geometric and kinematic models for detachment folds with fixed and variable detachment depths abstract detachment folds are defined by competent rock units and are cored by incompetent units deformed internally above a detachment horizon we have developed two geometric models to constrain possible geometries and kinematic paths for ideal detachment folds the models each independently relate fold geometry to shortening and to detachment depth model assumptions include plane strain constant competent bedlength constant cross sectional area chevron fold geometry and no bed parallel shear outside the fold detachment depth is constant in one model but may vary in the other thus allowing evaluation of the implications for fold geometry and kinematics of fixed vs variable detachment depth detachment folds formed above a detachment unit of constant thickness constant detachment depth must be initially symmetrical and cannot grow with fixed hinges fixed arc length or a self similar geometry detachment folds formed above a detachment unit of variable thickness variable detachment depth must also be initially symmetrical but any one fold geometry can have a range of possible initial and final detachment depths kinematic paths for folds with fixed hinges fixed arc lengths migrating hinges variable arc lengths and selfsimilar geometries are all possible if detachment depth varies the change in detachment depth during deformation can be determined using the variable detachment depth model if either initial or final detachment depth is known the models demonstrate a wider range of variability in the geometry and kinematics of ideal detachment folds particularly for the variable depth model than is the case for ideal fault bend and fault propagation folds this variability limits the usefulness of simple geometric models for reconstructing the geometry of natural detachment folds balancing cross sections over a sufficient area and evaluating strain may compensate for these limitations

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

alkane terpene and polycyclic aromatic hydrocarbon geochemistry of the mackenzie river and mackenzie shelf riverine contributions to beaufort sea coastal sediment abstract to study the largest source of river sediment to the arctic ocean we have collected suspended particulates from the mackenzie river in all seasons and sediments from the mackenzie shelf between the river mouth and the shelf edge these samples have been analyzed for alkanes triterpenes and polycyclic aromatic hydrocarbons pahs we found that naturally occurring hydrocarbons predominate in the river and on the shelf these hydrocarbons include biogenic alkanes and triterpenes with a higher plant peat origin diagenetic pahs from peat and plant detritus petrogenic alkanes triterpenes and pahs from oil seeps and or bitumens and combustion pahs that are likely relict in peat deposits because these components vary independently the season is found to strongly influence the concentration and composition of hydrocarbons in the mackenzie river while essentially the same pattern of alkanes diagenetic hopanes and alkyl pahs is observed in all river and most shelf sediment samples alkane and triterpene concentration variations are strongly linked to the relative amount of higher plant peat material polycyclic aromatic hydrocarbon molecular mass profiles also appear to be tied primarily to varying proportions of peat with an additional petrogenic component which is most likely associated with lithic material mobilized by the mackenzie river at freshet consistent with the general lack of alkyl pahs in peat the higher pahs found in the river are probably derived from forest and tundra fires a few anthropogenic pyrogenic compounds are manifest only at the shelf edge probably due to a weakening of the river influence we take this observation of pyrogenic pahs and the pronounced source differences between two sediment samples collected at the shelf edge as evidence of a transition from dominance by the mackenzie river to the geochemistry prevalent in arctic regions far removed from major rivers

tectonic and metasomatic mixing in a high t subduction zone melange insights into the geochemical evolution of the slab mantle interface abstract the catalina schist california contains an amphibolite grade 0 8 1 1 gpa 640 750 c melange unit consisting of mafic and ultramafic blocks in high mg schistose melange matrix with varying modal proportions of talc chlorite anthophyllite calcic amphibole enstatite and minor phases including zircon rutile apatite spinel and fe ni sulfides this melange unit is interpreted as a kilometer scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone the study of which may yield insight into chemical mixing processes at greater depths in subduction zones relationships among the major and trace element compositions of the mafic and ultramafic blocks in the melange the rinds developed at the margins of these blocks and the surrounding melange matrix are compatible with the evolution of the melange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing simple linear mixing models are compatible with the development of the melange matrix primarily through simple mixture of the ultramafic and mafic rocks with cr al ratios serving as indicators of the approximate proportions of the two lithologies this conclusion regarding mafic ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the melange matrix with rinds developed at the margins of mafic and ultramafic blocks the overall process involved development of metasomatic assemblages through complex fluid mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials which are rich in layer silicates and amphibole this deformation was sufficiently intense to transpose fabrics progressively disaggregate more rigid block derived materials in weaker chorite and talc rich melange and in some particularly weak lithologies e g chlorite talc and amphibole rich materials intimately juxtapose adjacent lithologies at the sub cm scale approaching grain scale sampled by the whole rock geochemical analyses chemical systematics of various elements in the melange matrix can be delineated based on the cr al based mixing model simple mixing relationships exhibited by al cr mg ni fe and zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the melange matrix the compositional patterns of many other elements are explained by either redistribution local stripping or enrichment at varying scales within the melange ca na k ba and sr or massive addition from external sources si and h2o the latter probably in infiltrating h2o rich fluids that produced the dramatic o and h isotopic shifts in the melange melange formation resulting in the production of high variance ultramafic assemblages with high volatile contents may aid retention of volatiles in this case h2o to greater depths in subduction zones than in original subducted mafic and sedimentary materials the presence of such assemblages i e containing minerals such as talc chlorite and mg rich amphiboles would impact the rheology of the slab mantle interface and perhaps contribute to the low velocity seismic structure observed at near the slab mantle interface in some subduction zones if operative along the slab mantle interface complex mixing processes such as these involving the interplay between fluid mediated metasomatism and deformation also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas producing fluids with geochemical signatures inherited from interactions with hybridized rock compositions

accessory minerals and subduction zone metasomatism a geochemical comparison of two melanges washington and california u s a abstract the ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks which can only be studied indirectly in contrast the role of accessory minerals in lower t and p metasomatic processes within paleo subduction zones can be studied directly in subduction zone metamorphic terranes the gee point iron mountain locality of the shuksan metamorphic suite north cascades washington state is a high t melange of metamafic blocks in a matrix of meta ultramafic rocks this melange is similar in geologic setting and petrology to the upper part of an unnamed amphibolite unit of the catalina schist santa catalina island southern california both are interpreted as shear zones between mantle and slab rocks that formed during the early stages of subduction some garnet amphibolite blocks from the gee point iron mountain locality display trace element enrichments similar to those in counterparts from the catalina schist some catalina blocks are highly enriched in th rare earth elements ree the high field strength elements ti nb ta zr and hf hfse u and sr compared to mid ocean ridge basalt morb and to other garnet amphibolite blocks in the same unit textural and geochemical data indicate that accessory minerals of metamorphic origin control the enrichment of th ree and hfse in blocks from both areas the mg rich rinds around blocks and the meta ultramafic matrix from both melanges are highly enriched in a large number of trace elements compared to harzburgites dunites and serpentinites evidence for recrystallization or formation of accessory minerals in the former rocks suggests that these minerals control some of the trace element enrichments data from the gee point and catalina melanges suggest that the accessory minerals titanite rutile apatite zircon and ree rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction related fluid rock interaction mobilization of incompatible elements and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid rich metamorphic environments in subduction zones

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

a geochemical investigation of carboxylic acids released via sequential treatments of two surficial sediments from the changjiang delta and east china sea two surface sediments from the delta of the changjiang river the fourth largest river in the world in terms of water discharge and the seventh in terms of sediment discharge and an adjacent area of the east china sea were subjected to sequential treatments in order to obtain complete quantitative and qualitative information on carboxylic acid moieties five successive treatments allowed for the release of all acid moieties occurring in each sample i the unbound acids isolated from extracts ii the oh labile acids released by classical saponification iii the oh ptc labile acids obtained via an additional saponification with a phase transfer catalyst iv the h labile acids released by a subsequent acid hydrolysis and v the tightly bound acids only released by thermolysis these five fractions correspond to distinct pools whose occurrence reflects diaerences in the mode of linkage of the acid moieties and or in the protection provided by the structures to which they are linked such analysis of acid moieties provided information on i the relative contributions from microalgae bacteria and higher plants in the delta and seaward stations ii the degree of early diagenetic alteration for the acids derived from these diaerent sources and iii the types of microalgal and bacterial species implicated these features were also compared with the results of the only previous study where the sequential treatments were applied on surficial sediments from a sharply diaerent environment the lena river delta arctic 2000 elsevier science ltd all rights reserved

