The Ediacaran volcanic rocks and associated mafic dykes of the Ouarzazate Group (Anti-Atlas, Morocco): Clinopyroxene composition, whole-rock geochemistry and Sr-Nd isotopes constraints from the Ouzellarh-Siroua salient (Tifnoute valley)

Belonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley...

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Bibliographic Details
Published in:Journal of African earth sciences (1994) 2017-03, Vol.127, p.113-135
Main Authors: Belkacim, Said, Gasquet, Dominique, Liégeois, Jean-Paul, Arai, Shoji, Gahlan, Hisham A., Ahmed, Hassan, Ishida, Yoshito, Ikenne, Moha
Format: Article
Language:English
Subjects:
Biodiversity and Ecology
Clinopyroxene chemistry
Ediacaran volcanism
Environment and Society
Environmental Engineering
Environmental Sciences
Geodynamics
Geography
Global Changes
Humanities and Social Sciences
Morocco
Nd-Sr isotopes
Ouarzazate Supergroup
Ouzellarh-Siroua salient
Tifnoute valley
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Summary:Belonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley volcanic rocks are located within a rigid salient of the Anti-Atlas that gives them special extreme characteristics. Due to the heavy greenschist alteration that affects this volcanic group, we focused the more immobile elements, but as REE can also be affected, we used the composition of unaltered clinopyroxene crystals to determine the nature of these volcanic rocks. The clinopyroxene is an augite diopside in the basalt, an augite in the andesite and an augite-salite in the dolerite. Petrography of the Tifnoute mafic volcanic rocks and clinopyroxene compositions indicate the presence of two magmatic series: (i) older high-K calc-alkaline (alkali-calcic) andesite and basalt characterized by the early crystallization of Fe-Ti oxides and of the late fractionation of plagioclase, the modal proportion of the latter increasing from the basalt to the andesite and (ii) younger alkalic dolerite dykes. With clinopyroxene trace element compositions obtained using laser ablation ICP-MS, we calculated the composition of the melts in equilibrium with the pyroxenes. The volcanic rocks of the Tifnoute Valley have positive εNd570 (+1.7 to +5.0), low Sri (
ISSN:1464-343X
1879-1956
DOI:10.1016/j.jafrearsci.2016.08.002