precambrian ophiolites cambrian island arc and variscan suture in the south carpathian balkan region a late proterozoic ophiolite in the south carpathian balkan region has a total surface outcrop area of 400 km 2 it is a complete ophiolitic section that includes mid ocean ridge basalts indicating that it was formed in a large ocean the oceanic crust is unconformably overlain by an ensimatic island arc of cambrian age the ophiolite island arc assemblage was obducted over the moesian platform during early ordovician time both sequences are now incorporated in a continental block as a result of intracontinental convergence which took place in variscan time the ophiolite is situated along the thracian suture which divides the moesian platform and the thracian continental fragment this suture is part of a larger one referred to as the south european suture that is situated between the thracian massif and the adriatic plate to the southwest and the moesian platform bohemian and central french massif to the northeast

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

evolution of the eclogites in the rhodope zone of northern greece abstract the polymetamorphic complex of rhodope in the southern balkan peninsula has been affected by three successive metamorphic episodes these are 1 a high pressure 2 a barrow type and 3 a greenschist facies retrograde metamorphic episode based on the different metamorphic grades of the barrovian metamorphism the rhodope zone can be subdivided into two tectonic units a lower and an upper one commonly amphibolitised eclogites of probable mesozoic age occur in both units a in the shape of lenses b as concordant interbeds with other rock types such as gneisses and marbles and c as metagabbroic dykes the high pressure mineral assemblage is garnet omphacite quartz ca amphibole clinozoisite zoisite rutile kyanite in eclogites of gabbroic origin igneous relics such as igneous plagioclase augite and ilmenite are sometimes preserved pt conditions of 14 kbar and 550 600 c were determined for the high pressure metamorphism in the lower tectonic unit symplectites of clinopyroxene plagioclase ca amphibole plagioclase biotite plagioclase and spinel plagioclase are common and are attributed to post eclogitic reactions during uplift changes in mineral composition of high pressure phases such as garnet ca amphibole and na pyroxene reflect a re equilibration tendency during unloading

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

the lunar wide effects of basin ejecta distribution on the early megaregolith the lunar surface is marked by at least 43 large and ancient impact basins each of which ejected a large amount of material that modified the areas surrounding each basin we present an analysis of the effects of basin formation on the entire lunar surface using a previously defined basin ejecta model our modeling includes several simplifying assumptions in order to quantify two aspects of basin formation across the entire lunar surface 1 the cumulative amount of material distributed across the surface and 2 the depth to which that basin material created a well mixed megaregolith we find that the asymmetric distribution of large basins across the moon creates a considerable nearside farside dichotomy in both the cumulative amount of basin ejecta and the depth of the megaregolith basins significantly modified a large portion of the nearside while the farside experienced relatively small degrees of basin modification following the formation of the large south pole aitken basin the regions of the moon with differing degrees of modification by basins correspond to regions thought to contain geochemical signatures remnant of early lunar crustal processes indicating that the degree of basin modification of the surface directly influenced the distribution of the geochemical terranes observed today additionally the modification of the lunar surface by basins suggests that the provenance of lunar highland samples currently in research collections is not representative of the entire lunar crust identifying locations on the lunar surface with unique modification histories will aid in selecting locations for future sample collection

rapid burial and exhumation during orogeny thickening and synconvergent exhumation of thermally weakened and thinned crust variscan orogen in western europe we present a model demonstrating that the presence of a thinned and thermally weakened crustal domain is a prerequisite for the formation of an orogenic root in mountain belts furthermore this mechanism permits burial to 50 to 70 km in time periods of less than 20 myr and exhumation from these depths in less than 10 myr our example from the variscan belt is based on field geology petrology of metamorphic rocks and detailed geochronology it describes an evolution from i sedimentation and magmatism during back arc extension ii compression leading to burial thickening of the lithosphere and granulite facies metamorphism followed by iii exhumation formation of dehydration melts migmatites and late intrusive granites the existing u pb ar ar data constrain this evolution to no more than 20 to 25 myr thermorheological modelling starts from a hot thinned crust forming a narrow 50 km wide orogenic root within 15 myr at a maximum of 50 km depth and subsequent exhumation by extrusion within 7 myr the model explains exhumation rates of 3 to 4 mm year by compressional extrusion and shows that extension cannot do the same job within the same time extrusion transported the internal thermal structure into the upper crust within a short time followed by rapid cooling whereas exhumation through extension would cause mantle upwelling and the formation of a long lived thermal anomaly the latter would contradict the geochronological and petrological database the model explains orogeny as a thermorheological process without needing to involve an external heat source from the mantle and presents a new explanation of the high temperature and low pressure conditions very typical of the variscan orogenic crust

the longevity of lunar volcanism implications of thermal evolution calculations with 2d and 3d mantle convection models abstract lunar volcanism as is generally accepted started well before the emplacement of the mare fill at 3 1 3 9 ga b p and likely extended well into the eratosthenian 3 1 1 1 ga b p the early volcanism is relatively easily understood the extension of the activity to possibly 1 5 ga b p albeit at a decreasing rate poses a problem since a relatively small body such as the moon may be expected to cool rapidly and freeze a partially molten mantle layer quickly we present thermal history models in which a region of partial melt forms in the mantle underneath the lithosphere almost immediately after the start of the model at depths between 300 and 700 km depending on the chosen initial depth of the magma ocean to calculate the thermal histories we use axisymmetric 2d and fully 3d spherical shell convection codes with viscosity depending on the azimuthally averaged temperature the thermal evolution of the moon is found to be characterized by the growth of a massive 700 to 800 km thick lithosphere while the lower mantle and core cool only by 100 200 k the partial melt zone decreases in thickness with time from top to bottom until it vanishes at times between 3 4 and 2 2 ga b p the maximum degree of partial melting is between roughly 10 and 20 the partial melt layer is initially global and is disrupted by cold downwellings as cooling proceeds the melt zone freezes from above due to the thickening of the lithosphere which implies that the source region of volcanic rock proceeds to increasing depth with time this corresponds nicely with the variation of titanium with age of lunar mare basalts mixing of the melt zone with the underlying mantle chemically rejuvenates the melt zone to some degree and thus the source region of the mare basalts

major lunar crustal terranes surface expressions and crust mantle origins in light of global remotely sensed data the igneous crust of the moon can no longer be viewed as a simple globally stratified cumulus structure composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual melt kreep sandwich horizon near the base of the lower crust instead global geochemical information derived from clementine multispectral data and lunar prospector gamma ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique 1 the procellarum kreep terrane pkt 2 the feldspathic high lands terrane fht and 3 the south pole aitken terrane spat the pkt is a mafic province coincident with the largely resurfaced area in the procellarum imbrium region whose petrogenesis relates to the early differentiation of the moon here some 40 of the th in the moon s crust is concentrated into a region that constitutes only about 10 of the crustal volume this concentration of th average 5 ppm and by implication the other heat producing elements u and k led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust lower crustal materials within the pkt likely interacted with underlying mantle materials to produce hybrid magmatism leading to the magnesian suite of lunar rocks and possibly kreep basalt although rare in the apollo sample collection widespread mare volcanic rocks having substantial th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources the fht is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation basin impacts into this region do not excavate significantly more mafic material suggesting a thickness of tens of kilometers of anorthositic crust the feldspathic lunar meteorites may represent samples from the anorthositic central region of the fht ejecta from deep penetrating basin impacts outside of the central anorthositic region however indicate an increasingly mafic composition with depth the spat a mafic anomaly of great magnitude may include material of the upper mantle as well as lower crust thus it is designated a separate terrane whether the spa basin impact simply uncovered lower crust such as we infer for the fht remains to be determined

