Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift

Abstract

The Study of Extension and maGmatism in Malawi aNd Tanzania (SEGMeNT) project acquired a comprehensive suite of geophysical and geochemical datasets across the northern Malawi (Nyasa) rift in the East Africa rift system. Onshore/offshore active and passive seismic data, long-period and wideband magnetotelluric data, continuous Global Positioning System data, and geochemical samples were acquired between 2012 and 2016. This combination of data is intended to elucidate the sedimentary, crustal, and upper-mantle architecture of the rift, patterns of active deformation, and the origin and age of rift-related magmatism. A unique component of our program was the acquisition of seismic data in Lake Malawi, including seismic reflection, onshore/offshore wide-angle seismic reflection/refraction, and broadband seismic data from lake-bottom seismometers, a towed streamer, and a large towed air-gun source. SCIENCE MOTIVATION AND EXPERIMENT SUMMARYThe primary scientific goal of the Study of Extension and maGmatism in Malawi aNd Tanzania (SEGMeNT) project is to examine the emergence and early evolution of two fundamental features of all divergent plate boundaries: magmatism and segmentation. Magmatism accommodates a significant percentage of plate separation at most midocean ridges and late-stage continental rifts. Likewise, transform faults demarcate discrete spreading segments in midocean ridges, which are broadly characterized by more robust magmatism at their centers than at their edges (Macdonald et al., 1988;Lin et al., 1990). Well-developed magmatic and tectonic segmentation is also observed in late-stage continental rifts and new ocean basins (Taylor et al., 1995;Ebinger and Casey, 2001;Keir et al., 2009), but little is known about the controls on the initiation and development of magmatism and segmentation in immature rifts. Our project is focused on addressing the following questions:• When, where, and why does magmatism initiate in rifts, and what is its role in accommodating extension? • What controls the development of tectonic segmentation in early-stage rifts? How is it manifested in 4D patterns of magmatism and deformation?To address the questions above, we acquired an integrated geophysical and geochemical dataset across the northern Malawi (Nyasa) rift in the southern part of the East Africa Rift system (EARS). Our team included universities and geological surveys in the United States, Malawi, and Tanzania. The following datasets were acquired as a part of the SEGMeNT project: onshore/offshore active and passive seismic data, long-period and wideband magnetotelluric (MT) data, continuous Global Positioning System (GPS) data, and geochemical samples. This is the first integrated geophysical and geochemical dataset acquired across and within any of the great African rift lakes that can constrain rift architecture and processes at a range of scales. TECTONIC BACKGROUNDThe northern Malawi (Nyasa) rift in the Western Branch of the EARS is an excellent locality to examine the early stages of rifting in str...

Depth Extent and Kinematics of Faulting in the Southern Tanganyika Rift, Africa

“…The initial model is adapted from the Accardo et al () velocity model with Moho depth from Hodgson et al (). The Pn (uppermost mantle) velocity is estimated from travel time analyses of record sections of well‐located earthquakes south of the TANGA14 array, but within the combined TANGA14 and SEGMeNT arrays (Shillington et al, ) (Figure S2), and comparison to Pn velocities from regional tomography analyses (O'Donnell et al, ).…”

Controls on Rift Faulting in the North Basin of the Malawi (Nyasa) Rift, East Africa

“…Multichannel seismic (MCS) reflection data and wide‐angle reflection/refraction data were acquired in the northern part of the Malawi Rift in March 2015 as a part of the Study of Extension and maGmatism in Malawi aNd Tanzania (SEGMeNT) project (Shillington et al, ). Here we focus on data acquired in the North Basin of the Malawi Rift (Figure b).…”

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

“…This contribution synthesizes our current understanding of crustal modification in tectonically active cratonic rift zones and mountain belts and lays out a road map for future studies of African rift and orogenic zones. Several large‐scale crust and mantle imaging experiments have acquired promising data sets in incipient and weakly extended, magma‐poor rift sectors (e.g., Gao et al, ; Hodgson et al, ; Shillington et al, ), but a synthesis of crustal structure of early stage rifts is premature. Our focus is to characterize crustal structure in zones of active deformation in the East African rift, Cameroon Volcanic Line (CVL), and Atlas Mountains.…”