co2 diffuse emission from maar lake an example in changbai volcanic field ne china abstract numerous maars and monogenetic volcanic cones are distributed in northeast china which are related to westward deep subduction of the pacific ocean lithosphere comprising a significant part of the pacific ring of fire it is well known that diffuse co2 emissions from monogenetic volcanoes including wet e g maar lake and dry degassing systems e g soil diffuse emission fault degassing etc may contribute to budget of globally nature derived greenhouse gases however their relationship between wet e g maar lake and concomitant dry degassing systems e g soil diffuse emission fault degassing etc related to monogenetic volcanic field is poorly understood yuanchi maar one of the typical monogenetic volcanic systems is located on the eastern flank of tianchi caldera in changbai volcanic field of northeast china which displays all of three forms of co2 degassing including the maar lake soil micro seepage and fault degassing measurements of efflux of co2 diffusion from the yuanchi maar system yms indicate that the average values of co2 emissions from soil micro seepage fault degassing and water air interface diffusion are 24 3 23 3 g m 2 d 1 39 2 22 4 g m 2 d 1 and 2 4 1 1 g m 2 d 1 respectively the minimum output of co2 diffuse emission from the yms to the atmosphere is about 176 1 88 3 ton yr of which 80 4 results from the dry degassing system degassing from the fault contributes to the most of co2 emissions in all of the three forms of degassing in the yms contributions of mantle crust air and organic co2 to the soil gas are 0 01 0 10 10 20 32 36 and 48 54 respectively which are quantitatively constrained by a he c isotope coupling calculation model we propose that co2 exsolves from the upper mantle melting beneath the tianchi caldera which migrates to the crustal magma chamber and further transports to the surface of yms along the deep fault system during the transportation processes the emission of gas experiences crustal contamination influence of magma chamber beneath the yms sub surface processes and air dilution

short paper the age and origin of boulders in the highland border complex constraints on terrane movements mid proterozoic rb sr muscovite ages on metasedimentary boulders within the highland border complex together with archean t dm ages on the same clasts provide constraints on terrane movements in the scottish caledonides an origin for these clasts from cratonic north america is ruled out combined radiometric age t dm and fauna1 province studies on basement materials provide a potentially productive method of determining the provenance of terranes

significance of the early fabric in the contact metamorphic aureole of the 590 ma ben vuirich granite perthshire scotland an early fabric is preserved in pseudomorphs of contact metamorphic cordierite and andalusite found in hornfelsed dalradian rocks at the nw margin of the ben vuirich granite as previous work had suggested that this fabric may be of regional tectonic d1 origin and taken as evidence that a pre 590 ma neoproterozoic orogenic event had affected the dalradian supergroup the textures found in the hornfelses and their porphryoblasts are illustrated and described in detail three types of hornfels are recorded unspotted cordierite and andalusite bearing cordierite was altered to mica garnet and kyanite and andalusite pseudomorphed by kyanite during the subsequent d2 regional metamorphism the early fabric is finely spaced and associated with a weak shape fabric except in the higher grade hornfelses where it is more intensely developed and formed during the deformation of irregularly shaped cross cutting granitic veinlets it is concluded that the hornfels fabric is probably bedding modified by intrusion related deformation rather than a d1 fabric parallel to bedding the implication of this finding is that intrusion of the ben vuirich granite occurred during the vendian c 650 ma rifting phase at about the time that the tayvallich lavas were being deposited and before any significant deformation of the dalradian rocks had taken place there is no unambiguous evidence to show that the early fabric in the hornfels at ben vuirich formed during a precambrian regional scale deformation of the dalradian block

testing for the presence of a terrane boundary within neoproterozoic dalradian to cambrian siliceous turbidites at callander perthshire scotland the southern highland group dalradian and keltie water grit formation which includes the lower cambrian leny limestone form an inverted 1 4 km thick largely arenaceous sequence at callander the grits have the same detrital mineralogy throughout mainly quartz plagioclase an 1 3 muscovite and biotite chlorite formed from detrital biotite during low grade regional metamorphism t 40 ar 39 ar laser fusion dating of detrital muscovites yields an age spectrum with a peak at 1600 1800 ma in the dalradian rocks similar old ages occur in the keltie water grits but are diluted by ages of 507 886 ma we interpret these new data as showing that the rocks were most likely deposited as a single sequence possibly with a disconformity in neoproterozoic to early cambrian times before the onset of grampian orogenesis in the early palaeozoic no major structural or stratigraphical breaks have been identified and there is no direct evidence for the presence of two separate terranes

review of eruptive activity at tianchi volcano changbaishan northeast china implications for possible future eruptions one of the largest explosive eruptions in the past several thousand years occurred at tianchi volcano also known as changbaishan on the china north korea border this historically active polygenetic central volcano consists of three parts a lower basaltic shield an upper trachytic composite cone and young comendite ash flows the millennium eruption occurred between 938 and 946 ad and was preceded by two smaller and chemically different rhyolitic pumice deposits there has been at least one additional small eruption in the last three centuries from 2002 to 2005 seismicity deformation and the helium and hydrogen gas contents of spring waters all increased markedly causing regional concern we attribute this event to magma recharge or volatile exhalation or both at depth followed by two episodes of addition of magmatic fluids into the overlying aquifer without a phreatic eruption the estimated present magma accumulation rate is too low by itself to account for the 2002 2005 unrest the most serious volcanic hazards are ash eruption and flows and lahars the available geological information and volcano monitoring data provide a baseline for comprehensive assessment of future episodes of unrest and possible eruptive activity

geochemically unravelling the sedimentary components of archaean metasediments from western australia major and trace elements of metasediments of the granulite facies narryer and the amphibolite facies jack hills metasediments have been used to devise plots which enable the original sedimentary components of these rocks to be unravelled despite their metamorphic state these plots overcome the predominant effect of quartz which ranges up to 100 and can be used to study other metasediment suites six components controlled the composition of the clastic metasediments 1 kaolinite 2 illite muscovite 3 chlorite montmorillonite 4 dolomite 5 quartz 6 resistant heavy minerals such as rutile zircon chromite and monazite identifying the first four of these components enables the trace element composition associated with the components to be estimated feldspar was largely destroyed by chemical weathering but there is a suggestion that traces of it formed a minor seventh component in the narryer rocks there was little or no mixing of the original kaolinite bearing and illite muscovite bearing samples indicating two distinct sources although both sets of samples contain 4 ga zircons suggesting a third zircon source the old zircons may have been derived from re worked sediment or metasediment as they occur in the matrix and in the quartzite clasts of conglomerates using bhatia9s criteria a passive margin is the likely site of deposition calc alkaline tholeiites in the narryer succession are intrusive and did not contribute to the sediments which were derived from extremely heavily weathered granites komatiites schists and reworked sandstones or quartzites

new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

mechanism of backarc opening in the japan sea role of asthenospheric injection abstract the process of backarc extension in the japan sea includes two modes of spreading the parallel and rotational or fan shape opening data from paleomagnetism for rocks on the northeast japan arc radiometric age determination for dredged volcanic rocks and heat flow in the basin have suggested that the parallel opening of the japan sea took place earlier than the rotational opening at 21 14 ma the mechanism of opening of the japan sea has been examined based on the secular change in the geometry of the subducted slab and in the volcanic activity on the northeast japan arc mechanisms of backarc rifting including mantle diapirism mantle flow induced by the slab subduction or interaction of the over and the underriding plates cannot reasonably explain the process of opening of the japan sea the most plausible mechanism operating in the spreading process of the japan sea is injection of the asthenosphere into the mantle wedge that forcefully pushed the subducted slab to cause both steepening of the slab and the backarc extension the asthenospheric current towards the northeast japan arc trench system may have been associated with the large scale upwelling of the asthenosphere beneath the northeastern china region that caused intra plate volcanism and produced continental rift systems in the region the present mechanism can also explain the active backarc rifting in the okinawa trough in the western pacific and the taupo depression in north island new zealand

geothermal he and co2 variations at changbaishan intra plate volcano ne china and the nature of the sub continental lithospheric mantle 1 we report new he and co2 data for geothermal fluids from changbaishan volcano located on the border of china and north korea helium isotope ratios reach a maximum of 5 4 ra where ra 3he 4he in air whereas carbon isotope values 13c fall between 2 and 7 vs pdb the ratio of co2 3he varies between 0 5 7 1 109 for gas samples but is considerably higher 1012 in waters the combined he co2 systematics reveal the clear imprint of a dominant subducted slab contribution to the total co2 inventory we conclude that these geothermal volatiles originate from the sub continental lithospheric mantle sclm in ne china and represent ancient fluids captured by prior metasomatic events

interaction of katabatic winds and near surface temperatures in the antarctic 1 a two dimensional mesoscale model was applied to simulate wintertime katabatic winds in the antarctic coastal region simulations were made for a constant slope angle with the slope height varying and for fixed slope heights with the slope angle varying thermal wind opposed the katabatic flow near the foot of the slope but enhanced it over the high plateau the steeper and higher the slope the stronger the effect on the plateau the 2 m potential temperature decreased down the slope toward sea ice because 1 the katabatic wind resulted in the accumulation of cold near surface air over the sea ice and the lower parts of the slope 2 over the flat sea ice zone the stratification was stronger and 3 the shallow slope was within the strong surface inversion from over the sea ice with a slope aspect ratio of 5 m km 1 and a slope height below 1000 m 2 m temperature t2m decreased down the slope but for slope heights of 1500 m and more t2m increased down the slope adiabatic warming and because of the stronger wind enhanced turbulent mixing of the warmer air from aloft contributed to the warming for slope angles ranging from 1 to 20 m km 1 with a small slope height of 500 m t2m decreased down the slope but not monotonically whereas with a slope height of 2000 m yielding stronger winds and larger adiabatic warming t2m increased monotonically down the slope the model results were supported by observations from several antarctic sites with different topographic conditions

helium and carbon isotope variations in liaodong peninsula ne china chemical and c he isotopic compositions have been measured for n2 rich hydrothermal gases from the liaodong abbreviation of east liaoning province peninsula from which the oldest crustal rocks in china with 3 8 ga outcrop with the exception of one sample containing tritogenic 3he and atmospheric 4he in liaoyang the observed 3he 4he ratios from 0 1 ra to 0 7 ra indicate 1 8 helium from mantle 92 98 from crust and 0 1 0 8 from atmosphere despite the lack of quaternary volcanism such 3he 4he ratios suggest together with geophysical evidences the existence of intrusive magmas that contain mantle helium and heat within the liaodong middle lower crust the 3he 4he ratios are high along the ne trending jinzhou faults and gradually decrease with the increase of distance from the faults such a spatial distribution suggests that the mantle helium exsolves from magmatic reservoir in the middle lower crust becomes focused into the root zones of jinzhou faults and subsequently traverses the crust via permeable fault zones when transversely migrated by groundwater circulation in near surface mantle helium with high 3he 4he ratio may have been further diluted to the observed values by addition of radiogenic helium produced in the crust this pattern shows strong evidence that the major faults played an important role on mantle derived components transport from mantle upwards

helium and carbon isotopes in the hot springs of changbaishan volcano northeastern china a material connection between changbaishan volcano and the west pacific plate abstract changbaishan volcano is located in northeastern china approximately 1400 km west of the west pacific subduction zone although the west pacific plate and changbaishan volcano are spatially associated with each other no previous evidence has demonstrated the existence of a direct material connection between the two in this study we utilize helium 3he 4he co2 3he and carbon isotopes 13c from the hot springs of changbaishan volcano to exclude the possibility of a direct material connection between the volcano and the west pacific plate at source a total of 22 gas samples were collected from three hot springs at changbaishan volcano in 2002 2006 2014 and 2015 isotopic and geochemical analyses were performed on these samples to trace the possible sources of these gases our analysis reveals that values for air corrected 3he 4he ratios range from 3 98 ra to 6 03 ra where ra represents the atmospheric 3he 4he ratio co2 3he ratios vary from 2 20 108 to 1 92 1011 and 13c values vary from 7 9 to 1 6 by comparing these measured values to those of typical mantle and crustal sources we can infer that hot spring gases from changbaishan volcano are mostly characterized by inputs from two isotopically distinct sources deep mantle fluids and shallower slab derived fluids fluids liberated from the shallower magma chamber are likely to include ancient izanagi subduction zone fluids whereas fluids originating from deeper magma chamber likely consist of morb like asthenospheric mantle fluids based on these results we suggest that helium and carbon isotopes in hot springs demonstrate the absence of a direct material connection between changbaishan volcano and the west pacific plate

short paper the depositional age of the dalradian supergroup u pb and sm nd isotopic studies of the tayvallich volcanics scotland zircons from a keratophyre associated with the tayvallich volcanics in the dalradian rocks of the sw scottish highlands have been dated by u pb methods yielding an age of 595 4 ma this age indicates that most or all of the dalradian is precambrian in age and that dalradian sedimentation may have lasted for about 200 million years the age also constrains the time interval between cessation of dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the grampian orogeny sm nd isotopic data for the tayvallich volcanins and related metadolerite sills yield initial ond values of 2 to 4 which are thought to reffect the effects of melting of lithospheric mantle

application of geochemistry to the stratigraphic correlation of appin and argyll group carbonate rocks from the dalradian of northeast scotland 240 samples from appin and argyll group carbonate rock units of the dalradian of northeast scotland have been analysed for 10 major oxides and 14 to 19 trace elements in order to classify and correlate them using geochemistry the carbonate rocks are chiefly limestones with some dolostones rocks with 0 38 mgo cao 0 03 are classed as dolomitic limestones those with mgo cao 0 38 are classed as dolostones the data have approximately lognormal distributions at a high level of significance except for cao mgo and sr cao and sr have negatively skewed distributions median values for groups of sample analyses plotted on normalized multi element variation diagrams and a nonlinear mapping nlm algorithm have been used to classify groups of samples in the appin group multi element diagram patterns are distinctive for each unit allowing correlations to be made though distinctive compositions do occur locally in argyll group carbonate rocks correlation on a regional scale is not possible the plot of nlm coordinates for suites of samples is consistent with the results from the spider diagrams suites of appin group samples cluster closely whereas there is wide spread in samples from the argyll group in several areas most notably at sandend bay the data have allowed reinterpretation of the stratigraphy the data are consistent with other geological data in suggesting that crustal conditions were relatively stable during the deposition of the appin group but not during the deposition of the argyll group

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

evidence for subduction related components in the subcontinental mantle from low 3he 4he and 40ar 36ar ratio in mantle xenoliths from far eastern russia abstract by applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases we have discovered 3he 4he ratios much lower than the atmospheric ratio 0 3 ra ra is the atmospheric 3he 4he ratio of 1 4 10 6 and relatively low 40ar 36ar ratios spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths liquid co2 inclusions and melt inclusions with shrinkage bubbles based on the crushing experiments it is inferred that the inclusions of liquid co2 have a 3he 4he ratio similar to that of morb and the component with the low 3he 4he ratio is derived from the shrinkage bubbles in the melt inclusions for the present samples the 40ar 36ar ratios obtained by crushing were less than 1000 suggesting incorporation of atmospheric components in the source materials since low 40ar 36ar ratios were observed irrespective of the occurrence of the liquid co2 inclusions the atmospheric component exists in the melt inclusions ne and xe isotopes are also consistent with incorporation of atmospheric components since the far eastern russia area was located at a subduction zone in the jurassic early cretaceous period it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low 3he 4he ratios have been derived from the jurassic cretaceous subducted slab although we cannot exclude the possibility that low 3he 4he ratios are due to the existence of minor u bearing minerals in the lithospheric continental mantle caused by metasomatism we have no petrographical evidence for such minerals in this area on the other hand 3he 4he ratios observed in the liquid co2 inclusions which are similar to the morb like value might reflect the general character of the upper mantle the far eastern russian mantle may therefore be a morb like source that has been partly infiltrated by subduction related fluids

source of the lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the delamerian ross fold belt during the cambrian ordovician the paleo pacific margin of gondwana underwent a rapid transition from a site of convergent deformation delamerian ross orogeny to one of sedimentation during which the thick turbiditic sequences of the adjacent basal lachlan fold belt were deposited laser probe 40 ar 39 ar data show that the synkinematic 523 486 ma mid crustal i and s type granites and metamorphic country rocks of the delamerian fold belt were rapidly cooled at 490 485 ma coincident with the intrusion of a suite of high level postkinematic a type granites and gabbros ca 497 481 ma 40 ar 39 ar data on detrital muscovites from the basal sections of the lachlan fold belt provide information on exhumation rather than cooling but yield an age pattern 507 480 ma identical to that of the delamerian fold belt demonstrating that this was the source of the sediments the combined data require that some 15 km of exhumation occurred very rapidly 5 15 mm yr 1 coincident as implied by overlapping ages with the cessation of convergent deformation and partial melting to form the postkinematic magmas this scenario implies a causative link which we infer to have been convective removal of lithospheric mantle following orogenic thickening the model is analogous to the tertiary uplift of the india asia orogen which provided the sediment source for the bengal fan our results suggest that similar processes were important in the evolution of mountain belts at least as far back as the early phanerozoic

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

metamorphism and cooling of the ne dalradian the buchan area of dalradian rocks represents a distinct tectonothermal domain within the scottish highlands and the portsoy duchray hill lineament on the western margin of this block is one of the best examples of a long lived domain boundary rb sr mica cooling ages from metamorphic rocks from across the trace of this lineament document a prolonged ordovician cooling history delayed but then relatively rapid cooling to the west of the portsoy duchray hill lineament is recognized whereas to the east the age data point to a high heat flow regime lasting more than 50 ma the isotopic ages suggest that c 460 ma was a time of active tectonism resulting in final cooling of the low grade rocks and differential uplift and rapid cooling of deeper structural levels to the west the radiometric ages do not support previous tectonic models for the region that have invoked thrust thickening along the line of the portsoy duchray hill lineament and a new model for the metamorphism is proposed the overprinting of andalusite bearing assemblages by kyanite to the west of the portsoy duchray hill lineament is linked to pressure increases associated with the intrusion of the newer gabbros and represents a magmatic loading related to the same tectonothermal event that generated the low pressure metamorphism rather than a separate tectonic episode

new uppermost cambrian u pb date from avalonian wales and age of the cambrian ordovician boundary a crystal rich volcaniclastic sandstone in the lower peltura scarabaeoideszone at ogof ddu near criccieth north wales yields a u pb zircon age of 491 1 ma this late late cambrian date indicates a remarkably young age for the cambrian ordovician boundary whose age must be less than 491 ma hence the revised duration of the post placentian trilobite bearing cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by ordovician graptolites and mesozoic ammonites

a pre d2 age for the 590 ma ben vuirich granite in the dalradian of scotland regional mapping demonstrates that s2 is the main fabric in the central highland dalradian and that it is this fabric not s3 as previously thought which overprints the 590 ma ben vuirich granite the granite appears to have been emplaced following a tectonic event d1 in the dalradian rocks for a finely spaced penetrative fabric seen in newly discovered hornfelses from the granite aureole is overgrown by contact metamorphic cordierite and andalusite porphyroblasts now both altered which predate the d2 metamorphism the ben vuirich granite cuts the neoproterozoic dalradian sequence of the central highlands of scotland fig 1 inset and was first recognized as an older foliated granite by barrow et al 1905 later workers bradbury et al 1976 bradbury 1978 concluded that the granite was intruded between d2 and d3 in the dalradian rocks harris et al 1976 and for many years an u pb zircon age of 514 7 ma from the intrusion pankhurst pidgeon 1976 provided a valuable datum point in the evolution of the scottish caledonides however dalradian chronology has recently undergone a radical revision following the determination of a precise u pb age of 590 2 ma for the emplacement of the ben vuirich granite rogers et al 1989 in accepting the interpretation of bradbury et al 1976 that the regional penetrative fabric which affects the country rocks and is continuous with that in the granite is of d3 age rogers et al were also guided by the conclusions of harte et al 1984 and dempster harte

age of the grampian event a discussion of new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

uplift patterns and orogenic evolution in the scottish dalradian rb sr and k ar mineral ages from the dalradian rocks of angus and perthshire indicate considerable diachronism of cooling following the caledonian regional metamorphism the oldest mineral ages 515 ma are similar to the independent estimates of peak metamorphic age and hence indicate very rapid cooling they occur in the highest grade samples of the angus region and are associated with localized uplift regional rapid uplift events at 460 440 ma and 410 390 ma may also be recognized and correlated with structural and igneous activity and metamorphic age dates within the scottish highlands thermal models show the importance of localized and discontinuous uplift in determining both the timing of metamorphism and the shape of the p t paths they suggest that the major diachronous metamorphism and granite production in the scottish highlands is depth controlled rather than representing major lateral diachronism of thickening or heat sources localized uplift may exercise considerable control on mineral facies variation within orogenic belts the local uplift in angus introduces hot high pressure tarfside nappe rocks into higher level tay nappe rocks thus the uniform block uplift models frequently used in the interpretation of metamorphic and structural phenomena in orogenic belts are an oversimplification of the real events

discussion on metamorphism and cooling of the ne dalradian and u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland authors reply

helium isotopes in peridotite mineral phases from hyblean plateau xenoliths south eastern sicily italy abstract fourteen he isotope and abundance analyses have been performed on olivine orthopyroxene and clinopyroxene grains from selected spinel facies peridotite xenoliths collected from the hyblean plateau southeastern sicily these peridotites consist of protogranular textured spinel facies lherzolites and lherzolitic harzburgites microthermometric data on olivine and pyroxenes reveal that the fluid inclusions fis are nearly pure co 2 with densities ranging from 0 76 to 1 15 g cm 3 the densest inclusion trail occurs in an orthopyroxene grain and indicates a trapping pressure of 0 98 1 14 gpa estimated equilibration temperature of 1000 c for pure co 2 system corresponding to a depth of 36 41 km for an average estimated density of the lithospheric column of 2 85 g cm 3 these are minimum estimates the near unimodal distribution of co 2 densities indicates that these xenoliths have been stored at the pressure interval of 0 75 0 95 gpa corresponding to a depth of 27 35 km crust mantle boundary or just below en route to the surface they have not had any significant interaction with shallower volatile reservoirs he trapped in co 2 rich fluid inclusions ranges in abundance from 1 8 to 86 6 10 9 cm 3 stp g with clinopyroxenes usually showing higher he contents than coexisting olivines and orthopyroxenes the inter mineral differences are due to physical properties of minerals in contrast he isotope ratios cover a narrow range 7 3 0 3 r a where r a air 3 he 4 he indicating isotopic equilibration between the mineral phases he composition indicates a morb type source for the metasomatic agent s influenced by relatively minor radiogenic production in the source therefore in closed system conditions the calculated helium residence time is 790 myr geophysical and geochemical studies suggest the existence of a common fluid reservoir in the mantle beneath the central mediterranean area the most pristine he signature for the mantle endmember is found on pantelleria island sicily channel this he ratio is similar to that found in hyblean peridotite minerals testifying to a common source history we conclude therefore that hyblean xenoliths can be used as a powerful tool in defining the geochemical features of this portion of the upper mantle

timescale and evolution of the intracontinental tianchi volcanic shield and ignimbrite forming eruption changbaishan northeast china abstract around the tianchi eruption cone the junjianshan formation which builds the tianchi basalt shield can be divided into three units they are from bottom to top the toudao baishan and laofangzixiaoshan units respectively individual basaltic flows of the tianchi shield vary significantly in volume and in spatial distribution from a few to dozens of kilometers in length hundreds to thousands of meters in width and a few to dozens of meters in thickness k ar age data indicate that the tianchi shield was formed within a very short time period between 2 77 0 08 and 0 31 0 002 ma our detailed mapping in combination with the k ar dating shows that the toudao unit erupted at 2 77 1 99 ma the baishan unit at 1 64 1 11 ma and the laofangzixiaoshan at 0 31 0 58 ma the huge millennium eruption from the tianchi volcano sustained a 35 km high column h t and lasted a few days producing the comenditic ignimbrite around the volcano wiggle matching measurements of a sample series of charcoal wood indicate the millennium eruption might have happened around 1024 ad features of eruptions stemming from the same source surrounding the tianchi volcano plus the volcanic evolution from effusive flows to explosive eruption are interpreted to reflect crustal thickening within this intracontinental tectonic environment field observations and lava compositional variations suggest that crystal fractionation and magma mixing or mingling process must have played an important role in the development and evolution of the tianchi volcano

hydrothermal he and co2 at wudalianchi intra plate volcano ne china 3 he abstract chemical and isotopic compositions have been measured for co2 rich bubbling gases discharging from cold springs in wudalianchi intra plate volcanic area ne china observed 3 he 4 he ratios 2 3 ra and d 13 c values of co2 5 to 3 indicate the occurrence of a mantle component released and trans ferred to the surface by the cenozoic extension related magmatic activities the co2 3 he ratios are in wide range of 0 4 97 10 9 based on the apparent mixing trend in a

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less

p wave tomography and origin of the changbai intraplate volcano in northeast asia abstract we present the first seismic image of the upper mantle beneath the active intraplate changbai volcano in northeast asia determined by teleseismic travel time tomography the data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations our results show a columnar low velocity anomaly extending to 400 km depth with a p wave velocity reduction of up to 3 high velocity anomalies are visible in the mantle transition zone and deep focus earthquakes occur at depths of 500 600 km under the region suggesting that the subducting pacific slab is stagnant in the transition zone as imaged clearly by global tomography these results suggest that the intraplate changbai volcano is not a hotspot like hawaii but a kind of back arc volcano related to the deep subduction and stagnancy of the pacific slab under northeast asia

formation of corrensite chlorite and chlorite mica stacks by replacement of detrital biotite in low grade pelitic rocks transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks illite crystallinity index 0 19 0 58 a28 from the gasp6 peninsula in quebec detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms 1 layer by layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite corrensite or smectite 2 dissolution transport precipitation resulted in the formation of relatively coarse grained aggregates of randomly orientated corrensite rich flakes and fine grained corrensite intergrown with chlorite and illite in the matrix the data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays subsequent prograde evolution of dioctahedral clays occurred through deformation dissolution and crystallization and overgrowth illite evolved to muscovite with k in part provided through biotite alteration and corrensite chlorite to homogeneous chlorite the alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks and pyrite calcite and anatase or rutile in the higher grade rocks the observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite rich metapelites originating in marginal basins the mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time