The fate of fluid inclusions during high‐temperature experimental deformation of olivine aggregates

Abstract

Torsion experiments on initially wet and dry olivine aggregates at equivalent deformation conditions investigated the fate of fluid inclusions (FIs) during high-temperature deformation. Wet samples were produced by adding water to San Carlos olivine powders before hot pressing; those hot pressed without water are considered dry. After hot pressing, wet and dry aggregates have comparable grain sizes, but wet aggregates have more abundant primary FIs. Talc jackets were fitted around some wet and dry samples prior to deformation to hydrate samples during deformation via talc dehydration at elevated temperature, whereas other samples were deformed without talc. At similar strain rates (~1.0 × 10 À4 s À1), the peak shear stress for the dry sample (no talc) was 190-220 MPa, whereas all other samples reached 180 MPa; the strengths of wet (± talc) and dry (+ talc) specimens appear similar. Deformed samples reveal abundant FIs, reduced grain size, shape preferred orientation of olivine, and a pervasive low-angle fabric (C′) to the shear plane defined by aligned FIs. Samples deformed with talc have FI-rich and FI-depleted domains; where FIs are abundant, the C′ fabric is better developed and grain size is smaller. Electron backscatter diffraction pole figures suggest that olivine deformed in the dislocation creep regime via the (010)[100] slip system. Results of these experiments suggest that FIs are redistributed during dislocation creep, leading to the development of grain-scale, high-diffusivity pathways.

Shallow melting of MORB‐like mantle under hot continental lithosphere, Central Anatolia

“…An alternative possibility for the relative enrichments in Ba without enrichments in LREE would be a component derived from (altered) oceanic crust during a past episode of subduction (Figure 9b). Melts of altered oceanic crust have too anomalously high Zr/Hf and Hf/Sm to be a likely candidate [Carter et al, 2015], whereas hydrous fluids derived from altered oceanic crust may account for some of the intraplate-like enrichment [Green and John, 2003]. We suggest below that the contribution from the intraplate-like component is greatest in melts that are mostly derived from a deep source, leading us to favor contributions from an intraplate mantle over contributions from a subducted slab.…”

“…Of these, the similarity between the Pb isotope signatures inferred for the subductionmodified mantle domain and eastern Mediterranean sediments, as well as the trend of e Hf and e Nd (Figure 4), suggest that Mediterranean Neotethyan sediments and/or derivative fluids are likely Geochemistry, Geophysics, Geosystems 10.1002/2016GC006772 responsible for the distinct chemical and isotopic characteristics of the subduction-related contribution to the Hasan Monogenetic Cluster basalts. Melts or fluids derived from oceanic crust [Elliott, 2003;Carter et al, 2015], in contrast, cannot account for the unradiogenic Nd and Hf isotopes of the subductionmodified mantle, nor its relatively high La/Sm and Th/Nb (Figures 7 and 9). Because certain trace element characteristics of the basalts, most notably La/Sm, overlap those of sediments, the agent for subductionrelated contamination of the mantle may be sediment melts, rather than sediments themselves.…”

Influence of Saline Fluids on the Electrical Conductivity of Olivine Aggregates at High Temperature and High Pressure and Its Geological Implications

“…The high-conductivity anomalies have been shown to occur in relatively cold subduction zones, which might be caused by the presence of aqueous fluids (Pommier and Evans, 2017). Previous studies of fluid inclusions in deep Earth rocks and hightemperature and high-pressure experiments have demonstrated that aqueous fluids with some form of volatile and salt species are abundant in subduction zones (Carter et al, 2015;Huang et al, 2019;Lacovino et al, 2020). NaCl-bearing aqueous fluids have been proposed to be the most significant saline fluid in subduction environments because Na + and Cl − are the most dominant ions in most saline fluid inclusions (Morikawa et al, 2016).…”