identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

major and trace element zoning in garnets from calcareous pelites in the nw shelburne falls quadrangle massachusetts garnet growth histories in retrograded rocks

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

approximate inversion of airborne em data from a multilayered ground1 a complex transfer function c or generalized skin depth can be derived from data for the secondary magnetic field measured by a dipole system with small coil spacing at height h above the ground this function has a useful property for a uniform or layered ground the real part of c yields the centroid depth z of the in phase current system as a function of frequency this parameter can be combined with the apparent resistivity a derived by conventional methods the function a z if known over a broad frequency range yields a smoothed approximation of the true distribution z without an initial model the relations between a z and z are studied for a number of multilayer models an example of the application of the a algorithm to data from a groundwater survey is given

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

chemistry and origin of monazites from carbonatite dikes in the hongcheon jaeun district korea abstract the hongcheon jaeun district is an important precambrian iron mineralization zone in korea fe rare earth elements ree ore bodies in the study area occur within carbonatite dikes composed mostly of fe dolomite these ore bodies shows orientations of n s to n10 e 30 nw are traced for 1 1 5 km and range from 15 to 50 m in thickness besides dolomite the most important minerals are magnetite monazite strontianite and barite monazite coexists with magnetite in early stage carbonatite and is associated with strontianite in late stage carbonatite in this area monazites in the study area have small positive or zero eu anomaly patterns and are similar to rocks of granitic or hydrothermal origin the high contents of rare earth and trace elements ba sr mo ni suggest that these compositions originated from magmatic carbonatite c 13 values range from 5 3 to 7 2 and o 18 values are from 8 4 to 10 1 these isotopic compositions from the fe ree ore deposit in the hongcheon jaeun district belong to the typical carbonatite field the textures monazite and stable isotopic compositions indicate that ree minerals were derived from carbonatite of igneous origin

discrete mineralization events at the hongtuling au mo vein deposit in the xiaoqinling district southern north china craton evidence from monazite u pb and molybdenite re os dating abstract the xiaoqinling district the second largest gold producer in china is situated on the southern margin of the north china craton and immediately to the north of the qinling orogen the timing and genesis of the gold deposits have been hotly debated because the area has undergone multiple tectono magmatic events since the stabilization of the north china craton in the early paleoproterozoic whether they are genetically related to the triassic orogeny that formed the qinling orogen or associated with the early cretaceous tectonic reactivation of the craton remains controversial here we present monazite u pb and molybdenite re os dating results from the hongtuling vein deposit in the eastern part of the xiaoqinling district to provide new insights into the age and tectonic setting of gold mineralization the hongtuling deposit consists of gold veins at the top and minor molybdenum veins at the bottom with molybdenum veins being locally crosscut by gold veins molybdenum veins mainly consist of calcite quartz k feldspar molybdenite and pyrite with minor amounts of galena and a variety of accessory minerals gold veins are dominated by quartz and pyrite with minor to trace amounts of chalcopyrite galena sphalerite and sericite monazite grains are well developed both in molybdenum and gold veins and are intergrown with molybdenite and pyrite respectively monazites from gold vein contain lower rees contents more prominent negative eu anomalies and higher th u ratios than those from molybdenum vein the textural and geochemical evidence indicates that monazites from both veins precipitated from contrasting ore forming fluids laser ablation icp ms u pb dating of monazite from the molybdenum vein yields a 206pb 238u age of 203 5 8 1 ma mswd 0 23 2 which is statistically indistinguishable from the molybdenite re os age of 204 ma in contrast monazite from the gold vein has a significantly younger 206pb 238u age of 130 4 5 3 ma mswd 0 99 2 results presented here combined with independent studies suggest that the molybdenum and gold veins of the hongtuling deposit and by inference the other deposits in the district formed in two discrete mineralization events in the late triassic and early cretaceous the molybdenum mineralization is most likely related to the post collisional magmatism associated with the qinling orogeny whereas gold mineralization occurred in an extensional setting associated with the decratonization of the north china craton

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

lewisian crustal history from in situ sims mineral chronometry and related metamorphic textures abstract a combination of detailed petrography and in situ sims 207 pb 206 pb micro chronometry of monazite has been carried out on samples from the lewisian high grade metamorphic terrain northwest scotland two episodes of granulite facies metamorphism have been recognized the thermal maxima of which are estimated at or before 2760 12 ma 2 and at 2526 8 ma respectively pegmatites at scourie crystallised at 2480 ma the amphibolite facies metamorphism of the main laxfordian event is estimated at 1752 12 ma and the formation of kyanite and staurolite is associated with this event the oldest ages of 2760 ma have been obtained from micro inclusions of monazite in garnet it appears that garnet which has a high closure temperature for the u pb system plays an important role in the behaviour of the monazite u pb system it serves to shield monazite from reaction with the other phases and to armour monazine from diffusive pb loss or from resetting

kinematics strain pattern and geochronology of the salem attur shear zone tectonic implications for the multiple sheared salem namakkal blocks of the southern granulite terrane india abstract structural mapping strain analysis and a variety of geochronological studies were carried out to determine the tectonothermal evolution of the salem attur shear zone in the southern granulite terrane of south india the salem namakkal blocks containing the shear zone consisted of quartzofeldspathic gneiss charnockite and mafic granulite and had undergone multiple phases of magmatism spanning over a period of 3 2 0 5 ga the rocks were deformed by four phases of deformation d1 d4 the d1 deformation was characterized by isoclinal and recumbent ne sw trending f1 fold with a pervasive subhorizontal axial planar granulitic fabric s1 and associated quartzofeldspathic leucosomes granulite metamorphism was dated at ca 2 5 2 3 ga the f1 fold and s1 fabric were coaxially refolded by tight to isoclinal upright to steeply inclined ne sw trending f2 folds during d2 deformation the d2 deformation was associated with f2 axial planar shear zones crenulations and leucosomes s2 fabric large scale d2 shear zones characterized by high temperature ductile shear fabric with a vertical flow host syntectonic syenite pluton which was dated at ca 2 5 2 4 ga a p t condition of 7 kb 600 c was inferred for the d2 deformation the d3 deformation was characterized by nw se to e w trending f3 folds and the salem attur shear zone the shear zone was a greenschist to amphibolite facies shear zone being characterized by mylonitic foliation and dominantly down dip stretching lineation defined by quartz biotite and hornblende minerals and dated at ca 2 0 ga it indicated n nne vergence of thrusting with the mean kinematic vorticity number wm as 0 7 suggesting general simple shear strain with 50 pure shear component the d4 deformation was manifested as nne ssw striking strike slip faults and nw se striking extensional normal faults pseudotachylite veins having an age of 1 9 ga injected during strike slip faulting and granite pegmatite veins showing age of 0 8 0 5 ga intruded during normal faulting the salem namakkal blocks thus recorded a long lived shearing history we suggest that the salem attur shear zone and other shear zones such as palghat cauvery moyar bhavani karur kambam painavu trichur and achankovil shear zones were paleoproterozoic intraterrane shear zones which were overprinted by meso neoproterozoic cambrian ductile and brittle deformations

contrasting p t t paths from the basement of the tisia unit slavonian mts ne croatia application of quantitative phase diagrams and monazite age dating abstract medium grade mica schists and intercalated paragneisses and amphibolites from the basement of the tisia unit slavonian mountains northeastern croatia contain complexly zoned garnets at the kutjevo locality mica schists are characterised by garnets with mn rich cores and ca rich rims mn decreases steadily from core to rim and ca increases abruptly this is in contrast to the paragneisses and amphibolites which contain garnets with smoothly decreasing ca from core to rim quantitative phase diagrams and garnet composition isopleths calculated from bulk rock analyses reveal that the ca poor garnet cores in the mica schists formed during an earlier event at 584 592 c and 6 4 7 8 kbar ca rich rims formed at conditions of 600 660 c and 11 12 kbar calculated using garnet isopleths and mineral thermobarometry the paragneiss and amphibolite provide similar p t information for the later peak event ca 650 c 10 12 kbar but do not preserve a record of the earlier lower p t event and modelling shows that garnet was not stable at these conditions contrary to previous studies on this outcrop and rock type no staurolite was observed and quantitative phase diagrams contoured for h 2 o mode isopleths indicate that the rock did not cross staurolite bearing fields during the retrograde p t path mica schists from the krndija locality contain zoned polyphase garnets phase diagram calculations reveal that ca rich garnet cores formed between 520 and 630 c and 7 8 kbar rims have a lower ca content and formed at considerably reduced pressures together with andalusite and staurolite at ca 530 570 c and 3 4 kbar since both localities were traditionally considered to be part of the same tectono metamorphic unit evidence presented here clearly shows that this cannot be the case emp monazite ages are variscan 350 ma in the krndija mica schists and around pre or early variscan 440 ma in the kutjevo mica schists we therefore propose a more complex internal structure and metamorphic history for this area than previously recognised suggesting a metamorphic evolution of the slavonian mountains that includes a pre variscan and a variscan cycle

th diffusion in monazite abstract diffusion of th has been characterized in synthetic monazite under dry conditions the synthetic monazites either pure cepo4 ndpo4 or a mixed lree phosphate containing ce nd and sm were grown via a na2co3 moo3 flux method the sources of diffusant for the experiments were either synthesized thsio4 or cath po4 2 powders mixed with cepo4 experiments were performed by placing source and monazite in pt capsules and annealing capsules in 1 atm furnaces for times ranging from 3 weeks to a few hours at temperatures from 1350 to 1550 c the th distributions in the monazite were profiled by rutherford backscattering spectrometry rbs the following arrhenius relation was obtained for th diffusion in monazite d 6 7 10 1 exp 740 63 kj mol 1 r t m 2 s 1 the diffusivity of th was found to be similar for monazites containing a single ree ce or nd and the mixed lree phosphates th diffusion was also similar for experiments run using the th silicate and ca th phosphate sources suggesting that the substitutional mechanism for th in monazite i e th 4 si 4 ree 3 p 5 for the thsio4 source and th 4 ca 2 2ree 3 for the cath po4 2 source does not significantly affect th diffusivities and that th is likely the rate limiting species in diffusion th diffusion in monazite is about 3 orders of magnitude slower than pb diffusion cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 this contrasts with findings of gardes et al gardes e jaoul o montel j m seydoux guillaume a m wirth r 2006 pb diffusion in monazite an experimental study of pb2 th4 2nd3 interdiffusion geochimica et cosmochimica acta 70 2325 2336 who determined that diffusivities measured in pb th ree exchange which would under most circumstances be rate limited by the slowest diffusing species are comparable to those measured by cherniak et al cherniak d j watson e b grove m harrison t m 2004a pb diffusion in monazite a combined rbs sims study geochimica et cosmochimica acta 68 829 840 for pb th diffusion in zircon cherniak d j hanchar j m watson e b 1997 diffusion of tetravalent cations in zircon contributions to mineralogy and petrology 127 383 390 is about an order of magnitude slower than in monazite but with similar activation energy for diffusion the lower diffusivities in zircon may be a consequence of the larger disparity in size between th and the zr site in zircon as compared with th and the ree site in monazite nonetheless th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions these findings may also have implications for containment of high level actinide based nuclear waste in monazite ceramic waste forms but it should be noted that mechanisms other than diffusive exchange e g recrystallization dissolution reprecipitation may be important to consider along with diffusion when evaluating the retentivity of monazite for th and other actinide elements

