crustal contamination in palaeogene east greenland flood basalts plumbing system evolution during continental rifting abstract palaeogene central east greenland flood basalts have sr nd and pb isotope characteristics consistent with crustal contamination of icelandic type basalts in the lower basalts of central east greenland amphibolite facies gneiss is the dominant contaminant at low stratigraphic levels whereas contamination with granulite facies gneiss prevails in the upper part of the lava succession the contamination probably occurred by partial melting of the crust and can be modelled by assimilation fractionation crystallisation processes similar contaminants have been detected in lavas from odp leg 152 off the se greenland coast although in a reverse sequence contamination in lower basalts and odp leg 152 lavas which erupted through an archaean proterozoic substrate differs from lavas in ne greenland which overly the caledonian fold belt and large mesozoic sediment deposits in the ne greenland lavas the dominant contaminant appears to be a dacitic component formed by partial melting of mesozoic sediments changes in magma supply rates from the mantle may be the determining factor for the sequence of contaminants and may also control the depth of ponding in crustal chambers the compositional variation of the least contaminated east greenland basalts suggests that melts were produced from mantle sources similar to present day iceland and north atlantic morb at the time of continental breakup but distinction between mantle sources is very complicated ree systematics indicate a maximum in initial depth of mantle melting at kangerlussuaq during formation of the east greenland flood basalts consistent with a plume being centered in that region

rare earth element characteristics and k ar ages of the band ziarat ophiolite complex southeastern iran the band ziarat complex of southeastern iran is located on the western boundary c f the jaz murian depression rand is bounded by two ma jar fault systems the principal rock units of this complex are a gabbro sequence that includcs low and high level cumulate gabbros a late intrusive sequence that consists of diorite and plagiogranite and a volcanic sequence that includes diabase dikes and a lesser anaount of basaltic lava mantle rocks are virtually absent because of the presence of the two bounding fault systems but we consider the complex to be an ophiolite in nature rare earth cleislcnt ree whole rock data clearly diffcremtiate the classic ophiolitic lithologies for the crustal rocks in this complex bas4 on the ree data there are two distinct types of basalt presenl at band ziarat i those that formed from an initial basaltic melt with a light rare earth element lree enriched signature similar to intraplate hasalts and ii those that have lree depleted patterns similar to normal mid ocean ridge basalts the data also suggest i that the gabbros are adcumulates and were derived from a source slightly enriched in lree with fractic natioam controlled by removal of clinopyroxene or hornblende and plagioclase and ii that the late intrusive rocks as well as a ma jority of the cliabnse dikes are cogenetic and were derived from thc same lree enriched source k ar ages ranging from 134 4 to 146 5 ma for lowlevel gabbros and from 821 4 to 930 4 ma for high level gabbros were measured on five hornblende and two whole rock samples which suggests that these rocks may have formed early in the cretaceous period

monoterpenylabietenoids novel biomarkers from extant and fossil taxodioideae and sedimentary rocks abstract the presence of 7 p cymenylferruginol and its diagenetic biomarkers occurring in cenozoic fossil plants and mesozoic siltstones and coals has been studied using gas chromatography mass spectrometry both 7 and 7 p cymenylferruginol isomers were the dominant natural products with two novel minor additional isomers namely 3 and 3 p cymenylferruginol and two hydrocarbons 7 and 7 p cymenyldehydroabietane the other tentatively assigned aromatic hydrocarbons were 9 10 p cymenylretene and 9 p cymenylsimonellite which were present in upper cretaceous and lower jurassic sedimentary rocks with their further dehydrogenation products diterpenoid dimers were also tentatively identified in trace amounts with 11 and 14 ferruginylferruginol as the dominant compounds our results show that the p cymenylferruginols and p cymenyldehydroabietanes are not thermally stable and that their occurrence in sedimentary rocks is controlled by the maturity of the organic matter om also chamaecydin identified for the first time in pre paleogene strata was not detectable when the om maturity based on vitrinite reflectance was higher than 0 45 0 5 rr

in situ trace element analysis of individual silicate melt inclusions by laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms this paper reports the successful application of laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms to the in situ analysis of a diverse suite of twenty trace elements including zr hf nb ta y and rees in individual silicate melt inclusions in phenocrysts from fantale volcano ethiopia the uv laser a frequency quadrupled nd yag operating at 266 nm significantly improves the ablation characteristics of minerals that do not absorb strongly at near ir wavelengths e g quartz and feldspar furthermore it allows for a significant reduction in ablation pit size to ca 10 m thereby permitting numerous applications that require high resolution sampling multiple ablations in individual melt inclusions in the size range 10 50 m demonstrate both the effectiveness of the technique and the generally homogeneous character of the inclusions comparison of the lam icp ms data for international reference material rgm 1 a rhyolite with recommended values indicates an analytical precision of 10 for most of the trace elements determined in this study the trace element abundances of the fantale melt inclusions determined by lam icp ms are typical of those of pantellerites i e peralkaline rhyolites and are consistent with their origin as tiny volumes of melt trapped in quartz and alkali feldspar phenocrysts during the final stage of fractional crystallization of the host peralkaline magma

the features of devonian coal bearing deposits in south china the people s republic of china abstract tectonic movements in south china had profound effects upon coal formation and the distribution of coal basins in that area as a result of the tectonic activity the devonian sea transgressed in a northeasterly direction in south china recent research indicates that devonian deposition in different regions of south china did not take place exactly at the same time deposition began in yunnan and guangxi provinces during the early devonian in hunan and jiangxi provinces during the middle devonian and in the lower yangtze region in the late devonian several paleodepositional environments were formed during the devonian period the devonian is one of several coal forming periods in china at this time the earliest known land plants grew along the coast of a shallow epeiric sea climatic conditions and depositional environments were considerably favorable to coal formation the middle devonian coal bearing deposits are present in yunnan and guangxi provinces these deposits are of littoral or neritic origin and the devonian coal beds contain a great deal of cuticles hence they are called cutinitic liptobiolith or luquanite upper devonian coal deposits occur as thin beds or lenses in hanshan anhui province and yixing jiangsu province in the lower yangtze valley the pattern of distribution illustrates that coal bearing formations of devonian age in china appear to migrate in a regular southwest northeast direction which corresponds to the direction of transgression of the devonian sea these features are believed to be related to tectonic activity marine transgression and paleodepositional environments

mid ocean ridge and island arc affinities in ophiolites from iran palaeographic implications complementary reference abstract fifty six samples of ophiolitic rocks from various late cretaceous eocene suture zones in iran have been analyzed for major and trace elements in order to assess their petrogenetic affinity and to determine their original tectonic setting in both southern baluchestan i e between the makran range and the lut block the fanuj maskutan sequence and northeastern baluchestan i e in the east iranian ranges the tchehel kureh sequence the ophiolitic complexes are well developed the rocks display affinities with mid ocean ridge tholeiites the basaltic rocks are comparable to respectively transitional fanuj maskutan and normal tchehel kureh morb in contrast the sequence along the zagros the sahneh sequence appears to have formed in an island arc setting in iranshar i e in southeastern baluchestan ophiolites are dismembered into a melange which includes cumulate intrusives similar to those from fanuj maskutan and lavas with island arc tholeiitic affinity a similar island arc origin may be inferred for the sabzevar ophiolitic sequence north of the lut block studied by other authors the chemical data thus help to elucidate the development of the jigsaw puzzle of microplates of gondwanian origin that during the mesozoic were intermediate in position between afro arabia india and eurasia and that now constitute the middle east ophiolite obduction in iran occurred during arc basin continent or ocean continent collisions in the late cretaceous early paleogene largely predating the final suturing between arabia and india with eurasia to which the intermediate microplates were already attached which did not take place before the neogene

major element and ree compositions of pliocene sediments in southwest japan implications for paleoweathering and paleoclimate abstract the history of the east asian monsoon and the relationship between the development of the monsoon climate tectonics and global climate are complicated and controversial earlier studies have indicated that the east asian monsoon fluctuated in the asian interior during the pliocene thus the chemical weathering record in coastal regions of east asia can be the key to elucidating its evolution as well as the kuroshio current variability the present study clarifies the chemical weathering conditions in southwest japan based on the concentrations of major elements and rare earth elements rees in lacustrine muddy sediments the chemical weathering was moderate between 4 4 and 3 8 ma between 3 8 and 3 4 ma chemical weathering significantly intensified as indicated by the high values of the chemical index of alteration that reached a maximum of 98 as well as the high concentrations of rees and light rees against heavy rees and kaolinite rich clay mineral compositions despite the wide variation in source rock compositions and grain sizes the degree of chemical weathering remained moderate during the early pleistocene the intense chemical weathering on land in southwest japan from 3 8 to 3 4 ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the kuroshio current and the intensification of the east asian summer monsoon

40ar39ar ages and tectonic setting of ophiolite from the neyriz area southeast zagros range iran abstract an ophiolite considered to be an allochthonous fragment of tethyan oceanic crust and mantle crops out near neyriz in the zagros range iran 40 ar 39 ar ages ranging from 76 8 23 8 ma to 105 23 3 ma were measured on hornblende from five samples of plagiogranite and diabase from the ophiolite the most precise ages are 85 9 3 8 ma for a diabase and 83 6 8 4 ma for a plagiogranite the weighted mean age of hornblende from the five samples is 87 5 7 2 ma which indicates that the igneous part of the neyriz ophiolite formed during the early part of the late cretaceous pargasite from amphibolite below peridotite of the neyriz ophiolite has a 40 ar 39 ar age of 94 9 7 6 ma the pargasite age agrees within analytical uncertainty with the ages measured on diabase and plagiogranite comparable ages have been measured on igneous rocks from the samail ophiolite of oman and on amphibolite below peridotite of the samail ophiolite

petrology geochemistry and tectonics of the sabzevar ophiolite north central iran abstract the sabzevar ophiolite is a highly dismembered ophiolite complex located along the northern boundary of the central iranian microcontinent cim and is one of the internal iranian group of ophiolites and colored melanges the igneous rocks of this complex consist of peridotites harzburgite dunite and lherzolite serpentinite minor pyroxenite gabbros and a volcanic sequence that exhibits a wide range of composition from basalts and basaltic andesites to rhyodacite dacites rhyolites and basanites sedimentary rocks include a variety of upper triassic to lower cretaceous deep and shallow marine rocks these include pelagic fossiliferous carbonates that are mixed with the pillow basalt and basaltic andesite as interlayers or exotic blocks ranging in size from 10 to 100 m also present are extensive units of radiolarian chert which are interbedded within the basalts and basaltic andesites a combination of petrographic observations and analyses of incompatible trace elements and rare earth elements indicates the presence of at least four different types of extrusive rocks in the sabzevar ophiolite the geochemical data clearly identifies some of the extrusive rocks to have formed from three distinct types of basaltic melts i the group 1 basaltic rocks which formed from an initial melt with n morb like lree depleted chemical signatures and are petrogenetically related to the gabbros ii group 2 basaltic rocks which have e morb chemical signatures and iii group 3 basaltic rocks with lree enriched signatures and incompatible trace element patterns that suggest an island arc affinity the data also suggest that the gabbros and the group 1 basaltic rocks are petrogenetically related and produced by fractionation of plagioclase and to a lesser extent clinopyroxene and hornblende similar to other studied iranian ophiolites e g khoy band e zeyarat dar anar neyriz kermanshah and baft the results from the sabzevar ophiolite demonstrate the presence of relics of mid ocean ridge basalt morb like signatures in the extrusive units of neo tethyan ophiolites and suggests that the fossil oceanic lithosphere preserved in these ophiolites developed at an oceanic spreading center in addition the sabzevar ophiolite contains other volcanic rocks that have non morb like geochemical signatures e g within plate island arc the differences between these geochemical signatures could be a result of a differing upper mantle composition or different degrees of partial melting of the same upper mantle the presence of sizable nb anomalies in the extended rare earth element ree patterns for andesites and the group 3 basalts is characteristic of volcanic arc magmas or possibly are products of the ascending magma that was modified by crustal contamination the presences of the basanites and the silica undersaturated rocks could be attributed to extrusive activity following ophiolite emplacement plate reconstructions suggest that rocks of the sabzevar ophiolite were part of the tethyan oceanic crust that was formed during rifting of a narrow but deep seaway that separated the cim from the eurasian plate the ophiolite was emplaced during northeast dipping subduction i e closure of this segment of the tethyan seaway sabzevar ocean

geochemistry and origins of petroleum in the neogene reservoirs of the baiyun sag pearl river mouth basin abstract a total of 25 light oils condensates 5 condensates from 2 new exploratory wells were collected from the baiyun sag in the pearl river mouth basin prmb in the south china sea and investigated to establish their origins and sources three oil families were identified among samples following analysis of various geochemical parameters using biomarkers stable carbon isotope compositions and hierarchical cluster analysis hca family i oils distributed in the northern structural belts are characterized by significantly high pristane to phytane pr ph ratios 4 77 7 93 moderate oleanane to c30 hopane ol c30h ratios 0 18 0 97 and raised bicadinane t c30h t c30h ratios 1 67 7 67 family ii oils are distributed along the eastern flank of the main sub sag towards the northeastern tectonic zones and have relatively high pr ph ratios 3 14 4 68 elevated ol c30h values 0 73 2 29 and moderate t c30h values 1 64 4 52 the geochemical characteristics of the oils suggest that oils of both family i and family ii are of terrestrial origin but from two entirely independent sources oils of family iii a newly discovered oil group have relatively lower pr ph ratios 0 89 1 99 moderate ol c30h values 0 13 0 82 and lower t c30h values 0 34 1 61 indicating a reduced contribution of higher plant organic matter in related source rocks family iii oils are consistent in geochemical characteristics with shallow lacustrine source rocks and their related oils discovered in the zhu i and iii depressions of the prmb suggesting that they are likely to be derived from source rocks deposited in a shallow lacustrine environment during the eocene wenchang enping period the oils of family iii mainly occur in the southwest flank of the baiyun sag which implies that this is the preferred direction for migration of lacustrine oils the discovery of lacustrine oil demonstrates that the baiyun sag possesses enormous exploration potential in lacustrine oils and that this may become the next favored petroleum exploration target

experimental melting of crustal xenoliths from kilbourne hole new mexico and implications for the contamination and genesis of magmas experiments p 6 9 kb t 900 1000 c on four crustal xenoliths from kilbourne hole demonstrate the varying melting behavior of relatively dry crustal lithologies in the region granodioritic gneisses samples kh 8 and kh 11 yield little melt 900 ppm ba in high temperature melts coexisting with a k feldspar free restite although ree were not measured in either feldspar or melt the high kspar melt kds for eu suggests that the melts coexisting with k feldspar will have strong negative eu anomalies isotopic and trace element models for magma contamination need to take into account the melting behavior of isotopic reservoirs for example the most radiogenic and incompatible element rich sample examined here the pelitic granulite 87sr 86sr 0 757 is refractory while samples with far less radiogenic sr 87sr 86sr 0 708 0 732 produced substantial melt this suggests that in this area the isotopic signature of contamination may be more subtle than expected the experimental results can be used to model the petrogenesis of oligocene volcanic rocks exposed 150 km to the nw of kilbourne hole in the black range in the mogollon datil volcanic field the experimental results suggest that a crustal melting origin for the kneeling nun and caballo blanco tuffs is unlikely even though such an interpretation is permitted by sr isotopes curstal contamination of a mantle derived magma best explains the chemical and isotopic characteristics of these tuffs both experimental and geochemical data suggest that the rhyolites of moccasin john canyon and diamond creek could represent direct melts of granodiorite basement similar but not identical to the kilbourne hole granodiorites perhaps slightly modified by crystal fractionation the absence of volcanic rocks having87sr 86sr 0 74 in the region is consistent with the refractory character of the pelitic granulite

geochemical characteristics 40ar 39ar ages and original tectonic setting of the band e zeyarat dar anar ophiolite makran accretionary prism s e iran abstract the makran accretionary prism in southeastern iran contains extensive mesozoic zones of melange and large intact ophiolites representing remnants of the tethys oceanic crust that was subducted beneath eurasia to the north of the makran accretionary prism lies the jaz murian depression which is a subduction related back arc basin the band e zeyarat dar anar ophiolite is one of the ophiolite complexes it is located on the west side of the makran accretionary prism and jaz murian depression and is bounded by two major fault systems the principal rock units of this complex are a gabbro sequence which includes low and high level gabbros an extensive sheeted diabase dike sequence late intrusive rocks which consist largely of trondhjemites and diorites and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks including radiolarian chert chondrite and primitive mantle normalized incompatible trace element data and age corrected nd pb and sr isotopic data indicate that the band e zeyarat dar anar ophiolite was derived from a midocean ridge basalt like mantle source the isotopic data also reveal that the source for basalts was indian ocean type mantle based on the rare earth element ree data and small isotopic range all the rocks from the band e zeyarat dar anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average e morb fractionation was controlled by the removal of clinopyroxene hornblende and plagioclase three 40ar 39ar plateau ages of 140 7 2 2 142 9 3 5 and 141 7 1 0 ma and five previously published k ar ages ranging from 121 4 to 146 5 ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the late jurassic early cretaceous plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the masirah ophiolite which has crystallization age of 150 ma like masirah the rocks from the band e zeyarat dar anar ophiolite complex represent southern tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90 100 ma bitlis zagros ophiolites including the samail ophiolite

geochemical modeling of low melt fraction anatexis in a peraluminous system the pena negra complex central spain abstract a study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt fraction cordieritic granites from migmatized meta greywackes the aims of the study were to 1 reveal the fractionation patterns of major and trace elements 2 compare the major element chemistry of leucogranites and the quantitative behavior of source minerals during anatexis inferred by mass balance adjustment with available experimental data for peraluminous systems and 3 discuss the behavior of trace elements in crustal melting by comparing the chemically determined composition of leucogranites with the results of three fractionation models two of these assume a perfect diffusive behavior of trace elements within residual solids but they use a different set of distribution coefficients the third assumes a perfect nondiffusive behavior in relation to their source rocks the leucogranites are strongly depleted in li transition elements and light rare earth elements but enriched in k2o sio2 and ba the k rb ratio in leucogranites is higher than in sources and reaches values typical of high grade metamorphism mass balance analysis using the anatexis mixing model shows that the chemistry of cordierite leucogranites is compatible with its having originated by closed system water undersaturated anatexis on previously migmatized meta greywackes leaving a residue enriched in cordierite plus biotite and exhausted in k feldspar biotite melts congruently unless important amounts of sillimanite were also present in the source compared with experimental melts obtained from sources with the same chemical composition but with a different femic mineralogy biotite sillimanite instead of cordierite biotite the pena negra leucogranites are richer in k2o and mgo with a lower fe fe mg ratio the differences in magnesium are believed to result from the changes in the mineral assemblage of the source rocks however the differences in potassium contents are still not well understood the behavior of trace elements during anatexis cannot be modeled by trace element fractionation equations because of the sluggish diffusion kinetics of trace elements at the temperature of anatexis making the melting rate of minerals greater than the diffusion rate of trace elements within minerals the behavior of trace elements essentially consists in following that of the minerals containing them

magma mixing in alkaline magmas an example from tenerife canary islands abstract the central region of tenerife canary islands offers a wide variety of alkaline rocks of intermediate composition between basalts and more differentiated magmas a recent less than 0 1 ma old eruption on the southwestern slopes of teide volcano produced separate felsic sio 2 59 and mafic sio 2 47 rocks as well as abundant hybrid inclusions sio 2 50 57 that show a wide range of geochemical and mineralogical variation between the end members mineralogical evidence reverse zoning skeletal and patchy feldspars incompatible assemblages mineral disequilibrium and geochemical data characteristic trends of major and trace elements ree ratios major and trace mass balance calculations support the generation of a mixing process we present a model in which basaltic magma entered a trachyte magma chamber which resulted in a stratified chamber of trachytic above more mafic hawaiitic melts the formation of hybrid magmas between these two end members is believed to involve some chemical diffusion across the interface between the two magmas before mechanical mixing a lowering of temperature due to the cooling effect of the trachytic magma and consequently a decrease in density by crystallization of plagioclase permitted the basaltic magma to penetrate through the trachyte which caused the eruption this natural example is in good agreement with the results obtained in experimental work on interdiffusion of silicate melts

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

geochemical and nd pb isotopic evidence for the provenance of the early proterozoic virginia formation minnesota implications for the tectonic setting of the animikie basin the early proterozoic animikie basin is located at a major crustal boundary between archean crust of the superior craton and penecontemporaneous early proterozoic crust of the wisconsin magmatic terranes the provenance of sedimentary rocks within the animikie basin constrains the tectonic evolution of the early proterozoic margin of the superior craton published geological petrographic and nd pb isotopic data indicate that the pokegama quartzite lower passive margin unit of the animikie group has a late archean provenance in contrast the virginia formation upper deep water turbidite shale unit of the animikie group was derived from dominantly early proterozoic sources with isotopic compositions similar to igneous rocks of the wisconsin magmatic terranes shales of the virginia formation have nd depleted mantle model ages 2 14 to 2 35 ga and mu 1 of 7 81 to 8 09 ashes within the virginia are more evolved geochemically than shales and have younger model ages of 1 86 and 1 99 ga and simila

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

petrology of the anorogenic oxidised jamon and musa granites amazonian craton implications for the genesis of proterozoic a type granites the 1 88 ga jamon and musa granites are magnetite bearing anorogenic a type granites of paleoproterozoic age they intrude the archaean rocks of the rio maria granite greenstone terrain in the eastern part of the amazonian craton in northern brazil a suite of biotite amphibole monzogranite to syenogranite with associated dacite porphyry dp and granite porphyry gp dykes dominates in these subalkaline granites that vary from metaluminous to peraluminous and show high feo feo mgo and k2o na2o in spite of their broad geochemical similarities the jamon and musa granites show some significant differences in their ree patterns and in the behaviour of y the jamon granites are related by fractional crystallisation of plagioclase potassium feldspar quartz biotite magnetite amphibole apatite ilmenite geochemical modelling and nd isotopic data indicate that the archaean granodiorites trondhjemites and tonalites of the rio maria region are not the source of the jamon granite and associated dyke magmas archaean quartz diorites differentiated from the mantle at least 1000 m y before the emplacement of the granites have a composition adequate to generate dp and the hornblende biotite monzogranite magmas by different degrees of partial melting a larger extent of amphibole fractionation during the evolution of the musa pluton can explain some of the observed differences between it and the jamon pluton the studied granites crystallised at relatively high fo2 and are anorogenic magnetite series granites in this aspect as well as concerning geochemical characteristics they display many affinities with the proterozoic a type granites of south western united states the jamon and musa granites differ from the anorthosite mangerite charnockite rapakivi granite suites of north eastern canada and from the reduced rapakivi granites of the fennoscandian shield in several aspects probably because of different magmatic sources

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

foraminiferal response to seasonality modulated by orbital cycles in the cretaceous mid latitudes the albian record from the lower saxony basin abstract the mid cretaceous serves as an excellent laboratory for testing the dynamics of the climate under greenhouse state of the earth this study is focused on the cyclicity record of foraminiferal assemblages in the lower saxony basin during the middle albian the short eccentricity obliquity and precession cycles are consistently recorded in absolute and relative abundance of most opportunistic benthic and planktic foraminifers the question is why foraminifers reacted to orbital cycles and what they actually record in the equable global climate it is suggested that seasonality changes modulated by orbital cycles are responsible for the milankovitch cyclicity records it is well known that the axial obliquity directly influences seasonal contrasts in mid and high latitudes the precession modulated by the eccentricity of the earth orbit further affects the contrast of seasons therefore seasonal dynamics of precipitation runoff and storm tracks patterns and to a lesser extent temperature contrasts are most likely factors controlling milankovitch scale cyclic fluctuations of foraminiferal assemblages and other proxies sensitive to productivity changes it can be deduced that periods of the highest seasonal contrasts were dominated by opportunistic abundant taxa such as benthic valvulineria gyroidinoides group and planktic hedbergellids which record the strongest obliquity signals the lower saxony and adjacent boreal basins were possibly controlled by humid climate with relatively dry summers and wet winter seasons this study confronted with the presented conceptual model and former climate models supports the conclusion that the temperate zone surrounding tethys was sensitive to seasonal changes modulated by orbital cyclicity the mid latitudinal climate of the greenhouse earth seems to be more dynamic and more seasonal than expected

petrogenesis and source characteristics of metatholeiites from the archean ramagiri schist belt eastern part of dharwar craton india the n s trending 2 4 km wide ramagiri schist belt is made up of three blocks dominated by metavolcanic rocks separated and surrounded by granitic rocks of distinct characteristics the metavolcanic rocks are tholeiitic in composition and are very similar in their major element composition as well as in their abundances of some trace elements however the rare earth elements ree require distinct sources the rocks of the amphibolite facies eastern block have lree depleted ree patterns ce yb 0 7 0 9 requiring derivation from depleted mantle like sources the greenschist facies metatholeiitic rocks of the central block have lree enriched ree patterns ce yb 3 6 reflecting the nature of their source s the nd isotopic data require that the lree enriched nature could not have been attained significantly prior to its melting the fine grained upper greenschist facies metatholeiites of the western block have flat to slightly lree depleted patterns ce yb 0 8 0 95 minor fractional crystallization of rock forming minerals may relate a few samples to each other among samples from each of the three blocks different extents of partial melting of distinct mantle sources have played a dominant role in the generation of the parent magmas to the central versus eastern and western block metatholeiites

testing crustal melting models for the origin of flood rhyolites a nd pb sr isotopic study of the tertiary davis mountains volcanic field west texas flood rhyolites are lavas that have areal extents similar to large ignimbrites the davis mountains volcanic field differs from most other cenozoic volcanic fields in the southwestern united states in that a major volume of the silicic rocks erupted there are flood rhyolites rather than ignimbrites a comparative isotopic study was made of a major flood rhyolite unit the star mountain and mafic to silicic rocks from three other magma systems the entire range in nd isotopic compositions found in the volcanic field is relatively small with n4 values ranging from about 2 in a basalt to between 1 0 and 1 5 in the silicic rocks including the star mountain rhyolite pb isotope ratios of the star mountain lavas 206 pb 204 pb 17 9 are considerably higher than those of xenoliths of proterozoic deep crustal granulites from the region 17 4 two types of crustal sources appear viable for the origin of the flood rhyolites first if the star mountain samples represent near primary melts from a crustal source then that source must have been cenozoic in age and silicic in composition second if the star mountain samples represent highly fractionated magmas then the crustal source could have been mafic but it could not have experienced the proterozoic granulite facies metamorphism known to have affected the basement the overall isotopic trends of the volcanic rocks are qualitatively consistent with the hypothesis that all the silicic rocks including the flood rhyolites evolved from mantle derived basalts with variable but generally small amounts of crustal contamination

geochemistry and sm nd isotopic characteristics of bimodal volcanic rocks of juscelândia goias brazil mesoproterozoic transition from continental rift to ocean basin abstract the ca 1 28 ga juscel ndia sequence in goias brazil comprises a unit of bimodal metavolcanic rocks amphibolite and felsic gneiss intercalated with metapelite and metachert the bimodal nature of the magmatism is evident as the metavolcanic rocks have basalt and rhyolite compositions bimodality is also shown by the trace elements and nd isotope data amphibolites yield positive e nd t values that can be separated into two groups in the first group amphibolite samples from lower and middle portion of the sequence are characterized by e nd between 2 8 and 5 4 these fairly positive values and enrichment in lree and lile suggest they were derived from a depleted mantle source with subsequent assimilation of continental crustal material the second group is formed by amphibolite of the upper portion of the sequence that have e nd around 6 0 and their low lile and lree contents resemble normal mid ocean ridge basalts n morb initial 143 nd 144 nd ratios represent the composition of the depleted mantle at 1 28 ga felsic rocks yield negative e nd t values between ca 2 8 and 4 5 and paleoproterozoic model ages t dm values in the interval between 1 8 and 2 1 ga the original felsic magmas represent the product of melting of older paleoproterozoic continental crust with trace element chemistry indicating that the felsic magmas were the product of continental crustal melts with small mantle contribution previous models proposing an oceanic setting for the origin of magmatism of the juscel ndia rocks within a mid ocean ridge or back arc basin are not supported by the data presented here transition from a continental rift to an ocean basin represents the most likely tectonic setting for the origin of the juscel ndia rocks

organic geochemistry of sediments in new zealand part i a biomarker study of the petroleum seepage at the geothermal region of waiotapu abstract the saturated hydrocarbons from the oil seepage at waiotapu in new zealand were examined by gc and gcms techniques of molecular fingerprinting the petroleum was characterised by a high ratio of phytane nc18 2 37 and low ratios of pr ph 0 64 and saturates aromatics 0 60 this study revealed that the oil was derived from terrigenous organic matter and it had neither migrated from its source nor suffered biodegradation the source rocks were deposited under anoxic conditions and these rocks lay within pleistocene sediments which were immature with respect to oil generation the location of the source rocks within a geothermal field had accelerated the generation of petroleum since the source rocks would have been too young and shallow to generate petroleum in the absence of geothermal energy

the extent of equilibration between melt and residuum during regional anatexis and its implications for differentiation of the continental crust a study of partially melted metapelitic enclaves thisstudy presentsthefirst precise evaluation of the extent ofchem ical equilibrium between felsic melt and crystalline residuumduring the crustal anatexis of metasediments the high precision ofthese resultsstemsfrom thefactthat in thiscase the meltsare repre sented by pristine glasses that occur in the matrices of partiallymelted metapelitic enclaves and as abundant glassy melt inclusionstrapped by different minerals in the same enclaves in previous stu dies of anatexis the composition of the melt has been approximatedby that of leucosomes in migmatites which do not necessarily repre sent the composition of the melt very well the present study isbased on laser ablation analyses of 35 trace elements in the glassand principal minerals of enclaves included within neogene peralu minous dacites exposed at el hoyazo se spain the enclaves which contain the assemblage plagioclase biotite sillimanite garnet glass ilmenite graphite k feldspar cordieritequartz represent fragments of metapelitic continental crust thatwaspartiallymeltedatpressuresof5 7kbarduringaregionalmeta morphic event matrix melt and melt inclusions within the enclaveswere quenched to glass upon eruption of the dacite the glasses inthe melt inclusions are interpreted as the remains of melt producedby an initial melting reaction involving a muscovite rich assemblageat 700 7508c whereasthe matrixglassesare consistent with con tinuedmeltingand oralatermeltdominatedbytheincipientmeltingof biotite at 800 8508c the distribution of trace elements be tween residuum and melt duringanatexis of the enclaves isdifferentfrom that predicted by disequilibrium models that consider effectivedistribution coefficients close to unity instead the bulk melt andthe major minerals plagioclase biotite alkali feldspar cordierite were close to equilibrium except for the case of garnet duringthe generation of the melt inclusions and matrix glasses thequenchedmelts meltinclusionsandparticularlythematrixglasses were not in equilibrium with accessory zircon and monazite andare depleted in zirconium and the light rare earth elements recrystallization of mineralsand diffusion in the melt were import ant controls during the redistribution of trace elements betweenthe solids and the bulk melt local disequilibrium processes alsotook place at mineral melt interfaces during the crystallizationof peritectic minerals and the recrystallization of residual phases as shown by the depletion of compatible elements in the meltinclusions

foraminiferal evidence for cenomanian sequence stratigraphy and palaeoceanography of the boulonnais paris basin northern france abstract a middle to upper cenomanian chalk succession in the northwestern european paris basin escalles section was investigated with respect to its sediment composition biofacies and foraminiferal content most planktic foraminifers exhibit a high frequency cyclicity in their distribution pattern and show little relationship to the sequence stratigraphic subdivision a few characteristic species of benthic foraminifers tritaxia pyramidata ataxophragmium compactum dorothia levis and gavelinella cenomana are related in their frequency distribution to certain systems tracts other benthic foraminiferal species are more evenly distributed through the systems tracts cluster analysis and factor analysis allow the separation of three benthic foraminiferal biofacies domains which exhibit a characteristic frequency distribution pattern with respect to sequence stratigraphy biofacies 1 is dominant in the highstand systems tract hst and biofacies 3 is characteristic for the transgressive systems tract tst biofacies 2 is most abundant around the maximum flooding downlap surface mfs and less abundant around the sequence boundary factor analysis shows that most of the variance in the data set is explained by variables related to plankton productivity variables related to changes in water depth and changes in sea level have minor influence on the variance of the whole data set but have some influence on the variance of the benthic foraminiferal data set the different reaction of benthic and planktic foraminifers to relative sea level changes is also recorded in the total number of foraminifers per gram sediment foraminiferal number and in the ratio between planktic and benthic foraminifers p b ratio the foraminiferal number is highest at the mfs and lowest at the sequence boundaries of the investigated depositional sequences the p b ratio has no correlation with the sequence stratigraphic subdivision but shows a high frequency cyclicity the abundance pattern of planktic foraminifers is controlled by changes in the productivity of calcareous plankton the regular variation in calcareous plankton productivity leads to marl low productivity chalk high productivity cycles that form conspicuous couplets in the section the productivity cycles are also recorded in gamma ray logs in the environmental setting of the escalles section in contrast the abundance patterns of benthic foraminifers are more influenced by relative sea level changes changes in water depth and variations in substrate composition the stacking of probably precession controlled development of couplets lead to a distinct 100 000 year cyclicity that does not match very well with published sequence stratigraphic subdivisions

geochemistry and u pb dating of felsic volcanic rocks in the riotinto nerva unit iberian pyrite belt spain crustal thinning progressive crustal melting and massive sulphide genesis abstract we present new geochemical sm nd and u pb data on the felsic volcanic rocks containing the world class volcanic hosted massive sulphide deposits in the riotinto nerva unit iberian pyrite belt spain three new u pb ages from older plagioclase quartz phyric dacites and plagioclase phyric rhyolites to youngest plagioclase quartz phyric rhyolites indicate a time span for felsic volcanism ranging from 351 5 0 4 to 345 7 0 6 ma the youngest felsic rocks exhibit lower e nd as well as contrasting ti sr zr hf and eu eu values we interpret that in the riotinto nerva unit crustal melting successively affected shallower more evolved horizons in the crust progressive crustal melting is consistent with current interpretations of the iberian pyrite belt in terms of a late devonian early carboniferous transtensional setting coupled with underplating by basic magma we suggest that low e nd evolved crustal magmatism could be used as a proxy in studies of the genesis of these and possibly other phanerozoic massive sulphide deposits supplementary material details of the analytical methods and whole rock data for basalts are available at http www geolsoc org uk sup18452

structure and origin of terpenoid hydrocarbons in some german coals abstract hydrocarbon extracts of coal samples from major coal fields in west germany have been investigated by gas chromatography mass spectrometry gc ms the samples are of carboniferous and tertiary age and derive from limnic and paralic environments the saar district the ruhr area and the lower rhine basin differences in facies maturity and age reflected in the distribution patterns of the extracted alkylcyclohexanes an unexpected occurrence of cyclic diterpenoid hydrocarbons in some samples of carboniferous age has been found the tetracyclic compounds mainly show phyllocladane type structures and can serve as source indicators hydrocarbons obtained from chemical degradation of the macromolecular material of the samples also revealed phyllocladane type compounds which are normally associated to resins of modern and extinct familes of conifers origin and structural variations of this class of hydrocarbons are discussed in terms of maturity and palaeobotanical implications

ree mobilization during small scale high pressure fluid rock interaction and zoisite fluid partitioning of la to eu a zoisite quartz segregation and its adjacent host metabasite from the tauern window austria have been investigated in detail to study the geochemical behaviour of ree during high pressure fluid rock interaction and the role of zoisite the segregation formed at t 500 to 550 c p 0 6 gpa because of decompressional dehydration of the host metabasite during the formation of the segregation the ree la to tb and dy to lu were geochemically decoupled in the metabasite la to tb are incorporated in allanite and were leached from the host rock by the fluid phase this decoupling and the leaching of la to tb significantly alter the ree patterns of the host rock in the immediate vicinity of the segregation from lree enriched to lree depleted based on a mass balance calculation for la ce nd sm and eu the composition of the fluid from which the segregation was precipitated is calculated the fluid is lree enriched with la sm n 3 7 individual ree contents range from eu 2 4 1 1 ppm up to ce 90 20 ppm ree 190 50 ppm calculated partition coefficients dreezoisite fluid are generally 1 and increase from dlazoisite fluid 0 08 0 02 to deuzoisite fluid 0 8 0 4 indicating a stronger preference of zoisite for mree than for lree to describe the fractionation of la relative to sm between zoisite and fluid the la sm exchange coefficient between zoisite and fluid is calculated the derived exchange coefficient kd la sm zoisite fluid 0 2 0 1 suggests that a fluid in equilibrium with zoisite will have a three to ten times higher la sm ratio than coexisting zoisite

origin of archean lamprophyre dykes superior province canada rare earth element and nd sr isotopic evidence hornblende and clinopyroxene phyric lamprophyre dykes exposed in the roaring river complex superior province are alkaline nepheline normative basaltic compositions 50 wt sio2 that range from primitive to fractionated mg mg total fe 0 66 0 40 ni 200 35 ppm and which have high abundances of light rare earth elements ree ce yb n 16 26 cen 60 300 n chondrite normalized sr 870 1 800 ppm p2o5 0 4 1 3 wt and ba 150 900 ppm crystal fractionation of the lamprophyres produced coeval gabbro and clinopyroxenite cumulate bodies a whole rock sm nd isochron for lamprophyres and gabbro pyroxenite yields a crystallization age of 2 667 51 ma ma i 0 50929 0 0004 nd 2 3 0 7 whole rock sr isotope data are scattered but suggest an initial 87sr 86sr ratio of 0 7012 similar to bulk earth the elevated levels of light rees and sr in the lamprophyres were not due to crustal contamination or mixing with contemporaneous monzodioritic magmas but a result of partial melting of a mantle source which was enriched in these and other large ion lithophile elements liles shortly before melting the lamprophyres were contemporaneous with mantle derived high mg lile enriched monzodiorite to granodiorite of the archean sanukitoid suite both suites have concave downward light ree profiles suggesting that depleted mantle was common to their source regions but the higher light ree abundances higher ba la ratios and lower nd values 1 3 0 3 of the parental monzodiorites suggest a more enriched source the lamprophyres and high mg monzodiorites were derived from a mineralogically and compositionally heterogeneous lile enriched mantle lithosphere that may have been part of a mantle wedge above a subducting plate in an arc environment

evolved granitic systems as a source of rare element deposits the ponte segade case galicia nw spain abstract in the ponte segade area galicia nw spain strongly differentiated granites often associated with rare element mineralization sn ta nb li be cs that could be of economic interest have recently been discovered these granites appear in the northern sector of the ollo de sapo antiform central iberian zone variscan orogen three different muscovite rich synkinematic and peraluminous types of leucogranite leucogranites s s albite rich leucogranites i and albite rich leucogranites ii and two pegmatite types associated with the albite rich leucogranites zoned and banded have been identified in the studied area the geochemistry of whole rock leucogranites indicates an enrichment in incompatible elements lithium rubidium beryllium cesium and hafnium al2o3 and na2o and an impoverishment in barium strontium zirconium cerium yttrium and sio2 geochemical studies of zircon muscovite k feldspar and tourmaline in the different types of granites and pegmatites indicate the grade of evolution of the granitic system with differentiation of the system the zircon is enriched in hafnium and uranium and is impoverished in zirconium in muscovite and k feldspar there is an increase in cesium and rubidium the opposite behavior is observed with regards to the mg fe and ti contents in the case of tourmaline the increase in li is the best indicator of the grade of evolution by contrast fe and mg decrease the sequence of evolution of the granitic system obtained from the geochemical studies indicates that the leucogranites s s are the least differentiated evolving gradually in accordance with field relationships to albite rich leucogranites i the albite rich leucogranites ii are the most evolved but no direct relationship between them and leucogranites s s has been found the banded pegmatites associated with the albite rich leucogranites ii are more differentiated than the zoned pegmatites associated with the albite rich leucogranites i but are the poorest in sn ta and nb

the geotectonic history of the makran and adjacent areas of southern iran abstract the makran mountain range in southern iran has been entirely covered by regional mapping on a scale of 1 250 000 but in contrast to the mapping of oman on the other side of the gulf the recent mapping is little known the cenozoic accretionary prism in the south fronts onto a mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver which is followed by a zone of largely intact mesozoic ophiolite complexes to the north of this lies the jaz murian depression a desert expanse with no bedrock outcrop the sanandaj sirjan bajgan dur kan microcontinental sliver which extends from turkey through the zagros to the makran is one of a number of microcontinents which detached from gondwana no later than the early triassic nw iran yazd tabas lut birk helmand farah during the mesozoic these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times ranging from early cretaceous to end palaeogene an analogy is drawn with the present day mediterranean the sistan ocean in the east was infilled with an immense thickness of abyssal turbidites during the eocene before it closed the field evidence indicates that there was a second cenozoic accretionary prism here but sedimentation ceased after the eocene on its collision with the back of the main makran prism this eastern sistan trough now completely occluded is compared with the still open tract separating the makran from oman at the present time and its northern extension which has been similarly occluded by collision beneath the zagros some residual very shallow inland seas persisted inland from the makran through the neogene the occurrence of blueschists in the inner ophiolite belt of the makran is discussed abyssal turbidite sedimentation continued in the main southern zone of the makran into the early miocene to be succeeded by thick shallow water sequences including reefal limestones intense tectonic dislocation at the end of the miocene was accompanied by a shift of the subduction front to its present position out in the indian ocean and uplift leading to the deposition of spectacular pliocene pleistocene fanglomerates

early forest soils and their role in devonian global change a paleosol in the middle devonian aztec siltstone of victoria land antarctica is the most ancient known soil of well drained forest ecosystems clay enrichment and chemical weathering of subsurface horizons in this and other devonian forested paleosols culminate a long term increase initiated during the silurian from silurian into devonian time red clayey calcareous paleosols show a greater volume of roots and a concomitant decline in the density of animal burrows these trends parallel the decline in atmospheric carbon dioxide determined from isotopic records of pedogenic carbonate in these same paleosols the drawdown of carbon dioxide began well before the devonian appearance of coals large logs and diverse terrestrial plants and animals and it did not correlate with temporal variation in volcanic or metamorphic activity the early paleozoic greenhouse may have been curbed by the evolution of rhizospheres with an increased ratio of primary to secondary production and by more effective silicate weathering during silurian time

coeval potassic and sodic calc alkaline series in the post collisional hercynian tanncherfi intrusive complex northeastern morocco geochemical isotopic and geochronological evidence abstract the post collisional late hercynian tanncherfi intrusive complex tic is part of a widespread intrusive episode in the moroccan meseta the complex contains a wide range of rock types from monzogabbros to monzogranites two distinct magmatic series are recognized 1 a potassic shoshonitic series consisting of monzogabbros quartz monzonites and monzogranites and 2 a sodic granodioritic series represented by quartz monzodiorites and granodiorites all the tanncherfi plutonic rocks display similar spider diagram profiles with lile and lree enrichment and nb ta ti depletion which are typical of subduction related magmas combined major trace element compositions and sr nd isotopic results indicate that the two series have been derived from a lile and lree enriched continental lithospheric mantle source under different partial melting and or depth conditions intrusion of the tanncherfi rocks was not temporally related to subduction and the enrichment of their source is likely to be linked to preceding subduction events the two series evolved by fractional crystallization of clinopyroxene plagioclase hornblende biotite k feldspar and accessories fe ti oxide minerals titanite apatite and zircon for the potassic series while the sodic series combined fractional crystallization with assimilation of felsic magmas with lower sr isotopic ratio than the more mafic term of the series the quartz monzodiorite the intrusion of the potassic magmas 344 6 ma marks a major change in the tectonic regime of eastern meseta these magmas intruded during post thickening uplift and extension both probably favored by convective thinning of the lithosphere this model provides a reasonable mechanism for the genesis of other hercynian intrusive complexes in morocco

petrogenesis of two granites from the nilgiri and madurai blocks southwestern india implications for charnockite calc alkaline granite and charnockite alkali a type granite link in high grade terrains abstract igneous charnockites share some of the characteristics of calc alkaline and alkali a type granites and together constitute important rock types in many high grade terrains the neoproterozoic kalpatta and munnar biotite hornblende granites intrude the upper amphibolite to granulite facies terrain of southwestern india geochemical characteristics of the kalpatta granite are similar to high k calc alkaline magnesian granitoids whereas those of the munnar granite are similar to alkali ferroan granitoids within the constraints imposed by the high temperature k rich nature of the magmas comparison with experimental studies on various granitoid source compositions and trace and rare earth element modeling the distinctive features of both granites reflect a source rock of charnockitic nature in this context the northern kerala nkm and cardamom hill cm charnockite massifs occurring near the granites were considered as probable source rock compositions both the nkm and cm charnockites consists of an intermediate low sio2 type and silicic high sio2 type with the intermediate type showing similarities to high ba sr granitoids with low k2o na2o ratios and the silicic type showing similarities to high ba sr granitoids with high k2o na2o ratios the proposed petrogenetic model involves partial melting of the intermediate nkm charnockite forming the kalpatta calc alkaline granite in contrast the munnar alkali a type granite was the product of melting followed by fractional crystallization of the intermediate cm charnockite it is suggested that granitoids that formed by melting of intermediate type charnockites show high k calc alkaline magnesian geochemical characteristics whereas those formed by intermediate type charnockite melting fractional crystallization show alkali ferroan geochemical characteristics

abundant tetracyclic terpenoids in a middle devonian foliated cuticular liptobiolite coal from northwestern china cuticular liptobiolite coal defined by its dominant cutinite is rare and only known in a few regions of the world an occurrence of this type of coal found in the devonian of the hefeng basin xinjiang northwestern china is described for the first time by organic petrography and biomarker analysis the cuticular liptobiolite has distinct sheet like layers and thus splits easily into leafy laminae which are segregated during weathering forming a so called paper coal it is comprised dominantly of cutinites 75 vol on a mineral free basis with minor vitrinites 20 lycopsids are suggested to be the dominant coal forming plants the aliphatic fractions of these samples contain only small amounts of n alkanes and common biomarkers such as steranes and hopanes tetracyclic diterpanes cnh2n 6 with mainly beyerane and atisane skeletons are the dominant constituents the abundant tetracyclic diterpanes present in this and other devonian cuticle rich coals indicate that their parent natural product precursors occurred abundantly in the early vascular land plants of the devonian i e lycopsid and psilopsid species it seems that these early land plants secreted massive amounts of resins from their vascular tissues coating their cuticle surfaces to protect against water evaporation massive cuticle accumulation in the middle devonian likely resulted from a simple assemblage of unique early land plants

trace element abundances of high mgo glasses from kilauea mauna loa and haleakala volcanoes hawaii we performed an ion microprobe study of eleven high mgo 6 7 14 8 wt tholeiite glasses from the hawaiian volcanoes kilauea mauna loa and haleakala we determined the rare earth re high field strength and other selected trace element abundances of these glasses and used the data to establish their relationship to typical hawaiian shield tholeiite and to infer characteristics of their source the glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites e g l light ree h heavy reec1 1 the kilauea and mauna loa glasses however display trace and major element characteristics that cross geochemical discriminants observed between kilauea and mauna loa shield lavas the glasses contain a blend of these discriminating chemical characteristics and are not exactly like the typical shield lavas from either volcano the production of these hybrid magmas likely requires a complexly zoned source rather than two unique sources when corrected for olivine fractionation the glass data show correlations between cao concentration and incompatible trace element abundances indicating that cao may behave incompatibly during melting of the tholeiite source furthermore the tholeiite source must contain residual garnet and clinopyroxene to account for the variation in trace element abundances of the kilauea glasses inversion modeling indicates that the kilauea source is flat relative to c1 chondrites and has a higher bulk distribution coefficient for the hree than the lree

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

the meta igneous granulite xenoliths from kerguelen archipelago evidence of a continent nucleation in an oceanic setting xenoliths of meta igneous origin occur as one of the two main types of ultramafic and mafic xenoliths entrained by alkaline lavas of the kerguelen islands these are designated type ii xenoliths and are subdivided into three mineralogical groups subtype iia and iic xenoliths are interpreted as crystallisation products of basaltic melts that were emplaced near the crust mantle boundary during the early tholeiitic transitional magmatic activity of the kerguelen islands younger magmatism became more alkaline and subtype iib xenoliths were formed as high pressure alkaline cumulates related to the last alkaline volcanic stage subsequently the plagioclase bearing type ii rocks have been re equilibrated under granulite facies conditions this addition of mafic material around the crust mantle boundary is consistent with seismic evidence for crustal thickening to 14 20 km calculated compressional seismic velocities vp for the basic granulites are consistent with the range of observed vp in the low velocity region underlying the oceanic crust such growth in the thickness of the oceanic crust may be caused by intrusion of basalts at different levels in the lithosphere and may provide the heat responsible for granulitic metamorphism in the oceanic setting this study suggests that basic granulites can account for the observed seismic characteristics of oceanic plateaux and can be important components of kerguelen oceanic lithosphere where there has been large scale magma production moreover we speculate that the kerguelen islands and perhaps the surrounding plateau represent a continental nucleation process

petrogenesis of the flood basalts forming the northern kerguelen archipelago implications for the kerguelen plume the thick 20 km crust of the kerguelen archipelago formed as the tectonic setting of the kerguelen plume changed from an oceanic ridge centered location at 43 ma to its present location beneath the antarctic plate the uppermost crust is dominantly flood basalt with a thickness of up to 10 km inverse isochron 40ar 39ar ages for upper and lower lavas in a 630 m section of basalt flows from mont bureau are 30 4 and 29 0 ma re os isotopic systematics are consistent with this age most of the lavas in two stratigraphic sections mont bureau and mont rabouillere from the northern part of the archipelago have sr nd and pb isotopic characteristics similar to the youngest upper miocene to pleistocene lavas erupted in the southeast part of the archipelago i e initial 87sr 86sr 0 7050 143nd 144nd 10 mgo alkalic lavas in the southeast province of the archipelago in these northern sections it is confined to transitional lavas with

petrology geochemistry and tectonic setting of the khoy ophiolite northwest iran implications for tethyan tectonics abstract the khoy ophiolite in northwestern iran represents a remnant of oceanic lithosphere formed in the mesozoic neo tethys this northwest southeast trending ophiolite complex consists from bottom to top east to west of a well defined basal metamorphic zone peridotites dunite harzburgite and serpentinized peridotite gabbros sheeted dikes pillow and massive lava flows and pelagic sedimentary rocks including radiolarian chert the rocks of the metamorphic zone have an inverse thermal gradient from amphibolite facies to greenschist facies the high grade metamorphic rocks are immediately adjacent to the peridotite and the gabbros and the low grade rocks are in contact with the precambrian kahar formation based on mantle normalized incompatible trace element diagrams there are two distinct types of basalt flows present at the khoy ophiolite 1 massive basalts that have patterns virtually identical to e morb and 2 pillow basalts that have more primitive chemical composition whose trace element patterns plot between e morb and n morb the chondrite normalized ree patterns for the pillow basalts are lree depleted lan smn ave 0 70 similar to patterns for the mean diabase composition for the oman ophiolite and lree depleted basalts of the band e zeyarat ophiolite of southern iran the ree patterns for the massive basalts are similar in general ree abundances to the pillow basalt patterns but they are slightly lree enriched lan smn ave 1 09 and their patterns cross those of the pillow basalts the ree patterns for the gabbros and diorites indicates that the crustal suite rocks were most likely derived by a process of fractional crystallization from a common basaltic melt this basaltic melt was most likely generated by approx 20 25 partial melting of a simple lherzolite source and had ree concentrations of roughly 10 chondrite a comparison between the results from the khoy ophiolite and the data from other iranian ophiolites reveals geochemical evidence to suggest a tectonic link between the khoy ophiolite and the rest of the iranian ophiolites our results suggest that khoy ophiolite is equivalent to the inner group of iranian ophiolites e g nain shahr babak sabzevar tchehel kureh and band e zeyarat and was formed as a result of closure of the northwestern branch of a narrow mesozoic seaway which once surrounded the central iranian microcontinent

the petrogenesis and tectonic setting of lavas from the baft ophiolitic melange southwest of kerman iran a late cretaceous ophiolite complex in the baft area southwest of kerman iran is characteristic of the central iranian ophiolitic melange belt which wraps around the lut block despite the extensive tectonic disruption of the baft complex most ophiolitic lithologies are present and many original igneous contacts are preserved a lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the baft spreading axis geochemical data confirm the presence of two distinct compositional groups in the mafic lavas 1 tholeiitic basalt and 2 transitional tholeiitic basalt the tholeiitic lavas are similar to typical mid ocean ridge basalt compositions whereas the transitional tholeiites are similar to intraplate basalts the available data suggest that the baft ophiolite complex formed in a small ocean basin possibly at or near a ridge transform intersection emplacement may have occurred as a result of conversion of the transform fault to a subduc

deciphering basaltic magmatism on the moon from the compositional variations in the apollo 15 very low ti picritic magmas picritic glass beads of volcanic origin have been interpreted as representing extremely primitive lunar magmas that approach primary magma compositions based on this they have been used for developing models for lunar magmatism estimating the mineralogical and chemical characteristics of their mantle sources constraining the dynamics and structure of the lunar mantle developing models for lunar core formation reconstructing the bulk composition of the moon and evaluating the genetic relationships between the earth and the moon yet we still do not truly understand many aspects of the compositional diversity among individual glass types or even within a single glass type using high precision ion microprobe techniques we have analyzed a total of forty very low ti glass beads from the apollo 15 a15 site and twenty additional picritic glass beads from other sampling sites for a suite of highly compatible ni co weakly compatible to weakly incompatible mn cr v and highly incompatible ce ti zr nb elements within the a15 very low ti glass population ni and co concentrations are positively correlated exhibit limited fractionation of ni co and are distinctive for individual glass groups as defined by major elements manganese is also colinear with both ni and co the highly incompatible elements also appear to be generally colinear with ni co and mn although there are distinguishable compositional offsets in the glass populations the ni co ratio does not differ dramatically among the very low ti glasses from other sampling sites although incompatible element concentrations may differ significantly these trace element data eliminate fractional crystallization and partial melting of a homogeneous source under extremely low fostaggered2 conditions as possible models for the origin of the compositional variations observed in the a15 very low ti glass population these data are consistent with the generation of these magmas through partial melting of a spatially restricted heterogeneous lunar magma ocean lmo cumulate sequence the compositional variation in these magmas can be produced by at least two different melting processes 1 partial melting of a cumulate sequence consisting of relatively early cumulates with a higher proportion of an intercumulus melt component green glass a d e and later cumulates with lower proportions of an intercumulus melt component green glass c 2 different degrees of partial melting of a cumulate sequence small degrees of partial melting less than 5 of a more primitive cumulate mantle source will generate one group of magmas green a d e whereas a group of other picritic magmas green c were produced by larger degrees of partial melting 10 to 20 of a mineralogically similar but a more evolved cumulate mantle source in both models the green b glass group is formed by either cumulate commingling or magma mixing processes these magmas cannot be rapidly transported from the source region to the lunar surface in a single eruptive event without extensive fractional crystallization yet the colinear relationship among ni co and mn is not compatible with extensive and variable fractional crystallization therefore a polybaric melting model as suggested by longhi 1992b appears to be the only alternative to producing relatively unfractionated apollo 15 very low ti picritic magmas with high pressure signatures the trace element data provides additional constrains for this type of model

occurrence and composition of solid bitumens from the bulonggoer devonian paleo oil reservoir north xinjiang china abstract the bulonggoer paleo oil reservoir bpr on the northwest junggar basin is the first devonian paleo oil reservoir discovered in north xinjiang china solid bitumens occur within sandstone pores and as veins filling fractures samples of both types were analyzed using stable carbon isotope and reflectance measurements as well as molecular biomarker parameters the extremely positive 13 c values and biomarker indicators of depositional environment lithology such as pristane phytane pr ph c 29 c 30 hopane diasteranes regular steranes and dibenzothiophene phenanthrene ratios indicate a siliciclastic source for the bpr and their deposition in a highly reducing hypersaline environment the presence of long chain n alkanes and abundant tetracyclic diterpanes c 20 c 21 tricyclic terpanes and perylene are indicators of higher plant organic matter input moreover the bimodal distribution of c 27 c 28 29 regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter the similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo petroleum which originated from peak oil window matured source rocks all solid bitumens from the bpr are characterized by relatively low bitumen reflectance values rb

orbitally mediated cycles from the turonian of southern england their potential for high resolution stratigraphic correlation detailed sampling of two sections of turonian aged chalk from southeast england for foraminifera has revealed that cyclical abundance changes in many species and genera were mediated by orbitally induced climatic cycles these cycles can be used for high resolution stratigraphic correlation of the two sections and as a possible means of re estimating the duration of the turonian period

rare earth element metasomatism in hydrothermal systems the willsboro lewis wollastonite ores new york usa abstract wollastonite ores and garnet pyroxene skarns in the willsboro lewis district new york usa were formed in a complex hydrothermal system associated with the emplacement of a large anorthosite pluton contact metamorphic marbles were replaced by wollastonite garnet and clinopyroxene during infiltration metasomatism involving large volumes of water of chiefly meteoric origin rare earth elements ree in these rocks show large departures from the protolith ree distribution indicative of substantial ree mobility three types of chondrite normalized ree distribution patterns are present the most common found in ores and skarns containing andradite rich garnet is convex up in the light ree lree with a maximum at pr and a positive eu anomaly europium anomalies and pr yb ratios are correlated with x ad in garnet this pattern type c results from uptake of ree from hydrothermal fluids by growing crystals of calcsilicate minerals principally andradite with amounts of lree controlled by the difference in ionic radius between ca and ree 3 in garnet x sites the eu anomaly results either from prior interaction of the fluids with plagioclase rich eu positive anorthositic rocks in and near the ore zone or by enrichment of divalent eu on growth surfaces of garnet followed by entrapment or both relative enrichment in heavy ree type h occurs in ores and skarn where calcsilicates including grossularitic garnet in contact metamorphic marble have been concentrated by dissolution of calcite in most cases a negative eu anomaly is inherited from the marble protolith skarns containing titanite and apatite exhibit high total ree relative light ree enrichment and negative eu anomalies type l these appear to be intrusive igneous rocks ferrodiorites or anorthositic gabbros that have been converted to skarn by ca metasomatism ree sequestered in titanite apatite and garnet preserve the approximate ree distribution pattern of the igneous protolith post ore granulite facies metamorphism homogenized zoned mineral grains without causing complete intergranular reequilibration and does not appear to have significantly affected the whole rock ree distributions these results demonstrate that extensive ree metasomatism can occur in hydrothermal systems at shallow to intermediate depths and that ree geochemistry may be useful in discerning the origin of skarns and skarn related ore deposits

geochemistry of cretaceous granites from mianning in the panxi region sichuan province southwestern china implications for their generation abstract the cretaceous granites of mianning located in the northern panxi region were emplaced after collision of the tibetan plateau and yangtze block these granites have very high k 2 o na 2 o ga zr nb y ree except eu and very low mgo cao p 2 o 5 and sr contents relative to m i or s type granites based on the chemical discrimination criteria of whalen et al whalen j b currie k l chappell b w 1987 a type granites geochemical characteristics distribution and petrogenesis contributions to mineralogy and petrology 95 407 419 most of them are a type granites moreover the granites plot in the range of post collision granites and belong to the a2 type elevated initial sr isotopic ratios 0 72 suggest their derivation dominantly from a crustal source these features are consistent with granite formation in a post orogenic setting such as after subduction or collision between of the tibetan plateau and yangtze block in addition the granites are characterized by low abundances of ba sr p ti and eu positive correlation between ba and eu anomalies and negative correlation between rb and k rb plots of rb vs sr suggest that fractional crystallization affected the final compositions of these granites after melting from a dominantly crustal source from the late proterozoic to late mesozoic the crustal composition compared to that of the mantle appears to have increased in the panxi region while the mantle component played an important part in the generation of cretaceous granites in southeastern china its influence was relatively minor in the panxi region thus there was a significant difference in mantle evolution between southeastern china and the panxi region which led to different metallogenic processes

the phillips pluton maine usa evidence of heterogeneous crustal sources and implications for granite ascent and emplacement mechanisms in convergent orogens the phillips pluton age of 403 8 1 3 ma was assembled at a crustal level below the contemporary brittle plastic transition during regional dextral reverse transpressive deformation the pluton is composed dominantly of medium to coarse grained leucogranite sensu lato s l but within its bounds includes decametric massive outcrop of fine to medium grained granodiorite s l in places the leucogranite contains centimetric enclaves apparently of the granodiorite granodiorite is host to more biotite than muscovite and more calcic oscillatory zoned plagioclase compared to the leucogranite pegmatitic granite and composite pegmatite aplite occur as metric sheets within the pluton and as larger bodies outside the pluton to the sw magmatic fabrics defined by biotite schlieren occur locally in the leucogranite the attitude of these fabrics and layering within the leucogranite are concordant with the ne striking steeply dipping country rock foliation k2o contents rb sr ratios rb sr and ba covariations and chondrite normalized rare earth element ree patterns of leucogranite are consistent with high to moderate a h2o muscovite dehydration equilibrium eutectic melting of a predominantly pelite source similar to metasedimentary rocks of the surrounding central maine belt cmb the ree patterns and rb sr ratios of granodiorite also suggest derivation from a metasedimentary source but more likely by moderate to low a h2o muscovite biotite dehydration equilibrium eutectic to non eutectic minimum melting of a protolith dominated by greywacke in which garnet and plagioclase were residual phases both granite s l types have heterogeneous initial nd isotope compositions samples of granodiorite define a range in end 404 ma of 1 8 to 0 1 0 3 2 uncertainty and samples of leucogranite define a range in end 404 ma of 8 0 to 5 3 0 3 2 uncertainty this bimodal distribution suggests that melts were derived from a minimum of two sources the data are consistent with these sources being cmb metasedimentary rocks end 404 ma 4 for the granodiorite the range of nd isotope compositions within each granite type most likely reflects isotopic heterogeneity inherited from the source these data imply that the integrity of individual melt batches was maintained during ascent and that extensive mixing of melt batches during emplacement at this level in the pluton did not occur although centimetric enclaves have intermediate nd isotope compositions consistent with small scale interactions between magmas we infer that the phillips pluton represents the root of a larger pluton and that what remains of this larger pluton is the feeder constructed from multiple melt batches arrested during waning flow of granite magma through a crustal scale shear zone system

organic geochemistry and coal petrology of tertiary brown coal in the zhoujing mine baise basin south china 4 biomarker sources inferred from stable carbon isotope compositions of individual compounds abstract carbon isotopic compositions of extractable compounds derived from higher land plants are within 2 0 00 of the bulk coal 13 c 27 0 0 00 from baise basin this data suggests that either similar species contributed these compounds or that the plants from which this coal was formed imposed similar biosynthetic fractionations the terpenoid hydrocarbons form two isotopically distinct groups the diterpenoids 13 c 25 0 1 4 0 00 and the sesquiterpenoids 13 c 25 9 1 5 0 00 are on 1 2 0 00 enriched in 13c compared to the bulk coal whereas the oleanane ursane lupane derivatives 13 c 29 0 0 8 0 00 are on average 1 2 0 00 depleted in 13c compared to the bulk coal the n alkanes ranging from c15 to c35 have a mean 13c value of 32 4 0 6 0 00 whereby averages for the c17 c22 and c23 c33n alkanes do not significantly differ from the overall average hopane derivatives in this coal extract are depleted in 13c compared to the bulk coal by 8 34 0 00 suggesting that bacterial cycling of methane played a role during formation of this coal

nature and depositional environment of devonian coals from western melville island arctic canada abstract the petrology and depositional environment of a suite of middle to upper devonian coals and carbonaceous shales from melville island has been studied the majority of the coals and carbonaceous shales are cannel coal and canneloids the sporinite content of cannel coal ranges as high as 80 the reflectance of vitrinite in cannel coals is suppressed compared with the normal coal from the same area these coals were deposited in fresh to slightly brackish water in interdelta lobe bays and lacutrine complexes associated with lower delta plain settings as indicated by the boron content 4 71 ppm petrology cannel and canneloid and sedimentology

differential early diagenetic low mg calcite cementation and rhythmic hardground development in campanian maastrichtian chalk abstract the campanian maastrichtian limestones in the south of the netherlands are well sorted fine grained mudstones and silt to fine sand sized bioclastic grainstones these limestones show a distinct lithological cyclicity manifested by fining upward grain size cycles with calcite cemented layers or hardgrounds capping each cycle in the lower part of the succession the cyclicity is further enhanced by nodular chert layers these fining upward cycles are caused by fair weather or storm wave related energy fluctuations and consequently changing rates of deposition differences in composition and texture and differences in the degree of early diagenesis cemented layers and hardgrounds are the result of differential early marine calcite cementation in these limestones early calcite cementation cannot be explained by the supply of cementing materials from saturated seawater an alternative model for early marine calcite cementation is proposed in which early calcite cementation occurred within the sediment at some distance below the seafloor as a result of organic matter degradation and internal redistribution of bioclastic carbonate bacterial organic matter degradation caused dissolution of relatively unstable high mg calcite and or aragonite in the oxic zone followed by precipitation of calcite cement as a consequence of bacterial iron reduction duringperiods with a lower sedimentation rate any significant early cementation and replacement of high mg calcite occurred when younger oxic burrows dissected older burrowed sediment with a more advanced stage of organic matter degradation in particular iron reduction cementation also occurred when redox boundaries repeatedly moved through the same layers during periods with low nett sedimentation and increased storm activity and erosion the differences in the degree of early diagenetic calcite cementation were further enhanced during paleocene karstification and development of secondary porosity by dissolution of remaining unstable carbonate grains and by associated meteoric water calcite cementation

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation