Palinspastic Reconstruction Research Articles

The Great Alaskan Terrane Wreck: reconciliation of paleomagnetic and geological data in the northern Cordillera

Paleomagnetic studies place much of the Cordilleran orogen ≥3000 km south, relative to autochthonous North America at 85 Ma. This conflicts with geological studies which have been interpreted to indicate minor displacement. The inability to reconcile these interpretations has precluded understanding the tectonic development of the Cordillera, and has cast doubt on global paleogeographic reconstructions which rely upon paleomagnetic studies. I demonstrate that Alaska and Yukon are divisible into a series of geological belts, including the northerly east–west-trending Arctic Alaska, the central southwest-trending Ruby, the southerly east-trending Dillinger and the southeast-trending Yukon–Tanana belts. Each belt is characterized by four regularly arranged rock sequences; (1) a Paleozoic continental margin strata, (2) a Devonian–Mississippian arc assemblage, (3) an ophiolite, and (4) an Early to mid-Cretaceous arc. These correlations greatly simplify the terrane nomenclature of the northern Cordillera and provide a basis for a new palinspastic reconstruction of the Cordillera. Continuity of the belts can be demonstrated through connecting oroclines, and facing a structural vergence directions vary in a consistent and predictable fashion indicating that the belts previously formed part of a linear ribbon continent. This ribbon continent, referred to here as SAYBIA, originally extended south from eastern Siberia and was ∼8000 km long. Northward translation in response to coupling with the Kula plate was accommodated by buckling (oroclinal orogeny) of SAYBIA, much like a derailing train, with scissored ‘cars’ forming much of Alaska. Oroclinal orogeny makes consistent interpretations of available geological and paleomagnetic data in the Cordillera, provides a means for the rapid construction of continent, and may have been an important process involved in the construction of ancient continental nuclei.

Paleogeography and catchment evolution in a mobile orogenic belt: the Central Alps in Oligo–Miocene times

In this study, we reconstruct the surface evolution of the Oligo–Miocene Central Alps using geochronological, geochemical and petrographical methods on the foreland basin sediments of both flanks of the mountain range. Our model is illustrated in four sketch maps of different time slices between mid-Oligocene to Middle Miocene times. For each time slice, we try to (1) give a palinspastic reconstruction of the Central Alps, based on the post-collisional lateral extrusion model, (2) show which tectonic units had become exposed to the surface due to exhumation processes in the Central Alps, (3) describe the thermochronologic evolution of lithological units formerly exposed but completely eroded today, (4) differentiate the catchment areas of the paleo-river systems which delivered debris to the foreland basins, and (5) describe the position of the main drainage divide relative to the exposed tectonic units.

Jurassic to Holocene tectonics, magmatism, and metallogeny of northwestern Mexico

The present metallic distribution in northwestern Mexico is the culmination of superposed magmatism, tectonism, erosion, and burial over more than 150 m.y. Detailed palinspastic reconstructions of preextensional configurations—the first study of its kind for this region—clarify the interplay among these features on the present distribution and character of mineralized geologic systems. This new synthesis goes beyond previous metallogenic investigations of northwestern Mexico by separating events into specific timing and structural relationships, and by restoring the geology to its preextensional configuration. Metallogenic factors such as enrichment, preservation, and erosion play major roles in the present distributions and for the first time are related to the overall metallogenic framework of northwestern Mexico. The analysis concludes that modern metallogenic patterns are the result of the complex superposition and subsequent redistribution of geologic systems in a way that is related directly to the regional history, rather than simply metallic belts or interpreted angle of a subducting slab. Three main extensional events in the Oligocene‐Holocene have been restored, and the palinspastic distributions have been analyzed. Reconstructions reveal the following: (1) Mineralization events, igneous centers, and sedimentary sequences are continuous across the Gulf of California and other areas with large amounts of extension. (2) Middle Tertiary gold-silver mineralization in Baja California may be the western part of the Sierra Madre Oc*Present address: BHP Billiton., Avenida America Vespucio Sur 100, 8th floor, Las Condes, Santiago, Chile; e-mail: John-Mark.G.Staude@ BHPBilliton.com. cidental metallogenic province, thus expanding the previously recognized extent of this province’s mineralization. (3) Late Cretaceous‐early Tertiary porphyry copper deposits and intrusive centers form a narrower belt than previously noted and are traceable for over 400 km, with parts of the belt buried beneath the younger Sierra Madre Occidental volcanic fields. (4) Interpreted alignments of older geologic features, including lineaments of ore deposits, are displaced in the reconstructions. (5) Sedimentary-rock‐hosted gold deposits and low-angle-detachment gold systems are closely related and occur around core complexes. By using structurally restored time slices, it becomes clear that older deposit types tend to be those formed at greater depths and more proximal to intrusions, whereas younger deposits formed at shallower depths are less eroded and are more commonly volcanic-rock hosted. These characteristics express themselves in the regional distribution of deposit types. Second, mineralization of widely differing ages is spatially superposed, commonly associated with coeval magmatic and tectonic events. The structural and magmatic events together with paleodistribution of ore deposits define a new framework to interpret the metallogenic history of northwestern Mexico.

