surface and subsurface data integration and geological modelling from the little ice age to the present in the ravenna coastal plain northwest adriatic sea emilia romagna italy abstract new geological analysis of the ravenna coastal plain has allowed a major update of the geological coastal model with anthropogenic overprints removed from an area heavily affected by human actions in the last four centuries a period in which the little ice age lia has had a large influence on the coastal dynamics the geological build up of the coastal plain is a natural occurrence that is important for understanding the present day coastal buildup however coastal zone anthropization has defined the actual coastal morphology canceling out most of surface expression needed to create an accurate coastal evolution model as the beach ridges morphology in the study area as the lack of surface expression due to the anthropogenic actions has changed the coastal zone under study it is not possible to only use geomorphological analysis to construct a local coastal evolution model because of this building a new model and understanding how coastal evolution would proceed without human influence would allow us to understand the interaction between natural forces and anthropogenic influence which has acted to shape the actual morphology of the study area from the lia period to the present days we therefore propose an integration of data using the following actual data from the surface such as the high resolution digital surface model dsm and the digital terrain model dtm the actual database from the emilia romagna region geological survey including the shapefile with the regional soil chart and the geological elements present in the study area knowledge from previous work carried out in the area and the subsurface data from ground penetrating radar gpr which would make the study the first to use a gpr survey of the coastal plain of the northwest adriatic in addition the work will follows a successful case study done in the southern brazilian coastal plain that integrated previous works done in the coastal plain with new methods such as gpr data acquisition the gpr data allows for corroboration of the interpretation of the coastal model constructed using the surface data finally the surface geological model proposed in this work may aid by providing the following i a new means for local coastal geology research ii a methodology to apply to other barrier lagoon systems around the world in order to update our knowledge about these systems and iii powerful information to support coastal managers and decision makers in constructing a long term master plan for effective integrated coastal zone management

new insights into the geologic evolution of the grenvillian trenton prong inlier central appalachian piedmont usa new geochemical and 40ar 39ar hornblende and biotite data from the grenvillian trenton prong inlier provide the first constraints for the identification of lithotectonic units their tectonic setti

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

crustal large scale serpentinized mantle peridotite body in the sulu ultrahigh pressure metamorphic belt eastern china evidence from gravity and magnetic anomalies abstract from analysis of the geological and geophysical data gravity magnetic seismic and petrophysics we propose that geophysical anomalies are produced by a serpentinized mantle peridotite body smpb situated in the middle to lower crust in the sulu belt the smpb was formed by crustal emplacement of mantle peridotites accompanied by ultrahigh pressure uhp metamorphism our finding suggests an emplacement mechanism for the serpentinized mantle wedge smw early in the subduction process this is different from the classic view which holds that the serpentinized forearc mantle is formed by in situ hydration processes blakely et al 2005 the petrophysical properties of the smpb are similar to those of the serpentinized forearc mantle or smw in modern subduction zones worldwide but the formation mechanisms for smpb and smw are different this observation is important for understanding the geodynamic processes that operated in the large uhp metamorphic belt in the dabie sulu area eastern china

trace element zoning in garnet as a monitor of crustal melting x ray composition maps of sc y p and cr in garnet have been measured using the electron microprobe zoning is discontinuous and is correlated with fluid absent crustal melting reactions the magnitude of the discontinuity is a function of the amount of muscovite that melts and the partition coefficients of solids versus melt trace element zoning is apparently not modified by diffusive processes so the zoning can be used to monitor the extent of melting and to examine kinetics of melting and the participation of accessory phases in crustal anatexis

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

eclogites and eclogites in the western gneiss region norwegian caledonides the western gneiss region wgr marks the outcrop of a composite terrane consisting of variably re worked proterozoic basement and parautochthonous or autochthonous cover units the wgr exhibits a gross structural petrographic and thermobarometric zonation from southeast to northwest reflecting an increasing intensity of scandian late palaeozoic

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

sequence stratigraphy of the punta ballena member of the jama formation early pleistocene ecuador insights from integrated sedimentologic taphonomic and paleoecologic analysis of molluscan shell concentrations abstract early pleistocene strata are well exposed along the uplifted eastern margin of the esmeraldas caraquez basin particularly on the coastal cliff west of the city of jama a type locality for shallow marine quaternary sedimentary exposures on north central ecuador here at least 180 m of sediments accumulated in inner shelf to subaerial settings are present jama formation this paper is concerned with the middle stratigraphic unit of the jama formation the punta ballena member pbm integrated sedimentologic paleontologic and stratigraphic observations reveal that the pbm is composed of eight disconformity bounded depositional sequences hiatal shell concentrations which formed as a consequence of landward and seaward stratal attenuation are associated with sequence bounding and intrasequence surfaces together with sedimentologic characteristics these fossiliferous levels are important indicators of facies architecture and therefore are useful tools for interpreting sequence stratigraphy according to their taphonomic features and taxonomic composition the hiatal shell concentrations occurring within the pbm may be grouped into two main types each of which occupies a predictable stratigraphic position within the sequences current wave winnowed beds at the cycle base and community shell concentrations in a roughly mid cycle position current wave winnowed beds commonly underlain by thalassinoides burrows that penetrate to depths of as much as 1 5 m below ravinement surfaces are transported skeletal concentrations and formed through physical processes in shallow high energy environments they comprise a time averaged mixture of specimens having different ecologies and states of preservation and accumulated mainly under conditions of total passing of siliciclastic sediment i e terrigenous sediments are delivered to the site as suspended load but owing to the high environmental energy failed to accumulate community shell concentrations occur in sparsely fossiliferous intervals and result from reduced net sedimentation within low energy relatively deeper settings they are composed of matrix supported loosely clustered life oriented and little disturbed fossil assemblages but are packed in excess of likely living densities and are visually dominated by successive generations of the infaunal bivalve raeta undulata which colonized a slowly aggrading muddy seafloor the sedimentological and paleontological evidence presented here not only supports the results of previous studies which demonstrate the value of condensed shell concentrations in the identification of stratigraphically significant surfaces but also provides adds to the distinctive features of these shell beds

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

sequence stratigraphic model for repeated butter shale lagerstatten in the ordovician katian of the cincinnati ohio region usa the butter shale lagerstatten of the cincinnati arch have produced an abundance of articulated trilobites along with assorted bivalves and cephalopods these bluish gray shales are rich in clay poorly calcified and show vague internal bedding in outcrop butter shales form a repetitive motif with similar lithological and paleontological characteristics suggesting conditions existed that can be explained by the interference between different orders of sequence stratigraphic cyclicity the characteristics that define butter shales include rarity of coarser interbeds homogenous fine grain size and abundance of burial horizons the overriding control is siliciclastic sediment supply during third order transgressions sediment supply to the basin is too low to produce thick shale prone intervals conversely during third order falling stages sediment supply is generally too high to favor butter shale deposition butter shales formed preferentially during a third order highstand systems tract and two subtly different variants resulted from the superimposed effects of higher order cycles highstands moderated by small scale transgressions are characterized by lower background sedimentation and fewer thinner mud deposition events superposition of small scale sea level fall on highstands produced increased background sedimentation higher silt and patchy fossil occurrences juxtaposition of various scaled highstand systems tracts provided the optimal butter shale conditions characterized by elevated mud influx and frequent episodic burial events leading to abundant articulated trilobites and associated fauna in these scenarios episodic events provide sufficient mud to smother local faunas and create a soft fine grained substrate that prohibited recolonization by taxa adapted to firm substrates each scenario differs from the others with respect to sedimentology and faunal composition

coastal dynamics under conditions of rapid sea level rise late pleistocene to early holocene evolution of barrier lagoon systems on the northern adriatic shelf italy this multidisciplinary case study of two preserved barrier systems combined the analysis of radiocarbon datings grain size distributions high resolution seismics and shelf bathymetry with reconstructions of palaeo environmental conditions tides waves sea level change and forward modelling of barrier lagoon systems to provide an integrated view of the coastal transgressive evolution of a large sector of the northern adriatic shelf between 15 and 8 ka bp palaeoenvironmental reconstructions point to increased tidal amplitude low energy wave climate and high rates of sea level rise up to 60 mm a during the formation of the oldest preserved barrier system not vert similar90 m water depth 14 3 cal ka bp a younger barrier system 42 m water depth 10 5 cal ka bp formed under conditions of lower tidal amplitude higher wave energy and a lower rate of sealevel rise 10 mm a forward modelling suggests that the probability of barrier island overstepping during transgression is inversely proportional to tidal amplitude if all other factors are assumed equal the oldest barrier lagoon system developed under conditions of large tidal amplitude which permitted rapid transgression however this system apparently failed to keep up with the anomalously high rate of sea level rise resulting from melt water pulse 1a the youngest barrier system appears to have drowned in place due to antecedent topography as the barrier system transgressed over an ancient pleistocene alluvial plain the rapid increase in backbarrier accommodation caused an abrupt disequilibrium between shoreface and backbarrier sedimentation which led to barrier overstepping although barsim modelling indicates that tidal deposition can reduce the probability of barrier overstepping there are other driving mechanisms in our case extremely rapid sea level rise and antecedent topography which are more determinative in explaining the transgressive coastal evolution of barrier lagoon systems in the northern adriatic sea grain size analysis of shoreface deposits sampled above the transgressive ravinement surface across the northern adriatic shelf indicate a distinct relation between the sediment grain size and the rate of sea level rise during deposition which implies that progressive sorting must have been highly effective

softening trigerred by eclogitization the first step toward exhumation during continental subduction direct observation of peak pressure deformation in exhumed subduction channels is difficult because little evidence of this deformation survives later syn exhumation deformation most ultrahigh pressure parageneses are found in continental derived metamorphic rocks making continental subduction the best context to observe peak pressure deformation whereas many studies have enlightened the main driving parameters of exhumation such as buoyancy forces low viscosity in the subduction channel overburden removal by erosion and normal faulting a basic question is seldom considered why is a tectonic unit disconnected from the descending lithosphere and why does it start its way towards the surface this event seminal to exhumation processes must involve some deformation and decoupling of the exhumed slice from the descending slab at peak pressure conditions or close to it our field observations in the bergen arc show that caledonian eclogitization and later amphibolitization of a granulitic terrane was achieved with a consistent component of simple shear compatible with the sense of the caledonian subduction thus the sequence of deformation preserved in the bergen arc documents the decoupling of subducted crustal material from the descending slab at the onset of exhumation this observation suggests that deformation in the subduction channel is largely controlled by kinematic boundary conditions i e underthrusting of the subducting slab in this context of simple shear metamorphic reactions assisted by fracturating fluid infiltration and ductile deformation lower the resistance of rocks and allow the localisation of shear zones and the decoupling of buoyant tectonic units from the subducting slab these tectonic units can then be incorporated into the channel circulation and start their upward travel

origin of graphite in the pickering gneiss and the franklin marble honey brook upland pennsylvania piedmont the graphite bearing pickering gneiss and intercalated franklin marble are part of an aggregation of crystalline rocks in the honey brook upland of the southeastern pennsylvania piedmont uplands that consists of a charnockitic basement overlain by a suite of volcanic rocks and intruded by the honey brook anorthosite massif carbon isotopic analysis indicates that graphite formation in the pickering gneiss and franklin marble is related to metamorphism of organic rich muds and carbonates accompanied by localized fluid flow associated with the development of anatectic pegmatites graphite in fine grained pickering gneisses of upper amphibolite and lower granulite facies has an average 13 c 23 8 per mil relative to pdb and ranges in value from 17 4 to 29 6 indicating an organic source calcite from the franklin marble and associated calcareous gneisses has an average 13 c 0 4 as would be expected with a sedimentary carbonate protolith coarse grained pickering gneisses termed anatectic pegmatites in this study of amphibolite facies have an average 13 c 18 7 and range in value from 14 0 to 26 9 whereas those of granulite facies have an average 13 c 10 9 and range in value from 8 9 to 12 4 at the time of anatexis metamorphic fluids may have facilitated exchange of high 13 c carbon from the carbonates with low 13 c carbon of the partially melted fine grained gneisses thus producing the intermediate values of 13 c of graphite in the anatectic pegmatites calcite graphite isotope thermometry yields estimates of 680 40 c for upper amphibolite facies and 748 40 c for granulite facies metamorphism in the upland

th diffusion in monazite abstract diffusion of th has been characterized in synthetic monazite under dry conditions the synthetic monazites either pure cepo4 ndpo4 or a mixed lree phosphate containing ce nd and sm were grown via a na2co3 moo3 flux method the sources of diffusant for the experiments were either synthesized thsio4 or cath po4 2 powders mixed with cepo4 experiments were performed by placing source and monazite in pt capsules and annealing capsules in 1 atm furnaces for times ranging from 3 weeks to a few hours at temperatures from 1350 to 1550 c the th distributions in the monazite were profiled by rutherford backscattering spectrometry rbs the following arrhenius relation was obtained for th diffusion in monazite d 6 7 10 1 exp 740 63 kj mol 1 r t m 2 s 1 the diffusivity of th was found to be similar for monazites containing a single ree ce or nd and the mixed lree phosphates th diffusion was also similar for experiments run using the th silicate and ca th phosphate sources suggesting that the substitutional mechanism for th in monazite i e th 4 si 4 ree 3 p 5 for the thsio4 source and th 4 ca 2 2ree 3 for the cath po4 2 source does not significantly affect th diffusivities and that th is likely the rate limiting species in diffusion th diffusion in monazite is about 3 orders of magnitude slower than pb diffusion cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 this contrasts with findings of gardes et al gardes e jaoul o montel j m seydoux guillaume a m wirth r 2006 pb diffusion in monazite an experimental study of pb2 th4 2nd3 interdiffusion geochimica et cosmochimica acta 70 2325 2336 who determined that diffusivities measured in pb th ree exchange which would under most circumstances be rate limited by the slowest diffusing species are comparable to those measured by cherniak et al cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 for pb th diffusion in zircon cherniak d j hanchar j m watson e b 1997 diffusion of tetravalent cations in zircon contributions to mineralogy and petrology 127 383 390 is about an order of magnitude slower than in monazite but with similar activation energy for diffusion the lower diffusivities in zircon may be a consequence of the larger disparity in size between th and the zr site in zircon as compared with th and the ree site in monazite nonetheless th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions these findings may also have implications for containment of high level actinide based nuclear waste in monazite ceramic waste forms but it should be noted that mechanisms other than diffusive exchange e g recrystallization dissolution reprecipitation may be important to consider along with diffusion when evaluating the retentivity of monazite for th and other actinide elements

monazite age constraints on the tectono thermal evolution of the central appalachian piedmont the central appalachian piedmont lies in the critical juncture between the northern and southern appalachians portions of the orogen with distinct middle to late paleozoic accretionary histories orogen scale compilation maps link the central and southern appalachians but until recently limited geochronological data prevented robust tectonic comparisons between high grade metamorphic rocks in different parts of the orogen we report the results of in situ u th total pb monazite geochronology that date significant deformation and metamorphism as middle silurian 425 ma through middle devonian 385 ma and demonstrate the diachronous nature of orogen development the rosemont shear zone is identified as a major tectonic boundary in southeastern pennsylvania and northern delaware separating the rifted laurentian margin from younger rock units that formed in a magmatic arc setting the laurentian margin rocks occur in a series of nappes in which the metamorphic grade decreases from the structurally highest nappe to the lowest the in situ monazite ages show that maximum temperature in the lowest nappe may have been attained some 15 million years after maximum temperature in the highest nappe we interpret this to be the result of successive nappe emplacement with the warmer overriding sheets contributing heat to lower levels combining geochronologic and thermobarometric results with the geometry of deformation results in a new picture of the tectonic development of the central appalachian piedmont that further links the evolution of the southern and northern appalachians for the laurentian margin rocks tectonism resulted from the approach and collision of peri gondwanan terranes during the silurian to early devonian in a dominantly sinistral transpressive tectonic regime this portion of the pennsylvania delaware piedmont inboard of the rosemont shear zone is contiguous with comparable rocks in the southern appalachians in contrast arc related rock units outboard of the rosemont shear zone experienced primarily thermal metamorphism in the silurian while crustal thickening and associated regional metamorphism is middle devonian in age and likely the result of the accretion of avalonia during the acadian orogeny these arc related and younger rocks probably originated to the north of their present location as part of the northern appalachians they were ultimately emplaced in a right lateral transcurrent regime sometime after the middle devonian thus it is in this portion of the central appalachian piedmont that the northern and southern appalachians are joined

exhumation mechanisms of melt bearing ultrahigh pressure crustal rocks during collision of spontaneously moving plates a series of 2d petrological thermomechanical numerical experiments was conducted to i characterize the variability of exhumation mechanisms of ultrahigh pressure metamorphic uhpm rocks during collision of spontaneously moving plates and ii study the possible geodynamic effects of melting at ultrahigh pressure conditions for the exhumation of high temperature ultrahigh pressure metamorphic ht uhpm rocks to this end the models include fluid and melt induced weakening of rocks five distinct modes of exhumation of u hpm rocks associated with changes in several parameters in the models of plate collision and continent subduction are identified as follows vertical crustal extrusion large scale crustal stacking shallow crustal delamination trans lithospheric diapirism and channel flow the variation in exhumation mechanisms for u hpm rocks in numerical models of collision driven by spontaneously moving plates contrasts with the domination of the channel flow mode of exhumation in a majority of the published results from numerical models of collision that used a prescribed plate convergence velocity and or did not include fluid and melt induced weakening of rocks this difference in the range of exhumation mechanisms suggests that the prescribed convergence velocity condition and the neglect of fluid and melt related weakening effects in the earlier models may inhibit development of several important collisional processes found in our experiments such as slab breakoff vertical crustal extrusion large scale stacking shallow crustal delamination and relamination and eduction of the continental plate consequently the significance of channel flow for the exhumation of uhpm rocks may have been overstated based on the results of the earlier numerical experiments in addition the results from this study extend over a larger proportion of the high temperature range of p t conditions documented from uhpm rocks including those retrieved from ht uhpm rocks than the results of experiments from previous numerical models in particular the highest peak metamorphic temperatures up to 1000 degrees c are recorded in the case of the vertical crustal extrusion model in which subducted continental crust is subjected to a period of prolonged heating by asthenospheric mantle abutting the continental side of the vertically hanging slab nonetheless some extreme temperature conditions which have been suggested for the kokchetav and bohemian massifs perhaps up to 1100 1200 degrees c are still to be achieved in experiments using numerical models

ti diffusion in quartz abstract we have measured ti diffusion in quartz under dry 1 atm conditions experiments were performed using synthetic and natural quartz and a tio2 powder source with ti profiles obtained by rutherford backscattering spectrometry rbs over the temperature range 700 1150 c the following arrhenius relation was obtained for diffusion parallel to 001 d ti 7 10 8 exp 273 12 kj mol 1 r t m 2 sec 1 similar diffusivities were obtained for both synthetic and natural quartz and for a range of ti source materials including natural titanite powder and rutile quartz single crystal diffusion couples although ti diffusion appears slightly slower in the direction normal to c this difference is not great using these diffusion parameters calculations indicate that distances over which diffusional alteration of ti concentrations in quartz could occur in a million years would be on order of 500 m at 800 c and 15 m at 600 c the arrhenius relation above should be broadly applicable and may find application in constraining metamorphic histories under conditions where the ti in quartz geothermometer can be reasonably applied this relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the ti depleted zone that develops around the growing needles finally these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz

high pressure rocks of the acatlan complex southern mexico large scale subducted ordovician rifted passive margin extruded into the upper plate during the devonian carboniferous abstract high pressure hp rocks in the paleozoic acatlan complex of southern mexico occur in a median belt extruded into the complex which is the root zone of a klippe to the west these hp rocks are predominantly clastic metasedimentary rocks and include a bimodal suite of amphibolites and granitoids u pb la icpms zircon dating indicates that one of the amphibolites was intruded at or before 461 2 ma and a megacrystic granitoid yielded an intrusive age of 488 8 7 ma which is within the 490 450 ma range of other dated hp megacrystic granitoids the amphibolites have a tholeiitic transitional to alkalic within plate chemistry derived from a heterogeneous mantle by various degrees of partial melting the host metasedimentary rocks contain detrital zircons derived both from the acatlan granitoids and the ca 1 0 1 3 ga oaxacan complex and are inferred to represent rifted passive margin sediments an age of 348 4 1 ma from zircons in a migmatized amphibolite is interpreted as the time of migmatization and dates decompression melting following peak pressure at depths of 45 55 km retrogression from 530 c to 370 c occurred between 343 and 335 ma the predominance of reasonably coherent rifted passive margin rocks over a surface area of 10 90 km suggests removal of a large slice of the upper plate during flat slab subduction this slice was subducted to depths of ca 45 55 km where it was underplated and transferred to the overriding plate the absence of oaxacan complex rocks in the hp belt suggests the oaxacan basement was subducted to greater depths underplating was followed by extrusion facilitated by extension in the upper plate that produced mississippian rift basins east of the median hp belt westward overthrusting of the hp rocks produced a klippe that overrode mississippian clastic wedge sediments

middle proterozoic age for the montpelier anorthosite goochland terrane eastern piedmont virginia uranium lead dating of zircons from the montpelier anorthosite confirms previous interpretations based on equivocal evidence that the goochland terrane in the eastern piedmont of virginia contains grenvillian basement rocks of middle proterozoic age a very few prismatic elongate euhedral zircons which contain 12 29 ppm uranium are interpreted to be igneous in origin the vast majority of zircons are more equant subangular to anhedral contain 38 52 ppm uranium and are interpreted to be metamorphic in origin one fraction of elongate zircon and four fragments of a very large zircon occurring in a nelsonite segregation yield an upper intercept age of 1045 10 ma interpreted as the time of anorthosite crystallization irregularly shaped metamorphic zircons are dated at 1011 2 ma weighted average of the 207pb 206pb ages the u pb isotopic systematics of metamorphic titanite were reset during the alleghanian orogeny at 297 5 ma these data provide a minimum age for gneisses of the goochland terrane that are intruded by the anorthosite middle proterozoic basement rocks of the goochland terrane may be correlative with those in the shenandoah massif of the blue ridge tectonic province as suggested by similarities between the montpelier anorthosite and the roseland anorthosite although the areal extent of middle proterozoic basement and basement cover relations in the eastern piedmont remain unresolved results of this investigation indicate that the goochland terrane is an internal massif of laurentian crust rather than an exotic accreted terrane

