Primary multiphase fluid inclusions (MFI) were studied in one eclogite and two granulites from the Cabo Ortegal Complex (COC, NW Spain) by means of Raman imaging, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM‐EDS) and Focused Ion Beam ‐ Scanning Electron Microscopy (FIB)‐SEM. Complementary, secondary MFI in pyroxenites from COC were also investigated. MFI hosted in eclogite and granulites occur along growth zones or in 3D clusters in garnet porphyroblasts suggesting a primary origin at high‐pressure (HP) metamorphic conditions. The mineral assemblage of MFI is mainly composed of Fe‐Mg‐Ca‐carbonates and phyllosilicates ± graphite ± quartz ± corundum ± pyrite ± apatite ± rutile and a fluid phase composed of nitrogen ± methane ± carbon‐dioxide. The mineral proportions vary among the lithologies. Dominant carbonates and hydrous silicates are interpreted as step‐daughter minerals (crystals formed in the MFI after entrapment as a result of fluid–host interaction), whereas apatite, quartz and rutile are considered in part as accidentally trapped minerals since they also occur as crystal inclusions together with MFI in each rock type. Quartz and corundum occur together in MFI in ultramafic granulite and are regarded as step‐daughter minerals in this lithology. These observations suggest that the MFI are products of post‐entrapment reactions of a homogeneous COHN fluid system with the host mineral. Thermodynamic calculations in the CaFMAS‐COHN system confirmed that bulk composition of the MFI in eclogite is similar to the host garnet+COHN composition except for a potential lost of H₂O. Carbonation and hydration reaction between the host (i.e. garnet or pyroxene) and the fluid inclusion results in the consumption of all CO₂ and part of the H₂O from the fluid phase producing Ca‐Fe‐Mg‐carbonates and hydrous step‐daughter minerals, mostly pyrophyllite and chlorite. Nitrogen content of the originally trapped COHN fluid in eclogite was estimated to have a maximum value of 10 mol% at peak HP conditions and 30–40 mol% at retrograde conditions that is within the range of the observed MFI in the residual fluid (13–68 mol%). Pseudosection modelling confirmed the stability of the phase assemblage in the MFI in a specific low‐pressure, low‐temperature stability field (between 300°C and 400°C at pressures < 1 GPa), caused by H₂O‐ and CO₂‐consuming reactions possibly in a single step. Our findings indicate that such processes in the exhuming HP units may play a role in global nitrogen and carbon cycling as well as potentially contributing to nitrogen and methane supply to subsurface–surface environments during devolatilization in the forearc regions of convergent plate margins.

In this study, we performed high resolution 3D Raman mapping on primary multiphase fluid inclusions from a granulite and an eclogite of the Cabo Ortegal Complex (NW Spain), the latter representing a former subduction zone environment. Several microns‐sized inclusions are great targets to test the advantages and limitations of 3D Raman mapping. We show how optical and Raman scattering properties of the phases inside the inclusions can affect the veracity of both 2D and 3D Raman maps. As an independent control, 3D Raman models were compared with focused ion beam‐scanning electron microscopy submicron‐scale slicing of three previously 3D Raman mapped inclusions, allowing us to optimize Raman spectroscopy data evaluation and provide volume proportion calculations. We found that a non‐optimized evaluation procedure might result in even an order of magnitude over‐ or underestimation of phase volume properties. We propose that correcting the Raman maps even with empirically determined Raman cross sections of the phases inside the inclusions can vastly improve the quality of the maps. The results provide valuable input data for thermodynamic modeling and draw implications for fluid/rock interactions.

Fluid and melt inclusions trapped in mantle xenoliths provide direct insights into the metasomatic agent in the lithospheric mantle, including its volatile content. We conducted 3D Raman mapping on fluid and melt inclusions in modally metasomatized mantle xenoliths from the Styrian Basin (W‐Carpathian Pannonian Region) to explore how this method can be utilized to study the role of fluids and melts in the upper mantle. 3D Raman mapping revealed complex phase assemblages of coexisting fluid and solid phases in the inclusions. Fluid phases are CO₂ (49.2–98.4 mol%, 19.1–61.0 vol%) and H₂O (1.5–50.8 mol%, 8.6–35.3 vol%). This H₂O concentration range is considerably higher than in most mantle fluids (∼10–15 mol%). Solid phases are silicates, carbonates, sulfides, and sulfates present in varying volume% (vol%). 3D Raman mapping shows that liquid H₂O wets other phases in the mapped fluid inclusions and may be preferentially lost compared to the CO₂‐rich phase during inclusion decrepitation. The accuracy of CO₂‐H₂O mol ratios from Raman 3D mapping in fluid inclusions can be affected by variable Raman cross‐sections of trapped phases. Therefore, thermodynamic modeling is recommended to validate measured CO₂‐H₂O mol ratios. 3D Raman mapping may underestimate low Raman scatterers like silicate glass in fluid inclusions, but their volumes can be corrected based on FIB‐SEM analyses. Thermodynamic modeling suggests that the fluid compositions in the Raman‐mapped fluid inclusions may reflect non‐equilibrium entrapment, whereas those in the melt inclusions reflect equilibrium entrapment in this mantle portion. The discovered C‐O‐H fluids provide new information on fluid‐rock reactions in the lithospheric mantle.

A Stájer-medence a Kárpát-Pannon régió nyugati szélén helyezkedik el, a Pannon-medence és a Keleti-Alpok közötti átmeneti zónában. A Stájer-medencében plio-pleisztocén alkáli bazaltok mintázták meg a medence alatti litoszféraköpenyt. A köpeny eredetű xenolitok közül ritkaságnak számító, modális metaszomatózison átesett, flogopit- és apatit-tartalmú amfibol-gazdag peridotitok is előkerültek. Jelen munkában egy ilyen, gazdagodott xenolit komplex fluidumzárvány vizsgálatát mutatjuk be. Fluidumzárványokat ortopiroxénben és amfibolban azonosítottunk. Utóbbi ásványban ritkán őrződnek meg köpenyfluidumok zárványai, ezért vizsgálatuk egyedi lehetőséget nyújt a köpenyben vándorló fluidumok megismerésére. Az elsődleges és álmásodlagos zárványok összetételét petrográfiai elemzések után mikrotermometriai és Raman-mikrospektroszkópiai mérések segítségével határoztuk meg. Az ortopiroxének zárványainak folyadék fázisában a nagy sűrűségű (~1 g/cm³) CO₂ a domináns komponens (>95 mol. %), ami mellett H₂O-t (<3,5 mol. %) és N₂-t (98 mol. %), ami mellett H₂O-t (<1,2 mol. %), N₂-t (<0,1 mol. %) és a vízben oldott SO₄^2--t azonosítottunk. A szilárd fázisok különböző karbonátokból (magnezit, Na-tartalmú dawsonit, nahkolit és nátrit) és szulfátokból (anhidrit, Na-tartalmú thenardit-burkeit) álló ásványegyüttest alkotnak. A klór-mentes, Na⁺ és SO₄^2--tartalmú fluidösszetétel egyedinek tekinthető köpenykörülmények között. A fluidum forrása egy illó-gazdag olvadék lehetett, amelyben az amfibol (valamint alárendelten flogopit és apatit) kristályosodása során feldúsultak az illók (C-O-N-S), Na⁺, HCO₃^- és SO₄^2-, amelyek csapdázódtak a keletkező amfibolban.