Isotope Data Research Articles

Early Ordovician to Early Permian tectonic evolution of the northern Western Kunlun Orogen (NW China): Insights from the Omixia Complex and surrounding rocks

The Palaeozoic tectonic evolution of the Western Kunlun Orogen plays an important role in deciphering the Tethyan tectonic evolution. This study provides new geochronology, geochemistry and Lu–Hf isotopic data of igneous rocks from the Omixia Complex in the eastern section of the northern Western Kunlun, as well as detrital zircon ages from turbidites and meta‐sediments north of it. From the Omixia Complex, the determined ages of five ultramafic–mafic rock samples are approximately 470, 456, 429, 401 and 382 Ma. Two samples of acidic rocks from the same complex yielded ages of approximately 438 and 378 Ma. One pegmatitic plagiogranite sample exhibits feature of accretionary arc granites, while other samples show geochemical characteristics of island arc tholeiite and E‐MORB. Additionally, four turbidite matrix and two limestone samples, with a major peak around ca. 480–500 Ma, have the youngest zircon ages ranging from ca. 481 to 387 Ma, paralleling the age range of igneous rocks in the ophiolitic mélange. The εHf(t) values of these samples reveal a broad spectrum of crustal and mantle processes. The youngest zircon ages of five meta‐sedimentary rock samples north of the Omixia Complex range from ca. 581 to 535 Ma, with peak ages concentrated around ca. 0.9–1.0 Ga. Their provenance characteristics differ from the turbidite matrix in the southern Omixia Complex and from the meta‐sediments in the northern Tiklik terrane with peak ages of ca. 0.8 Ga. A younger limestone sample yielded youngest zircon age of ca. 294 Ma, which is unconformably overlain the Omixia Complex and surrounding older rocks. Based on these new results, combined with previous data, we propose a new tectonic model for the eastern section of the northern Western Kunlun Orogen, suggesting a continuous evolution process of multi‐terrane subduction–accretion collage from the Early Ordovician to the Middle Devonian in the Paleo‐Tethys Ocean, which evolved into an Andean‐type active margin in the Early Permian, contributing to the substantial continental growth of the southern Tarim Craton.

First identification of late Mesozoic intraplate magmatism in the Chinese north Tianshan: implications for the orogenic architecture and crustal evolution

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical and Sr–Nd–Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced at c . 145–132 Ma. They have positive ε Nd ( t ) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk-rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are probably inherited from Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were probably triggered by thermal relaxation owing to crustal shortening and thickening. These data further imply that the Tianshan changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Supplementary material: LA-ICP-MS zircon U–Pb dating results, whole-rock major and trace element compositions, whole-rock Sr–Nd isotopic data and zircon Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.7167890 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Integrating radiometric and aeromagnetic data for assessment of geothermal potential: a case study in Central Eastern Desert, Egypt

Integrating radiometric and aeromagnetic data for assessment of geothermal potential: a case study in Central Eastern Desert, Egypt

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 effect on the anomalies of water: A corresponding states analysis.

Light and heavy water show similar anomalies in thermodynamic and dynamic properties, with a consistent trend of anomalies occurring at higher temperatures in heavy water. Viscosity also increases faster upon cooling in heavy water, causing a giant isotope effect, with a viscosity ratio near 2.4 at 244K. While a simple temperature shift apparently helps in collapsing experimental data for both isotopes, it lacks a clear justification, changes value with the property considered, and requires additional ad hoc scaling factors. Here, we use a corresponding states analysis based on the possible existence of a liquid-liquid critical point in supercooled water. This provides a coherent framework that leads to the collapse of thermodynamic data. The ratio between the dynamic properties of the isotopes is strongly reduced. In particular, the decoupling between viscosity η and self-diffusion D, measured as a function of temperature T by the Stokes-Einstein ratio Dη/T, is found to collapse after applying the corresponding states analysis. Our results are consistent with simulations and suggest that the various isotope effects mirror the one on the liquid-liquid transition.

