Main Episodes Research Articles

Emeishan felsic volcanism lasted until the Changhsingian? New evidence from volcanic ash in the northern South China block

The main episode of volcanism in the Emeishan large igneous province (ELIP) occurred ca. 260 Ma. However, the ending period of volcanism has not been well established. We present the SHRIMP and LA-ICP-MS zircon U–Pb geochronology, zircon Hf isotopes, and geochemistry of ashes in the Shuanghe and Xintang sections, northern South China block (SCB). The results show that the Al/Ti ratio and high field strength elements content of Changsingian ashes (253.5–253.0 Ma) are consistent with those of alkaline ashes in the Wuchiapingian coal measure of the western SCB. These volcanic rocks contain zircon grains with high εHf(t) values (mean + 2.53) and low Th/Nb ratios (mostly < 10), consistent with the origin from mantle-derived magmas within the plate. These magmas are interpreted to be related to the Emeishan felsic volcanism. Furthermore, the zircon grains separated from ashes at the Permian-Triassic boundary (PTB) (ca. 252 Ma) and the upper Longtan Formation (256.8 Ma), have low εHf(t) values (mean − 7.04) and high Th/Nb ratios (mostly greater than 40). These features are consistent with a magmatic arc source, and the arc was likely related to the subduction of Paleo-Tethys in the middle Wuchiapingian. Therefore, we propose that the waning stage of the Emeishan felsic volcanism continued until the middle Changhsingian (253 Ma), which is not a previously suggested older age of 257 Ma. However, the ashes near the PTB on the SCB should have come from the magmatic arc. The Emeishan volcanism may not be the main cause of the PTB extinction.

Filling critical gaps in the space-time record of High Lava Plains and co-Columbia River Basalt Group rhyolite volcanism

Miocene rhyolitic volcanism of eastern Oregon, USA, can be divided into two main episodes. Mantle plume upwelling is thought to have generated Columbia River Basalt Group (CRBG) lavas and coeval &amp;gt;16.5−15 Ma silicic volcanism trending north−south from northeast Oregon to northern Nevada. Rhyolite volcanism of the 12−0 Ma High Lava Plains province has been ascribed to either buoyancy-driven westward plume spreading or to slab rollback and mantle convection spanning from southeast Oregon to Newberry Volcano to the west. The apparent ca. 15−12 Ma eruptive hiatus suggests that rhyolites of these provinces were a product of separate processes, yet this gap was based on incomplete data. The lack of data on ∼33 of the total ∼50 rhyolitic eruptive centers in the area where the two provinces overlap (117−119°W, 43−44°N) yields only tenuous relationships between these two provinces. We acquired 40Ar/39Ar ages for 29 previously unanalyzed rhyolite centers that confirm the existence of a rhyolitic eruptive episode concurrent with CRBG flood basalt volcanism. Rhyolite eruptions gradually initiated at ca. 17.5 Ma, and our new ages indicate that peak intensity of the first eruptive episode occurred between 16.3 Ma and 14.4 Ma. We refine the ca. 15−12 Ma rhyolitic eruptive hiatus to 14.4−12.1 Ma, where strong recommencement of rhyolite eruptions began with Beatys Butte at 12.05 Ma. We find two prominent fluxes in rhyolitic eruptive activity after 12.1 Ma as opposed to one continuous, age-progressive trend, at 12.1−9.6 Ma and 7.7−5.1 Ma, which are separated by an ∼2 m.y. period of decreased rhyolite volcanism. Rhyolite eruptions were scarce after 5.1 Ma, at which point most eruptions were associated with Newberry Volcano. Periodicity of rhyolite volcanism along the High Lava Plains demands more punctuated basalt inputs than what continuous partial melting from west-spreading plume material should generate. Our new data suggest that regional rhyolite eruptions are a series of episodic events related to the arrival and storage of mafic mantle magmas. Paucity in rhyolite eruptions from 14.4 Ma to 12.1 Ma is related to decreased flux of CRBG flood basalt magmas at ca. 15 Ma. Strong recommencement of rhyolite volcanism at 12.1 Ma is related to continued Northwest Basin and Range extension and a peak rotation rate of Siletzia affecting regional lithosphere weakened by CRBG volcanism. Waning rhyolitic eruptive activity from ca. 9.6 Ma to 7.7 Ma reflects a regional transition in the primary mode of accommodation of extension from Northwest Basin and Range normal faulting to extension and shearing of the Brothers Fault Zone. Rhyolite volcanism between 7.7 Ma and 5.1 Ma was driven by continued regional extension in an area less affected by CRBG magmatism. Post-5.1 Ma rhyolite eruptions occurred within crust not influenced by CRBG magmatism but impacted by both regional extension and the Cascadia subduction zone.

