Lithospheric Controls on the Rifting of the Tanzanian Craton at the Eyasi Basin, Eastern Branch of the East African Rift System

Abstract

Continental rifts most often nucleate within orogenic belts. However, some studies in the East African rift system have shown that continental rifts can also develop within cratons. This work investigated the ~1.5‐Ma Eyasi basin, which propagates in a WSW direction into the Tanzanian craton. The basin is located where the eastern branch of the East African rift system transitions from a narrow rift (~70 km wide) to the wider (~300 km wide) North Tanzanian Divergence. Unlike the rest of the eastern branch segments, the Eyasi basin does not follow the Mozambique orogenic belt located on the eastern margin of the Tanzanian craton. This work generated lithospheric‐scale sections across the basin using (1) digital elevation model to map surface rift‐related brittle structures; (2) aeromagnetic data to determine the depth to the Precambrian basement; and (3) World Gravity Model 2012 to estimate crustal and lithospheric thickness by applying the two‐dimensional radially averaged power spectral analysis and two‐dimensional forward gravity modeling. These cross sections show that the Eyasi basin nucleates within a previously unidentified suture zone within the Tanzanian craton and that this suture zone is characterized by thinner lithosphere that can be as thin as ~95 km. This zone of thinner lithosphere is offset southeastward from the surface expression of the Eyasi basin and might have facilitated the formation of other basins further south. Furthermore, the lithospheric thickness map indicates that the Tanzanian craton is heterogeneous and possibly composed of multiple smaller cratonic fragments.

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

“…Our estimated exhumation magnitudes and rates determined from thermal history modeling along with the localized patterns seen in Cenozoic magmatism further emphasizes the physiographic differences that exist between the southern, central, and northern RGR. Although a detailed exploration of crustal inheritance and regional preexisting structure is beyond the scope of this work, we propose that crustal and lithospheric properties (i.e., thickness and potentially age and rheology) control rift accommodation and play a role in the orientation of faulting and magmatism along the RGR, as seen in continental rifts elsewhere (Figure ; e.g., Brun, ; Corti, ; Fletcher et al, ; Corti et al, ; Corti et al, ). Therefore, we suggest that differences in rift accommodation mechanisms (i.e., faulting vs. magmatism) are likely controlled by deep‐seated lithospheric‐scale properties and architecture, rather than progressive stages of rift development (e.g., Corti, ).…”

Lithospheric Structure of a Transitional Magmatic to Amagmatic Continental Rift System—Insights from Magnetotelluric and Local Tomography Studies in the North Tanzanian Divergence, East African Rift

“…An alternative is that 3-D geometry of units as craton or Proterozoic belt is more complex and differs from its surface expression. Recent study proposes [95] that the Mbulu domain mainly consists of Tanzanian Craton while the Proterozoic Belt only spreads over it as a thin superficial layer. The presence of a cratonic unit for the Manyara area can then more easily explain the magma trapping at depth.…”

Lithospheric Structure of the Malawi Rift: Implications for Magma‐Poor Rifting Processes

“…Similarly, we use seismically derived depth to LAB ranging between 150–170 km for profile A‐A′ and 170–210 km for profiles B‐B′ and C‐C′ (Fishwick, ) as initial constraints of the 2‐D forward modeling of the gravity data. The thickness and densities of the upper crust (2.76 g/cm 3 ), the lower crust (2.92 g/cm 3 ), and the lithospheric mantle (3.25 g/cm 3 ) were obtained from gravity and seismic studies of different parts of the EARS (e.g., Fletcher et al, ; Leseane et al, ; Mahatsente et al, ; Mickus et al, ; Simiyu & Keller, ). We determine the final gravity model by varying the initial crustal thickness and depth to LAB by ~10% and the initial densities of the different Earth layers by ~15%.…”

“…We use 2-D forward modeling of the gravity data along profiles A-A′, B-B′, and C-C′ (see Figure 3 for locations of the profiles) using the 2-D GYMSYS Oasis Montaj software (Talwani et al, 1959) to determine the lithospheric structure beneath the MR. Profiles A-A′ and C-C′ follow the passive seismic stations of the Seismic Arrays for African Rift Initiation experiment (Gao et al, 2013;Wang et al, 2019), and B-B′ is an east-west profile that cuts across the widest part of the MR and includes portions of the Luangwa Rift in Zambia. Gravity models have the limitation of nonunique solutions; however, we construct geological models by using realistic constraints on rock densities and lateral variations of rock units (e.g., Fletcher et al, 2018;Leseane et al, 2015;Mahatsente et al, 1999;Mickus et al, 2007;Simiyu & Keller, 2001). Because these constraints are not readily available in all parts of the MR and surrounding areas for the 2-D forward modeling of the gravity data, we used as initial constraints, estimates of crustal thicknesses obtained from the inversion of Rayleigh wave phase velocity maps constructed from ambient noise tomography recorded by broadband (Seismic Arrays for African Rift Initiation) seismic data sets, which range between 36-38 km for the A-A′ profile and 38-40 km for the B-B′ and C-C′ profiles (Wang et al, 2019).…”

“…(3.25 g/cm 3 ) were obtained from gravity and seismic studies of different parts of the EARS (e.g.,Fletcher et al, 2018;Leseane et al, 2015;Mahatsente et al, 1999;Mickus et al, 2007;Simiyu & Keller, 2001). We…”