crustal evolution in the early archaean of south america example of the sete voltas massif bahia state brazil the sete voltas massif sao francisco craton brazil appears as a composite crustal segment built in at least three successive accretional events dated by rb sr 207pb206pb monozircon and u pb shrimp methods a at ca 3 4 ga generation and emplacement of magmatic precursors to the old grey gneisses these are the oldest rocks so far recognized in south america their composition is typical of archaean ttg tonalite trondhjemite and granodiorite and geochemical modelling indicates that they were produced by partial melting of an archaean tholeiite leaving a hornblende garnet residue b between 3 17 and 3 15 ga younger grey gneisses and porphyritic granodiorites intruded the old grey gneisses their geochemical composition is clearly different from that of typical ttg and geochemical modelling shows that they were produced by partial melting of an older continental crust c grey granite dykes emplaced at ca 2 6 ga during a late stage magmatic event in the sete voltas massif all the units belonging to the sete voltas massif yield homogeneous tdm ages at 3 66 ga which are interpreted as reflecting derivation from older protoliths or rather their contamination by older pre existing continental crust it is tentatively proposed that a 3 66 ga old continental crust existed prior to the emplacement of the older grey gneisses although such crustal material is unknown at the present day in south america nutman and cordani 1993 have nevertheless reported a single zircon core from sete voltas giving a 207pb206pb age of 3 473 0 008 ga the present study together with some other recent data mougeot et al 1995 santos pinto et al 1995a indicates that the 3 4 ga old south american continental crust until now considered as of very small geographical extent in fact made up a true continental block corresponding in size to at least the whole present day gaviao block major and trace element petrogenetic modelling for the young grey gneisses and the porphyritic granodiorites indicates that the precursor magmas are derived from the melting of pre existing crustal rocks similar to the old grey gneisses this conclusion is supported by the intense migmatization of the old grey gneisses which took place before the intrusion of the younger intrusives the calculated residual mineral assemblage in equilibrium with the magmatic liquid is quartz hornblende plagioclase a condition that is achieved between p 10 kbar t 800 c 5 weight h2o or p 15 kbar t 700 c 15 weight h2o johnson and wyllie 1988 this suggests that the hydrous melting of the old grey gneisses occurred at ca 3 17 ga at depths of ca 30 45 km thus giving a minimum estimate of the thickness of this part of the archaean crust this estimate as well as the development of an intense migmatization and the strong foliation in the old grey gneisses can be interpreted as classical features of collisional thickening taken with the existence of horizontal tectonics in archaean cratons older than 3 0 ga such a conclusion indicates that more or less modern types of plate tectonic mechanisms operated in the early archaean in the studied terrain

field and geochronological evidence for origin of the contendas mirante supracrustal belt sao francisco craton brazil as a paleoproterozoic foreland basin abstract the low grade contendas mirante meta volcano sedimentary belt cmb was previously interpreted as an archean greenstone belt with the uppermost formation deposited in the paleoproterozoic new zircon u pb la icp ms ages on sedimentary groups and granite sheets intrusive in the belt constrain the timing of basin development phyllites of the lower group and meta arenites of the upper group yielded similar young zircon populations at ca 2080 ma which are interpreted as the maximum deposition age for the entire sequence the unique exception is the 3273 3338 ma zircon bearing quartzite that occurs in spatial association with the 3300 ma rhyolite a granite sheet intrusive into metagraywacke of the lower group constrains the minimum deposition age of 2045 26 ma for the cmb altogether four main age clusters of detrital zircon grains were recognized namely 2075 2200 ma 2200 2440 ma 2500 2770 ma 3270 3380 ma these age intervals match the ages of igneous and metamorphic rocks in the different terranes that comprise the sao francisco craton maximum deposition age for both groups indicates that sedimentation occurred immediately prior the high grade metamorphism in the adjacent archean paleoproterozoic jequie block and itabuna salvador curaca orogen these observations along with coarsening upwards in the sediments indicate that the cmb represents a foreland basin developed along the eastern margin of the gaviao block during plate convergence paleoarchean basement rocks were reactivated and emplaced into the cmb during basin inversion and is timely correlated with the granitic intrusion recognition of older supracrustal fragments is ambiguous one main example is the 3273 3338 ma zircon bearing quartzite which correlates with the northern jacobina basin along the contendas mirante lineament e g bahia gold belt and may represent part of an archean intracontinental rift sequence

