Abstract
The Doldrums Megatransform System (~7–8°N, Mid-Atlantic Ridge) shows a complex architecture including four intra-transform ridge segments bounded by five active transform faults. Lower ...crustal rocks are exposed along the Doldrums and Vernadsky transform walls that bound the northernmost intra-transform ridge segment. The recovered gabbros are characterized by variably evolved chemical compositions, ranging from olivine gabbros to gabbronorites and oxide gabbros, and lack the most primitive gabbroic endmembers (troctolites, dunites). Notably, the numerous recovered gabbronorites show up to 20 vol. % of coarse-grained orthopyroxene. Although covariations in mineral and bulk-rock chemical compositions of the olivine and oxide gabbros define trends of crystallization from a common parental melt, the gabbronorites show elevated light over heavy rare earth elements (LREE/HREE) ratios in both bulk-rock and mineral compositions. These features are not consistent with a petrological evolution driven solely by fractional crystallization, which cannot produce the preferential enrichments in highly incompatible elements documented in the orthopyroxene-bearing lithologies. We suggest that gabbronorites crystallized from evolved melts percolating and partly assimilating a pre-existing olivine gabbro matrix. Saturation in orthopyroxene and selective enrichments in LREE relative to M-HREE are both triggered by an increase in assimilated crystal mass, which ranges from negligible in the oxide-gabbros to abundant in the gabbronorites. This melt–rock reaction process has been related to lateral melt migration beneath ridge-transform intersections, where variably evolved melts injected from the peripheral parts of the melting region towards the transform zone may interact with a gabbroic crystal mush to form abundant oxide-bearing gabbronoritic associations.
Abstract
The Red Sea rift system represents a key case study of the transition from a continental to an oceanic rift. The Red Sea rifting initiated in Late Oligocene to Early Miocene (24–23 Ma) and ...was accompanied by extensive magmatism throughout the rifted basin, from Afar and Yemen to northern Egypt. Here, we present a petrological and geochemical study of two gabbro bodies and associated basalts from the Tihama Asir igneous complex, which formed at 24–20 Ma within the rifted Arabian-Nubian Shield (ANS). The Tihama Asir is therefore an ideal location to study the initial phase of syn-rift magmatism and its influence on the geodynamic evolution of the Red Sea rift system. The most primitive olivine gabbros present modal, bulk and mineral compositions consistent with formation from Mid-Ocean Ridge Basalt (MORB)-type parental melts, whereas the evolved olivine-free gabbros and oxide-bearing gabbros show saturation of phlogopite and a crystal line of descent diverging from fractional crystallization trends. In detail, whole-rock and mineral compositions in the most evolved lithologies show high Light over Middle Rare Earth Elements (LREE/MREE) ratios (LaN/SmN = 0.89–1.31) and selective enrichments in Sr, K and highly incompatible elements (Rb, Ba, U, Th). We relate these geochemical characteristics to a process of progressive assimilation of host continental crust during the emplacement of the gabbroic plutons. Interestingly, high LREE/MREE ratios (LaN/SmN = 1.45–4.58) and high Rb, Ba, Th and U contents also characterize the basaltic dike swarms associated to the gabbros. Incompatible trace element compositions of these basalts approach those of the melts that formed the most hybridized gabbros. Therefore, we propose that the dike swarms represent melts partially contaminated by assimilation of continental crust material, extracted from the underlying gabbroic crystal mush. Our results suggest that early syn-rift magmatism led to the partial replacement of the thinned continental crust by MORB-type gabbroic bodies, in turn suggesting that oceanic magmatism started prior to continental break-up. Extensive syn-rift magmatism is consistent with the interpretation of the southern Red Sea rift system as a volcanic rifted margin. One possible implication of this study is that extensive but diffuse syn-rift magmatism possibly hampered continental break-up, leading to a protracted rifting stage.
New multichannel seismic reflection profiles were acquired to unravel the structure of a portion of the eastern margin of the Tyrrhenian basin. This extensional feature is part of an Oligocene to ...Present back‐arc basin in the hangingwall of the west directed Apennines subduction system. The basin provides excellent conditions to investigate the early stage processes leading to the development of rifted passive margins and to the emplacement of oceanic crust in an oblique setting. The interpreted post‐stack‐migrated seismic profiles highlight the geometry and kinematics of the Pontine escarpment that connects the Latium‐Campania continental margin to the Vavilov basin. The latter is the main feature of the area, related to the early Pliocene extension of the Tyrrhenian Sea. Several morphological variations are pointed out along strike, mirroring different structural settings of the margin itself: a steeper margin to the north corresponds to high‐angle possibly transtensional faults, whereas a smooth slope in the southern portion corresponds to several more distributed listric faults. This work contributes to the understanding of the interplay between extensional and transtensional tectonics along the margins of an oblique back‐arc basin.
Key Points
Interpretation of new multichannel seismic profiles acquired in the eastern margin of the Tyrrhenian Sea
Reconstruction of the geometric and kinematics aspects of a segmented back‐arc margin
Interaction between extensional and transtensional tectonics along an oblique back‐arc basin setting
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This article presents results of the structural and morphological analysis of the fracture zones that are part of Doldrums Megatransform System (DMS), located in the northern part of the Equatorial ...Atlantic (6.5°–9° N) that include Vernadskiy and Bogdanov transform faults and the Doldrums and Pushcharovskiy megatransforms. Bathymetric map, based on the multibeam echo sounding data, collected during the 45th cruise of the R/V
Akademik Nikolaj Strakhov
was used for this analysis. It was established that large-scale variations in the width of fracture zone valleys are determined by the distribution of stresses perpendicular to the fracture zone. In the areas with compressive stresses, the fracture zone valleys are narrower and the extension areas are wider. The difference in geodynamic settings within the DMS is due to the difference in spreading directions, which change from
89° to
93° when moving from south to north. The depth of fracture zone valleys consistently increases from the periphery of the DMS (Bogdanov and Doldrums faults) to the center (Pushcharovskiy fracture zone) in accordance with a decrease in the upper mantle temperature. In each fracture zone, the valley depth decreases from the rift- fracture zone intersections towards the center of the active part to a certain background depth. It is assumed that this phenomenon is the result of the uplift of the valley bottom, which occurred due to the decompaction of the lithosphere, caused by the serpentinization of ultramafic rocks. The violation of the revealed variations in the width and depth of fracture zone valley patterns occurs as a result of various ridges and uplifts formation in the fracture zone. In the axial zones of the active parts of the fracture zone valleys median ridges are widespread, extending parallel to the fracture zone and representing serpentinite diapirs squeezed out above the bottom surface. Transverse ridges that were formed 10‒11 million years ago as a result of the lithospheric plate edge flexural bending under extensional conditions are now located in the western passive parts on the southern sides of the of Doldrums and Pushcharovskiy fracture zone valleys. The transverse ridge on the northern side of the Vernadskiy fracture zone, which includes Mount Peyve, was formed between 3.65‒2.4 Ma. Due to the frequent jumps of the spreading axis in this region, it was divided into three segments. There are interfracture zone ridges in megatransforms, which in the active part consist of two fracture zone valleys. The times of their formation were in the Pushcharovskiy megatransform, 30‒32 million years ago and in the Doldrums megatransform, about 4 million years ago. Due to the curvilinearity of the outlines and under the pressure of moving lithospheric plates, the interfracture zone ridges experience longitudinal (along the fault) compressive and tensile stresses, which are compensated by vertical uplifts of their separate blocks and the formation of depressions, pull apart depressions, and spreading centers (the latter are only in Pushcharovskiy megatransform). The structure-forming processes that determine the patterns and morphology of the fracture zones as a part of the DMS are related in their origin to the spreading and transform geodynamic systems.
The diagnostic sensitivity and specificity of antigen ELISA developed in the present study was found to be 97.4% and 99.0% respectively, with a Cohen’s kappa value of 0.96.
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•Antigen ...detecting ELISA has been developed using monoclonal antibodies.•The diagnostic sensitivity and specificity was found to be 97.4% and 99.0% respectively, with a Cohen’s kappa value of 0.96.•Dilution assay detected 11.5 trypanosomes per mL from blood, plasma and purified trypanosomes samples.•The developed assay can be explored in the detection of active infection of surra for field application.
Trypanosomosis, an endemic disease in Asia, America (central and south) and Africa causes havoc economical loss in livestock industry. The carrier animals which are symptomless and harbours low level of parasites can act as a source of infection. The level of parasitaemia fluctuates, especially during the latent infection; moreover the antibodies which are not found early in the infection may persit even after recovery or chemotherapy. The parasitological and/or serological tests always can not detect current infection or carrier animals. Hence, in the present study double antibody sandwitch antigen detection ELISA (Ag-ELISA) is developed to detect circulating trypanosomes. The new assay has been evaluated using 554 field samples comprising bovine and camel. The diagnostic sensitivity and specificity of the new assay was found to be 97.4% and 99.0% respectively, with a Cohen’s kappa value of 0.96. The developed assay could detect 11.5 Trypanosoma evansi per mL from the experimentally infected blood, buffy coat and purified T. evansi samples. The findings revealed that the developed assay can be exploited as a potential diagnostic tool in the detection of active trypanosomal infection.
