The Betic‐Rif orogen forms the western termination of the Alpine orogenic system in the Mediterranean region. The precise timing, structural evolution, and distribution of high‐grade metamorphic units (Alpine versus pre‐Alpine) in the inner zones of the orogen (Alboran Domain) remain controversial issues. In this paper we report occurrence of distinct generations of peraluminous granitic bodies intruded within Beni Bousera peridotites and their amphibolite‐to‐granulite facies envelope, in the core of the Alboran Domain of the Rif chain (northern Morocco). These granitic bodies are central to the reconstruction of the high‐grade evolution of the Alboran Domain because they provide first‐order structural markers to assess the P‐T‐t deformation history of the high‐grade terranes. Here we document the petrography and structural relationships with the host rocks and constrain the timing of granite emplacement using laser ablation–inductively coupled plasma–mass spectrometry U‐Pb zircon and/or monazite dating, complemented by 40Ar/39Ar dating. The results indicate that granite emplacement occurred in two major episodes of anatectic magmatism, during the Hercynian (circa 300 Ma) and Alpine (circa 22 Ma) periods, respectively. These data (1) provide conclusive evidence for an important phase of Hercynian magmatism and high‐grade metamorphism in the Alboran Domain and (2) permit a revaluation of the significance of the high‐grade early Miocene event documented in the Alboran Domain in terms of a late stage, thermal pulse that reworked a polymetamorphic (Hercynian and Alpine) nappe pile. These results provide new constraints for construction of a feasible tectonometamorphic model for the Alpine evolution of the western Mediterranean.
The Uluguru Mountains of eastern Tanzania represent a key area to unravel the tectonic history of Gondwana assembly along the Neoproterozoic East African Orogen. On the basis of combined structural and 40 Ar ⁄ 39 Ar geochronological investigations, we have re-interpreted the structural architecture of the region. Texturally-late, ductile to cataclastic low-angle tectonic contacts are recognized, which delimit the contacts between the main lithological units that form a post-metamorphic, NWverging nappe stack. 40 Ar ⁄ 39 Ar geochronology places this nappe-forming event at c. 550 Ma, post-dating tonalitic dyke emplacement at c. 580 Ma. Results from this study (i) demonstrate that a distinct and later episode of convergence occurred in the region at c. 550 Ma, when previous structural elements of the East African Orogen were finally juxtaposed; and (ii) extends models involving the polyphase assembly of Gondwana to East Africa.
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