Abstract
La Virgen tephra is the product of the youngest and most voluminous explosive eruption of Las Tres Vírgenes volcano (Baja California). Combined U–Th and (U–Th)/He zircon dating allows accurate correction for uranium-series disequilibrium, and yields an eruption age for La Virgen tephra of
30.7
−
1.4
+
1.8
ka
(2
σ). No difference in eruption ages was found between samples from proximal and distal La Virgen tephra. A previously undated tephra south of Las Tres Vírgenes volcano yielded U–Th and (U–Th)/He zircon ages overlapping those of La Virgen tephra, which suggests that both units are identical.
3He surface exposure ages (
T
3) of overlying mafic lavas are 25.5
±
4.4 and 22.0
±
2.5
ka, and agree within uncertainties with
21Ne exposure ages (
T
21).
T
3 and
T
21 ages for dome lava south of La Virgen are slightly older (
T
3
=
42.5
±
3.8
ka). (U–Th)/He and surface exposure ages are stratigraphically consistent, whereas a published Holocene
14C charcoal age from the distal site could not be confirmed. Instead, abundant zircon crystals with (U–Th)/He ages between ∼1 and 22
Ma are interpreted as undegassed detrital grains, suggesting reworking of pumice at the distal location. The results presented here underscore the potential of combined U–Th and (U–Th)/He zircon dating for Quaternary tephrochronology.