Eliseo Tesón

Inversion tectonics under increasing rates of shortening and sedimentation: Cenozoic example from the Eastern Cordillera of Colombia

Abstract The Northern Andes of Colombia is a key locality for understanding tectonic inversion of symmetric rifts. A review of available data on structural geometry and deformation timing, and new thermochronology and provenance data from selected localities, enable the construction of balanced cross-sections and shortening budgets. During early deformation in the Palaeocene, most shortening was focused in the western sector of the orogen, in the Central Cordillera and the Magdallena Valley, although widely spaced and mild inversion occur in areas as far to the east as the Llanos Basin. After a period of tectonic quiescence in the Middle Eocene, deformation resumed across a former early Mesozoic graben in the Eastern Cordillera. Peak shortening rates and out-of-sequence reactivation of the main inversion faults were in place in latest Miocene time, during a phase of topographical growth. Our results indicate that coeval activation of basement highs and adjacent slower-slip shortcuts appear to be characteristic of inverted symmetric grabens. However, before reactivation and brittle faulting occur, strain hardening is required. Deformation rates in the Eastern Cordillera correlate with the westwards velocity of the South American Plate. A threshold convergence rate of approximately 2 cm year−1 seems to be necessary to activate shortening in the upper plate.

Magnetostratigraphy of the Ouarzazate Basin: Implications for the timing of deformation and mountain building in the High Atlas Mountains of Morocco.

Two magnetostratigraphic profiles (450 samples) have been carried out to constrain the age of synorogenic formations in the southern foreland of the High Atlas of Morocco. The Amekchoud profile covers the Aït Ouglif and Aït Kandoula alluvial formations that form the bulk of the Ouarzazate basin fill, indicating an age between the upper Langhian and the Messinian (Miocene). Data obtained in the previously unexplored Hadida formation profile covers the oldest terms of the foreland basin succession, but the low quality of the magnetic record only allows proposing a tentative age between the middle Lutetian and an undetermined middle to late Eocene. The correlation of the Amekchoud profile is based on the recognition of the long C5n chron (Tortonian) in the middle part of the section studied and a new vertebrate locality of upper Tortonian age found in the upper part. These results indicate a discontinuous record of foreland basin development in the southern Atlas domain from mid Eocene to late Miocene times, punctuated by an intermediate large hiatus of 20-25 ma (late Eocene to mid Miocene). Thrusting in the Sub-Atlas frontal thrust belt began before the Aït Ouglif and Kandoula formations, probably during the Oligocene, and extends up to recent times. The alternation of periods of deposition with others of no sedimentary record, which does not coincide with specific tectonic events, results probably from the interference of orogenic deformation and the mantle-related thermal uplift events that have been described for the Moroccan Atlas.

Relationship of Mesozoic graben development, stress, shortening magnitude, and structural style in the Eastern Cordillera of the Colombian Andes

Abstract We use the Eastern Cordillera of Colombia as an example in early stages of inversion orogen showing still modest values of shortening. The style of deformation recorded in this orogenic chain seems to be strongly influenced by two main factors. The first is the pre-compression geometry of the rift basin, conditioning the strong heterogeneity imparted by a trough filled with Jurassic to Neocomian sediments limited by Precambrian and Palaeozoic high-angle walls. The second factor is the orientation of the stress regime with respect to the main normal faults during the inversion. If the stress field is of pure compression, the normal faults are not extensively inverted and the deformation is accommodated mainly in terms of footwall shortcuts. On the other hand, in transpressive regimes the inversion of the former normal faults is more common and the footwall shortcuts are not dominant structures. No significant lateral variations in tectonic shortening are found in the Eastern Cordillera. Finally we emphasize the role of buckle folds in the internal parts of the inversion orogens and give a cautionary note when interpreting these structures in terms of fault-related folding using the well-documented example of the Soapaga fault area.

Shortening, structural relief and drainage evolution in inverted rifts: insights from the Atlas Mountains, the Eastern Cordillera of Colombia and the Pyrenees

Abstract The Atlas, Eastern Cordillera and Pyrenees are thick-skinned thrust-fold belts formed by tectonic inversion of rift basins in continental settings. A comparison of shortening between them shows a gradation from 20–25% in the central High Atlas, to 25–30% in the Eastern Cordillera, and c. 40% in the Pyrenees. Accordingly, there is a structural variation from interior zones with low structural relief and isolated basement massifs in the first two cases, to an axial culmination of stacked basement thrust sheets in the Pyrenees. This results in marked topographic and drainage variation: the High Atlas and Eastern Cordillera contain axial plateaus dominated by structure-controlled longitudinal rivers and orogen flanks with slope-controlled transverse rivers, whereas the Pyrenees show a two-sided wedge profile dominated by transverse rivers. In spite of singularities exhibited by each orogen, we propose that this spatial variation can be understood as reflecting different degrees of evolution in mountain building. Rapidly incising, transverse rivers are capturing earlier longitudinal streams of the Atlas and Eastern Cordillera, thus reducing their axial plateaux, which will eventually disappear into a transverse-dominated drainage. This pattern of landscape evolution may be characteristic of inversion orogens as they develop from initial stages of inversion to full accretion.

