Assessing the Relationship Between Rift Magmatism and Differing Modes of Strain Distribution in an Advanced Continental Rift Setting: Manda Hararo, Afar

It has been recognized that episodes of increased rift magmatism are likely related to pulses of continental rift extension. The Afar Depression of the East African Rift offers the opportunity to investigate a recent pulse of extension and large volume magmatism followed by focused strain and small volume magmatism. Here, we examine a suite of basalts from three previously identified lava series found in Afar (The Afar Stratoid Series from 3.9 1.6 Ma, The Gulf Series from 2.8 0.3 Ma, and The Axial Series 0.7 Ma Present). We present petrographic and whole-rock geochemical data on 40 samples from basalts located in the Manda Hararo rift sector and fill gaps in the extant geochemical data for these lava series in Afar. Using mantle melting models, we explore whether the source of the volumetrically significant Afar Stratoid Series exhibits different conditions of melt generation when compared to the less volumetrically significant Gulf and Axial series. Our initial observations show little evidence of changes in the mantle source between the three magmatic series. Incompatible trace element concentrations of these basalts are broadly parallel and suggest similar degrees of mantle melting. We examine the possible reasons for observed similarities between lavas produced within the three different magmatic series. Our investigation shows that probing the melting processes is an important constraint in understanding the connection between pulses of extension and rift magmatism. Such observations are critical to establishing the relationship between the generation of magma, the mode of strain distribution, and the localization of strain during advanced continental rifting.