Crustal structure beneath the Tell and Atlas Mountains (Algeria and Tunisia) through the analysis of gravity data

Abstract Bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the Tell and Atlas Mountains of Algeria and Tunisia. Two-dimensional gravity models and profiles of topography, free-air and Bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation. The thickest crust (38–40 km) was found beneath the Saharian Atlas in northern Algeria, whereas under the Tunisian Atlas it is approximately 34–36 km. There is little evidence of crustal thickening due to the formation of the Tell Mountains. Large amplitude negative Bouguer, small amplitude, positive free-air gravity and small amplitude, positive isostatic residual gravity anomalies suggest that Saharian and Tunisian Atlas are partially isostatically compensated with regions of possible overcompensation in Algeria. The boundary between the Saharian and Tunisian Atlas is characterized by negative isostatic residual anomalies, suggesting overcompensation and a thick crustal root; however, the cause may be low density material in the upper crust. The amplitude and width of Bouguer gravity anomalies, and two-dimensional gravity models across the Saharian and Tunisian Atlas indicate that there was a greater amount of crustal shortening in Algeria than in Tunisia.

[1]  E. Mercier,et al.  Geometry and kinematics of the South Atlas Front, Algeria and Tunisia , 1995 .

[2]  N. L. Falcon.  International Tectonic Map of Africa , 1969 .

[3]  R. Clayton,et al.  Origin of High Mountains in the Continents: The Southern Sierra Nevada , 1996, Science.

[4]  J. E. Anderson.  The Neogene structural evolution of the western margin of the Pelagian platform, central Tunisia , 1996 .

[5]  P. A. Cross,et al.  Lecture notes in Earth sciences: Vol. 12. S. Turner (Editor), Applied Geodesy VIII, Springer, Berlin, F.R.G., 1987, 393pp, DM78.00, ISBN 3 540 182195 , 1989 .

[6]  R. Nicolich,et al.  A cross section of the lithosphere along the European Geotraverse Southern Segment (from the Alps to Tunisia) , 1990 .

[7]  R. J. Lillie.  Evolution of gravity anomalies across collisional mountain belts: Clues to the amount of continental convergence and underthrusting , 1991 .

[8]  S. Schamel,et al.  Neogene deformation in northern Tunisia: Origin of the eastern Atlas by microplate—continental margin collision , 1980 .

[9]  J. Dubois,et al.  Crustal anomalies under the Tunisian seismograph array using teleseismic P waves , 1985 .

[10]  C. Moreau,et al.  Post‐Hercynian tectonics in Northern and Western Africa , 1987 .

[11]  Walter Wildi.  La chaîne tello-rifaine (Algérie, Maroc, Tunisie): structure, stratigraphie et évolution du Trias au Miocène , 1983 .

[12]  R. Weijermars.  A revision of the Eurasian-African plate boundary in the western Mediterranean , 1987 .

[13]  M. Landisman,et al.  Rapid gravity computations for two‐dimensional bodies with application to the Mendocino submarine fracture zone , 1959 .

[14]  P. Coiffait,et al.  Characterisation of Mesozoic–Cenozoic deformations and palaeostress fields in the Central Constantinois, northeast Algeria , 1998 .

[15]  John E. Nafe,et al.  Variation with Depth in Shallow and Deep Water Marine Sediments of Porosity, Density and the Velocities of Compressional and Shear Waves , 1957 .

[16]  Ian Briggs.  Machine contouring using minimum curvature , 1974 .

[17]  W. K. Gealey.  Plate tectonic evolution of the Mediterranean-Middle East region , 1988 .

[18]  F. G. Stehli,et al.  The Ocean basins and margins , 1974 .

[19]  J. Makris,et al.  Deep seismic soundings in Morocco and a crust and upper mantle model deduced from seismic and gravity data , 1985 .

[20]  F. Lucazeau,et al.  Heat flow in the tectonic provinces crossed by the southern segment of the European Geotraverse , 1995 .

[21]  H. Herbig,et al.  Plate tectonics and intracratonic mountain ranges in Morocco - The mesozoic-cenozoic development of the Central High Atlas and the Middle Atlas , 1992 .

[22]  R. Simpson,et al.  A new isostatic residual gravity map of the conterminous United States with a discussion on the significance of isostatic residual anomalies , 1986 .

[23]  M. Boccaletti,et al.  First order kinematic elements in Tunisia and the Pelagian block , 1990 .

[24]  P. F. Burollet,et al.  Structures and tectonics of Tunisia , 1991 .

[25]  A. Galdeano,et al.  The aeromagnetic map of northern Algeria: Processing and interpretation , 1995 .

[26]  J. Dewey,et al.  Kinematics of the western Mediterranean , 1989, Geological Society, London, Special Publications.

[27]  C. Lepvrier,et al.  Geological constraints on the alpine evolution of the Mediterranean Tethys , 1986 .

[28]  A. Demnati,et al.  Intracontinental rifting and inversion; Missour Basin and Atlas Mountains, Morocco , 1996 .

[29]  Peter Giese,et al.  Crustal structure along a traverse across the Middle and High Atlas mountains derived from seismic refraction studies , 1992 .

[30]  V. Jacobshagen.  Geodynamic evolution of the Atlas system, Morocco: An introduction , 1988 .

[31]  M. Bott,et al.  The interior of the earth , 1971 .

[32]  V. Jacobshagen.  Major fracture zones of Morocco: The South Atlas and the Transalboran fault systems , 1992 .

[33]  S. Mueller,et al.  The Western Mediterranean Region as an upper-mantle transition zone between two lithospheric plates , 1985 .

[34]  P. Burollet,et al.  The Geology of the Pelagian Block: The Margins and Basins off Southern Tunisia and Tripolitania , 1978 .

[35]  Jean-Claude Sibuet,et al.  Geological evolution of the tethys belt from the atlantic to the pamirs since the LIAS , 1986 .

[36]  M. Meghraoui,et al.  Goringe-Alboran-Tell tectonic zone: A transpression system along the Africa-Eurasia plate boundary , 1996 .

[37]  P. Olivier,et al.  Role of strike-slip faults in the Betic-Rifian orogeny , 1984 .

[38]  R. J. Lillie,et al.  Gravity modelling of the lithosphere in the Eastern Alpine-Western Carpathian-Pannonian Basin region , 1994 .

[39]  Richard W. Allmendinger,et al.  Crustal shortening and vertical strain partitioning in the Middle Atlas Mountains of Morocco , 1998 .

[40]  M. J. R. Wortel,et al.  Regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle: The Mediterranean region , 1994 .