Peak Age Research Articles

Optical Microangiography and Progressive Retinal Nerve Fiber Layer Loss in Primary Angle-closure Glaucoma

Precis Younger patient age (coefficient: 0.10, P=0.04) and greater peak IOP during follow-up (coefficient: -0.14, P=0.03), but not baseline optical microangiography parameters, were significantly associated with a faster rate of RNFL loss in mild-moderate PACG. Purpose: To evaluate the association between optical microangiography (OMAG) measurements and progressive retinal nerve fiber layer (RNFL) loss in primary angle-closure glaucoma (PACG). Methods: In a prospective study, 45 eyes of 30 PACG patients (86 hemifields) with mild to moderate functional damage were longitudinally studied for at least 2 years and with a minimum of 3 optical coherence tomography (OCT) examinations. OMAG imaging was performed at the baseline visit. Effect of clinical parameters (age, gender, presence of systemic diseases, central corneal thickness, mean, peak and fluctuation of intraocular pressure during follow-up), baseline hemifield mean deviation (MD) and baseline OMAG (quadrant peripapillary and macular perfusion density [PD]) on the rate of RNFL change was evaluated using linear mixed models. Results: Average (±SD) hemifield MD, RNFL thickness, peripapillary PD and macular PD of the analyzed quadrants at baseline were -6.0±3.4 dB, 89±21 µm, 40.1±3.5% and 29.6±10.3%, respectively. Rate of quadrant RNFL change was -2.5±1.7 µm/year. Multivariate mixed models showed that younger patient age (coefficient: 0.10, P=0.04) and higher peak IOP during follow-up (coefficient: -0.14, P=0.03) were significantly associated with a faster rate of RNFL loss. Conclusions: Younger patient age and greater peak IOP during follow-up were significantly associated with a faster rate of RNFL loss in PACG patients with mild to moderate severity of functional damage. None of the OMAG parameters at baseline were associated with RNFL thinning suggesting a limited role of OCTA imaging in predicting structural progression in mild-moderate PACG.

Seawater retreated from the Tethyan Himalaya of south Tibet at ca. 49 Ma, not ca. 34 Ma

Timing of seawater retreat from the Tethyan Himalaya is of great importance, as it provides a minimum age control on the initial India-Asia collision. In south Tibet, however, it is still in dispute, with suggested ages ranging from >50 Ma to ca. 34 Ma. Here we present data of (1) larger benthic foraminifera from the topmost Zongpu Formation; (2) planktonic foraminifera; and (3) detrital zircon U-Pb ages from the Youxia and Shenkeza Formations at Guru, Tingri, and Gamba, with a special emphasis on the poorly studied Guru area. At Guru, existence of the Shallow Benthic Zonation (SBZ) 7 Zone index fossils of Alveolina moussoulensis Hottinger and Al. laxa Hottinger constrains the initial deposition of the Youxia Formation at ca. 54 Ma. Coexistence of the youngest planktonic foraminifera Acarinina boudreauxi Fleisher, Ac. coalingensis (Cushman and Hanna), and Ac. bullbrooki (Bolli) from the Youxia and Shenkeza Formations indicates their final deposition at ca. 49 Ma (E 7 Zone, where E stands for Eocene Planktonic foraminiferal Zone). Zircon U-Pb data are generally similar, with the youngest age peak of ca. 68−50 Ma resulting from input of the Gangdese Arc volcanic detritus. The complete lack of <49 Ma data among >1000 accepted ages implies that marine deposition probably ceased at ca. 49 Ma, consistent with the planktonic foraminiferal result. Integrating with previous results, we conclude that seawater retreated from both south Tibet and Zanskar at ca. 49 Ma. The initial collision happened quasi-simultaneously in the western and eastern Tethyan Himalaya, before ca. 49 Ma. Our findings do not support either a younger collisional age or a diachronous collisional process from the west to the east.

Continental-scale sediment mixing and dispersal across northern Gondwana: detrital zircon U-Pb-O-Hf isotopic evidence from the Cambro-Ordovician sandstones overlying the Arabian Shield

ABSTRACT The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post–Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process.

Petrogenesis and tectonic setting of mafic magmatism within the Laguna Amarga Metamorphic Complex, Andes of Catamarca, Argentina: Insights into the opening of the Cuyania/Precordillera terrane from the Ouachita rift

Neoproterozoic crystalline basement rocks are exposed as fault-bounded blocks over the high Andes of Catamarca. The crystalline basement is stratigraphically grouped into the unique Laguna Amarga Metamorphic Complex and represents the northern extension of the Cuyania/Precordillera terrane. Tabular bodies of meta-mafic rocks are widespread in the basement interspersed within a thick sequence of meta-sedimentary rocks derived from siliciclastic, calc-silicate, and limestone protoliths. Overall, the geochemical characteristics of meta-mafic rocks are in the compositional range of Normal-Mid Ocean Ridge Basalt (Normal-MORB), reflecting a common depleted-mantle source with varying degrees of partial melting. While preserving the typical bulk chemistry of MORB magmatism, some mafic magma underwent differentiation at emplacement, leading to the development of high-Ti mafic rocks. New U-Pb zircon geochronology reveals three distinct age peaks, with two coinciding with ages identified in the metasedimentary host rocks. The dominant Mesoproterozoic age cluster is linked to inherited zircon crystals assimilated within a single meta-mafic rock. In contrast, zircon ages from the late Ordovician to early Devonian are attributed to metamorphic overgrowths. Notably, the third age cluster, delineates a Late Neoproterozoic magmatic event, indicating the temporal span of mafic magmatism. The finding agrees with the best available age (576 ± 17 Ma) for mafic magmatism on the Precordillera Mafic-Ultramafic Belt. Stratigraphic relationships and geochemical fingerprints enable correlation among the meta-mafic rocks from Laguna Amarga, tracing a belt of mafic magmatism with an oceanic affinity that extends southward. Building upon previous works, this study reaffirms that the rift-drift transition of the Cuyania/Precordillera terrane, linked to the Ouachita rift opening from southeastern Grenville, evolved during the latest Neoproterozoic.

Influence of Triassic and Jurassic arc magmatism in Lower Jurassic Sierra de Santa Rosa Formation, northwestern México: Constraints from geochemistry and U-Pb geochronology

The Permo-Triassic and Lower Jurassic sedimentary succession of the El Antimonio Group in northern Sonora, Mexico is inferred to be deposited in a forearc basin and its age has been constrained by fossil assemblages and detrital zircon geochronology. In this work, petrography, geochemistry and detrital zircon U-Pb geochronology were undertaken on the Sierra de Santa Rosa Formation, the younger unit of the El Antimonio Group in the locality of the Sierra del Álamo, to constrain its tectonic setting, age, source area paleoweathering, and provenance. Sandstone of Sierra de Santa Rosa Formation is petrographically classified as arkose. The elemental ratios, REE patterns and Eu anomaly, as well as bivariate and ternary plots suggest igneous felsic sources subjected to weak to moderated chemical weathering under arid climatic conditions for detritus of the Sierra de Santa Rosa Formation. Detrital zircon U-Pb geochronology of seven sandstone samples of this unit record main populations of Proterozoic age (58% of the total grains) with age peaks at 1.68. 1.39 and 1.14 Ga and Triassic age (31% of total grains) with age peak at 219 Ma, and subordinate groups of Paleozoic, Jurassic and Archean ages. Main sources for the zircon grains are the regional nearby igneous-metamorphic Proterozoic basement rocks, recycled detritus from the Proterozoic and Paleozoic sedimentary cover, and the Permo-Triassic and Jurassic continental magmatic arcs of southwestern North America. The detrital zircon U-Pb geochronology of the dated samples allows to establish Sinemurian to early Toarcian maximum depositional ages for the Sierra de Santa Rosa Formation in the locality of the Sierra del Álamo.

Melting glaciers, emerging pandemics?

The world contains over 198,000 to 200,000 glaciers, covering in total over 726,000 square kilometers of Earth’s surface (Davies; “Glacier Quick Facts”). The repetitive cycle of snowfall forming layers and compressing into ice sheets over the course of centuries has allowed the formation of these unique, massive masses of ice. Apart from being huge reservoirs of water, glaciers are also hosts of many interconnected microbiomes, fostering active and dormant bacteria, fungi, viruses and other extremophiles. During the Last Glacial Maximum (LGM), or the peak of the ice age around 23,000-19,000 years ago, the sea surface temperature was at its lowest accompanied by low atmospheric Carbon Dioxide (CO2) concentration (“How Does Present Glacier Extent”; Quamar et al.). This was when glaciers covered over 32% of Earth’s total surface. However, today, glaciers account for just around 10% of land (“Glacier Quick Facts”). The rise of human choices, especially our indulgence in activities like industrialisation, consumerism and wastage have contributed to the emission of greenhouse gasses, which has in turn led to global warming. A consequence of this phenomenon is the melting of glaciers. Melting glaciers not only results in the release of water and rising sea levels, but also the unveiling of previously trapped microbiomes. This raised the hypothesis that melting glaciers, and other sections of the cryosphere can expose previously frozen, potentially pandemic-causing pathogens to the world. This descriptive research paper will serve the purpose of encapsulating existing research regarding whether the disintegration of the cryosphere can cause pandemics.

Early Specialization and Progress of Finalist Swimmers in World Championships and Olympic Games.

Background: The main objectives of this study were to analyze the effect of early specialization in swimming and to observe the general patterns of success of two different sport specialization models [Spanish (SPA) and United States of American (USA) swimmers] participating in World Championships (WCs) and Olympic Games (OGs) between the years 2006 and 2021 of all swimming strokes and distances. Methods: Descriptive analyses and contingency tables were examined for all the variables. Explanatory models of the z scores were estimated from age depending on the events' distances and strokes. Quadratic regression models were developed to capture the behavior of the variable time with parabolic functions, and the significance of the global model and the predictor variables (age) were also evaluated. In addition, the optimal age (peak performance) as well as the curvature of the model were analyzed. These models were compared between SPA and USA swimmers. Results: The results showed that the main differences in the patterns to success between SPA and USA were the earlier participation of USA swimmers in high-level competitions, as well as the greater number of participants for all the strokes, events, genders, and competitions. Age peak performance in short distances was lower for Spanish swimmers, obtaining the opposite situation for long distances. Conclusions: Being a finalist in junior WCs did not influence success in the finals of the senior WCs and OGs. Main differences in general patterns of success between SPA and USA showed younger swimmers participating in short-distance events, backstroke, and butterfly for USA swimmers and older swimmers taking part in butterfly and short-distance events for SPA.

Development and validation of a model for early survival prediction following liver transplantation based on donor and recipient characteristics

Background Circulating cytokine levels not only correlate with the progression of liver disease but also serve as indicators for the infection status of the body. Growing evidence points to the connection between donor cytokines and graft function following transplantation. This study set out to explore the clinical significance of donor cytokines in predicting liver transplantation prognosis. Methods Data from 172 deceased donor liver transplantations conducted between 2017 and 2022, with available donor serum cytokine information, were collected. The subjects were randomly divided into estimation (n = 120) and validation (n = 52) groups to establish and validate the model. The newly developed SA10 score was compared against established models EAD, MEAF, L-GrAFT7, and L-GrAFT10. Results Donor IL-10, along with donor age and recipient AST peak value within the first 7 days post-operation, was identified as an independent factor associated with recipient survival and was incorporated into the SA10 score. SA10 exhibited robust predictive capability, particularly for 1-month survival (AUC = 0.90, 95% CI = 0.84–0.96), outperforming EAD (AUC = 0.75, 95% CI = 0.60–0.90, p = 0.04) and L-GrAFT7 (AUC = 0.65, 95% CI = 0.49–0.81, p < 0.01). Comparable performance was observed between SA10, MEAF, and L-GrAFT10. Conclusion Donor IL-10 independently influences recipient survival, with the SA10 score demonstrating comparable and even superior predictive ability compared to existing models.

Hf Isotopes and Detrital Zircon Geochronology of the Silasia Formation, Midyan Terrane, Northwestern Arabian Shield: An Investigation of the Provenance History

ABSTRACTU–Pb ages and Hf isotopic data from detrital zircon of the Silasia Formation in the Midyan Terrane record evidence for the provenance and tectonic evolution of the northern Arabian Shield. Given that the youngest acknowledged age of these detritus sediments is 735 ± 13 Ma, it is likely that the Silasia Formation was deposited during the closure of the Mozambique Ocean. The U–Pb ages define a major Mesoproterozoic peak, with two minor peaks of Neoproterozoic and Archean age. Combined with zircon Hf isotopic compositions, the sedimentary detritus of the Silasia Formation was mainly derived from source rocks formed during the Grenville Orogeny during the assembly of Rodinia, with a minor contribution from Archean and Paleoproterozoic crustal material, in addition to a limited arc‐basement supply related to the early Mozambique Ocean. The youngest Concordia age of 735 ± 13 Ma with highly variable εHf(t) values (11 to −35) indicates a complex mixture of sources from juvenile to extremely ancient. The Concordia ages at 1113 ± 11 and 1046 ± 10 Ma have positive hafnium isotope signatures (up to +10.45) that are consistent with juvenile source rocks formed during the Grenville Orogeny. Several detrital zircons with ages of 2622 ± 22 Ma and 2690 ± 7 Ma are similar to those reported in Yemen, whereas 1818 ± 19 Ma, 2071 ± 8 Ma and 2001 ± 19 Ma Paleoproterozoic ages are similar to dated outcrops in the Khida terrane in the eastern Arabian Shield.

Generation of isotopically enriched giant Lincang Batholith by disequilibrium melting of the heterogeneous lower crust

Deciphering the origin of granitoids with enriched isotopic compositions is essential to understanding the mechanism of continental growth and reworking. Establishing their origin is also an effective solution to the decoupled interpretations between geochemical and isotopic observations in competing petrogenetic models. This paper reports on the whole-rock major and trace elements, Sr-Nd-Pb-Hf isotopes, and zircon UPb age and Hf isotope data of samples from the Late Triassic Lincang Batholith in SW China. The hornblende-bearing granodiorites are weakly peraluminous, whereas the coeval biotite monzogranites are generally strongly peraluminous. These two types of granitoids show identical and extremely enriched isotopic compositions with (87Sr/86Sr)i ratios of 0.71991 to 0.74302, whole-rock εNd(t) values of −13.5 to −10.1, and εHf(t) values of −13.4 to −10.3, as well as a large variation of zircon εHf(t) values of −17.6 to +0.6. The inherited zircons from both suites of samples show similar age peaks (ca. 950 Ma and ca. 1150 Ma), trace element concentrations, and εHf(t) variations to those of the detrital zircons from the Lancang Group. These similarities indicate that these rocks are most likely derived from the anatexis of the Lancang Group that is mainly composed of quartz schist, sericite schist, greenschist, chlorite albite schist, and minor eclogite. On the other hand, the Lancang Group is characterized by more enriched isotopic compositions than the granitic batholith with whole-rock εNd(225 Ma) value of −13.3 and εHf(225 Ma) value of −19.1, but identical to those of the average εHf(225 Ma) values of inherited and detrital zircons (−18.1 and − 16.3). This isotopic fractionation between the granitoids and the Lancang Group may result from disequilibrium melting of the Lancang Group with different dissolution behavior of accessory minerals (i.e., zircon, monazite, apatite, titanite, etc.). The Lincang Batholith is on average more silicic and richer in incompatible elements than the upper continental crust, suggesting that the isotopically enriched giant granitic batholith is a mature magmatic response to continental reactivation and reworking.

Geographic bias effects on interpretations of secular trends of Hf isotope times series in zircons

The analysis of εHf(t) time series data from zircon reveals notable discrepancies based on sample type (igneous versus detrital), statistical weighting methodology, and geographic sampling bias. These differences warrant caution when interpreting data in the context of tectonic settings and the history of supercontinents. In terms of tectonic setting, accretionary orogens dominate in both sedimentary basins that host detrital zircons and in igneous zircon sources. Because of differences between the various time series, emphasis in this study is on peaks, valleys and secular trends and not on absolute εHf(t) values. Specifically, the igneous time series for εHf(t) in zircons shows more peaks and valleys than corresponding detrital time series for both weighted and unweighted data (weighting corrects for disproportionate geographic sampling). Also, sample-based (each sample considered separately) and site-based (samples grouped by geographic location and age) results align closely to the igneous time series, whereas the site-based detrital series displays more negative εHf(t) values. Regardless of the type of time series, the failure to compensate for disproportionate geographic sampling increases the prospects of producing an unrepresentative time-series. Nine zircon age peaks (both detrital and igneous) have corresponding εHf(t) peaks (3200, 2700, 2500, 2150, 1500, 1100, 750 Ma) and two have corresponding age valleys (1800–2000, 550 Ma). With exception of a geographically widespread 1500 Ma peak, most of the εHf(t) peaks and valleys are controlled by specific geographic regions and are likely not be global in extent.Two distinct periods (200–0 and 1800–1600 Ma) display εHf(t) signatures that rise steadily for 100–200 Myr, coinciding with the final stages of supercontinent assembly and the transition to the retreat of exterior orogens. An εHf(t) peak at 750 Ma and a high at 1400–1100 Ma partly overlap with supercontinent breakup and valleys at 550 Ma and 900 Ma with supercontinent assembly. A large εHf(t) valley at 2000–1800 Ma corresponds with the onset of craton collisions that led to the final assembly of Columbia at 1800–1600 Ma. The steep rise in εHf(t) in the last 200 Myr in both igneous and detrital zircons is controlled by sites in Circum-Pacific orogens in North and South America and Southwest Asia, and it parallels the breakup of Pangea. The general increase in zircon εHf(t) in the last 500 Myr in both detrital and igneous data reflects an increase in the proportion of isotopically juvenile components in accretionary orogens.

Corrosion of aluminium alloy AA2024-Τ3 specimens subjected to different artificial ageing heat treatments

The effect of artificial-ageing on corrosion behaviour of aluminium alloy (AA)2024-T3 was investigated. The natural ageing which takes place during the aircraft's lifespan was simulated with isothermal heat-treatments at 190 °C. Electrochemical impedance spectroscopy measurements were performed in different heat-treated specimens to examine the prevailing corrosion mechanisms. Additionally, pre-corroded tensile specimens from different heat-treatment conditions were mechanically tested to assess the corrosion-induced degradation. Different forms of corrosion were revealed in the investigated ageing tempers; intense localized attack was noticed in the initial (T3) and under-aged (UA) tempers. UA condition exhibited the highest susceptibility to corrosion propagation followed by T3, according to the charge transfer resistance RCT and degradation rate of tensile elongation at fracture Af ( ≈ 0.118) and ( ≈ 0.103), respectively. Corrosion-induced degradation rates for the peak-aged (PA) and over-aged (OA) tempers ( ≈ 0.042 and 0.054, respectively) were almost one third of UA, attributed to volume fraction and size of the precipitated second-phase particles.

Detrital monazite evidence for crustal evolution of the North and South American continents during the Boring Billion

Orogenic processes associated with the supercontinent cycle play crucial roles in the evolution of continental crust and surface environments. Detrital zircon records, useful archives of orogenic history, have recently suggested the possibility of orogenic quiescence during the Mesoproterozoic, the so-called Boring Billion. However, detrital zircon may not always provide a precise record of crustal evolution due to preservation bias. Detrital monazite, another beneficial accessory mineral, can provide key archives for a better understanding of the continental crust evolution over geological history. Here, we present the U–Pb ages, trace element abundances, and Nd isotope compositions of detrital monazites from four major rivers on the North and South American continents: the Mackenzie, Mississippi, Amazon, and Paraná rivers. The monazite U–Pb age data showed an uneven distribution, with peaks even during the Mesoproterozoic. The age distribution of the detrital monazites was broadly consistent with that of the detrital zircons in the same rivers. However, the two mineral's different occurrences and preservation potentials result in significant differences. The trace element and Nd isotope data of the detrital monazites indicate that the monazite U–Pb age peaks reflect the timing of the collision stage rather than the subduction stage. We further found cyclic secular variations in the detrital monazite Nd isotope compositions: their 143Nd/144Nd averages shifted from juvenile to reworked crustal signatures during the interval of supercontinent assembly, including the Proterozoic period. The Nd isotope shifts can be interpreted as crustal maturation through crustal re-melting and metamorphism driven by orogenic events. The monazite U–Pb age peaks and Nd isotope shift during the Mesoproterozoic suggest sustained crustal evolution rather than orogenic quiescence during the Boring Billion.

Provenance evolution of the Fushan Sag (Hainan Island, Southern China): Constraints from U-Pb geochronology on detrital zircons

The Fushan Sag, situated on the southeast of the Beibuwan Basin in the northern Hainan Island, represents a semi-graben fault sag, characterized by a near NEE trend. In this study, we conducted LA-ICP-MS U-Pb age dating on detrital zircon from both the Liushagang and Weizhou formations in the Fushan Sag. By integrating our findings with previous research and considering the geological characteristics and bedrock conditions of the surrounding areas, we aimed to ascertain the provenance of the Fushan Sag. The obtained detrital zircon ages (1059 with 80% concordance) can be primarily categorized into three distinct age groups: Mesozoic (90–250 Ma), Paleozoic (250–450 Ma), and Proterozoic (450–2500 Ma). Specifically, detrital zircon grains from the Weizhou Formation reveal three prominent age peaks, approximately falling within the ranges of 100–150 Ma, 250–300 Ma, and 400–450 Ma. Conversely, the detrital zircon grains extracted from the Liushagang Formation predominantly exhibit two age peaks, approximately spanning 100–150 Ma and 200–300 Ma, with a weaker peak observed at 350–450 Ma in the second member, implying a potential change in provenance during this period. A comparative analysis of detrital zircon age characteristics strongly suggests that the primary provenance of the study area is Hainan Island, with the possibility of contributions from the YunKai Massif. Base on the preliminary geochronological data gathered, and in conjunction with extant scholarly research, an inference can be formulated regarding the paleogeographic evolution of the Beibuwan Basin spanning from the Eocene to the Oligocene. This analysis offers insights into the basin's geological history and dynamic changes over this extensive time frame.

Evidence for, and significance of, the Neoproterozoic Xuefeng Orogeny, South China

The recognition of unconformities is important for determining the long-term evolution of orogenic belts. We document an unconformity between Tonian and Cryogenian strata of the Nanhua Basin of South China. This stratigraphic break has previously been termed the Xuefeng Movement and is developed within the Yangtze Block and western Cathaysia Block. Deformation characteristics and detrital zircon U-Pb geochronology from rock units underlying and overlying the unconformity (i.e., the Niuguping and Gucheng formations, respectively) from the Anhua region of the northern Hunan Province in the southeastern Yangtze Block are documented. The Niuguping Formation displays a set of top-to-northwest imbricate thrust faults and related fault-propagation folds, NEE-plunging subparallel crenulation lineations, a foliation, and shows widespread greenschist facies metamorphism. In contrast, the overlying Gucheng Formation exhibits no obvious stratal deformation (apart from a mild inclination of bedding) and is unmetamorphosed. Detrital zircon age spectra of the samples from the Niuguping Formation are characterized by unimodal age peaks of ca. 750–730 Ma, while those of the samples from the Gucheng Formation yield a multimodal age distribution, with a few syn-sedimentary detrital zircons (<700 Ma), and much older zircons with age peaks of ca. 800 Ma, 2.1–1.9 Ga, and 2.6–2.3 Ga. Combining this data with previous geochronology indicates deposition of the Niuguping and Gucheng formations in the late Tonian (725–720 Ma) and Cryogenian (690–660 Ma), respectively. The time gap across the unconformity is some 30 Ma (720–690 Ma). The unconformity and associated structural and metamorphic break extend across the Yangtze Block and western Cathaysia Block, defining a major regional orogenic event. The significantly different detrital zircon spectra of strata across the unconformity suggest a dramatic change in the source due to the Xuefeng Orogeny in the Yangtze Block. Zircon U-Pb-Hf isotopic evidence indicates that detritus of the Niuguping Formation below the unconformity was derived from syn-depositional magmatic activity in the northern Yangtze Block, while a significant increase of Archean to Paleoproterozoic ages for the Gucheng Formation, suggests that the Xuefeng Orogeny resulted in crustal thickening and denudation in the northern Yangtze Block. These changes in provenance, along with changing deformational and metamorphic patterns, indicate evolution of the Nanhua Basin from a compressional to an extensional back-arc basin, which we infer is related to tectonic switching from an advancing to a retreating subduction system in the northern Yangtze Block at the time of the unconformity.

U–Pb apatite geochronology shows multiple thermal overprints within the Neoarchean foreland basement of the Faroe–Shetland Terrane

The Neoarchean foreland basement of the Faroe–Shetland terrane (FST) displays abundant evidence for isotopic resetting of U–Pb systems in apatite between c. 1800 and 200 Ma, interpreted to result from episodic heating pulses associated with regional-scale tectonic events. Major apparent age peaks of c. 1800–1600 Ma broadly correspond to the timing of Nagssugtoqidian–Laxfordian orogenesis &gt;225 km further south. These are thought to reflect widespread heating during late- to post-orogenic delamination that affected a wide area of the orogenic foreland and resulted in a low to middle greenschist-facies static overprint, affecting much of the FST basement. Late- to post-orogenic delamination might also account for major apparent age peaks at c. 1300–1100, 800 and 500–400 Ma, corresponding to, respectively, Grenvillian, Knoydartian and Caledonian orogenic events. However, east-dipping seismic reflectors in the basement west of Shetland may represent the northward extension of the Grenvillian Outer Hebrides Thrust (Zone) and/or Caledonian thrusts and so perturbation of isotherms during west-directed thrusting could therefore also account for these apparent age peaks. Minor apparent age peaks of c. 700, 600, 350 and 200 Ma are most easily interpreted as resulting from enhanced heat flux that accompanied periods of crustal extension prior to and following the Caledonian orogeny.

High-precision U-Pb zircon dating identifies a major magmatic event on the Moon at 4.338 Ga.

The Moon has had a complex history, with evidence of its primary crust formation obscured by later impacts. Existing U-Pb dates of >500 zircons from several locations on the lunar nearside reveal a pronounced age peak at 4.33 billion years (Ga), suggesting a major, potentially global magmatic event. However, the precision of existing geochronology is insufficient to determine whether this peak represents a brief event or a more protracted period of magmatism occurring over tens of millions of years. To improve the temporal resolution, we have analyzed Apollo 14, 15, and 17 zircons that were previously dated by ion microprobe at ~4.33 Ga using isotope dilution thermal ionization mass spectrometry. Concordant dates with sub-million-year uncertainty span ~4 million years from 4.338 to 4.334 Ga. Combined with Hf isotopic ratios and trace element concentrations, the data suggest zircon formation in a large impact melt sheet, possibly linked to the South Pole-Aitken basin.

Two distinct early Paleozoic subduction zones in the eastern Central Asian Orogenic Belt: Evidence of subduction recycling and arc evolution

This paper presents zircon U–Pb dating and Hf isotopic, and whole-rock geochemical and Sr–Nd isotopic data for early Paleozoic igneous rocks as well as zircon U–Pb dating for the sedimentary rocks of the Songnen Massif within the eastern Central Asian Orogenic Belt (CAOB), aiming to reveal arc magma evolution process. The zircon U–Pb dating results of the siltstone of the Xiaojingou Formation yielded 450 Ma, 471 Ma, 502 Ma, 773 Ma, 818 Ma and 949 Ma age peaks, as well as multi-episodic Paleo-proterozoic ages (2486-1612 Ma), implying its deposition time is younger than ∼ 450 Ma. The zircon U–Pb dating results reveal that the Songnen Massif exists three episodes of volcanic rocks of the middle Cambrian (502 Ma), Middle Ordovician (453-449 Ma) and the Silurian (435-420 Ma). The middle Cambrian basalts are low-K tholeiitic to calc-alkaline series, weakly depleted εHf(t) and εNd(t) values. They were derived from the weakly depleted mantle metasomatized by slab fluid in an immature island arc setting. The Middle Ordovician to Silurian volcanic rocks show SiO2 of 49.4–58.1 wt%, plotting into high-K calc-alkaline series, which are also featured by higher Th/Nd and (Hf/Sm)PM ratios, together with moderate depleted εNd(t) values, suggesting their derivation of the depleted mantle wedge metasomatized by sediment-derived melt. In contrast, coeval early Paleozoic volcanic rocks in the eastern Xing’an Massif with the MORB-like εNd(t) values are characterized by an origin of the depleted mantle wedge and the distinct interaction of oceanic crust melt and mantle peridotite. Combined with the variation of calculated crust thickness, we suggested that there was a continental arc in the eastern Songnen Massif, which developed from immaturity to maturity during middle Cambrian to Silurian, while the early Paleozoic island arc in the eastern Xing’an Massif is characterized by ocean ridge subduction process.

Earth’s metamorphic secular evolution accessed by rutile

Rutile provides crucial insights into the evolution of plate tectonics and variations in tectonomagmatic modes over Earth’s history primarily because rutile predominantly tracks higher-pressure metamorphism (>1.0–1.2 GPa). Comparison of rutile age and compositional data with diverse proxies tracks the presence of low temperature/pressure (T/P) metamorphic conditions, enabling the tracing of plate tectonics onset and evolution. We present a new compilation of rutile U-Pb ages that lag zircon ages by approximately 50 Myr, potentially indicating cooling ages of metamorphic belts. The earliest rutile age peak (ca. 1.8 Ga) aligns with the oldest evidence for low T/P metamorphic conditions. This coincides with a shift in the T/P distribution of rutile whereas the T/P of Archean rutile forms a tight normal distribution. In the Paleoproterozoic, the rutile T/P distribution is skewed to lower T/P, following the broader pattern of the full metamorphic record. The degree of lower T/P skew increases through time until the lower T/P population dominates the rutile record from the Neoproterozoic to the present. These data further highlight shifts in dominant metamorphic modes that can be tied to the evolution of the tectonic system, with early Archean metamorphism being associated with plume-driven vertical tectonics or hot, shallow subduction and post-Archean metamorphism being associated with progressive less plume-driven vertical tectonics and colder, steeper subduction. Although the frequency of rutile is lower during the Mesoproterozoic, the rutile T/P during this time follows the progressive skewing pattern from the Paleoproterozoic to the present and is likely inconsistent with a phase of interrupted tectonics characterized by stagnant lid.

Carboniferous rifting of the Lhasa Terrane (Tibet, China) and the break-up of East Gondwana based on detrital zircon analyses

The break-up processes of the northern margin of East Gondwana remain uncertain, especially regarding the Lhasa Terrane. In this paper, we conduct a systematic field geological survey, detrital zircon UPb dating, and zircon trace element and Hf isotope analyses in the Carboniferous rift basin in the eastern part of the Lhasa Terrane, including the Nuocuo and Laigu Formations, to reconstruct the break-up history of East Gondwana. The overall Carboniferous depositional environment in the eastern part of the Lhasa Terrane changed from near-shore and shallow marine to slope and moderately deep sea facies, reflecting a transgression. The weighted average age of several of the youngest detrital zircons from the Nuocuo Formation is 346.8 ± 6.4 Ma (4 grains), whereas that of the Laigu Formation is 328.7 ± 6.1 Ma (6 grains). The detrital zircon ages in the Carboniferous strata show similar distributions, dominated by zircons from the Indian continent (∼950 Ma), Australian continent (∼1170 Ma), and Lhasa Terrane (∼340 Ma). The paleogeographic position of the Lhasa Terrane was near the Indian and Australian continents during the Carboniferous. The increase of the ∼340 Ma detrital zircon age peak from the Mississippian to the Pennsylvanian demonstrated that the rift basin recorded a Mississippian magmatic event. The εHf(t) and oxygen fugacity values of partial zircons of ∼340 Ma are similar to those of zircons from intraplate magmatic rocks, further implying the intracontinental rifting in the Lhasa Terrane. Combined with the previous research on magmatic rocks in East Gondwana, including the Lhasa, South Qiangtang, and Himalayan Terranes, our study on sedimentation found that the Lhasa Terrane was in a passive continental margin rifting context during the Mississippian and the rift gradually expanded to become the Sumdo Paleo-Tethys Ocean basin.