Francesc Sàbat

Bed-by-bed fold growth by kink-band migration: Sant llorenç de Morunys, eastern Pyrenees

Ahstract<rowth strata deposited over and against the flank of the Sant Llorenc de Morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth. We use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding. The progressive restorations, as well as balanced forward modeling, show that the last few hundred meters of fold growth were dominated by kink-band migration of a sort that is typical of much faultrelated folding. The kink-band migration has produced complex anticlinal hinge-zone geometry, including segmented fold hinges linked by disconformities and unconformities, which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved-hinge kink-band migration rate. Large fluctuations in the convolution of non-steady sedimentation and deformation are demonstrated, although the absolute fluctuations in deformation and sedimentation are unknown. At a length scale of 100 m, kink-band migration with little or no deposition is interspersed with sedimentation with little or no deformation. At the length scale of 500 m, deposition ranges from 200% to 50% of uplift. 0 1997 Elsevier Science Ltd. All rights reserved.

A structural outline of the Serra de Tramuntana of Mallorca (Balearic Islands)

Abstract The structural and stratigraphic aspects of the Balearic Islands are described by outlining the geology of the Serra de Tramuntana. This range is part of the southeastern margin of the Valencia trough and has the typical features of thrust tectonic areas. A stratigraphic column, a structural map and three cross-sections show the main features of this range. Thrusts dip to the southeast and are arranged in an imbricate system with a transport direction to the NW. The thrusts recorded involve Upper Paleozoic to Middle Miocene rocks. Imbricates-bearing thin slices and duplexes developed where thin sequences with pronounced competency contrasts exist. Folds are also present: they usually trend NE-SW, except in local areas where they are interpreted as being associated with oblique ramps. Fold axes plunge sub-horizontally and folds face the northwest. Thrust displacements of up to 10 km are deduced from the existence of klippes and windows, and shortening of around 50% is deduced from a comparison of deformed and restored cross-sections. The onset of the main contractional event is pre-Miocene (probably Late Oligocene) in age, but major thrust emplacement occurred during the Middle Miocene. The widespread occurrence of compression structures in the Balearic Islands developed from late Oligocene to Middle Miocene put strong constraints on the models explaining the origin of both the Valencia trough and the Algerian basin. The first must be considered, at least in part, as the Balearic foreland basin and the second could be superimposed on the internal zone of the western Mediterranean orogenic belt.

Cenozoic tectosedimentary evolution of Mallorca island

AbstractThe results of recent biostratigraphic, sedimentologic and structural work concerning the island of Mallorca have led us to elaborate a synthesis of the Cenozoic tectosedimentary evolution of this area. The recognition in the field of several unconformities enabled us to distinguish four Depositional Sequences embracing the pre and syntectonic deposits.From Paleocene to part of Middle Eocene there was no sedimentation in the Mallorca area. This stratigraphie gap follows the onset of Africa-Europe convergence.The area was stable during the first sequence (Upper Lutetian-Bartonian), which is trangressive towards the NW. Tectonic activity is recorded by the conglomeratic wedges of Depositional Sequence 11 (Priabonian-Lower Chattian). A dramatic paleogeographic change ocurred between Depositional Sequence II and III. Observed thrusts and unstable platform sediments of Depositional Sequence III (Upper Chattian-Lo-wermost Burdigalian) indicate the onset of thrust tectonics in the area. Turbiditic deposi...

Lithostratigraphy of volcanic and sedimentary sequences in central Livingston Island, South Shetland Islands

Livingston Island contains several, distinctive sedimentary and volcanic sequences, which document the history and evolution of an important part of the South Shetland Islands magmatic arc. The turbiditic, late Palaeozoic-early Mesozoic Miers Bluff Formation (MBF) is divided into the Johnsons Dock and Napier Peak members, which may represent sedimentation in upper and lower mid-fan settings, respectively, prior to pre-late Jurassic polyphase deformation (dominated by open folding). The Moores Peak breccias are formed largely of coarse clasts reworked from the MBF. The breccias may be part of the MBF, a separate unit, or part of the Mount Bowles Formation. The structural position is similar to the terrigenous Lower Jurassic Botany Bay Group in the northern Antarctic Peninsula, but the precise stratigraphical relationships and age are unknown. The (?) Cretaceous Mount Bowles Formation is largely volcanic. Detritus in the volcaniclastic rocks was formed mainly during phreatomagmatic eruptions and redeposited by debris flows (lahars), whereas rare sandstone interbeds are arkosic and reflect a local provenance rooted in the MBF. The Pleistocene-Recent Inott Point Formation is dominated by multiple, basaltic tuff cone relicts in which distinctive vent and flank sequences are recognized. The geographical distribution of the Edinburgh Hill Formation is closely associated with faults, which may have been reactivated as dip-slip structures during Late Cenozoic extension (arc splitting).

Age and correlation of volcanism in central Livingston Island, South Shetland Islands: K-Ar and geochemical constraints

Volcanic sequences in central Livingston Island can be divided into two broad groups. The older group consists of basalt-dacite lavas, clastic rocks and associated hypabyssal intrusions. The lavas are lithologically and compositionally similar to other pre-Pliocene, volcanic arc lavas in the South Shetland Islands. The outcrops vary from relatively fresh (at Cape Shirreff, Hannah Point and Siddons Point) to indurated and pervasively altered (at Mount Bowles, Burdick Peak and Hurd Peninsula). Samples from the fresh outcrops yielded Late Cretaceous ages for eruption or intrusion, ranging from 90.2 ± 5.6 Ma at Cape Shirreff, to 73.0 ± 2.3 at Siddons Point. Chemical analyses of the lavas suggest that the sequences at these two outcrops can probably be correlated stratigraphically with the Byers Group and Coppermine Formation, respectively. Two samples from Hannah Point yielded conflicting ages of 87.9 ± 2.6 Ma and 67.5 ± 2.5 Ma from the centre and top of the sequence, respectively. The stratigraphical affinities of the Hannah Point sequence cannot yet be determined unambiguously but it is unlikely to be part of the Byers Group. All of the samples from the altered outcrops (which correspond to the Mount Bowles Formation) yielded Eocene-Oligocene K-Ar ages (44.4 to 35.0 Ma), interpreted as reset ages related to the emplacement and cooling of a nearby Eocene tonalite pluton responsible for much of the alteration, and also dated in this study (43.3 ± 2.8 Ma). A Cretaceous eruptive age (possibly Late Cretaceous) for the altered outcrops is likely but cannot yet be proven. By contrast, the younger group consists of degraded basalt lava flows, tuff cone and tuff ring remnants, which are part of the Inott Point Formation. The lavas are very fresh and Pleistocene or Recent in age (≤ 1 Ma). They are compositionally distinctive and are indistinguishable from supra-subduction alkali basalts preserved elsewhere in Livingston, Greenwich and Penguin islands.

Geomorphological and neotectonic features of Hurd Peninsula, Livingston Island, South Shetland Islands

On Hurd Peninsula (Livingston Island) neotectonic features, such as faults, affect the landforms and emerged marine levels. A detailed local study of these features provides information on the recent structural and geomorphological evolution of the area. We suggest that Hurd Peninsula is divided into several tectonic blocks separated by faults. Movement of the faults determines the relative altitude of these blocks and, in consequence, their susceptibility to glacial, periglacial or marine processes. Although some of the tectonic movements reflected in the landforms may have been inherited from former phases of deformation, some of the neotectonic faulting has a maximum lower Miocene age. A new method of correlation of emerged beach levels is suggested and the possibility of analysing the effects of neotectonic deformations from their analysis is discussed. The application of the methods tested here to other areas of the South Shetland archipelago could provide insights into the timing and mechanisms of recent tectonic evolution.

