The structuration of the External Rif (Rif belt: Northern Morocco). An insights from paleo-thermal and structural analyses

2021 ◽  
Author(s):  
Achraf Atouabat ◽  
Sveva Corrado ◽  
Dominique Frizon de Lamotte ◽  
Geoffroy Mohn ◽  
Faouziya Haissen ◽  
...  
Keyword(s):  
Upper Cretaceous ◽  
Vitrinite Reflectance ◽  
Structural Evolution ◽  
Structural Data ◽  
Passive Margin ◽  
Thermal Maturity ◽  
North African ◽  
Tectonic Structures ◽  
The North ◽  
Rif Belt

<p>Belonging to the Maghrebides system, the Rif belt (Northern Morocco) suffered an important Cenozoic Alpine compressional deformation as a consequence of the closure of the Maghrebian Tethys and the westward translation and docking of the Alboran Domain onto the African margin during the Late Burdigalian. The Mesozoic North African Margin is still partially preserved in the Eastern Rif (e.g., Senhadja Jurassic-Cretaceous unit) and inverted in its Central portion (North of the Nekor Fault Zone) due to the high shortening in this area. It is in agreement with sub-surface data suggesting that the thickest crust along the chain is located in the central Rif (Izzaren Area, External Rif), and can be interpreted as a deep-rooted crustal imbrication.</p><p>This contribution aims to characterize the role of the structural inheritance of the rifted North African margin in the development and the propagation of the Rif belt by the combination of paleothermal and structural data collected along a NE-SW regional transect (between Chefchaouen and Ouezzane provinces), focusing mainly on the external zones (namely, Intrarif, Mesorif and Prerif) sampling the deformed domains originally developed along the North African paleo-passive margin. A new paleo-thermal dataset of vitrinite reflectance (Ro%), micro-Raman spectroscopy on organic matter and XRD on clayey fraction of sediments displays levels of thermal maturity between early and deep diagenetic conditions (Ro% from 0.49% to 1.15%). The highest thermal maturity values along the section are concentrated in the Lower to middle Cretaceous Loukkos Intrarifain sub-unit that is structurally squeezed between Tangier Intrarif Upper Cretaceous sub-unit and the Mesorif “Izzaren Duplex”. It attests for an important amount of shortening leading to the development of an imbricate fan of thrusts.</p><p>The geometry of the “Izzaren Duplex”, limited at surface by two first-order thrust faults, is controlled by pre-existing tectonic structures, probably inherited by the former architecture of the North African paleomargin. Moreover, the Chattian-Middle Miocene siliciclastic succession filling the Zoumi basin is in a stratigraphic continuity with the Izzaren Upper Jurassic-Upper Cretaceous substratum, sheding new light on its geodynamic meaning. This observation is supported by the homogeneity of deformation and the absence of thermal jump between the Mesozoic and Cenozoic successions, attesting for an active compressive deformation in the area between the Late Serravalian and Late Tortonian.</p><p>In conclusion, the combination of paleo-thermal and structural analysis allowed to reconstruct robust tectono-thermal model in order to propose an accurate reconstruction of the structural evolution and a new geological restoration of the Rif belt with respect to the geometry of the rifted paleo-margin.</p>

Structural styles of the External Rif and Flysch Domain (Rif belt, northern Morocco) through thermal maturity and structural data

2020 ◽  
Author(s):  
Andrea Schito ◽  
Achraf Atouabat ◽  
Sveva Corrado ◽  
Faouziya Haissen ◽  
Geoffroy Mohn ◽  
...  
Keyword(s):  
Vitrinite Reflectance ◽  
Methodological Approach ◽  
Structural Evolution ◽  
Structural Data ◽  
Thermal Modelling ◽  
Thermal Maturity ◽  
North African ◽  
Data Set ◽  
The North ◽  
Rif Belt

<p>Located in northern Morocco, the Rif belt represents the western edge of the Maghrebides system. This domain underwent a significant Cenozoic alpine compressional deformation, due to the collision between the North African margin and the south-western margin of the exotic Alboran Domain. This collision led to the development of a nappe stack during the Miocene.</p><p>This contribution aims to characterize the main tectonic mechanisms driving the evolution of the Rifain wedge, its burial-exhumation paths and to understand the former architecture of the North African paleo-margin. The work focuses mainly on the Flysch domain, originated from the Maghrebian branch of the Tethys and on the External domain (namely Intrarif, Mesorif and Prerif) that belong to the former north African margin. To define the thrust sheet stacking pattern and their burial-exhumation paths, a regional transect from Chefchaouen and Ouezzane towns (Central Rif), crossing the orogenic wedge from the Flysch to the Prerif Units is constructed.</p><p>The methodological approach consists in combining petrography and Raman micro-spectroscopy on organic matter and 1D thermal modelling, together with field structural data.</p><p>A new paleo-thermal data set of vitrinite reflectance (Ro%) and Raman micro-spectroscopy displays levels of thermal maturity between early and deep diagenetic conditions (Ro% ranges from 0.50% to 1.15%).</p><p>Preliminary results show an abrupt change in the thermal maturity and the rate of shortening in the Loukkos sub-unit (Intrarif Domain) that is structurally squeezed between Tangier sub-unit (Intrarif Domain) and the “Izzaren Duplex” (Mesorif).</p><p>Furthermore, previous studies show that the thickest crust below the Rif fold-and-thrust belt is located below the Izzaren area, suggesting a deep crustal imbrication at the transition between the Intrarif and the Mesorif. These observations joined with the thermal maturity data and 1D thermal modelling allow revisiting the structural evolution of the central part of the Rif belt, by defining the rate of shortening and proposing a new geological restoration with respect to the Mesozoic North African margin structural original setting.</p>

New ophiolite slivers in the External Rif belt, and tentative restoration of a dual Tethyan suture in the western Maghrebides

2014 ◽  
Vol 185 (5) ◽  
pp. 313-328 ◽  
Author(s):  
André Michard ◽  
Abdelkader Mokhtari ◽  
Ahmed Chalouan ◽  
Omar Saddiqi ◽  
Philippe Rossi ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Suture Zone ◽  
Passive Margin ◽  
Transform Fault ◽  
North African ◽  
Structural Position ◽  
Passive Margins ◽  
The Core ◽  
The North ◽  
Rif Belt

AbstractOphiolite slivers have been described recently in the core of the External zones of the Central Rif belt. The present work aims at illustrating new ophiolite slivers further east and discussing the structural position and tectonic emplacement of all these oceanic floor remnants. Their basement consists of gabbros previously dated at 166±3 Ma and their cover includes mafic breccias, micrites and radiolarites. These oceanic slivers are located within the Mesorif nappe stack at the bottom of the Senhadja nappe that roots beneath the Intrarif Ketama unit and was thrust over the more external Mesorif and Prerif units during the Cenozoic inversion of the North African paleomargin. These oceanic crust (OC) slivers belong to the same Mesorif suture zone as the Beni Malek serpentinites and Ait Amrâne metabasites from eastern Rif that also include marbles with ophiolitic clasts and derive from an ocean-continent transition (OCT) domain. After examination of the varied hypotheses that have been suggested to account for the emplacement of these units in the External Rif, we propose that obduction sampled an oceanic corridor opened between the Mesorif and Intrarif domains at the emplacement of the Rif Triassic evaporite basin. The Intrarif block should have been then separated from the African passive margin and connected with the Flysch domain south of the passive margin of the Alboran domain. The pre-collision structure of the Rif transect would involve two hyper-extended passive margins separated by a narrow oceanic transform fault corridor. Therefore the Tethys suture in the western Maghrebides would be split by the Intrarif block and would involve the Flysch zone in the north and the ophiolite bearing Mesorif suture zone in the south.

scholarly journals Validating Structural Styles in the Flysch Basin Northern Rif (Morocco) by Means of Thermal Modeling

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 325
Author(s):  
Achraf Atouabat ◽  
Sveva Corrado ◽  
Andrea Schito ◽  
Faouziya Haissen ◽  
Oriol Gimeno-Vives ◽  
...  
Keyword(s):  
Vitrinite Reflectance ◽  
Thermal Modeling ◽  
Hydrocarbon Generation ◽  
Thermal Maturity ◽  
Data Set ◽  
The North ◽  
Frontal Part ◽  
Rif Belt ◽  
Thermal Indicators ◽  
North Western

Vitrinite reflectance and a micro-Raman spectroscopy parameters data set have been acquired on dispersed organic matter of the Maghrebian flysch basin and the Tangiers unit across a NE-SW section in the north-western Rif belt (North Morocco). Thermal maturity shows increasing values from the hinterland to the external unit (from NE to SW). Paleo-thermal indicators show that the internal flysch basin (i.e., the Mauretanian unit) is less mature than the external one, (i.e., the Massylian unit), with Ro% and Ro eq. Raman values ranging from 0.64% to 1.02% (from early mature to late mature stages of hydrocarbon generation). 1D thermal modeling estimates the overburden now totally eroded ranging from 3.1 km to 6.0 km, and has been used as constraint to reconstruct the complete thrust wedge geometry in Miocene times. The reconstructed geometry accounts for high shortening (about 63%) due to the development of an antiformal stack in the frontal part of the wedge made up by the flysch succession. This stacking is interpreted as a consequence of the western translation of the Alboran Domain in the core of the Betic-Rif orogenic system.

Thermal imprints along conjugated continental margins in response to the opening of the northern North Atlantic - case studies from eastern North Greenland and western Svalbard

2021 ◽  
Author(s):  
Katrin Meier ◽  
Paul O'Sullivan ◽  
Malte Jochmann ◽  
Patrick Monien ◽  
Karsten Piepjohn ◽  
...  
Keyword(s):  
Heat Flow ◽  
North Atlantic ◽  
Thermal History ◽  
Vitrinite Reflectance ◽  
Continental Margins ◽  
Thermal Maturity ◽  
Quartz Veins ◽  
The North ◽  
Reflectance Data ◽  
North Greenland

<p>Prior to break up of Greenland and Svalbard, the Wandel sea basin with Carboniferous to Cenozoic deposits formed in eastern North Greenland. These deposits were affected by the last major period of Arctic tectonism, the Eocene Eurekan deformation. Vitrinite reflectance data from late Cretaceous rocks long the east coast of North Greenland indicate unusual high thermal maturity in association with a swarm of quartz veins, which exceeds the thermal maturity associated with the Eurekan deformation further inland. This pattern is also observed in Cenozoic sediments further to the north as well as along the conjugated North Atlantic margin, in western Svalbard. However, cause and origin of the elevated heat flow indicated by thermal maturity values are not known so far and the timing is not well constrained. We test the hypothesis whether this pattern was established coevally along both margins of the North Atlantic and marks a post-Eurekan thermal event. Vitrinite reflectance data indicate temperatures high enough to reset low temperature chronometers, therefore we used apatite fission track (AFT) and (U-Th-Sm)/He (AHe) thermochronology to determine the age of the high thermal maturation and associated quartz veins formation.</p><p>Our data reveals a more complex thermal history than hypothesized:<br>For the eastern North Greenland margin thermal history modelling of the combined AFT and AHe ages indicates a pre-Eurekan phase of elevated heat flow between 72 Ma and 66 Ma causing the high vitrinite reflectance and the formation of the quartz veins in the late Cretaceous rocks. Additional petrographic and electron microprobe analysis reveals the growth of feldspar, hematite, amphibole, and tourmaline within the quartz veins. According to most paleogeographic reconstructions, northern Greenland was located to the south of Svalbard close to a volcanic province near Bear Island. Heating may thus be associated with incipient igneous activity of that area, related to initial North Atlantic opening. A second phase of elevated heat flow between 58 Ma and 52 Ma is indicated by thermal history modelling of the AFT and AHe ages from the Cenozoic rocks further north. This frames the timing of the initiation of the dextral displacement between Greenland and Svalbard and might be associated with heat transfer along the transform fault from the active spreading centres in the North Atlantic and the Arctic Ocean.<br>Contrasting to the results of North Greenland, thermal history modelling of AFT and AHe ages from the Cenozoic rocks of western Svalbard reveals heating throughout the Eocene and onset of cooling only during the early Oligocene for the Svalbard margin. Thus, even though we cannot exclude a similar thermal history during the Paleocene to early Eocene, the eastern North Greenland and western Svalbard margins are characterized by a differential thermal evolution during the ~middle Eocene to Oligocene.</p><p>In conclusion, our data show that the thermal history of the conjugated continental margins along the northern North Atlantic is characterized by episodic heat flow variations predominantly controlled by oceanic plate tectonic processes.</p>

The evolution of the Lansarine–Baouala salt canopy in the North African Cretaceous passive margin in Tunisia

2013 ◽  
Vol 150 (5) ◽  
pp. 835-861 ◽  
Author(s):  
AMARA MASROUHI ◽  
OLIVIER BELLIER ◽  
HEMIN KOYI ◽  
JEAN-MARIE VILA ◽  
MOHAMED GHANMI
Keyword(s):  
Geological Mapping ◽  
Passive Margin ◽  
Normal Faults ◽  
North African ◽  
The North ◽  
Extensional Tectonic ◽  
Two Factors ◽  
Salt Structure ◽  
Differential Sedimentation ◽  
Cretaceous Period

AbstractDetailed geological mapping, dating, and gravimetric and seismic data are used to interpret the Lansarine–Baouala salt structure (North Tunisia) as a salt canopy emplaced during the Cretaceous Period. The extensional tectonic regime related to the Cretaceous continental margin offered at least two factors that encouraged buried Triassic salt to extrude onto the sea floor and flow downslope: (i) extension induced normal faults that provided routes to the surface, and led to the formation of sub-marine slopes along which salt could flow; (ii) this structural setting led to differential sedimentation and consequently differential loading as a mechanism for salt movement. The present 40-km-long Lansarine–Baouala salt structure with its unique mass of allochthonous Triassic salt at surface was fed from at least four stems. The salt structure is recognized as one of the few examples worldwide of a subaerial salt canopy due to the coalescence of submarine sheets of Triassic salt extruded in Cretaceous times.

Active transcurrent fault system along the north African passive margin

1987 ◽  
Vol 141 (1-3) ◽  
pp. 249-260 ◽  
Author(s):  
Zvi Ben-Avraham ◽  
Amos Nur ◽  
Cello Giuseppe
Keyword(s):  
Passive Margin ◽  
Fault System ◽  
North African ◽  
The North ◽  
Transcurrent Fault

THE SUPPRESSION OF VITRINITE REFLECTANCE IN SOME NORTH WEST SHELF WELLS: BARROW-1, JUPITER-1 AND FLAMINGO-1

1992 ◽  
Vol 32 (1) ◽  
pp. 300 ◽  
Author(s):  
R.W.T. Wilkins ◽  
J.R. Wilmshurst ◽  
G. Hladky ◽  
M.V. Ellacott ◽  
C.P. Buckingham
Keyword(s):  
Organic Matter ◽  
Vitrinite Reflectance ◽  
Accurate Determination ◽  
Petroleum Exploration ◽  
Thermal Maturity ◽  
North West ◽  
The North ◽  
The Individual ◽  
Reflectance Data

The sediments of the North West Shelf pose several problems for the accurate determination of thermal maturity by vitrinite reflectance. There are some serious discrepancies between the results of different workers; in some wells there is a surprisingly small increase of reflectance with depth, and it is sometimes difficult to honour these data in thermal maturity modelling. There appear to be two major sources of error in the reflectance data. These are firstly, the effect known as 'suppression' of vitrinite reflectance, and secondly, the difficulty of identifying the vitrinite population in dispersed organic matter.These problems may be addressed by the fluorescence alteration technique which is closely related to vitrinite reflectance but has two special advantages. Firstly, it depends on an analysis of the fluorescence alteration response of a small representative population of organic matter in which the individual macerals need not be identified. Secondly, anomalous vitrinites with suppressed vitrinite reflectance are readily characterized, and the corrected equivalent reflectances determined.The technique has been tested on three North West Shelf petroleum exploration wells, Barrow-1, Jupiter-1 and Flamingo-1. Major discrepancies between measured and equivalent vitrinite reflectance appear to originate in part from the difficulty of identifying the vitrinite population in dispersed organic matter from marine sediments. There is also evidence of suppression of vitrinite reflectance in most samples from Barrow-1, in the Flamingo Group and Plover Formation of Flamingo-1, and in the upper part of the Mungaroo Formation of Jupiter-1.A model is proposed to facilitate the assessment of measured vitrinite reflectance data from Carnarvon or Bonaparte Basin wells. Suppression effects are likely to have influenced measured vitrinite reflectance results from wells for which the strongest data are obtained from the Lower Cretaceous fluvio-deltaic Barrow Group sediments or their equivalents.

The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin

2020 ◽  
Author(s):  
Oriol Gimeno ◽  
Dominique Frizon de Lamotte ◽  
Rémi Leprêtre ◽  
Faouziya Haissen ◽  
Achraf Atouabat ◽  
...  
Keyword(s):  
Late Eocene ◽  
West African ◽  
North African ◽  
Tectonic Event ◽  
North West ◽  
The North ◽  
Before And After ◽  
Rif Belt ◽  
Thrust Sheets ◽  
Gravity Driven

<p>The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process.  By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.</p>

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