Continental rifting at magmatic centres: structural implications from the Late Quaternary Menengai Caldera, central Kenya Rift

Abstract

The structural evolution of calderas in rifts helps to characterize the spatiotemporal relationships between magmatism, long wavelength crustal deformation and the formation of tectonic deformation zones along the rift axis. We document the structural characteristics of the c. 36 ka old Menengai Caldera located within a young zone of extension in the central Kenya Rift. Field mapping and high-resolution digital surface models show that NNE-striking Holocene normal faults perpendicular to the regional ESE–WNW extension direction dominate the interior sectors of the rift. Inside the caldera, these structures are overprinted by post-collapse doming and faulting of the magmatic centre, resulting in obliquely slipping normal faults bounding a resurgence horst. Radiocarbon dating of faulted units as young as 5 ka cal BP and the palaeo-shorelines of a lake formed during the African Humid Period in the Nakuru Basin indicate that volcanism and fault activity inside and in the vicinity of Menengai must have been sustained during the Holocene. Our analysis confirms that the caldera is located at the centre of an extending rift segment and suggests that other magmatic centres and young zones of faulting along the volcano-tectonic axis of the Kenya Rift may constitute nucleation points of faulting that ultimately foster future continental break-up. Supplementary material: 40 Ar/ 39 Ar radiometric dating data table is available at: https://doi.org/10.6084/m9.figshare.c.4647818

Mid‐Pleistocene to Recent Crustal Extension in the Inner Graben of the Northern Kenya Rift

“…It has, however, been suggested that due to the alternating layers of volcanics and sedimentary strata of the intrarift units of the NKR, such steep dip estimates from purely volcanic settings cannot be transferred to the NKR (Le Gall et al., 2000). At the surface, extensional fractures are suggested to partly accommodate the near‐surface extension at subvertical fault scarps (e.g., Acocella et al., 2003; Corti, 2009), and such extensional fractures are very common in the Kenya Rift (e.g., Atmaoui & Hollnack, 2003; Muirhead et al., 2016; Riedl et al., 2020).…”

A comprehensive database of active and potentially-active continental faults in Chile at 1:25,000 scale

“…We applied classical techniques in tectonic geomorphology summarized in seminal textbooks [45][46][47] for mapping newly-identified faults and remapping structures from previous studies at a uniform 1:25,000 scale. We rely on our past experience in mapping active faults in different tectonic environments using field observations and remote sensing data 16,[48][49][50][51][52][53][54][55][56] , in addition to the criteria used in previous active fault databases [57][58][59][60][61] . We paid special attention to interpreting fault trace continuity using a uniform mapping scale based on the surface expression of faults, not the inferred seismogenic expression at depth.…”

“…Further applications have been, for example, assessing anthropogenic factors in triggered and induced seismicity 12 such as stress changes to the crust caused by hydroelectric reservoirs, underground gas storage, groundwater pumping, or fracking 13 , 14 . Many geothermal fields occur in tectonically-active regions and maps of active faults have been used both for exploration and selection of drilling sites 15 , 16 as well as for reservoir modelling during exploitation 17 , 18 . Active fault databases have been also used in studies of volcanotectonic interactions and structural control on volcanism in rifts 19 and arcs 20 , in the interpretation of present-day stress indicators 21 , 22 as well as to infer sources of pre-instrumental earthquakes 23 and the response of groundwater to near and farfield earthquakes 24 .…”

Controls on Asymmetric Rift Dynamics: Numerical Modeling of Strain Localization and Fault Evolution in the Kenya Rift

“…As such, Quaternary volcano‐sedimentary units are areally restricted to the inner graben, which has been the focus of densely spaced normal faulting that has resulted in a horst‐and‐graben landscape (Hackman, 1988; McCall, 1967; Thompson & Dodson, 1963). Furthermore, the inner graben has been characterized by volcanic, seismic, and hydrothermal activity during the last 2 Ma (Clarke et al., 1990; Riedl et al., 2020; Tongue et al., 1992).…”