Geophysical and geological data from the North Mozambique Channel acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago. Here we identify and describe two major submarine tectono-volcanic fields: the N’Droundé province oriented N160°E north of Grande-Comore Island, and the Mwezi province oriented N130°E north of Anjouan and Mayotte Islands. The presence of popping basaltic rocks sampled in the Mwezi province suggests post-Pleistocene volcanic activity. The geometry and distribution of recent structures observed on the seafloor are consistent with a current regional dextral transtensional context. Their orientations change progressively from west to east (∼N160°E, ∼N130°E, ∼EW). The volcanism in the western part appears to be influenced by the pre-existing structural fabric of the Mesozoic crust. The 200 km-wide and 600 km-long tectono-volcanic corridor underlines the incipient Somalia–Lwandle dextral lithospheric plate boundary between the East-African Rift System and Madagascar. Supplementary Materials: Supplementary material for this article is supplied as a separate file: crgeos-159-suppl.pdf Des données géophysiques et géologiques ont été acquises lors de la campagne océanographique SISMAORE (2020–2021). Deux grands champs tectono-volcaniques sous-marins ont été découverts tout le long et principalement au nord de l’archipel des Comores : la province N’Droundé orientée N160°E au nord de Grande-Comore, et la province Mwezi orientée N130°E au nord d’Anjouan-Mayotte où des roches basaltiques de type popping-rocks suggèrent une activité volcanique possiblement actuelle à pléistocène. La géométrie et la distribution des structures récentes sont cohérentes avec un contexte régional actuel transtensif dextre. Leurs orientations évoluent d’Ouest en Est (∼N160°E, ∼N130°E, ∼EW), suggérant pour la partie occidentale, une mise en place du volcanisme influencée par la structuration crustale préexistante. Le corridor tectono-volcanique de 200 km de large et de 600 km de long dessine une limite de plaque lithosphérique Somalie-Lwandle immature en décrochante dextre entre le système du rift est-africain et Madagascar. Compléments : Des compléments sont fournis pour cet article dans le fichier séparé : crgeos-159-suppl.pdf

Geophysical and geological data from the North Mozambique Channel acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago. Here we identify and describe two major submarine tectono-volcanic fields: the N’Droundé province oriented N160°E north of Grande-Comore Island, and the Mwezi province oriented N130°E north of Anjouan and Mayotte Islands. The presence of popping basaltic rocks sampled in the Mwezi province suggests post-Pleistocene volcanic activity. The geometry and distribution of recent structures observed on the seafloor are consistent with a current regional dextral transtensional context. Their orientations change progressively from west to east (${\sim }$N160°E, ${\sim }$N130°E, ${\sim }$EW). The volcanism in the western part appears to be influenced by the pre-existing structural fabric of the Mesozoic crust. The 200 km-wide and 600 km-long tectono-volcanic corridor underlines the incipient Somalia–Lwandle dextral lithospheric plate boundary between the East-African Rift System and Madagascar.

Natural organic matter (NOM) is known to play an important role in the transport and binding of trace metal elements in aquatic and soil systems. Thallium is a pollutant for which the extent of the role played by NOM is poorly known. Consequently, this study investigates thallium(I) and its complexation to a purified humic substance as proxy for NOM. Experiments were performed with the Donnan Membrane Technique to separate, for the first time, the free Tl+ ion from its complexed form in the bulk solution. Various pH and concentrations were investigated at constant ionic strength and constant NOM proxy concentrations in solution. Experimental results were described with NICA-Donnan model. Thallium complexation was compared to silver complexation using literature data and using the same NICA-Donnan formalism. Parameters for these two cations (Tl+ and Ag+) are reported in this article, for the first time. Results display low thallium complexation to the NOM proxy while silver competes with divalent cations for the NOM binding sites. Calculated speciation for dissolved thallium highlights the dominance of free thallium (Tl+) in solution whereas Tl-NOM complexes contribute roughly 15% to total Tl(I) species in river and lake type waters. Similar results are obtained for soil solutions, Tl-bound to NOM < 30% of total, from UK soils with different land use and geochemistry.

Geothermal exploration of the Martinique Island (Lesser Antilles) focused, at first (1960-1980 years), on the Lamentin lowlands and on the Southern flank of the Mount Pelee volcano. In 2003, a new step was done with the identification of two areas of interest: the SW side of Mount Pelee dome and the surroundings of the Petite Anse - Diamant hot springs (Sanjuan et al., 2003). The 2012-2013 additional and combined - geological, hydrogeological, geochemical, geophysical - surface exploration results in a new insight of the Martinique geothermal systems, including Mount Pelee volcano, Petite Anse - Diamant area, Pitons du Carbet domes and Lamentin lowlands. High temperature geothermal systems are supposed to be active at both the former sites whereas only signs of medium to low temperature were detected at the Lamentin and Pitons du Carbet areas.

This is the first multidisciplinary study on the critical zone of the French volcanic island of Mayotte to address chemical weathering rates. Here we present the first estimation of chemical weathering rates using element fluxes transported in surface and subsurface waters, ranging from 49 to 306 t/km2/yr for rivers and 113 to 1,382 t/km2/yr for groundwater. These results are consistent with the weathering pattern of other tropical volcanic islands and support the hypothesis that subsurface waters transport more solutes to the ocean than surface waters. In addition, a helicopter-borne resistivity survey was correlated to borehole geological data to understand the hydrogeological functioning of the “deep critical zone”.

Guadeloupe, Martinique and Dominica islands, like numerous tropical environments, have extreme weathering regimes. Physical denudation is mainly controlled by landslides, which reflect the torrential dynamics of the rivers. In Guadeloupe, the mechanical weathering rates vary between 800 and 4000 t/km(2)/yr. The lithology is very porous with high infiltration rates, which suggests that most of the element fluxes are produced in the subsurface, with chemical erosion rates 2-5 times higher than the rates from surface water. We show how the kinetics of chemical weathering rates depend on the age of the lava and subsurface circulation. In addition, erosion timescales were calculated from U-series analyses of river sediments. Our results show a broad range: 0-150 ka in Martinique and 0-60 ka in Guadeloupe. We evaluated residence times in river water on the basis of the dissolved load analyses. It appears that water circulation is globally 3-fold longer for subsurface water than for surficial water (Rad et al. 2011a,b). Moreover, these islands are highly impacted by agriculture. However, contrary to what one might think, our results show that human activity does not disturb critical zone processes. Indeed, we show that among the combined impacts of all parameters (climate, runoff, slope, vegetation, etc.), the basin's age seems to be the control parameter for chemical weathering and land use the younger the basin, the higher the weathering rates. We could observe a combined effect between the higher erodibility and a higher climate erosivity of the younger reliefs. (C) 2013 Elsevier Ltd. All rights reserved.

ABSTRACTIn this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO2) involved in the neutralization reactions during water–rock interactions. The δ13C data span a large range of variations, from –19‰ to –5 · 2‰ for DIC (dissolved inorganic carbon) concentrations ranging from 11 μM to 2000 μM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO2 (enriched in heavy carbon (δ13C ≈ –3 · 5‰) and biogenic CO2 produced in soils (enriched in light carbon (δ13C < –17‰)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO2 consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first‐order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO2, either under hydrothermal (hot) or surficial (cold) weathering regimes.This study shows that the contribution of magmatic CO2 to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO2 to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone. Copyright © 2013 John Wiley & Sons, Ltd.

The Allier River is an important tributary of the Loire River, one of the major rivers in France. The Allier River presents both a natural environment upstream and a zone deeply impacted by mines and human activities. The δ13C and δ7Li combination show that the Allier River DIC is due to mixing of carbon from organic decay produced in a natural environment upstream, progressively enriched in DIC of anthropogenic origin downstream, and magmatic carbon inputs often associated with hydrothermal contributions.

Water-rock interactions produced in river catchment are accompanied by fractionation or changes in stable isotopes such as H, Li, C and O during chemical weathering processes. Li is a fluid-mobile element that tends to preferentially partition into the fluid phase during water-rock interaction. The relative mass difference between the two isotopes is considerable, generating large mass dependent fractionation during chemical weathering processes. The CO2 dissolves into the water providing the main acid that attack the rock during chemical weathering. Carbon stable isotopes and concentration of Dissolved Inorganic Carbon (DIC) in the river catchment can be used to determine the origin and consumption rates of CO2. In the present work, stable isotopes were analyzed in Allier River, one of the major river basins of France. The lithology is dominated by granite rocks within current upstream, while it is mainly basaltic and Oligocene sediments in the downstream with hydrothermal manifestations. We propose a new isotopic approach by combining δ7Li and δ13CDIC analyses in river catchment waters. A first method has been applied to volcanic tropical environments with Li concentrations correlated to δ13CDIC (Rad et al., 2011). Here, we have completed this approach by lithium isotopes. Water samples were collected during several field trips. Our results show a large variation in Li isotopes and C isotopes within the catchment from 3.3 ‰ to 30.3 ‰ and from -17.9‰ to -3.5‰, respectively. Chemical weathering rates linearly increase from upstream to downstream over 400km distance, whereas Li isotope signatures decrease and global C signature increases. This is due to low water-rock interaction dominated in upstream, whereas the downstream is punctually impacted by hydrothermalism. From Li and C isotopes, our results show 4 groups reflecting different chemical weathering processes: the first group with high fractionation of Li and C, for Li, the heavy lithium partitioned into surface waters, leaving lighter lithium behind in the weathered products, the signature of C is mainly due to organic matter or partially due to biochemical interaction with assimilation of CO2 by microorganism. The second group involves atmospheric equilibrium with CO2 degassing with organic origin or cold CO2 degassing with important fraction of Li. The third group present high fractionation of C, reflecting presence of superficial C with organic origin, with low fractionation of Li underling the hydrothermalism impact. Finally a fourth group with low fractionation mainly due to high temperature water-rock interaction. Therefore, the combination of the two tracers, Li and C isotopes, offers a powerful tool to discriminate chemical weathering processes from sources of alteration during water-rock interactions under multi-lithology terrains.

We report in this paper the results of a multidisciplinary project aiming at determining the rates of chemical and physical denudation in the Lesser Antilles and the carbon fluxes exported to the ocean in a volcanic arc setting (Guadeloupe, Martinique, Dominica). Chemical denudation rates, determined by using river dissolved load range from 30 to 600 t/km2/yr, are extremely variable as a result of highly variable runoff and of the variable input of groundwaters influenced by volcanic acids [1], [2]. Physical denudation was estimated using different methods. Temporal monitoring of selected watershed gives a first estimate over a relatively short observation period. Based on the chemistry of the bottom sands transported in rivers, we calculated the physical denudation rates expected for a weathering system at steady state by solving a mass budget between source rocks and erosion products. Results show that the volcanic relief of Guadeloupe is eroding both chemically and physically at rates ranging between 100 mm/kr and more than 1000 mm/yr from the northern (and older) part of the Island to the southern (and younger) part respectively. These rates are important at a global scale and show that volcanic arc islands are “hot spots” of chemical and physical denudation on Earth. The denudation of the Lesser Antilles Arc is 2-3 higher that the eruptive rate, or island construction rate, meaning that volcanic arc islands have a limited lifetime (of typically 1 to a couple of million years) at a geological time scale. In addition to be a locus of intense sediment production to the ocean, the Lesser Antilles have a significant role of carbon export to the ocean. In terms of atmospheric carbon sequestration, first results show that the sequestration of organic carbon (in both dissolved and suspended load) may be about the same order of magnitude than inorganic sequestration [3]. Hydrology, and particularly orographic precipitation are proposed to be the main drivers of the weathering and denudation of tropical volcanic islands. Progresses have to be done primarily to establish proper water budgets of volcanic island to separate the effect of surface waters from groundwaters and to monitor over long periods of time the exportation of solids and particulate carbon.

Geothermal exploration of Martinique Island started in 1967 but was interrupted successively at 3 times. Additional geothermal exploration program was conducted by BRGM, in 2001-2003 and recently in areas known for their geothermal interest: Mount Pelee volcano and Diamant. A complementary exploration is now proceed with new sites of interest such as du massif after recent dating (Germa et al., 2011). A conceptual model of reservoir was established for Mount Pelee volcano and on the Piton du Carbet massif, but the extension of these greenfield remains unknown. We propose new approach through geochemistry by the integration to the prospection of chemical compositions of river waters adding to hot springs and well waters. Rivers catchment in Lesser Antilles and their hydrothermal impact have been studied in order to quantify and identify the magmatic contribution into the river (Rad et al., 2011). Chemical analyses and new isotopic tools such as Lithium isotopes 7Li/6Li (expressed as δ7Li) are measured in river waters. Among these multi chemical parameters, isotopic in particular (H, Li, C, O, Sr...) the Li isotopic signature appear to be conservative and allows to identify new target with high temperature water-rock interactions or in case of high fractionation, reflecting low temperature water-rock interactions, to avoid an extended zone. These new technique was applied to the Mount Pelee and confirm the pre-existent model established in previous exploration campaign. For Pitons du Carbet massif all the river catchment of the massif have been sampled, first results show a potential western extension of the reservoir, confirm by an important gas leak of hydrothermal origin. For tropical volcanic environment with sharp relief, dense vegetation, and high precipitation, chemical and isotopic analyses, particularly lithium isotopes, in river waters, allow to identify zone of interest. To conclude, river catchment studies dedicate to geothermal exploration, especially in a context of difficult topography, seems to be a fast method and good indicator of hydrothermal manifestations at large scale before focusing on detail zones.

Les flux de sediments au sein des ensembles continentaux jouent un role majeur dans les cycles biogeochimiques et sont souvent a l'origine de la degradation des sols et de la pollution des eaux et des ecosystemes. Dans un contexte de changement climatique et de changement d'occupation des sols, il semble important de pouvoir quantifier les budgets sedimentaires aux echelles locales et globales afin de mieux apprehender les possibles impacts de ces changements a l'avenir. Beaucoup d'etudes se sont deja interessees aux exports de sediments a l'echelle des grands bassins fluviatiles ou continentaux ou a des echelles plus fines, de la parcelle experimentale a la parcelle culturale. Cependant, peu d'etudes se sont portees sur la connectivite des versants et au sein des masses d'eau les zones de stockage dans le but d'etablir des liens entre les differentes echelles. Dans ce contexte general, l'objectif de cette etude est de quantifier la part de sediments erodes sur les versants qui atteint les oceans et d'evaluer la pertinence de l'utilisation d'un concept tel que le Sediment delivery ratio (Walling, 1983) ou des calculs de flux pour realiser cette tâche. Une premiere etude a permis de mettre en exergue la contribution de la Loire aux exports de France Metropolitaine, aux environs de 1Mt/an (Delmas et al. in press). Il s'agit donc, dans un premier temps, d'estimer les charges annuelles de sediments a l'exutoire de sous-bassins (Figure 1) pour lesquels des donnees debits et matieres en suspensions sont disponibles dans les bases de donnees deja existantes (banque hydro/Osur2-web). Cependant, la faible resolution temporelle des donnees MES constitue une limite et ne permet de calculer des flux que pour une centaine de stations. Cette base de donnees permettra la calibration et la validation de cette approche. Sur cette base des quantites exportees, une typologie des bassins est ensuite proposee. Afin de prendre en compte les mecanismes et processus de redistribution des sediments au sein des versants et des cours d'eau, une approche de modelisation distribuee de la dynamique source-puit est developpee. Plusieurs parametres seront pris en compte tels que la connectivite hydrologique via l'etude de la dynamique ruissellement/infiltration ainsi que la connectivite sedimentaire. Les developpements conceptuels seront d'abord testes sur deux bassins pilotes. Nous montrerons des exemples sur un bassin versant de 80km², la Ligoire, qui a permis de mettre en avant les differentes sources potentielles des sediments exportes (erosion de surface et drains). En parallele, la mise en place de methode de tracage (Cesium 137, matiere organique...) permettra d'apporter un eclairage nouveau sur la provenance des sediments. Delmas M., Cerdan O., Cheviron B., Mouchel J.M, Eyrolle F. in press. Sediment exports of French rivers to the sea. Earth Surface Processes and Landforms. Walling D.E., 1983. The sediment delivery problem. Journal of hydrology 65, 209-237.

The Lesser Antilles have very high chemical weathering rates, with values that can reach 1290 t/km2/a. The tropical environment induces high precipitation rates, high temperature, dense vegetation, with sharp relief and thick soils. Because of volcanic activity, frequent pyroclastic flows produce very erodible and porous materials. In addition, agriculture induces important land use changes which replace existing native forest cover with banana and sugar cane plantations. Their surface can cover as much as 40% of the total area of a river basin. The aim of this study is to identify key parameters, either natural or anthropogenic, that control chemical weathering rates. Among the combined impact of all parameters (climate, runoff, slopes, vegetation etc.), basin age seems to be the control parameter: the younger the basin, the higher the weathering rate. A correlation between the chemical weathering rate and the basin age suggests that young volcanic rocks are more easily weathered than old ones: young fresh material is easily mobilized by erosion, while for older rocks with thick soil covers, chemical rates are much lower. A combined effect between the higher erodibility and a higher climate erosivity of the younger relief could be observed. Moreover, a correlation between banana plantations and the chemical weathering rates that can be explained by an increase of infiltration, due to stem flow processes is shown here. Banana plantations also have a correlation with the basin age, older basins being more favorable terrains for cultivation.

In this paper we present chemical composition data for major elements in rivers from three islands of the Lesser Antilles. The Lesser Antilles are a tropical volcanic subduction arc and are characterized by steep gradients of relief, bedrock age and precipitation. They constitute a natural laboratory where the response of the weathering engine to large variations of runoff can be understood. Data indicate that the Lesser Antilles are characterized by extremely variable chemical weathering (40-430 t/km2/a) and CO2 consumption (300-3500.103 mol/km2/a) rates, amongst the highest found on Earth and consistent with the previous studies on the weathering of volcanic rock. A noteworthy observation is that, along the runoff gradient, concentrations of rock-derived solutes do not follow a pure dilution law and that a buffering mechanism exists stabilizing solute concentrations. As a result concentrations vary much less than runoff and chemical weathering rates are mainly controlled by runoff. Precipitation patterns in the Lesser Antilles are essentially orographic and controlled by the adiabatic decompression of the water-saturated Atlantic air masses. The production of acidity by volcanic degassing is an additional factor that modulates the runoff effect. Two main conclusions can be drawn from this study. First, chemical weathering fluxes of oceanic islands are strongly dependent upon relief repartition, which cautions the use of regional mean values to compare volcanic islands. Second, volcanic activity in the Lesser Antilles subduction arc, by creating relief, promotes high orographic precipitation and/or infiltration regimes, that in turn results in elevated chemical weathering and atmospheric CO2 consumption fluxes. This feedback mechanism, implying mainly precipitation and relief, is proposed to act in complement to the temperature-related feedback proposed by previous authors for stabilizing the atmospheric CO2 content of the atmosphere in response to volcanic CO2 degassing. This study highlights the importance of the water cycle in controlling chemical weathering of volcanic arc islands and associated CO2 consumption rates.

Volcanic islands, being characterized by highly porous basaltic/andesitic lava flows and pyroclastic deposits, are subject to important chemical weathering by subsurface waters. Moreover, such subsurface weathering is impacted by hydrothermal springs in both active and non-active volcanic areas, thus increasing dissolved load concentrations. Here, we focus on the subsurface water chemistry in the volcanic islands of the Lesser Antilles and Réunion and on the origin of these subsurface flows. We are able, through the use of various isotopic tools (C, Sr, U–Th), to identify hydrothermal influences in river water. For example, Li concentrations show a positive correlation with temperature of hot and cold springs and also a relationship with δ 13 C; from this, we can show that several sources of hydrothermal activity influence the rivers of the Lesser Antilles and that some rivers also reveal an important organic influence. As much as 20% of the subsurface hydrothermal springs go to feed the rivers. The increasing temperatures result in more dissolved elements being mobilized and an increase in chemical weathering rates. In addition, using the ( 230 Th/ 238 U) isochron for the well and river dissolved loads in Martinique, Guadeloupe and Réunion, we can evaluate residence times in the river water, i.e. the average residence time in the water along the circulation path to the sampling point. Alteration takes longer when the water circulates through thick soil, for example, 400–5,000 years when circulating under an ash profile and 1,200–15,000 years when circulating through a collapse zone. It would appear that waters circulation is globally three times longer for subsurface water than for surficial water. The weathering regime in tropical volcanic environments seems to be controlled mainly by such subsurface circulation with high chemical concentration from hydrothermal inputs. The origin of these compositions is varied and not controlled by a single hydrothermal spring. Consequently, it is subsurface circulation that determines the weathering regime in tropical volcanic islands with the main controlling parameters being temperature and residence time.

We have re-assessed the Sr isotopic budget of the modern ocean taking into account the high erosion rates of volcanic islands, and especially of island arcs, emphasizing important contribution from subsurface weathering to global budgeting. We propose that intensive weathering on volcanic islands, island arcs and oceanic islands, coupled with large surface and subsurface water fluxes is the missing source of mantle-derived 87Sr/86Sr (0.703) in seawater Sr isotope balance. In our approach, it represents 60% of the actual mantle-like input of Sr to the oceans, the remaining 40% supplied by ridge-crest hydrothermal activity and sea-floor low-temperature alteration of basalts. The seawater Nd isotopic budget is consistent with this interpretation and explains well the regional contributions from ridge crest and island arc activity among the oceans.

Environmental aspects constitute main issues for our modern society in many ways, by the exploitation of natural resources or the development of road infrastructure. Studies of subsurface, called also Regolith, are at the crossroad of new geological point of view. Among wide range of geophysical methods, airborne geophysical tools is a fast method for providing informations about the near surface. Two different methods are been used: spectral radiometry and the time domain electromagnetic (TDEM). Spectral radiometry data were collected throughout “Région Centre” with a line space of 1km. The EM data were collected throughout three local boxes with a line spacing of 0.4 km. The three sites present very different geological and topographical characteristics. We have compared geological map with the two different airborne geophysical data. The three maps are consistent and show the same general structures but smallest structures are different. It appears that a decrease of resistivity a given geological formation is correlated with an increase of rock alteration. Moreover lowest potassium content seems to indicate the areas of accumulation of colluvial deposit. The 3D structure can be study with the TDEM data in regards of the resistivity variations.

The end of the Paleocene epoch (55.5 Ma) was marked by an abrupt episode of global warming (Palaeocene/Eocene Thermal Maximum; PETM) coincident with a large perturbation to the global carbon cycle. Because the PETM might represent an analogue in the past of the present anthropogenic accelerated emission of greenhouse gases, it has attracted a good deal of interest with both data collecting and modeling efforts. Most of the studies focused on ocean records through sediments, we propose here one of the first study on continental records during the PETM. We focus our study on silcretes sampled in north of France, rocks present on the Paleocene-Eocene boundary and on the silicification formed in the porosity during weathering processes. Stable isotopes of Si have been used as proxies for understanding the Si cycle and its variations in the past. Here we analyzed silicon isotopes of in situ quartz using a new generation secondary ion mass spectrometry apparatus. Secondary phases as overgrowths on primary detrital quartz and microcrystals of quartz have been measured. Our results are very unexpected : althought detrital quartz present same values than in other silcretes, secondary phases present very homogenuous signatures far from very negative values that can be reached (-8 ‰ in [1, 2]). It seems that the origin of silicium is not local as both primary and secondary phases are within the same range. The isotopic fractionnation link to the dissolution/precipitation phase during weathering processes is 1.5 ‰. The lack of a strongly 30Si-depleted reservoir with negative isotopic values seem to show a low intenisity of alteration during the PETM in continental context. [1] Basile-Doelsch et al.(2005) Nature 433, 399–402. [2] Basile-Doelsch (2006) Journal of Geochemical Exploration 88, 252-256.