3d litho constrained inversion model of southern sierra grande de san luis new insights into the famatinian tectonic setting abstract unravelling the orogenic structure of the sierra grande de san luis argentina is essential to understand the geological evolution of the famatinian orogen and the western margin of gondwana however its structural organization is still poorly known and widely debated in this contribution a new interpretation of the complex geological structures in the southern sector of the sierra grande de san luis is presented this work is based on a litho constrained joint inversion of gravity and magnetic datasets combining lithological structural and rock properties information results are consistent with a large scale doubly vergent structure caused by a compressional tectonic setting as a consequence of the collision between an allochthonous terrane cuyania precordillera and the proto margin of western gondwana a convex morphology of the indenter is proposed to be responsible for producing a significant clockwise rotation of the horizontal deviatoric stresses this stress field caused a small sinistral component of movement and gave rise to the doubly vergent transpressive mega structure

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

base metal skarns and au occurrences in the southern gaspe appalachians distal products of a faulted and displaced magmatic hydrothermal system along the grand pabos restigouche fault system in the southern gaspe appalachians base metal and au occurrences are spatially associated with the acadian dextral strike slip grand pabos and restigouche faults mineralization occurs as veins replacement zones and disseminations along the main structures and subsidiary faults with orientations compatible with the dextral strike slip kinematics along the main faults limestone of the upper ordovician lower silurian white head formation hosts numerous base metal skarns and au occurrences that are surrounded by halos of argillaceous alteration the reboul prospect is a type example of base metal skarns and consists of three types of mineralization 1 early strata bound disseminated cu zn ag associated with marble hornfels and skarn 2 northeast and northwest trending cu zn pb ag au and ag cu zn pb au sb veins parallel and perpendicular to the regional folding and 3 late ag au zn pb mineralized zones in quartz breccia veins parallel to the grand pabos fault crosscutting relationships fluid inclusion microthermometry mineralogy of the three types of mineralization and alteration patterns were used to define the timing of mineralizing processes which are 1 prograde metamorphism 2 metasomatism and hydrothermal alteration with high temperature skarn formation and cu zn ag mineralization 3 retrograde alteration with cu zn pb ag au and ag cu zn pb au sb veins and 4 late au precipitation at low temperature the saint andre de ristigouche prospect is the best example of au mineralization spatially associated with a base metal skarn in the area it consists of au sb as extensional veins and stockwork hosted by limestones felsic dikes associated with base metal skarns and a magmatic hydrothermal breccia at the reboul prospect are evidence for magmatic activity coincident with the mineralizing events argillaceous alteration high temperature and high salinity fluid inclusions and the pb isotope compositions of galena are compatible with a model linking the skarns and au occurrence to early to middle devonian magmatic activity at depth along the grand pabos and restigouche faults a palinspastic pre acadian strike slip reconstruction of the southern gaspe appalachians shows that all mineral occurrences hosted by the white head formation belong to the same mineralized area that might represent distal components of a magmatic hydrothermal system at depth

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

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

thrust tectonics in the north patagonian massif argentina implications for a patagonia plate 1 in the northeastern segment of the north patagonian massif southern argentina s to sw directed thrusting affected a late proterozoic to cambrian phyllite succession and the silurian to lower devonian sierra grande formation thrust tectonics was partly combined with the formation of mylonites and followed by the intrusion of the navarrete granodiorite mylonites of the tardugno granitoids are attributed to a ductile shear horizon in the subsurface as second stage of deformation after cessation of thrusting nw se compression led to the formation of widely distributed fold structures around ne sw trending axes as well as se directed reverse faults it was followed by the late kinematic intrusion of a porphyric granite as final pulse of the navarrete intrusive complex local folding around n s to nw se trending axes represents the final stage of the compressive deformational history thrust tectonics plus subsequent stages of deformation can be assigned to the late paleozoic time interval probably the permian they are seen in conjunction with the formation of granite mylonites within the north patagonian massif the cerro de los viejos granite mylonite of the la pampa province and the compressive structures in the sierras australes fold and thrust belt north of the boundary between patagonia and gondwana south america also the lack of early paleozoic famatinian deformation in this part of the north patagonian massif and the inferred boundary of the early paleozoic cuyania precordillera terrane north of patagonia support the interpretation that extra andean patagonia collided with gondwana south america during the gondwanide orogeny it is possible that patagonia was part of a plate and that the long gondwanide fold belt represented its collision zone

