m sosson

Abstract The ophiolites of NE Anatolia and of the Lesser Caucasus (NALC) evidence an obduction over ∼200 km of oceanic lithosphere of Middle Jurassic age (c. 175–165 Ma) along an entire tectonic boundary (>1000 km) at around 90 Ma. The obduction process is characterized by four first order geological constraints: (1) Ophiolites represent remnants of a single ophiolite nappe currently of only a few kilometres thick and 200 km long. The oceanic crust was old (∼80 Ma) at the time of its obduction. (2) The presence of OIB-type magmatism emplaced up to 10 Ma prior to obduction preserved on top of the ophiolites is indicative of mantle upwelling processes (hotspot). (3) The leading edge of the Taurides-Anatolides, represented by the South Armenian Block, did not experience pressures exceeding 0.8 GPa nor temperatures greater than ∼300 °C during underthrusting below the obducting oceanic lithosphere. (4) An oceanic domain of a maximum 1000 km (from north to south) remained between Taurides-Anatolides and Pontides-Southern Eurasian Margin after the obduction. We employ two-dimensional thermo-mechanical numerical modelling in order to investigate obduction dynamics of a re-heated oceanic lithosphere. Our results suggest that thermal rejuvenation (i.e. reheating) of the oceanic domain, tectonic compression, and the structure of the passive margin are essential ingredients for enabling obduction. Afterwards, extension induced by far-field plate kinematics (subduction below Southern Eurasian Margin), facilitates the thinning of the ophiolite, the transport of the ophiolite on the continental domain, and the exhumation of continental basement through the ophiolite. The combined action of thermal rejuvenation and compression are ascribed to a major change in tectonic motions occurring at 110–90 Ma, which led to simultaneous obductions in the Oman (Arabia) and NALC regions.

The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two‐dimensional thermo‐mechanical numerical modelling based on the geology of the Anatolia–Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far‐field plate kinematics appear to be essential for the obduction of ~80‐Ma‐old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10–20 Ma before obduction, at the onset of Africa–Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite‐free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far‐field plate kinematics resu...

Analysis of minors faults in the Colorado Plateau and determination of the displacement sense of structures in southeastern Arizona lead to distinguishing two different directions of compression in the western United States ranging in age from Middle Cretaceous to Upper Eocene. New structural data indicate a first Upper Cretaceous event with a N065˚E direction of shortening, then a second one trending N115˚E, Paleogene in age. The Colorado Plateau was reactivated by brittle deformation even though its southern boundary was affected by tangential, then transcurrent deformations, remobilizing prior crustal structures

In the tectonic evolution of the Black Sea (BS) there are several unsolved questions: 1) the timing of the BS opening and 2) the timing of the Cenozoic shortening of the northern margin of the Eastern BS (EBS) basin. Mainly, the age-frame of the main compressional deformations is assumed as Oligo-Miocene, related to the Greater Caucasus (GC) basin inversion. The Crimean Mountains (CM) is one of the key areas to fix the tectonic evolution of the BS therefore, we focus on an integrated onshore/offshore transect from the Eastern CM to the Sorokin trough (north of EBS). We used newly collected stratigraphic and structural data from the Eastern CM, and a new interpretation of multichannel seismic lines. We define 1) the seismic stratigraphy and constrain the relative chronology of deformations, 2) the age of seismic units by correlation of the seismic data with the Subbotina-403 well log, and 3) we construct an on-and-off shore transect of the Eastern CM - North of the EBS region. Our re...

Micropalaeontological age evidence for the sedimentary cover of ophiolites is important to understand the palaeogeographic and geodynamic evolution of Tethyan realms. The Stepanavan ophiolitic suite of Northern Armenia consists of peridotites, gabbros, plagiogranite and lavas with a radiolarite sedimentary cover. It is regarded as the northern extension of the Sevan Akera ophiolitic zone and may be considered as the eastern extension of the Izmir-Ankara suture zone. It represents the relics of a slow-spreading mid oceanic ridge that was active between Eurasia and the South-Armenian Block of Gondwanian origin. Radiolaria extracted from radiolarites of the Stepanavan ophiolite provide for the first time a Late Jurassic (late Kimmeridgian to early Tithonian) age constraint for this part of Tethyan oceanic crust preserved in Lesser Caucasus.

... On the geological features of Transcaucasian ophiolitic zones. Izvestia Acad. Sci. Armen-ian SSR, Nauki o Zemle, 4-5: 13-26 (in Russian). Avagyan A., Sosson M., Philip H., Karakhanian A., Rolland YA, Melkonyan R., Rebai S. and Davtyan V., 2005. ...

