Changes in the grain size distribution of river sediment have environmental, ecological and social implications. This study investigated the variation of the grain size of bulk samples, detrital zircons and rutiles from the mainstream and major tributaries of the Yangtze River. The mean size of bulk samples from the upper reaches is significantly higher than the mid-lower reaches. The Equivalent Spherical Diameter (ESD) of most zircons (from previous work) and rutile grains fall within the range of 32-250 μm with dominant size of 63-125 μm. Coarse-sized zircons and rutiles with ESD of 125-250 μm are found in higher proportions in the upper reaches than in the mid-lower reaches, and a significant grain size decrease is observed downstream of the Three Gorges Dam. The significantly decreasing in coarse grains downstream of the dam indicates that the massive sediment contributed by the Three Gorges Dam (TGD), especially coarse-sized sediment. Our study demonstrates that a complex sediment routing system like the Yangtze River is interrupted by the Three Gorges Dam. The problem of grain-size bias caused by human activities on age-data acquisition and interpretation of detrital minerals (rutile and zircon) from large rivers is not negligible and deserves more attention when using single grain geochronology to constrain sediment provenance and tectonic evolution.

We present Ar-40/Ar-39 ages of dacite domes and rare volcanic sanidine megacrysts from Ta & aacute;paca volcano (northern Chile) that record 1.3 m.y. of activity. Our focus is on 20 megacrysts from a single 32.9 ka eruption. We interpret that their surprisingly correlated Ba-rich and Ba-poor growth zones separated by resorption surfaces reflect frequent heat pulses with a uniform thermal history over >300 k.y. of growth. We infer extended storage in small (<400 m), shallow "hot" domains within a larger magma system. Our findings bear on the origin of K-feldspar megacrysts in plutonic rocks, thus linking volcanic and plutonic processes in shallow silicic magma systems, and support protracted residence of hot magma in small batches at upper-crustal levels to produce megacryst-bearing granitoid intrusive complexes.

Genesis and emplacement of Vredefort Granophyre, the impact melt rock exposed on the Vredefort Dome, the erosional remnant of the central uplift of the Vredefort impact structure, South Africa, have long been debated. This debate was recently reinvigorated by the discovery that besides the previously known felsic variety of >66 wt% SiO2, a second, somewhat more mafic phase of <66 wt% SiO2 occurs along a Granophyre dike on farms Kopjeskraal and Eldorado in the northwest sector of the dome. Two hypotheses have been put forward to explain the genesis and emplacement of this second phase: (1) successive injections of impact melt into extensional fractures opened in the course of central uplift formation/crater modification, with melts of distinct compositions derived from a differentiating impact melt body in the crater, and (2) generation of the more mafic phase as a product of admixture/assimilation of a mafic country rock component, either the so‐called epidiorite of possible Ventersdorp Supergroup affiliation or the Dominion Group meta‐lava (DGL), to Felsic Granophyre. In the latter model, contamination with mafic country rock would have occurred during downward intrusion and stoping into and below the crater floor. The so‐called Mafic Granophyre has previously only ever been sampled on a single site (Farm Kopjeskraal). In this study, samples of Granophyre occurring along the southerly extension of this dike on farm Rensburgdrif, and from a second dike on the Rietkuil property further southwest were investigated by field work, and petrographic, geochemical, and isotopic analysis. The mafic phase indeed occurs in the interior of the dike at Rensburgdrif, and also on Rietkuil. New geochemical and Sr‐Nd isotope data support the hypothesis that the Mafic Granophyre composition represents a mixture between Felsic Granophyre and a mafic country rock. A 20% admixture of epidiorite or DGL to Felsic Granophyre provides an excellent match for the chemical composition of the Mafic Granophyre. The Sr‐Nd isotope data indicate that this admixture likely involved the epidiorite component rather than DGL. Together with earlier Sr‐Nd‐Os‐Se isotopic data, and other geochemical data, these results further support formation of the Mafic Granophyre by local assimilation/admixture of epidiorite to Felsic Granophyre.

