Sediment Recycling Research Articles

Shallow recycling of lower continental crust: The Mahoney Seamount at the Southwest Indian Ridge

The Mahoney Seamount is a recently discovered volcanic edifice located 4 km north of the ultra-slow spreading Southwest Indian Ridge (SWIR). The SWIR is one of the slowest spreading ridges worldwide with a full spreading rate of ∼14 mm/year and low magmatic productivity. We report that highly vesicular basalts from the Mahoney Seamount have unradiogenic Nd-Hf together with radiogenic Sr isotopic compositions. Their distinct low 206Pb/204Pb isotope signature combined with high 207Pb/204Pb and 208Pb/204Pb is best explained by melting of a mantle that has been strongly influenced by stranded lower continental crust. The geographic distribution of the isotopic variability favors the idea of shallow recycling of lower continental crust isolated for a longer period contributing to melts forming Mahoney Seamount through off-axis fault systems. The isotopic composition of Mahoney Seamount lavas shares many characteristics with EM-1 sources and the DUPAL signature. Previous isotopic studies of the SWIR basalts proposed recycling of ancient subcontinental lithospheric mantle (SCLM) or pelagic sediments with oceanic crust to be responsible for this enriched isotopic signature. Lu/Hf and Sm/Nd ratios of pelagic sediments would result in decoupled 143Nd/144Nd and 176Hf/177Hf ratios. This decoupling is also observed in Ejeda-Bekily dikes from Madagascar, but those are believed to sample the SCLM dispersed in the Indian Ocean. However, Mahoney Seamount shows no decoupling in those isotopic systems and the restricted occurrence of the extreme lower continental crustal signature at Mahoney Seamount implies that the enriched isotopic signature has a different origin.

Recycling and optimum utilization of engineering sediment waste into low-carbon geopolymer paste for sustainable infrastructure

The development of underground space is an important trend for urban infrastructure in cities supporting socio-economic activities, while it also results in an enormous accumulation of sediment waste, which consumes vast land resources, causes serious environmental problems and endangers public safety. It is urgent to explore pathways of recycling sediment waste with low carbon impact for sustainable infrastructure. This study employed calcination and alkali activators to recycle sediment waste into geopolymer paste. The mechanical properties and working performance of recycled geopolymer paste were investigated and the underlying mechanism of this recycling scheme was revealed with microscale characterizations. Results showed that the compressive strength of recycled geopolymer paste could reach 50 MPa. The environmental impact of geopolymer paste and cement-based paste has been analyzed via life cycle assessment (LCA). Recycled geopolymer paste can save 310 kg CO2eq/t of carbon emissions, which is 39% lower than that of cement-based material. Moreover, the multi-criteria approach was adopted to evaluate geopolymer paste and cement paste considering mechanical properties, working performance, carbon emissions, energy consumption and cost, and geopolymer paste exhibits better overall performance. The findings inspire a construction waste management strategy and contribute to low-carbon construction materials for sustainable urban infrastructure.

Variable element enrichment sources and contributions to volcanic rocks along the Lesser Antilles Island Arc

Understanding relationships between different components involved in subduction-related recycling of sediment at arc volcanic systems has long been a focus of study. It is generally understood that volcanic arc lavas incorporate materials from the down-going slab including fluids, fluid mobile elements (FME), and fluid modified large ion lithophile elements (LILE), largely derived from subducted sediments and serpentinized ultramafic rocks. Past studies have presumed bulk sediment contributions rather than addressing localized variations in sediment composition. We examine trace element variability along the Lesser Antilles Island Arc (LAIA) and show that sediment inputs via fluid transfer to the mantle wedge are necessary to explain high B (up to 50 ppm), high B/La ratios, and higher As, Cs, Rb in the central LAIA. In contrast, the northern portion of LAIA is enriched in Ba, Sr and U/Th, with low FME. Grenada has low FME abundances, low Ba/La, but higher Sm/La. Our results suggest that modification of LAIA mantle source by fluid addition is important for the central islands but find that sediment enrichment is more likely in the northern section of the LAIA. Li/Yb ratios suggest the Grenada signature is chemically more comparable to sediment from DSDP Site 144 (Demerara Rise), while Martinique magmas in the central LAIA are affiliated to sediments from Site 543 (offshore Dominica). Unexpectedly, the northern portion of LAIA is not directly relatable to Site 543 sediments but instead trends back toward a sediment source similar in composition to Site 144 but with lower B, lower La/Sm and higher Ba. Binary mixing models suggest the northern islands are likely influenced by small amounts of sediment melt similar to average Site 144 sediments, but with Ba concentrations ranging from 1,250 to 1,500 ppm. Trace element ratios then likely result from different levels of contribution from sediment packages both spatially and temporally along the arc, with some variation evident among samples from the same island. We suggest that the process of recycling subducted sediment along the arc is variable along the length of the LAIA, wherein the trace element relationships are likely strongly influenced by the types of sediment being subducted along strike.

