the genesis of late hercynian granitoids from galicia northwestern spain inferences from ree studies two mica granites and biotite rich monzogranites and granodiorites constitute the main types of late to post kinematic hercynian intrusions in galicia northwestern iberian massif both rock types exhibit analogous total ree content although the two mica granites have generally more fractionated normalized spectra the hercynian granites studied can be modeled as partial melts which in some cases experienced feldspar dominated fractional crystallization model source materials may be compared to the rocks outcropping in the area studied these granites are not accurately described by the i and s type classification those with s type characteristics two mica granites are derived mainly from an orthogneiss rich model protolith i e i type source whereas those with i type affinities biotite rich granitoids may be modeled from mixtures of orthogneiss and graywacke eastern galicia or from orthogneiss rich protoliths containing only a small proportion of metabasite western galicia the propose

an isotopic mixing model for the origin of granitic rocks in southeastern australia a simple mixing process was a significant element in the genesis of many southeastern australian granitic rocks major and trace element abundances are near linearly correlated nd and sr initial isotopic compositions define a simple hyperbolic trend and many initial 87sr 86sr ratios are a regular function of rb sr ratios geological arguments and regression of geochemical variation diagrams place limits on the nature of the end members the high si end member is meta sedimentary derived magma comparable in composition to the cooma granodiorite the one pluton in the region surrounded by and clearly derived from regional metamorphic rocks the low si end member is basaltic material with similarities to rare gabbros also found in the area isotope dilution calculations based upon initial sr and nd isotopic compositions deduced for the end members yield realistic hypothetical sr and nd concentrations for the end members in a demonstration of the internal consistency of the model all of the granitic rocks from hornblende tonalites to cordierite granodiorites are a single broad family products of variable mixing between distinct batches of basaltic material and a uniform partial melt of the regional basement

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

fractionation hybridisation and magma mixing in the kialineq centre east greenland the igneous rocks of the kialineq centre on the coast of east greenland at 67 n include a number of quartz syenite and granite plutons intruded 35my bp these are subvolcanic bodies emplaced by cauldron subsidence and with ring dike and bell jar form associated with the major intrusions is an extensive acid basic mixed magma complex two liquid structures chilling of basic against acid magma pillows of basic in acid and net veining of basic by acid magma are superbly displayed the basic magma was of a transitional or alkaline type and underwent varying degrees of fractionation in a regime of repeated intrusions and diverse chambers heterogeneous hybrid rocks intermediate between basalt and quartz syenite are strongly developed and were formed by repeated mechanical mixing of contrasting magmas the energy for this mixing probably came in the main from cauldron block subsidence the quartz syenite magma which itself fractionated towards granite has initial 87sr 86sr ratios the same as the basic magma and is itself believed to be a fractionation product of alkali basalt magma

petrogenesis of the hercynian tichka plutonic complex western high atlas morocco trace element and rbzsr and smznd isotopic constraints the late tectonic hercynian tichka plutonic complex in morocco was emplaced in the lower cambrian volcanosedimentary sequence of the western high atlas and displays an exceptional acid basic association which consists of five well defined plutonic intrusions gabbros diorites granodiorites tonalites monzogranites and two types of leucogranites biotite amphibole leucogranites and two mica leucogranites with the exception of the late two mica leucogranites the plutonic suites present field relationships clearly indicating an almost synchronous magmatic emplacement the monzogranites and biotite amphibole leucogranites plot along the same rbzsr isochron and most of them also plot along the same smznd isochron yielding respectively ages of 291 5 ma and 283 24 ma with initial87sr 86sr and143nd 144nd ratios of 0 70348 4 and 0 51243 4 major and trace element data together with the rbzsr and smznd isotopic results rule out any genetic process involving a unique homogeneous source the smznd isotopic heterogeneity even at the scale of one unit implies the existence of contrasting source rocks and the combination of different mechanisms the gabbro and diorite magmas are assumed to be derived from the melting to different degrees of a depleted upper mantle source in a within plate geotectonic environment whereas a combined wallrock assimilation fractional crystallisation model is proposed for the evolution of the diorite suite in contrast the granitoids are mainly the result of the anatexis of a dominant basic to intermediate igneous heterogeneous continental crust

magma mixing origin of intermediate rocks and enclaves from volcanism to plutonism abstract intermediate magmatic rocks are rarely homogeneous a common example is the presence of magmatic enclaves volcanic examples show that they are indications of magma mixing processes mixing events in the trachyandesitic suites from the sancy volcano france the volcanic activity from sancy consists of several brief trachyandesitic cycles each of them begins with the eruption of highly heterogeneous benmoreites followed by more homogeneous mugearites light porphyritic trachyandesites enclose numerous inclusions of varied darker lavas the crenulated geometry of the contacts the presence of chilled margins the vesiculation of the core of the basic parts suggest that these different rock types were magmatic at the same time although under marked thermal disequilibrium xenocrysts are common partly resorbed sanidine rimmed with plagioclase in a basic matrix reactional olivines in tridymite bearing trachytes this shows that the mixing occurred between partially crystallized and fractionated magmas chemical compositions are continuously variable from basalts to trachytes within the same eruptive cycle all these facts might be interpreted as the result of a mechanical intermingling more or less achieved between two end members of contrasting composition in the reservoir in the sancy volcano this phenomenon occurred at least 4 or 5 times during a 600 000 y span mixing evidence in hercynian granodiorites from france similar observations may be described in granodioritic rocks the more widespread enclaves exhibit the same characteristics as their volcanic equivalents although most of them are small more important volumes of basic rocks may be associated in the same massif in the neighbourhood of such large bodies swarms of smaller enclaves recall the generation of basic pillows the nature of the contact between small microgranular enclaves and their host rocks the occurrence of xenocrysts with reaction rims rapakivi feldspars and quartz ocelli in a basic surrounding amphibole pyroxene clots in a granitic matrix and geochemical variations again suggest thermal and mineralogical disequilibrium such observations indicate the comagmatic character of enclaves with regard to their host rocks they cannot be interpreted as restites and are best described as co igneous inclusions resulting from non achieved mixing between coexisting magmas photonic rocks are less suitable to demonstrate such petrogenetic processes because they result from slow cooling and crystallization during a longer residence time in a magmatic chamber the successive mixing episodes giving rise to different generations of co igneous inclusions are also difficult to recognize on the other hand in volcanism this process is quenched and periodically sampled by eruptions in conclusion the heterogeneity and the variability of many intermediate rocks cannot be explained only in terms of simple partial fusion and fractional crystallization processes in a closed system volcanic examples point to a complex evolution of magmatic reservoirs that were continuously fractionated periodically tapped periodically refilled and mixed

origin of late variscan granitoids from ne bavaria germany exemplified by ree and nd isotope systematics sm nd isotopic results are presented for late and post tectonic granitoids comprising peraluminous granites and subordinate metaluminous dioritic rocks redwitzites from the fichtelgebirge fg and northern oberpfalz nop ne bavaria the data combined with a number of earlier geochromological studies on these granitoids place severe constraints on the crustal evolution of this region during the carboniferous and pre carboniferous epoch redwitzites range in nd t from 4 to 0 inclusive data from p k holl and coworkers the nd t values of the granites s s are restricted to overlapping ranges of 8 to 3 fg and 8 to 2 nop in both domains the older granites 330 325 ma are characterized by nd t values of 4 whilst the younger granites 315 305 and 290 ma have nd t values of 4 the diversity observed in nd isotopic characteristic is interpreted in terms of different source material the nd isotopic compositions of the redwitzites exhibit source heterogeneity suggesting mixing between mantle magma and crust the nd isotopic features of the older granites are consistent with the magmatic precursors having been generated by partial melting of pre existing mature crust variably contaminated by mantle material or alternatively by melting of chemically less evolved crust resembling paragneisses of teh zev structural unit the origin of the younger granites can be confidently linked to anatexis of common moldanubian and saxothuringian metasediments two stage nd model ages tdm of the granitoids are in the range 1 1 1 7 ga these ages provide further support of substantial involvement of pre phanerozoic crust in the generation of the granitoids the leuchtenberg granite and the g2 and g3 granites yield late variscan sm nd isochron ages which are concordant with previous rb sr data on these granites by contrast the nd isotopic data for barnau and flossenburg define pseudo isochrons suggestive of mixing between contrasting felsic melts

nature and evolution of the eastern margin of lapetus geochemical and isotopic constraints from siluro devonian granitoid plutons in the new brunswick appalachians in the gander zone ordovician to devonian metaluminous to slightly peraluminous plutons with within plate affinities intrude a lower paleozoic metasedimentary package during the siluro devonian end t and 18o values of the metasedimentary rocks would have been about 7 to 8 and 10 to 14 respectively granitoid end t values range from 0 3 to 4 2 18o values lie between 6 6 and 10 4 and published pb isotopic compositions are radiogenic 207pb 204pb 15 65 end t values of associated silurian gabbros are somewhat positive 1 2 to 2 3 some plutons exhibit evidence for comingling with this mafic component potential source materials include enriched mantle supracrustal and infracrustal sources although some constraints can be put on the first two sources the nature of infracrustal material is difficult to evaluate heterogeneous data obtained from silurian plutons can be explained by crust mantle mixing if some plutons contain a significant mantle component then mesoproterozoic o

chemical overprinting of magmatism by weathering a practical method for evaluating the degree of chemical weathering of granitoids abstract quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology and many weathering indices based on whole rock chemistry have been proposed however most classical indices are of limited application to granitoids in a wide area because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis the chemical evolution produced during rock weathering therefore overprints pre existing magmatic chemical variation this problem can cause many classical weathering indices to yield misleading results this study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index the method is based on a bivariate plot of the magmatic chemical variation mcv in granitoids and the degree of chemical weathering dcw the mcv axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering in this study tio 2 contents are utilized for the mcv the dcw axis is fundamentally defined by the ratios of more mobile to less mobile elements during weathering and hence many classical indices can be applied the improved value of the degree of chemical weathering dcw i for a weathered rock is derived by dcw i s mcv cv mcv 1 dcw 1 where mcv 1 is the measured composition e g tio 2 content of the weathered rock dcw 1 denotes the ratios of more mobile to less mobile elements of the weathered rock the s parameter is the slope of the least square linear regression for fresh granitoids in the mcv dcw relationship mcv cv is a correction factor which is given by the average point on the mcv axis e g average tio 2 of the fresh rocks this method is useful for evaluating the degree of weathering of various granitoids and enhances the practical application of many weathering indices

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

interaction among upper crustal lower crustal and mantle materials in the port mouton pluton meguma lithotectonic zone southwest nova scotia the port mouton pluton is unique among the late devonian peraluminous granitoid bodies in the meguma lithotectonic zone of southwestern nova scotia in its lithological heterogeneity extensive physical and chemical interac tion with the country rocks clear evidence for mingling and mixing with mafic magmas and highly abundant pegmatites new u pb age determinations on monazite establish an intrusion age of 373 1 ma similar to the ages of other meguma lithotectonic zone granitoid plutons and mafic intrusions field relations petrology and geochemistry define three stages of intrusion of the port mouton pluton i early stage discontinuously exposed around the outer margin of the pluton dominated by coarse grained tonalite granodiorite and with rb sr 0 40 and gdn lun 0 55 eu eu 2 and iii late stage consisting of abundant minor sheets throughout the pluton dominated by fine grained tonalite granodiorite and leucogranite that are similar to rocks of the early and middle stages the port mouton pluton shows a wider range of 87 sr 86 sri 0 7036 0 7154 and a wider range and generally higher endi 3 72 to 2 12 than other granitoid rocks in the meguma lithotectonic zone potentially reflecting a com plex partially equilibrated interaction among mantle lower crust and upper crust field petrological and chemical evi dence for the involvement of mantle derived magmas and melting of upper crust permit modelling of the port mouton pluton granitoid compositions by three simultaneous mixing equations these mixing model results suggest that the early stage granitoid rocks can form from simple three component mixing relationships when the bulk distribution coefficients between residuum and melt for sr and nd range from 1 05 to 1 18 or two component mixing combined with fraction ation of material like the known felsic lower crust the middle stage granitoid rocks only yield solutions involving two component mixing and fractionation of material unlike the known felsic lower crust we conclude that the late devonian mafic magmas played a major role in the formation of granitoid magmas in the meguma lithotectonic zone by supplying heat and material to cause partial fusion of the avalon lower crust

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

models for granitoid evolution and source compositions this paper critically examines the bases of various models for the chemical evolution of granitoid suites the proposed mineralogical textural and chemical criteria for the recognition of restite components are found to be equivocal and can be plausibly explained by crystal fractionation and accumulation as well as by magma mixing and assimilation of non restitic solids these processes demonstrably account for the bulk of the chemical variation in a variety of granitic suites although restite controlled variation may have played a role in some types of metasediment derived suites granitoid magmas with non minimum melt chemistry are probably rather common the petrographic geochemical and isotopic features of individual plutons should be assessed carefully to elucidate the relative importance of various mechanisms for chemical evolution conclusions as to the character of magma source materials and magma evolution paths that are based on the restite model should be treated with caution

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

granitoid chemistry and associated mineralization in the french variscan the orogenic granitoids of the french variscan are classified into three principal associations aluminopotassic subalkaline and calc alkaline each of these associations is characterized by the petrographical and geochemical composition of the members and the nature of the related mineralization aluminopotassic granitoids contain most of the observed sn w and u mineralization and all the be nb ta and li mineralization they are associated with two mica leucogranites with a separate occurrence of sn w li be nb ta mineralization related to evolved sodic leucogranites and u mineralization related to potassic leucogranites the cu and mo potential of the subalkaline granitoids is assessed by the occurrence of genetically related mineralized pegmatites and k feldspar veins and of postmagmatic veins and stockworks complex sn cu and w mo mineralization occurs in areas and bodies characterized by the emplacement of both subalkaline and aluminopotassic granitoids evolved subalkaline granites and leucogranites contain u mineralization occurrences deposits which can be enhanced by late aluminopotassic two mica leucogranite intrusions the calc alkaline granitoids are conspicuously barren except for some w skarn occurrences a type of mineralization which is also observed around subalkaline and aluminopotassic intrusions no cu mo porphyry mineralization is observed in either calc alkaline or subalkaline granitoids the regional pattern of distribution of the granitoids and their related mineralization leads to the definition of three principal regions which differ by the volumic development of the various granitoid associations and the related mineralization no clear magmatic or metalliferous polarity can be observed across the french variscan the observed pattern of distribution results from the ensialic evolution of the french variscan orogeny and from the mainly crustal origin of the granitoids emplaced between 280 and 360 ma in response to the postcollisional thrusting and shearing tectonics similar relationships between the mineralization and granitoid varieties are observed in the adjacent european segments of the french variscan other classification schemes suffer some limitations including being less discriminating so that comparisons are not always useful

sources of hercynian granitoids from the french massif central inferences from nd isotopes and consequences for crustal evolution the french massif central is characterized by a great abundance and variety of granitoids emplaced during hercynian times 360 280 ma distinct nd i and 87sr86sr i are not associated with particular petrographic types however lower nd i values 8 5 occur among the younger leucogranites from the western part of the massif intermediate nd i 6 correlate with aluminous monzogranites and higher values 6 to 3 with calc alkaline granodiorites in the eastern massif central nd i are homogeneous at the regional scale in the western massif central the leucogranites and the monzogranite granodiorites display different trends of nd i with emplacement ages from these results extreme models involving a depleted mantle or an old archean or early proterozoic source may be ruled out the trend of increasing nd i with decreasing age observed in the monzogranite granodiorite group suggests either an increasing contribution of a mantle component or the progressive melting of more mafic more refractory crustal sources or both the reverse trend displayed by the leucogranites might be explained in terms of the upward migration of partial melting across an isotopically zoned metasedimentary pile the large amount of granites may be the result of favourable processes during the collision tectonics combined with the unusual abundance of fertile materials enriched in water and heat producing elements in the pre carboniferous crust

a review of discrete element simulation of ice structure interaction sea ice loads on marine structures are caused by the failure process of ice against the structure the failure process is affected by both the structure and the ice thus is called icestructure int

inversion of the assimilation and fractional crystallization afc equations characterization of contaminants from isotope and trace element relationships in volcanic suites the assimilation and fractional crystallization afc equations of depaolo 1981 are inverted with the aim of characterizing the chemistry of contaminants involved in magma evolution from observed isotope and trace element relationships equations are derived for contours of the ratio of the rate of assimilation to the rate of fractional crystallization in the isotope or trace element region where the contaminant might be located even for volcanic suites in which afc is thought to have been the dominant process the characterization of the contaminant is poorly constrained although afc is likely to be a normal process it leaves a recognizable isotopic signature in volcanics only when magmas assimilate material derived from continental crust in subduction related volcanics this can be the case where the volcanic arc lies on or near continental crust

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

u pb zircon and monazite geochronology of post collisional hercynian granitoids from the central iberian zone northern portugal abstract in the central iberian zone ciz of the iberian massif large volumes of granitoids were emplaced during the post collisional stage of the hercynian orogeny syn to post d3 the last ductile deformation phase twelve granitic units and a quartz monzodiorite were selected for a u pb zircon and monazite geochronological study they represent successive stages of the d3 event the ucanha vilar lamego sameiro and refoios do lima plutons are coeval 313 2 ma 319 4 ma 316 2 ma and 314 2 ma respectively and belong to the earliest stage later on the braga massif was emplaced its different units yielding the same age 309 3 ma for the braga granite 309 1 ma for the gonca granite and 311 5 ma for a related quartz monzodiorite the braga massif is subcontemporaneous with the agrela and celeiros plutons 307 3 5 ma and 306 2 ma respectively in agreement with field data the briteiros granite is younger 300 1 ma followed by the emplacement of the peneda geres massif geres paufito illa and carris granites the geres granite emplaced at 296 2 ma seems to represent a first magmatic pulse immediately followed by the intrusion of the paufito granite at 290 2 5 ma for the carris granite a minimum emplacement age of 280 5 ma was obtained based on these results the following chronology is proposed 1 syn d3 biotite granitoids 313 319 ma 2 late d3 biotite dominant granitoids 306 311 ma 3 late to post d3 granitoids ca 300 ma 4 post d3 granitoids 290 296 ma these chronological data indicate that successive granitic intrusions were emplaced in the ciz during a short time span of about 30 ma that corresponds to the latest stages of the hercynian orogeny a rapid and drastic change occurred at about 300 ma between a compressive ductile tectonic regime d3 ca 300 320 ma associated to calc alkaline monzonitic and aluminopotassic plutonism and a fragile phase of deformation d4 which controlled the emplacement of the subalkaline ferro potassic plutonism at 290 296 ma

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

the nd and sr isotopic composition of i type microgranitoid enclaves and their host rocks from the swifts creek pluton southeast australia abstract initial nd and sr isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the siluro devonian swifts creek pluton within the lachlan fold belt of southeastern australia enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin host rocks range from tonalite to granite the isotopic data form an array in nd 87 sr 86 sr space with enclaves systematically displaced towards higher nd and lower 87 sr 86 sr values enclaves range in nd t 405 ma from 7 3 to 3 1 with a narrow range in 87 sr 86 sr from 0 70613 to 0 70718 whereas host rocks range from 9 0 to 6 4 and 0 70761 to 0 70946 in nd and 87 sr 86 sr respectively the isotopic relations rule out simple crystal liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks the data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility instead mixing between a mafic mantle derived and a crustal derived end member to generate the host rock enclave spectrum is compatible with the data because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks we favour the alternative view that both enclave and host rock magmas are of crustal origin consequently we avoid extrapolations to hypothetical end members we suggest that the enclaves from the swifts creek pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host rock spectrum the isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal liquid fractionation model ages tdm for enclaves and host rocks are almost identical averaging 1 7 and 1 6 ga respectively these model ages indicate that both the enclave and host rock protoliths were derived from a mantle reservoir during the proterozoic

geochemistry of hybrid granitoid rocks and of their biotites from central northern portugal and their petrogenesis abstract in the area of franzilhal s lourenco and pombal central northern portugal occur rocks ranging from hornblende biotite tonalite to muscovite biotite granite the distribution of some major and trace elements in the rocks and in the biotite shows an apparent calc alkalic trend of differentiation the behaviour of k li rb cs and k rb cr 103 fe3 ni 103 mg li 103 mg cs 103 k ratios of the rocks and of f of biotite cannot be explained by mineral fractionation but can be described in terms of hybridization the tonalite granodiorites and biotite muscovite granite are hybrid rocks formed by assimilation of pelitic sediments and dolomitic marbles by the granite magma the fo2 values range from 10 14 8 to 10 16 3 fo2 attains higher values during the crystallization of hybrid rocks than in the uncontaminated muscovite biotite granite giii magma the fh2o and ph2o values generally increase and the fh2o fhf ratio decreases in the hybrid rocks from tonalite to biotite muscovite bearing granodiorite and is smaller than in the uncontaminated granite magma

mantle and crustal sources in the genesis of late hercynian granitoids nw portugal geochemical and sr nd isotopic constraints abstract large volumes of granitoids were emplaced in the hercynian central iberian zone during the last ductile deformation phase d3 300 320 ma the biotite rich granitoids are the most abundant 1 syn d3 granodiorites monzogranites 313 319 ma with calc alkaline and aluminopotassic affinities 2 late d3 granodiorites monzogranites 306 311 ma related to subalkaline and aluminopotassic series these granitoids are associated with coeval gabbro norite to granodiorite bodies and or mafic microgranular enclaves both granitoids and basic intermediate rocks show petrological geochemical and isotopic evidence of interaction between felsic and mafic magmas the mantle derived melts represented by shoshonitic gabbro norites were probably derived from an enriched and isotopically homogeneous source sr i 0 7049 to 0 7053 e nd 2 1 to 2 5 in some syn and late d3 plutons there are evidences of essentially crustal granites represented by moderately peraluminous monzogranites of aluminopotassic affinity they have similar nd model ages 1 4 ga but different isotopic compositions sr i 0 7089 to 0 7106 e nd 5 6 to 6 8 revealing a heterogeneous crust potential protoliths are metasedimentary immature sediments and or felsic meta igneous lower crust materials large amounts of hybrid magmas were generated by the interaction of these coeval mantle and crust derived liquids giving rise to slightly peraluminous monzogranites granodiorites of calc alkaline and subalkaline affinities which display more depleted isotopic compositions than the crustal end members sr i 0 7064 to 0 7085 e nd 4 4 to 6 2 petrogenetic processes involving mingling and or mixing and fractional crystallization at variable degrees in multiple reservoirs are suggested a major crustal growth event occurred in late hercynian times 305 320 ma related to the input of juvenile mantle magmas and leading to the genesis of composite calc alkaline and subalkaline plutons largely represented in the central iberian zone

crustal origin of hercynian peraluminous granitic batholiths of central spain petrological geochemical and isotopic sr nd constraints abstract in central spain it is possible to distinguish two main types of peraluminous late hercynian granites the pi types and the ps types the distinction between both types is made on the basis of differences in peraluminosity ps types are more peraluminous than pi types and also on the appearance of some characteristic mafic minerals ps types have biotite cordierite and monazite as the most typical accessory phase whereas pi types have biotite amphibole in the less evolved facies and allanite as the accessory mineral both granite types have similar trace element ratios and initial sr nd and pb isotopic signatures initial 87sr 86sr ratios of both types exhibit a large range from 0 7073 to 0 7193 whereas initial end varies in a restricted range from 5 4 to 6 6 the scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite monzogranite parental magmas mixing and afc modelling of sr and nd isotopic data reveal an unrealistically high mantle contribution based on major and trace element and isotopic data an orthogneissic protolith for both granitic series is proposed nevertheless none of the metamorphic country rocks of central spain has the appropriate sr isotopic composition to satisfy the origin of these granitic rocks and so it is argued that progressive isotopic re equilibration of crustal material during the granulization of the lower hercynian crust together with the possibility of isotopic disequilibrium during melting as has been demonstrated in migmatitic terranes in nearby areas may explain the isotopic differences between the granites and the high level metamorphic country rocks

contribution of enclave studies to the understanding of origin and evolution of granitic magmas enclaves give important information on the origin and evolution of granitic magmas the presence in a granite of surmicaceous enclaves restites is good evidence of continental crust contribution to magma genesis the presence of dark microgranular enclaves is an indication of mantle contribution the joint presence in the same granite of the two types of enclaves indicates that its magma has probably more than one source dark microgranular enclaves and their host granites as well are hybridized rocks resulting from incomplete mixing or mingling of more acidic and basic components enclave studies allow one to specify mixing conditions when mixing occurs relatively early with respect to granite crystallization only earlier formed granitic minerals zircon apatite may be incorporated in the basic magma when mixing occurs later all granitic minerals may be involved when all the dark microgranular enclaves of a granite are similar the intervention of a single mixing event can be assumed on the contrary when several chemically and mineralogically contrasted varieties occur several mixing events can be assumed the order of these events may be deduced from the nature of the granitic minerals present in the enclaves early of late minerals or sometimes by observation of double enclaves enclave shapes bring information on the distance between the place of mixing and the place of observation enclaves with irregular or crenulated margins or with chilled margins as well always occur near mixing places the enclave transport in the magma makes these characteristics disappear in spite of hybridization processes the primitive composition of the basic component of the mixture may sometimes be recognized a systematic identification of this component in the different granites from the same orogen should allow to understand the space and time evolution of basic magmatism in an orogen magma mixing is a cause of heterogeneity in granites but it is also an important factor of homogenization as the thermal contribution of the basic magma produces new mingling of the components and sometimes new intrusive processes

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

h type hybrid granitoids a proposed revision of the granite type classification and nomenclature abstract recent studies on calc alkaline plutonic rocks reveal field and petrographic relationships with strong implications for the processes involved in their genesis the presence of magmatic inclusions and magma mingling zones in these rocks supports an origin by magma mixing compositional variations and isotopic anomalies are a good test for such petrogenetic models most of these calc alkaline plutonic rocks which characterize both collision related and active plate margin environments have been classically identified as i igneous type granitoids following chappell and white s 1974 classification and then interpreted as derived from partial melting of older igneous rocks restite model if the magma mixing origin of a type of granitoids can be demonstrated from field and petrographic evidence and supported by chemical and isotopic variations the nomenclature must be changed in this sense the new category of h hybrid type is tentatively introduced it includes most of the so called i type granitoids and some of the s type as deduced from field relationships of magma mingling zones a mixing model is suggested that can operate on a large scale to explain the petrogenesis of the hercynian calc alkaline granodiorites of iberia finally a modified classification of common plutonic rocks in orogenic environments is proposed

feasibility of afc models for the petrogenesis of calc alkaline magma series one of the most popular petrogenetic concepts is that of simultaneous assimilation and fractional crystallisation afc the equations governing these processes are well known and widely applied the power and attraction of the model are that with the minimum of constraints petrogenetic schemes can be erected for essentially any group of rocks these models are usually based on the observed variations in a small number of trace elements and or isotopic systems in this paper we have generated well constrained afc models for the variscan calc alkaline querigut complex in the french pyrenees our models are based on geological constraints on the identities of the parent magma and candidate assimilants and the sm nd and rb sr isotope systematics of the rocks the modelling is successful in mimicking the isotope array for the actual rocks however the results are massively inconsistent with those produced using the major and trace element concentrations our major conclusion is that afc modelling should be undertaken only with robust initial constraints on the compositions of the parent magma and the proposed assimilant with due respect for crystal liquid partition coefficients in so far as they are known the results should then be accepted only if the isotope based model parameters are consistent with those derived from major and trace element variations

neodymium and strontium isotope content of microdiorite enclaves points to mantle input to granitoid production microdiorite enclaves are arguably the most poorly understood of the more prominent features of granitoids surprisingly they have been invoked as support for completely different models for the origin of chemical zonation in granitoids depending on whether they are interpreted as restites syn plutonic blobs of magma remobilized cumulate or basified country rock xenoliths here we present the first detailed neodymium and strontium isotope study of suites of such enclaves from two plutons in both cases we find relatively high nd values most readily explained if enclaves represent syn plutonic injections of mafic magma into the host granitoid magma as such they are the tangible remains of a very important process of mantle derived heat and mass transfer operating in the generation of granitic magmas

a case study of the great plains low level jet using wind profiler network data and a high resolution mesoscale model abstract a detailed case study of one complete episode of a typical summertime great plains low level jet llj using data collected by the noaa wind profiler demonstration network is presented the high temporal and spatial resolution of the data from the profiler network permits a much more detailed picture of the great plains llj than is possible from previous studies of this phenomenon a three dimensional mesoscale numerical model is also used to simulate the episode and to provide information on the physical mechanisms responsible for the initiation evolution maintenance and decay of the llj the position and width of the jet core as well as the diurnal variation of wind speed and direction inside the jet core are well predicted by the model the analysis and modeling suggest that the diurnal oscillation of horizontal pressure gradient over sloping terrain is secondary to the inertial oscillation mechanism resulting from the release of frictional constraint in the evening and throughout the nigh

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

the genesis of felsic mafic plutonic associations a sr and nd isotopic study of the hercynian braga granitoid massif northern portugal abstract the late tectonic braga plutonic complex in the centro iberian zone north portugal was emplaced during the hercynian orogeny within a silurian sedimentary sequence and displays an acid basic association which consists of three well defined intrusions the biotite dominant braga granite minor bodies of gabbro to granodiorite composition and the mildly peraluminous gonca leucogranite these three plutonic suites present field relationships indicating a synchronous magmatic emplacement for which a rb sr age of 310 10 ma is obtained the distribution of the three plutonic units along regular curves in major and trace element diagrams suggests that the different units can be genetically related however the rb sr and sm nd isotopic results do not indicate a unique homogeneous source and a simple fractional crystallization process the gabbros have chemical characters high k ba sr and light rare earth elements and low nb ti and zr contents and isotopic compositions sri 0 70497 and nd 2 5 which suggest an alkaline magmatic affinity of shoshonitic type they are probably derived from an enriched mantle source in contrast the peraluminous gonca leucogranite sri 0 70933 and nd 6 8 is more likely the result of crustal anatexis the braga granite and the evolved members of the basic series have an intermediate isotopic composition sri 0 70532 to 0 70733 and nd 3 0 to 6 2 which can be interpreted in terms of an hybridization process between the two previous end members the chemical and sr nd isotopic compositions of the braga plutonic series can be explained by an assimilation fractional crystallization afc model between a mantle derived magma equivalent to the gabbros and a crust derived magma the gonca granite

geochemistry of granitoids and their minerals from rebordelo agrochao area northern portugal abstract deformed hercynian peraluminous granitoids ranging from tonalite to granite crop out in the rebordelo agrochao area northern portugal and some of them contain tonalitic and granodioritic enclaves variation diagrams of major and trace elements of the rocks biotites and sphenes show fractionation trends the most and the least deformed samples of granite and their biotites also define fractionation trends there is decrease in all rare earth element ree contents and increase in the eu anomaly in ree patterns from the most to the least deformed samples of granite all the granitoids define a whole rock rb sr errorchron a whole rock rb sr isochron for the least deformed samples of granite yields an age of 357 9 ma and an initial 87sr 86sr ratio of 0 7087 0 0007 geochemical modelling suggests that the tonalitic magma evolved by afc fractional crystallization of magnesiohornblende plagioclase quartz biotite and ilmenite and assimilation of metasediments to originate tonalitic and granodioritic enclaves granodiorite and granite 18o values support this mechanism the tonalite is hybrid and derived by interaction of a mantle derived magma and crustal materials

meta igneous origin of hercynian peraluminous granites in n w french massif central implications for crustal history reconstructions seventy samples of hercynian peraluminous granites gueret millevaches and saint sylvestre massifs and metamorphic units of the limousin area were analysed for rb sr and sm nd the source rocks of the peraluminous granites can be found in the metamorphic rocks of limousin among them meta igneous rocks were largely predominent over meta sedimentary rocks in the source of the three granites millevaches and gueret granites were generated by the partial melting of rocks comprising meta volcanics and meta sediments whereas the saint sylvestre granite was produced exclusively by the melting of late precambrian granites this leads to confusing t dm nd values the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites which leads to dramatic fractionation in sm nd ratios the data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates late precambrian time seems however to have been a period of extensive crustal generation in western europe

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma