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A six-step reconstruction of the South Pyrenean foreland fold-and-thrust belt in Spain delineates the topographic slope, basal dtcollement angie, internal deformation, and thrust- front advance from the Early Eocene until the end of contractional deformation in the Late Oligocene. Style of thrust- front advance, dip of the basal dtcollement, slope of the upper surface, and internal deformation are decoupled and not simply related. Internal deformation increased, decreased, and maintained surface slope angle at different stages. From the onset to the cessation of deformation, the basal dtcollement angle decreased overall suggesting translation of the thrust belt onto stronger crust with time. Taper angle of the Pyrenean thrust wedge was fundamentally controlled by the flexural rigidity of the lower plate, the relative rate of creation of structural relief in the rear versus the front of the wedge, the extent of deposition of eroded material within the deforming wedge, and the taper of the pretectonic stratigraphic wedge.

New mapping, structural analysis and magnetostratigraphy reveal a polyphase deformational history at the leading edge of the Spanish Pyrenean foreland fold-and-thrust belt. The present structural architecture is the consequence of three discrete periods of deformation. Map relationships between four syntectonic units and major structures provide tight geometric and age constraints for each deformational period (D1: 55 to 42 Ma; D2: 30.1 to 28.0 Ma; D3: 27.9 to < 25.8 Ma). Most of the shortening in the area accumulated during D2 thrusting at rates which varied from 0.7 mm y −1 to 2.8 mm y −1 along strike from northwest to southeast, respectively. Removal of D2 and D3 displacement on thrust faults restores folds formed during D1. A sequential kinematic history during which an individual structure accommodates shortening by folding, tightening of the fold and subsequent truncation by thrust faulting is inferred. Sequential restoration of three serial cross-sections demonstrates that nearly every structure active during D1 was also active during D2. Distributed deformation characterizes the temporal and spatial pattern on all time scales, from structures active during each individual deformational period to the long-term history encompassed by the total deformation.

The final, deformed state of a fold-and-thrust belt may be reached by an infinite number of kinematic paths. Two end-member kinematic paths are due to continuous or discontinuous rates of deformation. We have used a new magnetostratigraphic section from the Spanish Pyrenees to calibrate the emplacement history, over ≈10 m.y., of a major thrust sheet (the Sierras Marginales thrust sheet) and the deformation of both its hanging wall and footwall. Six time windows from before 36.5 Ma until after 24.7 Ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures. Footwall deformation of the Sierras Marginales thrust sheet occurred continuously on a detachment within the foreland-basin sequence (4.5 km net shortening; shortening rates steadily increased from 0.14 to 1.5 mm/yr with time). Although the detachments at the base of the foreland and the detachment at the base of the Sierras Marginales thrust sheet were active coevally, the rate of displacement on the Sierras Marginales detachment decayed with time and shows considerable variability. Emplacement of the thrust sheet may be divided into three distinct periods: a rapid 13.8 km translation from 37.0 to 36.5 Ma (27.6 mm/yr), a gradual climb of the toe of the thrust sheet up a 4.3-km-long ramp across the foreland-basin succession from 36.5 to 32.0 Ma (0.95 mm/yr), and a final 8.9 km translation from 32.0 to 29.5 Ma (3.56 mm/yr). Internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29.5 Ma. Shortening rates steadily decreased from 0.6 mm/yr between 29.5 and 27.8 Ma to 0.26 mm/yr from 27.8 until after 24.7 Ma. Only ≈1 km of shortening accumulated during each of the two periods; the last shortening localized on the most northerly thrust in the study area. Folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation. In contrast, translation followed by internal deformation on the hinterland side of the toe of the Sierras Marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time. Rate of deformation on both detachments was discontinuous and shows substantial variability about the mean. In general, the spatial and temporal pattern of deformation was distributed and continuous. In detail, however, shortening was spatially and temporally discontinuous above each detachment, and structures related to each one display distinctly different deformational patterns, rates, and styles.

