Abstract Rincón de Parangueo is a Quaternary maar that has been recently desiccated. The crater was partially occupied by a soda lake, and near the shoreline microbialites have formed. Evaporites (mainly trona and halite) precipitated as the water level dropped. Active subsidence of the lake floor ( c. 24 m since 1980) produced countless structures close to the lakeshore, where deformation is extensional. Closer to the depocentre, in the western half of the basin, gliding/spreading produced folds and mud-injection domes. The most remarkable structure throughout the basin is a monocline that forms a ring-like, nearly continuous scarp, approximately 15 m high, which in the eastern half of the basin was produced as a fault-propagation fold developed above the buried diatreme–country rock boundary. A more diffuse (wider) monocline, locally associated with compressive structures, occurs in the western half of the basin. These structures are interpreted as having developed above a gently inclined, irregular lake sediment–country rock (andesite) interphase. The monocline was modified by high-angle extensional faults/fractures with large heaves/apertures. In the eastern half of the basin, there is a second (outer) scarp, approximately 13 m high, formed by a high-angle, listric, normal fault. Rollover antiforms occur in the hanging wall of this structure. Rincón is an example of centripetal gravitational gliding/spreading.

Abstract The NE–SW-trending Grampian Fold Belt has anomalous features that set it apart from other belts in the Caledonides. It consists mainly of polyphase-deformed (D1–D4) Neoproterozoic–early Ordovician rocks (Dalradian Supergroup), deposited in a basin that formed behind a microcontinent detached from Laurentia during Iapetus opening. Detailed cross-strike structural traverses through the D1/D2 Tay Nappe in the SW Highlands show that part of the Ligurian-type basin floor (Highland Border Complex) was obducted on to the Laurentian margin prior to orogenesis. On the top limb of the nappe, δ-porphyroclasts give a top-to-the-SE shear sense for the D1 stretching lineation, whereas D2 microlithons within a zone of non-coaxial strain on the lower limb indicate top-to-the-east. Subduction was initially orthogonal to the Belt but became oblique during D2. Synchroneity at c. 470 Ma of deformation, regional metamorphism, magmatism, termination of sedimentation and formation of the Buchan Block was probably linked to subduction of the spreading ridge. The driving force was NW-directed Andean-type subduction of part of the basin floor, and later of the microcontinental margin. These events caused progressive, diachronous non-coaxial D1–D3 deformation of the hanging wall (Dalradian). Crustal thickening on the SE margin was balanced by thrusting on to the foreland.