strength of plate coupling in the southern ryukyu subduction zone abstract understanding the strength of a plate coupling is critical for assessing potential seismic and tsunamic hazards in subduction zones the interaction between an overriding plate and the associated subducting plate can be used to evaluate the strength of plate coupling by examining the mantle lithospheric buoyancy here we calculate the mantle lithosphere buoyancy across the northern portion of the southern ryukyu subduction zone based on gravity modeling with the constraints from a newly derived p wave seismic velocity model the result indicates that the strength of the plate coupling in the study area is relatively strong which is consistent with previous observations in the southernmost ryukyu subduction zone because few large earthquakes mw 7 have occurred in the southern ryukyu subduction zone a large amount of energy is locked and accumulated by plate coupling that could be released in the near future

the results of the taormina 2006 seismic survey possible implications for active tectonics in the messina straits abstract the straits of messina and its surroundings are considered as one of the most tectonically active area of the mediterranean but in spite of their hazard potential modern geophysical data aimed at investigating their hidden structures are lacking in order to bridge this gap we carried out a marine multichannel seismic survey primarily aimed at i studying the regional fault pattern in the area of the messina 1908 earthquake and ii checking the existence of a potentially seismogenic fault the taormina fault which many authors locate offshore along the coast between taormina and messina our seismic profiles show a great structural complexity within the messina straits with the best imaged faults occurring on the calabrian side in particular a more than 30 km long nw trending fault located at the sw tip of calabria is cutting the sea floor moreover our data did not image any extensional fault plane attributable to the taormina fault rather the whole slope has been tilted east ward the geodynamic implication is that extension in south eastern sicily on the ionian side of the hyblean plateau and extension in southern calabria and messina straits belong to two different tectonic systems and cannot be mechanically linked

lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone an example of decreasing plate coupling abstract the okinawa trough is a backarc basin located behind the ryukyu arc trench system the southernmost part of the okinawa trough spot displays different tectonic features from the rest of the okinawa trough the spot area includes abundant seamounts with active hydrothermal venting and high heat flow values to understand better the rifting and magmatism context of the spot area we examine the lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone the results show that beneath the spot area the continental crust and mantle lithosphere thickness of 25 30 and 120 km respectively are thick with little continental thinning the analysis of mantle lithosphere buoyancy across the southernmost ryukyu subduction zone shows strong plate coupling between the overriding and subducting plates however the two plates are actually decoupled as indicated by present day interface earthquakes this situation indicates that the southernmost ryukyu subduction zone displays a transitory case of a changing plate coupling from a strong to a weak plate coupling such a coupling decoupling transition is probably associated with the collision of the luzon arc with the asian continental margin additionally the curve of the mantle lithosphere buoyancy across the southernmost ryukyu subduction zone indicates that the submarine magmatism in the spot area is located within the volcanic arc area suggesting early arc magmatism in the spot area

temperature and density of the tyrrhenian lithosphere and slab and new interpretation of gravity field in the tyrrhenian basin abstract the gravity anomaly field of the tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the oligocene miocene they can resume in lithospheric thinning and asthenospheric rising beneath the tyrrhenian basin coexisting with the roll back subduction of the african plate margin westward sinking beneath the calabrian arc the geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects a model of the litho asthenospheric structure of this region is suggested showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro physical features of the mantle the first phase of this study consisted of the computation of the isotherms in the crust mantle system beneath the tyrrhenian basin and afterwards of the density distribution within the partially melted upwelling asthenosphere the second phase consisted of a temperature density modelling of the slab subducting beneath the calabrian arc finally a 21 2 interpretation of gravity data was carried out by including as constraints the results previously obtained thus the final result depicts a model matching both gravity thermal and petrographic data they provide a a better definition of the thermal regime of the passive mantle rise beneath the tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and b a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works

serpentinization of the fore arc mantle along the taiwan arc continent collision of the northern manila subduction zone inferred from gravity modeling abstract serpentinized peridotite in the fore arc has been observed in a number of subduction zones including the northern manila subduction zone which terminates northward in the taiwan arc continent collision how this zone of serpentinization changes northward from the subduction of thinned continental lithosphere to full arc continent collision in the taiwan orogeny is not well known in this paper we present 2 d gravity modeling along three p wave vp transects across the taiwan orogeny two of these transects were collected with ocean bottom seismometers these two transects provide good constraints on the velocity structure to the west of and on land southern taiwan conversion of vp to density in this area allows us to model the gravity anomaly with very little misfit along the subduction zone however the velocity models are poorly constrained in the upper mantle where an anomalous density unit has to be used in order to model the short wavelength gravity anomaly in this area a third transect across central taiwan that is derived from the taiger local tomography data provides good control on the crust and upper mantle vp structure that we use to place provide density constraints for modeling the gravity anomaly in this part of the collision zone in order to model the short wavelength gravity anomaly across the longitudinal valley and the southern longitudinal trough an anomalous density block is required beneath the fore arc region we interpret that the source of this anomalous density material could be serpentinized fore arc mantle similar to what is interpreted for the northern manila subduction zone farther south water released from the subduction of the extended crust of the continental margin results in the serpentinization of the fore arc area and may be driving the uplifting of the high pressure rocks