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

evidence for a scale limited low frequency earthquake source process we calculate the seismic moments for 34 264 low frequency earthquakes lfes beneath the olympic peninsula washington lfe moments range from 1 4 1010 to 1 9 1012 n m mw 0 7 2 1 while regular earthquakes follow a power law moment frequency distribution with a b value near 1 the number of events increases by a factor of 10 for each unit increase in mw we find that while for large lfes the b value is 6 for small lfes it is 1 the magnitude frequency distribution for all lfes is best fit by an exponential distribution with a mean seismic moment characteristic moment of 2 0 1011 n m the moment frequency distributions for each of the 43 lfe families or spots on the plate interface where lfes repeat can also be fit by exponential distributions an exponential moment frequency distribution implies a scale limited source process we consider two end member models where lfe moment is limited by 1 the amount of slip or 2 slip area we favor the area limited model based on the observed exponential distribution of lfe moment and geodetically observed total slip we estimate that the total area that slips within an lfe family has a diameter of 300 m assuming an area limited model we estimate the slips subpatch diameters stress drops and slip rates for lfes during episodic tremor and slip events we allow for lfes to rupture smaller subpatches within the lfe family patch models with 1 10 subpatches produce slips of 0 1 1 mm subpatch diameters of 80 275 m and stress drops of 30 1000 kpa while one subpatch is often assumed we believe 3 10 subpatches are more likely

vertical strain variations in the osen roa thrust sheet north western oslo fjord norway abstract vertical variations in deformation style and shortening within the osen roa thrust sheet are examined on the north western side of the oslo fjord using thrust distribution diagrams and graphs of throw against height in the stratigraphy particular formations are identified in which thrusts are either created or destroyed many thrusts are killed by a combination of 1 dissipation of slip by splaying of thrusts in shales and 2 the presence of a thick competent unit that requires a thrust to attain a specific displacement value in order to propagate through the unit in one jerk the upper didymograptus shales and ampyx limestone make an effective combination that kills thrusts with less than 50 m of throw within the thrust sheet deformation styles change vertically from imbricate slices pop up and triangle zones with tip line folds in the cambro ordovician shales and limestones to buckle folds in the silurian limestones sandstones and shales this change is accompanied by a decrease in shortening from 34 in the former to 17 in the latter hence one or several higher bedding parallel detachment horizons need to be invoked to separate areas of varying deformation character

experimental and field study of the effects of lithological contrasts on thrust related deformation 1 the influence of mechanical contrasts related to stratigraphy on thrust related deformation are investigated by sandbox modeling using combinations of granular materials possessing different mechanical properties and by structural analysis of a natural example from the spanish pyrenees the models used in this study consist of loose sand and glass microbeads in varied stratigraphic thicknesses and sequences and the natural example consists of a weakening upward sequence of sandstones and carbonates in both cases layers of different composition had a mechanical significance and accommodated shortening differently model sand and natural sandstone exhibited most shortening by thrust imbrication irrespective of stratigraphic position whereas glass microbeads and carbonates exhibited wider deformation zones and enhanced folding accompanied by displacement reduction along thrust surfaces cutting them transitions of structural style were guided by the stratigraphy rather than by a simple unidirectional propagation from a step up layer parallel shortening was accommodated by diverse mechanisms but did not vary significantly in layers which had different properties the magnitude with which mechanical contrasts were expressed in the models was influenced by the strength at the decollement zone the effect of mechanical contrast was more profound in models shortened above a low friction decollement

transfer of lipid molecules and polycyclic aromatic hydrocarbons to open marine waters by dense water cascading events abstract settling particles were collected by a set of moored sediment traps deployed during one year in the western gulf of lion along cap de creus and lacaze duthiers submarine canyons and on the adjacent southern open slope these traps collected particles during periods of pelagic settling and also during events of deep water flushing by dense shelf water cascading dswc analyses of lipid biomarkers n alkanes n alkan 1 ols sterols and c37 c38 alkenones and polycyclic aromatic hydrocarbons pahs showed much higher transfer of terrestrial lipids and pahs to open deep waters during dswc than in the absence of cascading the area of highest lateral fluxes was mostly located at 1000 m depth but also at 1500 m depth and extended along the canyons and to the adjacent slope higher fluxes were observed near the bottom 30 m above bottom mab than at intermediate waters 500 mab which is consistent with the formation and sinking of dense water over the continental shelf and its transport through the canyons towards the continental slope and deep basin dswc involved the highest settling fluxes of terrestrial lipids and pahs ever described in marine continental slopes and the pelagic domain as illustrated by peak values of c23 c33 odd carbon numbered alkanes 405 ng m 2 d 1 c22 c32 even carbon numbered alkan 1 ols 850 ng m 2 d 1 sitosterol sitostanol 4800 ng m 2 d 1 and pahs 55 g m 2 d 1 the algal lipids also showed higher transfer to deep waters during dswc but to a lower extent than the terrigenous compounds however the c37 c38 alkenones constituted an exception and their settling fluxes were not influenced by dswc the lack of influence of the dswc on the c37 c38 alkenone settling is consistent with absence of haptophyte algal inputs from the continental shelf and reinforces the reliability of these molecules for palaeothermometry and palaeoproductivity measurements in pelagic systems

centrifuge modelling of fold thrust structures in a tripartite stratigraphic succession abstract analog models measuring 127 76 mm in plan were deformed at 2500 4000 g in a centrifuge scaled stratigraphic sequences were constructed of anisotropic multilayers with individual layers of plasticine and silicone putty as thin as 40 m the plasticine silicone putty multilayers are analogs for interbedded competent carbonates and clastics and incompetent pelites given the model ratios of acceleration 2500 g length 5 10 6 specific gravity 0 6 time 10 10 modelling of fold thrust tectonics emphasizes the influence of stratigraphic succession on structural evolution the models are constructed with a tripartite stratigraphic succession comprising basal and upper well laminated and incompetent units and a middle somewhat more isotropic and competent unit the models deform by three mechanisms layer parallel shortening folding and thrust faulting they reproduce a number of fold thrust relationships that have been observed in nature folds are typically periclinal in en echelon arrays folds and thrusts are arcuate in plan reflecting differential shortening fold attitudes grade from upright at high levels to overturned at deeper levels within a structural panel reflecting drag against the basal decollement fold axial surfaces and thrust faults are listric while competent units may be offset by localized displacement on thrust faults the discrete faults may die out both upwards and downwards into regions of ductile strain in less competent units thrust faults appear to follow staircase trajectories through the strata transecting incompetent units at shallow angles to bedding and competent units at steeper angles however the apparent staircase pattern results from propagation of a fault along a relatively straight trajectory through previously folded strata foreland verging thrusts are more common than back thrusts the latter have steeper dips the models suggest a mechanism of thrust ramp nucleation following detachment folding long wavelength buckling of a competent unit can initiate localized strain folding and layer parallel shear in an underlying incompetent unit beneath the anticlines of the competent unit thrust faults propagate up section from these high strain zones through the foreland dipping limbs of buckle folds in the competent unit this mechanism may explain the commonly observed spatial periodicity of thrust ramps the model results bear similarities to natural fold thrust belts in which the stratigraphic succession consists of three mechanical units for example the asiak foreland and bear creek hills fold thrust belts of the slave province northwest territories canada

magnitudes and moment duration scaling of low frequency earthquakes beneath southern vancouver island we employ 130 low frequency earthquake lfe templates representing tremor sources on the plate boundary below southern vancouver island to examine lfe magnitudes each template is assembled from hundreds to thousands of individual lfes representing over 269 000 independent detections from major episodic tremor and slip ets events between 2003 and 2013 template displacement waveforms for direct p and s waves at near epicentral distances are remarkably simple at many stations approaching the zero phase single pulse expected for a point dislocation source in a homogeneous medium high spatiotemporal precision of template match filtered detections facilitates precise alignment of individual lfe detections and analysis of waveforms upon correction for 1 d geometrical spreading attenuation free surface magnification and radiation pattern we solve a large sparse linear system for 3 d path corrections and lfe magnitudes for all detections corresponding to a single ets template the spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12 24 h of lfe activity during an ets episode when tidal sensitivity is low the remainder is released in bursts over several days particularly as spatially extensive rapid tremor reversals rtrs during which tidal sensitivity is high rtrs are characterized by large magnitude lfes and are most strongly expressed in the updip portions of the ets transition zone and less organized at downdip levels lfe magnitude frequency relations are better described by power law than exponential distributions although they exhibit very high b values 5 we examine lfe moment duration scaling by generating templates using detections for limiting magnitude ranges mw 1 5 mw 2 0 lfe duration displays a weaker dependence upon moment than expected for self similarity suggesting that lfe asperities are limited in fault dimension and that moment variation is dominated by slip this behavior implies that lfes exhibit a scaling distinct from both large scale slow earthquakes and regular seismicity

fluid overpressure from chemical reactions in serpentinite within the source region of deep episodic tremor slow fault slip includes a range of transient phenomena that occur over timescales longer than those of standard earthquakes slow slip events are often closely associated with swarms of tectonic tremor deep episodic tremor and slip close to the slab mantle interface in subduction zones has been linked to high fluid pressures produced by dehydration of the subducting slab at greater depths the slab mantle interface is a fundamental chemical boundary where mantle rocks are sheared and mixed with oceanic slab lithologies in a highly reactive environment to form serpentinite here we present field and microstructural observations from the plate boundary scale crustal livingstone fault in new zealand that suggest chemical reactions involving serpentinite can promote rock hardening and generate in situ fluid overpressures we infer that these processes collectively can result in hydrofracturing and a transition from distributed creep to localized brittle failure and faulting serpentinite related reactions occur over a wide range of pressure and temperature conditions that overlap with those in many forearc mantle wedges we conclude that the release of fluids derived from such reactions may be an additional and widespread mechanism to generate high fluid pressure patches and brittle failure in the source region of deep tremor along the slab mantle interface chemical reactions between slab and mantle rocks may lead to brittle failure where deep episodic tremor occurs in subduction zones according to field and microstructural observations of a shear zone in new zealand

low frequency earthquakes at the southern cascadia margin we use seismic waveform data from the mendocino experiment to detect low frequency earthquakes lfes beneath northern california during the april 2008 tremor and slip episode in southern cascadia 59 templates were generated using iterative network cross correlation and stacking and grouped into 34 distinct lfe families the main front of tremor epicenters migrates along strike at 9 km d 1 we also find one instance of rapid tremor reversal observed to propagate in the opposite direction at 10 20 km h 1 as in other regions of cascadia lfe hypocenters from this study lie several kilometers above a recent plate interface model south of cascadia lfes were discovered on the maacama and bucknell creek faults the bucknell creek fault may be the youngest fault yet observed to host lfes these fault zones also host shallow earthquake swarms with repeating events that are distinct from lfes in their spectral and recurrence characteristics

secondary detachments within carbonates of the saraburi group triassic khao khwang fold and thrust belt thailand abstract permian limestones of the saraburi group in central thailand deformed during the triassic indosinian orogeny exhibit detachments formed in response to the following variations in lithology thin shale beds within a limestone sequence massive limestone overlaying well bedded limestone massive limestone overlying interbedded limestones and shales within well bedded limestones thin shales interbedded with limestones overlying limestones where shales are present the decoupling of layers is similar to examples previously described in the literature from outcrop and analogue models however more unusually detachments are also present within limestone units while detachment folds are typically developed above a basal weak unit usually salt or shale in the study area is an example developed entirely within well bedded limestones instead of flow of the weak unit into the core of the fold room problems in the core of the fold are accommodated by pressure solution parallel to bedding thrusts small fault propagation folds and intense folding variations in structural style are largely influenced by the spacing intensity of bedding limestone clay content and the efficiency of pressure solution during deformation and the presence absence and thickness of interbedded shales a ductile detachment zone is developed between well bedded limestones and overlying massive limestones the detachment zone separates highly folded sequence dominated by steep dips from a weakly folded sequence dominated by gentle dips pressure solution processes and variability in pressure solution intensity related to clay content play a very strong role in accommodating the difference in deformation styles across the detachment

tectonic tremor and deep slow slip on the alpine fault 1 tectonic tremor is characterized by persistent low frequency seismic energy seen at major plate boundaries although predominantly associated with subduction zones tremor also occurs along the deep extension of the strike slip san andreas fault here we present the first observations of tectonic tremor along new zealand s alpine fault a major transform boundary that is late in its earthquake cycle we report tectonic tremor that occurred on the central section of the alpine fault on 12 days between march 2009 and october 2011 tremor hypocenters concentrate in the lower crust at the downdip projection of the alpine fault coincide with a zone of high p wave attenuation low qp and bright seismic reflections occur in the 25 45 km depth range below the seismogenic zone and may define the deep plate boundary structure extending through the lower crust and into the upper mantle we infer this tremor to represent slow slip on the deep extent of the alpine fault in a fluid rich region marked by high attenuation and reflectivity these observations provide the first indication of present day displacement on the lower crustal portion of the australia pacific transform plate boundary

seismic wave triggering of nonvolcanic tremor episodic tremor and slip and earthquakes on vancouver island 1 we explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on vancouver island british columbia during and immediately after the arrival of large amplitude seismic waves from 30 teleseismic and 17 regional or local earthquakes we identify tremor triggered by four of the teleseismic earthquakes the close temporal and spatial proximity of triggered tremor to ambient tremor and aseismic slip indicates that when a fault is close to or undergoing failure it is particularly susceptible to triggering of further events the amplitude of the triggering waves also influences the likelihood of triggering both tremor and earthquakes such that large amplitude waves triggered tremor in the absence of detectable aseismic slip or ambient tremor tremor and energy radiated from regional local earthquakes share the same frequency passband so that tremor cannot be identified during these smaller more frequent events we confidently identify triggered local earthquakes following only one teleseism that with the largest amplitude and four regional or local events that generated vigorous aftershock sequences in their immediate vicinity earthquakes tend to be triggered in regions different from tremor and with high ambient seismicity rates we also note an interesting possible correlation between large teleseismic events and episodic tremor and slip ets episodes whereby ets events that are late and have built up more stress than normal are susceptible to triggering by the slight nudge of the shaking from a large distant event while ets events that are early or on time are not

the subduction plate interface rock record and mechanical coupling from long to short timescales abstract short and long term processes at or close to the subduction plate interface e g mineral transformations fluid release seismicity and more generally deformation might be more closely related than previously thought increasing evidence from the fossil rock record suggests that some episodes of their long geological evolution match or are close to timescales of the seismic cycle this contribution uses rocks recovered episodically from subduction zones together with insights from thermomechanical modelling to provide a new dynamic vision of the nature structure and properties of the plate interface and to bridge the gap between the mechanical behavior of active subduction zones e g coupling inferred from geophysical monitoring and fossil ones e g coupling required to detach and recover subducted slab fragments based on critical observations and an exhaustive compilation of worldwide subducted oceanic units for which the presence near the plate interface rock types pressure temperature t p gradients thickness and timing of detachment can be assessed the present study demonstrates how long term mechanical coupling exerts a key control on detachment from the slab and potential rock recovery critical assessment of rock t p characteristics indicates that these fragments can indeed be used as natural probes and provide reliable information on subduction interface dynamics down to 2 8 gpa rock clusters are identified at depths of 30 55 60 and 80 km with some differences between rock types data also reveal a first order evolution with subduction cooling in the first 5 myr which is interpreted as reflecting a systematic trend from strong to weak mechanical coupling after which subduction is lubricated and mostly inhibits rock recovery this contribution places bounds on the plate interface constitution regular thickness

abrupt wind regime changes in the north atlantic ocean during the past 30 000 60 000 years 1 the inputs of higher plants in blake outer ridge subtropical western north atlantic during marine isotope stage 3 mis3 have been recorded at high resolution by quantification of c23 c33 odd carbon numbered n alkanes and c20 c30 even carbon numbered n alkan 1 ols in sediment sections of ocean drilling program site 1060 the changes of these proxies at this open marine site are mainly related to eolian inputs their concentrations and fluxes exhibit major abrupt variations that are correlated with dansgaard oeschger d o patterns in greenland ice cores the ratios between interstadials and stadials range between 2 and 9 times the intense flux increases in the d o stadials are linked to strong enhancements of the westerly wind regime at these subtropical latitudes during stadials the observed variation was paralleled by changes in wind blown dust and the polar circulation index in greenland ice which is in agreement with previously hypothesized atmospheric teleconnections between northern and middle low latitudes of the northern hemisphere the close correspondence between sedimentary and ice core proxies is evidence that crossings of the glacial climate thresholds involved major reorganizations of the troposphere the observed large rise in higher plant biomarkers indicates that climate stabilization in the d o stadial conditions led to main increases in wind intensity

determination of the tectonic evolution from fractures faults and calcite twins on the southwestern margin of the indochina block in polyphase tectonic zones integrating a study of fault and fracture with calcite twin analysis can determine the evolving paleostress magnitudes and principle stress directions that affected the area this paper presents the results of the analyses of fractures striated faults and calcite twins collected within the khao khwang fold thrust belt in central thailand se asia here we attempt to reconstruct the orientation of the principal stresses that developed during the tectonic evolution of this highly deformed polyphase orogen tectonic data were collected in the permian carbonates of the khao khad formation of the saraburi group and five successive tectonic stages are determined that are interpreted to have developed before during and after the triassic indosinian orogeny the first three stages predate the main deformation event the first stage is interpreted as a pre indosinian n s extensional stage the second stage described a n s strike slip and compressional regime largely perpendicular to the fold axes of the main structures while the third stage is associated with an e w compressional strike slip phase a further two stages took place after or during the main folding event and correspond to n s compression and to an e w composite strike slip contractional stage the latter which is interpreted to represent cenozoic deformation related to the india asia collision

tectonic tremor along the northern hikurangi margin new zealand between 2010 and 2015 we present the first comprehensive tectonic tremor catalog for the northern hikurangi margin obtained from the systematic analysis of data from the new zealand seismic network between 2010 and 2015 the recent densification of this array along the northern hikurangi margin has allowed for the detection and location of tectonic tremor associated with 20 out of 26 identified transients in the continuous gps record along the east coast of the raukumara peninsula eighteen of these transients have never been reported in the literature and are likely to be slow slip events with magnitudes smaller than those previously studied we also investigate the spatiotemporal relationships between shallow offshore slow slip tectonic tremor and earthquakes for the duration of the study period

melange rheology and seismic style shear displacements in crustal fault zones are accommodated by a range of seismic styles including standard earthquakes non volcanic tremor and continuous and transitory aseismic slip subduction channel shear zones containing highly sheared fluid saturated trench fill sediments intermingled with fragments of oceanic crust are commonly inferred to occur along active subduction megathrusts if this interpretation is correct these plate boundary faults are not discrete planes but may resemble the melange shear zones commonly found in exhumed subduction related rock assemblages melange deformation appears to depend critically on the ratio of competent to incompetent material with shear surfaces localized along lithological contacts or within competent domains while matrix flow accommodates shearing by distributed strain if the style of strain and or displacement accommodation in a melange reflects the partitioning between aseismic and seismic slip the proportion of competent material seems likely to be a significant factor affecting seismic style within subduction channel shear zones and along comparable mixed lithology fault zones

understanding sibumasu in the context of ribbon continents abstract well described ribbon continent collision belts and modern examples with 2d seismic coverage particularly zealandia provide analogues for the permo triassic development of sibumasu two key parameters for the ribbon continents are their width and how rifting developed which in turn impact the structural metamorphic igneous and stratigraphic development of ribbon continents in ways that make them significantly different from the collisional development of major continents key characteristics of the tectonics of sibumasu are 1 a tendency towards basin inversion during the late triassic and possibly early jurassic and mixed thick skinned and thin skinned style deformation 2 extensional collapse around 215 ma is an important feature of sibumasu particularly in northern thailand and probably other areas too 3 slab delamination and extension related decompression melting were probably important mechanisms for generating granites in addition to crustal thickening 4 metamorphism is relatively high temperature lower pressure

on the role of incompetent strata in the structural evolution of the zagros fold thrust belt dezful embayment iran abstract the dezful embayment is the most important fertile oil province of the zagros fold thrust belt it includes several incompetent strata as basal and intermediate decollement levels that play a significant role on the structural styles and hydrocarbon preservation based on the interpretation of seismic profiles the influence of the gachsaran formation and the evaporitic kalhur member of the asmari formation on the geometry of deformation was investigated in different parts of the dezful embayment obtained results revealed that the thickness of the incompetent strata plays a crucial role in the formation and geometry of different types of fold structures e g rounded box chevron detachment fold in the dezful embayment there is a sharp difference between the geometry of surface and deep seated structures due to the existence of thick intermediate decollements e g gachsaran and kalhur in the dezful embayment therefore fault geometry and fold styles in upper and lower parts of these decollements are totally different in addition these incompetent strata act as a barrier level against the propagation of deep seated faults into the overlying layers therefore it seems that most of the faults exposed on the surface have originated from the upper decollement levels in the study area

crystallographic preferred orientation of talc determined by an improved ebsd procedure for sheet silicates implications for anisotropy at the slab mantle interface due to si metasomatism

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

chert geochemistry depositional setting stratigraphic and structural significance for the permian nong pong formation khao khwang fold and thrust belt saraburi thailand abstract the deepwater chert shale limestone tuff permian nong pong formation npf of the saraburi group is a major unit within the triassic indosinian orogeny khao khwang fold and thrust belt kkftb whether the npf was deposited in a continental margin or ocean basin remains uncertain and impacts structural sedimentary and stratigraphic interpretations of the kkftb this study investigates chert geochemistry from a 60 m section of the formation near muak lek town to determine its depositional environment radiolarian fauna from the chert beds includes follicucullus porrectus rudenko probable late guadalupian late middle permian indicating the npf is time equivalent to adjacent carbonate platform deposition khao khwang and khao khad formations high ratios of sio2 sio2 al2o3 fe2o3 and fe al mn plots indicate a biogenic origin radiolarians sponge spicules for the cherts far from a hydrothermal source trace element ratios for u th sc th and sr ba and ce anomalies in the nasc normalized ree distribution are ambiguous and range between shallow to deep ocean basin and continental margin settings major elements analysis of cherts show 1 high ratios of sio2 sio2 al2o3 fe2o3 range 0 60 0 82 0 76 average 2 al al fe mn range 0 67 0 82 and 3 average mno tio2 0 14 the mno tio2 and al2o3 al2o3 fe2o3 ratio 100 fe2o3 sio2 vs 100 al2o3 sio2 and fe2o3 100 sio2 vs al2o3 100 sio2 diagrams indicate deposition on a continental margin the lan cen versus al2o3 al2o3 fe2o3 discrimination diagram indicates a pelagic continental margin setting combined geochemical structural and sedimentary facies analyses suggests the npf was deposited in a deep marine normal fault bounded basin on a rifted ribbon continent margin where carbonate platforms grew on structural highs

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

sequential deformation from serpentinite mylonite to metasomatic rocks along the sashu fault sw japan the deformation of serpentinites along the sashu fault saganoseki peninsula sw japan involved both mylonitization and brecciation the brecciation was accompanied by metasomatism and the metasomatized rocks record additional ductile deformation serpentinite mylonite is composed mainly of antigorite with minor magnetite and cr spinel foliation and lineation in this rock type are defined by the shape preferred orientation of antigorite and the alignment of fine grained magnetite and carbonate minerals the antigorite also shows a lattice preferred orientation lpo as measured with a universal stage with c axes oriented near perpendicular to the foliation and b axes oriented parallel to the lineation brecciation is concentrated in the reaction zone along the boundary between serpentinites and surrounding country rocks talc and chlorite schists developed in this zone as a result of associated metasomatism and deformation consequently they contain composite planar fabrics and drag folds the breccias themselves are composed of serpentinite fragments cut by veins of calcite and talc analyses of fluid inclusions in calcite from the breccia indicate that brecciation occurred at 200 300 c at depths of 3 8 11 8 km metasomatic reactions particularly the formation of talc contributed to weakening of this serpentinite bearing fault zone

structure of the sibumasu indochina collision central thailand a section through the khao khwang fold and thrust belt abstract mainland se asia is composed of a number of continental fragments and volcanic arcs separated by oceanic suture zones which were accreted to the growing asian continent during the triassic indosinian orogeny the evolution of this orogeny has always been quite controversial indeed the effects of this orogeny in thailand have often been interpreted without considering the detailed tectonic evolution of the portion of the indochina block s margin formed by khao khwang platform area of the saraburi group in central thailand this area is unusual because 1 an extensive area representing a thin skinned fold and thrust belt is well exposed due to quarrying and 2 the fold and thrust belt displays a series of e w and wnw ese striking thrusts and associated folds that are not easily explained in the context of the traditional interpretation where the terranes have been accreted broadly along n s striking collisional zones detailed structural observations in numerous quarries around highway 21 in a 13 km long dip direction traverse have revealed that overall the thrust belt is composed of several large thrusts with an approximately northwards transport direction in the southern part of the area south verging structures are present although the dominant structural trend is northwards verging interference structures and late strike slip faults indicate there is more than one phase of structural development present

slab dehydration in warm subduction zones at depths of episodic slip and tremor abstract non volcanic tremor nvt and episodic slow slip events sses have been observed below the seismogenic zone of relatively warm subduction zones for the past 20 years geophysical and geologic observations show that this portion of the subduction interface is fluid rich and many models for these slip behaviors necessitate high pore fluid pressures however whether these fluids are sourced from local dehydration reactions in particular lithologies or require up dip transport from greater depths is not known we present thermodynamic models of the petrologic evolution of four lithologies typical of the plate interface average morb seafloor altered morb hydrated depleted morb mantle and metapelite along predicted plate boundary pressure temperature p t paths at several warm subduction segments where nvt and sses are observed at depths between 25 65 km the models suggest that 1 2 wt h2o is released at the depths of nvt sses in jalisco colima guerrero cascadia and shikoku due to punctuated dehydration reactions within morb primarily through chlorite and or lawsonite breakdown these reactions produce sufficient in situ fluid across a narrow p t range to cause high pore fluid pressures at nvt sse depths dehydration of hydrated peridotite is minimal at these depths for most margins and metapelite releases h2o

geometry and evolution of fold thrust structures at the boundaries between frictional and ductile detachments abstract fold thrust belts formed above a ductile detachment typically contain detachment folds whereas those formed above frictional detachments contain fault related fold complexes such as imbricate thrust systems analog models using silica sand to represent sediments and silicone gel to represent salt were conducted to study the fold geometry fold fault relations and sequential development of structures formed in each setting and at the boundaries between the two settings the results showed a relatively thinner wedge above a ductile detachment so that the deformation front propagated farther forward than that above a frictional detachment the thrust front connects across the two settings with a significant change in position and a resulting change in orientation the geometry of the deformation front is strongly controlled by that of the detachment boundary so that an oblique detachment boundary results in an oblique thrust front in the transition zone modifications in the taper geometry also result from the presence of a frictional belt behind a ductile belt the width of the ductile detachment which limits the location of the deformation front and the lateral propagation of thrust faults between the two regimes the experimental models can be used to explain observed geometries in natural examples of fold thrust belts marked by transitions between frictional and ductile detachments

characterization of the depositional environments of the ebro delta western mediterranean by the study of sedimentary lipid markers abstract thirty seven sediment samples from the fresh brackish water systems and the surrounding marine waters of the ebro delta have been analyzed for organic and inorganic carbon carbohydrates amino acids and lipids the study of individual lipid components showed autochthonous and allochthonous contributions of organic materials to the system namely higher plant residues allochthonous soil related components macrophytes unicellular algae and microbial residues however algal constituents are predominant in most sediments suggesting that decomposition and remineralization of allochthonous organic matter and subsequent enhancement of algal production may be one of the major processes of the carbon cycle in the delta the persistence of cycling intermediate and particularly labile compounds in the samples is constrained by environmental conditions of deposition accordingly six depositional environments have been characterized listed from more reducing to more oxic the coastal lagoons the bays the river bed the open sea area located around and far from the river mouth and the coastal sandy sediments

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions lorca basin murcia spain abstract free lipids sulphur bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a messinian sequence of lorca basin the high abundance of phytane 2 3 dimethyl 5 2 6 10 trimethylundecyl thiophene mid chain c 20 isoprenoid thiophenes and bithiophenes and bis o phytanyl and o phytanyl o sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions the isopranyl glycerol ethers are essentially found in the sulphur bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids however the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid shales and laminated carbonate and 3 7 11 15 19 pentamethyleicosanoic acid only in the laminated carbonate the bacterial inputs are represented by 2 hydroxytetracosanoic acid n octadec 11 enoic acid hopanoic acids and the distributions of iso and anteiso c 15 and c 17 homologues and minor amounts of iso c 16 and anteiso c 14 these branched fatty acids are characteristic of sulphate reducing bacteria the relative proportions of the iso and anteiso compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments

diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment recent sediments from an oligotrophic lake loch clair having uniform organic input for 2000 yr show changes in lipid abundance and composition with increasing depth attributed to diagenesis stability of free lipids decreases in the order n alkanes alkan 2 ones sterols n alkanoic acids n alkanols n alkenoic acids diagenetic loss of shorter chain homologues is complete within 400 yr stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter chain bound homologues in an eutrophic lake cross mere shorter chain free and bound sedimentary lipids show increased abundance compared with loch clair the relative importance of higher input of shorter chain lipids derived from aquatic detritus and slower initial diagenesis due to the anoxic hypolimnion as causative factors for this difference between lake types cannot yet be assessed

distinguishing coeval patterns of contraction and collapse around flow lobes in mass transport deposits abstract gravity driven mass transport deposits mtds form by the downslope directed movement of sediment associated with slope failure simple models suggest that extension forms at the upslope head area contraction is focussed in the downslope toe of the slump while differential shear associated with strike slip is restricted to the lateral margins of the slump although the head and toe are considered to be dominated by layer parallel shear lps differential layer normal shear lns may be generated around the lateral margins of slumps and potentially also within mtds where flow has been separated into different lobes despite this realisation that lns must form there has been little work into the geometries and spatial relationships of resulting structures using the late pleistocene lisan formation exposed around the dead sea basin as our case study we examine detailed

thermal and metamorphic environment of subduction zone episodic tremor and slip 1 episodic tremor and slip ets have been detected in the cascadia and southwest japan subduction zones where the subducting crust is relatively warm because of the young incoming lithosphere 20 ma and modest plate convergence rates 40 60 mm a in the southwest japan subduction zone low frequency earthquakes occur on the plate interface at depths of 30 35 km beneath shikoku where finite element thermal models predict temperatures of 425 c in the subducting oceanic crust and at depths of 30 40 km beneath the kii peninsula where predicted temperatures are 325 c warmer temperatures of 575 c are predicted at ets depths beneath southern vancouver island in the cascadia subduction zone but here tremor also occurs within the overlying fore arc crust where temperatures are lower in the southwest japan and cascadia subduction zones subducting oceanic crust passes through the blueschist greenschist and amphibolite metamorphic facies where mineral dehydration reactions are complex the different temperatures predicted for the two subduction zones suggest that ets does not coincide with a specific temperature or metamorphic reaction several lines of evidence indicate that a free h2o rich fluid is present at least transiently in subducting oceanic crust and fluids released by prograde metamorphic dehydration reactions may help trigger or enable ets within the subducting plate less clear is the role h2o may play in tremor observed in the cascadia fore arc crust where free h2o may exist locally in faults and fractures but retrograde hydration reactions are expected to consume h2o

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

development of schistosity by dissolution crystallization in a californian serpentinite gouge to understand the behaviour and deformation mechanisms of serpentinites in the seismogenic zone we study the deformation macro and microstructures of serpentinites along the santa ynez fault in the san andreas system at the outcrop scale deformation is localized in a gouge zone that shows three different structures 1 micrometric undeformed fragments clasts of the previously serpentinized peridotite 2 localized shear planes y and r and 3 a penetrative schistosity s observations under sem and tem reveal that the schistosity corresponds to serpentine fibres parallel to each other and whose orientation varies as they wrap around clasts tem micro textures indicate that these long fibres result from continuous syntectonic growth rather than from reorientation of pre existing fibres implying a slow transfer process that occurs at short distances we propose a dissolution diffusion crystallization process for the formation of the schistosity that corresponds to a low strain rate creeping process of deformation that can be effective in aseismic fault segments

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

cascadia subducting plate fluids channelled to fore arc mantle corner ets and silica deposition in this study we first summarize the constraints that on the cascadia subduction thrust there is a 70 km gap downdip between the megathrust seismogenic zone and the episodic tremor and slip ets that lies further landward there is not a continuous transition from unstable to conditionally stable sliding seismic rupture occurs mainly offshore for this hot subduction zone ets lies onshore we then suggest what does control the downdip position of ets we conclude that fluids from dehydration of the downgoing plate focused to rise above the fore arc mantle corner are responsible for ets there is a remarkable correspondence between the position of ets and this corner along the whole margin hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore arc mantle laboratory data show that such fore arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone at the fore arc mantle corner these fluids are released upward into the more permeable overlying fore arc crust an indication of this fluid flux comes from low poisson s ratios and vp vs found above the corner that may be explained by a concentration of quartz which has exceptionally low poisson s ratio the rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner

evidence of localized failure along altered basaltic blocks in tectonic melange at the updip limit of the seismogenic zone implications for the shallow slow earthquake source

