unraveling 470 m y of shortening in the central andes and documentation of type 0 superposed folding in the famatina ranges central andes of western argentina 470 m y of protracted shortening is recorded through episodic coaxial coplanar fold amplification ordovician anticlines within the east vergent thrust belt were refolded and tightened during later paleozoic and cenozoic shortening folding episodes are recorded in four major unconformities that can be measured on both flanks of one of these map scale anticlines superposed folding type 0 interpreted from mapping and bedding plots shows similar axial orientation in older and younger rocks throughout the different stratigraphic layers of the shortening 30 is pre cenozoic and allows the recording of episodic deformation during continuous plate convergence at the gondwana south american margin

foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

lithological discrimination based on statistical analysis of multi sensor drill core logging data in the matagami vms district quebec canada in mineral exploration traditional core logging is largely based on the visual inspection of drilled cores a process which is often subjective and non reproducible however a number of physical chemical and mineralogical properties of rocks can now be measured at high spatial resolution on drill cores the resulting large multiparameter databases can help geologists to quantitatively discriminate between lithologies study hydrothermal alteration and potentially vector towards mineralization multivariate statistical methods are important tools to assist geologists in interpreting such large databases we present an application of model based cluster analysis in the matagami base metal mining district more specifically to improve lithological discrimination at the zinc rich bracemac and mcleod volcanogenic massive sulfide vms deposits the model based cluster analysis method is able to efficiently discriminate different geological units encountered even in cases where two units are visually similar or in the presence of strong hydrothermal alteration

linking mid scale distributive fluvial systems to drainage basin area geomorphological and sedimentological evidence from the endorheic gastre basin argentina

multidomain petrophysically constrained inversion and geology differentiation using guided fuzzy c means clustering abstractgeophysical inversion methods are used as part of an interpretation process that seeks to differentiate geologic units to improve the reliability of geologic differentiation based on recovered images from geophysical inversions we have developed a multidomain clustering inversion algorithm that can incorporate statistical petrophysical data into a deterministic geophysical inversion framework through the use of the fuzzy c means clustering technique petrophysical data are treated in the parameter domain in the same way that geophysical data are treated in the spatial domain and these two different types of data are simultaneously inverted in their respective domains through the minimization of a single common objective function the resulting physical property model honors the geophysical and petrophysical data and therefore can represent the earth better than geophysical inversion models that solely honor the geophysical data geophysical inversion and geology differentiation are generally tr

stratigraphy and chronology of upper cretaceous lower paleogene strata in bolivia and northwest argentina integration of sequence stratigraphy magnetostratigraphy ar ar dating and paleontology considerably advances knowledge of the late cretaceous early paleogene chronostratigraphy and tectonic evolution of bolivia and adjacent areas the partly restricted marine el molino formation spans the maastrichtian and danian 73 60 0 ma deposition of the alluvial to lacustrine santa lucia formation occurred between 60 0 and 58 2 ma the widespread erosional unconformity at the base of the cayara formation is 58 2 ma this unconformity separates the upper puca and corocoro supersequences in bolivia and is thus coeval with the zuni tejas sequence boundary of north america the thick overlying potoco and camargo formations represent a late paleocene oligocene foreland fill the onset of shortening along the pacific margin at 89 ma initially produced rifting in the distal foreland santonian campanian eastward onlapping deposits indicate subsequent waning of tectonic activity along the margin significant tectonism and magmatism resumed along the margin at 73 ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin subsidence was maximum between 71 and 66 ma due to the early maastrichtian global sea level high marine waters ingressed from the northwest into this underfilled basin subsidence decreased during the late maastrichtian and was low during the danian it increased again in the latest danian for which a slight transgression is recorded and peaked in the early selandian tectonism between 59 5 and 58 2 ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the coastal batholith the subsequent 58 2 ma major unconformity marks the onset of continental foreland basin development which extended into andean bolivia during the late paleocene oligocene interval this basin underwent internal deformation as early as eocene time in the altiplano and cordillera oriental these early structures previously assigned to the late oligocene early miocene orogeny probably accommodated observed tectonic rotations in the eocene oligocene

