pre alpine variscan inheritance a key for the location of the future valaisan basin western alps the boundary between the helvetic and the penninic brianconnais zones has long been recognized as a major fault penninic front in the western alps a narrow oceanic domain has been postulated at least along part of this boundary the valaisan ocean however the information provided by the pre triassic basement has not been fully exploited and will be discussed here in detail the igneous and metamorphic history of the pre triassic basement shows significant differences between the external massifs from the helvetic zone with abundant late carboniferous granites and the basement of the brianconnais zone including the internal massifs dora maira gran paradiso monte rosa devoid of carboniferous granites a major coal bearing basin the zone houillere opened along this boundary this limnic intramontane basin has never been properly investigated the zone houillere is not comparable with the external paralic flexural basins on both sides of the variscan belt but shows similarities with the saar saale basin like the latter we interpret the zone houillere as a transtensional basin opened along a major crustal scale fault zone namely the east variscan shear zone the permian magmatism and sedimentation displays contrasting distributions being absent or very localized in the helvetic zone and widespread in the penninic zone the above data indicate that the structural inheritance from the variscan belt plays a major role in defining the future location of the valaisan basin i e the boundary between the european palaeomargin and the brianconnais microcontinent

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

role of crustal stretching on subsidence of the continental crust abstract the principal areas of subsidence of the continental crust are wide intracontinental basins and passive continental margins in many intracontinental basins crustal extension amounts to only a few percent and is unable to explain their subsidence as shown for the timan pechora pre caspian and west texas basins the deep black sea and south caspian basins are underlain by highly attenuated continental crust having velocities in the 7 km s range that shows no evidence for significant extension in passive margins upper crustal extension ranges between 10 and 40 whereas the lower crust is attenuated by 2 3 times e g campos basin north biscay margin large discrepancy between upper crustal stretching and lower crustal attenuation is seen in the crustal configuration of many intracontinental grabens e g baikal and dniepr prypyat basins only in highly extended areas such as the basin and range province and the east china rift system does crustal stretching account for the observed crustal thinning the observed discrepancy between upper extension and crustal thinning across intracontinental rifts and passive margins and particularly in some wide intracontinental basins suggests that crustal stretching alone cannot account for the subsidence of these basins phase transformations in the lower crust probably facilitated by the presence of hydrous fluids can cause rapid 1 ma as well as long term 200 1500 ma upward displacement of the moho discontinuity resulting in high amplitude subsidence of the crust in areas of crustal extension this mechanism can overprint subsidence induced by thermal relaxation of the lithosphere the case of the black sea and south caspian basins shows that density increase of the lithosphere can also occur independently of crustal stretching

upper plate magma poor rifted margins stratigraphic architecture and structural evolution abstract although it is generally accepted that many distal magma poor rifted margins are asymmetric and can be divided into lower and upper plate margins little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished this is due to the fact that most papers focused on the so called lower plate margins while the upper plate margins remained less well understood mainly due to the lack of public accessible drill hole data the aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate magma poor rifted margin in order to provide such a template we focused on 2 seismic sections the ion 1000 line east indian margin and the screech 2 line newfoundland margin and describe key km scale outcrops from the fossil european margin exposed in the western central alps all of which document classical upper plate margins based on these data we show that upper plate magma poor rifted margins can be characterized by a staircase type architecture with terraces t 1 t 2 t 3 and ramps r 1 r 2 that result as a consequence of an evolution through a coupling exhumation and breakup stage we also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin from these observations we develop a conceptual model for the evolution of upper plate margins and discuss the applicability of this model for different strain rates rates of subsidence and sedimentation rates

pre oceanic rifting in the alps abstract a review of mesozoic mainly earliest jurassic to mid jurassic rifting in the western and central alps normal faults with throws up to a few kilometers are moderately inclined and involve rotation of crustal blocks the amount of stretching and thinning of the crust by jurassic rifting is discussed the rifting 200 165 m y pre dates the opening of the alpine oceans by spreading and transform movements 165 110 m y

from faulted blocks to megamullions and megaboudins tethyan heritage in the structure of the western alps along the grenoble pelvoux viso transect in the western alps we schematize the geometrical relationships between 1 ductile marly calcareous sedimentary covers and 2 their more rigid substratum this substratum may be the pre alpine granitic gneissic basement the triassic dolomites or even the jurassic ophiolites basement mullions a few kilometer size are characteristic of the external part of the western alps arc dauphine zone they strongly contrast with the dolomitic or ophiolitic boudins also a few kilometer size in the inner part of the arc piedmont zone the dauphine megamullions formed and then became accentuated during the oligocene and then the neogene tectonic phases which correspond to the last major alpine contractions at relatively shallow structural levels in the sedimentary cover upright or inclined folds were associated with slaty or strain slip cleavage development and low grade metamorphism the corresponding stretching directions locally subvertical trend normal to the regional fold and mega mullions axes and to the mountain belt itself the piedmont megaboudinage took place during the earlier major eocene alpine phase which but for some exeptions did not affect the dauphine zone in the very ductile schistes lustres that surround the dolomitic and ophiolitic megaboudins generalized intrafolial recumbent folding was associated with blueschist metamorphism the deformation characteristic of a deep structural level was a strong flattening within a subhorizontal plane and a preferential elongation parallel to the fold axes owing to regional horizontal festooning those axes trend normal oblique or even parallel to the piedmont zone i e to the incipient mountain belt restored initial trends coeval megaboudinage was probably omnidirectional chocolate tablet pattern the eocene piedmont structure has not been really obliterated during the later alpine deformations leading to megamullions development in the dauphine zone we summarize the very numerous stratigraphical sedimentological and tectonic field observations which lead us to regard each dauphine megamullion as directly inherited from a previous pre alpine faulted block each piedmont megaboudin has a similar origin the corresponding paleofaults are in fact normal and or strike slip faults of truly tethyan age their synsedimentary offset occurred either during the liassic middle jurassic passive margin rifting evolution of the southern edge of the european continent or during the late jurassic opening up of the ligurian oceanic tethys we analyze how those tethyan faults partly induced the style of the alpine collisional structures according to the regional characters of the successive synmetamorphic deformations i e to their localization in the western alps mountain belt

measurement of in situ oxygen isotope ratios in monazite by shrimp ion microprobe standards protocols and implications abstract monazite forms at sub solidus conditions in a variety of metamorphic rocks and has been proven to be reactive to fluids and thus is a potential monitor of fluid rock interaction as monazite can preserve multiple growth zones in order to explore the potential of monazite as a fluid tracer in metamorphic conditions microbeam analysis is required we performed oxygen isotope analysis of monazite using the shrimp ion microprobe and newly characterized standards for which we obtained laser fluorination 18o values usgs 44069 monazite 7 67 0 26 and itambe monazite 0 46 0 20 reproducibility of 18o ion microprobe analyses for usgs 44069 and itambe monazites is in the order of 0 4 0 6 standard deviation at 95 c l similar to what is routinely obtained for silicates this reproducibility is comparable to that of the analyses of experimental p rich glasses which are assumed to be homogeneous and free of geological imperfections the variable composition of natural monazite has the potential to produce matrix effects during ion microprobe measurements monazite grains from the malagasy syenite madagascar and the dora maira whiteschists italy display a scatter in 18o values that show a negative correlation with th content and is related to the huttonite thsio4 and cheralite cath po4 2 substitutions in monazite the matrix effect on oxygen isotope measurements can be significant and is estimated to produce a shift in 18o of circa 0 85 or 1 9 for every 10 wt th introduced by the huttonite and cheralite components respectively corrections for this matrix effect are proposed on the basis of the natural samples investigated oxygen isotope fractionation factors for monazites of different compositions cheralite and huttonite were calculated with the increment method the results suggest that the substitution of trivalent lree by tetravalent ce and th results in consistent enrichment of 18o in the monazites whereas the substitution of tetravalent th by divalent ca results in the depletion of 18o in cheralite rich monazite monazites from high grade metasediments mount stafford central australia preserve inherited cores but are homogeneous in oxygen composition this suggests that diffusion may efficiently erase the oxygen isotope signature in monazite that experienced 800 c metamorphism

carbonate hosted siliceous crust type mineralization of carnic alps italy austria abstract a carbonate hosted stratabound siliceous crust type sct mineralization base metal sulphides barite fluorite occurs over large areas of carnic alps and karawanken in the eastern alps it concerns a pervasively silicified lithological unit up to some tens of metres thick which caps the unconformity landscapes developed on epicontinental devonian dinantian carbonates the sct mineralization is directly overlaid by different transgressive siliciclastic sediments which range from lower carboniferous to lower permian the presence of fragments of the sct mineralization in the transgressive siliciclastic sediment bounds its whole lithological evolution within a short stratigraphic interval of lower carboniferous age selected features of the regional and lithostratigraphic setting are discussed the chemical characterisation is based on the statistical evaluation of compositional data of 581 selected samples three significant groups of elements have been distinguished 1 the hydrological and metasomatically active elements si ba f which show a strong negative correlation amongst themselves and characterise the silica saturated aqueous solutions 2 the terrigenous elements al 2 o 3 k 2 o fe tot tio 2 b be ce la nb v y zr which suggest a continental margin environment for silica deposition 3 the sulphide metals cu pb zn ni sb as hg cd which define the metalliferous signature of the sct mineralization some consistent but still debatable genetic aspects of the sct mineralization are as follow 1 silica may be supplied by illitization of clay rich basinal sediments during their diagenesis 18 o of microcrystalline quartz ranges from 18 5 and 24 6 and is very similar to 18 o of authigenic quartz deriving from diagenetic processes of illitization of clay rich basinal sequences 2 the diagenetic evolution of these sediments may trigger off the movement of silica rich marine pore waters 34 s of barite ranges from 15 5 to 19 3 with an average of 17 7 and are in good agreement with 34 s of sulphate in ocean waters of upper devonian lower carboniferous age 3 a convective hydrological system connected with sinsedimentary transtensive tectonics active in the carnic alps since the frasnian may be the transport mechanism of aqueous solutions 4 a weak drop in ph in the dominant carbonate environment represents the conditions for silica precipitation sct mineralization showing persistent independent and distinct characters occurs over large areas also in other sites of the alpine belt and outside italy and austria therefore it points to important markers for some sedimentary sequences as well as to a worldwide significant cyclic metallogenic event it represents a new ore deposit type within the carbonate hosted mineralization

tectono thermal evolution of a distal rifted margin constraints from the calizzano massif prepiedmont brianconnais domain ligurian alps the thermal evolution of distal domains along rifted margins is at present poorly constrained in this study we show that a thermal pulse most likely triggered by lithospheric thinning and asthenospheric rise is recorded at upper crustal levels and may also influence the diagenetic processes in the overlying sediments thus representing a critical aspect for the evaluation of hydrocarbon systems the thermal history of a distal sector of the alpine tethys rifted margin preserved in the ligurian alps case tuberto calizzano unit is investigated with thermochronological methods and petrologic observations the studied unit is composed of a polymetamorphic basement and a sedimentary cover providing a complete section through the prerift synrift and postrift system zircon fission track analyses on basement rocks samples suggest that temperatures exceeding 240 25 c were reached before 150 160 ma upper jurassic at few kilometer depth neoformation of green biotite stable at temperatures of 350 to 450 c was synkinematic with this event the tectonic setting of the studied unit suggests that the heating cooling cycle took place during the formation of the distal rifted margin and terminated during late jurassic 150 160 ma major crustal and lithospheric thinning likely promoted high geothermal gradients 60 90 c km and triggered the circulation of hot deep seated fluids along brittle faults causing the observed thermal anomaly our results suggest that rifting can generate thermal perturbations at relatively high temperatures between 240 and 450 c at less than 3 km depth in the distal domains during major crustal thinning preceding breakup and onset of seafloor spreading

the structural evolution of the albula pass region graubunden eastern switzerland the origin of the various vergences in the structure of the alps the albula pass region lies between the lower austroalpine err nappe and the middle austroalpine silvretta nappe they will be treated here as the frame of the non to gently metamorphic sedimentary units between the two during the alpide times sedimentation started on a metamorphic hercynian basement during the latest carboniferous and continued into the permian then a sequence from the alpine buntsandstein to the medial jurassic to early cretaceous aptychenkalk maiolica and radiolarites were deposited in an environment of rifting and subsidence the succeeding palombini clastics were laid down after the aptychenkalk and mark the onset of shortening in the alpine realm the initial structures that formed were at least two north dipping normal faults which formed before the deposition of the jurassic sedimentary rocks when shortening set in the first structure that came into being was the south vergent elalbula nappe bending the normal faults into close antiforms it became further dismembered

