Fielding, S. Johnson, J. Zi, B. Rasmussen, J. Muhling, D. Dunkley, S. Sheppard, M.
Finally, the Amherst team investigated in detail the technical issues of electron microprobe monazite dating. They showed that the best analytical procedures must include at least: detailed chemical mapping, several interference corrections and special care for background measurements. With this machine, high precision ages can be obtained on well characterized individual grains in thin section, giving birth to a new era in geochronology of complex metamorphic rocks.
The Th-U-total Pb data collected by the EPMA for monazite have also been used to estimate the timing of its re growth by assuming no common Pb and no Pb-loss or by constructing a chemical isochron Cocherie et al. REE-Th-U and Nd isotope systematics of monazites in magnetite- and ilmenite-series granitic rocks of the Japan arc: Implications for its use as a tracer of magma evolution and detrital provenance.
Monazite [ Ce, La, Th PO4], a common accessory mineral in low-Ca felsic rocks and a wide range of metamorphic rocks, is suitable for in situ U-Pb dating, rare earth element REE geochemistry, and Nd isotope tracer studies. To link monazite composition with igneous petrogenesis and differentiation, we carried out comprehensive LA-ICP-MS measurements of REE-Th-U abundances and Sm-Nd isotope ratios in monazites from magnetite-series oxidized type and ilmenite-series reduced type granitic rocks across the Japan arc.
The data revealed systematic differences in monazite composition between magnetite-series and ilmenite-series samples, and between pegmatites and granites.
These geochemical variations were attributed to significant fractional crystallization of feldspars, monazite, xenotime, and garnet during differentiation in relatively reduced peraluminous granitic magmas. In contrast, there was no remarkable difference in the REE fractionation pattern between magnetite-series pegmatites and granites. Furthermore, the magnitudes of the negative Eu anomalies in the magnetite-series monazites were smaller than those observed in the ilmenite-series samples. These features were interpreted to reflect the suppression of monazite, xenotime, and garnet fractionation and limited Eu incorporation into fractionating feldspars in relatively oxidized and non-peraluminous magmas.
In addition, our data demonstrated intra-grain variations in REE-Th-U compositions in a monazite from the Masaki ilmenite-series pegmatite, despite its homogenous Nd isotope composition. These variations suggest that the core and rim of the grain crystallized from distinct magmas that were generated from similar crustal rocks, but were differentiated under different conditions.
A comparison of the present data with previously reported data indicates that igneous monazites from granitic rocks are distinct from a wide range of metamorphic monazites in REE-Th-U composition, especially due to their larger negative Eu anomalies.
This finding highlights the potential utility of monazite REE-Th-U systematics as a provenance indicator for detrital monazites. For background measurement of Pb Ma line, the exponential background fit was adopted to the curvature of the background values Jercinovic and Williams, ;Williams et al.
Geochemistry and chemical dating of uraninite in the Samarkiya area, central Rajasthan, northwestern India - Implication for geochemical and temporal evolution of uranium mineralization. Dipak C Pal T.
Xenotime is also known to be diagenetic: It may form as minute grains or as extremely thin (less than 10 µ) coatings on detrital zircon grains in siliciclastic sedimentary rocks. The importance of these diagenetic xenotime deposits in the radiometric dating of sedimentary rocks is only beginning to be thefoodlumscatering.comry: Phosphate minerals.
The present study aims to appraise the geochemical and temporal evolution of uranium mineralization from the basement and the adjoining supracrustals in the Samarkiya area integrating textural features, geochemistry, and in situ U-Th-PbTotal dating of uraninite.
Modified after Hiroi, The CHIME method has contributed to constraints on the structural-metamorphic-magmatic history of various terranes e. Timing and duration of regional metamorphism in the Kagasawa and Unazuki areas, Hida metamorphic complex, southwest Japan.
The granite intrusions into the Hida gneiss occurred at two different stages Ma and Ma and thermally affected the Hida gneiss. In the Unazuki area, situated at the northeast margin of the Hida metamorphic complex, a quartzo-feldspathic schist and a biotite granite containing a quartzo-feldspathic schist as xenolith yielded U-Pb zircon ages of The similarity between the geochemical compositions in whole rocks and zircons of the quartzo-feldspathic schist and the granite suggests that felsic volcanics were deposited on basement rocks at Although the time interval between protolith formation and post-peak regional metamorphism in the Unazuki area 0.
Ma is similar to that in the Kagasawa area Mathe different timing of the regional metamorphism indicates that the protolith of the Unazuki metasediments was deposited not on the proximal Hida metamorphic complex but on ancient rocks containing Eoarchean-Paleoproterozoic components of the North China Craton.
Ranchin analyzed uraninite in granite by using electron microprobe, and calculated the chemical ages of the uraninite through the results of U, Th, and total Pb contents. Since then, electron microprobe dating method on U-bearing minerals such as zircon, monazite and uraninite have been extensively studied Suzuki, ;Parrish, ;, Suzuki et al. In this study, age calculation of uranium minerals was calculated by the program ChemAge of Geisler Isotope geochronology, geochemistry, and mineral chemistry of the U-bearing and barren granites from the Zhuguangshan complex, South China: Implications for petrogenesis and uranium mineralization.
Monazite often contains significant quantity of thorium and uranium, while the amount of initial Pb is little compared to radiogenic Pb Williams et al. Mar Toshiaki Tsunogae. We use this setting to explore the evolution of monazite grain size, texture and composition, and variations in the whole-rock composition of eleven metapelite, metapsammite or metachert samples collected along the metamorphic field gradient. Monazite grain size increases with rising metamorphic grade, regardless of the whole-rock composition.
A succession of four compositional domains is recognized in monazite. In the highest-grade sample, zircon grains included in garnet or cordierite show metamorphic rims with sillimanite and Si-rich inclusions.
Monazite dating by electron microprobe and laser-ablation-mass-spectrometry reveals two age groups. When the Pb concentrations are near the detection limits, a considerable error arises on the ages Jercinovic et al.
In shear zones within Paleozoic and older orogens, monazite ages can record a polyphase evolution with several age generations below T c conditions and even involving the protolith history Shaw et al. Geochronology of shear zones - A review. Shear zones play a major role in the deformation of the crust at a variety of scales, as expressions of strain localization during orogeny and rifting, and also as reactivated structures.
They influence the geometry and evolution of orogenic belts and rifts, crustal rheology, magma ascent and emplacement, and fluid flow. Consequently, assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere. The interpretation of thermochronologic data from shear zones is, however, not straightforward.
In the first place, closure temperatures depend on a number of factors grain size, cooling rate, mineral composition and pressure, among others. On the other hand, deformation-related processes such as dynamic recrystallization, neocrystallization and fluid circulation seem to be crucial for isotopic systems and, thus, the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks.
For this reason, geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo- or recrystallization, fluid-assisted deformation and inheritance of the protolith age s. In addition, geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications. One of the most challenging cts that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored cts of isotopic diffusion, particularly the coupling with deformation processes, based on natural, theoretical and experimental data.
Future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks. The currently available data may be biased or may not encompass the actual compositional range for a particular rock type. For example, monazite trace element data have been less commonly reported than major element data, because most monazite studies have used electron microprobe techniques for geochemical characterization and chemical Th-U-total Pb isochron method CHIME dating  .