age of variscan magmatism from the balkan sector of the orogen central bulgaria abstract new high resolution secondary ion mass spectrometry u th pb data obtained from zircon and monazite from representative variscan intrusions in the balkan sector of the variscan orogen central bulgaria constrain the ages of magmatism to the interval 315 285 ma the samples investigated are granitoids from two contrasting intrusive suites calc alkaline granitoids of the first suite include the san nikola granite 311 9 4 1 ma and the petrohan granodiorite 304 6 4 0 ma from the balkan terrane and the smilovene 304 1 5 5 ma and hisara 303 5 3 3 ma granites from the sredna gora terrane zircons from these intrusions predominantly lack inherited cores the second suite consists of two mica leucocratic granites and includes the koprivshtitsa 312 0 5 4 ma and strelcha 289 5 7 8 ma plutons zircons from intrusions of the second suite are 80 90 xenocrystic apparent ages of inherited cores are the magmatic age and slightly older 300 400 ma to ordovician 450 ma ages and to neoproterozoic 600 900 ma ages gabbroic magmas related to the first suite are found only in the more northerly balkan terrane while the leucogranites occur only in the southerly sredna gora terrane although coeval the two suites of intrusions are not genetically related and furthermore were likely derived from different source regions via different melt generating mechanisms we propose a tectonic and petrogenetic model whereby following juxtaposition of the balkan and sredna gora terranes during variscan collision the two suites of magmas were generated by continued subduction under eastern europe due to the influx of mafic magmas into the base of the crust and by influx of water rich fluids into high grade metapsammitic rocks of the sredna gora metamorphic series the new ages are somewhat younger than ages for post collisional intrusions in the central european variscan massifs i e bohemian black forest and vosges where ages of intrusions are predominantly 340 320 ma although some younger intrusions may also occur within the intra alpine massifs both older 340 320 ma and younger 310 290 ma granitoids are present farther west intrusions in the iberian massif appear to be predominantly younger 325 290 ma similar to the intrusions of the balkans this may indicate that collision of adjacent crustal blocks culminated at earlier times in the central and more northerly portions of the orogen and moved both east west and south as the evolution of the orogen progressed

low temperature replacement of monazite in the ireteba granite southern nevada geochronological implications the ireteba pluton is a relatively homogeneous 64 ma zircon ion probe age two mica granite that was intruded by two 16 ma miocene plutons at depths ranging from 5 to 13 km deeper levels of the ireteba and miocene plutons were ductilely deformed at 15 16 ma at shallow levels remote from the miocene plutons the ireteba granite appears to have experienced little miocene heating and deformation monazites from different portions of the pluton reflect the different histories experienced by the host rock irregularly shaped patchy zones with high huttonite component thsio4 are widespread in monazite at deep levels adjacent to miocene plutons but less common in shallow level rock monazite grains with extensive replacement generally have irregular embayed surfaces in undeformed rocks distant from the miocene plutons monazites are less modified and more nearly euhedral though fine networks of replacement veins are common and irregular rims are evident in some grains secondary monazite from these samples is poorer in huttonite ion probe th pb dating yields 60 65 ma ages for magmatic and some replacement zones in monazite from the shallow samples and veins yield apparent ages as young as mid tertiary monazites from deep samples yield a few 55 65 ma ages for remnant magmatic zones and abundant miocene ages for replacement zones 14 18 ma these data demonstrate extensive miocene replacement of magmatic monazite especially at deep levels near miocene plutons and they suggest an early replacement episode as well both events were probably related to influxes of fluid the first may have been associated with initial solidification of the ireteba pluton and the second with the miocene plutons and or extensional deformation ambient temperatures at the time of replacement indicate that secondary monazite growth occurred at t as low as 400 c or less

lunar irregular mare patches classification characteristics geologic settings updated catalog origin and outstanding questions one of the most mysterious lunar features discovered during the apollo era was ina a 2 3 km depression composed of bleb like mounds surrounded by hummocky and blocky terrains subsequent studies identified dozens of similar features in lunar maria describing them as irregular mare patches imps due to the unusual and complex characteristics of imps their specific formation mechanism is debated to improve our understanding of the nature and origin of imps we undertook an updated search and geological characterization of all imps and established a classification approach encompassing the full spectrum of imps we present an updated catalog of 91 imps and survey the detailed characteristics of each imp we find that the majority of imps occur in maria emplaced over three billion years ago contemporaneous with the peak period of global lunar volcanism we utilized geologic context information and characteristics to establish two classification schemes for lunar imps 1 geologic context imps are categorized into a small shield volcano summit pit floor and flank b linear sinuous rille interior and adjacent exterior and c typical maria 2 characteristics imps are classified into a mound floor and b pit only types we showed the range of characteristics of lunar imps was consistent with the waning stage magmatic foam formation and extrusion scenario in different environments our updated catalog and classification raise several outstanding questions concerning the nature and origin of lunar imps assessing these questions will improve our knowledge of lunar thermal and geologic evolution 2020 american geophysical union all rights reserved

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

magma pulses in the central variscan belt episodic melt generation and emplacement during lithospheric thinning magmatism in the central part of the variscan orogenic belt in europe has occurred in several distinct episodes each episode spanned a few million years and was characterized by a distinct geochemical signature and geodynamic setting i between 340 and 330 ma visean high k diorites and granitoids within a zone extending parallel the orogen axis possibly tracing a palaeosuture ii at 310 307 ma westphalian calc alkaline granitoids in the intra alpine domain iii at 304 295 ma stephanian subalkaline granitoids in intra alpine and pennine domains and finally iv at 280 270 ma permian granitoids in pennine austroalpine and south alpine domains the generation and emplacement of granitoid melts in the variscan crust are suggested to be short term pulses that are controlled by extensional processes in the lithosphere such as thermal erosion and relaxation of the lithospheric mantle and decompressional melting

magma source transition of lunar mare volcanism at 2 3 ga mare basalts provide insights into the composition and thermal history of the lunar mantle the ages of mare basalts suggest a first peak of magma activity at 3 2 3 8 ga and a second peak at 2 ga in this study we reassess the correlation between the titanium contents and the eruption ages of mare basalt units using the compositional and chronological data updated by selene kaguya using morphological and geological criteria we calculated the titanium content of 261 mare units across a representative area of each mare unit in the procellarum kreep terrane where the latest eruptions are located an increase in the mean titanium content is observed during the eratosthenian period as reported by previous studies we found that the increase in the mean titanium content occurred within a relatively short period near approximately 2 3 ga suggesting that the magma source of the mare basalts changed at this particular age moreover the high titanium basaltic eruptions are correlated with a second peak in volcanic activity near 2 ga the high titanium basaltic eruptions occurring during the last volcanic activity period can be explained by the three possible scenarios 1 the ilmenite bearing cumulate rich layer in the core mantle boundary formed after the mantle overturn 2 the basaltic material layers beneath the lunar crust formed through upwelling magmas and 3 ilmenite bearing cumulate blocks remained in the upper mantle after the mantle overturn

metamorphism and diachronous cooling in a contractional orogen the strandja massif nw turkey the southern part of the strandja massif northern thrace turkey comprises a basement of various gneisses micaschists and rare amphibolite and a cover of metaconglomerate and metasandstone separated from each other by a pre metamorphic unconformity metamorphic grade decreases from the epidote amphibolite facies in the south to the albite epidote amphibolite greenschist facies transition in the north estimated p t conditions are 485 530 c and 0 60 0 80 gpa in the epidote amphibolite facies domain and decrease towards the transitional domain between greenschist and epidote amphibolite facies rb sr muscovite ages range from 162 9 1 6 ma to 149 1 2 1 ma and are significantly older 279 296 ma in the northernmost part of the study area the rb sr biotite ages decrease from 153 9 1 5 ma in the south to 134 4 1 3 ma in the north these age values in conjunction with the attained temperatures suggest that the peak metamorphism occurred at around 160 ma and cooling happened diachronously and rb sr muscovite ages were not reset during the metamorphism in the northernmost part structural features such as i consistent s dipping foliation and sw to se plunging stretching lineation ii top to the n shear sense and iii n vergent ductile shear zones and brittle thrusts suggest a n vergent compressional deformation coupled with exhumation we tentatively ascribe this metamorphism and subsequent diachronous cooling to the northward propagation of a thrust slice the compressional events in the strandja massif were most probably related to the coeval n vergent subduction collision system in the southerly lying rhodope massif

geomorphology of lowell crater region on the moon abstract surface topography surface morphology and crater chronology studies have been carried out for the lowell crater region occupying 198 198 km 2 in the northwestern quadrant of the orientale basin using kaguya tc dtm lro wac data and chandrayaan 1 m 3 750 nm image to characterize and date lowell impact event and to identify and assess the geological importance of the lowell crater and effect of pre existing geological conditions on the present day appearance of lowell crater the lowell crater has been found to be polygonal in shape with an average diameter of 69 03 km its average rim height and depth from pre existing surface are 1 02 km and 2 82 km respectively a prominent central peak with average height of 1 77 km above the crater floor is present which could have exposed undifferentiated mantle rocks the peak exhibits a pronounced v shaped slumped zone on the eastern side and a distinct v shaped depression in the adjacent region on the crater floor several other peculiarities noticed and mapped here include w e asymmetry in the degree of slumping of the walls and height of the topographic rim n s asymmetry in the proximal ejecta distribution with most of the material lying in the northern direction concentration of exterior melt pools in the northeastern direction only presence of several cross cutting pre existing lineaments on the crater walls presence of a superposed rayed crater on the eastern wall and a geologically interesting resurfaced unit which could be an outcome of recent volcanic activity in the region it has been inferred that the lowell crater formed due to impact of a 5 7 km diameter bolide in the montes rook region the impact occurred at an angle of 30 45 from the s sw direction the age of the lowell crater has been estimated as 374 28 ma therefore it is a younger copernican crater consistent with the possibility expressed by mcewen et al mcewen a s et al 1993 j geophys res 98 e9 17207 17231 pre existing topography and morphology has played a key role in shaping up the present day lowell crater

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

mineralogy of young lunar mare basalts assessment of temporal and spatial heterogeneity using m3 data from chandrayaan 1 abstract a comparative assessment of the mineralogy of young basalts 1 2 ga to 2 8 ga from the western nearside moscoviense basin and the orientale basin of the moon has been made using level 2 moon mineralogy mapper m3 data from the chandrayaan 1 mission spectral data characteristics of the individual units have been generated from fresh small craters to minimize the complications due to space weathering representative spectra for individual units and the derived spectral parameters band centers and integrated band depth ratio have been used to study composition of these young basalts a modified approach of gaffey et al gaffey m j cloutis e a kelley m s reed k l 2002 mineralogy of asteroids in asteroids iii the university of arizona press tucson pp 183 204 for olivine pyroxene mixtures and the methodology of adams adams j b 1974 j geophys res 79 4829 4836 http dx doi org 10 1029 jb079i032p04829 for interpreting pyroxene type have been used to improve our understanding of the spectral behavior of these basalts most of the young basalts of oceanus procellarum are characterized by abundant olivines and they show complex volcanic history vast exposures of olivine concentrated units having higher abundance of olivine content than high ca pyroxenes are emplaced in the northern oceanus procellarum region mostly they show distinct stratigraphic gradation with the immediately underlying units of relatively lower olivine content the moscoviense unit shows signatures of fe rich glasses along with clinopyroxenes the basalts of orientale basin are typically devoid of olivine and are rich in high ca pyroxene thus mineralogy of these mare basalts which erupted during the late stage volcanism vary across the moon s surface however broader observations reveal apparently higher feo content in the younger basalts of western nearside and orientale region

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

internal structures and dating of complex zircons from meissen massif monzonites saxony abstract u pb zircon ages were determined for accessory zircons from two monzonites from the meissen massif northern bohemian massif germany by shrimp ion microprobe bse and cl imaging revealed that the monzonite zircons showing oscillatory growth zoning often contain inherited cores raman microprobe measurements showed that zoned rims u 277 1426 ppm th 144 910 ppm are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states from well crystallized to highly metamict the radionuclide u th content of cores varies from a few hundred to more than 20 000 ppm shrimp ion probe measurements on zoned rims interpreted as zircon growth during crystallization of the monzonite magma gave concordant carboniferous 206 pb 238 u ages of 326 6 ma monzonite from leuben and 330 5 ma monzonite from heidenschanze 95 confidence respectively these ages are consistent with recently published 40 ar 39 ar ages of 329 1 2 8 to 330 4 2 8 ma 2 on amphiboles from the same rocks in contrast shrimp measurements on cores range from slightly discordant proterozoic relic ages in low u and th cores to highly discordant data in the most metamict cores previously obtained 207 pb 206 pb ages single zircon evaporation technique in the range 340 16 to 357 16 ma 1 are probably mixed ages between magmatic and inherited zircon components the u pb ages of the monzonite zircons postdate the upper devonian lower carboniferous subduction and collision events in the area by about 20 ma due to their shoshonitic chemical signature which is typical of rocks from destructive plate boundary settings the meissen massif monzonites might be interpreted as originating during these 350 ma events and the earlier 207 pb 206 pb ages appeared to confirm this interpretation however both the 40 ar 39 ar ages and our current results show that only the enrichment of the lithospheric mantle source but not the monzonite intrusion itself was directly related to these events the monzonite intrusion itself took place 330 ma ago in the framework of strike slip tectonics in the elbe valley zone widely occurring zircon cores are indicative of crustal contamination of the magma causing considerable modification of chemical signatures trace element content of the monzonites

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

middle triassic paleomagnetic data from northern bulgaria constraints on tethyan magnetostratigraphy and paleogeography magnetostratigraphic and biostratigraphic data are presented from the anisian middle triassic peri tethyan edivetur section of northwestern bulgaria a dual polarity component of magnetization carried by magnetite delineates a magnetic stratigraphy of mainly reversed polarity magnetozones are dated by means of foraminifer and conodont biostratigraphy data from edivetur are compared with data from middle triassic tethyan limestone sections with the aim of contributing to the completion of the middle triassic magnetic polarity time scale we also propose that paleomagnetic data from edivetur can be used as proxy data for the paleogeographic position of the moesian platform the moesian platform was located at 21 24 n along the southern margin of europe it was probably marginally separated but not detached or rotated away from europe by the north dobrugea transtensional trough which is interpreted as a back arc basin resulting from the northward subduction of the neo tethys vardar or paleo tethys ocean paleomagnetic data from this study and other minor tectonic elements are used to generate a paleogeographic sketch map of the pangea bounded western tethys and peri tethys at middle early late triassic time 2000 elsevier science b v all rights reserved

multistage variscan magmatism in the central tauern window austria unveiled by u pb shrimp zircon data u pb shrimp ages of nine variscan leucocratic orthogneisses from the central tauern window austria reveal three distinct pulses of magmatism in early carboniferous visean late carboniferous stephanian and early permian each involving granitoid intrusions and a contemporaneous opening of volcano sedimentary basins a similar relationship has been reported for the carboniferous parts of the basement of the alps further to the west e g the external massifs in switzerland after the intrusion of subduction related volcanic arc granitoids 374 10 ma zwolferkogel gneiss collisional intrusive granitic anatectic and extrusive rhyolitic dacitic rocks were produced over a short interval at ca 340 ma augengneiss of felbertauern 340 4 ma hochweisenfeld gneiss 342 5 ma falkenbachlappen gneiss 343 6 ma this early carboniferous magmatism which produced relatively small volumes of melt can be attributed to the amalgamation of the gondwana derived tauern window terrane with laurussia avalonia probably due to the oblique nature of the collision transtensional phenomena i e volcano sedimentary troughs and high level intrusives and transpressional regimes i e regional metamorphism and stacked nappes with anatexis next to thrust planes evolved contemporaneously the magmas are mainly of the high k i type and may have been generated during a short phase of decompressional melting of lithospheric mantle and lower crustal sources in the late carboniferous a second pulse of magmatism occurred producing batholiths of calc alkaline i type granitoids e g venediger tonalite 296 4 ma and minor coeval bodies of felsic and intermediate volcanics heuschartenkopf gneiss 299 4 ma peitingalm gneiss 300 5 ma prior to this magmatism several kilometres of upper crust must have been eroded because volcano sedimentary sequences hosting the heu schartenkopf and peitingalm gneisses rest unconformably on 340 ma old granitoids the youngest permian period of magma generation contains the intrusion of the s type granatspitz central gneiss at 271 4 ma and the extrusion of the rhyolitic schonbachwald gneiss protolith at 279 9 ma these magmatic rocks may have been associated with local extension along continental wrench zones through the variscan orogenic crust or with a permian rifting event the permian and the above mentioned late carboniferous volcano sedimentary sequences were probably deposited in intra continental graben structures which survived post variscan uplift and alpine compressional tectonics

