Studio delle emissioni gassose di CO2 e Radon al suolo e modellazione numerica del reservoir geotermico dell'area del Torrente Milia, Monterotondo Marittimo (GR)

RIASSUNTO. Negli ultimi 20 anni è stato riscontrato un crescente interesse nello studio del processo di degassamento di CO2 dalla geosfera in vari ambiti delle Scienze della Terra, con l’obiettivo di definire le relazioni tra i flussi di gas al suolo e le strutture tettoniche, di quantificare la CO2 di derivazione profonda rilasciata in atmosfera e di esaminare i processi di degassamento sia di natura vulcanica che non vulcanica (Cardellini et al., 2003). Mentre è ormai riconosciuto che il degassamento di origine vulcanica sia in grado di immettere in atmosfera enormi quantitativi di CO2, solo ricerche recenti (Kerrick et al.,1995; Seward & Kerrick, 1996) hanno dimostrato che il processo di degassamento non vulcanico può costituire un input di CO2 in atmosfera globalmente significante e che molte aree caratterizzate da rilevanti emissioni di CO2 non vulcanica sono in aggiunta contraddistinte da elevati valori di heat flow, presenza di magmi sub superficiali e regimi estensionali simicamente attivi (Kerrick et al., 1995). Inoltre la tecnica appare estremamente interessante nell’ottica dell’esplorazione geotermica, ai fini del riconoscimento delle principali strutture tettoniche presenti nel sottosuolo, dell’identificazione delle zone di risalita di fluidi e, in alcuni casi, dei reservoirs geotermici. La prima parte del presente lavoro di tesi ha riguardato l’esecuzione di un survey di misure al suolo di CO2 all’interno della zona geotermica di Larderello e più precisamente nel comune di Monterotondo Marittimo (GR). Tale lavoro si inquadra all’interno di un progetto più grande di valutazione del potenziale geotermico della zona in prossimità del Torrente Milia e ha costituito una delle metodologie utilizzate ai fini dell’ubicazione dei futuri pozzi geotermici. Le misure di CO2 al suolo sono state eseguite avvalendosi di un misuratore di flusso del tipo LICOR 8100 dotato di un analizzatore di gas all’infrarosso, che ha consentito la misura dei flussi di CO2 al suolo. La campagna, realizzata nel mese di Gennaio 2011, ha riguardato l’acquisizione di 63 punti nell’area del Torrente Milia, seguendo come riferimento una griglia di campionamento rettangolare con una maglia di lato pari a 250 m, per una lunghezza e una larghezza complessiva rispettivamente di 3000 m e 1250 m, con una superficie totale di 3,75 Km2. Al di fuori di quest’area sono inoltre state realizzate 20 misure di flusso con ubicazione nelle zone limitrofe ad alcuni pozzi ENEL (Carboli C bis, Poggio Travi e Lumiera 1bis), nelle aree considerate classicamente come ricarica del campo geotermico e presso le fumarole (Le Biancane). Dall’analisi dei valori di flusso di CO2 al suolo eseguita mediante il metodo grafico di analisi statistica (GSA) descritto da Chiodini et al. (1998) è emersa l’esistenza di quattro diverse popolazioni, ognuna contrassegnata da differenti caratteristiche e da diversa derivazione, mediante la cui identificazione è stato possibile eseguire una stima dell’output di CO2 giornaliero per l’intera area campionata del Torrente Milia, che ha fornito il valore di 145,45 t/d su una superficie di 3,75 Km2. Tali dati sono molto simili a quelli riscontrati da campagne eseguite in altre aree della Toscana termicamente anomale o contrassegnate dallo sviluppo di rilevanti discontinuità tettoniche ed evidenziano il problema legato all’immissione in atmosfera di gas serra. L’energia geotermica infatti rappresenta una fonte di energia a basso impatto ambientale, tuttavia il rilascio in atmosfera di CO2 dalle centrali è comunemente additato come uno degli effetti negativi derivanti dall’utilizzo della risorsa. La campagna condotta nell’area del Milia dimostra come anche aree di estensione limitata siano in grado di immettere naturalmente grandi quantitativi di CO2 in atmosfera. In effetti dati provenienti dalla letteratura scientifica attestano come il degassamento di CO2 di origine naturale ecceda, per molti campi geotermici