Microplastic particles are ubiquitous in our environment, having entered the air, the water, the soil, and ultimately our food chain. Owing to their small size, these particles can potentially enter the bloodstream and accumulate in the organs. To detect microplastics using existing methods, they must first be isolated. The aim of this study was to develop a non-destructive method for efficiently and affordably isolating plastic particles. We investigated the digestion of kidney, lung, liver, and brain samples from pigs. Kidney samples were analyzed using light microscopy after incubation with proteinase K, pepsin/pancreatin, and 10% potassium hydroxide (KOH) solution. Various KOH:tissue ratios were employed for the digestion of lung, liver, and brain samples. Additionally, we examined the effect of 10% KOH solution on added polystyrene microplastics using scanning electron microscopy. Our findings revealed that a 10% KOH solution is the most suitable for dissolving diverse organ samples, while enzymatic methods require further refinement. Moreover, we demonstrated that commonly used 1 µm polystyrene particles remain unaffected by 10% KOH solution even after 76 h of incubation. Digestion by KOH offers a simple and cost-effective approach for processing organ samples and holds potential for isolating plastic particles from meat products.

The presence of tektite-like glasses from a geographically restricted area in Belize (Central America) has been known for several decades. We comprehensively studied 18 such Belize glasses by a variety of petrographic and geochemical methods, including major and trace element analysis, radiogenic isotopic composition (Rb-Sr, Sm-Nd, and Re-Os), water content, oxidation state, and cosmogenic radionuclides. The aims were to determine their compositional variation, their mode of formation and possible source rocks, and their relation to known tektites, and to search for evidence of an extraterrestrial component.In terms of petrography, the samples are similar to tektites from the four “classical” strewn fields, with the presence of lechatelierites, schlieren, and vesicles; these are also widely accepted indicators of an impact origin. No close similarities to volcanic glasses are evident. Water contents are very low, and iron oxidation states are mostly reduced, in both cases similar to observations for other tektites. The geochemical and isotopic data presented, such as Cr, Co and Ni elemental abundances and interelement ratios, as well as trace element patterns are typical for local and regional volcanics from the active Central American Arc. Particular similarities to material comparable to volcanic rocks from Honduras or Guatemala are noted. This is confirmed by Sr-Nd isotope signatures of the Belize glasses, showing close similarities to Central American volcanics in general, and Honduran and Guatemalan volcanic, in particular. Osmium concentrations and 187Os/188Os ratios are comparable to arc volcanics from world-wide locations, but - in a few of the samples - elevated Ir concentrations, near-chondritic Pt/Ir and 187Os/188Os ratios can also be interpreted with the admixture of a minor meteoritic component to some of the Belize samples. 10Be concentrations are consistent with values typical of both, young or deeply buried soils and with values for Central American volcanics, which carry subducted 10Be.Geochemical data clearly indicate a source different from that of the Australasian tektites. Both isotope data sets for the Belize glasses indicate a close relationship to local arc lavas, especially those from Guatemala and Honduras, suggesting that the glasses were not deposited very far from their source. The main evidence that the Belize glasses are of impact origin are their petrographic characteristics and low water content. The evidence from 10Be is consistent with, but does not require, a model of formation for the Belize glasses by an impact on loosely consolidated surface sediments exposed to rain. A probable meteoritic component is low and heterogeneously distributed.

