defining a 3 dimensional trishear parameter space to understand the temporal evolution of fault propagation folds abstract the application of trishear in which deformation occurs in a triangular zone in front of a propagating fault tip is often used to understand fault related folding a key element of trishear in comparison to kink band methods is that non uniform deformation within the triangle zone allows the layer thickness and length to change during deformation by varying three controlling parameters independently trishear propagation slip ratio trishear apical angle and fault dip we construct a three dimensional parameter space to demonstrate the variability of resultant geometry feasible with trishear we plot published natural examples in this parameter space and identify two clusters and show that the most applicable typical trishear propagation slip ratio is 2 to 3 while the trishear apical angle varies from 30 to 100 we propose that these findings can help estimate the best fit parameters for natural structures we then consider the temporal evolution of specific geometric examples and factors that increase the complexity of trishear including 1 fault dip changes and 2 pre existing faults to illustrate the applicability of the parameter space and complex trishear models to natural examples we apply our results to a sub surface example from the qaidam basin in northern tibetan plateau

kinematics of the active west andean fold and thrust belt central chile structure and long term shortening rate west verging thrusts synthetic with the nazca south america subduction interface have been recently discovered at the western front of the andes at 33 30 s the active san ramon fault stands as the most frontal of these west verging structures and represents a major earthquake threat for santiago capital city of chile here we elaborate a detailed 3d structural map and a precise cross section of the west andean fold and thrust belt based on field observations satellite imagery and previous structural data together with digital topography we then reconstruct the evolution of this frontal belt using a trishear kinematic approach our reconstruction implies westward propagation of deformation with a total shortening of 9 15 km accumulated over the last 25 myr an overall long term shortening rate of 0 1 0 5 mm yr is deduced the maximum value of this shortening rate compares well with the rate that may be inferred from recent trench data across the san ramon fault and the slip associated with the two past mw 7 earthquakes this suggests that the san ramon fault is most probably the only presently active fault of the west andean fold and thrust belt and that most if not all the deformation is to be released seismically

quaternary palaeohydrological evolution of a playa lake salada mediana central ebro basin spain this research was partly funded by the national science foundation usa under the ear 941 8657 programme and by the eead csic project number z 5 96 this is limnological research center contribution number 527

penecontemporaneous diagenesis in continental saline sediments bloeditization in quero playa lake la mancha central spain abstract in most continental saline lakes of la mancha central spain bloedite has been identified as a part of recent saline deposits by means of a monitoring of the natural evaporation process of the brines in the quero playa lake has been observed the absence of this mineral as a primary phase in the sequence of saline precipitation however bloedite appears as one of the major components of the saline deposit originated during the aforementioned evaporation period the genesis of this bloedite is caused by a syndepositional diagenetic process we have called bloeditization this process in an early rapid diagenetic genesis of bloedite as a result of the reaction between the previously precipitated epsomite and the concentrating brines the replacement of the epsomite by bloedite leads to the release of magnesium chloride and water into the brine if we use a polythermal thermodynamic simulation of the studied evaporation process we obtain results consistent with observations of the brine precipitation paths and the mineralogical composition of the saline deposit

lateglacial and late holocene environmental and vegetational change in salada mediana central ebro basin spain the salada mediana lacustrine sequence central ebro basin spain 41330 10an 0344 w 350 m a s l provides an example of the potential and limitations of saline lake records as palaeoclimate proxies in the semi arid mediterranean region sedimentary facies analyses chemical stratigraphy stable isotopes d18o and d13c of authigenic carbonates d13c values of bulk organic matter and pollen analyses from sediment cores provide paleohydrological and vegetation change reconstructions for the lateglacial and late holocene in the central ebro basin a preliminary chronology is based on 210pb and 14c ams dates the lacustrine sequence is composed of three sedimentary sections the lower section was deposited in a permanent saline to brackish lake this stage represents the most humid period in the record and it was accompanied by the expansion of temperate trees particularly corylus the middle section was deposited in an ephemeral playa lake complex frequent subaerial exposure conditions favour the colonisation of the playa lake oor by chenopodiaceae during a low water table period this interval re ects the most arid conditions in the salada mediana record including the current environment a secondary temperate tree expansion occurred after the maximum aridity period aquatic plants and cyanobacterial mats spread in the lake during periods of raised water tables this paleohydrological and vegetational evolution attests to large changes in e ective moisture during the lateglacial in the semi arid northeastern spain the abundance of corylus during the lateglacial indicates that refugia for temperate trees were located along the ebro valley during the last glacial maximum the holocene sediments in the salada mediana records have been eroded and the upper section represents deposition during the last few centuries 2000 elsevier science ltd and inqua all rights reserved