macrostructures vs microstructures in evaporite detachments an example from the salt range pakistan abstract the salt range pakistan is the surface expression of an evaporite detachment over which the potwar plateau fold thrust belt has moved whilst previous publications regarding this region have focused on the petroleum prospectivity deformation and large scale processes this paper characterises the salt range detachment at the meso 10 cm to 10s of metres and micro scale cm to m and examines correlations to the macro scale 10s of metres to kms two detailed scaled cross sections are analysed alongside structural measurements to characterise the detachment at the meso scale with optical analysis of microstructures that formed during deformation characterising the micro scale both ductile and brittle features observed in cross section indicate composite deformation processes acting simultaneously this contrasts with models of salt detachments behaving homogeneously microstructural analysis indicates processes of grain boundary migration and crystal lattice distortions the microstructurally revealed competition between intra crystalline deformation and recrystallization at shallow depths and low temperatures links passes up scale to mesoscale evaporite mylonites and progressively in the weaker units whereas more brittle processes operate in the stronger lithologies in this near unique outcrop of a the emergent toe of a major salt bearing detachment fault

relationship between the cascadia fore arc mantle wedge nonvolcanic tremor and the downdip limit of seismogenic rupture great earthquakes anticipated on the cascadia subduction fault can potentially rupture beyond the geodetically and thermally inferred locked zone to the depths of episodic tremor and slip ets or to the even deeper fore arc mantle corner fmc to evaluate these extreme rupture limits we map the fmc from southern vancouver island to central oregon by combining published seismic velocity structures with a model of the juan de fuca plate these data indicate that the fmc is somewhat shallower beneath vancouver island 36 38 km and oregon 35 40 km and deeper beneath washington 41 43 km the updip edge of tremor follows the same general pattern overlying a slightly shallower juan de fuca plate beneath vancouver island and oregon 30 km and a deeper plate beneath washington 35 km similar to the nankai subduction zone the best constrained fmc depths correlate with the center of the tremor band suggesting that ets is controlled by conditions near the fmc rather than directly by temperature or pressure unlike nankai a gap as wide as 70 km exists between the downdip limit of the inferred locked zone and the fmc this gap also encompasses a 50 km wide gap between the inferred locked zones and the updip limit of tremor the separation of these features offers a natural laboratory for determining the key controls on downdip rupture limits

variations of fluid pressure within the subducting oceanic crust and slow earthquakes 1 we show fine scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high pressure fluids released by progressive metamorphic dehydration reactions in the subducting philippine sea plate in tokai district japan these zones have a strong correlation with the distribution of slow earthquakes including long term slow slip ltss and low frequency earthquakes lfes overpressured fluids in the ltss region appear to be trapped within the oceanic crust by an impermeable cap rock in the fore arc and impede intraslab earthquakes therein in contrast fluid pressures are reduced in the lfe zone which is deeper than the centroid of the ltss because there fluids are able to infiltrate into the narrow corner of the mantle wedge leading to mantle serpentinization the combination of fluids released from the subducting oceanic crust with heterogeneous fluid transport properties in the hanging wall generates variations of fluid pressures along the downgoing plate boundary which in turn control the occurrence of slow earthquakes

formation and inversion of salt detached ramp syncline basins results from analog modeling and application to the columbrets basin western mediterranean abstract the widespread extensional deformation that took place during jurassic to cretaceous times in western europe and the north atlantic margin resulted in the formation of several rift systems some of the resulting basins associated with these rifts show broad synclines detached on pre or syn kinematic permian or triassic salts and are filled by thick sedimentary successions the development of these salt detached ramp syncline basins has been associated to the extensional motion of ramp flat extensional sub salt faults the shape and kinematics of such faults have usually been established using the architecture of syn kinematic units and by assuming complete coupling of the hanging wall rocks therefore there are fault interpretations that do not consider the role played by the deep salt layers which clearly act as an effective detachment decoupling sub and supra salt deformations moreover the complexity of these scenarios further increases due to some of these basins which during latest cretaceous and cenozoic times were partially inverted and were often incorporated into fold and thrust belts based on analog models and using the mesozoic columbrets basin western mediterranean as a case study the aim of this research is to decipher the influence of the ramp flat extensional fault during the syncline development and the interaction with a pre kinematic salt and to infer how salt detached ramp syncline basins are subsequently inverted to achieve this goal we carried out an experimental program consisting of eight different sandbox models our results show that the main structure formed at the end of the extension is a salt detached ramp syncline and that its geometry not only depends on the dip and length of the fault panels but also on the fault displacement and salt thickness the inversion of these salt detached ramp synclines resulted in a major thick skinned fault bend anticline with minor thin skinned contractional structures

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

complex structure of an upper level shale detachment zone khao khwang fold and thrust belt central thailand abstract shale detachment zones have been previously described as largely mobile in character however increasing resolution of seismic images and understanding of these zones suggest brittle deformation may have a significant role in their deformational behaviour and in the deformation of overlying fold and thrust belts dependence on seismic imaging and other indirect and low resolution study methods has resulted from the lack of outcropping shale detachment zones both active and ancient for detailed study however a newly described upper level detachment zone in a shale unit in the khao khwang fold and thrust belt in central thailand is exceptionally well exposed we use detailed structural analysis to investigate deformational mechanisms of this ancient exhumed detachment zone as an analogue to active modern day examples through detailed field mapping we were able to construct multiple cross sections through the detachment zone these cross sections were subdivided into structural domains which display an increase in density and complexity of deformational structures folds faults and heterogeneity of their orientations toward the thrust at the base of the detachment zone contrasting strain rates in zones of continuous discontinuous deformation result from contrasting rock competencies through the sections we conclude that the fault damage zone in this study constitutes an upper level detachment and is potentially analogous to those in active collisional fold and thrust belts it displays mixed brittle ductile deformation and a complex three dimensional anastomosing fault system

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

chemical and carbon isotopic evolution of hydrocarbons during prograde metamorphism from 100 c to 550 c case study in the liassic black shale formation of central swiss alps abstract hydrocarbon distributions and stable isotope ratios of carbonates 13ccar 18ocar kerogen 13cker extractable organic matter 13ceom and individual hydrocarbons of liassic black shale samples from a prograde metamorphic sequence in the swiss alps were used to identify the major organic reactions with increasing metamorphic grade the studied samples range from the diagenetic zone 17 n alkanes suggests the occurrence of cracking reactions of high molecular weight compounds the isotopically heavier up to 5 6 c 13 n alkanes with metamorphism suggests progressive thermal release of kerogen linked fatty acid precursors and degradation of n alkanes changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures the absence of 18 h 22 29 30 trisnorneohopane ts the occurrence of 17 h trisnorhopane 17 h 21 h hopanes in the c29 to c31 range and 5 h 14 h 17 h 20r c27 c29 steranes in the low diagenetic samples the occurrence of specific hydrocarbons e g n alkylcyclopentanes cadalene hydrogenated aromatic compounds in metamorphic samples points to kerogen degradation reactions most probably occurring in the presence of water and under reducing conditions the changes of hydrocarbon distributions and carbon isotopic compositions of n alkanes related to metamorphism suggest that the organic geochemistry may help to evaluate the lowest grades of prograde metamorphism

syn deformation temperature and fossil fluid pathways along an exhumed detachment zone khao khwang fold thrust belt thailand abstract shale detachment zones their influence on deformational style and their internal mechanisms of deformation are an understudied aspect of fold thrust belts properties such as deformational temperature lithology and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold thrust belts however little work has been conducted on rock properties of known detachment zones a recently described upper level detachment zone in the exhumed khao khwang fold thrust belt of central thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone and association with its complex deformational style the low grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid rock interaction illite crystallinity data indicate deep diagenetic to low anchizonal conditions and temperatures of 160 210 c in the shale detachment interpreted as reflecting peak metamorphic conditions during the triassic indosinian orogeny no trend between the intensity spacing complexity of structures and illite crystallinty is observed however shale shear zones of continuous style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales we also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures data from limestones and syn tectonic vein fills detail the history of fluid rock interaction during early mesogenesis through to orogenesis the early covariant trend of increasingly negative 13 c and 18 o values is attributed to increasing burial while a divergent orogenic trend of increasingly negative 18 o values is interpreted as the result of a loss of matrix permeability and interruption of fluid rock re equilibration these hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

terrestrial and marine n alcohol inputs and degradation processes relating to a sudden turbidity current in the zaire canyon abstract n alcohol biomarkers from sediment trap samples collected during a turbiditic event and surficial sediments on a levee of the zaire canyon equatorial west african margin one of the world s largest and still very active deep sea fans were examined the initial goal was to study the benthic ecosystem in relation to organic matter inputs as the quantity and quality might influence its development two criteria were used the relative abundance of short 20 and long chain c 22 n alcohols derived from marine organisms and higher plants respectively and the ratio of odd to even carbon numbered 20 n alcohols to assess the extent of alteration the material collected in the trap 30 m above the bottom when the turbiditic current occurred exhibited a high abundance of terrigenous n alcohols this trap did collect the turbidity material in contrast to the one located at 400 m the influence of the turbidity current was also revealed in the surficial sediment sampled nine months after the event the initial turbiditic material from the 30 m trap settled on to the sediment and extensive degradation was apparent upon this settling assuming a first order degradation rate the degradation rate constants were 3 4 and 0 9 y 1 for 19 and c 22 n alcohols respectively

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

a geochemical study of long chain n aldehydes in washington coastal sediments a series of n aldehydes c20 to c32 with strong even to odd carbon preference was identified in the mixture of solvent extractable lipids isolated from various washington coastal sediments a limited survey of the lipid composition of surface waxes of foliage and cuticular waxes of pollen from several major plant species indigenous to the pacific northwest revealed that similar series of n aldehydes are intrinsic to regional vegetation debris from such plants discharged at the mouth of the columbia river represents a preformed source of the n aldehyde series accumulating in sediments from the washington coastal region although the evidence suggests n aldehydes are largely introduced erosionally to this region as a chemical component of land derived debris and are not formed in situ in the coastal sediments further study is warranted to establish the postdepositional stability of this series of compounds relative to other lipids of higher plantwax origin despite but few literature reports of the occurrence of these geochemicals long chain n aldehydes are very likely common in many sediments from environments that receive an input of detrital organic matter from higher plants

organic matter sources and early diagenetic alterations in arctic surface sediments lena river delta and laptev sea eastern siberia ii molecular and isotopic studies of hydrocarbons abstract the hydrocarbons extracted from three surface sediment samples from the delta of the lena river and adjacent areas of the laptev sea were examined to derive information on their source s natural vs anthropogenic terrestrial vs marine the abundance nature distribution and individual stable carbon isotope ratios of these hydrocarbons were determined it thus appeared that the laptev samples are characterized by i a negligible level of oil pollution due to anthropogenic and or natural petrogenic inputs ii an almost exclusive occurrence of long chain predominantly odd carbon numbered n alkanes and iii some differences in the level of bacterial alteration with a relatively higher degradation of the n alkanes in the seaward sediment a non terrestrial origin is proposed for these n alkanes based on the present results and on previous observations on carboxylic acid moieties and the pyrolysis products of the three surface sediments such hydrocarbons are probably not derived from the epicuticular waxes of higher plants but chiefly correspond to autochthonous products likely of algal origin these observations added to recent results on samples from other types of marine environments stress that an abundance of long chain predominantly odd n alkanes in extracts should not be systematically considered alone as evidence for a major contribution of higher plant waxes the relatively low contribution of terrestrial n alkanes in the laptev sediments should result from the combination of i a major dilution of the terrestrial input due to high primary productivity in summer promoted both by a large influx of nutrients provided by the lena river and by the specific conditions in such an arctic environment and ii the high level of degradation of the organic material transported by the lena river thus the latter probably provided a low input of lipids from terrestrial sources to the laptev samples

stratigraphy of deformed permian carbonate reefs in saraburi province thailand kilometre scale thrusts affect the stratigraphic order of the sedimentary rocks that form the khao khwang platform in central thailand the effect of these thrusts requires detailed analysis to unravel the original distribution of the sedimentary units and their associated facies the khao khwang platform comprises three carbonate dominated units identified previously as the phu phe khao khad and khao khwang formations these carbonates are intercalated with clastic mixed siliciclastic and carbonate sequences the sap bon pang asok and nong pong formations the palaeogeography of the area prior to the indosinian orogeny is poorly known and has herein been investigated by combining structural reconstructions microfacies and biostratigraphy in the saraburi area a stratigraphic model for the yakhtashian midian carbonate platform palaeogeography using the well developed exposed sections of the khao khwang platform located in the saraburi province of thailand is presented this has revealed the presence of several separate carbonate platforms dominated by four major middle permian facies peritidal platform interior algal reef and basin slope which are dated using foraminifera and algae this model integrates recent structural studies and considers their impact on the present day distribution of the facies in terms of platform development using biostratigraphy and detailed microfacies analysis supplementary material characteristic images of the six facies high resolution stratigraphic logs a timescale correlation chart and a table detailing the common fossils identified in this study are available at https doi org 10 6084 m9 figshare c 3861796

geochemical characterization of malm zeta laminated carbonates from the franconian alb sw germany ii abstract during jurassic times especially within the malm stage local depressions formed on the eastern bavarian carbonate platform that were surrounded by wall reefs this created a unique depositional environment where in an open marine setting stagnant and anoxic bottom waters developed in an intra reef depression anoxic conditions were stabilized below wave base by enhanced salinity in the bottom waters and establishment of a density stratification biomarker analysis was applied to characterize palaeosalinity and redox conditions utilizing organic sulfur compound methylated chroman hopanoid and saturated isoprenoid distributions prevention of terrigenous influx by protecting reef walls lead to iron deficiency in intra reefal sediments causing early diagenetic sulfurization of functionalized lipids absence of clay mineral catalysts and early sulfurization favored an unusual steroid distribution lacking rearranged analogues but providing coexistence of saturated steranes with and configuration 13 17 spirosterenes unknown sterenes and steradienes as well as mono di and triaromatic steroids desulfurization of the polar fraction was carried out for two samples to verify that palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distribution was not invalidated by sulfur quenching of selected compounds gammacerane was found to be the only component to occur exclusively in the sulfur bound fraction only minor amounts of hydrocarbons were released upon desulfurization implying that free bitumen analysis was applicable for organofacies characterization organic petrological investigation of organic mats revealed the presence of two different types of such structures comparison of organoclast fluorescence spectra with those of extracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial mats whereas algal dominated mats yield no porphyrins this aims towards a better localization of specific biomarker origin in geological samples

decollement in the alpine system an overview decollement in the alpine system is implied in the nappe concept jura decollement originally proposed bybuxtorf 1907 is the latest addition north of the alps the rheology of evaporites shows easy feasibility of jura decollement which is required by material balance in eastern switzerland the front of the alpine foreland thrust belt in the molasse is a typical triangle structure tectonic wedge an important decollement structure also in other places and scales the helvetic nappes are flat and ramp structures similar to the jura but translated by greater amounts and deformed under larger overburden corresponding basement deformation was largely ductile basement lobes and lagged behind the penninic nappes are usually metamorphosed in various degrees except some cover nappes transported far into the foreland coordination between basement and displaced cover is uncertain the austroalpine cover nappes of switzerland and adjacent austria as a rule are only weakly metamorphosed and resemble the southern alps in both stratigraphy and its expression in tectonics the basement part of both are essentially upright slivers not more than five kilometers thick with a frontal ramp fold splitting apart of the sedimentary sequence particularly in the carnian with tectonic wedging is frequent in both domains extensional decollement occasionally accompanied by tectonic denudation and high cooling rates occurred during several episodes most notably during early jurassic rifting and between the compressional phases gosau oligocene early miocene episodes the main strike slip elements of the transpressive neoalps are the insubric fault system with its dextral riedel shears and the dextrally arranged brachyanticlines of the late alpine windows which again imply decollement

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

chemical origin of tectonic tremor tectonic tremor may ultimately be caused by in situ fluid overpressure generated by chemical reactions between a subducting slab and the mantle according to field and microstructural observations of a shear zone

probing the transition between seismically coupled and decoupled segments along an ancient subduction interface the transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip as well as the focus site of episodic tremor and slip features exhumed remnants of the former alpine subduction zone found in the swiss alps allow analyzing fluid and deformation processes near the transition zone region 30 40 km paleodepth the dent blanche thrust dbt is a lower blueschist facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge we report field observations from the dbt region where multiple several tens of meters thick foliated cataclastic networks are interlayered within the basal dbt mylonites petrological results and microstructural observations indicate that the various cataclasis events took place at near peak metamorphic conditions 400 500 c 1 1 1 3 gpa during subduction of the tethyan seafloor in eocene times 42 48 ma some of these networks exhibit mutual crosscutting relationships between mylonites foliated cataclasites and vein systems indicating mutual overprinting between brittle deformation and ductile creep whole rock chemical compositions in situ 40ar 39ar age data of recrystallized phengite and sr isotopic signatures reveal that dbt rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the dbt from the rock fabrics we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates 10 12 s 1 accompanied by fluctuation of supralithostatic and quasi lithostatic fluid pressures 1 0 95 dbt brittle plastic deformation switches highlight the diversity of deformation processes and fluid rock interactions in the transition zone region of the subduction interface

structural and fluid evolution of saraburi group sedimentary carbonates central thailand a tectonically driven fluid system abstract a stable isotopic study focused on calcite cements vein fill calcite and various bioclasts was conducted on variably deformed and thrusted lower and middle permian carbonates of the saraburi group samples were collected in quarry faces across 3 areas in the saraburi lopburi region of central thailand stable isotope crossplots carbon and oxygen using texture aware isotope samples defined variable but related fluid cement histories which are tied to regional burial and then orogenic overprints driven by the indosinian triassic orogeny this was followed by telogenetic overprints driven by late cenozoic uplift the studied carbonates were deposited along the western margin of the indochina block where they were deposited as isolated calcareous algal sponge and fusilinid rimmed platforms on highs bound by extensional faults the platform areas passed laterally and vertically into more siliciclastic dominated sequences deposited in somewhat deeper waters within probable fault bound lows regional post depositional mesogenetic fluid rock re equilibration of the isotope values in ongoing calcite precipitates occurred until the matrix permeability was occluded via compaction and pressure solution this regional burial regime was followed by collision of the indochina and sibumasu blocks during the indosinian triassic blocks which drove a set of structurally focused thrust plane related increasingly warmer set of fluids through the studied sequences the final diagenetic overprint seen in the isotopic values of the latest calcite cements occurs in a telogenetic uplift setting driven by cenozoic tectonics and isostatic uplift integration of isotope data with its structural setting establishes a clear separation in fluid events related to two time separate tectonic episodes its fluid chemistry defines the permo triassic closure of the paleotethys and its subsequent reactivation during the tertiary collision of india and asia the c o covariant plot fields in the permian carbonates of central thailand are so distinct that it is possible to use their signatures to separate burial from meteoric cements in drill cuttings and hence recognise equivalent subsurface unconformities and likely zone of porosity development in possible buried hill plays in thailand

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

the geologic record of deep episodic tremor and slip transient and episodic slow slip accommodates a great deal of tectonic strain and may be mechanically linked with locked regions of seismically hazardous faults best documented in subduction zones and associated with nonvolcanic tremor most proposed mechanisms for slow slip revolve around the transition between stable and unstable frictional sliding the dilemma is that slow slip is generated at a wide range of crustal depths including at pressure temperature conditions where frictional deformation mechanisms give way to predominantly viscous ones we present a model for how fracture and viscous flow within mid crustal shear zones can produce episodic creep transients our model for such transients stems from geological examples of shear zones that formed at temperatures and pressures of 500 c and 0 6 gpa during early orogenesis following late cretaceous subduction of a backarc ocean basin within these shear zones relatively strong lenses of metabasalt localized fluid filled fractures that were subsequently deformed by viscous flow in surrounding quartzofeldspathic gneiss the spatial and temporal characteristics of the modeled creep events are similar to those of slow slip events observed in modern subduction zones we therefore suggest that some episodic tremor and slip can originate through combined fracture and viscous flow across shear zones comprising mixtures of strong and weak materials

serpentinization and infiltration metasomatism in the trinity peridotite klamath province northern california implications for subduction zones the trinity peridotite was emplaced over metabasalts and metasedimentary rocks of the central metamorphic belt along the devonian trinity thrust zone three metamorphic events can be recognized in the trinity peridotite 1 antigorite d 63 to 65 formation related to regional underthrusting of the central metamorphic belt 2 contact metamorphism associated with mesozoic dioritic plutons and 3 late stage formation of lizardite brucite and chrysotile d 127 to 175 due to infiltration of meteoric waters abundant relict phases indicate incomplete reactions and strongly suggest that the availability of h2o was a controlling factor during serpentinization antigorite event 1 formed as a result of infiltration into the trinity peridotite of mixed h2o co2 fluids derived from the underlying central metamorphic belt foliation defined by magnetite veins and shear zones within antigorite serpentinites are subparallel to the trinity thrust the assemblage fo atg chl mag tr carb reflects partial hydration of peridotite at 425 570 c talc rich serpentinite formed along the thrust as a result of the infiltration of silica bearing fluids metasomatic mass balance calculations based on silica solubilities and the extent of antigorite serpentinization suggest that 80 175 volumes of fluid have passed through a given volume of original peridotite at the trinity thrust the trinity thrust probably represents a devonian subduction zone thermodynamic calculations suggest that hydration reactions account for 30 35 of the total heat released by the cooling trinity peridotite by analogy similar hydration reactions are to be expected in the overlying mantle wedge of a subduction zone which act to retard cooling of the hanging wall just as dehydration reactions delay heating of the downgoing slab metasomatic zones formed in peridotite at the trinity thrust may reflect similar metasomatic processes to those proposed to occur in the mantle wedge above a subducting slab

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

palaeostress magnitudes in the khao khwang fold thrust belt new insights into the tectonic evolution of the indosinian orogeny in central thailand using the khao khwang fold thrust belt in central thailand as case study we handled data from calcite twinning analysis in order to propose the quantification of the effective principal palaeostresses magnitudes since the onset of the early stages of the indosinian orogeny we also combined the differential stress estimates from mechanically induced calcite twins with geochronological data in order to constrain the timing of the palaeoburial depth and subsequent uplift by folding within the khao khwang fold thrust belt the proposed mechanical scenario is based on the time constrained kinematic sequence of fracturing faulting and folding in the strata of the carbonate formations of the saraburi group cross checking the data on the palaeostress orientations regimes and differential stress magnitudes with rock mechanics analysis we provided data on the principal stress magnitudes for each tectonic stage that developed during the indosinian orogeny further 40ar 39ar and u pb geochronological data allowed to place reliable constraints on the amount and rate of vertical uplift of the carbonate formations of the saraburi group

frictional properties of actinolite chlorite gouge at hydrothermal conditions abstract exhumed subduction zones frequently show widespread actinolite chlorite act chl dominated compositions suggesting that this may play an important role in controlling megathrust fault slip we investigate the frictional behavior of simulated act chl 85 15 gouge mixtures derived from natural mafic metamorphic rocks under hydrothermal conditions using a ring shear deformation apparatus experiments were performed at effective normal stresses neff of 50 200 mpa pore fluid pressures pf of 50 200 mpa at temperatures t of 23 600 c in each experiment we applied a shear displacement x of 10 mm at a constant sliding velocity v of 10 m s followed by v stepping in the range 0 3 100 m s and slide hold slide shs tests with hold times t ranging from 3 s to 3000 s we quantified the rate and state dependent friction parameter a b and investigated the effect of t on fault healing pk the results showed no effects of temperature on the coefficient of friction 0 6 0 7 or on a b with some experiments showing persistent displacement hardening or weakening trends nonetheless effects of v and of normal stress n neff pf on a b fall into three temperature regimes 1 t 23 100 c 2 t 200 400 c and 3 t 500 600 c in regimes 1 and 3 a b 0 for all conditions tested whereas in regime 2 a b 0 at neff pf 50 mpa and v 0 3 3 m s we discuss on the origin of persistent displacement hardening or weakening trends observed and assess the implications of our data for subduction zone seismogenesis extrapolation of a b data using multiple linear regression suggests that high pore pressure ratios 0 9 are needed to promote seismogenesis in faults cutting actinolite chlorite compositions

analogue modeling of the role of multi level decollement layers on the geometry of orogenic wedge an application to the zagros fold thrust belt sw iran the presence of evaporate and incompetent formations i e decollement horizons within the sedimentary sequence of fold thrust belts can control their structural style and deformation evolution in the present study the influence of the decollement layers e g basal and internal decollement layers on the deformation style of several segments of the zagros fold thrust belt zftb sw iran e g fars arc dezful embayment and izeh zone was investigated using a series of analogue models of accretionary wedges the study of seismic profiles to understand the structural evolution of these segments of the belt where several decollement intervals acted as basal and internal decollements is complemented by the analogue model results the experimental results reveal that the thickness of the internal decollement layers influences the creation of fold dominated or thrust dominated deformations respectively experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation in sequence and or out of sequence faults into overlying strata towards southwest by fore deformation and control the rate of deformation propagation in the zftb the presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the zftb in addition the geometry spacing activity and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low frictional decollements geophys j int 165 1 336 356 2006 geochem geophys geosyst 14 1131 1155 2013 the seismic profiles of the zftb showed that in addition to lithological contrasts the existence and activity of deep seated and basement faults had a big impact on the structural styles of the region