Disorientation control on trace element segregation in fluid-affected low-angle boundaries in olivine

Abstract

The geometry and composition of deformation-related low-angle boundaries in naturally-10 deformed olivine were characterized by electron backscattered diffraction (EBSD) and atom probe 11 tomography (APT). EBSD data show the presence of discrete low-angle tilt boundaries, which formed 12 by sub-grain rotation recrystallisation associated with the (100)[001] slip system during fluid-13 catalysed metamorphism and deformation. APT analyses of these interfaces show the preferential 14 segregation of olivine-derived trace elements (Ca, Al, Ti, P, Mn, Na and Co) to the low-angle 15 boundaries. Boundaries with < 2° show marked enrichment associated with the presence of multiple, 16 non-parallel dislocation types. However, at larger disorientation angles (> 2°), the interfaces become 17 more ordered and linear enrichment of trace elements coincides with the orientation of dislocations 18 inferred from the EBSD data. These boundaries show a systematic increase of trace element 19 concentration with disorientation angle. Olivine-derived trace elements segregated to the low-angle 20 boundaries are interpreted to be captured and travel with dislocation as they migrate to the sub-grain 21 boundary interfaces. However, the presence of exotic trace elements Cl and H, also enriched in the 22 low-angle boundaries, likely reflect the contribution of an external fluid source during the fluid-23

Atomic-scale Element and Isotopic Investigation of 25Mg-rich Stardust from an H-burning Supernova

“…and conditions(Tacchetto et al 2021) demonstrates a similar stochiometric bias in the terrestrial olivine APT data, i.e., Si (14.94 at%), Mg (29.05 at%), Fe (9.04 at%), and O (46.98 at%). The quantification of oxygen anions via APT is known to be problematic due to the inability of APT to discriminate between the O + and O 2 ++ at a mass/charge of 16 Da (Reddy…”

Clustering and interfacial segregation of radiogenic Pb in a mineral host – inclusion system Tracing two-stage Pb and trace element mobility in monazite inclusions in rutile

“…Also, P and S have different degrees of segregation towards boundaries with different orientations in Ni (Larere et al, 1988) and it is apparent that trace elements segregate in different amounts in function to disorientation in olivine (Tacchetto et al, 2021). The segregation into boundaries for ionic systems is more complex since charge compensation needs to be considered (Kliewer, 1965;Sutton et al, 1995).…”

Rapid hydration and weakening of anhydrite under stress: Implications for natural hydration in the Earth’s crust and mantle

“…Further, segregation of (incompatible) elements and their enrichment in grain interfaces is considered to have a significant impact on the physical and chemical properties of mantle rocks (Hiraga et al, 2007). Interfacial segregation linked with grain boundary character distribution (GBCD) may lead to grain boundary energy minimization (Tacchetto et al, 2021).…”