Dating of a volcanic rock by electron spin resonance

The age of a volcanic rock has been determined by ESR dating using the Ge center in quartz. The total dose of natural radiation and the age obtained from the Ge center are 460 krad and 2.07 ± 0.50 Ma, respectively, and those from the unidentified defect at g = 2.011 are 484 krad and 2.16 ± 0.21 Ma, respectively. These dates agree well with the age of 2.0 ± 0.5 Ma determined by the fission-track method. High stress or temperature destroy these accumulated defects but, in the same time, produce a lot of new diamagnetic precursors which enable us to observe the clear ESR signal.     

Electron spin resonance spectra of marine and fresh-water manganese nodules

Eighty ferromanganese nodules from a wide variety of marine and fresh-water environments have been analyzed by electron spin resonance spectroscopy. The purpose has been to gain information on the forms in which the major constituents of manganese nodules are present. Contributions to ESR spectra of the nodules come mainly from Mn²⁺ and Fe³⁺. Deep-sea samples generally showed only broad resonance lines, and those with larger peaks close to g = 2.0 are believed to contain more Mn²⁺ than others. Some Antarctic and fresh-water nodules lack a strong Mn²⁺ resonance and have a peak around g = 4.0 which is most likely tetrahedral Fe³⁺. A number of smaller peaks in several samples could not be readily interpreted in terms of contributions from individual ionic species because of fundamental problems in preparing standards having the ion of interest in the same micro-environment as it experiences in the nodules.     

Simultaneous determination of alteration and eruption ages of volcanic rocks by electron spin resonance

The alteration and eruption ages of Japanese welded tuffs were estimated by the method of ESR using Ge, OHC and Al centers in quartz whose stabilities are different. The ages obtained from the Ge and OHC centers were 1–2 Ma, however the ages from the Al center varied from 0.059 to 1.36 Ma. The comparison of these ages with thermoluminescence (TL) and fission track (FT) ages proves that the ESR age of the Al center, which agrees with the TL age, shows the thermal history and, in an ideal case, gives the alteration age: those of the Ge and OHC centers, which agree with FT age, indicate the eruption age. Therefore, this method enables us to describe the thermal history of a rock.     

Electron paramagnetic resonance and electron spin echo spectroscopy study of natural bornite

Summary A minero-chemical and spectroscopic characterisation has been performed on a natural bornite sample from the Natural History Museum of the University of Florence, through the use of EPMA, XRD, continuous-wave (cw) and pulsed EPR spectroscopy. The use of different EPR techniques allowed to fully investigate the distribution and valence states of Cu and Fe and to study the early oxidation products of bornite. The microanalytical and XRD characterisation proved bornite to be homogeneous and stoichiometric. Cw-EPR measurements confirmed the presence of Fe(III) as fundamental valence state in bornite; moreover, no evidence of Cu(II) as a bulk transient species, due to a charge transfer process, has been revealed. The broadening of the Fe(III) EPR spectrum is ascribed to a partial transfer of spin density from Fe(III) to the surrounding cationic sublattice. In contrast, the pulsed EPR experiments, registered at 4.2 K, revealed the presence of both Fe(III) and Cu(II). These species were supposed to be present at the early stage of the surface alteration. The data provided by the electron spin-echo decay and modulation suggest both the oxidised Cu(II) and Fe(III) species to belong to premature surface water adducts (evidenced by proton nuclear modulation), which may evolve to sulphate species.     

Optical absorption and electron spin resonance in blue and green natural beryl

A comparative study of blue and green beryl crystals (from the region of Governador Valadares, Minas Gerais, Brazil) using electron paramagnetic resonance (EPR) and optical absorption (OA) spectroscopy is reported. The EPR spectra show that Fe³⁺ in blue beryl occupies a substitutional Al³⁺ site and in green beryl is localized in the structural channels between two O₆ planes. On the other hand the infrared spectra show that the alkali content in the blue beryl is mostly at substitutional and/or interstitial sites and in green beryl is mostly in the structural channels. The OA spectra show two types of Fe²⁺. Thermal treatments above 200° C in green beryl cause the reduction of Fe³⁺ into Fe²⁺ accompanied by a change of color to blue. The blue beryl color does not change on heating. The kinetics of the thermal conversion of Fe³⁺ into Fe²⁺ is composed of two first order processes; the first one has an activation energy ΔE ₁=0.30 eV and the second one has an activation energy ΔE ₂=0.46 eV.     

Magnesium stable isotope fractionation in marine biogenic calcite and aragonite

This survey of magnesium stable isotope compositions in marine biogenic aragonite and calcite includes samples from corals, sclerosponges, benthic porcelaneous and planktonic perforate foraminifera, coccolith oozes, red algae, and an echinoid and brachiopod test. The analyses were carried out using MC-ICP-MS with an external repeatability of ±0.22‰ (2SD for δ²⁶Mg; n = 37), obtained from a coral reference sample (JCp-1).Magnesium isotope fractionation in calcitic corals and sclerosponges agrees with published data for calcitic speleothems with an average Δ²⁶Mg_{calcite-seawater} = −2.6 ± 0.3‰ that appears to be weakly related to temperature. With one exception (Vaceletia spp.), aragonitic corals and sclerosponges also display uniform Mg isotope fractionations relative to seawater with Δ²⁶Mg_{biogenic aragonite-seawater} = −0.9 ± 0.2.Magnesium isotopes in high-Mg calcites from red algae, echinoids and perhaps some porcelaneous foraminifera as well as in all low-Mg calcites (perforate foraminifera, coccoliths and brachiopods) display significant biological influences. For planktonic foraminifera, the Mg isotope data is consistent with the fixation of Mg by organic material under equilibrium conditions, but appears to be inconsistent with Mg removal from vacuoles. Our preferred model, however, suggests that planktonic foraminifera synthesize biomolecules that increase the energetic barrier for Mg incorporation. In this model, the need to remove large quantities of Mg from vacuole solutions is avoided. For the high-Mg calcites from echinoids, the precipitation of amorphous calcium carbonate may be responsible for their weaker Mg isotope fractionation.Disregarding superimposed biological effects, it appears that cation light isotope enrichments in CaCO₃ principally result from a chemical kinetic isotope effect, related to the incorporation of cations at kink sites. In this model, the systematics of cation isotope fractionations in CaCO₃ relate to the activation energy required for cation incorporation, which probably reflects the dehydration of the cation and the crystal surface and bond formation at the incorporation site. This kinetic incorporation model predicts (i) no intrinsic dependence on growth rate, unless significant back reaction upon slow growth reduces the isotope fractionation towards that characteristic for equilibrium isotope partitioning (this may be observed for Ca isotopes in calcites), (ii) a small decrease of isotope fractionation with increasing temperature that may be amplified if higher temperatures promote back reaction and (iii) a sensitivity to changes in the activation barrier caused by additives such as anions or biomolecules or by the initial formation of amorphous CaCO₃.     

Effect of adsorbed iron on thermoluminescence and electron spin resonance spectra of Ca-Fe-exchanged montmorillonite

The electron spin resonance (ESR) spectra and the natural and gamma-induced thermoluminescence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 montmorillonite were examined. The ESR signal (g = 2) intensity associated with the surface Fe was found to increase linearly with surface Fe content up to a nominal concentration of 50% exchangeable Fe. At > 50% exchangeable Fe, no appreciable increase in the signal was noted. The TL intensity decreased linearly with increasing surface Fe up to 50% nominal exchangeable Fe. At > 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature peak, but irradiation produced an additional low-temperature peak. One month after gamma-irradiation, the integrated TL signal was still 10-100 times higher than that from the non-irradiated material. Thus, (1) surface iron clusters may form above a certain critical Fe concentration; (2) the Fe clusters are probably less effective in quenching TL than are single Fe atoms, implying interaction between surface Fe and the stored energy content of the material; and (3) the electronic energy stored in the material as the result of gamma-irradiation is only slowly dissipated.     

Elemental,infra-red spectrophotometric and electron spin resonance investigations of non-chemically isolated humic material

Naturally occurring organic material from a lake in the southeastern United States was isolated by ultrafiltration and analyzed by i.r. spectrophotometry and electron spin resonance spectrometry, and for its elemental composition without chemical pretreatment. The results of the study indicate the isolate is an apparent high molecular weight fulvic acid with associated, hydrated Mn²⁺ ion which does not appear strongly bound to the organic moiety.     

石英电子自旋共振（ESR）的地学研究现状与展望

电子自旋共振（ESR）是一种对断层物质、燧石、火山灰和沉积物（水系、风成、冰川）定年的重要方法,它广为接受的测年范围为第四纪。对断层泥和沉积物样品,石英ESR信号的不完全归零往往使ESR年龄偏老,多重ESR中心法和颗粒大小“平顶判据”是判断信号归零特征的两种有效方法。为将ESR测年范围拓展至前第四纪,通常采用石英氧空位在加热转化后极大增强的E’心作为测年信号,但由于石英氧空位形成转化机理不明确,加热后增强的ESR信号与地质年龄的相关性有待进一步验证。近期研究表明石英ESR的封闭温度为49 ℃～82 ℃,可在比磷灰石（U-Th）/He更低的温度区间内研究地球近地表的构造演化过程。释光技术热年代学研究发展迅速,与之测年原理接近的ESR在低温热年代学领域展现了良好的应用前景,它与释光及磷灰石（U-Th）/He可相互比对、共同提高地球近地表构造和地形演化问题的分析精度。     

Uptake of fluoride by aragonite

The uptake of F by aragonite is attributed to the ion-exchange process, in which one CO₃^2? ion in the structure is replaced by two F^? ions. Under the equilibrium condition at 15° C and 1 atm., the partition of F between aragonite and aqueous solution is described by:

$\text{log}\text{(}\text{[}\text{F}\text{]}\text{a}{}_{\mathrm{<mtext>F</mtext>}}\text{)=1.95 + 0.54}\text{log}\text{a}{}_{\mathrm{<mtext>Ca</mtext>}}$

were [F] denotes the F content of aragonite in mol/g, and a_F and a_Ca are the aqueous activities of F^? and Ca²⁺, respectively. The equation was successfully applied to estimating the F content of marine aragonite.     

An electron spin resonance spectrometric investigation of natural,extracted and thermally altered kerogenous materials

Core cuttings from three wells representing a 1000–7000-ft range of depths were examined by ESR spectroscopy. The spectral parameters of some of the series of samples follow trends, as suggested by the ESR kerogen method for paleotemperature estimation, while the spectral parameters of other series of samples do not. Samples extracted with mineral acids exhibit spectra parameters which follow the proposed trends somewhat better, but show large local variations which appear to be due to factors other than paleotemperature. Thermally treated samples show a general increase in free radical concentration, although there are several anomalies. While the ESR-kerogen method of paleotemperature estimation appears to have potential due to the large variations in some of the observed parameters, factors such as mineral acid extraction and sample lithology, among others, need further investigation to refine the technique.     

Coal inclusions of the Athabasca tar sands: characterization and direct determination of vanadyl porphyrin content by electron spin resonance

Electron spin resonance provides a sensitive and specific technique for the detection and approximate quantification of low concentrations of vanadyl porphyrins in Athabasca tar sands without recourse to extraction. The technique was successfully extended to coal inclusions of the tar sands and to extracts of these, which also clearly demonstrated the presence of lower concentrations of vanadyl porphyrins. These results were confirmed quantitatively and the fraction of complexed vanadyl was related to total vanadium present in all three sample types using neutron activation analysis. The fossiliferous inclusions are morphologically very similar to present day western hemlock, using scanning electron microscopy.     

Electron spin resonance optical dating of marine,estuarine, and aeolian sediments in Florida,USA

For the first time, electron spin resonance optical dating (ESROD) has been conducted on littorally transported and aeolian siliciclastic sediments in Florida. ESROD utilizes light-sensitive radiation-sensitive defects at silicon sites that have been replaced by aluminum and titanium atoms to give rise to a time-dependant signal. These defects saturate at higher levels of radiation dose, compared to optically stimulated luminescence, and therefore extend the optical dating range back into the millions of years. Our results show that the Trail Ridge Sequence is a multi-depositional unit that began deposition around 2.2 Ma and continued until 6 ka. The Osceola Cape, of the Effingham Sequence, was deposited around 1.5 Ma, and the Chatham Sequence was a multi-depositional terrace with at least three events preserved.     

Elasticity of single-crystal aragonite by Brillouin spectroscopy

The elastic constants of natural single-crystal aragonite (CaCO₃) have been measured by Brillouin spectroscopy at ambient conditions. The elastic constants C₁₁, C₂₂, C₃₃, C₄₄, C₅₅, C₆₆, C₁₂, C₁₃ and C₂₃ are 171.1±1.0, 110.1±0.9, 98.4±1.2, 39.3±0.6, 24.2±0.4, 40.2±0.6, 60.3±1.0, 27.8±1.6 and 41.9±2.0 GPa, respectively, for aragonite. The linear compressibilities of the a-, b- and c-axis for aragonite at ambient conditions were derived from our measured data to be 3.0±0.2, 4.2±0.2 and 7.3±0.6×10^–3 GPa^–1, respectively. The aggregate bulk and shear moduli for aragonite using the Voigt-Reuss-Hill (VRH) scheme are thus calculated to be 68.9±1.4 and 35.8±0.2 GPa, respectively. The value of bulk modulus is in remarkable contrast to the literature value of 46.9 GPa measured almost a century ago. Our new datum, however, is closer to that derived from recent atomistic simulation and static compression studies.     

Quantitative electron spin resonance (ESR) determinations of forms and total amounts of Mn in aqueous environmental samples

An electron spin resonance (ESR) method for determining quantitatively amounts and forms of Mn in 0.2 ml of marine and lacustrine waters with no chemical processing is described and applied to various samples from the Puget Sound region of western Washington state. Results over the 50 ppb15 ppm (0.9–270 μM) total Mn concentration range are reproducible to within ±3–5% and average 8 ± 7 and 13 ± 7% lower than inductively coupled plasma (ICP) determinations on marine and lacustrine pore waters, respectively. Main features in profiles of total Mn versus depth in Pacific Northwest pore waters resemble those in profiles from other coastal regions.The method reveals that 72–77% of total dissolved Mn is present as free Mn⁺⁺ in most seawaters, 14–16% is complexed with chloride, and 10–12% is complexed with sulfate. Less than 5% is associated with carbonate, bicarbonate or organic ligands. These results should significantly reduce uncertainties in equilibrium calculations of state of saturation of seawaters with respect to precipitation of various Mn-solids. The method can be easily extended to various ionic strengths and temperatures.     

Source indicators of humic substances and proto-kerogen. Stable isotope ratios,elemental compositions and electron spin resonance spectra

Stable isotope ratios of C, N and H, elemental compositions and electron spin resonance (ESR) data of humic acids and proto-kerogens from twelve widely varying sampling locations are presented. Humic acids and proto-kerogens from algal sources are more aliphatic and higher in N than those from higher plant sources. Oxygen content appears to represent a measure of maturation, even in Recent sediments and S content may reflect redox conditions in the environment of deposition. The ESR data indicate that the transformation of humic substances to proto-kerogens in Recent sediments is accompanied by an increase in aromatic character. A combination of δ¹³C and $\text{H}\text{C}$ ratio may be a simple but reliable source indicator which allows differentiation of marine-derived from terrestrially-derived organic matter. The δ¹⁵N values are useful indicators of nitrogen nutrient source. Deuterium/hydrogen isotope ratios appear to reflect variations in meteoric waters and are not reliable source indicators.     

祁连山夷平面形成时代的ESR年龄证据

青藏高原夷平面形成年代是确定高原起始隆升时代和抬升幅度的重要证据。青藏高原东北缘祁连山地区4100~4300 m的海拔高度上保留有大片平坦地形面构成的夷平面,地质与地貌调查表明,夷平面切削古生代花岗岩类侵入体及晚古生代-古近纪地层,被夷平的最新地层为始新世-渐新世火烧沟组。祁连山抬升导致河流下切与断陷作用并形成深切河谷及断陷盆地,充填于古河谷及断陷盆地中的渐新世-中新世白杨河组开始沉积时代,代表了夷平作用过程的终止年代及导致夷平面解体的构造隆升时代。29个ESR测年数据表明,白杨河组沉积时代为34.4~11.89 Ma。由此推论,祁连山夷平面形成于始新世末（34 Ma之前）,形成时其高度在1000 m左右,34 Ma左右祁连山夷平面开始解体并快速抬升。