Studying the migration behaviour of selenate in Boom Clay by electromigration

For the disposal of high-level waste (HLW) in a deep geological formation as Boom Clay, safety assessment studies have shown that long lived ⁷⁹Se is one of the more critical fission products. Therefore, the knowledge of its migration properties (diffusion, retention) through the geological barrier (Boom Clay) is of paramount importance. The migration behaviour of selenium strongly depends on its speciation. Under reducing conditions, selenide would be the dominant species and selenium migration would mainly be controlled by the low solubility of Se(−II)-bearing minerals. However Se species are often found in redox disequilibrium and more oxidized species might also coexist. Therefore, the study of selenate migration requires attention, as it might be the most mobile selenium species in the host rock. Electromigration experiments performed with a ⁷⁵Se-labeled selenate in Boom Clay indicate a high mobility for this species. The apparent diffusion coefficient (D_app) of selenate in Boom Clay is estimated from electromigration experiments performed under different electric fields. Using two independent approaches, the value of D_app for selenate is shown to fall in the range from 1.7×10⁻¹¹ to 6.2×10⁻¹¹ m² s⁻¹. Moreover, no reduction of selenate in Boom Clay was observed.     

Gum rosin (colophony): A suitable material for thermomechanical modelling of the lithosphere

We investigate the use of a ductile material with temperature-sensitive viscosity for thermomechanical modelling of the lithosphere. First, we consider the scaling of mechanical and thermal properties. For a normal field of gravity, the balance of stresses and body forces sets the stress scale, in proportion to the linear dimensions and the densities. The equation of thermal conduction sets the time scale. The activation enthalpy for creep sets the temperature scale; but the thermal expansivity provides an additional constraint on this temperature scale.

Gum rosin appears to be a suitable material for lithospheric modelling. We have measured its flow properties, at various temperatures, in a specially designed rotary viscometer with unusually low machine friction. The rosin is almost Newtonian. Strain rate depends upon stress to the power n, where 1.0 <n < 1.14. The viscosity varies over 5 orders of magnitude, from about 10² Pa s at 80°C, to about 10⁷ Pa s at 40°C. The activation enthalphy is thus about 250 kJ/mol. Measured with a needle probe, the thermal conductivity is 0.113 ± 0.001 W m⁻¹K⁻¹; the thermal diffusivity, (6±3) ×10⁻⁷ m² s⁻¹. Calculated from X-ray profiles, the thermal expansivity is about 3 × 10⁻⁴ K⁻¹. These thermal and mechanical properties make gum rosin suitable for thermomechanical models, where linear dimensions scale down by a factor of 10⁶; time, by 10¹¹; viscosity, by 10¹⁷; and temperature change, by 10¹.     

Application of in situ-produced cosmogenic Be and Al to the study of lateritic soil development in tropical forest: theory and examples from Cameroon and Gabon

Depth profiles of in situ-produced cosmogenic nuclides, including ¹⁰Be (T_1/2=1.5×10⁶ years) and ²⁶Al (T_1/20.73×10⁶ years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests.     

Geochemical constraints on the origin of Mesozoic alkaline intrusive complexes from the North China Craton and tectonic implications

Mesozoic alkaline intrusive complexes are widespread in the southern portion of the North China Craton and can provide some important constraints on the evolution of the Mesozoic lithosphere beneath the region. Three selected intrusive complexes (Tongshi, Hongshan, and Longbaoshan) are generally high in alkalis (K₂O+Na₂O=913 wt.%) and Al₂O₃ (1421.6 wt.%) and low in CaO and TiO₂ (<0.6 wt.%), with high and variable SiO₂ contents. Rocks from these complexes are all enriched in LREE and LILE (Cs, Rb, Ba, U, Th), depleted in Nb and Ti, have a highly positive Pb anomaly, and are characterized by lack of a clear Eu anomaly despite trace element abundances and isotopic ratios that vary greatly between complexes. The Tongshi complex has high Cs (2.68.5 ppm) and REE abundances (∑REE=112.6297 ppm, (La/Yb)_N=13.130.9) and MORB-like Sr–Nd–Pb isotopic ratios ((⁸⁷Sr/⁸⁶Sr)_i<0.704; ε_Nd>0; (²⁰⁶Pb/²⁰⁴Pb)_i>18). The Hongshan complex has low REE concentrations (∑REE=28.2118.7 ppm, (La/Yb)_N=4.614.7) and is moderately enriched as demonstrated by their Sr–Nd isotopic ratios ((⁸⁷Sr/⁸⁶Sr)_i>0.706; ε_Nd<−7). The Longbaoshan complex is extremely REE enriched (∑REE=211.3392.6 ppm, (La/Yb)_N=32.460.9) and has an EM2-like Sr–Nd isotopic character ((⁸⁷Sr/⁸⁶Sr)_i>0.7078; ε_Nd<−11). We suggest that the Tongshi complex originated from the asthenosphere and the Hongshan complex and the Longbaoshan complex were derived from the partial melting of previously subduction-modified lithospheric mantle, in response to post-collisional lithospheric extension and asthenospheric upwelling. The occurrence of these alkaline intrusive complexes demonstrates that the lithosphere beneath the region must have been considerably thinned at the time of intrusion of these complexes. This study also shed light on the temporal evolution of the Mesozoic lithosphere and the timing of the lithospheric thinning.     

Terrestrial Kr-Kr ages of Antarctic meteorites

The production rate of ³⁸Ar in meteorites—P(38)—has been determined, as a function of the sample's chemical composition, from ⁸¹Kr-Kr exposure ages of four eucrite falls. The cosmogenic ⁷⁸Kr/⁸³Kr ratio is used to estimate the shielding dependence of P(38).

From the “true” ³⁸Ar exposure ages and the apparent ⁸¹Kr-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 3 × 10⁵ a (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017 and A81009) have within the limits of error the same exposure age (15.2 × 10⁶ a) and the same terrestrial age (1.1 × 10⁵ a). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case are the Elephant Moraine polymict eucrites A79005, A79006 and 82600 with an exposure age of 26 × 10⁶ a and a terrestrial age of 1.8 × 10⁵ a. EETA79004 may be different from this group because its exposure age and terrestrial age are 21 × 10⁶ a and 2.5 × 10⁵ a, respectively.

The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: Directly deposited falls and meteorites transported to the Allan Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering “half-life” is about 1.6 × 10⁵ a. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.     

Magma–host interactions during differentiation and emplacement of a shallow-level, zoned granitic pluton (Tarçouate pluton, Morocco): implications for magma emplacement

The Tarçouate pluton (Anti-Atlas, Morocco) is an inversely zoned laccolith emplaced 583 Ma ago into low-grade metasediments, with the following succession: leucocratic granites, biotite–granodiorites (±monzodiorites), hornblende–granodiorites (±monzodiorites) and monzodiorites syn-plutonic dykes. These rocks form two distinct, chemically coherent, units:

(1) A main unit consists of layered (572<59 wt.%) and homogeneous (632<67%) hornblende–granodiorites, biotite–granodiorites (672<72%) and aplites (702<76%). All these rocks are metaluminous to peraluminous and display fractionated HREE depleted patterns (La/Yb_N=14–61; Yb_N=0.7–6.8). Initial ⁸⁷Sr/⁸⁶Sr ratios (0.7072 to 0.7080) increase, whereas _Nd(t) values (−1.7 to −2.8) decrease from the hornblende– to the biotite–granodiorites. Monzodiorites occur as mafic microgranular enclaves or syn-plutonic dykes.

(2) A subordinate unit consists of leucocratic, distinctly peraluminous, muscovite-bearing granites (722<75%) occurring at the northern edge of the pluton and as dykes in the surrounding schists towards the top of the pluton. These rocks are free of monzodioritic enclaves. They display less fractionated patterns with higher HREE contents (La/Yb_N=2–19; Yb_N=11–18), a distinct _Nd(t) value (−11.8) and a ⁸⁷Sr/⁸⁶Sr initial ratio (0.7480) within those of the surrounding schists (0.7393–0.7819).