The Tethyan geology of the Lesser Caucasus has a multiphase and complex history. The main lithotectonic domains that can be individualized during the presence of a Tethyan oceanic branch in the region are (i) the South Armenian Block (SAB), a Gondwanian remain that is mainly known by its characteristic Middle to Upper Palaeozoic sedimentary sequences; (ii) ophiolitic units, including their sedimentary cover, which record a complex history of geodynamic, magmatic and sedimentary events, and (iii) the Eurasian active margin, known essentially from its Middle Jurassic – Upper Cretaceous volcano-sedimentary sequences. Following the obduction of ophiolites onto the SAB during the Coniacian-Santonian interval and the subsequent Palaeocene-Lower Eocene collision of the South Armenian Block against Eurasia, widespread volcanic activity took place during the middle to late Eocene. Impressive quaternary volcanoes and recent tectonic activity along active faults attest on the geodynamic activity in relation to the collision with the Arabian plate.

In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the autochthonous South Armenian Block (SAB), a Gondwana-derived terrane; (2) the ophiolitic Sevan–Akera suture zone; and (3) the Eurasian plate. Based on our field work, new stratigraphical, petrological, geochemical and geochronological data combined with previous data we present new insights on the subduction, obduction and collision processes recorded in the Lesser Caucasus. Two subductions are clearly identified, one related to the Neotethys subduction beneath the Eurasian margin and one intra-oceanic (SSZ) responsible for the opening of a back-arc basin which corresponds to the ophiolites of the Lesser Caucasus. The obduction occurred during the Late Coniacian to Santonian and is responsible for the widespread ophiolitic nappe outcrop in front of the suture zone. Following the subduction of oceanic lithosphere remnants under Eurasia, the collision of the SAB with Eurasia started during the Paleocene...

... Version française abrégée. Introduction. Dans le Petit Caucase, les ophiolites de Stepanavan (Fig. 1) appartiennent à la zone de suture entre la marge eurasienne et lebloc sud-arménien, d'origine gondwanienne [5], [9], [16], [17], [18] and [20]. ...

This paper investigates the structure of the northern margin of the Ararat depression in a study area in SE Armenia. The depression is a Cenozoic intermontane basin located to the south of the Lesser Caucasus. The purpose is to improve understanding of the basin's structure and origin within a regional tectonic framework which has been dominated since the Late Cretaceous by the closure of Neotethys and the Arabia‐Eurasia collision. We suggest that the depression is not a graben controlled by normal faults; rather, based on detailed observations, structures in the study area are interpreted as oblique‐slip reverse and thrust faults activated in post Oligocene‐Miocene times. These compressional faults resulted in the formation of asymmetric fold structures including the Lanjanist and Urts anticlines which are well expressed in the surface relief to the north of the Ararat depression. In general the structural pattern is complicated by secondary normal faults which resulted in superimposed gravitational slope processes and erosion. Major structures in the study area originated in a compressional setting associated with the closure of Neotethys since the latest Cretaceous. Post‐collisional strike‐slip faulting was linked to convergence of the Arabian and Eurasian plate margins. Pliocene and Quaternary structures, some still active, show evidence of structural inheritance. The Armenian portion of the Ararat depression contains obduction‐related nappes, anticlines and thrust faults which have potential as structural traps for hydrocarbons. These should be investigated in detail using advanced geophysical methods including 2D and 3D seismic analyses.

Abstract The Eastern Pontides–Lesser Caucasus fold–thrust belt displays a peculiar northwards arc-shaped geometry that was defined as an orocline in earlier studies. The Lesser Caucasus was affected by two main tectonic events that could have caused orocline formation: (1) Paleocene–Eocene collision of the South Armenian Block with Eurasia; and (2) Oligocene–Miocene Arabia–Eurasia collision. We tested the hypothesis that the Lesser Caucasus is an orocline and aimed to time the formation of this orocline. To determine the vertical axis rotations, 37 sites were sampled for palaeomagnetism in rocks of Upper Cretaceous–Miocene age in Georgia and Armenia. In addition, we compiled a review of c. 100 available datasets. A strike test was applied to the remaining datasets, which were divided into four chronological sub-sets, leading us to conclude that the Eastern Pontides–Lesser Caucasus fold–thrust belt forms a progressive orocline. We concluded that: (1) some pre-existing curvature must have been present before the Late Cretaceous; (2) the orocline acquired part of its curvature after the Paleocene and before the Middle Eocene as a result of South Armenian Block–Eurasia collision; and (3) about 50% of the curvature formed after the Eocene and probably before the Late Miocene, probably as a result of Arabia–Eurasia collision. Supplementary material: Results from rock magnetic experiments, reversal and fold tests and equal area projections of the characteristic remanent magnetizations for each site, as well as biostratigraphic ages and a table with palaeomagnetic results from the literature review (with assigned numbers referred to in the text) are available at http://www.geolsoc.org.uk/SUP18852.