del mondo tra cui Larderello, quello legato allo sfruttamento della risorsa. Inoltre dai dati raccolti è stato verificato come le strutture tettoniche presenti, la geologia dell’area, le differenti caratteristiche del litotipo o i processi attivi nel sottosuolo potessero influenzare significativamente i valori di flusso registrati al suolo, sia per l’area in prossimità del Torrente Milia sia per la zona esterna. Questo ha consentito di poter determinare delle buone correlazioni tra i vari parametri. In aggiunta sono state condotte le repliche di 6 punti di misura alla fine del mese di Giugno, per verificare se esistesse una variazione dei flussi di CO2 legata alla stagionalità. Le misure di CO2 al suolo sono inoltre state affiancate da 7 misure di Radon (222Rn), effettuate mediante un detector per il Radon da campagna del tipo RTM 2100 della SARAD, ubicate in parte nell’area del Torrente Milia ed in parte al di fuori, nelle vicinanze dei pozzi Carboli C bis e Lumiera 1bis e nell’area di ricarica del campo geotermico. Questi dati hanno consentito di avanzare ulteriori interpretazioni per l’area oggetto di studio e di comprovare le ipotesi già avanzate con i soli dati inerenti le misure dei flussi di CO2. La seconda ed ultima parte del lavoro ha invece riguardato la modellazione del comportamento idrologico e delle caratteristiche termiche del serbatoio geotermico, costituito dalla formazione del Calcare Cavernoso, nella zona dove la campagna di misure al suolo era stata effettuata mediante una griglia di campionamento regolare. La simulazione numerica è stata eseguita su un modello tridimensionale avvalendosi del software PetraSim 5.1, utilizzando come simulatore di calcolo TOUGH2 e un’equazione di stato EOS1. Il modello concettuale è stato ideato avvalendosi dei dati fisici, geologico-strutturali, idrogeologici e geochimici a disposizione, ha dimensioni di 2,7 1 0,8 km ed è stato schematizzato come comprendente tre corpi fondamentali: copertura-serbatoio-basamento. Su questo è stata costruita una griglia di calcolo regolare formata da 3672 celle di forma rettangolare. La prima fase della simulazione numerica ha mirato a ricostruire lo stato imperturbato del modello di partenza, che ha costituito la base di partenza per una seconda fase inerente la simulazione di differenti scenari di sfruttamento dell’area a fini geotermici per un arco di tempo pari a 50 anni. ABSTRACT. In the last 20 years a growing interest is noticed in studying the process of carbon dioxide degassing from the geosphere in various field of Earth Sciences, with the aim of defining relationship between gas flux on the ground and tectonic structures, quantifying deeply derived CO2 released in to the atmosphere and studying volcanic degassing and nonvolcanic degassing processes (Cardellini et al., 2003). While it is already recognized that volcanic degassing can introduce huge quantities of carbon dioxide in to the atmosphere, only recent studies (Kerrick et al.,1995; Seward & Kerrick, 1996) have shown that nonvolcanic degassing may be a globally significant input of CO2 in to the atmosphere and that many areas where large emissions of non-volcanic carbon dioxide take place are also characterized by high heat flow values, by the presence of shallow magmas and seismically-active extensional tectonic regimes (Kerrick et al., 1995). Besides the technique is interesting for geothermal exploring, for recognizing the main tectonic structures in the subsurface, for identifying zones of ascent of fluids and, in certain cases, for locating geothermal reservoirs. In first part of this thesis a survey of measurements of carbon dioxide to the ground was performed in the geothermal area of Larderello and, more exactly in the town of Monterotondo Marittimo (GR). This work is framed within a larger project whose purpose is to assess the geothermal potential of the area near the torrent named Milia and was one of the methodologies used for location of future geothermal wells. The measurements of CO2 were performed using a flow meter of the type LICOR 8100 equipped with a gas analyzer, which allowed