stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

petrogenesis of the swaziland and northern natal rhyolites of the lebombo rifted volcanic margin south east africa thejozini and mbuluzi rhyolites and oribi beds of the southern lebombo monocline southeastern africa have geochemical characteristics that indicate they were derived by partial melting of a mixture of high ti zr and low ti zr sabie river basalt formation types compositional variations within the different rhyolite types can largely be explained by subsequent fractional crystallization the srand nd isotope composition of the rhyolites is unique amongst gondwana silicic large igneous provinces having end values close to bulk earth 0 94 to 0 35 and low but more variable initial sr sr ratios 0 7034 0 7080 quartz phenocryst do values indicate that the rhyolite magmas had do values between 5 3 and 6 7o consistent with derivation from a basaltic protolith with do values between 4 8 and 6 2o the low do rhyolites 56 0o come from the same stratigraphic horizon and are overlain and underlain by rhyolites with more normal do magma values these low do rhyolites cannot have been produced by fractional crystallization or partial melting of mantle derived basaltic material the rhyolites have low water contents making it unlikely that the low do values are the result of post emplacement alteration modification of the source by fluid rock interaction at elevated temperatures is the most plausible mechanism for lowering the do magma value it is proposed that the low do rhyolites were derived by melting of earlier altered rhyolite in calderas situated to the east which were not preserved after gondwana break up

controls on prolate and oblate geode geometries in the veia alta basalt flow largest world producer of amethyst parana volcanic province brazil abstract variable intensity of hydrothermal alteration of the veia alta basalt flow ametista do sul brazil exerted the fundamental control on the shape and size of the amethyst geodes the loss on ignition loi of the host basalt is used as a proxy for intensity of alteration and has direct relationship with the height of the geodes up to 150 cm in the three study mines and with the prolaticity of geodes all rocks with loi 5 wt host prolate geodes and all oblate geodes are hosted in rocks with loi 2 k 2 o and rb the hydrothermal origin of the geodic cavities is thus established and their shapes explained by the empirical observation of the results from a previous numerical simulation experiment

geochronology ar ar and k ar of the south atlantic post break up magmatism this work integrates the available geological information and geochronology data for the cretaceous recent magmatism in the south atlantic represented by onshore and offshore magmatic events including the oceanic islands along the transform faults and near the mid ocean ridge the analysis of the igneous rocks and their tectonic settings allows new insights into the evolution of the african and brazilian continental margins during the south atlantic opening following the abundant volcanism in the early cretaceous the magmatic quiescence during the aptian albian times is a common characteristic of almost all brazilian and west african marginal basins however rocks ascribed to the cabo granite 104 ma are observed in ne brazil in west africa sparse aptian albian ages are observed in a few coastal igneous centres in the se brazilian margin an east west alkaline magmatic trend is observed from pocos de caldas to cabo frio comprising igneous intrusions dated from 87 to 64 ma mafic dyke swarms trending nw also occur in the region extending from the cabo frio province towards the central brazilian craton on the west african side early cretaceous recent volcanism is observed in the walvis ridge 139 ma the st helena ridge 81 ma and the cameroon volcanic line early tertiary recent volcanic islands such as ascencion 1 0 0 65 ma tristao da cunha 2 5 0 13 ma and the st helena islands 12 ma most probably correspond to mantle plumes or hot spots presently located near the mid atlantic spreading centre within the south america platform and deep oceanic regions the following volcanic islands are observed the rio grande rise 88 86 ma abrolhos 54 44 ma the vitoria trindade chain no age trindade 2 8 1 2 ma and fernando de noronha 12 1 5 ma there are several volcanic features along the nw se trending cruzeiro do sul lineament from cabo frio to the rio grande rise but they have not been dated the only known occurrence of serpentinized mantle rocks in the south atlantic margin is associated with the saint peter and saint paul rocks located along the sao paulo fracture zone the cameroon volcanic line in nw africa is related to the magmatism that started in the late cretaceous and shows local manifestations up to the present the compilation of all available magmatic ages suggests an asymmetrical evolution between the african and south america platforms with more pre break up and post break up magmatism observed in the brazilian margin this is most likely to have resulted from the different geological processes operating during the south atlantic ocean opening shifts in the spreading centre and possibly the rising and waning of mantle plumes

petrology of serra geral parana continental flood basalts southern brazil crustal contamination source material and south atlantic magmatism the serra geral parana continental flood basalt sg cfb province in brazil is associated with the jurassic cretaceous breakup of gondwanaland and the transition of continental to oceanic magmatism during the opening of the south atlantic ocean a suite of 24 samples representative of the sg cfb in rio grande do sul southern brazil shows a compositional continuum from basalt 50 53 wt sio2 mg 60 45 to basaltic andesite to andesite rhyodacite and rhyolite 73 wt sio2 certain compositional aspects of the mafic rocks e g tio2 k2o cao zr nb zr y ti zr resemble those of basaltic dikes and flows associated with the opening of the north atlantic ocean

grain size and heavy minerals of the late quaternary eolian sediments from the imbituba jaguaruna coast southern brazil depositional controls linked to relative sea level changes abstract the stratigraphic subdivision and correlation of dune deposits is difficult especially when age datings are not available a better understanding of the controls on texture and composition of eolian sands is necessary to interpret ancient eolian sediments the imbituba jaguaruna coastal zone southern brazil 28 29 s stands out due to its four well preserved late pleistocene eolian generation 1 to holocene eolian units eolian generations 2 3 and 4 in this study we evaluate the grain size and heavy mineral characteristics of the imbituba jaguaruna eolian units through statistical analysis of hundreds of sediment samples grain size parameters and heavy mineral content allow us to distinguish the pleistocene from the holocene units the grain size displays a pattern of fining and better sorting from generation 1 older to 4 younger whereas the content of mechanically stable dense and hard heavy minerals decreases from eolian generation 1 to 4 the variation in grain size and heavy mineral content records shifts in the origin and balance input versus output of eolian sediment supply attributable mainly to relative sea level changes dunefields submitted to relative sea level lowstand conditions eolian generation 1 are characterized by lower accumulation rates and intense post depositional dissection by fluvial incision low accumulation rates favor deflation in the eolian system which promotes concentration of denser and stable heavy minerals increase of ztr index as well as coarsening of eolian sands dissection involves the selective removal of finer sediments and less dense heavy minerals to the coastal source area under a high rate of relative sea level rise and transgression eolian generation 2 coastal erosion prevents deflation through high input of sediments to the coastal eolian source this condition favors dunefield growth coastal erosion feeds sand from local sources to the eolian system including sands from previous dunefields eolian generation 1 and from drowned incised valleys therefore dunefields corresponding to transgressive phases inherit the grain size and heavy mineral characteristics of previous dunefields leading to selective enrichment of finer sands and lighter minerals eolian generations 3 and 4 developed during a regressive progradational phase holocene relative sea level highstand the high rate of sediment supply during the highstand phase prevents deflation the lack of coastal erosion favors sediment supply from distal sources fluvial sediments rich in unstable heavy minerals thus dunefields of transgressive and highstand systems tracts may be distinguished from dunefields of the lowstand systems tract through high rates of accumulation low deflation in the former the sediment source of the transgressive dunefields high input of previously deposited coastal sands differs from that of the highstand dunefields high input of fluvial distal sands based on this case study we propose a general framework for the relation between relative sea level sediment supply and the texture and mineralogy of eolian sediments deposited in siliciclastic wet coastal zones similar to the imbituba jaguaruna coast

