crustal versus mantle core complexes deep crustal and mantle rocks are exhumed in core complex mode of extension in three types of structures metamorphic core complexes oceanic core complexes and magma poor passive margins using available analogue and numerical models and their comparison with natural examples the present paper reviews the mechanical processes involved in these different types of extensional setting three main aspects are considered i the primary role of lithosphere rheology ii the lithosphere scale patterns of progressive deformation that lead to the exhumation of deep metamorphic or mantle rocks and iii the initiation and development of detachment zones crustal core complexes develop in continental lithospheres whose moho temperature is higher than 750 c with upper crust dominated strength profiles contrary to what is commonly believed it is argued from analogue and numerical models that detachments that accommodate exhumation of core complexes do not initiate at the onset of extension but in the course of progressive extension when the exhuming ductile crust reaches the surface in models convex upward detachments result from a rolling hinge process mantle core complexes develop in either the oceanic lithosphere at slow and ultra slow spreading ridges or in continental lithospheres whose initial moho temperature is lower than 750 c with sub moho mantle dominated strength profiles it is argued that the mechanism of mantle exhumation at passive margins is a nearly symmetrical necking process at lithosphere scale without major and permanent detachment except if strong strain localization could occur in the lithosphere mantle distributed crustal extension by upper crust faulting above a decollement along the ductile crust increases toward the rift axis up to crustal breakup mantle rocks exhume in the zone of crustal breakup accommodated by conjugate mantle shear zones that migrate with the rift axis during increasing extension

quasistatic propagation of a normal fault a fracture mechanics model abstract we have carried out boundary element calculations to simulate quasistatic propagation of a normal fault in the earth s crust under a horizontal tensile loading byerlee s frictional law is employed to describe the mechanical behavior of the fault surface we hypothesize that in order for a normal fault to grow quasistatically the mixed mode effective shear stress intensity factor must exceed a threshold value fracture toughness a crustal material property we suggest that the fault grows in a direction of local maximum shear stress the direction of fault propagation thus depends on the ratio of tensile and shear stress intensity factors a listric normal fault is likely to form in crustal material with a small shear fracture toughness a listric normal fault is also more likely to form in crustal material with a high degree of plasticity the propagation trajectory of an incrementally growing normal fault is examined as the normal fault extends to a greater depth the shear stress intensity factor drops owing to an increase in fault surface friction the equilibrium depth to which a normal fault will grow is controlled by the far field loading and the fracture mechanical property of the crustal material the decrease of shear stress intensity with fault length also stabilizes the fault growth

a finite element method for simulating fault block motion and hydrothermal fluid flow within rifting basins we study the influence of vertical fault block motion on the hydrodynamics of continental rift systems in this paper using finite element analysis numerical solutions to governing groundwater flow and heat transport equations within independently moving fault blocks are obtained using triangular elements hybrid four node slip elements developed for this study are employed along fault surfaces standard three node elements are used everywhere else the model is used in a sensitivity study to assess the effects of permeability variations subsidence erosion rates and water table configuration on basin hydrodynamics idealized simulations of rifting over a 1 5 m y period were constructed using two horst and graben fault blocks that are vertically offset by 4 5 km during the simulation period numerical results indicate that significant interaction between different fluid flow impelling mechanisms compaction topography and density driven flow occurs over a permeability range of 10 16 5 to 10 14 5 m2 many of the flow fields especially those in high permeability 10 14 5 m2 horst and graben blocks produce areas of high and low heat flow relative to conductive conditions models which incorporate alternating layers of permeable and less permeable layers indicate that the truncation reconnection of aquifers can induce transient thermal and hydrologie behavior the sensitivity results suggest a plausible mechanism for transient fluid flow on geologic timescales 105 to 107 years within faulted basins and may help to explain the occurrence of some banded ore deposits or multiple episodes of sediment diagenesis preserved within the sedimentary rock record

coseismic and postseismic slip distribution of the 2003 mw 6 5 chengkung earthquake in eastern taiwan elastic modeling from inversion of gps data abstract the chengkung earthquake with m l 6 6 occurred in eastern taiwan at 12 38 local time on december 10th 2003 based on the main shock relocation and aftershock distribution the chengkung earthquake occurred along the previously recognized n20 e trending chihshang fault this event did not cause human loss but significant cracks developed at the ground surface and damaged some buildings after 1951 taitung earthquake there was no larger m l 6 earthquake occurred in this region until the chengkung earthquake as a result the chengkung earthquake is a good opportunity to study the seismogenic structure of the chihshang fault the coseismic displacements recorded by gps show a fan shaped distribution with maximal displacement of about 30 cm near the epicenter the aftershocks of the chengkung earthquake revealing an apparent linear distribution helps us to construct the clear fault geometry of the chihshang fault in this study we employ a half space angular elastic dislocation model with gps observations to figure out the slip distribution and seismological behavior of the chengkung earthquake on the chihshang fault the elastic half space dislocation model reveals that the chengkung earthquake is a thrust event with minor left lateral strike slip component the maximum coseismic slip is located around the depth of 20 km and up to 1 1 m the slips are gradually decreased to less than 10 cm near the surface part of the chihshang fault the seismogenic fault plane which is constructed by the delineation of the aftershocks demonstrates that the chihshang fault is a high angle fault however the fault plane changes to a flat plane at depth of 20 km in addition a significant part of the measured deformation across the surface fault zone for this earthquake can be attributed to postseismic creep the postseismic elastic dislocation model shows that most afterslips are distributed to the upper level of the chihshang fault and most afterslips consist of both of dip and left lateral slip the model results show that the chihshang fault may be partially locked or damped near surface during coseismic slip after the mainshock the strain which cumulated near the surface was released by postseismic creep resulting in significant postseismic deformation

microearthquakes beneath median valley of mid atlantic ridge near 23 n tomography and tectonics data from a microearthquake experiment in the median valley of the mid atlantic ridge near 23 n in 1982 are used to measure earthquake source parameters to determine the laterally heterogeneous seismic velocity structure across the inner floor and to develop a kinematic tectonic model for this portion of the median valley fifty three microearthquakes occurred over a 10 day period beneath the median valley inner floor and eastern rift mountains twenty of 23 well located inner floor epicenters define a line of activity about 17 km long having a strike of n25 e and located near an along axis depression some 300 400 m deeper than surrounding regions earthquakes with well resolved hypocenters generally have focal depths of 4 8 km beneath the seafloor of both the inner floor and the rift mountains the hypocentral locations are robust with respect to plausible lateral variations in seismic velocity structure composite fault plane solutions for inner floor events indicate normal faulting on planes dipping at angles near 45 normal faulting mechanisms although poorly constrained are also indicated for the rift mountain microearthquakes seismic moments approximate fault dimensions and average stress drops for the largest events recorded are 1019 1020 dyn cm 200 400 m and 1 70 bars respectively a twodimensional tomographic inversion of p wave travel time residuals from microearthquakes and local shots indicates a well resolved lateral heterogeneity in crustal velocity structure across the median valley inner floor p wave velocities at 1 5 km depth within a zone less than 10 km wide beneath the central inner floor are lower by several percent than in surrounding regions the most likely explanation for the low velocities is that the region is the site of the most recent local magmatic injection and remains pervasively fractured as a result of rapid hydrothermal quenching of the newly emplaced crustal column by this view the seismic velocity structure at the ridge axis evolves probably by the sealing of cracks and pores within the first few hundred thousand years of crustal accretion consideration of the detailed sea beam bathymetry in this region of the inner floor the characteristics of large earthquakes that the region has experienced during the past 25 years and the results of the microearthquake and tomography analysis suggests that this section of the median valley has been undergoing continued horizontal extension and block faulting without significant crustal injection of magma for at least the past 104 years

core complex segmentation in north aegean a dynamic view the core complexes of the north aegean result from the gravity spreading of a thrust wedge driven by the hellenic slab rollback since middle eocene the development of the southern rhodope core complex occurred in two stages i core complex exhumation accommodated by the kerdylion detachment and ii steep normal faulting controlling the deposition of neogene sedimentary basins that segmented the core complex both stages have been controlled by a clockwise rotation of the detachment hanging wall the bulk amount of extension along the aegean coastline in northern greece reached 120 km the transition between the two stages occurred in middle miocene due to an increase in extensional displacement by a factor 5 this transition between two different modes of extension from localized detachment i e core complex mode to distributed steep normal faulting i e wide rift mode occurred at aegean scale as a result of an acceleration of slab rollback the neogene basins emplaced close to the detachment where brittle upper crust was thin around 7 km but containing weak marble layers allowing the formation of ramp flat extensional systems with rollover type basin fill since pliocene the stretching direction changed from ne sw to ns due to the propagation of the north anatolian fault in the north aegean domain

ductile and brittle deformations in the northern snake range nevada abstract the northern snake range east central nevada is one of the metamorphic core complexes of the sevier hinterland within the range a major decollement separates an upper plate composed of brittlely deformed paleozoic sedimentary rocks mostly carbonates from a lower plate composed of metamorphic upper precambrian lower cambrian rocks intruded by gneissic granites a study of the geometry and kinematics of structures and fabrics at outcrop scale and in thin sections indicates that the northern snake range decollement has been a zone of intense non coaxial e vergent shear and transport in a n115 e direction outstanding asymmetric boudinage within the marble sheet capping the lower plate testifies for late ductile shear strains of at least 20 the interface between brittlely and ductilely deformed rocks seems too sharp to represent a regional rheological transition but might result from two distinct phases of deformation ductile deformation in and below the decollement could have occurred before brittle deformation in the upper plate brittle faulting in the upper plate related to basin and range extension reactivated the upper surface of the ductile shear zone high topographic relief on the normal faults bounding the range triggered the slide of olistolites from the upper plate into the adjacent oligo miocene basins

