lithospheric structure and along strike segmentation of the central andean plateau seismic q magmatism flexure topography and tectonics the central andean plateau is a 300 km wide nearly 4 km high plateau which is situated above a 30 e dipping segment of the subducted nazca plate systematic changes in the topography the upper mantle seismic attenuation q structure the lithospheric flexural rigidity and the distribution and chemistry of back arc lavas indicate that the upper mantle structure changes along strike beneath the plateau south of 23 s the upper mantle beneath the plateau becomes hotter and the lithosphere becomes thinner and weaker this lateral variation in upper mantle structure coincides with variations in the tectonic style and timing of deformation in two physiographically distinct segments of the plateau and its adjacent foreland thrust belt to the east the bolivian altiplano and subandean ranges in the north and the argentine puna and santa barbara system in the south the segments different mantle lid thicknesses result in an altiplano supported mainly by crustal thickening and a puna supported by a combination of a crustal root and a thermal mantle root a thicker stronger foreland lithosphere in the north favors thin skinned underthrusting of the foreland beneath the plateau while to the south the thinner weaker lithosphere allows more basement involved shortening within the foreland and less underthrusting beneath the plateau a weaker lithosphere results in a longer period of compressional deformation and greater local and structural relief in the puna than in the relatively stable altiplano to the north ultimately this observed n s directed segmentation on the plateau and in the foreland may reflect the different responses of strong and weak continental lithosphere to an andean type subduction margin

crustal shortening at the sierra pie de palo sierras pampeanas argentina near surface basement folding and thrusting the sierras pampeanas consist of basement uplifts that are mainly controlled by w verging crustal thrusts one of these the sierra pie de palo is controlled by a blind thrust whose kinematics is debated we analysed the reverse faults located along the eastern side of the range and show that these are characterized by small displacements few hundreds of metres of the neogene and quaternary deposits controlled by the inherited basement metamorphic foliation and shear zones at the sierra scale the inherited foliation pattern appears already folded before the cenozoic shortening forming a series of antiforms and synforms with various wavelengths we propose that this structure is amplified during the plio quaternary shortening resulting in a large asymmetrical basement cored anticline where foliation parallel slip can act as folding mechanism the overall kinematics is consistent with an e verging fault propagation fold this proposed kinematics is an alternative to the frequently suggested w verging fault bend fold model finally we propose a new alternative and speculative crustal and lithospheric structure for this region consisting of two e verging basement thrusts coeval to w verging pampean thrusts both rooting below the precordillera above an eclogitized lower crust

pegmatite emplacement in the serido belt northeastern brazil late stage kinematics of the brasiliano orogen abstract geometric and kinematic analysis was performed in an area located in the central part of the serido belt ne brazil where supracrustal rocks affected by polyphase deformation are well exposed the first event recognized in this area and regionally known as the d 2 deformation is characterized by top to the south thrust tectonics while a second one d 3 deformation is marked by upright folds strike slip or transpressive shear zones and the development of flower structures major pegmatite swarms were emplaced during and late as regards the second event dated ca 580 ma being part of the brasiliano orogeny similar dyke swarms are known from the nigerian shield these pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the neoproterozoic trans sahara borborema collisional belt mineralogical geometric and kinematic features support two stages of pegmatite emplacement during the strike slip event i older syn d 3 homogeneous pegmatites intruded mostly along lithological and structural discontinuities such as foliation surfaces ii late d 3 heterogeneous pegmatites were emplaced along tension gashes and other dilation structures the heterogeneous pegmatites are economically more important being exploited for precious metals and stones as well as industrial minerals

damped regional scale stress inversions methodology and examples for southern california and the coalinga aftershock sequence 1 we present a new focal mechanism stress inversion technique to produce regional scale models of stress orientation containing the minimum complexity necessary to fit the data current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea this procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor to remove these artifacts while retaining any stress variations that are strongly required by the data we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas this method is conceptually similar to other geophysical inverse techniques that incorporate damping such as seismic tomography in checkerboard tests the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion while resolving sharper true stress rotations than a simple smoothed model or a moving window inversion we show an example of a spatially damped stress field for southern california the methodology can also be used to study temporal stress changes and an example for the coalinga california aftershock sequence is shown we recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field

spatial variations in stress within the 1987 whittier narrows california aftershock sequence new techniques and results the ml 5 9 whittier narrows california earthquake of october 1 1987 triggered a complex aftershock sequence the aftershocks had many different focal mechanisms including thrusting on e w striking north dipping planes similar to the main shock right lateral motion on nw se striking planes similar to the ml 5 3 aftershock on october 4 1987 thrusting on n s striking planes and left lateral motion on n s striking planes i attempt to interpret these mechanisms in terms of a stress field that may have caused them previously stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform in order to test for the spatially varying effect of the main shock s dislocation on the aftershocks focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field a series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field these simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses most importantly the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component the simulations also show that when applying the older stress inversion techniques one can determine if the results are valid and the amount of spatially varying stresses present by examining the misfit between the data and the model application of these techniques to the whittier narrows aftershocks suggests that the uniform component of the stress field and the complex faulting corresponds to the response of an elastic halfspace to a simple regional n s compression the misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at whittier narrows however their form as shown by the simulations can not be determined with this data set and these techniques

late quaternary to decadal velocity fields in asia 1 fields of crustal velocity and strain rate within asia averaged over horizontal distances of 300 km are calculated from estimates of quaternary slip rates on faults and rates of change of lengths of baselines between gps sites the calculated fields fit strain rate components estimated from quaternary slip rates within 95 confidence limits and fit the gps data with an rms residual of 2 5 mm yr 1 the strain rate field constrained only by quaternary slip rates of faults differs from the combined solution at the level of 20 nstrain yr 1 and the differences are explicable by the limited accuracy of geological estimates of slip rate therefore the strain rate fields determined by geodetic measurements taken on the 10 year timescale are consistent with geological observations on the 104 year timescale the combined solution for velocities shows plate or block like motion within deforming asia only in tarim south china and the amurian region elsewhere the kinematics of rigid blocks does not provide a useful description of the motion in particular velocities relative to eurasia point at high angles to contours of their magnitudes not parallel to them as they would if large regions moved as rigid blocks the axes of principal horizontal compressional strain align with topographic gradients in agreement with previous suggestions that asia deforms as a continuum under the influence of gravity

melt inclusions in pegmatite quartz complete miscibility between silicate melts and hydrous fluids at low pressure fluorine boron and phosphorus rich pegmatites of the variscan ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 c at a pressure of about 1 kbar pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth a silicate rich h2o poor melt and a silicate poor h2o rich melt both melts were simultaneously trapped on the solvus boundaries of the silicate fluorine boron phosphorus water system the partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 c in steps of 50 c by conventional rapid quench hydrothermal experiments glasses of completely rehomogenized inclusions were analyzed for h2o by raman spectroscopy and for major and some trace elements by emp electron microprobe both types of melt inclusions define a solvus boundary in an xh2o t pseudobinary system at 500 c the silicate rich melt contains about 2 5 wt h2o and the conjugate water rich melt about 47 wt h2o the solvus closes rapidly with increasing temperature at 650 c the water contents are about 10 and 32 wt respectively complete miscibility is attained at the critical point 712 c and 21 5 wt h2o many pegmatites show high concentrations of f b and p this is particularly true for those pegmatites associated with highly evolved peraluminous granites the presence of these elements dramatically reduces the critical pressure for fluid melt systems at shallow intrusion levels at t 720 c water is infinitely soluble in a f b and p rich melt simple cooling induces a separation into two coexisting melts accompanied with strong element fractionation on the water rich side of the solvus very volatile rich melts are produced that have vastly different physical properties as compared to normal silicate melts the density viscosity diffusivity and mobility of such hyper aqueous melts under these conditions are more comparable to an aqueous fluid

