The potential of
238U–
234U–
230Th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a ...125 kyr old Costa Rican alluvial terrace. Eighteen subsamples were collected from one section of the clast by drilling cores (4 mm in diameter and 5 mm depth) along two transects straddling the core–rind boundary. Variations of major and trace element concentrations along the two transects point out (a) intense loss of alkaline and alkaline-earth elements, (b) conservative behaviour of elements such as Zr, Hf and Th, and (c) external input of U into the rind without any evidence of U loss during basalt weathering. In addition, variations in U concentrations along the transects show that the main U–Th fractionation process associated with the weathering of the basaltic clast is an external input of U (without addition nor loss of Th) in the basalt rind transition zone, and that, once deposited U is immobile in the weathering rind. In the frame of this interpretation scheme, a weathering rate of 0.5
±
0.2 mm/kyr can be calculated for the studied clast, which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces. In addition, the variations in the (
234U/
238U) ratio along the analysed transects as well as the increase in Sr isotopic ratios within the weathering rind are best explained by temporal variation of the U activity ratios and Sr isotope ratios of the soil solutions brought into the rind. This work highlights how well detailed U–Th chronological studies of weathering rinds can (1) constrain the formation rates of weathering systems, and (2) record the time variation of isotopic composition of weathering fluids.
Basaltic bedrock dissolves quickly, and its weathering rate is therefore important towards controlling the composition of natural waters, soil formation, and CO2 concentrations in the atmosphere. ...Despite its importance, however, few reports of basalt or diabase and gabbro weathering rates exist in the literature, and most have been measured in laboratory dissolution experiments or based on watershed studies. Here, using elemental profiles measured through regolith on a Jurassic diabase dike in south-central Pennsylvania, we calculate time-integrated log dissolution rates (molm−2s−1) of the primary minerals plagioclase (−14.9s−1) and augite (−14.8), and of smectite (−17.6), a secondary clay mineral formed in the soil. Characteristic patterns in elemental profiles are consistent with preserved signatures of corestone formation. Elemental and mineral signatures of the soils relative to the parent rock are compared to predictions from citrate-containing basalt column dissolution experiments. Depletion of apatite and of Al, Fe, Mn, Ti, P, Y, Ni, Cr, Sc, V, Ga, Cu, Zn, and La are observed in the upper meter of the profile relative to the parent rock.
► Dissolution rates measured for primary and secondary minerals. ► Elemental soil depletion compared as a field test of organic-containing experiments. ► Elemental profiles are consistent with preserved signatures of corestone formation.
For the first time, we show that rind thicknesses developed on surfaces of a clast with different values of curvature can be used to estimate the duration of clast weathering. To obtain an analytical ...expression for the velocity of the curvilinear weathering front on a clast of arbitrary shape, we approximate our previous multi-mineral reactive-diffusion model and explore a simplified 2-D model numerically and analytically.
Our analysis documents that with increasing curvature of the weathering front, the mathematical description of weathering advance is equivalent to that derived for advection as the dominant solute transport mechanism, even for the case where transport is occurring by diffusion only. Specifically, for a curvilinear weathering front with constant curvature K<0, diffusivity (D), and porosity (ϕ), the normal component of the weathering advance rate can be calculated using an advection-like term where the advection velocity v can be expressed as v=Dϕ|K|. Therefore, at points along the rind–core interface with K<0, rind thickness is directly proportional to the absolute value of the curvature of the core–rind interface. The reaction front thickness also increases with K. These inferences are in agreement with field observations. This quantitative analysis allows an assessment of the duration of weathering if certain parameters are known. For example, using the difference in curvature observed at two positions for a clast that weathered in Guadeloupe (0.12mm−1 and 0.018mm−1) and the corresponding rind thickness difference (35.8mm and 20.6mm), we estimated the duration of weathering to be about 118ky, which is consistent with the weathering ages previously determined by U-series isotope disequilibrium.
•We performed a 2-D numerical and analytical investigation of weathering clasts.•The weathering front of a clast becomes curvilinear over time.•We analyze the effect of curvature on weathering.•The curvature of the weathering front affects its velocity.•Effect of curvature transforms the parabolic weathering rate law to the linear law.
prospective experimental study.
The purpose of this study was to evaluate feasibility and reliabil- ity of in vivo sentinel lymph node (SLN) mapping in patients with endometrial cancer and to verify ...a modified method of application of subserosal blue dye. Detection substance was applied subserosally in the uterine edges vicinity the round ligament of uterus and uterine vessels in the isthmic portion of the uterus.
Eighteen patients with intermediate and high-risk endome- trial cancer Stages I-II were subjected to staging laparotomy with intraoperative detection of SLNs and subsequent completion of the pelvic and para-aortic lymphadenectomies. Harvested SLN was routinely examined by classical haematoxylin eosin staining and in case of negativity, immunohistochemistry with anti-keratin antibodies AEl/AE3 was applied.
Total of 773 lymph nodes were removed in 18 patients: pelvic 420 (54%) and para-aortic 353 (46%). SLNs were detected in 16 of 18 patients totalling 59 nodes (7.6% of all nodes). Forty-eight were identified in the pelvic area (81%) and 11 nodes (19%) in the para-aortic area. Three metastatic SLNs were found in two patients (11%). No false negative nodes were demonstrated.
Experimental study results indicate that the proposed modified approach to label SLNs is applicable. The presented modified approach brings the highest added value namely in women with a myomatous uterus and scars from previous surgical procedures on the uterus.
Weathering rind thicknesses were measured on similar to 200 basaltic clasts collected from three regionally extensive alluvial fill terraces (Qt 1, Qt 2, and Qt 3) preserved along the Pacific coast ...of Costa Rica. Mass balance calculations suggest that conversion of unweathered basaltic core minerals (plagioclase and augite) to authigenic minerals in the porous rind (kaolinite, allophane, gibbsite, Fe oxyhydroxides) is iso-volumetric and Ti and Zr are relatively immobile. The hierarchy of cation mobility (Ca similar to Na > K similar to Mg > Si > Al > Fe similar to P) is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering (anorthite > albite similar to hypersthene > orthoclase >> apatite). Alteration profiles across the cm-thick rinds document dissolution of plagioclase and augite and the growth of kaolinite, with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age. The rate of weathering rind advance is evaluated using a diffusion-limited model which predicts a parabolic rate law for weathering rind thickness, r sub(r), as a function of time, t(r sub(r) =Kt), and an interface-limited model which predicts a linear rate law for weathering rind thickness as a function of time (r sub(r)i = k sub(app)t). In these rate laws, Kappa is a diffusion parameter and k sub(app) is an apparent rate constant. The rate of advance is best fit by the interface model. Terrace exposures are confined to the lower reaches of streams draining the Pacific slope near the coast where the stream gradient is less than similar to 3 m/km, and terrace deposition is influenced by eustatic sea level fluctuations. Geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest. Assigning the most weathered regionally extensive terrace Qt 1 (mean rind thickness 6.9 +/- 0. 6cm) to oxygen isotope stage (OIS) 7 (ca. 240 ka), and assuming that at TIME = 0 rind THICKNESS = 0, it is inferred that terrace Qt 2 (r sub(r) = 2.9 +/- 0.1 cm) is coincident with stage 5e (ca. 125 ka) and that Qt 3 (r sub(r) = 0.9 +/- 0.1 cm) is consistent with OIS 3 (ca. 37 ka). These assignments yield a value of k sub(app) of 8.6 x 10 super(-13) cm s super(-1) (R super(2) = 0.99). Only this value satisfies both the existing age controls and yields ages coincident with sea level maxima. Using this value, elemental weathering release fluxes across a weathering rind from Qt 2 range from 6.0 x 10 super(-9) mol Si m super(-2) s super(-1) to 2.5 x 10 super(-11) mol K m super(-2) s super(-1). The rate of rind advance for the Costa Rican terraces is 2.8 x 10 super(-7) m yr super(-1). Basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface-controlled weathering with an apparent activation energy of about 50 kJ mol super(-1). Rates of rind formation in Costa Rica are an order of magnitude slower than reported for global averages of soil formation rates.
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
V 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
d (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
−14
mol biotite
m
−2
s
−1. 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
−13
mol hornblende
m
−2
s
−1: 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
2 at the bedrock–saprolite interface.
Sorption-luminescent method for cerium determination based on natural Transcarpathian clinoptilolite without using of complex synthetic organic compounds and toxic solvents was proposed. Optimal ...luminophore preparation conditions are sorption of free Ce
3+
ions by zeolite in the solution with pH 4.5. For luminescence measurements excitation by quanta with wavelength of 255 nm were used. Luminescence intensity at λ = 346 nm was selected as analytical parameter for a quantitative cerium determination. Features characteristic to Ce
3+
and Ce
4+
oxidation states were identified in XPS spectra from as-grown and annealed samples. Definable range of Ce(III) concentration with the detection limit of 5 ng mL
–1
is within of 14–190 ng mL
–1
. The proposed method can be used for the cerium determination in the presence of many rare earths. Sorption-luminescent method can be applied for determination of trace cerium ions in synthetic water solutions containing rare earth elements of the cerium group. The proposed analytical method gave recoveries from 95 to 98.3% and relative standard deviation from 4.1% to 6.7% determination of cerium.
A clast of low porosity basaltic andesite collected from the B horizon of a soil developed on a late Quaternary volcaniclastic debris flow in the Bras David watershed on Basse-Terre Island, ...Guadeloupe, exhibits weathering like that observed in many weathered clasts of similar composition in other tropical locations. Specifically, elemental profiles measured across the core–rind interface document that primary minerals and glass weather to Fe oxyhydroxides, gibbsite and minor kaolinite in the rind. The earliest reaction identified in the core is oxidation of Fe in pyroxene but the earliest reaction that creates significant porosity is plagioclase dissolution. Elemental loss varies in the order Ca
≈
Na
>
K
≈
Mg
>
Si
>
Al
>
Fe
≈
P
≫
Ti, consistent with the relative reactivity of phases in the clast from plagioclase
≈
pyroxene
≈
glass
>
apatite
>
ilmenite. The rind surrounds a core of unaltered material that is more spherical than the original clast. The distance from the core–rind boundary to a visually prominent rind layer,
L, was measured as a proxy for the rind thickness at 36 locations on a slab cut vertically through the nominal center of the clast. This distance averaged 24.4
±
3.1
mm. Maximum and minimum values for
L, 35.8 and 20.6
mm, were observed where curvature of the core–rind boundary is greatest (0.12
mm
−
1) and smallest (0.018
mm
−
1) respectively. Extrapolating from other rinds in other locations, the rate of rind formation is estimated to vary by a factor of about 2 (from ∼
4 to 7
×
10
−
14
m
s
−
1) from low to high curvature. The observation of a higher rate of rind formation for a higher curvature interface is consistent with a diffusion-limited model for weathering rind formation. The diffusion-limited model predicts that, like rind thickness, values of the thickness of the reaction front (
h) for a given reaction, defined as the zone over which a parent mineral such as plagioclase completely weathers to rind material, should also increase with curvature. Values of
h were quantified as a function of interface curvature using bulk chemical analysis (500
<
h
<
2000
μm). Values of
h were also quantified by measuring loss of matrix glass and increase in porosity as a function of curvature. In contrast to rind thickness,
h shows no consistent increase with curvature. This contradiction is attributed to the mm-scale roughness of the interface which is related to phenocryst grain size. Therefore, the overall rind formation rate is strongly affected by curvature measured at the scale of the clast, while mineral reaction rates documented by reaction front thickness are strongly affected by curvature at the scale of phenocrysts. Similarly, the weathering advance rate (m
s
−
1) for the entire Bras David watershed can be extrapolated from the clast weathering rate if roughness at the watershed scale equals values of approximately 400–800.
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