the hydrogeological and contaminant transport properties of fractured champlain sea clay in eastern ontario part 1 hydrogeological properties hydrogeological and geochemical investigations were conducted on four fractured champlain sea clay deposits in eastern ontario the results from water level monitoring maximum seasonal variations and hydraulic head profiles revealed a hydraulically active fractured zone existing at all four sites the depth of this fractured zone varies from site to site ranging from 3 2 to 6 0 m slug test analysis indicated that bulk hydraulic conductivity values in the upper fractured zone range from 1 8 10 8 to 2 0 10 5 m s in contrast the measured hydraulic conductivity values from the deepest piezometers range from 8 2 10 10 to 1 4 10 9 m s the geochemical analysis indicated the presence of three hydrochemical facies a shallow active facies a deep inactive facies and an intermediate transition facies the presence of tritiated groundwater well below the groundwater table indicates that the upper fractured zone at all four sites is hydraulically active key words fractures champlain sea clay

shear wave splitting in northeast venezuela trinidad and the eastern caribbean abstract we present new measurements of splitting of core shear wave phases sks skks pks recorded at seven stations in the eastern caribbean region six stations in northeastern venezuela and trinidad constituted the secasa92 temporary broadband array the seventh station sjg is installed on puerto rico we also attempted to measure source side splitting of s waves from earthquakes in the lesser antilles subducted slab but with little success mean splitting parameters fast polarization direction and delay time t at the stations are consistently east west trending and over 1 s respectively delay times at the secasa92 array are amongst the highest yet measured reaching 2 1 s and generally over 1 5 s we note an approximately linear decrease in delay times here from maxima at the northernmost stations to a minimum at the southernmost the secasa92 array is situated in the wide south america caribbean sa ca plate boundary zone and sjg is within the north america caribbean na ca plate boundary zone in both cases trends are parallel to the plate boundary zones locally we interpret these results to indicate that the sa ca plate boundary deformation extends to depths of at least 200 km and that south american crust lithospheric mantle and asthenosphere are coherently deformed the extreme delay times we measure are probably the result of transpression in the sa ca plate boundary and overriding of the lesser antilles slab by south america compressional flattening results in extremes of foliation development and dextral shearing yields a strong lineation in upper mantle olivine by contrast the delay time at sjg 1 2 s is near the global average and reflects the fact that the na ca plate boundary zone is purely sinistral or includes minor transtension we note that recent counterclockwise rotation of puerto rico does not apparently affect upper mantle deformation beneath the island we suggest that this rotation is crustal driven by far field sinistral shear and partly decoupled from the mantle shear our results are consistent with the trench parallel mantle flow hypothesis russo and silver 1994 science 263 1105 1111 and indicate that asthenospheric mantle flow beneath the caribbean plate is eastward and probably drives the plate s eastward motion

spectral analysis of gravity anomalies and the architecture of tectonic wedging ne venezuela and trinidad we have analyzed the spectral content of free air gravity anomalies in the caribbean south american plate boundary zone in order to determine better the near surface 0 120 km distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region the plate boundary zone in northeastern venezuela and trinidad is the site of the world s sea level continental minimum of bouguer gravity anomalies yet the region is also one of mild topography mean value 43 m maximum 1200 m we find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone we interpret interfaces at 30 35 km and 32 km beneath the guyana shield and the aves ridge respectively to be the moho other shallow interfaces 5 14 km are most likely sediment cover basement contacts in the maturin foreland basin and southern grenada basin deeper interfaces 54 63 km we associate with loaded and downwarped continental and oceanic south american lithosphere the deepest boundaries at depths of 89 120 km may be related to detached or detaching oceanic lithosphere overridden by continental south america we use our results to test the tectonic wedging model of the plate boundary zone recently published by russo and speed 1992 we find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner guyana shield crust

halogen bearing minerals in syenites and high grade marbles of dronning maud land antarctica monitors of fluid compositional changes during late magmatic fluid rock interaction processes meta sedimentary rocks including marbles and calcsilicates in central dronning maud land cdml in east antarctica experienced a pan african granulite facies metamorphism with peak metamorphic conditions around 830 20 c at 6 8 0 5 kbar which was accompanied by the post kinematic intrusion of huge amounts of syenitic charnockitic magmas at 4 5 0 7 kbar the marbles and calcsilicates may represent meta evaporites as indicated by the occurrence of metamorphic gypsum anhydrite and cl rich scapolite that formed in the presence of saline fluids with x nacl in the range 0 15 0 27 the marbles and calcsilicates bear biotite tremolite and or hornblende and humite group minerals clinohumite chondrodite and humite which are inferred to have crystallized at about 650 c and 4 5 kbar the syenitic intrusives contain late magmatic biotite and amphibole formed between 750 and 800 c as well as relictic magmatic fayalite orthopyroxene and clinopyroxene two syenite and two calcsilicate samples contain fluorite corona textures in the marbles and calcsilicates suggest very low fluid rock ratios during the formation of the retrograde 650 c assemblages biotite in all but two syenite samples crystallized at log f h 2 o f hf ratios of 2 9 0 4 while in the calcsilicates both biotite and humite group minerals indicate generally higher log f h 2 o f hf values of up to 5 2 a few samples though overlap with the syenite values log f h 2 o f hcl derived from biotite covers the range 0 5 2 6 in all rock types within a single sample the calculated values for both parameters vary typically by 0 1 to 0 8 log units water and halogen acid fugacities calculated from biotite olivine orthopyroxene feldspar quartz equilibria and the above fugacity ratios are 1510 2790 bars for h2o 1 3 5 3 bars for hf and 7 600 bars for hcl the results are interpreted to reflect the reaction of relatively homogeneous magmatic fluids in terms of log f h 2 o f hf derived from the late magmatic stages of the syenites with both earlier crystallized still hotter parts of the syenites and with adjacent country rocks during down temperature fluid flow fluorine is successively removed from the fluid and incorporated into f bearing minerals close to the syenite into metamorphic fluorite in the course of this process log f h 2 o f hf increases significantly chlorine preferably partitions into the fluid and hence log f h 2 o f hcl does not change markedly during fluid rock interaction

the 1946 hispaniola earthquakes and the tectonics of the north america caribbean plate boundary zone northeastern hispaniola we have determined focal mechanisms for the largest earthquake ms 7 8 recorded instrumentally in the caribbean basin the august 4 1946 hispaniola earthquake and three of its large magnitude ms 6 1 aftershocks we also relocated 63 aftershocks and one foreshock of the event series the aftershock series is elongate trends wnw and is centered on the samana peninsula of northeast hispaniola shallow aftershocks are in a 75 km wide linear zone and intermediate depth 70 to 130 km aftershocks apparently delineate a moderately south or ssw dipping slab it is not clear however whether these events indicate active subduction of north american atlantic ocean lithosphere or are strike slip events on the interface between subducted but no longer sinking slab and caribbean mantle we constrained focal mechanisms of the main shock and three aftershocks by combining observed p and s polarities and amplitude ratios and also by waveform modeling the two methods yield consistent results the mechanisms include strike slip and thrust displacements on nw striking nodal planes fault dip is variable ne or sw the nw striking fault planes parallel mapped terrane boundaries and faults in the north america na caribbean ca plate boundary zone and are also parallel to the aftershock series trend we interpret the events to be motions on a wnw trending restraining bend segment of the na ca plate boundary in eastern hispaniola we have calculated magnitudes for eight of the earthquakes in the series for the three events including the main shock for which data are available our magnitudes are systematically less than the previously published magnitude estimates given the high magnitude and large aftershock area of the august 4 1946 event these earthquakes probably represent the true long term interplate motions between north america and the terranes in this portion of the plate boundary zone

the sarcheshmeh porphyry copper deposit kerman iran a mineralogical analysis of the igneous rocks and alteration zones including halogen element systematics related to cu mineralization processes abstract the giant sarcheshmeh porphyry copper deposit is located 65 km southwest of kerman city southeastern iran numerous miocene porphyry stocks and dykes intruded thick sequences of upper cretaceous sedimentary and eocene volcanic rocks hypogene and supergene porphyry cu mineralization occurs within the granodioritic porphyry and host rock sequence which was extensively altered to a dominantly potassic phyllic and argillic assemblage with interstitial to distal propylitic types biotite bearing assemblages occur as both primary phenocrysts and secondary replacements showing variable size colour and shape fluorine contents 0 22 to 1 33 wt and x mg 0 54 to 0 71 in biotites from the potassic and phyllic zones are higher than those of non mineralized granitoids f 0 09 to 0 56 wt x mg 0 43 to 0 54 whereas their cl contents cl 0 05 to 0 24 wt are lower than those of the non mineralized granitoids cl 0 11 to 0 45 the biotites from the phyllic zone have higher log f h 2 o f hf and log f h 2 o f hcl values than those of the potassic zone as well as the granitoid and andesitic dykes the log f hf f hcl values determined for the granitoid potassic and phyllic zones are similar though more negative than those of the andesitic dykes the log f hf f hcl values have a similar range for biotite from the granitoid and potassic and phyllic zones the halogen fugacity ratios established for fluids associated with the sarcheshmeh deposit from their f and cl contents in biotite show that the granitoid potassic zone and phyllic zone are increasingly affected by meteoric waters the fluids that circulated in the phyllic zone are predominantly of meteoric origin possibly overprinting original phyllic zone halogen contents the cl intercept values of biotite in the granitoid and phyllic and potassic are similar to other ore forming systems and tend to be more cl rich than cl intercept values of biotites in common igneous rocks calculated f cl intercept values for biotite in the granitoid and potassic zone are also consistent with many other porphyry copper forming systems