Furthermore, the application of other classification techniques, such as random forest, support vector machine, and sparse multinomial regression, would also be an interesting avenue for future research .
Feb Detrital monazite geochronology has been used in provenance studies. However, there are complexities in the interpretation of age spectra due to their wide occurrence in both igneous and metamorphic rocks. We use the multinomial logistic regression MLR and cross-validation CV techniques to establish a geochemical discrimination of monazite source rocks. The elemental abundance-based geochemical discrimination was tested by selecting 16 elements from granitic and metamorphic rocks.
We applied the discrimination model to detrital monazites from African rivers. The detrital monazites were mostly classified as granitic and of garnet-bearing metamorphic origins; however, their proportion of metamorphic origin was smaller than the proportion that was obtained by using the elemental-ratio-based discrimination proposed by Itano et al. Considering the occurrence of metamorphic rocks in the hinterlands and the different age spectra between monazite and zircon in the same rivers, a ratio-based discrimination would be more reliable.
Nevertheless, our study demonstrates the advantages of machine-learning-based approaches for the quantitative discrimination of monazite. Nov Schulz Joachim Krause Robert Zimmermann. Electron microprobe petrochronology of monazite-bearing garnet micaschists in the Oetztal-Stubai Complex Alpeiner Valley, Stubai.
Monazite dating in metapelites is an emerging method to investigate polymetamorphic areas. In this part, metabasites are alternating with metapelites. The micaschist samples with diverse modal compositions and variable bulk rock Ca contents of calculated assay, display distinct monazite microstructures, as quantified by automated SEM-MLA mineral liberation analysis routines.
Clusters of small monazite could indicate new crystallization and yielded isochrones at and Ma. In contrast, corona structures of apatite and allanite around large monazites with isochrones between and Ma suggest a decomposition during decreasing temperature.
Garnets in metapelitic assemblages display growth zonations with low pyrope contents in the cores and pyrope-rich rims. The P-T path entered the monazite stability field during the decompression. This signals a Carboniferous age of the metamorphism.
A minor population in one sample is composed of sporadic Permian single monazite ages. A Cretaceous monazite population is lacking.
In the wide parts of the Austroalpine basement with Carboniferous-to-Cretaceous mica mixing ages, monazite age populations allow to discriminate a distinct Permian metamorphic event. Dec Contributions to Mineralogy and Petrology, 52, 2, CHIME dating of monazite, xenotime, zircon and polycraseProtocol, pitfalls and chemical criterion of possibly discordant age data.
Gondwana Research, 14, Monazite and xenotime solubility in hydrous, boron-bearing rhyolitic melt. Monika Rusiecka D. In the presence of sufficient phosphorous, the concentration of LREE needed for monazite saturation is within uncertainty of the Y concentration needed from xenotime saturation and indicates that in the case of equilibrium crystallization the mineral that forms will only depend on the availability of LREE and Y and HREE.
Given the similarity of the solubility of xenotime to that of monazite, we propose that previously published models of monazite solubility in silicic melts can potentially be applied to xenotime, and could, like monazite, serve as a geothermometer. In the case of disequilibrium crystallization in front of rapidly growing crystals, Y will diffuse faster than LREE and xenotime will only crystalize when LREE are depleted.
We also found that the diffusion of Y is greater than diffusion of P from dissolving xenotime, unlike the similar diffusivities of LREE and P during monazite dissolution. The significant difference between Y and P diffusivities suggests that the components forming xenotime diffuse as separate entities rather than molecular complexes. The dissolution of phosphates monazite, xenotime, apatite in hydrous, silicic melts with addition of boron leads to liquid-liquid immiscibility at high temperatures where the saturation values of P and either light rare earth elements or Y are in the weight percent range.
Immiscibility is not observable at low, magmatic temperatures, most probably due to the lower concentrations of P2O5 necessary for phosphate saturation at these conditions, however addition of other components, notably F, may result in liquid-liquid immiscibility at magmatic temperatures. Keywords: monazite solubility, xenotime solubility, silicate melts, LREE diffusion, Y diffusion, liquid-liquid immiscibility.
Detrital monazite from Upper Jurassic sediments in the central part of the Frolov megadepression, Western Siberia: chemical dating and provenancesFig. Location of the studied wells within the West Siberian plate. Grains of detrital monazite in the matrix of Upper Jurassic sedimentary rocks of the Frolovsky megavpadin. The weighted average age of the detrital monazites from the Upper Jurassic deposits of the Frolovsky megavpadin.
May Detrital monazite from Upper Jurassic sediments in the central part of the Frolov megadepression, West Siberian megabasin, is studied. Chemical composition of the mineral is studied and data on its age chemical dating are presented. Most monazite clasts are characterized by low roundness and their age corresponds to the Lower Paleozoic. Upper Jurassic sediments were likely derived not only from the local Early Paleozoic rock complexes altaideswhich make up the pre-Jurassic basement of the Frolov megadepression, but also from rocks located east and south of this megadepression.
Errors in absolute ages in the range of Ma for each run are typically within the error limits obtained worldwide, suggesting a reasonable treatment scheme Cocherie et al. Ages were calculated using a modified version of Isoplot 3. Igor Likhanov M. The tectonic evolution of the Siberian Cratonic margins offers important clues for global paleogeographic reconstructions, within the complex continental collage of Central Asia.
Here we report the occurrence of A-type granites with geochemical features indicating intraplate setting from the Yenisey Ridge and provide evidence for rift-related magmatism. The magmatic events at Ma and - Ma along the western margin of the Siberian Craton and other continental blocks can be associated with the breakup of the Precambrian supercontinents Nuna-Columbia 1.
These pre-Grenville and post-Grenville episodes of regional crustal evolution are correlated with the synchronous successions and similar style of rocks along the Arctic margin of Nuna-Columbia and Rodinia and supports the spatial proximity of Siberia and North Atlantic cratons Laurentia and Baltica over the long period 1.
Our data confirm the proposed Neoproterozoic paleogeographic reconstructions of Columbia and Rodinia as constrained from the large igneous province LIP record. The spot age of individual analysis was computed using the formulae of Montel et al.
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. 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. 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. 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. 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.
Pseudotachylite veins having an age of 1. The Salem-Namakkal blocks thus recorded a longlived 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.
The concept of radiometric dating by determining the concentration of U, Th and Pb has been described previously by many authors e. The concept relies on two major assumptions i monazite behaves like a closed system, and ii absence of non-radiogenic lead in monazite or at least very little of it. Consistency in the geochronological data of the monazites from the geochronologically well-constrained high grade metamorphic terrain of Bundelkhand craton, north central India, confirms the reliability of the BHU-EPMA facility for the U-Th-Pb geochemical dating of monazite.
The EMP monazite dating technique has been a popular method for some time e. The provenance of sediments in western Taiwan has been the subject of debate in recent years. Previous investigators, solely based on the U-Pb zircon geochronology for the detrital grains, all advocated the important roles, but with varying emphasis, of drainage systems in the South China Block.
Influence of the Changjiang Yangtze River from the far-source Yangtze block versus nearby systems like Zhujiang, Minjiang and Jiulongjiang Rivers in the Cathaysia block has been the main issue. However, the fundamental question of whether the provenance is really the South China Block has never been evaluated.
