Publication Date:
2019
Description:
〈span〉The Turkana Depression of northern Kenya and southern Ethiopia contains voluminous
plume-related basalts that mark the onset of the Paleogene–recent East African Rift System
(EARS) at ca. 45 Ma. Thus, the Turkana Depression is crucial to understanding the inception
of intracontinental rifting. However, the precise chronology of early rift-basin formation
in Turkana is poorly constrained. We present apatite fission-track and (U-Th-Sm)/He
thermochronology data from basement rocks from the margins of the north-south–trending
Lokichar Basin that constrain the onset of rift-related cooling. Thermal history modeling
of these data documents pronounced Eocene to Miocene denudational cooling of the basin-bounding
Lokichar fault footwall. These results, along with ~7 km of Paleogene to middle
Miocene syn-rift strata preserved in the Lokichar fault hanging wall, suggest that formation
of the Lokichar Basin began as early as ca. 45–40 Ma. Preexisting lithospheric heterogeneities
inherited from earlier Mesozoic rifting and Eocene plume magmatism likely facilitated the
broadly concurrent nucleation of strain in the Turkana Depression, up to ~15 m.y. earlier
than EARS initiation elsewhere. Late Paleogene extension in the Lokichar Basin and other
parts of Turkana significantly predate the Miocene creation of pronounced plume-related
topography in East Africa, suggesting that other mechanism(s), such as far-field stresses or
mantle basal drag, likely played a critical role during EARS inception.〈/span〉
Print ISSN:
0091-7613
Electronic ISSN:
1943-2682
Topics:
Geosciences
