pinch and swell structures at the middle upper muschelkalk boundary triassic evidence of earthquake effects seismites in the germanic basin a limestone bed with synsedimentary deformations is described from the middle upper muschelkalk boundary middle triassic of thuringia germany the deformation structures have an elongated geometry in a preferential n s to nnw sse direction and are several metres across in size they are similar to ball and pillow structures but differ from these by absence of significant loading into underlying beds their development is interpreted as a result of bed internal deformation with bed thickening due to lateral contraction and bed thinning due to stretching this deformation mechanism is comparable to the one producing boudinage structures in particular pinch and swell structures the deformation style and size of these structures and their widespread occurrence together with other synsedimentary deformation structures support their interpretation as earthquake induced structures seismites synsedimentary deformation structures are common features that occur in a narrow stratigraphic unit at the middle upper muschelkalk boundary in different parts of the germanic basin and point to tectonically influenced changes in the depositional regime and basin organization further examples of pinch and swell structures from the lower and upper muschelkalk suggest that tectonics significantly influenced the sedimentation in the germanic basin during middle triassic time

complex concentric granitoid intrusions in the coastal mobile belt espirito santo brazil the santa angelica pluton an example the brazilian coastal mobile belt in southern espirito santo consists of archean to upper proterozoic units which have been metamorphosed and deformed to a gneiss migmatite and granulite facies rock assemblage during archean and proterozoic tectono thermal events

shallow marine carbonate sedimentation in a tectonically mobile basin the muschelkalk middle triassic of upper silesia southern poland abstract earthquakes and resulting tsunamis are important geological phenomena however their sedimentary paleorecord is difficult to identify because some fabrics can be generated by other processes and the criteria for discrimination of seismic and non seismic triggers are not fully established this paper presents several deformation and sedimentary structures in the middle triassic carbonates of upper silesia and discusses their seismogenic and tsunami origin and controls on the deformation type intensity preservation potential and geographic distribution the deformation type and intensity were controlled by the primary lithology whereas the lateral continuity of deformed horizons depended on the lateral extent of hosted facies the thickness and abundance of these structures increase towards the krakow lubliniec fault zone which bounded the area from the east and is considered as the main epicentrum of earthquakes and tsunami initiation the discussed fabrics have a universal significance and can potentially be found in other shallow marine carbonate successions

sedimentary structures tentatively attributed to seismic events abstract fingerprints of earthquakes in the sedimentary record are as yet difficult to identify this is particularly true for failure phenomena dewatering slumping fault graded and turbidite structures that could have been triggered also by other kinds of energy input other promising candidates are strange biostratinomic features convex down stacking of shells current orientation in wave ripple accumulations as well as certain preservational features found in geosynclinal pelagic limestones but in every case verification of the seismic origin is still needed

sedimentary features of tsunami backwash deposits in a shallow marine miocene setting mejillones peninsula northern chile abstract miocene shoreface sandstones in the caleta herradura half graben northern chile contain an exceptionally coarse deposit that based on sedimentologic and stratigraphic features is regarded as having been laid down during a tsunami event by non cohesive and sediment laden subaqueous density flows interpretations of the principal sediment depositing mechanisms effective in the tsunami surges rely largely on field observations of deposit geometry and internal sedimentary characteristics this example comprises two erosively based sedimentation units that were probably deposited by successive waves in the tsunami wave train the lower unit consists of a clast supported polymodal boulder bearing breccia composed mostly of angular clasts and fewer well rounded clasts framework components are mostly chaotic but may also exhibit either inverse to normal grading or crude normal grading laterally changes in characters of depositional facies are common and abrupt the sand sized bioclastic rich matrix is poorly sorted and very similar to the underlying lower shoreface bioclastic sandstone implying that soft sediments eroded at the lower erosional surface contributed to the tsunami deposit the bulk of the upper unit is a poorly sorted breccia bearing sandstone pebbles and cobbles are scattered massive or normally graded sporadic outsized boulders emplaced as debris fall deposits may occur along the erosional base an array of signatures such as unusually coarse grain size in comparison to the surrounding deposits erosional bases the mixed sources of sediments multiple erosional and depositional events normal size grading or massive texture are all considered distinctive features of tsunamigenic deposits backwash deposition is indicated by the incorporation within the tsunami deposits of sediments derived from mixed sources such as angular clasts from nearby subaerial settings rounded clasts reworked from beach gravels and bioclastic sand eroded from older and unconsolidated shoreface deposits notwithstanding the absence of soft sediment deformation features the marked facies change from a lower shoreface into an upper shoreface environment through the tsunamiites provides directional information about the origin of the tsunami wave it was most likely produced by a sea floor fault displacement associated with an episode of sudden probably coseismic coastal uplift

fractal analysis of mingled mixed magmas an example from the upper pollara eruption salina island southern tyrrhenian sea italy abstract upper pollara eruption products 13 ka salina island italy include both homogeneous and heterogeneous pumices resulting from mixing mingling processes between an hk andesite and a high sio2 rhyolite representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling mixing structures image analysis techniques are applied and eight grey color ranges classes are extracted from high resolution scans of pumice class 1 lighter colors and class 8 darker colors show end member glass compositions i e hk andesite and high sio2 rhyolite respectively these two classes show spot to cluster like morphological structures intermediate classes show an hk dacitic to rhyolitic composition and a banding to fold like morphology fractal analysis by box counting of the boundary pattern of eight grey classified images is performed over a length scale of 0 028 1 8 cm fractal dimension d is between 1 01 and 1 84 coupled fractal analysis and geochemical data reveal that d increases as the degree of magma interaction homogenization increases this feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection we conclude that the increase of d observed in the upper pollara samples reflects the transition from fractal mixing to homogenization end member magmas hk andesite and high sio2 rhyolite represent isolated mixing regions while homogenized magmas represent active mixing regions in the analyzed pumices isolated and active mixing regions coexist at scales between 10 4 and 10 2 m morphological and compositional features of the upper pollara pumices result from turbulence

