potential of pressure solution for strain localization in the baccu locci shear zone sardinia italy abstract the mylonites of the baccu locci shear zone blsz sardinia italy were deformed during thrusting along a bottom to top strain gradient in lower greenschist facies the microstructure of metavolcanic protoliths shows evidence for composite deformation accommodated by dislocation creep within strong quartz porphyroclasts and pressure solution in the finer grained matrix the evolution of mylonite is simulated in two sets of numerical experiments assuming either a constant width of the deforming zone model 1 or a narrowing shear zone model 2 a 2 5 mm y 1 constant external velocity boundary condition is applied on the basis of geologic constraints inputs to the models are provided by inverting paleostress values obtained from quartz recrystallized grain size paleopiezometry both models predict a significant stress drop across the shear zone however model 1 involves a dramatic decrease in strain rate towards the zone of apparent strain localization in contrast model 2 predicts an increase in strain rate with time from 10 14 to 10 12 s 1 which is consistent with stabilization of the shear zone profile and localization of deformation near the hanging wall extrapolating these results to the general context of crust strength suggests that pressure solution creep may be a critical process for strain softening and for the stabilization of deformation within shear zones

magnetic fabric of granitoids from southern corsica and northern sardinia and implications for late hercynian tectonic setting anisotropy of magnetic susceptibility ams data 180 sites from hercynian granitoids from southern corsica france and northern sardinia italy provide a high density net of structural information for this part of the european hercynian belt two main groups of granitoids defined according to petrography and relative chronology provide contrasting ams results for both groups shallowly dipping magnetic foliations and lineations suggest that these granitoids were emplaced as large scale shallowly dipping sheets or open funnel shaped structures at a high structural level in non leucocratic granitoids 305 300 ma foliation and lineation trajectory maps reveal antiforms and synforms with a n130 axial trace intersection of the foliation planes indicates a n120 low plunging fold axis revealing a n120 maximum stretching direction slightly younger leucocratic granitoids 295 285 ma bounded by late hercynian faults display n50 lineations parallel to the elongated shapes of these intrusions this structural pattern is undisturbed by the faults and suggests an intrusion in decakilometre scale tensional fractures indicating a n140 instantaneous stretching direction compatible with the stretching direction evidenced in non leucocratic granitoids a younger c n20 oriented permian dyke swarm confirms the permanence of this stretching direction over at least 35 ma and indicates a coaxial strain regime to integrate these new data within a broader context in the hercynian belt corsica has to be back rotated clockwise by 70 to its permian position which indicates a north to n30 stretching direction for the 305 285 ma interval compatible with the post collisional strain and stress fields of the french massif central at about the same period

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

tectonometamorphic evolution of an intracontinental orogeny inferred from p t t d paths of the metapelites from the rehamna massif morocco new petrographic and microstructural observations mineral equilibria modelling and u pb monazite geochronological studies were carried out to investigate relationship between deformation and metamorphism across the rehamna massif moroccan variscan belt in this area typical barrovian muscovite to staurolite zones developed in cambrian to carboniferous metasedimentary rocks that are distributed around a dome like structure first assemblages are characterized by the presence of locally preserved andalusite followed by prograde evolution culminating at 6 kbar and 620 c in the structurally deepest staurolite zone rocks this barrovian sequence was subsequently uplifted to supracrustal levels heterogeneously reworked at greenschist facies conditions which was followed locally by static growth of andalusite indicating heating to 2 5 4 kbar and 530 570 c the 206pb 238u monazite age of 298 3 4 1 ma is interpreted as minimum age of peak metamorphic conditions whereas the ages of 275 8 1 7 ma and 277 0 1 1 ma date decompression and heating at low pressure in agreement with previous dating of permian granitoids intruding the rehamna massif the prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust s1 horizontal schistosity the horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing n s compression the re heating of the massif follows late massive e w shortening refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of permian granitoids we argue that metamorphic evolution of the rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental gondwanan plate the tectonometamorphic history of the rehamna massif is put into palaeozoic plate tectonic perspective and late carboniferous reactivation of devonian early carboniferous basins formed during stretching of the north gondwana margin and formation of the palaeotethys ocean the inherited heat budget of these magma rich basins plays a role in the preferential location of this intracontinental orogen it is shown that rapid transition from lithospheric stretching to compression is characterized by specific ht type of barrovian metamorphism which markedly differs from similar barrovian sequences along palaeozoic plate boundaries reported from variscan europe this article is protected by copyright all rights reserved

ring complexes in the peninsular ranges batholith mexico and the usa magma plumbing systems in the middle and upper crust subvolcanic ring complexes are unusual in that they preserve a rapidly frozen record of intrusive events this sequential history is generally lost or complicated in plutons owing to mixing and mingling in a dynamic state thus subvolcanic ring complexes are more like erupted rocks in their preservation of instantaneous events but the self contained nature of the complexes allows detailed structural and chemical work to be conducted in environments where the relative timing between individual magmatic events is commonly well preserved we suggest that development of subvolcanic ring complexes in the western peninsular ranges batholith prb involved the following three stage generalized sequence 1 fracturing of the roof above a buoyant or overpressured magma chamber which resulted in moderately inward dipping conical fractures that locally hosted cone sheets 2 subsequent loss of magma from the chamber combined with degassing of the melt which facilitated collapse of the roof along near vertical ring faults that locally hosted ring dikes and 3 resurgence of the chamber and or intrusion of a broadly cogenetic nested pluton which locally destroyed evidence for the earlier history of the system this sequence has been repeated twice in one of the ring complexes that we have identified which resulted in nested intrusive centers calderas subvolcanic ring complexes and plutons may represent progressively deeper sections through linked magma plumbing systems and the systematic occurrences of these features in the western prb are consistent with progressively deeper along strike exposures of the batholith from south to north over a distance greater than 250 km in addition to subvolcanic complexes in the western prb deeper crustal levels exposed in the transition zone between eastern and western parts of the batholith preserve ring complexes emplaced at depths of up to 18 km occurrence of these deeper level complexes suggests either that caldera subsidence can extend to mid crustal levels or that other processes can produce ring complexes d 2002 elsevier science b v all rights reserved

telescoping of three distinct magmatic suites in an orogenic setting generation of hercynian igneous rocks of the albera massif eastern pyrenees abstract the petrogenesis of the hercynian magmatic rocks of the albera massif eastern pyrenees is investigated in this work in order to establish spatial and temporal relationships between deformation episodes high temperature low pressure metamorphism and igneous activity by using fieldwork together with petrological and geochemical methods hercynian magmatic rocks comprise i calc alkaline granitoids of la jonquera composed mainly by biotite and biotite hornblende granodiorites ii the leucogranitic pluton of el castellar iii small mafic complexes composed mainly by amphibole bearing gabbros and diorites and iv stocks of anatectic leucogranites hercynian deformation structures can be classified in two phases d1 and d2 both reflecting progressive deformation first compressional then transpressional closely linked to the development of regional metamorphism spatial relationships between igneous and metamorphic rocks suggest that the emplacement of magmatic bodies was a syn d2 event and was concomitant with the metamorphic climax of the country rocks the compositional and textural variation of the rocks of the mafic complexes is interpreted to reflect fractional crystallization of hydrous mafic magma with a composition similar to that of calc alkaline basalts documenting the involvement of basaltic magmas during the generation of hercynian crustal granitoids the anatectic leucogranites crystallized from peraluminous magmas produced by partial melting of metasediments and orthogneisses similar to those found in the local migmatite zone the similar sr and nd isotope signatures of the el castellar leucogranitic pluton some anatectic leucogranites and the orthogneissess supports the hypothesis that these leucogranites were generated by partial melting of the orthogneisses based on field petrographic geochemical and isotopic lines of evidence la jonquera granodiorite can be clearly distinguished from the gabbros and from the anatectic and el castellar leucogranites the high cao content of the granodiorites precludes an origin by partial melting of local metamorphic rocks and it is suggested that the calc alkaline granitoids la jonquera were produced by fractional crystallization of a granodioritic magma generated by partial melting of metatonalites in the lower crust although the magmatic rocks were emplaced contemporaneously at about 280 my based on rb sr whole rock data they reflect the occurrence of three genetically distinct igneous suites one granodioritic one leucogranitic and one mafic the metamorphic and igneous evolution documented in the albera massif bears strong similarities with those described in the neighbouring hercynian domains from the pyrenees the hercynian regional ht lp metamorphism and magmatism in the pyrenees are two processes linked to the same deep seated thermal anomaly that was generated in a transpressive context

petrogenesis of early permian olivine bearing cumulates and associated basalt dykes from bocca di tenda northern corsica implications for post collisional variscan evolution abstract the early permian gabbroic sequence of bocca di tenda northern corsica intrudes a plutonic suite made of hornblende granitoids and is crosscut by basalt dykes with chilled margins the gabbroic sequence includes olivine gabbronorite cumulates that consist mainly of euhedral olivine fo78 72 and plagioclase an68 61 and poikilitic clinopyroxene mg 0 85 0 80 orthopyroxene and ti pargasite pyroxenes from the olivine gabbronorites have 18 o values of 6 3 to 6 7 which are evidence for the involvement of a crustal component in the petrogenesis of these rocks the basalts have mg values of 57 to 53 and chondrite normalised patterns characterised by a steady decrease from lree to hree relative to modern n morb they show also moderate enrichment of nb and ta over zr and hf which are in turn slightly enriched over y and hree the olivine gabbronorites and basalts show overlapping nd isotopic compositions initial nd of 2 4 to 1 4 and of 3 0 to 1 5 respectively and have clinopyroxenes with nearly parallel incompatible trace element patterns thus revealing that these two rock types formed by melts with similar compositions most likely the primary melts of bocca di tenda gabbroic sequence were slightly enriched in most incompatible elements and nd isotopic compositions relative to modern n morb

igneous banding schlieren and mafic enclaves in calc alkaline granites the budduso pluton sardinia abstract this study deals with the origin of igneous layering in plutons and especially the extent layering is related to mafic silicic magma interactions the budduso pluton sardinia shows three main scales of organization i large scale lithological variations correspond to three main magmatic units with differentiation increasing from the outer hornblende bearing biotite granodiorite monzogranite to the middle biotite monzogranite and the inner leucomonzogranite units the striking homogeneity of 87 sr 86 sr initial ratios 0 7090 4 and e nd t values 5 6 0 1 strongly suggests that magma isotopic equilibration was achieved prior to emplacement whereas mixing mingling structures observed within the pluton reflect second stage processes involving broadly cogenetic components ii metre to decametre scale igneous layering may be isomodal or modally graded locally with cross layering biotite and plagioclase compositions are similar in both biotite rich and quartzofeldspathic layers as are the trace element patterns which differ only by relative abundances this precludes an origin by fractional crystallization a penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation iii composite layering and schlieren are commonly associated to mafic microgranular enclaves locally within synmagmatic shear zones or disrupted synplutonic dykes in that case there is a progressive shift in biotite x fe values from the core of enclave 0 65 to the host monzogranite 0 72 schlieren in the monzogranite show biotite x fe values similar to that of the host rock whereas schlieren close to mafic enclaves show lower x fe values 0 69 towards those of enclave rims these features can be ascribed to three main processes i assembly of differentiated mixed mingled magmatic pulses ii local hydrodynamic sorting related to density currents in a mush and segregation of residual melt iii mechanical disruption and chemical hybridization of mafic magmas during ascent or within the pluton related to magma dynamics none of these processes affect the whole pluton but they are limited to specific magmatic units therefore pluton growth by incremental assembly of magma batches is not incompatible with magma chamber processes

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

early permian 90 clockwise rotation of the maures esterel corsica sardinia block confirmed by new palaeomagnetic data and followed by a triassic 60 clockwise rotation

late orogenic heating during exhumation alpine ptt trajectories and thermomechanical models abstract during the alpine orogeny the penninic zone of the alps was affected by eoalpine high pressure metamorphism in the central and western alps this was followed by lepontine medium pressure high temperature metamorphism during exhumation we compare the pressure temperature time ptt trajectories established in two key areas in the central and western alps with 2 d numerical models of two possible causes of lepontine metamorphism 1 detachment or breakoff of a subducting slab and 2 the presence of a wedge of accreted radiogenic material numerical models show that both mechanisms are capable of producing significant heating during orogeny heating by slab detachment is fast and transient more than 100 c in up to 10 million years depending on the location whereas radiogenic heating requires time spans of the order of tens of millions of years and cessation of the subduction process the combination of ptt trajectories and synthetic pt paths deduced from our thermomechanical modelling results suggests that the metamorphism observed in the central alps has not been caused by radiogenic heating alone slab breakoff on the other hand seems a viable mechanism to account for the documented rise in metamorphic temperatures during exhumation in view of the time constraints posed by the geological data and acknowledging the effects of large scale block rotations and out of section transport slab detachment is also a more likely mechanism to have provided sufficient heat to cause re heating in the western alps

radiogenic heat production in the variscan crust new determinations and distribution models in corsica northwestern mediterranean abstract new heat production values of variscan volcanic rocks cropping out in the southern part of the corsican batholith were determined in the laboratory by analysing uranium thorium and potassium concentrations with gamma ray spectrometry they vary from a minimum of 0 2 for basalts to a maximum of 4 2 w m 3 for calc alkaline granites the th u ratio in variscan granitoids is slightly higher than normal generally our measurements yield values higher than those previously determined these data together with those available for the variscan massifs of the northwestern mediterranean were used for constructing models of distribution of radiogenic heat production of the crust the lithologic composition was deduced from available p wave velocity data by taking into account the pressure and temperature effects depending on the rate of decrease with depth of the radiogenic heat the crustal contribution in terms of heat flux ranges from 26 to 39 mw m 2 and on average is 33 mw m 2 the mean heat production of the crust is 1 0 w m 3 both average crustal heat source and crustal heat contribution are quite similar to those estimated with the heat production seismic velocity relationship

petrogenetic relationships between peralkaline rhyolite dykes and mafic rocks in the post variscan gabbroic complex from bocca di tenda northern corsica france the lower permian complex from bocca di tenda corsica island france consists of a gabbroic sequence crosscut by chilled dykes ranging in composition from basalt to trachyandesite and peralkaline rhyolite the gabbroic sequence is mostly composed of olivine gabbronorites quartz gabbronorites diorites locally displaying high ilmenite amounts and hornblende rich tonalites the quartz gabbronorites diorites and the hornblende rich tonalites have similar initial end values 0 9 to 1 1 and record a fractional crystallization process driven by separation of plagioclase pyroxene and ilmenite the olivine gabbronorites have slightly higher initial end than the quartz gabbronorites diorites and the hornblende rich tonalites thereby documenting that the early evolution of the melts that gave rise to the gabbroic sequence was controlled by concomitant fractional crystallization and crustal assimilation the trachyandesite dykes are rare and rich in dark mica the selected trachyandesite has initial end of 0 4 which is slightly lower than the end of the basalt dykes the basalt and the trachyandesite dykes are most likely genetically related through a process of fractional crystallization controlled by segregation of plagioclase clinopyroxene and minor ilmenite and assimilation of crustal material the peralkaline rhyolites have initial end values ranging from 0 3 to 0 3 whole rock chemical variations and trace element compositions of na amphibole arfvedsonite indicate that the peralkaline rhyolite dykes record a process of fractional crystallization mainly controlled by separation of alkali feldspar and minor ilmenite and arfvedsonite a plausible petrogenetic hypothesis for the genesis of the peralkaline rhyolite melts implies a protracted process of fractional crystallization from the trachyandesitic melts this fractionation process would be initially ruled by separation of plagioclase dark mica and minor ilmenite an alternative hypothesis for the origin of the peralkaline rhyolite melts implies partial melting of nearly coeval amphibole rich mafic intrusives which formed by crustally contaminated mantle derived melts the genesis of the peralkaline rhyolites is in any case correlated with mantle derived melts that experienced extensive crustal contamination

origin and timing of the post variscan gabbro granite complex of porto western corsica the post variscan complex of porto consists of metaluminous to slightly peraluminous a type biotite granites mingled with gabbro dioritic rocks and late dykes with basaltic to trachyandesitic composition u pb zircon dating by la icp ms on two mafic intrusive samples constrains the time of the gabbro granite crystallisation at 281 3 ma and 283 2 ma hornblende 40ar 39ar ages from a late trachyandesite dyke date the dyking event at 280 2 ma which is within error the u pb zircon ages of the intrusives biotite granites show variable major and trace element compositions and similar initial end 0 3 to 0 9 whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that the granites are genetically linked essentially through fractional crystallisation of feldspars and minor allanite on the basis of whole rock chemistry e g initial end 4 9 to 1 7 and trace element clinopyroxene compositions we have ascertained that the mafic intrusives and basic dykes formed from isotopically depleted mantle source derived melts with similar trace element signature these basic melts experienced slightly different evolutionary histories controlled by fractional crystallisation and crustal contamination mainly by the acid magma that gave rise to the associated biotite granites but also by the enclosing older variscan granitoids u pb zircon data suggest that the porto complex was affected by hydrothermal fluid circulation at 259 9 ma

evolution of the corsica sardinia batholith and late orogenic shearing of the variscides the corsica sardinia batholith formed in the late carboniferous permian along the northern gondwana margin one or more of the following processes may have raised the variscan geotherm enhancing melting of the crust and uppermost mantle such as i break off and detachment of the rheic oceanic slab ii mantle delamination due to gravitational re equilibration of thickened crust iii shear heating iv advection of mantle derived melts and v concentration of heat producing elements in this paper we present a simple one dimensional thermal model to explain the origin of the batholith in a geodynamic setting consistent with intraplate shearing between gondwana and cadomian avalonian blocks input parameters and boundary and initial conditions of the model crust are derived from a careful re examination of large petrological geochronological and structural datasets all parameters are varied within a range of geologically realistic values to reproduce thermal histories related to different tectonic processes and the reliability of models is quantitatively evaluated by comparing the simulated geotherms with a large dataset of pressure temperature time p t t constraints the best fit to p t t constraints is obtained for i break off in the late devonian early carboniferous ii decreasing exhumation rates from 340 to 280 ma and iii transpression at high average strain rates mostly coeval with the peak of high t low p metamorphism

timing of the ht lp transpression in the neoproterozoic serido belt borborema province brazil constraints from upb shrimp geochronology and implications for the connections between ne brazil and west africa abstract the serido schist belt is a classical domain of the borborema province ne brazil recording crustal melting at ht lp conditions in a tectonic setting dominated by dextral transpressive deformation a comparable tectonometamorphic setting has been described in the pan african igarra and ilesha schist belts of south nigeria africa the ht transpression of the serido has previously been imprecisely dated by using a range of isotopic methods on a suite of syntectonic granites we provide new u pb zircon ages of the acari granite and santa luzia migmatite that constrain the ht lp metamorphism of the serido at c 575 ma anisotropy of magnetic susceptibility of the santa luzia migmatite shows that the magnetic fabric records the ne trending dextral kinematics similar to those previously described in the acari pluton on the other hand the u pb ages of the totoro pluton provide evidence for an older mostly mafic to intermediate magmatism intruding the pelitic schist that precedes the ht lp metamorphism by approximately 15 m y in contrast with the acari pluton and santa luzia migmatite the magnetic fabrics of totoro show a concentric steep dipping structure apparently related to magma ascent thermobarometric studies in the serido igarra and ilesha schist belts indicate that a large domain in the northern borborema and south of the nigeria shields was deformed at a high temperature and at relatively shallow depths although the tectonic setting for such a post collision ht event remains an open issue it allows us nevertheless to refine the across atlantic geological correlation between the continents

modelling the thermal perturbation of the continental crust after intraplating of thick granitoid sheets a comparison with the crustal sections in calabria italy thick granitoid sheets represent a considerable percentage of palaeozoic crustal sections exposed in calabria high thermal gradients are recorded in upper and lower crustal regional metamorphic rocks lying at the roof and base of the granitoids ages of peak metamorphism and emplacement of granitoids are mostly overlapping suggesting a connection between magma intrusion and low pressure metamorphism to analyse this relationship thermal perturbation following granitoid emplacement has been modelled the simulation indicates that in the upper crust the thermal perturbation is short lived in contrast in the lower crust temperatures greater than 700 c are maintained for 12 ma explaining granulite formation anatexis and the following nearly isobaric cooling an even longer perturbation can be achieved introducing the effect of mantle lithosphere thinning into the model

genesis of a variscan batholith field petrological and mineralogical evidence from the corsica sardinia batholith abstract the genesis of the corsica sardinia batholith csb can be explained in a continental collision setting during the time of construction of the batholith which is dated at about 70 ma three magmatic associations were emplaced mg k calc alkaline u1 composite mafic silicic calc alkaline u2 and post collisional alkaline u3 in addition the level of intrusion became progressively shallower from 5 6 kbar for u1 to less than ikbar for u3 in a large scale uplift associations u1 and u2 exhibit non cogenetic mafic and felsic components the processes and products of interaction between mantle and crustal derived melts are however different and may be related to the thickness of the crust which controls both the parameters t pco2 ph2o andptot and the time of mingling of the products of anatexis and basaltic melts both u1 and u2 granitoids were formed by crystallization of a magma derived by fusion of a source of greywacke composition the melting occurred successively under granulitic u1 and amphibolite facies conditions u2 in association u1 basaltic melts displaying potassic lamprophyre like composition up to 8 k2o are of uncertain affinity furthermore crustal interaction with the basic magma precludes precise definition of the source in the u2 composite association the primary tholeiitic character of the mantle derived basic rocks is constrained by both mineralogical and geochemical data dry and hydrated subunits are distinguished among the basic rocks associated with the granitoids no hybridization processes have been identified in the core of the mafic complexes of the dry subunits but they are recognized at the level of emplacement at the margins at the contact with the granitoids contamination in the mafic hydrated subunit is due to the increase in water content of crustal origin in the magma during the ascent and emplacement of the basic complexes leading to the development of abundant green amphibole extensive hybridization is restricted to the base of the crust where it led to incomplete mixing yielding granodiorites and enclaves the genesis and emplacement of the composite calc alkaline u2 association took place in an extensional setting in an uplifting basement postdating a collisional event during the devonian an eastern austro alpine block was thrust onto the western ebro balearic continent the u1 mg k granitoids resulted from anatexis under conditions of pco2 ph2o this took place at the base of the austro alpine crust which was undergoing fusion due to its adiabatic ascent the u2 calc alkaline granitoid rocks were derived in a hydrated environment by fusion of the same austro alpine crust in corsica and of the ebro balearic crust on sardinia and in the pyrenees the conditions of interaction between mafic and felsic magmas may serve as a geodynamic marker providing information on the thickness of the crust in time and space and on the genesis of continental crust the persistence during the palaeozoic of dominantly tholeiitic mafic magmatism suggests that hot spot activity occurred in this area of southwestern europe during pre variscan and variscan times up to the time of opening of the liguro piedmontese ocean birthplace of the alpine orogen

heat flow heat production and fission track data from the hercynian basement around the provencal basin western mediterranean abstract in the complex structural framework of the western mediterranean hercynian areas are expected to be thermally preserved from the recent tectonic evolution the thermal regime of these areas is studied using heat flow heat production and fission track data the surface heat flow is significantly higher in corsica 76 10 mw m 2 than in the maures and esterel 58 2 mw m 2 neither heat production nor erosion subsequent to the alpine orogeny in corsica can explain such a difference it is suggested that a deep thermal source related to the asymmetric evolution of the provencal basin could explain the higher heat flow in corsica a model of thermal structure based on the present day thermal regime of the maures and esterei is proposed for the stable hercynian crust in this area the mantle heat flow is 20 25 mw m 2 and the temperature at moho level is 375 500 c depending on the thermal parameter distribution with depth

crustal thickness of the peninsular ranges and gulf extensional province in the californias we estimate crustal thickness along an east west transect of the baja california peninsula and gulf of california mexico and investigate its relationship to surface elevation and crustal extension we derive moho depth estimates from p to s converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at 318n latitude depth to the moho is 33 63 km near the pacific coast of baja california and increases gradually toward the east reaching a maximum depth of 40 64 km beneath the western part of the peninsular ranges batholith the crust then thins rapidly under the topographically high eastern peninsular ranges and across the main gulf escarpment crustal thickness is 15 18 62 km within and on the margins of the gulf of california the moho shallowing beneath the eastern peninsular ranges represents an average apparent westward dip of 258 this range of moho depths within the peninsula ranges as well as the sharp east west gradient in depth in the eastern part of the range is in agreement with earlier observations from north of the international border the moho depth variations do not correlate with topography of the eastern batholith these findings suggest that a steeply dipping moho is a regional feature beneath the eastern peninsular ranges and that a local airy crustal root does not support the highest elevations we suggest that moho shallowing under the eastern peninsular ranges reflects extensional deformation of the lower crust in response to adjacent rifting of the gulf extensional province that commenced in the late cenozoic support of the eastern peninsular ranges topography may be achieved through a combination of flexural support and lateral density variations in the crust and or upper mantle

the short term fate of fresh algal carbon in continental slope sediments emplacement of a tracer mixture containing 13c labeled green algae on the sea floor of the continental slope offshore of cape hatteras north carolina elicited a rapid response over 1 5 d from the dense benthic community certain deposit feeding annelids e g scalibregma injlatum and aricidea quadrilobata became heavily labeled with 13c as a result of ingestion of the algae 13c labeled organic matter was transported to a depth of at least 4 5 cm into the seabed during the 1 5 d period presumably as a consequence of a feedingassociated activity nonlocal transport produced subsurface peaks in organic 13c at 2 3 cm dissolved inorganic 13c produced by the oxidation of the labeled algae penetrated to lo cm depth the transport of highly reactive organic matter from the sediment surface at initial velocities 1 3 cm d l is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations anaerobic processes which are enhanced on the cape hatteras slope relative to adjacent areas may be promoted by the rapid injection of reactive material into subsurface sediments the transport in turn is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region

pre mesozoic alpine basements their place in the european paleozoic framework prior to their alpine overprinting most of the pre mesozoic basement areas in alpine orogenic structures shared a complex evolution starting with neoproterozoic sediments that are thought to have received detrital input from both west and east gondwanan cratonic sources a subsequent neoproterozoic cambrian active margin setting at the gondwana margin was followed by a cambrian ordovician rifting period including an ordovician cordillera like active margin setting during the late ordovician and silurian periods the future alpine domains recorded crustal extension along the gondwana margin announcing the future opening of the paleotethys oceanic domain most areas then underwent variscan orogenic events including continental subduction and collisions with avalonian type basement areas along laurussia and the juxtaposition and the duplication of terrane assemblages during strike slip accompanied by contemporaneous crustal shortening and the subduction of paleotethys under laurussia thereafter the final pangea assemblage underwent triassic and jurassic extension followed by tertiary shortening and leading to the buildup of the alpine mountain chain recent plate tectonic reconstructions place the alpine domains in their supposed initial cambrian ordovician positions in the eastern part of the gondwana margin where a stronger interference with the chinese blocks is proposed at least from the ordovician onward for the visean time of the variscan continental collision the distinction of the former tectonic lower plate situation is traceable but becomes blurred through the subsequent oblique subduction of paleotethys under laurussia accompanied by large scale strike slip since the pennsylvanian this global collisional scenario has been replaced by subsequent and ongoing shortening and strike slip under rising geothermal conditions and all of this occurred before all these puzzle elements underwent the complex alpine reorganization

dating shallow thrusts with zircon u th he thermochronometry the shear heating connection new zircon u th he zhe ages from a shallow 6 7 km thrust fault zone and surrounding wall rocks in the helminthoid flysch of the ligurian alps were measured to test the applicability of the thermochronometer for dating brittle or brittle ductile faults the ages are integrated with x ray diffraction analysis of clay minerals and fluid inclusion microthermometry on vein filling minerals to constrain the temperature conditions of the damage zone and the wall rocks during thrusting the wall rocks yield pre depositional inherited zhe ages 125 3 15 to 312 3 37 ma while ages from the fault core are reset 28 8 3 4 to 33 8 4 0 ma this is consistent with independent geological and thermochronometric evidence for early oligocene motion of the thrust this implies that the fault zone exceeded 200 c during faulting and confirms the illite crystallinity and fluid inclusion constraints which indicate temperatures of 220 300 c in the fault zone while in those the wall rocks were 180 200 c thermal modeling of the fault zone suggests that the shear heating associated with the fault motion is an efficient mechanism for generating temperature increases of 50 70 c during a displacement of 10 25 km in 2 10 m y our results underscore the validity of the zhe technique for dating brittle or brittle ductile faults characterized by relatively high strain rate

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

interaction between basic and acid magmas during the latest stages of the post collisional variscan evolution clues from the gabbro granite association of ota corsica sardinia batholith abstract the intrusive association of ota post variscan corsica sardinia batholith consists of mafic rocks and granites displaying mingling relations the mafic rocks are olivine gabbros to quartz diorites and the granites are subsolvus and characterised by biotite as the only mafic phase minor amounts of amphibole bearing granodiorites to granites develop along the contacts between mafic rocks and granites the rather high initial e nd 4 5 of the most primitive mafic sample indicates that parental basic melts had an extensive contribution from a depleted mantle source in the mafic rocks the decrease of initial e nd to 2 1 is associated with an increase of th and u concentrations in clinopyroxene thus indicating that the ota basic melts underwent a process of crustal contamination associated biotite granites have low initial e nd 0 4 and high th and u concentrations the chemical evolution of ota basic melts most likely occurred through fractional crystallisation and concomitant contamination with the acid magma that gave rise to associated biotite granites the incompatible element signature of late stage anhedral amphibole from variably evolved mafic rocks is similar thus suggesting that the whole ota mafic sequence recorded the contamination process possibly by percolation within the gabbroic crystal mush of a melt contaminated by the acid magma hybridisation between basic and acid magmas is also documented by contact amphibole bearing granitoids in particular major and trace element zoning of amphibole from granodiorites reveals that such a hybridisation was associated with reactions between crystals from the basic magma amphibole and clinopyroxene and the acid melt the occurrence of chemically homogeneous amphiboles in associated granites suggests that contact hybridisation comprised also a process of gradient induced chemical diffusion

geochronological constraints on post collisional shear zones in the variscides of sardinia italy terra nova 24 42 51 2012 abstract the post collisional tectonics in the inner zone of the variscan belt of corsica sardinia recorded a dextral transpression developed with an orogen parallel tectonic transport recent works documented the presence of nearly parallel dextral and sinistral crustal scale shear zones responsible for the exhumation of the metamorphic complexes to constrain for the first time the timing of both shear zones and the timing of the transpressional shearing zircons and monazites were collected for u th pb ages results indicate that the shear zones have been active at c 320 ma in a transpressional setting widespread in the southern european variscan belt

structural diversity and fate of intact polar lipids in marine sediments abstract marine sediments harbor an enormous quantity of microorganisms including a multitude of novel species the habitable zone of the marine sediment column begins at the sediment water interface and probably extends to depths of several thousands of meters studies of the microbial diversity in this ecosystem have mostly relied on molecular biological techniques we used a complementary method analysis of intact polar membrane lipids to characterize the in situ microbial community in sediments covering a wide range of environmental conditions from peru margin equatorial pacific hydrate ridge and juan de fuca ridge bacterial and eukaryotic phospholipids were only detected in surface sediments from the peru margin in contrast deeply buried sediments independent of their geographic location were dominated by archaeal diether and tetraether lipids with various polar head groups and core lipids we compared ring distributions of archaeal tetraether lipids derived from polar glycosidic precursors with those that are present as core lipids the distributions of these related compound pools were distinct suggestive of different archaeal sources i e the polar compounds derive from sedimentary communities and the core lipids are fossil remnants from planktonic communities with possible admixtures of decayed sedimentary archaea this in situ production of distinct archaeal lipid populations potentially affects applications of the tex86 paleotemperature proxy as demonstrated by offsets in reconstructed temperatures between both pools we evaluated how varying cell and lipid stabilities will influence the sedimentary pool by using a box model the results are consistent with i a requirement of continuous inputs of freshly synthesized lipids in subsurface sediments for explaining the observed distribution of intact polar lipids and ii decreasing lipid inputs with increasing burial depth

lithospheric shear zones as constant stress experiments below the seismogenic zone plate boundaries are defi ned by lithospheric ductile shear zones these localize strain and are the main reason that convective motions in the earth s interior are expressed at the surface as plate tectonics we argue here that lithospheric shear zones operate at approximately constant stress equal to the yield strength of the surrounding rocks this places constraints on the bulk strength of the lithosphere and allows us to calculate the cumulative width of the shear zones as a function of depth the concept applies most clearly to strike slip shear zones but is also applicable to thrust and normal sense shear zones although these evolve with time due to temperature changes associated with burial or exhumation if shear zones operate at constant stress this affects their microstructural evolution and hence their rheology decreases in grain size due to dynamic recrystallization may cause a switch in the dominant deformation mechanism to grain size sensitive creep leading to weakening and strain localization a common argument based on a constant strain rate approach has been that such transitions will be inhibited by grain growth in a constant stress shear zone however dynamic recrystallization continues to maintain the low grain size even after the switch has occurred grain growth is inhibited under these conditions and hence the switch is permanent as long as the boundary conditions remain the same grain size reduction in shear zones is therefore a critical factor in maintaining plate tectonic processes

shear heating during distributed fracturing and pulverization of rocks we provide estimates of temperature changes produced in fault damage zones during brittle deformation associated with distributed cracking and pulverization in contrast to localized faulting accompanied by significant frictional weakening the relatively high friction coefficient on the multitudinous small cracks generated in the fracturing process can lead to significant shear heating simple calculations with parameter values constrained by laboratory experiments and simulations indicate that the temperature can increase during the generation of rock damage and pulverization by 100 c or more the results can help explain signatures of elevated temperature observed in geometrically complex fault zone sections with significant rock damage and regions with broad distributed deformation

mass spectrometric characterization of 13c labeled lipid tracers and their degradation products in microcosm sediments abstract a gc ms approach was developed to characterize 13 c labeled tracers in microcosm sediments three major 13 c labeled fatty acids 16 1 7 16 0 and 18 1 9 and phytol in labeled microalgae added to sediments as organic substrate were distinguished from natural sedimentary counterparts during a series of incubations under various redox conditions oxic and anoxic and with and without the presence of macrofauna i e yoldia limiatula two newly produced 13 c labeled compounds iso 15 0 fatty acid and c 16 alcohol were identified from incubated sediments analyses of mass spectra showed that the iso 15 0 fatty acid was partially labeled while the c 16 alcohol was uniformly labeled with 13 c implying that the formation pathways of these two degradation products may be different estimates of degradation rate constants of planktonic lipids during these incubations showed that oxic conditions and the presence of yoldia significantly accelerated the degradation of planktonic lipids in sediments

mechanical anisotropies and mechanisms of mafic magma ascent in the middle continental crust the sondalo magmatic system n italy

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

emplacement of the arzachena pluton corsica sardinia batholith and the geodynamics of incoming pangaea abstract the assembly of the corsica sardinia batholith c sb coincides with final shaping of the variscan belt and represents a key structure to unravel the feedbacks between partial melting rheology and the evolution of collisional orogens this paper presents a model for the genesis of the arzachena pluton azn one of the major calc alkaline massifs of the c sb based on u pb zircon dating thermobarometry and structural analysis major and trace element compositions indicate that azn has hybrid characteristics between that of typical s and i type granites that could be explained in terms of incremental melting of a heterogeneous crustal source made of metatexites and ordovician calc alkaline granitoids growth of the pluton started around 320 315 ma with the emplacement at middle crustal level 0 37 0 4 gpa of granodioritic melts within narrow conjugate nw se sinistral and e w dextral shear zones the main growth stage 311 6 4 ma is marked by emplacement of large volumes of monzogranitic melts that induced a local decrease of the crustal strength expressed by horizontal channel flow driven by the gravity finally 307 6 3 5 ma leucogranites emplaced within radial and peripheral dilatant fractures developed during the cooling of the main body the transition from magmatic to sub magmatic and ht solid state fabric observed throughout azn indicates that deformation plays a non trivial role during the growth of the magmatic system restoring the position of the corsica sardinia block to early permian coordinates allow to recast the birth of the c sb in a consistent geodynamic framework that conciliates the development of conjugates strike slip structures the oroclinal bending of the chain and the thermal relaxation this study indicates that the c sb had an active role during post orogenic extension rather than being just a consequence of it

petrogenetic controls on the origin of tourmalinite veins from mandrolisai igneous massif central sardinia italy insights from tourmaline crystal chemistry abstract an inclusive study of tourmaline a well known petrogenetic indicator allowed the reconstruction of late stage evolution of b bearing variscan granodioritic magmas in sardinia batholith italy tourmaline samples from mandrolisai igneous massif were chemically and structurally investigated by electron microprobe analysis single crystal x ray diffraction mossbauer infrared and optical absorption spectroscopy tourmaline aggregates occur both as large crystals displaying graphic textures with quartz in aplite layers and pegmatite dykes within tonalitic granodiorite and as fine grained assemblages in tourmalinite veins crystallized along fractures within metamorphic country rocks tourmaline was identified as schorl in pegmatites and as dravite in veins both with relevant foitite and magnesio foitite components petrological and mineralogical constraints based on mineral oxythermobarometry and tourmaline crystal chemistry converged towards crystallization temperatures in the range 650 400 c at about 2 2 kbar under nno conditions that remained almost unvaried during the whole magma crystallization path in the reconstructed scenario mandrolisai tourmaline recorded the late stages of consolidation of a single granodioritic magma batch whose crystallization path locally led to residual concentration of b in the melt due to melt hydrous fluid immiscibility processes b enrichment promoted the crystallization of the large tourmaline quartz assemblages in pegmatites late b bearing fluids triggered metasomatic reactions and favored the precipitation of fine grained tourmaline in tourmalinite veins under a brittle solid state regime which overprinted a fracture network of the country rocks previously formed under magmatic flow conditions mandrolisai granodiorites are metaluminous asi 0 93 0 95 that is far from the compositional characters of typical b bearing magmas mostly felsic and markedly peraluminous asi 1 2 the uncommon occurrence of tourmaline bearing rocks in mandrolisai may be an evidence of the limited control exerted by al2o3 saturation on the origin of tourmaline conversely a more important role of b contents likely coming from crustal sources may be invoked for tourmaline saturation in the magma

decomposition of 14c labeled organic substances in marine sediments the depth variation of total organic carbon toc organic matter composition and porewater composition in marine sediments suggests that different components of the organic matter undergo decomposition at widely different rates the decomposition of 14c labeled organic substances was followed in sediment microcosms in the laboratory the substances used were chosen to simulate a portion of material settling to the sediment water interface a marine diatom or hypothesized components of refractory sediment organic matter melanoidins and a bacterial polymer the microcosms were found to be good models of the sediment water interface in terms of how well they mimicked sediment decomposition rates and processes the decomposition of the labeled material and the natural sediment toc were monitored over 1 month the water overlying the sediment remained oxic and net consumption of nitrate was small there was no detectable sulfate reduction the algae and the bacterial polymer were decomposed on average 9 x faster than the melanoidins and 90 x faster than the natural sediment toc the soluble fraction of the algae was decomposed more rapidly than the particulate material

change of nappe transport direction during the variscan collisional evolution of central southern sardinia italy abstract the collisional variscan early carboniferous evolution of the greenschist facies metamorphic basement of sardinia is characterized by three deformation phases and two 90 reorientations of shortening direction during the first phase of deformation n s shortening occurred with south facing isoclinal folding south directed nappe emplacement and mylonitization in central and southeastern sardinia and large scale e w striking upright folds in southwestern sardinia emplacement of the barbagia meana sardo gerrei and riu gruppa units took place during this event this deformation phase was followed by e w shortening with w directed emplacement of the sarrabus and arburese units along the villasalto thrust and upright to e dipping large scale n s striking upright folds in southwestern sardinia during the third deformation event the shortening direction again rotated 90 and n s shortening produced kilometer scale antiforms and synforms the most prominent features in the metamorphic basement of sardinia the limbs of the kilometer scale antiforms and synforms are vertically shortened during gravitational collapse with contemporaneous faulting and conjugate shear zone development presence of large scale e w oriented antiforms was therefore critical for the formation of late variscan extensional features such as e w striking low angle normal faulting

leucogranites in the black hills of south dakota the consequence of shear heating during continental collision leucogranites are common features of convergent orogens however the heat necessary for producing leucogranite magma from pelitic sources in convergent orogens is a major unresolved issue we suggest that the generation of the harney peak granite black hills south dakota during the proterozoic trans hudson orogeny is best explained by shear heating during thrusting of a proterozoic sedimentary sequence over the archean wyoming basement our thermotectonic model successfully reproduces pressure temperature time constraints on early regional metamorphism of schists and subsequent generation of the late orogenic harney peak granite the model is consistent with isotopic data for the granite which require both proterozoic and archean source rocks and its emplacement as small batches of melt the similarity of geologic relationships in the black hills to those of other collisional orogens suggests that shear heating may be a viable mechanism for leucogranite generation in thickened crusts

late palaeozoic palaeomagnetic and tectonic constraints for amalgamation of pangea supercontinent in the european variscan belt abstract this paper provides a review of the evolution of palaeomagnetic directions and sequence of tectonic events in the european variscan belt during late palaeozoic times these data are correlated with palaeomagnetic records from gondwana and baltica in order to provide a large scale geodynamic framework during the carboniferous to permian the early carboniferous palaeomagnetic records reported mainly from the rhenohercynian and saxothuringian magmatic arcs indicate a 70 anticlockwise rotation while late carboniferous to permian magnetic directions from various rocks of western and central europe are consistent with 120 clockwise rotation of the eastern and central parts of the variscan belt our review of the chronology of tectonic events is based on a robust database of geochronologically constrained deformation metamorphic and magmatic events which allow discretizing the 80 ma long orogenic evolution into five principal events in this scenario the variscan belt can be regarded as a linear sub plate isolated from gondwana and laurussia by the rhenohercynian and palaeotethysian oceans during devonian times this linear composite belt was segmented by transform faults and boundaries in the late devonian to early carboniferous times 360 335 ma during progressive e w closure of rhenohercynian ocean synchronously with collision between saxothuringian and moldanubian blocks subsequent relocation of subduction to the northern boundary palaeotethysian ocean was responsible for n s shortening almost orthogonal to the ancient sub plate n s elongation at around 335 325 ma this deformation resulted in dextral reactivation of transform boundaries associated with anticlockwise rotation of intermittent blocks at the end of this rotation the faults were parallelized to the teysseire tornquist zone the southern margin of baltica while the lozenge shaped blocks of the former variscan sub plate were further shortened during continuous contraction this evolution can fully explain the 70 anticlockwise rotation from cn3 to cn2 palaeomagnetic directions which are regarded as successive carboniferous magnetizations subsequently the variscan belt suffered a giant transtensional event from 325 to 310 ma that was related to the development of extensional syn magmatic core complexes over the whole belt and significant dextral reactivation of earlier nw se trending transform faults this extensional event was associated with important tilts recorded by cp magnetic overprint resulting from a major thermally induced remagnetization during this event new sets of sinistral transfer nne ssw trending faults originated that partly reactivated boundaries of the principal tectonic zones blocks delimited by second order sinistral and first order dextral faults then rotated in a clockwise manner by 80 the whole system subsequently suffered a period of nne ssw shortening that affected the variscan belt namely along the former laurussian and former variscan sub plate contact in the north and in the south where the giant cantabrian orocline developed at around 310 300 ma due to hard collision with gondwana this deformation is associated with the clockwise rotation of laurussia together with the accreted northern sector of the variscan belt and the anticlockwise of gondwana this clockwise 30 rotation is achieved by a1 remagnetizations while the southern part of iberia suffered anticlockwise rotation the final stage of rapid clockwise rotation affecting the northern limb of the iberian arc including corsica and sardinia is attributed to giant n s extension affecting the whole variscan belt at the onset of permo triassic opening of the tethys ocean this complex evolution is regarded as a result of the readjustment of inhomogeneous and thermally and mechanically instable mobile space in between reorganizing the gondwana and laurussia megaplates and the opening of the palaeotethys ocean during the final stages of formation of the pangea supercontinent finally the palaeomagnetically constrained rotations and tectonic evolution of the variscan belt are explained using a pinned model of internal and external rotations of blocks driven by activation of dextral shear zones by n s compression and e w transtension in particular

structure emplacement and lateral expansion of the san jose tonalite pluton peninsular ranges batholith baja california mexico abstract the 108 km2 san jose pluton forms part of the jurassic to cretaceous peninsular ranges batholith of northern baja california mexico the pluton was formed by three nested southward migrating intrusive pulses and the internal contacts between them indicate juxtaposition while the adjoining pulses were magmas shrimp u pb zircon data indicate that the entire pluton was emplaced in less than 4 4 m y ages of the individual pulses cannot be separated at the 95 confidence interval owing primarily to low uranium content of zircon detailed structural data and geologic mapping are consistent with a component of asymmetrical lateral expansion at the site of emplacement the direction of maximum lateral expansion may have been controlled by thermal compositional and resulting rheological gradients in the surrounding wall rocks a carapace of predominantly solid state deformation marks the northern two thirds of the pluton and the early stages of this fabric may have formed in the presence of a small amount of melt lack of evidence for syn to post emplacement regional ductile deformation around the pluton suggests that this carapace was deformed during the lateral expansion of the pluton

the atlas east variscan elbe shear system and its role in the formation of the pull apart late palaeozoic basins the variscan orogeny occurred as a result of the late devonian to late carboniferous collision and accretion of gondwana derived microcontinents and continental masses with those of laurussia the irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics accompanied by a complex pattern of intracontinental shear zones at the scale of the southern european variscides these shear zones and their configuration controlled the subsequent evolution of permian to middle triassic paleogeography the geographic distribution from morocco to the eastern alps of the late carboniferous permian up to triassic basins most of which are considered as pull apart basins was related with the development of the late palaeozoic intracontinental shear network our analysis of the stratigraphic tectonic and volcanic features of the late carboniferous permian continental basins across the laurussia gondwana boundary reveals the role of the east variscan shear zone during this time as a precursory lineament for the development of the permian to triassic rifting of pangaea and the following opening of oceanic basins e g the neothetyan ocean

importance of late magmatic and hydrothermal fluids on the sm nd isotope mineral systematics of hypersolvus granites abstract despite the significant impact of the sm nd radiometric system in various fields of isotope geochemistry very few attempts have been made to use it at the mineral scale in granite studies this approach has been used on two granites from the anorogenic province of corsica se france two statistically acceptable alignments were obtained in an isochron diagram for the hypersolvus fayalite bearing granite of mantelluccio alkali feldspar amphibole inclusion free zircon fluorite and fergusonite give an age of 331 10 ma whereas allanite whole rock amphibole and inclusion free zircon yield a significantly younger age at 291 13 ma the latter is validated by a zircon u pb age of 283 1 ma as the magmatic emplacement date of the granite the other alignment giving a 50 ma older age can be interpreted either as being inherited or more likely as the result of hydrothermal convection interacting with the country rocks at the end of granite crystallization the sm nd systematics of epidote records a second fluid rock event which probably occurred at least 200 ma after the emplacement of the granite extremely low 143 nd 144 nd ratio indicates that the epidote crystallized from a fluid that carried lanthanides in the crust over a distance of at least 1 km zircons with inclusions have a lower initial 143 nd 144 nd ratio than inclusion free zircons this feature is attributed to apatite and or zircon core inheritance through contamination during the ascent of the granitic melt in the crust two isochrons have been also obtained for the hypersolvus peralkaline granite of evisa amphibole fluorite sphene and fergusonite yield an age of 259 6 ma whereas the whole rock alkali feldspar and metamict zircon give an age at 209 14 ma in this case the former value is roughly in agreement with a possibly slightly rejuvenated whole rock rb sr date of 249 3 ma suggesting that it documents the magmatic crystallization age of the granite sm nd isotope systematics of the alkali feldspar metamict zircon and possibly allanite were re equilibrated during an important hydrothermal event that affected western europe in early jurassic times in both examples however it appears that the whole rock nd isotopic signatures were not strongly affected by the various fluid rock events indicating that they can still be used for petrogenetic investigations in contrast these results show that like k ar and rb sr the sm nd systematics of minerals with weak resistance to post magmatic processes can be used to trace and date hydrothermal events

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

finite element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting the development of shear zones initiating on random weaker initial perturbations is modelled numerically for low deborah number viscoelastic materials considering the influence of effective viscosity contrast power law rheology strain softening and different imposed bulk deformation geometries ranging from pure to simple shear conjugate shear zones initiate at 90 to one another and rotate with increasing bulk deformation the basic pattern not being markedly influenced by the vorticity of imposed deformation the rate of propagation of individual conjugate shear zones is little affected by increased effective viscosity contrast between matrix and inclusion but is promoted by power law rheology however the most marked effect is observed for strain softening behaviour where rapid propagation produces straighter and narrower shear zones the localisation of strain is reflected in a correspondingly heterogeneous stress distribution in particular mean stress or pressure is higher in the extending near planar weaker zones of localised shear melting of gneissic or pelitic compositions is pressure dependent with free water present increased pressure promotes melting whereas the opposite is true for water absent melting for water present conditions a positive feedback could develop between localised shearing increased pressure and partial melting this is potentially more effective in concentrating melt in shear zones than shear heating where melt related softening has a negative feedback effect

crust and mantle contributions to granite genesis an example from the variscan batholith of corsica france studied by trace element and ndsro isotope systematics the corsican batholith formed during the variscan orogeny was studied with particular emphasis on the respective roles played by crustal and mantle derived material in granite genesis major and trace element data identify the various types of magma and their genetic relationships the magmatic processes that gave rise to the observed rocks and the primitive liquids o sr nd isotope systematics constrain the origin of primitive liquids trace element models provide data on the various source materials and their possible geodynamic setting the evolution of two main calc alkaline plutonic associations is compared an older high mg k association u1 with both ultrapotassic mafic and silicic rocks the latter ranging from monzonite to leucosyenogranite and a younger calc alkaline composite association u2 involving a mafic cumulate sequence and granodiorite to leucomonzo granite both types of granite are accompanied by mafic units that were non cogenetic with surrounding granitic melts trace element calculations indicate that a primitive liquid of monzodioritic composition gave rise to the u1 mg k granite by fractional crystallization amphibole and titanite playing a major role which with increasing crystallization gave decreasing ree contents without a strong negative eu anomaly the u2 calc alkaline suite was formed by fractional crystallization involving feldspar and lree rich minerals i e monazite from a liquid of monzogranitic composition field and petrographical data identify magma mingling in both u1 and u2 between mafic and silicic rocks but geochemical data only indicate how magma mixing processes led to u2 granodiorite geochemical modelling shows that a single protolith of calculated graywacke composition yielded the two associations under different melting conditions the high mg k monzodiorite melt was formed after partial melting of a 30 non modal batch of granulite facies metamorphic protolith low ph2o but the calc alkaline monzogranite was formed by the same process in an amphibolite facies source of similar composition higher ph2o the primitive granite magmas of both associations show the same crustal characteristics i e sri 0 706 0 707 nd t 4 3 to 2 2 and 18o 7 to 8 this provides evidence that composition of both u1 and u2 granite melts probably was controlled by physico chemical fusion rather than protolith composition parameters the u1 ultrapotassic mafic rock is thought to be of mantle origin i e a deep source containing phlogopite garnet zone refining led to a significant increase of incompatible trace element contents during ascent of the magma mantle crust interaction lowered the la yb and 143nd144nd ratios but the 87sr86sr ratio increased nevertheless interaction with associated u1 mg k granite was not important and the crustal component is thought to be different from the associated granitic magma in u2 the mafic cumulate sequence clearly of mantle origin has e morb characteristics and seems the result of 10 non modal partial melting of a heterogeneous mantle of spinel or amphibole peridotite without garnet some interaction occurred with the associated granitic melt the e morb character of the mafic rock indicates that a large part of the batholith and at least the u2 magmatic association was generated under post collisional extensional conditions

late orogenic collapse and thermal doming in the northern gondwana margin incorporated in the variscan chain a case study from the ozieri metamorphic complex northern sardinia italy abstract a branch of the south european variscan chain is noticeably exposed in sardinia the early stage of collision between the northern gondwana margin and the armorica terrane assemblage ata generated syn metamorphic folding and thrusting the evidences of such deformation are well preserved in the nappe zone a structural domain characterized by stacking of different tectonic units under metamorphism of barrovian greenschist facies a late post nappe shortening under retrograde metamorphic conditions gave rise to wide upright n120 n160 trending antiforms that control the trend of the chain the structural analysis of the ozieri metamorphic complex omc shows evidence of an important phase of late variscan extensional tectonics deformation results in the formation of oppositely dipping normal shear zones which developed at upper and middle structural level along the limbs of major regional antiforms causing fabric reactivation crustal thinning and exhumation of the omc core within the omc the activity of the shear zones was coeval with ht lp metamorphism as suggests the occurrence of syn kinematic cordierite andalusite sillimanite biotite whereas syntectonic dykes and a tonalite body in the deeper part of the omc indicate that early emplacement of melt along shear zones and or in the antiform hinges possibly supplied the heat for the anomalous thermal gradient and triggered the exhumation of a core complex like structure

the late palaeozoic early mesozoic from the catalan pyrenees spain 60 myr of environmental evolution in the frame of the western peri tethyan palaeogeography the eastern catalan pyrenees form the southernmost segment of the pyrenean axial zone they experienced complex multistage process as the result of both the variscan and the pyrenean orogenic cycles after the late palaeozoic several small extensional sub basins were filled by continental successions as a response to the changing tectonic setting within the frame of the southwestern europe this stratigraphic record perfectly exposed in the studied eastern pyrenean areas preserves the signatures of the late palaeozoic pangea break up during the progressive dismantling of the variscan chain up to the triassic diffused extension despite structural network being severely affected by cenozoic reworking the stratigraphic framework can be unravelled by the detailed sedimentological and stratigraphical analysis of the well exposed sequences in short this paper addresses facies patterns and architectural elements of late carboniferous permian triassic continental sections studied in the catalan pyrenees and aims to use these signatures for correlation not only at a regional scale but also within the broader picture of the southwestern europe our stratigraphical reconstruction clearly demonstrates that the thick studied succession consists of fluvial lacustrine basal units affected by intense volcanic activity and overlaying predominantly fluvial fining upwards units for each unit several lithofacies architectural elements and bounding surfaces of different order have been identified and their lateral and vertical staking characterized deposition and erosion processes are controlled by alternating periods of tectonic activity producing different stages of high and low subsidence the uplift of the sub basin margins and subsequent extended erosive events marked by angular unconformities on the strength of the major rank bounding surfaces analysis the studied sedimentary packages have been grouped into different tectono stratigraphic units and then correlated they have been contextualized within the latest palaeogeographic reconstructions of the studied sector contributing to detail the role of the study area within the frame of the s european palaeogeography

petrology of the late carboniferous punta falcone gabbroic complex nothern sardinia italy the punta falcone gabbroic complex represents an evolved high alumina basalt which rose from the mantle through the lower crust and subsequently intruded a granite magma in middle crustal levels during the calc alkaline magmatic activity which took place in the sardinian and corsican islands in the carboniferous the gabbroic complex has a stratified sub vertical structure and consists of three zones developing from the bottom to the top of the magma chamber an interaction zone can be recognized along contacts with the surrounding granite stock and it is characterized by finer grained and more evolved rocks than the interior of the gabbroic complex processes occurring in its interior zone have been substantially different from those occurring in its marginal interaction zone petrographical and geochemical features indicate that the differentiation of the interior of the gabbroic complex can be accounted for by low pressure closed system in situ crystallization the different gabbroic units represent mixtures between cumulus phases and trapped liquid plagioclase pyroxenes and successively plagioclase calcic amphibole oxides nucleated and grew in situ on the floor and walls of the chamber floating of plagioclase towards the top of the magma chamber resulted in the accumulation of the denser liquid at the bottom compaction phenomena and convective fractionation processes permitted the development of the pile of cumulus crystals with their trapped liquid and the migration of part of this evolved liquid towards the top of the magma chamber on the basis of major and trace element modelling a mathematical artifice has been developed to evaluate cumulus intercumulus processes that occurred in the interior of the gabbroic complex accordingly the formation of the different units can be modelled by mixtures between the parental magma and different percentages of minerals formed during the first stages of crystallization contemporaneously with the differentiation of the interior zone the envelope of fine grained rocks enclosing and grading into the coarser inner part of the gabbroic complex experienced both chemical and physical processes chemical processes resulted in the evolution of the marginal interaction zone by crystal fractionation plus contamination by the acid magma physical processes were closely related to the thermodynamic instability of this marginal zone and consisted of mingling and back veining phenomena which developed interdigitations of granite veins along contacts in addition an increase of the melt fraction of the granite magma superheated by the latent heat of crystallization of the mafic magma caused the occurrence of tilting of the mafic magma chamber and resulted in the development of the sub vertical structure of the gabbroic complex

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

geochemical modeling of acid basic magma interaction in the sardinia corsica batholith the case study of sarrabus southeastern sardinia italy abstract the hercynian intrusive rocks outcropping in the sarrabus area southeastern sardinia italy consist of microgranular mafic enclave mme bearing granites 95 associated with coeval stratified gabbroic complexes and basic septa bs

geodynamic significance of early orogenic high k crustal and mantle melts example of the corsica batholith early post collision variscan magmatism in corsica france was characterised by high k granitic intrusions of namurian age they consist of quartz monzonites monzogranites and leuco monzogranites associated with vaugnerite meladiorites or hornblende biotite diorites intrusive stocks and enclaves the composition of the vaugnerites shows that they originated from slowly cooled syn magmatically amphibolitized lamprophyric magmas probably derived from enriched mantle melts that were injected into the lower crust and contributed to its extensive anatexis giving the high k granitic melts deep seated interactions between felsic and mafic magmas were responsible for the common characteristics of both magma suites the granitoid suite is characterised by high k and mg contents relatively high concentrations of th rb sr and ba la yb n from 10 to 20 lree enrichments lan 100 300 sri 0 707 18o 6 end 3 5 to 2 5 the mg rich minerals of the high k plutonic suite and the vaugnerites constrain emplacement conditions to 270 100 mpa al in hornblende geobarometer 675 25 c solidus temperature logfo2 16 and h2o contents in the range 3 4 wt k rich magmatism of carboniferous age mostly occurs in two parallel belts in the high grade zones of the variscan orogen it is interpreted as resulting from continental crust mantle interactions under high pressure conditions 1 5 gpa the chemical evolution of post collision plutonism is explained in terms of mantle crust interactions at decreasing depths during post orogenic extension

crustal exhumation during ongoing compression in the variscan maures tanneron massif france geological and thermo mechanical aspects abstract the maures tanneron massif mtm together with corsica and sardinia represent the southeastern branch of the huge european variscan belt a continuous evolution from continental collision to exhumation is described from ca 350 ma to ca 320 ma based on an extended compilation of available geological and geochronological data this geological compilation is complemented with thermo mechanical modelling that tests the conditions under which deep seated hp units can melt and exhume massively during continued convergence we simulate in two dimensions the development of gravitational instabilities in a partially melting crust depending on rheological layering and heat sources and accounting for temperature dependent elasto visco plastic rheologies in order to reproduce pt exhumation patterns in the mtm over the appropriate time scale 20 my and spatial extent 100 km a best fit was obtained with a convergence rate of 0 5 cm yr and moderate diffusive surface processes the contribution of radiogenic heating in the pre stacked felsic crustal units is crucial a lateral alternation with mafic units is also required in order to prevent lateral spreading of the orogen a low viscosity partially molten crust 1020 pa s thus rather felsic accompanies crustal exhumation in a decoupled mode from the deeper mantle a shallow asthenosphere below the orogen lab at 70 km depth e g shallow slab break off produces too warm and sudden exhumation as opposed to a competent mantle lithosphere 120 km depth lab that restrains it the mtm witnesses the typical competition between far field plate convergence and internal body forces and our study pleads for a progressive evolution of transpression towards perpendicular extension from ca 320 ma

alkali calcic and alkaline post orogenic po granite magmatism petrologic constraints and geodynamic settings abstract the end of an orogenic wilson cycle corresponds to amalgamation of terranes into a pangaea and is marked by widespread magmatism dominated by granitoids the post collision event starts with magmatic processes still influenced by subducted crustal materials the dominantly calc alkaline suites show a shift from normal to high k to very high k associations source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle affected by dehydration melting and generating more and more k and lile rich magmas in the vicinity of intra crustal magma chambers anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves the post collision event ends with emplacement of bimodal post orogenic po suites along transcurrent fault zones two suites are defined i the alkali calcic monzonite monzogranite syenogranite alkali feldspar granite association characterised by biotite plagioclase fractionation and moderate lile hfse enrichments and ii the alkaline monzonite syenite alkali feldspar granite association characterised by amphibole alkali feldspar fractionation and displaying two evolutionary trends one peralkaline with sodic mafic mineralogy and higher enrichments in hfse than in lile and the other aluminous biotite bearing marked by hfse depletion relative to lile due to accessory mineral precipitation alkali calcic and alkaline suites differ essentially in the amounts of water present within intra crustal magma chambers promoting crystallisation of various mineral assemblages the ultimate enriched and not depleted mantle source is identical for the two po suites the more primitive lile and hfse rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere present rock compositions are a mixture of major mantle contribution and various crustal components carried by f rich aqueous fluids circulating within convective cells created around magma chambers in favourable areas po suites pre date a new orogenic wilson cycle

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

the relationship between tectono metamorphic evolution and argon isotope records in white mica constraints from in situ 40ar 39ar laser analysis of the variscan basement of sardinia the basement of sardinia represents a nearly complete section of a segment of the variscan belt that experienced a polyphase tectonometamorphic evolution and barrovian metamorphism this basement is well suited to investigate the relationship between tectono metamorphic evolution and argon isotope records in white mica micaschists from the garnet zone maximum t of up to 520 560 c contain two texturally and chemically resolvable generations of white mica 1 deformed celadonite rich flakes defining a relict s1 foliation preserved within the main s2 foliation or enclosed in rotated albite porphyroblasts 2 celadonite poor white micas aligned along the main s2 foliation the s1 foliation developed earlier and at a deeper crustal level with respect to that at which the thermal peak was reached from the staurolite zone t of up to 590 625 c to the sillimanite k feldspar zone white mica is nearly uniform in composition muscovite and is predominantly aligned along the s2 foliation or is of later crystallization in situ ar ar laser analyses of white mica yielded ages of 340 315ma in the garnet zone and 320 300ma in the staurolite and sillimanite k feldspar zones results highlight a close link between argon isotope records in white mica and both textures and structure forming major elements the oldest ages were detected in samples where the earlier syn d1 white mica generation did not texturally and chemically re equilibrate at upper crustal levels this study suggests that the white micas that escaped recrystallization retain argon isotope records of an earlier metamorphic stage that survived a later event characterized by temperatures higher than 500 c

the arburese igneous complex sw sardinia italy an example of dominant igneous fractionation leading to peraluminous cordierite bearing leucogranites as residual melts abstract the arburese massif sw sardinia italy is a zoned shallow pluton emplaced in the frontal part of a nappe pile at the end of the hercynian orogeny its main lithologies are a pyroxene bearing biotite granodiorites and b cordierite bearing peraluminous leucogranites they form a sequence of sharply bounded multiple intrusions the leucogranites lg form the core of the intrusive complex and are younger than the granodiorites three types of granodiorites gd 1 gd 2 gd 3 have been distinguished on the basis of their field relations and their pyroxene content dark coloured enclaves are common in the granodiorites their compositions range from biotite bearing norite to pyroxene biotite quartzdiorite quartz monzodiorite a small body of olivine bearing quartz monzogabbro norite mg forms an independent intrusion in the border zone of the igneous massif it is crosscut by the granodiorite the whole rock sequence from mg to gd 3 is characterized by the same mafic assemblage opx cpx bt ilm it formed by dominant crystal liquid fractionation processes from a mantle derived olivine bearing magma from gd 3 to three types of leucogranites lg 1 lg 2 and lg 3 the rocks are progressively enriched in al reaching a peraluminous composition in the leucogranites cordierite makes its appearance among the primary mineral phases though confined to the later products of crystallization remarkably cordierite was also observed among the latest crystallization products in some granodiorites and even in some dark monzodioritic enclaves independent whole rock age determinations were made on the mg to gd 3 series and on the leucogranites these gave very similar values of 309 19 and 304 21 ma respectively some textural and mineralogical features common to both gd 3 granodiorite and the leucogranites e g both contain ti biotites characterized by a common trend of al and fe enrichment suggest a genetic linkage between these two rock types the extreme iron rich compositions displayed by the mafic minerals biotite cordierite of the leucogranites suggest that they crystallized from highly evolved melts petrochemical trace element and ree distribution patterns strongly support a common origin for the whole igneous sequence including the leucogranites strontium isotope compositions do not conflict with the above conclusion the oxygen isotopic composition changes progressively with time of emplacement 18 o increases from 7 6 in the granodiorites up to 11 9 in the leucogranites this probably reflects some degree of magma contamination due to assimilation of crustal material the sr and o isotope systematics reveal that the mg gd series is characterized by very small variations of the sr ratio and by pronounced changes in 18 o on account of the rather high sr initial ratios the observed trend is interpreted as due to afc assimilation fractional crystallization processes of a source contaminated parental magma modelling the evolution path from mg to lg in terms of afc processes shows the following a the assumed fractionation steps give realistic mineral assemblages compatible with the observed lithologies b they are able to produce high proportions of both leucogranitic and granodioritic rocks as observed in the field and c they can produce a progressive increase of alumina up to the peraluminous compositions observed in the more evolved members good results were also obtained by modelling the behaviour of trace elements such as rb sr and ba whose distribution is mainly governed by the major mineral phases the geochemical fingerprint of the whole igneous sequence is typical of a k rich calc alkaline series only some rare grey enclaves in the gd 3 granodiorite and in the leucogranites display a typical shoshonitic character their presence probably reflects the open system condition of the deep seated magma reservoir

structural setting of a transpressive shear zone insights from geological mapping quartz petrofabric and kinematic vorticity analysis in ne sardinia italy

selective aerobic and anaerobic degradation of lipids and palynomorphs in the eastern mediterranean since the onset of sapropel s1 deposition abstract selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle here we report on compositional changes between and within lipid classes and kerogen types represented by palynomorph groups in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early holocene for central eastern mediterranean site abc26 this includes the initially oxic but nowadays anoxic presapropelic interval the still unoxidised lower part of the organic rich s1 sapropel its postdepositionally oxidised and nowadays organic poor upper part as well as the overlying postsapropelic sediments which have always been oxic a general 2 3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon toc pollen spore dinoflagellate cyst n alkane n alkanol and n alkanoic acid concentration changes in the unoxidised part of the sapropel the long chain alkenones 1 15 diols and keto ols loliolides and sterols indicate that some plankton groups notably dinoflagellates may have increased much more apart from the terrestrial and surface water contributions to the sedimentary organic matter anomalous distributions and preservation of some c 23 c 27 alkanes alkanols and alkanoic acids have been observed which are interpreted as a contribution by organisms living in situ comparison of the unoxidised s1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs there seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation the n alkanes impagidinium and nematosphaeropsis are clearly more resistant than toc the n alkanols and n carboxylic acids are about equally resistant whereas the pollen all other dinoflagellate cysts and other lipids appear to degrade considerably faster which questions the practice of normalising to toc without taking diagenesis into account selective degradation also modifies the relative distributions within lipid classes whereby the longer chain alkanes alcohols and fatty acids disappear faster than their shorter chain equivalents accordingly interpretation of lipid and palynomorph assemblages in terms of pre or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent two lipid based preservation proxies are tested the diol keto ol oxidation index based on the 1 15c 30 diol and keto ols doxi and the alcohol preservation index api whereby the former seems to be the most promising

a further study on seismic response of a set of parallel rock fractures filled with viscoelastic materials the purpose of this study is to further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials following the work by zhu et al dry quartz sands are used to represent the viscoelastic materials the split hopkinson rock bar shrb technique is modified to simulate 1 d p wave propagation across the sand filled parallel fractures at first the displacement and stress discontinuity model dsdm describes the seismic response of a sand filled single fracture the modified recursive method mrm then predicts the seismic response of the sand filled parallel fractures the shrb tests verify the theoretical predictions by dsdm for the sand filled single fracture and by mrm for the sand filled parallel fractures the filling sands cause stress discontinuity across the fractures and promote displacement discontinuity the wave transmission coefficient for the sand filled parallel fractures depends on wave superposition between the fractures which is similar to the effect of fracture spacing on the wave transmission coefficient for the non filled parallel fractures