REFİK HALİD KARAY’IN BUGÜNÜN SARAYLISI ROMANINDA YAPI VE İZLEK

Millî Edebiyat Dönemi’nin önemli sanatçılarından olan Refik Halid Karay’ın Bugünün Saraylısı adlı romanında modernleşme sürecinin bireysel ve toplumsal düzeyde yarattığı etkiler anlatılır. Bu süreç içerisinde kültürel değerlerden uzaklaşmakla meydana gelen yozlaşma ve aidiyet problemi, romanda çatışma unsurunu sağlayan temel epizotlar olarak belirir. Ayrıca romanda bireysel ve toplumsal çözülmenin yanısıra aşk, kıskançlık gibi bireysel duygu ve yönelimlerin de ele alınması izleksel kurguya farklı bir yön kazandırır. Bu temel izlekleri eleştirel bir bakış açısı ile sunan Refik Halid Karay, diğer eserlerinde olduğu gibi Bugünün Saraylısı romanında da kendi dünya görüşünü ve yaşam üslubunu yansıtır. Nitekim okuyucuya vermek ve benimsetmek istediği düşünceyi, kurguladığı karakterler, zaman ve mekân algısı ile aktaran Refik Halid Karay’ın geleneksel olanın önemini ve değerini ortaya çıkarması bireysel bakış açısının yansımalarından izler taşır. Bu çalışmada hem geleneksel hem de modern yaşama ışık tutan Bugünün Saraylısı romanı sahip olduğu bütün bu içerik düzlemi ile birlikte yapısal unsurlar bakımından da tahlil edilecektir.

The Gymnesic Islands at the crossroads: Livestock body size as marker of social interactions during the first millennium BC

This study presents an analysis of 7575 individual sheep, goat, cattle and pig measurements from 22 sites from Mallorca and Menorca dating to different phases throughout the 1st millennium BC. Two main episodes of size change have been identified, although some variations in the speed and timing by species are noted. The earliest evidence for size change in cattle and sheep occurs between the 6–5th century BC and may be connected to the increase of trade exchanges and social interactions between Gymnesic Islands and the colonial area of influence of the Punics. This process of livestock size increasing probably occurred as a combined consequence of agricultural innovations, the increasing commercialisation of animal farming, and as the meat demands required by the expanding population. Subsequent size increases in livestock occurred as the process of integration continued to develop, reaching its peak at the end of the millennium with the Roman colonisation of the islands.

Evolutionary history of interactions among terrestrial arthropods.

The study of terrestrial arthopod fossils preserved with microscopic fidelity in amber and as permineralized replicas has been revolutionized by CT scanning. Fine preservation facilitates phylogenetic interpretation of fossils, but molecular divergence-time models still commonly use insufficient fossil calibrations, skewing estimates away from the direct (i.e.fossil, morphological) evidence. Interactions among terrestrial arthropods (predation, parasitoidism; phoresy, social symbionts) are briefly reviewed from the fossil record. Predation is the oldest and most widespread, originating with arachnids since probably the Silurian. The first phoretic arthropods were probably mites (Acari). Parasitoidism extends to the early Jurassic ~200 mya, with four main episodes proposed by [1•]. 100-myo Burmese amber, the most diverse Cretaceous paleobiota, is unique for our understanding of insect eusociality and interrelationships among terrestrial arthropods. Eusocial insect colonies are ecological sinks for thousands of symbiont species; ages of the major eusocial groups and some of their nest symbionts are discussed. Fossilized arthropod interrelationships in Miocene Dominican amber are presented as visual exemplars.

