dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

lunar core formation new constraints from metal silicate partitioning of siderophile elements abstract analyses of apollo era seismograms lunar laser ranging data and the lunar moment of inertia suggest the presence of a small at least partially molten fe rich metallic core in the moon but the chemical composition and formation conditions of this core are not well constrained here we assess whether pressure temperature conditions can be found at which the lunar silicate mantle equilibrated with a fe rich metallic liquid during core formation to this end we combine measurements of the metal silicate partitioning behavior of siderophile elements with the estimated depletion due to core formation in those elements in the silicate mantle of the moon we also explore how the presence of the light element sulfur suggested by seismic models to be present in the core at concentrations of up to 6 wt in the lunar core affects core formation models we use published metal silicate partitioning data for ni co w mo p v and cr in the lunar pressure range 1 atm 5 gpa and characterize the dependence of the metal silicate partition coefficients d on temperature pressure oxygen fugacity and composition of the silicate melt and the metal if the core is assumed to consist of pure iron core mantle equilibration conditions that best satisfy lunar mantle depletions of five siderophile elements ni co w mo and p are a pressure of 4 5 0 5 gpa and a temperature of 2200 k the lunar mantle depletions of cr and v are also consistent with metal silicate equilibration in this pressure and temperature range if 6 wt s is incorporated into the lunar core our results therefore suggest that metal silicate equilibrium during lunar core formation occurred at depths close to the present day lunar core mantle boundary this provides independent support for both the existence of a deep magma ocean in the moon in its early history and the presence of significant amounts of sulfur in the lunar core

genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth a case study from the huichizi pluton qinling orogen central china abstract adakitic rocks are often considered as a key to deciphering the genesis of archean ttgs and the early crustal growth granites from the huichizi pluton in the north qinling nq unit have high sr y and la yb n ratios similar to adakites their relatively high sio 2 k 2 o and na 2 o and very low mgo cr and ni contents are in the range of high sio 2 adakites and early archean ttgs and are compositionally similar to experimental melts derived from metabasalt sources new sims zircon u pb dating constrains the emplacement age of the huichizi pluton at 422 5 ma rock samples from the huichizi pluton have e nd t and zircon e hf t values similar to the neoproterozoic metabasalts in the nq unit in combination with their normal mantle like 18 o zir values these adakites are best explained by partial melting of the neoproterozoic mafic crustal root due to subduction of the shangdan ocean regional geological data suggest that the crust was probably thickened by a ca 490 ma arc collision process prior to the emplacement of the huichizi pluton our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust

tectonic evolution of the caribbean and northwestern south america the case for accretion of two late cretaceous oceanic plateaus it is widely accepted that the thickened oceanic crust of the caribbean plate its basaltic accreted margins and accreted mafic terranes in northwestern south america represent the remnants of a single ca 90 ma oceanic plateau we review geologic geochemical and paleomagnetic evidence that suggests that the caribbean colombian oceanic plateau in fact represents the remnants of two different oceanic plateaus both dated as ca 90 ma the first of these plateaus the caribbean plateau formed ca 90 ma in the vicinity of the present day galapagos hotspot northeastward movement of the farallon plate meant that this plateau collided with the proto caribbean arc and northwestern south america 10 m y after the plateau s main phase of formation paleomagnetic evidence suggests that the second of these plateaus the gorgona plateau formed at 268 308s possibly at the site of the present day sala y gomez hotspot over the next 45 m y this plateau was carried progressively northeastward on the farallon plate and collided in the middle eocene with the proto andean subduction zone in northwestern south america the recognition of a second ca 90 ma pacific oceanic plateau strengthens the link between plateau formation and global oceanic anoxic events

blueschists and associated rocks in eastern jamaica and their significance for cretaceous plate margin development in the northern caribbean blueschists and associated low grade greenschists and amphibolites occur in the blue mountains of eastern jamaica and are found in proximity to volcanic arc generated rocks in the blueschist and greenschist rocks known as the mount hibernia schists metamorphosed basalts gabbro and peridotites are found in a structurally disrupted region along with meta cherts marbles meta conglomerates and meta epiclastic rocks the amphibolite facies rocks known as the westphalia schists occur in a belt adjacent to the mount hibernia schists and consist of banded mafic to quartzofeldspathic schists a small outcrop of similar amphibolites also occurs in green bay several kilometres southwest of the blue mountains the metaigneous rocks of the mount hibernia schists have tholeiitic affinities but the westphalia schists seem to be more calc alkaline the mount hibernia blueschists contain minerals typical of high pressure low temperature terranes including crossite riebeckite pumpellyite and stilpnomelane the mount hibernia greenschists are low grade chlorite zone rocks lacking biotite in contrast the westphalia amphibolites typically contain the higher grade minerals hornblende biotite and plagioclase both groups of schists have a low grade greenschist overprint characterized by epidote chlorite and chloritoid the lithological associations chemical composition and metamorphism of these rocks strongly suggest that they were formed in the accretionary prism or subduction complex of the jamaica nicaragua rise island arc system the present geological setting and consideration of their thermal evolution indicate that these rocks probably recrystallized in early cretaceous time the metamorphic rocks are now juxtaposed against a campanian ophiolite body and are found in close association with upper cretaceous andesites and granodiorites a model for the genesis of the jamaican schist terrane describes the formation and subsequent erosion of these rocks in a pre campanian accretionary complex the tectonic regime changed in campanian time and involved the obduction of the ophiolite body and a 150 km outward stepping of the site of subduction and hence of volcanism this latter change resulted in the later cretaceous arc complex being superimposed on the lower cretaceous accretionary fore arc complex tertiary left lateral transcurrent faulting and consequent uplift and erosion exposed the present blueschist ophiolite magmatic arc complex

particle velocity generated by rockburst during exploitation of the longwall and its impact on the workings as a consequence of geomechanical and geotechnical conditions and also anthropogenic activities in mines of the ostrava karvina coal basin czech republic rockbursts have been recognized to be a serious seismic risk therefore local as well as regional monitoring arrays were deployed there in order to investigate the actual seismic activity continually one of the essential parameters which was observed at the seismic stations situated in situ was the particle velocity of p and s waves the aim of this paper is to derive some empirical dependences by determining the decrease of seismic wave amplitudes with distance from rockburst foci seismic energy local magnitude co ordinates of seismic stations rockburst foci and positions where damage to workings occurred were employed as additional imput moreover the degree of this damage was tested based on the values of particle velocity and simultaneously stress due to the loading of the workings by the stress wave was also calculated

formation of paleoarchean continental crust through infracrustal melting of enriched basalt abstract paleoarchean rocks of the tonalite trondhjemite granodiorite ttg series require a basaltic source region more enriched in k lile th and lree than the low k tholeiites typical of archean supracrustal sequences most ttg of the pilbara craton in northwestern australia formed between 3 5 and 3 42 ga through infracrustal melting of a source older than 3 5 ga basaltic to andesitic rocks of the 3 51 ga coucal formation at the base of the pilbara supergroup are amongst the only well preserved remnants of pre 3 5 ga supracrustal material on earth and may have formed a large proportion of pre 3 5 ga pilbara crust these rocks are significantly enriched in k lile th and lree compared to post 3 5 ga paleoarchean basalts and andesites and form a compositionally suitable source for ttg enrichment in these basalts was not the result of crustal assimilation but was inherited from a mantle source that was less depleted than modern morb source and was enriched in recycled crustal components we suggest that the formation of paleoarchean ttg and of their voluminous mafic source regions reflects both a primitive stage in the thermal and compositional evolution of the mantle and a significant prehistory of crustal recycling

experimental determination of the partitioning of gallium between solid iron metal and synthetic basaltic melt electron and ion microprobe study the distribution of ga between solid fe metal and synthetic basaltic melt has been investigated experimentally at two temperatures over a limited range of oxygen fugacities reversal experiments were conducted indicating a close approach to equilibrium analysis of run products was performed using an electron and an ion microprobe at 1 bar total pressure the solid metal silicate melt partition coefficient d ga is given by 1190 c logd ga 0 92 logfo2 11 91330 c logd ga 0 77 logfo2 8 8 for the common assumption of a valence state for ga of 3 in silicates and assuming ideal solution of ga in both phases a slope of 0 75 is predicted the slope obtained at 1300 c 0 77 is indistinguishable from this value while the slope at 1190 c 0 92 is somewhat higher henry s law is obeyed over the concentration range 0 007 wt to 0 15 wt ga in metal a factor of 20 in concentration these partition coefficients may be utilized to evaluate metal silicate fractionation processes in the earth moon and eucrite parent body the lunar mantle appears to be depleted in ga by a factor of 20 40 relative to ci abundances this depletion is consistent with extraction of ga into a geophysically plausible lunar core if ga was initially present at a subchondritic concentration a similar explanation probably accounts for the depletion of ga in the eucrite parent body the upper mantle of the earth appears to be depleted in ga by a factor of 4 7 relative to ci abundances this depletion is far smaller than would be expected as a result of core formation but is consistent with two quite different hypotheses i a small amount of solid metal and sulfur bearing metallic liquid was retained in the mantle after core formation or ii addition of a late stage chondritic component involving 5 to 10 of the upper mantle following core formation

evidence of impact melt sheet differentiation of the lunar south pole aitken basin the south pole aitken spa basin is the largest basin on the moon the basin forming impact likely melted the upper part of the mantle and formed an impact melt sheet impact melt of large terrestrial craters differentiated following a general magmatic differentiation sequence however it is still debated whether or not the spa melt sheet underwent differentiation to address this we investigated the vertical and lateral variations in mineral composition of the spa impact melt sheet area by analyzing the surface mineralogy including 277 post spa craters using remote sensing reflectance data we identified a 7 km thick high ca pyroxene rich layer and below that a 8 km thick low ca pyroxene rich layer both filled the entire impact melt sheet area 630 km in diameter considering the vast distribution of these two layers their thicknesses their feo abundances around 13 5 wt which are lower than most of the lunar mare basalt but within the estimated range of the differentiated spa impact melt and that the observed lithologies are consistent with a differentiation model we conclude that the spa impact melt was differentiated moreover based on the lunar magma ocean differentiation model al2o3 and cao abundances of the upper part of the mantle would be much lower after the mantle overturn if the spa impact occurred after overturn these elemental abundances of the initial impact melt would be much lower than that of the before overturn impact case and result in different solidified layers our observation matches only the after overturn case which may imply that the spa impact occurred after overturn

the moon a taylor perspective we address several current lunar problems the data suggest that the moon likely possesses an fe rich metallic core a few percent of lunar volume although definitive proof is lacking refractory elements appear to be enriched relative both to the composition of the primordial solar nebula ci and the earth very volatile elements appear to be depleted uniformly at high levels we adopt the single impact hypothesis for lunar origin which formed a high temperature silicate vapor disk mostly of metal poor silicate material from an impactor theia that was already depleted in volatiles we speculate that the curious lunar bulk composition resulted from condensation from high temperature vapor at around a few earth radii this could produce an enriched refractory element composition that cut off below 1000 k producing a uniform depletion in very volatile elements

do cenozoic analogues support a plate tectonic origin for earth s earliest continental crust archean continental crust largely comprises the trondhjemite tonalite and granodiorite dacite ttg d suite of igneous rocks formation of the earliest archean 3 5 ga ttg ds is controversial being attributed to either subduction zone processes with active plate tectonics or thermochemical mantle convection with no plate tectonic processes a suite of cenozoic adakite like lavas in jamaica has geochemical compositions comparable to early archean ttg d the data indicate that the adakites were generated by underthrusting or subducting and partial melting of oceanic plateau crust beneath jamaica this setting is analogous to proposed plate tectonic processes in the early archean where hot thick and more buoyant archean oceanic crust underthrusts adjacent plates the new adakite data imply that earliest archean ttg d continental crust could have formed above primitive subduction zones

secular changes in tonalite trondhjemite granodiorite composition as markers of the progressive cooling of earth archean tonalite trondhjemite granodiorite associations ttg are classically thought to generate through partial melting of hydrous metabasalts however the chemical composition of the least differentiated ttg parental magmas evolved from 4 0 to 2 5 ga during this interval the mg as well as the ni and cr contents increased which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite similarly cao na2o and sr also increased over time thus reflecting an increase in the abundance of plagioclase in the melt residue the presence or absence of residual plagioclase is interpreted in terms of melting depth the demonstrated interaction between ttg parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material at 4 0 ga earth s geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable consequently due to the small thickness of the overlying mantle wedge felsic magmas interacted little with the mantle at 2 5 ga however owing to lower geothermal gradients the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab as a result felsic magmas reacted strongly with the mantle peridotite the changes of ttg composition during archean time can be thus interpreted as reflecting the progressive cooling of earth

constraints on the moon s origin from the partitioning behaviour of tungsten the moon earth and eucritic meteorites display w la ratios which correspond to depletions of w relative to chondrites by factors of 19 ref 1 this depletion can be attributed to metal silicate fractionation ordinary chondrites and cl chondrites with widely varying metal contents and oxidation states have similar w la ratios suggesting that nebular fractionations were unimportant therefore assuming that both w and la are refractory and incompatible the depletions of w relative to la in the earth moon and eucrites are presumably due to separation of metal from silicate during planetary scale igneous events for the moon rammensee and wanke2 concluded that any geophysically reasonable metallic lunar core would be too small to explain the large lunar depletion of w it was therefore suggested2 that the moon acquired its depletion of w in a non lunar igneous event supporting the hypothesis that the moon formed by fission from the proto earth the upper portion of which was depleted in w due to terrestrial core formation3 5 we show here that this conclusion is implicity based on a special case namely equilibrium between metal and silicate phases with total melting of silicates in the geologically more general case where metal fractionates from silicate at relatively low degrees of partial melting the incompatible nature of w may negate this conclusion a geophysically plausible metallic core can account for the depletion of w in lunar surface and presumably lunar mantle rocks the low w la ratio in the moon cannot be used as unconditional evidence for a terrestrial origin of the moon

partial melting of subducting oceanic crust the conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two dimensional thermal models of subduction zones for porosities of 1 containing h20 the amount of partial melt generated at the wet basaltic solidus is limited to 100 mpa can be maintained by rocks close to or above their melting temperatures in the absence of high shear stresses substantial melting of the oceanic crust will only occur during subduction of very young 5 ma oceanic lithosphere partial melting of hydrated basalt amphibolites derived from the mid ocean ridge has been proposed e g 1 3 as being responsible for the generation of certain recent high al andesitic to dacitic volcanic rocks adakites three of these volcanic suites mount st helens southern chile and panama occur in volcanic arcs where oceanic crust 25 ma is being subducted at rates of 1 3 cm yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments however oceanic lithosphere is not currently being subducted beneath baja and new guinea where recent adakites are also present suggesting that some adakite magmas may form by water undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately

formation of earth s early archaean continental crust abstract subduction of oceanic crust at an unusually low angle has been proposed as a model for the growth of continental crust older than about 2 5 ga at modern zones of low angle or flat subduction magmatic additions to new crust come from partial melting of both the subducting oceanic crust slab and the thin wedge of mantle above the slab evidence for both a slab and wedge source is preserved in most late archaean 3 0 2 5 ga terrains but we find little evidence that a mantle wedge contributed to crustal growth prior to 3 1 ga this lack of evidence in part reflects a dearth of exposed crust aged between 3 0 and 3 3 ga but also suggests that subduction enriched mantle source regions did not develop before 3 3 ga and possibly not before 3 1 ga in contrast to most modern terrains and some late archaean terrains early archaean 3 3 ga continental crust evolved through direct melting of thick mafic crust we invoke a process of subduction that does not include the development of a mantle wedge and call this process archaean flat subduction to distinguish it from modern low angle subduction

thermal transport properties of major archean rock types to high temperature and implications for cratonic geotherms abstract the thermal structure of archean terranes depends in part on the thermal transport properties of their distinctive rock types we determined thermal diffusivity d of a suite of 14 greenstone mafic granulite and tonalite trondhjemite granodiorite ttg rocks at temperatures up to 1000 c at atmospheric pressure using laser flash analysis which lacks systematic errors associated with conventional contact techniques at room temperature d ranges from 3 8 mm 2 s 1 for banded iron formation to 0 8 mm 2 s 1 for a quartz poor trondjhemite for all samples thermal diffusivity decreases with increasing temperature such that d for the suite converges around 0 7 0 1 mm 2 s 1 at 700 c combining these results with measured density and heat capacity calculated from modal mineralogy provides thermal conductivity as a function of temperature for each rock suite whereas near surface thermal conductivity varies from 2 7 to 4 2 w m 1 k 1 depending on rock type thermal conductivity of the lower crust is 2 w m 1 k 1 and only weakly dependent on lithology which is more thermally resistive than the uppermost mantle 3 5 w m 1 k 1 use of temperature dependent thermal transport properties in numerical models reveals that surface geotherms can be relatively insensitive to crustal heat production because high heat producing ttg rocks typically have high thermal diffusivity and conductivity at low temperatures and consequently are more efficient conductors of the heat they produce this finding implies that calculations of crustal heat production from surface borehole measurements may entail significant uncertainties

space time variations of the frequency energy relation for mining induced seismicity in the ostrava karvina mining district the values of parameters of the relation logn a b loge characterize in general the level of seismicity of individual regions in the present paper a detailed analysis ofb values of the frequency energy distributions was carried out with the aid of a database of seismic events recorded by the seismological networks in the ostrava karvina coal mine district czech republic using the least squares regression and maximum likelihood method as well the determination ofb value was performed for a relatively large number of regions investigated and for different time series of observations special attention has been paid to induced seismic events statistics for the vicinity of one of the coalfaces in the lazy mine it could be generally stated that lowerb values correspond to a higher level of induced seismic activity while the higher ones correspond to a low and a moderate seismic activity

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

the geochemistry of young volcanism throughout western panama and southeastern costa rica an overview oblique aseismic subduction below western panama and southeastern costa rica has produced recent arc related volcanism the aseismicity is probably related to the subduction of relatively hot oceanic lithosphere the volcanism throughout this region over the past 2 ma has been quite distinct consisting of felsic magmas andesites to rhyolites but mainly dacites with geochemical signatures suggesting a metamorphosed basaltic source it is believed that the subduction of young oceanic crust sets up conditions under which the slab melts rather than the overlying mantle wedge rocks with slab melt geochemistries and associated with young subducted crust have been termed adakites elsewhere the young adakite melts are sometimes associated with a few rare young high nb basalts but there is no obvious genetic link between them through differentiation high nb basalts may also be derived from the partial melting of the subducted oceanic crust high nb basalt migmatites have been found with pegmatites of adakite compositions in the exposed subduction terrain of the catalina schist california alternatively the high nb basalts may be partial melts of phlogopite rich mantle that has previously reacted with adakite magmas eruption of adakites and high nb basalts was preceded by a 2 3 ma period of relative quiescence prior to this there was a 7 ma period of calc alkaline volcanism typical of the present day magmatism associated with a distinct benioff zone found throughout the central american arc the abrupt transition in volcanism with time from an early calc alkaline sequence to a later adakite high nb basalt sequence may record a change in the tectonic setting of western panama and southeastern costa rica over the past 12 ma

geochemical constraints on the origin of the moon abstract hypotheses for the origin of the moon involve variants on capture double planet and fission processes double planet and fission hypotheses are examined in the light of siderophile trace elements the siderophile trace elements chosen w re mo p ga ge have well understood geochemical behavior such that appropriate metal silicate partition coefficients are available and their abundances in the lunar and terrestrial mantles 4 4 4 5 109 years ago may be reasonably inferred the fission hypothesis of ringwood 1979 is not consistent with the behavior of re mo and p the hybrid fission hypothesis of wanke et al 1983 overcomes many of the deficiencies of ringwood s hypothesis but is not readily reconcilable with the behavior of re and ir the double planet hypothesis as most recently advanced by newsom and drake 1982 1983 appears to be consistent with siderophile element behavior in the moon

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

dehydration melting of a basaltic composition amphibolite at 1 5 and 2 0 gpa implications for the origin of adakites this study presents the results of dehydration melting experiments on a basaltic composition amphibolite under conditions appropriate to a hot slab geotherm 1 5 and 2 0 gpa and temperatures of 850 to 1150 c dehydration melting produces an omphacitic augite and garnet bearing residue coexisting with rhyolitic to andesitic composition melts at 1 5 gpa the amphibolite melts in two stages between 800 and 1025 c the 2 0 gpa data also define two melting stages at 2 0 gpa the first stage involves nearly modal melting of the original amphibolite minerals qtz pl amp to produce melt cpx grt during the second stage the eclogite restite melts non modally 0 86 cpx 0 14 grt 1 melt the experimental results were combined with data from the literature to generate a composite p t phase diagram for basaltic composition amphibolites over the 800 to 1100 c temperature range for pressures up to 2 0 gpa comparison of the major element compositions of the experimentally produced melts with compositions of presumed slab melts adakites shows that partial melting of amphibolite at conditions appropriate to a hot slab geotherm produces melts similar to andesitic and dacitic adakites except for significant mgo and cao depletions trace element modelling of amphibolite dehydration melting using the 2 0 gpa melting reactions produces ree abundances similar to those of adakites at 10 15 wt batch melting but the models do not reproduce the high sr y ratios characteristic of adakites taken together the major and trace element results are not consistent with the derivation of adakites by dehydration melting of the subducted slab with little or no interaction with the mantle wedge or crust if adakites are partial melts of the subducted slab they must undergo significant interaction with the mantle and or crust during which they acquire a number of their distinctive characteristics

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

on the formation of continental silicic melts in thermochemical mantle convection models implications for early earth abstract important constituents of archean cratons formed in the early and hot history of the earth are tonalite trondhjemite granodiorite ttg plutons and greenstone belts the formation of these granite greenstone terrains is often ascribed to plate tectonic processes buoyancy considerations however do not allow plate tectonics to take place in a significantly hotter earth we therefore propose an alternative mechanism for the coeval and proximate production of ttg plutons and greenstone like crustal successions that is when a locally anomalously thick basaltic crust has been produced by continued addition of extrusive or intrusive basalts due to partial melting of the underlying convecting mantle the transition of a sufficient amount of basalt in the lower crust to eclogite may trigger a resurfacing event in which a complete crustal section of over 1000 km long sinks into the mantle in less than 2 million years pressure release partial melting in the complementary upwelling mantle produces large volumes of basaltic material replacing the original crust partial melting at the base of this newly produced crust may generate felsic melts which are added as intrusives and or extrusives to the generally mafic crustal succession adding to what resembles a greenstone belt partial melting of metabasalt in the sinking crustal section produces a significant volume of ttg melt which is added to the crust directly above the location of subduction presumably in the form of a pluton this scenario is self consistently produced by numerical thermochemical mantle convection models presented in this paper including partial melting of mantle peridotite and crustal meta basalt the metamorphic p t conditions under which partial melting of metabasalt takes place in this scenario are consistent with geochemical trace element data for ttgs which indicate melting under amphibolite rather than eclogite facies other geodynamical settings which we have also investigated including partial melting in small scale delaminations of the lower crust at the base of a anomalously thick crust and due to the influx of a lower mantle diapir fail to reproduce this behavior unequivocally and mostly show melting of metabasalt in the eclogite stability field instead

experimental investigation of the partitioning of phosphorus between metal and silicate phases implications for the earth moon and eucrite parent body abstract the solid metal silicate melt partition coefficient for p d p has been determined experimentally at 1190 c and 1300 c the dependence of the partition coefficient on oxygen fugacity has been investigated and is consistent with a valence state of 5 for p in the silicate melt the experimental partition coefficients are given by log d p 1 21 log o 2 15 95 at 1190 c log d p 1 53 log o 2 17 73 at 1300 c the experimentally determined partition coefficients may be used to interpret the low p la ratios of the earth moon and eucrites relative to c1 chondrites the low p la ratios in the eucrites may be explained by partitioning of p into 5 to 25 of a sulfur bearing metallic liquid assuming equilibration and separation of the liquid metal from the silicates at low degrees of partial melting of the silicates the low w la ratios in the eucrites compared to c1 chondrites require the separation of an additional 2 to 10 solid metal the lowering of both p la and w la ratios in the moon may be explained by partitioning of p and w into metal during formation of a small core by separation of liquid metal from silicate at low degrees of partial melting of the silicates the w la ratios in the earth and moon are virtually indistinguishable while p la ratios differ by a factor of two the concentrations of feo also appear to be different these observations are difficult to reconcile with the hypothesis of a terrestrial origin of the moon following formation of the earth s core but are consistent with independent formation of the earth and moon

comparative geochemistry of basalts from the moon earth hed asteroid and mars implications for the origin of the moon abstract most hypotheses for the origin of the moon rotational fission co accretion and collisional ejection from the earth including giant impact call for the formation of the moon in a geocentric environment however key geochemical data for basaltic rocks from the moon earth the howardite eucrite diogenite hed meteorite parent body probably asteroid 4 vesta and the shergottite nakhlite chassignite snc meteorite parent body likely mars provide no evidence that the moon was derived from the earth and suggest that some objects with lunar like compositions were produced without involvement of the earth the source region compositions of basalts produced in the moon mare basalts were similar to those produced in the hed asteroid eucrites with regard to volatile lithophile elements na k rb cs and tl siderophile elements ni co ga ge re and ir and ferromagnesian elements mg fe cr and v and less similar to those in the earth or mars mare and eucrite basalts differ in their mn abundances fe mn values and isotopic composition suggesting that the moon and hed asteroid formed in different nebular locations however previous claims that the moon and hed parent body differ significantly in the abundances of some elements such as ni co cr and v are not supported by the data instead cr mg fe ni co abundance systematics suggest a close similarity between the source region compositions and conditions involved in producing mare and eucrite basalts and a significant difference from those of terrestrial basalts the data imply that the moon and hed asteroid experienced similar volatile element depletion and similar fractionation of metallic and mafic phases among hypotheses of lunar origin rotational fission and small impact collisional ejection seem less tenable than co accretion capture or a variant of giant impact collisional ejection in which the moon inherits the composition of the impactor both the moon and hed asteroid may have been derived from a class of objects that were common in the early solar system the most plausible model for the origin of the moon in line with geochemical and cosmochemical constraints is an impact induced fission of the proto earth wanke and dreibus 1986 clearly the moon and eucrite parent body resemble each other to a high degree nature produced such a composition not once but at least twice this calls into question an entire class of models that invoke ad hoc processes to explain the moon by a unique chance event anders 1977 the similarity between eucrites and lunar mare basalts are remarkable were it not for the differences in age and oxygen isotope signature it might be difficult to distinguish them on petrological or geochemical grounds taylor 1986

a potpourri of pristine moon rocks including a vhk mare basalt and a unique augite rich apollo 17 anorthosite analysis of previously unstudied apollo lithic fragments continues to yield surprising results among this year s samples is a small anorthosite fragment 76504 18 the first pristine anorthosit e found from apollo 17 this unique lithology strongly resembles the main type of apollo anorthosites ferroan anorthosites but 76504 18 has a far higher ratio about 9 of high ca pyroxene to low ca pyroxene higher na in its plagioclase higher contents of incompatible elements such as ree and a higher eu al ratio assuming that 76504 18 is a cumulate with less than 45 trapped liquid its parent melt probably had a negative eu anomaly in all these respects 76504 18 seems more likely than other ferroan anorthosites to be closely related to typical mare basalts apparently this anorthosite was among the latest to form by plagioclase flotation above a primordial magmasphere typical mare basalt source regions probably accumulated at about the same time or even earlier another previously unstudied fragment 14181c is a vhk very high potassium basalt that is similar in most respects to typical aluminous apollo 14 mare basalt but has a k la ratio of 1050 this lithology probably formed after a normal apollo 14 mare basaltic melt partially assimilated granite new data for siderophile elements in apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination

adakitic like magmatism in western ossa morena zone portugal geochemical and isotopic constraints of the pavia pluton abstract granitic rocks are a major component of the earth s continental crust and occur in a wide variety of tectonic settings their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation in this study we present the first whole rock chemical and isotopic sr nd o data for the pavia pluton 328 317 ma located near the western border of the ossa morena zone evora massif portugal major and trace element geochemistry suggests that the different granitic phases composing this intrusive body enclaves granites s l and crosscutting dikes represent independent magma pulses and the majority is similar to ttgs and adakites the little sr nd o isotopic variation with 87 sr 86 sr 328 0 70428 0 70560 end 328 ranging between 3 4 and 0 4 and 18 o varying from 5 6 to 8 4 implies an isotopically similar protolith for all phases the most viable mechanism for the generation of the pavia pluton adakitic like magmatism is assimilation fractional crystallization of a mantle derived magma this mechanism was also invoked to explain the genesis of other plutons within the evora massif but they have a distinct chemistry typical arc calc alkaline rocks the chemical differences between them and the pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle derived magmas by the sinking slab after subduction blocking and subsequent slab break off

highly depleted oceanic lithosphere in the rheic ocean implications for paleozoic plate reconstructions the rheic ocean formed at ca 500 ma when several peri gondwanan terranes e g avalonia and carolinia drifted from the northern margin of gondwana and were consumed during the late carboniferous collision between laurussia and gondwana a key event in the formation of pangea several mafic complexes ranging in age from ca 400 330 ma preserve many of the lithotectonic and or chemical characteristics of ophiolites they are characterized by anomalously high end values that are typically either between or above the widely accepted model depleted mantle curves these data indicate derivation from a highly depleted hd mantle and imply that i the mantle source of these complexes displays time integrated depletion in nd relative to sm and ii depletion is the result of an earlier melting event in the mantle from which basalt was extracted the extent of mantle depletion indicates that this melting event occurred in the neoproterozoic possibly up to 500 million years before the rheic ocean formed if so the mantle lithosphere that gave rise to the rheic ocean mafic complexes must have been captured from an adjacent older oceanic tract the transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved possible mesozoic cenozoic analogues include the capture of the caribbean plate or the scotia plate from the pacific to the atlantic oceanic realm our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the rheic ocean was consumed by subduction during laurentia gondwana convergence

geology of the ostrava karvina coalfield upper silesian basin czech republic and its influence on mining abstract the ostrava karvina coalfield represents the czechoslovak part of the upper silesian basin which is one of the most important european coal deposits it is an exception in europe as the major part of the coal reserves are of namurian age the formation of the upper silesian basin resulted largely from the tectonism that occurred during three periods these were the origin of the cadomian variscan and alpine structural stages the variscan evolution comprises the platform development middle devonian early carboniferous the period of marine molasse latest visean namurian a paralic molasse namurian a and terrigenous molasse namurian b and c westphalian two major basinal tectonic units with contrasting facies and tectonic structures originated in the latest visean as a result of the variscan mobilization the variscan foredeep along the western margin of the basin with thick coal bearing carboniferous and complicated fold and fault structures and the upper silesian stable block an extensive platform in the eastern part of the basin with a reduced thickness of sediments and simple tectonic structure the alpine tectonic movements rejuvenated the older major faults influenced the origin of a very sharply marked pre tertiary paleorelief formed on the top of carboniferous deposits and led to the nappe structure of the mesozoic and tertiary rocks which cover southern parts of the ostrava karvina coalfield the paralic ostrava formation namurian a is up to 3000 m thick with individual cycles varying from 6 to 20 m in thickness reflecting the broad variation in depositional environments it contains more than 170 coal seams with an average thickness of 73 cm about 80 marine and brackish horizons more than 100 freshwater horizons 16 coal tonsteins and 30 layers of whetstone rocks serve for correlation the continental karvina formation namurian b c and westphalian a deposited after tectonic inversion is up to 1000 m thick it contains up to 90 coal seams 180 cm thick on average maximum up to 16 m the cycles are thicker and laterally less stable than those in the ostrava formation and contain frequent layers of conglomerates and coarse grained sandstones only 25 freshwater horizons are known the typical feature of both formations is the frequent occurrence of tuffogenous layers whetstone rocks and tonsteins which are important strategraphic key horizons the coal seams mainly comprise bituminous coal at the lower boundary of the limnic karvina formation there is an abrupt increase in the abundance of inertinite up to 80 of the coal the majority of coals are of a high quality and can be used for coke production the sulphur and phosphorus content is very low less than 0 7 and 0 02 0 11 respectively the geological reserves are estimated to be about 16 000 million t of coal the variegated barren rocks the so called red beds have been recorded over the entire southwestern part of the basin the genesis of this rocks is discussed the following geological phenomena complicate the deep mining activity irregular development and distribution of the coal seams complex tectonic structure erosion wash outs the effect of the formation of red beds on coal beds gas rock and water bursts anomalous geomechanic features and the complicated paleorelief of the coal bearing carboniferous these phenomena and their influence on the mining activity are described

experimental determination of crystal melt partitioning of ga and ge in the system forsterite anorthite diopside the crystal liquid partitioning of ga and ge has been measured experimentally between forsterite diopside anorthite and spinel and melts in the pseudoternary system forsterite anorthite diopside at one atmosphere pressure and 1300 c gallium is incompatible with forsterite and diopside d ga 0 024 and 0 19 respectively is only slightly incompatible in anorthite d ga 0 86 and is highly compatible in spinel d ga 4 6 the partition coefficient for ge is within a factor of two of unity for forsterite diopside and anorthite d ge 0 62 1 4 and 0 51 respectively but ge is incompatible in spinel d ge 0 1 the coefficients for the exchange of ga and al and the exchange of ge and si between minerals and melts generally are within a factor of two of unity as is expected from the geochemical coherence of these element pairs in natural samples the application of our results to the interpretation of natural basaltic and mantle samples from the earth and basalts from the moon and the shergottite parent body demonstrates that it is possible to discriminate between different mantle source compositions using ga al and ge si ratios the ge variation among lunar mare basalts may be indicative of a heterogeneous lunar mantle the substantial depletion of ge in chassigny relative to the other snc meteorites may be evidence of either a heterogeneous shergottite parent body spb mantle or of different geochemical behavior for ge in the spb