Himalayan zircons resurface in Sumatran arc volcanoes through sediment recycling

Understanding the processes of subducted sediment recycling in subduction zones is vital to decipher Earth’s crust-mantle interactions. This study uses along-arc geochemical variations and zircon U-Pb-Hf-O isotopes of Quaternary arc basalts and andesites on Sumatra Island, Indonesia to assess the mode of sediment recycling in subduction zones. The Hf-O isotopes of inherited zircons of the basalts and andesites near the Toba Caldera indicate that some of them were derived from subducted terrigenous sediments mainly sourced from the (eastern) Himalaya. Hybridization of the subducted sediments with the mantle also accounts for the enriched Sr-Nd isotopic compositions of arc volcanic rocks near the Toba Caldera. Thermodynamic modeling indicates that the subducted sediments did not melt on the slab surface. Rather, geochemical evidence supports their formation as diapirs that rise buoyantly through the hot mantle wedge and contribute to ~30 to 45% of the magma source of the arc volcanic rocks near Toba.

Halogen (F, Cl, Br, and I) concentrations of the upper continental crust through time as recorded in ancient glacial diamictite composites

The continental crust is an important reservoir for incompatible elements, including the halogen elements (F, Cl, Br, and I), but their concentrations remain poorly known, thus hindering better understanding of the role of the crust in Earth’s halogen cycle. We present halogen data (F, Cl, Br, and I) for twenty-four well-characterized glacial diamictite composites that derive from the upper continental crust (UCC) and were deposited during discrete glacial events at ∼2.9 Ga, ∼2.4–2.2 Ga, 0.75–0.58 Ga, and ∼0.30 Ga. A good correlation between Cl and the highly soluble Na (R2 = 0.70), together with low and scattered Cl concentrations in the diamictites (2–279 ppm), indicates significant Cl loss during chemical weathering of the continents. The other halogens (F, Br, and I), however, are not strongly affected by chemical weathering as revealed by their correlations with less soluble elements like K, P, Nd, and Lu, which may be due to their retention in secondary minerals and/or organic matter. Increasing concentrations of F in the composites through time may reflect the evolving composition of the UCC. Using the median values of the Neoproterozoic and Paleozoic diamictite composites, halogen concentrations of the present-day weathered UCC are estimated to be: 575 ± 87 ppm F, 29 ± 20 ppm Cl, 0.65 ± 0.14 ppm Br, and 0.05 ± 0.01 ppm I (errors quoted at the median absolute deviation). Linear correlations between halogens and other elements provide estimates for minimum halogen concentrations of the present-day crystalline UCC: 394 ± 67 ppm F, 83 ± 24 ppm Cl, 0.41 ± 0.04 ppm Br, and 0.03 ± 0.01 ppm I (with 2σ uncertainties). These estimates are all lower than normalized concentrations of elements of similar incompatibility during igneous differentiation, which may reflect loss of halogens via magmatic degassing/exsolution and/or chemical weathering during the formation of the continental crust. The distinct behavior of Cl compared to Br and I during continental weathering leads to a wide range of Br/Cl (2–265 * 10−3) and I/Cl (122–197,952 * 10−6) ratios, and Br/I ratios that are distinctly higher than those of pelagic sediments and marine pore fluids. Similar halogen signals have been reported from the lithospheric mantle and may reflect recycling of terrigenous sediments. The calculated weathering flux of Cl from the continents is quite small compared to the total Cl content of seawater (<8–34 %), suggesting that Cl in seawater is mainly derived from outgassing of the mantle and/or late volatile accretion. On the other hand, the significantly higher Br and I contents in terrigenous organic-rich sediments compared to those of crystalline bedrocks suggest that significant amounts of Br and I were transported from the oceans to the continents.

The Carbon Emission and Environmental Benefit Analyses of the Qingxi River Sediment Treatment and Recycling Project in Dongguan, China

In this paper, the ability of resource treatment of black smelly river sediment to reduce life-cycle greenhouse gas (GHG) emissions and its environmental benefits were calculated using the US EPA life-cycle assessment (LCA) model. Different from previous studies, this paper used the willingness-to-pay method to determine the weight factors of various environmental impact types in this study and proposed a calculation model of carbon emissions and environmental benefits in the whole process of resource utilization of sediment, rather than a new method to treat black smelly river sediment. Take the Qingxi River sediment treatment and recycling project in Dongguan, China, as an example: the carbon reduction, environmental impact, and environmental benefit of different stages of sediment treatment are calculated. The results show that 93.419 kg of carbon dioxide, 0.202 kg of methane, and 0.001 kg of nitrous oxide are produced for 1 t of river sediment, in which the preparation process of unburned brick contributes 99% of carbon dioxide, 82.67% of methane, and 100% of nitrous oxide emissions and is the stage that produces the most greenhouse gases. The 1 t of sediment resource treatment can reduce the generation of 29.066 kg carbon dioxide and 0.855 kg of methane. The comprehensive net environmental benefit of processing 1 t of river sediment is 1.492 yuan, and the environmental benefit is 1.684 times the environmental cost. This study identified that the treatment and recycling of river sediment has better environmental benefits. The preparation process of unburned brick can be optimized to further reduce carbon emissions and produce better environmental benefits.

Tracing sediment provenance in the Yellow River, China: Insights from weathering, recycling, and rock compositions

Geochemical investigations of fluvial sediment help understand the provenance of sediment and surface processes taking place on the Earth at the watershed scale. This study is aimed at identifying the weathering and sedimentary recycling of the surface sediment of the Yellow River using the Chemical Index of Alteration (CIA), Weathering Index of Parker (WIP), Index of Compositional Variability (ICV), Mafic-Felsic-Weathering (MFW) ternary diagram, and Al-Ti-Zr ternary diagram. Source rocks compositions were clarified using Al2O3-CaO⁎+Na2O-K2O (A-CN-K), MFW, discriminant function, and Cr/V vs Y/Ni diagrams. The results demonstrated that the surface sediment of the Yellow River has experienced an overall low intensity of weathering and recycling. However, significant differences were observed in the characteristics of weathering and recycling among the upper, middle, and lower reaches, which is in turn associated with the differences in climatic conditions and tectonic settings. Source rocks manifested a typically mixed type composition, including felsic igneous rocks, intermediate igneous rocks, quartzose sedimentary rocks, and mafic components. Moreover, the sediment in the source area of the Yellow River may have originated from the clastics produced by the abrading of mountain glaciers. Sediment in the area in which the Yellow River flows through the Chinese Loess Plateau primarily originates from loess in the desert in Northwestern China. Sediment in the lower reaches does not only include the sorted sediment flowing down from the upper and middle reaches, but also that imported from regional rivers. This study can furnish a sound scientific basis for the reconstruction of the paleoclimatic and paleoenvironmental changes that affected large watersheds in arid and semi-arid areas.

Recycling of bottom sediment to agriculture: effects on plant growth and soil properties

PurposeThe use of bottom sediments in agriculture reduces the storage of excavated material and allows the nutrients it contains to be applied for soil fertilisation and improvement. However, the direct application of sediments to soil may cause numerous problems. Therefore, the addition of other waste materials may be a promising and useful method in the production of bottom-sediment-based growing media. The aim of the study was to evaluate the effect of growing media prepared on the basis of bottom sediments and various waste materials on the properties of soil as well as on the yield and chemical composition of courgette biomass.MethodsThe growing media were prepared with substrates in the form of mixtures with bottom sediments taken from the Rożnów reservoir. The effect of mixtures on plant growth was determined in a laboratory pot experiment. Air-dry mixtures (M1—bottom sediment with water treatment sludge (BS + SW); M2—bottom sediment with biomass ash (BS + BA); M3—bottom sediment with coffee hulls (BS + CH)) were mixed with soil (S) in the following proportions: combination I—25%, combination II—50%, combination III—75%, and combination IV—100% mixture.ResultsThe media did not have harmful effects on the plant or the soil environment. They had deacidifying properties; high contents of calcium, magnesium, potassium, and phosphorus; low total trace element content; and posed little risk of metal mobility. Heterocypris incongruens was the organism most sensitive to the substances contained in the studied media. The use of bottom-sediment-based media reduced the biomass of the test plant and, at the same time, limited the accumulation of trace elements in its aboveground parts.ConclusionMost of the analysed media were low-toxic to the test organisms and can potentially be used in agriculture, horticulture, or the reclamation of degraded land.

Volcanic and sedimentary rocks reveal the Paleozoic tectonic evolution of the Lhasa Terrane, Tibet

ABSTRACT The central Lhasa Terrane preserves the geological record of the opening, subduction, and closure of the Paleo-Tethys Ocean. However, the early tectonic history of the Paleo-Tethys Ocean remains unclear. Here, we present the results of a systematic study of Paleozoic volcanic-sedimentary rocks of the central Lhasa Terrane. The composition of Paleozoic sandstone includes quartz, potassium feldspar, plagioclase, lithic fragments, and a small amount of sericite. Qt-Ft-Lt Dickinson ternary diagrams reveal that the Paleozoic succession includes feldspatho-litho-quartzose sandstone (Gangsangmu and Yongzhu formations), litho-feldspatho-quartzose sandstone (Lower Laigu and Lower Laga formations), litho-quartzo-feldspathic sandstone (Upper Laigu and Upper Laga formations), and quartzo-litho-feldspathic sandstone (Luobadui formation). The Late Ordovician Gangsangmu formation shows passive margin characteristics controlled by sediment recycling. The Early Carboniferous–Late Carboniferous Yongzhu formation is derived from an evolved arc. The Late Carboniferous Lower Laigu and Lower Laga formations were associated with a passive margin controlled by sediment recycling. The Early Permian (Upper Laga, Upper Laigu, and Luobadui formations) represent active continental margin sedimentary rocks. The Early Permian volcanic rocks (287 ~ 274 Ma) belong to the calc-alkaline -potassic /shoshonitic series with high positive εHf(t) values. The Early Permian volcanic rocks have high LREE and LILE (e.g. Rb, Sr), and are depleted in HREE and HFSE (e.g. Nb and Ta, Ti), which indicate a subduction-related arc setting. Our findings, combined with previous studies, show that the northern margin of Gondwana was passive in the Late Ordovician. In the Early Carboniferous, a back-arc basin formed on this northern margin due to the subduction of the Paleo-Tethys Ocean. In the Late Carboniferous, the Sumdo Paleo-Tethys Ocean opened, and the southern edge of the central Lhasa Terrane was a passive margin. In the Early Permian, the Sumdo Paleo-Tethys Ocean began its initial northward subducted and formed the arc volcanic rocks on the central Lhasa Terrane.

‘I hate sand … it gets everywhere’—Phanerozoic sedimentary recycling from NW Africa

AbstractOver 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of north‐west Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across north‐west Africa indicate significant and sustained shifts in source regions in Meso‐Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from north‐west Africa—often described as the ‘Mesoproterozoic Gap’, which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa.

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments

Sediment provenances of a Mesozoic intracontinental basin enclosed by multiple orogenic belts, Junggar Basin, NW China: insights from detrital ilmenite, Cr-spinel geochemistry, and zircon U–Pb geochronology

