the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

mid to late holocene coastal environmental changes in southwest florida usa during the holocene florida experienced major changes in precipitation and runoff to better understand these processes shallow marine sediment cores from charlotte harbor southwest florida were studied covering approximately the past 9000 years whole core xrf scanning was applied to correlate different sediment cores on a river to sea transect biomarkers were used to identify periods with increased runoff and primary productivity the mid holocene sediments are characterized by a relatively large input of terrestrially derived organic matter with a maximum in precipitation and runoff around 5 kyr bp this maximum can be linked to large scale changes in the hydrological cycle involving shifts of the itcz bermuda azores high and polar front around 3 5 kyr bp charlotte harbor changed from a runoff dominated environment to a more oligotrophic and marine setting although other studies suggest that around this time precipitation in florida increased this is not reflected by the charlotte harbor

precipitates of α cristobalite and silicate glass in uhp clinopyroxene from a bohemian massif eclogite

the mw 5 4 reggio emilia 1996 earthquake active compressional tectonics in the po plain italy summary we have analysed the seismic sequence that occurred in october 1996 near the town of reggio emilia on the southern edge of the po plain the onset of the sequence was marked by a 5 4 moment magnitude main shock located at 15 km depth the main shock focal mechanism is a reverse solution with a strike slip component and the scalar moment is 1 46 1017 n m we used broad band digital recordings from a borehole station located at about 70 km from the epicentre for a spectral analysis in order to estimate attenuation and source parameters for the main shock in addition the empirical green s function method has been applied to evaluate the source time function in terms of both moment rate and stress rate we infer an asperity like rupture process for the main shock as suggested by the short duration of the stress release with respect to the overall duration of the moment rate function this analysis also allows us to estimate the average dynamic stress drop of the main shock 600 bar we analysed the digital recordings of the temporary local seismic network deployed after the main shock and of a permanent local network maintained by the italian petroleum agency agip during 15 days of field experiments we recorded more than 800 aftershocks which delineate a 9 km long ne elongated distribution confined between 12 and 15 km depth suggesting that the basement is involved in the deformation processes 102 focal mechanism of aftershocks have been computed from p wave polarities showing mainly pure reverse solutions we calculate the principal stress axes from a selected population of earthquakes providing a constraint on the stress regime of this part of the po plain the focal mechanisms are consistent with a n s subhorizontal 1 all the seismological data we have analysed confirm that this region is undergoing active compressional tectonics as already inferred from recent earthquakes geomorphological data and other stress indicators moreover the elongation of the reggio emilia aftershock sequence is consistent with the regional direction of the thrust fronts cropping out in the area suggesting that they are still active

fold fault relationships in low angle detachment systems a close kinematic and timing relationship between low angle extensional faulting and upright to moderately inclined folding with fold axes parallel to the extension direction is established for two well exposed neogene detachment systems in the simplon region of the alps and in the death valley region of california fold amplitude is largest in the oldest mylonitic foliation of the footwall these folds are transected by younger mylonitic foliation s and cataclastic detachment faults which are themselves folded about similar axes in general the amplitude decreases and the wavelength increases for progressively younger fold structures consistent with a history of progressive folding during faulting the interplay between folding and faulting in the footwall reflects a component of shortening perpendicular to fold axial surfaces during extension parallel to fold axes this strain pattern can develop in regions with a transcurrent component or during lateral extrusion and does not necessarily require overall crustal thinning

when did the northern apennine become a mountain chain abstract the purpose of the present paper is to bracket the age of the initial uplift of the northern apennine chain by means of all the available evidence the collected data show that the age of the lacustrine or fluvio lacustrine units which have aggraded in the intramontane basins is late pliocene in the northwestern tip of the northern apennine and mostly early pleistocene elsewhere the age of the oldest terraced fluvial deposits showing the initiation of incision is mostly middle pleistocene the uplift of the summit areas of low relief most likely took place during the middle pleistocene it is concluded that the uplift occurring during middle and upper pleistocene caused an area of rather low relief to become the northern apennine mountain chain an eastward shift of the uplift through time is likely

an integrated analysis of transverse structures in the northern apennines italy abstract the northern apennines have been the object of numerous studies both from a morphological and a structural point of view at present much debate is going on about the existence and interpretation of ne sw alignments described by geomorphologists boccaletti m coli m napoleone g 1977 nuovi allineamenti strutturali da immagini landsat e rapporti con l attivita sismica negli appennini boll soc geol it 96 679 694 signorini r 1953 linee tettoniche trasversali nell appennino settentrionale rend acc naz lincei 6 42 45 and partly denied by structural geologists we show new microtectonic and morphological data which contribute to a more comprehensive interpretation of these elements stress axis determination and different morphotectonic analyses have been combined the analysis of the drainage networks and of two different digital elevation models have also been considered the results lead us to interpret the ne sw alignments as large and diffuse deformation zones which may represent old transfer zones active with left lateral strike slip movements during the mountain building

study of plate deformation and stress in subduction processes using two dimensional numerical models two dimensional finite element modeling is used to model subduction of an oceanic lithospheric plate beneath continental lithosphere the subduction process is initiated along a preexisting inclined fault and continues until reaching 400 km of total convergence the lithosphere is assumed to be underlain by an in viscid asthenosphere different rheological laws have been considered for the lithosphere including elasticity and elastoplasticity the modeling shows that both the stress system in the plates and the surface topography are strongly dependent on two main parameters the density contrast between lithosphere and asthenosphere l a and the coefficient of friction along the subduction plane varying these two parameters allows explanation of the main characteristics of real subduction zones and results in two major regimes manifested by extension or compression in the arc back arc system extension and back arc rifting corresponds to a positive density contrast and a low coefficient of friction while negative values and or high friction leads to a compressional regime the coexistence of trench arc compression and back arc tension is only possible for a coefficient of friction lower than 0 1 the results of the numerical experiments agree with those of experimental modeling conducted under similar physical assumptions

crustal structure of the north iberian continental margin from seismic refraction wide angle reflection profiles abstract the structure and geodynamics of the southern margin of the bay of biscay have been investigated from a set of 11 multichannel seismic reflection profiles recorded also at wide angle offsets in an onshore offshore network of 24 obs obh and 46 land sites this contribution focuses on the analysis of the wide angle reflection refraction data along representative profiles the results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the iberian peninsula offshore the crust has a typical continental structure in the eastern tip of the bay which disappears smoothly towards the nw to reach crustal thickness close to 10 km at the edge of the studied area 45 n 6 w the analysis of the velocity depth profiles altogether with additional information provided by the multichannel seismic data and magnetic surveys led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic typical oceanic crust has not been imaged in the investigated area onshore the new results are in good agreement with previous results and document the indentation of the bay of biscay crust into the iberian crust forcing its subduction to the north the interpreted profiles show that the extent of the southward indentation is not uniform with an alpine root less developed in the central and western sector of the basque cantabrian basin n s to ne sw transfer structures seem to control those variations in the indentation degree

computer simulations of alaskan neotectonics ongoing deformation and fault slip neotectonics in the alaskan bering sea region were modeled with thin plate finite element methods by computing anelastic strain rate stress and velocity fields which represent time averages over several seismic cycles models included variable crust and lithosphere thickness heat flow and elevation and incorporated all faults known or thought to be active three sets of experiments totaling 46 models were computed with systematic variations of shear traction on the megathrust fault friction within north america internal friction of lithospheric blocks and mantle creep strength model quality was scored by comparing predictions to geologic data on fault slip rates the most compressive horizontal principal stress direction and geodimeter and very long baseline interferometry vlbi baseline rates best results were obtained with a driving traction of only 10 15 mpa on the aleutian megathrust and fault friction of only 0 17 within north america this is clearly a low stress model the fanning of away from the syntaxis was reproduced but does not imply high deviatoric stress magnitudes within the north american plate the aleutian forearc west of kodiak island moves westward along strike at rates which increase to 65 mm yr 1 in the komandorsky region however no crust is presently escaping westward from the alaskan syntaxis instead it is shortened and stacked by thrusting principally in the vicinity of the chugach and wrangell mountains because stresses in this model are low and are delicately balanced against topography it is likely that the present regime represents a transient response to plio pleistocene glacial mass redistribution and differs from typical tectonic flow in the tertiary

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

belt bending driven by lateral bending of subducting lithospheric slab geophysical evidences from the northern apennines italy abstract many of the mountain belts displaying a curved shape are oroclines i e are produced after progressive bending of an originally straight fold and thrust belt the bending process was previously explained as a consequence of several possible events taking place in the crustal orogenic wedge such as occurrence of obstacles non coaxial deformation and movements on wrench faults recent paleomagnetic results from the northern apenninic arc document that this belt is properly an orocline and results from late messinian early pliocene bending of a messinian straight belt foredeep system tomographic images in turn show the presence of a high velocity body interpreted as subducted slab in the upper mantle beneath the northern apennines between 35 and 670 km depth down to 100 km this body displays an arcuate shape which closely mirrors the geological outlines while it appears to be straight and parallel to the messinian pre rotated belt at depth we explore here the possibility that the arcuate shape of the northern apennines is a consequence closely following in time of much deeper processes than previously suggested i e the lateral bending of the subducting adriatic plate

deep seismic structure and thermo mechanical modelling of continental collision zones abstract a series of 2d thermo mechanical models are presented which quantify crustal thickening and the resulting temperature perturbations associated with thrusting in an attempt to constrain the existence of temperatures responsible for the generation of anatectic granites in a compressional environment deformation is assumed to occur in the crust by a simple thrusting mechanism the moho acting as a detachment surface as has been observed on deep seismic reflection data while the more ductile sub crustal lithosphere is assumed to behave elastically and deform in a pure shear manner investigated are the relative effects of the rate of crustal shortening the distribution of radioactive elements within the crust the reduced heat flow from the mantle isostasy and erosion our results show that previous oversimplified 1d models significantly overestimate the elevated temperatures in lower crustal regions caused by radiogenic heating and that this mechanism will only have a significant effect in regions of relatively thin lithosphere or where there are unusually high rates of radiogenic heating in the crust generation of synthetic p t t data for locations deep down in the lower crust enables us to quantify the temperatures produced following a period of compressional deformation providing insight into the time scales involved for the generation of crustal melt granites within an orogenic belt

