A comment on “Geomorphic development of the escarpment of the Eritrean margin, southern Red Sea from combined apatite fission-track and (U–Th)/He thermochronometry” by Balestrieri, M.L. et al. [Earth Planet. Sci. Lett. 231 (2005) 97–110]

Published without an abstract. From the introduction: The western Red Sea margin in Eritrea comprises 25 km of coastal lowlands backed by a deeply eroded escarpment that rises > 2.2 km in 40 km. The plateau atop this zone of Neogene uplift is capped by 30 Ma continental flood basalts (CFB). The CFBs rest conformably on thin Palaeogene (> 40 Ma) lateritic palaeosols [1], beneath which is a Neoproterozoic metamorphic complex. In the southern part, the laterites are separated from basement by discontinuous patches of Jurassic sandstones. The laterites observed in the field and on satellite images occur in this stratigraphic position throughout the hinterland of the western Red Sea margin from eastern Sudan [2] through Eritrea and northern Ethiopia [3] and [4] to the Blue Nile Gorge [5] (a N–S range of > 800 km), and further to the south [6]. Because they formed on a low-relief surface close to sea-level [7] across most of NE Africa and western Arabia [4], the laterites are an important datum for assessing the later effects of regional tectonics [3] and [8]. Post-30 Ma tectonics has displaced occurrences of this datum on the plateau and coastal lowlands by 2.2–2.8 km vertically. The opportunities presented by the laterite datum clearly encouraged Balestrieri et al. [9] and Abbate et al. [10] to analyse geomorphic processes at the western Red Sea margin thermochronologically. So too did previous work on the initiation of rifting in the Red Sea and Gulf of Aden areas [7], [11], [12] and [13], which converged on initiation of uplift and erosion from 25 to 20 Ma. On the basis of 13 apatite (U–Th)/He cooling ages (apatite He ages) from the Eritrean escarpment, Balestrieri et al. [9] conclude a 10 Ma younger age for the start of rifting in the southern Red Sea

Time constraints on exhumation of the East African Orogen from field observations and Ar-40/Ar-39 cooling ages of low-angle mylonites in Eritrea, NE Africa

Neoproterozoic high-grade metamorphic rocks of the lower to middle crust are exposed along parts of the East African Orogen (EAO). However, the mechanisms and rates of exhumation of these deep orogenic rocks remain unclear. In eastern Eritrea, the rocks of the EAO comprise two lithotectonic domains: Ghedem and Bizen. The Ghedem domain consists of low-angle mylonites among lower to middle crustal gneisses and schists that were metamorphosed at amphibolite facies conditions before being retrogressed locally. Here we quantitatively constrain time increments in the exhumation history of the low-angle Ghedem mylonites using Ar-40/Ar-39-cooling ages for metamorphic homblende and white mica samples extracted from them. The hornblende samples gave an average plateau age of about 579 6 Ma and the white mica samples an average plateau age of about 567 +/- 5 Ma. Geothermobarometry had already shown that these rocks experienced progressive syn-deformation metamorphism that peaked when P-T conditions were near 12 kbar and 650 degrees C at 593 +/- 5 Ma. These P-T conditions and the new Ar-40/Ar-39 cooling ages indicate that cooling and exhumation of the low-angle mylonites of the Ghedem domain were accomplished in three increments of different rate as they progressively rose from as deep as 45 km while the orogen was collapsing during the late Neoproterozoic. In the first increment, the rocks cooled similar to 11 degrees C/Ma as they rose at about 1.07 km/Ma to cool through 500 degrees C at a depth of 30 km at 579 5 Ma. In the second increment, the rocks cooled about similar to 10 degrees C/Ma after their exhumation rate increased to about 1.25 km/Ma so that they cooled through 300 degrees C at 567 5 Ma. A third increment, poorly constrained by unconformable Permo-Carboniferous sediments, implies minimum cooling rates of 1.4 degrees C/Ma and exhumation rates of only 0.06 km/Ma. The first two increments of exhumation occurred when the EAO in eastern Eritrea was undergoing gravitational collapse probablymuch faster and later than in the southern EAO. Such regional differences in gravitational collapse rates map local differences in maximum lithospheric thickness built by the final convergence of East and West Gondwana

Color Invariant Snakes

Snakes provide high-level information in the form of continuity constraints and minimum energy constraints related to the contour shape and image features. These image features are usually based on intensity edges. However, intensity edges may appear in the scene without a material/color transition to support it. As a consequence, when using intensity edges as image features, the image segmentation results obtained by snakes may be negatively affected by the imaging-process (e.g. shadows, shading and highlights) . In this paper, we aim at using color invariant gradient information to guide the deformation process to obtain snake boundaries which correspond to material boundaries in images discounting the disturbing influences of surface orientation, illumination, shadows and highlights. Experiments conducted on various color images show that the proposed color invariant snake successfully find material contours discounting other "accidental" edges types (e.g. shadows, shading and highlight transitions). Comparison with intensity-based snakes shows that the intensity-based snake is dramatically outperformed by the presented color invariant snake

Constraints for timing of extensional tectonics in the western margin of the Red Sea in Eritrea

Recent work on asthenosphere–lithosphere coupling reinforces past observations that active and passive rifting models do not adequately describe real rifts. There remains insufficient knowledge of fundamental controls on rift architecture. In the actively extending Red Sea margin of eastern Eritrea, which lies at the Red Sea/Danakil–Gulf of Aden and the East African rift triple junction zone, the geometry and kinematics of extension are complex and poorly defined due to large data gaps. Extension and sea-floor spreading in both the Red Sea and Gulf of Aden have influenced the Neogene tectonic development of Eritrea but many of the structures have Pan-African origins and do not follow normal plate opening geometries. To constrain the rifting history in eastern Eritrea, apatite fission-track thermochronologic data were measured for 22 Pan-African rock samples. Results identify late Oligocene–early Miocene cooling coincident with extension and erosion along the conjugate margin in Yemen. A younger age group, confined to Mt Ghedem, relates to an episode of fault reactivation and dyke injection that began ∼10 Ma coincident with rotation of the nearby Danakil block. Initially this was driven by onset of sea-floor spreading in the Gulf of Aden and later, in the Pliocene, aided by northward rifting in the Afar depression concomitant with spreading in the Red Sea. These different processes highlight the complex linkage between different extensional events and rift architecture

Cultuursensitief werken met alleenstaande jonge vluchtelingen

Alleenstaande minderjarige vreemdelingen (AMV’s) lopen een verhoogd risico op het ontwikkelen van psychische problematiek. Over de beste benadering van deze problematiek is nog veel onduidelijk. Aan de hand van een casus bespreken we hoe we cultuursensitief kunnen werken met een AMV die last heeft van traumagerelateerde klachten