Kooperativer Bibliotheksverbund

Language: English

In: Chemical Geology

Description: We conduct X-ray microprobe, chemical and U-series isotope analyses on an oriented weathering clast collected from the regolith of a weathered Quaternary volcanoclastic debris flow on Basse Terre Island, French Guadeloupe. The sample consists of an unweathered basaltic andesite core surrounded by a weathering rind, and an indurated crust that separates the rind from the overlying soil matrix. U/Th disequilibria dating indicates that rind age increases away from the core-rind boundary to a maximum of 66 ka. This translates to a rind-advance rate of ~0.2 mm kyr , broadly consistent with rind advance rates calculated elsewhere on Basse Terre Island. The overlying indurated crust is 72 ka, indicating a possible minimum duration of the rind formation. Elemental variations are constrained by a bulk chemical analysis along a vertical transects from the core to the overlying soil matrix and parallel electron microprobe analyses. The hierarchy of elemental loss across the core-rind boundary varies in the order Ca 〉 Na ≈ Mg 〉 K 〉 Mn 〉 Si 〉 Al 〉 Ti = 0 〉 P 〉 Fe, consistent with the relative loss of phases in the clast from plagioclase ≈ glass ≈ pyroxene 〉 apatite 〉 ilmenite. The abrupt, 〈900 μm wide, Ca, Na and porosity reaction fronts at the core-rind boundary approximately equal the length of the long dimension of plagioclase phenocrysts observed in the unweathered core. The 〈1000 μm wide reaction front at the rind-soil interface is marked by an indurated horizon with Fe and Mn enrichment that spans into enrichment of Mn, Ba, Al, Mg and K in the soil matrix. Unlike previously studied clasts, the preservation of the rind-soil interface permits characterization of weathering reactions and material exchanges between the weathering core, the rind, and the surrounding soil matrix, shedding insights into communication between the enveloping weathering rind and host regolith. The lack of an enrichment signal of Mn within the weathered rind suggests that weathering processes active within clasts are distinct from surrounding soil formation processes.

Keywords: Chemical Weathering ; Critical Zone ; Weathering Rinds ; Redox ; French Guadeloupe ; Geology

ISSN: 0009-2541

E-ISSN: 1872-6836

DOI: 10.1016/j.chemgeo.2018.08.015

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: Geochimica et Cosmochimica Acta, 2011, Vol.75(23), pp.7644-7667

Description: Saprolite formation rates influence many important geological and environmental issues ranging from agricultural productivity to landscape evolution. Here we investigate the chemical and physical transformations that occur during weathering by studying small-scale “saprolites” in the form of weathering rinds, which form on rock in soil or saprolite and grow in thickness without physical disturbance with time. We compare detailed observations of weathered basalt clasts from a chronosequence of alluvial terraces in Costa Rica to diffusion-reaction simulations of rind formation using the fully coupled reactive transport model CrunchFlow. The four characteristic features of the weathered basalts which were specifically used as criteria for model comparisons include (1) the mineralogy of weathering products, (2) weathering rind thickness, (3) the coincidence of plagioclase and augite reaction fronts, and (4) the thickness of the zones of mineral reaction, i.e. reaction fronts. Four model scenarios were completed with varying levels of complexity and degrees of success in matching the observations. To fit the model to all four criteria, however, it was necessary to (1) treat diffusivity using a threshold in which it increased once porosity exceeded a critical value of 9%, and (2) treat mineral surface area as a fitting factor. This latter approach was presumably necessary because the mineral-water surface area of the connected (accessible) porosity in the Costa Rica samples is much less than the total porosity ( ). The model-fit surface area, here termed reacting surface area, was much smaller than the BET-measured surface area determined for powdered basaltic material. In the parent basalt, reacting surface area and diffusivity are low due to low pore connectivity, and early weathering is therefore transport controlled. However, as pore connectivity increases as a result of weathering, the reacting surface area and diffusivity also increase and weathering becomes controlled by mineral reaction kinetics. The transition point between transport and kinetic control appears to be related to a critical porosity (9%) at which pore connectivity is high enough to allow rapid transport. Based on these simulations, we argue that the rate of weathering front advance is controlled by the rate at which porosity is created in the weathering interface, and that this porosity increases because of mineral dissolution following a rate that is largely surface-reaction controlled.

Keywords: Geology

ISSN: 0016-7037

E-ISSN: 1872-9533

DOI: 10.1016/j.gca.2011.09.033

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: Geochimica et Cosmochimica Acta, March 1, 2012, Vol.80, p.92(16)

Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2011.11.038 Byline: Lin Ma (a)(b)(c), Francois Chabaux (b), Eric Pelt (b), Mathieu Granet (b), Peter B. Sak (d), Jerome Gaillardet (e), Marina Lebedeva (a), Susan L. Brantley (a) Abstract: To quantify rates of rind formation on weathering clasts under tropical and humid climate and to determine factors that control weathering reactions, we analyzed Uranium series isotope compositions and trace element concentrations in a basaltic andesite weathering clast collected from Basse-Terre Island in Guadeloupe. U, Th, and Ti elemental profiles reveal that Th and Ti behave conservatively during rind formation, but that U is added from an external source to the rind. In the rind, weathering reactions include dissolution of primary minerals such as pyroxene, plagioclase, and glass matrix, as well as formation of Fe oxyhydroxides, gibbsite and minor kaolinite. Rare earth element (REE) profiles reveal a significant Eu negative anomaly formed during clast weathering, consistent with plagioclase dissolution. Significant porosity forms in the rind mostly due to plagioclase dissolution. The new porosity is inferred to allow influx of soil water carrying externally derived, dissolved U. Due to this influx, U precipitates along with newly formed clay minerals and oxyhydroxides in the rind. The conservative behavior of Th and the continuous addition of U into the rind adequately explain the observed systematic trends of (.sup.238U/.sup.232Th) and (.sup.230Th/.sup.232Th) activity ratios in the rind. Rind formation rates, determined from the measured U-series activity ratios with an open system U addition model, increase by a factor of [approximately equal to]1.3 (0.18-0.24mm/kyr) from a low curvature to a high curvature section (0.018-0.12mm.sup.-1) of the core-rind boundary, revealing that curvature affects rates of rind formation as expected for diffusion-limited rind formation. U-series geochronometry thus provides the first direct evidence that the curvature of the interface controls the rate of regolith formation at the clast scale. The weathering rates determined at the clast scale can be reconciled with the weathering rates determined at the watershed or soil profile scale if surface roughness equals values of approximately 1300-2200. Author Affiliation: (a) Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA (b) Laboratoire d'Hydrologie et de Geochimie de Strasbourg, EOST, University of Strasbourg and CNRS, Strasbourg, France (c) Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968-0555, USA (d) Department of Earth Sciences, Dickinson College, Carlisle, PA 17013, USA (e) Laboratoire de Geochimie et Cosmochimie, Institue de Physique du Globe de Paris, Paris, France Article History: Received 28 March 2011; Accepted 21 November 2011 Article Note: (miscellaneous) Associate editor: Eric H. Oelkers

Keywords: Clay Minerals -- Analysis ; Basalt -- Analysis ; Soil Moisture -- Analysis ; Uranium -- Analysis ; Porosity -- Analysis

ISSN: 0016-7037

Source: Cengage Learning, Inc.

Language: English

In: Geochimica et Cosmochimica Acta, 15 December 2016, Vol.195, pp.29-67

Description: Inside soil and saprolite, rock fragments can form weathering clasts (alteration rinds surrounding an unweathered core) and these weathering rinds provide an excellent field system for investigating the initiation of weathering and long term weathering rates. Recently, uranium-series (U-series) disequilibria have shown great potential for determining rind formation rates and quantifying factors controlling weathering advance rates in weathering rinds. To further investigate whether the U-series isotope technique can document differences in long term weathering rates as a function of precipitation, we conducted a new weathering rind study on tropical volcanic Basse-Terre Island in the Lesser Antilles Archipelago. In this study, for the first time we characterized weathering reactions and quantified weathering advance rates in multiple weathering rinds across a steep precipitation gradient. Electron microprobe (EMP) point measurements, bulk major element contents, and U-series isotope compositions were determined in two weathering clasts from the Deshaies watershed with mean annual precipitation (MAP) = 1800 mm and temperature (MAT) = 23 °C. On these clasts, five core-rind transects were measured for locations with different curvature (high, medium, and low) of the rind-core boundary. Results reveal that during rind formation the fraction of elemental loss decreases in the order: Ca ≈ Na 〉 K ≈ Mg 〉 Si ≈ Al 〉 Zr ≈ Ti ≈ Fe. Such observations are consistent with the sequence of reactions after the initiation of weathering: specifically, glass matrix and primary minerals (plagioclase, pyroxene) weather to produce Fe oxyhydroxides, gibbsite and minor kaolinite. Uranium shows addition profiles in the rind due to the infiltration of U-containing soil pore water into the rind as dissolved U phases. U is then incorporated into the rind as Fe-Al oxides precipitate. Such processes lead to significant U-series isotope disequilibria in the rinds. This is the first time that multiple weathering clasts from the same watershed were analyzed for U-series isotope disequlibrian and show consistent results. The U-series disequilibria allowed for the determination of rind formation ages and weathering advance rates with a U-series mass balance model. The weathering advance rates generally decreased with decreasing curvature: ∼0.17 ± 0.10 mm/kyr for high curvature, ∼0.12 ± 0.05 mm/kyr for medium curvature, and ∼0.11 ± 0.04, 0.08 ± 0.03, 0.06 ± 0.03 mm/kyr for low curvature locations. The observed positive correlation between the curvature and the weathering rates is well supported by predictions of weathering models, i.e., that the curvature of the rind-core boundary controls the porosity creation and weathering advance rates at the clast scale. At the watershed scale, the new weathering advance rates derived on the low curvature transects for the relatively dry Deshaies watershed (average rate of 0.08 mm/kyr; MAP = 1800 mm and MAT = 23 °C) are ∼60% slower than the rind formation rates previously determined in the much wetter Bras David watershed (∼0.18 mm/kyr, low curvature transect; MAP = 3400 mm and MAT = 23 °C) also on Basse-Terre Island. Thus, a doubling of MAP roughly correlates with a doubling of weathering advance rate. The new rind study highlights the effect of precipitation on weathering rates over a time scale of ∼100 kyr. Weathering rinds are thus a suitable system for investigating long-term chemical weathering across environmental gradients, complementing short-term riverine solute fluxes.

Keywords: U-Series Isotopes ; Weathering Rinds ; Weathering Rates ; Precipitation ; French Guadeloupe ; Geology

ISSN: 0016-7037

E-ISSN: 1872-9533

DOI: 10.1016/j.gca.2016.08.040

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: Geochimica et Cosmochimica Acta, 01 March 2012, Vol.80, pp.92-107

Description: To quantify rates of rind formation on weathering clasts under tropical and humid climate and to determine factors that control weathering reactions, we analyzed Uranium series isotope compositions and trace element concentrations in a basaltic andesite weathering clast collected from Basse-Terre Island in Guadeloupe. U, Th, and Ti elemental profiles reveal that Th and Ti behave conservatively during rind formation, but that U is added from an external source to the rind. In the rind, weathering reactions include dissolution of primary minerals such as pyroxene, plagioclase, and glass matrix, as well as formation of Fe oxyhydroxides, gibbsite and minor kaolinite. Rare earth element (REE) profiles reveal a significant Eu negative anomaly formed during clast weathering, consistent with plagioclase dissolution. Significant porosity forms in the rind mostly due to plagioclase dissolution. The new porosity is inferred to allow influx of soil water carrying externally derived, dissolved U. Due to this influx, U precipitates along with newly formed clay minerals and oxyhydroxides in the rind. The conservative behavior of Th and the continuous addition of U into the rind adequately explain the observed systematic trends of ( U/ Th) and ( Th/ Th) activity ratios in the rind. Rind formation rates, determined from the measured U-series activity ratios with an open system U addition model, increase by a factor of ∼1.3 (0.18–0.24 mm/kyr) from a low curvature to a high curvature section (0.018–0.12 mm ) of the core–rind boundary, revealing that curvature affects rates of rind formation as expected for diffusion-limited rind formation. U-series geochronometry thus provides the first direct evidence that the curvature of the interface controls the rate of regolith formation at the clast scale. The weathering rates determined at the clast scale can be reconciled with the weathering rates determined at the watershed or soil profile scale if surface roughness equals values of approximately 1300–2200.

