triassic liassic basins and climate of the atlantic passive margins as the laurasian plate tracked north over the new england hotspots in the latetriassic the heated and stretched crust failed along re activated basement structures including micro plate sutures and continental extensions of transforms this created the rifted passive margins of the atlantic and established the tectonic and climatic setting of wrench generated coastal ranges and detrital basins bordering vast salt flats that were overlain with waters from the tethys sea

le bassin de tizi n test haut atlas maroc exemple d evolution d un segment oblique au rift de l atlantique central au trias detailed mapping completed by a microtectonic study of the tizi n test triassic basin located along the tizi n test fault zone in the moroccan high atlas has allowed us to improve the knowledge on the geometry of the structures and the activity of faults during the triassic extensional events related to the rifting of the central atlantic the latter are reflected by the development of a rift at present inverted and deformed by the collision of africa and europe comprising kilometric scale grabens and half grabens bounded by major faults trending ene wsw with a dip towards the nnw and a dip slip syndepositional motion inverse analysis of fault slickenside populations shows a heterogeneous triassic state of stress however in the most significant measurement sites the maximum horizontal stress 1 is vertical while the minimum stress 3 is horizontal with a nw se trend the strike slip component appears to be very small during the triassic a noticeable fact because of the obliquity of the basin w

the south western branch of the variscan belt evidence from morocco abstract this work is based on the compilation and re evaluation of the most significant data either personal or from the literature concerning the moroccan variscides the latter constitute the only moderately disturbed or even undisturbed part of the south western branch of the variscan belt facing directly nw gondwana they include two orogenic segments namely the northern mauritanides and the meseta domain exposed in the saharan and atlas meseta regions respectively and a foreland belt cropping out essentially in the anti atlas the eastward thrust units of saharan morocco oulad dlim mostly originate from the west african craton wac border in an area of thin palaeozoic sedimentation thin skinned fold thrust foreland arcs develop progressively northward zemmour at the expense of the increasingly thick palaeozoic series whereas thick skinned deformation characterizes the inverted proximal paleomargin in the anti atlas domain as suggested by the meseta and anti atlas stratigraphic similarities the meseta domain corresponds to a collage of moderately displaced thinned crustal blocks from the distal gondwana paleomargin variscan deformation is dominated by nw verging thrusts and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth the meseta anti atlas boundary is a major ene trending transpressional dextral fault referred to as the south meseta fault smf discussing the correlations between the variscan segments of morocco and sw iberia allows us to suggest that a latitudinal transform zone similar to the smf separated these segments during the late palaeozoic subduction of the rheic ocean crust would have been directed se ward along both the iberian and moroccan meseta and nw ward south of the smf i e along the wac

paleostress evolution in the moroccan african margin from triassic to present abstract paleostresses were calculated from more than 1000 fault slip data on sites located in the rif moutains the middle and high atlas chains the occidental moroccan meseta and northeastern morocco we sorted the state of stress according to the main tectonic events in order to present new synthetic maps of paleostresses of morocco in the late triassic early cretaceous time nw se to ne sw extensions occurred they are consistent with the opening of the atlasic and atlantic rifts in the late cretaceous paleocene an e w to wnw ese compression took place conjugated strike slip faults developed in northeastern morocco and in the atlas chain this event was followed by a n s eocene compression where most of the reverse faults and the folds of the atlasic area developed together with strike slip faulting compression extended from oligocene to middle miocene with a ne sw direction in the rif chain the middle and high atlas and the coastal atlantic basins continuous deformation during the neogene in the atlasic area was responsible for shortening of the basement and detachment of the sedimentary cover thrust faults at the front of the atlas were either visible or blind in the lower tortonian nne ssw and ene wsw to e w compressions occurred respectively east and west of the nekor fault this tectonic regime led to the formation of post nappes basins separated by emerged lands in the tortonian early messinian the direction of compression varies from n s to nne ssw or ne sw east and west of the nekor fault respectively in the early messinian a large transgression occurred throughout the meseta domain and the middle atlas area in the late messinian a marine regression was synchronous with the mediterranean salinity crisis in the late miocene the atlas chain emerged and was progressively uplifted together with folding and thrusting of its foreland nappes involving paleozoic basement formed along the axis of the chain in the plio quaternary the compression varies from n s to n140 e and contributes to continuous uplift of the atlas chain

