alkalic to transitional ferrogabbro magma associated with paleohelikian anorthositic plutons in the flowers river area southeastern nain igneous complex labrador fine grained gabbroic chilled margins and crosscutting dikes are associated in space and time with three ca 1400 ma anorthositic plutons in the flowers river area southeastern nain igneous complex both the anorthositic and gabbroic rocks have distinctive compositions compared to rocks of similar age and lithology elsewhere in northcentral labrador the anorthositic rocks contain olivine and augite rather than orthopyroxene and fe ti oxides apatite and orthoclase are unusually abundant cumulus plagioclase is abnormally enriched in incompatible elements most of the gabbroic rocks are uniform in composition although the effects of contamination and fractionation are evident in some places they define a transitional to alkalic ferrogabbro magma that is strongly enriched in k p and incompatible trace elements the chemical characteristics of the ferrogabbro magma imply derivation from enriched mantle or involvement of a significant crustal component a parent daughter relationship between the ferrogabbro magma and anorthositic rocks is suggested by their compositional similarities and the fact that the gabbroic chilled margins and plagioclase rich pluton interiors appear to be completely gradational in composition and texture

the skaergaard liquid line of descent revisited there is a fundamental conflict between the suggestion that the iron content of skaergaard liquids increases during fe ti oxide fractionation and the observation that at the same time oxygen fugacity f text o text 2 drops by two log units below the fayalite magnetite quartz oxygen buffer fmq a new petrographic study of average skaergaard gabbros shows that the total modal content of fe ti oxides is about 22 in the early lzc and markedly decreases to below 5 in the uzc forward modeling based on these modal constraints as well as experimental results on skaergaard related dikes predicts that fractionation of troctolitic lza gabbros drives the derivative liquid towards a high iron content strong iron enrichment continues together with a small decline in silica during lzb crystallization due to the appearance of augite as a fractionating phase the fractionation of fe ti oxides in the lzc initially suppresses iron enrichment and reverses the silica trend to one of slight enrichment however continued evolution into the uz produces liquids with maximum uzc feo content of 23 25 wt and sio2 content of 53 wt feo is total iron as feo the maximum in feo is dependent on several factors of which the fe ti oxide mode has the strongest effect the f text o text 2 during crystallization of the lzc is widely thought to have been at or slightly below the fayalite magnetite quartz oxygen buffer fmq under closed system evolution incorporation of ferric iron into augite during formation of the lzb restricts the increase in f text o text 2 to about 0 1 log units above fmq 0 1 fmq likewise crystallization of the lzc through the uza involving fe ti oxide minerals leads to a decline in f text o text 2 of less than 0 1 fmq crystallization of the uzb c gabbros results in oxidation to a maximum of 0 5 fmq this behavior can account for the iron rich character of the uz gabbros as well as the low modal content of fe ti oxides thus evolved skaergaard liquids are high in iron and contain a modest amount of sio2 our modeling result do not account for a strong drop in f text o text 2 through the layered series such a drop would require an unacceptably high proportion of fe ti oxides and high magnetite content in the fractionating assemblage

geographical dependence observed in blocking high influence on the stratospheric variability through enhancement and suppression of upward planetary wave propagation abstractprevious studies have suggested the importance of blocking high bh development for the occurrence of stratospheric sudden warming ssw while there is a recent study that failed to identify their statistical linkage through composite analysis applied to high amplitude anticyclonic anomaly events observed around every grid point over the extratropical northern hemisphere the present study reveals a distinct geographical dependence of bh influence on the upward propagation of planetary waves pws into the stratosphere tropospheric bhs that develop over the euro atlantic sector tend to enhance upward pw propagation leading to the warming in the polar stratosphere and in some cases to major ssw events in contrast the upward pw propagation tends to be suppressed by bhs developing over the western pacific and the far east resulting in the polar stratospheric cooling this dependence is found to arise mainly from the sensitivity of the interference between the climatological pws and upward p

the system fayalite albite anorthite and the syenite problem the presence in a magma of fayalite the iron end member of the olivine binary series affects the feldspars at pressure by lowering the temperatures at which they crystallize from the magma starting with estimates from published literature it becomes obvious that at pressure fayalite becomes important because the pressure effects on the melting temperatures are very different large for albite and small for anorthite in this experimental study a powder of fayalite composition was combined with six finely ground natural feldspars from ab to an 97 to make six bulk compositions using graphite crucibles in piston cylinder apparatus at a pressure of 5 kbar a cotectic in the ternary system was found to range from 1141 c at an fa to 1124 c at ab fa with fayalite contents from 68 to 17 wt respectively the results can be used to show that ternary feldspars saturated with fayalite and fe monoclinic pyroxene will crystallize at a 5 kbar multiphase eutectic 1010 c 56 c below a calculated azeotropic point on the ab or join the results are used to compare the end points of two very different layered intrusions skaergaard and kiglapait and to illuminate the nature and origins of syenite and trachyte which are leucocratic rocks unsaturated with mafic minerals because fayalite saturated melts are responsive to pressure unequally on the feldspar end members olivine of intermediate composition will have a damped but potentially significant effect on feldspar fractionation in the lower crust of the earth possibly affecting the origin of anorthosite and syenite

partitioning of strontium between plagioclase and melt a comment abstract the origin of the partition coefficient d for sr in plagioclase is ascribed by blundy and wood 1991 mainly to the chemistry of the crystal rather than that of the liquid however a major data set used to support this conclusion also demonstrates an important correlation of d with the augite content of the liquid one truth cannot be used to deny another from the same data set moreover it appears that d has a limiting value of 1 0 in the system an ab confirming the importance of liquid composition the data base of natural magmas said to justify the conclusions of the paper omits the important troctolitic and noritic low augite varieties for which the augite effect was specifically claimed and therefore cannot be used to discount the effect the data base is skewed toward silicic igneous rocks for which a high value of d is experimentally known the attempt to rationalize the data from the kiglapait intrusion by supposing the escape of low sr material ignores the evidence of the chilled margin which matches the sr budget of the cumulates and neglects to mention that the vented mass would have to be equal to that of the entire intrusion to account for the small variation in sr observed much work remains to be done but it is clear that the liquid plays a much more important role in this partitioning effect than allowed by the authors

