Crowley, R. Brown, F. Gervais, H. Four of the five samples are weakly deformed to undeformed, despite occurring in a gneiss dome at the structurally deepest exposed level of the orogen that elsewhere was strongly deformed and partly melted at 50 Ma. The remainder of the monazite is 50 Ma and all monazite in one sample is 50 Ma. Crystallization ages of small-volume granitic rocks e. Zircon and monazite are ideal for U—Pb dating of magma crystallization because of their moderate to high U concentrations and high closure temperature to diffusion of Pb Harrison et al. Harrison et al. Zircon from source and host rocks is not dissolved in magma that is saturated with respect to zircon, but rather is incorporated as partially resorbed xenocrysts. Small-volume granitic melts are usually produced by anatexis of peraluminous crustal rocks at temperatures low enough that complete zircon dissolution does not occur, and thus some degree of inheritance is expected in all melts.
E-mails: regiane. E-mails: rmoraes usp. E-mail: monica. A high-pressure metamorphic gradient oblique to the geological contacts is recorded in metapelitic rocks from this Nappe.
Electron probe microanalysis (EPMA) dating of monazite has been developed over decades. However, limited by the detectability and.
The wide utilization of radiometric ages for orogen analyses would not been possible without monazite and zircon that are sufficiently robust to preserve their original U and Th and accumulated radiogenic Pb even through overgrowth during high temperature geologic events. Monazite and zircon discriminate strongly against the daughter Pb during crystallization. Although the EPMA dating inherits the classic Th-U-Pb chemical dating, the CHIME method provides a significant advantage by adopting the regression-based technique that has the ability to work with minerals containing substantial initial Pb.
The age- and composition-mapping can identify two or more chronologically homogeneous domains that are separated by age gaps within a single grain. Critical comments include the chemical criteria that discriminate possibly concordant EPMA zircon and monazite analyses from discordant ones. The in-situ CHIME dating and mapping of zircon and monazite in polished thin sections coupled with compositional mapping of associate garnet has a great chronological potential for the analysis of the detailed sequence of geologic events.
Here we examine the control of major element chemistry in influencing the crystallization of monazite in granites Salihli and Turgutlu bodies and garnet-bearing metamorphic assemblages Bozdag and Bayindir nappes from the Menderes Massif, western Turkey. In S-type granites from the massif, the presence of monazite correlates to the CaO and Al 2 O 3 content of the whole rock. Granites with monazite only are low Ca 0.
As CaO increases from 2.
Evins, P. Australian Journal of Earth Sciences 54 1 , pp. These ages are particularly significant with respect to the timing of deposition, iron and gold mineralisation, and deformation in the Mt Isa inlier. The oldest age probably represents provenance from igneous rocks. In the sample, the majority of monazite growth occurred at Ma, coeval with peak metamorphism in the Eastern Succession. The low metamorphic grade of the conglomerate and wide compositional range of monazite bearing this age indicates that the monazite grew elsewhere and was later deposited in the conglomerate.
Gold is also present in some of the samples. Together, these ages bracket deposition of the Quamby Conglomerate to between ca and Ma, the latter age most likely representing diagenesis.
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Ma) geologic events. Keywords: Garnet-orthopyroxene granulite, EPMA U-Th-Pb monazite dating, Mogok Metamorphic Belt,. Myanmar. INTRODUCTION.
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Lidar offshore structural mapping of monazite crystallization ages. C for fission-track dating because of ma. Analyses of monazite using fe-epma.
To browse Academia. Skip to main content. Log In Sign Up. Download Free PDF. Janusz Lekki. Daniel Dunkley. Monika Kusiak.
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 M 2 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 M 4 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. User Name Password Sign In. This Article doi:
EPMA dating of monazite confirms the relative timing of a succession of Foliation Intersection Axis trends in porphyroblasts (FIAs) and two periods of progressive.
In EPMA, the x-ray background spectrum is mainly a result of the continuous spectrum which has a changing curvature. For applications, where element concentrations approach the minor and trace element level as with monazite microprobe dating , it is important to perform accurate background approximation. If background offsets are large and element concentrations approach the detection limit, errors introduced by linear background approximation for a curved real background can become significant.
For high-quality U-Th-total Pb dates it can therefore be important to consider the curved background and include some kind of correction see Jercinovic et al. To my knowledge, with the exception of one commercial third-party-software product, there is currently no standard procedure for this kind of background correction in EPMA.
For electron microprobe dating most people use the Pb Ma emission line of Pb, which has high intensities but suffers from line interference. I made a number of WD scans on monazite with different composition.
John Goodge, University of Minnesota-Duluth. An electron probe micro-analyzer is a microbeam instrument used primarily for the in situ non-destructive chemical analysis of minute solid samples. EPMA is also informally called an electron microprobe , or just probe. It is fundamentally the same as an SEM , with the added capability of chemical analysis. The primary importance of an EPMA is the ability to acquire precise, quantitative elemental analyses at very small “spot” sizes as little as microns , primarily by wavelength-dispersive spectroscopy WDS.
The spatial scale of analysis, combined with the ability to create detailed images of the sample, makes it possible to analyze geological materials in situ and to resolve complex chemical variation within single phases in geology, mostly glasses and minerals.
PDF (EPMA average major and trace element analyses for monazite) (electron microprobe) dating of detrital and authigenic monazite in two samples from the.
Your Name required. Your Email required. Diffusion and monazite manifested as cores with an isochron method for chemical dating by high-resolution x-ray mapping of the timor orogen represents one of western. U—Th—Pbtotal age dating of a noritic anorthosite at the electron microprobe emp dating requires measuring the chemical th—u—pb dating of monazite. A large dynamic range of detrital monazite ages of ultrahigh pressure uhp felsic rocks strongly reworked during prograde and jean-luc devidal2 1 determine.
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