Intercalibration of standards, absolute ages and uncertainties in 40Ar/39Ar dating

Constraining timescales of focused magmatic accretion and extension in the Afar crust using lava geochronology

“…The oldest lavas in our geochronological data set were sampled B2 km from the edge of the graben and have 40 Ar- 39 Table 1). Although deformation of these flows by normal faulting currently prevents the reconstruction of individual eruptive systems, and it is, therefore, not possible to precisely locate the paleo-eruptive fissures, potential flow lengths can be estimated from the width of the current neovolcanic zone (assuming axial emplacement).…”

“…Future work involving detailed structural investigations and further geochronological analysis will build upon the constraints presented to develop understanding of how this and other mature rift systems develop during the latter phases of continental break-up. 40 Ar- 39 Ar geochronology. Samples were first inspected in thin section to select those with textures that were as close to holocrystalline and equigranular as possible and to identify the appropriate size fraction required for a groundmass separate.…”

“…This is partly due to the remoteness of this region, but also the analytical challenges associated with obtaining geochronological data for the young basaltic lavas that form the segment surface. In this paper, we present new 40 Ar/ 39 Ar plateau ages for basaltic lavas from the eastern rift flank that provide constraints on the timing of volcanic-tectonic processes and history of focused melt intrusion. 39 Ar geochronology.…”

“…Geochronology of low-K basaltic lavas remains analytically challenging, however meaningful age data can be obtained with suitable analytical techniques (Methods). 40 Ar-39 Ar step-heating experiments were performed on groundmass separates of eight lavas from the rift flank; 4 of which produced age-spectra suitable for plateau age determinations, while the remaining samples produced disturbed age-spectra unsuitable for a plateau age interpretation, most likely due to the effects of 39 Ar recoil during sample irradiation 24 . Age data from the successful step-heating experiments is listed in Table 1 and the age-spectra from the step-heating experiments shown in Fig.…”

Connecting local environmental sequences to global climate patterns: evidence from the hominin-bearing Hadar Formation, Ethiopia

“…For more accurate age determinations, as well as for comparison to the orbitally tuned marine record, ages for the Sidi Hakoma Tuff (SHT), the Kada Damum Basalt (KMB), Triple Tuff 4 (TT-4), the Kada Hadar Tuff (KHT), and the Bouroukie Tuffs 2L and 2U (BKT-2L and -2U) that had been published using the former Fish Canyon (FC) sanidine standard age of 27.84 Ma (Deino and Potts, 1990) were recalibrated using the revised standard age of 28.02 Ma (Renne et al, 1998) by multiplying the former age by 1.0065 (and supported by unpublished '^''Ar/^^Ar analysis by C.J.C). This standard date is also in closer accordance to the suggested FC age based upon orbitally tuned evidence (e.g., Hilgen et al, 1997;Kuiper et al, 2004).…”