Lunar meteorite Northwest Africa (NWA) 11962 is a regolith breccia with a diverse range of mineral and lithic clasts. For the present study, major and trace element contents and selected isotopic compositions were determined on a homogenized bulk powder of NWA 11962 by instrumental neutron activation analysis, thermal ionization mass spectrometry, and inductively coupled plasma mass spectrometry. The chemical composition of the sample points toward an origin of the meteorite from within the Procellarum KREEP terrane (PKT). Samarium-Nd and Rb-Sr isotopic compositions and concentrations show a similarity to those of Apollo 15 soils and KREEP basalt. Highly siderophile element (HSE) abundances and ratios, as well as the Re/Os isotopic system, are often used as tracers of different impactor types. The Os-187/Os-188 and Re-187/Os-188 isotopic ratios are within the range of ordinary chondrites, yet some of the siderophile element and highly siderophile element ratios are comparable to those of iron meteorites. Using Fe, Th, and Ti abundances of lunar surface regolith, measured by the Lunar Prospector gamma-ray spectrometer, we attempt to constrain potential lunar source regions for NWA 11962. By matching these possible source regions with coordinates of recently (<1 Ma) formed lunar impact craters (so-called lunar cold spots), we localized a potential source crater of NWA 11962 at the western rim of the PKT close to Sinus Medii.

The base of the Silvretta Nappe (Austroalpine Unit, Eastern Alps) has localized extensive deformation, including the occurrence of multiple generations of pseudotachylytes, alternating with (ultra)mylonites, in the host amphibolite and gneiss. Previous works attributed the formation of pseudotachylytes and associated ultra-mylonites to the Eoalpine deformation phase (mid. Cretaceous). In this work, we report the presence of a younger generation of pseudotachylytes, which overprints the previously characterized pseudotachylyte-ultramylonite association. A detailed petrographic study of selected samples from the Jamtal, Tyrol (Austria), provides further constraints on the possible tectonic evolution of the Silvretta Nappe. Contrary to the Eoalpine pseudotachylytes, the younger pseudotachylytes are not completely recrystallized, foliated, and epidotized, but rather preserve the typical features of frictional melts (e.g., micmlites, glassy gmundmass, evidence of melt immiscibility, etc.). This suggests formation in relatively shallow conditions, rather than under greenschist facies, as assumed for the Eoalpine pseudotachylytes. The "young" pseudotachylytes, commonly discordant to the foliation, thus likely formed during the final subduction of the Penninic Unit in the Paleogene. This occurrence lends further support to the localization of deformation at the base of the upper plate, in this case represented by the Silvretta Nappe, as observed in other portions of the Alps.

Additional information on methods, Figures S1–S3, and Tables S1–S4.

RationaleComplete decomposition of silicate rock matrices is crucial in determining their isotopic compositions, but acid dissolution in a high‐pressure steel‐jacketed bomb, which has been the only powerful, effective technique thus far, is time‐consuming and expensive. Rock dissolution using ammonium bifluoride (ABF), as described here, is a viable alternative.MethodsGeological reference materials (GRMs) were digested using ABF in closed Teflon beakers at temperatures of 220/230°C in a convection oven and subsequently treated with HNO3. Hf‐Sr‐Nd were separated and purified using ion‐exchange chemistry columns calibrated for 50–2 mg samples. The isotopic compositions of Sr‐Nd were measured by Thermal Ionization Mass Spectrometry, while that of Hf by Multi‐Collector Inductively Coupled Plasma Mass Spectrometry, both with normal 1011 Ω and gain calibrated 1013 Ω amplifiers.ResultsTotal procedural blanks of our protocol are 0.5 ng for Sr, 0.2 ng for Nd and <25 pg for Hf. Test runs with GRMs, ranging in composition from basic to felsic and dissolved in ABF, yield accurate 87Sr/86Sr, 143Nd/144Nd and 176Hf/177Hf isotope ratios as compared with those obtained with the bomb dissolution technique. Reproducibilities were comparable, on the order of 10–20 ppm. Our technique allows combined Hf‐Sr‐Nd isotope analyses of low‐mass (50–2 mg) samples.ConclusionsThe ABF digestion is an alternative technique to high‐pressure bomb dissolution in matrix decomposition for accurate and reproducible Hf‐Nd‐Sr isotope analyses of geological samples within a reasonable time (3–4 days), with high sample throughput and low costs in geochemistry and environmental sciences.

