The Triassic-Liassic volcanic sequence and rift evolution in the Saharan Atlas basins (Algeria). Eastward vanishing of the Central Atlantic magmatic province
Résumé
We investigate the Triassic-Liassic sequence in ten diapirs from the Saharan Atlas (Algeria). Based on detailed
mapping, two episodes are identified. The first one consists of a volcano-sedimentary sequence in which three
volcanic units were identified (lower, intermediate and upper units). They are interlayered and sometimes
imbricated with siliciclastic to evaporitic levels which record syn-sedimentary tectonics. This sequence was
deposited in a lagoonal-continental environment and is assigned to the Triassic magmatic rifting stage. The second
episode, lacking lava flows (post magmatic rifting stage), consists of carbonate levels deposited in a lagoonal to
marine environment during the Rhaetian-Hettangian. The volcanic units consist of several thin basaltic flows,
each 0.5 to 1m thick, with a total thickness of 10–15m. The basalts are low-Ti continental tholeiites, displaying
enrichment in large ion lithophile elements and light rare earth elements [(La/Yb)n= 2.5-6] with a negative Nb
anomaly. Upwards decrease of light-rare-earth-elements enrichment (e.g. La/Yb) is modelled through increasing
melting rate of a spinel-bearing lherzolite source from the lower (6–10wt.%) to the upper (15–20wt.%) unit. The
lava flows from the Saharan Atlas share the same geochemical characteristics and evolution as those from the
Moroccan Atlas assigned to the Central Atlantic magmatic province. They represent the easternmost witness of
this large igneous province so far known.
Domaines
Planète et Univers [physics]
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Meddah etal Geol Acta 2017 CAMP in Saharan Atlas.pdf (2.37 Mo)
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