Magma–host interactions are closely related to differentiation and occurred at different levels, but mainly before emplacement. Field relationships and petrogenetic modelling show that the bt–granodiorites formed at levels deeper than the level of emplacement, by fractional crystallisation (0.65

These data preclude any significant material transfer process for the emplacement of the Tarçouate pluton, but rather suggest assembly of successive pulses of variably differentiated crystal-poor magmas. These shallow level granitic plutons can be considered as an end-member of magma emplacement with minimum interactions with the country rocks.     

High-resolution methane profiles across anoxic brine–seawater boundaries in the Atlantis-II, Discovery, and Kebrit Deeps (Red Sea)

A decrease in temperature (ΔT up to 45.5 °C) and chloride concentration (ΔCl up to 4.65 mol/l) characterises the brine–seawater boundary in the Atlantis-II, Discovery, and Kebrit Deeps of the Red Sea, where redox conditions change from anoxic to oxic over a boundary layer several meters thick. High-resolution (100 cm) profiles of the methane concentration, stable carbon isotope ratio of methane, and redox-sensitive tracers (O₂, Mn⁴⁺/Mn²⁺, Fe³⁺/Fe²⁺, and SO₄²⁻) were measured across the brine–seawater boundary layer to investigate methane fluxes and secondary methane oxidation processes.

Substantial amounts of thermogenic hydrocarbons are found in the deep brines (mostly methane, with a maximum concentration up to 4.8×10⁵ nmol/l), and steep methane concentration gradients mainly controlled by diffusive flow characterize the brine–seawater boundary (maximum of 2×10⁵ nmol/l/m in Kebrit Deep). However, locally the actual methane concentration profiles deviate from theoretical diffusion-controlled concentration profiles and extremely positive δ¹³C–CH₄ values can be found (up to +49‰ PDB in the Discovery Deep). Both, the actual CH₄ concentration profiles and the carbon-13 enrichment in the residual CH₄ of the Atlantis-II and Discovery Deeps indicate consumption (oxidation) of ¹²C-rich CH₄ under suboxic conditions (probably utilizing readily available—up to 2000 μmol/l—Mn(IV)-oxihydroxides as electron acceptor). Thus, a combined diffusion–oxidation model was used to calculate methane fluxes of 0.3–393 kg/year across the brine–seawater boundary layer. Assuming steady-state conditions, this slow loss of methane from the brines into the Red Sea bottom water reflects a low thermogenic hydrocarbon input into the deep brines.     

皋兰山红黏土-黄土记录的上新世-更新世转型期C3/C4植被演化

上新世-更新世转型是上新世温暖气候向更新世冰期-间冰期旋回过渡的重要时段,与此同时,青藏高原的强烈隆升也深刻改变了高原及周边地区的地貌格局和生态环境面貌。因此,开展青藏高原东北缘地区上新世-更新世转型期的古气候变化研究是理解地球各圈层相互作用的重要切入点。而兰州盆地地处中国三大自然区的衔接位置,对气候变化和构造活动响应较为敏感,是探讨构造-气候-生态相互作用的理想区域。以兰州皋兰山红黏土-黄土岩芯为研究对象,在已有黄土高精度磁性地层年代学基础上,综合开展了有机碳同位素和长链正构烷烃碳同位素分析,重建了西部黄土高原上新世-更新世转型期（3.0~2.2 Ma）的C₃/C₄植被相对丰度演化历史。结果表明：皋兰山上新世-更新世转型期风成沉积中正构烷烃多以C₃₁为主峰的单峰模式,可能指示了草本植被的主要贡献。而典型黄土层位（L32和L33）的正构烷烃多呈现微生物降解的双鼓包模式,表明饱和烃受外源输入影响。综合对比常规指标、总有机碳和长链正构烷烃碳同位素后认为,皋兰山底部黄土的总有机碳同位素不能直接用于重建区域C₃/C₄植被演化。长链正构烷烃碳同位素研究表明：在3.0~2.2 Ma时期,皋兰山古生态整体以C₃植被为主;C₄植被扩张发生在3.0 Ma之前,3.0~2.9 Ma发生C₄植被快速减少事件,初步推测这可能与降温有关。     

Marginal mafic intrusions as indicators of downslope draining of dense residual melts in anorthositic diapirs?

