transmission electron microscopy of ejecta from the xvith century eruption of the soufriere guadeloupe microscopic evidence for magma mixing abstract pyroclastic products of the xvith century eruption of the soufriere of guadeloupe were examined in transmission electron microscopy features smaller than one micrometer inside the pyroxene and plagioclase phenocrysts were analyzed and provided information to constrain the mechanism and the chronology of the eruption the observations support a mechanism of triggering by injection of a hot andesitic magma into a chamber containing partly differentiated dacitic magma the analysis of the dusty zones in plagioclase phenocrysts suggests that the basic magma was about 200 c hotter than the resident magma the eruption probably had a very low chlorine yield and ended with a pyroclastic flow contemporaneous with the emplacement of the present dome

microgranitoid enclave swarms in granitic plutons central sierra nevada california abstract microgranitoid enclaves are common in granitic plutons worldwide occurring individually and in homogeneous or heterogeneous swarms three plutons in the central sierra nevada batholith contain swarms with mostly heterogeneous suites of enclaves in the intermediate composition range and occur in a number of two dimensional shapes specifically as dikes small rafts lenses pipe vortices and large massive shapes swarms are characterized by various features including the nature of their boundary with the host their planar or non planar character internal geometry density of enclave packing presence or absence of schlieren and crystal aggregates and axial ratios and degree of preferred alignment of enclaves we propose that heterogeneous enclave swarms form by one or some combination of the following mechanisms 1 velocity gradient sorting parallel or normal to the flow 2 gravitational sorting or 3 break up of heterogeneous dikes common sites where enclave swarms form include pluton margins or internal viscosity walls within fractures and near the pluton roof

flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

replenishment crystal accumulation and floor aggradation in the megacrystic kameruka suite australia detailed field evidence indicates that the kameruka suite plutons of the bega batholith eastern australia grew by crystal accumulation on the floor of a magma chamber depositional features in the plutons including mafic enclave channels asymmetric enclave pillows and exotic rafts load casts and flame structures and graded and trough cross beds indicate that the pluton built progressively upward the general eastward dip of depositional features in the main pluton implies a lower western and upper eastern contact consistent with a basal granite migmatite contact in the west and a sharp hornfelsic sidewall contact in the east mafic felsic and composite dykes most common near and below the basal western contact are interpreted as conduits for magma chamber replenishment and imply open system behaviour during pluton construction textural relations are also consistent with an open system cumulate origin typically centimetre scale grains of quartz plagioclase and megacrystic alkali feldspar form a touching framework with interstices filled with smaller biotite flakes and smaller intercumulus quartz and feldspar crystals alkali feldspar megacrysts vary from euhedral and unzoned to mantled and partially replaced by plagioclase to ovoid and completely pseudomorphed by quartz albite aggregates the common occurrence of mantled and pseudomorphed alkali feldspar in mafic enclaves and in hybrid tonalitic rocks forming the matrix to enclave swarms suggests that replacement or resorption of granitic primocrysts was associated with mafic replenishments the occurrence of all megacryst types at outcrop scale implies extended alkali feldspar crystallization in different parts of the chamber thorough stirring during or after periodic replenishment and final settling in a cumulate mush the bulk composition of the cumulate mush represented by granodiorite cannot represent the emplaced magma compositional variation can be modelled by variable degrees of crystal accumulation from a parental silica rich melt represented by the silicic dykes as dykes periodically fed the magma chamber crystals accumulated on the floor and more evolved melts probably erupted from its roof thus the average composition of the magma and the cumulus minerals may have remained relatively constant and the sublinear chemical trends that typify the kameruka suite simply reflect differing proportions of melt and cumulate material sublinear chemical trends can also be explained by a restite model however the distinctive ba light rare earth element and zr spikes at high silica can be explained only by a cumulate model which also explains why the low silica granites of the suite share the same chemical characteristics as the high silica granites

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

flexural eustatic numerical model for drowning of the eocene perialpine carbonate ramp and implications for alpine geodynamics the paleocene2eocene nummulitic limestone formation of the alpine periphery occupies the lowermost part of a stratigraphic trinity above a major basal unconformity it is thought to have accumulated as a foraminiferal carbonate ramp at the distal featheredge of the underfilled north alpine and southwest alpine foreland basin we present the results of a numerical model that links carbonate sedimentation at the distal featheredge of a peripheral foreland basin to the flexural subsidence of an elastic plate subjected to a distributed load with a superimposed eustatic sea level history carbonate accumulation is treated as depth dependent model parameters are constrained by geological and geophysical observations of the alpine orogen and its peripheral foreland basin and from literature on the ecology of benthic foraminifers the generic alpine model shows that the carbonate ramp accumulates as a number of sedimentary cycles before rapid drowning giving rise to a retrogradational stratigraphic package terminated by a surface of accelerated transgression and backstepping running the model with sets of parameter values appropriate to the paleocene to middle eocene nummulitic limestone in central eastern switzerland and the late eocene nummulitic limestone

mantle temperature as a control on the time scale of thermal evolution of extensional basins abstract extension of the lithosphere the thermo mechanical boundary layer above the convecting mantle is followed by cooling and subsidence the timescale of oceanic basin subsidence is 100 myr whereas basins of the continental interior often subside continuously for more than 200 myr after rifting using numerical modelling we show how these diverse rifting scenarios are unified when accounting for varying mantle potential temperature at a temperature of 1300 c cooling is plate like with nearly exponential subsidence as observed in oceanic basins at 1200 c subsidence is almost linear and continues for more than 800 myr the longevity of basin subsidence in the continental interior can therefore be explained by variation of mantle temperature an additional cause of the longevity of subsidence is related to the equilibrium thickness of the lithosphere which is increased by the local reduction of heat producing elements due to crustal thinning consequently the thermally mature lithosphere of an extensional basin can be thicker than the surrounding lithosphere this mechanism contributes to additional thermal subsidence compared to the case where the base of the lithosphere is assumed held at a constant depth

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

multistage magma mingling and the origin of flow banding in the aliso lava dome tumacacori mountains southern arizona flow banded rocks of the middle tertiary aliso lava dome in the tumacacori mountains of southern arizona contain light colored dacitic flow bands dark colored rhyolitic flow bands and dark colored ellipsoidal enclaves of rhyolite groundmass glass of the light and dark colored flow bands is trachyte and high silica rhyolite respectively enclaves are fine grained holocrystalline and phenocryst poor a two stage sequence of mixing and mingling of discrete magmas can account for the compositional and textural characteristics of the aliso rocks 1 enclave magma mixed with dark band magma and 2 the enclave dark band magma composite mingled with alkalic trachyte magma now represented by the light bands both mingling events may have happened in the magma chamber or partially in the magma chamber and partially in the volcanic conduit deformation of the magmas and the development of flow bands are likely to have occurred in the conduit during flow the highly crystalline enclave magma was slightly stretched and deformed contaminating the dark band magma the dark band magma deformed into thin bands decoupling in some instances from the rhyolitic enclaves which it hosted enclaves and phenocrysts from the dark band magma were locally captured by the light band magma calculations of viscosities of the three magmas across fanges of equilibration temperature strain rate water concentration and crystallinity indicate that magma viscosities are more strongly affected by water concentration and crystal abundance than by temperature or strain rate

a semi quantitative method for the reconstruction of eustatic sea level history from seismic profiles and its application to the southern south china sea abstract a quantitative model is proposed to estimate the magnitude of eustatic sea level fluctuations on the basis of definitions of relative and eustatic sea level in this model factors such as erosion sedimentation compaction basement tectonic and loading subsidence and paleo bathymetry are considered to estimate incremental changes in eustatic sea level we developed methods to solve for the variables involved in the model on the basis of interpretation of seismic profiles we reconstructed the onlap offlap points removed by erosion by fitting the effective thickness in areas without erosion with a piecewise defined function and extrapolating this function to zero thickness we used decompaction and backstripping algorithms to remove the effect of compaction and to calculate loading subsidence of the basement regional data however are needed to estimate the paleo water depths and the tectonic subsidence for this reason our methodology is considered semi qualitative as an application of this model an eustatic sea level curve since the pliocene 5 33 my was deduced from interpretation of our high resolution seismic data from the northern sunda shelf south china sea scs on this curve 36 fourth order sea level cycles were recognized with periods ranging from 0 08 to 0 29 my the curve matches well with the smoothed deep sea stable oxygen isotope curves from benthic foraminifera

sediment supply systems of the champion delta of nw borneo implications for deepwater reservoir sandstones abstract middle miocene to pliocene sedimentation on the nw borneo margin has been interpreted as the product of one relatively large deltaic system the champion delta however several lines of evidence indicate that the champion system was not a simple large delta its drainage basin was too small fluvial outcrops indicate multiple relatively small rivers and outcrop studies indicate the same facies associations as the diverse modern depositional systems the number and location of rivers reaching the shoreline changed as rapidly subsiding footwall synclines episodically active inversion anticlines and growth faults created an evolving structurally generated topography that not only controlled drainage pathways but also segregated champion strata into thick wave dominant and tide dominant successions although the principal rivers within the champion system the limbang padas and trusan rivers transport significant loads of coarse sediment the intermittent proximal ponding of sand in local basins as is currently occurring in brunei bay resulted in a variable delivery of sand to the shelf edge the number and distribution of shelf edge canyons also changed with time consequently the spatial and temporal distribution of deepwater sand accumulations sourced from the champion system are not solely related to relative sea level fluctuations such accumulations should be smaller and more scattered than those sourced from a large shelf edge delta because the catchments of the champion system s principal rivers represent different provenances the system s deepwater sands may carry the signal of specific rivers for example mineralogical contrasts between in the main reservoir sands of the deepwater gumusut and kikeh fields suggest that the relative contributions of the principal rivers shifted with time with the trusan and limbang rivers dominating sand supply for the youngest reservoirs at gumusut

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

provenance of igneous clasts in conglomerates of the archaean timiskaming group kirkland lake area abitibi greenstone belt canada four types of igneous clasts from timiskaming conglomerates of the kirkland lake area are identified calc alkaline porphyry trachyte k2o n2o 7 25 wt trondhjemite and tholeiitic basalt clasts derived from quartz carbonate veins and carbonatized porphyries and komatiites indicate co2 rich hydrothermal activity along the larder lake cadillac fault before sedimentation calc alkaline porphyry the predominant clast is similar in appearance to feldspar porphyry intrusions widely exposed in the area but the two are not related the porphyry clasts are cogenetic with diorite granodiorite intrusions and volcanic rocks of the greenstone belt andesite clasts are only observed near the base of the assemblage and the ratio of basalt to andesite increases up stratigraphic sections the change suggests progressive erosion of arc related volcanic rocks during sedimentation composition texture and mineralogy of the trondhjemite clasts are consistent with their derivation from the marginal phases of

mineralogy and geochemistry of microgranular enclaves in palaeoproterozoic malanjkhand granitoids central india evidence of magma mixing mingling and chemical equilibration palaeoproterozoic ca 2 480 ma felsic magmatism of malanjkhand region of central indian precambrian shield referred to as malanjkhand granitoids mg contain xenoliths of country rocks and mesocratic to melanocratic fine grained porphyritic microgranular enclaves me the shape of me is spheroidal ellipsoidal discoidal elongated and lenticular varying in size from a few centimeters to about 2 m across the contact of me with the host mg is commonly sharp crenulate and occasionally diffuse which we attribute to the undercooling and disaggregation of me globules within the cooler host mg the me as well as mg show hypidiomorphic texture with common mineral hbl bt kfs pl qtz assemblage but differ in modal proportions the variation in minerals composition presence of apatite needles elongated biotites resorbed plagiclase ocellar quartz and other mafic felsic xenocrysts strongly oppose the restite and cognate origins of me compositions of plagioclases an3 an29 amphiboles mg mg fe2 0 55 0 69 and biotites mg mg fe2 0 46 0 60 of me are slightly distinct or similar to those of mg which suggest partial to complete equilibration during mafic felsic magma interactions al in amphibole estimates the mg pluton emplacement at ca 3 4 0 5 kbar and therefore magma mixing and mingling must have occurred at or below this level the hbox fe rightleftharpoons hbox mg substitution in biotites of me and mg largely suggests subduction related calc alkaline metaluminous i type nature of felsic melts most major and trace elements against sio2 produce near linear variation trends for me and mg probably generated by the mixing of mafic and felsic magmas in various proportions trace including rare earth elements patterns of me mg pairs however show partial to complete equilibration most likely governed by different degrees of elemental diffusion the available evidence supports the model of me origin that coeval mafic enclave and felsic mg magmas produced a hybrid me magma layer which injected into cooler partly crystalline mg and dispersed mingled and undercooled as me globules in a convectively dynamic magma chamber

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

outer forearc high control in an erosional subduction regime the case of the central peruvian forearc 6 10 s abstract the forearc of the north central peruvian andes fncpa 6 10 s provides an exceptional opportunity to study the long term processes that affect a convergent plate boundary first it shows long term subsidence depocenter superimposition and individualization second although being mostly extensional and characterized as a typical erosive margin the fncpa shows complex uplifted regions older deformation is expressed by basement horst and grabens disposed in a complex geometry which onset may have resulted from strike slip tectonics a long lived episode of regional subsidence affected the forearc and led to the relatively thick and regional deposition of the lower miocene series coeval with a significant increase of the convergence velocity this period was followed by an episodic uplift of trench parallel corridors along the so called main deformation zone uplift ceased through the late miocene and restarted during pliocene and quaternary generating accommodation space by basin flank uplift for a forearc depocenter characterized by landward tilted strata significant along strike differences in the degree of uplift resulted in either uplifting series producing sharp seaward dipping erosional surfaces or less uplifted areas covered by seawards prograding clinoforms as a consequence of the shallow water marine setting the seismic strata geometry lateral extent and thickness of the deposits for the neogene successions in the fncpa have been also tightly controlled by accommodation changes uplift is uneven along strike independently of fault direction and closely followed the increase of the subsidence of the continental slope produced by subduction erosion therefore sediment underplating seems the most appropriate mechanism at the origin of uplift as observed in other parts of the peruvian and chilean margins although the erosive character of the margin the effects on basin geometry of the raised zone resemble that of typical outer forearc highs in accretionary margins such as in the kumano basin in japan

igneous and metamorphic enclaves in the s type deddick granodiorite lachlan fold belt se australia petrographic geochemical and nd sr isotopic evidence for crustal melting and magma mixing the deddick granodiorite a mafic s type pluton in the lachlan introduction fold belt contains abundant enclaves most are derived from enclaves in granites and volcanic rocks can provide high grade metasediments of pelitic psammitic composition and petrogenetic information not readily available from their migmatites are common among these discrete fragments of host rocks didier 1973 didier barbarin 1991 for melanosomes rich in cordierite and garnet are restites from partial example metasedimentary enclaves can place constraints melting however compositional and nd sr isotopic data indicate on the age composition and deformational history of they are not restite in equilibrium with the melt component of the magma source regions within continental crust fleming host magma but may have formed part of a spectrum of diverse 1991 steele et al 1991 enclaves formed by acmagma source lithologies alternatively they may be accidental cumulation of early phenocrysts autoliths document xenoliths regardless of their origin data for these enclaves suggest the early evolution of the host magma whereas others their precursors could represent deeply buried age equivalents of the may represent commingled magmas and illustrate the ubiquitous ordovician turbidites of the lachlan fold belt three possible role of hybridization didier 1987 types of microgranular enclaves with igneous textures are disenclave suites in the relatively mafic s type granitoids tinguished the most common type are small and rounded mafic of se australia are often diverse including abundant enclaves of tonalitic composition they carry xenocrysts derived from enclaves of metasedimentary origin and microgranular the host magma and some contain high mg pyroxene derived from enclaves phillips et al 1981 price 1983 chen et al a mafic magma isotopic data form an array with end from 6 to 1989 wyborn et al 1991 the metasedimentary en 12 and sr sr from 0 7130 to 0 7167 host rock 10 and claves are lithologically diverse including gneissic 0 715 respectively these enclaves formed as globules of hybrid migmatitic types and biotite rich surmicaceous types mafic magma commingled with and contaminated by the more apart from their potential as indicators of crustal structure felsic host magma other enclave types were derived from disrupted and composition they are of interest as possible fragments syn plutonic dykes having a distinct isotopic composition and from of source material and or refractory residue from which a cogenetic marginal facies of the host peraluminous melts were generated and extracted by

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

episodic intraplate deformation of stable continental margins evidence from late neogene and quaternary marine terraces cape liptrap southeastern australia the waratah fault is a northeast trending high angle reverse fault in the late paleozoic lachlan fold belt at cape liptrap on the southeastern australian coast it is susceptible to reactivation in the modern intraplate stress field in southeast australia and exhibits late pliocene to late pleistocene reactivation radiocarbon optically stimulated luminescence osl and cosmogenic radionuclide crn dating of marine terraces on cape liptrap are used to constrain rates of displacement across the reactivated waratah fault six marine terraces numbered qt6 tt1 youngest to oldest are well developed at cape liptrap with altitudes ranging from 1 5 m to 170 m amsl respectively on the lowest terrace qt6 barnacles in wave cut notches 1 5 m amsl yielded a radiocarbon age of 6090 5880 cal bp and reflect the local mid holocene sea level highstand qt5 yielded four osl ages from scattered locations around the cape ranging from 80 ka to 130 ka it formed during the last interglacial sea level highstand mis 5e at 125 ka inner edge elevations approximate paleo high tide line for qt5 occur at distinctly different elevations on opposite sides of the waratah fault offsets of the inner edges across the fault range from 1 3 m to 5 1 m with displacement rates ranging from 0 01 mm a to 0 04 mm a the most extensive terrace tt4 yielded four early pleistocene cosmogenic radionuclide crn ages two apparent burial ages of 0 858 ma 0 16 ma and 1 25 ma 0 265 ma and two apparent exposure ages of 1 071 ma 0 071 ma 10be and 0 798 ma 0 066 ma 26al allowing for muonic production effects from insufficient burial depths the depth corrected crn burial ages are 1 8 ma 0 56 ma and 2 52 ma 0 88 ma or late pliocene a late pliocene age is our preferred age offsets of tt4 across the waratah fault range from a minimum of 20 m for terrace surface treads to a maximum of 70 m for terrace bedrock straths calculated displacement rates for tt4 range from 0 01 mm a to 0 04 mm a using a late pliocene age 2 ma identical to the rates calculated for the last interglacial terrace qt5 this indicates that deformation at cape liptrap has been ongoing at similar time averaged rates at least since the late pliocene the upper terraces in the sequence tt3 110 m amsl tt2 140 m and tt1 180 m are undated but most likely correlate to sea level highstands in the neogene terraces tt1 tt4 show an increasing northward tilt with age the waratah fault forms a prominent structural boundary in the lachlan fold belt discernible from airborne magnetic and bouger gravity anomalies seismicity and deformation are episodic episodic movement on the waratah fault may be coincident with sea level highstands since the late pliocene possibly from increased loading and elevated pore pressure within the fault zone this suggests that intervals between major seismic events could be on the order of 100 ka

paleobiogeography of miocene equinae of north america a phylogenetic biogeographic analysis of the relative roles of climate vicariance and dispersal article i nfo the horse subfamily equinae underwent a major radiation during the miocene in north america diversifying from one species parahippus leonensis to 70 species this radiation has been linked to climatic and vegetation changes that occurred in north america during this time however the relationship between climate change and speciation has not previously been studied quantitatively using phylogenetic biogeography distribution and age range data were collected for all north american species within eighteen equine genera through a literature review and use of the paleobiology database fitch parsimony analysis of the taxon area cladogram indicate that speciation by dispersal allopatry model ii was more common in the evolution of the clade than speciation by vicariance allopatry model i distribution data were analyzed using the lieberman modified brooks parsimony analysis lbpa to determine patterns of vicariance and geodispersal using four constrained biogeographic regions within north america in the analysis the great plains the southwest the gulf coast and the southeast resulting general area cladograms are congruent with geological events such as uplift of the rocky mountains and climatic conditions such as the change from a warm and moist to cool and arid climate during the miocene well supported vicariance and geodispersal trees derived from the lbpa analysis are largely congruent with each other indicating that cyclical events in particular climate change during the miocene influenced the radiation of the clade

cenozoic evolution of sediment accumulation in deltaic and shore zone depositional systems northern gulf of mexico basin abstract paleogeographic and volumetric lithofacies mapping of 18 cenozoic genetic sequences within the northern gulf of mexico basin quantifies the proportional sequestering of sediment within wave dominated shore zone vs deltaic systems through time three long term depositional phases are revealed by plots based on paleogeographic and sediment isochore maps of total shore zone system area and volume to total delta system area and volume sz d 1 sz d area and volume ratios are highly variable in paleocene through eocene sequences however typical volume ratios for major genetic sequences upper middle and lower wilcox queen city qc and yegua range between 0 2 and 0 6 minor sequences sparta sp jackson js which record very low rates and volumes of sediment accumulation have the greatest variability in their ratios 2 oligocene and miocene sequences display consistently high proportions of shore zone sediment sz d area ratios range from 0 6 to 1 0 and volume ratios cluster between 0 4 and 0 8 3 a substantial late neogene decrease in sz d ratios is presaged in the late miocene sequence pliocene and pleistocene sequences are uniformly characterized by very low ratios of

development of igneous layering during growth of pluton the tarcouate laccolith morocco abstract we discuss the significance of igneous layering with respect to pluton growth processes the case study is the tarcouate laccolith morocco whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves contrasting with peripheral non layered biotite granodiorites with low amount of enclaves rhythmic layering with modal grading cross stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves its steep dips 45 result from tilting that occurred above solidus conditions as indicated by sub vertical and synmagmatic granite aplite and monzodiorite dykes cutting across the layering the systematic association of igneous layering with mafic enclaves in calc alkaline plutons suggests that layering originates from recurrent injection of mafic magma viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the tarcouate laccolith intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection formation of mafic enclaves and development of igneous layering through protracted crystallization

progressive hybridisation between late devonian mafic intermediate and felsic magmas in the meguma zone of nova scotia canada two felsic plutons of late devonian 385 370 ma age in the meguma zone of southwestern nova scotia contain three circa 376 ma synplutonic mafic intermediate intrusions that collectively record progressive stages of in situ hybridisation a 5 m wide spessartite dyke in the port mouton pluton probably underwent rapid cooling and crystallisation immediately after intrusion which heated and coarsened the adjacent tonalite an 85 m long sheet of pillowed kersantite also in tonalite of the port mouton pluton presumably contained residual magma after quenching and obtained k p ba rb more radiogenic sr zr nb and light ree from the tonalite during magma mingling the third synplutonic body a 100 m wide diorite sheet intrudes granodiorite of the adjacent shelburne pluton and has a circa 45 m wide gradational contact of metaluminous hornblende tonalite this tonalite dominantly records magma mixing by the transfer of ti mg fe ca and v in hornblende biotite plagioclase and at least in part apatite xenocrysts derived from dioritic pillows that were originally disaggregated in the granodiorite probably in response to convection scattered data points unusual concave down variation trends for al2o3 p2o5 and sr and non hyperbolic sr nd isotopic characteristics in the tonalite apparently reflect syn or post mixing fractionation and accumulation of xenocrysts from residual magma phosphorus may have assisted diffusion of sr zr nb and light ree and caused premature quenching of the hybrids at mcleods cove and birchtown during magma mingling and mixing

geochemistry and u pb shrimp zircon chronology of granitoids and microgranular enclaves from jhirgadandi pluton of mahakoshal belt central india tectonic zone india abstract the northern part of central india tectonic zone citz is delineated by an arc shaped supracrustal belt commonly referred to as mahakoshal belt which is considered as a product of intense rifting of sialic crust that occurred at ca 2400 2600 ma several granitoid plutons intrude the parsoi formation of mahakoshal belt among these an elliptical small stock like granitoid body trending e w is exposed in and around jhirgadandi region of mahakoshal belt referred herein as jhirgadandi pluton it is composed of minor amount of mafic rocks diorite and predominant granitoids country rock pelitic xenoliths and microgranular enclaves me are commonly hosted in granitoids but are absent in diorite the me exhibit typical magmatic texture with a bt cpx hbl pl kf qtz mag ap assemblage similar to that in host granitoids but with contrasting mineral proportions whole rock molar al 2 o 3 cao na 2 o k 2 o a cnk ratios of diorite 0 63 0 72 me 0 69 1 21 and granitoids 0 83 1 05 suggest their nature largely metaluminous i type to rarely peraluminous s type granitoids on most binary plots involving silica two distinct compositional paths can be recognized one formed by an array of differentiating diorite and me and another by fractionating granitoids gradually depleting in compatible elements it is most likely that me were generated by progressive and concurrent mixing of coeval pristine mafic diorite and granitoid magmas and fractionation processes however coherent and identical trace elements except for sr th y and ni and ree patterns for me granitoid pairs most likely suggest partial to near complete chemical equilibration through varying degrees of diffusion process across the me partly crystalline host granitoid boundary high precision u pb shrimp zircon 206 pb 238 u ages for me 1758 19 ma and host granitoid 1753 9 1 ma from jhirgadandi pluton further support the notion that they were coeval the obtained age 1750 ma of jhirgadandi pluton also points to the existence and role of super columbian continental component in the evolution of mahakoshal belt of the citz

plagioclase xenocrysts and mafic magmatic enclaves in some granitoids of the sierra nevada batholith california plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts an oscillatory locally patchy zoned andesine or more calcic core a ring with dusty calcic plagioclase and a normally zoned rim of sodic plagioclase although aspect of the calcic rings and width and zoning of the rims may slightly vary from the enclaves to the hosts cores of both phenocrysts and large plagioclase crystals show similar zoning and composition the andesine or more calcic cores are interpreted to have crystallized in the felsic or the mafic magma respectively and been incorporated into the coeval magma when the two magmas mixed introduction of the xenocrystic cores into a magma where they were not in equilibrium resulted in partial dissolution development of abundant patchy zoning and coating with dusty calcic plagioclase in both granitoids and mafic magmatic enclaves composition and zoning contrast between cores and rims of the plagioclase crystals reflect drastic changes in conditions of crystallization before and after the mechanical mixing event mixing of two magmas with contrasted compositions is suggested to be the major mechanism for generating complexly zoned plagioclase xenocrysts in granitoids and mafic magmatic enclaves this hypothesis is consistent with many recent models in which mixing of two contrasting components is proposed to play a fundamental part in the generation of calc alkaline granitoids and mafic magmatic enclaves of the sierra nevada batholith plagioclase xenocrysts may also provide information on the timing of the different mixing processes and on the magmatic evolution of the plutons

origin of minette by mixing of lamproite and dacite magmas in veliki majdan serbia composite dykes consisting of leucominette and dacite as well as discrete dykes and flows of minette and lamproite composition occur in the veliki majdan area western serbia this area is part of the serbian tertiary magmatic province which consists of numerous small occurrences of ultrapotassic igneous rocks the composite dykes have leucominette margins up to 150cm thick enclosing a central part of dacite up to 100m in width between these two lithologies a decimetre sized transition zone may occur petrography mineral chemistry and bulk rock geochemistry including sr nd and pb isotopes provide evidence that the minettes and leucominettes formed by hybridization between a felsic magma similar in composition to dacite and a mantle derived lamproitic magma the leucominettes and minettes contain all phenocryst types biotite plagioclase quartz present in the dacites but in partly resorbed and reacted form the mica displays a great diversity of resorption textures as a result of partial dissolution incipient melting and phlogopitization suggesting superheating of the felsic melt during hybridization the mineral modes and mineral compositions of the leucominettes and minettes resemble those in the lamproites a model for the modification of lamproite melt towards minette is presented in which minette is formed by mixing of lamproite and530 felsic magma the lack of any significant correlation between pb isotopic ratios and some of the mixing indices sio2 zr zr nb 143 nd 144 ndi recognized in the hybridization model for the veliki majdan dykes may be a result of similarity of the pb isotopic signature in the two end members highly phlogopitized biotite xenocrysts in the minettes are ascribed to the retention of volatile components after magma mixing and crystallization of a new generation of phlogopite from the hybridized magma the magma mixing model explains the reverse zoning and resorption features of phlogopite macrocrysts commonly recognized in calcalkaline lamprophyres elsewhere therefore this mixing mechanism may be globally applicable for the origin of minettes associated with calcalkaline granitic plutonism in postorogenic settings

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

on the origin of cenozoic and mesozoic third order eustatic sequences abstract the origin of third order eustatic sequences is reviewed by comparing recent sequence stratigraphic data to the latest best constrained astronomical model middle eocene to holocene icehouse sequences correspond to 1 2 myr obliquity cycles constraints from oxygen isotope records highlight the link between icehouse sea level lowerings sequence boundaries and 1 2 myr obliquity nodes mesozoic greenhouse sequences show some relation with the 2 4 myr eccentricity cycles suggesting that orbital forcing contribute to sea level change we suggest that during the icehouse large ice sheets associated with significant glacioeustatic changes 25 m up to 120 m changes were mainly governed by obliquity forcing during icehouse worlds obliquity forcing was the stongest control on global sea level and depositional sequences additionally during the middle eocene third order sequences were glacioeustatically driven in tune with 1 2 myr obliquity cycle suggesting that the presence of significant ice sheets is earlier than previously supposed i e early eocene in contrast during greenhouse worlds e g ephemeral small to medium sized or no ice sheets 0 25 m glacioeustatic changes the expression of obliquity in the sedimentary record is weak and intermittent instead the eccentricity signature which is the modulator of climatic precession is documented moreover we presume that greenhouse sequences on the myr scale are global and hence cannot be caused by regional tectonism e g intraplate stress or mantle hot blobs instead the eccentricity link implies a weaker glacioeustatic control because thermoeustasy is too small to explain the sea level changes stratigraphically well documented fourth order sequences may be linked to the astronomically stable strongest amplitude 405 kyr eccentricity cycle and possibly to 160 200 kyr obliquity modulation cycles fifth order sequences to the short 100 kyr eccentricity cycles and finally sixth order sequences to the fundamental obliquity 40 kyr and climatic precession 20 kyr cycles these astronomical cycles could be preserved in the sedimentary record and have been demonstrated to control sea level changes accordingly by placing depositional sequence orders into a high resolution temporal framework i e orbital periodicities standardization of eustatic sequence hierarchy may be possible

shallow burial dolomitisation of middle upper permian paleosols in an extensional tectonic context se iberian basin spain controls on temperature of precipitation and source of fluids this work is focused on carbonate paleosols developed in three stratigraphic sections landete talayuelas and henarejos of themiddle late permian alcotas formation in the se iberian basin the alcotas formation of alluvial origin was deposited in semi connected half grabens developed during the early stages of the permian triassic rifting stage that affected the iberian basin the studied sections were located in two of these half grabens the henarejos section being much closer to the basin boundary fault than the other two sections the mineralogy and texture of the carbonate precursor of paleosols in the three studied sections are not preserved because original carbonate is replaced by coarse crystals of dolomite and or magnesite dolomite crystals are typically euhedral displaying rhombohedral shapes and reddish luminescence although in the henarejos section dolomite displays non planar boundaries and frequently saddle habit micas are deformed and adapted to dolomite crystals which in turn are affected by stylolites suggesting that dolomite precipitated before mechanical and chemical compaction carbon and oxygen isotopic compositions of dolomite fromthe three sections showdifferent values 13cvpdb mean values 6 7 5 5 and 7 5 18ovpdb mean values 4 0 5 6 and 8 2 at landete talayuelas and henarejos sections respectively the 87sr 86sr ratios are similar in the three sections yielding values between 0 71391 and 0 72213 the petrographic and geochemical features of dolomite in the three studied sections suggest precipitation fromsimilar fluids and during shallow burial diagenesis assuming that theminimum temperature for dolomite precipitation in the henarejos sectionwas 60 c as suggested by the presence of non planar saddle habit and that the dolomitizing fluid had similar 18o values at the three localities then dolomite in the talayuelas and landete sections precipitated at temperatures around 16 and 25 c cooler respectively in addition the 18ovsmow values of the water from which dolomite precipitated would have ranged between 0 3 and 2 9 dolomite is partially or totally replaced by non to dark dull luminescent magnesite in the landete and talayuelas sections magnesite crystals are affected by stylolites indicating that it precipitated before chemical compaction the 13c mean values are 6 5 and 6 0 and the 18ovpdb mean values are 6 7 and 7 8 in the landete and talayuelas sections respectively the 87sr 86sr ratios of magnesite are similar in both sections yielding values between 0 71258 and 0 72508 this suggests that they probably precipitated from similar fluids during progressive burial and at higher temperatures than dolomites at the same sections assuming thatmagnesite precipitated froma fluid with similar 18o values in both sections then it had to precipitate at a temperature around 8 c higher in talayuelas than in the landete section dolomitisation and magnesite precipitation probably occurred via reflux of saline to hypersaline brines from the overlying mid late triassic muschelkalk and or keuper facies the temperatures inferred for dolomite precipitation however are too high for shallow burial if a normal geothermal gradient is applied thus it can be inferred that salinefluidswere heated as theyflowed through the syn sedimentary extensional faults that controlledmiddle permian to middle triassic sedimentation consequently fluidswould have been at higher temperatures near the henarejos area which was closer to the basin boundary fault than at the talayuelas and landete areas whichwere situated further away this contention is in agreement with recent studies which demonstrate that an important thermal event took place during late triassic early jurassic times in the iberian peninsula

late neogene recent uplift of the cabo de gata volcanic province almeria se spain abstract cabo de gata is a miocene volcanic province in the betic cordillera in southeastern spain the distribution of coastal deposits in the successive marine sedimentary units overlying the last volcanic episode about 7 5 ma old has been used to reconstruct the post volcanic palaeogeographic evolution of the region during the late neogene the current elevation of well dated shoreline marker rocks has been used to estimate uplift amount and rates since the late tortonian a n45 e aligned the strike of the carboneras fault system topographic relief was emergent in the cabo de gata region the extension and height of this island increased throughout the late neogene smaller independent islands were emergent and finally became connected to the main island during the messinian the carboneras and agua amarga pliocene sub basins were the last two marine basins prior to the final emergence of the region since the last volcanic eruption ca 7 5 ma maximum uplift of sedimentary rocks in cabo de gata has taken place on the western margin of the n45 e aligned palaeorelief the altitude of the shoreline marker rocks in the successive sedimentary units decreases eastwards to the present day coast and northwards of the rambla del plomo uplift rates since deposition remain nearly constant for the successive messinian rocks and decrease slightly for the lower pliocene outcrops most of the uplift took place before the pliocene while the main island enlarged uplift amounts and rates since deposition of the upper neogene sedimentary units in the cabo de gata area are similar to the ones estimated for laterally equivalent units in the eastern betic basins approximately 50 m ma despite its volcanic nature and the occurrence of the carboneras fault system the cabo de gata probably became elevated as a consequence of regional uplift in connection with the rest of the betic cordillera

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

integrated stratigraphic studies of paleocene lowermost eocene sequences new jersey coastal plain evidence for glacioeustatic control 1 we describe seven paleocene to lowermost eocene sequences in core holes at island beach bass river ancora millville and sea girt nj ocean drilling program leg 150x 174ax and analyze benthic foraminiferal assemblages to assess paleodepth changes within sequences these sequences are referred to as pa0 pa1a pa1b pa2a pa2b pa3a and pa3b paleocene sequence boundaries are identified by unconformities and variations in benthic foraminiferal biofacies we used q mode factor analysis and paleoslope modeling to identify three distinct middle outer neritic benthic foraminiferal assemblages and their associated water depths paleodepths during the early paleocene and deposition of pa0 pa1a and pa2b were 80 m with 20 m changes across sequence boundaries a long term shallowing occurred through the late paleocene where paleodepths were 50 70 m in pa3a this trend drastically changes in the earliest eocene where the paleodepths of sequence pa3b were 120 150 m new jersey paleocene sequence boundaries correlate with those in other regions and with 18o increases in the deep sea suggesting paleocene eustatic lowerings were associated with ice growth events

cenozoic range front faulting and development of the transantarctic mountains near cape surprise antarctica thermochronologic and geomorphologic constraints 1 the transantarctic mountains tam define the western flank of the west antarctic rift system cape surprise near the shackleton glacier in the central tam is the only location along the range s 3500 km length where upper paleozoic beacon supergroup strata are down faulted to near sea level previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the tam front in this region the history of rock uplift is debated suggested as early as mesozoic typically cenozoic or even pliocene or younger structural observations apatite fission track aft thermochronology and geomorphologic mapping undertaken within the tam front east of the shackleton glacier indicate extension faulting and denudation was mostly late eocene late oligocene and likely into the early miocene an exhumed aft partial annealing zone is found at the coast and traced 50 km inland the base of that exhumed partial annealing zone indicates denudation accelerated at 40 ma near the coast and at 30 35 ma on the inland side of the tam front vertically offset aft isochrones across the tam front reveal a step faulted architecture rather than a single master fault the cumulative vertical offset of the 55 ma isochrone is 2 3 2 7 km compared to 2 4 2 6 km offset of beacon strata indicating that all significant normal faulting is cenozoic and not related to mesozoic extension within the west antarctic rift system denudation from 26 ma to 14 ma produced a locally preserved erosion surface within the tam front erosion surface remnants indicate the tam front has undergone minimal internal deformation and only 290 790 m of surface uplift along offshore faults since the middle miocene

high temperature fracturing and ductile deformation during cooling of a pluton the lake edison granodiorite sierra nevada batholith california abstract in the bear creek area of the sierra nevada batholith california the high temperature postmagmatic deformation structures of the lake edison granodiorite include steeply dipping orthogneiss foliations joints and ductile shear zones that nucleated on joints and leucocratic dykes exploitation of segmented joints resulted in sharply bounded thin shear zones and in large slip gradients near the shear zone tips causing the deformation of the host rock at contractional domains the orthogneiss foliation intensifies towards the contact with the younger mono creek granite and locally defines the dextral rosy finch shear zone rfsz a major kilometre wide zone crosscutting the pluton contacts joints predominantly strike at n70 90 e over most of the lake edison pluton and are exploited as sinistral shear zones both within and outside the rfsz in a narrow 250 m thick zone at the contact with the younger mono creek granite within the rfsz the lake edison granodiorite includes different sets of dextral and sinistral shear zones joints the latter corresponding to the set that dominates over the rest of the lake edison pluton these shear zones joints potentially fit with a composite y r r shear fracture pattern associated with the rfsz or with a pattern consisting of y r shear fractures and rotated t mode i extensional fractures the mineral assemblage of shear zones and the microstructure and texture of quartz mylonites indicate that ductile deformation occurred above 500 c joints and ductile shearing alternated and developed coevally the existing kinematic models do not fully capture the structural complexity of the area or the spatial distribution of the deformation and magmatic structures future models should account more completely for the character of ductile and brittle deformation as these plutons were emplaced and cooled

magmatic structures in the krkonose jizera plutonic complex bohemian massif evidence for localized multiphase flow and small scale thermal mechanical instabilities in a granitic magma chamber abstract the present paper examines magmatic structures in the jizera and liberec granites of the krkonose jizera plutonic complex bohemian massif the magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal rich mushes and to capture the evolution of physical processes in an ancient granitic magma chamber we propose that after chamber wide mixing and hybridization as suggested by recent petrological studies laminar magma flow became highly localized to weaker channel like domains within the higher strength crystal framework mafic schlieren formed at flow rims and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure after the cessation or deceleration of channel flow gravity driven processes settling of crystals and enclaves gravitational differentiation development of downward dripping instabilities accompanied by compaction filter pressing and melt segregation dominated in the crystal mush within the flow channels subsequently magmatic folds developed in schlieren layers and the magma chamber recorded complex late magmatic strains at high magma crystallinities late stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization we emphasize that the most favorable environments for the formation and preservation of magmatic structures such as those hosted in the jizera and liberec granites are slowly cooling crystal rich mushes therefore where preserved in plutons these structures may lend strong support for a mush model of magmatic systems

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

relationships between calc alkaline acidic and basic mantle derived magmas in late archaean composite dykes kambalda goldfield western australia abstract composite dykes from the north dome area kambalda comprise basic spessartite hornblende plagioclase lamprophyre 56 sio 2 with mg numbers cr and ni contents typical of primitive mantle derived rocks and more acidic plagioclase phyric quartz andesite 66 sio 2 together with felsic net veins and hornblendic patches suggesting local differentiation the spessartites can be regarded chemically as volatile lile and incompatible element enriched versions of siliceous high magnesian basalts from the local greenstone sequence a pb pb isochron on one dyke yields an age of 2636 27 ma making this the oldest composite dyke so far dated field and geochemical evidence including identical pb initial ratios for the constituent rock types virtually indistinguishable ree spectra and tight linear trends on plots such as y versus ti and ce cr versus ti cr suggests that the two magmas lamprophyric and acidic were genetically related and were emplaced contemporaneously into the same fracture quantitative least squares modelling of whole rock and mineral compositions suggests that the acidic components resulted mainly from fractionation of hornblende from parental spessartite magmas together with a possible contribution from mixing of the same spessartite magma with crustally derived acidic e g trondjhemitic magma the latter is represented by separate dykes and stocks in the kambalda area close similarities between the kambalda composite dykes and archaean tertiary composite dykes in other parts of the world imply a persistent role for mantle derived magmas such as lamprophyres in the genesis of the dominant intermediate acidic e g granitoid magmas in many calc alkaline provinces

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

back to basics of sequence stratigraphy early miocene and mid cretaceous examples from the new jersey paleoshelf abstract many sequence stratigraphic approaches have used relative sea level curves that are dependent on models or preconceived notions to recognize depositional sequences key stratal surfaces and systems tracts leading to contradictory interpretations here we urge following basic sequence stratigraphic principles independent of sea level curves using seismic terminations facies successions and stacking patterns from well logs and sections and chronostratigraphic data to recognize sequence boundaries other stratal surfaces parasequences and systems tracts we provide examples from the new jersey siliciclastic paleoshelf from the 1 early miocene using academic based chronostratigraphic seismic core downhole and core log data and 2 mid cretaceous using commercial well log seismic and biostratigraphic data we use classic criteria to identify sequence boundaries on seismic profiles by reflection terminations onlap downlap erosional truncation and toplap in cores by surfaces of erosion associated with hiatuses detected using biostratigraphy and sr isotope stratigraphy and changes in stacking patterns and in logs by changes in stacking patterns maximum flooding surfaces mfss are major seismic downlap surfaces associated with changes from retrogradational to progradational parasequence stacking patterns systems tracts are identified by their bounding surfaces and fining generally deepening and coarsening generally shallowing upward trends in cores and well log stacking patterns our miocene examples of sequences m5 4 17 7 16 1 ma and m5 8 20 1 19 2 ma illustrate how basic sequence stratigraphic techniques reveal higher order sequences within myr scale composite sequences our mid cretaceous examples from the new jersey shelf provide a paleoshelf transect spanning the great stone dome to the outer continental shelf to identify parasequences sequences and systems tracts this sequence stratigraphic framework provides insights into myr scale coeval depositional environments across the paleoshelf and reservoir continuity and highlights the application of basic sequence stratigraphic criteria to reservoir scale evaluation not only for oil and gas resources but also for carbon storage

palaeobiogeographic relationships and palaeoenvironmental implications of an earliest oligocene tethyan ichthyofauna from egypt the fayum depression of egypt has produced a great diversity of fossil material including marine and freshwater fishes in contrast to the eocene formations of the fayum the oligocene jbel qatrani formation has been more or less consistently considered to be deposited in a freshwater environment however the ichthyofauna indicates a more complex picture cenozoic fishes have been convincingly used to interpret the palaeoenvironment in which sediments were deposited based on the elasmobranch and osteichthyan faunas of the jbel qatrani formation we interpret that this formation was not deposited entirely in fresh waters but had some marine influence particularly in the lower part of the formation the mixture of freshwater elements such as polypterids and alestids with brackish and marine elements including myliobatid stingrays in the quarry e site suggests a local palaeoenvironment that was very close to the shoreline in a less protected area or under more seasonal influence than the rest of t

long term and short term global cenozoic sea level estimates backstripping analysis of three continuously cored well dated boreholes from the new jersey coastal plain ocean drilling program odp leg 150x indicates a long term 10 8 n10 7 yr eustatic fall of 100 m since 55 ma early eocene and suggests short term 0 5n3 m y eustatic falls of less than 70 m eustatic estimates are calculated from residuals between the decompacted unloaded and paleodepth corrected records and tectonic subsidence assuming a cooling lithospheric plate because the residuals are similar among the three sites we interpret them as an approximation of the eustatic signal

astronomical calibration of the toarcian stage implications for sequence stratigraphy and duration of the early toarcian oae the toarcian oceanic anoxic event t oae of the early jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 ma recorded by a pronounced negative carbon isotope excursion cie numerous studies have focused on potential causes of the t oae and cie but are hampered by an uncertain timescale here we present high resolution 2 kyr magnetic susceptibility ms measurements from the marine marls of the sancerre couy drill core southern paris basin spanning the entire toarcian stage the ms variations document a rich series of sub milankovitch to milankovitch frequencies precession obliquity and eccentricity with the periodic g2 g5 405 kyr and quasi periodic g g 2 4 myr cenozoic mean periodicity eccentricity terms being the most prominent the ms related g g variation reflects third order eustatic sequences and constrains the sequence stratigraphic framework of the toarcian stage in addition ms variations reveal a modulation of g g by g g eccentricity related cycles suggesting that sea level change was the main control on the deposition of the toarcian sancerre marls in tune with the astro climatic frequencies the stable 405 kyr cyclicity constrains a minimum duration of the toarcian stage to 8 3 myr and the well documented cie associated with the t oae to 300 to 500 kyr the 405 kyr ms timescale calibrates the periodicity of the prominent high frequency c cycles that occur in the decreasing part of the cie to 30 to 34 kyr consistent with the toarcian obliquity period predicted for an earth experiencing sustained tidal dissipation

hybridization between felsic and mafic magmas in calc alkaline granitoids a case study in northern sardinia italy abstract two examples of felsic mafic association resulting from a magma mingling mechanism have been studied in carboniferous calc alkaline granitoids from sardinia using mineralogical and geochemical techniques 1 the centimetric to decimetric magmatic mafic enclaves from the reversely zoned tonalitic santa restituta pluton this type of enclave which is common in calc alkaline granitoids represents blobs of mafic magma incorporated into a silicic host magma 2 the osidda mafic complex about one kilometre in diameter enclosed in the benettuti granodiorite this study intends to compare these two types of felsic mafic association in order 1 to clarify the nature of the interaction processes which occurred between the two magmatic components 2 to test the influence of the degree of fragmentation of the mafic component into the felsic matrix on the intensity of such processes the santa restituta enclaves sre and the osidda mafic complex omc exhibit the same general mineral assemblage plagioclase biotite hornblende quartz this assemblage is similar to that of the corresponding host granitoids however the sre and the omc are characterized by a greater abundance of biotite and hornblende the mineralogical study reveals the presence of two types of crystals the first type corresponds to minerals typical of the mafic or the felsic component in the mafic magma they are represented by remnants of an rich plagioclase by hornblende clots presumably pyroxene relicts and by orthopyroxene observed only in one facies of the omc these crystals represent remnants of phenocrysts present in the mafic component prior to the mingling event in the felsic component the first type of crystals is represented by quartz ocelli which are sometimes incorporated in the mafic magma as xenocrysts surrounded by a reaction rim of biotite and hornblende the second type comprises minerals which are found indiscriminantly in both magmatic components and which formed during the mingling event mingling minerals they include plagioclase an52 35 biotite hornblende quartz mineralogical data indicate that thermal equilibrium occurred between the mafic magma and the felsic matrix that equilibration was reached in the sre is shown by the compositional similarity of the mingling minerals of the enclaves and their host rocks however due to a lesser degree of fragmentation thermal equilibration was not reached in the omc geochemical data however do reveal close relationships between the two magmas which appear therefore to have both been hybridized by mutual chemical interaction a chemical comparison between the sre and the omc shows that in both cases the same qualitative interaction mechanisms operated between the host granitoids and either a voluminous mafic body osidda or a highly fragmented mafic component santa restituta enclaves however the intensity of hybridization is minor in the omc as compared with the sre it is suggested that hybridization of the host granitoids involves 1 mass to mass mixing due to disaggregation and dispersal of the mafic magma in the host granitoid resulting from mechanical stirring during the pluton s genesis from the initial meeting of the two magmas to the pluton s final emplacement 2 loss of certain elements si k rb ba li zr p nb ree which migrated towards the mafic magma through diffusion due to compositional gradients fluid transfer as a consequence the composition of the host granitoids is linked to that of their magmatic enclaves the enclaves with the lowest feo tot mgo ratios are enclosed in the least felsic granitoids and vice versa hybridization of the mafic component involves 1 mechanical transfer of crystals quartz from the host granitoid 2 enrichment in numerous elements migrating from the felsic component this is expressed mineralogically by the crystallization of numerous anhedral phases such as quartz sio2 biotite k rb h2o hornblende h2o apatite p and zircon zr 3 loss of ca and sr by the mafic component the nature of the processes of chemical migration are discussed the importance of the continuous renewal of the contact surface between the two components is emphasized the original compositions of the interacting mafic and granitic components become therefore highly modified this phenomenon can probably be generalized to apply to calc alkaline granitoids as a whole which are in fact characterized by the common occurrence of magma mingling

chemical and isotopic evidence for major mass transfer between mafic enclaves and felsic magma abstract in both the strontian and criffell zoned granitoid plutons certain chemical elements notably k rb ca sr and pb display a correlation between their concentration in microdiorite enclaves and their concentration in the immediately enclosing host granitic rock this appears to represent the effects of post incorporation mixing and exchange between the enclave and its host magma enclave initial 87 sr 86 sr ratios are indistinguishable from those of the host while enclave initial 143 nd 144 nd ratios are systematically more radiogenic establishing that these enclaves are not melt segregations nor restite the isotopic data are in agreement with the chemical data in indicating that sr is almost entirely derived from the host despite clear evidence of major mass transfer of alkali metals alkali earths and transition metals a comparison of the concentrations and ratios of hfse and ree and nd isotopic ratios with those of a number of potential starting protoliths allows the enclave precursors to be positively discriminated in this regard enclave hfse and ree compositions may allow for models of granitoid production by the injection of hot mantle derived magmas into the crust to be tested

mixing between granitic and dioritic crystal mushes guernsey channel islands uk abstract the contact zone between the cobo granite and bordeaux diorite complex of guernsey channel islands uk displays numerous features which result from the interaction of these two penecontemporaneously emplaced intermediate to felsic magmas initial interaction resulted in the formation of chilled mafic enclaves in granite magma as thermal equilibrium was approached some physical mixing took place to produce a heterogeneous marginal facies continued interaction resulted in incorporation of previously mixed magma into intruding magma the early mixed material is locally preserved as enclaves but more commonly underwent disaggregation promoted by its incompletely crystallised nature the mineral components becoming distributed as xenocrysts and often as microenclaves or glomeroxenocrysts into surrounding magma further modification within the contact zone was brought about by the infiltration of melt through the interconnected pore space of the magma mushes on the scale of centimetres to hundreds of metres these processes produced geochemical profiles which do not exhibit perfect mixing trends the petrographic and geochemical features described not only demonstrate the efficacy of mixing between partially crystallised magma mushes of broadly similar composition but also provide criteria by which such interaction may be recognised elsewhere many features in particular mineral scale disequilibria and small scale modal heterogeneity bear striking similarities to those which occur widely in granite plutons where obvious evidence for magma mixing is absent as such it is possible that many granite bodies preserve a subtle record of hitherto overlooked mixing events

buried fluvial incisions as a record of middle late miocene eustasy fall on the armorican shelf bay of biscay france high resolution seismic data have been acquired in june 2008 on the armorican shelf as in the northern bay of biscay in order to reassess its stratigraphic architecture in detail and to study the impact of eustasy tectonic and sediment delivery on the margin sedimentary record several profiles show fluvial type incisions of several tens of meters up to 54 m associated to a widespread erosion surface several hypotheses are proposed for the stratigraphic position of this surface and incisions we suggest middle to late miocene age considering the relatively quiescent tectonic activity of the margin we infer that the relative sea level fall responsible of aerial incision on the miocene shelf is eustasy related we propose the attested serravallian tortonian eustatic lowstand c 11 6 ma as the key event responsible of such erosion and incision this event marks the early beginning of the high amplitude sea level fluctuations that culminated during the pleistocene and significantly controlled the present day as morphology the variability of vertical incision observed along single reaches can be explained by the confluence of several tributaries the sinuosity of the channel and can be amplified by the unconsolidated nature of the miocene substratum the main pathways of the fluvial network corresponding to these buried valleys have been reconstructed and connections to other existing networks are proposed

granitoid emplacement and deformation along a major crustal lineament the cordillera blanca peru abstract the cordillera blanca batholith and ignimbrites of the intermountain callejon de huaylas basin represent the last magmatic event in the andean cycle of central northern peru this most spectacular example of an extensional regime is characterised by acid magmatism spanning some 10 ma with both magma emplacement and subsequent deformation being fundamentally controlled by a ca 300 km lineament known as the cordillera blanca fault complex the western margin of the batholith has been strongly deformed by the cordillera blanca fault resulting in a series of ductile to brittle structures that increase with intensity away from the relatively undeformed core towards the margin the late stage brittle fabrics are coeval with extensional structures in the callejon de huaylas basin and relate to uplift and extension along the fault zone the more ductile fabrics as indicated by combined k ar and 40 ar 39 ar mineral dates formed earlier in the intrusion history and are consistent with emplacement into an active dextral strike slip shear zone the rapid uplift and high erosion rates seen from the late miocene onwards and the current state of stress in this region of thickened crust are due to gravitational instability body forces set up at high topographical levels and buoyancy forces resulting from the intrusion of young acid magmas at high crustal levels

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

global implications of lower to middle eocene sequence boundaries on the new jersey coastal plain the icehouse cometh wedocumentninelower middleeocenesequencesonthenewjerseycoastalplainand comparethemwithglobal d 18 oandhaqetal records earlyeocenehiatusesdonotmatch d 18 ochanges anditisunlikelythattheyaretheresultofglacioeustasy consistentwithan ice free early eocene early middle eocene 49 43 ma evidence for a link between sequencesand d 18 oisequivocal andthepresenceoflargeicesheetsisuncertain beginning in the late middle eocene 43 42 ma concomitant increases in planktonic and benthic d 18 o records coincide with the timing of hiatuses on the new jersey coastal plain and a change from carbonate dominated to siliciclastic dominated sedimentation these represent the development of the antarctic ice cap and the beginning of the icehouse world of the 14 sequences predicted by haq et al for this interval 9 are resolvable on the new jersey margin and the other 5 appear to be combined with others we conclude that although ice volume changes controlled sequences since at least 42 ma mechanisms for sea level change prior to then are still not fully understood

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

coupled sr o isotope variations as an indicator of source heterogeneity for the northern peninsular ranges batholith primary 18o values for tonalitic rocks from the san jacinto intrusive complex range from 9 0 to 10 6 initial87sr 86sr for the same samples varies from 0 7058 to 0 7076 rocks with low 18o tend to have higher initial87sr 86sr the majority of samples have a limited range of 18o values 10 0 10 4 that is anticorrelated with colour index this variation is compatible with crystallization of rocks with varying mineral abundances from an homogeneous for oxygen reservoir more mafic rocks show a large range of 18o values reflecting original variations in source material compositions the combined sr o isotope data demonstrate that three or more distinct components were involved in the genesis of these rocks these three components are also seen in batholithic rocks from the mojave block and sierra nevada to the north these data are interpreted as indicating a 0 35 oxygen atom basis contribution to the san jacinto rocks from an old continental lithosphere source

magmatic inclusions in rhyolites of the spor mountain formation western utah limitations on compositional inferences from inclusions in granitic rocks inclusions of quenched mafic magma occur in a 21 ma rhyolite lava and precursory non welded tuff that form the spor mountain formation in west central utah the mafic inclusions are not lithic inclusions no comparable volcanic unit was present at the surface when the spor mountain formation erupted mineral and bulk compositions preclude liquid immiscibility the mafic inclusions show clear morphologic and textural effects of magma mingling shortly before eruption of the rhyolite globular inclusions from both units are vesicular phenocryst poor plagioclase sanidine clinopyroxene orthopyroxene magnetite ilmenite latites and trachytes with quench temperatures of about 1000 c although overlapping in sio2 tio2 zr and hf concentrations inclusions from the underlying tuff lack negative eu anomalies and are enriched in p2o5 k2o al2o3 sr pb cr and ni whereas those hosted in the overlying lava have small negative eu anomalies and two fold enrichments in fe2o3 mno hree y ta th rb and cs the most reasonable explanation for the differences between the two sets of inclusions lies in selective chemical exchange between the rhyolite lava and the mafic inclusions after eruption limited mechanical mixing occurred after the inclusions solidified and became chemically modified the textures of the inclusions in the lavas and the elements selectively mobilized in the inclusions imply that vapor phase transport occurred in this low pressure volcanic environment if such substantial variations in inclusion compositions can arise during what must have been a short period of time before chemical reactions were halted by rapid cooling it seems unlikely that the compositions of mafic inclusions formed by magma mingling in slowly cooled granites preserve their original compositions mineralogies or information about their ultimate sources using the compositions of such chemically modified inclusions as end members for mixing calculations may lead to erroneous results regarding the significance of magma mixing in plutonic rocks

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

interaction between felsic and mafic magmas in the salmas intrusive complex northwestern iran constraints from petrography and geochemistry abstract the salmas plutonic complex in the northernmost part of sanandaj sirjan zone of iran provides evidence for magma interaction processes the complex contains mafic intermediate hybrid and felsic rocks which intruded into the paleozoic metamorphic complex they show typical relationships described in many mafic felsic mingling and mixing zones worldwide such as mafic microgranular enclaves in felsic and hybrid rocks mafic sheets and hybrid rocks the mafic microgranular enclaves mmes are characterized by fine grained equigranular and hypidiomorphic texture and some special types of microscopic textures e g quartz xenocrysts oscillatory zoned plagioclase small lath shaped plagioclase in large plagioclase spike zones in plagioclase and spongy cellular plagioclase textures rounded plagioclase megacrysts blade shaped biotite acicular apatite the mafic sheets and mmes in granites mme gr which indicated magma mingling structures show isr values and end i similar to diorites the hybrid rocks and their mafic enclaves mme h show isotope signatures similar to each other granites have isotope signatures higher 87sr 86sr i 0 70788 0 71075 and lower end i 2 4 to 4 2 distinct to those of the all rock types and mmes major trace and ree modeling show that hybrid rocks are generated via 40 60 mixing of mafic dioritic and felsic granitic end members all the geochemical data suggest that underplating of dioritic magma which has been produced by fractional crystallization of gabbros under the lower crust caused its melting to make felsic granitic magma injection of dioritic magma into the base of the felsic magma chamber and a limited mixing of two end members the lower crust derived magma and mantle derived melts formed hybrid magma and their enclaves injections of new mafic magma pulses into hybrid magma generated mafic enclaves into them the injections of denser dioritic magma pulses into a felsic magma chamber and spreading of it at the level of rheological contrast have been formed mafic sheets and mmes in granites