mica liquid trace elements partitioning and the granite pegmatite connection the st sylvestre complex western french massif central abstract we constrain the genetic relation between granite and pegmatite parental melts from the variscan saint sylvestre leucogranite complex and associated pegmatite bodies massif central france through compositions of micas using mica trace element concentrations and available partition coefficients for li rb ba cs and f we calculated the trace element contents of granitic and pegmatitic melts at equilibrium with micas biotite in leucogranites and pegmatites ranges mostly from fe biotite to siderophyllite more evolved facies contain protolithionite and zinnwaldite and lepidolite occurs in the most fractionated pegmatite white micas have homogeneous compositions from muscovite to li phengite in granites biotite and muscovite trace element distributions are clustered in pegmatites mica trace element contents globally follow differentiation from the least to the most evolved body the reconstructed pegmatitic and granitic melts present strong compositional similarities such as enrichments in li rb cs and depletion in ba that suggest a similar origin however micas are shown to have selectively equilibrated with the last melt or fluid in contact and so trace element concentrations of early magmatic liquids are rarely preserved inversion of the mica data constrains the composition of parental melts and the trace element evolutions during crystallization leucogranite and pegmatite melts show mutual incompatible element evolutions inconsistent with a parent daughter genetic relation the data and the modelling suggest that they represent non cogenetic melts generated by discrete episodes of partial melting differentiation is thus inherited from source processes rather than being the consequence of fractional crystallization of a common parental melt magma we suggest that both the leucogranites and the pegmatites originate from partial melting of a heterogeneous source rather than pegmatites being the product of granite crystallization

chemical signature of quartz from s and a type rare metal granites a summary abstract about 800 new and 1200 already published laser ablation inductively coupled plasma mass spectrometry analyses of quartz from rare metal granites and related greisens quartz tourmaline rocks and quartz veins were evaluated in order to define typical trace element signatures of quartz of different origin the studied dataset comprises typical examples of sub aluminous to slightly peraluminous plutons a type granites of the kimi stock finland eastern erzgebirge czech republic orlovka russia and ongon chairchan mongolia and strongly peraluminous plutons s type granites of beauvoir france cornwall england panasqueira and argemela portugal western erzgebirge czech republic additional 700 mostly already published analyses of quartz from barren granites of all geochemical types i s a type rhyolites and barren and rare element pegmatites were evaluated for comparison compiled data reveal high diversity in the contents of trace elements in quartz even among rocks of similar geochemical composition the most common trace elements in magmatic quartz are al li and ti with medians of 447 39 6 and 17 4 ppm in s type rare metal granites and 160 15 and 6 6 ppm in a type rare metal granites the contents of all these elements in greisens and quartz veins are significantly lower than in their parental granites al contents above 450 ppm should serve as a reliable indicator of s affinity of the analyzed granite while contents

from magmatic to hydrothermal sn li nb ta w mineralization the argemela area central portugal abstract the argemela mineralized area ama central portugal exhibits a nearly continuous magmatic to hydrothermal ore forming sequence typical of variscan granite related rare metal deposits disseminated and vein type mineralization are distributed in two systems the argemela mine am and the cabeco da argemela ca disseminated mineralization includes montebrasite cassiterite and columbite tantalite dispersed in rare metal granites vein type mineralization occurs both in granites and country rocks the ca system exposes three generations of intragranitic veins with montebrasite in the two earliest and montebrasite wolframite cassiterite and columbite tantalite in the latest country rock veins include a swarm of cassiterite and montebrasite veins am and rare isolated wolframite veins ca disseminated cassiterites are enriched in ta2o5 and nb2o5 compared to vein cassiterites disseminated columbite tantalites evolve toward mn and ta rich chemistries that contrast with the more fe and nb rich compositions in intragranitic veins in the ca system both intragranitic and country rock veins crystallize early mn rich wolframites followed by late more fe rich compositions associated with nb ta poor cassiterite the later replaced by stannite field relations structural mineralogical and geochemical data suggest that the disseminated and vein type mineralization are expressions of a continuous metallogenic evolution initiated at the magmatic stage pursued during the magmatic hydrothermal transition and ended with hydrothermal circulations in country rock the two mineralized systems share similarities but they also show major differences structural analysis demonstrates that the intragranitic veins in the ca and the country rock veins in the am were emplaced under the same tectonic regime therefore the two systems are variants of the same local metallogenic evolution sn and w show markedly contrasted behaviors both have a magmatic source but only sn reaches concentrations leading to saturation of the melt with cassiterite w is deposited later and preferentially to sn in intragranitic veins at the hydrothermal stage cassiterite and wolframite deposition are disconnected and overall wolframite occurs only in minor amounts the metallogenic model proposed for the ama emphasizes magmatic rare metal concentration processes exsolution of magmatic fluids and selective deposition of metals during the magmatic hydrothermal and later hydrothermal stages the sn li nb ta dominated and w poor signature of the ama makes it similar to lct pegmatites of the central iberian zone but is distinctive from the world class w sn cu panasqueira deposit nearby

magmatic fractionation and the magmatic hydrothermal transition in rare metal granites evidence from argemela central portugal abstract rare metal granites rmgs are highly evolved intrusions with specific geochemical signatures that are the result of combined magmatic and hydrothermal processes in most examples the early evolution is overprinted by late subsolidus transformations and the role of magmatic and magmatic hydrothermal fractionation processes remains unclear the origin of fluids involved in magmatic hydrothermal systems is also an open question the argemela rmg portugal is a small subvolcanic intrusion which exposes in remarkable continuity a sequence of magmatic magmatic hydrothermal and early hydrothermal processes the intrusion comprises a main granitic facies and a border unit made of a complex alternation of aplitic and pegmatitic facies plus three generations of intragranitic veins the granitic mineral assemblage includes quartz k feldspar albite muscovite and accessory montebrasite cassiterite and columbite tantalite the whole rock chemistry is strongly peraluminous with very high p2o5 li and f enrichments elevated rare metal sn nb ta w concentrations and strong depletions in ca fe ti mg trace element zonation in minerals mainly muscovite and quartz record crystallization fractionation processes along the magmatic hydrothermal transition three main stages are recognized magmatic crystal fractionation and accessory minor mineral saturation magmatic hydrothermal fluid melt element partitioning and early hydrothermal corresponding to the segregation and collection of magmatic fluids in the intragranitic vein system those are followed by limited metasomatic transformations and a late sulphide stage stable isotope o h data demonstrate a magmatic origin for the early fluids and a granite buffered signature for the vein forming fluids the fractionation of rare elements sn nb ta li w mn b rb cs from the magmatic to the early hydrothermal stage is quantitatively modelled from the combination of three mechanisms crystal fractionation magmatic crystallization of accessory minor phase mcma and fluid melt partitioning sn and w show a markedly contrasted behaviour with sn precipitated as disseminated mineralization within the intrusion and w partitioned toward the magmatic fluid and extracted from the intrusion geochemical trends along the magmatic hydrothermal transition do not require phases with unusual properties such as immiscible hydrous melts to be explained and they do not necessarily result in an amplification of initial rare metal melt enrichments the argemela rmg stresses the importance of mcma to generate magmatic rare element pre concentrations which later can be hydrothermally redistributed to form large economic deposits

missing molluscs as evidence of large scale early skeletal aragonite dissolution in a silurian sea in the silurian carbonate platform succession of gotland sweden interreef limestone and marl sequences have shallow marine shelly assemblages dominated by brachiopods typical of many paleozoic benthic faunas locally from similar facies where early skeletal silicification occurred associated with bentonites there are rich and diverse assemblages of originally aragonitic molluscs quantitative faunal analysis suggests that massive depletion of skeletal aragonite chiefly molluscs took place and the entire molluscan fauna may generally be underrepresented by at least 100 fold previous workers on the gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization our findings indicate molluscs as the probable source of this diagenetic calcite not aragonite mud as was previously thought the taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original silurian shelf benthos and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect

a tin mineralized topaz rhyolite dike with coeval topaz granite enclaves at qiguling in the qitianling tin district southern china abstract the qiguling topaz rhyolite is present as a dike within the qitianling biotite granite batholith of the nanling range of southern china here the rhyolitic dike 4 5 m wide and 500 m long contains enclaves of topaz granite these rhyolites contain up to 72 wt sio 2 have alumina saturation index asi 1 1 and have groundmasses with estimated fluorine contents of approximately 1 5 wt textural relationships provide evidence of a quenched silicate melt that contains quartz k feldspar albite and zinnwaldite phenocrysts in a groundmass containing abundant topaz the rhyolites in the study area are also strongly enriched in tin 90 2700 ppm and generally have a close association between cassiterite and zinnwaldite although cassiterite is also present as sponge textured fills between rock forming minerals granite enclaves and their hosted rhyolite have similar major geochemical compositions and mineralogies to each other zircon u pb dating indicates that the topaz rhyolite 147 150 ma and topaz granite enclaves 154 ma were formed contemporaneously with ages that overlap within analytical uncertainty in addition the major and trace element compositions of the rhyolite and their granite enclaves are dissimilar to those of the hosting qitianling biotite granite this discovery of granite enclaves within rhyolite dikes suggests the presence of a topaz bearing granite body at depth that may host tin mineralization the expected hidden tin granite may be of great interest in the further exploration

contrasting evolution of fluorine and boron rich tin systems individual sn provinces or regions within provinces are sometimes enriched in fluorine or boron giving rise to fluorine rich and boron rich environments the structural styles of mineralisation within these environments are similar except that hydrothermal intrusive breccia pipes are more common in boron rich environments and apogranite massive greisen systems are more common in fluorine rich environments the increased solubility of h2o in b bearing magmas compared to f bearing magmas may play a role in the structural evolution of the mineralising systems the greater mechanical energy produced during crystallisation of b rich magmas provides a mechanism for breccia pipe and stockwork formation while the more passive crystallisation of f rich magmas often results in the formation of disseminated mineralisation the partitioning of boron toward the aqueous fluid phase and the enhanced solubility of silica in the fluid phase frequently results in tourmalinisation and silicification of the wall rocks in b rich environments in contrast feldspathic and sericitic alterations usually predominate in f rich environments

the greer lake leucogranite manitoba and the origin of lepidolite subtype granitic pegmatites abstract the archean greer lake leucogranite intruded metabasalts of the bird river greenstone belt in the southwestern part of the superior province of southeastern manitoba the considerably evolved multiphase peraluminous b p and s poor leucogranite k rb 132 to 24 was probably generated by fault friction assisted anatexis of dominantly metatonalitic rocks and subsequent differentiation the leucogranite produced interior transitional non crosscutting pods of barren beryl columbite and lepidolite subtype pegmatites that solidified from local segregations of highly fractionated residual melt steep fractionation gradients characterize the granite to pegmatite transition most conspicuously so in the case of the most evolved li rb cs be mn sn nb ta f rich lepidolite subtype pod ac 3 with k rb 16 and cs 330 ppmwt in accessory k feldspar 2 5 and 11 200 ppmwt respectively in lepidolite cs 28 000 ppmwt in beryl and ta ta nb at 0 95 in manganotantalite the greer lake example documents beyond any doubt the igneous derivation of lepidolite subtype pegmatites from a plutonic parent most cases of generally very scarce lepidolite subtype pegmatites obscure this relationship as the volatile rich highly fluid melts stable to relatively low temperatures commonly migrate to great distances from their plutonic sources

the h f ratio as an indicator of contrasted wolframite deposition mechanisms abstract understanding wolframite deposition mechanisms is a key to develop reliable exploration guides for w in quartz veins from the variscan belt of europe and elsewhere wolframites have a wide range of compositions from hubnerite mnwo4 to ferberite rich fewo4 deposition style source of mn and fe distance from the heat fluid source and temperature have been proposed to govern the wolframite h f hubnerite ferberite ratio defined as 100 at mn fe mn the argemela mineralized district located near the world class panasqueira w mine in portugal exposes a quartz wolframite vein system in close spatial and genetic association with a rare metal granite wolframite is absent as a magmatic phase but w rich whole rock chemical data suggest that the granite magma is the source of w wolframite occurs as large homogeneous hubnerites h f 64 75 coexisting with montebrasite k feldspar and cassiterite in the latest generation of intragranitic veins corresponding to magmatic fluids exsolved from the granite locally early hubnerites evolve to late more fe rich compositions h f 45 55 in a country rock vein an early generation of fe rich hubnerites h f 50 63 is followed by late ferberites h f 6 23 most argemela wolframites have h f ratios higher than at panasqueira and other variscan quartz vein deposits which dominantly host ferberites in greisens or pegmatitic veins wolframites generally have intermediate h f ratios in those deposits fluid rock interactions either involving country rocks quartz veins or granite greisens control w deposition in contrast at argemela wolframite from intragranitic veins was deposited from a magmatic fluid differentiation of highly evolved peraluminous crustal magmas led to high mn fe in the fluid which promoted the deposition of hubnerite therefore the h f ratio can be used to distinguish between contrasted deposition environments in perigranitic w ore forming systems hubnerite is a simple mineralogical indicator for a strong magmatic control on w deposition

liquidus equilibria in the system k2o na2o al2o3 sio2 f2o 1 h2o to 100 mpa ii differentiation paths of fluorosilicic magmas in hydrous systems we investigated phase equilibria in the six component system na2o k2o al2o3 sio2 f2o 1 h2o at 100mpa to characterize differentiation paths of natural fluorine bearing granitic and rhyolitic magmas topaz and cryolite are stable saturating solid phases in calcium poor systems at 100mpa the maximum solidus depression and fluorine solubility in evolving silicic melts are controlled by the eutectics haplogranite cryolite h2o at 6408c and 4 wt f and haplogranite topaz h2o at 6408c and 2 wt f topaz and cryolite form a binary peralkaline eutectic at 6608c 100mpa and fluid saturation the low temperature nature of this invariant point causes displacement of multiphase eutectics with quartz and alkali feldspar towards the topaz cryolite join and enables the silicate liquidus and cotectic surfaces to extend to very high fluorine concentrations more than 30 wt f for weakly peraluminous and subaluminous compositions the differentiation of fluorine bearing magmas follows two distinct paths of fluorine behavior depending on whether additional minerals buffer the alkali alumina ratio in the melt in systems with micas or aluminosilicates that buffer the activity of alumina magmatic crystallization will reach either topaz or cryolite saturation and the system solidifies at low fluorine concentration in leucogranitic suites precipitating quartz and feldspar only the liquid line of descent will reach topaz or cryolite but fluorine will continue to increase until the quaternary eutectic with two fluorine bearing solid phases is reached at 5408c 100mpa and aqueous fluid saturation the maximum water solubility in the haplogranitic melts increases with the fluorine content and reaches 12 5 0 5 wt h2oat the quartz cryolite topaz eutectic composition a continuous transition between hydrous fluorosilicate melts and solute rich aqueous fluids is not documented by this study our experimental results are applicable to leucocratic fluorosilicic magmas in multicomponent systems however the presence of calcium may severely limit enrichment of fluorine by crystallization of fluorite

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

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

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

scaling of sedimentation rates and drowning of reefs and carbonate platforms the rule that sedimentation rates decrease as the time interval increases has been examined by a procedure that avoids the mathematical problem of plotting a variable time against its inverse the test confirms that the scaling trend has real physical meaning in the time range of 10 1 108 yr sedimentation rates change roughly proportionally to the inverse of the square root of time this report proposes and evaluates the hypothesis that the growth potential of reefs and carbonate platforms follows the same scaling trend the trend implies that a growth of 104 m yr sustained over 103 yr an upper limit of reef growth in the holocene translates into 102 m yr sustained over 107 yr decrease of the growth potential with increasing time solves the paradox of drowned platforms if the decrease results largely from environmental factors and not simply from increase of the time fraction of subaerial exposure

evolution of the ordovician through middle pennsylvanian carbonate shelf in east central california carbonate shelf rocks marked by various sedimentary features suggesting intertidal to supratidal deposition or bearing rich benthic faunas and their corresponding slope and basin rock sequences containing planktic fossils and sediment gravity flow deposits have been identified in the inyo mountains argus range region of east central california for all of the paleozoic from ordovician through middle pennsylvanian four major depositional sequences each beginning with a marine transgression and all but the third ending with a progradation were developed representing 1 early ordovician into early silurian time 2 early silurian into earliest middle devonian time 3 middle to late devonian time and 4 early to middle late mississippian time a period of basinal infilling in the late mississippian was followed by a fifth major marine transgression in the early pennsylvanian the carbonate shelf itself evolved from a homoclinal ramp in the ordovician to an accretionary rimmed margin by the early devonian this margin was drowned probably in the middle devonian by the early mississippian a new homoclinal ramp had been developed before the end of the mississippian this ramp became distally steepened and then was transformed into an accretionary rimmed margin the early to middle pennsylvanian marine transgression gave rise to still another homoclinal carbonate ramp subsidence of 2 300 m occurred between early ordovician and middle pennsylvanian time in the area immediately east of the inyo mountains it increased westward to probably 3 500 m at the edge of the owens valley as the continental margin subsided and bent downward 1 between early ordovician and middle late mississippian time as a result of subsidence and relatively low rates of sedimentation the water depth in the western part of the study area increased from close to sea level at the beginning of the ordovician to as much as 3 000 m in the late mississippian because of higher rates of sediment accumulation and lower rates of subsidence in the eastern part of the region shallow water environments were maintained throughout most of this time interval even so the shelf slope break retreated at least 45 km southeastward from middle ordovician to middle late mississippian time and at least 35 km farther southeastward by middle pennsylvanian time

mineralogy and geochemistry of pegmatite hosted sn ta nb and zr hf bearing minerals from the southeastern part of the bastar malkangiri pegmatite belt central india abstract primary tin and rare metal mineralization in the bastar malkangiri pegmatite belt central india is associated with granitic pegmatites hosted by metabasic and metasedimentary rocks the rare metal minerals identified from six mineralized pegmatites at govindpal mundaguda mundval dhuramagurah haladikunda and bacheli include cassiterite columbite tantalite wodginite microlite fersmite and hf zircon ta nb poor cassiterite is ubiquitous and the most abundant ore mineral in all the mineralized pegmatites subtle differences are noted in the ore mineral assemblages and in the compositions of individual minerals in different pegmatites ta nb oxides are represented by microlite wodginite manganotantalite in li f p bearing lct pegmatites govindpal mundaguda and mundval in contrast least evolved members of the lct type pegmatites are characterized by the presence of ferrocolumbite dhuramgurah haladikunda and rare ferrotantalite bacheli the compositional variations of columbite tantalite in terms of ta ta nb and mn mn fe ratios and zircon in terms of hf contents from different pegmatites correlate with the degree of fractionation of the pegmatitic melt in the govindpal pegmatite ta nb poor cassiterite occurs as aggregates of grains small pockets and veinlets in the intermediate and core zone the ta nb oxides are restricted to the core margin texturally and compositionally distinct ta nb rich cassiterite along with ta nb oxides and hf zircon occur as irregular inclusions in ta nb poor cassiterite at the core margin the field evidence textural relations and compositions of the ore minerals suggest that the main mineralizing event was associated with hydrothermal precipitation of ta nb poor cassiterite which postdated precipitation of manganotantalite wodginite microlite hf zircon and ta nb rich cassiterite in the govindpal pegmatite the crystallization of ta nb oxides was facilitated possibly by the removal of li and f from the melt and that of ta nb rich cassiterite by increasing oxygen fugacity calculated higher fe 3 fe 2 in wodginite compared to manganotantalite suggests such a possible increase in oxygen fugacity anastomosing veins of microlite in ta nb poor cassiterite was the last mineralizing event in this pegmatite the consistently high ti contents of this subsolidus vein microlite compared to primary ta nb oxides manganotantalite wodginite and microlite might suggest contamination by ingress of metamorphic fluid during its formation

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

life span and fate of basins the life span of each main class of sedimentary basin is estimated from published data life spans vary over at least three orders of magnitude from 100 m y for passive margin and intracratonic basins the life span estimates are used to calibrate a chart of basin groups that focuses on the likely basin fates i e depositional deformational or thermal consequent fates predetermined by the tectonic setting of a particular basin class are distinguished from contingent fates which are independent of basin type accretion of trench basin fill is for example a consequent fate whereas inversion far field shortening of a rift basin is a contingent fate life span data are also used to calibrate the wilson cycle and indicate that it has an average duration of 260 m y this is certainly an underestimate because basin life spans are an imperfect proxy for the duration of subduction and collision zones

acidity salinity diagrams application to greisen and porphyry deposits to a first approximation alteration minerals in greisen and related fluorine rich porphyry deposits lie in the system k 2 o al 2 o 3 sio 2 h 2 o f 2 o sub 1 equilibria in this model system can be depicted on quartz and fluid saturated chemical potential diagrams whose axes are mu hf acidity where mu hf mu hcl mu sub fcl sub 1 and mu kf salinity where mu kf mu nacl mu sub kna sub 1 mu sub fcl sub 1 advantages of this approach are that it reflects the fact that the anion f unlike cl is incorporated in greisen minerals mainly topaz fluorite and micas and that mineral stabilities can be correlated with possible ore forming processes the most important of these processes is probably vapor phase separation from an aqueous brine or magma first or second boiling fluid inclusion studies have shown that boiling occurs in all porphyry and many but not all greisen deposits vapor phase separation from a magma pneumatolysis must similarly be responsible for the formation of greisenlike mineral assemblages in miarolitic topaz rhyolite lava flows and is presumably also responsible for the formation of gem pockets in more deeply seated pegmatites and granites the result of boiling is an increase in mu hf and a decrease in mu kf in the vapor phase and the opposite in the residual brine or magma in deep greisen veins the muscovite stability field is encountered between the k feldspar and topaz fields whereas in f rich relatively shallow porphyry deposits such as henderson colorado boiling causes aqueous fluids to pass directly from the k feldspar ore zone to the overlying topaz magnetite zone muscovite or f bearing mn fe garnet is only encountered farther out as the fluids are condensed neutralized and diluted by cooler meteoric waters when ca fe mn be w o 2 s 2 and co 2 are added to the greisen model system scheelite is shown to transform to wolframite with increasing mu hf and beryl to phenakite with increasing mu hf or mu kf biotite transforms to magnetite hematite siderite pyrite chlorite or fayalite beyond the k feldspar field its stability is enhanced by high mu hf and chlorite cordierite or mn fe garnet transform to an mn fe carbonate oxide or sulfide or biotite beyond the al silicate field the ca content of plagioclase coexisting with fluorite decreases with an increase in either mu hf or mu kf and thus provides an indicator of total fluorine in both acid and neutral species

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

paleolatitudinal sampling bias phanerozoic species diversity and the end permian extinction species diversity varies with latitude almost all marine sedimentary rock in the paleozoic of europe and north america was deposited in the tropics whereas only 24 was deposited in these latitudes during mesozoic and tertiary time a new plot of species diversity through the phanerozoic takes into account the paleolatitudinal distribution of marine sedimentary rock this plot indicates that the permian witnessed the acme of species diversity prior to the cretaceous and that the triassic recovery following the end permian extinction was much less pronounced than suggested by previous studies

time partitioning in cratonic carbonate rocks dissimilarity in relations between thickness duration and accumulation rate in holocene sections metre scale phanerozoic cycles and epoch interval phanerozoic sequences reflects variation in the distribution of depositional and hiatal time at different scales of observation modern accumulation rates are strongly dependent on duration of deposition lower rates correspond to longer durations phanerozoic cycle thicknesses are similar to those of holocene sections suggesting that both formed while filling similar amounts of accommodation space however accumulation rates of phanerozoic cycles and sequences are about two orders of magnitude less than in modern settings and they show neither strong dependence on duration of accumulation nor significant variation over phanerozoic time hence net accumulation is primarily controlled by regional subsidence rate these relations also allow for determination of that fraction of cycle period recorded as rock and that corresponding to hiatal time at intercycle boundaries depending on subsidence rate and amount of compaction most cratonic carbonate units accumulated over 3 to 30 of the time represented by sequences in which they occur

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

global tectonics and eustasy for the past 2 billion years abstract continental freeboard and eustasy as gauged by the relative position of the world shelf break with respect to sea level have varied by 250 m from today s ice free shelf break depth of 200 m during the past 600 ma assuming constant or uniformly accreting continental crust and ocean water volume in an ice free world sea level fluctuations can be attributed to variation in the world ocean basin volume caused by changes in either its area or its depth relative to the world shelf break an increase in volume and lowering of sea level occur as 1 the world ocean floor ages cools and subsides 2 accreting continents collide thicken and decrease in area and 3 poorly conductive continental platforms become thermally elevated due to a size induced stasis over the mantle conversely a decrease in the age of the world ocean floor attenuation of continental crust during rifting and an increase in continent number and mobility will reduce the world ocean basin volume and raise sea level theoretical sea level calculated from these principles correlates well with calibrated first order cycles of eustatic sea level change for the phanerozoic the record closely fits a simple model of retardation and acceleration of terrestrial heat loss during alternating periods of supercontinent accretion and fragmentation calibrated to sea level highstands successive first order marine transgressions and orogenic pangea regressions characterize a self sustaining 440 ma plate tectonic cycle for the late precambrian and phanerozoic the cycle can be recognized as far back as 2 ga from the tectonic evidence of continental collision and rifting recorded in global orogenic peaks and mafic dike swarms and may be related to major episodes of glaciation and evolutional biogenesis

partitioning of sn and w between granitic melt and aqueous fluid abstract hydrothermal granite related sn and w deposits typically show predominance of one metal over the other at the intrusion and deposit scale this separation may reflect contrasting behavior of these elements during late stage magmatic processes in our experimental study we determined fluid melt partition coefficients of sn and w at 750 c 200 mpa as function of the alumina saturation index asi of the melt for nacl kcl hcl fluids two sets of data were obtained one from analysis of fluid inclusions trapped in glass and the other based on analysis of the quenched fluid our data indicate slight partitioning of sn into the melt and at asi of 0 99 1 16 strong partitioning of w into the aqueous fluid the effect of quenching was evident for tungsten which indicates that fluid melt partition coefficients of w reported in the literature are underestimated the contrasting fluid melt partitioning of sn and w implies that hydrothermal sn and w mineralization is rarely cogenetic furthermore contrasting fluid melt partitioning accounts for the separation and zonation of these metals on the deposit scale and the different style of predominant mineralization tin precipitates from the granitic melt as cassiterite or is incorporated in biotite and other minerals later exsolution of hcl bearing magmatic fluids can efficiently mobilize sn from the granite or the wall rock of the intrusion but can transport sn only over relatively short distances due to reaction of the fluid with feldspar greisenization which results in precipitation of cassiterite and formation of tin greisens tungsten is partitioned into the magmatic fluid and will be lost from the intrusion along with this fluid because greisenization reactions do usually not result in tungsten mineralization w can be transported farther away from the intrusion than sn and is deposited in scheelite bearing skarns or upon cooling in quartz wolframite veins

crystallisation of magmatic topaz and implications for nb ta w mineralisation in f rich silicic melts the ary bulak ongonite massif textural mineralogical and geochemical data on f rich rhyolite ongonite from the ary bulak massif of eastern transbaikalia help constrain the formation of magmatic topaz in these rocks topaz occurs as phenocrysts thus providing compelling evidence for crystallisation at the orthomagmatic stage cathodoluminescence images of topaz and quartz reveal growth textures with multiple truncation events in single grains indicative of a dynamic system that shifted from saturated to undersaturated conditions with respect to topaz and quartz electron microprobe and raman analyses of topaz indicate near pure f composition al2sio4f2 with very limited oh replacement laser ablation icp ms traverses revealed the presence of a large number of trace elements present at sub ppm to hundreds of ppm levels the chemical zoning of topaz records trace element fluctuations in the coexisting melt concentrations of some trace elements li ga nb ta and w are correlated with cathodoluminescence intensity thus suggesting that some of these elements act as cl activators in topaz the study of melt inclusions indicates that melts with different f contents were trapped at different stages during formation of quartz and topaz phenocrysts respectively electron microprobe analyses of glass in subhedral quartz hosted melt inclusions indicate f 1 2 wt whereas irregular shaped melt inclusions hosted in both topaz and quartz have f 9 wt cryolithionite na3li3al2f12 coexists with glass in irregular inclusions implying high li contents in the melt the very high f contents would have increased the solubility of nb ta and w in the melt thus allowing progressive concentration of these elements during magma evolution crystallisation of nb ta w oxides w ixiolite and tantalite columbite may have been triggered by separation of cryolithionite which would have caused f and li depletion and consequent drop in the solubility of these elements

the beauvoir topaz lepidolite albite granite massif central france the disseminated magmatic sn li ta nb be mineralization the beauvoir topaz lepidolite albite granite french massif central is the latest intrusion in a variscan peraluminous granitic complex composed of three units successively emplaced the concealed la bosse granite the colettes two mica granite and the beauvoir granite the 900 m deep drill hole of the geologie profonde de la france deep drilling program of the continental crust has provided a continuously cored section of the beauvoir granite the exposed section of the beauvoir granite is presently mined for kaolin in the upper 200 m it also represents a huge subeconomic disseminated li sn ta be deposit sharing many characteristics with rare metal bearing pegmatites compared to similar li f rich igneous bodies the beauvoir granite is strongly enriched in sn 200 1 400 ppm ta 20 400 ppm and be 20 300 ppm li is located in lepidolite and amblygonite ta and nb mainly in columbo tantalite and uranium rich microlite and sn in cassiterite be is located in lepidolite crystals and in unidentified mineral s the major element composition of the beauvoir granite is similar to that of macusani volcanic glasses of peru and ongonite subvolcanic rocks of mongolia the main structural textural mineralogical and geochemical characteristics of the beauvoir granite can be explained by extreme fractionation of f and li rich magmas and associated fluid phases most trace elements show a strong upward enrichment the high f sub o 2 low solidus temperature and high fluorine content of the beauvoir magma have considerably reduced sn and w fractionation in the expelled magmatic fluid despite its high chlorine content 25 30 wt nacl equiv however f and li enriched geochemical halos have developed in the enclosing mica schist in response to the boiling of the magmatic fluid the relatively deep emplacement of the granite 3 km has limited the development of hydraulic fracturing and subsequent hydrothermal circulation and mineralization thus despite the very high specialization of the beauvoir granite no significant vein type mineralization is directly related to it the la bosse quartz ferberite stockwork was developed before the emplacement of the colettes and beauvoir granites and is related to the earlier concealed la bosse granite

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

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

mineralogical evidence for two magmatic stages in the evolution of an extremely fractionated p rich rare metal granite the podlesi stock krusne hory czech republic have the oh f sites fully occupied by fluorine also accessory the podlesi granite stock in the western krusne hory erzgebirge phosphates were formed during late magmatic crystallization of the mountains czech republic represents an extremely fractionated strongly p f enriched residual melt thus the mineralogical data strongly peraluminous fand p rich rare metal granite system of reflect the presence of two crystallization events within the dyke late variscan age the stock studied in drill core of 300 m length granite and pegmatite the presence of two melts parental and is formed by albite protolithionite topaz granite stock granite residual the latter strongly enriched in phosphorus has been also depth 50 300 m and shows geochemical and textural zoning the confirmed by study of melt inclusions in quartz from samples of stock granite is rich in p 0 5 wt f 0 5 1 2 wt rb the stock granite in its dyke bearing uppermost part mineral melt 1000 ppm li 500 1000 ppm and cs 100 150 ppm inclusion and whole rock chemical data from all rock types provide and poor in ti mg fe ca sr ba zr and rare earth elements evidence for two stages of granite evolution namely crystallization ree within the uppermost part of the stock depth 57 115 m from parental and residual melts this means that in addition to the stock granite is intercalated with albite zinnwaldite topaz dyke the granites in beauvoir france and argemela portugal the granite layers of 0 5 7 m thickness and a few thin flat dykes of podlesi stock is another well documented example of a two stage pegmatite the dyke granite and pegmatite are even more enriched evolution of a p rich granite system in p 1 wt p2o5 f 1 0 1 5 wt and rb up to 3000 ppm and are also rich in nb up to 100 ppm and ta up to 50 ppm the chemical data for the rock forming minerals show distinct differences between the stock granite and the dyke granite and pegmatite no chemical zoning of the rock forming minerals either from the upper rapidly cooled or from the lower slowly

tin tantalum niobium mineralization in the penouta deposit nw spain textural features and mineral chemistry to unravel the genesis and evolution of cassiterite and columbite group minerals in a peraluminous system abstract the sn ta nb penouta granite is a highly evolved rare metal post kinematic leucogranite located in north western spain which was intermittently mined from roman times until 1985 when falling metal prices led to the closure of most mines in the country mineralization consists mainly of cassiterite cassiterite i and columbite group minerals cgm disseminated in the leucogranite that increase in abundance and crystal size towards the upper part of the granitic cupola especially in banded pegmatite like dikes upwards quartz veins and greisen zones associated with the wall rock mainly augen gneisses were developed containing coarse grained cassiterite cassiterite ii in contrast to nearly homogenous cassiterite chemistry cgm may show complex compositional zonation patterns in relation with compositional variations of the leucogranite taking into account the mineral chemistry and textural features of cgm two main groups were distinguished i the first one group i follows a general main trend from columbite fe to columbite mn and finally to tantalite mn which is in accordance with the evolution of the magma observed from the less to the more evolved zones of the leucogranite and from bottom to top of the body and responds to common fractionation patterns of decreasing nb ta ratios in the melt and ii a second group group ii with intermediate values of mn mn fe and ta ta nb due to local supersaturation effects of the melt during crystallization resulting in complex oscillatory zoned cgm crystals textural and chemical features of cassiterite and cgm support the magmatic origin for both minerals although cassiterite crystallized later in the sequence in both generations mineral chemistry evolution of cgm is in good agreement with a greater solubility of tantalite in the melt at the upper levels where besides the fluorine contents of apatite and muscovite were increased and the onset of fluorite crystallization occurred so the fluorine enrichment in the upper levels seems likely to be an important component to explain the mineral chemistry of the penouta granite although the same mineral chemistry scheme could also be explained in terms of white mica fractionation upwards furthermore the absence of typical textures originated by fluids in the cgm as well as the lack of these minerals in the quartz veins point to a low influence of the hydrothermal fluids in dissolution and recrystallization processes of the primary oxides

ta and sn concentration by muscovite fractionation and degassing in a lens like granite body the case study of the penouta rare metal albite granite nw spain abstract the penouta peraluminous low phosphorous granite is the most important low grade high tonnage sn ta nb bearing albite granite from the iberian massif a sheet or laccolith shape instead of a stock is inferred for the penouta granite maybe in relation with the low viscosity and high mobility of a fluorine bearing melt subhorizontal lateral extension of the magma is also inferred via vertical and horizontal geochemical variations the absence of compositional gaps in variation diagrams coupled with continuous evolutionary trends of compatible and incompatible elements with height discard a multi pulse intrusion and point to a single magma pulse mineral chemistry trace element and least squares mass balance modelling support a differentiation process from bottom to top in the emplacement place the absence of switch from incompatible to compatible behaviour bell shaped trends in sn nb and ta variation diagrams coupled to experimental constraints on tantalite and cassiterite saturation suggest that nb ta oxides and probably cassiterite were not fractionated mineral phases their crystallisation being related to concentration gradients within a trapped intercumulus melt major and trace element modelling support that the concentration upwards of ta and the ta nb ratio could be a consequence of mineral fractionation with a key role of muscovite mainly primary for the ta nb ratio as this mineral has a higher partition coefficient for nb than ta our results suggest that fluorine and peraluminosity had a limited effect in the ta nb ratio variations hence ta enrichment is mainly controlled by fractional crystallisation processes in most cases sn enrichment was also concomitant with ta indicating that crystal melt fractionation processes also played an important role in sn concentration nevertheless the strongest sn enrichment in the granite e g central part of the granite body does not correspond to a significant ta enrichment the high affinity of sn for fluids and the high partitioning of ta for melt could explain this decoupling nevertheless the magmatic signature of cassiterites in these strongly sn enriched zones central part of the granite body rules out a hydrothermal subsolidus origin for this fluid by analogy with models carried out in sill like bodies it seems likely that the sn enrichment in the central part of the granite body is related to fluid saturation degassing occurred in the lower margin as a consequence of cooling and crystallisation of mostly anhydrous minerals i e second boiling the vapour exsolved migrated into the hotter melt up to the central part where it probably was reabsorbed yielding cassiterite with a magmatic signature moreover we suggest that heat loss in the upper margin of the granite body might also contribute to the formation of a second fluid saturated zone as a result pegmo aplites and greisen were developed

a new look at sedimentation rates and the completeness of the stratigraphic record several recent papers have suggested that completeness of stratigraphic sections can be estimated by using the ratio of long term sedimentation rates to short term rates we show that the median short term sedimentation rates used in these papers are erroneous and are mostly an artifact arising from improper data manipulation to demonstrate the artificial character of short term median rates we have generated a series of plots assuming a constant sedimentation rate with fixed variance and defined limits of measurement precision these plots demonstrate that increasing variance in the time required to deposit sediments will result in spuriously high short term median sedimentation rates a new method for calculating median sedimentation rates which eliminates the problem of spurious median rates is then applied to make an improved estimate of expected completeness recalculated median values show that sedimentation rates for pelagic sediments are close to identical for both short term and long term tim

the role of fractional crystallization in the genesis of early syn d3 tin mineralized variscan two mica granites from the carrazeda de ansiaes area northern portugal abstract a multiphase granitic complex g1 g6 in the carrazeda de ansiaes area central iberian zone was emplaced during syn kinematic stages of the variscan orogeny between 329 9 0 8 ma and 318 9 1 9 ma as determined by id tims u pb on zircon and monazite the complex intruded the metasedimentary douro group in a nw trending antiform formed during the d 1 and d 3 deformation phases but was itself affected by ductile and brittle deformation the granites have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves and more rarely xenoliths schlieren and microgranular enclaves they are s type mainly alkaline calcic and peraluminous with asi ranging between 1 21 and 1 45 and normative corundum of 2 63 4 77 they are enriched in lree relatively to hree with negative eu anomalies 87 sr 86 sr i 0 7097 0 7159 end 6 2 to 9 1 and 18 o 10 96 11 81 geochemical and isotopic characteristics show that granites g1 g2 g4 and g5 correspond to distinct pulses of magma formed by partial melting of heterogeneous metasedimentary material geochemical fractionation trends recorded by whole rocks and minerals permit to distinguish and model two fractional crystallization series g2 g3 and g5 g6 the latter also affected by crustal assimilation during fractionation granites g1 g2 g3 and g6 have 20 ppm sn and g5 16 ppm sn they are also associated with mineralized sn and w bearing quartz veins fractional crystallization was the responsible process for the increase in sn content in granites from the series and their micas

stratigraphic paleoecology bathymetric signatures and sequence overprint of mollusk associations from upper quaternary sequences of the po plain italy upper quaternary sequences of the po plain italy were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns three densely sampled cores 89 samples 98 genera 23 280 specimens dominated by extant mollusk species with known environmental distributions were analyzed with detrended correspondence analysis dca the dca scores calibrated using extant genera provided outstanding estimates of bathymetry 3 m and related environmental parameters depth related successions of mollusk associations delineated by using dca were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques e g depth estimates for maximum flooding surfaces the dca ordination demonstrates the severity of the sequence stratigraphic overprint samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts when analyzed across comparable systems tracts similar species associations repeat during the last and current interglacial cycles suggesting that po plain mollusk associations have remained remarkably stable over the past 125 k y the results are consistent with the bathymetric interpretation of the dc axis 1 postulated previously for the paleozoic fossil record demonstrate the sequence stratigraphic overprint of paleoecological patterns predicted by computer modeling and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations

tectonic cycles and the history of the earth s biogeochemical and paleoceanographic record an integrated approach to earth history for the last 2 5 b y reveals the strong interdependence of all geologic variables three earth history components are identified and interrelated secular trends as the earth ages recurring events of a previously proposed supercontinent megacycle worsley et al 1984 1985 and nonrecurring environmental shifts declining secular trends are endogenic heat production atmospheric carbon dioxide levels and surface temperatures continental differentiation enzyme efficiency atmospheric oxygen levels and solar luminosity are increasing secular trends four phases of a supercontinent cycle supercontinent fragmentation maximum continent dispersal continental assembly and supercontinental stasis recur with a 0 5 b y period and are correlated with tectonism cratonic sediment preservation atmospheric and hydrospheric evolution and the distribution of marine platform stable isotopes these correlations reflect coupling among the various oceanic and continental constituents during consecutive supercontinent assemblies and fragmentations nonrecurring shifts are unique and irreversible events in earth history e g development of photosynthesis occurrence of banded iron formations and deposition of detrital uraninite that represent periods of rapid geochemical adjustment to biospheric evolution earth s tectonobiogeochemical history is then synthesized by integrating secular trends and nonrecurring events with the supercontinent cycle emphasizing the preferentially preserved periods of fragmentation and continental dispersal paleoceanographic consequences of the megacycle are considered to reflect the stepwise coupling of secular trends and nonrecurring events to a biotically controlled phosphorus organic carbon climate linkage required to maintain earth s post archean surface temperature

granitic pegmatites in science and industry p cěrný editor mineralogical association of canada short course handbook vol 8 mineralogical association of canada m a c winnipeg man 1982 xiii 555 pp can 15 00 paperback available from the business manager m a c c o department of mineralogy royal ontario museum 100 queen s park toronto ont m5s 2c6 canada

spodumene pegmatites from the pusila pluton in the higher himalaya south tibet lithium mineralization in a highly fractionated leucogranite batholith abstract the himalayan leucogranite belt is evaluated as a prospect for rare metal mineralization the pusila pluton is located 44 km northwest of mount everest and consists of two mica granite muscovite granite albite granite and pegmatites numerous pegmatite dikes have intruded the higher himalayan crystalline sequence and the granites oligocene pegmatites in the chomogu and cuore areas which we constrain to have formed at ca 25 23 ma were investigated in this study because they are strongly enriched in li up to 8460 ppm and contain abundant spodumene petalite lithium was progressively enriched from the two mica granite to the muscovite granite and finally li mineralization occurred in the highly fractionated pegmatites the chomogu no 1 pegmatite is a well zoned dike that hosts beryl columbite cassiterite and li minerals which are concentrated in the inner parts of the dike scanning electron microscopy and cathodoluminescence images reveal two stages of li mineralization primary spodumene spd 1 crystallized in the magmatic stage whereas secondary spodumene spd 2 and petalite formed later in the hydrothermal stage the pusila pluton is thus an important site of li mineralization in the himalayan leucogranite belt

paleoclimatic and tectonic control on the accumulation of north american cratonic sediment variation in accumulation rate as a function of depositional latitude has been determined for north american limestone dolostone sand stone gray black shale red shale and evaporite rocks from tabulations by ronov and co workers from data in lexicons of united states and canadian stratigraphy and from isopach and lithofacies maps published in 1975 by cook and bally phanerozoic sediment is similar to that on other continents consisting of 63 terrigenous elastic facies 23 sandstone 40 shale 36 carbonate and 1 chert evaporite and other minor rock types latitudinal variation in accumulation rate is influenced primarily by past positions of foreland and intracratonic basins additional variation related to paleoclimate is recorded as strong dependence of limestone dolostone red shale and evaporite deposition on latitudes of accumulation a relation reflecting the importance of ambient temperature and meteoric precipitation on the formation of various authigenic phases poleward increase in dolostone total carbonate ratio in both hemispheres implicates the importance of syndepositional diagenesis in the formation of most dolostone sequences the ratio of sandstone total terrigenous clastic sediment exhibits little variation with latitude a constancy indicating that most sand and mud is derived from older sediment rather than from the weathering of crystalline rock as a result terrigenous lithofacies record little climatic influence in the proportional delivery of mechanically versus chemically derived weathering products to basins of accumulation

models for simulating the fossil record computer modeling of the distribution of fossils within depositional sequences provides a means for generating hypotheses and increasing understanding of the fossil record the simulation presented here joins the basin scale stratigraphic modeling program strata a random branching model of species origination and extinction and a model relating the probability of species occurrence to sedimentary facies model results indicate that facies sensitivity of species has the strongest control on range offset i e the time between last appearance in a stratigraphic column and the time of extinction within a basin or the time between first appearance in a column and time of origination in a basin model results also predict the distribution of zones of increased range offset within depositional sequences in the results presented here increased range offset occurs within the transgressive systems tract of the deep basin in far updip settings and near the shelf break of the late highstand to early lowstand the model also demonstrates how incompleteness of the fossil record is partitioned among sampling bias facies bias and unconformity bias in this simulation sampling bias and facies bias are roughly equal in magnitude and constant across the basin but unconformity bias increasingly dominates over these two in updip positions

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

solubility of cassiterite in evolved granitic melts effect of t fo2 and additional volatiles abstract the aim of this experimental study was to determine the solubility of cassiterite in natural topaz and cassiterite bearing granite melts at temperatures close to the solidus profiles of sn concentrations at glass crystal sno 2 interface were determined following the method of harrison t m watson e b 1983 kinetics of zircon dissolution and zirconium diffusion in granitic melts of variable water content contributions to mineralogy and petrology 84 66 72 the cassiterite concentration calculated at the sno 2 glass interface is the sno 2 solubility experiments were performed at 700 850 c and 2 kbar using a natural f bearing peraluminous granitic melt with 2 8 wt normative corundum slightly h 2 o undersaturated to h 2 o saturated melt compositions were chosen in order to minimize the loss of sn to the noble element capsule walls at the nickel nickel oxide assemblage ni nio oxygen fugacity buffer the solubility of cassiterite in melts containing 1 12 wt f increases from 0 32 to 1 20 wt sno 2 with an increasing temperature from 700 to 850 c at the ni nio buffer and a given corundum content sno 2 solubility increases by 10 to 20 relative to an increase of f from 0 to 1 12 wt sno 2 solubility increases by 20 relative to increasing cl content from 0 to 0 37 wt in synthetic granitic melts at 850 c we show that cl is at least as important as f in controlling sno 2 solubility in evolved peraluminous melts at oxygen fugacities close to the ni nio buffer in addition to the strong effects of temperature and f o 2 on sno 2 solubility an additional controlling parameter is the amount of excess al corundum content at ni nio and 850 c sno 2 solubility increases from 0 47 to 1 10 wt sno 2 as the normative corundum content increases from 0 1 to 2 8 wt at oxidizing conditions ni nio 2 to 3 sn is mainly incorporated as sn 4 and the effect of excess al seems to be significantly weaker than at reducing conditions

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

sea level cycles during the growth of atlantic type oceans abstract first order changes in global sea level are commonly thought to be the result of short term fluctuations in oceanic spreading rate however eustatic high stands have occurred only twice in phanerozoic time and in both cases have followed supercontinent break up by a lag period of 50 100 ma therefore if pulses in spreading rate were the primary control of eustasy then for some reason rate increases would have had to have occurred with predictable periodicity with respect to major rifting events alternatively we propose that the major control on first order sea level cycles is the formation of atlantic type oceans with its attendant changes in the area age distribution of the global ocean floor and the formation of extensional passive margins our calculations indicate that both the approximate magnitude and relative timing of sea level highstands relative to supercontinent break up are predicted by this mechanism thus the importance of short term spreading rate variations in eustatic cycles becomes secondary

a geological numerical model for paleozoic global evaporite deposition a geologically driven model for evaporative deposition of marine sulfate and other sulfur fluxes roughly reproduces the observed stratigraphic record of paleozoic global evaporite depositional rates and the observed delta 34 s age curve erosional and depositional fluxes in this model are controlled by areas available for erosion and deposition which are in turn controlled by sea level global hypsography and plate tectonic movement of the continents through low latitude evaporite belts sea level also provides the record of seafloor spreading rates needed to determine fluxes at mid ocean ridges the success of this geologically driven model as opposed to geochemical models dependent on isotopic compositions or reservoir contents to determine fluxes suggests the possibility of modeling fluxes of elements that have no useful isotopic record it also suggests that variability of the stratigraphic record of evaporite deposition is not entirely the result of accidents of erosion and preservation bu

response of late ordovician paleoceanography to changes in sea level continental drift and atmospheric pco2 potential causes for long term cooling and glaciation abstract we performed sensitivity experiments using an ocean general circulation model at two stages of the late ordovician caradoc 454 ma ashgill 446 ma under a range of atmospheric pco2 values 8 18 pal pre industrial atmospheric level at high and low sea level the model results indicate that the long term cooling trend during the late ordovician can be explained by progressive cooling of the global ocean in response to falling levels of atmospheric pco2 sea level change and paleogeographic change these results also explain the occurrence of low latitude cool water carbonates in north america in all simulations a drop in sea level led to a reduction in poleward ocean heat transport this indicates a possible positive feedback that could have enhanced global cooling in response to sea level drop during the late ordovician alterations in poleward ocean heat transport linked to changes of atmospheric pco2 also indicate that there is a threshold of 10 pal above which ocean current change cannot be responsible for glaciation in the late ordovician continental drift could explain the observed global cooling trend in the late ordovician through a combined poleward ocean heat transport feedback and increased ice albedo effect if atmospheric pco2 was low during the entire late ordovician the model results further indicate that the response of meridional overturning to changes in paleogeography atmospheric pco2 and sea level is stronger than the response of surface circulation to these perturbations because the overturning circulation is so strong meridional overturning was the dominant mechanism for described changes in heat transport in the late ordovician

textural and chemical constraints on the formation of disseminated granite hosted w ta nb mineralization at the dajishan deposit nanling range southeastern china the dajishan deposit located in the nanling range of southeastern china is the largest wolframite deposit in the world approximately two thirds of the tungsten resource is contained in large quartz wolframite k feldspar muscovite scheelite sulfide beryl veins but the remainder occurs as wolframite and lesser scheelite disseminated through the nb ta mineralized no 69 granite which is characterized by abundant snowball quartz crystals disseminated granite hosted wolframite mostly occurs as a replacement after lath shaped muscovite although an interstitial variety is present in some samples the major element chemistry of the disseminated and vein hosted wolframite is similar however the former has one to two orders of magnitude higher concentrations of high field strength elements hfse including nb and ta disseminated muscovite in the no 69 granite is fe and mg rich replacement rims on these muscovite crystals are enriched in ta sn and cs but more depleted in nb related to the original phase vein hosted muscovite is characterized by lower nb ta rb and cs contents than the granite hosted muscovite although sn and w concentrations are comparable columbite mn is the principal nb ta ore mineral and occurs disseminated through the no 69 granite where it is hosted by snowball quartz crystals some of the columbite has been altered and overgrown by wodginite the restriction of these altered columbite crystals to within snowball quartz along with the ta and sn enrichment of the alteration rims on muscovite tie the formation of snowball quartz to a ta sn metasomatic event high ge ti and al ti ratios in the snowball quartz relative to interstitial quartz are also consistent with a late stage of formation for the former variety the disseminated granite hosted w mineralization formed through fluid rock interaction the fluids that precipitated the disseminated wolframite were most likely those that formed the veins but were modified through reaction with the hfse enriched no 69 granite nb ta mineralization however is represented by magmatic columbite and by a later metasomatic stage of wodginite the low solubility of ta in aqueous fluids combined with the evidence for ta sn metasomatism suggests that the ta sn metasomatic event was caused by hydrosilicate liquids a transitional fluid that lies compositionally between silicate magmas and hydrothermal fluids whole rock and mineral chemistry both suggest that deep level fractional crystallization of the no 69 granite was required to elevate ta and nb concentrations to allow saturation of columbite