the measure of CO2 fluxes to the ground. During the survey, conducted in January 2011, 63 measurements of CO2 flux were taken in the area near the torrent Milia, using as a reference a rectangular sampling grid with a mesh side equal to 250 m, with an overall length and width of 3000 m and 1250 m respectively, with a total area of about 3,75 km2. Outside this area 20 measurements of carbon dioxide flux were also done with location in the zone near certain wells ENEL (Carboli C bis, Poggio Travi e Lumiera 1bis), in areas classically considered as recharge of the geothermal field and in the area of fumaroles (“Le Biancane”). Analysis of the flux values made by graphical statistical analysis method (GSA) described by Chiodini et al. (1998) revealed the existence of four different populations, each of them marked by different characteristics and origin; the identification of these geochemical families allowed to estimate for the sampled area of Milia the daily carbon dioxide output which provided the value of 145,45 t/d over an area of 3,75 km2. Those data are very similar to those obtained by other CO2 flux survey carried out in other Tuscan thermally anomalous areas or in zone characterised by the development of major tectonic discontinuities and also highlight the problem of putting greenhouse gases in to the atmosphere. Geothermal energy is, as a matter of fact, a source of power with low environmental impact, however the release of carbon dioxide in to the atmosphere by power plants is commonly pointed out as one of the negative effects arising from the use of resource. The survey performed in the area near the Milia torrent proves that also area with small extension are able to enter naturally large amounts of CO2 in to the atmosphere. Indeed data from scientific literature certify that carbon dioxide degassing of natural origin exceeds the one produced with the exploitation of geothermal resource, for many geothermal fields included Larderello. From collected data was furthermore verified as the tectonic structures, the geology of zone, the different characteristics of rocks or the processes active in the subsurface environment could substantially influence the CO2 flux measured to the ground, both for the area near the Milia torrent but also for the outer zone. This has allowed to determine good relationship between various parameters. In addition 6 replicas of measured points were carried out at the end of June to verify if there was a variation in CO2 fluxes due to seasonality. Measurements of carbon dioxide flux were also accompanied by 7 Radon (222Rn) measurements, conducted using a portable detector type RTM 2100 produced by SARAD, placed in the area near Milia torrent and partly in the outer zone near the wells Carboli C bis and Lumiera 1bis and in the recharge area of the geothermal field. These data have allowed to advance further interpretations for the studied area and to prove the hypothesis already made by using data from CO2 flux measurements. The second and last part of the work concerned the modelling of the hydrological behaviour and the thermal characteristics of the geothermal reservoir, consisting of the formation of Calcare Cavernoso, in the zone where the survey of CO2 measurements was carried out using a regular sampling grid. Numerical simulation was performed on a three-dimensional model employing the software PetraSim 5.1 and using TOUGH2 as a simulator and a equation of state EOS1. The conceptual model was created with physical, geological-structural, hydrogeological and geochemical available data, it has a length of 2,7 km, a width of 1 km and a thickness of 0,8 km and has been modelled as comprising three fundamental bodies: cap-reservoirbasement. On this model a computational grid consisted of 3672 regular rectangular cells was built. The first phase of numerical simulation aimed to model the current natural state of the initial model, which constituted the basis for a second phase concerning the simulation of different scenarios of exploitation for geothermal purposes for a defined period of time equal to 50 years

