Melting Events Research Articles

Geochemical insights and petrogenetic processes of ophiolitic fragments from Avajiq and Silvana: implications for Neo-Tethyan Evolution in northwest Iran

ABSTRACT The Avajiq and Silvana ophiolites are part of the Late Cretaceous Neo-Tethyan ophiolitic belt located in northwestern Iran, between the Sevan-Akera suture to the north and the Bitlis-Zagros suture in the southwest. The Avajiq ophiolite formed between the South Armenian Block (SAB) with a Gondwanan origin to the north and the Eastern Anatolian Plateau (EAP) to the south and west. In contrast, the Silvana ophiolite is situated at the juncture of the EAP and the Sanandaj-Sirjan Zone (SaSiZ). The mantle sequences of both ophiolites are composed of harzburgites with various degrees of refertilization. The compositions of olivine (Fo: 90–90.8), spinel (Mg#: 0.49 to 0.69 and Cr#: 0.25 to 0.59), orthopyroxene (Mg#: 0.90–0.96), and clinopyroxene (Mg#: 0.91–0.94), along with the bulk geochemistry of highly serpentinized ultramafic rocks, were evaluated to distinguish the tectonic settings of both ophiolites. The spinel composition indicates that the harzburgites represent mantle residuum formed after moderate to high degrees of partial melting (16–19% for the Avajiq and 10–17% for the Silvana). This is supported by the low bulk rock content of incompatible elements such as Ti and heavy rare earth elements (REE). Harzburgites generally display U-shaped chondrite-normalized REE patterns, with elevated light REE (LaN/SmN = 3.5–4), reflecting early partial melting events and multiple episodes of depletion, modified by subsequent melt/fluid-dominated metasomatism. The observed moderate to significant enrichment in fluid-mobile elements, such as U, Pb, Ba, and Sr, in the harzburgites are linked to serpentinization/refertilization resulting from fluid/melt-rock interactions. Field relationship and geochemical comparisons with other Neo-Tethyan ophiolites suggest that most samples from the Silvana ophiolite along with those from the Zagros ophiolites, predominantly exhibit abyssal characteristics, although some may be more closely related to fore-arc settings. In contrast, the Avajiq fore-arc ophiolite is associated with the Khoy-Maku back-arc basin, situated far from the southern and northern Neo-Tethyan sutures.

The initial solar system abundance of 60Fe and early core formation of the first asteroids.

High-precision Ni isotope analyses of the differentiated andesitic meteorite Erg Chech 002 (EC 002), the oldest known crustal fragment of a planetesimal, show that short-lived 60Fe was present in the early solar system with an initial 60Fe/56Fe ratio of (7.71 ± 0.47) × 10-9, which is five times more precise than previous estimates and is proposed to be the reference value for further studies. Using this ratio, the Ni isotopic composition of EC 002 implies that metal segregation in the source of the EC 002 parental melts took place [Formula: see text] million years (Myr) after solar system formation, and similar very early metal-silicate differentiation ages are obtained for 4-Vesta ([Formula: see text] Myr) and the angrite parent body ([Formula: see text] Myr). Such an early age dictates a specific accretion and differentiation history for the EC 002 parent body, with metal segregation occurring at relatively low temperatures (1000° to 1200°C), followed by a high-temperature silicate melting event.

Concurrent Bering Sea and Labrador Sea ice melt extremes in March 2023: a confluence of meteorological events aligned with stratosphere–troposphere interactions

Abstract. Today's Arctic is characterized by a lengthening of the sea ice melt season, as well as by fast and at times unseasonal melt events. Such anomalous melt cases have been identified in Pacific and Atlantic Arctic sector sea ice studies. Through observational analyses, we document an unprecedented, concurrent marginal ice zone melt event in the Bering Sea and Labrador Sea in March of 2023. Taken independently, variability in the cold-season ice edge at synoptic timescales is common. However, such anomalous, short-term ice loss over either region during the climatological sea ice maxima is uncommon, and the tandem ice loss that occurred qualifies this as a rare event. The atmospheric setting that supported the unseasonal melt events was preceded by a sudden stratospheric warming event amidst background La Niña conditions that led to positive tropospheric height anomalies across much of the Arctic and the development of anomalous mid-troposphere ridges over the ice loss regions. These large-scale anticyclonic centers funneled extremely warm and moist airstreams onto the ice causing melt. Further analysis identified the presence of atmospheric rivers within these warm airstreams whose characteristics likely contributed to this bi-regional ice melt event. Whether such a confluence of anomalous wintertime events associated with troposphere–stratosphere coupling may occur more often in a warming Arctic remains a research area ripe for further exploration.

The geochronology and cooling history of type 7 chondrites: Insights into the early impact events on chondritic parent body

Type 7 chondrites, which record a higher degree of heating process than typical type 3 to type 6 chondrites, are characterized with textures and petrography of partial melting. Understanding the timing and cooling history of incipient melting event for type 7 chondrites could provide insights into the complex thermal process of the early solar system. Here, we studied two chondrites NWA 12272 and NWA 11021. Both samples display partial melting characteristics of LL chondrites, including interconnected plagioclase/high-Ca pyroxene network, zoned plagioclase and lack of chondrules, which concurs with their classification of LL7 chondrites in the Meteoritical Bulletin Database. The 53Mn-53Cr isotopic data of NWA 12272, determined by mineral separates and bulk samples, yielded an isochron with a 53Mn/55Mn ratio of (1.40 ± 0.59) × 10-6 and a corresponding absolute age of 4558.8 ± 2.3 Ma (anchored to D’Orbigny angrite). Combined with the cooling rate estimated by the integration of REE-in-two-pyroxene thermometry and two-pyroxene thermometry, Mn-Cr isochron age of 4558.8 ± 2.3 Ma and Ca-phosphate Pb-Pb age of 4517 ± 6 Ma, we suggest that NWA 12272 experienced a two-stage cooling process after the incipient melting: it exposed to a relatively cold environment with a rapid cooling rate of ∼ 30-100°C/yr at 1150–1000 °C, and soon reburied with a slower cooling rate of ∼ 13 °C/Ma at 1000–475 °C. Although the Mn-Cr isotopic study was not conducted for NWA 11021, the average Ca-phosphate Pb-Pb age of 4509 ± 7 Ma and high-temperature cooling rate (∼1-30°C/yr) of NWA 11021 are indistinguishable from or slightly lower than those of NWA 12272. Assuming NWA 11021 cooled from the same incipient melting event as NWA 12272, it could have recorded a similar two-stage cooling process. We suggest that the studied LL7 chondrites were most likely formed in the early solar system when additional impact heat overlapped on the “heated” type 5–6 chondrites. Integrated with the previous cooling rates of LL6-7 chondrites, the prevailing two-stage cooling rates of LL chondrites provide compelling evidence for the fragmentation-re-accretion process in the early history of LL chondrite parent body. This early impact event also happened in other ordinary chondrite groups and some iron meteorites.

Petrogenesis of ultramafic rocks from the Neoproterozoic Bou Azzer Ophiolite (Morocco): new insights into a long-standing geodynamic question

ABSTRACT The Neoproterozoic Bou Azzer Ophiolite, located in the Pan-African orogen of the Anti-Atlas, Morocco, exposes a well-preserved mantle section of the ophiolitic sequence. Although ultramafic rocks are the most common rock types in the sequence, they have received less attention in previous studies. In this work, we investigate the petrogenesis of these ultramafic rocks in detail, including their petrology, mineralogy, and whole rock geochemistry. The mineral assemblages are mainly formed by antigorite with minor lizardite, chlorite, and accessory Cr-spinel. The only preserved primary mantle mineral is Cr-spinel, which shows unaltered cores with Cr# between 0.61 and 0.71 and alteration rims to ferrian chromite and magnetite. Whole rock analyses indicate almost total serpentinization and, locally, strong carbonation (mass loss of ignition between 11.94 and 22.20 wt%). The non-carbonated samples preserve protolith signatures, with decreased MgO/SiO2 suggesting metasomatic processes related to serpentinization. Immobile trace elements compare well with fore-arc peridotites, while melting modelling indicates intense and polyphasic melting events. We propose polyphase melting in a subduction-initiation setting, with a first stage of 14–23% anhydrous melting, forming fore-arc basalts, and a second stage of 15–25% melting with 1 wt% H2O, forming boninites. The Bou Azzer ultramafic rocks represent the fore-arc region of a supra-subduction zone, challenging previous interpretations that suggested a back-arc position.

Multi-Stage Evolution of the Oceanic Lithosphere beneath Heard Island, Southern Indian Ocean

Abstract The Kerguelen Plateau is the second biggest submarine large igneous province (LIP) on Earth, however, the nature of the lithospheric mantle source underlying it remains poorly constrained. In this contribution, we provide novel insights into the oceanic lithospheric mantle underlying Heard Island (southern Indian Ocean), which represents the most recent and active phase of volcanic activity (<1 Ma) in the Kerguelen Plateau. We present petrographic and geochemical data for a suite of spinel-bearing harzburgite xenoliths hosted in basanite lavas and provide detailed constraints for distinguishing in situ mantle metasomatism from post-entrapment modification of the xenoliths following interaction with the host magma. We demonstrate that the xenolith mineral compositions and textures preserve a complex multistage history of different modal and cryptic transformations that occurred in the mantle due to: i) high degrees of partial melting that produced highly refractory whole-rock Mg# (Mg# = (Mg + Fe)/Mg × 100; 88–92), major element (FeO/MgO = 0.17) and mineral compositions (e.g. highly forsteritic olivine; Fo = (Mg + Fe)/Mg × 100; 91–92 mol %); ii) solid-state re-equilibration reactions during decompression that caused exsolution of clinopyroxene and Cr-spinel from xenolith orthopyroxene to form symplectite intergrowths; iii) cryptic metasomatism affecting the composition of xenolith clinopyroxene (i.e. enrichment in Na, Th, U and light rare earth elements, and depletion in Rb, Nb, Zr, Hf and Ti) due to interaction with carbonatitic melts in the mantle. Mantle fragments, entrapped by ascending basanite magmas as xenoliths were further modified by reactions with the host magma. This resulted in the partial dissolution of mantle orthopyroxene and replacement by newly formed and compositionally distinct assemblages of clinopyroxene (Mg# 87–91), olivine (Fo: 81–88 mol %) and Cr-spinel (i.e. ‘wehrlitisation’ of the xenoliths). This study highlights the utility of combining petrography and mineral chemistry to decipher the complex and sometimes overprinting and masking effects that different processes (e.g. melting events, metasomatism) exert on the lithospheric mantle, as well as constrain the processes that modify the xenoliths during transport towards the surface.

Silica spherules in Late Pleistocene‑Holocene glaciomarine sediments from the Ross Sea, Antarctica: insights into the formation and significance

In this study, we investigate silica spherules with a diameter <1.25 mm from sediment cores retrieved from the northern Drygalski Trough, during the Italian Antarctic Research Programme (PNRA) expeditions in 1999 and 2002. In the past, these unique spherules have been a subject of interest due to their distinctive characteristics. Despite previous hypotheses on their origin, a comprehensive discussion on their formation mechanism and implications in marine sediments was lacking. Our analysis encompasses the depositional environment, morphology, internal texture, major element composition, and age determination through radiocarbon dating (14C) and 40Ar‑39Ar dating of spherule-containing sediments. By integrating our findings with a critical review of existing literature, we propose that spherules form by cyclical chemical precipitation of silica when silica‑rich freshwater mixed with seawater during extensive events of ice melting. We also tentatively suggest that these spherules possibly represent a proxy for significant meltwater production and discharge into the Antarctic Ocean. This research contributes to a better understanding of silica spherules in polar marine environments and their implications for past climate conditions.

Remote Forcing for a Circulation Pattern Favorable to Surface Melt over the Ross Ice Shelf

Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasigeostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño–related sea surface temperature (SST) anomalies in the tropical central–eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to the Ross Sea. The northerly flow toward the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS. Significance Statement During austral summer, surface melt occurs over the Ross Ice Shelf, accelerates ice loss, and poses ice-sheet destabilization risks in a warming world. The northerly wind anomaly over the Ross sector provides strong poleward heat and moisture transport and is favorable for the surface melt. This wind anomaly is influenced by two remote forcings, El Niño and heating anomaly over western Australia, through generating Rossby wave trains from the tropics and subtropical Australia. This study reveals a previously unexplored relationship that atmospheric heating over western Australia influences large-scale circulation, contributing to surface melt.

Rising Extreme Meltwater Trends in Greenland Ice Sheet (1950–2022): Surface Energy Balance and Large-Scale Circulation Changes

Abstract The Greenland Ice Sheet (GrIS) meltwater runoff has increased considerably since the 1990s, leading to implications for the ice sheet mass balance and ecosystem dynamics in ice-free areas. Extreme weather events will likely continue to occur in the coming decades. Therefore, a more thorough understanding of the spatiotemporal patterns of extreme melting events is of interest. This study aims to analyze the evolution of extreme melting events across the GrIS and determine the climatic factors that drive them. Specifically, we have analyzed extreme melting events (90th percentile) across the GrIS from 1950 to 2022 and examined their links to the surface energy balance (SEB) and large-scale atmospheric circulation. Extreme melting days account for approximately 35%–40% of the total accumulated melting per season. We found that extreme melting frequency, intensity, and contribution to the total accumulated June–August (summer) melting show a statistically significant upward trend at a 95% confidence level. The largest trends are detected across the northern GrIS. The trends are independent of the extreme melting percentile rank (90th, 97th, or 99th) analyzed and are consistent with average melting trends that exhibit an increase in similar magnitude and spatial configuration. Radiation plays a dominant role in controlling the SEB during extreme melting days. The increase in extreme melting frequency and intensity is driven by the increase in anticyclonic weather types during summer and more energy available for melting. Our results help to enhance the understanding of extreme events in the Arctic.

A 3.3‐Million‐Year Record of Antarctic Iceberg Rafted Debris and Ice Sheet Evolution Quantified by Machine Learning

AbstractOver the last 3.3 million years, the Antarctic Ice Sheet (AIS) has undergone phases of ice sheet growth and decay, impacting sea level and climate globally. Presently, the largely marine‐terminating AIS loses mass primarily by iceberg calving and basal melt of ice shelves. Quantifying past rates and timing of AIS melt is vital to understanding future cryosphere and sea level changes. One proxy for past ice sheet instabilities is iceberg rafted debris (IRD) fluxes. However, traditional methods of IRD quantification are labor‐intensive. Here, we present a new method of identifying IRD grains in sediment core X‐ray images using a convolutional neural network machine learning algorithm. We present a 3.3‐million‐year record of AIS IRD melt events using sediment cores from International Ocean Discovery Program Sites U1536, U1537, and U1538 in the Southern Ocean's “Iceberg Alley.” We identify two increases in the IRD fluxes throughout this period, at ∼1.8 and 0.43 Ma. We propose that after 1.8 Ma, the AIS expanded and transitioned from a primarily terrestrial‐terminating to a primarily marine‐terminating ice sheet. Therefore, after 1.8 Ma, glacial terminations and AIS iceberg discharge are associated with variations in global ice volume, presumably through the mechanism of sea level and, therefore, grounding line change. The second AIS regime change occurs during the Mid‐Brunhes Event (∼0.43 Ma). After this time, there are heightened and continuous IRD fluxes at each glacial termination, indicating increased AIS size and instability after this time.

A Mechanism for Ice Layer Formation in Glacial Firn

AbstractThere is ample evidence for ice layers and lenses within glacial firn. The standard model for ice layer formation localizes the refreezing by perching of meltwater on pre‐existing discontinuities. Here we argue that even extreme melting events provide insufficient flux for this mechanism. Using a thermomechanical model we demonstrate a different mechanism of ice layer formation. After a melting event when the drying front catches up with the wetting front and arrests melt percolation, conductive heat loss freezes the remaining melt in place to form an ice layer. This model reproduces the depth of a new ice layer at the Dye‐2 site in Greenland. It provides a deeper insight into the interpretation of firn stratigraphy and past climate variability. It also improves the simulation of firn densification processes, a key source of uncertainty in assessing and attributing ice sheet mass balance based on satellite altimetry and gravimetry data.

Assessment of various microwave brightness temperature products and methods for surface melt detection over Greenland ice sheet

Microwave brightness temperature have widely been used for the detection of the ice sheet's surface melt conditions and understanding their spatio-temporal variability. In this study, we investigated the sensitivity of microwave brightness temperature products from three different sensors, namely, Advanced Microwave Scanning Radiometer-2 (AMSR2), Special Sensor Microwave Imager/Sounder (SSMIS) and Indian scatterometer satellite (SCATSAT-1) for surface melt detection over the Greenland ice sheet (GrIS). In-situ air temperature measurements from GC-Net AWSs were used for sensitivity and inter-comparison analysis. Our findings show that brightness temperature (Tb) from SSMIS better correlates (Pcoef = 0.81 for 19 GHz) with air temperature measurements in comparison to AMSR2 (Pcoef = 0.7 for 18 GHz) and SCATSAT-1 (Pcoef = 0.67). However, interestingly, AMSR2 and SCATSAT-1 uniquely discriminated the surface conditions during pre- and post-melt period, due to their heterogeneity in Tb values during the two period. Error analysis with respect to AWS melt days shows that SSMIS 19 GHz Tb (Tb/SSMIS/19H) products with TED method giving the most promising observations. A wide variability in Tb values is observed during the melt season across the various AWS sites depending upon the elevation, location and frequency. During our study period, using Tb/SSMIS/19H for TED method, we observed the highest melt extent area for the extreme melt event in year 2019 (∼1.12 million km2), followed by another melt event year 2021 when it went as high as ∼1.02 million km2.

Melting of W/Cu flat type component for main limiter and its impact on plasma operation in EAST experiments

A type of actively cooled W/Cu flat-type component with high heat exhaust capacity was installed as limiter during the EAST spring plasma campaign in 2022, aiming to support the long pulse operation. Unfortunately, severe melting phenomena with obvious droplets ejection of the flat-type W/Cu limiter was repeatedly monitored by CCD and IR cameras, which not only induced the failure of component but also seriously influenced plasma operation. The high temperature around midplane of W/Cu flat-type main limiter is identified to be closely connected with ICRF induced fast ions loss. Indeed, the surface temperature of W/Cu flat-type main limiter was too high to ignore. The damage of flat-type structure, however, usually started between the joint interface of W plates and CuCrZr heat sink material. Such damage would in turn lead to the gradual increase of surface temperature which eventually would cause melting of W plates. Once melting events occurred on the W/Cu flat-type main limiter, the vast majority of cases would result in plasma disruption. Moreover, the damage of main limiter would rapidly deteriorate. Hence, more attention should be paid to how to improve the fatigue lifetime of the joint interface. Such test results of flat-type W/Cu component for limiter are important references for the improvement and application of W/Cu flat-type component for high heat flux area in fusion devices.

The late Archaean granite paradox: A case study from the Zimbabwe Craton

Late- to post-tectonic high-K granites are found in many Archaean cratons and are thought to be the product of a major, crustal-scale melting event in the underlying TTG crust leading to the stabilisation of the craton. However, despite the TTG melting model being an obvious explanation for the origin of late-Archaean high-K post-tectonic granites, experimental studies show that TTGs are insufficiently fertile to produce large volumes of potassic granites. This is the late Archaean granite paradox. Here we argue that the paradox can be resolved if the TTG protolith is more potassic than might be expected from a straightforward partial melt of an Archaean basalt. We propose that a likely fertile protolith for late Archaean granites is TTG crust which has incorporated a partial melt of older felsic crust during its emplacement. This hypothesis is validated with a case study from the Neoarchaean rocks of the Zimbabwe Craton.This paradox reflects a more fundamental problem when considering the origin of Archaean TTGs, for the ‘enriched’ basaltic protolith invoked in many models of TTG genesis is not abundant in Archaean terrains, nor should it be if the basaltic protolith is a melt of primitive or depleted mantle. This means that fertile, K-rich, TTGs are not simply the product of the melting of a basaltic protolith, but involve an additional process. Three models of TTG petrogenesis are discussed which might lead to K-enrichment in the melt – the hydrothermal potassic enrichment of the basaltic protolith and the influences of fractional crystallisation and/or crustal contamination on the TTG magmas. We conclude that to produce a sufficiently fertile, K-rich TTG source in the Zimbabwe Craton the contribution of a melt phase from older TTG crust is most consistent with the major and trace element and isotopic geochemistry.

The importance of cloud properties when assessing surface melting in an offline-coupled firn model over Ross Ice shelf, West Antarctica

Abstract. The Ross Ice Shelf, West Antarctica, experienced an extensive melt event in January 2016. We examine the representation of this event by the HIRHAM5 and MetUM high-resolution regional atmospheric models, as well as a sophisticated offline-coupled firn model forced with their outputs. The model results are compared with satellite-based estimates of melt days. The firn model estimates of the number of melt days are in good agreement with the observations over the eastern and central sectors of the ice shelf, while the HIRHAM5 and MetUM estimates based on their own surface schemes are considerably underestimated, possibly due to deficiencies in these schemes and an absence of spin-up. However, the firn model simulates sustained melting over the western sector of the ice shelf, in disagreement with the observations that show this region as being a melt-free area. This is attributed to deficiencies in the HIRHAM5 and MetUM output and particularly a likely overestimation of night-time net surface radiative flux. This occurs in response to an increase in night-time downwelling longwave flux from around 180–200 to 280 W m−2 over the course of a few days, leading to an excessive amount of energy at the surface available for melt. Satellite-based observations show that this change coincides with a transition from clear-sky to cloudy conditions, with clouds containing both liquid water and ice water. The models capture the initial clear-sky conditions but seemingly struggle to correctly represent cloud properties associated with the cloudy conditions, which we suggest is responsible for the radiative flux errors.

Accretion of “young” Phanerozoic subcontinental lithospheric mantle triggered by back-arc extension—the case of the Ivrea-Verbano Zone

The subcontinental lithospheric mantle (SCLM) beneath Phanerozoic regions is mostly constituted by fertile lherzolites, which sharply contrast with cratonic mantle made of highly-depleted peridotites. The question of whether this chemical difference results from lower degrees of melting associated with the formation of Phanerozoic SCLM or from the refertilization of ancient depleted SCLM remains a subject of debate. Additionally, the timing and geodynamic environment of accretion of the fertile SCLM in many Phanerozoic regions are poorly constrained. We here document new geochemical and Nd-Hf isotopic data for orogenic lherzolite massifs from the Ivrea-Verbano Zone (IVZ), Southern Alps. Even though a few Proterozoic Re depletion ages are locally preserved in these mantle bodies, our data reveal that the IVZ lherzolitic massifs were “recently” accreted to the SCLM in the Upper Devonian (ca. 370 Ma) during Pangea amalgamation, with a petrochemical evolution characterized by low-degree (~ 5–12%) depletion and nearly contemporaneous pervasive to focused melt migration. The lithospheric accretion putatively took place through asthenospheric upwelling triggered by Variscan intra-continental extension in a back-arc setting related to the subduction of the Rheic Ocean. We thus conclude that the fertile sections of Phanerozoic SCLM can be accreted during “recent” events of back-arc continental extension, even where Os isotopes preserve memories of melting events in much older times.

Isotope-Edited Variable Temperature Infrared Spectroscopy for Measuring Transition Temperatures of Single A-T Watson-Crick Base Pairs in DNA Duplexes.

Experimental methods to determine transition temperatures for individual base pair melting events in DNA duplexes are lacking despite intense interest in these thermodynamic parameters. Here, we determine the dimensions of the thymine (T) C2═O stretching vibration when it is within the DNA duplex via isotopic substitutions at other atomic positions in the structure. First, we determined that this stretching state was localized enough to specific atoms in the molecule to make submolecular scale measurements of local structure and stability in high molecular weight complexes. Next, we develop a new isotope-edited variable temperature infrared method to measure melting transitions at various locations in a DNA structure. As an initial test of this "sub-molecular scale thermometer", we applied our T13C2 difference infrared signal to measure location-dependent melting temperatures (TmL) in a DNA duplex via variable temperature attenuated total reflectance Fourier transform infrared (VT-ATR-FTIR) spectroscopy. We report that the TmL of a single Watson-Crick A-T base pair near the end of an A-T rich sequence (poly T) is ∼34.9 ± 0.7°C. This is slightly lower than the TmL of a single base pair near the middle position of the poly T sequence (TmL ∼35.6±0.2°C). In addition, we also report that the TmL of a single Watson-Crick A-T base pair near the end of a 50% G-C sequence (12-mer) is ∼52.5 ± 0.3°C, which is slightly lower than the global melting Tm of the 12-mer sequence (TmL ∼54.0±0.9°C). Our results provide direct physical evidence for end fraying in DNA sequences with our novel spectroscopic methods.

The hydrological response of melting ephemeral snowpacks compared to winter rainfall events in a mid-mountainous Pyrenean catchment

AbstractThe hydrological role of ephemeral snowpacks and their differences in stormflow and sediment transport characteristics compared to events triggered by winter rainfall conditions have received limited attention. This study aims to analyze the hydrological and sediment transport responses to rain-on-snow (ROS), melt, mixed, and rainfall events in the Araguás Catchment, situated in a mid-mountain site of the Central Spanish Pyrenees, with a climate strongly influenced by Mediterranean conditions. This catchment represents the transition from a winter ephemeral snow environment to a fully rainfall-dominated site. Results indicate that snowmelt has a modest yet measurable impact on the annual water balance, averaging 10% and rising to 30% during winter (December to February). ROS and melt events consistently exhibited higher mean and maximum discharge and elevated stormflow coefficients compared to mixed and rainfall events. The lowest water infiltration into the soil was observed during melt events, attributed to the potential for frequent freezing soils, specific poor edaphic conditions, and the rapid snowmelt in the area. Consequently, melting events displayed the shortest flood hydrographs among the four analyzed events. The study also underscores precipitation’s almost negligible erodibility capacity in the solid phase and emphasizes the protective role of snow cover in preventing soil erosion. It is important to note that the presented results are significantly influenced by the physiographic, lithological, and edaphic characteristics of the Araguás Catchment. This highlights the importance of conducting more detailed analyses of ephemeral snowpacks in experimental sites under a broader range of environmental conditions for a comprehensive understanding.

Towards a greater understanding of the deep eutectic phenomenon through examination of the lidocaine-NSAID therapeutic deep eutectic systems

Therapeutic deep eutectic solvents (THEDES) have been attracting increasing attention in the pharmaceutical literature as a promising enabling technology capable of improving physicochemical and biopharmaceutical properties for difficult-to-deliver drug compounds. The current literature has explored amide local anaesthetics and carboxylic acid nonsteroidal anti-inflammatories (NSAIDs) as commonly used THEDES formers for their active hydrogen-bonding functionality. However, little is known about what happens within the “deep eutectic” region where a range of binary compositions present simply as a liquid with no melting events detectable across experimentally achievable conditions. There is also very limited understanding of how parent compounds’ physicochemical properties could impact upon the formation, interaction mechanism, and stability of the formed liquid systems, despite the significance of these information in dose adjustment, industrial handling, and scaling-up of these liquids.In the current work, we probed the “deep eutectic” phenomenon by investigating the formation and physicochemical behaviours of some chosen lidocaine-NSAID systems across a wide range of composition ratios. Our data revealed that successfully formed THEDES exhibited composition dependent Tg variations with strong positive deviations from predicted Tg values using the Gordon-Taylor theory, suggesting substantial interactions within the formed supramolecular structure. Interestingly, it was found that the parent compound’s glass forming ability had a noticeable impact upon such profound interaction and hence could dictate the success of THEDES formation. It has also been confirmed that all successful systems were formed based on charge-assisted hydrogen bonding within their THEDES network, affirming the significant role of partial protonisation on achieving a profound melting point depression. More importantly, the work found that within the “deep eutectic” region there was still an ideal, or thermodynamically preferrable “THEDES point”, which would exhibit excellent stability upon exposure to stress storage conditions.The discoveries of this study bring the literature one step closer to fully understanding the “therapeutic deep eutectic” phenomenon. Through correlation between parent reagents’ physicochemical properties and the synthesised products’ characteristics, we establish a more educated process for the prediction and engineering of THEDES.

The formation of the granite complex in the Wuhe Mari area of Bayankala Mountain on the northeastern margin of the Tibetan Plateau: constraints from lithogeochemistry and U–Pb zircon dating

The granite complex in the Wuhe Mari area lies in the tectonic magma belt of the North Bayankala Mountains on the northeastern edge of the Qinghai-Tibet Plateau. It is located in the middle of the first member of the Changmahe Formation of the Early and Middle Triassic Bayankala Mountains Group. This article presents a systematic study of the petrological and geochemical characteristics and chronology of porphyrite granilite, monzogranite, porphyritic monzogranite and diorite in the granite complex in Wuhe Mari area. The genetic relationship between these four rock types as well as the type of source area and tectonic environment are clarified. Zircon LA-ICP-MS-U–Pb dating shows that the porphyritic granodiorite, monzogranite, porphyritic monzogranite and diorite have ages of 221.0 ± 2.7 Ma, 219.8 ± 3.0 Ma, 216.6 ± 4.3 Ma and 213.4 ± 1.6 Ma, respectively. The petrogeochemical characteristics show that the porphyritic granodiorite, monzogranite and porphyritic monzogranite in the granite complex have the characteristics of high Si, Al2O3, K, low Na, Ca, Mg, Fe, K, Rb and Th—Content in the strongly incompatible elements of the granite complex have three, the relative loss of Ba, Ta, Nb, Ce, slight enrichment or no anomaly, the loss of Sm, Hf and Zr, the strong loss of Y and Yb and the aluminum saturation index < 1.1. Combined with the geological data all three samples belong to Type I granite formed in the same collision environment. Based on the lithogeochemical characteristics and the results of U–Pb chronology, these three rock formations are believed to have been formed by a series of magmatic melting events and are the result of homologous magma crystallization and differentiation. The diorite forms in an intraplate tectonic setting as a result of the evolution of co-collision granite to intraplate granite.