Recent fieldwork, geochemistry, and U–Pb geochronology in the Palaeoproterozoic Ketilidian orogen provide substantial insights into the timing and mechanisms of its magmatic, sedimentary, and tectonic accretion. From north to south the orogen comprises an Archaean foreland and Border Zone, a calc-alkaline arc, and a migmatized fore arc. Contrasting the marginally older Nagssugtoqidian orogen of central West Greenland, the Ketilidian orogen is juvenile, lacks evidence of continent–continent collision, and probably evolved during northward subduction of an oceanic plate under the Archaean craton, with a suture south of the present orogen. Palaeoproterozoic dolerite dyke emplacement into the cratonic margin was followed by deposition of Ketilidian cover rocks. Thrusting and dextral transpression before 1848 Ma in the northwest may correlate with 1895–1870 Ma dextral transpression in the Makkovik orogen, Labrador. Sinistral transpression and I-type granite emplacement followed at 1848–1805 Ma. In the northeast, limited geochronology indicates deformation and metamorphism at ca. 1800 Ma. The calc-alkaline Julianehåb batholith was largely emplaced between 1854–1795 Ma during sinistral transpression, giving rise to steep magmatic fabrics and northeast-trending shear zones. Until 1790 Ma, the proximal fore-arc basin (Psammite Zone) received coarse detritus from the batholith, and turbidity currents swept sands and muds into distal parts. Fore-arc sedimentation, pervasive deformation, high temperature – low pressure (HT–LP) metamorphism and anatexis occurred at 1795–1785 Ma: flat-lying planar fabrics with top-to-northeast transport were due to tectonic decoupling at the outboard batholith margin during continued transpression. Rapakivi granite sheets were emplaced at 1755–1732 Ma and folded into broad arches and narrow synclinal cusps compatible with late-stage sinistral transpression.

Three fault systems were responsible for Permian to Late Cretaceous deformation of the overriding plate of the Andean convergent margin in the Coastal Cordillera of northern Chile (25°30′ to 27°00′S). Displacements were linked to crustal growth expressed by the emplacement of a sequence of magmatic arcs. The Tigrillo Fault System, active from Triassic to Early Cretaceous time, was characterized by arc-normal extension with increasing left-oblique extension (transtension) from Early Jurassic to Early Cretaceous time. Stretching of the crust created space for Triassic, Early Jurassic and Early Cretaceous arc basins where epiclastic, volcaniclastic and volcanic sequences accumulated in continental to shallow marine environments. Tabular plutonic complexes were emplaced by roof uplift–floor subsidence that allowed a vertical transfer of material in the crust without significant horizontal extension. The Atacama Fault System was initiated at c. 132 Ma as a (mainly) left strike-slip fault during left-oblique extension of the margin. Elongate, tabular plutonic complexes were emplaced within the Atacama Fault System between c. 132 and c. 106 Ma, again by roof uplift–floor subsidence mechanisms. Ductile–brittle transitions in synplutonic mylonitic rocks of the Atacama Fault System provided the setting for Kiruna-type Fe-apatite, and Fe oxide (with Cu and/or Au) ores. The Chivato Fault System was active as an extensional fault system at the eastern side of the Coastal Cordillera during displacement on the Tigrillo Fault System and later, between c. 125 and c. 93 Ma, as a partitioned left-oblique extensional fault system. In post-Early Cretaceous time the Chivato Fault System was inverted by left-oblique contraction (transpression) when NW-trending transfer faults, some probably reactivated lateral ramps in the Tigrillo Fault System, accommodated clockwise vertical-axis rotations of 35–45°. Contraction inverted the Atacama Fault System and Tigrillo Fault System and was responsible for west-vergent, thin-skinned, fold–thrust deformation in stratified rocks throughout the margin.

From Middle Jurassic to Late Cretaceous time the African-European Rift Zone (AERZ), a seaway connecting the western part of the Tethys Ocean to the embryonic Atlantic Ocean, was characterized by sinistral transtension. On the African margin of the AERZ this caused break-up of Tethyan Triassic and Lower Jurassic evaporite and carbonate platform sequences by linked, strike-slip and normal-slip fault displacements that delineated a system of sedimentary basins separated by horsts. The Zaghouan-Ressas Structural Belt (ZRSB) in northern Tunisia was initiated as a north-tapering horst in this system, bounded to the northwest by a pelagic basin (the Tunisian Trough) in which thick Lower Cretaceous sequences were deposited and to the east by a north-south trending system of reactivated Tethyan margin faults. Thickness variations in syn-rift stratigraphy led to lateral flow in underlying Triassic evaporitic sequences and the initiation of pillows and, perhaps, piercement diapirs. Mid- to latest Cretaceous post-rift sequences onlapped syn-rift fault blocks, but the post-rift period is complicated by a reversal in the displacement sense across the AERZ leading to dextral transpression and local fault inversion. In Paleocene and Eocene time, northern Tunisia was characterized by northeast-southwest extension accommodated by displacements on linked systems of reactivated AERZ-related and Tethyan margin faults at the southern margin of Mesogea. This was associated with drift of the Apulian microplate into eventual collision with the European margin to form the Western Alps. Further west, convergence of Africa relative to Europe was initially taken up by subduction of oceanic lithosphere in the remnant AERZ. The Oligo-Miocene evolution of the western Mediterranean reflects the destruction of this oceanic lithosphere and its successor oceanic basin, the Proto-Mediterranean. The Atlassic orogeny in northern Tunisia began in Oligocene time as a result of collision of microplates rifted off the European margin with the North African margin, and coincided with the progressive elimination of Proto-Mediterranean lithosphere from west to east along the African margin. Evidence of the contractional deformation is the development of an Oligocene-Miocene foreland basin in northern Tunisia and its deformation in the Atlas fold-thrust belt of mid- to Upper Miocene age. Within this tectonic framework, two models for the structural evolution of the ZRSB during the Atlassic orogeny are evaluated. The first recognizes the importance of facies variation in controlling thrust geometry, but is essentially a thin-skinned model in which detachment on incompetent Triassic strata forms the main control of structural style. The second model emphazises reactivation of AERZ-related basin margin faults during contraction and accounts for the major folds in the ZRSB at Djebel Zaghouan and Djebel Ressas as forced folds formed by fault inversion. Anticlines at Hamman Zriba, and east of Grombalia, are also interpreted as fault-inversion folds formed in normal sequence on the external side of the ZRSB. Flow of Triassic strata into the cores of these folds may have been assisted by tectonic loading during fault inversion along the ZRSB. Subsequently, structures in the ZRSB were dissected by northeast-southwest-trending faults that propagated through the post-rift sequence during post-Miocene reactivation of syn-rift extensional faults. These faults accommodated dextral oblique-slip displacement and were linked to extension in northwest-southeast-trending graben that cut the ZRSB and the Intermediate Atlas Zone.

No abstract

Paleomagnetic analyses of Mesozoic lavas and dike swarms from the northern Chilean Coastal Cordillera, between 25.4°S and 26.4°S, reveal a clockwise rotation of about 42°. Magnetizations from lava flows of andesitic‐basaltic composition of the Middle Jurassic La Negra Formation pass both fold and reversal tests and are interpreted as prefolding remanences. Five dike swarms of Middle Jurassic to Early Cretaceous age yield similar directions to that obtained from the La Negra Formation. Four of the five swarms have mixed polarity, suggesting that they too carry a primary or very early remanence. The structural setting of the dikes suggests that they have not suffered any substantial tilting about nonvertical axes since acquisition of the remanence. The clockwise rotation of the area is believed to have been the consequence of transpressional deformation of mid–Late Cretaceous age, post‐100 Ma, associated with abandonment of the Jurassic–Early Cretaceous magmatic arc in this region and its eastward migration to form a new mid–Late Cretaceous magmatic arc in the former back arc region. This younger arc is located east of the Coastal Cordillera and lies in the Central Valley region. The clockwise sense of rotation is consistent with other paleomagnetic data from northern Chile and southern Bolivia, south of the Arica Deflection in the Andean margin, although it is the largest yet reported. To the north of the Arica Deflection, paleomagnetic studies report counterclockwise rotations, and several large‐scale models have been proposed to explain the overall pattern of rotations. Models include oroclinal bending of an originally straight margin, differential shortening across the margin at a preexisting bend which is subsequently tightened by the passive rotation of the limbs of the bend, and distributed shear throughout the margin as a consequence of oblique convergence at a preexisting bend. In contrast to these models, several workers have argued that rotation is better explained in terms of localized in situ rotations. We review these models in light of our results and present a domino‐type model with blocks bounded by left‐lateral faults and rotating clockwise in response to mid‐Late Cretaceous transpression within a crustal scale shear zone. This is consistent with the observed strike‐slip fault systems identified in the Coastal Cordillera.