the quartz dioritic hospitais intrusion sw iberian massif and its mafic microgranular enclaves evidence for mineral clustering abstract the hospitais pluton is an elliptical body with its long axis oriented wnw ese that belongs to the evora massif iberian variscan belt this intrusion has a quartz dioritic composition with plagioclase quartz amphibole hornblende but locally also cummingtonite and biotite as the main mineral phases mafic microgranular enclaves in the quartz diorite show the same minerals as the host but with a greater abundance of amphibole and lower proportions of felsic minerals especially quartz u pb zircon ages obtained in one sample of the quartz diorite and one sample of a mafic microgranular enclave gave identical ages within error of ca 337 ma geochemical data show that the quartz diorite has a calc alkaline signature with moderate enrichment in lile hfse ratio thn yn 2 71 11 43 and clear negative ti and nb ta anomalies thn nbn 1 33 6 22 the composition of the enclaves shows that they do not represent direct melt compositions instead their geochemical features namely the abundances of fe and mn in variation diagrams and ree patterns in primitive mantle normalized diagrams suggest that they correspond to mineral clustering formed during the previous crystallization stage of quartz dioritic magma overlapping of mineral chemistry and sr nd isotope compositions in the quartz diorite and the enclaves provides further support to that conclusion the values for 87sr 86sr i and endi calculated for 337 ma in the quartz diorite vary from 0 706147 to 0 706491 and from 1 87 to 3 22 respectively this isotope composition may be explained either by differentiation of a mafic magma extracted from a mantle wedge enriched by long lasting subduction processes or by mixing between a mafic magma from a depleted mantle source and a crustal melt in the second case the most likely source for the felsic component should be meta igneous rocks like the lower cambrian alcacovas orthogneisses that outcrop in neighbouring areas

characterization of magma from inclusions in zircon apatite and biotite work well feldspar less so detrital zircon grains are employed to decipher sediment provenances and crustal evolution and they provide unique evidence of hadean crust mantle differentiation processes we demonstrate that mineral inclusions in zircon provide valuable information on the conditions under which zircon crystallized zircon grains from selected plutonic rocks from dronning maud land antarctica contain inclusions of apatite biotite amphibole and pyroxenes that accurately reflect the chemical compositions of the equivalent phases in the host rock matrix and the compositions of the whole rocks high concentrations of y and low concentrations of sr in apatite inclusions in zircon are diagnostic of evolved felsic granitoid host rocks in contrast the relative abundances and compositions of plagioclase and alkali feldspar inclusions in zircon are decoupled from the composition of the whole rock and they are generally indicative of granitic melts regardless of the bulk rock this is best explained by the late crystallization of zircon relative to the bulk of the feldspars we conclude that inclusions of apatite and mafic phases in zircon constrain the potential source rocks of detrital zircon whereas feldspar inclusions do not

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

geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

oxygen isotopes in titanite and apatite and their potential for crustal evolution research abstract oxygen isotope analysis of zircon often combined with geochronology and hf isotope analysis has been pivotal in understanding the evolution of continental crust in this contribution we expand the use of underexplored accessory phases titanite and apatite by demonstrating that their oxygen isotope systems can be robust and by developing geochemical indicators involving o isotopes and trace element concentrations to better constrain magma petrogenesis these minerals have the advantage over zircon of being present in less evolved magmas and being more responsive to igneous processes and crustal metamorphism we present new data on titanite apatite and zircon from carefully selected granitoids through geological time the phanerozoic high ba sr granites caledonian province scotland archean sanukitoids karelia province finland and a neoproterozoic basalt andesite dacite rhyolite suite badr guernsey channel island we demonstrate i that 18o values of the studied accessory minerals are not affected by crystal fractionation ii a strong correlation between 18o in all three accessory minerals showing that apatite and titanite can faithfully record the magmatic 18o iii that these accessory minerals can also record metamorphic and or fluid circulation events during the syn to post magmatic history of granitoids

s type granite generation and emplacement during a regional switch from extensional to contractional deformation central iberian zone iberian autochthonous domain variscan orogeny zircon grains extracted from s type granites of the meda escalhao penedono massif central iberian zone variscan orogen constrain the timing of emplacement and provide information about potential magma sources simple and composite zircon grains from three samples of s type granite were analyzed by la icp ms new u pb data indicate that granites crystallized in the bashkirian 318 7 4 8 ma overlapping the proposed age range of ca 321 317 ma of the nearby s type granitic rocks of the carrazeda de anciaes lamego and ucanha vilar massifs the timing of emplacement of such s type granites seems to coincide with the waning stages of activity of a d2 extensional shear zone i e pinhel shear zone developed in metamorphic conditions that reached partial melting and anatexis ca 321 317 ma dykes of two mica granites resembling diatexite migmatite are concordant and discordant to the compositional layering and s2 main foliation of the high grade metamorphic rocks of the pinhel shear zone much of the planar fabric in these dykes was formed during magmatic crystallization and subsequent solid state deformation field relationships suggest contemporaneity between the ca 319 317 ma old magmatism of the study area and the switch from late d2 extensional deformation to early d3 contractional deformation inherited zircon cores are well preserved in these late d2 early d3 s type granite plutons u pb ages of inherited zircon cores range from ca 2576 to ca 421 ma the spectra of inherited cores overlap closely the range of detrital and magmatic zircon grains displayed by the ediacaran to silurian metasedimentary and metaigneous rocks of the iberian autochthonous and parautochthonous domains this is evidence of a genetic relationship between s type granites and the host metamorphic rocks there is no substantial evidence for the addition of mantle derived material in the genesis of these late d2 early d3 s type granitic rocks the end arrays of heterogeneous crustal anatectic melts may be just inherited from the source probably reflecting mixing of a range of crustal materials with different ages and primary isotopic signatures the generation of the bashkirian s type granites has been dominated by continental crust recycling rather than the addition of new material from mantle sources

variscan intra orogenic extensional tectonics in the ossa morena zone evora aracena lora del rio metamorphic belt sw iberian massif shrimp zircon u th pb geochronology

a granitic inclusion suite within igneous zircons from a 3 81 ga tonalite w greenland restrictions for hadean crustal evolution studies using detrital zircons abstract this paper presents an electron microprobe study of inclusions within igneous zircons from ca 3800 ma metatonalite sample g97 18 crystalline inclusions are k feldspar plagioclase quartz hornblende biotite ilmenite and apatite additionally one globular polymineralic inclusion interpreted as crystallised melt occurs at the surface of a polished grain mount this consists of plagioclase quartz k feldspar around a biotite lath other similar but rare globular inclusions were seen buried within other zircons below the polished surface these inclusions particularly the presence of k feldspar and plagioclase in broadly equal amounts entail crystallisation of the zircons from a residual granitic sensu stricto melt rather than a tonalitic melt shrimp sensitive high resolution ion microprobe u pb dating of zircons with inclusions indicates that they grew at ca 3800 ma the accepted igneous age of the rock this inclusion suite is compatible with the low ti in zircon temperatures for g97 18 igneous zircon hiess et al 2008 therefore low ti in zircon temperatures and granitic inclusions found in hadean detrital zircons do not necessitate crystallisation from low temperature granites because such features would also be found if hadean zircons had crystallised late from higher temperature zircon undersaturated melts of tonalitic composition

accessory minerals and subduction zone metasomatism a geochemical comparison of two melanges washington and california u s a abstract the ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks which can only be studied indirectly in contrast the role of accessory minerals in lower t and p metasomatic processes within paleo subduction zones can be studied directly in subduction zone metamorphic terranes the gee point iron mountain locality of the shuksan metamorphic suite north cascades washington state is a high t melange of metamafic blocks in a matrix of meta ultramafic rocks this melange is similar in geologic setting and petrology to the upper part of an unnamed amphibolite unit of the catalina schist santa catalina island southern california both are interpreted as shear zones between mantle and slab rocks that formed during the early stages of subduction some garnet amphibolite blocks from the gee point iron mountain locality display trace element enrichments similar to those in counterparts from the catalina schist some catalina blocks are highly enriched in th rare earth elements ree the high field strength elements ti nb ta zr and hf hfse u and sr compared to mid ocean ridge basalt morb and to other garnet amphibolite blocks in the same unit textural and geochemical data indicate that accessory minerals of metamorphic origin control the enrichment of th ree and hfse in blocks from both areas the mg rich rinds around blocks and the meta ultramafic matrix from both melanges are highly enriched in a large number of trace elements compared to harzburgites dunites and serpentinites evidence for recrystallization or formation of accessory minerals in the former rocks suggests that these minerals control some of the trace element enrichments data from the gee point and catalina melanges suggest that the accessory minerals titanite rutile apatite zircon and ree rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction related fluid rock interaction mobilization of incompatible elements and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid rich metamorphic environments in subduction zones

the origin and spread of grass dominated ecosystems in the late tertiary of north america preliminary results concerning the evolution of hypsodonty abstract sediment samples were collected in northwestern nebraska from the following lithologic units 1 the upper oligocene monroe creek formation the lower miocene harrison formation and upper harrison beds of the arikaree group and 2 the lower miocene runningwater formation and the dawes clay member box butte formation of the ogallala group the samples were processed using heavy liquid extraction and analyzed for siliceous plant microfossils phytoliths all samples yielded well preserved and diverse assemblages dominated by grass phytoliths but included phytoliths produced by woody and herbaceous dicotyledons palms and sedges the abundance of woody dicotyledons and palms decreased up section the grass assemblages consisted mainly of festucoid c3 phytolith morphotypes an index assessing the amount of tree cover d p the ratio of dicotyledon phytoliths to grass phytoliths was employed to interpret the data according to this analysis there was open c3 dominated grassland in the study area between 25 and 17 ma at least 7 ma before supposed adaptations to grasslands in ungulates hypsodonty originate

comment on rheic ocean ophiolitic remnants in southern iberia questioned by shrimp u pb zircon ages on the beja acebuches amphibolites by a azor et al

apatite composition tracing petrogenetic processes in transhimalayan granitoids apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements in this study electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of thetranshimalayan igneous plutonic suite s type granites the i type gangdese batholith and postcollisional adakites f mn sr and rare earth elements ree in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers more specifically the f and mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index combined with sr and ree data which show significant variations in apatite from different rock types these elements are useful for constructing discrimination diagrams this study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution systematic variations of sr and ree in apatite with bulk rock aluminosity are the results of partition competition with pre existing and coexisting major and accessory minerals in silicate melts and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing which is signaled by inconsistent eu anomalies sr abundances and ree patterns relative to bulkrock compositions

apatite chemical composition determined by electron microprobe and laser ablation inductively coupled plasma mass spectrometry as a probe into granite petrogenesis abstract major minor and trace element abundances in apatites from various i and s type igneous and sedimentary granites of the lachlan fold belt have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometer the results show that apatite can accommodate many minor and trace elements whose concentrations and ratios are relatively sensitive to factors controlling many of the fundamental differences between i and s type granites apatites from s type granites generally have higher f but lower cl contents than those from i type granites which is ascribed mainly to the loss of cl during the weathering processes forming the source rocks of s type granites although fractional crystallisation can cause significant enrichment in f as well high mn and fe contents in apatites from s type granites and high s and as abundances in apatites from mafic i type granites result from different oxygen fugacities and degrees of al saturation or aluminosity between metaluminous mafic i type magmas and peraluminous s type and felsic i type magmas there are systematic and distinctive differences in absolute rare earth element ree abundances ree distribution patterns and element ratios e g la y sm nd etc between apatites from different types of granite the strong eu depletion that characterises apatites from s and felsic i type granites is interpreted here to be a result of the uniqueness of crystal chemistry of apatite and high eu2 eu3 ratios in s type and felsic i type magmas which are more reduced and peraluminous than mafic i type magmas strong ree la to eu and th enrichment in apatites from mafic i type granites and marked nd depletion in apatites from most s type and felsic i type granites are caused by the precipitation and fractionation of monazite in the parental magmas of the latter rocks substitution mechanisms are responsible for high na in apatites from s type and felsic i type granites and for high si in apatites from mafic i type granites and may also have important effects on ree partitioning between apatite and melt thus apatite chemistry can be used as an excellent indicator of granite petrogenesis the results have important implications for identifying different types of granite and are potentially significant for determining the provenance of sedimentary rocks

episodic intrusion internal differentiation and hydrothermal alteration of the miocene tatoosh intrusive suite south of mount rainier washington the miocene tatoosh intrusive suite south of mount rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral cascades arc magmatism tatoosh intrusive suite plutons have individually diagnostic characteristics including texture mineralogy and geochemistry and apparently lack internal contacts new ion microprobe u pb zircon ages indicate crystallization of the stevens pluton ca 19 2 ma reflection pyramid pluton ca 18 5 ma and nisqually pluton ca 17 5 ma the stevens pluton includes rare statistically distinct ca 20 1 ma zircon antecrysts wide ranging zircon rare earth element ree hf u and th concentrations suggest late crystallization from variably evolved residual liquids zircon eu eu hf covariation is distinct for each of the reflection pyramid nisqually and stevens plutons although most tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration and sparse mineralized veins cut some of these rocks significant base or precious metal mineralization is absent at the time of shallow emplacement each of these magma bodies was largely homogeneous in bulk composition and petrographic features but prior to final solidification each of the tatoosh intrusive suite plutons developed internal compositional variation geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt possibly represented by late aplite dikes or erupted as rhyolite from crystal rich magma crystal rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth assembled by episodic intrusion the tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes

solution properties of rare earth elements in silicate melts inferences from immiscible liquids abstract the partitioning behavior of rare earth elements ree between immiscible silicate liquids was investigated as a function of temperature and total ree oxide concentration ree preferentially partition into the end member liquids that are rich in network modifying cations with two liquid partition coefficients greater than any other cation the two liquid partition coefficients of ree in a given experiment are essentially identical to one another no evidence was seen to suggest that the solution mechanisms of ree in high silica liquids vary with differences in their ionic radii two lattice models of trace element solution behavior fail to remove the compositional dependence of ree two liquid partition coefficients due to the assumption that all network forming and network modifying cations mix ideally with one another as a result it is probably incorrect to derive physical interpretations from the results of the application of two lattice models the results are applied to the origins of the lree enriched phenocryst matrix partition coefficients seen for some ferromagnesian minerals in high silica rhyolites since liquids with extremely high concentrations of t o t linkages do not strongly discriminate between the ree on the basis of their ionic radii the anomalous ree crystal matrix partition coefficient patterns are best explained as the result of contamination of these minerals by lree accessory phases

dissecting complex magmatic processes an in depth u pb study of the pavia pluton ossa morena zone portugal the build up of large magmatic complexes can proceed piecemeal over periods of several million years through sequences of complex processes of magma production differentiation assimilation final crystallization and subsequent metasomatic modification all these stages can produce or modify minerals used as geochronometers such as zircon monazite and titanite the present study exemplifies such complex relationships also demonstrating how a systematic approach with comprehensive sampling and careful high resolution u pb analyses can yield a coherent picture of the entire magmatic process the study was conducted on the pavia pluton an elongated variscan intrusion in the ossa morena zone of portugal the geochronological data show that the pavia pluton was emplaced by the amalgamation of multiple magma pulses into the crust over a period of c 11 myr an early event at 340 ma revealed by xenocrystic zircon preceded the magmatic activity at the exposed level of the pluton but is recognized as the main magmatic event elsewhere in the ossa morena zone a second event at 328 ma formed tonalite trondhjemite and granodiorite and subordinate differentiates in the central domains of the pluton units i and ii a third event at c 324 ma emplaced granodiorite in the flanking domains iii v and the contemporaneous and widespread two mica granite in domainvi together with late rhyodacite porphyries microgranodiorites aplite pegmatite and pegmatite dikes a fourth event at 319 317 ma was characterized by the emplacement of some microgranites and pegmatite dikes these two last magmatic events also had an effect on the previously emplaced rocks causing local overgrowths and isotopic resetting of minerals the occurrence of a fifth magmatic event at depth at 313 ma is the inferred cause of the hydrothermal activity responsible for local zircon monazite and titanite resorption and or recrystallization and for some of the textures exhibited by the main rock forming minerals the magmatic episodes were interspersed with periods of quiescence this cyclicity presumably reflects an external control by the transtensional tectonic regime of the ossa morena zone

timing of normal faulting along the indus suture in pakistan himalaya and a case of major 231 pa 235 u initial disequilibrium in zircon we report age data by tims u pb la icp ms and 39ar 40ar techniques for main magmatic events in the lower swat region of pakistan in order to constrain the tectonic evolution of the northwestern himalaya the pre himalayan history of the indian continent is documented by single zircon u pb results from the peraluminous choga granite gneiss which yielded a 468 5 ma lower concordia intercept interpreted to approximate the time of magmatic emplacement the presence of a well defined 870 7 ma inherited component upper intercept suggests a plutonic or volcanic protolith residing at unexposed levels of the indian crust zircon data for the swat granite gneiss from the northern part of the loe sar dome give an emplacement age of 267 6 3 ma which is at variance with earlier correlations favoring an early paleozoic origin subsequent to metamorphic overprint by the himalayan orogeny the swat granite was intruded by late kinematic alkali granite dykes single zircons from one of these dykes show reproducible 206pb 238u data giving a precise mean age of 29 26 0 12 ma whereas the 207pb 235u ages scatter between 34 and 81 ma pointing to huge and variable enrichment in 207pb the unsupported 207pb can be explained by incorporation of 231pa an intermediate long lived daughter nuclide in the 235u decay chain in excess of the secular equilibrium ratio la icp ms measurements confirm the presence of unsupported 207pb but do not show any correlation between the latter and other selected trace element concentrations in these zircons a concordant ar ar muscovite age of 28 4 1 1 ma obtained for the same dyke postdates regional mica cooling ages and indicates a lack of younger regional events capable of resetting the k ar system in muscovite because the dyke is pre to synkinematic relative to normal faulting and related north vergent folds its emplacement age provides a maximum age for this event or reflects already ongoing local extension a lower limit of 15 ma has previously been established by apatite fission track analysis the 29 15 ma age bracket for normal faulting is coeval with extension along the south tibetan detachment system stds on the north side of the high himalaya this suggests that the indus suture in pakistan has acted as a western continuation of the stds and that related faulting was roughly contemporaneous over most of the himalaya

variscan ophiolite belts in the ossa morena zone southwest iberia geological characterization and geodynamic significance abstract the boundary between the iberian and south portuguese terranes in sw iberia is traced by a suture recording the closure of rheic and related oceans through nne directed subduction the western segment of the suture comprises imbrications of the iberian terrane relative autochthon neoproterozoic lower palaeozoic and allochthonous complexes the iberian terrane relative autochthon is overlain by lower middle devonian metasediments and an unconformable cover of lower carboniferous calc alkaline volcano sedimentary complexes both preserving evidence of very low grade metamorphism the allochthonous complexes include disrupted slivers of eclogite ca 370 ma klippen and slices of an internal ophiolite sequence iomzos a basal tectonic melange moura phyllonitic complex and an external ophiolite beja acebuches complex baoc a large layered gabbroic sequence lgs whereas part of the beja igneous complex intruded ca 350 340 ma the sw suture domains the iomzos represents obducted remnants of the rheic ocean for which available shrimp u pb data indicate an age of 479 5 ma this ocean which separated iberia from a promontory of gondwana and avalonia now represented by the south portuguese terrane opened near the cambrian ordovician boundary through a rift jump from an intra cratonic setting within the iberian terrane to oceanic rifting the baoc displays geochemical features compatible with derivation from a short lived back arc basin lower middle devonian t dm sm nd 380 440 ma the variscan ophiolite belts preserved along the sw variscides were emplaced by antithetic obduction in two stages both with shearing sense towards the nne the first stage which involved iomzos cold obduction exhumed hp rocks ca 370 ma and created a foreland bulge towards the iberian terrane s sw flank this mechanism controlled the development of the volcanic related carbonate shelves and the contemporaneous terena flysch trough to the ne the second stage corresponds to baoc hot obduction carrying the iomzos klippen in piggy back style and affecting the southern margin of the lgs at ca 350 340 ma

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

understanding preservation of primary signatures in apatite by comparing matrix and zircon hosted crystals from the eoarchean acasta gneiss complex canada

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

an apatite for progress inclusions in zircon and titanite constrain petrogenesis and provenance apatite has recently gained considerable attention as a mineral with many uses within the earth and planetary sciences apatite chemistry has recently given new insight into a wide range of geological processes and tools for example magmatism metasomatism planetary geochemistry and geochronology we expand the utility of apatite here by presenting a novel way to fingerprint magma chemistry and petrogenesis using apatite inclusions within robust titanite and zircon we present trace element data from apatite mineral inclusions shielded within magmatic zircon and titanite importantly apatite inclusion and host titanite chemistries detailed in this study allow estimation of the whole rock sr and sio2 we show how these data can be used to assess the degree of fractionation of the host magma and to calculate key trace element abundances and ratios we demonstrate that the inclusions can be linked to discrete periods in the crystallization history of the host phases thus providing insight into petrogenesis the results highlight that apatite compositions might discriminate modern granitoids younger than 2 5 ga from archean proterozoic transitional granitoid compositions sanukitoid signatures development of such a petrological tool has important potential for interpretation of provenance and a better understanding of the secular evolution of the continental crust including that of early earth

zircon and titanite recording 1 5 million years of magma accretion crystallization and initial cooling in a composite pluton southern adamello batholith northern italy abstract the southern part of the adamello batholith the so called re di castello unit is an example of a composite pluton ranging from gabbro to granodiorite in composition u pb dating of single zircon crystals from four tonalitic to granodioritic lithologies reveals that zircon crystallization is protracted in all studied lithologies showing apparent durations of growth between 90 and 700 ka the youngest zircons crystallized near the solidus and yield identical or slightly older ages than titanite the formation of these autocrystic zircons is considered to approximate the age of emplacement of the melt and its final crystallization in contrast to antecrystic zircons present in the same sample which had formed earlier in the magmatic column or were derived from re mobilized earlier magma the autocryst derived emplacement ages range from 42 43 0 09 ma to 40 90 0 05 ma recording 1 5 ma of intrusion and crystallization history we anticipate that extended periods of zircon crystallization may be common in silicic rocks whereas the zircons from residual melts from initially undersaturated mafic liquids should yield far more precise emplacement ages within our present analytical uncertainties of 0 1 0 2 in 206 pb 238 u age decreasing th u ratios of dated zircons within one melt batch document the depletion of the residual melt portion in th due to the contemporaneous crystallization of titanite preliminary hf isotopic compositions of the dated zircon grains suggest that the early stage melts of the southern re di castello unit represent hybrid melts with an important crustal component e hf between 2 8 and 3 0 subsequently emplaced melts are more juvenile at e hf values at 6 4 to 8 9 and may thus reflect the addition of large volumes of mafic melt to the magmatic system

impact melt sheet zircons and their implications for the hadean crust impacts may have been important mechanisms of crustal redistribution and differentiation particularly during intense postaccretionary bombardment between 4 5 ga and 3 9 ga ago evidence of crustal processes during this period is largely provided by detrital zircons from the yilgarn craton australia trace element compositions crystallization temperatures and inclusion populations of these ancient zircons have been taken as evidence for predominantly granitic source magmas implying widespread felsic continental crust on the early earth however there is little knowledge of zircons formed in impact melt sheets a potential source for the hadean zircons here we present ti thermometry trace elements and inclusion populations of zircons from the 1 85 ga sudbury impact melt sheet ontario canada our results demonstrate that large variations in zircon crystallization temperature and composition will be an inevitable consequence of the evolution of such magmatic systems we also show that zircons in mafic rocks crystallize in residual liquids of granitic composition producing inclusion assemblages that are remarkably similar to those reported for the ancient yilgarn grains thus we conclude that the trace element compositions and inclusion populations of the hadean zircons are consistent with crystallization from more mafic melts than previously recognized although high crystallization temperature distributions of sudbury zircons indicate that impact melt sheets were not a dominant source for the grains older than 3 9 ga

diet reconstruction for an extinct deer cervidae cetartiodactyla from the quaternary of south america abstract among the extinct cervids of the pleistocene in south america morenelaphus has the most abundant fossil record and the broadest geographic distribution however the paleoecology of morenelaphus is poorly known especially its dietary patterns thus this study aims to recognize the feeding habits of this extinct cervid through analysis of microwear the microwear analysis indicated a mixed feeder diet for morenelaphus both high pit values and frequency of individuals with low number of fine scratches indicated the consumption of grasses possibly including grit siliciclastic sediment ingested during feeding also our results suggest that morenelaphus possibly went extinct at the pleistocene holocene transition as a result of climate environmental changes and or a physiological nutritional crisis

time space distribution of silicic plutonism in a gneiss dome of the iberian variscan belt the evora massif ossa morena zone portugal abstract in the iberian variscan belt polyphasic deformation has been recognized as comprising an early phase of crustal thickening followed by an intermediate phase of crustal extension and doming and a later phase of shortening the evora massif is a gneiss dome of the westernmost domains of the ossa morena zone sw iberia which provides a remarkable insight into the late paleozoic deep crustal structure of the variscan continental crust of northern gondwana in this study we bring new structural and geochronological u pb data for the northern hanging wall of the evora massif we describe the existence of low dipping d2 extensional shear zones associated with buchan type metamorphism m2 this enables three tectono metamorphic units to be distinguished the lower gneiss unit the intermediate schist unit and the upper slate unit d2 m2 structures experienced subhorizontal shortening d3 and were transposed by low plunging folding thrusting and strike slip faulting zircon grains extracted from pavia quartz feldspathic gneiss of the lower gneiss unit yielded a crystallization age of ca 521 ma cambrian stage 2 3 which establishes a correlation with tectono metamorphic units of the footwall and southern hanging wall of the evora massif u pb zircon dating of divor foliated quartz diorite 339 7 ma malarranha weakly foliated biotite rich granite 322 3 ma and undeformed porphyritic granite of the pavia pluton 314 4 ma constrain the timing of emplacement of granitic magmas synchronously with doming carboniferous magmatism initiated with doming me1 ca 343 335 ma continued through d2 m2 me2 ca 328 319 ma and lasted until the waning stage of crustal extension me3 ca 317 313 ma the evora massif gneiss dome probably formed as result of the combined effect of gravitational collapse of the thickened crust and buoyancy driven gravitational instability developed in the partially molten continental crust influenced by the transfer of heat from rising mantle derived i e dioritic gabbroic magmas rocks found in the footwall of the evora massif

adakitic like magmatism in western ossa morena zone portugal geochemical and isotopic constraints of the pavia pluton abstract granitic rocks are a major component of the earth s continental crust and occur in a wide variety of tectonic settings their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation in this study we present the first whole rock chemical and isotopic sr nd o data for the pavia pluton 328 317 ma located near the western border of the ossa morena zone evora massif portugal major and trace element geochemistry suggests that the different granitic phases composing this intrusive body enclaves granites s l and crosscutting dikes represent independent magma pulses and the majority is similar to ttgs and adakites the little sr nd o isotopic variation with 87 sr 86 sr 328 0 70428 0 70560 end 328 ranging between 3 4 and 0 4 and 18 o varying from 5 6 to 8 4 implies an isotopically similar protolith for all phases the most viable mechanism for the generation of the pavia pluton adakitic like magmatism is assimilation fractional crystallization of a mantle derived magma this mechanism was also invoked to explain the genesis of other plutons within the evora massif but they have a distinct chemistry typical arc calc alkaline rocks the chemical differences between them and the pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle derived magmas by the sinking slab after subduction blocking and subsequent slab break off

mechanisms and duration of non tectonically assisted magma emplacement in the upper crust the black mesa pluton henry mountains utah abstract a new study of black mesa pluton henry mountains colorado plateau utah usa indicates that it is a classic example of a small upper crustal pluton assembled over a few years by incremental amalgamation of discrete magma pulses the results of our petrostructural study of the pluton interior allow us to constrain the geometry kinematics and timing of the processes the symmetric internal fabric is interpreted as an evidence for a feeding by below and not laterally the observed rotation of the lineation from wnw ese on the very top to nne ssw below lead us to propose that the fabric at the base of the pluton is a record of magma infilling process and the fabric at the very top is a record of the strain due to the relative movement between magma and wallrocks a consequence is that except at the contact between pluton and wallrocks top and margins the stretching direction recorded by the lineation is not parallel to the flow direction of the magma i e displacement the black mesa pluton is a sheeted laccolith on its western edge and a bysmalith on its eastern edge this e w asymmetry in pluton geometry construction and the symmetrical internal fabric indicates that the apparently different west and east growth histories could have occurred simultaneously our field data indicate pluton growth through an asymmetric vertical stacking of sill like horizontal magma sheets one dimensional thermal models of the pluton provide maximum limits on the duration of its growth we have constrained the number the thickness and the frequency of magma pulses with our structural observations including 1 the emplacement of the pluton by under accretion of successive magma pulses 2 the absence of solid state deformation textures at internal contacts and 3 the apparent absence of significant recrystallization in the wallrocks our results suggest that the emplacement of the black mesa pluton was an extremely rapid event with a maximum duration on the order of 100 years which requires a minimum vertical displacement rate of the wallrocks immediately above the pluton greater than 2 m yr finally our data show that the rates of plutonic and volcanic processes could be similar a significant result for interpretation of magma transfer in arc systems

petrogenesis of the nanling mountains granites from south china constraints from systematic apatite geochemistry and whole rock geochemical and sr nd isotope compositions abstract the widespread mesozoic granitoids in south china 135 300 km2 were emplaced in three main periods triassic 16 of the total surface area of mesozoic granitoids jurassic 47 and cretaceous 37 though much study has been conducted on the most abundant jurassic nanling mountains nlm granites their rock affinities relative to the triassic darongshan drs and cretaceous fuzhou zhangzhou complex fzc granites which are typical s and i type respectively and the issue of their petrogenetic evolution is still the subject of much debate in this study we discuss the petrogenesis of nlm granites using apatite geochemistry combined with whole rock geochemical and sr nd isotope compositions sixteen apatite samples from six granite batholiths one gabbro and three syenite bodies in the nlm area were analyzed for their major and trace element abundances and compared with those collected from drs n 7 and fzc n 6 granites the apatite geochemistry reveals that na si s mn sr u th concentrations and ree distribution patterns for apatites from drs and fzc granites basically are similar to the s and i granite types of the lachlan fold belt australia whereas those from nlm granites have intermediate properties and cannot be correlated directly with these granite types according to some indications set by the apatite geochemistry e g lower u and higher eu abundances nlm apatites appear to have formed under oxidizing conditions in addition we further found that their ree distribution patterns are closely related to aluminum saturation index asi and nd isotope composition rather than sio2 content or degree of differentiation of the host rock the majority of apatites from nlm granites asi 0 97 1 08 and end t 8 8 to 11 6 display slightly right inclined apatite ree patterns distinguishable from the typical s and i type however those from few granites with asi 1 1 and end t 6 6 and gabbro and syenite are similar to fzc apatites strongly right inclined in light of sr and nd isotope compositions magmas of nlm intrusives except gabbro and syenite and few granites with end t 8 generally do not involve a mantle component instead they fit with a melt derived largely from in situ melting or anatexis of the pre mesozoic mainly caledonian granitic crust with subordinate pre yanshanian mainly indosinian granitic crust we suggest that an application using combined whole rock asi and end t values is as useful as the apatite geochemistry for recognizing possible sources for the nlm granites

decoding whole rock plagioclase zircon and apatite isotopic and geochemical signatures from variably contaminated dioritic magmas zircon and apatite grains from three types of variably contaminated quartz diorite were analyzed in the gesiniec intrusion sw poland the zircon isotopic compositions ehf300 5 5 0 and 18o 5 6 9 3 are consistent with contamination processes zircon is characterized by an increase in u th pb and ree from the least to the most evolved quartz diorite type apatite is characterized by ranges in trace element concentrations and with the progress of contamination its composition evolves from those typical for i type granites toward those typical for s type isotopic and trace element variations in zircon and apatite correlate with sr isotopic composition of plagioclase 87sr 86sr300 0 7069 0 7084 pietranik and waight 2008 however both sr isotopic composition of plagioclase and trace element composition of apatite could be homogenized by late stage resorption leaving zircon as the only record of contamination processes that predate resorption comparison between plagioclase and zircon isotopic composition is consistent with both plagioclase cores and zircons recording similar stages of magma contamination comparison between plagioclase and apatite composition indicates that crystallization of apatite was contemporaneous with crystallization of plagioclase rims the preferred interpretation of isotopic and trace element variations observed in different grains is a two stage contamination by crustally derived magmas early contamination was probably dominated by material typical of the lower crust i e with none or only small amounts of a sedimentary component as indicated by low 18o in zircon 5 6 6 5 in both the least and the most contaminated types later contamination was dominated by crustally derived magmas containing more than 20 of a sedimentary component as the most contaminated sample includes zircon with 18o up to 9 3 partial melts generated from an s type granite source are the most probable contaminant for this second stage contamination as indicated by apatite trace element composition in general isotopic and chemical composition of plagioclase zircon and apatite provides complementary information on magmatic processes but records a longer time span than a single mineral only due to their diachronous crystallization histories

detrital apatite u pb and trace element analysis as a provenance tool insights from the yenisey ridge siberia abstract the use of zircon u pb geochronology to study the provenance of sediment is well established yet there are fundamental biases that are hard to avoid these biases are due in part to the limited range of magmatic compositions from which zircon will crystallise this can manifest as the over under representation of particular age populations i e sediment sources in the data the analysis of apatite a mineral found in a wide variety of igneous rocks can help to address this bias in detrital geochronology in this study we combine geochemical and u pb la icp ms analysis of individual apatite grains to characterise the potential source rocks this information is integrated with zircon u pb data from the same samples in order to demonstrate the complementary provenance information that can be derived from apatite and zircon archives the analysis of detrital apatite from sedimentary rocks in the yenisey ridge siberia found two main u pb age populations an apatite u pb population at 880 720 ma corresponds to neoproterozoic magmatism in the yenisey ridge and a second at 1800 ma to magmatism related to the assembly of the siberian craton abundant neoproterozoic apatites many of which have chemistries indicative of crystallising from a mafic magma are considerably more common than the relatively rare zircons of the same age the ability of apatite analysis to detect mafic magmatic sources is one of the strengths of this approach that makes it particularly useful when used in combination with zircon u pb geochronology this study shows that multi method analysis of detrital apatite has the potential to be an important tool in conjunction with detrital zircon analysis in future efforts to understand the provenance of sedimentary rocks

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

paleodietary reconstruction of fossil horses from the eocene through pleistocene of north america paleodietary trends for north american horses from hyracotherium early eocene through equus late pleistocene were examined using dental microwear analysis over 1200 fossil specimens were analyzed for enamel microwear and results were compared to an extensive microwear database of extant ungulates this study tests the hypothesis that eocene horses browsed on low abrasion foods whereas oligocene and later horses had more abrasive diets concomitant with the spread of more open habitats and examines the correlation between the acquisition of hypsodonty and the beginning of grazing microwear results indicate that early to middle eocene species engaged mostly in fruit browsing in contrast late eocene to oligocene taxa have microwear scratch numbers typical of grazing and mixed feeding ungulates but with very fine scratch textures which are unusual in modern c4 grazers and indicate consumption of relatively low abrasion grasses an increase in overall dietary abrasion is evident beginning in the early miocene but members of the anchitherinae sensu stricto engaged in leaf browsing while other forms committed to grazing or alternating between grass and leaves anchitherinae ss continue to rely on leaves until they became extinct in the late miocene while members of the equinae were either grazing or mixed feeding through the pleistocene dietary abrasion increased further beginning in the late miocene and continued to increase through the pleistocene most pleistocene horses were not grazing but rather alternating between grass and leaves or even browsing increased pitting of dental enamel and coarser scratch textures in plio pleistocene horses reinforces the idea that increased abrasion may be due to grit encroachment on food items and or a shift toward coarser grasses than due to a steady increase in the amount of grass consumed

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

the pannonian c hipparions from the vienna basin abstract the hipparion datum has been recognized as being a key geochronologic marker for early late miocene eurasian and african horizons the vienna basin pannonian c hipparions are the stratigraphically oldest basal mn9 ca 11 4 11 0 ma and we contend herein the most primitive of all old world hipparions we evaluate the stratigraphic context cheek tooth morphological characters paleodietary and paleoenvironmental context of the three pannonian c hipparion assemblages from gaiselberg atzelsdorf and mariathal austria we find that the gaiselberg and atzelsdorf are slightly more primitive than the mariathal hipparion assemblage and refer the first two assemblages to hippotherium sp while the mariathal assemblage is referred to hippotherium aff primigenium exhibiting some advanced characters that presage austrian and german later vallesian age we review the chronology and biogeography of the old world hipparion datum and evolutionary relationships of first occurring european west and south asian and north african hipparion to north american cormohipparion we evaluate and expand upon earlier paleodietary studies of pannonian c hipparions and determine that they were browser dominant mixed opportunistic feeders

evolution of grasses and grassland ecosystems the evolution and subsequent ecological expansion of grasses poaceae since the late cretaceous have resulted in the establishment of one of earth s dominant biomes the temperate and tropical grasslands at the expense of forests in the past decades several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation the data indicate that the development of grassland ecosystems on most continents was a multistage process involving the paleogene appearance of c3 and c4 open habitat grasses the mid late cenozoic spread of c3 grass dominated habitats and finally the late neogene expansion of c4 grasses at tropical subtropical latitudes the evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open habitat grasses in addition the timing of these evolutionary and ecological events varied between regions consequently region by region investigations using both direct plant fossil

accessory mineral chemistry as a monitor of petrogenetic and metallogenetic processes a comparative study of zircon and apatite from wushan cu and zhuxiling w mo mineralization related granitoids abstract in this study we explore the chemistry of accessory apatite and zircon as tools to monitor the petrogenetic and metallogenetic processes involved in the formation of the wushan cu and zhuxiling w mo mineralization related granodiorite porphyry the wushan granitoids are metaluminous with a cnk of 0 88 1 01 and the zhuxiling intrusions are weakly peraluminous with higher a cnk values 1 02 1 12 the wushan granitoids have end t values of 4 6 to 4 7 which combined with the relatively elevated mg values 57 62 and adakitic features high sr y ratios of 51 60 indicate that they were derived from melting of a thickened lower crust of the yangtze block with addition of small amounts of mantle components compared to the wushan granitoids the zhuxiling granitoids have relatively high 87sr 86sr i 0 70945 0 70951 and low end t values 5 9 to 6 3 and zircon ehf t values 3 8 to 9 0 suggesting their derivation dominantly from partial melting of the neoproterozoic crust the apatites from the zhuxiling samples are characterized by relatively high mno and feo variable y and low ce which is consistent with the weakly peraluminous feature of whole rock chemistry these apatites show notable depletion of th and lree with a lower la sm n ratio 0 74 1 44 and la yb n ratio 6 2 17 9 relative to those of the host rock 3 04 3 61 and 19 1 23 4 respectively suggesting early crystallization of some lree and th enriched minerals such as allanite monazite before apatite crystallization the steep trend of ce sm versus yb gd ratios shown by zircons from the zhuxiling granitoids suggests that the crystallization of zircon is affected by the crystallization of titanite and apatite thus the crystallization sequence of accessory minerals in the zhuxiling intrusion is allanite apatite titanite and zircon the apatites from the wushan granitoids however show strongly lree enriched ree patterns with weak negative eu anomalies which indicate minor feldspar fractionation and mildly magmatic differentiation the flat trend of ce sm versus yb gd ratios shown by zircon from the wushan pluton indicates that its ree composition is affected by hornblende saturation zircon grains from the metaluminous wushan granitoids exhibit remarkably higher ce4 ce3 ratios and weaker eu eu anomalies than those of the peraluminous zhuxiling samples and the apatites from the wushan samples show higher eu eu 0 55 0 62 and lower ce ce 0 91 1 04 and mno 0 05 0 09 compared to those of the zhuxiling pluton with eu eu 0 41 0 50 ce ce 1 06 1 11 and mno 0 15 0 18 respectively the apatite and zircon chemistry suggest that the cu bearing granitoid formed at an oxygen fugacity higher than the w bearing granitoid which agrees with the fact that the wushan granitoids show whole rock fe3 fe2 ratios higher than the zhuxiling granitoids in addition apatites from the wushan intrusion show enrichment of cl and higher f cl ratios compared to those of the zhuxiling samples suggesting that a water rich parental magma with relatively high cl content is favourable for copper mineralization this case study shows that apatite and zircon chemistry could reflect the geochemical characteristics of their host rock and magma evolution moreover they provide insights into the oxidation state halogen fugacity and magma differentiation of the magmatic system which are key factors for mineralization our data suggest that magma associated with cu mineralization is relatively oxidizing chlorine enriched and less fractionated compared to w bearing magma

reply to comment by c pin and j rodriguez on rheic ocean ophiolitic remnants in southern iberia questioned by shrimp u pb zircon ages on the beja acebuches amphibolites

birth and demise of the rheic ocean magmatic arc s combined u pb and hf isotope analyses in detrital zircon from sw iberia siliciclastic strata paleozoic continental reconstructions indicate that subduction of rheic oceanic lithosphere led to collision between laurussia and gondwana which was a major event in the formation of the ouachita appalachian variscan orogenic belt and the amalgamation of pangea however arc systems which record rheic ocean subduction are poorly preserved the preservation of devonian detrital zircon in late devonian early carboniferous siliciclastic rocks of sw iberia rather than arc related igneous rocks indicates that direct evidence of the arc system may have been largely destroyed by erosion here we report in situ detrital zircon u pb isotopic analyses of late devonian early carboniferous siliciclastic rocks from the pulo do lobo zone which is a reworked late paleozoic suture zone located between laurussia and gondwana detrital zircon age spectra from the pulo do lobo zone frasnian formations show striking similarities revealing a wide range of ages dominated by neoproterozoic and paleoproterozoic grains sourced from rocks typical of peri gondwanan terranes such as avalonia the meguma terrane and the ossa morena zone pulo do lobo rocks also include representative populations of mesoproterozoic and early silurian zircons that are typical of avalonia and the meguma terrane which are absent in the ossa morena zone the famennian tournaisian formations from the pulo do lobo zone however contain more abundant middle late devonian zircon indicating the contribution from a previously unrecognized source probably related to the rheic ocean magmatic arc s the middle late devonian to early carboniferous zircon ages from the siliciclastic rocks of sw iberia south portuguese pulo do lobo and ossa morena zones have a wide range in ehft values 8 2 to 8 3 indicating the likely crystallization from magmas formed in a convergent setting the missing rheic ocean arc was probably built on a meguma avalonia type basement we propose for the pulo do lobo zone that the frasnian sedimentation occurred through the opening of a back arc basin formed along the laurussian active margin during rheic ocean subduction as has been recently proposed for the rhenohercynian zone in central europe detrital zircon ages in the frasnian siliciclastic rocks indicate provenance in the meguma terrane avalonia and devonian rheic ocean arc s as a result of back arc basin inversion the frasnian formations underwent deformation metamorphism and denudation and were unconformably overlain by famennian to visean siliciclastic strata including the phyllite quartzite formation of the south portuguese zone the latest devonian early carboniferous detritus were probably shed to the pulo do lobo zone represa and santa iria formations by recycling of devonian siliciclastic rocks from the south portuguese zone meguma terrane and from a new distinct source with baltica laurentia derivation preserved in the horta da torre formation and alajar melange

early carboniferous visean emplacement of the collisional klodzko zloty stok granitoids sudetes sw poland constraints from geochemical data and zircon u pb ages sensitive high resolution ion microprobe zircon u pb dating and geochemical data of igneous rocks from the composite klodzko zloty stok kzs granite pluton sudetic block indicate that the granitoids represent an early carboniferous visean phase of variscan metaluminous high k i type syn collisional granite magmatism within the saxothuringian zone of the central european variscides igneous zircon records hypabyssal magmatism that produced various granitoids and lamprophyre spessartite emplaced from ca 340 to 331 ma the kzs granitoids have compositions ranging from granodiorite to monzonite low a cnk ratios 1 and are associated with abundant mafic members most of them are alkaline highly potassic and moderately evolved the major and trace element contents of the kzs granitoids suggest geochemical heterogeneity and the hybrid nature of magmas derived from a range of sources in the middle crust with a strong input of material from the upper mantle mixing of magmas of mantle origin with high k material from partly melted continental crust was probably a more important factor than fractional crystallization in controlling the evolution of the magmas the mean pb u ages of the main population of igneous zircon from a quartz monzodiorite elazno and hornblende monzonite droszkow are 340 2 2 5 ma and 339 5 3 1 ma respectively a slightly younger biotite hornblende granodiorite from chwalislaw 336 7 2 5 ma was cut by a spessartite dyke at 333 1 3 1 ma this indicates that mafic magmas were immediately intruded into fractured probably incompletely solidified granodiorites the lamprophyric dyke also contains igneous zircon of neoproterozoic age 566 3 6 4 ma typical of the crust in the saxothuringian zone tonalite from ptasznik hill near droszkow is of similar age to the spessartite 331 5 2 6 ma high ree contents in the tonalite and its igneous zircon indicate advanced differentiation of granitic magma producing a more leucocratic melt associated with post magmatic activity including abundant late crosscutting pegmatites and quartz veins and contact metasomatic mineralization the kzs granitoids have rather similar petrographic and geochemical characteristics to granitoids from other parts of the central european variscides where a thickened orogenic root caused a substantial rise in crustal temperatures producing granitoid magmas closely correlated with regional tectonic activity between the saxothuringian and brunovistulia terranes at the ne margin of the bohemian massif

tectonic evolution of variscan iberia gondwana laurussia collision revisited an integrated interpretation of the late paleozoic structural and geochronological record of the iberian massif is presented and discussed under the perspective of a gondwana laurussia collision giving way to the variscan orogen compressional and extensional structures developed during the building of the variscan orogenic crust of iberia are linked together into major tectonic events operating at lithosphere scale a review of the tectonometamorphic and magmatic evolution of the iberian massif reveals backs and forths in the overall convergence between gondwana and laurussia during the amalgamation of pangea in late paleozoic times stages dominated by lithosphere compression are characterized by subduction both oceanic and continental development of magmatic arcs over and under thrusting of continental lithosphere and folding variscan convergence resulted in the eventual transference of a large allochthonous set of peri gondwanan terranes the iberian allochthon onto the gondwana mainland the iberian allochthon bears the imprint of previous interaction between gondwana and laurussia including their juxtaposition after the closure of the rheic ocean in lower devonian times stages governed by lithosphere extension are featured by the opening of two short lived oceanic basins that dissected previous variscan orogenic crust first in the lower middle devonian following the closure of the rheic ocean and then in the early carboniferous following the emplacement of the peri gondwanan allochthon an additional major intra orogenic extensional event in the early middle carboniferous dismembered the iberian allochthon into individual thrust stacks separated by extensional faults and domes lateral tectonics played an important role through the variscan orogenesis especially during the creation of new tectonic blocks separated by intracontinental strike slip shear zones in the late stages of continental convergence

a new stable isotope record of neogene paleoenvironments and mammalian paleoecologies in the western great plains during the expansion of c4 grasslands abstract stable isotopes in horse teeth from the north american great plains show that equids began to incorporate c4 plants in their diets about 6 5 million years ago as c4 grasslands expanded however the ecological response of many other ungulates to this expansion is poorly documented we use stable carbon isotopes in mammalian tooth enamel to test whether other ungulates adapted by incorporating c4 vegetation in their diets the openness of habitats before the expansion of c4 grasslands is uncertain with plant phytolith studies suggesting a patchy environment with open habitat grasses and forest and pollen and macrofloral studies suggesting more forested habitats to address this problem we use a model that predicts carbon isotope values for tooth enamel for a variety of environments based on values in modern plants carbon and oxygen isotopes were analyzed in medium to large herbivores from three late miocene and three pliocene local faunas comprising a total of 13 and 7 genera respectively and 59 and 42 individuals results indicate that before the expansion of c4 grasslands taxa with high crowned teeth were consuming predominantly c3 vegetation in contrast by the late pliocene most taxa studied were consuming a component of c4 vegetation and only the peccary platygonus sp had a pure c3 diet c4 consumption increased in the late pliocene 3 0 ma big springs local fauna probably in response to increased c4 biomass most landscapes in the late miocene of nebraska were open such as woodland savanna or c3 grassland although low carbon values from the pratt slide local fauna suggest a denser presumably forested area this general pattern suggests an expansion of open habitats no later than 12 ma early clarendonian through the miocene pliocene transition there was an overall shift to lower 18o enamel values which parallels the long term decrease in global mean annual temperature inferred from the marine record our results indicate that major changes in the diets of medium and large herbivores broadly corresponded with increased c4 biomass and cooling climate from the latest miocene to the late pliocene

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

dietary reconstruction of hezhengia bohlini artiodactyla bovidae from the late miocene linxia basin of china using enamel microwear abstract dietary behavior of the middle late miocene bovid hezhengia bohlini from the linxia basin liushu formation of china was reconstructed using enamel microwear results were compared to a large comparative database of known ungulate microwear patterns results indicate a dietary regime that included both grass and browse while scratch numbers reflect this heterogeneous dietary pattern scratch width scores of h bohlini are more typical of extant grazers also enamel surfaces did not display the heavy pitting and large pits and gouges typical of extensive grit consumption indicating that fairly abrasive browse and or grass was likely consumed these results are consistent with paleohabitat reconstructions of the late miocene linxia basin as mixed habitat including woodland grassland mosaics

u pb id tims dating applied to u rich inclusions in garnet garnet has long been recognized as an important mineral in metamorphic petrology thanks to its widespread distribution and successful use in the reconstruction of p t t paths however the potential of garnet to solve geological problems may have been underestimated in this paper we make use of the role of garnet as a safe container of u rich inclusions that despite being metamict are screened from pb loss causing processes and can be dated by isotope dilution thermal ionization mass spectrometry garnet itself is not a true u pb geochronometer as it normally contains no uranium but it represents a vessel that protects u rich inclusions from later disturbances garnet is virtually free of common pb it is clean and transparent and provides a good control for the selection of suitable grains in this study inclusions such as uranitite in garnet were successfully used to obtain a precise u pb age of 318 36 0 32 ma of a pegmatite vein evora portugal which otherwise would have been undatable due to the absence and or strong alteration of common geochronometers such as zircon

variability over time in the sources of south portuguese zone turbidites evidence of denudation of different crustal blocks during the assembly of pangaea this study combines geochemical and geochronological data in order to decipher the provenance of carboniferous turbidites from the south portuguese zone sw iberia major and trace elements of 25 samples of graywackes and mudstones from the mertola visean mira serpukhovian and brejeira moscovian formations were analyzed and 363 u pb ages were obtained on detrital zircons from five samples of graywackes from the mira and brejeira formations using la icpms the results indicate that turbiditic sedimentation during the carboniferous was marked by variability in the sources involving the denudation of different crustal blocks and a break in synorogenic volcanism the visean is characterized by the accumulation of immature turbidites mertola formation and the base of the mira formation inherited from a terrane with intermediate to mafic source rocks these source rocks were probably formed in relation to devonian magmatic arcs poorly influenced by sedimentary recycling as indicated by the almost total absence of pre devonian zircons typical of the gondwana and or laurussia basements the presence of carboniferous grains in visean turbidites indicates that volcanism was active at this time later serpukhovian to moscovian turbiditic sedimentation mira and brejeira formations included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism the abundance of precambrian and paleozoic zircons reveals strong recycling of the gondwana and or laurussia basements a peri gondwanan provenance is indicated by zircon populations with neoproterozoic cadomian avalonian and pan african zircon forming events paleoproterozoic and archean ages the presence of late ordovician and silurian detrital zircons in brejeira turbidites which have no correspondence in the gondwana basement of sw iberia indicates laurussia as their most probable source

the multistage crystallization of zircon in calc alkaline granitoids u pb age constraints on the timing of variscan tectonic activity in sw iberia cl imaging and u th pb data for a population of zircons from two of the evora massif granitoids ossa morena zone sw iberia show that both calc alkaline granitoids have zircon populations dominated by grains with cores and rims either showing or not showing differences in th u ratio and having ages in the range ca 350 335 ma early carboniferous multistage crystallization of zircon is revealed in two main growth stages ca 344 342 ma and ca 336 335 ma well represented by morphologically complex zircons with cores and rims with different ages and different th u ratios that can be explained by 1 crystallization from melts with different compositions felsic peraluminous to felsic intermediate metaluminous 0 001 837 c granulite facies and or because they were derived from inheritance poor felsic and mafic rocks from a previous cycle as suggested by the internal structures of zircon cores these variscan magmatic rocks with crystallization ages estimated at ca 336 335 ma are spatially and temporally related to high temperature metamorphism anatexis processes of interaction between crustal and mantle derived magmas and intra orogenic extension that acted in sw iberia during the early carboniferous

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

investigating equid mobility in miocene florida usa using strontium isotope ratios abstract despite extensive research on the evolutionary history and ecology of horses surprisingly little is known about the daily and seasonal movements i e mobility of extinct species we used strontium isotope ratios 87sr 86sr in tooth enamel to estimate mobility patterns of equids from two miocene fossil sites in northern florida usa thomas farm ca 18 ma and love bone bed ca 9 5 9 ma the species included in our sample have a range of body sizes 45 252 kg and reconstructed diets gomphotheres and tapirs from love bone bed were also included to represent browsers based on modern species behavior we predicted small bodied and browsing taxa living in closed habitats had limited mobility and 87sr 86sr similar to local northern florida limestone we anticipated larger bodied and grazing taxa living in open environments had increased mobility with higher and more variable 87sr 86sr reflecting larger movements across differing geologies contrary to expectations the majority of taxa at both sites have higher 87sr 86sr than expected for local eocene bedrock and instead are similar to contemporary late oligocene to mid miocene seawater the most plausible explanation for these findings is that most individuals foraged close to the paleo coastline where vegetation would have been influenced by marine derived strontium via sea spray or precipitation tapirs have considerably higher and more variable 87sr 86sr than horses or gomphotheres at love bone bed which may reflect foraging on aquatic vegetation in the river channel that is preserved at the site our results suggest that horses were relatively sedentary in florida even during their peak radiation

paleoecology δ 13 c and δ 18 o stable isotopes analysis of a mammalian assemblage from the late pleistocene of hidalgo central mexico and implications for a better understanding of environmental conditions in temperate north america 18 36 n lat abstract paleoenvironmental interpretations inferred by the isotopic ecology of mammalian assemblages from the quaternary of mexico are scarce carbon 13 c and oxygen 18 o stable isotope analysis is performed on six late pleistocene localities from central mexico the objectives of the study are 1 to reconstruct the dietary traits and habitat of a mammalian community from the late pleistocene of southeastern hidalgo and 2 to characterize the paleoenvironments that existed in the region as well as placing them in the context of the paleoenvironmental conditions of temperate north america during the late pleistocene the carbon isotope composition shows a large diversity of dietary preferences including c3 intermediate c3 c4 and c4 feeders however c3 feeders are the most abundant in the assemblage the oxygen isotope composition also indicates a diversity of preferences for habitats including open habitats as well as humid and closed habitats the study reveals the presence of heterogeneous vegetation consisting of both woodland and grassland habitats during the late pleistocene the results obtained for the hidalgoan assemblage fit within the paleoenvironmental pattern known for other localities in temperate north america in particular those located in the western and central part between the coast of california the southern great plains and texas gulf coast i e grassland and mixed woodland grassland habitats

was grass more prevalent in the pronghorn past an assessment of the dietary adaptations of miocene to recent antilocapridae mammalia artiodactyla abstract molar teeth of both tertiary and quaternary representatives of the family antilocapridae were examined using mesowear and light stereomicroscopy microwear taxa from the central and southern great plains and the northern and southern great basin were included in the analyses and results compared to those obtained on the modern pronghorn antilocapra americana species included spanned from the early miocene late hemingfordian to the late pleistocene rancholabrean results are concordant with well known trends toward increasing aridity and shifts in vegetational structure in the late miocene early pliocene of north america both mesowear and microwear results indicate a shift toward more abrasive diets beginning in the hemphillian late miocene pliocene and then a return to a less abrasive dietary regime for the duration of the pleistocene and into the recent the more derived antilocaprines more hypsodont relatively longer limbs apparently depended more on grass than the less advanced merycodontines but even the earliest of the latter seem to have relied more on grass as a dietary staple than the modern pronghorn seasonal grit encroachment on food items encountered by fossil antilocaprids coupled with a heavier reliance on grasses may provide a possible explanation for the extreme hypsodonty present in the modern pronghorn despite its mainly browsing dietary behavior

transcurrent continental tectonics model for the ossa morena zone neoproterozoic paleozoic evolution sw iberian massif portugal the ossa morena zone sw iberian massif was affected by continuous orogen parallel transcurrent continental tectonics from the neoproterozoic to the carboniferous times involving transtension tt and transpression tp processes that co existed together occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically a first stage of transpression tp1 took place during the late neoproterozoic lower cambrian as a result of cadomian arc continent collisional processes structures generated by transtension tt1 from cambrian to lower devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments tilting rifting and important tectono thermal diachronic processes denudation phenomena and inhibition of sedimentation related with thermal uplift asthenosphere upwelling and consequent subsidence caused by isostatic equilibrium involving generalized transgressions were processes responsible for major unconformities the variscan tp2 tt2 episodes that followed diachronically tp1 tt1 by maintaining the orogen parallel transport direction were concomitant with syntectonic deposition of continental basins in the omz and foreland basins in the spz tt2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones favoured the opening of tectonic troughs filled up by sediments and volcanism tp2 shortening have generated fold axes parallel to the orogen strike and composite dissymmetric flower structures

ungulate diets reveal patterns of grassland evolution in north america abstract equids from the late miocene hemphillian north american land mammal age of texas evolved c4 dominated diets earlier than their nebraska counterparts leading researchers to hypothesize a northward expansion of c4 grasses between 8 and 6 ma however competing hypotheses from multiple paleoecological proxies support one of three hypotheses that northward c4 expansion occurred at the expense of c3 woodlands c3 grasslands or was not occurring during the hemphillian we test these alternative hypotheses by comparing the ecosystems of hemphillian texas and nebraska 6 3 7 5 ma using hoofed mammal dietary reconstruction hypsodonty and digestive strategy and by incorporating published tooth enamel isotopes paleosol isotopes and phytolith assemblage data we also use hypsodonty mesowear and microwear in a detailed comparison of two localities that are roughly contemporary cambridge nebraska at 7 ma and coffee ranch texas at 6 6 ma to rule out time averaging as an explanatory variable through analogy with modern african communities we reconstruct texas and nebraska ecosystems as bushland and woodland respectively using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217 mm year for nebraska and 1368 mm year for texas using rarefaction we also do not find differences in the richness of brachydont hypsodont and hindgut fermenting taxa we therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late miocene when compared to published paleosol and phytolith data which show no differences in c3 c4 biomass among latitudes our results allow us to reject hypotheses of northward c4 expansion during the late miocene we therefore suggest that the equid enamel isotopes may have been biased by two potential factors the primary reliance on a single locality of appropriate age and possible behavioural lag in c4 feeding among nebraska equids these results suggest that the formation of a modern c3 c4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes

incremental growth of the patagonian torres del paine laccolith over 90 k y the miocene paine granite in the torres del paine intrusive complex southern chile is an extraordinary example of an upper crustal mafic and granitic intrusion the granite intruded as a series of three sheets each one underplating the previous sheet along the top of the basal paine mafic complex high precision u pb geochronology on single zircons using isotope dilution thermal ionization mass spectrometry yields distinct ages of 12 59 0 02 ma and 12 50 0 02 ma respectively for the first and last sheet of the laccolith this age relationship is consistent with field observations the zircon ages define a time frame of 90 40 k y for the emplacement of a 2000 m thick granite laccolith these precise u pb zircon ages permit identification of the pulses in a 20 k y range the data obtained for the paine granite fill the gap between 100 k y and 100 1000 yr pulses described in the literature for crustal magma chambers

reply to discussion on detrital zircon geochronology of the carboniferous baixo alentejo flysch group south portugal constraints on the provenance and geodynamic evolution of the south portuguese zone journal of the geological society 172 294 308 we would like to thank pereira 2015 for his interest in our work and appreciate the opportunity to clarify some aspects of the rodrigues et al 2015 study here we dispute several fundamental assertions made in the discussion of our original paper

layered granitoids interaction between continental crust recycling processes and mantle derived magmatism examples from the evora massif ossa morena zone southwest iberia portugal abstract in this paper field petrographic mineralogical geochemical and isotopic rb sr and sm nd information from three areas within the evora massif iberian variscan orogen is presented and discussed aiming at to unravel the relationships between granitoids and units mapped as migmatites and also to evaluate the interplay between mantle and crustal derived magmas one of the areas almansor displays a well developed compositional layering concordant with the regional variscan structure which was considered in previous works as an alternation of leucosome and melanosome in this study the layering is described as intercalation of diatexites weakly foliated granitoids and trondhjemitic veins diatexites have characteristics of crustal melts plus restitic material and according to geochemical and isotopic evidence result from anatexis of ediacaran metasediments weakly foliated granitoids and trondhjemitic veins from almansor have calc alkaline signatures and may be related to each other by crystal fractionation processes however the mixing between mafic mantle derived and felsic diatexitic melt magmas revealed by the isotopic data may also explain their genesis in the alto de sao bento area several igneous lithologies tonalites granodiorites porphyritic granites and leucogranites are present and show typical isotropic igneous textures despite structural and textural differences geochemical data support for most rocks an origin from the same calk alkaline suite also present at almansor the alto de sao bento leucogranites have an isotopic signature that although different from that obtained in the almansor diatexites is still compatible with an origin involving melting of ediacaran metasediments compositions with very low contents of usually incompatible elements flat normalized ree patterns and strong negative eu anomalies suggest that the anatectic melt has undergone crystal fractionation processes before reaching the composition of the leucogranite magma the almansor outcrop is then interpreted as the remnants of a shear zone that operated as a pathway for melts that moved upward through the crust providing the locus for differentiation and mingling mixing of magmas whilst alto de sao bento would correspond to the zone at a higher crustal level where magmas were trapped and forced to spread horizontally at valverde the third area foliated and non foliated granitoids are spatially related and field criteria links these rocks to metamorphic protolith and anatectic melt respectively however petrographic geochemical and isotopic information shows that they all are compositionally identical trondhjemites with no evidence of metamorphic fabric in the foliated rocks mesoscopic features are interpreted as resulting from melt segregation structures formed in a crystallizing mush in contrast to the previous areas the valverde trondhjemites probably do not belong to the main calc alkaline plutonic suite of the evora massif since they have a distinct sr and nd isotope signature

trace element partitioning between apatite and silicate melts we present new experimental apatite melt trace element partition coefficients for a large number of trace elements cs rb ba la ce pr sm gd lu y sr zr hf nb ta u pb and th the experiments were conducted at pressures of 1 0 gpa and temperatures of 1250 c the rare earth elements la ce pr sm gd and lu y and sr are compatible in apatite whereas the larger lithophile elements cs rb and ba are strongly incompatible other trace elements such as u th and pb have partition coefficients close to unity

emplacement of magma pulses and growth of magma bodies magmatism is responsible for the formation of continental and oceanic crusts it is the main agent of mass and heat transfers from the mantle towards the crust the hydrosphere oceanic and continental hydrothermalism and the atmosphere emissions of volcanic gas and ashes its expressions are the crystallization of intrusive rocks and the eruption of volcanic products however with a ratio between the volumes of extrusive and intrusive magmatic rocks estimated to be of the order of 1 5 for most magmatic systems white et al 2006 one of the main characteristics of magmatism is that magmas rarely reach the earth s surface this suggests that the prevailing conditions in the crust are not favourable to the arrival of magma on the earth s surface but instead lean heavily towards the formation of intrusive bodies in the crust these intrusive bodies referred to here as plutons constitute the elementary building brick of the continental crust an increasing number of geophyscial and geochronological data as well as geological observations is currently modifying our understanding of pluton construction when plutons were initially envisaged as quasi spherical bodies growing slowly and essentially by an overall inflation they are now recognized as growing incrementally by the accretion of successive and relatively small magma pulses over variable periods of time from hundred to millions of years depending on geodynamic setting and source fertility this brings new challenges and has far reaching implications according to this new model of plutonism the evolution of magma bodies is related to the processes that control the timescale and the spatial distribution of the successive pulses depending on their emplacement rate and on their ability to amalgamate repeated magma pulses can either rapidly solidify or ultimately build up an active magma chamber thus understanding how magma bodies grow has fundamental implications for the link between volcanism and plutonism as well as for magma differentiation and ultimately for our understanding of the growth and evolution of the earth crusts the concept of pluton incremental growth challenges our understanding as well as our field interpretations of the processes involved during pluton construction indeed these processes and how they operate in governing the emplacement and growth of plutons both in space and time are still debated a state of the art session on these very issues was held at the 2008 general assembly of the european geosciences union as a follow up of this session this special volume emplacement of magma pulses and growth of magma bodies brings together both theoretical models and field studies that cover most aspects of the emplacement and growth of plutons

differentiated impact melt sheets may be a potential source of hadean detrital zircon constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of earth s very early crust and hadean geodynamics previous applications of the ti in zircon thermometer to 4 ga zircons have identified a population with relatively low crystallization temperatures graphic 1 of 685 c this could possibly indicate wet minimum melting conditions producing granitic melts implying very different hadean terrestrial geology from that of other rocky planets here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated sudbury impact melt sheet ontario canada the new zircon ti results and corresponding graphic 2 fully overlap with those of the hadean zircon population previous studies that measured ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true ti content it is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low graphic 3 in zircons from the most evolved rocks on earth melt sheet differentiation is strongest in subaqueous impact basins thus not all hadean detrital zircon with low ti necessarily formed during melting at plate boundaries but at least some could also have crystallized in melt sheets caused by intense meteorite bombardment of the early hydrosphere covered protocrust 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

rare earth elements and sm nd isotope redistribution in apatite and accessory minerals in retrogressed lower crust material bergen arcs norway in the bergen arcs norway grenvillian granulite retrogressed under eclogite and amphibolite facies conditions during caledonian subduction collision offer a unique opportunity to investigate rare earth elements ree and sm nd isotope redistribution in accessory minerals during fluid assisted metamorphism our sampling targeted apatite bearing ree rich protoliths mangerite and jotunite that preserve distinct mineral assemblages depending on the external fluid availability and metamorphic conditions ree concentrations in apatite are the highest in the granulite two populations are present magmatic apatite ap1 relics that occur as inclusions in ilmenite hematite and intergranular apatite ap2 formed under granulite facies conditions the presence of abundant needle like monazite and sulphide inclusions in ap2 indicate that granulite reactions were fluid assisted a thin typically 10 m rim of ree rich epidote ep1 commonly surrounds ap2 in these accessory minerals u and th contents are too low or grains are too small for in situ u th pb dating sm nd isotope data of ap2 monazite and ep1 give an isochron age of 601 69 ma which is interpreted to represent a partially reset grenvillian age affected by caledonian fluid assisted mineral growth in amphibolitized samples granulite ap2 is replaced by apatite ap3 with lower ree contents and no monazite inclusions the ree released by this replacement are redistributed in a corona of epidote group minerals ep2 surrounding ap3 the in situ sm nd isotope data for ep2 and titanite found in replacement of ilmenite hematite return an isochron age of 395 65 ma recording the timing of amphibolite facies mineral growth when fluids were introduced into the rock in eclogitized samples eclogitic apatite ap4 occurs as polycrystalline aggregates suggesting for a complex replacement process during deformation ree contents of ap4 are low as ree originally contained in the precursor apatite were redistributed mainly into zoisite apatite shielded as inclusions in ilmenite and garnet preserve the ree rich signature of the initial magmatic ap1 and granulite ap2 apatite indicating these grains did not undergo further re equilibration during caledonian metamorphism the resistance of apatite to compositional re equilibration in this case confirms the petrological potential of apatite inclusions shielded in chemically inert minerals to track early magmatic or metamorphic crystallisation stages

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

structural environment around th4 in silicate glasses implications for the geochemistry of incompatible me4 elements the structural environment around th4 in several silicate glasses containing 1 3 wt th4 was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy one set of glasses had the bulk chemical composition of monticellite mo diopside di anorthite an albite al olivine basalt o bas tholeiitic basalt t bas calc alkaline dacite dac and calc alkaline rhyolite rhy a second set of th bearing glasses had the bulk al composition but also contained either 5 5 wt f or 2000 ppm cl in glasses containing 3 wt th th coordination varies from 8 d viiith o 2 41 0 02 a in mo and di to a mixture of 8 and 6 coordinations d vi viiith o 2 35 2 36 0 02 a in all other compositions the presence of viiith is related to the thorianite tho2 saturation in the glass in al glasses containing 1 wt th 6 fold coordinated th dominates d vith o 2 32 0 02 a no clear evidence for f or cl complexes around th is observed in any of the halogen containing glasses weak but significant interactions of th with tetrahedral si al network and or alkali elements are observed especially in highly polymerized compositions rhy in which th si ai na k contributions are detected between 3 25 and 3 50 0 05 a these results suggest that in this set of glasses th does not form complexes but rather acts as a weak network modifier the presence of vith in silicate glasses an unusual low coordination for th suggests that the ionic radius of th in magmatic systems is lower than previously reported rth 0 94 a the resulting high th o bond strength 0 7 vu unknown in minerals may explain the observed low crystal melt partition coefficients of th4 i e its incompatible character during magmatic differentiation increasing polymerization is predicted to favor higher coordination around th viii ix as a result of a shortage of nbo to which th preferentially bonds hence dramatic changes in the crystal chemistry of th are predicted i e the incorporation of th in minerals comparison with u4 suggests that vith is less abundant in similar glass melt systems compared with viu this may explain the u th fractionation often observed in zircon as well as the preferential incorporation of th in accessory minerals containing large sites in which th4 can be substituted e g the ca2 site in titanite apatite or zirkelite

rheic ocean ophiolitic remnants in southern iberia questioned by shrimp u pb zircon ages on the beja acebuches amphibolites 1 the rheic ocean was a major oceanic domain between avalonia and gondwana in ordovician silurian times most of the paleozoic plate reconstructions assume that the rheic ocean suture lies within southern iberia coinciding with the contact between the south portuguese zone and the ossa morena zone this paper reports four sensitive high resolution ion micro probe shrimp u pb zircon ages from mid ocean ridge basalt morb featured rocks of the beja acebuches amphibolite unit which crops out along the boundary between the ossa morena and the south portuguese zone and is considered its most conspicuous suture unit the obtained ages range from 332 3 to 340 4 ma corresponding to the crystallization of the mafic protoliths these early carboniferous ages for the beja acebuches amphibolites imply that this unit can no longer be viewed as an ophiolite belonging to the rheic ocean suture since this oceanic domain was presumably closed in devonian times tectonic reconstructions joining in a single suture line the beja acebuches amphibolite unit in southern iberia to either the devonian lizard ophiolite in southern england or the root zone of the devonian ordovician ophiolitic units in northwest iberia must be therefore reconsidered because of the age difference we interpret the beja acebuches amphibolite unit to represent a narrow and very ephemeral realm of oceanic like crust that opened in early carboniferous times after total consumption of the rheic ocean we suggest that a mantle plume underneath southern iberia in early carboniferous times is the most plausible large scale geodynamic scenario for the formation of these morb featured rocks

trends in the paleodietary habits of fossil camels from the tertiary and quaternary of north america abstract dietary adaptations of both tertiary and quaternary representatives of north american camelidae were examined through deep evolutionary time via hypsodonty index though ecological time via mesowear analysis and through the last few days of life via microwear by examining molar teeth fossil samples are from the great plains great basin arizona and florida and span from the early late eocene late chadronian early orellan to the late pleistocene rancholabrean results were compared to those obtained on modern camels and llamas and other ungulates of known dietary behavior camels apparently exploited open habitats early on in their evolution as evidenced by the extreme pitting of their enamel surfaces grasses were likely consumed early on in their history e g poebrotherium but the vast majority of taxa were committed browsers results show that the hypsodonty pattern deep time adaptation and mesowear pattern cumulative abrasion index are very similar hypsodonty indices and mesowear scores decrease in the middle miocene a time when a few taxa also incorporate fruit and or seeds in their browse crown height and dietary abrasion increase in the late miocene and pliocene a time when some grazers and mixed feeders also appear but then decrease in pleistocene and recent forms

evidence for geographic variation in the diets of late pleistocene and early holocene bison in north america and differences from the diets of recent bison abstract during the late pleistocene and early holocene bison was widely dispersed across north america and occupied most regions not covered by ice sheets a dietary study on bison paleopopulations from alaska new mexico florida and texas was performed using two methods that relate dental wear patterns to diet mesowear analysis and microwear analysis these data were compared to a mixed sample of extant bison from the north american central plains extant wood bison from alberta canada and a variety of other modern ungulates mesowear relates macroscopic molar facet shape to levels of dietary abrasion the mesowear signature observed on fossil bison differs significantly from the hyper abrasive grazing diet of extant bison tooth microwear examines wear on the surface of enamel at a microscopic scale the microwear signal of fossil samples resembles to modern bison but the fossil samples show a greater diversity of features suggesting that fossil bison populations regularly consumed food items that are texturally inconsistent with the short grass diet typical of modern plains bison mesowear and microwear signals of fossil bison samples most closely resemble a variety of typical mixed feeding ungulates all with diets that are substantially less abrasive than what is typical for modern plains bison furthermore statistical tests suggest significant differences between the microwear signatures of the fossil samples thus revealing geographic variability in pleistocene bison diets this study reveals that fossils are of value in developing an understanding of the dietary breadth and ecological versatility of species that in recent times are rare endangered and occupy only a small remnant of their former ranges

niche modeling reveals lack of broad scale habitat partitioning in extinct horses of north america abstract the classic traits of modern horses equidae large body size high crowned teeth hypsodonty and a single toe monodactyly are often considered adaptations to grassland environments however extinct horses that varied in these three traits overlapped geographically for millions of years during the miocene and pliocene it has been hypothesized that co occurring horse species partitioned habitats with large bodied hypsodont and monodactyl equids dominating open grasslands while equids with different combinations of traits lived in more wooded areas we tested for the presence of broad scale habitat partitioning by compiling a large database of north american horse fossil occurrences with data on trait state body size hypsodonty index and toe number and paleoenvironment derived from paleovegetation records null modeling of niche overlap in each of the north american land mammal ages of the miocene and pliocene revealed that taxonomic and trait based groups show no differences in habitat occupancy cluster dendrograms visualizing niche overlap showed that some ecological guilds shared derived traits but derived traits were not associated exclusively with grassland habitats trait values are not predicted by the proportion of grassland habitats in time bins further the three traits show no co evolution across the equid tree when corrected for phylogenetic relatedness together these results suggest that the evolution of large body size hypsodonty and monodactyly in equids was not due to a shared selective regime in response to expanding grassland habitats instead these traits may have evolved separately likely due to a variety of small scale selective pressures acting across the variety of habitats present in the miocene and pliocene

rare earth element partitioning between titanite and silicate melts henry s law revisited we present detailed experimental results on the partitioning of rare earth elements ree between titanite and a range of different silicate melts our results show that henry s law of trace element partitioning depends on bulk composition the available partners for heterovalent substitution crystal composition and melt composition we illustrate that the partition coefficients for sm depend very strongly on the bulk concentration of sm in the system the substitution mechanism by which rare earth elements are incorporated into the crystal structure plays an important role for trace element partitioning and also for the onset of henry s law our data show that there are clear differences between substitution mechanisms of major elements compared to elements which are present only as traces our experiments also clearly show that the onset of henry s law depends on the concentrations of the sum of all trace elements which are incorporated into the crystal by the same substitution mechanism for geochemical modelling of magmatic processes involving titanite and indeed other accessory phases it is of crucial importance to first evaluate whether the ree and other trace elements are present as traces or as major elements only then appropriate d values may be chosen

implications of incremental emplacement of magma bodies for magma differentiation thermal aureole dimensions and plutonism volcanism relationships abstract field observations and geophysical data indicate that many igneous bodies grow by amalgamation of successive magma pulses that commonly take the shape of horizontal sheets sills emplacement styles and emplacement rates of magma bodies have fundamental implications on magma differentiation country rock metamorphism and assimilation and for the formation of large magma chambers in the upper crust when a magma body begins to grow by slow accretion of sills each successive intrusion solidifies before the injection of the next one when the system is thermally mature sill temperatures equilibrate above the solidus melts accumulate and older sills can re melt the time needed for each magma injection to cool down and equilibrate with its surrounding is short relatively to the total emplacement time of the body the transition from a mafic crystal poor magma to a partially molten rock that retains a highly differentiated melt is fast whereas the resulting evolved residual melt can reside in the crust for protracted periods as long as temperatures in the system are relatively low highly differentiated melts are generated which may explain the bi modal character and the absence of intermediate compositions in some magmatic provinces the level of emplacement of successive magma pulses controls the shape of the thermal anomaly associated with the magma body growth metamorphism partial melting and assimilation of the country rock are favoured if successive magma sheets are emplaced at or close to the country rock magma body boundary if the magma emplacement rate is low the size of the thermal aureole is controlled by the size of one pulse and not by the size of the entire igneous body understanding emplacement of magma bodies is fundamental for our understanding of the plutonism volcanism relationship magma emplacement rates of several centimetres per year are needed for a magma body to evolve into a large magma chamber able to feed large silicic explosive eruptions the time averaged emplacement rates of plutons are lower than this critical emplacement rate eruptions of 100s to 1000s cubic kilometres of silicic products show that such high volumes of magmas can accumulate in the upper crust this suggests that the emplacement of magma bodies is a multi timescale process with the development of large magma chambers corresponding to the highest magma fluxes because they control magmatic processes and the impact of magma intrusion on the country rock future studies should focus on magma emplacement rates and on magma emplacement geometries these studies should integrate field observation on plutons and geophysical data on active magmatic systems coupled with laboratory experiments and numerical simulations

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

dental histology of late miocene hipparionins compared with extant equus and its implications for equidae life history abstract hipparionins were a dominant element of the late miocene faunas of europe however their biology and ecology remain incompletely understood in this paper we explore the pace of life history of different sized hipparionin horses using dental histology and compare it with extant equids in doing so we consider i the size diversity of hipparionins ii their generally smaller size compared to extant equids and iii the allometric coupling between size and life history in particular we reconstruct the dental growth in lower first second molars and in later formed lower third molars for three hipparionin taxa two dwarf species hipparion periafricanum and h gromovae and a larger species h concudense we also analyze dental growth in an extant zebra equus quagga for comparative purposes our results reveal that within each species there are differences in enamel growth parameters between the first second molars and third molars these results illustrate the differences in the developmental timing of these teeth and the existence of a relationship between dental growth parameters with somatic growth we also find that hipparionin teeth grow at slower rates and tend to erupt later in time than in extant equus dwarf hipparionins moreover exhibit lower enamel extension rates than the larger species but similar formation and eruption times considering the link between dental development and life history these results suggest a slower pace of growth of selected hipparionins compared to extant equids and a further slower life history than expected for their size in the two dwarf forms

two models for the formation of magma reservoirs by small increments abstract it is now clear that magma reservoirs develop over long time intervals out of a large number of individual intrusions evidence from some large volcanic deposits including those of the bishop tuff california and fish canyon tuff colorado indicates that such reservoirs may experience pervasive and rapid heating before catastrophic eruptions injection of hot primitive melt in the reservoir is often invoked to explain these observations but this requires the rapid emplacement of a large magma volume at least 25 km 3 in less than 100 years for the bishop tuff and efficient heat transfer through a thick cumulate pile within a magma body that grows incrementally temperatures rise progressively and may eventually lead to a permanent volume of melt temperature and crystallization follow two completely different paths depending on the thickness of individual intrusive sheets in one limit corresponding to thick sheets crystallization proceeds at equilibrium initial magma batches crystallize completely and a permanent body of melt develops progressively once ambient temperatures in the complex rise above the solidus in the other limit corresponding to thin sheets crystallization is kinetically controlled such that initial intrusions do not crystallize completely and preserve a glassy residue once temperatures within the growing magma pile reach a certain threshold value nucleation and growth of crystals get reactivated in the residual glass crystallization then proceeds catastrophically in a positive feedback loop involving latent heat release and temperature rise thus an initial phase with no evolved melt present ends with the sudden formation of a large volume of evolved melt in a crystal mush after this initial phase new intrusions get emplaced in heated surroundings and follow a thermal path similar to that of the equilibrium case with melts that become increasingly more primitive with time evidence for kinetic controls on crystallization in the natural environment is provided by the significant amounts of glass up to 40 that are found in thin isolated basaltic sills and dykes owing to sluggish crystallization kinetics more glass should be generated in andesitic and dacitic magmas emplaced in similar conditions devitrification of such quantities of glass accounts for the rapid heating of a thick sill complex the two models of magma reservoir formation involve different requirements the intrusion thickness must be smaller than a critical value in the kinetic model and the average magma input rate must exceed a threshold value in the equilibrium model for a given injection rate a permanent magma reservoir forms in a shorter time interval and over a smaller cumulative magma thickness in the kinetic model than in the equilibrium one the kinetic model is such that the amount of evolved melt generated increases with decreasing injection rate in contrast to the equilibrium model for which the opposite relationship holds

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

time constraints on the building of the serre batholith consequences for the thermal evolution of the hercynian continental crust exposed in calabria southern italy abstractnew laser ablation inductively coupled plasma mass spectrometry u pb dating on zircon and monazite was performed to estimate the time required for the building of the serre batholith in calabria age spectra from the bottom and top of the pluton are characterized by two main peaks at 306 and 295 ma resulting from a mutual interference between serial intrusive events on this basis the emplacement of the top granodiorite layer postdates by about 10 m yr emplacement of the lower tonalite layer these results have been incorporated into a two dimensional numerical thermal model assuming overaccretion of a batholith in an extensional tectonic regime with this approach it was possible to reproduce pressure temperature paths for various levels of the continental crust and define timing for low pressure regional and contact metamorphism in a unique tectonomagmatic scenario the model reproduces regional low pressure metamorphic effects in the lower to intermediate continental crust and with a time