emplacement of mantle peridotite in the lower continental crust ivrea verbano zone northwest italy the ivrea verbano zone has been cited repeatedly as an exposed pre alpine crust mantle transition on the basis in part of the presence of lenses of mantle peridotite and a possible petrologic moho a 10 km thick mafic complex has been described as an intrusion at the contact between the mantle and a thick crustal sequence of metamorphosed wacke and pelitic rocks the significance of these features is now challenged by new mapping that demonstrates that mantle peridotites in the southern ivrea verbano zone were lenses tectonically interfingered with metasedimentary rocks prior to intrusion of the gabbroic complex although it remains possible that the ivrea verbano section exposes part of a complex crust mantle interface within which crustal and mantle rocks were interleaved the association of peridotite and metasedimentary rocks is also consistent with assembly in an accretionary wedge in either case present exposures are from an unknown distance above the pre alpine contiguous mantle and reference to the section as a complete crust mantle transition could be misleading

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

p and s wave velocities and densities in silicate and calcite rocks from the peloritani mountains sicily italy the effect of pressure temperature and the direction of wave propagation abstract the peloritani mountain belt north eastern sicily represents the connection between the southern appenninic range and the appenninic maghrebid chain the lithotypes outcropping in a 36 km long and approximately 8 km wide area in the eastern part of the peloritani mountains are considered to represent most properly the composition of the lower crust we selected 7 representative samples of silicate rocks amphibolite paragneisses augen gneiss phyllitic quartzite pegmatitic rock and 3 samples of calcite rocks calc schist marbles for the petrophysical measurements measurements were done on sample cubes of dry rocks in a multi anvil apparatus raising of pressure gives rise to velocity increase but the rate is different in the silicate and calcite rocks and closely related to progressive closure of microcracks linear behaviour is approached above about 200 mpa increasing temperature at 600 mpa decreases velocities in most silicate and in the calcite rocks with almost linear slopes substantial anisotropy of p and s wave velocities and shear wave splitting is found in both rock types the residual anisotropy observed above about 200 mpa is attributed to lattice preferred orientations lpo of major minerals 3d velocity calculations for an amphibolite a paragneiss and a marble sample based on the lpo of hornblende biotite and calcite respectively confirm the experimental findings of a close relationship between velocity anisotropy shear wave splitting shear wave polarization lattice preferred orientation and the structural frame of the rocks foliation lineation in the silicate rocks the intrinsic 600 mpa average p wave velocities and poisson s vp vs ratios exhibit a tendency for a linear increase with densities whereas the three calcite rocks cluster at markedly higher p wave velocities and poisson s vp vs ratios compared to their densities in the silicate rocks there is also a linear trend for an inverse relationship between the sio2 content density and the poisson s vp vs ratio respectively

modal mineralogy and chemical composition of the uralide lower crust determined from physical properties data abstract modeling of rock physical properties of the uralide lower crust is carried out using the physprops excel worksheet which calculates its p wave vp s wave vs poisson s ratio and density the mineral modal abundance and composition of mafic granulite mafic garnet granulite amphibolite and gabbronorite is modeled and the composition of each is determined by converting the aggregate mineralogy into wt oxides the modeled wt oxide composition of mafic garnet granulite fit well with those estimated for post archean terrains and all are within 1 of the average of all lower crustal xenoliths the modeled gabbronorite also shows a reasonable fit with these estimates the modeled amphibolite compositions show variations in the wt sio2 feo and mgo with respect to the estimates of mafic granulite and amphibolite the differences in the composition across the uralide lower crust are largely due to the presence or absence of garnet in the mafic granulite which may be a result of higher temperatures having been reached in the interior part of the orogen

paleozoic evolution of southern alpine crust northern italy as indicated by contrasting granitoid suites abstract the western southalpine crust of northern italy and southern switzerland consists of high grade ivrea verbano and medium grade rocks serie dei laghi the latter contains ordovician og and permian granitoids pg the og which range in composition from diorite to leucogranite show a calcalkaline metaluminous character the felsic lithologies yield a rb sr w r isochron of 466 5 ma with i r of 0 7087 the most mafic lithologies do not plot on the isochron but arrange on a mixing line indicating mantle crust interaction 87 sr 86 sr i 0 704 0 709 their initial pb isotope ratios 206 pb 204 pb i 17 47 18 00 207 pb 204 pb i 15 55 15 63 208 pb 204 pb i 37 66 38 12 fall within typical values of the lower crust linear trends in the pb pb diagrams are in agreement with a mantle crust interaction the pg consist of mafic to intermediate dykes and granitic plutons with calcalkaline and weakly peraluminous character two felsic plutons give two whole rock isochrons at 276 7 and 277 8 ma with the same i r of 0 710 the mafic dykes show sr isotopic variations indicating mantle crust interaction 87 sr 86 sr i 0 705 0 710 the pb isotope ratios of pg 206 pb 204 pb i 18 12 18 53 207 pb 204 pb i 15 63 15 73 208 pb 204 pb i 38 08 38 73 are distinctly higher than those of og and similar to those of the ivrea verbano metasediments og are depleted in both lile and hfse show less pronounced negative anomalies of sr p and ti and have lower sr and pb isotope ratios than pg for both og and pg we suggest that the most mafic representatives were generated through interaction of mantle derived magma and crustal material while the granitoids derived from the resulting hybrid magma mainly through crystal fractionation the ultimate sources of the ordovician and permian magmatisms were different both geochemically and isotopically reflecting two different geodynamic environments a convergent plate boundary in an accretionary terrane in the ordovician a post orogenic extensional regime in cratonized continental crust in the permian geological data are compatible with such environments

moho vs crust mantle boundary evolution of an idea abstract the concept that the mohorovicic discontinuity moho does not necessarily coincide with the base of the continental crust as defined by rock type compositions was introduced in the early 1980s this had an important impact on understanding the nature of the crust mantle boundary using information from seismology and from deep seated samples brought to the surface as xenoliths in magmas or as tectonic terranes the use of empirically constrained p t estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment the xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere and revealed that the crust mantle boundary in off craton regions commonly is transitional over a depth range of about 5 20 km early seismic reflection data showed common layering near the moho correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust mantle boundary developments in seismology petrophysics and experimental petrology have refined interpretation of lithospheric domains the expansion of in situ geochronology especially zircon u pb ages and hf isotopes os isotopes of mantle sulfides has defined tectonic events that affected whole crust mantle sections and revealed that the crust mantle boundary can change in depth through time however the nature of the crust mantle boundary in cratonic regions remains enigmatic mainly due to lack of key xenoliths or exposed sections the observation that the moho may lie significantly deeper than the crust mantle boundary has important implications for modeling the volume of the crust mapping the crust using seismic techniques alone without consideration of the petrological problems may lead to an overestimation of crustal thickness by 15 30 this will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust formation processes and the composition of the convecting mantle

the evolution of the serie dei laghi strona ceneri and scisti dei laghi the upper component of the ivrea verbano crustal section southern alps north italy and ticino switzerland abstract the serie dei laghi is the upper intermediate component of the exposed crustal section of massiccio dei laghi in the southern alps the latter including also the ivrea verbano zone its oldest event is a sedimentary cycle at least of early paleozoic age it starts with a pelitic sequence scisti dei laghi that later suffered a tectono metamorphic event of rather high pressure this event is recorded by rare mineral and textural relics detected in the scisti dei laghi of the m gambarogno area later an arenaceous sequence strona ceneri was deposited it is now represented at the base by basaltic metatuffites resulting from the reworking of an ophiolite belt then followed by paragneisses with detrital phenoclasts ceneri gneiss and by fine grained gneisses gneiss minuti during the ordovician conspicuous tonalitic to granitic masses were emplaced the induced thermal disturbance and the circulation of pegmatitic stage magmatic residuals caused contact metamorphism and granitization in the sedimentary country rocks during the hercynian a main prograde event generated the regional foliation with isoclinal geometry and transposed character a syn kinematic stage produced medium grade parageneses of relatively high pressure static recrystallization and sillimanite growth then followed during the uplift due to the combined action of hydration and decompression margarite bearing coronitic textures grew around kyanite a retrograde metamorphism was then recorded by the appearance of greenschist facies parageneses at particular structural sites the formation of the cossato mergozzo brissago cmb and pogallo fault system against the ivrea verbano zone as well as the schlingen folds in the northeast is of late hercynian age along the cmb fault calc alkaline dykes and stocks appinites were intruded probably towards the end of the upheaval but deep enough to induce partial melting in their country rocks between val d ossola and valsesia the hercynian evolution is concluded by the early permian magmatic cycle that gave rise to both extrusive rhyolitic sheets and to granitic epiplutonic bodies accompanied by mafic dykes in mesozoic times the serie dei laghi was dissected by many extensional faults these partly reactivated the hercynian lineaments such as the cmb and pogallo lines during the alpine orogenic cycle the serie dei laghi was affected by s verging cataclastic overthrusts

contribution of crystallographic preferred orientation to seismic anisotropy across a surface analog of the continental moho at cabo ortegal spain the lithostratigraphic sequence of the upper allochthon of the cabo ortegal complex in northwestern spain provides an excel lent analog for the direct study of petrophysical properties of the continental moho transition the various lithologies present were sampled for velocity measurements on minicores and determination of seismic veloc ities through microstructural analyses with emphasis on the crustal part of the sequence here we present data from electron backscatter diffraction ebsd to determine the crystallographic preferred orientation of all major rock forming minerals the orientation data are then combined with the elastic properties densities and modal fractions of the mineral phases to calculate p wave and s wave velocities calculated velocities coincide very well with direct measurements made on minicores of the same samples in the high pressure laboratory the threedimensional velocity patterns show the signifi cant contribution of the crystallographic preferred orientation of certain constituent minerals on the bulk properties of the rock the bulk anisotropic signal is dominated by highly anisotropic phases that are susceptible to both shape and crystal preferred orientation factors of particular importance are small modal fractions of micas in gneisses and amphiboles and clinopyroxenes in eclogites and high pressure granulites in the lower crustal rocks the direction of maximum p wave velocities although contained in the foliation plane does not coincide with the orientation of the mineral and stretching lineation and therefore cannot be used as an indicator of the main strain direction in rocks the maximum seismic birefringence is often contained within the foliation plane but very rarely coincides with the lineation our data set also illustrates the strong effect of the breakdown reactions of clinopyroxene and the appearance of plagioclase on the petrophysical properties of mafi c lower crustal rocks while it does not enhance anisotropy it does produce a drop in velocity and as a consequence enhances the refl ectivity of the contact between lower crustal rocks and ultra mafi cs from the mantle

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

the tectonic and rheological evolution of an attenuated cross section of the continental crust ivrea crustal section southern alps northwestern italy and southern switzerland the tectonic and rheological evolution of the southern alpine continental crust is reconstructed from structural petrological and radiometric studies in the ivrea and strona ceneri basement units the deep crust of the southern alps acquired its present compositional and metamorphic zonation during paleozoic magmatism and amphibolite to granulite facies regional metamorphism inferred strength contrasts between lower crustal and upper mantle rocks in the ivrea zone are low at the high temperatures of regional metamorphism late paleozoic transtension and basic to intermediate magmatism in all crustal levels preceded extensional faulting associated with the formation of a passive continental margin during early mesozoic time extensional uplift and cooling of the basement section is coupled with crustal scale trends of increasing rheological stratification grain size reduction and strain localization mylonitic shear zones in the lower crust and a broad zone of noncoaxial shear at the base of the intermediate crust in the ivrea zone are inferred to have controlled the high strain rheology of the attenuating southern alpine crust the deep crust in the thinned ivrea crustal cross section transferred noncoaxial strain from the upper mantle to the intermediate and upper crust final uplift and exposure of the deep southern alpine crust occurred during late cretaceous to tertiary alpine thrusting

crystallographic preferred orientation magnetic and seismic anisotropy in rocks from the finero peridotite ivrea verbano zone northern italy interplay of anisotropy contributions from different minerals abstract mineral alignment can provide valuable information on a rock s geological history many structural tectonic or geodynamic studies rely on determining the preferred orientation of rock forming minerals either by direct texture determination or using anisotropy measurements as proxies robust interpretations of anisotropy require detailed understanding of its relationship with texture this study investigates the texture magnetic and seismic anisotropies of ultramafic rocks from the ivrea verbano zone ivz northern italy with a special focus on the interplay between anisotropy contributions carried by different minerals texture was obtained from electron backscatter diffraction magnetic anisotropy from low and high field anisotropy of susceptibility measurements and seismic anisotropy from p and s wave velocities along the three principal directions of the macroscopic fabric using 22 mm diameter cores texture based models of magnetic anisotropy agree well with corresponding measurements larger variability is observed for seismic anisotropy possible explanations are 1 velocities were measured in three directions insufficient to determine the full elasticity tensor and 2 seismic anisotropy depends on grain boundaries pores and cracks in addition to crystallographic preferred orientation the contributions to magnetic and seismic anisotropy of each constituent mineral can interfere positively leading to a larger overall anisotropy or negatively resulting in a weaker anisotropy seismic anisotropy is mostly controlled by olivine whereas magnetic anisotropy can be dominated by olivine pyroxene or hornblende this study illustrates that although the relationship between texture and anisotropy can be complex it is possible to quantitatively predict magnetic and to a lesser degree seismic anisotropy from texture data even though both magnetic and seismic anisotropies are common proxies for texture they are not coaxial and no simple relationship between the degree of magnetic and seismic anisotropy was found these results underline the importance of understanding different minerals contributions to anisotropy in upper mantle rocks

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

regional granulite facies metamorphism in the ivrea zone is the mafic complex the smoking gun or a red herring one widely accepted paradigm for the development of continental lower crust is that regional granulite facies metamorphism is caused by intrusion of mafic magma beneath or into the crust magmatic accretion the amphibolite to granulite facies supracrustal section exposed in the ivrea zone southern alps northern italy is commonly cited as a classic example establishing this postulated genetic relationship our interpretation of the pattern of metamorphic isograds compositional trends in high grade metasedimentary rocks and textural evidence in metapelite however indicates that final emplacement of the mafic plutonic rocks the mafic complex occurred subsequent to the regional thermal maximum field and petrographic relations suggest that a spatially restricted contact melting event in crustal rocks accompanied the emplacement of the mafic complex this inference is consistent with leucosome compositions in migmatites and a low pressure high temperature metamorphic overprint recorded by mineral assemblages in wall rocks proximal to the intrusion therefore evidence of anatexis and metamorphism of crustal rocks associated unequivocally with emplacement of the mafic complex is found only within an 2 km wide contact aureole overlying the intrusion the narrow aureole associated with emplacement of the mafic complex demonstrates that in some cases emplacement of large volumes of mafic magma within the crust does not inexorably lead to regional scale granulite facies metamorphism and large ion lithophile element depletion by melt loss

elastic properties fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity in this paper the elastic properties of amphibolites from the serie dei laghi and the ivrea zone southern alps n italy were investigated as a function of their mineralogical composition microfabric and density three orthogonal cores were cut parallel and normal to foliation and lineation from those bulk and grain density were measured and the interconnected porosity was calculated bulk density varies from 2 75 to 3 07 g cm 3 and calculated porosity ranges from 0 02 to 0 88 the same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 mpa at high pressure the matrix properties are separated from the crack induced properties p wave velocity varies with respect to the direction of propagation the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation the mineral lineation is typically defined by the elongation of amphibole crystals in which the fastest vp direction is parallel to the c axis that is also the elongation axis the vp ranges between 6 76 and 7 54 km s in the direction parallel to lineation and between 6 32 and 7 06 km s in the direction normal to foliation this defines a vp anisotropy of up to 14 whose shape varies from orthorhombic to axially symmetric either prolate or flattened it was observed that both vp and vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase moreover the c axis distribution of amphiboles is responsible of the vp anisotropy intensity and shape in agreement with observations from previous studies the seismic properties calculated with the approach of mainprice 1990 using the fabric data the elastic constants and the modal composition gave results in good agreement with the measurements exposed rocks in the ivrea and serie dei laghi zones show that amphibolites are interlayered with metapelites on a scale from 1 to 100 m because of the very large acoustic impedance contrast 20 34 1 75 for amphibolites 17 16 0 4 for metapelites they represent a very reflective portion in the middle lower crust 2007 elsevier b v all rights reserved

faunal transport within event horizons in the british upper silurian many marine fossil concentrations are considered the result of episodic sedimentological events and in particular those due to storms most storm or tempestite concentrations are identified as autochthonous or parautochthonous assemblages created by a variety of winnowing processes within shallow water environments in contrast samples described here from both a shelf and a basinal setting within the ludlow upper silurian succession of the welsh basin reveal the presence of a biota transported by tempestite activity into a setting dominated by a more offshore biota tempestite horizons from within an outer shelf mud dominated setting include shelly lenses with a transported fauna abounding in gastropods tentaculitids and atrypid brachiopods the background sediment being rich in graptolites cephalopods and small strophomenid brachiopods within the basinal area distal tempestites range from minor siltstone layers to thicker bioclastic limestone lenses the siltstones are largely graptolitic dominated by bohemograptus with some small brachiopods whilst saetograptus colonus is the only common graptolite in the limestones which also contain a fauna of broken brachiopods and bryozoa the transport of assemblages distally into a variety of settings represents a potential source of error in palaeoecological analysis transported assemblages may however provide evidence of the composition of both benthic and pelagic shallower water faunas no longer known in situ

at sea measurements of sound penetration into sediments using a buried vertical synthetic array at sea measurements were conducted to understand the propagation of sound into sediments these investigations used a new buried vertical synthetic array system developed and built at the naval research laboratory the design of this at sea system is based on a system developed for laboratory experiments that utilized a two dimensional synthetic array technique j acoust soc am 107 2000 for the measurements reported here the hydrophone was water jetted into the sediment to a depth of 2 m once buried the hydrophone was mounted to a vertical robotics stage that pulled the hydrophone up in 1 cm increments a spherical source positioned 50 cm above the interface was used to ensonify the sediment the ensonification angle was varied by changing the horizontal distance of the source from the insertion point in this manner several measurements were made with ensonification angles above and below the critical angle in addition the enhancement of sound penetration due to interface roughness was investigated this new system along with the results of the measurements will be discussed work supported by onr

a quantitative evaluation of the contribution of crustal rocks to the shear wave splitting of teleseismic sks waves abstract the seismic elastic properties of the crust have been modelled using hypothetical polycrystals with typical crustal compositions and commonly measured petrofabrics this modelling allows us to better evaluate and quantify the crustal contribution to splitting of teleseismic sks waves mafic rocks such as anorthosite or pyroxene bearing gabbros have complex s waves properties i e with small shear wave anisotropies

synthetic seismic reflection profile through the ivrea zone serie dei laghi continental crustal section northwestern italy a geologic cross section restored to its original horizontal orientation in permian triassic time has been constructed for the middle and lower continental crustal rocks of the ivrea verbano zone and the adjacent serie dei laghi of northwestern italy seismic p wave velocities of a representative suite of rock samples were measured to high pressure and high temperature conditions a synthetic seismic reflection profile 76 km long and 30 km thick was computed to compare what can be deduced from the seismic profile with what is known in much more detail from geologic mapping imaged features correspond closely to those seen on many present day profiles and the broad features of the tectonic evolution would be correctly interpreted but important recumbent fold structures would be missed and relationships between intrusive bodies and their country rocks would be unclear

lg wave attenuation in the australian crust abstract we estimate the lg wave quality factor q across the australian continent from vertical component lg waveforms a tomographic inversion is performed to construct an lg attenuation model for 58 frequencies between 0 05 and 10 0 hz the available spatial resolution is approximately 1 5 1 5 for the 0 5 2 0 hz band at 1 0 hz the lg wave q over the whole island continent varies from 50 to 1250 with an average value of 850 significant regional variations in the lg wave q images tie well with many geological features and boundaries in australia the cratons in western northern and southern parts of australia usually have higher q values 700 1250 while the volcanic regions sedimentary basins and orogenic areas in eastern australia are characterized by increased attenuation lower q values 50 650 we determine the frequency dependent q of lg waves for different blocks across australia and find the frequency dependence of q is much more complex than the traditional single power law representation when combined with the assumed geometrical spreading relation the lg q maps provide a new way of assessing potential ground motion across the continent for any event location

large scale folding in the upper part of the ivrea verbano zone nw italy new geological mapping has led to a new interpretation of the large scale superimposed folding in the upper part of the ivrea verbano zone italian alps the region is widely held to represent an upended section through lower continental crust of northern italy the dominant fold structure extending some 40 km along strike is the massone tight to isoclinal antiform with a hinge line strongly curved through 115 this folds pre existing large scale folds that formed during regional migmatization probably during the hercynian orogeny to form a type 2 interference geometry the region then suffered post orogenic mafic magmatic underplating and other magmatism accompanied by crustal stretching with contact metamorphism and migmatization causing the imposition of the final pattern of metamorphic isograds the ivrea verbano zone was brought into contact with the overlying metamorphic rocks of the serie dei laghi on a major shear zone sub solidus stretching continued though displacements on low angle high temperature shear zones most of the ivrea verbano zone was finally tilted to the vertical and emplaced into its present position after the mesozoic era and probably during alpine orogenesis forming the vertical limb of a crustal scale double kink

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

laboratory measurements of p wave and s wave velocities across a surface analog of the continental crust mantle boundary cabo ortegal spain the paleozoic cabo ortegal complex of nw spain provides an exposed analog of the continental crust mantle transition it is composed of an overturned section that at its base begins with felsic gneisses followed upward by eclogites intermediate and mafic granulties and ultramafic rocks peak metamorphic conditions reached c 800 c and 1 7 gpa in the middle to late devonian fourteen samples were analysed for p wave and s wave velocities as well as density at the high pressure lab at dalhousie university canada seismic velocities were measured at pressures of 10 to 600 mpa at a temperature of 20 c when possible measurements were made parallel and perpendicular to banding and parallel to the lineation the major element composition of each sample was measured by xrf at the university of barcelona spain samples display a broad range of p wave and s wave velocities 6 2 to 8 2 km s and 3 2 to 4 6 km s at 600 mpa respectively that generally increase with density 2 7 to 3 4 g cm3 and reflect an overall increase from middle to lower crustal velocities in the felsic gneisses and intermediate to mafic granulites to mantle velocities in the eclogites and ultramafic rocks the seismic moho p wave velocity 7 6 km s is reached at the mappable contact between the gneisses and the eclogite whereas the compositional moho or crust mantle transition occurs at the transitional contact between the mafic granulites and peridotites between 200 and 600 mpa p wave anisotropy ranges from between 2 and 8 whereas s wave anisotropy ranges from 1 to around 8 according to rock type poisson s ratios calculated from the laboratory measurements are within the range of those determined from field experiments elsewhere p wave reflection coefficients between the various lithologies range from 0 21 to 0 08 these laboratory data provide a calibration for the physical properties and the nature of reflectivity of the in situ lower continental crust and upper mantle transition

seismic and magnetic susceptibility anisotropy of middle lower continental crust insights for their potential relationship from a study of intrusive rocks from the serre massif calabria southern italy abstract we investigated the relationships between fabric seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the serre massif southern italy in particular from five granitoids and one metagabbro cubes were cut according to the fabric elements and seismic properties up to 400 mpa confining pressure were measured with a triaxial multi anvil apparatus we also calculated the elastic properties based on the mineral content and composition in granitoids measured average compressional wave velocity vp of the fracture free aggregate at 400 mpa is 6 2 km s whereas average shear wave velocity vs is 3 6 km s with poisson s ratio ranging from 0 240 to 0 257 related to the modal proportions of quartz in metagabbro average vp and vs at 400 mpa are 6 9 km s and 3 7 km s respectively results showed that intrinsic velocity distribution after microcracks closure depends on progressive alignment of anisotropic minerals such as biotite amphibole and pyroxene with maxima velocities localized within the foliation plane mean magnetic susceptibility k m of the granitic rocks is 6 si units indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties moreover a positive correlation between seismic and magnetic anisotropy has been recognized indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust conversely in metagabbro the anisotropy of magnetic susceptibility ams is controlled by magnetite and pyrrhotite although these form

discontinuous change in temperature derivative of vp in lower crustal rocks 1 compressional wave velocities vp of gabbronorite pyroxene granulite wehrlite and websterite were measured up to 1000 c at 1 gpa during heating and cooling the wehrlite and websterite which contain secondary hydrous minerals show irreversible change in temperature derivative of vp vp t during heating these rocks show sudden decrease in vp when dehydration reactions took place during cooling the rocks show a linear increase in vp in contrast the gabbronorite and pyroxene granulite which are nearly dry crystalline assemblage show reversible and discontinuous change in vp t at around 400 c it changes from 2 4 and 2 1 10 4 km s 1 c 1 to 4 7 and 4 5 10 4 km s 1 c 1 this reversible and discontinuous change in vp t is difficult to explain by the previously proposed mechanisms such as thermal cracking dehydration reaction and or partial melting the data suggest that this reversible and discontinuous change would be associated with phase transition in plagioclase

the continental crust as a source of sand southern alps cross section northern italy abstract all tectonostratigraphic levels of the continental crust from carbonate platforms in the dolomites to granulites in the ivrea zone are exposed along strike in the world famous southern alps cross section in this extraordinary natural laboratory we studied the composition of modern stream sands shed by each distinct type of source rock in order to improve on existing models of sediment provenance and specifically to reconstruct the step by step changes of detrital signatures ideally produced during unroofing of a continental block detritus from progressively deeper crustal levels of the southern alps changes systematically from lithic sedimentaclastic unmetamorphosed cover sequences to lithoquartzose quartzolithic and quartzofeldspathic metamorphiclastic greenschist facies to amphibolite facies basement units and finally to feldspathoquartzose and feldspathic composition granulite facies basement units six progressively richer types of heavy mineral assemblages ztr brookite garnet

simultaneous high p t measurements of ultrasonic compressional and shear wave velocities in ichino megata mafic xenoliths their bearings on seismic velocity perturbations in lower crust of northeast japan arc 1 simultaneous measurements of ultrasonic compressional vp and shear wave velocities vs were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast japan arc crust for comparison with the observed seismic heterogeneity of the lower crust of the northeast japan arc the velocity deviations dvp and dvs of the xenoliths were calculated using the average reference vp 6 61 0 1 km s and vs 3 76 0 1 km s the dvp and dvs values of the xenoliths at 700 c and 0 8 gpa are 0 8 and 1 2 for hornblende gabbro 4 8 and 4 0 for hornblende pyroxene gabbro 0 9 and 1 5 for amphibolite 2 5 and 1 7 for pyroxene amphibolite and 0 9 and 5 6 for hornblendite respectively we compared the velocity perturbations in the lower crust determined by seismic tomography with dvp and dvs of the xenoliths using vp vs vp vs deviation diagrams on the basis of our measurements we suggest that 1 the seismically high vp and vs regions beneath the tobishima basin consist of hornblende pyroxene gabbro 2 hornblende gabbro is a predominant rock type beneath the dewa hills and ou backbone range 3 the low velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro and 4 the low vp and high vs regions beneath the kitakami mountains consist of quartz plagioclase bearing rocks our data demonstrate that the seismic heterogeneity in the lower crust of the northeast japan arc reflects variations in rock composition and temperature that are related to the regional geological history

some attributes of wavefields scattered from ivrea type lower crust abstract the ivrea zone in northern italy is a well studied sliver of extended lower continental crust which was brought to the surface in the course of alpine lithospheric shortening based on two 1 25 000 geological maps from the central ivrea zone and petrophysical parameters of the corresponding lithologies we have constructed geologically constrained stochastic seismic models of ivrea type lower crust a stochastic rather than a deterministic approach is applied due to the limited availability of detailed geological maps and the high degree of small scale structural and petrophysical complexity of the ivrea zone the primary characteristic of the resulting model is its layered self affine or fractal structure and its bimodal velocity distribution while we are not suggesting that ivrea type structure is universal for extended lower continental crust synthetic seismograms may help to constrain some pertinent quantitative aspects observed in deep seismic reflection data 1 1 ivrea type lower crust can explain the igh observed reflection coefficients and bright reflectivity in the lower crust 2 2 observed lower crustal q factors can be largely explained by scattering losses and intrinsic q factors of reflective lower crust are likely to be larger than 1000 which is incompatible with the presence of free volatiles 3 3 in agreement with recent broad band studies of the lower crust ivrea type lower crust does not create any tuning effects and 4 4 for ivrea type heterogeneity the lateral correlation of the reflected signal is largely independent of the lateral characteristic scale of the scattering structures which suggests that multiple scattering may be important in the reflective lower crust

p and s wave velocities of the lowermost crustal rocks from the kohistan arc implications for seismic moho discontinuity attributed to abundant garnet abstract p vp and s wave vs velocities of garnet free two pyroxene granulite and garnet bearing garnet granulite and garnet pyroxenite lowermost crustal rocks collected from the kohistan arc northern pakistan were measured at 0 1 1 0 gpa and 25 400 c garnet granulite had higher vp 0 31 km s and vs 0 27 km s than two pyroxene granulite although vp and vs increased with increasing volume percent of garnet plagioclase free garnet pyroxenite showed significantly higher vp and vs than plagioclase rich garnet granulite mainly due to the low vp and vs of plagioclase in contrast we observed two quasi linear relationships between vp vs and sio2 content for the garnet bearing and garnet free rocks the garnet bearing rocks had relatively higher vp and vs and stronger sio2 dependences than the garnet free rocks the stronger sio2 dependences of vp and vs in the garnet bearing rocks suggest that the garnet formation in mafic to ultramafic rocks e g pyroxenite and hornblendite having relatively lower sio2 leads to more pronounced increases in vp and vs than that of relatively felsic rocks e g felsic to mafic granulite indeed the vp and vs of the garnet pyroxenite were significantly higher than those of garnet granulite but comparable to those of dunite the significantly high vp and vs of the garnet pyroxenite yielded high reflection coefficients between the garnet granulite and garnet pyroxenite of up to 0 13 for p waves and 0 14 for s waves comparable to values expected for moho reflection thus the lithological boundary between plagioclase rich garnet granulite and plagioclase free garnet pyroxenite in the lowermost crust of the kohistan arc corresponds to the seismic moho discontinuity

magmatic underplating extension and crustal reequilibration insights from a cross section through the ivrea zone and strona ceneri zone northern italy the thermal impact of magmatic underplating at various crustal levels is studied along a traverse through the ivrea verbano zone and strona ceneri zone in northern italy geochronological and petrologic data are compared to a two dimensional thermal kinematic model field data and numerical simulation show the strong disturbance of the temperature field in the lower and intermediate crust in relation to magmatic underplating leading to granulite to amphibolite facies metamorphism as well as reequilibration of mineral chemical and isotopic systems magmatic underplating leaves a crust with an apparently heterogeneous tectonometamorphic evolution as information on the earlier history is preserved only at upper crustal levels

structural geometry lower crustal magmatic underplating and lithospheric stretching in the ivrea verbano zone northern italy abstract the ivrea verbano zone is believed to represent an up ended cross section through the lower continental crust as it existed at the end of the hercynian orogeny in the southern alps structurally oriented geological mapping has been carried out in the central and northern parts of the ivrea verbano zone a region some 30 km along strike the geology of the southern half of the zone is dominated by a large basic ultrabasic complex the mafic formation which is in contact with a strongly banded metasedimentary metabasic sequence to the north particular attention was paid to a the structural relationship between the rocks of the mafic formation and their envelope of high grade metasedimentary and metabasic rocks b the geometrical configuration throughout the ivrea verbano zone of high temperature shear zones which accommodated post hercynian crustal extension and c the geometry of late low temperature faulting the effects of which have been removed in order to produce a restoration of the structure as it existed during the post hercynian extensional phase the intrusion of large volumes of basic magma ca 50 of the outcrop area to form the rocks of the mafic formation appears to be coeval with the onset of extension ca 280 ma the main basic body has a laccolithic form which was originally more than 10 km thick overfolding developed at the northern margin of the laccolith and is interpreted in terms of the gravitational collapse of the hot immediately subsolidus or partially molten body incorporating its envelope of hot metasediments into a large originally recumbent fold a geometrical association with a high temperature low angle fault zone suggests that faulting was subsequently localized by the several km of uplift associated with the laccolithic intrusion the ivrea verbano zone may therefore demonstrate at least one particular geometry of lower crustal magmatic underplating which may aid in the interpretation of present day deep seismic profiles it also demonstrates the geometry of a network of conjugate high temperature low angle shear zones in a well layered lower crustal section

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

physical properties of ultrahigh pressure metamorphic rocks from the sulu terrain eastern central china implications for the seismic structure at the donghai ccsd drilling site about 30 samples representing major lithologies of sulu ultrahigh pressure uhp metamorphic rocks were collected from surface exposures and exploration wells and compressional vp and shear wave vs velocities and their directional dependence anisotropy were determined over a range of constant confining pressures up to 600 mpa and temperatures ranging from 20 to 600 degreesc samples range in composition from acidic to ultramafic p and s wave velocities measured at 600 mpa vary from 5 08 to 8 64 km s and 2 34 to 4 93 km s respectively densities are in the range from 2 60 to 3 68 g cm 3 to make a direct tie between seismic measurements refraction and reflection and subsurface lithologies the experimental velocity data corresponding to shallow depths were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000 m chinese continental scientific drilling program ccsd crustal segment comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks the strongly reflective zone beneath the donghai drill site can be explained by the impedance contrasts between the different lithologies contacts between eclogite peridotite and felsic rocks gt gneiss granitic gneiss in particular may give rise to strong seismic reflections in addition shear induced lattice preferred orientation lpo related seismic anisotropy can increase reflectivity for the explanation of the high velocity bodies 6 4 km s around 1000 m and below 3200 m depth large proportions of eclogite peridotite about 40 and 30 vol respectively are needed c 2002 elsevier science b v all rights reserved

petrogenesis and tectonic significance of amphibolites interlayered with metasedimentary gneisses in the ivrea zone southern alps northwest italy abstract amphibolites occurring as elongate lenses and boudins within the metasedimentary kinzigite formation of the ivrea zone are all of igneous parentage a detailed study of their trace element characteristics shows that they can be divided into two groups type 1 amphibolites occur as layers up to 100 m thick and have trace element distributions showing depletion in incompatible elements typical of normal n type mid ocean ridge basalts type 2 amphibolites occur as thinner layers and boudins and have higher levels of the more incompatible elements similar to transitional or enriched e type ocean basalts although metamorphism appears to have resulted in loss of sio 2 and variable enrichment in na k rb ba sr and locally ca the less mobile elements including the rare earth elements have preserved the primary basaltic geochemical characteristics the tectonic model which best explains the assemblage of slivers of morb like amphibolites within extremely highly deformed semi pelitic metasediments is that of an accretionary sedimentary wedge formed at a palaeozoic subduction zone

variation in amphibole and plagioclase composition with deformation investigation of the mineral chemistry of a shear zone in an amphibolite facies metagabbro has shown that the composition of the amphibole and plagioclase varies with deformation chemical analyses of the rocks indicate that the shear zone approximates an isochemical system the amphibole varies progressively from an initial magnesio hornblende to a ferroan pargasitic hornblende in the shear zone alkalies ti and fe2 fe2 mg increasing while the plagioclase becomes more anorthitic varying from labradorite to bytownite these changes in composition of amphibole and plagioclase from metabasic rocks are normally associated with increasing temperature in prograde regional metamorphic terrains such chemical variations observed in localized shear zones would suggest that shearing stress in regional metamorphism may play an important role in producing the documented discrepancies in amphibole chemistry between different metamorphic belts

stochastic modeling of the reflective lower crust petrophysical and geological evidence from the ivera zone northern italy crustal scale seismic wave equation modeling demonstrates that wavelength scale velocity fluctuations can dominate the seismic response over a wide range of offsets and that a wide range of velocity distributions qualitatively can explain deep seismic data this range can be narrowed by studying the detailed petrophysical and structural properties of middle and lower crustal exposures the ivrea zone in the southern alps is a well studied sliver of extended lower continental crust brought into its present upright position as a result of late alpine lithospheric shortening the high degree of structural and petrophysical complexity and in particular the limited exposure of the ivrea zone favor a statistical rather than deterministic approach to develop a two dimensional crustal scale seismic model for this purpose we digitized two 1 25 000 geological maps from the central ivrea zone on a 60 m grid we find that the ivrea zone is characterized by a bimodal velocity distribution and a band limited self affine structure having a fractal dimension of 2 7 a characteristic horizontal scale of 500 to 1000 m and an aspect ratio around 4 0 assuming statistical stationarity a realization of this stochastic model was used to develop synthetic seismograms typical of ivrea type lower continental crust our results indicate that 1 ivrea type lower crust can explain qualitatively commonly observed lower crustal reflectivity 2 relatively minor changes in bulk composition and or metamorphic grade may lead to dramatic changes in reflectivity which cannot be explained by current generic models on the origin of lower crustal reflections and 3 travel time interpretation of the synthetic wide angle data may lead to erroneous large scale velocity structures

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

petrophysical analysis of a mid crustal reflector in the iberseis profile sw spain abstract the origin of strong crustal reflectors in vertical incidence reflection seismic data is generally attributed to either rock layering deformation fabrics in shear zones fluids or igneous intrusions the iberseis normal incidence reflection and wide angle seismic profiles in sw spain imaged a large high velocity subhorizontal reflector in the middle crust the iberseis reflective body whose origin has been attributed to a mafic intrusion in order to test this hypothesis in this paper we present laboratory measurements of vp vs and density from 17 samples of mafic igneous and metamorphic rocks and metasediments that are thought to be equivalent to the proposed iberseis reflective body these measurements are then corrected to 400 c at 600 mpa and used to calculate poisson s ratio and to compare it vp and vs to values measured in situ by wide angle data finally normal incidence reflection coefficients are calculated to test if the measured lithologies could reproduce the reflectivity imaged in the vertical incidence reflection seismic data for the iberseis reflective body our physical property measurements are very similar to those modeled from the wide angle data and our reflection coefficients are sufficiently high to cause strong mid crustal reflectivity our data indicate therefore that previous interpretations of the iberseis reflective body as a mafic sill are quite reasonable

seismic properties of highly strained marbles from the splugenpass central alps abstract seismic reflection profiling across the central alps nfp20 shows strong reflectors some of which correspond to a mesozoic marble zone which underlies the contact between the tambo and suretta nappes by means of experimental velocity measurements at confining pressures up to 300 mpa on rock samples collected in the marble zone we determined the seismic properties of these marbles and calculated their reflection coefficients in order better to constrain the seismic interpretation the main findings are as follows 1 a marbles exhibit v p anisotropy up to 9 with orthorhombic or transverse isotropic tetragonal symmetry due to the crystallographic preferred orientation of calcite 2 b compressional waves shear waves and shear wave splitting are very sensitive to the type of fabric presence or absence of an r axes concentration 3 c interfaces between marbles and amphibolites or orthogneisses could be good reflectors in normal incidence reflection

pogallo line south alps northern italy an intermediate crystal level low angle normal fault the pogallo line is a major crustal shear zone in the crystalline south alps of northern italy which separates middle amphibolite granulite facies rocks of the ivrea zone from lower middle amphibolite facies rocks of the strona ceneri zone u pb rb sr and k ar whole rock and mineral ages for samples from this region indicate that the two zones pursued different time temperature paths after caledonian peak metamorphism cooling curves for the two terrains finally converge in the late triassic early jurassic a time of large scale crustal extension in the south alps that anticipated the opening of the western tethys we suggest that the pogallo line may represent a low angle normal fault that developed at intermediate crustal levels during this period of extension and attained its present subvertical orientation during alpine deformation

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

shear strain localization from the upper mantle to the middle crust of the kohistan arc pakistan shear structures from mantle to middle crust levels of the kohistan palaeo island arc in pakistan are described pre himalayan ductile shear zones show a wide variety in size and shape and developed from gabbro subsolidus to amphibolite facies conditions their lithological context and geological history give insights into mechanisms that initiate shear strain localization factors that control stabilization of deformation in shear zones and flow properties at the mantle crust transition shear strain localization began within compositional gradients gabbros were more prone to localization into anastomosing patterns than diorites and granites which show more homogeneous strain shear strain localization during cooling led to less numerous but longer and thicker shear zones viscous heating within shear zones resulted in melt production and segregation in deformation structures and seems to have taken part in the plutonic history of the arc using kohistan as an example we suggest that the plutonic lower crust of arcs is strongly affected by subhorizontal synmagmatic shear zones probably consistent with the bulk flow direction of the subduction zone these features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision

magmatic plumbing of a large permian caldera exposed to a depth of 25 km we report evidence for a 13 km diameter permian caldera associated with a renowned section through the continental crust comprising the ivrea verbano zone and serie dei laghi of northwest italy correlation of ages of volcanic and middle to deep crustal plutonic rocks suggests that they constitute an unprecedented exposure of a subcaldera magmatic plumbing system to a depth of 25 km and points to a cause and effect link between intrusion of mantle derived basalt in the deep crust and large scale silicic volcanism

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

a new calibration of seismic velocities anisotropy fabrics and elastic moduli of amphibole rich rocks 1 a large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase we have measured p and s wave velocities vp and vs and anisotropy of 17 amphibole rich rock samples containing 34 80 vol amphibole at hydrostatic pressures p up to 650 mpa combined petrophysical and geochemical analyses provide a new calibration for mean density average major element contents mean vp p and vs p coefficients intrinsic vp and vs anisotropy poisson s ratios the logarithmic ratio rs p and elastic moduli of amphibole rich rocks the vp values decrease with increasing sio2 and na2o k2o contents but increase with increasing mgo and cao contents the maximum 0 38 0 40 km s and minimum s wave birefringence values occur generally in the propagation direction parallel to y and normal to foliation respectively amphibole plays a critical role in the formation of seismic anisotropy whereas the presence of plagioclase quartz pyroxene and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations cpos the cpo variations cause different anisotropy patterns illustrated in the flinn diagram of vp x vp y vp y vp z plots the results make it possible to distinguish in terms of seismic properties the amphibolites from other categories of lithology such as granite granodiorite diorite gabbro diabase felsic gneiss mafic gneiss eclogite and peridotite within the earth s crust hence amphibole aligned by dislocation creep anisotropic growth or rigid body rotation is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs which contains rather little phyllosilicates such as mica or chlorite

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

planar microstructures in zircon from paleo seismic zones pseudotachylytes resulted from frictional melts associated with ultramylonites in high grade metapelitic rocks from the ivrea verbano zone in the southern alps northern italy were studied with focus on the deformation microstructures in zircon the aims were to investigate the characteristics of zircon deformation in seismic zones and to recognize specific microstructures generated in zircon during earthquakes which could be useful for mineral dating of paleo seismic events helps to understand how seismic energy is released at depth and interacts with metamorphic processes the interior of polished zircon grains ranging from 30 to 150 m in length were investigated with optical microscope and scanning electron microscope sem techniques including secondary electron se backscattered electron bse forward scattered electron fse cathodoluminescence cl imaging and crystallographic orientation mapping by electron backscatter diffraction analysis ebsd grains were studied in situ and as separated fractions embedded in epoxy disks among different cataclastic and crystal plastic deformation microstructures in zircon we identified characteristic planar deformation bands pdbs planar fractures pfs and curviplanar fractures cfs planar deformation bands in zircon are crystallographically controlled planar lattice volumes with misorientation from the host grain which varies from 0 4 to 2 7 pdbs are usually parallel to 100 crystallographic planes have width from 0 3 to 1 m and average spacing of 5 m in 2d sections planar deformation bands appear as contrast lamellae in orientation contrast images and in ebsd maps and in rare cases can be observed with the optical microscope pdbs form in specifically oriented grains due to high differential stresses high temperatures and high strain rates generated in seismically active environment and or due to shearing in the vicinity of frictional melts discovered structures represent a result of crystal plastic deformation of zircon grains with operating dislocations having 010 glide system and misorientation axis therefore they can be classified as a new type 4 lattice distortion pattern according to the existing classification for zircon piazolo et al 2012 kovaleva et al 2014 we have demonstrated that formation of planar fractures in zircon takes place not only during impacts but also in seismically active zones we observe at least two cases of formation of pfs with 100 orientation 1 as a result of evolution of pdbs and 2 as micro cleavage this study demonstrates that planar microstructures in terrestrial zircon do not exclusively form during impact events but also as a result of seismic events at depth due to unusually high differential stress strain rate and temperature according to the new findings pdbs in zircon from the deep crust are supposed to represent newly recognized evidence of seismicity

seismic anisotropy of metapelites from the ivrea verbano zone and serie dei laghi northern italy abstract laboratory measurements of compressional and shear wave velocities up to 600 mpa confining pressure were carried out on amphibolite to granulite facies metapelites from the serie dei laghi and ivrea verbano zone northern italy the metapelite samples show moderate to high compressional wave anisotropy and significant shear wave splitting for propagation directions parallel to foliation serie dei laghi samples are generally transversely isotropic for compressional wave propagation a pattern that based on calculated velocities is the consequence of strong preferred orientation of micas ivrea verbano samples generally have an orthorhombic anisotropy pattern for compressional waves that is caused by the preferred orientation of both mica and sillimanite shear wave anisotropy and shear wave splitting patterns differ significantly for the two fabric types intense static recrystallization can obliterate seismic anisotropy but partial static recrystallization does not appreciably reduce anisotropy we conclude that seismic anisotropy may occur in mid to lower continental crust where it is predominantly composed of metapelitic rocks and if there is a consistent regional fabric this seismic anisotropy may be diminished if there is no consistent regional fabric or if postmetamorphic intrusions have caused static recrystallization

high pressure high temperature seismic velocity structure of the midcrustal and lower crustal rocks of the ivrea verbano zone and serie dei laghi nw italy the ivrea verbano zone and the adjacent serie dei laghi in the inner arc of the western alps nw italy display an upended cross section through much of the thickness of the continental crust as it existed in that region in triassic jurassic time we collected a suite of oriented rock samples that represent most of the volume of the rocks of the region p and s wave velocity measurements were made in three orthogonal directions related to the mesoscopic fabric of the rocks at room temperature and up to 550 mpa confining pressure combined high temperature and high pressure measurements were made up to 700 c on a subset of the samples the lithologic units were divided into 23 different principal rock types and we present velocity data averaged in terms of these groups vertical and horizontal velocity and anisotropy sections are computed from the measured velocity data based on a restored geologic section these show that vp and vs both increase and anisotropy decreases systematically with depth of burial reflecting variations in rock type and metamorphic grade with depth vp and vs anisotropy arises mainly because of crystallographic preferred orientation or mineralogical banding with the slowest direction tending to be normal to the foliation or banding the vp velocity sections were used to compute synthetic seismic reflection profiles for the region when it lay at the bottom of the continental crust these correspond well with contemporary deep reflection profiles for regions of comparable tectonic evolution

3d seismic study of a ductile shear zone from laboratory and petrofabric data saint barthelemy massif northern pyrenees france in order to constrain interpretations of seismic reflection records more effectively the seismic properties of a middle crustal section exposed in the saint barthelemy massif have been determined the massif transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties seismic velocities vp v5 shear wave birefringence have been measured on five representative samples to 600 mpa and 600 c simultaneously in the three structural directions x y and z for two samples the expep mental data have been compared with calculated values based on petrofabric analyses the lattice preferred orientation lpo is determined using universal stage electron channelling microscopy and neutron diffraction goniometry using the experimental and calculated velocity data we establish a lateral homogeneous anisotropie model

the cossato mergozzo brissago line and the pogallo line southern alps northern italy and their relationships with the late hercynian magmatic and metamorphic events abstract the hercynian basement of the southern alps west of lago di lugano consists of two units the ivrea verbano which is well known for its lower crust and upper mantle rocks and as the seat of a marked gravimetric positive anomaly and the serie dei laghi an intermediate to upper crustal metasedimentary and metagranitic complex the contact between them is a subvertical tectonic discontinuity the cossato mergozzo brissago line cmb and pogallo line recently the subject of considerable interest as the possible analogue of a low angle normal fault later tilted to the present upright position such as those increasingly revealed by the deep reflection seismics in thinned continental crust late hercynian igneous activity mainly took place along this lineament the contact is however very complex the cossato lower valsesia segment is poorly exposed and has been reactivated by a younger fault cremosina line in the valsesia val d ossola toce river segment the cmb line is expressed as a strong structural and lithological contrast as well as by a narrow belt of mylonites in the val cannobina lago maggiore sector the mylonites are distributed over a considerable thickness mostly within the serie dei laghi they are connected with large scale ductile folding on nearly vertical axes schlingenbau the cmb line is dissected by several orthogonal and oblique subvertical faults grottaccio quarna val lessa val pogallo faults the presence of appinitic calcalkaline dykes and stocks of about 285 ma intruded along particular segments of the cmb isolated by those faults suggests that the attitude of the main tectonic boundary was upright at the time of intrusion the intrusion apparently occurred in a transtensional environment and induced a temperature increase in the country rocks causing a low pressure metamorphic overprint in the val cannobina lago maggiore segment and dehydration melting in a belt 2 3 km wide between valsesia and val d ossola the pogallo line cuts across the cmb line with a sinistral horizontal slip of about 11 km and is also characterized by amphibolite facies mylonites the absence of mylonitic appinites and consistent geologic evidence point to formation of the fault before 285 ma a significant mesozoic displacement along both faults is therefore excluded even though post permian reactivations are demonstrated by the presence of rb sr and k ar mica mixed ages along the cmb line a new evolutionary model can be proposed to account for most of the geological petrological and geophysical data early paleozoic continental accretion subduction and magmatic arc followed by a more external probably oblique hercynian reactivation inducing important transcurrent movements along cmb and pogallo before the early permian magmatic phase

amphibolite facies pseudotachylytes in premosello metagabbro and felsic mylonites ivrea zone italy abstract pseudotachylytes solidified friction induced melts produced during seismic slip that formed under high temperature ambient conditions might retain information on earthquake mechanics beneath the brittle ductile elasto frictional viscous plastic transition in the crust thin sharply bounded pseudotachylytes and ultramylonites occur together inside the granulite facies premosello metagabbro and inside country felsic mylonites of the ivrea zone italian southern alps petrographic and microstructural data indicate that the studied pseudotachylytes and ultramylonites are coeval and developed under amphibolite facies 500 650 c metamorphic conditions the occurrence of foliated pseudotachylytes and of local remnants of cataclastic microstructures within ultramylonites suggests that pseudotachylytes might have represented planar heterogeneities for nucleation of ultramylonites the association of coeval pseudotachylyte and mylonites is interpreted as caused by cyclic stages of coseismic high strain rate transients related to downward propagation of seismic ruptures from the upper brittle crust followed by post seismic stress relaxation by ductile flow

synmagmatic deformation in the underplated igneous complex of the ivrea verbano zone the ivrea verbano zone northern italy contains an igneous complex up to 10 km thick that is thought to have been intruded near the interface between the continental crust and mantle during the late paleozoic new data indicate that this complex is pervasively deformed and concentrically foliated widespread deformation under hypersolidus conditions is indicated by growth of undeformed poikilitic phases across the foliation and segregation of late stage melts into high temperature faults and pressure shadows of boudins the presence of analogous features in ophiolitic gabbros suggests that emplacement of the ivrea verbano zone plutonic rocks involved large scale flow of crystal mush in a dynamic and possibly extensional tectonic environment