bathymetry of mariana trench arc system and formation of the challenger deep as a consequence of weak plate coupling 1 the challenger deep in the southernmost mariana trench western pacific ocean is the deepest point on the earth s surface 10 920 m below sea level its location within a subduction trench where one plate bends and descends below another is not surprising however why is it located in the southernmost mariana trench and not at its central part where the rate of subduction is higher where the lithosphere is the oldest and densest on the earth and where the subducted lithosphere pulling down is the longest in the earth 1000 km or more according to seismic tomography we suggest that although subduction rate and slab age generally control trench depth the width of the plate coupling zone is more important beneath the central marianas the subducted slab is attached to the upper plate along a 150 km wide surface that holds the shallow portion of the subducted plate nearly horizontal in spite of its great load and thus counters trench deepening in contrast along the south mariana trench the subducted length of the lithosphere is much shorter but its attachment to the upper plate is only along a relatively narrow 50 km wide surface in addition a tear in the slab beneath this region helps it to sink rapidly through the mantle and this combination of circumstances allows the slab to steepen and form the deepest trench on the earth in a wider perspective the interrelations shown here between trench deepening ridge shallowing slab steepening and forearc narrowing may shed light on other subduction zones located near edges of rapidly steepening slabs

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

lateral spreading phenomena and weathering processes from the tropea area calabria southern italy this paper describes the lateral spreading landslides the weathering processes and the hydrogeological risk patterns of the nw sector of monte poro calabria southern italy based on the development of a multidisciplinary research the tectonic uplift of the area combined with the litho structural features of the sedimentary deposits overlying the intensely weathered granitoid complex produces important gravitational phenomena characterized by lateral spreading kinematics the contact between deposits with a different behaviour together with the high slope energy related to the tectonic uplift processes is the main cause of widespread fracturing and disjoint of the lithologies associated with lateral spreading phenomena these phenomena are also testified by the various trenches and cracks characterized by a parallel orientation relatively to the main fluvial incisions measures of these deformations were obtained with a quantitative result by the use of interferometric stacking methods the experimental results confirm this morphological scenario characterized by strain values ranging between 20 and 25 mm year relatively to the landslides detected geomorphological analysis of the drainage basins in the study area indicates a juvenile stage of the stream networks this pattern is consistent with the high rate of tectonic uplift of the area hence the continuous rejuvenation of the stream networks and their low level of hierarchy these conditions of geomorphic equilibrium of the stream networks the widespread occurrence of geological instability in continuous evolution are the main causes of high hydrogeological risk conditions for this coastal area

superimposed cycles of composite marine terraces the example of cutro terrace calabria southern italy abstract marine terraces are a valuable archive of information in the reconstruction of uplift and sea level history of coastal areas especially when they can be correlated with specific highstands of the eustatic curve usually the correlation is based on the assumption that any morphological terrace is the result of a single sea level fluctuation however if the surface of a terrace is reoccupied during successive transgressions the result may be a single morphological terrace which has in fact been generated by several superimposed sea level fluctuations this study illustrates what type of stratigraphic architecture may be recorded in the deposits of such composite marine terraces focusing on identification and interpretation of discontinuity surfaces and facies analysis the examined example is the marine terrace of cutro the highest and most extensive of five terraces preserved in a step like sequence along the coast of the crotone peninsula calabria southern italy the sedimentary cover of the cutro marine terrace had generally been regarded as the result of a single sea level oscillation but stratigraphic analysis and correlation of several sections has enabled the recognition of three distinct transgressive regressive sequences these cycles display an overall shallowing trend from shelf deposits represented in the first cycle by algal carbonate buildups to shoreface and alluvial deposits in the younger cycles the succession is now interpreted as a response to high frequency sea level fluctuations occurring during a long term interglacial such as those documented during marine isotope stage mis 7

propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy the rollback of a segmented slab of oceanic lithosphere is typically accompanied by vertical lithospheric tear fault s along the lateral slab edge s and by strike slip movement in the upper plate defined as a step fault subduction tear edge propagator the neogene evolution of the central mediterranean is dominated by the interaction between the slow africa eurasia convergence and the se ward rollback of the ionian slab that leads to the back arc opening of the tyrrhenian sea here we present post stack time migrated and pre stack depth migrated archimede 1997 multichannel seismic lines that were acquired offshore eastern sicily at the foot of the malta escarpment first we identify the recent deformation along the lateral ramp of the calabrian accretionary wedge towards the east the calabrian wedge is formed by the accretion of the post evaporitic sediments above a decollement at the base of the messinian evaporites at the latitude of syracuse 50 km east of the malta escarpment a major n150 degrees e trending crustal scale and vertical fault slices through the entire accretionary wedge this fault cuts by several kilometers through the pre evaporitic messinian sediments and into the basement the vertical offset along this vertical fault decreases from north to south and the fault is no longer observed on the seismic lines 50 km se of the alfeo seamount a previously published moho depth isocontour map offshore sicily and the recent gps data combined with the presence of strike slip movements ne onshore sicily allow us to identify this 200 km long crustal scale fault as the surface expression of a step fault the presence of syntectonic pleistocene sediments on top this crustal scale fault suggests a recent lithospheric vertical movement of the step fault in response to the rollback of the ionian slab and to the se ward advance of the calabria peloritan block

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

holocene tectonic uplift patterns in northeastern sicily evidence from marine notches in coastal outcrops abstract marine notches are groove like features formed in rocky coastal outcrops in relation to past sea levels and are widely used as indicators of rates and patterns of tectonic activity examination of uplifted notches in the complex plate boundary setting of northeast sicily reveals the need for considerable care in their interpretation present notch forming processes are dominated by carbonate dissolution aided by microbial activity as waves surge and recede at the base of the cliffs and produce notches approximately 0 5 m above present biological mean sea level i e above an organic constructional rim of coralline algae used to define sea level at sea level dissolution is restricted through saturation and the bedrock protected by the outbuilding algal rim this assemblage varies in response to fetch exposure and uplift rate typically producing a complex band of uplifted notch features exposed above sea level correlations based on height of the shallow and discontinuous notch indentations within this band are unreliable however the upper margin of the band marked by the roof of the uppermost notch is a prominent and laterally persistent feature easily recognised as the boundary between subaerial and marine processes we propose that this is an approximately coeval datum formed when post glacial sea level rise decelerated in the mid holocene to match the rate of tectonic uplift a notion strengthened by the available dates of about 5 ka for this feature subsequent uplift outpaced later sea level rise taking the notches above sea level this proposed datum varies in height from about 2 m at capo milazzo on the north coast to about 5 m on the east coast bordered by the messina fault system the height differential is consistent with the respective elevations of nearby marine terraces dating from the last interglacial at about 125 ka but also exhibits shorter term variations suggesting holocene increases in activity rates on more localised structures affecting the localities involved regionally northeast sicily is characterised by long term differential uplift rather than behaving as a coherent block the highest uplift rate probably exceeding 2 mm a 1 calculated using the sea level curve from fairbanks r g 1989 a 17000 year glacio eustatic sea level record influence of glacial melting rates on the younger dryas event and deep ocean circulation nature 342 637 642 is suggested for a notch locality on the upthrown side of the malta escarpment rates of about 2 mm a 1 are indicated by the 5 m notch at localities bordered by the messina fault system and a rate close to 1 mm a 1 is suggested for the undated 2 m notch at capo milazzo

evolution of the grenada and tobago basins and implications for arc migration abstract the tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood this paper presents an integrated stratigraphic and tectonic evolution of late cretaceous to recent volcanic arcs and associated basins in the southeastern caribbean sea using seismic reflection data wide angle seismic refraction data well data and onland geologic data we propose a new tectonic model for the opening of the grenada and tobago basins and the 50 250 km eastward jump of arc volcanism from the late cretaceous aves ridge to the miocene to recent lesser antilles arc in the southeast caribbean based on the mapping of three seismic megasequences the striking similarity of the half graben structure of the grenada and tobago basins that flank the lesser antilles arc their similar smooth basement character their similar deep marine seismic facies and their similar paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single saucer shaped oceanic crust paleogene forearc basin adjacent to the now dormant aves ridge this single forearc basin continued to extend and widen through flexural subsidence during the early to middle eocene probably because of slow rollback of the subducting atlantic oceanic slab rollback may have been accelerated by oblique collision of the southern aves ridge and southern lesser antilles arc with the south american continent uplift and growth of the southern lesser antilles arc divided the grenada and tobago basins by early to middle miocene time inversion of normal faults and uplift effects along both edges of the lesser antilles arc are most pronounced in its southern zone of arc collision with the south american continent the late miocene to recent depositional histories of the grenada and tobago basins are distinct because of isolation of the grenada basin by growth and uplift of the neogene lesser antilles volcanic ridge