gravity tectonics driven by quaternary uplift in the northern apennines insights from the la spezia reggio emilia geo transect abstract the neotectonics of the northern apennines is illustrated using a crustal scale geoseismic cross section based on seismic profiles and field mapping the geological profile crosses a variety of tectonic settings from the val di vara and val magra vv vm grabens in the inner side of the apennines to the pede apennine thrust fronts ptf and finally to the external fronts of the apennines both the vv vm extensional system and the ptf show evidence of early pleistocene tectonic activity whereas thrusting in the external apennine ended by late pliocene the sole decollement of the external thrusts cuts down westwards into the basement to a depth of about 15 km whereas the ptf joins a shallower detachment surface that follows the top of the basement this basal surface also represents the basal detachment of the vv vm extensional system with the vv vm and ptf defining a large scale gravitational spreading system we hypothesise that the regional quaternary uplift that affected the internal sector of the apennines promoted a gravitational spreading in the upper part of the orogenic wedge accounting for the coeval extension in the vv vm and shortening at the ptf and applicable to a 100 km long sector of the northern apennines

contemporaneous extension and compression in the northern apennines from earthquake fault plane solutions summary the northern apenninic arc belongs to the deformation zones surrounding the adriatic plate which behaves as a rigid block it is a ne verging fold and thrust belt which developed since the miocene with the migration of an extensional compressional pair previous seismological data are roughly in agreement with this deformation picture although the outer compressional front was not clearly defined by the few available solutions in this work we confirm the existence of two adjacent zones of contemporaneous extension and compression in the northern apennines defining the extent of these two zones and their interim1 deformation better than was previously done this is accomplished through the analysis of 125 new focal mechanisms of earthquakes 2 6 md 4 8 recorded by the national network of the lstituto nazionale di geofisica in the period 1988 1995 the two deformation zones are clearly separated and lie very close to each other with a partial overlapping in the emilian tuscan apennines strikeslip events are scattered in most of the study area thrust faulting earthquakes are located in the internal part of the most recently active thrust front middle upper pleistocene there is a general trend of the compressional p axes of thrust fault and strike slip solutions to be perpendicular to the apenninic direction in the external zone while the tensional axes of the normal fault and strike slip solutions in the belt do not show a uniform orientation however clearly evident is the ene direction of extension in the peri tyrrhenian region consistent with the direction of shmln in the quaternary volcanoes of this region inferred from borehole breakouts and microearthquake fault plane solutions we determined the orientation of the stress tensor in the two main deformation zones by inversion of the 125 fault plane solutions determined in this study we found that the external belt is characterized by ne sw compression ol horizontal oriented n45 e while a normal faulting regime with o3 e w oriented is characteristic of the umbria tuscany back arc region

driving mechanism of tectonic activity in the northern apennines quantitative insights from numerical modeling 1 it is shown by numerical modeling that the recent deformation pattern observed in the northern apennines mainly characterized by progressive eastward migration and bowing of the belt thrusting activity along its external front and tensional tectonics in the internal area can be reproduced at a first approximation by applying a belt parallel se nw compression to the chain which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones the above compressional regime obtained by imposing kinematic boundary conditions to the model causes the outward escape of crustal wedges from the chain in particular the northeastward displacement of the romagna marche umbria units and the counterclockwise rotation and northwestward displacement of the ligurian units this kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area in line with the observed features that concern both strain style and orientation of principal strains evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central apennines on tectonic and seismic activity in the northern apennines

intracontinental tectonic melange in southern apennines on the axial zone of the southern apennines the major tectonic boundary between the inner platform western platform unit and the pelagic lagonegro units domains is represented by a thick level of highly deformed rock assemblage structural analysis reveals that this tectonic unit represents an intracontinental melange complex characterized by a block in matrix fabric that contains blocks from both hangingwall platform and footwall basin units this unit comprises different sets of structures that caused by shearing processes developed at depths ranging from about 8 9 km to the surface these tectonites represent the product of a crustal shear zone developed at the major boundary between platform basin domains of adria during the thick skinned tectonic processes controlling the southern apennines mountain building

considerations on the seismotectonics of the northern apennines abstract the northern apennines have been subdivided into homogeneous zones on the basis of recent structural evolution and crustal structure in which the earthquake distribution can find a coherent framework these zones whose physiography is in strict connection with their structure are the internal peri tyrrhenian belt the external or main belt the buried belt and the pede alpine homocline earthquake activity has a tendency to cluster along well defined bands particularly in the easternmost border of the peri tyrrhenian belt as well as along the zone between the external belt and the buried belt i e along the padanian margin of the northern apennines a minimum of seismic activity seems to be correlated with some zones of the external belt as well as with the late tertiary and quaternary magmatic province of tyrrhenian southern tuscany the fault plane solutions are coherent with the structural picture a tentative seismotectonic model of the northern apennines is discussed

climate agriculture and cycles of human occupation over the last 4000 yr in southern zacatecas mexico scholars attribute the growth and decline of classic period ad 200 900 settlements in the semi arid northern frontier zone of mesoamerica to rainfall cycles that controlled the extent of arable land however there is little empirical evidence to support this claim we present phytolith organic carbon and magnetic susceptibility analyses of a 4000 yr alluvial record of climate and human land use from the malpaso valley the site of one such classic frontier community the earliest farming occupation is detected around 500 bc and appears related to a slight increase of aridity similar to the level of the modern day valley by ad 500 the valley s classic period mesoamerican settlements were founded under these same dry conditions which continued into the postclassic period this indicates that the la quemada occupation did not develop during a period of increased rainfall but rather an arid phase the most dramatic changes detected in the valley resulted from the erosion associated with spanish colonial grazing and deforestation that began in the 16th century the landscape of the modern malpaso valley is thus primarily the product of a series of intense and rapid transformations that were concentrated within the last 400 yr

the victor hensen seahill central ionian sea morphology and structural aspects abstract a seabeam based bathymetric map from the victor hensen seahill is presented 3 5 khz sonar profiles show the structural relations of the near surface sedimentary sequences of the surrounding abyssal plain and between abyssal plain and seahill the structures are interpreted to be caused by tensional tectonics acting up to the present

neogene quaternary tectonic evolution of the southern apennines 1 in this paper we present a study of a segment of the southern apennine mountain belt which extends from the pollino mountain range to the south and the sele valley to the north combining regional data and structural information with the results based on the interpretation of several seismic reflection lines and many deep well logs three regional cross sections have been constructed the cross sections highlight the overall architecture of the orogenic belt which is constituted by a thin tectonic layer of allochthonous nappes represented by remnants of the neotethyan accretionary wedge e g liguride and sicilide units resting above a thick imbricated thrust belt this latter comprises distinct units represented by platform carbonates western platform monte alpi costamolina and tempa rossa units and pelagic basin domains lagonegro campomaggiore and faeto units deriving from the late tortonian quaternary deformation of the adria paleomargin the restoration of the three cross sections furnished information on the primary geometry of the adria paleomargin which was characterized by the occurrence of a large platform domain dissected by distinct pelagic basins with complex and irregular margins represented by pelagic embayments and platform promontories developed during the mesozoic and the late cretaceous tertiary times the reconstructed geometry of the paleomargin provided moreover useful insights to evaluate the mode of deformation and the rates of shortening of the thrust belt and to explain the neogene stratigraphy of the distinct platform domains the mode of deformation of this portion of the southern apennines was dominated by the occurrence of crustal thrusts located along previous weakness zones represented by the boundaries between platform and pelagic domains these crustal thrusts caused the complete closure of the basin areas and the direct overthrusting of the different buoyant platform domains with contractional rates characterized by values ranging from 3 1 to 4 3 cm yr finally a geodynamic model in which the southern apennine mountain belt is considered the result of lateral extrusion produced by the indentation of the pelagian block and by the consequent opening of the tyrrhenian sea is also proposed

architecture and seismotectonics of a regional low angle normal fault zone in central italy information from surface geology subsurface geology boreholes seismic reflection and refraction profiles and seismicity are used to depict the geometry and the possible seismogenic role of the altotiberina fault af a low angle normal fault in central italy the af extends along the inner umbria region for a length of 70 km with an average dip of 30 and an horizontal displacement up to 5 km it emerges west of the inner border of the tiber basin and deepens beneath the umbria marche carbonate fold and thrust belt to a depth of 12 14 km close to the af surface trace low angle synthetic east dipping normal faults extensively outcrop whereas high angle antithetic west dipping normal faults prevail farther east integrating geological and seismologic information it can be stated that the af behaves as an active extensional fault zone and represents the basal detachment of the west dipping seismogenic normal faults of the umbria marche region the af belongs to a regional ne dipping low angle normal fault system etrurian fault system efs which extends for 350 km from northwestern tuscany to southern umbria early preliminary considerations suggest that the efs may play an important role in controlling active extension and related seismicity in northern central italy

magnetic anisotropy of plio pleistocene sediments from the adriatic margin of the northern apennines italy implications for the time space evolution of the stress field abstract the anisotropy of magnetic susceptibility ams of the marine fine grained plio pleistocene sediments that crop out at the eastern adriatic front of the central northern apennines italy indicates a prevalent sedimentary compactional magnetic fabric with variable overprint of the tectonic strain the degree of anisotropy and the geometry of the ams ellipsoids suggest a subdivision of the studied sediments in two distinct ages early middle pliocene and late pliocene early pleistocene the early middle pliocene sediments show a weak but well defined magnetic lineation parallel to the main fold and thrust axes throughout the region analogously to the messinian sediments located in a more internal western position of the apenninic chain since the late pliocene the ams data are not regionally coherent and indicate a reduced and locally variable tectonic influence on the magnetic fabrics the ams data have been integrated with the available geophysical information of the present day stress in the region with the aim to reconstruct the time spatial evolution of the stress field in the adriatic margin of the central northern apennines during the past 5 ma the present day stress field was evaluated using borehole breakout in deep wells about 50 wells focal mechanisms of crustal earthquakes 2 5 m d

