Contrasting styles of silicic magma mixing dynamics in Turkana Basin, Kenya: Insights from high-resolution tephrochronological tools
Saini Samim, Hayden Dalton, David Phillips, Janet Hergt
Affiliations: School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Australia
Presentation type: Talk
Presentation time: Monday 11:00 - 11:15, Room R280
Programme No: 1.7.3
Abstract
Distal volcanic products are crucial for building a tephrochronological framework and can serve as important messengers of the volcanic processes that produced them. The Turkana Basin, NW Kenya, located within the East African Rift System has been subjected to multiple episodes of silicic volcanism, resulting in numerous volcanic ash layers (tuffs) intercalated with paleoanthropologically significant fossiliferous horizons. Whilst the tuffs and their entrained pumice clasts have been frequently targeted for tephrochronological reasons, there is limited knowledge on the petrological implications of these volcanic products. Here we provide a comprehensive study on the feldspars, pumice and tuff glass chemistry of two distinct tuff layers- the Middle Nariokotome (MNK) and the Morutot tuffs - by utilizing a combined methodology of high-precision 40Ar/39Ar geochronology, and shard-specific major and LA-ICP-MS trace element geochemistry. High-precision ages from individual feldspar grains reveals significant age dispersions (~206kyr for MNK and ~60kyr for Morutot) suggesting 'cold storage' of feldspar crystals. In addition, pumice and tuff glass geochemistry indicate contributions of less evolved silicic magmas leading to heterogeneous geochemical signatures on a clast-scale and possibly triggering eruptions. For the MNK tuff, we see two distinct geochemical components, suspected to result from mingling of magmas. In contrast, the Morutot volcanic products reveals evidence of chemical mixing of magmas through chaotic dynamics, leaving complex signatures typified by contemporaneous pumice clasts that exhibit either intra-clast heterogeneity or homogeneity. Altogether, this integrated approach refines the tephrochronology of the Turkana Basin and also provides critical insights into the regional silicic magma dynamic processes.