geochemistry of s type granitic rocks from the reversely zoned castelo branco pluton central portugal abstract the zoned pluton from castelo branco consists of variscan peraluminous s type granitic rocks a muscovite biotite granite in the pluton s core is surrounded successively by biotite muscovite granodiorite porphyritic biotite muscovite granodiorite grading to biotite muscovite granite and finally by muscovite biotite granite id tims u pb ages for zircon and monazite indicate that all phases of the pluton formed at 310 1 ma whole rock analyses show slight variation in 87 sr 86 sr 310 ma between 0 708 and 0 712 nd 310 ma values between 1 and 4 and 18 o values between 12 2 and 13 6 these geological mineralogical geochemical and isotopic data indicate a crustal origin of the suite probably from partial melting of heterogeneous early paleozoic pelitic country rock in detail there is evidence for derivation from different sources but also fractional crystallization linking some of internal plutonic phases least squares analysis of major elements and modelling of trace elements indicate that the porphyritic granodiorite and biotite muscovite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz biotite and ilmenite by contrast variation diagrams of major and trace elements in biotite and muscovite the behaviours of ba in microcline and whole rock 18 o the ree patterns of rocks and isotopic data indicate that both muscovite dominant granites were probably originated by two distinct pulses of granite magma

magmatic graphite inclusions in mn fe rich fluorapatite of perphosphorus granites the belvis pluton variscan iberian belt three mn fe rich fluorapatite types have been found in the highly evolved peraluminous and perphosphorous granites of the belvis pluton one of these apatite types includes abundant graphite microinclusions suggestive of a magmatic origin for the graphite the belvis pluton is a reversely zoned massif composed by four highly fractionated granite units showing a varied accessory phosphate phases u rich monazite u rich xenotime u rich fluorapatite and late eosphorite childrenite the strong peraluminous character of the granites determines an earlier monazite and xenotime crystallization so the three types of fluorapatite record late stages of phosphate crystallization the earlier type 1 apatite is mostly euhedral small and clear type 2 apatite is dusty large 2800 m and mostly anhedral with strong interlobates interfaces with the main granite minerals more abundant in the less fractionated units and absent in the most evolved unit type 3 is subeuhedral to anhedral shows feathery aggregate texture and only appears in the most evolved unit apatite composition was acquired by electron microprobe analyses laser ablation inductively coupled plasma mass spectrometry and electron energy loss spectroscopy type 1 and type 2 apatite display similar broad compositional ranges showing high mno up to 4 30 wt and feo up to 2 88 wt contents without traces of carbon in apatite structure type 2 differs from type 1 by having slightly higher lree and sr contents ree spectra also differ with type 1 displaying both variable lree slope and negative eu anomaly whereas type 2 shows constant lree slope and higher negative eu anomaly although both display similar hree slope type 3 apatite displays higher feo contents up to 5 09 wt positively correlated with higher cl na li be b zn contents and extremely low y ree contents when compared to the other apatite types cation substitution indicates that part of the fe content is as fe graphite has been found exclusively as abundant microinclusions in type 2 apatite parallel or randomly distributed and heterogeneously grouped in clusters within the crystals high resolution electronic images show that graphite occurs with unusual habits filaments of stacked hexagonal flakes up to 15 m length and up to 0 5 m width textural and chemical features suggest a highly crystallized melt which favor compartmentalizing in compositional microdomains where the apatite types would have crystallized the cocrystallization of type 2 apatite and graphite suggests a c f p rich melt sufficiently saturated to acquire an immiscible character with the highly evolved silicate melt in late magmatic stages as type 2 differs from type 1 apatite by higher lree and sr contents we interpret that fluxing components were favorably concentrated in those residual less depleted lree sr fraction melts once monazite and zircon and xenotime would have crystallized type 3 apatite records a change in the ultimate melt stage an increase of the oxygen fugacity coupled with high undercooling by volatile lost of highly fractionated residual cl richer melts the presence of biogenic carbon in granite peraluminous melts derived from metasedimentary sources and its later crystallization as graphite filaments opens a discussion on the carbon behavior during magma evolution especially in highly polymerized melt framework

turbidite provenance in the lower palaeozoic manx group isle of man implications for the tectonic setting of eastern avalonia the provenance of turbidites from the predominantly arenig aged manx group has been constrained using petrographical and geochemical techniques petrographical analysis of sandstones reveals that mono and poly crystalline quartz grains of cratonic origin are dominant major trace and rare earth element concentrations in both sandstones and mudstones complement the petrographical data indicating that the source of the sediments consisted of quartzose basement and mature sedimentary rocks there is little evidence of a juvenile volcanic input but a minor palaeovolcanic component of active continental margin affinity is present there are indications of a more immature character in the oldest units but on the whole geochemical data from the manx group suggest an overall passive margin setting these results suggest that eastern avalonia was attached to gondwana during deposition of the manx group and that iapetus oceanic crust did not subduct beneath the region before the end of the arenig

the timing of ordovician magmatism in the english lake district and cross fell inliers volcanic and hypabyssal intrusive rocks of the lower palaeozoic english lake district and cross fell inliers are elements of the ordovician destructive plate margin system of microcontinental avalonia two igneous sheets within the marine sedimentary skiddaw group of these inliers previously described as lavas are reinterpreted as sills sedimentary rocks enclosing these sills are of late tremadoc early arenig c 493 ma and early llanvirn 476 ma age and breccias along the upper contacts of both were produced by steam explosivity and fluidization ahead of theadvancing tips of the intrusions previous interpretation of the breccias on the older sheet as sediment deposited on the eroded top of a lava flow implied an early ordovician onset of arc magmatism such early magmatism would have been virtually coincident with the latest tremadoc initiation of arc magmatism in wales but evidence for such a near synchronous response tothe putative onset of subduction is lacking respective onsets of magmatismwere probably separated by at least 17 m y and possibly by as much as 29 m y the apparent contemporaneity of mid and late ordovician volcanic episodes in england and wales and similarities in extensional tectonic style suggest that the two areas then were part of the same subduction system responding similarly to plate scale magma generating and tectonic processes the early ordovician situation is uncertain but the absence of arc volcanic rocks of this age in the english lake district suggests that this area and wales are not tectonically juxtaposed elements of a former simple linear arc

emerald deposits and occurrences a review abstract emerald the green gem variety of beryl is the third most valuable gemstone after diamond and ruby although it is difficult to obtain accurate statistics colombia supplies most an estimated 60 worth more than 500 000 000 per year of the world s emeralds however there is speculation that the emerald mines in colombia are becoming depleted brazil currently accounts for approximately 10 of world emerald production emeralds have also been mined in afghanistan australia austria bulgaria china india madagascar namibia nigeria pakistan south africa spain tanzania the united states and zimbabwe because it is difficult to obtain accurate analyses of beryllium most published analyses of beryl are renormalized on the basis of 18 oxygen and 3 be atoms per formula unit the color of emerald is due to trace amounts of chromium and or vanadium replacing aluminum at the y site in most cases the cr content is much greater than that of v to achieve charge balance the substitution of divalent cations at the y site is coupled with the substitution of a monovalent cation for a vacancy at a channel site beryl is relatively rare because there is very little be in the upper continental crust unusual geologic and geochemical conditions are required for be and cr and or v to meet in the classic model be bearing pegmatites interact with cr bearing ultrama c or ma c rocks however in the colombian deposits there is no evidence of magmatic activity and it has been demonstrated that circulation processes within the host black shales were sufficient to form emerald in addition researchers are recognizing that regional metamorphism and tectonometamorphic processes such as shear zone formation may play a signi cant role in certain emerald deposits a number of genetic classification schemes have been proposed for emerald deposits most are ambiguous when it comes to understanding the mechanisms and conditions that lead to the formation of an emerald deposit studies of individual emerald deposits show that in most cases a combination of mechanisms magmatic hydrothermal and metamorphic were needed to bring be into contact with the chromophores this suggests the need for a more flexible classification scheme based on mode of formation stable isotopes can be used to estimate the contribution of each mechanism in the formation of a particular deposit such estimates could perhaps be more precisely defined using trace element data which should reflect the mode of formation emerald may be identified in the field by color hardness and form it will tend to show up in stream sediment samples but because its specific gravity is relatively low it will not concentrate in the heavy mineral fraction in colombia structural geology the sodium content of stream sediment samples and the lithium sodium and lead contents of soil samples have all been used to find emerald occurrences exploration for gem beryl could result in the discovery of new occurrences of non gem beryl or other be minerals that could become new sources of be and be oxide future efforts should go towards creating a comprehensive data base of emerald compositions including trace elements determination of the role of metamorphism in the formation of some emerald deposits improved classification schemes and more effective exploration guidelines

the stability of zincian spinels in sulfide systems and their potential as exploration guides for metamorphosed massive sulfide deposits zincian spinel zn fe mg al 2 o 4 is found in a variety of geologic settings including metamorphosed massive sulfide deposits aluminous metasediments pegmatites and marbles many spinels in and near metamorphosed massive sulfides have formed by desulfidation and oxidation reactions that involve members of the system zn fe al si s o experimental reversals of the simplified reaction zns fes 2al 2 o 3 o 2 znal 2 o sub 4 feal 2 o 4 s 2 using hydrothermal techniques have been obtained at 2 and 5 kb and various temperatures using fe sub 1 x s fes 2 fe 3 o 4 as a buffer calculated positions of the spinel sphalerite equilibria in f sub o 2 f sub s 2 x space for ideal behavior along the znal 2 o 4 feal 2 o 4 join as is suggested by octahedral site preference energies agree with experimental results and theoretical calculations depending on the choice of the free energy of formation of hercynite the compositions of spinels in equilibrium with sphalerite and either pyrite or pyrrhotite become more zn enriched with increasing f sub s 2 and f sub o 2 values and can be used as a measure of f sub o 2 during metamorphism spinel associated with metamorphosed massive sulfide deposits marbles and aluminous metasediments is enriched in the gahnite znal 2 o 4 spinel mgal 2 o 4 and hercynite feal 2 o 4 molecules respectively whereas spinel associated with pegmatites is depleted in the spinel molecule such variability in composition constitutes a potential exploration guide for metamorphosed massive sulfide deposits

uranium rich accessory minerals in the peraluminous and perphosphorous belvis de monroy pluton iberian variscan belt the strongly peraluminous perphosphorous 0 85 wt p2o5 and low ca granites from the belvis de monroy pluton contain the most u rich monazite ce and xenotime known in igneous rocks along with these accessory minerals p rich zircon occurs reaching uncommon compositions particularly in the more fractionated units of this zoned pluton monazite displays a wide compositional variation of uo2 23 13 wt and tho2 19 58 wt positively correlated with ca si p y and ree xenotime shows a high uo2 content 2 37 13 34 wt with parallel increases of lree ca and si zircon contains comparatively much lower uo2 1 53 wt but high p2o5 14 91 wt al2o3 6 96 wt feo 2 93 wt and cao 2 24 wt contents the main mechanism of incorporating large u and th amounts in studied monazite and u in xenotime is the cheralite type th u 4 ca2 2 y ree 3 substitution zircon requires several coupled mechanisms to charge balance the p substitution resulting in non stoichiometric compositions with low analytical totals compositional variations in the studied accessory phases indicate that the substitution mechanisms during crystal growth depend on the availability of non formula elements the strong p rich character of the studied granites increases monazite crystallization triggering a progressive impoverishment in th and lree in the residual melts and consequently increasing extraordinarily the u content in monazite and xenotime this is in marked contrast to other peraluminous i type or p poor s type granite series the p rich and low ca peraluminous melt inhibits uraninite crystallization so contributing to the u availability for monazite and xenotime

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

an experimental study of element partitioning among biotite muscovite and coexisting peraluminous silicic melt at 200 mpa h2o

gahnite chrysoberyl and beryl co occurrence as accessory minerals in a highly evolved peraluminous pluton the belvis de monroy leucogranite caceres spain abstract gahnite znal 2 o 4 chrysoberyl beal 2 o 4 and beryl be 3 al 2 si 6 o 18 have been found as accessory minerals in the external highly fractionated leucogranitic unit within the hercynian reversely zoned belvis de monroy pluton westernmost part of the montes de toledo batholith caceres spain the highly felsic sio 2 72 wt and peraluminous acnk 1 2 character of this leucogranite together with the high content of some incompatible elements f li b and p seems to be a primary consequence of fractional crystallization in a magmatic closed system the high be contents and zn fe total ratio 0 01 are relevant factors which have favoured the precipitation of these minerals moreover the si al p b and f activities might be high favouring the magmatic crystallization of such exotic mineral phases together with be rich cordierite f rich micas sillimanite and al rich phosphates in fact the interplay between the silica and alumina activities likely controls the stabilization and the preferential crystallization of gahnite chrysoberyl or beryl chrysoberyl assemblages in mm sized microdomains the p t crystallization conditions are constrained by the muscovite and sillimanite stability fields and the minimum granite al 2 o 3 saturated solidus and have been estimated at temperatures between 670 and 700 c and pressures between 1 and 2 kbar

thermal state under the tohoko arc with consideration of crustal heat generation abstract the thermal structure beneath subduction zones plays a key role in aiding understanding of tectonic activities such as seismicity volcanism arc formation and genesis of back arc basins around subduction zones many simulations have been made to estimate the thermal process in the mantle wedge which causes the surface activities in the tohoku arc many heat flow measurements have been made and the heat flow profile from the trench to the back arc has been constructed in this study the thermal structure in the crust of northeast japan is investigated to account for the surface heat flow data to estimate the contribution of the heat generation in the crust to the surface heat flow the heat production rate was obtained on granitic and metamorphic rocks collected from the hidaka metamorphic zone hokkaido japan where the vertical crustal section of an island arc is understood to be exposed at the surface instrumentation neutron activation analysis and gamma ray spectrometry were adopted to analyze the concentration of heat producing elements the obtained rate of heat generation and its decrease with increasing depth for the upper part of the crust were found to be similar to those estimated for stable continental areas but the heat generation rate was almost constant in the lower part of the crust the vertical distribution of the heat production rate in the crust of the northeastern japan arc was estimated from the present results and previous estimates of heat production rates in various rocks using the crustal structure determined by explosion seismology the total heat generation in the crust thus estimated is about 30 mw m 2 with the surface heat flow data and estimated heat generation distribution in the crust the thermal structure in the crust was simulated numerically modeling calculations were made on a cross section along the line from the japan trench to the japan sea a direction parallel to the direction of convergence of the pacific and eurasian plates the models were two dimensional and included frictional heating at the upper surface of the slab the calculated thermal structure in the crust shows that the temperature at the moho is about 850 c and almost about 250 c lower than previous estimates the magnitude of the interplate stress was derived by considering the rate of frictional heating at the interface between the plates in order to explain the surface heat flow between the trench and aseismic front the interplate stress should be less than 20 mpa at depth in the crust

solubility and stability of beryl in granitic melts beryllium contents of granitic melts at saturation in beryl or chrysoberyl phenakite or quartz have been determined by forward and reverse direction experiments at 650 850 degrees c and 200 mpa using natural beryl or the compositionally equivalent mixture of phenakite alumina quartz added to metaluminous haplogranite peraluminous haplogranite and macusanite a peraluminous li b f and p enriched rhyolite obsidian from macusani peru chrysoberyl coexists with beryl or quartz in moderately to strongly peraluminous systems asi approximately or 1 05 the assemblage phenakite beryl chrysoberyl is stable in silica undersaturated bulk composition the beo content of the melts which ranged between 0 03 0 40 wt varies principally with temperature the solubility of beryl falls with decreasing t and with the activity product of beryl alpha beo 3 alpha al2o3 alpha sio2 6 beryllia contents are lowest in strongly peraluminous and quartz saturated haplogranite melts however the highest beo content measured in glass products occurs for the strongly peraluminous macusanite at 850 degrees c 4016 ppm we infer that the greater solubility of beryl in macusanite melt results from melt speciation reactions involving li f b and p for all bulk compositions studied the beo content of melt projects to a narrow range of similar values at low t near the solidus of haplogranite thus metaluminous to peraluminous granitic magmas with and without common volatile and fluxing components will if cooled to subsolidus temperatures have similarly low beo requirements for beryl saturation the small beo content of melt near the solidus of haplogranite results in a minor 10 degrees c depression of the freezing point compared to be free haplogranite melt the mean melt composition at the beryl saturated granite minimum shifts slightly toward quartz beryl is common in peraluminous granitic rocks in part because lower beo contents are required to saturate these melts in beryl and possibly because these melts acquire higher beo contents by mica melting reactions at their sources beryl is also a common constituent of border facies assemblages in granitic pegmatite dikes regardless of their asi values this early crystallization of beryl results from the low beo content required to saturate any granitic melt in beryl at the low t environments in which pegmatite dikes solidify

the early palaeozoic geography of europe in the early ordovician three main continents are recognized by faunas in europe laurentia northwest of the closed suture of the iapetus ocean which was tropical baltica north of the general area of the trans european suture zone which was temperate and gondwana south of the tesz which was high latitude as the ordovician progressed various terranes separated and drifted away from the gondwana supercontinent at different times namely avalonia which was probably originally part of gondwana near south america iberia armorica perunica bohemia and various alpine fragments each terrane developed progressively different faunas as time went by avalonia collided with baltica near the end of ordovician confirmed by faunas tectonics and palaeomagnetism and subsequently avalonia baltica collided with laurentia to form laurussia from the mid silurian to the early devonian the ibero armorica perunica and alpine terranes did not join the european collage until the devonian the modern sites of the terrane boundaries bear little direct relationships to the original palaeogeographical boundaries in the early palaeozoic

stability of andalusite and sillimanite and the al_ 2 sio_ 5 triple point constraints from the ballachulish aureole scotland andalusite and and sillimanite sil occur in well defined zones in the ballachulish aureole in most of the aureole s sillimanite bearing rocks sillimanite grain diameters range from 2 m to 10 m the boundary between prograde andalusite and prograde sillimanite is constrained to a zone of max 30 m width upgrade of the muscovite quartz andalusite k feldspar h 2 o reaction isograd this boundary is interpreted to correspond to the and sil equilibrium the common occurrence of andalusite well upgrade of the first occurrence of sillimanite is ascribed to sluggish kinetics of the polymorphic inversion the p t position of the and sil equilibrium in the aureole is estimated as 645 20 c and 3 0 0 4 kbar based on a combination of 1 location of the ms qtz and kfs h 2 o reaction corrected for non end member fluid and mineral compositions and 2 independent pressure estimates obtained from equilibria in metapelites marbles calcsilcates and granitoids all in exce

geochemical evolution of the tertiary succession of the nw shelf bengal basin bangladesh implications for provenance paleoweathering and himalayan erosion abstract whole rock major trace and rare earth element ree compositions of paleogene to neogene sedimentary rocks of the nw shelf succession province 1 of bangladesh contain a record of interaction of the india and asian plates himalayan tectonism and climatic development analyses of 66 sandstones and mudrocks from the tertiary succession of bangladesh were made to examine provenance source weathering and the influence of paleoclimate and tectonism the sediments display linear geochemical trends due to quartz dilution and varying quartz clay ratios produced by hydrodynamic sorting chondrite normalized ree patterns for both sandstones and mudrocks from different groups are similar to upper continental crust with moderate to high lree enrichment lithotypes within formations average lan ybn 5 31 11 41 and marked negative eu anomalies eu eu 0 51 0 69 based on geochemical criteria the succession can be divided into three parts jaintia barail surma and dupi tila very high silica contents in jaintia tura sandstones and high chemical index of alteration cia indices in kopili mudrocks fe shales suggest derivation from a deeply weathered and stable cratonic source india the tura sandstones are interpreted as first cycle quartz arenites produced while the indian plate drifted across equatorial regions during the paleocene eocene thermal maximum petm the barail surma and dupi tila sediments were derived from a felsic orogen the himalaya the barail surma sediments were mainly derived from the trans himalayan batholith and associated granitoids with significant contribution from the lesser himalaya mafic input is also evident probably from intraoceanic arc material within the himalaya barail mudrocks have uniformly high cia values 92 95 suggesting intense steady state weathering of their proto himalayan source and warm and humid climate in contrast cia values of surma mudrocks range from 66 to 93 average 84 suggesting non steady state weathering related to active uplift in the himalaya the dupi tila sediments were derived from a more felsic lesser himalaya source with significant contribution from the trans himalaya and very little or no ophiolitic or arc material dupi tila mudrocks have cia ratios of 62 99 average 72 also indicating non steady state weathering in the rising himalayan source geochemical compositions of the nw shelf sediments are comparable to coeval successions in the surma basin province 2 of bangladesh and the siwaliks india indicating similar source evolution of the indian monsoon and associated high precipitation caused intense chemical weathering of the surma and dupi tila source despite rapid uplift the surma group thus bears the signature of evolution of the asian monsoon in the bengal basin at 21 ma simultaneous with the development of the east asian monsoon this supports proposals that both monsoon systems developed at the same time

experimental partitioning of rb cs sr and ba between alkali feldspar and peraluminous melt hydrous partial melting experiments performed between 650 and 750 c at 200 mpa h20 on synthetic metapelite compositions quartz albite muscovite biotite mineral mixtures doped with ba sr rb and cs yielded alkali feldspar crystals with a wide range of compositions in equilibrium at their rims with peraluminous melt measured partition coefficients for normally trace lithophile elements between feldspar and melt d m fsp gl m ba sr rb cs do not depend on either temperature or bulk composition of melt for the compositions studied values of d sr fsp gl are between 10 and 14 and appear to be independent of the albite and orthoclase contents of the feldspar crystals in contrast values of d ba fsp gl and d rb fsp glare strongly dependent on the orthoclase content of feldspar relationships that can be expressed by the following linear equations d ba fsp gl 0 07 0 25 orthoclase and d rb fsp gl 0 03 0 0 1 orthoclase where orthoclase is in mole percent these equations reproduce the range of previously reported values for d ba and d rb determined on natural and synthetic samples a single partition coefficient for cs was also determined at d cs fsp gl 0 13 these data can be used in conjunction with recently published partition coefficients for muscovite biotite and plagioclase feldspars blundy and wood 1991 icenhower and london 1995 to model quantitatively the trace element signatures of peraluminous magmas during anatexis and crystallization depending on bulk composition and pressuretemperature trajectories during episodes of partial melting ba and sr and to a lesser extent rb are retained at the source while cs and li are enriched in the first melts these results explain why peraluminous granitic magmas with s type sedimentary sources carry a distinctive enrichment in li and cs

petrography and geochemistry of the cambro ordovician wajid sandstone southwest saudi arabia implications for provenance and tectonic setting abstract the wajid sandstone of probable cambro ordovician age rests unconformably on peneplained precambrian crystalline rocks on the southeastern margin of the arabian shield the sandstone is composed of varicolored siliciclastic rocks mainly coarse to fine grained sandstones with granule conglomerate and siltstone interbeds displaying diverse sedimentary primary structures such as planar and trough cross bedding and flat bedding they form repeated fining upward cycles typical of deposition from braided streams current indicators indicate that flow was from sw to nne petrographically all samples of the wajid sandstone are of quartz arenite type highly enriched in quartz but poor in heavy minerals feldspar and lithic fragments the provenance and tectonic setting of the wajid sandstone have been assessed using integrated petrographic and geochemical studies petrographic analysis reveals that mono and poly crystalline quartz grains and heavy minerals from metamorphic and igneous rocks of a craton interior setting were the dominant sources chemically major and trace element concentrations in the rocks of the wajid sandstone indicate deposition in a passive continental margin setting petrographic and geochemical data suggest that the sediments were derived from metamorphic and igneous rocks forming the adjacent precambrian basement rocks of the arabian shield and were deposited on a passive continental margin deposition took place after stabilization of the arabian shield following the late precambrian pan african orogeny the wajid sandstone can be correlated with similar deposits elsewhere in arabia and north africa which were deposited on a low lying landmass forming the stable continental margin of the arabian nubian shield flanking the southern margin of the paleo tethys ocean

lithofacies of lower palaeozoic deep marine sediments in the isle of man a new map and stratigraphic model of the manx group

be daughter minerals in fluid and melt inclusions implications for the enrichment of be in granite pegmatite systems the study of re homogenized melt inclusions in the same growth planes of quartz of pegmatites genetically linked to the variscan granite of the ehrenfriedersdorf complex erzgebirge germany by ion microprobe analyses has determined high concentrations of be up to 10 000 ppm in one type of melt inclusion as well as moderate concentrations in the 100 ppm range in a second type of melt inclusion generally the high be concentrations are associated with the h2o and other volatile rich type b melt inclusions and the lower be concentration levels are connected to h2o poor type a melt inclusions both inclusion types representing conjugate melt pairs are formed by a liquid liquid immiscibility separation process this extremely strong and very systematic scattering in be provides insights into the origin of be concentration and transport mechanisms in pegmatite forming melts in this contribution we present more than 250 new analytical data and show with ion microprobe and fs la icpms studies on quenched glasses as well as with confocal raman spectroscopy of daughter minerals in unheated melt inclusions that the concentrations of be may achieve such extreme levels during melt melt immiscibility of h2o b f p li enriched pegmatite forming magmas starting from host granite with about 10 ppm be melt inclusions with 10 000 ppm be correspond to enrichment by a factor of over 1 000 this strong enrichment of be is the result of processes of fractional crystallization and further enrichment in melt patches of pegmatite bodies due to melt melt immiscibility at fluid saturation we also draw additional conclusions regarding the speciation of be in pegmatite forming melt systems from investigation of the be bearing daughter mineral phases in the most h2o rich melt inclusions in the case of evolved volatile and h2o rich pegmatite systems b p and carbonates are important for the enrichment and formation of stable be complexes

the p fe diagram for k feldspars a preliminary approach in the discrimination of pegmatites abstract pegmatites are extremely coarse grained and heterogeneous rocks in which quantitative measurements of mineral proportions and chemical compositions of the whole rock are virtually impossible to acquire thus conventional criteria such as bulk compositions and modal mineralogy used for the classifications of igneous rocks simply cannot be applied for pegmatites an alternative is to use the mineralogical and chemical attributes of k rich feldspars the only mineral that is omnipresent in pegmatites we have used this approach to test a possible discriminant among four groups of pegmatites on the basis of major petrological features such as the abundance of quartz feldspars micas and phosphates group i is represented by relatively flux poor and silica poor pegmatites in most cases with hypersolvus feldspars devoid of quartz and with minor biotite which are common in rift settings as in the coldwell alkaline complex in northwestern ontario canada group ii comprises relatively flux poor silica rich pegmatites with quartz subsolvus feldspars and biotite as major primary minerals typically occurring in the asymmetric collisional grenville orogeny group iii comprises relatively flux rich silica rich p poor pegmatites with quartz subsolvus feldspars and muscovite as the major primary minerals finally group iv consists of relatively flux rich silica rich p rich pegmatites with the same previous major minerals as in group iii but with abundant phosphates group iii and iv are found in most symmetric collisional orogens such as in the eastern brazilian pegmatite province as the result of the collision of cratons mainly formed by igneous and metamorphic rock of archean and early proterozoic age we have selected specimens of blocky perthitic k rich feldspar from the inner part of thirty one pegmatites belonging to these four categories occurring worldwide to cover a wide range of mineralogy geological age geotectonic setting and geographical positions concentrations of major elements si al k na ca fe mg mn ti and p were obtained by x ray fluorescence xrf and those of minor and trace elements p fe li ge ga rb sr ba tl pb y cs ba la ce pr nd sm eu gd tb dy ho er tm yb and lu were established by laser ablation inductively coupled plasma mass spectrometry la icp ms in areas free of coarse na feldspar veins or patches we show that the four groups have very different average values of the minor and trace elements however only the cations occupying tetrahedral sites particularly the fe and p are sufficiently immobile to show distinct differences among pegmatites hence we propose a p fe diagram to discriminate among the four groups of pegmatites as a possible criterion with which to classify pegmatites

tectonic controls of ordovician arc and marginal basin volcanism in wales ensialic destructive plate margin volcanism persisted in wales from late tremadoc to caradoc times late tremadoc uplift and erosion in nw wales is attributable to onset of subduction and development of a frontal ridge system fore arc south east of this in the vicinity of the harlech dome and in sw wales more localized uplift was associated with the development of arc volcanoes at a volcanic front in north wales the arc volcanism occurred in a regime of e w crustal extension and was centred on a deep crustal discontinuity during arenig times the arc terrane was transgressed subsequently marine conditions with local and temporary emergence persisted through arenig to caradoc episodes of marginal basin volcanism while there was widespread and persistent subsidence in wales during development of the marginal basin the volcanism occurred mainly along complex and relatively narrow grabens which were sites of repeated channelling of magmas and pronounced subsidence the grabens mark the sites of deep and steep crustal discontinuities fractures one of which controlled the earlier arc volcanism changing sites of volcanism in wales can now be seen as due to transfer of active extension from one fracture to another there is evidence that the fractures were present by tremadoc times and they almost certainly formed before development of the cambrian marine rift basin they are most likely to have been strike slip faults or shear zones and their pattern in wales indicates that they may represent part of a complicated deep crustal strike slip duplex system the volcanically active grabens of the marginal basin are considered to reflect upward propagation of splay faults flower structure which channelled magmas through the cover during extension across the fractures the fractures and associated grabens strongly influenced the location and orientation of zones of relatively high strain that developed during late caledonian compression and transpression in north wales the volcanically active grabens trended broadly n s oblique to the exposed ne sw basement tectonic grain and dominantly e w extension seems to have persisted throughout the ordovician volcanism while there is considerable uncertainty concerning ordovician plate tectonic configurations and displacements the extension is best explained by invoking a n s convergence vector between the oceanic and over riding microcontinental plates with resultant sinistral shear stress in the latter and sinistral transtensional displacements across the arc and marginal basin the model highlights the suspect nature of the relationship between the welsh ordovician terrane and others to the north

a model for monazite melt equilibrium and application to the generation of granitic magmas abstract in order to model the behaviour of zr hf ti p u th y and the rare earth elements ree in the continental crust the parameters which control the equilibria between accessory minerals and granitic melts must be determined this paper proposes equations for the equilibrium between monazite and ca poor felsic melts in a first step all the light ree are considered as a single component and an equation describing monazite solubility is deduced from the available experimental data in a second step the fractionation of ree by monazite is investigated on the basis of a natural example of coexisting monazite and obsidian from macusani peru the solubility of monazite can be used as a thermometer based on the total ree content of natural magmatic rocks application of ree thermometry to various peraluminous rock series suggests that it is a reliable tool for determining temperatures of magmatic processes the equation governing ree fractionation by monazite is used to discuss genetic relationships between a melt and a presumed parental rock using the composition of the monazite in the parental rocks and the ree pattern of the daughter rock this method has been applied successfully to high himalayan manaslu and tibetan slab granites it is suggested that detailed petrographical work on monazite including electron microprobe analyses and sem imaging of its internal structures combined with the model presented here can be a useful tool for deciphering the genesis and the differentiation of peraluminous granitic magmas in the continental crust

the miocene pliocene macusani volcanics se peru i mineralogy and magmatic evolution of a two mica aluminosilicate bearing ignimbrite suite

formation and evolution of the hogtuva beryllium deposit norway metagranite in the hogtuva tectonic window nordland norway hosts several spatially restricted be mineralisations with phenakite as the main ore mineral geochronology of magmatic zircon zircon i indicates crystallisation of phenakite bearing and beryl free metaluminous granite at 1787 57 ma and of phenakite and beryl beryl i bearing peraluminous aplites and pegmatites at 1710 59 ma crystallisation of texturally distinct zircon zircon ii cogenetic with fluorite in peraluminous aplites and pegmatites occurred at 434 14 ma during caledonian metamorphism in be mineralised and barren metagranite breakdown of phenakite post dates growth of zircon ii and resulted in the crystallisation of metamorphic hogtuvaite ca2 text fe 3 2 text fe 3 3 si4bealo20 in metaluminous metagranite and metamorphic beryl beryl ii in peraluminous metamorphosed aplites and pegmatites qualitative and quantitative assessment of mineral reactions implies that be has not been mobilised to significant degrees during metamorphism in spite of the presence of a fluorine rich fluid and that phenakite underwent in situ metamorphic reactions hogtuvaite crystallised as a metamorphic phase at the expense of phenakite the anorthite component in albitic plagioclase magnetite and possibly clinopyroxene in peraluminous environments the breakdown of phenakite to metamorphic beryl ii is accompanied by the formation of albite a decreasing activity ratio of a k h in the metamorphic fluid results in the reaction of k feldspar and phenakite to beryl ii further decrease in a k h finally results in complete transformation of the remaining k feldspar into albite the metamorphic breakdown of phenakite in the distinct be mineralisation types at hogtuva is probably controlled by changes in the activities of na k and h in the coexisting metamorphic fluid

variability over time in the sources of south portuguese zone turbidites evidence of denudation of different crustal blocks during the assembly of pangaea this study combines geochemical and geochronological data in order to decipher the provenance of carboniferous turbidites from the south portuguese zone sw iberia major and trace elements of 25 samples of graywackes and mudstones from the mertola visean mira serpukhovian and brejeira moscovian formations were analyzed and 363 u pb ages were obtained on detrital zircons from five samples of graywackes from the mira and brejeira formations using la icpms the results indicate that turbiditic sedimentation during the carboniferous was marked by variability in the sources involving the denudation of different crustal blocks and a break in synorogenic volcanism the visean is characterized by the accumulation of immature turbidites mertola formation and the base of the mira formation inherited from a terrane with intermediate to mafic source rocks these source rocks were probably formed in relation to devonian magmatic arcs poorly influenced by sedimentary recycling as indicated by the almost total absence of pre devonian zircons typical of the gondwana and or laurussia basements the presence of carboniferous grains in visean turbidites indicates that volcanism was active at this time later serpukhovian to moscovian turbiditic sedimentation mira and brejeira formations included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism the abundance of precambrian and paleozoic zircons reveals strong recycling of the gondwana and or laurussia basements a peri gondwanan provenance is indicated by zircon populations with neoproterozoic cadomian avalonian and pan african zircon forming events paleoproterozoic and archean ages the presence of late ordovician and silurian detrital zircons in brejeira turbidites which have no correspondence in the gondwana basement of sw iberia indicates laurussia as their most probable source

cryptic trace element variation as an indicator of reverse zoning in a granitic pluton the ricany granite czech republic cryptic variation recognized on the basis of trace element patterns shows the oieany granite in the northeastern part of the hercynian central bohemian pluton to be a reversely zoned high level intrusion unlike many other reversely zoned plutons there are no marked differences in modal composition between the margins and the centre of the intrusion the granite is generally peraluminous and geochemically evolved as demonstrated by its restricted and high sio 2 range and low k rb ratio coupled with a c two fold variation in ba and sr concentrations modelling shows that the geochemical variations can be most readily explained by k feldspar dominated fractionation in a magma chamber below the present level of exposure the reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient the least evolved magma was emplaced in the centre of the high level pluton with the more evolved magma around it recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement

the stratigraphy correlation provenance and palaeogeography of the skiddaw group ordovician in the english lake district a new lithostratigraphy is presented for the skiddaw group lower ordovician of the english lake district two stratigraphical belts are described five formations are defined in the northern fells belt ranging in age from tremadoc to early llanvirn they are all mudstone or sandstone dominated of turbidite origin in ascending order they are named the bitter beck watch hill hope beck loweswater and kirk stile formations two formations are defined in the central fells belt ranging in age from late arenig to llanvirn these are the buttermere formation a major olistostrome deposit overlain by the tarn moor formation consisting of turbidite mudstones with volcaniclastic turbidite sandstone beds a revised graptolite and new acritarch biostratigraphy for the skiddaw group is presented with eight graptolite biozones and thirteen acritarch assemblages and sub assemblages the provenance of the group is assessed from detailed petrographical and geochemical work this suggests derivation in the early ordovician largely from an old inactive continental arc terrane lying to the south east with the appearance of juvenile volcanic material in the llanvirn comparisons and correlations of the skiddaw group are made with the isle of man and eastern ireland

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

what controls chemical variation in granitic magmas abstract consideration of the models that have been applied to explain the chemical variations within granitic rock suites shows that most are inadequate to account for the main variations this stems from a variety of model deficiencies ranging from physical or energetic inadequacies to incompatibility with the chemical data or internal inconsistency between models based on for example isotope or trace element data and major element data we contend that any model that fails any of these tests of internal consistency cannot be considered further thus although we can point to examples in which many of the traditionally accepted mechanisms have played secondary roles in producing variation there presently remains but one viable choice for the primary mechanism by which most granitic magmas acquire compositions beyond the range defined by the compositions of crustal melts that primary mechanism is peritectic assemblage entrainment pae we infer that once a partial melt has formed in a crustal protolith it may segregate from its complementary solid residue carrying small crystals of the peritectic phase assemblage formed in the melting reaction and that the ratios of individual peritectic minerals in the entrained assemblage remains fixed in the ratio decreed by the stoichiometry of the melting reaction for those elements with low solubilities in granitic melts pae in varying degrees accompanied by co entrainment of accessory minerals is responsible for most of the primary elemental variation in granitic magmas in contrast the concentrations of elements with high solubilities in silicic melts reflect the protolith compositions in a simple and direct way the source is the primary control on granite magma chemistry it dictates what is available to dissolve in the melt and what will be formed as the entrainable peritectic assemblage the apparent complexity in granitic rock suites is largely a consequence of these processes in the source all other mechanisms contribute only as a secondary overlay

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

discussion unraveling the provenance of eocene oligocene sandstones of the thrace basin north east greece by caracciolo et al 2011 sedimentology 58 1988 2011

exceptions to the relationship between plate tectonics and sandstone composition abstract routine use of qfl qplsmlvm and lmlslv plate tectonic provenance diagrams has led to the recognition of error populations for these sandstones the interpretation of tectonic setting based on data exclusive of petrography does not coincide with the interpretation of tectonic setting based on their location on compositional diagrams the anomalous sandstones can be separated into at least four categories i sandstones deposited during the transition between tectonic regimes may be derived in part from relict source rocks ii the relative enrichment of sandstones in detrital quartz by weathering and or depositional reworking may lead to an inaccurate interpretation of tectonic setting from compositional data iii sandstones deposited in tectonic settings as yet unrepresented on he provenance diagrams may plot between the provenance fields or overlap existing fields iv the role of detrital carbonate rock fragments directly affects the location of data points on provenance diagrams and is an unresolved problem the first two categories represent permanent problems in the use of sandstone composition as an indicator of plate tectonic setting whereas the last two may only be temporary problems that can be solved by more data and a consensus on determining detrital modes recognition of anomalous sandstones in the rock record will reduce the probability of erroneous interpretations of tectonic setting and enhance the use of sandstone petrology as an indicator of plate tectonic setting

experimental partitioning of be cs and other trace elements between cordierite and felsic melt and the chemical signature of s type granite the trace element signature that cordierite crd imparts to silicic magmas was evaluated by experiment using metapelite mineral mixtures to produce cordierite bearing peraluminous granitic melts at 200 mpa ph2o from 700 to 850 c most elemental partition coefficients vary with t beryllium is strongly compatible with dbecrd melt values decreasing linearly from 202 0 to 6 7 as t rises from 700 to 850 c manganese is compatible dmncrd melt 7 67 to 1 92 over the same range of t and shows similar values to those reported for biotite in silicic melts incompatible components include li rb b f and p although cs is nearly compatible in cordierite especially at higher t dcscrd melt 0 19 to 0 60 where the large alkalis are better accommodated structurally cordierite appears to be the most effective crystalline reservoir of be and cs in metapelites and their anatectic melts natural data support the hypothesis that crd when present in granitic melts sequesters be cs and in the absence of garnet mn s type granitic rocks containing crd show consistently low be contents mean 0 8 ppm be with an average range of 1 to 1 20 whereas crd free granites e g containing accessory garnet exhibit distinctly higher be contents mean 6 ppm be with an average range of 3 to 12 these values increase further in evolved facies mean 69 ppm be with a an average range of 11 to 145 which commonly give rise to beryl bearing pegmatites whole rock signatures of be discriminate source environments of silicic magmas at a resolution equal to the boundaries of the cordierite stability field e g at the p t x conditions where cordierite gives rise to garnet aluminum silicate cordierite bearing granitic rocks contain low cs contents mean 1 8 ppm cs compared to the crd free equivalents mean 18 ppm cs mn contents also correlate with the presence mean 0 01 wt mno or absence of crd mean 0 09 wt mno depending on its contribution to anatexis cordierite may either give or take s type chemical character from granitic liquids resulting in a distinctive crd associated group of s type elements this signature is different from that of micas high li f and to a lesser degree be and mn whole rock compositions of granites coupled with notable absences of beryl in their associated pegmatites indicate that a sizable population of s type granites originated from crd bearing sources the normative crd component of silicic peraluminous melts is 4 wt to 850 c higher modal contents of cordierite reflect either restite entrainment or peritectic reactions which produce crd after magma ascent to shallow depths the distinctive trace element signature of cordierite now provides improved resolution of the source mineralogy for s type magmas

the provenance and crustal residence ages of british sediments in relation to palaeogeographic reconstructions 24 smnd isotope analyses of fine grained phanerozoic and modern clastic sediments from britain and quebec are presented in combination with published data they have been used to calculate crustal residence ages tcr and to assess the provenance of the british sedimentary mass sediments now preserved on either side of the suture formed by the closure of the iapetus ocean ca 400 ma ago were derived from isotopically distinct source regions sediments north of the suture are characterised by1 7 tcr 2 8 ga whereas those to the south exhibit a smaller range and an average value of 1 6 ga the northern and southern source regions were most probably laurentia and gondwana respectively it seems likely that a third source perhaps baltica provided the lower palaeozoic southern uplands succession sediments deposited in southern britain after the closure of iapetus were derived mainly from the recycling of older sediments the tectonic rearrangements which occurred during the phanerozoic are not reflected in the smnd isotopic structure of the southern british sedimentary mass suggesting that the caledonian and hercynian orogenies and even the grenville orogeny involved minimal accretion of new mantle derived material into the british and adjacent continental crust smnd analyses of fine grained clastic sediments provide a powerful sedimentological tool for elucidating palaeogeography clastic source areas sediment recycling and maturity and some aspects of sediment transport

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

experimental silicate mineral melt partition coefficients for beryllium and the crustal be cycle from migmatite to pegmatite partition coefficients dbemineral melt for beryllium between hydrous granitic melt and alkali feldspars plagioclase feldspars quartz dark mica and white mica were determined by experiment at 200 mpa h2o as a function of temperature 650 900 c activity of be in melt trace levels to beryl saturation bulk composition and thermal run direction at trace levels be is compatible in plagioclase of an31 1 84 at 700 c and muscovite 1 35 at 700 c but incompatible in biotite 0 39 0 54 from 650 800 c alkali feldspar 0 38 0 19 from 680 850 c quartz 0 24 at 800 c and albite 0 10 at 750 c the partition coefficients are different at saturation of the melt in beryl lower in the case of plagioclase of an31 0 89 at 700 c muscovite 0 87 at 700 c biotite 0 18 0 08 from 675 800 c alkali feldspar 0 18 0 14 from 680 700 c and quartz 0 17 0 08 from 750 800 c but higher in the case of albite 0 37 at 750 c with other data sources these new partition coefficients were utilized to track first the distribution of be between aluminous quartzofeldspathic source rocks and their anatectic melts and second the dispersion or concentration of be in melt through igneous crystal fractionation of different magma types e g s type i type up to beryl saturated granitic pegmatites and finally into their hydrothermal aureoles among the rock forming minerals cordierite calcic oligoclase and muscovite in this order control the fate of be because of the compatibility of be in these phases in general beryl bearing pegmatites can arise only after extended crystal fractionation of large magma batches to f fraction of melt remaining 0 05 granitic magmas that originate from cordierite bearing protoliths or that contain large modal quantities of calcic oligoclase will not achieve beryl saturation at any point in their evolution

beryllium in silicic magmas and the origin of beryl bearing pegmatites this chapter addresses the portion of the geochemical cycle of beryllium that entails its transfer through the continental crust by the generation and migration of silicic magmas which will be referred to loosely as granitic but will include all of the textural variants of rocks derived from the granitic bulk compositions within the granite system we will examine the distribution of be between anatectic melts and residual crystals and we will track the accumulation of be in melt via crystal fractionation culminating in the saturation of pegmatite forming melts in the mineral beryl beryl is unquestionably the most common manifestation of be enrichment and the most abundant of the phases that contain essential beryllium see cern this volume to explain the presence of beryl in pegmatites we pose four questions 1 how much be does it take to saturate a granitic pegmatite forming melt in beryl 2 how much be is likely to be incorporated in silicic partial melts at their source 3 consequently how much fractionation of a typical granitic magma must occur to achieve beryl saturation in pegmatitic derivatives or is beryl saturation possible without extended magmatic fractionation 4 and should all granitic magmas be expected to achieve beryl saturation eventually or are there special attributes of the source material or crystalline phases in the magma that predetermine the likelihood of forming beryl in pegmatitic differentiates to address these questions we start with a review of beryl saturation in pegmatites we then examine the likely abundance of be derived by anatexis at the sources of granitic magmas with the two ends of the system bracketed we can then subject be fractionation to conventional modeling methods to ascertain how much fractionation must take place to bring granitic melts to beryl saturation as a review this chapter relies as much as possible on readily available publications

phase relations of a f enriched peraluminous granite an experimental study of the kymi topaz granite stock southern finland phase relations of f rich kymi equigranular topaz granite have been investigated experimentally at 100 500 mpa as a function of water activity and f content fluorite and topaz can crystallize as liquidus phases in f rich peraluminous systems but the f content of the melt should exceed 2 5 3 0 wt for the crystallization of topaz in peraluminous f bearing melts containing more than 1 wt f topaz and muscovite are expected to be the first f bearing phases to crystallize at high pressure whereas fluorite and topaz should crystallize first at low pressure following reaction models the saturation of fluorite and topaz caal2si2o8 plagioclase 2 alf3 melt caf2 fluorite 2al2sio4f2 topaz the obtained partition coefficient for f between biotite and glass d f bt glass ranges from 1 89 to 0 80 average value 1 29 and can be used as an empirical fluormeter to determine the f content of coexisting melts combined petrological and experimental studies of the kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water saturated fluid saturated conditions and that the f content of the melt was at least 2 wt the mean f content of natural biotite 3 92 wt suggests that the late stage crystallization of biotite occurred in melts containing about 3 wt f the early crystallization of biotite and the presence of muscovite in our experiments at 200 mpa contrasts with the late stage crystallization of biotite and the absence of muscovite in the natural assemblage indicating that crystallization pressure may have been lower than 200 mpa for the granite

rifting during separation of eastern avalonia from gondwana evidence from subsidence analysis subsidence curves for cambrian ordovician sequences from the anglo welsh segment of the paleocontinent of avalonia reveal two periods of regionally enhanced basement subsidence early cambrian 545 518 ma and late cambrian to early tremadocian 505 490 ma the earlier event may record transtension following the avalonian cadomian orogeny the second event may be a transtensional precursor to the late tremadocian volcanic arc on eastern avalonia however paleomagnetic faunal volcanic and sedimentary evidence suggests that the main separation of eastern avalonia from gondwana occurred after middle arenigian time rifting during separation is probably recorded by localized middle arenigian to llanvirnian 480 462 ma subsidence along the welsh basin margin but rifting must have occurred mainly on the now obscured southern margin of the avalonian continent pronounced caradocian 462 449 ma subsidence is associated with back arc rifting after separation from gondwana