fractal structure of heterogeneous ejecta from the me akan volcano eastern hokkaido japan implications for mixing mechanism in a volcanic conduit abstract during the somma building activity about 13 ka of the me akan volcano eastern hokkaido simultaneous eruptions of basaltic andesite andesite and dacite magmas yielded a variety of heterogeneous juvenile ejecta these heterogeneous ejecta ranging from mafic scoria to dacite pumice can be divided into three types based on the morphological structure of the pumicescoria boundary type 1 is characterized by a spot pattern type 2 by a banded pattern containing streaky dense banded and vortical structures and type 3 by irregular lumps with fingering patterns these structures and the eruptive sequence suggest that the basaltic andesite magma was injected into or drawn up with the dacite magma within the volcanic conduit beneath the nakamachineshiri crater a fractal analysis of boundary patterns of the heterogeneous ejecta was performed by a counting method over a length scale of 0 2 mm to 17 mm in order to characterize the mixing mechanism in the conduit the morphological patterns of heterogeneous ejecta have a self similar structure with fractal dimensions of d 0 9 to 1 2 for type 1 d 1 2 to 1 6 for type 2 and of d 1 2 to 1 4 for type 3 the mean value of d 1 37 0 11 for types 2 and 3 ejecta is almost the same as the value measured for fluid turbulence structures such as clouds or jets thus we infer that formation of banded and irregular lump structures was probably produced by turbulent entrainment of dacite magma into basaltic andesite magma in the conduit the lower fractal dimension of type 1 d 1 11 0 08 is due to weakly turbulent or nearly laminar processes homogeneous andesite magma is inferred to result from complete vigorous turbulent mixing

use of soils and colluvial deposits in analyzing tectonic events the southern arava rift israel abstract buried soils in colluvium units developed on downthrown fault blocks have been presumed to form during periods of tectonic quiescence this assumes however that all colluvial units on a fault scarp are tectonically induced particularly for a multiple event fault scarp to test this hypothesis we compared the colluvial stratigraphy and pattern of soil development on two non tectonic scarps terrace risers and a nearby multiple event fault scarp on the same alluvial fan surface both slopes developed under extremely and climatic conditions the colluvial stratigraphy and soil catenary relationship developed on terrace risers were found to be substantially different from those on the multiple event fault scarp the fault scarp colluvium contained several colluvial units separated by soils whereas only two colluvial units without buried soils were found on the terrace risers the colluvial units on the fault scarp were triangular in shape while those on the terrace riser were concave and overlapped up the slope cumulic soils indicating a continuous and low rate of deposition during pedogenesis were formed along the terrace riser in contrast buried soils indicating episodic deposition occurred on the downthrown block of the multiple event fault scarp accordingly the colluvial stratigraphy developed on the fault scarp can be viewed as a record of distinct tectonic events with no climatically controlled deposition the data indicate that soils and sedimentary stratigraphy can serve as useful indicators to distinguish terrace risers and single event fault scarps from multiple event fault scarps these indicators can be helpful in distinguishing phases of tectonic activity and in evaluating recurrence intervals on a multiple fault scarp

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

late neoproterozoic cambrian granitic magmatism in the aracuai orogen brazil the eastern brazilian pegmatite province and related mineral resources

tsunami induced conglomerates in miocene upper bathyal deposits chita peninsula central japan abstract the tsubutegaura conglomeratic tsunamiites occur in the middle section of the miocene storm related sand silt alternation system in the chita peninsula central japan deposition of the system in the upper bathyal environment in a bay and synsedimentary seismic activity has been elucidated by palaeontological palaeogeographical and sedimentological studies two coupled units each built up by a conglomerate layer with an overlying sandstone layer and the alignment of lenticular sedimentary bodies are exceptional in this sequence some typical lenticular bodies confined within sedimentary troughs consist of a boulder bearing conglomerate layer and calcareous sandstone layer of the lower couple and another conglomerate layer of the upper couple the tuffaceous sandstone layer of the upper couple is distributed more widely than the other lithologies the framework gravels in the coupled conglomerates form a clast supported fabric and are quite notably monomictic the clasts are angular and imbricated partly forming peculiar gravel clusters due to traction current transportation conspicuous laminations develop in the coupled sandstone layers antidunes with chute and pool structure in the upper couple sandstone layer indicate deposition from an upper flow regime current on the other hand the calcareous composition of the lower couple sandstone layer reveals shallow water provenance thixotropic deformations and diastasis cracks in the siltstone bed immediately beneath the layers of the couples show that a severe earthquake tremor and a rapid change of water pressure occurred just before the deposition of the tsunamiites submarine debris flows due to collapse of a fault scarp in a shallow bank and the ensuing wash by two pulses of the tsunami induced ebb current comprise the scenario for the formation of the tsubutegaura conglomeratic tsunamiites

interactions between rhyolitic and basaltic melts unraveled by chaotic mixing experiments abstract magma mixing may operate at any stage in the evolution of a magmatic system the development of mixing is strongly controlled by fluid dynamics and its understanding requires a comprehensive physico chemical approach in order to identify and interpret its occurrence in nature here we experimentally study the physical and chemical interplays during the mixing of basaltic and rhyolitic natural melts from the snake river plains usa in particular we present the results of the first high temperature mixing experiments performed under controlled chaotic dynamic conditions providing a new methodological approach to constrain the complexities of the mixing process between natural silicate melts the mixing process is initially governed by the dynamics of stretching and folding of the melts producing alternating flow bands these bands increase the contact area between the end members which subsequently enhance chemical exchanges and thus contribute to the generation of regions with variable degrees of hybridization we quantified the mobility of major and trace elements across contact areas and analyzed the concentration variance decay induced by chemical diffusion the analysis shows that elements diffuse with different efficiencies as the chemical gradient evolves and therefore the achievement of hybrid compositions contrasts between elements the approach introduced in this study can in principle be applied to mixing trends observed in nature in order to estimate the time scales and degree of magma mixing evidenced across volcanic rocks deposits

