jotunites from the grenville province quebec petrological characteristics and implications for massif anorthosite petrogenesis abstract we report new results on the geology mineralogy and chemical compositions of jotunites mainly pyroxene monzodiorites from the morin st urbain and labrieville anorthosite complexes all in the grenville province of quebec jotunites occur between anorthosite and mangerite as marginal units to anorthosite or mangerite plutons or as fine grained dikes in either rock type some occurrences are probably cumulates but the dikes indicate the existence of jotunitic liquids jotunites consist predominantly of sodic plagioclase an25 an45 clinopyroxene and orthopyroxene having intermediate xmg e g en60 en40 along with significant ilmenite magnetite and apatite most samples contain small amounts of k feldspar locally mesoperthite and quartz it is noteworthy that plagioclase and pyroxene compositions in jotunites lie between those in associated anorthosite and mangerite jotunites from all areas span a similar range in sio2 content 40 55 wt and are characterized by high levels of fe2o3 t 30 wt tio2 6 wt and p2o5 3 25 wt all samples are alkalic with k2o 3 6 wt increasing in the sequence morin st urbain labrieville they contain high sr up to 1400 ppm and ba up to 4600 ppm and concentrations correlate well with those in associated anorthosite in each case jotunites also are high in ga high ga al zr zn y and ree but low in rb high k rb u th ni cr co sc and v high ti v jotunites can be linked spatially mineralogically and chemically with associated anorthosite and mangerite and we interpret them as transitional rocks in a largely comagmatic sequence from anorthosite to mangerite we postulate a model for andesine anorthosite petrogenesis involving early crystallization and accumulation of plagioclase from parental magmas of intermediate sio2 content broadly dioritic in composition resulting in fe ti and p enrichment in the remaining magma leading to jotunite high o2 table causes early crystallization of fe ti oxides which suppresses fe mg enrichment in pyroxene fractionation of fe ti oxides pyroxene and apatite ultimately results in si and k enrichment in residual liquids leading to quartz mangerite significantly liquids follow an initial trend of si depletion fe enrichment followed by a reversal of this trend this view contrasts strongly with current models that regard anorthosite jotunite and mangerite as unrelated products of bimodal magmatism

paleoproterozoic tectonic transition from collision to extension in the eastern cathaysia block south china evidence from geochemistry zircon u pb geochronology and nd hf isotopes of a granite charnockite suite in southwestern zhejiang abstract the badu complex and associated paleoproterozoic granitoids are among the oldest known rocks in the cathaysia block in south china the paleoproterozoic units of the badu complex are dominantly composed of metapelitic rocks and meta greywackes here we report la ss icp ms laser ablation split stream inductively coupled plasma mass spectrometry zircon u pb data from a newly discovered garnet bearing granite which show an emplacement age of 1929 15 ma and metamorphism at 1872 34 ma we also report u pb ages of 1886 16 ma 1858 7 ma 1848 11 ma from a gneissic granodiorite and two charnockites respectively the garnet bearing granite is peraluminous with a cnk range from 1 1 to 1 3 the rock shows relatively high sio2 k2o and rb contents and low total ree sr cao and ferromagnesian components typical of leucogranites the whole rock nd two stage model age tdm2 nd of this rock is ca 2 7 ga zircon hf crustal model ages tdmc hf peak at about 2 7 ga and abundant inherited zircons occur with u pb ages in the range of 2044 to 2803 ma evidences from zircon u pb age and hf isotope compositions whole rock nd isotopes and whole rock major and trace elements suggest a metasedimentary protolith and that the garnet bearing granite leucogranite was derived by partial melting in a thickened crust at about 1 93 ga the gneissic granodiorite and charnockites show indistinguishable major and trace element features as well as zircon hf and whole rock nd isotope compositions indicating that they were generated from the same source rocks the gneissic granodiorite and charnockites are ferroan calc alkalic and metaluminous with a cnk range from 0 80 to 0 98 they display relatively low sio2 contents and ga al ratios suggesting their a type affinity their zircon tdmc hf age peak is 2 9 ga and whole rock tdm2 nd ages range from 2 8 to 2 9 ga these high temperature rocks were generated possibly through the partial melting of ancient amphibolites 2 9 ga with heat input from asthenosphere upwelling and magmatic underplating in an extensional setting at about 1 85 1 88 ga combined with data from previous studies we suggest three episodes of major crustal growth in this region at 1 8 1 9 ga 2 7 ga and 2 9 ga during the 1 8 1 9 ga event extensive reworking also took place from the 1 93 ga syn collision leucogranite garnet bearing granite the 1 88 1 85 ga post collision a type granites and charnockites the granite charnockite suite and the1 85 1 77 ga intraplate basaltic rocks li 1997 and xiang et al 2008 in the region a paleoproterozoic orogenic cycle can be deciphered in the cathaysia block the rapid transition of tectonic regime from collision to post collisional extension can be correlated to the assembly of the supercontinent columbia

derivation of the 1 0 0 9 ga ferro potassic a type granitoids of southern norway by extreme differentiation from basic magmas major and trace elements sr and nd isotopic data as well as mineral compositions are presented for a selection of the 1 0 0 9 ferro potassic a type granitoids bessefjellet rustfjellet verhuskjerringi valle holum svofjell handeland tveit aseral lyngdal gabbronorites that occur close to the mandal ustaoset line mul of southern norway these hornblende biotite granitoids hbg define an extensive differentiation trend ranging from gabbronorites 50 wt sio 2 to granites 77 wt sio2 this trend is interpreted as resulting from extreme fractional crystallization of several basaltic magma batches with similar major and trace elements compositions at 930 ma the hbg suite displays a narrower range in isr 0 7027 0 7056 than in end t 1 97 down to 4 90 suggesting some assimilation of a rb depleted lower crust afc process or and source variability an age of 929 47 ma is given by a rb sr isochron on the holum granite sri 0 7046 0 0006 mswd 1 7 geothermobarometers indicate a low pressure of emplacement 1 3 2 7 kbar and an oxygen fugacity close to nno high liquidus temperatures are given by the apatite saturation thermometer 1005 1054 c and are in agreement with results from other studies the basaltic parent magmas of the hbg suite are partial melts of an hydrous mafic potassic source lying either in the lithospheric upper mantle or in the mafic lower crust derived from it this contrasts with the 930 ma anorthosite mangerite charnockite suite amc suite of the rogaland province for which a depleted lower crustal anhydrous gabbronoritic source has been indicated the present data imply the penecontemporaneous melting of two contrasting sources in southern norway the source duality could result from an increasing degree of metamorphism amphibolite to granulite from east to west an horizontal stratification of the lower crust or from the stratification of the lithosphere melting of the lower crust or upper mantle it may also indicate that the amc and hbg suites formed in two distinct crustal segments the linear alignment of the hbg suite along the mandal ustaoset shear zone suggests that a linear uprise of the asthenosphere following a lithospheric delamination under this structure could be the vector of the mantle heat 2003 elsevier science b v all rights reserved

ferro potassic a type granites and related rocks in ne poland and s lithuania west of the east european craton the present study of monzodiorite quartz monzodiorite monzonite quartz syenite granodiorite and rapakivi like granite surrounding the suwalki ketrzyn and sejny anorthosite norite and gabbro plutons or forming separate bodies in northern poland and southern lithuania has resulted in the recognition of a specific suite with amcg affinity the bodies belonging to the mazury and veisiejai complexes are aligned to e w trending lineaments in southern lithuania and northern poland with a continuation through the baltic sea into south central sweden in the west and into nw belarus in the east the rocks of the suite form a continuous series ranging from 45 to 75 sio2 with no indication of the classical daly gap between mafic and felsic rocks the mazury and veisiejai complexes chemically belong to the ferro potassic alkali calcic type of rocks and are comparable with the amcg suite e g in rogaland southern norway the most acidic varieties of the granitoids approach the classic rapakivi granites in their petrogenetic characteristics elevated contents of incompatible elements and ree and hence have a type affinities the granitoids are assigned to the post collisional granite field the overall evolution from mafic to acidic rocks is characterized by well defined trends which most probably represent a liquid line of descent fractional crystallization with or without assimilation and hybridization can account for the continuous evolution from mafic to acidic members the formation of the suite is concentrated in the timespan covering almost 50 myr from 1 55 to 1 5 ga the most felsic rocks yield ages of ca 1 5 ga which are very similar to the kabeliai granites further east in southeastern lithuania cooling and local mylonitization proceeded until 1 4 ga hornblende and biotite 40 ar 39 ar ages

isotopic constraints on the genesis of the rogaland anorthositic suite southwest norway demaiffe d weis d michot j and duchesne j c 1986 isotopic constraints on the genesis of the rogaland anorthositic suite southwest norway in s deutsch and a w hofmann editors isotopes in geology picciotto volume chem geol 57 167 179 isotopic data were obtained on the sveconorwegian 1200 900 ma anorthosites and associated norites and charnockites of the rogaland igneous complex sw norway the isotopic data isr 0 703 0 7077 end 0 4 to 5 5 suf 4pb 1 8 1 8 2 so 5 2 to 6 6 c suggest an upper mantle origin for the parental magma of the anorthosites and related norites and jotunites or an origin in the lower crust by melting of mantle derived basic rocks shortly after their formation in two well documented cases the egersund ogna and the hidra bodies a progressive contamination by u depleted but not rb depleted lower crustal material is apparent during the differentiation process the late stage liquids have higher i up to 0 7086 lower but still slightly positive end less radiogenic pb isotopic composition the intrusive acidic rocks some of them of the charnockitic type display variable isotopic data is 0 7055 0 709 end 0 5 to 0 8 pb isotopic compositions comparable to that of some of the surrounding gneisses suggesting that there are in general no direct cogenetic relations between the anorthosites and the charnockites our data point to an origin of some of these acidic rocks by anatectic melting of the surrounding high grade metamorphic gneisses

visible and near infrared reflectance spectroscopy of pyroxene bearing rocks new constraints for understanding planetary surface compositions 1 laboratory visible and near infrared reflectance spectra of solid rock slabs mineral separates and systematic mixtures were simultaneously investigated we apply an empirical approach to evaluate spectra in order to achieve qualitative and quantitative information we use cumulates mostly norites leuconorites melanorites and anorthosites belonging to the bjerkreim sokndal layered intrusion a sequence of genetically related rocks with simple textures laboratory spectra are measured on slightly polished rock slabs in the 350 to 2500 nm interval and directional hemispherical reflectance geometry composition is determined using traditional techniques other than reflectance spectroscopy we find that 1 band minima measured on rock spectra are strongly influenced by the concurrent effects due to modal abundance of the spectroscopically active mineral and mineral chemistry 2 band depths can be used for semiquantitative analyses limited to the set of rocks investigated 3 the spectral parameters derived from powdered pyroxene are in agreement with previously published calibrations 4 the mineral mixture systematics can be reasonably considered as linear when pyroxene is mixed with neutral components and 5 the empirical evaluation of solid rock surface spectra needs further insights to give a great improvement to planetary researches in addition genetic sequences of rocks should be investigated in detail to help the geological interpretation of planetary evolution therefore more laboratory and analytical studies are required in order to understand the influence of composition and petrographic textures on the spectral analysis

a strontium isotopic investigation of the bjerkreim sokndal layered instrusion southwest norway the 230 km 2 proterozoic bjerkreim sokndal layered instrusion has a monzonoritic bulk composition and comprises a 6 km thick broadly leuconoritic layered series ls overlain by unlayered mangerite and quartz mangerite in the bjerkreim lobe the ls comprises six megacyclic units mcu 0 ia ib ii 11 and iv in a syncline this lobe is surrounded by migmatitic gneisses the roof to the instrusion is missing the mg number opx an and whole rock initial 87 sr 86 sr isotope ratios sr 0 display broadly parallel trends through mcus ii and iii and into mcu iv with decreasing mg number 75 58 and an 50 40 accompanying increasing sr 0 0 7050 0 7085 this correlation breaks down in the upper part of mcu iv and mangerite the quartz mangerite has sr 0 values of 0 7085 abrupt reversals occur across the mcu boundaries the ls crystallized on the floor of a periodically replenished magma chamber that was continually assimilating country rock gneisses strong compositional zoning of the magma developed as a result of repeated replenishments with relatively dense primitive ferrobasaltic magma sr 0 0 7049 along the floor and the development of extensive buoyant roof melts assimilation took place on a massive scale up to 50 in the upper parts of the chamber

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

petrogenesis and tectonic implications of the charnockites in the yishui terrane north china craton abstract a combined study of zircon u pb ages lu hf isotopes and whole rock geochemistry was carried out for representative charnockites from the yishui terrane in the western shandong province ncc the results demonstrate that the charnockites in the yishui terrane are of igneous origin rather than derivation from remelting or metamorphism of supracrustal rocks zircon u pb dating for the charnockites in the yishui terrane indicates protolith emplacement around 2 52 2 56 ga and synchronous metamorphism around 2 50 2 53 ga zircon lu hf isotopes analyses show that the charnockites have positive e hf t values with an average 4 03 and depleted mantle two stage zircon hf model ages t dm2 mainly cluster around 2 7 3 0 ga indicative of a source of juvenile crust formed around 2 7 3 0 ga furthermore the charnockites with 2 tend to be magnesian calcic to calc alkalic and metaluminous only a small population of the charnockites with 70 wt sio 2 are ferroan alkali calcic and weakly peraluminous which are consistent with geochemical features of cordilleran type granitoids suggesting a deeply eroded magmatic arc derived from remelting of juvenile crust mainly formed around 2 7 3 0 ga taken the comprehensives of available whole rock geochemical and zircon lu hf isotopic data of the charnockites synchronous emplacement and metamorphism high temperature setting of charnockites granulite facies metamorphism of anticlockwise p t path in the yishui terrane as well as the whole ncc we conclude that the combined geodynamics of mantle plume and oceanic crust subduction might contribute to the formation of the charnockites in the yishui terrane as well as similar late archean charnockites in other areas of the ncc further implying extensive occurrences of modern style plate tectonic accretions in late archean in the ncc

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

1 88 1 87 ga post kinematic intrusions of the central finland granitoid complex a shift from c type to a type magmatism during lithospheric convergence abstract the evolution of the svecofennian orogen spans from 1 95 ga to 1 80 ga with the main crust forming activity having taken place 1 90 1 87 ga ago subsequent deformation was largely concentrated to southern finland where transpressional structures indicate lithospheric convergence until 1 80 ga much of the svecofennian orogen in finland is occupied by the central finland granitoid complex cfgc that mainly consists of i type granodiorite and granite these 1 89 1 88 ga intrusive rocks are typically foliated and considered synkinematic a distinct suite of post kinematic undeformed or slightly foliated plutons crosscut the synkinematic rocks they are predominantly quartz monzonites and monzogranites and have been divided into three types according to their petrographic mineral and chemical characteristics compared to the calc alkaline synkinematic granitoids the post kinematic suite generally has an alkaline affinity with higher fe ti k ba zr and nb and lower mg ca and sr at a given sio 2 content the type 1 post kinematic plutons are peraluminous and contained a prominent sedimentary component in their source the types 2 and 3 plutons are marginally metaluminous to peraluminous the type 2 granites especially those in the western cfgc approach the classic 1 65 1 54 ga rapakivi granites of southern finland in their petrographic characteristics magmatic association tholeiitic mafic rocks and elevated contents of incompatible elements and hence have a type characteristics the type 3 plutons contain a pyroxene bearing margin type 3a or contain pyroxene throughout type 3b the type 3b rocks have c type charnockite magma type affinities and some plutons of this subgroup are alkaline the type 3a plutons appear to be transitional between the type 2 and type 3b plutons the synkinematic magmatic episode in the cfgc area probably involved partial melting of intermediate high k rocks in the lower crust with a magmatic addition from a mafic underplate this magmatic episode left a hornblende and biotite poor granulitic residue in the lower crust heat from the mafic underplate triggered partial melting of the granulite to produce the post kinematic magmatism and also introduced mafic material into the post kinematic magmas the post kinematic magmatism took place over quite a short time period ca 15 ma during overall lithospheric convergence it extended beyond the cfgc area and registers a temporal shift from the northeast toward the west and a general change in the character of magmatism from c type to a type the post kinematic magmatism probably resulted from extensional or transtensional events modifying the tectonically thickened crust partial melting of the mafic lower crust produced c type magmatism soon after the first melting episode the crust was already rather rigid and allowed the mafic magmas to follow a tholeiitic trend when the bimodal a type magmas were formed in the western cfgc

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

space and time in granite plutonism granitic suites formed in the last 2500 ma are either calc alkaline or less commonly alkalic the space time trends of granitoid rocks from modern compressional arcs include variations towards more silicic and potassic products but even the most mature magmas of these arcs have fe mg ratios near to 1 in contrast with the strongly iron enriched alkalic suites that characterize zones of crustal extension both calc alkaline and alkalic suites are mainly mantle derived they evolved respectively from tholeiitic and alkali basalt parental magmas which have been subject in most examples to a two stage fractionation history other factors that may influence the evolution of these parental magmas include first the addition of variable but minor amounts of crustal melt and secondly the persistence of refractory mineral phases in the zone of melting contributions from subducted continental detritus are thought to be of minor significance a long term trend over the entire history of the crust from more sodic to more potassic calc alkaline magmatism may reflect the declining importance of subducted ocean lithosphere in magma generation and the increasing role of the overlying volatile fluxed mantle wedge this trend and in particular the widespread development of alkalic granite suites in mid proterozoic times may be linked to the declining vigour of tectonic and associated magmatic processes during the earth s history these alkalic suites may indicate a period when the continental lithosphere had become stable enough to resist fragmentation leading to intracontinental rift and swell zones of magmatism in some cases new plate cycles with more normal calcalkaline igneous rocks seem to have occurred in the same zones although much of the evidence favours the operation of plate tectonic and subduction processes in magma generation during archaean and early proterozoic times this link cannot be taken as proved except for the last ca 1000 ma

influence of co2 on melting of model granulite facies assemblages a model for the genesis of charnockites it is shown that partial melting studies at crustal pressures in sio2 rich portions of the system kalsio4 mg2sio2 h2o co2 can be used in modeling the anatectic origin of charnockites the univariant reaction phlogopite sanidine quartz vapor enstatite liquid yields an sio2 rich melt granite analog at 3 kbar the vapor composition at the solidus is buffered to high h2o contents by virtue of the coexistence of phlogopite with its breakdown products with higher pressures 8 and 15 kbar the fluid phase is buffered to higher co2 contents and the melt composition becomes enriched in k2o and mgo charnockite analog melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure it is noted that partial melts generated at the base of the crust in the presence of co2 rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures co2 saturated melting of similar sio2 rich bulk compositions phlogopite absent through the reaction enstatite sanidine quartz co2 liquid occurs at temperatures above 1000 c to about 15 kbar

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

igneous charnockites and related rocks from the bjerkreim sokndal layered intrusion southwest norway a jotunite hypersthene monzodiorite derived a type granitoid suite the upper part of the bjerkreim sokndal layered intrusion bksk introduction comprises a suite of charnockitic granitoids mangerite quartz charnockitic granitoids are a major component of mangerite and charnockite with some jotunites the petrology and anorthosite mangerite charnockite rapakivi granite geochemistry major and trace elements of eight main rock types amcg complexes and therefore play a crucial role in 88 samples are considered the rocks form a suite of k2o rich the formation and evolution of the proterozoic crust alkali calcic granitoids of a type deriving from jotunitic magma their origin has been long debated though intimately two trends of inferred liquids are distinguished the main liquid associated with massif anorthosites they are generally line of descent which passes from jotunites through two pyroxene considered to be derived from distinct parental magmas quartz mangerites to amphibole charnockites the second one which generated in different sources emslie 1978 1991 morse encompasses olivine bearing quartz mangerites and charnockites and 1982 duchesne 1984 wiebe 1992 ashwal 1993 it is rooted into mangeritic liquids comparison with the tellnes rock has however been recognized that some charnockitic series reveals that contamination by leucogranitic material has taken rocks could also be derived from an intermediate monplace simultaneously with fractional crystallization in both bksk zodioritic to ferrodioritic jotunitic magma duchesne trends zr rb cs and th are particularly sensitive to assimilation et al 1989 wilmart et al 1989 owens et al 1993 and the higher water content in bksk zircon and apatite have whose origin is also controversial the jotunitic magma saturated at the liquidus of quartz mangerite around 900 c close could either be derived from a crustal source by the to the fayalite magnetite quartz fmq buffer the two pyroxene partial melting of basic rocks duchesne et al 1989 quartz mangerites cannot have been equilibrated with the mangerite duchesne 1990 or be residual magmas after the forcumulates on which they rest a major influx of magma took place mation of massif anorthosites which have been conwhen mangeritic cumulates were being deposited it mingled and partly mixed with the resident contaminated magma taminated to various degrees by crustal material emslie et al 1994 the latter hypothesis seems to explain a large number of amcg complexes in the grenville and nain provinces and elsewhere accepting that some charnockites are derived from jotunites there is a logical

petrogenesis of monzonoritic dykes in the egersund ogna anorthosite rogaland s w norway trace elements and isotopic sr pb constraints two major monzonoritic dykes occur in the egersund ogna anorthositic massif s w norway the lomland dyke which varies from norite to monzonite and the vettaland ferronoritic dyke they are characterized by high fe ti and p contents low sio2 variable k2o 0 5 4 5 and high fe mg ratios small variations in ree distribution are observed inside the lomland dyke la yb 12 lree ca 150 180 chondrite normalized values neutral to slightly positive eu anomaly part of the vettaland dyke is severely depleted in zr rb and ree and shows a positive eu anomaly all rocks are depleted in u and th and show very low cr and ni contents as well as high sr contents 400 600 ppm variation within the lomland dyke is satisfactorily ex plained through subtraction of an apatite bearing noritic cumulate the role of apatite is predominant in controlling the ree behaviour eutectic partial melting of a fe rich noritic cumulate containing apatite under low ph2o conditions is suggested for the vettaland dyke by ree modelling sr isotopic initial ratios are different in lomland ca 0 708 and vettaland ca 0 706 dykes these values preclude direct derivation from the mantle as well as comagmatic relationship with anorthosite contamination of a mantle derived magma by deep crustal material or anatexis of the lil depleted lower crust is compatible with the low u and th contents and with the pb isotopic ratios the vettaland partial melting process is extended to all monzonoritic types the necessary heat being provided by the high temperature anorthositic crystal mush

imaging downward granitic magma transport in the rogaland igneous complex sw norway combining geological mapping and petrological structural and geophysical gravity and seismic data already available for the late proterozoic rogaland igneous complex of norway allows the 3d shape of the bjerkreim sokndal layered intrusion to be modelled as a thick cumulate series capped by massive granitic rocks using the latter data along with the spectacular convergent linear flow pattern that covers both the cumulates and the felsic rocks of this chamber evidence is presented to show that the granitic material was downdragged through the sinking of its high density mafic floor into lower density anorthosites and granulitic gneisses this example illustrates that downward gravity driven flows of rocks were active in addition to upward flows in the building of the early crust up to late proterozoic times helping to explain the geochemical and structural complexities of the old crust

fluid inclusions in charnockites from the bjerkreim sokndal massif rogaland southwestern norway fluid origin and in situ evolution fluid inclusions and mineral associations were studied in late stage charnockitic granites from the bjerkreim sokndal lopolith rogaland anorthosite province because the magmatic and tectonic evolutions of this complex appear to be relatively simple these rocks are a suitable case for investigation of the origin and evolution of granulitic fluids fluid inclusions primarily contained in quartz can be divided into four types carbonic type i n2 bearing type ii co2 h2o type iii and aqueous inclusions type iv for each type the role of leakage and fluid mixing are discussed from microthermometric and raman spectrometric data the most striking features of co2 rich inclusions the predominant fluid is the presence of graphite in numerous trail bound inclusions ib and its absence in a few isolated very dense d 1 16 pure co2 inclusions ia and in the late carbonic inclusions ic fluid chronology and mineral assemblages suggest that carbonic ia inclusions represent the first fluid pure co2 trapped at or close to magmatic conditions t 780 830 c fo2 10 15 atm and p 7 4 1 kb outside the graphite stability field in contrast type ib inclusions enclosed graphite particles from a channelized fluid during retrograde rock evolution p 3 4 kb and t 600 c decreases in t fo2 could explain a progressive evolution from a co2 rich fluid to an h2o rich fluid in a closed c o h system however graphite destabilization observed in type ic inclusions implies some late introduction of external water during the last stage of retrogression the main results of this study are the following 1 a carbonic fluid was present in an early stage of rock evolution probably in the charnockitic magma and 2 this granulite occurrence offers good evidence of crossing the graphite stability field during post magmatic evolution

petrology and u pb geochronology of the telohat migmatites aleksod central hoggar algeria the aleksod region is composed of metasedimentary rocks and large areas of biotite and hornblende bearing migmatites anatexis associated with the main deformation stages occurred under high pressure and temperature conditions estimated at 13 2 kbar and 750 50 c the bulk mineralogical composition of the telohat migmatites shows that their protolith was granodioritic internal structures of zircons and u pb data suggest a polyphased evolution with a 2131 12 ma age for the protolith and a 609 17 ma age for the pan african tectono metamorphic evolution thus precluding any kibaran event in the aleksod area leucosomes are richer in sr and display lower rb zr nb y th u and ree contents than melanosomes wherein accessory phases are stored eu contents are also lower in the leucosomes but in lesser proportion than the other rare earth s leading to a significant positive anomaly petrogenetic modelling accounting for accessory mineral phases clearly shows that the trace element contents of leucosomes and melanosomes follow a distribution law consistent neither with equilibrium nor fractional melting their trace element patterns are best explained by the model of disequilibrium melting with mixing of a few residual phases the present results and previous sr isotopic data as well raise the question of disequilibrium melting in anatexis of crustal material

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

the nain churchill boundary and the nain plutonic suite a regional perspective on the geologic setting of the voisey s bay ni cu co deposit northern labrador is the site of two major lithotectonic elements of eastern canadian shield geology first it encompasses a paleoproterozoic continental suture zone archean rocks of the nain province tectonically juxtaposed against paleoproterozoic and reworked archean rocks of the churchill province the nain churchill suture evolved between 1860 and 1740 ma impressing upon the archean and paleoproterozoic rocks a regional metamorphic and tectonic signature referred to as the torngat orogen an important component of the torngat orogen is the tasiuyak gneiss a paleoproterozoic metasedimentary unit that occupies most of the eastern margin of the churchill province second northern labrador is the site of a world renowned terrane of mesoproterozoic anorogenic igneous rocks the nain plutonic suite that sits astride the suture and acts as a stitching batholith between the nain and churchill provinces the nain plutonic suite comprising amalgamated granitic anorthositic dioritic and troctolitic intrusions largely obscures the suture for nearly half of its total length the suite evolved between 1350 and 1290 ma and is interpreted as a product of magmatism associated with limited intracontinental rifting of the conjoined nain churchill crust above a mantle plume the voisey s bay ni cu co deposit serendipitously discovered in 1993 resides within one of the oldest troctolitic intrusions of the nain plutonic suite a 1334 ma intrusion that transgresses a contact between archean and paleoproterozoic gneisses genetic controls on the setting of mineralization have been built upon the nain churchill boundary as a zone of weakness that was exploited by mantle magmas and have implicated the tasiuyak gneiss as a crustal sulfur source although the archean paleoproterozoic junction at voisey s bay is presently interpreted as representing the nain churchill boundary in reality the provincial affinity of the archean gneisses is equivocal this uncertainty dictates caution in assigning the nain churchill boundary as the convenient transcrustal conduit that allowed the voisey s bay mafic intrusions rapid transit from their mantle staging area modeling the sulfide deposit as being solely a result of sulfur saturation of mafic magma by proximal paleoproterozoic tasiuyak paragneisses is also questionable because other genetic processes may have been responsible for example desilication of gneiss is strongly indicated by aluminous refractory minerals in vestiges of fused tasiuyak gneiss the spatial distribution of the mineralized rock at voisey s bay apparently within the subchamber plumbing system feeding a larger intrusion and within remnants of the larger intrusion itself may serve as a paradigm for similar deposits in the nain area but the preerosional comparative morphology of that larger intrusion relative to the better preserved ones may never be known a thorough understanding of the setting and genesis of the voisey s bay deposit will better facilitate establishing exploration targets in other parts of the nain region in labrador as a whole and in other geologically similar regions of the world

geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent whole rock major element compositions are investigated in 99 cumulates from the proterozoic bjerkreim sokndal layered intrusion rogaland anorthosite province sw norway which results from the crystallization of a jotunite fe ti p rich hypersthene monzodiorite parental magma the scattering of cumulate compositions covers three types of cumulates 1 ilmenite leuconorite with plagioclase ilmenite and ca poor pyroxene as cumulus minerals 2 magnetite leuconorite with the same minerals plus magnetite and 3 gabbronorite made up of plagioclase ca poor and ca rich pyroxenes ilmenite ti magnetite and apatite each type of cumulate displays a linear trend in variation diagrams one pole of the linear trends is represented by plagioclase and the other by a mixture of the mafic minerals in constant proportion the mafic minerals were not sorted during cumulate formation though they display large density differences this suggests that crystal settling did not operate during cumulate formation and that in situ crystallization with variable nucleation rate for plagioclase was the dominant formation mechanism the trapped liquid fraction of the cumulate plays a negligible role for the cumulate major element composition each linear trend is a locus for the cotectic composition of the cumulates this property permits reconstruction by graphical mass balance calculation of the first two stages of the liquid line of descent starting from a primitive jotunite the tjfrn parental magma another type of cumulate called jotunite cumulate and defined by the mineral association from the transition zone of the intrusion has to be subtracted to simulate the most evolved part of the liquid line of descent the proposed model demonstrates that average cumulate compositions represent cotectic compositions when the number of samples is large n 40 the model however does not account for the k2o evolution suggesting that the system was open to contamination by roof melts the liquid line of descent corresponding to the bjerkreim sokndal cumulates differs slightly from that obtained for jotunitic dykes in that the most ti p and fe rich melts evolved jotunite are lacking the constant composition of the mafic poles during intervals where cryptic layering is conspicuous is explained by a

zircon in charnockitic rocks from rogaland southwest norway petrogenetic implications zircons separated from monzonoritic rocks and quartz mangerites igneous and metamorphic have been studied for various mineralogical chemical and physical properties colour zoning presence of core u distribution morphology lattice parameters thermoluminescence to determine the relationships with chemical composition of the host rocks and geological setting the zircons grade from nearly perfectly crystalline to slightly metamict types the crystal morphology shows prismatic habits and a striking lack of well developed pyramidal faces possibly indicating growth in a dry formation environment the zircons can be divided into two groups the first one comprises zircons from monzonoritic rocks they are unzoned devoid of brownish core with a uniform u distribution and low u content except in hidra the second group comprises zircons from igneous and metamorphic quartz mangerites they contain brownish zoned u rich cores in rocks where temperature of crystallization can be determined watson and harrison s 1983 experimental data indicate strong zircon saturation the cores are considered as inherited a fact that can be accounted for either by dry anatexis or bulk contamination in the bjerkreim sokndal layered lopolith previous isotopic data are confirmed which indicate that the acidic upper part of the massif is not comagmatic with the anorthosito noritic lower part and the monzonoritic rocks

petrogenesis of two granites from the nilgiri and madurai blocks southwestern india implications for charnockite calc alkaline granite and charnockite alkali a type granite link in high grade terrains abstract igneous charnockites share some of the characteristics of calc alkaline and alkali a type granites and together constitute important rock types in many high grade terrains the neoproterozoic kalpatta and munnar biotite hornblende granites intrude the upper amphibolite to granulite facies terrain of southwestern india geochemical characteristics of the kalpatta granite are similar to high k calc alkaline magnesian granitoids whereas those of the munnar granite are similar to alkali ferroan granitoids within the constraints imposed by the high temperature k rich nature of the magmas comparison with experimental studies on various granitoid source compositions and trace and rare earth element modeling the distinctive features of both granites reflect a source rock of charnockitic nature in this context the northern kerala nkm and cardamom hill cm charnockite massifs occurring near the granites were considered as probable source rock compositions both the nkm and cm charnockites consists of an intermediate low sio2 type and silicic high sio2 type with the intermediate type showing similarities to high ba sr granitoids with low k2o na2o ratios and the silicic type showing similarities to high ba sr granitoids with high k2o na2o ratios the proposed petrogenetic model involves partial melting of the intermediate nkm charnockite forming the kalpatta calc alkaline granite in contrast the munnar alkali a type granite was the product of melting followed by fractional crystallization of the intermediate cm charnockite it is suggested that granitoids that formed by melting of intermediate type charnockites show high k calc alkaline magnesian geochemical characteristics whereas those formed by intermediate type charnockite melting fractional crystallization show alkali ferroan geochemical characteristics

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

geochemical constraints on the genesis of the tellnes ilmenite deposit southwest norway the ilmenite norite of the tellnes fe ti deposit in the aana sira massif type anorthosite is connected to a main dike which varies in composition from monzonorite to quartz mangerite fine grained satellite dikes also occur in the vicinity of the main dike a number of rock samples have been analyzed for 36 major and trace elements an rb sr whole rock isochron 12 samples gives an age of 930 ma initial sr isotope compositions of the ilmenite noritc the main dike and the satellite dikes are 0 7050 0 7069 and 0 7100 respectively thus precluding a comagmatic origin without invoking contamination the evolution of the main dike can be accounted for by a closed system fractional crystallization of a monzonoritic magma that is without progressive contamination which gave rise to a series of liquids prior to intrusion mass balance calculation permits a two stage process in which noritic cumulates were subtracted trace element behavior is also consistent with such a model the satellite dikes represent undifferentiated monzonorites with trace elements and isotopic ratios implying a source material quite different from that of the main dike monzonorite the orebody is made up of ilmenite norite and small amounts of more plagioclase rich rocks which plot on linear trends in variation diagrams it is interpreted as a noritic cumulate which was enriched in dense oxide rich magma before being emplaced as a crystal mush the parental magma was noritic in composition unsaturated in apatite and probably derived from the crystallization of the enclosing massif anorthosite it is not precluded either that it could have given rise to the main dike monzonoritic liquid after being contaminated by lower crustal material nevertheless as an alternative it is not possible to reject two distinct parental magmas for the orebody and the main dike they would have evolved in two separated magma chambers before the tapping of these chambers and simultaneous injection of their contents in the dike the main dike illustrates the process by which a quartz mangerite can derive from a monzonoritic magma and gives support to a comagmatic origin of charnockitic and monzonoritic rocks

significance of 1 5 ga zircon and monazite ages from charnockites in southern lithuania and ne poland abstract the presence of 1 52 1 50 ga charnockites from the anorthosite mangerite charnockite granite amcg mazury complex in southern lithuania and ne poland in the western east european craton eec is revealed by secondary ion mass spectrometry sims and epma geochronology early 1 85 1 82 ga charnockites are related to major orogeny in the region whereas the newly studied charnockites intrude the already consolidated crust the 1 52 1 50 ga charnockite magmatism sims data on zircon was followed by high grade metamorphism epma data on monazite which strongly affected the surrounding rocks the 1 85 1 81 ga zircon cores in lazdijai and 1 81 ga monazite domains in the lanowicze charnockites represent the protolith age of a volcanic island arc the 1 52 1 50 ga charnockite magmatism and metamorphism are likely related to the distal danopolonian orogeny further to the west at the margin of baltica the c 1 52 1 50 ga amcg magmatism and metamorphism in the western eec as well as the paired accretionary rapakivi suites in amazonia may be the inboard manifestations of the same early mesoproterozoic orogeny associated with the juxtaposition of amazonia and baltica during the amalgamation of the supercontinent columbia

the umarizal igneous association borborema province ne brazil implications for the genesis of a type granites abstract the umarizal igneous association ne brazil consists of three a type plutons intruded over an interval of about 15 ma during the post collisional phase of the brasiliano orogeny all the plutons have sr isotopic compositions which indicate important or dominant crustal contributions crystallization of the umarizal sill formed of fayalite quartz syenite and syenogranite and of the lagoa stocks formed by mangerite and granite commenced under water undersaturated conditions at pressures around 700 800 mpa and temperatures around 900 c and continued during magma rise with the crystallization of hornblende at about 480 570 mpa crystallization of the acao stock which contains a rapakivi like facies commenced at similar temperatures and hornblende appeared at slightly less than 800 c and around 500 mpa different f o2 conditions controlled the compositions of the ferromagnesian phases and the nature of the oxide mineral assemblage simple fractional crystallization models from homogeneous parent magmas are insufficient to explain the chemical variation of the rocks suites

the environment in the caucasus in the upper paleolithic late pleistocene evidence from the small mammals from dzudzuana cave georgia abstract the mis 3 2 transition denekamp interstadial and beginning of the lgm is a crucial point in time for understanding adaptation of modern humans to climate the southern caucasus is a unique place to study human ecology within this time period because it served as a refugium during the last glacial maximum lgm and thus allows us to study how human populations responded to the climatic shifts during the last glacial this study presents the results of the paleoecological analysis of dzudzuana cave during the mis 3 2 transition using small mammal community structure as a proxy for paleoenvironment of the four units in dzudzuana units a through d unit c divided into subunits c5 to c1 has been dated to 27 24 ka cal bp and the mis 3 2 transition thus unit c allows for a diachronic analysis throughout this important time period small mammals were found primarily in subunit c2 and c1 analysis of the small mammal assemblages of dzudzuana subunits c2 and c1 confirm the paleoecological reconstruction obtained from macrobotanical remains and suggest a refugium habitat during the last phase of mis 3 and the onset of the lgm comparison with a contemporaneous site in the region satsurblia suggests a high spatial temporal mosaic habitat in the region small refugium areas within the rioni river valley and its tributaries that enjoyed ameliorated climatic conditions and proximity to water resources may have promoted local human habitation furthermore results suggest that the small mammal assemblages of dzudzuana are non analogue communities typical of european denekamp assemblages and provide a new datum point for the faunal remains during this time period

commingling of magmas in the bjerkrem sogndal lopolith southwest norway evidence for the compositions of residual liquids a detailed re examination of some of the more fractionated portions of the bjerkrem sogndal lopolith bsl has provided evidence for widespread mixing between quartz mangeritic and monzonoritic eia rekefjord magmas the higher temperature monzonoritic liquids are preserved as chilled pillows within quartz mangerite chemical compositions of these and other fine grained monzonorites suggest that they are chilled residual liquids related to the bsl and that they were in equilibrium with the more fractionated cumulates of the bsl the chilled monzonoritic liquids appear to define a fractionation trend of increasing sio2 up to 60 wt the quartz mangerites appear to represent separate partial melts derived from the country rock

chemical exchange in migmatites during cooling abstract the chemistry of the leucosome components in limited size migmatitic associations is generally believed to reflect the composition of the partial melt that could have been extracted to yield an anatectic magma several well documented studies of migmatites indicate that the distributions of some trace elements in leucosome melanosome pairs are inconsistent with equilibrium partial melting but are rather in agreement with chemical reequilibration during cooling in migmatites the liquid fraction does not leave the system this may induce an alteration of the chemical composition of the whole migmatite system by extensive chemical exchange between the liquid and the solid residue during cooling if this is the case the leucosome and melanosome components are not representative of the chemical composition of the liquid and solid residue respectively at the time of partial melting a rough evaluation of the residences time of the melt fractions in cooling in situ migmatitic bodies yields minimum estimates of 1 to 10 ma for such time spans the characteristics distances of diffusion distances of diffusion induced chemical transfer exceed the sizes of individual mineral grains which is consistent with a re equilibration process the release of latent heat of crystallization in cooling migmatitic systems and the presence of an interstitial liquid phase are critical in determining the extent and scale of chemical exchange the mechanism involves 1 reducing the cooling rate and 2 promoting the efficiency of chemical diffusion through the liquid phase thus some doubt is cast on the ability of small scale migmatitic systems to provide relevant information about chemical mass balance during partial crustal melting

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

the tortonian reference section at monte dei corvi italy evidence for early remanence acquisition in greigite bearing sediments summary the reliability of primary natural remanent magnetization nrm signals in greigite bearing sediments has been frequently questioned here we show that the stable nrm in the deep marine middle to late miocene sediments at monte dei corvi northern italy is mainly carried by greigite combined rock magnetic experiments and scanning electron microscopy successfully enabled discrimination between two greigite populations one fine grained and relatively well dispersed greigite population grain size between 60 and 200 nm is most likely of magnetotactic origin the second greigite population with larger grain sizes typically 700 nm to 1 m is most likely of authigenic bacterially mediated origin and is related to post depositional sulphidization processes greigite is the main magnetic remanence carrier in the older part of the section 12 8 to 8 7 ma whereas greigite and fine grained presumably magnetotactic magnetite are present in the younger part of the section 8 7 to 6 9 ma similar remanent magnetization directions of the magnetite and greigite components and the likelihood of a magnetotactic origin suggests that the nrm is of syn depositional age we suggest that moderate methane seepage from the underlying sediments may have occurred that resulted in the preservation of pristine greigite this corroborates the reliability of the previously established magnetostratigraphy at monte dei corvi

relationship between the layered series and the overlying evolved rocks in the bjerkreim sokndal intrusion southern norway abstract the bjerkreim sokndal layered intrusion bksk consists of a 7000 m thick layered series comprising anorthosites leuconorites troctolites norites gabbronorites and jotunites hypersthene monzodiorites overlain by an unknown thickness of massive evolved rocks mangerites hypersthene monzonites mg quartz mangerites qmg and charnockites ch the layered series is subdivided into six megacyclic units that represent the crystallisation products of successive major influxes of magma we have studied a ca 2000 m thick section that straddles the sequence from the uppermost part of the layered series to the qmg in the northern part of the intrusion mineral compositions in 37 samples change continuously in the lower part of the sequence up to the middle of the mg unit plagioclase an37 18 olivine fo40 7 ca poor pyroxene mg 57 15 ca rich pyroxene mg 65 21 above this compositions are essentially constant in the upper part of the mg unit and in the qmg an21 13 fo6 4 mg opx17 13 mg cpx25 20 the amount of interstitial quartz and the amount of normative orthoclase however both increase systematically upwards through the qmg unit implying that these rocks are cumulates there is no evidence of a compositional break in the mg qmg sequence that could reflect influx of relatively primitive magma two types of qmg ch are known in the uppermost part of bksk olivine bearing types are comagmatic with the underlying layered series the studied stratigraphic sequence belongs to this suite two pyroxene qmg and amphibole ch define a separate compositional lineage related to jotunites an intrusive unit of dominantly two pyroxene qmg is discordant to the olivine bearing jotunite mg qmg sequence near rapstad confirming the presence of two compositionally distinct suites of qmg and related lithologies in the upper part of bksk a xenolith rich unit near the olivine bearing mg qmg boundary represents a major collapse of the roof of the magma chamber during the final stages of crystallisation

high temperature metamorphism and the role of magmatic heat sources at the rogaland anorthosite complex in southwestern norway the rogaland complex covers 1000 km in southwestern norway and consists mainly of anorthosite massifs and the layered bjerkreim sokndal lopolith bsl these rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites high temperature mineral isograds pigeonite osumilite and orthopyroxene in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex p t estimates from the country rocks show a roughly linear increase in temperature towards the bsl consistent with the distribution of isograds the peak p t conditions at 20 and 2 5 km from the contact at 5 kbar range from 700 to 41000 c field relations and age determinations link the high t metamorphism and the magmatism the two dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures two magmatic episodes separated by 3myr however can account for the high temperature metamorphism in this model the emplacement and crystallization of the anorthosite produces a regional thermal gradient from 750 to 600 c after a brief hiatus a second smaller body bsl provides an additional thermal input that results in an array of high temperature isograds and country rock temperatures 41000 c

the norite mangerite relationships in the bjerkreim sokndal layered lopolith southwest norway the transition zone between the anorthositic noritic rhythmic units and the mangeritic unit of the bjerkreim sokndal layered lopolith southwest norway is characterized by thick layers of ultramafic rock uml interleaved with norites in the lower part and mangerites in the upper part in the latter rocks large mesoperthite crystals occur in a fine grained groundmass porphyritic texture rapid variations in chemical composition are shown by the mafic minerals especially by olivine fos0 to fo19 and by ti magnetite 10 19 tio the whole rock composition of the uml does not change in the upper part of the transition zone and the fe fe mg ratio of the mangerites remains constant bowen trend formation of the uml through liquid immiscibility is rejected because 1 the liquidus minerals are not always identical in the fe rich and associated silica rich rocks 2 the distribution of p205 ree and ba between associated rocks are not in agreement with experimental data 3 the major elements vary along parallel trends in the creigh diagram cumulative processes and adcumulus growth can best explain the uml oscillatory nucleation can account for the norites and flotation of mesoperthite is plausible in the mangerites where accumulation of feldspar is evidenced by a strong positive eu anomaly and porphyritic textures the mangeritic unit of the lopolith is interpreted as a flotation cumulate at the roof of the magma chamber the residual liquids of the bjerkreim sokndal differentiation were either trapped in the mangerites or expelled in the form of dykes or were mixed with quartz mangeritic liquids above the intrusion

post collisional melting of crustal sources constraints from geochronology petrology and sr nd isotope geochemistry of the variscan sichevita and poniasca granitoid plutons south carpathians romania the sichevita and poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the getic nappe in the south carpathians the present work provides shrimp age data for the zircon population from a poniasca biotite diorite and geochemical analyses major and trace elements sr nd isotopes of representative rock types from the two intrusions grading from biotite diorite to biotite k feldspar porphyritic monzogranite u pb zircon data yielded 311 2 ma for the intrusion of the biotite diorite granites are mostly high k leucogranites and biotite diorites are magnesian and calcic to calc alkaline sr and nd isotope and trace element data ree th ta cr ba and rb permit distinguishing five different groups of rocks corresponding to several magma batches the poniasca biotite diorite p1 shows a clear crustal character while the poniasca granite p2 is more juvenile conversely sichevita biotite diorite s1 and a granite s2 are more juvenile than the other sichevita granites s2 geochemical modelling of major elements and ree suggests that fractional crystallization can account for variations within p1 and s1 groups dehydration melting of a number of protoliths may be the source of these magma batches the variscan basement a subduction accretion wedge could correspond to such a heterogeneous source the intrusion of the sichevita poniasca plutons took place in the final stages of the variscan orogeny as is the case for a series of european granites around 310 ma ago especially in bulgaria and in iberia no alleghenian granitoids late carboniferous early permian times being known in the getic nappe the geodynamical environment of sichevita poniasca was typically post collisional of the variscan orogenic phase

diffusion controlled growth of pyroxene bearing margins on amphibolite bands in the granulite facies of rogaland southwestern norway implications for granulite formation in the rogaland granulites of southern norway thin anhydrous pyroxene bearing margins 5 10 mm are observed mainly in migmatitic banded gneisses at the contact between hornblende rich metabasites and charnockites according to field data the development of these margins post dates any deformation petrographic data show that they are zoned three different types have been recognized 1 metabasite plagioclase orthopyroxene plagioclase clinopyroxene gneiss 2 metabasite plagioclase orthopyroxene clinopyroxene plagioclase clinopyroxene gneiss 3 metabasite plagioclase orthopyroxene gneiss

metasedimentary melting in the formation of charnockite petrological and zircon u pb hf o isotope evidence from the darongshan s type granitic complex in southern china abstract charnockites are opx bearing igneous rocks commonly found in high grade metamorphic terranes despite being volumetrically minor they show a wide range in both bulk geochemistry and intensive parameters they form a characteristic component of the amcg anorthosite mangerite charnockite granite suite but their association with typical s type granites is less well known the darongshan s type granitic complex dsgc in guangxi province southern china contains granites varying in mafic silicate mineral assemblages from bt crd darongshan suite to opx grt bt crd jiuzhou suite and opx crd bt taima suite corresponding to a geochemical transition from magnesian calc alkalic to ferroan calc alkalic however its genesis even the accurate age of intrusion remains highly contentious despite intensive research in order to understand the genesis of charnockite and its genetic relationship with s type granite here we first determined zircon u pb ages of each suite using a sims on the basis of a detailed petrological study zircon u pb ages show that all suites of the complex were emplaced contemporaneously at ca 249 ma monazite apparent u pb ages are indistinguishable from zircon u pb ages within analytical error further in situ zircon hf o isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks 18ozircon ca 11 ehf t zircon ca 10 log fmq 0 mn in apatite oxybarometer with rare material input from the mantle the variation in 18o 7 8 12 9 is more likely a result of hybridization whereas that in ehf t 31 9 to 1 8 is a result of both hybridization and disequilibrium melting the variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite dehydration melting nevertheless heat input from mantle through basaltic intrusion underplating is considered to play a major role in high temperature 850 c melting at mid crustal levels i e the cordierite stable field for generation of the granitic complex we interpret that the granites were intruded in a back arc setting and basaltic magmatism was directly associated with slab roll back and tearing during the latest permian and early triassic times

crystallization processes in the bjerkreim sokndal layered intrusion south norway evidence from the boundary between two macrocyclic units the bjerkreim sokndal bksk layered intrusion belongs to the rogaland anorthosite province in southern norway the northwestern part of bksk consists of a ca 6 km thick layered series made up of macrocyclic units mcu arranged in a syncline each mcu which resulted from the crystallization of a major magma influx can be subdivided into a series of cumulate zones the mcu iii iv boundary has been studied in seven profiles across its strike length of 24 km massive pic1 at the base of mcu iv overlies laminated and modally layered phimc in the central part of the chamber and phimacc towards the flanks there is a discordance of between 2 and 6 between the base of mcu iv and phase layering in mcu iii the mcu iv pic is overlain by 75 100 m of massive poic the svaalestad unit of michot 1960 a similar olivine bearing unit occurs near the base of mcu iii which has more primitive compositions than the underlying pic this is followed by laminated and modally layered phic phimc and phimacc the reversal to more primitive mineral assemblages across the mcu iii iv boundary is accompanied by a cryptic reversal plagioclase and ca poor pyroxene have compositions of about an 44 mg no 71 at the top mcu iii and about an 52 mg no 77 near the base of mcu iv olivines in the mcu iv poic vary unsystematically from fo 66 to 76 macrocyclic units iii and iv crystallized from monzonoritic parental magma the bksk magma chamber had a broad saucer like shape with a small thickness to breadth ratio the magma in the chamber during crystallization of mcu iii was compositionally zoned and crystallized on an inward sloping floor by down dip accretion just before the major magma influx at the base of mcu iv phimc was crystallizing from the basal magma layer at the centre of the chamber while phimacc was crystallizing towards the flanks the new dense magma fountained into and mixed with the basal magma layers already in the chamber this hybrid magma crystallized during continued influx to produce massive pic at the base of mcu iv this hybrid unit is thickest near the centre of the chamber and smoothed out the floor to an essentially horizontal surface continued influx resulted in the dense primitive magma ponding on the floor this crystallized fairly rapidly to produce the massive poic unit the return of normal fractional crystallization conditions is marked by the overlying sequence of modally and cryptically layered cumulates which duplicate the succession in mcu iii the variation in thickness of the upper part of mcu iv indicates that crystallization of the bksk layered series was accompanied by sinking of the floor at a greater rate near the centre of the chamber than towards the flanks this was accompanied by compaction of the underlying cumulates promoting the development of lamination and the expulsion of intercumulus melt to encourage the development of adcumulates

magma influx and mixing in the bjerkreim sokndal layered intrusion south norway evidence from the boundary between two megacyclic units at storeknuten abstract the bjerkreim sokndal layered intrusion belongs to the proterozoic anorthositic province in the rogaland area of southern norway the northwestern part of the intrusion comprises a ca 6 km thick layered series made up of megacyclic units mcu arranged in a syncline each megacyclic unit reflects the influx of fresh magma into the chamber the boundary between megacyclic units iii and iv has been studied in detail at storeknuten on the southern flank of the syncline the megacyclic units can be subdivided into a series of cumulate stratigraphic zones the interval from the top of zone iiie to the base of zone ivd is exposed in the storeknuten area modally layered plagioclase hypersthene ilmenite magnetite augite apatite cumulates belonging to zone iiie are overlain by 30 m of massive plagioclase rich rocks commonly containing ilmenite and or hypersthene constituting zone iva the entry of cumulus olivine defines the base of zone ivb dominantly plagioclase olivine ilmenite cumulates which is about 100 m thick many of the olivines are partly or completely replaced by ca poor pyroxene fe ti oxide symplectites this massive leucotroctolitic zone is overlain by modally layered laminated plagioclase hypersthene ilmenite cumulates of zone ivc the successive entry of magnetite apatite accompanied by ca rich pyroxene and inverted pigeonite defines zones ivd e and f respectively the entry of k feldspar accompanied by fe rich olivine defines the base of a jotunitic transition zone which passes upwards into mangerites and quartz mangerites there is a compositional regression through zone iva the upper part of zone iiie has ca poor pyroxene with about en68 plagioclase with an44 48 and a sr isotope ratio of about 0 7062 while the base of zone ivb has olivine with fo75 together with en78 an53 and 0 7050 respectively similar reversals are shown by the minor element compositions of plagioclase and fe ti oxides sr isotope ratios increase systematically up through zone ivb reaching 0 7058 in zone ivd while an and sr in plagioclase and ni and cr in fe ti oxides decrease olivine compositions vary unsystematically and are believed to have changed their fe mg ratios as a result of trapped liquid shift the magma residing in the chamber when the influx at the base of megacyclic unit iv took place was compositionally zoned and assimilation of gneissic country rock at the roof had resulted in the sr isotope ratio increasing up through the magma column the new magma had a sr isotope ratio of about 0 7050 while the resident magma had a ratio of 0 7062 at the floor increasing upwards the new magma mixed with the basal layer s of the compositionally zoned resident magma and crystallization of this hybrid magma during influx and mixing produced the compositional regression in zone iva when magma influx ceased olivine bearing rocks began to crystallize at the base of zone ivb the leucotroctolites at the base of this zone are the most primitive rocks in the entire intrusion the systematic increase in sr isotope ratios up through zone ivb resulted from progressive mixing between new and resident magma this mixing either took place during magma influx or by the progressive mixing of overlying resident magma layers during crystallization calculations based on geochemical modelling the thickness of cumulate stratigraphy repeated and sr isotope ratios indicate that the new magma influx had a thickness of 350 500 m in the storeknuten section and that the leucotroctolites of zone ivb represent about 20 30 crystallization of this influx

magnetic fabric and deformation in charnockitic igneous rocks of the bjerkreim sokndal layered intrusion rogaland southwest norway abstract the bjerkreim sokndal intrusion bksk belongs to the proterozoic rogaland igneous complex of southwest norway the bksk displays an anorthosite to mangerite cumulate series folded into a syncline in the core of which crop out massive acidic rocks of quartz mangerite to charnockite composition we present a study which focuses on the acidic rocks in which we use the low field anisotropy of magnetic susceptibility ams technique systematic microscope examination of the samples collected at 148 ams stations and considerations based on mineral intrinsic magnetic susceptibilities reveal magnetic mineralogy and anisotropy controlled by magnetite macro to micro scale petrofabrics and magnetic fabrics indicate that the acidic rocks which intruded after deposition of the underlying cumulate series were also affected by the syn to post magmatic folding event which gave rise to the bksk syncline in absence of any recognized plate scale regional stress field it is suggested that this folding results from a gravity induced subsidence linked to the final stage of diapiric emplacement of huge neighbouring anorthosite plutons this model is mainly supported by the structural pattern in the bksk which reveals a convergent flow towards a central trough where lineations are sub vertical

proterozoic ferroan feldspathic magmatism abstract the proterozoic eon is characterized by an unusual abundance of ferroan feldspathic rocks that range in composition from granite to quartz syenites to feldspathoid bearing syenites three associations of ferroan rocks may be recognized on the basis of major element compositions 1 metaluminous alkalic to alkali calcic syenites and granites associated with anorthosites and iron rich basaltic rocks 2 alkaline intrusions in continental rifts and 3 calc alkalic metaluminous to peraluminous granitoid plutons that are less strongly ferroan than the other two groups the first two groups form by differentiation of tholeiitic to alkali basaltic parental magmas the third by partial melting of quartzo feldspathic crust although all three associations may form in intraplate settings only the alkaline intrusions which typically contain high incompatible trace element abundances plot entirely within the within plate granite fields on trace element discrimination diagrams processes of crustal melting and magma mixing have had a greater effect on the trace element compositions of ferroan granitoids from the other two associations causing some rocks to plot outside this field of these three associations the granitoids associated with anorthosites are the most voluminous and are essentially restricted to the proterozoic special conditions perhaps related to the presence of a long lived supercontinent under which widespread mantle upwelling took place appear required to explain the abundance of these rocks ferroan alkaline rocks although rarely preserved in archean crust are present in proterozoic and phanerozoic rifts the earliest alkaline intrusions thus may mark the establishment of rigid continents capable of rifting the formation of ferroan calc alkalic granites does not appear to be time dependent these granites have been generated throughout earth history in response to crustal melting

monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites duchesne j c wilmart e demaiffe d and hertogen j 1989 monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites precambrian res 45 111 128 monzonorites members of the anorthositic suite of rocks are usually considered as residual after the formation of massif type anorthosites in rogaland s w norway they occur as large dykes intrusions and chilled margins to differentiated massifs emplaced during and soon after the main anorthosite massifs in granulite facies conditions ti p and fe are enriched in monzonorites and steadily decrease towards quartz mangerites the feo feo mgo ratios varying slightly during alkali enrichment bowen trend trace element spidergrams show deep troughs in rb th nb ta sr zr hf and ti the ree slightly decrease in the evolution with la yb s ratios about 9 and neutral to positive eu anomalies several occurrences however show highly contrasted trace element features sr isotope ratios st show a wide interval of variation 0 704 0 710 between the various dykes and intrusions without any correlation with the elements indicative of crustal contamination in the tellnes main dyke evolution towards acidic rocks occurs without contamination and variation in isr fractional crystallization with subtraction of apatite bearing noritic cumulates can account for the major and trace element evolution from monzonorite to quartz mangerite but is unable to explain the large differences between occurrences it is concluded that monzonorites cannot be comagmatic though coeval with massif type anorthosites they result from the crystallization of distinct magma batches possibly formed through partial melting of basic to intermediate rocks in the lower crust