Responses of both modern and ancient fluvial depositional systems to growing folds can be interpreted in terms of interactions among competing controlling variables which can be incorporated into simple conceptual models. The ratio of the rate of sediment accumulation to the rate of structural uplift determines whether a fold develops a topographic expression above local base level. The balance between (a) stream power and rates of upstream deposition vs. (b) bedrock resistance and rates of crestal uplift and of fold widening determines whether an antecedent stream maintains its course or is defeated by a growing structure. Modern drainage configurations in actively folding landscapes can often be interpreted in terms of these competing variables, and through analysis of digital topography, detailed topographic characteristics of these folds can be quantified. Modern examples of growing folds display both defeated and persistent antecedent rivers, deflected drainages and laterally propagating structures. The topography associated with a defeated antecedent river at Wheeler Ridge, California, is consistent with a model in which defeat results from forced aggradation in the piggyback basin, without the need to vary discharge or uplift rate. Reconstruction of the long-term interplay between a depositional system and evolving folds requires a stratigraphic perspective, such as that provided by syntectonic strata which are directly juxtaposed with ancient folds and faults. Analysis of Palaeogene growth strata bounding the Catalan Coastal Ranges of NE Spain demonstrates the synchronous growth and the kinematic history of multiple folds and faults in the proximal foreland basin. Although dominated by transverse rivers which crossed fold crests, palaeovalleys, interfan lows, structural re-entrants and saddles, and rising anticlines diverted flow and influenced local deposition. In the ancient record, drainage-network events, such as avulsion or defeat of a transverse stream, usually cannot be unambiguously attributed to a single cause. Examination of ancient syntectonic strata from a geomorphological perspective, however, permits successive reconstructions of synorogenic topography, landscapes and depositional systems.

[1] Active mountain building associated with the accretion of the Yakutat microplate (YT) in southern Alaska is characterized through the combination of a new balanced cross section and new low-temperature cooling ages. This analysis constrains the amount and timing of shortening, the spatial and temporal trends of exhumation, and the interplay between structural development and exhumation. A fold-and-thrust belt comprising three principal thrust sheets (the Hope Creek, Sullivan, and an offshore thrust sheet from north to south) characterizes the YT internal structure, which has absorbed a minimum of ∼82 km shortening. Assuming shortening and foreland basin development occurred contemporaneously, the shortening rate across the YT is ∼13–14 mm/a after 5.6 Ma. Detrital apatite fission track ages, from south to north, are unreset along the southern edge of the Sullivan thrust sheet at the coast, are reset and have ages younger than 6.3 Ma within the thrust belt, and have reset cooling ages of ∼13 Ma in the North American upper plate. Only the zircon samples from the northern, internal YT are potentially reset. Exhumation rates within the thrust belt vary from 0.3 ± 0.1 mm/a to 4 ± 1.8 mm/a. Combining the thermochronometric and structural data indicate that wedge exhumation since ∼6 Ma is 500 km2 and that particle trajectories have larger horizontal than vertical components. Whereas exhumation and shortening have been focused on the windward side of the Chugach/St. Elias Range since ∼6 Ma, the cooling ages do not uniquely distinguish between orographically versus tectonically controlled erosion.

Three independent data sets from northwestern India and Pakistan suggest initial displacement along >1000 km of the Main Boundary thrust prior to 10 Ma, at least 5 m.y. earlier than previously reported. Regionally extensive changes in the depositional characteristics and rates of the foreland-basinfill between 11 and 9.5 Ma are interpreted to reflect new hinterland loading due to the formation of the Main Boundary thrust. Sediment-accumulation rates, sandstone-siltstone ratios, and thickness and amalgamation of individual sandstone bodies all substantially increase after 11 Ma in well-dated stratigraphic sections from Pakistan to Nepal across the Indo-Gangetic foreland basin. In the Himachal Pradesh reentrant of northwestern India, a newly discovered 8.7 Ma conglomerate derived from the hanging wall of the Main Boundary thrust indicates that source-area uplift and denudation must have occurred prior to 9 Ma and probably prior to 10 Ma, assuming a gravelprogradationrateof3cm/yr.Threeapatitefission-trackages fromstructuresattheleadingedgeoftheMainBoundarythrustin the Kohat region of northwest Pakistan indicate that rapid cooling below ;105 C1‐2 m.y. earlier. These data indicate that the Main Boundary thrust in the western Himalaya formed synchronously along strike in the middle-late Miocene, has a displacement rate of ;10 mm/yr, and has a displacement history that is coeval with late displacement on the Main Central thrust.