quantitative nannofossil correlation to open ocean deep sea sections from plio pleistocene boundary at vrica italy although numerous studies have been performed on material from the vrica section southern italy1 3 with a view to establishing its suitability as a type section for the plio pleistocene boundary these studies have failed either to establish the age of the boundary or to achieve accurate correlation to other regions we report here quantitative studies of selected nannofossil species in this section which unambiguously correlate it with open ocean piston cores in which an accurate chronology has been established the age of the plio pleistocene boundary as proposed by colalongo et al 4 is estimated to be 1 6 myr

periodicities of caco3cycles in the pliocene of sicily discrepancies with the quasi periods of the earth s orbital cycles a high resolution caco3 record in combination with a detailed magnetostratigraphy is presented for the rhythmically bedded marly sequence of the pliocene trubi formation on sicily italy magnetostratigraphic age calibration and subsequent spectral analysis of the variatrions in caco3 content yield a remarkably consistent discrepancy between the resulting periodicities and the corresponding quasi periods of the earth s orbital cycles this discrepancy can only be explained by assuming that ages assigned to polarity reversal boundaries in the geomagnetic polarity time scale lack sufficient precision a new polarity time scale is presented for the major part of the gilbert and gauss chron using the radiometrically dated gilbert gauss chron boundary at 3 40 ma as an age reference point and extrapolating an average quasi period of 21 7 kyr of the precession cycle as the periodicity of small scale colour annex caco3 cycles

unraveling tectonic and climatic controls on synorogenic growth strata northern apennines italy we develop a new high resolution stratigraphic age model to unravel the contributions of tectonic and climatic processes on early to late pleistocene synorogenic growth strata we capitalize on excellent continuous exposures along the flank of the po foreland in northern italy to elucidate hydrologic geomorphic and sedimentologic processes that are regularly attributed to but rarely proven to be caused by glacial interglacial climatic changes and unsteady rock uplift we perform our analysis on the enza section a succession of marine and terrestrial strata exposed along the enza river between parma and reggio emilia northern italy bedding in the enza section displays synorogenic growth strata geometry with bedding dips that range from 2 to 55 that becomes progressively shallower upsection we develop an age model that incorporates biostratigraphy magnetostratigraphy rock magnetic cyclostratigraphy cosmogenic radionuclide burial dating and optically stimulated luminescence dating and shows that the enza section spans the interval between 0 04 and 1 65 ma furthermore the age model pins the time of deposition for several lithostratigraphic units of regional significance and shows that sediment accumulation was unsteady ranging from 14 31 cm k y in the marine part of the section to 5 362 cm k y in the overlying littoral and terrestrial part of the section unsteady deposition is most pronounced in the terrestrial deposits where thick fluvial gravel packages accumulated in short 10 15 k y time periods that coincide with quaternary glacial intervals there is direct evidence for a dominant tectonic control in the older marine part of the section here sediment accumulation rates on the limb of the fold growing along this portion of the northern apennine mountain front show that between 1 07 and 1 65 ma repetitive progradation of neritic sand units directly followed pulses of rapid punctuated uplift in contrast the cyclic terrestrial facies variations in the enza section reveal that once the section became emergent at ca 1 ma and uplift slowed climate was the dominant control on sediment production and deposition

vitric compositions in the onaping formation and their relationship to the sudbury igneous complex sudbury structure the 1 85 ga sudbury structure is the largest well preserved exposed example of a terrestrial impact crater it contains world class ni cu platinum group element pge ores associated with the igneous component a new understanding of the geology and geochemistry of the vitric crater fill sequence the onaping formation provides constraints on the evolution of 1 85 ga igneous rocks in the sudbury structure the onaping formation has a well defined mappable stratigraphy composed of three members seven stratigraphic units and two types of intraformational dikes that are overprinted by an impact generated hydrothermal system stratigraphic and alteration mapping provided a basis for well constrained sampling and allowed the definition of the geochemical characteristics of the less altered rocks from each unit including vitric bombs and blocks and intraformational vitric dikes significantly the identification of a least altered composition of the vitric onaping formation enabled an investigation of the link between the early formed vitric melt phase in the impact crater fill sequence and the sudbury igneous complex and offset dikes the least altered vitric onaping formation represented by the massive xenolith poor cores of vitric bombs blocks and intraformational dikes is andesitic in composition consistent with a crustally derived melt the melt composition 61 6 wt sio 2 4 28 mgo 60 ppm ni is remarkably uniform throughout the onaping formation with a typical enrichment of large ion lithophile and light rare earth elements and pronounced negative nb and ti anomalies incompatible trace element ratios and bulk concentrations of the onaping formation coincide with the main mass norite and offset quartz diorite compositions of the underlying sudbury igneous complex but differ distinctly from the granophyre and quartz gabbro root mean squared differences in composition of the vitric onaping formation with the units of the sudbury igneous complex and quartz diorite offset dikes show that the vitric onaping formation does not directly match any of these igneous units but more closely resembles the composition of the ministic and manchester offset dikes the quartz diorite offset dikes have been proposed as representative of the bulk composition of the original melt of the sudbury igneous complex in detail there are small compositional differences between north and south range offset dikes and between these offset dikes and the concentric manchester offset dike however such differences are lacking in the onaping formation we propose that the least altered vitric composition of the onaping formation represents the best estimate of the bulk composition of an initial quenched melt or shock melt formed early in the evolution of the sudbury structure and is a logical starting liquid to model the evolution of the sudbury main mass and offset dikes the offset dike compositions can be derived from onaping formation vitric shock melt by assimilation of progressively greater amounts of mafic material at deeper levels in the crater this mafic contaminated melt or impact melt developed at the base of the melt sheet and was injected into the offset dikes both prior to and contemporaneously with the earliest stages of sulfide precipitation from the sudbury complex fractionation of the mafic contaminated melt by plagioclase and pyroxene accumulation produced the north range felsic and mafic norite and the south range norites the chalcophile metal content of the onaping formation vitric phase closely reflects the overall metal ratios of the magmatic sulfide ores the vitric onaping formation and unmineralized offset dikes have low liquidus temperatures 1 115 1 125 c and if these units represent the source of metals in the sulfide deposits unusually high mass distribution coefficients for cu and ni and high r factors are necessary to account for the metal endowment

the nature age and petrogenesis of the cartier batholith northern flank of the sudbury structure ontario canada abstract the cartier batholith exposed about 50 km northwest of sudbury ontario canada is a late archean k rich granitic batholith along with the levack gneiss complex it forms the footwall of the north range of the sudbury igneous complex the cartier batholith dominantly monzogranitic to granodioritic is relatively homogeneous unfoliated and contains k feldspar megacrysts it shows several distinctive chemical features including high concentrations of zr th u and lree and low concentrations of nb ti and hree several discriminants suggest a post orogenic tectonic environment for the batholith this inference is consistent with a u pb age of 2642 1 ma obtained on zircon only slightly younger than the inferred timing of high grade metamorphism of the levack gneiss complex the cartier batholith could have formed as a result of approximately 33 partial melting of the levack gneiss complex

geochemical relationships in the sudbury igneous complex origin of the main mass and offset dikes petrological models relating the different rock types constituting the 1 85 ga sudbury igneous complex are constrained with extensive new geochemical data we show that the main mass felsic norite transition zone quartz gabbro and granophyre have similar ratios of the highly incompatible trace elements e g la sm 4 5 7 la nb 2 8 4 2 th zr 0 04 0 05 and that these variations are consistent with the crystallization and differentiation of magma types largely 80 derived from the upper crust with a smaller contribution from a mantle source although there is presently no conclusive proof that magma was generated in situ as a melt sheet produced by meteorite impact we find no principal reason why this model should be rejected however we propose that a small contribution of mantle derived picritic magma is required to explain the abundant ni cu and platinum group elements pge in the sudbury deposits as well as the compositions of the ultramafic inclusions mgo 12 36 wt fo sub 68 87 olivines with 450 3 700 ppm ni and abundant chrome rich spinel and the magnesian composition of the mafic norite 8 14 wt mgo and the sublayer 6 12 wt mgo we believe that the main mass of the sudbury complex achieved its present composition through incorporation of up to 20 percent mantle derived picritic magma emplaced along crustal fractures produced by the impact event these picritic magmas entered the melt sheet as a dense plume vigorously mixing with it and due to the marked compositional shift the mixed magma formed magmatic sulfides which sank through the magma column depleting the melt in ni cu and pge since both the felsic norite and granophyre have indistinguishable ratios of the incompatible trace elements we see no requirement to derive these units of rock by the crystallization of magmas derived from different sources rather the compositional difference between the felsic norite and granophyre is attributed to the in situ differentiation of the magma we show that the main mass has many compositional traits similar to those of most of the offset dike quartz diorites e g the parkin offset dike la sm 6 3 la nb 4 5 th zr 0 05 and of embayment related leucocratic norites from the whistle mine la sm 6 2 la nb 5 0 th zr 0 02 these rocks have compositions intermediate between the felsic norite and the granophyre and therefore crystallized from the same magma type arguably the unmineralized quartz diorites provide the best possible estimate of the original magma from which the sudbury complex crystallized in detail there are subtle variations in composition within and between offset dikes with the largest difference being between the north and south range offsets the north range offset dikes cut archean granitoids and gneisses and have elevated sr la yb la sm and gd yb and low tio 2 whereas the south range dikes cut early proterozoic sediments mafic volcanics and intrusions and have low sr la yb gd yb la sm and high tio 2 these differences may be caused by the assimilation of different country rocks during emplacement of the dike a strongly mineralized offset dike at the creighton mine has geochemical variations that are different when compared to the main mass and in the case of creighton are more similar to the local mineralized sublayer these data suggest that mineralized and barren quartz diorites have different geochemical compositions and that these traits may be of value in mineral exploration

magnetic fabric and microstructural evidence for a tectono thermal overprint of the early proterozoic murray pluton central ontario canada abstract the 2 38 ga old murray granite pluton intruded the southern footwall of the sudbury igneous complex and was subjected to repeated ductile deformation its nw and se domains display differences in strain state ams signature and the nature and distribution of fe oxide minerals the magnetic foliation is parallel to the visible foliation in the nw domain but discordant to it in the se domain microstructural data show that the magnetic fabric in the nw domain coincides with a foliation formed at high temperature probably in response to thermal softening during the emplacement of the adjacent sudbury igneous complex this tectono thermal overprint affected pre existing shape fabrics and was facilitated by incipient melting of the granite near the intrusive contact with the sudbury igneous complex rocks of the se domain are only partially overprinted and two mineral subfabrics are preserved prolate susceptibility ellipsoids and clusters of maximum susceptibility directions at the intersections of the two planar fabrics suggest oblique superposition of strain increments increases in bulk magnetic susceptibility and magnetic anisotropy degree towards the intrusive contact with the sudbury igneous complex can be explained by respective increases in the proportion of magnetite over ilmenite and strain intensity in the murray pluton

mid crustal deformation at the southern flank of the sudbury basin central ontario canada a field based structural analysis was made in the southern footwall of the sudbury basin to facilitate a reassessment of the igneous emplacement mechanism of the 1 85 ga sudbury norite i e synfold intrusion impact melt ponding more specifically we wanted to discern whether attitude and curvature of the norite shell were primary or produced mainly by noncylindrical folding the southern footwall of the sudbury basin is composed of paleoproterozoic metavolcanic rocks of the lower huronian supergroup that host the 2 3 ga creighton and murray plutons the geometry of foliation trajectories and other structural evidence reveal that the plutons were emplaced into ductilely deforming host rocks during the blezardian tectonic pulse 2 4 2 2 ga this deformation led to a southward overturn of huronian metavolcanic rocks and was accompanied by amphibolite facies metamorphism static greenschist facies metamorphism in metavolcanic and granitoid rocks was prompted by penokean northward thrusting after subconcordant emplacement of the norite the lack of evidence for penokean folding of huronian footwall rocks suggests that the curvilinear shape of the norite shell is primary this in turn constitutes evidence against impact melt ponding and lends indirect support to an intrusive origin

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

structural characteristics of the sudbury impact structure canada impact induced versus orogenic deformation a review orogenic deformation both preceding and following the impact event at sudbury strongly hinders a straightforward assessment of impact induced geological processes that generated the sudbury impact structure central to understanding these processes is the state of strain of the sudbury igneous complex the solidified impact melt sheet its underlying target rocks overlying impact breccias and post impact sedimentary rocks this review addresses 1 major structural metamorphic and magmatic characteristics of the impact melt sheet and associated dikes 2 attempts that have been made to constrain the primary geometry of the igneous complex 3 modes of impact induced deformation as well as 4 mechanisms of pre and post impact orogenic deformation the latter have important consequences for estimating parameters such as magnitude of structural uplift tilting of pre impact huronian strata and displacement on major discontinuities which collectively have not yet been considered in impact models in this regard a mechanism for the emplacement of offset dikes is suggested that accounts for the geometry of the dikes and magmatic characteristics as well as the occurrence of sulfides in the dikes moreover re interpretation of published paleomagnetic data suggests that orogenic folding of the solidified melt sheet commenced shortly after the impact uncertainties still exist as to whether the sudbury impact structure was a peak ring or a multi ring basin and the deformation mechanisms of rock flow during transient cavity formation and crater modification

late gauss to early matuyama invasions of neogloboquadrina atlantica in the mediterranean and associated record of climatic change a well dated high resolution record of climatic change is presented for the late pliocene mediterranean principal component analysis on abundances of 14 planktonic foraminiferal species reveals a series of late gauss to early matuyama surface water cooling events which can be correlated with north atlantic glacial isotope stages 108 to 94 the abundance record of the benthic foraminifer trifarina angulosa suggests lowered bottom water temperatures at times of surface water cooling the record of surface water oxygen and carbon isotopes shows an inverse pattern with 18o maxima and 13c minima at times of cool sea surface temperature conditions concomitant decrease in p b value and increased admixtures of clastic material suggest that late gauss to early matuyama surface water cooling events in the mediterranean are accompanied with glacioeustatic sea level low stands major surface water cooling events are associated with invasions of neogloboquadrina atlantica this north atlantic mid to high latitude species is at 2 55 ma close to the gibraltar portal whereafter it could invade the mediterranean repeatedly during periods of climatic cooling until it disappears from all over the north atlantic and mediterranean at the end of glacial stage 96

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

integrated magnetostratigraphy and biostratigraphy of the upper pliocene lower pleistocene from the monte singa and crotone areas in calabria italy the results of a detailed magnetostratigraphic and biostratigraphic study of late pliocene to early pleistocene marine marl sequences from the monte singa and crotone areas in calabria italy are presented the magnetostratigraphy from the monte singa sequence ranges from below the gauss matuyama boundary up to and including the lower olduvai boundary normal polarities at a level corresponding to isotope stage 81 most probably represent the r union subchron from the lower olduvai boundary upward a reliable magnetostratigraphy could not be established due to increased weathering of the marls resulting in mainly secondary magnetizations the magnetostratigraphy from the composite sequence of the crotone area belongs to a large part of the matuyama chron and includes the olduvai subchron the position of the lower and upper boundaries of the olduvai subzone could be established more precisely than from earlier results moreover the upper boundary of the olduvai subzone poses an ambiguity a relatively long normal polarity interval representing the main olduvai subchron and corresponding to a duration of 115 ka is followed by a short 30 ka reversed subchron and the short 15 ka normal vrica subchron another option and more in accordance with the duration of the olduvai subchron in literature would be to consider the complete n r n polarity succession with a total duration of 160 ka as representing the olduvai subchron implying that this olduvai subchron has a short reversed interval in its upper part linear interpolation and extrapolation yield ages for the most important late pliocene early pleistocene biostratigraphic datum levels an age of 1 69 ma is found for the pliocene pleistocene boundary using the conventional polarity time scale dated with radiometric results however hilgen 1 in correlating the sapropel groups and patterns to the precession curve of the earth s orbit obtained significantly different ages for the polarity transitions of the present study according to this astronomically calibrated polarity time scale the age of the pliocene pleistocene boundary is 1 81 ma

a refined pliocene to early pleistocene chronostratigraphic frame at odp hole 653a west mediterranean abstract two planktonic foraminiferal oxygen isotope records of odp hole 653a tyrrhenian sea are presented for the time period extending from approximately 0 8 to 3 0 ma six generally accepted synchronous bioevents were used to precise the oxygen isotope chronology and to identify the oxygen isotope stages 22 down to 114 subsequently this oxygen isotope chronology was used to determine the synchronism or diachronism of various other biostratigraphic events with those recorded in the singa and ficarazzi land sections italy and those in other dsdp odp sites new results concern the diachronity of the fod of the planktonic foraminiferal species n atlantica g truncatulinoides truncatulinoides and g inflata between odp hole 653a and the italian landsections because many species entered the mediterranean in short term fluxes strongly related to the southward migration of cool north atlantic surface waters their time distribution through the pliocene pleistocene generally corresponds to alternated intervals of presence and absence this should explain most of the apparently diachronous appearances and disappearances alternating presence absence patterns are of less importance for the various nannofossil events the lod of d surculus occurs during the transition of stage 100 to 101 in both odp hole 653a and the singa section which is in perfect agreement with the disappearance of this species from the open ocean the lod of d pentaradiatus in the mediterranean occurs in stages 100 99 which seems to be consistent with the extinction of this species in the southern hemisphere g oceanica which corresponds to the 4 m gephyrocapsa spp m is recorded in stages 65 to 64 at odp hole 653a the gephyrocapsa spp 5 5 m first occurred in stage 51 at hole 653a which fits within the uncertainty interval for this event stretching from stage 51 to 47 in the open ocean and seems therefore a useful tool for conventional biostratigraphy in the mediterranean

structural analysis of the central and southwestern sudbury structure southern province canadian shield the sudbury structure ss is an unusual crater structure which acquired its present oval surface shape during northwest directed ductile thrusting lower amphibolite facies metamorphism accompanied the thrusting which generated a major reverse shear zone at least 50 km long the south range shear zone srsz transects the south range of the sudbury structure and exhumes a low level of the sudbury igneous complex sic assuming heterogeneous simple shear in the northwest southeast vertical plane on northeasterly striking glide surfaces minimal estimates of net displacement across the srsz exceed 8 km this displacement magnitude and the map pattern of the sic require the southwest closure of the ss to be steeply plunging in accord with a hypothetical funnel shape of the sic the rocks of the metasedimentary core of the ss are deformed into a family of second order buckle folds the tangent surface of which forms an upright open flexure within the first order structure of the sudbury synclinorium the

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

geochemical stratigraphy of the huronian continental volcanics at thessalon ontario contributions of two stage crustal fusion the 1500 m thick sequence of huronian continental volcanics at thessalon ontario is subdivided into 4 volcanic cycles each of which includes abundant early mafic end members central intermediate flows and late rhyolite units major and trace element concentrations are dominated by extensive gabbroic fractionation trends that ultimately produced two types of felsic flows 1 rhyolites with high light rare earth element lree and relatively low large ion lithophile element lile concentrations high lree low lile rhyolites and 2 following late separation of ree rich accessory phases rhyolites depleted in lree low lree high lile rhyolites mafic end members of individual volcanic cycle are progressively less siliceous and less enriched in lile and lree with height in the stratigraphic section ti zr ratios gradually rise from 35 in early mafic flows to stabilize at about 85 in late units while average sio2 contents decrease from 56 to about 50 and mg rises from about 48 to 52 nd values are consistently negative indicating variable degrees of pre fractionation crustal contamination of the end member magmas during their uprise through the crust mixing models are consistent with up to 50 contamination by crustal material of tonalitic hornblende gneiss composition a progressive increase in nd from about 5 0 to 0 5 upward in the volcanic succession reflects a decreasing degree of crustal contamination due to development of insulating layers along margins of the feeder system detailed stratigraphic variations suggest that successive magmas batches were intercepted by a progressively fractionating periodically replenished magma source giving rise to open system magmatism despite the prevalence of crustal assimilation in the huronian lavas la sr n ratios are too low in least contaminated end members to be explained by contamination of tholeiitic magmas the late basalts resemble instead modern island are basalts and it is suggested that the subcontinental mantle source was enriched by subduction related processes during crustal formation within individual volcanic cycles gabbroic fractionation trends systematically deviate from calculated factors toward compositions characteristic of hornblende gneiss such relations suggest that further crustal contamination of the magmas occurred simultaneous with crystal fractionation probably within undulating sills at upper crustal levels quantitative analysis suggests assimilation fractional crystallization a fc ratios of about 0 45 as a result of extensive two stage contamination rhyolites from the initial volcanic cycle incorporate a total of over 60 of crust

magnetic fabric constraints on friction melt flow regimes and ore emplacement direction within the south range breccia belt sudbury impact structure abstract magnetic fabric analysis and petrography have been carried out on 1100 samples from the south range breccia belt srbb a 45 km long arc of huronian supergroup breccia fragments and crystallized friction melt pseudotachylyte sub concentric to the 1 85 ga sudbury impact structure optical petrography and analytical sem analyses show the pseudotachylyte to consist of fine grained quartz biotite and ilmenite with minor plagioclase apatite zircon pyrite and pyrrhotite alternating field and thermal demagnetization spectra indicate that the principal magnetic carrier in the matrix is pyrrhotite while clasts can contain either pyrrhotite or magnetite mean magnetic susceptibilities in the matrix are generally on the order of 10 4 si two ams anisotropy of magnetic susceptibility fabrics have been determined in the matrix the most common is an oblate sub vertical foliation sub parallel to the local strike of the srbb with anisotropies p ranging from 1 08 to 1 20 the second ams fabric is a weakly to strongly prolate sub vertical lineation with generally higher p values of 1 2 to 1 55 both fabrics are coaxial to the petrofabric in the matrix huronian clasts exhibit scattered heterogeneous ams fabrics distinct from those found in the srbb matrix the strongly prolate t 0 73 and anisotropic p 1 55 ams fabric found directly over the giant frood stobie ni cu pge deposit hosted within the srbb suggests that sulfide droplets were injected and or squeezed into the matrix above the deposit samples containing pyrrhotite from the edges of the deposit do not exhibit this magnetic signature similar prolate moderately anisotropic lineations are also found further to the east of the frood stobie mine and appear to be associated with a magnetotelluric conductor at depth it is suggested that these lineations are due to injection of material from depth into the srbb during failure of the inner rim of the sudbury impact structure during the crater modification stage the oblate magnetic fabric found within the srbb is consistent with frictional comminution and melting of the wall rock lithologies during collapse of the transient cavity and subsequent slumping of the crater walls however subsequent deformation of the sudbury structure by late penokean folding and thrusting to the nw could produce a similar oblate fabric tight clustering of the maximum principal axes of the magnetic susceptibility could be interpreted as being consistent with tectonometamorphic transposition of the matrix petrofabric as well as generation by slumping and friction melt flow during failure of the hanging wall further work is needed on undeformed impact structures of similar size to sudbury in order to constrain the petro and magnetic fabrics produced during rim collapse additional work in the westerly trending srbb along the edge of the creighton pluton would help to determine if the dominant ne sw trending matrix fabric is regional in origin or is controlled by the current orientation of portions of the srbb

comment on effective thermal expansivity of maxwellian oceanic lithosphere by jun korenaga earth planet sci lett 257 343 349 2007 abstract korenaga korenaga j effective thermal expansivity of maxwellian ocean lithosphere earth planet sci lett 257 2007 343 349 apparently unaware of pollack pollack h n on the use of the volumetric thermal expansion coefficient in models of ocean floor topography tectonophysics 64 1980 t45 47 has confirmed pollack s essential result the apparent volumetric thermal expansivity of oceanic lithosphere is less than the intrinsic value indicated by mineral physics data and less than the value suggested by models in which oceanic lithosphere is treated as a fully relaxed fluid

increasing seasonal upwelling in the subtropical south atlantic over the past 700 000 yrs evidence from deep living planktonic foraminifera abstract the distribution and character of deep living planktonic foraminifera such asgloborotalia truncatulinoides andg hirsuta are particularly sensitive to the structure of the upper ocean because of the wide range of water depths over which their life cycles extend like other planktonic foraminifera the deep living species begin growing in shallow surface waters but unlike the other species they continue growing while sinking into much deeper water their reproduction is synchronized with the seasonal deep mixing and upwelling of nutrient rich waters that precedes spring bloom where deep mixing is curtailed the abundances of the deeper dwelling species g hirsuta the deeper dwelling varieties e g left coilingg truncatulinoides and the larger presumably faster sinking shells are reduced leading to an apparent acceleration in shell development these changes are observed today in transects from the seasonally deep mixed subtropical gyres to the seasonally stable surface waters equatorward of the subtropical convergences past changes in the abundance and character of these deep living planktonic foraminifera have been measured in a late pleistocene record from the subtropical western south atlantic ocean over the past 700 kyrs abundances of these species have increased g truncatulinoides has changed from the predominantly shallower dwelling right coiling to the deeper dwelling left coiling variety and the accelerated shell development characteristic of shallow mixing has shifted toward the rates normally associated with deep mixing all this indicates that the structure of the upper ocean in the subtropical south atlantic before 700 kyrs ago was more like that nearer the equator today where mixing is limited to the upper 100 200 m since that time the scale of mixing has gradually increased to more than 400 m this implies a gradual increase through the late pleistocene in the seasonal upwelling of nutrients in the subtropical south atlantic and consequently in the intensity of the seasonal maximum in organic productivity

geochemical evolution of a 10 m thick intrusive body the south brenterc h diabase dyke western armorican massif france the south brenterc h 9 5 m thick diabase dyke belongs to the intermediate ti quartz normative tholeiitic magmatism which has intruded the western end of britanny france near the trias lias boundary it has been previously identified as a simple dyke resulting from a single magmatic injection the present study is based on ten samples collected along a half transverse section of this dyke geochemical analyses and some textural parameters have been used to point out two flow related differentiation processes partially masked by alteration these late magmatic mechanisms have induced subtle geochemical variations among samples which sometime counteract each other the processes pointed out here are i expulsion of phenocrysts from the borders during flow differentiation likely by the way of an hydrodynamic grain dispersive pressure and ii emplacement of a more evolved magma in the central part of the intrusion probably due to a viscosity segregation mechanism during the flow

differentiation and emplacement of the worthington offset dike of the sudbury impact structure ontario the offset dikes of the 1 85 ga sudbury igneous complex sic constitute a key topic in understanding the chemical evolution of the impact melt its mineralization and the interplay between melt migration and impact induced deformation the origin of the melt rocks in offset dikes as well as mode and timing of their emplacement are still a matter of debate like many other offset dikes the worthington is composed of an early emplaced texturally rather homogeneous quartz diorite qd phase at the dike margin and an inclusion and sulfide rich quartz diorite iqd phase emplaced later and mostly in the centre of the dike the chemical heterogeneity within and between qd and iqd is mainly attributed to variable assimilation of host rocks at the base of the sic prior to emplacement of the melt into the dike petrological data suggest that the parental magma of the worthington dike mainly developed during the pre liquidus temperature interval of the thermal evolution of the impact melt sheet 1200 c based on thermal models of the cooling history of the sic the two stage emplacement of the worthington dike occurred likely thousands to about ten thousand years after impact structural analysis indicates that an alignment of minerals and host rock fragments within the worthington dike was caused by ductile deformation under greenschist facies metamorphic conditions rather than flow during melt emplacement it is concluded that the worthington offset dike resulted from crater floor fracturing possibly driven by late stage isostatic readjustment of crust underlying the impact structure

the onset of major northern hemisphere glaciations and their impact on dinoflagellate cysts and acritarchs from the singa section calabria southern italy and dsdp holes 607 607a north atlantic abstract the climatic deterioration related to the onset of northern hemisphere glaciations circa 2 52 ma b p must have lead to reorganization and relocation of species associations and may have enhanced species turnover the present study investigates how this deterioration affects the dinoflagellate cyst and acritarch assemblages from two locations dsdp site 607 north atlantic and the singa section southern italy the records from these locations cover the interval from 2 8 to 2 2 ma with at least a 5 ka resolution and they have been correlated to the milankovitch periodicities on a cycle to cycle basis by means of integrated high resolution stable isotope calcium carbonate foraminiferal palynological and magnetostratigraphical datasets in the present study this high resolution stratigraphic framework is used for a detailed correlation of events occurring in each of the depositional sequences it also enables further assessment of the palaeoenvironmental preferences of some dinoflagellate cyst forms comparison of the two palynological records reveals a close correspondence in the timing of major assemblage changes and extinction events confirming their milankovitch cycle based correlation a close link between periods of northern hemisphere cooling at oxygen isotope stages 110 104 and 100 96 and increased dinoflagellate cyst turnover appears to be present for both dsdp site 607 and the singa section the turnover events can also be recognized in the records of planktic foraminifera and calcareous nannoplankton comparison of the singa section with site 607 and with other time equivalent marine palynological data sets shows that some oceanic taxa respond similarly over a large area the biostratigraphical implications are discussed notably the last occurrence of invertocysta lacrymosa appears to be a valuable marker for isotope stage 110 in the mediterranean and north atlantic

origin and emplacement of offset dykes in the sudbury impact structure constraints from hess the hess offset is a steeply dipping dyke located 12 15 km north of the 1 85 ga sudbury igneous complex sic within the 200 250 km diameter sudbury impact structure it is up to 60 m wide and strikes subconcentrically to the sic for at least 23 km the main phase of the dyke is granodioritic but it conforms with what is locally referred to as quartz diorite a term used for all the offset dykes of the sudbury impact structure rare earth element data shows that the hess offset is genetically related to the sic hess is most closely affiliated with an evolved felsic norite component of sic and not bulk impact melt this indicates that hess was emplaced during fractionation of the impact melt sheet rather than immediately following impact the main quartz diorite phase of the dyke comprises a quartz plagioclase hornblende biotite clinopyroxene orthopyroxene assemblage critically the hess offset occupies a concentric fault system that marks the northern limit of a pseudotachylyte rich shatter cone bearing annulus about the sic this fault system was active during the modification stage of the impact process

the mechanisms of petrogenesis of the archaean continental crust comparison with modern processes the petrographic and chemical composition of magmatic rocks generated during the archaean appears to be different from that of post archaean rocks komatiites are widespread before 2 5 ga and rarely occur afterwards in addition the archaean continental crust is primarily ttg tonalitic trondhjemitic and granodioritic in composition exhibiting typical trondhjemitic differentiation trends whereas modern equivalents are granodioritic to granitic following classical calc alkaline differentiation trends this distinction becomes more prominent when rare earth elements ree are taken into account archaean ttg are yb poor ybn 8 5 and have high layb ratios 5 layb n 150 in comparison the post 2 5 ga granitoids emplaced in subduction zone geodynamic environments have high yb content 4 5 ybn 20 with very low layb n ratios 20 theoretical calculations and experimental petrology have shown that the ttg can be produced by partial melting of an archaean tholeiite transformed into garnet bearing amphibolite consequently the low heavy ree content of the ttg is explained by the influence of both residual garnet and hornblende in their source after 2 5 ga the role of these minerals in calc alkaline magma genesis becomes progressively less important which is interpreted in terms of a cooling earth model in modern subduction zone environments the subducted oceanic slab is relatively old and cold and the geothermal gradient along the benioff plane in low ca 10 c km consequently the down going lithosphere undergoes dehydration before partial melting is able to occur the liberated fluids are light ree and lile enriched and ascend into the overlying mantle wedge where they induced partial fusion the produced magmas separate from their mantle source region leaving a residue mainly composed of olivine and pyroxenes mantle derived magmas typically exhibit high yb contents due to low kdyb values for olivine and pyroxenes during the archaean the subducted lithosphere was relatively young and hot providing high geothermal gradients along the benioff zone thus partial melting of the subducted slab was possible at lower temperatures before dehydration would take place garnet and hornblende are the main residual phases accounting for the low yb contents of the archaean ttg this model can be tested using a modern analogue of archaean like subduction processes in south chile an oceanic ridge has subducted and all thermodynamic calculations indicate that this creates locally high geothermal gradients along the benioff zone thus in very small areas archaean like environments may be simulated in modern subduction zones the modern andesites produced in this environment show archaean geochemical characteristics with low ybn 5 whereas the majority of andesites along the andean arc have modern patterns with ybn ranging from 8 to more than 17 this conclusion was generalised to all young subducted lithospheres all over the world in conclusion it appears that since the archaean there has been a change in the site of continental crust genesis the location of calc alkaline magma source in subduction zone environments has migrated through time from the subducted slab to the mantle wedge this is a direct consequence of the progressive cooling of the earth

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

age of the plio pleistocene boundary in the vrica section southern italy new palaeomagnetic data from the proposed plio pleistocene boundary stratotype section vrica section southern italy are presented here in order to improve the correlation of these sediments to the magnetic polarity time scale if the interpretation preferred here is correct the boundary falls above the olduvai normal subchron at approximately 1 6 myr

the south range breccia belt of the sudbury impact structure a possible terrace collapse feature the south range breccia belt srbb is an arcuate 45 km long zone of sudbury breccia in the south range of the 1 85 ga sudbury impact structure the belt varies in thickness between tens of meters to hundreds of meters and is composed of a polymict assemblage of huronian supergroup 2 49 2 20 ga nipissing diabase 2 2 ga and proterozoic granitoid breccia fragments ranging in size from a few millimeters to tens of meters the srbb matrix is composed of a fine grained 100 m assemblage of biotite quartz and ilmenite with trace amounts of plagioclase zircon titanite epidote pyrite chalcopyrite pyrrhotite and occasionally chlorite the srbb hosts the frood stobie vermilion and kirkwood quartz diorite offset dykes the former being associated with one of the largest ni cu pge sulphide deposits in the world optical petrography and whole rock geochemistry concur with previous studies that have suggested that the matrix of the srbb is derived from comminution and at least partial frictional melting of the wall rock huronian supergroup lithologies rare earth element ree data from all sampled lithologies associated with the srbb exhibit crustal signatures when normalized to c1 chondrite values additionally ree data from the quartz diorites disseminated sulphides in sudbury breccia and a sample of an aphanitic biotite hornblende tonalite dyke exhibit flat slopes when compared to the mafic and felsic norites quartz gabbro and granophyre units of the sudbury igneous complex sic which suggests that these lithologies are representative of bulk sic melt we suggest that the srbb was formed by high strain rate 1 m s gravity driven seismogenic slip of the inner ring of the sudbury impact structure during postimpact crustal readjustment crater modification stage failure of the hanging wall may have facilitated the injection of bulk sic melt into the srbb along with the ni cu pge sulphides of the frood stobie deposit postimpact penokean 1 9 1 7 ga tectonism particularly northwest directed shearing along the south range shear zone and associated thrust faulting could account for the present subvertical orientation of the srbb and the apparent lack of a connection at depth with the sic

mediterranean neogene planktonic foraminifer biozonation and biochronology abstract planktonic foraminifera are widely used for biostratigraphy and correlation of mediterranean neogene marine sediments and are a fundamental component in the astronomical tuning of the neogene time scale recent developments in high resolution studies focused on the astronomical calibration of cyclically marine sediments cropping out in land based sections and recovered from deep sea successions increased the accuracy of stratigraphic ranges of planktonic foraminiferal species improving the biostratigraphic resolution and biochronology the large amount of data on planktonic foraminifera obtained through quantitative semiquantitative analyses published in the recent years allowed the revision of many biohorizons and their calibrations we incorporate these developments and emendments into the existing mediterranean planktonic foraminiferal biozonation therefore in this paper we present an emended standard mediterranean planktonic foraminiferal biozonation with a detailed description of zones and subzones within the framework of the astronomical tuned neogene time scale 2004 and 2012 atnts2004 atnts2012 and we provide the range chart of the most common planktonic foraminiferal taxa and the quantitative distribution pattern of selected marker species twenty two biozones and thirty one subzones that span the past 23 million years have been identified we distinguished them using the following code system mmi1 to mmi13 and ndz for the time interval related to the messinian salinity crisis mediterranean miocene biozones mpl1 to mpl6 mediterranean pliocene biozones according to the gelasian as the uppermost stage of the pliocene series epoch and mple1 to mple2 mediterranean pleistocene biozones according to the calabrian as the lowermost stage of the pleistocene series epoch we assembled 118 neogene planktonic foraminiferal biohorizons from multiple datasets and incorporated the calibration of these bioevents into a revised neogene planktonic foraminiferal biochronology the revised and recalibrated data provide a major progress in biostratigraphic and biochronologic resolution and a template for future progress of the neogene time scale unfortunately two main gaps of planktonic foraminiferal quantitative data occur in the late burdigalian between 16 12 ma and 17 23 ma and at aquitanian burdigalian boundary between 19 74 ma and 20 66 ma due to the absence of high resolution studies of these time intervals in the mediterranean

partial melt topology in statically and dynamically recrystallized granite microstructures of the murray granite pluton central ontario canada show evidence of both static and dynamic crystallization subsequent to partial melting backscattered electron analyses reveal interstitial k feldspar and plagioclase at triple junctions of strain free isometric quartz grains the geometry of the quartz feldspar boundaries mimics the original topology of the quartz melt contacts during crystallization this conclusion is suggested by the occurrence of both rounded and planar faces of quartz grains and by low 27 dihedral angles of quartz quartz feldspar boundaries similar to dihedral angles in experimentally crystallized quartz quartz silicic melt systems in contrast feldspar seams in deformed granites have high axial ratios are usually elongated perpendicular to the foliation plane and are located preferentially along individual grain boundaries quartz grains are dynamically recrystallized and occasionally transected by feldspar seams indicating that fracturing occurred in the presence of melt during crystal plastic deformation of quartz the subparallel orientation in quartz grains of intragranular feldspar bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular and intergranular fractures respectively partial melt topology was therefore controlled by intergranular and occasionally by intragranular fracturing

calcareous plankton biostratigraphy and biochronology of the pliocene lower pleistocene succession of the capo rossello area sicily abstract in the first part of this paper we present the calcareous nannofossil biostratigraphy of the capo rossello section sicily which suggests that a sedimentary gap exists at the contact between the trubi and the overlying monte narbone formation close to the top of the proposed zanclean stratotype this suggestion is supported by the planktonic foraminiferal results and field observations in contrast the transition from the trubi to the monte narbone formation is well exposed gradational and biostratigraphically continuous in the nearby section of punta piccola a composite of the capo rossello and punta piccola sections serves as a good biostratigraphic reference for the pliocene of the mediterranean in a second part of this paper we have attempted to update the mediterranean pliocene time framework by integrating all of the available biostratigraphic biochronologic chronostratigraphic paleomagnetic and radiometric data

recrystallized impact glasses of the onaping formation and the sudbury igneous complex sudbury structure ontario canada abstract the origin of the sudbury structure and of the associated heterolithic breccias of the onaping formation and the sudbury igneous complex have been controversial while an impact origin of the structure has gained wide acceptance over the last 15 years the origin of the recrystallized onaping formation glasses and of the igneous complex is still being debated recently the interpretation of the breccias of the onaping formation as suevitic fall back impact breccias has been challenged the igneous complex is interpreted either as a differentiated impact melt sheet or as a combination of an upper impact melt represented by the granophyre and a lower impact triggered magmatic body consisting of the norite sublayer formations the onaping formation contains glasses as fluidal and nonfluidal fragments of various shapes and sizes they are recrystallized and our research indicates that they are petrographically heterogeneous and span a wide range of chemical compositions these characteristics are not known from glasses of volcanic deposits this suggests an origin by shock vitrification an interpretation consistent with their association with numerous and varied country rock clasts that exhibit microscopic shock metamorphic features the recrystallized glass fragments represent individual solid state and liquid state vitrified rocks or relatively small melt pods the basal member lies beneath the gray and black members of the onaping formation and where not metamorphic has an igneous matrix igneous textured melt bodies occur in the upper two members and above the basal member a comparison of the chemical compositions of recrystallized glasses and of the matrices of the basal member and the melt bodies with the components and the bulk composition of the igneous complex is inconclusive as to the origin of the igneous complex basal member matrix and melt bodies on average are chemically similar to the granophyre of the sudbury igneous complex suggesting that they are genetically related our chemical results allow interpretation of the entire igneous complex as a differentiated impact melt however they are also consistent with the granophyre alone being the impact melt and the norite and quartz gabbro beneath it representing an impact triggered magmatic body this interpretation is preferred as it is consistent with a number of field observations a re evaluation and extension of structural field studies and of geochemical data as well as a systematic study of the contact relationships of the various igneous phases of the igneous complex are needed to establish a sudbury impact model consistent with all data and observations

deep geometry of the sudbury structure from seismic reflection profiling seismic reflection data show the deep geometry of the sudbury structure to be markedly asymmetric the sudbury north range comprises shallowly south dipping sedimentary strata overlying a thick unit of heterolithic breccia and melt bodies layered rocks of the sudbury igneous complex and footwall gneiss reflections from the upper layers are interrupted by faults near the center of the sudbury basin whereas the basal mafic units and footwall gneiss continue dipping southward and appear to be tightly folded or truncated near the creighton fault in contrast the seismic image of the south range is dominated by a distinctive series of moderately south dipping reflections interpreted as thrust faults or shear zones on which severe telescoping and imbrication of lithological units and considerable northwest southeast shortening of the sudbury structure have occurred such shortening explains the noncircular shape of the structure and thus removes a critical objection to the sudbury impact crater hypothesis the new structural model is shown to be consistent with regional magnetic and gravity fields a large hidden ultramfic mafic mass is no longer required to explain the potential field data

low temperature deformation mechanisms at a lithotectonic interface near the sudbury basin eastern penokean orogen canada abstract southwest of the sudbury basin variations in macroscopic strain microstructure and deformation mechanisms within archaean granitoid basement and overlying proterozoic rocks suggest that rock strength was strongly influenced by large amounts of fluids ductilely deformed granitoids with strong shape fabrics are concentrated in a 150 200 m wide zone parallel to the subvertical basement cover interface high fluid activity in this zone is indicated by 1 thickness and close spacing of foliation parallel quartz veins 2 abundant fluid inclusion trails in quartz 3 quartz c axis fabrics and 4 transformation of feldspar into phyllosilicates under middle greenschist facies metamorphic conditions away from this zone brittle ductile deformation in archaean granitoids caused grain size reduction of feldspar by fracturing and crystal plastic deformation of quartz indicating largely dry conditions strain was concentrated at the interface in a region of bulk horizontal shortening and linked kinematically to large scale shortening of the sudbury igneous complex and thrusting in the south range shear zone after early open buckling of the sudbury igneous complex reverse shearing in this zone may have been controlled by ductile deformation at the basement cover interface physical continuity of and age constraints on strain fabrics suggest that the south range shear zone represents a segment of a large ductile deformation zone which is most likely linked to the murray fault and on which higher grade rocks ascended between 1 85 and 1 23 ga ago

differentiation and source of the nipissing diabase intrusions ontario canada major and trace element data are presented for 2 2 ga proterozoic diabase sills from across the nipissing magmatic province of ontario in situ differentiation of the magma coupled with assimilation of huronian supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions uniform trace element and isotope ratio signatures such as la sm 2 8 3 7 and endchur 2 7 to 5 9 characterize chilled margins and undifferentiated quartz diabases these chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province this magma has higher la sm and lower ti y than primitive mantle and is displaced towards the composition of shales most chilled diabases and quartz diabases have a similar mg 0 64 and 0 60 and ni content 98 and 127 ppm and it is argued that the magma differentiated at depth and was emplaced as a uniform low mg magma

geochemistry of drill core samples from yaxcopoil 1 chicxulub impact crater mexico the chemical composition of suevites displaced cretaceous target rocks and impactgenerated dikes within these rocks from the yaxcopoil 1 yax 1 drill core chicxulub impact crater mexico is reported and compared with the data from the yucatn 6 y6 samples within the six suevite subunits of yax 1 four units with different chemical compositions can be distinguished a upper lower sorted and upper suevite depth of 795846 m b middle suevite depth of 846861 m c brecciated impact melt rock depth of 861885 m and d lower suevite depth of 885895 m the suevite sequence a b and d display an increase of the cao content and a decrease of the silicate basement component from top to bottom in contrast the suevite of y6 shows an inverse trend the different distances of the yax 1 and y6 drilling sites from the crater center 60 and 47 km respectively lead to different suevite sequences within the cretaceous rocks of yax 1 a suevitic dike depth of 916 m does not display chemical differences when compared with the suevite while an impact melt rock dike depth of 1348 m is significantly enriched in immobile elements a clastic breccia dike depth of 1316 m is dominated by material derived locally from the host rock while the silicate rich component is similar to that found in the suevite significant enrichments of the k2o content were observed in the yax 1 suevite and the impact generated dikes all impactites of yax 1 and y6 are mixtures of a crystalline basement and a carbonate component from the sedimentary cover an anhydrite component in the impactites is missing yax 1 or negligible y6

rare earth element characteristics and origin of the sudbury igneous complex ontario canada abstract systematic geochemical studies have been carried out on the sudbury igneous complex sic and its country rocks the two main rock types of the sic norite and granophyre show contrasting chemical features the norite contains 54 58 wt sio2 whereas the granophyre has a sio2 content of 65 71 wt all rocks are characterized by high absolute rare earth element contents ree 63 314 ppm the granophyre having more than twice the ree contents of the norite and by lree enriched chondrite normalized distribution patterns huronian volcanic rocks and huronian plutonic granites have the highest ree contents and hree enrichment among the country rocks archean rocks are characterized by very steep ree patterns and positive eu anomalies nipissing diabase contains the lowest ree contents and has a flat ree pattern within the sic the ree values are more or less constant through the norite but the abundances of some elements such as ce and yb decrease slightly upward with stratigraphy ree contents increase sharply in passing from norite to granophyre and the eu eu ratio decreases from around unity to 0 66 the contrasting ree contents of the norite and granophyre combined with their distinctive major and trace element contents are considered to indicate that they resulted from two separate batches of magma probably emplaced at about the same time the previous models in which the sic was considered to originate from a single magma either contaminated mantle magma or crustal melt are not adequate a new hypothesis is developed based on the chemical features observed in this study the sic is considered to have comprised two independent intrusions the norite was derived from a heavily contaminated mantle magma 30 60 the main contaminant being archean granulite facies rocks of the lower crust the granophyre represents a crustal melt 75 archean rocks and 25 huronian granite induced by meteorite impact the new hypothesis better accounts for the large proportion of granophyre in relation to norite and for the ni cu sulfide mineralization associated with the sic it is also favored by the rb sr isotopic data

the sudbury igneous complex a differentiated impact melt sheet the sudbury structure ontario is the remnant of a 1 85 ga old impact crater which originally had a diameter of 200 to 250 km the sudbury igneous complex occurs within the sudbury structure the sudbury igneous complex is a 2 5 to 3 0 km thick 60 27 km elliptical igneous rock body which consists of four major lithologies from top to bottom traditionally termed granophyre quartz gabbro norite and contact sublayer sulfide and inclusion bearing noritic rock with the exception of the latter all these lithologies are continuous across the structure modal analyses reveal that following the iugs system of nomenclature quartz gabbro samples are in fact quartz monzogabbros a few of the norite samples are quartz gabbros and most norite samples are quartz monzogabbros in view of these observations and in order to clarify the nomenclature an updated terminology is proposed from top to bottom upper unit middle unit lower unit and contact sublayer the bulk composition of the sudbury igneous complex from north range data is granodioritic continuous and gradational mineralogical and geochemical variations between the lithological units are evidence that the complex behaved as a single melt system all the sudbury igneous complex lithologies have the same light to heavy rare earth element ree ratio and an overall pattern of increased light ree and depleted heavy ree the occurrence of primary hydrous minerals hornblende and biotite deuteric alteration and abundant micrographic and granophyric intergrowths demonstrate that the melt was rich in h2o moreover the granophyric and other far from equilibrium textures are most likely due to rapid crystallization triggered by exsolution of a volatile phase the sudbury igneous complex differs from traditional layered mafic complexes in the following aspects it has an overall intermediate composition a hydrous nature a crustal isotopic signature normative corundum and an unusually large volume of granophyre the sudbury complex differs from known terrestrial impact melt sheets only by its great thickness and the presence of chemical and therefore mineralogical layering reported here for the first time and similar to those found in impact melt rocks elsewhere are the occurrences of plagioclase xenocrysts with complex twinning and zoning patterns and planar deformation features in quartz xenocrysts the well known ore deposits of the sudbury region are directly related to the genesis of the sudbury igneous complex some ores precipitated from the sudbury melt whereas others were concentrated by hydrothermal fluids that percolated through the crystallized complex it is concluded that the sudbury igneous complex is the best exposed and only well documented to date terrestrial impact melt sheet to have differentiated