Neodymium diffusion in orthopyroxene: Experimental studies and applications to geological and planetary problems

摘要: Abstract We have determined the Nd 3+ diffusion kinetics in natural enstatite crystals as a function of temperature, f (O 2 ) and crystallographic direction at 1 bar pressure applied these data to several terrestrial planetary problems. The is found be anisotropic with parallel c -axial being significantly greater than that - b -axis. Also, D (// likely somewhat ). Diffusion experiments do not show significant dependence (Nd on within range defined by IW buffer 1.5 log unit above WM buffer. observed anisotropy weak effect may understood considering crystal structure pathways. Using experimental for ), we calculated closure temperature Sm–Nd geochronological system during cooling rate, grain size geometry, initial (peak) direction. also evaluated approximate domain validity temperatures basis an infinite plane sheet model finite sheets showing diffusion. These results provide quantitative framework interpretation mineral ages orthopyroxene samples. discuss implications our problems melting subsolidus mantle rocks, resetting mesosiderites. It proposed earlier [Ganguly J., Yang H., Ghose S., 1994. Thermal history mesosiderites: Quantitative constraints from compositional zoning Fe–Mg ordering orthopyroxene. Geochim. Cosmochim. Acta 58, 2711–2723] could lead ∼90 Ma difference between U–Pb age mesosiderites, thus obviating need “impulsive disturbance” [Prinzhoffer A, Papanastassiou D.A, Wasserburg G.J., 1992. Samarium–neodymium evolution meteorites. 56, 797–815].