Comparison of fatty acid profile in lamb meat and baby food based on lamb meat

The aim of this study was to compare the fatty acid (FA) profile of fresh lamb meat with those of baby foods based on lamb meat. For this purpose, samples of commercial homogenized (HO) and lyophilized (LIO) baby food based on lamb meat and fresh lamb meat (FM) were analyzed for their FA composition. All fatty acids, except for oleic acid and conjugated linoleic acid (CLA), differed among the three baby products tested. The sum of omega-6 FA and the ratio omega 6/omega 3 FA were lower in FM and LIO meat compared to HO samples. The content of total PUFA n-3 was the highest in FM, because of its highest content of C18:3 n3, EPA, DPA and DHA compared to LIO and HO baby food. The content of arachidonic acid was more than 6-fold higher in FM compared to LIO and HO. This study evidenced the possibility of enhancing the FA profile of commercial baby food based on lamb meat by using meat with healthier FA profile

Heterogeneous mantle domains in a modern OCT: new insights from the west Iberian margin (ODP Legs 149 and 173)

Magma-poor ocean-continent transition zones (OCTs) represent wide areas of tectonically uplifted mantle. While an important body of literature has dealt with the investigation of fossil analogues (e.g. Picazo et. al., 2016, and references therein), studies on mantle sequences exhumed in modern OCTs remain a few (e.g. McCarthy et al., 2020), leaving our knowledge somehow fragmentary. In particular, how, where and when lithospheric breakup occurs, the timing of melt production, and the nature of the mantle source involved remain hotly debated issues. Among the best-documented continental margins worldwide, the West Iberian margin represents a unique site where mantle has been accessed through scientific drilling more than three decades ago (e.g. Boillot et al., 1989). However, these peridotites have remained poorly characterized, partly because of their pervasive serpentinization. In this contribution, we present the results of an in situ petrological and geochemical study performed on a set of mantle peridotites from ODP Holes 899B, 1068A, and 1070A. In Hole 899B, relatively fresh spineland plagioclase-bearing harzburgites (cpx ≈ 2-8 vol.%) occur. In contrast, highly serpentinized plagioclase lherzolites and spinel harzburgites were sampled in Holes 1068A and 1070A. Hole 899B spinel harzburgites bear refractory compositions, as attested by the low clinopyroxene contents (≈ 2-3 vol.%), coupled to moderate spinel Cr# (0.230-0.343) and low pyroxene YbN (≈ 1-2). Geochemical modeling based on pyroxene trace element compositions points to significant degrees of melt extraction (up to ≈ 15%), starting in the garnet stability field, followed by post-melting metasomatism. Holes 899B and 1068A plagioclase-bearing samples share remarkable similarities, i.e. frequent occurrence of (altered) plagioclase rims mantling elongated dark spinel, Na2O- and Al2O3-rich clinopyroxene associated with high TiO2 spinel (up to 0.66 wt%). Clinopyroxene shows convex-upward REE patterns, yielding negative Eu anomalies and higher HREE contents compared to abyssal peridotites. Hence, these peridotites are not simple partial melting residues but experienced melt-rock interaction processes and re-equilibration in the plagioclase stability field. Hole 1070A peridotites exhibit contrasting signatures, as highlighted by the presence of Na2O-rich, Al2O3-poor clinopyroxene coupled to spinel with high Cr# (0.246-0.428) and TiO2 below the detection limit. Orthopyroxene trace element investigation of these samples revealed hump-shaped patterns with variable LREE-MREE fractionation (LaN/SmN= 0.003- 0.16) and low YbN (≈ 1-2). Our new data attest a wide spectrum of petrological and geochemical characters shown by mantle rocks exhumed in a modern OCT. This heterogeneous nature possibly reflects a complex interplay between riftingrelated processes and previous depletion history inherited from the last Wilson cycle

Temperatures and cooling rates recorded by the New Caledonia ophiolite: implications for cooling mechanisms in young forearc sequences.

To unveil how forearc lithosphere cools and re-equilibrates, we carried out a comprehensive geothermometric investigation of the New Caledonia ophiolite, which represents a rare example of proto-arc section generated during subduction infancy. A large dataset, including more than eighty samples (peridotites and mafic-ultramafic intrusives), was considered. Closure temperatures calculated for the lherzolites using slow (TREE-Y) and fast diffusing (TCa-in-Opx, TBKN, TCa-in-Ol, TOl-Sp) geothermometers provide some of the highest values ever documented for ophiolitic peridotites, akin to modern sub-oceanic mantle. Cooling rates deduced from TREE-Y and TBKN yield values of ≈ 10-3 °C/y, similar to those obtained with TCa-in-Ol. These features are consistent with a post-melting history of emplacement, possibly along a transform fault, and thermal re-equilibration via conduction. Cpx-free harzburgites register a high-T evolution, followed by quenching and obduction. The relatively high TCa-in-Ol, TOl-Sp and cooling rates computed from TCa-in-Ol (≈ 10-3 °C/y) are atypical for this geodynamic setting, mirroring the development of an ephemeral subduction system, uplift and emplacement of the Peridotite Nappe. Temperature profiles across the crust-mantle transect point to high closure temperatures, with limited variations with depth. These results are indicative of injection and crystallization of non-cogenetic magma batches in the forearc lithosphere, followed by thermal re-equilibration at rates of ≈ 10-4-10-3 °C/y. Our study shows that the thermal conditions recorded by forearc sequences are intimately related to specific areal processes and previous lithospheric evolution. Thus, detailed sampling and exhaustive knowledge of the geological background are critical to unravel the cooling mechanisms in this geodynamic setting

Pb isotope composition of recycled mantle pyroxenites: insights into the HIMU source of oceanic basalts?”

Recycled mantle pyroxenites are believed to play a key role in the magma genesis contributing to the radiogenic Pb signatures within the sources of oceanic basalts. In particular, a garnet pyroxenite component derived from recycling of aged oceanic crust is widely advocated to explain the HIMU end-member in the OIB sources. However, natural examples of recycled pyroxenites are rare and the known examples do not meet the required Nd-Hf-Pb isotope characteristics of this component (e.g., Varas Reus et al., 2018). Here, we present Pb isotope systematics of garnet clinopyroxenites and websterites enclosed in fertile mantle sequences of the External Ligurian ophiolites (Northern Apennine). The garnet clinopyroxenite layers have gabbroic crustal precursors that experienced a long-lived evolution of recycling into the mantle (1.5-1.0 Ga), as inferred from Sm-Nd and Lu-Hf isotope systematics, which in addition point to a HIMU affinity (Montanini & Tribuzio, 2015). The garnet clinopyroxenites originated by crystallization of melts produced by partial melting of gabbro-derived eclogites, whereas the websterites were interpreted as secondary pyroxenites with a crustal geochemical fingerprint and a peridotite contribution. Highly radiogenic present-day Pb isotope compositions were obtained for bulk rocks and clinopyroxene separates from garnet clinopyroxenites. In Pb isotope diagrams, samples exhibit a good positive correlation, with 206Pb/204Pb extending from MORB field toward the most extreme HIMU components (i.e., St. Helena and Mangaia hotspots). In particular, the pyroxenites and the clinopyroxene separates display somewhat higher 207Pb/204Pb and lower 208Pb/204Pb for a given 206Pb/204Pb than HIMU-type basalts. The less radiogenic values are shown by the websterites containing a peridotite component. Age-corrected Pb isotope compositions of clinopyroxene separates, assuming a melting event at 220 Ma as inferred from Nd-Hf isotopes, are strikingly similar to the most extreme HIMU-type basalts. High-precision LA-ICP-MS analyses of elemental Pb were also performed on the primary HP assemblage of the garnet clinopyroxenites (Al-rich clinopyroxene, garnet and Fe-Ni-Cu sulfides). The results show that clinopyroxene is the main carrier of Pb, whereas Pb is typically below detection limits in sulfides, in contrast with recent measurements on sulfides from abyssal peridotites and pyroxenites (e.g. D’Errico et al., 2019). The Pb isotope compositions of studied pyroxenites require a long-term evolution of recycled MORB-type gabbros with high and variable U/Pb and Th/Pb ratios. We conclude that these rocks represent a special and rare combination of age and composition of subduction-modified recycled oceanic crust

