Geochronology, geochemistry and isotopic compositions of the volcanic rocks from oceanic (Hawaii) and continental (Eifel) intra-plate environments

The Eifel volcanism is part of the Central European Volcanic Province (CEVP) and is located in the Rhenish Massif, close to the Rhine and Leine Grabens. The Quaternary Eifel volcanism appears to be related to a mantle plume activity. However, the causes of the Tertiary Hocheifel volcanism remain debated. We present geochronological, geochemical and isotope data to assess the geotectonic settings of the Tertiary Eifel volcanism. Based on 40Ar/39Ar dating, we were able to identify two periods in the Hocheifel activity: from 43.6 to 39.0 Ma and from 37.5 to 35.0 Ma. We also show that the pre-rifting volcanism in the northernmost Upper Rhine Graben (59 to 47 Ma) closely precede the Hocheifel volcanic activity. In addition, the volcanism propagates from south to north within the older phase of the Hocheifel activity. At the time of Hocheifel volcanism, the tectonic activity in the Hocheifel was controlled by stress field conditions identical to those of the Upper Rhine Graben. Therefore, magma generation in the Hocheifel appears to be caused by decompression due to Middle to Late Eocene extension. Our geochemical data indicate that the Hocheifel magmas were produced by partial melting of a garnet peridotite at 75-90 km depth. We also show that crustal contamination is minor although the magmas erupted through a relatively thick continental lithosphere. Sr, Nd and Pb isotopic compositions suggest that the source of the Hocheifel magmas is a mixing between depleted FOZO or HIMU-like material and enriched EM2-like material. The Tertiary Hocheifel and the Quaternary Eifel lavas appear to have a common enriched end-member. However, the other sources are likely to be distinct. In addition, the Hocheifel lavas share a depleted component with the other Tertiary CEVP lavas. Although the Tertiary Hocheifel and the Quaternary Eifel lavas appear to originate from different sources, the potential involvement of a FOZO-like component would indicate the contribution of deep mantle material. Thus, on the basis of the geochemical and isotope data, we cannot rule out the involvement of plume-type material in the Hocheifel magmas. The Ko’olau Scientific Drilling Project (KSDP) has been initiated in order to evaluate the long-term evolution of Ko’olau volcano and obtain information about the Hawaiian mantle plume. High precision Pb triple spike data, as well as Sr and Nd isotope data on KSDP lavas and Honolulu Volcanics (HVS) reveal compositional source variations during Ko’olau growth. Pb isotopic compositions indicate that, at least, three Pb end-members are present in Ko’olau lavas. Changes in the contributions of each component are recorded in the Pb, Sr and Nd isotopes stratigraphy. The radiogenic component is present, at variable proportion, in all three stages of Ko’olau growth. It shows affinities with the least radiogenic “Kea-lo8” lavas present in Mauna Kea. The first unradiogenic component was present in the main-shield stage of Ko’olau growth but its contribution decreased with time. It has EM1 type characteristics and corresponds to the “Ko’olau” component of Hawaiian mantle plume. The second unradiogenic end-member, so far only sampled by Honololu lavas, has isotopic characteristics similar to those of a depleted mantle. However, they are different from those of the recent Pacific lithosphere (EPR MORB) indicating that the HVS are not derived from MORB-related source. We suggest, instead, that the HVS result from melting of a plume material. Thus the evolution of a single Hawaiian volcano records the geochemical and isotopic changes within the Hawaiian plume

Using a combined stable isotope -speciation approach to understand the impact of long-term spreading of organic effluents on agricultural soils

