HR: 15:10h
AN: S52G-06    [PDF]
TI: Initiation and Along-Axis Segmentation of Seaward-Dipping Volcanic Sequences Captured in Afar
AU: * Ebinger, C
EM: cindy@gl.rhul.ac.uk
AF: Royal Holloway U of London, Department of Geology, Egham, TW20 0EX United Kingdom
AU: Wolfenden, E
EM: ellenwolfenden@yahoo.co.uk
AF: Royal Holloway U of London, Department of Geology, Egham, TW20 0EX United Kingdom
AU: Yirgu, G
EM: yirgu.g@geol.aau.edu.et
AF: Addis Ababa University, Department of Geology and Geophysics, Addis Ababa, N Ethiopia
AU: Keir, D
EM: d.keir@gl.rhul.ac.uk
AF: Royal Holloway U of London, Department of Geology, Egham, TW20 0EX United Kingdom
AB: The Afar triple junction zone provides a unique opportunity to examine the early development of magmatic margins, as respective limbs of the triple junction capture different stages of the breakup process. Initial rifting in the southernmost Red Sea occurred concurrent with, or soon after flood basaltic magmatism at ~31 Ma in the Ethiopia-Yemen plume province, whereas the northern part of the Main Ethiopian rift initiated after 12 Ma. Both rift systems initiated with the development of high-angle border fault systems bounding broad basins, but 8-10 My after rifting we see riftward migration of strain from the western border fault to narrow zones of increasingly more basaltic magmatism. These localised zones of faulting and volcanism (magmatic segments) show a segmentation independent of the border fault segmentation. The much older, more evolved magmatic segments in the southern Red Sea, where not onlapped by Pliocene-Recent sedimentary strata, dip steeply riftward and define a regional eastward flexure into transitional oceanic crust, as indicated by gravity models constrained by seismic refraction and receiver function data. The southern Red Sea magmatic segments have been abandoned in Pliocene-Recent triple junction reorganisations, whereas the process of seaward-dipping volcanic sequence emplacement is ongoing in the seismically and volcanically active Main Ethiopian rift. Field, remote sensing, gravity, and seismicity data from the Main Ethiopian and southern Red Sea rifts indicate that seaward-dipping volcanic sequences initiate in moderately stretched continental crust above a narrow zone of dike-intrusion. Our comparison of active and ancient magmatic segments show that they are the precursors to seaward-dipping volcanic sequences analogous to those seen on passive continental margins, and provides insights into the initiation of along-axis segmentation of seafloor-spreading centers.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8180 Tomography
SC: Seismology [S]
MN: 2003 Fall Meeting