forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

late archean mantle composition and crustal growth in the western superior province of canada neodymium and lead isotopic evidence from the wawa quetico and wabigoon subprovinces abstract neodymium and lead isotopes are presented for late archean rocks from the wawa quetico and wabigoon subprovinces sp in the western superior province ontario canada the isotopic compositions were determined on greenstone volcanic sequences pre tectonic 2 73 2 69 ga trondhjemite tonalite granodiorite ttg suites metasedimentary rocks and post tectonic 2 69 2 67 ga dioritic to granitic plutons in order to characterize the mantle and crustal reservoirs involved in the evolution of the southern part of the western superior province although derived from a depleted mantle almost all the greenstone volcanism and pre tectonic ttg suites record contamination by crustal material as old as 3 2 ga neodymium and lead isotopic compositions of the pre tectonic ttg can be modeled as products of the melting of amphibolitic crust e g subducted basalts contaminated by 1 10 of subducted sediments moreover lead isotopes of ttg suites provide evidence that the isotopic compositions of these subducted sediments varied as a result of the addition of new ca 2 7 ga juvenile material in agreement with neodymium isotopic differences recorded by sedimentary units of the quetico sp 50 50 mix of young old crusts and wawa sp 75 25 young old neodymium and lead isotopes of the post tectonic ree enriched archean sanukitoid suites define an isotopic trend which is distinct from that of the ttg suites and which is interpreted to reflect the importance of crustal assimilation in the evolution of these suites furthemore such plutons found in the wawa sp have more juvenile neodymium and lead isotopic compositions and higher nd contents than those intruded into the quetico and wabigoon sp which have more crustal isotopic signatures and lower nd concentrations this geographical difference could be due either to differences in nd contents of initial archean sanukitoid magmas lesser assimilation in the wawa sp or more probably because the wawa crust is on average more juvenile than the quetico and wabigoon crusts in agreement with the fact that the geographical difference mirrors that recorded by metasedimentary rocks deposited in quetico and wawa sp

spatial variation in solutional denudation and soil moisture over a hillslope hollow a spatial pattern of relative solutional denudation is described for a hillslope hollow and adjacent spurs at bicknoller combe somerset the pattern was obtained from a network of micro weight loss rock tablets emplaced in the soil the results show that the hollow is the main locus of solutional denudation the soil moisture distribution over the hollow indicates that it is a transmission zone for acid soil water percolating from the adjacent spurs to the saturated wedge at the base of the hollow the wetter acid soils in the hollow are responsible for the relatively higher solutional denudation taking place in the hollow

petrogenetic constraints for the genesis of archaean sanukitoid suites geochemistry and isotopic evidence from karelia baltic shield new sm nd isotope data are presented for late archaean sanukitoid suites of the karelian granite greenstone terrane of the baltic shield within the terrane there are regional variations in the nd isotope compositions of the sanukitoids sanukitoids in the youngest central karelian domain have nd isotope characteristics similar to depleted mantle whereas those from the older west karelian and vodlozero domains have lower initial end values the isotopic heterogeneity of the sanukitoids is interpreted to result from variations in the time interval between mantle source enrichment and the partial melting that produced the sanukitoid magmas we therefore suggest a two stage model of the generation of sanukitoid magmas during first stage the mantle was metasomatised by fluids and or melts generated during subduction or tectonic underplating later between 2 74 and 2 70 ga a tectonothermal anomaly generated the sanukitoid magmas by melting of the previously metasomatised mantle most of the sanukitoid intrusions are cut by calc alkaline lamprophyre dykes that have the similar geochemical signatures to their sanukitoid wall rocks new sm nd isotope data for these lamprophyres suggest a genetic kinship between the sanukitoids and the lamprophyres comparison between chemical signatures of sanukitoids and modern subduction related magmas shows that archaean sanukitoids actually have no modern analogues sanukitoid melts can be modelled as partial melts of mantle that had been metasomatised a short time previously the melts could have been in equilibrium with residues containing ol cpx plus minor phl and grt at a pressure of about 2 5 gpa and a temperature of 1150 1230 8c the small percentage of residual phlogopite would retain rb in the mantle and explain the peculiar signature of low rb and high ba and sr characteristic of the sanukitoids we envisage a temporal evolution of the composition of the mantle in this region this pattern of evolution controlled production of the sanukitoid melts and explains why the sanukitoids have such a restricted range of ages sanukitoid magma production must have followed from a major global mantle enrichment event these magmas could not have been produced earlier because the archaean mantle had not become sufficiently enriched before 2 7 ga we suggest that their scarcity after the major period of sanukitoid magmatism may be due to the increased thickness of overlying crust which can inhibit mantle enrichment

the use of rock hard sodium sulphate tablets for quickly determining preferential water flow routes in soils subsurface water flow routes have been inferred from gypsum sphere weight loss with minimal disturbance to soil structure or flow nets crabtree and trudgill 1984 this technique is limited by the relatively slow fixed dissolution of gypsum a solution is to use tablets consisting of durham s rock hard water putty and sodium sulphate laboratory tests indicate that tablet dissolution is controlled by the ratio of rock hard to sodium sulphate and is proportional to net throughflow yet independent of throughflow ph between 3 0 and 9 0 and throughflow rate at rates 0 04 1 hr 1 the tablets are also mechanically stable economical and environmentally safe field study results using the rock hard sodium sulphate tablets are consistent with both the laboratory findings and the results of previous investigators

geochemical characteristics of granitoid rocks from within the archean michipicoten greenstone belt wawa subprovince superior province canada implications for source regions and tectonic evolution three distinct tonalite trondhjemite granodiorite ttg magma series occur syngenetically with bimodal mafic felsic cyclical volcanics in the middle to late archean michipicoten greenstone belt mgb canada between 2 72 and 2 60 ga two additional series are recognised as pre tectonic late tectonic and post tectonic syenite quartz monzonite granitoid stocks smg series and an alkali feldspar syenite alkali feldspar quartz syenite stock ss series the synvolcanic ttg series such as the hawk lake granitic complex and the jubilee lake stock are characterised by moderate to low k2o 2 5 wt rb 60 ppm and sr concentrations 400 ppm moderate tio2 levels 0 1 1 0 wt lasm 2 12 and gdyb 0 8 2 9 moderate to large negative eu anomalies and small negative ta nb troughs on ocean ridge granite org normalised plots the ttg series are compositionally similar to synvolcanic mgb felsic volcanics of cycles 1 to 3 the high lasm lata and low zrth are features of sialic crust a contribution of ancient sialic crust in the genesis of the felsic volcanics and ttg series granitoids of all three felsic volcanic cycles and synvolcanic ttg stocks is required in the mgb the parental magma like that of the ttg series of the abitibi greenstone belt agb may originate in oceanic mantle the smg series have elevated k2o 2 0 6 3 wt rb 40 280 ppm ba 10 2800 ppm and sr 250 1350 ppm steep ree patterns reflected in elevated lasm 3 12 and gdyb 1 8 5 0 without eu anomalies a moderate to large negative ta nb trough on ocean ridge granite normalised plots and low tio2 0 5 wt and cao na2o k2o the smg series is compositionally different to the mgb felsic volcanic rocks and to the ttg series granitoids the source is tentatively placed in the mantle wedge overlying a southward dipping subducted plate of oceanic crust and the elevated lile signature is attributed to metasomatism of this source by fluids derived from the subducted slab of oceanic crust the smg series granitoids like those of the abitibi are different when compared to the sanukitoids in that they are compositionally more evolved however they may be related to these rocks by low pressure fractionation and may be derivatives of sanukitoid like magmas the alkali feldspar syenite alkali feldspar quartz syenite represented by the herman lake stock of the ss series has a primitive composition 60 wt sio2 with low ree abundances and relatively flat lree and hree but steep mree profiles these rocks are strongly lile enriched but do not develop pronounced ta nb troughs on org normalised profiles these rocks may be derived by low degrees of partial melting of a depleted mantle wedge previously metasomatised by alkali rich fluids released from a subducting slab the elevated tiy and zry of these rocks appear to suggest that small amounts of partial melting were responsible for the genesis of these rocks the granitoid rocks record an overall progression from contributions made from the continental crust in a continental margin environment to magmas dominated by contributions from subducted crust or the overlying variably metasomatised mantle wedge during the terminal phase of arc continent collision

the use of gypsum spheres for identifying water flow routes in soils gypsum plaster of paris has been cast into spheres and placed in soils weight loss has been used to identify relative water flow routes theoretical considerations and laboratory experimentation show that solutional weight loss of the material used increases with increasing water flow but is independent of ph above ph 4 results for gypsum sphere weight loss are presented for soils where moisture conditions have been measured independently using tensiometers the data suggest that the weight loss method provides a viable time integrated demonstration of relative water flow routes

multi element geochemical modelling of crust mantle interactions during late archaean crustal growth the closepet granite south india the closepet granite in the dharwar craton of south india is a large late archaean magmatic body its composition can be explained as a result of interactions between mantle derived melts and pre existing continental crust ttg gneisses using geochemical modelling based upon major and trace element compositions the following petrogenetic model is proposed for the formation of the batholith i an enriched mantle garnet and amphibole bearing lherzolite melts to produce a basaltic liquid ii the basaltic liquid undergoes limited fractional crystallization of biotite and amphibole f 0 9 iii the differentiated liquid rises into the old continental crust and induces water saturated anatexis of the ttg gneisses k feldspar qtz plagioclase melt iv both mantle derived and anatectic liquid mix and give rise to magma compositions ranging from quartz monzonite to granite the origin of the mantle enrichment is discussed in the context of the regional geological setting the most likely possibility seems to be metasomatism by slab melts the metasomatism of a mantle wedge by slab melts this suggests a two stage evolution for the dharwar craton during the late archaean i a subduction related event with the formation of ttgs sanukitoids and with associated mantle metasomatism and ii re melting of the metasomatized mantle this evolutionary history implies that at least some of the k rich late archaean granites are juvenile rather than products of intracrustal reworking as frequently assumed

the archaean sanukitoid series of the baltic shield geological setting geochemical characteristics and implications for their origin abstract archaean high mg granitoids sanukitoids occur in the karelian granite greenstone terrain in the baltic shield in two distinct zones in the west of the shield sanukitoid intrusions formed between 2700 and 2720 ma and consist of a single igneous phase that varies in composition from diorite to granite in the eastern part of the shield sanukitoid intrusions formed between 2730 and 2745 ma and are strongly differentiated varying in composition from ultramafic to felsic all the sanukitoids are enriched in light rare earth elements lree la 80 ppm ce 150 ppm la n yb n 30 40 sr 2000 ppm ba 2500 ppm p 2 o 5 1 5 alkalis na 2 o k 2 o 5 10 possess high mg values 0 50 0 65 and show a negative nb ta anomaly they are spatially and temporally related to syenite intrusions and lamprophyre dykes sanukitoid intrusions in the western and eastern zones differ in composition in the west they have higher sio 2 mainly 60 and lower alkalis sr ba lree than in the eastern zone intrusions the most differentiated intrusion the panozero intrusion in the eastern zone was formed in two magmatic cycles separated by ductile deformation in the first cycle ultramafic to monzonitic rocks formed whereas in the second cycle the magmas were monzodioritic to quartz monzonite ultramafic and mafic rocks make up about 10 of the outcrop and occur as enclaves in monzonites and monzodiorites and as dykes implies a number of discrete magmatic events all rocks of the panozero intrusion have high k 2 o and the composition of the initial melt calculated from the weighted average of the first cycle magmas is monzodiorite sio 2 52 mg 0 55 na 2 o k 2 o 6 the presence of magmatic hornblende and biotite a high carbonate content widely distributed explosive breccias and evidence of liquid immiscibility are consistent with a high h 2 o co 2 content in the sanukitoid melt the geodynamic model which most satisfactorily explains our geological and geochemical observations is the formation of the karelian sanukitoids in a cratonic environment adjacent to the belomorian karelian suture

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

the temporal evolution of sanukitoids in the karelian craton baltic shield an ion microprobe u th pb isotopic study of zircons abstract the u th pb isotopic systematics of zircons from six sanukitoid intrusions in the karelian craton has been investigated using the secondary ion mass spectrometer sims our results show that karelian sanukitoids formed between 2745 and 2705 ma ago and that there is an age difference of about 30 ma between sanukitoids in the eastern and western karelia results for intrusions made up of a number of magmatic phases show no internal age variation in the east of the study region zircons from a monzodiorite and two quartz monzonites from the panozero pluton were dated at 2737 11 2739 11 and 2741 8 ma in the hautavaara pluton a monzodiorite and a subalkaline granite were dated at 2743 8 and 2742 23 ma and a quartz diorite from the elmus pluton gave an age of 2741 7 ma in addition a lamprophyre dyke within the sjargozero pluton gave an age of 2742 14 ma in the west zircons from a quartz monzonite and a granodiorite in the njuk intrusion gave ages of 2709 10 and 2716 11 ma in the kurgelampi pluton zircons from a diorite and two granodiorites were dated at 2707 9 2719 6 and 2712 9 ma respectively zircons from the granodiorites and the alkaline granites contain older cores with 207 pb 206 pb ages greater than 2800 ma the absence of inherited zircons in the more mafic sanukitoids is attributed to their higher saturation levels for zirconium sanukitoid zircons have th u ratios above 0 5 and often higher whereas nearby tonalite tondhjemite granodiorites ttgs have th u ratios below 0 5 typically tonalites are older than sanukitoids by more than 100 ma and it is possible that tectonic processes associated with the collision of the belomorian mobile belt provided the heat necessary to initiate the generation of the sanukitoid melts

hillslope hydrochemistry and stream response on a wooded permeable bedrock the role of stemflow abstract the hillslope hydrochemical processes operating on a permeable carbonate bedrock can be linked to the hydrochemical response which a slope foot stream shows to rainfall events solute sources hydrochemical inputs and outputs and storm responses have been evaluated for a wooded hillslope section the data could not be interpreted in terms of a throughflow soil water movement mechanism storm events produced a rapid input of solute rich water to the stream by vertical percolation in the bedrock and subsequent lateral movement at depth the solute rich nature of the response implies that a displacement mechanism operates the rapid response from the hillslope may be initiated by stemflow which produces large concentrated point source inputs to the soil by passing the soil matrix baseflow runoff is produced by throughfall percolating through the soil matrix stemflow may be used to explain the different hydrochemical responses of the wooded hillslope and the non wooded upper portion of the catchment

archean crustal evolution of the suomussalmi district as part of the kianta complex karelia constraints from geochemistry and isotopes of granitoids abstract this study presents new geochemical and isotopic data from granitoids belonging to the kianta complex of the western karelian terrane collected from the suomussalmi district in eastern finland geochemically the archean granitoids can be divided into five groups ttgs tonalite trondhjemite granodiorite sensu stricto transitional ttgs sanukitoids high mg granitoids quartz diorites and anatectic leucogranitoids this study includes chemical data for the first four and isotopic data for all the suites the majority 78 out of 80 samples of ttgs sensu stricto k2o na2o 0 5 display higher lile concentrations but otherwise closely resemble the ttgs sensu stricto sanukitoids and quartz diorites have moderate la yb n 6 50 and higher hree cr and ni than the ttgs sanukitoids can be differentiated from quartz diorites based on higher ba averages 1453 vs 626 ppm k2o averages 3 02 vs 1 94 and lree lan averages 141 vs 92 contents although overlap between these two suites exists ttg magmatism in suomussalmi and the surrounding parts of kianta complex can be divided into three major phases ca 2 95 ga 2 83 2 78 ga and 2 76 2 74 ga sanukitoid magmatism 2 73 2 71 ga partly overlaps in error limits with quartz diorites aged 2 70 ga and is coeval with one transitional ttg sample 2 72 ga migmatization of older rocks and intrusion of leucogranitoids took place at 2 70 2 69 ga geochemistry inherited zircons

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

single grain zircon u pb age constraints of the western and eastern sanukitoid zones in the finnish part of the karelian province abstract a single grain zircon u pb secondary ion mass spectrometer sims study of nine granitoid intrusions with sanukitoid geochemistry from the finnish part of the karelian province shows their time limited emplacement the age results indicate emplacement at 2715 and 2745 ma we observed also a significant number of relict cores in the zircons with 207 pb 206 pb ages up to 3 2 ga emphasizing the importance of inheritance processes in the petrogenesis of the sanukitoids compiled single grain age data of the finnish and russian bibikova et al 2005a parts of the karelian province confirm the occurrence of two temporally diverging sanukitoid zones throughout the province the western zone shows a younger average age 2718 ma and the eastern zone an older average age 2740 ma with an apparent age difference of 20 ma between the zones most of the sanukitoid intrusions in finland belong to the western sanukitoid zone but the southernmost intrusions can be regarded as a part of the eastern sanukitoid zone the boundary between the sanukitoid zones specifies the boundary of the western and central karelian terranes worldwide sanukitoid magmatism at 2 95 2 55 ga as reported from several archean blocks followed sharply after prolonged tonalite trondhjemite granodiorite ttg magmatism indicating a short lived tectonomagmatic phenomenon at the end of convergent accretion

neoarchean sanukitoids and associated rocks from the tengzhou pingyi intrusive complex north china craton insights into petrogenesis and crust mantle interactions abstract quartz monzodiorites granodiorites and monzogranites constitute the dominant lithological assemblage in the neoarchean tengzhou pingyi intrusive complex tpic in the southwestern part of western shandong province wsp in the eastern part of the north china craton ncc and mafic magmatic enclaves mmes are widely developed only in granodiorites of the tpic la icp ms zircon u pb isotopic dating reveals that the tpic was emplaced at 2 54 2 52 ga the 2 54 ga monzogranites display geochemical affinities with high k granites and they were likely derived from the partial melting of metamorphic greywackes at lower crustal levels the 2 54 2 52 ga quartz monzodiorites and granodiorites show significant geochemical similarities to the archean sanukitoids of the western karelian province of finland with higher mg 43 57 values cr 24 88 ppm sr 547 1154 ppm and ba 662 1961 ppm contents and k2o na2o 0 42 1 00 ratios therefore we define the quartz monzodiorites and granodiorites as neoarchean sanukitoids based on their lithological assemblages and geochemical characteristics these sanukitoids can be subdivided into sanukitoid quartz monzodiorites sqms and porphyritic sanukitoid granodiorites psgs the sqms exhibit higher positive hf t2 values from 1 9 to 3 6 with tdm values of 2 70 to 2 77 ga and are strongly enriched in light rare earth elements lrees and large ion lithophile elements liles implying a mantle source that was enriched by either fluids or melts the psgs have a wide range of hf t2 values from 3 4 to 3 8 suggesting that they were formed by crust mantle magma mixing this interpretation is also supported by the petrological textural and compositional disequilibrium of plagioclase phenocrysts from the psgs moreover the mmes and their host psgs have identical crystallization ages 2 54 ga similar mineral chemistries and zircon lu hf isotopic compositions indicating that the mmes are cumulates from the earlier host psgs magma petrogenetic studies and zircon lu hf isotopic features of these lithological assemblages indicate that the interval of 2 55 2 52 ga in the tpic represents an important period of crustal growth and crust mantle interactions considering the spatial temporal relationships and the petrogenesis of the diverse lithological assemblages we propose that the neoarchean tpic was most likely formed in an active continental margin setting

weathering and durability of the goldsworthy chalk stones south downs west sussex england the goldsworthy chalk stones 14 roughly shaped balls of chalk each approximately 2 m in diameter were installed in june 2002 initial assessments by the artist andy goldsworthy and the strange partners commissioning team concluded that they would last for about 2 years the balls disintegration has been measured as part of an ongoing scientific monitoring programme designed to assess their durability and to study controls on rates of chalk weathering preliminary assessment of the first 3 years of data shows that 76 of the total mass loss occurred during year 1 19 during year 2 and 5 during year 3 this might reflect the fact that winter rainfall amounts decreased substantially over the period of study the west facing sides of the balls have tended to show greater mass loss than those facing east which might also be a function of exposure to rain judging from their present slow rates of weathering the balls will last for over 200 years but an exceptionally cold wet winter might cause sudden and massive breakdown three models of chalk mass weathering are presented the ongoing scientific monitoring programme will focus experimental work on four key research themes process lithology environment and stress history

experimental evidence against co2 promoted deep crustal melting there has been considerable controversy regarding the role of carbon dioxide in the metamorphism and melting of the earth s crust fuelled principally by reports of experimental evidence for co2 enhanced partial melting of the assemblage phlogopite mica quartz in the model system kalo2 mgo sio2h2o co21 2 the analogous process in the crust would lead to the formation of granulite facies rocks at temperatures characteristic of amphibolite facies metamorphism the granulite fades3 5 would thus be indicative not of unusually high temperatures but of the influx of carbonic fluids4 6 moreover the similarity of their low temperature melts to the compositions of some calc alkaline lamprophyres led peterson and newton2 to suggest that such magmas might be generated by the introduction of co2 rich fluids providing a means of large scale mass transfer in the deep crust these ideas have been highly influential6 but there are aspects of peterson and newton s results that are hard to reconcile with other available data i have accordingly tried to replicate the results of refs 1 and 2 but as i report here have been unable to do so the present results thus cast doubt on the general idea of melt fluxing by co2 and the formation of magnesium and co2 rich magmas at crustal pressures

chemical denudation on a magnesian limestone hillslope field evidence and implications for modelling the pattern of relative denudation at the soil bedrock interface over a wooded magnesian limestone hillslope was investigated using micro weight loss bedrock tablets the resulting pattern of weight loss after emplacement for one year indicated a consistent upslope increase in solutional denudation results from tablets emplaced for two years confirmed this dye tracing and gypsum sphere weight loss results showed that water movement over the slope was by vertical percolation and not by throughflow the pattern of solutional denudation was related to changes in soil type and associated changes in soil ph continued slope development by solutional denudation will ultimately lead to slope decline comparison with a similar study suggests that a general soil chemistry based model of hillslope solutional denudation can be proposed

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

petrogenesis of mantle derived lile enriched archean monzodiorites and trachyandesites sanukitoids in southwestern superior province reply in southwestern superior province diorite monzodiorite and trachyandesite sanukitoids occurring within syn to post tectonic intrusive complexes and within greenstone belts have the following chemical characteristics 55 60 wt sio2 mgo 6 wt mg 0 60 ni and cr both 100 ppm na2o k2o 6 wt sr and ba both 600 1800 ppm and rare earth element ree patterns that are strongly light rare earth element lree enriched cen 80 250 ybn 4 10 and show no eu anomalies sanukitoids and their granodioritic derivatives constitute at least 5 of the exposed crust in the study area the sanukitoids cannot be derived by melting fractionation or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids crustal contamination of komatiites fails to explain the high large ion lithophile element lile contents of the sanukitoids rather we suggest that the sanukitoids were derived by hydrous melting of lile enriched mantle peridotite at pressures between 10 and

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

mixed layer shear generated by wind stress in the central equatorial pacific abstract sixteen months of wind and current profile observations in the central equatorial pacific show the response of the upper ocean shear to local wind forcing the shear at the ocean surface is significantly correlated with the wind stress in direction but not in magnitude implying that the vertical eddy viscosity coefficient is proportional to the square of the wind speed or to the stress using this variable eddy viscosity coefficient in stommel s model of the equatorial undercurrent we calculate shears in the mixed layer that compare well with the observations the flow is downwind on the equator and tends toward and ekman spiral off the equator