(U-Th)/He Geochronology Constraints on Lateritic Duricrust Formation on the Guiana Shield

Thick regoliths developed under tropical climate, namely, laterites, resulting from long-term and pronounced geochemical and mineralogical rearrangement of the parent rock in response to environmental changes. Little information is available on the timing of laterite and bauxite formations, especially on the chronology of the main weathering episodes responsible for lateritic cover formation on the Guiana shield. For this purpose, we focused on both lateritic and bauxitic duricrusts developed over the Paleoproterozoic Greenstone Belt in the Brownsberg, Suriname. The duricrust samples have a relatively simple mineralogy (i.e., goethite, gibbsite, hematite, and kaolinite) but reveal, when observed at a microscopic scale, a complex history of formation with multiple episodes of dissolution/reprecipitation. The (U-Th)/He dating of 179 Fe-oxides subsamples shows that duricrusts sampled at the top of the Brownsberg plateau have ages ranging from &amp;lt;0.8 Ma to ∼19 Ma. In contrast, Fe-oxides extracted from detrital duricrust boulders collected downslope indicate formation ages up to 36 Ma. This age discrepancy may indicate that a main episode of physical erosion affected this region between ca. 30 and 20 Ma. Consistently, the bauxite sampled at the mountaintop indicates a younger phase of formation, with Fe-oxides recementing fragments of a preexisting bauxitic material older than ∼15 Ma. Geochronological data also reveal a long-lasting weathering history until the present day, with multiple generations of Fe-oxides in the bauxite and the duricrusts resulting from successive cycles of dissolution and reprecipitation of Fe-oxides associated with redox cycles. This long-lasting weathering history led to geochemical remobilization and apparent enrichment in some relatively immobile elements, such as REE, aluminum, and vanadium, especially in the duricrust sampled at the mountaintop. Our geochronological, mineralogical, and geochemical study of Fe- and Al-crusts from the Brownsberg mountain provide constraints on the evolution of environmental conditions prevailing since the early Oligocene in Suriname.

Plio-Quaternary sequences and tectonic events in the northern Adriatic Sea (northern Italy)

The analysis of multichannel seismic profiles and their correlation with well data in the northern Adriatic Sea (Northern Italy) has allowed to document Plio-Quaternary episodes of tectonic subsidence and uplift. They affected the sedimentation above the Mesozoic to lower Eocene Friuli-Dinaric Carbonate Platform (FDCP) and the unit composed of the Eocene Trieste Flysch and the Miocene Molassa (TFM), as well as the sedimentary succession lying SW of the FDCP. In particular, the early Zanclean reflooding that postdated the Messinian Salinity Crisis, was followed by the SW-ward progradation of a highstand to forced regressive shelf-slope system (Sequence 1). Forced regression was controlled by a main episode of tectonic uplift that occurred at the end of the Zanclean. This tectonic event also led to the formation of the sequence boundary separating the two main sequences that compose the Plio-Quaternary succession. The lower part of Sequence 2 (Piacenzian to late Pleistocene) recorded a two-step subsidence phase, which led to drowning episodes during Piacenzian and in particular late Gelasian (transgressive systems tract of Sequence 2). They were associated with the partial flooding of the TFM and the Miocene deposits overlying the FDPC, and with a downward bending of the pre-Calabrian succession toward the Apennine chain. The accommodation created during the late Gelasian drowning event was filled in part by an Alpine-sourced, SW-ward prograding system, and in part by the NE-ward paleo-Po prograding system (highstand systems tract of Sequence 2). The most recent part of Sequence 2 documents the last glacio-eustatic cycles in a physiographic context characterized by a very low gradient.

The VMC survey – XLVIII. Classical cepheids unveil the 3D geometry of the LMC

ABSTRACT We employed the VISTA near-infrared YJKssurvey of the Magellanic System (VMC) to analyse the $Y,\, J,~\mathrm{ and}~ K_\mathrm{s}$ light curves of δ Cepheid stars (DCEPs) in the Large Magellanic Cloud (LMC). Our sample consists of 4408 objects accounting for 97 per cent of the combined list of OGLE IV and Gaia DR2 DCEPs. We determined a variety of period–luminosity (PL) and period–Wesenheit PW relationships for Fundamental (F) and First Overtone (1O) pulsators. We discovered for the first time a break in these relationships for 1O DCEPs at P= 0.58 d. We derived relative individual distances for DCEPs in the LMC with a precision of ∼1 kpc, calculating the position angle of the line of nodes and inclination of the galaxy: θ = 145.6 ± 1.0 deg and i = 25.7 ± 0.4 deg. The bar and the disc are seen under different viewing angles. We calculated the ages of the pulsators, finding two main episodes of DCEP formation lasting ∼40 Myr which happened 93 and 159 Myr ago. Likely as a result of its past interactions with the SMC, the LMC shows a non-planar distribution, with considerable structuring: the bar is divided into two distinct portions, the eastern and the western displaced by more than 1 kpc from each other. Similar behaviour is shown by the spiral arms. The LMC disc appears ‘flared’ and thick, with a disc scale height of h ∼ 0.97 kpc. This feature can be explained by strong tidal interactions with the Milky Way and/or the Small Magellanic Cloud or past merging events with now disrupted LMC satellites.

Elite Struggle and Journalism in Russia in the Period of Nation Building

In the article the author presents the main stages and certain episodes of the struggle inside the ruling elite in the Russian Empire starting with 1820-ies and up to 1880-ies. The author studies the activity of the two main directions (groups) in Russian political elite, – nationally oriented and cosmopolitan ones, - who struggled for control over periodical press and public opinion. Ht pays special attention to the participation in this struggle of the III Section of His Majesty Imperial Chancellery, of S.S. Uvarov and other directors of the Ministry of National Education, of the Minister of Internal Affairs L.P. Perovsky and the Minister of State Property P.D. Kiselev. The author also examines the role in this struggle of certain official and private editions, their editors and publicists.

«Слушая великого художника, я нашел что-то великое и нужное…»: Письма Семена Фикса — Горькому и о Горьком (по материалам Архива А.М. Горького)

This publication of materials from A.M. Gorky’s archive supplements studies related to the name of the artist Simon Fix, new facts and details of his life and work. The only mention of Fix’s name in Gorky's letter to the publisher A. Kogan (the publication of L. Fleishman in 1979) remained without comment for a long time and scattered information about the artist left significant gaps in his biography. V. Khazan's research, supplemented by the publication of Fix’s letters to R. Friedlander and N. Friedlander, kept in the archives of David and Yevsey Shor (National Library of Israel, Jerusalem), recreates the main episodes of the artist's creative biography. Letters stored in the A.M. Gorky’s Archive reveal the details of a previously unknown acquaintance between the artist and the writer. Presented corpus of Fix’s letters — three letters to Gorky and four letters to relatives — testifies to their rather long acquaintance and Gorky’s obvious interest in works and personality of the young painter. The content of Fix’s letter to Gorky dated January 28, 1936 continues the theme of the conversation with Gorky during the meeting in Sorrento, which Fix described to his relatives in April 1928. It is logical to assume that its topics — art education and the position of artists in Soviet society — were discussed with Gorky also in the period between these two dates: perhaps researchers will have a chance to verify it.

The History of One Personal Copy: Esper E. Ukhtomsky (1861–1921) — His life, His Buddhist Collection, and the Study of Buddhism in Russia

The article focuses on the contribution of Esper E. Ukhtomsky, an outstanding collector of Buddhist sculpture and painting in pre-revolutionary Russia, to the study of Buddhist art. In addition to the main episodes of the biography, little covered earlier in research, the author examines how Ukhtomsky, who had the largest private Buddhist collection in the Russian Empire, contributed to the study of Buddhist art and collaborated with Albert Grunwedel, to whom he provided part of his collection, resulting in the famous Grunwedel’s work “The Mythology of Buddhism in Tibet and Mongolia”. Ukhtomsky himself published pamphlets in which he contributed to the clarification and understanding of Buddhism and the East by the reading public. In 1890–1891 Ukhtomsky was one of the retinues that accompanied the future Emperor Nicholas II, his brother and the Greek Prince on a journey to the East. It was Ukhtomsky who had the honor to write a trip report — “Journey to the East of His Imperial Highness the Sovereign Heir Tsesarevich” in three volumes. The article shows how Ukhtomsky worked with Asian material on the example of the book by Archbishop Nilus “Buddhism, Considered in Relation to Its Followers Living in Siberia” (1858), where Ukhtomsky left numerous marginalia. In his marginal notes, the author translated Mongolian terms into Russian, quoted major authors of Buddhist studies, and left his own reflections on what Archbishop Nilus, who was engaged in missionary activity in Siberia, managed to learn and understand.

НАУЧНЫЙ ЭНТУЗИАЗМ И МОТИВАЦИЯ: ОПЫТ АКАДЕМИКА В.М. АЛЕКСЕЕВА И ОПЫТ АКАДЕМИКА ГО МОЖО

Aims of the research: 1) to problematize the topic of science and education and propose an alternative, Chinese-specific approach to science and education; 2) to identify the characteristics of scientific enthusiasm and motivation of the most prominent Chinologists - V.M. Alekseyev and Guo Moruo, to consider their experience and scientific worldview as examples of scientists looking for ways to scientific enthusiasm and motivation in education. The topic of scientific enthusiasm and motivation is highlighted in the context of modern, stressful conditions for science, when the life of researchers in various fields enables not scientific activity, which is specified in writing and publishing articles in scientific publications, but more pressing issues, for example, of finance and overcoming the difficulties of the COVID pandemic. The topic of the crisis of Western culture is problematized, the possibility of studying alternative worldview systems and methodologies is substantiated. The research describes the life path and systematizes the scientific worldview of academician V.M. Alekseyev, a great Russian Chinologist, as well as the factors that inspired his scientific activity. We describe the main episodes of the life and scientific path of the outstanding Chinese academician Guo Moruo, widely known at one time in the USSR and the People's Republic of China, and now all over the world. The life milestones of Guo Moruo are briefly outlined, his characteristics as a scientist and writer, a public figure are given, the peculiarities of his personality and creativity are studied; the factors that influenced his personality are summarized in his scientific achievements. His scientific methodology is reconstructed and his main ideological positions and character traits that have become factors of his scientific, creative and social activities are formulated.

Saint Jerome’s Posthumous Life: Aspects of His Reception in the Twentieth Century

The paper examines three examples of Saint Jerome’s contemporary reception. First, in Sous l’invocation de Saint Jérôme, the essay by the French writer and translator Valery Larbaud (1946), Jerome’s life is imagined as the large city of Hiéronymopolis where three itineraries are possible: one that is imaginary to Stridon, Rome, and Bethlehem; one that is iconographical through the paintings of Raffaello, Correggio, and Domenichino, and one that is literary through Jerome’s works, divided into many “city districts,” where an impressive bridge, the Vulgata, connects Jerusalem to Rome. – In the eccentric novel Jérôme ou de la traduction by the French-Canadian writer Jean Marcel (1990), Hieronymus’s famous lion narrates the main episodes of the Saint’s life, especially regarding his translations. This is an existential metaphor for the passage from the ancient eastern world to early Christian Rome. – The poetic movie by the Brasilian director Júlio Bressane, São Jerônimo (1999), is not a biographical reconstruction of Jerome’s life, but rather a fresco, which consists of some moments of his life and some iconic symbols (the skull, the lion, the desert).

A Brief, Individualized Exercise Program at Intensities Below the Ventilatory Threshold Exerts Therapeutic Effects for Depression: A Pilot Study.

Due to the fact that existing pharmacological treatments for depression are not ideal, effort has been devoted to the development of complementary, alternative therapies such as physical exercise. The antidepressant effect of exercise is well documented. However, current recommendations and prescriptions of exercise may be too demanding for depressed patients, as some complain about the design of exercise programs and depression is associated with reduced motivation and capacity to exercise. Therefore, appropriately designed, patient-friendly exercise programs may prove critical for the long-term maintenance and therapeutic effects of exercise. In this pilot study, we developed an exercise program based on patients’ individual level of ventilatory threshold (VT), a submaximal index of aerobic capacity measured by Cardiopulmonary Exercise Testing (CPX). Compared to traditional measures, CPX provides more trustable indices of aerobic capacity and more homogenous exercise prescriptions. The main episode of the program consisted of 15–25 min of cycling twice a week at an intensity that approached but never went higher than subjects’ VT (considered low to moderate in intensity). We found that in patients diagnosed with major depressive disorder or persistent depressive disorder (n = 8), the program resulted in a significant reduction in depressive symptoms at week 8, which was maintained at week 16. Meanwhile, patients’ social functioning, quality of life, and cognitive functions improved. Although we used a single arm, non-randomized design, our results suggest that even a brief, low to moderate intensity exercise program may exert therapeutic effects for depression and CPX may be a useful tool for exercise prescriptions.

«Свои поганые» Киевской земли: этапы заселения и ландшафтно-географическая ниша кочевников в земледельческом обществе

The paper analyzes the issue of the spatial and ecological niche of the nomadic population of the south of the Kiev principality (“Black Hats”), as well as the dynamics of the settling in the Ros’ river basin in the 11th—13th centuries. An important part in the spatial organization of the Ros’ river basin was the multi-row system of long walls, which divided the steppe zone into closed sectors. Nomadic burials were not discovered yet in the large northern sector (“Perepetovo Pole”), it was used as a buffer between nomads and farmers of the Stugna river basin. The area of burial mounds concentration is characterized by a lower amount of precipitation and a higher winter temperature, which makes it suitable for winter pastures. The more humid northwestern part with single burials was used for seasonal migrations in summer. There are four main episodes of the nomad influx in the Ros’ river basin detected. The wave of the 11 th century were Torks and Pechenegs, they occupied the space between the Rosava and the Dnieper. Migrants of the 12 th century wave were added to the Rosava basin, but they also left burials near Vyshgorod. The third big wave of the Cuman origin came in 1223—1241. They occupy both the main area of the “Black Hats” and new sectors along western Ros’. The Yablunivka burial ground of the 2nd half of the 13th—14th centuries should be withdrawn from the list of the “Our Pagans” sites. It arose after the migration of a group of the North Caucasian population during the Golden Horde stage.

Prerequisites for self-determination and the sovereignty of Tuva (Russia) in 1921

The article analyzes the prerequisites of self-determination and sovereignty of Tuva in 1921. Briefly, the general context of events is revealed, the main episodes and key personalities are listed. Using historical-genetic, comparative-historical and problem-chronological methods, the positions of Mongolia and Soviet Russia and their relationship on the status of Tuva, the organization and convocation of the All-Tuva Constituent Khural, which proclaimed the independence of Tuva, as well as the consequences of the declaration of independence of Tuva, were reconstructed. The role of the authorized representative of the Sibrevkom in Uryanhai I.G. Safyanov in this process is shown. In conclusion, the authors conclude that the emergence of a sovereign Tuva state was made possible both due to the contradictory political situation in Asia and due to the role of I.G. Safyanov in history. Since 1921, Tuva began to live and develop in the political and economic conditions created by the Constituent Khural.

General-relativistic treatment of tidal g-mode resonances in coalescing binaries of neutron stars – II. As triggers for precursor flares of short gamma-ray bursts

ABSTRACT In some short gamma-ray bursts, precursor flares occurring ∼ seconds prior to the main episode have been observed. These flares may then be associated with the last few cycles of the inspiral when the orbital frequency is a few hundred Hz. During these final cycles, tidal forces can resonantly excite quasi-normal modes in the inspiralling stars, leading to a rapid increase in their amplitude. It has been shown that these modes can exert sufficiently strong strains on to the neutron star crust to instigate yieldings. Due to the typical frequencies of g- modes being ∼100 Hz, their resonances with the orbital frequency match the precursor timings and warrant further investigation. Adopting realistic equations of state and solving the general-relativistic pulsation equations, we study g-mode resonances in coalescing quasi-circular binaries, where we consider various stellar rotation rates, degrees of stratification, and magnetic field structures. We show that for some combination of stellar parameters, the resonantly excited g1 and g2 modes may lead to crustal failure and trigger precursor flares.

Distance and extinction to the Milky Way spiral arms along the Galactic centre line of sight

Context. The position of the Sun inside the disc of the Milky Way significantly hampers the study of the spiral arm structure given the high amount of dust and gas along the line of sight, and the overall structure of this disc has therefore not yet been fully characterised. Aims. We aim to analyse the spiral arms in the line of sight towards the Galactic centre (GC) in order to determine their distance, extinction, and stellar population. Methods. We use the GALACTICNUCLEUS survey, a JHKs high-angular-resolution photometric catalogue (0.2″) for the innermost regions of the Galaxy. We fitted simple synthetic colour-magnitude models to our data via χ2 minimisation. We computed the distance and extinction to the detected spiral arms. We also analysed the extinction curve and the relative extinction between the detected features. Finally, we studied extinction-corrected Ks luminosity functions (KLFs) to study the stellar populations present in the second and third spiral arm features. Results. We determined the mean distances to the spiral arms: d1 = 1.6 ± 0.2 kpc, d2 = 2.6 ± 0.2 kpc, d3 = 3.9 ± 0.3 kpc, and d4 = 4.5 ± 0.2 kpc, and the mean extinctions: AH1 = 0.35 ± 0.08 mag, AH2 = 0.77 ± 0.08 mag, AH3 = 1.68 ± 0.08 mag, and AH4 = 2.30 ± 0.08 mag. We analysed the extinction curve in the near-infrared for the stars in the spiral arms and find mean values of AJ/AH = 1.89 ± 0.11 and AH/AKs = 1.86 ± 0.11, in agreement with the results obtained for the GC. This implies that the shape of the extinction curve does not depend on distance or absolute extinction. We also built extinction maps for each spiral arm and find them to be homogeneous and that they might correspond to independent extinction layers. Finally, analysing the KLFs from the second and third spiral arms, we find that they have similar stellar populations. We obtain two main episodes of star formation: &gt; 6 Gyr (∼60 − 70% of the stellar mass), and 1.5 − 4 Gyr (∼20 − 30% of the stellar mass), compatible with previous work. We also detect recent star formation at a lower level (∼10%) for the third spiral arm.

Chemical-Abrasion U-Pb zircon geochronology reveals 150 Myr of partial melting events in the Archean crust of the São Francisco Craton

Field observations and CA-LA-ICP-MS U–Pb zircon ages and Hf isotope compositions obtained from migmatitic orthogneisses and granitoids from the Belo Horizonte Complex, southern São Francisco Craton, indicate a major period of partial melting and production of felsic rocks in the Neoarchean. Our observations show that the complex is an important site for studying partial melting processes of Archean crystalline crust. Much of the complex exposes fine-grained stromatic migmatites that are intruded by multiple leucogranitic veins and sheeted dikes. Both migmatites and leucogranite sheets are crosscut by several phases of granitoid batholiths and small granitic bodies; both of which are closely associated with the host banded gneisses. Chemical abrasion followed by detailed cathodoluminescence imaging revealed a wide variety of zircon textures that are consistent with a long-lived period of partial melting and crustal remobilization. Results of U-Pb and Hf isotopes disclose the complex as part of a much wider crustal segment, encompassing the entire southern part of the São Francisco Craton. Compilation of available U-Pb ages suggests that this crustal segment was consolidated sometime between 3000 Ma and 2900 Ma and that it experienced three main episodes of partial melting before stabilization at 2600 Ma. The partial melting episodes took place between 2750 Ma and 2600 Ma as a result of tectonic accretion and peeling off the lithospheric mantle and lower crust. This process is likely responsible for the emplacement of voluminous potassic granitoids across the entire São Francisco Craton. We believe that the partial melting of Meso-Archean crystalline crust and production of potassic granitoids are linked to a fundamental shift in the tectonics of the craton, which was also responsible for the widespread intrusion of large syenitic bodies in the northern part of the craton, and the construction of layered mafic–ultramafic intrusions to the south of the BHC.

Mechanisms of sulfate formation in acidic hydrothermal sites of Iceland, Lassen, Valles Caldera, and Yellowstone: Implications for possible oxidation pathways in martian volcanic settings

Sulfate (SO42−) has been found in elevated concentrations on the surface of Mars and linked to oxidation of volcanically derived sulfur (S) in the past, with the best examples of hydrothermal S-rich deposits in Gusev crater. However, the oxidation mechanisms of volcanic S are unclear due to the lack of abundant molecular oxygen (O2) in the Martian atmosphere. To address this uncertainty, we investigated the mechanisms of hydrogen sulfide (H2S) oxidation to SO42− in O2-depleted acidic hydrothermal systems of Iceland and the United States (Valles Caldera, Lassen, and Yellowstone) as geochemical analogs. Approximately 50 water and sediment samples were collected for chemical and stable isotope analyses (δ34S, δ18O, δ2H). At the time of sampling, the measured dissolved O2 (DO) concentrations were low (0.01 to 1.03 mg/L) because of elevated temperatures (60 to 90 °C) and did not account for high concentrations of SO42− (up to 24,461 mg/L) in the acidic hot springs and mud pots. However, high concentrations of leachable iron (Fe) were present in the hydrothermal water and sediments (average of 158 mg/L and 71,302 mg/kg, respectively), implying that in addition to atmospheric O2, the Fe-driven oxidation of H2S via ferric Fe reduction to ferrous Fe is likely involved. Our laboratory experiments studying H2S oxidation carried out in a wide temperature range (25 °C, 50 °C, 90 °C) and low pH of 2 suggest that under acidic hydrothermal conditions, ferric Fe reduction involves stepwise oxidation of H2S with preferential formation of insoluble elemental S, which is later oxidized to SO42−. In contrast, the Gusev hydrothermal sediments on Mars appear to be enriched in Fe3+-sulfates with minor amounts of Ca-Mg-sulfates and negligible elemental S. This implies that the Gusev sediments must have experienced subsequent oxidation, most likely after the main episode of hydrothermal activity.