copper isotope fractionation in the meiduk porphyry copper deposit northwest of kerman cenozoic magmatic arc iran the meiduk deposit possesses three different cu reservoirs each with a unique cu isotope signature 65cu for the leached cap minerals ranges from 2 5 to 0 49 to 0 45 to 0 3 for hypogene minerals and from 1 3 to 4 4 for supergene enrichment minerals oxidation of hypogene sulphides and effective trapping of copper from solutions derived from the leached cap in the supergene enrichment zone caused this relationship a systematic pattern of low cu isotope values close to the surface and higher isotope values with depth reveals a palaeo fluid pathway in the northwest southeast direction over the deposit thus the copper isotope data from leached cap and enrichment minerals can be used to monitor copper migration during supergene weathering at the meiduk deposit

the bright moho reflection in the 1986 nevada passcal seismic experiment abstract detailed study of the reflected phases from the moho identified in the seismic reflection recordings of the 1986 nevada passcal lithospheric seismic experiment place important constraints on the fine structure and geological nature of the mohorovicic discontinuity two different spectral ratio techniques are used to estimate the reflectivity of the moho we evaluate the ratio of the reflected pmp phase to the incident source amplitude we also calculated the spectral ratio of the pmp phase with a reference reflection reflectivity estimates calculated using both spectral ratio techniques are very consistent high reflectivity within the range 0 28 0 39 was obtained the analysis of the spectral characteristics suggests a layered structure for the moho with an average thickness between 85 and 250 m these results require a layered moho structure with high impedance contrasts amplitude modeling using a reflectivity algorithm demonstrates that constructive interference from a 1 0 1 5 km thick layered structure produces amplitudes and waveforms comparable to the data to achieve such high reflectivities 20 25 of the moho consists of layers with velocities below 6 5 km s the remaining layers have velocities between 7 7 and 8 1 km s geologically the low velocities are consistent with velocities characteristic of basaltic magmas partial melts the high velocities are characteristic of mantle material the partial melts may represent an expression of present day underplating

crustal structure and surface zonation of the canadian appalachians implications of deep seismic reflection data in 1986 1181 km of marine seismic reflection data was collected to 18 20 s of two way traveltime in the gulf of st lawrence area the seismic profiles sample all major surface tectono stratigraphic zones of the canadian appalachians they complement the 1984 deep reflection survey northeast of newfoundland together the seismic profiles reveal the regional three dimensional geometry of the orogen three lower crustal blocks are distinguished on the seismic data they are referred to as the grenville central and avalon blocks from west to east the grenville block is wedge shaped in section and its subsurface edge follows the form of the appalachian structural front the grenville block abuts the central block at mid crustal to mantle depths the avalon block meets the central block at a steep junction that penetrates the entire crust consistent differences in the seismic character of the moho help identify boundaries of the deep crustal blocks the moho signature varies from uniform over extended di

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

geophysical studies of the structure of the appalachian orogen in the atlantic borderlands of canada results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the appalachian orogen in eastern canada wide angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins high velocity lower crust attributed to underplating is found below the former laurentian continental margin in newfoundland and below the magdalen basin potential field data are used to trace the surface zones of the orogen from the northeast newfoundland shelf to cape breton but extrapolation to new brunswick and quebec is unclear because of late paleozoic basin development the central mobile belt of the orogen is only a few tens of kilometres wide in southwest newfoundland and cape breton but broadens substantially to around 200 km elsewhere reflection images show a strong deep crustal fabric that runs along the orogen with a margin that crosses into the avalon zone in southern newfoundland but coincides with the avalon gander zone boundary el

geochemical and isotopic nd o data from ordovician felsic plutonic and volcanic rocks of the miramichi highlands petrogenetic and metallogenic implications for the bathurst mining camp middle ordovician felsic magmatism contemporaneous with bathurst camp pb zn volcanogenic massive sulphide vms deposits consists of strongly altered volcanic to subvolcanic rocks belonging to the tetagouche group and relativelyunaltered granitoid plutons which are divided into northern central and southern groups within the miramichi highlands calc alkalic felsic volcanic rocks and northern plus central plutons have epsilonnd t values ranging from 8 2 to 1 9 and 4 0 to 0 3 respectively they exhibit within plate type volcanic and transitional i to a type granite geochemical characteristics granitoid rock delta18o values range from 8 0 to 10 1 published granitoid rock pb isotopic compositions overlapunpublished galena data from bathurst vms deposits field geochemical and isotopic evidence indicate that these volcanicand granitoids rocks are consanguineous and mainly derived from proterozoic orolder infracrustal sources alkalic felsic volcanic rocks and associated alkaline basaltic rock

devonian extension in northwestern newfoundland 40ar 39ar and u pb data from the ming s bight area baie verte peninsula abstract the ming s bight group of northwestern newfoundland an outlier of humber zone continental margin rocks is entirely surrounded by ophiolitic rocks of the dunnage zone structures in the ming s bight group and adjacent units record three main phases of deformation the earliest structures relate to silurian sinistral transpression previously documented in the region two later phases of extensional deformation produced a series of dextral oblique normal shear zones and faults that now separate the ming s bight group in the footwall from ophiolitic and granitoid rocks in the hangingwall 40ar 39ar and u pb data constrain the times of oblique normal shear and cooling metagabbro in the point rousse ophiolite complex which lies in the hangingwall preserves disturbed ordovician hornblende 40ar 39ar ages whereas adjacent shear zones record devonian ages hornblendes in pacquet harbour group amphibolites within extensional shear zones mainly record 40ar 39ar ages of 390 380 ma synkinematic titanite

estimating the near surface amplification factor to minimize earthquake damage a case study at west wadi hagoul area egypt the damage caused by earthquake occurrences in different localities all over the world necessitates the evaluation of the underground and or sub soil structure for strategic projects the case study is the proposed area for a new factory construction that lies 3 km west of suez cement factory in the area between kottamiya and ain sokhna the shallow seismic refraction survey was carried out through 10 major lines grid lines comprising 30 seismic profiles the microtremor measurements were done at 25 locations at the grid intersection points the obtained compressional p and horizontal shear sh wave velocities with the horizontal to vertical h v spectral ratios are used to deduce the subsurface structures to evaluate the elastic and dynamic properties and the transfer function at both the surface and bedrock the results illustrate that there is a good correlation between the fundamental frequencies deduced through the theoretical transfer function and the h v spectral ratio the maximum value of ground motion amplification factor of the study area is 3 3 at a corresponding frequency of 7 8 hz

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

early silurian orogenic andesites from the central quebec appalachians the pointe aux trembles formation is a deep to shallow water volcaniclastic apron with massive lava flows deposited in early silurian time the apron deposits extend laterally to a deep water accu

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

nature and evolution of the eastern margin of lapetus geochemical and isotopic constraints from siluro devonian granitoid plutons in the new brunswick appalachians in the gander zone ordovician to devonian metaluminous to slightly peraluminous plutons with within plate affinities intrude a lower paleozoic metasedimentary package during the siluro devonian end t and 18o values of the metasedimentary rocks would have been about 7 to 8 and 10 to 14 respectively granitoid end t values range from 0 3 to 4 2 18o values lie between 6 6 and 10 4 and published pb isotopic compositions are radiogenic 207pb 204pb 15 65 end t values of associated silurian gabbros are somewhat positive 1 2 to 2 3 some plutons exhibit evidence for comingling with this mafic component potential source materials include enriched mantle supracrustal and infracrustal sources although some constraints can be put on the first two sources the nature of infracrustal material is difficult to evaluate heterogeneous data obtained from silurian plutons can be explained by crust mantle mixing if some plutons contain a significant mantle component then mesoproterozoic o

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

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

silurian extension in the upper connecticut valley united states and the origin of middle paleozoic basins in the quebec embayment pre silurian strata of the bronson hill arch bha in the upper connecticut valley nh vt are host to the latest ludlow comerford intrusive suite consisting east to west of a mafic dike swarm with sheeted dikes and an intrusive complex the rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite the suite is truncated on the west by the monroe fault a late acadian thrust that carries rocks of the bha westward over silurian devonian strata of the connecticut valley gaspetrough cvgt dikes intrude folded strata with a pre intrusion metamorphic fabric taconian but they experienced acadian deforma tion twenty fractions of zircon and baddeleyite from three sample sites of gabbro diorite spanning nearly 40 km yield a weighted 207 pb 206 pb age of 419 1m a greenschist facies dikes sampled over a strike distance of 35 km were tholeiitic basalts formed by partial melting of asthenospheric mantle with little or no influence from mantle or crustal lithosphere the dike chemistry is similar to mid ocean ridge within plate and back arc basin basalts parent magmas originated in the astheno sphere and were erupted through severely thinned lithosphere adjacent to the cvgt extensive middle paleozoic basins in the internides of the appalachian orogen are restricted to the quebec embayment of the laurentian rifted margin and include the cvgt and the central maine trough cmt separated from the bha by a silurian tectonic hinge the ne trending comerford intrusions parallel the cvgt cmt and the tectonic hinge and indicate nw se extension during post taconian convergence the irregular margins of composite laurentia and avalon permitted continued colli sion in newfoundland st lawrence promontory and coeval extension in the quebec embayment extension may be related to hinge retreat of the northwest directed brunswick subduction complex and rise of the asthenosphere following slab break off an alternative hypothesis is that the basins originated as pull apart basins between northwest trending left stepping sinistral strike slip faults along the southern flanks of the new york and st lawrence promontories

patterns in the copper isotope composition of minerals in porphyry copper deposits in southwestern united states cu isotope measurements of minerals from american southwest porphyry cu deposits reveal a positive relationship with the grade of cu and display spatial patterns we measured the cu isotope composition of 87 minerals contained within veins from drill core and hand specimen samples from three deposits the silver bell ray and morenci mines the overall range of cu isotope ratios varies from 13 5 to 8 3 per mil the deposits possess three different cu reservoirs in which each has unique cu isotope signatures where 65cu for leach cap minerals hypogene minerals supergene enrichment minerals the pattern exists in all three deposits and resulted from oxidative weathering of cu at surface and reprecipitation of cu at depth a rayleigh distillation model mimics the cu isotope patterns found in the leach cap and quantifies the degree of leaching a comparison of the isotopic composition of the three reservoirs among the three deposits reveals distinct differences the silver bell mine possesses leach cap minerals that are more depleted in 65cu and enrichment minerals that are more enriched in 65cu than both the morenci and ray mines a possible explanation for the difference among the deposits could indicate that the silver bell deposit experienced a greater degree of leaching than the ray and morenci deposits the comparative analysis of the cu isotope data reveals the exploration potential of using cu isotope fractionation in the supergene environments

remnants of a fossil alluvial fan landscape of miocene age in the atacama desert of northern chile using cosmogenic nuclide exposure age dating we have used cosmogenic nuclides to estimate limits on the surface exposure durations and erosion rates of alluvial fans and bedrock surfaces in the atacama desert in chile the oldest landforms we studied are extensive alluvial fans referred to as atacama gravels with the exception of samples collected in antarctica the cobbles collected on these alluvial surfaces have the lowest erosion rates of any samples as determined by cosmogenic nuclides analyzed to date the oldest cobble has a model surface exposure age of 9 myr based on combined measurements of cosmogenic 10be 26al and 21ne concentrations cobbles from the alluvial fans are eroding slower than the surrounding steep mountainous bedrock surfaces maximum erosion rates for cobbles on alluvial surfaces are uniformly 0 1 m myr the survival of these gravels specifically and more generally the stability of landform features in this geographic area is made possible by the attainment of hyperarid conditions in the atacama desert resulting from global climatic cooling about 15 myr ago combined with the rain shadow effect caused by uplift of the central andes the landform features observed presently in the atacama desert are remarkably stable and despite the inevitable erosion that is detectable using cosmogenic nuclides undoubtedly bear considerable resemblance to conditions as they existed in the miocene over geologic time the atacama landscape is evolving in such a manner as to erode the higher bedrock ridges relative to the more stable but stratigraphically lower depositional surfaces through which clastic detritus now travels occasionally along the floors of incised drainage systems leaving the older permeable alluvial fan surfaces largely intact as widespread remnants of a miocene fossil landscape

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

the use of seismic shear waves and compressional waves for lithological problems of shallow sediments from a great variety of in situ shear wave experiments i e reflection refraction and borehole surveys in the shallow sediments of the north german plains several specific properties have been derived shear waves s differ from compressional waves p in that correlations have been established between v s and the confining pressure and between reduced v s values and several lithological parameters like the grain size of sandy material more lithological and hydrological information is obtained by using s and p wave surveys along the same profile the best information on a sedimentological structure is obtained by the simultaneous observation of v s v p q s and q p

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

paleohydrologic evolution and geochemical dynamics of cumulative supergene metal enrichment at la escondida atacama desert northern chile quantitative limonite mapping within the leached capping of the porphyry copper deposit at la escondida chile permits reconstruction of the paleohydrologic and chemical evolution of a well developed supergene ore forming system the mineralogy textures and relative abundance of supergene limonite minerals hematite goethite and jarosite are used to reconstruct the former ratio of pyrite to chalcocite and the preoxidation copper grade based on empirical limonite sulfide correlations after locke 1926 blanchard 1968 and loghry 1972 estimates of preoxidation copper grades in surface exposures and tops of drill holes at la escondida are significantly lower than actual copper grades in the underlying enrichment blanket at depth this apparent inconsistency is explained by a progressive increase in the copper grade of the sulfide enrichment blanket as it descended to its present location in response to a descending water table this systematic trend of reconstructed grades of supergene enriched copper sulfide increasing with depth offers the first quantitative proof of cumulative downward enrichment in a supergene profile as proposed by locke 1926 the consistent trends of limonite mineralogy and abundance in vertical profiles indicate that water table descent at la escondida was relatively continuous in space although not necessarily in time evidence for cumulative downward enrichment in vertical profiles through leached capping allows quantitative analysis of chemical mass balance in dynamic supergene systems slopes of linear regressions for profiles of reconstructed enriched copper grades vs depth indicate lateral fluxes into or out of a given vertical profile this method provides independent verification of conclusions from a previous study of copper mass balance at la escondida brimhall et al 1985 which showed that lateral fluxes of copper were a significant factor during supergene leaching and enrichment

post taconian shortening inversion and strike slip in the stephenville area western newfoundland appalachians deformed terrigenous and carbonate sedimentary rocks representing the early paleozoic laurentian continental margin form a series of elongate fault bounded blocks that plunge north beneath the humber arm allochthon in the stephenville area west newfoundland appalachians the continental shelf succession was folded and thrust faulted after emplacement of the humber arm allochthon in the west of the area table mountain is cut by a pop up structure bounded by downward converging reverse faults structures at the east margin of table mountain indicate both dextral and reverse slip the phillips brook structure farther east contains multiple fault bounded carbonate slices one slice carried by the west blanche brook fault is thrust over the humber arm allochthon the western edge of the indian head massif consisting of grenville basement is also a thrust contact these reverse faults and thrusts which cut the carbonate succession and postdate emplacement of the humber arm allochthon are in turn

iodine rich waters involved in supergene enrichment of the mantos de la luna argentiferous copper deposit atacama desert chile recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting cu assemblages to form atacamite during supergene oxidation of cu deposits in the atacama region in this report we document the occurrence of ag i inclusions hosted by supergene chalcocite from mantos de la luna an argentiferous upper jurassic stratabound cu deposit in the coastal range of northern chile the presence of this unusual mineral assemblage indicates that iodargyrite precipitated from reducing iodine rich waters suggesting that the fluids involved in supergene enrichment of cu deposits in the coastal range were more complex than previously thought this suggests the prevalence of hyperarid conditions during the latest stages of supergene enrichment of the mantos de la luna cu deposit in the atacama region supporting the notion that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of meteoric water

chronology of exotic mineralization at el salvador chile by 40ar 39ar dating of copper wad and supergene alunite exotic copper mineralization is a complex hydrochemical process linking supergene enrichment lateral copper transport and precipitation of copper oxide minerals in the drainage network of a porphyry copper deposit at the el salvador porphyry copper deposit in northern chile the majority of the exotic ore comprised a mixture of copper bearing manganese oxyhydrates termed copper wad x ray diffraction scanning electron microscopy and electron probe microanalysis show that the copper wad is composed of copper bearing cryptomelane k1 2 mn3 mn4 8o16 x h2o and birnessite k0 33 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mn 7 3 9 end document o14 7h2o structures these natural occurrences within the exotic ore provide the opportunity to directly date the formation of these deposits using recent advances in 40ar 39ar geochronology of supergene k mn oxides formed by weathering a suite of copper bearing cryptomelane and birnessite samples from exotic deposits within the el salvador district were characterized and dated by 40ar 39ar laser step heating supergene alunite kal3 so4 2 oh 6 found in paleospring feeder systems leading from the source zones of copper outward to the exotic mineralization was dated to independently constrain the age of exotic ore formation although the ar retentivity of the layered birnessite structure has been questioned by others the ar retentivity of these samples is thought to be a function of their natural preservation and limited postcrystallization ground water interaction in the hyperarid atacama desert the 40ar 39ar analytical results show that ar and or k losses after crystallization excess 40ar and 39ar recoil do not pose significant problems therefore in the context of exotic copper deposits within hyperarid environments this dating method is applicable to both cryptomelane and birnessite within copper wad the 40ar 39ar dating of exotic mineralization at el salvador indicates that supergene and exotic mineralization processes were active at 35 ma about 5 m y after the emplacement of hydrothermal mineralization and continued until the middle miocene the majority of exotic mineralization extends from the oligocene miocene 24 ma boundary through the middle miocene 11 ma and relates to supergene fluid emanating in multiple directions from the source of copper in indio muerto which represents a topographic high above the exotic deposits one reconnaissance date of exotic mineralization at the chuquicamata porphyry copper deposit yielded an age of 17 03 0 03 ma coincident with the known supergene alunite dates for this deposit reconnaissance dating at exotica mina sur and el abra proved problematic due to the presence of contaminant silicate minerals within the copper wad ages derived here for exotic mineralization are similar to the known supergene ages throughout northern chile the dates indicate that supergene exotic mineralization began at the eocene oligocene boundary and continued through the oligocene eventually ceasing in the middle miocene due to desiccation of the atacama desert a series of 10 cm thick supergene alunite veins were microsampled across their widths and dated to address the kinetics of alunite vein growth apparent growth rates of the veins vary from 71 to 100 mm m y in the horizontal direction to 24 mm m y in the vertical presumably caused by differences in pressure regimes due to their orientation

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

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

age and composition of the ruisseau isabelle melange along the shickshock sud fault zone constraints on the timing of melanges formation in the gaspe appalachians melanges are common in the humber and dunnage zones of the quebec appalachians humber zone melanges are spatially associated with taconian nappes and believed to be of tectonic origin dunnage zone melanges are interpreted as relicts of an ordovician accretionary prism the ruisseau isabelle melange rim in the gaspe ap palachians was first interpreted as a dunnage zone melange because of its tectonic position along the baie verte brompton line and lithological components such as dark mudstone blocks of ultramafic rocks and greenish chromite bearing sandstone the rim comprises sedimentary rock assemblages composite shale black shale and chromite bearing sandstone assemblages an exotic block a pebbly mudstone assemblage and slivers of serpentinized peridotite and metamorphic tectonite most melanges of the dunnage zone in the quebec appalachians contain partly similar rocks but their age is not well constrained recent work on the rim and cap chat melange of the humber zone and new fossil finds in the rim rock assemblages allow us to conclude that previous distinction between melanges of the dunnage and humber zones on the basis of rock type associations is not valid according to the age of the rim rock assemblages melanges in the northern gaspe appalachians continued forming after the mid caradocian later than the dunnage zone melanges of southern gaspe appalachians the juxtaposition and structural features of the rim rock assemblages result from repeated faulting along the shickshock sud fault from late ordovi cian to middle devonian

brittle faulting in the canadian appalachians and the interpretation of reflection seismic data abstract brittle faults in the canadian appalachians mostly late devonian or younger in age are divided into two groups on the basis of their movement vectors a strike slip group and a dip slip group the two groups are subdivided on the basis of orientation and sense of movement they are interpreted in terms of palaeozoic transpression and mesozoic extension during atlantic opening the palaeozoic faults comprise strike slip and reverse faults which were active in devono carboniferous times mesozoic strike slip faults are interpreted as transfer faults and they are coupled with normal faults many of which developed by reactivation of earlier reverse faults or steeply dipping surfaces including bedding and earlier foliations together these mesozoic faults comprise an adequate mechanism for crustal extension perpendicular to the orogen evidence for listric normal faults is rare in the older rocks of the orogen and it is suggested that this is due to the adequacy of the deformation mechanisms afforded by the pre existing planes of weakness the data presented demonstrate clearly that geological structures are commonly repeated at all scales from outcrop to regional following this principle prominent shallowly dipping reflectors imaged in the lithoprobe east seismic profiles are interpreted as large scale representatives of the palaeozoic reverse faults seen in outcrop that were reactivated as normal faults during atlantic opening it is suggested that reverse faulting is to be expected as a deformation mechanism in general in the late stages of a collisional orogen we draw attention to the importance of the mesozoic faults in modifying the attitude of earlier surfaces such a bedding foliations and faults

late silurian early devonian rifting during dextral transpression in the southern gaspe peninsula quebec petrogenesis of volcanic rocks the upper silurian lower devonian volcanic rocks in the southern gaspe peninsula of the quebec appalachians crop out at the northeast end of the connecticut valley gaspe synclinorium these shallow marine and subaerial sequences reach a thickness of up to at least 2000 m and comprise two groups 1 the late silurian volcanic rocks which are mainly transitional alkalic tholeiitic basalts with steeply sloping ree patterns 2 the early devonian volcanic rocks which include a significant proportion of intermediate rocks in addition to tholeiitic basalts compared with the silurian rocks the devonian basalts have lower abundances of strongly incompatible trace elements such as ba th ta nb and light ree and relatively flat heavy ree patterns basalts of both groups display negative nb and ta anomalies relative to th and la although the basalts of both sequences were derived from lithospheric mantle the silurian basalts were generated from garnet peridotite at 80 km depth while the devonian ba

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 hydrostatic corer selcore a tool for sediment sampling and geophysical site characterization hydrostatic energy is used to power an active device for sediment sampling and geophysical site characterization in the selcore design a steel tank with built in drive unit constitutes the core head the difference between ambient water pressure and atmospheric pressure in the tank provides the energy the selcore prototype enters the seabed as a gravity corer and automatically shifts into pile driving mode with up to 52 duty cycles without the need for an external trigger mechanism the corer has operated in water depths from 300 to 3500 m operation at depths shallower than 300 m including on dry land can be facilitated using auxiliary water pressure penetration and recovery is generally more than two times the performance of a gravity corer of equivalent weight the added utilization of hydrostatic energy has particular advantage in cases of relatively high shear strength sediments as well as attempts to core shallow bedrock below a sediment cover selcore has potential as a seabed seismic hammer source and initial land tests show good signal repeatability estimates of sediment thickness and seismic velocity obtained from the inversion and interpretation of the dominant rayleigh surface waves corresponds closely to the shallow borehole stratigraphy at a land test site

late devonian palinspastic reconstruction of the avalon meguma terrane boundary implications for terrane accretion and basin development in the appalachian orogen abstract a late devonian early carboniferous palinspastic reconstruction of atlantic canada restoring subsequent motion along the avalon meguma terrane boundary and other major faults facilitates re examination of the spatial distribution of important accretionary and post accretionary events in the northern appalachian orogen the reconstruction suggests a genetic relationship between 415 and 360 ma tectonothermal activity in both these terranes and the collision between laurentia and gondwana in a zone of anomalously intense shortening opposite the st lawrence promontory in the appalachian orogen erosional products of this collision are an order of magnitude greater than the thin ca 1 km veneer of latest devonian early carboniferous clastic rocks that were deposited in intermontane basins across the orogen this missing detritus may be found in the thick deposits of the catskill clastic wedge in the central appalachians

regional metamorphism of the appalachian humber zone of gaspe peninsula 40ar 39ar evidence for crustal thickening during the taconian orogeny geochronological studies on the timing of deformation and metamorphism along the laurentian margin have shown that the ages of metamorphic events change along strike within the newfoundland southern quebec segment of the canadian appalachians the gaspe peninsula is located at mid point of the two extremities of this segment new single grain laser 40ar 39ar plateau ages solely reflect latest middle late ordovician metamorphism samples taken within the internal humber zone in the shickshock group rocks yield 40ar 39ar muscovite and hornblende ages ranging from 457 to 454 ma samples from the amphibolite du diable the metamorphic sole of the mont albert ophiolite yield 40ar 39ar muscovite and hornblende ages ranging from 459 to 457 ma ordovician ages of the internal humber zone are consistent with 40ar 39ar ages from southern quebec and are interpreted as the result of the emplacement onto the margin of both the ophiolite and its metamorphic sole

ordovician arc collision and foredeep evolution in the gaspe peninsula quebec the taconic orogeny in canada and its bearing on the grampian orogeny in scotland the middle to upper ordovician deslandes cloridorme and garin formations in the eastern gaspe peninsula quebec are some of the most extensively exposed foredeep successions along the northern appalachian portion of the taconic caledonian orogen their depositional and biostratigraphic frameworks n gracilis to c spiniferus zones approximate correlatives to the n gracilis to d clingani british zones indicate that foredeep evolution spanned c 10 ma and was essentially synchronous with the convergence and accretion of the popelogan arc to the laurentian margin during the caradoc c 458 449 ma these results when combined with metamorphic and radiometric age data synthesized from across the laurentian segments of the northern appalachian and northwestern ireland taconic caledonian orogen further substantiate that orogenesis consisted of several short lived c 10 20 ma deformational episodes confined to arenig through ashgill time c 485 440 ma this indicates that the total duration of orogeny as recorded by arc magmatism metamorphism and laurentian foredeep development spanned no more than c 45 ma in that the scottish caledonides are a consanguineous part of this orogen their tectonostratigraphic evolution i e grampian orogeny should be similar accordingly the results detailed above are geodynamically compatible with and thereby support tectonic models that define the grampian orogeny in scotland as a mostly early to mid ordovician c 480 460 ma tectonic episode of short rather than long duration

radiation and receiver pattern of shear and compressional waves as a function of poisson s ratio shear s wave studies in addition to compressional p wave surveys have revealed that s wave velocities are much more variable than p wave velocities this strongly affects poisson s ratio especially in young sediments it is shown that has a great influence on the directivity pattern i e on the radiation and receiving characteristic of horizontal sources and receivers for their calculation well known surface boundary conditions and white s statement of the reciprocity relation white 1965 are used they also form the basis for the combination of source and receiver patterns essential for practical field work the various combinations of horizontally and vertically arranged sources and receivers are investigated with regard to their directivity pattern their amplitude ratio and in general to their usefulness in seismic prospecting

preliminary fractionaltion patterns of ore metals through earth history abstract a systematic method of comparing fractionation patterns of ore metals to those of common rock forming elements is developed using the coherent electronic framework provided by the periodic table through its progressive filling of transition metal d and f orbitals four generalized fractionation processes in earth history are addressed 1 nebular condensation and accretion 2 core mantle interaction 3 continental crustal growth and 4 ore formation in supracrustal environments through each of these simplified processes preliminary fractionation patterns of ore metals within periods appear to vary smoothly with atomic number fractionation trends for each of these four processes can be ascribed respectively to 1 differential condensation volatility 2 multiple stages of core formation with partial separation of highly siderophile metals into the core 3 enrichment of the continental crust in ore metals and incompatible elements by ascent of mantle derived magmas and 4 efficient multistage magmatic and hydrochemical ore forming processes within the crust fractionation trends of ore metals are contiguous and collinear with those of rock forming metals in the same period implying common geochemical controls the systematic variation of enrichment and depletion factors across groups of elements within the same period are termed chemical fractionation spectra

paleogeography of the matapedia basin in the gaspe appalachians initiation of the gaspe belt successor basin the matapedia basin consists of the uppermost ordovician lowermost silurian deep water fine grained carbonate siliciclastic rocks of the honorat garin formation and matapedia groups pabos and white head formations the lower rock assemblage of the gaspe belt in the gaspe appalachians paleogeographic maps of eight time slices from the caradocian to the llandoverian are presented to better understand the tectonosedimentary evolution of the matapedia basin deposition evolved from siliciclastic garin fm to argillaceous limestones pabos fm to limestones white head fm the overall change from terrigenous garin fm to limestone facies white head fm reflects a change in the source area paleocurrent directions and composition of sandstones indicate an orogenic source area to the south for the garin formation which is believed to be the inliers of the humber and dunnage zones in the southern gaspe and new brunswick appalachians lime muds deposited by turbidity currents coming from the nor

development of inverted metamorphic gradient in the internal domain of the taconian belt gaspe peninsula the mont logan nappe is part of the taconian internal domain of the quebec appalachians and is entirely made up of synrift to passive margin elastics and volcanics of the shickshock group rocks o

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

atacamite formation by deep saline waters in copper deposits from the atacama desert chile evidence from fluid inclusions groundwater geochemistry tem and 36 cl data the presence of large amounts of atacamite in oxide zones from ore deposits in the atacama desert of northern chile requires saline solutions for its formation and hyperarid climate conditions for its preservation we investigated the nature and origin of atacamite forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data high resolution mineralogical observations and chlorine 36 36cl data in atacamite from the mantos blancos and spence cu deposits in both deposits the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes the average salinity of fluid inclusions in atacamite for the mantos blancos and spence deposits 7 9 and 2 3 wt nacleq respectively are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits total dissolved solids 5 9 and 1 3 wt nacleq respectively this correlation is confirmed by transmission electron microscopy observations of atacamite bearing samples revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale 36cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry cu deposits from the atacama desert all atacamite samples show very low 36cl to cl ratios 11 10 15 to 28 10 15 at at 1 comparable to previously reported 36cl to cl ratios of deep formation waters and old groundwaters in addition 36cl to cl ratios in atacamite correlate with u and th concentration in the host rocks but are independent from distance to the ocean this trend supports an interpretation of the low 36cl to cl ratios in atacamite as representing subsurface production of fissiogenic 36cl in secular equilibrium with the solutions involved in atacamite formation therefore 36cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old 1 5 ma but that atacamite formation occurred more recently 1 5 ma than suggested in previous interpretations our data provide new constraints on the origin of atacamite in cu deposits from the atacama desert and support the recent notion that the formation of atacamite in hyperarid climates such as the atacama desert is an ongoing process that has occurred intermittently since the onset of hyperaridity

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

stratigraphy depositional setting and diagenetic history of the saint jules formation upper devonian or mississippian a newly identified post acadian red clastic unit in the southern gaspe peninsula quebec the saint jules formation a post acadian continental clastic unit previously mapped as part of the bonaventure formation pre namurian unit was recently identified in the southern gaspe peninsula of quebec the saint jules formation in the study area is confined to a small post sedimentary graben the unit is characterized by fault controlled oxidized and poorly sorted detritus that underwent short transportation by fluvial processes the saint jules formation is locally overlain by a massive groundwater calcrete several metres in thickness which is tenta tively correlated with the calcretization event that has affected the base of the la coulee formation grey clastics pre namurian unit the calcrete has developed within the karstified upper beds of the saint jules formation which brings new insights into the potential hosts of such calcretes and on the potential stratigraphic confusion that such diagenetic overprints can create partial erosion of both the la coulee and saint jules clastic rocks as well as the mas sive groundwater calcretes occurred prior to deposition of the bonaventure formation like the la coulee and bonaventure formations the saint jules is undated but unconformably overlies acadian structures middle devonian and predates mabou group units namurian

analysis of supergene ore forming processes and ground water solute transport using mass balance principles analysis of metal distribution in weathering profiles developed above ore deposits provides a simple and direct method to determine the geologic controls on surficial leaching and enrichment of metals by supergene descending fluids this approach offers an understanding of the interrelationships of metal concentration zone thicknesses and bulk rock density of the various zones within a weathered rock column analytical solutions to mass balance equations provide expressions describing the chemical evolution paths of enrichment blanket metal grade b in terms of original protore metal grade p leached zone metal grade 1 and the ratio of total leached zone column height to blanket thickness l o t b neglecting density terms for the sake of simplicity this function is expressed as b p l o t b p 1 linear data arrays in the coordinate system b versus p 1 for groups of drill holes in individual geologic domains e g wall rock types strongly suggest that enrichment blanket metal grades evolve from a protore metal grade p with a fairly constant slope of l o t b to a final value b determined by the extent of metal leaching in the zone of oxidation the constancy of the ratio l o t b within geologic domains indicates a simultaneous deepening of the zone of oxidation and thickening of the enrichment blanket under conditions of a descending ground water table analysis of metal mass balance in drilling profiles also provides a means of reconstructing paleosurficial topography at the time of active oxidation even in highly eroded terrains application of these methods using rock density and assay data from the butte district of montana shows the paleo oxidation surface to have been eroded by as much as 450 ft down to the present unconformity between weathered bedrock and overlying tertiary gravels geomorphic stability and slow erosion rates often thought necessary for effective chemical weathering are therefore questioned we propose instead a general balance of rates of erosion and descent of the ground water table for optimal enrichment preservation of the fossil weathering profiles occurs by submergence of the zone of oxidation below the paleoground water table resulting in cessation of supergene oxidation and preservation of the blanket the mass balance methods derived in this study also relate overall leaching efficiency to protore characteristics showing a strong hypogene alteration control at butte as described by mcclave 1973 lateral copper transport is evaluated by identifying local anomalies in the computed oxidation surface zones of copper introduction near faults and zones of high permeability appear as apparent topographic highs whereas zones of depletion appear as topographic depressions preliminary analysis of this type at the porphyry copper deposit at la escondida chile indicates deeper oxidation and leaching effects than at butte the assumption of vertically homogeneous protore copper grades leads to the conclusion that erosion of at least 200 m of leached capping has occurred throughout much of the la escondida district geologic domains defined by computed values of l o t b correlate well with hypogene alteration zoning computation of the magnitude and direction of overall subsurface lateral metal fluxes indicates transport distances of at least 1 km in directions consistent with present surface topography and fracture patterns there is a strong correlation of the thickest and highest grade enrichment zones with inferred positive lateral fluxes whereas the most thoroughly leached cap rocks make up zones of inferred negative lateral flux which are likely source regions alternative explanations to the lateral flux hypothesis are evaluated including assessment of variations in protore metal grade projections both in vertical and horizontal directions despite the approximations involved in the present calculations the lateral flux pattern appears to be the most likely interpretation of the present metal distribution in the supergene system at la escondida

structural evolution and tectonic significance of the eastern highlands shear zone in cape breton island the canadian appalachians the eastern highlands shear zone in cape breton island of the canadian appalachians is characterized by an amphibolite facies deformation zone over 5 km wide overprinted by a greenschist facies mylonite zone about 1 km wide deformation zones in both metamorphic grades dip steeply to the southeast with movement direction pitching steeply to the southwest and shear sense indicators indicate the same sense of shear that is an east over west dip slip movement with minor sinistral strike slip component deformation in both conditions is constrained to the late silurian to early devonian mainly late silurian it is suggested that the greenschist facies deformation represents the last stage of a single episode of deformation that occurred initially under amphibolite facies conditions the west vergent shearing along the shear zone is antithetic to the westward subduction that led to the silurian continent continent collision which is interpreted by tectonic wedging in this part of the canadian appalachians

geochemical modeling of steady state fluid flow and chemical reaction during supergene enrichment of porphyry copper deposits in this study motivated by detailed field work and laboratory analysis we numerically simulate the supergene enrichment of porphyry copper deposits we utilize a new program developed to model simultaneously advective solute transport in variably saturated porous media and chemical fluid rock interactions incorporating mineral dissolution kinetics field and laboratory analytic and mineralogic data from supergene enrichment systems at butte montana and ok tedi located in western papua new guinea are used to provide geochemical lithologic and hydrologic initial and boundary conditions required for geologically relevant modeling we have simulated the weathering and supergene enrichment of porphyry copper potassium silicate proto ore or protore containing disseminated pyrite and chalcopyrite in a one dimensional vertically oriented flow region under steady flow conditions for a total model time of about 12 000 yr during this time primary chalcopyrite dissolves completely from the leached and blanket zones pyrite is destroyed in the leached zone and magnetite dissolves from the entire flow region we therefore investigate both supergene enrichment processes and the response of the system to complete dissolution of a protore reactant computed mineral assemblages are generally in excellent agreement with those observed in natural systems although copper is remobilized in the simulation by leaching above the model ground water table and reprecipitation below it the resulting differentiated weathering profile is chemically closed with respect to copper this is because nearly all of the transported copper is fixed below the ground water table by secondary sulfide precipitation therefore an important conclusion to be drawn from the modeling is that in natural oxidative weathering vertical copper fluxes out of supergene systems are probably negligible even over extremely long periods of geologic time these theoretical results confirm earlier calculations of amounts of erosion and erosion rates and reconstructions of paleotopography assuming copper mass balance in regions of vertical fluid flow brimhall et al 1985 alpers and brimhall 1988 1989 sulfur in contrast is mobile during the simulation and significant quantities of sulfate leave the flow region with time modeling results indicate that the dominant source of sulfur for secondary copper sulfide mineral formation in the enrichment blanket is the preexisting protore sulfides not electrochemical reduction of the sulfate transported out of the leached zone the numerical simulation demonstrates that oxygen fugacity is the primary control governing the nature and extent of low temperature reequilibration of the fossil magmatic hydrothermal system in the near surface weathering environment

patterns of mineralization and alteration below the porphyry copper orebody at el salvador chile three diamond drill holes angled below the lowest haulage level at el salvador have doubled the vertical exposure of the deposit and revealed very different features of alteration and mineralization below this major porphyry copper orebody sulfide assemblages persist with depth but the total sulfide content diminishes magnetite becomes a part of all sulfide assemblages except very late pyritic d veins residual traces of pyrrhotite chalcopyrite found locked in quartz and as abundant and wide spread inclusions in pyrite apparently represent the remains of an early prograde mineralization obliterated by intense sulfidation of subsequent events relicts of specularite veinlets may be a similar phenomenon vein types change newly recognized early biotitic eb veinlets with and without sulfides quartz albite anhydrite and actinolite have varied alteration halos containing albite k feldspar biotite green sericite anhydrite and andalusite they appear to be deeper equivalents of a quartz veins veinlets descriptively similar to both eb and a quartz veins formed as a second generation within the young intramineral l porphyry complex which truncates similar veinlets in older and better mineralized rocks granular a quartz k feldspar sulfide anhydrite veins diminish in abundance and in content of sulfide and k feldspar with depth and are hard to distinguish from b quartz anhydrite veins with characteristic molybdenite the latter have much better developed k feldspar alteration halos than seen above younger g sulfide veins with green sericite biotite and anhydrite and halos with green sericite alkali feldspar and andalusite cut b veins they are older than relatively sparse d pyrite quartz veins with sericite pyrite calcite anhydrite halos and occasional tourmaline pervasive sericite chlorite in the pyritic fringe terminates downward and biotitic alteration of andesite diminishes revealing more restricted and residual actinolite hornfels ilmenite and then sphene appear as residual accessory minerals and minor vein constituents minor andalusite with alkali feldspar extends to deepest exposures mostly within halos of b and c veins traces of corundum and cordierite occur with andalusite

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

p and sv velocity structure of the south portuguese zone fold and thrust belt sw iberia from traveltime tomography imaging the architecture of the shallow crust of the south portuguese zone fold and thrust belt is essential to extend surface mapped geological information to depth and to help in developing model

supergene enrichment of copper deposits since the onset of modern hyperaridity in the atacama desert chile supergene enrichment of cu deposits in the atacama desert has played a critical role in making this the prime cu producing province of the world previously this has been believed to have occurred exclusively over a long period from the middle eocene to the late miocene which ended when climatic conditions changed from arid to hyperarid here we report u series disequilibrium ages in atacamite bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the atacama desert 230th 234u ages of gypsum intergrown with atacamite in supergene veins from cu deposits cluster at 240 ka chuquicamata 130 ka mantos blancos spence and 80 ka mantos de la luna michilla when coupled with previous data these results indicate that supergene enrichment of cu deposits did not cease after the onset of hyperaridity we propose that supergene enrichment in the atacama region developed in two main stages the main phase caused by downward circulation of meteoric waters in a semi arid setting was active from 45 until 9 ma with a last pulse ca 5 ma in the southern atacama desert during this phase atacamite bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water this was followed by a second stage starting at 2 1 5 ma and continuing until at least the late pleistocene when deep formation waters derived from the basement passed up through and modified the pre existing supergene cu oxide minerals atacamite has then been preserved in the prevailing hyperarid climate

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

a special issue devoted to porphyry copper deposits of northern chile chile is known worldwide as the site of one of the largest copper concentrations on earth a total resource including production of about 400 million tons mt of fine copper has been identified in 50 porphyry copper deposits and numerous prospects fig 1 considering 10 mt of contained fine copper as a minimum tonnage to classify a porphyry copper deposit as a giant ore deposit the chilean cordillera contains nine of the 16 giant porphyries along the circum pacific belt among them are the three largest of all el teniente rio blanco los bronces and chuquicamata fig 1 all containing resources plus production of more than 50 mt of fine copper currently chile annually produces about 4 6 mt of fine copper that represents about 37 percent of the world production this enormous geologic potential has triggered numerous international mining companies to concentrate their exploration efforts in the central andes with emphasis in chile during the past 25 years exploration expenditures have surpassed a figure on the order of us 2 billion as a result a total of 76 copper and gold discoveries have been made 24 of which are already in production cabello 2000 among them the most relevant discoveries are the porphyries at la escondida escondida norte zaldivar rosario and ujina in the collahuasi mining district quebrada blanca lomas bayas and in the last 5 years spence and gaby sur the presence of such a significant number and large size of copper porphyries intrigued several generations of researchers during the twentieth century the ongoing exploration efforts have enhanced the interest in understanding the andean geological evolution and metallogenesis the geological processes that are common factors in controlling the emplacement of these orebodies have been the subject of research by numerous individuals in chile and elsewhere the support of mining companies has been

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

carbonate sedimentation in an extensional tectonic regime the lower devonian upper gaspe limestones quebec appalachians carbonate sedimentation occurred over most of eastern gaspe peninsula in early devonian time the resulting succession known as the upper gaspe limestones is a 500 1800 m thick unit outcropping in the connecticut valley gaspe synclinorium detailed stratigraphic and sedimentologic work allows recognition of important thickness and lithofacies variations in a north south oriented transect in the eastern part of the peninsula variations are spatially associated with acadian middle devonian dextral strike slip faults three lithotectonic domains are proposed and interpreted they are from north to south 1 a proximal outer shelf 2 a distal gently sloping outer shelf and 3 a slope or slope toe field mapping and reinterpretation of seismic profiles from this area have shown that the faults bounding the three domains are reactivated normal listric faults early devonian vertical movement along these faults caused accelerated subsidence of the central and southern segments of the sedimentary ba

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

late silurian early devonian transpressional rift origin of the quebec reentrant northern appalachians constraints from geochemistry of volcanic rocks silurian devonian rocks in the northwestern mainland appalachians form part of an overstep sequence deposited across the vestiges of iapetus after the collision of laurentia and gondwana they occur in three synclinoria gasl connecticut valley merrimack aroostook and fredericton synclinoria separated by two anticlinoria munsungun pennington boundary mountain bronson hill and miramichi silurian rocks in gasp6 connecticut valley and merrimack aroostook synclinoria consist of shelf and trough sediments derived mainly from laurentia to the northwest with some local contributions from an ephemeral landmass appalaclfia and from the miramiclfi highlands in contrast early devonian rocks in all three synclinoria are mainly flysch derived froxn the southeast in avalonia interbedded volcanic rocks are predominantly late silurian early devonian in age they are generally bimodal with the mafic rocks exhibiting a change from transitional alkalic tholeiitic to tholeiitic around the siluro devonian boundary broadly coincident with the salinic disturbance in the gaspe peninsula the geochemical characteristics of the basalts indicate that they were erupted in a continental intraplate environment with melting migrating upward through time across the garnet to spinel phase boundary as stretclfing increased thermal uplift during rifting is inferred to have led to erosion associated with the salinic disturbance the start of the volcanism appears to coincide with a switch from sinistral to dextral transpression along the orogen that may be related to the change from clockwise to anticlockwise rotation of laurentia relative to gondwana the effects of dextral transpression vary with the trend of the orogen intense deformation and metamorplfism occurred in the central mobile belt opposite the new york and st lawrence promontories whereas rifting developed in the quebec reentrant leading to tlfinning of the crest up welling of the asthenosphere melting and magmatism

bacterially mediated supergene alteration and redistribution of copper in mineralised rocks at the salobo iocg deposit brazil abstract the primary ore at the giant salobo iron oxide copper gold iocg deposit in brazil is dominated by magnetite and fe rich silicates with minor 1 disseminated cu fe sulphides and a distinctive absence of pyrite supergene fe silicate and sulphide oxidation has been mediated by bacteria commonly within micrometre scale acidic environments but silicate dominated acid neutralisation has maintained ambient circumneutral ph supergene cu mobility has been controlled by the highly localised fe dominated biogeochemical processes with cu redistribution on the micrometre to metre scales and negligible supergene cu enrichment silicates especially the phyllosilicates biotite and chlorite have variably altered to the clay minerals vermiculite and or smectite and ultimately to kaolinite leaching of mn fe mg and si accompanied silicate alteration with minor addition of cu to clay mineral structures and along cleavage planes iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite with up to 10 wt cu most cu and mn mobilised in localised acidic environments were precipitated nearby metre scale at circumneutral ph and reflect the immediate supergene biogeochemical environments cu carbonates pseudomalachite chrysocolla and cu mn oxides copper wad the early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron oxidising strain of acidithiobacillus ferrooxidans previously cultured from the salobo site bacterially mediated precipitation of ferrihydrite commonly cu bearing in these experiments strongly resembles that seen in the natural outcrops these leaching experiments confirmed the effectiveness of silicate dominated acid neutralisation especially when accompanied by bornite oxidation which is also acid consuming in contrast chalcopyrite oxidation is acid producing and leads to more effective localised cu mobility in solution our combination of field and laboratory observations at the salobo iocg deposit shows that the biogeochemical environment dominated by fe silicates with little sulphides typical for these systems has led to an entirely different style of supergene cu redistribution from that seen at many other cu deposits such as chalcopyrite and pyrite rich porphyry copper deposits where substantial supergene cu enrichment has occurred

chlorine isotope fractionation recorded in atacamite during supergene copper oxidation abstract in the atacama desert of northern chile large amounts of the copper hydroxy chloride mineral atacamite cu2cl oh 3 are formed in the supergene oxidation zone of cu deposits since atacamite requires saline water to form and is commonly preserved under hyperarid conditions it has been proposed as a climate sensitive mineral marker that can also provide relevant geochemical information regarding halogen in particular chlorine fluid sources during supergene cu oxidation however chlorine stable isotope data for atacamite in cu deposits are scarce and no experimental data for chlorine isotope fractionation between atacamite and water are currently available that could provide constraints on the possible mechanisms of fractionation in this study we report 37cl values of atacamite along a thick 100 m and well developed supergene enrichment profile at the barreal seco iron oxide copper gold iocg deposit in the atacama desert the 37cl values of atacamite along this profile range from 2 1 to 0 6 mean 0 4 0 7 median 0 3 and show a distinct trend with depth characterized by higher 37cl values towards the top of the profile with lower values at the bottom in addition the chlorine isotope compositions of experimentally synthetized atacamite crystals and coexisting cucl2 solutions were determined at room temperature 23 c the per mil fractionation factor 37clatacamite cl was determined at 0 75 showing that the heavy isotope 37cl is preferentially incorporated into atacamite we used numerical models to test two possible scenarios that might explain the observed 37cl profile at barreal seco a first scenario involves lowering of the water table with concomitant precipitation of atacamite which removes cl from solution following a rayleigh fractionation process this model qualitatively fits our observations but does not explain the full magnitude of the observed 37cl shift along the supergene profile in contrast a model that simulates cl diffusion following the upward injection of a deep brine that overlies fresh groundwater reproduces well the observed 37cl data suggesting that seismic pumping of basinal brines followed by cl diffusion is a feasible mechanism to explain the formation of atacamite at barreal seco these data are a first step towards interpreting 37cl profiles of atacamite in cu deposits in the atacama desert and exploring the potential use of stable chlorine isotopes to monitor cu weathering and enrichment in supergene environments

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

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

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

a lost arc back arc terrane of the dunnage oceanic tract recorded in clasts from the garin formation and mccrea melange in the gaspe appalachians of quebec upper ordovician garin conglomerates base of the gaspe belt quebec appalachians contain three igneous clast populations 1 calc alkaline intermediat felsic rocks resemble exploits new brunswick maine and notre dame quebec newfoundland subzone lavas clasts monzonite rhyodacite give u pb zircon ages between 465 and 466 ma precluding correlation with exploits rocks we suggest that the suite represents peri laurentian continental arc magmas coeval with the red indian lake group of newfoundland correlation of lavas from a gaspe well with the popelogan arc implies that the red indian line passes through southern gaspe 2 mafic tholeiitic to alkaline clasts resemble new brunswick and maine exploits subzone alkaline lavas we interpret them as magmas associated with initiation of a back arc basin possibly on the laurentian margin 3 mafic intermediate tholeiitic to calc alkaline clasts have an oceanic subduction component and correlate with notre dame subzone lavas quebec newfoundland they are interpreted as products of spreading and off axis magmatism of a peri laurentian back arc basin we correlate mccrea melange lavas to the calc alkaline intermediat felsic and mafic intermediate suites and interpret them as samples of a notre dame subzone terrane coeval with the red indian lake group of newfoundland during initiation of a successor arc back arc a terrane which is no longer preserved in new brunswick and maine but that provides some evidence for possible extensions of newfoundland9s geology into the gaspe appalachians of quebec a mid ocean ridge basalt like intrusion in the mccrea melange ar ar age 471 2 11 2 ma is coeval with peri laurentian ophiolites in newfoundland and may record a back arc opening event

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