ABSTRACT The Junggar Basin was an intracontinental basin enclosed by multiple orogenies in the Mesozoic. Unravelling the provenances development in the western Junggar Basin enclosed by the West Junggar Orogenic Belt (WJOB) and Tianshan Orogenic Belt (TSOB) would elucidate the exhumation history of these orogenic belts during the post-orogenic period. The TSOB includes Central Tianshan which includes a continental block with the Precambrian to early Palaeozoic metamorphic basements, while the WJOB includes Palaeozoic accretionary complexes. Given their contrasting geological histories, we use detrital garnets, metamorphic ilmenites, epidotes, and Precambrian zircons to distinguish the TSOB and detrital Cr-spinel to distinguish the WJOB. Combined with sedimentary analysis, palaeocurrents, heavy mineral data, seismic profiles, and zircon U-Pb geochronology, here we reconstruct a four-phase source-to-sink model. During the syn-rift phase, the southern basin was stably fed by the TSOB in the Triassic, evidenced by high Garnet-zircon index and stable single-peak Carboniferous detrital zircon age spectra. During the post-rift sag basin phase, the source-to-sink system experienced a significant change, because detrital zircon age spectra change into multiple peaks. During the transpressional basin phase, the WJOB replaced the TSOB as the dominant provenance in the late Middle Jurassic and the TSOB became the dominant provenance again in the Late Jurassic. Syndepositional volcanic materials provided a large amount of sediments. During the sag basin phase, lake transgression happened and the TSOB provenance could not reach the northern basin. We concluded that the WJOB experienced transpression and obvious denudation in the late Middle Jurassic, and the TSOB uplifted under transpression in the Late Jurassic. The transpression controlled the change of major provenances. The aridification in the Late Jurassic was recorded by the decrease in the Zircon-Tourmaline-Rutile index and the increase in epidotes and magnetites. The humidification in the Early Cretaceous was responded to by lake transgression and sediment recycling.

Diverse manifestations of silicate weathering responses to late Neogene cooling within a tectonically active setting

The relationship between tectonic uplift, climate change and continental silicate weathering has long been debated because deconstructing the tectonic and climatic impacts on continental silicate weathering is challenging. To address this issue, we present long-term climatic and silicate weathering records since 7.3 Ma on tectonically active NE Tibet retrieved from the SG-1 and SG-1b lake sediment drill cores in the western Qaidam Basin. We find distinct correlations between silicate weathering and regional climate on long-term (>106 years) and short-term (105–106 years) time scales. On long-term scales, silicate weathering intensity exhibits a consistent evolution with regional climate, both of which are dominantly controlled by global climate change. This evolution resulted in a stable weathering intensity during 7.3–~3.6 Ma and a weakening of weathering intensity since ~3.6 Ma, followed by a continuous decreasing trend after 2.6 Ma. However, on short-term scales, silicate weathering intensity displays out-of-phase changes with the regional climate at 6.9–3.7 Ma and 0.2–0.1 Ma and in-phase changes at 7.3–6.9 Ma and 3.7–0.2 Ma. We attribute this long-term consistency between the weathering intensity and climate to aridification in inland Asia, but the short-term inconsistencies at 6.9–3.7 Ma and 0.2–0.1 Ma to the change in the sediment routing system impacted by the regional climate within a tectonically active setting. Such a change in the sediment routing system along with sediment recycling may bias weathering indication on orbital time scales, and our study therefore suggests a more complex response of silicate weathering to tectonic and climatic forcings.

Petrographical and Geochemical Study of Syn-Rift Sediments, Pranhita-Godavari Intracratonic Gondwana Basin, India: Genesis and Paleo-Environmental Implications

The approximately 2 km thick fluvio-lacustrine deposits of Pranhita-Godavari Gondwana syn-rift basin, ranging in age from 235 to 196 Ma, track the compositional changes from the Middle Triassic to Early Jurassic. Mineralogical and geochemical investigations, as well as paleocurrent data of the siliciclastic deposits of the four conformable formations—Yerrapalli, Bhimaram, Maleri and Dharmaram—trace the source of sediments to the south and southwest of the Gondwana basin. The dominance of arkosic to sub-arkosic sandstones in all the formations suggests mostly felsic sources. The high value of Zr/Sc, as well a high content of Hf, reflects the addition of zircon by sediment recycling. The index of compositional variability (ICV) and chemical index of alteration (CIA) values of these Gondwana samples suggest intermediate weathering of Proterozoic shales, granites and gneisses. The concentration of Cr and Ni, ratios of Eu/Eu* and (GdN/YbN) suggest a dominant post-Archean source. The insignificant variation in ICV and CIA values across the studied Mesozoic formations corroborates the continuation of syn-rift tectonics of the Pranhita-Godavari Gondwana basin since the Late Paleozoic. Sandstone samples show a gradual shift from arkose to subarkose in Yerrapalli, Barakar and Maleri formations, and to sublithic arenite sandstones in the younger Dharmaram formation, indicating recycling. However, the insignificant variation of feldspar and/or quartz content throughout these Mesozoic formations suggests lesser tectonic activity. The paleocurrent direction, shifting from NNW to NE direction, suggests a change in basin tectonism and/or sediment supply, which is corroborated by mineralogical and geochemical data.

Sedimentary geochemistry of Late Cretaceous-Paleocene deposits at the southwestern margin of the Anambra Basin (Nigeria): Implications for paleoenvironmental reconstructions

The Campano-Maastrichtian deposits of the Nkporo and Mamu formations of the Anambra Basin represent prospective hydrocarbon resources in southern Nigeria. In order to reveal the paleoclimate, sediment recycling and paleoenvironment during the deposition of these formations in the southwestern portion of the Anambra Basin, a detailed geochemical analysis was performed using major elements, trace elements and rare earth element data, as well as the mineralogical characterization of 20 samples from two wells. The combination of geochemical ratios (Rb/Sr, Th/U, and C-value) and weathering indices (CIA, CIW, and PIA) demonstrates that the region experienced a warm, humid tropical paleoclimate throughout the Late Cretaceous. Furthermore, West Africa experienced strong precipitation during the Cretaceous, leading to intense chemical weathering in the region, as documented by the geochemically matured sediments.The paleosalinity (Sr/Ba) and paleoproductivity (Ba/Al and P/Ti) proxies show that the studied mudrocks were deposited primarily in brackish to shallow-marine settings, with poor primary productivity due to terrestrial clastic influx and hydrodynamic influence. Using multiple paleoredox indicators, deposition under oxic conditions is detected. The low authigenic U enrichment and depleted V and Cr values normalized to UCC standards further support oxic bottom water conditions. Wavy laminations observed in the mudrocks indicate retreating seawater and high hydrodynamic conditions. Ultimately, the southwestern Anambra Basin reveals Late Cretaceous-Paleocene deposits of a shallow sea controlled by a strong hydrodynamic regime.

Barium stable isotopic composition of chondrites and its implication for the Earth

Barium is a refractory and fluid mobile element that is highly incompatible in basaltic systems. The elemental and isotopic compositions of Ba are used to trace fluid processes or sediment recycling during subduction. However, the Ba isotopic composition of primitive meteorites (chondrites), which represents the possible building blocks of terrestrial planets, is presently poorly known. Here, we report high precision Ba isotopic compositions of major types of chondrites using a double-spike method. Chondritic meteorites without clear terrestrial weathering show relatively homogeneous Ba isotopic distributions and have an average δ137/134Ba (the permil deviation of the 137Ba/134Ba ratio from the SRM3104a standard) value of 0.09 ± 0.09‰ (2SD, N = 14). Given the refractory and lithophile behavior of Ba and the limited variations of Ba isotope composition between various chondrite groups, this value can represent the Ba isotopic composition of the bulk Earth and the Bulk Silicate Earth (BSE). It is actually consistent with the present estimate of BSE (0.05 ± 0.06‰, Li et al., 2020; Nan et al., 2022) based on the measurements of mid-ocean ridge basalts and carbonatites. Small Ba isotope variations are observed between carbonaceous chondrite groups where CO and CV show slightly heavier (by 0.09‰) Ba isotopic compositions than CI and CM. Significant light stable Ba isotopes enrichment has previously been documented in calcium, aluminum-rich inclusions (CAIs) in the Allende CV chondrite, and the Ba isotopic differences between CO and CV might result from the various proportions of CAIs based on a mass balance calculation. However, the parent body of CI and CM might have experienced aqueous alteration and secondary carbonates are most likely responsible for their light Ba isotopic signatures.

Decoupled Trace Element and Isotope Compositions Recorded in Orthopyroxene and Clinopyroxene in Composite Pyroxenite Veins from the Xiugugabu Ophiolite (SW Tibet)

Abstract Pyroxenite veins and dikes are commonly observed in the mantle section of ophiolites. Because of their mantle occurrence, these pyroxenites are free from crustal contamination and offer a unique opportunity for studying mantle compositions and melt–rock interaction processes. We conducted an integrated petrological and geochemical study of a suite of composite orthopyroxenite, websterite, and pyroxene-bearing dunite veins from the Xiugugabu ophiolite located on the western segment of Yarlung–Zangbo Suture Zone. The dunite is separated from the host peridotite by a layer of pyroxenite, forming a composite vein system. Systematic variations in major, minor, and trace element compositions in minerals across the composite veins are observed. Two generations of orthopyroxenes in the pyroxenites are characterized by high Mg#, low TiO2 concentrations, and depleted patterns of incompatible trace elements. Clinopyroxenes in the pyroxenites are characterized by high Mg#, low contents of TiO2 and Na2O, spooned shaped REE patterns, and a negative Zr anomaly. Through major and trace element modeling, we showed that both orthopyroxene and clinopyroxene were in equilibrium with melts with different compositions. This hypothesis is further confirmed by distinct initial Nd and Hf isotope ratios in the two pyroxenes. A model for the formation of composite pyroxenite veins is developed, whereby hydrous and silica-rich melts percolate along the margins of a dunite channel. The orthopyroxenite was formed by the reaction between a hydrous, silica-rich melt and the surrounding peridotite. The websterite is formed by reactive crystallization of a hybrid melt produced by mixing silica-rich melt and the melt formed by remelting of previously depleted peridotite in the deeper part of the mantle column. The extremely enriched Nd–Hf isotope compositions of the pyroxenite veins (εNd = −20.3 to +11.5 and εHf = −13.2 to +25.3, 125 million years ago) can be explained by the addition of ancient, recycled sediments to the mantle source in a supra-subduction setting. Based on the low-Cr# spinel in the Xiugugabu dunites (Cr# = 19–50) and the depleted nature of the parental melt of the Xiugugabu pyroxenites, we deduced that the formation of pyroxenites postdate the formation of the Xiugugabu ophiolite at ~125–130 Ma. Collectively, results from this study have provided support to the hypothesis that the Xiugugabu ophiolite experience a two-stage evolution, i.e., firstly formed in a mid-ocean ridge setting and subsequently modified in a supra subduction zone.

Sedimentologic and Petrographic Study of Outcrops of Ajali Sandstone in Okigwe, Uturu and Isiukwuato, Anambra Basin Southeastern Nigeria

The Ajali Formation outcrops at Okigwe, Ihube, Onyekaba mine, Uturu and Isiukwuato in the Anambra Basin southeastern Nigeria were evaluated for an integrated field, sedimentologic and petrograpic methods. The study was aimed at presenting a better understanding of the depositional processes and provenance. Five lithofacies were altogether described namely: planar Cross bedded sandstone facies A, Massive sandstone facies B, Ferruginized sandstone facies C, herringbone cross bedded sandstone facies D, and Bioturbated sandstone facies E. The facies were deposited in a fluvially influenced shallow marine environment. The overall grain size interpretation shows that sediments from the study area are fine to coarse grained with values ranging from 0.2 to 2.0Φ, poorly sorted to very well sorted with range value of 0.28 to 1.2Φ, nearly symmetrical to strongly fine skewed with values of -0.04 to 0.59Φ and platykurtic to very leptokurtic with values of 0.79 to 2.46Φ. An inspection of the cumulative frequency curves of the studied samples shows that the sediment population is dominated by saltation population. Texturally, the sandstone sediments are sub-mature containing grains that are moderately to poorly sorted and not well rounded. The Mineral Maturity Index of the sandstone in the study area ranges from 24-49 which falls within the mature to super mature class. The high quartz content and insignificant amount of feldspar and rock fragments further support this assertion. The study suggest the sandstones must have been subjected to substantial high degree of reworking that resulted in the removal of the ferromagnesian minerals and feldspar typical of recycled sediments.

Detrital zircon in an active sedimentary recycling system: Challenging the ‘source‐to‐sink’ approach to zircon‐based provenance analysis

ABSTRACTThe age and properties of detrital zircon in a sediment reflect properties of the rocks in which the zircon crystallized, and not necessarily the immediate precursor of the host sediment. Where clastic sediments are recycled, these properties are preserved so that U‐Pb ages and Lu‐Hf data on zircon grains will no longer give information on the routing of detritus. Because the crustal evolution and sedimentary recycling history of Southern Africa is well‐established, Holocene sediments in the region provide a good test example for detrital zircon geochronology applied to sands or sandstones with a complex recycling history. Data from 16 samples of unconsolidated sand, including dunes from the southern part of the Kalahari Basin, beach sands at the Atlantic coast, and isolated inland dune occurrences, yield ranges of early Mesozoic to late Archaean ages. Uranium–lead and lutetium–hafnium isotope data provide no evidence of direct derivation of zircon from protosources in crystalline bedrock. The complex distribution patterns can be decomposed into seven ‘provenance components’ that have previously been encountered in Palaeoproterozoic to Jurassic sedimentary rocks in the region. These components occur in non‐random combinations, in proportions that suggest mixing of recycled material from different sedimentary precursors. Taking pre‐Cenozoic geology, Cretaceous to Pleistocene drainage history of southern Africa and Holocene wind and current patterns into account, it is possible to work out a consistent model for transport of detritus from sedimentary precursors into the basin, followed by aeolian remobilization within the basin itself. The detrital zircon distributions can thus be interpreted from prior knowledge of the basin filling history, regional geology, geomorphology, drainage evolution and wind pattern. This amounts to a line of reasoning from ‘sink back to (intermediate) ‘source’, which is the opposite of the ‘(proto)source‐to‐sink’ paradigm commonly invoked in detrital zircon studies.

Combined U-Pb ages and Lu-Hf systematics of detrital zircons from Early Cambrian Gondwanan siliciclastic rocks in S Turkey: Provenance and correlations with coeval successions in peri-Gondwanan terranes

Detrital U-Pb age peaks and εHf(t) and TDM(Hf) of peri-Gondwanan units of S Turkey indicate that they may have been derived from Neoproterozoic igneous suites in the Sinai Peninsula (Egypt), Israel (Elat) and Eastern Desert (Egypt) part of the Nubian Shield. Early Cambrian siliciclastics in the peri-Gondwanan units of S Turkey consist of quartzites in the Menderes Massif of the Tauride-Anatolide Platform (TAP), meta-quartz arenites in the different Alpine tectonic slivers of the TAP-margin and quartz-arenites in the Southeast Anatolian Autochthon Belt (SAAB). Geochemical data indicate that these sediments are likely to be derived from sedimentary recycling processes in oxic depositional basins within a continental back-arc tectonic setting. They were opened after the formation of the Avalonian-Cadomian magmatic arc. In the TAP, the youngest detrital zircon 238U/206Pb ages are range from 530.6 + 6.3/-12.0 Ma to 549.4 ± 10 Ma and from 551.9 + 7.9/-8.4 Ma to 545.8 ± 11 Ma in the SAAB verifying the Early Cambrian maximum depositional ages for the sampled siliciclastic successions. In the TAP, meta-quartz arenites, Neoproterozoic detrital zircons make up about 75% of the total grains, whereas they constitute about 88 % in the SAAB sedimentary rocks. Tonian zircons in the TAP (>40 %) and SAAB (<32 %) reveal key populations to determine their provenance and the paleotectonic positions of the respective terranes. The combination of U-Pb age and Lu-Hf systematics in the detrital zircons of the TAP and SAAB show that age groups at 535 to 562 Ma and 888 to 3370 Ma are mainly represented by the zircons derived from evolved sources with a limited juvenile component. The predominant zircon age groups between 577 and 854 Ma in the TAP and SAAB, on the other hand, were derived from juvenile to evolved sources. Non-parametric Kolmogorov-Smirnov tests suggest that Early Cambrian successions in the TAP (except Kocaosman-Isparta) may have been located in similar paleogeographic locations with coeval successions in the SAAB during the Early Cambrian. U-Pb geochronology and Lu-Hf systematics of the Early Cambrian successions in the TAP and SAAB indicate that the dominant detrital zircon age groups were mainly sourced and transported to continental back-arc fluvial to shallow marine sedimentary environments from igneous rocks of the Nubian Shield and the Saharan Metacraton by a combination of the glaciers, eolian events and multiple-stage erosional and sedimentary recycling processes during the Early Cambrian (ca 520 Ma). The provenance of the Early Cambrian successions in the TAP and SAAB correlate with the provenance areas of the coeval siliciclastic sequences in Israel and Jordan (Arabian Shield), Iraq and Iran and the peri-Gondwanan Carpathians, rather than the Early Cambrian successions in the central and southern European peri-Gondwanan terranes.