Here we report both the U-Pb zircon and Electron MicroProbe EMP monazite age data for seven sediment samples from two sides of the Taiwan Strait and synthesize the published data for all these rivers and sedimentary strata in western Taiwan to tackle this problem.
With reference to the tectonic evolution of the coastal southeast China-Taiwan region during Early Cretaceous to recent time, we propose a new explanation that invokes a now-concealed microcontinent along the Manila Trench. It then drifted away sometime after Ma and split into two parts with one becoming today's Palawan-Mindoro terrain of the Philippines. Both the Peikang and Kuanyin basement highs in the offshore western Taiwan represent the unsubducted remnants of this microcontinent and also the major suppliers of Late Oligocene-Miocene sediments in western Taiwan.
On the other hand, the Eocene-Early Oligocene strata of the Hsuehshan Range in central Taiwan show both zircon and monazite age patterns resembling the Eocene-Early Oligocene and recent sediments of the Zhujiang drainage system, indicating the southwestern origin of the protolith Taiwan. This scenario also matches the recent proposition that part of the Central Range belongs to the deep-level accretionary prism of a Miocene subduction system. Mylonitized quartz-biotite schist, Metasediments, PPL.
Neoproterozoic arc sedimentation, metamorphism and collision: Evidence from the northern tip of the Arabian-Nubian Shield and implication for the terminal collision between East and West Gondwana.
Ahmed S. Abu Sharib Ayman E. The metasediments bear the geochemical signature of a first depositional cycle in two distinct continental island arc settings that derived from incipiently-to moderately-weathered intermediate to felsic sources under generally warm and humid conditions.
The metapelitic succession records three distinct episodes of metamorphism, M1-M3, whereas the molasse-type succession records only the last metamorphic episode, M3.
M3 is a hornblende hornfels facies thermal metamorphism related to the intrusion of the post-orogenic, Neoproterozoic The silicon concentrations were also determined to assess the validity of the in-situ titanium concentration as the measurement of a low silicon would imply the unexpected analysis of fluid inclusion in quartz cf.
Suzuki and Kato, An abrupt decrease in the silicon intensity would demonstrate the decomposition of the quartz crystal due to the electron beam. Crystallization processes of quartz in a granitic magma: Cathodoluminescence zonation pattern controlled by temperature and titanium diffusivity. Quartz from a granitic pluton is found to have formed through sequential growth events under different mechanisms and crystallization temperatures, which can provide new insights into magmatic processes of granitic magmas that were eventually consolidified into plutons.
The events were identified using 1 the description of crystal shape and occurrence, 2 the study of the internal structure with cathodoluminescence CLand 3 derivation of the crystallization temperatures based on TitaniQ thermometry. The magmatic quartz crystals from the Toki granite, central Japan, are characterized as having the following internal structures: oscillatory zonation, no-oscillatory zonation with luminescence gradation gradational zonationand heterogeneous CL.
The CL zonation pattern was controlled by the temperature conditions and titanium diffusivity in the melt magma. The crystallization process of quartz within the Toki granite reveals the cooling processes of the granitic pluton; the lithofacies with a high frequency of oscillatory-zoned quartz underwent slower cooling under the OZT conditions than those in other lithofacies. Hrinchenko S.
Bondarenko T. Composition of granites, genetically associated pegmatites and superimposed metasomatites distributed within Shpoliano-Tashlyk ore area Ingul megablock is considered. It is established, that on the basis of similarity in their petrographic and petrochemical features granitoids of the area can be related to single complex.
Features of ore mineralization are defined by both composition of granitoids Sgranites after which rare-metal pegmatites are formed and intensity of superimposed metasomatic alterations. Depending on geological setting such ore minerals as tapiolite, ixiolite, cassiterite, uraninite, nigerite, gahnite are commonly found in association with these minerals.
Chemical composion of tantalo-niobates sampled from ore-bearing pegmatites and metasomatites is investigated by microprobe analysis.
Most minerals of columbite-tantalite series are characterized by distinct and rhythmic internal zonality and contrasting mosaic structure which are related to considerable heterogeneities of their chemical composition.
Scandium ores occur as scandium-rich minerals that are mostly confined to the minerals of columbite-tantalite series found in Polohivka ore field. On the Ukrainian Shield high contents of Sc2O3 in tantalo-niobates are established for the first time. Minerals of ilmenorutile-struverite series do not quantitatively yield to minerals of columbite-tantalite series. Minerals of pyrochlore-microlite series are of subordinate importance. Dicton Saikia. U-Th-Pb total age determinations in monazite in a noritic anorthosite at the margin of the Koraput anorthosite pluton constrain the time of emplacement and sub-solidus chemical modifications in the Grenvillian-age anorthosite pluton in the Eastern Ghats Province EGPIndia.
Based on the textural-chemical heterogeneities, these monazites are classified into three groups. The U-Th-Pb total chemical ages obtained using electron probe microanalyses exhibit four age clusters. Vera Vital'evna Khiller K.
Ivanov Yuriy Viktorovich Erokhin. This work is made relevant by the necessity to improve chemical dating methods, when applied to high atomic and thorium zircons, for which isotopic methods cannot be used. The purpose of the work is to study the chemical composition of the accessory zircon cyrtolite from granitic pegmatites in the north-eastern part of the Aduisky massif in the Middle Urals and determine how best to date it.
According to the microprobe analysis, the impurity content of ThO2, UO2 and PbO in the zircon varied significantly, within the ranges 0. The dating calculation was carried out for each mineral in which the analysis took place. Their age was found to be between and Ma. Dating calculations show that veined pegmatites and host granites were formed almost simultaneously at least, in this part of the Aduisky massif.
This situation justifies microprobe dating of the U-Th zircon content because the minerals are usually in a metamict state and not suitable for accurate age determination. It comprises two plutons, Nikeiba basement rock complexes and Fileita Nubian sandstone. It is composed of metavolcanics, syenogranite, alkali feldspar granite and quartz syenite intruded by felsite and dolerite dikes and quartz veins at Nikeiba plutons which non-conformable overlain by Nubian sandstones at Fileita area.
Purpose of the work. The present work of this paper is to elucidate the interaction between inherited ductile fabrics and overprinting brittle structures. It is important to reconstruct the tectonic evolution of Wadi Road El-Sayalla area which help in constraining the mineralization trends in the study area.
Research methods. The folding related to ductile structures were analyzed using stereographic projection software packages GE Orient version 9.
The fracture analyses related to brittle structures were carried out quantitatively using the paleostress analyses of the different sets to calculate the tensors related to the different compressional and extensional events using Tensor program. E2: Late-tectonic granite; upright folding episode associated with compression and shortening to the NE-SW direction.
E3: Post-tectonic granite intrusion episode produced syenogranite and alkali feldspar granite of Nikeiba. Accessories as thorite, uranothorite, monazite, zircon, allanite, yttrocolombite and fluorite appear to be structurally controlled by the interaction between inherited ductile fabrics and overprinting brittle structures.
Vladimir Ponomarev Vera V. Khiller Yuriy Viktorovich Erokhin. Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex amphibolite facies, NE-striking and the Yunkai Group greenschist facies, NW-striking of this massif and adjacent undeformed granites.
Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at - Ma and - Ma, respectively. They also yield ages of - Ma for core domain gneissic granites and - Ma for undefomed granites.
Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic 1. Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited.
With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province E-LIP. Suzuki M. Mineralogical and radiometric studies of monazite and sphene occurrences in the Namib Desert, South-West Africa.
