Metamorphic evolution, partial melting and Miocene exhumation of lower crust in the Edough metamorphic core complex, west Mediterranean orogen, eastern Algeria

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• 作者：Caby ; R. ; Hammor ; D. ; Delor ; C.
• 关键词：Edough ; Maghrebides ; Transtension ; Metamorphic core complex ; Exhumation ; Tectonic denudation
• 刊名：Tectonophysics
• 出版年：2001
• 出版时间：December, 2001
• 年：2001
• 卷：342
• 期：3-4
• 页码：239-273
• 全文大小：2.06 M

文摘

The Edough massif is the easternmost crystalline massif of the Maghrebides which represent the southeastern part of the west Mediterranean orogen. It emerges from below the greenschist–facies Tellian units that represent the thrusted Mesozoic to Eocene passive paleomargin of northern Africa deposited on the thinned continental crust. The top of the crystalline pile of the Edough massif is characterised by metasedimentary rocks affected by medium- to high-pressure (12–14 kbar) and medium-temperature metamorphic conditions of ca. 600 °C. The northern part of the massif as well as the overlying allochthonous amphibole–peridotite unit in the north is characterised by high-pressure granulite facies (T800 °C and P≥12 kbar). Nearly isothermal decompression is documented in metapelites by late- to post-kinematic crystallisation of sillimanite and andalusite overprinting kyanite. The core of the dome comprises essentially diatexite and granite gneisses. A late low-pressure evolution and overprinting (2–3 kbar) took place in Paleozoic rocks in proximity to granite–gneisses. The predominant igneous mineralogy of granite–gneisses suggests that they represent synmetamorphic and syn-kinematic sheeted intrusions generated through a high-degree melting of metasediments. Geochronology of the metamorphic rocks (U–Pb on monazite, Sm–Nd on garnet–WR pairs, ⁴⁰Ar/³⁹Ar on amphiboles and micas) yields ages bracketed between 24 and 16 Ma, suggesting that regional metamorphism of the Edough massif took place during the Late Tertiary, synchronous with the greenschist–facies metamorphism recorded in the overlying Mesozoic Tellian units. The Edough massif represents a metamorphic core complex exhumed through tectonic denudation assisted by syn- to late-metamorphic low-angle, N-dipping normal ductile shear zones. An exhumation rate of 6–8 km/Ma and associated cooling rate of 200–300 °C/Ma is implied. We conclude that the Edough massif represents part of the former thinned continental crust of Africa involved in a Late Eocene northward subduction beneath the suboceanic domain that separated Paleo-Europe and Africa in Mesozoic time. The upward syn-metamorphic tectonic emplacement at 40–45 km depth of slices of spinel peridotites detached from the lower mantle may be responsible for the local granulite facies occurrences. Their emplacement is a consequence of the long-lived transtensional (sinistral, then dextral) kinematics having taken place between the African and European plates.