Nonmonotonic thermal histories and contrasting kinetics of multiple thermochronometers

Evidence for shock heating and constraints on Martian surface temperatures revealed by 40Ar/39Ar thermochronometry of Martian meteorites

“…Brief heating above the diffusive "kinetic crossover" observed on Arrhenius plots. As a result of apparent differences in diffusion kinetics between glass (or plagioclase) and pyroxene (i.e., strongly contrasting E a ), 40 Ar* may diffuse more rapidly from pyroxene under certain high-temperature conditions (i.e., above the temperature at which the extrapolated Ar Arrhenius relationships intersect; the "kinetic crossover", as recently discussed by Reiners, 2009). In Fig.…”

Thermochronology in Orogenic Systems

“…However, the notion that the effective diffusion dimension is an intrinsic property of a mineral-isotopic system seems unlikely, given that subgrain structures in minerals are demonstrably a function of their thermal and deformational histories. Other researchers have found evidence that a does correspond to the half-grain size for most mineral-isotopic systems (e.g., Farley, 2000;Goodwin and Renne, 1991;Hames and Bowring, 1994;Hess et al, 1993;Hodges and Bowring, 1995;Hodges et al, 1994;Onstott et al, 1991;Reiners andFarley, 1999, 2001;Reiners et al, 2004), but this relationship breaks down in samples subjected to intensive ductile or brittle deformation (e.g., Arnaud and Eide, 2000;Kramar et al, 2001;Mulch et al, 2002). In general, it seems prudent to assume that a is related to the physical grain size when applying eqns [18] and [20] unless samples show textural evidence for the extensive development of subgrain boundaries that may act as fast diffusion pathways, orin the case of K-feldspar -show direct evidence of the existence of multiple diffusion domains during incremental heating experiments.…”

“…Although such exercises sometimes can be complicated by episodic reheating events that can change the expected sequence of closure temperatures because of the differing kinetic properties of the thermochronometers (Reiners, 2009), such studies are a time-honored tradition among thermochronologists (e.g., Hurford, 1991;Wagner et al, 1977). However, three alternative approaches have Table 2.…”

A lattice Boltzmann model for noble gas diffusion in solids: The importance of domain shape and diffusive anisotropy and implications for thermochronometry

“…4). The Arrhenius relationships intersect (define a "kinetic crossover"; Reiners, 2009) at 800°C. Thus at lower temperatures diffusion proceeds primarily along the short axis and at higher temperatures diffusion proceeds primarily along the long axis.…”