bloedite sedimentation in a seasonally dry saline lake salada mediana spain abstract salt crusts covering the surface of the salada mediana a seasonally dry saline lake in northern spain consist predominantly of bloedite na2mg so4 2 4h2o microscopic features of the crust were investigated to understand processes of bloedite sedimentation this study was combined with satellite and airborne observations revealing asymmetrical concentric and parallel linear patterns related to wind action gypsum caso4 h2o and glauberite na2ca so4 2 in the calcareous sediments below the crust and abundant eugsterite na4ca so4 3 2h2o along the base of the crust largely formed at a different stage than bloedite the main part of the crust consists predominantly of coarse crystalline xenotopic hypidiotopic bloedite but fan like aggregates with downward widening radial aggregates surface layers with vertically aligned elongated crystals and partially epitaxial coatings occur as well the upper part of the crust is marked by a bloedite thenardite na2so4 association recording a change in brine composition that is not in agreement with results of modelling of local brine evolution a thin fine grained thenardite dominated surface formed in part by subaqueous settling of crystals but there are also indications for development by transformation of bloedite surface features include fan like bloedite aggregates with upward widening formed by bottom growth overall the salada mediana crusts record a complex history of bloedite and thenardite precipitation by various processes

the west andean thrust the san ramon fault and the seismic hazard for santiago chile 1 the importance of west verging structures at the western flank of the andes parallel to the subduction zone appears currently minimized this hampers our understanding of the andes altiplano one of the most significant mountain belts on earth we analyze a key tectonic section of the andes at latitude 33 5 s where the belt is in an early stage of its evolution with the aim of resolving the primary architecture of the orogen we focus on the active fault propagation fold system in the andean cover behind the san ramon fault which is critical for the seismic hazard in the city of santiago and crucial to decipher the structure of the west andean thrust wat the san ramon fault is a thrust ramp at the front of a basal detachment with average slip rate of 0 4 mm yr young scarps at various scales imply plausible seismic events up to mw 7 4 the wat steps down eastward from the san ramon fault crossing 12 km of andean cover to root beneath the frontal cordillera basement anticline a range 5 km high and 700 km long we propose a first order tectonic model of the andes involving an embryonic intracontinental subduction consistent with geological and geophysical observations the stage of primary westward vergence with dominance of the wat at 33 5 s is evolving into a doubly vergent configuration a growth model for the wat altiplano similar to the himalaya tibet is deduced we suggest that the intracontinental subduction at the wat is a mechanical substitute of a collision zone rendering the andean orogeny paradigm obsolete

a reappraisal of episodic burial metamorphism in the andes of central chile the jurassic to miocene sequences of the central andes east of santiago reputedly show repeated cycles of episodic sub greenschist facies burial metamorphism that are identified by sharp breaks in metamorphic grade at major stratigraphic boundaries this paper presents the first detailed petrochemical analysis of these low grade metamorphic sequences by examining the progressive development of secondary minerals reaction progress in mafic phyllosilicates and topological variations in the low grade assemblages as a means of testing this model the results indicate a progressive increase from zeolite facies through to close to the onset of greenschist facies from miocene to jurassic rocks combined analysis of reaction progress in mafic phyllosilicates and petrochemical relationships of chlorite pumpellyite actinolite in metabasites provides no evidence for sharp metamorphic breaks at major stratigraphic boundaries integrating the results presented here with the most recent models of stratigraphic tectonic development of the central andes shows that the metamorphism took place in two episodes and was not episodic on a 40 million year cycle an absence of sharp breaks in metamorphic grade in any part of the succession as demonstrated here shows that the original petrographic establishment of low grade facies provided insufficient resolution of changes in metamorphic conditions to establish definitive evidence of such breaks accordingly this study suggests that re assessment of metamorphic breaks reputedly developed in other areas of the andean cordillera is imperative in order to resolve the questions raised here about the origin of the low grade metamorphism

crustal scale structural architecture in central chile based on seismicity and surface geology implications for andean mountain building 1 we document a crustal scale structural model for the central chile andes based on seismicity and surface geology which consists in a major east verging ramp detachment structure connecting the subduction zone with the cordillera the ramp rises from the subducting slab at 60 km depth to 15 20 km below the western edge of the cordillera extending eastward as a 10 km depth flat detachment this structure plays a fundamental role in the andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a simple shear deformation mode indeed despite shortening distribution being very asymmetric 16 km versus 70 km in the western and eastern side respectively the western side is higher and thicker than what is expected yield strength envelopes show strong rheological control on this structure vp and vp vs variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab which coincides with the blueschist eclogite transition therefore subduction processes would control the depth where the major east verging structure may merge with the slab such a ramp flat structure is observed in other parts of the chilean margin hence it seems to be a first order feature in the andean subduction zone this structure delimitates upward the rocks transmitting part of the plate convergence stress from the plate interface and controls mountain building tectonics thus playing a key role in the andean orogeny

the development of a burkeite dominated salt crust an example of evaporite sedimentation in a saline pan with non monomineralic deposits a salt crust from an ephemeral saline lake in northern namibia includes a basal thenardite layer na2so4 followed by intervals consisting of burkeite na6 co3 so4 2 with a palisade type fabric that are separated by layers of fine grained burkeite all palisade burkeite formed as coatings along the sides of the neighbouring intervals and around thin lenses of fine grained burkeite during the development of these coatings the original constituents of the intervals that they now occupy were dissolved textural features indicate that the dissolved deposits were composed at least in part of halite crystals the study of this crust illustrates the complexity of evaporite sedimentation in ephemeral saline lakes where more than one dominant mineral is formed in the studied basin selective dissolution of the most soluble salts occurred during flooding stages partly affecting subsurface occurrences that consisted of continuous beds the final product is a nearly monomineralic deposit derived from a layered non monomineralic formation the deposit developed to a large extent by subsurface crystal growth in a subaqueous setting rather than by mineral formation along the brine sediment interface or under subaerial conditions

active transpressional tectonics in the andean forearc of southern peru quantified by 10be surface exposure dating of an active fault scarp our understanding of the style and rate of quaternary tectonic deformation in the forearc of the central andes is hampered by a lack of field observations and constraints on neotectonic structures here we present a detailed analysis of the purgatorio fault a recently recognized active fault located in the forearc of southern peru based on field and remote sensing analysis pleiades dem we define the purgatorio fault as a subvertical structure trending nw se to w e along its 60km length connecting on its eastern end to the crustal incapuquio fault system the purgatorio fault accommodates right lateral transpressional deformation as shown by the numerous lateral and vertical plurimetric offsets recorded along strike in particular scarp with a 5m cumulative throw is preserved and displays cobbles that are cut and covered by slickensides cosmogenic radionuclide exposure dating be 10 of quartzite cobbles along the vertical fault scarp yields young exposure ages that can be bracketed between 0 to 6ka depending on the inheritance model that is applied our preferred scenario which takes in account our geomorphic observations implies at least two distinct rupture events each associated with similar to 3 and similar to 2m of vertical offset these two events plausibly occurred during the last thousand years nevertheless an interpretation invoking more tectonic events along the fault cannot be ruled out this work affirms crustal deformation along active faults in the andean forearc of southern peru during the last thousand years

magmatic and hydrothermal chronology of the giant rio blanco porphyry copper deposit central chile implications of an integrated u pb and 40ar 39ar database the history of hypabyssal intrusion and hydrothermal activity in the northeastern and central parts of the be hemothian sensu clark 1993 rio blanco los bronces porphyry copper molybdenum deposit is clarified on the basis of integrated u pb and 40ar 39ar geochronology isotope dilution thermal ion mass spectrometry id tims u pb dates for zircon separates and id tims and sensitive high resolution ion microprobe shrimp dates for single zircon grains in pre syn and late mineralization volcanic and intrusive host rocks in the rio blanco don luis and sur sur mining sectors provide a temporal framework for interpretation of incremental heating and spot fusion 40ar 39ar dates for respectively magmatic biotite and hydrothermal biotite muscovite and orthoclase the ore deposit is hosted in part by 16 77 0 25 to 17 20 0 05 2 ma andesitic volcanic strata of the farellones formation but the major host rocks are units of the san francisco batholith including the 11 96 0 40 ma rio blanco granodiorite mine terminology the 8 40 0 23 ma cascada granodiorite and the 8 16 0 45 ma diorite hypabyssal dacitic intrusions late porphyries emplaced into the batholith yield 206pb 238u id tims dates ranging from 6 32 0 09 ma quartz monzonite porphyry through 5 84 0 03 ma feldspar porphyry to 5 23 0 07 ma don luis porphyry the late mineralization rio blanco dacite plug yields a shrimp zircon age of 4 92 0 09 ma the 40ar 39ar plateau ages for phenocrystic biotites in quartz monzonite porphyry feldspar porphyry and don luis porphyry as well as the preore diorite range only from 5 12 0 07 to 4 57 0 06 ma all are significantly younger than the corresponding zircons and exhibit no correlation with intrusive sequence the 40ar 39ar ages for hydrothermal biotite and orthoclase veins within the san francisco batholith units fall in a narrow interval from 5 32 0 27 to 4 59 0 11 ma hydrothermal sericites muscovite one associated with chalcopyrite yielded spot fusion ages of 4 40 0 15 ma rio blanco granodiorite hosted and 4 37 0 06 ma don luis porphyry hosted comparison with the id tims and shrimp zircon ages indicates that most of the 40ar 39ar ages even 95 percent plateaus do not record initial magmatic cooling or hydrothermal alteration mineralization events evidence for quasipervasive reheating to at least 300 c by successive intrusions published re os ages for two molybdenite samples range from 5 4 to 6 3 ma and overlap extensively with the zircon u pb ages for the late porphyries they imply that cu mo mineralization overlapped temporally with the emplacement of at least quartz monzonite porphyry and feldspar porphyry units of the late porphyry suite and was therefore contemporaneous with the rise of dacitic melts to subvolcanic levels hydrothermal activity is inferred to have continued until 4 37 0 06 ma following intrusion of the don luis porphyry and the early stages of emplacement of the rio blanco dacite plug complex hypogene cu mo mineralization therefore probably persisted for 2 m y the geochronologic data do not resolve whether ore formation was continuous or episodic but the observed crosscutting relationships between intensely altered and mineralized country rocks and less altered and mineralized late porphyry bodies support a model in which the ascent of metal rich brines from an unexposed zone of the parental magma chamber was periodically stimulated by magma perturbation and hypabyssal intrusion

cenozoic deformation and tectonic style of the andes between 33 and 34 south latitude 1 the andes of argentina and chile between latitudes 33 and 34 s are composed from west to east of an oligocene to miocene volcanic arcs and the neogene east vergent aconcagua fold and thrust belt of the cordillera principal and the basement block faulted cordillera frontal a regional cross section suggests that shortening across the andes was achieved by thrusting along detachments at several levels in the crust while thin skinned deformation along newly formed thrusts occurred in mesozoic sequences of the eastern cordillera principal reactivation of preexisting jurassic and oligocene normal faults has resulted in additional hybrid thick and thin skinned structures in the western cordillera principal five major thrusting events are recognized in this part of the andes 1 early to middle miocene tectonic inversion of the extensional faults in the western cordillera principal 2 middle to late miocene development of the aconcagua fold and thrust belt 3 late miocene uplift of cordillera frontal 4 late miocene early pliocene out of sequence thrusting in the cordillera principal and 5 pliocene to present deformation of the foreland

criteria for the recognition of salt pan evaporites layered evaporites can accumulate in 1 ephemeral saline pans 2 shallow perennial lagoons or lakes and 3 deep perennial basins criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated the characteristics of the ephemeral saline pan setting have been determined by examining eight holocene halite dominated pans salt pans and their deposits marine and non marine from the u s mexico egypt and bolivia these salt pans are typified by alternating periods of flooding resulting in a temporary brackish lake evaporative concentration when the lake becomes saline and desiccation which produces a dry pan fed only by groundwater the resulting deposits consist of alternating layers millimetres to decimetres of halite and mud the layers of halite are characterized by 1 vertical and horizontal cavities rounded crystal edges and horizontal truncation surfaces due to dissolution during flooding 2 vertical chevrons and cornets grown syntaxially on the bottom during the saline lake stage 3 halite cements overgrowths and euhedral cavity linings and disruption of layering into metre scale polygons produced during the desiccation stage the muddy interbeds are characterized by displacive growth of halite during the desiccation stage immediately below the surface of the pan the halite layers are matured by repeated episodes of dissolution and diagenetic crystal growth this results in porous crusts with patches of chevron and cornet crystals truncated by dissolution clear diagenetic halite cement and internal sediment these layers of mature halite closely resemble the patchy cloudy and clear textures of ancient halite deposits holocene salt pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick so they are realistic models for ancient evaporites in scale e g permian salado formation of new mexico texas which preserves many primary salt pan features

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

application of trishear fault propagation folding to active reverse faults examples from the dalong fault gansu province nw china abstract determining accurate fault slip rates at 1 ka to 1 ma timescales requires well constrained palinspastic reconstructions of dateable geomorphic and or geologic markers although general kinematic models have been developed to simultaneously reconstruct both bedrock e g bedding and fault attitudes and neotectonic markers e g strath terraces along active strike slip and thrust faults it is not clear if these models can also account for deformation along steeply dipping 45 reverse faults to address this problem we have investigated the active 50 dipping dalong reverse fault system this 40 km long fault system forms part of the aksai restraining stepover along the active left slip altyn tagh fault in northwestern china our geometric and kinematic analyses show that conventional fault bend fold models cannot satisfy the steeply dipping fault geometry we observe in the bedrock record likewise standard fault propagation fold models fail to match our measurements of a set of fluvial terraces however by expanding the trishear model of fault propagation folding to track both bedrock and neotectonic markers we are able to match both sets of records in particular we have developed trishear kinematic models for two sites liuchenzi and qingyazi using the numerical modeling program fault fold v 5 0 this work indicates that an important implication of active trishear fault propagation folding is that terrace deformation extends for over 1 km on either side of the fault trace thus to accurately measure the total magnitude of vertical separation between matching terraces in the hanging wall and footwall terrace profiles across active reverse faults must extend 1 2 km on either side of this zone of deformation

revisiting the crustal structure and kinematics of the central andes at 33 5 s implications for the mechanics of andean mountain building the andean belt is the only present day active case example of a subduction type orogeny however an existing controversy opposes classical views of andean growth as an east verging retro wedge against a recently proposed bi vergent model involving a primary west vergent crustal scale thrust synthetic to the subduction we examine these diverging views by quantitatively re evaluating the orogen structural geometry and kinematics at the latitude of 33 5 s we first provide a 3d geological map and build an updated section of the east vergent aconcagua fold and thrust belt aconcagua ftb which appears as a critical structural unit in this controversy we combine these data with geological constraints on nearby structures to derive a complete and larger scale section of the principal cordillera within the forearc region we restore our section and integrate published chronological constraints to build an evolutionary model showing the evolving shortening of this forearc part of the andes the proposed kinematics implies uplift of the frontal cordillera basement since 20 25 ma supported by westward thrusting over a crustal ramp that transfers shortening further west across the principal cordillera the aconcagua ftb is evidenced as a secondary east verging roof thrust atop the large scale basement antiform culmination of the frontal cordillera we estimate a shortening of 27 42 km across the principal cordillera of which only 30 is absorbed by the aconcagua ftb finally we combine these findings with published geological data on the structure of the eastern back arc andean mountain front and build a crustal scale cross section of the entire andes at 33 5 s we estimate a total orogenic shortening of 31 55km mainly absorbed by crustal west vergent structures synthetic to the subduction our results provide quantitative key geological inferences to revisit this subduction type orogeny and compare it to collisional alpine type orogenic belts

backlimb trishear a kinematic model for curved folds developed over angular fault bends abstract numerous analog models and some natural examples display smoothly curving backlimb fold hinges over sharp angular bends in the underlying thrust surface we present a new kinematic model that can reproduce this geometry by defining a triangular zone focused on the fault bend the model presupposes incompressible flow in the triangular zone and makes common assumptions about velocities on either side of the fault bend either symmetric or asymmetric triangular zones can be defined with parallel kink folding and similar folding being special cases of the two respectively where the apical angle of the triangular zone is zero the results of the numerical model compare well to analog experiments the model is conceptually analogous to forelimb trishear at the tip of a propagating fault and hence we refer to it as backlimb trishear

tertiary volcanism during extension in the andean foothills of central chile 33 15 33 45 s this lithologic and geochemical study treats two tertiary volcanic formations in the andean foothills of central chile deposited during and after an inferred culmination of crustal attenuation the abanico and farellones formations which are described in their type localities just east of santiago formed from volcanic arcs in continental basins during the oligocene and early miocene respectively aphyric basic lavas of tholeiitic affinity acid pyroclastic rocks and lacustrine deposits constitute the 3100 m thick abanico formation the overlying 2100 m thick farellones formation consists of calc alkaline lavas basalts absent with thick pyroclastic deposits at the base both formations have nd sr isotope signatures within the mantle array the abanico rocks end 5 7 plot closer to n morb normal mid oceanic ridge basalt than the farellones rocks end 3 9 to 5 1 the ree rare earth element patterns indicate greater depth to the mantle source and a smaller degree of partial melting with time the abanico lavas segregated within the stability field of spinel whereas the lavas of the upper farellones member show residual garnet in their source geochemical changes with time are systematic the greatest contrast is between the middle and upper farellones members in 1 2 m y e g for basaltic andesites la yb increases from 4 3 abanico to 5 6 6 0 and 11 6 lower middle and upper farellones members the bimodal composition of the abanico formation and the lower farellones member indicates that volcanism took place during episodes of extensional conditions extension with subsidence is independently shown by the burial metamorphic pattern voluminous pyroclastic flows structural relationships and other evidence suggest recurrent caldera collapse the first extensional episode ended with contraction and folding of the abanico rocks and the second episode resulted in uplift of the lower and middle farellones members followed by a more passive tectonic regime sequences showing many similarities with the abanico and farellones formations occur along the andean foothills of chile they decrease in age from late cretaceous paleocene at 23 s to early miocene late miocene at 35 s and might be explained by oblique subduction of oceanic ridge

evaporite minerals and geochemistry of the upper 400 m sediments in a core from the western qaidam basin tibet qaidam basin is a tectonically controlled depression on the northern margin of the tibetan plateau in 2008 a long core was drilled in the qahansilatu sub basin in the western qaidam basin the sediment layers in the upper 400 m alternate between evaporite mineral layers and carbonaceous clay layers the detailed mineralogical investigation focused on evaporite minerals including halite gypsum mirabilite thenardite glauberite eugsterite and bloedite gypsum and halite make up the majority of the evaporate minerals environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated gypsum has prismatic and pyramid habits such as disc pyramid stubby prismatic slender prismatic visible isolated gypsum and aggregates rosette radial and twins are mostly scattered in carbonaceous clay layers suggesting that secondary gypsum is well developed gypsum may be a precursor mineral of glauberite and thenardite is the precursor of bloedite as a metastable and rare mineral eugsterite does not appear in other tibetan areas it forms at the expense of pre existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature the presence of eugsterite indicates a warm and or hot climate at its deposition time

orbital and suborbital scale changes in the east asian summer monsoon since the last deglaciation the variability of the east asian summer monsoon easm has far reaching effects on the global climate system and the environment and full understanding of the variability and dynamics of the easm contributes to predictions of its future behavior here we present a well dated mineralogical and total organic carbon record from a saline inland lake in northern china which provides a robust archive of the easm evolution since 16 0 cal ka bp our record reveals a series of rapid and frequent millennial scale climatic fluctuations during the last deglaciation these fluctuations are documented by changes in the abundances of mirabilite bloedite and gypsum which appear to record the oldest dryas the bolling allerod warm period and the younger dryas the peak easm moisture occurred in the early and middle holocene which was punctuated by a prominent and abrupt weak monsoon interval that occurred synchronously with the 8 2 cal ka bp cold event this moisture maximum was terminated at 6 9 5 9 cal ka bp

facies identification within the playa lakes of the monegros desert spain from field and satellite data abstract the monegros desert and its saline wetlands called saladas literally translated as the salties are a unique european landscape of great scientific and ecological value the saladas i e playa lakes and other small saline depressions are dynamic environments changing their surface morphology on a seasonal diurnal basis in response to both climate and groundwater fluxes to depict changes in these natural systems we have identified five surface facies classes which are detectable both in the field and from remote sensing data these facies are crucial for describing and promoting the protection of these habitats remote sensing has provided worthwhile historical data and additional information that compensate for scarce field records combined field and satellite criteria are used to catalog these facies with a new conceptual integration that manages the asynchronism between the field and satellite data the catalog of facies is intended to be helpful for monitoring these wetlands and for understanding the current hydrological patterns and trends in the playa lakes this work will serve as a baseline for studying the future evolution of the saladas which may soon fall under manmade environmental forces such as increased water input from adjacent newly irrigated lands it is hoped that identification of these facies will be useful with minor adaptations in using more advanced sensors or in studying similar habitats

detrital thermochronology reveals major middle miocene exhumation of the eastern flank ofthe andes that predates the pampeanflat slab 33 33 5 s fil lossada ana clara consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de estudios andinos don pablo groeber universidad de buenos aires facultad de ciencias exactas y naturales instituto de estudios andinos don pablo groeber argentina universidad de buenos aires facultad de ciencias exactas y naturales departamento de geologia argentina

syntectonic sedimentation effects on the growth of fold and thrust belts we use two dimensional mechanical models to investigate the effects of syntectonic sedimentation on fold and thrust belt development testing variable syntectonic wedge top and foredeep sediment thicknesses and flexural rigidities model results indicate a first order control of syntectonic sedimentation on thrust sheet length and thrust spacing thrust sheets are longer when syntectonic sediment thickness and or flexural rigidity increase comparison with observations from several fold and thrust belts confirms this first order control of syntectonic sedimentation

the tectonic development of albania explanation and prediction of structural styles abstract this paper summarises the results of a study of the regional geological development of albania carried out with the objective to develop a better understanding of the complicated geometry and kinematics within the framework of the tectonic development the available geological information has been integrated into a model that is consistent with all the data the data included the geological map of albania well data interpreted satellite imagery existing and new shell seismic offshore and onshore published paleomagnetic data and radiometric ages and own field work the model offers a geomechanical explanation for the tectonic style and kinematics of the albanian fold and thrust belt this includes an explanation for out of sequence thrusting as a function of the mechanical stratigraphy brittle limestones and viscous salt and the structural style in the peri adriatic depression the timing of the tectonic events is consistent with plate tectonic movements as modelled for the eastern mediterranean the result of the study demonstrates the value of regional geology for a better understanding of the local geology and the importance of an integrated approach

surface crusts on soils sediments of the southern aral sea basin uzbekistan soils and sediments of the southern aral sea basin of central asia are commonly covered by salt bearing surface crusts these crusts represent a potential source of salt rich dust that can contribute to salinisation of soils in a large area crust types include takyric crusts surface crusts on solonchaks and salt crusts covering dry parts of the lake bed the takyric crusts are structural crusts showing features related to flooding and shrinkage gypsum formed within the sediment matrix is the only evaporite mineral they contain one studied solonchak crust is fine grained with a thin thenardite and bloedite coating along the irregular surface and halite coatings along the sides of pores all salts in this crust formed by evaporation of solutions contained in the groundmass a solonchak crust with a sandy texture contains prismatic gypsum crystals that formed in a water saturated surface layer as well as bloedite eugsterite and halite formed by evaporation of interstitial brines the lake bed crust is a pure accumulation of salt minerals bloedite hexahydrite halite kainite with synsedimentary and diagenetic features salt mineral assemblages in the three crust types are those that form during successive stages of evaporation of aral sea waters in agreement with published theoretical predictions

the relationships between tectonics climate and exhumation in the central andes 18 36 s evidence from low temperature thermochronology abstract the central andes between 18 s and 36 s latitude strike north south for 2000 km along the chilean subduction margin cross several climate zones from hyperarid to humid and exhibit mean elevations in excess of 4000 m a s l here we investigate the relationships between tectonics climate and exhumation by inverting low temperature thermochronological data compiled from the literature 824 ages from 549 samples and new data 238 ages from 146 samples to quantify the exhumation rate history of the central andes since 80 ma our inferred exhumation rates west of the drainage divide and between 18 and 32 s did not exceed 0 25 km ma such low exhumation rates are consistent with low shortening rates and arid conditions in this region local pulses of exhumation occurred only during the eocene as response to active deformation and during the miocene probably as response to uplift of the western andean slope east of the drainage divide between 18 and 28 s the observed exhumation pattern reflects the onset and eastward propagation of deformation here exhumation occurred locally since the middle to late eocene in the eastern cordillera and the altiplano puna and subsequently affected larger parts of these regions and the north western sierra pampeanas during the oligocene in the early miocene 20 ma the interandean zone started exhuming and at 12 10 ma exhumation propagated into the subandean zone enhanced shortening rates and intensified precipitation along the eastern deformation front associated with the onset of the south american monsoon led to increased exhumation rates in the eastern interandean and the subandean zones in the plio pleistocene 0 6 km ma higher pleistocene exhumation rates are also observed in the northern sierra pampeanas 1 5 km ma that can be related to rock uplift along steep reverse faults coupled with high precipitation south of 32 s on the western side exhumation rates in the principal cordillera increased from ca 0 25 km ma in the miocene to rates locally exceeding 2 km ma in the pleistocene whereas the tectonic regime in the southern principal cordillera remained unchanged since the late miocene these higher rates are likely associated with enhanced erosion resulting from intensified pleistocene precipitation and glacial growth in this region reinforced by isostatic rock uplift and active tectonics our study shows that the onset of exhumation correlates mainly with the initiation of horizontal shortening and crustal thickening whereas the magnitude of exhumation is largely set by the amount of precipitation and glacial erosion and by the style of deformation which is controlled by inherited structures and the amount of sediments in the foreland

probing large intraplate earthquakes at the west flank of the andes estimating the potential for the occurrence of large earthquakes on slow slip rate faults in continental interiors away from plate boundaries is possible only if the long term geological record of past events is available however our knowledge of strong earthquakes appears to be incomplete for thrust faults flanking large actively growing mountain ranges such as those surrounding tibet and the andes mountains we present a paleoseismic study of a prominent fault scarp at the west flank of the andes in santiago chile the evidence demonstrates recur rent faulting with displacement of 5 m in each event with two large earthquake ruptures within the past 17 19 k y and the last event occurring 8 k y ago the fault appears to be ripe for another large earthquake moment magnitude m w 7 5 these results emphasize the potential danger of intraplate continental faults particularly those associated with youthful mountain fronts

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

faulting and erosion in the argentine precordillera during changes in subduction regime reconciling bedrock cooling and detrital records abstract the argentine precordillera is an archetypal retroarc fold and thrust belt that records tectonics associated with changing subduction regimes the interactions between exhumation and faulting in the precordillera were investigated using apatite and zircon u th sm he and apatite fission track thermochronometry from the precordillera and adjacent geologic domains inverse modeling of thermal histories constrains eastward in sequence rock cooling associated with deformation and erosion from 18 to 2 ma across the central precordillera tracking thrusting during this time the youngest ahe ages 5 2 ma and highest erosion rates are located in the eastern and western extremities of the precordillera and indicate that recent denudation is concentrated at its structural boundaries moreover synchronous rapid pliocene cooling of the frontal cordillera eastern precordillera and sierra del valle fertil was coeval with initiation of basement involved faulting in the foreland detrital zircon u pb geochronology from the ca 16 8 1 ma bermejo foreland basin strata suggests fluvial connectivity westward beyond the frontal cordillera to the main cordillera and coast range followed by an important shift in sediment provenance at ca 10 ma at this time we suggest that a substantial decrease in permo triassic igneous sources in the frontal cordillera and concurrent increase in recycled zircons signatures of paleozoic strata are best explained by uplift and erosion of the precordillera during widening of the thrust belt bedrock thermochronology and modeling indicate a 2 6 myr lag time between faulting related cooling in the hinterland and the detrital record of deformation in the foreland basin suggesting that for tectonically active semi arid settings bedrock cooling may be more sensitive to onset of faulting we suggest that high erosion rates in the frontal cordillera and eastern precordillera are associated with increased interplate coupling during shallowing of the subducting nazca plate that may concentrate stress along weak structural boundaries of the precordillera

climate surface pore water interactions on a salt crusted playa implications for crust pattern and surface roughness development measured using terrestrial laser scanning sodium accumulating playas also termed sodic or natric playas are typically covered by polygonal crusts with different pattern characteristics but little is known about the short term hours dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness it is important to understand these interactions because playa crust surface pore water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity here we present the first high resolution 10 3m hours co located measurements of changing moisture and salt crust topography using terrestrial laser scanning tls and infra red imagery for sua pan botswana maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity these peaks experienced non elastic expansion overnight of up to 30 mm and up to an average of 1 5 mm night during the 39 day measurement period continuous crusts on the other hand showed little nocturnal change in moisture or elevation the dynamic nature of salt crusts and the complex feedback patterns identified emphasise how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles

influence of overlapping decollements syntectonic sedimentation and structural inheritance in the evolution of a contractional system the central kuqa fold and thrust belt tian shan mountains nw china

horizontal velocities and propagation directions of gravity waves in the ionosphere over the czech republic 1 using a five point continuous doppler sounding system operating at 3 59 mhz developed at the institute of atmospheric physics as cr iap we investigate propagation directions and velocities of gravity waves gws at altitudes from 150 to 250 km over the western part of the czech republic the velocities and directions are computed from the time delays between the observations of corresponding gws at different reflection points that correspond to various sounding paths we focused on the gws that produce an s shaped trace in doppler shift spectrograms and are observed close to sunrise and sunset we have selected about 100 of such events our results show that the analyzed gws propagate with typical horizontal velocities from 100 to 200 m s the north south component of gw velocities depends on the season it is directed northward in the summer and southward in the winter at the same time the north south component of the neutral winds calculated by the horizontal wind model hwm07 has the opposite sign typical observed periods of the analyzed waves range from 10 to 30 min

estimation of fault propagation distance from fold shape implications for earthquake hazard assessment a numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault propagation fold the propagation distance defines the initial position of the tip line at the onset of slip in the santa fe springs anticline of the los angeles basin we show that the tip line of the underlying puente hills thrust fault initiated at the same position as the 1987 magnitude 6 0 whittier narrows earthquake

quaternary tectonics and seismic potential of the andean retrowedge at 33 34 s the andean retrowedge located between 338s and 348s lies in the transition region of the pampean flat slab subduction zone to the north and a normal subduction zone to the south neo tectonic structures and shallow seismicity are very common north of this segment and become pro gressively less frequent southwards the frontal cordillera and the cerrilladas pedemontanas are the main morphostructures involved in the quaternary deformation of this region the frontal cor dillera is a thick skinned fold and thrust belt uplifted since late miocene time the cerrilladas pedemontanas are low relief hills that represent the mild inversion of the cuyo triassic rift depo centre since pliocene time middle miocene holocene synorogenic strata cover the cuyo basin and surrounding foreland areas the quaternary tectonic evolution of this area has been established through integration of new data from fieldwork in the frontal cordillera piedmont with subsurface information and previously published data mean late pleistocene uplift rates ranging between 0 21 and 0 92 mm a 21 and earthquake minimum moment magnitudes mw o fc 6 4 6 7 have been estimated for the morphostructural units analysed in this manuscript

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

mineralogical chemical and morphological features of salt accumulations in the flumen monegros district ne spain abstract relationships among the mineralogy morphology and the formation processes of salt accumulations were studied in three sampling areas in the flumen monegros district which represent three geochemical environments na so4 cl na mg so4 cl and na co3 so4 cl according to chemical and mineralogical results the samples included both natural ones and others that were obtained in the laboratory by the crystallization of brines with and without substrate a climatic chamber was used to reproduce the environmental conditions laboratory crystallization of brines without soil substrate does not always reproduce the natural mineral associations such associations were reproduced however when the crystallization was carried out with the epipedon new morphologies are described for bloedite radiating prismatic and foliated rosette like and burkeite book plates and spheroidal association of plates the latter formed through capillary evaporation x ray diffraction scanning electron microscopy se and bse modes energy dispersive x ray spectrometry and polarized light microscopy were some of the techniques used supplemented by chemical data

cenozoic tectonics of the high andes of west central argentina 30 36 s latitude abstract the structure of the central andes shows three distinctive segments characterized by different geometries these geometries are superimposed on the present large scale plate tectonic setting characterized by distinct subduction segments the northern la ramada segment is a thick skinned fold and thrust belt formed by tectonic inversion of a late triassic rift the central aconcagua segment consists of a thin skinned fold and thrust belt while the southern malargue segment like the first one is a thick skinned fold and thrust belt developed by tectonic inversion of a late triassic early jurassic rift system during late cenozoic times the amount of shortening gradually decreases from north to south as indicated by the crustal roots of the central andes the different geometries along the principal cordillera controlled the abrupt changes in the shortening among segments the structure of precordillera and sierras pampeanas has also been considered in order to account for the total shortening in the la ramada segment the main shortening occurred in the precordillera in the aconcagua segment in the principal cordillera while in the malargue segment the shortening is widely distributed in a broader principal cordillera because south of the flat slab subduction segment the precordillera and sierras pampeanas are missing

textural features of holocene perennial saline lake deposits of the taoudenni agorgott basin northern mali abstract the holocene salt lake deposits of the taoudenni agorgott basin northern mali mainly consist of sediments with a high glauberite na2ca so4 2 content the remainder of the deposits largely consists of salt beds with a bloedite na2mg so4 2 4h2o thenardite na2so4 or halite nacl composition a petrographical study of the deposits demonstrates that they formed in a perennial lake that experienced a gradual decrease in water depth textural features of the glauberite dominated deposits are found to be related to water depth through the control that this factor exerts on the sensitivity of the lake to changes in water supply and to short term variations in evaporation rates in this way layering due to variations in glauberite content and crystal size is inferred to be typical of deposits that formed in shallow water whereas unstratified deposits are the product of high lake level stages halite textures are found to be indicative of the place within the water column where crystal growth occurred along the lake bottom or higher which is mainly determined by water depth and partly by evaporation rates the oldest halite beds are largely unaltered cumulate deposits whereas the youngest layers developed exclusively through bottom growth the basal part of one thick halite bed at a level between these two groups of halite layers developed by an alternation of both types of growth in response to variations in evaporation rates variations in mineralogical composition between and within the salt beds that formed during the earliest periods with a higher salinity up to the first stage with halite formation record a change in lake water chemistry with time but they are in one instance also determined by an early diagenetic mineral transformation

the crustal seismicity of the western andean thrust central chile 33 34 s implications for regional tectonics and seismic hazard in the santiago areathe crustal seismicity of the western andean thrust central chile 33 34 s