Andean topographic growth and basement uplift in southern Colombia: Implications for the evolution of the Magdalena, Orinoco, and Amazon river systems

Surface uplift of the Garzon Massif in the northern Andes formed a critical orographic barrier (2500–3000 m elevation) that generated a deep rain shadow and strongly influenced the evolution of the largest river systems draining northern South America. This basement massif and its corresponding foreland basement high define the headwaters and drainage divides of the Amazon, Orinoco, and Magdalena Rivers. Despite its pivotal role, the exhumation history of the Garzon Massif and its relationships to the structural evolution of the broader Eastern Cordillera fold-thrust belt remain unclear. The northern Andes underwent major Cenozoic shortening, with considerable thin-skinned and thick-skinned deformation and topographic development in the Eastern Cordillera focused during late Miocene time. On the basis of widespread coarse-grained nonmarine sedimentation, previous studies have inferred that uplift of the Garzon Massif began during the late Miocene, coincident with rapid elevation gain elsewhere in the Eastern Cordillera. We take an integrated, multiproxy approach to better reconstruct Andean topographic growth and distinguish between exhumation and surface uplift of the Garzon Massif. We present new U-Pb detrital zircon provenance data, sandstone petrographic data, and paleoprecipitation data from upper Miocene clastic fill of the Neiva Basin within the adjacent Upper Magdalena Valley of the modern hinterland. In addition, six new apatite fission track (AFT) ages from the central segment of the northeast-trending Garzon Massif (Jurassic granite and Proterozoic gneiss and schist) directly constrain its Neogene exhumation history. The results indicate that early exhumation may have initiated by ca. 12.5 Ma, but a substantial orographic barrier was not fully established until ca. 6–3 Ma, when >1 km/m.y. of material was exhumed. Thermal history modeling of the AFT data suggests diminished exhumation thereafter (3–0 Ma), during latest Cenozoic oblique Nazca–South America convergence. This exhumation history is consistent with paleontological data suggesting late Miocene divergence of the three river systems, with associated transcontinental drainage of the Amazon River.

Interaction between thin- and thick-skinned tectonics in the foothill areas of an inverted graben. The Middle Magdalena Foothill belt

Abstract The Magdalena Valley fold-and-thrust belt is a tectonic province associated with inverted rift zones. This belt displays a narrow and discontinuous deformation front indicating association with inversion tectonics. We show the differences with an analogue belt on the eastern side of the Eastern Cordillera (Llanos foothills). To do that we use structural data (seismic, wells and geological maps) which characterize different structural geometries as well as palaeocurrents, provenance and thermochronology to analyse the timing of deformation. The new datasets allowed us to detect that inversion is limited whenever the stresses are more orthogonal to the rift structures, whereas the mountain front is more segmented in comparison to the Eastern Foothills because of the absence of a continuous low basal friction detachment horizon and a pronounced eastwards basement dip. These two factors favoured fault hard linkage. It is remarkable that, in spite of the distinct segmentation, all the different segments in the Magdalena belt are coeval. Supplementary material: U–Pb Zircon data are available at: http://www.geolsoc.org.uk/SUP18630.

Segmentation and growth of foothill thrust-belts adjacent to inverted grabens: the case of the Colombian Llanos foothills

Abstract The geometry, kinematics and evolution of thick- and thin-skinned fold and thrust-belts have been characterized for many tectonic provinces. However, the impact of prior extension in the structural evolution of fold and thrust-belts remains under-appreciated. We use a series of balanced cross sections across areas of thin- and thick-skinned tectonics superimposed over former extensional structures in order to characterize the style of deformation, segmentation and displacement magnitude. We detect the style of fault linkage in foothill settings adjacent to inversion belts. The most relevant aspect is the presence of inherited ‘soft linkages’ generating zones of displacement deficit, which in contraction interact laterally with en-echelon inverted segments via ‘detachment linkages’. We document the temporal development and interaction between inverted faults and fault splays branching from them where both are coeval but where the frontal fault tips propagate more slowly during Oligocene and Early Miocene times. Later, during the Neogene, the frontal fault splays slip faster than the main inversion fault. The structural style of thrust-belt development displays along-strike variations, which reflect the changes in sedimentation rates and mechanical conditions of deformation. However, the timing and magnitude of shortening remain uniform along-strike.

Intraplate tectonics:: insights from mountain building in the Moroccan Atlas and related subsidence in the Ouarzazate foreland basin .

Los braquiopodos retzidinos son una fraccion menor de las faunas devonicas de la CordilleraCantabrica (Norte de Espana). Aparte de un par de formas raras, impublicadas, del Praguiense delDominio Palentino y del Emsiense inferior del Astur-Leones, proximas al genero Rhynchospirina, ellinaje alcanzo su maximo de diversidad en la parte superior del Emsiense, con dos especies del generoRetzia, R. adrieni y R. cf. prominula, Cooperispira subferita y, quizas, una forma impublicada dePlectospira. El grupo no es conocido en el resto del Devonico y reaparece en el Pensilvaniense con algunasformas del genero Hustedia. En este trabajo se propone un nuevo taxon de la Familia Retziidae,Argovejia n.gen., de la parte final del Emsiense superior de Asturias y Leon, constituido por su especietipo,A. talenti n.sp. y, quizas, por las formas del Emsiense superior del Macizo Armoricano (Francia)Retzia haidingeri var. armoricana y Retzia haidingeri var. dichotoma.The Ronda Depression is filled by Neogene sediments on the boundary between Subbeticreliefs, with NE-SW structural trends, and the frontal Subbetic Chaotic Complexes. The folding stylein the Subbetic Units of Western Betics is strongly controlled by the rheology of the rocks: thick andmassive beds of Jurassic limestones over Triassic marls and gypsum with plastic behaviour. Main deformationstructures in the sedimentary infill of the Ronda depression are simultaneous box folds withNNE-SSW and WNW-ESE trends that only affect its southwestern part. This distribution of folds isa consequence of the inherited fold trend that affected the basement during Early Burdigalian age.