evidence from precise earthquake hypocenters for segmentation of the san andreas fault in san gorgonio pass we use precise hypocenter patterns and focal mechanisms to investigate the presence or absence of a continuous strike slip fault at depth connecting the san bernardino strand of the san andreas fault with the coachella valley segment of the banning fault we inverted 560 000 arrival times from 23 000 earthquakes 1981 1993 for high quality hypocenters and three dimensional p wave velocity structure in a 1 by 2 area centered on the san gorgonio pass cross sectional plots of relocated earthquakes reveal an abrupt 5 to 7 km high step in the maximum depth of hypocenters the step riser defines a near vertical locally curved surface that extends westerly more than 60 km from the coachella valley segment of the san andreas fault to the san jacinto fault a hypothetical continuous vertical san andreas fault through san gorgonio pass would cross the step at an oblique angle we suggest that the step is the expression of the contact between different basement rock types juxtaposed by large scale right slip motion on the ancestral san andreas fault south of the step in peninsular ranges type basement intrusives brittle failure occurs down to about 20 km depth while north of the step in san bernardino type basement pelona schist brittle failure occurs to only about 13 km depth the step provides a piercing plane that should be offset about 3 km right laterally by an active continuous vertical san andreas fault within the resolution of our mapping the step is not offset in this manner implying either that there has not been a throughgoing vertical fault at depth that a throughgoing fault has not experienced enough slip to offset the step or that a throughgoing fault is not vertical and dips north over the top of the step hypocentral patterns and focal mechanisms indicate distributed deformation thrust normal and strike slip faulting over a large volume in the san gorgonio pass region there is no evidence of hypocenter or slip vector alignments that would indicate a throughgoing continuous near vertical san andreas fault in summary we find no evidence indicating a continuous fault at seismogenic depth connecting the san bernardino strand and coachella valley segment of the san andreas fault zone we speculate that this is because the 3 km of right slip on the san bernardino stand of the san andreas fault and coachella valley segment of the banning fault has not been sufficient to form a single new structure through the 15 to 20 km gap between the two previously unconnected segments this implies that large earthquake rupture on the san andreas fault may be inhibited from propagating through san gorgonio pass thus limiting the maximum magnitudes on the southern san andreas fault

potentially toxic elements ptes associated with asbestos chrysotile tremolite and actinolite in the calabria region italy abstract potentially toxic elements ptes hosted in asbestos elongate mineral particles is one of the factors that determines their toxic pathogenic effects this study quantifies and compares these elements in terms of major minor and trace element concentrations si mg ca al fe mn cr co ni cu zn be v as rb sb ba pb sr in various types of asbestos using micro x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms in order to understand how they contribute to asbestos related diseases chrysotile tremolite asbestos and actinolite asbestos extracted from the gimigliano mount reventino unit calabria region southern italy were used for this study in the minerals analysed high concentrations of cr 171 ppm and be 2 9 ppm were found in tremolite asbestos and chrysotile respectively when calculating the pseudo total concentrations of trace elements in the samples the largest amounts were detected in tremolite asbestos followed by actinolite asbestos and chrysotile however since other metals such as mn and fe minor elements are known to induce toxicity and considering their input to the overall balance actinolite contained the largest amount of ptes and in this case chrysotile proved to be more toxic than tremolite asbestos furthermore the potential leaching of ptes released by chrysotile tremolite and actinolite asbestos containing rocks into the soil and water supply is also discussed since asbestos elongate mineral particles can be widespread in the environment i e air rocks soil water it is essential to quantify the toxic elements present in asbestos elongate mineral particles in order to prevent asbestos related diseases the knowledge obtained from this study will provide us with a better understanding of asbestos related lung cancer

deciphering the tectonic geodynamic context of the gem quality noble serpentine deposit formation combining microstructural chemical and micro raman analyses in palaeozoic olivine bearing marbles and serpentine hosting rocks pizzo tremogge margna unit austroalpine val malenco central alps italy abstract the gem quality noble serpentine of pizzo tremogge val malenco italy is included in palaeozoic olivine bearing marbles occurring in the margna unit central austroalpine domain a detailed inspection of serpentine samples reveals the presence of the three serpentine species lizardite chrysotile and antigorite occurring in different microstructural domains serpentine samples were investigated to obtain microstructural information preserved in the serpentine species by optical microscopy x ray powder diffraction electron microprobe spectrometry and micro raman spectroscopy the last of which is considered a reliable method for the identification of the different serpentine species two types of noble serpentine have been identified the yellow green type characterized by fine grained aggregates in marbles and the green type localized in fibrous veins in association with calcite and quartz the identification of the different serpentine types allowed us to recognize three stages of mineral crystallization characterized by i the formation of olivine bearing marbles stage 1 ii the growth of lizardite after olivine or within lizardite rich veins stage 2 and iii the replacement of lizardite by antigorite in marbles and by antigorite clinohumite in veins stage 3 these stages clarify the complex geodynamic tectonic evolution of the margna malenco system the paleozoic olivine bearing marbles margna protoliths stage 1 are subjected to extensional tectonics that brings the margna protoliths close to the malenco in a thinned extended type passive margin stage 2 finally an inversion of tectonics leads to the subduction and collision of the margna malenco system during alpine convergence stage 3 all this suggests that gem quality noble serpentine deposits may be related to different geological contexts

quantitative determination of chrysotile in massive serpentinites using dta implications for asbestos determinations there is increasing concern about the health hazard of asbestos from natural geologic deposits such as greenstones natural occurring asbestos noa therefore quantitative determination of the chrysotile asbestos content within massive serpentinites is a recurrent requirement of recent asbestos inherent law regulations due to the possible health hazard associated with the release of chrysotile fibers unfortunately the obtainment of accurate and precise quantitative figures of the actual chrysotile content is strongly complicated by typical serpentinite textures consisting of fine to ultrafine intergrowths of fibrous and non fibrous serpentine minerals often difficult to identify by conventional methods such as x ray diffraction or microanalytical approaches in this paper we propose a reliable and straightforward method for the quantitative determination of chrysotile asbestos within bulk massive serpentinites based on thermal analysis data and specifically on the distinctive thermal behavior of chrysotile lizardite and antigorite during dehydroxylation at 500 800 c deconvolution processing of dta endothermic signals in the dehydroxylation temperature range revealed good linear correlation between peak area ratios and chrysotile content for both lizardite chrysotile and antigorite chrysotile samples the dta correlation curves have been used to determine the chrysotile content in two test serpentinites revealing surprisingly high chrysotile content this novel method is of vast importance as it represents one of the most promising tools for chrysotile quantitative determinations in massive serpentinites providing unbiased and accurate responses to recent asbestos related law requirements

morphology of large scale traveling atmospheric disturbances in the polar thermosphere using a fully coupled thermosphere ionosphere plasmasphere model we investigate the morphology of modelled large scale traveling atmospheric disturbances ls tads hereinafter tads propagating both poleward and equatorward from auroral sources we confirm observational evidence of daytime ion drag reducing equatorward far field tad activity we further suggest an additional source dependent mechanism that associates tads propagating preferentially poleward with an auroral electric field burst that contains an eastward rather than a westward component these poleward tads are superimposed on the high speed neutral air winds in the polar cap originating from the day night plasma convection and exhibit speed and spatial resonance effects with the neutral wind the direction of propagation is affected by coriolis forcing due to the earth s rotation

asbestos and other fibrous minerals contained in the serpentinites of the gimigliano mount reventino unit calabria s italy serpentinites are metamorphic rocks with good technological properties and valuable ornamental characteristics which have been exploited since ancient times actually their use is limited and monitored in several countries worldwide because they can contain fibrous asbestos minerals that may be carcinogenic furthermore certain types of fibrous minerals can be confused with asbestos and must therefore be carefully investigated we have investigated the possible presence of the asbestos and non asbestos fibrous phases contained in serpentinitic rocks in a meta ophiolitic sequence from the gimigliano mount reventino unit southern italy which had not been previously assessed the detection and quantification of asbestos and the correct distinction of the fibrous non asbestos minerals are very important not only from a scientific point of view but also from a legislative one this is especially the case for the administrative agencies that have to take decisions with regards to the implementation of public and occupational health protection measures e g in road yards and quarry excavations as a consequence of this serpentinitic rock samples have been characterized in detail through x ray powder diffraction scanning and transmission electron microscopy combined with energy dispersive spectrometry analytical electron microscopy sem eds and tem aem differential scanning calorimetry thermogravimetry and micro raman spectroscopy two kinds of asbestos and four kinds of non asbestos fibrous silicates have been detected in the examined samples in order of decreasing abundance these are polygonal serpentine chrysotile fibrous antigorite tremolite gedrite and magnesiohornblende the size morphology crystallinity and chemical composition of the fibres were also discussed in the light of the possible role these properties could play in the carcinogenic effect on human health

natural radioactivity levels k th u and rn in the cecita lake area sila massif calabria southern italy an attempt to discover correlations with soil features on a statistical base soils can exhibit a complex range of physical mineralogical and chemical features depending on many interrelated factors such as parental rock composition and mineralogy climate topography vegetation amounts and types water infiltration versus runoff soil moisture organic matter presence and types of anthropogenic contaminants and many others radioactivity as measured on these complex systems is consequently perturbed by several mixed effects in order to find out a possible potential relationship among soil properties and experimental data attributable to radioactivities of k th u and rn a detailed investigation has been performed in the cecita lake basin sila grande calabria southern italy most of the soil types outcropping in the cecita lake surroundings belong to the entisol and inceptisol orders usda united states department of agriculture 2006 keys to soil taxonomy 10th edit usda soil survey staff natural resources conservation service washington d c 333 pp representing relatively young poorly to moderately differentiated soils showing features strongly dependent on the nature of the parent rock and the climatic conditions disintegrations contributed by k th u and rn measured respectively in k ppm u and th and kbq m3 rn have been related to 13 a priori known soil unit groups with well defined general features and spatial position the data have been analysed by using graphical and numerical statistical procedures able to manage compositional data in a correct sample space the paper summarises the results of this research and highlights the conclusions drawn from these investigations particularly concerning i the modelling of the high u variability a behaviour that tends to homogenise the differences potentially attributable to soil features with the exception of situations where uranium could be enriched due to adsorption onto iron oxi hydroxides and or clay minerals or concentrated in argillic horizons due to illuviation ii the discovering of the discriminative effect of the k th ratio values particularly for soil groups where th behaviour as other tetravalent actinides is strongly affected by the presence of mineral colloids or where the presence of clays affects the trapping of k iii the clustering of the a priori known soil groups in four new sets characterised by internal similarities for rn values for which the morphology appears to be the most important discriminative effect

san andreas fault geometry through the san gorgonio pass california three dimensional numerical models are needed to investigate the role of nonvertical strike slip fault segments on the deformation within restraining bends numerical models simulate geologic deformation of two alternative three dimensional present day configurations for the san andreas fault through the restraining bend within the san gorgonio pass region sgpr in southern california both models produce decreasing strike slip rates southward along the san bernardino strand of the san andreas fault similar to geologic data the north dipping san andreas fault model better matches the available strike slip data as well as the geologic uplift data for the southern san bernardino mountains than the vertical san andreas fault model we conclude that a north dipping fault configuration is preferred for models of the san andreas fault in the sgpr the complexity of the active fault geometry at the sgpr promotes the transfer of strike slip from the san andreas fault to the nearby but unconnected san jacinto fault slip rates and uplift patterns are sensitive to fault geometry within strike slip restraining bends

lithospheric instability beneath the transverse ranges of california recent high resolution seismic experiments reveal that the crust beneath the san gabriel mountains portion of the transverse ranges thickens by 10 15 km contrary to earlier studies associated with the transverse ranges there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle this high velocity anomaly has previously been interpreted as a lithospheric downwelling both lithospheric downwelling and crustal thickening are associated with the oblique convergence of pacific and north america plates across the san andreas fault though it seems likely that the lithospheric downwelling is driven at least partly by gravitational instability of the cold lithospheric mantle we show by means of numerical experiment that the balance between buoyancy forces that drive deformation and viscous stresses that resist deformation determines the geometry of crustal thickening and mantle downwelling we use a simple two layered lithospheric model in which dense lithospheric mantle overlies relatively inviscid and less dense asthenosphere and is overlain by buoyant crust external plate motion drives convergence which is constrained by boundary conditions to occur within a central convergent zone of specified width a fundamental transition in the geometry of downwelling is revealed by our experiments for slow convergence or low crustal viscosity downwelling occurs as multiple sheets on the margins of the convergent zone for fast convergence or crust that is stronger than mantle lithosphere a single downwelling occurs beneath the center of the convergent zone this complexity in the evolution of the system is attributed to the interaction of crustal buoyancy with the evolving gravitational instability in order for a narrow downwelling slab to have formed beneath the transverse ranges within the last 5 myr the effective lithospheric viscosity of the convergent region is at most about 10 20 pa s

tectonic and volcanic evolution of dark terrain and its implications for the internal structure and evolution of ganymede furrows in ancient dark terrain on ganymede form three systems that are each hemispheric or greater in scale the oldest of the systems designated system iii is dominated by approximately concentric troughs centered on about 60 n 50 w system i in the anti jovian hemisphere contains concentric and subradial furrows arrayed around a large degraded palimpsest centered at 15 s 165 w furrows in each system formed on and locally are buried by dark volcanic materials that embay and infill preexisting topographic features they crosscut extremely few well preserved older craters and they occur on surfaces having significantly different relative crater ages system ii also in the anti jovian hemisphere contains widely spaced radially arrayed furrows commonly 500 2000 km in length which are organized around a large area of dark smooth resurfacing material intense dark terrain fracturing and some of the globally oldest light material the total thickness of dark terrain resurfacing estimated using the stratigraphy of different dark material deposits and the rim heights of the largest crater size class whose density was depleted by each deposit is probably in the range of 3 8 km multiple models of the origin of each furrow system were tested using observed geologic features and patterns systems i and iii were found to be most consistent with reactivation of impact generated multiringed structures by endogenic global extension during a period of widespread dark material volcanism that obliterated a dense ancient crater population system ii was found to be most consistent with fracturing of a single circular isostatic uplift covering an entire hemisphere on the basis of geologic observations and interpretations and theoretical models of convection in spheres it is hypothesized that the uplift developed by long term warming of the upwelling current of a single axisymmetric convection cell in an initially cooler undifferentiated interior such wanning would also have created global expansion and supplied the tensional stress inferred to have formed systems i and iii this hypothesis is supported by the concentration around the center of system ii of intense fracturing and relatively young dark volcanic deposits suggestive of high lithospheric heat flow lithospheric thinning and stress concentration an observed long term decrease in the width of extensional tectonic features interpreted to be of endogenic origin is also consistent with lithospheric thinning due to warming of a cool interior

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

use of mean residence time of water flowrate and equilibrium temperature indicated by water geothermometers to rank geothermal resources application to the thermal water circuits of northern calabria abstract a new hydro geochemical survey was carried out on the thermal sites of northern calabria by use of new and historical data it was possible to improve the knowledge on the deep systems of interest first thermal waters were characterized by means of a classical approach including water classifications use of the triangular diagram of cl li b and geothermometry through suitably selected functions then the tritium based mean residence time and flowrate of the thermal waters of northern calabria were used to evaluate the volume of the geothermal reservoir and its component terms based on these results the heat stored in the geothermal reservoir was computed by means of the volume method their natural heat discharge was also calculated these parameters as well as the reservoir temperature indicated by water geothermometers were used to rank the geothermal resources of northern calabria sambiase resulted to be the thermal circuit of highest geothermal potential

asbestiform and non asbestiform morphologies in a talc and vermiculite mine from the province of cordoba argentina a case study in this work a talc and vermiculite mine from the province of cordoba argentina was investigated with special emphasis on the occurrence of asbestiform and non asbestiform phases the meta ultramafic rock was studied by a multimethodological approach complementing field studies with petrographic mineralogical compositional and morphological analyses samples were examined by stereomicroscopy polarizing light microscopy sem eds xrd dsc tga and ftir complementary compositional and textural analyses were performed with fe sem eds and epma talc rich veins with a laminar and fibrous appearance were at first recognized however the fibrous morphology observed both in the field and by microscopy is due to an apparent habit because of the sample orientation to avoid erroneous interpretations studies by secondary electron images sem are fundamental to carrying out this type of analysis tremolite was identified in different zones of the outcrop however only 40 of the crystals located in the vermiculite zone have dimensions to be considered as asbestiform fibres in the range of respirable particles in these types of complex deposits affected by superimposed metamorphic igneous and deformational events multimethodological approaches are necessary to develop models of occurrence of asbestiform morphologies that may be applicable to other with similar characteristics

complexities of the san andreas fault near san gorgonio pass implications for large earthquakes 1 geologic relationships and patterns of crustal seismicity constrain the three dimensional geometry of the active portions of san andreas fault zone near san gorgonio pass southern california within a 20 km wide contractional stepover between two segments of the fault zone the san bernardino and coachella valley segments folds and dextral reverse and dextral normal faults form an east west belt of active structures the dominant active structure within the stepover is the san gorgonio pass garnet hill faults a dextral reverse fault system that dips moderately northward within the hanging wall block of the san gorgonio pass garnet hill fault system are subsidiary active dextral and dextral normal faults these faults relate in complex but understandable ways to the strike slip faults that bound the stepover the pattern of crustal seismicity beneath these structures includes a 5 8 km high east west striking step in the base of crustal seismicity which corresponds to the downdip limit of rupture of the 1986 north palm springs earthquake we infer that this step has been produced by slip on the linked san gorgonio pass garnet hill coachella valley banning sgp gh cvb fault this association enables us to construct a structure contour map of the fault plane the large step in the base of seismicity downdip from the sgp gh cvb fault system probably reflects a several kilometers offset of the midcrustal brittle plastic transition u th he thermochronometry supports our interpretation that this south under north thickening of the crust has created the region s 3 km of topographic relief we conclude that future large earthquakes generated along the san andreas fault in this region will have a multiplicity of mostly specifiable sources having dimensions of 1 20 km two tasks in seismic hazard evaluation may now be attempted with greater confidence first the construction of synthetic seismograms that make useful predictions of ground shaking and second theoretical investigations of the role of this complexity in retarding the propagation of future seismic ruptures

the carbonate tectonic units of northern calabria italy a record of apulian palaeomargin evolution and miocene convergence continental crust subduction and exhumation of hp lt rocks in northern calabria italy the metasedimentary succession of the lungro verbicaro tectonic unit preserves mineral assemblages suggesting underthrusting to depths in excess of 40 km internal deformation of these rocks occurred continuously during the following decompression index mineral composition associated with progressively younger tectonic fabrics indicates that a substantial part of the structural evolution took place within the blueschist facies p t field despite their tectonic and metamorphic history the rocks of the lungro verbicaro unit preserve significant sedimentary and palaeontological features allowing correlations with successions included in adjacent thrust sheets and the reconstruction of the mesozoic continental margin architecture the subduction exhumation cycle recorded by the lungro verbicaro unit is entirely of miocene age this portion of the apulia continental palaeomargin was involved in convergence related deformation not earlier than the aquitanian the integration of our results with available constraints on the tectonic evolution of the apennine calabrian arc system suggests that subduction and most of the subsequent exhumation of the lungro verbicaro unit occurred up to langhian time at maximum vertical rates in excess of 15 mm a 1 the exhumation process was then completed at much slower rates 1 in late miocene time as indicated by both apatite fission track data and stratigraphic information

structure of the monte reventino greenschist folds a contribution to untangling the tectonic transport history of calabria a key element in italian tectonics abstract calabria an anomalous pile of largely crystalline nappes resting on top of the mostly sedimentary fold thrust belts of the apennines and the sicilian maghebides has moved several hundred kilometers southeastward opening the tyrrhenian sea in its wake this study treats the monte reventino area in the northern third of crystalline calabria where pre mesozoic schist appears to rest on deep water mesozoic sedimentary rocks along a thrust surface marked by discontinuous bodies of serpentinite and banded greenschist with a complex internal structure detailed mapping led to a structural analysis of an unusual pattern of folds in the banded greenschist resulting from twisting of opposite major fold limbs in opposite directions a useful aspect of this fold distortion is that the sense of rotation of minor fold axes enables one to determine the sense of tectonic transport in this case it was generally westward for many years the structure of calabria has been thought of as a pile of nappes emplaced through entirely compressional thrusting recently some geologists have begun to reinterpret the structure as resulting from large scale low angle extensional faulting that has stretched and torn apart the nappe edifice monte reventino appears to be a key location for evaluating this possibility

predictive assessment of the asbestos content in the western italian alps an essential tool for an effective approach to risk analysis and management in tunneling operations and muck reuse the modern approach to the design and management of tunnel excavation and muck reuse can be influenced to a great extent by the possible presence of rock formations containing asbestos minerals this situation creates problems concerning the protection of the workers health and the expectable environmental criticalities while a drastic re consideration of the muck destination is necessary since in the case of carcinogens corrective action following exposure or dispersion is not acceptable detailed knowledge of the characteristics of the material to be excavated is all the more essential only on this basis it is possible to design the tunneling operations in a prevention through design approach so that the tunnel driving techniques fittings and technologies and special equipment and modus operandi can grant where necessary minimized risk conditions and make a correct decision on whether how and when these measures must be fully activated since such an approach involves a remarkable impact on costs and work organization in the western alps a detailed identification and quantification of the asbestos content in rocks is a difficult task due to the fact that the asbestos in the host rocks mainly serpentinite shows a highly variable distribution typical of ophiolitic belts throughout the world as it is mostly associated with joints and shear zones the possibilities of a predictive assessment of the asbestos content in the formations to be excavated are here discussed with special reference to the reliability of the achievable results

serpentine minerals discrimination by thermal analysis this paper reports a complete set of tg dtg and dta data coupled with emitted gas analysis for well constrained almost pure serpentine samples serpentine dehydroxylation takes place between 550 and 800 c with dtg and dta peak temperatures progressively decreasing from antigorite 720 and 715 c respectively to lizardite 708 and 714 c polygonal serpentine 685 and 691 c and chrysotile 650 and 654 c antigorite has an additional diagnostic signal at 740 760 c always absent in the other serpentines and dependent on antigorite superperiodicity t shift of 20 c from 36 to 49 a modulation wavelength a sharp exothermic peak occurs at extremely constant temperatures 820 c independently from the starting serpentine structure the high t mineral assemblage is always represented by forsterite and enstatite based on the observed relationships between serpentine structures and dtg dta dehydroxylation temperatures thermal analysis may represent a useful tool for serpentine identification particularly in the case of natural massive samples where different varieties are mutually intermixed the accurate definition of serpentine mineralogy would have obvious implications in both geological petrological and health related issues

late cenozoic tectonics of the northwestern san bernardino mountains southern california the late cenozoic structural and stratigraphic history of the northwestern san bernardino mountains supports two distinct episodes of uplift in late miocene to earliest pliocene and quaternary time that we hypothesize are related to movements on low angle structures beneath the range in this paper we document the nature distribution and timing of late cenozoic deformation and deposition in the northwestern san bernardino mountains and we illustrate the neotectonic evolution of the area in a series of interpretive paleotectonic block diagrams in the first episode of deformation late miocene to earliest pliocene motion on the south southwest directed squaw peak thrust system disrupted drainage in pre existing miocene nonmarine basins and uplifted the western third of the present range to form the ancestral san bernardino mountains crystalline rocks of the san bernardino mountains were thrust southward across the present site of the san andreas fault between 9 5 and 4 1 ma at a time when the san gabriel fault was the active strand of the san andreas transform system we speculate that the liebre mountain crystalline block at the northern margin of the ridge basin may be the missing upper plate of the squaw peak thrust now offset along the san andreas fault the second episode of deformation began with uplift of the northern plateau of the modern san bernardino mountains on north directed range front thrusts in early pleistocene time between 2 0 and 1 5 ma synchronous uplift of the northern plateau recorded in early pleistocene fanglomerates on the northwestern margin of the range is interpreted to be the result of movement of a relatively coherent crustal block northward up a south dipping detachment ramp beneath the central range in middle pleistocene time activity on the northern range front began to wane and the locus of uplift shifted to a narrow zone of arching and northward tilting adjacent to the san andreas fault which subsequently migrated rapidly northwestward along the san andreas fault from the western san bernardino mountains into the northeastern san gabriel mountains we attribute this pattern of deformation to the passage of a bulge or strike slip ramp attached to the southwest side of the san andreas fault at depth

dissolution rate of antigorite from a whole rock experimental study of serpentinite dissolution from 2 ph 9 at 25 c implications for carbon mitigation via enhanced serpentinite weathering serpentinite rock dissolution experiments at 25 c and 2 ph 9 were used to retrieve antigorite dissolution rates as its high abundance and comparatively fast dissolution dominate element release from the rock retrieved antigorite dissolution rates at ph 2 02 and 3 06 are similar to previous literature data for serpentine minerals at corresponding ph in contrast retrieved rates at higher ph are considerably lower than corresponding literature data nonetheless the retrieved rates at ph 5 76 and 7 28 are consistent with the linear log rate ph relationship of orlando et al 2011 suggesting that rates follow a single acidic mechanism to a ph of at least 7 3 the relatively low dissolution rates of serpentine minerals found in this study suggests that significantly more time is required for serpentine weathering than that estimated using the dissolution rates of these solids reported by marini 2006 based on a review of literature data as such using enhanced serpentine weathering as a carbon capture storage strategy may be less efficient than previously assumed

hydrogeochemical study of an ophiolitic aquifer a case study of lago southern italy calabria a hydrogeochemical survey was carried out in the area of lago calabria region southern italy and outcropping geological units were classified from the hydrogeological point of view to explain the evolution of local groundwaters in addition reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local metabasalts phyllites and serpentinites by means of the eq3 6 software package version 8 0 simulations were carried at constant temperature of 14 1 c which reproduces the average temperature of local groundwaters three different simulations have been performed for the average metabasalt fixing the fugacity of co2 at either 10 2 4 bar mean value 10 2 0 bar mean value 1 or 10 2 9 bar mean value 1 the simulation for the average serpentinite and phyllite was carried out at the mean value of the fugacity of co2 10 2 4 bar all evidences acquired in this study namely the hydrogeological framework the chemical analysis of local groundwaters and the results of reaction path modeling consistently point out that groundwater circulation under ordinary hydraulic gradient primarily occurs in the ophiolitic sub complex and that dissolution of metabasalts and serpentinites controls the chemical characteristics of the groundwaters from the study area

seismic heterogeneity and small scale convection in the southern california upper mantle we invert traveltime residuals of teleseismic p and s phases for 3 d perturbations in vp vs and vp vs structures in the southern california upper mantle the tomographic inversion uses frequency dependent 3 d sensitivity kernels to interpret traveltime residuals measured in multiple frequency bands and recent advances in regional crustal thickness and velocity models to better isolate the mantle component of traveltime residuals in addition to separate vp and vs tomography we jointly invert the p and s data sets for vp vs perturbations by imposing a smoothness constraint on the lnvs lnvp field the regional upper mantle is very heterogeneous with the greatest amplitude of velocity and vp vs perturbations in the upper 200 km and mantle structures that correlate spatially with the major physiographic provinces of southern california our imaging improves the resolution of the geometry and amplitude of these features in addition to the major structures imaged and discussed in previous papers we find a large high velocity anomaly at depths between 340 and 500 km beneath the borderland transverse ranges and northern peninsular ranges this anomaly is separate from the well known uppermost mantle transverse ranges anomaly which extends no deeper than 175 200 km the strongest low velocity high vp vs anomaly is found beneath and west of the salton trough and is attributed to relatively high partial melt in the asthenosphere as a result of lithospheric thinning the magnitudes of vp vs and vp vs perturbations and knowledge of regional 1 d velocity and attenuation lead us to conclude that the asthenosphere contains up to 1 partial melt extending to depths as great as 150 200 km

implications of volcanism in coastal california for the neogene deformation history of western north america 1 the geologic record of coastal california includes evidence of numerous volcanic centers younger than 30 ma that do not appear to have erupted in an arc setting by correlating these volcanic centers with specific slab windows predicted from analysis of magnetic anomalies on the pacific plate we add new constraints to tectonic reconstructions since 30 ma our correlations such as erupting the morro rock islay hill complex south of the pioneer fracture zone and the iversen basalt south of the mendocino fracture zone require larger displacements within western north america than advocated by most previous authors specifically we infer at least 315 km of motion between the sierra nevada and rigid north america at an azimuth of about n60 w and at least 515 km between baja california and rigid north america in a similar direction a consequence of inferring a large displacement of baja california is that the pacific north american plate boundary must have developed most of its current form prior to 10 ma we interpret a slab window developing between cocos and monterey plates after 19 ma that reconstructs under nearly all of the southern california volcanic centers dated at 18 14 ma most of the sedimentary basins associated with volcanic rocks show brief periods of rapid subsidence synchronous with volcanism followed by slow subsidence of variable but often extended duration consistent with rapid extension of cold lithosphere over recently introduced hot asthenosphere

geophysical evidence for wedging in the san gorgonio pass structural knot southern san andreas fault zone southern california geophysical data and surface geology define intertonguing thrust wedges that form the upper crust in the san gorgonio pass region this picture serves as the basis for inferring past fault movements within the san andreas system which are fundamental to understanding the tectonic evolution of the san gorgonio pass region interpretation of gravity data indicates that sedimentary rocks have been thrust at least 5 km in the central part of san gorgonio pass beneath basement rocks of the southeast san bernardino mountains subtle long wavelength magnetic anomalies indicate that a magnetic body extends in the subsurface north of san gorgonio pass and south under peninsular ranges basement and has a southern edge that is roughly parallel to but 5 6 km south of the surface trace of the banning fault this deep magnetic body is composed either of upper plate rocks of san gabriel mountains basement or rocks of san bernardino mountains basement or both we suggest that transpression across the san gorgonio pass region drove a wedge of peninsular ranges basement and its overlying sedimentary cover northward into the san bernardino mountains during the neogene offsetting the banning fault at shallow depth average rates of convergence implied by this offset are broadly consistent with estimates of convergence from other geologic and geodetic data seismicity suggests a deeper detachment surface beneath the deep magnetic body this interpretation suggests that the fault mapped at the surface evolved not only in map but also in cross sectional view given the multilayered nature of deformation it is unlikely that the san andreas fault will rupture cleanly through the complex structures in san gorgonio pass

a new perspective on the geometry of the san andreas fault in southern california and its relationship to lithospheric structure the widely held perception that the san andreas fault saf is vertical or steeply dipping in most places in southern california may not be correct from studies of potential field data active source imaging and seismicity the dip of the saf is significantly nonvertical in many locations the direction of dip appears to change in a systematic way through the transverse ranges moderately southwest 55 75 in the western bend of the saf in the transverse ranges big bend vertical to steep in the mojave desert and moderately northeast 37 65 in a region extending from san bernardino to the salton sea spanning the eastern bend of the saf in the transverse ranges the shape of the modeled saf is crudely that of a propeller if confirmed by further studies the geometry of the modeled saf would have important implications for tectonics and strong ground motions from saf earthquakes the saf can be traced or projected through the crust to the north side of a well documented high velocity body hvb in the upper mantle beneath the transverse ranges the north side of this hvb may be an extension of the plate boundary into the mantle and the hvb would appear to be part of the pacific plate