aftershock pattern of the july 9 1997 mw 6 9 cariaco earthquake in northeastern venezuela abstract the mw 6 9 cariaco earthquake of july 9 1997 was the strongest earthquake that occurred on the el pilar fault between cumana and the gulf of paria in the 20th century the el pilar fault is the most prominent strike slip fault in the transition zone between the caribbean plate and the south american plate in this region we installed 18 seismic and 10 strong motion stations for recording aftershocks we calculated the hypocenters of 1306 aftershocks with magnitudes between 0 5 and 4 1 most aftershocks concentrated near the documented trace of the el pilar fault the spatial distribution of the aftershocks allowed us to separate the aftershock region on the el pilar fault into six segments with different dip angles we computed and classified fault plane solutions of 222 aftershocks the majority of fault plane solutions are of strike slip type some segments show differences in the dominating type of focal mechanisms from the aftershock distribution and spatial variation of b values we inferred a rupture length of the cariaco earthquake of 60 km and thus an average displacement of 1 3 m during the main shock is estimated two out of four stepovers which were found on this length were seismically activated during the monitoring time interval the b value distribution on the fault plane appears to define two areas of major stress relaxation beneath cariaco and half way between casanay and el pilar close to the surface

quick clay a case study of chemical perspective in southwest sweden quick clay a soil that changes from normal firm ground to a liquid mass when it is disturbed has been involved in most of the large and serious clay slides in sweden norway and canada the location time of occurrence and size of quick clay slides are difficult to predict and large slides may cause great devastation some geochemical studies of swedish quick clay were done in the 1960s and early 1970s but no systematic studies of the interrelationships of pore water chemistry mineralogy geotechnical properties and other parameters on quick clays in sweden have been published such studies are of national and general interest because of the many combinations of rock flour source areas and sedimentation conditions that occurred across central sweden and into the baltic sea area during deglaciation in this study geotechnical properties related to the in situ chemistry at one quick clay site were extensively studied and spot sampling was conducted at two other locations in southwest sweden in this area the clay minerals mainly are non expanding phyllosilicate minerals illite and primary minerals quartz feldspar which is consistent with previous studies of quick clay mineralogy extensive leaching has occurred at all three locations at the extensively studied site surte the lowest salinity was found at the greatest depth inferring that the leaching by fresh water was accomplished by water movement upward and laterally through the sediment from the underlying bedrock this is consistent with the local setting where bedrock hills rise sharply to over 100 m above the marine sediment surface an artesian pressure would also be anticipated at this location there is a correlation negative between sensitivity and salinity but there is an indication that the maximum salinity or electrical conductivity consistent with the quick clay behaviour is higher than reported elsewhere however for high sensitivities the salinity is about the same as reported elsewhere in the deepest part of the borehole there is a higher content of fe and al in the pore water indicating reduced state further work is needed to confirm the difference in salinity and to investigate the possible interplay of salinity and potential dispersing agents such as the role of anoxic conditions in this region further work is especially needed in the locations where the sediment accumulation occurred under lower salinity conditions at all three locations high remoulded shear strength and low sensitivity have been seen near the surface together with a decrease in pore water cation concentrations

a multiscale study of the permeability of a thick clayey till we describe and evaluate two previously undocumented methods of bulk permeability k determination and compare results obtained with results of conventional smaller scale tests on the same thick clayey till deposit analysis of the downward propagation of seasonal water table fluctuations yielded bulk k of approximately 10 10 m s 1 in close agreement with results of laboratory consolidation and permeameter tests slug tests and distribution of vertical hydraulic gradient with depth in the deposit this agreement suggests that for such materials high gradient tests conducted at small scales of distance and time can provide reasonable estimates of bulk k the results also imply groundwater residence times in the till of thousands of years the flow pattern observed near a large excavation in the till was consistent with the initial recoveries of piezometers installed in much smaller boreholes assuming perturbation of hydraulic head in the formation due to borehole excavation time scales of these perturbations which prevent interpretation of measured hydraulic head using conventional well hydraulic methods varied from months to tens of years

origin and movement of groundwater and major ions in a thick deposit of champlain sea clay near montreal at a site near montreal piezometers and core samples were used to assess the origin age and rate of groundwater movement in a 28 m thick deposit of champlain sea clay 3h occurs only within the upper 3 4 m which indicates that groundwater below this surficial weathered zone originated prior to 1952 concentrations of 18o na and cl in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33 seawater and 67 freshwater profiles of several major ions show a gradual increase in concentration with depth mathematical simulations of vertical migration of ca2 mg2 k na and cl provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a when the downward advection rate of 0 13 cm a 1 obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model the simulated major ion profile

mercury intrusion and permeability of louiseville clay several theories have been proposed to correlate the permeability hydraulic conductivity with the pore size distribution of soils and it seemed interesting to determine if these theories could be applied to natural clays for this purpose permeability and mercury intrusion porosimetry tests were performed on a champlain sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42 the results show that for either intact or remoulded soil conditions there is a relationship between the pore size parameters and the permeability of the clay however there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies consequently mercury intrusion porosimetry alone cannot be usepto evaluate the permeability of soils in general plusieurs thkories ont ctc proposces pour corrcler la permiabilite conductivitk hydraulique avec la distribution des grosseurs de pore des sols et il a semblc intiressant de verifier si ces theories pourraient 2tre appliquees aux argiles naturelles a cette fin des essais de permcabilitc et de porosimctrie a intrusion de mercure okt ctc rcaliscs sur l argile de la mer champlain dans des conditions tant intactes que remanikes apris la compression des specimens a des dcformations variant de 0 a 42 les rcsultats demontrent que pour des conditions soit intactes ou remanices il existe une relation entre les paramitres de grosseur de pore et la permcabilitc de l argile cependant il n existe pas de relation unique pour les argiles tant intactes que remanices et pour le limon et l argile ctudics antkrieurement en conscquence la porosimctrie a intrusion de mercure ne peut pas a elle seule tre utilisce pour cvaluer la permcabilitc des sols en general mots clds permcabilitc argile porosimctrie a intrusion de mercure structure traduit par la rcdaction

the major features of the crustal structure in north eastern venezuela from deep wide angle seismic observations and gravity modelling abstract venezuela is located on the plate boundary zone between the south american continent and the caribbean plate a relative movement of 2 cm year is accommodated by a system of strike slip faults running from the andes to the gulf of paria the interior range a moderate height mountain range separates the oriental basin from the caribbean to the south predominantly precambrian rocks are outcropping in the guayana shield south of the orinoco river results of deep wide angle seismic measurements for the region were obtained during field campaigns in 1998 ecoguay for the guayana shield and in 2001 ecco for the oriental basin the total crustal thickness decreases from 45 km beneath the guayana shield to 39 km at the orinoco river and 36 km close to el tigre in the center of the oriental basin the average crustal velocity decreases in the same sense from 6 5 to 5 95 km s detailed information was obtained on the velocity distribution within the oriental basin velocities are as low as 2 2 km s for the uppermost 2 km 4 5 km s down to 4 km in depth and a maximum depth of 13 km was derived for material with seismic velocities up to 5 9 km s interpreted as the base of the sedimentary basin a gravimetric model confirms the structures derived from the seismic data discrete increases in sedimentary thickness along the basin may be associated to extension processes during the passive margin phase in the cretaceous or during earlier extension phases

characteristics of high resolution hydraulic head profiles and vertical gradients in fractured sedimentary rocks summary accurately identifying the position of vertical hydraulic conductivity k v contrasts is critical to the delineation of hydrogeologic units that serve as the basis for conceptual and numerical models of groundwater flow high resolution head profiles have identified the position and thickness of k v contrasts in clayey aquitards but this potential has not yet been thoroughly evaluated in sedimentary rocks this paper describes an experiment in which head profiles with the highest technically feasible resolution were obtained using westbay multilevel systems mls installed in 15 cored holes at three sedimentary rock research sites with contrasting geologic and flow system conditions mlss were installed to maximum depths between 90 and 260 m with 2 5 monitoring zones per 10 m head profiles were measured over multiyear periods the vertical component of hydraulic gradient i e vertical gradient was calculated for each pair of adjacent monitoring intervals in every mls and then categorized based on its repeatability to facilitate interpretation of k v contrasts and comparisons within boreholes between boreholes at the same site and between sites the head and vertical gradient profiles from all three sites display systematic i e simple geometric shapes defined by repeatable intervals of no to minimal vertical gradient indicating relatively high k v units bounded by shorter depth intervals with large up to 50 m m vertical gradients indicating relatively low k v units the systematic nature of the profiles suggests flow in regular and interconnected fracture networks rather than dominated by a few key fractures with irregular orientations the low k v units were typically thin with their positions and thicknesses not predicted by lithostratigraphy or detailed lithologic geophysical and horizontal hydraulic conductivity data hence the position and thickness of units with contrasting k v would not be evident if mlss with the conventional number of monitoring zones had been used furthermore the detailed profiles can be strongly diagnostic of hydrogeologic unit boundaries or layers and can be used to improve the quantitative assessment of flow system conditions that is foundational to understanding contaminant plume migration

historical seismicity of the southeastern caribbean and tectonic implications we have relocated the twenty eight largest magnitude 4 3 ms 7 3 historical 1922 1963 earthquakes of the southeastern caribbean we also present new focal mechanisms for seven of these events the relocations are based on reported issp ands arrival times that we analyzed using generalized linear inversion techniques the new focal mechanisms were constrained by first motionp polarities as reported by the iss and as picked by us where records were available and by the polarities and ratios ofsh andssh andsv andssv arrivals that we determined from seismograms the results of the relocations are commensurate with the distribution of seismicity observed in the recent era hypocenters are shallow and intermediate in depth 0 200 km and the events occur almost exclusively in areas known to be currently seismic the frequent seismic activity in the vicinity of the paria peninsula venezuela is clearly a persistent feature of the regional earthquake pattern intermediate depth earthquakes indicative of subduction beneath the caribbean plate occur here and along the lesser antilles arc the grenadines seismic gap is confirmed as an area of low seismic moment release throughout the historical era trinidad and the eastern gulf of paria were also largely quiescent

p wave velocity tomography of the venezuelan region from local arrival times arrival times from the local seismological network of venezuela were used to estimate a three dimensional p wave velocity model for the region between longitude 60 74 w and latitude 6 14 n to a depth of more than 80 km the inversion was carried out by damped least squares describing the media by homogeneous velocity blocks the resolved lateral velocity variations in the first layer 0 30 km depth showed a correlation with the main stratigraphic features of the area while second layer 30 50 km depth showed the influence of moho depth variations through the region generating a pattern well correlated to the bouguer anomaly map lithospheric seismic velocities below the moho appear to be influenced by the major crustal fault systems an important low velocity zone is present below the triple junction of the fault systems of oca bocono and moron in northwestern venezuela farther south a similar low velocity zone is present below the junction of the bocono and the santa marta fault systems those are the two continental corners of the triangular maracaibo block below 80 km depth the fourth layer the low velocity zones show a connected pattern that follows or is adjacent to the crustal fault zones the presence of subducted atlantic lithosphere below the eastern venezuelan basin could explain the high velocity zone at this location a similar interpretation emerges from the tectonic wedging model previously proposed to explain the pronounced minimum of the gravity anomaly

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

mineralogy chemistry and physical properties interrelationships of some sensitive clays from eastern canada this paper describes the use of quantitative mineralogy and specific surface area in interpreting the index properties of clayey soils from nine sites in eastern canada samples representative of t

influence of porefluid salinity on instability of sensitive marine clays a new approach to an old problem the geographic association between earthflow occurrence sensitivity of the sediment and salinity of the interstitial fluid has been examined in an area of exposed marine champlain sea deposits in the lachute region northwest of montreal quebec mapping of earth resistivity as a means of calculating porefluid salinity revealed that areas of large earthflows 20 ha coincided with sediment of very low porefluid salinity earthflow scars were absent from intervening areas of higher salinity 5 gl 1 mapping of the thickness of the clay deposit by seismic refraction showed furthermore that low porefluid salinity occurred only in areas of relatively thin 25 m deposits resting upon more permeable drift or rock finally laboratory tests confirmed that high sensitivity was restricted to areas of low porefluid salinity the study thus provides a geomorphological verification of the importance of salt depletion as a prerequisite for earthflow occurrence and by implication presents mapping of porefluid salinity as a method of delineating zones which should be safe from landslide retrogression in this type of sediment

structure and deformation history of the northern range of trinidad and adjacent areas conflicting models have been proposed for both the evolution of northern south america and the neotectonics of the south caribbean plate boundary zone the trinidadian portion of the margin is particularly controversial but surprisingly it has been little studied we present a structural analysis of trinidad s northern range pertinent updates of the island s stratigraphy and sedimentology and new zircon fission track age determinations and use them to constrain trinidad s geologic history and to better understand the controlling tectonic processes in our interpretation trinidad s three e ene striking ranges which are separated by late neogene recent depocenters expose 1 the northern range group generally greenschist metamorphosed upper jurassic to cretaceous north facing continental slope sediments of the northern range deposited on the northern south american passive margin 200 400 km to the wnw and 2 the trinidad group cretaceous paleogene shelf slope sediments of the central and southern trinidad deposited less than 100 km wnw of their present location a small allochthon composing the sans souci group cretaceous tholeiitic volcaniclastic basaltic and gabbroic rocks sans souci formation and sediments toco formation now in the northeastern northern range has been transported hundreds of kilometers from the west with the caribbean plate despite earlier references to cretaceous orogenesis all deformation in trinidad is of cenozoic age the first deformation in the northern range d1 formed north vergent nappes and induced greenschist metamorphism probably in the late eocene or oligocene the nappes developed either by the underthrusting of the proto caribbean crust beneath south america due to convergence between north and south america or as gravity slides caused by oversteepening induced by this convergence and or the passage of the caribbean plate s peripheral bulge and arrival of its foredeep northern range d2 deformation is south vergent and represents the incorporation of northern range metasediments into the caribbean accretionary prism the transition to d3 brittle transpressive right lateral strike slip faulting is interpreted to be due to the uplift and east southeastward transpressive emplacement of northern range caribbean prism rocks onto the south american stepped shelf this emplacement formed the miocene transpressive thrust belts and foreland basin in central and southern trinidad in the final phase of northern range deformation d4 e w normal faults and shear zones and conjugate nnw sse and ne sw normal faults developed and displacement on preexisting e w right lateral strike slip faults continued the 11 ma northern range zircon fission track ages suggest rapid uplift from the late miocene to recent late miocene subsidence of the tobago platform immediately to the north of the northern range and greater than 3 km of normal down to the north displacement indicated for the north coast fault zone separating the northern range and tobago platform leads us to postulate that the rapid uplift of the northern range was in response to the northward detachment of the tobago platform from above the northern range along the north dipping transtensional north coast fault zone this late miocene change in deformation style can be explained by a change from caribbean south american right lateral transpression to right lateral strike slip generally striking 080 this has generally induced a component of extension on pre existing faults striking at greater than 080 and a component of compression on faults striking at less than 080

origine de la preconsolidation des argiles du saguenay quebec the clays of eastern canada and in particular the saint jean vianney clay in the saguenay region have often been described as clays with a preconsolidation due partly to cementation in order to check this assumption the geological history and the geomorphology of the saguenay region have been analyzed further to the evidence of significant erosion available geotechnical data in the form of variations of water content undrained shear strength and preconsolidation pressure have been analyzed to determine the elevation of the original ground surface in the hypothesis of a preconsolidation resulting from deposition and erosion the results of this analysis are in good agreement with the geological and geomorphological data and they suggest that cementation has had a negligible effect on the preconsolidation of the saguenay clays a regional map of preconsolidation pressures is also presented keywords clay preconsolidation geomorphology erosion shear strength journal translation

probabilistic seismic hazard assessment at the eastern caribbean islands a probabilistic seismic hazard analysis has been performed to compute probabilistic seismic hazard maps for the eastern caribbean region 10 n 19 n 59 w 64 w which includes in the north the leeward islands from anguilla to dominica and in the south the windward islands from martinique to grenada barbados trinidad and tobago the analysis has been conducted using a standard logic tree approach that allowed systematically taking into account the model based i e epistemic uncertainty and its influence on the computed ground motion param eters hazard computations have been performed using a grid of sites with a space resolution of 0 025 degrees covering the territory of the considered islands two different computation methodologies have been adopted the standard cornell mcguire approach cornell 1968 mcguire 1976 based on the definition of appropriate seismogenic zones sz and the zone free approach developed by woo 1996 which overcomes the ambiguities related with the definition of seis mic sources the interplay and complexities between shallow crustal intraplate and interface subduction seismicity of the caribbean region have been thoroughly investigated by merging all available databases a comprehensive and updated earthquake catalog for the region has been compiled also a thorough investigation has been undertaken to identify the most suitable ground motion prediction equa tions to be used in the analyses uniform hazard spectra have been calculated for the horizontal component of ground motion rock and level site conditions 4 return periods rp 95 475 975 and 2475 yr and 22 spectral accelerations sa with structural periods ranging from 0 to 3 s sas at 0 2 and 1 0 s for 2475 yr rp have been calculated to allow the definition of seismic hazard in the region of study according to the international building code ibc international code council icc 2009

hydraulic transience and the role of bedding fractures in a bedrock aquitard southeastern wisconsin usa 1 hydraulic heads in a dolomitic shale bedrock aquitard in wisconsin usa are apparently not in equilibrium with drawdown in the underlying aquifer system caused by pumping for municipal supply over the last century measurements of head with depth downhole geophysical logs and estimates of hydraulic conductivity indicate very low vertical hydraulic diffusivity and show that high horizontal permeability within the aquitard due to bedding plane fracture zones can allow lateral groundwater flow unlike the hydrogeological conceptual models used in many investigations flow in aquitards cannot always be inferred to be primarily one dimensional and vertical failure to account for transient conditions and lateral flow in similar settings of intensive groundwater pumping could lead to error in estimates of aquitard leakage and underlying aquifer properties

evolution of the grenada and tobago basins and implications for arc migration abstract the tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood this paper presents an integrated stratigraphic and tectonic evolution of late cretaceous to recent volcanic arcs and associated basins in the southeastern caribbean sea using seismic reflection data wide angle seismic refraction data well data and onland geologic data we propose a new tectonic model for the opening of the grenada and tobago basins and the 50 250 km eastward jump of arc volcanism from the late cretaceous aves ridge to the miocene to recent lesser antilles arc in the southeast caribbean based on the mapping of three seismic megasequences the striking similarity of the half graben structure of the grenada and tobago basins that flank the lesser antilles arc their similar smooth basement character their similar deep marine seismic facies and their similar paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single saucer shaped oceanic crust paleogene forearc basin adjacent to the now dormant aves ridge this single forearc basin continued to extend and widen through flexural subsidence during the early to middle eocene probably because of slow rollback of the subducting atlantic oceanic slab rollback may have been accelerated by oblique collision of the southern aves ridge and southern lesser antilles arc with the south american continent uplift and growth of the southern lesser antilles arc divided the grenada and tobago basins by early to middle miocene time inversion of normal faults and uplift effects along both edges of the lesser antilles arc are most pronounced in its southern zone of arc collision with the south american continent the late miocene to recent depositional histories of the grenada and tobago basins are distinct because of isolation of the grenada basin by growth and uplift of the neogene lesser antilles volcanic ridge

assessing the flow regime in a contaminated fractured and karstic dolostone aquifer supplying municipal water the silurian dolostone bedrock in ontario canada is a broad 400 km long swath northward from niagara falls through the bruce peninsula that represents an important water source for municipal industrial and agricultural uses where the quaternary overburden is thin or absent karst is common this study concerns an urban area where the dolostone aquifer is 100 m thick beneath up to 50 m thick quaternary deposits and where karst features identified by borehole information are common hydraulic tests show moderate to large bulk rock hydraulic conductivity and rock core tests indicate much smaller matrix hydraulic conductivity than the bulk rock values therefore the aquifer is essentially a dual permeability fully saturated system in which conduits occur within a network of ubiquitous extensive horizontally and vertically interconnected fractures karst features are concentrated in a thin zone at the top of rock likely representing former epikarst and also in a thicker zone in the middle of the aquifer some pumping test results and large yields of some municipal wells are consistent with conduit occurrences however atmospheric tritium distributed source contamination cl view the mathml source and a point source pesticide plume metolachlor show detailed concentration distributions lacking influence of flow in conduits detailed hydraulic head profiles also show no influence of conduit flow this study shows that when designing monitoring networks for groundwater quality and source water protection in similar contexts locating conduits is not necessary because contaminant distributions are governed by the combined influences of the rock matrix fractures and conduits the hydraulic boundary conditions and the interconnected fracture network with only minimal conduit effects prior to glaciations an integrated karstic aquifer could develop with flow controlled by conduits however this original converging flow system became non functional when the quaternary sediments drastically modified the boundary hydrologic conditions and the head distribution

source processes of large m 6 5 earthquakes of the southeastern caribbean 1926 1960 we have conducted body waveform modeling studies of 13 historic earthquakes to provide a better understanding of the long term spatial and temporal pattern of seismicity and deformation within a region extending from barbuda lesser antilles to cumana venezuela our results suggest that shallow earthquakes 50 km deep along the south american caribbean plate margin reflect right lateral and extensional deformation intermediate depth events 100 km show left lateral strike slip motion beneath the paria peninsula of venezuela in the lesser antilles the 1960 barbuda and 1946 martinique earthquakes appear to be interplate thrust events however the greatest moment release in the region has occurred at intermediate depths as a mixture of normal and strike slip faulting generally along trends oblique to the arc the deformation rate estimated from the seismic moment release between 1926 and 1960 is only 1 to 10 of the estimated plate convergence rate for the region

crustal structure of the caribbean northeastern south america arc continent collision zone 1 we present the results of a 568 km long regional wide angle seismic profile conducted in the southeastern caribbean that crosses an active island arc a remnant arc two basins possibly floored by oceanic crust an allochthonous terrane of forearc affinity and the passive margin of northern south america the velocity structures of the late cretaceous aves ridge remnant arc and miocene and younger lesser antilles arc are remarkably similar which implies that magmatic processes have remained moderately steady over time crustal thickness is 26 km at the aves ridge and 24 km at the lesser antilles arc in comparison to the izu bonin and aleutian arcs the lesser antilles arc is thinner and has no evidence for a lower crustal cumulate layer which is consistent with the estimated low magma production rates of the lesser antilles arc crustal thickness beneath the grenada and tobago basins is 4 10 km and the velocity structure suggests that these basins could be floored by oceanic crust a decrease of 1 km s in average seismic velocity of the upper crust is observed from nw to se across the north coast fault zone we argue that this marks the suture between the far traveled caribbean arc and the passive margin of the south american continent current strike slip motion between the caribbean and south american plates is located 30 km to the south and thus material originally deposited on the south american passive margin has now been transferred to the caribbean plate

tectonic inversion in the caribbean south american plate boundary gps geodesy seismology and tectonics of the mw 6 7 22 april 1997 tobago earthquake on 22 april 1997 the largest earthquake recorded in the trinidad tobago segment of the caribbean south american plate boundary zone mw 6 7 ruptured a shallow 9 km ene striking 250 azimuth shallowly dipping 28 dextral normal fault 10 km south of tobago in this study we describe this earthquake and related foreshock and aftershock seismicity derive coseismic offsets using gps data and model the fault plane and magnitude of slip for this earthquake coseismic slip estimated at our episodic gps sites indicates movement of tobago 135 6 to 68 6 mm nne and subsidence of 7 9 to 0 mm this earthquake was anomalous and is of interest because 1 its large component of normal slip and ene strike are unexpected given the active e w dextral shearing across the caribbean south american plate boundary zone 2 it ruptured a normal fault plane with a low 28 dip angle and 3 it reactivated and inverted the preexisting tobago terrrane south america ocean continent thrust boundary that formed during early tertiary oblique plate convergence

slope instability and valley formation in canadian soft clay deposits the purposes of the paper are to examine the deepening of valleys in clay deposits of eastern canada and in particular to look at the changes in the groundwater regime and slope stability conditions during valley formation field observations and laboratory testing indicate that the rate of valley deepening in champlain clay deposits is of the order of only a few millimetres a year owing to the low erodibility of the intact clay the clay banks are however more erodible owing to alteration and fissuration the stratigraphy of eastern canadian clay deposits can be simplified by considering it to be a stratum of low permeabilityconfined between two boundary layers of relatively high permeability which are the till layer at the base and a weathered crust or coarse grained layer at the top as the valley bottom get closer to the bottom till layer the groundwater regime and consequently the stability conditions are modified during the process of valley formation the groundwater regime passes through a

timing and duration of north american glacial lake discharges and the younger dryas climate reversal abstract radiocarbon dated sediment cores from the champlain valley northeastern usa contain stratigraphic and micropaleontologic evidence for multiple high magnitude freshwater discharges from north american proglacial lakes to the north atlantic of particular interest are two large closely spaced outflows that entered the north atlantic ocean via the st lawrence estuary about 13 200 12 900 cal yr bp near the beginning of the younger dryas cold event we estimate from varve chronology sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0 1 sv 1 sverdrup 106 m3 s 1 the second outflow lasted about a century with a sustained discharge sufficient to keep the champlain sea relatively fresh for its duration according to climate models both outflows may have had sufficient discharge duration and timing to affect meridional ocean circulation and climate in this report we compare the proglacial lake discharge record in the champlain and st lawrence valleys to paleoclimate records from greenland ice cores and cariaco basin and discuss the two step nature of the inception of the younger dryas

estimation of the intrinsic absorption and scattering attenuation in northeastern venezuela southeastern caribbean using coda waves northeastern venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short period seismic network the studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters coda q 1 q c 1 has been obtained using the single scattering theory the contribution of the intrinsic absorption q i 1 and scattering q s 1 to total attenuation q t 1 has been estimated by means of a multiple lapse time window method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers results show significant spatial variations of attenuation the estimates for intermediate depth events and for shallow events present major differences this fact may be related to different tectonic characteristics that may be due to the presence of the lesser antilles subduction zone because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc

retrogression of staurolite schists and the sources of infiltrating fluids during metamorphism staurolite kyanite schists from the dalradian of scotland and ireland show two types of retrograde alteration in the irish examples staurolite and kyanite are replaced by muscovite and paragonite often with margarite and sometimes chloritoid plagioclase in these samples may be albitized in contrast one scottish sample shows replacement of both staurolite and plagioclase by muscovite retrogression resulted from infiltration of fluid but while in some samples the large number of retrograde phases internally buffered the fluid composition and cation metasomatism cannot be proven in others the fluid composition was externally controlled and there was cation metasomatism indicating more extensive infiltration it is demonstrated by the use of activity diagrams showing the relationships between al silicate white mica and alkali feldspar that wholesale alteration to muscovite was most likely caused by fluids moving down temperature from a granitic or arkosic source in contrast if growth of retrograde albite is actually accompanied by na metasomatism then the infiltrating fluids are likely to have been moving up temperature through pelitic lithologies large fluid rock ratios of around 10 1 are needed to achieve significant alkali metasomatism except in extreme situations of large temperature changes and highly concentrated fluids

on the long term hydraulic gradient in the thick clayey aquitard in the sarnia region ontario much of the southwestern part of ontario between lake huron and lake erie has a thin freshwater aquifer overlain by an aquitard of late pleistocene clayey glaciolacustrine deposits and underlain by

