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We explore the connections between crustal shortening, volcanism, and mantle dynamics in the Atlas of Morocco. In response to compressional forces and strain localization, this intraplate orogen has evolved far from convergent plate margins. Convective effects, such as lithospheric weakening and plume‐related volcanism, contributed in important ways to the building of high topography. We seek to better understand how crustal and mantle processes interacted during the Atlas' orogeny by combining multiple strands of observations, including new and published data. Constraints on crustal and thermal evolution are combined with new analyses of topographic evolution, petrological, and geochemical data from the Anti‐Atlas volcanic fields, and a simple numerical model of the interactions among crustal deformation, a mantle plume, and volcanism. Our findings substantiate that: (a) crustal deformation and exhumation accelerated during the middle/late Miocene, contemporaneous with the onset of volcanism; (b) volcanism has an anorogenic signature with a deep source; (c) a dynamic mantle upwelling supports the high topography. We propose that a mantle plume and the related volcanism weakened the lithosphere beneath the Atlas and that this favored the localization of crustal shortening along pre‐existing structures during plate convergence. This convective‐tectonic sequence may represent a general mechanism for the modification of continental plates throughout the thermo‐chemical evolution of the supercontinental cycle. Key Points: Crustal thickening is limited and cannot account for the topography elevation of the Atlas systemResumption of volcanism is contemporaneous with the acceleration of crustal deformation and topography growingThe erosion and weakening of the lower lithosphere, as a consequence of mantle plume, may enhance crustal deformation and exhumation [ABSTRACT FROM AUTHOR]

Abstract We explore the connections between crustal shortening, volcanism, and mantle dynamics in the Atlas of Morocco. In response to compressional forces and strain localization, this intraplate orogen has evolved far from convergent plate margins. Convective effects, such as lithospheric weakening and plume‐related volcanism, contributed in important ways to the building of high topography. We seek to better understand how crustal and mantle processes interacted during the Atlas' orogeny by combining multiple strands of observations, including new and published data. Constraints on crustal and thermal evolution are combined with new analyses of topographic evolution, petrological, and geochemical data from the Anti‐Atlas volcanic fields, and a simple numerical model of the interactions among crustal deformation, a mantle plume, and volcanism. Our findings substantiate that: (a) crustal deformation and exhumation accelerated during the middle/late Miocene, contemporaneous with the onset of volcanism; (b) volcanism has an anorogenic signature with a deep source; (c) a dynamic mantle upwelling supports the high topography. We propose that a mantle plume and the related volcanism weakened the lithosphere beneath the Atlas and that this favored the localization of crustal shortening along pre‐existing structures during plate convergence. This convective‐tectonic sequence may represent a general mechanism for the modification of continental plates throughout the thermo‐chemical evolution of the supercontinental cycle.

An abnormally odd and rare occurrence of a basaltic body has been discovered in the middle of the Gercus Formation within the large, double-plunging NW-SE trending Bekhair Anticline to the north of Duhok city, northern Iraq. This is the first discovery of such a volcanic body within the widely exposed Gercus Formation in northern Iraq, southeastern Turkey, and western Iran. This volcanic body, named by the authors the Gercus Basalt, has a long tabular/lenticular shape with a total length of ~4.5 km and a thickness ranging between 1 to 16 m. It is exposed on both limbs of the anticline and has a conformable relation with the terrigenous beds of the Gercus Formation. The basalt is greenish to grayish black in color, vesicular, amygdaloidal and porphyritic in texture, and consists of feldspar (Ab85 An2Or13), pyroxene (Wo49En40Fs11), olivine (Fo87.2-Fa12.6-Tp0.2 ), and their alteration products. Postemplacement hydrothermal fluids resulted in pervasive alteration of the Gercus Basalt and introduction of copper mineralization filling joints, fractures, and adjacent vesicles. The alteration processes are dominated by calcitization, zeolitization, serpentinization, chloritization, silicification, iddingsitization, and copper mineralization. Seventeen basalts have been analyzed for 63 major and trace elements including REEs and PGEs. The Gercus Basalt has very similar geochemical compositions to that of OIB. Excluding Cr, Co, Ni, and PGEs, it is enriched in all other analyzed major and trace elements relative to primitive mantle. The chondrite-normalized distribution of REEs shows a smooth pattern, high La/Yb(N) ratio of 23, and LREE enrichment relative to HREE, indicating alkaline magmatic origin. The studied rocks are basanites, alkaline basalts, melanephelinites, and picrites with an OIB-like anorogenic geochemical signature. The Gercus Basalt was derived from amphibole-bearing garnet-lherzolite subcontinental asthenospheric mantle, enriched with silicate metasomatism. [ABSTRACT FROM AUTHOR]

This study discusses the geochemical features of the Early-Middle Miocene and Pliocene basaltic (SiO 2  = ~46–52; MgO = ~6–10 wt%) to andesitic (SiO 2  = ~59; MgO = ~4 wt%) rocks exposed in the Gürün and Kangal basins (Sivas, eastern part of central Anatolia), respectively. The basaltic rocks are characterized by alkaline to tholeiitic affinities, while the more evolved andesitic samples show calc-alkaline affinity. Trace element variations reveal that they can be evaluated in three sub-groups, each represented by different contents of trace elements for given Nb contents. Primary magmas of each groups were likely produced by different degrees of partial melting (~1–2, 2–3, 7–10% respectively) from a common mantle source, subsequently underwent different degrees of fractionation and crustal contamination. Derivation from a common mantle source of the primitive magmas of each group is supported by similar Sr, Nd and Pb isotopic ratios. Increasing degrees of partial melting seem to be responsible for the alkaline to tholeiitic variation among the basaltic samples, while higher degrees of crustal contamination (AFC) resulted in calc-alkaline affinity of the more evolved samples. Most primitive Pliocene samples show intra-plate (anorogenic) geochemical features, while the more evolved Miocene calc-alkaline samples resemble geochemically subduction-related (orogenic) magmatic rocks. However, on the basis of detailed geochemical models, we propose that the calc-alkaline affinity among the Miocene samples can also be gained by crustal contamination of their primary magmas which were also anorogenic in character. If this is true, overall, the Miocene and Pliocene basaltic to andesitic rocks in the Gürün and Kangal basins appear to may have formed by variable degrees of partial melting of a common anorogenic mantle that had not been subject to subduction-related metasomatism. This is an alternative approach to the general view assuming the Early-Middle Miocene magmatic activity in the region was derived from subduction-modified mantle sources in response to subduction of the Arabian Plate under the Anatolian Plate. This hypothesis further implies that either delamination of the sub-continental lithosphere or slab break-off processes beneath the central to eastern Anatolia might took place well before the Miocene, thus allowing upwelling unaltered mantle to provide the source of the Miocene to Pliocene volcanic rocks. [ABSTRACT FROM AUTHOR]