Geochemical and isotopic investigation of three small mafic intrusions (Løyning: 1250 × 150 m, Hogstad: 2000 × 200 m, Koldal: 1250 × 500 m) in the marginal zones of the Egersund-Ogna (Løyning, Koldal) and Åna-Sira massif-type anorthosites (Hogstad) (Rogaland Anorthositic Province, south Norway: 930 Ma) provides new insights into the late evolution of anorthositic diapirs. These layered mafic intrusions are essentially of norite, gabbronorite as well as leuconorite and display conspicuous evidence of subsolidus recrystallization. In Løyning and Hogstad, the modal layering is parallel to the subvertical foliation in the enclosing anorthosite. The northern part of the Koldal intrusion cuts across the foliation of the anorthosite, whereas in its southern part the subvertical layering is parallel to the anorthosite's foliation. The regularity of the layered structures suggests that the layering was initially acquired horizontally and later tilted during the final movements of the diapirs.

The least differentiated compositions of plagioclase and orthopyroxene in the three intrusions (An₅₉–En₆₈ in Løyning, An₄₉–En₆₄ in Hogstad and An₄₄–En₆₁ in Koldal) and the REE contents in apatite (Hogstad) indicate that their parent magmas were progressively more differentiated in the sequence Løyning–Hogstad–Koldal. Isotopic data (Løyning: ⁸⁷Sr/⁸⁶Sr: 0.70376–0.70457, ε_Ndt: + 6.8 to + 2.7; Hogstad: ⁸⁷Sr/⁸⁶Sr: 0.70537–0.70588, ε_Ndt: + 2.1 to − 0.5; Koldal: ⁸⁷Sr/⁸⁶Sr: 0.70659–0.70911, ε_Ndt: + 3.5 to − 1.6) also indicate that in this sequence, parent magmas were characterized by a progressively more enriched Sr and Nd isotopic signature. In Løyning, the parent magma was slightly more magnesian and anorthitic than a primitive jotunite; in Hogstad, it is a primitive jotunite; and, in Koldal, an evolved jotunite. Given that plagioclase and orthopyroxene of the three intrusions display more differentiated compositions than the orthopyroxene and plagioclase megacryts of the enclosing anorthosites, it is suggested that the parent magmas of the small intrusions are residual melts after anorthosite formation which were entrained in the anorthositic diapir during its rise from lower crustal chambers.

Calculated densities of primitive jotunites (2.73–2.74 at FMQ, 0.15% H₂O, 200 ppm CO₂, 435 ppm F, 1150 °C, 3 kb) and evolved jotunites (2.75–2.76 at FMQ, 0.30% H₂O, 400 ppm CO₂, 870 ppm F, 1135 °C, 3 kb) demonstrate that they are much denser than the plagioclase of the surrounding anorthositic crystal mush (2.61–2.65). Efficient migration and draining of dense residual melts through the anorthositic crystal mush could have taken place along sloping floors (zones of lesser permeability in the mush), which occur along the margins of the rising anorthositic diapirs. This process takes into account the restricted occurrence of the mafic intrusions in the margins of the massif anorthosites. In a later stage, when the anorthosite was nearly consolidated, the residual melts were more differentiated (evolved jotunites) and could have been extracted into extensional fractures in the cooling and contracting anorthositic body in a similar way as aplitic dikes are emplaced in granitic plutons. As in the Rogaland Anorthositic Province, these dikes are much more abundant than the small mafic intrusions, collection and transport along dikes was probably more efficient than draining through the crystal mush.     

Seismic activity along the central america volcanic arc: is it related to subduction of the Cocos plate?

We determine seismic strain rate of tectonic earthquakes along the Central America Volcanic Arc. We then compare this result to those obtained from earthquakes related to the convergence of the Cocos and Caribbean plates and to earthquakes in the back-arc region of northern Central America.

The seismic strain-rate tensor for shallow-focus earthquakes along the Central America volcanic arc since 1700, has a compressive eigenvector with a magnitude of 0.7 × 10⁻⁸ year⁻¹, and oriented in a 357° azimuth. The extensive eigenvector is oriented in a 86° azimuth, with a magnitude of 0.82 × 10⁻⁸ year⁻¹. When only Centroid Moment-tensor solutions (CMT) are considered, the respective eigenvectors are 1.2 × 10⁻⁸ year⁻¹ and 1.0 × 10⁻⁸ year⁻¹.

The compressive eigenvector from the seismic strain-rate tensor for earthquakes along the Cocos-Caribbean convergent margin is 2.0 × 10⁻⁸ year⁻¹, plunging at 25°, and oriented in a 29° azimuth. Its magnitude and direction are similar to those of the compressive eigenvector for earthquakes along the volcanic arc. The extensive eigenvector along the convergent margin, on the other hand, has a large vertical component. The compressive and extensive eigevenvectors are 4.9 × 10⁻⁸ year⁻¹ and 4.6 × 10⁻⁸ year⁻¹, using only CMTs as the database.

Earthquakes along the grabens of northern Central America yield a seismic strain-rate tensor whose extensive eigenvector has a magnitude of 2.4 × 10⁻⁸ year⁻¹, oriented in a 109° azimuth. Magnitude and direction are similar to those of the extensive eigenvector for earthquakes along the volcanic arc. The compressive eigenvector along the grabens is practically vertical.

Similarities in magnitudes and directions for compressive and extensive eigenvectors suggest to us that the strain field along the Central America volcanic arc is the result of compression along the convergent Cocos-Caribbean margin, and extension in the back-arc region, along the grabens of northern Central America. This field is resolved as strike-slip faulting along the arc.     

水驱对原油饱和烃馏分影响的分子地球化学表征

利用GC、GC/MS分析技术,对水驱开发的曲9油藏进行了原油饱和烃馏分的动态变化对比。研究表明,随着水驱推进,在9个多月的动态监测中,原油饱和烃馏份表现出明显的变化规律,逐渐升高的有饱和烃相对含量、C₁₅-RD/C₁₅-D、C₁₅8β（H）-D/C₁₆8β（H）-HD、TTs/17α-H、RS/17α-H等比值;逐渐降低的有芳烃相对含量、轻重比参数∑nC_21-/∑nC₂₂₊、∑nC_14-/∑nC₁₅₊;基本保持稳定不变的有异构烷烃比值Pr/Ph、iC₁₈/Pr、iC₁₈/Ph,萜烷比值C₂₁/C₂₂TT、C₂₄/C₂₃TT、∑C_19-26/∑C_28-29TTs、C₃₀*/C₂₉Ts、C₃₅R/C₃₄R、Ol/C₃₀H、G/C₃₁R、C₃₁22S/（22S+22R）、C₃₀M/C₃₀H、Ts/（Ts+Tm）、C₂₉Ts/（C₂₉Ts+C₂₉H）,甾烷比值C₂₇-DS/C₂₇-RS、C₂₉20S/（20S+20R）、C₂₉ββ/（ββ+αα）、C₂₇-重排甾烷20S/（20S+20R）等;先升高再降低,或先降低再升高的分异变化的有Pr/nC₁₇和Ph/nC₁₈。水洗作用造成芳烃相对含量与轻重比的降低,生物降解作用引起了三环萜烷与规则甾烷相对藿烷的富集,二者虽然对相近碳数的异构烷烃、萜烷、甾烷比值影响甚微,却合力促使了补身烷参数的升高。注水过程中的色层效应进一步导致了饱和烃馏分的分异。     

Comprehensive chemical analyses of natural cordierites: implications for exchange mechanisms

Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H₂O and CO₂ (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg₋₁ and MnMg₋₁ on the octahedral site, some minor KNa₋₁ on the Ch0 channel site, and Fe³⁺Al₋₁ on the T₁1 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□₋₁Mg₋₁), and of Be and other divalent cations on the tetrahedral T₁1 site (NaBe□₋₁Al₋₁ and Na(Mg,Fe²⁺)□₋₁Al₋₁). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: ^Ch(Na,K)_0–1 ^VI(Mg,Fe²⁺,Mn,Li)₂ ^IVSi₅ ^IVAl₃ ^IV(Al, Be, Mg, Fe²⁺, Fe³⁺)O₁₈ *x^Ch(H₂O, CO₂…). Our results show that the population of (Mg, Fe²⁺) on the T₁1-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M²⁺–Na.     

Crustal structure of the Balearic sea

Within the frame of the German-French project ANNA-1970, two long refraction profiles were investigated north and south of the island of Majorca.

For the southern Balearic Basin an oceanic crust can be derived from the travel-time curves consisting of a 4.0 km thick Cenozoic sedimentary layer with: V_p = 2.35 (km/sec) + 0.35 (sec⁻¹) × Z (km) and a 5 km thick layer with: V_p = 4.0 (km/sec) + 0.28 (sec⁻¹) × Z (km)

The transition to the upper mantle takes place at a depth of 12 km. Directly south of Majorca a crustal thickening was measured which may be caused by the process of crustal shortening. P]In the northern Balearic Basin a faulted transitional type of crust has been observed indicating probably an embryonic and juvenile ocean expansion.     

盐湖相低熟油脂肪酸的组成与分布特征

对泌阳凹陷碱性盐湖相、舞阳凹陷盐湖相、襄城凹陷膏盐湖相、南阳凹陷淡水湖相低熟油脂肪酸组成和分布特征进行了分析与研究。结果表明这些不同盐湖相的低熟原油的脂肪酸为丰度不同的饱和正构酸、不饱和正构酸、少量异构酸、类异戊二烯酸及脂肪酸乙酯系列化合物。脂肪酸的组成和分布反映了原始有机质的来源。     

天津平原区浅层地下水水化学特征及碳酸盐风化碳汇研究

大气 CO₂浓度在控制全球气候变化方面具有至关重要的作用,研究碳循环、CO₂收支平衡和精确评估是制定区域CO₂减排策略和寻找新的碳汇途径最重要的组成部分。碳酸盐风化碳汇是全球碳循环研究的一个重要方向。为此,本研究以天津平原区浅层地下水为研究对象,通过对地下水调查及水样的采集与分析,运用水化学分析方法分析了地下水水化学特征,并估算了地下水总储存量、DIC储量和碳酸盐风化碳汇量。研究结果表明:浅层地下水化学场自北部山前平原向南部冲积平原和滨海平原,呈现出自北而南和由北西向南东的水平水化学分带规律,地下水由低浓度的淡水、微咸水变为高浓度咸水,沿此方向水化学类型由HCO₃-Ca·Na·Mg→Cl·SO₄-Na→Cl·HCO₃-Na→Cl-Na型转变;淡水区、微咸水区和咸水区面积分别为733、3 034和6 564 km²。地下水水化学组分中Ca²⁺、Mg²⁺和 {\mathrm{HCO}}_3^{-}主要来源于碳酸盐的溶解作用。研究区浅层地下水总储存量为2 241 640万m³,总DIC储量为8.13×10⁶ t,总碳汇量为4.11×10⁶ t。研究区浅层地下水淡水区、微咸水区和咸水区地下水储存量分别为157 799万、6 245 936万和1 459 247万 m³,DIC浓度分别为19200、19200和19342 mg/L,DIC储量分别为0.67×10⁶、1.65×10⁶和0.58×10⁶ t,碳汇量分别为0.22×10⁶、0.90×10⁶和2.98×10⁶ t。沿地下水流向,DIC、储量和碳汇量的空间分布均呈现出由低到高的趋势。     

Hydrothermal gases offshore Milos Island, Greece

Hydrothermal fluids emerge from the seafloor of Paleohori Bay on Milos. The gases in these fluids contain mostly CO₂ but CH₄ concentrations up to 2% are present. The stable carbon isotopic composition of the CO₂ (near 0%) indicates an inorganic carbon source (dissociation of underlying marine carbonates). The carbon and hydrogen isotopes of most CH₄ samples are enriched in the heavy species (δ¹³C = −9.4 to −17.8‰; δD = −102 to −189‰) which is believed to be characteristic for an abiogenic production of CH₄ by CO₂-reduction (Fischer-Tropsch reactions). Depletions in the deuterium content of three CH₄ samples (to −377%) are probably caused by unknown subsurface rock alteration processes. Secondary hydrogen isotope exchange processes between methane, hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures.