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

chronostratigraphy and tectonostratigraphy of the columbus basin eastern offshore trinidad the columbus basin forming the easternmost part of the eastern venezuela basin is situated along the obliquely converging margins of the caribbean and south american plates the two primary structural elements that characterize the basin are 1 transpressional northeast southwest trending anticlines and 2 northwest southeast oriented down to the northeast extension normal faults the basin was filled throughout the pliocene and pleistocene by more than 40 000 ft 12 200 m of clastic sediment supplied primarily by the paleo orinoco delta system the delta prograded eastward over a storm influenced and current influenced shelf during the pliocene pleistocene depositing marine and terrestrial clastic megasequences as a series of prograding wedges atop a lower pliocene to pre pliocene mobile shale facies biostratigraphic and well log data from 41 wells were integrated with thousands of kilometers of interpreted two dimensional and three dimensional seismic data to construct a chronostratigraphic framework for the basin as a result several observations were made regarding the basin s geology that have a bearing on exploration risk and success 1 megasequences wedge bidirectionally 2 consideration of hydrocarbon system risk across any area requires looking at these sequences as complete paleofeatures 3 reservoir location is influenced by structural elements in the basin 4 the lower limit of a good quality reservoir in any megasequence deepens the closer it comes to the normal fault bounding the wedge in a proximal location 5 reservoir quality of deep marine strata is strongly influenced by both the type of shelf system developed bypass or aggradational and the location of both subaerial and submarine highs and 6 submarine surfaces of erosion partition the megasequences and influence hydrostatic pressure migration and trapping of hydrocarbons and the distribution of hydrocarbon type begin page 1906

differential response of zircon u pb isotopic systematics to metamorphism across a lithologic boundary an example from the hope valley shear zone southeastern massachusetts usa a detailed morphological chemical and isotopic study of zircons from a single outcrop of two mineralogically and chemically distinct units of the late precambrian ponaganset gneiss was undertaken to investigate the effects of mylonitization and metamorphism on u pb isotopic systematics late paleozoic amphibolite grade approx 600 c mylonitization of the ponaganset gneiss at this locality is associated with movement along the hope valley shear zone the response of zircon to metamorphism in each gneiss unit is distinct zircons in gray augen gneiss are uncorroded and not overgrown whereas zircons from fluorite bearing pink granitic gneiss are variably corroded and over 50 bear opaque overgrowths the zircon overgrowths are chemically distinct from the primary cores and contain high conentrations of hf u hree and th mylonite derived from the gray gneiss contains only a small population of hf u rich metamorphic zircon but zircons in the pink gneiss derived mylonite are dominated by the hf u rich metamorphic component in terms of their u pb isotopic systematics overgrowth free zircons from both units are markedly discordant gray 10 20 pink 35 but overgrown zircons from the pink gneiss are up to 70 discordant zircons from the mylonites yield younger pb pb and u pb ages than those of the protolith gneisses and isotopic data from each gneiss mylonite pair define a linear array on concordia plots upper intercept ages of the gray gneiss 621 27 ma and the pink gneiss 635 50 ma indicate that the crystallization of both units was coeval and the lower intercept ages gray 270 92 ma pink 285 26 ma fall within the range of other published age estimates for alleghanian metamorphism in southeastern new england e g zartman et al 1988 new growth of zircon suggests that zr was mobile during metamorphism the presence of fluorite in the pink gneiss and a discontinuity in log left f text h text 2 text o mathord left vphantom f text h text 2 text o f text hf right kern nulldelimiterspace f text hf right values obtained from biotite across the pink gneiss gray gneiss contact indicates that dissolution and reprecipitation of zircon may be related to local variations in hf fugacity zircon dissolution reprecipitation in the pink gneiss and the lack of similar features in the contiguous gray gneiss suggests that the degree of isotopic perturbation of zircon during metamorphism is related to bulk chemistry fluid chemistry and or the degree of fluid rock interaction

the causes and effects of aging in quick clays the physicochemical properties of a clay from la baie quebec were found to be typical of champlain quick clays very low plasticity liquidity index greater than 3 sensitivity greater than 500 and ph of about 9 5 the mineralogy is characterized by the abundance of primary or rock flour minerals such as feldspar quartz amphibole and calcite with illite as the principal clay mineral the pore water chemistry consists predominantly of sodium bicarbonate low concentrations of sulfate calcium and magnesium and high alkalinity and ph are attributed in part to anaerobic sulfate reduction processes taking place in situ quick clay samples stored in the laboratory showed signs of aging regardless of the storage procedure the remoulded strength and the liquid limit increased with time whereas the sensitivity the liquidity index and the ph decreased the water content plastic limit and undisturbed strength remained practically unchanged the pore water concentrations of calcium magnesium and su

evaluation of preconsolidation pressure and the overconsolidation ratio from piezocone tests of clay deposits in quebec the preconsolidation pressure and overconsolidation ratio profiles are the most important factors related to the mechanical behaviour of clay deposits they are interpreted on the basis of a limited number of laboratory tests but the near continuous information provided by the piezocone can allow local data to be extrapolated to an entire site numerous methods have been proposed for relating piezocone data to preconsolidation pressure and the overconsolidation ratio but their validity is still uncertain in this paper nine methods are compared on the basis of data collected on 31 sensitive clay sites in quebec whose preconsolidation pressure profiles are well known each method is briefly presented and the most promising are identified the simplest method which directly relates preconsolidation pressure to net tip resistance also appears to be the most effective key words clay preconsolidation pressure overconsolidation ratio piezocone correlations

identification and tectonic implications of a tear in the south american plate at the southern end of the lesser antilles 1 in the southeast corner of the caribbean westward subduction of atlantic oceanic south america beneath the lesser antilles transitions to east west transform motion between continental south america and the caribbean plate this geometry requires negatively buoyant subducting oceanic south american lithosphere to progressively detach from positively buoyant continental south american lithosphere the most widely accepted model is slab break off with oblique arc continent collision and northwest dipping continental subduction precipitating narrow rifting in the subducting slab in contrast the subduction transform edge propagator step model conceptualizes progressive detachment along a vertical dip slip tear through the lithosphere with stress focused at the edge of the propagating transform boundary we present four types of seismic data to resolve the ongoing lithospheric detachment local seismicity receiver functions wide angle seismic velocity inversion and a regional balanced cross section constrained by petroleum industry data these four data sets image a near vertical tear extending through the entire lithosphere revealing a key mechanism for the structural evolution of venezuela

pore pressure response to barometric pressure change in champlain clay prediction of the clay elastic properties abstract champlain sea clay deposits play a crucial role in limiting contaminant migration to underlying aquifers in the saint lawrence river valley champlain sea clays are well known as being prone to landslide and sample disturbance estimation of their elastic properties using their in situ loading efficiency would provide mechanical properties for the soil dynamic analyses and immediate settlement calculations encountered in geotechnical projects determination of loading efficiency can be envisioned as a very small strain test in this paper we describe a detailed monitoring program for 10 vibrating wire piezometers installed within sealed boreholes on 5 study sites near montreal in quebec canada the pore pressure response to barometric pressure variation was analyzed with three methods linear regression visual inspection and multiple regression which gave loading efficiencies between 0 7 and 0 95 these values were then used to estimate the elastic properties of the clay formation vertical compressibility and specific storage on the order of 1 10 6 kpa 1 and 1 10 5 m 1 were respectively obtained for most of the monitoring sites a comparison of compressibility values derived from the in situ loading efficiency method with those obtained with pressuremeter oedometer and pulse tests confirmed that clay compressibility is strain dependent the pore pressures measured on the study sites have been corrected by applying the multiple regression and visual inspection methods for most piezometers both methods provided nearly identical results however for deep piezometers the multiple regression method provided smoother pore pressure time series than the visual inspection method the vertical hydraulic gradient obtained with corrected pressure data was shown to change significantly on some test sites during the monitoring period

a 3 d lithospheric model of the caribbean south american plate boundary a 3 d structural model of the caribbean south american plate boundary was constructed by gravity modeling the model was constrained by four wide angle seismic refraction sections moho depth estimations from receiver functions and additionally seismological hypocenters surface geology and geodynamic information density values were calculated from empirical velocity density functions and mineralogical chemical composition considering specific p t conditions we tested different structural models for western and eastern venezuela in the final model the fit of the measured and modeled gravity fields for a long caribbean slab in western venezuela was better than the fit obtained for a short one this interpretation is consistent with the constraining data the slab is interpreted to extend further to the south beneath northern colombia and culminates in the area of the seismic cluster of the bucaramanga nest the modeling estimates a slab dip angle under maracaibo and merida andes of 15 which increases to 32 below 100 km depth the dip direction of approx n150 e 5 increases lightly eastward in eastern venezuela considering its short wavelength lineaments analyzed from gravity data by curvature methods and euler deconvolution seem to be related to shallow structures and density contrast in the serrania del interior and not from a deep detached slab beneath the continental crust it is deduced from modeling results that this slab configuration has a very small influence on the gravity field the slab was modeled according to the subduction transform propagation model with purely westward subduction and a slab break off along a vertical dip slip tear through the lithosphere

methods of interpretation of borehole falling head tests performed in compacted clay liners the interpretation of falling head tests in cased boreholes is discussed these tests are commonly used to measure hydraulic conductivity of compacted clay liners and are often part of the construction quality assurance program three methods of interpretation are reviewed with data sets collected from real tests two of these methods have been the subject of past research by other authors the hvorslev or time lag method and the velocity method after the limitations of these two approaches have been underlined a third method is proposed it uses a best linear unbiased estimator to fit the theoretical head difference function in a plot of falling water column elevation as a function of time z t method the hvorslev method is found unreliable and is not recommended the velocity method is theoretically sound but statistical uncertainty can become high when this method is used in testing materials with low hydraulic conductivity such as clay liners materials with low hydraulic conductivity tend to

regional structure and tectonic history of the obliquely colliding columbus foreland basin offshore trinidad and venezuela abstract cenozoic eastward migration of the caribbean plate relative to the south american plate is recorded by an 1100 km long venezuela trinidad foreland basin which is oldest in western venezuela 65 55 ma of intermediate age in eastern venezuela 34 20 ma and youngest beneath the shelf and slope area of eastern offshore trinidad submarine columbus basin 15 0 ma recent in this study of the regional structure fault families and chronology of faulting and tectonic events affecting the hydrocarbon rich columbus foreland basin of eastern offshore trinidad we have integrated approximately 775 km of deep penetration 2d seismic lines acquired by the 2004 broadband ocean land investigations of venezuela and the antilles arc region bolivar survey 325 km of vintage gulfrex seismic data collected by gulf oil company in 1974 and published industry well data that can be tied to some of the seismic reflection lines top cretaceous depth structure maps in the columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11 15 km thick and highly asymmetrical middle miocene recent depocenter of the columbus basin the main depocenter located 150 200 km east of trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the orinoco delta the submarine darien ridge exhibits moderate 20 140 m seafloor relief forms the steep 12 24 northern structural boundary of the columbus basin and is known from industry wells to be composed of 0 5 4 5 km thick folded and thrust imbricated hydrocarbon bearing section of cretaceous and early tertiary limestones and clastic rocks the eastern and southern boundaries of the basin are formed by the gently 1 7 4 5 northward dipping cretaceous paleogene passive margin of south america that is in turn underlain by precambrian rocks of the guyana shield interpretation of seismic sections tied to wells reveals the following fault chronology 1 middle miocene thrusting along the darien ridge related to highly oblique convergence between the caribbean plate and the passive margin of northern south america continuing thrusting and transpression in an oblique foreland basin setting through the early pleistocene 2 early pliocene recent low angle normal faults along the top of the cretaceous passive margin these faults were triggered by oversteepening related to formation of the downdip structurally and bathymetrically deeper and more seaward columbus basin large transfer faults with dominantly strike slip displacements connect gravity driven normal faults that cluster near the modern shelf slope break and trend in the downslope direction to the south no normal faults are present because the top cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin 3 early pliocene recent strike slip faults parallel the trend of the darien ridge and accommodate present day plate motions

biotite equilibria and fluid circulation in the klokken intrusion chemical variation in biotite from the kjokken gabbro syenite intrusion in the proterozoic gardar province in south greenland has been investigated by electron probe and for f and li ion microprobe most mica occurs in small amounts as fringes on ilmenomagnetite or fayalite rarely as an intercumulus or poikilitic phase the micas range continuously from phlog70ann30 in a gabbro to phlog4ann96 in the most evolved slightly persilicic and peralkaline syenite in the syenites fe mg partitioning between biotite and olivine can be described by a single distribution coefficient k6 xfi x x xf 3 suggesting that these reactant phases mix ideally at the reaction t experimental data for fe mg exchange via aqueous chloride solutions schulien 1980 imply low t 320 q f was absent in the experiments and may significantly affect the exchange equilibrium k6 in the gabbros is 1 consistent with equilibrium via a fluid depleted in f because of crystallization of large amounts of amphibole al mn and ti vary regularly throughout the series and can be used as markers of cryptic variation in the layered syenites al si 22 o is always in the range 7 7 7 85 a1 a1 si decreases from o31 in gabbros to 0 25 in the most fe rich micas li is always 300 c subsolidus even when texturally intercumulus stable isotope data are consistent with the separation and retention of a deuteric fluid during the final stage of magmatic crystallization klokken was not generally subject to the pervasive long range in both distance and time dydrothermal interactions demonstrated in

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

halogen geochemistry of fluid during amphibolite granulite metamorphism as indicated by apatite and hydrous silicates in basic rocks from the bamble sector south norway abstract the halogen chemistry of apatites biotites amphiboles and titanites from metabasites in the proterozoic bamble sector amphibolite granulite facies transition zone norway has been studied to gather data on the behaviour of halogens during original magmatism and subsequent metamorphism three groups of apatites could be recognized 1 f oh apatites with more than 50 mole f and virtually no cl 2 f oh apatites with up to 15 mole of cl 3 cl rich apatites with up to 6 73 wt cl the latter are the most cl rich metamorphic apatites ever reported the f contents of coexisting biotite do not follow this division but their cl contents do log z sfnc hf z sfnc h 2 o values for the coexisting fluid phase calculated from biotite are slightly lower than those calculated from apatite log z sfnc hcl z sfnc h 2 o values in the coexisting fluid phase calculated from biotite are substantially higher than those calculated from apatite the log z sfnc hf z sfnc h 2 o reflects the composition of the peak metamorphic fluid phase the apatites show three types of patterns of f contents 1 w shaped 2 rimward increasing and 3 rimward decreasing pattern 2 reflects progressive metamorphism pattern 3 is thought to reflect growth starting near peak metamorphism and going on during retrograde dilution of the peak metamorphic fluid by a newly introduced aqueous one some apatites show local resorption effects along cracks no regional trend in calculated log z sfnc hf z sfnc h 2 o values is present as different from other granulite terrains the bamble biotites and amphiboles from granulite facies samples do not have higher halogen contents as those from the amphibolite facies area the samples show that halogen bearing fluids were controlled at a very restricted scale during peak as well as retrograde metamorphism

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

semi periodic sequences and extraneous events in earthquake forecasting ii application forecasts for japan and venezuela in order to analyze observed seismicity in central japan and venezuela we applied a new method to identify semi periodic sequences in the occurrence times of large earthquakes which allows for the presence of multiple periodic sequences and or events not belonging to any sequence in the time series we also explored a scheme for diminishing the effects of a sharp cutoff magnitude threshold in selecting the events to analyze a main four event sequence with probability p c 0 991 of not having occurred by chance was identified for earthquakes with m 8 0 in central japan venezuela is divided from west to east into four regions for each of these the magnitude ranges and identified sequences are as follows region 1 m 6 0 a six event sequence with p c 0 923 and a four event sequence with p c 0 706 region 2 m 5 6 a five event sequence with p c 0 942 region 3 m 5 6 a four event sequence with p c 0 882 region 4 m 6 0 a five event sequence with p c 0 891 forecasts are made and evaluated for all identified sequences having four or more events and probabilities 0 5 the last event of all these sequences was satisfactorily aftcast by previous events whether the identified sequences do in fact correspond to physical processes resulting in semi periodic seismicity is of course an open question but the forecasts properly used may be useful as a factor in seismic hazard estimation

regional hydrogeology of the silurian and ordovician sedimentary rock underlying niagara falls ontario canada abstract due to concern over the potential for widespread groundwater contamination in the sedimentary rock underlying the niagara falls area this study was done to investigate the hydrogeology of the silurian and ordovician stratigraphy underlying the upper niagara river and the eastern niagara peninsula seven boreholes up to 150 m deep were drilled instrumented with multiple packer casing tested for permeability sampled for inorganic and organic solutes and monitored for hydraulic head to provide data for a conceptual model of regional groundwater flow results show that there are at least three distinct groundwater flow regimes in the bedrock the uppermost regime consists of fracture zones in the guelph and lockport formations within which hydraulic conductivity hydraulic head measurements and geochemical analyses indicate active groundwater circulation primarily discharging towards the niagara gorge and escarpment underlying the lockport formation are an overpressured high hydraulic head regime in the clinton upper cataract lower queenston formation and an underpressured low hydraulic head regime in the lower cataract upper queenston formation in both regimes geochemical analyses and permeability measurements indicate very old and saline groundwater which probably has undergone minimal migration since pre pleistocene time the implication based on the study so far is that potential groundwater contamination below the bottom of the lockport formation is probably not significant in the niagara falls area except adjacent to the niagara gorge where vertical permeability in the lower flow regimes may be enhanced

enhanced detection of hydraulically active fractures by temperature profiling in lined heated bedrock boreholes summary the effectiveness of borehole profiling using a temperature probe for identifying hydraulically active fractures in rock has improved due to the combination of two advances improved temperature sensors with resolution on the order of 0 001 c and temperature profiling within water inflated flexible impermeable liners used to temporarily seal boreholes from hydraulic cross connection the open hole cross connection effects dissipate after inflation so that both the groundwater flow regime and the temperature distribution return to the ambient background condition this paper introduces a third advancement the use of an electrical heating cable that quickly increases the temperature of the entire static water column within the lined hole and thus places the entire borehole and its immediate vicinity into thermal disequilibrium with the broader rock mass after heating for 4 6 h profiling is conducted several times over a 24 h period as the temperature returns to background conditions this procedure referred to as the active line source als method offers two key improvements over prior methods first there is no depth limit for detection of fractures with flow second both identification and qualitative comparison of evidence for ambient groundwater flow in fractures is improved throughout the entire test interval the benefits of the als method are demonstrated by comparing results from two boreholes tested to depths of 90 and 120 m in a dolostone aquifer used for municipal water supply and in which most groundwater flow occurs in fractures temperature logging in the lined holes shows many fractures in the heterothermic zone both with and without heating but only the als method shows many hydraulically active fractures in the deeper homothermic portion of the hole the identification of discrete groundwater flow at many depths is supported by additional evidence concerning fracture occurrence including continuous core visual inspection acoustic televiewer logs and tests for hydraulic conductivity using straddle packers as well as rock core voc data where available that show deep penetration and many migration pathways confidence in the use of temperature profiles and the conceptual model is provided by numerical simulation and the demonstrated reproducibility of the evolution of the temperature signal measured in the lined holes with and without heating this approach for using temperature profiling in lined holes with heating is a practical advance in fractured rock hydrogeology because the liners are readily available the equipment needed for heating is low cost and rugged and the time needed to obtain the profiles is not excessive for most projects

metamorphism of the pelitic rocks of the snyder group in the contact aureole of the kiglapait layered intrusion labrador effects of buffering partial pressures of water the petrography and mineral chemistries of the aphebian snyder group pelitic rocks in the contact aureole of the kiglapait layered intrusion labrador reveal a rapid increase in metamorphic grade o

strength development with burial in fine grained sediments from the saguenay fjord quebec following a sedimentological and geotechnical investigation two main types of materials were identified in the saguenay fjord 1 organic rich sediments deposited by continuous sedimentation and 2 unbioturbated sediments deposited rapidly by episodic events the consolidation state of sediments with depth were analysed in all subsurface deposits sediments are overconsolidated irrespective of the depositional processes however in continuously deposited sediments strength develops more rapidly than in turbidites or mass flows in the surficial bioturbated layer strength and liquidity index gradients are at a maximum and the rate of strength variation can reach values as high as 9 kpa kpa results from one dimensional creep tests suggest that in the organic poor turbidites the strength development is controlled at least partly by thixotropic strengthening for bioturbated clays it appears that the viscosity and the aggregating potential of organic matter controls the evolution of the strength

monitoring well into abandoned deep well disposal formations at sarnia ontario a 300 m deep monitoring well was completed to the detroit river group of formations in sarnia ontario to evaluate the potential near surface impacts resulting from previous deep injection of industrial waste detailed logging testing and sampling were performed to evaluate the vertical distribution of industrial waste and to determine hydraulic conductivity and hydraulic head in the disposal horizon and in the confining formations results of hydraulic testing indicate the hydraulic conductivity of the disposal formation is 2 10 9 to 2 10 7 m s and that of most of the confining shale and limestone formations is less than 1 10 10 m s analyses of groundwater samples and results from other studies show that industrial waste characterized by elevated phenol concentrations is present in a 10 m horizon in the lucas dolomite disposal formation at 192 m depth waste is also likely present within 2 3 m thick high permeability limestone layers at 74 and 123 m depth in the confining units of the hamilt

relocated aftershocks of the march 10 1988 trinidad earthquake normal faulting slab detachment and extension at upper mantle depths abstract we relocated aftershocks of the march 10 1988 earthquake off the east coast of trinidad in order to determine the fault plane for the main shock and to understand this anomalous earthquake series the march 10 main shock m w 6 6 was the first significant instrumentally recorded earthquake to occur in the epicentral region east of trinidad the reported depth of the main shock 53 km by the international seismological centre isc is unusual but is consistent with observations of pp p times the main shock harvard centroid moment tensor cmt solution nearly pure normal faulting on nodal planes striking ene is also unusual given the depths of the seisms and the rarity of extensional faulting at these depths using p arrival times tabulated by the isc we relocated the aftershocks using the joint hypocentral determination method to find new locations relative to the main shock in map view the relocated epicenters form a tight elliptical cluster with major axis trending wnw ese and minor axis nne ssw virtually all the seisms in the earthquake series occurred at depths ranging from 30 to 60 km deeper than normal crustal earthquakes in an area previously not considered a locus of subducting lithosphere the aftershocks define a distinct plane dipping 34 nw this dip is consistent with the harvard cmt focal mechanism of the main shock one cmt nodal plane dips 38 n and strikes ene very close to our estimate of the active fault plane thus the march 10 aftershocks are consistent with slip on the north dipping plane of the main shock because the earthquake series occurred 100 km se of oceanic south american slab subducting beneath the caribbean plate at a depth generally inconsistent with shallow normal faulting outside of slabs we interpret the main shock as having occurred deep 50 km in south american lithosphere currently moving nw into the subduction zone the occurrence of this earthquake indicates an extensional stress applied to the lithosphere of the south american plate likely related to a combination of slab pull to the nw as the slab subducts beneath the caribbean plate and to detachment of the subducting lithosphere from buoyant continental south america

calcite and quartz microstructural geothermometry of low grade metasedimentary rocks northern range trinidad abstract the northern range of trinidad is a mountainous exposure of deformed metasedimentary rocks with mesozoic depositional ages and tertiary metamorphic ages located in the caribbean south american plate boundary zone these rocks lack precise mineralogical indicators of metamorphic grade using temperature sensitive quartz and calcite microstructures and fission track data we identify describe quantify and map a nearly continuous spectrum of relatively low l50 c to relatively high 250 400 c deformation temperatures from east to west across the range average estimated rock exhumation rates also increase systematically along this trend the analysis illuminates a sharp east west trending major thermal discontinuity i e a fault along the southern boundary of the range kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80 85 and accommodated normal dip slip at rates that decreased from west to east earlier experimental studies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions our work indicates a possible strong temperature control for quartz microstructural transitions at natural strain rates

geochemical evidence for magmatic fluids in porphyry copper mineralization the koloula igneous complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes cycle 1 intrusions 4 5 ma and cycle 2 intrusions 2 4 to 1 5 ma the cycle 2 intrusions are further divided into the inamumu zoned pluton izp which is composed of 6 concentrically disposed quartz diorite and tonalite units and several satellite intrusions the izp is host to porphyry copper mineralization whereas the cycle 1 and cycle 2 satellite intrusions are barren presently exposed mineralization in the izp a system represents the deeply eroded core of a porphyry copper system where widely spaced veinlet alteration envelopes 1 mm thick are separated by large volumes of unaltered rock

oblique collision and tectonic wedging of the south american continent and caribbean terranes our studies of the surface structures seismicity and gravity anomalies of the caribbean south american plate boundary zone of northeast venezuela and trinidad show that the crustal and upper lithospheric structure and kinematics of this zone are complex and differ markedly along strike we propose a model of the zone9s lateral transition from near trinidad west to caracas emphasizing three concepts 1 the steepening detachment and then sinking away of atlantic oceanic lithosphere that is was attached to the northern edge of continental south america 2 the wedging seaward and imbricate thickening of the northern margin of the continent in the region of the detaching atlantic slab the continental wedge overrides the slab and is overridden by terranes attached to the caribbean plate and 3 that the structural and kinematic transitions are a consequence of the progressive oblique collision between continental south america and the overriding caribbean terranes

the lachenaie clay deposit some geochemical and geotechnical properties in relation to the salt leaching process this paper summarizes a detailed geotechnical and geochemical characterization program for the champlain clay deposit in lachenaie quebec presently the clay pore water is saline the main objective of the testing program was to study the leaching of the clay saline pore water since its deposition four issues are discussed in this paper first the deposit is shown to comprise two distinct clay layers with contrasting geotechnical properties the liquid limit and grain size distribution are the properties that best distinguish the two materials the upper layer is more plastic while the lower one is relatively silty the occurrence of these two layers is shown to be in agreement with some recent findings in quaternary geology second the relatively high pre consolidation pressures of the clay in the lachenaie area are shown to be coherent with an erosion scenario and the elevation of a neighbouring bluff previously interpreted as an erosion terrace third the relatively constant hydraulic conductivit

detailed hydraulic head profiles as essential data for defining hydrogeologic units in layered fractured sedimentary rock this paper describes a study in southern wisconsin where vertical hydraulic head profiles measured in exceptional detail provided the key data for defining hydrogeologic units hgus in a layered sequence of sandstone siltstone shale and dolostone the most important data were obtained from corehole mp 6 which was cored 131 m into bedrock and instrumented using a westbay multilevel system with 36 depth discrete monitoring intervals the resulting head profile is consistant over time and shows eight distinct inflections in hydraulic head several of the inflections occur between adjacent permeable units and are likely due to poor vertical connectivity of fracture sets rather than distinct lower permeability layers or aquitards in the conventional sense no other type of data was capable of identifying the position of such distinct hydrogeologic features these zones of abrupt head loss provide the primary dataset for delineation of eleven hgus at mp 6 and are supported by less detailed head profiles at other locations although the detailed head profiles are essential core logs and geophysical logs from other boreholes are nessessary to fully establish the lateral continuity of the hgus

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

halogen chemistry as an indicator of metamorphic fluid interaction with the ponder pluton coast plutonic complex british columbia canada during hydrothermal fluid activity associated with the intrusion of the ponder pluton coast plutonic complex british columbia canada the halogen composition of biotite amphibole and apatite is controlled by the composition of the metamorphic fluid the core of the pluton was not affected by infiltrating fluids and the fluorine composition of biotite was controlled by the biotite fe mg ratio the edge of the cooling crystallized pluton interacted with a chlorine rich fluorine poor fluid which changed the halogen composition of biotite and amphibole the composition of the metamorphic fluid derived from biotite and apatite compositions was relatively high in chlorine and low in fluorine the concentration of chlorine in the metamorphic fluid increases towards the pluton whereas fluorine remains constant this suggests that the metamorphic fluid near the pluton had the greatest potential for masstransfer of metals

gneiss domes metamorphic core complexes and wrench zones thermal and structural evolution of the nigde massif central anatolia 1 the nigde massif a migmatite cored structural dome in south central turkey was metamorphosed deformed intruded and exhumed in an oblique tectonic regime involving a switch from transpression prograde metamorphism to transtension exhumation an 80 ma history of transpression and transtension is recorded in metamorphic rocks of the massif and the last 50 ma are recorded in both basement and overlying basin deposits nigde metamorphic rocks record a high temperature top to north syntranspression ductile fabric that was overprinted by lower grade top to south syntranstension ductile shear zones the 40ar 39ar data for hornblende muscovite and biotite document rapid late cretaceous cooling with the oldest ar hornblende ages 88 79 ma overlapping u pb ages in monazite and zircon 92 78 ma muscovite ar ages are dominantly 81 79 ma suggesting a short time between crystallization of high temperature metamorphic rocks and their cooling biotite ar ages are 79 74 ma with the exception of disturbed samples from the eastern margin of the massif and from eocene granitic stocks in the dome core the eastern margin adjacent to the sinistral central anatolian fault zone records another cycle of burial and exhumation that overprinted earlier fabrics and disturbed isotopic systems these two cycles of burial exhumation took place repeatedly along the same zone this may be characteristic of highly oblique tectonic regimes in the nigde massif burial and exhumation became more localized and of lower amplitude over time suggesting stabilization of the crust

the permeability of natural soft clays part ii permeability characteristics reply the permeability characteristics of a number of intact natural soft clays from quebec the usa and sweden have been investigated in the laboratory the variation of permeability with void ratio is best represented in terms of a linear e vs lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice the permeability at the in situ void ratio is shown to be a complex function of such parameters as the void ratio the clay fraction the plasticity index and the fabric of the clay permeability anisotropy is negligible in marine clays the e vs lg k relationships of the various clays tested are well ordered in terms of an empirical parameter ip clay fraction irrespective of the geological origin of the clay the slope of the e vs lg k relationship referred to as permeability change index ck is simply related to the initial void ratio by ck 0 5eo keywords permeability clays laboratory tests permeability anisotropy permeability void ratio re

seismicity and tectonics of the southeastern caribbean we present 33 new focal mechanisms for se caribbean earthquakes 1963 1988 we use these mechanisms in conjunction with 28 previously available mechanisms to distinguish between two models of plate boundary zone interaction in the se caribbean the trench trench transform and hinge faulting model and the right oblique collision model shallow 0 70 km and intermediate 70 200 km depth earthquakes occur in the study region we focus on the tectonic causes of these events and the motions they delineate the shallow earthquakes are in a broad linear zone which trends ne from the paria peninsula of venezuela towards barbados intermediate depth earthquakes cluster beneath and nw of the peninsula and deepen to the nw perpendicular to the ne trending shallow events the vertical distribution of the earthquakes suggests a slab with steep nw dip shallow dextral strike slip on e striking faults is restricted to a 60 km wide linear zone between the gulf of cariaco and the western margin of the gulf of paria dextral strike slip is active only as far east as the gulf of paria and not within or east of trinidad shallow thrust events with ene striking planes distributed between the araya peninsula and the gulf of paria indicate collision at crustal levels between south america and caribbean and that folding and thrusting are still active over a 60 km interval south of the araya paria isthmus active thrusting in venezuela corroborates predictions of transpression between caribbean and south america and discounts transtensional motions between the two plates in the se caribbean the conjunction of shallow thrust strike slip and normal earthquakes in the gulf of paria at around 62 3 may be the expression of unpartitioned oblique compressive deformation in the plate boundary zone intermediate 165 km h 70 km depth thrust and dip slip events within the nw dipping slab indicate that oceanic lithosphere probably originally attached to south america subducts to the nw beneath the caribbean plate shallow normal faulting events e and ne of trinidad are expressions of plate bending about near horizontal axes parallel to the lesser antilles subduction zone we conclude that the earthquake mechanisms provide strong support for the right oblique collision model of caribbean south american plate interaction

triangulation to gps and gps to gps geodesy in trinidad west indies neotectonics seismic risk and geologic implications we estimated horizontal velocities at 25 sites first surveyed in a 1901 1903 british ordnance survey triangulation and then resurveyed with gps in 1994 1995 to identify trinidad s principal active on land faults quantify fault slip rates and test for elastic locking our best fit single fault elastic dislocation model put 12 3 mm yr of dextral strike slip on the central range fault 1 2 km locking depth an apparently aseismic active fault the estimated motions also showed statistically insignificant horizontal motion 2 2 1 8 mm yr of right slip 2 7 2 0 mm yr of n s shortening on the eastward on strike extension of the el pilar fault known to be the active transform fault in venezuela repeat gps measurements made between 1994 and 2005 at two sites spanning the island north to south showed a1 4 3 mm yr eastward plate motion parallel dextral velocity differential consistent with our best fit historic 1901 1995 fault slip rate paleoseismology trenching demonstrates that the central range fault cuts 5000 year old sediment and is capped by w550 year old sediment suggesting that it may be locked and may have ruptured at least once during this time interval about w5 mm yr of slip could be taken up on the los bajos fault and additional faults in the offshore south of trinidad the existing 1901 1995 and 1994 2005 geodetic data alone cannot resolve whether the central range fault is

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

tectonic wedges geometry and kinematic interpretation abstract the geometry of several tectonic wedge combinations was studied in an outcrop in the basque basin western pyrenees three types of tectonic wedges were distinguished simple double and triple wedge on the surface the geometry of the observed tectonic wedges is always highly elemental emergent thrust horse or klippe the final stage in the evolution of a tectonic wedge is its delamination this can occur by the spreading of the thrusts which conform the wedge or by the development of back thrusts associated to them the relative age of the back thrust with respect to the thrust indicates whether the original structure was a simple thrust or a tectonic wedge if this criterion is applied to the pyrenean orogen this range corresponds to a tectonic wedge

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

aseismic continuation of the lesser antilles slab beneath continental south america 1 we present results of travel time inversions of teleseismic p and s waves recorded at the secasa92 southeast caribbean south america 1992 temporary broadband array in northeastern venezuela and trinidad the inversions reveal the unusual structure of the southern termination of the lesser antilles subduction zone a minimum 2 relatively high velocity anomaly trends wsw from the seismically defined lesser antilles slab beneath and nw of the paria peninsula to a point below the venezuelan serrania del interior well south of the caribbean coast resolution tests utilizing actual ray geometries and densities of the source data indicate that the regional scale structure beneath the study area is reasonably well resolved thus a detached and detaching subducted south american slab appears to lie beneath continental south america we infer that oceanic south american lithosphere has been overridden to a significant degree by continental south america the detached slab now lying beneath continental south america was driven into its current position after detaching from the former eastward striking mesozoic ocean continent passive margin as this margin entered the subduction zone because oceanic and continental south america are still attached without apparent relative motion between them along the atlantic passive margin southeast of our study region the slab must be the actively moving element during continental overriding thus the slab and its surrounding mantle both caribbean and south america beneath northeastern south america are mobile and have moved ese relative to the stable guyana shield craton

quaternary fault kinematics and stress tensors along the southern caribbean from fault slip data and focal mechanism solutions deformation along the southern caribbean coast as confirmed by the compilation of stress tensors derived from fault plane kinematic indicators microtectonics and further supported by focal mechanism solutions herein presented results from a compressive strike slip transpressional senso lato regime characterized by a nnw sse maximum horizontal stress 1h 11 and or an ene wsw minimum 1h 13 or 12 horizontal stress which is responsible for present activity and kinematics of six sets of brittle features east west right lateral faults nw se right lateral faults synthetic riedel shears ene wsw to east west dextral faults p shears nnw sse normal faults almost north south left lateral faults antithetic riedel shears and ene wsw reverse faults sub parallel to fold axes and mostly in the subsurface the latter ones being associated to ene wsw trending folding in this particular region the brittle deformation obeys the simple shear model although not all the deformation can be accounted for it since partitioning is also taking place regional folding and thrusting is essentially due to the normal to structure component of the partitioned maximum horizontal stress conversely the maximum horizontal stress on

on the use of the kozeny carman equation to predict the hydraulic conductivity of soils the saturated hydraulic conductivity of a soil can be predicted using empirical relationships capillary models statistical models and hydraulic radius theories a well known relationship between permeability and the properties of pores was proposed by kozeny and later modified by carman the resulting equation is largely known as the kozeny carman kc equation although the two authors never published together in the geotechnical literature there is a large consensus that the kc equation applies to sands but not to clays this view however is supported only by partial demonstration this paper evaluates the background and the validity of the kc equation using laboratory permeability tests test results were taken from publications that provided all of the information needed to make a prediction void ratio and either the measured specific surface for cohesive soils or the gradation curve for noncohesive soils the paper shows how to estimate the specific surface of a noncohesive soil from its g

surface rupture of the cariaco july 09 1997 earthquake on the el pilar fault northeastern venezuela abstract this paper discusses the surface rupture of the cariaco july 09 1997 ms 6 8 earthquake in northeastern venezuela located at 10 545 n and 63 515 w and about 10 km deep the field reconnaissance of the ground breaks confirms that this event took place on the ene wsw trending onshore portion of the dextral el pilar fault between the gulfs of cariaco and paria which is part of the major wrenching system within the caribbean south america plate boundary zone dextral slip along this fault was further supported by the structural style of this rupture en echelon right lateral r shears connected by mole tracks at restraining stepovers and by larger geometric complexities pop ups at las manoas and guarapiche as well as by the focal mechanism solutions determined for the event by several authors this 1997 surface ruptre comprised two distinct sections from west to east a a main very conspicuous continuous 30 km long rather straight 075 n trending alignment of en echelon surface breaks with a rather constant purely dextral coseismic slip of about 25 cm but reaching a maximum value of 40 cm slightly northwest of pantono and b a secondary discontinuous 10 km long boomerang shaped rupture with a maximum coseismic slip of 20 cm at guarapiche the onshore extent of the surface rupture totalled 36 km but may continue westward underwater as suggested by the very shallow aftershock seismicity this aftershock activity also clearly defined the steep north dip of the fault plane along the western rupture suggesting tectonic inheritance on this major fault from many locals accounts the rupture seems to have propagated from pantono to the west highly asymmetric bidirectionality this suggests that earthquake nucleation happened at or near the casanay guarapiche restraining bend and rupture quickly propagated westward allowing only a small fraction to progress eastwards beyond the bend additionally the large fraction of after slip or creep released is to be related to such restraining bend which seems to have partly locked slip during rupture