Late Triassic to Early Jurassic carbon isotope chemostratigraphy and organo-facies evolution in a distal to proximal transect of the North German Basin

AbstractThroughout the Latest Triassic and the Early Jurassic, major changes in paleogeography, climate and eustatic sea-level impacted on the development of shelf depositional environments. Secular trends in environmental conditions were punctuated by transient perturbations that occurred in relation to large-scale volcanic events, such as the emplacement of the Central Atlantic Magmatic Province at the Triassic/Jurassic boundary and the Karoo–Ferrar Large Igneous Province in the early Toarcian. We here present bulk organic (HAWK programmed pyrolysis) and organic carbon isotope (δ13Corg) data for three drill cores recovering Latest Triassic and Early Jurassic strata (Rhaetian to Toarcian). Study sites are located in the northeastern part of the Central European Epicontinental Sea and were positioned along a distal–proximal transect of the North German Basin. This allows discussing the differential response of depositional settings and organo-facies toward secular and transient environmental change. Biostratigraphically anchored trends in δ13Corg values allow the precise correlation along the transect, as well as with distant sites. At all North German locations, diagnostic secular trends in δ13Corg are punctuated by transient negative carbon isotope excursions, reflecting perturbations of the global carbon cycle at the Triassic/Jurassic boundary and in the early Toarcian. Stratigraphic gaps occurred during sea-level lowstands and are most pronounced at shallow proximal sites. Programmed pyrolysis data indicate spatiotemporal organo-facies trends that on a temporal scale occurred in response to sea-level and climate trends, while spatial patterns were governed by basin morphology and paleobathymetry. Substantial marine organic matter accumulations occurred at high sea level during the Toarcian only, and were most continuous at distal sites. Graphical Abstract

Back-arc magmatism of the Proto-Tethys Ocean in the West Kunlun Orogenic Belt: evidence from the Ordovician Nanpingxueshan Nb-enriched gabbros

ABSTRACT The West Kunlun Orogenic Belt (WKOB) in the northwestern Tibetan Plateau records key information about the tectonic evolution of the Proto-Tethys Ocean. To further constrain the Early Palaeozoic tectonic evolution of the WKOB, we report petrography, geochronology, whole-rock geochemistry, and Sr-Nd-Hf-O isotope data of the newly identified Ordovician Nanpingxueshan gabbros in the southern WKOB. Laser ablation-inductively coupled plasma-mass spectroscopy (LA-MC-ICP-MS) U-Pb zircon dating reveals that the gabbroic intrusion was emplaced during 476–471 Ma. Geochemically, the gabbroic rocks exhibit a tholeiitic signature and can be subdivided into two groups, i.e. normal arc-like gabbros (AGs) and Nb-enriched gabbros (NEGs). The AGs have TiO2 (1.20–1.64%), P2O5 (0.18–0.25%), and Nb (4.60–7.64 ppm) contents, fractionated REE patterns ((La/Yb)N = 2.64–4.11), and Nb-Ta depletion (Nb/La = 0.37–0.50). Compared with AGs, the NEGs have higher TiO2 (1.74–2.68%), P2O5 (0.34–0.55%), and Nb (10.79–14.08 ppm) contents and Nb/La ratios of 0.45–0.53, which are similar to typical Nb-enriched arc basalts. Isotopically, the AGs have depleted whole-rock εNd(t) values of 3.22 to 4.04 and negative to positive zircon εHf(t) values of −1.8 to 7.8, while the NEGs exhibit slightly lower whole-rock εNd(t) values of 0.69 to 3.18, zircon εHf(t) values of −7.8 to 4.6, and mostly δ18O values greater than those of normal mantle zircon. Integrated analyses reveal that the AGs and NEGs can be attributed to a similar mantle source metasomatized by different proportions of subducted sediment-derived melt during the subduction process. Our new data, combined with the results of previous studies, suggest that the southward subduction of the Proto-Tethys Ocean under the WKOB initiated at ca. 530 Ma. The long-term southward subduction led to the formation of the massive Early Palaeozoic accretionary complex in the South Kunlun Terrane, while trench retreat led to migration of the arc magmatism northward from the Mazar – Tianshuihai Terrane to the South Kunlun Terrane, as well as back-arc extension in the Mazar – Tianshuihai Terrane.