structural evolution of the lucanian apennines southern italy abstract in this paper we present a study of an entire segment of the southern apennines of italy extending from the pollino mountain range to the south to the agri valley to the north in which all the units of the chain are represented combining regional information with detailed structural data obtained from the different tectonic units forming the orogenic belt the structure as well as the tectonic evolution of this portion of the orogenic belt are proposed the overall architecture of this segment of the southern apennines mountain chain represents the result of a complete orogenic cycle in which oceanic subduction syn collisional and post collisional events are well recorded structurally this segment of the orogenic belt exhibits two distinct structural levels separated by a major detachment surface the sole thrust of the accretionary wedge that occur at the surface in the allochthonous nappes and at depth in the adria continental margin the upper level is characterized by an imbricated fan system affecting the allochthonous terranes emplaced during oceanic subduction and the first stages of continent continent collision the lower level is represented by a duplex geometry that has developed in the post collisional stage during evolution of the foreland migrating thrust system involving the carbonate platform basin system of the adria block during the last stages of the mountain building process when the foreland thrust migration was locked by the thickening of the colliding continental crusts the southern apennines were thus affected by a severe strike slip tectonics that dissects the entire mountain belt deeply modifying the previous thrust geometry

crustal velocity field of western europe from permanent gps array solutions 1996 2001 we derive a new geodetic velocity field for western europe and the western mediterranean by rigorously combining 1 a selection of 36 itrf2000 sites 2 a solution from a subset of sites of the european permanent gps network euref epn 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy of the order of i mm yr 1 or better its analysis shows that central europe defined as east of the rhine graben and north of the alps and the carpathians behaves rigidly at a 0 4 mm yr 1 level and defines a stable europe reference frame in that reference frame we find no significant motion at sites located west of the rhine graben and on the iberian peninsula which sets an upper bound of 0 6 mm yr 1 on horizontal motion across the rhine graben and the pyrenees we find that the current strain pattern in the western alps combines e w extension and right lateral shear we confirm a counterclockwise rotation of the adriatic microplate which appears to control the strain pattern along its boundaries in the friuli area the alps and the apennines our results also suggest that the africa eurasia plate motion in the western mediterranean may be 40 50 per cent slower that the nuvel1a plate motion model and rotated 20 30 counterclockwise

long term elasticity in the continental lithosphere modelling the aden ridge propagation and the anatolian extrusion process summary the evolution of the gulf of aden and the anatolian fault systems are modelled using the principles of elastic fracture mechanics usually applied to smaller scale cracks or faults the lithosphere is treated as a plate and simple boundary conditions are applied that correspond to the known plate boundary geometry and slip vectors the models provide a simple explanation for many observed geological features for the gulf of aden the model predicts why the ridge propagated from east to west from the owen fracture zone towards the afar and the overall form of its path the smaller en echelon offsets can be explained by upward propagation from the initially created mantle dyke while the larger ones may be attributed to the propagating rupture interacting with pre existing structures for anatolia the modelling suggests that the east anatolian fault was created before the north anatolian fault could form once both faults were formed however activity could switch between them the time scales over which this should take place are not known but evidence for switching can be found in the historical seismicity for aden and anatolia pre existing structures or inhomogeneous stress fields left from earlier orogenic events have modified the processes of propagation and without an understanding of the existence of such features the propagation processes cannot be fully understood furthermore a propagating fault can extend into an active region where it would not have initiated the north anatolian fault encountered slow but active extension when it entered the aegean about 5 ma and the stress field associated with the extending fault has progressively modified aegean extension in the central aegean activity has been reduced while to the north west on features such as the gulfs of evvia and corinth activity has been increased the field observation that major structures propagate and the success of simple elastic models suggest that the continental crust behaves in an elastic brittle or elastic plastic fashion even though laboratory tests may be interpreted to suggest viscous behaviour there are major problems in scaling from the behaviour of small homogeneous samples to the large heterogeneous mantle and large scale observations should be treated more seriously than extrapolations of the behaviour of laboratory experiments over many orders of magnitude in space and time the retention of long term elasticity and localised failure suggests a similar gross rheology for the oceanic and continental lithospheres even though it is incorrect to attribute differences in behaviour to the former being rigid i e elastic and the latter viscous oceanic and continental lithosphere behave in different ways unlike oceanic crust continental crust is buoyant and cannot be simply created or destroyed the process of thickening or thinning works against gravity preventing large displacements on extensional or contractional features in the upper mantle the equivalents of ridge or subduction systems are suppressed before they can accommodate large displacements and activity must shift elsewhere on the other hand strike slip boundaries and extrusion processes are favoured

ductile and brittle shortening extension parallel folds and maintenance of crustal thickness in the central aegean cyclades greece in contrast to previous studies that concentrated on the two dimensional crustal strain in the central aegean region cyclades it is shown that nne ssw extension via ductile and brittle stretching and low angle detachments was accompanied and or alternated with horizontal shortening perpendicular to the stretching direction since at least the early miocene roughly e w directed ductile shortening produced large scale overturned and upright folds having axes parallel or slightly oblique to the stretching lineation upright folding and arching of low angle normal faults occurred above the brittle ductile transition and brittle e w compression culminated with vertical axis block rotations strike slip faults and minor thrusts since at least the early miocene the structure of the cycladic massif evolved through alternating and or coeval increments of horizontal shortening and vertical thinning associated with an approximately constant nne ssw stretching exact magnitudes of the vertical and horizontal deformational components are difficult to assess nevertheless we note that extensional tectonics that affected the cyclades during the last 15 20 m y have produced no net crustal thinning we suggest that crustal thickness was maintained by extension parallel folds which represent true contractional structures and that crust was fed into the extended region from its margins

crustal section based on crop seismic data across the north tyrrhenian northern apennines adriatic sea abstract using deep seismic reflection data from the italian lithospheric exploration project crop in the central mediterranean region a 400 km long section composed of three different profiles crossing the northern tyrrhenian sea crop m 12a profile the northern apennines crop 03 and the adriatic sea crop m 16 is reconstructed and discussed new data allow us to outline a seismically consistent tectono stratigraphic setting for the crust and upper mantle of the northern apennines thrust belt system and its adriatic foreland time space analysis of the deformation of the investigated chain and identification of existing macrostratigraphic crustal intervals and tectonic units allow a reasonably controlled interpretation of the geodynamic evolution and of the main orogenic stages careful seismic reprocessing and application of advanced techniques to key zones of the explored area such as the tuscan archipelago were determinants in obtaining fundamental information for understanding of the complex lithospheric structures and their evolution profile interpretation supports that the northern apennine chain is dominated by a compressive thrust system crustal extension assumed by some authors as the dominating tectonic process for the whole tuscan apennine area represents a subordinate geodynamic event of the last stage tyrrhenian in the early cretaceous late jurassic the paleogeographic framework consisted of the europe and adria plates separated by the alpine tethys ocean during the late cretaceous early eocene adria europe convergence eo alpine stage and subduction beneath the adria plate closed the alpine tethys sea with the tethyan slab being clearly seismically imaged the first apenninic geodynamic stage occurred in the late oligocene early miocene with the opening of the balearic basin which generated a first lithospheric root of the apenninic chain in the tuscan archipelago area this root is represented by adria verging thrust faults that progressively flatten eastward upper parts of the west verging eo alpine thrust blocks were truncated by the east verging thrust faults of the balearic stage a deeper seismic reflector attributed to the top of the asthenosphere forms a mantle high below the elba island from the late miocene to present the corsica basin and western hinterland area were affected by extensional tectonics related to the tyrrhenian opening whereas compressional tectonics continued in the eastern hinterland and mostly on the eastward migrating foreland with development of a second lithospheric root constituted by high angle thrust faults these faults give rise to a huge basement culmination below the main apennines watershed impressive e directed gravity sliding of sedimentary blocks over their sloping basement occur generating the umbria marche shallow seismicity crustal shortening of the apennines system amounts to 170 km 14 km of which are due to the eo alpine stage 71 km to the balearic and 85 km to the tyrrhenian one in the frame of africa europe convergence the tyrrhenian apennines tectonodynamics were mainly conditioned by the mesozoic paleogeography

preliminary results from laguna minucua a potentially annually resolved record of climate and environmental change for the past 5000 years in the mixteca alta of oaxaca mexico abstract despite several decades of research focusing on prehispanic human ecology debate continues over the impact of climatic and anthropogenic landscape change on human populations in mesoamerica one problem in identifying the cause of this change is the lack of high resolution paleo environmental data from many regions the southern mexican highlands in particular have yielded few paleoenvironment data yet have a rich and diverse cultural history the sedimentary record from laguna minucua located within the sierra madre del sur oaxaca offers an exceptional opportunity to address human and environmental interactions in the region minucua is a small 0 25 ha currently shallow pond with no apparent inlets or outlets we retrieved two sediment cores from the site 3 5 m and 5 6 m long the cores are highly laminated core chronology was developed with paleomagnetic secular variation data and compared with couplet counts and limited radiometric measurements these data indicate that the minucua record at least spans the last 4500 100 years we discuss preliminary results that assess long term environmental change for the region through examination of geochemical and magnetic susceptibility data in particular we discuss in more detail a 500 year time slice which encompasses the period known as the classic collapse the record indicates overall dry conditions but with two extended wet periods experienced between 1160 and 1120 cal yr bp and 1060 1000 cal yr bp we place our findings in the context of current archaeological and paleoclimatological research in oaxaca

late neogene sequence stratigraphy of a carbonate siliciclastic transition southwest florida a network of high resolution seismic profiles and 23 lithologically and or geophysically logged boreholes have been analyzed in order to evaluate the effects of sea level cyclicity karstification and an intercalated carbonate to siliciclastic transition on the late miocene to quaternary stratigraphy of the charlotte harbor area in southwest florida six late neogene disconformity bounded depositional sequences are identified between two regional unconformities the lower regional unconformity r 3 varies from about 20 m to more than 115 m below sea level the lows are present as northwest southeast and northeast southwest trending troughs and the high areas as sharp irregular reflections and isolated sinkholes indicative of subaerial exposure the r 2 unconformity which overlies and truncates the late neogene sequences occurs as a strong flat lying reflector seaward of the present coastline and a series of downcutting channel complexes in back barrier areas the six depositional sequences prograde to the south southeast with a proximal distal transition from short steeply dipping oblique clinoforms to long low angle clinoforms three lithofacies which generally occur in a vertical sequence are from the bottom up 1 quartz dominated sand with phosphate sand and gravel 2 calcareous clays and 3 poorly indurated to well indurated sandy molluscan calcirudite the pebbley sand facies are transgressive lags gradationally overlain by prograding laminated clays deposited in an estuarine to prodelta shoreface environment the calcirudite transitionally overlies the clay facies and was deposited in a shallow subtidal to subaerial chenier like setting which may be indurated and or indicate subaerial exposure and may form the base of another sequence the karstified antecedent topography has controlled the distribution of the depositional sequences in two ways first fluvial systems are localized in the antecedent lows which restricts the distribution of fluvially transported sands second the relatively impermeable clays which occur as thin beds outside the lows thicken to 20 40 m within the karstic depressions the clay deposits limit vertical drainage and initiate the development of fluvial systems on the carbonate terrain the sequences were deposited during the late miocene tortonian stage which is increasingly viewed as a time of high frequency glacio eustatic sea level fluctuations although high resolution chronostratigraphic data are not available the sequences contain thin and or poorly preserved transgressive sands overlain by prograding regressive sediments and they represent discrete sea level cycles a regional pattern of karstic dissolution has controlled the transition by localizing deposition of impermeable prodelta clays and the developing paleo fluvial system the introduction of quartz sand into the carbonate terrain was in turn controlled by the karstic relief and a localized sediment supply derived from the paleo fluvial systems

are s c structures duplexes and conjugate shear zones different manifestations of the same scale invariant phenomenon abstract by measuring s spacing c spacing and the s c angle in deformed rocks this paper investigates the geometry of previously published examples of s c and s c like structures on a scale range between micrometres and several hundred kilometres the results indicate that common s c fabrics of thin section hand specimen and outcrop scale and conjugate fault mylonite zones of map scale define a simple function c spacing 2 s spacing which depicts a scale invariant geometry over ten orders of magnitude logarithmic plots of cumulative frequency suggest that the s c fractal set d 0 13 is restricted to the scale range between 600 800 m and 1 km where genuine s c structures characterized by antithetic shear on the s planes can be formed below 600 800 m grain scale processes seem to influence the development of s c structures above the upper limit 1 km only s c like structures with duplex kinematics synthetic shear on s planes occur the s c and s c c fractals are envisaged as self similar structures where the foliations work as both s or c planes depending on which scale is considered

present state of tectonic stress of the friuli area eastern southern alps stress orientations are determined for the friuli area from focal mechanisms using the inversion technique of gephart and forsyth 1984 the data consist of 244 fault plane solutions selected for the period 1988 1995 where the data coverage was poor this period was extended to 1978 1996 local magnitude ranges from 2 0 to 4 3 and the depths extend from 4 to 16 km the friuli area is subdivided into five seismotectonic zones on the basis of tectonic characteristics seismic activity and focal mechanisms and for each zone a stress tensor is determined the results show that the active tectonic stress in the friuli area is heterogeneous and conditioned by the complex structural pattern which is characterized by two indented tectonic wedges the western and central parts of the area are mainly affected by a compressional state of stress while in the eastern part a strike slip state of stress prevails the orientation of the principal stresses varies from the western to the eastern part of the area and differences are also noticeable with depth in the central part of the friuli area the maximum compressional stress is n s trending at shallow depths 10 km changing to nw se at deeper levels the maximum compressional stress is nw se oriented in the western part while in the eastern part it is n s oriented

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

multiproxy paleoecological reconstruction of prehistoric land use history in the western region of the lower rio verde valley oaxaca mexico paleoecological archives from three paleomeander sites and one archeological feature located in the lower rio verde valley oaxaca mexico are used to develop a spatial understanding of the patter

potential field constraints on the deep structure of the lugo gneiss dome nw spain abstract the lugo gneiss dome in the nw iberian massif spain is a variscan structure developed during late stages of orogenic collapse crustal extension was mainly accomplished by two kilometre scale conjugate extensional shear zones and by the late development of the dome and a huge normal fault these structures overprint previous contractional recumbent folds and a thrust fault the lugo dome and its southward continuation the sanabria dome are the site of the conspicuous eastern galicia magnetic anomaly egma a n s band 50 km wide and 190 km long with a maximum amplitude of 190 nt integrated potential field modelling of the egma and its corresponding gravity signature have been carried out aided by constraints provided by the measurement of c 900 magnetic susceptibilities and by previous geophysical data mainly seismic refraction and reflection profiles results suggest that a large volume of low density migmatites and associated inhomogeneous granites are the main source of the magnetic anomaly small massifs of basic and ultrabasic rocks inside the migmatites and high susceptibility iron ore bodies sparsely distributed in low grade middle ordovician slates are also thought to contribute to the anomaly but to a minor extent although otherwise similar to other gneiss domes the lugo dome is accompanied by a striking magnetic anomaly whose origin is discussed in terms of the tectonic evolution of this structure and the provenance of the magnetite bearing migmatites and inhomogeneous granites that core it

geomagnetic and mineral magnetic characterization of the anthropocene geomagnetic and mineral magnetic data provide geological indices that are both independent of human impact i e geomagnetic and respond to human induced environmental impact i e mineral magnetic we provide the first discussion of such magnetic events for help in defining the anthropocene within the holocene a potential geomagnetic marker for the anthropocene is the low dipole latitude at c 2700 cal a bp which is associated with distinct palaeosecular variation features in northerly mid to high latitude sites mineral magnetic records from lake and marine sediments identify major deforestation and soil delivery events from catchment systems in many parts of the world during the last 4000 years in europe clusters of these events occur around both 2600 cal a bp and ad 1100 the former coinciding with a low in geomagnetic field dipole latitude and peak intensity mineral magnetic records in peats and lake sediments can reflect particulate pollution from fossil fuel burning the expansion of major coal burning began c ad 1800 in western europe and eastern north america but around ad 1900 this expanded due to more widely distributed coal use and this event is the most clear mineral magnetic marker for the base of the anthropocene

lateral variations of thermo mechanical properties in the tyrrhenian northern apennine region abstract we present lithospheric strength profiles calculated for a transect running from the island of corsica in the west to the apennine foredeep in the east strength profiles are constructed at locations selected on the basis of the availability of seismic heat flow gravity data and earthquake foci distribution rheological modelling points to the presence of strong lateral variations in the thermo mechanical state of the lithosphere the tyrrhenian tuscany area has a low rigidity in relation with the intense stretching active from the early miocene and with very high heat flow associated with asthenospheric rise on the contrary hinterland corsica and apenninic foreland areas adriatic area show a higher level of lithospheric strength effective elastic thickness estimates confirm this scenario exhibiting a strong reduction from the northern tyrrhenian to the inner apennines and then an abrupt increase in correspondence of the adriatic plate the distribution of earthquake focal depths confirms the presence of a brittle rheology in the first kilometres of the crust in the tuscany area whereas close to the plate boundary much lower thermal gradients partly induced by the westward plunging adriatic plate enable seismic activity to occur at larger depths

tectonics of the umbria marche romagna arc central northern apennines italy new paleomagnetic constraints we present the results of a paleomagnetic study carried out on 32 sites from mainly messinian clayey sediments distributed throughout the external umbria marche romagna arc umra these data together with published results from coeval sediments demonstrate that this arc is an orocline in its central northern sector bending not well constrained in time was due to about 15 clockwise rotations of the central part of this arc and to counterclockwise rotations farther north in this latter area post messinian counterclockwise rotations are of the same amplitude as those calculated for some classic mesozoic paleomagnetic sections in northern umbria suggesting a plio pleistocene age for the rotations reported from the older sequences

paleomagnetic evidence for a neogene two phase counterclockwise tectonic rotation in the northern apennines italy paleomagnetic directions have been determined for a new collection of early oligocene and late miocene pliocene epiligurian clastic sediments from the frontal portions of the northern apennines these results are combined with cenozoic data from the literature to evaluate whether rotations of units in this region are related to the oligomiocene corsica sardinia rotation and or to younger phases of deformation of the apennine chain when corsica sardinia moved counterclockwise ov the coast of france the ligurian units located at its front were presumably pushed eastward and rotated counterclockwise above a main boundary thrust onto the adria africa margin we propose that about 24 out of a total of 52 of rotation observed in the epiligurian units can be related to the oligo miocene motion of the corsica sardinia block in partial agreement with previous conclusions and the remaining 28 to the pliocene tectonic phase at the apennine chain front which may have re activated thrust planes in the adria africa succession below the ligurian wedge 2000 elsevier science b v all rights reserved

late miocene uplift in the romagnan apennines and the detachment of subducted lithosphere abstract we report part of a test of the hypothesis that detachment of subducted lithosphere may be a process of lateral propagation of a horizontal tear wortel and spakman proc kon ned akad wetensch 95 1992 325 347 we have used the apennines as a test area the test procedure consists of the comparison of hypothetical vertical motions predicted from the expected redistribution of slab pull forces with observed vertical motions we demonstrate that a late miocene depocentre migration from the northern towards the central apennines is associated with uplift of the fore arc of the northern apennines such a combination of a depocentre shift and uplift is thought to be diagnostic for lateral migration of slab detachment the depocentre migration was identified in earlier work van der meulen et al earth planet sci lett 154 1998 203 219 this contribution focuses on uplift which has primarily been identified through the geohistory analysis of the monte del casino section romagnan apennines northern italy owing to methodological problems the start and duration of the uplift phase could not be constrained and only a minimum estimate of the total amount of uplift 483 180 m is obtained the data do allow for an estimate of the uplift rate 163 61 cm ky a review of regional data results in better constraints on the timing of the above lateral reorganisation of the fore arc and on the spatial extent of the uplifted area depocentre development in the central apennines began between 8 6 and 8 3 ma b p uplift started between 9 and 8 ma b p and affected the entire northernmost apennines