regional deformation and offshore crustal local faulting as combined processes to explain uplift through time constrained by investigating differentially uplifted late quaternary palaeoshorelines the foreland hyblean plateau se sicily

tomographic evidence of slab detachment beneath eastern turkey and the caucasus summary teleseismic phase readings from the eastern turkey seismic experiment etse have been inverted using teleseismic tomography in order to create a 3 d image of the underlying mantle beneath eastern turkey the aim was to investigate the existence of an upper mantle negative velocity anomaly that is used to explain the uplift of eastern anatolian plateau and the potential pieces of detached oceanic slabs related to neo tethyan subduction suggested by previous studies using teleseismic waveforms from the 29 stations of the eastern turkey seismic experiment 2926 direct p phases from 146 events were picked by using adaptive stacking techniques in order to increase the station coverage and resolve the surrounding area the phase readings from the international seismological center isc bulletin have also been added the data set consists of 9571 p and pkp phase readings of 79 stations from 503 teleseismic events this study develops the first highresolution 3 d upper mantle p wave tomographic model for this region the tomographic results show the existence of an upper mantle negative velocity anomaly to a depth of 200 km beneath the eastern anatolian accreationary complex eaac as commonly observed in the previous studies that suggest a shallow partially molten asthenosphere the slab like high velocity anomalies beneath the eaac pontides and caucasus are interpreted as the detached southern and northern neo tethys slabs

plate detachment asthenosphere upwelling and topography across subduction zones this study analyzes the topography across subduction zones considering the separate contributions of the crust and the mantle lithosphere to the observed surface elevation we have found a transition from a region where the overriding plate is coupled to the descending slab and pulled down along with it to a region where the overriding plate floats freely on the asthenosphere when the subducting slab retreats oceanward rapidly this transition is abrupt and the edge of the overriding plate is uplifted we propose that at some point during rapid slab rollback the overriding plate detaches and rebounds like a boat released from its keel this event is associated with suction of asthenospheric material into the gap that is opened between the plates up to the base of the crust as a result the forearc uplifts and magmatism in the arc increases

new structural and seismological evidence and interpretation of a lithospheric scale shear zone at the southern edge of the ionian subduction system central eastern sicily italy we performed an integrative analysis of geological gravimetric and seismological data analyzed data depicted a not well known wrench zone in the central eastern sicily our findings enabled us to interpret this shear zone as a plio pleistocene step fault

mesozoic to recent evolution of intraplate stress fields under multiple remote stresses the case of signy island south orkney microcontinent antarctica abstract palaeostresses inferred from approximately 3200 brittle mesostructures measured at 43 sites in signy island show a stress field characterized by compressional strike slip and extensional stress states there is a dominant nw se horizontal compression direction as well as three nnw sse wnw ese and ene wsw secondary 1 horizontal stress directions orientation of 3 shows a main mode trending nw se together with secondary north south and ne sw extensional stress directions the nnw sse horizontal compression is consistent with the stretching shearing direction defined from the fold axis trend this is owing to a subduction related tectonic regime during early to middle jurassic times in middle jurassic early cretaceous times the tectonic regime changes to extensional with north south extensional stress directions the early processes of subduction of the northern sector of the weddell sea oceanic crust below the south orkney microcontinent from the paleocene until the middle miocene is related to the 1 direction wnw ese to nw se the spreading of powell basin took place from the late eocene to the early miocene and is the cause of east west and ne sw extensional processes in the southern south orkney microcontinent finally the nw se 3 direction is related to the current left lateral strike slip movement between the scotia and antarctic plates

southwestward weakening of wyoming lithosphere during the laramide orogeny the mechanism of laramide deformation in the central rocky mountains remains enigmatic it is generally agreed that the deformation resulted from low angle subduction of the farallon plate beneath the north american plate during the latest cretaceous early eocene however recent studies have suggested the importance of slab removal or slab rollback in causing this deformation here we infer wyoming lithosphere structure and surface deformation pattern by conducting 2 d flexural subsidence modeling in order to provide constraints on the mechanism of laramide deformation we assume that wyoming lithosphere behaved as an infinite elastic plate subject to tectonic loading of mountain ranges and conduct 2 d flexural subsidence modeling to major laramide basins to document lithospheric stiffness and mountain load height our results show that the stiffness of wyoming lithosphere varied slightly in each basin during the 30 myr duration of the laramide deformation and decreased from northeastern wyoming te 32 46 km to southwestern wyoming te 6 9 km our results also imply that the increase of equivalent load height of major laramide ranges accelerated during the early eocene we propose that the bending stresses induced by the topographic load of the sevier fold and thrust belt combined with crust mantle decoupling initiated by the overthickened sevier hinterland and the end loads due to the low angle subduction at the western edge of the thick wyoming craton have caused the southwestward decrease of lithospheric stiffness in wyoming moreover we attribute the accelerated load height gain during the early eocene to both dynamic and isostatic effects associated with slab rollback