Triassic palaeogeography of Tunisia

A stratigraphic, palaeogeographic and palinspastic synthesis of the Triassic successions in Tunisia is herein documented from a SSE–NNN oriented profile (Saharan Platform, Gulf of Gabes offshore, Tunisian Atlas, Tellian Units) across the northern boundary of the Gondwana Plate and the future South-Tethyan Margin. It is principally based on a reinvestigation of old data and on recent results, particularly related to new lithostratigraphic subdivisions and palaeontologic datings obtained from assemblages of benthic foraminifera, algae, palynomorphs, ammonites and brachiopods. The various Triassic successions of Tunisia are compared at the scale of the formations and sequences in the most possible precise biochronologic framework. The corresponding chart is used as reference to seven maps of the dominating depositional environments, during the following time intervals: Induan/Olenekian, Anisian, Lower Ladinian, Middle–Upper Carnian, ‘Norian’, ‘lowermost part of Rhaetian’ and ‘uppermost part of Rhaetian’. In a Peri-Tethyan domain controlled both by eustasy and extensional tectonics, the proposed maps show the alternation of regressions (marked by fluvio-deltaic siliciclastics and paralic sebkha-type evaporites) and transgressions (marked by foraminifera-bearing limestones/dolomites of internal/proximal platform, sometimes open to pelagic influences). The transgressions were particularly widespread during Carnian and ‘Rhaetian’ times and probably came from a deeper trough situated towards ENE. During a first rifting phase, the motion of normal crustal faults, strongly inclined towards the north, induced well-marked differential subsidences. In conclusion, a new palinspastic reconstruction along a south–north/SSE–NNW oriented profile is proposed. It shows a succession of shoals (flanked by lateral steps), such as the Tebaga of Medenine shoal, sub-basins (Atlas) and tilted blocks (Hairech–Ichkeul) heralding the structuring of the South-Tethyan Margin during Jurassic times.

Retrograde metamorphism of eclogite in the southern Appalachian Mountains, U.S.A.–A case involving seamount subduction?

AbstractThis work supports a growing body of evidence that the Ashe Metamorphic Suite (AMS) of the eastern Blue Ridge province in North Carolina has an ensimatic origin and is part of a subduction‐related accretionary mélange, marking the Taconic suture between the North American craton and the Inner Piedmont. In a palinspastic reconstruction, the thrust fault at the base of the AMS appears to have intercepted the greatest depths (i.e. highest‐P metamorphic rocks) beneath parts of the AMS now exposed adjacent to the Grandfather Mountain window. The greatest volume of mafic rock is found in these same areas. We suggest that the nascent, subduction‐related, basal thrust fault was deflected downward by an obstacle in the form of an isolated, mafic volcanic edifice on the oceanic crust–a sea mount.Pelitic and mafic rocks dominate the AMS. North of the Grandfather Mountain window, retrograded eclogite occurs in the amphibolite near the base of the AMS. Textures and mineralogy indicate that an original eclogite assemblage was subjected to the following sequence of parageneses:(a) Eclogite(I) facies: omphacite+garnet+quartz,(b) Eclogite(II) facies: omphacite+garnet+epidote+quartz,(c) Symplectic (diopside+plagioclase)+garnet+epidote+quartz,(d) Amphibolite facies: (diopside+plagioclase)+garnet+epidote+hornblende+quartz,(e) Amphibolite facies: plagioclase+garnet+epidote+hornblende+quartz. P–T conditions, estimated from geothermobarometry applied to relevant mineral compositions, are c.720 °C and c.16 kbar for (b) eclogite(II) facies; c.655 °C and c.8.5 kbar for (e) amphibolite facies.