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

geodynamic mechanism and classification of basins in the earth system abstract the sedimentary basin is a basic geological unit in the earth system its formation and evolution are controlled mainly by plate tectonics and geodynamics which have produced a variety of basin types the development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric and earth surface actions basin classification schemes based on the theories of platform geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution from the viewpoint of earth system we proposed a new basin classification scheme based on geodynamic mechanism that is lithospheric plate sublithospheric and earth surface actions in our geodynamic classification we employed a series of geodynamic settings of basin formation and evolution including the lithospheric plate sublithospheric and earth surface environments the dynamic regimes of basin formation and evolution such as tectonic setting extension compression and shearing the thermal processes and gravity effects the various natures of basin basement and crustal types continental oceanic or transitional crust and the history of basin sedimentary filling and tectonic paleogeography successively as the controlling factors for basin classification this new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the earth surface actions on controlling the basin formation and evolution the basic dynamic types of basin classification include the prototype basin forming under a single tectonic thermal or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and or tectonic regimes thus this classification scheme could provide an evolving understanding of lithosphere crust mantle interaction and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources

rift and thrust tectonics associated with a translational block slide abbotsford new zealand the east abbotsford translational block landslide failed suddenly on 8 august 1979 after months and probably years of slowly accelerating movement a displacement of about 50 m occurred on a bedding plane dipping 7 about 30 m below ground surface at or very near the contact between two formations the complex graben formed around the head of the landslide is a small scale example of extensional rift tectonics a wedge and prism model is developed to fit the geometry and meet the constraints of preserving the cross sectional area and stratal length of the beds involved and also to account for the sequential retrogressive failures of the trailing edge of the sliding block reconstruction of the failure sequence at the toe shows the compressional zone to be dominated by overthrusting on upward sloping surfaces or ramps with subsidiary backthrusting and buckling the energy expended in overthrusting coupled with the decrease in mass and hence driving force resulting from the retrogressive spalling of the trailing edge of the slide block indicates that the phase of rapid movement was accompanied by a sudden decrease in resistance on the failure surface for a movement of 50 m to have occurred both the rift and thrust structures associated with the landslide have large scale tectonic analogues

implications of selected subsurface data on the structural form and evolution of some basins in the northern basin and range province nevada and utah

constraints on the seismogenic faults of the 2003 2004 delingha earthquakes by insar and modeling abstract the 2003 m w 6 3 delingha earthquake happened at the dacaidan zongwulong fault system which is an important active tectonic belt on the northeastern margin of tibetan plateau until the end of 2004 6 approximately m w 5 0 aftershocks occurred on almost the same seismogenic fault the conventional viewpoint is that the seismic hazard near the continental seismogenic fault will be reduced in decades or centuries after rupture why did so many large earthquakes happen on almost the same seismogenic fault within a short temporal interval the seismogenic fault information and the character of the co seismic slip distribution are the keys to answer this problem in this paper the co seismic slip distribution of the 2003 m w 6 3 delingha earthquake was inverted using 18 teleseismic broadband p waveforms 8 sh waveforms and 28 long period surface waveforms data the peak slip concentrates at 12 km depth beneath the epicenter and the slip decreases gradually from 6 km depth to surface and beneath 12 km depth the shallow slip deficit of the co seismic slip distribution may be caused by inelastic failures in the uppermost crust beneath 12 km depth the strain energy may be accumulated by the velocity strengthening frition behavior and may trigger aftershock three post seismic insar interferograms spanning the most aftershocks were formed through analysis on the aftershock distribution and the focal mechanisms of m w 4 9 aftershocks two 3d finite element models containing topography were built and used to simulate the insar observations comparing the modeled results with the insar observations we obtained the seismic source of the 2003 2004 delingha earthqakes it consists of two southwest dipping seismogenic faults named the west fault and the east fault the east fault extends beneath the west fault the 2003 m w 6 3 delingha earthquake occurred on the west fault while 6 large aftershocks occurred on the east fault this shows that the complex spatial location relationship between the seismogenic faults may be an important factor to the large earthquake occurrence with high frequency at almost the same locality due to special tectonic setting and complex structure the dacaidan zongwulong fault system will be a high seismic risk zone in the future

variation in extensional fault geometry related to heterogeneities within basement and sedimentary sequences abstract fault patterns of extensional basins are strongly influenced by the presence of lithological heterogeneities within their sedimentary fill as well as by discontinuities within the basement and at the basement sediment contact low angle detachment surfaces can play an important role in the structural style of extensional basins extensional flat and ramp geometry and superposed extensional sedimentary sequences must be taken into consideration in the case of basins which are characterized by several detachment surfaces

late orogenic plastic to brittle extension along the robertson lake shear zone implications for the style of deep crustal extension in the grenville orogen canada rocks regionally metamorphosed and deformed at middle to lower crustal levels in the contraction dominated mesoproterozoic grenville orogen are exposed in southern ontario canada investigation of the robertson lake shear zone rlsz indicates that extension is a significant component in the late tectonic evolution of this deeply eroded orogen the rlsz is a discrete zone 0 5 1 0 km thick that can be traced for nearly 100 km cross cutting regional structures and lithologic units the zone is composed of a thick mylonite zone and a narrow overlying brecciated zone mylonite foliation shallowly dips east southeast and contains a down dip lineation mylonites are characterized by microstructures indicative of crystal plastic deformation and contain a variety of shear sense indicators including s c and c c composite fabrics sigma porphyroclasts mica fish and other shape fabrics oblique to shear planes consistently indicating a normal down to the east sense of shear a zone of cataclastic structures overlies the mylonite zone and brittle deformation overprints the mylonitic fabrics slickensides in the zone generally strike parallel to foliation in the mylonites but have steeper dips sense of slip indicators and brittle fault orientations also indicate down to the east displacement during east west extension juxtaposition of brittle and crystal plastic structures is resolved with a model of displacement during exhumation whereby localization of cataclasis occurred along a previously active mylonite zone metamorphic facies are upper greenschist in the hanging wall and upper amphibolite in the footwall and metamorphic grade increases from west to east in both the hanging wall and footwall the regional variations in metamorphic grade and the low angle shear zone geometry are a result of isostatic flexural rotations that accompanied extension combined with the crystal plastic to cataclastic nature of the rlsz new 40ar 39ar isotope data from biotite constrain the timing of shear zone displacement until at least 901 1 ma late in the evolution of the grenville orogen

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

rift tectonics on the passive continental margin off galicia spain abstract new migrated multichannel seismic profiles on the starved passive continental margin off galicia spain illustrate the tectonic style of the early cretaceous rifting event which preceded the separation of iberia and north america the main episode of rifting was preceded by other tensional episodes probably of earliest cretaceous and late jurassic age listric faulting associated with rifting was accompanied by large scale mass movements from the crests of the tilted blocks two subaerial erosional surfaces are visible one of late jurassic or earliest cretaceous age was affected by the final faulting episode the other was synchronous with the main phase of rifting and is present only on the upper part of the margin because the central trough was under deep water the significance of a ridge near the ocean continent boundary where altered lherzolite has been dredged and cored is discussed below the tilted blocks which include the basement rocks the seismic horizon s is visible as on the armorican margin its significance is also discussed

an automatic method for determining three dimensional normal fault geometries we describe a general kinematic method for automatically determining the three dimensional 3 d geometry of normal faults at depth from the 3 d geometry of deformed hanging wall horizons the method should be applicable to normal faults which do not change shape as deformation proceeds it is a generalization of two dimensional models and assumes that the hanging wall deforms by arbitrarily inclined bulk simple shear deformation in three dimensions is parameterized by the three euler angles which describe the horizontal slip vector the rake angle and the inclination of shear planes as in two dimensions differential compaction can be included by assuming that the axis of shortening is parallel to the direction of shear three dimensional fault geometry and the three euler angles can all be automatically determined provided the geometries of two or more hanging wall horizons are known here the method is tested on both synthetic data and on 3 d sand box models synthetic modeling shows that unique solutions can be found and more importantly that the horizontal slip vector can be constrained solutions obtained from sand box models are also encouraging in most cases the method can predict automatically the correct direction of extension and a 3 d fault geometry close to the fault geometry used hence arbitrarily inclined bulk simple shear appears to be a good approximation of hanging wall deformation in three dimensions this general method will allow 3 d palinspastic analysis to be undertaken on 3 d seismic reflection data sets

