Search

Quantified balanced and restored crustal cross-sections across the NW Zagros Mountains are presented in this work integrating geological and geophysical local and global datasets. The balanced crustal cross-section reproduces the surficial folding and thrusting of the thick cover succession, including the near top of the Sarvak Formation (~90 Ma) that forms the top of the restored crustal cross-section. The base of the Arabian crust in the balanced cross-section is constrained by recently published seismic receiver function results showing a deepening of the Moho from 42 ± 2 km in the undeformed foreland basin to 56 ± 2 km beneath the High Zagros. The internal parts of the deformed crustal cross-section are constrained by new seismic tomographic sections imaging a ~50° NE-dipping sharp contact between the Arabian and Iranian crusts. These surfaces bound an area of 10800 km2 that should be kept constant during the Zagros orogeny. The Arabian crustal cross-section is restored using six different tectonosedimentary domains according to their sedimentary facies and palaeobathymetries, and assuming Airy isostasy and area conservation. While the two southwestern domains were directly determined from well-constrained surface data, the reconstruction of the distal domains to the NE was made using the recent margin model of Wrobel-Daveau et al. (2010) and fitting the total area calculated in the balanced cross-section. The Arabian continental–oceanic boundary, at the time corresponding to the near top of the Sarvak Formation, is located 169 km to the NE of the trace of the Main Recent Fault. Shortening is estimated at ~180 km for the cover rocks and ~149 km for the Arabian basement, including all compressional events from Late Cretaceous to Recent time, with an average shortening rate of ~2 mm yr−1 for the last 90 Ma. [ABSTRACT FROM AUTHOR]

We present balanced and restored cross-sections across the Western Cuba fold and thrust belt, based on MCS profiles, field data and balancing techniques. The cross-section intersects the Los Palacios Basin, the Sierra del Rosario antiformal stack, the Bahía Honda unit, the frontal imbricated thrust sheets, the foredeep basin and a buried, geometrically inferred duplex. The minimum calculated shortening is 130 km. Syntectonic deposits and a forward kinematic model provide a good constraint for the Cenozoic tectonic evolution of the orogen, from the emplacement of the Bahía Honda unit to the final infill of the foredeep. [ABSTRACT FROM AUTHOR]

ABSTRACT The timing of deformation in the northern Zagros Folded Belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences. The foreland basin infill in the northern part of the Fars arc is composed of supratidal sabkha deposits (Razak Fm), medium-grained deltaic deposits (Agha Jari Fm) and coarse conglomerates of nearshore fan delta deposits at the base (Bakhtyari Fm, Bk1) and continental alluvial deposits at the top of the section (Bakhtyari Fm, Bk2). A magnetostratigraphic study was carried out in a composite section spanning about 1300 m on the northern flank of the Chahar-Makan syncline. Magnetostratigraphic correlation of the Razak Fm with chron C6n yields an age of 19.7 Ma at the base of the composite section. The transition to Agha Jari Fm is correlated with chron C5Cn, yielding an age of 16.6 Ma. The transition to the conglomerates of the Bakhtyari Fm (Bk1) correlates with the chron C5AD at approximately 14.8 Ma, which is considerably older than previously thought. The base of the Bakhtyari Fm growth strata, and thus the beginning of the deformation in northern Fars, is dated at 14-15 Ma. The topmost preserved Bakhtyari Fm (Bk1) is folded and unconformably overlain by Bakhtyari Fm (Bk2) conglomerates. This indicates that tectonic deformation in northern Zagros was already underway in the Middle Miocene. [ABSTRACT FROM AUTHOR]

The characteristics of folds of the southern Lurestan province have been studied in terms of wavelength and axial-length distribution. The large variability of these parameters occurs in relation to facies changes within the Cretaceous Bangestan group which acts as the competent carbonate unit that governs bucking in this region. Disharmonic folding of the overlying Asmari formation occurs where the thickness of the interposed incompetent units exceeds a critical thickness that leaves the Asmari limestone outside of the zone of contact strain of the Bangestan buckles. [ABSTRACT FROM AUTHOR]

A sequential restoration based on combined backstripping and unfolding methods affords the opportunity to study the Cenozoic evolution of two low amplitude domes in the Mid-Norwegian extensional margin, the Helland Hansen Arch and the Vema Dome. The integration of growth strata geometries observed in both flanks of the domes demonstrate that the structures grew by a variable combination of tectonics and differential compaction mechanisms. Sequential restoration shows that the Helland Hansen Arch grew between Early Oligocene and earliest Late Pliocene times (33–1.9 Ma). During the first phase of growth (33–9 Ma), the tectonic compression accounted for a minimum of 27% of the total dome amplitude. During Late Miocene to Pliocene times (9–1.9 Ma), differential compaction was the mechanism for dome growth. During Late Pliocene times, the Helland Hansen Arch grew with the highest rates coinciding with initial deposition of prograding wedges (3.6–1.9 Ma). In contrast, the Vema Dome started to develop in Early Eocene times and grew at a fairly constant rate up to Early Pliocene times at 3.6 Ma. The amplification of the Vema Dome took place through both differential compaction and tectonics between Early Eocene and Late Miocene times (54.8–7 Ma). The tectonic contribution accounted for a minimum of a 37% of the total dome amplitude. During Pleistocene times, the progradation of clastic wedges led to a decrease of the amplitudes of both the Helland Hansen Arch and the Vema Dome. The different timing of tectonic growth for analysed domes and arches suggest that a small and protracted phase of compression affected the Mid-Norwegian Margin. This agrees with well-known widespread contractional deformation affecting the Atlantic Margin of the European Plate during the Tertiary. [ABSTRACT FROM AUTHOR]