the western alps from the jurassic to oligocene spatio temporal constraints and evolutionary reconstructions abstract despite extensive research in the last 150 years the regional tectonic reconstruction of the western alps has remained controversial the curved orogenic belt consists of several ribbon like continental terranes sesia austroalpine internal crystalline massifs brianconnais which are separated by two or more ophiolitic sutures piemonte valais antrona lanzo canavese high pressure hp metamorphism of each terrane occurred during distinct orogenic episodes at 65 ma in the sesia austroalpine at 45 ma in the piemonte zone and at 35 ma in the internal crystalline massifs it is suggested that these events reflect individual accretionary episodes which together with kinematic indicators and the speed and direction of plate motions provide constraints for the discussed reconstruction model the model involves a prolonged orogenic history that took place during relative convergence of europe and adria here considered as a promontory of the african plate the first accretionary event involved the sesia austroalpine terrane final closure of the piemonte ocean occurred during the eocene 45 ma and involved ultra high pressure uhp metamorphism of the piemonte oceanic crust incorporation of the brianconnais terrane in the accretionary wedge occurred thereafter possibly during or after subduction of the valais ocean in the late eocene 45 35 ma this subduction was terminated at ca 35 ma when the internal crystalline massifs i e the assumed internal parts of the brianconnais terrane were buried into great depths and underwent hp and uhp metamorphism

breccias of the adnet formation indicators of a mid liassic tectonic event in the northern calcareous alps salzburg austria stratigraphy lithology and depositional structures of liassic red limestone breccias of the adnet formation including the adnet scheck were studied at several outcrops of the northern calcareous alps nca south east of salzburg a four fold lithostratigraphic division is proposed for the adnet formation of the osterhorn mountains the hemipelagic schmiedwirt sinemurian and kehlbach carixian members are separated from the pelagic saubach member toarcian by a layer of amalgamated breccias scheck member probably domerian to early toarcian several other breccia beds occur locally from the base of the kehlbach member up to the lower saubach member although the sediments overlying the scheck member breccias are of coeval age the ages of the underlying strata are very different this can be explained by submarine liassic erosion during a period of resedimentation from the middle carixian until the early toarcian at least 10 15 m of partly lithified sediments were eroded by gravity flows the entire kehlbach member and up to two thirds of the schmiedwirt member were removed at adnet the breccias originated from submarine debris flows repeated flows over a long period and the depositional setting exclude a triggering by sea level fluctuations most probably they arose from tectonically triggered slumps and slides of superficial sediments the scheck was initiated on the steep upper slope of the drowned triassic adnet reef and flowed to the north east the pliensbachian to early toarcian period of tectonic activity indicated by the breccias was the most important during the liassic in the osterhorn mountains and other parts of the nca from the large scale regional distribution of the breccias and in accord with published data a roughly northeast trending strike slip fault zone is proposed crossing the nca south of the osterhorn block with a peaking activity during the pliensbachian to early toarcian as the cause of the tectonic movements

early history of the atlantic ocean and gas hydrates on the blake outer ridge results of the deep sea drilling project leg 76 leg 76 of the deep sea drilling project achieved two major scientific objectives the first objective was met at site 533 where on the blake outer ridge gas hydrates were identified by geophysical geochemical and geological studies gas hydrate decomposition produced a volumetric expansion of 20 1 of gas volume to pore fluid volume this expansion exceeded by about a factor of four the volume of gas that could be released from solution in pore water under similar conditions the gas hydrate includes methane ethane propane and isobutane but apparently excluded normal butane and higher molecular weight hydrocarbons as predicted from gas hydrate crystallography for the first time marine gas hydrates were tested with a pressure core barrel the second objective was achieved when coring at site 534 in the blake bahama basin sampled the oldest oceanic sediments yet recovered the sequence of oceanic basement and overlying sediments documents the geologic history of the early stages of the opening of the north atlantic ocean in detail the oldest oceanic sediments are red claystones and laminated green and brown claystones of middle callovian age this finding supports the interpretation that the beginning of the modern north atlantic occurred in the early callovian 155 m y b p as much as 20 m y later in time than often previously thought

kinematic linkage between internal zone extension and shortening in more external units in the nw alps in the alps a major extensional shear zone unroofed eclogites in its footwall from 30 kbar to c 10 kbar implying of the order of 60 km of relative vertical movement in the period 45 36 ma the horizontal component of divergence was of the order of 100 km we use the foreland basin sedimentary record to prove that the extension was contemporaneous with thrusting in units structurally beneath the eclogites the brianconnais and or external zones this thrust related convergence during that time period was of the order of 44 56 km and therefore of the same order of magnitude as internal zone divergence extension may have been driven by internal density contrasts buoyant continental crust underneath the mafic eclogites or dense subducted slab offset from the orogen can induce extension any dynamic model must account for the comparable magnitudes of extension and shortening in adjacent parts of the orogen relative plate motions in the period 45 36 ma played a subsidiary role

fossil oceanic core complexes recognized in the blueschist metaophiolites of western alps and corsica tethyan ophiolites show an apparent poorly organized association of ultramafic andmafic rocks by contrast tothe complete mantle crustal sections of semail type ophiolite sheets tethyan ophiolites are characterized by asmaller amount of mafic rocks gabbros and basalts by the absence of any sheeted dyke complex and by thefrequent occurrence of oceanic sediments stratigraphically overlying mantle derived peridotites and associatedgabbroic intrusions therefore they are considered as typical remnants of oceanic lithosphere formed in slowspreadingenvironment or in ocean continent transition at distal passive margins in the very first models offormation of the tethyan ophiolites in the years 1980 the geodynamical processes leading to mantle unroofingwere poorly understood due to the paucity of data and concepts available at that time from the present dayoceans in particular at that time little work had focused on the distribution origin and significance ofmafic rocks with respect to the dominant surrounding ultramafics here we reconsider the geology of sometypical metaophiolites from the western alps and corsica and we show how results from the past decadeobtained in the current oceans ask for reassessing the significance of the tethyan ophiolites in general revisitedexamples include a set of representative metaophiolites from the blueschists units of the western alps queyrasregion and from alpine corsica golo valley field relationships between the ophiolitic basement andthe metasedimentary metavolcanic oceanic cover are described outlining a typical character of the tethyanophiolite lithological associations jurassic marbles and polymictic ophiolite metabreccias are unconformablyoverlying the mantle gabbo basement in a way strictly similar to what is observed in the non metamorphicappennine ophiolites or chenaillet massif this confirms that very early tectonic juxtaposition of ultramafic andmafic rocks occurred in the oceanic domain before subduction this juxtaposition resulted from tectonic activitythat is now assigned to the development of detachment faults and to the formation of oceanic core complexes occs at the axis of slow spreading ridges this fundamental plate tectonics process is responsible for the exhumationand for the axial denudation of mantle rocks and gabbros at diverging plate boundaries in addition fieldrelationships between the discontinuous basaltic formations and the ultramafic mafic basement indicate that thistectonic stage is followed or not by a volcanic stage we discuss this issue in the light of available field constraints

different metamorphic evolutions in the alpine apenninic ophiolites france italy switzerland austria abstract the metamorphic evolution of the alpine apennine ophiolites from calabria to the eastern alps is reviewed with special emphasis laid on the western alpine ophiolites after the oceanic metamorphic phases marked differences appeared in the metamorphic evolution 1 1 the units that contain eclogite associations zermatt zone including the voltri group internal liguria lower zone in the tauern window are distinguished from the sediment rich units devoid of eclogites most of which also contain ophiolite olistoliths and or tectonic slices and interlayered ophiolitoids e g combin zone in the western alps 2 2 the externai units can be further separated into units showing initial late cretaceous eo alpine associations of either glaucophane jadeite lawsonite glaucophane greenschist or prehnite pumpellyite 3 3 all units shared a more or less common cainozoic meso and neo alpine history of a grade roughly controlled by the distance to the ticino thermal culmination both the development of very high pressure conditions and the existence of domains with different evolutions are accounted for by the marginal sea setting now envisaged for the alpine apenninic oceanic domains

a local dust storm in the chryse region of mars viking orbiter observations a local dust storm was observed near the viking lander 1 site by viking orbiter l in september 1977 when the areocentric longitude of the sun ls was 340 shortly before vernal equinox the orbiter observations which consisted of a time sequence of pictures show that the storm moved at about 50 m sec to the ene from the lunae planum region into the chryse basin both baroclinic waves and topography may have been associated with the generation of the storm