morphochemistry of patterns produced by mixing of rhyolitic and basaltic melts abstract in this work we present the results of time series experiments performed by mixing basaltic and rhyolitic melts at high temperature using a device recently developed to trigger chaotic dynamics in a mixing system the morphology of mixing patterns is quantified at different times by measuring their fractal dimension and a linear relationship is derived between mixing time and morphological complexity the complexity of mixing patterns is also compared to the degree of homogenization of chemical elements during mixing and empirical relationships are established between the fractal dimension and the temporal variation of concentration variance of elements new concepts and tools to study the magma mixing process unfold from the experimental results presented in this work the first one is that the mixing patterns are fractals and they can be quantified by measuring their fractal dimension this represents a further step in the quantification of the magma mixing process the second outcome is that the relationship between the fractal dimension of the mixing patterns and mixing time is linear this has important volcanological implications as the analyses of the morphology of mixing patterns in volcanic rocks can be complemented by experiments to build a new chronometer to estimate the mixing to eruption time a further result from this work is the relationship between the fractal dimension of mixing patterns and concentration variance of chemical elements this represents the first morphochemical study in igneous petrology bringing with it the potential to infer the relative mobility of chemical elements during the time progression of mixing by analyzing the morphology of mixing patterns in the rocks

the lower permian freshwater carbonates of the slawkow graben southern poland sedimentary facies context and stable isotope study abstract during early permian times the post hercynian rift valley known as the slawkow graben was filled with typical continental molasse deposits including fanglomerates and olistolites playa flat sediments with evaporites volcaniclastics and carbonates deposited in small spring fed basins oasis environment lithofacies variability lithofacies relationships sedimentary structures and paleokarst data indicate a highly changeable sedimentary environment controlled by climate syndepositional faulting and accompanying volcanism differential uplift resulted in a high relief topography the basin margin mountains probably having a relative altitude of up to 1000 m the stable isotopic composition 13 c 18 o of the spring related carbonates indicate seasonal temperature differences of up to 15 c a value that is close to the average annual temperature amplitude in the present day subtropical zone other environmental indicators e g red beds evaporites braided stream sediments corroborate the isotopic interpretation a longer term 6 7 year cycle reflected in 18 o composition of the carbonate is attributed to rainfall fluctuations

late quaternary sediment sediment mass flow processes and slope stability on the scotian slope canada the study area just to the west of the verrill canyon on the scotian slope eastern canada exhibits both large and small scale sediment mass movement features study of high resolution seismic reflection and sidescan sonar data shows that a large portion approximately 70 of the near surface sediment 20 m in the area has undergone erosion rotational slumping and internal deformation remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores sediment physical properties are highly dependent on sediment type lithofacies frequent facies changes both temporally and spatially make correlation between cores difficult although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels the triggering mechanisms for the large scale events are less obvious slope stability analyses indicate that at present the seabed is stable the most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock our analyses demonstrate that it is unlikely that large magnitude distant earthquakes such as those previously proposed in the laurentian slope seismic zone lsp model could initiate failure of sediment in the study region our data support the interpretation that more frequent lower magnitude earthquakes closer to the study region as previously proposed in the eastern slope experimental source zone esx model are the likely causes of large scale slope failures furthermore excess pore pressures resulting from shallow gas and or high sedimentation rates during deglaciation contribute to slope failure

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

time evolution of chemical exchanges during mixing of rhyolitic and basaltic melts we present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts the mixing process is triggered by a recently developed apparatus that generates chaotic streamlines in the melts mimicking the development of magma mixing in nature the study of the interplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing experiments under controlled chaotic dynamic conditions the variation of major and trace elements is studied in detail by electron microprobe and laser ablation icp ms the mobility of each element during mixing is estimated by calculating the decrease in the concentration variance in time both major and trace element variances decay exponentially with the value of exponent of the exponential function quantifying the element mobility our results confirm and quantify how different chemical elements homogenize in the melt at differing rates the differential mobility of elements in the mixing system is considered to be responsible for the highly variable degree of correlation linear nonlinear or scattered of chemical elements in many published inter elemental plots elements with similar mobility tend to be linearly correlated whereas as the difference in mobility increases the plots become progressively more nonlinear and or scattered the results from this study indicate that the decay of concentration variance is in fact a robust tool for obtaining new insights into chemical exchanges during mixing of silicate melts concentration variance is in a single measure an expression of the influence of all possible factors e g viscosity composition and fluid dynamic regime controlling the mobility of chemical elements and thus can be an additional petrologic tool to address the great complexity characterizing magma mixing processes

depositional events and their records an introduction abstract event deposits of some lateral extent as defined here occur almost in all types of sedimentary basins the reflect either local intra basinal processes or they are associated with regional or global mechanisms some types of event beds such as sediment gravity flows sandy and muddy turbidites are common and usually well preserved they make up large proportions of basin fills whereas others e g tsunami deposits and in situ earthquake structures appear to be less frequent or rare in the geological record volume frequency and facies of event deposits are controlled by several processes pre event sediment accumulation triggering and transport mechanisms and mode of final deposition

