assessment of heavy metal distribution pattern in the sediments of tamirabarani river and estuary east coast of tamil nadu india the present study aims to investigate the concentration and spatial distribution of trace metals in tamirabarani river and estuary located in the southeast coast of india sediment samples collected from sixteen locations were analysed for cu ni cr pb zn and cd the extent of pollution in these sediments was assessed using enrichment factor ef contamination factor cf geo accumulation index i geo the ef shows enrichment of ni in the northern part of the estuary and that of cu in the south and it is mainly due to the process of weathering the contamination factor indicates cd is more highly contaminated than other metals i geo index shows that cd is moderately polluted and its spatial distributions clearly indicate that it is found in estuarine region the comparison of metal concentration with other estuaries of india indicates that these metals are well below the permissible limit the metals in the estuary of the study area indicate more of the predominance of natural process than other estuaries in india it is evident that the samples of river and estuary area are dominantly due to the natural process rather than anthropogenic activity

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

origin and evolution of avalonia evidence from u pb and lu hf isotopes in zircon from the mira terrane canada and the stavelot venn massif belgium laser ablation inductively coupled plasma mass spectrometry u pb and lu hf isotope analyses of detrital zircon from neoproterozoic cambrian clastic sedimentary rocks in the mira terrane cape breton island nova scotia canada west avalonia and the stavelot venn massif east belgium east avalonia support deposition on an originally coherent microcontinent crustal evolution trends defined by hf t values varying with age reflect juvenile magma production in the source continent at 1 2 2 2 and 2 4 3 1 ga mixing of juvenile and recycled crust in continental magmatic arcs is recognized at 0 5 0 72 1 4 1 7 1 8 2 2 and 2 4 2 7 ga these results concur with the crustal evolution in amazonia the likely parent craton crustal evolution in avalonia is recorded in detrital and magmatic zircon from neoproterozoic arcs 680 550 ma positive hf t values suggest juvenile input and mixing with recycled crust most negative hf t values represent recycling of predominantly mesoproterozoic underlying crust avalonian arc magmatism was followed by late neoproterozoic early cambrian sedimentation in various belts in west avalonia these belts were juxtaposed by strike slip during late early cambrian deposition in a rift basin the youngest detrital zircon population c 517 ma probably represents synrift magmatism before break up of avalonia migmatization at 406 2 ma in a xenolith from the east avalonian crust reflects post collisional heating supplementary materials details of sample locations and analytical results are available at www geolsoc org uk sup18641

preservation of old prograde metamorphic u th pb ages in unshielded monazite from the high pressure paragneisses of the variscan ulten zone italy abstract three samples of garnet kyanite paragneiss from the variscan ulten zone northern italy were studied in detail for u th pb monazite dating monazite in these gneisses is abundant shows highly variable grain size and occupies different textural positions within the matrix as inclusion in garnet and kyanite within apatite aggregates monazite shows different deformation features as a function of the textural position enclosed shielded monazite is generally more fractured than matrix unshielded monazite the integration of textural information with deformation features and in situ u th pb analyses by la icp ms indicates that there is no direct correlation between textural site and monazite ages old ages of 351 343 ma determined on portions of large matrix unshielded monazite and on rare domains of monazite shielded by garnet have been related to a prograde stage of the variscan metamorphic evolution of the ulten zone ages of 330 326 ma which are related to the thermal peak are recorded by small matrix monazite external domains of large matrix monazite and by domains of fractured monazite enclosed in garnet and kyanite large old unshielded grains formed as blasts during the prograde metamorphic history and survived the peak metamorphism during which crystallisation re crystallisation partially occurred

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

alteration and breakdown of xenotime y and monazite ce in granitic rocks of the western carpathians slovakia abstract in the granitic rocks of the western carpathians xenotime y occurs both as a late stage magmatic mineral and as a secondary post magmatic phase magmatic xenotime occurs with monazite and displays minor compositional zonation involving si th and u the source of elements for the formation of secondary xenotime y in the granitic rocks results from leaching of p and y ree mainly from zircon and apatite both xenotime y and monazite ce are unstable during fluid activated overprinting low temperature alteration of monazite in s type granites leads to the formation of apatite enriched in the britholite component but low to medium grades of metamorphism result in the formation of apatite and lree enriched epidote partly allanite as a corona enclosing the monazite ce core xenotime y shows a similar alteration pattern but with different ree distributions within the products at greenschist amphibolite facies rims of secondary y rich apatite and y rich epidote form around xenotime y in low ca granites however apatite is missing from this alteration assemblage as xenotime y breaks down directly to y enriched epidote the relative mobilities of the heavy and light ree are different during breakdown of monazite and xenotime the fluid responsible for the breakdown of monazite and xenotime contains elements released from alteration of anorthite ca and biotite si al and f

partially retrograded eclogites of the munchberg massif germany records of a multi stage variscan uplift history in the bohemian massif eclogites with a wide range in bulk composition are present in the munchberg massif part of the variscan basement of the bohemian massif in north east bavaria new analyses of the primary phases garnet omphacite phengite and amphibole as well as the secondary phases clinopyroxene ii various amphiboles biotite phlogopite plagioclase margarite paragonite prehnite and pumpellyite reveal a complex uplift history new discoveries were made of samples with very jadeite rich primary omphacite as well as a secondary omphacite in a symplectite with albite various geothermobarometric techniques together with thermodynamic databases incorporating separately determined activity composition values and experimental data have clustered the minimum conditions for the primary assemblages to the p t range 650 60 c 14 3 1 kbar however jadeite in omphacite kyanite paragonite in phengite and zoisite grossular in garnet kyanite quartz relationships suggests pressures of 25 28 kbar at the same temperatures the fact that the secondary omphacite plagioclase assemblage yields pressures within a few hundred bars of the minimum pressures for the plagioclase free assemblages strongly suggests that the minimum values are serious underestimates zoning inclusion suites and breakdown reactions of primary phases in addition to new minerals formed during uplift define a polyphase metamorphic evolution which from geochronological evidence occurred solely within the variscan cycle the complex breakdown in other bohemian massif eclogites and the distinct variation in their temperatures during uplift suggest a multi stage thrusting model for the regional evolution of the eclogites such an evolution has significance with respect to incorporation of mantle slices into crustal sequences and fluid derivation from successively subducted units possibly driving the breakdown reactions

p t evolution and fluid inclusion characteristics of retrograded eclogites munchberg gneiss complex germany kyanite eclogites occur as part of the munchberger nappe pile in ne bavaria west germany eclogites are overprinted by subsequent amphibolite facies metamorphism the preservation of primary eclogitic textures as well as symplectitic textures are indicative of rapid decompression eclogite formation is estimated to have occurred under conditions of high h2o activities at pressures between 20 and 26 kbar and temperatures ranging between 590 and 660 c as is shown by the coexistence of omphacite jd 50 kyanite zoisite and quartz minimum pressure estimates independent of the water activity range between 9 and 16 kbar at the relevant temperatures detailed studies of fluid inclusion reveal two predominant groups of aqueous brine inclusions high salinity 14 17 wt nacl equiv and low salinity 0 8 wt nacl equiv inclusions fluid compositions of both groups of inclusions yield isochores passing close to the estimated amphibolite facies pt field the compositions of these fluids are in good agreement with fluid compositions considered from mineral equilibria none of the fluid inclusions has densities appropriate for eclogite facies metamorphism but probably reflect later amphibolite facies metamorphism

probable anticlockwise p t evolution in extending crust hlinsko region bohemian massif in the hlinsko region variscan bohemian massif czech republic a major extensional shear zone separates low grade metasedimentary series hlinsko schists and high grade rocks of the moldanubian terrane svratka crystalline unit during late variscan extension a tonalite intruded syntectonically into the normal ductile shear zone and caused contact metamorphism of the overlying schists concurrent syntectonic sedimentation of a flysch series took place at the top of the hangingwall schists in order to decipher the detailed petrological evolution of the hlinsko unit situated in the hangingwall of this tectonic contact a phase diagram approach and pctrogenetic grids calculated with the thermocalc computer program were used the crystallization deformation relationships and the paragenetic analysis of the hlinsko schists define a p t path with an initial minor increase in pressure followed by cooling calculated pseudosections constrain this anticlockwise p t evolution to the upper part of the andalusite field between 0 36 and 0 40 gpa for temperatures ranging from 570 to 530 c a low uhz0 is required to explain the presence of andalusite biotite bearing assemblages and could be related to the presence of abundant graphite in contrast the footwall rocks of the svratka crystalline unit record decompression from around 0 8 gpa at a relatively constant temperature followed by cooling thus the footwall and the hangingwall units display opposite but convergent p thistories decompression in the footwall rocks is related to a rapid exhumation we propose that the inverse anticlockwise p t path recorded in the hangingwall pelites is related to the rapid extension controlled sedimentation of the overlying flysch series

the palu metamorphic complex nw sulawesi indonesia origin and evolution of a young metamorphic terrane with links to gondwana and sundaland abstract the palu metamorphic complex pmc is exposed in a late cenozoic orogenic belt in nw sulawesi indonesia it is a composite terrane comprising a gneiss unit of gondwana origin a schist unit composed of meta sediments deposited along the se sundaland margin in the late cretaceous and early tertiary and one or more slivers of amphibolite with oceanic crust characteristics the gneiss unit forms part of the west sulawesi block underlying the northern and central sections of the western sulawesi province the presence of late triassic granitoids and recycled proterozoic zircons in this unit combined with its isotopic signature suggests that the west sulawesi block has its origin in the new guinea margin from which it rifted in the late mesozoic it docked with sundaland sometime during the late cretaceous u th pb dating results for monazite suggest that another continental fragment may have collided with the sundaland margin in the earliest miocene high pressure hp and ultrahigh pressure uhp rocks granulite peridotite eclogite are found as tectonic slices within the pmc mostly along the palu koro fault zone a major strike slip fault that cuts the complex mineralogical and textural features suggest that some of these rocks resided at depths of 60 120 km during a part of their histories thermochronological data u th pb zircon and 40ar 39ar from the metamorphic rocks indicate a latest miocene to mid pliocene metamorphic event which was accompanied by widespread granitoid magmatism and took place in an extensional tectonic setting it caused recrystallization of and new overgrowths on pre existing zircon crystals and produced andalusite cordierite sillimanite staurolite assemblages in pelitic protoliths indicating ht lp buchan type metamorphism the pmc was exhumed as a core complex at moderate rates c 0 7 1 0 mm yr accompanied by rapid cooling in the plio pleistocene some of the uhp rocks were transported to the surface at significantly higher rates 16 mm yr the results of our study do not support recent plate tectonic reconstructions that propose a nw australia margin origin for the west sulawesi block e g hall et al 2009

different age response of zircon and monazite during the tectono metamorphic evolution of a high grade paragneiss from the ruhla crystalline complex central germany results of tims sims and sem analyses show that zircon and monazite in a high grade paragneiss of the ruhla crystalline complex central germany were formed and or altered during different stages of a tectono metamorphic history between early devonian and permian times detrital zircon cores of 460 ma place an older limit on the age of anatexis and show that the paragneiss sequence contains rocks at least as young as early cambrian metamorphic zircon growth commenced at 365 ma peaking at 360 355 ma at the same time that granite dykes were emplaced in contrast monazite in the paragneiss preserves little record of the metamorphic peak most monazite grains grew or were recrystallised in the lower carboniferous at 339 ma contemporaneous with the emplacement of voluminous diorite and granite bodies these intrusions and related tectonics caused some of the high u zircon overgrowths to undergo moderate to severe pb loss a second pb loss event between 300 and 280 ma can be related to late carboniferous early permian large scale block faulting

time of formation and peak of variscan hp ht metamorphism of quartz feldspar rocks in the central erzgebirge saxony germany the variscan erzgebirge represents an antiform with a core of gneisses and mica schists surrounded by a phyllitic mantle the gneiss eclogite unit geu in the central part is a composite tectonometamorphic assemblage characterized by a hp ht imprint and comprises migmatitic para and orthogneisses ht mylonites hp granulites eclogites and garnet peridotites it is tectonically sandwiched between two major units with distinctly lower pt histories the geu experienced a characteristic kinked retrograde pt path after hp ht equilibration with 1 strong near isothermal decompression at high temperatures 2 extensive re equilibration at medium pressures followed 3 by rapid cooling during continued uplift we dated zircons pb pb evaporation from granitoid orthogneisses and metapelites of the geu the orthogneisses contain euhedral long prismatic zircons of igneous origin that provided protolith ages between 470 and 524 ma metapelites retain well preserved granulite facies mineral assemblages and contain spherical multifaceted metamorphic zircons that grew near the peak of hp ht metamorphism inclusions of prograde hp phengite 15 kbar and rutile are included in one such zircon metamorphic zircons of three samples from different localities yielded identical 207pb 206pb ages of 340 5 0 7 ma 341 2 0 5 ma and 341 6 0 5 ma respectively consideration of these zircon ages with published 39ar 40ar white mica ages suggests fast cooling and uplift rates in excess of 50 c ma and 4 km ma this is typical for large scale extensional tectonic unroofing of the ultra deep part of a fossil thickened variscan continental crust 60 km during continuing continental collision and orogenic collapse

inferring protoliths of high grade metamorphic gneisses of the erzgebirge using zirconology geochemistry and comparison with lower grade rocks from lusatia saxothuringia germany protoliths of highly metamorphosed gneisses from the erzgebirge are deduced from the morphology age and chemistry of zircons as well as from whole rock geochemistry and are compared with lower grade rocks of lusatia gneisses with similar structural appearance and or geochemical pattern may have quite different protoliths the oldest rocks in the erzgebirge are paragneisses representing meta greywackes and meta conglomerates the youngest group of zircon of meta greywackes that did not undergo pb loss represents the youngest igneous component for source rocks about 575 ma similar ages and zircon morphology reflect the subordinate formation of new zircon grains or only zircon rims in the augengneiss from barenstein and wolkenstein which probably represent metamorphic equivalents to lower cambrian two mica granodiorites from lusatia bulk rock chemistry intense fracturing and high u and th concentrations of zircons suggest deformation induced and fluid enhanced recrystallisation of zircon grains temperatures during tectonic overprinting too low to reset zircon ages indicate mid or upper crustal levels for shearing recorded in these augengneisses lower cambrian 540 ma granodiorites are widespread in lusatia but are exclusively represented by the freiberg gneiss dome in the eastern erzgebirge ordovician protolith ages were recorded by zircons from the augengneisses of the reitzenhain catherine dome and the schwarzenberg dome western erzgebirge documenting significant regional differences between the eastern and the western erzgebirge 540 vs 490 ma in the western erzgebirge most meta volcanic rocks muscovite gneisses and meta granites mainly red augengneisses yield ordovician zircon ages whereas in the eastern part similar rocks mainly recorded lower cambrian protolith ages zircon overprinting was highest within discrete tectonic zones where the combination of fluid infiltration and deformation induced variable degrees of recrystallisation and formation of a new augengneiss structure variable degrees of pb loss caused age shifts that do not correspond to changes in zircon morphology but may be associated with u and th enrichments major changes in bulk rock composition appear to be restricted to discrete zones and to u hp nappes whereas gneisses with a mp mt metamorphic overprint basically show no geochemical modifications

two stage collision exploring the birth of pangea in the variscan terranes abstract the variscan suture exposed in nw iberia contains a stack of terranes including two allochthonous units with continental affinity and gondwanan provenance upper and basal units separated by an ophiolite belt where the most common units show protolith ages at c 395 ma recent lu hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust hence the ophiolites could not have originated in a deep ocean basin associated with a mature mid ocean ridge or intraoceanic subduction the tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction the upper units record an initial high p ultra high p metamorphic event that occurred before 400 390 ma while the basal units were affected by a second high p low to intermediate t metamorphic event dated at c 370 ma continental subduction affected the most external margin of gondwana and developed in a setting of dextral convergence with laurussia development of the two high p events alternated with the opening of an ephemeral oceanic basin probably of pull apart type in early devonian times this ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the variscan suture current ideas for the assembly of pangea advocate a single collisional event between gondwana and laurussia in the carboniferous however the new evidence from the allochthonous terranes of the variscan belt suggests a more complex scenario for the assembly of the supercontinent with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered based on modern analogs of continental interaction the development of complex collisions as here suggested for gondwana and laurussia during the assembly of pangea could have been the norm rather than the exception throughout earth history

retrograde evolution of eclogites evidences from microstructures and 40ar 39ar white mica dates munchberg massif northern bavaria phengites from eclogites and pegmatites 3t 2m1 coarse grained and recrystallized of the munchberg massif weissenstein and oberkotzau have been dated by the 40ar 39ar method 3t micas from the eclogites yielded plateau and isochron ages of 365 7 ma 2m1 micas show disturbed degassing spectra micas from pegmatites show a slight excess ar component with an isochron age of 353 to 351 3 ma an age component of approximately 300 ma was also detected in combination with age values from the literature the cooling history of the munchberg massif from eclogite facies conditions 390 ma to cooling below 350 c 350 ma is documented the age component of 300 ma is attributed to a low grade stage of mineral growth accompanied by a transitional ductile brittle deformation the petrological effects include formation of pumpellyite prehnite facies minerals frequently precipitated in microcraks and cleavage planes of earlier formed minerals this stage has to be seen in conjunction with the intrusions of the fichtelgebirge granite

high pressure relics in meta sediments intercalated with the weissenstein eclogite munchberg gneiss complex bavaria the mineral assemblages in the eclogites and meta sediments of the munchberg gneiss complex suggest minimum pressures of about 15 kbar and temperatures of 600 30 c for the eclogite facies metamorphism both rock types underwent a subsequent amphibolite facies metamorphism at almost the same temperature range in the weissenstein borehole the eclogites and meta sediments show an intimate interlayering on a centimetre scale contacts between the two rock types are often sharp and untectonized suggesting in situ metamorphism of the eclogites the following features indicate that the gneisses were subjected to eclogite facies metamorphism 1 phengite relics and phengite inclusions in garnet contain up to 3 45 si per formula unit while amphibolite facies phengites have considerably lower si contents 3 0 3 25 p f u 2 omphacite relics occur in the form of na augite 6 9 mol jadeite oligoclase symplectites 3 garnets with up to 40 mol of the pyrope component occur

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

monazite in a variscan mylonitic paragneiss from the munchberg metamorphic complex ne bavaria records cadomian protolith ages small oval shaped unshielded monazite grains found in a variscan garnet muscovite bearing mylonitic paragneiss from the liegendserie unit of the munchberg metamorphic complex mmc in the northwestern bohemian massif central europe yield only pre variscan ages these ages determined with the electron microprobe have maxima at about 545 520 and 495 ma and two side maxima at 455 and 575 ma and are comparable with previously determined ages of detrital zircon reported from paragneisses elsewhere in the nw bohemian massif the pressure p temperature t history of this mylonitic paragneiss determined from contoured p t pseudosections involved an initial stage at 6 kbar 600 c reaching peak p t conditions of 12 5 kbar 670 c with partial melting followed by mylonitization and retrogression to 9 kbar 610 c the monazite representing detrital grains derived from igneous rocks of a cadomian provenance between 575 455 ma has survived these variscan metamorphic deformational events unchanged because this mineral has probably never been outside its p t stability field during metamorphism this article is protected by copyright all rights reserved

convergent hydraulics at horseshoe steps in bedrock rivers abstract horseshoe waterfalls are a common feature of steep bedrock rivers as a first step toward understanding their geomorphology a detailed study of the fluid mechanics at a 0 91 m vertical drop horseshoe waterfall was performed in a 2 75 m wide flume five non dimensional upstream energy levels each with 3 5 non dimensional downstream tailwater depths 21 runs total were assessed for water surface topography via digital elevation modeling flow dynamics via digital videography and overall energy dissipation via an energy and momentum conservation model regardless of tail depth the horseshoe waterfall was found to have three distinct zones beyond the step brink 1 a nappe whose degree of convergence depends on upstream energy and brink configuration 2 a convergence zone whose features vary strongly with upstream energy brink configuration and tail depth and 3 a downstream tailwater region whose dynamics primarily depend on tail depth the centerline nappe profile and brink velocity were reasonably predicted using rouse s jet trajectory equations when h p h 2 peripheral profiles were not predictable using existing equations for any arbitrary broad crested step brink configuration maximum energy dissipation was found to occur when no jump was present and downstream tail depth was exactly critical rather than providing maximal energy dissipation hydraulic jumps below steps provide efficient conversion of kinetic energy to potential energy

ductile deformation of garnet in mylonitic gneisses from the munchberg massif germany abstract mylonitic gneisses from the munchberg massif contain single grains type i and polycrystalline aggregates type ii of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation lattice preferred orientations of quartz textures symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments garnet textures measured by ebsd together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation 1 for the single grains stretching can be attributed to diffusion creep along grain boundary zones coble creep the related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing 2 for the polycrystalline garnet aggregates consisting of cores grading into fine grained mantles dislocation creep and associated rotation recrystallization can be assumed continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are 100 and equivalent systems according to the cubic lattice symmetry the same holds for garnets which appear to be completely recrystallized for this type of fine grained aggregates an alternative nucleation model is discussed due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation primary growth zones are strongly disturbed since for the considered rock unit of the munchberg massif peak metamorphic temperatures between 630 and 670 c can be assumed this study clearly demonstrates that the inferred processes of ductile garnet deformation can occur not only in ht regimes as often suggested in the literature even if embedded within a matrix of low strength minerals like quartz feldspars and micas

thermochemistry of monazite la and dissakisite la implications for monazite and allanite stability in metapelites thermochemical properties have been either measured or estimated for synthetic monazite lapo4 and dissakisite calamgal2 sio4 3oh the mg equivalent of allanite a dissakisite formation enthalpy of 6 976 5 10 0 kj mol 1 was derived from high temperature drop solution measurements in lead borate at 975 k a third law entropy value of 104 9 1 6 j mol 1 k 1 was retrieved from low temperature heat capacity c p measured on synthetic lapo4 with an adiabatic calorimeter in the 30 300 k range the c p values of lanthanum phases were measured in the 143 723 k range by differential scanning calorimetry in this study la oh 3 appeared as suitable for drop solution in lead borate and represents an attractive alternative to la2o3 pseudo sections were calculated with the theriak domino software using the thermochemical data retrieved here for a simplified metapelitic composition la ree y and considering monazite and fe free epidotes along the dissakisite clinozoisite join as the only ree bearing minerals calculation shows a stability window for dissakisite clinozoisite epidotes t between 250 and 550 c and p between 1 and 16 kbar included in a wide monazite field the p t extension of this stability window depends on the bulk rock ca content assuming that synthetic lapo4 and dissakisite la are good analogues of natural monazite and allanite these results are consistent with the ree mineralogy sequence observed in metapelites where 1 monazite is found to be stable below 250 c 2 around 250 450 c depending on the pressure allanite forms at the expense of monazite and 3 towards amphibolite conditions monazite reappears at the expense of allanite