metalliferous mining geophysics state of the art after a decade in the new millennium mining exploration was very active during the first decade of the twenty first century because there were numerous advances in the science and technology that geophysicists were using for mineral exploration development came from different sources instrumentation improvements new numerical algorithms and cross fertilization with the seismic industry in gravity gradiometry kept its promise and is on the cusp of becoming a key technology for mining exploration in potential field methods in general numerous techniques have been developed for automatic interpretation and 3d inversion schemes came into frequent use these inversions will have even greater use when geologic constraints can be applied easily in airborne electromagnetic em methods the development of time domain helicopter em systems changed the industry in parallel improvements in em modeling and interpretation occurred in particular the strengths and weaknesses of the various algorithms became better understood simpler imaging schemes came into standard use whereas layered inversion seldom is used in the mining industry today improvements in ground em methods were associated with the development of squid technology and distributed acquisition systems the latter also impacted ground induced polarization ip methods developments in borehole geophysics for mining and exploration were numerous borehole logging to measure physical properties received significant interest perhaps one reason for that interest was the desire to develop links between geophysical and geologic results which also is a topic of great importance to mining geologists and geophysicists

the spectrem airborne electromagnetic system further developments the spectrem airborne electromagnetic aem system has been in full production in canada and africa since 1989 the prototype built by a cubed of mississauga canada was subject to two major upgrades by anglo american corp staff to produce the spectrem ii instrument that located the photo lake and konuto lake orebodies in manitoba canada subsequent work in tropical africa has made it desirable to further increase the transmitter power and use greater available computer power in the aircraft to substantially improve the ability of the system to reject sferic noise although there appears to be a limiting sferic level above which current filtering methods are ineffective although designed to detect massive sulfide bodies deep below conductive overburden techniques have been developed to map the regolith in particular to compute resistivity depth sections using an approximate but fast method a comparison is presented of such a section with the same section flown and processed using a frequency domai

geochronology and geochemistry of multiple generations of monazite from the wepawaug schist connecticut usa implications for monazite stability in metamorphic rocks u pb isotope analyses rare earth and trace element analyses and petrographic observations are presented for monazites from the wepawaug schist in southern connecticut usa two samples of kyanite zone schist were collected less than a meter apart each sample contains a different variety of monazite with distinct morphology chemistry and pb isotopic composition one sample preserves a largely amphibolite facies mineralogy including kyanite staurolite garnet biotite and chlorite with little textural evidence of later shearing monazites from this sample are xenoblastic with about 1 wt tho2 0 3 wt cao and a more lree enriched pattern than monazites from the second sample these xenoblastic monazites preserve textural evidence of a retrograde reaction to apatite which involves chlorite indicating that these monazites became unstable during retrograde chloritization of biotite these monazites give strongly discordant u pb ages which fit a chord with an upper intercept age of 411 18 ma interpreted as the minimum growth age of these xenoblastic monazites perhaps during amphibolite facies metamorphism the second sample contains s c banding evidence of dynamic recrystallization and abundant retrograde chlorite this sample contains idioblastic monazites with about 3 wt tho2 0 8 wt cao and with less fractionated ree patterns these monazites give close to concordant u pb ages with a mean 207pb 206pb age of 388 2 ma this age is interpreted as probably representing the time of monazite growth during retrogression of the sample from an amphibolite to greenschist facies mineralogy

detrital and newly formed metamorphic monazite in amphibolite facies metapelites from the motajica massif bosnia abstract the motajica massif in bosnia situated in the sava zone between the tisza unit and the dinarides hosts a late cretaceous flysch series which is partly preserved in an anchimetamorphic state partly affected by amphibolite facies overprint samples from both parts contain abundant accessory monazite which was investigated by means of the electron microprobe with reference to age and composition in the amphibolite facies samples new metamorphic monazite has formed chemical th u pb monazite ages indicate that the regional metamorphic event happened in the late cretaceous or the early palaeogene in addition inherited detrital monazite of permian age has been identified based on various observations it is argued that the detrital monazite was not the direct precursor to the metamorphic monazite the latter may rather have grown from other more reactive ree carrier minerals either detrital ones e g detrital allanite or such that formed during diagenesis and low grade metamorphism a later greenschist facies event that occurred in connection with a ca 27 ma old granodiorite intrusion led in some samples to the formation of late fluorapatite allanite coronas around both detrital and newly formed monazites the anchimetamorphic samples contain exclusively detrital monazite these are partly of permian as well as jurassic to early cretaceous age based on their compositional and textural features the jurassic to early cretaceous monazite relics are considered to be mainly derived from metamorphic rocks the permian monazite displays high yttrium content up to ca 3 5 wt y 2 o 3 indicating a high formation temperature 650 c and therefore probably a magmatic origin apart from almost ubiquitous permian high y monazite the motajica flysch also contains large permian xenotime with magmatic zoning patterns fluorapatite with parasitic monazite inclusions formerly ree rich fluorapatite and zircon with a type granite morphology this accessory mineral spectrum implies that among others rift related ree rich permian a type granites or rhyolites should be considered as a source for the sava zone flysch

monazite chemical composition some implications for monazite geochronology an investigation of the chemical composition of monazite from a number of localities has been carried out samples used include monazites from metamorphic rocks granitic rocks and a hydrothermal ore deposit the ree distribution pattern of monazite varies greatly in accordance with its geological environment a remarkable feature of the monazites studied is that their chondrite normalised ree distribution patterns are mostly uniform between grains within the same sample but differ significantly from sample to sample this characteristic apparently indicates that there is an important effect on the ree distribution of monazite exerted by the host rock or source material from which monazite crystallised another important feature shown by the monazites studied is that monazites in rocks containing garnet as a major mineral show extreme depletion of hree whereas monazites in rocks without garnet or monazite that formed after the garnet breakdown contain significantly higher amounts of y and hree this suggests that the phase assemblage especially garnet plays an important role in the ree distribution of monazites in these rocks the value of ree distribution in monazite is exemplified with regard to the origin of monazite in the lewisian metamorphic rocks which is a fundamental issue in monazite geochronology

direct dating of left lateral deformation along the red river shear zone china and vietnam 1 exposures of high grade midcrustal rocks within the red river shear zone rrsz which separates the indochina and south china blocks exhibit clear evidence of left lateral ductile deformation assuming that the south china sea represents a pull apart basin formed at the southeastern termination of the rrsz it has been argued that seafloor magnetic anomalies constrain the timing of sinistral slip accommodated by the rrsz between 32 and 17 ma at a rate of 4 cm yr while 40ar 39ar thermochronometry indicates that left lateral slip occurred along the rrsz between 25 and 17 ma the timing of earlier high temperature deformation has not been directly constrained in situ th pb ion microprobe dating of monazite inclusions in garnets allows direct assessment of the timing of amphibolite grade metamorphism and synchronous left lateral shearing results from northern segments of the rrsz in yunnan china indicate that synkinematic garnet growth occurred between 34 and 21 ma and are the first to document late oligocene metamorphism and left lateral shearing data from the southern rrsz within vietnam are complicated by tertiary overprinting of rocks that experienced amphibolite facies metamorphism during the indosinian orogeny 220 ma the period during which sinistral deformation is now constrained to have occurred along the rrsz i e 34 17 ma is essentially coincident with spreading of the south china seafloor 32 17 ma this temporal and kinematic link between left lateral shearing along the rrsz and opening of the south china sea supports the view that indochina was extruded from asia as a block along lithospheric scale strike slip faults

direct shear fabric dating constrains early oligocene onset of the south tibetan detachment in the western nepal himalaya a newly identified and dated segment of the south tibetan detachment in the karnali klippe western nepal himalaya constrains initiation of mid crustal tectonically driven exhumation to the early oligocene the folded top to the northeast high temperature 600 c shear zone separates amphibolite facies rocks with a ca 36 30 ma prograde metamorphic history in the footwall from weakly to non metamorphosed upper crustal rocks in the hanging wall in situ dating of syn kinematic post metamorphic peak monazite indicates that the base of the shear zone was active from ca 30 29 to 24 ma and a post deformation muscovite cooling age implies that ductile shearing had ceased by ca 19 ma deformation along the south tibetan detachment in western nepal was thus synchronous with thrust sense shearing along the lower boundary of a zone of migmatitic rocks compatible with tectonic models involving mid crustal channelized flow during the oligocene along with other published data from the himalayan range this suggests that the south tibetan detachment actively exhumed the middle crust for almost 20 m y

the behaviour of monazite from greenschist facies phyllites to anatectic gneisses an example from the chugach metamorphic complex southern alaska monazite is a common accessory mineral in various metamorphic and magmatic rocks and is widely used for u pb geochronology however linking monazite u pb ages with the pt evolution of the rock is not always straightforward we investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses which is exposed in the eocene chugach metamorphic complex of southern alaska we investigated textures chemical compositions and u pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade with particular focus on the relationship between monazite and other ree bearing minerals such as allanite and xenotime in the greenschist facies phyllites detrital and metamorphic allanite is present whereas monazite is absent in lower amphibolites facies schists 550 650 c and 3 4 kbar small medium y monazite is wide spread mnz1 indicating monazite growth prior and or simultaneous with growth of garnet and andalusite in anatectic gneisses new low y high th monazite mnz2 crystallised from partial melts and a third high y low th monazite generation mnz3 formed during initial cooling and garnet resorption u pb shrimp analysis of the second and third monazite generations yields ages of 55 50 ma monazite became unstable and was overgrown by allanite and or allanite epidote apatite coronas within retrograde muscovite and or chlorite bearing shear zones this study documents polyphase complex monazite growth and dissolution during a single relatively short lived metamorphic cycle

two generations of variscan garnet implications from a petrochronological study of a high grade avalonia derived paragneiss from the drosendorf unit bohemian massif abstract garnets in metapelitic paragneisses from the southern drosendorf unit in the austrian part of the bohemian massif exhibit two episodes of growth during the variscan orogeny which can be distinguished on textural and chemical grounds the first garnet grt1 records evidence of high grade metamorphism in the late devonian frasnian famennian while the second garnet grt2 formed by a second high grade event in the early carboniferous visean both garnet generations contain abundant inclusions of which monazite rutile and crystallised melt droplets are particularly useful for reconstructing p t t conditions the late devonian age 373 9 ma for the first episode of garnet growth was obtained from chemical dating of monazite inclusions in grt1 metamorphic conditions during the first episode of garnet growth are estimated to have been between 0 7 and 0 8 gpa at 680 700 c and 0 95 1 10 gpa at 745 785 c there followed a phase of cooling and exhumation after which the second garnet grt2 were formed beginning under amphibolite facies conditions and continuing prograde to peak conditions of 0 95 1 10 gpa and 745 785 c which are similar to those of the first garnet forming event subsequently the rocks experienced near isothermal decompression to 0 5 0 8 gpa chemical dating of both monazite inclusions in grt2 and the matrix provide a visean age 343 3 ma a study of detrital zircons in these paragneisses revealed zircon forming events at around 1 2 1 5 and 1 8 ga suggesting an avalonian provenance the lack of zircons younger than 1 ga and the presence of cadomian metamorphic monazite relics 652 15 ma indicates an early neoproterozoic deposition age for the sedimentary protolith likely our documentation of a late devonian high grade metamorphic event in rocks derived from avalonian corroborates tectonic models which assume that frontal parts of the armorican terrane had already docked with avalonia by this time

metamorphism of the ca 3800 ma supracrustal rocks at isua west greenland implications for early archaean crustal evolution a detailed mineralogical and petrological study has been carried out on samples from two clastic metasedimentary lithologies from the 3800 ma isua supracrustal belt west greenland semipelitic to pelitic garnet biotite schist contains the limiting akfm assemblage muscovite biotite garnet staurolite quartz plagioclase ilmenite whereas muscovite biotite gneiss derived from felsic volcanogenic graywacke locally contains kyanite quartz plagioclase ca mn rich garnet temperatures calculated from fe mg partitioning between coexisting garnet biotite indicate equilibration for garnet coresat t 550 c and 460 c for garnet rims we interpret the higher t as a minimum estimate for prograde regional metamorphism which we argue occurred before 3600 ma whereas the lower t reflects later retrogression as indicated by the development of chlorite sericite in many samples the presence of kyanite as the stable aluminosilicate polymorph combined with phase assemblage data indicate p 5 kbar during prograde metamorphism and a depthof burial of at least 15 km the isua supracrustals are the oldest comprehensively dated rocks on earth and the metamorphic mineral assemblages reported here constitute the earliest direct record of thermal regimes in archaean crust therefore characterization of the metamorphic history of the isua region places an important constraint on models of early earth history our data and observations indicate that prograde regional metamorphism at isua occurred at conditions which are considered normal for an orogenic system with a metamorphic thermal gradient 35 c km moreover our results contraindicate the universal occurrence of thin archaean crust and excessively steep crustal thermal gradients as proposed by some investigators such conclusion appears at odds with estimates for higher terrestrial heat production during the early archaean but can be resolved by appealing to more rapid convection and generation of oceanic crustas a means of dissipating excess heat from the earth s interior as opposed to conduction through the crust

zoned porphyroblasts of metamorphic monazite in the anakeesta formation great smoky mountains north carolina monazite has widespread occurrence in pelitic schists of the anakeesta formation which were metamorphosed to staurolite kyanite grade this monazite is of strictly metamorphic origin in a few very graphitic metashales monazite forms zoned euhedral porphyroblasts 50 150 g m in size microprobe analyses of these porphyroblasts for p ca th y and the rare earth elements la ce pr nd sm and gd revealed significant relations among the elements virtually all thorium is accommodated by the charge coupled substitution tha caz 2ree3 zonation for th and ca is sharply gradational and separates distinct cores and rims cores show thorium enrichment over rims by a factor of 2 5 increase in thorium content correlates with a small increase in average atomic number of analyzed ree from 58 65 to 58 76 and is most clearly seen in enrichment in gadolinium and depletion in lanthanum these trends can be explained by a decrease in ionic size with increasing atomic number of rare earth elements and a slight decrease in unit cell dimensions of monazite due to increased content of th and ca however yttrium is slightly enriched in the rims and does not follow this trend

monazite behaviour and age significance in poly metamorphic high grade terrains a case study from the western musgrave block central australia abstract integrated in situ textural chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western musgrave block central australia has identified evidence for multiple events of growth and recrystallisation during poly metamorphism in the mesoproterozoic garnet sillimanite bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 ma with monazite grains in leucosome recording crystallisation at 1300 ma monazite breakdown during melting is inferred to have occurred in the palaeosome during a subsequent granulite facies event at 1200 ma deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 ma monazite in leucosome growth of new high y hree monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel as a result of post peak isothermal decompression diffusive enrichment of resorbed garnet rims in y hree suggests garnet breakdown occurred slower than volume diffusion of ree monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150 1130 ma the intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or fertile local environments provided by the palaeosome mesosome volumes which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite like reaction textures it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite ree and u th pb chemistry and hence ages

the differential parameter method for multifrequency airborne resistivity mapping helicopter em resistivity mapping began to be accepted as a means of geologic mapping in the late 1970s the data were first displayed as plan maps and images some 10 years later sectional resistivity displays became available using the same pseudolayer half space resistivity algorithm developed by fraser and the new centroid depth algorithm developed by sengpiel known as sengpiel resistivity sections these resistivity depth images proved to be popular for the display of helicopter electromagnetic em data in conductive environments a limitation of the above resistivity and depth algorithms is that the resulting sengpiel section may imply that the depth of exploration of the em system is substantially less than is actually the case for example a target at depth may be expressed in the raw data but its appearance on the sengpiel section may be too shallow which is a problem with the depth algorithm or it may not even appear at all which is a problem with the resistivity algorithm an algorith

trace element zoning in pelitic garnet of the black hills south dakota trace element ree cr ti y y and zr analysis of garnet from the garnet staurolite and lower sillimanite zones of an aluminous schist of the black hills south dakota indicates that ree zoning varies as a function of grade garnet zone garnet has high concentrations of rees cr ti y y and zr in the cores and low concentrations in the rims profiles of heavy rees contain inflections between the cores and rims which are approximately symmetric about the cores staurolite zone garnet contains cores enriched with y and heavy rees which decrease toward the rim and increase again at the rim edges but to lower concentrations than in the cores cr y ti zr and light ree zoning is less pronounced than heavy ree zoning and is less symmetric about the garnet cores almandine rich garnet of the lower sillimanite zone displays no major element zonation trace element ti cr y and zr concentrations are minimal and the zoning is irregular and not symmetric about the garnet cores garnet from all three zones has core to rim fe fe mg profiles that suggestgarnet growth was uninterrupted with respect to major element components and that mn zoning formed by a fractionation process analysis of trace element zoning in this garnet reveals that the major element zoning was relatively unaffected by volume diffusion reequilibration trace element zonation of all samples of garnet is best explained by a fractionation mechanism in conjunction with limited intergranular diffusion and changing partition coefficients during garnet growth heavy ree partitioning is especially dependent on the major element composition of garnet this research complements previous research by others on the use of trace elements as metamorphic petrogenetic indicators which demonstrated the importance of bulk rock composition and phase assemblage on trace element partitioning

monazite paragenesis and u pb systematics in rocks of the eastern mojave desert california u s a implications for thermochronometry abstract studies of the paragenesis and u pb systematics of monazite in rocks from the eastern mojave desert california corroborate its potential usefulness as a prograde thermochronometer and in dating granite inheritance unmetamorphosed latham shale and its equivalents at grades ranging from greenschist to upper amphibolite facies are virtually identical in composition monazite is absent in the shale and low grade schists but it is abundant in schists at staurolite and higher grades lower grade schists instead include minute th and ce oxides and unidentified ce poor lree phosphates that apparently are lower temperature precursors to monazite thus monazite originates when the pelite passes through lower amphibolite facies conditions monazites from three upper cretaceous granites yield ages that are strongly discordant upper intercepts of 1 6 1 7 ga are similar to those defined by u pb data for coexisting zircons and coincide with a period of copious magmatism in the mojave crust as the host upper cretaceous granitic magmas were all above 700 c effective closure of the restitic monazites to pb loss must be well in excess of this temperature u pb compositions of monazite from proterozoic granitoids and schist also indicate high pb retentivity taken together these studies support the suggestion that monazite can be an effective prograde thermochronometer at least in pelites it is not usually retained as a detrital mineral but rather forms during moderate temperature metamorphism its u pb system should not be reset by subsequent higher grade metamorphism

zoned monazite and zircon as monitors for the thermal history of granulite terranes an example from the central indian tectonic zone the growth and dissolution behaviour of detrital metamorphic and magmatic monazite and zircon during granulite facies anatexis in pelitic and psammo pelitic granulites and in garnetiferous granite from the southern margin of the central indian tectonic zone citz have been investigated using reconstructed metamorphic reaction history monazite electron microprobe dating and sensitive high resolution ion microprobe shrimp u pb zircon geochronology whereas the pelitic granulites record medium pressure granulite facies metamorphism bm1 stage the psammo pelitic granulite reached ultrahigh temperatures tmax 880 c at 8 7 kbar the meta psammite additionally records two stages of granulite facies recrystallization bm2 and bm3 irrespective of variations in the bulk rock compositions and peak metamorphic conditions monazite is highly reactive during the bm1 event producing complex chemically zoned crystals textural compositional and chemical ages of these grains indicate the stability of six compositional domains cd1 to cd6 in the paragenetic sequence of which cd1 represents pre metamorphic detrital cores of paleoproterozoic age cd2 and cd3 combined mean age of 1612 14 ma mark two stages of recrystallization of detrital monazite cores during prograde events rims of cd4 monazite ages between 1615 14 and 1586 14 ma on partially to completely equilibrated cores indicate melt crystallization at or immediately following peak bm1p metamorphism cd5 monazite age of 1574 7 ma is restricted to the psammo pelitic granulites and marks final melt crystallization at the solidus during post peak cooling bm1r stage where r represents retrograde metamorphism the metamorphic rim of cd6 monazite age of 1539 24 ma around partially resorbed cd5 domains is linked to the decomposition of bm1 garnet during the terminal hydration event as part of a granulite facies recrystallization event compositionally homogeneous monazite and rims of chemically zoned monazite grains in granite together record a magmatic crystallization age of 1604 9 ma shrimp u pb zircon dating of the psammo pelitic granulite and garnetiferous granite indicates detrital or inherited cores of paleo to neoarchean age 3584 3 to 2530 3 ma which have been variously recrystallized and overgrown by new zircon 1 at 1658 12 ma 2 between 1595 5 and 1590 6 ma 3 at 1574 9 ma these zircon dates are correlated with the timing of the following 1 the protoliths of precursor sediments of the metasedimentary granulites deposited between 2530 and 1658 ma 2 a short lived high grade event 65 70 myr before the culmination of the bm1 granulite facies event 3 a high t anatectic event corresponding to the peak bm1p metamorphism at tmax 900 c 4 final crystallization of anatectic melt at the solidus cf bm1r metamorphic stage these chronological constraints from monazite and zircon when integrated with the metamorphic reaction history and published geochronological data allow recognition of three episodes of granulite facies metamorphism in the citz at 1658 ma pre bm1 event between 1612 and 1574 ma bm1 event and between 1572 and 1539 ma combined bm2 and bm3 events as part of a latest paleoproterozoic to early mesoproterozoic orogenic event this orogeny is linked to the growth of the proto greater indian landmass

monazite u pb dating of staurolite grade metamorphism in pelitic schists a study of the occurrence of and relations between rare earth element ree minerals in pelitic schists indicates that monazite forms at or near the p and t of the staurolite isograd samples at staurolite grade from the silurian perry mountain formation in the rumford quadrangle of maine yield monazite in sufficient quantities to permit accurate dating of the metamorphic events forming the monazites the bulk chemistry of the metapelites as seen in the major element abundances and ree patterns does not vary significantly across the study area thus the appearance and disappearance of ree phases is assumed to reflect changes in metamorphic grade in a sample from the biotite zone scanning electron microscope and microprobe studies show allanite and monazite intimately associated on a 10 m scale the texture suggest that metastable detrital monazite breaks down distributing its ree components to allanite from samples below staurolite grade in which monazite is not present our observations suggest that rees are partitioned into allanite at or near the staurolite isograd monazite forms as a metamorphic mineral initiating its role as a geochronometer garnet biotite geothermometry on samples at this grade from this and other studies places constraints on the minimum temperature necessary to form monazite 525 c 25 c at 3 1 0 25 kbar a total of 15 separates from nine schist samples ranging up to sillimanite grade have been dated each date is remarkably concordant even though petrologic and textural studies by previous workers have shown that the rocks in the area have been affected by at least three metamorphic episodes calculations indicate insignificant th disequilibrium in these monazites the conditions associated with the metamorphic events suggest that monazite remains closed to lead loss provided that subsequent metamorphisms are at or below sillimanite grade two distinct metamorphic events are resolved one at around 400 ma and one at about 370 ma the latter was due to thermal effects of a nearby pluton that yields concordant monazite ages of 363 ma this work suggests that in addition to dating plutonism and high grade metamorphism monazite should be viewed as a reliable geochronometer for moderate metamorphism of pelitic schists

a long lived tectono metamorphic event in the late paleoproterozoic evidence from sims u th pb dating of monazite from metapelite in central south trans north china orogen abstract as a key accessory mineral in metapelite monazite forms in the metamorphic event and therefore places important direct constraint on the timing of the tectono metamorphic event in this study we investigate four representative metapelites from different metamorphic terranes in the central south trans north china orogen tnco applying secondary ion mass spectrometry sims u th pb dating on monazite the dating results reveal that monazite collected from the huashan luoning zanhuang and wutai metamorphic complexes record the metamorphic ages of 1 83 ga 1 95 ga 1 85 ga and 1 91 to 1 83 ga respectively combined with the literature data of metamorphic geochronology on the discrete terranes within the tnco it is suggested that the amalgamation between the western and eastern blocks of the north china craton along the nearly ns trending tnco stared as earlier as 1 97 ga and continued to as late as 1 80 ga which was in fact a long lived tectono metamorphic event

are discontinuous chondrite normalized ree patterns in pegmatitic granite systems the results of monazite fractionation abstract all 14 stable rare earth elements rees in biotite muscovite granite and tourmaline rich granite of the harney peak granite black hills south dakota usa have been analyzed using inductively coupled plasma mass spectrometry chrondrite normalized ree patterns of the tourmaline rich granites are discontinuous between nd and sm the discontinuity was modeled successfully by the fractional crystallization of monazite from a biotite muscovite granite initial composition this explanation may also apply to the development of such discontinuous patterns in other highly evolved rocks

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

zonation of monazite in metamorphic rocks and its implications for high temperature thermochronology a case study from the lewisian terrain abstract monazite is a valuable chronometer for many geological processes and a proper interpretation for the age derived from monazite requires an adequate understanding of the behaviour of this phase and its chemical and isotopic systems during geological processes this contribution reports the results of a detailed study on chemical and isotopic zonation of monazite in lewisian granulites which is of general significance for monazite geochronology in high grade metamorphic rocks detailed investigations on two lewisian granulite samples using sem epma and sims have revealed that lewisian monazites frequently show petrographic chemical and age zonation the petrographical zonation which reflects the chemical compositional variation can be characterised as follows on the basis of the bse images 1 concentric zoning 2 patchy zoning and 3 intergrowth like zoning the chondrite normalised ree distribution patterns are remarkably similar between different zones of single monazite grains this rules out the possibility that any portion of a zoned monazite in these two samples is detrital in origin some possible mechanisms are proposed for the formation of monazite zonation these include 1 intergrowth of monazite crystals with different composition 2 episodic growth or regrowth of monazite in response to the change of environment conditions during thermal event s which may involve recrystallisation or replacement of the original crystals in short the diversity of zoning patterns in monazites observed in this study cannot be explained assuming a single mechanism accordingly interpretation of the chemical and age information from any zoned monazite requires an adequate understanding of its formation mechanism line scans of th u pb la ce nd sm ca and si across monazite zones have been performed on two monazite grains which experienced granulite facies metamorphism the very sharp boundaries in these line scans indicate that the diffusive transport of these elements in monazite is low even at the temperature of granulite facies metamorphism the effective closure of monazite grains may also depend upon other factors such as the armouring effects of the host phase and recrystallisation of the mineral itself thus great care needs to be taken for geological application of the closure temperature concept

large scale inversion of ztem data a z axis tipper electromagnetic technique ztem survey is an airborne natural source electromagnetic survey that relates the vertical magnetic field to the horizontal magnetic fields measured at a reference station on the ground for large airborne surveys the high number of cells required to discretize the entire area at a reasonable resolution can make the computational cost of inverting the data set all at once prohibitively expensive we present an iterative methodology that can be used to invert large natural source surveys by using a combination of coarse and fine meshes as well as a domain decomposition that allows the full model area to be split into smaller subproblems which can be run in parallel for this procedure the entire data set is first inverted on a coarse mesh the recovered coarse model and computed fields are used as starting models and source terms in the subsequent tiled inversions after each round of tiled inversions the tiles are merged together to form an update model which is then forward modeled to determine if the model achieves the target misfit following this procedure we first invert the data computed from a large synthetic model of the noranda mining camp the inverted models from this example are consistent among our different tiling choices the recovered models show excellent large scale agreement with the true model and they also recover several of the mineralized zones that were not apparent from the initial coarse inversion finally we invert a 30 30 km block of the 2010 ztem survey collected over the porphyry pebble deposit in alaska the inverted ztem results are consistent with the results obtained using other electromagnetic methods

dating rock deformation with monazite the impact of dissolution precipitation creep abstract the u th pb system of monazite behaves differently dependent on the deformation mechanism dissolution precipitation creep dpc or dislocation creep activated in the hosting metamorphic rocks this can be exploited to use monazite for dating deformation as is shown in rocks subsequently deformed by dislocation creep and dpc in rock layers intensely deformed by dpc mineral reactions particularly the dissolution of feldspar and apatite increased the alkali content and reactivity of the fluid this in turn led to dissolution of old predeformative monazite grains new synmetamorphic monazite grains formed as the result of inter grain transport of material over distances within the grain scale this process efficiently led to complete resetting of the monazite u th pb system even at temperatures prevailing during greenschist facies conditions the chemical composition of the new monazite records the dissolution of the old feldspar by a less pronounced negative eu anomaly compared to old monazite the shape of the monazite grains that precipitated during creep indicates the sense of shear in the shear zone thus linking the obtained ages directly to the map scale tectonic transport in rock layers predominantly deformed by dislocation creep old monazite grains survived intense mylonitization and high strain and show a core rim structure the cores are patchy reflecting intra grain coupled dissolution reprecipitation replacement processes a wide range in apparent geologically inaccurate th pb and u pb ages among the patchy zones is the result of incomplete removal of in situ grown radiogenic pb from the patchy domains depletion of th and u and the redistribution of th and u among the domains exclusively in the rims of the old monazite the chemical composition correlates to that of the syndeformative monazites and the u th pb system reflects the subsequent dpc accordingly rocks pervasively deformed by dpc should be preferably used to obtain monazite most suitable for precise dating of creep episodes linked to shear deformation and for determination of deformation rates

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

significance of in situ sims chronometry of zoned monazite from the lewisian granulites northwest scotland abstract in situ studies of lewisian metamorphic monazites show them to be strongly zones in th content th u ratio and 207 pb 206 pb age traverses across compositional zones of individual monazites by sims and empa show that there are no resolvable shifts between 232 th 238 u and 208 pb 206 pb ratios and between th and pb contents in any of the profiles obtained furthermore the difference in 208 pb 232 th ages between two zones of monazites in the same thin section is indistinguishable from the difference in 207 pb 206 pb ages determined by sims these observations together with simple models suggest that transport of pb relative to th and u did not occur significantly during younger e g the laxfordian events in the lewisian and the ages preserved in these zoned monazites are close to concordant moreover monazites having different compositions yield indistinguishable 207 pb 206 pb ages which suggests that the closure temperature of the u pb system in these monazites is not significantly dependent upon their composition consequently the pattern of age distribution observed in the monazites is taken to reflect the metamorphic history of the lewisian the results are consistent with the recent interpretations of the lewisian thermal history which suggest two high grade metamorphic events separated by 200 ma

unravelling dates through the ages geochronology of the scottish metamorphic complexes the paper by giletti et al 1961 is seen as a major landmark in the evolution of dating techniques in polymetamorphic terrains we consider certain critical issues from each of the main complexes of the scottish highlands studied by giletti et al to illustrate how subsequent developments in geochronological methodology have influenced our understanding of metamorphic belts lewisian examples focus on the formation of archaean crust and the age of the main high grade metamorphism and the scourie dyke swarm the antiquity of moinian sedimentation its relationship to the torridonian sandstones and the timing of precambrian metamorphism have been controversial issues the timing and nature of caledonian orogenesis most clearly expressed in the dalradian complex have been the focal points for the refinement of radiometric investigation these complexes have been subject to successive developments in methodology with ever tighter constraints from rb sr and k ar mineral dating through rb sr and pb pb whole rock studies u pb dating of bulk zircon fractions and sm nd whole rock and mineral investigation up to the latest technologies of single grain zircon and ion microprobe analysis the rocks have released their secrets reluctantly and many of the questions posed in 1961 have still not been definitively answered however the hope of unambiguous solution leads towards greater efforts ever more reliable data and a clearer evolutionary picture

sources and distribution of fresh water around cape farewell in 2014 we investigate the origin of fresh water on the shelves near cape farewell south greenland using sections of three hydrographic cruises in may hud2014007 and june 2014 jr302 and geovide we partition the fresh water between meteoric water sources and sea ice melt or brine formation using the 18o of sea water the sections illustrate the presence of the east greenland coastal current egcc close to shore east of cape farewell west of cape farewell it partially joins the shelf break with a weaker near surface remnant of the egcc observed on the shelf southwest and west of cape farewell the egcc traps the freshest waters close to greenland and carries a brine signature below 50 m depth the cruises illustrate a strong increase in meteoric water of the shelf upper layer by more than a factor 2 between early may and late june likely to result from east and south greenland spring melt there was also a contribution of sea ice melt near the surface but with large variability both spatially and also between the two june cruises furthermore gradients in the freshwater distribution and its contributions are larger east of cape farewell than west of cape farewell which is related to the egcc being more intense and closer to the coast east of cape farewell than west of it large temporal variability in the currents is found between different sections to the east and southeast of cape farewell likely related to changes in wind conditions

age trends in garnet hosted monazite inclusions from upper amphibolite facies schist in the northern grouse creek mountains utah we performed in situ th pb dating of monazite in upper amphibolite facies pelitic schist from the grouse creek mountains in northwest utah sixty six ages from inclusions in four garnet grains range from 37 to 72 ma and decrease with radial distance from garnet cores the age range of 30 matrix monazite grains overlaps and extends to younger ages than inclusions 25 58 ma the monazite grains are not intersected by cracks in the garnets through which dissolution reprecipitation or pb loss might occur and are generally too small 20 lm to allow for more than one age determination on any one grain processes that might explain inclusion ages that decrease with radial distance from garnet cores include 1 pb diffusion in monazite 2 dissolution and reprecipitation of monazite and 3 co crystallization of monazite and garnet after consideration of these possibilities it is concluded that the co crystallization of monazite and garnet is the most plausible with monazite neoblasts deriving rees from the breakdown of muscovite garnet ages derived by regression of the inclusion ages and assuming a constant rate of volume increase during garnet growth yield model ages with a maximum difference between core and rim of 22 m y

a geological assessment of airborne electromagnetics for mineral exploration through deeply weathered profiles in the southeast yilgarn cratonic margin western australia abstract mineral exploration in regolith dominated environments is challenging requiring the development of new technical tools and approaches when airborne electromagnetics aem is combined with information on stratigraphy mineralogy geochemistry drilling and landscape observations in a geological context it becomes a powerful approach to describe the architecture of the regolith cover this has significant implications for mineral exploration in any regolith dominated terrain rdt this research presents two case studies of aem data integrated in a geological context for mineral exploration in the yilgarn craton margin albany fraser orogen afo in one of the study sites presented study site 1 neale tenement the availability of aem data allowed for lateral and vertical extrapolation of the information contained in datasets at specific locations thereby creating a 2d architectural model for the regolith cover in addition it was determined 1 the total thickness of the regolith cover and its variability between 2 m and 65 m 2 that low conductivity transported overburden and silcrete units with a total thickness between 5 and 45 m is widely distributed capping the upper saprolite and 3 that the silcrete unit varies laterally from being completely cemented to permeable and that these permeable areas windows coincide vertically with mineralogical textural moisture salt content changes in the underlying saprolite resulting in increased conductivity this has been interpreted as resulting from more intense vertical weathering and consequently a higher vertical geochemical dispersion of the basement signature towards surface aem has been used to assist in identifying and describing the lateral continuity of these windows in areas with no direct field observations surface geochemical sampling above these permeable areas may deliver more reliable geochemical basement signatures in the second study site silver lake tenement the aem data was strongly influenced by the high conductivity of the hypersaline groundwater this had a significant effect on the aem response resulting in reduced depth penetration and reduced resolution of subtle conductivity contrasts between cover units despite this the aem data set combined with geological observations in the area was able to map the presence and extent of a buried palaeochannel network the most significant architectural sedimentary feature in the cover this interpretation allowed for a more efficient drilling campaign to be designed to sample the fresh basement rock suites in the area by avoiding drilling into palaeochannels integrated and constrained by the geological context the application of aem conductivity models by geologists is envisioned as one of the most promising tools within the exploration geologist toolbox to understand the architecture of the cover

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

interpretation of monazite ages obtained via in situ analysis abstract monazite grains from nepal and vietnam were compositionally analyzed with an electron microprobe and dated th pb with an ion microprobe five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population 1 pb loss due to diffusion 2 dissolution reprecipitation reactions along a retrograde path 3 analytical uncertainties 4 analyses of overlapping age domains and 5 episodic monazite growth the influence of these factors is sample dependent but can be evaluated 1 using peak metamorphic conditions and x ray element maps to assess potential polymetamorphism or retrogression 2 obtaining other geochronologic data including previous work or dating other minerals in the sample 3 evaluating any method related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses and 4 ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element ree oxide or allanite chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms instead of relying on monazite chemical composition major mn fe mg ca and minor y element garnet zoning patterns and peak p t conditions should be used to facilitate age interpretation this thermobarometric data records the sample s thermal history changes in garnet growth rate and mechanisms and accessory mineral breakdown

fluid induced disturbance of the monazite th pb chronometer in situ dating and element mapping in pegmatites from the rhodope greece bulgaria abstract the monazite th pb chronometer is widely used in a variety of geological contexts but may be affected by interaction with fluids in the central part of the rhodope massif greece bulgaria synfolial pegmatite veins were emplaced within two major synmetamorphic shear zones in the chepelare shear zone czs which displays no evidence of post metamorphic fluid flow consistent monazite th pb ages of 36 ma are interpreted as dating vein emplacement higher in the metamorphic pile zircon and monazite give u th pb ages of 42 ma for vein emplacement in the nestos shear zone nsz pegmatites show evidence of post emplacement interaction with fluids during greenschist facies ductile deformation evidence for this includes the precipitation of calcite in microscale tension gashes within feldspar porphyroclasts and the oxygen isotope disequilibrium between quartz and feldspar aqueous carbonic fluids deriving from carbonate lithologies in the footwall of the nsz are identifiable in the pegmatites by the high 18 o value of quartz up to 21 8 and the presence of calcium in calcite veinlets in these samples some of the monazite grains show large intragrain scattering of th pb age spanning up to 12 ma with intergrain scattering reaching 16 ma from 39 to 55 ma within individual grains age domains correlate with chemical heterogeneities and some show a characteristic ca excess these chemical and isotopic alterations are interpreted to be caused by interaction with fluids derived from carbonate lithologies complementary u pb data on zircons from the nsz pegmatites yield mostly mesozoic ages related to an older metamorphic cycle and an age of 48 ma for one grain with typical magmatic zoning the th pb ages of 49 3 1 6 to 54 9 1 7 ma probably relate to the emplacement of the pegmatites the spread of younger th pb ages from 38 6 1 1 to 46 2 1 6 ma probably reflects the period of fluid circulation during progressive cooling to greenschist facies conditions or variable perturbations of the monazite isotope system during fluid assisted greenschist facies deformation this is consistent with 39 ar 40 ar mica ages of 32 to 34 ma interpreted as a tighter constraint for the timing of the greenschist facies metamorphism this study illustrates the capacity of monazite to record distinct events in a single rock and highlights the need for identifying the potential involvement of fluids in order to interpret monazite ages

comparative isotopic and chemical geochronometry of monazite with implications for u th pb dating by electron microprobe an example from metamorphic rocks of the eastern wyoming craton u s a polygenetic monazite grains in diverse precambrian crystalline rocks from the black hills south dakota have been analyzed in situ by ion and electron microprobe methods shrimp and emp to evaluate the accuracy and precision of emp ages determined using a new analytical protocol that incorporates improved background acquisition and interference corrections parallel evaluations were conducted by comparing emp chemical and shrimp isotopic ages at regional rock and grainscales the monazite data set includes 354 emp chemical analyses from 26 grains in six metamorphic rocks which resolve into 54 age composition domains and 31 shrimp isotopic ages from 13 grains in one of the rocks with six grains microanalyzed in common by the two methods the data set also includes monazite bearing garnets in two of the rocks whose isotopic compositions were analyzed using pb stepwise leaching pbsl methods both the emp and shrimp data sets reveal a continuum of apparent monazite ages spanning a 1790 1680 ma timeframe with a relatively high probability of ages at 1755 and 1715 ma that correspond spatially to core and rim domains pbsl ages of 1742 and 1734 ma obtained from monazite bearing garnet in two rocks are intermediate compared to the corresponding emp ages and are thereby interpreted as mixed ages emp data for two grains in the structurally deepest of the six rocks record 1785 and 1755 ma ages in the cores and higher y and lower th rims respectively and these results are duplicated by shrimp ages in these and or other grains from the same rock overall the emp shrimp and pbsl ages are internally consistent at the various scales of observation which serves to validate emp chemical dating as an accurate and precise method of discerning monazite age populations in polymetamorphic terrains the emp data set is interpreted geologically as res ecting multiple episodes of monazite growth that are provisionally related to known metamorphic events in the black hills taking the most precise emp data at face value it is possible to resolve the timing of the two older events at 1784 4 ma or 1786 6 ma and 1756 3 ma or 1753 4 ma with 95 con dence these events are considered to be related to sequential episodes of n directed thrusting and e w compression associated with paleoproterozoic crustal assembly in the mid continent a younger metamorphism related to granite intrusion known to have occurred at 1715 3 ma is dated independently at 1717 2 ma from the emp monazite ages

accessory phase controls on the geochemistry of crustal melts and restites produced during water undersaturated partial melting the profound geochemical conseqences of accessory phase behaviour during partial melting of highgrade metapelites are demonstrated with reference to two geochemically distinct crustal melts produced by biotite dehydration melting reactions under granulite facies kbar 860 cc conditions these two leucogneiss suites from the brattstrand bluffs coastline eastern antarctica have similar field relations transport distances 10 100 s of metres and major element chemistry type 1 leucogneisses have low zr th and lree positive eu anomalies and zr zr and lreet lreet values less than 1 0 i e less than required to saturate the melt mass balance constraints suggest that these melts have been extracted before equilibration with host melanosomes the dry peraluminous nature of vapour undersaturated melts inhibits monazite and zircon solubility and results in concentration of these phases in the residue melts are consequently depleted in lree and hree melanosomes show complementary enrichment in lree while hree patterns are dominated by residual garnet type 2 leucogneisses in contrast have strongly enriched zr th and lree abundances negative eu anomalies and zr zr and lreet lreet 1 resulting from accessory phase entrainment vapour absent partial melting under moderate 6 8 kbar pressure granulite facies conditions of a pelitic source containing monazite is likely to give disequilibrium melts depleted in lree and hree as monazite and garnet are concentrated in the residue if temperatures are high enough 850 870 c to permit relatively large degrees of partial melting then the feldspar component of the source will be removed almost completely giving melts with large positive eu anomalies melts formed under vapour present conditions are unlikely to show such extreme lree and hree depletion or positive eu anomalies even at high degrees of partial melting disequilibrium melting coupled with source entrainment could fortuitously produce ree and trace element signatures similar to those typical of s type granites and usually ascribed to equilibrium melting conditions

electron probe ultrachron microchronometry of metamorphic monazite unraveling the timing of polyphase thermotectonism in the easternmost wyoming craton black hills south dakota a metapelite from the easternmost wyoming craton black hills south dakota has been analyzed by microstructural methods to unravel polyphase deformational history associated with 1800 1700 ma assembly of southern laurentia three deformational fabrics are recognized in oriented thin sections an ene trending s 1 fabric preserved as oblique inclusion trails in garnet porphyroblasts a nnw trending s 2 fabric preserved as microlithons in the rock matrix and a flattening fabric s 3 which transposed s 1 s 2 and dominates the matrix a complex monazite porphyroblast has been analyzed in situ with the electron microprobe ultrachron to constrain the timing of s 1 s 3 fabric formation associated with monazite growth the core of this grain uniquely preserves the s 1 s 2 fabrics as sigmoidal inclusion trails the mean total pb age of this domain is 1750 10 ma all dates reported at 95 confidence n 39 spots which is equivalent to the published 2 0 7 pb 2 0 6 pb age for the same domain these results validate the total pb dating method in general and the ultrachron in particular for reliable age determination in low th monazite and are interpreted as 1750 ma minimum ages for the s 1 s 2 fabrics and sequential d 1 d 2 collisional events that imposed them n directed arc accretion and e w continental collision respectively a higher th y rim of this same rosetta grain truncates the s 1 s 2 sigmoid and is associated with resorption textures in garnet porphyroblasts coupled release of y and an s 3 fabric that pervasively overprinted s 1 s 2 in the rock matrix the mean ultrachron date of this domain is 1692 5 ma n 17 spots which is slightly younger that the published isotopic age for all monazite rims combined these results support a 1715 1690 ma timeframe for localized doming d 3 related to granite magmatism the onset of which has been dated independently at 1715 3 ma the timing of post d 3 cooling through 350 and 300 c is constrained by 4 0 ar 3 9 ar dates of 1610 and 1480 ma obtained for separates of d 3 matrix muscovite and biotite respectively which are interpreted as closure ages this study shows that fabrics in poly deformed rocks can be dated by linking monazite spot ages to key microtextures further the results of this micrometer scale study enhance previous knowledge of local thermotectonism black hills and regional terrane assembly laurentia

monazite ages and the evolution of the menderes massif western turkey the menderes massif experienced polyphase deformation but distinguishing pan african events from alpine tectono metamorphic evolution and discriminating eocene oligocene shortening from recent extension remain controversial to address this monazite in garnet bearing rocks from the massif s gordes central and cine sections were dated in thin section in situ using the th pb ion microprobe method cambro ordovician monazite inclusions in cine and central menderes massif garnets are 450 m y older than matrix grains monazites in reaction with allanite from the kuzey detachment which bounds the northern edge of the central menderes massif are 17 5 ma and 4 5 1 0 ma the pliocene result shows that dating of monazite can record the time of extension the kuzey detachment might have exhumed rocks a lateral distance of 53 km at a rapid rate of 12 mm year assuming the present 20 ramp dip pliocene monazite crystallization at 450 c and a geothermal gradient of 25 c km assuming an angle of 60 the rate decreases to 5 mm year with the detachment surface at 21 km depth in the pliocene two gordes massif monazites show a similar allanite monazite reaction relationship and are 29 6 1 1 ma and 27 9 1 0 ma suggesting that the cenozoic extension in the gordes massif and possibly the entire menderes massif might have begun in the late oligocene

sm nd isotope systematics of high ree accessory minerals and major phases id tims la icp ms and epma data constrain multiple permian triassic pegmatite emplacement in the koralpe eastern alps abstract detailed sm nd mineral id tims empa and la icp ms analysis of meta pegmatite minerals from the koralpe stubalpe area austria involving single crystal separation step wise dissolution and acid leaching techniques yielded i information about the partitioning of ree between accessory and major mineral phases in meta pegmatites and ii age constraints on the long lasting permian triassic event in the austroalpine basement units of the eastern alps internal sm nd mineral isochrons performed on porphyroclast domains from the three localities rostockbach kuppergrund and wildbachgraben including garnet xenotime apatite monazite and feldspar indicate multiple emplacement of pegmatoid melts between 273 2 and 258 3 ma other localities yielded younger ages indicating that magmatic garnet crystallisation persisted from 251 7 to c 230 ma ages calculated between high ree accessories monazite apatite xenotime and the low ree major phases feldspar and garnet are largely consistent zircon however plots clearly off the internal regression line h 2 so 4 leaching experiments on meta pegmatite garnet rich in micron sized xenotime and apatite inclusions locally affected by dynamic recrystallisation yielded information about the behaviour of the sm nd system during strong tectono metamorphic overprinting the data suggest multiple injections of pegmatite melts at distinctly different times during protracted crustal thinning and heating in the permian triassic ky paramorphs after andalusite and micro inclusions of kyanite staurolite and sillimanite in magmatic garnet indicate crystallisation of the garnet at moderately high but variable pressure conditions during subsequent eclogite facies overprinting peak pt c 700 c 2 2 gpa and intense deformation in cretaceous time the magmatic chemical and isotopic signatures of porphyroclasts were largely preserved except for localized within grain micro shear zones and outermost rim domains whereas part of the feldspar rich matrix recrystallised during pervasive mylonitisation along the eclogite to amphibolite facies grade exhumation path

a textural and geochemical guide to the identification of hydrothermal monazite criteria for selection of samples for dating epigenetic hydrothermal ore deposits hydrothermal monazite is one of the most reliable geochronometers for u pb dating of epigenetic or hydrothermal ore deposits because its blocking temperature at ca 700 c is higher than that of most metamorphic conditions although igneous monazite is routinely used for age dating igneous rocks only a few ore deposits have been dated by hydrothermal monazite this is due to the similar morphology of hydrothermal and igneous monazite which prevents the reliable distinction of hydrothermal monazite in particular we demonstrate that hydrothermal monazite can be distinguished from igneous monazite by its unique geochemical signature its local abundance and to common association with hydrothermal mineral assemblages our data and the data of others reported in the literature suggest that the low tho 2 content of hydrothermal monazite 0 1 wt is distinct from that of igneous monazite 3 to 5 wt and may be used to determine their genesis

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

metalliferous mining geophysics state of the art in the last decade of the 20th century and the beginning of the new millennium the downturn in mining activity experienced during the 1990s did not preclude significant new developments in various areas of mining geophysics the methodology for acquiring and compiling data has kept pace with the latest technological developments from global positioning system navigation to raster displays and parallel computing wavelet transforms principal component analysis and fractals have begun to find successful applications in both processing and interpretation of geophysical data methods of quantitatively interpreting inverting anomalies in terms of 2 d and 3 d models of causative bodies are becoming common for the first time it is possible to make airborne gravity gradient measurements suitable for use in mineral exploration lower transmitter frequencies for airborne time domain electromagnetic em systems have enabled surveys in areas where conductive cover previously screened basement conductors the use of approximation algorithms has allowed the transformation of either time domai

sources to the east greenland current and its contribution to the denmark strait overflow data from the east greenland current in 2002 are evaluated using optimum multiparameter analysis the current is followed from north of fram strait to the denmark strait sill and the contributions of different source waters in mass fractions are deduced from the results it can be concluded that at least in spring 2002 the east greenland current was the main source for the waters found at the denmark strait sill contributing to the overflow into the north atlantic the east greenland current carried water masses from different source regions in the arctic ocean the west spitsbergen current and the greenland sea the results agree well with the known circulation of the western nordic seas but also add knowledge both to the quantification and to the mixing processes showing the importance of the locally formed greenland sea arctic intermediate water for the east greenland current and the denmark strait

polymetamorphic evolution of the lewisian complex nw scotland as recorded by u pb isotopic compositions of zircon titanite and rutile u pb isotopic relations in zircon and titanite of granulite and amphibolite gneisses in the lewisian complex and bordering laxford front reveal complex discordance patterns indicating multiple late archean and early proterozoic crystallization overgrowth and pb loss events the earliest stages in the evolution of the complex remain poorly resolved zircon ages of 2710 ma date high grade metamorphism and magmatism probably related to tectonic and magmatic accretion in a continental arc setting a distinct event at 2490 2480 ma possibly initiated by metamorphism and deformation at high grade conditions caused amphibolitization of the granulites and emplacement of granitic pegmatites this event can be correlated with development of inverian shear zones and formation of granitoid layers along the laxford front the emplacement of a younger generation of granitoid sheets during the laxfordian event fromed hydrothermal titanite at 1754 ma in gneisses south of the laxford bridge and partially reset older titanite at scourie growth of secondary titanite and rutile also occurred during subsequent low grade metamorphism at 1690 1670 ma

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part i the monazite ce brabantite solid solution series peraluminous granites of the erzgebirge fichtelgebirge germany are hosts of various members of the monazite group of minerals that display an unprecedented compositional diversity the eibenstock s type granite constitutes the third reported occurrence worldwide of brabantite and the first occurrence of this mineral in a granite many new occurrences of cheralite ce as well as a monazite group mineral intermediate between monazite ce and huttonite for which the term huttonitic monazite is proposed were discovered even common monazite ce may show extreme ranges of actinide and lanthanide element concentrations the granites that host brabantite and cheralite ce are highly differentiated strongly peraluminous low temperature residual melts of s type affinity which are rich in fluorine and other volatile constituents but depleted in thorium and the light rare earth elements such highly evolved volatile rich compositions resemble rare element pegmatites and appear favorable for the precipitation of cheralite ce and brabantite but not of monazite with large amounts of huttonitic substitution instead these minerals occur preferentially in f poor biotite and f rich li mica granites of a type affinity irrespective of the level of uranium in silicate melts which may exceed that of thorium the substitution of uranium in monazite remains limited the compositional data reported here are consistent with complete miscibility in the monazite ce brabantite solid solution series under magmatic conditions these granites contain monazites that span almost the entire compositional range reported for monazite group minerals worldwide and therefore granites appear to be ideal rocks in which to study the crystal chemistry of this mineral group in general

an anticlockwise p t t path at high pressure high temperature conditions for a migmatitic gneiss from the island of fjortoft western gneiss region norway indicates two burial events during the caledonian orogeny

matrix effects and calibration limitations in ion probe u pb and th pb dating of monazite abstract monazite can be used for u pb and th pb dating of a wide variety of rocks and geological processes particularly metamorphism in many instances ion microprobe analysis is the preferred method for dating monazite combining good analytical precision with m scale spatial resolution however ion microprobe dates can be compromised by matrix effects on the ionisation efficiencies of different secondary ionic species which can bias monazite pb tho n and pb uo n data by as much as 40 and 30 respectively for known monazite compositions these effects appear to be entirely attributable to the sputtering process in which case similar effects exist in data from all ion probes the effects on data ratios are modified sometimes exacerbated or reversed when data are subjected to the correlation based pb th and pb u calibrations that are now commonly used one dimensional calibrations of 206 pb 270 uo 2 and 208 pb 264 tho 2 are recommended corrections derived from data for a suite of reference materials with diverse compositions can reduce biases in 208 pb 232 th ages to 206 pb 238 u ages to 204 pb can be addressed without iterative data reduction

crystal chemistry of the monazite and xenotime structures monazite and xenotime the re p04 dimorphs are the most ubiquitous rare earth re minerals yet accurate structure studies of the natural phases have not been reported here we report the results of high precision structure studies of both the natural phases and the synthetic re p04 phases for all individual stable rare earth elements monazite is monoclinic p2 n and xenotime is isostructural with zircon space group 14 amd both atomic arrangements are based on 001 chains of intervening phosphate tetrahedra and re polyhedra with a reogpolyhedron in xenotime that accommodates the heavy lanthanides tb lu in the synthetic phases and a re09 polyhedron in monazite that preferentially incorporates the larger light rare earth elements la gd as the structure transforms from xenotime to monazite the crystallographic properties are comparable along the 00i chains with structural adjustments to the different sizes of re atoms occurring principally in 00i there are distinct similarities between the structures that are evident when their atomic arrangements are projected down 001 in that projection the chains exist in 100 planes with two planes per unit cell in monazite the planes are offset by 2 2 a along 010 relative to those in xenotime in order to accommodate the larger light re atoms the shift of the planes in monazite allows the re atom in that phase to bond to an additional 02 atom to complete the re09 polyhedron

u pb geochronological constraints on the timing of episodic regional metamorphism and rapid high t exhumation of the grand forks complex british columbia abstract the grand forks complex gfc is a fault bounded metamorphic core complex in the southern omineca belt of british columbia canada it experienced prograde metamorphism ranging from upper amphibolite to granulite facies conditions during the mesozoic to early tertiary compressional stage of the cordilleran orogeny peak metamorphism was followed by multi stage exhumation in the early eocene this study provides u pb monazite and zircon constraints on the timing of metamorphic episodes in the gfc and subsequent high t amphibolite facies decompression in the early eocene monazite la icp ms ages from metapelitic gneisses record episodic metamorphism from the late jurassic to paleocene with peak metamorphism occurring between 59 and 50 ma peak metamorphism was followed by rapid near isothermal decompression of the gfc between 52 and 50 ma and leucosome crystallization at 50 ma thermodynamic modeling of metapelites in the system mnnckfmashpyce predicts that monazite was not stable at peak metamorphic conditions consistent with the dominant population of 59 ma ages representing growth along the prograde path most likely at subsolidus conditions growth of widespread high y monazite rims 50 ma is predicted along suprasolidus decompression and cooling paths zircon shrimp ages from igneous bodies in the gfc and hanging wall of the bounding kettle river fault krf suggest ductile deformation related to high t decompression of the gfc was ongoing at 51 ma but had ceased by 50 ma truncated by post kinematic granitoids this high t deformation predates subsequent greenschist facies extension on the overlying krf a pre krf hanging wall ductile shear zone is constrained to 59 51 ma it deforms 59 ma ladybird suite leucogranites and may be related to high t exhumation of the core complex rapid 100 c ma cooling rates are required to accommodate high t amphibolite facies exhumation of the gfc at 52 50 ma followed by low t greenschist facies exhumation at 49 ma

complexity in the behavior and recrystallization of monazite during high t metamorphism and fluid infiltration abstract a detailed study of monazite grains in silica undersaturated and quartz bearing mg al metapelite from the oygarden group of islands east antarctica reveals a complex history of growth and recrystallization during two separate events in the neoproterozoic and earliest cambrian monazite grains from garnet poor and garnet rich metapelite preserve core domains that have ages corresponding to growth and or recrystallization at granulite facies p 9 1 0 gpa t 850 900 c conditions during the rayner structural episode between 930 and 890 ma high th rims 22 wt tho 2 that are in textural equilibrium with sapphirine orthopyroxene symplectites formed after garnet during late rayner decompression occur on monazite grains in garnet rich assemblages and give electron microprobe ages 883 18 ma within error of core domains 903 14 ma these high th rim domains are interpreted to have formed through recrystallization of liberated inclusions via a process dominated by coupled dissolution reprecipitation reactions facilitated by transient fluid films on the large surface areas in the symplectite and not by new growth in garnet poor metapelite monazite grains that have grain boundaries in textural equilibrium with the granulite facies assemblage also show alteration to higher th compositions on rims and along vein like fractures this compositional shift is accompanied by partial to complete resetting of ages to 500 ma along with minor modification of core domain ages textures and patterns of chemical age resetting are interpreted to also be the result of a coupled dissolution reprecipitation reaction process but in contrast to garnet bearing assemblages this alteration occurred during a fluid influx at lower temperatures during regional pan african tectonism this study highlights the susceptibility of monazite to resetting with fluid present conditions dramatically increasing the potential for recrystallization

kinematic metamorphic and age constraints on the miyar thrust zone implications for the eohimalayan history of the high himalayan crystalline of nw india

in situ shrimp u pb dating of monazite integrated with petrology and textures does bulk composition control whether monazite forms in low ca pelitic rocks during amphibolite facies metamorphism abstract bulk composition and specific reaction history among common silicate minerals have been proposed as controls on monazite growth in metapelitic rocks during amphibolite facies metamorphism it has also been implied that monazite that formed during greenschist facies metamorphism may be preserved unchanged under upper amphibolite facies conditions if correct this would make the interpretation of monazite ages in polymetamorphic rocks exceedingly difficult because isotopic dates could vary significantly in rocks that have experienced identical metamorphic conditions but differ only slightly in whole rock composition low ca pelitic schists from the mount barren group in southwestern australia display a range of whole rock compositions in afm space and different peak mineral assemblages resulting from amphibolite facies metamorphism 8 kb 650 c in this study we test whether bulk composition controls the formation of monazite through geochronology and textural evidence linking monazite growth with deformation and peak metamorphism x ray element mapping of monazite from the metapelitic rocks reveals concentric zoning in many grains with compositionally distinct cores and rims in situ shrimp u pb geochronology of monazite yields two 207 pb 206 pb age populations the cores and texturally early monazite give an age of 1209 10 ma interpreted to record prograde metamorphism whereas the rims and late monazite define a single population of 1186 6 ma which is considered the likely age of peak thermal metamorphism the growth of monazite was widespread in low ca pelitic schists representing a broad range of compositions in afm space indicating that variations in bulk composition in afm space did not control the formation of monazite during amphibolite facies metamorphism in the mount barren group

upb pbpb and smnd dating of authigenic monazite implications for the diagenetic evolution of the welsh basin abstract authigenic monazite nodules from silurian turbiditic rocks in the central welsh basin are zoned with respect to nd isotope composition the cores are relatively radiogenic and the rim to core trend projects toward the composition of associated very early authigenic apatite concretions these authigenic phases therefore equilibrated with changing fluid composition as they formed the apatites and the monazite nodule cores may have included significant nd from organic matter or seawater whereas the rees in the outer parts of the monazite nodules were derived from clastic detritus the apparent sm nd age obtained from these phosphates is a mixing line which gives an ordovician age for these silurian rocks the u pb isotope system does not show similar trends and shows promise as an alternative method for dating such phosphates a date of 417 11 ma 2 mswd 107 agrees well with recent estimates of the time of the diagenetic smectite illite transition in the rocks of this study a pb pb isochron gave an age of 422 24 ma 2 mswd 0 9 this shows that the pb is in isotopic equilibrium and is undisturbed and that the elevated mswd of the u pb regression is caused by slight subsequent mobility in the u pb system the event dated by the monazite is probably compactional dewatering during accelerated mid silurian sediment loading in the central welsh basin

oligocene initiation of the south tibetan detachment system constraints from syn tectonic leucogranites in the kampa dome northern himalaya abstract himalayan leucogranites provide a robust record of the thermal and tectonic processes that occurred during convergence of the eurasian and indian tectonic plates we present structural petrological mineralogical whole rock geochemical sr nd isotope and geochronological results for cenozoic leucogranites from the kampa dome northern himalaya the kampa leucogranites are typical syn tectonic granites and occur as a series of sills dikes and puddings in the kampa shear zone which is considered to be the exhumed portion of the south tibetan detachment system stds in the northern himalaya the kampa syn tectonic leucogranites provide information about the timing and nature of regional kinematics and record thermal conditions and the initiation of the stds whole rock geochemistry and sr nd isotope analyses show that the kampa leucogranites are characterized by the following 1 they are peraluminous and have high sio2 al2o3 and a cnk low tio2 mgo p2o5 and tfe2o3 and variable cao na2o k2o and total alkalis 2 they are enriched in large ion lithophile elements e g k and rb and depleted in high field strength elements e g zr and ti with negative eu anomalies and 3 they display variable initial 87sr 86sr compositions 0 7507580 826065 and their end i values range between 7 6 and 12 2 anatexis of graywackes and metapelites in the great himalayan crystalline series played an important role in the formation of the kampa leucogranites anatexis was controlled by fluid absent partial melting of muscovite mineralogical and petrological analyses show that zircons belong to an early crystallization phase whereas monazites are remnants of the final crystallization phase of the granitic melt zircon u pb dating reveals that anatexis in the deep himalayan crust occurred at ca 32 23 ma during the oligocene monazites yield homogeneous 208pb 232th ages of ca 23 5 ma and record rapid emplacement in the kampa shear zone these results indicate that movement on the stds was initiated during the early oligocene and became well developed during the late oligocene in the kampa region the oligocene was a unique period of counterbalance between continued plate convergence and intense extension in the himalayan orogen

constraints on fluid evolution during metamorphism from u th pb systematics in alpine hydrothermal monazite abstract the timing and duration of hydrothermal activity during orogenesis are difficult to constrain because such systems are open and multistage using mm sized monazite crystals from two alpine clefts from the central alps switzerland we demonstrate that combined u th pb isotopic systematics of hydrothermal monazite can constrain both timing and fluid evolution during crystallization our data highlight four major characteristics of the cleft monazites i extreme th u ratios ii significant common pb in the u system up to 39 206 pb iii excess 206 pb up to 54 and iv precise and reliable th pb ages comparison of our results with literature data indicates that th u in monazite is a remarkable discriminant of geological conditions capable of distinguishing metasedimentary magmatic and hydrothermal origin hydrothermal monazite crystals are characterized by th u ratios up to 629 among the highest values ever reported extreme th u ratios in monazite enhance incorporation of 230 th a short lived intermediate product in the 238 u 206 pb decay chain generating 206 pb excess which if not accounted for results in 206 pb 238 u ages that are too old for example in the samples investigated here by as much as 300 for the two zoned monazite crystals studied in detail 208 pb 232 th ages are reliable for the different compositional domains visible in back scattered electron bse images 232 th 208 pb ages for the older domains 15 2 0 3 ma and 14 1 0 3 ma respectively are consistent with the structural relationships of the hydrothermal veins indicating early retrograde genesis the youngest rim age at 13 5 0 4 ma for the blauberg crystal marks termination of monazite precipitation the resolvable age difference is interpreted to reflect pulsed monazite growth over an extended period of hydrothermal activity in both crystals the outer rims have the highest 206 pb excess confirming a two stage crystallization two scenarios are envisaged to account for the 206 pb excess evolution in the first increasing 206 pb excess is caused by a modification of the th u fractionation between monazite and fluid due to an evolution of the fluid towards more oxidizing conditions that favor partitioning of hexavalent u into the fluid alternatively it is possible that 230 th increased with time in the fluid in this second case monazite growth would have occurred in a closed system from a fluid that was initially in disequilibrium with the 238 u 206 pb decay chain and progressively equilibrated t

ion microprobe determinations of trace element concentrations in garnets from anatectic assemblages abstract trace element data for garnet cordierite plagioclase alkali feldspar and tourmaline have been obtained by ion microprobe analysis of assemblages from a pelite derived leucogranite a sillimanite grade anatectic gneiss and a kyanite grade sub solidus schist from the high himalaya results confirm that for equilibrium melting residual plagioclase will cause depletion in sr and eu in the melt and residual garnet will result in strong depletion of y and hree consistent with their published partition coefficients all trace elements of interest are strongly incompatible in cordierite implying that for equilibrium fractional melting of pelites at shallow depths hree concentrations in garnets from metasediments are independent of metamorphic grade but the metamorphic garnets are significantly less enriched in hree than is the leucogranite garnet this suggests either that the leucogranite is derived from a source with lower modal abundances of garnet than the analysed metasediments or that garnet from the anatectic gneiss has not reached chemical equilibrium with a granitic melt the latter possibility is consistent with sluggish self diffusion rates in garnets for ree at temperatures of 5 kbar

heavy mineral based provenance analysis of mesozoic continental marine sediments at the western edge of the bohemian massif se germany with special reference to fe ti minerals and the crystal morphology of heavy minerals during the mesozoic the epicontinental germanic basin and the regensburg strait the latter being an embayment of the tethys ocean that had subsided into the moldanubian zone of the central european variscides were filled with terrigenous continental marine sediments both sediments heavy mineral hm grains and aggregates have been studied in a drill section in the wackersdorf area se germany the majority of them belong to the semi opaque group of fe ti minerals in wackersdorf the entire stratigraphy of the basin fill which occurred between the triassic and the late cretaceous is well exposed in addition to the chemical composition of hm the morphology and texture of zircon apatite and fe ti compounds have been studied in a provenance related mineral classification provenance analysis has yielded five discrete source rock lithologies 1 moldanubian h t metamorphics 2 late paleozoic sub volcanic rocks 3 gneisses of the tepla barrandian unit 4 ophiolites of the tepla barrandian unit 5 silicified shear zones and quartz cores of pegmatites the detrital minerals include zircon tourmaline dravite schoerl apatite monazite ce th la nd xenotime biotite rutile ilmenite nigrine ilmenite rutile intergrowth sphene amphibole staurolite garnet and spinel cr mg al based on the allogenic ti and fe minerals a magnetite type source area eh 0 near surface felsic to intermediate sub volcanic rocks was distinguished from an ilmenite type source area eh 0 deeply eroded crystalline basement rocks gneiss granite shear zones the latter may be subdivided into nigrine i deep and nigrine ii intermediate subtypes according to the level of erosion in the source area at the jurassic cretaceous transition extrabasinal erosion provoked a noticeable variation of allogenic heavy minerals with the incisions of rivers into source rock lithologies 4 and 5 uplift and erosion along the western edge of the bohemian massif took place contemporaneously with spreading and closure in the central parts of the adjacent tethys ocean

a metamorphic history from micron scale 207pb 206pb chronometry of archean monazite ion microprobe measurements of pb isotope ratios in monazites have been obtained in situ from thin sections using the cambridge isolab 120 molecular interferences are sufficiently resolved at an rp of 6500 to allow 2 7pb z 6pb dating of monazite with precisions as low as 4 5 ma 2 r the results presented here provide important information on the chronological history of the late archean metamorphism of the wind river range wyoming usa matrix monazites and monazite inclusions in garnets from a metapelite from the northern wind river range have been analysed by sims in a previous study peak metamorphic conditions t 800 c p 8 1 kb were estimated using inclusion assemblages in garnets from this same sample isolated monazite inclusions in garnet yield 2 7pb z 6pb age estimates of 2781 6 to 2809 10 ma those along fractures yield lower ages 2603 2687 ma which are similar to tims and sims ages of matrix monazites a single large 500 xm monazite grain locally preserves growth zoning but has a recrystallised core and a resorbed recrystallised rim age estimates for these three regions are 2788 9 ma 2663 4 and 2523 6 ma respectively thus the inclusion assemblages of sharp and essene may record peak metamorphic conditions at ca 2 8 ga and indicate a phase of metamorphism that predates by over 100 ma the emplacement of the bridget batholith the major lithologic component of the northern wind river range the analysed monazite grains appear to preserve ca 300 ma history even within a single grain monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth even in high grade terranes where most chronometers are reset the age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure instead a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis

versatile monazite resolving geological records and solving challenges in materials science generalizations about monazite implications for geochronologic studies with the advent of techniques that preclude mineral separation ages from specific compositional domains in monazite ce la th po 4 have provided a wealth of information regarding the timing of the geologic evolution of numerous regions however confusion can arise when single grains show large differences in age that fail to correlate to chemistry or location within the monazite generalizations that lead to incorrect age interpretations include that monazite zoning in y th and or the rare earth elements ree always identify 1 distinct tectonic events 2 environment of crystallization and 3 provenance of detrital grains increasing th contents in monazite do not always reflect 1 increasing grade in metamorphic grains 2 changes in silicate melt composition in igneous grains 3 make the mineral more susceptible to alteration nor 4 control the mineral s uptake of ree metamorphic monazites from himalayan garnet bearing rocks with coexisting allanite show no relationship between th content and ree instead chondrite normalized ree patterns of the allanite mirror those of the monazite indicating the variations are related to the reactant that formed the mineral generalizations about pb behavior in monazite remain problematic incorporation of pb into monazite has thus far been precluded by experimental studies yet common pb has been measured in many studies of natural monazite a clear understanding about controls of monazite composition and the role of the chemical and or pressure temperature p t environment of the rocks in which it forms is required to correctly interpret the meaning of the mineral s age s

3d inversion of airborne electromagnetic data abstracttime domain airborne surveys gather hundreds of thousands of multichannel multicomponent samples the volume of data and other complications have made 1d inversions and transforms the only viable method to interpret these data in spite of their limitations we have developed a practical methodology to perform full 3d inversions of entire time or frequency domain airborne electromagnetic aem surveys our methodology is based on the concept of a moving footprint that reduces the computation requirements by several orders of magnitude the 3d aem responses and sensitivities are computed using a frequency domain total field integral equation technique for time domain aem responses and sensitivities the frequency domain responses and sensitivities are transformed to the time domain via a cosine transform and convolution with the system waveform we demonstrate the efficiency of our methodology with a model study relevant to the abitibi greenstone belt and a case study from the reid mahaffy test

monazite controlled sm nd fractionation in leucogranites an ion microprobe study of garnet phenocrysts rare earth element ree abundances in four garnet phenocrysts from two monazite bearing leucogranites from southern british columbia have been measured with an ion microprobe this study examines the effect of monazite crystallization on the lrees by using garnet as a monitor of elemental variations in the liquid this approach virtually eliminates uncertainties associated with source induced lree fractionation the garnets examined are spessartine rich alm70 75sps18 22pyp3 4grs3 4 phenocrysts that show primary igneous zoning and lack monazite inclusions garnet rims have zoning profiles i e eu to ce that are depleted by factors of five to ten relative to cores of the three models investigated to constrain processes controlling lree zoning in garnet 1 1 variations in the garnet melt distribution coefficients 2 2 liquid diffusion controlled partitioning and 3 3 crystal diffusion controlled partitioning the latter model best explains the observed zoning this model is consistent with experimental studies suggesting that monazite has a low solubility in granitic melts these results suggest that nd model ages calculated using measured 147sm144nd in leucogranites should be viewed with caution as is demonstrated by neodymium isotopic data from southern british columbia and the central nepalese himalaya

rare earth element minerals in martian breccia meteorites nwa 7034 and 7533 implications for fluid rock interaction in the martian crust paired martian breccia meteorites northwest africa nwa 7034 and 7533 are the first martian rocks found to contain rare earth element ree phosphates and silicates the most common occurrence is as clusters of anhedral monazite ce inclusions in apatite occasionally zoned irregular merrillite inclusions are also present in apatite monazite bearing apatite is sometimes associated with alkali feldspar and fe oxide apatite near merrillite and monazite generally contains more f and oh f rich region than the main chlorapatite host and forms irregular boundaries with the main host locally the composition of f rich regions can reach pure fluorapatite the chlorapatite hosts are similar in composition to isolated apatite without monazite inclusions and to euhedral apatite in lithic clasts the u th total pb ages of monazite in three apatite are 1 0 0 4ga 2 1 1 0 5ga 2 and 2 8 0 7ga 2 confirming a martian origin the texture and composition of monazite inclusions are mostly consistent with their formation by the dissolution of apatite and or merrillite by fluid at elevated temperatures 100 c in nwa 7034 we observed a monazite chevkinite perrierite bearing benmoreite or trachyandesite clast anhedral monazite and chevkinite perrierite grains occur in a matrix of sub micrometer ree phases and silicates inside the clast monazite ce and nd and chevkinite perrierite ce and nd display unusual la and ce depletion relative to sm and nd in addition one xenotime y bearing pyrite ilmenite zircon clast with small amounts of feldspar and augite occurs in nwa 7034 one xenotime crystal was observed at the edge of an altered zircon grain and a cluster of xenotime crystals resides in a mixture of alteration materials pyrite ilmenite and zircon in this clast are all highly altered zircon being the most likely source of y and hree now present in xenotime the association of xenotime with zircon low u and th contents and the low yb content relative to gd and dy in xenotime suggest the possible formation of xenotime as a byproduct of fluid zircon reactions on the basis of relatively fresh apatite grains and lithic clasts in the same samples we propose that the fluid rock mineral reactions occurred in the source rocks before their inclusion in nwa 7034 and 7533 additionally monazite bearing apatite and ree mineral bearing clasts are possibly derived from different crustal origins thus our results imply the wide occurrence of hydrothermal fluids in the martian crust at 1 ga or older which were probably induced by impacts or large igneous intrusions

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

recent changes in the freshwater composition east of greenland results from three hydrographic surveys across the east greenland current between 2011 and 2013 are presented with focus on the freshwater sources end member analysis using salinity 18o and nutrient data shows that while meteoric water dominated the freshwater content a significant amount of pacific freshwater was present near denmark strait with a maximum in august 2013 while in 2011 and 2012 the net sea ice melt was dominated by brine in 2013 it became close to zero the amount of pacific freshwater observed near denmark strait in 2013 is as large as the previous maximum in 1998 this together with the decrease in meteoric water and brine suggests a larger contribution from the canadian basin we hypothesize that the increase of pacific freshwater is the result of enhanced flux through bering strait and a shorter pathway of pacific water through the interior arctic to fram strait

repeated syn and post orogenic gold mineralization events between 1 92 and 1 76 ga along the kiistala shear zone in the central lapland greenstone belt northern finland abstract the central lapland greenstone belt clgb is well endowed with orogenic gold deposits along major shear zones and structural lineaments in the northern part of the belt the kiistala shear zone kisz hosts the suurikuusikko gold deposit kittila mine currently the largest gold producer in europe the iso kuotko deposit is located 10 km to the north of suurikuusikko along the same shear zone gold mineralization at iso kuotko formed in two major stages an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at suurikuusikko and a late main stage mineralization with free gold in carbonate quartz veins with abundant pyrrhotite native bismuth and other sulphide minerals this latter ore is absent at suurikuusikko based on u pb dating as well as re os and pb isotope systematics of rock forming and hydrothermal minerals we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late palaeoproterozoic in the northern part of the clgb results from in situ u pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by la icpms and model age calculations using re os isotopic data for arsenopyrite and in situ pb isotope data for galena from the iso kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the kisz data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault dominated n s shearing associated with early micro continent accretion ushering in the svecofennian orogeny this includes the formation of refractory gold ores at suurikuusikko 1916 19 ma and iso kuotko 1868 15 ma subordinate barren veining took place at 1830 ma during transient extension between the accretion and final collision stage xenotime in late stage veins with visible gold at iso kuotko yield u pb ages between 1761 9 and 1770 7 ma this time interval is concurrent with widespread granitoid emplacement at the close of the svecofennian orogeny disturbance of the re os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post orogenic hydrothermal system in situ u pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in paleoproterozoic orogenic systems results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the central lapland greenstone belt