The Edembo Murzukian (575-545 Ma) monophase high-temperature amphibolite metamorphism (Eastern Hoggar, Algeria): a key for understanding the development of the Saharan metacraton during the Gondwana supercontinent amalgamation
| dc.contributor.author | Bendaoud, A. | |
| dc.contributor.author | Liégeois, J.P. | |
| dc.contributor.author | Sergeev, S. | |
| dc.contributor.author | Kienast, J.R. | |
| dc.contributor.author | Drareni, A. | |
| dc.contributor.author | Ouzegane, K. | |
| dc.date | 2016 | |
| dc.date.accessioned | 2024-03-14T13:06:32Z | |
| dc.date.available | 2024-03-14T13:06:32Z | |
| dc.identifier.uri | https://orfeo.belnet.be/handle/internal/11610 | |
| dc.description | Eastern Hoggar was for long considered as "cratonized" at c. 730 Ma (Caby et al., 1987) due to a rigid behavior during the main Pan-African collision (630-580 Ma) that affected the Tuareg shield. Indeed, west of the Raghane shear zone (running along the 8°30' longitude), the Pharusian belt, the In Ouzzal and LATEA metacratons, were at that period either generated or weakly to strongly reactivated during this convergence marked by a northerly tectonic escape (Black et al., 1994; Liégeois et al., 2003). Conversely, at that time, Eastern Hoggar was covered by an extensive sedimentary basin (Tiririne-Djanet Group), which was actually the molasse of Central Hoggar (Fezaa et al., 2010), only crosscut by granitoids close to the Raghane shear zone at 600-580 Ma (Henry et al., 2009; Nouar et al., 2011). Recently, it was confirmed that eastern Hoggar behaved as a rigid block during the Neoproterozoic until at least 595 Ma, the age of the youngest detrital zircon in the metasedimentary Djanet Group, but that it was later affected by an orogenic event during the 575-550 Ma period (Fezaa et al., 2010). Eastern Hoggar is composed of three terranes, from W to E: Aouzegueur, Edembo and Djanet. The easternmost Djanet terrane has been subjected to greenschist facies metamorphism and is crosscut by various granitoids, from batholith to dykes during that 575-555 Ma period (Fezaa et al., 2010). The here studied Edembo terrane, separated from the Djanet terrane by shear zones, is characterized by a higher grade metamorphism, by anatectic granitoids (biotite-plagioclase-K-feldspar-quartz ± amphibole) and intrusive norite (orthopyroxene-clinopyroxene-plagioclase-amphibole). The Edembo metamorphism is typically monophase. A garnet-biotite-plagioclase-K-feldspar-quartz paragenesis indicates amphibolite facies P-T conditions of 750 to 850°C and 6-7 kbar. In these migmatites, the presence of quartz, plagioclase and biotite inclusions within garnet indicates that the prograde reaction responsible of melting and garnet growth is probably: biotite + plagioclase + quartz ==> garnet + K-feldspar + melt. Only a superimposed local greenschist facies metamorphism is present in the northern part of the terrane. This is much higher that the greenschist metamorphism (chlorite-quartz-andalusite-graphite assemblage) that affected the Djanet terrane. We dated (SHRIMP U-Pb ages on zircon) several of these deep-seated intrusions. These zircons display large cores giving inherited ages while rims and some well crystallized crystals give the intrusion ages: the Aledema norite at 557 ±4 Ma (concordant inherited zircons at 0.76, 0.81 and 2.7 Ga) and two garnet gneisses at 553 ±4 Ma (inherited zircons at 1.9 Ga) and 552 ±7 Ma (inherited zircons at 0.62, 0.66 and 2.06 Ga). These ages allows getting a good date of 550-560 Ma for these intrusions and the contemporaneous HT metamorphism. The inherited ages, devoid of Mesoproterozoic ages, are typical of the LATEA metacraton to the west that fed the Djanet Group (Fezaa et al., 2010). We can confirm here that the protolith of the Edembo metamorphic series corresponds to the molassic Tiririne/Djanet Group deposited onto the Eastern Hoggar basement at around c.600 Ma (Fezaa et al., 2010). This is in agreement with the monophase character of the Edembo metamorphism, its late age at 550-560 Ma, the presence of metasediments such as marbles and the peraluminous composition of the magmatism (norite, garnet gneisses) and the total absence of lithologies with oceanic affinities. This means that Eastern Hoggar behaved as a rigid cratonic block during the main Pan-African orogeny that occurred to the west (Central and West Hoggar) and during the 630-580 Ma (Liégeois et al., 2003) where it ceased at c. 580 Ma (Abdallah et al., 2007). Later, Eastern Hoggar was reactivated by the Murzukian orogeny (Fezaa et al., 2010), generating HT metamorphism and peraluminous crustal magmatism at 560-550 Ma in the Edembo terrane. The Murzukian orogeny appears to be of intracontinental nature and corresponds to a metacratonic process (Liégeois et al., 2013). The cause of that metacratonization cannot be the far field stress related to the convergence in the west of the West African craton since it ended earlier, at c. 580 Ma. It can instead be attributed to the newly discovered Murzuq craton (Fezaa et al., 2010), now considered to be a cratonic remnant within the Saharan metacraton (Liégeois et al., 2013). However, considering the absence of any late Neoproterozoic oceanic rocks on all its margins, the Murzuq craton can only have acted as a rigid relay for the pushing of an indenter located to the NE, over the Sirte basin, which is a weak zone of the African lithosphere. We propose that this indenter could be the Siberian craton, which is at the right latitude and in the area when considering the paleogeographic reconstructions at c. 550 Ma (e.g. Cocks & Torsvik, 2005; Levashova et al., 2011). Only a small change in longitude is needed relatively to their reconstruction. With the Siberian craton located on its northern margin, the Saharan metacraton would have been surrounded by cratons on all its margins with no escape possibilities and so squeezed during the Gondwana supercontinent amalgamation. This could be an explanation for the development of the so large Saharan metacraton (5,000,000 km2). | |
| dc.language | eng | |
| dc.publisher | USTHB | |
| dc.title | The Edembo Murzukian (575-545 Ma) monophase high-temperature amphibolite metamorphism (Eastern Hoggar, Algeria): a key for understanding the development of the Saharan metacraton during the Gondwana supercontinent amalgamation | |
| dc.type | Conference | |
| dc.subject.frascati | Earth and related Environmental sciences | |
| dc.audience | Scientific | |
| dc.subject.free | Geodynamics and mineral resources | |
| dc.source.title | 1st Arab Geoscience Union International Conference (AIC-1) | |
| Orfeo.peerreviewed | Yes | |
| dc.identifier.rmca | 4814 |
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