TY - JOUR
T1 - 40Ar/ 39Ar ages in mantle xenolith phlogopites
T2 - Determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands
AU - Wartho, Jo Anne
AU - Kelley, Simon P.
PY - 2003/12/1
Y1 - 2003/12/1
N2 - Kimberlites are extraordinary natural phenomena, ascending through the Earth's lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to test whether other mantle phlogopite cores may yield meaningful ages. Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9-6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2-15 hours (assuming the same magma temperature).
AB - Kimberlites are extraordinary natural phenomena, ascending through the Earth's lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to test whether other mantle phlogopite cores may yield meaningful ages. Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9-6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2-15 hours (assuming the same magma temperature).
UR - http://www.scopus.com/inward/record.url?scp=0348225373&partnerID=8YFLogxK
U2 - 10.1144/GSL.SP.2003.220.01.14
DO - 10.1144/GSL.SP.2003.220.01.14
M3 - Article
AN - SCOPUS:0348225373
VL - 220
SP - 231
EP - 248
JO - Geological Society Special Publications
JF - Geological Society Special Publications
SN - 0305-8719
ER -