Abstract This chapter shows, from the theoretical point of view, that growth strata geometries above angular unconformities depend on the modification of initial unconformity angles due to different folding mechanisms operating in underlying layers. This theory is applied to the Sant Llorenç de Morunys growth structure, where the analysis of the unconformity angles shows that classic folding mechanisms, such as layer-parallel simple shear in both angular and curved folds, and tangential-longitudinal strain operated in the forelimb of a fault-propagation fold. These folding mechanisms, inferred from changes in unconformity angles, are consistent with the minor structures and lithological features of the involved stratigraphic units. Forward modeling, including limb rotation, hinge migration, and the above-mentioned folding mechanisms, explains the main structural features of the syntectonic sediments in the Sant Llorenç de Morunys fault-propagation fold.

Abstract The largest rivers that drain the Argentine Andean Ranges are characterized by incised valleys in high mountains and by a variety of Quaternary terraces. The terraces display a fan geometry with the apex located upstream of a tributary junction. Their convex-up morphology suggests that these terraces are related to a series of alluvial fans developed where the tributaries join the main river. The succession of alluvial aggradation and degradation is controlled by local base-level variation conditioned by temporary lake development in the main river valley. All these factors give rise to the inset segmented (terraced) morphology of the fan surfaces, yielding a telescopic-like relationship. The variation in the morphology and number of terraces suggests that they are not controlled by a general/regional base level. Neither tectonic activity nor significant climatic changes account for the alluvial fans at the confluences of the tributaries and the main river. Significant variations in rainfall or thunderstorms induced by the El Niño Southern Oscillation (ENSO) could explain the genesis of these telescopic-like alluvial fans.

Abstract The East African–Antarctica Orogen resulted from the continent–continent collision of East and West Gondwana, or parts thereof, during the Pan-African event at c . 650–510 Ma. The collision overprinted large areas of older, mainly Mesoproterozoic, crust up to granulite facies grade in East Antarctica. The collision history is well documented by folding and thrusting, isothermal decompression and metamorphic zircon growth at c . 580–560 Ma (Pan-African I). The convergence was succeeded by an extensional phase, probably representing orogenic collapse. This Pan-African II event at c . 530–510 Ma is characterized by large-scale extensional structures, finally resulting in the post-tectonic intrusion of voluminous A2-type granitoids. In central Dronning Maud Land the Pan-African II event started with the intrusion of syntectonic igneous rocks within an overall extensional setting. Two new SHRIMP data from gabbro zircons of the Zwiesel Gabbro give ages of 521±5.6 and 527±5.1 Ma. These ages are interpreted as crystallization ages and confirm the interpretation that the gabbro was emplaced early during the Pan-African II event. The gabbro was intruded by a network of leucogranite dykes and veins. Whereas the gabbro appears entirely undeformed, the leucogranite dykes are strongly mylonitized along extensional shear zones, indicating pronounced strain partitioning of the gabbro complex. Within the leucogranite mylonites, large tension gashes developed during mylonitization, indicating very high strain rates. Quartz c-axis orientations from quartz of the tension gashes show a distinct cross-girdle that formed during pure shear deformation. Fluid inclusion data from the leucogranite mylonites and the associated tension gashes mainly reveal recrystallization-related intracrystalline CO 2 -dominant inclusions with relatively low densities of < 1 g cm −3 . The fluid inclusion data are interpreted to represent the last stages of a retrograde P–T path that is characterized by simultaneous cooling and decompression during extensional exhumation, probably succeeding the collapse of overthickened crust. A comparable orogenic collapse of the East African–Antarctic Orogen is reported from other parts of the orogen, such as from western Madagascar and the northern Arabian–Nubian Shield.