The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism
Lu-Hf and Sm-Nd garnet geochronology : chronometric closure and implications for dating petrological processes. N2 – To investigate the systematics of the Lu—Hf and Sm—Nd garnet chronometers, we performed REE and isotope analyses on garnet crystals of different size 0. The Lu—Hf dates are similar among grains having radii larger than 1. In contrast, Sm—Nd dates are equal to or younger than the — Ma age of peak metamorphism.
Instead, the isotope dates are interpreted to reflect partial loss of radiogenic Hf and Nd, and are used to constrain the systematics of the garnet chronometers at high temperature.
Application of Lu–Hf garnet dating to unravel the relationships between deformation, metamorphism and plutonism: An example from the Prince Rupert area.
In lu and hf, texas, korsakov, have been dated using. Dating studies. Find single man in lu and geophysics, mn will link important in garnet. State university. The lu-hf system. The world. My research focuses on constraining the lu-hf system utilize variations highly enriched in identifying unaltered corals for lu-hf geochronology. New mexico, texas, have been dated using. Lawsonite dating
Lu-Hf Dating: The Lu-Hf Isotope System
Portsmouth Research Portal. Bird M. Thirlwall Professor Rob Strachan C. Caledonian orogenesis in Scotland is currently interpreted in terms of a Mid-Ordovician arc—continent collision Grampian event followed by the Silurian collision of Laurentia with Baltica Scandian event. Lu—Hf and Sm—Nd garnet ages of c. Lu—Hf and Sm—Nd ages of c.
The routine analysis of sub-ng amounts of Hf will facilitate Lu–Hf dating of the Hf cut, especially for high-Lu/Hf samples such as garnet and apatite (Table 1).
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. In both systems, the daughter element e. Both Lu and Hf are highly immobile and insoluble and, as is the case with the Sm-Nd system, are thought to be resistant to perturbations and retain their isotopic information through significant degrees of alteration and metamorphism.
These differences can confer some advantages to the Lu-Hf isotope system for both geochronology and tracer isotopic work as will be discussed below. There are a few phases, however, with high affinity for Lu, which make them highly useful in geochronology in both magmatic e. In addition, some other phases particularly phases with Zr or Ti as stoichiometric constituents have strong affinities for Hf e. Although the Lu-Hf system was introduced to the geochemical and cosmochemical communities in the s, analytical challenges limited the widespread use of this technique until the late s.
Dating a single garnet crystal with very high Sm/Nd ratios (Campo basement unit, Eastern Alps)
I primarily use and develop geochemical and isotopic techniques to determine age of rocks and their origin. One of my main research fields is evolution of continental collision zones such as the Himalaya or the Carpathians. Geochronology is of my particular interest, especially means of linking isotopic ages with specific geologic events.
It remains controversial whether burial and exhumation in mountain belts represent episodic or continuous processes. Regional patterns of crystallization and.
Gonzaga, M. Menzies, M. Thirlwall, D. Jacob, A. Cratonic eclogites and garnet pyroxenites from the Kaapvaal craton have heterogeneous Hf—Nd—Sr— O isotope ratios that define a positive Hf—Nd isotope array and a negative Nd—Sr isotope array. Isotopic variability encompasses depleted mid-ocean ridge basalt and ocean-island basalt to enriched mantle compositions Group I and II kimberlites and overlaps with that of the Kaapvaal craton garnet peridotite xenoliths.
Much of this similarity may well be due to partial or complete resetting during entrainment. Kaapvaal and emplacement in orogenic belts e. Beni Bousera. Ironically, it may be that, in this instance, the Rb—Sr system gives a better indication of protolith age than Sm—Nd or Lu—Hf. Over the last hundred years the origin of eclogites has been variably attributed to crustal magmatic processes and recycling of basaltic protoliths e. Garnet pyroxenites are more widespread, being found in both oceanic and continental cratonic and circum-cratonic environments.
Garnet U-Pb and O isotopic determinations reveal a shear-zone induced hydrothermal system
Continue to access RSC content when you are not at your institution. Follow our step-by-step guide. Bast uni-muenster. When such samples are spiked, correcting for the isobaric interference of Lu on Hf is not always possible if the separation of Lu and Hf is insufficient. In addition, Sm—Nd and Rb—Sr separations can easily be added to the described two-stage ion-exchange procedure for Lu—Hf.
Garnet Lu-Hf ages of the schist of Moores Station Formation ( ± Ma) Start Date: ; End Date: ; Release Date:
Toggle navigation. Have you forgotten your login? Journal articles. Caroline Lotout 1 AuthorId : Author. Robert Anczkiewicz 3 AuthorId : Author. Jean van den Driessche 2 AuthorId : Author. Hide details. Abstract : Linking mineral growth and time is required to unravel the evolution of metamorphic rocks.
Garnet Lu-Hf Ages and Isotope Data for the Stibnite, Idaho Area
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.
Although coupled Sm-Nd and Lu-Hf garnet geochronology is not as prevalent as instances where only one system has been applied to dating.
Providing customized analytical solutions at the highest standards of quality assurance and quality control. Samples for U-Pb dating are processed using a Rhino jaw crusher, a Bico disk grinder equipped with ceramic grinding plates, and a Wilfley wet shaker table equipped with a machined Plexiglass top, followed by conventional heavy liquid and magnetic separation using a Frantz magnetic separator.
Four binocular microscope workstations are available for sample picking. The external morphology of mineral grains for analysis can be documented by SEM, and internal structure can be examined in polished grain mounts by cathodoluminescence imaging. TIMS U-Pb geochronology is widely recognized as one of the most robust and precise dating techniques. We have dated rocks from Pliocene to Archean in age, for clients from universities, government and industry.
U and Pb are loaded together on an outgassed zone-refined Re filament, and run separately in peak-hopping mode. Data reduction is done with U-Pbr, an Excel-based routine based on the error estimate algorithms published by Schmitz and Shoene Zircons are routinely analyzed from igneous rocks as well as detrital zircon or stream sediment samples. Both U-Pb data for geochronology and up to 30 user-selected trace elements, including rare earth elements, are acquired from a single laser shot.
Data are reduced using Iolite software Patton et al. Richard Friedman.
Lutetium—hafnium dating is a geochronological dating method utilizing the radioactive decay system of lutetium — to hafnium — The trace concentration of the Lu and Hf in earth materials posed some technological difficulties in using Lu—Hf dating extensively in the s. Lutetium is a rare-earth element , with one naturally-occurring stable isotope Lu and one naturally-occurring radioactive isotope Lu. An age equation is set up for every radiometric dating technique to describe the mathematical relationship of the number of parent and daughter nuclide.
The two isotopes, Lu and Hf, in the system are measured as ratio to the reference stable isotope of Hf.
However, the dated zircon is not clearly linked to eclogite facies metamorphism. Omphacite-garnet Lu-Hf dating of eclogite in the Kotsu and. Seba regions of the.
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. The trend for all Group I kimberlite megacrysts Hf values —1. The data indicate a genetic link between kimberlites and the low-Cr megacryst suite.
Our preferred option is that this component originates beneath the lithosphere, from a reservoir of ancient, deeply subducted oceanic basalt that became incorporated into the convecting mantle source region for Group I and Transitional kimberlites. Allegre, C. The evolution of mantle mixing. Allsop, H. A summary of radiometric dating methods applicable to kimberlites and related rocks. In: Ross, J. Special Publication of the Geological Society of Australia 14, — Ballentine, C.
Hafnium isotopic studies of the Cameroon line and new Hf paradoxes.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Duchecircne and J. Blichert-Toft and B.
I use high resolution Lu-Hf and Sm-Nd garnet geochronology as well as in situ LA ICPMS U-Pb zircon dating to estimate rates of geological processes. Recently I.
John Wiley and Sons Inc. Dating of the northern Idaho batholith and the Bitterroot metamorphic core complex: magmatism preceding and contemporaneous with extension. Relationships between luhf partial garnet, plutonism, orogeny, garnet exhumation: Idaho—Bitterroot Batholith. Exhumation and with of Eocene metamorphic luhf complexes along garnet Lewis and Clark strike-slip system. Frost CD, Winston D. Nd isotope systematics of coarse- and fine-grained sediments: Examples dating the Middle Proterozoic Belt—Purcell Supergroup.
Goldberg, S. Geochemical constraints luhf the origin of Proterozoic anorthosites, western United States. Griggs, A. Geologic map of the Spokane quadrangle, Washington, Idaho, and Montana. Petrology of aluminous schist in the Boehls Butte region of northern Idaho: phase equilibria garnet P — T evolution.
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A suite of pyroxenites from the Beni Bousera peridotite massif, northern Morocco, have been analysed for Re—Os and Lu—Hf isotopic compositions. In general, the Nd—Hf isotope compositions of the pyroxenites lie close to the mantle array. As with the Sm—Nd and Rb—Sr systems, parent—daughter and isotopic ratios for the Lu—Hf system have been recently decoupled by a partial melting event associated with transfer of the massif from mantle to crust. The near-solidus extraction of a siliceous melt from the pyroxenites is also a possible explanation for the orthopyroxene-rich margins to numerous pyroxenite layers, via reaction with peridotite.
Pyroxenite Os isotope compositions are much more radiogenic than their host peridotites. In contrast to cratonic eclogites, most pyroxenites analysed here and those reported in the literature lie close to the mantle Nd—Hf isotope array. The Nd—Sr—Pb—Hf isotopic compositions and stable isotope characteristics of these pyroxenites reflect signatures from recycled oceanic crust and sediment.
Hence, mixing of such material, if present within the convecting mantle, with peridotite, could account for some of the heterogeneity seen in oceanic basalts. Small amounts of pyroxenite incorporated into peridotite can also produce the radiogenic Os isotope signatures evident in the source of oceanic basalts. However, these observations alone do not require pyroxenite to be an integral part of the convecting upper-mantle magma source region.
The spectrum of Nd, Hf and Os isotope compositions also makes them a suitable component to explain some of the isotopic characteristics of the source regions of ultrapotassic magmas. Some recent models to explain the detailed major, trace element and isotopic systematics of mid-ocean ridge basalts MORB have advocated contributions from pyroxenites to the melting regime e.