We show that excess helium, slightly enriched in ³He, is present in the hydrothermal fluids emerging the seafloor of Paleohori Bay. When the isotopic ratio of the excess component is calculated a ³He/⁴He_excess of 3.6 · 10⁻⁶ is obtained: This indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium. We infer that the mantle-derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface.     

Determining mineral weathering rates based on solid and solute weathering gradients and velocities: application to biotite weathering in saprolites

Chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths. An increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change. The solid-state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration. These relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients. Contemporary weathering rates based on solute residence times can be directly compared to long-term past weathering based on changes in regolith composition. Both rates incorporate identical parameters describing mineral abundance, stoichiometry, and surface area.

Weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the Piedmont of Northern Georgia, USA and in Luquillo Mountains of Puerto Rico. Solid-state weathering gradients for Mg and K at Panola produced reaction rates of 3 to 6×10⁻¹⁷ mol m⁻² s⁻¹ for biotite. Faster weathering rates of 1.8 to 3.6×10⁻¹⁶ mol m⁻² s⁻¹ are calculated based on Mg and K pore water gradients in the Rio Icacos regolith. The relative rates are in agreement with a warmer and wetter tropical climate in Puerto Rico. Both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering.     

Effect of Fe on garnet–melt trace element partitioning: experiments in FCMAS and quantification of crystal-chemical controls in natural systems

Garnet–melt trace element partitioning experiments were performed in the system FeO–CaO–MgO–Al₂O₃–SiO₂ (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe²⁺ content on partition coefficients (D^Grt/Melt). D^Grt/Melt, measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal–melt partition coefficients from elastic moduli. Nature 372, 452–454], which describes partitioning of an element i with radius r_i and valency Z in terms of three parameters: the effective radius of the site r₀(Z), the strain-free partition coefficient D₀(Z) for a cation with radius r₀(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus E_X(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838–847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r₀(3+) and E_X(3+) as a function of garnet composition (X) and pressure (P):

r₀(3+) [Å]=0.930X_Py+0.993X_Gr+0.916X_Alm+0.946X_Spes+1.05(X_And+X_Uv)−0.005(P [GPa]−3.0)(±0.005 Å)

E_X(3+) [GPa]=3.5×10¹²(1.38+r₀(3+) [Å])^−26.7(±30 GPa)

Accuracy of these equations is shown by application to the existing garnet–melt partitioning database, covering a wide range of P and T conditions (1.8 GPa<P<5.0 GPa; 975°C<T<1640°C). D^Grt/Melt for all 3+ elements entering the X-site (REE, Sc and Y) are predicted to within 10–40% at given P, T, and X, when D^Grt/Melt for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. D_Sm^Grt/Melt/D_Nd^Grt/Melt) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r₀(3+) for garnets ranges from 0.939±0.005 to 0.953±0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet–melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting D^Grt/Melt for these elements as a function of P, T and X.     

Strontium diffusion in sanidine and albite, and general comments on strontium diffusion in alkali feldspars

Strontium chemical diffusion has been measured in albite and sanidine under dry, 1 atm, and QFM buffered conditions. Strontium oxide-aluminosilicate powdered sources were used to introduce the diffusant and Rutherford Backscattering Spectroscopy (RBS) used to measure diffusion profiles. For the 1 atm experiments, the following Arrhenius relations were obtained:

Sanidine (Or₆₁), temperature range 725–1075°C, diffusion normal to (001): D=8.4 exp(−450±13 kJ mol⁻¹/RT) m²s⁻¹. Albite (Or₁), temperature range 675–1025°C, diffusion normal to (001): D=2.9 × exp(−224±11 kJ mol⁻¹/RT) m²s⁻¹.

The alkali feldspars in this and earlier work display a broad range of activation energies for Sr diffusion, which may be a consequence of the thermodynamic non-ideality of the alkali feldspar system and/or the mixed alkali effect.