Mantle rocks exhumed along an ocean-continent transition: revisiting the Iberian margin peridotites (ODP Leg 149 and 173)

Investigating peridotite samples exposed along ocean-continent transitions is crucial to shed light on processes occurring in the upper mantle during lithospheric breakup, unravelling, at the same time, source heterogeneity and inheritance. More than three decades ago, mantle rocks were recovered along the West Iberian margin during several ODP cruises (Leg 103, 149, and 173; see Abe, 2001; Chazot et al., 2005). Despite being one of the few sites worldwide where mantle has been accessed through scientific drilling, Iberian peridotites remain poorly characterized. Here, we revisit Iberian peridotites through a combined petrological and geochemical study performed on a new set of mantle samples from ODP Holes 899B, 1068A, and 1070A. Hole 899B peridotites are relatively fresh, clinopyroxene-rich (≈ 5-8 vol.%) tectonite harzburgites. They mostly consist of deformed olivine (≈ 80- 85 vol.%), showing variable Fo contents (89.1-92.1), and low amount (≈ 10-12 vol.%) of exsolved, Mg-rich orthopyroxene. Dark brown spinel (< 1 vol.%, Cr#=0.198-0.483; TiO2=0.10-0.72) mainly occurs as elongated grains, sometimes rimmed by altered plagioclase. In contrast to Hole 899B, peridotites from Holes 1068A and 1070A are highly serpentinized. Samples from Hole 1068A have chromian spinel (Cr#=0.253-0.376) mantled by a fine-grain white rim, possibly representing a pseudomorph after plagioclase. Clinopyroxene relics display highly variable Al2O3 (3.77-7.25 wt.%) and TiO2 contents (0.38-0.75 wt.%), in contrast to the lower and more homogenous values of Hole 1070A samples (3.87-4.70 wt.% and 0.14-0.20 wt.% for Al2O3 and TiO2, respectively). High Mg# (0.915-0.920) olivine and orthopyroxene with low- to moderate Al2O3 contents (2.52-3.70 wt.%) are only preserved in Hole 1070A. In situ trace element investigation revealed convex-upward patterns for Holes 899B and 1068A clinopyroxene, in the range of modern abyssal peridotites. Clinopyroxene shows LREE-depleted segments (LaN/SmN = 0.01-0.27) and flat HREE for YbN ≈ 10, coupled to Eu negative anomalies. Orthopyroxene of Hole 899B yields low REE concentrations (HREEN ≤ 1) and spoon-shaped patterns, except for the plagioclasebearing sample, which exhibits a straight pattern (LaN/YbN = 0.001-0.02) and negative Eu anomalies. Humpshaped REE patterns with steep LREE slopes (LaN/SmN = 0.003-0.01) and flat HREE segments are observed for Hole 1070A orthopyroxene. Our preliminary results indicate that the mantle exhumed along the ocean-continent transition of the Iberian margin experienced variable degrees of depletion and melt/rock interaction

Fatty acids composition of Colonnata Lard from two different swine breeds

The study compares the fatty acid composition of the Colonnata lard obtained from two different swine breeds, Large White (LW) and Cinta Senese (CS), during a one year long curing period. Samples of backfat were obtained from the carcass of three animals per breed and disposed into six different marble boxes according to the procedure of the disciplinary production of PGI "Lardo di Colonnata". During curing period individual lard samples were collected monthly from each marble box. The fatty acid composition of pig backfat reflected the differences in the dietary regimen and in the rearing system of the two breeds. LW swine, in fact, were fed a commercial concentrate and reared in an intensive system, whereas CS swine were fed a diet composed by a commercial concentrate supplemented with acorn and reared in an outdoor system. Lard from LW contained higher amount of saturated fatty acids than lard from CS, whereas the content of unsaturated fatty acids (mainly monounsaturated fatty acids) was lower. During the curing period the trend of lard fatty acids composition was different in the two breeds: the lard from CS seemed to be more susceptible to a faster hydrolysis of fatty acids than lard from LW, especially for the monounsaturated fatty acids, while the lard from LW seemed to be more susceptible to a faster hydrolysis of PUFA n-3

Supra-subduction mantle pyroxenites in an infant subduction system: the New Caledonia ophiolite record

Pyroxenites constitute the major form of heterogeneity in the upper mantle. Their occurrence in supra-subduction zone settings is mostly testified by veins and layers in refractory ophiolitic peridotites, where they represent a crucial witness of melt migration in the forearc/subarc environment [1,2]. The New Caledonia ophiolite hosts one of the largest forearc mantle section worldwide, providing a unique perspective into upper mantle processes. The sequence is dominated by ultra-depleted harzburgites [3], locally overlain by mafic-ultramafic cumulates [4,5,6]. The harzburgites are highly refractory residues that register a multi-phase evolution, including fluid-assisted melting in a forearc environment and contamination by fluid- and melt inputs triggered by Eocene subduction [1]. Pyroxenitic rocks intruding the harzburgites are only known in the Bogota peninsula shear zone, which records HT deformation along a paleotransform fault [7]. In this contribution, we report a comprehensive petrological and geochemical characterization on a new set of pyroxenites from this locality. The pyroxenites (~5-15 cm-thick) generally cut the peridotite foliation at variable angles, but concordant, locally boudinaged, layers also occur. Pyroxenite textures range from cumulitic to porphyroclastic or granoblastic-polygonal. The studied samples mostly consist of amphibole-bearing (5-44 vol.%) websterites, with variable amounts of orthopyroxene (27-67 vol.%) and almost constant clinopyroxene contents (~ 25-29 vol.%). Minor olivine-bearing orthopyroxenites are also present. Accessory phases include high-Ca (An= 82-86 mol%) plagioclase, Cr-rich spinel (Cr# = 50-61), sulfides and, occasionally, apatite. Pyroxenes displays high Mg# (Mg# Opx= 91-92; Mg# Cpx= 84-93), coupled with low Al2O3 contents (0.97-1.92 wt% and 1-2.42 wt% for orthopyroxene and clinopyroxene, respectively). Amphibole is high Mg# edenite. Application of conventional pyroxene thermometry yield equilibration temperatures ranging between 930-1040°C, comparable to the enclosing harzburgites (~ 950°C), whereas amphibole-plagioclase geothermometer provides lower temperatures (~ 800°C). Bulk rock composition of the websterites show variable Mg# (82-91) and REE concentrations ranging between 1 to 10 times chondritic values. They are characterized by flat to LREE-depleted (LaN/SmN 0.28-0.92) patterns, coupled to weak MREE-HREE fractionation (GdN/YbN = 1.73-1.92) and Eu negative anomalies. By contrast, orthopyroxenites display notably lower concentrations (0.1≤REE≤1 chondrite abundances). As a whole, clinopyroxene REE patterns of the websterites mirror bulk rocks at higher absolute values. Putative melts in equilibrium with clinopyroxene indicate strongly enriched compositions (up to 300 times chondritic values) coupled to variable LREE-HREE fractionation (LaN/LuN = 3-19) and flat to fractionated HREE (GdN/LuN 1-2). Such enriched liquids, which show some analogies with pre-obduction adakite-like dikes [8], have never been recorded in the MTZ cumulitic sequence of the New Caledonia ophiolite and shed new light on the magmatic activity in the early stage of subduction