Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting

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Authors
Toummite, A.
Liégeois, J.P.
Gasquet, D.
Bruguier, O.
Beraaouz, E.H.
Ikenne, M.
Discipline
Earth and related Environmental sciences
Subject
Geodynamics and mineral resources
Audience
Scientific
Date
2013Publisher
Springer Verlag
Metadata
Show full item recordDescription
In the Tifnoute Valley, three plutonic units have been  defined: the Askaoun intrusion, the Imourkhssen intrusion and  the Ougougane group of small intrusions. They are made of  quartz diorite, granodiorite and granite and all contain abundant  mafic microgranular enclaves (MME). The Askaoun granodiorite  and the Imourkhssen granite have been dated by LA-ICPMS  on zircon at 558±2Ma and 561±3Ma, respectively. These  granitic intrusions are subcontemporaneous to the widespread  volcanic and volcano-detrital rocks from the Ouarzazate Group  (580 545 Ma), marking the post-collisional transtensional  period in the Anti-Atlas and which evolved towards alkaline  and tholeiitic lavas in minor volume at the beginning of the  Cambrian anorogenic intraplate extensional period.  Geochemically, the Tifnoute Valley granitoids belong to an  alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta  negative anomalies and no alkaline affinities. Granitoids and  enclaves display positive εNd-560Ma (+0.8 to +3.5) with young  Nd-TDM between 800 and 1200Ma and relatively low87Sr/86Sr  initial ratios (Sri: 0.7034 and 0.7065). These values indicate a  mainly juvenile source corresponding to a Pan-African metasomatized  lithospheric mantle partly mixed with an old crustal  component from the underlying West African Craton (WAC).  Preservation in the Anti-Atlas of pre-Pan-African lithologies (c.  2.03 Ga basement, c. 800 Ma passive margin greenschist-facies  sediments, allochthonous 750 700 Ma ophiolitic sequences)  indicates that the Anti-Atlas lithosphere has not been thickened  and was never an active margin during the Neoproterozoic.  After a transpressive period, the late Ediacaran period (580   545Ma) is marked by movement on near vertical transtensional  faults, synchronous with the emplacement of the huge  Ouarzazate Group and the Tifnoute Valley granitoids. We propose  here a geodynamical model where the Tifnoute Valley  granitoids as well as the Ouarzazate Group were generated  during the post-collisional metacratonic evolution of the northern  boundary of theWest African craton. The convergence with  the peri-Gondwanan active margin produced brittle fracturing  of the cratonic boundary without thickening, allowing rising of  magmas. The Tifnoute Valley granitoids display a metasomatized  lithospheric mantle source mixed with a minor ancient  (2 Ga) continental crust component from the underlying WAC.
Citation
Toummite, A.; Liégeois, J.P.; Gasquet, D.; Bruguier, O.; Beraaouz, E.H.; Ikenne, M. (2013). Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting. , Mineralogy and Petrology, Vol. 107, 739-763, Springer Verlag, DOI: DOI 10.1007/s00710-012-0245-3.Identifiers
Type
Article
Peer-Review
Yes
Language
eng
