HR: 0830h
AN: S51C-0074 [PDF]
TI: Temporal compositional variation of early syn-rift rhyolites along the western margin of the southern
Red Sea and northern Main Ethiopian rift
AU: Ayalew, D
EM: dereayal@geol.aau.edu.et
AF: Addis Ababa University, Department of Geology and Geophysics, PO Box 1176, Addis Ababa, N
Ethiopia
AU: * Bourdon, E
EM: e.bourdon@gl.rhul.ac.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, PO Box 1176, Addis Ababa, N
Ethiopia
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
AB:
New structural and geochronological analyses indicate that the felsic volcanism at the top of the Oligocene flood basalt
sequences along the western margin of the Afar Depression marks the onset of rifting in the southern Red Sea.
Geochronological studies show a pattern of riftward migration of the locus of magmatism and faulting from 28 Ma to
present-day. Preliminary geochemical analyses (trace and major elements; Sr, Nd and O isotopic compositions) of syn-rift
rhyolites ranging in age from 28 to 2.5 Ma indicate that the rhyolites are derived from mantle-sourced basaltic magma through
fractional crystallization accompanied by variable amounts of crustal contamination (e.g. $^{87}$Sr/$^{86}$Sr =
0.705445-0.706508; $^{143}$Nd/$^{144}$Nd = 0.512576-0.512836). The input of crust tends to increase with time, which
suggests the weakening and heating of the crust in response to lithospheric thinning and magma injection in the past ~30 My.
These results support earlier structural and thermo-mechanical models for rift formation in the southern Red Sea rift and
the younger, less-evolved northern Main Ethiopian rift system.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8180 Tomography
DE: 8439 Physics and chemistry of magma bodies
SC: Seismology [S]
MN: 2003 Fall Meeting