The Los Angeles martian diabase: Phosphate U-Th-Pb geochronology and mantle source constraints

In situ laser ablation inductively coupled mass spectrometry (LA ICP-MS) is used to determine the U-Th-Pb age of phosphates ferromerrillite and apatite in Los Angeles shergottitic meteorite. The initial 207Pb/206Pb was refined by analyzing K-rich diaplectic glass. LA ICP-MS mapping document zones elevated U Th content establish textural controls on isotope ages. By critically assessing dispersion dataset due Pb-diffusion during high-temperature shock metamorphism, as a result subsequent terrestrial contamination, we obtain best-estimate U-Pb 169 ± 5 Ma anchored at an 0.98390 0.00018. This statistically indistinguishable from joint-isochron 179 6 with 208Pb/206Pb 2.5151 0.0028. These results complement previously determined Rb-Sr Sm-Nd ages provide independent evidence for having crystallized medium-grained basic rock thick lava flow or high-level intrusion late Amazonian ∼170 Ma. context martian mantle evolution, common-Pb values suggest that originated source (µ2 ∼ 3.2) similar enriched members shergottite meteorite clan. systematics both were locally affected diffusive Pb-loss thin U-enriched marginal domains more profoundly shock-induced melt pockets where temperatures briefly exceeded 2000 °C. reveal: (1) how precise can be attained phosphates; (2) importance microtextural contextualization data; (3) timescales cooling conditions sufficient promote local re-equilibration Pb over 10 s microns; (4) locate highest U/Pb Th/Pb, which increases precision lower intercept isochron regression lines.