Keywords: Geology

ISSN: 0016-7037

E-ISSN: 1872-9533

DOI: 10.1016/j.gca.2011.11.038

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: Geoderma, 01 July 2016, Vol.273, pp.83-97

Description: At Earth's surface, bedrock transforms to regolith in a process that has many implications for water storage, soil formation, and nutrient availability to ecosystems. To understand deep regolith formation, we investigate three zones demarcating changes in mineralogy, chemistry and Fe isotopic composition in a 4-m thick regolith profile developed at a ridge top in Pennsylvania (U.S.A.) that is underlain entirely by diabase. Relative to the unweathered diabase, Zone 1 at the bottom is characterized by major element depletion, abrupt oxidation of Fe(II), a rapid decrease in sulfur concentrations and the presence of short-range ordered (SRO) Fe with depleted δ Fe values relative to unweathered diabase. We attribute many of the observations at this depth (which we refer to as the lithogenic zone) to the effects of spheroidal weathering, which may be releasing a flux of Fe(II) with low δ Fe values as the mineral pyroxene is weathered. This Fe(II) is oxidized due to the presence of oxygen at the bottom of the profile and is likely precipitated as isotopically light SRO Fe phases, which then recrystallize with time. Zone 2 is interpreted as a region of crystallization in which minimal bulk chemical changes occur. Finally, SRO Fe isotopic compositions become lighter again near the land surface in Zone 3, the zone of most intense biogenic weathering. Biological Fe weathering likely involves enhanced microbial activity, exudation of protons and organic acids by plant roots and fungi, and plant uptake. This pattern of SRO Fe isotopic variability (with isotopically depleted values both at depth and near the surface) has been observed in another regolith profile on spheroidally weathering bedrock in Puerto Rico. We further used pore-water concentrations and soil chemistry to calculate rates of diabase weathering. While pore-water concentrations yield modern rates, soil chemistry concentrations indicate longer-term rates. The similarity in the diabase dissolution rates using modern pore fluids and soil chemistry is consistent with steady-state weathering. Similar approaches can be applied to other Appalachian soil profiles in the future.

Keywords: Fe Isotopes ; Deep Regolith ; Chemical Weathering ; Diabase ; Spheroidal Weathering ; Preferential Flow ; Agriculture

ISSN: 0016-7061

E-ISSN: 1872-6259

DOI: 10.1016/j.geoderma.2016.03.004

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: Geology, Jan, 2008, Vol.36(1), p.67(4)

Description: Where Martian rocks have been exposed to liquid water, chemistry versus depth profiles could elucidate both Martian climate history and potential for life. The persistence of primary minerals in weathered profiles constrains the exposure time to liquid water: on Earth, mineral persistence times range from ~10 k.y. (olivine) to ~250 k.y. (glass) to ~1 m.y. (pyroxene) to ~5 m.y. (plagioclase). Such persistence times suggest mineral persistence minima on Mars. However, Martian solutions may have been more acidic than on Earth. Relative mineral weathering rates observed for basalt in Svalbard (Norway) and Costa Rica demonstrate that laboratory pH trends can be used to estimate exposure to liquid water both qualitatively (mineral absence or presence) and quantitatively (using reactive transport models). Qualitatively, if the Martian solution pH 〉~2, glass should persist longer than olivine; therefore, persistence of glass may be a pH indicator. With evidence for the pH of weathering, the reactive transport code CrunchFlow can quantitatively calculate the minimum duration of exposure to liquid water consistent with a chemical profile. For the profile measured on the surface of the exposed Martian rock known as Humphrey in Gusev Crater, the calculated exposure time is 22 k.y., which is a minimum due to physical erosion. If correct, this estimate is consistent with short-term, episodic alteration accompanied by ongoing surface erosion. More of these depth profiles should be measured to illuminate the weathering history of Mars. Keywords: Mars, basalt, weathering reactive transport modeling, weathering rind, pH.

Keywords: Mars (Planet) -- Natural History ; Basalt -- Properties ; Weathering -- Evaluation ; Impact Craters -- Properties

ISSN: 0091-7613

E-ISSN: 19432682

DOI: 10.1130/G24238A.1

Language: English

In: Geochimica et Cosmochimica Acta, 2008, Vol.72(18), pp.4488-4507

Description: In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2–2 m thick zone of partially weathered rock layers (∼2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive Δ of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in (0 0 1) from 10.0 to 10.5 Å, forming “altered biotite”. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 × 10 mol biotite m s . Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 μm resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet–saprolite interface, hornblende dissolves to completion at a rate of 6.3 × 10 mol hornblende m s : the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O at the bedrock–saprolite interface.

Keywords: Geology

ISSN: 0016-7037

E-ISSN: 1872-9533

DOI: 10.1016/j.gca.2008.06.020

Source: ScienceDirect Journals (Elsevier)

URL: View record in ScienceDirect (Access to full text may be restricted)

Language: English

In: American Journal of Science, 09/2018, Vol.318(7), pp.727-763

Description: Weathering-induced fracturing (WIF) has been posited to be a mechanism that develops secondary porosity when mineral reaction fronts separate over depth intervals in regolith, and, in particular, when oxidation (which can promote porosity development through volume expansion) occurs deeper than dissolution (which grows porosity through material removal). If this is true, then the protolith's capacity to reduce O (sub 2) [for example, the Fe(II) content] and O (sub 2) availability should affect WIF. This study explores the hypothesis that if the ratio of pO (sub 2) to pCO (sub 2) , in soil water, R' (sub (aq)) , is greater than the ratio of the capacity of the protolith to consume O (sub 2) and CO (sub 2) , R (super 0) , then WIF is more likely to occur, and regolith will become thicker. We evaluated this hypothesis by measuring the bulk geochemistry of regolith and rock and monitoring soil gas at three sites, encompassing a wide range of FeO concentrations and regolith thickness: a Pennsylvania (PA) diabase (10.15%; 3.8 m), a Virginia (VA) diabase (10.49%; 1.4 m), and a VA granite (1.45%; 20 m). We inferred soil water O (sub 2) concentrations from calculated equilibrium with the measured soil gas pO (sub 2) . We observed WIF in the VA granite and PA diabase where R' (sub (aq)) 〉R (super 0) , while at the site that lacked WIF--the VA diabase--R' (sub (aq)) 〈R (super 0) , particularly during the wet season. In the VA diabase, the presence of swelling clays (smectite) limits the ability of the oxidant (O (sub 2) ) to diffuse deeper into the weathering profile during the wet season and microbially accelerated iron oxidation rapidly consumes O (sub 2) , limiting O (sub 2) availability for WIF. Smectite has little to no observable effect on O (sub 2) consumption in the PA diabase because the PA diabase is more fractured. A compilation of dissolved soil gas oxidation ratios, the stoichiometric ratio of O (sub 2) consumed to CO (sub 2) produced, shows that for unsaturated conditions, the mean is -1.45+ or -0.88, which is consistent with aerobic root and microbial respiration and the oxidation of organic matter. For near-saturated conditions, the mean oxidation ratio of the compilation is -3.46+ or -1.79, which is consistent with Fe redox and microbial metabolism under reducing conditions. The consistency between the VA and PA data presented here and the compilation suggests that soil water surplus drives coupled Fe-redox reactions that may act as a negative feedback, limiting O (sub 2) supply and WIF under wetter soil moisture conditions. We defined Rz, the ratio of O (sub 2) consumption to CO (sub 2) consumption during weathering for each depth interval, z. For all profiles, R' (sub (aq)) 〉Rz near the surface but R' (sub (aq)) approaches Rz in the saprolite. We suggest that R' (sub (aq)) 〉Rz in the soil reflects consumption of O (sub 2) and production of CO (sub 2) due to biotic processes whereas R' (sub (aq)) approaching Rz suggests that low fluxes at depth are at least partly dictated by rock and regolith composition, notably tortuosity of pores. In the VA diabase, we observed R' (sub (aq)) 〈Rz occasionally during the wet season in the lowermost soil and saprolite. Thus, at times the O (sub 2) availability may be less than the O (sub 2) consumption at that depth, consistent with Fe(II) loss and a lack of WIF. Mass-balance calculations show Fe loss in the VA diabase. The influence of rock composition on aqueous O (sub 2) /CO (sub 2) concentrations in saprolite is consistent with the hypothesis that the protolith's capacity to consume O (sub 2) and CO (sub 2) has some effect on oxidation and acid consumption deep in the weathering profile.

Keywords: Soils ; Geochemistry Of Rocks, Soils, And Sediments ; Appalachians ; Bedrock ; Carbon Dioxide ; Case Studies ; Chemical Reactions ; Diabase ; Fracturing ; Geochemistry ; Granites ; Igneous Rocks ; North America ; Oxygen ; Parent Materials ; Pennsylvania ; Piedmont ; Plutonic Rocks ; Regolith ; Soil Gases ; Soils ; United States ; Valley And Ridge Province ; Virginia ; Weathering;

ISSN: 0002-9599

E-ISSN: 1945-452X

DOI: 10.2475/07.2018.01

Source: CrossRef

Language: English

In: Geochimica et Cosmochimica Acta, 15 February 2019, Vol.247, pp.1-26

Description: To quantify chemical weathering processes, it is essential to develop and utilize new geochemical tools that can provide information about chemical weathering in the field. U-series isotopes have emerged as a useful chronometer to directly constrain the rates and duration of chemical weathering. However, the conventional solution-based MC-ICPMS method involves a long and expensive sample processing procedure that restricts the numbers of measurements of samples by U-series analysis that can be completed. Here, we report measurements of U-series disequilibria obtained with laser ablation (LA)-MC-ICPMS on weathering rinds collected from the tropical island of Basse-Terre in the archipelago of French Guadeloupe. We characterized two weathering rinds for U-series isotope compositions and elemental distributions with LA-MC-ICPMS and LA-Q-ICPMS. The measurements of U-series disequilibria were consistent with the previous bulk measurements obtained by conventional solution MC-ICPMS despite the larger analytical uncertainties. The LA technique allowed a greater number of measurements that accelerated sample throughput and improved spatial resolution of measurement. The rind formation age, weathering rates, and U-series mobility parameters modeled in this study are comparable to the results from previous studies conducted on the same clasts, and also reveal new insights on rind formation such as the impact of micro-fractures on weathering history and U-series ratios. The improved spatial resolution available with LA Q-ICPMS helps distinguish between linear and power law rind thickness-age relationships that were unresolvable using conventional solution-based MC-ICPMS. measurements with LA-Q-ICPMS in these weathering rinds also elucidates the sequences of mineral reactions during chemical weathering. The LA-Q-ICPMS maps of major and trace elements and elemental ratios reveal details about the rind formation processes at the weathering interfaces of clasts such as dissolution of primary phases, formation of new phases, development of porosity, and mobility behavior of U. This study demonstrates a new analytical method for determining weathering rates in rinds rapidly and accurately that can be used in a large number of rinds, providing key information at the clast scale.

Keywords: Geology

ISSN: 0016-7037

E-ISSN: 1872-9533

DOI: 10.1016/j.gca.2018.12.020

URL: View record in ScienceDirect (Access to full text may be restricted)