crossing the several scales of strain accomplishing mechanisms in the hinterland of the central andean fold thrust belt bolivia depictions of structures at outcrop regional and tectonic scales enforce horizontal shortening and vertical thickening as the predominant style of deformation at all scales within the hinterland of the central andean fold thrust belt outcrop scale structures document a progression of strain that created 1 flexural slip folds 2 fold flattening via axial planar cleavage 3 vertical stretching via boudinage and late stage faulting and finally 4 kink folding these examples of intraformational deformation are generally concentrated just beyond the tip lines of thrust faults where fault propagation folds and related structures are well developed fault propagation folding accommodated the accrual of strain indicated by outcrop scale structures while the structures themselves indicate how deformation developed within each individual fold fault propagation fold geometries at a regional scale emerge from the construction of regional balanced cross sections the sections were drawn with careful attention to 1 known map relationships 2 field inspection of key contacts 3 bedding orientation data 4 local seismic control and 5 principles of balance the pervasive ese wnw shortening and vertical elongation seen at the outcrop and regional scales developed during the formation of the central andean backthrust belt in the hinterland of the andes the central andean backthrust belt is a large scale west vergent thrust system along the western side of the eastern cordillera in the generally east vergent andean fold thrust belt of bolivia strain accrual within this west verging zone of deformation is proposed to be a taper building mechanism that allowed the fold thrust belt to continue propagating eastward

thermochronological investigation of fault zones abstract the timing of faulting episodes can be constrained by radiometric dating of fault zone rocks fault zone material suitable for dating is produced by tectonic processes such as 1 fragmentation of host rocks followed by grain size reduction and recrystallization to form mica and clay minerals 2 secondary heating melting of host rocks by frictional fault motions and 3 mineral vein formation as a result of fluid advection associated with the fault motions the thermal regime of fault zones consists primarily of the following three factors a regional geothermal structure across the fault zone and background thermal history of studied province bounded by fault systems b frictional heating of wall rocks by fault motions and c heating of host rocks by hot fluid advection in and around the fault zone thermochronological methods widely applied in fault zones are k ar 40ar 39ar fission track and u th methods for which methodological principles as well as analytical procedures are briefly described the thermal sensitivities of individual thermochronological systems are then reviewed which critically control the response of each method against the thermal processes based on the knowledge above representative examples as well as key issues are highlighted to date fault gouges pseudotachylytes mylonites and carbonate veins placing new constraints upon geological geomorphological and seismological frames finally the nojima fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone

deep crustal expressions of exhumed strike slip fault systems shear zone initiation on rheological boundaries abstract the formation of major exhumed strike slip faults represents one of the most important dynamic processes affecting the evolution of the earth s lithosphere detailed models of the potential initiation their properties and architecture of orogen scale exhumed strike slip faults which are often subparallel to mountain ranges are rare the initiation of strike slip faults is at depth where temperature controlled rheological weakening mechanisms play the essential role localizing future strike slip faults in this review study we highlight that in pluton and metamorphic core complex mcc controlled tectonic settings as end members the initiation of strike slip faults occurs by rheological weakening along hot to cold contacts deep within the crust and mantle lithosphere respectively these endmember processes are potential mechanisms for the initiation of orogen scale exhumed strike slip faults at depth result in a specific thermal and structural architecture similar processes guide the overall displacement and ultimately the exhumation at such deep levels these types of exhumed strike slip dominated fault zones expose a wide variety of mylonitic cataclastic and non cohesive fault rocks on the surface which were formed at different structural levels of the crust during various stages of faulting and exhumation exhumation of mylonitic rocks is therefore a common feature of such reverse oblique slip strike slip faults implying major transtensive and or transpressive processes accompany pure strike slip motion during exhumation a major aspect of many exhumed strike slip faults is their lateral thermal gradient induced by the lateral juxtaposition of hot and cold levels of the crust controlling relevant properties of such fault zones and thus the overall fault architecture e g fault core damage zone shear lenses fault rocks and its thermal structure these properties of the overall fault architecture include strength of fault rocks permeability and porosity the hydrological regime as well as the nature and origin of circulating hydrothermal fluids

the chamberlin 1910 balanced section context contribution and critical reassessment abstract chamberlin 1910 was the first to quantitatively predict the shape and position of a basal detachment from detailed surface observations his predicted detachment beneath the appalachian valley and ridge fold thrust belt of central pennsylvania is substantially deeper and differs in geometry from the current interpretation the modern profile by faill and nickelsen 1999 across the same area shows a much shallower planar lower detachment and the presence of a duplex below the surface folds a significant conceptual difference from the chamberlin profile two assumptions prove to be critical in causing the discrepancies the width of the segments used as the unit of analysis and the assumption of constant bed length the segmentation scheme led to an erroneous conjugate fault detachment geometry the depth discrepancy is primarily due to ignoring the layer parallel strain the duplex is of the coupled roof style and not responsible for the differences a result supported by an experimental model we use the modern profile and the area depth relationship to quantify the effects of uncertainty on profile geometry and estimates of orogenic shortening small differences in the assumptions inference error lead to significant differences in displacement detachment location and layer parallel strain our best area balanced interpretation is a slightly modified version of the faill and nickelsen profile

weak faults rotten cores earthquakes are triggered when crustal deformation produces displacements along fault zones the rock in these zones is found to be weaker than adjacent material but what are the mechanisms of this loss of strength in his perspective holdsworth 1 discusses how recent studies of exposed ancient fault zones combined with laboratory analyses are revealing that rock properties at the grain scale can determine the large scale behavior of crustal deformation 1 http www sciencemag org cgi content full 303 5655 181

the role of basement involved normal faults in the recent tectonics of western taiwan in the foreland area of western taiwan some of the pre orogenic basement involved normal faults were reactivated during the subsequent compressional tectonics the main purpose of this paper is to investigate the role played by the pre existing normal faults in the recent tectonics of western taiwan in nw taiwan reactivated normal faults with a strike slip component have developed by linkage of reactivated single pre existing normal faults in the foreland basin and acted as transverse structures for low angle thrusts in the outer fold and thrust belt in the later stage of their development the transverse structures were thrusted and appear underneath the low angle thrusts or became tear faults in the inner fold and thrust belt in sw taiwan where the foreland basin is lacking normal fault reactivation the pre existing normal faults passively acted as ramp for the low angle thrusts in the inner fold and thrust belt some of the active faults in western taiwan may also be related to reactivated normal faults with right lateral slip component some main earthquake shocks related to either strike slip or thrust fault plane solution occurred on reactivated normal faults implying a relationship between the pre existing normal fault and the triggering of the recent major earthquakes along strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western taiwan variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre existing normal faults deformed in response to orogenic contraction

gaspe belt subsurface geometry in the northern quebec appalachians as revealed by an integrated geophysical and geological study 2 seismic interpretation and potential field modelling results abstract geological information seismic reflection profiles and potential field data are used to study the geometry of the middle paleozoic gaspe belt eastern canada that has been interpreted in various ways in the past on the western edge of the gaspe belt in the matapedia area growth strata are imaged on seismic profiles and testify of normal or transtensional motion during the period spanning the silurian and possibly late ordovician to earliest devonian along several faults including the shickshock sud fault in this area acadian deformation during the middle to late devonian is associated with relatively modest shortening less than 20 accommodated by broad open folds steeply dipping neo formed faults and inversion of previously formed faults neo formed faults cut the entire middle paleozoic succession and offset the ordovician taconian unconformity suggesting that no sedimentary interval acted as an efficient decollement level toward the se the sainte florence fault divides rock assemblages with different paleogeographic settings and structural styles increase in tectonic complexity and amount of shortening to the south of the fault is interpreted as resulting of a vise effect between two basement blocks

cover deformation above a blind duplex an example from west virginia u s a abstract pretectonic cover above blind thrust systems responds to underlying thrusting by combinations of forethrusting backthrusting and coupling the role of these responses was examined in the hanging rock cacapon mountain anticlinorium of the central appalachians this cover fold consists of middle ordovician and younger sedimentary rocks above a blind horse of cambro ordovician carbonates the cover has abundant folding and subsidiary faulting cover cleavage in carbonate and fine grained clastic rocks formed before regional folding in response to layer parallel shortening lps this 15 lps also produced grain suturing and fluid inclusion trails in quartzarenites the lps formed during cover forethrusting accommodating older blind horses in the hinterland with the formation of the underlying horse cover coupling occurred with bending folding additional secondary buckling and cleavage rotation by flexural flow with perhaps minor flattening this cover coupling was insufficient to accommodate horse formation no evidence exists for backthrusting but forelandwards abundant subsurface evidence exists for cover forethrusting with imbricate thrusting this thrusting accommodates horse formation and differs in style from the lps of the older forethrusting event so for this blind system the cover responded with a combination of coupling and forethrusting