some aspects of the recent tectonics in the strait of messina italy abstract during pliocene and pleistocene times the strait of messina was subjected to extensional tectonism which was contemporaneous with marine sedimentary processes various tectonic sedimentary features created by this combination of processes are reviewed depocentres synsedimentary truncations and the association of sedimentary dykes related to extensional fissuring and hydraulic fracturing these features are regarded as characteristic accompaniments to extensional block faulting the recent structural evolution of the strait of messina margins provides an illustration of high magnitude vertical movements occurring within a short time interval the subsidence phase is related to fault movements which generate important fault scarps and sedimentary dykes phases of upheaval in contrast correspond to a general uplift of the margins unrelated to the local fault movements

earthquakes as a triggering mechanism for debris flows and turbidites on the calabrian ridge abstract debris flows and turbidites have been described in piston cores bottom photographs and side looking sonar records from basin floors amid the rugged irregular topography of the calabrian ridge a sediment transport process is inferred which began with a rotational slump on the steep basin wall subsequently transformed into a debris flow and turbid cloud such events occurred approximately every 1500 years because the debris flow turbidite deposits are correlative between basins some relatively widespread mechanism such as an earthquake is required to initiate the slope failure the estimated intensity of ground shaking as a result of historical earthquakes on the nearby calabrian and hellenic arcs has been used to develop a relationship between frequency of occurrence and intensity of ground shaking extrapolation of this relation to infrequent large magnitude events shows that the 1500 yr event is small enough to be geologically plausible but large enough to cause slope failure on basin walls it is possible that the historical record fortuitously contains one of these large magnitude long repeat time events which may have caused the most recent of the observed debris flows in 1903

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

late middle to late ordovician seismites of kentucky southwest ohio and virginia sedimentary recorders of earthquakes in the appalachian basin synsedimentary ball and pillow beds breccias and faults in late middle to late ordovician foreland basin rocks of kentucky southwest ohio and virginia indicate broad zones of seismicity near the cincinnati arch and taconic orogenic front during deposition earthquake induced liquefaction formed seismites that include ball and pillow beds and rare sedimentary breccias that are correlative over large areas hundreds to thousands of square kilometers comparison of these features with liquefaction structures in holocene sediments indicates that the ordovician ball and pillow beds were probably generated by large earthquakes magnitudes 6 the ordovician seismites also provide information about epicenter location and the recurrence interval of large earthquakes in the ordovician foreland basin some were produced by faulting in the foreland and accretionary prism however horizons of resedimented lithoclastic breccias in the jeptha knob cryptoexplosive structure appear to correlate with several ball and pillow beds on jessamine dome along the cincinnati arch suggesting that some of the seismites may be genetically related to this enigmatic structure

isotopic evolution of the mantle the role of magma mixing trace element and isotopic data for magmas from the two major mantle reservoirs appear to be inconsistent the incompatible elements and sr and nd isotopes show that abyssal tholeiities morb are form a reservoir that has current and time integrated depletions of the elements that are fractionated into a melt morb however have206pb 204pb and207pb 204pb ratios suggesting long term enrichment in u pb i e future single stage ages alkali basalts and tholeiities from continents and oceanic islands are derived from lile and u pb enriched reservoirs sr and nd isotopic ratios however appear to indicate that some of these basalts are derived from unfractionated reservoirs and others from reservoirs with time integrated depletions the apparent stages of the mantle reservoirs are much younger than the ages of continental shields these inconsistencies can be reconciled by assuming that oceanic and continental basalts are mixtures of magmas from depleted and enriched reservoirs morb are slightly contaminated depleted magmas while ocean island and continental basalts are mixtures of morb or a depleted picritic parent magma and an enriched end member having trace element patterns similar to high k magmas such as kimberlites or nephelinites the mixing relations are such that mixtures can be enriched in u pb rb sr nd sm 206pb 204pb relative to primitive mantle yet appear to have time integrated depletions in143nd 144nd and87sr 86sr a small amount of contamination by material from an enriched reservoir can explain the pb results for morb depleted basalts are more sensitive to pb than to rb or nd contamination the238u 204pb of uncontaminated morb may be about 7 compared to 7 9 for the primary growth curve and 10 for the enriched reservoirs similarly continental and ocean island basalts may represent mixtures of enriched and depleted magmas if so the ages of mantle reservoirs have been underestimated we propose that both of the major mantle magmas source are in the upper mantle and that both are global in extent the shallower one 200 km depth is inhomogenous having been enriched metasomatised at various time by fluids from the depleting layer it may also be the sink of subducted sediments and hydrothermally altered oceanic crust the deeper source 220 670 km depth is more homogenous more garnet rich and provides depleted magmas which however become contaminated as they rise through the shallow encriched layer partial melting and diapiric ascent originated in the thermal boundary layer between the two chemically distinct layers magma mixing prior to eruption is an inevitable consequence of a chemically layered mantle with depleted magmas rising through an enriched uppermost mantle this allows quantification of the heretofore nebolous concept of mantle metasomatism

architecture of late orogenic plutons in the aracuai ribeira fold belt southeast brazil abstract post collisional to late orogenic magmatism 580 to 480 ma in the aracuai ribeira fold belt se brazil is characterized by the predominance of high k metaluminous allanite titanite bearing granitoids small lenses of coronitic gabbro anorthosite pyroxenite and phlogopite peridotite are also common in deeper exposed areas of this fold belt in the region of southern espirito santo state the deep erosional level associated with a steep topography reveals the internal architecture of the intrusions a tendency to funnel shaped bodies with sub vertical hemi ellipsoidal conical roots changing upwards to shallow dipping tops associated stocks sills and dykes of basic and acid rocks generally intrude the enclosing gneisses along the foliation planes local ductile shear zones and parallel to fold hinges the contact between intrusions and the enclosing rocks is sharp in deeply eroded plutons e g santa angelica venda nova mimoso do sul and varzea alegre but at shallow levels e g castelo pedra azul and conceicao de muqui agmatic stoping zones occur along the borders a magmatic foliation within the granitoids is usually well marked but the schistosity in the surrounding gneisses wraps around the plutons the intrusions have a bimodal chemical distribution and generally are reversely zoned with mafic cores gabbro diorite to tonalite surrounded by a mingled marble cake zone where basic and acid rocks are interfingered and an external zone of syenomonzonite and granite widespread evidence of mingling and mixing between contrasting magmas of gabbroic and granitic and or syenomonzonitic compositions is characteristic for all intrusive complexes we suggest that replacement of lithospheric mantle by hot asthenospheric mantle induced partial melting of the crust the mantle exchange was due to lithospheric mantle delamination and slab breakoff following collisional orogenesis the bimodal plutons result from interaction among the contrasting magmas ascent and emplacement followed older regional structures such as regional fold hinges and ductile shear zones

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

enhancement of magma mixing efficiency by chaotic dynamics an experimental study magma mixing is common in the earth understanding the dynamics of the mixing process is necessary for dealing with the likely consequences of mixing events in the petrogenesis of igneous rocks and the physics of volcanic eruptive triggers here a new apparatus has been developed in order to perform chaotic mixing experiments in systems of melts with high viscosity contrast the apparatus consists of an outer and an inner cylinder which can be independently rotated at finite strains to generate chaotic streamlines the two cylinder axes are offset experiments have been performed for ca 2 h at 1 400 c under laminar fluid dynamic conditions re 10 7 two end member silicate melt compositions were synthesized 1 a peralkaline haplogranite and 2 a haplobasalt the viscosity ratio between these two melts was of the order of 103 optical analysis of post experimental samples reveals a complex pattern of mingled filaments forming a scale invariant i e fractal distribution down to the m scale as commonly observed in natural samples this is due to the development in space and time of stretching and folding of the two melts chemical analysis shows strong non linear correlations in inter elemental plots the original end member compositions have nearly entirely disappeared from the filaments the generation of thin layers of widely compositionally contrasting interfaces strongly enhances chemical diffusion producing a remarkable modulation of compositional fields over a short length scale notably diffusive fractionation generates highly heterogeneous pockets of melt in which depletion or enrichment of chemical elements occur depending on their potential to spread via chemical diffusion within the magma mixing system results presented in this work offer new insights into the complexity of processes expected to be operating during magma mixing and may have important petrological implications in particular 1 it is shown that in contrast with current thinking rheologically contrasting magmas can mix i e with large proportions of felsic magmas and high viscosity ratios thus extending significantly the spectrum of geological conditions under which magma mixing processes can occur efficiently 2 the mixing process cannot be modeled using the classical linear two end member mixing model and 3 the chemical compositions on short length scales represent snapshots within the process of mixing and therefore may not reflect the final composition of the magmatic system this study implies that microanalysis on short length scales may provide misleading information on the parental composition of magmas

compositional variations and magma mixing in the 1991 eruptions of hudson volcano chile the august 1991 eruptions of hudson volcano produced 2 7 km3 dense rock equivalent dre of basaltic to trachyandesitic pyroclastic deposits making it one of the largest historical eruptions in south america phase 1 of the eruption p1 april 8 involved both lava flows and a phreatomagmatic eruption from a fissure located in the nw corner of the caldera the paroxysmal phase p2 began several days later april 12 with a plinian style eruption from a different vent 4 km to the south southeast tephra from the 1991 eruption ranges in composition from basalt phase 1 to trachyandesite phase 2 with a distinct gap between the two erupted phases from 54 60 wt sio2 a trend of decreasing sio2 is evident from the earliest part of the phase 2 eruption unit a 63 65 wt sio2 to the end unit d 60 63 wt sio2 melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases the basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes a combination of observed phase assemblages inferred water content crystallinity and geothermometry estimates suggest pre eruptive storage of the phase 2 trachyandesite at pressures between 50 100 megapascal mpa at 972 26 c under water saturated conditions log fo2 10 33 0 2 it is proposed that rising p1 basaltic magma intersected the lower part of the p2 magma storage region between 2 and 3 km depth subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the hudson caldera the presence of tachylite in the p1 products suggests that some of the magma was stalled close to the surface 0 5 km prior to eruption seismicity related to magma movement and the p1 eruption combined with chamber overpressure associated with basalt injection may have created a pathway to the surface for the trachyandesite magma and subsequent p2 eruption at a different vent 4 km to the south southeast

evolution of the silicoflagellate naviculopsid skeletal morphology in the cenozoic abstract the naviculopsid morphology which consists of an arch across the minor axis of a basal ring with two corners and sides is the simplest of the cenozoic silicoflagellate skeletal designs that include an apical structure this skeletal design is most often associated with the genus naviculopsis geologic range middle paleocene to early miocene but also occurs among other silicoflagellate genera this paper interprets the evolutionary history for silicoflagellates of naviculopsid morphology beginning with a group of large two sided silicoflagellates from the late early paleocene recently placed in genus pseudonaviculopsis and ending with a late miocene group of naviculopsid morphologies associated with bachmnnocena diodon subsp nodosa between these is naviculopsis which has more than twenty species recognized in deep sea sediments a significant portion of the naviculopsis taxa discussed in this paper are associated with plexus episodes of abundant and unusual variability from the late paleocene late eocene and early miocene a possible explanation of the development of this skeletal morphology as well as silicoflagellates with more complicated apical structures is a need to decrease the size of portals which may better support the cell boundary during mitosis

the middle triassic magnetostratigraphy from the peri tethys basin in poland abstract the paper presents the first complete magnetic polarity scale obtained for the middle triassic of the northern peri tethys area the roetian and muschelkalk deposits of southern poland upper silesia the holy cross mountains were studied paleomagnetically the obtained paleopole a 52 n 143 e fits well to the middle triassic ca 240 ma segment of the stable european apwp a set of various quality characteristic directions isolated in 106 samples was used for construction of the composite polarity scale this peritethyan scale has been tied with conodont zonation and referred to the scale erected earlier in the tethyan realm comparison of both scales indicates that the whole roetian succession in the southern polish basin should be correlated with the latest olenekian the normal marine sedimentation ceased in the polish basin as early as in the late fassanian time the obtained magnetostratigraphic scale combined with the sequence stratigraphic framework enables a reliable chronological correlation of the late olenekian ladinian succession over the entire peri tethys basin

depositional facies and sedimentary successions of earthquake induced tsunami deposits in upper pleistocene incised valley fills central japan abstract two anomalous deposits with well preserved sedimentary structures were discovered in a drowned valley and in relict barrier sand body deposits in the furuya mud and kyomatsubara sand of the upper pleistocene incised valley fills the sedimentary features of both deposits are interpreted as earthquake induced tsunami deposits which were deposited in incised valley fills the tsunami deposit in the drowned valley furuya mud is 150 cm thick and shows a contorted structured bed in the lower part and cross laminated sand in the upper part the tsunami deposit in barrier sand body kyomatsubara sand is 270 cm thick and shows structureless sand with mud clasts in the lower part cross laminated sand with mud drapes in the middle part and mud with small wave ripples in the upper part taken together these sedimentary features suggest a model for the composite succession which is comprised of three units a lower earthquake shock influenced anomalous convoluted part a middle part dominated by tsunami generated tractional currents and an upper suspended sediment part the lower part is interpreted as earthquake event deposits seismites and the middle and upper parts as tsunami current deposits tsunamiites

trace element mobility during magma mixing preliminary experimental results abstract magma mixing tests have been performed experimentally in a taylor couette like experimental setting the variation of trace element concentrations along transects crossing the resultant melt column has been measured results indicate a strongly variable mobility of the different trace elements in the same mixing system such a different behaviour of trace elements tends to be enhanced as the mixing time increases leading to the production of highly heterogeneous volumes of melts in which depletion and enrichment of trace elements occurred depending on their potential of spreading across the magma mixing system the results presented here offer new insights into the complexity of processes expected to be operating during mixing of magmas it is demonstrated that on short mixing times also the trace elements may become highly non correlated this is due to the development of chaotic advection diffusion processes in the system these results indicate that the onset of diffusive fractionation processes may strongly influence the patterns of data on inter elemental diagrams depending on the relative mobility of the different elements

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

sedimentologic and geomorphologic tsunami imprints worldwide a review abstract tsunami events with extreme effects on sedimentary transport or considerable alterations of the coastal configuration are rather rare regarding human history but considering geological timescales they occur frequently at least 100 megatsunami in different parts of the world have been recorded in the past 2000 years but presumably far more have failed to be noticed during historical times and are not mentioned either in written or oral ancient records therefore the topic of paleotsunami requires inevitable sedimentological and geomorphological research however field research concerning paleotsunami is astonishingly rare within the scientific approach and only 5 of the existing tsunami literature is related to this subject future efforts in paleotsunami research should focus on the geological evidence of these mega events to clarify their contribution to coastal forming processes this paper reviews the state of the art knowledge of sedimentologic and geomorphic imprints of tsunami along the world s coastlines in order to highlight the need for more detailed studies of paleotsunami depositional and geomorphological traces

soft sediment deformation structures in late albian to cenomanian deposits sao luis basin northern brazil evidence for palaeoseismicity soft sediment deformation structures from the alc ntara formation late albian to cenomanian sao luis basin northern brazil consist of 1 contorted structures which include convolute folds ball and pillow structures concave up paths with consolidation lamination recumbently folded cross stratification and irregular convolute stratification that grades into massive beds 2 intruded structures which include pillars dykes cusps and subsidence lobes and 3 brittle structures represented by fractures and faults displaying planes with a delicate ragged morphology and sharp peaks these structures result from a complex combination of processes mostly including reverse density gradients fluidization and liquefaction reverse density gradients promoted by differential liquefaction associated with different degrees of sediment compaction led to the genesis of convolute folds more intense deformation promoted the development of ball and pillow structures subsidence lobes and sand rolls which are attributed to denser and thus more compacted less liquefied portions that sank down into less dense more liquefied sediments irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation the subsidence of beds was accompanied by lateral current drag and fluid escape from water saturated sands in addition the fractures and faults record brittle deformation penecontemporaneous with sediment deposition all these mechanisms were triggered by a seismic agent as suggested by a combination of criteria including 1 the position of the study area at the edge of a major strike slip fault zone that was reactivated several times from the albian to the holocene 2 a relative increase in the degree of deformation in sites located closer to the fault zone 3 continuity of the deformed beds over large distances several kilometres 4 restriction of soft sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata 5 recurrence through time and 6 similarities to many other earthquake induced deformational structures

