Crustal structure and upper mantle anisotropy of the Afar triple junction

U Kumar,C P Legendre,B S Huang

doi:10.1186/s40623-021-01495-0

Abstract

The Afar region is a tectonically distinct area useful for studying continental break-up and rifting. Various conflicting models have been suggested to explain the lateral variations of the anisotropy in this region. To address this issue, we investigated the tectonics of the Afar region using receiver function and shear-wave splitting measurements based on broadband seismic data from 227 stations in the region. Further, the receiver function results were inverted to obtain the crustal thickness and Vp/Vs ratio of the region. Our results reveal a thick African crust (thicker than 40 km) with typical Vp/Vs values for the continental crust, elongated down to 21 km along the rift system with very high Vp/Vs values near the fractured zones, suggesting crustal thinning near the fractured zones. Our shear-wave splitting measurements indicate a general fast axis orientation of N030E. However, substantial disparities in the fast anisotropy direction exist in the triple junction region, with some stations displaying a direction of N120E, which is perpendicular to the fast directions measured at the surrounding stations. In addition, many stations located close to the rifts and within the Arabian Plate provide mostly null measurements, indicating the presence of fluids or isotropic media. This study uses several methodologies to unravel the structure and evolution of the Afar region, providing valuable insight into the Afar, a tectonically distinct region, which will be useful for elucidating the mechanisms and characteristics of a continental break-up and the rifting process.

Highlights

Geological settings The Afar triple junction (Fig. 1) is located in East Africa connecting three branches of a complex rift system
Our results suggest that regional thick continental crust exists beneath the African and Arabian plates, which agrees with previous measurements (Dugda et al 2005; Dugda and Nyblade 2006; Hammond et al 2011; Reed et al 2014; Thompson et al 2015)
Hammond et al (2011) found that the crustal thickness ranged from 16 km down the spreading centers in the northern Afar region to

Summary

Introduction

Geological settings The Afar triple junction (Fig. 1) is located in East Africa connecting three branches of a complex rift system. This area is an example of the last stage of continental rifting and the early stage of seafloor spreading, leading to the creation of oceanic crust (Mohr 1970; Tesfaye et al 2003; Rychert et al 2012). The Afar hotspot is located at the triple junction between the Red Sea rift, the Gulf of Aden, and the Ethiopian rift zone (Mohr 1970; Legendre 2013). The early stage of the collision between the Mediterranean and Biltis segments (McQuarrie et al 2003) occurred

Results

Discussion

Conclusion