tectonic control on peritidal carbonate parasequence formation an investigation using forward tectono stratigraphic modelling studies of quaternary extensional faults indicate that they have instantaneous amounts of throw 0 4 to 4 m average slip rates 0 05 to 2 8 m kyr 1 and frequency of recurrence 40 000 years accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences pcps hangingwall sites and graben are characterized by fault down dropping together with regional subsidence and footwall sites and horsts by fault related uplift alternating with periods of regional subsidence the relative sea level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program sedtec2000 to simulate how fault related changes in accommodation space can account for high frequency pcp formation each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings high frequency cycles in hangingwall sites are either symmetric deepening then shallowing upward or asymmetric shallowing upward the major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space high frequency cycles in footwall sites and horsts comprise shallow subtidal facies with no distinctive bathymetric trends capped by erosional boundaries generated by footwall uplift the modelled cycles are of the same thickness with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea level changes or autocyclic processes these numerical experiments demonstrate that high frequency pcps can be generated by tectonic fault related processes a hypothesis that is frequently discounted

kinematics of pre miocene ductile deformation in the santa catalina core complex and adjacent regions this paper describes structures within mylonites and metamorphic rocks from the santa catalina and tortolita suizo metamorphic core complexes southeastern arizona united states in these areas mylonitic rocks constitute an easterly low dipping slab more than 4 km thick mapping of principal strain directions and analysis of shear sense have been carried out through the whole pile of mylonites it is shown that although the stretching lineation appears to have a uniform mean sw ne trend three successive shearing events are involved the first shearing event is toward the west and is accompanied in part by the emplacement of the leatherwood quartz diorite dated at 64 ma the second shearing event is toward the ne and is accompanied by the emplacement of the wilderness granitic suite dated at 49 ma the third shearing event is localized and directed toward the sw the top to west shearing and top to ne shearing are possibly related to laramide thrusting the last ductile shearing is related to post eocene extension

40ar 39ar thermochronology from the northwestern dabie shan constraints on the evolution of qinling dabie orogenic belt east central china abstract seven structural units with distinct kinematics have been recognized in the northwestern dabie shan 114 e 115 e and 31 n 32 n east central china they are from north to south 1 the north verging mafan fold belt mfb involving early paleozoic metamorphic rocks 2 the liangting melange belt lmb which is separated from the mfb by a south dipping thrust and consists of gneissic and marble blocks surrounded by highly sheared greenschist 3 the north verging laoshan ductile fold belt lfb which was thrust northward over the liangting melange belt and involves proterozoic schists 4 the suhe thrust sheet sts which consists of phyllite and slate above a folded thrust fault dipping both to the north and south 5 the 5 8 km wide huwan shear belt hsb in the footwall of the folded thrust consisting of mylonitic gneisses and sheared ecologite 6 the kafang eclogite bearing gneiss dome kgd which is defined by broadly warped foliations and 7 the 10 km wide pendian ductile shear belt psb characterized by dextral strike slip deformation nine phengite and muscovite samples in eclogites mylonitic shear zones and metamorphic gneisses from four of the seven structural units have been dated by the 40ar 39ar step heating method phengites from deformed eclogites in the hsb yield complex age spectra that we interpret as most likely indicating closure with respect to ar loss between 350 and 430 ma the rock samples collected from the eclogite bearing gneiss display a significant static recrystallization of quartz which suggests temperatures in excess of ca 350 400 c the ages of 350 430 ma from samples 9669b and 9669c are therefore interpreted as retrograde metamorphic ages for the eclogites six additional phengites sampled from mylonitic rocks yield two groups of ages 263 249 and 236 214 ma the older group samples 96 5 9667 and 9692 were collected from mylonitic rocks with top to north shear sense in the lmb hsb and kgd respectively 9667 and 9692 exhibit a strong static recrystallization which means that ductile deformation took place at a temperature in excess of 350 400 c we therefore adopt the age of 263 249 ma as the cooling ages of white micas considering sample 96 5 shows microfabrics formed at lower temperature around or slight below the closure temperature of white mica there is a strong possibility that the age of 254 1 ma represents a crystallization age rather than a cooling age because these samples are taken from the top to north shear zones we also interpret the 263 249 ma event as a result of thrusting induced denudation the younger group samples 96106 96124 and 96113 collected from dextral shear belts in the hsb and psb exhibit a strong static recrystallization at a temperature in excess of 350 400 c their ages 236 214 ma are therefore interpreted as the cooling ages related to later dextral strike slip faulting sample 96101 collected from weakly foliated rock without penetrative deformation on the north limb of the kgd shows poorly recovered quartz microfabrics at the temperature around or slightly below the closure temperature of white mica its age of 187 1 ma is therefore interpreted as crystallization age during the downdip detachment event related to doming the 40ar 39ar data from the northwestern dabie shan suggest four distinctive cooling events on the basis of the local structural framework and regional tectonic relationships we suggest that the 410 350 ma cooling event was related to either subduction of an oceanic plate beneath the sino korean plate or collision between the sino korean plate and a microcontinental block in the middle paleozoic the three younger episodes of cooling between the late permian and the late triassic may all have been related to the collision between the sino korean and yangtze plates specifically the 263 249 ma event could have been a result of thrusting induced denudation whereas the 236 214 ma cooling event is likely related to strike slip faulting the younger ages of 195 187 ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the sino korean and yangtze plates

new constraints on the formation of the non volcanic continental galicia flemish cap conjugate margins numerous multichannel seismic data acquired on the starved continental margin off galicia show that the prominent intra crustal s reflector is observed only below the oceanward portion of the continental margin close to the ocean continent boundary superficial extension has been computed from the geometry of the well imaged tilted fault blocks of the entire margin by using a series of parallel seismic lines specifically designed for this purpose the pure shear model clearly accounts for the lithospheric extension of the continentward portion of the continental margin but not for the oceanward portion of the continental margin where the s reflector is present the s reflector is a detachment zone which presents a decreasing offset in the direction of the continent and this detachment zone has been active since the beginning of rifting recent kinematic reconstructions show that the conjugate margin to galicia is the southeastern flemish cap margin from the few seismic profiles available on this canadian margin a major master fault is observed beneath the continental slope and is interpreted as the outcropping portion of a main detachment zone identified on the galicia margin as the s reflector the proposed mechanism of extension for these two conjugate margins is pure shear which affects the whole lithosphere but in the upper part of the crust the rifting mechanism is either pure shear for the continentward portion of the galicia margin or simple shear for the oceanward portion of the galicia and the whole southeastern flemish cap margins where the detachment zone is active i consider that pure shear is the basic lithospheric mechanism and that simple shear is a mechanism which affects only the upper crust

kaapvaal craton changing first and second order controls on sea level from c 3 0 ga to 2 0 ga abstract well preserved supracrustal basin fills including the oldest large depository witwatersrand known makes the kaapvaal craton an ideal example for studying controls on first and second order stratigraphic cyclicity the duration of the three basins studied witwatersrand ventersdorp and transvaal from c 3 0 to c 2 0 ga is almost twice that of the entire phanerozoic period from which the paradigms of classical sequence stratigraphy have been derived amongst these is an assumption that cyclicity at specific hierarchical levels is predictable and repetitive through earth history this does not appear to be borne out by the precambrian record studied here instead a hierarchical order of cycles based on relative importance of sequences allied to a more flexible approach to controls on stratigraphic cyclicity at first and second orders is preferred first order cycles within the c 3 0 2 0 ga period on kaapvaal are synonymous with the entire evolution of a supracrustal basin fill defined by a specific basin type second order cycles define basin fill packages of unique character which reflect large scale shifts in the accommodation sedimentation balance early to middle archaean evolution of the kaapvaal craton encompassed amalgamation of a mosaic of subdomains to produce an early south southeastern nucleus by c 3 1 ga accretion of composite terranes from both north and west followed from c 3 0 2 7 ga this was contemporaneous with evolution of the c 3 0 2 8 ga witwatersrand basin the high grade limpopo terrane was amalgamated with the kaapvaal craton between 2 95 and 2 69 ga although a younger age for this orogensis is also possible the witwatersrand first order depositional cycle was controlled largely by subduction related tectonic loading and had a duration of c 190 my the c 5 my first order cycle of the c 2 7 ga ventersdorp basin was essentially controlled by thermal uplift induced extensional subsidence and that of the c 650 my transvaal basin by extensional and subsequent thermal subsidence it is noteworthy in the three basins examined that first order cycles controlled by plate tectonics witwatersrand and transvaal basins were about two orders of magnitude longer relative to the ventersdorp plume tectonic cycle second order cycles also varied greatly from c 100 my to c 1 my within the witwatersrand and transvaal basins subsidence allowed extensive seaways to develop within which classical sequence stratigraphic systems tracts can be recognized reflecting different stages of shoreline shifts within the short lived ventersdorp continental basin system sedimentological criteria can be used to discriminate high and low accommodation systems tracts the transvaal first order cycle was terminated at c 2 0 ga by the bushveld complex plume event