strain fabric analysis applied to hydrothermal ore deposits emplaced during changing geodynamical conditions infiernillo and las picazas san rafael massif argentina abstract infiernillo and las picazas are two small hydrothermal ore deposits in the northern san rafael massif argentina they are genetically linked to the permian choiyoi volcanic province which reflects the transition from a convergent plate margin to an extensional regime calc alkaline early permian lower choiyoi magmatism was syntectonic with transpressional deformation of the san rafael orogeny whereas transitional late permian upper choiyoi sequences were emplaced under a transtensional regime during the post san rafael extension infiernillo is a cu mo porphyry type deposit hosted by pyroclastic rocks of the lower choiyoi it consists of a central quartz plug surrounded by a potassic and a phyllic halo and a set of peripheral polymetallic cu pb zn veins cropping out close to the alteration zone the las picazas deposit consists of a group of low sulfidation epithermal galena bearing veins hosted by early palaeozoic meta sediments strain fabric and available 2 d and 3 d kinematic analyses were performed in order to define the relationships between both deposits and the geodynamic scenario these data reveal that a porphyry emplacement at infiernillo occurred during the declination of the san rafael orogeny shortly before the change in stress regime and b las picazas low sulfidation epithermal veins were emplaced during the subsequent transtensional post san rafael regime these results prove that each ore deposit is linked to a different stress regime reflecting the change in geodynamical conditions that prevailed during the emplacement of the choiyoi volcanism thus strain fabric analysis at both ore deposits allows us to confirm that the tectonic regime is a major factor in controlling the mineralization style of hydrothermal ore deposits

apatite fission track thermochronology of the sierras pampeanas central western argentina implications for the mechanism of plateau uplift in the andes over much of its length the andean orogen is characterized by a generally east vergent geometry and a progressive eastward cratonward migration of individual arc orogenic elements a departure from this model occurs in the sierras pampeanas region of central western argentina where a terrane of active basement uplifts is currently developing to the east of the main cordillera apatite fission track data from uplifted precambrian and phanerozoic basement rocks of the sierras pampeanas constrain the tectonic development of this terrane and indicate that deformation associated with exhumation may have propagated broadly westward since the late miocene two pre andean cooling events during the carboniferous permian ca 300 280 ma and the early jurassic middle jurassic ca 200 174 ma have been identified the onset of andean deformation is represented by a cooling event during the late paleocene middle eocene this cooling was followed by a period of middle miocene late miocene reheating during foreland basin style sedimentation exhumation and possible westward migration of the exhumation front in the sierras pampeanas commenced during the late miocene pliocene to the east of the dominantly east vergent precordillera fold and thrust belt the apparent convergence of deformation in these two terranes and the progressive closure of miocene pliocene intermontane basins in the sierras pampeanas may reflect the early stages of andean plateau uplift the relative timing of plateau development along strike suggests that lateral thickening of the orogen is progressing southward at least from the latitude of central bolivia ca 20 s furthermore the time space coincidence between basement uplift and flattening of the subducted slab beneath the sierras pampeanas suggests that a relationship exists between westward displacement of the terrane and the dynamics of plate interaction

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

un coupled thrust belt foreland deformation in the northern patagonian andes new insights from the esquel gastre sector 41 30 43 s the patagonian andes represent a unique natural laboratory to study surface deformation in relation to deep slab dynamics in the sector comprised between latitudes 41 30 and 43 s new apatite u th he ages indicate a markedly different unroofing pattern between the broken foreland area characterized by late cretaceous to paleogene exhumation and the adjacent andean sector to the west which is dominated by miocene pliocene exhumation these unroofing stages can be confidently ascribed to inversion tectonics involving reverse fault related uplift and concomitant erosion late cretaceous paleogene shortening and exhumation are well known to have affected also the thrust belt sector of the study area during a prolonged stage of flat slab subduction therefore the different ages of near surface unroofing documented in this study suggest coupling of the deformation between the thrust belt and its foreland during periods of flat slab subduction e g during late cretaceous paleogene times and dominant uncoupling during periods of steep slab subduction and rollback even when these are associated with high convergence rates i e 4 cm year as those documented in miocene times for the patagonian andes

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

neogene paleoelevation of intermontane basins in a narrow compressional mountain range southern central andes of argentina the topographic growth of mountain ranges at convergent margins results from the complex interaction between the motion of lithospheric plates crustal shortening rock uplift and exhumation constraints on the timing and magnitude of elevation change gleaned from isotopic archives preserved in sedimentary sequences provide insight into how these processes interact over different timescales to create topography and potentially decipher the impact of topography on atmospheric circulation and superposed exhumation this study uses stable isotope data from pedogenic carbonates collected from seven different stratigraphic sections spanning different tectonic and topographic positions in the range today to examine the middle to late miocene history of elevation change in the central andes thrust belt which is located immediately to the south of the altiplano puna plateau the world s second largest orogenic plateau paleoelevations are calculated using previously published local isotope elevation gradients observed in modern rainfall and carbonate formation temperatures determined from clumped isotope studies in modern soils calculated neogene basin paleoelevations are between 1 km and 1 9 km for basins that today are located between 1500 and 3400 m elevation considering the modern elevation and 18o values of precipitation at the sampling sites three of the intermontane basins experienced surface uplift between the end of deposition during the late miocene and present the timing of elevation change cannot be linked to any documented episodes of large magnitude crustal shortening paradoxically the maximum inferred surface uplift in the core of the range is greatest where the crust is thinnest the spatial pattern of surface uplift is best explained by eastward migration of a crustal root via ductile deformation in the lower crust and is not related to flat slab subduction

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

method for estimating the stress field from seismic moment tensor data based on the flow rule in plasticity theory the stress field is a key factor controlling earthquake occurrence and crustal evolution in this study we propose an approach for determining the stress field in a region using seismic moment tensors based on the classical equation in plasticity theory seismic activity is a phenomenon that relaxes crustal stress and creates plastic strain in a medium because of faulting which suggests that the medium could behave as a plastic body using the constitutive relation in plastic theory the increment of the plastic strain tensor is proportional to the deviatoric stress tensor simple mathematical manipulation enables the development of an inversion method for estimating the stress field in a region the method is tested on shallow earthquakes occurring on kyushu island japan

delamination of southern puna lithosphere revealed by body wave attenuation tomography the southern puna plateau has been proposed to result from a major pliocene delamination event that has previously been inferred from geochemical geological and some preliminary geophysical data seventy five seismic stations were deployed across the southern puna plateau in 2007 2009 by scientists from the u s germany chile and argentina to test the delamination model for the region the puna passive seismic stations were located between 25 and 28 s using the seismic waveform data collected from the puna experiment we employ attenuation tomography methods to resolve both compressional and shear quality factors qp and qs respectively in the crust and uppermost mantle the images clearly show a high q nazca slab subducting eastward beneath the puna plateau and another high q block with a westward dip beneath the eastern cordillera we suggest that the latter is a piece of delaminated south american lithosphere a significant low q zone lies between the nazca slab and the south american lithosphere and extends southward from the northern margin of the seismic array at 25 s before vanishing around 27 5 s this low q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array the low q zone reaches 100 km depth beneath the northern part of the array but only 50 km depth in the south lateral variations of the low q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration the depth of the nazca slab as defined by q images decreases from north to south beneath the plateau which is consistent with the steep flat transition of the angle of the subducting slab as defined by previous earthquake studies

