American Journal of Science. The Journal’s web site is located at http: The HP pelitic granulites contain four distinct mineral assemblages: The origin of these HP granulites is important for understanding the tectonic evolution of the Jiao-Liao-Ji Belt, but the timing of the HP event still remains unknown. The oldest ages of to Ma were yielded from high-Y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite, and thus interpreted as the time of the HP M2 granulite-facies metamorphism. The youngest age group of to Ma obtained from low-Y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism M4 that occurred when the HP pelitic granulites were exhumed to the upper crust. The presence of Paleoproterozoic HP mafic and pelitic granulites in the southern segment of the Jiao-Liao-Ji Belt suggests that the evolution of the Jiao-Liao-Ji Belt in the Eastern Block of the North China Craton must have been involved in subduction- or collision-related tectonic processes.
CU Boulder â Electron Microprobe Laboratory – JEOL JXA-8230
It provides precise and accurate chemical composition for elements Be to U at the micron-scale of a large variety of solid materials such as minerals, glasses, alloys, and ceramics. The primary advantage of EMP analysis is the non-destructive and in-situ character of the analysis. All you need is a well-polished, flat sample, such as a regular petrographic thin section or an epoxy mount. EMP is the ideal technique for analyzing chemically zoned crystals, for testing a material’s homogeneity, for sampling delicately intermixed phases, or for identifying and characterizing phases chemistry, size, shape.
As it is an in-situ technique, information on texture and deformation can be preserved.
EPMA (Electron Probe Micro Analyzer) dating of monazite combining BSE (Back scattered Electron) information has been carried out on migmatite and granitoid samples from the Hercynian Belt in the French Massif Central (south of ca Ma Velay dome).
Geology of the concerned area is focused mainly on the younger granite of Gabal Gattar. Gabal Gattar represent the northern parts of a big pink granite batholith. This granite mass occurs as mountain terrain forming moderate to high relief hills, ridges and multi-peaks. It is composed mainly of younger granite forming marginal sharp intrusive contacts with the surrounding countryrocks which include; metavolcanics, diorite and Hammamat sediments Figure 3 , after Rose .
Younger granite range in colors from pale pink to pink and sometime show reddish pink color along fault planes and shear zones. They are massive, varying in grain size from coarse-grained pegmatitic texture to fine-grained, but medium-grained is the prevailing one and show few mafic minerals. Silicification, hematitization, Kaolinization, chloritization, fluoritzation and episyentization are the most common alteration features recognized along the major faults and shear zone dissected Gattar younger granites.
Pegmatites, quartz veins and aplites dykes are the most abundance encountered at the marginal parts of this granites. Dykes show variable distribution and composition in Gattar area. They represented by two main groups, the first group acidic dykes which comprising granite porphyry and granophyres dykes, while the second group represented by intermediate dykes which include basaltic and andesitic dykes.
Canadian Journal of Earth Sciences
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Furthermore, validation for age estimations for this study was performed by comparing data obtained from monazite EPMA dating of the Sukhda tuff (this study) with data obtained by Patranabis-Deb et al. from zircon grains using the SHRIMP method.
However, zircon U-Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. Documenting the composition and mineralogy of these Pb-enriched domains is essential for understanding the processes of Pb redistribution in zircon and its effects on geochronology. Using high-resolution scanning transmission electron microscopy, we show that Pb-rich domains previously identified in zircons from East Antarctic granulites are nm nanospheres of metallic Pb.
They are randomly dist However, studies of the diversity of monazite chemical compositions associated with fluid-flow at low temperatures and basinal brine circulation are scarce, due to the difficulty of isolating single monazite grain generations as representative of distinct fluid events. This study describes the chemical composition of monazite grains from permeable sandstone units in the Grinnell Formation of the Belt-Purcell Supergroup BPS , Western North America, to evaluate their efficacy as a proxy for describing the characteristics of basinal brine circulation along these regional -scale pipelines.
CU Boulder â Electron Microprobe Laboratory – JEOL JXA-8230
During analysis, a set of differing monazite standard reference materials with established isotopic ages are measured at the start of the session. These measurements are used to test the analytical set-up and, if necessary, to calculate MARC factors that can be applied to monazite samples. The MARC is not intended as a way to correct systematic errors due to problems in set-up, but rather as a fine-scale adjustment for factors that cannot be readily assessed during single sessions.
Long-term, multi-session calculation of MARC factors allows for precise monitoring of anomalous behavior among monazite age reference materials during individual sessions. The method can also assist in the identification of chemical inhomogeneity in monazite, such as that commonly produced by interaction with metasomatic fluids. Additional modifications to analytic protocols are proposed, including a corrections for count rate increases during long beam dwell times, and b improved estimation of background values at line positions by accounting for the effect of mean atomic number.
improved monazite dating by EPMA that includes a ‘monazite age reference correction’ (MARC) consistent analytical method for monazite age determination correction of Th, U, Pb and Y count-rate increase over long acquisitions.
The Chadormalu magnetite-apatite deposit in Bafq metallogenic province, Central Iran, is hosted in the late Precambrian-lower Cambrian volcano-sedimentary rocks with sodic, calcic, and potassic alterations characteristic of iron oxide copper-gold IOCG and iron oxide-apatite IOA ore systems. Apatite occurs as scattered irregular veinlets and disseminated grains, respectively, within and in the marginal parts of the main ore-body, as well as apatite-magnetite veins in altered wall rocks.
Our data suggest that hydrothermal magmatic fluids contributed to formation of the primary fluorapatite, and sodic and calcic alterations. The primary apatite reequilibrated with basinal brines in at least two regional extensions and basin developments in Silurian and Triassic in Central Iran. Introduction The formation of apatite-bearing iron deposits is a current topic of debate.
The deposits are characterized by large masses of Ti-rich to Ti-poor Fe oxides essentially magnetite and subordinate phosphates, in particular apatite, and are known as Kiruna-type magnetite-apatite e. However, the deposits are considered by other researchers e. Apatite is a common accessory mineral in a wide range of magmatic, sedimentary, and metamorphic rocks. Apatites can serve as a useful indicator mineral for IOCG- and IOA-type deposits, recording the origin and nature of the associated host rocks and the volatile contents of the ore fluids e.
The composition and crystal structure of apatite favors substitution of light rare earth elements LREE. Monazite and xenotime inclusions typically nucleate as a product of fluid-induced multi-elements redistribution within apatite e. Apatite can serve as a fingerprint for metasomatic reactions, and provides information on the temperature, composition, and nature of the fluids, as well as timing and duration of metasomatic processes [ 13 ].
Apatite chemistry can be used as a tool to investigate the nature of fluids involved in alteration-mineralization and development of REE-enriched apatite in IOA deposits.
CU Boulder â Electron Microprobe Laboratory – JEOL JXA-8230
The terrane is underlain by heterogeneous isobarically cooled orthogneisses termed the Mary batholith. A transect across the batholith documents early, penetrative subhorizontal to gently dipping gneissic foliation S1. L1 coincides with garnet aggregates, elongate mafic enclaves, and core-and-mantle structure in feldspar porphyroclasts. Lineations are coaxial with hinges of isoclinally folded layering F1.
L1 is interpreted as a composite mineral lineation with intersection and stretching components. Kinematics are uniformly top-to-the-ESE.
Electron probe microanalysis (EPMA) of accessory minerals such as monazite, xenotime, and thorite for minor- and trace-element concentrations and geochronology, requires consideration of beam irradiation effects (increasing heat and charge) as higher current densities and lengthy counting times.
Dumplin on west, Central Maine and Conant Brook on east of opposing shear sense enclosing the Monson orthogneiss. Research was designed to establish the timing of deformation to test the hypothesis that strain in transpressional systems occurs contemporaneously. An understanding of the timing of deformation in this zone could elucidate the mechanisms that formed the zone and contribute to a greater overall understanding of fabric evolution in transpressional systems.
Plutons that contain all fabrics associated with progressive transpression — lineations ranging from subhorizontal initial to steeply-plunging parallel to dip final — mark the maximum age of deformation. Ages range from Ma in the Hardwick tonalite, Wachusett tonalite, West Warren diorite, Walker Mountain orthogneiss, and Nichewaug diorite, and indicate transpression in the PZoT initiated after ca. Monazite from Rangeley paragneisses and schists selected in the context of petrofabrics and syn-deformational mineral assemblages yield U-Th-Pb EPMA chemical ages that indicate dextral transpression occurred continuously from to Ma.
Monazite chemical ages also indicate that sinistral lateral displacement in the west-bounding Mt. Dumplin high strain zone initiated ca. The data for the Central Maine zone, Conant Brook shear zone, and Greenwich syncline support the idea of contemporaneous deformation across the compartmentalized zones of a transpressive system Ma , while the ages for the Mt. Dumplin high strain zone indicate sinistral lateral displacement overlapped dextral transpression by about 10 m.
Theses and Dissertations–Earth and Environmental Sciences.
Mineralogical, geochronological, and geochemical characterization of Early Devonian aquamarine-bearing dykes of the Zealand Station beryl and molybdenite deposit, west central New Brunswick Kristy-Lee Beal, a David R. Lentz, a Douglas C. Paper handled by associate editor Victor Owen Published on the web 28 June Canadian Journal of Earth Sciences, , 47 6: A late-stage, southeast-trending, pegmatite—aplite dyke has abundant aquamarine associated with pegmatitic sections.
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The Igralishte pluton Ograzhden block, Serbo-Macedonian massif is built-up of twomica S-type granite with age of The most significant alterations of the plutonic rocks are caused by postmagmatic high-temperature alkaline K and Na metasomatism. Besides, a tectonic and hydrothermal overprint at Monazite brings clear signs of hydrothermal alteration being presented by randomly shaped relics of the mineral surrounded by pseudomorphic dispersed aggregates of secondary products.
In backscattered electron BSE images these aggregates appear as much darker areas than those of the monazite relics and contain very small lighter spots with increased content of Th, REE, Si and Y. According to EPMA data, the major part of the aggregates corresponds to apatite containing variable quantity of britholite molecule.
Advanced Search Abstract 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.
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.
These zircon dates are correlated with the timing of the following: 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 Ma pre-BM1 event , between and Ma BM1 event , and between and Ma combined BM2 and BM3 events , as part of a latest Paleoproterozoic to Early Mesoproterozoic orogenic event.
Microstructural observation and chemical dating on monazite from the Shilu Group, Hainan Province of South China: implications for origin and evolution of the Shilu Fe-Co-Cu ore district. Lithos ; accepted.
Please complete our online readership survey by clicking the button below We appreciate your comments and feedback so we can continue to improve our magazine. Nevertheless, there are only scarce geochronological data on the timing of formation for the majority of Australian uranium deposits. Because uraninite is commonly a major ore constituent of many primary uranium deposits its geochronology has the potential to provide a direct age of mineralisation.
This contrasts with other geochronological studies of mineral deposits where the age of mineralisation is based on the inference that the dated mineral such as muscovite, biotite, monazite and xenotime crystallised at the same time as the ore. Additionally, the high concentration of uranium in uraninite requires only a relatively short time period for the accumulation of significant concentrations of radiogenic lead.
To encourage exploration for uranium, Geoscience Australia researchers undertook dating of selected uranium deposits as a part of its Onshore Energy Security Program to ; Skirrow This article outlines the results from the Kintyre deposit in Western Australia and the Oasis deposit in Queensland where the timing of uranium mineralisation was directly dated using Electron-Probe Micro-analysis EPMA chemical uranium-thorium-lead U-Th-Pb uraninite analysis.
This analysis measures the natural radioactive decay of uranium and thorium to lead to measure time.