Sobre la Presencia de Fallas de edad Precretácica y Post- Girón (Jura-triásico) en el Flanco W del Macizo de Santander (Cordillera Oriental, Colombia)

Two faults in which it has been pointed out the existen ce of a movement previous to the Cretacic and posterior to the Girón (Jura-Triassic) were studied. One of them (Aratoca's Fault) has not had any movement after the Cretacic and it is unconformably covered by the Cretacic. The other one (Matanza's Fault ) again was in movement after the Cretacic, having moved in opposed direction to the irritial movement ; this fact is indicated by the sudden disappearance of the Giron E of such fault. These pre-cretacic fauIts have pararelism with the general post-cretacic faulting. Also Matanza's fauIt shows the existence of faults with double movement pre and post-cretacic, this together with the analysis of disposition of overthrust sides in the post-cretacic fauIts, demostrates that the double movement of the Matanza's fault is not an isolated fact buy probably makes up a general feature of the tectonic of this region. Therefore after the Girón or during its own deposition, took place a period of distention with formation of normal faults which can he related to the tilting affecting the Girón and with the formation of a depressed area between the Macizo of Santander and the Colombian Cordillera Central; the great part of these fauIts moved as thrust faults with posteriority to the Cretacic and they are tied to tbe stage of folding of the Cordillera OrientalSe estudian dos fallas en las que se ha puesto de manifiesto la existencia de un juego anterior al cretácico y posterior al Girón (jura-triásico) Una de ellas (Falla de Aratoca) no ha tenido ningún juego con posterioridad al cretáceo; la base del cretácico la cubre discordantemente. La otra (falla de Matanza) ha sido nuevamente puesta en movimiento; este hecho se pone de manifiesto por la desaparición brusca del Girón al E de dicha falla. Estas fallas pre-cretácicas guardan paralelismo con la dirección general de fracturación post-cretácica, Esto, unido al hecho de que la Falla de Matanza demuestra que han existido fallas con doble juego, pre y post-cretácico, y unido al análisis de la disposición de los labios hundidos, permite afirmar que el fenómeno del doble juego de la falla de Matanza no es un hecho aislado sino que probablemente constituye un rasgo general de la tectónica de esta región. Así pues con posterioridad al Girón, o durante el depósito del mismo, tuvo lugar una etapa de distensión que se puede relacionar con las basculaciones que afectan al Girón y con la formación de una área deprimida entre el anticlinal de fondo del Macizo de Santander y la Cordillera Central Colombiana; estas fallas en gran parte jugaron como fallas inversas con posterioridad al cretácico y en relación con la etapa de plegamiento de la Cordillera Oriental

Sobre la Presencia de Fallas de edad Precretácica y Post- Girón (Jura-triásico) en el Flanco W del Macizo de Santander (Cordillera Oriental, Colombia)

Two faults in which it has been pointed out the existen ce of a movement previous to the Cretacic and posterior to the Girón (Jura-Triassic) were studied. One of them (Aratoca's Fault) has not had any movement after the Cretacic and it is unconformably covered by the Cretacic. The other one (Matanza's Fault ) again was in movement after the Cretacic, having moved in opposed direction to the irritial movement ; this fact is indicated by the sudden disappearance of the Giron E of such fault. These pre-cretacic fauIts have pararelism with the general post-cretacic faulting. Also Matanza's fauIt shows the existence of faults with double movement pre and post-cretacic, this together with the analysis of disposition of overthrust sides in the post-cretacic fauIts, demostrates that the double movement of the Matanza's fault is not an isolated fact buy probably makes up a general feature of the tectonic of this region. Therefore after the Girón or during its own deposition, took place a period of distention with formation of normal faults which can he related to the tilting affecting the Girón and with the formation of a depressed area between the Macizo of Santander and the Colombian Cordillera Central; the great part of these fauIts moved as thrust faults with posteriority to the Cretacic and they are tied to tbe stage of folding of the Cordillera OrientalSe estudian dos fallas en las que se ha puesto de manifiesto la existencia de un juego anterior al cretácico y posterior al Girón (jura-triásico) Una de ellas (Falla de Aratoca) no ha tenido ningún juego con posterioridad al cretáceo; la base del cretácico la cubre discordantemente. La otra (falla de Matanza) ha sido nuevamente puesta en movimiento; este hecho se pone de manifiesto por la desaparición brusca del Girón al E de dicha falla. Estas fallas pre-cretácicas guardan paralelismo con la dirección general de fracturación post-cretácica, Esto, unido al hecho de que la Falla de Matanza demuestra que han existido fallas con doble juego, pre y post-cretácico, y unido al análisis de la disposición de los labios hundidos, permite afirmar que el fenómeno del doble juego de la falla de Matanza no es un hecho aislado sino que probablemente constituye un rasgo general de la tectónica de esta región. Así pues con posterioridad al Girón, o durante el depósito del mismo, tuvo lugar una etapa de distensión que se puede relacionar con las basculaciones que afectan al Girón y con la formación de una área deprimida entre el anticlinal de fondo del Macizo de Santander y la Cordillera Central Colombiana; estas fallas en gran parte jugaron como fallas inversas con posterioridad al cretácico y en relación con la etapa de plegamiento de la Cordillera Oriental

Constraints on the Cenozoic Deformation of the Northern Eastern Cordillera, Colombia

The Eastern Cordillera of Colombia rose to maximum elevations of >5 km during the Cenozoic by inversion of a Mesozoic rift basin. Previous studies proposed that the exhumation of the Eastern Cordillera increased from ~6 Ma to the present due to the interplay between tectonic shortening and climate. In this study, we integrate new field observations, structural data, low-temperature thermochronology, thermobarometry, and vitrinite reflectance along a section through the Tablazo, Cocuy, and Llanos regions to estimate the amount of shortening and the exhumation history. Our results indicate that shortening started as early as the latest Maastrichtian-Paleocene in the Tablazo and Cocuy regions. Exhumation migrated eastward, starting in the Paleocene in the west and continuing in the Miocene in the east. The amount and rate of exhumation peaked in the Cocuy region with values of <5 km and < 0.4 km/Ma, respectively. At the highest elevations in the Cocuy Sierra, we also found evidence of a low-pressure/high-temperature metamorphic overprint, possibly related to shallow and local magmatic intrusions that occurred in the Late Miocene. Our cross-section interpretation suggests a low amount of shortening (13%) that is mainly accommodated by high-angle inverted faults and by the frontal thrust system. The presence of shallow magmatic bodies, moderate exhumation, and low shortening raises questions about the processes (isostatic versus dynamic) that drove the topographic growth of the high Cocuy Sierra

Status of Basement Terranes in Orogens: Insights From the Cadomian Domain of the North Armorican Variscides, Western France

International audienceThe stable versus mobile behavior of basement terranes in orogens is discussed about the North Armorican Cadomian floored domain (NAD) in the Armorican Variscides, Western France. Our onshore/offshore structural study demonstrates the heterogeneous nature of the NAD which comprises: (a) a southern part which remained stable during both the Paleozoic extensional and compressional (Variscan) events and (b) a northern part which was initially the locus of extensive Paleozoic sedimentary basins before recording Variscan deformation. Our work supplies a more complete structural picture of the Variscan pattern in Northern Armorica as a whole: (a) as precising the spatial distribution of Variscan strain, (b) as emphasizing its importance with a bulk shortening estimated at 30% in the North Cotentin fold and thrust belt, and (c) as regarding a newly identified pattern of sinistral ductile shear zones in the Morlaix area as lateral ramps that parallel the western edge of the rigid (southern) Cadomian block in a indenter kinematic setting. At a wider scale, compiling structural data set from others Cadomian terranes in the Variscan belt of Central (Bohemia) and Western (Iberia) Europe leads us to hypothetize that their stability versus reworking during the Variscan orogeny relies primarily on the mechanical/thermal state of their lithosphere at the end of the Paleozoic extensional stage