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

new time constraints on dyke swarms related to the parana etendeka magmatic province and subsequent south atlantic opening southeastern brazil abstract 40 ar 39 ar incremental heating analyses were carried out on tholeiitic dyke swarms of santa catalina florianopolis and rio de janeiro and alkaline dykes from the proximity of rio de janeiro city southeastern brazil most of the plagioclases from the tholeiitic dykes display disturbed age spectra with younger apparent ages most often clearly correlated with alteration phases however a calculated weighted mean age from the less disturbed released fractions of the ne oriented santa catarina dyke swarm gives an age of 129 4 0 3 ma which is contemporaneous with the ponta grossa dyke swarm pgds and at least the northern parana continental flood basalts cfb the rio de janeiro tholeiitic dykes display age spectra affected by alteration and probably excess argon but with low temperature mini plateau ages between 130 6 and 129 8 ma which are concordant with previous data obtained on the pgds and rio de janeiro dyke swarms by renne et al 1996a and turner et al 1994 these new geochronological data when added to the previous ones show that the initiation of gondwana s breakup in the region was characterized by a volcano tectonic system with a geometry more complicated than the rift rift rift system suggested by many authors the different rift arms of this structural feature were operating during a brief time period mainly from 131 5 to 129 ma and were contemporaneous at least with the northern part of the parana etendeka province pep single grain and bulk sample biotite from the alkaline mainly coast parallel dyke swarm near rio de janeiro city display plateau ages around 80 ma 81 8 1 8 and 78 8 2 8 ma and 70 ma 72 5 0 5 and 69 7 0 2 ma these magmatic intrusions refer to late cretaceous flexuring and vertical movements and rift basin formations almeida 1976 due the northward progressing rifting motions separating south america and africa during south atlantic ocean formation

nanoscale constraints on a fluid induced transformation of monazite during postmagmatic alteration a case of the jawornik granitoid ne orlica śnieznik dome sudetes sw poland abstract two monazite grains altered during postmagmatic hydrothermal processes in the variscan jawornik granitoid ne orlica nieznik dome sudetes sw poland were investigated different assemblages of secondary phases replacing and forming close to altered monazite indicate two different courses of the mineral fluid reactions the first monazite is surrounded by two zones comprising rhabdophane group minerals rhabdophane henceforth and hematite inner zone and allanite outer zone that form a concentric corona texture the growth of secondary phases is interpreted as being related to decreasing temperatures below ca 500 c the inner zone formed due to alteration of the monazite that was driven by fluid induced coupled dissolution reprecipitation reactions this alteration resulted in the progression of partial replacement by submicron layers of rhabdophane along the monazite surface and pseudomorphic replacement of a substantial part of the monazite by rhabdophane and hematite the presence of the hematite suggests oxygen fugacity above the hematite magnetite buffer alteration of the second investigated monazite is related to dissolution induced by a k bearing alkali fluid partial replacement by thorianite tho2 and overgrowth by k feldspar with minor titanite formed during the chloritization of biotite and the alteration of feldspars these results demonstrate that the local character of mineral fluid reactions can take an entirely different course at the microscale within a distance of several hundreds of microns the assemblages of secondary phases replacing two investigated monazite grains indicate that the alteration processes are related to moderate temperature

geochemical and scintillometric characterization and correlation of amethyst geode bearing parana lavas from the quarai and los catalanes districts brazil and uruguay geochemical studies of the six lowermost lava flows of the cretaceous serra geral formation parana volcanic province in quarai brazil and artigas uruguay were combined with flow by flow field studies of structures and scintillometric profiles to establish a consistent regional stratigraphic framework over at least 100 km this greatly improves exploration capability for amethyst and agate geodes a basalt colada mata olho alegrete facies serra geral formation was the first lava to flow over the ancient botucatu desert in the region but an andesite colada catalan overstepped this basalt in many places perhaps palaeohighs four basaltic andesites complete the lava stratigraphy in this formation adding up to 300 m of lavas the stratigraphic sequence of contrasting lava compositions is 51 0 wt sio 2 in the first lava followed by 57 5 52 5 56 0 53 0 and finally 54 5 wt sio 2 overall mgo variation is between 2 and 7 wt all lavas in the two districts are low ti 2 of the gramado type the characteristic contents of most major and trace elements 124 rock samples analysed allow the ready identification of each lava contrasting rock chemistry also results in strong variation in scintillometric values 270 points measured in the field and nineteen continuous borehole profiles from bottom to top of the stratigraphy the cps values are 49 3 2 123 10 3 62 4 7 94 4 6 45 and 85 colada catalan has the structure of aa lava particularly the contorted igneous banding and autobreccias in the upper and lower crusts in some places a 2 m thick silicified sandstone layer lies on top of some coladas and silicified sandstone forms breccias with volcanic rocks geochemistry of the six lavas indicates complex evolution involving melting of lithospheric mantle injection into the crust and assimilation of crust followed by fractional crystallization this study indicates the possibility of world class deposits of amethyst geodes on the brazilian side of the border with uruguay

geological relationships of basalts andesites and sand injectites at the base of the parana volcanic province torres brazil abstract the cretaceous interaction of the heated giant guarani aquifer with lavas dikes and sills of the parana volcanic province is here evaluated based on the description of the large exposures in torres southernmost brazil chalcedony silicified sandstone dikes sills and breccias containing volcanic clasts in a sandstone matrix are common in the parana volcanic province sandstone layers mark either the contact between lava flows or the base of the vertically jointed massive core in torres one basaltic andesite and one andesite lava flow of the low ti gramado type and basalt and basaltic andesite sills and dikes are correlated over 10 km with rocks in the graxaim quarry scintillometric emission rates vary systematically with contents of k th and u and are characteristic of each lava or intrusive rock major and trace elements are also characteristic of each lava three large outcrops of breccias display angular amygdaloidal volcanic clasts immersed in a silicified sandstone matrix no evidence was found of high temperature 1150 c interaction of the lava with the loose erg of the botucatu formation such as fluidal volcanic clasts quenched rims or thermal recrystallization of the sand only a thin 5 mm layer of thermally modified sand is present on top of a paleodune in torres in torres the interaction of andesite with wet sand occurred after degassing of the lava because the breccia clasts are amygdaloidal all evidence points to hydrothermal processes for the formation of the breccias such as lozenge fractures filled with silicified sandstone preserved detrital characteristics of the sandstone grains and cold below 130 c contact between the volcanic rock and the sand most significant is the timing of sand intrusion because thin 1 mm dikes of silicified sandstone cut fractures in the rock and the zeolite filled amygdales the sandstone dikes sills and breccias are interpreted as a result of the ascent of overpressured heated water and its vapor from the huge underlying guarani aquifer carrying fluidized sand and continuously silicifying the intruded sand the three breccias are sills intruded into cold lava flows the description and correlation of the magmatic bodies and the field relationships of the silicified sandstones establish the stratigraphy of the parana volcanic province in torres and elucidate the processes responsible for the injection and effusion of sand in the cretaceous

lower cretaceous tholeiitic dyke swarms from the ponta grossa arch southeast brazil petrology sr nd isotopes and genetic relationships with the parana flood volcanics the lower cretaceous dykes of the ponta grossa arch the most important dyke swarms in brazil are associated with the flood basalts and rare acid flows of the northern parana basin the ponta grossa pg dykes are formed by two pyroxene tholeiites and rare acid rocks the basaltic dykes may be distinguished into two main groups a dominant high tio2 2 wt hti group and a subordinate low tio2 2 wt lti group characterized for similar mgo content by high and low incompatible element contents respectively most pg dykes do not show chemical and isotope evidence supporting important crustal contamination pg dykes with 87sr86sr 0 0 7060 plot in the mantle array sr 17 and nd 3 and can be considered virtually uncontaminated intra dyke chemical variations suggest that the normal or reverse differentiation trends may be related to pre emplacement low pressure differentiation processes the important chemical differences between incompatible element poor and incompatible element rich basaltic dykes cannot be accounted for in terms of fractional crystallization but are compatible with different melting degrees of a garnet peridotite mantle source e g 9 and 20 melting for the hti and lti tholeiites respectively field distribution of the magmatism chemistry and sr nd isotope compositions support that the pg dykes may be related to the flood volcanics of northern parana and not to those of the central and southern parana paleomagnetic data indicate that pg dykes are younger than the parana volcanics all the results suggest that pg dykes were probably feeders of the stratoid volcanics erupted in northern parana towards the continental margin and later eroded chemistry and isotopic data reveal that asthenospheric mantle components were not significant factors in the genesis of pg dykes dyke emplacement occurred during early phases of rifting and or flexuring cutting flood volcanic suites

geodynamics of rapid voluminous felsic magmatism through time abstract two end member geodynamic settings produce the observed examples of rapid voluminous felsic rhyolitic magmatism through time the first is driven by mantle plume head arrival underneath a continent and has operated in an identifiable and regular manner since at least 2 45 ga this style produces high temperature 1100 c low aspect ratio rheoignimbrites and lavas that exhibit high sio 2 al 2 o 3 ratios high k 2 o na 2 o ratios and where available data exists high ga al 2 o 3 ratios 1 5 with high f in thousands of parts per million and low water content f concentration is significant as it depolymerizes the silicate melt influencing the magmas physical behavior during development and emplacement these rhyolites are erupted as part of rapidly emplaced 10 15 myr mafic lips and are formed primarily by efficient assimilation fractional crystallization processes from a mafic mantle parent the second is driven by lithospheric extension during continental rifting or back arc evolution and is exclusive to the phanerozoic slips silicic large igneous provinces develop over periods 2 al 2 o 3 ratios and lower k 2 o na 2 o ratios rapid voluminous felsic magmatism represents both extreme examples of continental growth since the archean and also dramatic periods of crustal recycling and maturation during the phanerozoic

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

chemical weathering rate denudation rate and atmospheric and soil co2 consumption of parana flood basalts in sao paulo state brazil abstract the chemical weathering rate and atmospheric soil co 2 consumption of parana flood basalts in the preto stream basin sao paulo state brazil were evaluated using major elements as natural tracers surface and rain water samples were collected in 2006 and analyses were performed to assess ph temperature dissolved oxygen do electrical conductivity ec and total dissolved solids tds including so 4 2 no 3 po 4 3 hco 3 cl sio 2 ca 2 mg 2 na and k fresh rocks and c horizon samples were also collected taking into account their geological context abundance and spatial distribution to analyze major elements and mineralogy the preto stream downstream from the city of ribeirao preto receives several elements compounds as a result of anthropogenic activities with only sulfate yielding negative flux values the negative flux of so 4 2 can be attributed to atmospheric loading that is mainly related to anthropogenic inputs after corrections were made for atmospheric inputs the riverine transport of dissolved material was found to be 30 t km 2 y 1 with the majority of the dissolved material transported during the summer wet months the chemical weathering rate and atmospheric soil co 2 consumption were 6 m ma and 0 4 10 6 mol km 2 y 1 respectively the chemical weathering rate falls within the lower range of parana flood basalt denudation rates between 135 and 35 ma previously inferred from chronological studies this comparison suggests that rates of basalt weathering in brazil s present day tropical climate differ by at most one order of magnitude from those prevalent at the time of hothouse earth the main weathering process is the monosiallitization of anorthoclase augite anorthite and microcline magnetite is not weathered and thus remains in the soil profile

amethyst geodes in the basaltic flow from triz quarry at ametista do sul rio grande do sul brazil magmatic source of silica for the amethyst crystallizations the amethyst geodes observed in the tholeiitic basaltic flow from the triz quarry at ametista do sul rio grande do sul brazil show particular wall layering infillings with from the outside inwards celadonite chalcedony fine grained quartz and large sized amethyst crystals the primary fluid inclusions analysed in the amethyst crystals yield a 152 to 238 c crystallization temperature range the amethyst geodes are always located in the massive fracture free basaltic part of the lava flows and surrounded by a limited wall lining alteration halo the thickness of which depends on the geode radius the geochemical balances calculated from fresh to altered basalt in the geode environment indicate that the amount of sio 2 released from the alteration halo is always sufficient to produce the siliceous rims in the geodes without requirement for extraneous silica supply the results point to a volcanic origin for the amethyst geode infillings through basalt autoalteration by authigenic high temperature hydrothermal fluids these fluids can originate from 1 unmixing of volatile coumpounds from melt through pressure release 2 cooling to supercritical hydrous fluids with autoalteration of the surrounding basalt and 3 migration of the residual hot fluids from the basalt to the geodic cavities through the pressure gradient between the geodic cavity and the rock

emplacement of ophiolite in papua new guinea summary the major ophiolite complexes of papua new guinea lie on the northeastern margin of the australian craton and are flanked externally by palaeogene volcanic arcs the ophiolites are segments of oceanic lithosphere which occupied the forearc zone prior to arc continent collision in the case of the easternmost ophiolite the papuan ultramafic belt there is evidence that emplacement was preceded by development of a secondary rupture in the down going plate at some distance from the subduction zone and was followed by extension buoyant emergence and reversed movement of the ophiolite the westernmost ophiolite april ultramafics has more complex structure and probably developed as a series of thrust sheets in a subduction system the thrust sheets were subjected to renewed deformation and thrusting by continued convergence after arc continent collision

hydrocarbon generation in the permian irati organic rich shales under the influence of the early cretaceous parana large igneous province abstract the increasing global demand for natural gas and petroleum byproducts is turning organic rich shales into an important target for hydrocarbon exploration and production current understanding about hydrocarbon generation in unconventional plays such as oil shales and gas shales is still evolving especially in sedimentary basins where hydrocarbon generation is influenced by magmatism this is the case for the permian oil shales of the irati formation in the parana basin southern south america the irati shales are considered an atypical petroleum system due to thermal effects of the parana large igneous province lip emplaced during the early cretaceous in this context the focus of this study was to characterize the thermal conditions of hydrocarbon generation in the irati formation as well as the composition of related aqueous diagenetic fluids the kerogen from the irati organic rich shales has an aromaticity around 30 ar 30 as determined by carbon nuclear magnetic resonance 13c nmr and vitrinite reflectance ro of around 0 6 fluid inclusions in calcite and quartz veins present aqueous fluids with salinity of 0 5 wt of nacl equivalent and homogenization temperatures greater than 250 c hydrocarbon fluid inclusions were classified as black oil through their vapor fraction volumes fv 1 6 9 1 and homogenization temperatures th in the 60 80 c range methane ch4 or carbon dioxide co2 fluid inclusions were absent within the analyzed calcite and quartz veins the pvt model for trapped fluid inclusions suggests a shallow hydrocarbon petroleum system 2 5 km depth active during the early cretaceous synchronous with the parana lip

asthenosphere and lithosphere structure controls on early onset oceanic crust production in the southern south atlantic abstract the southern south atlantic has often been considered a classic example of continental break up in the presence of a starting mantle plume evidence for a mantle plume includes the parana etendeka continental flood basalts which are associated with the rio grande rise and walvis ridge and the wide spread presence of seaward dipping reflectors and high velocity lower crustal bodies along the conjugate margins observations from seaward dipping reflector distributions suggested that lithospheric segmentation played a major role in the pattern of volcanism during break up in this region and consequent numerical modelling was used to test this we tested this hypothesis ourselves by measuring the thickness of the earliest oceanic crust generated this was done through the use of 37 measurements of initial oceanic crustal thickness from wide angle and multichannel seismic profiles collected along the conjugate margins these measurements show that at 450 km south of the parana etendeka flood basalts the oceanic crust is thicker than the global average at 11 7 km farther south the oceanic crust thins reaching 6 1 km at a distance of 2300 km along strike overall the along strike trend of oceanic crustal thickness is linear with a regression coefficient of 0 7 and little indication of segmentation from numerical models representing extension of the lithosphere we find that observed melt volumes are matched with the presence of a hot layer if we assume this region of hot mantle has a thickness of 100 km its excess temperature relative to the asthenosphere has to decrease from 200 to 50 c north to south this decrease in temperature also seen in published thermobarometry results suggests that temperature was the primary control of volcanism during the opening of the southern south atlantic

petrology of the alkaline rocks of the macau volcanic field ne brazil the macau volcanic field mvf in the borborema province ne brazil contains multiple centres of volcanic activity of early to late cenozoic ages we present element and sr nd pb isotope geochemical data for four of the few most prominent basalt types of this volcanic field serrote preto type serra aguda type pico do cabugi type and serra preta type in order to assess their magmatic history from source to crystallization and the evolution of the mantle beneath the borborema province the basalts are basically sodic nephelinitic basanitic alkali olivine basalts enriched in lile and in nb ta the serra preta cabugi and serra aguda types demonstrate compositions close to primitive characteristics with 10 mgo 15 wt and 200 ppm ni 500 ppm and experienced limited fractional crystallization of olivine clinopyroxene plagioclase oxides with negligible wall rock assimilation rb sr and ba rb constraints support the generation of sio2 undersaturated magmas from mantle melting of amphibole bearing peridotites with minor phlogopite the source for the basanites and alkali basalts is estimated to be a garnet bearing domain around the lithosphere asthenosphere boundary 80 93 km deep while the nephelinites are derived from the adiabatic asthenosphere at 105 km with temperatures of 1480 c their incompatible trace element patterns and sr nd pb isotopic compositions are similar to fozo and em type oib magmas from the comparison of data with those of the ceara mirim dyke swarm we propose that there is a ubiquitous fozo reservoir in the sclm beneath the borborema province this fozo signature characterized the upwelling asthenosphere during the lithospheric extension and thinning at the opening of the equatorial atlantic and is clearly represented in the mesozoic olivine tholeiites of ceara mirim the upwelled asthenosphere cooled as a rigid sclm since the cretaceous and has preserved its fozo signature evident in the macau cenozoic basalts the em signatures in mvf lavas probably represent a deep component derived from metasomatizing fluid melts that have interacted with an originally old oib type mantle to produce metasomatic minerals such as k rich amphibole mica with highly incompatible trace elements contents which enhanced the generation of alkaline magmas through mantle melting

chemical stratigraphy of the parana lavas south america classification of magma types and their spatial distribution a new classification scheme has been developed to assign the lava flows of the parana continental flood basalt province south america into geochemically distinct magma types with six basaltic major and trace element abundances and or ratios by mapping out the spatial distribution of these magma types within the lava sequences it has been possible to determine the internal stratigraphy of the lava pile on a regional scale previous studies on road profiles traversing the well exposed coastal serra geral escarpment of southern brazil are summarised together with results from some new sampled sections more widespread stratigraphical investigations of the parana lavas have been hampered by the lack of sufficient topographic relief and the cover of sedimentary rocks however access to drill core chippings from nine boreholes in the central parana region has provided a unique opportunity to investigate the stratigraphy of the otherwise inaccessible deeper levels of the lava pile and to map out stratigraphic variations in three dimensions the borehole samples have indicated cated a stacking of units of different magma types all overlapping towards the north which suggests that the main locus of magmatism moved northwards with time within the parana basin this migration could be related to the northward propagation of rifting during the initiation of the south atlantic ocean maps of the surface distribution of samples of each magma type show a pattern consistent with the stratigraphy inferred from the boreholes although suggesting that the shift in magmatism may have been towards the northwest on the basis of geochemical similarities between magma types and their inferred stratigraphical relationships it is proposed that the parana can be divided into two principal magmatic centres 1 an older one in the south comprising the gramado esmeralda and urubici magma types and 2 a younger one developed about 750 km to the north formed by the pitanga paranapanema and ribeira magma types

mantle plumes and flood basalt stratigraphy in the parana south america geochemical studies of the parana continental flood basalts in brazil have led to the recognition of distinct magma types which have been used to infer the internal stratigraphy of the lava pile the overstepping of stratigraphic units toward the north and a similar compositional change in sills within the underlying parana basin sedimentary rocks imply that the site of magnatism migrated 750 km toward the north during this volcanic event this has important implications for recent plume related models that have argued whether fithospheric rifting must accompany the presence of a mantle plume in order to generate continental flood basalt magmatism it is difficult to ascribe the magnitude and direction of the shift in the locus of the parana magmatism to movement of the brazilian lithosphere relative to the underlying tristan mantle plume instead it is suggested that the observed lava distribution and internal structure of the parana etendeka flood basalt province were imposed by the intracacies of the rifting process during the initial opening of the south atlantic ocean

long distance lava correlation in the parana volcanic province along the serra geral cuesta southeastern brazil the capability of determining the flow by flow stratigraphy and the long distance correlation of lava flows in large continental volcanic provinces leads to a considerable advance in the understanding of processes related to generation and evolution of the lavas the parana volcanic province is exposed along the serra geral cuesta of southern brazil in a steeply inclined 1 000 m high section starting 40 m above sea level each of the 10 20 pahoehoe flows and rhyodacite flow units has a unique chemical composition integrated with field stratigraphy and gamma spectrometric measurements this leads to the establishment of the correct stratigraphic sequence in each of three different vertical sections the number of flows integrating the three serras is 26 serra is a mountain range in portuguese each serra has basaltic andesites at the base whereas rhyodacites are intercalated with basaltic andesites at the top three basaltic andesite flows and one rhyodacite flow unit are correlated between serra umbu and serra boa vista 10 km in the serra faxinal a thick 170 m sill at the base correlates with flow 13f whereas a dike sill in the graxaim quarry 24 km distance correlates with flow 3f one basaltic andesite and two rhyodacite flow units correlate between serra faxinal and serra umbu 50 km the results are most significant for the understanding of large tracts of continental volcanic provinces with use of common geochemical and gamma spectrometric techniques

a reappraisal of the high ti and low ti classification of basalts and petrogenetic linkage between basalts and mafic ultramafic intrusions in the emeishan large igneous province sw china abstract based on published data we reappraise the classification of high ti and low ti basalt from the emeishan large igneous province elip and the correlations between basalts and mafic ultramafic intrusions because of the lack of clear spatial and temporal variations of different types of basalts we suggest that the basalts in the elip cannot be classified into high ti and low ti groups by tio 2 contents and or ti y ratios the distinctive characteristics of these high ti and low ti lavas probably result largely from the different fractionating assemblages whether or not fractional crystallization of the fe ti oxides occurred probably is the key factor that controls the ti abundances and ti y ratios in the residual melts e g lavas although the nature of the mantle sources variable degrees of partial melting of mantle and crustal contamination also influence the geochemical signatures of the lavas therefore neither ti abundance nor ti y ratios in basalts can reflect the nature of their mantle source moreover the different types of mafic ultramafic intrusions in the elip cannot simply be attributed to be genetically related special types of basalts either high ti or low ti basalts it is likely that they are merely the cumulus phases i e chamber or conduit of the basaltic lavas hence caution should be exercised in the use of high ti or low ti basalts as prospecting vectors for ore deposits in the region potential implications are proposed that both the fe v ti oxide and cu ni pge sulfide mineralization in the elip intrusions is largely due to the variable differentiation and crustal contamination during magmatic processes

tectonic significance of the florianopolis dyke swarm parana etendeka magmatic province a reappraisal based on precise u pb dating abstract the first precise id tims u pb baddeleyite zircon dating of dykes representative of the main activity in the florianopolis dyke swarm parana etendeka magmatic province south brazil reveals a restricted age range 134 7 0 3 to 133 9 0 7 ma this is at least 5 ma older than indicated by previous 40 ar 39 ar stepwise heating dating and precludes a direct relationship with syn rifting magmatism connected with opening the south atlantic ocean instead as indicated by their age and geochemical signature these dykes are feeders to the nearby urubici lavas and coeval khumib lavas in etendeka these new geochronological results also cast doubt on a large 10 ma time span for the emplacement of the florianopolis dyke swarm implied by 40 ar 39 ar dates but the determination of its upper age limit still requires accurate dating of younger low volume fine grained dykes with distinct low ti chemistry crystals suitable to u pb dating were not obtained thus far from these dykes

geological controls of copper gold and silver in the serra geral group realeza region parana brazil abstract the serra geral group has high cu concentrations in southern brazil including the realeza parana region where au and ag also occur the basalts 46 7 50 8 wt sio 2 have breccias at the top of 10 out of 31 studied flows in the realeza section and at the top of 5 out of 7 analyzed flows in the capanema section sand injectites occur at the top of basalts in 18 out of 23 flows from the realeza section the average content of cu in three samples of mineralized breccias is 3788 ppm one sample from a silicified sandstone sill intruded at the top of a basalt flow has up to 0 66 ppm au k 2 o was not leached during basalt alteration the hydrothermal breccias particularly when sand is present show enrichment in u which leads to higher values of scintillometry rate of emission of k u and th in the basalts breccias and sandstones pd 17 5 8 4 ppb is higher than pt 12 5 5 ppb suggesting a hydrothermal remobilization of the metals the serra geral group is thus shown to have high potential for precious and base metal deposits

petrogenesis of the flood basalts from the early permian panjal traps kashmir india geochemical evidence for shallow melting of the mantle article i nfo the early permian panjal traps of northern india represent a significant eruption of volcanic rocks which occurred during the opening of the neotethys ocean basaltic basaltic andesites dacitic and rhyolitic rocks collected from guryal ravine and pahalgam show evidence for subaerial and subaqueous eruptions indicating that they are contemporaneous with the formation of a shallow marine basin the major and trace element geochemistry of the basalts is consistent with a within plate setting and there are basalts which have high ti tio2 n 2 0 wt and low ti tio2 b 1 8 wt compositions the high ti basalts are similar to oib whereas the low ti basalts are similar to continental tholeiites the identification of high and low ti basalts within the panjal traps is analogous to other large igneous provinces e g karoo deccan parana emeishan the sr nd isotopic values end t 5 3 to 1 3 isr 0 70432 to 0 71168 of both types of basalts overlap indicating that the rocks may have originated from the same ancient subcontinental lithospheric i e emii like mantle source tdm 2000 ma the two groups of basalts can be modeled by using a primitive mantle source and different degrees of partial melting where the high tirocksare producedby 1 partial melting of a spinel peridotite source where as the low ti rocks are produced by 8 partial melting trace elemental and isotope modeling indicatesthat some of the basalts assimilated 10 crustal material in contrast the basaltic andesites are likely formed by mixing be tween basaltic magmas and crustal melts which produced rocks with higher sio2 55 wt content and enriched isotopic signatures end t 6 1 isr 0 70992 the panjal trap volcanism was likely due to partial melting of the sclm within a passive extensional setting related to the rifting of cimmeria from gondwana contemporaneous volcanic and plutonic granitic rocks throughout the himalaya are probably not petrogenetically related but are likely part of the same regional tectonic regime

compositional and kinetic controls on liquid immiscibility in ferrobasalt rhyolite volcanic and plutonic series we present major element compositions of basalts and their differentiation products for some major tholeiitic series the dry low pressure liquid lines of descent are shown to approach or intersect the experimentally defined compositional space of silicate liquid immiscibility ferrobasalt rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts unmixed melt inclusions in cumulus phases of major layered intrusions such as skaergaard and sept iles and oxide rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust liquid immiscibility is promoted by low pressure anhydrous fractional crystallization that drives the low al2o3 high feo liquids into the two liquid field kinetic controls can be important in the development of two liquid separation the undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature in contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions a feature of many tholeiitic provinces the compositions of experimental unmixed silica rich melts coincide with those of natural rhyolites and plagiogranites with high feotot and low al2o3 suggesting the potential role of large scale separation of immiscible si rich liquid in the petrogenesis of late stage residual melts no trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics instead fe ti p rich gabbros are the cumulate products of immiscible fe rich melts in plutonic settings the immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions the two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium even if segregated both melts evolve on the binodal surface and exsolve continuously with decreasing temperature the two liquids do not differentiate independently and keep crystallizing the same phases with differentiation further evolution by fractional crystallization potentially drives the bulk liquid out of the twoliquid field so that very late stage liquids could evolve into the single melt phase stability field

global dispersal of pb by large volume silicic eruptions in the parana etendeka large igneous province volcanism from large igneous provinces is often inferred to have had a significant global environmental impact but demonstrating synchronicity between the volcanism and sedimentary records of environmental change is not straightforward several studies use sediment pb isotopes to fingerprint the timing of input of volcanic pb from a particular large igneous province published data on ocean drilling program site 1149b sediments in the pacific ocean associated with the valanginian 13 c excursion that has been linked to the parana etendeka volcanism in central south america and namibia require input of radiogenic pb the pb isotope analyses of parana etendeka lavas show that this radiogenic pb is uniquely associated with the large volume silicic eruptions rather than the effusive basaltic lavas this strengthens the case for a temporal link between the parana etendeka volcanism and the valanginian 13 c excursion although basaltic magmatism dominates the province 95 there is no evidence for pb associated with volatile metal degassing from such eruptions in the site 1149b sediments on the other side of the globe suggesting that eruption columns produced by the basaltic eruptions did not reach the stratosphere instead the widespread global dispersal of pb is apparently linked to the ability of large volume 1000 km 3 silicic eruptions to loft aerosols into the upper stratosphere

generation of block and ash flows at the onset of silicic volcanism in the parana magmatic province brazil evidence from photoanalysis of caxias do sul breccias in this work we perform textural analysis on volcanic breccias related to the silicic magmatism in the region of sao marcos southern brazil parana magmatic province the breccias are matrix supported coarse grained poorly sorted with angular to rounded fragments in a fine grained matrix juvenile fragments are dense to pumiceous massive to banded dacites lithic fragments were not recognised the analyses were performed on field photographs grain size distribution gsd analysis showed maximum fragment sizes between 8 and 9 5 and smallest recognised sizes between 3 and 1 5 due to the spatial resolution limit of the photographs and the weathered condition of the matrix the fine fragments from the matrix were not analysed the gsd fractality could be quantified by a single power law with low moderate d values of 1 9 2 3 vesicle size distribution vsd and shape parameters of both fragments and vesicles were also measured the fragments are typically low vesicularity with median vesicle area fractions around 5 for all samples but pumiceous fragments with up to 43 area are found vsds exhibit single exponential concave upwards curves with vesicles becoming more deformed complex with increasing size suggesting a single continuous process of nucleation and growth under low degrees of shear regarding the fragments shape parameters all samples have high values of solidity which together with the low vesicularity of the fragments suggest brittle fragmentation of poorly vesicular material and the operation of secondary fragmentation processes during transport that round and smooth the clasts however field evidence for local conduit systems together with the gsd fractality suggest that these may be proximal deposits without substantial transport history based on a comparison of the deposits characteristics with several types of volcanic breccias we propose a block and ash flow source for these breccias that indicate the presence of nearby lava domes providing evidence for high viscosity low flux dacitic volcanism in the parana magmatic province

effusive silicic volcanism in the parana magmatic province south brazil evidence for locally fed lava flows and domes from detailed field work abstract lava flows and dome complexes of silicic composition were identified in the lower cretaceous parana magmatic province pmp at rio grande do sul state southern brazil detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments likely representing the fissural systems that fed the three palmas type silicic units different structures indicative of effusive emplacement lava domes lobated flows sheet flows and autobreccias are very common in the study area and are probably also more abundant than previously thought in whole pmp silicic magmatism in fact effusive deposits seem predominant in the three distinct silicic units identified in the area since no remnants of pyroclastic components have been identified the vitreous dacites that make up the upper flows of the basaltic andesite to dacite barros cassal sequence are clearly effusive as indicated by their occurrence as thin sheet flows the much thicker early caxias do sul dacites occur mostly as lava flow lobes and pancake like of low to moderate viscosity and lava domes the younger high sio2 santa maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion as lobated flows formed by vesicle rich obsidian in spite of higher viscosities relative to the previous units 106 pa s it is probable that the very low h2o contents 1 wt of these rhyolite melts associated with high discharge rates resulted in an effusive nature in most to this unit

volcanic glass in cretaceous dacites and rhyolites of the parana magmatic province southern brazil characterization and quantification by xrd rietveld abstract acidic rocks are a significant component of the cretaceous parana magmatic province occurring in different stratigraphic positions and often forming deposits of complex and as yet poorly defined architecture vitrophyric varieties are surprisingly abundant for a volcanic sequence of this age and are composed of predominant glass plus plagioclase labradorite andesine pyroxenes augite pigeonite and orthopyroxene ti rich magnetite and traces of apatite hypocrystalline rocks largely derived from devitrification additionally contain sanidine cristobalite and quartz the negative correlation between the abundance of these minerals and the amount of glass suggests that these latter phases formed by devitrification modal analysis using a combined xrd rietveld rir method detected glass contents between 0 and 85 wt in a set of representative samples of palmas type acidic rocks from southern brazil with dacite to rhyolite composition modal compositions determined by xrd and by scanning electron microscope are in good agreement with each other and were checked against whole rock xrf chemical data water contents up to 4 wt show a positive linear correlation with the amount of glass and are inferred to be mostly secondary as original pre eruptive h2o dissolved in melts is inferred to have been

petrological reconstruction of triassic seamounts oceanic islands within the palaeotethys geochemical implications from the karakaya subduction accretion complex northern turkey abstract subduction accretion complexes provide unique insight into the tectonic assembly of continental margins and oceanic basins as they record the tectonic stacking and juxtaposition of materials derived from distinct tectonic environments the karakaya complex exposed throughout northern turkey is a good example of an ancient subduction accretion complex that includes a number of pre liassic units that characterize the closure of palaeotethys defining the components of this complex is of crucial importance to understanding the geodynamic evolution of palaeotethys in the eastern mediterranean region in this study we explore the geochemistry of metabasic rocks within the karakaya complex redefining and evaluating one of its main constituents known as the nilufer unit new geochemical results combined with previously published data suggest that the nilufer unit is dominated by oceanic island basalt oib and enriched mid ocean ridge basalt e morb type metabasic rocks which are variably enriched in the most highly incompatible elements relative to normal morb n morb associated alkaline oib type basalts are characterized by highly fractionated and variable rare earth element ree patterns la yb n 4 8 16 2 suggesting melting across the garnet spinel transition derivation from a heterogeneous mantle source and or dynamic melting of a homogeneous source similar nb y zr y systematics of spatially associated oib and e morb type samples may indicate involvement of a shared enriched mantle source s combining both geological and geochemical evidence we suggest that the oib and e morb type assemblages defining the nilufer unit represent seamounts and oceanic islands formed on palaeotethyan oceanic crust which was finally incorporated into a forearc accretionary prism during latest triassic and became a component of the karakaya complex

paleoenvironmental dynamics of low order paleovalleys in the late quaternary palmas cacador summit surface southern brazil abstract the quaternary dynamics of landscapes in the subtropical continental region of brazil is not still well understood pedostratigraphic records of low order paleovalleys paleovalley heads and 1st and 2nd order paleovalleys of the palmas cacador summit surface serve as important resources for the identification of landscape component responses relief soil sediment and vegetation of plateau areas of southern brazil in the light of environmental changes driven by climatic variations of the late quaternary we integrated litho pedo allo and chronostratigraphic descriptions with carbon stable isotope analysis phytoliths indices and 14c and osl dating we found that at 44 86 ky bp there was a change in the hydrodynamics of 2nd order perennial channels humid climate controlled possibly by tectonics at 28 35 to 23 69 to 28 ky bp regressive pedogenesis in dry climate began with a predominance of erosion by overland flows at 2 60 to 23 69 ky bp full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between 4 60 and 19 77 ky bp echoing the results postulated by the knox s model during this period the most pronounced modifications to the landscape were made with a change in vegetation from campo cerrado to campo limpo with changes in erosion patterns caused first by overland flows and then earthflows debris flows and with the gradual silting filling and burying of gullies valley heads and 1st and 2nd order valley bases since 2 60 ky bp the area returned to a predominance of progressive pedogenesis in wet and cold climates finally we found that at the local scale low order basins

origin of the silicic volcanic rocks of the early permian panjal traps kashmir india abstract the panjal traps of kashmir india represent a significant outpouring of mafic and silicic volcanic rocks during the early permian and are synchronous with the opening of the neotethys ocean previous studies have suggested that the silicic volcanic rocks are derived by differentiation of mafic magmas dacites and rhyolites collected from the lower portions of the volcanic pile near pampore kashmir are peraluminous anck 1 0 in composition their calculated whole rock i sr values are variable i sr 0 69307 to 0 71825 and indicate open system behavior of either rb or sr or both whereas their nd isotope compositions end t 8 6 to 8 9 are nearly uniform the end t values and trace element th nb pm 4 nb u 8 ratios suggest the rocks are derived partially or wholly from the crust least squares and melts modeling indicate that the likely source of the silicic rocks is the middle crust rather than the lower or upper crust furthermore the silicic panjal traps have trace element compositions similar to some felsic volcanic rocks and a type granitic rocks from other large igneous provinces e g karoo parana and camp the paleoproterozoic t dm ages t dm 1836 to 1937 ma indicate that the rocks were likely derived from an ancient crustal source which experienced multiple episodes of recycling in contrast to silicic volcanic rocks from other lips the silicic panjal traps are unusual in that they did not involve mantle source material the heat required to melt the crust was likely due to the continuous injection of contemporaneous basaltic magmas which formed the majority of the mafic panjal traps

gravity signature of the western parana basin brazil abstract volcanism in the parana basin one of the largest continental flood basalt provinces on earth was contemporaneous with the early cretaceous opening of the south atlantic ocean problematic is the lack of crustal extension associated with this flood basalt event although three palaeozoic jurassic extensional episodes have been reported in parts of the basin gravity measurements at 185 new stations were established to constrain the geometry and magnitude of bouguer anomalies that characterise the poorly understood western portion of the parana basin and to interpret new and existing data in light of its poly phase extensional history the bouguer map of the parana basin is characterised by two gravity lows up to 100 mgal in the eastern and western portions with a relative high in its centre around 50 mgal the spectral characteristics of the n s oriented western gravity lows and flanking regions suggest density contrasts at 7 4 4 km which we interpret as variable depth to basement beneath the palaeozoic cretaceous sedimentary and cretaceous volcanic rocks forward modelling 2 5 d of two profiles across the n s trending western gravity low shows that the low can be explained by shallow steeply deepening structures bounding what we believe to be a rift basin buried beneath the mesozoic flood basalts and sedimentary strata comparison with other gravity data heat flow contour maps of crustal extension basement and structural maps all support our interpretation of a pre cretaceous rift basin we also compare our results to palaeozoic mesozoic rift basins in brazil the north sea and central africa with similar gravity signatures and better subsurface control these comparisons also support a 3 5 km deep thick rift sequence beneath the western parana basin sequences

sm nd isotopic investigation of neoproterozoic and cretaceous igneous rocks from southern brazil a study of magmatic processes abstract nd evolutionary paths for diversified igneous suites from southern brazil are here re evaluated using published results we interpret the end paths considering the secondary fractionation of 147sm 144nd due to major petrogenetic processes the inclusion of nd isotopes and geochemical data for precambrian and mesozoic basic rocks allow improving the discussion on the subcontinental lithosphere beneath southern brazil late neoproterozoic rocks mostly granitoids are exposed in two regions of the southern brazilian shield an eastern collisional belt and a western foreland the latter included two geotectonic domains amalgamated at this time the sao gabriel arc 900 700 ma and the taquarembo cratonic block magma genesis mainly involved mixture of crustal and incompatible element enriched mantle components both with a long residence time continental segments are the neoarchaean paleoproterozoic lower crust ca 2 55 ga in the western foreland and paleoproterozoic neoproterozoic recycled crust 2 1 0 8 ga in the collisional belt granitoids with a single crustal derivation are limited in the southern brazilian shield mixing processes are well registered in the western foreland where the re enriched old mantle was probably mixed with a 900 700 ma old subducted lithosphere and a 2 55 ga old lower crust the contribution of the latter increased from the early 605 580 ma to the later 575 550 ma neoproterozoic events which may be due either to crustal thickening or to delamination of the lithosphere magma sources were diversified in the 660 630 ma collisional belt initially they involved the mixing between two components with similar nd isotopic ratios a 2 1 0 8 ga old recycled crust and a subduction processed old mantle regional heating and abundant production of granitic melts with diversified contribution of enriched mantle components mark the end of the collisional period at 630 580 ma we can also attribute this to the delamination of the lithosphere so that the same geodynamic process may explain the magmatism in the whole shield at the end of the dom feliciano orogeny mesozoic rocks include flood basalts from the cretaceous parana province and sub coeval alkalic suites multiple processes of metasomatism affected the lithospheric mantle resulting in some complexity but they mainly register two enriched mantle components both generated during neoarchaean paleoproterozoic events one end member has a more pronounced subduction signature the other one probably resulted from the re enrichment of the first component at the end of the camboriu collisional orogeny 2 0 ga

a revised chemo chrono stratigraphic 4 d model for the extrusive rocks of the parana igneous province abstract the statistical analysis of a lithogeochemical database from whole parana igneous province pip containing 5974 outcrop and drillhole samples stresses natural gaps separating sio2 zr tio2 and p2o5 in high and low values their combination delimits 16 chemical types which have been adopted to classify a sub set of extrusive rocks with

origin composition and relative timing of seaward dipping reflectors on the pelotas rifted margin abstract the mechanism by which seaward dipping reflectors sdrs are formed is a topic of debate two contrasting models exist for their formation the volcanic faulting model and the volcanic loading model each of these models has important implications for the processes which control the structure and formation of magma rich rifted continental margins we have examined high quality deep seismic reflection data across the pelotas basin offshore brazil these data reveal a remarkable set of sdrs for which we have investigated the likely nature of their formation the total package of sdrs has an across strike width of 200 km and a variable vertical thickness of 10 17 km previously interpreted as volcanic flows detailed observations however show changes in seismic character and geometry within the sdr package which suggest a complex and varied evolution we have used gravity anomaly inversion and seismic observations together to investigate the likely composition of the sdrs by determining the proportion of basaltic material to sedimentary volcaniclastic material basalt fraction within the sdrs this has been achieved by minimising the difference between the depth of the gravity moho and seismic moho in order to quantify the lateral variation in basalt fraction taken to be proportional to the bulk density of the package the density of the sdr package together with seismic interpretation is then used to infer the composition depositional environment source and time of formation relative to breakup our analysis suggests that the overall sdr basalt fraction and bulk density decrease oceanwards possibly due a change in the type of volcanic deposits from predominantly subaerial to volcaniclastics possibly deposited subaqueously the sdrs can be split into three sub packages the two inner sdr packages are interpreted to consist of lava flows sourced from syn tectonic subaerial eruptions associated with the onshore parana large igneous province flowing eastwards into an extensional basin the outer sdr package shows reflector geometries that progressively offlap oceanwards interpreted as extrusives sourced from an eastwards migrating newly formed ocean ridge our analysis suggests that both the volcanic faulting and volcanic loading models for sdr formation are applicable to the pelotas rifted margin recording distinct syn rift and syn breakup magmatic events we show that both sdr formation models can be recognised in a naturally occurring example and can coexist on the same margin

flow and fragmentation patterns in the silicic feeder system and related deposits in the parana etendeka magmatic province sao marcos south brazil voluminous silicic volcanic products from the paran etendeka magmatic province are exposed in the southern brazil a regional synformal structure torres syncline controls a tick sequence of these units in the region of sao marcos rio grande do sul parallel to the axis of torres syncline a nw se trending zone constituted by the alignment of complex structures was interpreted as the feeding system of silicic volcanism characterized as fissural through a combination of field mapping and determination of fractal dimension fd we have identified and described distinct intermingled morphological domains one related to flow processes and one related to fragmentation processes vertical flow directions in this zone exhibit two preferential directions nw ranging from n272 degrees to n 355 degrees and ne varying from n20 degrees to n85 degrees the systematic repetition and crosscutting relations of domains point towards a cydicity of flow and fragmentation processes in this zone this feeder system intrudes previous basaltic and silicic volcanic rocks the later being composed by banded deposits interpreted as rheoignimbrites and proximal volcanic breccias this set is overlapped by hybrid deposits lava flows and finally massive deposits the silicic volcanism can be summarized at an early pyrodastic stage characterized by rheoignimbrites and proximal volcanic breccias a transition between explosive and effusive events is suggested by the occurrence of hybrid deposits which gradually give place to lobated lavas local alternation with new possibly rheoignimbritic deposits suggests oscillatory fragmentation processes at the conduit related to decompression and volatiles ex solution in an effective permeable system

peperite formed by lava flows over sediments an example from the central parana continental flood basalts brazil pahoehoe flows interbedded with sediments have been identified in the superior portion of parana continental flood basalts pcfb west portion of parana state southern brazil in the study area peperites are generated by the interaction between lava flows and wet lacustrine sediments silt and clay evidence that the sediments were unconsolidated or poorly consolidated and wet when the lava flowed over them includes vesiculated sediment sediment in vesicles and fractures in lava flow and in juvenile clasts in the peperite and soft sediment deformation hydrodynamic mingling of lava and wet sediments coarse mingling is predominant and volcanic rocks and textures related to explosive phase of molten fuel coolant interaction mfci are not observed in study area locally centimeter sized areas display direct contact between ash sized juvenile clasts and sediments formed by the collapse of a vapor film the textures of fluidal peperites in the central pcfb indicate that the relevant factors that led to a coarse mingling between lava sediment are 1 lava properties low viscosity 2 fine grained unconsolidated or poorly consolidated wet sediment and 3 a single episode of interaction between lava flows and sediment

tectonic controls on magmatism associated with continental break up an example from the parana etendeka province the high and low ti basalts of the parana etendeka province were primarily derived from old trace element enriched source regions in the lithospheric mantle and they are associated with dyke swarms of different orientations these swarms appear to reflect different amounts of extension and it is inferred that the high and low ti magma types were characterised by different melt generation rates of 0 15 km3 yr 1 and 0 4 km3 yr 1 respectively stewart et al earth planet sci lett 143 1996 95 109 there is probably a gap of 2 myr between the end of the main phase of cfb magmatism and the oldest rocks on the adjacent ocean floor a simple numerical model has been used to constrain the amounts and rates of melt generated from the continental lithosphere and asthenosphere under finite duration extension melting in the mantle is assumed to be controlled by the dry peridotite solidus in the asthenosphere and the hydrous 0 2 h2o peridotite solidus in the lithosphere for a maximum of 4 and a duration of extension of 10 myr the derivation of melt from the asthenosphere by dry peridotite melting depends primarily on potential temperature tp and is relatively insensitive to the thickness of the mbl while the converse is the case for melt derived from the lithosphere by hydrous peridotite melting for a tp of 1450 50 c inferred from the crustal thickness estimates along the rio grande rise and walvis ridge the model successfully generates 2 4 km of lithosphere derived melt before producing significant volumes of asthenosphere derived melt it is concluded that increases of melt volume with time can be generated by decompression melting of the mantle lithosphere critically in areas of significant melt generation within the mantle lithosphere during extension and break up there is likely to be a gap in the volcanic record between the end of melt generation in the lithosphere and the onset of melting in the underlying asthenosphere no such gap is present if all melts are generated within the mantle plume and thus these models may in principle be tested in the geologic record

the deccan traps an interpretation in terms of progressive lithospheric flexure in response to a migrating load abstract structural and geochemical data from the western ghats india have been used to construct an accurate north south section of the volcanic stratigraphy of the southwest part of the deccan province the characteristic style of the section is one of southerly dip reversing in the extreme south southward overstep of higher units onto pre deccan rocks and down dip thinning of individual formations in contrast an east west section shows continuity of essentially horizontal stratigraphic units without overstepping relationships previous authors have interpreted these data in terms of the progressive southward migration of the volcanic source as india drifted northwards over a hot spot now centered beneath reunion we have compared the observed stratigraphy to the predictions of a geophysical model based on the flexural response of the continental lithosphere to a migrating volcanic load the best fit to the observed section is for the structurally lowest part of the modelled sections with an elastic thickness of the lithosphere of 100 km this value explains the present day width of the traps in peninsula india but requires that up to 5 5 km of the upper part of the flank section has been removed by erosion the origin of the erosion is not clear but it may be related to flexural rebound following removal of the cone loads that formed along the trace of the plume the model cannot explain the subsidence of the traps beneath the shelf off bombay or the rim uplift of the traps in the western ghats we attribute these modifications of the stratigraphy to vertical movements uplift and subsidence that followed rifting of india from the mascarene plateau during the eocene

basalt stratigraphy and silica gossans in campo grande and serra de maracaju mato grosso do sul parana volcanic province abstract thousands of silica gossans are exposed at the top of the lower cretaceous basalt hills in the parana volcanic province strongly indicating the presence of calcite amethyst and agate geode deposits along with native copper mineralization the embrapa silica gossan in the northwestern portion of the province campo grande region is an excellent example of such novel geological structure in the continental flood basalts this silica gossan has a size of 450 350 m standing out as a treeless area in the densely wooded savanna and makes part of the stratigraphy of six basalt flows of paranapanema intermediate ti chemical type the base of the volcanic column is constituted by two pitanga types and the overlying column is paranapanema type every basalt flow has a silicified sand layer or breccia at the top and these are fed by abundant sand dikes the anel viario norte avn flow is the most intensely altered by hydrothermal fluids producing voluminous secondary calcite infillings in the amygdales and fractures in this region the basalts contain higher copper content than the average of the volcanic province the studied silica gossans display negative anomalies in gamma spectrometry as a response to k u and th depletion during alteration we propose a new exploration methodology by observing googleearth images complemented with field studies and geochemistry to readily locate favorable areas for amethyst and agate geode deposits and native copper mineralization

an ams study of different silicic units from the southern parana etendeka magmatic province in brazil implications for the identification of flow directions and local sources abstract in the southern portion of the parana etendeka magmatic province in brazil extensive silicic dacite rhyolite deposits occur at the top of a sequence of low ti pahoehoe to rubbly basalts the internal architecture of the silicic deposits and their eruptive style as well as the location of their sources are still unsatisfactorily known in an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive and test the hypothesis of local sources we carried out anisotropy of magnetic susceptibility ams studies on the two main silicic units caxias do sul dacites and santa maria rhyolites with the best exposures in an area previously mapped in detail magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites rock magnetism properties indicate that pseudo single domain magnetite carries the fabrics and the remanence magnetic fabrics were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm both ams and aarm tensors are coaxial indicating that the ams fabric is not affected by the effect of magnetite single domain grains magnetic data from several dacitic coulees caxias do sul unit indicate flows from se to nw the location and spatial distribution of these lavas support the hypothesis of local sources aligned along a ne sw trend these data are in agreement with the alignments of structures dome shaped hills observed in field work and dem images on the other hand magnetic data obtained in santa maria rhyolites indicate that flow directions in two different areas are distinct towards nw ne and w suggesting that they derived from different emission centers so regarding the silicic volcanism in the studied region our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit in contrast we propose the occurrence of local volcanic events implying in the existence of different sources possibly characterized by local emission centers

precambrian acid volcanism in central india geochemistry and origin abstract the early proterozoic bijli rhyolites 2180 25 ma constitute an important part of the nandgaon group in the central indian craton a tectonically active block sandwiched between the dharwar craton in the south and the bundelkhand craton in the north the rhyolites are chemically heterogeneous they have high sio 2 74 4 k 2 o 4 41 ba 834 ppm and low mgo 0 22 cao 1 0 iron 2 8 v cr and ni 5 6 and 1 ppm respectively they contain moderate sr 88 ppm rb 140 ppm th 27 ppm and u 6 ppm total ree ranges from 223 ppm to 453 ppm with high lree lree 307 and all the rhyolites have low to high negative europium anomalies eu eu 0 03 to 0 77 the overall chemical signatures support a crustal anatectic origin for the rhyolites from a source of intermediate composition basalt pooling below the crust and associated rifting most likely initiated anatexis

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

anisotropy of magnetic susceptibility of silicic rocks from quarries in the vicinity of sao marcos rio grande do sul south brazil implications for emplacement mechanisms abstract the parana etendeka large igneous province includes acid volcanic rocks that can be found throughout its extension several aspects concerning those rocks remain controversial including their mechanism of emplacement and location of their eruptive sources opening of several quarries of dimension stone near the city of sao marcos rio grande do sul brazil offers a unique opportunity to study in detail the acid products here we present the results of a study of the anisotropy of magnetic susceptibility ams completed in some rocks that had been interpreted as the roots of volcanic conduits our results and reexamination of the textural features of the rocks lead to a reinterpretation that suggests that these rocks were emplaced subaerially and involved assimilation and remelting of clastic components of previous products due to the inferred conditions of emplacement it is unlikely that the eruptive vents are located far from the area of study therefore ruling out the long travelled nature of these products

oxygen isotope geochemistry of the silicic volcanic rocks of the etendeka parana province source constraints oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the cretaceous etendeka parana flood basalt province namibia south america are believed to reflect the delta sup 18 o values of the original magmas the authors recognize a high delta sup 18 o value type delta sup 18 o pyroxene approximately 10 per thousand found in the south of both regions and a low delta sup 18 o value type delta sup 18 o pyroxene approximately 6 5 per thousand found in the north other differences between thee two rhyolite types include higher concentrations of incompatible elements and lower initial sup 87 sr sup 86 sr ratios in the low delta sup 18 o value type the authors suggest that the regional distribution of rhyolite types reflects differences in source composition which can best be explained if the sources are lower crustal late proterozoic mobile belt material high delta sup 18 o and archean lower crust low delta sup 18 o

regional correlation of grande ronde basalt flows columbia river basalt group washington oregon and idaho the tholeiitic flood basalts of the columbia river basalt group of middle and late miocene age cover more than 200 000 km2 in washington oregon and idaho the most voluminous formation of the group the grande ronde basalt erupted for 2 m y from north northwest trending fissure systems concentrated in southeast washington and adjacent oregon and idaho four magnetostratigraphic units designated r1 n1 r2 and n2 from oldest to youngest are recognized on the basis of polarity in the grande ronde and provide the broad stratigraphic framework for the formation in this study major element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the grande ronde basalt on a regional scale systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings which are distinguished primarily by small but significant variations in mgo tio2 and p2o5 content in addition four minor chemical types local to the eastern part of the province have been identified feeder dikes of each chemical type have also been located flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical stratigraphic subunits these subunits consist of several flows collectively 30 150 m thick subunits of most chemical types are repeated at irregular intervals throughout the formation no progressive chemical trend occurs within the grande ronde many of the chemical stratigraphic subunits extend to the margins of the province although most are confined to the source region in eastern washington although the total number of subunits is less in the west away from the fissure systems the total thicknesses of the n2 and r2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern washington the greatest thicknesses occur in the central part of the province within the pasco basin the distribution of basalt relative to the location of vents as well as the relative east west thicknesses suggests that basalt flowed hundreds of kilometres westward during the most voluminous grande ronde eruptions ponding against the irregular margin of the cascade range and being diverted through the ancestral columbia gorge toward the washington oregon coast between these huge sheetflood events smaller eruptions blanketed areas within the source region and ongoing regional subsidence created a shallow westward draining basin in the center of the province

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

a new approach for electron microprobe zircon fission track thermochronology abstract fission track thermochronology ftt has been applied for decades to quantify rates and timing of processes in the shallow crust the most widely used approach is the external detector method edm in this conventional approach an age is obtained by counting both the fossil 238u spontaneous fission and the induced 235u induced fission tracks using an optical microscope the induced tracks are obtained through the irradiation of the sample with thermal neutrons in the nuclear reactor which causes fission of 235u based on the studies carried out by gombosi et al 2014 we present an alternative method of dating zircons using electron probe microprobe analysis epma to measure uranium concentration u the electron microprobe analysis fission track epma ft method was applied to three samples of rapidly cooled zircons the fish canyon tuff pocos de caldas syenite and serra geral zircons the analyses were performed using two approaches 1 using the age equation described in gombosi et al 2014 and 2 using a new age equation calibration developed for this work the results using the gombosi et al 2014 age equation were 26 7 4 1 ma 80 6 12 8 ma and 130 9 20 1 ma respectively and the results using the age equation from this work were 27 8 1 9 ma 83 8 7 7 ma and 136 12 ma respectively the uncertainty of the age is affected mainly by 238u concentration and s the spontaneous fission track density determinations other factors can affect the uncertainty of the age but their contributions are smaller for all samples the yield ages found by the two methods are consistent and overlap within two standard deviations of published reference ages determined from other radiometric techniques i e k ar 40ar 39ar and or u pb and traditional ftt by the edm

calculating earth moon system parameters from sub yearly tidal deposit records an example from the carboniferous tradewater formation abstract the secular evolution of the earth moon system remains poorly constrained largely because there are few continuous tidal rhythmite or foreset bundle sequences that preserve deposition over more than several neap spring tidal cycles deposits recording less than one year of deposition do not facilitate direct calculation of past lunar distance directly from kepler s laws but may prove necessary to reconstruct lunar orbital evolution because they are far more common than longer records a method is demonstrated to make use of shorter tidal deposit sequences by utilizing conservation of angular momentum between the earth and moon and estimating the solar component of tidal deposition while assuming a constant moment of inertia for earth since the proterozoic the precision and accuracy of spectral estimates obtained from short records are considered as are the limitations of subsequent calculations of earth moon parameters the late carboniferous abbott sandstone of the tradewater formation in the illinois basin preserves just over 6 apparently continuous neap spring cycles in its semidiurnal deposits the quality of these data as assessed via sedimentological evidence and statistical time series properties produces spectral estimates that are likely within at least 5 of the actual underlying periodicity 90 accuracy to test the usefulness of such records we assessed the possible scenarios of 90 and 95 accuracy at 90 accuracy the error bounds on earth moon parameter estimates become rather large and render individual data sets to be of limited use at 95 accuracy very general inferences about the evolution of the earth moon system may be made calculated mean lunar orbital distance at 315 ma is 3 798 10 8 m with error bounds of 0 086 10 8 m and 0 046 10 8 m we conclude that short sequences of cyclic tidal deposits offer rather limited resolution of lunar distance estimates utilizing multiple sub yearly data of similar age in ensemble may prove necessary if further investigations of secular changes in earth moon parameters are to proceed

pillow lavas and fluvio lacustrine deposits in the northeast of parana continental magmatic province brazil abstract the northeast edge of the parana continental magmatic province was marked by a topographical barrier that gave rise to a predominantly peridesertic environment this high allowed the recurrent of above average rainfall in this area of the province in contrast with other areas where many evidences indicate that lava flows have settled in an arid climate in a desert environment as a result alluvial fan debris flows and fluvio lacustrine systems developed occasionally this paper presents one of these sequences which is remarkable for the presence of sedimentary rocks and two sets of pillow lavas both sets of pillow lavas show interaction with the fluvio lacustrine sediments with distinctive grain size from pebbly sand to clay that locally preserve the original sedimentary structures such as bedding and lamination this interaction gives rise to peperites which show a diversity of textures for different sedimentary granulometries hyaloclastites and fragments of lava also occur in the interpillow material and may be intricately mixed with sediment these features based mainly on detailed field observations in the northeastern region demonstrate that the palaeorelief sedimentary environment stratigraphy and morphology of sedimentary units and basaltic flows are contrasting from the central and southern regions of the parana continental magmatic province

pre rift tectonic scenario of the eo cretaceous gondwana break up along se brazil sw africa insights from tholeiitic mafic dyke swarms