Strong Anomalies Research Articles

Origin of the Permian high silica A-type granites in Halajun, South Tienshan, NW China: Implications for crystal-liquid segregation and rare metal fertilization

High silica A-type granites (HSAGs) are important carriers of rare metal elements. Formation of HSAGs by crystal-liquid segregation would facilitate fertilization of rare metals and rare earth elements (REE). In this work, we present detailed petrology, whole-rock geochemistry, and in-situ zircon UPb ages and HfO isotopic compositions of the Halajun HSAGs in the South Tienshan Orogenic Belt (STOB). In combination with the previous study of the Halajun syenite and monzonite, we unravel the genetic connection of these granitoids and further explore the metallogenetic potentiality of HSAGs along the STOB in China. The Halajun granites have geochemical affinities of HSAGs with high SiO2 contents (> 70 wt%), whole-rock zirconium saturation thermometry (680–860 °C), high Ga/Al ratios and high field strength elements (HFSE) contents. The HSAGs (273–279 Ma), monzonite (280 Ma) and syenite (283 Ma) have similar formation ages, identical mineral assemblages, and consistent variations in major elements, implying a common magma reservoir of their parental magma. The Tamu and Huoshibulake HSAGs have high SiO2 (74.5–78.1 wt%) contents, low Sr (5–28 ppm) and Ba (7–60 ppm) contents, high Rb/Sr ratios (11.6–87.5), and strong negative Eu anomalies (0.01–0.08). Combined with the petrographic features, these geochemical variations suggest that they are the extracted melt. Conversely, the geochemical (high Sr and Ba concentrations, and Eu/Eu* near unity) and petrographic features of monzonite and syenite represent the residual silicic cumulate (crystals ± trapped melt). The Kezi'ertuo and Halajun II HSAGs have SiO2 (71.9–76.5 wt%) contents, Sr (35–101 ppm) and Ba (60–541 ppm) contents, Rb/Sr ratios (1.9–8.9), and negative Eu anomalies (0.04–0.43), indicating the intermediate component (extracted melt + fractional crystals) in the consecutive system of crystal-liquid segregation. In-situ zircon HfO isotopes for the Halajun granitoids indicate a complex trans-crustal magmatic process involving crystal-liquid segregation and wall-rock assimilation. The long-time span of Tarim Large Igneous Province (TLIP) sustained injection of mantle-derived magma and/or advective heat to the magma chamber (> 1 Ma). Owing to the prolonged magma evolution, the highly fractionated silicic magma with high incompatible elements and F contents was extracted from the magma mush, and formed the HSAGs.

Crustal Velocity Structure of the Sichuan–Yunnan Block Revealed by High-Quality Crustal Phase Travel Time

Abstract The Sichuan–Yunnan block is located at the southeastern margin of the Tibetan Plateau, which is the key area as a transition belt from the active plate extrusion zone to the stable Yangtze Craton. Using a semiautomatic measuring method based on a graphical interface, we pick 81,585 precise travel times from 449 local earthquake records and finally obtain a crustal 3D P-wave velocity model of the Sichuan–Yunnan block. The model reveals an unexpected velocity contrast between the shallower and deeper crusts. It is summarized as weakly perturbed low-velocity belts encircling a high-velocity zone in the upper crust and strongly perturbed low-velocity anomalies in the mid-lower crust, respectively. The weak low-velocity anomalies are revealed along the major strike-slip faults, and their small perturbations may imply a slip-driven mechanism. The strong low-velocity anomalies are distributed extensively in the Sichuan–Yunnan block, and their great perturbations may be related to the partial melting of weak material extruded from Tibet. Besides, our result shows noticeable high-velocity anomalies in the core zone of the Emeishan Large Igneous Province (ELIP), which may be an indication of magma solidification from the ancient mantle plume. The result further exhibits an interesting pattern that the strong low-velocity anomalies are partially separated by the high-velocity anomalies in the ELIP. Such a specific pattern probably reflects that the stable zone in the ELIP leads to the bifurcation of weak Tibetan material.

The Role of the Stratosphere in Teleconnections Arising From Fast and Slow MJO Episodes

AbstractThe Madden‐Julian Oscillation (MJO) can influence the extratropical circulation on timescales up to several weeks, with a dependence on the MJO characteristics: MJO episodes that propagate slowly across the Maritime Continent have a stronger impact on Euro‐Atlantic weather than fast MJO episodes. While the tropospheric pathway for MJO teleconnections with varying phase speeds is well understood, in this study, we investigate the contribution of the Northern Hemisphere stratospheric pathway for fast versus slow MJO episodes. During slow MJO episodes, Phases 5–6 lead to increased upward wave propagation in the North Pacific sector, and subsequently enhanced heat flux at 100 hPa, leading to the weakening of the polar vortex. The results suggest a clear role of stratosphere‐troposphere coupling for slow MJO episodes, which is proposed as a mechanism for anomalously strong positive polar cap height anomalies in MJO Phases 7–8.

Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

Petrogenesis and metallogenic significance of late Mesozoic granites in the Akjilga mining area, Tajikistan: constraints from geochronology and geochemistry

The Akjilga (Акджилга) mining area in Tajikistan sits in the central part of the Pamir syntaxis in the western part of the Indo–Eurasia collisional orogenic belt. Recently, the mineralization phenomena of skarn-type tin polymetallic ore bodies and dolomite-type rare-earth metals in the copper polymetallic mining area have been reported. However, the limited knowledge on the genesis of granite and its relationship with mineralization in this area hinders further research. Here, the Late Mesozoic granite rocks in the mining area were studied by petrology, geochemistry, and zircon U–Pb dating. The results showed that the rocks comprise majorly porphyric biotite syenogranite and minorly porphyric biotite monzogranite. The zircon U–Pb age of the porphyric biotite syenogranite was 108.3 ± 2.0 Ma, highlighting the Early Cretaceous period. The porphyric biotite syenogranite features high silicon and potassium contents and low iron, magnesium, calcium, sodium, titanium, and phosphorus contents. Furthermore, their aluminum saturation indexes were 1.11–1.21. Therefore, they were classified as high-potassium calc-alkaline strong peraluminous rocks. Trace-element analysis showed the enrichment of large ionic lithophile elements and light rare-earth elements (REEs); the deficiency of high-field-strength elements and heavy REEs; and the negative anomalies of Nb, P, and Ti. Compared with ordinary granites, the porphyric biotite syenogranite exhibits a higher differentiation index (91.20–93.96) and strong negative Eu anomaly (0.05–0.26), as well as a low Zr content and abnormally low Nb/Ta, Zr/Hf, Y/Ho, ∑LREE/∑HREE ratios. Therefore, the rocks are considered highly differentiated I-type granites with good Sn polymetallic and rare-metal prospecting potentials, and it resulted in the subduction-collision of the Rushan-Pshart ocean between the Middle Pamir block and the South Pamir block during the northward subduction process of the Late Mesozoic New Tethys ocean (Shyok ocean).

Lithospheric delamination as the driving mechanism of intermediate-depth seismicity in the Bucaramanga Nest, Colombia

The Bucaramanga nest (BN) is an area of exceptionally strong intermediate-depth seismicity localized in a narrow zone at 150–170 km depth beneath the continental plate in Colombia. To explain the very unusual mantle seismicity cluster in this area, we built a seismic velocity model in the vicinity of BN with the use of local earthquake tomography and developed a numerical hydromechanical model. Our seismic model shows a strong high-velocity anomaly at 130–167 km coinciding with the BN seismicity. The relocated seismicity can be separated in two clusters. We propose that the upper BN cluster at ~ 130 km depth is attributed to dehydration embrittlement, whereas the lower BN cluster at ~ 150 km depth coinciding with the high-velocity body is caused by lithospheric delamination, creating a “drip” that falls down over the subducting oceanic plate, enhancing fluid release from the slab, potentially increasing seismicity.

Fingerprints of the COVID-19 economic downturn and recovery on ozone anomalies at high-elevation sites in North America and western Europe

Abstract. With a few exceptions, most studies on tropospheric ozone (O3) variability during and following the COrona VIrus Disease (COVID-19) economic downturn focused on high-emission regions or urban environments. In this work, we investigated the impact of the societal restriction measures during the COVID-19 pandemic on surface O3 at several high-elevation sites across North America and western Europe. Monthly O3 anomalies were calculated for 2020 and 2021, with respect to the baseline period 2000–2019, to explore the impact of the economic downturn initiated in 2020 and its recovery in 2021. In total, 41 high-elevation sites were analyzed: 5 rural or mountaintop stations in western Europe, 19 rural sites in the western US, 4 sites in the western US downwind of highly polluted source regions, and 4 rural sites in the eastern US, plus 9 mountaintop or high-elevation sites outside Europe and the United States to provide a “global” reference. In 2020, the European high-elevation sites showed persistent negative surface O3 anomalies during spring (March–May, i.e., MAM) and summer (June–August, i.e., JJA), except for April. The pattern was similar in 2021, except for June. The rural sites in the western US showed similar behavior, with negative anomalies in MAM and JJA 2020 (except for August) and MAM 2021. The JJA 2021 seasonal mean was influenced by strong positive anomalies in July due to large and widespread wildfires across the western US. The polluted sites in the western US showed negative O3 anomalies during MAM 2020 and a slight recovery in 2021, resulting in a positive mean anomaly for MAM 2021 and a pronounced month-to-month variability in JJA 2021 anomalies. The eastern US sites were also characterized by below-mean O3 for both MAM and JJA 2020, while in 2021 the negative values exhibited an opposite structure compared to the western US sites, which were influenced by wildfires. Concerning the rest of the world, a global picture could not be drawn, as the sites, spanning a range of different environments, did not show consistent anomalies, with a few sites not experiencing any notable variation. Moreover, we also compared our surface anomalies to the variability of mid-tropospheric O3 detected by the IASI (Infrared Atmospheric Sounding Interferometer) satellite instrument. Negative anomalies were observed by IASI, consistent with published satellite and modeling studies, suggesting that the anomalies can be largely attributed to the reduction of O3 precursor emissions in 2020.

Tonian rifting coeval with the last stages of amalgamation of Rodinia: Evidence from southern Borborema province, northeastern Brazil

During the last stages of assembly of the Rodinia supercontinent at 1000-900 Ma, rifting processes were occurring in places that would be part of Gondwana in the late Neoproterozoic. In the Borborema Province, northeastern Brazil, this event is known as Cariris Velhos. It is represented in the Alto-Pajeú Domain from the Central subprovince by a 700 km-long, 70 km-wide NE-SW belt comprising bimodal metavolcanic rocks and granitic orthogneisses. Orthogneisses with similar ages were found in previous works in the western Pernambuco-Alagoas Domain from the Southern subprovince immediately to the south of the ESE-trending dextral West Pernambuco shear zone. The Airi Complex comprises several elongate bodies that extend for at least 80 km. It consists of a bimodal sequence of metafelsic (granitic orthogneisses) associated with layers and enclaves of metamafic (amphibolites) rocks. Seven orthogneiss samples dated by LA-ICPMS yielded zircon U–Pb crystallization ages of 950–1011 Ma. Zircon Hf analyses from two samples yielded εHf(t) values ranging from −1.4 to 2.1 and TDM model ages of 1.7–1.9 Ga. Geochemical analyses allow to distinct different source rocks for the protoliths of the orthogneisses. Orthogneisses derived from metasedimentary sources have modal muscovite ± garnet, are ferroan, alkali-calcic and predominantly peraluminous, exhibiting strong negative Eu anomalies in chondrite-normalized rare earth elements diagrams. Orthogneisses derived from high-K mafic rocks are calc-alkalic, slightly peraluminous, with small or absent negative Eu anomalies. Orthogneisses from tonalitic sources are magnesian, calc-alkalic to alkali-calcic, and slightly peraluminous, without Eu anomalies. There is no correlation between crystallization ages and source rock types. The results indicate that the Airi Complex originated through partial melting of ancient heterogenous crustal sources. Therefore, its geochemistry reflects the nature of these sources, not the tectonic setting of intrusion. Emplacement of the complex was broadly coeval with well-documented extensional processes in the São Francisco/Congo Craton and represents a failed attempt to break-up a larger paleocontinent encompassing this craton and the basement of the Borborema Province.

Rayleigh wave group velocities in North-West Iran: SOLA Backus-Gilbert vs. Fast Marching tomographic methods

In this study, we focus on Northwest Iran and exploit a dataset of Rayleigh-wave group-velocity measurements obtained from ambient noise cross-correlations and earthquakes.We build group-velocity maps using the recently developed SOLA Backus-Gilbert linear tomographic scheme as well as the more traditional Fast-marching Surface-wave Tomography method.The SOLA approach produces robust, unbiased local averages of group velocities with detailed information on their local resolution and uncertainty; however, it does not as yet allow ray-path updates in the inversion process. The Fast-marching method, on the other hand, does allow ray-path updates, although it does not provide information on the resolution and uncertainties of the resulting models (at least not without great computational cost) and may suffer from bias due to model regularisation.The core of this work consists in comparing these two tomographic methods, in particular how they perform in the case of strong vs. weak seismic-velocity contrasts and good vs. poor data coverage. We demonstrate that the only case in which the Fast-marching inversion outperforms the SOLA inversion is for strong anomaly contrasts in regions with good path coverage; in all other configurations, the SOLA inversion produces more coherent anomalies with fewer artefacts.

Application of Borehole Geophysical Prospecting Method in Pile Foundation Detection of Existing Buildings

It is particularly important to find out the pile foundation of existing buildings for building safety protection and engineering construction safety during the development and utilization of urban underground space. As a non-destructive, efficient and economic method, the borehole geophysical techniques such as magnetic gradient method, ground penetrating radar method and parallel seismic test method are used to detect the pile foundation of existing buildings, which have obvious advantages. According to the combined abnormal characteristics such as "strong magnetic anomaly, electromagnetic wave in-phase axis change and diffraction wave anomaly at the pile end, P-wave velocity variation", the pile foundation length can be judged.

New heat flow data on the South Balearic margin: Evidence of regional fluid circulation system

Crustal heat loss processes in contexts other than mid-ocean ridge flanks are still poorly understood and described in the literature. In this work, we present 54 new surface heat flow measurements recorded along the South Balearic margin and across the Hannibal High area, in the Western Mediterranean Sea, away from spreading centres. The South Balearic margin is a narrow continental margin expressed on the seabed topography by the steep Emile Baudot Escarpment while the Hannibal High area, further south, is a presumed volcanic oceanic crust zone. Recent heat flow studies pointed out the presence of strong local thermal anomalies, imprinted in regional deep basin heat flow increasing from the eastern to the western Algerian basins (70–90 to 100–130 mW/m2). The new data in this study confirm local anomalies around the Emile Baudot seamounts and allow the delineation of some low and high heat zones. We show that (1) a correlation exists between the heat flow variability and the sedimentary cover thickness, and (2) the most pronounced anomaly is a low heat flow zone (30 km wide) observed in the mid-slope South Formentera basin, close to the basaltic basement of the Los Martines volcano. The correlation of heat flow with sedimentary thickness, the lateral extent of the heat flow anomalies, the flux peak magnitudes, and the co-existence of both low and high anomalies suggest the presence of an active fluid circulation system. Based on the arrangement of the anomalies in relation to the basaltic basement seamounts, we consider a syphon-type circulation system in the Formentera basin. Reduced heat flow suggests a recharge zone close to the Los Martines seamount, while local high heat flow located close to a smaller seamount could be a potential zone of fluid discharge. Although different buoyancy-driven circulations could occur in the South Balearic margin, we believe that a syphon-type hydrothermal circulation along permeable basaltic mounds and sealed basement conduits, similar to the off-axis oceanic crust, is best developed in the young marginal basin of the South Balearic margin.

Geochemical Evidence for Genesis of Nb–Ta–Be Rare Metal Mineralization in Highly Fractionated Leucogranites at the Lalong Dome, Tethyan Himalaya, China

Leucogranites in the Lalong Dome are composed of two-mica granite, muscovite granite, albite granite, and pegmatite from core to rim. Albite granite-type Be–Nb–Ta rare metal ore bodies are hosted by albite granite and pegmatite. Based on field and petrographic observations and whole-rock geochemical data, highly differentiated leucogranites have been identified in the Lalong Dome. Two-mica granites, albite granites, and pegmatites yielded monazite ages of 23.6 Ma, 21.9 Ma, and 20.6 Ma, respectively. The timing of rare metal mineralization is 20.9 Ma using U–Pb columbite dating. Leucogranites have the following characteristics: high SiO2 content (>73 wt.%); peraluminosity with high Al2O3 content (13.6–15.2 wt.%) and A/CNK (mostly > 1.1); low TiO2, CaO, and MgO content; enrichment of Rb, Th, and U; depletion of Ba, Nb, Zr, Sr, and Ti; strong negative Eu anomalies; low εNd(t) values ranging from −12.7 to −9.77. These features show that the leucogranites are crust-derived high-potassium calc-alkaline and peraluminous S-type granites derived from muscovite dehydration melting under the water-absent condition, which possibly resulted from structural decompression responding to the activity of the South Tibetan detachment system (STDS). Geochemical data imply a continuous magma fractional crystallization process from two-mica granites through muscovite granites to albite granites and pegmatites. The differentiation index (Di) gradually strengthens from two-mica granite, muscovite granite, and albite granite to pegmatite, in which albite granite and pegmatite are highest (Di = 94). The Nb/Ta and Zr/Hf ratios of albite granite and pegmatite were less than 5 and 18, respectively, which suggests that albite granite and pegmatite belong to rare metal granites and have excellent potential for rare metal mineralization.

Contrasting the Impacts of Intraseasonal Oscillations on Yangtze Precipitation during the Summer of 1998 and 2016

In 1998 and 2016, boreal summer intraseasonal oscillation (BSISO) could reach the middle-lower reaches of the Yangtze River basin (YRB), leading to extreme precipitation. Based on multiple daily data, this study reveals the differences in BSISO events and mechanisms between 1998 and 2016. In June–July of 1998 (2016), YRB precipitation was impacted by 30–60-day oscillation, i.e., BSISO1 (10–30-day oscillation, i.e., BSISO2), with two strong (three) precipitation events occurring. In 1998, when BSISO1 was in phases 1–4 (phases 5–8), the YRB experienced a wet (dry) episode. In 2016, when BSISO2 was in phases 1–2 and 7–8 (phases 3–6), the YRB experienced a wet (dry) episode. In 1998, in event 1, the active convection of the YRB first originated in the South China Sea–western Pacific (SCS–WP) and then in the tropical Indian Ocean (IO). In 1998, in event 2, the active convection of the YRB originated in the SCS–WP. In 2016, in events 1 and 3, the active convection of the YRB originated from the SCS–WP. In 2016, in event 2, the active convection of the YRB originated from the tropical IO and the extratropical WP. Different SST and atmospheric circulations explain different BSISO modes that dominate in the YRB. In 1998 (2016), in summer, (no) strong easterly wind anomalies occurred in the SCS–WP, which are favorable (unfavorable) for the enhancement of BSISO1. Accompanying the suppressed BSISO1, BSISO2 was enhanced in 2016.

Stratosphere-troposphere coupling during stratospheric extremes in the 2022/23 winter

Using the ERA5 reanalysis, sea surface temperature, sea ice observations, and the real-time multivariate Madden-Julian Oscillation (MJO) index, the evolution of the stratospheric extreme circulation in the winter of 2022/2023 is explored. The stratospheric polar vortex was disturbed three times in the 2022/23 winter, contrasted with only one disturbance during the other three recent winters with an SSW. Possible favorable conditions for the strong stratospheric disturbances and their effects on stratospheric ozone, water vapor distribution, and near-surface temperature were examined. Around 7 December 2022 when a short but strong pulse of planetary wavenumber 2 appeared from the troposphere to stratosphere, a weakened and elongated stratospheric polar vortex formed at 10 hPa. This pulse is related to the intensifying Ural ridge and the deepening East Asian trough. After the first stratospheric disturbance, a large fraction of cold anomalies occurred in the Eurasian continent. A lagged impact after these stratospheric disturbances was observed as strong cold anomalies formed in North America from 13 to 23 December. On 28 January 2023, a minor SSW event occurred due to a displacement of the stratospheric polar vortex. A strong pulse of eddy heat flux contributed alternately by planetary wavenumber 1 and 2 showed a large accumulative effect on the stratospheric disturbance. However, the downward impact of this second disturbance was weak, and cold surges were not noticeable after this minor SSW. The third stratospheric disturbance this winter is a major displace-type SSW that occurred on 16 February 2023, and the total eddy heat flux primarily contributed by planetary wavenumber 1 increased rapidly. Following the major SSW, the North American continent was covered by large patches of strong cold anomalies until the end of March. During the three disturbances, the residual circulation correspondingly strengthened. The water vapor and ozone in the middle and lower layers of the polar stratosphere showed positive anomaly disturbances, especially after the major SSW onset. The unprecedented frequent stratospheric disturbances in winter 2022/23 were accompanied by severe loss of Barents-Laptev Sea ice and anomalously cold tropical Pacific sea surface temperatures (La Niña), which have been reported to be conducive to the enhancement of planetary waves 1 and 2 respectively. Further, two weeks before the major SSW, existing MJO developed into phases 4–6, also contributing to the occurrence of major SSW.

The increased summer monsoon rainfall in Northwest India: Coupling with the Northwestern Arabian Sea warming and modulated by the Silk Road Pattern since 2000

This study investigates changes in rainfall patterns over Northwest India (NWI) and the warming of the Northwestern Arabian Sea (NWAS) since 2000. These changes are attributed to the Silk Road Pattern (SRP) phase change in the late 1990s. The SRP positive phase triggers geostrophic deformation over the Tibetan Plateau (TP) by inducing an anomalous circulation pattern along the westerly jet, at 200 hPa. This deformation along the westerly Jet leads to Jet streaks and thermally indirect ageostrophic circulation over TP. In addition, the intensified heating over the TP led to a westward shift of the South Asian High (SAH). Associated with this, the interaction of positive temperature advection and northward ageostrophic wind (Jet entrance) over south-central Asia generates a southward component of ageostrophic wind (Jet Exit), causing upper-level convergence at southeast TP, excites the sinking cold air thereby strengthen the surface pressure below, over TP. This amplifies the anomalous anticyclone effect over there resulting in strong easterly wind anomalies along the monsoon trough at 850 hPa, disrupting the monsoon circulation. These anomalies, combined with a poleward shifting moisture-laden Low-Level Jet (LLJ), contribute to the warming of the NWAS and increased rainfall over NWI. The NWAS has shown significant summer warming over the past two decades. The poleward shift of the LLJ and SRP-induced circulation changes also impact the ocean dynamics. Given the occurrence of severe floods in this region of the Indian subcontinent, these findings have broader implications for predicting and projecting monsoon variability and extremes.

Do variations in anomalous mortality in Europe in fall and winter of 2019–2020 tell us anything on the timing of SARS‐CoV‐2 outbreak?

AbstractThe present study makes a part of the already ample discussion on the subject of identification of the beginnings of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) coronavirus pandemics in the world and considers the following question: do the anomalies in death rates in the earlier periods bring any new knowledge of the subject? With the ultimate purpose of answering this question, spatial differences are analysed of excess mortality for the first time at such a detailed spatial scale in Europe. As it is known, according to current knowledge, a strong increase in coronavirus disease‐2019 mortality occurred in Lombardy, Italy, from about mid‐March (Week 11–12 of 2020), followed by Spain and Belgium. It was decided, in the context of the present study, to see if similarly strong mortality anomalies, not assigned to this factor, were not present earlier. This could constitute circumstantial evidence that SARS‐CoV‐2 coronavirus was present in Europe on a much larger scale earlier than it is commonly believed. The study, therefore, looks at whether there were local outbreaks of elevated deaths between November 2019 and March 2020. The analysis used available Eurostat data for 34 European countries according to the NUTS1, NUTS2 and NUTS3 divisions based on 918 units with more than 100,000 inhabitants. The number of deaths was analysed over consecutive 24 weeks of autumn–winter (7 October 2019–22 March 2020, i.e., W41‐2019 to W12‐2020) and were compared with the respective data for the 3‐year reference period 2016–2018. The method used identifies geographically concentrated areas with excess deaths over short periods relative to the reference period. It was shown that 44 regions between W41‐2019 and W08‐2020 (i.e., before February 23) had elevated mortality (115% or more relative to the reference period). In the 44 NUTS3 regions mentioned, excess deaths during the autumn–winter period amounted to 96,000–126,000 when compared with the 2016–2018 baseline period (mainly in Spain, France, Italy, United Kingdom). It cannot be excluded that to some extent this could have been due to SARS‐CoV‐2 coronavirus infections. To confirm or deny this more clearly, detailed studies of the recorded causes of death in the indicated 44 regions are needed.

Petrogenesis of Late Cretaceous A-type plutonic rocks from the Eastern Pontides Orogenic Belt (NE Turkey): constraints from zircon U-Pb geochronology, zircon Lu-Hf and whole-rock Sr-Nd-Pb-Hf isotopes

ABSTRACT The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes.

Magnetic field map of the Wilhelm Archipelago shelf zone, West Antarctica

The Antarctic Digital Magnetic Anomaly Project is an international research effort to construct a magnetic map of the continent based on ground, satellite, marine, and aeromagnetic surveys. This paper reports the magnetic mapping of the shelf zone in the SE part of the Wilhelm Archipelago, West Antarctica, based on magnetic surveys conducted with Zodiac boats. A spectacular feature of this area is the strong magnetic anomaly of the Antarctic Peninsula (AP) batholith, which was the product of subduction-related Mesozoic–Cenozoic arc magmatism on the former margin of Western Gondwana. We constructed and analyzed a detailed magnetic map of magnetic field anomalies using field observations of rock exposures on the islands and magnetic properties of rocks from laboratory data. The oldest volcanic rocks of Jurassic to Lower Cretaceous age relate to N-NE trending bands of negative magnetic field. The largest feature in the study area is an Upper Cretaceous/Paleogene granodiorite complex that produces a positive magnetic anomaly. Many smaller anomalies are also present over gabbroid bodies of Cretaceous age. Two-dimensional magnetic modeling shows that heterogeneities in the upper crust may have magnetic susceptibilities in the range of 0.005–0.13 SI. Magnetic field anomalies also delineate an orthogonal system of tectonic faults, including the main NE fault along the Penola Strait (sub-parallel to the AP coastline) and four intersecting faults. These fault systems may be associated with different stages of continental margin evolution along the Antarctic Peninsula.

Extremely long-lived marine heatwave in South China Sea during summer 2020: Combined effects of the seasonal and intraseasonal variations

South China Sea (SCS) experienced an exceptionally long-lived marine heatwave (MHW) event in summer 2020, which broke the historical records in terms of its time duration since 1982. This long-lasting MHW was primarily attributed to the combined effects of the seasonal cycle (SC) and 30–60-day intraseasonal oscillation (ISO) components of anomalous atmospheric circulations. During the SC developing phase, the superimposed anticyclonic circulation regimes of the SC and 30–60-day ISO jointly contributed to the first warming sea surface temperature (SST) peak over the central SCS in July, via the combined effects of net downward shortwave radiation (SWR) and latent heat flux (LHF) anomalies. In contrast, during the SC decaying phase, the SCS MHW-related warming SST tendency was mostly due to 30–60-day ISO signals. During the growth phase of ISO, the joint warming effect of the SWR and LHF anomalies was the dominant factor maintaining the SCS MHW. In the decaying phase of 30–60-day ISO, however, the second MHW-related warming peak around Beibu Gulf in September was mainly contributed by the sharply reduced LHF loss due to strong southwesterly anomalies over the northern SCS on the 30–60-day timescale. The varying SC component plays a crucial role in the occurrence and maintenance of MHWs, while the 30–60-day ISO can effectively regulate the development and pattern of SCS MHWs. These results suggest that, besides the vital role of the SC component, the 30–60-day ISO should also be considered for fully understanding the extreme MHW events.

Reconnaissance Basement Geology and Tectonics of North Zealandia

AbstractNew rock dredge samples supply key information to establish the tectonic and geological framework of the northern two‐thirds of the 95% submerged Zealandia continent. The R/V Investigator voyage IN2016T01 to the Fairway Ridge, Coral Sea, obtained poorly sorted poly‐lithologic pebbly to cobbly sandstones, well sorted fine grained sandstones, mudstones, bioclastic limestones, and basaltic lavas. Post‐cruise analytical work comprised petrography, whole rock geochemical and Sr and Nd isotopic analyses, and U‐Pb zircon, Rb‐Sr, and Ar‐Ar geochronology. A Fairway Ridge cobbly sandstone has a ∼95 Ma (early Late Cretaceous) depositional age; two biotite granite cobbles are 111 ± 1 and 128 ± 1 Ma in age, and some volcanic pebbles are also likely Early Cretaceous. Fairway Ridge basalts have intraplate alkaline chemistry and are of Late Eocene age (∼40–36 Ma). By analogy with South Zealandia, we interpret strong positive continental magnetic anomalies of North Zealandia to mainly result from Late Cretaceous to Cenozoic intraplate basalts, many of them rift‐related lavas. A new basement geological map of North Zealandia shows the position of the Mesozoic Gondwana magmatic arc axis (Median Batholith) and other major geological units. This study completes onland and offshore reconnaissance geological mapping of the entire 5 Mkm2 Zealandia continent.