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

transpressional tectonics in the marrakech high atlas insight by the geomorphic evolution of drainage basins the ouzzelarh massif extends across the marrakech high atlas mha and forms the highest elevated mountain belt to better understand the evolution of collision related topography we present the results of a geomorphological study in which elevation changes generated by reactivated pre alpine variscan and triassic jurassic faults drive a landscape evolution model we aim to evaluate the relationship between the geometry of the drainage network and the main fault systems in this region new insight into geomorphological changes in drainage patterns and related landforms is based on geological fieldwork combined with dem analysis to quantitatively measure landscape features we used several classical geomorphic indices spacing ratio hypsometric curves and integral stream frequency drainage stream length gradient the ouzzelarh massif is bounded to the north by the tizi n test fault zone ttfz and to the south by the sour fault zone sfz these faults delimit a pop up structure by using the above geomorphic parameters we ascertained that the ouzzelarh massif is affected by a high spatial variability of uplift the actual landscape of the ouzzelarh massif reveals remnants of an uplifted ancient erosional surface and the heterogeneity of exposed rocks in the range explaining the possibility that the topographic asymmetry between north and south flanks is due to differences in lithology controlled resistance to erosion drainage topography and fault pattern all concur to show uplifted rhomboidal shaped blocks it exhibits high stream frequency drainage and uplift in separate tectonically uplifted blocks such as jebel toubkal which is characterized by asymmetric drainage basins

mid jurassic events in the western high atlas morocco angular unconformities time gaps and progressive increase of thickness in the mesozoic sedimentary pile of the western high atlas morocco point to mid jurassic tectonic pulses in this area red beds middle jurassic in age were deposited in the nearshore agadir essaouira basin in contrast to transgressive tendencies of the eustatic curve these phenomena are easily explained by uplift and erosion in the central part of the mountain belt even in the middle jurassic thus a rift stage permian to early jurassic in the tectonic history of the western high atlas was followed by a gulf stage late jurassic to middle cretaceous until later the high mountain range generated by inversion in late cretaceous and neogene to recent times tensional forces that created the mobile rift belt were superimposed by vertical uplift during the middle jurassic that gave rise to a nne ssw stretching high even in the present day high mountain range this area called the ancient massif is strongly elevated thus the evaluation of the geological history of the western high atlas seems much complicated

the inverted triassic rift of the marrakech high atlas a reappraisal of basin geometries and faulting histories the high atlas of morocco is an aborted rift developed during the triassic jurassic and moderately inverted during the cenozoic the marrakech high atlas with large exposures of basement and triassic early syn rift deposits is ideal to investigate the geometries of the deepest parts of a rift constituting a good analogue for pre salt domains it allows unraveling geometries and kinematics of the extensional and compressional structures and the influence that they exert over one another a detailed structural study of the main triassic basins and basin margin faults of the marrakech high atlas shows that only a few rift faults were reactivated during the cenozoic compressional stage in contrast to previous interpretations and emphasizes that fault reactivation cannot be taken for granted in inverted rift systems preserved extensional features demonstrate a dominant dip slip opening kinematics with strike slip playing a minor role at variance to models proposing a major strike slip component along the main basin bounding faults including faults belonging to the tizi n test fault zone a new middle triassic paleogeographic reconstruction shows that the marrakech high atlas was a narrow and segmented orthogonal rift sub perpendicular to the main regional extension direction which was nw se in contrast to the central and eastern segments of the atlas rift which developed obliquely this difference in orientation is attributed to the indented ouzellarh precambrian salient part of the west african craton which deflected the general rift trend in the area evidencing the major role of inherited lithospheric anisotropies in rift direction and evolution as for the cenozoic inversion total orogenic shortening is moderate 16 and appears accommodated by basement involved large scale folding and by newly formed shortcut and by pass thrusting with rare left lateral strike slip indicators triassic faults commonly acted as buttresses

salt tectonics along the atlantic margin of morocco abstract the moroccan salt basin appears to be very unique in the sense that it is not sedimentary loading but tectonic inversion which appears to drive the latest stages of salt related deformation in the central part of the basin the gravity potential to maintain salt tectonics is provided by the differential uplift of the atlas mountains located adjacent and striking almost perpendicular to the margin along the offshore part of the moroccan salt basin there are many play types most of them related to the triassic syn rift salt toe thrust anticlines at the basinwards edge of the salt basin form very large structures traps associated with salt tongues and diapirs define a more classical salt flank play numerous salt tongues sheets and canopy complexes provide for a gulf of mexico style subsalt play despite the numerous untested play types there have been only four deep water exploration wells drilled in the entire moroccan salt basin none of them having subsalt penetrations

can moroccan atlas lithospheric thinning and volcanism be induced by edge driven convection terra nova 24 27 33 2012 abstract the moroccan lithosphere is characterized by an anomalously thinned area located beneath the atlas domains which forms a singular narrow ne sw directed strip overlain by cenozoic alkaline volcanism the origin of this thinning and volcanism is still a matter of debate the proposed models invoke processes either related to the mediterranean slab or mantle plumes herein we propose an alternative edge driven convection edc model involving small scale convection at the boundary between the west african craton and the atlas lithosphere our comparison of the atlas lithosphere velocity and volcanism episodes during the last 80 ma points out that volcanism occurs when plate moves at velocities c 1 cm a 1 a velocity sufficiently low to trigger edc this is the first process that could explain the c 20 ma volcanism shutdown separating the two volcanic episodes of the atlas in addition it may successfully account for the lithosphere thinning location and geometry and volcanism geochemistry

the role of inherited tectono sedimentary architecture in the development of the central andean mountain belt insights from the cordillera de domeyko abstract the structure of the cordillera de domeyko is dominated by a number of elongated n s trending basement ridges these ridges were uplifted by steep reverse n s faults that deformed the mesozoic cenozoic cover the vergence of the fault system varies along strike conferring an apparent doubly vergent pop up geometry to the axial zone two mesozoic pre compressional extensional events were recorded in the area new structural data presented in this paper indicate that most of the generated n s trending thrusts and related folds were controlled by the inversion of the pre existing mesozoic extensional faults thin skin structures in the mesozoic cenozoic cover are genetically linked to major basement upthrusts which could be interpreted as basement short cuts formed during inversion rather than as uplifted blocks associated with major cenozoic strike slip faults growth strata geometries date the beginning of the andean compressional event which generates the chilean precordillera as far back as 90 ma ago the resulting structural architecture is strongly controlled by inherited pre andean extensional structures the association of porphyry intrusives with major reverse faults suggests that the emplacement of the eocene oligocene porphyry cu mo deposits in northern chile can be explained by an oblique inversion tectonics model the upper eocene lower oligocene giant porphyry copper bodies chuquicamata la escondida el salvador located in the cordillera de domeyko show an adakitic affinity this magma affinity together with structural evidence presented in this work indicates that porphyry emplacement occurred at the end of the basement involved contractional stage that generates the anomalous thickened crust needed to generate these magmas this tectonic evolution is coherent with the existence of a flat slab subducting beneath the central andes 22 26 s during early cenozoic that will also produce the eastward migrating of the compressional regime in the upper plate since late cretaceous

cenozoic denudation in the marrakech high atlas morocco insight from apatite fission track thermochronology in north africa the high atlas belt culminates at more than 4000 m in morocco recent work shows that a lithospheric thinning explains about 1000 m of the mean topography the remaining topography being related to crustal shortening we combine regional geology with new apatite fission track aft ages to constrain the timing of these events in the marrakech high atlas mha in the inner belt 10 aft ages are comprised between 9 1 and 27 3 ma these neogene ages indicate that the mha underwent significant denudation during that time in the southern foreland domain of the belt three samples give scattered aft ages between 27 2 and 87 5 ma geological evidences allow us to constrain the age of a major denudation event during middle miocene age we propose that it is linked to the thermal doming highlighted in the whole moroccan atlas domain

syn to post rift diapirism and minibasins of the central high atlas morocco the changing face of a mountain belt the atlas mountains are classically regarded as a failed mesozoic rift arm subject to alpine inversion folding and thrusting here we present new integrated structural and sedimentological studies that have revealed numerous early middle jurassic diapiric ridges and minibasins characterized by distinctive halokinetic structures diachroneity in halokinesis is observed across the central high atlas waning first in the sw during the early middle jurassic jbel azourki and tazoult ridges and continuing to late middle jurassic towards the ne imilchil region the halokinetic structures are readily differentiated from the effects of later alpine deformation allowing a new picture of the central high atlas to emerge the most pervasive deformation in the central high atlas is associated with early middle jurassic diapirism whereas the impact of alpine inversion is mostly focused at the basin margins this new understanding helps explain previously problematic aspects of the atlas mountains which we now recognize as an exceptionally well exposed natural laboratory for understanding the interactions between halokinesis tectonics and sedimentation

mid triassic to early liassic clastic evaporitic deposits over the maghreb platform abstract the development of triassic to lower liassic clastic evaporitic series over the epicratonic maghreb platform is closely associated with the eastern opening of a tethyan marine domain between africa and europe west of the platform morocco became separated from north america in late triassic times by rifting along the axis of the proto atlantic ocean in addition ne sw and ene wsw trending atlasic half grabens formed essentially in morocco as part of a late triassic early liassic atlas rifting episode this is the tectonic context in which the red bed to evaporite sequences were deposited a first depositional pattern is illustrated by the areally extensive onlapping of upper triassic clastic evaporitic series over the algerian saharan platform from the carnian to the norian distal mudflats and evaporites graded westward i e landward into proximal fluvial facies seven stratigraphic cycles formed part of a general base level rise of a major retrogradational clastic to evaporitic cycle indicative of general tectonic subsidence of the algerian platform as a whole the evaporites are thus interpreted as markers of persistent onlapping occurring at the edge of the basin as clastic influxes gradually diminished a second depositional pattern is provided by ladinian to rhaetian clastic evaporitic carbonate transgressive sequences of the atlasic domain in tunisia these terminate characteristically in marine facies in this domain intense tectonic activity was consistently offset by a high rate of evaporitic or clastic sedimentation in shallow water environments a third depositional pattern is illustrated in the moroccan high atlas in the central part of this range carnian red conglomerates and sheet like sandstones of a distal braided fluvial plain were deposited in tectonic troughs that linked together as part of a rift system episodic connections occurred with the tethyan domain to the northeast in the western high atlas an upper carnian norian sequence several hundred meters thick displays a general trend from clastics to evaporites reflecting the development of arid paleoclimatic conditions the moroccan meseta provides examples of clastic evaporitic depositional patterns within intracratonic troughs clastic filling of rift induced troughs in the oujda mountains exhibits significant facies and thickness variations ranging from local proximal alluvial and distal anastomosed channel systems through to dominant mudflat systems in the 1000 m thick series of the 60 km long khemisset basin facies range from red beds located mainly along the basin margins to salt dominated deposits in the basin center increasing accommodation controlled the deposition of evaporites and the maximum flooding surface is to be found in typical halite deposits with interbedded bands of clays at that time greater tectonic subsidence rates allowed more marked episodic marine incursions clastic evaporitic series from the passive margin of the moroccan atlantic coast are known only from bore holes and onshore and offshore seismic data recent papers have reported interesting sections across strongly subsiding grabens or tilted blocks related to predominantly ssw nne faults

syn and postrift evolution of the el jadida agadir basin morocco constraints for the rifting models of the central atlantic the el jadida agadir basin shows an evolution related to that of the central atlantic rifting history the synrift period late early triassic to earliest jurassic is dominated by deposition of red clastic sediments and evaporites which are overlain by or intercalated with basalt flows two intense extensional phases are recognized the first probably in middle triassic times is oriented north northwest south southeast and resulted in the formation of east northeast west southwest oriented grabens and half grabens the second a widespread northwest southeast trending extension is ladinian to earliest liassic and induced the formation of westward dipping half grabens extensional tectonics initiated in the southern part of the basin and migrated northwards contrary to classical ideas proposing rifting from north to south the postrift evolution is characterized by jurassic to eocene subsidence tectonism appears to have been restricted to a narrow area close to the present day coast subsidence h

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

synsedimentary faulting and palaeocurrent patterns in the triassic sandstones of the high atlas morocco the influence of syndepositional fault patterns on palaeocurrents is demonstrated in fluvial to shallow marine sandstones of upper triassic basins in the high atlas the synsedimentary nature of faults is deduced from hydroplastic slickensides thickness variations due to block tilting and dislocation of layers next to the fault scarp on a regional scale it is shown that the major normal fault trend of n050 070 controlled the overall palaeocurrent pattern which was directed towards the west southwest i e in the direction of the future atlantic ocean some anomalies in the palaeocurrent pattern could be related to an increase in subsidence which induced a general coarsening of sediment towards the top of the triassic

role of synsedimentary strike slip faults in the formation of moroccan triassic basins upper triassic sandstone and siltstone infilled basins in the massif ancien of the high atlas morocco are distributed along a complex east northeast trough at the boundary between the hercynian orogen and the west african craton the formation of these basins involved a dense pattern of pre existing faults hydroplastic slickensides which affect nonlithified sediments help identify not only dip slip but also strike slip faults together with other tectonic and sedimentary structures the directional distribution of these faults leads to a model in which extension varies from north northwest during lower unit sandstone infilling to northwest during upper unit siltstone infilling the latter direction is compatible with the formation of the lower liassic intrusional doleritic dikes of the anti atlas