Feedback between topography and lithosphere–asthenosphere dynamics beneath the Yerer‐Tulu Wellel volcano‐tectonic lineament: Insights from apatite thermochronology and basalt geochemistry

Abstract

Ethiopian topography is dominated by an ~2‐km high plateau that underwent uplift and incision after or during the Cenozoic Flood Basalt event in the Early Oligocene; however, the timing and drivers of plateau dynamics are poorly constrained. We constrain the onset and causal mechanism of plateau uplift using thermochronologic and basaltic geochemical techniques. We performed low‐temperature apatite fission track and (U–Th)/He thermochronologic dating on three Neoproterozoic basement rocks from the Yerer‐Tullu Wellel volcano‐tectonic lineament, directly west of Addis Ababa. Thermal models based on these results suggest this part of the plateau underwent slight heating in the Oligocene through Late Miocene, followed by rapid and recent cooling until the present day. To determine the nature of these Cenozoic thermal events, we compiled and reinterpreted a suite of partially published basaltic geochemical data. These geochemical data suggest this part of the plateau is underlain by a metasomatized and pyroxenite‐rich lower lithosphere that began to drip into the asthenosphere in the Miocene. Fault‐facilitated release of the lithospheric drip in the Late Cenozoic encouraged basin inversion, driving rapid cooling and incision within the last 5 Ma. Our study suggests that a direct coupling between lithospheric removal and topographic response highlights significant plateau formation around the Yerer‐Tullu Wellel volcano‐tectonic lineament zone within the Pliocene.

Geodynamic Controls on Basaltic Volcanism in the Arabian Peninsula: Evolution of Harrat Uwayrid, Saudi Arabia

“…A similar geochemical pattern attributed to metasomatism by hydrous fluids is observed in mafic volcanics of the Yerer–Tulul Wellel Volcano‐Tectonic Lineament in Ethiopia (Bowden et al., 2022; Rooney et al., 2017). This region is underlain by the same Arabian‐Nubian Shield basement and has likely undergone the same orogenic history that characterizes the Harrat Uwayrid region (Bowden et al., 2020).…”

“…First‐order morphological features of Harrat Uwayrid are also consistent with geophysical models of laminar lithospheric removal: the upper lithosphere in areas undergoing lithospheric removal will initially experience a >∼120 m depression as the lower lithosphere begins to be removed; after detachment, topographic rebound may return the elevation to heights greater than the unperturbed level (Elkins‐Tanton, 2005). These predictions are met at several localities that are interpreted to have experienced recent lithospheric removal (e.g., Ethiopia: Bowden et al., 2022; the Anatolian Plateau: Gall et al., 2021, Göğüş et al., 2017). The youngest volcanism at Harrat Uwayrid is restricted to topographic depressions, most notably the ∼60 km across, ∼200 m deep Al Jaww in the center of the harrat (Figure 2).…”