jupiter s main auroral oval observed with hst stis 1 an extended series of fuv images obtained on 7 days during winter 2000 2001 with fixed pointing yielded highly accurate tracking of emisson features as jupiter rotated they provided newly detailed measurements of the degree of corotation of auroral emissions and their variations with changing central meridian longitude this 2 month data set provides a statistical average location of the auroral emission and leads to the definition of new reference ovals the overall auroral morphology pattern is shown to be fixed in system iii longitude and unchanged over a 5 year period when arranged in central meridian longitude ranges the images show a significant contraction of the northern main oval as the central meridian longitude increases from 115 to 255 the main auroral oval brightness is globally very stable in comparison with its terrestrial counterpart it is shown to vary with magnetic local time increasing from noon to dusk and then decreasing again in the magnetic evening hectometric emissions observed simultaneously with galileo and cassini reveal interplanetary shocks propagating outward from the sun which may be related to the contraction of the main auroral oval observed in the hst images taken on 14 december 2000 in addition we find that a brightening and a significant contraction of the main oval observed on 13 january 2001 corresponded to a time of increased solar wind dynamic pressure

chromite geochemistry and pge fractionation in the campo formoso complex and ipueira medrado sill bahia state brazil two districts of stratiform chromite deposits are situated near the northern margin of the sao francisco craton the ultramafic host rocks are remnants of early precambrian layered complexes that intruded archean gneissic blocks prior to transamazonian collisional events the intrusions contain abundant chromite exhibit orthopyroxene rich sequences and are similar geochemically with highly magnesian bulk compositions mg mg fe 0 91 0 67 and fractionation trends consistent with komatiitic parent magmas the intrusion form alteration history and current metamorphic grade of each are distinct at the ipueira medrado mines representative of the jacurici valley district a folded segment of a 200 to 250 m thick ultramafic mafic sill contains a 5 to 8 m thick highly massive chromitite layer green spinel in the orthopyroxene rich peridotite and ubiquitous granoblastic textures indicate recrystallization during upper amphibolite or granulite facies metamorphism now with incomplete retrograde alteration and serpentinization in campo formoso a deeply eroded stratiform complex contains at least seven different economic chromite seams comprising varying proportions of disseminated net textured layered and massive ores here greenschist alteration of the ultramafic host rocks is complete apart from orthopyroxene relicts in an upper unit at the cascabulhos mine microprobe studies of chromite rich specimens from representative stratigraphic sections of each intrusion suggest that unusually low tio2 levels 0 9 wt combined with high cr2o3 contents 45 55 wt reflect the primitive parental magma composition in both intrusions core compositions of chromite from cascabulhos retain high xcr 0 57 0 72 but show a wide range of xmg 0 21 0 47 consistent with fe mg exchange at grades at or below amphibolite facies some relict igneous fractionation is preserved since tio2 increases 0 2 0 4 wt while cr al or xcr decreases 0 70 0 55 from the massive chromitites hosted by serpentinite through the disseminated seams above to the two high level seams in pyroxenite chromite from ipueira medrado is more magnesian xmg 0 57 0 64 but also more aluminous xcr 0 60 0 64 when massive types are compared here the submassive minor seams stratigraphically above and below the main seam both have relatively lower xmg and xcr 0 36 0 45 and 0 45 0 57 this suggests that combined cr al and mg fe exchange occurred between chromite and silicates during postemplacement progressive metamorphism of the seams close spaced sampling of representative drill core sections at 2 or 4 m intervals has allowed the precious metal potential of each intrusion to be assessed in both cases the highest total platinum group element pge concentrations occur exclusively in chromitite illustrating the well known phenomenon of chromite control the ipueira medrado chromitite contains lower concentrations 350 ppb and has unfractionated pge patterns chalcophile element analyses provide little evidence of precious metal scavenging by immiscible sulfide segregation and so indicate little potential for mineralization elsewhere in the sill at campo formoso the alternation of pge enriched chromitite and barren silicates is suggestive of repeated influxes of primitive magma during open system fractionation an increase in the pt pd and rh tenor of the chromitite to ca 1 ppm occurs from the lower massive group through the upper disseminated group to the high level seams hosted by pyroxenite thus upward evolution of the host chromite mineral compositions is matched by increasing pt pd ru os ir ru ratio the covariation of pge ratios with chromite mineral chemistry is analogous to that occurring over the sequence of chromitite seams in the lower critical zone of the bushveld complex this provides evidence for a fundamental link in the fractionation processes controlling chromite and pge mineralization in stratiform intrusions which has clear implications for exploration models