Abstract: The present-day thermal and compositional 3D structure of the lithosphere beneath the Atlantic–Mediterranean Transition Region and the lithosphere–asthenosphere interaction from Jurassic times to present has been studied. The Atlantic–Mediterranean Transition Region comprises the western segment of the Africa–Eurasia plate boundary, encompassing two main large-scale tectonic domains: the Gibraltar Arc System and the Atlas Mountains. An integrated and self-consistent geophysical–petrological methodology (LitMod3D) has been applied that combines elevation, gravity, geoid, surface heat flow, and seismic data and allows modelling of compositional heterogeneities within the lithospheric mantle. Our results reveal large variations in the depth of the Moho and the lithosphere–asthenosphere boundary (LAB) as well as a lack of spatial correlation between the thicknesses of these two boundaries. The Moho essentially mimics the topography with depths ranging from ∼10km beneath the oceanic domains of the Atlantic abyssal plains and the Algerian Basin to >34km in the Eastern Betics and Rif, the High Atlas mountains, and the Sahara Platform. In contrast, the LAB is shallower beneath the central and eastern Alboran Basin (∼70km) and all along the High, Middle and Anti Atlas (<100km) coinciding with the loci of Cenozoic volcanism. Deeper LAB depths are found along the central and western Betics and the Moroccan Atlantic margin (>140km) with values exceeding 230km beneath the Rif and the Sahara Platform. The average bulk composition of the lithospheric mantle corresponds to that of a typical Tecton (i.e. Phanerozoic) domain, with the exceptions of the Sahara Platform, the Alboran Basin, and Atlas Mountains. Distinct mantle compositions are required in these areas to make model predictions and geophysical observables compatible. It is proposed that the highly irregular LAB topography is the result of the superposition of three different geodynamic processes: i) shortening and thickening related to NW–SE Iberia–Africa convergence lasting from Late Cretaceous to Recent, ii) impingement of a baby-like mantle plume or small-scale convection beneath the High-Middle Atlas and Anti Atlas commencing in the mid Eocene, and iii) slab roll-back or mantle delamination in the Betic–Rif–Alboran realm acting from early to late Miocene. [Copyright &y& Elsevier]

Abstract: Detailed information on lateral variations in lithospheric properties can aid in understanding how surface deformation relates to deep Earth processes. The effective elastic thickness, T e , of the lithosphere is a proxy for lithospheric strength. Here, we present a new T e map of the African lithosphere estimated from coherence analysis of topography and Bouguer anomaly data. The latter data set derives from the EGM 2008 model, the highest resolution gravity database over Africa, enabling a significant improvement in lateral resolution of T e . The methodology used for T e estimation improves upon earlier approaches by optimally combining estimates from several different window sizes and correcting for an estimation bias term. Our analysis finds that T e is high, ~100 km, in the West African, Congo, Kalahari and Tanzania cratons. Of these, the Kalahari exhibits the lowest T e . Based in part on published seismic and mineral physics constraints, we suggest this may reflect modification of Kalahari lithosphere by anomalously hot asthenospheric mantle. Similarly, the Tanzania craton exhibits relatively lower T e east of Lake Victoria, where a centre of seismic radial anisotropy beneath the craton has been located and identified with a plume head, thus suggesting that here too, low T e reflects modification of cratonic lithosphere by an underlying hot mantle. The lowest T e in Africa occurs in the Afar and Main Ethiopian rifts, where lithospheric extension is maximum. In the western Ethiopian plateau a local T e minimum coincides with published images of a low P and S seismic velocity anomaly extending to ~400 km depth. Finally, the Darfur, Tibesti, Hoggar and Cameroon line volcanic provinces are characterised by low T e and no deep-seated seismic anomalies in the mantle. Corridors of relatively low T e connect these volcanic provinces to the local T e minima within the western Ethiopian plateau. We interpret the low T e to indicate thinner lithosphere within the corridors than in the surrounding cratons. We speculate that these corridors may provide potential conduits for hot asthenospheric material to flow from the western Ethiopian plateau to the volcanic provinces of central and western Africa. [Copyright &y& Elsevier]