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

dynamics of sediment subduction accretion at convergent margins short term modes long term deformation and tectonic implications a conceptual model is proposed for the short term operation of subduction accretion systems at convergent margins the operation is described in terms of the mass fluxes among the four system components namely the accretionary or prowedge wedge p an uplifted plug u a retrowedge r and the subduction zone the latter consists of a conduit c of slowly moving and deforming material and an underlying subduction channel where material moves and deforms more rapidly a broad range of convergent margin types can be accommodated within the conceptual model framework with differing short term modes that depend on which of the p u r c components that are active finite element geodynamical model experiments are used to investigate whether these modes are dynamically feasible these experiments determine excitation of modes under controls that include model entry and exit mass fluxes flexural loading by accreted material and slab pull forces boundary velocities corresponding to subduction and subduction zone advance retreat distribution thickness and density of accreted sediment and internal frictional properties of the coulomb sediments that all modes with the exception of p in which only a prowedge is created are seen in the models provides support for the concepts and allows conditions that favor particular modes to be recognized in addition the finite deformation predicted by the models is used to infer the long term tectonic styles associated with both single mode evolutions and those that exhibit mode switching a steady state mass balance can occur for modes 0 pure subduction p c i e where components p and c are active or other modes when the surface mass denudation plus the subduction flux balances accretion plus tectonic underplating the p c mode is favored by subduction zone retreat and or an increasing subduction load and creates an apparent landward dipping backstop p u c is predicted to be the most common mode and it creates an apparent seaward dipping backstop p u r c is an inefficient mode but is favored by easily detached retrocrust or sediment and or a decreasing subduction load

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

deciphering multiple mesoproterozoic and paleozoic events recorded in zircon and titanite from the baltimore gneiss maryland sem imaging shrimp u pb geochronology and emp analysis

global sea level control on local parasequence architecture from the holocene record of the po plain italy abstract holocene deposits exhibit distinct predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record in this study we examined the sedimentary response of the po plain coastal system to short term millennial scale relative fluctuations of sea level through high resolution sequence stratigraphic analysis of the holocene succession meters thick parasequences form the building blocks of stratigraphic architecture above the younger dryas paleosol a prominent stratigraphic marker that demarcates the transgressive surface early holocene parasequences s 1 3 record alternating periods of rapid flooding and gradual shoaling and are stacked in a retrogradational pattern that mostly reflects stepped post glacial eustatic rise conversely middle to late holocene parasequences s 4 8 record a complex pattern of coastal progradation and delta upbuilding that took place following sea level stabilization at highstand starting at about 7 cal ky bp the prominent transgressive surface at the base of parasequence 1 correlates with the period of rapid global sea level rise at the onset of the holocene mwp 1b whereas flooding surfaces associated with parasequences 2 and 3 apparently reflect minor early holocene eustatic jumps reported in the literature changes in shoreline trajectory parasequence architecture and lithofacies distribution during the following eustatic highstand had instead an overwhelming autogenic component mostly driven by river avulsions delta lobe switching local subsidence and sediment compaction we document a 1000 year delayed response of the coastal depositional system to marine incursion farther inland from the maximum landward position of the shoreline a dramatic reduction in sediment flux due to fluvial avulsion resulted in marine inundation in back barrier position whereas coastal progradation was simultaneously taking place basinwards we demonstrate that the landward equivalents of marine flooding surfaces parasequence boundaries may be defined by brackish and freshwater fossil assemblages and traced for tens of kilometers into the non marine realm this makes millennial scale parasequences whether auto or allogenic in origin much more powerful than systems tracts for mapping detailed extents and volumes of sediment bodies the holocene parasequences of the po coastal plain with strong age control and a detailed understanding of sea level variation may provide insight into the driving mechanisms and predictability of successions characterized by similar depositional styles but with poor age constraint resulting in more robust interpretations of the ancient record

metamorphic discontinuities in the pennsylvania delaware piedmont evidence for early paleozoic assembly interpretation of the early paleozoic tectonic history of the appalachian piedmont is commonly complicated by post taconian deformation that has disrupted and obscured early paleozoic structure blocks that lie between zones where later deformation has been concentrated however may preserve evidence of taconian high grade metamorphism in these cases analysis of metamorphism allows an interpretation of the early paleozoic tectonic history of the block and its surrounding region a block of this type in the pennsylvania delaware piedmont includes three tectonic units 1 the basement cored massifs of southeastern pennsylvania with grenvillian gneiss unconformably overlain by the setters formation and cockeysville marble 2 the wilmington complex arc terrane and 3 the wissahickon group and associated metaigneous rocks a metamorphic gradient and inferred temperature inversion within the wissahickon group and a metamorphic discontinuity at the wissahickon group cockeysville marble contact are used t

the 127 ma gold mineralization in the wulong deposit liaodong peninsula china constraints from molybdenite re os monazite u th pb and zircon u pb geochronology abstract the wulong deposit is a large tonnage deposit 80 t of au characterized by quartz vein style of gold mineralization in the liaodong peninsula china the auriferous quartz veins are mainly hosted by late jurassic gneissic two mica granite 165 157 ma and early cretaceous granodiorite 129 ma and are structurally controlled by nne and nw trending faults previous attempts to date the gold mineralization yielded ambiguous results 135 112 ma here we report the first in situ and direct age constraint for gold mineralization at wulong five molybdenite samples from mo bearing quartz pyrite veins yielded an isochron age of 127 6 2 3 ma in situ sims u th pb dating of hydrothermal monazite that coexists with gold bearing pyrite and quartz yielded a 208pb 232th age of 126 7 3 2 ma these robust ages together with new age data of the wulong host intrusion and post ore dike allow for a better interpretation of the ore genesis of the wulong deposit relative to a well constrained sequence of regional geological events zircon u pb dating of the wulong host intrusion gneissic two mica granite representing the oldest magmatic event at wulong gave a weighted mean age of 159 3 1 4 ma that is interpreted to be the magma emplacement age subsequent magmatic events are recorded by the early cretaceous dikes with zircon u pb ages between 127 and 113 ma a post ore diorite porphyry dike that crosscuts the early cretaceous dikes has a u pb zircon age of 121 5 1 5 ma all the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the early cretaceous magmatism in the wulong orefield this episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern north china craton which is triggered by the subduction of the paleo pacific plate

coexisting monazite and allanite in peraluminous granitoids of the tribec mountains western carpathians monazite a typical light rare earth element lree mineral of s type granitoids in the western carpathians was found in the peraluminous biotite granodiorite tonalite in the tribec mountains commonly containing polymineralic inclusions these inclusions are dominated by anhedral allanite although allanite also occurs rarely as discrete grains not enclosed by monazite the monazite studied here is relatively homogeneous and characterized by high th contents with proportions of huttonite thsio4 and brabantite cath po4 2 up to 14 6 and 9 3 respectively the discrete allanite grains are highly aluminous with a composition consistent with the peraluminous type of host rock however allanite included in monazite is extremely variable in lree al fe and mg contents this variation is interpreted to result from entrapment of allanite melt in monazite before local equilibrium was attained the change from allanite to monazite as the stable lree rich phase is related to an overall decrease in ca concentration caused by the onset of plagioclase crystallization the early precipitation of allanite was possible because of the high lree concentrations in the melt the crystallization temperature of allanite must have been higher than monazite saturation 856 845 c and 798 790 c for two analyzed samples the zr saturation temperature based on zircon solubility and ree thermometry based on monazite solubility reflect an increase in temperature from the edge to the center of the pluton which coincides with an increase in the huttonite content in monazite the primary lree assemblage is accompanied by small grains of late huttonite replacing monazite and brabantite replacing allanite

definition of sequences through ichnocoenoses and taphofacies an example from the sacaras formation early cretaceous eastern spain abstract an integrated taphonomical ichnological and sedimentological analysis has been carried out on the albian deposits of the sierra helada section province of alicante southeastern spain this allowed recognition and detailed characterization of the shallowing and coarsening upward sequences present in these deposits twenty sequences were detected throughout the section they contain the following from bottom to top 1 the bottom of the sequence characterized by very fine grained marls rich in echinoid tests and echinoid trace fossils with very little evidence of physical reworking it records a distal platform low energy environment 2 marls interbedded with fine grained calcarenites rich in large thalassinoides and slightly reworked echinoid tests with common bioclast armored tubes ereipichnus geladensis recording low energy background conditions but increasing energy of the sedimentary events 3 coarse grained calcarenites rich in different types of small to large thalassinoides and e geladensis horizons showing the intense and frequent action of storms and directed currents on the seafloor and 4 coarse grained cross bedded calcarenites rich in ophiomorpha nodosa deposited under high energy background conditions in the shallowest part of the sequence recording the presence of shifting dunes in the inner platform occasionally also the record of a rapid transgression has been pointed out through the presence of condensed tapho and sedimentary facies and mixed ichnocoenoses at the top of the sequence just after an erosive surface the defined ichnoceonoses and their distribution throughout the sequence reflect the shifting from a distal expression of the cruziana ichnofacies to the shallower archetypal cruziana ichnofacies and finally to the high energy shallow water skolithos ichnofacies the distribution of taphofacies and ichnocoenoses and development of the sequences all through the section show a general transgression followed by a regressive phase which fit with the third order curves described for the area on the basis of pure sedimentological analysis in previous studies castro et al 2008

sedimentary response to late quaternary sea level changes in the romagna coastal plain northern italy data from 17 continuously cored boreholes 40 170 m deep reveal the subsurface stratigraphy of the romagna coastal plain sedimentological and microfaunal data allow the distinction of eight facies associations of late pleistocene holocene age including 18 lithofacies and 16 faunal associations ten 14c dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky bp of the last glacio eustatic cycle the eight facies associations can be grouped into lowstand transgressive and highstand systems tracts the upper part of the lowstand systems tract consists of alluvial plain deposits these accumulated during the late pleistocene when the shoreline was 250 km south of its present day position a pronounced stratigraphic hiatus between 25 and 8 8 ky bp is invariably recorded at the upper boundary transgressive surface of these pleistocene indurated and locally pedogenized alluvial deposits the succeeding postglacial history is represented by a well developed transgressive regressive cycle transgressive deposits interpreted to reflect the rapid landward migration of a barrier lagoon system include two wedge shaped paralic and marine units these thicken in opposite directions and are separated by a ravinement surface above the transgressive deposits the maximum flooding surface mfs marks the change from a transgressive barrier lagoon complex to a prograding wave dominated delta system early po delta the mfs can be traced landwards where it constitutes the base of lagoonal deposits an aggradational to progradational stacking pattern of upper delta plain marsh lower delta plain lagoon bay and delta front beach ridge deposits reflects the progressive increase in the sediment supply accommodation ratio during the following highstand the alluvial deposits capping the sequence accumulated by the 13th century ad in response to an avulsion event that caused abandonment of the former po delta lobe and the northward migration of the po river towards its present position

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

on the origin of orogens in order to understand how orogens work a quantitative approach demonstrating proof of concept is essential our goal is to reconcile the diverse array of tectonic features observed in natural orogens in the context of working numerical models that are consistent with both the underlying physics and first order geological constraints we present a simple conceptual temperature magnitude t m framework for orogenesis in terms of the progression from small cold to large hot orogens and we use forward numerical models to test hypotheses corresponding to specific stages along the t m spectrum small cold orogens are analyzed using crustal scale singularity s point models in which suborogenic mantle lithosphere is kinematically subducted beneath crust that deforms by critical wedge mechanics the transition from oceanic subduction to continental collision and the subsequent evolution of large hot orogens has been investigated using both crustal and upper mantle scale models the latter including dynamic subduction of suborogenic mantle lithosphere large hot orogens with thick crust are characterized by elevated plateaus with a strong superstructure underlain by hot weak lower crustal infrastructure beneath plateaus tectonic processes are dominated by ductile flow of weak crust in response to differential pressure while plateau flanks form external thrust sense wedges we discuss four topical issues in orogenic tectonics including the response of the suborogenic mantle lithosphere to convergence the interaction of climate and tectonics the current debate concerning wedge versus channel flow models to explain the himalayan tibetan system and the interpretation of metamorphic architecture in terms of orogenic processes we conclude that collisional orogenesis is driven largely by subduction and accretion of material at convergent margins accompanied by shortening thickening and heating of deformed crust

anomalous mesozoic thermal regime central appalachian piedmont evidence from sphene and zircon fission track dating a total of 17 sphene and 45 zircon fission track ages fta are reported from the piedmont province of pennsylvania delaware and maryland the reading prong of new jersey and the newark basin of pennsylvania with the exception of one sphene sample fta fall within a relatively restricted age range sphene 190 217 ma average 199 ma and zircon 143 218 ma average 184 ma near concordance of fta over a large tract of crystalline basement sim20 000 km 2 and within upper triassic sediments in the newark basin indicates late triassic early jurassic total resetting of the fission track clocks followed by regional cooling between sphene sim275 pm 25 circ c to zircon sim 220 pm 40 circ c closure temperatures at rates of 4 8 c ma fourteen rb sr whole rock mica ages together with previously reported 40 ar 39 ar biotite and hornblende ages generally indicate no regional mesozoic resetting thus the maximum temperature experienced by the samples was 300 c sphene fta clo

systematic vertical and lateral changes in quality and time resolution of the macrofossil record insights from holocene transgressive deposits po coastal plain italy abstract in siliciclastic marine settings skeletal concentrations are a characteristic feature of transgressive intervals that provide insights into biological and sequence stratigraphic processes to investigate taphonomic signatures of transgressive intervals we analysed three cores along a depositional profile from the high resolution chrono and stratigraphic framework of the holocene po coastal plain in northern italy coupled multivariate taphonomic and bathymetric trends delineated spatial and temporal gradients in sediment starvation bypassing suggesting that quality and resolution of the fossil record vary predictably along the studied depositional profile moreover integration of taphonomic bathymetric and fossil density trends across the study area reveals distinctive signatures useful in characterizing facies associations and determining surfaces and intervals of sequence stratigraphic significance within the southern po plain succession taphonomic degradation of macroskeletal remains increases from proximal nearshore to distal offshore locations this trend is discernible for both biologically driven bioerosion and physically driven e g dissolution abrasion shell alterations compared to the up dip most proximal core the down dip core is distinguished by shell rich lithosomes affected by ecological condensation co occurrence of environmentally non overlapping taxa and by higher taphonomic alteration the onshore offshore taphonomic trend likely reflects variation in sediment accumulation along the depositional profile of the holocene northern adriatic shelf with surface near surface residence time of macroskeletal remains increasing down dip due to lower accumulation rates these results indicate that during transgressive phases changes in sea level base level are likely to produce down dip taphonomic gradients across shelves where the quality and resolution of the fossil record both deteriorate distally radiocarbon calibrated amino acid racemisation dates on individual bivalve specimens and the chronostratigraphic framework for this profile suggest jointly that the high levels of taphonomic degradation observed distally developed over millennial time scales 8ky whereas in proximal setting overall low taphonomic degradation and geochronologic constrains point to centennial scale time averaging during the late transgression phase patterns documented in the holocene transgressive and lowermost regressive deposits of the southern po plain may be characteristic of siliciclastic dominated depositional systems that experience high frequency base level fluctuations

monazite xenotime miscibility gap thermometry i an empirical calibration rare earth element ree and yttrium concentrations of coexisting monazite and xenotime were determined from a suite of seven metapelites from the variscan fold belt in ne bavaria germany the metapelites include a continuous prograde mainly low p 3 5 kbar metamorphic profile from greenschist c 400 c to lower granulite facies conditions c 700 c the lree la sm are incorporated preferentially in monoclinic monazite reo9 polyhedron whereas the hree plus y are concentrated in tetragonal xenotime reo8 polyhedron the major element concentrations of both phases in all rocks are very similar and do not depend on metamorphic grade monazite consists mainly of la ce and nd la0 20 0 23 ce0 41 0 45 nd0 15 0 18 po4 all other elements are below 6 mol likewise xenotime consists mainly of ypo4 with some dy and gd solid solutions y0 76 0 80 dy0 05 0 07 gd0 04 0 06 in contrast the minor hree concentrations in monazite increase strongly with increasing metamorphic grade y dy and gd increase by a factor of 3 5 from greenschist to granulite facies rocks monazite crystals often show zonation with cores low in hree and rims high in hree that is interpreted as growth zonation attained during prograde metamorphism similarly sm and nd in xenotimes increase by a factor of 3 4 with increasing metamorphic grade prograde zonation in single crystals of xenotime was not observed the xhree y in monazite and xlree in xenotime of the seven rocks define two limbs along the strongly asymmetric miscibility gap from c 400 c to 700 c the empirical calibration of the monazite miscibility gap limb coexisting with xenotime is appropriate for geothermometry due to its contents of u and th monazite has often been used for u pb age determination the combination of our empirical thermometer on prograde zoned monazite along with possible age determination of zoned single crystals may provide information about prograde branches of temperature time paths

a multidisciplinary study of ecosystem evolution through early pleistocene climate change from the marine arda river section italy the arda river marine succession italy is an excellent site to apply an integrated approach to paleoenvironmental reconstructions combining the results of sedimentology body fossil paleontology and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early pleistocene climate change and tectonic activity the succession represents a subaqueous extension of a fluvial system originated during phases of advance of fan deltas affected by high density flows triggered by river floods and overlain by continental conglomerates indicating a relative sea level fall and the establishment of a continental environment an overall regressive trend is observed through the section from prodelta to delta front and intertidal settings the hydrodynamic energy and the sedimentation rate are not constant through the section but they are influenced by hyperpycnal flows whose sediments were mainly supplied by an increase in apennine uplift and erosion especially after 1 80 ma the arda section documents the same evolutionary history of coeval successions in the paleo adriatic region as well as the climatic changes of the early pleistocene the different approaches used complement quite well one another giving strength and robustness to the obtained results

the alps 2 controls on crustal subduction and ultra high pressure rock exhumation in alpine type orogens building on our previous results we use 2 d upper mantle scale thermomechanical numerical models to explore key controls on the evolution of alpine type orogens and the alps per se focusing on ultra high pressure u hp metamorphic rocks the models show that uhp rocks form and exhume by burial and subsequent buoyant ascent of continental crust in the subduction conduit here we test the sensitivity of the models to surface erosion rate crustal heat production plate convergence divergence rates geometry of the subducting continental margin and strength of the retrocontinent surface erosion affects crustal exhumation but not early buoyant exhumation metamorphic temperatures increase with crustal radioactive heat production maximum burial depth prior to exhumation increases with plate convergence rates but exhumation rates are only weakly dependent on subduction rates onset of absolute plate divergence does not trigger exhumation in these models we conclude that contrasting peak pressures exhumation rates and volumes of u hp crust exhumed in the alps orogen primarily reflect along strike contrasts in the geometry thermal structure and or strength of the subducting microcontinent brianconnais and continental european margin crust the experiments also support the interpretation that the western alps u hp internal crystalline massifs exhumed as composite stacked plumes and that these plumes drove local crustal extension during orogen scale shortening for weak upper plate retrocrusts postexhumation retrothrusting forms a retrowedge overall these results are consistent with predictions using the exhumation number ratio of buoyancy to side traction forces in the conduit which expresses the combined parameter control of the depth volume of crustal subduction and the transition to buoyant exhumation

paradigms new and old for ultrahigh pressure tectonism regional ultrahigh pressure uhp metamorphic terranes exhibit a spectrum of lithological structural and petrological characteristics that result from the geodynamic processes that formed and exhumed them at least six geodynamic processes can be envisioned to have carried continental rocks to mantle depths i continental margin subduction ii microcontinent subduction iii sediment subduction iv intracontinental subduction v subduction erosion and vi foundering of a crustal root most of these processes have been investigated through numerical or analog models and most have been invoked for one or more specific occurrences of uhp rocks at least six geodynamic processes can be envisioned to have exhumed uhp continental rocks i eduction ii microplate rotation iii crustal stacking iv slab rollback v channel flow and vi trans mantle diapirs most of these processes have also been investigated through numerical or analog models and all have been invoked to explain the exhumation of at least one uhp terrane more detailed and systematic field investigations are warranted to assess the predictions of numerical models and more sophisticated and realistic numerical models are required to replicate and explain the petrological structural and chronological data obtained from uhp terranes

a geologic history of the north central appalachians part 3 the alleghany orogeny the north central appalachians occupy a critical position within the 3000 km long appalachian orogen lying southwest of the boundary between the central and northern appalachians cnab the one billion year long history of tectonic activity in eastern laurentia includes the creation and evolution of the appalachian orogen during the paleozoic and the mesozoic transformation of the orogen into a passive margin during pangea9s disassembly a most important ingredient in the evolution of the orogen was the alleghany orogeny which was driven by the convergence and collision between laurentia laurussia and west gondwana africa the alleghany orogeny in the central and southern appalachians was a decollement tectonism that involved a larger part of eastern laurentia than had the previous three orogenies the fundamental element was a very low angle thrust decollement that originated in mid crustal levels east of the presently exposed appalachians and rose westwardly to progressively higher levels in the upper crust and the supra crustal paleozoic section alleghany deformation was widely developed in the hanging wall block allochthon primarily in the form of thrust faults and fold and thrust structures both of which splayed upward from the basal decollement the youngest manifestations of the alleghany orogeny were northeast trending strike slip faults and dextral shear zones in the piedmont in the north central appalachians the exposed allochthon consists of two parts the sedimentary externides appalachian plateau and valley and ridge provinces and the crystalline externides reading prong blue ridge belt and piedmont province long thrust cored anticlines predominate in the sedimentary externides a widespread layer parallel shortening preceded the folding it is largely coaxial with the folding but extends considerably farther to the northwest toward the craton it is hypothesized that the folding developed in reverse order sequentially from the northwest to the southeast the crystalline externides are dominated by low angle thrust faults and upright folds trending east northeast the first order valley and ridge folds on the northwest side acted as a buttress and diverted the crystalline externides rocks north northwestwardly onto the topographic low area over the anthracite region this thrusting of the crystalline externides caused anthracitization of the coals within the pennsylvanian rocks there metamorphism and magmatism were significant events during the earlier phase of the alleghany orogeny in the southern appalachians whatever magmatism and medium to high grade metamorphism developed in the north central appalachians are in the covered internides to the southeast the alleghany orogeny of the north central appalachians occurred during the early permian erosion of anticlinal crests probably began as the folds grew with accumulation of this locally derived sediment in the intervening synclines a regional alluvial plain coalesced above the partially eroded externides structures as erosion of the pre alleghany highland and the alleghany hinterland mountains continued to the southeast spreading sediment to the northwest this erosion and northwest transport probably persisted with diminishing intensity throughout the remainder of the permian and into the mesozoic and changed only with the beginning of crustal extension during the late triassic

retroward extrusion of high pressure rocks an example from the hellenides pelion blueschist nappe nw aegean current tectonic models interpret the hellenides as a unidirectional sw vergent orogenic belt new micro structural and amphibole chemistry analyses show instead that the exhumation of the pelion blueschist nappe pbn of the internal hellenides was achieved by retroward ene directed ductile extrusion which opposes the principal proward orogenic vergence retroward extrusion occurred between two sub parallel major ductile shear zones basal thrust and upper detachment with opposite shear senses which operated simultaneously under blueschist to greenschist facies conditions during the late eocene oligocene because the pbn is tectonically sandwiched between pelagonian basement rocks we suggest that the pbn protolith was accumulated during the late cretaceous in an incipient backarc basin developed above the ne dipping subduction of the pindos ocean beneath the pelagonian microcontinent subsequent apulian pelagonian collision triggered basin inversion and the proward dipping intracontinental subduction that caused the early middle eocene blueschist facies metamorphism followed by the retroward extrusion of the pbn this article is protected by copyright all rights reserved

remarks on sequence stratigraphy and taphonomy of the malvinokaffric shelly fauna during the kacak event in the apucarana sub basin parana basin brazil the eifelian givetian middle devonian transition constituted an important paleoenvironmental event for the malvinokaffric realm in the apucarana sub basin parana basin this study highlights integration between taphonomy and sequence stratigraphy and four depositional sequences are identified during the transition in sequence 1 the presence of a typical normal sized malvinokaffric fauna is recorded in the transgressive systems tract tst of sequence 2 no benthic fossils are present and this is interpreted as a stratigraphic marker of an event of significant paleoenvironmental change kacak event in sequence 3 the tst has abundant bioclasts which become rarer toward the top of the section i e within the transgressive systems tract the original habitat of this autochthonous to parautochthonous fauna was a low energy environment between the fair weather wave base and the storm wave base of the devonian epicontinental sea in the highstand systems tract of this sequence the presence of normal sized pennaia paulianna and lingulids demonstrates the return of more ambient conditions sequence 4 is of carboniferous age its limit is a second order sequence boundary recording a lowstand systems tract formed by a fluvial depositional system the low diversity and the disappearance of taxa are not the result of a taphonomic bias but reflect the post kacak event

diagnosing non meteorically induced variations in the chemistry of saline springs of the vrancea seismic area romania a monitoring operation conducted over more than seven years has been addressing chemical fluctuations displayed by several cool low discharge springs located close to the highly seismic vrancea area romania those outflows compositions proved to be strongly controlled by binary essentially isochemical mixing between a deep origin brine and meteoric freshwater by taking advantage of this particular setting there have been constructed diagrams aimed at investigating how the groundwater discharges na k mg geothermometric parameters fluctuated as a function of the chloride content taken to be an estimator of the freshwater induced dilution we made use of the reciprocal algebraic relationships existing between the equations describing the na k mg geothermometric parameters na k temperature and k mg temperature on the one hand and the so called maturity index mi on the other in an accordingly derived plot of mi against the logarithm of the chloride concentration a series of data points being quite uniformly off set from the mi dilution curve constructed for an apparently regular period suggested that episodically all concerned springwaters were simultaneously subject to some similar changes in the controlling geochemical processes one such modification intervened 3 4 months before the occurrence of the strongest earthquake m text w 5 8 of the hydrochemical monitoring period the consequently derived interpretation was that then the numerical values of certain geothermometric coefficients were likely altered such a process could be consistent with changes in the alkali feldspars solubility relationships possibly in response to episodic al si complexing which might develop within a hypothesised still active exhumation channel

a low seasonality scenario in the mediterranean sea during the calabrian early pleistocene inferred from fossil arctica islandica shells understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems here we estimate seasonal water temperature amplitudes from stable oxygen isotope 18oshell values of fossil shells of arctica islandica assuming 18owater 0 9 0 1 v smow specimens were collected from three pleistocene successions emilian and sicilian substages of the calabrian in central and southern italy i e rome lecce and sicily biostratigraphic analyses from rome quarry deposits indicate an age between 1 6 and 1 2 ma whereas sicily and lecce successions are slightly more recent between 1 1 and 0 62 ma prior to carbonate geochemical analysis we checked the shells for potential diagenetic alterations e g from aragonite to calcite using confocal raman microscopy 18oshell transects indicate an annual temperature amplitude of about 3 c during the early pleistocene this is in sharp contrast to reconstructions based on faunal assemblages according to which the simultaneous occurrence of boreal and warm water species in the calabrian mediterranean sea suggests a much higher seasonality ca 10 c the low seasonality and the relatively cold water 9 10 c indicate the outcrops represent colder climatic conditions compared to modern times and suggest the occurrence of a maximum glacial phase

recycling of crustal materials through study of ultrahigh pressure minerals in collisional orogens ophiolites and mantle xenoliths a review abstract newly recognized occurrences of ultrahigh pressure uh p minerals including diamonds in ultrahigh temperature uh t felsic granulites of orogenic belts in chromitites associated with ophiolitic complexes and in mantle xenoliths suggest the recycling of crustal materials through deep subduction mantle upwelling and return to the earth s surface this circulation process is supported by crust derived mineral inclusions in deep seated zircons chromites and diamonds from collision type orogens from eclogitic xenoliths in kimberlites and from chromitities of several alpine himalayan and polar ural ophiolites some of these minerals contain low atomic number elements typified by crustal isotopic signatures ophiolite type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone in addition to ringwoodite and inferred stishovite a number of nanometric minerals have been identified as inclusions employing state of the art analytical tools reconstitution of now exsolved precursor uh p phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier uh p conditions for example tibetan chromites containing exsolution lamellae of coesite diopside suggest that the original chromitites formed at p 9 10 gpa at depths of 250 300 km the precursor phase most likely had a ca ferrite or a ca titanite structure both are polymorphs of chromite and at 2000 c would have formed at minimum pressures of p 12 5 or 20 gpa respectively some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin including zircon feldspars garnet kyanite andalusite quartz and rutile the zircons possess much older u pb ages than the time of ophiolite formation these uh p mineral bearing chromitite hosts evidently had a deep seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes these new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere recycling of surface organic carbon into the lower mantle and ascent to the earth s surface through mantle upwelling intensified study of uh p granulite facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

direct dating of adirondack massif anorthosite by u pb shrimp analysis of igneous zircon implications for amcg complexes the low abundance of igneous zircon in proterozoic massif anorthosites has presented a major obstacle to the acquisition of direct absolute ages of crystallization for these important rocks indirect dating that relies on zircon ages from associated mangerite charnockite granite granitoids assumes that they have a coeval relationship with anorthosite that requires documentation shrimp sensitive high resolution ion microprobe u pb zircon dating techniques provide a powerful means for directly dating the small populations of zircons in anorthositic rocks and for resolving problems with inheritance within the adirondack mountains 10 samples of massif anorthosite have yielded more than sufficient quantities of igneous zircon to establish directly the ages of the region9s classic anorthosite occurrences e g the marcy and oregon dome massifs in addition a ferrogabbro a ferrodiorite and a coronitic olivine metagabbro all crosscutting massif anorthosite were dated the average age of this suite of 13 anorthositic samples is 1154 6 ma mswd mean square of weighted deviates 0 26 probability 0 99 in addition eight associated granitoids have been dated by shrimp techniques and complement another five previously dated by multi grain thermal ionization mass spectrometry tims methods the 13 granitoids yield an average age of 1158 5 mswd 0 89 probability 0 60 and are broadly coeval with the massif anorthosite the overlapping ages provide evidence that these rocks constitute a single composite anorthosite mangerite charnockite granite amcg suite intruded at ca 1155 ma an age corresponding to the ages of major amcg suites in the grenville province in canada e g morin and lac st jean although rocks of the adirondack amcg suite are now documented as broadly coeval it does not follow that the constituent amcg lithologies were comagmatic field relationships and mineral disequilibria in transitional zones are inconsistent with derivation from a single parental magma moreover the presence of older ca 1 2 1 3 ga inherited cores in some zircons from amcg granitoids conflicts with derivation of these rocks from magmas that formed anorthosite gabbro or ferrodiorite or jotunite in which zircons are highly soluble the slightly older ca 1158 ma average age of the mangeritic and charnockitic members of the amcg suite is consistent with an origin as early lower crustal anatectites that left behind pyroxene plagioclase restites this refractory material then reacted by assimilation fractional crystallization afc with ponded mantle derived gabbroic magmas to produce plagioclase rich crystal mushes with crustal isotopic signatures as proposed much earlier by r f emslie these magmas are considered to be parental to the adirondack anorthosite and upon ascent they were emplaced in proximity to still hot earlier mangeritic and charnockitic bodies where they underwent further fractionation the composite nature of the marcy massif documents that this process was repeated in several sequential pulses

consequences of progressive eclogitization on crustal exhumation a mechanical study summary the very low water content of the granulitic unit of holsnoy in the bergen arcs norway caused its partial metastable preservation throughout caledonian burial end exhumation leading to the observed mixture of completely eclogitized and uneclogitized rocks the eclogitization of the granulite facies protolith led to a density increase 10 but also to a large rheological weakening that resulted in the localization of all deep ductile deformation in the eclogite fraction we address the consequences on subduction dynamics of the concomitant evolution of large scale density and rheology during progressive eclogitization of crust by comparing the behaviour of buried crust with various properties in the channel flow model large scale buoyancy and density are integrated in a single adimensional parameter the exhumation number which describes the capacity of the crust to exhume for a crust whose eclogitization causes a very large viscosity decrease burial resistant end member goes through a maximum in the partially eclogitized zone that is there is a given proportion of eclogite for which the crust is strongly weakened but still significantly lighter than surrounding mantle for this partially eclogitized crust with max the maximum possible downward flow is very low this zone acts as a bottleneck and all incoming crust in excess is forced backwards and starts exhuming this return flow zone is bounded downwards in the partially eclogitized zone by max while its upper limit propagates upwards at a constant rate the curve eclogite fraction controls the maximum proportion of eclogite of the crust that can be exhumed we also demonstrate that large exhumation rates reached by certain uhp units are incompatible with any stationary flow regime whatever the nature of subducted crust the additional presence of a weak layer on top of the channel favours burial for narrow channels and exhumation for large ones but does not qualitatively change the dynamics of the subduction channel this study shows that deep crustal circulation in subduction zones and exhumation from large depths are controlled by the evolution of large scale crustal properties with progressive eclogitization

experimental examination of two pyroxene graphical thermometers using natural pyroxenes with application to metaigneous pyroxenes from the adirondack mountains new york clinopyroxene with exsolved orthopyroxene and coexisting orthopyroxene with exsolved clinopyroxene inverted pigeonite in metaigneous rocks from the adirondacks new york were experimentally homogenized at temperatures near those inferred for their original crystallization the purposes were several 1 to test the graphical two pyroxene geothermometer of lindsley 1983 2 to test the hypothesis of bohlen and essene 1978 that these were originally igneous pyroxenes and 3 to test whether modal recombination of complexly exsolved pyroxenes yields realistic compositions experiments on fe rich compositions at 930 and 870 c 1 gpa are compatible with the graphical thermometer of lindsley 1983 however this graphical thermometer yields apparent temperatures approximately 50 c too high for experiments at 1050 c and 1100 c 0 mpa this suggests that at intermediate mg fe the augite isotherms for these temperatures lie at lower wollastonite compositions than shown by lindsley the results are however in good agreement with isotherms derived from the solution model of davidson 1985 when these isotherms are applied to a variety of terrestrial and lunar igneous rocks and the metaigneous rocks from the adirondacks temperatures given by augite and pigeonite compositions from coexisting pairs are similar comparison of the experimentally homogenized compositions with modally recombined compositions of bohlen and essene 1978 show that discrepancies between augite and pigeonite temperatures may nevertheless arise if pyroxene grains formed by granular exsolution are not correctly reintegrated

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part i the monazite ce brabantite solid solution series peraluminous granites of the erzgebirge fichtelgebirge germany are hosts of various members of the monazite group of minerals that display an unprecedented compositional diversity the eibenstock s type granite constitutes the third reported occurrence worldwide of brabantite and the first occurrence of this mineral in a granite many new occurrences of cheralite ce as well as a monazite group mineral intermediate between monazite ce and huttonite for which the term huttonitic monazite is proposed were discovered even common monazite ce may show extreme ranges of actinide and lanthanide element concentrations the granites that host brabantite and cheralite ce are highly differentiated strongly peraluminous low temperature residual melts of s type affinity which are rich in fluorine and other volatile constituents but depleted in thorium and the light rare earth elements such highly evolved volatile rich compositions resemble rare element pegmatites and appear favorable for the precipitation of cheralite ce and brabantite but not of monazite with large amounts of huttonitic substitution instead these minerals occur preferentially in f poor biotite and f rich li mica granites of a type affinity irrespective of the level of uranium in silicate melts which may exceed that of thorium the substitution of uranium in monazite remains limited the compositional data reported here are consistent with complete miscibility in the monazite ce brabantite solid solution series under magmatic conditions these granites contain monazites that span almost the entire compositional range reported for monazite group minerals worldwide and therefore granites appear to be ideal rocks in which to study the crystal chemistry of this mineral group in general

stratigraphic paleoecology bathymetric signatures and sequence overprint of mollusk associations from upper quaternary sequences of the po plain italy upper quaternary sequences of the po plain italy were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns three densely sampled cores 89 samples 98 genera 23 280 specimens dominated by extant mollusk species with known environmental distributions were analyzed with detrended correspondence analysis dca the dca scores calibrated using extant genera provided outstanding estimates of bathymetry 3 m and related environmental parameters depth related successions of mollusk associations delineated by using dca were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques e g depth estimates for maximum flooding surfaces the dca ordination demonstrates the severity of the sequence stratigraphic overprint samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts when analyzed across comparable systems tracts similar species associations repeat during the last and current interglacial cycles suggesting that po plain mollusk associations have remained remarkably stable over the past 125 k y the results are consistent with the bathymetric interpretation of the dc axis 1 postulated previously for the paleozoic fossil record demonstrate the sequence stratigraphic overprint of paleoecological patterns predicted by computer modeling and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations

stratigraphic paleoecology of the valle di manche section crotone basin italy a candidate gssp of the middle pleistocene abstract macro benthic assemblages from the lower to middle pleistocene of the valle di manche vdm section crotone basin southern italy were used to assess the value of merging paleoecological quantitative patterns into a sequence stratigraphic framework two way cluster and detrended correspondence dca analyses were applied to the macrofossil data matrix comprising 22 samples 157 species and 5761 specimens specifically two way cluster analysis allowed for the characterization of five shelf related biofacies and four sub biofacies along section biofacies change along the vdm generally supported previous sequence stratigraphic interpretations and suggests that faunal turnover is the result of habitat tracking dca stratigraphic curves dc1 sample scores calibrated to the depth preferences of extant species provided quantitative estimates of bathymetry and the assessment of related parameters e g grain size sedimentation turbidity when plotted stratigraphically calibrated dc1 scores highlight the magnitude of relative sea level fluctuations at the scale of the section as well as individual sequences and systems tracts additionally dca derived paleobathymetric trends track the oscillations of the 18 o record indicative of global sea level change based on this comparison it is held that macro benthic assemblages once supported by a robust statistical interpretation can be employed successfully as a proxy for 18 o depicting the variability in local water depths the potential of this approach is especially high for studies in shallow water depositional settings where dependable 18 o data are typically difficult to obtain

crustal emplacement of exhuming ultra high pressure rocks will that be pro or retro side ultra high pressure u hp rocks form and exhume from deep within subduction channels but subsequent horizontal transport in the shallower orogenic crust makes it difficult to reconstruct their tectonic histories we use a conceptual framework and numerical models to show that buoyant exhumation from within a subduction conduit formed during one sided subduction may lead to emplacement of u hp rocks into either the lower plate prowedge or upper plate retrowedge of an orogen depending on whether the upper plate crust deforms or acts as a backstop during exhumation both modes may operate at different positions or different times within an orogen leading to emplacement of u hp rocks into both plates without changing subduction geometry we propose that retrotransport during exhumation may explain some u hp rocks e g liverpool land situated in the upper plate of the greenland norwegian caledonides

mineral zoning p t x m phase relations and metamorphic evolution of some adirondack granulites new york detailed petrologic analysis of ten meta anorthosites and related introduction rocks from the adirondack highlands new york has been used to the adirondack highlands of new york are one of constrain the p t history of the region metamorphic orthopyroxene the best studied granulite facies terranes of the world and clinopyroxene occur in aggregates of 1 mm diameter grains e g bohlen et al 1985 valley et al 1990 and that are zoned concentrically with decreasing al and fe fe mg references therein based on this considerable volume and increasing ca towards the rim moreover zoning is not related of work the peak metamorphic conditions in the to the presence of garnet zoning is interpreted to have been produced adirondack highlands have been fairly well constrained during growth by the reaction igneous pyroxene plagioclase at pressures of 7 8 kbar crustal depths of 25 30 metamorphic opx metamorphic cpx along a cooling path with a km and temperatures that range from 775 c in slope of 6 bars c starting at 850 c and 6 5 8 kbar garnet the central highlands to t 675 c in the southern occurs as isolated clusters of 5 25 grains of 1 mm diameter adirondacks e g bohlen et al 1985 p t paths have crystals and as necklaces of 1 mm diameter crystals surrounding been shown to follow nearly isobaric cooling trajectories metamorphic pyroxenes or oxides plagioclase quartz typically e g bohlen 1987 because of this wealth of inseparates garnet from pyroxene but locally garnet embays metaformation some fundamental questions about the origin morphic pyroxene suggesting that garnet grew at the expense of of the adirondack granulite facies terrane have emerged pyroxene garnet clusters have slightly lower fe fe mg than e g bohlen et al 1985 how did the crust achieve garnet in necklaces fe fe mg 0 73 and 0 75 0 78 rethe relatively high temperature conditions necessary to spectively and slightly higher grossular xgrs 0 20 vs 0 19 produce granulite facies rocks at depths of 25 30 km neither is zoned in mn and zoning towards increasing fe and what is the relative importance of magmatic fe mg is restricted to contacts with biotite and locally clinoheating vs continental burial in this process pyroxene biotite adjacent to garnet is zoned towards decreasing this study will present new data on mineral comfe fe mg production of garnet in necklaces is interpreted position and element zoning in garnet pyroxene to be the result of the continuous fe mg reaction opx pl biotite amphibole and plagioclase from adirondack grt cpx qtz p t x m modeling of this reaction reveals a meta anorthosite and related rocks with the goal of p t path with a slope of 6 bars c no evidence for early prefurther constraining the metamorphic evolution of this metamorphic peak garnet is observed which rules out any possibility terrane mineral compositions will be used to construct of early higher pressure metamorphism the p t path is therefore phase diagrams in an attempt to evaluate approach to inferred to be counterclockwise with loading to 6 5 8 kbar at a chemical equilibrium theoretical analysis will be used maximum temperature of 850 c occurring during or immediately to construct p t x m phase diagrams depicting how following an influx of heat presumably from early orogenic plutons mineral composition and modes change with p and t this theoretical analysis will then be applied to the mineral zoning to constrain the p t path and the results will be discussed in the context of a tectonic

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

bulk chemical control on metamorphic monazite growth in pelitic schists and implications for u pb age data several petrographic studies have linked accessory monazite growth in pelitic schist to metamorphic reactions involving major rock forming minerals but little attention has been paid to the control that bulk composition might have on these reactions in this study we use chemographic projections and pseudosections to argue that discrepant monazite ages from the mount barren group of the albany fraser orogen western australia reflect differing bulk compositions a new sensitive high mass resolution ion microprobe shrimp u pb monazite age of 1027 8 ma for pelitic schist from the mount barren group contrasts markedly with previously published shrimp u pb monazite and xenotime ages of c 1200 ma for the same area all dated samples experienced identical metamorphic conditions but preserve different mineral assemblages due to variable bulk composition monazite grains dated at c 1200 ma are from relatively magnesian rocks dominated by biotite kyanite and or staurolite whilst c 1027 ma grains are from a ferroan rock dominated by garnet and staurolite the latter monazite population is likely to have grown when staurolite was produced at the expense of garnet and chlorite but this reaction was not intersected by more magnesian compositions which are instead dominated by monazite that grew during an earlier greenschist facies metamorphic event these results imply that monazite ages from pelitic schist can vary depending on the bulk composition of the host rock samples containing both garnet and staurolite are the most likely to yield monazite ages that approximate the timing of peak metamorphism in amphibolite facies terranes samples too magnesian to ever grow garnet or too iron rich to undergo garnet breakdown are likely to yield older monazite and the age difference can be significant in terranes with a polymetamorphic history

yttrium zoning in garnet coupling of major and accessory phases during metamorphic reactions the concentration of yttrium in pelitic garnets as a function of metamorphic grade has been examined in relation to the distribution of xenotime ypo 4 in samples from new england and british columbia samples with xenotime present only as inclusions in garnet generally possess high y cores and concentrations that drop off discontinuously along zoning shoulders of variable width to low y outboard regions samples with matrix xenotime are restricted to the garnet zone y concentration of these garnets generally decreases smoothly from core to rim xenotime may also be present in reaction zones around garnet in xenotime bearing samples y g r t is strongly temperature dependent and ranges from 5000 ppm in the garnet zone to 150 ppm in the sillimanite zone measured yttrium zoning profiles in xenotime absent samples are reproduced with both rayleigh fractionation and diffusion models but p t histories of the samples examined favor the rayleigh model with garnet volume bulk rock yttrium and mode of y hree accessory phases controlling the profile shape high yttrium annuli in staurolite zone samples may form by garnet overgrowth of proximal matrix enriched in yttrium due to garnet consumption during discontinuous staurolite forming reactions an increase in y g r t and hree g r t in garnet from anatectic samples is related to dissolution of phosphates in vapor absent peraluminous melt with partitioning of highly compatible y and hree into garnet grown during anatexis textural analysis reveals that phosphates are absent from regions of garnet grown in equilibrium with melt a main result of this study is identification of an intimate coupling between major pelite phases and accessory phases during reaction progress this coupling is of great advantage in that it may be used to 1 calibrate sensitive geothermometers and geobarometers 2 identify particular regions of garnet grown in different garnet producing reactions over a range of grades and 3 reveal portions of pelite reaction history invisible to major elements

palaeoecology taphonomy and preservation of a lower pliocene shell bed coquina from a volcanic oceanic island santa maria island azores abstract massive fossil shell accumulations require particular conditions to be formed and may provide valuable insights into the sedimentary environments favouring such concentrations shallow water shell beds appear to be particularly rare on reefless volcanic oceanic islands on account of narrow steep and highly energetic insular shelves where the potential for preservation is limited the occurrence of an exceptional coquina pedra que pica within the miocene pliocene deposits of santa maria island azores therefore provides a rare opportunity to understand the conditions that led to the formation and preservation of a massive shell bed at mid ocean insular setting this study provides a detailed analysis regarding a 10 11 m thick bivalve dominated fossil assemblage exposed at pedra que pica on santa maria island in the azores integration of taphonomical palaeoecological and sedimentological observations are used to reconstruct the genesis of the coquina bed and related events and to discuss why such exceptional sedimentary bodies are so rare on shelves around reefless volcanic oceanic islands the sequence at pedra que pica demonstrates a complex succession of sedimentary environments in response to the drowning of an existing coastline during a period of rapid sea level rise the pedra que pica shell bed incorporates storm related materials and possible debris falls that originated nearby in a shallow and highly productive carbonate factory deposition took place below fair weather wave base at around 50 m depth as inferred from the overlying volcanic succession the preservation of this coquina was favoured by deposition on a platform laterally protected by a rocky spur combined with rapid burial by water settled volcanic tuffs and subsequent volcanic effusive sequences the recent exhumation of the deposit is the result of island uplift and subsequent erosion

sequence stratigraphy and the resolution of the fossil record sequence stratigraphy a major theoretical achievement of earth sciences integrates facies associations and stratal architecture within a chronological framework of the geological record the sequence stratigraphic model implies that sediment supply to the basin preservation potential of individual horizons and the resolution of paleontological data co vary with base level fluctuations especially for siliciclastic depositional systems using holocene transgressive regressive successions of the po plain italy we assessed the model s hypotheses by analyzing 249 marine mollusk shells dated individually using 14 c calibrated amino acid racemization methods as postulated by the model the temporal resolution of the fossil record frequency of depositional events and net accumulation rates decreased upward concomitantly through the transgressive systems tract reaching minima in the condensed section maximum flooding zone the reverse trend with increasingly frequent thicker and less time averaged beds was observed throughout the overlying highstand systems tract the results quantify the postulated sequence stratigraphic asymmetry in temporal resolution of the fossil and sedimentary records

hydrothermal alteration of monazite in the precambrian crystalline basement of the athabasca basin saskatchewan canada implications for the formation of unconformity related uranium deposits microanalytical studies of basement rocks below the athabasca sandstone basin indicate that monazite is the dominant uranium bearing mineral in the study area drill core samples of hydrothermally altered basement show that monazite is commonly altered to a th silicate phase and uranium has been significantly mobilized on average 75 of the uranium bound to monazite is leached out during monazite alteration in contrast no substantial mobilization of uranium from detrital minerals e g zircon has yet been observed in the athabasca sandstones it is suggested that hydrothermal alteration of granitic rocks especially potassic pegmatoids and potassic orthogneisses of the sub athabasca basement represents the most important uranium source for the unconformity type deposits

quantitative bathymetric models for late quaternary transgressive regressive cycles of the po plain italy abstractin marine settings quantitative bathymetric models can be developed using various water depth proxies including epibiont distribution sedimentologic features and the distribution of benthic taxa in time and space here the late quaternary bathymetric history of the po coastal plain italy has been reconstructed using mollusk samples from a network of 16 cores multiple analytical approaches have been applied in a comparative fashion a direct ordination approach was used to estimate sample bathymetry using weighted averaging of genera with known preferred depth weighted averaging carries an advantage of analytical simplicity and produces direct ordination models expressed in environmentally meaningful units indirect ordination methods based on depth estimates developed using posteriori calibrated ordination strategies correspondence and detrended correspondence analysis calibrated against present day bathymetric data yielded results consistent with weighted averaging regardless of the

styles of post subduction collisional orogeny influence of convergence velocity crustal rheology and radiogenic heat production abstract a number of models of continental collision already exist but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored in addition heat generation by radioactive decay may be quite variable for example our geochemical data from low to high grade metamorphic rocks of the lesser and higher himalayan sequences reveal measured heat production values on the order 4 5 w m 3 which is considerably higher than normal inferred upper crustal values 3 therefore we performed 2d numerical experiments of oceanic continental subduction followed by continental collision for varying continental lower crustal strength convergence velocity and radiogenic heating rate oceanic subduction produces thinning and upwarping of the overriding lithospheric wedge such as is observed in andean type collisional settings cascadia and central andes after collision two main orogenic styles develop depending on the values of key parameters either a slow convergence rates weak shear heating and consequently strong rheological coupling between plates and or a weak lower crust generate a two sided thick and narrow symmetrical collisional zone or b high convergence rates strong shear heating and therefore weak rheological coupling between plates and a strong lower crust produce a one sided thin and broad asymmetrical collisional zone in this case a vertical lithospheric body divides two upper crustal wedges that develop distinct deformation patterns in both cases enhanced radiogenic heating favors the formation of midcrustal partially melted channels that propagate toward the surface and the pro foreland partial melting triggers lateral extrusion of metamorphic rocks from different depths 15 23 kbar 700 c on top of coherent lp lt units the geometry of metamorphic isograds inverted shapes of p t paths at different grades and exhumation rates are similar to those observed in parts of the himalayan chain indicating that the models capture the essence of real systems the model results demonstrate that internal heat production rate is a crucial parameter in determining the timing of slab breakoff polarity reversal and exhumation of the inverted metamorphic sequence with respect to the timing of partial melting late stages of some numerical experiments showed interesting geodynamical evolution of the collisional zone with the appearance of polarity reversal roll over of both plates and roll back of the subducting slab irrespective of these details hundreds of km of continental lithosphere are recycled into the mantle in all models supporting the idea that continental crustal consumption is indeed a common and considerable process during collision this affects inferences about extents of convergence and or shortening during orogenesis moreover crustal recycling into the deep mantle during collisional orogeny needs to be considered in models of crustal growth and evolution

sampling species abundance and the stratigraphic signature of mass extinction a test using holocene tidal flat molluscs assume that a catastrophe caused the sudden extinction of the molluscan biota of a holocene tidal flat would this event be recorded accurately in the stratigraphic record how accurately would the extinction of rare species be recorded how would sudden gradual and stepwise patterns of extinction compare bivalve and gastropod species occurrences were recorded from eight tidal channel sediment cores up to 70 cm long from bahia la choya northern gulf of california the distribution of last occurrences of 45 species suggests that a sudden extinction would appear to be gradual in the stratigraphic record due to error in biostratigraphic range end points signor lipps effect extinction is typically not accurately recorded for species with less than 15 stratigraphic abundance i e occurring in less than 15 of the sample intervals 71 of the species the data were subjected to simulations of stepwise and gradual extinction differences between the sudden stepwise and gradual scenarios are apparent in 1 frequency distributions of biostratigraphic last occurrences 2 graphic relations between stratigraphic abundance and last occurrence and 3 patterns of apparent diversity decline below the extinction boundary extinction studies in outcrops and cores could utilize last occurrence and stratigraphic abundance data readily available in the fossil record to distinguish among sudden stepwise and gradual patterns of extinction

an empirical garnet yag xenotime thermometer a pronounced negative correlation between the yttrium concentration in garnet y grt and temperature has been observed in xenotime ypo4 bearing metapelites from central new england usa the y grt decreases roughly two orders of magnitude 5500 to less than 100 ppm y over a 150 c interval a regression of ln y grt against estimated reciprocal temperature yields the following relationship

constraints on fluid evolution during metamorphism from u th pb systematics in alpine hydrothermal monazite abstract the timing and duration of hydrothermal activity during orogenesis are difficult to constrain because such systems are open and multistage using mm sized monazite crystals from two alpine clefts from the central alps switzerland we demonstrate that combined u th pb isotopic systematics of hydrothermal monazite can constrain both timing and fluid evolution during crystallization our data highlight four major characteristics of the cleft monazites i extreme th u ratios ii significant common pb in the u system up to 39 206 pb iii excess 206 pb up to 54 and iv precise and reliable th pb ages comparison of our results with literature data indicates that th u in monazite is a remarkable discriminant of geological conditions capable of distinguishing metasedimentary magmatic and hydrothermal origin hydrothermal monazite crystals are characterized by th u ratios up to 629 among the highest values ever reported extreme th u ratios in monazite enhance incorporation of 230 th a short lived intermediate product in the 238 u 206 pb decay chain generating 206 pb excess which if not accounted for results in 206 pb 238 u ages that are too old for example in the samples investigated here by as much as 300 for the two zoned monazite crystals studied in detail 208 pb 232 th ages are reliable for the different compositional domains visible in back scattered electron bse images 232 th 208 pb ages for the older domains 15 2 0 3 ma and 14 1 0 3 ma respectively are consistent with the structural relationships of the hydrothermal veins indicating early retrograde genesis the youngest rim age at 13 5 0 4 ma for the blauberg crystal marks termination of monazite precipitation the resolvable age difference is interpreted to reflect pulsed monazite growth over an extended period of hydrothermal activity in both crystals the outer rims have the highest 206 pb excess confirming a two stage crystallization two scenarios are envisaged to account for the 206 pb excess evolution in the first increasing 206 pb excess is caused by a modification of the th u fractionation between monazite and fluid due to an evolution of the fluid towards more oxidizing conditions that favor partitioning of hexavalent u into the fluid alternatively it is possible that 230 th increased with time in the fluid in this second case monazite growth would have occurred in a closed system from a fluid that was initially in disequilibrium with the 238 u 206 pb decay chain and progressively equilibrated t

constraints on the subduction erosion extrusion cycle in the paleozoic acatlan complex of southern mexico geochemistry and geochronology of the type piaxtla suite abstract the type high pressure hp piaxtla suite in the acatlan complex of southern mexico consists of retrogressed eclogite amphibolite megacrystic granitoids and high grade meta sedimentary rocks exhumation of these hp rocks has recently been interpreted as the result of extrusion into the upper plate rather than by return flow up the subduction zone geochemical analyses of the retrograde eclogites indicate that they have a rift tholeiitic transitional alkalic composition these are closely associated with a megacrystic meta granitoid that has yielded an intrusive age of 452 6 ma concordant u pb zircon analyses with inherited zircon populations at ca 800 950 ma and 1000 1200 ma derived from the underlying basement probably the oaxacan complex which borders the acatlan complex to the east the bimodal nature of these igneous rocks and their spatial and temporal close association with continentally derived sedimentary rocks is similar to most hp rocks in the acatlan complex derived from a rifted passive margin the youngest detrital zircon population in a meta psammite sample yielded a u pb age of 365 15 ma with older analyses distributed along a chord with an upper intercept of 1287 29 ma the ca 365 ma age provides a maximum age for the time of deposition of this sample 40 ar 39 ar ages from the retrogressed eclogites provided hornblende plateau ages of 342 2 ma and 344 2 ma whereas muscovite from the granitoid and meta psammite yielded 334 2 ma plateau ages these data constrain the subduction erosion extrusion cycle to 35 ma during which the rocks were taken to a depth of ca 40 km at a rate of 2 7 km ma and back to the surface at 2 4 km ma such exhumation rates are slower than those in continent continent collision zones but similar to those in the iberia czech variscan belt where tectonic interpretation also suggests extrusion into the upper plate

dynamics of benthic marine communities across the early middle pleistocene boundary in the mediterranean region valle di manche southern italy biotic and stratigraphic implications abstract the valle di manche vdm section calabria southern italy offers the opportunity to investigate the ostracod turnover along a continuous shelf succession straddling the early middle pleistocene boundary and compare it against other paleoenvironmental i e mollusks and paleoclimatic uvigerina peregrina 18o records high resolution ca 1 sample m ostracod fauna quantitative data coupled with gradient analysis detrended correspondence analysis and non metric multi dimensional scaling document a strong relationship between changes in faunal composition and lithofacies vertical stacking patterns the comparison between the mollusk and ostracod derived ordination data demonstrates that the meio and macro faunal turnover is guided by a common complex gradient bathymetry the integrated ostracod mollusk gradient analysis also provides a trend in water depths along the section highlighting to what extent such multivariate approach can improve the paleoenvironmental and sequence stratigraphic interpretation of ancient shallow marine successions when plotted stratigraphically ordination major axis sample scores reveal two increasing decreasing patterns in water depth that fit well with the t r cycles previously identified paleobathymetric estimates combined with the vertical distribution of key ostracod groups i e epiphytic taxa on sandy substrates vs deep sea mud related taxa allow refining depositional trends stratal stacking patterns and position of previously not well resolved sequence stratigraphic surfaces within each t r cycle e g transgressive surface ts indeed two rapid increases in water depth values mark the tss that separate shallowing upward progradational rst from deepening upward retrogradational tst stratal stacking patterns of shelf deposits the tss which underline fine grained successions dominated by deep sea mud lover taxa are invariably constrained to the inception of interglacials marine isotope stages mis 21 and 19 identified within the vdm section by benthic foraminifera 18o values within both the vdm t r cycles the deepest conditions ca 140 m of water depth are invariably identified within the neopycnodonte unit slightly above the lightest 18o intervals the overlying decreasing bathymetric trend coupled with shifts in ostracod ecological groups allows to identify in the bryozoans lithofacies the stillstand falling of the relative sea level also tracked by a progressively heavier 18o record more stable paleobathymetric conditions around 40 45 m of water depth characterize the overlying silt sand deposits dominated by epiphytic species and showing the heaviest 18o values

crustal structure a key constraint on the mechanism of ultra high pressure rock exhumation abstract the distribution of ultra high pressure uhp metamorphic rocks demonstrates that burial to 100 km and rapid exhumation 1 cm a 1 of continental crust is a normal part of early 10 ma continental collision currently there is no comprehensive model for this fundamental tectonic process that also satisfactorily explains the upper crustal structures resulting from early collisional uhp rock exhumation characteristic features requiring explanation include structural domes that are cored by uhp nappes associated medium to high pressure nappes displaying a distinct pressure gap overlying lower grade rocks including suture zone ophiolites and coeval foreland directed thrust faults and syn exhumation normal faults we present a geodynamical model involving crustal burial and exhumation in a subduction channel below an accretionary wedge competition between down channel shear traction and up channel buoyancy forces expressed as the exhumation number e controls burial and exhumation leading to rapid up channel flow when e 1 exhuming uhp material forms a nappe stack and structural dome as it penetrates and destabilises the overlying wedge driving thrusting and extension this solution is compelling because it explains both the geology and the petrology of the tso morari and other uhp complexes and because it demonstrates that pulse like buoyant exhumation from deep in the subduction channel creates observed upper crustal structures this places constraints on the exhumation mechanism and provides a test of alternative models other proposed mechanisms such as continuous circulation in a lithospheric scale wedge or overpressured subduction channel predict different types of upper crustal structures and are therefore unsatisfactory explanations for early collisional exhumation of uhp terranes

late paleozoic transcurrent tectonic assembly of the central appalachian piedmont recent investigations in south eastern pennsylvania and northern maryland have demonstrated a major anastomosing strike slip shear system the pleasant grove huntingdon valley shear system emerges from beneath the coastal plain cover at trenton new jersey and extends to the area west of baltimore maryland where it is overlain by the culpepper mesozoic rift basin the sense of offset across this system is dextral in the susquehanna river region and north of the shear zone the rocks of the octoraro formation contain evidence for two metamorphisms and deformations prior to strike slip shearing whereas south of the shear zone the peters creek formation contains evidence for only one the discordance in metamorphic and deformational history across the shear zone suggests the now juxtaposed rocks originated in different parts of the orogen although conclusive ages for the strike slip deformation do not exist at this time the timing of deformation is loosely constrained where the shear system crosscuts known taconian structures in the piedmont comparison of deformation style with other regions in the appalachian suggests the pleasant grove huntingdon valley shear system is related to alleghanian transcurrent tectonics in the piedmont palinspastic reconstruction of the pleasant grove huntingdon valley shear system reveals fundamental problems in current tectonic models for the central appalachian piedmont a minimum of 150 km of dextral offset is proposed for the pleasant grove huntingdon valley shear system based on reconstruction of the cambrian ordovician shelf edge between northern maryland and southeastern new york displacement of this magnitude can account for the previously proposed tectonic models that portray a failed iapetan rift block and microcontinent that contains the baltimore grenvillian massifs even though a history of early orthogonal collision is preserved within discrete structural blocks transcurrent shearing has greatly influenced the distribution of those blocks models not including the strike slip component of tectonic assembly need serious reconsideration as evidence grows that the magnitude of orogen parallel displacement is equal to or larger than the orthogonal component

temperature time paths from phosphate accessory phase paragenesis in the honey brook upland and associated cover sequence se pennsylvania usa abstract analysis of monazite bearing lithologies from the precambrian honey brook upland hbu and overlying metasedimentary paleozoic chester valley sequence cvs se pa usa reveals overprinting of primary major and accessory phase parageneses by texturally and compositionally disparate secondary accessory phase parageneses two pyroxene temperatures of 915 945 c for reconstituted pyroxene reflect emplacement temperatures of felsic plutonic rocks opdalite charnockite prior to mesoproterozoic metamorphism monazite in metavolcanic felsic gneiss yields three age domains at 1009 4 ma 2 s e 965 6 and 876 10 ma the first two domains record metamorphism of the hbu after anorthosite intrusion peak monazite xenotime temperatures for the monazite core domain are 700 c and high th u values in the second overgrowth age domain likely reflect a second high t monazite growth episode formation of cummingtonite coronas on orthopyroxene in opdalite constrains maximum 1010 ma metamorphic temperatures in the granulite facies terrane to 730 740 c evidence of increased cl fluid activity in the 965 ma metamorphism includes higher cl content of matrix apatite relative to garnet included apatite metavolcanics and cl bearing k hornblende succeeding cummingtonite in coronal overgrowths opdalite extreme monazite th u values 75 250 in the rim domain suggest growth during low t hydrothermal alteration in the opdalite secondary singe grain monazite and monazite xenotime metasomites in apatite yield ages of 714 24 and 586 88 ma temperatures of 325 425 c and are interpreted to reflect thermal disturbances associated with late proterozoic plutonic and volcanic activity in the upland this thermal disturbance may be recorded by rb sr age of 567 ma for biotite from a hbu gneiss monazite age domains in metaquartzite 378 28 272 44 ma suggest that low grade metamorphism 260 320 c mnz xno thermometry of the cvs is not a result of taconian orogenesis

fluid induced nucleation of y ree phosphate minerals within apatite nature and experiment part i chlorapatite this study investigates chlorapatite ideally ca10 po4 6cl2 from two spatially separated locations in the odegardens verk apatite mine bamble sector se norway which was partially metasomatized under amphibolite facies conditions relative to the original chlorapatite metasomatized areas in sample dl136 are enriched in oh and f depleted in na si and y ree and contain numerous inclusions 1 15 m of monazite and xenotime in contrast metasomatized areas in sample tn174 are enriched in f and si depleted in na show y ree abundances similar to the original chlorapatite and host only a few monazite and xenotime grains in order to define the role of fluids in the formation of y ree phosphate minerals associated with apatite a series of experiments covering wide ranges of temperature 900 300 c and pressure 1000 500 mpa for a series of fluid compositions pure h2o a 50 50 molar mix of h2o and caf2 and co2 with 1 2 wt h2o were conducted on unaltered chlorapatite from the odegardens verk in the h2o experiments features due to metasomatic alteration depletion in na si and y ree as well as numerous monazite and xenotime inclusions as observed in the natural sample dl136 were fully reproduced monazite and xenotime grains were also observed growing on the surface of the apatite in dissolution embayments in metasomatized areas in the 50 50 caf2 h2o experiments metasomatized regions are strongly enriched in f and si depleted in na show unchanged y ree abundances and contain only a very few small monazite and xenotime grains similar to what was observed in sample tn174 natural and experimental observation imply the presence of two coupled substitutions na y ree 3 2 ca2 and si4 y ree 3 p5 ca2 in the case of dl136 and h2o fluid experiments na and si4 went into solution whereas the released y ree contributed to the growth of monazite and xenotime within the metasomatized apatite structure for sample tn174 and the 50 50 caf2 h2o fluid experiments na in apatite became depleted but si was enriched thereby stabilizing the y ree in the now recrystallized fluor hydroxylapatite structure which retarded the growth of monazite or xenotime inclusions the basic conclusion of this study is that nucleation of monazite and xenotime in the metasomatized chlorapatite is principally a function of the composition of the infiltrating fluid and to a much lesser extent temperature and pressure