the effects of k metasomatism on the mineralogy and geochemistry of silicic ignimbrites near socorro new mexico abstract k metasomatism of the upper lemitar and hells mesa silicic ignimbrites near socorro new mexico is thought to be the result of downward percolation of alkaline saline brines in a hydrologically closed basin chapin c e lindley j i 1986 potassium metasomatism of igneous and sedimentary rocks in detachment terranes and other sedimentary basins economic implications arizona geological society digest xvi 118 126 during the chemical changes associated with metasomatism na rich phases primarily plagioclase are replaced by secondary mineral phases adularia a low temperature k feldspar is the dominant mineral formed during k metasomatic alteration but mixed layer i s discrete smectite and kaolinite can also be present in the assemblage the formation of discrete smectite within the assemblage during k metasomatism may have occurred during periods of low cation h ratios in the alkaline saline brine upon an increase in the cation h ratio such as could occur during evaporation of the alkaline lake the solution may have become sufficiently concentrated to cause illitization of smectite resulting in the formation of mixed layer i s within the assemblage distribution of phases in the alteration assemblage strongly suggests a dissolution precipitation reaction for k metasomatism in the socorro area as indicated by the presence of dissolution embayments in plagioclase crystals the presence of euhedral adularia and the common occurrence of authigenic clay minerals in the assemblage k metasomatism causes significant chemical modification of the silicic ignimbrite particularly increases in k 2 o and rb and depletion of na 2 o and sr with increasing adularia abundance the correlation between rb and k 2 o suggests that rb is enriched during alteration due to substitution for k in adularia the effect of hydrothermal activity either prior to or following metasomatism is also observed in some samples as shown by high concentrations of elements such as ba as sb pb and cs enrichment of middle and hree in the upper lemitar tuff samples and depletion of middle and hree in hells mesa tuff samples suggests attempted re equilibration between the secondary alteration assemblage and the metasomatizing fluid preliminary data indicate clay minerals within the secondary assemblage may have played an important role in the incorporation of ree during redistribution

experimental results on the influence of gas on the mechanical response of peats direct observation of gas in peat layers generated by slow degradation in anoxic conditions raised concern in the netherlands about its potential impact on the geotechnical response of dykes foun

migratory tectonic switching western svecofennian orogen central sweden constraints from u pb zircon and titanite geochronology abstract the forsmark area in the western part of the svecofennian orogen central sweden is situated between two major palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity ductile deformation and metamorphism geological features common to both the adjacent domains are found at forsmark which consequently is a key area for understanding the tectonic evolution of the svecofennian orogen in this region new sims and tims geochronological data from several samples in a limited area at forsmark constrain the timing of igneous activity ductile deformation and metamorphism in this area u pb zircon dating in combination with field studies reveals the existence of two calk alkaline igneous suites at forsmark the older and most voluminous plutonic suite intruded at 1 89 1 87 ga and is affected by penetrative yet variably intense ductile deformation with the development of a ductile grain shape fabric under amphibolite facies metamorphic conditions and folding the younger and less voluminous hypabyssal suite intruded at 1 86 1 85 ga during the waning stages of this penetrative deformational phase furthermore u pb titanite dating shows that the area has been affected by one or more tectonothermal events after regional fabric development and possibly even after 1 83 ga the deformation during these events involved more restricted strain along discrete zones the forsmark data in combination with a compilation and evaluation of available geochronological data from the time interval 1 91 1 84 ga in central sweden points to the existence of at least two major tectonic cycles in this region each cycle is characterised by igneous activity associated at least partly with extension a short interval of compressional deformation and migration of the tectonic activity in this paper we discuss two highly contrasting tectonic models that may explain the cyclic tectonic evolution of the western part of the svecofennian orogen in central sweden the favoured model involves continuous subduction with a constant polarity beneath a single active continental margin combined with alternating subduction hinge retreat and advance the model involves migration of what has been described as tectonic switching in the younger accretionary orogenic systems of eastern australia palaeozoic lachlan orogen and new zealand

seafloor instabilities and sediment deformation processes the need for integrated multi disciplinary investigations abstract in this paper we present the current practice of investigations of seafloor instabilities and deformation processes based on extensive research conducted over the last years which sets the scene for future research activities in this field the mapping of the continental margins and coastal areas with ever increasing resolution systematically reveals evidence of instabilities and deformation processes both active and palaeo features in order to properly assess the hazards and risks related to these features an integrated and multi disciplinary approach is essential but challenging such an approach consists of combining field data geophysics geology sedimentology geochemistry and geotechnical data with numerical simulations constrained by results from laboratory data as such it is of paramount importance to build a common knowledge base and understanding that unify these disciplines into more complete and conceptual models constrained by all the data we review the status of this integrated approach adapted to palaeo landslides e g storegga ana vesteralen and recent deformations finneidfjord nice gulf of guinea allowing to identify gaps in our knowledge at these sites by reviewing these case studies one can conclude that each case remains highly site specific in which both the regional and local geological tectonic settings have a distinct effect of the type of instability or deformation taking place or that can take place our knowledge on the actual triggers remains poorly constrained and there is even ambiguity for historic landslides e g finneidfjord also our knowledge of the preconditioning factors is incomplete there is a general lack of geotechnical data both in situ and from laboratory and therefore modelling the dynamics e g rheology of the instabilities relies on a number of assumptions rather than facts in addition excess pore pressure and its evolution is one of the key parameters driving instabilities despite this fact in situ excess pore pressure is rarely measured or monitored much work remains to be done to relate and integrate geotechnical data with geophysics e g through inversion and rock physical models in order to obtain additional quantitative information from the sub surface but also with respect to partial saturation free gas hydrate and pore pressure behaviour or lithologies it is of critical importance to be able to identify the different processes which can lead to hazardous situations which include establishing recurrence intervals timing and frequencies through event recognition and age control and magnitudes so that proper mitigation measures can be developed in this perspective the smaller scale instabilities deserve much attention as there are many instances where such features had far reaching consequences for society e g nice finneidfjord in that perspective human interferences e g exploitation drilling blasting loading must be one of the factors that should be taken into consideration

mud volcanism by repeated roof collapse 3d architecture and evolution of a mud volcano cluster offshore nigeria abstract using 3d seismic data we document the subsurface architecture of a cluster of 3 mud volcanoes located on the upper continental slope offshore nigeria in a background of gently dipping stratified sediments the subsurface of the cluster contains 8 seismic sequences made of one subcircular syncline 1 3 km in diameter and adjoining unstratified units synclines flatten out upward through intercalation of unstratified concave up lenses between stratified units and are eventually filled by a convex up unstratified lens onlapped by background sediments the lower boundary of each sequence is a 0 5 1 5 km deep bowl shaped unconformity across which high dip strata rest above truncated low dip series we interpret each seismic sequence as a mud volcano system mvs sourced from a connected region and evolving through episodes of roof collapse three are associated with the surface mud volcanoes and another 4 to fossil ones mud volcano systems are dynamic features that record the evolution of 1 the material extruded from one single connected source region depletion zone as it grows downwards and stepwise becomes depleted 2 the basal unconformity which joins strata originally separated by material evacuated in the remobilization process by analogy with salt tectonics we propose to call it a mud weld 3 the conduits and 4 the successive collapsed roofs of the depletion zone the evolution of each mud volcano system in this interpretation records progressive growth of the depletion zone by downbuilding punctuated by episodes of roof collapse and extrusion the geometry and evolution of this type of mvs can be interpreted in the light of analogue models of magmatic caldera development in early stages the thin roof experiences downsagging while remobilized material is extruded through an axial pipe like conduit in later stages the thickened roof undergoes piston like subsidence and mud extrusion occurs along the peripheral fault

the undrained shear strength of soils containing large gas bubbles measurements of undrained shear strength are reported from a series of triaxial tests on reconstituted soil samples containing large bubbles of methane gas the experimental results indicate that the undrained strength can be either increased or reduced by the presence of large gas bubbles depending upon the values of the consolidation pressure and the initial pore water pressure a conceptual model for soils containing large gas bubbles developed in the companion paper is analysed to provide theoretical predictions for the undrained shear strength the analysis leads to theoretical upper and lower bounds for the undrained strength which show good agreement with the experimental data the experimental and theoretical developments have led to a better understanding of the strength of soils containing large gas bubbles this could be of considerable benefit to the offshore construction industry if platforms pipelines and other structures are to be built in areas of gas bearing sediments l article pre

the undrained equilibrium behaviour of gassy sediments gassy soils are defined as those soils which contain a relatively large amount of gas dissolved in the pore fluid examples include the alberta oil sands marine sediments from deep ocean locations

red staining of the wall rock and its influence on the reducing capacity around water conducting fractures abstract red staining and alteration of wall rock is common around water conducting fractures in the laxemar simpevarp area se sweden which is currently being investigated by the swedish nuclear fuel and waste management co skb in common with many other places red staining is often interpreted as a clear sign of oxidation but relevant analyses are seldom performed the area is dominated by palaeoproterozoic crystalline rocks ranging in composition from quartz monzodiorite to granite in this study wall rock samples have been compared with reference samples from within 0 1 to 1 m of the red stained rock in order to describe mineralogical and geochemical changes but also changes in redox conditions a methodology for tracing changes in mineralogy mineral and whole rock chemistry and fe3 fetot ratio in silicates and oxides in the red stained wall rock and the reference rock is reported the results show that the red stained rock adjacent to the fractures displays major changes in mineralogy biotite plagioclase and magnetite have been altered and chlorite k feldspar albite sericite prehnite epidote and hematite have been formed the changes in chemistry are however moderate k enrichment ca depletion and constant fetot are documented the fe3 fetot ratio in the oxide phase is higher in the red stained samples whereas the fe3 fetot ratio in the silicate phase is largely similar in the wall rock and the reference samples because most of the fe is hosted in the silicate phase the decrease in reducing capacity fe2 if any in the red stained wall rock is very small and not as high as macroscopic observations might suggest instead the mineralogical changes in combination with the modest oxidation and formation of minute hematite grains in porous secondary minerals in pseudomorphs after plagioclase have produced the red staining increased porosity is also characteristic for the red stained rock moderate alteration in the macroscopically fresh reference rock shows that the hydrothermal alteration reaches further from the fracture than the red staining the extent of the red staining can therefore not be used in the same way as the extent of the alteration adjacent to a fracture the increase in porosity in the red stained rock may result in enhanced retention of radio nuclides due to an increased sorptivity and diffusion close to the fracture the hydrothermal alteration causing the red staining is thought to have occurred at temperatures of about 250 400 c based on the secondary mineralogy the major part of this alteration in the area is assumed to be related to fluid circulation associated with the intrusion of the mesoproterozoic gotemar and uthammar granites nearby

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

penetrative ductile deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield the svecofennian orogen in the fennosandian shield consists of several palaeoproterozoic meta igneous provinces that generally young progressively southwards and westwards the understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of ductile deformation and metamorphism within them in the western part of the orogen in central sweden ductile deformation and metamorphism is conventionally thought to have occurred after 1 85 ga and mainly around 1 82 1 80 ga at forsmark in central sweden we have dated two undeformed granite dykes that cross cut the tectonic fabric in their host rocks to 1851 15 and 1855 6 ma respectively since the former shows an unequivocal field relationship with respect to the tectonic fabric we establish that penetrative ductile deformation under amphibolite facies metamorphic conditions occurred prior to 1851 5 ma this u pb zircon minimum age for the timing of ductile deformation is supported by a u pb titanite age of 1844 4 ma these data as well as the field relationships at forsmark indicate that an early phase of penetrative deformation and metamorphism affected the svecofennian bedrock in the western part of the fennoscandian shield and was overprinted after 1851 5 ma by spatially more confined deformational events in conjunction with earlier results our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the svecofennian orogen c 2006 elsevier b v all rights reserved less

characterisation of pore water in crystalline rocks abstract the mass of pore water present in the rock matrix of a crystalline rock mass is significant and its influence on fracture groundwater and future deep repositories needs to be understood yet the rock matrix has a hydraulic transmissivity generally well below 10 10 m 2 s 1 inhibiting sampling of pore water by conventional sampling techniques various innovative techniques for the chemical and isotopic characterisation of pore water in crystalline rocks are applied and evaluated direct sampling of pore water was facilitated by collecting seepage water in a specially designed borehole located at a depth of 420 m in the aspo underground research laboratory aspo hrl sweden over a period of 7 5 a during the entire time span seepage waters collected from different sampling sections showed constant but individual chemical and isotopic compositions compositional differences compared to nearby fracture groundwaters indicate that the collected waters originated from the low permeability rock mass without mutual influence via more conductive microfractures within the metre scale they are interpreted as representing pore water in a transient state of diffusive interaction with different types of old palaeowaters which have periodically characterised the fracture network at the aspo hrl over geological times thousands to hundreds of thousands of years pore water compositions derived by indirect methods out diffusion and diffusive isotope equilibration experiments from originally saturated drillcore samples collected at the laxemar and forsmark sites sweden can be interpreted within a wider palaeohydrogeological framework the chemical and isotope compositions of the pore water show distinct trends related to rock type and with depth becoming more saline at greater depth at both sites concentration gradients established between pore water and fracture groundwater commonly coincide with higher fracture frequency and transmissivity in the host rocks differences developed in the attainment of near steady state conditions between pore water and fracture water from laxemar and forsmark support a different hydrogeological and therefore hydrogeochemical evolution at least during holocene times the observed compositional differences between pore water and fracture groundwater support diffusion dominated solute transport in the low permeable rock masses which is consistent with measured and experimentally derived hydraulic properties from the present investigations it can be concluded that in such rock masses the diffusion accessible porosity extends over significant distances of at least metres to tens of metres

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

fracture related hydrothermal alteration of metagranitic rock and associated changes in mineralogy geochemistry and degree of oxidation a case study at forsmark central sweden red staining of rocks due to fluid rock interaction during hydrothermal circulation in fractures is a common feature in crystalline sequences in this study red stained metagranitic rock adjacent to fractures in forsmark central sweden has been studied with emphasis on the mineral reactions and associated element mobility occurring during the alteration the main mineral reactions associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization of biotite magnetite has been partly replaced by hematite whereas quartz and k feldspar were relatively unaffected by the hydrothermal alteration we show that redistribution of elements on the whole rock scale was very limited and is mainly manifested by enrichment of na2o and volatiles and depletion of cao feo and sio2 in the red stained rock however on the microscale element redistribution was more extensive with both intragranular and intergranular migration of e g ca k na al si fe ba cs rb sr ti and rees the altered rock shows a shift towards higher total oxidation factors but the change is smaller than 1 and the red staining of the rock is due to hematite dissemination rather than a significant oxidation of the rock an increase in the connected porosity is also observed in the altered rock

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

sediment damage caused by gas exsolution a key mechanism for mud volcano formation abstract gassy sediments are common in marine environments and are characterized by a specific mechanical behavior significantly different from that of water saturated sediments it is shown that gas causes damage and initiates fractures in sediments to define the controlling parameters dominating the damage process during gas exsolution and its consequences in terms of hydro mechanical behavior we developed a specific consolidation apparatus to test sediments collected from the active absheron mud volcano indeed mud volcano formation is initiated by gas exsolution and subsequent mud generation at depth from stratified sediments gas was generated in the samples by circulating carbonated water through the fine grained sediments then decreasing the total pressure particular attention was given to the impact of gas saturation and associated damage and fractures on p wave velocity sediment compressibility permeability and preconsolidation pressure results show that fracture geometry is mainly controlled by the degree of gas saturation and preconsolidation pressure the damage level increases with the degree of gas saturation while the elastic modulus of sediments is degraded experimental data show that sediments do not entirely recover their original mechanical behavior when gas dissipates finally the experimental data confirm that gas exsolution and expansion is a key mechanism for mud generation

oxygen isotope zoning profiles in hydrothermally altered feldspars estimating the duration of water rock interaction the characterization of intragrain mineralogical and isotopic zoning patterns provides the basis for estimating the duration of fluid rock interaction associated with mineral replacement reactions in the rico colorado hydrothermal system oxygen isotope ratios in reaction rims on partially reacted plagioclase feldspar exhibit some of the largest gradients yet reported for individual grains to 15 o the extent of rim formation and accompanying isotopic exchange vary across the system as a function of temperature fluid isotope composition and the local fluid rock ratio distal feldspars show narrow rims with 1 8 o enrichments relative to pristine feldspars feldspars intermediate or proximal to the system s center have wide reaction rims or are completely exchanged and show 180 depletions formation times of reaction rims and associated isotopic patterns have been estimated with a coupled reaction diffusion model that suggests that hotter 250 350 c hydrothermal circulation was active for 100 300 k y in the center part of the system perhaps only while the igneous heat engine was still magma cooler 150 200 c circulation was widespread lasting for 1000 k y

hydrothermal fluids responsible for the formation of precious minerals in the nigerian younger granite province preliminary investigations in the younger granite province of nigeria have revealed that precious and semi precious minerals like rubies sapphires emeralds aquamarine zircon and fluorite can be found in the region the gem minerals are shown to have been produced either by direct deposition along fissures veins and greisens by hydrothermal fluids or as a result of hydrothermal fluids reacting with wall rocks these wall rocks are either biotite granites from which the hydrothermal fluids originated or basement rocks or any other rocks which the biotite granites intrude and their residual hydrothermal fluids have invaded the hydrothermal fluids appear to have been rich in alkalis na k etc rare elements be zr f ree etc and siliceous as these fluids rose through fractures and channel ways through the rocks they either deposited the gem minerals in the fractures at the appropriate stability conditions or reacted with the wall rocks producing the gem minerals at the expense of elements like ca and a1 in the minerals of these rocks

sediment undulations induced by free gas in muddy marine sediments a modeling approach 1 sediment undulations observed on the continental shelf in muddy prodeltas are often marked by the presence of gas in the upslope location the growth and migration of bubbles within fine grained muddy sediments are associated with sediment fracturing that damages the sediment and changes its effective mechanical properties the presented theoretical investigation demonstrates by modeling that undulations may be induced by creep deformations downslope from the region with gas presence comparison of the dimensions of the modeled undulations with the observed ones suggests that the undulations may be enhanced over time by different processes e g by the different types of the sediment deposition

isocon analysis of migmatization in the front range colorado usa isocon analysis has been applied to five sets of leucosome mafic selvages and immediately adjacent mesosome in the migmatites from a 15 m outcrop in the colorado front range the results show i mafic selvages formed from the adjacent mesosome by loss of felsic components and therefore the mesosomes are indeed palaeosomes or protoliths ii the leucosomes did not form in a closed system from the palaeosome in which case the material lost from the palaeosome during selvage formation would become the leucosome the observed volumes and compositions of leucosomes require that the present leucosome must contain some material in addition to the felsic components lost from the selvages the materials that must be added are leucotonalitic to granitic in composition varying greatly in k na ca ratio the trend in leucosome composition can be reproduced by assuming that a metasomatic exchange kna ca modified originally leucotonalitic leucosomes to more k rich compositions these leucosomes most likely formed by injection of silicate melts accompanied or followed by metasomatism the trend of leucosome compositions in this study reflects the general trend in the leucosome compositions which have been published from other areas indicating that the proposed mechanism can be applicable to other regional migmatites

mechanical behaviour of gas charged marine plastic sediments understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue special triaxial tests were carried out on natural sediments recovered from the gulf of guinea special attention was devoted to the laboratory preparation procedure involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of a the increase in the isotropic compressibility and decrease in the preconsolidation pressure and b the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing the experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments

thermodynamic analysis of fe and mg partitioning between plagioclase and silicate liquid thermodynamic analysis of fe and mg bearing plagioclase and silicate liquid was carried out based on reported element partitioning data between plagioclase and silicate liquid in reduced conditions solution properties of ternary feldspar standard state properties of plagioclase endmembers and solution properties of multicomponent silicate liquid derived mixing properties of fe and mg bearing plagioclase are in harmony with estimated results from synthetic experiments in the systems caal2si2o8 cafesi3o8 and caal2si2o8 camgsi3o8 based on the determined solution properties of the plagioclase a computer program to calculate the element partition relationships between fe and mg bearing plagioclase and multicomponent silicate liquid was developed the feo mgo and mgo mgo feo in plagioclase predicted from known liquid compositions and pressure are in agreement with measurements within 0 2 wt 0 1 wt and 0 1 mol ratio respectively the fe3 content in plagioclase crystallized at high oxygen fugacity can be estimated with this program the fe3 total fe ratio in plagioclase crystallized near the quartz fayalite magnetite buffer ranges from 0 to 0 5 which is consistent with previous study on natural plagioclase in submarine basalt derived solution properties of the fe and mg bearing plagioclase are also used to calculate equilibrium composition relationship between olivine and plagioclase change of xfo in olivine coexisting with plagioclase affects mgo and feo contents in plagioclase greatly the present model predicts xfo of coexisting olivine from the chemical composition of plagioclase to 0 1 accuracy at given pressure and temperature

biotite chloritization process in hydrothermally altered granites abstract chloritization of biotite in a hydrothermal environment was studied in two granitic rocks of the massif central france four types of transformation were observed 1 mg chlorite growth upon 001 biotite planes in contact with quartz 2 biotite pseudomorphosed by a corrensite residual biotite assemblage 3 corrensite residual biotite pseudomorphosed by a ferromagnesian chlorite and 4 biotite pseudomorphosed by chlorite these transformations induce an expansion of the site of the ferromagnesian minerals which can be observed by the corrosion of neighbouring minerals and fracturation of the rock around the new chlorites open fractures or chloritic veinlets if al is considered as a strictly inert component the reaction biotite chlorite produces a decrease of the ferromagnesian mineral volume of 13 ferry 1979 this is not in agreement with petrographic observations of the rocks studied here therefore writing of a chloritization reaction must take into account a volume increase in this case al does not behave as an inert component but as a mobile one at the scale of the microsystem biotite neighbouring crystals albitization of plagioclase which occurs simultaneously with the chloritization process is the al furnisher in addition fe and mg must be brought into the microsystem during the transformation of biotite into chlorite this explains why the mg mg fe ratio is not the same between biotite chlorite growths and chlorite pseudomorphs because the bulk rock composition is enriched in these components the hydrothermal fluids must contain fe and mg before they flow into the rock chloritization in propylitized granites is not an isochemical process

observations of wave influence on alongshore ebb tidal delta morphodynamics at oregon inlet nc abstract a radar inlet observation system rios collected hourly x band radar data at the wave dominated oregon inlet nc for 9 months from september 2016 to may 2017 the intensity of the radar backscatter predominantly associated with surface wave shoaling and breaking was time averaged to provide an implied measure of bedforms superimposed on the ebb tidal delta eulerian and lagrangian motion tracking analyses determined the bedform alongshore migration rates over the study period these were found to be significantly correlated to estimates of longshore sediment flux based on offshore wave parameters given by ashton and murray 2006 although the exact magnitude of sediment transport cannot be directly estimated from bedform migration the correlation does support an underlying assumption that sediment transport varies proportionally in both magnitude and direction to average bedform movements the implications of these findings were further explored through application of the sediment transport model to a year long period of continuous offshore wave data 20 oct 2016 to 20 oct 2017 the predicted net transport of 90 000 m3 southward during this year is consistent with a previous estimate of inlet bypassing dolan and glassen 1973 however pronounced and opposing seasonal transport patterns were an order of magnitude higher than the yearly net and could lead to significant inter annual variability in alongshore sediment transport with similar dynamic response in ebb delta morphodynamics at oregon inlet

cyclic liquefaction of loose gassy sand gas can be found in many soils but none more common than in seabed soils gas charged sediments are known to be widely distributed throughout the world s oceans numerous research programs have studied saturated soil response to cyclic loading however little is known about the behavior of gassy soils subjected to cyclic loading the response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program triaxial tests were performed on specimens of reconstituted ottawa sand prepared to various gas contents and densities the specimens were consolidated and then sheared under undrained cyclic loading gas content was measured at the beginning and end of each test using time domain reflectometry the response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity duration and frequency of the cyclic loading the propensity of a soil to liquefy is represented by a cyclic resistance ratio defined as the cyclic stres

on the undrained unloading behaviour of gassy sands soils that contain large amounts of dissolved gas within the pore fluid are called gassy soils gassy soils are common in marine environments and it is important to further our understanding of the unloading behaviour of gassy soils because of their potential to initiate and propagate submarine slope failures this paper focuses on the pore pressure responses and volumetric strains of loose gassy sands under different undrained unloading stress paths in laboratory specimens special attention was given to the constant deviatoric stress q constant undrained unloading stress path as it simulates the stress condition imposed by tidal drawdown one of the potential triggers of landslides in gaseous marine sediments gas exsolution was observed when the pore pressure was reduced below the liquid gas saturation pressure upon further decreases in total stress the resulting pore pressure change was much less than the total stress change hence effective stress decreased rapidly and at a certain point the sa

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

stress dilatancy behaviour of bubbled fine grained sediments abstract although the strength and stiffness of fine grained gassy soil have been relatively well characterised its dilatancy remains poorly understood this study aimed to understand and formulate the stress dilatancy behaviour of fine grained gassy soil through a series of triaxial tests 19 in total conducted on fine grained gassy specimens where different initial gas volume fractions 0 and initial pore water pressures uw0 were considered compared to the stress dilatancy relation of saturated fine grained soil the addition of gas bubbles was found to result in more contractive or dilative soil behaviour depending on the combination of 0 and uw0 these distinct features cannot be captured by the existing stress dilatancy functions for fine grained saturated soils which solely depend on the stress ratio therefore a new stress dilatancy function is proposed within the framework of critical state soil mechanics to quantify the distinct modification effects of bubbles which either suppress or enhance dilatancy on the dilatancy of gassy soils with different 0 and uw0 values in a unified manner this new function has been validated and can be readily implemented in critical state based constitutive models for predicting the shear behaviour of fine grained gassy soil and therefore the response of various offshore structures i e foundations and pipelines founded on a gas bearing seabed

biotite and muscovite 40ar 39ar geochronological constraints on the post svecofennian tectonothermal evolution forsmark site central sweden in order to characterize the post svecofennian tectonothermal evolution of the fennoscandian shield 40ar 39ar biotite and some 40ar 39ar muscovite geochronological data are reported from a total of 30 surface outcrop and 1000 m long borehole samples at forsmark central sweden the thirteen surface samples were collected across three branches of a major wnw to nw trending system of deformation zones whereas the boreholes were drilled within a tectonic lens in between two of these zones the 40ar 39ar biotite ages indicate that the present erosion surface in central sweden cooled below 300 c at 1 73 1 66 ga and that the rocks could respond to stress by brittle deformation between 1 8 and 1 7 ga the variation in surface ages is suggested to be due to faulting along the large wnw to nw trending deformation zones following the establishment of a sub cambrian peneplain the minor variation of ages within a single crustal block may be due to disturbance along ene to nne trending fracture zones possible cooling paths derived from 40ar 39ar hornblende muscovite and biotite ages were calculated for the time interval from 1 80 to 1 66 ga when the area cooled from 500 c to 300 c between 1 70 and 1 64 ga uplift rates of c 22 m m y were calculated from borehole 40ar 39ar biotite data tectonothermal histories inferred from the combined cooling and uplift rates are related to simple slow cooling after the svecofennian orogeny to crustal movement in response to far field effects of c 1 7 ga orogenic activity further to the west or to a combination of these possibilities less

effect of initial pore pressure on undrained shear behaviour of fine grained gassy soil many of the world reserves of fossil fuels are located at various water depths in fine grained sediment under the seabed the fine grained sediment contains relatively large biogas bubbles which has been posing challenges to the stability of offshore foundations supporting oil and gas platforms although fine grained gassy soil was found to exhibit different undrained shear strengths cu by altering the initial pore pressure ui relevant to water depth systematic studies concerning the effect of ui on undrained shear behaviours of the soil are still lacking this study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine grained gassy soil with the same consolidation pressure p c but at a wide range of varying ui 0 1000 kpa the shearing induced excess pore pressure u in the gassy specimens highly depends on ui it can be either smaller than that of the saturated specimen with the same p c due to partial dissipation of u int