late pleistocene and holocene paleoenvironments of chalco lake central mexico abstract in order to establish paleoenvironmental conditions during the late quaternary four cores from the basin of mexico central mexico were drilled in chalco lake located in the southeastern part of the basin the upper 8 m of two parallel cores were studied using paleomagnetic loss on ignition pollen and diatom analyses based on 11 14c ages the analyzed record spans the last 19 000 14c yr b p volcanic activity has affected microfossil abundances both directly and indirectly resulting in absence or reduction of pollen and diatom assemblages important volcanic activity took place between 19 000 and 15 000 yr b p when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry cold climate during this interval abrupt environmental changes with increasing moisture occurred from 15 000 until 12 500 yr b p the lake level increased and the pollen indicates wetter conditions the highest lake level is registered from 12 500 to ca 9000 yr b p the end of the pleistocene is characterized by an increase in humidity from 9000 until ca 3000 yr b p chalco lake was a saline marsh and the pollen record indicates warmer conditions after 3000 yr b p the lake level increased and human disturbance dominates the lacustrine record

internal anatomy of a mixed siliciclastic carbonate platform the late cenomanian mid turonian at the southern margin of the spanish central system the late cenomanian mid turonian succession in central spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments alluvial plain estuarine lagoon shoreface offshore hemipelagic and carbonate ramp three depositional sequences third order are recognized the atienza patones and el molar sequences the patones sequence contains five fourth order parasequence sets while a single parasequence set is recognized in the atienza and el molar sequences systems tracts can be recognized both in the sequences and parasequence sets the lowstand systems tracts only recognized for atienza and patones sequences are related to erosion and sequence boundary formation transgressive systems tracts are related to marine transgression and shoreface retreat the highstand systems tracts are related to shoreface extension and progradation and to carbonate production and ramp progradation sequences are bounded by erosion or emergence surfaces whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea level transgressive surfaces are subordinate erosion and or omission surfaces with a landward facies shift interpreted as parasequence set boundaries the co existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland and dolomite probably derived from bioclastic material siliciclastic flux to coastal areas is highly variable the maximum flux postdates relative sea level falls carbonate production in these areas may be constant but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect carbonate ramps were detached from the coastal system and separated by a fringe of offshore fine grained muds and silts as distinct facies belts the growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth order parasequence sets during the growth of these ramps some sediment starvation occurred basinwards progradation and retrogradation of the different belts occur simultaneously suggesting a sea level control on sedimentation in the study area the co existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea level cycles and occurred mainly when the second order third order and fourth order cycles showed highstand conditions

short and long term deformation patterns in the aegean anatolian systems insights from space geodetic data gps geodetic measurements gps in the eastern mediterranean suggest higher rates of motion of about 10 mm yr in the aegean western anatolian zone with respect to those in the central eastern anatolia in this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post seismic relaxation processes induced by the seismic activation of the north anatolian fault since 1939 the major implications of this hypothesis are tentatively quantified by a simplified model constituted by an elastic lithosphere 100 km thick coupled with a viscous asthenosphere 250 km thick with a viscosity of 10 19 pas the predicted perturbation of the displacement and stress fields is consistent with geodetic velocities and could also account for the major features of seismic activity in the period considered

chronology of deformation and analogue modelling of the plio pleistocene tiber basin implications for the evolution of the northern apennines italy abstract the late miocene quaternary hinterland basins located in the western sector of the northern appennines have been considered either as the surficial effect of the back arc extension related to the tyrrhenian basin opening or related to late orogenic gravity spreading conversely some authors recently suggested that they formed in a compressional regime and underwent a complex tectonic history in this frame the controversial origin of these hinterland basins is the subject of this paper a structural study of the plio pleistocene continental tiber basin tb one of the most important ones has been carried out allowing to establish the role of lateral compressional and extensional deformations both of which have been affecting the continental deposits during basin evolution on the basis of field mapping and structural analysis the development during early middle pliocene of the three main branches constituting the tb has been referred to a compressive regime related to the emplacement of a crustal thrust the area was only later during the early pleistocene affected by extension characterised by nw se trending normal faults as well as fault controlled basins these structures in fact obliquely cross cut the nnw trending older tb branches the area was further affected by a ne oriented shortening phase at the boundary between early and middle pleistocene which produced the partial inversion of the southwestern tb branch deruta terni sector the pleistocene tectonic evolution of this sector has been also investigated by means of analogue modelling experiments whose results support the hypothesised tectonic evolution a succession of stress fields ranging from tb development up to middle late pleistocene has been reconstructed they are characterised by a ne to ene trending direction of compression or extension and the variation through time of the stress field led to the reactivation of suitably oriented pre existing structures the proposed tectonic evolution of the tb indicates a rejuvenating of thrust activity in the study area as well as a retard of normal faulting with respect to the hypotheses proposed by previous authors

stress field in friuli ne italy from fault plane solutions of activity following the 1976 main shock abstract fault plane solutions of 78 earthquakes with magnitude larger than 3 2 which occurred in friuli between may 1976 and august 1979 have been used to estimate the orientations of the principal stress axes by an inversion technique the analysis of the confidence limits and the average angular misfit of the solution found when inverting the entire data set revealed that faulting was not produced by a uniform stress distribution subdivision of the study area into smaller volumes did not lead to significant improvements in terms of stress uniformity whereas temporal subdivision of the sample reduced significantly misfit and confidence areas of the solution for some data sets therefore we conclude that the stress directions changed as a function of time a nearly uniform stress direction compatible with tectonic models proposed for the study area ca n s convergence of the adriatic and south alpine units was found between the main event of 6 may 1976 m l 6 4 and the strong aftershocks of mid september 1976 5 1 m l 6 1 the analysis of the individual misfit cumulative pattern reveals that some degree of stress heterogeneity appeared in july 1976 which is explained here in terms of heterogeneous local responses of the stress field to the seismic activity superimposed to the regional compressive factor the degree of perturbation of the principal stress directions by local effects increased with time and showed in particular a clear variation after the strong earthquakes of mid september 1976 the perturbations appear to be reflected by low magnitude quakes whereas the faulting in strong events is compatible with the regional stress field

cover thrust reactivations related to internal basement involvement during neogene quaternary evolution of the northern apennines up to recently the neogene quaternary evolution of the northern apennines italy has been described by the classic model of a migrating eastward compressive external front with an extensional regime in the back areas connected with the tyrrhenian basin formation however in the last few years new structural data have been collected in the internal marine and continental episutural basins and in the external exposed thrust belt a complex structural evolution has now been reconstructed with coeval main tectonic phases that affect both areas with stress field change four main tectonic phases have been identified since late tortonian times these are dated as messinian late pliocene middle and late pleistocene the thrust belt has a complex evolution detected in a wide external area of the chain after the first emplacement of the main thrust sheets with reactivations and out of sequence thrusting these reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins suggesting a direct relationship within a single evolutive model the increased knowledge of the deep structure of the northern apennines through geophysical and subsurface data acquired in the last few years indicates the basement involvement at least for the internal side of the northern apennines this basement involvement also played an important role in the tectonic evolution of the external sector of the apennines in this paper a new model is proposed that integrates field data geophysical evidence and geodynamic constraints the thrust reactivations and the out of sequence structures of the external area are related to internal crustal thrust activity the deformed sediments of the neogene quaternary basins are dating the thrust activity all the evidences point to a late neogene rejuvenation of the tectonic evolution but some inferences can be drawn on the development of the foredeep

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

geomorphological evidence for anti apennine faults in the umbro marchean apennines and in the peri adriatic basin italy abstract the apennines are a relatively recent mountain chain which has been affected by uplift movements since the upper pliocene in fact the remnants of an erosional surface reduced close to base level is preserved at the top of the relief there is no general agreement on the geodynamic stress field and mechanisms which are creating the chain however it is largely accepted that uplift occurred together with the activation on the western side of the chain of extensive faults oriented in the apennine direction nw se which have been linked to the opening of the tyrrhenian sea a great debate is going on about the presence and significance of anti apennine faults ne sw which have been observed by some authors but completely denied by others the main evidence is represented by 1 block faulting of the remnants of the erosional surface along the marchean ridge more elevated relief delimiting relatively depressed areas was created in correspondence with the sibillini mts and mt s vicino similar evidence has been found in the umbro marchean ridge locally more than 1500 metres of displacement have been observed between more and less uplifted remnants 2 block faulting of fan deltas and related beaches of sicilian to crotonian age with more elevated sediments preserved between the tronto and tenna rivers and between the musone and esino rivers maximum displacement along a transect parallel to the coast is 200 metres 3 fault scarps affecting the middle pleistocene river terraces as observed along the esino the tronto the chienti and the tenna river valleys maximum displacements are in the order of 50 metres 4 faulting of horizontal karst galleries and reorientation of the cave network as in the frasassi gorge maximum displacements are about 100 metres 5 captures and alignments in the drainage network of the main river courses 6 large scale gravitational movements as in the ancona landslide and along the chienti and esino rivers their activation occurred in most cases after the lower pleistocene and although their displacements may be of relatively limited extent dispite their recent activity they played a major role in the modelling of the landscape these faults display transtensive extensional and trascurrent movements apart from the controversial geodynamic significance of these faults from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the apennine chain the importance and timing of activity of these faults in the quaternary geomorphological evolution of the umbria marchean apennines is demonstrated using evidence usually underestimated by structural geologists which can contribute to a debate based on a multidisciplinary approach

late holocene estuarine inner shelf interactions is there evidence of an estuarine retreat path for tampa bay florida abstract the purpose of this study was to determine if and how a large modern estuarine system situated in the middle of an ancient carbonate platform has affected its adjacent inner shelf both in the past during the last post glacial sea level rise and during the present an additional purpose was to determine if and how this inner shelf seaward of a major estuary differed from the inner shelves located just to the north and south but seaward of barrier island shorelines through side scan sonar mosaicking bathymetric studies and ground truthing using surface grab samples as well as diver observations two large submarine sand plains were mapped one being the modern ebb tidal delta and the other interpreted to be a relict ebb tidal delta formed earlier in the holocene the most seaward portion of the inner shelf studied consists of a field of lobate bathymetrically elevated fine sand accumulations which were interpreted to be sediment starved 3d dunes surrounded by small 2d dunes composed of coarse molluscan shell gravel additionally exposed limestone hardbottoms supporting living benthic communities were found as well this modern shelf sedimentary environment is situated on a large buried shelf valley which extends eastward beneath the modern tampa bay estuary these observations plus the absence of an incised shelf valley having surficial bathymetric expression and the absence of sand bodies normally associated with back tracking estuarine systems indicate that there was no cross shelf estuarine retreat path formed during the last rise in sea level instead the modern tampa bay formed within a mid platform low relief depression which was flooded by rising marine waters late in the holocene with continued sea level rise in the late holocene this early embayment was translated eastward or landward to its present position whereby a larger ebb tidal delta prograded out onto the inner shelf extensive linear sand ridges common to the inner shelves to the north and south did not form in this shelf province because it was a low energy open embayment lacking the wave climate and nearshore zone necessary to create such sand bodies the distribution of bedforms on the inner shelf and the absence of seaward oriented 2d dunes on the modern ebb tidal delta indicate that the modern estuarine system has had little effect on its adjacent inner shelf

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

scismotectonics of the northwest external dinarides abstract the region of the tectonic contact between the alps and the dinarides is studied comparing all the available geological geophysical and seismological data the peculiar crustal structures in particular the difference in thickness of the alps dinarides and pannonian basin can be correlated to the seismically active zones the highest seismicity is related to the adria microplate underthrusting the southern alps beneath the friulian piedmont arc this movement produces a composite lateral slip and an underthrust which is subparallel to the dinarides along the yugoslav coast the seismicity in western yugoslavia is more diffuse than in friuli although it is possible to pick out three narrow parallel bands with dextral shear subparallel to the periadriatic vardar fault system which separate the apulia from the pannonian area the interaction of this system with the sinistral strike slip faults of the western carpathians belt enhances the seismicity of the easternmost sector of the alps analogies and differences in the seismotectonic behaviour between central friuli and western yugoslavia are studied and a unique model with a vertical mechanical disengagement at the rear of the compressive fronts of the southern alps and external dinarides is proposed

interplay of late cenozoic siliciclastic supply and carbonate response on the southeast florida platform abstract high resolution seismic reflection data collected along the length of the caloosahatchee river in southwestern florida have been correlated to nannofossil biostratigraphy and strontium isotope chemostratigraphy at six continuously cored boreholes these data are interpreted to show a major late miocene to early pliocene fluvial deltaic depositional system that prograded southward across the carbonate florida platform interrupting nearly continuous carbonate deposition since early in the cretaceous connection of the platform top to a continental source of siliciclastics and significant paleotopography combined to focus accumulation of an immense supply of siliciclastics on the southeastern part of the florida platform the remarkably thick 100 m sand rich depositional system which is characterized by clinoformal progradation filled in deep accommodation while antecedent paleotopography directed deltaic progradation southward within the middle of the present day florida peninsula the deltaic depositional system may have prograded about 200 km southward to the middle and upper florida keys where late miocene to pliocene siliciclastics form the foundation of the quaternary carbonate shelf and shelf margin of the florida keys these far traveled siliciclastic deposits filled accommodation on the southeastern part of the florida platform so that paleobathymetry was sufficiently shallow to allow quaternary recovery of carbonate sedimentation in the area of southern peninsular florida and the florida keys

thrust belt development in the central apennines italy northward polarity of thrusting and out of sequence deformations in the gran sasso chain the lazio abruzzi carbonate platform overrides the outermost sectors of the foreland fold and thrust belt of the central apennines of italy along an arcuate thrust front which swings from e w to nnw sse orientation the e w striking north verging thrust faults of the gran sasso cut in their footwall the n s oriented east verging imbricates of the marche thrust belt and the adjacent adriatic foredeep our field mapping of the gran sasso imbricate system shows an array of six major thrust faults crosscutting each other in such a way that oblique propagation of higher thrust faults across the preexisting thrust sheets causes rethrusting of earlier imbricated units decapitation of previous folds and superposition of younger on older beds deformation in the gran sasso thrust belt mainly occurred between messinian and middle pliocene times and is partly synchronous with the development of the marche thrust belt thus implying that shortening resulted from a complex combination of northward and eastward propagating thrust systems increasing west to east shortening along the gran sasso thrust front indicates large differential anticlockwise rotation by decoupling along a n s transpressive right lateral shear zone this mechanism could have been induced by the maiella foreland uplift acting as a buttress against which the lazio abruzzi carbonate platform was stacked and forced to rotate anticlockwise with consequent shortening by out of sequence thrust propagation

paleoecological studies at lake patzcuaro on the west central mexican plateau and at chalco in the basin of mexico abstract a 1520 cm sediment core from lake patzcuaro michoacan mexico is 44 000 yr old at the base all parts of the core have abundant pollen of pinus pine alnus alder and quercus oak with frequent abies fir the interval dated from 44 000 to 11 000 yr ago has a homogeneous flora characterized by abundant juniperus juniper pollen and frequent artemisia sagebrush it is believed to represent an appreciably drier and colder climate than at present the holocene at lake patzcuaro is characterized by a moderate increase in pinus pollen and the loss of juniperus pollen as the modern type of climate succeeded alnus was abundant until about 5000 yr ago its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake shore and stream course alder communities for agricultural purposes or it may simply reflect a drying tendency in the climate pollen of zea corn appears at lake patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr b p apparently recording a human population large enough to modify the natural environment as well as the beginning of agriculture a rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion in the most recent period corn is absent from the sediments perhaps reflecting a change in agricultural practices the environment changes at lake patzcuaro are similar to and correlate with those in the cuenca de mexico where diatom stratigraphy from the chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture before 10 000 yr ago climates there were cool and dry and the chalco basin was occupied by a shallow freshwater marsh that drained north to lake texcoco where saline water accumulated by evaporation increases in effective moisture and possible melting of glaciers during the holocene caused lake levels to rise throughout the cuenca de mexico and lake texcoco flooded the chalco basin with brackish water after 5000 yr ago such flooding decreased and shallow freshwater ponds and marshes were restored in the chalco basin this environmental change coincides with the appearance of zea pollen and suggests cultural control of lake levels and salinity

fault geometry and earthquakes in continental interiors abstract although large earthquakes in continental interiors are much less frequent than those along plate boundaries they have been responsible for a disproportionate amount of destruction i present a testable model for strain accumulation and seismicity in the upper crust of continental interiors intersecting faults provide a focus for strain build up resulting in local pockets of high strain accumulation rigid plates typically deform at strain rates 10 10 to 10 9 strain yr 1 but at intersecting fault zones strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr 1 i e the strain rates are comparable with those at plate boundaries the resulting large earthquakes are associated with relatively short return times hundreds of years typically one of the intersecting faults appears to split and to offset the other main fault defined as a fault on which the larger offset occurs forming two parallel strands separated by a jog i also observe a rotation of one leg of the main fault with respect to the other the region of intersection is usually associated with intense fracturing increased microseismicity and uplift

inversion of source parameters from near and far field observations an application to the 1915 fucino earthquake central apennines italy we use a nonlinear inversion approach for determining source parameters of the fucino m s 6 9 earthquake that occurred along central apennines italy in 1915 taking into account both near field surface deformations and far field first motion polarities this event was one of the most destructive in italy this century causing over 30 000 casualties altitude and leveling measurements were performed before 1862 and after 1917 the event along a circular route consisting of 18 benchmarks polarities of first arrivals do not constrain a unique fault plane solution while the one obtained by inverting geodetic data with relevant constraints provided by neotectonic data disagrees with p wave polarities our joint inversion based on a robust fitting technique has resulted in only one well defined solution satisfying geophysical data as well as surface faulting distribution and paleoseismological information

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

effects of uplift and tilting in the central northern apennines italy abstract the morphotectonics of the central northern apennines reflect the effects of pliocene pleistocene regional uplift and tectonics high uplift rates and extensional tectonics prevailed in the axial sector while lesser uplifting eastward tilting and gravity sliding affected the periadriatic belt the axial sector has a chocolate slab pattern of blocks with intermontane depressions bounded by normal faults and characterized by differential vertical movements the periadriatic belt is a ne dipping monocline broken by transverse faults into separate blocks with different evolutionary development the evolution of the axial sector can be correlated with that of the periadriatic sector because the unconformities in the marine succession of the periadriatic basin are linked to pulses of uplift in the axial chain the amounts of coarse grained sediments in intermontane depressions and in the periadriatic belt are correlated with the erosion processes affecting the axial sector this morphostructural pattern may be connected with the formation of a long wavelength bulge associated with mantle upwelling

classification of seismic strain estimates in the mediterranean region from a bootstrap approach summary the uncertainty that may affect seismic strain estimates in the mediterranean is investigated using a distribution free numerical approach based on the bootstrap resampling technique applied to more than 2000 seismic source mechanisms of shallow earthquakes that occurred from the azores to iran in the period 1905 1999 this analysis shows that the short time interval covered by the available data set may be the main source of uncertainty on long term strain estimates since it could imply a biased representation of contributions from large earthquakes our results also indicate that as a possible consequence of this bias the condition of strain field uniformity is poorly verified in most of the zones considered the confidence limits obtained for scalar strains and directions of principal strain axes indicate that both the amount and the style of seismic deformation are poorly defined for roughly half of the zones considered mostly located in the western and central mediterranean area these results suggest that one should be cautious in using seismic strain estimates when not accompanied by satisfactorily uncertainty evaluation

stratigraphic evidence for anthropogenically induced coastal environmental change from oaxaca mexico abstract previous interdisciplinary paleoenvironmental and archaeological research along the rio verde valley of oaxaca mexico showed that holocene erosion in the highland valleys of the upper drainage basin triggered geomorphic changes in the river s coastal floodplain this article uses stratigraphic data from sediment cores extracted from laguna pastoria an estuary in the lower rio verde valley to examine changes in coastal geomorphology potentially triggered by highland erosion coastal lagoon sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene times three distinct storm facies are identified from sediment cores obtained from laguna pastoria which indicate that profound coastal environmental changes occurred within the region and are correlated with increased sediment supplied from highland erosion the chione laevicardium facies was deposited in an open bay while the mytella barnacle facies and sand facies were deposited in an enclosed lagoon following bay barrier formation we argue that highland erosion triggered major geomorphic changes in the lowlands including bay barrier formation by 2500 cal yr b p these environmental changes may have had significant effects on human populations in the region the lagoon stratigraphy further indicates an increase in mid late holocene hurricane activity possibly caused by increased el nino frequencies

some problems in the late quaternary pollen records of central mexico basins of mexico and zacapu most pollen analyses of late quaternary sediments have been carried out in closed basins of the trans mexican neovolcanic belt in central mexico climatic changes have been inferred from these pollen data however some problems arise from reinvestigations the dominance of a few pollen types in general pinus quercus and alnus is almost constant among these records in spite of the importance of vulcanism and tectonism in the evolution of this region no effects of these factors are evident from the pollen records some of the problems are illustrated in the pollen records from lake texcoco and lake chalco in the basin of mexico and lake zacapu in michoacan

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

sensitivity of bulk sedimentary stable carbon isotopes to prehistoric forest clearance and maize agriculture the stable carbon isotope compositions d 13 c of tropical lake sediments and soils have been used to reconstruct the occurrence of prehistoric maize cultivation and its relative importance through time this study assesses some of the possible variables affecting the response of lake sediment bulk organic carbon isotope d 13 ctoc values to variations in the scale of prehistoric maize cultivation and the potential of this proxy to yield quantitative estimates of the scale of prehistoric maize agriculture in small tropical watersheds high resolution analyses of d 13 ctoc values maize pollen concentrations and mineral influx were conducted on sediments deposited during a w220 year period of prehistoric maize agriculture in the watershed of laguna castilla a small lake in the mid elevations of the cordillera central dominican republic close correspondence between d 13 ctoc values and maize pollen concentrations in the laguna castilla sediment record indicates a close relationship between the isotopic values and the scale of prehistoric maize cultivation correlations between the d 13 ctoc signature and mineral influx indicate that the isotope record is also sensitive to variations in allochthonous carbon delivery this study establishes that sedimentary d 13 ctoc values can provide a highly sensitive proxy of the spatial scale of prehistoric maize agriculture in small tropical watersheds but

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

tectonic role of ophiolite bearing terranes in the development of the southern apennines orogenic belt new data on ophiolite bearing terranes of the liguride complex together with some information on the terranes of the sicilide complex result in a better understanding of the role and tectonic significance of these units in the construction of the southern apennines orogenic belt the liguride complex is composed of two main tectonic units overlain by a thick turbiditic sequence of late oligocene middle miocene age the uppermost one frido unit is a polydeformed and polymetamorphosed sequence composed of two tectonic subunits of shales and calc schists respectively containing blocks of ophiolite garnet gneiss amphibolites and granitoids this unit is thrust over the un metamorphosed terranes calabro lucano flysch unit consisting of a broken formation with blocks of late jurassic ophiolite and their sedimentary cover cretaceous eocene pelagic sediments and late oligocene volcaniclastic deposits the frido unit underwent hp lt metamorphism p 8 10 kb t 400 500 c resulting in glaucophane and lawsonite assemblages in the ophiolitic rocks and aragonite in the meta limestones and calc schists followed by greenschist fades metamorphism p 4 kb t 300 350 c from a structural point of view units of the liguride complex comprise structures developed at different structural levels indicating progressive non coaxial deformation in response to tectonic transport towards the n ne the ophiolite bearing terranes of the liguride complex can be considered as a remnant of an accretionary complex in which the calabro lucano flysch unit represents the toe of the wedge where frontal accretion processes occur and the frido unit is a deeper portion emplacement of the frido unit is explained as being due to formation of a deep duplex structure during the early stage of continental collision processes the polarity of tectonic transport provides new evidence that the liguride complex represents a suture zone between the apulian and the calabrian blocks the age of collision appears to be not older than late oligocene the allochtonous terranes of the liguride and sicilide complexes therefore represent a complete accretionary wedge which records first subduction of the neotethys ocean beneath the calabrian europe continental margin and later continental collision with the african block

insights into present day crustal motion in the central mediterranean area from gps surveys summary in this paper we present observations of crustal motion related to a large gps network located in the central western mediterranean area velocities are obtained by the analysis of more than 30 observing sites at which at least three different gps campaigns were carried out in the time span 1991 1999 the results are presented both in the itrf96 reference frame and with respect to a eurasian fixed reference frame the sites located along the northern african margin in sicily and southern italy show prevalent northeastward movements with a mean velocity of roughly 0 7 cm yr 1 the relatively dense network available in the southern apennines led us to try a tentative estimate of the average strain rate in this zone resulting in a maximum extension of 0 021 0 006 10 6 yr 1 normal to the chain in ionian greece the two sites located south of the kephallinia discontinuity lefkas and kastro ilias consistently indicate a south to southwestward motion at an average rate of roughly 15 mm yr 1

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

fault geometries from the space distribution of the 1990 1997 sannio benevento earthquakes inferences on the active deformation in southern apennines in this study we analyze the recent 1990 1997 seismicity that affected the northern sector sannio benevento area of the southern apennines chain we applied the best estimate method bem which collapses hypocentral clouds to the events of low energy md max 4 1 seismic sequences in order to constrain the location and geometry of the seismogenetic structures the results indicate that earthquakes aligned along three main structures two sub parallel structures striking nw se 1990 1992 benevento sequence and one structure striking ne sw 1997 sannio sequence the southernmost nw se structure which dips towards ne overlies the fault that is likely to be responsible for a larger historical earthquake io max xi mcs 1688 earthquake the northernmost nw se striking structure dips towards sw the ne sw striking structure is sub vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake the spatio temporal evolution of the 1990 1997 seismicity indicates a progressive migration from se benevento to nw sannio associated to a deepening of hypocenters i e from about 5 to 12 km hypocenters cluster at the interface between the major structural discontinuities e g pre existing thrust surfaces or within higher rigidity layers e g the apulia carbonates available focal mechanisms from earthquakes occurred on the recognized nw se and ne sw faults are consistent with dip slip normal solutions this evidences the occurrence of coexisting nw se and ne sw extensions in southern apennines

injection of indian crust into tibetan lower crust a two dimensional finite element model study we propose a model in which the stronger indian crust injects into the weaker lower crust of tibet if the viscosity of the tibetan lower crust is below a critical value the continuous advancing of the indian crust beneath tibet would produce negligible variation in stresses on the bottom of the stronger brittle tibetan upper crust and would result in a spatially uniform uplift and a virtually undisturbed tibetan plateau surface this process is analogous to that of a piston rising in a hydraulic jack as additional fluid is forced into the chamber we find that if the viscosity of the tibetan lower crust is assumed to be constant throughout the computed critical viscosity is 6 1018 pa s for the present day lower crustal thickness of 58 km in addition to uniform viscosity two hypothetical depth dependent viscosities are also tested which give rise to essentially the same distribution of stress along the bottom of brittle upper crust our model also interprets the 4 km elevation contrast between the tibetan plateau and the tarim block a 1 160 viscosity contrast between the tibetan and tarim lower crust is required in order to maintain the current thickening rate of the tibetan crust 1 2 mm yr while keeping the thickness of the tarim crust unchanged

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

pleistocene strike slip tectonics in the lucanian apennine southern italy structural studies carried out in the lucanian apennines southern italy show that strike slip faulting was the principal mode of deformation of this area during middle upper pleistocene time w nw to e se trending left strike slip fault systems dissect the entire apennine mountain belt and affect the preexisting thrust geometry strike slip faults activated by a roughly e w shortening are characterized by different geometries representing the surface response to lateral motion occurring along deep seated structures the occurrence of different structural patterns which characterize different segments of strike slip system is related to 1 the depth of a major decoupling surface which separates the upper tectonic multilayered horizon apennines thrust belt system from the lower rigid horizon apulian belt in which strike slip structures have originated and 2 the geometric relationships between the strike slip faults and the thrust belt pattern which characterize the upper horizon the different segments of the strike slip system are interpreted as internal deformation developed within a crustal shear zone this zone which corresponds to the boundary between the apulian block and the apennine chain is characterized by sinistral movement as a response to the northwesterly convergent motion of the african plate with respect to europe

average strain rate in the italian crust inferred from a permanent gps network ii strain rate versus seismicity and structural geology summary high quality weekly solutions for the coordinates of 45 permanent gps stations spanning 1 6 years and covering the alpine mediterranean area are used to estimate a horizontal velocity field aligned with the itrf2000 velocity datum after subtracting model velocities for the eurasian plate we show that the residual velocity field north of the apennines in the adriatic dinaric region describes a nne trending tectonic flow with a negative velocity gradient from 6 mm yr 1 ne of the apennines to virtually zero ne of the dinarids in the calabria region we observe a divergent pattern with nnw orientation which turns to west as one moves north towards tuscany very small residual velocities are observed for stations in the sardinia corsica block spain southern france and north of the alps this regional pattern of velocities defines areas of intraplate strain on the basis of good station coverage and of a strain rate value above a threshold we define five provinces calabria central apennines both in the extensional regime and north adriatic eastern alps and south adriatic under compression we show that the orientations of the principal strain rate axes agree with the stress pattern that is inferred from local seismicity a comparison of the geodetically determined strain rate with the strain rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface strain for example the umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large but concentrated over a short time interval so that the equivalent coseismic strain rate was larger than the value observed geodetically on average depending on the assumptions on the seismogenic volume and time span 70 100 per cent of the surface strain seems to be accommodated by the release of seismic moment in the upper italian crust