determining changes in the state of stress associated with an earthquake via combined focal mechanism and moment tensor analysis application to the 2013 awaji island earthquake japan abstract one approach that can be used to evaluate the potential for an earthquake occurrence is the detection of the stress concentration at an earthquake fault while the stress fields for pre and post seismic event stages differ this change cannot provide information regarding the potential for an earthquake here we propose a detection method for states of stress that uses focal mechanism data from microearthquakes the state of stress can be defined both by the background stress and by a moment tensor equivalent to the stress concentration we applied this method to actual focal mechanism data from the 2013 awaji island earthquake m6 3 japan and the results showed the presence of stress concentration around the earthquake fault before the mainshock in addition the regional differential stress was shown to be about 13 mpa the magnitude of the obtained stress concentration in the focal area and the high dip angle of the mainshock fault imply that the faulting occurred in the crust where it was overpressurized to a level near the lithostatic pressure

cmt data inversion using a bayesian information criterion to estimate seismogenic stress fields summary we developed an inversion method to estimate the stress fields related to earthquake generation seismogenic stress fields from the centroid moment tensors cmt of seismic events by using akaike s bayesian information criterion abic on the idea that the occurrence of an earthquake releases some part of the seismogenic stress field around its hypocentre we define the cmt of a seismic event by a weighted volume integral of the true but unknown seismogenic stress field representing each component of the seismogenic stress field by the superposition of a finite number of 3 d basis functions tri cubic b splines we obtain a set of linear observation equations to be solved for the expansion coefficients model parameters we introduce prior constraint on the roughness of the seismogenic stress field and combine it with observed data to construct a bayesian model with hierarchic highly flexible structure controlled by hyper parameters the optimum values of the hyper parameters are objectively determined form observed data by using abic given the optimum values of the hyper parameters we can obtain the best estimates of model parameters by using a maximum likelihood algorithm we tested the validity of the inversion method through numerical experiments on two synthetic cmt data sets assuming the distribution of fault orientations to be aligned with the maximum shear stress plane in one case and to be random in the other case then we applied the inversion method to actual cmt data in northeast japan and obtained the pattern of the seismogenic stress field consistent with geophysical and geological observations

water in granite and pegmatite forming melts article i nfo in this paper we have compiled water concentration data obtained from melt inclusion in minerals mostly quartz and topaz from granites and pegmatites a small number of data come from analysis of natural glasses about 4600 melt inclusions are from granites and about 2100 melt inclusions are from pegmatites another 4159 values are from melt inclusions and glasses of rocks with more than 66 g g sio2 are added belonging to a recent compilation the total of 10 859 melt inclusions provides a statistically significant basis from which to derive some conclusions generally the water concentration in granite melt inclusion is b10 g g with three maxima at 4 0 1 3 5 9 1 2 and 8 1 1 1 g g water for pegmatites a larger range of water contents was found from 2 to more than 50 g g water with two distinct maxima at 10 5 8 1 and 26 2 14 3 g g we show that the great spread and the generally high water content of the pegmatite forming melts as sampled by melt inclusions are the result of melt melt immiscibility pro cesses connected with the formation of conjugate melt fraction with contrasting physical and chemical char acteristics which have also a major influence on the element partitioning between such fractions in this paper we also discuss viscosity as an important transport property of natural silicate melts and we show that due to high primary water concentration in the pegmatite forming melts their viscosity is very low over a wide range of temperatures in the case of water rich peralkaline melt fractions the viscosity can decrease still further together these suggest that liquidus undercooling as the major cause of pegmatite textures is redundant furthermore we demonstrate that the effect of boron carbonates and bicarbonates on pegmatite melts these two last mostly ignored in the past have a large influence on the melt structure and they enable pegmatite formation in the absence of the usual discussed fluxing elements such as f and p

the miarolitic pegmatites from the konigshain a contribution to understanding the genesis of pegmatites in this paper we show that the crystallization of miarolitic pegmatites at konigshain started at about 700 c in melts containing up to 30 mass water such high water concentration at low pressures 1 3 kbar is only possible if the melts are peralkaline such peralkaline melts are highly corrosive and reacted with the wall rock here the granite host forming the graphic granite zone in part via a magmatic metasomatic reaction with cooling the water concentration in some melt fractions increased up to 50 mass h2o the melt dominated system ends below 600 c and passes into a fluid dominated system the beginning of which is characterized by strong pressure fluctuations caused by the change of oh and co32 in the melt to molecular water and co2 we note two generations of smoky quartz one crystallized above the transition of quartz 573 c and one below both of which contain melt inclusions this indicates that some melt fraction remains during at least the higher temperature portion of the growth of minerals into the miarolitic cavity contradicting the view that minerals growing into a pegmatite chamber only do so from aqueous fluids we show that the konigshain miarolitic pegmatites are part of the broad spectrum of pegmatite types and the processes active at konigshain are representative of processes found in most granitic pegmatites and are thus instructive in the understanding of pegmatite formation in general and constraining the composition and characteristics of pegmatite forming melts

dynamics of deformation and sedimentation in the northern sierras pampeanas an integrated study of the neogene fiambala basin nw argentina reply the thick skinned sierras pampeanas morphotectonic domain of western and northwestern argentina 27 s 33 s is characterized by reverse fault bounded basement blocks that delimit internally deformed neogene sedimentary basins foreland basin evolution in this part of the andes is still not very well understood for example challenging questions exist as to how thick skinned deformation develops if there are distinct spatiotemporal trends in deformation and exhumation how such deformation styles influence sedimentation patterns and whether or not broken foreland basins are related to regional plate tectonic processes such as flat slab subduction the fiambala basin of the northwestern sierras pampeanas is the largest of several intermontane basins in the transition to the southern margin of the puna plateau this basin preserves a thick continental neogene sequence that provides information on the dynamics of thick skinned deformation and resulting sedimentation the fiambala basin contains 4 km of fluvial alluvial sedimentary rocks that comprise the tamberia guanchin and punaschotter formations u pb geochronology of ashes intercalated within the fiambala stratigraphic sequence demonstrates that these sedimentary rocks are late miocene to pliocene 8 2 0 3 ma to 3 05 0 4 ma in age sedimentology and provenance data indicate that the source of the tamberia formation was located to the west of the modern western basin bounding range the guanchin and punaschotter formations record input from local sources including the modern basin bounding range to the west and the southern puna plateau to the north suggesting reorganization of the catchment area at ca 5 5 ma the coarsening upward trends recorded by the fluvial tamberia and guanchin formations indicate enhanced tectonics and relief during sedimentation the punaschot ter conglomerates record alluvial fan sedimentation and local sources fault kinematic data document a contractional regime characterized by e w and ne sw shortening active throughout the middle late miocene and pliocene furthermore a comparison between the fiambala basin and similar sedimentary basins in the sierras pampeanas e g bermejo foreland basin and the eastern cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland basin system thin skinned for much of its early history our data suggest coeval intrabasin deformation along strike from the bermejo region northward to the eastern cordillera the coeval change at ca 6 ma from a regional to more compartmentalized thick skinned tectono sedimentary environment in the regions adjacent to the eastern cordillera the southern puna margin and other sectors within the sierras pampeanas domain may thus reflect a regional tectonic process related to flat subduction our data combined with existing sedimentological and petrological evidence imply that the passage from steep to flat subduction occurred synchronously from 30 s to 26 s

exhumation and uplift of the sierras pampeanas preliminary implications from k ar fault gouge dating and low t thermochronology in the sierra de comechingones argentina the sierras pampeanas in central and north western argentina constitute a distinct morphotectonic feature between 27 s and 33 s the last stage of uplift and deformation in this area are interpreted to be closely related to the andean flat slab subduction of the nazca plate beneath the south american plate k ar fault gouge dating and low temperature thermochronology along two transects within the sierra de comechingones reveal a minimum age for the onset of brittle deformation about 340 ma very low exhumation rates since late paleozoic time as well as a total exhumation of about 2 3 km since the late cretaceous new ar ar ages 7 54 1 91 ma of volcanic rocks from the san luis volcanic belt support the eastward propagation of the flat slab magmatic front confirming the onset of flat slab related deformation in this region at 11 2 ma although low temperature thermochronology does not clearly constrain the signal of the andean uplift it is understood that the current structural relief related to the comechingones range has been achieved after the exhumation of both fault walls circa 80 70 ma

miocene forebulge development previous to broken foreland partitioning in the southern central andes west central argentina 1 in the distal region of the modern flat slab segment in the southern central andes an unusual stack of middle miocene paleosols together with regional upwarping and normal faulting indicate episodic aggradation and condensed sedimentation contemporaneous with the principal stage of foreland basin development associated with foreland flexure farther to the west these features are consistent with development of a forebulge zone during the early stages of a proposed asymmetric foreland basin system sedimentary thickness farther east and far from the cordilleran tectonic loads suggests accommodation and preservation driven by nonisostatic dynamic subsidence regional overlapping relationships and basin modeling suggest that the modern broken foreland present sierras pampeanas can be interpreted as a reactivation of a formerly partitioned broad forebulge

the role of magmatic and hydrothermal processes in the evolution of be bearing pegmatites evidence from beryl and its breakdown products beryl and euclase crystals from the mina do santino and the jacu pegmatites in the borborema pegmatite province in northeastern brazil contain several generations of melt and fluid inclusions which allow interpretation of p t x conditions responsible for beryl crystallization and for alteration of a primary pegmatitic mineral assemblage to a mixture of hydrothermal minerals euclase bertrandite kaolinite and quartz primary melt and fluid inclusions hosted by beryl were trapped simultaneously however their homogenization temperatures are significantly higher 870 900 c than the values previously reported for pegmatitic systems 712 c and should be treated with caution an isobaric drop of temperature resulted in the exsolution of a fluid a low salinity co2 enriched phase and a saline water rich phase were trapped in pseudosecondary inclusions in beryl at a pressure of 2 1 2 7 kbar and temperature of 390 480 c cooling of the country rocks below 400 c caused a ductile to brittle transition and allowed infiltration of cold groundwater which further decreased the temperature in the system to 190 240 c at the same time the pressure dropped from a lithostatic 2 1 2 7 kbar to a hydrostatic value 0 57 0 73 kbar consequently minerals deposited under magmatic conditions feldspars and beryl became unstable and a newly formed hydrothermal mineral paragenesis euclase bertrandite kaolinite and quartz overprinted the earlier one the hydrothermal fluids responsible for the alteration differ from the earlier exsolved fluids in having a lower salinity lower homogenization temperature the absence of co2 and the presence of ch4

tectonic and dynamic controls on the topography and subsidence of the argentine pampas the role of the flat slab abstract we analyze the pampean foreland the pampas along the modern flat slab segment of the south central andes between 31 and 33 south latitude and to the east of the argentine flat slab province using flexural and gravity studies and computations of dynamic topography bouguer anomalies and flexural analysis predict a foredeep of 250 km width and a peripheral bulge amplitude of 25 m which match the regional morphologies of the modern argentine pampean plain however these studies do not account for the subsurface miocene quaternary basin preservation represented by sedimentary thicknesses 400 m and with depocenters 400 km eastward with respect to flexural models the discrepancy suggests that two mechanisms acting at different wavelengths influence the argentine pampas the basin preservation is likely the result of a large scale geodynamic forcing models of mantle flow driven by realistic flat slab subduction geometry and density contrasts reproduce the depocenter location and the wavelength of subsidence as well as most of the remaining amplitude nonetheless more sophisticated studies e g considering lateral viscosity variations in the mantle wedge might help reduce the dynamic amplitudes and better reproduce the observed geological record

the diversity of b isotope variations in tourmaline from rare element pegmatites in the borborema province of brazil abstract tourmaline chemical and b isotope compositions have been determined from 4 rare element pegmatites and 1 barren pegmatite in the borborema pegmatite province of ne brazil and also from a leucogranite considered to be parental to the pegmatites the rare element pegmatites are of the lct lithium cesium tantalum class and they display a classic zoning structure with tourmaline present in all units but the quartz core tourmaline major element composition varies systematically from schorl dravite in the border and wall zones to varicolored elbaite in the inner zones consistent with increasing differentiation of a pegmatite magma previous studies supposed a continuous variation in li contents from schorl dravite to elbaite but the sims data instead show a major gap between 0 07 wt and 0 72 wt li 2 o followed by a continuous variation to the maximum value of 1 8 wt the barren pegmatite and leucogranite contain schorl dravite only the full range of 11 b values in tourmaline from the borborema pegmatites is from 20 2 to 1 6 n 62 which comes close to the total known diversity of pegmatite tourmalines worldwide and is much broader than the range of the associated leucogranite 15 1 to 13 4 n 3 however more than 80 of the pegmatite tourmalines define a main range between 17 and 9 11 b the average value of the latter 13 5 s d 2 3 n 50 is identical within error with the leucogranite supporting suggestions of a genetic relationship the b isotope compositions of barren and mineralized pegmatites overlap within the main range we find no correlation between chemical composition and b isotope ratios famous for the borboreman province are gem quality crystals of blue paraiba type elbaite the 11 b values of blue tourmaline from the capoeira pegmatite also fall within the main range 16 4 to 11 9 n 5 four of the 5 pegmatites studied are heterogeneous in 11 b with typical variations of 6 however there are no consistent trends in these examples from outer to inner units or from core to rim of zoned crystals that would fit any one scenario of melt evolution instead the factors controlling b isotope evolution e g crystallization fluid exsolution or mixing with external b reservoirs appear to vary locally and can be specific to the individual pegmatite or internal zone within it for example the carrascao pegmatite shows a shift from higher to lower 11 b values in tourmaline from the outer to inner zone 14 9 to 9 1 vs 20 2 to 13 9 resp and there is a parallel trend of lighter rims in zoned elbaite from the inner intemediate zone these trends are consistent with 11 b removal by tourmaline crystallization and or fluid exsolution an opposite trend in isotopic variation was found in zoned tourmaline from the wall zone of the boqueirao pegmatite whose core compositions are in the main range 15 1 to 14 9 and whose rims are much heavier 5 5 to 1 7 similarly high 11 b values about 10 beyond the main range were found in wall zone tourmaline in the barren fazenda turmalina pegmatite 6 0 to 1 6 the patchy distribution of heavy b isotopic compositions found only in outer zones of pegmatites and the strong isotopic contrast with the main range suggest the possibility of mixing with heavy b from the country rocks a potential source being layers of marble and calc silicate rocks

latitudinal variation of denudation in the evolution of the bolivian andes latitudinal gradients in topography relief climate and deformation have been used to suggest that climate driven erosion has exerted a first order control on the development of the central andes we synthesize the spatial and temporal variations in denudation across the eastern bolivian andes 14 22 s from new and existing estimates to test whether physical evidence exists to support the hypothesis that erosion influences thrust belt evolution basin morphometry channel network indices climate and longitudinal river profiles indicate a northward increase in relative relief fluvial incision and denudation short term denudation rate averages from landslide mapping and sediment flux data range from 1 to 9 mm yr in the north compared to 0 3 to 0 4 mm yr in the south long term denudation rate estimates from thermochronology cosmogenic radionuclides foreland basin sediment volumes stra tigraphy paleoerosion surface degradation and balanced cross sections range from 0 04 to 1 6 mm yr with rates up to more than twice as fast in the north when comparing estimates from the same method the shorter term denudation rates exhibit the greatest variance our denudation synthesis shows that an along strike disparity in denudation greater in the north has existed throughout the holocene and perhaps existed since as early as the late miocene our denudation synthesis also suggests that the disparity and denudation rates have increased to the present correlations between the thrust belt geology geometry geomorphology climate and kinematics of the orogenic wedge provides a case study in observing the regional scale interactions between uplift climate and erosion we conclude that the denudation history uplift history and tectonic geomorphic correlations suggest that models of the evolution of the bolivian andes should incorporate a latitudinal erosion gradient for the last 10 kyrs to perhaps 10 myrs

matrix deformation in a basement involved fold and thrust belt a case study in the central andes malargue argentina abstract an analysis of the anisotropy of magnetic susceptibility ams is used to investigate the matrix strain record of weakly deformed clastic rocks including sandstones and shales along a cross section of the malargue fold and thrust belt mftb argentina we collected 339 oriented cores from the tres esquinas sandstones the red beds of the tordillo and neuquen formations as well as from shales silts of the mendoza group overall 90 of the magnetic fabrics are well defined and are related to the strain imprint of the layer parallel shortening among the tectonic related fabrics 40 show the development of a magnetic lineation at right angle of the shortening type ii 38 display an apparent loss of magnetic foliation type iii and 21 develops a magnetic foliation at right angle of the shortening type iv there is no lithological control on magnetic fabric typology despite contrasting ferromagnetic mineralogy between the red sandstones and dark shales thin section observations highlight the good match between the orientation of both the susceptibility ellipsoid and microstructure orientation which enables us to infer the preferred orientations of the petrofabric i e finite strain directions in this way two trends can be recognized in the study area shortening directions trending n110 in the north and trending n80 in the south in addition the spatial distribution of magnetic fabric typology and burial data suggests an atypical pattern of deformation from the foreland to hinterland such a pattern contrasts with previous studies in fold thrust belt settings suggesting that at the matrix scale the deformation even in a pre folding setting is compartmentalized and controlled by the occurrence of deep seated thrusts localized along inherited structures from the analysis of cross sections we can distinguish several domains each of them reflecting distinct states of matrix deformation

reconstructing the thermal and exhumation history of the sierras pampeanas through low temperature thermochronology a case study from the sierra de velasco

modeling heterogeneous deviatoric stress field around the hypocentral area of the 2005 fukuoka earthquake m7 0 by spatially distributed moment tensors 1 recent studies on the stress field in a seismogenic zone revealed a heterogeneous feature around a fault to model the stress field around a fault zone we have developed an inversion method that can be applied to focal mechanism data on microearthquakes and slip data on faults the modeling scheme takes an objective approach without an a priori model such as the existence of faults or a magma source the stress variation resulting from inelastic deformation in a medium e g fault slip and magma intrusion can be expressed as equivalent body forces in the medium thus we attempted to model the stress field through the estimation of parameters of the regional stress and spatially distributed moment sources the method was applied to the focal mechanism data of the aftershocks of the 2005 fukuoka earthquake m7 0 in japan the direction obtained for the minimum regional principal stress i e nnw sse was as expected from the general tendency of the focal mechanisms the results revealed that the stress field was distorted by the fault slip in the middle segment of the earthquake fault the slip detected at the deep part of the fault is located away from the coseismic slip area suggesting a possibility of either preseismic or postseismic slip around the initiation point of the main shock rupture in contrast the stress accumulation rises at the folding point of the aftershock alignment and the stress relaxation area is found at the deeper edge where the largest aftershock occurred and strong heterogeneous medium exists

tectonic shortening and crustal thickness in the central andes how good is the correlation exceptional thickening of continental crust beneath the central andes is believed to be mainly a result of tectonic shortening of the south american plate in neogene time this shortening has been estimated to have contributed as much as 70 80 of the present crustal volume a compilation of published shortening values and our own estimates based on balanced cross sections from the central andes between lat 3 s and 40 s suggest that 70 80 is a maximum rather than an average value for this part of the andes tectonic shortening and the crustal cross section area are only loosely correlated variations in tectonic shortening are more abrupt than those of crustal areas particularly near the northern and southern ends of the altiplano puna high plateau where thick crust is associated with relatively small amounts of shortening shortening there may account for no more than about 30 of the present crustal cross section area the processes that created the remaining crustal area are not clear but are likely to involve poorly constrained pre neogene tectonic shortening moderate magmatic additions to the crust tectonic underplating of material derived from the forearc and possible flow of ductile lower crust along strike

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

the serido group of ne brazil a late neoproterozoic pre to syn collisional basin in west gondwana insights from shrimp u pb detrital zircon ages and sm nd crustal residence tdm ages abstract the serido group is a deformed and metamorphosed metasedimentary sequence that overlies early paleoproterozoic to archean basement of the rio grande do norte domain in the borborema province of ne brazil the age of the serido group has been disputed over the past two decades with preferred sedimentation ages being either paleoproterozoic or neoproterozoic most samples of the serido formation the upper part of the serido group have sm nd tdm ages between 1200 and 1600 ma most samples of the jucurutu formation the lower part of the serido group have tdm ages ranging from 1500 to 1600 ma some basal units have tdm ages as old as 2600 ma reflecting proximal basement thus based on sm nd data most if not all of the serido group was deposited after 1600 ma and upper parts must be younger than 1200 ma cathodoluminescence photos of detrital zircons show very small to no overgrowths produced during ca 600 ma brasiliano deformation and metamorphism so that shrimp and isotope dilution u pb ages must represent crystallization ages of the detrital zircons zircons from meta arkose near the base of the jucurutu formation yield two groups of ages ca 2200 ma and ca 1800 ma in contrast zircons from a metasedimentary gneiss higher in the jucurutu formation yield much younger ages with clusters at ca 1000 ma and ca 650 ma zircons from metasedimentary and metatuffaceous units in the serido formation also yield ages primarily between 1000 and 650 ma with clusters at 950 1000 800 750 and 650 ma thus most if not all of the serido group must be younger than 650 ma because these units were deformed and metamorphosed in the ca 600 ma brasiliano fold belt during assembly of west gondwana deposition probably occurred ca 610 650 ma soon after crystallization of the youngest population of zircons and before or during the onset of brasiliano deformation the serido group was deposited upon paleoproterozoic basement in a basin receiving detritus from a variety of sources the jucurutu formation includes some basal volcanic rocks and initially received detritus from proximal 2 2 2 0 ga transamazonian to late paleoproterozoic 1 8 1 7 ga basement provenance for the upper jucurutu formation and all of the serido formation was dominated by more distal and younger sources ranging in age from 1000 to 650 ma we suggest that the serido basin may have developed as the result of late neoproterozoic extension of a pre existing continental basement with formation of small marine basins that were largely floored by cratonic basement subjacent oceanic crust has not yet been found immature sediment was initially derived from surrounding land as the basin evolved much of the detritus probably came from highlands to the south present coordinates alternatively if the patos shear zone is a major terrane boundary the basin may have formed as an early collisional foredeep associated with south dipping subduction in any case within 30 million years the region was compressed deformed and metamorphosed during final assembly of west gondwana and formation of the brasiliano pan african fold belts

the 3 d tectonic stress fields in and around japan inverted from centroid moment tensor data of seismic events 1 we can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture in the framework of linear elasticity any indigenous source including earthquake rupture is represented by a moment tensor the moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source and so we can quantitatively relate the centroid moment tensor cmt of seismic events with an unknown tectonic stress field on the basis of such an idea and bayesian statistical inference theory we developed an inversion method to estimate the 3 d pattern of tectonic stress from cmt data applying the cmt data inversion method to 12 500 seismic events in and around japan we obtained precise 3 d tectonic stress patterns that illuminate the present day quaternary complex tectonic motion of japanese islands the stress pattern of the kuril japan nankai arc is basically e w compression but the direction of intermediate principal stress changes from n s reverse faulting type in northeast japan to vertical strike slip faulting type in southwest japan on the other hand the stress pattern of the ryukyu and izu bonin back arc regions is basically trench perpendicular tension normal faulting type in addition to these basic stress patterns governed by mechanical interaction between the eurasian north american pacific and philippine sea plates we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the kuril fore arc sliver the collision of the izu peninsula with the mainland of japan and the opening of the beppu shimabara rift zone

