Hotspot Activity Research Articles

Hybrid Plasmonic Symmetry-Protected Bound state in the Continuum Entering the Zeptomolar Biodetection Range.

Photonics bound states in the continuum (BICs) are peculiar localized states in the continuum of free-space waves, unaffected by far-field radiation loss. Although plasmonic nano-antennas squeeze the optical field to nanoscale volumes, engineering the emergence of quasi-BICs with plasmonic hotspots remains challenging. Here, the origin of symmetry-protected (SP) quasi-BICs in a 2D system of silver-filled dimers, quasi-embedded in a high-index dielectric waveguide, is investigated through the strong coupling between photonic and plasmonic modes. By tailoring the hybridizing plasmonic/photonic fractions, a trade-off is selected at which the quasi-BIC exhibits both high intrinsic Q-factor and strong near-field enhancement because of dimer-gap hotspot activation. Not only radiation loss is damped but in a configuration sustaining a lattice of plasmonic hotspots. This leads to an advantageous small modal volume for enhancing light-matter interaction. The layout of nearly embedded dimers is designed to maximize the spatial overlap between the optical field and the target molecules, enhancing reactive sensing efficiency. The architecture is evaluated for its ability to detect transactive response DNA-binding protein 43. The refractometric sensitivity outperforms current label-free biosensing platforms, reaching the zeptomolar range. The approach highlights the potential of combining plasmonic and dielectric nanomaterials for advanced sensing technologies.

Zircon Xenocrysts From Easter Island (Rapa Nui) Reveal Hotspot Activity Since the Middle Jurassic

AbstractWe report the finding of mantle‐derived zircon grains retrieved from red soils, regoliths, and beach sands from Easter Island, that are much older than the island volcanism (0–2.5 Ma) and its underlying lithosphere (Pliocene, 3–4.8 Ma). A large population of 0–165 Ma old zircons have coherent oxygen (δ18O 3.8–5.9‰) and hafnium (εHf(t)+3.5–+12.5) mantle isotopic signatures. These results are consistent with the crystallization of zircon from plume‐related melts. In addition, a chemically diverse population with ages from the Paleozoic to the Archean was found. These older populations are enigmatic but they could represent remnants of ancient subducted sediments. Meanwhile, the ∼0–165 Ma population is interpreted as plume‐derived, suggesting that the hotspot started at least ∼165 Ma ago. A spike of ∼164–160 Ma zircons could represent a Large Igneous Province (LIP) stage upon the first arrival of the plume. We use plate reconstructions to show that such a LIP would have formed on the Phoenix Plate and would have subducted below the Antarctic Peninsula around 100–105 Ma. There, LIP subduction would offer a solution for the enigmatic Palmer Land deformation event, previously proposed to result from a collision with an unknown indenter. The here‐reported “ghost” of a prolonged hotspot activity suggests that fragments of the Easter plume and of the ambient sub‐lithospheric mantle stored and re‐sampled zircon xenocrysts due to convective (re)circulation at the scale of the plume head. Our study demonstrates how zircon geochronology and geochemistry provide novel insights into global‐scale geodynamics, offering new perspectives on the dynamics of mantle plumes and hotspot activity.

Selectivity and Switchability of Hot Spot Activation in Nanolens-like Nanosphere Heterotrimers

Selectivity and Switchability of Hot Spot Activation in Nanolens-like Nanosphere Heterotrimers

Geochemical and Isotopic evidence for volcanism on the Alleppey Terrace, southwest Indian continental margin

The Arabian Sea consists of prominent undersea bathymetric highs whose genesis is often attributed to volcanism either related to the 90-85 Ma Marion or the 70-65 Ma Reunion hot spot activity on the Indian Plate. The enigmatic Alleppey Terrace (AT) is one such significant bathymetric high in the southwestern continental margin of India. We studied the siliciclastic sediments deposited on the AT and the adjacent shelf region using major/trace element, and Sr-Nd isotope geochemistry to decipher their provenances and implications of the findings for the origin of the Terrace. Geochemical data suggest that the AT sediments are chemically distinct from the adjacent shelf sediments, with the former having been sourced from juvenile mafic rocks and the latter from significantly older, felsic continental crustal rocks. Although currently located at a water depth of ∼300 m, AT was likely exposed above the sea level in the past and had undergone subaerial weathering and lateritization. The εNd of AT sediments (−17.1 to −10.9), which is much radiogenic than that of the shelf sediments (−26.4 to −22.2), indicates significant presence of a juvenile basaltic component - likely derived from in situ weathering of the local seafloor/basement. The common component in both the terrace and shelf sediments appears to be terrigenous, deposited by the local rivers draining the Western Ghats. Conspicuous similarities of trace element ratios and isotopic compositions of the terrace sediments with those of the volcanic rocks temporally and spatially related to the Deccan volcanism suggest that the AT may contain traces of the end Cretaceous Reunion-Deccan plume/hotspot activity on the India subcontinent.

Periodicity in the Deccan Volcanism Modulated by Plume Perturbations at the Mid‐Mantle Transition Zone

AbstractIn peninsular India, the Deccan Traps record massive, continental‐scale volcanism in a sequence of magmatic events that corresponds with the timing of mass extinction at the Cretaceous‐Paleogene boundary. Although the Deccan volcanism is linked with the Réunion hotspot, the origin of its periodic magmatic pulses is still debated. We developed a numerical model replicating the geodynamic scenario of the African superplume underneath a moving Indian plate to explore the mechanism of magmatic pulse generation during the Deccan volcanism. Our model results revealed a connection between the Réunion hotspot and the African large low shear‐wave velocity province (LLSVP), suggesting that the pulses were produced from a thermochemical plume originated in the lower mantle. The ascending plume had stagnation at 660 km due to phase changes in the transition zone, and its head eventually underwent detachment from the tail under the influence of Indian plate movement to produce sequentially four major pulses (periodicity: 5–8 Ma), each giving rise to multiple secondary magmatic pulses at a time interval of ∼0.15–0.4 Ma. This study sheds a new light on the mechanism of periodic hotspot activities from a global perspective.

Development of one-step roll-to-roll system with incorporated vacuum sputtering for large-scale production of plasmonic sensing chips

The trade-off relationship between cost and performance is a major challenge in the development of surface-enhanced Raman spectroscopy (SERS) sensors for practical applications. We propose a roll-to-roll system with incorporated vacuum sputtering to manufacture Ag-coated nanodimples (Ag/NDs) on A4-scale films in a single step. The Ag/ND SERS platforms were prepared via O2 ion beam sputtering and Ag sputtering deposition. The concave three-dimensional spaces in the Ag/NDs functioned as hotspots, and their optimal fabrication conditions were investigated with two variables: moving speed and Ag thickness. The entire process was automated, which resulted in highly consistent optical responses (i.e., relative standard deviation of ∼10%). The activation of plasmonic hotspots was demonstrated by electric-field profiles calculated via the finite-difference time-domain method. The wavelength dependency of the Ag/ND platforms was also examined by dark-field microscopy. The results indicate that the developed engineering technique for the large-scale production of Ag/ND plasmonic chips would likely be competitive in the commercial market.

Complete transition from mantle plume to mantle exhumation on the Central Atlantic Guyana/Suriname margin

Modern data are clarifying tectonic transitions from continents to oceans. The importance of magmatic additions relative to mechanical extension varies between cases and through time based on observations of isolated margins and ridges. Magma poor spreading centers and magma rich continental margins are both well known. Here we present data to document the complete and continuous evolution from a magma rich Central Atlantic margin to a magma-starved ocean floor. Tectonic changes correlate with separation rate changes. Early Jurassic hotspot volcanism initially overwhelmed slow extension to build the Demerara Plateau at the eastern edge of the margin, but hotspot activity waned near the end of the Middle Jurassic. Normal spreading rates and normal thickness oceanic crust prevailed through most of the Oxfordian. Spreading slowed in the Kimmeridgian but magmatic addition slowed even more, evidenced by normal faults that offset the full oceanic crust and by outboard exhumed mantle.

Abstract WP73: Temporal Effects on Mobile Stroke “Hot” Zones Using a Geo-Spatial Software Analysis

Background: We sought to identify variations of mobile stroke unit (MSU) hotspot activity based on time of day by using a geospatial analysis software. Methods: The Mobile Stroke Treatment Unit of metropolitan Columbus, Ohio, provides emergency stroke care coverage for 325 square miles which spans 47 zip codes. Our MSU is operational from 0700-1900 and is dispatched for all 911 calls designated as probable or possible strokes. We retrospectively reviewed all MSU calls from May 2019 to June 2022. The calls were organized into zip codes and 3 time epochs (0700-1100, 1101-1500, 1501-1900). Our endpoint was to determine hotspots of MSU activity during these epochs using the ESRI/ArcGIS Online geospatial analysis software. Statistically significant hotspots are qualitatively defined as clustered regions with high activity and quantitatively defined as having a Gi Bin score > 2, which correlates to statistical confidence > 95%. Results: We received 5198 calls during our study period; 1535 from 0700-1100; 2002 from 1101-1500; 1661 from 1501-1900. All hotspots had an average separation of 6.2 miles. From 0700-1100, 5 zip codes (12.9% of calls) were considered hotpots (Figure-Top). From 1101-1500, 15 zip codes (44.7% of calls) were considered hotspots (Figure-Middle). From 1501-1900, 9 zip codes (34.1% of calls) were considered hotspots (Figure-Bottom). Five zip codes were statistical hotspots during the entire coverage period. Four additional zip codes also showed hotspot activity and overlapped 1101-1900 time epochs. Conclusions: Our study showed that hotspot activity can vary throughout the day and must be considered for strategic MSU deployment. Prospective validation is needed to determine if such strategic deployment is feasible and can improve clinical outcomes.

Toxic metal contamination effects mediated by hotspot intensity of soil enzymes and microbial community structure

Metal contamination from mine waste is a widespread threat to soil health. Understanding of the effects of toxic metals from mine waste on the spatial patterning of rhizosphere enzymes and the rhizosphere microbiome remains elusive. Using zymography and high-throughput sequencing, we conducted a mesocosm experiment with mine-contaminated soil, to compare the effects of different concentrations of toxic metals on exoenzyme kinetics, microbial communities, and maize growth. The negative effects of toxic metals exerted their effects largely on enzymatic hotspots in the rhizosphere zone, affecting both resistance and the area of hotspots. This study thus revealed the key importance of such hotspots in overall changes in soil enzymatic activity under metal toxicity. Statistical and functional guild analysis suggested that these enzymatic changes and associated microbial community changes were involved in the inhibition of maize growth. Keystone species of bacteria displayed negative correlations with toxic metals and positive correlations with the activity of enzymatic hotspots, suggesting a potential role. This study contributes to an emerging paradigm, that changes both in the activity of soil enzymes and soil biota – whether due to substrate addition or in this case toxicity – are largely confined to enzymatic hotspot areas.

Comparison of Otsu and an adapted Chan–Vese method to determine thyroid active volume using Monte Carlo generated SPECT images

BackgroundThe Otsu method and the Chan–Vese model are two methods proven to perform well in determining volumes of different organs and specific tissue fractions. This study aimed to compare the performance of the two methods regarding segmentation of active thyroid gland volumes, reflecting different clinical settings by varying the parameters: gland size, gland activity concentration, background activity concentration and gland activity concentration heterogeneity.MethodsA computed tomography was performed on three playdough thyroid phantoms with volumes 20, 35 and 50 ml. The image data were separated into playdough and water based on Hounsfield values. Sixty single photon emission computed tomography (SPECT) projections were simulated by Monte Carlo method with isotope Technetium-99 m (^{text {99m}}Tc). Linear combinations of SPECT images were made, generating 12 different combinations of volume and background: each with both homogeneous thyroid activity concentration and three hotspots of different relative activity concentrations (48 SPECT images in total). The relative background levels chosen were 5 %, 10 %, 15 % and 20 % of the phantom activity concentration and the hotspot activities were 100 % (homogeneous case) 150 %, 200 % and 250 %. Poisson noise, (coefficient of variation of 0.8 at a 20 % background level, scattering excluded), was added before reconstruction was done with the Monte Carlo-based SPECT reconstruction algorithm Sahlgrenska Academy reconstruction code (SARec). Two different segmentation algorithms were applied: Otsu’s threshold selection method and an adaptation of the Chan–Vese model for active contours without edges; the results were evaluated concerning relative volume, mean absolute error and standard deviation per thyroid volume, as well as dice similarity coefficient.ResultsBoth methods segment the images well and deviate similarly from the true volumes. They seem to slightly overestimate small volumes and underestimate large ones. Different background levels affect the two methods similarly as well. However, the Chan–Vese model deviates less and paired t-testing showed significant difference between distributions of dice similarity coefficients (p-value <0.01).ConclusionsThe investigations indicate that the Chan–Vese model performs better and is slightly more robust, while being more challenging to implement and use clinically. There is a trade-off between performance and user-friendliness.

Galvanically Replaced Au/Ag Nanostructures as a SERS‐Active Substrate with Progressive Interior Hotspots

AbstractInterior hotspots in surface‐enhanced Raman spectroscopy (SERS) platforms have attracted intensive attention because they enable facile methodologies and exhibit excellent sensing behavior. Molecules surrounded by plasmonic materials exhibit dual functions as field‐confined regions and analytes, and their domain consistency eventually triggers the amplification of SERS signals. In this study, to conveniently realize interior hotspots, hollow regions such as voids and interstitials are strategically introduced via a galvanic reaction (GR) as a result of the difference in reduction potential between Au and Ag. The imbalanced stoichiometric ratio and diffusion fluxes induce the Kirkendall effect in conjunction with the GR between Au and Ag. SERS platforms with narrow and densified interior hotspots are optimized by controlling the reaction time. The activation of interior hotspots is confirmed using the finite‐difference time‐domain method, which indicates a theoretical enhancement factor of 1.07 × 107 based on a fourth‐power approximation. The spontaneous GR reaction enables sensing operation with high reproducibility (relative standard deviation of &lt;10%). The proposed bimetallic platforms are used to trace methylene blue and rhodamine 6G dyes until their concentrations reach 50 nm. Therefore, the GR methodology for interior hotspot engineering demonstrates the potential for enabling the fabrication of SERS platforms with practical applications.

Structure of the Lithosphere and Conditions of Formation of Oceanic Rises in the Sub-Antarctic Sector of the South Atlantic Using Density and Physical Modeling

The kinematic reorganization of plate boundaries, accompanied by the cessation of old spreading centers and the formation of new ones, and manifestations of plume magmatic activity in the southeastern part of the Antarctic sector of the South Atlantic led to the formation of a complex structural plan of the region. As a result of these processes, a system of ridges, rises, and plateaus with varying morphological expressions and different geophysical characteristics were formed. Results of density modeling of the crust and lithosphere structure along profiles extending from the Falkland Plateau to the Mozambique Ridge and crossing a series of rises and ridges separated by deepwater basins showed that rises have different crustal structures, indicating different origins. The conditions for the formation of different types of submarine rises were studied based on physical modeling. A new experimental model of lithosphere and submarine rises formation in the region was constructed, in which the fracture of the large Agulhas magmatic province into the Agulhas Plateau and the Northeast Georgia rise played an important role, as did the accretion of oceanic crust on the Agulhas spreading ridge and subsequent jump of the spreading axis, leading to the cessation of spreading on this ridge and the formation of the southern segment of the Mid-Atlantic Ridge and its associated Meteor and Islas Orcadas rises. Jumps of spreading axes, accompanied by the periodic activity of hotspots, played an important role in the formation of submarine rises of different genetic types, which determined the different structures of their crust.

Short-range axono-cortical evoked-potentials in brain tumor surgery: Waveform characteristics as markers of direct connectivity

ObjectiveIntraoperative measurement of axono-cortical evoked potentials (ACEP) has emerged as a promising tool for studying neural connectivity. However, it is often difficult to determine if the activity recorded by cortical grids is generated by stimulated tracts or by spurious phenomena. This study aimed to identify criteria that would indicate a direct neurophysiological connection between a recording contact and a stimulated pathway. MethodsElectrical stimulation was applied to white matter fascicles within the resection cavity, while the evoked response was recorded at the cortical level in seven patients. ResultsBy analyzing the ACEP recordings, we identified a main epicenter characterized by a very early positive (or negative) evoked response occurring just after the stimulation artifact (<5 ms, |Amplitude| > 100 µV) followed by an early and large negative (or positive) monophasic evoked response (<40 ms; |Amplitude| > 300 µV). The neighboring activity had a different waveform and was attenuated compared to the hot-spot activity. ConclusionsIt is possible to distinguish the hotspot with direct connectivity to the stimulated site from neighboring activity using the identified criteria. SignificanceThe electrogenesis of the ACEP at the hotspot and neighboring activity is discussed.

Importance of DICER1 pathogenic variants in non-small cell lung cancer.

e20602 Background: DICER1 encodes a miRNA processing enzyme involved in regulation of cell proliferation and differentiation. The role of DICER1 pathogenic variants (PVs) in non-small cell lung cancer (NSCLC) is relatively unknown. Germline and/or somatic PVs have been reported in pleuropulmonary blastoma, pulmonary blastoma (PB), and low-grade/well-differentiated fetal adenocarcinoma (WDFLAC), with clustering of somatic PVs at specific metal ion binding residues referred to as hotspot alterations. PVs in CTNNB1, resulting in constitutive activation of the WNT signaling pathway, have also been implicated in PB and WDFLAC. This study seeks to establish the frequency of somatic DICER1 hotspot PVs that occur in all NSCLCs, their co-occurrence with other PVs in DICER1 and with alterations of CTNNB1/WNT signaling, and their histologic correlates. Methods: Molecular sequencing data collected from 12,146 NSCLCs at Caris Life Sciences were queried for cases featuring somatic DICER1 variants. For those tumors harboring hotspot PVs, sequencing for CTNNB1 and APC mutations was performed, as well as histological review, including examination of beta-catenin immunohistochemical (IHC) staining. Results: Of the 12,146 NSCLCs analyzed, 235 (1.9%) were found to have one or more DICER1 PVs. Of these 235, 225 cases demonstrated one variant, while 10 tumors featured two. Gene analysis revealed that 8 of the observed PVs cases contained hotspot alterations: 2 in the single variant cases and 6 in the double variant cases. The remaining 4 double variant cases harbored a combination of truncating, non-hotspot missense, or splice variants. No significant differences were observed for age or smoking status between DICER1 hotspot-positive and hotspot-negative groups. All but one tumor were considered to be in histologic spectrum of PB/WDFLAC. Of the 8 DICER1 hotspot-positive cases, 1 had a PV in APC, 4 had a CTNNB1 PV, 1 had a PV in both APC and CTNNB1, and 2 had neither. Beta-catenin IHC showed nuclear positivity in 5 tumors that had a PV in either CTNNB1 and/or APC.. Conclusions: This study demonstrates that DICER1 somatic hotspots select for morphologic features of tumor types such as PB and WDFLAC, but are not implicated in the most common forms of NSCLC. Furthermore, DICER1 hotspot-positive NSCLCs frequently harbor CTNNB1 and/or APC alterations, with many cases exhibiting nuclear staining by beta-catenin IHC, suggesting a possible synergistic relationship between DICER1 hotspot PVs and activation of the WNT signaling pathway in the formation of pulmonary tumors. These findings emphasize the importance of molecular testing in clinical practice such that detecting somatic DICER1 hotspot alterations aids in the diagnosis of rare lung cancers, which ultimately require special consideration with respect to disease severity and treatment.

Thermochronology and U–Pb dating of detrital zircons from the Demerara Plateau (French Guiana‐Suriname): Implications for the provenance of the Early Cretaceous syn‐rift sedimentation

AbstractThe provenance of Early Cretaceous sandstones dredged on the northern margin of the Demerara Plateau, offshore French Guiana and Suriname, reveals the sediment routing system that prevailed through the Equatorial Atlantic rifting. Fission‐track analysis and U–Pb dating of 310 and 111 detrital zircons, respectively, have been performed. Microfacies analysis and inherited cooling ages suggest that the sandstones were deposited in shallow marine environments during the Early Cretaceous, before the Late Albian drowning of the marginal plateau. Most of the U–Pb zircon crystallisation ages are comprised of between 700 and 600 Ma and are attributed to the Pan‐African‐Brasiliano orogeny. Statistical and chronological evidence suggest that the zircon fission‐track cooling ages were inherited from source materials. Triassic peak ages (&gt;50% of the population) are attributed to the early phase of Central Atlantic rifting. One sample records a cooling phase at ca. 170 Ma, presumably following volcanic hotspot activity and the opening of the Central Atlantic Ocean. Two other samples record the rapid exhumation of the French Guiana transform margin during the Equatorial Atlantic rifting (127 ± 11 and 106 ± 8 Ma). We propose a source‐to‐sink model in which the Pan‐African‐Brasiliano basement of the margin was eroded as a result of flexural uplift along the French Guiana margin, and the detrital material funnelled in the Cacipore graben sustained the Early Cretaceous syn‐rift sedimentation on the marginal plateau.

The effect of DNA polymorphisms and natural variation on crossover hotspot activity in Arabidopsis hybrids

In hybrid organisms, genetically divergent homologous chromosomes pair and recombine during meiosis; however, the effect of specific types of polymorphisms on crossover is poorly understood. Here, to analyze this in Arabidopsis, we develop the seed-typing method that enables the massively parallel fine-mapping of crossovers by sequencing. We show that structural variants, observed in one of the generated intervals, do not change crossover frequency unless they are located directly within crossover hotspots. Both natural and Cas9-induced deletions result in lower hotspot activity but are not compensated by increases in immediately adjacent hotspots. To examine the effect of single nucleotide polymorphisms on crossover formation, we analyze hotspot activity in mismatch detection-deficient msh2 mutants. Surprisingly, polymorphic hotspots show reduced activity in msh2. In lines where only the hotspot-containing interval is heterozygous, crossover numbers increase above those in the inbred (homozygous). We conclude that MSH2 shapes crossover distribution by stimulating hotspot activity at polymorphic regions.

A flexible RecC surface loop required for Chi hotspot control of RecBCD enzyme.

Escherichia coli RecBCD helicase-nuclease promotes vital homologous recombination-based repair of DNA double-strand breaks. The RecB nuclease domain (Nuc) is connected to the RecB helicase domain by a 19-amino-acid tether. When DNA binds to RecBCD, published evidence suggests that Nuc moves ∼50 Å from the exit of a RecC tunnel, from which the 3'-ended strand emerges during unwinding, to a distant position on RecC's surface. During subsequent ATP-dependent unwinding of DNA, Nuc nicks the 3'-ended strand near 5'-GCTGGTGG-3' (Chi recombination hotspot). Here, we test our model of Nuc swinging on the tether from the RecC tunnel exit to the RecC distant surface and back to the RecC tunnel exit to cut at Chi. We identify positions in a flexible surface loop on RecC and on RecB Nuc with complementary charges, mutation of which strongly reduces but does not eliminate Chi hotspot activity in cells. The recC loop mutation interacts with recB mutations hypothesized to be in the Chi-activated intramolecular signal transduction pathway; the double mutants, but not the single mutants, eliminate Chi hotspot activity. A RecC amino acid near the flexible loop is also essential for full Chi activity; its alteration likewise synergizes with a signal transduction mutation to eliminate Chi activity. We infer that altering the RecC surface loop reduces coordination among the subunits, which is critical for Chi hotspot activity. We discuss other RecBCD mutants with related properties.

Rapid Evolution of the Fine-scale Recombination Landscape in Wild House Mouse (Mus musculus) Populations.

Meiotic recombination is an important evolutionary force and an essential meiotic process. In many species, recombination events concentrate into hotspots defined by the site-specific binding of PRMD9. Rapid evolution of Prdm9's zinc finger DNA-binding array leads to remarkably abrupt shifts in the genomic distribution of hotspots between species, but the question of how Prdm9 allelic variation shapes the landscape of recombination between populations remains less well understood. Wild house mice (Mus musculus) harbor exceptional Prdm9 diversity, with >150 alleles identified to date, and pose a particularly powerful system for addressing this open question. We employed a coalescent-based approach to construct broad- and fine-scale sex-averaged recombination maps from contemporary patterns of linkage disequilibrium in nine geographically isolated wild house mouse populations, including multiple populations from each of three subspecies. Comparing maps between wild mouse populations and subspecies reveals several themes. First, we report weak fine- and broad-scale recombination map conservation across subspecies and populations, with genetic divergence offering no clear prediction for recombination map divergence. Second, most hotspots are unique to one population, an outcome consistent with minimal sharing of Prdm9 alleles between surveyed populations. Finally, by contrasting aggregate hotspot activity on the X versus autosomes, we uncover evidence for population-specific differences in the degree and direction of sex dimorphism for recombination. Overall, our findings illuminate the variability of both the broad- and fine-scale recombination landscape in M. musculus and underscore the functional impact of Prdm9 allelic variation in wild mouse populations.

Cretaceous intraplate volcanism of Govorov Guyot and formation models of the Magellan seamounts, Pacific Ocean

ABSTRACT The OIB-type volcanic rocks of Govorov Guyot in Magellan Seamounts (Pacific Ocean) include basalts, trachybasalts, basaltic trachyandesites, and trachyandesites dated by the 40Ar-39Ar plateau from 121 ± 2.8 to 98.5 ± 1.4 Ma. Some rocks bear amphibole-spinel wehrlite xenoliths and clinopyroxene-amphibole (Cpx-Amp) mantle vein fragments in xenoliths and xenocrysts, which are remnants of metasomatized oceanic lithosphere. The pressure and temperature crystallization for pargasitic amphibole were the highest (1170–1130°C and 2.5–1.6 GPa, 73–53 km depth) in wehrlite peridotite and the lowest (1.6–1.1 GPa, shallower than 52 km, and 1070–980°C) in Cpx-Amp metasomatic mantle veins. Ti-bearing Amp phenocrysts and microlites crystallized from the parent melts of basaltic rocks at 1060–910°C and 1.2–0.4 GPa (40–15 km). The ascending basaltic melts lost H2O from 8.6 ± 1.2 to 2.6 ± 0.4 wt% upon decompression. Amphibole mantle xenocrysts became replaced by Ti-magnetite- and rhönite-bearing mineral assemblages in intermediate magma chambers within oceanic crust (3–7 km). Pargasitic Amp in wehrlite and metasomatic mantle veins may have crystallized at different depths from hydrous (6–4.5 ± 0.7 wt% H2O) mafic melts that percolated through peridotite. The sources of heat and metasomatic agents (silicate melts and/or fluids enriched in volatiles) most likely had no relation to the Pacific Plate subduction but may be associated with the Southern Pacific Superplume in the South Pacific Thermal and Isotopic Anomaly region, or may be located at the Lithosphere-Asthenosphere Boundary (LAB) level in the plume absence. Repeated events of Cretaceous intraplate volcanism in the Magellan guyots can be explained in terms of plume (hotspot) activity or decompression partial melting of enriched or metasomatized asthenosphere and/or metasomatized oceanic lithosphere caused by Pacific Plate deformation and fracturing from the LAB level.

Geochemistry and geochronology of the Rajmahal Flood Basalt Province, northeastern India: Genetic links to Kerguelen hotspot activity

Geochemistry and geochronology of the Rajmahal Flood Basalt Province, northeastern India: Genetic links to Kerguelen hotspot activity