the early metamorphic history of the haast schists and related rocks of new zealand rare but widespread relics of sodic amphibole occur in metabasites and metacherts of the haast schists and related caples terrane rocks present main stage metamorphic assemblages are frequently chemically equivalent to earlier sodic amphibole bearing assemblages indicating that these rocks underwent an earlier higher p tmetamorphism prior to formation of the present pumpellyite actinolite and greenschist facies assemblages the earlier assemblages were stable during and after early isoclinal folding but were replaced by the present moderate p t assemblages prior to the last major fabric forming deformation the change in conditions was due to thermal relaxation probably accompanied by uplift and erosion and peak metamorphic temperatures were about 350 370 c in the pumpellyite actinolite zone of the caples terrane and near 390 c in the greenschist facies chlorite zone near queenstown according to henley 1975 these greenschist facies rocks attained a pressure of at least 6 4 0 4 kb during their history but a pressure of 4 6 0 6 kb has been estimated for a chlorite zone rock from middlemarch and so the 6 4 kb estimate probably refers to the maximum pressure attained during the earlier higher p t metamorphism similar changes in metamorphic facies series with time occur in some older and more complex metamorphic belts such as the caledonides and this study suggests that it may be possible to interpret particular elements in the metamorphic development of such belts in terms of specific circum pacific analogues

geochemistry of the shuksan greenschists and blueschists north cascades washington variably fractionated and altered metabasalts of oceanic affinity the shuksan schist comprises a structurally coherent metabasaltic member of the easton formation the uppermost allochthon shuksan thrust plate in the thrust system of the western north cascades of washington state late jurassic metamorphism at moderately high p t produced interlayering of actinolite bearing greenschist assemblages with blue amphibole bearing rocks major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated type i morb to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages

amphibole compositions and metamorphic history of the rand schist and the greenschist unit of the catalina schist southern california the catalina schist and rand schist are two high p t terranes in southern california the catalina schist is correlated with the franciscan complex and occurs in the continental borderland it consists of a blueschist facies melange tectonically overlain by a greenschist unit which in turn is overthrust by an amphibolite unit the greenschist unit itself is inversely zoned from epidote amphibolite fades at the top through greenschist facies in the center to transitional blueschist greenschist facies at the base the rand schist is part of the eugeoclinal pelona orocopia schist terrane which lies interior to the present continental margin structurally beneath precambrian to mesozoic sialic basement the rand schist is inversely zoned from epidote amphibolite facies to transitional blueschist greenschist facies similar to the greenschist unit of the catalina schist

high pressure metamorphism in mafic schist from northern vermont the only confirmed occurrence of glaucophane and omphacite in the appalachian mountains of new england is in mafic schist from tillotson peak 44 48 72 33 north central vermont mineral assemblages observed all with epidote sphene magnetite phengitic muscovite carbonate calcite or dolomite apatite sulfide are 1 actinolite glaucophane chlorite garnet quartz 2 actinolite glaucophane chlorite albite garnet 3 actinolite glaucophane omphacite garnet 4 glaucophane chlorite garnet quartz 5 glaucophane omphacite quartz 6 albite glaucophane chlorite quartz and 7 albite paragonite chlorite quartz electron microprobe investigations show that plagioclase chlorite sphene white mica carbonate and magnetite grains are relatively homogeneous however amphibole pyroxene epidote and garnet grains are zoned indicating incomplete equilibration and changing physical conditions during metamorphism glaucophane in assemblage 6 has the general formula rim composition na 1 9 m4 ca 0 1 mg 1 8fe 1 2 2 al 1 0 vi fe 0 3 3 si 7 9 al 0 1 iv o 22 oh 2 glaucophane in assemblages 1 to 5 is somewhat poorer in the glaucophane endmember and richer in actinolite ca rich amphibole grains are zoned extensively with barroisite cores and actinolite rims omphacite grains in assemblages 3 and 5 have the general formula rim composition na 0 5 ca 0 5 mg 0 4 fe 0 1 2 al 0 4 vi fe 0 1 3 si 2o 6 in spite of the significant zoning the partitioning of elements among the minerals at their grain margins suggests that all seven assemblages above may coexist at the same physical conditions of metamorphism in mafic rocks with a relatively small range in bulk composition correlation of mineral compositions and assemblages with mineral stability data suggests high pressure facies series metamorphism at about 9 2 kb and 450 100 c with p h2o p total it is proposed that the metamorphism occurred during the ordovician

petrological evidence for the development of refolded folds during a single deformational event abstract the pelona schist which forms the lower plate of the vincent thrust in the san gabriel mountains of southern california has undergone a complex history of folding the youngest folds in the schist style 2 folds range in shape from open to tight and fold both compositional layering and schistosity these are superposed upon isoclinal folds with axial plane schistosity style 1 folds that in turn overprint older isoclinal folds also called style 1 folds samples from the hinges of style 2 folds contain two generations of muscovite muscovites of the older generation are parallel to the folded style 1 schistosity the newer muscovites recrystallized during and or after style 2 folding microprobe analysis indicates that the two generations of muscovite are very similar in composition although the new muscovites tend to have slightly higher paragonite and celadonite contents than the old muscovites from the gross similarity of the two groups of muscovite it is concluded that the style 1 and style 2 folds were produced during a single progressive deformation the slightly higher paragonite and celadonite contents of the new muscovites are thought to indicate that both pressure and temperature were increasing during the deformation this is consistent with the deformation being due to underthrusting of the pelona schist beneath the upper plate of the vincent thrust

structural geology of the pelona schist and vincent thrust san gabriel mountains california the vincent thrust of the san gabriel mountains southern california separates an upper plate that contains abundant granitic rocks from a lower plate composed of metagraywackes and metabasites pelona schist the vincent thrust is part of a regional thrust system of late cretaceous early tertiary age vincent chocolate mountain thrust several earlier workers have concluded that the upper plate was derived from the southwest implying the former presence of continental rocks separated from north america by a marginal oceanic basin other workers consider that regional correlations indicate thrusting of the opposite sense the pelona schist of the san gabriel mountains has undergone a complex structural history the earliest recognized structures are tight synmetamorphic isoclinal folds style 1 folds these folds are present throughout the entire 4 km of presently exposed section and do not become more appressed or more abundant near the thrust isoclinally refolded folds and sheath folds were observed at several localities textural observations indicate that the present schistosity of the pelona schist formed by the extreme flattening of crenulations developed in an earlier schistosity this is evidence that the isoclinally refolded folds although only infrequently noticed in the field are actually widespread the isoclinal folding was followed by the development of a macroscopic synform narrows synform and associated minor folds in the 700 m of pelona schist closest to the upper plate these folds style 2 folds are more open than the style 1 folds and do not have a well developed axial planar schistosity they are generally parallel in orientation to the style 1 folds both style 1 and style 2 folds are in turn parallel to tight folds in mylonitic rocks present at the base of the upper plate it is believed that the three groups of folds are cogenetic and possibly were produced in a subduction zone the sheath folds and other evidence of stretching parallel to fold axes might indicate that fold axes were rotated into the direction of thrusting on the other hand the parallelism of the early isoclinal folds and the later relatively open style 2 folds is evidence against rotation thus the orientation of fold axes relative to the thrusting direction is not clear subsequent to metamorphism the pelona schist and the mylonites were folded into a broad arch style 3 folding uncertainty as to the orientation of the axes of style 1 and 2 folds relative to the thrusting direction the presence of the style 3 folding and recently described paleomagnetic evidence of large scale rotation of crustal blocks in southern california make determination of thrusting direction impossible at the present time thus no evidence was found either to support or to invalidate the marginal basin model for the origin of the pelona schist

structural and metamorphic history of the shuksan metamorphic suite in the mount watson and gee point areas north cascades washington the blueschist facies shuksan metamorphic suite of the north cascades has relict stratigraphy and sediment composition suggesting that it is of oceanic origin broadly defined the first metamorphic event affecting the rocks which probably occurred on the sea floor is a static epidote metasomatism of wide extent the earliest penetrative structures l 1 s 1 formed during latest jurassic early cretaceous blueschist facies metamorphism which is inferred to have occurred during subduction in this event recrystallization and intense penetrative strain were closely linked late metamorphic isoclinal fold axes f 2 and later crenulations l 3 formed at high angles to the l 1 lineation f 2 folds reflect extreme shortening perpendicular to the axis of the shuksan belt microscopic textural relations indicate that ca amphibole not na amphibole was stable during the development of f 2 and suggest that these structures record events related to uplift of the suite l 1 and f 2 structures can be interpreted to indicate either that uplift was the result of a distinct tectonic event or that metamorphism and uplift were part of a continuous tectonic process with no change in the stress field final emplacement of the shuksan suite occurred along a fault system which at least locally is high angle and includes zones of tectonic melange

controls on p t t deformation path from amphibole zonation during progressive metamorphism of basic rocks estuary of the river vilaine south brittany france edenite tremolite and edenite magnesio hornblende in equilibrium with plagioclase chlorite epidote quartz and vapour involve several types of reactions for which kd can be related to t and p thermodynamic calculation of these equilibria leads to isopleth systems given knowledge of the progressive changes of end member activities in zoned ca mg amphiboles based on microprobe analyses it is possible to construct precise pressure temperature time paths p t t paths which have been followed by metabasites during polyphase metamorphism when applied to basic rocks from the river vilaine area this method allows us to construct a p t t path that can be compared directly to the p t t path constructed from interbedded acid rocks aluminous micaschists in the same structural unit through time both basic and acid rocks underwent the same complex deformation history that can be described conveniently in the l s fabric system of flinn this allows us to construct a p t t deformation path for this structural unit these paths are interpreted in terms of an under overthrusting continental collision belt the hercynian belt and represent an illustration of the time delay caused by stacking of more than two crustal units

oceans in the icy galilean satellites of jupiter abstract equilibrium models of heat transfer by heat conduction and thermal convection show that the three satellites of jupiter europa ganymede and callisto may have internal oceans underneath ice shells tens of kilometers to more than a hundred kilometers thick a wide range of rheology and heat transfer parameter values and present day heat production rates have been considered the rheology was cast in terms of a reference viscosity 0 calculated at the melting temperature and the rate of change a of viscosity with inverse homologous temperature the temperature dependence of the thermal conductivity k of ice i has been taken into account by calculating the average conductivity along the temperature profile heating rates are based on a chondritic radiogenic heating rate of 4 5 pw kg 1 but have been varied around this value over a wide range the phase diagrams of h2o ice i and h2o 5 wt nh3 ice have been considered the ice i models are worst case scenarios for the existence of a subsurface liquid water ocean because ice i has the highest possible melting temperature and the highest thermal conductivity of candidate ices and the assumption of equilibrium ignores the contribution to ice shell heating from deep interior cooling in the context of ice i models we find that europa is the satellite most likely to have a subsurface liquid ocean even with radiogenic heating alone the ocean is tens of kilometers thick in the nominal model if tidal heating is invoked the ocean will be much thicker and the ice shell will be a few tens of kilometers thick ganymede and callisto have frozen their oceans in the nominal ice i models but since these models represent the worst case scenario it is conceivable that these satellites also have oceans at the present time the most important factor working against the existence of subsurface oceans is contamination of the outer ice shell by rock rock increases the density and the pressure gradient and shifts the triple point of ice i to shallower depths where the temperature is likely to be lower then the triple point temperature according to present knowledge of ice phase diagrams ammonia produces one of the largest reductions of the melting temperature if we assume a bulk concentration of 5 wt ammonia we find that all the satellites have substantial oceans for a model of europa heated only by radiogenic decay the ice shell will be a few tens of kilometers thinner than in the ice i case the underlying rock mantle will limit the depth of the ocean to 80 100 km for ganymede and callisto the ice i shell on top of the h2o nh3 ocean will be around 60 to 80 km thick and the oceans may be 200 to 350 km deep previous models have suggested that efficient convection in the ice will freeze any existing ocean the present conclusions are different mainly because they are based on a parameterization of convective heat transport in fluids with strongly temperature dependent viscosity rather than a parameterization derived from constant viscosity convection models the present parameterization introduces a conductive stagnant lid at the expense of the thickness of the convecting sublayer if the latter exists at all the stagnant lid causes the temperature in the sublayer to be warmer than in a comparable constant viscosity convecting layer we have further modified the parameterization to account for the strong increase in homologous temperature and therefore decrease in viscosity with depth along an adiabat this modification causes even thicker stagnant lids and further elevated temperatures in the well mixed sublayer it is the stagnant lid and the comparatively large temperature in the sublayer that frustrates ocean freezing

stagnant lid convection in bottom heated thin 3 d spherical shells influence of curvature and implications for dwarf planets and icy moons because the viscosity of ice is strongly temperature dependent convection in the ice layers of icy moons and dwarf planets likely operates in the stagnant lid regime in which a rigid lid forms at the top of the fluid and reduces the heat transfer a detailed modeling of the thermal history and radial structure of icy moons and dwarf planets thus requires an accurate description of stagnant lid convection we performed numerical experiments of stagnant lid convection in 3 d spherical geometries for various ice shell curvatures f measured as the ratio between the inner and outer radii effective rayleigh number ram and viscosity contrast from our results we derived scaling laws for the average temperature of the well mixed interior m and the heat flux transported through the shell the nondimensional temperature difference across the bottom thermal boundary layer is well described by 1 m 1 23 f 1 5

an example of high pressure low temperature metamorphic rocks from an island arc the paikon series innermost hellenides greece the paikon series is considered to be a volcanic arc sequence with a mainly neritic sedimentary sequence and bimodal tholeiitic volcanism of early mesozoic age the metamorphic assemblages are syn to post kinematic with respect to a pre tithonian tectonic phase and range from the lawsonite chlorite albite facies through transitional na amphibole greenschist facies to the chlorite sub zone of the greenschist facies the metamorphic imprint of the paikon series corresponds to a temperature range from less than 330 c to 450 c under a total pressure from 3 kbar to 6 7 kbar the overprinting of these facies on an earlier blueschist assemblage related either to a subduction zone or to a tectonic overpressure caused by thrusting is suspected

tidal resonance in icy satellites with subsurface oceans tidal dissipation is a major heat source for the icy satellites of the giant planets several icy satellites likely possess a subsurface ocean underneath an ice shell previous studies of tidal dissipation on icy satellites however have either assumed a static ocean or ignored the effect of the ice lid on subsurface ocean dynamics in this study we examine inertial effects on tidal deformation of satellites with a dynamic ocean overlain by an ice lid based on viscoelasto gravitational theory although ocean dynamics is treated in a simplified fashion we find a resonant configuration when the phase velocity of ocean gravity waves is similar to that of the tidal bulge this condition is achieved when a subsurface ocean is thin 1 km the enhanced deformation increased h2 and k2 love numbers near the resonant configuration would lead to enhanced tidal heating in the solid lid a static ocean formulation gives an accurate result only if the ocean thickness is much larger than the resonant thickness the resonant configuration strongly depends on the properties of the shell demonstrating the importance of the presence of a shell on tidal dissipation

the tidal response of europa the tidal response of europa to a time varying potential is determined by solving the quasi static equilibrium equations for a body composed of several uniform maxwell viscoelastic layers models in which europa s surface ice extends all the way to the silicate mantle have weak tidal responses 1 m vertical deflection while models in which a liquid ocean underlies the ice have about 30 m peak vertical deflection the phase lag of the tidal response is very small 2 in the case of an ocean but may be large if there is no ocean and the ice has a viscosity around 1013 pa s for models with an ocean the product of the thickness and strength of the ice determines the tidal response making it difficult to determine the thickness of the ice by observing the tidal deflection of europa

the effects of laterally varying icy shell structure on the tidal response of ganymede and europa we use a finite element model to solve for the response of ganymede and europa to tidal forcing from jupiter using various icy shell models with laterally variable 3 d structure in all cases the shell is assumed to be underlain by a liquid water ocean icy shells with laterally varying thickness are derived from a thermal conduction model three dimensional shear modulus profiles for the shell are built either from a conduction model or for europa by assuming a hemispherical difference in composition icy shell structures with a nonglobal ocean are built for ganymede using these shell structures to calculate the tidal response of ganymede and europa we conclude the following 1 the presence of lateral variations in thickness or in shear modulus would not degrade future attempts to use tidal observations to decide on the existence or absence of a liquid ocean and to determine the mean icy shell thickness 2 given accurate enough observations the presence of lateral variations in thickness or in shear modulus could be determined by searching for nondegree 2 components in the tidal response 3 in the absence of significant viscous convective flow in the shell the effects of a laterally varying shear modulus on the tidal response would be smaller than those of a laterally varying shell thickness 4 if the shell is partially grounded tidal observations of either gravity or uplift would be able to roughly differentiate regions where the ice is grounded from those where it is floating

the tidal response of ganymede and callisto with and without liquid water oceans calculations of the tidal responses of ganymede and callisto reveal that tidal amplitudes on these bodies may be as large as a few meters if a liquid ocean exists to decouple the surface ice from the interior tides on ganymede s surface can exceed 7 m peak to peak variation while on callisto the tidal amplitude can exceed 5 m in the presence of a liquid ocean without an ocean tidal amplitudes are less than 0 5 m on ganymede and less than 0 3 m on callisto an orbiting spacecraft using an altimeter for crossover analysis and doppler tracking from earth should be able to achieve sufficient accuracy to identify the tidal amplitude to within about a meter over the course of a few months observing tens of tidal cycles

tidal deformation of ganymede sensitivity of love numbers on the interior structure tidal deformation of icy satellites provides crucial information on their subsurface structures in this study we investigate the parameter dependence of the tidal displacement and potential love numbers i e h2 and k2 respectively of ganymede our results indicate that love numbers for ganymede models without a subsurface ocean are not necessarily smaller than those with a subsurface ocean the phase lag however depends primarily on the presence absence of a subsurface ocean thus the determination of the phase lag would be of importance to infer whether ganymede possesses a subsurface ocean or not based only on geodetic measurements our results also indicate that the major control on love numbers is the thickness of the ice shell if ganymede possesses a subsurface ocean this result however does not necessarily indicate that measurement of either of h2 or k2 alone is sufficient to estimate the shell thickness while a thin shell leads to large h2 and k2 independent of parameters a thick shell does not necessarily lead to small h2 and k2 we found that to reduce the uncertainty in the shell thickness constraining k2 in addition to h2 is necessary highlighting the importance of collaborative analyses of topography and gravity field data

theoretical investigation of the ocean coast effect at a passive continental margin abstract the idea that oceanic lithosphere is thinner than continental lithosphere is widely accepted even though one would like to see clearer evidence to support it in fact the very concept of lithosphere is still a matter of some debate if there is indeed a variation in the thickness of the lithosphere at continental margins and if this change is associated with a lateral variation in electrical conductivity one may envisage detecting it with electromagnetic soundings methods a model of a passive continental margin has therefore been investigated to test whether this would be feasible it has been found that the well known but strong ocean coast effect masks the minor lithospheric effect in magnetotelluric soundings performed on the shore inductive soundings on the other hand are highly sensitive to lateral variations in electrical conductivity an analysis in terms of the induction arrow has shown that such soundings carried out on land would be perfectly suitable to reveal a changing lithospheric thickness if the continents merely extended to the oceanic coast however the presence of only a narrow continental shelf of 100 km width under 250 m of sea water produces an overriding coast effect ahead of the margin and thus renders electromagnetic methods unsuited to reveal a changing lithospheric thickness

geophysical investigations of habitability in ice covered ocean worlds geophysical measurements can reveal the structures and thermal states of icy ocean worlds the interior density temperature sound speed and electrical conductivity thus characterize their habitability we explore the variability and correlation of these parameters using 1 d internal structure models we invoke thermodynamic consistency using available thermodynamics of aqueous mgso 4 nacl as seawater and nh 3 pure water ice phases i ii iii v and vi silicates and any metallic core that may be present model results suggest for europa that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by mgso 4 from a more reduced ocean dominated by nacl in contrast with jupiter s icy ocean moons titan and enceladus have low density rocky interiors with minimal or no metallic core the low density rocky core of enceladus may comprise hydrated minerals or anhydrous minerals with high porosity cassini gravity data for titan indicate a high tidal potential love number k 2 0 6 which requires a dense internal ocean ocean 1 200 kg m 3 and icy lithosphere thinner than 100 km in that case titan may have little or no high pressure ice or a surprisingly deep water rock interface more than 500 km below the surface covered only by ice vi ganymede s water rock interface is the deepest among known ocean worlds at around 800 km its ocean may contain multiple phases of high pressure ice which will become buoyant if the ocean is sufficiently salty callisto s interior structure may be intermediate to those of titan and europa with a water rock interface 250 km below the surface covered by ice v but not ice vi

ocean tidal heating in icy satellites with solid shells abstract as a long term energy source tidal heating in subsurface oceans of icy satellites can influence their thermal rotational and orbital evolution and the sustainability of oceans we present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness the stabilizing effect of an overlying shell damps ocean tides reducing tidal heating this effect is more pronounced on enceladus than on europa because the effective rigidity on a small body like enceladus is larger for the range of likely shell and ocean thicknesses of enceladus and europa the thin shell approximation of beuthe 2016 is generally accurate to less than about 4 explaining enceladus endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints the time averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell with higher dissipation near the equator and poles for eccentricity and obliquity forcing respectively this can lead to unique horizontal shell thickness variations if the shell is conductive the surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response for europa and enceladus eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values despite the small obliquity values obliquity forcing generally produces larger phase lags due to the generation of rossby haurwitz waves if europa s shell and ocean are respectively 10 and 100 km thick the tide amplitude and phase lag are 26 5 m and

complex refolding history of the pelona orocopia and rand schists southern california previous workers studying the structural geology of the pelona and related schists of southern california and southwestern arizona have generally reported two important sets of folds an early group of isoclinal folds and a set of later more open folds field and petrographic evidence presented here indicates the existence of additional isoclinal folds predating the ones already described all folds are thought to have formed during underthrusting of the pelona schist in a subduction zone

the orbital thermal evolution and global expansion of ganymede article history the tectonically and cryovolcanically resurfaced terrains of ganymede attest to the satellite s turbulent geologic history yet the ultimate cause of its geologic violence remains unknown one plausible scenario suggests that the galilean satellites passed through one or more laplace like resonances before evolving into the current laplace resonance passage through such a resonance can excite ganymede s eccentricity leading to tidal dissipation within the ice shell to evaluate the effects of resonance passage on ganymede s thermal history we model the coupled orbital thermal evolution of ganymede both with and without passage through a laplace like resonance in the absence of tidal dissipation radiogenic heating alone is capable of creating large internal oceans within ganymede if the ice grain size is 1 mm or greater for larger grain sizes oceans will exist into the present epoch the inclusion of tidal dissipation significantly alters ganymede s thermal history and for some parameters e g ice grain size tidal q of jupiter a thin ice shell 5 to 20 km can be maintained throughout the period of resonance passage the pulse of tidal heating that accompanies laplace like resonance capture can cause up to 2 5 volumetric expansion of the satellite and contemporaneous formation of near surface partial melt the presence of a thin ice shell and high satellite orbital eccentricity would generate moderate diurnal tidal stresses in ganymede s ice shell larger stresses result if the ice shell rotates non synchronously the combined effects of satellite expansion its associated tensile stress rapid formation of near surface partial melt and tidal stress due to an eccentric orbit may be responsible for creating ganymede s unique surface features

zoned sodic amphibole petrologic indicator of changing pressure and temperature during tectonism in the bathurst area new brunswick canada amphibole zoned from an actinolite core through a barroisite layer to a crossite or ferroglaucophane rim coexists with epidote chlorite albite quartz phengite sphene magnetite and calcite in metabasites of the tetagouche group near bathurst new brunswick stratigraphic structural and regional metamorphic evidence suggests that these rocks were situated in the hangingwall of a se dipping subduction zone during the taconian orogeny using microprobe analyses of the coexisting minerals a dehydration reaction and a subsequent hydration reaction have been balanced in the system sio2 al2o3 tio2 fe2o3 fe mg mn o cao na2o k2o h2o so as to describe the development of the zoned amphiboles relatively large coefficients for magnetite in these reactions accord with the absence of sodic amphibole in associated magnetite free metabasites indicating that ferric iron has a significant effect on the transition from greenschist to epidote blueschist fades relatively small residuals of feo mgo and mno show that these components are only weakly partitioned between the reactant and product assemblages the procedure of holland and richardson 1979 has been used to calculate apparentp t paths that trace the growth histories of the zoned amphiboles from a low p environment to a high p environment although the apparent pressure change is implausibly large and the final temperature implausibly low it is clear that the bathurst metabasites followed a very differentp t path than those of the austrian alps despite their identical mineral assemblage

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

tides on europa and the thickness of europa s icy shell 1 it has been shown previously that measurements of tides on jupiter s moon europa can be used to determine whether there is a liquid ocean beneath this moon s icy outer shell in this paper we examine the further possibility of constraining the thickness of the icy shell in the case where a liquid ocean exists by combining measurements of tidal gravity obtained from tracking an orbiting spacecraft with measurements of vertical tidal surface displacements obtained from a precise onboard altimeter by simulating a 1 month europa mapping mission we demonstrate that this combination of tidal measurements would provide a much better estimate of ice thickness than could be obtained using either tracking or altimeter measurements alone the thickness value inferred from the combined data would also require an estimate of the shear modulus of europa s icy shell this introduces an additional uncertainty in the thickness estimate that is approximately proportional to the uncertainty in the inverse of the shear modulus