circulation in drake passage revisited using new current time series and satellite altimetry 1 the yaghan basin circulation in the yaghan basin

shisha pangma leucogranite south tibetan himalaya field relations geochemistry age origin and emplacement the shisha pangma pluton forming most of the xixabangma 8027 m massif in south tibet is one of the 20 larger leucogranite intrusives that mark the highest structural levels of the himalayan metamorphic core the pluton occurs immediately below the shisha pangma detachment a strand of the south tibetan detachment std system a low angle 30 north dipping normal fault placing paleozoic black slates atop sillimanite grade pelites and calc silicate rocks k feldspar augen gneisses containing fibrolite and sillimanite paragneisses along the footwall show strong internal s c fabrics indicative of down to the north extension the shisha pangma leucogranite is a heterogeneous polyphase intrusion with an earlier foliated biotite rich phase and a later tourmaline muscovite rich phase typically containing the assemblage kfs pl qtz ms tur gt bt sil ap the highly peraluminous granites have high 87sr 86sr ratios 0 738 0 750 typical of pelite derived anatectites nd depleted mantle model

boron cycling by subducted lithosphere insights from diamondiferous tourmaline from the kokchetav ultrahigh pressure metamorphic belt abstract subduction of lithosphere involving surficial materials into the deep mantle is fundamental to the chemical evolution of the earth however the chemical evolution of the lithosphere during subduction to depth remains equivocal in order to identify materials subjected to geological processes near the surface and at depths in subduction zones we examined b and li isotopes behavior in a unique diamondiferous k rich tourmaline k tourmaline from the kokchetav ultrahigh pressure metamorphic belt the k tourmaline which includes microdiamonds in its core is enriched in 11b relative to 10b 11b 1 2 to 7 7 and 7li relative to 6li 7li 1 1 to 3 1 it is suggested that the k tourmaline crystallized at high pressure in the diamond stability field from a silicate melt generated at high pressure and temperature conditions of the kokchetav peak metamorphism the heavy isotope signature of this k tourmaline differs from that of ordinary na tourmalines in crustal rocks enriched in the light b isotope 11b 16 6 to 2 3 which experienced isotope fractionation through metamorphic dehydration reactions a possible source of the heavy b isotope signature is serpentine in the subducted lithospheric mantle serpentinization of the lithospheric mantle with enrichment of heavy b isotope can be produced by normal faulting at trench outer rise or trench slope regions followed by penetration of seawater into the lithospheric mantle serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy b isotope signature which was acquired during the serpentinization prior to subduction the fluids could ascend and cause partial melting of the overlying crustal layer and the resultant silicate melt could inherit the heavy b isotope signature the subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle

badrinath gangotri plutons garhwal india petrological and geochemical evidence for fractionation processes in a high himalayan leucogranite the gangotri leucogranite is the western end of the badrinath granite one of the largest bodies of the high himalayan leucogranite belt hhl it is a typical fine grained tourmaline muscovite biotite leucogranite the petrography shows a lack of restitic phases the inferred crystallization sequence is characterized by the early appearance of plagioclase quartz and biotite and by the late crystallization of the k feldspar this suggests that in spite of being of near minimum melt composition the granite probably had long crystallization or melting interval in agreement with previous experimental studies tourmaline and muscovite have a mainly magmatic origin even though the major element composition is homogeneous there are several geochemical trends when cao decreases there is an increase in na2o rb sn u b f and a decrease in k2o fe2o3 tio2 sr ba zr ree th which are best explained by a fractionation process with early crystallizing phases experimental solubility models for zircon and monazite in felsic melt support a magmatic origin for these two accessory phases as well rb sr isotope data show this granite to have like other hhl heterogeneous isotopic values for sr initial 87sr 86sr ratios calculated at 20 ma range between 0 765 and 0 785 therefore no mixing i e no convection occurred between the different batches of magma in contrast 18o data show little variation 13 04 0 25 implying a source with homogeneous 18o values differences in timing between fluid infiltration and the onset of melting related to differences in temperature of the source could explain why source homogenization occurred for the gangotri and not for the manaslu granite the use of experimental results for solubility and the position of the accessory minerals during melting predict a low viscosity for the melt during its extraction this in turn explains the lack of restitic phases major and accessory in the granite as well as some field features lensoid shape pronounced magmatic layering based on the petrographic and isotopic studies it is suggested that the mechanism of ascent was not diapiric but rather that the melt ascended along several fractures and the level of emplacement was partialy controlled by the density contrast between the melt and host rocks