lunar mare basalt flow units thicknesses determined from crater size frequency distributions accurate lava flow unit thicknesses estimates are necessary to place constraints on volcanic flux estimates we refine the technique of using the shape of crater size frequency distribution csfd curves to estimate the thickness of individual lunar mare flow units we find that a characteristic knee often observed in csfd curves is reasonably interpreted to represent the presence of two lava flow units separated in time and that the diameter at which this knee occurs is related to the thickness of the overlying flow unit examination of 58 curves with this characteristic knee in several lunar nearside basins oceanus procellarum imbrium tranquillitatis humorum cognitum nubium and insularum allowed us to identify flow units that have not been detected in low sun images we found that the range of flow unit thickness is 20 220 m and the average is 30 60 m this technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the moon and planets

geochronology and nd sr systematics of lusatian granitoids significance for the evolution of the variscan orogen in east central europe a variety of pre variscan granitoids and two variscan monzogranites occurring in the central and western parts of the lusatian granodiorite complex lgc saxonia were dated by the single zircon evaporation method complemented by whole rock nd isotopic data and rb sr whole rock and mineral ages the virtually undeformed pre variscan granitoids constitute a genetically related mostly peraluminous magmatic suite ranging in composition from two mica granodiorite muscovitebearing biotite quartz diorite tonalite and granodiorite to biotite granodiorite and monozogranite

palaeozoic terranes of the balkan peninsula in the framework of pangea assembly abstract the presence of three gondwanan palaeozoic terranes in the basement of the eastern part of the balkan peninsula is revealed by sedimentological palaeoclimatological biogeographical and magnetic data the terranes are from north to south the moesian balkan and thracian terranes they originate from different parts of gondwana and perigondwana regional data indicate an en echelon movement of the moesian and balkan incl thracian terranes from the southern humid zone in the ordovician through the southern arid zone moesian terrane during the devonian and the equatorial zone during the carboniferous to the northern arid zone in the permian devonian convergence brought the moesian terrane and the dobrudgea periphery of palaeo europe into collisional contact the collision between the moesian and balkan incl thracian terranes took place during the late carboniferous and permian and was related to the formation of the variscan orogeny upper palaeozoic molasse sediments blanket a palaeo relief in predominantly continental environments both the collision of the perigondwanan moesian and balkan terranes as well as their accretion to palaeo europe are confirmed by the presence of a megaflora and palynomorphs similar to those in other pangea land areas of similar climatic and hypsometric conditions this study attempts to improve the understanding of the palaeogeographic evolution of the balkan area it further tries to explain the regional processes and stages of formation of pangea

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

implications of shear sense criteria for the tectonic evolution of the central rhodope massif southern bulgaria a systematic record of sense of shear criteria associated with peak conditions of amphibolite facies metamorphism from the central rhodope massif bulgaria gives evidence for superposition of two distinct terranes the lower terrane is characterized by south vergent flat lying thrusting that involved eclogites the upper terrane is characterized by east vergent flat lying shearing possibly associated with crustal extension we suggest that both regional metamorphism and deformation may be cretaceous in age there was erosion prior to emplacement of several crystalline sheets at shallow depths during the early cenozoic this was followed by oligocene extension and rhyolitic volcanism the rhodope massif can no longer be regarded as a stable paleozoic or older microcontinent

oil and gas developments in new zealand and southwest pacific islands in 1988 in new zealand a total of 17 licenses were granted 8 in the east coast region 7 in taranaki 1 in northland and 1 in murchison although 10 licenses were relinquished 8 offshore a net increase in area under license resulted particularly onshore seismic exploration activity totaled 519 km onshore and 2 403 km offshore drilling decreased slightly with 10 onshore and 6 offshore wells totaling 46 584 m much of the drilling involved appraisals of the kupe south field waihapa field and kora structure all in the taranaki basin total petroleum production remained steady at 4 716 million m3 of gas 1 221 m3 of condensate and 752 m3 of oil a decision on whether to construct the maui b platform awaits the outcome of pending negotiat ons papua new guinea had increased exploration activity in 1988 resulting in 15 wells drilled or spudded of these 11 were field extensions three were suspended as producers and the remaining 8 were abandoned of 4 new field wildcats drilled 1 was a gas discovery the only offshore well and the only one drilled outside the papuan fold belt the total depth drilled 30 000 m was double 1987 s total seismic surveys amounted to 1 220 km onshore a 43 increase and 1 317 km offshore a 72 decrease the hides gas and condensate field in the highlands has been scheduled for development and will be the first commercially produced field in papua new guinea a route has been surveyed for the proposed pipeline connecting the iagifu and hedinia oil and gas fields with a terminal at the gulf f papua there was little activity in tonga fiji vanuatu and the solomon islands although some basic research was published

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

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

the age of the kagenfels granite northern vosges and its bearing on the intrusion scheme of late variscan granitoids in the saxothuringian part of the vosges france a first series of variscan plutonic rocks diorites to granites has been intruded by several younger granites rocks of both the older generations have been cross cut by the late orogenic kagenfels granite the averages of the hitherto published mineral ages of the earlier rock generations are 331 and 334 ma respectively whereas rb sr and k ar dates around 290 ma have been reported for the kagenfels granite because of the unlikely large age hiatus a redetermination of the intrusion age of the kagenfels granite formation appeared to be irrevocable the newly obtained mineral ages on the kagenfels granite k ar and 40ar 39ar biotite ages as well as single zircon radiogenic 207pb 206pb data 331 5 ma are about 40 ma older than the previous results they are interpreted as giving the time of emplacement of the kagenfels granite during the latest viscan the mineral ages of the earlier plutonic rocks in this part of the variscan orogeny in all probability are not significantly different from their ages of intrusion therefore the age concordance of all three granitoid generations constrains a rather narrow time interval of orogenic magmatism close to the lower upper carboniferous boundary

isotopic age determinations of crystalline rocks of the upper harz mountains germany dating of crystalline rocks occurring in the upper harz mountains was carried out by means of u pb isotope investigations on zircons and sphene as well as by rb sr isotope measurements on whole rock samples and biotites

u pb zircon and monazite geochronology of variscan magmatism related to syn convergence extension in central northern portugal abstract the viseu area is located in the central iberian zone of the iberian variscan belt and hosts numerous post thickening collision related granitoids intruded into upper and middle crustal levels the present paper reports high precision u pb zircon and monazite ages for four plutons of the viseu area the syn kinematic granitoids of maceira 314 5 ma casal vasco 311 1 ma and junqueira 307 8 0 7 ma and the late kinematic biotite monzogranites of cota 306 9 ma this points to a synchronous emplacement of the different syn kinematic plutons shortly followed by the intrusion of the late kinematic granites and shows that the upper carboniferous plutonism occurred within a short time span of ca 10 million years the ascent of granite magmas took place after an extensional tectonic event d 2 and is coeval with dextral and sinistral crustal scale transcurrent shearing d 3 field and petrographical evidence suggest a narrow time span between peak t metamorphic conditions and the intrusion of granitic melts which implies very fast uplift rates accommodated through active tectonic exhumation magma compositions evolve through time reflecting an increasing involvement of mid crustal sources and the underplating effect of an upwelling asthenospheric mantle at the base of a thinning and stretching continental crust

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

lateral heterogeneity of lunar volcanic activity according to volumes of mare basalts in the farside basins estimates for volumes of mare basalts are essential to understand the thermal conditions of the lunar mantle and its lateral heterogeneity in this study we estimated the thicknesses and volumes of mare basalts within five farside basins apollo ingenii poincare freundlich sharonov and mendel rydberg using pre mare craters buried by mare basalts and post mare craters that penetrated non penetrated mare basalts employing topographic and multiband image data obtained by selene kaguya furthermore using the grail crustal thickness model and the mare volumes estimated by this and previous studies we investigated the relationship between the volumes of the mare basalts and the crustal thicknesses the results suggest that the minimum crustal thicknesses within the basins were a dominant factor determining whether magma erupted at the surface and that the critical crustal thicknesses for magma eruption were 10 km on the farside and 20 km on the nearside the total areas of the regions in which magmas could erupt at the surface are 10 times larger on the nearside than on the farside a comparison between the mare volumes within the mare basins on the nearside and the farside shows that magma production in the farside mantle might have been 20 times smaller than that in the nearside mantle implying a stronger dichotomy than previously estimated these results suggest that the mare hemispherical asymmetry should be attributed to both the difference in the crustal thickness distribution and the difference in the quantity of magma production between the nearside and farside mantles

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

magma mixing in the genesis of hercynian calc alkaline granitoids an integrated petrographic and geochemical study of the sazava intrusion central bohemian pluton czech republic the devonian early carboniferous 354 1 3 5 ma conventional zircon u pb age sazava intrusion biotite amphibole quartz diorite tonalite and granodiorite of the central bohemian pluton cbp associated with bodies of olivine pyroxene amphibole gabbro gabbrodiorite quartz diorite and rare hornblendite gives an opportunity for a comparative study of a rather shallow calc alkaline magma mixing zone at two levels separated by a vertical difference of approximately 1 km the deeper section p ibram displays the direct evidence for the existence of a long lived periodically tapped and replenished floored magma chamber masli the contacts between the subhorizontal sheet like basic bodies and the surrounding commonly cumulus rich sazava granitoid are arcuate and cut by a series of veins and ascending pipes shallow dipping swarms of strongly elongated and flow aligned mafic microgranular enclaves mme concordant with the contacts of the basic bodies are commonplace the higher level teletin section shows relatively independent basic intrusions some of them distinctly hybrid in character and mainly of quartz dioritic composition surrounded by relatively homogeneous nearly cumulus free sazava tonalite rich in texturally variable mme larger quartz microdiorite bodies and the mme both interpreted as hybrids contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning particularly well shown by cathodoluminescence cl most often the megacrysts have cores of labradorite anorthite partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth also characteristic are long prisms of apatite oikocrysts of quartz and k feldspar and zoned amphibole the latter has brown pargasite and magnesiohastingsite cores resorbed and overgrown by magnesiohornblende compositionally similar to the amphibole in the sazava tonalite the brown cores are probably relics of a higher p t stage with temperature exceeding 900 c plots of major element analyses of the teletin quartz microdiorite and the mme fall close to the line joining the compositions of the evolved sazava granodiorite tonalite and the associated gabbros the estimated minimal proportions of the acidic end member range from ca 15 to 20 for the quartz microdiorite and ca 40 to 60 for the enclaves field relationships macroscopic and mineralogical features and whole rock geochemistry are consistent with a hybrid origin of the quartz microdiorite masses and enclaves unzoned calcic plagioclase cores are interpreted as having crystallized from a basic magma prior to its injection into a high level acidic magma chamber the sudden decrease in ca activity and introduction of water due to magma mixing with tonalitic melt led to their resorption and brecciation quartz ocelli that are abundant locally in some basic bodies are most likely xenocrysts introduced from the felsic magma in the basic melt they were resorbed and became a substrate for heterogeneous nucleation of the amphibole or pyroxene coronas strong undercooling of the basic magma resulted in the growth of long prismatic apatite together with dendritic boxy cellular plagioclase both types of plagioclase cores were subsequently overgrown by more sodic mantles at the same time small unzoned plagioclase crystals nucleated in the groundmass following thermal re adjustment crystallization of the hybrid magma ended with considerably slower growth of quartz and k feldspar oikocrysts

the procellarum kreep terrane implications for mare volcanism and lunar evolution geophysical remote sensing and sample data demonstrate that the procellarum and imbrium regions of the moon make up a unique geochemical crustal province here dubbed the procellarum kreep terrane geochemical studies of imbrium s ejecta and the crustal structure of the imbrium and serenitatis basins both suggest that a large portion of the lunar crust in this locale is composed of a material similar in composition to apollo 15 kreep basalt kreep basalt has about 300 times more uranium and thorium than chondrites so this implies that a large portion of moon s heat producing elements is located within this single crustal province the spatial distribution of mare volcanism closely parallels the confines of the procellarum kreep terrane and this suggests a causal relationship between the two phenomena we have modeled the moon s thermal evolution using a simple thermal conduction model and show that as a result of the high abundance of heat producing elements that are found in the procellarum kreep terrane partial melting of the underlying mantle is an inevitable outcome specifically by placing a 10 km kreep basalt layer at the base of the crust there our model predicts that mare volcanism should span most of the moon s history and that the depth of melting should increase with time to a maximum depth of about 600 km we suggest that the 500 km seismic discontinuity that is observed in the apollo seismic data may represent this maximum depth of melting our model also predicts that the kreep basalt layer should remain partially molten for a few billion years thus the imbrium impact event most likely excavated into a partially molten kreep basalt magma chamber we postulate that the kreep basalt composition is a by product of mixing urkreep with shallow partial melts of the underlying mantle since mg suite rocks are likely derived from crystallizing kreep basalt the provenance of these plutonic rocks is likely to be unique to this region of the moon

long lived volcanism on the lunar farside revealed by selene terrain camera we determined model ages of mare deposits on the farside of the moon on the basis of the crater frequency distributions in 10 meter resolution images obtained by the terrain camera on selene selenological and engineering explorer kaguya most mare volcanism that formed mare deposits on the lunar farside ceased at 3 0 billion years ago suggesting that mare volcanism on the moon was markedly reduced globally during this period however several mare deposits at various locations on the lunar farside also show a much younger age clustering at 2 5 billion years ago these young ages indicate that mare volcanism on the lunar farside lasted longer than was previously considered and may have occurred episodically

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

constraining the prograde and retrograde p t t path of eocene hp rocks by shrimp dating of different zircon domains inferred rates of heating burial cooling and exhumation for central rhodope northern greece ion microprobe shrimp dating was carried out on different zircon domains from metamorphic rocks of the hp ht terrane of central rhodope northern greece to constrain the timing of prograde and retrograde stages within a single tectono metamorphic cycle a well determined p t t relative path for the metamorphic rocks of this terrane was used as a petrological basis for the geochronological investigations ion microprobe work was assisted by cathodoluminescence cl images of the zircon crystals the geochronological results revealed that hercynian continental crust was subducted during the eocene several stages of the eocene tectono metamorphic cycle including both the prograde and retrograde parts of the p t path above ca 300 c 0 3 gpa were dated using zircons from the following rock types 1 a deformed quartz vein probably formed at ca 300 c 0 3 gpa zircons in this vein precipitated from a hydrothermal fluid they yielded an age of 45 3 0 9 ma which corresponds to the time of a low t prograde stage of metamorphism 2 in kyanite eclogites zircons were entirely reset during eclogite facies metamorphism resetting was very probably enhanced by the presence of fluids derived by h2o liberating reactions close to the p peak they yielded an age of 42 2 0 9 ma 3 orthogneisses surrounding the kyanite eclogites contained zircons with magmatic oscillatory zoned cores which yielded hercynian ages of 294 8 ma age of granitic protolith formation whereas cl bright metamorphic rims yielded like the eclogite zircons ages of 42 0 1 1 ma therefore both the eclogites and orthogneisses are interpreted to have approached maximum depth at around 42 ma 4 in a leucosome of a migmatized orthogneiss oscillatory zoned zircons yielded an age of 40 0 1 0 ma at this time the rocks reached maximum temperatures during early decompression 5 a late pegmatite crosscutting the schistosity of amphibolites contained oscillatory zoned zircons that yielded a crystallization age of 36 1 1 2 ma thus the whole tectono metamorphic cycle above ca 300 c 0 3 gpa lasted from 45 3 0 9 ma to 36 1 1 2 ma that is 9 2 ma with an extreme error value of 2 1 ma based on combined shrimp and petrological data the average rates of heating and burial during subduction above ca 300 c 0 3 gpa are 94 c ma and 15 mm a respectively rates of cooling and exhumation also above 300 c 0 3 gpa are calculated to be 128 c ma and 7 7 mm a the eocene age of metamorphism in central rhodope implies that the terrane of at least central rhodope and the cyclades very probably was part of the same continental crust

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

the protomoesian microcontinent of the balkan peninsula a peri gondwanaland piece abstract based on differences in their pre palaeozoic and palaeozoic development the protomoesian microcontinent is divided into two terranes the balkan and the moesian a precambrian cambrian ophiolite island arc assemblage unconformably overlain by a palaeozoic sequence forms the first terrane the pre palaeozoic basement of the moesian terrane consists of proterozoic vendian metamorphics of continental origin the differences in the development of the palaeozoic rocks are also significant reason for dividing the balkan and the moesian terrane numerous features of the palaeozoic sediments palaeoclimatologic palaeobiogeographic palaeomagnetic from both terranes and the pan african affiliations of the ophiolite island arc assemblage identify the protomoesian microcontinent as a peri gondwanaland piece

modelling diverse processes in the petrogenesis of a composite batholith the central bohemian pluton central european hercynides the multiple intrusions making up the central bohemian pluton in the central european hercynides have petrographic and geochemical features consistent with the presence of four main granitoid suites major element trace element and sr nd isotopic compositions are used to model their petrogenesis partial melting of metabasic locks or of a chur like mantle source are interpreted to have produced melts parental to the most primitive calc alkaline sazava suite interaction of basic with more acidic magmas followed by extensive amphibole plagioclase dominated fractionation accounts for the production of trondhjemites alternatively the trondhjemites correspond to small degree melts of a metabasic source afc assimilation fractional crystallization modelling with a paragneiss as a contaminant and increasing d nd values simulates the characteristics of the blatna suite closed system fractionation of strongly enriched mantle derived magmas or their interaction with leucogranitic melts is deduced for the petrogenesis of the shoshonitic certovo bremeno suite partial melting of a metasedimentary source followed by k feldspar dominated fractionation accounts for the granites of rite ricany suite the progression from relatively primitive calc alkaline granitoids towards evolved k rich calc alkaline and shoshonitic rocks is interpreted to reflect the increasing enriched mantle input in the petrogenesis of the later suites the evidence for hercynian subduction is equivocal and the mantle enrichment could have been significantly older

high mg potassic rocks in the balkan segment of the variscan belt bulgaria implications for the genesis of orogenic lamproite magmas ultrapotassic plutons from several domains of the variscan orogenic belt have been in turn interpreted as syn to post orogenic due to their age spread but assessment of their geodynamic setting and source regions is still open to interpretation in the svoge region bulgaria at the southern margin of the balkan orogen peralkalic plutons are hosted within ordovician pelites the main intrusion with lamproitic affinity which hosts monzodiorite xenoliths and a polyphase syenite suite was emplaced at a shallow level 40 ar 39 ar dating by step heating of amphibole and biotite yielded a early carboniferous intrusion age for the main body 337 4 and 339 1 1 6 ma the lamproite intrusion is silica rich compared with bona fide lamproites and characterized by moderate lile and la n yb n enrichments sr and nd isotopic data initial nd in the range 4 87 to 5 88 suggest an origin in a depleted lithospheric mantle possibly refertilized by eo variscan subduction the high k syn tectonic plutonism in several zones of the variscan orogen bohemian austro alpine vosges french and corsica domains is consistent with a derivation of high k magmatism from partial melting of metasomatized mantle following the subduction along the collision front between gondwana and laurasia

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

geodynamic evolution of the european variscan fold belt palaeomagnetic and geological constraints the variscan fold belt of europe resulted from the collision of africa baltica laurentia and the intervening microplates in early paleozoic times over the past few years many geological palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt whereas it is now fairly well established that avalonia drifted from the northern margin of gondwana in early ordovician times and collided with baltica in the late ordovician early silurian the nature of the gondwana derived armorican microplate is more enigmatic geological and new palaeomagnetic data suggest armorica comprises an assemblage of terranes or microblocks palaeobiogeographic data indicate that these terranes had similar drift histories and the rheic ocean separating avalonia from the armorican terrane assemblage closed in late silurian early devonian times an early to mid devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow rhenohercynian basin which closed progressively between the late devonian and early carboniferous in this contribution we review the constraints provided by palaeomagnetic data compare these with geological and palaeobiogeographic evidence and present a sequence of palaeogeographic reconstructions for these circum atlantic plates and microplates from ordovician through to devonian times

precambrian to early cretaceous rocks of the strandja massif northwestern turkey evolution of a long lasting magmatic arc1 the strandja massif northwestern turkey forms a link between the balkan zone of bulgaria which is correlated with the variscan orogen in europe and the pontides where cimmerian structures are

post collisional melting of crustal sources constraints from geochronology petrology and sr nd isotope geochemistry of the variscan sichevita and poniasca granitoid plutons south carpathians romania the sichevita and poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the getic nappe in the south carpathians the present work provides shrimp age data for the zircon population from a poniasca biotite diorite and geochemical analyses major and trace elements sr nd isotopes of representative rock types from the two intrusions grading from biotite diorite to biotite k feldspar porphyritic monzogranite u pb zircon data yielded 311 2 ma for the intrusion of the biotite diorite granites are mostly high k leucogranites and biotite diorites are magnesian and calcic to calc alkaline sr and nd isotope and trace element data ree th ta cr ba and rb permit distinguishing five different groups of rocks corresponding to several magma batches the poniasca biotite diorite p1 shows a clear crustal character while the poniasca granite p2 is more juvenile conversely sichevita biotite diorite s1 and a granite s2 are more juvenile than the other sichevita granites s2 geochemical modelling of major elements and ree suggests that fractional crystallization can account for variations within p1 and s1 groups dehydration melting of a number of protoliths may be the source of these magma batches the variscan basement a subduction accretion wedge could correspond to such a heterogeneous source the intrusion of the sichevita poniasca plutons took place in the final stages of the variscan orogeny as is the case for a series of european granites around 310 ma ago especially in bulgaria and in iberia no alleghenian granitoids late carboniferous early permian times being known in the getic nappe the geodynamical environment of sichevita poniasca was typically post collisional of the variscan orogenic phase

iron distribution of the moon observed by the kaguya gamma ray spectrometer geological implications for the south pole aitken basin the orientale basin and the tycho crater abstract in this study we describe the distribution of iron on the moon as obtained by the kaguya high energy resolution gamma ray spectrometer kgrs we achieved for the first time the identification of iron based on the fast neutron flux obtained by the kgrs the iron distribution obtained by kgrs is compared to that of the lunar prospector gamma ray spectrometer lp grs showing that the feo distributions observed by kgrs and lp grs in general are in good agreement furthermore we compare the iron content data obtained by kgrs and lp grs to spectral reflectance measurements of the clementine kaguya and chandrayaan 1 spacecraft as well as those inferred from returned samples we found differences in feo concentration and distribution in areas of moderate abundance 6 15 wt of the south pole aitken basin mare orientale and around the crater tycho crater it implies that high concentrations of feo at mare ingenii in the south pole aitken basin and mare orientale are due to the presence of mare basalts whereas the enriched feo content in the central depression of the south pole aitken basin and the tycho crater indicates the presence of mafic materials such as impact melt breccia

young mare volcanism in the orientale region contemporary with the procellarum kreep terrane pkt volcanism peak period 2 billion years ago 1 the crater retention ages of the mare deposits within the orientale multi ring impact basin are investigated using 10 m resolution images obtained by the selene kaguya spacecraft in order to constrain the volcanic history of the moon around the nearside farside boundary precise crater counting analyses reveal that mare deposits in the orientale region are much younger than previously estimated 2 9 ga mare basalt in the eastern part of mare orientale and 1 8 2 2 ga mare deposits in lacus veris and lacus autumni maria along the northeastern rings of the basin the latter age estimates indicate that the orientale region experienced volcanic activities 2 billion years after the basin formation impact the dominance of a uniform surface age across the mare deposits in the peripheral regions strongly suggests that these volcanic eruptions are contemporary with the elevated volcanic activity episode proposed for the procellarum kreep terrane on the lunar nearside at 2 ga and that this activity peak is much more widespread than previously estimated the longevity of mare volcanism in the orientale region further suggests high initial temperatures and or high content of heat producing elements in the underlying mantle of this region

timing and characteristics of the latest mare eruption on the moon unraveling the timing and duration of mare volcanism on the moon is essential for understanding its thermal evolution the end of mare volcanism is poorly constrained because mare basalts are incompletely sampled in this study employing selene kaguya high resolution images we performed new crater size frequency measurements for 49 young mare units 3 0 ga in the procellarum kreep terrane pkt in which the latest magma eruption of the moon occurred mare volcanism in this region continued until 1 5 ga suggesting that volcanic activity in this region ceased 1 0 ga after the magma eruption had globally ceased 2 5 3 0 ga volcanic activity may have peaked 1 8 2 2 ga ago the youngest basalts occur around the aristarchus plateau and the kepler crater which are located in the central region of the pkt it is likely that heating in the crust due to the concentration of heat producing elements in the pkt delayed cooling of a partial melting zone in the underlying mantle in contrast with previous basalt dating in this region our results indicate a higher correlation between ages and spectral types of mare basalts the young mare units in the pkt tend to have spectral types corresponding to high titanium contents while low titanium basalts occur mainly in the early stage the titanium variation in mare basalts may reflect vertical heterogeneity in tio2 content in the upper mantle beneath the pkt

the uniform k distribution of the mare deposits in the orientale basin insights from chang e 2 gamma ray spectrometer the composition of mare basalt units in the orientale basin are investigated by using the potassium k map derived from chang e 2 gamma ray spectrometer ce 2 grs and feo map derived from clementine uv vis data set together with crater retention ages of the mare basalts from literature data we aim to investigate possible magma sources underneath the orientale basin and their chemical evolution over time analyses of the chemical composition of the resurfaced mare basalts together with the reported eruption ages suggest a unique magma generating process for the resurfaced mare deposits the early mare basalts in the central mare orientale and the later resurfaced mare deposits probably derived from magma generated by heat release due to high radioactive element concentrations based on forward modeling the similar k abundances observed in the small mare deposits of the sw polygon area lacus veris and lacus autumni and those in the central mare orientale imply the same heat source for these lava eruptions the chemical similarities e g k feo and tio2 of these regions suggest that mare basalts within the orientate basin are a result of multiple eruptions from a relatively homogeneous source underneath the basin c 2014 elsevier b v all rights reserved

lunar mare deposits associated with the orientale impact basin new insights into mineralogy history mode of emplacement and relation to orientale basin evolution from moon mineralogy mapper m3 data from chandrayaan 1 1 moon mineralogy mapper m3 image and spectral reflectance data are combined to analyze mare basalt units in and adjacent to the orientale multiring impact basin models are assessed for the relationships between basin formation and mare basalt emplacement mare basalt emplacement on the western nearside limb began prior to the orientale event as evidenced by the presence of cryptomaria the earliest post orientale event mare basalt emplacement occurred in the center of the basin mare orientale and postdated the formation of the orientale basin by about 60 100 ma over the next several hundred million years basalt patches were emplaced first along the base of the outer rook ring lacus veris and then along the base of the cordillera ring lacus autumni with some overlap in ages the latest basalt patches are as young as some of the youngest basalt deposits on the lunar nearside m3 data show several previously undetected mare patches on the southwestern margins of the basin interior regardless the previously documented increase in mare abundance from the southwest toward the northeast is still prominent we attribute this to crustal and lithospheric trends moving from the farside to the nearside with correspondingly shallower density and thermal barriers to basaltic magma ascent and eruption toward the nearside the wide range of model ages for orientale mare deposits 3 70 1 66 ga mirrors the range of nearside mare ages indicating that the small amount of mare fill in orientale is not due to early cessation of mare emplacement but rather to limited volumes of extrusion for each phase during the entire period of nearside mare basalt volcanism this suggests that nearside and farside source regions may be similar but that other factors such as thermal and crustal thickness barriers to magma ascent and eruption may be determining the abundance of surface deposits on the limbs and farside the sequence timing and elevation of mare basalt deposits suggest that regional basin related stresses exerted control on their distribution our analysis clearly shows that orientale serves as an excellent example of the early stages of the filling of impact basins with mare basalt

variscan orogeny in the black sea region two gondwana derived paleozoic belts rim the archean paleoproterozoic nucleus of the east european platform in the black sea region in the north is a belt of paleozoic passive margin type sedimentary rocks which extends from moesia to the istanbul zone and to parts of the scythian platform the mois block this belt constituted the south facing continental margin of the laurussia during the late paleozoic this margin was deformed during the carboniferous by folding and thrusting and forms the variscan foreland in the south is a belt of metamorphic and granitic rocks which extends from the balkanides through strandja sakarya to the caucasus bassac block the protoliths of the metamorphic rocks are predominantly late neoproterozoic granites and paleozoic sedimentary and igneous rocks which were deformed and metamorphosed during the early carboniferous there are also minor eclogites and serpentinites mostly confined to the northern margin of the bassac block typical metamorphism is of low pressure high temperature type and occurred during the early carboniferous visean 340 330 ma coevally with that observed in the central europe volumetrically more than half of the crystalline belt is made up of carboniferous earliest permian 335 294 ma granites the type of metamorphism its concurrent nature over 1800 km length of the bassac block and voluminous acidic magmatism suggest that the thermal event probably occurred in the deep levels of a continental magmatic arc the bassac arc collided with laurussia in the mid carboniferous leading to the foreland deformation the ensuing uplift in the permian resulted in the deposition of continental red beds which are associated with acidic magmatic rocks observed over the foreland as well as over the bassac block in the black sea region there was no terminal collision of laurussia with gondwana during the late paleozoic and the laurussia margin continued to face the paleo tethyan ocean in the south

late cambrian ordovician northeastern gondwanan terranes in the basement of the apuseni mountains romania abstract the pre alpine basement of the apuseni mountains romanian carpathians comprises three terranes somes baia de aries and biharia metaigneous rocks within these terranes record late cambrian ordovician u pb zircon crystallization ages two samples from an orthogneiss layer in the somes terrane yielded an age of 459 8 2 7 ma in the baia de aries terrane an augen gneiss yielded an age of 470 8 3 8 ma a porphyroid yielded an age of 467 8 3 8 ma and two metagranites yielded ages of 467 8 4 7 ma and 467 1 3 9 ma respectively three samples from a metagranitoid outcrop located in the lower part of the biharia terrane yielded an age of 495 0 2 1 ma three other samples from a metabasite layer situated lithostratigraphically several hundred metres above the metagranitoid yielded an age of 477 8 3 2 ma detrital u pb zircon ages from a paragneiss interlayered within the baia de aries terrane scatter between 548 and 3518 ma detrital zircon ages together with the inherited ages recorded by magmatic zircon populations suggest a northeastern gondwanan provenance for the somes baia de aries and biharia terranes adjacent to the arabian nubian shield lead loss in some zircons is interpreted to have taken place during the variscan orogeny supplementary material coordinates for samples from the apuseni mountains palaeozoic palaeogeographical models of gondwana laurentia and baltica to the formation of pangaea sample preparation and analytical procedures sample description and age measurements of zircon grains are available at http www geolsoc org uk sup18425

erratum to early permian pangea b to late permian pangea a earth planet sci lett 215 2003 379 394 a dipartimento di scienze della terra universita di milano via mangiagalli 34 20133 milan italy b lamont doherty earth observatory palisades ny 10964 usa c department of geological sciences rutgers university piscataway nj 08854 usa d dipartimento di scienze geologiche e geotecnologie universita di milano bicocca piazza della scienza 4 20126 milan italy e departement erdwissenschaften eth zentrum ch 8092 zu rich switzerland f department of earth sciences aarhus university aarhus denmark

paleomagnetic investigations and k ar dating on the variscan plutonic massif of the champ du feu and its volcanic sedimentary environment northern vosges france abstract paleomagnetic investigations have been carried out on samples from the plutonic series of the champ du feu massif and the devonian ordovician host rocks in order to date the different phases of magnetization a series of samples has been selected for k ar analysis on micas amphiboles and feldspars the diorites granodiorites diabases and hornfelses are characterized by high susceptibilities of up to 10 1 si thermal demagnetization reveals several groups of directions of characteristic magnetization the a direction d 202 i 23 49 n 153 e is consistent with the permian virtual geomagnetic pole for europe the b 1 direction d 59 i 22 11 n 128 5 e was obtained from the effusive parts of the kagenfels granite dated at 284 ma diorites microdiorites and volcanics emplaced a short time after the intrusion of the natzwiller granite dated at 344 and 351 ma display three groups of directions the c 1 direction d 328 i 15 27 n 223 5 e the c 2 d 323 i 38 13 s 222 e and the c 3 d 272 i 41 16 s 260 e the c 1 and c 2 directions agree well with those obtained previously for visean volcanics from the southern vosges in the host rocks we have identified b and c overprintings despite the lack of tectonic control the paleomagnetic data demonstrate at least two important motions of the vosges first a rotation of undetermined direction relative to stable europe which affected the variscan belt between the late visean and 320 ma and second a clockwise rotation which occurred during the stephanian autunian in late variscan time

precise upb chronometry of 345 340 ma old magmatism related to syn convergence extension in the southern vosges central variscan belt abstract the southern vosges host a large volcano sedimentary basin which contains clastic sediments of famennian late devonian ca 365 ma to late visean ca 340 335 ma age the basin is bordered by an exhumed high grade basement complex and intruded by several granitoid plutons a chronology for basin evolution and magmatism was established dating volcanic rocks of the basin as well as cross cutting granitoid rocks by the u pb technique applied to zircon and titanite the basin evolution started with olistolithic deposits and overlying marine shales that have a famennian fauna ca 365 ma and contain detrital zircons with an age of 386 ma the lowermost rhyolite flows interlayered with the basin sediments and tholeiitic basalts yielded an age of 345 2 ma following a tectonic event at the bottom of the upper visean the rates of sedimentation and volcanism were strongly enhanced leading to basin emersion and were concluded by the extrusion of the uppermost ignimbrite molkenrain rhyolite emplaced at 340 2 ma the whole volcano sedimentary association was subsequently intruded by melts of the ballons and cre tes granites as well as by small monzodioritic and dioritic satellite intrusions along the border of the ballons granite within 3 2 myr 342 1 to 339 5 2 5 ma the zircons of most of the volcanic and plutonic rocks investigated contain inherited lead of 0 6 and 2 1 ga age the differences in initial nd isotopic composition of the ballons and cre tes granites can be explained by differential uptake of crustal material during magma genesis the precise age data prove that magmatism and basin formation in the southern vosges were extremely short lived and coeval to the exhumation of adjacent high grade gneiss terrains revealing an episode of extension at the end of the lower carboniferous between 345 and 340 ma visean the tectonic regime in the internal part of the variscan orogen is that of extension and strike slip while convergent tectonics were still ongoing in the external part of the variscan orogen

galileo imaging observations of lunar maria and related deposits the galileo spacecraft imaged parts of the western limb and far side of the moon in december 1990 ratios of 0 41 0 56 gin filter images from the solid state hnaging ssi experiment provided information on the titanium content of mare deposits ratios of the 0 76 0 99 gm images indicated 1 gin absorptions associated with fe 2 in mafic minerals mare ages were derived froin crater statistics obtained from lunar orbiter images results on mare coinpositions in western oceanus procellarum and the humorurn basin are consistent with previous earth based observations thus providing confidence in the use of galileo data to extract compositional information mare units in the grimaldi and riccioli basins range in age froin 3 25 to 3 48 ga and consist of medium to medium high titanium 4 to 7 tio2 content lavas the schiller zucchius basin shows a higher 0 76 0 99 gm ratio than the surrounding highlands indicating a potentially higher mafic mineral content consistent with previous interpretations that the area includes mare deposits blanketed by highland ejecta and light plains materials the oldest mare materials in the orientale basin occur in south central mare orientale and are 3 7 ga old youngest mare materials are in lacus autumni and are 2 85 ga old these units are medium to medium high titanium 4 to 7 tio2 basalts thus volcanism was active in orientale for 0 85 ca but lavas were relatively constant in composition galileo data suggest that mendel rydberg mare is similar to mare orientale cryptomare are present as well thus the mare lavas on the western limb and far side to 178oe are remarkably uniform in coinposition being generally of medium to medium high titanium content and having relatively low 0 76 0 99 gin ratios this region of the moon is between two postulated large impact structures the procellarum and the south pole aitken basins and may have a relatively thick crust in areas underlain by an inferred thinner crust i e zones within large basins as at apollo titanium content is often higher however no mare deposits with titanium abundances approaching those of the high titanium 9 to 14 tio2 apollo 11 and 17 basalts nor of the high titanium regions of central oceanus procellarum are seen on the western limb or eastern far side light plains deposits are generally indistinct froin the surrounding highlands in the ssi data and are inferred to be derived primarily from the same material that forins the highlands some of the light plains are too young to be related to basin forming impacts suggesting possible volcanic origin dark mantle deposit compositions derived from ssi data are consistent with earth based observations of similar near side deposits and are interpreted to be pyroclastic materials however the modernitc albedo and 1 gin absorption of the dark mantle deposit on the southwest margin of the orientale basin suggest it is a local pyroclastic deposit contaminated with underlying highland materials from the orientale impact

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

multistage geochronological evolution of the velka fatra mountains a combined tims and ion microprobe study on zircons abstract new isotopic and geochronological data from the velka fatra mountains tatric unit of the central western carpathians are presented and discussed with a focus on the variscan orogeny and events during permian and early triassic times the investigated samples are meta to per aluminous granitoids and their trace element patterns indicate a volcanic arc origin this study presents u pb single zircon data measured on tims as well as on an ion microprobe sims the zircon age determinations were additionally constrained by cathodoluminescence cl most of the investigated granitoids yield variscan emplacement ages of about 310 ma however for the lubochna leucogranite a triassic crystallisation age at 231 17 ma was found the presence of such young slightly discordant zircon ages gives evidence for a so far unknown late permian early triassic magmatic event in the western carpathians

cadomian lower crustal contributions to variscan granite petrogenesis south bohemian pluton austria constraints from zircon typology and geochronology whole rock and feldspar pb sr isotope systematics zircons show a mean pb pb evaporation age of 355 a hybrid pyroxene bearing weinsberg type granitoid of the south 9 ma interpreted as the age of zircon growth during a carboniferous bohemian batholith austria consists of two independent mineral partial melting event in the lower crust granite emplacement at assemblages that were formed during two different magmatic events 345 5 ma is inferred from u pb analysis of the anhedral the older inherited assemblage forms unevenly distributed millimetrezircon population the comparably low radiogenic common pb sized multi grain patches of quartz mesoperthitic alkali feldspar isotope composition of megacrystic alkali feldspars suggests that at andesine bytownite clinopyroxene xmg 0 50 0 54 least some domains of these crystals are inherited from the older orthopyroxene xmg 0 35 0 42 ilmenite accessories pyroxene bearing mineral assemblage rb sr whole rock dating is it is interpreted to represent remnants of a mangeritic igneous thus severely jeopardized by the presence of the inherited alkali rock with a superimposed granulite facies re equilibration texture feldspar crystals leading to widely scattering data points and characterized by unzoned pyroxenes and plagioclase the enclosing errorchron ages of no geological significance younger assemblage with alkali feldspar oligoclase andesine quartz biotite accessories crystallized from a biotite bearing granitic melt with feldspars exhibiting typical magmatic zoning