Thibaud Simon-labric - Academia.edu (original) (raw)

Papers by Thibaud Simon-labric

Lithosphere, 2014

Physical and numerical simulations of the development of mountain topography predict that asymmet... more Physical and numerical simulations of the development of mountain topography predict that asymmetric distributions of precipitation over a mountain range induce a migration of its drainage divide toward the driest flank in order to equilibrate erosion rates across the divide. Such migration is often inferred from existing asymmetries, but direct evidence for the migration is often lacking. New low-temperature apatite cooling ages from a transect across the northern North Cascades range (Washington, NW USA) and from two elevation profiles in the Skagit River valley record faster denudation on the western, wetter side of the range and lower denudation rates on the lee side of the range. This difference has already been documented further south along another transect across the range; however, in the south, the shift from young cooling ages to older ages occurs across the modern drainage divide. Here, further north, the shift occurs along a range-transverse valley within the Skagit Gorge. It has been proposed that the upper Skagit drainage was once a part of the leeward side of the range but started to drain toward the western side of the range across the Skagit Gorge in Quaternary time. Age-elevation profiles along the former drainage and in the Skagit Gorge restrict the onset of Skagit Gorge incision to the last 2 m.y., in agreement with 4 He/ 3 He data for the gorge floor. Breaching of the range drainage resulted in its displacement 40 km further east into the dry side of the range. In the 2000-m-deep, V-shaped Skagit Gorge, river stream power is still high, suggesting that incision of the gorge is still ongoing. Several other similar events have occurred along the range during the Pleistocene, supporting the proposed hypothesis that the repeated southward incursions of the Cordilleran ice sheet during this period triggered divide breaching and drainage reorganization by overflow of ice-dammed lakes at the front of the growing ice sheet. Since these events systematically rerouted streams toward the wet side of the range and resulted in leeward migration of the divide, we propose that in fact the Cordilleran ice sheet advance essentially catalyzed the adjustment of the mountain chain topography to the current orographic precipitation pattern.

Basin Research, 2011

Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonl... more Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record.We provide ¢eld evidence of the reorganization of a Miocene drainage network in response to strike^slip and vertical displacements in Guatemala.The drainage was deeply incised into a 50-km-wide orogen located along the North America^Caribbean plate boundary. It rearranged twice, ¢rst during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults.The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, ¢eld mapping, sediment provenance study, grainsize analysis and Ar 40 /Ar 39 dating from paleovalleys and their ¢ll reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runo¡, are not su⁄cient to produce the observed diversions.The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution-triggered or deformation-triggered permeability have helped breaching of inter£uves.The diversions are also related temporally and spatially to the accumulation of sediment ¢lls in the valleys, upstream of the rising structures.We infer that the breaching of the inter£uves was achieved by headward erosion along tributaries fed by groundwater £ow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley ¢lls provided the head pressure that enhanced groundwater circulation.The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater £ow between catchments.

Tectonics, 2011

The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between... more The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between the North American and Caribbean plates. To the west, it interacts with the subduction of the Cocos plate, with which it forms a triple junction of subduction-subduction-transform type (SST). The North American plate moves westward relative to the Caribbean plate. However, this differential displacement of the two overriding plates does not result in a wrenching of the subducted Cocos plate. This implies that this deformation is accommodated entirely within the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements to understand how this triple junction has evolved during the late Cenozoic. In Miocene time, extension and shortening occurred respectively to the south and north of the Motagua fault. This strain parting shifted northward onto the Polochic fault after the Late Miocene. This shift is interpreted as the result of the "pulling-up" of North American blocks and their attachment to the Caribbean domain. In the west the PMFS interacts with a trench-parallel fault zone that comprises the Tonala fault and the Jalpatagua fault. These faults delimitate landward a forearc sliver that is shared by the two overriding plates. We propose that the dextral Japatagua fault merges with the sinistral PMFS, leaving behind a suture, the Tonala fault. This tectonic "zipping" allows the triple junction to migrate towards the Caribbean Plate. As a result, the forearc sliver comes into contact with the North American plate and helps maintaining a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates. distance to the Cocos subduction zone as the Jalpatagua fault [Guzmán-Spéciale and Meneses-Rocha, 2000; Witt et al., in review].

Terra Nova, 2009

Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar... more Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar ⁄ 39 Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite-phengite thermobarometry yields 10-15 km and T 280°C, while 40 Ar ⁄ 39 Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40 Ar ⁄ 39 Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.

Lithosphere, 2014

Physical and numerical simulations of the development of mountain topography predict that asymmet... more Physical and numerical simulations of the development of mountain topography predict that asymmetric distributions of precipitation over a mountain range induce a migration of its drainage divide toward the driest flank in order to equilibrate erosion rates across the divide. Such migration is often inferred from existing asymmetries, but direct evidence for the migration is often lacking. New low-temperature apatite cooling ages from a transect across the northern North Cascades range (Washington, NW USA) and from two elevation profiles in the Skagit River valley record faster denudation on the western, wetter side of the range and lower denudation rates on the lee side of the range. This difference has already been documented further south along another transect across the range; however, in the south, the shift from young cooling ages to older ages occurs across the modern drainage divide. Here, further north, the shift occurs along a range-transverse valley within the Skagit Gorge. It has been proposed that the upper Skagit drainage was once a part of the leeward side of the range but started to drain toward the western side of the range across the Skagit Gorge in Quaternary time. Age-elevation profiles along the former drainage and in the Skagit Gorge restrict the onset of Skagit Gorge incision to the last 2 m.y., in agreement with 4 He/ 3 He data for the gorge floor. Breaching of the range drainage resulted in its displacement 40 km further east into the dry side of the range. In the 2000-m-deep, V-shaped Skagit Gorge, river stream power is still high, suggesting that incision of the gorge is still ongoing. Several other similar events have occurred along the range during the Pleistocene, supporting the proposed hypothesis that the repeated southward incursions of the Cordilleran ice sheet during this period triggered divide breaching and drainage reorganization by overflow of ice-dammed lakes at the front of the growing ice sheet. Since these events systematically rerouted streams toward the wet side of the range and resulted in leeward migration of the divide, we propose that in fact the Cordilleran ice sheet advance essentially catalyzed the adjustment of the mountain chain topography to the current orographic precipitation pattern.

Terra Nova, 2009

Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar... more Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar ⁄ 39 Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite-phengite thermobarometry yields 10-15 km and T 280°C, while 40 Ar ⁄ 39 Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40 Ar ⁄ 39 Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.

Tectonics, 2011

The initial propagation of the Western Alpine orogen was directed northwestwards, as shown by bas... more The initial propagation of the Western Alpine orogen was directed northwestwards, as shown by basementinvolved and Mesozoic sedimentary cover compressional structures, and by the early foreland basins evolution. The crystalline basement of the Dauphiné zone recorded three shortening episodes : pre-Priabonian deformation D1 (coeval with the Pyrenean-Provence orogeny), and Alpine shortening events D2 (N-NW directed) and D3 (W-directed). The early Oligocene D2 structures are trending sub-perpendicular to the more recent, arcuate orogen and are interfering with (or truncated by) D3, which marks the onset of westward lateral extrusion. The NW-ward propagating Alpine flexural basin shows earliest Oligocene thin-skinned compressional deformation, with syn-depositional basin-floor tilting and submarine removal of the basin infill above active structures. Gravity enhanced submarine erosion gave birth locally to steep submarine slopes overlain by kilometric-scale blocks slided from the orogenic wedge. The deformations of the basin floor and the associated sedimentary and erosional features indicate a N-NW-ward directed propagation, consistent with D2 in the Dauphiné foreland. The Internal zones represent the paleo-accretionary prism developped during this early Alpine continental subduction stage. The early buildup has been curved in the arc and rapidly exhumed during the Oligocene collision stage. Westward extrusion and indenting by the Apulian lithosphere allowed the modern arc to crosscut the western, lateral termination of the ancient orogen from ~32 Ma onwards. This contrasted evolution leads to propose a palinspastic restoration taking in account important northward transport of the distal passive margin fragments (Briançonnais) involved in the accretionnary prism before the formation of the Western Alps arc.

Tectonics, 2011

The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between... more The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between the North American and Caribbean plates. To the west, it interacts with the subduction of the Cocos plate, with which it forms a triple junction of subduction-subduction-transform type (SST). The North American plate moves westward relative to the Caribbean plate. However, this differential displacement of the two overriding plates does not result in a wrenching of the subducted Cocos plate. This implies that this deformation is accommodated entirely within the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements to understand how this triple junction has evolved during the late Cenozoic. In Miocene time, extension and shortening occurred respectively to the south and north of the Motagua fault. This strain parting shifted northward onto the Polochic fault after the Late Miocene. This shift is interpreted as the result of the "pulling-up" of North American blocks and their attachment to the Caribbean domain. In the west the PMFS interacts with a trench-parallel fault zone that comprises the Tonala fault and the Jalpatagua fault. These faults delimitate landward a forearc sliver that is shared by the two overriding plates. We propose that the dextral Japatagua fault merges with the sinistral PMFS, leaving behind a suture, the Tonala fault. This tectonic "zipping" allows the triple junction to migrate towards the Caribbean Plate. As a result, the forearc sliver comes into contact with the North American plate and helps maintaining a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates. distance to the Cocos subduction zone as the Jalpatagua fault [Guzmán-Spéciale and Meneses-Rocha, 2000; Witt et al., in review].

Journal of Geodynamics, 2012

The northwestwards-directed Eocene propagation of the Western Alpine orogen is linked with (1) co... more The northwestwards-directed Eocene propagation of the Western Alpine orogen is linked with (1) compressional structures in the basement and the Mesozoic sedimentary cover of the European foreland, well preserved in the External Zone (or Dauphiné Zone) of the Western Alps, and (2) tectono-sedimentary features associated with the displacement of the early Tertiary foreland basin. Three major shortening episodes are identified: A pre-Priabonian deformation D1 (N-S shortening), supposedly linked with the Pyrenean-Provence orogeny, and two Alpine shortening events D2 (N-to NW-directed) and D3 (W-directed). The change afficher lignesfrom D2 to D3, which occurred during early Oligocene time in the Dauphiné zone, is demonstrated by a high obliquity between the trends of the D3 folds and thrusts, which follow the arcuate orogen, and of the D2 structures which are crosscut by them. This change is also recorded in the evolution of the Alpine foreland basins: the flexural basin propagating NW-wards from Eocene to earliest Oligocene shows thin-skinned compressional deformation, with syn-depositional basin-floor tilting and submarine removal of the basin infill above active structures. Locally, a steep submarine slope scar is overlain by kilometricscale blocks slided NW-wards from the orogenic wedge. The deformations of the basin floor and the associated sedimentary and erosional features are kinematically consistent with D2 in the Dauphiné foreland. Since ~32 Ma ago, the previously subsiding areas were uplifted and the syntectonic sedimentation shifted westwards. Simultaneously, the paleo-accretionnary prism which developped during the previous, continental subduction stage was rapidly exhumed during the Oligocene collision stage due to westward indenting by the Adriatic lithosphere, which likely enhanced the relief and erosion rate. The proposed palinspastic restoration takes into account this two-stage evolution, with important northward transport of the distal passive margin fragments (Briançonnais) involved in the accretionnary prism before the formation of the western arc, which now crosscuts the westward termination of the ancient orogen. By early Oligocene, the Ivrea body indentation which was kinematically linked with the Insubric line activation initiated the westward escape and the curvature of the arc was progressively acquired, as recorded by southward increasing counter-clockwise rotations in the internal nappes. We propose that the present N-S trend of the Ivrea lithospheric mantle indenter which appears roughly rectilinear at ~15 km depth could be a relict of the western transform boundary of Adria during its northward Eocene drift. The renewed Oligocene Alpine kinematics and the related change in the mode of accomodation of Africa-Europe convergence can be correlated with deep lithospheric causes, i.e. partial detachment of the Tethyan slab and/or a change in motion of the Adria plate, and was enhanced by the Edirected rollback of the eastern Ligurian oceanic domain and the incipient Ligurian rifting.

Geophysical Research Letters, 2013

1] Geological observations of mantle flow-driven dynamic topography are numerous, especially in t... more 1] Geological observations of mantle flow-driven dynamic topography are numerous, especially in the stratigraphy of sedimentary basins; on the contrary, when it leads to subaerial exposure of rocks, dynamic topography must be substantially eroded to leave a noticeable trace in the geological record. Here, we demonstrate that despite its low amplitude and long wavelength and thus very low slopes, dynamic topography is efficiently eroded by fluvial erosion, providing that drainage is strongly perturbed by the mantle flow driven surface uplift. Using simple scaling arguments, as well as a very efficient surface processes model, we show that dynamic topography erodes in direct proportion to its wavelength. We demonstrate that the recent deep erosion experienced in the Colorado Plateau and in central Patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling.

Earth and Planetary Science Letters, 2013

Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology ... more Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology a b s t r a c t

Basin Research, 2011

Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonl... more Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record.We provide ¢eld evidence of the reorganization of a Miocene drainage network in response to strike^slip and vertical displacements in Guatemala.The drainage was deeply incised into a 50-km-wide orogen located along the North America^Caribbean plate boundary. It rearranged twice, ¢rst during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults.The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, ¢eld mapping, sediment provenance study, grainsize analysis and Ar 40 /Ar 39 dating from paleovalleys and their ¢ll reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runo¡, are not su⁄cient to produce the observed diversions.The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution-triggered or deformation-triggered permeability have helped breaching of inter£uves.The diversions are also related temporally and spatially to the accumulation of sediment ¢lls in the valleys, upstream of the rising structures.We infer that the breaching of the inter£uves was achieved by headward erosion along tributaries fed by groundwater £ow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley ¢lls provided the head pressure that enhanced groundwater circulation.The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater £ow between catchments.

Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology ... more Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology a b s t r a c t

Lithosphere, 2014

Physical and numerical simulations of the development of mountain topography predict that asymmet... more Physical and numerical simulations of the development of mountain topography predict that asymmetric distributions of precipitation over a mountain range induce a migration of its drainage divide toward the driest flank in order to equilibrate erosion rates across the divide. Such migration is often inferred from existing asymmetries, but direct evidence for the migration is often lacking. New low-temperature apatite cooling ages from a transect across the northern North Cascades range (Washington, NW USA) and from two elevation profiles in the Skagit River valley record faster denudation on the western, wetter side of the range and lower denudation rates on the lee side of the range. This difference has already been documented further south along another transect across the range; however, in the south, the shift from young cooling ages to older ages occurs across the modern drainage divide. Here, further north, the shift occurs along a range-transverse valley within the Skagit Gorge. It has been proposed that the upper Skagit drainage was once a part of the leeward side of the range but started to drain toward the western side of the range across the Skagit Gorge in Quaternary time. Age-elevation profiles along the former drainage and in the Skagit Gorge restrict the onset of Skagit Gorge incision to the last 2 m.y., in agreement with 4 He/ 3 He data for the gorge floor. Breaching of the range drainage resulted in its displacement 40 km further east into the dry side of the range. In the 2000-m-deep, V-shaped Skagit Gorge, river stream power is still high, suggesting that incision of the gorge is still ongoing. Several other similar events have occurred along the range during the Pleistocene, supporting the proposed hypothesis that the repeated southward incursions of the Cordilleran ice sheet during this period triggered divide breaching and drainage reorganization by overflow of ice-dammed lakes at the front of the growing ice sheet. Since these events systematically rerouted streams toward the wet side of the range and resulted in leeward migration of the divide, we propose that in fact the Cordilleran ice sheet advance essentially catalyzed the adjustment of the mountain chain topography to the current orographic precipitation pattern.

Basin Research, 2011

Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonl... more Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record.We provide ¢eld evidence of the reorganization of a Miocene drainage network in response to strike^slip and vertical displacements in Guatemala.The drainage was deeply incised into a 50-km-wide orogen located along the North America^Caribbean plate boundary. It rearranged twice, ¢rst during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults.The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, ¢eld mapping, sediment provenance study, grainsize analysis and Ar 40 /Ar 39 dating from paleovalleys and their ¢ll reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runo¡, are not su⁄cient to produce the observed diversions.The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution-triggered or deformation-triggered permeability have helped breaching of inter£uves.The diversions are also related temporally and spatially to the accumulation of sediment ¢lls in the valleys, upstream of the rising structures.We infer that the breaching of the inter£uves was achieved by headward erosion along tributaries fed by groundwater £ow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley ¢lls provided the head pressure that enhanced groundwater circulation.The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater £ow between catchments.

Tectonics, 2011

The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between... more The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between the North American and Caribbean plates. To the west, it interacts with the subduction of the Cocos plate, with which it forms a triple junction of subduction-subduction-transform type (SST). The North American plate moves westward relative to the Caribbean plate. However, this differential displacement of the two overriding plates does not result in a wrenching of the subducted Cocos plate. This implies that this deformation is accommodated entirely within the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements to understand how this triple junction has evolved during the late Cenozoic. In Miocene time, extension and shortening occurred respectively to the south and north of the Motagua fault. This strain parting shifted northward onto the Polochic fault after the Late Miocene. This shift is interpreted as the result of the "pulling-up" of North American blocks and their attachment to the Caribbean domain. In the west the PMFS interacts with a trench-parallel fault zone that comprises the Tonala fault and the Jalpatagua fault. These faults delimitate landward a forearc sliver that is shared by the two overriding plates. We propose that the dextral Japatagua fault merges with the sinistral PMFS, leaving behind a suture, the Tonala fault. This tectonic "zipping" allows the triple junction to migrate towards the Caribbean Plate. As a result, the forearc sliver comes into contact with the North American plate and helps maintaining a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates. distance to the Cocos subduction zone as the Jalpatagua fault [Guzmán-Spéciale and Meneses-Rocha, 2000; Witt et al., in review].

Terra Nova, 2009

Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar... more Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar ⁄ 39 Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite-phengite thermobarometry yields 10-15 km and T 280°C, while 40 Ar ⁄ 39 Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40 Ar ⁄ 39 Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.

Lithosphere, 2014

Physical and numerical simulations of the development of mountain topography predict that asymmet... more Physical and numerical simulations of the development of mountain topography predict that asymmetric distributions of precipitation over a mountain range induce a migration of its drainage divide toward the driest flank in order to equilibrate erosion rates across the divide. Such migration is often inferred from existing asymmetries, but direct evidence for the migration is often lacking. New low-temperature apatite cooling ages from a transect across the northern North Cascades range (Washington, NW USA) and from two elevation profiles in the Skagit River valley record faster denudation on the western, wetter side of the range and lower denudation rates on the lee side of the range. This difference has already been documented further south along another transect across the range; however, in the south, the shift from young cooling ages to older ages occurs across the modern drainage divide. Here, further north, the shift occurs along a range-transverse valley within the Skagit Gorge. It has been proposed that the upper Skagit drainage was once a part of the leeward side of the range but started to drain toward the western side of the range across the Skagit Gorge in Quaternary time. Age-elevation profiles along the former drainage and in the Skagit Gorge restrict the onset of Skagit Gorge incision to the last 2 m.y., in agreement with 4 He/ 3 He data for the gorge floor. Breaching of the range drainage resulted in its displacement 40 km further east into the dry side of the range. In the 2000-m-deep, V-shaped Skagit Gorge, river stream power is still high, suggesting that incision of the gorge is still ongoing. Several other similar events have occurred along the range during the Pleistocene, supporting the proposed hypothesis that the repeated southward incursions of the Cordilleran ice sheet during this period triggered divide breaching and drainage reorganization by overflow of ice-dammed lakes at the front of the growing ice sheet. Since these events systematically rerouted streams toward the wet side of the range and resulted in leeward migration of the divide, we propose that in fact the Cordilleran ice sheet advance essentially catalyzed the adjustment of the mountain chain topography to the current orographic precipitation pattern.

