a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

experimental development of patch perthite from synthetic cryptoperthite microstructural evolution and chemical re equilibration in this study deuteric coarsening of a lamellar cryptoperthite to a patch perthite has been experimentally induced for the first time an homogeneous alkali feldspar bulk composition ab60or40 was produced by molten salt ion exchange with a gem quality orthoclase from madagascar this was then annealed isothermally for 32 days at 550 c this resulted in a coherent lamellar cryptoperthite periodicity 28 nm probably by spinodal decomposition and subsequent coarsening the cryptoperthite was then reacted with 20 wt h2o or 0 1 m hcl at 400 and 500 c at 200 400 and 1000 mpa for 96 h and for 192 h at 1500 mpa at 1000 and 1500 mpa and 500 c the cryptoperthitic crystal fragments were partially replaced by a mosaic of albite and sanidine subgrains in the form of a patch perthite other than the gibb s free energy of reaction as derived from the chemical potentials of the reactant and product phases the second principle mechanism responsible for driving this reaction is interface coupled dissolution reprecipitation driven by a reduction in the coherency strain energy stored within the initial cryptoperthite the main indicator of this is a change in the microtexture due to the destruction of the coherent lamellar cryptoperthite and its replacement by an assemblage of incoherent subgrains detailed mass balancing based on xrd and epma data indicate that conversion of cryptoperthite to patch perthite is not isochemical experimental formation of patch perthite appears to take place in two steps between the original cryptoperthite and the patch perthite tem investigation identified a transition zone characterized by a significant coarsening of the preexisting lamellar microstructure without any sign of a loss in lattice coherency this zone is probably the result of hydrous species diffusing into the cryptoperthite causing the h2o enhanced diffusion of na and k and hence lamellar coarsening in the second step this coarsened microstructure is replaced by the patch perthite the polycrystalline patch perthite is characterized by a very complex distribution of albite and sanidine sub grains even the larger albite or sanidine patches are polycrystalline this inevitably results in a three dimensional network of grain boundaries characterized by high defect densities resulting from the structural misfit between the albite and sanidine sub grains an increase in average grain size with distance from the interface indicates that secondary coarsening of the initially very fine grained intergrowth occurred this was driven by the reduction of interface and surface energy similar to the coarsening observed in multiphase ceramics in addition the newly formed patch perthite is highly porous despite the fact that the results obtained in this study show that the replacement of cryptoperthite by patch perthite is nearly isovolumetric v 0 6 the observed reaction induced porosity results from differences in relative solubilities between the cryptoperthite and the patch perthite porosity abundance has been estimated at approximately 10 to 11 vol based on the amount of quartz formed during the experiments three dimensional investigations via fib serial sectioning indicate almost no interconnectivity between pores a consequence of albite and sanidine sub grain coarsening is the constant redistribution of the porosity and the sub grain boundaries within the patch perthite mosaic over time this suggests that a dynamically evolving porosity could provide an important transport mechanism for fluid transport through rocks even when the abundance and interconnectivity of the reaction induced porosity is low

corundum and kyanite bearing anatexites from the precambrian of tanzania abstract in the precambrian near morogoro east tanzania there are anatectic gneisses which are composed of two different domains 1 medium grained gneiss with the assemblage rutile baddeleyite albite ab 95 an 03 or 02 muscovite phlogopite ss corundum and albite ab 88 an 09 or 03 kyanite or sillimanite phlogopite ss 2 coarse grained nests of corundum and antiperthite with minor albite muscovite phlogopite rutile baddeleyite and tourmaline the bulk composition of the antiperthite id ab 75 an 02 or 23 the composition of the na phase ab 95 an 03 or 02 that of the k phase ab 13 an 00 or 87 phase relationship of the rock can be modelled in the na rich si undersaturated part of the knash system p t conditions are close to the intersection of the melting curve muscovite ss h 2 o corundum liquid with the kyanite sillimanite transition i e 7 7 kb 695 c assuming a h 2 o 1

nanotunnels and pull aparts defects of exsolution lamellae in alkali feldspars we have studied defects associated with flat lens shaped perthitic albite lamellae in alkali feldspars using sem and tem in orthoclase phenocrysts from the shap granite cumbria nw england bulk composition or 70 20 ab 29 05 an 0 85 no dislocations were found even in optically fresh parts of grains instead dissolution inferred to be localized on edge dislocation loops has created tiny nanotunnels typically t effect of the 1 an in the feldspars is taken into account for commencement of coherent exsolution the orientation of the pericline twins was fixed shortly after coherent exsolution began previous work has indicated that edge dislocations would start to form during cooling at 400 c so that nanotunnels form at still lower t dry heating experiments were carried out to establish the stability of the defects and the homogenization behavior of the exsolution lamellae na k exchange is rapid on heating above the coherent solvus and chemical homogenization of lamellae is complete after 24 h at 700 c in contrast nanotunnels persist for 148 h at 1000 c and 5748 h at 700 c below the coherent solvus exsolution lamellae thin on heating leaving nanotunnels stranded in the orthoclase matrix microtextures related to si al ordering patterns in the framework such as albite twins are not eliminated forming ghost like lamellar strain patterns in chemically homogeneous feldspar the presence of nanotunnels in optically fresh alkali feldspars shows that not only granites but also granulite facies rocks have been pervasively affected by fluids at low t both nanotunnels and pull aparts have important implications for feldspar reactivity in the upper crust for 18 o exchange and for transport of 40 ar both in nature and in laboratory step heating

eight phase alkali feldspars low temperature cryptoperthite peristerite and multiple replacement reactions in the klokken intrusion eight feldspar phases have been distinguished within individual alkali feldspar primocrysts in laminated syenite members of the layered syenite series of the klokken intrusion the processes leading to the formation of the first four phases have been described previously the feldspars crystallized as homogeneous sodian sanidine and exsolved by spinodal decomposition between 750 and 600 c depending on bulk composition to give fully coherent strain controlled braid cryptoperthites with sub m periodicities below 500 c in the microcline field these underwent a process of partial mutual replacement in a deuteric fluid producing coarse up to mm scale turbid incoherent patch perthites we here describe exsolution and replacement processes that occurred after patch perthite formation both or and ab rich patches underwent a new phase of coherent exsolution by volume diffusion or rich patches began to exsolve albite lamellae by coherent nucleation in the range 460 340 c depending on patch composition leading to film perthite with 1 m periodicities below 300 c misfit dislocation loops formed which were subsequently enlarged to nanotunnels ab rich patches bulk composition ab91or1an8 in one sample exsolved giving peristerite with one strong modulation with a periodicity of 17 nm and a pervasive tweed microtexture the ab rich patches formed with metastable disorder below the peristerite solvus and intersected the peristerite conditional spinodal at 450 c this is the first time peristerite has been imaged using tem within any perthite and the first time peristerite has been found in a relatively rapidly cooled geological environment the lamellar periodicities of film perthite and peristerite are consistent with experimentally determined diffusion coefficients and a calculated cooling history of the intrusion all the preceding textures were in places affected by a phase of replacement correlating with regions of extreme optical turbidity we term this material ultra porous late feldspar uplf it is composed predominantly of regions of microporous very or rich feldspar mean ab2 5or97 4an0 1 associated with very pure porous albite ab97 0or1 6an1 4 implying replacement below 170 90 c depending on degree of order in tem uplf has complex irregular diffraction contrast similar to that previously associated with low temperature albitization and diagenetic overgrowths replacement by uplf seems to have been piecemeal in character ghost like textural pseudomorphs of both braid and film parents occur formation of patch perthite film perthite and peristerite occurred 104 105 year after emplacement but there are no microtextural constraints on the age of uplf formation

shock melting of k feldspar and interlacing with cataclastically deformed plagioclase in granitic rocks at toqqusap nunaa southern west greenland implications for the genesis of the maniitsoq structure abstract folded sheets of mesoarchaean leucocratic plagioclase k feldspar mesoperthite bearing granitic rocks in the toqqusap nunaa area of the maniitsoq structure west greenland are characterised by their very fine grain sizes and microstructures without normal igneous or planar linear tectonic fabrics quartz forms equidimensional and branching ductilely deformed aggregates and bifurcating panels with protrusions constrictions and chains of ball shaped grains with healed radiating intergranular fractures plagioclase an10 20 was cataclastically deformed and comminuted whereas k feldspar and mesoperthite are devoid of cataclastic microstructures k feldspar forms dispersed highly irregular grains with numerous cusps and saddles indicating almost ubiquitous direct shock melting of this mineral it is commonly located along former fractures in plagioclase resulting in an interlaced feldspar microstructure with contact shapes indicating subsequent melting of plagioclase directly adjacent to k feldspar mesoperthite forms separate rounded and irregular grains with protrusions and cusped margins indicating crystallisation from melts some mesoperthite grains are texturally and compositionally heterogeneous and contain internal lenses of k feldspar and or plagioclase other mesoperthite grains comprise coarsened unzipped areas presumably due to localised fluid controlled dissolution reprecipitation processes the ternary feldspar precursor of the mesoperthite is interpreted as having crystallised from variably effectively mixed k feldspar shock melts and plagioclase contact melts direct melting of k feldspar but no whole rock melting requires shock metamorphism with a short lived temperature excursion to above the melting temperature of k feldspar 1300 c the presence of three different feldspar species and absence of chemical zonation magmatic mantling or metamorphic coronas furthermore hinders interpretations solely by means of endogenic magmatic or ultrametamorphic processes the feldspar microstructures with direct k feldspar melts in the leucocratic orthogneisses of the toqqusap nunaa area thus confirm that the recently discovered maniitsoq structure represents the deep crustal remnants of a giant mesoarchaean meteorite impact

flow of variable density formation water in deep sloping aquifers minimizing the error in representation and analysis when using hydraulic head distributions abstract although not fully adequate freshwater hydraulic heads have been used historically to represent and analyze variable density flow in sloping aquifers in sedimentary basins the use of environmental heads is valid only for strictly vertical flow in unconfined aquifers while using variable density hydraulic heads contravenes darcy s law although the use of hydraulic head surfaces is the simplest and quickest means of flow analysis and interpretation preceding other methods such as numerical modeling it introduces some errors that should be assessed and minimized in order to provide the most accurate flow representation a first error is introduced when approximating the potential and buoyancy components along aquifer slope of the flow driving force with their projections onto the horizontal plane this error is most probably negligibly small for sloping aquifers in undisturbed sedimentary basins but may be significant for aquifers dipping at a significant angle such as in folded strata a second error is introduced when using only hydraulic heads in the representation and analysis and neglecting the buoyancy component of the flow driving force the significance of this error can be assessed by performing a driving force ratio dfr analysis there is no single or critical value of the dfr below which the error in using hydraulic heads alone is negligible and above which it is not acceptable anymore rather the decision regarding the error acceptability should and can be made on a case by case basis the dfr hence the errors in flow direction and magnitude can be minimized for any given aquifer by using an optimum reference density in hydraulic head calculations that is the areally weighted average density of formation water in that aquifer in flow analyses based on potentiometric surfaces the use of freshwater as the reference density actually maximizes the errors introduced by the neglect of the buoyancy component of the flow driving force because it is either at the low end of the density variation spectrum or outside it

precipitation in pores a geochemical frontier the purpose of this article is to review some of the recent research in which geochemists have examined precipitation of solid phases in porous media particularly in pores a few nanometers in diameter nanopores while this is a review it is actually more forward looking in that the list of things about this phenomenon that we do not know or cannot control at this time is likely longer than what we do know and can control for example there are three directly contradictory theories on how to predict how precipitation proceeds in a medium of varying pore size as will be discussed below the confusion on this subject likely stems from the complexity of the phenomenon itself one can easily clog a porous medium by inducing a rapid homogeneous precipitation directly from solution or have limited precipitation occur that does not affect permeability or even porosity substantially it is more difficult to engineer mineral precipitation in order to obtain a specific outcome such as filling all available pore space over a targeted area for the purposes of contaminant sequestration however breakthrough discoveries could occur in the next five to ten years that enhance our ability to predict robustly and finely control precipitation in porous media by understanding how porosity and permeability evolve in response to system perturbations these discoveries will likely stem at least in part from advances in our ability to 1 perform and interpret x ray neutron scattering experiments that reveal the extent of precipitation and its locales within porous media anovitz and cole 2015 this volume and 2 utilize increasingly powerful simulations to test concepts and models about the evolution of porosity and permeability as precipitation occurs steefel et al 2015 this volume a further important technique to isolate specific phenomena and understand reactivity is also microfluidics cell

plagioclase hosted fe ti oxide micro inclusions in an oceanic gabbro plagiogranite association from the mid atlantic ridge at 13 34 n

using hydrogeochemistry to understand inter aquifer mixing in the on shore part of the gippsland basin southeast australia groundwater in the latrobe valley in the gippsland basin of southeast australia is important for domestic agricultural and industrial uses this sedimentary basin contains a number of aquifers that are used for water supply dewatered for open pit coal mining and which are potentially influenced by off shore oil and gas production major ion chemistry together with stable and sr isotope data imply that the main hydrogeochemical processes are evapotranspiration with minor silicate and carbonate weathering methanogenesis and so4 reduction in reduced groundwater associated with coal deposits have also occurred groundwater has estimated 14c ages of up to 36ka and is largely 3h free carbon 14 ages are irregularly distributed and poorly correlated with depth and distance from the basin margins the observations that the geochemistry of groundwater in aquifers with different mineralogies are similar and the distribution of 14c ages is irregular implies that the aquifers are hydraulically connected and horizontal as well as vertical inter aquifer mixing occurs the connection of shallow and deeper aquifers poses a risk for the groundwater resources in gippsland as contaminants can migrate across aquifers and dewatering of shallow units may impact deeper parts of the groundwater system

site characterisation of a basin scale co2 geological storage system gippsland basin southeast australia geological storage of co2 in the offshore gippsland basin australia is being investigated by the cooperative research centre for greenhouse gas technologies co2crc as a possible method for storing the very large volumes of co2 emissions from the nearby latrobe valley area a storage capacity of about 50 million tonnes of co2 per annum for a 40 year injection period is required which will necessitate several individual storage sites to be used both sequentially and simultaneously but timed such that existing hydrocarbon assets will not be compromised detailed characterisation focussed on the kingfish field area as the first site to be potentially used in the anticipation that this oil field will be depleted within the period 2015 2025 the potential injection targets are the interbedded sandstones of the paleocene eocene upper latrobe group regionally sealed by the lakes entrance formation the research identified several features to the offshore gippsland basin that make it particularly favourable for co2 storage these include a complex stratigraphic architecture that provides baffles which slow vertical migration and increase residual gas trapping and dissolution non reactive reservoir units that have high injectivity a thin suitably reactive lower permeability marginal reservoir just below the regional seal providing mineral trapping several depleted oil fields that provide storage capacity coupled with a transient production induced flow regime that enhances containment and long migration pathways beneath a competent regional seal this study has shown that the gippsland basin has sufficient capacity to store very large volumes of co2 it may provide a solution to the problem of substantially reducing greenhouse gas emissions from future coal developments in the latrobe valley

present day stress analysis of the st lawrence lowlands sedimentary basin canada and implications for caprock integrity during co2 injection operations abstract a geomechanical analysis of the st lawrence lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for co 2 injection that will not reactivate pre existing faults in the caprock thereby inducing a breeched co 2 reservoir this requires the determination of prevailing stresses orientations and magnitudes fault and fractures geometries and rock strengths the average maximum horizontal stress orientation s hmax is estimated n59 e 20 in the st lawrence lowlands the stress orientations were obtained from stress induced wellbore breakouts inferred from four arm dipmeter caliper data in 17 wells these wellbore failure features are confined to paleozoic lithological units of the st lawrence platform succession and frontal thrusts of the quebec appalachians at depths from 250 m to 4 km our results are consistent with the regional ne sw s hmax stress orientation trend that is generally observed in eastern canada and the u s the stresses pressure gradients estimated for the st lawrence lowlands depths hmin 20 5 3 kpa m s v 25 6 kpa m s hmax 40 7 5 kpa m pore pressure p p 9 8 kpa m indicating a strike slip stress regime s hmin v hmax the high angle ne sw regional faults and fractures in the paleozoic sedimentary succession and the grenvillian basement are oblique to the s hmax stress orientations 10 to 36 and could be reactivated slip tendency 0 34 to 0 58 under the present day stress field if fluid pressures exceeded the critical threshold further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults the regional pore pressure stress coupling ratio under assumed parameters is about 0 5 0 65 and may contribute to reduce the risk of shear reactivation of faults and fractures the maximum sustainable p p that would not cause opening of vertical tensile fractures during co 2 operations is about 18 5 20 mpa for the depth of 1 km

intracrystalline microstructures in alkali feldspars from fluid deficient felsic granulites a mineral chemical and tem study samples of essentially dry high pressure felsic granulites from the bohemian massif variscan belt of central europe contain up to 2 mm large perthitic alkali feldspars with several generations of plagioclase precipitates in an orthoclase rich host the first generation takes the form of lenses homogeneous in size whereas the size of a second generation of very thin albite rich precipitates is more variable with comparatively high aspect ratios in the vicinity of large kyanite garnet or quartz inclusions the first generation of plagioclase precipitates is significantly less abundant the microstructure is coarser than in the remainder of the perthitic grain and the host is a tweed orthoclase the first generation of precipitates formed at around 850 c during the high pressure stage 16 18 kbar of metamorphism primary exsolution was followed by primary coarsening of the plagioclase precipitates which still took place at high temperatures 850 700 c the coarsening was pronounced due to the access of fluids in the outer portions of the perthitic alkali feldspar and in more internal regions around large inclusions the second generation of albite rich precipitates was formed at around 570 c tem investigations revealed that the interfaces between the second generation plagioclase lamellae and the orthoclase rich host are coherent or semi coherent during late evolutionary stages of the perthite albite linings were formed at phase boundaries and the perthitic microstructure was partially replaced by irregularly shaped precipitates of pure albite with incoherent interfaces the albitization occurred below 400 c and was linked to fluid infiltration in the course of deuteric alteration based on size distribution analysis it is inferred that the precipitates of the first generation were most probably formed by spinodal decomposition whereas the precipitates of the second generation rather were formed by nucleation and growth

flow of variable density formation water in deep sloping aquifers review of methods of representation with case studies abstract distributions of freshwater hydraulic heads have been and continue to be used in the representation and analysis of groundwater flow including the flow of variable properties formation water in deep sloping aquifers because of variations in pressure temperature and salinity the flow of formation waters in sedimentary basins is driven by potential forces resulting from pressure and elevation topography differences by buoyancy resulting from density differences and by osmosis caused by temperature and concentration gradients because of variations in both fluid and rock properties it is not possible to define a flow potential to be used in representing and analysing the flow neither is there a force potential from which a flow driving force can be derived and which could be used in flow representation and analysis even if osmotic effects are neglected buoyancy still plays a role which in certain cases may be important in horizontal or near horizontal aquifers the lateral flow of variable density water is correctly represented by freshwater potentiometric surfaces and the vertical flow may be analysed using environmental hydraulic head distributions however the flow of formation waters in sedimentary basins is mostly along bedding in confined sloping aquifers in this case short of calculating and representing either the velocity or the impelling force distribution freshwater hydraulic heads remain the only tool available for representing and analysing the flow by neglecting buoyancy errors in flow strength and direction are introduced which become significant if a dimensionless driving force ratio exceeds a threshold value estimated to be around 0 5 the review of representation and analysis methods for the flow of variable properties formation water in deep sloping aquifers is illustrated with two case studies from the alberta and llanos sedimentary basins

low temperature coherent exsolution in alkali feldspars from high grade metamorphic rocks of sri lanka in the alkali feldspars of the amphibolite and granulite facies rocks of sri lanka a late stage final exsolution event is observed which produced film lamellae and fine scale spindles these were investigated by optical microprobe single crystal transmission electron microscopy and atomic resolution microscopy techniques the lamellae and spindles exsolved below the coherent solvus at temperatures as low as 300 to 350 c precession photographs and arm micrographs show that the intergrowth is perfectly coherent in sections 010 the rhombic section of the pericline twins corresponds to analbite or high albite the albite lamellae and spindles nucleated and grew at low temperatures in a metastable disordered structural state within a tweed orthoclase matrix and became periodically twinned analbite or high albite which subsequently developed only a slight increase in al si order the relationship between twin periodicity and lamellar width predicted for coherent intergrowths by willaime and gandais 1972 is obeyed in or rich grains in which coherent exsolution is the only exsolution event the film lamellae tend to be restricted to the rim the fine scale spindles to the centre of the grains the films nucleated heterogeneously at grain boundaries and grew towards the grain centres fine scale spindles probably nucleated homogeneously in the interior part of grains heterogeneous nucleation and coherent growth are not mutually exclusive

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

exsolution and coarsening mechanisms and kinetics in an ordered cryptoperthite series cryptoperthites from the klokken layered syenite intrusion were examined by tem to determine the role of exsolution ordering and twinning in the development of the coherent microtextures during slow cooling the stratigraphic position of the samples in the layered series giving an independent variable in determining their evolution both periodicity primary and secondary and morphology change with distance from the top of the series most samples contain low microcline in the diagonal association

late cretaceous paleogene palaeoclimate reconstruction of the gippsland basin se australia abstract the cretaceous paleogene palaeovegetation and palaeoclimate in the gippsland basin was reconstructed using vascular plant derived biomarkers and are consistent with other proxy evidence for palaeoclimate e g spore pollen assemblages and plankton foraminifera oxygen isotopes variation in the higher plant derived aliphatic and aromatic sesquiterpenoids diterpenoids and triterpenoids resulted from vegetation succession and is different in the t lilliei f longus l balmei m diversus p asperopolus and n asperus palynological biozones analyses of the oleanane index the higher plant parameter the higher plant index the higher plant fingerprint and various aliphatic and aromatic angiosperm gymnosperm indices indicate the late cretaceous paleogene ca 80 40 ma palaeoclimate in the gippsland basin was initially warm campanian t lilliei biozone and then changed in this way cool maastrichtian upper f longus biozone warm paleocene l balmei biozone hot early eocene m diversus and p asperopolus biozones warm and then cool middle eocene n asperus biozone this changing climate trend is mostly consistent with global climate changes in comparison to the analogous taranaki basin western new zealand the gippsland basin is inferred to have had a less gymnosperm dominated rainforest and a warmer climate in the late cretaceous during the paleogene the palaeoclimate was similar in the two basins as deduced from the angiosperm gymnosperm indices of the sedimentary rocks

zoned ternary feldspars in the klokken intrusion exsolution microtextures and mechanisms the microtextures developed during relatively slow cooling as a function of bulk composition in zoned ternary feldspars from syenodiorites and syenites in the klokken intrusion described in the preceding paper were determined by tem and their origin and evolution deduced the feldspars normally have a plagioclase core and an alkali feldspar rim cores become smaller and rims larger and the an content of both decrease with distance from the contact of the intrusion the following microtextural sequence was observed the inner plagioclase cores are homogeneous oligoclase andesine with albite growth twins only but are crypto antiperthitic towards the outer core at first small platelets of low sanidine a few nanometres thick and up to 10 nm long occur sporadically only on albite twin composition planes with further increase in bulk or they are homogeneously distributed in the plagioclase thicker through going plates in platelet free areas are found which induce albite twins in the surrounding plagioclase the microtextures in the rims are regular cryptomesoperthitic with 601 lenses or lamellae depending on the bulk or content of low sanidine in albite twinned low oligoclase andesine albite and pericline twins in plagioclase in an m twin relationship together with lenticular low sanidine were found in only one small area the overall diffraction symmetry of the mesoperthites is monoclinic showing that exsolution started in a monoclinic feldspar whereas that of the antiperthites is triclinic the intermediate zone between the core and rim is more complex and microtextures vary over distances of a few micrometres the cryptomesoperthites are very regular where or rich and probably arose by spinodal decomposition the platelets in the outer cores arose by heterogeneous nucleation on twin composition planes and by homogeneous nucleation elsewhere near the intermediate zone they coarsened to give larger plates which induced albite twins in the plagioclase because of the zoning microtextures that were initiated in areas of given composition can propagate laterally into zones of different composition a diagram is given showing the relationship between ternary bulk composition and the microtexture developed in coherent perthitic alkali feldspars and plagioclases from slowly cooled rocks

cenozoic structural history of the gippsland basin early oligocene onset for compressional tectonics in se australia abstract the gippsland basin contains some of the largest hydrocarbon accumulations in australia and has been in production since the 1920 s these hydrocarbons are trapped by large growth anticlines offshore in reservoirs of the cretaceous to eocene aged latrobe group despite the obvious importance of these growth anticlines the timing of their formation and the overall cenozoic tectonic history of the basin is not well understood here we present a detailed growth strata analysis of the faults and anticlines within the cenozoic sediments of the gippsland basin this indicates two major phases of tectonism in the basin 1 late cretaceous to eocene extension and 2 oligocene to holocene compression detailed analysis of the extensional phase indicates the development of numerous normal growth faults which display an overall reduction in the magnitude of extension from the late cretaceous to the eocene commonly terminating at the top of the latrobe group the shift to compressional tectonism occurred at approximately the eocene oligocene boundary 34 ma a major and widespread episode of compression then occurred with evidence of growth on anticlines and reverse faults beginning in the early oligocene this previously unrecognized early oligocene event produced significant growth 20 50 total growth of the major anticlines which host hydrocarbon accumulations the early oligocene event represents the first phase of the compressional tectonic regime that continues to the present day in se australia it appears likely that this oligocene event affected other basins in se australia and probably contributed to uplift of the eastern highlands the underlying tectonic cause for this oligocene compressional regime is enigmatic and may be related to far field tectonic processes a second pulse of compressional tectonism and anticline growth occurred during the mid miocene and is generally more significant in the onshore regions of the basin the youngest phase of compressional tectonism beginning in the late miocene 10 ma is also more intense in onshore regions and is marked by an unconformity that is widespread in se australia

microstructural evolution during experimental albitization of k rich alkali feldspar crystals of k feldspar c2 m in contact with highly concentrated aqueous nacl solutions at 500 c and 200 mpa are pseudomorphically replaced by high albite c bar 1 as a result of an interface coupled dissolution reprecipitation process the reaction occurs at an extremely sharp reaction front 10 nm and involves the complete breakdown of the initial framework structure this results in the release of tetrahedrally incorporated elements such as fe3 and ti4 and a significant increase in si al disorder across the reaction interface the evolving microstructure is controlled by crystallographic relations between the phases this leads to highly anisotropic sawtooth shaped intergrowths of albite and initial k feldspar resulting in the least structural misfit between the two framework structures as a result the newly formed interfaces appear to be semicoherent and cracks across the reaction fronts even indicate elastic strain the reaction produces 2 distinctive albite types albite 1 and albite 2 both are polycrystalline with albite 2 showing significantly larger subgrain sizes this indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product the reaction also produces a highly porous rim however the porosity is not evenly distributed resulting in a porous albite 1 and a non porous albite 2 that mostly surrounds large euhedral pores despite the substantial volume fraction of porosity in albite 1 no significant 3d interconnectivity could be detected making the presence of a pervasive porosity unlikely however the result of coarsening is the continuous modification of the 3d porosity distribution this could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved

experimental na k exchange between alkali feldspar and an nacl kcl salt melt chemically induced fracturing and element partitioning the exchange of na and k between alkali feldspar and a nacl kcl salt melt has been investigated experimentally run conditions were at ambient pressure and 850 c as well as 1 000 c cation exchange occurred by interdiffusion of na and k on the feldspar sub lattice while the si al framework remained unaffected due to the compositional dependence of the lattice parameters compositional heterogeneities resulting from na k interdiffusion induced coherency stress and associated fracturing depending on the sense of chemical shift different crack patterns developed for the geometrically most regular case that developed when potassic alkali feldspar was shifted toward more sodium rich compositions a prominent set of cracks corresponding to tension cracks opened perpendicular to the direction of maximum tensile stress and did not follow any of the feldspar cleavage planes the critical stress needed to initiate fracturing in a general direction of the feldspar lattice was estimated at 0 35 gpa fracturing provided fast pathways for penetration of salt melt or vapor into grain interiors enhancing overall cation exchange the na k partitioning between feldspar and the salt melt attained equilibrium values in the exchanged portions of the grains allowing for extraction of the alkali feldspar mixing properties

coarsening kinetics of coexisting peristerite and film microperthite over 104 to 105 years alkali feldspar crystals from the klokken syenite pluton south greenland have a coarse patch perthite exsolution texture on the scale of hundreds of micrometers produced by dissolution reprecipitation reactions at 500 c we have discovered that ab rich patches ab92an7or1 subsequently exsolved by spinodal decomposition to give peristerite with a periodicity of 17 nm this is the first time a peristerite has been characterized by tem within a perthite and the first peristerite to be found outside regional metamorphic rocks and pegmatites the coexisting or rich patches ab16or84 an0 3 unmixed over the same temperature interval to yield coherent film microperthite with periodicities 1 m because the peristerite and film perthite from a single hand specimen from the klokken intrusion have shared exactly the same cooling history they provide a novel opportunity to test the utility of diffusion coefficients obtained in the laboratory for prediction of coarsening rates over 105 yr time scales in the light of a calculated cooling trajectory for the pluton we find good agreement between observed and predicted periodicities for the film perthite which began to exsolve by coherent nucleation at the coherent solvus for ordered feldspars at 420 c 32 000 yr after crystal growth and took a further 13 000 39 000 yr to coarsen to a periodicity of 1 m peristerite exsolution began at the conditional spinodal at 450 c but on the basis of the best existing experimental data would have taken 520 000 4 600 000 yr to coarsen incompatible with the cooling history we speculate on changes to these best parameter values to describe nasi caal interdiffusion that would lead to peristerite coarsening rates compatible with the cooling history of the klokken intrusion we find that an interdiffusion expression batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathit d nasi caal 9 times 10 12 exp 220 000 mathit rt end document where d and the pre exponential term a are in units of m2 s and the activation energy e a is in j mol leads to coarsening rates compatible with the experimental data the cooling path of the klokken intrusion and the coarsening rate of the coexisting film perthite the new interdiffusion parameters are consistent with fine scale peristerite intergrowths in low grade metamorphic rocks and with the existence of the coarsest known peristerite in the light of our discovery it seems likely that peristerite is commonplace in albitic plagioclase in granitic rocks

exsolution by spinodal decomposition ii perthite formation during slow cooling of anatexites from ngoronghoro tanzania perthites in slowly cooled granulite facies rocks from the ngoronghoro structure tanzania show complex microstructures reflecting several stages of exsolution and coarsening mesoperthites with an integrated bulk composition of or26 5ab71an2 5 are comprised of lamellar intergrowth of 5 to 10 m wide orthoclase rich and albite rich lamellae spindle perthites with a bulk composition of or67ab31 5an1 5 are comprised of 2 to 10 m wide and several 109s of m long albite rich spindles in an orthoclase rich host in the mesoperthite primary exsolution occurred by spinodal decomposition whereas the spindle perthite formed by a nucleation and growth mechanism the interfaces between the exsolved phases are generally incoherent unmixing and coarsening of the mesoperthite is discussed in the light of non linear uphill diffusion the microstructure evolution and successive chemical separation of the exsolved phases during cooling are modeled based on cahn hilliard theory we find that coarsening primarily occurs during the first 20 c to 30 c of cooling after the homogeneous precursor feldspar has entered the coherent spinodal the extent of coarsening and the characteristic size of the exsolved phases depend on the cooling rate over this temperature interval for geologically relevant cooling rates on the order of 5 c ma to 50 c ma the compositions of the exsolved phases develop along the solvus down to about 480 c to 530 c and are frozen in only at lower temperatures the compositions that are finally preserved in the orthoclase rich and in the albite rich phases depend on cooling rate over this temperature interval both the characteristic lamella width of the mesoperthite as well as the compositions of the exsolved phases indicate slow cooling at 5 c ma during the coarsening stage and down to about 450 c during later stages of the cooling history the albite rich phase of the mesoperthite exsolved about the peristerite gap and the orthoclase rich host of the spindle perthite exsolved a second generation of coherent albite rich spindles the incoherent phase boundaries of the primary perthite microstructures served as passageways for fluids during late stage deuteric alteration which lead to secondary coarsening in the mesoperthite and to alteration of the albite rich precipitates in the spindle perthite finally both types of perthites were replaced by coarse grained patch perthite during deuteric alteration