Elephanta Island near Mumbai is an important area for understanding the stratigraphic and structural framework of the Deccan flood basalt province in the tectonically disturbed Panvel flexure zone on the western Indian rifted margin. Elephanta exposes a west-dipping, 66–65 Ma sequence of tholeiitic lava flows and dykes. Geochemical correlations with the thick, horizontal, 66–65 Ma Western Ghats sequence to the east show that lava flows of the Khandala and Ambenali formations are present at Elephanta, with two lava flows probably being locally derived. The Elephanta tholeiites have experienced crystal fractionation and accumulation, particularly of olivine. They have εNd(t) ranging from +5.4 to −7.9 and (87Sr/86Sr)t from 0.70391 to 0.70784, with most tholeiites little contaminated by continental lithosphere, probably lower crust. Field and geochemical data indicate a normal fault along the central part of Elephanta with a 220 m downthrow, consistent with a domino-type block-faulted structure of Elephanta, and the surrounding area as previously known. Seventeen of the 20 analyzed Elephanta intrusions, striking ~N–S, belong to the Coastal dyke swarm of the western Deccan province. Several of these are probable feeders to the Ambenali Formation in the Western Ghats sequence, requiring reconsideration of the current view that the voluminous Wai Subgroup lavas of the Western Ghats were erupted without organized crustal extension. East–west-directed extensional strain was already active at 66–65 Ma along this future (62.5 Ma) rifted continental margin. A young (~62 Ma) ankaramite dyke on Elephanta Island is a probable feeder to the Powai ankaramite flow in the 62.5 Ma Mumbai sequence 20 km to the northwest.

The Banded Gneissic Complex of the Aravalli Craton of northwestern India comprises Palaeo‐ to Neoarchaean (3.3–2.7 Ga) gneisses, including tonalite–trondhjemite–granodiorite (TTG) gneisses, intruded by Neoarchaean (2.6–2.5 Ga) TTGs, sanukitoids, and potassic granites. The latter include the Malola granite that crops out near Bhilwara and forms the basement for the Mesoproterozoic Pur‐Banera mineralized belt. The granite has experienced three deformation events, represented by an S 1 foliation and superimposed open folds and dextral shears. Textural evidence and thermobarometry indicate that prograde metamorphism initially forming actinolite and subsequently diopside, and culminating in the upper amphibolite facies, was followed by retrograde metamorphism in the greenschist facies with fluid influx, forming zoisite. Zircon geochronology yields a crystallization age of 2,538 ± 11 Ma and indicates a prominent metamorphic overprint in the region at 1,307 ± 9 Ma. The Malola granite has low Sr–Nd isotopic ratios, enrichments in fluid‐mobile elements (Cs, Rb, Ba, Th, and Pb), and depletions in alteration‐resistant elements (Nb, Ta, and Ti). These characteristics combined with mineralogical evidence suggest that the granite was derived by anatexis of older crystalline crust (possibly granulitic lower crust) in the same subduction zone setting inferred previously for other Neoarchean granitoids in this region. Geochemical and Sr–Nd–Hf isotopic similarities between the Malola granite and Neoarchaean granitoids of the Aravalli, Bundelkhand, Bastar, Dharwar, and Congo cratons indicate a major role for anatectic crustal reworking in their genesis.

The Deccan Traps continental flood basalt (CFB) province of India contains several dyke swarms, which are dominated by tholeiitic basalts and basaltic andesites. The Southeastern Saurashtra dyke swarm, containing mainly these rock types, also contains an andesite and several rhyolites. Based on petrographic, mineral chemical, and whole-rock major and trace element and Sr-Nd isotopic data, we discuss the magmatic evolution and pressure-temperature conditions of crystallisation of these dyke magmas. The tholeiitic basalts and basaltic andesites have low to moderate TiO2 contents. The andesite and the rhyolites have low CaO, MgO, Fe(2)O(3)t, TiO2 and P2O5, and high K2O, Rb, Ba and light rare earth element contents. Thermobarometric calculations for equilibrium mineral-whole-rock pairs indicate plagioclase crystallisation at 1200-1170 degrees C, overlapping with clinopyroxene crystallisation at 1181-1143 degrees C, and a pressure range of 0.1-3.6 kbar indicating crystallisation during magma ascent or storage at shallow crustal levels. Major and trace element modelling is consistent with the rhyolites being produced by advanced fractional crystallisation of basaltic parental magmas. However, a broad trend of increasingly radiogenic Sr and nonradiogenic Nd isotopic ratios, fromthemafic rocks through the andesite to the rhyolites, suggests a combined assimilation and fractional crystallisation (AFC) process between basaltic magma and ancient granitic crust. The rhyolites contain the largest crustal contributions and display the most "enriched" Sr-Nd isotopic characteristics yet recorded from the Deccan Traps (epsilon(Nd)t =-20.6, (Sr-87/Sr-86)(t) = 0.74855). The widespread occurrence of mafic enclaves in the rhyolite dykes suggests that processes such as magma mixing may also be responsible for some of the andesitic rocks known in Saurashtra. (C) 2020 Elsevier B.V. All rights reserved.

Mineral dust in ice cores provides insight into past atmospheric circulation patterns provided that the source(s) of these aerosols can be identified. Isotopes of strontium, neodymium and lead are frequently used for source discrimination in ice cores, while those of hafnium much less so. This is because of the extremely low (1-5 ng) amounts of Hf present in 5-10 mg dust samples usually available for isotopic analyses from the dustiest periods of past glaciations, e.g. the Last Glacial Maximum. The use of 176Hf/177Hf isotopic ratios in dust fingerprinting is crucial in situations when Sr-Nd isotopes are inconclusive in source identification. The overall Hf budget is dominated by the heavy mineral zircon in silt-sized, wind-blown material, while it is significantly depleted in the finer (<5 µm) fractions and the effects of other minerals (apatite, sphene, monazite, xenotime and clay minerals) become increasingly important. Since the major hosts of Hf are refractory heavy minerals, the complete digestion of dust material is crucial in determining reliable Hf isotope ratios. Here we introduce a closed vessel ammonium bifluoride (NH4HF2) digestion method (220 °C), which is a fast and low blank (0.5 ng for Sr, 0.2 ng for Nd, and <25 pg for Hf) technique for dust dissolution, prior to column chemistry for combined Hf-Sr-Nd isotope analyses. Repeated measurements of the Hf isotope ratios of USGS geological reference materials (AGV-2, BCR-2 and GSP-2) demonstrate that raw, non fractionation corrected 176Hf/177Hf ratios are accurate within 5-50 ppm, while the JMC-475 fractionation corrected values are accurate to 5-10 ppm, compared to reference values using our ion exchange chemistry setup. This methodology also allows separating Sr and Nd from the same samples, and analysing the 87Sr/86Sr and 143Nd/144Nd isotopic compositions. Here we discuss mass spectrometry issues (including sensitivity) of TIMS and two different MC-ICP-MS instruments, and major limitations on dust sample size for Hf-Sr-Nd isotope analyses. Furthermore, the mineralogical background of Hf isotopic compositions, including zircon depletion effects and clay mineralogy (illite) control will be demonstrated. Hf isotope data obtained from four NorthGRIP ice core samples will be presented. This study was financially supported by the FWF Austria through a Lise Meitner grant (project nr. M 2503-N29) and the European Regional Development Fund in the project of GINOP-2.3.2.-15-2016-00009 ‘ICER’.

The geochemical conditions conducive to dolomite formation in shallow evaporitic environments along the Triassic Tethyan margin are still poorly understood. Large parts of the Triassic dolomites in the Austroalpine and the southern Alpine realm are affected by late diagenetic or hydrothermal overprinting, but recent studies from the Carnian Travenanzes Formation (southern Alps) provide evidence of primary dolomite. Here a petrographic and geochemical study of dolomites intercalated in a 100 m thick Carnian sequence of distal alluvial plain deposits is presented to gain better insight into the conditions and processes of dolomite formation. The dolomites occur as 10 to 50 cm thick homogeneous beds, millimetre-scale laminated beds, and nodules associated with palaeosols. The dolomite is nearly stoichiometric with slightly attenuated ordering reflections. Sedimentary structures indicate that the initial primary dolomite or precursor phase consisted largely of unlithified mud. Strontium isotope ratios (87Sr∕86Sr) of homogeneous and laminated dolomites reflect Triassic seawater composition, suggesting precipitation in evaporating seawater in a coastal ephemeral lake or sabkha system. However, the setting differed from modern sabkha or coastal ephemeral lake systems by being exposed to seasonally wet conditions with significant siliciclastic input and the inhibition of significant lateral groundwater flow by impermeable clay deposits. Thus, the ancient Tethyan margin was different from modern analogues of primary dolomite formation.

ABSTRACT The complete and well-studied pelagic carbonate successions from the Umbria-Marche basin (Italy) permit the study of the event-rich stratigraphic interval around the Cretaceous-Paleogene boundary (e.g., Deccan volcanism, boundary impact, Paleocene recovery, and climate). To test the robustness of various proxy records (bulk carbonate δ13C, δ18O, 87Sr/86Sr, and Ca, Fe, Sr, and Mn concentrations) inside the Umbria-Marche basin, several stratigraphically equivalent sections were investigated (Bottaccione Gorge, Contessa Highway, Fornaci East quarry, Frontale, Morello, and Petriccio core). Besides the classical Gubbio sections of Bottaccione and Contessa, the new Morello section is put forward as an alternative location for this stratigraphic interval because it is less altered by burial diagenesis. Elemental profiles (Ca, Fe, Sr, Mn) acquired by handheld X-ray fluorescence (pXRF) efficiently provide regional chemostratigraphic and paleoenvironmental information. The Deccan volcanism, the Cretaceous-Paleogene boundary, the characteristic pattern of the Sr/Ca profile across the boundary driven by the extinction and recovery of coccolithophores, and the Dan-C2 hyperthermal event are examples of such recorded paleoenvironmental events. Moreover, cyclostratigraphic analyses of proxies of detrital input (magnetic susceptibility and Fe concentrations) show the imprint in the sedimentary record of a 2.4 m.y. eccentricity minimum around 66.45–66.25 Ma, and suggest that the occurrence of the Dan-C2 hyperthermal event was astronomically paced.

Combined Sr‐Nd‐Hf isotopic data of two reference materials (AGV‐1/BCR2) and 50, 10, and 5 mg aliquots of carbonate‐free fine grain (<10 μm) separates of three loess samples (Central Europe/NUS, China/BEI, USA/JUD) are presented. Good agreement between measured and reference Sr‐Nd‐Hf isotopic compositions (ICs) demonstrate that robust isotopic ratios can be obtained from 5 to 10 mg size rock samples using the ion exchange/mass spectrometry techniques applied. While 87 Sr/ 86 Sr ratios of dust aluminosilicate fractions are affected by even small changes in pretreatments, Nd isotopic ratios are found to be insensitive to acid leaching, grain‐size or weathering effects. However, the Nd isotopic tracer is sometimes inconclusive in dust source fingerprinting (BEI and NUS both close to ɛNd(0) –10). Hafnium isotopic values (<10 μm fractions) are homogenous for NUS, while highly variable for BEI. This heterogeneity and vertical arrays of Hf isotopic data suggest zircon depletion effects toward the clay fractions (<2 μm). Monte Carlo simulations demonstrate that the Hf IC of the dust <10 μm fraction is influenced by both the abundance of zircons present and maturity of crustal rocks supplying this heavy mineral, while the <2 μm fraction is almost unaffected. Thus, ɛHf(0) variations in the clay fraction are largely controlled by the Hf IC of clays/heavy minerals having high Lu/Hf and radiogenic 176 Hf/ 177 Hf IC. Future work should be focused on Hf IC of both the <10 and <2 μm fractions of dust from potential source areas to gain more insight into the origin of last glacial dust in Greenland ice cores.