diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

strain partitioning and progressive deformation history in a transpressive belt northern appalachians abstract syntectonic fibres within rocks of the gaspetrough a mid paleozoic slate belt within part of the acadian orogen of the canadian appalachians record the complex structural evolution of a transpressive belt the fibres occur around pyrite framboids and can be divided into five segments which record four distinct structural stages all four structural stages are related to a single progressive deformation since fibre segments can be traced continuously from the first segments to the last fibre growth patterns within the gaspetrough clearly indicate that folding occurred during coaxial deformation during the first three structural stages these structural stages are 1 layer parallel shortening 2 combined flattening and rigid body rotation and 3 cleavage development strain associated with vertical extension during these three stages accounts for approximately 50 shortening within the slate belt during the last structural stage deformation resulting from regional simple shear continued to affect the entire slate belt as local flattening within cleavage planes produced horizontal extension and brought about further tightening of folds strain recorded by the horizontal fibre increments produced during simple shear accounts for 25 shortening in this part of the appalachians oblique convergence during the acadian orogeny was partitioned in time between strike slip and reverse faulting convergence was accommodated by folding flattening and reverse faulting during the first part of the deformation and later on by flattening and dextral transcurrent faulting

record of late mississippian tectonics in the new perce group visean of eastern gaspesie quebec visean clastic units and structures at the northwest margin of the upper paleozoic maritimes basin provide information on tectonic events that are only poorly recorded in more central parts of the basin these continental units are time equivalent to marine sediments of the windsor group of nova scotia they are herein assigned to the new perce group which includes the la coulee and bonaventure formations as well as a new unit the cap d espoir for mation the latter unit unconformably underlies the bonaventure formation in a small but thick sub basin of the ristigouche basin in eastern quebec it is characterized by a succession of sandstone and mudstone rhythmites that contrast with the coarse alluvial fan deposits of the overlying bonaventure formation the cap d espoir formation was sourced from a broad area of subdued topography occupied by the visean la coulee formation and underlying units erosional remnants of the la coulee formation are unconformably overlain by the bonaventure formation in marginal parts of the ristigouche basin whereas these units are separated by the cap d espoir formation in more central areas of the basin the la coulee and cap d espoir formations underwent tilting and erosion during a normal faulting event that preceded deposition of the fault controlled bonaventure formation this series of events is interpreted to represent different steps in the reactivation of a pre carboniferous dextral strike slip system in response to northwest southeast compression during the visean in gaspesie resume des unites clastiques viseennes et leurs structures intrinseques dans la marge nord ouest du bassin des mari times paleozoique superieur illustrent des evenements tectoniques qui ne sont que pauvrement enregistres dans les parties plus centrales du bassin ces unites continentales sont chronologiquement equivalentes aux sediments marins du groupe de windsor en nouvelle ecosse elles sont ici assignees au nouveau groupe de perce lequel inclut les forma tions de la coulee et de bonaventure ainsi qu une nouvelle unite la formation de cap d espoir cette derniere est re couverte en discordance par la formation de bonaventure a l interieur d un petit mais relativement epais sous bassin du bassin de ristigouche dans l est du quebec elle est caracterisee par une succession de depots rythmiques de gres et de mudstone qui contraste avec les depots grossiers de cones alluviaux de la formation de bonaventure sus jacente la formation de cap d espoir est le produit de l erosion d une region source de grande etendue et a faible gradient topo graphique laquelle etait occupee par la formation de la coulee et les unites qui lui sont sous jacentes les reliques d erosion de la formation de la coulee sont recouvertes de facon discordante par la formation de bonaventure dans les parties marginales du bassin de ristigouche alors que ces unites sont separees par la formation de cap d espoir dans les parties plus centrales du bassin les formations de la coulee et de cap d espoir ont ete basculees et partiel lement erodees a l interieur d un evenement de fracturation ayant precede le depot de la formation de bonaventure dont les facies ont ete controles par des escarpements de failles cette serie d evenements est consideree comme etant le resultat de differentes etapes dans la reactivation d un systeme de coulissage dextre pre carbonifere en reponse a des contraintes orientees nw se durant le viseen en gaspesie

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

cleavage fold relationships and their implications for transected folds an example from southwest virginia u s a abstract a non coaxial deformation involving pre folding initiation of cleavage perpendicular to bedding is proposed to explain non axial planar cleavage associated with mesoscopic folds in part of the appalachian foreland thrust belt of southwest virginia folds are gently plunging asymmetric upright to slightly inclined sinusoidal forms with non axial fanning cleavage they show extreme local variations in type and degree of transection and the consistency of transection direction these relations are further complicated by hinge migration cleavage fan angles bedding cleavage angles and transection values appear influenced by fold tightness and in part by fold flattening strain fold flattening increments are considered simultaneous with folding axial surface traces and not cleavage traces coincide with the principal extension direction in fold profiles geometric modelling of cleavage fanning and bedding cleavage angle variations for various theoretical folding modes suggest that folding in limestone and sandstone layers was by tangential longitudinal strain significant shape modification and change in bedding cleavage relations occurred after limb dips of 40 and 50 were attained in limestone and sandstone respectively mud rock class 1c folds with convergent cleavage fans show features transitional between buckling and flexural flow initiation of cleavage fabrics during layer parallel shortening prior to significant folding may be important for cleavage evolution in some deformed rocks

age and correlation of the honorat group southern gaspe peninsula the honorat group of southern gaspe consists of two formations the arsenault and the garin the arsenault formation heretofore considered barren has yielded a graptolite faunule indicative of a llanvirn llandeilo age early middle ordovician suggesting a correlation with the lower mictaw group of gaspe as revised by de broucker a hiatus of indeterminate magnitude corresponding to the taconic unconformity probably separates the arsenault formation from the overlying garin formation the garin has yielded graptolites ranging from the upper climacograptus spiniferus zone to the paraclimatograptus manitoulinensis zone late middle to early late ordovician the c spiniferus zone graptolites are identical to those of the upper sequence of the cloridorme formation of northern gaspe and the blind brook formation of the munsungun anticlinorium of maine but differ somewhat from those from the upper tetagouche group of new brunswick which are closer to those from the summerford and exploits groups of no

riedel shear a mechanism for crenulation cleavage drag folds 1 from the microfaulting of inclined markers distinguish crenulation cleavage from other cleavage types cleavage as riedel r shears nucleates obliquely to planar anisotropy of foliated rocks and at various angles related to to the shear zone boundaries folds 2 with axes parallel to the instantaneous 1 at high angle and partway with r shears are formed in the xz plane of strain ellipsoid the angle between folds and cleavage is changed in the progressive deformation the largest antithetic counterclockwise r shears rotation and largest opening of initial angle between folds and fractures up to 170 is achieved in the progressive transtension 1 this is not geometrically possible in the simple shear and transpression but forward rotation of the r shears of excess length is prevented by the constant or diminishing thickness of the shear zone the crenulation folds 3 amplify the drag folds of the inclined faulted marker and nucleate with axial planes parallel to the cleavage at higher strains the cleavage propagates further as p shears parallel to flanks of tightened crenulation folds the r shears are in higher order folds 4 reoriented into the axial planar position by pure shear in the yz plane of the first incremental deformational ellipsoid and by the shear induced by flexural slip along the layer boundaries the stretching of the fold limbs and the non coaxial ductile deformation of microlithons in their slip perpendicular to fold axis deform former drag and crenulation folds to a characteristic pattern striation and or faint lineation preserved in the cleavage plane trace the shear directions the shear sense is indicated by the cleavage folds transection and by the asymmetrical structures in the plane cut perpendicularly to clevage and parallel to striations

reconstruction of taconian and acadian paleostress regimes in the quebec and northern new brunswick appalachians a numerical analysis of fault populations was applied in the quebec and northern new brunswick appalachians to characterize paleostress fields attributed to the taconian and acadian orogenies the first brittle deformation documented in the external domain of the humber zone is associated with the thin skinned tectonics of the taconian orogen the taconian brittle deformation characterized by north south to ne sw reverse conjugated brittle faults evolved under a pure shear compressional regime vertical 3 axes with 1 axes oriented ese wnw the ene wsw dextral and nw se sinistral faults that are observed in the st lawrence lowlands are also attributed to taconian compression the first brittle deformation recognized in the dunnage zone and the gaspe belt is attributed to an ese wnw compression during the acadian orogeny in the dunnage zone of southern quebec the acadian paleostress axes are similar to the directions of 1 axes and to the pure shear compressional regime computed for the silurian and devonian rocks of the gaspe belt in the gaspe peninsula the acadian stresses are oriented ese wnw and are mechanically compatible with transpressional regimes reverse brittle faults and pure shear stress are identified along regional and secondary sets of ne sw brittle faults whereas a strike slip stress regime is reconstructed along major east west faults in the humber zone of the quebec appalachians a second compression is identified it is characterized by conjugate ene wsw dextral and nw se sinistral strike slip faults that crosscut taconian thrust faults this late deformation event is attributed to a distal expression of the acadian orogeny

alleghanian deformation in the eastern gaspe peninsula of quebec canada juxtaposition of the mississippian risti gouche and cannes de roches basins which are subbasins of the composite late paleozoic maritimes basin occurred through dextral movement along the north west striking percefault system in the east ern gaspepeninsula of quebec the north west striking faults are truncated by small north northwest striking dextral strike slip faults which probably developed as region al stress gradually rotated clockwise from north northwest south southeast to north east southwest this study provides the first evidence in eastern quebec for significant post acadian block displacement other than normal faulting and indicates that al leghanian deformation extended much far ther north than previously thought iden tification of these structures formed during the alleghanian orogeny but more than 1000 km away from areas of peak allegh anian metamorphism in the southeastern united states underlines the far reaching effects of continental collisions it also casts doubt on the age attribution of brittle strike slip faults elsewhere in the gaspe peninsula away from mississippian expo sures such brittle faults were previously associated with late stages of the acadian orogeny but could in fact be considerably younger

a reevaluation of the position of the baie verte brompton line in the quebec appalachians the influence of middle devonian strike slip faulting in gaspe peninsula the baie verte brompton line bbl the surface expression of the taconian suture in the canadian appalachian orogen extends from southern quebec to the northeast end of newfoundland in the que

acadian strike slip tectonics in the gaspe region quebec appalachians at the southern margin of the cambro ordovician humber zone in the quebec appalachians on gaspe peninsula three structural units of middle ordovician to middle devonian cover rocks of the gaspe belt are in large part bounded by long straight longitudinal faults in one of these units the aroostook perce anticlinorium several structural features which can be ascribed to acadian deformation are controlled by three subparallel dextral strike slip longitudinal faults grande riviere grand pabos and riviere garin these faults follow bands of intense deformation contrasting with the mildly to moderately deformed intervals that separate them most of the structural features observed rotated oblique folds and cleavage subsidiary riedel and tension faults and offsets of markers can be integrated in a model of strike slip tectonics that operated in ductile brittle conditions a late increment of deformation in the form of conjugate cleavages and minor faults is restricted to the bands of high strain an anticlockwise transection of the synfolding cleavage in relation to the oblique hinges may be a feature of the rotational deformation the combined dextral strike slip that can be measured within the three major longitudinal fault zones amounts to 138 km to which can be added 17 km of ductile movement in the intervals for a total of 155 km

vertical and fold axis parallel extension within a slate belt in a transpressive setting northern appalachians abstract an incremental and finite strain study of a mid paleozoic slate belt in a transpressive setting in gaspe canadian appalachians has been undertaken using syntectonic fibers from pyrite type pressure shadows regionally strain estimates are quite consistent and reflect only slightly higher strain in the central part of the anticlinorial structure defining the slate belt extensions of up to 160 vertically and 110 parallel to the fold axis were recorded in the slate belt combined with an estimated overall regional shortening of 80 the fibers first rotated toward the final position of the cleavage within a vertical section normal to the cleavage and then rotated from a vertical to a horizontal orientation this change in fiber orientation observed in cleavage parallel sections indicates an abrupt change in the incremental stretching direction from sub vertical to sub horizontal fold axis parallel the vertical extension is related to folding and cleavage development during coaxial flattening the horizontal extension reflects the strain imposed on the rocks during regional simple shear which produced strike slip faulting and further tightening of the folds folding cleavage development fold axis parallel extension and faulting are all related to oblique convergence during the middle devonian acadian orogeny in this part of the canadian appalachians and clearly indicate an overall transition from a pure shortening deformation to a simple shear dominant deformation in an overall transpressive setting

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

a 40ar 39ar study of oceanic and continental deformation processes during an oblique collision taconian orogeny in the quebec reentrant of the canadian appalachians received 7 december 2006 revised 9 january 2008 accepted 10 march 2008 published 1 july 2008 1 two phases of penetrative deformation are documented in the taconian hinterland of the appalachian orogen in the gaspepeninsula d1 is associated with the obduction of the mont albert ophiolite onto the paleozoic laurentian margin whereas d2 corresponds to later transport of allochthons across the margin in the metamorphic sole s1 is a se dipping mylonitic fabric with a downdip lineation in underlying metabasalts d1 is characterized by nw overturned and recumbent folds and a subhorizontal s1 schistosity with an ene trending orogen parallel lineation d2 is characterized by a s2 steeply dipping penetrative axial planar crenulation cleavage and ne trending f2 folds the intraoceanic thrusting of ophiolite is dated at 465 ma early d1 whereas emplacement of ophiolite andsubsequentdeformationofthemarginwasrecorded by isotopic signatures between 459 and 456 ma late d1 d2 is dated at 448 ma throughout the hinterland taconian transpressive deformation is related to an oblique collision within the quebec reentrant of the canadian appalachians during the ordovician citation malo m g ruffet a pincivy and a tremblay 2008 a 40 ar 39 ar study of oceanic and continental deformation processes during an oblique collision taconian orogeny in the quebec reentrant of the canadian appalachians tectonics 27 tc4001 doi 10 1029 2006tc002094

along strike acadian structural variations in the quebec appalachians consequence of a collision along an irregular margin the quebec appalachians have been shaped by two major orogenies the middle to late ordovician taconian and the middle devonian acadian thrust faults and nappe structures characterized the taconian deformation throughout the quebec appalachians whereas structural styles pertaining to the acadian orogeny differ from southern quebec to the gaspe peninsula structural analysis of late ordovician to middle devonian supracrustal rocks shows two different acadian deformational regimes strike slip tectonics in the gaspe peninsula and thrust or dip slip tectonics in southern quebec in southern quebec acadian regional deformation produced folds which vary from upright to overturned and tight to isoclinal from the nw to the se major faults e g la guadeloupe are northwestward directed thrust faults marked by highly ductile shear zones outlined by mylonite in the gaspe peninsula structural trend is ne and major e w dextral strike slip faults transect this trend folds are open and upright inclined and tighter near the major faults where they have a clockwise rotation like the regional cleavage major faults e g grand pabos follow corridors delimiting high strain zones where the fabrics developed are indicative of a ductilebrittle regime of deformation in the temiscouata region major structural features of both southern quebec and the gaspe peninsula are recognized structures of this region consist of ene trending dextral strike slip faults and high angle wnw verging reverse faults parallel to major nne folds these structures reflect the transition from purely horizontal movement along major strike slip faults of the gaspe peninsula to vertical movement along thrust faults in southern quebec acadian structural variations within the quebec appalachians are interpreted in terms of a continental collision of gondwana along the irregular margin of laurentian and its taconian accreted terranes

mean annual temperature in new zealand during the last glacial maximum derived from dissolved noble gases in groundwater abstract this study presents a reconstruction of mean annual surface temperature in new zealand over the last glacial period using groundwater noble gas paleothermometry low resolution 14c derived mean recharge ages of groundwater from the deep moutere deep wairau and taranaki aquifers range from roughly 41 500 yr to present including the last glacial maximum lgm modeled noble gas temperatures of probable glacial age samples range from roughly 3 7 6 2 c cooler than present we present an error weighted mean cooling of 4 6 0 5 c relative to present during last glacial period the screened depth intervals of some wells sampled in this study allow for a degree of mixing during extraction between groundwater layers of different recharge age mixing with modern groundwater may slightly elevate the noble gas temperatures ngts of glacial age samples while making them appear substantially younger given the uncertainty in dating we cannot rule out a larger lgm temperature depression of up to 6 c the 4 6 c cooling estimate agrees with a number of terrestrial paleoclimate reconstructions near the study area as well as the majority of nearby paleoceanographic temperature studies

petrochemistry and u pb zircon age of porphyry dykes at the mckenzie gulch porphyry skarn cu ag au deposit north central new brunswick canada implications for emplacement age tectonic setting and mineralization potential north to northeast trending intermediate to felsic porphyry dykes in the mckenzie gulch mg area intrude upper ordovician through silurian calcareous sedimentary rocks of the matapedia group the

ophiolite obduction in the quebec appalachians canada 40 ar 39 ar age constraints and evidence for syn tectonic erosion and sedimentation 1 2 3 detailed field work conducted in the dunnage zone of the quebec appalachians is herein combined with 40 ar 39 ar dating on a series of ophiolitic massifs crosscutting granites and associated metamorphic rocks occurring along the baie verte brompton line the taconian suture between laurentia and lower paleozoic peri laurentian oceanic terranes studied massifs are the lac brompton ophiolite and the riviere des plante ultramafic complex in southern quebec and the nadeau ophiolitic melange in the gaspe peninsula our work suggests that these massifs form remnants of eroded ophiolitic nappes which are unconformably overlain by the saint daniel and riviere port daniel melanges and correlate with the thetford mines and mont albert ophiolitic complexes our 40 ar 39 ar data and compiled regional age constraints indicate that ophiolite obduction was diachronous along the strike of the orogen the timing of obduction and melange formation varies according to the irregular geometry of the early paleozoic laurentian margin with earlier collision occurring along or at the margins of promontories obduction was initiated with the formation of infraophio litic metamorphic soles between ca 479 and 472 ma in southern quebec and the nadeau ophiolitic melange and pos sibly as late as ca 470 466 ma for the mont albert complex these sole rocks were later exhumed and translated onto the laurentian margin with the overlying ophiolites between 475 and 460 457 ma the uplifting and erosion of the orogenic wedge during the waning stages of obduction has resulted in the sedimentation of olistostromal melanges and onlapping flysch units above the ophiolitic nappes as well as foredeep flysch successions during the latest arenig to earliest caradoc