carlin type gold mineralization at saint andre de ristigouche gaspe peninsula quebec canadian appalachians the gaspe peninsula in the canadian appalachians hosts a variety of mineral occurrences that are spatially associated with the grand pabos and restigouche faults among these occurrences the saint andre de ristigouche gold sar au showing has peculiar features comparable with carlin type gold deposits at the regional district and prospect scales the most striking ones are 1 the calcareous nature of the host rocks 2 the au as sb hg metallic signature with absence of base metals and ag 3 the association with a crustal scale fault zone 4 the hydrothermal alteration characterized by silicification calcite and quartz veinlets at the margin of the au bearing zones and the occurrence of kaolinite in large halos of argillic alteration 5 numerous felsic dikes 6 the occurrence of au in as rich pyrite forming overgrowths on premineralization as free pyrite and in arsenopyrite 7 hydrothermal fluids equilibrated with host rocks at high temperature 200 which cooled to precipitate arsenopyrite and then mixed with evolved meteoric water to precipitate stibnite in veins although the sar au showing is relatively small analogies with carlin type mineralization encourage exploration in the gaspe peninsula and in similar settings elsewhere in the appalachians

neoproterozoic to early palaeozoic events in the sierra de san luis implications for the famatinian geodynamics in the eastern sierras pampeanas argentina the application of the sensitive high resolution ion microprobe shrimp u pb dating technique to zircon and monazites of different rock types of the sierra de san luis provides an important insight into the provenance and timing of deposition of the sedimentary precursors as well as the metamorphic and igneous history of the various basement domains additional constraints on the famatinian metamorphic episode are provided by pb pb stepwise leaching experiments on one staurolite and two garnet separates the results indicate that the sedimentary precursors of the conlara metamorphic complex have a maximum age of c 590 ma whereas the pringles metamorphic complex metasediments appear to be sourced from the pampean orogen in the early cambrian folded xenoliths within the c 496 ma el penon pluton suggest that the host conlara metamorphic complex underwent a pampean compression from a 208 pb 232 th monazite age of 478 ma for a migmatite from the nogoli metamorphic complex the structural evolution of this basement complex appears to be entirely post pampean onset of the famatinian high grade metamorphism between c 500 ma and c 450 ma follows a period of crustal extension on the western outboard of gondwana and might not be related directly to a mid ordovician accretion of the cuyania terrane

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

early paleozoic orogeny in southern south america abstract in northwest argentina weakly metamorphic clastic and calcareous sedimentary rocks of latest precambrian to lower cambrian age puncoviscana formation and related units contain an abundant ichnofauna of both chronostratigraphic and paleoenvironmental value in the western and central sierras pampeanas metasedimentary and metavolcanic rocks are considered to form part of the same geotectonic unit this pampean orogenic cycle includes geosynclinal sedimentation of latest precambrian to lower cambrian age as well as magmatism metamorphism and deformation of middle to upper cambrian age documented by an angular unconformity below the upper cambrian to devonian rocks of the famatinian orogenic cycle in some of the metamorphic rocks of the pampean cycle a pre ordovician folding is also distinguished from a later tectonic overprinting hence the concept of a pampean cycle differs from other concepts of late precambrian orogenic cycles of south america which are only defined by radiometric ages the pampean orogenesis may be compared with the ross orogenesis of the transantarctic mts the tyennan orogenesis of australia and some of the deformation phases of the damara orogen in namibia

pampean deformation in the sierra norte de cordoba argentina implications for the collisional history at the western pre andean gondwana margin 1 in the sierra norte de cordoba argentina at the inferred western pre andean gondwana margin structural analyses show that upper proterozoic lower cambrian strips of metamorphic clastic rocks underwent two stages of a compressive deformational history the d1 deformation led to the formation of an s1 cleavage foliation and affected an older granite it is related to f1 folding around n s to ne sw trending axes that partly record a steep plunge reconstructed fold structures display maximum wavelengths and amplitudes on a scale of hundreds of meters to kilometers a steep to overturned dip of thick packages of metaconglomerates and metasandstones is related to this folding event also because of variably oriented l1 lineations and dextral shearing structures of the d1 deformation are assigned to different structural domains interpreted as the result of strain partitioning during dextral transpression strips of post d1 granite and clastic mylonites with a dextral sense of shear are attributed to the second stage deformational event the late stage dextral shearing and mylonitization locally affected intrusions of granites and dacitic porphyries in the country rocks it took place along preexisting s1 planes or locally developed s2 c2 planes related to f2 fold structures with steeply plunging axes the regional metamorphism accompanying the deformation was in the range of the subgreenschist facies greenschist facies transition and greenschist facies the emplacement of synkinematic intrusions presumably followed active dextral shear zones it cannot be excluded that during compressive deformation older normal fault lines were reactivated and caused strain partitioning and later dextral shearing after cessation of compressive deformation granites and granodiorites intruded the deformed clastic succession and led to contact metamorphism of variable extent younger high level intrusions record chilled margins also at angular xenoliths isotopic dates from granitoids dacites and metaclastic rocks in the sierra norte area and surroundings suggest that compressive deformations and metamorphism took place during the early cambrian pampean orogeny the deformational and metamorphic history can be attributed to either ridge subduction collision or collision of the pampean terrane with the western pre andean gondwana margin the two stage kinematics suggests that oblique collision was followed by a change to dextral displacements in the upper plate during the final state of and after collisional tectonics the sierra norte area represented the upper eastern plate as supposed part of the rio de la plata craton and its cover overriding the lower plate that consisted of an accretionary complex in the west

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

orogenic development of the argentinian chilean andes during the palaeozoic the geological development of the basement of the argentinian chilean andes during the palaeozoic is characterized by an almost continuous structural metamorphic and plutonic mobility ultrabasic magmatism occurred only in a few regions terrigenic psammopelitic sequences are widespread at all times metamorphism is mostly of low to intermediate pressure but of variable temperature late palaeozoic high pressure metamorphism only took place near the present pacific coast there are about four culminations of orogenic activity varying in space and time from the mid cambrian to the mid ordovician from the silurian to the mid devonian during the early carboniferous and at the permian triassic boundary fold structures strike in variable directions at different times on the whole the pacific margin of gondwana consolidated continuously from the shield region in the e towards the pacific during the palaeozoic

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

the role of tectonic deformation on rock avalanche occurrence in the pampeanas ranges argentina abstract both tectonic and long term gravitational slope deformation in several mountain settings have been shown to be key drivers of large scale slope instability the roles of both mechanisms are investigated in this study of the potrero de leyes rock avalanche one of the largest and better preserved slope failures in the pampeanas ranges in argentina this rock avalanche involved 0 25 km3 of highly fractured granitic rocks cropping out on an uplifted planation surface the rock avalanche left a lobate deposit up to 4 km run out into the piedmont a field survey 3d terrestrial lidar photogrammetry and gigapixel panoramic photos allowed us to map the structures on the headscarp and on the planation surface we observed a dense network of fractures with joints sets striking nne ssw ene wsw and nw se respectively representing foliation riedel and anti riedel structures that developed during the paleozoic as suggested by previous studies the decrease of rock mass strength caused by tectonic fracturing the exposure of those highly fractured rocks along a tectonically active mountain front and potential deep seated gravitational deformation occurring along nne ssw foliation planes along the mountain front suggest that tectonic and gravitational processes were key causal factors leading to the occurrence of the potrero de leyes rock avalanche

gaspe belt subsurface geometry in the northern quebec appalachians as revealed by an integrated geophysical and geological study 1 potential field mapping abstract together recent gravity and high resolution aeromagnetic datasets are used to qualitatively investigate the upper and middle crustal geometry of the middle paleozoic gaspe belt in the northern appalachians long wavelength potential field anomalies define two sub basins that are divided by northeast trending gravity highs for each sub basins gravity lows correlate with the youngest rock units maps that highlight anomalies associated with near surface features at the expense of those related to deeper sources provide an important supplement to the spatially discrete observations derived from bedrock mapping analysis of such maps indicates that the sub basins are characterized by different structural patterns and that faults trending obliquely compared to the main structural grain have been previously underestimated the geometry of the gaspe belt as revealed by this integrated geophysical and geological study bears similarities with orogens exhibiting lateral extrusion this geometry is interpreted as the result of a heterogeneous strain regime in front of an indenter corresponding to the early paleozoic gander dunnage crustal block the indentation tectonic model is supported by 1 the various strike and kinematic of faults that suggest a strongly heterogeneous strain regime 2 the greater geological complexity and the occurrence of faults with a significant thrust component in front of the indenter 3 the predominance of dextral strike slip faults in the eastern gaspe peninsula that result in lateral material transport away from the indenter 4 the location of abundant devonian magmatic dykes sills and stocks in a fault bounded zone that experienced local extension 5 the occurrence of block rotation

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

the early paleozoic evolution of the argentine precordillera as a laurentian rifted drifted and collided terrane a geodynamic model paleontologic and stratigraphic evidence points to the early paleozoic precordilleran terrane of western argentina as being the conjugate rift pair of the appalachians stratigraphic similarities of the cambrian and early arenig carbonate series and very strong affinities among trilobite conodont and brachiopod faunas show their close relationship the most probable provenance areas are the appalachian ouachita rifted margin and the newfoundland appalachians although the former fits better with geometric and drifting paths suggested by faunal affinities increasing celtic and baltic brachiopod genera and divergent stratigraphy since the arenig indicate the drifting of the precordilleran terrane collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed the collision of the precordillera with western gondwana occurred during the mid llanvirn to llandeilo a magmatic arc related to eastward subduction present coordinates was active in the famatina range east of the precordillera this region of celtic affinity shows faunal exchange with the precordilleran terrane since the late arenig and may represent accreted intra iapetus volcanic island arc complexes the rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the precordilleran terrane from periequatorial to peripolar latitudes between the cambrian and latest ordovician the deep ocean to the west of the precordillera started to close by the late ordovician with the eastward drift of the chilenian terrane absence of volcanic or pyroclastic arc derived rocks in the precordillera indicate west dipping subduction as chilenia approached the continental margin a new forebulge was established on the former collided precordilleran terrane developing an erosional unconformity in central precordillera talacasto tambolar arch a gondwanic signature was fully developed by the middle silurian when the malvinokaffric clarkeia fauna flourished before then the late ordovician glacial record and associated hirnantia fauna were the first clear tie to gondwana during the silurian the marginal basin behaved as a foreland with lithosphere rheology and eustasy governing the sequence stratigraphy wrench faulting along its eastern boundary displaced the precordillera toward the south continued shortening during closure with the chilenian terrane in the mid devonian produced thrust loading of the basin and generated a thick graywacke succession final accretion of chilenia late devonian generated a regional angular unconformity between the lower and upper paleozoic new eastward subduction was initiated west of the accreted chilenian terrane during the late permian triassic as indicated by the choiyoi volcanic complex which presently outcrops in the frontal cordillera

early paleozoic structural and metamorphic evolution of western sierra de san luis argentina in relation to cuyania accretion abstract structural metamorphic and isotopic data obtained from the nogoli metamorphic complex of western sierra de san luis indicate that the early paleozoic famatinian orogeny overprinted an already structured and metamorphosed older basement the older geological features are relict nw trending fabric associated with high grade amphibolite facies regional metamorphism preserved within thin strips of schists and paragneisses and in the core of mafic to ultramafic lenses arc magmatism medium p barrovian type high t amphibolite to granulite facies regional metamorphism and penetrative nne to ne trending foliation are related to the building of the famatinian orogenic belt the p t conditions of the famatinian prograde metamorphism reached a pressure peak of ca 8 kb with a thermal peak from 750 c up to 820 c u pb conventional and chemical dating and ar ar plateau ages constrain the peak of the main orogenic phase related to the famatinian belt to 470 457 ma early to mid ordovician greenschist facies retrograde metamorphism closely associated with shear zones and secondary ar ar plateau and sm nd ages suggest that a late to post orogenic phase of the famatinian belt was active at least since 445 ma this phase continued during the silurian to late devonian times through multiple reactivation of early shear zones the famatinian orogeny reset a previous thermal history and therefore the timing of the relict fabric could not be constrained conclusively with radiometric dates despite this difficulty a range of 520 to 490 ma suggests some inheritance from pampean events registered by the older nw se fabric the early to mid ordovician regional metamorphism and ductile deformation of the western sierra de san luis is interpreted as the orogenic effects of the collision of the allochthonous cuyania terrane with the autochthonous proto pacific margin of gondwana during the famatinian orogeny

ages of metamorphic and deformational events in the sierra de ancasti pampean ranges argentina metamorphic rocks of the sierra de ancasti catamarca province northwestern argentina were investigated by means of the rb sr method three phases of metamorphism can be distinguished a first possible homogenization of sr possibly took place 524 m y ago a second one can be subdivided into a mean metamorphism at 472 m y and a statical recrystallization at about 450 m y a last weak metamorphism at about 420 m y can be recognized only by ages of cooling of biotites the relations of the metamorphic rocks to granitic intrusions and regional comparisons support this subdivision similar ages have been reported from various regions of the gondwana continent

self consistent generation of tectonic plates in three dimensional mantle convection abstract despite the fundamental importance of plates in the earth s mantle convection plates have not generally been included in numerical convection models or analog laboratory experiments mainly because the physical properties which lead to plate tectonic behavior are not well understood strongly temperature dependent viscosity results in an immobile rigid lid so that plates where included at all in 3 d models have always been imposed by hand an important challenge is thus to develop a physically reasonable material description which allows plates to develop self consistently this paper focuses on the role of ductile shear localization in two dimensional geometry it is well established that strain rate softening non newtonian rheologies e g power law visco plastic cause weak zones and strain rate localization above up and down wellings resulting in a rudimentary approximation of plates three dimensional geometry however is fundamentally different due to the presence of transform plate boundaries with associated toroidal motion since power law and visco plastic rheologies do not have the property of producing shear localization it is not surprising that they do not produce good plate like behavior in three dimensional calculations here it is argued that a strain rate weakening rheology previously shown to produce plate like behavior in a two dimensional sheet representing the lithosphere is a reasonable generic description of various weakening processes observed in nature one and two dimensional models are used to show how this leads to shear localization and the formation of faults this rheology is then applied to the high viscosity lithosphere of 3 d mantle convection calculations and the velocity pressure viscosity solution for the entire 3 d domain lid and underlying mantle is solved self consistently it is found that the lithosphere divides into a number of very high viscosity plates separated by narrow sharply defined weak zones with a viscosity many orders of magnitude less than the plate interiors broad weak zones with dominant convergent divergent motion above up and down wellings are interconnected by a network of narrow weak zones with dominant strike slip motion passive spreading centers are formed in internally heated cases while the resulting plates are not fully realistic these results show that self consistent plate generation is a realizable goal in three dimensional mantle convection and provide a promising avenue for future research

role of grain size in phyllonitisation insights from mineralogy microstructures strain analyses and numerical modeling abstract brittle y and p planes exist in an exposure of greywacke in the garhwal lesser himalaya india although y planes are well developed throughout the p planes are prominent only in some parts domain a and not elsewhere domain b to investigate why the p planes developed selectively the following studies were undertaken 1 clay separated xrd analyses clinochlore and illite are present in both the domains 2 strain analyses by rf method it deduces strain magnitudes of 1 8 for the ductile deformed quartz grains from both the domains a and b 3 grain size analyses of quartz clasts domain a is mostly composed of finer grains area up to 40 000 m2 whereas domain b consists of a population of coarser grains area 45 000 m2 a 2d finite element modeling of linear elastic material was performed using comsol software to investigate the control of grain size variation on the generation brittle shear planes the results of numerical modeling corroborate the known fact that an increase in grain size reduces the elastic strain energy density a broader grain size distribution increases the effects of diffusion creep and resists the onset of dislocation creep thus rocks with coarser grain population domain b tend to resist the generation of shear fractures unlike their fine grained counterpart domain a

syn deformational anatexis along the santa rosa river section argentina feedback relations between deformation metamorphism and melt extraction abstract mass transference from lower to upper crustal levels requires an efficient network of pathways that act as channels for draining melts from the source and transferring magmas through the crust we report on a mid crustal section in the santa rosa river from the eastern pampean ranges that underwent partial melting under active deformation the study focuses on the feedback relations between structural features and the position and shape of leucosomes that record the remnant magma network in both metasedimentary and meta igneous rocks a complete range of migmatites encompassing from patch to stromatic metatexite to schollen schlieren and nebulitic diatexite formed during a single high grade metamorphic event that postdated a previous sub solid evolution the diversity in migmatites structures suggests that the layered sequence behaved heterogeneously under a non coaxial deformational regime of progressive deformation the relationships between migmatitic structures and the progressive production of melts resulted in feedback relations that persisted as a time marker during the pampean event u pb dating of leucogranitic zircons allows constraining the time of melt generation and segregation to the lower cambrian 534 520 ma migmatites in the lower crust of the pampean orogen acted as channels of melt migration towards upper crustal levels

paleostress analysis of atlantic crustal extension in the quebec appalachians abstract a paleostress analysis using normal fault slip data and jurassic dike trends has been conducted in the quebec and new england appalachians stress tensor analysis of fault slip by a numerical inversion method has distinguished homogeneous and directionally consistent e w and nw se oriented extensional stress regimes in the quebec appalachians and st lawrence lowlands the directions of extension compare well with the mean direction of extensional stress inferred from the jurassic dolerite dike trend in new england both extensions are interpreted as the result of rift related stress associated with the separation of north america and africa early in the late triassic early jurassic fragmentation of pangea the paleostress field configuration is assumed to be related to the direction of divergent plate motion the n s and ne sw late proterozoic faults that bordered the quebec reentrant and taconian acadian structures of the quebec appalachians appear to have played a significant role in the dis

the pacific gondwana margin in the late neoproterozoic early paleozoic detrital zircon u pb ages from metasediments in northwest argentina reveal their maximum age provenance and tectonic setting abstract u pb detrital zircon ages are reported from puncoviscana formation late neoproterozoic early cambrian and meson group late cambrian greywackes of northwest argentina to constrain provenance and depositional environment the new data are combined with previously published detrital zircon ages to show that puncoviscana formation age patterns contain two broad groups late mesoproterozoic early neoproterozoic 1150 850 ma and late neoproterozoic early cambrian 650 520 ma with their relative proportions varying inversely with youngest component age the 1150 850 ma age components are dominant in greywackes with oldest late neoproterozoic components 600 ma the former diminish considerably when late neoproteozoic components become dominant and younger to 520 ma a northernmost greywacke sample from purmamarca jujuy is distinctive whilst its zircon age pattern partly resembles other puncoviscana formation samples it contains no cambrian late neoproterozoic ages the youngest ages being early neoproterozoic this may reflect an early neoproterozoic passive margin depocentre for the formation or an older early neoproterozoic succession within it which may predate the brasiliano orogeny in brazil the youngest age components c 520 ma in a greywacke from rancagua cachi salta province dominate an almost unimodal pattern suggestive of contemporary volcanic sources at a late early cambrian depocentre detrital zircon age patterns of the meson group lizoite formation have major cambrian latest neoproterozoic components resembling those of the puncoviscana formation but its mesoproterozoic component is diminished and there are no significant age components of this age small youngest components at c 500 ma suggest a maximum late cambrian stratigraphic age the puncoviscana formation detrital zircon patterns suggest a provenance in a continental hinterland having a stabilised extensive late mesoproterozoic orogen with minor paleoproterozoic and archean precursors and a more variable late neoproterozoic orogen containing an evolving sequence of less extensive subcomponents a direct relationship with the brazilian shield is suggested with sediment supplies originating within active margin orogens of the interior and collisional orogens at the suture between african and south american cratons but ultimate deposition in passive margin environments of western gondwanaland

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

evolution of the sierras de cordoba argentina abstract located in the southeastern part of the sierras pampeanas argentina the pampean ranges of cordoba show the evolution at the western margin of the rio de la plata craton from extensional stages during neoproterozoic times to compressive stages during the pampean orogeny the cumbre de gaspar group represents distal deep sea clastic sedimentation deposited in a passive margin environment very possibly during a time of incipient oceanization the santa sabina group representing shelf sedimentation rests conformably on the cumbre de gaspar group stocks of granites and granodiorites of calc alkaline affinity intruded the cumbre de gaspar group during the early pampean or earlier the polyphase pampean orogeny involves several distinct metamorphic and orogenic events metamorphism is discussed using the chemical composition of minerals the major effect of the pampean orogeny was the formation of a pile of westward thrust blocks the rio de la plata craton thrust above its marginal basin forms the uppermost unit the intrusion of the el pilon granite dated at 520 5 ma post dates these tectonic and metamorphic events after this main orogenic event the domain remained permanently located on the cratonic side of younger famatinian and andean orogenic events the mermela group probably corresponds to the molasse of the pampean orogeny and to the base of a new sedimentary cycle it is difficult to distinguish famatinian tectonics in the sierras de cordoba because the main orogeny occurred further west however this orogenic cycle is marked by the intrusion of the large achala batholith during the late palaeozoic and mesozoic the sierras de cordoba remained a stable platform the whole region was rejuvenated by the andean orogeny which induced tilted blocks in its foreland and the pocho volcanics of shoshonitic affinities

across strike geometry of the grand pabos fault zone evidence for devonian dextral transpression in the quebec appalachians the principal faults of southeastern gaspe peninsula in quebec consist of a central high strain zone that is characterized by mainly ductile deformation structures and bordered by low strain zones each dominated by brittle deformation structures the overall geometry of shear fractures within the low strain zones is quite similar to the expected geometry of riedel shear fractures the brittle structures overprint the dominant c s type fabric of the high strain zone which implies that brittle deformation outlasted ductile deformation the asymmetry of local micro to meso scale deformation features along the fault zones reflects the non coaxiality of the shear other features described within the fault zone stylolitic cleavage shear bands and reverse faults are evidence for a component of shortening perpendicular or oblique to the fault zone the geometry of the grand pabos fault zone gpfz a major fault of southern gaspe indicates that deeper seated fault rocks high strain zone have been brought

paleomagnetic constraints on siluro devonian laurentian margin tectonics from northern appalachian volcanics abstract paleomagnetic analyses of silurian mafic volcanics from the overstep sequence of sedimentary and volcanic rocks deposited over the central mobile belt of the northern appalachians provide insight into the mid paleozoic tectonic history of the laurentian margin stepwise thermal demagnetization of the subaerial mafic volcanics of the ludlovian fivemile brook formation of northwestern maine reveals two ancient high temperature dual polarity remanences a tilt corrected mean direction yields an inclination of 41 i 3 9 n 4 sites and the magnetization is interpreted as a near primary magnetization acquired well before the end of early devonian deformation an in situ mean direction d 165 i 35 95 6 k 65 n 10 entries from 8 sites is interpreted as a secondary overprint with a pole 22 s 306 e near the early carboniferous segment of the north american apparent polar wander path apwp conglomerate and fold tests of the high temperature characteristic remanence preserved in wenlockian subaerial mafic volcanics of the bryant point formation and a red bed of the south charlo formation both of the chaleur group of northeastern new brunswick constrain paleolatitude and deformational age the inclination only fold test peaks at 50 unfolding with a mean inclination of 35 i 8 5 n 148 synfolding acquisition of magnetization is wenlockian based on a negative conglomerate test at the base of the section and a positive conglomerate test at the top of the section clockwise streaking of site mean directions away from a predominantly northerly declination is consistent with post middle wenlockian dextral shear in the chaleur bay region comparison of a locus of paleomagnetic pole positions with the north american apwp supports a silurian age of the magnetization of the chaleur group the age and synfolding nature of this remanence furthermore requires that deformation associated with the acadian orogeny in new brunswick began by mid silurian times moreover inclinations from these units indicate that within paleomagnetic resolution there has been no significant latitudinal displacement with respect to stable north america since the silurian

crustal provenance and cooling of the basement complexes of the sierra de san luis an insight into the tectonic history of the pro to andean margin of gondwana abstract the sierra de san luis constitutes the southernmost tip of the eastern sierras pampeanas its palaeozoic metamorphic basement units define a key location for the understanding of the accretional history along the proto andean margin of gondwana although it is largely accepted that the polyphase accretional history of the sierras pampeanas is preluded by the docking of the pampean terrane followed by the famatinian orogenic cycle that involves subduction along the margin of gondwana and the accretion of the precordillera cuyania terrane and finally ceased with the collision of the chilenia terrane a vast amount of controversial information concerning the timing and mode of collisions as well as the origin of the different involved crustal fragments within the eastern sierras pampeanas is published in this paper those different hypothesis are presented and evaluated under the light of new isotopic data of the sierra de san luis nd systematics of the metasedimentary sequences of the sierra de san luis indicate that the studied sequences were developed on the pampean terrane an amazonian origin of the pampean terrane that was probably detached from the arequipa antofalla craton is proposed furthermore the correlation of two low grade phyllitic belts san luis formation with the widespread puncoviscana formation is not supported by sm nd data it is suggested that the sedimentary precursors of the pringles metamorphic complex and the topping phyllites were sourced on the pampean orogen and accommodated in a newly formed back arc basin during the early famatinian the cooling history of the basement complex is recorded by an extensive amount of k ar muscovite and biotite ages a high variability in muscovite ages is only partly related to different intrusion times of two pegmatoid generations post famatinian to achalian crustal scale mylonite formation 359 ma and a rotational exhumation of the central basement unit are causal for the observed k ar muscovite age pattern in the range from 395 ma to 447 ma therefore the decrease in metamorphic degree from west to east is the result of the erosion level of a crustal profile from the mid lower crust to the upper crust an even higher variability in k ar biotite cooling ages covering the range from 315 ma to 418 ma is related to the slow cooling after the famatinian orogenic cycle or reheating during the achalian orogenic cycle and consequent variable reset of the isotopic system however ages recorded by biotite booklets substantiate the hypothesis of a differential exhumation of the basement of the sierra de san luis

structural evolution of the sierra de san luis eastern sierras pampeanas argentina implications for the proto andean margin of gondwana

crystallochemical indexes and geothermobarometric calculations as a multiproxy approach to p t condition of the low grade metamorphism the case of the san luis formation eastern sierras pampeanas of argentina abstract in this work crystallochemical indexes and geothermobarometric calculations are used together to estimate the p t condition in low grade metamorphic units of the san luis formation from sierra de san luis eastern sierras pampeanas of argentina phyllites and slates from this formation record at least two episodes of white mica wm and chlorite chl growth associated with main d1 s1 wm2 chl1 and local d2 s2 wm3 chl2 stages mean kicis values of 0 30 western belt and 0 23 2 eastern belt were determined for the the identification of increasing p t condition paths in low grade metasedimentary successions is not easy in the absence of higher grade rocks in these situations a systematic sampling and analysis of dozens of samples must be carried out the very good correlation between crystallochemical index values kubler index and white mica b parameter and thermobarometric calculations empirical and semi empirical chlorite thermometers and thermobarometry for chlorite white mica quartz h2o equilibrium presented in this work argues in favor of the development of a multiproxy study strategy in this type of low grade metasedimentary successions that involve 1 a systematic sampling of metapelite levels for x ray diffraction study mineralogical and crystallochemical indexes with a rapid implementation allowing a dense systematic sampling 2 the recognition of variations in the p t conditions from ki and b parameter values and the consequent selection of metapelitic samples for analyzing mineral chemistry and thermobarometric calculations in order to facilitate these calculations a user friendly spreadsheet for crystallochemical indexes and chlorite thermometry calculations is also provided

taconian and acadian transpression between the internal humber zone and the gaspe belt in the gaspe peninsula tectonic history of the shickshock sud fault zone the shickshock sud fault has a history of ordovician taconian silurian salinic and devonian acadian movements taconian deformation involving ductile dextral oblique slip faulting is recorded in cambrian rocks in the footwall of the shickshock sud fault metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist shear bands asymmetric garnet porphyroclasts c s fabrics and mica fish textures indicate dextral shearing the regional sense of shear is top to west and southwest on generally southeast dipping shear zones hornblende of metabasalt yielded an 40ar 39ar age of 455 9 2 ma and muscovite from the mylonitic schist yielded an 40ar 39ar age of 454 3 0 9 ma which indicate metamorphism and deformation during the taconian orogeny evidence for silurian activity is indicated by the salinic unconformity to the south related to normal block faulting deformation features in the ordovician and silurian devonian rocks in the hanging wall were predominantl

basement tectonics of the southern pampean ranges argentina upper precambrian to lower paleozoic crystalline basement of the southern pampean ranges is composed of 1 a narrow western zone having low to medium grade metamorphic rocks and relatively few granites and migmatites and 2 a wide central eastern hercynotype low pressure zone with abundant granitoids the internal structures fall into three distinct domains characterized by the following orientations dl nearly e w d2 nnw sse and d3 nne ssw the tectonic evolution is interpreted as having begun in an upper precambrian orogenic cycle commencing with lithospheric rifting followed by compression forming d1 structures next was a mobile belt cycle composed of two main stages the first one which generated the main tectonic features d2 of the igneous metamorphic complex coincided with a syntectonic to late tectonic granitic intrusive event with the principal metamorphic episode and with paleozoic andean tectonic trends related to the activity of the gondwanaland pacific margin the last one was a fracturing and an open weak folding d3 event with local low grade metamorphism it occurred during the silurian

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

the proto andean margin of gondwana an introduction a basic background is presented for the discussion of the early palaeozoic geology of western argentina covered by this book this includes the definition and terminology of orogenic cycles on this part of the gondwana margin represented by the eastern sierras pampeanas the pampean orogeny early cambrian relates to an intense but short lived period of terrane collision predating the rifting of the precordillera terrane from laurentia the famatinian cycle is predominantly represented by intense subductionrelated magmatism of early middle ordovician age developed on the continental margin of gondwana during the rifting and drifting of the precordillera terrane the grenvillian basement of the latter is further exemplified by a new rb sr whole rock isochron age of 1021 12 ma for orthogneisses from the western sierras pampeanas a mid ordovician granite in this area dated at 481 6 ma by u pb ion microprobe data may be related to rifting while the precordillera terrane was still attached to laurentia a divergence of opinion is pointed out between some authors in this book who favour mid ordovician collision of the precordillera with gondwana and others who place it much latter in silurian or devonian times