shallow marine tsunami deposits in teluk banten nw java indonesia generated by the 1883 krakatau eruption teluk banten tb is a tropical shallow marine embayment with coral reef islands close to the krakatau volcanic complex the 1883 krakatau eruption generated a tsunami which had a devastating effect on the neighboring coastal areas the effects of the 1883 krakatau eruption and the associated tsunami on the bottom sediments in tb are assessed using textural compositional and 210 pb geochronological data an important diagnostic criterion consists of the occurrence of tephra conform descriptions of the 1883 eruption tephra the tsunamite consists of a sandy layer with abundant reworked shell and other carbonate fragments coarse components in the tsunamite consist of locally derived material eroded from the seabed land derived components are incorporated in the tsunamite only in close proximity to the coast the tsunamite is thickest in localized areas of the central part of the bay along the northern open sea facing slope of tb the tsunamite is relatively thin 6 7 cm thick but well preserved as little postdepositional modifications have occurred in the eastern bay area recent erosion since the redirection of the ciujung river in the 1920s has removed the krakatau tsunamite along the west coast of tb the only signature of the 1883 krakatau eruption consists of tephra and evidence for a high energy event is lacking presumably the western area was sheltered from the tsunami wave coming from the northwest at the shallower stations with low accumulation rates the tephra has been thoroughly mixed by bioturbation 2003 elsevier science b v all rights reserved

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

chaotic flow patterns from a deep plutonic environment a case study on natural magma mixing this work focuses on the mixing between basalt and granite in a deep plutonic environment the description of mixing patterns and measurements of fractal dimensions and the evaluation of geochemical data from a cambro ordovician granitic pluton are summarized and discussed different morphologic domains within the pluton reveal concentric fragmented and or folded layers of granite in a gabbro granite mixed matrix this stands in contrast to two predominantly regular gabbroic regions these regular regions are separated by tightly stretched filament areas in which mixing is enhanced sharp and gradational contacts between granitic and gabbroic domains depict the interplay among frozen flows mingling and convection enhanced diffusion processes mixing measurements of fractal dimensions at different scales and analysis of normalized concentration variance for major elements point towards magma mixing the compositional variability and flow patterns of the studied pluton have been greatly controlled by a natural chaotic mixing process between a granitic and a basaltic end member during the mixing process coeval fractional crystallization no doubt contributed to increasing the complexity of the system however since flow and therefore mixing stops with temperature decrease flow patterns must have retained the predominant morphology and composition of the moment at which both contrasting magmas came together and froze flow patterns have been preserved with further temperature decrease fractional crystallization took over and hybrid rocks were generated from the fractionation of magmas previously mixed in different proportions

high frequency depositional cycles in the muschelkalk middle triassic of southern poland origin and implications for germanic basin astrochronological scales abstract high frequency depositional cycles are often used for long distance correlations within sedimentary basins and constructing high resolution chronostratigraphic scales calibrated to the orbital clock such an approach has been used for the tropical epicontinental muschelkalk sea covering most of europe in the middle triassic this paper aims at establishing the spatial extent and internal architecture of shallow marine muschelkalk cycles within a small 120 by 50 km area of the germanic basin to identify their local vs regional distribution and cycle forming mechanisms three groups of cycles are distinguished 1 peritidal cycles representing a tidal flat lagoon system which experienced longer periods of emersion 2 shallow subtidal cycles formed around the fair weather wave base and 3 deep subtidal cycles developed around the storm wave base the three cycle types differ markedly in the composition facies homogeneity sedimentary trends hierarchical organization continuity and degree of lateral changeability and complexity which collectively translates into the ease of cycle recognition despite the differences the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities sedimentary trends and thicknesses this variability resulted from more or less mosaic infilling of accommodation space reflecting local bathymetry physicochemical conditions and carbonate production and accumulation rates on the platform accommodation space evolved by the interplay of eustatic sea level fluctuations regional subsidence and synsedimentary tectonic block movements but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes the study shows that middle triassic cycles of the germanic basin have a local to sub regional distribution and thereby are inappropriate for basin wide correlations and chronostratigraphic inferences it also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

analysis and simulation of magma mixing processes in 3d abstract magma mixing structures from the lava flow of lesbos greece are analyzed in three dimensions using a technique that starting from the serial sections of rock cubes allows the reconstruction of the spatial distribution of magmas inside rocks two main kinds of coexisting structures are observed i active regions ar in which magmas mix intimately generating wide contact surfaces and ii coherent regions cr of more mafic magma that have a globular shape and do not show large deformations the intensity of mingling is quantified by calculating both the interfacial area ia between interacting magmas and the fractal dimension of the reconstructed structures results show that the fractal dimension is linearly correlated with the logarithm of interfacial area allowing discrimination among different intensities of mingling the process of mingling of magmas is simulated using a three dimensional chaotic dynamical system consisting of stretching and folding processes the intensity of mingling is measured by calculating the interfacial area between interacting magmas and the fractal dimension as for natural magma mixing structures results suggest that as in the natural case the fractal dimension is linearly correlated with the logarithm of the interfacial area allowing to conclude that magma mixing can be regarded as a chaotic process since chemical exchange and physical dispersion of one magma inside another by stretching and folding are closely related we performed coupled numerical simulations of chaotic advection and chemical diffusion in three dimensions our analysis reveals the occurrence in the same system of active mixing regions and coherent regions analogous to those observed in nature we will show that the dynamic processes are able to generate magmas with wide spatial heterogeneity related to the occurrence of magmatic enclaves inside host rocks in both plutonic and volcanic environments

