Paleomagnetic and geochronological identification of the Reunion subchron in Ethiopian Afar

This paper reports the paleomagnetic and geochronological analysis of a sui te of samples from a basaltic fault-related scarp of Pliocene age in the ce ntral part of the Afar depression (Ethiopia). Paleomagnetic work uncovers a clear characteristic remanent magnetization carried by (titano-) magnetite s, with high unblocking temperatures, close to the Curie temperature of pur e magnetite. The characteristic direction, based on 27 non transitional flo ws, is D=8.1 degrees, I=10.1 degrees (alpha(95)=4.1 degrees). This is consi stent with earlier determinations of the clockwise tectonic rotation, due t o rift propagation and overlap, of the block to which the section belongs. Magnetic stratigraphy consists of a succession from bottom to top of 16 rev ersed, 7 normal, and 4 reversed flows. One flow at the upper normal to reve rse transition demonstrates complex behavior upon thermal and alternating f ield (AF) demagnetization, which is due to remagnetization by the overlying flow. K/Ar dating of five samples provides consistent determinations, aver aging 2.07 +/- 0.05 Ma. All ages agree with this average, given their rathe r large individual uncertainties (from 0.04 to 0.08 Ma at the 1 sigma level ). Comparison with recent reference geomagnetic polarity timescales (GPTS) indicates that the normal subchron recorded in the Gamarri section must be linked with tone of the Reunion event(s). The normal subchron and an earlie r episode of large secular variation could provide the best volcanic record of a double Reunion event. Although uncertainties in ages are too large to allow unequivocal inferences, our age determination for the Reunion event is in better agreement with earlier determinations of McDougall and Watkins [1973] than with a more recent value proposed by Baksi et al. [1993] and u sed in the GPTS.