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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.
The prospects of garnet-based Lu-Hf geochronology returning accurate ages using garnet. Whereas the U-Pb system showed early promise for dating garnet.
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.
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.
Second, the new MC-ICPMS instrumentation also facilitated the analysis of high Lu-Hf, but Hf-poor, phases like garnet or apatite, which made.
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.
Garnet Lu-Hf Ages and Isotope Data for the Stibnite, Idaho 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.
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The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism
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Lu-Hf garnet dating provides high precision age information, which is competitive even for the most precise geochronometers. Accuracy of garnet geochronology.
The absolute crystallization ages of minerals from hydrothermal fluids measured in situ can unravel the timing of key events leading to the formation of, for instance, ore deposits and hydrothermally derived geological terrains. This skarn age instead correlates with the occurrence of strike-slip and thrust faulting in the region. The low oxygen isotopic composition indicates the role of meteoric water in the garnet formation.
Meteoric water in this hydrothermal system would leach cations from the meta-volcano-sedimentary rocks necessary for mineralization. Silica-rich hydrothermal fluid reacts with calcic-rich materials in the meta-volcano-sedimentary rocks, depositing the garnet and magnetite. Our work suggests that the shear zone is rich in ores, rendering this deposit for NW China a prospective source for future mineral resource exploration.
Garnet is an abundant mineral phase found in a range geological settings, from skarn-type ore deposits, granite, and low- and high-grade metamorphic rocks, to the upper mantle. It is a widely used proxy in geothermobarometry 1 , 2. The stability and generally porphyroblastic nature of garnet makes it an ideal mineral for tracking the evolution of crystallization by measuring the elemental and isotopic compositions of different crystallization zones in garnet 3.
On the other hand, heavy rare-earth elements are compatible in garnet, which can provide absolute age constraints using, for instance, the Lu-Hf and Sm-Nd isotopic systems 4 , 5.
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.
Both have proven successful not merely in dating garnet growth itself, but For analyses of bulk garnet that grew over a protracted interval, Lu-Hf dates are.
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.
High-pressure polybaric fractionation of mafic or ultramafic magmas in the mantle e.
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.
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.
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. However, dating early metamorphic stages is a challenge, due to subsequent retrograde overprinting.
In the retrogressed sample, most of the zircon grains are characterized by negative Eu anomalies and HREE enrichment, and yield an Ordovician U-Pb date of In agreement with other data available for the Variscan belt, and based on zircon trace elements record and whole rock geochemistry, this age is considered to represent the magmatism associated with the extreme thinning of the continental margins during the Ordovician.
Fresh and retrogressed samples yield respectively Apatite grains from the retrogressed sample give a mean age of
Garnet U-Pb and O isotopic determinations reveal a shear-zone induced hydrothermal system
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.
It remains controversial whether burial and exhumation in mountain belts represent episodic or continuous processes. Regional patterns of crystallization and.
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.
The reason for this is that Hf has a very high first ionization potential 6.