tectonic implications of paleomagnetic and geochronologic data from the yukon koyukuk province alaska the paleomagnetic and geochronologic record of alaska is complicated by overprints that make it difficult to relate the terranes of northern and southern alaska to each other and to north america to better understand these relationships and the overprinting paleomagnetic and k ar dating samples were analyzed from the three major geologic units of the yukon koyukuk province ykp of central alaska these units consist of a basal jurassic early cretaceous volcanic island arc assemblage albian cenomanian clastic sedimentary rocks and bimodal eocene volcanic rocks k ar age determinations of the early tertiary volcanic rocks form two distinct groups the older group 65 49 ma is mostly felsic and probably represents the maximum inboard penetration of low angle subduction related volcanism these older rocks were deformed during the regional deformation of the ykp the younger group 44 43 ma is post deformational and composed dominantly of basalt these results bracket a time 49 44 ma when deformation ceased in the province this time interval is coincident with a major transition from convergence to strike slip and extensional tectonic style throughout alaska the geologic units of the ykp display two characteristic paleomagnetic signatures primary directions based on positive reversal conglomerate and or bedding tilt stability tests were obtained from the albian cenomanian sedimentary rocks and eocene volcanic rocks the mid cretaceous sedimentary rocks show about 15 of poleward motion between 90 56 ma a time of high rates of convergence between alaska and the pacific and eurasian plates age equivalent rocks from neighboring regions st matthew island and the alaskan north slope also indicate similar amounts of poleward northward motion which suggests that the whole of western and northern alaska may have moved northward about 10 relative to north america as a more or less coherent block paleomagnetic results from the eocene volcanic rocks indicate that the ykp was in place by 56 ma and formed part of the accretionary nucleus that served as a backstop for the accreted terranes of southern alaska secondary remagnetized directions are recorded in the basal island arc assemblage and in albian cenomanian sediments near younger igneous occurrences the clustering of secondary directions in the geographic reference frame indicates that they were acquired after deformation ceased 49 44 ma which is consistent with the coincidence of the mean of these directions and the 54 44 ma north american reference direction

accretion of southern alaska abstract paleomagnetic data from southern alaska indicate that the wrangellia and peninsular terranes collided with central alaska probably by 65 ma ago and certainly no later than 55 ma ago the accretion of these terranes to the mainland was followed by the arrival of the ghost rocks volcanic assemblage at the southern margin of kodiak island poleward movement of these terranes can be explained by rapid motion of the kula oceanic plate mainly from 85 to 43 ma ago according to recent reconstructions derived from the hot spot reference frame after accretion much of southwestern alaska underwent a counterclockwise rotation of about 50 as indicated by paleomagnetic poles from volcanic rocks of late cretaceous and early tertiary age compression between north america and asia during opening of the north atlantic 68 44 ma ago may account for the rotation

fluid inclusions of the high pressure granulites from the namche barwa complex of the eastern himalayan syntaxis tibet fluid composition and evolution in the continental subduction zone abstract the namche barwa complex in the eastern himalayan syntaxis has experienced high medium pressure granulite facies and amphibolite facies metamorphism the high pressure granulites contain complex fluid inclusion assemblages including h 2 o co 2 ch 4 carbonic co 2 ch 4 n 2 co 2 solid brine medium to low salinity aqueous inclusions and low density gaseous inclusions textural evidence suggests that the isolated h 2 o co 2 ch 4 inclusions occurring in quartz blebs enclosed in garnet porphyroblasts were trapped in the peak metamorphic stage whereas isolated and trail bound co 2 inclusions along intragranular fractures in quartz plagioclase and garnet were mainly trapped during the early decompression stage of the high pressure granulites although some co 2 rich inclusions have formed by selective leakage of h 2 o out of h 2 o co 2 inclusions this together with wide variations in homogenization temperatures indicates modifications and density resetting of the fluid inclusions during exhumation in contrast to the common presence of high density co 2 fluid inclusions in granulite terrains worldwide the high pressure granulites in the namche barwa complex contain dominantly medium to low density h 2 o co 2 ch 4 and co 2 inclusions this may be explained as that the high pressure granulites occur in the continental subduction zone tectonic setting

primary carbonate co2 inclusions in sapphirine bearing granulites from central sri lanka high density co2 rich fluid inclusions from a sapphirine bearing granulite hakurutale sri lanka have been studied by microthermometry raman spectrometry and sem analysis based on textural evidence two groups of inclusions can be identified primary negative crystal shaped inclusions group i and pseudo secondary inclusions which experienced a local limited post trapping modification group ii both groups contain magnesite as a daughter mineral occurring in a relatively constant fluid solid inclusion volume ratio volsolid 0 15 total volume co2 densities for group i and ii differ only slightly both groups contain a fluid which was initially trapped at peak metamorphic conditions as a homogeneous co2 mgco3 mixture thermodynamic calculations suggest that such a fluid co2 15 vol mgco3 is stable under granulite facies conditions after trapping magnesite separated upon cooling while the remaining co2 density suffered minor re adjustments a model isochore based on the integration of the magnesite molar volume in the co2 fluid passes about 1 5 2 kbar below peak metamorphic conditions this remaining discrepancy can be explained by the possible role of a small quantity of additional water

low density carbonic fluids in the archean granulite facies terrain of the jequie complex bahia brazil the 2 7 ga old high grade metamorphic rocks of the jequi complex of bahia include charnockites enderbites and late pink potassic granites mineralogic p t determinations for the granite terrain yield 4 5 kb 750 850c for the peak of metamorphism microthermometry of fluid inclusions in quartz was performed on different rock types early co 2 rich fluids have densities around 0 85 g cm 3 and may represent synmetamorphic fluids since the isochores cross the inferred p t box late fluids are of lower density and correspond to the waning phase of metamorphism the correspondence in the jequte complex of the relatively low p t conditions with the low density co 2 rich fluids provides evidence that the trapped fluids are to some degree representative of the granulite facies metamorphism though they may have been modified by post metamorphic processes

fluid influence on mineral reactions in ultrahigh pressure granulites a case study in the śnieznik mts west sudetes poland small tectonic slices of undeformed eclogites and ultrahigh pressure granulites occur in three tectonic units of the nieznik mts sw poland ultrahigh pressure granulite eclogite transitions with peak metamorphic conditions between 21 and 28 kbar at 800 to 1000 c occur only in the zlote unit conventional u pb multigrain analyses of zircons from a mafic granulite provided 207pb 206pb ages between 360 to 369 ma which are interpreted to approximate timing of original crystallisation from a melt diffusion kinetics and the restricted availability of a fluid phase mainly controlled the conversion from granulite to eclogite although some bulk chemical differences were also recognised the ultrahigh pressure granulites from the zlote unit exclusively contain h2o rich inclusions with variable salinities which distinguishes them from high temperature ht granulites world wide this is also in contrast to the fluid regime h2o n2 co2 recognised in the lower temperature eclogites 600 800 c from the closely associated miedzygorze and nieznik units the variation in fluid composition between the lower temperature eclogites and ultrahigh pressure granulites on the one hand and ultrahigh pressure granulites and ht granulites on the other hand probably indicates contrasting p t t paths as a result of different tectonic environments

cordierite gneisses of southern kerala india petrology fluid inclusions and implications for crustal uplift history the cordierite bearing gneisses occurring as elongate patches in an 8 to 10 km wide zone along the achankovil fault lineament at the northern margin of the southern kerala crustal segment represent an important lithological unit in the archaean granulite terrane of south india the textural relationships in these rocks are consistent with the following main reactions 1 garnet quartz cordierite hypersthene 2 garnet sillimanite quartz cordierite 3 hypersthene sillimanite quartz cordierite 4 sillimanite spinel cordierite corundum and 5 biotite quartz sillimanite cordierite k feldspar many of the mineral associations and reaction textures including the remarkable preservation of symplectites are indicative of partial replacement of high pressure assemblages by cordierite bearing lower pressure ones during an event of rapid decompression temperature estimates from coexisting mineral phases show 710 garnet biotite 791 garnet cordierite and 788 c garnet orthopyroxene pressure estimates from mineral assemblages range from 5 4 to 7 kb detailed fluid inclusion studies in quartz associated with cordierite show high density co2 0 80 0 95 g cm3 as the dominant fluid phase with traces of probable ch4 in the sillimanite bearing rocks the isochore for the higher density fluid inclusions defines a pressure of 5 5 kb the fracture bound co2 and co2 h2o ch4 inclusions indicate simultaneous entrapment at 400 c and 1 7 kb in the cordierite hypersthene assemblage and 340 c and 1 2 kb in the cordierite sillimanite assemblage the p t path delineated from combined solid and fluid data corresponds to the piezothermic array of the gneisses and is characterized by t convex nature indicative of rapid and virtually isothermal crustal uplift probably aided by extensional tectonics

tectonic evolution of northeastern siberia and adjacent regions abstract previous models for the tectonic evolution of northeastern siberia have proposed the existence of a kolyma plate composed of the kolyma and omolon massifs of presumed precambrian age lithologic similarities between the siberian platform and the cherskiy mountains and the presence of oceanic and island arc type deposits in the kolyma indigirka interfluve suggest that no such plate exists the eastern margin of the siberian plate is suggested to lie along a line between the ulakhan sis range the alazeya uplift and the arga tas range the cherskiy mountains and the verkhoyansk fold belt are parts of the siberian plate the paleozoic deposits of the omolon massif are unlike those found in the cherskiys or siberia paleomagnetic data from the omolon massif are discordant from data from siberia it is suggested that the omolon massif represents a microplate which accreted onto siberia in the jurassic ophiolites in central chukotka are of the same emplacement age as in the western brooks range and may have been emplaced at the initiation of the rotation of arctic alaska geometric and limited stratigraphic data suggest that the east siberian sea may be floored by oceanic crust left by an incomplete closure between arctic alaska siberia and omolon the tectonic position of the prikolymsk massif remains ambiguous

early cretaceous paleolatitude of the yukon koyukuk province alaska we report results from a paleomagnetic study of the yukon koyukuk province a key region for reconstructing the cretaceous paleogeography of northern alaska and northeastern asia the province lies between the displaced continental fragment of arctic alaska and the accreted terranes of southern alaska although lower cretaceous volcanogenic rocks of the yukon koyukuk province preserve primary remanent magnetizations the primary component is masked by a pervasive overprint the over printing magnetization which has dual polarity was acquired after a late cretaceous orogeny left the region highly deformed by fitting planes to tilt corrected thermal demagnetization data and solving for the best intersection of the corresponding remagnetization circles we separated the primary component presumably a vestige of the original thermoremanent magnetization from the overprinting component of the natural remanence the primary magnetization corresponds to a mean paleopole of early cretaceous age at 60 2 n 159 e the mean paleolatitude is 69 n with the 95 confidence ellipse ranging from 60 to 75 n this analysis was successful because the tilt corrections of the sampled strata had sufficient variation to ensure a strong intersection of the remagnetization circles we infer that lower cretaceous rocks of the brooks range and the yukon koyukuk province were once separated by a wide ocean basin that was closed by subduction probably during the cretaceous the northern limb of the angayucham terrane which lies between the brooks range and the yukon koyukuk province may contain remnants of the now closed ocean basin

calculation of co 2 activities using scapolite equilibria constraints on the presence and composition of a fluid phase during high grade metamorphism thermodynamic and phase equilibrium data for scapolite have been used to calculate co2 activities aco2 and to evaluate the presence or absence of a fluid phase in high grade scapolite bearing meta anorthosite granulites calc silicates and mafix xenoliths the assemblage scapolite plagioclase garnet quartz may be used to calculate or limit aco2 by the reaction meionite quartz grossular anorthite co2 granulites from four high grade terranes grenville province canada sargut belt india furua complex tanzania bergen arcs norway yield aco2 0 4 1 with most 0 7 for scapolite bearing granulites from the furua complex in which aco2 0 9 calculated h2o activities ah2o based on phlogopite dehydration equilibria are uniformly low 0 1 0 2 the aco2 calculated for meta anorthosite from the grenville province ontario ranges from 0 2 to 0 8 for grenville meta anorthosite also containing epidote the ah2o calculated from clinozoisite dehydration ranges from 0 2 to 0 6 calc silicates from the grenville sargur and furua terranes mostly yield aco2 1 the calculated fluid activities are consistent with metamorphism 1 in the presence of a mixed co2 h2o fluid phase in which co2 is the dominant fluid species but other c o h s species are minor 2 in the absence of a bulk fluid phase fluid absent metamorphism or 3 in the presence of a fluid bearing melt phase the results for many granulites and grenville meta anorthosite are consistent with the presence of a co2 rich mixed co2 h2o fluid phase in contrast the relatively restricted and low values of aco2 for calc silicates require an h2o rich fluid or absence of a fluid phase during metamorphism the range of values for xenoliths are most consistent with absence of a fluid phase the primary implication of these results is that a co2 rich fluid accounts for the reduced ah2o in scapolite bearing granulites however scapolite may be stable with a wide range of fluid compositions or in the absence of a fluid phase and the presence of scapolite is not a priori evidence of a co2 rich fluid phase in addition close association of scapolite free mafic granulites with scapolite bearing granulites having identical mineral compositions in the furua complex and the absence of scapolite from most granulite terranes implies that a co2 rich fluid phase is not pervasive on an outcrop scale or common to all granulite terranes

remote detection of fumarolic gas chemistry at vulcano italy using an ft ir spectral radiometer abstract an infrared absorption spectroscopy remote sensing technique was used to determine the so 2 hcl ratio in fumarolic plumes at vulcano italy the measurements were made from the southern crater rim of fossa grande crater about 400 m from the fumarolic area in the crater infrared absorption spectra of hcl and so 2 were observed for four fumaroles a few tens of metres apart using the hot fumarolic surface as an infrared light source the measured so 2 hcl ratios in the fa f47 fw and lower parti of the f21 fumaroles were 4 5 5 4 3 5 9 5 11 2 and 5 8 respectively the so 2 hcl ratio of the fa fumarole was higher than that of the gas collected directly in the fumarolic vent so 2 hcl ratio 2 9 and was closer to the s total hcl ratio 4 6 of the collected gas our results show that the so 2 hcl ratios of two fumaroles only a few tens of metres apart exhibits differences of about twofold this suggests that this remote monitoring technique is capable of detecting spatial distribution in the so 2 hcl ratios of volcanic plumes because temporal variations in s cl ratios can provide precursory signals for volcanic eruptions 1 3 this remote sensing technique can used efficiently for evaluation of volcanic activity

co2 rich fluid inclusions in the whitestone anorthosite implications for the retrograde history of the parry sound shear zone grenville province canada the whitestone anorthosite wsa located in southern ontario underwent granulite facies metamorphism during the grenville orogeny at 1 16 ga during the waning stages of metamorphism fluids infiltrated the outer portions of the anorthosite and promoted the formation of an envelope comprised of upper amphibolite facies mineral assemblages also this envelope corresponds to portions of the anorthosite that underwent deformation related to movement along a high grade ductile shear zone samples from this portion of the anorthosite the margin contain co2 rich inclusions in plagioclase porphyroclasts relict igneous phenocrysts matrix plagioclase and garnet these inclusions have features which normally are interpreted as indicating that they are texturally primary but they have relatively low co2 densities 0 61 0 95 g cm 3 plagioclase from the anorthosite interior contains texturally secondary inclusions with relatively high co2 densities generally from 0 99 to 1 10 g cm 3 the high co2 densities suggest that the inclusions in the plagioclase of the anorthosite core formed prior to inclusions in porphyroclast minerals of the outer portions of the anorthosite an interpretation that is apparently inconsistent with inclusion textures this apparent paradox indicates that most fluid inclusions from the anorthosite margin were formed during or were modified by the dynamic recrystallization that affected this portion of the wsa in either case late formation or modification the texturally primary fluid inclusions do not contain pristine samples of the peak metamorphic fluid furthermore because shear related deformation is apparently associated with entrapment of the lowest fluid densities some strain localization persisted to relatively low temperatures e g less than approximately 500 c these results constrain a part of the retrograde p t path for this portion of the grenville orogen to temperatures of approximately 400 500 c at pressures of approximately 1 2 kbar

tectonic implications of paleomagnetic poles from lower tertiary volcanic rocks south central alaska we have determined the paleolatitude of lower tertiary volcanic rocks in southern alaska to measure possible poleward translation of the wrangellia and the peninsular terranes after 50 m y ago previous paleomagnetic studies have shown that in triassic and jurassic time these terranes were located near the equator and have moved at least 3000 km poleward relative to the north american craton our sample localities are in the northern talkeetna mountains in mildly deformed andesite and dacite flows 50 4 51 3 53 9 and 56 3 m y by k ar that overlap lower cretaceous flysch lower permian volcanic rocks of wrangellia and upper triassic pillow basalt of the susitna terrane results from 26 cooling units 23 of reversed polarity and 3 of normal polarity give a mean paleomagnetic pole at 69 5 n 179 6 e 95 12 2 stratigraphic sections from opposite limbs of a syncline yield directional paths that pass the fold test satisfying a necessary condition for primary origin of the magnetization the corresponding mean paleolatitude 76 n of the northern talkeetna mountains is 8 10 higher than the latitude predicted from the eocene reference pole for north america therefore northward drift of the talkeetna superterrane which is the amalgamation of the wrangellia and peninsular terranes during and after middle jurassic time was probably complete by 50 m y ago our results are consistent with paleomagnetic poles from uppermost cretaceous and paleocene volcanic sequences in denali national park the lake clark region northern bristol bay region and near mcgrath these poles generally lie south of the cratonic poles suggesting that the region between the kaltag bruin bay and castle mountain faults has rotated counterclockwise relative to north america since the early eocene

the sulfur and carbon isotope composition of scapolite rich granulites from southern tanzania sulfur and carbon isotope data are presented of 15 granulite samples from the furua complex southern tanzania in which scapolite is a primary and major rock forming constituent up to 30 vol from these data the isotopic composition is deduced of the sulfate and carbonate group in the scapolite structure subsequently the composition and origin is discussed of the volatile species that are present in the deep crustal environment in which these scapolites formed

co2transfer between the upper mantle and the atmosphere temporary storage in the lower continental crust the co2 atmospheric content has shown large variations over geological times high contents up to one order of magnitude more than present day values ultimately correspond to discrete episodes of mantle degassing either juvenile or subduction related carbon recycling a number of arguments e g the continuous volume increase of carbonate bearing sediments with time suggest that throughout the earth s history juvenile co2 has formed a major contribution to the global carbon budget of the earth the absence of a direct relationship between major volcanic episodes and the average co2 atmospheric content suggests that volcanoes might not be the only way by which mantle co2 is transported to the surface it is proposed that large quantities of juvenile co2 could temporarily be stored in the lower continental crust during major episodes of granulite formation these are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of co2 bearing mantle derived magmas most of the co2 migrates through the crust during post metamorphic evolution and isostatic restoration of the normal continental thickness however large quantities of co2 can still be present in some areas notably as high density fluids enclosed in minerals

carbonic fluid inclusions in granulites from tanzania a comparison of geobarometric methods based on fluid density and mineral chemistry abstract high density carbonic fluid inclusions with well developed negative crystal shape occur in host quartz plagioclase and garnet in intermediate to high pressure granulites from the furua granulite complex southern tanzania they are most abundant in intercalated metapelitic units detailed microthermometric data on inclusions in combination with electron microprobe analyses of associated solid phases are presented for a kyanite bearing garnet granulite and a garnet two pyroxene granulite both selected from the same locality the inclusions contain virtually pure co2 and are believed to be of primary syngenetic origin this is indicated by their distribution in the host minerals and by the homogenization temperatures which give well defined single maxima between 30 and 50 c the corresponding fluid pressures are only 1 3 kbar lower than the pressure range of 10 13 kbar that is inferred from the solid phase geobarometers based on element partitioning in garnet kyanite plagioclase and orthopyroxene clinopyroxene garnet plagioclase assemblages associated temperature estimates of 770 870 c are based on the compositions of garnet biotite garnet clinopyroxene and orthopyroxene clinopyroxene pairs although the co2 density data fit within the regional pressure regime of 7 12 kbar for the metamorphism in the furua area the detailed comparison with solid phase geobarometers at the scale of a single outcrop reveals a small underestimate of pressure which may be explained by minor adjustment of the inclusions after peak metamorphism or by partial h2o pressures in the order of 0 1ptot to 0 2ptot

high density early co2 fluids in the ultrahigh temperature granulites of ihouhaouene in ouzzal algeria abstract fluid inclusion studies in rocks from the lower proterozoic granulites from western hoggar algeria provide new evidence for the hypothesis that a co 2 rich h 2 o poor fluid was present during the high grade metamorphism co 2 inclusions represent the main fluid trapped in the ihouhaouene ultrahigh temperature over 1000 c and high pressure 10 to 14 kbar granulites the microthermometric and raman microspectrometric measurements indicate that the carbonic fluid is mainly composed of co 2 with minor amounts of ch 4 and n 2 detected in some inclusions 4 carbonic fluid densities range from 1 18 to 0 57 g cm 3 the highest densities are recorded in superdense carbonic inclusions presenting evidence of the earliest trapping and they correspond to the fluid densities expected for the p t conditions of the peak of metamorphism in the area previously determined from mineral geothermobarometers lower densities of carbonic fluids mainly result from the reequilibration of earlier trapped fluid inclusions during retrograde metamorphism and final uplift of the metamorphic terrane but a new influx of carbonic fluids during the retrograde event remains possible carbonic fluids can be produced in situ from decarbonation reactions in interlayered impure marbles during the prograde event or derived from co 2 flushing from underlying basic intrusions the aqueous fluids present large variations of composition 0 5 to 30 wt nacl equivalent and densities 1 16 to 0 57 g cm 3 they clearly correspond to post metamorphic fluids because they mainly occur along microfractures they do not show any evidence of immiscibility with the carbonic fluids and mixed aquo carbonic inclusions have not been observed the percolation of aqueous fluids is related to the pan african tectonometamorphic event

rotation of the colorado plateau an analysis of paleomagnetic data hamilton 1981 has proposed that the colorado plateau has rotated clockwise relative to cratonic north america by a total of 5 7 since mid cretaceous time a rotation this small is unresolvable by most paleomagnetic studies in this paper we present a new method for simultaneously comparing all of the available paleomagnetic data from on and off the plateau in order to estimate rotation of the colorado plateau our new method examines the effect of various hypothetical plateau rotations on the dispersion of data fit to a smooth model of apparent polar wander a maximum likelihood criterion is used to estimate the amount of rotation confidence limits are found using an f ratio test assuming the plateau craton euler pole to be located at 37 n 103 w we applied this method to north american paleomagnetic data of carboniferous to cretaceous age the best paleomagnetic estimate of the rotation is 3 9 clockwise with a 95 confidence interval of 1 4 6 6 clockwise in good agreement with geologic estimates of rotation because of the dependence of published north american apparent polar wander paths on data from the colorado plateau the existence of such a rotation requires a minor revision in the apparent polar wander path the largest change being a 3 9 eastward shift of the cusp connecting the carboniferous permian triassic and jurassic cretaceous tracks

texturally early fluid inclusions in garnets evidence of the prograde metamorphic path well formed texturally early fluid inclusions in garnets from the archean pikwitonei granulite domain manitoba canada have been analyzed using microthermometric methods the mean co2 homogenization temperature to liquid for inclusions in 12 of 13 samples from the cauchon lake nelson river area is 15 2 c n 125 2 8 2 c corresponding to a co2 density of 0 82 g cm3 inclusions in the remaining sample have somewhat lower co2 homogenization temperatures mean 5 4 c n 24 the studied inclusions contain an estimated 10 to 20 vol percent h2o with minor amounts of other fluid species such as ch4 n2 and or h2s the fluid inclusions were probably trapped during early garnet growth at relatively low pressures 5 kbar if at 750 c and appear to have undergone only limited or possibly no subsequent re equilibration this interpretation is consistent with the anti clock wise p t t path heating before loading determined for the pikwitonei region by other workers for such a prograde path inclusions entrapped early at high temperatures but at relatively low pressures would experience internal underpressures during most of the subsequent prograde and retrograde phases of metamorphism the texturally early fluid inclusions in garnets from the pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions 750 c and 7 kbar however the results obtained in this study suggest that texturally early fluid inclusions in garnets may in some cases retain evidence of the prograde metamorphic path

palaeomagnetism of lower cretaceous tuffs from yukon kuskokwim delta region western alaska during the past decade the prescient arguments1 3 for the allochthoneity of large portions of southern alaska have been corroborated by detailed geological and palaeomagnetic studies in south central alaska4 9 the alaska peninsula10 kodiak island11 12 and the prince william sound area13 fig 1 these investigations have demonstrated sizeable northward displacements for rocks of late palaeozoic mesozoic and early tertiary age in those regions with northward motion at times culminating in collision of the allochthonous terranes against the backstop of nuclear alaska14 15 a fundamental question is which parts of alaska underwent significantly less latitudinal translation relative to the stable north american continent thereby serving as the accretionary nucleus into which the displaced microplates 16 were eventually incorporated17 18 here we present new palaeomagnetic results from tuffs and associated volcaniclastic rocks of early cretaceous age from the yukon kuskokwin delta region in western alaska these rocks were probably overprinted during the cretaceous long normal polarity interval although a remagnetization event as recent as palaeocene cannot be ruled out this overprint direction is not appreciably discordant from the expected late cretaceous direction for cratonal north america the implied absence of appreciable northward displacement for this region is consistent with the general late mesozoic early tertiary tectonic pattern for alaska based on more definitive studies little to no poleward displacement for central alaska though substantially more northward drift for the southern alaska terranes comprising alaska peninsula kodiak island prince william sound area and matunuska valley since late cretaceous to palaeocene time

post metamorphic co2 rich fluid inclusions in granulites in granulite facies samples from the adirondack mountains ny estimates of peak metamorphic co2 fugacities based on mineral equilibria are not consistent with estimates based on data for high density co2 rich fluid inclusions of the 21 adirondack samples investigated for this study all contain co2 rich inclusions inclusions occur in quartz apatite and garnet they range in size from 3 to 50 m and are without visible h2o in a few of the inclusions freezing point determinations and preliminary laser raman spectroscopy show the presence of small amounts 3 of other fluids n2 and h2s co2 liquid vapor homogenization temperatures are between 46 and 31 c corresponding to densities between 1 14 and 0 5 gm cc some of these densities are consistent with peak metamorphic entrapment 1 06 to 1 1 gm cc

radioactive element distribution in the archean granulite terrane of jequie bahia brazil the radioactive element distribution in the archean granulite facies rocks of jequie brazil has been determined the k rb ratios show a large spread with majority of the values falling within the normal field k rb 300 the th u ratios fall into two groups one group with values in the range of 1 7 to 2 6 whereas the other group show th u values greater than 7 7 to 25 these distributions can be explained on the basis of the presence of accessory minerals apatite and zircon the relatively high concentrations of the radioactive and other elements in jequie granulites probably represents the relict primary geochemical character little modified during metamorphism the radiogenic heat production data for the area are calculated and using the measured regional heat flow value from nearby area an estimate of the relative thickness of the continental lithosphere is made using the model developed by oxburgh 1981

relative motions between eurasia and north america in the bering sea region knowledge of the relative motion of the north american and eurasian plates during the late mesozoic and cenozoic provides insight into the observed timing and style of deformational events in the bering sea region periods of strong convergence from 70 to 50 ma maastrichtian to paleocene are correlated with compressional deformation between the chukotsk peninsula and northern alaska and movement along the denali fault the convergence may also be the cause of a previously proposed counterclockwise rotation of western alaska transform motion between these plates from 50 to 38 ma middle to late eocene correlates with subsidence of the bering shelf creation of a series of pull apart basins along the bering margin and cessation of calc alkaline volcanism in western alaska slight compressive convergence from 37 ma to the present may be responsible for the anticlinal deformation of basin filling sediments in the anadyr and khatyrka basins

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

paleolatitudes versus time for southern alaska paleomagnetic determinations of the inclination of the ancient geomagnetic field for localities in the alaska peninsula wrangellia chugach and kuskokwim tectonostratigraphic terranes of alaska show systematic northward motion from late cretaceous time until the present prior to this the ambiguity of polarity of the ancient geomagnetic field allow several interpretations however the preferred interpretation involves southerly motion of the terranes from triassic to early jurrassic time and steady northward motion from then up to the present the latitudinal rate is about 6 cm yr

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

sulphide formation from granulite facies s rich scapolite breakdown scapolite in granulite facies terranes provides a reservoir for volatile components such as sulfur and carbon in rocks that are otherwise considered dry formed at lower crustal conditions the high s endmember of scapolite silvialite is a major host of sulfur in granulites compositional and textural changes involving scapolite reveal that s rich scapolite becomes unstable during hydration and deformation at amphibolite facies conditions either scapolite changes composition whereby so42 is exchanged for co32 or cl in its structure or scapolite is replaced by amphibole and or epidote sulfur that is released from silvialite is deposited as sulfides within the original silvialite grain boundaries and can remain relatively immobile in undeformed anorthosites however increased sulfide mobility is evident in areas of increased deformation and hydration reactions involving s bearing scapolite not only have important implications for sulfide deposition and the s cycle but may also influence conductivity variation in the lower crust this article is protected by copyright all rights reserved

early tertiary paleomagnetic evidence and the displacement of southern alaska paleomagnetic data from early paleocene lavas a few kilometers north of lake clark just inboard of the peninsular terrane indicate modest post early tertiary latitudinal displacement and about 55 sup 0 of counterclockwise rotation of this region with respect to north america a nearby middle eocene sequence of lava flows however gives no indication of displacement or rotation south of lake clark the paleomagnetism of five paleogene 30 to 40 ma volcanic sequences that are a part of the peninsular terrane proper shows no northward translation and no rotation a major part of the northward movement documented by other studies in the gulf of alaska region may be accounted for by cumulatively significant intraterrane displacements 32 references 3 figures 1 table

arrested charnockite formation in southern india and sri lanka arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high grade terrains of southern india and sri lanka two major kinds of orthopyroxene producing reactions are recognized breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic granitic gray gneiss produced the regional orthopyroxene isograd manifest in charnockitic mottling and veining of mixed facies exposures as at kabbal karnataka and in the kurunegala district of the sri lanka central highlands chemical and modal analyses of carefully chosen immediately adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of cao mgo and feo and gains of sio2 and na2o rb and y are depleted in the charnockite another kind of charnockitization is found in paragneisses throughout the southern high grade area and involves the reaction of biotite and quartz garnet to produce orthopyroxene and k feldspar although charnockite formation along shears and other deformation zones at such localities as ponmudi kerala is highly reminiscent of kabbal close pair analyses are not as suggestive of open system behavior this type of charnockite formation is found in granulite facies areas where no prograde amphibole bearing gneisses exist and connotes a higher grade reaction than that of the orthopyroxene isograd metamorphic conditions of both kabbaltype and ponmudi type localities were 700 800 c and 5 6 kbar lower p h2o in the ponmudi type metamorphism was probably the definitive factor

the relationship between metamorphic charnockite and marble near speculator central adirondack mountains new york granites and charaockites with similar bulk compositions are exposed in a series of roadcuts along rt 8 3 east of the central adirondack town of speculator the mineralogy of these rocks is correlated with their associated rock types with the orthopyroxene bearing varieties occurring in the marble rich portion of the sequence mineral assemblages in a charnockite boudin enclosed in marble appear to be consistent with equilibration with a co 2 rich fluid under high grade t 700 c p 7 kb conditions while high density co 2 rich fluid inclusions occur in a quartz vein enclosed within the boudin it is suggested that small amounts of charnockite may have been produced in this area by the influx of co 2 produced by devolatilization reactions in the marble however carbonic metamorphism in the adirondacks appears to have been at most a minor local process and did not operate on the regional scale that has been suggested for some other granulite terranes thus the presence of abund

nitrogen in fluids effecting retrogression of granulite facies gneisses a debatable mantle connection abstract the abundance patterns of nitrogen and chlorine in retrogressed granulite facies gneisses from southern east greenland exhibit strong enrichment in the vicinity of small scale shear zones sulfur in the shear zones occurs at the same concentration levels as in the adjacent country rock but is depleted in the transition zone between shear zone and country rock within the shear zone sulfur occurs as sulfate whereas in the country rock granulites it occurs as sulfide recrystallization of rock in the shear zone to scapolite bearing hornblende absent assemblages along with changes in the major element chemistry demonstrates that these zones define migration pathways of chemically reactive fluids consideration of the computed fluid compositions and of the mass ratios of chlorine sulfur and nitrogen sulfur demonstrate that the fluid equilibrated with continental crust prior to its passage through gneisses in the study area previous suggestions have been made that the mantle may act as a source region for nitrogen rich fluids however equilibration of these s n and cl rich fluids with crustal material precludes the use of element abundances to identify a mantle signature the bulk of these fluid constituents must be considered crustal derived

origin of granites in an archean high grade terrane southern india archean deep level granites in southern india are similar geochemically to young granites from continentalmargin arc systems they exhibit light ree enriched patterns with variable but chiefly positive eu anomalies this is in striking contrast to the negative eu anomalies typical in high level archean granites in addition the deep level granites are relatively enriched in ba and sr and depleted in total ree and high field strength elements hfse one pluton the sankari granite has unusually low contents of ree and hfse most of the deep level granites appear to represent cumulates with variable amounts of trapped liquid and of minor phases resulting from fractional crystallization of a granitic parent such parental granitic magmas can be produced by batch melting of archean tonalite at middle to lower crustal depths the sankari granite requires a tonalitic source depleted in ree and hfse archean tonalites and tonalitic charnockites exhibit original igneous geochemical signatures and their average composition does not show a significant eu anomaly hence they cannot represent the positive eu anomaly complement to the negative eu anomaly high level granites our results suggest that archean deep level granites may represent this complement such granite may form in waterrich zones in the middle or lower crust and be produced in response to dehydration of the lower crust by a rising co2 rich fluid phase

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

stratigraphy and sedimentology of the mid cretaceous deposits of the yukon koyukuk basin west central alaska the northeast trending yukon koyukuk basin of west central alaska consists of two subbasins the kobuk koyukuk subbasin to the north and east and the lower yukon subbasin to the southwest the subbasins are separated by an arcuate lower cretaceous volcanic pile the hogatza trend which is thought to be an accreted volcanic arc the oldest part of the sedimentary fill of the subbasins consists of valanginian to lower albian volcaniclastic rocks deposited on the flanks of the hogatza trend following subsidence of the hogatza trend mid cretaceous clastic sedimentary strata of mainly albian and cenomanian age and possibly as thick as 8000 m were shed into the basin these deposits were derived from surrounding uplands or borderlands in the seward peninsula to the west the brooks range to the north and the ruby geanticline to the southeast these mid cretaceous basin fill deposits can be divided into four main facies 1 basin margin conglomerate facies chiefly alluvial fan deposits that were transported basinward and rest in part unconformably on the surrounding uplands 2 shelf facies chiefly cross stratified and hummocky cross stratified sandstone deposited by wave generated currents on a shelf that rimmed the basin on its western and northern margins 3 deltaic facies chiefly sandstone and shale deposited in delta plain and delta front environments on a large constructional delta that prograded westward from the eastern basin margin across both subbasins and across the subsided southern part of the hogatza trend and 4 turbidite facies chiefly interbedded sandstone and shale deposited as elongate deep sea fans and related deep sea clastic systems by flows that transported sediment to the axial parts of both subbasins northeastward in the lower yukon subbasin and eastward to southward in the kobuk koyukuk subbasin sedimentation appears to have ended in the santonian followed by uplift folding and faulting of the basin fill less deformed lower tertiary nonmarine volcanic and volcaniclastic rocks unconformably overlie the more highly deformed cretaceous strata

carbonic metamorphism at ultrahigh temperatures evidence from north china craton abstract the north china craton ncc constitutes one of the fundamental precambrian nuclei of asia the paleoproterozoic khondalite belt along the northern margin of the ncc shows evidence for extreme crustal metamorphism at temperatures exceeding 1000 c and pressures of 10 12 kbar with the formation of diagnostic ultrahigh temperature uht mineral assemblages including sapphirine quartz high alumina orthopyroxene sillimanite and high temperature mesoperthites here we record for the first time the common occurrence of co2 rich fluid inclusions in peak uht minerals in the mg al granulites of ncc and trace the fluid evolution history from microthermometric and laser raman spectroscopic studies we show that the syn metamorphic fluid in the uht rocks was pure co2 while very high density carbonic fluids are preserved in some cases corresponding to entrapment at peak conditions many of the inclusions underwent density modification during the rapid and near isothermal exhumation of the rocks following peak uht metamorphism and initial cooling at depth the present study area within the northern margin of the ncc defines a collisional orogenic belt where continental collision and deep subduction were possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusions of paleoproterozoic age that are seen emplaced within the granulite facies supracrustals the thermal anomaly displayed by the uht granulites may thus correlate with asthenospheric upwelling and emplacement of mafic magmas possibly associated with plume activity which provided the heat and co2 input to achieve extreme crustal metamorphism and generation of dry granulite facies assemblages our study is the first report of syn metamorphic co2 rich fluids in uht granulites from a paleoproterozoic ca 1 92 ga terrane and provide evidence for carbonic metamorphism at ultrahigh temperatures as north china craton joined the columbia supercontinent amalgam

petrology and fluid inclusions in garnetiferous gneisses and charnockites from weddagala ratnapura district sri lanka fluid inclusions have been studied in garnetiferous gneisses and igneous charnockites from weddagala sri lanka fluid distribution brines in metasediments co 2 in charnockites compares well with other regions notably bamble southern norway for the brines it suggests an ultimate pre metamorphic origin and for co 2 initial entrapment during metamorphic crystallization the fluid density has been completely reset during post metamorphic evolution maximum co 2 densities indicate much lower pressure than those at peak metamorphic conditions recorded by the solid assemblages about 5 vs 8 kbars the evolution of co 2 densities with time suggests a post metamorphic trajectory concave toward the pressure axis adiabatic uplift and local redistribution and reequilibration of co 2 inclusions between 500 and 600 c fluid movements were mostly limited to grain scale millimeter order of magnitude and did not transgress the lithological boundaries