Trypanosoma evansi, a haemoflagellated protozoan parasite, is responsible for chronic as well as the acute debilitating disease called surra in a wide range of herbivores and carnivores including ...domestic and wild animals. Since the parasite is having wide host range, there is a need for diagnostic test which can detect the T. evansi specific antibody in different species of animals for generating sero-surveillance data. In the present study we developed and evaluated competitive enzyme immunoassay using monoclonal antibodies (MAbs) raised against recombinant variable surface glycoprotein (rVSG) of T. evansi. The immunoreactivity of the developed MAbs (IgG3-subtype) was evaluated by immunoblot as well as ELISA and subsequently used in the development and standardization of competitive ELISA (C-ELISA). Further, the serological data generated from the C-ELISA using reference samples constituting true positive or surely infected (35), true negative (45), sero-positive (225) and sero-negative (215) samples and was analyzed statistically. The true positivity/negativity was determined by thin blood smear examination and diagnostic PCR assay, While, seropositivity/seronegativity of the reference samples was determined through standard reference tests. The data showed the diagnostic sensitivity of 92.6% and specificity of 96.4% with Cohen's kappa value of 0.88. In order to determine the utility of C-ELISA in detecting T. evansi antibodies in different species of animals, the assay was further evaluated with 1361 field sera sample comprising bovine, horse, donkey and camel. Since the C-ELISA described herein has showed high sensitivity and specificity, this single test can be explored in the sero-surveillance of T. evansi in a wide range of animals.
Frequency distribution graph establishing diagnostic sensitivity and specificity of Competitive ELISA. Display omitted
•Monoclonal antibody production•CI-ELISA development•Exhibit high sensitivity and specificity
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•Antigen ELISA has been developed using monoclonal antibodies raised against recombinant VSG of T. evansi.•The assay has been evaluated using 652 blood samples collected from cattle, ...buffalo, horse and camel.•The diagnostic sensitivity and specificity of the assay was found to be 97.4% and 96.4% respectively, with a positive-negative cut-off OD value >0.28.
Trypanosoma evansi, a haemo-flagellated protozoan parasite causes chronic wasting disease in a wide range of animals. For its diagnosis, blood smear examination is useful in clinical cases for direct identification of the parasite but in latent infection the carrier animals are difficult to screen out by conventional blood smear test. Harboring low level of parasites and showing no symptom, the carrier animals for surra can act as a source of infection. The level of parasitaemia fluctuates, especially during latent infection; moreover the antibodies which are not found early in the infection may persist even after recovery or chemotherapy. In the present study a double antibody sandwich ELISA exploring, monoclonal antibodies and hyperimmune serum, raised against recombinant variable surface glycoprotein has been developed to detect circulating trypanosome antigens. The developed antigen detection ELISA (Ag-ELISA) was evaluated using 652 blood samples collected from cattle, buffalo, equine and camel. The statistical analysis of the data showed diagnostic sensitivity and specificity at 97.4% and 96.4% respectively, with a positive-negative cut-off OD value >0.28. Furthermore, the detection limit of the assay was found to 7.15 trypanosomes per mL. The present finding revealed that the developed assay can be exploited as a potential diagnostic test in the detection of circulating trypanosome antigens and also can be used as a population screening test for multiple animal species for detection of active infection for further treatment and control of the disease.
The paper presents new data on the Doldrums megatransform fault located in the northern Equatorial Atlantic (6.5°–9° N), which consists of four transform faults with large offsets: Doldrums, ...Vernadsky, Pushcharovsky, and Bogdanov. Several types of spreading segments of the Mid-Atlantic Ridge (MAR) displaced by transform faults were identified by analyzing seafloor bathymetric survey results from a multibeam echo sounder on cruise 45 of the R/V
Akademik Nikolaj Strakhov
in 2019. Depending on the depth of the axial spreading zone, the structure of segments varies from typical for mid-oceanic ridges to intratransform spreading centers. The shallowest spreading segments south of the Bogdanov FZ and north of the Vernadsky FZ correspond to spreading cells with small neovolcanic rises and abyssal hills in combination with oceanic core complexes on the flanks of the MAR. The deepest intra-transform spreading center formed between two branches of the double Pushcharovsky FZ. This center is characterized by the largest neovolcanic rise, a nonstationary position, and origination of new spreading centers in areas of pull-apart basins, which form under the influence of extension directed towards the intra-transform domain of the Pushcharovsky FZ. Segments intermediate in depth and structure form between the Vernadsky, Pushcharovsky, and Bogdanov Fracture zones. The segments are characterized by large neovolcanic rises in the axial zone and asymmetrical structure of the flanks. The eastern flank exhibits oval rises, which are mostly composed of serpentinized ultramafic rocks; the western flank shows rare rift ridges (former neovolcanic rises). We analyzed the oblique structures with respect to the spreading direction, which are abundant in the studied region, and considered possible reasons for their origination in Equatorial Atlantic.
Flagellar (FLA) protein of T. evansi was isolated and purified and its related monoclonal antibody (MAbs) was produced. Later, FLA antigen and its related MAbs were used for the development of ...CI-ELISA. While comparing the developed test with CATT/T. evansi antigen from reference laboratory, it was found that the developed test is having sensitivity of 95.8% and specificity of 94.4%, to detect the antibodies against T. evansi in different species of animals. The Cohen’s kappa value was recorded as high of 0.83. The data from the present study suggested that the developed test has the potentiality to use in sero surveillance of surra in animals.
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•Flagellar antigen and monoclonal antibody (MAb) based CI-ELISA was developed for detection of surra antibodies in animals.•The test showed 95.8% sensitivity, 94.4% specificity and 0.83 Cohen’s kappa value when compared with standard test.•The data suggested that the developed test has the potentiality to use in sero surveillance of ‘surra’ in animals.
Trypanosoma evansi causes a disease known as ‘surra’ in wide range of domesticated and wild animals including cattle, buffaloes, horses, camels etc. The disease is transmitted through the bites of haematophagous tabanid flies and is characterized by undulating fever, chronic progressive weakness, and hypoglycemia leading to low productivity in animals. In the present study, monoclonal antibodies (MAbs) have been produced (IgG3 sub-type) against purified flagellar (FLA) protein of T. evansi and its immunoreactivity was evaluated by serological tests. MAb and purified protein were then exploited in the development of CI-ELISA and the diagnostic potentiality of the new ELISA test has been evaluated using 1230 sera samples from field animals including cattle, buffaloes, camels, horses and donkeys. The statistical analysis of the data showed optimum combination of sensitivity and specificity at 95.8 and 94.4, respectively. The positive–negative cut off percentage inhibition (PI) value was found to be >55, with a Cohen’s Kappa value of 0.83. The study showed that the new assay has potential for application in sero-diagnosis as well as sero-surveillance of surra.
Strong acceleration of abyssal flows in narrow deep‐water channels and fracture zones is a key feature of bottom circulation in the Atlantic Ocean. In the Equatorial Atlantic, these bottom currents ...transport Antarctic Bottom Water (AABW) over the Mid‐Atlantic Ridge from west to east. The main pathway for Antarctic waters in this region is the Romanche Fracture Zone. The deepest point of this fracture zone is the Vema Deep; its maximum depth based on the published data is 7,856 m. This deep basin is filled by waters of Antarctic origin overflowing a sill in a narrow channel. During the expedition on the R/V Akademik Ioffe (August 2022), we revealed a strong flow in the middle part of the Romanche Fracture Zone and collected new data on thermohaline and kinematic structures of this gravity current. Our survey is the first observational evidence of the intense flow into the Vema Deep. At the sill, the flow splits into branches flowing through three distinct channels of intricate configuration located in the southern transform valley of the fracture zone. The northern channel is proved to be the main pathway of the coldest and densest bottom waters to the Vema Deep. We also found that vertical structure of the flow is presented by two individual jets, namely the deep and bottom jets. The total transport of AABW through the Romanche Fracture Zone at this location was estimated at 1.40 Sv; the velocities exceeding 10 cm/s were found at depths greater than 5,000 m.
Plain Language Summary
Abyssal basins of the Atlantic Ocean are filled with cold and dense Antarctic waters. Propagation of these waters plays an important role in the heat transport of the ocean and influences the Earth's climate. The most intense bottom currents of Antarctic waters are formed in the narrow abyssal channels connecting deep ocean basins. In particular, fracture zones of the Mid‐Atlantic Ridge connect deep basins of the western and eastern Atlantic. The equatorial Romanche Fracture Zone is the deepest fracture zone in the tropical Atlantic and provides transport of the coldest bottom waters from the Brazil to the Guinea and Sierra Leone basins. Direct measurements from ships remain the main source of information about the structure of currents in the abyssal fracture zones. In this work, we present new field observations at the entrance to the Vema Deep, which is the deepest point of the Romanche Fracture Zone. New measurements revealed several jets of the Antarctic Bottom Water flow guided by distinct channels in the bottom topography. It was also shown that the location of the abyssal pycnocline affects the vertical structure of the abyssal currents in this region. Comparison with historical measurements shows an increase in bottom temperatures exceeding 0.06°C.
Key Points
Flow of the Antarctic Bottom Water (AABW) in the Romanche Fracture Zone intensifies at the entrance to the Vema Deep
The flow splits into multiple jets observed in three distinct channels of the fracture zone
AABW temperatures in the Vema Deep increased by 0.066°C over the last 30 years
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