a three stage structural evolution of the quadrilatero ferriifero consequences for the neoproterozoic age and the formation of gold concentrations of the ouro preto area minas gerais brazil abstract the quadrilatero ferrifero occurs in the southern part of the sao francisco craton brazil where three major proterozoic supracrustal units the rio das velhas minas and itacolomi supergroups are exposed together with archaean to palaeoproterozoic granito gneissic basement microtectonic and kinematic analyses have been undertaken in the area close to ouro preto in order to precise the tectonic evolution and to distinguish the tectonic features related to the transamazonian and brasiliano orogenies respectively 2000 and 600 ma three main tectonic events have been recognized the earlier event de is clearly expressed within basement rocks of the bacao complex and surrounding supracrustal units a stretching lineation le lineation roughly oriented n s can be observed numerous shear criteria such as drag folds and asymmetric pressure shadows indicate a top to the south sense of movement along the southern border of the bacao complex this event was developed within amphibolite facies conditions fact confirmed by quartz c axis fabrics this earlier deformation is related to plutonic activity and reactivation of the archaean basement expressed by the occurrence of scarce leucocratic granitoid rocks intruded within the bacao gneisses it is here attributed to the transamazonian orogeny in agreement with recent u pb dating 2000 ma the large scale folds i e mariana anticline dom bosco syncline which define the dominant structural geometry of the quadrilatero ferrifero were formed during this event the second tectonic event dm has been defined as a major thrusting towards the wnw related to the brasiliano cycle a well expressed stretching and mineral lineation oriented e w to nw se lm lineation and associated nw verging shear criteria characterize this event occurrence of muscovite biotite and more scarcely sillimanite indicate that deformation developed in upper greenschist lower amphibolite facies quartz c axis fabrics confirm the sense of shearing but the large scattering of several fabrics traduces a weak intensity of strain all supracrustal and gneiss formations were affected by the thrusting which is developed on a folded surface previously formed during the de event the third event dm is characterized by hangingwall down movement of the nappe pile in response to relaxation of the brasiliano compressional dm forces this event developed in greenschist facies is marked by the occurrence of metre scale drag folds sometimes associated to the development of a new lineation lm gold mineralization which occurs along the main mineralized contact located between the minas and rio das velhas supergroups is found within late veins which comprise large recrystallized quartz carbonate sulphide chlorite and tourmaline microscopic analysis and veins geometry allow us to conclude that the veins were emplaced mostly after the ductile dm deformation it is proposed that the veins were formed by filling of open cavities created during dm tectonics this study highlights that the northwest verging thrusting which is the main tectonic event of the quadrilatero ferrifero is only relevant of the brasiliano orogeny a model of structural evolution which involves plutonic activity at 2000 ma within the archaean bacao complex followed by neoproterozoic thrust tectonics brasiliano is proposed and discussed the age of gold concentration assumed to be achieved during the relaxation that occurred in response to the thrusting event is re interpreted and related to the late stage of the brasiliano tectonics

effects of turbulence on the transport of individual particles as bedload in a gravel bed river this study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel bed river the experimental design implemented in the eaton north river quebec canada is based on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical flow velocity components using a vertical array of three electromagnetic current meters ecms the frequency and distance of displacement of particles larger than 20 mm that were sliding or rolling on the bed were measured from a 10 minutes long film mean and turbulent flow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling when particles are sliding weak differences are present for the mean streamwise velocity and normal vertical stresses instantaneous reynolds shear stresses are significantly lower for sliding events which was not expected but could be explained by the important dominance of quadrant 3 events inward interactions when particles are rolling only the vertical normal stresses show a weak difference from those observed in the absence of transport but they tend to occur when quadrant 2 ejections dominate the flow field for both sliding and rolling particles vertical and or streamwise fluid accelerations show high magnitude values when compared to periods without transport for sliding particles streamwise acceleration is mostly negative and combines most of the time with a positive vertical acceleration for rolling particles streamwise and vertical acceleration are predominantly of opposite sign these results suggest that fluid acceleration or deceleration in the streamwise and vertical directions is affecting the pressure field around particles in this study fluid acceleration seems to play a more important role than reynolds shear stress or normal stresses for bedload movements copyright 2010 john wiley sons ltd

measurements of turbulence in the benthic boundary layer over a gravel bed and comparison between acoustic measurements and predictions of the bedload transport of marine gravels articles originaux williams j j thorne p d heathershaw a d 1989a sedimentology 36 959 971 1989b sedimentology 36 973 979

jupiter s interior and deep atmosphere the initial pole to pole passes with the juno spacecraft on 27 august 2016 the juno spacecraft acquired science observations of jupiter passing less than 5000 kilometers above the equatorial cloud tops images of jupiter s poles show a chaotic scene unlike saturn s poles microwave sounding reveals weather features at pressures deeper than 100 bars dominated by an ammonia rich narrow low latitude plume resembling a deeper wider version of earth s hadley cell near infrared mapping reveals the relative humidity within prominent downwelling regions juno s measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise this has implications for the distribution of heavy elements in the interior including the existence and mass of jupiter s core the observed magnetic field exhibits smaller spatial variations than expected indicative of a rich harmonic content

u pb rb sr and sm nd chronology of granitic basement hydrothermal albitites and uranium mineralization lagoa real south bahia brazil the granites orthogneisses hydrothermal albitities and rocks which have suffered uranium mineralization from the lagoa real district south state of bahia brazil have been investigated by u pb rb sr and sm nd techniques u pb values on zircons from the granitic protolith give an age of 1725 ma u pb on u mineralization dates the primary mineralization at 1395 ma and indicates a reworking at 480 ma which may represent the age of the thrusting of the lagoa real complex over espinhaco metasediments during the brazilian orogeny these two dates are given by rb sr on albitites but from sparse information and are not supported by unequivocal arguments the uranium deposition and sodium metasomatism however cannot be linked either with the thermal history of the granite or with brazilian thrusting sm nd gives scattered results which are suggestive of autochtonous reworkings of rees these results lead to the following suggestions 1 magmatic activity of subalkaline affinity existed within the sao francisco craton at about 1 7 ga 2 such subalkaline plutons are likely sources for u mineralization 3 at about 1 4 ga an unknown event caused hydrothermal activity leading to u deposition at lagoa real 4 brazilian overthrusting at about 480 ma did not play any genetic role in the hydrothermal activity

where are the eburnian transamazonian collisional belts the reconstruction of early proterozoic crustal evolution and geodynamic environments in africa and south america is incomplete if cratonic areas alone are studied if the presence of high grade

the rio itapicuru greenstone belt bahia brazil structure and stratigraphical outline abstract the rio itapicuru greenstone belt is situated within the sao francisco craton and is the largest of a series of n s trending volcanosedimentary sequences surrounded by gneisses and granitoids pb pb and rb sr dating of andesitic lavas within the supracrustal sequence yielded ages of 2 1 ga with late tectonic granitoids emplaced about the same time the succession appears to be developed on a sialic basement represented by the santa luz gneiss complex although the actual contact between basement and supracrustals has not been observed there is a sharp contrast in strain and metamorphic conditions near to the contact zone a 2 9 ga u pb age obtained from a gneissic raft within the intrusive ambrosio dome is interpreted as a basement to the greenstone sequence and was plucked from a lower crustal level by the ascending magma the itapicuru river section provides good exposures along an e w profile and has been used to attempt a reconstruction of the lithostratigraphy in this area where the supracrustals reach a maximum thickness of 9 5 km rare stratigraphic facing and structural data indicate that the base of the sequence is marked by an intrusive granitoid above this contact is a 5 0 km thick succession of tholeiitic subaqueous basalts with rare cherts banded iron formation pelites andesitic lavas and tuffs this mafic domain is overlain by a 3 5 km thick sequence of andesites tuffs and volcanogenic sediments with rare dacites and laminated cherts a silica gap between 55 and 60 sio2 characterises the lavas as a bimodal sequence two small ultramafic bodies with komatiitic chemistry also occur in the andesitic volcanic domain the uppermost 1 0 km consists of volcanogenic siltstones and shales with rare arkoses tuffs and basalts localised bedding parallel shear zones are the earliest deformation features observed the shear zones may be up to 200 m thick and were important in controlling subsequent lode gold mineralisation in the north central sector of the greenstone belt these shear zones were deformed by n s trending east verging folds with 20 km wavelength the main greenstone sequence in the itapicuru river section lies on the overturned limb of a syncline and the ambrosio dome occupies the adjoining anticline in the southern part of the greenstone belt the initial deformation produced a major shear zone striking e w with a 40 s dip and a subhorizontal e w stretching lineation north verging folds and thrusts produced the present e w trend a late upright ne sw trending fold phase terminated the ductile deformation greenschist facies metamorphism affected the major part of the belt during deformation with amphibolite facies assemblages developed around the margins and thermal aureoles developed around intrusions metamorphic fluids transported gold to higher crustal levels via pre existing steeply dipping shear zones and faults and produced the large fazenda brasileiro deposit along with many smaller deposits

h3 as an ionospheric sounder of jupiter and giant planets an observational perspective thirty years of observations of h3 on jupiter have addressed many complex questions about the physics of the ionospheres of the giant planets spectroscopy imaging and imaging spectroscopy in the

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

the miocene pliocene macusani volcanics se peru i mineralogy and magmatic evolution of a two mica aluminosilicate bearing ignimbrite suite

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

the geologic evolution of the ancient granite greenstone terrane of central southern bahia brazil abstract the granite greenstone terrain of central southern bahia belongs to the sao francisco craton and is a key area for the understanding of the archaean and lower proterozoic of south america in addition it is in an area of great metallogenic potential the granitic migmatitic gneissic basement complex is intimately associated with low to medium grade metasedimentary and metavolcanic sequences such as the brumado umburanas and contendas mirante in all of these sequences the metasedimentary rocks predominate although acid metavolcanics constitute a significant fraction of the contendas sequence and ultrabasic rocks occur in several isolated units early archaean granitoid rocks rb sr isochron ages older than 3 ga occur in some regions such as mata verde boa vista lagoa do morro and sete voltas extensive granitic intrusive activity with associated medium grade metamorphism and metasomatism occurred in most of the area 2 7 ga ago and the resulting terrain is taken to be the basement at least for the contendas mirante sequence the relationships to the brumado and umburanas metamorphic complexes are not clear and these sequences may be of archaean age the contendas mirante sequence was affected by strong lower proterozoic deformation 2 ga ago and contemporaneous granitic intrusions like the gameleira granite large domal structures interpreted as mantled gneiss domes such as those associated with the boa vista and sete voltas granitoid rocks also formed at this time a late proterozoic to early palaeozoic thermal event affected the southwestern part of the region at 0 5 0 7 ga ago as revealed by mica k ar ages

geochemical comparison between himalayan and hercynian leucogranites abstract isotopic sr pb nd o ree and trace element data from three himalayan nepal and six hercynian brittany france leucogranites are compared for the himalayan granites makulu mustang and especially manaslu the 87sr 86sr versus 87rb 86sr scatter diagrams and hence variability of the initial 87sr 86sr ratios reflect heterogeneity of the source materials these ratios are very high 0 730 0 770 for manaslu the very high 207pb 204pb ratios 15 8 at the corresponding 206pb 204pb ratio of 18 8 the very low 143nd 144nd ratios i nd 13 to 17 and the very high 18o 16o ratios 12 confirm the crustal origin with the paragneisses of the tibetan slab formation i as the probable parent source for the six hercynian granites with an individual rb sr isochron established for many of them the initial 87sr 86sr ratios range from 0 706 to 0 717 the lead neodymium and oxygen isotope compositions confirm their crustal source of presumably palaeozoic age but not specifically identified the rare earth patterns and thorium contents are comparable to those for himalayan granites the similarities of the geochemical signatures isotopes and trace elements of the himalayan and hercynian leucogranites suggest that the petrogenetic processes were comparable and that the himalayan continental collision model can be applied to the hercynian the depletion in ree and th implies either interaction of the granitic liquids with fluid or more probably early precipitation of monazite the increase in sm nd in the granites compared to their parent materials implies that the neodymium model ages of primary mantle extraction are maximum rather than minimum ages in contrast to the hercynian leucogranites the extremely radiogenic sr of the himalayan leucogranites reflects the very long crustal residence time before the melting event the apparent uniformity of the initial 87sr 86sr ratios of the individual hercynian granites may be related to an aging effect where the straight line fitting improves with increase in age of the pluton

hydrogen and oxygen isotope variations in the high himalaya peraluminous manaslu leucogranite evidence for heterogeneous sedimentary source abstract the manaslu granite belongs to the high himalaya leucogranitic belt which was produced by melting of the crust during postcollisional thrusting d and 18o values have been determined for whole rock and coexisting minerals from the 8 km thick manaslu massif and its 50 km long dyke sheet its country rocks and the formation 1 f1 paragneisses which are the source of the granite for the granite dmusc range from 70 to 85 and 18o w r from 10 9 to 12 8 h and o isotope fractionations among minerals are consistent with high temperature equilibrium and for oxygen closed system evolution a few samples coming mainly from the dyke swarm have very low d values down to 188 and biotite muscovite h isotope fractionations indicative of disequilibrium the d h ratios of associated magmatic tourmaline are essentially unmodified from the distribution of d values in the granite and its country rocks circulation of very low deuterium meteoric hydrothermal waters was extremely localized because these waters are depleted in deuterium by up to 50 relative to modern meteoric waters the manaslu area was either at an altitude substantially higher than that of today 2500 6000 m for the analyzed samples or a mountain chain once existed to the south the f1 gneisses have 18oquartz between 12 and 14 3 which confirms that the granite was generated from f1 but d values are 20 higher than in the granite such a difference can be a result of degassing of the magma and or introduction of fluid in the melting zone infiltration of low d fluid 90 into the hot but dry f1 probably triggered partial melting these fluids could have come from the dehydration of the midlands sediments which are separated from the overlying f1 by the main central thrust the correlations among 18o 87 sr 86 sr 20 ma and nd values in both f1 and the granite indicate that the variations of these isotopic ratios in the manaslu are inherited from those in f1 at the time of melting in turn these ratios in f1 are related to the proportion of quartz and phyllosilicates for the isotopic ratios of nd and o and to the quantity of radiogenic sr generated within the sediment which is a function of age and rb content amount of phyllosilicate some other himalayan leucogranites require either other crustal source rocks or the 18o and 87 sr 86 sr ratios of f1 vary along the himalaya

probabilistic description of grain resistance from simultaneous flow field and grain motion measurements experiments were carried out using a mobile gravel bed placed in a tilting flume with a modified particle image velocimetry piv system individual grain movements were surveyed using data from time series of images near bed velocity flow field measurements were made simultaneously above the same area of the sediment surface by applying cross correlation techniques to the collected plan view images statistics of grain motions were collected through a semiautomatic procedure significant changes in the flow field were observed in the proximity of the entrained or deposited particles a strong correlation is shown between the changes in the local streamwise and lateral velocity and the movement of the grains the theory of grass is revisited and developed based on the experimental results the probability distribution of individual grain resistance has been derived from the statistics of the near bed velocity field and of the entrainment risk

the 2 ga peraluminous magmatism of the jacobina contendas mirante belt bahia brazil major and trace element geochemistry and metallogenic potential abstract the jacobina contendas mirante belt represents a transamazonian 2 ga n s 500 km long elongated orogenic domain in the central part of the sao francisco craton bahia state numerous syntectonic to post tectonic peraluminous leucogranites were emplaced along the major structures of the belt their mineralogical and geochemical and some of their metallogenetic characteristics are very similar to their hercynian and himalayan equivalents however their average peraluminous index varies from one granitic pluton to another and biotite is on average slightly more magnesian in the transamazonian leucogranites higher oxygen fugacity is indicated by the general occurrence of magnetite the stability of allanite and sometimes epidote in most of the plutons and by biotite chemistry the peraluminous magmatism of the jacobina contendas mirante belt results from crustal partial melting during a continental collision event at 2 ga trace element geochemistry implies variable source composition and or melting conditions for the different granitic plutons and some different facies within the same plutonic unit the scarcity of ilmenite the general occurrence of magnetite and the relatively low peraluminous index of some of these granites suggest that graphite beating sediments are not a significantly source material from their mineralogical and geochemical characteristics acid meta igneous rocks such as the sete voltas ttg suite of presumed archaean age seem to represent a suitable source for these granites sn w li f and be enrichment of most transamazonian leucogranites is much weaker than in the mineralized variscan equivalents the caetano alianca and riacho das pedras granites represent the most specialized granitic bodies beryl emerald molybdenite and scheelite mineralizations are related to some of these granites which intrude ultrabasic formations the campo formoso and the carnaiba granites in many of these granites uranium content is comparable to values measured in mineralized hercynian leucogranites the occurrence of hexavalent uranium minerals mineralization and episyenitic alteration are favourable criteria for finding variscan type uranium ore deposits

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

emerald dating through 40ar 39ar step heating and laser spot analysis of syngenetic phlogopite emerald occurring in k metasomatic rocks developed at the contact of the carnaiba leucogranite with serpentinite bahia state brazil has been dated using an original 40ar 39ar procedure it combines step heating and spot fusion experiments on two types of phlogopite crystals 1 bulk samples and individual grains extracted from the enclosing k metasomatic host rocks and 2 syngenetic solid inclusions precipitated along growing zones of the emerald host crystals the second procedure uses in situ laser probe experiments on rock sections in spite of the huge amounts of excess 40ar detected in adjacent emerald we could measure reliable ages of 1951 8 ma and 1934 8 ma for the trecho velho and braulia occurrences respectively spot fusion data had higher discrepancy than the step heating data but minute crystals of phlogopite included in emeralds bearing excess argon do not reveal excess argon a muscovite belonging to the same granite hydrothermal complex gave a plateau age of 1976 8 ma which may correspond to a higher closure temperature of the kar system during the cooling of the whole pluton and associated hydrothermal halo these accurate measurements lead to the following conclusions 1 direct emerald dating is possible 2 in spite of a polyphase history during the transamazonian orogenesis 2 ga combined step heating and spot fusion experiments give a better precision for granite related emerald mineralization than the scattered ages obtained by rb sr and k ar methods 3 the late transamazonian tectonothermal retrograde event which probably caused the dispersion of previous rb sr and k ar data is not revealed by our procedure 4 the emerald mineralization and k metamorphism appear to be linked with the thermal history of the leucogranite 5 in addition to its use in polyphase crustal domains accurate 40ar 39ar dating is of major interest in the field of metallogenic models even for instance for mineralizations characterized by disturbed isotopic systems which record effects as excess argon

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

the 2 ga peraluminous magmatism of the jacobina contendas mirante belts bahia brazil geologic and isotopic constraints on the sources abstract a 500 km north south alignment of granitic intrusions cross cuts the central part of the sao francisco craton these late to post tectonic granitic bodies are emplaced between two archean blocks jequie and gaviao blocks and cross cut the contendas mirante volcano sedimentary sequence and the metasedimentary rocks of the serra de jacobina they are two mica or muscovite garnet bearing peraluminous granites rb sr systematics show that these granites were emplaced during the transamazonian orogeny 1 9 ga the high initial 87 sr 86 sr ratios 0 706 0 748 and the very low nd t 13 to 5 indicate a crustal origin possible sources are 1 the jequie block 2 the contendas mirante sequence and 3 the gaviao block including some early archean domes trondhjemitic tonalitic granodioritic ttg boa vista type which were tectonically emplaced within the volcano sedimentary sequence the currently available rb sr and sm nd data are not consistent with reworking of the 3 5 ga ttg the combination of field and isotopic constraints preclude the jequie block and the contendas mirante sequence and favour instead the gaviao block medium grade terrains as the source for the peraluminous granitic line the available data suggest that a continent continent collision occurred during the transamazonian orogeny which followed subduction obduction marked by volcanism arc tholeiitic calc alkaline and shoshonitic and related plutonism

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

preliminary jiram results from juno polar observations 2 analysis of the jupiter southern h3 emissions and comparison with the north aurora the jupiter infrared auroral mapper jiram aboard juno observed the jovian south pole aurora during the first orbit of the mission h3 trihydrogen cation and ch4 methane emissions have been identified and measured the observations have been carried out in nadir and slant viewing both by a l filtered imager and a 2 5 m spectrometer results from the spectral analysis of the all observations taken over the south pole by the instrument are reported the coverage of the southern aurora during these measurements has been partial but sufficient to determine different regions of temperature and abundance of the h3 ion from its emission lines in the 3 4 m wavelength range finally the results from the southern aurora are also compared with those from the northern ones from the data taken during the same perijove pass and reported by dinelli et al 2017

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