TY - JOUR
T1 - A volcanic district between the Hoggar uplift and the Tenere Rifts
T2 - volcanology, geochemistry and age of the In-Ezzane lavas (Algerian Sahara)
AU - Yahiaoui, Rachid
AU - Dautria, Jean Marie
AU - Alard, Olivier
AU - Bosch, Delphine
AU - Azzouni-Sekkal, Abla
AU - Bodinier, Jean Louis
PY - 2014/4
Y1 - 2014/4
N2 - The In-Ezzane volcanic district (EZD), located at the triple junction of Algeria, Niger and Libya belongs to the Eastern Hoggar, covers 350km2 and includes 9 volcanic edifices that are probably aligned along NW-SE faults, parallel to the Tafassasset valley. The low volume (0.7 and 1km3) of emitted lavas, the similar morphology of the monogenic cones and the lack of differentiated rocks indicate that the volcanic activity of the EZD was restricted in time and volume. The new K-Ar age (i.e. 2.86±0.07Ma) indicates that the EZD is contemporaneous with the last alkali volcanism paroxysm in Hoggar and with the nearby Libyan volcanics. The EZD alkali basalts (mainly basanite) show a remarkable homogeneous compositions both in major elements (44.8≤SiO2≤45.8wt.%; 5.2≤(Na2O+K2O)≤6.2wt.%), trace elements (4.3≤Th≤5.5ppm; 34.7≤La≤44.7ppm; 16.1<La/Yb(N)<21.6) and radiogenic isotopes (0.70285<87Sr/86Sr<0.70303; 0.51298<143Nd/144Nd<0.51301; (19.212<206Pb/204Pb<19.340, 15.589<207Pb/204Pb<15.602 and 38.834<208Pb/204Pb<38.903). Relative to the Hoggar alkaly basalts the EZD basalts appear systematically impoverished in incompatible elements and show a depleted signature both in Sr and Nd isotopes (almost MORB-like). The Pb isotopes are relatively enriched and intermediate between tholeiites and alkali basalts of the Hoggar. This unusual geochemical signature, is uneasy to reconcile with the known characteristics of the Hoggar swell, and would rather fingerprint a circum cratonic mantle lying beneath the west border of the Murzuq craton (Libya).
AB - The In-Ezzane volcanic district (EZD), located at the triple junction of Algeria, Niger and Libya belongs to the Eastern Hoggar, covers 350km2 and includes 9 volcanic edifices that are probably aligned along NW-SE faults, parallel to the Tafassasset valley. The low volume (0.7 and 1km3) of emitted lavas, the similar morphology of the monogenic cones and the lack of differentiated rocks indicate that the volcanic activity of the EZD was restricted in time and volume. The new K-Ar age (i.e. 2.86±0.07Ma) indicates that the EZD is contemporaneous with the last alkali volcanism paroxysm in Hoggar and with the nearby Libyan volcanics. The EZD alkali basalts (mainly basanite) show a remarkable homogeneous compositions both in major elements (44.8≤SiO2≤45.8wt.%; 5.2≤(Na2O+K2O)≤6.2wt.%), trace elements (4.3≤Th≤5.5ppm; 34.7≤La≤44.7ppm; 16.1<La/Yb(N)<21.6) and radiogenic isotopes (0.70285<87Sr/86Sr<0.70303; 0.51298<143Nd/144Nd<0.51301; (19.212<206Pb/204Pb<19.340, 15.589<207Pb/204Pb<15.602 and 38.834<208Pb/204Pb<38.903). Relative to the Hoggar alkaly basalts the EZD basalts appear systematically impoverished in incompatible elements and show a depleted signature both in Sr and Nd isotopes (almost MORB-like). The Pb isotopes are relatively enriched and intermediate between tholeiites and alkali basalts of the Hoggar. This unusual geochemical signature, is uneasy to reconcile with the known characteristics of the Hoggar swell, and would rather fingerprint a circum cratonic mantle lying beneath the west border of the Murzuq craton (Libya).
KW - Algeria
KW - basalts
KW - hoggar
KW - mantle
KW - tuareg shield
UR - http://www.scopus.com/inward/record.url?scp=84893480011&partnerID=8YFLogxK
U2 - 10.1016/j.jafrearsci.2013.12.001
DO - 10.1016/j.jafrearsci.2013.12.001
M3 - Article
AN - SCOPUS:84893480011
SN - 1464-343X
VL - 92
SP - 14
EP - 20
JO - Journal of African Earth Sciences
JF - Journal of African Earth Sciences
ER -