Reconstitution, en Corse, au Jurassique moyen–supérieur, de la marge européenne de l'océan Liguro-Piémontais, grâce à des niveaux repères à Praekurnubia crusei (foraminifère)

By means of the Upper Bathonian–Callovian isochron time-line marked by some calcareous key-beds bearing Praekurnubia crusei Redmond (benthonic Foraminifer), identified both in the ophiolitic ‘Balagne Nappe’ and in the continental ‘Prepiedmontese Zone’, an attempt of palinspastic reconstruction of the European margin of the Ligurian-Piedmont Ocean, in Corsica, during Middle–Upper Jurassic times, is herein proposed. The bayonet transect reaches to the west the autochthonous cover of the Hercynian Corsica. It shows, during the syn-rift phase (Dogger), the subdivision of the margin into tilted blocks inducing strong differential subsidences (particularly between the Caporalino half-horst and the adjacent half-grabens) and, during the post-rift phase (Malm), the sealing of the previous palaeostructures by the Kimmeridgian shelf-type limestones preceeding the general flooding of the Lowermost Cretaceous times. Grâce à l'isochrone du Bathonien supérieur–Callovien constitué par quelques bancs-repères calcaires à Praekurnubia crusei Redmond (foraminifère benthique), identifiés tant dans la nappe ophiolitique de Balagne que dans la zone continentale prépiémontaise, est proposé un essai de reconstitution palinspastique, au Jurassique moyen–supérieur, de la marge occidentale européenne de l'océan Liguro-Piémontais en Corse. Son transect en baı̈onnette débute, à l'ouest, dans l'Autochtone de la Corse ancienne. Il montre, en phase syn-rift (Dogger), le découpage de la marge en blocs basculés, expliquant les fortes subsidences différentielles (notamment entre le demi-horst de Caporalino et les demi-grabens adjacents) et, en phase post-rift (Malm), le scellement de ces paléostructures par les calcaires kimméridgiens de plate-forme avant l'ennoiement généralisé du début du Crétacé.

Miocene high-pressure metamorphism in the Cyclades and Crete, Aegean Sea, Greece: Evidence for large-magnitude displacement on the Cretan detachment

Research Article| May 01, 2001 Miocene high-pressure metamorphism in the Cyclades and Crete, Aegean Sea, Greece: Evidence for large-magnitude displacement on the Cretan detachment Uwe Ring; Uwe Ring 1Institut für Geowissenschaften, Johannes Gutenberg-Universität, 55099 Mainz, Germany Search for other works by this author on: GSW Google Scholar Paul W. Layer; Paul W. Layer 2Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska 99775, USA Search for other works by this author on: GSW Google Scholar Thomas Reischmann Thomas Reischmann 3Institut für Geowissenschaften, Johannes Gutenberg-Universität, 55099 Mainz, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Uwe Ring 1Institut für Geowissenschaften, Johannes Gutenberg-Universität, 55099 Mainz, Germany Paul W. Layer 2Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska 99775, USA Thomas Reischmann 3Institut für Geowissenschaften, Johannes Gutenberg-Universität, 55099 Mainz, Germany Publisher: Geological Society of America Received: 06 Sep 2000 Revision Received: 23 Jan 2001 Accepted: 24 Jan 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2001) 29 (5): 395–398. https://doi.org/10.1130/0091-7613(2001)029<0395:MHPMIT>2.0.CO;2 Article history Received: 06 Sep 2000 Revision Received: 23 Jan 2001 Accepted: 24 Jan 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Uwe Ring, Paul W. Layer, Thomas Reischmann; Miocene high-pressure metamorphism in the Cyclades and Crete, Aegean Sea, Greece: Evidence for large-magnitude displacement on the Cretan detachment. Geology 2001;; 29 (5): 395–398. doi: https://doi.org/10.1130/0091-7613(2001)029<0395:MHPMIT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Cyclades in the backarc region of the present Hellenic subduction zone are known for widespread Late Cretaceous to Eocene high-pressure metamorphism in the Cycladic blueschist unit. We report 40Ar/39Ar and Rb/Sr phengite ages of 24–21 Ma for high- pressure metamorphism (8–10 kbar, 350–400 °C) in the lowest tectonic unit in the Cyclades, the Basal unit, which structurally underlies the Cycladic blueschist unit. The Basal unit is correlated with the Tripolitza unit of the External Hellenides in the forearc region of the Hellenic subduction zone. The Tripolitza unit is unmetamorphosed on Crete, where it is separated from the underlying high-pressure (8–10 kbar, 300–400 °C) Plattenkalk and Phyllite-Quartzite units by the extensional Cretan detachment. The age for high- pressure metamorphism in the latter units is similar to our age for the Basal unit in the Cyclades. Because pressure-temperature conditions in the Plattenkalk and Phyllite- Quartzite units on Crete and the Basal unit in the Cyclades are also similar, they must have been in close proximity in the early Miocene Hellenic subduction zone. A palinspastic reconstruction suggests a subsequent displacement of >100 km on the Cretan detachment. This is one of the greatest displacement magnitudes ever reported from detachment faults. Because of this large offset, the Cretan detachment was an efficient agent for exhuming high-pressure rocks. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A North Louisiana Gas-Prone Hosston Slope-Basin Sand Trend

