.In general, all these wadis have contributed to the formation of the flood plain of the Nile because they usually transport clayey, sandy and gravelly deposits. The main channels of the seasonal wadis reveal parallel and dendritic patterns of drainage which are characteristic in the upper reaches of Abu Gadad valley and the middle channel of Abu Gaduiem valley, and the radial pattern in Musa, Shuluk, and Sada wadis which drain the volcanic plateau . Morphometrical analysis of Abu Gaidoum and Abu Gadad wadis revealed that Abu Gaidoum is more developed than Abu Gadad, and morphometrical differences between these two wadis could be attributed to area factor. The research arrived at the conclusion that seasonal wadis of Sabaloka area could be considered as part of the paleo drainage systems of the River Nile, the Sahara and Red Sea Hills, and that paleoclimate and geological structure have significantly determined the geomorphological and morphometrical characteristics of these wadis and the differences between them.

Papanin Ridge and Ojin Rise Seamounts (Northwest Pacific): Dual Hotspot Tracks Formed by the Shatsky Plume

AbstractAlthough previous findings support an origin of the Shatsky Rise igneous plateau (Northwest Pacific) through interaction of a mantle plume with a mid‐ocean ridge triple junction, the evidence for the involvement of a mantle plume is equivocal. The identification of an intraplate hotspot track emanating from the plateau could solve this controversy. Here we present major and trace element geochemical data from two different bathymetric features that emanate from the youngest end of Shatsky Rise: Papanin Ridge and the Ojin Rise Seamount province. Combining our results with plate tectonic reconstructions, we conclude that Papanin Ridge represents a hotspot track formed by plume‐ridge interaction. Whereas the southwestern part was formed along the path of the retreating Pacific‐Farallon‐Izanagi triple junction, the northeastern part was built by preferential drainage into its Pacific‐Farallon branch. In contrast, the Ojin Rise Seamounts formed as a true intraplate hotspot track of the Shatsky plume tail. Our wide‐ranging study reveals systematic spatial geochemical variations, consistent with a lithospheric thickness control on magma composition derived from melting a heterogeneous plume source. The recognition of two hotspot tracks and in particular of the Ojin Rise Seamounts as an intraplate hotspot track that is directly linked to Shatsky plateau volcanism both in terms of geochemistry and plate tectonic reconstructions confirms the long‐disputed involvement of a mantle plume for the formation of Shatsky Rise.

Culture-independent assessment of the diazotrophic Bradyrhizobium communities in the Pampa and Atlantic Forest Biomes localities in southern Brazil

The isolation of rhizobial strains from the root and stem nodules remains a commonly used method despite its limitations as it enables the identification of mainly dominant symbiotic groups within rhizobial communities. To overcome these limitations, we used genus-specific nifD primers in a culture-independent assessment of Bradyrhizobium communities inhabiting soils in southern Brazil. The majority of nifD sequences were generated from DNA isolated from tropical-lowland pasture soils, although some soil samples originated from the Campos de Cima da Serra volcanic plateau. In the nifD tree, all the bradyrhizobial sequences comprised 38 clades, including 18 new clades. The sequences generated in this study were resolved into 22 clades and 21 singletons. The nifD bradyrhizobial assemblage contained Azorhizobium and α-proteobacterial methylotrophic genera, suggesting that these genera may have acquired their nif loci from Bradyrhizobium donors. The most common in the lowland pasture soils subclade III.3D branch comprises the isolates of mainly an American origin. On the other hand, subclade III.4, which was earlier detected in Brazil among Bradyrhizobium isolates nodulating native lupins, appears more common in the Campos de Cima da Serra soils. The second-largest group, Clade XXXVIII, has not yet been reported in culture-dependent studies, while another common group called Clade I represents a symbiovar predominating in Australia. The identification of the diverse nifD Clade I haplotypes in the tropical-lowland pastures infested by Australian Acacia spp implies that the introduction of these legumes to southern Brazil has resulted in the dissemination of their bradyrhizobial symbionts.

Geomorphological description of the biome Pampa (Brazil) with support of digital elevation model and geographic information system

In Brazil, the Pampa Biome is restricted to the far south in the state of Rio Grande do Sul, where it occupies an area of 176,496 km², which corresponds to 63% of the territory state and 2.07% of the Brazilian territory. The biome is characterized by the predominance of native fields with the presence of riparian forests, hillside forests, dwarf-palms fields, xerophyte bushes, wetlands, rocky outcrops, etc. Geomorphologically the landscape of the biome is very varied due to the lithological and structural conditions that interacted in the performance of surface processes. The landscapes consists of plains areas associated with Quaternary deposits; undulating reliefs associated with the sedimentary Basins, which consists of a volcano-sedimentary sequence by rocks formed in different depositional environments of the Paraná Basin and by rocks that represent a Plateau Volcanism and; a dissected plateau relief associated with the Precambrian crystalline basement. This paper describes quantitatively the relief through equations using Geographic Information Systems and the representation of the earth surface in the form of numerical digital models. Digital processing as well as the database were organized and managed by GIS, ArcGIS 10.3®, with spatial analysis and three-dimensional analysis tools. For each of the large geomorphological compartments that make up the Biome, a description of the landforms, and landforms elements were established and mapped. Relief shapes are described by the amplitude and slope of the terrain defined in flat areas, slightly undulations hills, undulating hills and large hills and buttes. For the determination of the relief elements the difference of topographic height, distance and the direction angle of the neighboring points in relation to the central cell (zenith and nadir angles) was used, through online application, available in the website << http://sil.uc.edu/geom/app >>. The relief elements determined are the flat, peak, ridge, shouder, spur, slope, hollow, footslope, valley, pit. The grouping of landforms and landform elements allowed the distinction of predominant morphological patterns for each geomorphological compartment in the Pampa Biome.

Mantle metasomatic influence on water contents in continental lithosphere: New constraints from garnet pyroxenite xenoliths (France & Cameroon volcanic provinces)

Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, mantle composition, and related physical properties. Most mantle lithologies (peridotite) contain little water (~50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous (~300 ppm) relative to the mantle rocks. Pyroxenites also melt at lower temperatures than peridotites and are thus important to magma genesis. Thus, quantifying pyroxenite water contents provides new information on the distribution of water in the mantle. Here, we present phase-specific FTIR measurements of the water contents in pyroxenite mantle xenoliths from two continental lithospheric domains that experienced intense metasomatism: the French Massif Central (FMC, France) and the Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet pyroxenites are more hydrated ([H2O]Clinopyroxene = 386–685 ppm; [H2O]Orthopyroxene = 124–155 ppm; [H2O]Garnet < 0.5 ppm) than FMC ones ([H2O]Clinopyroxene = 112–465 ppm; [H2O]Orthopyroxene = 61–104 ppm; [H2O]Garnet < 0.5 ppm). These water concentrations are homogenous at the grain and correlate with equilibrated major element concentrations, indicating that they are representative of lithospheric water, although the FMC pyroxenites were dehydrated during metasomatism by a carbonatitic fluid (based on the correlation between LaN/SmN and Ti/Eu ratios); the water contents of AVP pyroxenites were likely not affected by metasomatism. FMC pyroxenites show peculiar FTIR spectra that may reflect the preferential dehydration of specific sites in the pyroxene structure. In both regions, metasomatism modified the light rare Earth element contents (e.g., Ce) of the pyroxenites, resulting in highly variable H2O/Ce ratios. Therefore, we conclude that the utility of the H2O/Ce ratio to identify the involvement of pyroxenites in magmas genesis is limited.

The Systematics of Chlorine, Lithium, and Boron andδ37Cl,δ7Li, and δ11B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

AbstractChlorine, lithium, and boron are trace elements in rhyolite but are enriched in groundwater flowing through rhyolite because they tend to partition into the fluid phase during high‐temperature fluid‐rock reactions. We present a large data set of major element and δ37Cl, δ7Li, and δ11B compositions of thermal water and rhyolite from Yellowstone Plateau Volcanic Field (YPVF). The Cl/B, Cl/Li, δ37Cl (−0.2‰ to +0.7‰), and δ11B (−6.2‰ to −5.9‰) values of alkaline‐chloride thermal waters reflect high‐temperature leaching of chlorine, lithium, and boron from rhyolite that has δ37Cl and δ11B values of +0.1‰ to +0.9‰ and −6.3‰ to −6.2‰, respectively. Chlorine and boron are not reactive, but lithium incorporation into hydrothermal alteration minerals result​s in a large range of Cl/Li, B/Li, and δ7Li (−1.2‰ to +3.8‰) values in thermal waters. The relatively large range in δ7Li values of thermal waters reflects a large range of values in rhyolite. Large volumes of rhyolite must be leached to account for the chloride, lithium and boron fluxes, implying deep groundwater flow through rhyolite flows and tuffs representing Yellowstone's three eruptive cycles (∼2.1 Ma). Lower Cl/B values in acid‐sulfate waters result from preferential partitioning of boron into the vapor phase and enrichment in the near‐surface water condensate. The Cl/B, Cl/Li, δ7Li (−0.3‰ to +2.1‰), and δ11B (−8.0‰ to −8.1‰) values of travertine depositing calcium‐carbonate thermal waters which discharge in the northern and southern YPVF suggest that chlorine, lithium, and boron are derived from Mesozoic siliciclastic sediments which contain detrital material from the underlying metamorphic basement.

Diversity and phylogenetic affinities of Bradyrhizobium isolates from Pampa and Atlantic Forest Biomes

In this work, we investigated Bradyrhizobium strains isolated from soils collected from the rhizosphere of native and exotic legumes species inhabiting two ecoclimatic zones – asubtropical-lowland pasture (Pampa Biome) and a volcanic plateau covered by Araucaria Moist Forests (Atlantic Forest Biome). The rhizobial strains were isolated from the nodules of seven native and one exotic legume species used as rhizobium traps. Single-gene (recA, glnII, dnaK) and combined-gene MLSA analyses (dnaK-glnII-gyrB-recA-rpoB) revealed that nearly 85% of the isolates clustered in B. elkanii supergroup, while the remaining (except for two isolates) in B. japonicum supergroup, albeit, in most cases, separately from the type strains of Bradyrhizobium species. As a symbiotic gene marker, a portion of nifD gene was sequenced for 194 strains. In the nifD-tree, an American branch III.3D (104 isolates), was the most numerous among the isolates. A significant portion of the isolates clustered in American groups; subclade III.4 (40 strains), Clade VII (3 strains), and a new Clade XX (4 strains). Most of the remaining strains belonged to a pantropical III.3C branch (39 isolates). On the other hand, identification of isolates belonging, respectively, to Clade I and Clade II may result of spreading of the Australian (Clade I) and European (Clade II) bradyrhizobia following the introduction of their legume hosts. Our study indicated that the American groups predominated in the symbiotic Bradyrhizobium communities in southern Brazil. However, there is a significant component of exotic lineages, resulting from the dispersal of pantropical Fabaceae taxa and the introduction of exotic legumes.