Terra Nova, 2009

Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar... more Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40 Ar ⁄ 39 Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite-phengite thermobarometry yields 10-15 km and T 280°C, while 40 Ar ⁄ 39 Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40 Ar ⁄ 39 Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.

Tectonics, 2011

The initial propagation of the Western Alpine orogen was directed northwestwards, as shown by bas... more The initial propagation of the Western Alpine orogen was directed northwestwards, as shown by basementinvolved and Mesozoic sedimentary cover compressional structures, and by the early foreland basins evolution. The crystalline basement of the Dauphiné zone recorded three shortening episodes : pre-Priabonian deformation D1 (coeval with the Pyrenean-Provence orogeny), and Alpine shortening events D2 (N-NW directed) and D3 (W-directed). The early Oligocene D2 structures are trending sub-perpendicular to the more recent, arcuate orogen and are interfering with (or truncated by) D3, which marks the onset of westward lateral extrusion. The NW-ward propagating Alpine flexural basin shows earliest Oligocene thin-skinned compressional deformation, with syn-depositional basin-floor tilting and submarine removal of the basin infill above active structures. Gravity enhanced submarine erosion gave birth locally to steep submarine slopes overlain by kilometric-scale blocks slided from the orogenic wedge. The deformations of the basin floor and the associated sedimentary and erosional features indicate a N-NW-ward directed propagation, consistent with D2 in the Dauphiné foreland. The Internal zones represent the paleo-accretionary prism developped during this early Alpine continental subduction stage. The early buildup has been curved in the arc and rapidly exhumed during the Oligocene collision stage. Westward extrusion and indenting by the Apulian lithosphere allowed the modern arc to crosscut the western, lateral termination of the ancient orogen from ~32 Ma onwards. This contrasted evolution leads to propose a palinspastic restoration taking in account important northward transport of the distal passive margin fragments (Briançonnais) involved in the accretionnary prism before the formation of the Western Alps arc.

Tectonics, 2011

The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between... more The Polochic-Motagua fault system (PMFS) is a segment of the sinistral transform boundary between the North American and Caribbean plates. To the west, it interacts with the subduction of the Cocos plate, with which it forms a triple junction of subduction-subduction-transform type (SST). The North American plate moves westward relative to the Caribbean plate. However, this differential displacement of the two overriding plates does not result in a wrenching of the subducted Cocos plate. This implies that this deformation is accommodated entirely within the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements to understand how this triple junction has evolved during the late Cenozoic. In Miocene time, extension and shortening occurred respectively to the south and north of the Motagua fault. This strain parting shifted northward onto the Polochic fault after the Late Miocene. This shift is interpreted as the result of the "pulling-up" of North American blocks and their attachment to the Caribbean domain. In the west the PMFS interacts with a trench-parallel fault zone that comprises the Tonala fault and the Jalpatagua fault. These faults delimitate landward a forearc sliver that is shared by the two overriding plates. We propose that the dextral Japatagua fault merges with the sinistral PMFS, leaving behind a suture, the Tonala fault. This tectonic "zipping" allows the triple junction to migrate towards the Caribbean Plate. As a result, the forearc sliver comes into contact with the North American plate and helps maintaining a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates. distance to the Cocos subduction zone as the Jalpatagua fault [Guzmán-Spéciale and Meneses-Rocha, 2000; Witt et al., in review].

Journal of Geodynamics, 2012

The northwestwards-directed Eocene propagation of the Western Alpine orogen is linked with (1) co... more The northwestwards-directed Eocene propagation of the Western Alpine orogen is linked with (1) compressional structures in the basement and the Mesozoic sedimentary cover of the European foreland, well preserved in the External Zone (or Dauphiné Zone) of the Western Alps, and (2) tectono-sedimentary features associated with the displacement of the early Tertiary foreland basin. Three major shortening episodes are identified: A pre-Priabonian deformation D1 (N-S shortening), supposedly linked with the Pyrenean-Provence orogeny, and two Alpine shortening events D2 (N-to NW-directed) and D3 (W-directed). The change afficher lignesfrom D2 to D3, which occurred during early Oligocene time in the Dauphiné zone, is demonstrated by a high obliquity between the trends of the D3 folds and thrusts, which follow the arcuate orogen, and of the D2 structures which are crosscut by them. This change is also recorded in the evolution of the Alpine foreland basins: the flexural basin propagating NW-wards from Eocene to earliest Oligocene shows thin-skinned compressional deformation, with syn-depositional basin-floor tilting and submarine removal of the basin infill above active structures. Locally, a steep submarine slope scar is overlain by kilometricscale blocks slided NW-wards from the orogenic wedge. The deformations of the basin floor and the associated sedimentary and erosional features are kinematically consistent with D2 in the Dauphiné foreland. Since ~32 Ma ago, the previously subsiding areas were uplifted and the syntectonic sedimentation shifted westwards. Simultaneously, the paleo-accretionnary prism which developped during the previous, continental subduction stage was rapidly exhumed during the Oligocene collision stage due to westward indenting by the Adriatic lithosphere, which likely enhanced the relief and erosion rate. The proposed palinspastic restoration takes into account this two-stage evolution, with important northward transport of the distal passive margin fragments (Briançonnais) involved in the accretionnary prism before the formation of the western arc, which now crosscuts the westward termination of the ancient orogen. By early Oligocene, the Ivrea body indentation which was kinematically linked with the Insubric line activation initiated the westward escape and the curvature of the arc was progressively acquired, as recorded by southward increasing counter-clockwise rotations in the internal nappes. We propose that the present N-S trend of the Ivrea lithospheric mantle indenter which appears roughly rectilinear at ~15 km depth could be a relict of the western transform boundary of Adria during its northward Eocene drift. The renewed Oligocene Alpine kinematics and the related change in the mode of accomodation of Africa-Europe convergence can be correlated with deep lithospheric causes, i.e. partial detachment of the Tethyan slab and/or a change in motion of the Adria plate, and was enhanced by the Edirected rollback of the eastern Ligurian oceanic domain and the incipient Ligurian rifting.

Geophysical Research Letters, 2013

1] Geological observations of mantle flow-driven dynamic topography are numerous, especially in t... more 1] Geological observations of mantle flow-driven dynamic topography are numerous, especially in the stratigraphy of sedimentary basins; on the contrary, when it leads to subaerial exposure of rocks, dynamic topography must be substantially eroded to leave a noticeable trace in the geological record. Here, we demonstrate that despite its low amplitude and long wavelength and thus very low slopes, dynamic topography is efficiently eroded by fluvial erosion, providing that drainage is strongly perturbed by the mantle flow driven surface uplift. Using simple scaling arguments, as well as a very efficient surface processes model, we show that dynamic topography erodes in direct proportion to its wavelength. We demonstrate that the recent deep erosion experienced in the Colorado Plateau and in central Patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling.

Earth and Planetary Science Letters, 2013

Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology ... more Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology a b s t r a c t

Basin Research, 2011

Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonl... more Deeply incised drainage networks are thought to be robust and not easily modi¢ed, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record.We provide ¢eld evidence of the reorganization of a Miocene drainage network in response to strike^slip and vertical displacements in Guatemala.The drainage was deeply incised into a 50-km-wide orogen located along the North America^Caribbean plate boundary. It rearranged twice, ¢rst during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults.The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, ¢eld mapping, sediment provenance study, grainsize analysis and Ar 40 /Ar 39 dating from paleovalleys and their ¢ll reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runo¡, are not su⁄cient to produce the observed diversions.The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution-triggered or deformation-triggered permeability have helped breaching of inter£uves.The diversions are also related temporally and spatially to the accumulation of sediment ¢lls in the valleys, upstream of the rising structures.We infer that the breaching of the inter£uves was achieved by headward erosion along tributaries fed by groundwater £ow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley ¢lls provided the head pressure that enhanced groundwater circulation.The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater £ow between catchments.

Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology ... more Keywords: subduction slab window Patagonia dynamic topography apatite (U-Th)/He thermochronology a b s t r a c t