Syn-tectonic garnet in the Prince Rupert area has Lu—Hf ages of Porphyroblast—matrix relationships in these samples, and samples from the same outcrops, indicate syn-tectonic garnet growth. These relationships imply that the garnet ages directly date the development of the metamorphic foliations. The data show that the older Lu—Hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement. Contractional and transpressional deformation occurred throughout much of the North American Cordillera at this time, from southeastern Alaska to the Baja Peninsula in Mexico. Left-lateral transpression dominated the Canadian Cordillera, whereas, right-lateral transpression affected areas south of the Idaho—Salmon River suture zone, including the Sierra Nevada batholith. This reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first-order feature of the geology of the North American Cordillera during the Cretaceous. Previous article in issue.
Isotopic Analysis: Fundamentals and Applications Using ICP-MS
In addition to tetrahedral and octahedral sites, such as those seen in spinels, garnets have dodecahedral coordinated sites. The net… General considerations Garnets, favoured by lapidaries since ancient times and used widely as an abrasive , occur in rocks of each of the major classes. In most rocks, however, garnets occur in only minor amounts—i. Nevertheless, as a consequence of their distinctive appearances, they are frequently recognized in hand specimens and become part of the name of the rock in which they are contained—e.
Garnet Lu–Hf and Sm–Nd geochronology on granulite unveil chronometer systematics. • Lu–Hf dates Ga garnet growth, Sm–Nd dates Ga high-T overprinting. • Sm–Nd more susceptible to diffusion but still robust in most crustal rocks. • Hf/ Hf potentially heterogeneous on a mineral scale down to lithospheric mantle.
Physical characteristics[ edit ] Pieces of Hafnium Hafnium is a shiny, silvery, ductile metal that is corrosion -resistant and chemically similar to zirconium  due to its having the same number of valence electrons , being in the same group, but also to relativistic effects ; the expected expansion of atomic radii from period 5 to 6 is almost exactly cancelled out by the lanthanide contraction.
The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity. The most notable nuclear properties of hafnium are its high thermal neutron-capture cross-section and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece. Hafnium dioxide Hafnium reacts in air to form a protective film that inhibits further corrosion.
The metal is not readily attacked by acids but can be oxidized with halogens or it can be burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air, producing an effect similar to that obtained in Dragon’s Breath. The chemistry of hafnium and zirconium is so similar that the two cannot be separated on the basis of differing chemical reactions. The melting points and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.
Isotopes of hafnium At least 34 isotopes of hafnium have been observed, ranging in mass number from to A potential source of hafnium is trachyte tuffs containing rare zircon-hafnium silicates eudialyte or armstrongite, at Dubbo in New South Wales , Australia. Production[ edit ] Melted tip of a hafnium consumable electrode used in an ebeam remelting furnace, a 1 cm cube, and an oxided hafnium ebeam remelted ingot left to right The heavy mineral sands ore deposits of the titanium ores ilmenite and rutile yield most of the mined zirconium, and therefore also most of the hafnium.
However, because of hafnium’s neutron-absorbing properties, hafnium impurities in zirconium would cause it to be far less useful for nuclear-reactor applications. Thus, a nearly complete separation of zirconium and hafnium is necessary for their use in nuclear power. The production of hafnium-free zirconium is the main source for hafnium.
Chalcophile Elements and Sulfides in the Upper Mantle
One of presumed terrane boundaries occurs in the Orlica Mts, along the contact between the phyllite-amphibolite complex Neoproterozoic? The synmetamorphic structural evolution of both adjacent units comprised four deformation events. The original overthrust contact was subsequently modified by a dextral shear-dominated event D2 , which produced a 1—2 km wide shear zone at the boundary of both units, in which earlier fabric elements were overprinted and mostly obliterated.
Lu–Hf dating of the felsic granulite resulted in Ma age, which in the context of the trace element study is interpreted as constraining the time of the prograde metamorphic path of UHP–UHT granulites. Importantly, the same age component was recorded by Sm–Nd system in garnet from the metapelitic inlier in the host orthogneisses.
Over the last decades a large number of geochronological studies have Over the last decades a large number of geochronological studies have elucidated its evolution, as summarised by Kinny et al. The Lewisian thus provides an important link between Laurentia and Baltica during the Proterozoic Most of the Lewisian Gneiss Complex was formed during the Meso- to Neoarchaean, as a series of crustal terranes that were largely amalgamated at the end of the Archaean to form part of the North Atlantic Craton.
Here, we provide an overview of the Proterozoic history, based on information from the literature and new geochronological data Goodenough et al. Juvenile magmas were emplaced into many parts of the Lewisian Gneiss Complex in the period c. Magmatism at this time has now been recognised along most terrane boundaries in the Lewisian. This magmatic activity was related to the development of continental arcs during the accretion of the Columbia supercontinent, and may be correlated with the Ketilidian or Nagssugtoqidian events in Greenland and the Svecofennian and Lapland-Kola belts in Scandinavia.
Subsequently, the Lewisian Gneiss Complex was affected by a crustal thickening and heating event or events during the period Ma.
Chalcophile Elements and Sulfides in the Upper Mantle
They are observed in upper-mantle peridotites and oceanic basalts, in mantle xenoliths, and are also the most common mineral inclusion in diamonds. Thus, sulfides control the behaviour of the chalcophile elements during magmatic processes. Periodic table showing chalcophile elements highlighted in yellow. In addition to their economic importance, residual sulfides exert a strong control on the budget of chalcophile elements during partial melting and crustal differentiation and, hence, have a profound effect on the trace-element concentrations found in erupted magmas.
Sulfides in the upper mantle Sulfides are ubiquitous accessory phases in all types of mantle xenoliths.
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Full citation Abstract Pan-African high-grade metamorphism in the Proterozoic Damara orogen Namibia led to formation of garnet-bearing leucosomes in potassic meta-igneous gneisses producing a meta-igneous migmatite. In addition, the migmatite gneiss mesosome plus leucosome was intruded by small-scale leucogranitic melts with a high amount of accumulated biotite and garnet. U-Pb zircon ages obtained on the mesosome and the leucosome indicate late Proterozoic ca.
High precision Lu-Hf garnet-whole rock dating gave ages of In addition, it is suggested that melting and intrusion was coeval and occurred probably shortly after the main peak of metamorphism which occurred at c. P-T estimates obtained by conventional thermobarometry c. Outcrop evidence diffuse relationship between the gneiss domain and the leucosomes, similar size of the leucosomes, homogeneous distribution of leucosomes on the sample scale suggests that minor melt segregation had occurred.
Whole rock Sr, Nd, Hf and O isotope data of the mesosome indicate that it belongs to basement rocks from this area. Geochemical and isotope data obtained on the leucosomes argue for derivation by in-situ melting of the mesosome. Both, leucosome and leucogranite originated from the same source rock but the leucogranite represents an accumulated melt that was able to segregate and to intrude the gneiss domain. The similar isotope features of the mesosome, leucosome and leucogranite indicate a direct relationship for the gneiss and the melts.
Isotopes of lutetium Lutetium occurs on the Earth in form of two isotopes: Out of these two, only the former is stable, making the element monoisotopic. The latter one, lutetium , decays via beta decay with a half-life of 3. The most stable of them are lutetium m, with half-life of Urbain chose neoytterbium and lutecium,  whereas Welsbach chose aldebaranium and cassiopeium after Aldebaran and Cassiopeia.
Dating of garnets with Lu–Hf could provide information of history of garnet growth during prograde metamorphism and peak P-T conditions. With the help of garnet Lu/Hf ages, a study on Lago di Cignana, western Alps, Italy, an age of ± million yr for lower boundary of garnet .
Timing of eclogite-facies metamorphism of mafic and ultramafic rocks from the Pohorje Mountains Eastern Alps, Slovenia based on Lu—Hf garnet geochronometry. Lithos, , , doi: High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps Etirol-Levaz Slice, Valtournenche, Italy.
Late Miocene to Early Pliocene blueschist from Taiwan and its exhumation via forearc extraction. Terra Nova, 27, , doi: Dating the initiation of Piemont-Liguria Ocean subduction: Lu-Hf garnet systematics of a polymetamorphic basement unit: Geologica Carpathica, 61, 6, Late Miocene to Early Pliocene blueschist from Taiwan and its exhumation via forearc subduction. TSK , Bonn, Germany. Late Ceratceous eclogite in the Eastern Rhodopes Bulgaria: GeoBerlin , Berlin, Germany.
Alpine metamorphism in the continental Etirol-Levaz slice Western Alps, Italy — Insights from petrological, thermodynamic and geochronological investigations.
Geochronology and Thermochronology
The giant Beiya Au skarn deposit over tonnes Au metal reserve is located in the middle part of the Jinshajiang-Ailaoshan alkaline porphyry metallogenic belt. The deposit is the largest Au skarn deposit and third largest Au deposit in China. In this paper, we present garnet U-Pb ages and trace element geochemical data from two types of skarn-related U-rich garnet from Beiya, and discuss their implications on skarn metallogenesis.
Based on optical characteristics and major element compositions, the older Grt I and the younger Grt II both belong to the grossular-andradite solid solution are distinguishable:
Request article pdf on, jeff vervoort and others published lu-hf lu-hf garnet dating dating the lu-hf isotope system. Lu-hf high lu hf ratios found in make these minerals useful for lu hf dating of metamorphic tes from three units of the.
When we review graduate-student applications, we evaluate your GPA; GRE scores; breadth, depth and difficulty of completed course work; reference letters from scientists; and statement of purpose. Direct dating of deformation using titanite. Former graduate students Robert Holder Ph. Geochronology, geochemistry and petrology. Postdoctoral scholar, Penn State University. Himalaya gneiss dome formation, focused radiogenic heating in southern Madagascar, and fertilization of the Neoproterozoic ocean by mantle-derived phosphorus.
Genesis and Evolution of the Pamir Plateau: Professor, Utah Valley University. Examples from the Western Gneiss Region, Norway. Editor, US Geological Survey. Geologist, Campbell Geo, Inc. Visiting Assistant Professor, Bucknell University.
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Abstract Introduction Methods Results Discussion Acknowledgements Author Contributions References Supplementary Information Constraining the thermal and temporal evolution of the deep arc lithosphere is critical to understanding the magmatic evolution of a volcanic arc. The Sierra Nevada batholith is one of only a few places world-wide to study deep crustal and lithospheric evolution of an arc because of the availability of lower crustal and mantle xenoliths Dodge et al. Xenoliths in a volcanic pipe near Big Creek, California.
Geological Society of America Bulletin , Journal of Petrology 35, Evidence from xenolith thermobarometry.
Lu-Hf has several advantages over other systems for dating Grt, notably better age resolution at lower ages, high closure temperature, and better tolerance for certain types of inclusions.
Radioactive decay[ edit ] Example of a radioactive decay chain from lead Pb to lead Pb. The final decay product, lead Pb , is stable and can no longer undergo spontaneous radioactive decay. All ordinary matter is made up of combinations of chemical elements , each with its own atomic number , indicating the number of protons in the atomic nucleus.
Additionally, elements may exist in different isotopes , with each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of a particular element is called a nuclide. Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide. This transformation may be accomplished in a number of different ways, including alpha decay emission of alpha particles and beta decay electron emission, positron emission, or electron capture.