diversity of neogene seismites of the northwest red sea egypt a characteristic sedimentary expression of rifting abstract the syn rift neogene sediments outcropping along the northwest red sea coast exhibit a series of early remobilization structures formed close to the paleo sediment water interface developed both in inclined and in subhorizontal sedimentary substrates their origins cannot be explained only by simple gravity movement they are formed in a variety of sediments including floodplain mudstones shallow marine sandstones and micritic limestones as well as in nonlithified conglomerates although the type of sediment undoubtedly determines in part their preservation they are not limited to any particular sedimentary environment among the twelve types of deformational structures described the most frequent are various types of breccia which generally have a clearly defined base brecciation is most intense at the base and often tends to grade up into undisturbed beds there being no sharp break at the top these breccias have not been transported and adjacent elements may be fitted together giving asymmetric brecciated folds nonbrecciated fold structures are also common especially in continental floodplain mudstones which have been deposited on subhorizontal surfaces other remobilisation structures include load casts and other hydroplastic phenomena affecting individual beds certain sandstone horizons have been completely homogenized due to fluidification finally sedimentary dykes and other fracture fillings up to 10 m in height are also frequent certain structures especially the cm scale reverse faults exhibit both compressional and dilatory movements their stratiform disposition and independance with respect to paleoslopes suggest that these synsedimentary remobilization structures express periodic instability which is best explained by repeated earthquake shocks their similitude with respect to structures resulting from recent earthquakes at el asnam algeria and near the san andreas fault california tend to confirm this interpretation although they have not yet been related to particular structural elements their frequence indicates that these seismite structures are a characteristic expression of red sea rifting

the interplay between crystallization replenishment and hybridization in large felsic magma chambers abstract while hybridized granitoid magmas are readily identifiable the mechanisms of hybridization in large crustal magma chambers are so not clearly understood characteristic features of hybrid granitoids are 1 both the granitoid and included enclaves are commonly hybrids as shown by mineralogy geochemistry and isotopes 2 mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early 3 zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution 4 mafic end members in hybrids are commonly fractionated magmas and 5 stratification in subvolcanic granitoid magma chambers is not uncommon and stratification has been identified in some deeper level plutons hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma experimental work with magma analogues and theoretical considerations reveal very severe thermal rheological and dynamical limitations on mixing only very similar composition temperature magmas are likely to mix to homogeneity and only moderately silicic hybrids are likely to be produced however impossibly silicic hybrids do exist synchronous interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas in the following manner a mafic magma intrudes into the base of a stratified felsic magma and is cooled against it crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber subsequently melt released by crystallization pf this now hybrid zone mixes with adjacent more felsic zones thus a suite of hybrid magmas are progressively formed density inhibitions are overcome by the generation of relatively low density residual melts as crystallization proceeds later injections are preserved as dykes and enclaves composed of hybrid magma in this process only physically adjacent and dynamically thermally similar magmas directly interact and so may mix to homogeneity finally not simply felsic and mafic endmembers mix but a whole suite of intermediate endmembers participate ranging from relatively mafic through to felsic pairs of magmas direct mixing between the primary magmas only occurs at the beginning

chaotic advection fractals and diffusion during mixing of magmas evidence from lava flows structures of magma mixing from three different lava flows have been analyzed and the degree of mingling has been quantified by measuring the contact perimeter between magmas and the fractal dimension of structures in each lava flow the values of these parameters suggest that the magma mixing structures were produced by chaotic dynamics induced by stretching and folding processes between the interacting magmas the mingling of magmas has been simulated using a chaotic dynamical system consisting of repeated stretching and folding processes the simulation shows the same patterns of variation of contact perimeter and fractal dimension as those observed in natural structures and indicates that magma interaction processes acted with different intensities in the three lava flows in response to different magmatic interaction regimes since physical dispersion of one magma inside another through stretching and folding processes and chemical exchanges are closely related we performed coupled numerical simulations of chaotic advection and chemical diffusion the results show a good agreement between the computed and natural structures in particular the occurrence in the same system of well and poorly mixed regions it is shown that magma interaction processes are able to generate magmatic masses having wide spatial heterogenity at many length scales this occurrence can account for the presence of magmatic enclaves inside host rocks showing a variable degree of hybridization in both plutonic and volcanic environments

coastal uplift and mortality of intertidal organisms caused by the september 1985 mexico earthquakes coastal uplift associated with the great mexican earthquake of 19 september 1985 and its principal aftershock produced widespread mortality of intertidal organisms along the coast of the states of michoacan and guerrero mexico measurements of the vertical extent of mortality at ten sites provided estimates of the magnitude of the vertical component of deformation along the coast within the affected area uplift ranged from about 12 centimeters to about 1 meter and no subsidence was observed the observations are consistent with models of the tectonic deformation that results from buried slip on a shallow dipping underthrust fault

the space and time complexity of chaotic mixing of silicate melts implications for igneous petrology abstract we present new experimental results on the study of the space and time modulation of compositional fields during chaotic mixing between mafic and felsic silicate melts the experimental strategy was planned using numerical simulations performed using the experimental geometry these mixing experiments were performed using a recently developed experimental apparatus which is capable of mixing high viscosity silicate melts at high temperatures and under precisely controlled conditions of fluid dynamics and strain the compositional variability produced by the mixing process was investigated both along linear analytical transects and on high resolution 2d x ray maps covering the mixing patterns our results indicate that chaotic flow fields represent very powerful dynamics to blend silicate melts even under laminar fluid dynamic conditions reynolds number ca 10 7 and for dissimilar melts with high viscosity ratios on the order of 103 the repetition of stretching and folding processes between the two melts induced a strong increase of contact interfaces thus favoring efficient chemical exchanges as a result the initial mafic composition is no longer detectable in the mixing system after ca 2 h i e the duration of the experiment a further important result is the observation of highly non linear patterns in inter elemental plots produced by the onset of diffusive fractionation processes this is contrary to common thinking that magma mixing should always produce linear trends between pairs of chemical elements a new measure the concentration variance is proposed to quantify chemical element mobility during the mixing process this measure is statistically robust and can be quantitatively used to measure chemical element mobility independently of the geometry in which the compositional variation i e transects areas etc is embedded or the local strain history of the mingling our results highlight concentration variance as a robust probe of the as yet poorly understood processes involved in the common petrological process of magma mixing

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved