fluid absent melting of a layered crustal protolith implications for the generation of anatectic granites we report the result of h2o undersaturated melting experiments on charges consisting of a layer of powdered sillimanite bearing metapelite hq36 and a layer of powdered tonalitic gneiss agc150 experiments were conducted at 10 kbar at 900 925 and 950 c when run alone the pelite yielded 40 vol strongly peraluminous granitic melt at 900 c while the tonalite produced only 5 vol weakly peraluminous granitic melt at 950 c the pelite and the tonalite yielded 50 vol and 7 vol granitic melt respectively when run side by side the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone in the pelite the melt abundance increased by 25 vol when run alone biotite dehydration melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt when run side by side only garnet was produced in addition to granitic melt experiments of relatively short duration however also contained al rich orthopyroxene we suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of al2o3 in the melt which lowers the temperature of the biotite dehydration melting reaction in the pelite the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite layer to the pelite layer this has the effect of changing the bulk composition of this layer in the direction of minimum temperature granitic liquids our results show that rocks which are poor melt producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase s and facilitate dehydration melting because of this effect the continental crust may have an even greater potential for granitoid melt production than previously thought our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks which will be reflected in their isotopic and geochemical compositions

three s type volcanic suites from the lachlan fold belt southeast australia the concept that granitoids of the lachlan fold belt in southeast australia are derived from either igneous or sedimentary source rocks i or s type can be extended to volcanic rocks of the same age three suites of late silurian s type volcanics are described two of which can be matched quite closely with plutonic equivalents a large part of the paleozoic continental margin volcanic activity in southeast australia consisted of the magmatic recycling of old metasedimentary crust probably of late proterozoic age the three volcanic suites are moderately to strongly peraluminous with the corresponding presence of al rich minerals variation within the volcanic suites is ascribed chiefly to progressive removal of restite or source material residual from partial melting the most mafic suite the hawkins suite contains plagioclase cordierite orthopyroxene biotite and quartz as restite components with less abundant almandine these rocks are chemically equivalent to mafic biotite rich and cordierite bearing granitoids from parts of the berridale and murrumbidgee batholiths garnet is absent from the goobarragandra suite volcanics which are a little more felsic and close in compositon to granitoids of the young and maragle batholiths the s type character of the laidlaw suite is less pronounced although a sedimentary source seems to be established such a source would be less mature than those for the other two volcanic suites the laidlaw suite resembles but cannot be closely identified with felsic s type granitoids of the murrumbidgee and berridale batholiths low grade regional metamorphism in most of the volcanic rocks has resulted in much mineralogical alteration and mobility of alkali and alkaline earth elements despite this alteration unaltered rocks are present in all three suites compositional data for the phenocryst phases within the unaltered rocks has allowed estimation of some intensive parameters hawkins suite volcanics were extruded directly from their source region and preserve phenocryst equilibria established at 5 6 kbar at 800 c the laidlaw and goobarragandra suites reequilibrated at lower pressures than their source before extrusion the laidlaw suite reequilibrated at estimated temperatures of 725 730 c o2 of 10 15 5 to 10 14 bars and h2o of 2 to 2 5 kbar differing mineral compositions in the three suites are related to differing source rock compositons and oxygen fugacities relative biotite and orthopyroxene mg is possibly pressure dependent

andalusite and na and li rich cordierite in the la costa pluton sierras pampeanas argentina textural and chemical evidence for a magmatic origin the la costa pluton in the sierra de velasco nw argentina consists of s type granitoids that can be grouped into three igneous facies the alkali rich santa cruz facies scf sio2 67 wt distinguished by the presence of andalusite and na and li rich cordierite na2o 1 55 1 77 wt and li2o 0 14 0 66 wt the anillaco facies sio2 74 wt with a significant proportion of mn rich garnet and the anjullon facies sio2 75 wt with abundant albitic plagioclase the petrography mineral chemistry and whole rock geochemistry of the scf are compatible with magmatic crystallization of na and li rich cordierite andalusite and muscovite from the peraluminous magma under moderate p t conditions 1 9 kbar and ca 735 c the high li content of cordierite in the scf is unusual for granitic rocks of intermediate composition

dissolution of corundum and andalusite in h2o saturated haplogranitic melts at 800 c and 200 mpa constraints on diffusivities and the generation of peraluminous melts of h2o in the aluminum alkali eigenvector could not be obtained the mechanisms and kinetics of equilibration between peraluminous from our results we propose that some h2o may provide charge minerals and granitic melt were investigated experimentally by balance for excess aluminum multicomponent diffusion models the dissolution of corundum and andalusite into h2o saturated yield eigenvalues for the corresponding aluminum alkali eigenvector metaluminous haplogranitic melt at 800 c and 200 mpa mineral of 0 3 10 to 1 9 10 cm s calculated effective and haplogranitic glass rods were juxtaposed inside platinum binary diffusion coefficients for al2o3 are higher 1 0 10 to capsules and then subjected to experimental conditions for times 3 6 10 cm s these diffusion coefficients are used to ranging from 12 to 2900 h upon melting the mineral melt calculate equilibration times between peraluminous minerals and interface retreats with the square root of time the composition of granitic melts in a model system in which two grains of corundum the melt at the interface changes with time but its asi aluminum or andalusite 1 cm apart are connected via a narrow melt column saturation index molar al2o3 cao na2o k2o at the conditions of the experiments diffusive equilibrium through remains constant at 1 20 after 480 h this value is close to initially metaluminous h2o saturated melt would be attained within the asi of an h2o saturated haplogranitic melt in equilibrium with 10 10 years at h2o activity well below saturation of the corundum or andalusite which may indicate that the composition of melt lower diffusivity of all components may increase the time to the melt at the interface follows the liquidus of these minerals in equilibration to 10 10 years approaching possible time frames the system sodium and potassium diffuse rapidly uphill across the for the generation and extraction of crustal melts entire length of the charge towards the interface resulting in a rapid and uniform increase in asi throughout the entire melt column this uphill diffusion of alkalis is due to coupling with excess aluminum entering the melt at the interface and involves long range

assessing bulk assimilation in cordierite bearing granitoids from the central system batholith spain experimental geochemical and geochronological constraints

geochemical evidence for relict degassing pathways preserved in andesite andesitic arc volcanoes degas large quantities of volatiles evidence for vapour transport in the erupted lavas is rarely preserved and poorly understood but is crucial for understanding eruption style we present geochemical evidence for the transport of metal bearing vapour in shear zones preserved in lavas erupted from soufriere hills volcano montserrat textural evidence suggests that shear induced brittle failure occurred in a narrow zone at the conduit wall or in the lava dome elevated metal concentrations cu au ag pb zn within the zones indicate that the fractures acted as a transient pathway for metal bearing magmatic gases during slip frictional heating to temperatures of 1000 c caused partial melting at the slip surface resorption of volatiles and metals into the partial melt preserved the geochemical signature of magmatic vapour in the shear zone cordierite which is highly unusual in volcanic rocks crystallised from the peraluminous partial melt with metal bearing sulphides and oxides the shear zones provide the first geochemical evidence for vapour segregation and transport through viscous andesite magmas and provide an insight into controls on eruption style

multipolarization radar images for geologic mapping and vegetation discrimination the nasa jpl airborne synthetic aperture radar system produces radar image data simultaneously in four linear polarizations hh vv vh hv at 24 6 cm wavelength l band with 10 m resolution across a swath width of approximately 10 km the signal data are recorded optically and digitally and annotated in each of the channels to facilitate a completely automated digital correlation both standard amplitude and also phase difference images are produced in the correlation process individual polarization and range dependent gain functions improve the effective dynamic range but as yet do not permit absolute quantitative measurements of the scattering coefficients however comparison of the relative intensities of the different polarizations in individual black and white and color composite images provides discriminatory mapping information in the death valley california area rough surfaces of young alluvial deposits produce strong responses at all polarizations smoother surfaces of older alluvial deposits show significantly lower responses evaporite deposits of different types and moisture contents have distinct polarization signatures in the wind river basin wyoming sedimentary rock units show polarization responses that relate to differences in weathering local intensity variations in like polarization images result from topographic effects strong cross polarization responses denote the effects of vegetation cover and in some cases possible scattering from the subsurface in the savannah river plant south carolina forest cover characteristics are discriminated by polarization responses that reflect the density and structure of the canopy and the presence or absence of standing water beneath the canopy

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

phase equilibria and compositions of fe mg al minerals and melts in water saturated peraluminous granitic systems phase assemblages and phase compositions were studied experimentally in water saturated biotite bearing peraluminous granitic melts as a function of alumina excess and temperature the runs were performed at 2 and 5 kbars under nno buffer biotite was stable only in composition containing 5 of normative corundum it coexisted with cordierite and hercynite at 2 kbars and with hercynite at 5 kbars in composition containing 10 of normative corundum biotite was not observed abundant cordierite and hercynite were the only fe mg al minerals these relationships show that at constant pressure the amount of cordierite increases with increasing excess of alumina simultaneously the stability of biotite decreases due to preferential partitioning of mg into cordierite and fe into biotite besides the distribution of fe mg and al among the coexisting solid phases solubility of these elements in the melts is given below 900 c melts are poor in iron and magnesium and correspond in terms of these elements to leucogranites it is suggested that the leucogranitic magmas such as parental magmas of european hercynian and himalayan leucogranites must have been formed through highly efficient separation of partial melt from restite in which ferromagnesian components are concentrated peraluminous granites rich in ferromagnesian minerals originate supposedly from restite bearing magmas

origin and evolution of a peraluminous silicic ignimbrite suite the violet town volcanics the violet town volcanics are a 373 ma old comagmatic s type volcanic sequence mainly comprising crystal rich intracaldera ignimbrites rock types vary from rhyolites to rhyodacites all containing magmatic cordierite and garnet phenocrysts variation in the suite is primarily due to fractionation of early crystallized quartz plagioclase and biotite plus minor accessory phases in a high level magma chamber prior to eruption early magmatic crystallization occurred at around 4 kb and 850 c with melt water contents between 2 8 and 4 wt this high temperature markedly water undersaturated restite poor granitic magma was generated by partial melting reactions involving biotite breakdown in a dominantly quartzofeldspathic source terrain leaving a granulite facies residue

origin and evolution of mid cretaceous garnet bearing intermediate and silicic volcanics from canterbury new zealand abstract the mt somers volcanics are part of a suite of mid cretaceous 89 2 ma intermediate to silicic volcanics erupted onto an eroded surface of torlesse sediments rock types vary from basaltic andesite to high silica rhyolite andesites are medium to high k with phenocrysts of plagioclase orthopyroxene and pigeonite dacites are peraluminous and commonly contain granulite facies xenoliths and garnet xenocrysts equilibrium mineral assemblages indicate metamorphic pressures of close to 6 kbar at 800 c rhyolites are peraluminous with phenocrysts of quartz sanidine plagioclase biotite garnet and orthopyroxene the ferromagnesian phases show textural evidence of magmatic crystallization and are chemically distinct from xenocryst phases in dacites equilibrium assemblages indicate that early magmatic crystallization occurred at close to 7 kbar 20 km depth at above 850 c with melt water contents of less than 3 5 major element contents trace element contents and an initial 87 sr 86 sr ratio of 0 7085 indicate that the rhyolites formed by partial melting of dominantly quartzo feldspathic torlesse sediments leaving a granulite facies residue the chemical variation displayed by the rhyolites is best explained by fractional crystallization of the observed high pressure phenocryst assemblage most elements show a compositional gap between rhyolite and dacite the major element trace element and sr isotope compositions of the intermediate lavas are best explained by assimilation of lower crustal material combined with fractional crystallization in mantle derived tholeiitic magmas magmatism was the result of heat and magma flux from the mantle during the change from compressive to extensional tectonics after the culmination of the rangitata orogeny

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

petrology of the coyaguayma ignimbrite northern puna of argentina origin and evolution of a peraluminous high sio2 rhyolite magma abstract the coyaguayma ignimbrite is a strongly peraluminous sp sillimanite garnet bearing silicic rhyolite which erupted in the northern puna segment of the central andean plateau in the upper miocene 11 ma a period that was characterized by the eruption of voluminous 100s to 1000s km3 dacitic ignimbrites of high k calc alkaline affinity in this region the sp magmatic rocks are both rare and small but their importance is potentially much greater as rocks of this type are usually interpreted as products of crustal melting and therefore useful for addressing mantle addition vs crustal recycling in the central andes the phenocryst assemblage of the coyaguayma ignimbrite comprises plagioclase an26 18 quartz ba rich and ba poor sanidine minor al rich ferromagnesian minerals alt and alvi rich biotite almandine spessartine garnet and sillimanite as well as accessory zircon and monazite textural relations suggest that the accessory and ferromagnesian phases crystallized before quartz and feldspars mineral equilibria suggest that crystallization of the rhyolite magma began at 5 kbar and 800 c and continued almost isobarically to 720 c causing the residual liquid to increase h2o contents from 4 5 to 7 5 before eruption most major features e g high sio2 a cnk 1 3 low cao mgo tio2 and feo and trace element patterns low ba sr th lree and eu eu high rb u y and nb along with the thermobarometric constraints on magmatic p t and water contents are consistent with an origin by mica dehydration melting of metapelitic sources e g typical biotite muscovite gneisses from the outcropping s puna basement however the relatively low initial 87sr 86sr 0 7125 and high 143nd 144nd 0 512200 ratios invalidate a pure crustal origin instead we propose contamination of calc alkaline dacitic magmas similar to typical puna ignimbrites by metapelite at mid crustal settings 18 km depth geochemical modeling that satisfies the chemical and isotopic data suggests mixing of 70 dacite and 30 of metapelite partial melts followed by extensive 70 fractionation of plagioclase k feldspar quartz and biotite with minor magnetite and apatite from the hybrid magma sillimanite in the coyaguayma rhyolite is interpreted as a restite mineral or a product of incongruent melting of the metapelite which was preserved intact in the hybrid melt due to local equilibrium this petrogenetic model explains most characteristics of crystal poor sp rhyolites from the puna plateau e g tocomar ramadas rhyolites and it may be more generally applicable to occurrences of sp magmas in andean type continental arcs dominated by calc alkaline magmatism

radar polarimetry analysis tools and applications the authors have developed several techniques to analyze polarimetric radar data from the nasa jpl airborne sar for earth science applications the techniques determine the heterogeneity of scatterers with subregions optimize the return power from these areas and identify probable scattering mechanisms for each pixel in a radar image these techniques are applied to the discrimination and characterization of geologic surfaces and vegetation cover and it is found that their utility varies depending on the terrain type it is concluded that there are several classes of problems amenable to single frequency polarimetric data analysis including characterization of surface roughness and vegetation structure and estimation of vegetation density polarimetric radar remote sensing can thus be a useful tool for monitoring a set of earth science parameters

s type granites and their probable absence in southwestern north america criteria that have been and still are used to characterize s type granites of the lachlan fold belt lfb of southeastern australia are reviewed and comparisons are made with various peraluminous granites of southwestern north america some of which have been classified as s types on the basis of insufficient data virtually all of the vast volume of s type granites in the lfb are near surface batholithic granites that are commonly associated with s type volcanics and are not associated with regional metamorphic rocks and migmatites they are strongly peraluminous as shown by the presence of cordierite granites with primary muscovite are rare all are low in na ca and sr as a result of chemical weathering during formation of the sedimentary sources peraluminous granites of various ages in southwestern north america are distinctly different they rarely contain cordierite a mineral characteristic of lfb s types but some are highly evolved such that fe mn rich garnet has crystallized they are dominantly two mica granites indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the lfb cordierite bearing volcanics s types have not been reported sodium is generally high in the peraluminous granites of southwestern north america some of these rocks have trondhjemitic affinities the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks locally some peraluminous rocks marginal to metaluminous types may owe their compositions to high level contamination of i types these are not s type rocks no compelling evidence has been presented that any of the peraluminous granites of southwestern north america are s types

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

multisensor classification of sedimentary rocks abstract this paper compares linear discriminant analysis and supervised classification results based on signatures from the landsat thematic mapper tm the thermal infrared multispectral scanner tims and airborne synthetic aperture radar sar alone and combined into extended spectral signatures for seven sedimentary rock units exposed on the margin of the wind river basin wyoming results from a linear discriminant analysis showed that training area classification accuracies based on the multisensor data were improved an average of 15 over tm alone 24 over tims alone and 46 over sar alone with similar improvement resulting when supervised multisensor classification maps were compared to supervised individual sensor classification maps when training area signatures were used to map spectrally similar materials in an adjacent area the average classification accuracy improved 19 using the multisensor data over tm alone 2 over tims alone and 11 over sar alone the conclusion of this study is that certain sedimentary lithologies may be accurately mapped using a single sensor but classification of a variety of rock types can be improved using multisensor data sets that are sensitive to different characteristics such as mineralogy and surface roughness

petrology of spinel granulites from araku eastern ghats india and a petrogenetic grid for sapphirine free rocks in the system fmas spinel quartz cordierite and spinel quartz are found as relic prograde assemblages in fe rich granulites from the araku area eastern ghats belt india subsequent reactions produced orthopyroxene sillimanite in the former association and garnet sillimanite in the latter the first reaction is univariant in the fmas system but is trivariant in the present case because of the presence of zn and fe3 in spinel the second reaction also has high variance because of zn and fe3 but also because of the presence of ca in garnet thermobarometry shows that the metamorphic conditions were approximately 950 c and 8 5 kbar and the fo2 was near the nno buffer in fe rich bulk compositions and low p high t conditions of metamorphism two of the univariant reactions around the invariant point sa namely sa hy and sa cd change topology due to reverse partitioning of fe mg between coexisting garnet and spinel an alternative partial petrogenetic grid in the system fmas is constructed for such conditions and is applied satisfactorily to several sapphirine free spinel granulites it is shown that bulk composition xfe and zn exerts greater control on the stability of spinel quartz than fo2 the effect of the presence of zn and fe3 in spinel on the proposed grid is evaluated reaction textures in the araku spinel granulites can be explained from the petrogenetic grid as due to near isobaric cooling

calculated relationships between activity of alumina and phase assemblages of silica saturated igneous rocks petrogenetic implications of magmatic cordierite garnet and aluminosilicate abstract many peraluminous igneous rocks are characterized by the presence of al rich minerals such as cordierite garnet and aluminosilicate polymorphs clearly one of the important thermodynamic intensive variables controlling the stability of these minerals relative to al poor phases such as ortho and clinopyroxene must be the activity of al 2 o 3 a al 2 o 3 in the melt calculated phase relationships of anhydrous mineral assemblages in equilibrium with quartz saturated liquids show that at crustal pressures less than about 10 kbar garnet cordierite and aluminosilicate are only likely to crystallize from melts in which a al 2 o 3 is up to one order of magnitude higher than that required for orthopyroxene clinopyroxene crystallization in spite of this peraluminous granitoid liquids saturated with orthopyroxene garnet or orthopyroxene cordierite do not ordinarily contain significantly larger amounts of excess al al in excess of that required to form feldspars than peraluminous liquids saturated with orthopyroxene clinopyroxene these observations indicate that there must be profound compositional controls on the activity coefficient of al in silicic melts and the strongest of such controls appears to be the total alkali content of the melt the activity coefficient of al in silicic melts varies directly with total alkali oxide content so that alkali poor melts can become markedly peraluminous without ever becoming saturated in aluminous phases whereas alkali rich melts of similar normative corundum content can crystallize garnet cordierite or even aluminosilicate because activity of alumina in a silicic melt is not a simple function of excess al content classification schemes for silicic igneous rocks based on model mineralogical assemblages which reflect the value of the thermodynamic effective concentration of al during crystallization convey more petrologic information than those based on chemical parameters such as normative corundum content or alumina saturation index

petrology geochemistry and genesis of high al tonalite and trondhjemites of the cornucopia stock blue mountains northeastern oregon tonalitic and trondhjemitic compositions span a narrow range of trondhjemite sio2 content 65 74 wt and exhibit characteristics of a highal tonalite trondhjemite granitoid ttg suite including light rare earth element lree enrichment low y nb and rb sr and high al2o3 and sr these compositions are consistent with an

composition and origin of garnet from the antarctic peninsula volcanic group of trinity peninsula garnet is widely found as a minor constituent in rocks of the antarctic peninsula volcanic group apvg of trinity peninsula it occurs as conspicuous megacrysts or in xenoliths within volcanic rocks of andesitic rhyolitic composition and as detrital grains in the associated terrestrial sediments it is also found as an accessory mineral in many plutonic rocks from the e coast of the antarctic peninsula evidence is presented to show that the garnet can be divided petrographically and chemically into two main groups type a almandine rich primary igneous garnet and type b less almandine and more pyrope rich garnet as xenocrysts or included in xenoliths within the volcanic rocks comparison with published experimental data on garnet occurrence in acidic igneous rocks suggests that high almandine low spessartine garnet in volcanic rocks is a remnant phase of high pressure crystallization from magma at pressures of 7 kbar garnet with a higher pyrope content is regarded as xenocrystal in origin having been derived from garnet bearing country rocks at depth either as accidental inclusions or through direct partial melting restite of the lower crust and implies that a considerable thickness 25 km of crustal material was in existence before the generation of the mesozoic magmatic arc the origin of these calc alkaline magmas may therefore be due at least in part to partial melting of pre existing sialic crustal material

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

on the application of sar interferometry to geomorphological studies estimation of landform attributes and mass movements this paper presents two examples of application of synthetic aperture radar sar interferometry insar to typical geomorphological problems the principles of insar are introduced taking care to clarify the limits and the potential of this technique for geomorphological studies the application of insar to the quantification of landform attributes such as the slope and to the estimation of landform variations is investigated two case studies are presented a first case study focuses on the problem of measuring landform attributes by interferometric sar data the interferometric result is compared with the corresponding one obtained by a digital elevation model dem in the second case study the use of insar for the estimation of landform variations caused by a landslide is detailed

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

emplacement of ultramafic carbonatite intrusions along reactivated north american mid continent rift structures abstract understanding the various emplacement pathways of ultramafic carbonatite intrusive complexes and mapping of their global distribution are in an early stage discerning the pattern of their emplacement can reveal information about earth s dynamics and guide exploration for associated economic deposits here we apply multiple spatial analysis methods and synthetic aperture radar sar data to assess the correlation between outcrops of ultramafic carbonatite intrusives and regional craton scale fractures and assign targets for further exploration kernel density cluster two point azimuth and the fry method two dimension spatial analyses are applied to 58 known outcrops of intrusives in the avon volcanic district avd southeast missouri usa the results of the spatial analysis show linear trends among the outcrops with three primary orientations northwest northeast and east west and a strong correlation with regional fault zones sar data processing and analysis guided by the spatial results reveals rhombic lineament patterns with sides that parallel the northwest northeast emplacement patterns of the avd these rhombic structures are related to possible extensional stepover duplexes likely formed during precambrian north american plate rifting along transfer faults reactivation of the precambrian structures during high angle dip slip and wrench faulting that was penecontemporaneous with emplacement of the avd in the devonian likely provided pathways for the mantle derived intrusives these findings can guide exploration efforts and help us understand the emplacement of a unique intracontinental intrusive complex

knowledge based land cover classification using ers 1 jers 1 sar composites land cover classification of an ers 1 jers 1 composite is explored in the context of regional to global scale applicability each of these orbiting synthetic aperture radars provide somewhat complementary information since data is collected using significantly different frequencies polarizations and look angles ers 1 c band vv polarization 23 spl deg jers 1 l band hh polarization 35 spl deg this results in a classification procedure for the composite image a co registered pair from the same season that is superior to that obtained from either of the two sensors alone a conceptual model is presented to show how simple structural attributes of terrain surfaces and vegetation cover relate to the data from these two sensors the conceptual model is knowledge based and it is supported by both theoretical considerations and experimental observations the knowledge based conceptual model is incorporated into a classifier that uses hierarchical decision rules to differentiate land cover classes the land cover classes are defined on the basis of generalized structural properties of widespread applicability the classifier operates sequentially and produces two levels of classification at level 2 terrain is structurally differentiated into man made features urban surfaces short vegetation and tall vegetation at level 2 the tall vegetation class is differentiated on the basis of plant architectural properties of the woody stems and foliage growth forms of woody stems include excurrent i e pines decurrent i e oaks and columnar i e palm architecture two classes of leaves are considered broadleaf and needle leaf the composite classifier yields overall accuracies in excess of 90 for a test site in northern michigan located along the southern ecotone of the boreal forest for the area examined the sar based classification is superior to unsupervised classification of multitemporal avhrr data supplemented with a priori information on elevation climate and ecoregion

the significance of garnet in the permo carboniferous volcanic rocks of the pyrenees garnet occurs within rhyolitic to dacitic lavas ignimbrites and volcaniclastic sediments of the pyrenean calc alkaline permo carboniferous volcanic rocks on the basis of texture and major and trace element composition the garnet is interpreted as having a phenocrystal as opposed to a xenocrystal or restite origin the pyrenean silicic volcanics are strongly peraluminous consistent with derivation as a partial melt from a sedimentary source they were erupted contemporaneously with the hercynian thermal anomaly which produced regional granulite facies metamorphism and anatectic granites the late hercynian granodiorites were also intruded at about this time geochemical data suggest that the petrogenesis of the volcanic rocks differed from that of the granodiorites ree garnet matrix partition coefficients for garnets from a welded rhyolitic ignimbrite are similar to those reported for other phenocrystal garnets in rhyolites ree abundances imply that the garnets crystallized from a hree depleted melt and this is considered to reflect the effects of garnet in the restite experimental constraints suggest that the garnet crystallized at pressures 4 5kb implying that the rhyolites originated from 14 17km depth and were erupted rapidly from these depths in order for the garnet to survive these figures place constraints on the thermal regime prevailing in the late stages of the hercynian orogeny

using full polarimetric sar data to characterize the surface sediments in desert areas a case study in el gallaba plain egypt abstract mapping and characterizing surface sediment of desert environments in terms of surface texture and grain sizes provide important information on the geomorphology and depositional history to assess their potential for economic development accurate maps of surface sediment are often not available at the desired scales using conventional field surveys optical and radar remote sensors are increasingly used as an alternative method for rapid delineation and classification of surface sediments however each sensor provides different levels of information and accuracy in this research work six datasets alos avnir 2 aster avnir 2 palsar aster palsar quad polarized alos palsar and quad polarized radarsat 2 were prepared to run unsupervised and supervised classifications to compare their accuracy for mapping surface sediment in the non vegetated el gallaba plain of the western desert of egypt particularly in terms of grain size and surface roughness the accuracy level of all classification outputs as well as the official geologic map in comparison with the reference field information is empirically evaluated using the standard accuracy assessment method confusion matrices the best overall accuracy and dataset is the supervised classification using the complex coherence matrix t3 of the full polarimetric radarsat 2 which is 96 43 with kappa coefficient of 0 929 therefore the zonal statistics method is applied between the final supervised classification map with its five classes and the generated entropy h alpha anisotropy a and the shuttle radar topography mission srtm to extract information regarding the polarimetric response as well as the elevation of each sediment class in addition the polarization signatures of these five classes are extracted in order to examine their scattering mechanism and to distinguish the differences between them in terms of differences in their surface roughness and grain sizes in addition the low frequency alos palsar data reveal a set of linear features that are hidden under windblown sand and are not visible in the field or in other datasets these hidden lineament features were confirmed in the field by a ground penetrating radar survey using 100 mhz shielded gssi antenna the gpr profiles show very clear discontinuities in the subsurface layers which are covered by a thin sand sheet furthermore the complicated depositional history of these surface sediments is proposed based on field work and remote sensing analyses consequently the results show that el gallaba plain has high potential for agricultural production using its groundwater resources

separation of vegetation and rock signatures in thematic mapper and polarimetric sar images abstract a technique for separating classes of surface roughness and vegetation in semiarid regions using polarimetric synthetic aperture radar sar and thematic mapper tm data has been developed we conclude that polarimetric sar data may be used to separate areas with vegetation cover where one suite of model inversions may be applicable for derivation of surface roughness in more vegetated regions visible near infrared nir data will provide a mechanism for determining the relative contribution of vegetation to multiple scattering in the sar data thus the synergistic use of the two data sets provides a more complete characterization of surface units and cover this result while important for geologic interpretations is even more critical when trying to monitor dielectric constant variations related to changes in moisture content of soil and vegetation cover in arid to semiarid regions a strategy for automating a procedure for measurement of surface roughness is proposed

radar polarization properties of volcanic and playa surfaces applications to terrestrial remote sensing and venus data interpretation the radar polarization properties of lava flows in hawaii kilauea and arizona sp flow and two play a surfaces lunar lake nevada and lavic lake california are compared to the predicted behaviors of theoretical scattering models at 5 7 cm and 24 cm wavelengths kilauea lava flows can be modeled by a combination of facet and diffuse dipole like scattering scattering by rock faces on the scale of the radar wavelength is proposed to account for much of the facet return the radar echoes at 24 cm wavelength from sp flow are on average consistent with entirely diffuse scattering but there are regions within the flow where circular polarization ratios exceed unity suggesting a coherent scattering effect 68 cm data for the lava flows show evidence of radar penetration and volume scattering the playa surfaces are characterized by polarization properties which in some cases are qualitatively consistent with the first order small perturbation model but the echoes do not closely match the predictions of this model for any reasonable dielectric constant value these results show that it may be difficult to construct invertible models for the polarization behavior of some surfaces the playas whereas for others the kilauea lava flows the scattering properties can be successfully modeled the first order small perturbation model is not appropriate for inverse modeling of most terrestrial lava flows though very smooth surfaces on venus may be amenable to the use of this model high circular polarization ratios observed for sp flow tentatively attributed here to coherent backscatter may be analogous to arecibo observations of high reflectivity areas on venus

anatexis of interlayered amphibolite and pelite at 10 kbar effect of diffusion of major components on phase relations and melt fraction we have conducted h2o undersaturated melting experiments on charges consisting of a layer of a sillimanite bearing metapelite and a layer of garnet bearing amphibolite with the goal of studying how layered metamorphic rocks interact during anatexis experiments with the layered charges were performed at 10 kbar 1 gpa at 900 c 334 h 925 c 341 h and 950 c 50 161 332 h dehydration melting of the amphibolite alone and of the pelite alone were studied at the same p t conditions when run alone at 900 c the pelite and the amphibolite yielded ca 40 vol and 15 vol melt respectively corresponding melt fractions at 950 c were ca 50 vol and 30 vol when run side by side melt abundance in the pelite is fairly uniform and ca 20 vol higher than in the solo runs at all temperatures studied in contrast complex zoning patterns parallel to the interface develop in the amphibolite layer far from the interface the melt fraction is 5 10 vol lower than in the amphibolite solo runs closer to the interface the melt fraction in the amphibolite layers are comparable to or somewhat higher than in the amphibolite solo runs and both clinopyroxene and plagioclase react out and are replaced by orthopyroxene and quartz melt fraction closest to the interface reaches 65 70 vol and the only crystalline phase present is garnet with hollow cores the increase in melt fraction in the pelite layers of the layered runs is caused by transfer of na from the amphibolite to the pelite which forces biotite to be eliminated at lower temperature along the biotite garnet reaction boundary k is transferred from the pelite to the amphibolite and the lower melt fraction in the distal end of the amphibolite layers is caused by faster diffusion of na compared to k which results in a net depletion of alkalies ca is transferred from the amphibolite to the pelite and the resulting changes in cao concentrations affect the stabilities of plagioclase pyroxenes garnet and quartz and cause the observed zoning in the amphibolite layer ca entering the pelite layer induces crystallization of large plagioclase neoblasts radiating from the interface into the pelite layer these results show that diffusion of components between contiguous lithologies undergoing anatexis can cause profound changes in phase relations melt fractions and restite compositions

origin of peraluminous granites and granodiorites iberian massif spain an experimental test of granite petrogenesis the discrimination between potential source materials involved in the genesis of iberian granites and granodiorites as well as the role of mantle crust inter actions are examined using constraints imposed by melting experiments melting assimilation experiments and sr nd isotope systematics the sr nd isotope re lationships indicate the existence of diaerent genetic trends in which juvenile mantle materials are involved by diaerent mechanisms 1 a source trend traced by a particular evolution of the pre hercynian basement and indicating mantle participation at the time of sedimen tation 2 a set of magmatic trends traced by gabbro tonalite enclave granodiorite associations implying the incorporation of new mantle material at the time of granite generation these relationships strongly support a pure crustal origin for the peraluminous leucogranites derived from partial melting of crustal protoliths and a hybrid origin for the peraluminous granodiorites these granodiorites are the most abundant granitic rocks of the central iberian zone ciz of the iberian massif implying that processes of hybridisation by assimilation and or magma mixing played an important role in granitoid production during the hercynian orogeny these hypotheses have been tested by means of melting and assimilation experiments melting experiments in the range 800 900 c and at pressures of 3 6 10 and 15 kbar indicate that 1 several potential source materials such as bt ms gneisses and metagreywackes are suitable for the production of peraluminous leucogranite melts 2 the melt compositions are always leucogranitic re gardless of pressure 3 pressure exerts a strong influ ence on the fertility of the source experiments at 3 kbar produce more than 20 vol of melt compared with less than 5 vol of melt produced at 10 and 15 kbar and at the same temperature the melting assimilation experi ments carried out at 1000 c and 4 7 and 10 kbar and using a proportion of 50 gabbro and 50 gneiss give high melt proportions more than 50 vol and noritic residues these melts have the composition of le ucogranodiorites and overlap with part of the compo sitional range of peraluminous granodiorites of the iberian massif the generation of more mafic granodiorites may be explained by the incorporation of some residual orthopyroxene to the granodiorite mag mas the low solubility of fe mg prevents the gen eration of granodiorite melts with more than 3 wt of mgo feo at all crustal pressures the large volumes of peraluminous hybrid granodiorites produced by assimilation of crustal rocks by mantle magmas imply that an important episode of crustal growth took place during the late palaeozoic hercynian orogeny in the iberian massif