boron in granitic magmas stability of tourmaline in equilibrium with biotite and cordierite experiments at 750 c 200 mpa h2o a h2o 1 and fo2 ni nio established that the equilibrium among tourmaline biotite cordierite and melt spinel aluminosilicate or corundum occurs with 2 wt b2o3 in strongly peraluminous melt with an aluminosity measured by the parameter asi of 1 2 the experiments demonstrate the relationship of tourmaline stability to the activity product of the tourmaline components boron and aluminum which are inversely related to one another tourmaline is unstable in metaluminous to mildly peraluminous melts asi 2 wt b2o3 in their bulk magmas

differentiation of strongly peraluminous perphosphorus granites the pedrobernardo pluton central spain the pedrobernardo pluton 295 2 ma initial 87sr 86sr 0 7122 is a layered sheet like granite body with distinct vertical zoning biotite muscovite bearing granites in the lower zone muscovite biotite leucogranites in the middle zone and muscovite bearing aplites and pegmatites in the upper zone the magma was anatectically generated intruded almost free of restite and evolved as a closed system by crystallization in situ geochemical modelling indicates that the lower and middle zones followed an equilibrium crystallization path with no separation between solids and melt and the upper zone followed a fractional crystallization path magmatic fractionation produced leucocratic differentiates with high p concentrations and a p ca ratio higher than in apatite the excess p is located in plagioclase and k feldspar monazite apatite fractionation in the lower and middle zones produced extreme depletions in th u y and the rees and chondrite normalized ree patterns with low lrees hrees and a slight discontinuity between nd and sm about 90 of the th u y and rees reside in accessory minerals especially in monazite biotite and muscovite have very low ree contents with small positive or no eu anomalies k feldspar and plagioclase in both the lower and upper zones have moderate ree contents with positive eu anomalies feldspars from the upper zone in contrast have negative eu anomalies and have very low ree contents compared to available data from literature dsr ba th u y reesbio mineral are lower by one to three orders of magnitude and dreesplag kfsp are also lower by one order of magnitude these huge discrepancies are attributed not only to contamination with ree rich inclusions in mineral concentrates used in previous studies but to real differences in geochemical behavior of trace elements in peraluminous systems with respect to subaluminous systems biotite melt and probably k feldspar melt distribution coefficients for th u y and the rees in peraluminous magmas must be much lower than previously considered

the geochemistry of phosphorus in granite rocks and the effect of aluminium phosphorus has been shown to have a profound influence on the evolution of silicate melt systems it also controls the geochemical behavior of rare earths uranium thorium strontium and other elements through the relationships between melt and accessory phosphates based on experimental data harrison and watson 1984 proposed a model of saturation behavior of apatite in crustal melts as a function of temperature and silica content subaluminous granites fit in well with such a model but departures are evident in the case of peraluminous granites a systematic study of the distribution of p2o5 in granitoids from all over the world shows that there are two modes to describe phosphorus enrichment in peraluminous granitic rocks 1 the hoyos type trend which is parallel to the one in harrison and watson s hw model but with higher p2o5 concentrations at the same silica contents and 2 the pedrobernardo type trend implying an increase in phosphorus in the most sio2 rich differentiates of strongly peraluminous low ca granites pedrobernardo type leucogranites are characterized by the presence of rare phosphates or p rich feld spars since they have excess p2o5 over cao to form normative apatite we here propose the term perphosphorous granites high phosphorus contents appear to be due to elevated apatite solubility in peraluminous granitic melts rather than to high amounts of restitic apatite both the hoyos and pedrobernardo type departures from the hw model can be corrected by using the expression p2o5corrected p2o5hw efactor where p2o5hw is the prediction according to the hw model and factor is asi 1 6429t asi being the al2o3 cao na2o k2o molar ratio we suggest that such departures could be caused by a decrease in the ca activity in the melt as a result of increased peraluminousity the pedrobernardo type trend is a limiting case in which ca activity in the melt is nearly zero and calcium instead of phosphorus becomes the essential structural constituent esc of the apatite when this happens phosphorus starts behaving as an incompatible element that is concentrated in late fluids high p2o5 contents are more characteristic of s than other granite types no significant departures from the hw model have been found for i a or m type granites in central iberia granites associated with u sn and w mineralizations usually have high phosphorus contents values of p2o50 5 wt at sio270 wt are good indicators of economic mineralization

geochemical modeling of low melt fraction anatexis in a peraluminous system the pena negra complex central spain abstract a study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt fraction cordieritic granites from migmatized meta greywackes the aims of the study were to 1 reveal the fractionation patterns of major and trace elements 2 compare the major element chemistry of leucogranites and the quantitative behavior of source minerals during anatexis inferred by mass balance adjustment with available experimental data for peraluminous systems and 3 discuss the behavior of trace elements in crustal melting by comparing the chemically determined composition of leucogranites with the results of three fractionation models two of these assume a perfect diffusive behavior of trace elements within residual solids but they use a different set of distribution coefficients the third assumes a perfect nondiffusive behavior in relation to their source rocks the leucogranites are strongly depleted in li transition elements and light rare earth elements but enriched in k2o sio2 and ba the k rb ratio in leucogranites is higher than in sources and reaches values typical of high grade metamorphism mass balance analysis using the anatexis mixing model shows that the chemistry of cordierite leucogranites is compatible with its having originated by closed system water undersaturated anatexis on previously migmatized meta greywackes leaving a residue enriched in cordierite plus biotite and exhausted in k feldspar biotite melts congruently unless important amounts of sillimanite were also present in the source compared with experimental melts obtained from sources with the same chemical composition but with a different femic mineralogy biotite sillimanite instead of cordierite biotite the pena negra leucogranites are richer in k2o and mgo with a lower fe fe mg ratio the differences in magnesium are believed to result from the changes in the mineral assemblage of the source rocks however the differences in potassium contents are still not well understood the behavior of trace elements during anatexis cannot be modeled by trace element fractionation equations because of the sluggish diffusion kinetics of trace elements at the temperature of anatexis making the melting rate of minerals greater than the diffusion rate of trace elements within minerals the behavior of trace elements essentially consists in following that of the minerals containing them

compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites examples from the bohemian massif czech republic two distinct textural types of tourmaline were distinguished in leucocratic granites of the bohemian massif moldanubicum saxothuringicum i commonly euhedral disseminated tourmaline dt crystallized in relatively early stage of the granite consolidation and ii typically interstitial nodular tourmaline nt formed during the stage transitional from late solidus to early subsolidus crystallization very similar chemical composition and similar fractionation trends in both dt and nt tourmaline types indicate crystallization in a quasi closed system from early solidus to early subsolidus stage of granite consolidation the substitutions in tourmaline from nt granites in the moldanubicum are more similar to the substitutions in tourmaline from li poor granitic pegmatites in the same region relative to tourmaline from dt granites plotting of emp analyses of tourmaline in diverse diagrams strongly suggests using combination of ternary diagrams al fe mg and na ca xsite vacancy and simple plots involving single cations elements such as na al f na fe mg rather then more complicated diagrams e g r1 r2 r3 to characterize chemical composition and to derive substitution mechanisms in ca poor tourmaline from granitic rocks the complex diagrams e g r1 r2 versus r3 do not enable to investigate compositional evolution in the xsite and wsite properly and oversimplifies the real substitutions we recommend using specific diagrams for specific tourmaline compositions e g carich lirich

two mica and tourmaline leucogranites from the everest makalu region nepal tibet himalayan leucogranite genesis by isobaric heating in the higher himalaya of the region from cho oyu to the arun valley northeast of makalu the miocene leucogranites are not hosted only in the upper high himalayan crystallines hhc a network of dykes also cuts the lower hhc and the lesser himalayan crystallines lhc the plutons and dykes are mainly composed of two mica muscovite biotite tourmaline cordierite andalusite sillimanite leucogranite with tourmaline 2 6 and biotite 1 5 modal and tourmaline muscovite tourmaline biotite sillimanite garnet kyanite andalusite spinel corundum leucogranite with tourmaline 2 2 and biotite 1 5 modal both leucogranite types were produced by partial melting in the andalusite sillimanite facies series under lp ht conditions constrained by the occurrence of peritectic andalusite and cordierite the geochemical features of the leucogranites suggest that tourmaline leucogranite was produced by muscovite dehydration melting in muscovite rich metapelites at p 350 mpa and t 640 c whereas two mica leucogranite was produced by biotite dehydration melting in biotite rich metapelites at p 300 mpa and t 660 710 c melting in fertile muscovite rich metapelites of the top of both the hhc and lhc produced magmas which were emplaced at the same structural level in which they had been generated melting in the biotite rich gneiss of both the hhc and lhc produced hotter magmas which were transported upwards by dyking and eventually coalesced in the plutons of the upper hhc a similar process also produced a network of two mica granite at the top of the lhc in the ama drime nyonno ri range northeast of makalu the prograde character of leucogranite melt producing reactions in the everest makalu area suggests that here the generation of miocene leucogranites took place in a regime of nearly isobaric heating following nearly adiabatic decompression

matrix analysis of metamorphic mineral assemblages and reactions assemblage diagrams are widely used in interpreting metamorphic mineral assemblages in simple systems they can help to identify assemblages which may represent equilibrium states to determine whether differences between assemblages reflect changes in metamorphic grade or variations in bulk composition and to characterize isograd reactions in multicomponent assemblages these questions can be approached by investigating the rank composition space range and reaction space null space of a matrix representing the compositions of the phases involved singular value decomposition svd provides an elegant way of 1 finding the rank of a matrix and detemining orthonormal bases for both the composition space and the reaction space needed to represent an assemblage or pair of assemblages and 2 finding a model matrix of specified rank which is closest in a least squares sense to an observed assemblage although closely related to least squares techniques the svd approach has the advantages that it tolerates errors in all observations and is computationally simpler and more stable than non linear least squares algorithms models of this sort can be used to interpret multicomponent mineral assemblages by straightforward generalizations of the methods used to interpret assemblage diagrams in simpler systems svd analysis of mineral assemblages described by lang and rice 1985 demonstrates the utility of the approach

geochemical constraints on the bimodal origin of high himalayan leucogranites major and trace element and rb sr isotope systematics of the manaslu leucogranite central nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis biotite and tourmaline are for the most part mutually exclusive with a predominance of two mica leucogranites over tourmaline leucogranites the 87sr86sr initial isotopic ratios sri indicate that leucogranitic melts were derived from two different sources the two mica leucogranites having a metagreywacke origin with sri 0 752 nd 15 such a bimodal nature of the source zone does not directly influence the magmatic evolution except that probably the higher initial boron content in the metapelitic rocks may increase the na2ok2o ratio in contrast the amount of water present during melting principally controls in part anatectic processes and element behaviour water saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two mica leucogranites whereas water absent conditions prevailed during melting of metapelitic layers and favoured biotite plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite

luminescence dating at the archaeological and human burial site at roonka south australia abstract roonka the aboriginal habitation and burial site on the river murray south australia was excavated from 1968 to 1983 in 1983 thermoluminescence tl ages were obtained for several fireplaces at the east bank site sandy dune sediments collected from east bank were also analysed using traditional tl methods and ages were found at depths down to the base at 2 6 m now 20 years on with optical dating methods well established it seemed instructive to repeat the measurements using new techniques specifically the single aliquot regeneration dose protocol this has provided confirmation of the tl ages and provided an age framework for both the archaeological and geological aspects of roonka the ages confirm the archaeological description of the structure of the dune and show that only the top 20 is the holocene bunyip formation the lower part is assigned to the woorinen formation formed during and after the last glacial maximum burials at east bank took place between about 16 and 20 ka substantially earlier than those on the roonka flat but consistent with the earliest evidence of occupation on the flat they are one of the very few securely dated pleistocene burials in australia whether the individuals were gracile or robust is not known

petrologic and geochemical links between the post collisional proterozoic harney peak leucogranite south dakota usa and its source rocks abstract the proterozoic terrane of the black hills south dakota includes the composite harney peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes available dates indicate that granite generation post dated regional metamorphism and deformation that have been attributed to collision of the wyoming and superior cratons at 1760 ma previous radiogenic and stable isotope work indicates that the exposed metasedimentary rocks are equivalent to sources of the leucogranites in this study whole rock and mineral compositions of the metasedimentary rocks were used to calculate the likely average residue mineralogies and melt fractions that would be generated by muscovite dehydration melting of the rocks these were then used to model observed trace element compositions of the granites using published mineral melt distribution coefficients model trace element melt compositions using pelitic and graywacke protoliths yield similar results the models reproduce well the observed depletion of transition metals and ba in the granites relative to metasedimentary protoliths the depletion is due mainly to high proportion of biotite with variable amounts of k feldspar in the model residue sr is also depleted in the granites compared to source rocks but to a lesser relative extent than ba this is because of the low biotite melt distribution coefficient for sr and because high proportion of plagioclase in the residue is compensated by high sr concentrations in protoliths rubidium cs and ta behaved as slightly compatible to incompatible elements and therefore were not strongly fractionated during melting of the considered elements only b appears to have been highly incompatible relative to residue during melting the protoliths had sufficient b to allow tourmaline crystallization in those parts of the harney peak granite in which ti concentration was sufficiently low not to enhance crystallization of biotite the reproducibility of observed trace element concentrations in the harney peak granite by the models supports the often made proposition that metapelites and metagraywackes are common sources for leucogranites this argues against mass input from the mantle into metagraywacke and metapelitic crustal sources or melting of amphibolites to generate the post collisional harney peak and other similar peraluminous granite suites

titanium substitution in biotite an empirical model with applications to thermometry o2 and h2o barometries and consequences for biotite stability abstract an empirical model for solution of ti in biotite is developed and calibrated on the basis of various equilibria among biotite and ti saturating assemblages sources of data used for the calibration include both experimental products and published analyses of natural assemblages ti solution in biotite can be satisfactorily modelled by means of the exchange component tife 2 whose non ideal behavior can be approximated empirically by means of a linear function of the relative concentrations of ti and octahedral al in biotite within assemblages which fix the chemical potential of the exchange component tife 2 the concentration of this component in biotite is very sensitive to temperature and oxygen fugacity making it possible to use biotite oxide assemblages to obtain reliable t and f o 2 estimates in igneous and metamorphic rocks in assemblages which also contain alkali feldspar it is possible to use breakdown equilibria of ti additive components in biotite to estimate h 2 o fugacity such uses are likely to find important applications in rocks in which other assemblages sensitive to temperature f o 2 and or f h 2 o are absent in general rocks containing a single oxide phase plus biotite as the only mafic silicate phase alkali feldspar the empirical model for solution of ti in biotite also allows to calculate the loci of various terminal reactions for the assemblage titanian biotite quartz which by comparison with equivalent equilibria in ti free systems provide insight into the effect of ti on the stability of biotite solubility of ti in biotite increases with temperature in a strongly non linear fashion as a consequence calculations predict that the effect of ti on the stability of biotite is very small up to conditions typical of the beginning of the granulite facies of metamorphism but beyond those conditions ti concentration increases markedly and biotite is rendered very refractory at mid to deep crustal pressures 10 kbar the vapor absent solidus of biotite quartz in rocks containing ti saturating phases is likely to exceed 900 c even in bulk compositions with subequal concentrations of fe and mg

the generation and crystallization conditions of the proterozoic harney peak leucogranite black hills south dakota usa petrologic and geochemical constraints the mineralogy petrology and geochemistry of the proterozoic harney peak granite black hills south dakota were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare element pegmatites the granite was emplaced at 3 4 kbar as multiple sills and dikes into quartz mica schists at the culmination of a regional high temperature low pressure metamorphic event principally along the periphery of the main pluton and in satellite intrusions the sills segregated into granite pegmatite couplets the major minerals include quartz k feldspar sodic plagioclase and muscovite biotite mg no molar mgo mgo feo 0 32 0 38 is the predominant ferromagnesian mineral in the granite s core whereas at the periphery of the main pluton and in the satellite intrusions tourmaline mg no 0 18 0 48 is the dominant ferromagnesian phase almandine spessartine garnet is also found in the outer intrusions there is virtually a complete overlap in the wide concentration ranges of sio2 cao mgo feo sr zr w of the biotite and tourmaline bearing granite suites with no discernable differentiation trends on harker diagrams precluding the derivation of one suite from the other by differentiation following emplacement this is consistent with the oxygen isotope compositions which are 11 5 0 6 for the biotite granites and 13 2 0 8 for the tourmaline granites suggesting derivation from different sources the concentrations of tio2 and possibly ba are higher and of mno and b are lower in the biotite granites the normative orthoclase albite ratio is extremely variable ranging from 0 26 to 1 65 in the biotite granites to 0 01 1 75 in the tourmaline granites very few sample compositions fall near the high pressure watersaturated haplogranite minima eutectic trend indicating that the granites for the most part are not minimum melts generated under conditions with a text h text 2 text o 1 instead most biotite granites are more potassic than the water saturated minima and eutectics and in analogy with experimentally produced granitic melts they are best explained by melting at 6 kbar a text h text 2 text o 1 and temperatures 800 c such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals nabelek et al 1992 several of the tourmaline granite samples contain virtually no k feldspar and have oxygen isotope equilibration temperatures 716 775 c therefore they must represent high temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water saturated haplogranite minima or during fractionation of intruded melts into granite pegmatite couplets accompanied by volatile aided differentiation of the alkali elements the indicated high temperatures a text h text 2 text o 1 the relatively high tio2 and ba concentrations and the relatively low partial 18 text o values of the biotite granites suggest that they were generated by high extent biotite dehydration melting of an immature archean metasedimentary source the ascent of the hot melts may have triggered low extent muscovite dehydration melting of schists higher in the crust producing the high b low ti melts comprising the periphery of the main pluton and the satellite intrusions alternatively the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse with the low partial 18 text o biotite granites generated at a deeper hotter region and the high partial 18 text o tourmaline granites at a higher cooler region of the crust the low ti and high b concentrations in the high partial 18 text o melts resulted in the crystallization of tourmaline rather than biotite which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions

on the occurrence and boron isotopic composition of tourmaline in ultra high pressure metamorphic rocks abstract the extensive p t stability and the high chemical variability of tourmaline tur together with its common occurrence in metasediments proves its high potential for petrological and isotope geochemical studies on fluid rock interaction in subduction and collision related rocks this paper reviews the occurrence major element chemistry and boron isotopic composition of tur in high and ultrahigh pressure metamorphic uhpm rocks in addition it presents a new discovery of coesite bearing tur schorl from the erzgebirge germany as well as tur dravite related to the retrograde history of coesite and diamond bearing rocks from the erzgebirge and the kokchetav massif kazakhstan the scarce data on worldwide occurrences of u hpm tur reveal a high occupation of the crystallographic x site dominated by na and the possible presence of excess b with little further distinctiveness in its major element composition when compared with tur from medium grade rocks high k 2 o contents in tur are probably not related to uhp growth or equilibration the b isotopic composition of u hpm tur ranges in 11 b from 16 to 1 with many samples in or below the range of continental crust in contrast tur formed during retrograde fluid influx typically shows high 11 b values up to 28 suggesting heavy b fluids infiltrating the exhuming u hpm units coesite inclusions in tur characterized by raman spectroscopy are regarded as the best indicator for its uhp stability supplementary material analytical methods tourmaline compositions and boron isotope values are available at http www geolsoc org uk sup18354

phase relations of tourmaline leucogranites and the significance of tourmaline in silicic magmas by means of melting and recrystallization tourmaline seeded experiments phase relations of two natural tourmaline bearing fe rich members of the schorl dravite series leucogranites have been determined between 1 and 3 kbar under h2o saturation with fo2 close to ni nio the presence of tourmaline slightly lowers the solidus temperatures of both samples from 5 to 20 c compared to the corresponding tourmaline free solidus quartz k feldspar and plagioclase phase relations are not significantly dependent on the presence of tourmaline tourmaline is the last major phase to disappear for both samples and a demonstrated liquidus phase exists for one in the recrystallization experiments the compositions of the tourmalines growing from the melt change from more mg rich at high temperatures to more fe rich at lower temperatures the tourmalines are always richer in mg than the melt is but fe and mg are not especially partitioned between crystallizing tourmaline and melt melt compositions do not depart

syn collisional extensional collapse parallel to the orogenic trend in a domain of steep tectonics the salamanca detachment zone central iberian zone spain the area south of the town of salamanca is a zone of the spanish variscan belt characterized by a first compressional event which gave rise to steep structures followed by the development of an extensional ductile shear zone more than 4 km thick that is described as the salamanca detachment zone the strain associated to the detachment is analyzed using quartz pebbles in conglomerates comparing the measured strain values with theoretical strain paths leads to the conclusion that the deformation was approximately of plane strain type quartz c axis fabrics and kinematic criteria indicate that simple shear was a very important component of the deformation though coaxial components were probably involved the extensional character of the detachment is indicated by the geometry of the metamorphic zones and the metamorphic evolution taken together the data indicate that the extensional event was related to gravitational collapse induced by the thickening of the continental crust and that it was syn collisional the movement of the hangingwall unit was to the southeast parallel to the trend of the fold belt and the translation was of the order of one to a few dozens of km though important this is not exceedingly large and allowed the preservation of low grade metamorphic conditions in the hangingwall preventing it from being affected by extensive brittle tectonic processes

evaluating the controls on tourmaline formation in granitic systems a case study on peraluminous granites from the central iberian zone ciz western spain

causes of geochemical diversity in peraluminous granitic plutons the jalama pluton central iberian zone spain and portugal abstract the jalama pluton jp is one of the best examples of the late hercynian two mica granites of the central iberian zone ciz of the hesperian massif spain and portugal this pluton is a multiphase intrusion that consists of three intrusive units 1 the external unit eu comprises three main facies a two mica coarse grained porphyritic granite pg a two mica coarse grained equigranular granite eg and a tourmaline bearing muscovite leucogranite tl which define both vertical and horizontal zonation the main petrographic and compositional characteristics of the eu can be explained by a fractional crystallization process that takes place in independent magma batches generated from heterogeneous source rocks 2 the sillimanite monzogranite sm is distinguished by the presence of micaceous aggregates composed of biotite muscovite and sillimanite based on major and trace element data the compositional variability within the sm has been ascribed to inheritance from compositionally heterogeneous source rocks 3 the late leucogranites ll appear mainly as dykes intruded in the pg from a comparison with this pg it can be deduced that the ll represent derivative liquids segregated after important fractionation from magmas equivalent to pg magmas but at deeper levels the most important implication of our study is that the jalama granites were generated by partial melting of high grade metamorphic peraluminous rocks that were compositionally heterogeneous on different scales during this small scale intracrustal melting event temperature was the limiting factor for the degree of melting

boron geochemistry of the lower crust evidence from granulite terranes and deep crustal xenoliths abstract boron contents are uniformly low in more than 100 granulites from exposed terranes in india norway and scotland and from xenolith suites in the western usa averages for the terranes 2 5 ppm and for xenoliths 1 2 ppm suggest maximum b contents of about 2 1 ppm for the lower crust abundance distributions from exposed terranes are skewed to higher values as b has been added to some samples via retrograde fluids during decompression the samples studied include mafic to felsic lithologies of both igneous and sedimentary origin there is no correlation of b content with bulk composition or with protolith type in any of the suites studied boron is apparently depleted in all granulite protoliths during prograde metamorphism and dehydration similar depletions of b and other fluid mobile elements e g u cs with respect to rare earth elements ree zr ba rb and k 2 o are seemingly inconsistent with origin of granulites primarily via extraction of silicate melts these distinctive geochemical features are attributed to selective element transport in fluids released by devolatilization reactions anatexis is not necessarily precluded but dehydration of the subsolidus protolith normally would precede melting and lead to depletion of the fluid mobile elements compositions of any melts and restites eventually formed would reflect the effects of this antecedent process the systematic depletion of b and cs in granulites contrasts with the highly variable contents of most other incompatible elements determined for this reason the estimated lower crust abundance for b is relatively well constrained whereas abundance estimates for many other elements are model dependent have large uncertainties and are unlikely to be globally representative