International audienceRecycling of organic waste (OW) as fertilizers on farmlands is a common practice as it provides a cost effective and sustainable way of managing OW. However, it represents a major source of contaminants such as copper (Cu) and zinc (Zn) that may pose potentially negative environmental impacts (Lavado et al., 2005). To limit the environmental impact of OW spreading on farmlands, agronomical doses are calculated based on the nitrogen, phosphorus and potassium requirements of crops. Consequently, lower quantities of Cu and Zn are introduced in soil following OW application (López-Rayo et al., 2016). However, the long-term impacts of OW spreading at the set agronomical doses on the accumulation and fate of Cu and Zn in soils are scant. This study was designed to fill this gap by using a combination of Cu and Zn speciation characterization and isotopic compositions in OW and soils. We studied four soils with contrasting physicochemical properties (luvisols, nitisols, calcisols and arenosols) and the OW used in four long-term field experiments. We observed, in agreement with published literature, that in OW, Cu and Zn speciation is affected by the OW treatment (anaerobic digestion and composting) and by the physicochemical conditions during storage. In the studied OW samples, Cu and Zn occurred mainly or entirely as sulfides in raw and anaerobically digested pig slurries whereas only oxidized species were present in composted household wastes (Zn-phosphate, Cu bound to organic matter). In two field experiments selected for this study, little or no change in Cu and Zn speciation was observed between control and amended soil due to OW application at agronomical doses. Thus, the interest in analyzing the isotopic signatures to investigate whether Cu and Zn originating from OW application can be traced in such cases

Using a combined stable isotope -speciation approach to understand the impact of long-term spreading of organic effluents on agricultural soils

Recycling of organic waste (OW) as fertilizers on farmlands is a common practice as it provides a cost effective and sustainable way of managing OW. However, it represents a major source of contaminants such as copper (Cu) and zinc (Zn) that may pose potentially negative environmental impacts (Lavado et al., 2005). To limit the environmental impact of OW spreading on farmlands, agronomical doses are calculated based on the nitrogen, phosphorus and potassium requirements of crops. Consequently, lower quantities of Cu and Zn are introduced in soil following OW application (López-Rayo et al., 2016). However, the long-term impacts of OW spreading at the set agronomical doses on the accumulation and fate of Cu and Zn in soils are scant. This study was designed to fill this gap by using a combination of Cu and Zn speciation characterization and isotopic compositions in OW and soils. We studied four soils with contrasting physicochemical properties (luvisols, nitisols, calcisols and arenosols) and the OW used in four long-term field experiments. We observed, in agreement with published literature, that in OW, Cu and Zn speciation is affected by the OW treatment (anaerobic digestion and composting) and by the physicochemical conditions during storage. In the studied OW samples, Cu and Zn occurred mainly or entirely as sulfides in raw and anaerobically digested pig slurries whereas only oxidized species were present in composted household wastes (Zn-phosphate, Cu bound to organic matter). In two field experiments selected for this study, little or no change in Cu and Zn speciation was observed between control and amended soil due to OW application at agronomical doses. Thus, the interest in analyzing the isotopic signatures to investigate whether Cu and Zn originating from OW application can be traced in such cases

Zn isotopes as tracers of a 166-year old Pb-Ag contamination in soils in National Parc of Calanques, France

International audienc

Using a combined stable isotope -speciation approach to understand the impact of long-term spreading of organic effluents on agricultural soils

Recycling of organic waste (OW) as fertilizers on farmlands is a common practice as it provides a cost effective and sustainable way of managing OW. However, it represents a major source of contaminants such as copper (Cu) and zinc (Zn) that may pose potentially negative environmental impacts (Lavado et al., 2005). To limit the environmental impact of OW spreading on farmlands, agronomical doses are calculated based on the nitrogen, phosphorus and potassium requirements of crops. Consequently, lower quantities of Cu and Zn are introduced in soil following OW application (López-Rayo et al., 2016). However, the long-term impacts of OW spreading at the set agronomical doses on the accumulation and fate of Cu and Zn in soils are scant. This study was designed to fill this gap by using a combination of Cu and Zn speciation characterization and isotopic compositions in OW and soils. We studied four soils with contrasting physicochemical properties (luvisols, nitisols, calcisols and arenosols) and the OW used in four long-term field experiments. We observed, in agreement with published literature, that in OW, Cu and Zn speciation is affected by the OW treatment (anaerobic digestion and composting) and by the physicochemical conditions during storage. In the studied OW samples, Cu and Zn occurred mainly or entirely as sulfides in raw and anaerobically digested pig slurries whereas only oxidized species were present in composted household wastes (Zn-phosphate, Cu bound to organic matter). In two field experiments selected for this study, little or no change in Cu and Zn speciation was observed between control and amended soil due to OW application at agronomical doses. Thus, the interest in analyzing the isotopic signatures to investigate whether Cu and Zn originating from OW application can be traced in such cases

Zn isotopes as tracers of a 166-year old Pb-Ag contamination in soils in National Parc of Calanques, France

International audienc