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

a statistical methodology for deriving reservoir properties from seismic data the use of seismic data to better constrain the reservoir model between wells has become an important goal for seismic interpretation we propose a methodology for deriving soft geologic information from seismic data and discuss its application through a case study in offshore congo the methodology combines seismic facies analysis and statistical calibration techniques applied to seismic attributes characterizing the traces at the reservoir level we built statistical relationships between seismic attributes and reservoir properties from a calibration population consisting of wells and their adjacent traces the correlation studies are based on the canonical correlation analysis technique while the statistical model comes from a multivariate regression between the canonical seismic variables and the reservoir properties whenever they are predictable in the case study we predicted estimates and associated uncertainties on the lithofacies thicknesses cumulated over the reservoir interval from the seism

heat flow gravity and structure of the abitibi belt superior province canada implications for mantle heat flow the results of new heat flow measurements are presented for eleven sites located in the abitibi greenstone belt of the archean superior province these new and previously published heat flow data are used with gravity and seismic data to constrain the crustal structure and composition of the abitibi subprovince and to determine the mantle heat flow beneath the canadian shield in order to analyze the long wavelength variations in heat flow and bouguer gravity anomaly the crust was divided into three layers with distinctive composition and physical properties average density heat production and thickness for each layer were varied within a range compatible with measurements and yielded crustal models consistent with gravity and heat flow data the dominant contribution to crustal heat production is that of a tonalitic type layer which has the lowest density the models require mantle heat flow to range between 10 and 14 mw m 2 the westward increase in heat flow requires the tonalitic layer to thicken from the grenville front toward the kapuskasing uplift at the expense of the greenstone supracrustals long wavelength gravity data are more affected by changes in crustal thickness than by composition and the low bouguer anomaly near the eastern grenville front is caused by 5 6 km of crustal thickening in greenstone terranes the long wavelength variations in heat flow are more useful for determining average crustal composition and the thickness of supracrustals than the gravity data

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

porosity prediction from seismic data the inversion of seismic traces allows the estimation of reservoir porosity from an analysis of transit times derived from the pseudo velocity logs a four step computational procedure is illustrated consisting of i inversion of seismic traces and calculation of interval velocities ii accurate stratigraphic interpretation iii determination of the petrophysical parameters for the porosity evaluation iv analysis of the reliability of the results and final corrections both the possibilities and the limits of the method are discussed one of the causes of error is the fact that impedances and not velocities are readily obtainable from seismic data moreover the porosity due to fracturation contributes only slightly to velocity while it often contributes most importantly to the permeability results are shown for two of the most significant reservoir types i e carbonatic and clastic two cases belonging to the latter type will be examined in the first case the primary porosity is dominant the second case is very complex and both primary and secondary porosity are present

application of seismic reflection data to discriminate subsurface lithostratigraphy a correlation between lithology and quantitative parameters abstracted from seismic reflection data is established the concept and methodology developed on synthetic data has been successfully applied to discriminate between two different kinds of lithologies a particular hydrocarbon bearing formation in a sedimentary basin in western india has been considered part of which is dominantly sandy lithological composition sand 53 percent shale 21 percent coal 26 percent and another part which is dominantly shaly sand 37 percent shale 60 percent coal 3 percent these two different lithologies are mathematically modeled using one step markov chains their seismic responses when scrutinized in time and frequency domain and subjected to statistical discriminant analysis give a fair idea about synthetic subsurface lithostratigraphy seismic reflection data from the same area were considered for a similar analysis on subjecting the data to discriminant analysis it was again possible to dis

numerical zonation of log suites and logfacies recognition by multivariate clustering zonation of well logs and the correlation of zones between wells are routine fundamental tasks in subsurface geological analysis objective numerical multivariate clustering is an effective procedure to simultaneously comprehend a suite of well logs and partition it into geologically meaningful zones and for identifying zone specific logfacies discrimination of zones and logfacies from log suites was established by a hierarchical clustering algorithm that defines clusters so that their within cluster dispersion is minimal logfacies are defined by an unconstrained analysis of unzoned data whereas the special requirements of the stratigraphic context of the zonation are observed by an adjacency constraint which prohibits merging individual depth levels or lower order clu ters if their members are not vertically contiguous two test cases one involving a succession composed of several alternating lithologies and the other entailing a uniform carbonate sequence with only subtle changes demonstrate the applicability and efficacy of the method in both cases the numerical zonation matched the manual lithostratigraphic division extremely well the geological validity of the numerically defined zones was also borne out by density neutron crossplots the unconstrained analysis successfully identified logfacies which are zone specific indicating that logfacies can serve as important leads for the recognition of reverse faults in boreholes and for interwell correlations

electrical resistivities of crustal fluids results of calculations on the electrical resistivities of crustal fluids as a function of temperature pressure and fluid composition indicate that crustal fluids can range in resistivity from approximately 1 m the dominant contribution to decreasing the resistivities of crustal fluids comes from increased concentrations of chloride and bicarbonate salts and increased temperature and density of the fluids calculations indicate that the sharpest decrease in fluid resistivity occurs at shallow depths 10 km and temperatures 300 c can not be readily explained as a product of variations in resistivities of crustal fluids these results indicate that a transition in mineralogy or pore shape geometry is more likely responsible for the observed decrease in electrical resistivity of the middle crust than a major change in fluid resistivity

heat flow and structure of the lithosphere in the eastern canadian shield twenty two new determinations of heat flow and radiogenic heat production in the superior and grenville provinces of the canadian shield are presented the new data and previously published measurements strongly constrain the thermal structure of the eastern canadian shield in the abitibi greenstone belt heat flow gradually increases from 29 mw m 2 near the grenville front to 44 mw m 2 east of the kapuskasing uplift this heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1 1 w m 3 this interpretation based on estimated heat production of major rock types in the region is consistent with crustal models derived from recent seismic reflection and refraction studies it also leads to an estimate of about 12 mw m 2 for the mantle heat flow beneath the area the average heat flow in the grenville province 41 10 mw m 2 is the same as that of the superior province this similarity and the lack of significant variation of heat flow across the grenville front indicate that the crust on both sides of the front has similar heat production and thus composition in the western part of the grenville province heat flow reaches high values in the vicinity of the boundary between the allochtonous polycyclic and monocyclic belts where enriched granitic plutons are found in the crystalline terranes in the central part of the grenville province heat flow and heat production are related to each other the parameters of the linear heat flow heat production relationship qr 30 2 in mw m 2 and d 7 1 1 7 km are close to those of the much younger appalachian province implying that the higher appalachian heat flow is due solely to higher heat production in the upper crust the data provide no evidence for variation of mantle heat flow between the superior grenville and appalachian provinces whose tectonic ages range between 2700 and 400 ma the small value of the mantle heat flow about 12 mw m 2 implies that the depth to the 450 c isotherm which controls the effective elastic thickness of the lithosphere is very sensitive to crustal heat production

