The regions north, south, and east of the Grand Canyon host hundreds of solution-collapse breccia pipes . Six decades of exploration across the region has found that most of these breccia pipes are not mineralized or substantially mineralized, and only a small percentage of the breccia pipes contain ore-grade uranium deposits. The mineralized breccia pipes contain concentrations of uranium, arsenic, copper, silver, lead, zinc, cobalt, and nickel minerals , which is reflected in the data sets of Van Gosen and others . An earlier-published data release provides the geochemical analyses of 63 elements for 35 drill core samples of the Canyon deposit that were collected by the USGS. X-ray diffraction analyses were performed on 28 of these samples to examine their mineralogy; the raw XRD data are provided in Van Gosen and others . In addition to the XRD analyses, ore mineralogy was also determined by examinations of thin sections of 21 of the ore samples using a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS).
Dacites and rhyolites may be the result of further fractional crystallization of basaltic andesites (high-Al basalts) and andesites. Mixing of magmas at various stages along the fractionation course of basaltic andesites (high-Al basalts) toward rhyolites promotes the trend of the calc-alkaline series. 1.7(gros+andr)5spes5.6alm87.7 and pyr1.2(gros+andr)5.5spes6.7alm86.6, respectively. These compositions in a sillimanite-garnet-muscovite migmatite are pyr4(gros+andr)2.7spes2.7alm90.6 and pyr2.7(gros+andr)4spes3.2alm90.1, respectively. We used this information to decipher the P-T evolution of the rocks applying P-T and T-H2O pseudosections with the PERPLE_X computer software package taking into consideration deformational microstructures.
Although, the accuracy on measured ages obtained using EPMA is considered to be poor compared to isotopic ages, the superior spatial resolution, ability to integrate textural and age information by in-situ measurement, lack of sample damage and easier and cheaper data generation in EPMA make chemical dating a very valuable tool to decipher diverse petrological processes. Graduate rather than the total numbers and it is pleasing to note that there is growing evidence of first class products in the Faculties. There have been two Rhodes Scholars in a matter of several years, but other awards of significance are also coming to light. This data release compiles the electron microprobe spot analyses of U, Th, and Pb concentrations in uraninite particles, and corresponding calculated age determinations, measured in samples of ore from two uranium-copper breccia pipe ore bodies, the Canyon and Hack II deposits.
Likewise, high Ca/Al melts will saturate clinopyroxene earlier than low Ca/Al melts and their crystallization may provide an explanation for high Mg# clinopyroxene in oceanic gabbros. The newly calibrated geobarometer gives lower crystallization pressures for MORB at the slow-spreading SWIR than previous calibrations, but still suggests relatively higher pressures of crystallization with decreasing spreading rate. As mentioned above, the pseudosections described in the previous section were contoured by isopleths relevant to constrain the metamorphic P-T paths or crystallization conditions of the analyzed samples (Fig. 11a–c). 2-foliation, demonstrated by deformational microstructures, occurred during the exhumation of the studied area from depths of ~18km to ~8km in the time interval 2.01–1.90Ga.
Electron Microprobe Analysis of REE in Apatite, Monazite and Xenotime: Protocols and Pitfalls
Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, Massachusetts 01003, U.S.A. Williams M L, Jercinovic M J, Harlov D E, Budzyń B and Hetherington C J 2011 Resetting monazite ages during fluid-related alteration; Chem. Ni Y, Hughes J M and Mariano A N 1995 Crystal chemistry of the monazite and xenotime structures; Am.
Towards Synthesis and Usage of Actinide-Bearing REE Phosphate age Standards: A Progress Report
The leucogranite records an isothermal decompression from 5.3 to 3.8kbar at 665°C. The garnet-biotite migmatite was exhumed from 5.5kbar at 630°C to 4.3kbar at 615°C and the sillimanite-garnet-muscovite migmatite from supersolidus conditions of 670°C and 3.6kbar to 625°C at 2.4kbar. Of India and Director, NCESS, Thiruvananthapuram for providing funds and unconditional support to carry out the work. They are also thankful to Dr V Nandakumar, and Dr J K Tomson for their cooperation during the journey.
Contrasted monazite alteration and mechanisms and their geochemical implications
Finally, a date cannot be interpreted as an age without the proper context, and several key factors in the interpretation are discussed and illustrated with several case studies. We obtain the compositions of the Archean lower crust of the North China Craton based on the Archean Wutai-Jining section by compiling the average tonalite–trondhjemite–granodiorite components, average mafic granulite components, and average gcruise can’t edit profile sedimentary rock components. The modeling results show that the generation of high-Al basalts, basaltic andesites and andesites can be attributed to assimilation by high-Mg basalts of relatively high-Al2O3 thickened lower crust and the subsequent crystallization of prevailing mafic mineral phases, while Al2O3-rich plagioclase crystallization is suppressed under high-pressure and nearly water-saturated conditions.
NS was involved in setting up the EPMA laboratory at NCESS, Thiruvananthapuram and devised the conceptual ideas to design the study. NCP gave critical feedback to setup the monazite protocol more accurately. NS, NCP and AD provided critical feedback and helped to shape the research, analysis and manuscript. Montel J M, Foret S, Veschambre M, Nicollet C and Provost A 1996 Electron microprobe dating of monazite; Chem. The change in the stability field of clinopyroxene in mid-ocean ridge basalt as a function of pressure has been used widely as a geobarometer. Based on results from crystallization experiments using MORB-like compositions it has been suggested that MORB differentiation occurs at relatively high pressures at ultraslow- and slow-spreading ridges.
Suzuki K and Adachi M 1991 The chemical Th–U–total Pb isochron ages of zircon and monazite from the Gray Granite of the Hida terrane; Japan Earth Sci. Spear F S, Pyle J M and Cherniak D 2009 Limitations of chemical dating of monazite; Chem. The Canyon mine sample (CMCH A) yielded generally consistent age results whether spots were divided by textural type or lumped together. Only those analyses from uraninite as inclusions in chalcopyrite had unusual scatter, possibly due to Pb loss to the sulfide host. The full CMCH A data set provide a remarkably consistent estimated date at 118.0 ± 4.5 million years ago with a mean square of weighted deviates of 0.35 based on 44 of 47 measurements .
By applying the same analytical setup of chemical dating, the monazites from metapelites of Madurai Block of Southern Granulite Terrain, India yield two peak ages in probability density diagram of ca. 590 Ma which is similar to the 206Pb/238U age (ca. 506 Ma and ca. 585 Ma; 34 spots) obtained by LA-ICPMS. The successful elucidation of the formation of modern orogenic belts can be a complex task because an interdisciplinary approach from different fields of geosciences is required. The study of cratonized ancient orogenic belts can be even more complex because after collision of terranes and exhumation of enormous volumes of upper crustal rocks much more information is lost compared to very young orogens.
This latter significantly improves the accuracy of minor and trace element analysis in complex matrices, as demonstrated by the analysis of Rare Earth Elements in REE-silicates and phosphates and of trace elements in scheelite. Major and trace element analyses of monazite by electron probe microanalyzer are routinely carried out for several decades. U–Th–total Pb method of monazite dating is currently considered as a reliable and acceptable tool to decipher the time of geological events. The purpose of the present study is to establish the quantification conditions of monazite chronology using SXFive tactis EPMA, recently installed at the National Centre for Earth Science Studies, Thiruvananthapuram, India. Consistency in the chemical-chronological data of the monazites starting from the chronologically well-constrained Maocyr monazite data followed by the analysis of monazite from the garnet-cordierite gneiss of the Kerala Khondalite Belt confirms the reliability of the NCESS-EPMA facility for the U–Th–total Pb chemical age dating of monazite.