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

paleomagnetism and paleogeography of the northern calcareous alps austria prefolding magnetization components have been resolved at 38 sites of liassic adnet limestones in the central northern calcareous alps nca and at one site in the drauzug the site mean directions are northeasterly and down and are closer to coeval european directions than to southern alpine african directions the western end of both the nca and of the drauzug yield different site mean directions and negative fold tests indicating remagnetization the sampling localities have been rotated relative to one another during thrusting however comparison of paleomagnetic poles with the european apparent polar wander path implies an average clockwise rotation of about 30 for the nca relative to europe larger scale clockwise rotations in excess of 80 relative to the southern alps are implied by comparison with the southern alpine african polar wander path facies analysis of jurassic and lower cretaceous basinal sediments in the central part of the nca suggests that liassic subsidence was related to presently e w sinistral strike slip faults whereas malm berriasian subsidence was controlled by presently e w south dipping normal faults both paleomagnetic and facies data tend to indicate that the nca did not undergo the african rotation seen in southern alpine paleomagnetic data this implies the existence of a short lived tract of triassic jurassic ocean floor between the nca and the southern alps which linked the pindos ocean to the ligurian trough and allowed adria to rotate independently from the nca during the late jurassic eo alpine deformation and metamorphism are associated with the early cretaceous closure of this hallstatt trough

pogallo line south alps northern italy an intermediate crystal level low angle normal fault the pogallo line is a major crustal shear zone in the crystalline south alps of northern italy which separates middle amphibolite granulite facies rocks of the ivrea zone from lower middle amphibolite facies rocks of the strona ceneri zone u pb rb sr and k ar whole rock and mineral ages for samples from this region indicate that the two zones pursued different time temperature paths after caledonian peak metamorphism cooling curves for the two terrains finally converge in the late triassic early jurassic a time of large scale crustal extension in the south alps that anticipated the opening of the western tethys we suggest that the pogallo line may represent a low angle normal fault that developed at intermediate crustal levels during this period of extension and attained its present subvertical orientation during alpine deformation

carbonate turbidite sequences deposited in rift basins of the jurassic tethys ocean eastern alps switzerland syn rift sediments in basins formed along the future southern continental margin of the jurassic tethys ocean comprise in the eastern alps of switzerland up to 500 m thick carbonate turbidite sequences interbedded with bioturbated marls and limestones in the fault bounded troughs no submarine fans developed in contrast the fault scarps acted as a line source and the asymmetric geometry as well as the evolution of the basin determined the distribution of redeposited carbonates the most abundant redeposits are bio and lithoclastic grainstones and packstones with sedimentary structures indicating a wide range of transport mechanisms from grain flow to high and low density turbidity currents huge chaotic megabreccias record catastrophic depositional events their main detrital components are upper triassic shallow water carbonates and skeletal debris from nearby submarine highs after an event of extensional tectonism sedimentary prisms accumulated in the basins along the faults each prism is wedge shaped with a horizontal upper boundary and consists of a thinning and fining upward megacycle within each megacycle six facies associations are distinguished at the base of the fault scarp an association of breccias was first deposited by submarine rockfall and rockfall avalanches a narrow approximately 4000 m wide depression along the fault was subsequently filled by the megabreccia association in which huge megabreccias interfinger with thin bedded turbidites and hemipelagic limestones the thick bedded turbidite association covered the megabreccias or formed farther basinward the base of the sedimentary column within the thick bedded turbidites thinning and fining upward cycles are common the overlying thin bedded turbidite association shows nearly no cyclicity and the monotonous sequence of fine grained calciturbidites covers most of the basin area with continuous filling and diminishing sediment supply a basin plain association developed comprising fine grained and thin bedded turbidites intercalated with bioturbated marls and limestones on the gentle slopes opposite the fault escarpment redeposited beds are scarce and marl limestone alternations as well as weakly nodular limestones prevail

area of mixed marine faunas between two major paleogeographical realms exemplified by the early jurassic late sinemurian and pliensbachian ammonites in the alps abstract the late sinemurian and pliensbachian ammonite faunas of the alpine range yield a good opportunity to study an area of mixed marine fauna the faunas of the 4 major paleogeographical alpine units from southern alps to delphino helvetic are illustrated by fifteen recently investigated outcrops moreover information provided by the alpine units is compared with both northern and southern surroundings these data areaanalyzed here through a qualitative and quantitative approach two main patterns of distribution are recognizable the first one mainly ammonitina versus phylloceratina and lytoceratina shows a rather gradual decrease of ammonitina to the south and of phylloceratina lytoceratina to the north the second pattern well exemplified if we consider euroboreal vs tethyan ammonitina corresponds to abrupt faunal changes the pattern of the first suggests that ecological depth of water currents siliciclastic sedimentation constraints are stronger than competition between the two considered groups in the second case competition between ammonites seems more important than ecological constraints at last redundancies in patterns of faunal distribution reveal that only two paleogeographical areas correspond to important faunal changes the first one is probably located on the brianconnais area and the second one is situated between upper austroalpine and southern alps areas if the brianconnais is classically considered as a possible barrier the second faunal boundary is more enigmatic because palinspastic reconstructions hardly suggested any physical barrier at this place except perhaps the vardar ocean

tethyan ophiolites and tethyan seaways tethyan ophiolites have played a major role in the development of the ophiolite concept during the past 200 years and contributed significantly to the formulations of the suprasubduction zone ssz ophiolite paradigm and the plate tectonics theory their melt evolution and magmatic construction witnessed the dispersal of the supercontinent pangaea via continental rifting and seafloor spreading opening and closure of multiple seaways in an eastward widening latitudinal ocean basin neotethys and deep mantle recycling processes through subduction zone tectonics and plume activities neotethyan ophiolites are highly diverse in their crustal mantle structures and compositions pointing to major differences in their melt sources and tectonic settings of magmatic construction the papers in this thematic set demonstrate these differences in the neotethyan ophiolite record through new structural geochemical isotopic and geochronological data and interpretations the jurassic western alpine ophiolites formed in a narrow basin alpine tethys that developed between europe and north africa adria iberia their peridotites represent exhumed continental lithospheric mantle the triassic jurassic and cretaceous ophiolites east of adria formed in different neotethyan seaways and their ssz magmatic construction involved multiple episodes of melting depletion and refertilization of subduction modified oceanic mantle the late cretaceous peri arabian and peri indian ophiolites which are discontinuously exposed along a c 9000 km long belt from sw anatolia to se tibet formed above a trans tethyan subduction accretion system within southern neotethys diachronous collisions of arabia and india with this intraoceanic subduction accretion system in the latest mesozoic and the paleogene respectively resulted in diachronous ophiolite emplacement in the mediterranean and tibetan himalayan orogenic belts thematic collection this article is part of the tethyan ophiolites and tethyan seaways collection available at https www lyellcollection org cc tethyan ophiolites and tethyan seaways

thermochronological constraints on the multiphase exhumation history of the ivrea verbano zone of the southern alps abstract the ivrea verbano zone of the western southern alps nw italy exposes a well preserved tilted section across the lower continental crust making it a key region for studying deep crustal and exhumation processes this paper refines the cooling and exhumation history of the ivrea verbano zone using k ar dating of mica and illite rich fault gouges as well as zircon fission track and u th he thermochronology the adjacent strona ceneri zone sesia lanzo zone and lower penninic nappes are included in the study to derive a broader picture of the low temperature history of the area in the strona profile of the ivrea verbano unit the biotite k ar zircon fission track and u th he geochronometers show well preserved but unusually wide partial retention zones the youngest ages representing the formerly deepest position are situated along the insubric line the main foliation of the ivrea verbano zone is vertical the exhumation of the ivrea verbano zone which section has a horizontal position on the surface now took place in three steps during jurassic time the ivrea verbano zone was exhumed to a shallow to mid crustal position by continental scale extension in this displacement the pogallo line probably played a dominant role the studied section occupied an oblique position with a calculated angle of ca 15 to 23 in the jurassic later the ivrea verbano zone experienced a minor cooling event in the late eocene 38 ma zircon fission track ages that was probably related to thrusting and erosion the final exhumation towards the surface took place in the mid miocene as documented by the ca 14 ma zircon u th he ages and a 12 8 ma k ar fault gouge age the magnitude and the high rate of final exhumation suggest orogen parallel extension as a driving force which is widespread in the alps in the lower to middle miocene and is most probably connected to orogenic collapse

mesozoic architecture of a tract of the european iberian continental margin insights from preserved submarine palaeotopography in the longobucco basin calabria southern italy abstract the sedimentary successions exposed in northeast calabria document the jurassic early cretaceous tectonic sedimentary evolution of a former segment of the european iberian continental margin they are juxtaposed today to units representing the deformation of the african and adriatic plates margins as a product of apenninic crustal shortening a complex pattern of unconformities reveals a multi stage tectonic evolution during the early jurassic which affected the facies and geometries of siliciclastic and carbonate successions deposited in syn and post rift environments ranging from fluvial to deep marine late sinemurian early pliensbachian normal faulting resulted in exposure of the hercynian basement at the sea floor which was onlapped by marine basin fill units shallow water carbonate aprons and reefs developed in response to the production of new accommodation space fringing the newborn islands which represent structural highs made of paleozoic crystalline and metamorphic rock their drowning and fragmentation in the toarcian led to the development of thin caps of rosso ammonitico facies coeval to these deposits a thick 1 km hemipelagic siliciclastic succession was sedimented in neighboring hanging wall basins which would ultimately merge with the structural high successions footwall blocks of the early jurassic rift made of paleozoic basement and basin margin border faults with their onlapping basin fill formations are found today at the hanging wall of miocene thrusts overlying younger middle late jurassic to late paleogene folded basinal sediments this paper makes use of selected case examples to describe the richly diverse set of features ranging from paleontology to sedimentology to structural geology which are associated with the field identification of basin margin unconformities our data provide key constraints for restoring the pre orogenic architecture of a continental margin facing a branch of the liguria piedmont ocean in the western tethys and for estimating displacements and slip rates along synsedimentary faults

the association of continental crust rocks with ophiolites in the northern apennines italy implications for the continent ocean transition in the western tethys abstract the late cretaceous sedimentary melanges from the external liguride units of the northern apennines include large slide blocks of ophiolites and lower and upper continental crust rocks representative of a continent ocean transition between the internal liguride oceanic domain and the thinned continental margin of the adria plate the slide blocks preserve a record of the long lived history of rifting which led to opening of the jurassic western tethys basin the external liguride ophiolites consist of 1 undepleted spinel peridoties partly re equilibrated under plagioclase facies conditions which were interpreted as unroofed subcontinental mantle 2 rare gabbroic rocks mainly troctolite to olivine bearing gabbro probably crystallised from n morb magmas and 3 basalts with n to t morb affinity covered by late callovian early oxfordian radiolarian cherts both gabbroic rocks and basalts locally intrude the mantle peridotites and postdate their re equilibration to plagioclase facies conditions the slide blocks of lower continental crust are composed of gabbro derived mafic granulites and felsic granulites the latter include quartzo feldspathic granulites and rare quartz poor to quartz free charnockitic rocks in both mafic and felsic granulites granulite facies re equilibration was followed by a retrograde metamorphic evolution to amphibolite greenschist and subgreenschist facies conditions retrogression is commonly accompanied by deformations progressively changing from plastic to brittle the upper crustal rocks occurring as slide blocks consist of hercynian granitoids with orogenic affinity mainly biotite bearing granodiorites and peraluminous two mica leucogranites locally the granitoids are intruded by basaltic dykes or capped by basaltic flows and radiolarian cherts the granitoids underwent polyphase brittle deformations under subgreenschist facies conditions which predated the basalt emplacement the tectono metamorphic evolution recorded by the slide blocks of the external liguride units started in the late carboniferous early permian about 290 ma with the emplacement at deep crustal levels of the gabbroic protoliths for the mafic granulites the associated felsic granulites likely represent the remnants of the lower continental crust intruded by the gabbro derived granulites mafic and felsic granulites subsequently underwent tectonic exhumation in permo triassic times as testified by the development of granulite to amphibolite facies ductile shear zones the granulites were finally exhumed to shallow levels probably in association with the subcontinental mantle in late triassic middle jurassic times the latter period was most likely characterized by extensive brittle faulting at shallow crustal levels thus giving rise to extensional allochthons formed by stretched slices of granitoids the western tethys opening is finally testified by the basalt intrusion and effusion in the late jurassic followed by deep sea pelagic sedimentation the external liguride crustal stratigraphy can be regarded as a fossil example of the transitional realm at the continent ocean boundary this reconstruction fits well with the available data on the present day continental margins derived from passive lithosphere stretching