Density intrusions with large relative thickness

Previous analyses of density intrusions indicate that only relatively thin intrusions are allowed, to satisfy a momentum balance at the current head. These constraints can be relaxed somewhat by various modifications to the basic theory, but are inconsistent with experimental observations indicating that intrusions occupying nearly the entire flow depth can be produced. An alternative theory of density current propagation does not possess these restrictions on intrusion layer thickness and provides a more satisfactory explanation of experimental observations. New experimental results are presented to corrborate this interpretation.     

Sodic amphiboles and pyroxenes from fenites in East Africa

During alkali metasomatism of the country-rock associated with ijolite-carbonatite complexes the development of sodic amphibole and/or pyroxene is characteristic. In this paper, some new chemical analyses of these minerals, together with published analyses from fenites of Kenya, Uganda and Tanzania, include those of co-existing pairs of amphibole and pyroxene. The common amphiboles of the fenites are magnesioarfvedsonites with 100 Mg: Mg+Fe+Mn ranging from 67 to 36. They co-exist with aegirines having 0.75 to 0.89 ions Fe⁺³. Most of these minerals are poor in Ca; co-existing pairs tend to show corresponding increases in Ca and in Fe⁺². In the syenitic fenites of Tororo and Budeda, considered to have formed at higher temperatures, the stable mineral is aegirine-augite. New analyses of richterite, magnesioarfvedsonite and aegirine from carbonate-rich rocks are also presented, and the relation between fenites and carbonatites is discussed.     

Accuracy of a pre-trained sentiment analysis (SA) classification model on tweets related to emergency response and early recovery assessment: the case of 2019 Albanian earthquake

Traditionally, earthquake impact assessments have been made via fieldwork by non-governmental organisations (NGO's) sponsored data collection; however, this approach is time-consuming, expensive and often limited. Recently, social media (SM) has become a valuable tool for quickly collecting large amounts of first-hand data after a disaster and shows great potential for decision-making. Nevertheless, extracting meaningful information from SM is an ongoing area of research. This paper tests the accuracy of the pre-trained sentiment analysis (SA) model developed by the no-code machine learning platform MonkeyLearn using the text data related to the emergency response and early recovery phase of the three major earthquakes that struck Albania on the 26th November 2019. These events caused 51 deaths, 3000 injuries and extensive damage. We obtained 695 tweets with the hashtags: #Albania #AlbanianEarthquake, and #albanianearthquake from the 26th November 2019 to the 3rd February 2020. We used these data to test the accuracy of the pre-trained SA classification model developed by MonkeyLearn to identify polarity in text data. This test explores the feasibility to automate the classification process to extract meaningful information from text data from SM in real-time in the future. We tested the no-code machine learning platform's performance using a confusion matrix. We obtained an overall accuracy (ACC) of 63% and a misclassification rate of 37%. We conclude that the ACC of the unsupervised classification is sufficient for a preliminary assessment, but further research is needed to determine if the accuracy is improved by customising the training model of the machine learning platform.

     

Late Pleistocene–Holocene environmental and climatic history of a freshwater paramo ecosystem in the northern Andes

This study presents the first multi-proxy palaeoenvironmental and palaeoclimatic history for northern South America based on the palaeolimnological reconstruction of a pond located in a dry paramo at 3570 masl. During the Last Glacial Maximum (LGM), the study area was under glacial conditions, then during global events Heinrich Stadial 1 (HS1), Bølling–Allerød (BA), and the Younger Dryas (YD), the pond expanded, accumulation rates and proxies for erosion reached the highest values, indicative of humid conditions, with maxima in humidity during the BA and YD. Dry conditions and pond desiccation occurred in the Greenlandian–Northgrippian and by 6010 cal a bp the area was transformed into the mire of today. Comparisons with records from other sites in South America indicate that changes in humidity are most likely controlled by the Intertropical Convergence Zone, mainly during the glacial and postglacial, and by changes in the Pacific Ocean, more pronounced after the YD.     

Late Neoproterozoic crustal growth in the European Variscides: Nd isotope and geochemical evidence from the Sierra de Córdoba Andesites (Ossa-Morena Zone, Southern Spain)

Because the Hercynian overprint was extremely weak, the Sierra de Córdoba (southeastern Ossa-Morena Zone, OMZ) provides an excellent opportunity to study the tectonic evolution of sequences deposited close to the Late Neoproterozoic–Early Palaeozoic boundary. In order to put constraints on the sources and geodynamic significance of the Late Proterozoic magmatism, a representative set of 18 igneous rocks, and 3 interbedded sedimentary rocks from the San Jerónimo Formation have been studied for major and trace element geochemistry and for the Sm–Nd isotopic systematics. The igneous rocks are generally porphyritic to microporphyritic andesites, with abundant plagioclase (±amphibole) phenocrysts. With the exception of two intrusive rocks, possibly not related to the Late Proterozoic episode, all the samples display positive _{Nd550 Ma} values, ranging from +2.9 to +7.6. Most of them, with +4<_{Nd550 Ma}<+6, exhibit LREE enrichment, high La/Nb ratios, and elevated Zr/Nb ratios ranging from 21 to 32. There is no obvious correlation between the shape of REE patterns, La/Nb ratios and _{Nd550 Ma} values, precluding simple models of late-stage interaction with typical crustal components having low _Nd and high LREE/HREE and La/Nb ratios. Based on their major element composition and enriched, continental crust-like trace element characteristics, combined with distinctly positive _Nd initial values, the Córdoba andesites document an episode of crustal growth through the addition of calc-alkaline magmas, extracted from a mantle reservoir which was strongly depleted in LREE on a time-integrated basis. The occurrence of interlayered sediments of continental provenance (negative _Nd values) does not favour a purely ensimatic arc setting, remote from continental land masses, for this subduction-related magmatism, but the geochemical data suggest an active margin environment located on relatively juvenile crust. In any case, the Córdoba andesites document the addition of materials chemically similar to the bulk continental crust which were extracted from mantle sources with strong time-integrated LREE depletion. Therefore, they provide evidence for crustal growth related to Cadomian orogenic events during Late Proterozoic times.     

Spatially distributed rainfall thresholds for the initiation of shallow landslides

The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key feature of the code is the capability of evaluating the time t _p required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds. In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios.     

A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia

Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots.