al coordination and speciation in calcium aluminosilicate glasses effects of composition determined by 27al mq mas nmr and raman spectroscopy the structure and properties of glasses and melts in the cao al2o3 sio2 cas system play an important role in earth and material sciences aluminum has a crucial role in this ternary system and its environment is still questioned in this paper we present new results using raman spectroscopy and 27al nuclear magnetic resonance on cas glasses obtained by classic and rapid quenching methods we propose an al si tetrahedral distribution in the glass network in different qn species in this system we show that al and si are mainly in q4 species along the join r cao al2o3 1 and in depolymerized q2 and q3 units at high cao content for other joins r 1 57 and 3 five 5 al and six fold 6 al coordinated aluminum can be detected in the peraluminous glasses r 1 except for glasses with low silica and high cao content the presence of 5 al is related to viscous flow mechanisms while in highly depolymerized glasses the absence of 5 al may indicate different mechanisms for melts to flow this systematic study on the cas system modifies the simple picture of aluminosilicate glasses and the existence of 5 al should be included by geochemists geophysicists and glass scientists to model appropriately the physical properties of aluminosilicate glasses and melts

model for the evolution of the avalonian cadomian belt the inception and termination of the ca 670 550 ma avalonian cadomian orogenic cycle are interpreted in terms of the amalgamation and breakup of a late precambrian supercontinent synorogenic arc related volcano sedimentary and granitoid rocks are attributed to oblique southward directed subduction along the margin of the supercontinent after its amalgamation breakup of the supercontinent and inception of the iapetus cycle led to termination of subduction and its replacement by transform activity the resulting closure of late precambrian arc related basins and the development of early cambrian platform successions with acado baltic fauna accompanied the formation of iapetus but took place on the active margin of a preexisting ocean and do not record the evolution of its rifted european flank

extent of disorder in iron bearing albite and anorthite melts insights from multi nuclear 29si 27al and 17o solid state nmr study of iron bearing naalsi3o8 and caal2si2o8 glasses abstract knowledge of the detailed structure of iron bearing aluminosilicate glasses is essential to unraveling the effects of iron on the macroscopic properties of natural silicate glasses and melts however the local structures around the framework cations such as al and si and the extent of network polymerization in iron bearing aluminosilicate glasses are not well understood this is mainly because the high resolution solid state nmr one of the effective probes of the structures of aluminosilicate glasses has limited utility in delving into the local configurations of oxide glasses with paramagnetic elements i e iron here we use multi nuclear 29si 27al and 17o high resolution solid state nmr to investigate the effect of iron content on the local structure around framework cations and oxygen species in na al1 xfex si3o8 glasses with varying x fe al fe fe3 fe 0 8 naalsi3o8 glasses with varying fe2o3 naalsi3o8 fe2o3 fe3 fe 0 5 and caal2si2o8 glasses with varying fe2o3 caal2si2o8 fe2o3 fe3 fe 0 3 the nmr results for na al1 xfex si3o8 glasses reveal preferential interaction between fe3 and si rich framework and thus an extensive mixing between 4 si and 4 fe3 the presence of a small amount of 5 al in na al0 5fe0 5 si3o8 glass suggests that the extent of disorder around al increases by al fe3 substitution the nmr results for naalsi3o8 fe2o3 glasses suggest that fe2 interacts more strongly with al rich framework and reveal the presence of a non negligible fraction of na nbo confirming fe2 induced structural disorder the absence of 5 al in naalsi3o8 fe2o3 glasses indicates that fe3 is more likely to form a highly coordinated framework i e 5 fe3 when excess fe3 is added to charge balanced glasses the nmr spectra for caalsi2o8 fe2o3 glasses showed an iron induced increase in the 5 al fraction and confirmed that the overall degree of disorder increases with increasing fe2o3 content the noble nmr results for iron bearing aluminosilicate glasses revealed the nature of diverse aspect of iron induced structural disorder mainly characterized by the intermixing between si and fe3 preferential interaction between al and fe2 and formation of highly coordinated 5 fe3 the detailed iron induced structural evolution is largely dependent on the composition of melts as well as the valence state of iron the observed increase in the extent of structural disorder in charge balanced na and ca aluminosilicate glasses with increasing fe2 and fe3 can account for the iron induced decrease in viscosity of the corresponding iron bearing aluminosilicate melts

provenance of neoproterozoic and early paleozoic siliciclastic rocks of the tepla barrandian unit bohemian massif evidence from u pb detrital zircon ages abstract new la icp ms u pb detrital zircon ages from ediacaran and paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the tepla barrandian unit tbu in the centre of the bohemian massif central europe czech republic the samples taken span the period from 635 ma to 385 ma and permit recognition of provenance changes that reflect changes in geotectonic regime detrital zircon age spectra of two ediacaran one lower cambrian and three upper ordovician samples resemble the ages known from the nw african proportion of gondwana particularly the trans saharan belt while three rocks from higher lower cambrian to lowermost ordovician strata contain detritus that may have been derived exclusively from local sources the age spectrum of the devonian rock is a combination of the nw gondwanan and local features these new findings in combination with a wide range of published data are in agreement with a neoproterozoic subduction related setting at the margin of gondwana followed by a cambrian early ordovician rifting stage and an ordovician passive margin setting furthermore the data are in favour of a position of the tbu at the gondwanan margin throughout pre variscan times

detrital zircon u pb geochronology of pennsylvanian permian sandstones from the turnaicum and meliaticum western carpathians slovakia provenance and tectonic implications the blueschist bearing borka nappe regarded as a part of the meliaticum unit s l and the turnaicum unit in its hanging wall were thrusted together to the north on the inner western carpathians basement during the orogenic events of the late jurassic early cretaceous a new u pb sensitive high resolution ion microprobe shrimp magmatic as well as detrital zircon ages were used to constrain provenance and paleogeography the detrital zircon age spectrum of the studied metasediments contains mainly ages of the ediacaran cryogenian 550 720 ma and tonian stenian 0 9 1 1 ga which correspond to the pan african belt and saharan metacraton subordinate archean ages were likely derived from the saharan metacraton of north gondwana 1 7 2 2 and 2 5 2 7 ga the 273 2 ma zircon age of a metarhyolite along with the youngest detrital zircon of 265 4 ma from the associated metasediments specify the maximum depositional age of the bucina fm from the borka nappe to the guadalupian the rhyolite olistoliths from the middle late jurassic meliaticum olistostrome yielded the latest cambrian earliest ordovician 488 6 ma and middle ordovician 465 ma zircon ages this is consistent with the u pb zircon ages from the foot walling southern gemericum basement metavolcanites which are therefore regarded as a potential source the obtained zircon ages confirm the provenance from the southern gemericum basement and its permian envelope for the meliaticum borka nappe and turnaicum sedimentary embayment

permian continental basins in the southern alps italy and peri mediterranean correlations the late carboniferous to permian continental successions of the southern alps can be subdivided into two main tectono sedimentary cycles separated by a marked unconformity sealing a middle permian time gap generally estimated at over 10 ma the lower cycle 1 between the variscan crystalline basement and the early permian is mainly characterised by fluvio lacustrine and volcanic deposits of calc alkaline acidic to intermediate composition which range up to a maximum thickness of more than 2 000 m the upper cycle 2 which is devoid of volcanics is mostly dominated through the mid late permian by alluvial sedimentation which covered the previous basins and the surrounding highs giving rise to the subaerial verrucano lombardo val gardena groden red beds up to about 800 m thick the palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro and microfloras and tetrapod footprints the age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings however some sections are also controlled by radiometric calibrations the comparison with some selected continental successions in southern europe allows to determine their evolution and set up correlations a marked stratigraphic gap shows everywhere between the above mentioned cycles 1 and 2 as in the southern alps the gap reaches the greatest extent during the mid permian near the illawarra reversal geomagnetic event 265 ma in western europe however such as in provence and sardinia the discussed gap persists upwardly to late permian and early triassic or slightly younger times i e to the onset of the alpine sedimentary cycle even though in northeastern spain iberian ranges balearic islands this gap results clearly interrupted by late guadalupian lopingian deposits the above two major tectonosedimentary cycles reflect in our view two main geodynamic events that affected the southern europe after the variscan orogenesis the late carboniferous early permian transformation of the gondwana eurasia collisional margin into a diffuse dextral transform margin and the middle late permian opening of the neotethys ocean with the onset of a generalised extensional tectonic regime and the progressive westward marine ingression

