Ar Dating Research Articles

Rb–Sr geochronology of metamorphic rocks from the Central Indonesian Accretionary Collision Complex: Additional age constraints for the Meratus and Luk Ulo complexes (South Kalimantan and Central Java)

Metamorphic rocks of the Central Indonesian Accretionary Collision Complex are exposed in widely scattered occurrences on the islands of Java, Sulawesi, and Kalimantan. Their relationship to one or more subduction zones is controversial which can partly be explained by insufficient geochronological investigation. Using Rb–Sr geochronology we have dated various schists from the Meratus Complex, South Kalimantan, and the Luk Ulo Complex, Central Java. The Meratus schists first experienced high-pressure/low-temperature (HP/LT) metamorphism and were later overprinted at medium pressure conditions. Due to the rarity and poor preservation of such rocks, isotopic ages for well-preserved HP/LT rocks could not be determined yet. Previously obtained K–Ar white mica dates (180–160 Ma) were attributed to the HP/LT event, however, this was speculative as the dated rocks only record greenschist- to amphibolite-facies P–T conditions. A newly dated partially overprinted but still glaucophane-rich sample yielded a well-defined Rb–Sr isochron age (phengite, epidote) of 112.9 ± 0.7 Ma (all uncertainties on Rb–Sr dates indicate 95% confidence level), providing a minimum age for the HP/LT stage. Internal mineral isochrons of more severely overprinted samples show poor linear fits between mica and associated phases indicating incomplete resetting of the Rb–Sr isotope system during the later lower pressure metamorphic event. Isochrons that are derived only from different grain-size fractions of white mica indicate dates between 115 and 110 Ma (± 3 to 6 Ma). In contrast to previous interpretations that linked high-grade rocks of the Meratus Complex to collision-induced crustal thickening it is here considered more likely that these rocks either represent exotic fragments from NW Australia or the metamorphic sole of the Meratus ophiolite. Differences in temperature estimates for HP/LT rocks from the Luk Ulo Complex probably indicate erroneous textural interpretation of equilibrium mineral assemblages and/or compositions. Neither petrological analysis nor geochronological dating has yet unambiguously confirmed different P–T–t paths for eclogites with and without tourmaline (Trm) from the Luk Ulo area. The newly dated Trm-bearing epidote blueschist from the serpentinitic Muncar River mélange yielded a well-defined Rb–Sr isochron of 119.0 ± 0.7 Ma (phengite, epidote, tourmaline) that perfectly matches with existing K–Ar and Rb–Sr data for Trm-free HP/LT rocks. Two samples of the more widespread garnet-phengite schists of the Luk Ulo area yielded Rb–Sr ages (phengite, feldspar) of 118.0 ± 0.8 Ma and 114.7 ± 1.3 Ma. A meter-sized epidote amphibolite block included in these clastic metasedimentary rocks provided a Rb–Sr isochron age of 116.8 ± 0.7 Ma (phengite, epidote, whole rock). These ages match existing K–Ar data for severely overprinted rocks from the Luk Ulo area and further corroborate the geological significance of Early Cretaceous metamorphism in Central Java. Petrological and geochronological data of the Meratus and Luk Ulo complexes are in accordance with a model suggesting that both occurrences belong to the same Cretaceous subduction system. The existence of an additional Cretaceous suture zone cutting through Sulawesi is considered likely.

A new understanding of Demala Group complex in Chayu Area, southeastern Qinghai-Tibet Plateau: Evidence from zircon U-Pb and mica 40Ar/39Ar dating

The Chayu area is located at the southeastern margin of the Qinghai-Tibet Plateau. This region was considered to be in the southeastward extension of the Lhasa Block, bounded by Nujiang suture zone in the north and Yarlung Zangbo suture zone in the south. The Demala Group complex, a set of high-grade metamorphic gneisses widely distributed in the Chayu area, is known as the Precambrian metamorphic basement of the Lhasa Block in the area. According to field-based investigations and microstructure analysis, the Demala Group complex is considered to mainly consist of banded biotite plagiogneisses, biotite quartzofeldspathic gneiss, granitic gneiss, amphibolite, mica schist, and quartz schist, with many leucogranite veins. The zircon U-Pb ages of two granitic gneiss samples are 205 ± 1 Ma and 218 ± 1 Ma, respectively, representing the ages of their protoliths. The zircons from two biotite plagiogneisses samples show core-rim structures. The U-Pb ages of the cores are mainly 644–446 Ma, 1213–865 Ma, and 1780–1400 Ma, reflecting the age characteristics of clastic zircons during sedimentation of the original rocks. The U-Pb ages of the rims are from 203 ± 2 Ma to 190 ± 1 Ma, which represent the age of metamorphism. The zircon U-Pb ages of one sample taken from the leucogranite veins that cut through granitic gneiss foliation range from 24 Ma to 22 Ma, interpreted as the age of the anatexis in the Demala Group complex. Biotite and muscovite separates were selected from the granitic gneiss, banded gneiss, and leucogranite veins for ⁴⁰Ar/³⁹Ar dating. The plateau ages of three muscovite samples are 16.56 ± 0.21 Ma, 16.90 ± 0.21 Ma, and 23.40 ± 0.31 Ma, and the plateau ages of four biotite samples are 16.70 ± 0.24 Ma, 16.14 ± 0.19 Ma, 15.88 ± 0.20 Ma, and 14.39 ± 0.20 Ma. The mica Ar-Ar ages can reveal the exhumation and cooling history of the Demala Group complex. Combined with the previous research results of the Demala Group complex, the authors refer that the Demala Group complex should be a set of metamorphic complex. The complex includes not only Precambrian basement metamorphic rock series, but also Paleozoic sedimentary rock and Mesozoic granitic rock. Based on the deformation characteristics, the authors concluded that two stages of the metamorphism and deformation can be revealed in the Demala Group complex since the Mesozoic, namely Late Triassic-Early Jurassic (203–190 Ma) and Oligocene–Miocene (24–14 Ma). The early stage of metamorphism (ranging from 203–190 Ma) was related to the Late Triassic tectono-magmatism in the area. The anatexis and uplifting-exhumation of the later stage (24–14 Ma) were related to the shearing of the Jiali strike-slip fault zone. The Miocene structures are response to the large-scale southeastward escape of crustal materials and block rotation in Southeast Tibet after India-Eurasia collision.

Optimization of irradiation parameters for 40Ar/39Ar dating by Argus VI multi-collector mass spectrometry

In 40Ar/39Ar dating, 39ArK generated is dependent on irradiation conditions, and the accumulation fast neutron fluence is a critical parameter for 40Ar/39Ar dating.

Continental flood basalt magmatism contemporaneous with Deccan traps in the Mannar basin, offshore Sri Lanka

AbstractThe Gulf of Mannar and adjoining Cauvery basin to the north between India and Sri Lanka are associated with a failed rift, which initiated during the late Jurassic to early Cretaceous as a precursor to the breakup of East Gondwana. Despite the occurrence of igneous rocks that can be noted in seismic profiles, offshore, and deep seated occurrence of those have lead only to the limited understanding of igneous activity in the Mannar basin. Rock cuttings recovered in the Barracuda exploratory well in the Mannar basin shows approximately 700 m thick basalt rock sequence interlayered with sediments at a depth of 3500–4200 m below mean sea level. Here, we analyzed samples recovered from the Barracuda well for major and trace element composition. Major and trace element data suggest that the basalts were crystallized from two different degrees of partial melts from a similar source. Chondrite normalized rare earth element (REE) patterns indicate that the basalts are similar to continental flood basalt, though they show a distinct Ba positive anomaly. Importantly, supported with previously available K–Ar data, we decipher that these basalts are contemporaneous with the Deccan traps. Rifting between Seychelles and India which had occurred at ~62 Ma approximately 3.5 Ma after the main Deccan eruption is synchronous with the Barracuda volcanism suggesting coeval rifting between Seychelles–India and India–Sri Lanka. Thus, our data suggest simultaneous rifting between Seychelles–India and India–Sri Lanka. Large plate reorganizations that took place during this time period in the Indian Ocean have likely caused consequent passive rifting in the Mannar basin.

Early Cretaceous deformation in the southern Tashkorgan region: Implications for the tectonic evolution of the northeastern Pamir

The Pamir Plateau comprises a series of crustal fragments that successively accreted to the Eurasian margin preceded the India-Asia collision, is an ideal place to study the Mesozoic tectonics. The authors investigate the southern Tashkorgan area, northeastern Pamir Plateau, where Mesozoic metamorphic and igneous rocks are exposed. New structural and biotite 40Ar-39Ar age data are presented. Two stages of intense deformation in the metamorphic rocks are identified, which are unconformably covered by the Early Cretaceous sediment. Two high-grade metamorphic rocks yielding 128.4 ± 0.8 Ma and 144.5 ± 0.9 Ma 40Ar-39Ar ages indicate that the samples experienced an Early Cretaceous cooling event. Combined with previous studies, it is proposed that the Early Cretaceous tectonic records in the southern Tashkorgan region are associated with Andean-style orogenesis. They are the results of the flat/low-angle subduction of the Neotethyan oceanic lithosphere.

Геохронология мезозойского щелочного магматизма для Тыркандинской и Амгинской тектонических зон (Алданский щит): новые U-Pb и Ar-Ar данные

Геохронология мезозойского щелочного магматизма для Тыркандинской и Амгинской тектонических зон (Алданский щит): новые U-Pb и Ar-Ar данные

Reappraisal of the oldest high-pressure type schist in Japan: New zircon U-Pb age of the Kitomyo Schist of the Kurosegawa Belt

The Kitomyo Schist from Kurosegawa Belt, Shikoku, has been long considered as the oldest records of subduction metamorphism in Japan, based on an early 1970s K–Ar dating of white mica. The schist consists of mafic and pelitic layers and occurs as a tectonic block within serpentinite. Reappraisal of the schist confirmed the schist is characterized by an epidote-amphibolite peak metamorphic facies. The mafic portion is characterized by zoned amphibole + epidote + chlorite + titanite ± phengite ± rutile. The presences of relict rutile surrounded by titanite and the barroisitic cores of zoned amphibole suggest a high-pressure intermediate type metamorphism at the metamorphic peak (P = ~0.8–1.5 GPa and T = ~500–570 °C). The presence of Mn-rich garnet and the lack of biotite, oligoclase and paragonite also support high-pressure intermediate type metamorphism that eliminate the possibility of a typical blueschist-facies metamorphism. New SHRIMP and LA-ICPMS zircon U–Pb geochronology on a pelitic sample show detrital grains of Mesoproterozoic and Early Paleozoic ages, suggesting a maximum deposition age for the trench-fill sediment of ~440 Ma. Also the U–Pb data confirmed ~360 Ma overgrown rims that might have formed during the subduction zone epidote-amphibolite facies metamorphism. Reappraisal revealed that the Kitomyo Schist is not the oldest high-pressure type schist in Japan and rather comparable to the Late Paleozoic Renge Metamorphic Rocks and their equivalents in the Kurosegawa Belt. The Devono–Carboniferous high-pressure metamorphic rocks in Japan might have been paired with their coeval batholiths along the ‘Greater South China’ margin that was extensively eroded during later tectonic processes.

Structural and Crystal-Chemical Features and Rb–Sr Age of Globular Glauconite in the Ust-Il’ya Formation (Lower Riphean, Anabar Uplift)

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio KAl = (VIAl / (VIFe3+ + VIAl) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 A and K2O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mossbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.

Timing of multiple magma events and duration of the hydrothermal system at the Yu’erya gold deposit, eastern Hebei Province, China: Constraints from U–Pb and Ar–Ar dating

The Yu’erya deposit is a large granite–hosted gold deposit in the eastern Hebei Province classified as an intrusion–related gold system. The Yu’erya complex contains the causative intrusion which was the source of hydrothermal metal-bearing fluids. This composite granite complex contains miarolitic pegmatite(–like) cavities and pegmatite veins. A combination of detailed field observations and U–Pb dating by SHRIMP and LA–ICP–MS is used to document multiple magmatic events which occurred at 210–220, 175–173, 171–170, 167–166 and ~161 Ma formed the Yu’erya granite complex. The initiation of the hydrothermal system, as determined via Ar–Ar dating, is closely related to the exsolution of a magmatic volatile phase from the G1 granite at ca.176 Ma. The hydrothermal system operated for ~16 my (176–160 Ma) and produced multiple mineralising events (~176, 172–168 and 162–160 Ma) linked to emplacement of repeated magma pulses from 175 Ma to 161 Ma. Our results suggest that multiple magmatic–hydrothermal events over a time period of several million years may be a fundamental factor responsible for the enrichment process during formation of intrusion-related gold deposits and thus may be a requirement for forming economic orebodies.

Expanding the toolbox for dating basaltic lava sequences: 40 Ar– 39 Ar dating of silicic volcanic glass from interbeds

40 Ar– 39 Ar dating of glass shards from silicic tuffs of the Ellensburg Formation (NW, USA) interbedding basaltic lavas yielded accurate, precise, reproducible plateau and isochron ages that are within error at the 2σ level. The age-spectra have flat plateaus and the inverse isochrons have atmospheric 40 Ar/ 36 Ar at the 2σ level. Ages of 12.00 ± 0.24, 11.37 ± 0.15, 10.67 ± 0.21 and 10.70 ± 0.18 Ma are consistent with the stratigraphy of four of the dated layers; the age of 10.77 ± 0.18 Ma for a fifth layer is at odds with the stratigraphy. This discrepancy arises due to the effect of glass alteration that induced K- and Ar-loss. There is no evidence of excess 40 Ar or 39 Ar recoil. The new ages indirectly constrain the timing of eruption of the lavas above and below the ash beds. This demonstrates that volcanic glass from interbeds can be used as an additional tool for indirectly dating basaltic lava sequences, which is independent of the lavas and complementary to other materials. Considering the numerous studies in which volcanic glass failed to provide reliable 40 Ar– 39 Ar ages, additional and supportive constraints are still needed to assess the validity of the ages from glass shards. Supplementary material : A1 – sample location, stratigraphic position and depositional environments; A2 – electron microprobe information with calibration and sample data; A3 – Ar isotopic data of blanks and samples, data reduction software, J values, criteria for age calculation and images of age spectra and inverse isochrons are available at https://doi.org/10.6084/m9.figshare.c.5077705

Illite 40 Ar– 39 Ar dating of Eocene deformation in the Chiapas Fold and Thrust Belt, southern Mexico

Abstract The Chiapas Fold and Thrust Belt (CFTB) of southern Mexico underwent widespread contraction during the well-documented middle Miocene ‘Chiapanecan’ Orogeny. However, earlier phases of folding have been documented in the region and might have affected the belt before the Miocene. We carried out a stratigraphic review and a structural analysis of the belt, complemented by 40 Ar– 39 Ar dating of synorogenic illite to identify the successive pulses of deformation. Reliable radiometric ages were obtained in three folds from the southern portion of the belt, and in one thrust gouge near the front of the belt. Authigenic illite-rich samples were located in Upper Cretaceous limestone successions that experienced bed-parallel shear during folding and thrusting. They yielded ages ranging from 35 to 40 Ma in the folds and 54.5 ± 7 Ma in the thrust, documenting thin-skinned folding and thrusting in the belt mostly in Eocene time. Some of the basement faults of the belt may have been active during this phase. However, most of the pervasive lateral faults that cross-cut the regional folds in the belt were mostly active from the Miocene onwards, causing transpression and fold amplification.

Immunohistological Expression of SOX-10 in Triple-Negative Breast Cancer: A Descriptive Analysis of 113 Samples.

Background: SRY-related HMG-box 10 (SOX-10) is commonly expressed in triple negative breast cancer (TNBC). However, data on the biological significance of SOX-10 expression is limited. Therefore, we investigated immunhistological SOX-10 expression in TNBC and correlated the results with genetic alterations and clinical data. Methods: A tissue microarray including 113 TNBC cases was stained by SOX-10. Immunohistological data of AR, BCL2, CD117, p53 and Vimentin was available from a previous study. Semiconductor-based panel sequencing data including commonly altered breast cancer genes was also available from a previous investigation. SOX-10 expression was correlated with clinicopathological, immunohistochemical and genetic data. Results: SOX-10 was significantly associated with CD117 and Vimentin, but not with AR expression. An association of SOX-10 with BCL2, EGFR or p53 staining was not observed. SOX-10-positive tumors harbored more often TP53 mutations but less frequent mutations of PIK3CA or alterations of the PIK3K pathway. SOX-10 expression had no prognostic impact either on disease-free, distant disease-free, or overall survival. Conclusions: While there might be a value of SOX-10 as a differential diagnostic marker to identify metastases of TNBC, its biological role remains to be investigated.

Long‐distance fluid migration defines the diagenetic history of unique Ediacaran sediments in the East European Craton

AbstractThe diagenetic history of the Ediacaran sedimentary rocks in the East European Craton (EEC) over the area extending from Arkhangelsk (Russia) in the north to Podolia (Ukraine) in the south was revealed by means of the XRD characterization and K–Ar dating of clay fractions, mudstone porosity measurements and organic geochemistry investigations. Mudstone porosity measurements produced direct evidence of shallow maximum burial of the Ediacaran sediments on the craton (Russia, Lithuania, Belarus, Volyn), not exceeding 1.5 km, and much deeper burial at the cratonic margin, in Podolia and Poland. In general, illitization of smectite and biomarker indices indicates more advanced diagenesis at the cratonic margin.K–Ar dating of authigenic illite–smectite and aluminoceladonite revealed the Palaeozoic age of mineral diagenesis (ca. 450–300 Ma) both on the craton and its margin, with older ages generally observed in the north. When the maximum palaeotemperatures were evaluated from illite–smectite and biomarkers, based on the calibrations from the conventional burial diagenetic sections, a major mismatch was detected for the cratonic area: 100°C–130°C from illite––smectite and tens of oC lower from the lipid biomarkers. This diagenetic pattern was interpreted as the result of short‐lasting (in ky scale) pulses of potassium‐bearing hot fluids migrating from the Caledonian and Variscan orogens deep in the craton interior, effectively promoting illitization in porous rocks without altering the organic matter. Analogous short pulses of fluids were responsible for numerous diagenetic phenomena, including Mississippi Valley‐Type ore deposits, in the American Midwest, in front of the Appalachians. K–Ar dating indicates that the entire Proterozoic sedimentary cover of the Great Unconformity on the EEC remained untouched by measureable post‐sedimentary changes until the early Palaeozoic, thus for over 1000 My, which is an unprecedented finding.

Two-stages of plume tail volcanism formed Ojin Rise Seamounts adjoining Shatsky Rise

Many groups or chains of seamounts border, or are associated with, oceanic plateaus but their origin and relationship with plateau volcanism are debated. An example is Ojin Rise Seamounts, a group of ~80 seamounts located northeast of the 147–134 Ma Shatsky Rise, an oceanic plateau that was formed along the trace of a triple junction in the northwest Pacific Ocean. A notable topographic feature of Ojin Rise Seamounts is that they are distributed in such a way that they appear to be connected to another oceanic plateau in the east, the ~100 Ma Hess Rise. Many seamounts are arranged in a NW–SE direction (almost in the same absolute plate motion direction) and some are organized into seamount chains consisting of several volcanic cones connected by a common platform, reflecting a complex volcanic history. Here we report petrography as well as major and trace element, Sr, Nd, Pb, and Hf isotope, and 40Ar-39Ar age data for basalts dredged from five seamounts in the western part of Ojin Rise Seamounts. We found that the 40Ar-39Ar ages of the cones (123.7–120.7 Ma) are distinctly younger than the magnetic lineation age (M9-M7; 134–132 Ma) around the chain. The younger age suggests either a protracted development for the seamount chain, previously proposed to have formed near-ridge, or age difference between the platform and cones. The morphological and age differences are supported by petrography and geochemistry: platform basalts are aphyric, whereas cone basalts are slightly to highly plagioclase-phyric (up to 48 vol%); platform basalts are depleted in trace element and isotope composition, but cone basalts are enriched with high Nb/Ti and 87Sr/86Sr, and low 143Nd/144Nd and 176Hf/177Hf ratios. The depleted signature of the platform basalts is similar to that of the abundant normal type basalts of Shatsky Rise with an isotope composition that overlaps with that of normal mid-ocean ridge basalts (N-MORB), whereas trace elements are enriched (e.g., higher Nb/Zr and Nb/Ti than N-MORB). However, slight geochemical differences between the Ojin platform basalts and Shatsky normal type basalts exist and are expressed in higher 208Pb/204Pb isotope ratios of the former. The depleted signature implies shallow mantle dilution of the (enriched) Shatsky plume tail near a ridge. In contrast, the enriched signature of the cone basalts indicates little contribution from N-MORB source mantle as (enriched) plume volcanism moved away from the ridge. The enriched features (Nb/Zr and 176Hf/177Hf) of the Ojin Rise cone basalts increase with increasing distance from Shatsky Rise and conform with a geochemical evolution model that involves increasing contribution from a highly enriched Hess Rise source component with time.

Geological anatomy of the Upper Triassic sequence in southeastern Tibet: Implication for tectonic evolution of the eastern Himalayan Orogen

Located south of the Yarlung‐Tsangpo Suture Zone (YTSZ), the Upper Triassic rocks of the Tethyan Himalayan Sequence (THS) in the Shannan area, southeastern Tibet, serve as an ideal geologic entity to investigate the post‐collisional evolution of the eastern Tethyan Himalayan realm. Detailed field observations suggest that D2 north‐verging folds and thrusts dominate the deformational pattern of the newly named Luolin Group, while D1 south‐verging imbricated structures characterize the Langjiexue Group and the Nieru Unit. Illite crystallinity measurements in pelitic samples indicate that the metamorphic grade decreases from epizonal in the Luolin Group to anchizonal facies in the Langjiexue‐Nieru Unit. Fluid inclusions from two stages of syn‐deformational quartz veins are characterized by moderate homogenization temperature (~260°C) and low salinity (5% NaCleqv). Electron microprobe analyses (EMPA) of garnet amphibolites show metamorphic temperature of ~510°C. The age of D1 event is determined by 40Ar–39Ar dating of phyllite sample at ca. 47 Ma. Correlations with regional deformational events through the THS demonstrate that the D2 event occurred between ca. 30 and 22 Ma. These data imply that the Upper Triassic sequence is part of the fold‐thrust belt of the Himalayan Orogen, rather than the accretionary mélange within the YTSZ.

Is the High-Resolution Coronal Imager Resolving Coronal Strands? Results from AR 12712

Abstract Following the success of the first mission, the High-Resolution Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1) on 2018 May 29 from the White Sands Missile Range, NM, USA. On this occasion, 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of ≈4 s, and a plate scale of 0.″129 pixel−1. Using data captured by Hi-C 2.1 and co-aligned observations from SDO/AIA 17.1 nm, we investigate the widths of 49 coronal strands. We search for evidence of substructure within the strands that is not detected by AIA, and further consider whether these strands are fully resolved by Hi-C 2.1. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss are studied. A comparison is made between these low-emission strands and those from regions of higher emission within the target active region. It is found that Hi-C 2.1 can resolve individual strands as small as ≈202 km, though the more typical strand widths seen are ≈513 km. For coronal strands within the region of low emission, the most likely width is significantly narrower than the high-emission strands at ≈388 km. This places the low-emission coronal strands beneath the resolving capabilities of SDO/AIA, highlighting the need for a permanent solar observatory with the resolving power of Hi-C.

The Effect of Resampling on Data-imbalanced Conditions for Prediction towards Nuclear Receptor Profiling Using Deep Learning.

In toxicity evaluation based on the nuclear receptor signalling pathway, in silico prediction tools are used for the detection of the early stages of long-term toxicities, the prioritization of newly synthesized chemicals and the acquisition of the selectivity and sensitivity. Computational prediction model is one of the promising tools for the toxicity screening of the chemical-protein interaction as deep learning has been improved the prediction accuracies. However, the challenge is that data-imbalanced conditions, where the volume of toxic chemical compound dataset is much smaller than the nontoxic dataset, result in low prediction accuracy of the toxic dataset providing valid information to toxicity hazard. In this paper, we have examined the effect of data imbalance in the toxicity assessment data of AR (LBD), ER (LBD), AhR, and PPAR as nuclear receptors, and identified the severe imbalance between the prediction of the toxic and nontoxic datasets. As the acquisition of the balanced selectivity and sensitivity is required for the assessment of toxicity hazards, data resampling methods have been investigated in order to improve the bias problem in binary classification for toxicity hazard profiling of nuclear receptor. The experimental results achieved a sensitivity of 0.714 and a specificity of 0.787, with an overall accuracy of 0.829 and a ROC-AUC of 0.822 by the simple resampling methods.

Tephrochronology and chronostratigraphy of the Miocene Chilcatay and Pisco formations (East Pisco Basin, Peru)

Strata of Chilcatay and Pisco formations exposed in the Ica Desert (East Pisco Basin, southern Peru) preserve one of the most complete and rich records of Miocene marine vertebrates of the world. Despite its exceptional importance, the chronostratigraphy of these fossil-bearing deposits has been only sporadically studied in the literature until recently. This work presents a detailed reconstruction of the chronostratigraphic framework, achieved by mapping and measuring of seven sections (totaling a height of almost 1000 m) of the Miocene Chilcatay and Pisco formations along the western side of the Ica River. The Chilcatay Formation consists of two allomembers, namely Ct1 and Ct2, bounded at the base by unconformities CE0.1 and CE0.2, respectively. Similarly, the immediately overlying Pisco Formation is divided into allomembers P0, P1, and P2, bounded at the base by unconformities PE0.0, PE0.1 and PE0.2, respectively. The new 39Ar–40Ar results presented here, combined with ages of previous work, provide precise constraints on the age of several stratigraphically referenced volcanic ash layers intercalated in the studied fossil-bearing succession, placing its vertebrate fossil fauna within a refined temporal framework and laying the solid ground for its detailed regional and global comparison. The ages of the allomembers, and thus their associated faunas, can be reliably estimated by the combination of 39Ar–40Ar dating on tephra layers with diatom biostratigraphy. In the study area, two methods are mutually consistent and constrain the deposition of the Chilcatay Formation between 19.2 and 18.0 Ma, that of P1 between 9.5 and 8.6 Ma, and that of P2 between 8.4 and 6.7 Ma. In the absence of direct dating of the P0 allomember, which lacks both preserved tephra suitable for 39Ar–40Ar dating and microfossils, its age can be constrained to the temporal gap between the youngest age available from the underlying Chilcatay strata (18.0 Ma) and the oldest age available from the overlying P1 strata (9.5 Ma).

Contemporaneous intraplate magmatism on conjugate South Atlantic margins: A hotspot conundrum

Intraplate magmatism is enigmatic in origin despite its importance in our understanding of crustal cycling through the deep mantle. A mantle plume origin is justified for some intraplate magmatism, but not in the case of a large number of occurrences. Here we present a novel explanation for intraplate magmatism in situations where evidence for a plume origin is either lacking or equivocal. Specifically, we highlight two voluminous, long-lived intraplate magmatic provinces located on the precisely conjugate continental margins of Cameroon and NE Brazil and which lasted, respectively, from 65 and 52 Ma to the present. New Ar dating and geochemical data show that magmatism in the two provinces was contemporaneous, identical in incompatible-element composition, and started >40 Myr after continental separation, when the two margins were ∼2000 km apart. Lack of age progression in magmatic activity rules out a mantle plume origin. We propose an origin in sub-continental lithospheric mantle that was thickened during Gondwana supercontinent assembly. Thermal re-equilibration of the thickened lithosphere accompanied by percolation of carbonate-rich melt led to the formation of a thick zone of newly created, enriched asthenosphere that is held in place by buoyancy, prevented from dispersing by adjacent lithospheric blocks, and heated by radioactive decay. Following continental breakup at 105 Ma, slow outward drainage of this enriched and heated asthenosphere was channelled into thinner parts of the continental and oceanic lithosphere. Sublithospheric drainage and decompression melting of this enriched mantle provides a viable explanation for these and many other intraplate magmatic occurrences.

40 Ar/ 39 Ar mica dating of late Cenozoic sediments in SE Tibet: implications for sediment recycling and drainage evolution

The Indo-Asia collision significantly changed the topography and drainage network of rivers around the Tibetan Plateau. Debate continues as to when and how the current drainage system of the Yangtze River was formed. Here we use 40 Ar/ 39 Ar dating of detrital micas (muscovite and biotite) to constrain provenances of the Pliocene sediments from the Jianchuan and Yuanmou basins in SE Tibet. Muscovite and biotite data of the same Pliocene samples from the Jianchuan Basin suggest contrasting distal v. local sources, respectively. Similarly, muscovite data of the Yuanmou Basin suggest a derivation of sediments from the Yalong River, but the characteristics of the Pliocene cobbles (palaeocurrent and subrounded cobbles) suggest that these sediments are locally sourced. Sediment reworking is proposed as an explanation for the different sediment provenance signals in the Jianchuan and Yuanmou basins that have led to the controversy of an either Pleistocene or pre-Miocene age of formation of the current Yangtze. Based on sediment provenance constraints, the evolution of the Jinsha River is reconstructed. The upper Jinsha River lost its connection with the southward flowing Red River upstream from the Jianchuan basin at least before the Pliocene. At the same time a parallel site in the Yuanmou Basin shows that the Yalong River stopped flowing southward into this basin. Detrital mica from early Pleistocene sediments at the Panzhihua site between the Jianchuan and Yuanmou basins is sourced from the current Jinsha and Yalong rivers. These results would suggest that the current upper Yangtze drainage system should have been established before the Pliocene. Supplementary material: Muscovite 40 Ar/ 39 Ar data, biotite 40 Ar/ 39 Ar data and muscovite geochemistry are available at https://doi.org/10.6084/m9.figshare.c.4821573