ABSTRACT Regional palinspastic reconstructions of north Louisiana's down-dip Hosston strata offer a basis for predicting the most likely area that might have contained deep-water sand deposition at the beginning of early Cretaceous time. Since the area's deep well control to the base of the Hosston is very limited, future regional 3-D seismic surveys will remain the preferred way of predicting individual sand trends. However, an in-depth integrated modeling and simulation analysis of the regional stratigraphic, structural, and thermal history provides one method of defining the main potential prospective trend. Furthermore, this type of analysis, in conjunction with conventional petrophysical log analysis, provides a method for (1) determining the location of specific trend segments that appear more sandprone, and (2) defining the confining window of thermal maturation where hydrocarbon potential still may remain. A predicted trend area for deep-water sand development, compatible with the present hydrocarbon maturation window, covers a gross area with dimensions of 20-40 miles (32-64 km) in width and 110-140 miles (177-225 km) in length. The area extends eastward across the State from the south flank of the Sabine uplift. Up-dip, the area is situated mainly within the southern confines of the North Louisiana Salt Dome Basin and extends down-dip to the northern edge of the South Louisiana Salt Dome Basin. On the north, its limit is expected to be governed by individual sand bodies encased and terminated in fore-shelf claystones. The trend's southern limit can be defined by its containment within thermally over-matured strata which create an economic drilling barrier.

Cenozoic tectonism in the central Basin and Range; magnitude, rate, and distribution of upper crustal strain

A wealth of pre-Cenozoic geologic markers across the central Basin and Range province, defined mainly by thrust faults developed within a miogeoclinal wedge, makes it one of the best areas on Earth to reconstruct large-scale continental extension. We use this ~100,000 km^2 region, bounded by the southern Sierra Nevada on the west and the Colorado Plateau on the east, to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions. The results indicate ~250 to 300 km of west-northwest motion of the Sierra away from the Plateau, accommodated by both crustal thinning and north-south shortening. Tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion. Most of the westward motion occurred between 16 and 5 Ma, at rates near 2 cm/yr, slowing to 1 to 1.5 cm/yr in the last 5 Ma. We have quantified the partitioning of strain between vertical crustal thinning (via normal faults) and map-view plane strain (via conjugate strike-slip faults) by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present-day grids. This analysis yields a maximum finite elongation of the Basin and Range at 36°N to 37°N of 3.4, oriented N73°W. Map-view area balance shows that 20 percent of this elongation is compensated by ~north-south shortening, and 80 percent by crustal thinning. This yields an average thinning factor for the upper crust of 2.7 between the Sierra and Plateau, inconsistent with the hypothesis that Neogene deformation in the central Basin and Range is predominantly dextral-shear plane strain. These results, in concert with the observation that the southern Sierra Nevada has similar crustal thickness to the central Basin and Range, support the hypothesis of large-scale eastward flow of Sierran deep crust during extension.

Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions

Abstract Nd crustal residence ages combined with xenocrystic and detrital zircon ages of Neoproterozoic and early Palaeozoic granitoid gneisses and metasediments from the NE Bohemian Massif (West Sudetes and Erzgebirge) suggest an origin from a basement with significant Grenvillian and Svecofennian-Birimian-Amazonian age components. Large contributions from Archaean crust appear to be missing. Nd model ages of 1.4–1.7 Ga as well as Meso- to Palaeoproterozoic zircon xenocrysts ages for the Lugian Domain (Jizerské, Krkonoše, and Orlica-Sniezník Mountains) are interpreted as evidence for a predominantly Palaeoproterozoic basement that underwent rejuvenation during Meso- and Neoproterozoic-Ordovician magmatic events. Our interpretation of the Nd model ages may be relevant for the western part of the Variscan Belt, where a similar range of Nd model ages characterizes large crustal segments. Samples from the Silesian Domain (Desná Dome Staré Město Belt, Velké Vrbno Unit) of the Brunia Microcontinent, in thrust contact with the Lugian Domain, yielded Nd crustal residence ages of 1.1–1.3 Ga, which coincide with the oldest ages of xenocrystic zircons. Brunia is interpreted as a predominantly juvenile Grenvillian-age crustal segment, possibly constituting a former arc batholith outboard from the more ensialic setting of the Lugian Domain. Nd crustal residence ages for our 77 whole-rock samples, including 41 new data, as well as 185 xenocrystic and detrital zircon ages from the northern and northeastern Bohemian Massif agree with those of Neoproterozoic rocks from northern South America and support an origin from a northwest Gondwana palaeogeographical location.