Massive crustal carbon mobilization and emission driven by India underthrusting Asia

The active Himalayan-Tibetan orogen, where India underthrusts into Asia, is an important geological source of carbon dioxide (CO2) emission into Earth’s atmosphere. However, the extent to which Indian underthrusting could stimulate the mobilization of deeply-sourced carbon and its subsequent emission remains unknown. Here, we use a combination of field observations coupled with in-situ CO2 flux measurements and helium and carbon isotopic data, to study the controls on CO2 origins and fluxes in a 400-kilometre-long rift transecting northern Himalaya and southern Tibet. High diffuse CO2 fluxes sustained by pure crustal fluids are confined to rift segments in the northern Himalaya, while toward southern Tibet, CO2 fluxes become lower but mantle fluid inputs are identified. Such rift-related CO2 degassing profile suggests metamorphic decarbonation and release of carbon-bearing fluids enhanced by the underthrusting Indian lower crust, agreeing well with Himalayan metamorphism and orogen-parallel lithospheric extension. Deep CO2 fluxes from extensional tectonics in northern Himalaya and southern Tibet, primarily of crustal origins, are comparable to mantle CO2 fluxes from global mid-ocean ridges. Our findings demonstrate that geophysical and geo-tectonic responses to continental underthrusting could facilitate massive crustal carbon mobilization and emission, making active collisional orogens globally important carbon sources.

Tracing the Origin and Magmatic Evolution of the Rejuvenated Volcanism in Santa Clara Island, Juan Fernández Ridge, SE Pacific

Oceanic intraplate volcanoes sometimes experience late-stage eruptive activity known as rejuvenated volcanism, and contrasting interpretations for its petrogenesis depend on the compositional characteristics. In the Juan Fernández Ridge (JFR), a volcanic chain approximately 800 km in length emplaced on the Nazca Plate, some subaerial occurrences of rejuvenated volcanism have been recognized on the Robinson Crusoe and Santa Clara Islands, both part of the same deeply eroded shield volcano complex. This study aims to understand the origin and magmatic evolution of rejuvenated volcanism on Santa Clara Island, emplaced after ~2.15 Ma of quiescence above the shield sequence, mainly via the analysis of unpublished geochemical and isotopic data. Field reconnaissance identified two nearly coeval rejuvenated sequences on Santa Clara Island: Bahía W (BW) and Morro Spartan (MS), both formed by basanitic and picro-basaltic lava flows with brecciated levels and local intercalations of sedimentary and pyroclastic deposits. In comparison to the chemical signature of the preceding shield-building stage (comprised mainly of basalts and picrites), the two rejuvenated sequences exhibit a notable enrichment in incompatible elements, but the Sr, Nd, and Pb isotopes are very similar to the FOZO mantle endmember, with an apparent additional contribution of HIMU and EM1 components. The geochemistry of lavas revealed the involvement of various processes, including contamination by ultramafic xenoliths, high-pressure fractional crystallization of olivine and clinopyroxene, and potential partial assimilation of oceanic lithospheric components. While the oceanic lithosphere has been considered as a potential source, the isotopic data from Santa Clara lies outside of the mixing curve between depleted mantle (DM, here represented by the North Chile Rise and the East Pacific Rise) and the previous shield stage, suggesting that a lithospheric mantle is not the primary source for the rejuvenated stage volcanism. Therefore, we favor an origin of the rejuvenated volcanism from the mantle plume forming the JFR, supported by similarities in isotopic signatures with the shield stage and high values of 208Pb/204Pb (only comparable to San Félix—San Ambrosio in the vicinity of JFR), implying the presence of a regional source with radiogenic 208Pb/204Pb isotope ratios. In addition, isotopic variations are subparallel to the mixing line between HIMU and EM1 components, whose participation in different proportions might explain the observed trends. In conclusion, we propose that the source of the rejuvenated volcanism on Santa Clara Island is a heterogeneous mantle plume, the same one that fed the shield stage. The rejuvenated volcanism is derived from a secondary melting zone away from the main axis of the plume.

