section S1. Sample 15498
section S2. NRM behavior
section S3. Paleointensity
section S4. Rock magnetic properties
section S5. 40Ar/39Ar and 38Ar/37Ar thermochronology
fig. S1. Apollo 15 landing site and 15498 sampling context.
fig. S2. Sample 15498.
fig. S3. Backscattered scanning electron microscopy images of 15498 matrix showing absence of post-lithification microfracturing.
fig. S4. BSEM images of FeNi grains in 15498.
fig. S5. Equal-area stereographic projections of LC/LT and MC/MT magnetization components observed for peripheral subsamples of 15498.
fig. S6. AF demagnetization of sample 15498,282a over the range of the HC component.
fig. S7. Thellier-Thellier paleointensity experiments for subsamples 15498,313k1 and 15498,313k2 following the IZZI variant.
fig. S8. Paleointensity fidelity limit tests for 15498.
fig. S9. FORC distribution for sample 15498,287b1.
fig. S10. Rock magnetic experiments on 15498,282a.
fig. S11. PRM acquisition by 15498 subsample 15498,282a.
fig. S12. VRM decay experiment on sample 15498,282c.
fig. S13. The predicted effects of 600 Ma of solar heating at the lunar surface, calculated using the 15498 MP-MDD model.
fig. S14. Arrhenius plots with calculated diffusion coefficients for 39Ar and 37Ar released during the first 20 release steps.
fig. S15. Schematic depicting time-temperature conditions underlying our thermochronological models.
fig. S16. 15498 MP-MDD model predictions for diffusion of 40Ar* resulting from impact heating at 2000 Ma (to temperatures ranging between 450° and 675°C), followed by daytime heating to an effective mean temperature of 69°C after 600 Ma.
fig. S17. 15498 MP-MDD model predictions for diffusion of 40Ar* resulting from impact heating at various times in lunar history (to temperatures ranging between 450° and 675°C), followed by daytime heating to effective mean temperatures ranging between 35° and 56°C after 600 Ma.
fig. S18. 15498 MP-MDD model age spectra incorporating diffusion of 40Ar* resulting from impact heating at 650 Ma (to temperatures ranging between 450° and 675°C), followed by daytime heating to an effective mean temperature of 25°C after 600 Ma.
table S1. WDS measurements of metal grains in 15498 thin sections 298 and 299.
table S2A. NRM components identified for interior matrix glass subsamples of 15498.
table S2B. NRM components identified for peripheral matrix glass subsamples of 15498.
table S2C. Fisher mean component directions derived from 15498 data in table S2A.
table S3A. Thellier-Thellier paleointensity determinations for 15498 subsamples.
table S3B. Comparison of pTRM and pTRM check values for 15498 subsamples.
table S3C. ARM paleointensity determinations for 15498 subsamples.
table S3D. IRM paleointensity determinations for 15498 subsamples.
table S4. Rock magnetic and hysteresis parameters.
table S5. Anisotropy of ARM (85-mT ac field with 0.01-mT dc field).
table S6. Complete 40Ar/39Ar incremental heating results.
table S7. Oxide weight percent compositions of K-bearing phases in basalt clast 15498-282-1.
table S8. Summary of MP-MDD model parameters with cosmogenic 38Ar production rates for 15498.
table S9. Summary of 40Ar/39Ar chronology for 15498.
table S10. Reduced χ2 misfit statistics for best-fit thermochronometry models for a variety of breccia formation ages.
data file S1. 15498 demagnetization data sets.
data file S2. 15498 Thellier-Thellier paleointensity data sets.