timing and kinematics of caledonian thrusting and extensional collapse southern norway evidence from 40ar 39ar thermochronology 40ar 39ar dating methods have been applied to rocks across the caledonian orogen in southwestern norway in the eastern nappe area k feldspar thermochronological modeling microfabric characteristics and conodont color alteration together indicate that temperatures were not above the closure temperature of muscovite for any significant period of time two groups of muscovite and biotite ages from this area 415 408 for most samples with top to the se fabrics and 402 394 for samples with top to the nw fabrics are therefore interpreted as ages of contractional thrusting and extensional hinterland directed nappe translation deformation respectively in the west hinterland peak caledonian temperatures were higher and 40ar 39ar plateau ages are generally interpreted as cooling ages the western basement and lower nappes cooled rapidly through 500 c basement at 404 ma and 350 c basement and lower nappes shortly after i e during extensional top to the nw transport of the orogenic wedge in addition tectonostratigraphically higher nappes in the hinterland show evidence of earlier cooling probably following ordovician orogenic activity prior to the main collisional stage the new 40ar 39ar data conform to kinematic observations that contraction and extension in the caledonian nappe region were sequential and that the change from contraction convergence to extension divergence was quick between 408 and 402 ma

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

spectral analysis of topography and gravity in the basin and range province abstract a two dimensional spectral analysis has been carried out for the topography and the bouguer gravity anomaly of the basin and range province in western north america the aim was to investigate the possible presence of dominant wavelengths in the deformation pattern at the surface and at the depth of compensation the results suggest that a 200 km wavelength in the deep compensating mass distribution has been inherited from an early tectonic phase of extension at an azimuth n65 e the corresponding surface topography exhibits prominent overtones at wavelength of 100 75 and possibly 45 km it is argued that these characterize the non linear rheology of the upper crust the short wavelengths in the topography reflect the present phase of deformation mixed with the results of the older deformations these results point to a need to extend the physical models of lithospheric stretching beyond the presently available one phase scenario however they show that the boudinage instability concept is consistent with the data

tertiary structural development of selected valleys based on seismic data basin and range province northeastern nevada reflexion seismic data in railroad diamond mary s river and goshute valleys provide information on their structural development that cannot be deduced solely from outcrop and well data these valleys contain tertiary sediments that in dip section define an asymmetrical basin bounded along the eastern flank by a major listric normal fault with about 3 0 4 5 km of displacement the west flank is defined by a gentle east dipping ramp seismically the trace of the listric fault is interpreted to dip westward and sole into the palaeozoic section exploiting regionally recognized mesozoic decollement surfaces the tertiary depocentre adjacent to this fault shifted from west to east with continued slippage through time the greatest movement occurring in the miocene and post miocene in the strike direction the valleys are separated into at least two subbasins by an east west structurally high axis the axis is postulated to be the result of a tear fault associated with movement along the listric normal fault tertiary stratigraphy varies between valleys and between sub basins in a given valley all the valleys contain miocene and younger rocks however not all sub basins contain the pre miocene section suggesting a complex scheme of structural development

deep structure and seismogenesis of the north south seismic zone in southwest china 1 to understand the deep structure and seismogenesis in the north south seismic zone nssz in southwest china we collected a large number of p and s wave arrival time data from both local earthquakes and teleseismic events to invert simultaneously for the three dimensional p and s wave velocity vp vs structures in the crust and upper mantle the obtained vp and vs models are generally coherent with each other from the crust to the mantle transition zone the nssz is characterized by strong structural heterogeneities from the mountainous areas of southeastern tibet to the yangtze platform low vp and low vs anomalies are generally imaged in the upper crust under the sichuan basin showing good agreement with the surface geological features that the foreland basin contains primarily mesozoic and paleozoic sedimentary rocks with a thickness of several kilometers the deep part of the yangtze platform is characterized by a cratonic lithospheric body dipping southwestward down to 400 km depth beneath the southeastern margin of the tibetan plateau in sharp contrast to low velocity anomalies in the upper mantle beneath the songpan ganzi fold system and the northwest qiangtang block at depths of the lower crust and uppermost mantle a layer with low vp and low vs 1 2 is revealed under a region west of the yangtze platform which may reflect the ductile flow in the lower crust our results indicate that the seismotectonics in the nssz is affected significantly by the ductile flow in the lower crust and strong heterogeneities in the upper mantle under southwest china in addition to the dominant role of the india asia collision

image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis results from the campo felice fault central apennines italy abstract morphologic investigations along the campo felice cf fault central apennines italy have been made in order to develop a procedure for the paleoseismological analysis of bedrock fault scarps the cf fault has been responsible for the formation of an impressive limestone fault scarp geomorphologic work on the cf basin and related fault indicated that the scarp originated from tectonic fault displacements three morphologic units have been distinguished along the fault scarp and defined as morphosome m1 lowest part of the scarp m2 and m3 the uppermost part these units display different karstic features which are the result of their different duration of exposure to weathering micromorphologic analyses focused on the morphosome m1 along which the cf fault plane is exposed for a height ranging between 4 and 7 m these analyses were aimed at defining differently weathered bands located at various heights and parallel to the fault scarp top and base the presence of these bands suggests repeated fault movements the exposed fault surface displays a low grade biokarstic weathering due to the action of epilithic and endolithic organisms the biokarst distribution is however inhomogeneous and conditioned by the presence of nourishing elements moisture and by light intensity an area preferentially affected by the biokarstic processes develops as a band at the bedrock soil contact at the base of the scarp roughness and colour analyses were made to identify uplifted bands which previously formed at the bedrock soil contact the roughness analysis was made using a microroughness meter along 20 cm long horizontal transects repeated each 20 cm of fault height for the entire morphosome m1 at various sites along the scarp the roughness variance data plotted vs the fault height failed to identify differently weathered bands of paleoseismological interest this result is probably due to the complex distribution of biokarst along the investigated fault plane more reliable results have been obtained by areal analysis of the variation of the colour rendering of the rocks exposed along the fault plane at different sites photographic images of large portions of fault surfaces have been processed with standard graphic computer programs the variations of colour indicated the presence of bands at various heights along the fault plane two uplifted bands have been recognised at all the investigated sites suggesting two displacement events e1 and e2 a preliminary chronological framework for these two events the youngest of which affected the cf fault can be derived from the paleoseismological data available for the southernmost branch of the regional fault system that includes the cf fault according to these data e1 may have occurred between 860 and 1300 ad while e2 may have occurred at about 1900 bc work is in progress to define surface exposure ages of different parts of the fault plane by means of in situ produced cosmogenic 36 cl this procedure will give further chronological constraints for the age of e1 and e2 and will also permit to test the validity of the micromorphologic analysis of bedrock fault scarps for paleoseismological aims

palaeostresses inferred from macrofractures colorado plateau western u s a abstract in order to 1 understand the tectonic significance of jointing and 2 reconstruct the regional palaeostress history we have studied macrofractures especially joints in the colorado plateau nine major joint set trends have been identified in the colorado plateau each set includes joints that may differ in significance and in age the joints are commonly extensional joints but shear joints were also found the main tectonic events reconstructed from macrofractures analysis include 1 a pre laramide compressional event with 1 n 45 e 2 three laramide compressional events with 1 n 65 e n 95 e and n 115 e successively and 3 three neogene extensional events with 3 n 65 e n 85 e and n 120 e successively these events are correlated with major tectonic events described in neighbouring areas of the western american cordillera

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

extensional layer parallel shear and normal faulting abstract an extensional fault system in bare mountain nevada u s a contains abundant evidence of layer parallel shear deformation contemporaneous with faulting layer parallel shear is manifest by deformation of pre faulting fabrics and cleavage at low angles to bedding that indicate shear in the down dip direction perpendicular to fault bedding intersections layer parallel shear along discrete bedding planes locally offsets normal faults and shear distributed within layers reorients block bounding normal faults in simple rigid block models of extension accommodated by normal faults above a low angle detachment or decollement extension causes faults to rotate to progressively shallower dips while originally horizontal beds rotate to steeper dips these rotations reorient faults out of originally optimum conditions for slip into orientations of a lower slip tendency whereas bedding rotates to steeper dips with progressively higher slip tendency the timing or amount of rotation before the initiation of layer parallel shear depends on the frictional resistance to sliding or resistance to shearing within layering in fault blocks offset or deflection of block bounding normal faults may cause faults to lock as extension increases alternatively bedding and faults may become simultaneously active progressively lowering dips of faults and bedding until neither is well oriented for slip at which point new faults are required to accommodate additional extension at bare mountain early extension within the fault system was accomplished by fault slip and associated block rotation continued extension took place by slip along bedding within fault blocks

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 2 coeruptive deflation july august 2008 1 a hydrovolcanic eruption near cone d on the floor of okmok caldera alaska began on 12 july 2008 and continued until late august 2008 the eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and 3 km below sea level bsl which began immediately after okmok s previous eruption in 1997 in this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar insar techniques to produce a suite of 2008 coeruption deformation maps most of the surface deformation that occurred during the eruption is explained by deflation of a mogi type source located beneath the center of the caldera and 2 3 km bsl i e essentially the same source that inflated prior to the eruption during the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1 e time constant of 13 days we envision a sponge like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath okmok caldera the rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface a similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring fracture system

probing into extensional sedimentary basins comparison of recent data and derivation of tentative models abstract more and more deep seismic profiling is revealing the complex evolution of the continental crust which bears the imprints of former plate movements previous subduction zones and mountain belts affected the crust before the formation of intra cratonic sedimentary basins or passive margins therefore the former geological setting must always be taken into account in deep reflection studies of such areas recent deep seismic profiles in europe and other parts of the world have demonstrated the largely heterogeneous nature of the continental crust with dipping reflectors within the crust while bedding heterogeneities or intrusive sill complexes may be invoked these reflectors are most often associated with inherited thrust planes related to crustal shortening during previous orogenies some of these inherited faults have been imaged beneath sedimentary basins with contrasting styles and their reactivation depends on their strike in relation to the regional stress field these pre existing zones of weakness induce a heterogeneity in the upper crust which may control the geometry of future extensional tectonics when the strike of the inherited faults is perpendicular to the extensional stress field they may be reactivated as a detachment surface controlling the sedimentary infill more often the obliquity of these structures induces local changes and segmentation of the rif when they are crossed in such a case they correspond to transfer faults acting as relays between major normal faults or to twist zones where changes occur in the throw of the normal faults sometimes evolving to an inversion of the polarity in the tilting of the major blocks during extension the top of the lower crust may act as a mechanical decoupling boundary separating asymmetrical brittle failure within the upper crust and symmetrical ductile creep within the lower crust extensional modes may explain the great values of crustal thinning observed in both upper and lower crusts beneath rifts and passive margins related to the opening of an oceanic domain it is more difficult to explain the comparatively small amount of horizontal extension generally observed

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

deformation partitioning in a slow spreading ridge undergoing oblique extension mohns ridge norwegian sea although oceanic spreading is often perpendicular to the ridge trends in some cases the angle between these two directions can be significantly less than 90 40 50 this occurs because of either a bend of the ridge trend or a change of the spreading direction we here describe oblique spreading in the mohns ridge resulting in deformation partitioning between the valley walls which are dominantly affected by strike slip displacements and the axial valley which is subject to nearly pure extension the axial valley walls are characterized by en echelon normal faults affecting the walls while the axial valley is affected by parallel faults grouped into oblique sets these fault sets define different structures horst or tilted blocks that are regularly spaced inside the axial valley moreover some ridge segments mainly undergo pure extension whereas others are affected by oblique extension we explain this faulting pattern including the along strike and transverse variations as a consequence of depth variations of the brittle ductile transition

basin and range large scale tectonics constraints from gravity and reflection seismology two geophysical informations constrain the mechanical state of the lithosphere in the basin and range province cocorp reflection seismic structure across nevada shows a rather smooth reflector at about 30 km depth which can be interpreted as indicative of a rather flat moho on the other hand the bouguer map exhibits two marked troughs in the same region and filtering techniques reveal a predominant 200 km wavelength of the deep compensating masses of the topography this paper attributes these deep heterogeneities to lateral thermal variations created by boudinage type instabilities of the stretched mantle lithosphere

pn anisotropic tomography and dynamics under eastern tibetan plateau we present a new anisotropic tomographic model of the uppermost mantle around eastern tibet using pn traveltime data from a newly deployed temporary seismic array and recent observation bulletins of chinese provincial networks our results are generally consistent with previous results but provide new insights into the dynamics of tibetan plateau prominent high velocity high v anomalies are visible under alashan block and qaidam and sichuan basins which clearly outline their tectonic margins a distinct high v zone representing the double sided subduction of indo eurasian plates is imaged from lhasa block to the south of qaidam basin a pronounced low velocity low v zone is observed from songpan ganzi block to southern chuan dian diamond block suggesting the existence of hot material upwelling there crustal strong earthquakes frequently occurred around high v anomalies or transition zones from high v to low v anomalies suggesting that these earthquakes could be related to lateral heterogeneities in the mantle the pn fast direction approximately rotates around eastern himalayan syntaxis and it is tangential to the margins of sichuan basin suggesting that the mantle material flow of tibetan plateau may have affected east china in the yunnan region to the south of 26 n the pn fast direction is different from sks splitting results indicating that the mantle lithosphere could be mechanically decoupled at certain depth below the uppermost mantle which might be attributable to the subduction of indian or burma slab although the correlation between anisotropy and velocity is complicated anisotropy strength could be associated with the pattern of velocity anomalies in the region

aerobic biomineralization of mg rich carbonates implications for natural environments we studied the formation of mg rich carbonate in culture experiments using different aerobic bacterial strains and aqueous mg ca ratios 2 to 11 5 at earth surface conditions these bacteria promoted the formation of microenvironments that facilitate the precipitation of mineral phases dolomite huntite high mg calcite and hydromagnesite that were undersaturated in the bulk solution or kinetically inhibited dolomite huntite high mg calcite hydromagnesite and struvite precipitated in different proportions and at different times depending on the composition of the medium the mg content of dolomite and calcite decreased with an increasing ca concentration in the medium the stable carbon isotope composition of the mg rich carbonate precipitates reflected the isotope composition of the organic compounds present in the media suggesting that microbial metabolism strongly influenced the carbon isotope composition of biomediated carbonates we observed that ca enriched carbonate precipitates have relatively low carbon isotope composition these results provide insights into the mechanism s of carbonate formation in natural systems and they are of fundamental importance for understanding modern environments in which carbonate minerals form as a window into the geologic past

the plant debris beds of the early cretaceous barremian wessex formation of the isle of wight southern england their genesis and palaeontological significance abstract the early cretaceous barremian wessex formation of the isle of wight primarily represents high sinuosity fluvial but also lacustrine and terrestrial deposition on a low relief floodplain occupying half grabens with active normal faults immediately to the north plant debris beds form a very small proportion of the succession but are the main source of vertebrate fossils including dinosaurs these conspicuous but thin grey units are distributed randomly throughout the wessex formation and are of limited lateral extent the lower part of most plant debris beds comprises a poorly sorted matrix supported conglomerate the upper part of most consists of structureless mudstone which usually grades up into colour mottled but predominantly red and purple floodplain mudstones the plant debris beds contain an unusual mixture of freshwater molluscs diverse aquatic and terrestrial vertebrates and mainly terrestrial plants with a variable quality of preservation we conclude that each plant debris bed represents a locally generated sheetflood which was then transformed on the floodplain into a debris flow by the acquisition of surface material the debris flows surged into and were deposited in depressions on the alluvial plain including abandoned chute and cut off channels oxbows and ponds these units are therefore intrabasinal and interfluvial and the fossils that they contain are locally derived similar deposits of palaeontological significance have not been reported elsewhere in the literature in view of this their origin and sedimentology their palaeontological significance and the taphonomy of the flora and fauna they contain are discussed

static stress interactions in extensional earthquake sequences an example from the south lunggar rift tibet 1 an extensional earthquake sequence occurred in 2004 8 across a graben in the south lunggar rift on the tibetan plateau we use insar data to determine the location fault geometry and slip distribution of these earthquakes and to test whether the sequence is compatible with static stress triggering the mw 6 2 and 6 3 earthquakes in 2004 and 2005 both ruptured west dipping faults on the east side of a graben in 2008 a mw 6 7 earthquake ruptured a pair of east dipping fault segments on the other side of the graben offset from the earlier ruptures we compute first order dislocation models of stress change and demonstrate that the order and spatial configuration of this sequence of events is compatible with triggering by static stress transfer a continuation of the sequence would be most likely to occur on the northern extension of the 2008 rupture although variable slip rate along the rift may mean that the sequence has run its course the insar data for the 2008 earthquake also reveal slip on a fault that cuts the graben at a highly oblique angle we suggest that this is a release fault accommodating differential throw in the hanging wall and associate the deformation with a mw 6 0 aftershock activity on such a release fault has not been directly imaged before the zhongba sequence is one of several examples of recent clustered normal fault earthquakes on the plateau and may be an example of phase locking of similar faults

tectono sedimentary evolution of the eastern gulf of aden conjugate passive margins narrowness and asymmetry in oblique rifting context abstract here we focus on the yet unexplored eastern gulf of aden on socotra island yemen southeastern oman and offshore conjugate passive margins between the socotra hadbeen shfz and the eastern gulf of aden fracture zones our interpretation leads to onshore offshore stratigraphic correlation between the passive margins we present a new map reflecting the boundaries between the crustal domains proximal necking hyper extended exhumed mantle proto oceanic and oceanic domains and structures using bathymetry magnetic surveys and seismic reflection data the most striking result is that the magma poor conjugate margins exhibit asymmetrical architecture since the thinning phase upper rupelian burdigalian their necking domains are sharp 40 10 km wide and their hyper extended domains are narrow and asymmetric 10 40 km wide on the socotra margin and 50 80 km wide on the omani margin we suggest that this asymmetry is related to the migration of the rift center producing significant lower crustal flow and sequential faulting in the hyper extended domain throughout the oligo miocene rifting far field forces dominate and the deformation is accommodated along ew to n110 e northward dipping low angle normal faults convection in the mantle near the shfz may be responsible of change in fault dip polarity in the omani hyper extended domain we show the existence of a northward dipping detachment fault formed at the beginning of the exhumation phase burdigalien it separates the northern upper plate oman from southern lower plate socotra island and may have generated rift induced decompression melting and volcanism affecting the upper plate we highlight multiple generations of detachment faults exhuming serpentinized subcontinental mantle in the ocean continent transition associated to significant decompression melting final detachment fault may have triggered the formation of a proto oceanic crust at 17 6 ma and induced late volcanism up to 10 ma finally the setting up of a steady state oceanic spreading center occurs at 17 ma

tectonics of slow spreading mid ocean ridges and consequences of a variable depth to the brittle ductile transition geophysical evidence especially microearthquakes that extend into the upper mantle beneath the inner floor of the mid atlantic and gorda ridges indicates that the axial magma chamber episodically freezes beneath slow spreading ridges freezing of the axial magma chamber will result in a variable thermal structure that has important tectonic consequences most importantly large near axis faults will intersect as the brittle ductile transition deepens causing some of the faults to become locked the topographic effect of fault locking will be a variation in the width of the inner floor from narrow 10 km when a magma chamber is absent the deep microearthquakes also imply that faults at slow spreading ridges extend into the upper mantle the nature of these faults at depth is unknown but the following hypotheses are presented 1 the faults may be planar and pass downward into aseismic ductile shear zones and 2 the faults may sole into a flat detachment fault defining a sharp boundary between brittle faulting and homogeneous ductile flow such low angle normal faults are common in continental extensional domains large scale tilting 50 70 is probably common at slow spreading ridges and implies either listric faulting or rotation of planar faults and fault blocks similar to toppling dominoes calculations of temperatures at the brittle ductile transition are made assuming olivine and diabase rheologies for the mantle and crust respectively the temperature is approximately 800 c when the transition is at 8 km depth and approximately 600 when the transition is at 2 km depth the strength of the lithosphere varies dramatically with the rise and fall of the brittle ductile transition as magma chambers form and subsequently freeze strong lateral temperature gradients will be present when a magma chamber is formed resulting in localization of faulting within thin weak crust above the chamber when the magma chamber freezes lateral temperature gradients will be small and the strength of the lithosphere will be similar over a wide area this results in active faulting occurring over a width of as much as 60 km some ophiolites possibly provide insights to the tectonic processes at slow spreading ridges the entire crustal section of the josephine ophiolite was tilted by approximately 50 prior to deposition of overlying pelagic sediments this tilting probably took place by faulting suggesting that oceanic faults extended into the upper mantle possible oceanic faults have been identified in the josephine ophiolite but their oceanic origin cannot be established beyond doubt

sandbox experiments on gravitational spreading and gliding in the presence of fluid overpressures whereas in previous analogue experiments on gravitational spreading and gliding detachment occurred on a ductile layer we have used a relatively new technique of injecting compressed air into sand packs so as to simulate the effects of fluid overpressures in sedimentary strata and to trigger slope instabilities in our experiments the governing equations yield scales for dimensions stresses and fluid pressure however the more transitory phenomena of production and decrease of overpressure cannot be suitably scaled by using layers of differing permeability we are able to produce sharp detachments in models made of sand alone the experiments involve gravity spreading or gravity gliding in gravity spreading propagation of the detachment and of extensional deformation depends on the fluid pressure for medium values of fluid overpressure normal faults are closely spaced numerous and bound rotated blocks they propagate progressively toward the back of the model for the highest pressures the deformation propagates very fast and faults bound non rotated blocks which slide on an efficient basal detachment fault dips are also controlled by fluid pressure and by frictional resistance at the base to model gravitational gliding required an apparatus with a more complex system of air injection we did a series of experiments using injection windows of various lengths and compared the results with predictions from a quasi 3d analytical model of sliding in contrast with predictions for an infinite slope sliding depends on 1 the fluid overpressure on the detachment 2 the fluid overpressure in the body of the sliding sheet and 3 the shape of the detachment surface in particular we show that frictional resistance at the lower edge is a primary control on the dynamics of gliding

rifting and shallow dipping detachments clues from the corinth rift and the aegean the corinth rift is superimposed on the hellenic nappe stack that formed at the expense of the apulian continental crust above the subducting african slab extension started in the pliocene and the major steep normal faults that control the geometry of the present day rift were born very recently some 600 kyr ago only they root into a shallow dipping zone of microseismicity recorded near the base of the upper crust the significance of this seismogenic zone is debated considering the northward dip of the zone of microseismicity the depth of microearthquakes and their focal mechanisms we observe a strong similarity with the northern cycladic detachments in terms of expected pressure temperature conditions and kinematics we herein show 1 that the formation of the corinth rift can be considered a part of a continuum of extension that started some 30 35 ma in the aegean and that was recently localised in a more restricted area 2 that the present day structure and kinematics of the corinth rift can be explained with a series of decollements relayed by steeper ramps that altogether formed a mechanically weak crustal scale detachment and 3 that the deformation fluid behaviour and metamorphic features seen in the northern cycladic metamorphic core complexes can be good analogues of the processes at work below the corinth rift

evolution of deep crustal normal faults constraints from thermobarometry in the grenville orogen ontario canada abstract the robertson lake shear zone rlsz is a low angle 30 dip plastic to brittle extensional shear zone located in the southeastern grenville orogen ontario canada thermobarometric data have been collected to evaluate the effects of extension on regional metamorphic field gradients upper greenschist facies metamorphic conditions are preserved in the footwall and upper amphibolite facies metamorphic conditions in the hanging wall however steep gradients in metamorphic pressure are present adjacent to the robertson lake shear zone in the footwall pressures increase from 550 mpa to 800 mpa within 8 km of the rlsz and in the hanging wall pressures decrease from 900 mpa to 500 mpa within 12 km of the rlsz the pressure gradients are interpreted to be a product of isostatic flexural rotations in response to extension along the zone the degree of rotation indicated by the baric gradients in the hanging wall and footwall are compatible and require an initial shear zone orientation of 60 90 which suggests reactivation of an initially high angle terrane boundary previous studies provide constraints of a depth extent of 40 km for the rlsz and crustal thickness of 60 km during extension thus extensional rotations were accommodated by decoupling and regional scale flow in the lower third of the crust

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

testing of permian lower triassic stratigraphic data in a half graben tilt block system evidence for the initial rifting phase in antalya nappes testing of middle permian lower triassic stratigraphic data from the antalya nappes in a half graben tilt block system has revealed the presence of episodic rifting events separated by periods of

applications of bacterial carbonatogenesis to the protection and regeneration of limestones in buildings and historic patrimony abstract the ability of the so called carbonatogenic bacteria may be used for producing surficial protecting coatings biocalcin on limestones buildings monuments and statuary this is the concept of biomineralisation laboratory experiments were undertaken in order to choose the most active bacterial strains and to improve the composition of the nutritional media suitable for stimulating the nitrogen cycle metabolic pathways which are the only ones to be used in aerobic and or microaerophilic conditions life size experiments subsequent measurements and observations show that this natural process of biomineralisation is feasible within the frame of industrial constraints this concept of further developments includes the creation of patinas and the manufacturing of biological mortars and cements which were also improved in the laboratory the biomineralisation recreates a material that is remarkably similar to the limestone substrate because it uses natural microbial mediation which follows the same natural processes that formed many limestones

paleozoic and grenvillian structures in the southern appalachians extended interpretation of seismic reflection data interpretive reprocessing of seismic reflection data has elucidated paleozoic and grenvillian structures in the southern appalachians the seismic data include a 7500 km grid of adcoh seisdata and cocorp reflection profiles that traverse the blue ridge and inner picdmont geologic provinces of north carolina south carolina and georgia surface geology and potential field data were used to constrain the interpretation the reprocessed seismic reflection data have delineated the internal and external geometry of the crystalline blue ridge inner piedmont allochthon including the locations of the blue ridge master decollement haycsville fault and brevard fault zone on the basis of the reprocessed data all of the major faults within the allochthonous upper crust sole in the blue ridge master decollement reflections extending to the southeast from beneath the surface location of the hayesville fault to the blue ridge thrust might be the seismic signature of a high strain zone this implies that internal deformation of the blue ridge allochthon associated with the alleghanian orogeny might have occurred farther to the west than has been previously documented from field studies relative amplitude seismic data enabled the discrimination between blue ridge inner piedmont crystalline rocks and underlying lower paleozoic shelf strata thereby delineating the blue ridge thrust the interpreted geometry constrains the top of the shelf sequence beneath the blue ridge to depths of less than 3 km this relatively shallow depth of the shelf strata together with the presence of duplex structures and bright spots that are imaged within the sequence might imply favorable conditions for hydrocarbon exploration beneath the blue ridge midcrustal reflections from within the upper to iower crust are interpreted to originate from preserved grenvillian structures that were reactivated at the basement surface during late proterozoic early cambrian extension reflection continuity is occasionally disrupted by interpreted post grenvillian pre early cambrian low density intrusions topography at the basement surface possibly caused by the intrusions is interpreted to have controlled the formation of some of the structures within the overlying allochthon including blue ridge and brevard fault zone ramps correlation of seismic time structure contour maps with available gravity data and two dimensional gravity modeling suggest that anomalies in the gravity field can be attributed to low density sources within the autochthonous crust discontinuous reflection packages from depths of 36 42 km are interpreted to originate from the mohorovi i discontinuity the reflectors trend about n15 e with a true dip of approximately 15 nw

the influence of tectonics on early cretaceous sedimentation in bedfordshire england the lower cretaceous sediments of the bedfordshire area are aptian and albian in age during this time the area was situated within an extensional tectonic regime and the pattern of sedimentation in terms of lateral variation both in sediment type and thickness reflects the influence of normal faulting jurassic topography created by block faulting and erosion controlled the distribution of later facies largely by continued tectonic processes especially the reactivation of the jurassic fault block system which produced syn sedimentary faulting of the overlying sequence thus the traditional view of the infill of an erosional basin by the lower greensand is challenged

extension on the tibetan plateau recent normal faulting measured by insar and body wave seismology we use insar and body wave modelling to determine the faulting parameters for a series of five mw 5 9 7 1 normal faulting earthquakes that occurred during 2008 including the march 20 yutian earthquake mw 7 1 one of the largest normal faulting events to have occurred recently on the continents we also study three earlier normal faulting earthquakes that occurred in southern tibet between 1992 and 2005 coseismic deformation for each of these eight events is measured with ascending and descending interferograms from envisat ers and alos sar data elastic dislocation modelling of the line of sight insar displacements and body wave seismological modelling of p and sh waves are used to estimate fault parameters and are found to be in good agreement for all the events studied the use of insar to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity only five of the eight events are associated with a clear surface topographic feature suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone the observations in all cases are consistent with slip on planar surfaces with dips in the range 40 50 that penetrates the uppermost crust to a depth of 10 15 km we find no evidence for active low angle dip less than 30 normal faulting the contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3 4 mm yr 1 or 15 20 per cent of the rates of extension measured across the plateau using gps 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km this observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere

identification of ordovician block tilting in the hercynian fold belt of central brittany france field evidence and computer models abstract the significance of the brioverian lower ordovician unconformity in central brittany has been discussed by many authors a new interpretation in terms of extensional tectonics is presented based on structural sedimentological and stratigraphical data however because sedimentary formations have been strongly folded by hercynian deformation extensional structures are obscured and difficult to recognize to identify the normal faults the geological map is compared with computer models of the folded tilted blocks it is shown that major normal faults had a mean n70 trend dipping toward the se with an almost regular spacing of 7 8 km

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

the 1996 mw 6 6 lijiang earthquake application of jers 1 sar interferometry on a typical normal faulting event in the northwestern yunnan rift zone sw china abstract the northwestern yunnan rift zone in the yunnan province of china is a seismically active region located along the western boundary of the sichuan yunnan block on the eastern margin of the qinghai tibetan plateau an earthquake with a magnitude of 6 6 mw occurred in this region on february 3 1996 the lijiang earthquake was the largest normal faulting event to occur along the western boundary of the sichuan yunnan block in the last 40 years in this study we used l band jers 1 japanese earth resources satellite 1 sar data sets from two descending orbits to detect surface deformation signals surrounding the epicentral region in order to estimate the source parameters through an inversion of the displacement fields the results indicated that the earthquake can be explained by slip along two segments of the n s trending listric normal fault named the lijiang daju fault coseismic deformation patterns and slip distributions revealed that the earthquake consisted of two sub events which were also suggested by seismological results based on an analysis of the static coulomb stress change the second sub event was likely triggered by the first sub event the central segment of the lijiang daju fault which has an eastward convex geometry did not rupture during the earthquake this phenomenon was probably related to a geometrical discontinuity at the fault bend area of the lijiang daju fault

ca carbonates precipitation and limestone genesis the microbiogeologist point of view abstract experiments show that the production of carbonate particles by heterotrophic bacteria follows different ways in heterotrophy the passive carbonatogenesis is generated by modifications of the medium that lead to the accumulation of carbonate and bicarbonate ions and to the precipitation of solid particles it is induced by several metabolic pathways of the nitrogen cycle ammonification of amino acids degradation of urea and uric acid dissimilatory reduction of nitrates and of the sulphur cycle dissimilatory reduction of sulphates the active carbonatogenesis is independent of the mentioned metabolic pathways the carbonate particles are produced by ionic exchanges through the cell membrane following still poorly known mechanisms in autotrophy non methylotrophic methanogenesis and cyanobacterial photosynthesis also may contribute to the precipitation of carbonates autotrophic carbonates as carbonatogenesis is neither restricted to particular taxonomic groups of bacteria nor to specific environments it has been an ubiquitous phenomenon since precambrian times carbonatogenesis is the response of heterotrophic bacterial communities to an enrichment of the milieu in organic matter after a phase of latency there is an exponential increase of bacterial numbers together with the accumulation of metabolic end products these induce a ph increase and an accumulation of carbonate and hydrogenocarbonate ions in the medium this phase ends into a steady state when most part of the initial enrichment is consumed and there is a balance between death and growth in bacterial populations particulate carbonatogenesis occurs during the exponential phase and ends more or less after the beginning of the steady state the active carbonatogenesis seems to start first and to be followed by the passive one which induces the growth of initially produced particles in eutrophic conditions the first solid products are patches that appear on the surface of the bacterial bodies and coalesce until forming a rigid coating and or particles excreted from the cell all these tiny particles assemble into biomineral aggregates which often display precrystalline structures these aggregates grow and form biocrystalline build ups which progressively display more crystalline structures with growth in oligotrophic conditions the primary solid products are rapidly smoothed in the crystalline structure and leave no trace in present aqueous environments apart from deep ocean the potential efficiency of heterotrophic bacterial carbonatogenesis in ca carbonate sedimentation is much higher than autotrophic or abiotic processes it much more likely accounts for extensive apparently abiotic limestone formation than any of the latter as far as biodetrital particles are concerned it may be observed that the shells and tests of organisms are built from the activity of cellular organites which are nowadays considered by a number of biologists as endosymbiotic bacteria thus apart from probably mythical purely evaporitic and autotrophic ones most limestones must be considered as principally of heterotrophic bacterial origin as the carbon of limestones is issued from organic matter bacterial heterotrophic carbonatogenesis appears as a fundamental phenomenon in the relationships between atmosphere and lithosphere during the biogeological evolution of the earth

pre eruption deformation caused by dike intrusion beneath kizimen volcano kamchatka russia observed by insar abstract interferometric synthetic aperture radar insar images reveal a pre eruption deformation signal at kizimen volcano kamchatka russia where an ongoing eruption began in mid november 2010 the previous eruption of this basaltic andesite to dacite stratovolcano occurred in 1927 1928 insar images from both ascending and descending orbital passes of envisat and alos palsar satellites show as much as 6 cm of line of sight shortening from september 2008 to september 2010 in a broad area centered at kizimen about 20 cm of opening of a nearly vertical dike provides an adequate fit to the surface deformation pattern the model dike is approximately 14 km long 10 km high centered 13 km beneath kizimen and strikes ne sw time series analysis of multi temporal interferograms indicates that 1 intrusion started sometime between late 2008 and july 2009 2 continued at a nearly constant rate and 3 resulted in a volume expansion of 3 2 107 m3 by september 2010 i e about two months before the onset of the 2010 eruption earthquakes located above the tip of the dike accompanied the intrusion eventually magma pressure in the dike exceeded the confining strength of the host rock triggering the 2010 eruption our results provide insight into the intrusion process that preceded an explosive eruption at a pacific rim stratovolcano following nearly a century of quiescence and therefore have implications for monitoring and hazards assessment at similar volcanoes elsewhere

normal faulting block tilting and decollement in a stretched crust extensional tectonics cover a wide range of crustal structures from narrow continental rifts to large continental areas if we except continental and oceanic rifts stretched portions of the crust exhibit complex faulting patterns at upper levels with high angle and low angle normal faults very little is known concerning the geometry of structures and physical processes at depth it is therefore difficult to extrapolate surface observations to the crustal scale five general models are proposed that combine continuous and discontinuous deformation and geometrical and geological tests are proposed two natural examples the west armorican atlantic margin and eldorado mountains basin and range province are presented they are characterized by an association of high angle normal faults tilted blocks and low angle normal faults field and geometrical arguments are given to demonstrate that low angle faults are controlled by decollement surfaces along preexisting interfaces geometrical implications of the tilted block pattern are presented and the gravity gliding hypothesis is proposed as a possible explanation of block tilting when associated with low angle normal faults in such cases the amount of stretching cannot be related to bulk thinning of the crust

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

tension fractures and extensional tectonics a characteristic pattern of normal faults that we have studied in several regions illustrates successive geometries relating to increasing amounts of extension from 10 50 gulf of suez egypt to 50 100 western gulf of california mexico up to 200 southern basin and range usa tension fractures formed at an early stage of extension have an essential role the resulting structure is described as a multiple tilted packs of cards model in which rotational deformation within the major blocks is accommodated by normal faulting on previously formed tension fractures thus defining smaller blocks of second and third generation

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

effect of ductile and frictional decollements on style of extension abstract scaled analogue models were used to study the effect of frictional and ductile detachments on thin skinned extension models consisted of two halves one half is the ductile and the other has a frictional detachment extension occurred above two different basal configurations a stretchable rubber sheet and a folded banded sheet intended to produce homogeneous and heterogeneous extension respectively model parameters varied systematically and included the brittle ductile thickness ratio rheologies and bulk strain structures in the two halves are compared in profiles and plan views a series of graben developed above both halves of models extended above a banded sheet although there were differences in style propagation rate and width of the deformation zone between the two halves different rates of propagation of structures in the two halves led to the formation of an accommodation or transfer zone parallel to the extension direction most relay ramps and inflection of normal faults in this zone indicate differential extension between the two halves in contrast in models extended above a stretchable rubber sheet extensional structures such as horst and graben developed only above the ductile detachment model results indicate that heterogeneous mechanical stratigraphy and displacement rate have no effect on extensional structure above a rubber sheet however above 20 bulk extension deformation becomes heterogeneous along multiple sets of conjugate faults oblique to the extension direction

displacement and strain patterns of extensional orogens rock fabrics that result from displacement in extensional orogens provide a means of identifying geometric models responsible for extension of continental crust strain compatibility arguments indicate that a finite extension can be accommodated by displacements across 1 planar nonrotating faults or ductile shear zones 2 shear zones which rotate above a horizontal detachment the domino model or 3 shear zones which rotate as a result of a horizontally oriented pure shear stretching component the plastic model listric normal shear zone geometries may develop as the result of a depth dependent change in the pure shear component in the plastic model or the area loss component in the planar shear zone model within the geometric framework of these various models the effects of superposed simple shear pure shear extension and area change on the rock fabric are investigated these displacement components which may be superposed sequentially or simultaneously determine the state of finite strain associated with a given magnitude of tectonic extension the relationships between displacement and strain are expressed as graphs of foliation dip or strain ratio versus shear strain and as graphs of foliation dip or strain ratio versus tectonic extension the shear strain graphs illustrate the effects of the different displacement components on the rock fabric in a single shear zone whereas the tectonic extension graphs better illustrate these effects on the regional scale the shear strain and tectonic extension graphs can be used by field geologists 1 to determine tectonic extension across a region from measurements of strain ratio or orientation and fluctuation of foliation 2 to distinguish between possible extension models from field data and 3 to evaluate the influence of shear zone attitude and thickness upon the amount of displacement applications of these methods are illustrated for field areas in metamorphic core complexes of arizona and in the basin and range province of the north america cordillera

origin of rectangular and aligned lakes in the beni basin of bolivia abstract the origin of aligned rectangular shaped lakes in the beni basin of bolivia has been investigated utilizing landsat imagery shuttle imaging radar and the available scientific literature the lakes tend to line up in two preferred orientations northwest and northeast they occur in cenozoic sediments of the beni basin situated between the brazilian shield and the andean foredeep available evidence suggests that the shapes and orientations of the lakes are primarily controlled by a nearly orthogonal fracture pattern propagated upward from the underlying granitic brazilian shield basement these orientations and shapes may reflect a reactivated ancient global fracture pattern or may be the result of an e w greatest principal compressive stress 1 and subsequent downwarping and uplifting of the beni basin during the cenozoic andean orogeny the lakes themselves may occupy down dropped basement blocks induced in the gently upwarped basement while unusual these lakes are not unique this suggests that transmission of basement structure through overlying sediments may occur in other regions but that special conditions such as little or no lateral compression of the sediments the absence of high trees and vegetation stability of surface material from drifting and a high water table are necessary to preserve and enhance such surface features

finite deformation and displacement fields on the southern yemen margin using satellite images topographic data and a restoration method abstract geological interpretations of processed satellite images and structural field measurements were used to calculate the amount of extension and the finite displacement field of two stretched areas located on the northern margin of the gulf of aden in yemen this calculation was done by a comparison between the deformed and the undeformed states of each studied area the structural setting established from satellite image interpretations and fieldwork yields a detailed geometry of the deformed state the undeformed state was reconstructed from reference layers chosen on satellite images from folded and faulted geological markers the strike and dip of those layers were computed directly from dip indicator measurements identified on three dimensional 3d realistic views of the sites derived from spot stereoscopic views and topographic data and controlled by field measurements from the previous structural data a numerical model of the deformed state was prepared with respect to the structural setting the two stretched areas were then restored to their undeformed state successively by 1 an unfolding method use of the unfold program on each folded piece bounded by faults and 2 a best fit method fitting along the boundary of the unfolded pieces the comparison between the deformed and undeformed states leads to quantifying the amount of strain and to establishing the total finite displacement field the results point to differences in the amount of extension and in the finite displacement field between the two areas studied within the regional context of the afar triple junction kinematics this leads to the conclusion that there was an early extensional tectonic phase recorded on the southern yemen margin probably linked to the earlier opening of the gulf of aden

the influence of mechanically weak layers in controlling fault kinematics and graben configurations examples from analog experiments and the norwegian continental margin fault systems in extensional basins commonly display geometries that vary with depth reflecting depth and lithology dependent mechanical strength using an experimental approach we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle ductile sand silicone polymer sequences subject to single and polyphase deformation the experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature the latter being representative of decollement horizons experiments series 1 s1 using homogeneous and stratified quartz and feldspar sand produced asymmetric composite single grabens with diverse fault frequencies and fault styles for the graben margin faults for the mechanically stratified experiments with one decollement level series 2 contrasting graben configurations were produced in that the lowermost sequence was characterized by graben geometries of similar type to that of the s1 experiments whereas the sequence above the decollement was characterized by large fault blocks delineated by steepened or oversteepened faults the experiments with two decollements series 3 were displayed similarly but included graben geometries that widened upward with each level being characterized by independent fault systems the results can be used to explain strata bound fault patterns and depth dependent extension as seen in several places along the norwegian continental margin and elsewhere

effects of strain gradients on asymmetry of experimental normal fault systems abstract sandbox experiments were carried out to investigate the influence of horizontal strain gradients on the asymmetry of normal fault systems in regions of crustal extension during the experiments faults facing in the direction of higher strain were preferentially developed the results show that the horizontal strain gradient is an important factor in controlling the asymmetry of normal fault systems the experiments also relate the degree of asymmetry to the horizontal strain gradient the results may be applicable to the formation of asymmetric normal fault systems on either side of the axes of mid oceanic ridges extensional back arc regions and continental rifts

lithospheric stress and deformation the study of the mechanisms magnitudes and modes of lithospheric stress and deformation occupies a central position in the discipline of tectonophysics it is therefore difficult in assembling a comprehensive review to place limits on what should be included for example one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors once admitting to the importance of rheological considerations in discussing stress and deformation one is then compelled to include information relating to the thermal state of the lithosphere since temperature is one of the foremost environmental variables controlling rheology furthermore lithospheric processes cannot be considered in isolation from those affecting the asthenosphere since surely there exists some coupling between the motion of the lithosphere and convection in the earth s interior in fact an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth the topic of this report cannot even be cleanly separated from reviews in other disciplines such as seismology and geodesy the magnitude and orientation of lithospheric stress is often indicated by earthquakes while lithospheric strain can be observed geodetically the philosophy i have adopted here is that some overlap with other review papers in this series is unavoidable and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere s state of stress and mechanisms of deformation i have however resisted the temptation to include extraterrestrial studies presumably covered in the planetary section despite the similar causes for deviatoric stress and deformational mechanisms operating on other terrestrial planets certainly ideas of how silicate materials behave and how lithosphere responds to internal forces benefit from the perspective of omparative planetology finally in defining the scope of this portion of the u s national report to the iugg i did not consciously exclude papers by non u s citizens work done at non u s institutions projects not funded by the u s government or however else foreign might be defined topics in geophysical research cannot be divided along political boundaries however i did not attempt to seek out articles written in languages other than english or published in journals not readily available in the united states and i apologise for this obvious shortcoming