Compositional Diversity of Early Mesozoic Granites in South Qinling: Derivation from Heterogenous Basement Rocks in the Orogenic Belt

Granitic rocks forming in the syn- to post-orogenic stages can trace the compositional and structural complexity of the crust beneath an orogenic belt. The Qinling orogenic belt undertook multiple stages of tectonics and magmatism, resulting in the multifaceted evolution and compositional diversity of the crust. In the present study, the Guangtoushan and Miba plutons in South Qinling were chosen to reveal the crustal heterogeneity in study area via isotopic geochemistry and zircon geochronology. The Guangtoushan pluton was emplaced between ~215 Ma and ~202 Ma and the Miba pluton formed at ~213 Ma, as constrained by zircon U-Pb isotopic dating. Granitic rocks of the Miba pluton are characterized by amphibole bearing and homogeneous composition, with relatively depleted Sr-Nd isotopic compositions (initial 87Sr/86Sr values of 0.7060 to 0.7084 and initial εNd values of −5.4 to −9.5) and high Pb isotopic values. The Guangtoushan pluton contains muscovite and complex inherited zircon grains and has variable Sr-Nd isotopic composition (initial 87Sr/86Sr values of 0.7050 to 0.7091 and initial εNd values of −4.5 to −12.9) and low Pb isotopic values. Felsic magmas of the Guangtoushan pluton should be derived mainly from meta-sedimentary rocks beneath South Qinling, while the Miba pluton originated primarily from partial melting of meta-igneous rocks. The compositional diversity recorded in the Early Mesozoic plutons was caused by the heterogeneous crust, and partial melting was induced by heating of the up-welling asthenosphere in a post-collision setting.

Stable Isotope Variation in East and Southeast Asian Marine Ecosystems and its Relevance for Archaeological Analysis

ABSTRACT This paper delves into the utilisation of stable isotope analysis as a tool for understanding ancient human adaptations to diverse marine environments, with a specific geographical focus on Southeast Asia and the Pacific. It analyzes stable isotope data from modern fish bones and tooth enamel, focusing on δ13C, δ15N, and δ18O values. The data confirm the reliability of δ13C as a proxy for marine consumption in archaeological contexts and emphasises the potential of combining δ13C and δ15N measurements to reconstruct marine food consumption and trophic level. This, in turn, helps us gain insights into ancient marine consumption and ecosystems in Southeast Asia. While distinctions between marine niches are not clear, δ15N shows potential for distinguishing feeding behaviours among fish species. The data also suggests geographical and ecological variations in stable isotope values, highlighting the need for locally-based baseline datasets in archaeological studies of marine subsistence strategies.

Origin of the Site U1504 alkaline basalts in the South China Sea continental margin: Insights on deep mantle diversity and subduction dynamics under continental arcs