faulting and erosion in the argentine precordillera during changes in subduction regime reconciling bedrock cooling and detrital records abstract the argentine precordillera is an archetypal retroarc fold and thrust belt that records tectonics associated with changing subduction regimes the interactions between exhumation and faulting in the precordillera were investigated using apatite and zircon u th sm he and apatite fission track thermochronometry from the precordillera and adjacent geologic domains inverse modeling of thermal histories constrains eastward in sequence rock cooling associated with deformation and erosion from 18 to 2 ma across the central precordillera tracking thrusting during this time the youngest ahe ages 5 2 ma and highest erosion rates are located in the eastern and western extremities of the precordillera and indicate that recent denudation is concentrated at its structural boundaries moreover synchronous rapid pliocene cooling of the frontal cordillera eastern precordillera and sierra del valle fertil was coeval with initiation of basement involved faulting in the foreland detrital zircon u pb geochronology from the ca 16 8 1 ma bermejo foreland basin strata suggests fluvial connectivity westward beyond the frontal cordillera to the main cordillera and coast range followed by an important shift in sediment provenance at ca 10 ma at this time we suggest that a substantial decrease in permo triassic igneous sources in the frontal cordillera and concurrent increase in recycled zircons signatures of paleozoic strata are best explained by uplift and erosion of the precordillera during widening of the thrust belt bedrock thermochronology and modeling indicate a 2 6 myr lag time between faulting related cooling in the hinterland and the detrital record of deformation in the foreland basin suggesting that for tectonically active semi arid settings bedrock cooling may be more sensitive to onset of faulting we suggest that high erosion rates in the frontal cordillera and eastern precordillera are associated with increased interplate coupling during shallowing of the subducting nazca plate that may concentrate stress along weak structural boundaries of the precordillera

experiments on silicate melt immiscibility in the system fe2sio4 kalsi3o8 sio2 cao mgo tio2 p2o5 and implications for natural magmas the effect of cao and mgo with or without tio2 and p2o5 on the two melt field in the simplified system fe2sio4 kalsi3o8 sio2 has been experimentally determined at 1 050 1 240 c 400 mpa despite the suppressing effect of mgo cao and pressure on silicate melt immiscibility our experiments show that this process is still viable at mid crustal pressures when small amounts 0 6 2 0 wt of p2o5 and tio2 are present our data stress that the major element partition coefficients between the two melts are highly correlated with the degree of polymerisation nbo t of the sio2 rich melt whatever temperature pressure or exact composition experimental immiscible melt compositions in natural systems at 0 1 mpa from the literature lunar and tholeiitic basalts plot on similar but distinct curves compared to the simplified system these relations between melt polymerisation and partition coefficients which hold for a large range of compositions and fo2 are extended to various volcanic and plutonic rocks this analysis strengthens the proposal that silicate melt immiscibility can be important in volcanic rocks of various compositions from tholeiitic basalts to lamprophyres however the majority of proposed immiscible compositions in plutonic rocks are at least not coexisting melts but may have suffered accumulation of early crystallized minerals

horizontal subduction zones convergence velocity and the building of the andes we discuss the relationships between andean shortening plate velocities at the trench and slab geometry beneath south america although some correlation exists between the convergence velocity and the westward motion of south america on the one hand and the shortening of the continental plate on the other hand plate kinematics neither gives a satisfactory explanation to the andean segmentation in general nor explains the development of the bolivian orocline in paleogene times we discuss the cenozoic history of horizontal slab segments below south america arguing that they result from the subduction of oceanic plateaus whose effect is to switch the buoyancy of the young subducting plate to positive we argue that the existence of horizontal slab segments below the central andes during eocene oligocene times and below peru and north central chile since pliocene resulted 1 in the shortening of the continental plate interiors at a large distance from the trench 2 in stronger interplate coupling and ultimately 3 in a decrease of the trenchward velocity of the oceanic plate present day horizontal slab segments may thus explain the diminution of the convergence velocity between the nazca and south american plates since late miocene

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

exhumation history of the andean broken foreland revisited the andean broken foreland in west central argentina located 400 800 km from the peru chile trench is associated with flat subduction linked to collision of the oceanic juan fernandez ridge while the conditions associated with flat subduction would be expected to produce increases in rock uplift and exhumation where thrusting and dynamic forces work together a prevalence of pre cenozoic apatite fission track aft cooling ages suggests that there is no such link the lack of cenozoic cooling ages is at odds with structural reconstructions and basin studies along the foreland that show several kilometers of exhumation this paradox can be reconciled by taking into account the thermal effects of flat subduction that removed the mantle wedge and a significant source of heat flow into the crust reinterpretation of published aft exhumation data 320 ages using more realistic lower geothermal gradient values allows for substantial exhumation and explains the lack of cenozoic exhumation ages across the foreland region

fluid inclusion microthermometry in be ta li sn bearing pegmatites from the borborema province northeast brazil abstract fluid inclusions in be ta li sn bearing pegmatites have been reported in the literature as hypersaline aqueous brines or low salinity aqueous or aqueous carbonic fluids the evolution paths of volatile fluids in equilibrium with the different crystallizing phases of rare element pegmatites do not seem to be unique the aim of this work is to contribute to this discussion on the basis of fluid inclusion information from the borborema pegmatite province bpp in northeast brazil some well known heterogeneous be ta li sn mineralized pegmatites of this province were systematically sampled along cross sections with the purpose of studying the fluid inclusions in the different pegmatite zones i muscovite rich contact zone ii homogeneous or graphic pegmatite iii blocky feldspar zone and iv quartz core the observed fluid inclusions mainly in quartz were almost always secondary or pseudosecondary grouped along healed fractures with random orientation even some trails paralleling quartz grain limits were not undoubtedly primary almost all these fluid inclusions were filled with low salinity aqueous or aqueous carbonic fluids primary inclusions were recognized only in some well formed crystals from druses with erratic distribution in the pegmatites microthermometric data from these samples confirm that the various crystallizing phases of the pegmatites were in equilibrium with low salinity aqueous or aqueous carbonic fluids with insignificant n 2 or ch 4 contents with frequent accidentally trapped solids the various types of primary inclusions found in these crystals compare well with the types of secondary inclusions of the samples from the systematic cross sections the relative age of the crystals hosting primary fluid inclusions the relative age of primary inclusion types in successive crystal growth zones the relative age of secondary fluid inclusion trails and the corresponding microthermometric data allowed to establish the most probable evolution of the fluid characteristics during pegmatite crystallization an early low salinity aqueous carbonic fluid with co 2 contents of 20 mol was present during the crystallization of early minerals such as garnet and tourmaline of the border zone and graphic quartz beryl manganotantalite and blue tourmaline of zones ii and iii the end of zone iii crystallization occurred in the presence of a low salinity aqueous fluid with very low co 2 contents as indicated by inclusions in the smoky core of quartz crystals at the limit between zones iii and iv later aqueous fluids barren in co 2 and with salinities increasing from 5 to 20 coexisted with the formation of the pegmatite nucleus and replacement bodies as indicated by inclusions in the border of these crystals and in euclase the estimated trapping conditions of 3 5 kbar and 580 c for the earliest inclusion types agree with the regional metamorphic conditions and with the known liquidus conditions of rare element bearing pegmatite crystallization the trapping conditions of inclusions in euclase and coexisting quartz crystal rims in the pegmatitic core at 3 5 kbar and 400 c are slightly below the conditions admitted for the solidus of rare element pegmatites and indicate an isobaric cooling during pegmatite crystallization

be minerals synthesis stability and occurrence in metamorphic rocks a major interest in beryllium minerals which are rock forming constituents in certain metamorphic hydrothermal and igneous environments comes from their use as ore materials for be as single crystal material for special optical purposes and as gemstones beryl ideally al2be3si6o18 bertrandite be4si2o7 oh 2 and phenakite be2sio4 are mined and processed as ores of be beryl and chrysoberyl are used as maser and laser crystals and bromellite beo has outstanding properties such as exceptionally high electrical conductivity and speed of sound propagation in combination with great strength and chemical resistance be minerals find wide use as gemstones emerald and alexandrite are among the most highly prized for all these reasons a large amount of experimental work has been reported on the synthesis of these minerals the interest in be minerals for petrology comes from the fact that be can be a minor component in several rock forming silicates such as sapphirine margarite and cordierite and can have an important influence on the phase relations of these minerals the study of the behavior of be and be minerals may give an important insight in the history of magmatic and metamorphic rocks one of the key questions for the natural occurrences is the problem of enrichment of be so that either be minerals can be formed or that common rock forming minerals such as cordierite contain an appreciable amount of be we start with a review of experimental work about synthesis of be minerals in various simplified systems their phase equilibria and their compositional variation thermodynamic data and calorimetric work are reviewed by barton and young this volume in the second part we review the geological setting and mineralogical characteristics of be mineralizations in regional metamorphic terrains and on hydrothermal be occurrences metamorphosed be rich pegmatites leucogranites and

neogene and quaternary tectonics of the eastern sierras pampeanas argentina active intraplate deformation inboard of flat slab subduction 1 the ranges of the eastern sierras pampeanas are located 600 km east of the andean cordillera in central argentina and have been interpreted to be a response to shortening related to flat slab subduction of the nazca plate uplift of the ranges has been broadly documented to occur during neogene time but many questions remain regarding the timing and style of deformation and the subsurface structural configuration in this study we address these unknowns with observations at multiple scales integrate our results into a tectonic model for the area and discuss how our structural interpretation fits with more regional tectonic models our major findings are 1 the range bounding faults thrust late proterozoic to cambrian schist and gneiss over poorly dated pliocene to pleistocene alluvial strata the timing of fault displacement and age of footwall strata suggest that deformation may have been active at least by pliocene time 2 apatite and zircon u th he thermochronometry exhibits cooling ages that range from permian to early jurassic time and suggests that rock exhumation in the area is less than 2 3 km since that time 3 deploying a local seismic array allowed for locating seismicity and calculating receiver functions these observations indicate that the moho lies at a depth of 37 km and that a midcrustal discontinuity appears to correspond to a detachment zone between 15 and 20 km depth and aligns with a plane of seismicity in our tectonic model the craton appears to act as a rigid backstop to the eastward propagation of stresses from the shallowly subducting slab deformation then propagates back to the west via westward verging faults along a midcrustal detachment

deformation of an island arc rates of moment release and crustal shortening in intraplate japan determined from seismicity and quaternary fault data the historical record of large m 6 9 earthquakes and geologically determined rates of slip on quaternary faults in intraplate japan honshu and shikoku are used to estimate the average rate of seismic moment release m for the last 400 years and during the late quaternary respectively values of m estimated from the two data sets are similar in regions where seismic activity is concentrated on land we interpret this observation to suggest that m in intraplate japan has been constant during the late quaternary and is relatively free from secular variation when averaged over periods of several hundreds of years m in shikoku may be attributed almost solely to right lateral slip of the median tectonic line mtl the easterly strike of the mtl is consistent with a compressive stress field that trends northwest crustal shortening of the izu peninsula taken up on a set of strike slip faults that show north by northwest compression is 1 mm yr northeast honshu is characterized by a set of reverse type faults that trend northerly conversion of m in northeast japan to strain rates suggests that about 5 of the relative plate motion between japan and the pacific plate 9 7 cm yr is accommodated as a permanent east west shortening 5 mm yr of northeast honshu the predominant deformation in central and western honshu takes place as slip on a conjugate system of strike slip faults that strike northeast and southeast and show right lateral and left lateral motion respectively crustal shortening resulting from slip on faults in central and western honshu is 5 and 0 5 mm yr respectively in an easterly direction central and western honshu are in closest proximity to the nankai trough and hence the stress field in these regions cannot simply be attributed to the accommodation of the relative northwesterly convergence of the philippine sea plate the northward impingement of the izu peninsula into honshu may influence stresses in central and western japan but a conclusive explanation of the stress field in central and western honshu remains an enigma

geometry and brittle deformation of the subducting nazca plate central chile and argentina summary we use data from the chile argentina geophysical experiment charge broad band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the south american subduction zone between 30 s and 36 s this region contains a zone of flat slab subduction where the subducting nazca plate flattens at a depth of 100 km and extends 300 km eastward before continuing its descent into the mantle we use a grid search multiple event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the wadati benioff zone these contours reflect slab geometries from previous studies of intermediate depth seismicity in this region with some small but important deviations our hypocentres indicate that the shallowest portion of the flat slab is a

anatomy and global context of the andes main geologic features and the andean orogenic cycle the andes make up the largest orogenic system developed by subduction of oceanic crust along a continental margin subduction began soon after the breakup of rodinia in late proterozoic times and since that time it has been intermittently active up to the present the evolution of the pacifi c margin of south america during the paleozoic occurred in the following stages 1 initial proterozoic rifting followed by subduction and fi nal re amalgamation of the margin in early cambrian times as depicted by the puncoviscana and tucavaca basins and related granitoids in southern bolivia and northern argentina 2 a later phase of rifting in the middle cambrian and subsequent collisions in middle ordovician times of parautochthonous terranes derived from gondwana such as paracas arequipa and antofalla and exotic terranes originating in laurentia such as cuyania chilenia and chibcha 3 fi nal permian collision between south america and north america to form pangea during the alleghanides orogeny leaving behind rifted pieces of laurentia as the tahami and tahuin terranes in the northern andes and other poorly known orthogneisses in the cordillera real of ecuador in the late permian early triassic and 4 amalgamation of the mejillonia and patagonia terranes in early permian times representing the last convergence episodes recorded in the margin during the gondwanides orogeny these rifting episodes and subsequent collisions along the continental margin were the result of changes of the absolute motion of gondwana related to global plate reorganizations during proterozoic to paleozoic times generalized rifting during pangea breakup in the triassic concentrated extension in the hanging wall of the sutures that amalgamated the paleozoic terranes the opening of the indian ocean in early jurassic times was associated with a new phase of subduction along the continental margin the northeastward absolute motion of western gondwana produced a negative trench roll back velocity that controlled subduction under an extensional regime until late early cretaceous times the northern andes of venezuela colombia and ecuador record a series of collisions of island arcs and oceanic plateaus from the early cretaceous to the middle miocene as a result of interaction with the caribbean plate the remaining central and southern andes record periods of orogenesis and mountain building alternating with periods of quiescence and absence of deformation as recorded in parts of the oligocene based on the generalized occurrence of fl at slab subduction episodes through time as recorded in most ramos v a 2009 anatomy and global context of the andes main geologic features and the andean orogenic cycle in kay s m ramos v a and dickinson w r eds backbone of the americas shallow subduction plateau uplift and ridge and terrane collision geological society of america memoir 204 p 31 65 doi 10 1130 2009 1204 02 for permission to copy contact editing geosociety org 2009 the geological society of america all rights reserved

magnetic anomaly interpretation across the southern central andes 32 34 s the role of the juan fernandez ridge in the late tertiary evolution of the margin marine and terrestrial magnetic surveys have been integrated to study the tectonic structure of the convergent margin of chile between 32 34 s three magnetic domains have been identified oceanic continental margin and subaerial the oceanic domain has seafloor spreading anomalies 16 37 ma to 18 39 5 ma disturbed by anomalies of the juan fernandez hot spot chain in the continental margin the most prominent fabric are e w anomalies in the upper slope corresponding to onshore e w anomalies of large intrusive bodies onshore a n s lineament of short wavelength anomalies defines the roots of a cretaceous volcanic arc a resembling lineament offshore indicates a submerged older volcanic arc and that continental basement extends to 50 km landward of the trench absolute cenozoic plate motion for nazca and south american plates and dating of the juan fernandez chain provide a kinematic model of ridge continent collision the reconstruction indicates rapid southward migration of the collision point along 1400 km of the margin from 20 to 11 ma 20 cm yr 1 from 11 ma to present the collison point has migrated at a slower rate along 375 km of the margin 3 5 cm yr 1 the predicted location of the subducted portion of the juan fernandez chain coincides with the south edge of the southward migrating flat slab segment of the subducted lithosphere and with a cluster of deep earthquakes indicating a causal relationship in the last 10 myr the ridge has separated a sediment starved trench to the north where subduction erosion may dominate from a sediment filled trench to the south where recent sediment accretion dominates these observations indicate that subduction of the juan fernandez chain plays a major role in arc forearc tectonics

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

uplift analysis on a pericratonic region an example in the sierras de cordoba 29 34 s argentina abstract the sierras de cordoba argentina is a mountain belt located in the most distal pericratonic part of the south central andean foreland in the easternmost end of the sierras pampeanas pampean ranges broken foreland although this region is considered an excellent example for settings where basement thrusting generates relief and intermontane basin systems hundreds of kilometers away from the cordilleran front the driving mechanisms and main controls on topography are still poorly understood given that the landscape and particularly the rivers react to changes in climate and tectonics on timescales between 103 and 106 yrs we used dem based morphometry elevation patterns local relief and analysis of 242 longitudinal stream profiles to evaluate the main controls on modern topography we focus on the morphologies of the main streams and their tributaries using metrics of the channel concavity and normalized channel steepness index ksn the distribution of local relief concavity and ksn values was compared with the present day topography tectonic structures rock type and modern rainfall patterns the stream longitudinal profiles show homogeneous concavities and ksn background values with some local anomalies local structures east and west vergent thrusts in the sierras de cordoba seem to be the most fundamental controls on the formation of these anomalies slope break knickpoints as well as deep incision high local relief this suggests localized and accelerated rock uplift rates which produce localized increases in the gradient along the longitudinal stream profile it is important to notice that the highest ksn values were reported on the eastern range flanks coincident with the highest values of mean annual rainfall however high ksn values appear to be maintained even with greater rainfall our study provides new insights on the neogene sierra de cordoba uplift evolution which will assist future sampling and modelling cosmogenic nuclides analysis thermochronology and gps analysis

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

late paleozoic deformation and exhumation in the sierras pampeanas argentina 40 ar 39 ar feldspar dating constraints systematic 40ar 39ar feldspar data obtained from the sierras pampeanas are presented filling the gap between available high 300 c and low temperature 150 c thermochronological data results show silurian devonian exhumation related to the late stages of the famatinian ocloyic orogeny for the sierra de pocho and the sierra de pie de palo regions whereas the sierras de san luis and the sierra de comechingones regions record exhumation during the carboniferous comparison between new and available data points to a carboniferous tectonic event in the sierras pampeanas which represents a key period to constrain the early evolution of the proto andean margin of gondwana this event was probably transtensional and played a major role during the evolution of the paganzo basin as well as during the emplacement of alkaline magmatism in the retroarc

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

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

active basement uplift of sierra pie de palo northwestern argentina rates and inception from10be cosmogenic nuclide concentrations quaternary tectonic and denudation rates are investigated for an actively growing basement anticline the sierra pie de palo range which belongs to the andean foreland of northwestern argentina 28 s 33 s in this study a detailed morphometric analysis of the topography is combined with in situ produced cosmogenic10be concentrations measured in 1 surface boulders abandoned on alluvial terraces affected by fault activity along the north bounding fault and growth of the basement fold along the southeastern border 2 bedrock outcrops corresponding to an exhumed and folded regional erosion surface and 3 fluvial sediments sampled at the outlets of several watersheds along the eastern and northern borders of the range incision and uplift rates have been estimated at approximately 0 5 and 1 mm yr when integrated on holocene and pleistocene time scales in close agreement with both long term structural and basin evolution data and short term gps derived velocity field analyses cosmogenic derived denudation and uplift rates combined with geomorphic characteristics of watersheds and river channels allows estimating the onset of the uplift at 4 6 ma followed by a more recent period of topographic rejuvenation at roughly 1 2 ma probably synchronous with steepening of the eastern and northern flanks of the anticline

cosmogenic 10 be denudation rates and geomorphometric analysis in the ambato range 28 29 s sierras pampeanas argentina abstract quantifying denudation rates along orogenic systems is crucial to understand how tectonics and climate interact with each other to create topography long term mean denudation rates estimated from geologic data in the ambato range sierras pampeanas is 0 34 mm yr when compared with short term denudation rates from other studies northward and southward along the argentine south central andes foreland our results are similar to those found in regions with higher mean annual precipitation here we utilize concentrations of 10be cosmogenic radionuclide crn in river sediments from catchments along the eastern slope of the ambato range to understand the relationship among short term 102 104 yrs catchment wide denudation rates and long term denudation rates estimated from geologic data crn denudation rates range between 0 038 and 0 12 mm yr the relationship between geomorphometric parameters local relief slope hypsometric integral and catchment mean channel steepness index ksn and crn denudation rates shows linear behavior the best correlation concerned ksn indicating a strong connection in the ambato range between tectonics and denudation when analyzed together with denudation rates from other studies northward and southward along the south central andes foreland our results are similar to those found in more arid regions and suggest that bedrock strength variations should be contemplated in a regional analysis as well as climate

vapor undersaturated experiments with macusani glass h 2 o at 200 mpa and the internal differentiation of granitic pegmatites vapor undersaturated fractional crystallization experiments with macusani glass macusanite a peraluminous rhyolite obsidian at 200 mpa yield mineralogical fabrics and zonation and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition typically peraluminous li be ta rich deposits the zonation from the edge of charges inward is characterized by 1 fine grained sodic feldspar quartz border zones 2 a fringe of very coarse grained graphic quartz feldspar intergrowths that flair radially toward melt and terminate with nearly monophase k feldspar 3 cores of very coarse grained nearly monominerallic quartz or virgilite lialsi5o12 mica and 4 late stage fine grained albite mica intergrowths that are deposited from alkaline na rich interstitial melt at vapor saturation similar experimental products have been observed in compositionally simpler less evolved systems liquid lines of descent from initially h2o undersaturated runs are marked by a decrease in sio2 and increases in na k b p f h2o and a variety of trace lithophile cations these trends are believed to be governed by three factors 1 disequilibrium growth of feldspars quartz via metastable supersaturation 2 fractionation of melt toward sio2 depleted na rich compositions due to increases in b p and f and 3 changes in nucleation and growth rates mostly as a function of the h2o content of melt x w m in contrast experiments that are cooled below the liquidus from the field of melt aqueous vapor london et al 1988 fail to replicate pegmatitic characteristics in most respects on the basis of these and other experiments we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile rich melts and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline silica depleted compositions although vapor saturation at near solidus and subsolidus conditions may promote extensive recrystallization an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites