The northern Wyoming province preserves a long history of tectonic activity during the Proterozoic. The details of these geological events, particularly at the NW margin, remain elusive. Geochronologic results were integrated with phase equilibria modeling in order to place constraints on the P-T-t paths. Samples from three areas across the range were investigated. The western side of the range contains Grt-Sil-Bt paragneisses and Grt-St-Crd orthoamphibolites that record protracted monazite growth between 1. Inclusions in garnet and matrix grains record similar ages. In the south-central part of the range, Grt-Sil-Bt-Ksp migmatitic paragneisses and Grt-Crd orthoamphibolites record growth at 1.
U-PB AND LU-HF GEOCHRONOLOGIC CONSTRAINTS ON THE PROTEROZOIC EVOLUTION OF THE RUBY RANGE, MONTANA
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Here we report lutetium–hafnium (Lu–Hf) mineral ages on eclogites from the Alps as obtained by plasma-source mass spectrometry. We find that.
Jingao Liu, D. Alard, O. Project : Research. N2 – Highly depleted Archean peridotites have proven very amenable to Re-Os model age dating. In contrast, due to the increasing heterogeneity of mantle Os isotope compositions with time, the Re-Os system has not been as effective in dating post-Archean peridotites. The timing of depletion and accretion of post-Archean lithospheric mantle around cratons is important to understand within the context of the evolution of the continents.
In an attempt to precisely date post-Archean peridotite xenoliths, we present a study of the petrology, mineralogy and geochemistry, including whole-rock Re-Os isotopes, highly siderophile elements and clinopyroxene-orthopyroxene Sr-Nd-Hf isotopes of peridotite xenoliths from Lake Nyos in the Cameroon Volcanic Line CVL. Eight Nyos peridotite xenoliths, all fresh spinel lherzolites, are characterized by low to moderate olivine Fo contents However, trace element patterns of both clinopyroxene and orthopyroxene are not a pristine reflection of melt depletion but instead show various extents of evidence of metasomatic enrichment.
Because of these metasomatic effects, the Sr-Nd isotope systematics in pyroxenes cannot sufficiently reflect melt depletion signatures. Unlike Sr-Nd isotopes, the Lu-Hf isotope system is less sensitive to recent metasomatic overprinting. The reconstructed Nyos Lu-Hf isochron from ortho- and clinopyroxenes gives an age of 2.
With regards to the origin of the CVL, our data reveal that the Hf isotopic compositions of the Nyos peridotites are too radiogenic to be the main source of the CVL basalts.
Lu-Hf Dating: The Lu-Hf Isotope System
Anczkiewicz, R. Lu-Hf geochronology and trace element distribution in garnet: Implications for uplift and exhumation of ultra-high pressure granulites in the Sudetes, SW Poland. Lithos , 95 pp. The surrounding rocks were metamorphosed at the same time as indicated by The second metamorphic episode, which affected most of the lower crust in the Orlica-Snieznik Massif OSM occurred at ca.
Keywords: Gondwanan magmatism, Geochemistry, U-Pb SHRIMP dating, Lu-Hf isotope, NW Argentina. Abstract. 1. Introduction. A long and discontinuous.
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Hf-w dating Iowa
Kimberlites from Southern Africa, along with their low-Cr megacrysts, have unusual Hf—Nd isotopic characteristics. Group I kimberlites have Hf values varying from —1. Low-Cr megacryst suites from individual Group I kimberlites have compositions that overlap those of their host kimberlites.
This research will develop and refine the technique of dating lawsonite by the Lu/Hf method. Lawsonite forms at distinct pressure and temperature conditions.
Subduction zones are places on the Earth where dense ocean crust descends or subducts beneath more buoyant continental or oceanic crust. Active subduction zones are responsible for most of Earth’s large earthquakes and explosive volcanic eruptions. Ancient subduction zones now exposed at the Earth’s surface provide important information on the processes, both physical and chemical, occurring within active subduction zones.
Determining the timing and rates of past events in these ancient subduction zones, however, has proven extremely difficult. This proposed research will develop a new technique to determine ages on lawsonite, an important mineral that forms during metamorphism associated with subduction zones. Dating lawsonite, therefore, provides geologists the ability to determine the timing and rates of ancient subduction processes.
Lawsonite forms at distinct pressure and temperature conditions during the metamorphic history of a rock. The Franciscan Complex contains Lawsonite-bearing rocks that are of similar metamorphic age but that preserve different metamorphic histories. These rocks also contain both garnet and epidote, making the Franciscan Complex an ideal place to examine lawsonite growth with respect to these minerals.
The Sivrihisar Massif contains garnet and lawsonite-bearing rocks that formed under a large range of pressures and temperatures and is therefore ideally suited to compare the relative closure temperatures of Lu and Hf in garnet and lawsonite. The dating will be combined with quantitative thermodynamic models to directly relate the ages to the metamorphic history of a given sample.
The results of this study can be applied to other lawsonite-bearing localities and will further develop this powerful tool for dating subduction zone metamorphism.
Extending In-Situ Dating to New Geochronometers: Pb-Pb, Sm-Nd, Re-Os, and LuHf
Brouwer , M. Groen, O. Nebel, J. Wijbrans , H.
Molybdenite Re–Os, zircon U–Pb dating and Lu-Hf isotopic analysis of the Xiaerchulu Au deposit, Inner Mongolia Province, China. PDF version. GEOSCIENCE.
Peter D. Reviews in Mineralogy and Geochemistry ; 53 1 : — As a significant carrier of uranium, thorium and the rare earth elements REEs at ppm level, and hafnium at the percent level, zircon hosts a remarkable number of long-lived radioactive isotopes and their stable decay products. These include U, U and Th which decay via intermediate steps to Pb, Pb and Pb, respectively, Lu which decays to Hf, Sm which decays to Nd, and La which undergoes branched decay to Ce and Ba.
This combination makes zircon one of the most versatile minerals available to the geochronologist Shibboleth Sign In. OpenAthens Sign In. Institutional Sign In. Sign In or Create an Account. User Tools.
Thorsten J Nagel
The Lu-Hf isotope system, with applications to geo- and cosmochemistry, was first investigated in the early s Patchett b ; Patchett and Tatsumoto a, b , c , following the successful implementation of the Rb-Sr and Sm-Nd isotope systems several years earlier. There are some obvious similarities between the Lu-Hf and Sm-Nd isotope systems and, as a result, they have long been used in concert in a wide range of studies e.
In these two systems all elements are lithophile and refractory with high condensation temperatures. Because of these characteristics it has long been assumed that their abundances in the Earth can be approximated by chondritic meteorites see discussion below. In addition, all elements in these systems behave incompatibly during melting and are concentrated in the melt over the residual solid.
Therefore, it’s not surprising that Lu-Hf dating is yet another target for the wrath of young-Earth creationists. Nevertheless, the only response that Woodmorappe.
Author contributions: T. Yet the data interpretation requires a well-defined hafnium isotope growth curve of the bulk Earth, which is notoriously difficult to reconstruct from the variable bulk compositions of undifferentiated chondrite meteorites. Here we use lutetium—hafnium systematics of meteorite zircon crystals to define the initial hafnium isotope composition of the Solar System and further to identify pristine chondrites that are the best representative of the lutetium—hafnium system of the bulk Earth.
Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess Hf due to the accelerated decay of Lu resulting from photoexcitation to a short-lived isomer. Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.
Initial Hf isotope ratios in meteoritic samples as a function of age. Thus, meteorite zircon would provide the most direct and robust Hf isotope record of the early Solar System 1.