146Sm-142Nd formation interval for the lunar mantle

A Rb–Sr and Sm–Nd isotope geochronology and trace element study of lunar meteorite LaPaz Icefield 02205

“…The latter can therefore be used to estimate the shielding depth of LAP 02205 without introducing large errors. From Figure 4 of Lingenfelter et al (1972), the ε 149 Sm = -3.5 is consistent with 3 Ga irradiation at a shielding depth of ~800 g/cm 2 , or ~2.7 m below the surface in a rock with the density for LAP 02205 in this study from the isotopic shift of the samarium isotopes (Nyquist et al, 1995). This correction term is similar to the external 2σ-reproducibility of the standard (4.5 and 3.9 ppm for the AMES 97 and La Jolla isotope standards, respectively).…”

“…(Rankenburg et al, 2006). The formation interval for the lunar mantle, however, is model dependent and ranges between 30 to 50 Ma after solar system formation from Hf-W isotopes (Kleine et al, 2005;Shearer and Newsom, 2000) and 215 to 250 Ma from 146,147 Sm/ 142,143 Nd isotopes (Nyquist et al, 1995;Rankenburg et al, 2006). For the two-stage mixing model on the basis of Sm-Nd isotopes ( Figure 8B), a lunar mantle formation interval of 215 Ma (Rankenburg et al, 2006) (Table 3).…”

“…The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic evolution of the lunar mantle source regions of the LAP parent magma, Apollo 12 and 15 olivine basalts, and KREEP are modeled assuming two-stage models ( Figure 8A and B) with the mixing parameters listed in Table 3 (data from this study, Borg et al, 2004;Gnos et al, 2004;Jolliff et al, 2003;Neal, 2001;Nyquist and Shih, 1992;Nyquist et al, 1995;Rankenburg et al, 2006;Snyder et al, 1997). Because the trace element abundances in the SaU 169 impact melt breccia are the highest among the KREEP-rich samples, it probably represents a relatively 'pure' KREEP composition, and the REE and Sr concentrations of SaU 169 (Gnos et al, 2004) are therefore used in the mixing calculations.…”

Constraints on Martian differentiation processes from RbSr and SmNd isotopic analyses of the basaltic shergottite QUE 94201

“…A model age for the depletion event can be calculated using the techniques outlined in Nyquist et al (1995b), and by assuming values are similar to the most depleted lunar sources postulated to exist at 4.4 to 4.5 Ga by Misawa et al (1993) and Snyder et al (1994) and inferred from the 142Nd data of lunar basalts (Nyquist et al, 1995b (Table 3). Likewise, only the proportions of garnet in the source and in the melt assemblage will effect the Sm and Nd abundances in the modeled melts (Table 3).…”

Feldspathic clasts in Yamato-86032: Remnants of the lunar crust with implications for its formation and impact history

“…They also are signficantly less than for most Apollo returned samples. Of the 14 mare basalts for which Nyquist et al (1995) reported Sm-isotopic data, for example, only three of them have neutron-capture induced 149 Sm anomalies of <~-1 ε-unit: 70135, 74255, and lunar meteorite Asuka-881757. Of these, ε 149 Sm = -1.2±0.4 for basalt 70135 is the closest match to the Y-86032 data.…”