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

lithologic tomography an application to geophysical data from the cadomian belt of northern brittany france abstract a probabilistic description of subsurface lithologic structures can be established by inverting multidisciplinary geophysical data constrained by geological and geostatistical priors the methodology is based on the joint modelling of several media properties and on a statistical description of the relationships between them the information provided by the geophysical data and the geological and geostatistical priors is represented by probability density functions pdf that are combined into a posterior pdf composed by 1 a prior pdf in the space of the primary lithologic model parameters 2 a pdf of the secondary physical model parameters conditional to the primary model parameters and 3 a joint likelihood function that is the product of the independent likelihood functions for each observed geophysical field applying a markov chain sampling method enables a large sample of joint models to be generated from the posterior pdf the true configuration of the media is then determined from the representation of models pulled from the chain and the elaboration of statistics from the large sample of posterior joint models the method was used to invert gravity and magnetic data jointly characterising the mass density field the magnetic susceptibility field and the lithotype field along two 2 d sections of the geological units in the cadomian belt of northern brittany besides generating 10 6 joint models consistent with the observations and priors some features of the joint models and the statistical tomographic images provided additional insights to the geologic configuration of the area for example the main cadomian thrust shows an irregular geometry that could have resulted from the belt emplacement and or from variscan tectonism and the hercynian granitic intrusion shows a deep subsurface continuation the cosimulation of magnetic susceptibility and mass density inside each lithologic region was performed according to a multivariate gaussian model or a mixed multivariate gaussian functions model that was developed specially to describe multimodal distributed properties

measurement of thermal properties of select intact and weathered granulites and their relationship to rock properties abstractunderstanding the thermal properties of granulites a group of high grade metamorphic rocks representing composition of lower crust of the earth is necessary to arrive at effective crustal heat flow modeling however the thermal conductivity and diffusivity of intact and weathered granulites and parameters that influence them are poorly known the above properties for a few felsic mafic and intermediate granulites and associated soils from the southern granulite terrain india were investigated using a cost effective self fabricated setup the results generated by this technique were precise reproducible and comparable with other published procedures and values because the samples analyzed were of intact in situ specimens the thermal conductivity and diffusivity could be directly used in practical applications among several parameters it was observed that sio2 mgo fe2o3 ratio grain size and bulk density were the principal factors to influence the conductivity and diffusivity of fresh

lithology discrimination from physical rock properties the estimation of lithology from multiple geophysical survey methods needs to be addressed to develop advanced tomographic methods an initial requirement for lithology discrimination is that lithology should be discriminable from the media properties physically related to the geophysical observations to test this condition for different combinations of the most common crustal rocks we performed several lithology discrimination exercises on rock samples under laboratory conditions the physical properties included mass density compressional velocity shear velocity electric conductivity thermal conductivity and magnetic susceptibility a categorical description of the sample lithology was followed hence the inference consisted of predicting the sample rock category lithotype membership the joint information provided by the physical properties of the rocks allowed us to discriminate the sample lithotype correctly with an overall success rate of 100 in the most favorable situation and over 85 in the least favorable situation we obtained successful classification results for a variety of common lithotypes granite gabbro limestone tuff marble basalt and gneiss using three common classification methods clustering analysis gaussian classification and discriminant analysis although discrimination was positive with each of these multivariate classification techniques discriminant analysis showed some advantages for the classification and graphic analysis of the data these results support our postulate that lithology can be estimated reliably if multiple geophysical observations are considered jointly

trace based and geostatistical inversion of 3 d seismic data for thin sand delineation an application in san jorge basin argentina argentina s san jorge basin which straddles the southern provinces of chubut and santa cruz in the heart of patagonia has been producing hydrocarbons since 1907 the region currently accounts for 32 of the country s production the existence and early geologic evolution of the basin is due to the same rift process responsible for the opening of the atlantic ocean in early jurassic times extensive direct faulting and local erosion accompanied the rift evolution thereby facilitating the accumulation of chiefly nonmarine terrigenous sediments well into the early cretaceous at this point andean tectonism became a major source of pyroclastic concentration in the sedimentary column it was also responsible for pervasive batholitic intrusions clastic deposition in the hydrocarbon producing zone is characterized by thick shale laminations of lacustrine and floodplain origin interspersed with much thinner and laterally sparse sand bodies the hydrocarbon reservoirs

hinge migration as a mechanism of superimposed folding abstract paraffin wax analogue modelling of superimposed folding shows how early fold shape and orientation determine fold axis orientation type of interference pattern and mechanism of superposed folding during two successive deformations the behaviour depends on the angle between the first and second compression directions i when they are perpendicular to each other classic superposed folding with either domes and basins or folds with vertical axes develop depending on whether the earlier folds were open or closed ii when the two compression directions are oblique the earlier folds rotate the degree of rotation depends on the angle between the first folds and the later compression direction and is proportional to the amount of strain the orientations of the new folds are close to those of the earlier open folds the final deformation pattern consists of domains where the orientations of the axes depend on whether the early folds were previously either open or closed many early folds are reused to become later folds by the mechanism of hinge migration these results are consistent with the pattern of superimposed folding observed in the devoluy structure of the french alps they show that simply by studying the directions of fold axes in areas of superposed folding it is not possible to define compression directions moreover there is the possibility that superposed folding may go unnoticed if hinge migration has occurred

new heat flow density and radiogenic heat production data in the canadian shield and the quebec appalachians new heat flow density hfd measurements were performed at 10 sites in quebec for five of the sites located in the superior province the heat flow density varies between 24 and 35 mw m2 26 and 37 mw m2 after adjustment for pleistocene climatic variations in the grenville province the values obtained range between 25 and 28 mw m2 29 and 31 mw m2 after adjustment for two nearby sites in the gaspe region appalachians the heat flow density is 47 mw m2 48 mw m2 after adjustment radiogenic heat production was also measured at the sites located in the meta volcano sedimentary sequences of the superior province the heat production is low 0 1 0 6 w m3 and it does not always correlate with the surface heat flow in the grenville province the hfd is close to slightly higher than the reduced heat flow of the superior the higher hfd in the appalachians is partly explained by the higher crustal heat production and partly by higher deep heat flow

along strike segmentation of the andean foreland causes and consequences abstract thrust belts of tertiary age characterize the east flank of the andes and part of the adjacent foreland from venezuela to the southern tip of south america this foreland deformation comprises three basically different structural styles 1 thin skinned thrust belts detached within the sedimentary cover 2 thick skinned thrust belts with an inferred basal detachment in the basement at 10 20 km depth and 3 foreland basement thrusts which possibly affect the entire crust alternating foreland structural styles along the orogen often with sharp boundaries produce a segmentation of the andean foreland the changes in structural style are interpreted to be primarily controlled by inherited stratigraphic and structural features of the south american plate for instance thin skinned thrust belts appear to require a more or less conformable sedimentary cover at least some 3 km thick over a metamorphic crystalline basement unaffected by mesozoic extension in areas of mesozoic rifting normal faults have been reactivated during tertiary contraction resulting in the formation of thick skinned thrust belts the basement becomes involved even if potential decollement levels are present deep seated foreland basement thrusts tend to form over basement arches with a thin sedimentary cover the three basic structural styles are unequally efficient in terms of shortening thin skinned belts are typically shortened by 40 70 thick skinned belts by 20 35 and areas of foreland thrusts by less than 10 the structural segmentation of the foreland therefore implies strong along strike variations in the amount of shortening available estimates of shortening along the central andes actually suggest that shortening does not vary steadily but has several maxima and minima strongly and weakly shortened foreland segments correlate poorly with the segmentation of the subducted plate in steeper and subhorizontal segments flat slabs but closely with lithospheric structure the most strongly shortened segment coincides with thick mantle lithosphere suggesting that shortening of the edge of the south american plate has resulted in substantial underthrusting of lithospheric mantle beneath part of the andes this underthrusting of thick lithosphere may have caused steepening of a formerly flat slab in the arica bend region to the normal 25 30 dip presently observed

a three dimensional gravity inversion applied to sao miguel island azores gravimetric studies are becoming more and more widely acknowledged as a useful tool for studying and modeling the distributions of subsurface masses that are associated with volcanic activity in this paper new gravimetric data for the volcanic island of sao miguel azores were analyzed and interpreted by a stabilized linear inversion methodology an inversion model of higher resolution was calculated for the caldera of furnas which has a larger density of data in order to filter out the noncorrelatable anomalies least squares prediction was used resulting in a correlated gravimetric signal model with an accuracy of the order of 0 9 mgal the gravimetric inversion technique is based on the adjustment of a three dimensional 3 d model of cubes of unknown density that represents the island s subsurface the problem of non uniqueness is solved by minimization with appropriate covariance matrices of the data resulting from the least squares prediction and of the unknowns we also propose a criterion for choosing a balance between the data fit which in this case corresponds to residues with rms of the order of 0 6 mgal and the smoothness of the solution the global model of the island includes a low density zone in a wnw ese direction and a depth of the order of 20 km associated with the terceira rift spreading center the minimums located at a depth of 4 km may be associated with shallow magmatic chambers beneath the main volcanoes of the island the main high density area is related to the nordeste basaltic shield with regard to the caldera furnas in addition to the minimum that can be associated with a magmatic chamber there are other shallow minimums that correspond to eruptive processes

early evolution of the proto andean margin of south america from a detailed study of a 500 km transect in the sierras pampeanas central west argentina two pre silurian tectono magmatic episodes are recognized and defined each culminating in micro continental collisions against the proto andean margin of gondwana the pampean orogeny started in early cambrian time with short lived subduction indicated by ca 535 ma calc alkaline granitoids following pampean terrane collision burial to granulite facies conditions ca 9 kbar generated widespread migmatites and ca 520 ma highly peraluminous granites in the eastern sierras pampeanas after brief quiescence a second major episode the famatinian orogeny started with subduction ca 490 ma forming a wide continental arc and ensialic backarc basin this heralded the approach of laurentia to gondwana during which the precordillera terrane separated from the southern appalachian region finally colliding with gondwana in silurian devonian time

two dimensional refold interference patterns abstract when a rock undergoes two generations of folding complex three dimensional refolded structures result if such a structure is then sectioned two dimensional interference patterns result these patterns have been discussed before but the incredible variety and complexities of these patterns can be shown only with a large number of diagrams using a computer simulation various refolded structures have been sliced at every unique 30 combination of strike and dip thirty sections per structure the characteristics of the patterns observed are discussed and recurring recognizable patterns are identified

an integrated approach to lithologic inversion part i theory for the complex problem of lithologic inversion a new formalism is proposed using a spatial distribution of seismic velocities cp cs and densities as input at each subsurface grid point the inversion result consists of the most likely lithotype gas sand shale etc together with its related litho parameters frame strength porosity etc the inversion method is based on the bayesian theory of parameter estimation allowing specification of inaccuracies in the input and the incorporation of geological knowledge an important advantage of the proposed inversion method is that for each practical situation the necessary accuracy of cp cs and can be predetermined to distinguish between specific lithotypes or to estimate a specific litho parameter with a prespecified accuracy for instance inversion results show that water saturation can only be estimated for an unrealistic accurate input on the other hand for the estimation of porosities it is generally sufficient to have compressional ve

multivariate analysis of cross hole georadar velocity and attenuation tomograms for aquifer zonation 1 we have investigated the potential of combining cross hole georadar velocity and attenuation tomography as a method for characterizing heterogeneous alluvial aquifers a multivariate statistical technique known as k means cluster analysis is used to correlate and integrate information contained in velocity and attenuation tomograms cluster analysis allows us to identify objectively the major common trends in the tomographic data and thus to reduce the information to a limited number of characteristic parameter combinations the application of this procedure to two synthetic data sets indicates that it is a powerful tool for converting the complex relationships between the tomographically derived velocity and attenuation structures into a lithologically and hydrologically meaningful zonation of the probed region in addition these synthetic examples allow us to evaluate the reliability of further petrophysical parameter estimates we find that although absolute values of the tomographically inferred petrophysical parameters often differ significantly from the actual parameters the clustering approach enables us to reliably identify the major trends in the petrophysical properties finally we have applied the approach to a cross hole georadar data set collected in a well studied alluvial aquifer a comparison of the clustered tomographic section with well log data demonstrates that our approach delineates the hydrostratigraphic zonation

ordovician collision of the argentine precordillera with gondwana independent of laurentian taconic orogeny abstract the argentine precordillera a rifted fragment of laurentian crust and sedimentary cover collided with gondwana in middle ordovician time the time of collision ocloyic orogeny is similar to that of the taconic orogeny of eastern laurentia three hypotheses have been proposed to explain ordovician docking of the precordillera with western gondwana a the precordillera microcontinent was rifted from laurentia in cambrian time and following solitary drift collided with gondwana independent of the laurentian taconic orogeny b a continent continent collision of laurentia with gondwana producing a continuous taconic ocloyic orogenic belt was followed by rifting that left the precordillera attached to gondwana and c the precordillera at the tip of a distal plateau on greatly stretched laurentian crust collided with gondwana and subsequently separated from laurentia contrasts in several aspects of taconic and ocloyic orogenic history provide for discrimination between the microcontinent and continent continent collision hypotheses stratigraphic gradients and lithologic assemblages within the synorogenic clastic wedges are incompatible with a single continuous orogenic belt which in palinspastic location places the thin fine grained southern fringe of the taconic clastic wedge adjacent to the thickest and coarsest part of the ocloyic clastic wedge separate temporal and spatial distribution patterns of volcanic ash bentonite beds in laurentia and the precordillera indicate originally separate dispersal systems late ordovician hirnantian gondwanan glacial deposits in the precordillera indicate substantial latitudinal separation from laurentia post collision faults with large vertical separation in the precordillera have no coeval counterparts on the laurentian foreland these contrasts indicate originally separate not initially continuous and subsequently dismembered orogenic belts favoring the microcontinent hypothesis and eliminating the continent continent collision hypothesis initial taconic tectonic loading near the southern corner of the alabama promontory of laurentia and the lack of post taconic extension there are inconsistent with the tectonic history required by the plateau hypothesis but are consistent with the tectonic history required by the microcontinent hypothesis paleobiogeography distribution of bentonite beds and the hirnantian glacial deposits all indicate wide separation iapetus ocean between the precordillera and southern laurentia at the time of the ocloyic and taconic orogenies further favoring the microcontinent hypothesis

three dimensional massively parallel electromagnetic inversion ii analysis of a crosswell electromagnetic experiment summary a 3 d electromagnetic inversion scheme has been successfully applied to crosswell electromagnetic data collected at the richmond field station near berkeley california by comparing images of data collected before and after the injection of 50000 gallons of salt water a 3 d image of the plume has been developed which shows the location of zones of maximum permeability surrounding the injection well through which the salt water has migrated a resolution analysis has determined that the location of the plume is fairly accurate however the image of the geology will be distorted due to incomplete data coverage this latter problem is further complicated by the fact that data residuals indicate that the wells deviate from the vertical these deviations have been shown to cause artefacts within the images and thus further reduce the accuracy of the images with respect to the geology

laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data the campi flegrei caldera located near the city of naples italy has shown signs of unrest characterized by large ground deformation seismic activity and changes in the hydrothermal system since 1970 any attempt to model the processes giving rise to these phenomena requires some knowledge of the subsurface structure and of the physical properties of the rocks at depth in this study we report the results of laboratory measurements of ultrasonic compressional and shear wave velocities in rock samples cored in 4 different geothermal wells reaching a maximun depth of 3 km the wells are located in the san vito sv and mofete mf areas at about 3 km north and 4 km west respectively from the center of the caldera we selected 10 core samples 7 from the sv wells and 3 from the mf wells the attention being focused on the most important rock formations underneath campi flegrei and on the lower sections of the wells where data had been lacking the measurements involved the transmission of ultrasonic waves along three orthogonal directions through dry and water saturated rocks at room conditions the samples are only moderately anisotropic 13 for one sv sample and 8 for all the other samples wave velocities generally increase with the depth of the sample the range of velocities is 3 5 4 km s 1 for p waves and 1 5 2 9 km s 1 for s waves for the sv samples water saturation generally implies slightly larger 10 vp values and smaller 20 vs values as compared with dry velocities for the mf samples water saturation implies both higher vp and vs velocities up to 35 and 18 respectively these results may be explained by the different type of porosity of the sv samples vesicular and the mf samples fissurai the ultrasonic measurements on water saturated samples are slightly higher than the available in situ vp sonic measurements 25 for one sv sample and 15 for all the other samples these differences can be explained by velocity dispersion between ultrasonic and sonic frequencies and by the different pressure temperature conditions existing at depth

multivariate statistical analyses applied to seismic facies recognition one of the most important goals of seismic stratigraphy is to recognize and analyze seismic facies with regard to the geologic environment the first problem is to determine which seismic parameters are discriminant for characterizing the facies then to take into account all those parameters simultaneously the second problem is to be sure that there is a link between the seismic parameters and the geologic facies we are investigating this paper presents a methodology for automatic facies recognition based upon two steps the first or learning step begins with the definition of learning seismic traces for each facies we wish to recognize the choice of learning traces is based upon either well data or a seismic stratigraphic interpretation a large number of seismic parameters are then computed from the learning traces multidimensional analyses are carried out in order to validate the choice of learning traces and to select among all the available parameters those that discriminate best at this st

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

geophysical inversions applied to 3d geology characterization of an iron oxide copper gold deposit in brazil abstract mineral exploration dynamics often requires an efficient and objective means of evaluating a prospect in early exploration stages when few holes have been drilled in the case of deep prospects or prospects under cover this evaluation will mostly be based on geophysical data to develop an objective interpretation method capable of combining all the information available we have developed an integrated interpretation scheme of geophysical models and sparse geologic data our method is based on the relationship between recovered physical properties obtained from 2d and 3d inversions aiming to find patterns associated with geologic units such as iron formation copper ore and host rock the interpretation is guided by theoretical relations of the minerals of interest chalcopyrite and magnetite and the sparse geologic information available it is suitable for prospects in the initial stages of exploration when only limited mineralogical information is available from say one drillhole we h

integrated data analysis for mineral exploration a case study of clustering satellite imagery airborne gamma ray and regional geochemical data suites abstractpartitioning cluster algorithms have proven to be powerful tools for data driven integration of large geoscientific databases we used fuzzy gustafson kessel cluster analysis to integrate landsat imagery airborne radiometric and regional geochemical data to aid in the interpretation of a multimethod database the survey area extends over 3700 km2 and is located in the northern cape province south africa we carefully selected five variables for cluster analysis to avoid the clustering results being dominated by spatially high correlated data sets that were present in our database unlike other more popular cluster algorithms such as k means or fuzzy c means the gustafson kessel algorithm requires no preclustering data processing such as scaling or adjustment of histographic data distributions the outcome of cluster analysis was a classified map that delineates prominent near to surface structures to add value to the classified map we compared the detected structures to mapped geology an

porosity from seismic data a geostatistical approach using a geostatistical technique called cokriging the areal distribution of porosity is estimated first in a numerically simulated reservoir model then in an oil bearing channel sand of alberta canada the cokriging method consistently integrates 3 d reflection seismic data with well measurements of the porosity and provides error qualified linear mean square estimates of this parameter in contrast to traditional seismically assisted porosity mapping techniques that treat the data as spatially independent observations the geostatistical approach uses spatial autocorrelation and crosscorrelation functions to model the lateral variations of the reservoir properties in the simulated model the experimental root mean square porosity error with cokriging is 50 percent smaller than the error in predictions relying on a least squares regression of porosity on seismically derived transit time in the reservoir interval in the alberta reservoir a cross validation study at the wells demonstrates that the co