segmentation of the caledonian orogenic infrastructure and exhumation of the western gneiss region during transtensional collapse the ultra high pressure western gneiss region of the norwegian caledonides represents an archetypical orogenic infrastructure of a continent continent collision zone to test established exhumation models we synthesize the geochronology and structures of major basement windows and provide new ages from poorly dated areas migmatite u pb zircon samples date melt crystallization at c 405 ma in the oygarden complex expanding the spatial extent of devonian migmatization micas from shear zones in the oygarden and gulen domes yield 40ar 39ar ages mostly between 405 and 398 ma recording the exhumation of metamorphic core complexes on a larger scale the youngest ages of various geochronometers in different segments of the western gneiss region show abrupt breaks 10 30 myr across low angle detachments and sinistral transfer zones which also correspond to metamorphic and structural discontinuities we explain the segmentation of the orogenic infrastructure by partitioned post orogenic transtension due to lateral and vertical rheological contrasts in the orogenic edifice strong cratonic foreland and orogenic wedge v soft infrastructure differential crustal stretching dragged out deep levels of the orogenic crust below low angle detachments and became progressively dominated by sinistral transfer zones collapse obliterated the syn collisional structure of the orogenic root and resulted in the diachronous exhumation of distinct infrastructure segments supplementary material complete analytical results are available at https doi org 10 6084 m9 figshare c 5241710

textural and age relations of polymetamorphic rocks in the hp meliata unit western carpathians abstract slices and tectonic blocks of amphibolite facies crustal rocks overprinted by blueschist facies metamorphism occur in the middle jurassic meliata high pressure unit of the western carpathians the early paleozoic age for relic muscovite is known from some micaschists with blueschist facies overpint in the eastern sector of the meliata unit based on lithology some amphibolite facies rocks are comparable with the early paleozoic basement rocks in the gemeric unit in this work we present results of petrology and ar ar and rb sr geochronology from blueschist facies rocks with relicts of hornblende muscovite garnet and rutile the older amphibolite facies metamorphism was followed by retrogression prior to the blueschist facies overprint the blueschist facies metamorphic minerals are ca rich garnet glaucophane phengite and albite the coarse grained relict muscovite indicates an early paleozoic age using the ar ar method and a middle jurassic age using the rb sr technique the presence of amphibolite facies rocks within the meliata unit is interpreted as involvment of variscan pre variscan basement unit rocks in the middle jurassic subduction of the meliata hallstatt oceanic basin

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

detrital muscovite 40ar 39ar ages from carboniferous sandstones of the british isles provenance and implications for the uplift history of orogenic belts major progradations of clastic sediments are recorded in the sedimentary record of the famennian and the visean namurian of the united kingdom and surrounding waters we have determined 40ar 39ar ages of 162 detrital muscovites from 11 coarse sandstones which were deposited between 370 and 465 ma spanning both progradations detrital mica ages are dominated by a peak at 415 ma with minor peaks at 440 ma and 390 ma the 415 ma muscovites are derived from the unroofing of the scandian nappes during the compressional phase of the caledonian orogeny in scandinavia the 440 ma muscovites record pre scandian orogenic activity which is rarely preserved in the orogenic record thermochronological evidence suggests that episodic postorogenic uplift and exhumation events kept the scandian orogen a major topographic feature and likely a sediment source for over 100 million years after nappe emplacement and implicates tectonic rather than climatic control on the clastic sediment progradations the near total absence of detrital muscovites with ages 415 ma suggests that the scandian nappes had not been entirely eroded despite repeated uplift during the postorogenic extension the river s which supplied the sediments probably ran parallel to the strike of the major scandian thrusts along the length of the caledonian orogen in a manner analogous to the major river systems of contemporary orogenic highlands

exhumation of the high pressure tsakkok lens swedish caledonides insights from the structural and white mica 40ar 39ar geochronological record

mantle fragments in the scandinavian caledonides abstract mantle fragments of ultramafic composition are widespread in the scandinavian caledonides sc lenses and boudins of alpine type peridotites in the scandinavian caledonides represent parts of dismembered ophiolite sequences and fragments of sub continental upper mantle metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope usually caledonian metasediments but in places also precambrian metagranitoids forming the basement cores of the nappes caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope metaperidotites of the external massifs display at least a two stage metamorphic history an early caledonian high pressure high temperature phase related to early crustal stacking and a late caledonian regional metamorphic overprint which produced a regular barrovian type metamorphic pattern of in situ metamorphism metaperidotites from nappes in intermediate positions iapetus ocean ophiolites and ultramafic rocks from island arc environments show strongly diverging histories metaperidotites from internal ophiolites oceanic ophiolites koli lack any evidence of subduction metamorphism are serpentinized to various degrees show abundant primary mantle relic mineralogies and the caledonian metamorphic overprint is low metaperidotites from external island arc ophiolites and other associations seve often show relic high pressure metamorphism related to the finnmarkian phase of the caledonian orogeny the seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late caledonian regional metamorphism alpine type peridotites are absent in the foreland of the baltic shield and in the innermost nappes lofoten the metamorphic characteristics and evolution recorded by the metaperidotites in the scandinavian caledonides allow a general reconstruction of the dynamics of collision belt formation

extensional deformation along the late precambrian cambrian baltoscandian passive margin the sarektjakka nappe swedish caledonides the structural evolution of a part of the late precambrian baltoscandian passive margin just before the inception of seafloor spreading is described recording the change from deformation by faulting to dominantly magmatic extension of the crust the allochthon of the scandinavian caledonides contains the imbricated passive margin of continental baltica overlain by various exotic terranes the sarektjakka nappe in the seve nappe complex which contains the outer parts of baltica s passive margin consists of sedimentary rocks occurring as screens between vendian 573 74 ma diabase dykes these dykes constitute 70 80 of the nappe and locally form sheeted dyke complexes the sarektjakka nappe largely escaped penetrative caledonian deformation and preserves igneous metamorphic and structural elements that are linked to the evolution of a pre caledonian rift to a passive continental margin extensional deformation before dyke emplacement is recorded by normal faults pull apart structures and folds unconformities dykes affected by brittle deformation and fluidization of sediments during dyke emplacement indicate close relations between the deposition of sediments extensional deformation and dyke emplacement the sarektjakka nappe is compared with other parts of the baltica s passive margin and its tectonic evolution is discussed

40ar 39ar polyorogenic mineral age record within the central mauritanide orogen west africa the central mauritanide orogen in the vicinity of magta lahjar is characterized by several internally imbricated polydeformed and variably metamorphosed infrastructural allochthons which include 1 a calc alkaline igneous complex kelbe intrusive and el hneik t extrusive sequences 2 portions of an ophiolitic sequence el aoueija and oued amour units and 3 continental margin rift sequences fark ka association which include amphibolite low ti continental tholeiite dike protoliths mylonitic quartzite and kyanite schist several variably meta morphosed quartzitic supracrustal nappes g oua and sangarafa allochthons structurally overlie the infrastructural units 40 ar 39 ar incremental release ages have been determined for 10 hornblende and 22 muscovite concentrates prepared from various units of the infrastructural and supra structural allochthons hornblende from fark ka amphibolite is characterized by internally discordant spectra reflecting wide spread contamination with extraneous argon 36 ar 40 ar versus 39 ar 40 ar isotopic correlations are well defined for several concentrates and the resultant ages suggest that post metamorphic cooling occurred following distinct late proterozoic tectonothermal events at ca 700 720 ma and ca 640 650 ma muscovite within fark ka lithologies initially cooled through argon closure temperatures between ca 570 and 595 ma muscovite records similar post metamorphic cooling ages in the other infrastructural allochthons and in the g oua suprastructural allochthon these muscovite ages are interpreted to reflect cooling associated with widespread post orogenic uplift and are consistent with deposition of upper proterozoic lower paleozoic flysch in the proximal foreland tichilit el beida group the tichilit el beida group and correlative parautochthonous sequences djon ba group were penetratively deformed prior to the early ordovician 40 ar 39 ar incremental release analyses of 6 very fine grained white mica concentrates from mylonitic quartzite along thrust faults within the parautochthon indicate that this deformation occurred prior to ca 540 550 ma there is no clear thermal record of this orogenic activity in either infrastructural or suprastructural allochthons suggesting that it must have occurred at relatively high structural levels and was probably largely of intracontinental character all foreland units were affected by post emsian folding effects of this tectonic activity are widespread throughout the parautochthon and western metamorphic sequences these effects include emplacement of the suprastructural allochthons into their present structural positions at ca 300 325 ma with an associated partial rejuvenation of muscovite argon systems proximal to basal thrust faults local reactivation of older thrust faults within the parautochthon and infrastructural allochthons is also indicated by variable 300 325 ma rejuvenation of muscovite argon systems within some fault zones muscovite within westernmost exposures of the infra structural allochthons was totally rejuvenated during the early carboniferous and records 300 m y plateau ages the early tectonic history recorded within the central mauritanide orogen appears to have been related to restricted rifting of a western crustal block from the west african craton and formation of a limited intervening oceanic domain subsequent closure resulted in compression and imbrication of continental crust with resultant development of an ensialic volcanic arc calc alkaline sequences within the infrastructural allochthons together with widespread metamorphism and deformation between ca 700 and 650 ma later orogenesis at ca 550 ma could have reflected distal effects of collisional events which dominate the rokelide orogen in sierra leon and guinea late paleozoic tectonotherma activity within the central mauritanides is interpreted to have developed as a result of a renewed translation between the western continental block and the west african craton during final collision of laurentia arc gondwana

ordovician and cretaceous tectonothermal history of the southern gemericum unit from microprobe monazite geochronology western carpathians slovakia the southern gemericum basement in the inner western carpathians experienced a polyphase regional deformation differences in the pre alpine and alpine events have been constantly discussed to address this monazites from metapelites and acid metavolcanic rocks were dated using the th u pb electron microprobe method three monazite generations such as precambrian early paleozoic and alpine have been recognized in the greenschist facies pelites and acid metavolcanic rocks of the southern gemericum basement both inherited magmatic monazite grains in metavolcanites and rare relics of detrital monazites within the polyphase monazite grains in metapelites yielded the precambrian age in the time span of 550 660 ma they prove the provenance and derivation from deeper crustal cadomian fragments high y magmatic monazites of early paleozoic age 444 13 and 477 7 ma have been recorded in the acid metavolcanites and their metavolcaniclastics these ages roughly fit within the previously published magmatic zircon age determinations at 494 1 7 and 464 1 7 ma that clearly indicate two phase volcanic activity in the early paleozoic southern gemericum basin the early paleozoic magmatic monazites were partly overprinted by the low y alpine monazites 133 5 and 184 16 ma at their rims in al rich metapelites the newly formed low y monazites of alpine age commonly occur reflecting the polystage compression geodynamic evolution with three distinct peaks at 100 8 133 5 and 190 16 ma respectively no data as the evidence of the pre alpine metamorphic events were observed in metapelites only some monazites yield the age indications for the permian extensional thermal re heating 260 290 ma the monazite age data from the southern gemericum basement indicate the strong overprinting due to the polyphase alpine deformation at least in the greenschist facies conditions

aluminum coordination in rhyolite and andesite glasses and melts effect of temperature pressure composition and water content abstract the coordination state of the network formers si and al is one of the primary parameters describing the structure of silicate glasses and melts in this experimental study we use 27al mas nmr spectroscopy to investigate the effect of temperature pressure and composition on the coordination of al in dry and hydrous rhyolite and andesite glasses quenched from pressures of up to 3 5 gpa the spectra were collected at a high magnetic field of 20 tesla to increase spectral resolution and allow for a direct quantification of the different al coordinations the disorder around 4 al increases with increasing fictive temperature and pressure and with decreasing water content or peralkalinity al is predominantly 98 in fourfold coordination in all investigated samples nevertheless systematic trends in al coordination have been observed as a function of pressure composition and water content for the investigated pressure range the proportion of 5 al increases with increasing pressure but decreases with increasing water content and proximity to the metaluminous join for rhyolite glasses within analytical uncertainty the amount of 5 al is independent of fictive temperature the addition of water to andesite glasses does not decrease the amount of 5 al in contrast to the rhyolite glasses based on the glass data we conclude that the majority of al and si will be present in fourfold coordination in metaluminous dry and hydrous rhyolite magmas at the temperature and pressure conditions relevant for the crust and the subducting slab up to 3 5 gpa however consistent with previous predictions from model systems more higher coordinated al may be present in andesite and peralkaline or peraluminous rhyolite melts although the exact concentrations cannot be predicted accurately from the available data compared to more depolymerized melts rhyolite melts can accommodate a higher degree of densification without a significant increase in al coordination

late cambrian ordovician magmatic arc type volcanism in the southern gemericum basement western carpathians slovakia u pb shrimp data from zircons the low grade crystalline basement of the southern gemeric unit inner western carpathians consists mainly of siliciclastic deep water turbidite sequence associated with a huge mass of redeposited rhyolite dacite volcanics and their volcaniclastics in situ u pb shrimp zircon dating applied to metavolcanic rocks contributed to specification of the southern gemeric crystalline basement stratigraphy the gelnica group zircon populations from ten samples of three lithostratigraphic units of the gelnica group rock complex have been analysed the zircons presented significant magmatic zoning part of the magmatic zircons contained inherited older cores the vlachovo formation gives the 494 1 6 ma zircon average age the bystr potok formation gives 465 8 1 5 ma and the drnava formation 463 9 1 7 ma average age the geochemical data are compatible with an orogenic geodynamic setting dominant rhyolite dacite volcanites belong to the peraluminous calc alkaline high k magmatic series the age data let us presume two phase longlasting magmatic activity starting in the late cambrian and continuing to the middle late ordovician thus the studied late cambrian volcanic sequence of the gelnica group reflects the active continental margin setting the second middle ordovician volcanic phase documents an assumed rifting stage accompanied by a strong volcanic activity with inherited features of the late cambrian magmatic arc the inherited cores of magmatic zircons have proterozoic 600 760 1 000 1 400 2 000 2 700 ma and archean 3 099 3 164 ma ages

cretaceous collision and indentation in the west carpathians view based on structural analysis and numerical modeling 1 a model of indentation of a rigid promontory into weak metasedimentary rocks during cretaceous convergence is suggested for tectonic evolution of southern part of west carpathians an early arcuate cleavage fan has developed in front of northward moving southern rigid basement block the interaction of the moving indenter with western stationary basement promontory is responsible for development of the boundary parallel shear zone along which the main southern indenter is shifted to the east this results in development of a new steep transpressional cleavage overprinting the early fabric eastward displacement of the southern indenter causes the development of a thrust zone parallel to the margin of the eastern stationary promontory a proposed numerical model of the deformation of a thin viscous sheet in front of oval rigid indenter reliably simulates the development of the observed deformation pattern modeled discrete partitioning between the western promontory and the indenting block fully agrees with the observed secondary cleavage associated with the transpressional shear zone our numerical model interconnects this complex kinematic frame with finite strain pattern which was to date possible only for simple boundary conditions in addition the model explains the polyphase cleavage patterns in terms of complex shapes of promontories and changes in movements of indenting blocks

thermal history of thrust sheets in an orogenic wedge 40ar 39ar data from the polymetamorphic seve nappe complex northern swedish caledonides the seve nappe complex in the scandinavian caledonides contains the fragmented late precambrian continent ocean transition between baltica and the iapetus ocean this passive margin was fragmented and thrust eastwards over the baltic shield during caledonian orogenesis the individual thrust sheets in the seve nappe complex went through different p t t evolutions resulting in dramatic metamorphic contrasts eclogite bearing nappes are juxtaposed with nappes showing no evidence of caledonian deformation or metamorphism in their interiors strain localization to the marginal parts of the thrust sheets left records of both pre orogenic rift and early orogenic subduction and subsequent uplift processes in the thrust sheets of the seve nappe complex even though it has been transported several hundred kilometres only the margins of the eastern part of the sarektjakka nappe are affected by penetrative caledonian deformation this part of the sarektjakka nappe is dominated by pristine tholeiitic dykes and cross bedded sandstones the dykes are 608 1 ma old and make up 70 80 of the nappe widely spaced thin shear zones of the ruopsok fault system represent the only caledonian penetrative deformation in the interior of the nappe previously published ar ar dates indicate cooling below the closure temperature of hornblende at c 470 ma but numerous ages have been recorded ar dating of biotite and muscovite from a cross laminated metapsammite in the sarektjakka nappe gave well defined ages of 428 5 3 6 and 432 4 3 8 ma respectively muscovite from a shear zone in the ruopsok fault system gave 428 2 4 0 ma whereas hornblende from the same locality did not yield interpretable data the results indicate that these rocks were completely degassed at some unknown time presumably at the emplacement of the dyke swarm no subsequent excess argon contamination can be detected a likely candidate for the degassing event is the emplacement of the dykes at 608 ma the interior of the nappe and thus the entire nappe complex cooled below 350 c at around 430 ma cooling from more than 500 c at c 470 ma to 350 c at c 430 ma suggests an average cooling rate of 4 c ma a prolonged period of slow cooling exhumation following the initial rapid uplift of the eclogite bearing nappes and early ordovician construction of the seve nappe complex is suggested

protracted shearing at midcrustal conditions during large scale thrusting in the scandinavian caledonides during continental collision large tracts of crust are mobilised along major shear zones the metamorphic conditions at which these zones operate the duration of thrusting and the deformation processes that facilitated hundreds of km of tectonic transport are still unclear in the scandinavian caledonides the lower seve nappe displays a main mylonitic foliation with thickness of 1 km this foliation is overprinted by a brittle to ductile deformation pattern localized in c and c type shear bands proximal to the tectonic contact with the underlying sarv nappe thermobarometry of amphibolites and micaschists suggest a first high pressure stage at 400 500 c and 1 1 3 gpa recorded in mineral relics the main mylonitic foliation developed under epidote amphibolite facies conditions along the retrograde path from 600 c and 1 gpa to 500 c and 0 5 gpa age dating of synkinematic titanite grains in the amphibolites indicates that this mylonitic fabric formed at around 417 9 ma but older ages spanning 460 430 ma could represent earlier stages of mylonitization the shear bands developed at lower metamorphic conditions of 300 400 c and 0 3 gpa in the micaschists the recrystallized grain size of quartz decreases towards the shear bands monomineralic quartz layers are eventually dismembered to form polyphase aggregates deforming by dominant grain size sensitive creep accompanied by slip in muscovite and chlorite plagioclase zoning truncations suggest that the shear bands originated by fracturing followed by ductile deformation the results suggest protracted and long lasting shearing under amphibolite to greenschist facies conditions during the juxtaposition stacking and exhumation of the lower seve nappe

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

illawarra reversal the fingerprint of a superplume that triggered pangean breakup and the end guadalupian permian mass extinction abstract the permian magnetostratigraphic record demonstrates that a remarkable change in geomagnetism occurred in the late guadalupian middle permian ca 265 ma from the long term stable kiaman reverse superchron throughout the late carboniferous and early middle permian to the permian triassic mixed superchron with frequent polarity changes in the late permian and triassic this unique episode called the illawarra reversal probably reflects a significant change in the geodynamo in the outer core of the planet after a 50 million years of stable geomagnetism the illawarra reversal was likely led by the appearance of a thermal instability at the 2900 km deep core mantle boundary in connection with mantle superplume activity the illawarra reversal and the guadalupian lopingian boundary event record the significant transition processes from the paleozoic to mesozoic modern world one of the major global environmental changes in the phanerozoic occurred almost simultaneously in the latest guadalupian as recorded in 1 mass extinction 2 ocean redox change 3 sharp isotopic excursions c and sr 4 sea level drop and 5 plume related volcanism in addition to the claimed possible links between the above listed environmental changes and mantle superplume activity i propose here an extra explanation that a change in the core s geodynamo may have played an important role in determining the course of the earth s surface climate and biotic extinction evolution when a superplume is launched from the core mantle boundary the resultant thermal instability makes the geodynamo s dipole of the outer core unstable and lowers the geomagnetic intensity being modulated by the geo and heliomagnetism the galactic cosmic ray flux into the earth s atmosphere changes with time the more cosmic rays penetrate through the atmosphere the more clouds develop to increase the albedo thus enhancing cooling of the earth s surface the illawarra reversal the kamura cooling event and other unique geologic phenomena in the late guadalupian are all concordantly explained as consequences of the superplume activity that initially triggered the breakup of pangea the secular change in cosmic radiation may explain not only the extinction related global climatic changes in the end guadalupian but also the long term global warming cooling trend in earth s history in terms of cloud coverage over the planet

the caledonian heilhornet pluton north central norway geological setting radiometric age and implications for the scandinavian caledonides the heilhornet pluton is a medium sized c 50 km 2 sub circular discordant intrusion which penetrates the thrust zone separating the helgeland nappe complex from paragneisses in the vestranden region north central norway the intrusion consists of biotite hornblende granite and ranges in composition from 61 5 to 72 5 wt si0 2 the initial sr ratio c 0 7070 shows that crustal sources have been involved in the petrogenesis of the granite a u pb zircon age of 444 11 ma for the pluton indicates that juxtaposition of the nappe complex with metasedimentary rocks in vestranden took place prior to or during the late ordovician a consequence of this is that the general correlation of the metasedimentary rocks in vestranden with the seve nappes must be revised final eastward thrusting of the complex together with a yet unknown part of the vestranden supracrustal sequence probably took place during the middle silurian to early devonian scandian orogenic event

microdiamond on areskutan confirms regional uhp metamorphism in the seve nappe complex of the scandinavian caledonides metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust here we present a new occurrence of diamond within the seve nappe complex snc of the scandinavian caledonides on areskutan in jamtland county sweden microdiamond is found in situ as single and composite diamond carbonate inclusions within garnet in kyanite bearing paragneisses the rocks preserve the primary peak pressure assemblage of ca mg rich garnet phengite kyanite rutile with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite calculated p t conditions for this stage are 830 840 c and 4 1 4 2 gpa in the diamond stability field the ultrahigh pressure uhp assemblage has been variably overprinted under granulite facies conditions of 850 860 c and 1 0 1 1 gpa leading to formation of ca mg poor garnet biotite plagioclase k feldspar sillimanite ilmenite quartz this overprint was the result of nearly isothermal decompression which is corroborated by ti in quartz thermometry chemical th u pb dating of monazite yields ages between 445 and 435 ma which are interpreted to record post uhp exhumation of the diamond bearing rocks the new discovery of microdiamond on areskutan together with other evidence of ultrahigh pressure metamorphism uhpm within gneisses eclogites and peridotites elsewhere in the snc provide compelling arguments for regional at least 200 km along strike of the unit uhpm of substantial parts of this far travelled allochthon the occurrence of uhpm in both rheologically weak gneisses and strong lithologies eclogites peridotites speaks against the presence of large tectonic overpressure during metamorphism

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

tectonics of the scandian orogeny and the western gneiss region in southern norway two crust forming events dominate the precambrian history of the western gneiss region wgr at about 1800 1600 ma and 1550 1400 ma the influence of the sveconorwegian orogeny 1200 900 ma is restricted to the region south of moldefjord romsdalen a series of anorthosites and related intrusives are present possibly derived from the now lost western margin of the baltic craton that may have been emplaced in the wgr as an allochthonous unit before the ordovician

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

pb ages of detrital zircons in relation to geodynamic evolution paleozoic of the northern gemericum western carpathians slovakia abstract new u pb sensitive high resolution ion microprobe shrimp detrital zircon ages from early paleozoic to permian siliciclastic metasediments are used to constrain provenance and paleogeographic affinity of the northern gemericum unit ngu in the western carpathians central europe the samples span the time period from 480 ma to 260 ma and permit the recognition of provenance changes that reflect the realm s geodynamic evolution the detrital zircon age spectrum of one early paleozoic sample resembles the neoproterozoic and archean ages of the cadomian belt 550 650 ma and the west african craton provenances 1 8 2 7 ga the origin of the early paleozoic ngu rakovec basin is inferred to be the rifting as followed by back arc spreading which occurred at the cambrian ordovician boundary ca 480 ma as continental pieces started to split off from the gondwanan margin the deformation and closure of the early paleozoic basin is coincident with the 355 ma peak of the post tournaisian detrital zircon age assemblage the detrital zircon age spectra of two post mississippian and two post artinskian samples indicate high exhumation and erosion rates in the variscan collision belt pennsylvanian permian sedimentary troughs formed between 318 and 275 ma record contemporaneous unroofing of the variscan collision belt and magmatic activity during post orogenic transtensional tectonics zircon age spectra reflect these three paleozoic 480 419 ma 340 380 ma 320 275 ma tectono thermal events and permit the recognition of provenances both of which supporting the interpreted changes in geotectonic regime from ordovician rifting to variscan compression and the subsequent extension the zircon age data constrain the provenance linkage of the low grade ngu basement to the cadomian fragments within the west european variscides

petrological and kar and40ar39ar age constraints for the tectonothermal evolution of the high pressure meliata unit western carpathians slovakia abstract the meliata high pressure unit exposed in the southern part of the western carpathians consists of four groups of rocks which are characterized by different lithologies and metamorphic histories 1 the most common are triassic marbles intercalated with metabasalts and glaucophane bearing phyllites phengite from metabasalts and phyllites record k ar and40ar 39ar plateau ages of 152 155 ma which are interpreted to date the high pressure metamorphism 2 blueschist facies mafic rocks and subordinate glaucophane bearing micaschists devoid of marbles which contain relic low si muscovite and newly formed high si phengite the40ar 39ar data obtained for the micas indicate palaeozoic ages of 375 380 ma for the early amphibolite facies muscovite and a 250 ma age for the secondary blueschist facies phengite 3 glaucophane free phyllites and phengite quartzite with low si and high si micas respectively textural features indicate a polyphase evolution characterized by a greenschist facies metamorphism followed by a blueschist facies overprint the high si micas provide evidence for an early middle jurassic age 172 ma of the high pressure metamorphism 4 amphibolite facies slices and blocks overprinted by blueschist facies metamorphism represent old basement rocks regarding the differences in lithologies metamorphic conditions and radiometric ages of high pressure micas older age for continental vs younger age for oceanic rocks subduction of a continental wedge prior to that of oceanic crust can be assumed this interpretation is based also on palaeogeographical reconstruction of the mesozoic western tethys between the apulian promontory and the tisza bihor continental block

the laidlaw volcanics a late silurian point on the geological time scale mapping mineralogical and chemical studies of an area west and northwest of canberra southeastern australia have shownthat the laidlaw volcanics are unique in the region and that their age is tightly controlled stratigraphically as they lie both above and below early ludlow late silurian fossiliferous sediments k ar mineral analyses previously published rb sr mineral analyses and new rb sr wholerock and mineral analyses together give the laidlaw volcanics an age of 420 7 2 2 m y this result for the early ludlow is identical numerically with a recently published age of 421 3 m y for the ashgillian late ordovician stockdale rhyolite and suggests either that the time interval between the ashgill and ludlow does not exceed a few million yearsor that the age estimate for the stockdale rhyolite is too young

the evolution of the meliata hallstatt ocean and its significance for the early evolution of the eastern alps and western carpathians abstract the evolution of the meliata hallstatt ocean and of its southern and northern margin in the inner western carpathians are described the main rifting began during the pelsonian and the sea floor spreading ended at the beginning of the middle carnian contemporaneously with the raibl event the subduction began in the latest triassic and the final closing of the ocean accompanied by uplift of the adjacent marginal areas was dated as basal oxfordian remnants of the oceanic suboceanic sequence occur in two tectonic positions 1 obducted nappes that contain mostly as tectonic melanges the whole middle triassic to middle jurassic sequence including large bodies of dismembered ophiolites of ladinian to early carnian age 2 evaporite melanges at the base of nappes that are derived from the northern margin of the ocean these evaporite melanges consist of late permian evaporitic matrix and blocks of a dismembered ladinian to lower carnian ophiolitic sequence in the inner western carpathians both the northern and southern marginal sequences of the meliata hallstatt ocean and the transitions into the carbonate platforms are present in different nappes the southern marginal development is characterized by middle carnian distal clastic raibl beds and by middle jurassic rhyolithic volcanism both missing in the northern marginal development because the subduction related middle jurassic volcanism contemporaneous with the turbidites in the southern meliaticum is restricted to the marginal area south of the meliata hallstatt ocean southward directed subduction is indicated to the south on the adjacent carbonate platform a jurassic basin with aalenian to bajocian ophiolites opened this may be a back arc basin in the eastern alps only the northern marginal zone and the adjacent carbonate platform are preserved but parts of the dismembered ophiolites in the haselgebirge may be of ladinian to late carnian age like in evaporitic melanges in the same tectonic position in the inner western carpathians the final closing of the meliata hallstatt ocean is indicated by the abrupt end of the turbiditic sedimentntation in the oceanic suboceanic domain and by uplift in the marginal areas where lower oxfordian radiolarites are overlain by shallow water upper oxfordian to tithonian or neocomian limestones silica nappe hallstatt nappes with the evidence of the final closing of the meliata hallstatt ocean near the middle late jurassic boundary the cimmerian orogenesis in the genetic sense of engor 1984 1985 is now also proven in the inner western carpathians and in the eastern alps a continuation of the meliata hallstatt ocean into the pontide paleotethys cimmerian ocean sensu kozur 1990 through the transylbanian oceanic domain and the strandzha unit is assumed a connecction with the vardar ocean is impossible because in the vardar zone no triassic ophiolites or basic volcanics are present and the ophiolites have jurassic age

p t paths in the handl area central scandinavia record of caledonian accretion of outboard rocks to the baltoscandian margin the seve koli nappe complex is widespread in the scandinavian caledonides and is composed of units representing parts of the baltoscandian margin seve nappes now overlain by magmatic sedimentary rocks koli nappes derived from west of this margin the metamorphic evolution of koli and seve units has been studied in the handol area central scandinavian caledonides where a fragmented ophiolite with cover sequence in the lower koli units is thrust over the higher grade seve units thermobarometry constrains metamorphic conditions to 490 570 c 950 600 mpa with a slight downwards increase in grade for the lower koli bunnerviken lens 520 620 c 1000 600 mpa for the upper seve taljstensvalen complex 630 740 c 750 650 mpa for the middle seve snasahogarna nappe and 480 600 c 1150 1000 mpa for the lower seve blahammarfjallet nappe p t paths during garnet growth have been constructed for all units except the highest grade middle seve these paths record heating at the base of the koli and cooling in the underlying seve units pressure increase during garnet growth is indicated for all units leading to anticlockwise p t paths in the seve the results imply thermal convergence with time for all units and spatial convergence in metamorphic grade in the koli it is suggested that the contrasting metamorphic histories on either side of the seve koli boundary resulted from the emplacement of relatively colder koli rocks on top of relatively hotter seve rocks and that emplacement of structurally higher units contributed to the increase in pressure

the influence of si b substitution and of the nature of network modifying cations on the properties and structure of borosilicate glasses and melts abstract the influence of the si b substitution and of the nature of network modifying cations on viscosities and heat capacities of ternary borosilicate melts has been investigated for two series of melts containing either 20 mol na 2 o or 33 mol bao the measurements have been made near the glass transition and above the liquidus for viscosities and from 300 to 1073 k for heat capacities they have been used to determine the configurational entropies of the melts from adam and gibbs theory of relaxation processes to complete these observations the room temperature raman spectra of the glasses have also been recorded the observed increase in the configurational heat capacity of melts with b 2 o 3 content indicates the existence of strong temperature induced structural changes induced by the presence of boron correlatively the viscosity variations with composition can be related to the existence of distinct coordination environments for boron as for the effects of barium and sodium they are similar in silicate and borosilicate melts and depend mainly on the field strength of the cation

mesozoic plate tectonic reconstruction of the carpathian region abstract palaeomagnetic palaeobiogeographic and structural comparisons of different parts of the alpine carpathian region suggest that four terranes comprise this area the alcapa tisza dacia and adria terranes these terranes are composed of different mesozoic continental and oceanic fragments that were each assembled during a complex late jurassic cretaceous palaeogene history palaeomagnetic and tectonic data suggest that the carpathians are built up by two major oroclinal bends the alcapa bend has the meliata oceanic unit correlated with the dinaric vardar ophiolite in its core it is composed of the western carpathians eastern alps and southern alcapa units transdanubian range bukk this terrane finds its continuation in the high karst margin of the dinarides further elements of the alcapa terrane are thought to be derived from collided microcontinents czorsztyn in the n and a carbonate unit tisza in the se the tisza dacia bend has the vardar oceanic unit in its core it is composed of the bihor and getic microcontinents this terrane finds its continuation in the serbo macedonian massif of the balkans the bihor getic microcontinent originally laid east of the western carpathians and filled the present carpathian embayment in the late palaeozoic early mesozoic the vardar ocean occupied an intermediate position between the western carpathian austroalpine transdanubian high karst margin and the bihor getic serbo macedonian microcontinent the vardar and pindos oceans were opened in the heart of the mediterranean adriatic microcontinent in the late permian middle triassic vardar subducted by the end of jurassic causing the bihor getic serbo macedonian microcontinent to collide with the internal dinaric western carpathian margin an external penninic vahic ocean tract began opening in the early jurassic separating the austroalpine western carpathian microcontinent and its fauna from the european shelf further east the severin ceahlau magura also began opening in the early jurassic but final separation of the bihor getic ribbon and its fauna from the european shelf did not take place until the late middle jurassic the alcapa and the tisza dacia were bending during the albian maastrichtian the two oroclinal bends were finally opposed and pushed into the gates of the carpathian embayment during the palaeogene and neogene at that time the main n s shortening in distant alpine and hellenic sectors was linked by a broader right lateral shear zone along the former vardar suture

devonian mississippian i type granitoids in the western carpathians a subduction related hybrid magmatism abstract sims zircon u pb dating of i type granitoids from four variscan crystalline basement outcrops in the western carpathians tribec nizke tatry cierna hora and slovenske rudohorie mts implies that they originated between 367 and 353 ma therefore they belong to the earliest variscan i type granitoids the oldest devonian age at ca 367 364 ma is obtained from an enclave bearing tonalite and associated dikes of the tribec mts several granodiorites from the nizke tatry vepor and cierna hora mts 353 357 ma show younger early carboniferous ages these data require a re assessment of older models that explained the genesis of i type granitoids in the western carpathians based on the assumption of younger middle to upper carboniferous ages the i type granite massifs of the western carpathians most probably originated in an arc related environment within the galatian superterrane an assemblage of gondwana derived fragments the early age of i type magmatism in the western carpathians marks the beginning of a north dipping subduction of the paleotethys ocean under ibero ligerian and intra alpine terranes we suggest a term proto tatricum for that part of the galatian superterrane where devonian mississippian i type granitoids were emplaced now the granitoids are incorporated as a part of crystalline basement into the alpine tatric and veporic units within present west carpathian mountain chain

the influence of composition on the local structure around yttrium in quenched silicate melts insights from exafs abstract the structural environment around y in silicate and aluminosilicate glasses containing 5000 ppm y was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy the used glass compositions were taken from prowatke and klemme 2005 varying in the aluminum saturation index asi molar ratio of al 2 o 3 na 2 o k 2 o cao from 0 115 to 0 768 furthermore a set of glass compositions from the system cao al 2 o 3 sio 2 cas was used for which structural data from computer simulations are available haigis et al 2013 this issue structural parameters of the y o pair correlation of the first coordination shell were determined from the exafs based on a gamma like distribution function that accounts for the large static disorder and non gaussian pair distributions the analysis shows an increase in the coordination number from 6 to 8 along with an increase of the average y o distance by 0 13 a for the composition of prowatke and klemme 2005 for the cas composition an increase of the coordination number from 6 to 7 along with an increase of the average y o distance by 0 06 a is obtained the change of these parameters is associated with a considerable increase in the asymmetry and width of the y o pair distribution due to its size and charge 6 fold coordinated y will preferentially bond to non bridging oxygens of the polymeric melt network to form a stable configuration as is the case for the less polymerized melts with low asi in highly polymerized melts with asi values close to one 6 fold coordination of y is not possible because almost only bridging oxygens are available consequently over bonding of bridging oxygens around y is counterbalanced by an increase of coordination number and y o distance to satisfy local charge balance requirements

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

noble gas and halogen evidence for the origin of scandinavian sandstone hosted pb zn deposits abstract fluid origins in the sandstone hosted pb zn class of ore deposit have been investigated in three deposits from scandinavia laisvall vassbo and osen the deposits studied are hosted by autochthonous cambrian sandstones that preserve a near original structural relationship to the underlying precambrian basement enabling the role of basement interaction to be assessed mineral samples have been collected from across the paragenetic sequence sphalerite galena pyrite fluorite and barite of impregnation and related joint hosted mineralization fluid inclusion halogen cl br and i and noble gas isotope 40 ar 36 ar 84 kr compositions were determined simultaneously by noble gas mass spectrometry of irradiated sample splits complementary he isotope analyses are obtained from nonirradiated splits of the same samples 3 he 4 he values at laisvall and osen are highly radiogenic 0 02 ra and the 4 he 40 ar ratio extends to values greater than the crustal production value of 5 characteristic of low temperature crustal fluids at vassbo a slightly elevated 3 he 4 he ratio of 0 1 0 3 ra is compatible with a very minor mantle component 1 4 suggesting a distal source for the basinal brine dominated fluid br cl molar ratios 3 2 8 2 10 3 are greater than the present seawater value of 1 54 10 3 and correspond with i cl molar ratios in the range 64 1600 10 6 the upper limits of both the i cl and br cl values are amongst the highest measured in crustal fluids together the data indicate acquisition of salinity by the evaporation of seawater beyond the point of halite saturation and subsequent fluid interaction with i rich organic matter in the subsurface the data are compatible with the independent transport of sulfate and sulfide and indicate that fluids responsible for joint hosted mineralization were distinct to those responsible for impregnation mineralization all three deposits preserve fluids with 40 ar 36 ar in the range of 6 000 10 000 and fluid inclusion 40 ar concentrations of 0 02 0 05 cm 3 cm 3 fluid inclusion 4 he concentrations are also extremely elevated with maximum values of 0 1 cm 3 cm 3 in laisvall fluorite and sphalerite the high 40 ar 36 ar values together with the high 4 he and 40 ar concentrations result from a very long premineralization crustal residence time on the order of 100 200 ma together the noble gas and halogen data are compatible with a caledonian mineralization event 425 ma caused by mixing of two or more long lived hydrothermal basinal brines and pore fluids at the sites of mineralization the data suggest negligible recharge of the basinal brines by meteoric water and indicate extensive fluid basement interaction before mineralization the similar noble gas composition of each deposit suggests that similar processes operated at all three deposits and favors a single pass fluid flow model for mineralization

protolith ages and exhumation histories of ultra high pressure rocks across the western gneiss region norway the timing of protolith formation ultrahigh pressure uhp subduction and subsequent exhumation for the ultrahigh pressure to high pressure units across the eastern part of the western gneiss region norway were assessed using u pb zircon th pb monazite and 40 ar 39 ar white mica ages u pb zircon ages from eclogites demonstrate that oceanic and continental allochthons were emplaced onto the baltica basement before the entire mass was subducted to ultra high pressure eclogites within the allochthons across the entire western gneiss region are caledonian and show a degree of zircon re crystallization that increases with peak pressure permitting the interpretation that the entire region underwent synchronous subduction 40 ar 39 ar white mica ages of 399 ma indicate that the eastern part of the western gneiss region had been exhumed to shallow crustal levels while uhp metamorphism was ongoing farther west indicating a westward dip to the slab the 40 ar 39 ar white mica ages also show a clear east to west gradient across the entire western gneiss region indicating that the western gneiss region rose diachronously to crustal levels from east to west between 399 and 390 ma

structure and properties of lime alumino borate glasses the aim of our study is to investigate the structural effects of the substitution of aluminum by boron in lime alumino borate glasses in this case a competition between two network formers can be observed it was proven that aluminum can be in four five and six fold coordination in calcium aluminate and aluminosilicate glasses whereas boron can be in three and four fold coordination in borate and borosilicate glasses to understand what happens when boron replaces aluminum different glasses were made starting with ca aluminate glass c12al14o33 i e c12a7 in cement nomenclature and then progressively substituting aluminum by boron until b fully replaces al raman 11b nmr and 27al nmr spectroscopies were used to investigate the structure of these glasses at medium and short range order respectively density dsc measurements were also done in order to characterize properties at a macroscopic scale nmr and raman spectra show that aluminum in ca aluminate glass c12a7 is in four fold coordination more precisely in t3 and t4 species tn indicates aluminum in tetrahedral sites with n bridging oxygens whereas when boron replaces aluminum bo3 are the main species formed in good agreement with the two spectroscopic methods these triangular units break the tetrahedral network already formed by alo4 leading to an important drop of tg as the concentration of boron increases nbos are formed to create bo4 tetrahedral units with the presence of calcium acting as a charge compensator these tetrahedral structures start to increase the polymerization of the network glass transition temperature tg continues to decrease but with a slower decline in this study we will present all these results and discuss the influence of the structure of the network on the macroscopic parameters

40ar 39ar incremental release age of biotite from a gabbro of the shabogamo intrusive suite southwestern labrador biotite from a gabbro sill of the shabogamo intrusive suite in southwestern labrador records a well defined 40ar 39ar plateau age of 1353 17 ma this is similar to the 1375 60 ma dates recorded by sm nd and rb sr whole rock isotopic systems of the suite together recent radiometric results suggest that members of the suite were emplaced at approximately 1375 ma and cooled quickly at shallow crustal levels

40ar 39ar and rb sr age determinations on quaternary volcanic rocks 40 ar 39 ar and rb sr ages have been measured on separated minerals from the potassic volcanics of the roman comagmatic region to test the ability of these methods to accurately data quaternary geological events the very high k and rb contents of the roman magmas present particularly favorable situations in which the very high concentrations of the radioactive nuclides 40 k and 87 rb result in well resolved in situ enrichments of the daughter isotopes despite the very young ages six leucite separates contained ar with very high bulk 40 36 ratios above 1000 and in which the 40 ar and the 39 ar were very well correlated yielding well defined ages averaging 3 38 0 08 10 5 years two leucites contained ar with lower bulk 40 36 ratios 400 and in at least two release steps from these leucites the 40 ar 36 ar ratio was significantly lower than atmospheric despite the uncertainty in the composition of the trapped component these two leucites have ages that do not differ significantly from the ages of the other leucites for the biotites it was not possible to obtain through stepwise degassing a good separation of in situ radiogenic 40 ar from trapped 40 ar and therefore the calculated ages are not as precise as those of the leucites in three cases the biotite age agrees with the age of the cogenetic leucite but in the remaining two cases discordant ages are obtained suggesting caution when using biotites as quaternary age indicators rb sr measurements on leucite biotite and pyroxene separates hand picked from each of three tuff samples yielded a dispersion in 87 sr 86 sr as large as 16 parts in 10 4 and 87 rb 86 sr as high as 218 for leucites and permitted the determination of internal isochron ages the ages obtained range from 3 8 0 2 10 5 to 3 3 0 2 10 5 years and are in good agreement with the 40 ar 39 ar ages on the leucites the data for each tuff sample yield a well defined uniform initial 87 sr 86 sr however different tuffs show small differences in initial 87 sr 86 sr pointing to distinct sources or to assimilation of different materials during the extrusion of the tuffs these measurements demonstrate the possibility of dating quaternary materials by both the 40 ar 39 ar method and the rb sr method the observation of concordant ages with a precision of a few percent represents a powerful tool in quaternary stratigraphy

early palaeozoic tectonothermal events in basement complexes of the eastern greywacke zone eastern alps evidence from u pb zircon data field observations and u pb zircon data yield evidence that the kaintaleck complex represents a distinct crystalline basement unit of the eastern greywacke zone and contrasts partly with other pre alpine basement complexes of the eastern alps the age data indicate possible late archean rock formation several magmatic and metamorphic events in the early palaeozoic ca 520 490 and ca 400 360 ma and low grade metamorphic overprint in the cretaceous zircons from a garnet gneiss layer in a plagioclase gneiss and amphibolite sequence yield an upper intercept age of ca 2 55 ga which is interpreted as a possible protolith age the lower intercept age at 514 ma represents either 1 a magmatic event or 2 a metamorphic overprint within amphibolite facies conditions magmatic zircons derived from granitic orthogneiss boulders of the kalwang conglomerate which covers the crystalline basement crystallised at ca 500 ma the lower discordia intercepts of the orthogneiss boulders mark the cretaceous low grade metamorphic overprint the lower intercept age of paragneiss zircons from another slice of the kaintaleck complex suggests a likely devonian metamorphic event at ca 390 400 ma the new data demonstrate that the kaintaleck complex experienced several stages of tectonothermal evolutions which are in contrast to the evolution of the main mass of the austroalpine basement the data constrain linkages of this part of the austroalpine basement to the cordillere ligerienne and cadomian block within west european variscides

pre variscan geological events in the austrian part of the bohemian massif deduced from u pb zircon ages in an attempt to elucidate the pre variscan evolution history of the various geological units in the austrian part of the bohemian massif we have analysed zircons from 12 rocks mainly orthogneisses by means of shrimp conventional multi grain and single grain u pb isotope dilution mass spectrometry two of the orthogneisses studied represent cadomian metagranitoids that formed at ca 610 ma spitz gneiss and ca 580 ma bittesch gneiss a metagranite from the thaya batholith also gave a cadomian zircon age 567 5 ma traces of neoproterozoic zircon growth were also identified in several other samples underlining the great importance of the cadomian orogeny for the evolution of crust in the southern bohemian massif however important magmatic events also occurred in the early palaeozoic a sample of the gfohl gneiss was recognised as a 488 6 ma old granite a tonalite gneiss from the realm of the south bohemian batholith was dated at 456 3 ma and zircon cores in a moldanubian metagranitic granulite gave similar ages of 440 450 ma this ordovician phase of magmatism in the moldanubian unit is tentatively interpreted as related to the rifting and drift of south armorica from the african gondwana margin the oldest inherited zircons in a migmatite from the south bohemian batholith yielded an age of ca 2 6 ga and many zircon cores in both moravian and moldanubian meta granitoid rocks gave ages around 2 0 ga however rocks from the moldanubian unit show a striking lack of zircon ages between 1 8 and 1 0 ga reflecting an ancestry from armorica and the north african part of gondwana respectively whereas the moravian bittesch gneiss contains many inherited zircons with mesoproterozoic and early palaeoproterozoic ages of ca 1 2 1 5 and 1 65 1 8 ga indicating a derivation from the south american part of gondwana

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

structure of type a cai like melts a view from multi nuclear nmr study of melilite ca2al2sio7 ca2mgsi2o7 glasses abstract exploring the polymerization and structural disorder of ca al rich inclusion cai like melts is a key question in cosmochemistry due to strong implications for macroscopic properties of melts i e viscosity and diffusivity here we report experimental results showing the effect of composition on the structure of melilite glasses and melts akermanite ak ca2mgsi2o7 gehlenite gh ca2al2sio7 in type a cais with varying composition using high resolution solid state nuclear magnetic resonance nmr the 27al magic angle spinning mas and 3q triple quantum mas nmr spectra of melilite glasses show predominant 4 al a non negligible fraction of 5 al is observed in ak50gh50 and ak72gh28 glasses and it slightly increases with increasing akermanite content the 17o 3qmas nmr spectra of melilite glasses show that bridging oxygens bos si o si al o al and si o al and non bridging oxygens nbos ca o si ca o al and mixed ca mg nbo are partially resolved despite the strong preference of si over al for nbos for the first time ca o al is observed in natural melts i e gehlenite and ak25gh75 glasses and melts the results show that al nbo 150 ppm in mas dimension can be distinguished from si nbo 110 ppm in melilite glasses and melts the fraction of nbo increases with increasing akermanite content the experimental results suggest that composition induced structural changes should be considered to interpret the melt viscosity diffusivity and oxygen isotopic composition of cai like melts in the early solar system

recognition of extraneous argon components through incremental release 40ar39ar analysis of biotite and hornblende across the grenvillian metamorphic gradient in southwestern labrador 40ar39ar incremental release ages have been determined for 15 hornblende and 20 biotite concentrates separated from rocks collected across the garnet and kyanite zones of grenvillian metamorphism in southwestern labrador most hornblende spectra from the kyanite zone are slightly discordant with low temperature increments yielding ages older than the ca 1000 ma date suggested for culmination of grenvillian metamorphism in the area however all the hornblende concentrates record well defined plateau ages these range from 968 to 905 ma across the kyanite zone and date times of diachronous post metamorphic cooling the discordant spectra are interpreted to result from low temperature liberation of excess 40ar components from grain margins two hornblende concentrates from the garnet zone display very discordant spectra total gas ages of 2100 and 3017 ma in which incremental dates systematically decrease during analysis this pattern of discordance suggests that excess argon components are inhomogeneously distributed throughout these hornblende grains most biotites from the garnet and kyanite zones record total gas or plateau ages in excess of 1000 ma 2066 857 ma reflecting the widespread presence of excess argon components because most of the 40ar39ar age spectra are internally concordant the ratios of excess 40ar relative to radiogenic 40ar must have been uniform in the various gas fractions liberated from each sample this is also reflected in the inability of isotope correlation diagrams to differentiate between excess radiogenic and atmospheric argon components the biotite total gas or plateau dates show marked local variation this is interpreted to indicate that the biotite grains were in contact with a post metamorphic intergranular vapor phase that was characterized by large and variable 40ar36ar ratios such ratios most likely resulted from widespread diffusion of the argon liberated from adjacent archean basement gneisses during the grenvillian metamorphic overprint

raman spectra and structure of baosio2 srosio2 and caosio2 melts to 1600 c abstract raman spectra were collected for barium silicate strontium silicate and calcium silicate melts at temperatures ranging from the glass transition region to temperatures as high as 1600 c for melts less polymerized than disilicate the spectra were used to determine the relative abundances of the q3 q2 and q1 tetrahedra and the si2o52 sio32 and si2o76 structural units in the melts a concentration constant was computed for the reaction 4 sio 2 3 sio 2 5 si 2 o 6 7 and was found to vary with composition from approximately log10kc 0 5 for barium silicate melts with nbo si 1 143 to log10kc 1 75 for calcium metasilicate melts with nbo si 2 little difference was found to exist in the structural behavior of the melts on the three alkaline earth silicate binary joins activity coefficients were computed for the sio2 3 structural unit as a function of bulk composition the logarithm of the activity coefficients and mole fraction of the structural unit are linearly correlated

phase petrology and p t conditions of mafic blueschists from the meliata unit west carpathians slovakia blueschists occurring as layers in calcite marbles of the meliata unit occur along the so called roznava tectonic line situated in the southern part of the gemericum slovakia mineral assemblages and compositions from seven blueschists localities and one occurrence of amphibolite facies rocks overprinted by blueschist metamorphism were investigated the most common minerals in the blueschists are blue amphibole epidote and albite some fe2 and al rich rocks also contain garnet and chloritoid respectively na pyroxene with a maximum 50 jadeite component was also found the blue amphiboles correspond mostly to crossite and also to glaucophane and ferroglaucophane in some samples almandine and spessartine rich garnet has very low mgo content 3 wt the si content in phengite ranges between 3 3 and 3 5 pfu calculated on the basis of 11 oxygens the zoning patterns of blue amphibole garnet and chloritoid suggest their formation during a prograde stage of metamorphism the p t conditions of metamorphism are estimated to be about 380 460 c and 10 13 kbar pressures of 7 5 8 5 kbar and temperatures of 350 370 c were obtained for some actinolite and aegirine rich rocks apart from chlorite other mafic minerals formed during retrograde metamorphism are biotite and occasionally also actinolite

40ar 39ar incremental release ages of biotite from a progressively remetamorphosed archean basement terrane in southwestern labrador abstract gneisses within an archean basement terrane adjacent to the southwestern portion of the labrador trough were variably retrograded during a regional metamorphism of grenville age ca 1000 ma biotites from non retrograded segments of the gneiss terrane record 40 ar 39 ar plateau and isochron ages which date times of cooling following an episode of the kenoran orogeny 2376 2391 ma a suite of gneiss samples displaying varying degrees of retrograde alteration was collected across the grenville metamorphic gradient biotites in these samples show no petrographic evidence of retrograde alteration however they do record internally discordant 40 ar 39 ar age spectra although the extent of internal discordance is variable the overall character of the release patterns is similar with younger apparent ages recorded in intermediate temperature gas fractions the total gas dates range from 2257 27 ma northwest to 1751 23 ma southeast suggesting that variable quantities of radiogenic argon were lost from the archean biotites during grenville metamorphism the saddle shaped nature of the discordant spectra indicates that argon loss was not accomplished through single stage volume diffusion processes biotites in portions of the gneiss terrane which were completely recrystallized during grenville metamorphism are petrographically and texturally distinct a representative of this phase records a 40 ar 39 ar plateau age of 2674 28 ma this date is markedly inconsistent with regional constraints on the timing of grenville metamorphism and indicates the presence of extraneous argon components both the extraneous and radiogenic argon components must have been liberated in constant proportions during experimental heating because the argon isotopic data yield a well defined 40 ar 36 ar vs 39 ar 36 ar isochron corresponding to an age 2658 23 ma similar to that defined by the plateau portion of the spectrum the 40 ar 39 ar biotite dates suggest that the effects of grenville metamorphism extent 15 20 km northward into the superior province the limit of this overprint is approximately coincident with the northernmost development of grenville age thrust faults in the archean terrane therefore it is proposed that the northern margin of the grenville province in southwestern labrador should be located along the northernmost grenville thrust fault because this represents both a structural and a thermal discontinuity

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less

al and sr environment in tectosilicate glasses and melts viscosity raman and nmr investigation structure and properties of sro al 2 o 3 sio 2 glasses and melts were investigated along the tectosilicate join sro al 2 o 3 1 varying the amount of silica the structure of the glasses was studied by means of various spectroscopic techniques raman 27 al nmr and xas at the sr k edge raman spectroscopy revealed that the fraction of high membered tetrahedral rings diminishes upon substitution of sio 2 by sral 2 o 4 favouring the formation of low membered rings sr k edge xanes shows that the strontium coordination number is around 9 based on the spectrum similarity with the one obtained for crystalline strontianite 27 al nmr spectroscopy indicates the presence of four and five coordinated aluminium the latter being found in small quantities 5 i e smaller than for analogous mg and ca based aluminosilicate glasses a minimum in t g is found when the alo 5 content is maximum both in sr and ca aluminosilicates this fact indicates the importance of minor species such as five fold aluminium in activating viscous flow similarly to what has been proposed for five fold silicon by farnan and stebbins 1994 increase of t g at low silica content was correlated to a decrease in alo 5 content as well as to a decrease of a number of different structural units and as a consequence an ordering of the system

the middle to late devonian hoybakken detachment central norway 40ar 39ar evidence for prolonged late post scandian extension and uplift the regionally significant 0 5 2 km thick hoybakken detachment in central norway bounds the southern margin of the central norway basement window and exhibits a well developed top to the wsw fabric characteristic of late scandian devonian ductile extension 40 ar 39 ar data obtained from hornblende mica and k feldspar mineral separates of rocks collected in a transect through the hoybakken detachment yield well defined plateau and isochron mineral ages early devonian exhumation and cooling of the hoybakken detachment footwall is recorded by hornblende ages of 400 ma and mica ages of 390 ma the mylonitic fabric overlying the footwall records younger middle devonian mica crystallization ages of 384 381 ma that are among the youngest extensional ductile fabrics dated in the caledonides and suggest prolonged extensional activity on the hoybakken detachment after inferred cessation of ductile extension at 381 ma the rate of uplift and cooling was reduced and the footwall records late devonian to early carboniferous k feldspar ages of 371 356 ma prolonged extensional activity at hoybakken is compatible with recent u pb ages of deformed titanite crystals and established rb sr ages of white mica in shear related pegmatites both from the southwestern part of the fosen peninsula and 40 ar 39 ar ages of syn tectonic mica overgrowth from the adjacent hitra snasa fault together these ages suggest the onset of ductile extension soon after 401 ma and with the middle devonian crystallization ages determined here suggest that ductile extension on the hoybakken detachment had a duration of 11 20 ma the youngest age of 320 ma was obtained from a k feldspar in a cataclastic granite of the hoybakken detachment s hangingwall and is considered to date a phase of post scandian brittle deformation that overprinted the mylonitic shear fabric

geochronology of the swift current granite and host volcanic rocks of the love cove group southwestern avalon zone newfoundland evidence of a late proterozoic volcanic subvolcanic association zircon fractions from the variably deformed and metamorphosed swift current granite and host volcanic rocks of the love cove group record individually discordant u pb ages with well defined upper c

early ordovician u pb metamorphic ages of the eclogite bearing seve nappes northern scandinavian caledonides eclogite grade metamorphism of the seve nappe complex snc in norrbotten sweden records the attempted subduction of the baltic continental margin during the early palaeozoic evolution of the iapetus ocean metamorphic titanite sampled from several calcsilicate gneisses of the snc in norrbotten occurs as part of a prograde eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant u pb ages of 500 475 ma later structural disruption of these rocks occurred during the siluro devonian scandian phase of the caledonide orogeny but the u pb systematics show no evidence of a second generation metamorphic or recrystallized of titanite or of post early ordovician disturbance through pb loss hence the u pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the snc these results support earlier sm nd and 40ar 39ar studies indicating an early ordovician metamorphic age for the eclogitic norrbotten snc and confirm the early ordovician destruction of at least this segment of the palaeozoic passive margin of baltica these results indicate that the snc in the northern scandinavian caledonides was subducted and metamorphosed to high grade some 50 70 myr prior to the high grade metamorphism of the snc in the central scandinavian caledonides this result requires significantly different early palaeozoic tectonic histories for rocks mapped as snc in the northern caledonides and those in the central caledonides despite a seemingly similar tectonostratigraphic position and broadly similar high grade metamorphism

early permian pangea b to late permian pangea a the pre drift wegenerian model of pangea is almost universally accepted but debate exists on its pre jurassic configuration since tedirving introd ucedpangea b by placing gond wana farther to the east by v3000 km with respect to laurasia on the basis of paleomagnetic data new paleomagnetic data from radiometrically dated early permian volcanic rocks from parts of adria that are tectonically coherent with africa gondwana integrated with published coeval data from gondwana and laurasia again only from igneous rocks fully support a pangea b configuration in the early permian the use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for pangea b the ultimate option to reject pangea b is to abandon the geocentric axial dipole hypothesis by introducing a significant non dipole zonal octupole component in the late paleozoic time averaged geomagnetic field we demonstrate however by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from gondwana as well as laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for pangea b in the early permian we therefore regard the paleomagnetic evidence for an early permian pangea b as robust the transformation from pangea b to pangea a took place during the permian because late permian paleomagnetic data allow a pangea a configuration we therefore review geological evidence from the literature in support of an intra pangea dextral megashear system the transformation occurred after the cooling of the variscan mega suture andlasted v20 myr in this interval the neotethys ocean opened between india arabia and the cimmerian microcontinents in the east while widespread lithospheric wrenching and magmatism took place in the west around the adriatic promontory the general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right lateral shear couple between gondwana and laurasia during the permian transcurrent plate boundaries associated with the pangea transformation reactivated variscan shear zones andwere subsequently exploitedby the opening of western neotethyan seaways in the jurassic

40ar 39ar dating of the inner carpathians variscan basement and alpine mylonitic overprinting abstract the 40ar 39ar dating method has been applied to mylonitic rocks from the carpathian mountains these are variscan metamorphic and magmatic rocks that were overprinted during the alpine orogeny the inner western carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike slip and normal faulting resulting in the formation of mylonitic rocks precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of alpine events such as the pre gosauian phase during the turonian 90 ma the 40ar 39ar method allows to define the age of the ancient variscan basement and the ages of the alpine overprinting in the high and low tatras mineral ages of around 340 350 ma are yielded by gneisses micaschists and amphibolites providing a younger limit for the variscan metamorphism the emplacement cooling of the variscan granites is defined between 305 and 335 ma these rocks are overprinted by several alpine tectonothermal events the major events are dated at 65 and 86 88 ma during which the mylonites were generated an older event around 140 ma earlier defined by the rb sr method is now confirmed by the 40ar 39ar method dating of phengites extracted from high pressure metamorphic triassic rocks from the kosice area yields new data for the age of this event at 155 ma