composition and origin of intermediate solid solutions in the system thorite xenotime zircon coffinite abstract a comprehensive survey of the accessory mineral assemblages in variscan granites of the german erzgebirge and pan african granites from jordan revealed the occurrence of intermediate solid solutions of the tetragonal thorite xenotime zircon coffinite mineral group with partially novel compositions these solid solutions preferentially formed in evolved and metasomatically altered p poor leucogranites of either i or a type affinity thorite from the erzgebirge contained up to 18 8 wt y2o3 16 1 wt zro2 and 23 3 wt uo2 xenotime and zircon have incorporated th in abundances up to 36 3 wt and 41 8 wt tho2 respectively extended compositional gradation with only minor gaps is confined to hydrated members of this mineral group and is observed to exist between thorite and xenotime thorite and coffinite and y hree bearing thorite and zircon complex hydrous solid solutions containing elevated abundances of three or more of the endmembers are subordinate previously reported intermediate solid solutions between anhydrous zircon and xenotime and anhydrous zircon and thorite are not observed and are in conflict with experimental work demonstrating very limited miscibility between anhydrous species of endmember composition the majority of hydrous intermediate solid solutions in the th y zr u system are likely thermodynamically unstable instead they are probably metastable responses to unusual physico chemical conditions involving various parameters and conditions the relative importance of which is incompletely known leaching and dissolution of preexisting accessory phases during interaction with f bearing hydrous fluids enriched in th y hree zr and or u and common deposition of the various elements at disequilibrium supersaturation seems to play a key role but other processes may be of similar importance experimental work involving hydrous conditions and complex systems composed of more than two endmembers are needed to shed light into the stability relations of the chemically uncommon compositions treated in this study

origin of the herman norcross tintah sequence of lake agassiz beaches in manitoba canada abstract the giant glacial lake agassiz basin is fringed by many strandlines which have long been used to trace the paleogeography of the former lake over its 5000 year history the oldest and highest of these strandlines were placed into three groups by warren upham in the 1890 s the herman norcross and tintah and form a staircase of small landforms the formation of these old strandlines began as early as 13 9 cal 12 0 14 c kyr bp and ended 12 8 cal 10 8 14 c kyr bp based on osl dates and the history of lake level in the agassiz basin new mapping and augering of beach ridges in southern manitoba canada associated with the earliest phase of the lake indicate that there are a series of up to 28 small discontinuous beach ridges that are generally only a few metres high and a few tens of metres wide these beaches mainly consist of weakly defined beds of poorly sorted sediments in many cases a central sandy diamicton unit lies stratigraphically between overlying beach sediments and clay diamicton till below spatially ridges are separated by silty or sandy units or gravel lags inter beach lagoonal organics were not found we discuss the possible origin of these lake agassiz beaches concluding that they were deposited over a few centuries by episodic storm events as lake level slowly declined we base this conclusion on the nature of the sediments in the beach ridges and the regional geomorphology as well theoretical considerations about sedimentation along a regressing shoreline of a large lake other origins are rejected although some other factors may have contributed to formation of some of the beaches such as temporary increases in sediment supply variable rate of outlet erosion and short increases in lake level that reworked sediment upslope into ridges using the time frame of 13 9 to 12 8 cal kyr bp for the formation of the beaches the average interval between formation of each beach is 39 years

igcp project 510 a type granites and related rocks through time abstract this introductory article of the igcp 510 special issue of lithos presents the goals of igcp project 510 a type granites and related rocks through time activities in the first two years 2005 2006 of the project and plans for the years 2007 2009 the 11 research papers in this issue are based on papers presented at the inaugural meeting of igcp 510 in conjunction with the 15th goldschmidt conference in moscow idaho usa in 2005

structure and chemistry of zircon and zircon group minerals zircon zrsio4 is a common accessory mineral in nature occurring in a wide variety of sedimentary igneous and metamorphic rocks known to incorporate an assortment of minor and trace elements zircon has the ability to retain substantial chemical and isotopic information leading to its use in a wide range of geochemical investigations including studies on the evolution of earth s crust and mantle e g hanchar et al 1994 bowring 1995 vervoort et al 1996 hoskin and schaltegger this volume valley this volume as well as age dating e g gibson and ireland 1995 bowring et al 1998 solar et al 1998 bowring and schmitz this volume ireland and williams this volume parrish et al this volume the physical and chemical durability of zircon is a major factor in it being the mineral by which many of earth s oldest known rocks have been dated bowring et al 1989 maas et al 1992 buick et al 1995 bowring and williams 1999 wilde et al 2001 and is also an important factor in zircon being proposed as a candidate waste form for the geologic disposal of excess plutonium from dismantled nuclear weapons ewing and lutze 1997 ewing 1999 burakov et al 2002 burakov et al 2003 ewing et al this volume the chemical and physical properties of zircon and its ability to incorporate and retain trace elements are largely determined by its crystal structure the zircon structure is adopted by numerous minerals and synthetic compounds with the general formula at o4 in which high field strength t site cations occupy isolated tetrahedra and a site cations occupy larger eight coordinated structural sites zircon type compounds share many physical properties as well as displaying variable degrees of solid solution among end members

