Apatite u thhe dating

Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. PY - 2015Y1 - 2015N2 - Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity.

Melt sheets are amenable to high-precision dating by the U-Pb and 40Ar/39Ar methods, but many impact events do not produce them, or they are not preserved.

In contrast, five apatites from this sample yield dates between 205.9 ± 6.5 and 162.0 ± 5.3 Ma (2s), indicating variable postimpact helium loss due to low-temperature thermal disturbance. In cases where high-temperature shock metamorphism of the target materials has occurred without widespread melting, these isotopic chronometers may be partially reset and yield dates that are difficult to interpret unambiguously as the age of impact.

Preimpact titanite crystals from a shocked meta-anorthosite sample yield two dates consistent with the impact age, at 212 ± 27 and 214 ± 13 Ma (2s), and two younger dates of 189.6 ± 6.9 and 192.2 ± 9.8 Ma (2s), suggestive of postimpact helium loss. However, the (U-Th)/He chronometer is sensitive to thermal resetting and can provide a powerful new tool for dating impactites.

In cases where high-temperature shock metamorphism of the target materials has occurred without widespread melting, these isotopic chronometers may be partially reset and yield dates that are difficult to interpret unambiguously as the age of impact.

However, the (U-Th)/He chronometer is sensitive to thermal resetting and can provide a powerful new tool for dating impactites.

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