subduction of the lithosphere and back arc dynamics insights from physical modeling physical modeling of the subduction of an elastico plastic lithosphere underlained by a low viscosity asthenosphere and driven by both horizontal compressional force and gravitational sinking of the subducting plate has shown the subduction regime to be strongly affected by 1 a where a and 1 are the asthenosphere and lithosphere densities at 0 a steady state process develops which requires a horizontal lithosphere compression of h 0 3 0 4 s 108 pa where s is the lithosphere yield limit the central part of the leading wedge of the overriding plate is nonisostatically elevated in this case especially in the region of the frontal arc which corresponds to a free air gravity anomaly maximum of 200 400 mgal a decrease in 0 compression of the overriding plate is considerably less from the onset of subduction and then decreases during subduction at some point compression changes into tension tensional nonhydrostatic stresses grow during the process to a value near h 0 1 0 2 s 0 4 108 pa both subsidence of the overriding wedge below the isostatic equilibrium level and an increase in the benioif dip angle accompany this process the gravity anomaly maximum is displaced into the volcanic arc in this subduction regime where it is normally less than 150 mgal if some weaknesses are present in the overriding plate tensional stresses result in a failure of the lithosphere at these locations and the broken lithosphere segment the arc plate starts to move counter to the subduction plate the arc plate slides along the underthrusting plate s surface without loss of contact and causes back arc opening hydrostatic suction prevents the plates from being separated this effect is caused by the peculiarity of a mechanical system whereby a low viscosity asthenosphere and a plastic lithosphere which effective yield limit is considerably lower than the hydrostatic stresses in the plate if the overriding lithosphere is not weakened enough to fail under the existing tension then the hanging slab breaks down under its own weight when it reaches a specific length both interacting plates undergo isostatic recovery in this case and the whole cycle is repeated again the hydrostatic suction effect also provides back arc tension under other conditions such as when asthenospheric flow forces the subducted plate to move away from the island arc

late holocene vegetation change in the sierra madre oriental of central mexico abstract past vegetation and climate changes reconstructed from a sediment core from laguna atezca molango mexico provide new insights into the environmental and cultural histories of the sierra madre oriental during the last 1700 yr pollen microscopic charcoal sediment chemistry loss on ignition and magnetic susceptibility indicate that three phases of human occupation deforestation and erosion ca a d 280 890 ca a d 1030 1420 and ca a d 1680 present alternate with two phases of abandonment ca a d 890 1030 and ca a d 1420 1680 forest composition of the two abandonment phases differed with cloud forest taxa liquidambar ostrya carpinus ulmus etc dominating the pollen record during the first phase and quercus and pinus pollen characterizing phase two these differences may reflect a climate change in which the second phase was drier than the first alternatively the increase in pinus and quercus may have been caused by a human induced decline in soil fertility the laguna atezca record also differs from several other mesoamerican paleoenvironmental records in that it shows no evidence of drought at the end of the classic period ca a d 900

a new proposal for the late cenozoic geodynamic evolution of the western mediterranean a simple mechanism of arcuate fold belt and back arc basin formation is presented based on the opening of mega continental tension gashes along pre existing deep parallel and steep faults that separate lithospheric units with different properties if plate convergence is parallel to these faults the fault bounded units open at right angles to the convergence vector adopting an arcuate shape with thrusting in front of the bowed out units and extensional basin opening between the separated units this model is applied to the cenozoic geodynamic evolution of the western mediterranean after the iberian collision 35 30 ma several ellipsoidal basins valencia alboran north algerian and liguro provencal developed by 10 ma along the eastern margin of the iberian plate the formation of these basins is attributed to an increase in ne sw horizontal tectonic palaeostress during early middle miocene times resulting from the post subduction collision of the tethyan oceanic lithosphere

deep structure of the campanian lucanian arc southern apennine italy abstract recent exploration activities and successful discovery of large oil fields in the upper val d agri area southern apennine italy have encouraged the collection of large quantities of geological and geophysical data and their integration into comprehensive geological models here we present a series of structural profiles based on several hundred kilometres of seismic lines two and three dimensional and the results of many deep wells the best seismic lines have been extensively reprocessed and also tied to magnetotelluric data geological interpretations of those lines have been interactively tested and verified by gravity and magnetic modelling and structural balancing the wells and seismic data demonstrate that the fundamental tracts of the deep architecture of the orogen as it appears today were developed only at the end of the late pliocene the final closure of the ensialic shear zone responsible for the subduction of at least 150 km of continental lithosphere originally underlying the lagonegro basin can be dated as early pliocene the involvement of the inner apulian platform in the core of the belt and the activation of a new and more external left lateral oblique ensialic shear zone can be constrained to the late pliocene pleistocene the seismic profiles clearly show the underthrusting of the outer apulian platform unit beneath the inner apulian platform unit the thick skinned character of the plio pleistocene contractional structures is evident from the structural profiles this geometry is constrained by gravity magnetic data and structural considerations according to the relatively steep angle of dip about 10 of the apulian foreland beneath the chain the structural profiles depict the general architecture of the campanian lucanian arc the apennine platform and lagonegro unit are largely allochthonous and a part of the lagonegro basement could be buried below the apennine platform sole thrust the neogene plastic successions of the apennine platform and lagonegro basin were detached and now outcrop in the bradanic foredeep the inner apulian platform constitutes a huge thrust sheet structured as a wide antiform in the core of the belt its regional culmination roughly corresponds to the val d agri area extensional and transtensional structures cross cut the pre existing compressional structures as shown by the quaternary valleys of vallo di diano and val d agri the profiles shown also highlight the existing contrast between the deep structures in the core of the belt and the tectonic style of the lagonegro liguride and sicilide units these units were in fact subjected to brittle ductile deformation under metamorphic part of liguridi units and deep diagenetic to anchizonal conditions lagonegro units and were affected by a general overthrust shear directed towards the ne the inner apulian platform was on the contrary involved in the thrust belt together with its basement whereas the outer apulian platform affected by a subduction underwent a regional bending with associated normal faulting

active oblique extension in the central apennines italy evidence from the fucino region the fucino basin is a flat quaternary depression within the central apennines it is surrounded by active normal faults with small oblique slip components surface faulting was observed along the east side of the basin during the ms 7 0 avezzano earthquake of 1915 in order to understand the kinematics of recent strain better and to assess the seismic hazard of this region we carried out a detailed geomorphic and structural study of the faults around the basin fault scarp heights were accurately measured with total station profiles and vertical slip rates were estimated assuming slope offsets to post date the end of periglacial abrasion 14 4 kyr bp to the north the most prominent fault the magnola fault appears to have an average postglacial throw rate of 0 7 0 3 mm yr 1 and together with the velino fault to be capable of generating earthquakes of maximum magnitudes of 6 9 7 3 with recurrence intervals of 1000 3000 yr east of the basin the serrone parasano and ventrino faults form a right stepping horsetail of the giovenco fault current vertical slip rates on the three former faults appear to be between 0 5 and 1 4 0 5 and 1 0 and 0 3 and 1 1 mm yr 1 respectively infrequent maximum magnitude earthquakes on them may also exceed 7 particularly in the case of coupled rupture with loosely constrained recurrence intervals up to several thousand years the right lateral slip components implied by the most recent slickensides and by geomorphic offsets on the nw se trending normal faults of the area suggest that the blocks they bound rotate counterclockwise consistent with oblique left slip on the nnw sse trending giovenco and ovindoli faults to the east sinistral shear parallel to the latter faults the maximum relief across the magnola fault and the postglacial slope offsets measured suggest that the extension rate across the central apennines might be of the order of 6 3 mm yr 1 in a n20 10 e direction more northerly than hitherto inferred

post seismic relaxation and earthquake triggering in the southern adriatic region summary an attempt at quantifying post seismic relaxation triggered by decoupling earthquakes along the eastern thrusting border of the adriatic plate southern dinarides is carried out by finite element modelling with a model constituted by an elastic lithosphere riding on a viscous asthenosphere in particular it is investigated the possibility that the above phenomenon is responsible for the fact that in the last two centuries most major earthquakes in the southern dinarides ms 6 have been followed within a few years by intense mainly tensional earthquakes in southern italy i e the zone lying on the opposite margin of the adriatic plate this analysis has been applied to the last example of the supposed seismic interrelation i e the triggering 1979 april 15 montenegro event ms 6 7 and the presumably induced 1980 november 23 irpinia earthquake in the southern apennines ms 6 9 results indicate that the strain induced in the southern apennines by the triggering event has significant amplitude since it largely exceeds the effect of earth tides and the principal stress axes are consistent with those of southern apenninic earthquakes the order of magnitude of the time delay between the montenegro and irpinia events 1 6 yr could be explained by assuming that earthquake triggering is most probable when the highest values of the induced strain rate reach the southern apennines in particular this interpretation predicts the observed time delay when a model diffusivity of 400 m2 s 1 is assumed the constraints that this diffusivity value may pose on the structural and rheological features of the crust upper mantle system in the study area are discussed it is shown that the effects of the montenegro event on the present velocity field are comparable to though systematically lower than the velocities suggested by geodetic observations in the italian region this suggests that geodynamic interpretations of geodetic data given without taking into account possible transient effects on the kinematic pattern as those related to post seismic relaxation may be incorrect experiments carried out by tentatively simulating the presence of subducted lithosphere along the western margin of the adriatic plate as a lateral variation of diffusivity have shown that this structural feature may emphasize e w tensional strains in the southern apennines