Burger O. Von Knorring T. Microprobe analysis of REE minerals using empirical correction factors. Microprobe analyses of zircons in some granitic rocks with special reference to the distribution of uranium. Suzuki S. A study of inherited and newly formed zircons from paragneisses and granitised sediments of the Strona-Ceneri-Zone Southern Alps.
Tanaka M. Santosh K. Yokoyama Alan Stephen Collins. We report U-Pb electron microprobe ages for zircon and monazite from two granitic plutons from southern India, the Vattamalai granite within the Palghat-Cauvery Shear Zone system and the Pathanapuram granite within the Achankovil Shear Zone.
Monazites from the Vattamalai granite show a small range of ages between S20 Ma. PbO vs. Monazite cores from the granite lie in the range of Ma, whereas rims and bright overgrowths range from Ma. These monazites define two linear arrays in PbO vs. The age data from the granite plutons indicate multiplethermal imprints in southern India with the latest orogeny during the Late Neoproterozoic-Cambrian Pan-African.
The older zircon cores up to Ma from the Pathanapuram pluton suggest inherited components of late Mesoproterozoic age, caught up within the granite magma. However, the dominant Ma ages obtained from both zircons and monazites closely compare with similar ages for magmatism and metamorphism from throughout the East African Orogen.
Late Neoproterozoic-Cambrian felsic magmatism occurred along both the Palghat-Cauvery Shear System and the Achankovil Shear Zone, indicating that these shears were active at this time and may have served as pathways for the emplacement of magmas generated at depth.
The magmatism represents part of the various collisional-extensional episodes that marked the final amalgamation of the Gondwana supercontinent. Discordant distribution of U and Pb in zircon of Naegi granite: A possible indication of Rn migration through radiation damage. Kazuhiro Suzuki. The Pb content of some portions in each grain is equivalent to what has been generated by the radioactive decay of co-existing U and Th since the granite crystallization, but other portions evidently show either deficient or excess Pb with respect to the U and Th contents.
The granite has not undergone any thermal event after the intrusion. The Pb-deficiency and -excess arc explained in terms of Pb-loss and -gain owing to the migration of gaseous daughters Rn through radiation damage. The Rn atoms that entered into a network of radiation damage by recoil at the birth can move at random: they are adsorbed for a moment on the walls of radiation damage, and then re-emitted in random directions. Their residence time on the walls depends on the heat of adsorption which increases with increasing number of irregular sites on the walls, so that Rn atoms tends to decay on irregular walls as compared with smooth walls.
This process disturbs the distribution of radiogenic Pb, and brings forth the enrichment and depletion of Pb with respect to the U and Th contents of zircon. Isotopic ages of zircon from granites and pegmatites. Tilton G. Davis G.
The younger age of xenotime growth at ca. Ma, obtained from multiple grains, is attributed to a second, discrete hydrothermal event, probably dating emplacement of the ankerite-quartz veins, and is within uncertainty of xenotime rims in the auriferous quartz-sulfide vein (GSWA ).Cited by: Jul 02, Diagenetic xenotime is common in siliciclastic sedimentary rocks, where it starts to form on detrital zircon shortly after sediment deposition. It is possible to estimate the age of sedimentary rocks by in situ uranium-lead analysis of that xenotime. Two Proterozoic sandstone units from northwestern Australia, previously constrained to the age interval of to million years ago, have Cited by: Nov 06, More details on the dating protocol are described in Takahata et al. Matrix effect could affect the accuracy of in-situ monazite and xenotime U-Pb dating due to variations of U and Th (Fletcher et al., , Li et al., ). The accuracy of monazite U-Pb dating using NanoSIMS at AORI had been carefully evaluated in Sano et thefoodlumscatering.com: Yung-Hsin Liu, Der-Chuen Lee, Chen-Feng You, Naoto Takahata, Yoshiyuki Iizuka, Yuji Sano, Chuanming.
Wetherill L. Joseph D. Geller Charles Herrington. Reducing the measurement uncertainty of quantitative analyses made using electron probe microanalyzers EPMA requires a careful study of the individual uncertainties from each definable step of the measurement. Those steps include measuring the incident electron beam current and voltage, knowing the angle between the electron beam and the sample takeoff anglecollecting the emitted x rays from the sample, comparing the emitted x-ray flux to known standards to determine the k-ratio and transformation of the k-ratio to concentration using algorithms which includes, as a minimum, the atomic number, absorption, and fluorescence corrections.
This paper discusses the collection and counting of the emitted x rays, which are diffracted into the gas flow or sealed proportional x-ray detectors.
The representation of the uncertainty in the number of collected x rays collected reduces as the number of counts increase. The uncertainty of the collected signal is fully described by Poisson statistics. Increasing the number of x rays collected involves either counting longer or at a higher counting rate.
Counting longer means the analysis time increases and may become excessive to get to the desired uncertainty. Instrument drift also becomes an issue. Counting at higher rates has its limitations, which are a function of the detector physics and the detecting electronics. Since the beginning of EPMA analysis, analog electronics have been used to amplify and discriminate the x-ray induced ionizations within the proportional counter.
This paper will discuss the use of digital electronics for this purpose. These electronics are similar to that used for energy dispersive analysis of x rays with either Si Li or Ge Li detectors except that the shaping time constants are much smaller. Precambrian provenance and Silurian metamorphism of the Tsubonosawa Paragneiss in the South Kitakami Terrane, Northeast Japan, revealed by the chemical Th-U-total Pb isochron ages of monazite, zircon and xenotime.
Kazuhiro Suzuki Mamoru Adachi. Data points are arrayed linearly and enable us to define an isochron which passes through the origin. The chemical Th-U-total Pb isochron ages coincide well with mineral and whole-rock ages isotopically determined for the same samples.
The chemical Th-U-total Pb isochron method was applied to the age determination of monazite, zircon and xenotime from the Tsubonosawa paragneiss and the host Hikami granite in the South Kitakami terrane of Northeast Japan. The Ma event corresponds to the intrusion of the Hikami granite, and the Ma one to the intrusion of the Cretaceous Kesengawa granite. The and Ma events may correspond in age to the main metamorphic event and subsequent igneous activity in the Hida terrane, central Japan.
The chemical Th-U-total Pb isochron age in terms of the precise microprobe analysis of low-level Th, U and Pb will open a new vista on the Paleozoic-Mesozoic tectonics of the Japanese Islands.
The intra-grain distribution of rare earth elements REEs in coexisting apatite, monazite, xenotime and zircon was determined by electron microprobe for a sample of Cretaceous Busetsu Granite, Okazaki, Japan.
The REE distribution suggests that these accessory minerals did not originate as a restite component, but crystallized successively from magmatic melt despite of their possible cotectic relationships. The crystallization sequence is early zircon and euhedral apatite, followed by monazite, xenotime and anhedral apatite.
The REE distribution in these accessory minerals is closely related to the sequence of their crystallization. The successive appearance and disappearance of accessory minerals in the crystallization sequence are explained in terms of deviation from cotectic saturation levels owing to kinetic crystallization from the supersaturated melt. Any laboratory that does not meet these standards has had difficulties adopting the CHIME dating method.
We have developed a working standard technique for CHIME dating to prepare standard materials without use of nuclear fuel materials. Mineral samples, such as small pieces of monazite that are homogeneous in X-ray intensities, are calibrated using well-characterized primary standards in one laboratory.
Once this procedure is done, they can be readily usable as working standards in the other laboratories, only with measurement of X-ray intensities. This method is applicable in preparing standard materials for both chemical compositions and determination of X-ray interference correction factors, and it is independent from chemical composition of mineral standard.
Differential REE uptake by sector growth of monazite. Cressey F. Wall B. Monazite- Ce from a dolomite carbonatite at Kangankunde, Malawi, is sector-zoned with variation in La2O3 of up to 6. Single crystal X-ray diffraction, backscattered electron imaging and microprobe analysis have been used to establish the relationship between the morphology and sector chemistry of this low-Th monazite, Ce,La,Nd PO4.
There appears to be a distinct relationship between the size of the REE ion and the probability of uptake via the different growth surfaces. Interpretation of this uptake behaviour, based on theories involving 'protosites', involves an investigation of the possible kink site geometries at edge-steps during growth.
The overall morphology and sector growth is suggested to be a function of uptake chemistry. Steiger, R. Subcommission on geochronology: convention of the use of decay constants in geo- and cosmochronology.
Earth Planet. Steiger E. Dieter Rhede I. Wendt H. Previous theoretical considerations on the chemical U-Th-total Pb dating method failed to distinguish between thorogenic and uranogenic lead.
The U-Th-Pb and (U-Th)/He dating methods applied to apatite, monazite, and xenotime have as their basis the decay series of the long-lived isotopes of uranium, U and U, and of thorium, Th. These decay at a known rate through a series of short-lived radionuclides ultimately to Pb isotopes. Anushka 22 Private Escorts Bandra, Mumbai. Hi dear, My name is Anushka, a 22 Dating Xenotime years old bachelorette in Mumbai. I am extremely hot and Dating Xenotime a co-operative girl with a cute smiling face. Do you want to see passionate personalities to give you complete relaxation from your hectic schedule?/ The Xenotime+dating solution is to dress nice, appear charming and funny, be completely honest about your intentions and be Xenotime+dating ready to spend like a drunken sailor. The hard truth is that women know exactly what you want and they are not going to give it up Xenotime+dating for free/
The method described in this paper is applied to monazites from the Hercynian G4-granite of the Fichtelgebirge Germany. The intercept value close to zero indicates that no significant amounts of common lead are present in the monazites studied.
Grain-boundary enrichment of incompatible elements in some mantle peridotites. Whereas both rocks contain an appreciable amount of K2O, P2O5 and TiO2, the constituent minerals contain only trace amounts of these elements.
Microprobe analyses across the grain boundaries on polished sections and on mineral surfaces before and after acid leaching show that most of the incompatible elements in the rocks are contained within a surface film. It could be an adsorbate on the irregular sites of crystal surfaces, and was probably formed by any of: diffusion from interiors of minerals i.
The contribution of incompatible elements from the grain boundaries into partial melts has been documented by heating experiments on peridotite chips under controlled fo2. Grain boundaries are an important storage of incompatible elements in peridotites and they in turn can be the dominant source of these elements in magmas during partial melting of the upper mantle. Bence Arden Albee. Joseph M. Four distinct generations of monazite growth have been identified in samples from the Chesham Pond Nappe, and three monazite compositional domains 2, 3, and 4 have been correlated with both temperature and mineral assemblage.
Domain 1 cores were interpreted previously to be detrital relics or vestiges of an earlier Acadian metamorphism. Temperature-time paths calculated with monazite ages and monazite thermometry indicate that 1 plutonism at ca. Monazite ages in the Chesham Pond Nappe and adjacent structural units to the west constrain the commencement of nappe overthrusting to roughly Ma.
New Accurate Bence-Albee? Takenori Kato. A new a-factor table for the Bence-Albee correction method of quantitative electron microprobe analysis is presented for an accelerating voltage of 15 W and a take-off angle of 40 degrees. The a-factors were calculated from the full PAP correction with least squares fitting in the range 0.
Recently determined mass attenuation coefficients were chosen. X-ray intensities were calculated for binary oxide-oxide, oxide-anion and anion-anion systems. The new a-factor table improves the accuracy of the Bence-Albee method compared with previous studies, and provides results as accurate as the full PAP correction when absorption is not large. Ages based on electron microprobe analysis using the chemical Th-U-total Pb isochron method CHIME were determined for monazite and zircon in 12 granulite-facies paragneiss samples from four exposures on or near the coast of East Antarctica: Mt.
Monazite occurs in textural equilibrium with silicate minerals in all samples and as inclusions in garnet in three of these and is presumed to have crystallized under granulite-facies conditions. Most of the analyzed monazite grains appear to be chronologically homogeneous, but many others are markedly zoned. The Neoproterozoic ages on monazite cores suggest the intriguing possibility that the area between 45degrees E west of Alasheyev Bight and 25degrees E within the Sor Rondane Mountains constitutes a Cambrian monometamorphic belt in which sediments were deposited during the Neoproterozoic or early Cambrian with much less involvement of older rocks; i.
The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings.
Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with wt.
High concentrations of Rb ppmSr - ppmBa - ppm and Zr ppmwith low concentrations of Y mostly. Analyzed monazite is characterized by mosaic zoning rather than simple core-to-rim growth, and strontium contents of up to ppm.
Contrasting ages between isotopic chronometers in granulites: Monazite dating and metamorphism in the Higo Complex, Japan. Daniel J Dunkley K.
Suzuki Monika A. Kusiak Tomokazu Hokada. The Higo Complex of west-central Kyushu, western Japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south, where granitoids are emplaced along the southern margin.
The timing of granulite metamorphism has been extensively investigated and debated. Previously published Sm-Nd mineral isochrons for garnet-bearing metapelite yielded ca. Ion and electron microprobe analyses on zircon have yielded detrital grains with rim ages of ca.
Electron microprobe ages from monazite and xenotime are consistently - Ma. Two models have been proposed: 1 high-grade metamorphism and tectonism at ca. These models are evaluated through petrographic investigation and electron microprobe Th-U-total Pb dating of monazite in metapelitic migmatites and associated lithologies. In-situ investigation of monazite reveals growth and dissolution features associated with prograde and retrograde stages of progressive metamorphism and deformation.
Monazite Th-U-Pb isochrons from metapelite, diatexite and late-deformational felsic dykes consistently yield ca. Earlier and later stages of monazite growth cannot be temporally resolved.
The preservation of petrogenetic relationships, coupled with the low diffusion rate of Pb at. Neoproterozoic alkaline magmatism at Sivamalai, southern India. U-Pb TIMS dating of zircon from a pegmatitic syenite sample in the complex yields a concordant age of The Pan-African high-grade metamorphism and ductile deformation has thus most likely affected the alkaline rocks.
This is supported by the presence of a metamorphic foliation and extensive recrystallisation textures seen in the rocks. The major and trace element concentrations measured on selected samples reveals the presence of both enriched and depleted rock types.
The enriched group includes ferrosyenite and nepheline syenite while the depleted group has only nepheline syenites. The trace element depletion of some nepheline syenites is interpreted to be a result of fractional crystallization involving the removal of accessory phases like zircon, titanite, apatite and allanite.
Rogers M. Yokoyama S. We report age data on zircon, monazite, uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern India using an electron microprobe technique. The rocks analysed in this study cover all of the major lithounits in these terrains and include garnet-bearing and garnet-free charnockites, garnet-biotite gneisses, khondalites, calc-silicate rocks, and a suite of orthogneisses biotite gneiss, biotite-hornblende gneiss.
Two pink metagranites representing the magmatic phase were also analysed. Zircons from the Madras Block yield well-defined isochrons at 2.
Core to rim analyses of single zircon grains show age zoning with 2. Detrital zircons show age up to ca. Monazites in this block have cores and rims with 2.
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A suite of 19 samples from the Madurai Block brings out the multiple tectonothermal events in this terrain. Zircons from an orthogneiss yield well-defined isochrons at 1.
Zircon grains in other rocks preserve either core or secondary growth ages at 0. Zircons in a pink metagranite from this block show sharply defined isochrons of 0.
A late Pan-African overprint is observed throughout this block with zircon rims, monazite, uraninite and huttonite yielding age values in the range of 0. Zircons from both the Trivandrum and Nagercoil blocks show a major tectonothermal event at 0.
Monazite data from both the Trivandrum and Nagercoil blocks are essentially similar to those from the Madurai Block except for presence of relic monazite in the former.
An improved U-Th-Pb age calculation for electron microprobe dating of monazite. The method is rapid and reliable, both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization.
The main limitation of the method is its rather poor precision, i. With complex polygenetic monazite, in which either the points show large scattering indicated by a large MSWD or the regression line exhibits a slope very different from neighbour theoretical isochrons, the procedure must be applied separately on homogeneous domains only.
Several examples are given to illustrate these systematics. Age dating of individual grains of uraninite in rocks from electron microprobe analyses. It is shown that an electron microprobe analysis of the U, Th and Pb content of a single uraninite UO2 grain may be used to calculate the age of formation of that grain.
This is known as a chemical age. Examples are shown for a range of natural samples with a wide range of ages. Comparison with ages derived from isotopic measurements shows the results to be valid. Approximate formulae which have been proposed for the calculation of the chemical age are not sufficiently reliable, especially where the Th content is high and for older ages.
A method for calculating the age by iteration is presented; this uses the full and exact formula and is shown to produce a reliable age for the uraninite compared to isotopic measurements.
The method is particularly useful for samples where the minerals and mineral textures record information on more than one event. Two examples of samples recording information on dual ages are discussed to show how these ages can be related to events in the formation of the host rocks.
In one example an alluvial heavy-mineral concentrate is shown to contain uraninites from two distinct sources with significantly different ages. In the other example two phases of U mineralisation are distinguished in the same rock sample; one phase relates to the genesis of the sediments from which the rock was formed; the second phase records remobilisation of the U during later tectonic movement.
Yokoyama M. Zircons from six granitoid plutons, occurring in the northern part of the Delhi Fold Belt, NW India, have been chemically dated using an electron microprobe. Most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1. Monazite and zircons from the metasediments of Delhi Supergroup adjacent to the granitoids were also analyzed.
The older age of 1. The geochemical signatures of these granitoids are consistent with an extensional tectonic regime. The new geochronologic information on these granitoids in the northern part of the Delhi Fold Belt and their comparison with other correlative events establishes a widespread thermal event during late Paleoproterozoic. Middle Precambrian provenance of Jurassic sandstone in the Mino Terrane, central Japan: Th-U-total Pb evidence from an electron microprobe monazite study.
Other grains show the ratio of about 0. The ratio of 0. Gold is rarely observed in hand specimen in the Upper zone, but petrographic studies show that early gold forms rounded inclusions within pyrite crystals and displays simple monocrystalline twinned microstructures with silver contents of 8. A second phase of gold formed along fractures and at grain boundaries where the pyrite is brecciated.
This style of gold is typically associated with chalcopyrite and pyrrhotite, and has a lower silver content, ranging from 6. The stylolites and wall-rock inclusions are associated with abundant free gold Fielding and Stokes,with silver contents between 6. Proximal to the Paulsens mineralization, regional-scale greenschist facies metamorphic assemblages are overprinted by a hydrothermal alteration assemblage that is associated with gold mineralization.
Primary mineral assemblages within the Paulsens gabbro are almost entirely replaced, with plagioclase altered to muscovite, and pyroxene replaced mainly by ankerite but with patches of muscovite-quartz-ankerite.
Iron oxide minerals, possibly originally ilmenite and titanomagnetite, have been totally altered to leucoxene. Alteration distal to the orebody is difficult to differentiate from the regional metamorphic background; however, a change from ankerite to calcite along with an increase in.
They share many characteristics of Paulsens, but have not been subject to the same degree of deformation, which allows more straightforward determination of timing relationships between ore formation and the regional geologic history. Gabbro Offset is located m southwest of the main Paulsens orebody and consists of a series of parallel quartz-carbonate-sulfide veins within the Paulsens gabbro.
Mineralized veins are typically narrow, usually between 0. Petrographic examination of pyrite from samples GSWA from Gabbro Offset reveals two styles of native gold inclusions within the pyrite. Rounded blebs of native gold and chalcopyrite within the cores are interpreted to be primary inclusions Fig. The pyrite is locally brecciated, and chalcopyrite, pyrrhotite, and gold occur along fractures and pyrite grain boundaries Fig.
Although there is some evidence for gold remobilization from the rounded gold inclusions in the cores of pyrites at a local scale Fig. Paulsens East mineralization is located approximately 1 km east of the main Paulsens orebody Fig. Mineralization is hosted within parallel, steeply NE dipping, 1- to 5-m-wide veins comprising quartz, carbonate, and oxidized sulfides that are hosted within the Melrose argillite on the northern side of the Hardey fault.
The Paulsens deposit exhibits many of the characteristics of a typical orogenic gold deposit. Orogenic gold deposits form in the upper to middle crust in compressional tectonic settings related to accretionary or collisional orogenesis and tend to have a close spatial relationship to transcrustal structures which mark the boundaries between continental blocks Groves et al.
Host rocks are varied, with Archean deposits commonly formed in volcanic-dominated sequences and Paleoproterozoic and Phanerozoic deposits formed in siliciclastic sequences Goldfarb and Groves, Unlike other styles of mineralization e. Paulsens has many of these traits: a spatial relationship to the mantle-tapping Nanjilgardy fault, siliciclastic sedimentary host rocks that have been metamorphosed to greenschist facies, the high-grade nature of gold mineralization average 8.
A list of dated samples is provided in Table 1. Appendix 1 describes the methodology in detail. Detrital zircons were separated from sedimentary host rocks using standard magnetic and density techniques. Zircons, together with zircon reference materials BR and OGCwere cast in mm epoxy mounts and polished to expose the interiors of the crystals. Each mount was gold coated and characterized using transmitted light, reflected light, and cathodoluminescence CL images Fig.
U-Th-Pb analysis of monazite, xenotime, and baddeleyite was conducted in situ in order to preserve textural context.
Grains for analysis were identified using a scanning electron microscope SEM in polished thin sections, and 2- or 3-mm-diameter plugs were extracted from the polished thin sections with a hollow-core rotary drill and mounted in mm-diameter epoxy discs. The mounts were cleaned and gold coated before each analytical session. Reference materials were set into separate mounts and gold coated simultaneously with sample mounts. Standard and sample mounts were loaded together into the SHRIMP for concurrent analysis during each analytical session.
Detrital zircons from two Hardey Formation sandstone samples Table 1 were dated to provide a maximum depositional age for the supracrustal rocks into which the Paulsens gabbro was emplaced.
GSWA -quartz sandstone, Hardey Formation: Medium-grained, strongly cleaved, quartz sandstone of the Melrose argillite member of the Hardey Formation was collected from The zircons range in age from ca.
GSWA -quartz sandstone, Hardey Formation: Medium- and fine-grained quartz sandstone, with very fine grained matrix, from the Melrose argillite member was collected from the hanging wall to the Gabbro Offset deposit from drill core PLDDW1 between GSWA -altered dolerite, Paulsens gabbro : A finegrained, dark-colored portion of the Paulsens gabbro that is host to the Gabbro Offset deposit was collected from The outer surfaces of baddeleyite grains are commonly altered to very fine grained aggregates of zircon Fig.
Seventeen analyses were made of 11 baddeleyite grains. These veins are part of the Gabbro Offset deposit and share similarities to Paulsens Upper zone mineralization. A massive sulfide vein was sampled for geochronology Table 1the lower 10 cm of which contained xenotime. The sample is associated with gold grades of 21 ppm, with gold formed as rounded inclusions within pyrite crystals Fig. The sample comprises an interlocking assemblage of quartz and pyrite, and contains xenotime in a number of textural settings: as euhedral grains enclosed entirely within pyrite Fig.
Commonly, the matrix xenotime grains are chemically zoned, showing core and rim growth structures Fig. Eighty analyses were made on 37 grains, with multiple analyses performed within or across single grains.
Irrespective of age or site of analysis, uranium and thorium contents range from to ppm and 2 to ppm, respectively. Twenty-six analyses of euhedral xenotime grains entirely enclosed within pyrite grains or as core zones of matrix xenotime present along brecciated pyrite grain boundaries Fig. We interpret these two dates to represent times of xenotime growth and subsequent dissolution- reprecipitation during two discrete periods of hydrothermal activity. The first event at ca. The second date at ca.
Assays from depths between and m returned up to 48 ppm Au. Seven analyses were made on seven xenotime grains. Uranium and thorium contents vary from to ppm and to 1, ppm, respectively. There are no textural or chemical differences between this grain and the others analyzed. The older xenotime date corresponds with the age of monazite in the altered host gabbro GSWA a and is interpreted to be inherited from the hydrothermally altered host rocks.
The younger age of xenotime growth at ca. GSWA -carbonaceous phyllite, Hardey Formation: Very fine grained, black, carbonaceous, quartz-muscovite-chlorite phyllite of the Melrose argillite member was sampled from drill core PDU between The sample contains randomly distributed, 1-mm-long, elongate porphyroblasts consisting of intergrown monazite and apatite, in equal amounts, with lesser chlorite and quartz. It is possible that the apatite has replaced monazite, a common reaction during greenschist to amphibolite facies metamorphism and hydrothermal alteration Finger et al.
However, it is not clear whether the monazites are primary metamorphic or hydrothermal porphyroblasts or whether they replaced former regional-scale peak-metamorphic porphyroblasts such as andalusite?
Monazite within two porphyroblasts was analyzed, with five spots on each. Uranium and thorium contents are to ppm and 2, to 10, ppm, respectively.
These two analyses are not considered to be geologically significant and were not included in the age analysis. This date is indistinguishable from that obtained on xenotime interpreted to date the timing of emplacement of the auriferous quartz-sulfide vein GSWA This sample is located 1 m above gabbro sample GSWAwhich yielded a baddeleyite crystallization age of ca.
Eight analyses were made of five monazite grains. Uranium and thorium contents are 30 to ppm and 15, to 55, ppm, respectively. Among the eight analyses, one indicates high common Pb and is excluded. This age is indistinguishable from that obtained from hydrothermal monazite in sample GSWA and the age of xenotime cores in the auriferous quartz-sulfide vein GSWA GSWA -carbonaceous phyllite, Hardey Formation: A fine-grained, strongly foliated, black carbonaceous muscovite phyllite of the Melrose argillite member was sampled from drill core PDU between The sample also contains elongate porphyroblasts up to 3 mm long comprising intergrowths of monazite and florencite in subequal amounts with lesser quartz and chlorite.
In this sample, it appears that the monazite is partially replaced by florencite, which is common during greenschist facies metamorphism Rasmussen and Muhling, However, it is unclear if the growth of monazite is related to low-grade metamorphism and deformation associated with fault reactivation or if it has locally replaced former regional-scale peak metamorphic porphyroblasts such as andalusite [?
Twenty-two analyses were made on three monazite grains within the porphyroblasts. Uranium and thorium contents vary from 50 to ppm and 3, to 14, ppm, respectively.
This date is interpreted as the age of monazite growth during hydrothermal alteration of the carbonaceous phyllite, possibly during fault reactivation. GSWA, and -micaceous phyllites, Hardey Formation: Fine-grained and slightly weathered phyllites were collected from shallow adits at Paulsens East Table 1 in a 0.
Samples and contain large monazite grains up to 3 mm long, intergrown with minerals that define the main hydrothermal alteration assemblage muscovite, quartz, and pyrite; Fig.
The quartz-sulfide veins yielded rock-chip assays up to 6. Sixteen analyses were made on seven monazite grains. Uranium and thorium contents of the samples varied from 30 to ppm and to 5, ppm, respectively. This date is interpreted to represent the timing of hydrothermal alteration associated with the emplacement of the auriferous quartz-sulfide veins at Paulsens East and is within uncertainty of ages of hydrothermal monazite from altered samples at the Gabbro Offset deposit GSWA and a as well as ages of xenotime cores from the auriferous quartz-sulfide vein at Gabbro Offset GSWA Samples GSWA and also contain abundant 1- to 3-mm-long, elongate porphyroblasts of interlocking monazite-florencite Fig.
Fifteen analyses were made on three monazite porphyroblasts. Uranium and thorium contents vary from to 1, ppm and to 8, ppm, respectively. Because sample GSWA also contains abundant, coarse-grained ca. SHRIMP U-Th-Pb geochronology has been used to define the age of the host rocks to gold mineralization at the Gabbro Offset deposit, as well as the timing of regional-scale hydrothermal activity associated with the emplacement of the auriferous quartz-sulfide veins and subsequent regional-scale hydrothermal events Fig.
Sedimentary rocks of the Hardey Formation were deposited between ca. The detrital zircon data presented here from two quartz sandstone samples from near the middle of the Hardey Formation Melrose argillite have relatively similar detrital age modes Fig.
Despite these differences, the similarity in age modes at ca. The crystallization age of the Paulsens gabbro suggests it may have been a feeder to mafic volcanic horizons in the to Ma Jeerinah Formation Trendall et al. These grains only occur within the quartz matrix or at the margins of brecciated sulfide grains, suggesting that this date represents a second period of hydrothermal alteration during which ca. Gold mineralization at Gabbro Offset is present in two distinct forms: 1 as rounded inclusions within euhedral pyrite grains Fig.
Because the euhedral pyrite is intergrown with and contains euhedral grains of xenotime dated at ca. However, where the pyrite is locally fractured or brecciated, containing flakes of free gold Fig. This suggests that these rocks were subjected to a secondary hydrothermal event responsible for the brittle deformation of pyrite grains, xenotime dissolution, and reprecipitation, and either the local remobilization Fig. This indicates that this second hydrothermal event was also responsible for the emplacement of gold-bearing ankerite-quartz veins.
A study on the mineralogy and chemistry of gold at the main Paulsens lode indicates that the youngest phase of gold mineralization is also associated with free gold with elevated Hg and Ag which formed in pyrite fractures and along stylolites Hancock and Thorne,indicating a commonality between the youngest gold mineralizing event at the main Paulsens lode and the secondary event at the Gabbro Offset deposit.
Our in situ dating of monazite and xenotime at the Paulsens deposit has identified three discrete hydrothermal events at ca.
The first hydrothermal event at ca. The timing of the mineralizing hydrothermal event ca. However, cryptic events, including the growth of monazite in phyllitic rocks across the Pilbara region from Whim Creek in the north to Mt. Tom Price in the south Rasmussen et al. The age of monazite growth decreases progressively southward Rasmussen et al.
Tom Price, located km to the east of the Paulsens deposit Rasmussen et al. In the Pilbara region, the cause of this cryptic event is currently unknown, but indirect evidence for a tectonic event at ca. A study of detrital zircons from the matrix of the Meteorite Bore Member of the Kungarra Formation in the to Ma Turee Creek Group indicates that they were sourced, together with abundant rhyolite clasts, from the to Ma Woongarra Rhyolite Blake and Barley, ; Takahara et al.
In the Hardey syncline, from where the samples were taken, the Woongarra Rhyolite is situated 1, m stratigraphically below the Meteorite Bore Member, implying at least to 1, m of uplift and erosion of sedimentary rocks along the southern Pilbara margin between ca.
Our data show that this event was associated with the emplacement of quartz-sulfide veins during extensive hydrothermal activity and gold mineralization at Paulsens Fig. However, we note that this event is within uncertainty of dextral strike-slip faulting and hydrothermal gold mineralization at the Mt. This hydrothermal event appears to have been responsible for the local brecciation and fracturing of pyrite grains in the quartz-sulfide vein and for the local remobilization of gold Fig.
However, it is possible that this event was also responsible for the introduction of new gold precipitated as free gold in pyrite fractures and within stylolites at the main Paulsens lode Hancock and Thorne, This event is coincident with medium- to high-grade metamorphism, deformation, and magmatism during the to Ma Mangaroon Orogeny Sheppard et al.
Colorado Monazite - Xenotime
Rasmussen et al. Tom Price iron ore mine. The structural effect of this event at Paulsens is not known, but may have resulted in the reactivation of preexisting faults, such as the Nanjilgardy and Hardey faults.
Importantly, we find no evidence for hydrothermal activity related to either the to Ma Ophthalmia Orogeny or the to Ma Capricorn Orogeny. This is surprising because these events played a significant role in the tectonic evolution of the region elsewhere in the southern Pilbara craton and northern Capricorn Orogen Young et al.
Our results reveal a significantly different and more complicated low-temperature tectonothermal evolution for the southern Pilbara region than had been thought. Previous studies e. Results from this study show that two gold mineralizing events occurred at Paulsens. Primary gold mineralization at Paulsens was much older, occurring at ca. However, uplift, erosion, and hydrothermal activity throughout the Pilbara craton may reflect a previously unrecognized orogenic event at ca.
The second gold event, at ca. Recognition of a new orogenic event has important implications for exploration targeting of orogenic gold deposits in the northern Capricorn Orogen. Previously, rocks affected by the Capricorn Orogeny, up to and including the Ashburton Formation, were considered the most prospective for orogenic gold mineralization similar to that at Paulsens.
However, we have demonstrated that the primary mineralization at Paulsens, which shares many of the characteristics of orogenic gold deposits, occurred at ca. Therefore, older rocks of the Fortescue and Hamersley groups are more likely candidates to host significant gold mineralization similar to that at Paulsens.
The second gold event occurring at ca. This event, at least locally, caused the remobilization of preexisting gold, but may also have been responsible for the introduction of new gold along these mantle-tapping structures.
Nevertheless, the age constraints for mineralization at Paulsens differ from those proposed by Young et al.
For exploration of orogenic gold, it is critical to have an understanding of the distribution of mineralization through both space and time. In situ geochronology of monazite and xenotime has important implications for exploration targeting by providing absolute ages for orogenic gold mineralization and allowing mineralization to be linked to specific orogenic events.
EPMA U-Th-Pbtotal dating in U- and Th bearing minerals (e.g., monazite, zircon, and xenotime) is a low-cost and reliable technique used for retrieving age information from detrital, diagenetic and. Xenotime Dating thefoodlumscatering.com we are committed to providing you with the best selection of local Shemales, TS, TV, CD, transvestites, transgender, TS Girls, Cross Dresser and ladyboy escorts that are driven to make Xenotime Dating sure you are satisfied with the time you spend together and strive to ensure that your experience is one that / It used to Xenotime Dating be so hard for me to get laid - until I found MeetnFuck. Honestly, I didn't want to tell my friends about this site, but after I fucked my local bank teller in a Starbucks bathroom, I /
In turn, this allows explorers to minimize their exploration search area by targeting the most prospective tectono-thermal events and host stratigraphy. This research is part of a Ph. We thank NSR for samples and for permission to publish, and A.
White, D. Huston, and an anonymous reviewer for their helpful comments. Analytical methods for U-Pb zircon geochronology are described in detail by Wingate and Luand only a summary is provided here. Data were collected in sets of six scans, with reference standards analyzed after every five sample analyses.
Count times per scan for Pb isotopesbackground positions U-Th-Pb ratios and absolute abundances were determined relative to the BR standard zircon Ma, ppm U; Stern,analyses of which were interspersed with those of unknown zircons. Measured compositions were corrected for common Pb using nonradiogenic Pb and contemporaneous Pb composition according to the terrestrial Pb evolution model of Stacey and Kramers Background counts from scattered ions were reduced using a flight retardation lens, which is known to cause slight sessiondependent IMF of Pb isotopes.
Data were collected in sets of eight scans, with monazite, xenotime, or baddeleyite reference material analyzed every four to six sample analyses. Count times per scan for Pb isotopesbackground position Baddeleyite was analyzed using the conventional zircon 9-peak run table, calibrated against baddeleyite reference material Phalaborwa Heaman and LeCheminant, Monazite was analyzed with a peak run table as defined in Fletcher et al.
Xenotime was analyzed with a 9-peak run table following analytical protocols in Fletcher et al. Raw data from analyses on baddeleyite, monazite, and xenotime were processed using the SQUID 2 add-in v. Matrix effect corrections were made for all monazite and xenotime data using procedures described by Fletcher et al. Regional geologic setting of the northern Capricorn Orogen, showing the location of the Paulsens gold mine.
Local geologic map of the northwest corner of the Wyloo Inlier, showing the location of the Paulsens, Gabbro Offset, and Paulsens East deposits. Coordinates are in meters MGA94 zone Lithostratigraphic column and chronology of events for units in the northern Capricorn Orogen. Lithostratigraphic column, ages, and depositional environments for the Fortescue Group adapted from Thorne et al.
Schematic vertical cross section of the Paulsens deposit adapted from Fielding and Stokes, Viewed southeast with no vertical exaggeration.