An Improved Method for Reconstructing the Stratigraphy and Bathymetry of Continental Margins: Application to the Cenozoic Tectonic and Sedimentary History of the Congo Margin

A number of techniques, such as backstripping and forward modeling, have been previously used to reconstruct the tectonic, sedimentary, and thermal history at passive margins. Still, these techniques are generally inaccurate in places such as the west African margin where the stratigraphic record is disrupted by continuous faulting of the sediment pile caused by salt tectonics and by erosional unconformities. The ability to reconstruct the stratigraphy, salt thickness, and water depth along profiles of these types of margins is important for determining the factors controlling the geological history of the margin and the evolution of hydrocarbon systems. To reconstruct the stratigraphy, paleowater depths, and salt flowage on a profile across the Congo margin, we combined backstripping and palinspastic reconstruction. This enabled us to restore the faulting and salt flowage and simultaneously to take into account the isostatic response of the lithosphere to sediment loading and unloading. This method allowed us to estimate the paleowater depth, as well as the stratigraphy, and the geometry of the sedimentary section on the profile through time. The determination of the regional isostatic response of the lithosphere is performed with the use of a new model to estimate the flexural rigidity of continental lithosphere. To demonstrate this method, we perform the Cenozoic reconstruction of the Congo margin. The results yield a coherent geological history of the margin from the Eocene to the present. In the Eocene the margin was a carbonate ramp with a deep-seated shelf break (600 m). During the Eocene-Oligocene transition, intermediate water-depth oceanic currents triggered submarine erosion of the Eocene slope and shelf. From the Miocene to the present, we observe a large increase in the input of terrigenous clastic sediments. As a result, the shelf prograded 40 km across the Eocene ramp. As the clastic sediments prograded across the margin into the deep basin, faulting of the sediment pile and salt withdrawal caused the formation of grabens in places where salt swells had previously formed. Finally, the reconstruction suggests that the Congo margin was uplifted by at least 330 m between the late Oligocene and the middle Miocene.

ABSTRACT: Stratigraphic Zone-Depth Predictions for Louisiana's Probable Hydrocarbon Exploration Floor

Abstract Question: To what maximum drilling depth might one reasonably expect to have some chance of finding gas in commercial quantities anywhere in Louisiana? In the final analysis, economic factors define the ultimate depth to which exploration for hydrocarbons can be conducted in any given area. However, the determination of one physical condition--the depth at which natural in situ hydrocarbon destruction would commence--is paramount when evaluating the practicality of even attempting to explore for gas reservoirs in the deeper parts of sedimentary basins. In basins such as those in Louisiana, with their thick sedimentary sections and presently active hydrocarbon generation windows, even gas-bearing reservoir host strata would loose commercial viability because of the onset of hydrocarbon destruction and overwhelming reservoir porosity-permeability degradation brought on by hostile burial conditions. Exploration drilling has not reached the base of the present hydrocarbon generation window in many parts of Louisiana, therefore a statewide basin analysis has been conducted in order to predict the stratigraphic zone and depth at which hydrocarbon destruction begins. The predictions from this analysis are facilitated by palinspastic reconstructions based on well data and the use of projected regional subsurface data beyond where the drill has reached. A subsurface network of sea-level referenced geologic time-depth profiles provides the basic stratigraphic framework from which such predictions are possible. The maximum depths, at which presently active conditions exist that would terminally destroy hydrocarbons, are predicted to vary between less than 15,000 ft (4572 m) in the pre-Louann Salt section (pre-Jurassic) of northwest and central north Louisiana, to more than 35,000 ft (10668 m ) in the lower Miocene of the extreme southern part of the state in Terrebonne, Lafourche, Jefferson, and Plaquemines parishes. A gradual south-north progression between these two stratigraphic zone-depth endpoints defines the probable hydrocarbon exploration floor across Louisiana.

Emplacement of the Resurrection Peninsula ophiolite in the southern Alaska forearc during a ridge‐trench encounter

The 57±1 Ma Resurrection Peninsula ophiolite of southern Alaska's Chugach terrane formed in a near‐trench environment as the Kula‐Farallon ridge was being subducted beneath North America. The magmatic sequence includes pillow lavas, sheeted dikes, gabbros, trondhjemites, and a poorly‐exposed ultramafic section. The lavas show mid‐ocean ridge basalt and arc‐like geochemical signatures, interpreted to reflect compositionally diverse melts derived from near‐fractional melting of a variably depleted mantle source, mixed with variable amounts of assimilated continentally‐derived flysch. A sedimentary sequence overlying the ophiolite, here named the Humpy Cove Formation of the Orca Group, preserves a continuous 3.6 plusmn;1.4 Ma record of turbidite sediments that were deposited on the ophiolite as it was transported to North America and emplaced in the Chugach accretionary prism. A transition from thinly bedded turbidites at the base of the section to thickly bedded turbidites is interpreted as a distal to proximal facies change recording the migration of the ophiolite toward the continent. Chemical trends vertically through the sedimentary sequence show an increasing biogenic component diluting terrigenous matter 950 m above ophiolitic basalt, signaling a change to more favorable biologic conditions or increased preservation of biogenic matter with proximity to the continent. Hydrothermal metals are not resolvable in sediments interbedded with pillow lavas or in sediments above the ophiolite, suggesting that they were diluted by turbidite sedimentation. The top of the section is truncated by the Fox Island shear zone, a 1 km thick, greenschist‐facies, west‐over‐east thrust related to the emplacement of the ophiolite into the accretionary wedge. The Fox Island shear zone is intruded by a 53.4±0.9 Ma granite, showing that the ophiolite formed, was transported to the North American continent, overthrust by a major accretionary prism‐related thrust, and intruded by granite all within 3.6±1.4 Ma. Using these estimates for the timing of formation and emplacement of the ophiolite, with palinspastic reconstructions and plate motion vector triangles, we suggest that the Resurrection Peninsula ophiolite was transported up to 500 km (461±79 km) relative to North America from the place of its formation at the Kula‐Farallon ridge prior to its emplacement into the North American margin. Since the best estimates of the amount of translation of the Chugach terrane come from paleomagnetism of the Resurrection Peninsula ophiolite, current estimates of margin‐parallel strike slip need to be reduced considerably.

Thrust-top lacustrine–lagoonal basin development in accretionary wedges: late Messinian (Lago-Mare) episode in the central Apennines (Italy)

We analysed in detail the geometry, sedimentology and palaeontology (both mollusc and ostracod assemblages) of a small lacustrine–lagoonal basin located at about 1100 m a.s.l. in the Marsica region of the Apennines, at Le Vicenne locality (L'Aquila, Abruzzo, central Italy). The structure of the basin infill deposits outlines an open syncline with an E–W axis. Polygenic conglomerates interbedded with clay levels and sandy marls, which constitute roughly coarsening-upward progradational sequences, are the dominant lithologies. These sequences are interpreted as lacustrine to coastal lagoon deposits with episodic fan delta supplies. This sedimentological interpretation is also supported by mollusc and ostracod assemblages, which suggest that the sedimentary environment was characterized by a mesohaline closed water body, with salinity probably ranging from 10‰ to 13‰. Both mollusc and ostracod assemblages show a clear Paratethyan influence. In the ostracod assemblage ten species out of the fourteen collected forms belong to the Loxoconcha djaffarovi Zone as defined by Carbonnel (1978). Thus, it is possible to refer the siltitic–clayey intercalations of Le Vicenne to the top of the Messinian (post-salinity crisis). The presence of a strong angular unconformity at the base of the basin, together with the structural setting of its deposits, suggesting a light compressive deformation, are common features in all the thrust-top basins recognized in the central Apennines. Taking into account the regional data, the age of the youngest deposit involved in the substratum (siliciclastic turbidites which recorded the Messinian salinity crisis) and the palaeobiological indications given by the mollusc and ostracod assemblages, it is possible to constrain the origin of the Le Vicenne basin to the Messinian Lago-Mare–Early Pliocene tectono-sedimentary event of the Apennines. The recognition in the Marsica range of this thrust-top basin allows us to attempt a palinspastic reconstruction locating the Marsica region in the latest Miocene–Early Pliocene active thrust zone of the Apennine accretionary wedge.

Aspects of the three-dimensional structure of the Alberta Foothills and Front Ranges

Ever more detailed subsurface images of the Alberta Foothills and Front Ranges obtained from improving seismic techniques, coupled with an ever expanding base of information from deep wells and improved structural analysis techniques, have produced an understanding of fold-thrust deformation that is probably applicable to other fold-thrust belts. Comprehensive subsurface data obtained by the petroleum industry are used to outline and analyze the three-dimensional configuration of fold-thrust deformation of Paleozoic carbonate strata. These data indicate that displacement changes smoothly along individual thrusts, but displacement changes along strike may be large, marked by considerable horizontal rotation (20°–30° or more) of hanging-wall stratigraphic cutoffs relative to the footwalls. Stacking of thrusts with varying displacements has produced summed horizontal rotations of hanging-wall cutoffs of as much as 45°–50°. The three-dimensional trajectories of the thrusts through the stratigraphy are smooth for large distances, interrupted by abrupt offsets at lateral and oblique ramps. These are more common than previously realized. The intersections of these ramps with other thrusts produce complex three-dimensional links between thrusts with concomitant abrupt displacement changes. Some simple examples of these linkages are examined with a three-dimensional geometric analysis. The predictions of the analysis are consistent with structural geometries observed in two case studies of subsurface structures. The links at lateral ramps imply simultaneous displacement on parts of the thrusts connected by the ramps. Since the ramps extend downdip 20 km or more, displacement occurred simultaneously on structures occupying relatively interior and exterior positions in the thrust belt. The smooth and long radius-of-curvature folding of many upper detachments indicated by reflection seismic data also is consistent with simultaneous or overlapping periods of motion on groups of thrusts distributed along regional dip. Most major Alberta Foothills thrust sheets terminate southward at lateral ramps at the Paleozoic level. The abrupt southwest-northeast offsets at these features are most clearly apparent on a palinspastic reconstruction. These offsets cause the Paleozoic deformation front to step out east and northeast around the southern and eastern margins of the main arc of the Foothills. In contrast, northward thrust terminations at the Paleozoic level commonly occur at both tip lines and lateral ramps. Subsurface data reveal that there have been some misconceptions regarding large-scale structural relationships. For example, the McConnell and Livingstone sheets are actually portions of the same thrust sheet, as are the Bighorn and Nikanassin sheets. When corrected for these misconceptions, the data from the Alberta Foothills suggest that maximum displacement has a nonlinear relationship to thrust length, although a linear relationship cannot be ruled out.

West‐northwest directed obduction of the Batain Group on the eastern Oman continental margin at the Cretaceous‐Tertiary boundary

The Batain coast area in eastern Oman is dominated by allochthonous Permian to Late Maastrichtian sedimentary and volcanic rocks (Batain Group), unconformably overlain by neoautochthonous Tertiary sediments. The allochthonous rocks of the Batain coast were previously attributed to the Hawasina complex, the Permian to Coniacian/Santonian sedimentary infill of the neo‐Tethyan Hawasina basin off northern Oman. Previous structural interpretations suggested that the Batain Group, along with the Hawasina complex and the Semail ophiolite, was obducted in the Coniacian to Campanian from NE to SW onto the northern Oman continental margin. Results of our work in the Batain area differ from previous interpretations, with most significant differences concerning timing and direction of obduction. Our results show that WNW directed tectonic movements formed a fold‐and‐thrust belt and led to the obduction of allochthonous rocks onto the east Oman continental margin during latest Maastrichtian/earliest Paleocene times. This is coeval with emplacement of ophiolitic fragments along the eastern coast of Oman (eastern ophiolite belt) but is about 15–20 Myr later than emplacement of Hawasina complex and Semail ophiolite in northern Oman. Postemplacement structural evolution during the Tertiary involved intraplate extension, possibly reflecting the Red Sea/Gulf of Aden opening, and late Tertiary shortening related to convergence between Arabia and Eurasia. Late Tertiary contractional deformation resulted in refolding of the Batain nappes and in folding of the overlying Tertiary sediments. A palinspastic reconstruction of the Batain area indicates that the Permian to Upper Cretaceous sediments were formerly deposited in the Batain basin, a part of the proto‐Indian Ocean, along the present‐day eastern Oman margin. This leads us to propose that Permian breakup of Gondwanaland created both continental margins of Oman and led to the opening of two major basins: the neo‐Tethyan Hawasina basin in the north and the proto‐Indian Ocean Batain basin in the east, the latter separating Arabia from greater India.

Interaction between faulting, drainage and sedimentation in extensional hanging-wall syncline basins: example of the Oligocene Matelles basin (Gulf of Lion rifted margin, SE France)

Abstract A tectono-sedimentary model for hanging-wall syncline basins emphasizing the role of erosion in the basin architecture is proposed, based on the well-exposed Matelles basin. Detailed geological mapping is the base for the analysis of the extensional double ramp-flat Matelles fault system, hanging-wall deformation and relationships between faulting/drainage/sedimentation. Displacement of the hanging-wall above the fault resulted in the formation of (a) upper and lower rollovers associated with the upper and lower rampflat couples, (b) a hanging-wall ramp syncline above the lower ramp and (c) a half graben associated with the emergent ramp and upper flat couple. Only the hanging-wall ramp syncline and the lower rollover are preserved. Ramp syncline basin-fill architecture is characterized by progressive unconformity and faultward migration of the growth synclines ‘climbing up’ the monoclinal prerift strata corresponding to the ramp-side limb of the ramp syncline. Clast composition analysis of the synrift deposits indicates that sediments were mainly supplied from the hanging-wall flat, and allows to propose palinspastic reconstructions of the hanging wall in order to establish the palaeo-drainage system and its evolution. ‘Upper hanging-wall flat catchments’ and ‘lower rollover catchments’ are proposed as main features of the drainage system in extensional hanging-wall syncline basins.

Palinspastic reconstruction and topographic evolution of the Eastern Alps during late Tertiary tectonic extrusion

This paper presents a new palinspastic restoration of the Eastern Alps for Neogene time and an attempt to reconstruct the Neogene palaeogeology, palaeotopography and palaeohydrography in connection with the structural evolution. The Eastern Alps underwent radical horizontal displacement during the Neogene due to large strike-slip systems and formation of structural windows. Our palinspastic reconstruction considers: (a) the rearrangement of tectonic units dismembered during tectonic extrusion, (b) the tectonic denudation driven by displacement of the crystalline blocks, (c) geochronological arguments, and (d) the sedimentary record of the syn-extrusion basins. The rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre-Miocene unstretched pattern of the Eastern Alps, reduced to 65% of its present-day E–W elongation. Using this structural frame and considering the sedimentary record, a set of palaeogeologic and palaeotopographic sketch maps with the palaeo-river systems is presented for three time slices (pre-, syn- and post-extension situation). In Late Oligocene and Early Miocene times, the western Eastern Alps were already mountainous, whereas the eastern part of the orogen formed lowlands or hilly areas. Enhanced block movement in the course of the extrusion process around the Early/Middle Miocene boundary led to the formation of intramontane sedimentary basins and a fault-induced reorientation of the drainage pattern, which forms the basis of the modern river system in the area east of the Tauern window. This region, where pre-Miocene land surfaces are preserved, probably became a mountainous area not before Late Miocene time and never reached the elevations of the areas further west.

Crustal structure of the Himalayan orogen at ∼90° east longitude from Project INDEPTH deep reflection profiles

International Deep Profiling of Tibet and the Himalaya (INDEPTH) deep seismic reflection profiles show that the Indian lithosphere is underthrusting the central Himalaya along a gently north dipping decollement that is traceable northward beneath the Tethyan belt to ∼28.6°N and to a depth of about 45 km. The decollement carries in its hanging wall a near‐crustal‐thickness slice of internally deformed Indian continental basement and cover represented in outcrop by the Greater Himalayan belt and structurally overlying Tethyan belt. Geometric relationships suggest that the decollement probably ramps downward beneath the northern Tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from Indian mantle lithosphere that presently underlies southern Tibet to the north. The North Himalayan anticlinorium (Kangmar dome) appears to be a large duplex ramp anticline in the hanging wall of the decollement. The South Tibetan Detachment appears to have been imaged in two areas. In the Wagye La area it appears to follow the Tethyan belt/Greater Himalayan belt contact northward in the subsurface and to have been folded over the Kangmar dome. In the Zherger La area it appears to have been active relatively recently as a ∼30° north dipping normal fault that cuts deeply into the Greater Himalayan belt allochthon. Palinspastic reconstruction indicates a minimum of about 326 km of shortening of the Indian basement across the Himalaya since the initiation of the Main Central Thrust. Hence Indian continental lithosphere, largely stripped of its overlying crust, can extend northward beneath the Tibetan plateau to at least 32°N, where earthquake seismological observations show that the properties of the upper mantle change markedly [e.g., McNamara et al., 1995]. Taken together, the seismic reflection and earthquake seismological observations lend support for the view that the Indian mantle lid mechanically underplates roughly the southern half of the Tibetan plateau. The INDEPTH reflection data do not show that Indian crust attached to this lithosphere extends north of southernmost Tibet (Kangmar dome), nor do they negate this possibility. Similarly, the reflection data do not yield direct evidence for or against lower‐crustal subduction beneath the Himalaya.

Crustal structure and orogenic material budget in the west central Pyrenees

Surface and subsurface data are combined to construct a crustal‐scale cross section of the western central Pyrenees (France and Spain) at the boundary between the European and Iberian plates. The position of Moho reflections in the ECORS‐Arzacq reflection profile suggests a tectonic wedge of European crust and upper mantle had indented the Iberian plate at lower crustal levels. The European wedge is overlain by an upper, Iberian wedge thus constituting a double (stacked) wedge geometry. The upper wedge was delaminated and deformed giving rise to the Pyrenean orogenic prism, manifested as a bivergent fan in upper crustal levels. The underthrust lower Iberian plate has been imaged to depths of 55–60 km, but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km. Total orogenic contraction calculated from surface structures is about 75–80 km, which was accomplished between the latest Cretaceous and the early Miocene at an averaged rate of 1.2 mm/yr. Consistent with these moderate values, exhumation of the orogen is much less than in the more shortened eastern parts of the range. Paleozoic basement and preorogenic Mesozoic rocks are little eroded, and much of the exhumation involved cannibalization of early foreland basins, which once covered the entire, poorly emergent orogen at this transect. This resulted in a continuous process of sediment recycling and, coupled with a considerable lateral arrival of material, a bulk negative erosion‐sedimentation budget.