escherer

Prof. Erik E. Scherer

Westfälische Wilhelms-Universität Münster - Geochemistry

Principal Investigator

Institut für Mineralogie, Corrensstrasse 24, D-48149 Münster
Tel.: +49 251-8333504, e-mail: escherer@unimuenster.de

Summary

Lunar impact basins and their deposits represent the most detailed and best-preserved record of the timing, flux, and composition of late accretion in the inner solar system. However, reconciling interpretations of isotopic ages (suggesting a late heavy bombardment at 3.9 Ga) with the cratering record remains controversial. Thus, applying improved methods and novel approaches to the geochronology of ancient (>3.8 Ga) lunar impact rocks will produce new constraints for models of the lunar accretion history between 4.5 and 3.8 Ga. New Lu-Hf, Sm-Nd, Rb-Sr, and Pb-Pb ages and applying in situ U-Pb dating of zircons in lunar impactites by ion microprobe will provide new insight into the significance of ages of impact events and isochron resetting due to late basin-forming impacts. In particular the U-Pb zircon and Lu-Hf systems are characterized by high closure temperatures, and will likely display a different response to secondary overprints by later impacts compared to the Ar-Ar plagioclase chronometer. The samples we will analyse have siderophile element compositions that may be related to specific impactors, include samples that have yielded ambiguous Ar-Ar dates, or apparently predate the ~3.9 Ga distribution peak that is dominated by Ar-Ar ages. Linking the new data to impact rocks with specific highly siderophile element (HSE) and siderophile volatile element (SVE) compositions (subproject B1) may also place constraints on the flux of volatile rich planetesimals during late accretion. Another objective will be to provide new data to improve the chronology function of the lunar cratering record, in particular for older geologic units that comprise ejecta deposits. The lunar chronology function, established in the early 1980s, provides the basis for ages of other bodies of the inner solar system that were determined by crater counting. Some ages used for the chronology function were obtained on lunar impactites from the Apollo 16 landing site. However, the significance of many of the ages obtained in the 1970s is unclear. Thus, here we will use multiple decay systems to date petrographically well-characterized impact melt rocks and breccias, both simple and complex. By offering updated constraints on the lunar accretion history, this new data will then be used to test different models of post-4.5 Ga mass accretion rates in the inner solar system (A2, A3).

 
Publications

Bast, R., Scherer, E. E., Sprung, P., Mezger, K., Fischer-Gödde, M., 2017: Reconciliation of the excess 176Hf conundrum in meteorites: Recent disturbances of the Lu-Hf and Sm-Nd isotope systematicsGeochimica et Cosmochimica Acta, Vol. 212, pp. 303-323. 10.1016/j.gca.2017.05.043

Bast, R., Scherer, E. E., Bischoff, A., 2017: The 176Lu-176Hf systematics of ALM-A: A sample of the recent Almahata Sitta meteorite fall. Geochemical Perspectives Letters, Vol. 3, pp. 45-54. 10.7185/geochemlet.1705

 
Conferences

Haber, T. and E. E. Scherer (2019): A History of Outhouse Rock.  GeoMünster.

Haber, T. and E. E. Scherer (2019): Multi-system chronometry of lunar breccia 67955.  Goldschmidt conference, Barcelona.

Haber, T. and E. E. Scherer (2018): One Rock – Two Dates: The Curious Case of Feldspathic Granulitic Breccia 77017. Poster presentation at the American Geophysical Union, Fall Meeting, Washington D.C.

Haber, T. and E. E. Scherer (2018): The age of lunar impact melt rock 67935 – Imbrium or not? Oral presentation at the European Planetary Science Congress, Berlin.

Borisov, D., Hiesinger, H., Iqbal, W., Scherer, E. E., Haber, T., van der Bogert, C. H. (2018): An interdisciplinary re-investigation of the Apollo 14 landing site - Pb-Pb chronology of the impact melt rock 14310 and new crater size-frequency distribution measurements. 49th Lunar and Planetary Science Conference, the Woodlands, TX, USA.

Haber, T. and E. E. Scherer (2017): Separating ≤20 µm sized mineral fractions for geochronology of lunar sample 67935. Paneth Kolloquium, Nördlingen, Germany

Haber, T. and Scherer, E. E., Bast, R. and P. Sprung (2017): 176Lu-176Hf Isochron Dating of Strongly Cosmic Ray Exposed Samples – A case study on Apollo 14 Impact Melt Rock 14310.  48th Lunar and Planetary Science Conference, the Woodlands, TX, USA.