Basin fragmentation controlled by tectonic inversion and basement uplift in Sierras Pampeanas and Santa Bárbara System, northwest Argentina

Abstract The study area is located within the Central Andes, a complex region composed of different structural styles. The region is characterized by highly elevated basement cored ranges, which abruptly break the foreland plain. These ranges were uplifted mainly by deep detached high-angle faults or by the inversion of former extensional faults of the Cretaceous rift. Palaeozoic orogenies generated crustal scale discontinuities in the basement, some of them reactivated during the Andean orogeny. Sedimentary sequences and layers architecture in the basins bordering ranges recorded the tectonic evolution of the region. Basement, syn–rift, post-rift and three foreland stages were interpreted in the seismic sections according to the arrangement of the horizons and the main outcropping geological units in bordering ranges. Based on seismic data sets and field data, here we document a particular style of activation of basement faults. Thick-skinned structures that are not always related to the tectonic inversion but to the reactivation of older basement anisotropies represent a paradox since they were not active during the rifting stage. A flat slab subduction and a subsequent angle recovery conditioned the structural evolution of the area.

Fold amplification history unravelled from growth strata: the Dorood anticline, NW Persian Gulf

Abstract: The origin and kinematic evolution of the Dorood growth anticline, a kilometre-scale fold located in the Iranian NW part of the Persian Gulf on the Zagros front, is discussed based on the geological interpretation of a seismic section and subsequent application of a number of techniques such as depth to detachment estimations, sequential cross-section restoration, estimations of crestal structural relief, shortening, wavelength and fold core area in various stages of fold amplification, and comparison between functions derived from the anticline analysis and functions for theoretical folds. Long-term fold growth rates indicate a slow amplification for c. 88.6 Ma punctuated by two periods of faster growth during the Late Cretaceous and from the Late Miocene to the present day. The kinematic evolution proposed involves vertical push related to reactivation of a basement fault during the oldest amplification event and fold tightening owing to buckling as a consequence of horizontal compression in the youngest event, both causing evaporite motion. Fold amplification took place by a combination of hinge migration and limb rotation.

An example of three-dimensional analysis of thrust-related tectonites

Abstract A spaced pressure-solution cleavage related to Alpine thrusts in Mallorca (Balearic Isles) is deformed by several sets of shear planes and minor folds. All these structures formed synchronously, related to the thrust sheet movement. Shear plane sets show different orientations irrespective of the cleavage disposition. Slip along these shear planes shows that deformation did not result in plane strain. Minor fold axes show a wide range of orientations. Neither folds nor shear planes enable us to directly deduce the sense of thrust motion, indicating that these criteria must be used with care. Previous strain characterization is required for definite conclusions to be reached.

Synorogenic basins of central Cuba and collision between the Caribbean and North American plates

The synorogenic basins of central Cuba formed in a collision-related system. A tectono-stratigraphic analysis of these basins allows us to distinguish different structural styles along the Central Cuban Orogenic Belt. We recognize three distinct structural domains: (1) the Escambray Metamorphic Complex, (2) the Axial Zone, and (3) the Northern Deformation Belt. The structural evolution of the Escambray Metamorphic Complex includes a latest Cretaceous compressional phase followed by a Palaeogene extensional phase. Contraction created an antiformal stack in a subduction environment, and extension produced exhumation in an intra-arc setting. The Axial Zone was strongly deformed and shortened from the latest Cretaceous to Eocene. Compression occurred in an initial phase and subsequent transpressive deformation took place in the middle Eocene. The Northern Deformation Belt consists of a thin-skinned thrust fault system formed during the Palaeocene to middle Eocene; folding and faulting occurred in a piggyback sequence with tectonic transport towards the NNE. In the Central Cuban Orogenic Belt, some major SW–NE structures are coeval with the Cuban NW–SE striking folds and thrusts, and form tectonic corridors and/or transfer faults that facilitated strain-partitioning regime attending the collision. The shortening direction rotated clockwise during deformation from SSW–NNE to WSW–ENE. The synchronicity of compression in the north with extension in the south is consistent with the opening of the Yucatan Basin; the evolution from compression–extension to transpression is in keeping with the increase in obliquity in the collision between the Caribbean and North American plates.