To better constrain the Euler pole describing the recent motion of the Pacific plate relative to the Rivera plate, total- field magnetic data, multi-beam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May of 2002 in the area surrounding the Moctezuma Spreading Segment of the East

The Pacific margin of Baja California is one of the few examples of an active margin that evolved from a convergent margin (before 12 Ma) to a transform margin (12-5 Ma). The amount of motion along the transform zone, which mainly occurred along the Tosco-Abreojos fault, is still debated, as well as the time of the transfer of Baja California to the Pacific plate. During the FAMEX cruise (L'Atalante, April 2002), swath bathymetry data were acquired along the Baja California margin from 23N to 27N. Several seismic profiles were also collected across the margin, using 300 inch3 GI guns tuned in harmonic mode and a streamer with six 50m-long channels. The 10s pop-rate at a 10 knots speed allowed a 3-fold coverage with a record-length of 4s. One profile clearly evidence the flat top of the subducted slab that can be followed 20 km landward. The lower part of a large pre-Upper Miocene mass-wasting is missing from the paleo-trench fill, and there is no evidence for an accretionary pr...

The first proposal of an intra-transform spreading center along the Rivera transform at 108°15'W was based on microseismicity data. During projects BART and FAMEX, conducted during 2002 aboard the N/O L'Atalante, 100% of the Rivera transform was covered by multibeam bathymetric and seafloor reflectivity data. These data show that the Rivera transform is marked by a broad, deep basin between 107°30'W and 109°12'W and can be subdivided into two smaller basins based on morphologic characteristics. The previous proposed intra-transform spreading center is located within the eastern basin which lies between 107°30'W and 108°35'W. This basin is approximately 110 km long, 18 to 20 km wide and exhibits a rhomboidal shape elongated in a NW-SE direction. Broad sediment filled depressions lie at the basin's eastern and western sides. The surface sediments in these depressions are undisrupted. Narrow bathymetric troughs lying at the base of prominent escarpmen...

During the FAMEX cruise of the R/V L'Atalante (April 2002), swath bathymetry and seismic profiles were recorded along the Baja California margin from 23° to 27°N. The upper-slope of the margin exhibits active faulting of recent sediments along the Tosco-Abreojos fault system (TAFS). Flower structures evidence strike-slip motion along the TAFS. Right lateral strike slip faulting, associated in places with

Dating radiolarites in the ophiolitic sequences of Alpine mountain belts is important for the geodynamic reconstruction of Neo-Tethys in the Lesser Caucasus. However, radiolarian data from Karabagh are very rare. A moderately well-preserved radiolarian ...

... Eduardo López1, Jean-Yves Collot1, & Marc Sosson1 ... accreted against the western border of the South American plate, during the Late Cenozoic to Early Paleogene (Kerr et al, 2002), (Marcaillou, 2003; Escovar et al, 1992; Evans and Whittaker, 1982). Despite the extensive ...

In number of orogens (e.g. Alps, Norwegian Caledonides, Dabie Shan) exhumation of UHP/LT rocks was followed by HT metamorphism and magmatic events both suggesting heating of the crust. We present a geodynamical model based on the thermo-mechanical analogue experiments that allow us to account for this relation between the exhumation and temperature increase. According to the model the continental crust

The relative motion between the Rivera and Pacific plates is currently the subject of debate. To resolve this debate, multibeam bathymetry and seafloor reflectivity data was collected along the entire extent of the Rivera Transform during project BART (BAthymetry of the Rivera Transform); funded by CONACyT and CNRS. The survey was conducted in April 2002 aboard the N/O L'ATALANTE employing a dual Simrad EM-12 system. These data were processed by IFREMER during the survey, producing a grid of bathymetric values (gid spacing 200m x 200m) and a mosaic of the seafloor reflectivity data. The transform displays four distinct morphotectonic zones. East of 107.1W the transform is, for the most part, marked by a narrow, continuous trough. Between 107.1W and 109.27W the transform zone is marked by a broad, deep basin. Within this basin east of 108.58W, the morphology is indicative of seafloor spreading/crustal extension. Surface magnetic data do not clearly delineate the location of the ...