thermal constriction and slab tearing at the origin of a superinflated spreading ridge marsili volcano tyrrhenian sea 1 recently acquired swath bathymetry of the marsili basin has offered an unprecedented opportunity to study the processes of back arc ocean basin development in the tyrrhenian sea in particular the detailed morphology of marsili seamount a large strongly elongated volcano located in an axial position within the 2 ma ocean crust floored marsili basin is a key to understanding the mechanisms governing lithosphere formation in this young basin the basin is near circular in shape with diameter on the order of 120 km and is positioned in the southern tyrrhenian sea above the steeply dipping ionian oceanic slab of mesozoic age it is bounded southward by the aeolian volcanic arc and the calabrian accretionary wedge surface evidence of the northwesterly directed subduction the most outstanding feature of the basin is the elongated 3000 m high marsili volcano which reveals distinctive morphology strikingly akin to the high order segmentation and volcanic landforms described in mid ocean slow spreading ridges on the basis of its distinctive morphology and incremental growth relationship we propose that marsili volcano represents a superinflated spreading ridge resulting from a distinct thermal pulse of increased melt production occurring within the young and immature marsili basin surrounding cooler continental lithosphere thermally constricts ridge propagation and crust production in marsili basin to the finite scale of marsili volcano increased melt production to feed the superinflated marsili ridge is generated by deep lateral asthenospheric mantle flow produced at the edges of tears that bound the subducting ocean crust of the ionian plate slow spreading plate separation outpaced by the increase in magma generation results in vertical accretion to produce the superinflated ridge the existence of dip directed tears delimiting the narrow ionian slab is supported by the geological evolution of the surrounding foreland and apennine maghrebid mountain belt during early middle pleistocene i e the time of formation of the marsili volcano present day structure and volcanism furnish direct and indirect surface evidence of the presence and location of the slab tears

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

chronology of the middle upper pliocene succession in the strongoli area constraints on the geological evolution of the crotone basin southern italy the aim of this study is to reconstruct the evolution of the strongoli area a critical sector of the crotone basin calabria southern italy where a thick middle upper pliocene marine succession is present the strongoli succession shows prominent changes in the sedimentary environment that are partly forced by tectonics major tectonostratigraphic events have been recognized that might correlate with spreading pulses in the back arc tyrrhenian sea in particular we demonstrate that a dramatic basinal collapse at c 2 3 ma correlates with the so called calabrian transgression auctorum and is close in age to the oceanization of the marsili basin

mantle wedge dynamics versus crustal seismicity in the apennines italy 1 in the apennines subduction italy earthquakes mainly occur within the overriding plate along the chain axis the events concentrate in the upper 15 km of the crust above the mantle wedge and focal solutions indicate normal faulting in the foreland the seismogenic volume affects the upper 35 km of the crust focal solutions indicate prevailing reverse faulting in the northern foreland and strike slip faulting in the southern one the deepening of the seismogenic volume from the chain axis to the foreland follows the deepening of the moho and isotherms the seismicity above the mantle wedge is associated with uplift of the chain axial zone volcanism high co2 flux and extension the upward pushing of the asthenospheric mantle and the mantle derived co2 rich fluids trapped within the crust below the chain axis causes this seismicity all these features indicate that the axial zone of apennines is affected by early rifting processes in northern italy the widespread and deeper seismicity in the foreland reflects active accretion processes in the southern foreland the observed dextral strike slip faulting and the lack of reverse focal solutions suggest that accretion processes are not active at present in our interpretation of the apennines subduction the shallower seismicity of the overriding plate is due to the dynamics uprising and eastward migration of the asthenospheric wedge

early cretaceous tectonomagmatic evolution and basin development of western bangong nujiang suture a complete history of soft collision abstract uncertainty surrounding the early cretaceous tectonomagmatic evolution and basin development of the bangong nujiang suture zone bnsz limits understanding of the history of meso tethys ocean and the initial uplift and large scale metallogenesis of the tibetan plateau during the mesozoic here we present new geochronological geochemical and isotopic data for the early cretaceous volcano intrusive rocks including quartz diorites tholeiitic andesites and bajaitic latites around the western segment of the bnsz w bnsz we also report an early cretaceous deep water volcano stratigraphic section newly identified in this region based on these new data and information available for the bnsz we propose that the w bnsz and surrounding regions had already entered a stage of soft collisional land locked basin evolution during the early cretaceous the land locked basin underwent limited uplift related to the initial soft collision during the earliest early cretaceous resulting in the formation of a regional unconformity between shamuluo formation shallow marine sedimentary rocks and underlying ophiolitic melange subsequently the basin experienced continuous subsidence related to sinking and rollback of the bangong oceanic slab leading to the occurrence of deep water flysch deposits e g the zhaga formation the bangong oceanic slab was completely detached from the overlying soft collision zone at ca 113 ma resulting in the strong isostatic uplift of the whole soft collision zone consequently seawater receded from w bnsz and surrounding regions during the late early cretaceous late cretaceous our study also shows that the western segment of the south qiangtang terrane experienced long lived intermediate magmatism 130 104 ma under this soft collision regime intermediate magmas of this age originated from partial melting of juvenile lower crust fractional crystallization of mantle derived mafic magmas and partial melting of metasomatized mantle wedge peridotites and these processes were driven by the break off rollback and complete detachment of the bangong oceanic slab respectively

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

slab behaviour and its surface expression new insights from gravity modelling in the se carpathians abstract we use lithosphere scale gravity models to calculate gravity anomalies resulting from oceanic subduction continental collision slab steepening delamination and break off local isostasy was assumed for determining vertical movements caused by mass changes related to these tectonic processes our results show that subduction is accompanied by basin subsidence on the upper plate caused by the heavy lithospheric root of the subducting slab the basin evolution goes parallel with the slab evolution and shows considerable modifications when the processes at depth change slab steepening delamination break off characteristic gravity anomaly curves were acquired for the different tectonic scenarios these curves together with other data e g basin evolution on the upper and the lower plate were used for the reconstruction of the tectonic evolution of the se carpathians which includes tertiary subduction and collision followed by slab steepening and delamination

paleogeographic record of eocene farallon slab rollback beneath western north america eocene terrestrial strata in western north america are now dated with sufficient precision to examine the hypothesis that rollback of the farallon flat slab created a trenchward migrating wave of dynamic and thermal topography we use patterns of accumulation and unconformity lake type stratigraphy and physical and isotopic provenance tools to track its migration across the laramide foreland between 53 ma and 47 ma hydrologic ponding and coincident unconformity development began at 53 ma culminating at 51 8 ma in the hydrologic closure of an 900 000 km2 area between the cordilleran and rocky mountain divides four subsequent stream diversions and a southwest expanding regional unconformity record trenchward migration of uplift from 50 to 47 ma volcaniclastic detritus from magmatic centers coincident with the uplifted region progressively filled the green river formation lakes from north to south these findings are consistent with recent numerical and conceptual models of slab rollback that predict initial dynamic subsidence above the slab hinge followed by uplift and volcanism triggered by influx of asthenosphere beneath the overriding plate based on the surface record rollback proceeded systematically at a rate of 6 cm yr across the wyoming craton from 53 to 47 ma resulting in removal of the entire shatsky conjugate oceanic plateau from the base of the north american lithosphere

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

why is the challenger deep so deep abstract recent sidescan surveys of the deepest segment of the southern mariana trench in the western pacific ocean provide the first detailed images of this plate boundary which includes the world s greatest ocean depth the challenger deep the surveys reveal details of the southern mariana plate margin identify another deep rivaling the challenger and document widespread deformation of the overriding plate our data show a subduction generated deep ocean trench not the transform fault boundary suggested by other work d e karig geol soc am bull 82 1971 323 344 d e karig et al j geophys res 83 1978 1213 1226 d e karig b ranken in the tectonic and geologic evolution of southeast asian seas and islands part 2 american geophysical union washington dc 1983 pp 266 280 k fujioka et al geophys res lett 19 2002 1 4 we present the geological characteristics of the region including seismic evidence for a tear in the subducting plate that has influenced the deformation of the overriding plate the rollback caused by this tear creates greater depths along the southern part of the trench than elsewhere along its length

three dimensional visualization of a near vertical slab tear beneath the southern mariana arc the use of a three dimensional ray tracing inversion algorithm has greatly enhanced the resolution of gradients and strong variations in wave speeds to create improved p wave tomographic images of the mariana arc region the images obtained from the mariana arc region show relatively low amplitudes of heterogeneity due to the limited number of seismic stations in the area despite these limitations detailed interpretations of the three dimensional geometry and morphology of the pacific plate subducting beneath the philippine sea plate have provided a three dimensional model of the steep dip of the pacific plate and the curvature of the slab beneath the mariana arc in unprecedented detail the new p wave tomography and seismicity depict a previously unidentified e w trending near vertical tear in the subducting plate at the southern end of the mariana arc that divides the arc into two distinct segments a steeply dipping curved slab penetrating the lower mantle and a short 250 km depth slab along the challenger deep segment of the arc the slab tear is likely to be the result of the need to accommodate the reduced volume the slab must occupy as it is subducted beneath the philippine sea plate along a curved arc

evolution of the southern tyrrhenian slab tear and active tectonics along the western edge of the tyrrhenian subducted slab abstract the evolution of the southern tyrrhenian subduction has been possibly controlled by distinct episodes of slab break off as indicated by a critical review of the geological literature and by the analysis of purposely acquired multichannel seismic profiles within the proposed interpretation the first episode occurred from 8 5 to 4 0 ma and affected the segment of the slab located in the sardinia channel causing the abandonment of the adventure thrust front in western sicily the second episode occurred between 2 5 and 1 6 ma affecting the segment of slab located north of sicily and was preceeded by rifting in the strait of sicily the space and time location of these episodes appear controlled by discontinuities pre existing within the subducted african plate that trend at high angle to the advancing subduction front these discontinuities delimit segment of subducted slab that can be affected by slab break off and can act as wayouts for magma and mantle derived he the major of these discontinuities the malta escarpment has been reactivated in the quaternary as a trench perpendicular tear step faults ultimately the hierarchy in strength of these trench perpendicular features could have affected the timing and amount of trench retreat and backarc opening

a thermomechanical model of exhumation of high pressure hp and ultra high pressure uhp metamorphic rocks in alpine type collision belts using a fully coupled numerical thermomechanical model handling strain localization surface processes and ultra high viscosity contrasts 11 orders of magnitude we test a number of possible mechanisms of high pressure hp low temperature lt high temperature ht exhumation in continental collision zones the model considers two end member cases low or high buoyancy of the downgoing crust the first model case predicts three levels of exhumation in the same collisional context the classical corner flow lp lt low pressure low temperature exhumation in the accretionary prism deeper 70 km hp ht exhumation for the thickened subducting crustal sedimentary wedge and ultra hp ht exhumation from the lower crustal chamber forming at the depth of 100 120 km and separated from the upper one by a narrow crustal channel the width of this channel can oscillate in the process of shortening thus controlling the quantity of the crustal material exchanged between the crustal wedge and the lower crustal chamber although both zones of crustal accumulation and the narrow channel between them resemble a vortex shaped nozzle this nozzle appears to be too soft to produce any significant overpressures from the upper crustal wedge the material is exhumed following the ascending shear flow created by the overriding plate assisted by positive buoyancy of the heated crustal material from the lower crustal chamber the material is transported upward to the upper crustal wedge by a flow induced by the asthenospheric traction and a small scale convective instability forming in the lower crustal chamber due to its heating by the overriding asthenosphere in the second modelled case of high buoyancy the latter mechanisms become dominant resulting in hyper fast exhumation of the crust to the surface accelerated or slowed subduction in case of full or partial crustal decoupling respectively and upper plate extension d 2001 elsevier science b v all rights reserved

petrogenesis and metallogenesis of the yaxi gabbroic intrusion associated with fe ti v p ores in eastern tianshan nw china abstract an fe ti v p ore deposit hosted by the yaxi layered gabbroic intrusion was recently discovered in eastern tianshan of the central asian orogenic belt caob the yaxi intrusion is composed of interlayered leucogabbro and melagabbro and the fe ti v p ore layers are mainly hosted at the bottom of the melagabbro layers we have studied the geology petrology mineralogy and geochemistry of the yaxi gabbroic rocks and associated ore igneous zircons separated from a gabbro sample yield a sims u pb age of 308 7 1 4 ma indicating that the yaxi ore bearing intrusion was emplaced during the late carboniferous postcollisional stage the yaxi gabbroic intrusion is characterized by enrichment in large ion lithophile elements and depletion of high field strength elements positive zircon ehf t values 2 5 to 11 5 positive end t values 1 69 to 4 02 low initial 87sr 86sr ratios 0 7054 to 0 7061 and low initial 206pb 204pb ratios 17 1 to 18 2 these results suggest that the parental magma was produced by interactions between metasomatized lithospheric mantle and depleted asthenospheric melts at the early postcollisional stage the parental magma experienced extensive fractional crystallization in a deep magma chamber becoming oxidized and enriched in metallogenic elements and volatiles during emplacement extensive crystallization and accumulation of plagioclase from the highly evolved parental magma caused metallogenic elements and volatiles to become further enriched in the residual melts leading to fe ti v p mineralization therefore the yaxi fe ti v p ore deposit benefited from extensive fractional crystallization in a deep magma chamber and accumulation of plagioclase during emplacement