dissolution of quartz albite and orthoclase in h2o saturated haplogranitic melt at 800 c and 200 mpa diffusive transport properties of granitic melts at crustal anatectic conditions we have conducted experiments on dissolution of quartz albite orthoclase and corundum into h2o saturated haplogranite melt at 800 c and 200mpa over a duration of 120 1488h with the aim of ascertaining the diffusive transport properties of granitic melts at crustal anatectic temperatures cylinders of anhydrous starting glass and a single mineral phase quartz or feldspar were juxtaposed along flat and polished surfaces inside gold or platinum capsules with 10 wt added h2o concentration profiles in glass quenched melt perpendicular to the mineral glass interfaces and comparison with relevant phase diagrams suggest that melts at the interface are saturated in the dissolving phases after 384h and with longer durations the concentration profiles are controlled only by diffusion of components in the melt the evolution of the concentration profiles with time indicates that uncoupled diffusion in the melt takes place along the following four linearly independent directions in oxide composition space sio2 n a2o and k2o axes si na and k eigenvectors respectively and a direction between the al2o3 na2o and k2o axes al eigenvector such that the al na molar ratio is equal to that of the bulk melt and the al na k molar ratio is equal to the equilibrium asi mol al2o3 na2o k2o of the melt experiments in which a glass cylinder was sandwiched between two mineral cylinders quartz and albite quartz and k feldspar or albite and corundum tested the validity of the inferred directions of uncoupled diffusion and explored longrange chemical communication in the melt via chemical potential gradients the application of available solutions to the diffusion equations for the experimental quartz and feldspar dissolution data provides diffusivities along the directions of the si eigenvector and al eigenvector of 2 0 2 8 10 15 m 2 s and 0 6 2 4 10 14 m 2 s respectively minimum diffusivities of alkalis 3 9 10 11 m 2 s are orders of magnitude greater than the tetrahedral components of the melt the information provided here determines the rate at which crustal anatexis can occur when sufficient heat is supplied and diffusion is the only mass transport mixing process in the melt the calculated diffusivities imply that a quartzo feldspathic source rock with initial grain size of 2 3mm undergoing hydrostatic h2o saturated melting at 800 c infinite heat supply could produce 20 30 vol of homogeneous melt in less than 1 10 years slower diffusion in h2o undersaturated melts will increase this time frame

vapour absent melting from 10 to 20 kbar of crustal rocks that contain multiple hydrous phases implications for anatexis in the deep to very deep continental crust and active continental margins

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

sar studies in the yuma desert arizona sand penetration geology and the detection of military ordnance debris abstract synthetic aperture radar sar images acquired over part of the yuma desert in southwestern arizona demonstrate the ability of c band 5 7 cm wavelength l band 24 5 cm and p band 68 cm airsar signals to backscatter from increasingly greater depths reaching several meters in blow sand and sandy alluvium airsar images obtained within the barry m goldwater bombing and gunnery range near yuma arizona show a total reversal of c and p band backscatter contrast image tone for three distinct geologic units this phenomenon results from an increasingly greater depth of radar imaging with increasing radar wavelength in the case of sandy and small pebble alluvium surfaces mantled by up to several meters of blow sand backscatter increases directly with sar wavelength as a result of volume scattering from a calcic soil horizon at shallow depth and by volume scattering from the root mounds of healthy desert vegetation that locally stabilize blow sand airsar images obtained within the military range are also shown to be useful for detecting metallic military ordnance debris that is located either at the surface or covered by tens of centimeters to several meters of blow sand the degree of detectability of this ordnance increases with sar wavelength and is clearly maximized on p band images that are processed in the cross polarized mode hv this effect is attributed to maximum signal penetration at p band and the enhanced phv image contrast between the radar bright ordnance debris and the radar dark sandy desert this article focuses on the interpretation of high resolution airsar images but also compares these airborne sar images with those acquired from spacecraft sensors such as ers sar and space radar laboratory sir c x sar

petrological evolution of a suite of spinel granulites from vizianagram eastern ghats belt india and genesis of sapphirine bearing assemblages a suite of spinel cordierite granulites from viziangram eastern ghats belt india preserve mineral assemblages and reaction textures indicative of peak metamorphic conditions of 1000 c 8 10 kbar followed successively by near isobaric cooling down to 750 800 c near isothermal decompression to 4 5 kbar and late hydration p t conditions of each stage are evaluated through a combination of petrogenetic grid approach and thermobarometry sapphirine is developed in sillimanite bearing acid pegmatite veins that intruded the spinel cordierite granulite close to peak metamorphic conditions and also in the host rock in immediate contact with the pegmatite both sillimanite and sapphirine in the pegmatite are considered to be magmatic phases field observations and textural characteristics suggest that al metasomatism of the spinel cordierite granulite due to the intrusion of pegmatite was responsible for sapphirine formation in the spinel granulite

sequence stratigraphy of the upper part of the plio pleistocene kakegawa group western shizuoka japan abstract the kakegawa group is exposed in shizuoka central japan it is the fill of a plio pleistocene fore arc basin and constitutes a third order sequence 2 6 1 0 m y the upper kakegawa group consists of a transgressive systems tract tst and a highstand systems tract hst the tst comprises parasequence sets that are retrogradational on the shelf and progradational on the slope the shelf parasequences consist of upward coarsening facies of tempestites bounded by ravinement surfaces the shelf parasequences can be traced downslope where they comprise upward thinning turbidite successions fourth or fifth order transgression containing backstepping sand dominated intervals and silt dominated upward thickening successions regression the hst consists of progradational parasequence sets the shelf parasequences are similar to those of the tst except for greater basinward distribution of shelf sand outer shelf to upper slope parasequences incorporate silt dominated upward thinning successions transgression and overlying upward thickening turbidite successions regression including sand dominated intervals at their tops the upward thinning successions are much thinner than those in the tst a condensed interval dividing these systems tracts consists of bioturbated silt and might include the maximum flooding surface in the tst parasequences slope sand packets are thicker are present on the lower slope and were formed during fourth or fifth order transgression in contrast the hst slope turbidite sands are thinner are present on the outer shelf to upper slope and were deposited during fourth or fifth order regression during transgression the large volumes of sediment derived from intense shoreface erosion bypassed the narrow shelf ca 10 km wide and contributed to channeling on the upper slope and accumulation of larger packets on the lower slope in the hst deposition of slope turbidites was induced by progradation of shelf sand during regression smaller rate supply of sandy sediment to the slope resulted in deposition of smaller packets the sand might have been deposited at the o ter edge of a wider shelf 15 20 km of the hst

occurrence and origin of andalusite in peraluminous felsic igneous rocks andalusite occurs as an accessory mineral in many types of peraluminous felsic igneous rocks including rhyolites aplites granites pegmatites and anatectic migmatites some published stability curves for and sil and the water saturated granite solidus permit a small stability field for andalusite in equilibrium with felsic melts we examine 108 samples of andalusite bearing felsic rocks from more than 40 localities world wide our purpose is to determine the origin of andalusite including the t p x controls on andalusite formation using eight textural and chemical criteria size compatibility with grain sizes of igneous minerals in the same rock shape ranging from euhedral to anhedral with no simple correlation with origin state of aggregation single grains or clusters of grains association with muscovite with or without rims of monocrystalline or polycrystalline muscovite inclusions rare mineral inclusions and melt inclusions chemical composition andalusite with little significant chemical variation except in iron content 008 171 wt feo compositional zoning concentric sector patchy oscillatory zoning cryptically reflect growth conditions compositions of coexisting phases biotites with high siderophyllite eastonite contents aliv 268 007 atoms per formula unit muscovites with 057 401 wt feo and 002 285 wt tio2 and apatites with 353 018 wt f coexisting muscovite biotite pairs have a wide range of f contents and fbt 1612fms 0015 most coexisting minerals have compositions consistent with equilibration at magmatic conditions the three principal genetic types of andalusite in felsic igneous rocks are type 1 metamorphic a prograde metamorphic in thermally metamorphosed peraluminous granites b retrograde metamorphic inversion from sillimanite of unspecified origin c xenocrystic derivation from local country rocks and d restitic derivation from source regions type 2 magmatic a peritectic water undersaturated t associated with leucosomes in migmatites b peritectic water undersaturated t as reaction rims on garnet or cordierite c cotectic water undersaturated t direct crystallization from a silicate melt and d pegmatitic watersaturated t associated with aplite pegmatite contacts or pegmatitic portion alone type 3 metasomatic water saturated magma absent spatially related to structural discontinuities in host replacement of feldspar and or biotite intergrowths with quartz the great majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin of the many possible controls on the formation of andalusite excess al2o3 water concentration and fluid evolution high be b li p high f high fe mn ti and kinetic considerations the two most important factors appear to be excess al2o3 and the effect of releasing water either to strip alkalis from the melt or to reduce alumina solubility in the melt of particular importance is the evidence for magmatic andalusite in granites showing no significant depression of the solidus suggesting that the and sil equilibrium must cross the granite solidus rather than lie below it magmatic andalusite however formed is susceptible to supra or sub solidus reaction to produce muscovite in many cases textural evidence of this reaction remains but in other cases muscovite may completely replace andalusite leaving little or no evidence of its former existence

aluminum in zircon as evidence for peraluminous and metaluminous melts from the hadean to present zircon structurally accommodates a range of trace impurities into its lattice a feature which is used extensively to investigate the evolution of silicate magmas one key compositional boundary of magmas is defined by whether the molar ratio of al2o3 cao na2o k2o is larger or smaller than unity here we report 800 al in zircon concentrations from 19 different rocks from the lachlan fold belt southeastern australia new england usa and arunachal leucogranites eastern himalaya with al2o3 cao na2o k2o whole rock values that range from 0 88 to 1 6 zircons from peraluminous rocks yield an average al concentration of 10 ppm which distinguishes them from crystals found in metaluminous rocks 1 3 ppm this difference is related to the materials involved in the melting assimilation and or magma differentiation processes for example magmas that assimilate al rich material such as metapelites are expected to produce melts with elevated alumina activities and thus zircons with high al concentrations these observations are applied to the archean and hadean jack hills detrital zircon record detrital archean zircons with ages from about 3 30 to 3 75 ga yield al in zircon concentrations consistent with origins in peraluminous rocks in 8 of the cases n 236 a single zircon from the pre 3 9 ga age group n 39 contains elevated al contents which suggests that metaluminous crustal rocks were more common than peraluminous rocks in the hadean weathered material assimilated into these hadean source melts was not dominated by al rich source material

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water