Metamorphic Ages Derived from Meteorites

 Meteorites are commonly dated using the 182Hf-182W decay (t1/2 = 8.9 Myr), a radiogenic process which is used to date the timing of core formation in terrestrial planets and other planetary bodies. Short-lived nuclides are optimal for dating processes that occurred within a relatively short time frame during the early Solar System because they can provide a high-resolution time scale for comparison (Holst et al., 2013). 

Calcium-Aluminum rich inclusions (CAIs) are the oldest known rock particles that condensed in our Solar System, and their remains can be found in primitive meteorites. Thus, a common method of dating chondrites is to analyze the difference in time since formation for bulk and/or metal separates and the CAIs found within the same sample.

The graph below records the Hf-W ages derived via bulk chondritic analyses from a suite of H and CR chondrites, and comparing the ε182-W of each separate to the ε182-W of the bulk chondrite and the initial ε182-W of CAIs. (Archer et al., 2019). 

Each shape represents a different chondrite which is named along the y-axis. The x-axis measures time since the last significant metamorphic event (in millions of years), which can also be considered time since CAI formation for meteorites which have remained relatively undisturbed since the early Solar System era. 

Section (a) houses the slope-derived ages for non-magnetic (NM) and slightly magnetic (SM) bulk separates. In section (b), the solid fills represent coarse metal grain separates (>150 um) and the shaded fills represent the finer grains (<150um). 

The error bars are the uncertainties for CAI ages calculated using the reported values from Kruijer et al. (2014). 

References

1. Archer G., Walker R., Tino J., Blackburn T., Kruijer T., Hellmann J. 2019. Siderophile element constraints on the thermal history of the H chondrite parent body. Geochimica et Cosmochimica Acta 245 pp 556-576

2. Holst J., Olsen M., Paton C., Nagashima K., Schiller M., Wieland D., Larsen K., Connelly J., Jorgensen J., Krot A., Nordlund A., Bizzarro M. 2013. 182Hf-182W age dating of a 26Al-poor inclusion and implications for the origin of short-lived radioisotopes in the early solar system. Proceedings of the National Academy of Sciences of the United States of America v110 n22 (20130528): pp 8819-8823

3. Kruijer T. S., Kleine T., Fischer-Go¨dde M., Burkhardt C., Wieler R. (2014) Nucleosynthetic W isotope anomalies and the Hf-W chronometry of Ca-Al-rich inclusions. Earth Planet. Sci. Lett. 403, 317–327.