geochemistry and tectonic implications of the early carboniferous keketuobie intrusion in the west junggar foldbelt nw china abstract the keketuobie intrusion is situated in the northern part of the west junggar foldbelt at the southern margin of the central asian orogeic belt the intrusion consists of medium to coarse grained gabbro fine grained gabbro and diorite igneous zircons from the medium to coarse grained gabbro yielded a la icp ms u pb age of 320 8 5 7 ma indicating that the intrusion was emplaced in the early carboniferous the intrusive contact between the medium to coarse grained gabbro and the fine grained gabbro indicates they formed from distinct magma pulses magnetite crystals from the fine grained gabbro have lower v 2 o 3 but higher tio 2 and al 2 o 3 contents than those of the medium to coarse grained gabbro suggesting that the fine grained gabbro crystallized in a relatively higher fo 2 and temperature magma than the medium to coarse grained gabbro the keketuobie intrusive rocks are characterized by enriched large ion lithophile elements and depleted high field strength elements relative to n morb with restricted 87 sr 86 sr t ratios 0 70370 0 70400 and end t values 5 85 to 6 97 the petrography and geochemistry are comparable to those of subduction related volcanic rocks the trace elements and isotopic compositions of the mafic intrusive rocks suggest that the primary magmas were derived from mixing of metasomatized lithospheric mantle and depleted asthenospheric melts perhaps triggered by slab break off the keketuobie intrusion is younger than adjacent ophiolite sequences island arc volcanic rocks and porphyry deposits but predates the post collisional a type granites and bimodal volcanic rocks in the district suggesting that the keketuobie intrusion likely formed in a syn collisional setting

distinguishing between tectonic and lithologic controls on bedrock channel longitudinal profiles using cosmogenic 10be erosion rates and channel steepness index abstract knickpoints in fluvial channel longitudinal profiles and channel steepness index values derived from digital elevation data can be used to detect tectonic structures and infer spatial patterns of uplift however changes in lithologic resistance to channel incision can also influence the morphology of longitudinal profiles we compare the spatial patterns of both channel steepness index and cosmogenic 10be determined erosion rates from four landscapes in italy where the geology and tectonics are well constrained to four theoretical predictions of channel morphologies which can be interpreted as the result of primarily tectonic or lithologic controls these data indicate that longitudinal profile forms controlled by unsteady or nonuniform tectonics can be distinguished from those controlled by nonuniform lithologic resistance in each landscape the distribution of channel steepness index and erosion rates is consistent with model predictions and demonstrates that cosmogenic nuclide methods can be applied to distinguish between these two controlling factors

isostasy flexure and dynamic topography abstract a fundamental scientific question is what controls the earth s topography although the theoretical principles of isostasy flexure and dynamic topography are widely discussed the parameters needed to apply these principles are frequently not available isostatic factors controlling lithospheric buoyancy are frequently uncertain and non isostatic factors such as lithospheric bending towards subduction zones and dynamic topography are hard to distinguish the question discussed here is whether a set of simple rules that relate topography to lithospheric structure in various tectonic environments can be deduced in a way that missing parameters can be approximated or does each area behave differently making generalizations problematic we contribute to this issue analyzing the asia africa arabia europe domain following a top down strategy we compile a new crustal thickness map and remove the contribution of the crust from the observed elevation then the challenge is to interpret the residual topography in terms of mantle lithosphere buoyancy and dynamics based on systematic relationships between tectonic environments and factors controlling topography we argue that crustal buoyancy and mantle lithospheric density can be approximated from available geological data and that regions near mantle upwelling or downwelling are easily identified by their extreme residual topography yet even for other areas calculating lithospheric thickness from residual topography is problematic because distinguishing variations in mantle lithosphere thickness from sub lithospheric dynamics is difficult fortunately the area studied here provides an opportunity to examine this issue based on the conjunction between the afar plume and the mid ocean ridge in the nearby gulf of aden and southern red sea we constrain the maximal amplitude of dynamic topography to 1 km this estimate is based on a narrow definition of dynamic topography that only includes sub lithospheric processes and using mid ocean ridges as reference where mantle lithosphere buoyancy is zero