Primary CO2-bearing fluid inclusions in granulitic garnet usually do not survive

Carvalho, Bruna B.; Bartoli, Omar; Cesare, Bernardo; Tacchetto, Tommaso; Gianola, Omar; Ferri, F.; Aradi, László Előd; Szabó, Csaba

doi:10.1016/j.epsl.2020.116170

Cited by 33 publications

(26 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although H 2 O as a free phase has never been demonstrated by Raman spectroscopy within the measured FI of the Gruf Complex, its occurrence at the nanometric scale cannot be excluded (see also Esposito et al., 2016; Lamadrid, Lamb, Santosh, & Bodnar, 2014). On the other hand, carbonates and phyllosilicates are interpreted as re‐speciation products after post‐entrapment carbonation and hydration reactions between garnet host and fluid, as it has been suggested also for other HT/UHT terranes (Carvalho et al., 2019, 2020; Ferrero et al., 2014; Tacchetto et al., 2019). Hence, the different densities displayed by the FI are a direct consequence of incomplete reactions, which leave a variable amount of CO 2 in the residual fluid.…”

Section: Discussionmentioning

confidence: 79%

Anatectic melt inclusions in ultra high temperature granulites

Gianola

Bartoli

Ferri

et al. 2020

Journal Metamorphic Geology

Self Cite

View full text Add to dashboard Cite

Partial melting up to ultra high temperature (UHT) conditions is one of the major processes for the geochemical differentiation and reworking of the mid‐ to lower continental crust, with relevant implications on its rheological behaviour. UHT granulites from the Gruf Complex (European Central Alps) display garnet and sapphirine porphyroblasts containing a variety of primary melt inclusions (MI). Typically, MI in garnet occur as glassy and polycrystalline inclusions (i.e. nanogranitoids), the latter commonly organized in mm‐sized clusters associated with primary fluid inclusions (FI). Nanogranitoids are characterized by an elliptical faceted shape, with variable sizes ranging from 2 to 115 µm, while glassy inclusions show negative crystal shapes that usually never exceed 15 µm in diameter and present CO2‐rich shrinkage bubbles. The characteristic mineral assemblage observed in nanogranitoids consists of quartz, biotite, muscovite, plagioclase, K‐feldspar, kokchetavite and rarely aluminosilicates. Glassy and re‐homogenized MI are peraluminous and rhyolitic in composition, with SiO2 = 69 − 80 wt% and Na2O + K2O = 5 − 12 wt%. Commonly, the analysed MI have very high K2O (>6 wt%) and very low Na2O (<2 wt%) contents, indicative for potassic to ultrapotassic melts. Measured H2O contents of the melts range from 2.9 to 8.8 wt%, whereas CO2 concentrations are between 160 and 1738 ppm. Accordingly, calculated viscosities for re‐homogenized MI vary between 104 and 105 Pa·s. Related primary FI mainly contain CO2, with rare occurrence of CO and N2, and are commonly associated with quartz, as well as different carbonates and phyllosilicates. It is assumed that the source for the carbonic fluid was external and probably related to the degassing lithospheric mantle. Consequently, it is argued that anatexis was initially triggered by incongruent dehydration melting reactions involving biotite breakdown and proceeded in the presence of an externally derived COH‐bearing fluid. The coexistence of COH‐bearing fluid and MI indicates that partial melting occurred under conditions of fluid − melt immiscibility. Potassic to ultrapotassic MI in UHT granulites suggests that lower crustal anatexis may play a significant role in the redistribution of heat‐producing elements (such as K2O), potentially influencing the thermal structure of the continental crust.

show abstract

Section: Discussionmentioning

confidence: 79%

Anatectic melt inclusions in ultra high temperature granulites

Gianola

Bartoli

Ferri

et al. 2020

Journal Metamorphic Geology

Self Cite

View full text Add to dashboard Cite

show abstract

“…Multiphase inclusions were previously recorded in HT granulite facies rocks that experienced anatexis (Carvalho et al, 2019; Ferrero et al, 2014; Tacchetto et al, 2019). These MFI generally coexist with nanogranitoids (Acosta‐Vigil et al, 2016; Carvalho et al, 2019, 2020; Cesare et al, 2007, 2015; Ferrero et al, 2014; Tacchetto et al, 2019), in which inclusions are defined as crystallized silicate melt, thus indicating fluid‐melt immiscibility (Cesare et al, 2015; Korsakov & Hermann, 2006). In our study, however, no petrographic evidence of partial melting and no nanogranitoid inclusions were observed.…”

Section: Discussionmentioning

confidence: 99%

“…This discrepancy can be explained by the modelled chlorite composition, which is poorer in silica (2.0 Si apfu) relative to the measured composition (2.7-2.9 Si apfu; see Tables S2 and S8). The production of carbonates and hydrous silicates through the carbonation and hydration reaction of the almandine endmember in garnet with CO 2 and H 2 O was previously proposed by thermodynamic calculations in simple systems (Carvalho et al, 2020;Marini, 2007). At peak conditions (1.8 GPa, 800 C), the modelled assemblage is largely (>85 vol.%) formed by garnet and a COHN-fluid (Figure 10b) supporting a homogeneous entrapment of a fluid composed mostly of H 2 O (56 mol%) and CO 2 (34 mol%) with additional N 2 (10 mol%, Figure 10c, Table 3).…”

Section: Origin Of Mfi and Fluid Compositionmentioning

confidence: 94%

Abiotic passive nitrogen and methane enrichment during exhumation of subducted rocks: Primary multiphase fluid inclusions in high‐pressure rocks from the Cabo Ortegal Complex, NW Spain

Spránitz

Padrón‐Navarta

Szabó

et al. 2022

Journal Metamorphic Geology

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…Similarly, most of the mineral phases observed in the investigated FI (i.e. pyrophyllite, carbonates, quartz and phlogopite) were not present during inclusion formation but are to be considered as stepdaughter minerals resulting from the interaction of the trapped COH-fluid and the host/garnet during cooling, in analogy with the recent work of Carvalho et al (2020).…”

Section: Discussion and Perspectivesmentioning

confidence: 53%

Mesoarchean melt and fluid inclusions in garnet from the Kangerlussuaq basement, Southeast Greenland

2022

View full text Add to dashboard Cite

The present work reports the first anatectic melt inclusions found so far in the Mesoarchean basement in East Greenland. Using optical microscope observations and MicroRaman spectroscopy, we show that garnets in metasedimentary migmatite contain primary polycrystalline aggregates which can be confidently interpreted as former droplets of anatectic melt, i.e. nanogranitoids. In some cases, they coexist with coeval fluid inclusions under conditions of primary fluid-melt immiscibility. The re-evaluation of the metamorphic pressure and temperature conditions with up-to-date phase equilibria modelling, combined with the identification of nanogranitoids and fluid inclusions, suggests metamorphic peak equilibration and partial melting in presence of a COH-fluid at T ~1000°C and P > 7 kbar. To date, this is the oldest verified occurrence of nanogranitoids and fluid-melt immiscibility during garnet growth in a partially molten environment.

show abstract

Primary CO2-bearing fluid inclusions in granulitic garnet usually do not survive

Cited by 33 publications

References 43 publications

Anatectic melt inclusions in ultra high temperature granulites

Anatectic melt inclusions in ultra high temperature granulites

Abiotic passive nitrogen and methane enrichment during exhumation of subducted rocks: Primary multiphase fluid inclusions in high‐pressure rocks from the Cabo Ortegal Complex, NW Spain

Mesoarchean melt and fluid inclusions in garnet from the Kangerlussuaq basement, Southeast Greenland

Contact Info

Product

Resources

About