evolution of the caldera forming eruption at crater lake oregon indicated by component analysis of lithic fragments crater lake caldera 8 10 km formed 6845 years b p 14c age during the climactic eruption of the volcanic edifice known as mount mazama is intermediate in size between small calderas associated with central vent eruptions and large calderas that have ring fracture vent systems our quantitative study of lithic fragments in the ejecta confirms the existing model of changes in vent configuration during the climactic eruption of mount mazama initial activity was from a single vent that produced a rhyodacite pumice fall from a plinian column altered preexisting volcanic rocks are the predominant lithic type in the plinian deposit and their extensive hydrothermal alteration is considered as evidence of their relatively deep origin the wineglass welded tuff lies atop the plinian deposit and contains a higher proportion of fresh volcanic rocks suggesting enlargement of the single vent by slumping of its walls this same vent enlargement caused the plinian eruption column to collapse and feed valley hugging pyroclastic flows that deposited the wineglass welded tuff when enough material was erupted from the shallow magma chamber that its roof was no longer adequately supported mount mazama collapsed to form the caldera while highly energetic pyroclastic flows produced the climactic ignimbrite a lag breccia that represents the proximal facies of the compositionally zoned climactic ignimbrite lies atop the wineglass welded tuff and contains predominantly altered volcanic rocks of deeper origin accompanied by minor granitoids from the magma chamber walls azimuthal differences in lithic component proportions in the lag breccia correlate well with the geology of the caldera walls indicating that the climactic ignimbrite was ejected by multiple vents along a ring fracture system systematic lithic component changes within the lag breccia suggest different quarrying levels that reflect waxing and waning of the discharge rate during the caldera collapse phase of the climactic eruption our lithic component analysis demonstrates that calderas that may be too small to experience structural resurgence such as crater lake nevertheless may form by syneruptive subsidence along ring fractures

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

geochemical specialization of the tin bearing granitoid massifs of nw bohemia the geochemistry of hercynian tin bearing granitoid massifs of the krusne hory mts erzgebirge slavkovsk les forest kaiserwald and smrciny eastern fichtelgebirge is compared by statistical processing of 270 analyses including a wide spectrum of major and trace elements seven different types of granites are distinguished out of these five types represent the successive differentiation of the largest massif of nw bohemia the karlovy vary karlsbad massif this comprises strongly differentiated peraluminous granites evolving towards extreme li rb cs f and sn enrichment in the youngest members which are albite topaz zinwaldite lithium granites the sixth and seventh types are different from the former by their location in the eastern krusne hory and tectonic setting and they display geochemical features of anorogenic granites they are metaluminous albite zinwaldite granites with marked enrichment of nb y and hree in addition to li rb cs f and sn indicating contamination by sub crustal material sn w mineralizations including flat peri contact greisen bodies steep greisen veins and tourmalinized phyllites are all intimately associated with the most strongly differentiated granites the li granite and the cinovec granite respectively

extreme fractionation from zircon to hafnon in the koktokay no 1 granitic pegmatite altai northwestern china the koktokay no 1 pegmatite is a li cs ta rich granitic pegmatite located in altai northwestern china zircon is present in most textural zones of this pegmatite and in its contact zone with surrounding metagabbro here we describe the detailed associations of zircon with other minerals and the internal textures and chemistry of the zircons most zircon grains from the contact zone have relatively low hfo 2 2 18 0 18 7 wt zircon grains from the aplite zone contain 2 although their thin and bright rims have higher hfo 2 10 8 13 0 wt most zircon grains from the quartz muscovite zone have complex internal textures and have hfo 2 contents of 2 up to 36 1 wt zircon sl from the cleavelandite quartz spodumene zone can be divided into two types based on petrography and chemistry one group of zircons appears to be typical magmatic zircon and are greater than 100 m in size closely associated with albite and have hfo 2 contents of 13 0 19 5 wt the second group of zircons is typically associated with muscovite and or spodumene is small in size down to a few micrometers and may exhibit zoning or alteration textures the hfo 2 contents of this second zircon group are 19 8 58 9 wt indicating the presence of hafnian zircon to zirconian hafnon large hfo 2 content variations of up to 34 8 wt were also observed within single zoned crystals we suggest that the increase of hfo 2 in the magmatic zircon from 9 4 wt in the contact zone to 19 5 wt in the cleavelandite quartz spodumene zone mainly reflects fractional crystallization of pegmatite magma however the occurrence of hafnian zircon and hafnon in the cleavelandite quartz spodumene zone is likely related to coupled li f fluxing effects in the pegmatite magma

petrogenetic and mineralization processes in paleo to mesoproterozoic rapakivi granites examples from pitinga and goias brazil abstract the 1 8 ga pitinga granites agua boa and madeira massifs in amazonas northern brazil are within plate shallow level rapakivi granites associated with an extensional fracture system they comprise an early facies of pyterlitic to wiborgitic rapakivi granite a fine to medium grained biotite granite as well as topaz granite agua boa massif and albite granite madeira massif the granites are usually metaluminous to peraluminous the albite granite however is peralkaline they are enriched in sio2 k2o na2o f rb th nb y zr and the rare earth element ree and impoverished in mgo tio2 p2o5 and sr as the majority of sn mineralized granites sn contents range from 1 ppm in the rapakivi facies to 3400 ppm in the albite granite end at 1 8 ga values vary from 2 2 to 0 4 and nd model ages lie between 2 4 and 2 1 ga mineralization in the madeira massif includes disseminated magmatic cryolite zircon cassiterite pyrochlore columbite tantalite and xenotime and massive cryolite bodies in the f rich peralkaline albite granite in the agua boa massif sn mineralization is associated with greisens and episyenite the 1 77 ga g1 and 1 58 1 57 ga g2 rapakivi granites of goias central brazil are coeval with the arai rift basin granites of the g1 suite are metaluminous and alkaline while the g2 suite is metaluminous to peraluminous both are enriched in f sn rb y th nb ga and the ree primary micas range from fe rich biotite to zinnwaldite the micas of the more evolved granites and the metasomatic micas are strongly enriched in f with f li between 2 and 10 the initial end values of both suites show a considerable range 14 to 0 and indicate substantial compositional variation in source sn deposits in goias are hosted mainly by greisens indium is concentrated in quartz topaz rock and albitized g2d granite of the mangabeira massif and is always related to a cassiterite sulfide association this quartz topaz rock is of metasomatic origin probably generated by a hydrothermal fluid derived from the topaz albite granite mineralization in the studied deposits was essentially associated with f enrichment in the peralkaline madeira albite granite extremely high f contents favored disseminated mineralization while in the goias tin province gtp and agua boa massif greisenization was related to early fluid saturation the gtp and pitinga granites display tectonic petrogenetic geochemical isotopic and metallogenic similarities that can be applied in search of sn and rare metal deposits

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

extreme p bi nb sc u and f rich zircon from fractionated perphosphorous granites the peraluminous podlesi granite system czech republic abstract the strongly peraluminous and p rich protolithionite and zinnwaldite leucogranites from podlesi western krusne hory mts czech republic contain accessory zircon with extraordinary enrichment of several elements which constitute trace elements in common zircon elements showing a not yet reported anomalous enrichment include p up to 20 2 wt p2o5 equivalent to 0 60 apfu formula calculated on the basis of 4 oxygen atoms bi up to 9 0 wt bi2o3 0 086 apfu nb up to 6 7 wt nb2o5 0 12 apfu sc up to 3 45 wt sc2o3 0 10 apfu u up to 14 8 wt uo2 0 12 apfu and f up to 3 81 wt f 0 42 apfu strong enrichment of p preferentially involved the berlinite type substitution 2 si4 p5 al3 implying that significant al may enter the si position in zircon incorporation of other exotic elements is primarily governed by the xenotime si4 zr4 p5 y3 pretulite sc3 p5 zr4 si4 brabantite type ca2 u th 4 2p5 2zr4 2si4 and ximengite type bi3 p5 zr4 si4 substitution reactions one part of the anomalous zircons formed late magmatically from a strongly peraluminous p f u rich hydrous residual melt that gave rise to the zinnwaldite granite interaction with aggressive residual fluids and metamictization have further aided in element enrichment or depletion particularly in altered parts of zircon contained in the protolithionite granite most of the zircon from f rich greisens have a composition close to endmember zrsio4 and are chemically distinct from zircon in its granite parent this discrepancy implies that at podlesi granitic zircon became unstable and completely dissolved during greisenization part of the mobilized elements was reprecipitated in newly grown hydrothermal zircon

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

a new understanding of the provinces of the amazon craton based on integration of field mapping and u pb and sm nd geochronology abstract new conventional and sensitive high resolution ion microprobe zircon u pb dating has led to a new understanding of the subdivision and evolution of the amazon craton during precambrian time with major improvements and changes made to the previous rb sr based model the interpretation of u pb and sm nd isotopic data identifies eight main precambrian tectonic provinces in the craton with ages ranging from 3 1 to 0 99 ga some of the provinces were generated by accretional arc related processes carajas transamazonic tapajos parima and rondonia juruena and others by recycling of continental crust central amazon rio negro and sunsas the exposed archean crust is restricted to the east carajas and south amapa in brazil and north imataca in venezuela of the craton indicating that the amazon craton is largely a proterozoic crust the carajas imataca 3 10 2 53 ga and transamazonian 2 25 2 00 ga provinces are composed predominantly of granite greenstone terranes the tapajos parima 2 10 1 87 ga and rondonia juruena 1 75 1 47 ga provinces represent new crust added as orogenic belts while the rio negro 1 86 1 52 ga and sunsas 1 33 0 99 ga provinces originated mainly by magmatic tectonic recycling of the above two orogenic belts the only zone with a prominent northeast trend is the poorly known k mudku shear belt characterized by a 1 20 ga shear zone which deforms the rocks of at least three different provinces rio negro tapajos parima and transamazonic the central amazon province comprises mostly orosirian volcano plutonic rocks uatuma magmatism and is a terrane in which the exposed crustal structure and deformation are pluton related the sm nd tdm model ages and nd suggest that the central amazon province was generated by the partial melting of archean continental crust carajas province perhaps related to underplating that began at the end of the tapajos parima orogeny 1 88 1 86 ga

rare earth elements in synthetic zircon part 1 synthesis and rare earth element and phosphorus doping zircon crystals were grown from a li mo flux 7 5 mol li2moo4 86 5 mol moo3 to which equal molar proportions zro2 and li2sio3 were added 3 mol each the crystals were initially grown undoped but later dy was added to the flux without any other charge compensating species with dy and p added in equal molar proportions the zircon crystals incorporated 1 37 mol 6 99 wt dy and 1 36 mol 1 33 wt p a factor of 5 3 increase in dy over the crystals grown without p intentionally added to the flux the other p ree doped zircon crystals displayed an approximately 1000 fold increase in ree and p from la through lu a result of decreasing ionic radii the incorporation of p5 allowed in a general sense the xenotime type coupled substitution of ree3 y3 p5 zr4 si4 from la to nd however p exceeds ree from sm to gd the ree are generally equal to p and from tb to lu the ree exceed p the y and p doped zircon behaved more like middle ree mree doped zircon than heavy ree hree doped zircon crystals in their ability to incorporate y and p and to maintain charge neutrality to investigate the incorporation of dy with no p added to the flux the p to lree excess and the hree to p excess in the doped zircon secondary ion mass spectrometry sims analyses were completed on selected crystals in the dy doped crystals the sims analyses revealed minor amounts of p li and mo in the crystals these elements contributed to charge balance required by the excess dy in ree and p doped zircon the sims analyses detected li and mo and the li and mo may also provide charge balance for excess ree in the hree p doped crystals

variscan silicic magmatism and related tin tungsten mineralization in the erzgebirge slavkovský les metallogenic province integration of geochemical mineralogical isotopic and geochronological data with geodynamic considerations suggests that the variscan granites in the erzgebirge slavkovsk les domain originated from repeated melting events and were emplaced over a period of about 40 ma 330 290 ma several lines of evidence exist supporting the idea that erzgebirge granites assigned to different types biotite granites two mica granites strongly peraluminous p rich li mica granites and slightly peraluminous p poor granites are in most cases not genetically related via continuous fractional crystallization from a common magmatic reservoir the genesis of the slavkovsky les granites however might be discussed in terms of an uninterrupted fractionation series geological models of sn w deposits based upon geochemical and structural results imply that the main ore depositional events followed immediately the emplacement and solidification processes of melt via fluid melt immiscibility breccia pipe formation and or pervasive rock fluid interactions

carboniferous permian volcanic evolution in central europe u pb ages of volcanic rocks in saxony germany and northern bohemia czech republic nine shrimp u pb ages on zircon and two pb pb single zircon ages have been determined from late paleozoic volcanic rocks from saxony and northern bohemia samples came from the teplice altenberg volcanic complex the meissen volcanic complex the chemnitz basin the dohlen basin the brandov olbernhau basin and the north saxon volcanic complex the teplice altenberg volcanic complex is subdivided into an early namurian phase mikulov ignimbrite 326 8 4 3 ma thus older than assumed by previous studies and a late caldera forming phase teplice ignimbrite 308 8 4 9 ma the age of the latter however is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint the leutewitz ignimbrite product of an early explosive volcanic episode of the meissen volcanic complex yielded an age of 302 9 2 5 ma stephanian a volcanic rocks intercalated in the brandov olbernhau basin bob 302 2 8 ma chemnitz basin cb 296 6 3 0 ma dohlen basin db 296 3 0 ma and the north saxon volcanic complex nsvc c 300 290 ma yielded well constrained stephanian to sakmarian ages the largest late paleozoic ignimbrite forming eruption in central europe the rochlitz ignimbrite has a well defined middle asselian age of 294 4 1 8 ma ages of palingenic zircon revealed that the namurian westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous paleozoic geodynamic phases the precambrian inherited ages support the chronostratigraphic structure assumed for the saxo thuringian zone of the variscan orogen the present results help to improve the chronostratigraphic allocation of the late paleozoic volcanic zones in central europe at the same time the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the variscan orogeny

chemical characteristics of zircon from a type granites and comparison to zircon of s type granites abstract the trace element content in zircons from a type granites and rhyolites was investigated by using back scattered electron images and electron microprobe analyses the studied proterozoic wiborg batholith finland and para amazonas and goias states brazil and variscan krusne hory erzgebirge czech republic and germany plutons cover a wide range of rocks from large rapakivi textured geochemically primitive plutons to small intrusions of f li sn nb ta and u enriched rare metal granites while zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites it is a late crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification the early crystals are included in mica quartz and feldspar the late grains are included in fluorite or cryolite or are interstitial the zircon in hornblende biotite and biotite granites from the non mineralized plutons is poor in minor and trace elements the zircon in moderately fractionated granite varieties is slightly enriched in hf th u y and hrees whereas the zircon in highly fractionated ore bearing granites may be strongly enriched in hf up to 10 wt hfo 2 th up to 10 wt tho 2 u up to 10 wt uo 2 y up to 12 wt y 2 o 3 sc up to 3 wt sc 2 o 3 nb up to 5 wt nb 2 o 5 ta up to 1 wt ta 2 o 5 w up to 3 wt wo 3 f up to 2 5 wt f p up to 11 wt p 2 o 5 and as up to 1 wt as 2 o 5 metamictized zircons may also be enriched in bi ca fe and al the increase in the hf content coupled with the decrease in the zr hf value in zircon is one of the most reliable indicators of granitic magma evolution in the zircon of a type granites the zr hf value decreases from 41 67 porphyritic granite to 16 19 equigranular granite in the kymi stock finland and from 49 52 biotite granite to 18 36 leucogranite in the pedra branca pluton brazil in the in situ strongly fractionated cinovec cupola erzgebirge the zr hf value decreases from 33 51 in the protolithionite granite at a depth of 1255 m to 7 5 25 in the zinnwaldite granite at a depth of 40 m at the scale of individual crystals the zr hf value decreases from 86 to 68 from the cores to the rims of the zircons from the teplice rhyolite and from 64 to 33 in the zircons from the biotite granite at krupka erzgebirge the contents of hf and u in zircon are dependent mainly on the degree of granite fractionation and the nature and volume of the volatile phases and are independent of the a or s character of the parental melt the zircon zr hf ratios 55 and 25 are proposed to approximately distinguish common moderately evolved and highly evolved granites zircons from the moderately and highly evolved granites of a and s type can be discriminated on the basis of their hree content and the u th ratios nb ta and w are present in zircon from the highly evolved granites from all studied areas while high as bi and sc contents are typical only for the erzgebirge

accessory mineral behavior during differentiation of a granite suite monazite xenotime and zircon in the sweetwater wash pluton southeastern california u s a abstract compositional and textural characteristics of the accessory minerals monazite xenotime and zircon in the sweetwater wash granites and related aplites indicate that these phases not only controlled much of the trace element geochemistry of the suite but that they also record the melt compositional changes that occurred during magmatic differentiation fractionation of monazite due to decreasing saturation levels of its essential structural constituents with falling temperature was likely responsible for an ongoing trend of light rare earth element ree depletion this was accompanied by increasing heavy ree concentrations until xenotime joined the crystallizing assemblage subsequently combined monazite xenotime fractionation resulted in lowering of the entire ree budget zircon which contains inherited cores that were apparently resorbed and rounded during initial anatexis was saturated throughout the differentiation history of the sweetwater wash suite accessory phases in granite and aplite exhibit strong compositional differences at a variety of scales the differences are best displayed by monazite on average crystals in more differentiated rocks aplites are relatively depleted in light ree s and contain higher concentrations of the substituting elements u and th zircon displays complimentary increases in hf and y while xenotime shows a slight increase in th and in gd ho ratios both phases also exhibit higher u concentrations in aplites than in granites these differences in accessory mineral compositions are observed not only between granites and the more differentiated aplites but also within individual thin sections due to in situ fractionation on an even smaller scale strong compositional variations are present within single crystals possibly due to diffusion controlled melt compositional gradients in the regions a adjacent to growing major phases and b adjacent to the growing accessory crystal itself our observations indicate that compositional variations among accessory minerals are potentially useful for tracking of magmatic processes but that the scale of observed variations must be carefully considered

archean crustal sources for paleoproterozoic tin mineralized granites in the carajas province sse para brazil pb pb geochronology and nd isotope geochemistry whole rock and k feldspar pb single zircon pb evaporation and nd whole rock isotopic data are presented for granites of the velho guilherme intrusive suite and the volcanic rocks of the uatumagroup in the carajas mineral province southern para brazil pb pb zircon ages of 18679 4 ma 18629 16 ma and 18669 3 ma for the antonio vicente mocambo and rio xingu granite massifs respectively show that the granites were emplaced at 1870 ma pb pb whole rock reference age of the uatumavolcanic rocks 18759 158 ma is comparable within the limits of the error 1870 ma thus represents the time of an important magmatic event in the eastern part of the amazonian craton nd model ages of the granites 3 0 3 2 ga and volcanic rocks 2 9 3 1 ga and their strongly negative initial ond values indicate that the magmas were derived from mesoarchean rocks with a long crustal residence time a mantle contribution cannot be completely ruled out however 2002 elsevier science b v all rights reserved

well preserved late paleoproterozoic volcanic centers in the sao felix do xingu region amazonian craton brazil abstract the amazonian craton in the sao felix do xingu city southeast region of the para state north of brazil hosts exceptionally well preserved paleoproterozoic bimodal magmatic units grouped in the sobreiro and santa rosa formations these formations are correlated to the uatuma magmatic event which is largely distributed in the amazonian craton occupying more than 1 500 000 km 2 geological mapping and petrographical observations reveal distinct spectra of volcanic facies in both formations the basal calc alkaline sobreiro formation is composed mainly of andesitic and dacitic lava flows and associated volcaniclastic facies of autoclastic origin with subordinate pyroclastic flow deposits this formation shows inferred eruption style that is similar to those in flood basalt provinces with rare scutulum type lava shields the upper a type santa rosa formation was generated by multicyclic explosive and effusive episodes predominantly associated with large fissures and is materialized by voluminous ignimbrites with subordinated ash fall tuff crystal tuff lapilli tuff co ignimbritic breccias rhyolitic dikes and domes and associated granitic porphyries and equigranular granitic intrusions ignimbrite and rhyolite dikes reveal conspicuous vertical flow pattern pointing to a fissure controlled eruption similar to sierra madre occidental ignimbrite province the proposed evolutionary model for the sao felix do xingu units differs from those of other occurrences related to the uatuma magmatic event in the amazonian craton characterized by predominance of a type volcanism and contemporaneous granites

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

granitic systems a special issue in honor of ilmari haapala abstract this paper is an introduction to the special issue of lithos honoring ilmari haapala the 1982 2002 professor of geology and mineralogy of the department of geology university of helsinki the articles in the issue are based on invited presentations given at a january 12 14 2003 symposium granitic systems state of the art and future avenues that was held at the department of geology university of helsinki on the occasion of ilmari haapala s december 31 2002 retirement the scientific achievements of professor haapala are briefly reviewed and the main results of the papers that comprise the volume are discussed

zircon rock partition coefficients of rees y th u nb and ta in granitic rocks uses for provenance and mineral exploration purposes abstract the trace element composition of magmatic zircon is highly variable even within the same grain and its study is complicated by the abundance of microinclusions metamict portions and strong compositional zoning among other factors to contribute to the understanding of the geochemistry of trace elements in zircon we determined the rare earth y nb ta th and u contents in zircon grains by laser ablation inductively coupled plasma mass spectrometry la icp ms with the use of cathodoluminescence and backscattered mev images zircon rock partition coefficients were determined in nine different types of granitoids and compared with experimental and natural data the obtained data are comparable with those reported by other authors by using the partition coefficient we estimated the composition of the host granitoids based on the zircon grain composition which was interpreted as evidence that the patterns of the trace elements in zircon grains are controlled by the liquid composition at the moment of crystallization a new set of partition coefficients for rees y nb ta th and u is suggested for provenance and exploratory studies la 0 8 ce 1 7 pr 2 1 nd 3 4 sm 9 8 eu 7 9 gd 24 tb 37 dy 69 ho 117 er 167 tm 281 yb 379 lu 437 nb 1 6 ta 2 9 th 27 u 177 and y 109 trace element diagrams eu eu vs yb nb vs th and y 200 lu 10 nb vs nb ce are proposed for discriminating zircon from different types of granitoids particularly for a type i type and shoshonitic rocks the trace element patterns of zircon are useful as a tool for mineral exploration studies because they often reproduce the patterns of mineralized granites

magmatic vs hydrothermal origins for zircon associated with tantalum mineralization in the tanco pegmatite manitoba canada complex textures in zircon associated with ta oxides have been used to assess the processes at the origin of zircon crystallization and associated ta mineralization in pegmatites in particular the role of magmatic vs hydrothermal processes the tanco pegmatite is used as an example because its zircon is devoid of post magmatic alteration and its petrogenesis is well constrained zircon in primary units is metamict with high u pb th contents by contrast in secondary assemblages affected by late magmatic micaceous alteration zircon is devoid of radiogenic elements but it may contain abundant ta2o5 up to 4 7 wt the incorporation of ta into zircon may occur through coupled substitution mechanisms involving other minor elements such as p al mn or li the presence of ta accounts for the distorted structures in the ta rich zircon as revealed in high resolution tem images four zircon types occur sequentially in single zircon crystals which permits a new model for zircon growth and evolution in rare element pegmatites to be advanced 1 zircon z1 is ta rich and crystallized possibly before discrete ta phases 2 z1 was overgrown by regularly zoned zircon z2 and z3 which show lower ta and extreme zr hf fractionation hfo2 up to 38 9 wt suggesting crystallization from a highly fractionated melt possibly at the onset of ta mineralization and 3 close to the solidus the aqueous fluid at the origin of micaceous alteration corroded the distorted structure of z1 and a low ta zircon z4 replaced z1 by dissolution reprecipitation whereas z2 and z3 resisted this alteration tantalum was no longer stable in the zircon structure and crystallized as ta oxide inclusions in the reequilibrated zircon z4

geochemical evidence for a multistage magmatic genesis of ta sn li mineralization in the granite at beauvoir french massif central the beauvoir rare metal granite at the southern edge of the echassieres granite massif french massif central is mineralized by disseminated ta sn and li the granite body formed from an independent melt which was emplaced soon after the main granite facies of the massif the geochemistry of the beauvoir granite relates it to the phosphorus rich type of ta bearing granites and geochemical and mineralogical data establish its similarity to pegmatite melts the beauvoir granite results built up from two distinct intrusions both intrusions are cogenetic and were emplaced within a short time interval a geochemical study of a deep drill hole bored down to 900 m under the surface to the floor of the granite sheet with selected key zones observed in greater detail has allowed the recreation step by step of a long process leading to the economic concentration of ta sn and li the comparison of major element trace element and isotopic geochemistry with the petrology makes it possible to unravel the numerous processes contributing to the ore formation local events need to be determined before main events can be identified constraints on the interpretation of the ore genesis are provided by a careful observation of data interpretations of these observations are strongly backed up by experimental data e g keppler 1993 the source rock was most likely enriched in sn and w at about 10 ppm precluding a slightly enriched granitic melt by partial melting it is not known whether the melt was already enriched in ta but this is not a prerequisite subsequently deep seated fractional crystallization produced granitic magma similar in composition ta nearly equal 9 m to the adjacent colettes granite and further fractionation processes led to a melt already strongly enriched in ta ca 40 ppm strongly peraluminous and enriched in the depolymerizing elements f and p the viscosity was therefore very low allowing easy ascent during transport small scale fluctuations in the viscosity were amplified by upward movement leading to an f and p rich melt preceding the magma batch this less viscous melt again underwent crystallization while moving through the upper

petrogenesis of the paleoproterozoic rapakivi a type granites of the archean carajas metallogenic province brazil three paleoproterozoic a type rapakivi granite suites jamon serra dos carajas and velho guilherme are found in the carajas metallogenic province eastern amazonian craton liquidus temperatures in the 900 870 c range characterize the jamon suite those for serra dos carajas and velho guilherme are somewhat lower pressures of emplacement decrease from jamon 3 2 0 7 kbar through serra dos carajas 2 0 1 0 kbar to velho guilherme 1 0 0 5 kbar oxidizing conditions nno 0 5 characterized the crystallization of the jamon magma the velho guilherme magmas were reducing marginally below fmq and the serra dos carajas magmas were intermediate between the two in this respect the three granite suites have archean tdm model ages and strongly negative nd values 12 to 8 at 1880 ma and they were derived from archean crust the jamon granite suite may have been derived from a quartz dioritic source and the velho guilherme granites from k feldspar bearing granitoid rocks with some sedimentary input the serra dos carajas granites either had a somewhat more mafic source than velho guilherme or were derived by a larger degree of melting underplating of mafic magma was probably the heat source for the melting the petrological and geochemical characteristics of the carajas granite suites imply considerable compositional variation in the archean of the eastern amazonian craton the oxidized jamon suite granites are similar to the mesoproterozoic magnetite series granites of laurentia and they were derived from archean igneous sources that were more oxidized than the sources of the fennoscandian rapakivi granites the serra dos carajas and velho guilherme granites approach the classic reduced rapakivi series of fennoscandia and laurentia no counterparts of the mesoproterozoic two mica granites of laurentia have been found however following the model of hoffman hoffman p 1989 speculations on laurentia s first gigayear 2 0 to 1 0 ga geology 17 135 138 the origin of the 1 88 ga carajas granites is related to a mantle superswell beneath the trans amazonian supercontinent this caused breakup of the continent and was associated with magmatic underplating and resultant crustal melting and generation of a type granite magmas the paleoproterozoic continent that included the archean and trans amazonian domains of the amazonian craton was assembled at 2 0 ga its disruption was initiated at 1 88 ga at least 200 ma earlier than in laurentia and fennoscandia the carajas granites were related to the breakup of the supercontinent not to subduction processes

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

oxidized magnetite series rapakivi type granites of carajas brazil implications for classification and petrogenesis of a type granites abstract the varying geochemical and petrogenetic nature of a type granites is a controversial issue the oxidized magnetite series a type granites defined by anderson and bender anderson j l bender e e 1989 nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america lithos 23 19 52 are the most problematic as they do not strictly follow the original definition of a type granites and approach calc alkaline and i type granites in some aspects the oxidized jamon suite a type granites of the carajas province of the amazonian craton are compared with the magnetite series granites of laurentia and other representative a type granites including finnish rapakivi and lachlan fold belt a type granites as well as with calc alkaline i type orogenic granites the geochemistry and petrogenesis of different groups of a types granites are discussed with an emphasis on oxidized a type granites in order to define their geochemical signatures and to clarify the processes involved in their petrogenesis oxidized a type granites are clearly distinguished from calc alkaline cordilleran granites not only regarding trace element composition as previously demonstrated but also in their major element geochemistry oxidized a type granites have high whole rock feo t feo t mgo tio 2 mgo and k 2 o na 2 o and low al 2 o 3 and cao compared to calc alkaline granites the contrast of al 2 o 3 contents in these two granite groups is remarkable the cao feo t mgo tio 2 vs cao al 2 o 3 and cao feo t mgo tio 2 vs al 2 o 3 diagrams are proposed to distinguish a type and calc alkaline granites whole rock feo t feo t mgo and the feo t feo t mgo vs al 2 o 3 and feo t feo t mgo vs al 2 o 3 k 2 o na 2 o diagrams are suggested for discrimination of oxidized and reduced a type granites experimental data indicate that besides pressure the nature of a type granites is dependent of o 2 conditions and the water content of magma sources oxidized a type magmas are considered to be derived from melts with appreciable water contents 4 wt originating from lower crustal quartz feldspathic igneous sources under oxidizing conditions and which had clinopyroxene as an important residual phase reduced a type granites may be derived from quartz feldspathic igneous sources with a metasedimentary component or alternatively from differentiated tholeiitic sources the imprint of the different magma sources is largely responsible for the geochemical and petrological contrasts between distinct a type granite groups assuming conditions near the nno buffer as a minimum for oxidized granites magnetite bearing granites formed near fmq buffer conditions are not stricto sensu oxidized granites and a correspondence between oxidized and reduced a type granites and respectively magnetite series and ilmenite series granites is not always observed

sn polymetallic greisen type deposits associated with late stage rapakivi granites brazil fluid inclusion and stable isotope characteristics tin polymetallic greisen type deposits in the itu rapakivi province and rondonia tin province brazil are associated with late stage rapakivi fluorine rich peraluminous alkali feldspar granites these granites contain topaz and or muscovite or zinnwaldite and have geochemical characteristics comparable to the low p sub type topaz bearing granites stockworks and veins are common in oriente novo rondonia tin province and correas itu rapakivi province deposits but in the santa barbara deposit rondonia tin province a preserved cupola with associated bed like greisen is predominant the contrasting mineralization styles reflect different depths of formation spatial relationship to tin granites and different wall rock fluid proportions the deposits contain a similar rare metal suite that includes sn fw fta fnb and base metal suite zn cu pb is present only in correas deposit the early fluid inclusions of the correas and oriente novo deposits are 1 low to moderate salinity 0 19 wt nacl eq co2 bearing aqueous fluids homogenizing at 245 450 8c and 2 aqueous solutions with low co2 low to moderate salinity 0 14 wt nacl eq which homogenize between 100 and 340 8c in the santa barbara deposit the early inclusions are represented by 1 low salinity 5 12 wt nacl eq aqueous fluids with variable co2 contents homogenizing at 340 to 390 8c and 2 low salinity 0 3 wt nacl eq aqueous fluid inclusions which homogenize at 320 380 8c cassiterite wolframite columbite tantalite scheelite and sulfide assemblages accompany these fluids the late fluid in the oriente novo and correas deposit was a low salinity 0 6 wt nacl eq co2 free aqueous solution which homogenizes at 100 260 8c and characterizes the sulfide fluorite sericite association in the correas deposit the late fluid in the santa barbara deposit has lower salinity 0 3 wt nacl eq and characterizes the late barren quartz muscovite and kaolinite veins oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240 450 8c and 1 0 2 6 kbar fluid pressure at correas and oriente novo the hydrogen isotope composition of breccia greisen stockwork and vein fluids