40ar 39ar chronology of the nain anorthosites canada a hornblende 40ar 39ar age of 1328 8 ma has been obtained from the contact aureole of the bird lake massif confirming it as one of the oldest members of the nain plutonic suite this age constrains the timing of the early stage magma activity of the nain plutonic suite plagioclase samples from the intrusions yield either u shaped or staircase shaped 40ar 39ar age spectra and most of them have two isochrons of similar age but greatly different initial argon composition most plagioclase closure ages are 95 of either the hornblende age from a contact aureole or coexisting biotite ages and appear to reflect single cooling events for each intrusion two major stages of emplacement for the nain anorthosites are identified an older anorthosite event and a main anorthosite event in agreement with results from earlier field studies the port manvers run paul island and nukasorsuktokh island intrusions yield much younger plagioclase ages than any previously established intrusion ages probably reflecti

tropospheric precursors and stratospheric warmings abstractmany tropospheric arctic oscillation ao events are preceded by stratospheric ao events and even earlier in time by anomalous upward energy flux associated with rossby waves in the troposphere this study identifies lower tropospheric circulation anomalies that precede large ao events in both the troposphere and stratosphere and the anomalous upward energy flux compositing analysis of stratospheric warming events identifies regional tropospheric precursors which precede stratospheric warmings the tropospheric precursor is found to vary when compositing over polar vortex displacements and splits separately prior to vortex displacements the main anomaly sea level pressure center of the tropospheric precursor is located across northwest eurasia and is associated with the siberian high prior to vortex splits a similar anomaly center is identified in the tropospheric precursor but is weaker and appears to be more strongly related to a shift in the storm tracks differences in the sea level pressu

analysis of factors influencing tunnel deformation in loess deposits by data mining a deformation prediction model abstract due to the special properties of loess the deformation of tunnels constructed in loess is generally large and easily induced to control deformation during construction the degree of influence of multiple factors on tunnel deformation is analyzed by data mining and a deformation prediction model is established based on tunnels along the menghua railway of china both objective environment and manual operation are considered the surrounding rock level groundwater condition burial depth excavation method and support close time are selected as the main factors influencing tunnel deformation the influence degree of each factor is calculated through mining statistical data collected from the project finally using influencing factors as evaluation indices a rough set extension model for predicting loess tunnel deformation is established and tested results obtained via the prediction model are in good agreement with field observations the study quantifies the influence degree of each selected factor on deformation of the loess tunnel which in turn can help in deformation control efforts moreover the rough set extension model realizes a multi criteria prediction of the loess tunnel s deformation and provides a practical guide for construction of similar projects

stratospheric connection to the abrupt end of the 2016 2017 iberian drought southwestern europe experienced extraordinary rainy and windy conditions in march 2018 leading to the end of the most severe drought since 1970 at continental scale this anomalous weather was linked to a persistent negative north atlantic oscillation pattern two weeks earlier a sudden stratospheric warming ssw took place preceded by the strongest planetary wave activity on record in this study we explore the connection between the ssw and the weather shift by employing a weather regime approach and flow analogues the timing of the downward propagation of the stratospheric anomalies the transition to and persistence of the negative north atlantic oscillation weather regime and the sudden precipitation increase are all consistent with the typical tropospheric state after ssws our results evidence a significant role of the 2018 ssw in the record breaking precipitation event

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

kiglapait mineralogy iv the augite series based on twenty five new chemical analyses augites from the upper zone of the kiglapait layered intrusion labrador span the range from en 7 3 to en 0 disposed about a straight line sloping slightly upward from wo 4 0 to wo 4 2 in the pyroxene quadrilateral they contain little tetrahedral al which decreases with fe enrichment as tetrahedral ferric fe 3 increases little or no jadeite or ca tschermaks component is present titanium rises only slightly with fe and the acmite component is scattered near mole fraction 0 03 excess cations relative to 6 oxygen atoms occur chiefly by solid solution toward olivine the only co crystallizing mafic silicate phase values of n increase linearly over the range 1 670 at fictive en 1 0 0 to 1 7448 at en 0 the position of the 150 powder x ray diffraction peak shifts regularly from 5 0372 to 4 1727 degrees away from the 220 peak of silicon metal over the same composition range exsolution of orthopyroxene near 100 is succeeded up stratigraphy by that of pigeonite near 001 and the switch occurs at about the same augite composition as the switch from external orthopyroxene to pigeonite in the skaergaard intrusion exsolution of ilmenite in or near 100 and magnetite ulvospinel near the a and c directions in 010 produces the black color of these augites in hand specimen subsolidus augite olivine tie lines and exchange relations in fe mg allow the distinction between equilibrium pairs and those affected by exchange with external fe ti oxide minerals or with intercumulus liquid in upper border zone lithologies liquids producing augite and olivine with plagioclase follow a ca depletion trend until crystallization of abundant olivine and titanomagnetite drives them on a ca enrichment trend to a point near mg free augite activities of silica consistent with augite olivine pairs range from 0 6 to 0 98 the kiglapait augite series exemplifies the crystallization of a magma occupying the narrow regime between silica saturation and undersaturation in extreme fractionation from troctolite to mg free syenite

fractional crystallization and magma mixing in the tigalak layered intrusion the nain anorthosite complex labrador the tigalak intrusion is a dominantly dioritic layered body about 80 km2 in area which ranges in composition from norite to granodiorite local areas of the layered rocks display upward fractionation from norite to ferrodiorite periodic reversals of mineral composition trends record the emplacement of less fractionated dioritic magma heterogeneous mixtures of dioritic and granodioritic rocks occur widely in mappable lenses and layers that alternate up section and along the strike with more uniformly layered rocks in these mixtures chilled dioritic pillows occur abundantly in a hybrid cumulate matrix of granodiorite to diorite composition cross cutting granodioritic dikes grade upward into stratigraphically bound lensoid masses of the hybrid cumulates it appears that the hybrid rocks formed as a result of the emplacement of the granodioritic magma through lower cumulates into the dioritic magma chamber and that the dioritic pillows represent chilled bodies of ferich dioritic magma that commingled with cooler granodioritic magma and settled to the floor of the tigalak magma chamber

plagioclase fractionation in troctolitic magma troctolitic intrusive rocks poor in augite are common in certain proterozoic anorthosite complexes and related rocks the lower zone of the kiglapait intrusion labrador consists of 1570 km troctolite today and possibly 2900 km before erosion in this augite free lower zone plagioclase fractionation is as low as 1 6 an km of cumulate thickness and averages 3 an km when augite crystallizes after 84 of the magma has crystallized the fractionation becomes as much as 17 an km of cumulate why such a difference it is clear from first principles of phase equilibria that fractionation accelerates with saturation in augite but not so clear that the difference should be so great the answer is to be found in the silica poor nature of troctolitic magma that is critically undersaturated in silica this low silica effect reduces the activity of the nasi albite component relative to the caal anorthite component in the plagioclase thereby favoring the an component of the liquid and crystals and weakening the fractionation process as the normative augite component in the magma rises from the base of the lower zone to the base of the upper zone the activity of silica also rises slightly and its consequent effect on plagioclase composition tends to diminish liquid fractionation paths derived from observed crystal paths when plotted in the system diopside anorthite albite rise across the liquidus fractionation lines toward diopside and reach augite saturation near the 1atm cotectic they produce plagioclase compositions 10 mol higher in an than pure liquidus fractionation lines predict the key criterion for the troctolitic fractionation of plagioclase composition is the absence of ca poor pyroxene from the rocks noritic magmas by contrast have higher activities of silica and more effective fractionation of plagioclase a parallel fractionation of olivine is also retarded in the lower zone by the accumulation of ferric iron in the liquid until augite and titanomagnetite crystallize in the upper zone key word plagioclase fractionation troctolite melts silica activity layered intrusions kiglapait intrusion

kiglapait geochemistry iii potassium and rubidium abstract the regular geometry and completeness of the kiglapait intrusion permit its bulk composition to be obtained by summation and the composition of successive liquids to be obtained by subtraction the summations for k and rb give 1806 and 1 08 ppm yielding r frsol k rb 1670 for the intrusion taken as equal to the parent magma r increases slightly from this initial value to 2000 at the end of crystallization where mgo approaches zero in the rocks k and rb are therefore closely coherent and their distribution coefficients can differ only by a small amount in the kiglapait system apparent feldspar liquid distribution coefficients d f l can be estimated from detailed plots of feldspar and liquid compositions against f l the kiglapait data imply that these coefficients are linear 1 1 functions of plagioclase composition within experimental error having values given by d k f l 1 42 x an d rb f l 1 13 x an with minimum values of 0 75 and 0 49 respectively the ratio r f r l lies in the range of 1 53 0 03 for the plagioclase composition range x an 0 34 to 0 67 showing that high r rocks such as anorthosite crystallized from high r liquids the apparent feldspar distribution coefficients are much closer to 1 0 than common literature values they can be reduced by assuming that the cumulate pile was continuously recharged by the circulating magma until an advanced stage of differentiation was reached and assuming that alkalies were exchanged to the feldspars from the magma when such an aquifer recharge model is calibrated using olivine liquid equilibria as a time marker for the liquid the inferred minimum equilibrium values of the distribution coefficients are d k f l 0 42 d rb f l 0 25 at the base of the intrusion their variation is given by d k f l 1 66 1 88x an d rb f l 1 17 1 41x an the equilibrium values are considered to be appropriate for deducing liquid compositions in plutonic bodies where alkali exchange can be shown or inferred to have been inhibited such as in small intrusions the apparent values are considered to be appropriate even though they may be artificial for large intrusions similar to the kiglapait the bulk k and rb concentrations in the kiglapait intrusion are consistent with a plagioclase rich abyssal tholeiite magma clinopyroxene and olivine fractionation in the mantle may contribute to the production of such high r magmas

microstructural evolution of silicate immiscible liquids in ferrobasalts an experimental study of the microstructural evolution of an immiscible basaltic emulsion shows that the fe rich liquid forms homogeneously nucleated droplets dispersed in a continuous si rich liquid together with droplets heterogeneously nucleated on plagioclase magnetite and pyroxene heterogeneous nucleation is likely promoted by localised compositional heterogeneities around growing crystals the wetting angle of fe rich droplets on both plagioclase and magnetite increases with decreasing temperature droplet coarsening occurs by a combination of diffusion controlled growth and ostwald ripening with an insignificant contribution from coalescence characteristic microstructures resulting from the interaction of immiscible fe rich liquid with crystal grains during crystal growth can potentially be used as an indicator of liquid unmixing in fully crystallised natural samples in magma bodies 10 m in size gravitationally driven segregation of immiscible fe rich droplets is unlikely to be significant

the deformation evaluation of kizlac t3a tunnel osmaniye turkey abstract this study covers the graphical analysis of deformation values measured in the kizlac t3a tunnel osmaniye turkey which was built as a part of the tarsus adana gaziantep motorway project excavation was performed through a sequence which was composed of sandstone shale alternation sandstone and dolerite dyke horizontal longitudinal and settlement deformation values were optically read and recorded daily on a computer these data were evaluated according to new austrian tunneling method total deformation measurement risky area determination and forecast of transitions between weak and stiff rock stiff and weak rock were assessed as a result of deformation evaluation for tunnel stability safety and economy the largest resultant deformation value 13 mm was measured in the sandstone shale alternation between chainage 500 and 550 m which was highly weathered by groundwater and affected by local tectonic disturbance the smallest deformation value was observed in a stiff dolerite dyke between 370 and 430 m where at times the deformation values decreased to zero in the sandstone small resultant deformation values 2 4 mm were also recorded the 500 550 m interval of tunnel alignment had the highest risk for tunnel instability in the studied section but the deformation values maximum 13 mm were within the tolerable deformation range 10 cm small negative longitudinal deformation values decreasing between chainage 320 and 370 m and small positive longitudinal deformation values decreasing between 420 and 480 m indicate the sandstone shale alternation weak rock and the dyke stiff rock and sandstone stiff rock and the sandstone shale alternation with a fault gauge zone weak rock respectively these longitudinal deformations needed probable to predict the lithological transitions ahead of the face which in timely were used to determination of the tunnel support system

experimental equilibrium tested by plagioclase loop widths are solid and liquid respectively and an is the mole fraction or per cent an an ab it is measured from the plagioclase composition and an estimate of the liquid composition based on standard assumptions rooted in the norm recalculation routine a survey of a large new database allows study of the 1 atm experimental literature involving 819 experiments the approach to equilibrium is tested empirically by the loop width and its transform the linear partitioning function kd this function is the exchange coefficient formed as the intercept at pure an s from the array over all x s of the partition coefficient d when defined as x s x l w herex is the mole fraction d and kd are thus limited to lie between zero and 1 0 the results show a 1atm loop width ranging from 0 2t o 68 mol a n with associated kd 0 03 0 98 these extrema represent loops both far too small and far too large to represent stable equilibrium between plagioclase and liquid some of the higher values lie near the persodic limit because the an component of the liquid is scarce and the liquid composition is ab rich the loops from ne normative liquids span the range from 40 to 90 mol an in the crystal with loops 2 50 mol wide a baseline for loop width is derived from the precise synthetic study of the system di an ab at 1atm and an array of high pressure data that extrapolates to the same value of kd 0 26 at 1atm many of the 1atm experimental data fall far outside any reasonable uncertainty limits on the baseline causes of departure include crystal disequilibrium that can lead to errors in both directions and compositional problems comparison of the values of kd with liquid compositions in silica oxygen fugacity temperature kinetics and sodium reveals the common presence of sodium deficiency a crystallinity study shows a definite decrease in sodium content with liquid evolution whereas the sodium content should increase or at least remain nearly constant with evolution of the melt a selection of self consistent 1atm data from a few laboratories shows a close correspondence to the standard distribution of loop widths and indeed most literature data lie within the limited range of kd 0 26 0 4 experiments known to be hydrous show very low values of kd and corresponding large loop widths as previously understood from literature data when data limited to nearbaseline kd values are plotted against temperature they yield expected thermal slopes and concave up curves of temperature plotted against plagioclase composition literature data show a positive correlation of kd with dry pressure and a separate database from 2 to 15 kbar shows that more than half the data comport with this pressure effect a different group ranges down to kd as low as 0 2 with increasing loop widths some of these are alkalic and hence rich in the ab component of the liquid others were obtained in fe containers that control the oxygen fugacity to low values and convert the fayalite component of the liquid to iron oxygen and silica this reaction increases the activity of silica and in turn the activity of ab in the melt thus widening the loop thermodynamic studies concerned with plagioclase melt equilibria will profit from an awareness of these effects

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

crystallization sequence and magma chamber processes in the ferrobasaltic sept iles layered intrusion canada the sept iles layered intrusion quebec canada 564 ma is a large plutonic body with a diameter of 80 km and a thickness of 6 km made up from its base to top of a layered series with troctolite and gabbro and an upper border series with anorthosite capped by cupolas of a type granite chilled margin compositions suggest a ferrobasaltic parental magma close to that of the skaergaard intrusion but much richer in iron and titanium samples from drill cores and surface sampling of the 4 7 km thick layered series reveal a succession of massive troctolites and layered gabbros that contain 24 fe ti oxide layers cm to m thick and many anorthositic autolithic blocks the sequence of crystallization in the layered series is plagioclase an72 34 and olivine fo75 21 followed by magnetite and ilmenite then ca rich pyroxene and finally apatite an olivine gap is observed between fo66 and fo59 the saturation of fe ti oxides before ca rich pyroxene is interpreted to be the result of the high feot and tio2 contents and the low cao content of the parental magma contamination by old continental crust has occurred during crystallization of the layered series as indicated by sr isotopic compositions 87sr 86sr564 0 70360 0 70497 the differentiation trend of the intrusion is interrupted by two large and many small reversals to more primitive compositions of cumulus phases cr content of magnetite and lower sr isotope ratios these reversals and the intermittent disappearance of some phases are interpreted as resulting from magma chamber replenishments by undifferentiated primitive basaltic magma and mixing with the resident magma the author 2010 published by oxford university press all rights reserved for permissions please e mail journals permissions oxfordjournals org

solidification of trapped liquid in rocks and crystals trapped liquid in an igneous cumulate solidifies over a range of time and temperature that can be retrieved by use of the lever rule in binary solutions applied to plagioclase using the range in the an content found for the individual rock studied the an range so called when measured in sufficient detail defines the solidification history the instantaneous solid composition along the solidus defines the zoning of the plagioclase as it follows the trapped liquid on the liquidus the reference bulk composition of the trapped liquid is given by an intercept on the initial solid liquid lever defined by the fraction of plagioclase in the trapped parent magma times the residual porosity the mafic fraction is assumed to solidify by reaction independently of the plagioclase zoning the residual porosity is estimated from the content of evolved components in the trapped liquid and can also be calculated from the an range itself when that is calibrated to a value independently determined from the evolved components examples from a recent treatment of residual porosity are given for the solidification of selected rock compositions from the kiglapait and skaergaard intrusions the same principles apply to the solidification of melt inclusions with the difference that the latter tends to sample an evolved sheath by capture rather than a parent magma trapped by closure of a cumulate because only the cumulate has had time to exchange the evolved rejected solute owing to its slow solidification experimental examples of melt inclusions trapped at liquidus conditions demonstrate the highly evolved composition of the sheath compared to the bulk glass composition the application of the solidification principle to presumed liquid immiscibility in the skaergaard intrusion suggests that the melt inclusions are evolved during the capture process and then solidified as given by the an range in the plagioclase the hypothesis of liquid immiscibility is not needed in this analysis the very different end stage feldspar histories of the two intrusions is attributed to the sequestering of low melting feldspar components in the trapped liquids of the skaergaard cumulates compared to the lesser amounts trapped in the kiglapait cumulates

a partisan review of proterozoic anorthosites most anorthosites of the massif type crystallized in the episode 1 7 1 2 gyr with a pronounced peak of the age distribution near 1 4 gyr they were emplaced anorogenically at depths as shallow as 7 km where the ambient temperature of country rocks was probably less than 250 c depths of emplacement may have been as great as 25 km or more in rare cases the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths but in any case they are demonstrably not required or characteristic of anorthosite emplacement penetrative deformation and metamorphism of anorthosites are post emplacement accidents of the local geologic history and are not directly caused by the presence of anorthosites granitic rocks mangerite charnockite suite associated with anorthosite are in general later or contemporaneous products of crustal anatexis with chemical and isotopic signatures distinct from the anorthosites and their residua such granitic rocks should not therefore be summed with the anorthositic rocks to obtain bulk compositions the magmas that produced most anorthosites were dry as shown by high temperature mineralogy and anhydrous mineral assemblages in contact aureoles residua from their crystallization are ferrodiorites to ferrosyenites typical of closed system fractionation these residua were locally and frequently ejected into contemporaneously molten granite where they formed pillows and cooled rapidly the overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle olivine bearing magmas locally ranged from leucotroctolite anorthosite to later but coexisting picrite or melatroctolite in the same pluton confirming a wide spectrum of magma types a signal feature of troctolitic and noritic magmas is their low augite content implying high content of spinel component large anorthosite complexes such as nain and harp lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry the abundant true anorthosites richer in plagioclase than magmas cosaturated with a mafic phase must represent plagioclase enrichment by either mechanical or chemical processes or both the role of kinetics in nucleation and solidification of such rocks may be centrally important it is proposed that hyperfeldspathic plagioclase supersaturated liquids were generated by quasi isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth s mantle

geochemistry of the nain massif anorthosite labrador magma diversity in five intrusions abstract the petrography and major and trace element concentrations of the anorthositic bird lake massif blm susie brook slab sbs lister massif lm port man vers run pmr and kikkertavak area kik in the nain plutonic suite nps labrador delineate the mineralogical and composition ranges of these large intrusions from these a variety of magmas and staging histories can be inferred the blm and sbs are mainly noritic anorthosites of the western region exposed along tikkoatokhakh bay tik tilting and stretching deformation distinguish sbs from blm but the two units show no mineralogical or chemical differences the kik and pmr intrusions are mainly troctolitic to noritic anorthosites of the eastern region and they contain more mafic components than the tik bodies chemically all the anorthositic rocks are high in ba sr and the ratio k rb and low in zr rb and rb sr the three plutonic bodies blm sbs and lm along tik are similar and can be clearly distinguished from kik and pmr intrusions by element concentrations and ratios diagrams of element pairs show that each intrusion or group has its own evolutionary trend and variable style indicating that they represent independent magma batches rather than fractionally related volumes of the same magma ree patterns show light ree enrichment and heavy ree depletion and strong positive eu anomalies correlated with cumulus plagioclase in chemical comparison with adjacent plutons one pmr chilled leucotroctolite after subtraction of 18 cumulus plagioclase is similar to the kiglapait magma ki one melatroctolite in kik is close to the comb layered melatroctolite of the snowflake zone in the hettasch intrusion hi and the average leucotroctolite and leuconorite in kik are similar to the leucotroctolite unit and the upper leuconorite respectively at paul island pi therefore the magmas from pmr and kik are similar to those of wellknown troctolitic bodies and their feldspar rich cumulates kik differs from pmr in having somewhat higher an and xmg values all these lines of evidence show that at least three types of magma existed in the study area sodic noritic magma accumulating plagioclase in tik troctolitic magma in kik and a magma similar to but more evolved than kik in pmr the methods used also illustrate the feasibility of characterizing magma compositions from diverse types of cumulates regional differences in modal and chemical composition occur in the nps noritic compositions with pale plagioclase are located in the western and southern regions and troctolitic compositions with darker plagioclase are located in the eastern region a reasonably accurate boundary can now be drawn between the two regions which differ in the nature of their transport from the mantle in comparison with a primitive mantle composition high ba pb k sr ti and low rb nb zr in the nain anorthositic rocks are distinctive these anomalies and the isotopic results of other investigators are consistent with mantle source enrichment followed by variable contamination during magma ponding at the base of the depleted crust

mining induced fault reactivation associated with the main conveyor belt roadway and safety of the barapukuria coal mine in bangladesh constraints from bem simulations fault reactivation during underground mining is a critical problem in coal mines worldwide this paper investigates the mining induced reactivation of faults associated with the main conveyor belt roadway cbr of the barapukuria coal mine in bangladesh the stress characteristics and deformation around the faults were investigated by boundary element method bem numerical modeling the model consists of a simple geometry with two faults fb and fb1 near the cbr and the surrounding rock strata a mohr coulomb failure criterion with bulk rock properties is applied to analyze the stability and safety around the fault zones as well as for the entire mining operation the simulation results illustrate that the mining induced redistribution of stresses causes significant deformation within and around the two faults the horizontal and vertical stresses influence the faults and higher stresses are concentrated near the ends of the two faults higher vertical tensional stress is prominent at the upper end of fault fb high deviatoric stress values that concentrated at the ends of faults fb and fb1 indicate the tendency towards block failure around the fault zones the deviatoric stress patterns imply that the reinforcement strength to support the roof of the roadway should be greater than 55 mpa along the fault core zone and should be more than 20 mpa adjacent to the damage zone of the fault failure trajectories that extend towards the roof and left side of fault fb indicate that mining induced reactivation of faults is not sufficient to generate water inflow into the mine however if movement of strata occurs along the fault planes due to regional earthquakes and if the faults intersect the overlying lower dupi tila aquiclude then liquefaction could occur along the fault zones and enhance water inflow into the mine the study also reveals that the hydraulic gradient and the general direction of groundwater flow are almost at right angles with the trends of faults fb and fb1 which could act as barriers to groundwater flow into the mines

regional ai fe mafic magmas associated with anorthosite bearing terranes proterozoic anorthosite massifs are nearly monomineralic accumulations of plagioclase feldspar which must result from unusual conditions of crystallization and emplacement1 2 their chemistry is compatible with derivation from a high alumina basalt parent of mantle origin1 and mafic magmas rich in aluminium and iron have long been suspected of having an important connection to anorthosites and their parent magmas1 4 regional examples of mafic magmas clearly compatible with an anorthosite lineage have not been generally recognized3 in part because of the paucity of candidates within the anorthosite massifs themselves samples of such magmas should also be sought in the country rocks surrounding the massifs here we report the widespread occurrence of al fe mafic magmas in the anorthosite bearing adirondack highlands of new york state they are chemically distinct from typical high ai basalt fe basalt and most common magma types identification of similar al fe basaltic magmas in other areas suggests that such magmas are characteristic of anorthosite bearing terranes

the internal magma reservoir of large intrusions revealed by multiphase rayleigh fractionation the fractionation progress of a crystallizing basaltic magma is recorded in the changing mineral compositions of binary solutions that form a part of plagioclase olivine and augite when such compositional data are plotted against an independent measure of progress such as volume they can often be described by a rayleigh equation that reveals details of the crystallization history a binary solution crystallizing by itself follows a path determined by the rayleigh exponent d 1 where d is the partition coefficient x1 x1 l x is mole fraction 1 is low melting component l is liquid s is solid in company with another phase however such a binary solution may follow a wide range of paths in an envelope about d 1 ranging from a f d 1 to b d 1 f where f is the fraction of the active phasecthe binary solution under consideration the upper limiting curve an extended fractionation path is given by a above whereas a full x2 depletion path b defines the lower limit this range of alternatives is here codified and supplemented by considerations of residual porosity the result is a rayleigh equation in five variables that can illuminate magmatic history including the probability of the existence of an internal reservoir that damps the depletion effect the range of paths can help to identify evidence for and causes of leading edge fractionation of ascending magma small packet crystallization pressure variations off cotectic excursions and oscillating modal variation

plagioclase an range and residual porosity in igneous cumulates of the kiglapait intrusion the range in an content of plagioclase in grain mounts of igneous cumulates provides a measure of diversity that is uniquely preserved in plagioclase because of its well known refractory nature to a first approximation such data provide when calibrated an estimate of the residual porosity or fraction of trapped liquid in each specimen the ensemble of specimens then provides a model for the stratigraphic variation of residual porosity the raw data however include pre cumulus zoning that can be isolated from in situ zoning by textural analysis in thin section the baseline of residual porosity determinations was earlier determined for the lower zone of the kiglapait intrusion from the content of excluded components in the solid rock compared with their content in the melt as calculated by summation and rayleigh fractionation the baseline equation was then used to calibrate the residual porosity obtained from the an range in grain mounts this calibration is now extended to the remainder of the intrusion the an range and the calculated residual porosity decrease to zero at 99 solidified pcs and then rise to the end of crystallization the data suggest initial porosities smaller than 0 35 allowing for pre cumulus zoning the data suggest a dominance of adcumulates in the intrusion and these impermeable barriers occupy 75 of the rocks in the lower zone they occur at intervals of 1 to rarely 15 m and thereby restrict the likelihood of compaction over thick mushy zones variations in the fo range of olivine are also observed in grain mounts and they follow those in plagioclase however they are in part due to subsolidus equilibration with fe ti oxides and augite the new calibration is successfully applied to the skaergaard intrusion to supplement the published results from excluded components with some interesting contradictions

anorthosites of diverse magma types in the puttuaaluk lake area nain complex labrador helikian anorthositic rocks in the puttuaaluk lake area labrador are in contact with granitic rocks of similar age and basement granulites of archean age internal variation within the anorthositic rocks has led to their subdivision into anorthosite leuconorite and oxide rich anorthosite which suggests three separate intrusive events and at least three magma types the major differences among the anorthositic rocks are that anorthosite typically carries augite leuconorite carries orthopyroxene augite and oxide rich anorthosite carries ilmenite magnetite with minor orthopyroxene plagioclase compositions plotted in the system ab an or lie within 3 mol or of the ab an join and regression analyses for anorthosite and leuconorite show a slight decrease of k with decreasing an hence a distribution coefficient dkplag liq 1 0 is implied for the anorthositic parent magmas the average modal composition of the leuconorite assuming 1 ilmenite is 23 orthopyroxene and 76 plagioclase volume per

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

further work on experimental plagioclase equilibria and the skaergaard liquidus temperature equilibria between plagioclase and ferrobasaltic melt in low pressure dry melting experiments can be demonstrated near the liquidus further analyses of melting experiments using optimized beam conditions reveals that previous data for understanding the skaergaard intrusion potentially suffered from the analytical inclusion of non equilibrated components in the average plagioclase compositions new reversal experiments demonstrate convergence between plagioclase rim compositions in melting and crystallization products for a ferrobasaltic melt and thus support equilibrium relations the new data set provides tighter bounds on experimental plagioclase composition and documents composition dependent partitioning of na and ca between plagioclase and melt application of the results to modeling the skaergaard requires only minor adjustments to the previously proposed liquidus temperatures and liquid line of descent

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

isotopic evidence from the eastern canadian shield for geochemical discontinuity in the proterozoic mantle most workers agree that proterozoic anorthosite massifs represent the crystallization products of mantle derived magmas1 2 although the composition of the parental melts is a major unsolved petrological problem3 as mantle derived rocks the massifs can be used as geochemical probes of their late precambrian upper mantle sources we report here nd and sr isotopic compositions of anorthosites and related rocks from the grenville and nain provinces of the eastern canadian shield here 75 of the earth s known anorthosite is found in a 1 600 km belt from the adirondack mountains of northern new york state to the eastern coast of labrador4 fig 1 the results indicate that the massifs were derived from at least two distinct mantle source regions which were established before 1 650 myr ago and were episodically involved in magmatism over 500 myr one reservoir below the grenville province and probably below much of the eastern superior province was isotopically similar to the depleted modern day mid ocean ridge basalt morb source the other reservoir was chondritic to moderately enriched and is most easily identified in the nain province but may have occurred scattered throughout the superior province

proterozoic massif type anorthosites as the archetypes of long lived 100 myr magmatic systems new evidence from the kunene anorthosite complex angola abstract proterozoic massif type anorthosites are voluminous plagioclase dominated plutonic suites with characteristic intermediate compositions an50 10 that represent mantle derived magmas ponded at moho depths and crystallized polybarically until emplacement at mid crustal levels we present new id tims and la icpms u pb ages as well as detailed field observations from the kunene anorthosite complex kac of sw angola our main objective in this work is to contextualize a variety of important petrographic and geochronological features of the kac that have implications for proterozoic anorthosite petrogenesis and the geological evolution of the sw congo craton high precision u pb zircon and baddeleyite ages for anorthositic rocks from across the complex n 11 range between 1376 and 1438 ma a period of 60 myr showing that such systems may be remarkably long lived dating of magmatic zircons from a comagmatic pegmatoidal enclave in the kac which also contains high al orthopyroxene megacrysts haom gives an age of 1500 ma indicating as much as 120 myr between some of the earliest and latest crystallization products of the system these enclaves provide a snapshot of the liquid line of descent of the anorthosites and are compelling evidence for the comagmatic nature of the haom field evidence for block structure magma mingling and extreme textural heterogeneity in the kac supports emplacement as multiple influxes of magma of various volumes carrying variable proportions of crystals and autoliths from below we infer that the kac represents a long lived mushy magmatic system that was likely emplaced in distinct pulses these observations refine our understanding of proterozoic anorthosite petrogenesis they also provide evidence for an array of magmatic processes operating at various levels of crystallinity that may create textural and chemical heterogeneity in evolving magma products at lower to mid crustal levels

kiglapait geochemistry vii yttrium and the rare earth elements abstract based on 51 wholerock analyses by xrf and summation over the layered group the kiglapait intrusion contains 4 7 1 6 1 2 ppm y which resides principally in augite and apatite using liquid compositions calculated by summation the partition coefficient daug ly is 0 95 0 12 from 84 to 97 pcs percent solidified and 1 5 0 4 above 97 pcs for feldspar the most likely value for d is 0 028 0 02 n 6 ree analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs pcs summations over the rocks of the layered group gave la 2 5 ce 5 8 nd 3 9 sm 1 0 eu 0 8 tb 0 17 yb 0 37 and lu 0 06 ppm with 2 s d errors near 30 all these elements are highly incompatible until the arrival of augite which affects chiefly the hree and apatite which affects all but more strongly the lree the net result is that after apatite arrival at 94 pcs the liquid compositions are nearly constant hence dwr lree 1 0 these results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar olivine augite apatite and fe ti oxide minerals for pre apatite liquids dfsp lree vary regularly with the normative di content of the liquid and change by an order of magnitude hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids the eu anomaly at first decreases in kiglapait liquids due to plagioclase fractionation but then increases due to removal of augite and apatite with negative eu anomalies the features dominantly responsible for eu partitioning are liquid structure and for monoclinic ternary feldspars crystal structure the former is best monitored by the augite or diopside content of the liquid and the latter by the k content of the feldspar the chondrite normalized ree pattern for the intrusion has lan 7 4 lun 1 6 ce yb n 3 6 and eu eu 2 4 indicating its feldspar rich nature the chilled margin of the nearby hettasch intrusion has a similar but more evolved pattern corresponding roughly to the kiglapait liquid at 70 pcs as with other data those for the ree suggest source differences for the two intrusions rather than a relationship due to fractionation

kiglapait mineralogy v feldspars in a hot dry magma the lithology of the 1 305 ga kiglapait intrusion is dominated by a lower zone of troctolite succeeded by an upper zone of olivine gabbro ferrodiorite and syenite with olivine composition of pure fayalite the feldspar composition of the intrusion varies from an 68 to an 9 over a thickness of 8 4 km from the base to a sandwich horizon under an upper border zone the anhydrous nature of the kiglapait syenites is shown by their high temperature by the loss of minor biotite up stratigraphy in the intrusion and the absence of amphibole the end stage feldspar of the kiglapait syenites is that of a solidus embedded in a solvus in a 3 kbar eutectic at 1000 c the end member assemblage at temperature and pressure is invariant the final bulk composition is relatively an rich an 11 with a composition of x or 1 3 when projected to the ab or sideline the experimental feldspar solvus when corrected for the effects of an and ba and referred to 3 kbar penetrates the solidus and fits the experimental tie lines these conditions precede a stage of local coarsening under subsolidus conditions that is found in colloform symplectites invading mesoperthite the oligoclase orthoclase symplectites are iso compositional with their host mesoperthites the coarsening is assumed to be related to a plausibly f rich vapor phase that is locally consumed with time the observed phase compositions indicate the end of exsolution at 800 c at 3 kbar on the binodal solvus

marginal rocks resembling the estimated bulk composition of the kiglapait intrusion abstract the southern margin of the kiglapait intrusion labrador contains fine grained rocks 5 6 m above a contact with anorthosite of the nain complex and a laminated unit 3 m from the contact three fine grained samples and one of the laminated unit have a mean composition closely resembling that previously calculated by summation of the exposed layered group analyzed values agree closely with the earlier estimates for alkalies sr and y thus they support the mineral liquid partition coefficients previously calculated for these elements and for the rare earth elements based on new calculations the value for ferric oxide is revised to 1 04 from its original value of 1 91 the new samples are depleted in the incompatible elements titanium and phosphorus suggesting that they have lost some residual liquid by sidewall fractional crystallization and downward motion of rejected solute the marginal rocks provide no evidence for repeated injection of magma during lower zone time

sr nd and pb isotopes in proterozoic intrusives astride the grenville front in labrador implications for crustal contamination and basement mapping abstract we report sr nd and pb isotopic compositions of mid proterozoic anorthosites and related rocks 1 45 1 65 ga and of younger olivine diabase dikes 1 4 ga from two complexes on either side of the grenville front in labrador anorthositic or diabasic samples from the mealy mountains grenville province and harp lake nain churchill provinces complexes have very similar major minor and trace element compositions but distinctly different isotopic signatures all mealy mountains samples have isr 0 7025 0 7033 end 0 6 to 5 6 and pb isotopic compositions consistent with derivation from a mantle source depleted with respect to nd sm and rb sr pb isotopic compositions for the mealy mountains samples are slightly more radiogenic than model mantle compositions all harp lake samples have isr 0 7032 0 7066 end 0 3 to 4 4 and variable but generally unradiogenic 207pb 204pb and 206pb 204pb compared to model mantle suggesting mixing between a mantle derived component and a u depleted crustal contaminant crustal contaminants are probably a variety of archean high grade quartzofeldspathic gneisses with low u pb ratios and include a component that must be isotopically similar to the early archean 3 6 ga uivak gneisses of labrador or the amitsoq gneisses of west greenland this would imply that the ancient gneiss complex of coastal labrador and greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the labrador trough if harp lake and mealy mountains samples were subjected to the same degree of contamination as suggested by their chemical similarities then the mealy contaminants must be much younger probably early or middle proterozoic in age the labrador segment of the grenville front therefore appears to coincide with the southern margin of the archean north atlantic craton and may represent a pre mid proterozoic suture