variation in quartz arenite deformation mechanisms between a roof sequence and duplexes abstract microstructural abundances and histories in quartz arenite of the lower silurian tuscarora sandstone were used to determine the nature and role of microscale deformation in a cover sequence and underlying thrust system and to assess the degree to which the cover sequence accommodated emplacement of the thrust system sandstone samples are located across the transition from the central to southern appalachian foreland thrust system where the thrusts change from blind to emergent southwards and where southern deformation of early alleghanian age has been previously shown to be overprinted by central deformation of alleghanian age microstructures observed with transmitted light and cathodoluminescence microscopy indicate that grain scale deformation occurred by dislocation flow pressure solution and microfracturing with the last being generally the most important the sequence of deformation mechanisms is the same for the cover sequence and the thrust system pressure solution during sedimentary compaction dislocation flow during layer parallel shortening and localized microfracturing with limited pressure solution near major thrust ramps and in steep fold limbs a greater abundance of dislocation flow microstructures in the cover sequence from layer parallel shortening indicates grain scale accommodation in the tuscarora sandstone of some shortening associated with emplacement of the thrust system the transition zone between the central and southern appalachians contains the greatest occurrence of every microstructure which is consistent with the area having been affected by diachronous central and southern alleghanian deformations

the kinematic paradox of the san andreas fault the pacific north america plate boundary along the san andreas fault system is notoriously a right lateral transpressive margin where both almost pure thrust and strike slip tectonics take place the pacific plate travels wnw forming an angle of about 25 with the boundary since the pacific is moving wnw faster than north america right lateral transtension should result along the san andreas system north america in turn travels westward obliquely to the boundary and a left lateral transpressive component would be expected along the same margin therefore the right lateral transpression of the san andreas system can be partitioned into i a sinistral transpression along the southwestern margin of the north america plate obliquely overriding ii a faster right lateral transtension occurring along the transfer margin of the pacific plate between the east pacific rise in the california gulf and the gorda ridge to the north west this is due to the oblique trend of the pacific and north america plate margins with respect to their motion in a absolute reference frame the geodynamics of california is marked by a unique setting in which there is a special subduction where in contrast with classic subduction zones the footwall of the subduction plane is obliquely diverging from the hanging wall in an e w section while it is converging at slower rates in a ne sw direction the extensional e w component is absorbed into the basin and range rifting whereas the compressive ne sw component is mainly expressed in the coast ranges and california offshore the compression perpendicular to the san andreas is then not intrinsic in the strike slip movement but it is rather an independent tectonic factor therefore the san andreas system cannot be considered as an archetype of a pure strike slip fault

mechanical stratigraphy and fault fold interaction absaroka thrust sheet salt river range wyoming abstract a distinct contrast in deformation style from tightly folded and faulted cambrian through ordovician strata to broadly folded and faulted mississippian and younger strata is displayed in the hanging wall of the absaroka thrust salt river range wyoming based on style the paleozoic section can be divided into two main structural lithic units each unit is characterized by a relatively weak ductile anisotropic lower section and a relatively strong brittle more isotropic upper section where the two units were stacked within the thrust sheet inverted fault propagation folds formed in the center of each unit and the overall transition upward from close to wide spaced folds and imbricate faults developed in the multilayer where the upper unit was isolated deformation was dominated by imbricate faulting with little associated folding and inverted fault propagation folds did not form observations illustrate that the mechanical interaction between the two units and boundary conditions imposed on them were significant to defining the deformation response it is note worthy that the boundary between the two structural lithic unts in part defined by the roof thrust of the stewart passive roof duplex occurs within a dolostone rather than in overlying shale of the darby formation i propose that the roof thrust and other detachments in dolostone reflect the relatively low frictional strength of dolostone under shallow crustal conditions cross cutting relations suggest that the absaroka sheet was cut by large imbricate faults during late stage movement over a major dip ramp a high deviatoric and low mean compressive stress state just beyond the upper ramp flat corner promoted break back imbrication and allowed tectonic thickening of the thrust wedge necessary to reestablish critical taper and for forward translation

synkinematic magmatism heterogeneous deformation and progressive strain localization in a strike slip shear zone the case of the right lateral karakorum fault 1 new structural observations coupled with 15 u pb and 24 ar ar new ages from the karakorum shear zone ksz constrain the timing and slip rate of the right lateral karakorum fault zone kfz one of the great continental asian strike slip faults in the tangtse darbuk area the tangtse sw and muglib ne mylonitic strands of the ksz frame the less deformed pangong range inherited u pb ages show that granitic protoliths are mostly from the karakorum and ladakh batoliths with a major miocene melting event lasting from 21 5 to 13 5 ma some of the miocene granitic bodies show structural evidence for intrusion synkinematic to the ksz the oldest of these granitoids is 18 8 0 4 ma old implying that deformation started prior to 19 ma microstructural data show that right lateral deformation pursued during cooling ar ar data show that ductile deformation stopped earlier in the tangtse 11 ma than in the muglib strand 7 ma deformation ended at 11 ma in the tangtse strand while it is still active in the muglib strand suggesting a progressive localization of deformation when merged with published observations along the kfz these data suggest that the kfz nucleated in the north ayilari range at least 22 ma ago the long term fault rate is 0 84 to 1 3 cm yr considering a total offset of 200 to 240 km the ksz collected magma produced within the shear zone and or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow

seismic reflection images of the crust of the northern part of the chugach terrane alaska results of a survey for the trans alaska crustal transect tact deep crustal seismic reflection data show strong reflections from the middle and lower crust of the convergent continental margin near the eastern end of the aleutian trench these data were collected across the border ranges fault system a major suture zone that separates the peninsular and chugach tectonostratigraphic terranes the chugach terrane consists of metamorphosed strongly deformed flysch subduction melange as well as blueschist and greenschist facies rocks even so highly reflective rocks lie at great depth within or beneath this terrane the shallow part of the seismic section 0 5 s reveals only a few reflections which undulate and interweave indicating that some of them originate outside of the plane of the seismic section other undulating events could reveal early cenozoic granitic plutons or antiformal stacks of rock imbricated along thrust faults in contrast to this shallow reflection pattern three reflection bands contain most of the events on the middle part of the seismic section 5 12 s or 12 34 km we interpret divergent reflections within the uppermost band 5 5 5 s as gently north dipping thrust faults and subparallel reflections truncated at the boundaries of the upper and middle bands may image a metamorphic foliation or thrust faults if the truncated reflections represent thrust faults then the reflection geometry suggests that subparallel roof and floor thrust faults bound imbricated rocks forming duplex structures the upper and middle bands are separated by an area on the seismic section that reveals few reflections this area correlates approximately in depth with a high velocity 7 5 km s layer evident in refraction models the poorly reflective high velocity unit might be volcanic rocks like those exposed in the structurally lowest part of the chugach terrane if so then the bottom of the poorly reflective rocks indicates the base of the chugach terrane rocks that cause the upper and middle reflection bands and the intervening poorly reflective volcanic rocks may form a midcrustal shear zone that is about 10 km thick the deepest band of subparallel reflections 30 35 km correlates closely in depth with the top of the wadati benioff zone associated with the underthrusting pacific plate the reflections probably stem from the decollement that separates lithospheric plates within the subduction zone this reflection band increases abruptly in thickness possibly indicating local underplating of subducted sediment no events from the oceanic moho have been recognized neither the border ranges fault system the suture between the chugach and peninsular terranes nor deep crustal layers of the peninsular terrane are evident in these seismic reflection data

strain paths of three small folds from the appalachian valley and ridge maryland structural analysis indicates that for a given set of conditions subtle differences in layer configuration and rheology can result in major differences in fold kinematics we studied three hand sample scale folds from the maryland valley and ridge province in an effort to understand the accommodation of folding on meso and microscopic scales and to constrain the deformation histories of the folds sampled two single layer folds and one multilayer fold were taken from two nearby outcrops of the wills mountain anticline and are therefore interpreted to have developed under virtually identical pressure and temperature conditions although all three folds are dominated by carbonate material structural fabrics are unique for each fold indicating rheological contributions to and local structural control of fabric development both single layer folds have asymmetric vein distributions that are consistent with strain directions expected from asymmetric flexural flow slickenlines on one sample and cleavage in an adjacent layer in the other sample support this interpretation the first of these folds appears to have undergone late stage hinge tightening as evidenced by the development of crosscutting bed normal stylolites in contrast veins stylolites and the intracrystalline deformation in the multilayer fold are suggestive of symmetric tangential longitudinal strain followed by heterogeneous sub horizontal flattening the three folds are interpreted to be buckle folds with differing mechanisms accommodating strain within the competent layers

exhumation of the diancang shan metamorphic complex along the ailao shan red river belt southwestern yunnan china evidence from 40ar 39ar thermochronology abstract exhumation of the high grade metamorphic rocks from deep to shallow crustal levels in the diancang shan dcs massif is evident by the temporal transition from shearing and mylonitization at the amphibolite facies in the lower to middle crust through retrograde ductile brittle faulting at greenschist facies in the middle crust and brittle faulting near the surface new 40ar 39ar ages of amphibole muscovite biotite and k feldspar mostly from mylonitic rocks help constrain the thermal evolution of the massif during its exhumation the thermochronologic studies have shown at least three stages of exhumation and cooling from late oligocene to pliocene e g 28 13 ma 13 4 ma and 4 0 ma respectively the initiation of the unroofing history of the dcs massif resulted from ductile left lateral shearing along the ailao shan red river shear zone asrr since the late oligocene diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history of the massif the first stage of exhumation might have stopped due to the cessation of the left lateral shearing at ca 21 ma although cooling continued until 13 ma ago to relatively low temperature conditions the second and third stages of cooling started from 13 ma and lasted until the recent active faulting the diversity of cooling rates during the second stage from 13 to 4 ma suggests differences in exhumation rates at various localities ductile to brittle shearing along the eastern flank retrograde normal shear zone is the best explanation for the exhumation during this stage the inhomogeneous cooling and exhumation of the lower plate of the normal fault zone possibly resulted from the tilting of the lower plate or differential exhumation of slabs in the lower plate during the third stage cooling and exhumation of the dcs massif since 4 ma ago is recognized when higher temperature cooling paths are extended and plotted at a lower temperature of about 16 c the present day average surface temperature therefore the diachronous cooling and exhumation continuously spanned to the surface the tectonic exhumation of the dcs massif constitutes a part of the tectono thermal evolution and diachronous exhumation of the metamorphic complexes in the fan shaped area bounded broadly in se asia by the red river fault zone and sagaing fault zone since 36 ma extrusion induced strike slip shearing and rotation associated normal faulting played important roles in the diachronous cooling and exhumation of the dcs massif and other metamorphic complexes in se asia

relationships between kinematics of arc continent collision and kinematics of thrust faults folds shear zones and foliations in the nevadan orogen northern sierra nevada california abstract the mesozoic nevadan orogeny in the northern sierra nevada metamorphic belt california may be attributed to arc continent collision stratigraphic data and macroscopic cross cutting relations suggest successive accretion of two arcs along an active continental margin the younger accretion event involved the early jurassic slate creek terrane which is a 3 5 km thick pseudostratigraphic arc fragment the slate creek thrust an isoclinally folded fault with a subhorizontal median surface carries the slate creek terrane at least 40 km eastward continentward over the pre existing continental margin terrane amalgam no rock units can be correlated across the slate creek thrust which is thus interpreted as an arc continent suture in addition to the slate creek thrust the nevadan orogen includes a major east vergent imbricate thrust set east of and beneath the slate creek thrust and steep west vergent reverse shear zones macroscopic upright folds and steep foliations that overprint and cut the east vergent structures these data suggest a model for the relationships between the kinematics of arc collision and nevadan orogenic structures the slate creek arc terrane accreted by westward partial subduction of the continental margin along the east vergent slate creek thrust the continental margin was imbricated along an east vergent thrust set the structurally higher inactive slate creek thrust suture was deformed by steep west vergent shear zones folds and foliations which may have accommodated shortening of the east vergent thrust sheet this deformation occurred within an active continental margin arc that probably initiated by subduction flip after collision of the slate creek arc this kinematic model is consistent with the structural geometry and chronology of the nevadan orogen while qualitatively maintaining lithosphere scale strain compatibility this model has implications for problems related to emplacement of large crystalline thrust sheets displacements beneath and at the margins of shortened crustal segments and interaction of oppositely verging structures the nevadan orogen is a slate belt and the structural plate tectonic model presented for the nevadan orogeny may be testable in slate belts of other orogens

active faulting and deformation of the coalinga anticline as interpreted from three dimensional velocity structure and seismicity this work gives a clear picture of the geometry of aftershock seismicity in a large thrust earthquake interpretation of hypocenters and fault plane solutions from the 1983 coalinga coast range california earthquake sequence in combination with the three dimensional velocity structure shows that the active faulting beneath the fold primarily consists of a set of southwest dipping thrusts uplifting blocks of higher velocity material above the main listric blind thrust there is a conjugate fault steeply northeast dipping that provides the western limit of the aftershocks within the coalinga anticline and that corresponds in location and spatial extent with the adjacent pleasant valley syncline the character of the seismicity varies with the degree of previous deformation on each section of the anticline where the previous uplift was largest the shallow seismicity shows secondary faulting on either side of the fold with orientations that correspond to the preexisting geologic structure diffuse seismicity characterizes the area with the least previous deformation the mainshock rupture terminated where the fold trend was no longer uniform but had competing north and west trending features the upward extent of the mainshock rupture ended at the approximate boundary between franciscan and great valley sequence rocks above that depth the main thrust appears to splay into a steeper segment and a near horizontal segment thus the extent of rupture area is limited by the area of uniform structural orientation and by the variation in the type of material with the three dimensional velocity model each individual hypocenter moved slightly 0 2 km in accord with the details of the surrounding velocity structure so that secondary features in the seismicity pattern are more detailed than with a local one dimensional model and station corrections the overall character of the fault plane solutions was not altered by the three dimensional model but the more accurate ray paths did result in distinct changes in particular the mainshock has a fault plane dipping 30 southwest instead of the 23 obtained with the one dimensional model

contrasting tectonic and sedimentary history of the central and eastern parts of the polish carpathian foredeep basin results of seismic data interpretation polish carpathian foredeep basin pcfb is located at the junction between western and eastern european platforms such location caused different evolution of various parts of this basin in the central part of the pcfb growth fault propagation folds related to latest badenian stages of thrusting in this segment of the carpathians developed only minor normal faulting related to miocene reactivation of older basement faults was detected paleovalleys mapped within the mesozoic basement were interpreted as palaeogene tectonically controlled erosional features developed after inversion of the polish trough in the central pcfb post evaporitic sediments were supplied into the foredeep basin from south from the eroded carpathians in the eastern part of the pcfb a system of large normal faults related to miocene flexure induced reactivation of inherited mesozoic faults was identified within the hangingwall of this system reverse faults rotated blocks and basement pop up structures were described their formation was related to combined effect of compressional stresses transferred from the carpathian collision zone and reactivation of older large scale fault caused by both flexural extension and strike slip movements during deposition of the miocene foredeep sediments differential compaction also played an important role gentle onlap of the middle badenian evaporites by post evaporitic sediments towards the nw was interpreted as a result of tectonically driven relative sea level rise and re establishment of marine connections with eastern paratethys

late cenozoic extension and crustal doming in the india eurasia collision zone new thermochronologic constraints from the ne chinese pamir 1 the northward motion of the pamir indenter with respect to eurasia has resulted in coeval thrusting strike slip faulting and normal faulting the eastern pamir is currently deformed by east west oriented extension accompanied by uplift and exhumation of the kongur shan 7719 m and muztagh ata 7546 m gneiss domes both domes are an integral part of the footwall of the kongur shan extensional fault system kes a 250 km long north south oriented graben why active normal faulting within the pamir is primarily localized along the kes and not distributed more widely throughout the orogen has remained unclear in addition relatively little is known about how deformation has evolved throughout the cenozoic despite refined estimates on present day crustal deformation rates and microseismicity which indicate where crustal deformation is presently being accommodated to better constrain the spatiotemporal evolution of faulting along the kes we present 39 new apatite fission track zircon u th sm he and 40ar 39ar cooling ages from a series of footwall transects along the kes graben shoulder combining these data with present day topographic relief 1 d thermokinematic and exhumational modeling documents successive stages rather than synchronous deformation and gneiss dome exhumation while the exhumation of the kongur shan commenced during the late miocene extensional processes in the muztagh ata massif began earlier and have slowed down since the late miocene we present a new model of synorogenic extension suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting alai slab localize extensional upper plate deformation along the kes and decouple crustal motion between the central western pamir and eastern pamir tarim basin

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

geometry and kinematic evolution of passive roof duplexes deduced from cross section balancing example from the foreland thrust system of the southern bolivian subandean zone the subandean zone of bolivia is a foreland fold and thrust belt which forms the eastern edge of the central andes mountains between 19 s and 22 s latitude the construction of five balanced cross sections shows that the n s trending subandean zone is characterized by the existence of passive roof duplexes these complex structures can be distinguished by the lithotectonic unit within which duplexing occurs the five balanced cross sections permit the geometric and kinematic analyses of these passive roof duplexes the sequential restorations of certain cross sections reveal a possible development of a piggy back sequence of three passive roof duplexes apparently these passive roof duplexes propagated toward the foreland from deeper and deeper lithotectonic units while a passive roof duplex was developing the sole thrust stuck and the major horizontal displacements were then transferred either to out of sequence thrusts or to a new sole thrust in a deeper detachment horizon therefore each passive roof duplex would correspond to the orogenic front of the andean range at one very particular time in the history of the subandean zone of southern bolivia from south to north the quantitative analysis by cross section balancing shows a transfer of displacement from the hinterland structures to the passive roof duplex that forms the present orogenic front available data do not permit us to explain completely this phenomenom

distinguishing lateral folds in thrust systems examples from corbieres sw france and betic cordilleras se spain abstract folds with axes almost parallel to the mean tectonic transport direction are frequent in fold thrust belts particularly along the borders of arcuate belts such structures have been frequently explained in terms of superimposed tectonic events but in some cases they are most realistically understood in terms of lateral folds inherited from lateral footwall ramps and initiated subparallel to the tectonic transport direction in order to distinguish frontal and lateral folds we have established criteria based on field examples from two regions where folds occur parallel to the regional transport direction the betic cordilleras southern spain and the corbieres thrust front northeast pyrenees france the main differences between frontal and lateral folds concern the geometry the evolution of the structures and the modes of strain accommodation in the roof strata enveloping imbricate stacks recalling that above a duplex or even on individual horse the roof layers are thinned along sections normal to transport we examine the precise location where the extension is expressed illustrated by examples from the two regions this leads us to address some tectonic problems of these erogenic zones such as the thrust sequence and development of thrust related cleavage

capture of an olivine micrometeoroid by spacecraft in low earth orbit particulates associated with an impact feature in the solar maximum satellite meb thermal control blanket are identified as magnesium rich mg mg fe2 0 66 0 83 olivine and confirm that the impact feature was caused by an olivine micrometeoroid at a relative impact velocity of 7 km s a considerable portion of the micrometeoroid was lost due to back splattering analytical electron microscope analysis of recovered particulates show several degrees of mineralogical and chemical degradation such as mechanical fragmentation melting loss of sulfur and iron and formation of fe ni grains the results indicate that recovery of information is sufficient to establish the character of the impacted micrometeoroid

long term continental deformation associated with transpressive plate motion the san andreas fault a synthesis of transpressive mountain building as evidenced by rock uplift and topography along the entire san andreas fault reveals a complex crustal response to oblique plate motion convergent deformation increases toward the fault but does not correlate with the angle of plate motion obliquity the shortening estimated from rock uplift is also insufficient to account for the fault normal motion based on relative plate velocity this suggests that near field convergence is influenced by local structural complexity and is not purely driven by regional transpression and that the fault normal component of plate motion is partly accommodated elsewhere heterogeneity in deformation and degree of slip partitioning highlight the importance of other factors in shaping transpressive continental deformation including surface processes material anisotropy and strain weakening

strain variations and three dimensional strain factorization at the transition from the southern to the central appalachians abstract the transition between the southern and the central appalachian foreland thrust system is a region subjected to at least two non coaxial deformations where typical two dimensional analyses such as cross section balancing or plane strain retro deformation cannot be applied three dimensional factorization can simulate the non coaxial strain history simulation results for compaction and layer parallel shortening lps were compared to finite strains of 16 quartz arenite samples from the tuscarora sandstone successful simulations indicate in the southern appalachians 30 35 total compaction by volume loss including a 4 5 9 e w horizontal shortening during lithification and 5 lps along 150 330 by plane strain or axial symmetric flattening in the central appalachians 30 35 total compaction by volume loss including a 3 7 n s horizontal shortening during lithification and 10 lps along 120 300 by plane strain or axial symmetric flattening in the transition zone 30 compaction by volume loss including a 3 e w horizontal shortening during lithification 5 southern lps along 150 330 by axial symmetric flattening and 5 10 central shortening along 130 or 140 by plane strain or axial symmetric flattening at 10 to the normal central trend from the simulations horizontal shortening in the southern appalachians during lithification in the mississippian was greater than the later alleghanian deformation this shortening probably represents a very early lps developed in unlithified sand that required less deviatoric stress to deform than did the cemented quartz arenites during later tectonic deformation also the oblique and weaker central tectonic lps in the transition zone probably represents behavior at the limits of central appalachian deformation finally the lps simulations indicate that axial symmetric flattening oblate strain is more successful than plane strain as the representative behavior so caution is recommended in assuming plane strain as the dominant strain behavior in orogenic forelands

flexural rift flank uplift at the rio grande rift new mexico like other cenozoic continental rifts the rio grande rift in colorado and new mexico exhibits prominent flanking uplifts several driving stresses and thermal mechanical processes have been proposed to explain the origin of rift flank relief which can be modeled to infer lithospheric structure although we have identified multiple uplift styles at the rio grande rift only one range the sacramento mountains is attributable to flexural upwarping of the lithosphere the process most suitable for geodynamic modeling and interpretation we demonstrate that two common assumptions in such modeling potentially introduce serious errors first presuming only one mechanism acts to uplift the flanks is inappropriate various forces influence flank topography at different depths and wavelengths and no single one is dominant second the end member boundary conditions of complete mechanical continuity or discontinuity broken plate at the range bounding normal fault are in general not applicable at rift flanks we examine alternative analytic plate flexure solutions by comparing them to finite element models of footwall flexure at a normal fault in a two dimensional elastic plate undergoing extension these simulations indicate that broken plate fits to rift flanks underestimate the plate thickness unless the uplift is large at least 1 km which promotes decoupling between the hanging wall and footwall if denudation dominates the flank unloading as may commonly be the case the best fit broken plate thickness error can be even greater our flexural analysis of the sacramento mountains suggests that the pecos river valley originated as a flexural down warp adjacent to the rift flank sensitivity tests of least squares fits to the sacramento mountains imply typical plate thickness errors of 20 although in extreme cases the combined errors may be 50 the average effective elastic lithosphere thickness is 23 km we find that elastic plastic models of rift flank flexure are unable to provide meaningful constraints on the thermal structure of continental lithosphere

stratigraphic and structural controls on gold mineralization in the pilgrim s rest goldfield eastern transvaal south africa abstract since 1872 approximately 185 metric tons of gold and a significant amount of silver have been won from numerous stratiform ore bodies within the pilgrim s rest goldfield the epigenetic stratiform ore bodies are found primarily in the malmani dolomite subgroup a laterally extensive lower proterozoic carbonate platform succession a strong relationship exists between the presence of stratiform ore bodies and environment of deposition and structural deformation analysis of the host sediments indicates deposition in a retrogradational followed by an aggradational sequence that comprises supratidal sabkha siliciclastic sediments to midshelf carbonates the retrogradational and aggradational sequences are characterized by numerous higher frequency transgressive and regressive cycles mineralization is with few exceptions restricted to shallow water siliciclastic sediments deeper water carbonates are barren more importantly siliciclastic mudstones and sandstones have acted as zones of detachment for thin skinned thrust fault deformation resulting in the development of conformable passageways in which fluids concentrated their auriferous lodes evidence of shallow hinterland dipping duplex antiformal stack and imbricate thrust systems abounds in several underground and field exposures the gold silver emplacement model for the pilgrim s rest goldfield infers fluids derived from a deep seated magmatic source oxygen isotopic compositions of the mineralizing fluids recalculated from 18o quartz 12 1 to 19 5 point to a magmatic source and subsequent mixing with saline evolved formation water a magmatic origin is also supported by the high homogenization temperature gradient displayed by the fluid inclusions 100 c km the bushveld igneous complex rustenburg layered suite to the west of pilgrim s rest is thought to be the source of the auriferous hydrothermal solutions and its emplacement was the driving mechanism of thrust fault deformation in the pilgrim s rest goldfield

formation of a metamorphic complex along an obliquely convergent margin structural and thermochronological evolution of the chugach metamorphic complex southern alaska this study documents the structural and metamorphic evolution of middle to lower crust along an oblique convergent curved continental margin during a time span of 60 myr our study documents the importance of variable obliquity during convergence which led to the development of overprinting fabrics and distinct exhumation histories along strike of the margin we present structural analyses 40ar 39ar rb sr and zircon fission track ages from middle to lower crust exposed along the southern alaskan margin in the chugach metamorphic complex together with the metamorphic history and additional geochronology from the literature we derive the following tectonic evolution for this area accretion of sediments during dextrally oblique convergence led to strain partitioned d 1 structures and greenschist facies metamorphism prior to circa 55 ma at 55 51 ma a margin parallel stretching phase with vertical thinning d 2 affected the margin and led to andalusite sillimanite grade metamorphism and the onset of partial melting a switch back to dextral transpression d 3 shortly after d 2 led to rapid cooling of the western and central parts of the complex associated with exhumation of parts of the core of the complex until circa 46 ma the southeastern part of the complex cooled and exhumed regularly and slowly until circa 5 ma due to its highly oblique orientation relative to the convergence direction an increase in cooling and exhumation occurred after circa 5 ma in the entire southeastern part of the complex associated with the neogene collision of the yakutat terrane

coseismic and blind fault of the 2015 pishan mw 6 5 earthquake implications for the sedimentary tectonic framework of the western kunlun mountains northern tibetan plateau on 3 july 2015 the mw 6 5 pishan earthquake occurred in the western kunlun mountains front at the northern margin of the tibetan plateau to reveal the sedimentary tectonic framework of the seismically active structure three high resolution seismic reflection profiles and well drilling data were collected for seismic interpretation the western kunlun mountains and tarim basin have two gypseous detachments and one basement detachment that control the tectonic framework and structural deformation the upper gypseous detachment d1 is in the lower paleocene and the middle gypseous detachment d2 is in the middle to lower cambrian a neogene shallow thrust system is developing above d1 and includes the zepu fault f2 and mazar tagh fault f3 a deep thrust system is developing between d1 and d2 and forms a large scale structural wedge beneath the western kunlun mountains front the pishan mw 6 5 earthquake was triggered on a frontal blind fault of this deep thrust system the lower detachment is in the proterozoic basement d3 which extends into the tarim basin and develops another deep thrust f4 beneath the f3 belt d1 d2 d3 and the tiekelike fault f1 merge together at depth crustal shortening of the western kunlun mountains front continues for approximately 54 km two tectonic evolutionary stages have occurred since the miocene according to sedimentary unconformity axial analysis and fault interpretation the results of this study indicate a regime of episodic growth of the western kunlun mountains and tarim basin during the cenozoic

triangle zone and displacement transfer structures in the eastern front ranges southern canadian rocky mountains the geometry of a relict triangle zone at the boundary of the foothills and front ranges in the southern canadian rocky mountains is constrained by detailed surface mapping over 700 m of relief and by seismic reflection data the geometry and progressive development of the triangle zone along a strike length of 15 20 km in the displacement transfer zone between the coleman and misty thrusts is illustrated using closely spaced balanced cross sections palinspastic restorations and a sequentially restored cross section structural geometries show that a northeast foreland verging mainly carbonate wedge of mississippian to triassic rock was inserted along a major upper detachment zone in shale near the base of the jurassic cretaceous clastic package this was accompanied by southwest hinterland verging displacements along the upper detachment zone tectonic thickening of the clastic package exceeding 200 and backthrusting later northeast verging deformation slightly modified the triangle zone by steepening structures tightening folds and minor thrusting recognition of relict triangle zones within the fold and thrust belt may document important changes in the rate of thrust front advancement and aid in the delineation of potential hydrocarbon traps similar to those discovered along th present day thrust belt margin in the southern canadian rocky mountains

the effect of convergence angle on the kinematic evolution of strain partitioning in transpressional brittle wedges insight from analog modeling and high resoluiton digital image analysis 1 using analog modeling aided by digital image analysis dpiv we constrained the long term kinematic evolution of strain partitioning in transpressional brittle wedges as a function of convergence angle we ran a series of dry quartz sand experiments representing highly oblique continent continent collision convergence angles of 4 to 30 the digital image analysis provided high resolution constraints on the long term kinematic evolution of these wedges which could be subdivided in distinct kinematic stages comprising 1 an initial distributed strain stage and 2 an oblique wedge stage before 3 the stage of strain partitioning is reached thus we document the evolution of different deformation stages from a single plate tectonic boundary condition in addition the relationship between convergence angle kinematic stages and wedge geometry including fault dips and fault hierarchy was established the modeling results show that smaller convergence angles lead to steeper faults besides for a constant convergence angle the proshears that evolved during the strain partitioning stage were less steep than those formed during the oblique wedge stage the fault slip vector on individual fault segments was derived from the dpiv data set for each time increment quantifying the magnitude and orientation of slip on fault segments during the different kinematic stages in addition in the 7 5 and 15 models rotation of the slip vector by up to 40 was observed on a single proshear during the strain partitioning stage these observations allow to some degree a validation of existing analytical models of strain partitioning in particular the assumption of steady state

evidence for major shortening on the eastern edge of the bolivian altiplano the calazaya nappe abstract for the first time evidence is presented of major shortening on the eastern edge of the altiplano in bolivia a tectonic nappe showing at least 40 km of horizontal displacement towards the east is revealed at the altiplano cordillera oriental transition 20 s analysis of the differences in stratigraphy sedimentology and structure between allochthonous and autochthonous units confirms the 40 km of overthrust a geometric analysis of the thrust structures has been made to interpret the three dimensional geometry of the nappe and a deformation sequence is suggested the nappe emplacement is related to the eastward transport of a large allochthonous domain during the late oligocene early miocene the sole thrust of this allocthtonous domain is located in a stratigraphie unit whose three dimensional basin geometry controlled the deformation the existence of the calazaya nappe allows us to explain the exceptional thickness of the altiplano 55 70 km as mainly resulting from the neogene shortening that occurred between the altiplano and the cordillera oriental

morphostructural evidence of late quaternary tectonics at the po plain northern apennines border lombardy italy abstract the landscape of foreland basins adjacent to active mountain ranges evolves under the control of basinward tectonic propagation of the structural fronts in competition with climate dynamics the resulting palimpsest landscapes record the sequence of geomorphic evolutionary steps and the spatial temporal relations between the active geological processes however a precise evolutionary sequence is hard to decipher from low relief settings like the wide alluvial plains worldwide about these topics we investigate the sequence of tectonic and climate driven processes which shaped the palimpsest landscape of a large quaternary foreland basin the po plain in northern italy above the average glacio fluvial and alluvial plain of the basin late quaternary intra basin reliefs emerge owing to syndepositional ramp folding and uplift driven by n wards propagation of the outermost thrust fronts of the active n apennine chain the incremental tectono morphological and depositional history of the region permits to describe the propagation of the structural front as a polyphase process involving uplift wrenching and late collapse of the reliefs this history is documented by relicts of uplifted planation surfaces covered by latest pleistocene weathered loess units polygonal facets landslides and slope wedges along faults delineating the slopes of the largest among the intra basin reliefs san colombano hill hydrographic anomalies on the relief network river diversions piracy and perching of valleys paleovalley fills river diversions and cross cut relations on the adjacent alluvial plain these features testify the thrust fold related pre lgm uplift of the late pleistocene alluvial stratigraphy the subsequent segmentation of the relief in differently uplifting blocks along riedel faults owing to activation of a transfer fault zone and the lgm extensional collapse of the relief along inherited fault systems a late post glacial outwards propagation of the apennine thrusts was buttressed by the opponent alpine thrust belt front and induced the entrenchment of the river network river diversions on the plain were controlled by the orientation of the san colombano hill fault systems the distribution of historical earthquakes and the present day geodetic data are coherent with this evolution the study documents how in foreland basins the syndepositional propagation of blind orogenic fronts shapes the palimpsest landscape with superimposed morphological tectonic and stratigraphic features of paleoseismic significance and permits comparisons with the other low relief basin settings worldwide

central and southern appalachian water and wind gap origins review and new data abstract the origin and evolution of transverse drainage were stumbling blocks to classical historical geomorphologists and many problems still remain decollements that upramp laterally transported at depth tectonic sheets in the central and southern appalachians have produced structural geomorphic fronts that are prominent features often of regional or subregional extent cf blue ridge north mountain allegheny as these structural geomorphic fronts likely were features that developed significant cover relief during the alleghanian orogeny they may hold clues to incipient landscape development during and soon after orogenesis unless buried by thick sediment cover where these fronts are crossed by transverse drainage lines spectacular water gaps that frequently expose complex structural features are produced there are many other transverse water gaps not located across decollement structures in the region these gaps display complex features that shatter bedrock and must also be accounted for in any comprehensive hypothesis of transverse water gap origin lineaments including both cross strike structural discontinuities and disturbed zones are present in the appalachians and coincide with a number of transverse water gaps the positioning of weakened bedrock zones high on structures where downcutting streams had access to them permits a localizing mechanism such as structural ensnarement to operate local sedimentary patterns may also have played roles in drainage localization major unsolved problems include post alleghanian tectonic effects rates and timings of uplift erosion and deposition whether lithotectonic weaknesses are most pronounced in gap areas and establishing a numerical chronology for drainage development whereas lithotectonic influence upon drainage development is stressed in this chapter the importance of other factors e g climate catastrophic events as documented by others in this volume is fully recognized

plutonism oblique subduction and continental growth an example from the mesozoic of california major episodes of mesozoic plutonism in california correlate with periods of oblique subduction and trench parallel transport of western california along intrabatholithic faults major episodes of plutonism occurred in the late jurassic during left oblique convergence and in the mid cretaceous during right oblique convergence in contrast a conspicuous lull in plutonism but continuation of volcanism in the earliest cretaceous coincides with a time when the north america farallon convergence vector although large in magnitude was oriented perpendicular to the trench this correlation suggests that plutonism is facilitated by strike slip faulting within the batholithic belt one explanation which helps to solve the plutonic room problem is that plutons are passively emplaced at releasing bends in the strike slip faults and volume is conserved by thrusting at the trench if this correlation is generally applicable then it implies that mid crustal plutonism is limited beneath areas in which the convergence vector is subperpendicular to the trench continental growth in such areas may occur dominantly by volcanism

weak ductile shear zone beneath a major strike slip fault inferences from earthquake cycle model constrained by geodetic observations of the western north anatolian fault zone gps data before and after the 1999 izmit duzce earthquakes on the north anatolian fault zone turkey reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient using 3 d finite element calculations of the earthquake cycle in an idealized model of the crust comprising elastic above maxwell viscoelastic layers we show that spatially varying viscosity in the crust can explain these observations depth dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities a localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths and the ratio of relaxation time to earthquake repeat time ranges from 0 005 to 0 01 for weak zone widths of 24 and 40 km respectively in the weakened domain and greater than 1 0 elsewhere corresponding to viscosities of 1018 0 3 pa s and greater than 1020 pa s models with sharp weak zone boundaries fit the data better than those with a smooth viscosity increase away from the fault implying that the weak zone may be bounded by a relatively abrupt change in material properties such a change might result from lithological contrast grain size reduction fabric development or water content in addition to any effects from shear heating our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

coexistence of thin and thick skinned tectonics in zakynthos area western greece insights from seismic sections and regional seismicity abstract the structural style of the fold and thrust belt in the western part of the hellenic foreland in an area offshore the zakynthos island is assessed on the basis of two lithoseismic profiles earthquake data and field data in the broader area the compressional deformation in the area is due to the late phases of subduction and collision between aegean and african plates shortening is affecting a 6 7 km thick sedimentary succession of mesozoic carbonate rocks and evaporites as well as miocene to pleistocene foredeep clastic deposits structures accommodating shortening in the pre apulian and ionian zones comprise a blind imbricate thrust system and fault propagation folds that formed over a 10 11 km deep detachment the thrust system comprises an array of forward verging thrust faults which sole out in a low angle hinterland dipping decollement separating the mesozoic cover from the pre mesozoic basement in this tectonic context the triassic evaporitic layers seem to play an important role in the vertical partitioning of the deformation style acting as either detachment horizons or lining the imbricate thrust surfaces the concentration of recent seismic activity at a depth between 6 and 16 km implies that the pre mesozoic basement is also involved in the deformation in the form of upthrust basement slices suggesting a combination of thick and thin skinned deformation across this domain of the external hellenides fold and thrust belt the frontal part of the belt shows higher seismic activity along a low angle blind thrust as well as also in the areas where the individual thrust planes branch at depth to the basal decollement

carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles we have studied nineteen anhydrous chondritic interplanetary dust particles idps using analytical electron microscopy we have determined a method for quantitative light element edx analysis of small particles and have applied these techniques to a group of idps our results show that some idps have significantly higher bulk carbon abundances than do carbonaceous chondrites we have also identified a relationship between carbon abundance and silicate mineralogy in our set of anhydrous idps in general these particles are dominated by pyroxene olivine or a subequal mixture of olivine and pyroxene the pyroxene dominated idps have a higher carbon abundance than those dominated by olivines members of the mixed mineralogy idps can be grouped with either the pyroxene or olivine dominated particles based on their carbon abundance the high carbon pyroxene dominated particles have primitive mineralogies and bulk compositions which show strong similarities to cometary dust particles we believe that the lower carbon olivine dominated idps are probably derived from asteroids based on carbon abundances the mixed mineralogy group represents particles derived from either comets or asteroids we believe that the high carbon pyroxene rich anhydrous idps are the best candidates for cometary dust

fractal strain distribution and its implications for cross section balancing abstract rock units having different physical properties show contrasts in structural styles massive competent rocks have relatively simple geometry and control the structural framework whereas thin bedded less competent units are characterized by complex deformation at smaller scales these contrasting structural styles can be quantified by a fractal dimension d a fold profile with a d close to 1 has a simple geometry a value of 2 d 1 indicates a fractal profile a fractal profile has a fractal strain distribution such that the measured shortening increases with resolution for rock units having different values of d the shortening strains measured with the same resolution cannot be compared because a significant amount of deformation takes place at smaller scales for these units with a larger d proper balancing requires high resolution analysis for these units to resolve strain at smaller scales in the central appalachians west virginia the cacapon mountain anticlinorium has a large ramp anticline in cambrian ordovician rocks which has a net shortening of 10 510 km as measured by section restoration in contrast restoration of the overlying complexly folded and faulted upper ordovician through devonian units indicated a 3 660 km shortening thin section analysis revealed a 15 20 strain equivalent to another 3 km shortening and the remaining difference in shortening between the cover and the underlying blind thrust sheet has been previously attributed to forethrusting fractal analysis indicates that the cambrian ordovician thrust sheet has a d 1 001 and the cover fold profile has a d 1 072 which indicates a fractal geometry if thin section scale through outcrop scale to map scale strains are included in the cross section balancing the cover sequence has a comparable shortening to that in the underlying thrust sheet

kinematic model for the curvature of the northern subalpine chain france abstract analyses of cross sectional shortening mapped faults and calcite twin strain are used in conjunction with geometric kinematic modeling to interpret the mechanism of curvature formation in the northern subalpine chain of france there is a 45 change in strike around the chain that is convex towards the foreland northwest five models for fold thrust belt curvature are applied to the northern subalpine chain they can reproduce the geometry and the kinematic history of a curved fold thrust belt and can be used to predict the magnitude and orientations of strains and the three dimensional geometry of the curvature the models are pure bending radial thrusting curve parallel simple shear uniform displacement uniform shortening and transport parallel simple shear two principal criteria for distinguishing among the models geometrically are the horizontal tangential strain extension or contraction parallel to strike and cross sectional shortening the transport parallel simple shear model predicts no tangential extension in the central domain and greater radial shortening and significant tangential extension in the northeastern and southern domains this is the pattern observed in the northern subalpine chain therefore the curvature of the northern subalpine chain is attributed to a transport parallel simple shear mechanism

phase transformation and nanometric flow cause extreme weakening during fault slip faults weaken during earthquakes laboratory simulations of earthquake rupture show that the nanometric scale fault gouge created during slip is inherently weak and flows by grain boundary sliding providing a mechanism to weaken faults

blind thrust systems blind faults are documented from 20 thrust systems throughout the world they occur as single faults sets of faults or entire thrust systems the overlying cover responds to the formation of the blind system by backthrusting coupling forethrusting and deposition the relative importance of the first three responses for pretectonic cover is represented in a ternary backthrusting coupling forethrusting diagram pretectonic cover of blind systems deforms by either a combination of coupling and forethrusting or a combination of backthrusting and coupling

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

mechanics of triangle zones and passive roof duplexes implications of finite element models abstract finite element models of passive roof duplexes simulate the evolution and distribution of fault slip and deformation as functions of boundary conditions friction on the roof fault cover strength and amount of overburden a foreland buttress is essential for backthrust displacement in the models this foreland buttress is analogous to a pin line between the cover and footwall forelandward of the triangle zone in a balanced cross section and could be caused by a stratigraphic pinchout of the upper detachment or a strong cover in the foreland with boundary conditions that prevent the cover from slipping toward the hinterland relative to the wedge incipient forethrust and backthrust ramps zones of high equivalent plastic strain cut through the cover in the models there is more backthrust displacement with a lower friction coefficient on the upper detachment and with a stronger cover because of pressure dependence both fault strength and material strength increase with increasing overburden therefore the effect of overburden on backthrust displacement is determined by the nature of the pressure dependencies for fault friction and material strength in models with multiple imbricate faults the distribution of equivalent plastic strain adjacent to each fault is similar to that in single fault models with differences resulting from bending strains in the wedge and cover the strain distribution in the cover of the models is similar to that above natural passive roof duplexes characterized by layer parallel shortening above the tip of each horse in the duplex

kinematic model of detachment folding including limb rotation fixed hinges and layer parallel strain abstract detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will in general require layer parallel shortening a kinematic model for detachment folds is presented that has planar limbs and is area balanced but requires bed length changes that can be expressed as layer parallel strain the fold grows primarily by limb rotation not by limb lengthening at constant dip the kinematic evolution of the geometry and strain is examined fold geometry is well predicted and the strain estimated in applications of the model to two map scale detachment folds a triangle zone from the front of the wyoming thrust belt and a duplex cored anticline from the appalachian plateau

the giant shakhdara migmatitic gneiss dome pamir india asia collision zone 1 geometry and kinematics 1 cenozoic gneiss domes comprise one third of the surface exposure of the pamir and provide a window into the deep crustal processes of the india asia collision the largest of these are the doubly vergent composite shakhdara alichur domes of the southwestern pamir tajikistan and afghanistan they are separated by a low strain horst top to sse noncoaxial pervasive flow over the up to 4 km thick south pamir shear zone exhumed crust from 30 40 km depth in the 250 80 km shakhdara dome the top to nne alichur shear zone exposed upper crustal rocks in the 125 25 km alichur dome the gunt shear zone bounds the shakhdara dome in the north and records alternations of normal shear and dextral transpression it contributed little to bulk exhumation footwall exhumation along two low angle normal sense detachments resulted in up to 90 km syn orogenic n s extension extension in the southwestern pamir opposes shortening in a fold thrust belt north of the domes and in particular in the tajik depression where an evaporitic decollement facilitated upper crustal shortening gravitational collapse of the pamir plateau margin drove core complex formation in the southwestern pamir and shortening of the weak foreland adjacent to the plateau overall this geometry defines a vertical extrusion scenario comprising frontal and basal underthrusting and thickening and hanging gravitationally driven normal shear in contrast to the himalayan vertical extrusion scenario erosion in the pamir was minor preserving most of the extruded deep crust including the top of the south pamir shear zone at peak elevations throughout the dome

exhumation of high pressure rocks under continuous compression a working hypothesis for the southern hellenides central crete greece combined kinematic structural and palaeostress calcite twinning fault slip data analyses are used to study the exhumation mechanism of the high pressure rocks exposed on the island of crete southern aegean greece our study shows that the evolution of windows in central crete was controlled by two main contractional phases of deformation the first phase d1 was related to the ductile stage of exhumation nnw sse compression during d1 caused layer and transport parallel shortening in the upper thrust sheets resulting in nappe stacking via low angle thrusting synchronously intracontinental subduction led to high pressure metamorphism which however did not affect the most external parts of the southern hellenides subsequent upward ductile extrusion of high pressure rocks was characterized by both down section increase of strain and up section increase of the pure shear component the second phase d2 was associated with the brittle stage of exhumation d2 was governed by nne ssw compression and involved conspicuous thrust related folding considerable tectonic imbrication and formation of a middle miocene basin the major d2 related psiloritis thrust cross cuts the entire nappe pile and its trajectory partially follows and reworks the d1 related contact between upper and lower high pressure tectonic units eduction and doming of the talea window was accompanied by gravity sliding of the upper thrust sheets and by out of the syncline thrusting late orogenic collapse also contributed to the exhumation process therefore it seems that the high pressure rocks of central crete were exhumed under continuous compression and that the role of extension was previously overestimated

a crustal scale orogen parallel strike slip fault in the middle urals age magnitude of displacement and geodynamic significance the kinematic evolution of an orogen parallel strike slip fault in the middle urals demonstrates that orogen parallel mass transfer was an important previously underestimated process during the syncollisional evolution of the middle urals the kyshtym strike slip fault extends nne parallel and adjacent to the main uralian fault which is the main suture of the uralide orogen the kyshtym fault is interpreted as one of two conjugate strike slip fault zones that have accomodated the longitudinal transfer of material along the margins of a rigid indenter belonging to the east european craton the dextral kyshtym shear zone was active under retrograde lower amphibolite to middle lower greenschist facies conditions four metagranitic muscovite bearing mylonites yielded rb sr internal mineral isochron ages of 247 5 2 9 244 5 6 5 240 0 1 4 and 240 4 2 3 ma whereas a biotite rich sample without muscovite gave a mineral isochron age of 229 1 3 2 ma the results indicate almost complete sr isotopic reequilibration on the hand specimen scale during mylonitization the muscovite ages are interpreted as deformation ages and demonstrate a late permian early triassic age for the kyshtym shear zone the shear zone transects a pre orogenic syenite intrusion of ordovician age a maximum shear strain of 7 3 is estimated from the shape of the ductily deformed syenite body in map view and from the length width ratios of deformed amphibolite bodies in the country rock this shear strain suggests a maximum displacement of 28 12 km for the 4 km thick kyshtym shear zone a younger brittle fault oriented subparallel to the shear zone accomplished an additional horizontal displacement of 15 3 km thus the total displacement along the fault system is 43 15 km

deformation behavior during blind thrust translation as a function of fault strength deformation partitioning between translation and distortion for a thrust sheet and for the roof sequence above a moving thrust horse were analyzed in terms of the role of fault strength using finite element models greater frictional resistance on the thrust decollement decreased fault translation increased distortion of the thrust sheet and roof sequence and increased the ratio of backthrusting to forethrusting for the roof sequence in all models with weak decollements 0 35 the ratio of tip line propagation to thrust displacement is very high during initial thrust movement but decreases significantly during later fault motion this observation supports interpretations in natural thrust systems where thrust faults propagate large distances before accumulating significant displacements the tip lines for weak decollements also propagated into the foreland well in advance of the distortion front in the overlying thrust sheet or roof sequence this result does not support interpretations from natural systems for the existence of ductile beads in front of propagating thrusts but rather suggests that recent models for fault arrest or displacement gradient folds may be mechanically valid in addition no model for roof sequences yielded a simple end member response of only backthrusting or forethrusting suggesting that the many blind thrust belts where only one response has been interpreted may need to be re examined finally in those cases where more than one thrust flat moves simultaneously in the models partitioning of displacement and distortion in space and time changes significantly this result supports interpretations from natural systems where more than one thrust is thought to move at once

how much magma is required to rift a continent article i nfo article history many continental rifts are associated with and preceded by the formation of large igneous provinces partial melting of a large region of anomalously hot upwelling mantle isrequired to explain these huge volumes of pre and syn rift basaltic magma the uplift associated with a shallow region of hot mantle is often invoked as a cause of the rift push force that may drive the observed extension the rift push force is likely to be an order of magnitude toosmall todrive tectonicstretching of normal continentallithosphere but may besufficient to drive opening of lithosphere cutting dikes intrusion of a sequence of such dikes along a narrow zone may provide enough heat to significantly weaken the lithosphere here we use a newly developed 2d numerical approach in which magma filled dikes open in continental lithosphere in response to an evolving model stress field and the advection and diffusion of heat is tracked to investigate the relation between the volume of magma and the amount of lithospheric weakening the available rifting force lithospheric structure and parameters controlling magma flux are varied in the numerical simulations for continental lithosphere 60 km thick hl h1200 c heat diffusion is unimportant and only a small amount of magma is required 10 20 m y similar to magmatic rifts like the red sea

far field lithospheric deformation in tibet during continental collision 1 crustal deformation along the present day northern margin of the tibetan plateau has occurred since mid to late eocene time soon after india collided with eurasia assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet we show that far field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins when a strong region analogous to cratonic lithosphere like that of the tarim basin is included in the calculations shear and vertical strain rates concentrate along the southern edge of the strong region resulting in enhanced deformation there in calculations scaled to the dimensions of india and the tibetan plateau shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins crustal thickening accelerates later in the calculations we propose that the apparent increased exhumation and perhaps surface uplift around 10 ma may signal the arrival of the thickening front

the 1987 whittier narrows earthquake sequence in los angeles southern california seismological and tectonic analysis the october 1 1987 whittier narrows earthquake m l 5 9 was located at 34 2 96 n 118 4 86 w at a depth of 14 6 0 5 km in the northeastern los angeles basin the focal mechanism of the mainshock derived from first motion polarities shows pure thrust motion on west striking nodal planes with dips of 25 5 and 65 5 respectively the aftershocks define an approximately circular surface that dips gently to the north centered at the hypocenter of the mainshock with a diameter of 4 6 km hence the spatial distribution of the mainshock and aftershocks as well as the focal mechanisms of the mainshock indicate that the causative fault was a 25 north dipping thrust fault striking west and is confined to depths from 10 to 16 km although most of the 59 aftershock focal mechanisms presented here document a complex sequence of faulting they are consistent with deformation of the hanging wall caused by the thrust faulting observed in the mainshock a cluster of reverse faulting events on north striking planes occurred within hours after the mainshock 2 km to the west of the mainshock the largest aftershock m l 5 3 occurred on october 4 and showed mostly right lateral faulting on the same north northwest striking plane within the hanging wall similarly several left lateral focal mechanisms are observed near the eastern edge of the mainshock rupture the earthquake and calibration blast arrival time data were inverted to obtain two refined crustal velocity models and a set of station delays when relocating the blast using the new models and delays the absolute hypocentral location bias is less than 0 5 km the mainshock was followed by nearly 500 locatable aftershocks which is a small number of aftershocks for this magnitude mainshock the decay rate of aftershock occurrences with time was fast while the b value was low 0 67 0 05 for a los angeles basin sequence

normal vs strike slip faulting during rift development in east africa the malawi rift kinematic analysis of neogene and quaternary faults demonstrates that the direction of extension in the malawi rift rotated from east northeast to southeast rift development commenced with the formation of half grabens bounded by northwest north and northeast striking normal faults owing to slightly oblique rifting the northwest striking faults in the northernmost rift segment show a small dextral oblique slip component whereas north and northeast oriented faults in the central part of the rift display a sinistral oblique slip component this first event resulted in block faulting and basin subsidence which is largely responsible for the present day basin morphology of lake malawi a major change in fault kinematics occurred because of rotation of the extension direction and permutation of the principal compressive and intermediate axes the structural pattern inherited from the first rifting phase was no longer suitably oriented to accommodate extensional deformation and strike slip faulting assumed a major role the strike slip regime amplified uplift of basement ridges within the rift in regions of local transpression but it also created alluvial basins because of local transtension this new kinematic style is compatible with the recent seismicity older faults that show mainly the first deformational increment are restricted to the outermost parts of the rift toward the center the faults depict an increase in strike slip components of movement suggesting deformation propagation toward the rift center which results in a narrowing of the active rift environments with time

roof sequence response to emplacement of the wills mountain duplex the roles of forethrusting and scales of deformation abstract this paper focuses on the behavior of a roof sequence in the appalachian plateau of west virginia u s a and emplacement of the wills mountain duplex with 17 5 km of displacement unlike the plateau along strike in pennsylvania and new york where forethrusting was previously documented this roof sequence lacks an underlying salt dominated roof decollement kinematic analyses reveal that the roof sequence in the west virginian plateau accommodated about two thirds of the 17 5 km of shortening by the adjacent wills mountain duplex as a forethrusting kinematic response the remaining shortening imbalance of about 5 km between the duplexes and younger roof sequence rocks is accommodated by additional forethrusting further into the foreland and local compensation this kinematic response matches that along strike in the central appalachians despite the loss of the salt decollement we interpret that an ordovician shale dominated formation was sufficiently weak to substitute for the salt horizon thus a weak mechanical unit rather than specifically a salt decollement is a necessary prerequisite for forethrusting a contributing factor to forethrusting may be the subvertical front of the wills mountain duplex which inhibited other responses by the roof sequence mesoscale and smaller processes including grain to grain pressure solution twinning and cleavage formation account for over 75 of the shortening in the roof sequence and if ignored would result in an erroneous interpretation of backthrusting or local compensation this result suggests that failure to consider all deformation scales could lead to incorrect kinematic conclusions in other tectonic systems

migration of deformation fronts during progressive deformation evidence from detailed structural studies in the pennsylvania anthracite region u s a abstract detailed study of selected outcrops in the pennsylvania anthracite region has resulted in identification of five at least partly continuous stages of alleghanian progressive deformation these structural stages are in sequence a layer parallel shortening and top to the foreland layer parallel shear b a second episode of layer parallel shortening c flexural slip and flexural flow folding d fold modification and late thrust faulting and e late veining and fracturing at each outcrop an average shortening direction was determined for each observed structural stage the mean regional shortening direction for each structural stage was calculated and maps showing the spatial distribution of the shortening directions for each stage were constructed the mean regional shortening directions for the five structural stages successively rotated 25 30 clockwise during the evolution of the fold and thrust belt shortening directions for structural stages b and c over the region show a systematic clockwise change in orientation from hinterland to foreland indicating that these structural stages of progressive deformation were time transgressive on a regional scale

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

tectonic wedge geometry at bardas blancas southern andes 36 s argentina abstract a tectonic wedge at the mountain front of the cordillera principal mendoza province argentina shows some geometrical features that depart from examples described elsewhere this wedge underthrusts the roof sequence beneath a blind thrust the wedge is deformed by imbricate backthrusting that branches into the hangingwall ramp of the leading horse this backthrust system contributed to the uplift and shortening of the mountain front

first deep seismic reflection images of the eastern alps reveal giant crustal wedges and transcrustal ramps 1 the alps are considered as a classical example for an orogen created by continental plate collision in this study we present new images obtained from deep seismic reflection profiling in the eastern alps between munich and venice which give rise to examine and revise existing concepts the seismic sections exhibit a prominent bi verging reflection pattern at crustal scale a major ramp like structure outcropping at the inn valley fault can be traced southward over 80 km into the mountain root where relics of the subducted penninic ocean are expected new models of the evolution of the eastern alps show an upper lower crustal decoupling along transcrustal thrust faults with opposite thrust directions of both the european and the adriatic african continents

fault related rocks suggestions for terminology many traditional terms for fault related rocks have undergone recent dynamic metamorphism under high pressure discussions by various groups of specialists a generally acceptable simplified framework encompassing these and associated structural terms is now needed for many geologic engineering and legal purposes such a framework is proposed here focusing on a rate of strain versus rate of recovery diagram and relating this framework to the products of brittle and ductile deformation along faults

impact fracturing and structural modification of sedimentary rocks at meteor crater arizona 1 meteor crater provides a rare opportunity to study impact deformation of sedimentary target rocks and isolate those features from preexisting tectonic deformation and impact generated reactivation of preexisting tectonic features this study reports over 2500 new measurements of orientations of bedding faults and fractures in crater walls and in surrounding bedrock target rocks are characterized by horizontal bedding planes that are cut by at least three prominent sets of preimpact tectonic fracture systems the crater rim is also cut by three distinct groups of fractures radial concentric and conical fractures when the crater rim is restored to preimpact condition the radial and concentric fractures resemble preimpact fracture populations indicating that crater wall deformation and rim uplift were partly accommodated by activation of preexisting fractures in contrast the conical fractures are dissimilar to the preimpact fractures and apparently formed as a direct result of impact deformation some of the preimpact fractures were transformed into tear faults during the impact event and motion along those faults appears to have controlled the geometry of the impact deformational features the crater rim is thus square in plan view rather than circular faults occurring in the crater diagonals are prominent ones allowing greater vertical displacement the deformation pattern of meteor crater is different from that at lonar crater which was excavated in basalt with fewer preimpact fractures the differences between deformation at meteor crater and lonar crater may reflect the same disparities seen in simple craters produced in different target lithologies on mars and other planetary surfaces

passive roof duplexes under the rocky mountain foreland basin alberta seismic reflection data in the central alberta foothills near edson reveal the presence of small passive roof duplexes in upper cretaceous rocks within the otherwise undeformed foreland basin as much as 40 km northeast of the mountain front monocline the tops and bottoms of the duplexes are defined by backthrusts and sole thrusts which follow bedding planes within upper cretaceous strata overlying the structures is an essentially uncontracted 1 8 km thick section of upper cretaceous and tertiary rocks which is passively uplifted over the thickened duplexes the underlying autochthonous sequence of mesozoic and paleozoic rocks exhibits some minor folding but is also uncontracted our interpretation extends both the upper and lower detachments of the widely accepted triangle zone model more than 30 km farther under the foreland basin than has previously been supposed the seismic data illustrate relatively clearly the form of the leading edge of the last phase of rocky mountain thrusting we expect that similar features will be observed elsewhere in the rocky mountain foothills and probably at other mountain fronts worldwide

distribution of fault slip in outcrop scale fault related folds appalachian mountains abstract current kinematic models of ramp related folds predict a direct relationship between ramp angle and fold shape and imply specific sequences of deformation analyses of outcrop scale structures in the valley and ridge province of the appalachians reveal configurations that depart from model predictions the models fail to account for the presence of footwall synclines and are inconsistent with measured displacement distributions on some natural faults observations support the interpretation that faults can grow by propagation both up and down dip from a nucleation point fault propagation in either direction may result in the formation of folds primarily on the side of the fault that is displaced in the direction of fault propagation