We performed deformation and grain growth experiments on natural olivine aggregates with olivine water contents (C OH = 600 ± 300 H/10 6 Si) similar to upper mantle olivine, at 1000-1200°C and 1,400 ± 100 MPa confining pressure. Our experiments differ from published grain growth studies in that most were (1) conducted on natural olivine cores rather than hot-pressed aggregates and (2) dynamically recrystallized prior to or during grain growth. We combine our results with similar experiments performed at 1200-1300°C and fit the data to a grain growth relationship, yielding a growth exponent (p) of 3.2, activation energy (E G) 620 ± 145 kJ mol −1 (570 ± 145 kJ mol −1 when accounting for the role of temperature on water content), activation volume (V G)~5 × 10 −6 m 3 mol −1 , and rate constant (k 0) 1.8 × 10 3 m p s −1. Our E G is within uncertainty of that predicted for dislocation creep of wet olivine (E* = 480 ± 40 kJ mol −1). Grain size in strain rate-stepping samples adjusted to the olivine piezometer within 1.3-7.9% strain. The active grain boundary migration processes during deformation and dynamic recrystallization affect the kinetics of postdeformation grain growth, as grain boundary migration driven by strain energy density (ρGBM) may delay the onset of grain growth driven by interfacial energy (γGBM). We compared our postdeformation grain growth rates with data from previously published hydrostatic annealing experiments on synthetic olivine. At geologic timescales, the growth rates are much slower than predicted by the existing wet olivine grain growth law.

The Beypazarı granitoid is emplaced in a Late Cretaceous volcanic arc in north central Turkey and provides evidence for processes that occurred during the closure of the Neo-Tethys Ocean. Zircons from its northern granodiorite and quartz monzonite exposure are dated in rock thin section and display characteristic igneous zoning in cathodoluminescence (CL). Its oldest Late Cretaceous ages (95.4 ± 4.2-91.3 ± 6.5 Ma, 238 U/ 206 Pb, ±1σ) time early crystallization from rising melts, but inspection of the youngest grains in composite CL-secondary electron images shows they are located along grain boundaries surrounded by alteration textures and were possibly affected by fluid-driven metamorphism. Ages obtained from zircon mid-rims (82.7 ± 6.0-70.5 ± 3.4 Ma) record continuous crystallization of the pluton. Here, we model the Late Cretaceous development of the Beypazarı granitoid wherein subduction of Neo-Tethyan oceanic plate, multiple injections and mixing of magma, and crustal contribution during ascent are the cause of geochemical heterogeneities within the pluton and account for protracted zircon crystallization. The model speculates that the pluton is in the overriding tectonic plate of a series of stacked, north-dipping subduction zones that record the closure of Neo-Tethyan ocean basins during the geologic assembly of Turkey.

We performed deformation and grain growth experiments on natural olivine aggregates with moderate olivine water contents (COH = 600±300 ppm H/Si) at 1000-1200°C and a confining pressure of 1400±100 MPa. Our experiments differ from published grain growth studies in that most were: 1) conducted on natural olivine cores rather than hot-pressed aggregates, and 2) dynamically recrystallized prior to or during grain growth. The active grain boundary migration processes during deformation and dynamic recrystallization affect the kinetics of post-deformation grain growth, as grain boundary migration driven by strain energy density (⍴GBM) may delay the onset of grain growth driven by interfacial energy (γGBM). We compared our post-deformation grain growth rates with data from previously published hydrostatic annealing experiments on synthetic olivine. At geologic timescales, the growth rates are slower than predicted by the existing wet olivine grain growth law.

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