Alkaline basalts produced in continental arcs should contain information different from the arc tholeiite-calc-alkaline-series magmas, and their origin could provide unique constraints on deep mantle composition and material cycling. However, due to their sparse occurrence, alkaline basalts in continental arcs have not been studied thoroughly, which hinders our understanding of the mantle diversity and subduction dynamics under continental arcs. In this study, we present new 40Ar/39Ar ages, major and trace elements, and Sr-Nd-Hf isotopic data for the International Ocean Discovery Program Site U1504 alkaline basalts in the continental arc developed on the South China Block (SCB). These alkaline basalts were generated at ca. 121 Ma and display typical oceanic-island basalt geochemical characteristics. Their relatively high εNd(t) (3.5−3.7) and low (87Sr/86Sr)i (0.7034−0.7040) and La/Nb (0.5−1.0) values suggest that they were mainly derived from an asthenosphere mantle source. Compared to alkaline basalts in the SCB inland, U1504 alkaline basalts exhibit lower K2O/Na2O, Zr/Sm, Zr/Y, εNd(t), and εHf(t) values, indicating the addition of minor sub-continental lithospheric mantle. The enrichment of Nb, Ta, light rare earth elements, and slight depletion of Zr, Hf, and Ti, as well as elevated Fe/Mn and Sm/Yb and low CaO, indicate that their mantle lithology was mainly garnet pyroxenite. Based upon these findings and previous studies, the garnet pyroxenite was probably formed by the interaction of upwelling asthenosphere with slab edges in the scenario of break-off of the Paleo-Pacific Plate, and such interaction diversified the mantle chemistry beneath continental arcs. In conjunction with other reported alkaline basalt data, it is proposed that the enriched asthenosphere mantle beneath the SCB had formed sequentially from inland to coastal since the late Mesozoic, and this may be related to lateral and vertical flow in the deep asthenosphere controlled by the break-off of subducted plates.

Potential historically intertropical stable areas during the Late Quaternary of South America

AbstractSouth America is a pivotal paleontological setting for Late Quaternary megafaunal research. Nonetheless, its paleobiogeography and paleoecology, and the causes for the recent extinction of megafauna in the Late Pleistocene/Early Holocene are not yet fully understood. This study aimed to investigate the potential geographical distribution and historically intertropical stable areas (HISAs) of South American megafauna. We generated maps using Paleo‐Species Distribution Models for 12 megafaunal taxa (11 herbivores and one carnivore) during interglacial and glacial periods in the Late Quaternary: 120 and 21 ka. Our models, together with isotopic data, show that the HSIAs occurred mainly in low‐altitude plains (<1000 m) and were superimposed on seasonal dry forest biomes. We propose the occurrence of two HSIAs: the West Intertropical Region and the Brazilian Intertropical Region, the latter being redefined. We suggest that the Brazilian Intertropical Region is much smaller than previously proposed, but was still a key zoogeographical region for megafauna in South America during the Late Pleistocene.

The response of ostracod faunal assemblages to hydrology, lake level, and carbon cycling in a Jamaican marl lake: a palaeolimnological investigation

Abstract. Ostracod taxa from shallow freshwater lakes are sensitive to a range of limnological factors including temperature, hydrological habitat, lake level, and the distribution of aquatic plants. Ostracod assemblages preserved in Quaternary lake sediments can be used to reconstruct limnological change and are therefore potentially valuable palaeoenvironmental proxies. However, lack of autecological information about some taxa may limit the validity of such reconstructions. We use fossil ostracod assemblages recovered from radiocarbon-dated late Holocene sediments from Wallywash Great Pond, a small, shallow freshwater lake in southwestern Jamaica, to reconstruct limnological change over the past ∼ 1800 years. We circumvent ongoing taxonomic and ecological uncertainties associated with the identification of fossil ostracod taxa by drawing on observations of the ecology of ostracods found living in Jamaican water bodies. By combining this information with limnological data from the extant lake, and with sedimentological and isotopic data from the lake sediments, we show that a published interpretation of ostracod assemblages for the late Quaternary of Wallywash Great Pond is simplistic, at least for the late Holocene section of the sediment record. We conclude that changes in ostracod assemblages are linked to variations in the input of undersaturated groundwater to the northern part of the lake from which the core was recovered. These variations, which were driven by changes in the precipitation / evaporation ratio (effective moisture), also controlled sedimentation, with reduced effective moisture and a decline in undersaturated groundwater input favouring marl precipitation, whereas organic sediments are linked to increased effective moisture and enhanced groundwater input. Our findings suggest that the dramatic shifts in ostracod assemblages at this site are a complex response to changes in hydrology, sedimentology, and carbonate saturation rather than being a simple indicator of lake-level change. Combining ostracod assemblage data with the results of other palaeolimnological analyses also allows more detailed reconstructions to be made for this lake, and such a multiproxy approach is recommended for similar lakes elsewhere.

Quantifying Nitrogen Treatment by an In-stream Bioreactor in a Watershed Served by Septic Systems

Septic systems are potentially significant sources of nitrogen to groundwater and surface water. In-stream practices, such as in-stream bioreactors (IBRs), that promote or enhance nitrogen treatment are promising solutions to reduce nitrogen loads to nutrient-sensitive water. More work is needed to evaluate the efficiency of IBRs in new applications, such as residential sub-watersheds with a high-density of septic systems. The goal of this study was to quantify nitrogen treatment by an in-stream bioreactor (IBR) during baseflow conditions. The IBR was constructed in March 2017 when approximately 1 m of streambed sediment was excavated and backfilled with 0.75 m of woodchips capped by 0.2 m of rotary-kiln, expanded slate and boulder-sized riprap. Samples were collected monthly from July 2017 – March 2019 including IBR inflow, monitoring ports within the IBR, groundwater seeps draining to the IBR, and IBR outflow. Water samples were analyzed for total dissolved nitrogen (TDN), nitrate, ammonium, dissolved organic carbon, chloride, and nitrate isotopic fractionation. The IBR reduced the median concentration of TDN and nitrate by 40% and 77%, respectively. The median mass removal of TDN and nitrate was 26 and 5.2 g day− 1, respectively. Nitrogen-chloride ratios and isotopic fractionation data suggest that denitrification was likely a predominant nitrogen reduction mechanism. In addition to nitrogen treatment, the IBR provided other benefits by improving erosion control, streambank stabilization, and increased bank-full storage from 6 m3 to 19.2 m3. Results indicated that the IBR improved water quality and other residential sub-watersheds with septic systems would benefit from similar practices.

Ma/Ca Ratio in Stalagmites as a Potential Palaeo‐Temperature Indicator

AbstractMg/Ca ratio in stalagmites primarily serves as an indicator of past hydrological conditions rather than temperature variations. Here, we present an Mg/Ca ratio record in a stalagmite from northern China, spanning ice age termination II. A unique finding is that Mg/Ca ratio shows a moderately strong positive correlation with cave air temperature obtained from clumped isotopes data in the same stalagmite. The stable hydrogeochemistry of source water and high temperature sensitivity of Mg partition coefficient plausibly explain this temperature dependence. Furthermore, we establish an Mg/Ca‐temperature calibration for stalagmites from mid‐latitudes, encompassing a temperature range between ∼2 and ∼15°C, where Mg/Ca = 14.221 × e0.073×T (R2 = 0.40). Applying this function to Mg/Ca ratio from similar stalagmites could tentatively provide a quantitative regional temperature record over millennial and centennial timescales. This research highlights Mg/Ca ratio in stalagmites as a potential palaeo‐temperature proxy and introduces, for the first time, a tentative Mg/Ca‐temperature calibration function for speleothems.

Constraints on crustal compositional architecture across the North China-Altaids transition and implications for craton margin reworking

Abstract The phase of secular evolution of continents is manifested as the degree of compositional differentiation, modification, and maturation of continental crusts, which is vital in understanding the mechanism of continental evolution but is difficult to quantify. Here we use integrated passive- and active-source seismic profiling to conduct joint analysis and inversion and derive Vs and Vp/Vs section models across the North China craton (NCC) to southeastern Altaids boundary zone that bears a tectonic transition from a reworked ancient craton margin to a Phanerozoic accretionary orogen. We systematically exploited the imaged multiple physical properties as precise and delicate proxies to constrain the compositional architecture in the crust across this important tectonic transition subject to various crustal evolutional phases. Our Vs and Vp/Vs imaging, together with the existing isotopic data, characterizes the Yin Shan-Yan Shan belt as the northern NCC margin with layered homogeneous compositions that point to an evolved crust. However, the lower-crustal low-Vs/high-Vp/Vs signature that overlaps the shallowly dipping to horizontal reflective fabrics suggests the crust of the northern NCC margin has undergone considerable reworking through lower-crustal-stretching assisted melt migration and mixing since the late-Paleozoic to Mesozoic era. The process probably involved crust-mantle interaction and thus resulted in a compositionally modified ancient crustal basement. On the contrary, the southeastern Altaids domain manifests crustal complexity in compositions and structures inferred to be indicative of a juvenile crust of the Phanerozoic accretionary orogen. Our results provide deep physical-property constraints that shed new light on the crustal evolution of a complex craton margin.

The First Results of U–Th–Pb Isotopic Dating of Detrital Zircons from the Chenka Sandstones: A Contribution to the Stratigraphy of the Cimmerides of Mountainous Crimea

The First Results of U–Th–Pb Isotopic Dating of Detrital Zircons from the Chenka Sandstones: A Contribution to the Stratigraphy of the Cimmerides of Mountainous Crimea

Elemental and oxygen isotopic fractionation recorded in highly vaporized cosmic spherules from Widerøefjellet, Sør Rondane Mountains (East Antarctica)

AbstractUpon passage through Earth's atmosphere, micrometeorites undergo variable degrees of melting and evaporation. Among the various textural and chemical groups recognized among cosmic spherules, that is, melted micrometeorites, a subset of particles may indicate anomalously high degrees of vaporization based on their chemical and isotopic properties. Here, a selection of such refractory element‐enriched cosmic spherules from Widerøefjellet (Sør Rondane Mountains, East Antarctica) is characterized for their petrographic features, major and trace element concentrations (N = 35), and oxygen isotopic compositions (N = 23). Following chemical classification, the highly vaporized particles can be assigned to either the “CAT‐like” or the “High Ca‐Al” cosmic spherule groups. However, through the combination of major and trace element concentrations and oxygen isotopic data, a larger diversity of processes and precursor materials are identified that lead to the final compositions of refractory element‐enriched particles. These include fragmentation, disproportional sampling of specific mineral constituents, differential melting, metal bead extraction, redox shifts, and evaporation. Based on specific element concentrations (e.g., Sc, Zr, Eu, Tm) and ratios (e.g., Fe/Mg, CaO + Al2O3/Sc + Y + Zr + Hf), and variations of O isotope compositions, “CAT‐like” and “High Ca‐Al” cosmic spherules likely represent a continuum between mineral endmembers from both primitive and differentiated parent bodies that experienced variable degrees of evaporation.

980-970 Ma Sette-Daban event of the Siberian craton: new geochronological and geochemical data, relationship to LIP and potential connection with other LIPs

ABSTRACT The paper presents new geological, geochronological, geochemical and Nd-Sr isotopic data on the Meso- Neoproterozoic dolerites of the Siberian Craton. New U-Pb baddeleyite and apatite ages of a E-W-trending dyke and two sills from southeastern Siberia are 982 ± 11, 977 ± 7, 970 ± 31 and 972 ± 60 Ma, respectively, extending the area of distribution of the event by more than 100 km to the north. The Sette-Daban intrusions are subalkalic mostly low-Ti dolerites, although high-Ti dolerites have been locally documented as well. Trace element abundances in dolerites vary from typical to E-MORB to OIB with arc-like signatures represented by high Th/Yb and low TiO2/Yb ratios. All dolerite samples display moderately positive εNd(t) values varying from +3.3 to +7.7 and indicating the magmas were derived from a depleted mantle source. E-MORB and OIB intrusions are attributed to the different degree of interaction of magma between the depleted asthenospheric mantle and regions within the sub-continental lithospheric mantle (SCLM) that were metasomatically enriched during earlier subduction events. Available data on Sette-Daban event distribution, composition and duration satisfy the characteristics of a typical Large Igneous Province (LIP). Similar age 1000–950 Ma mafic magmatism is also recognized in the Baltic and Amazonian cratons and can be potentially correlated with the Sette-Daban event.