Lu-hf garnet dating

B 52, — These results indicate that the Alpine high- Structure and energetics of neutral and negatively charged C60 dimers.

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What is the lowest-energy isomer of the C60 dimer? A , — With the discovery of the coesite-bearing quartzites of Dora Synthesis of oxo- and methylene-bridged C60 dimers, the first well-characterized species containing fullerene-fullerene of the Alps provided fresh insight into alpine tectonic processes. Published data, however, emphasize both the extent of inconsis- The first [60]fullerene dimer with cages bis-linked by furanoid bridges. Coalescence reactions of fullerenes. Nature and its far-reaching geodynamic implications2—5.

The Eoalpine age , 44—47 Mass peak assignment for C60 polymer generated in an Ar plasma. The solid-phase reaction of [60]fullerene: Water continuing subduction of the oceanic Tethyan lithosphere under the soluble buckminsterfullerene-g-cyclodextrin inclusion complexes via a solid-solid reaction.

Eclogite burial and exhumation also appear to be State Ionics 74, 47—51 Cyanodihydrofullerenes and dicyanodihydro- fullerene: Pb ages in the range 60— Myr refs 10— In contrast, the Late NMR and Raman characterization of pressure polymerized C Eocene—Early Oligocene age found for Dora Maira13,14 —as a lower , — B 54, ellenbergerite, which was later confirmed by U—Pb ion-probe data R—R Thermal decomposition of polymeric C Infrared study of vibrational property and polymerization of C60 and C70 under from other eclogite localities in the western and central Alps16— Polymerized fullerene facies during the Oligocene 25—35 Myr ago at the latest7,19, the structures.

The Lu-Hf dating of garnets and the ages of the Alpine high-pressure metamorphis

All-carbon polymers polyfullerenes from photochemical reactions of fullerene clusters in room-temperature solvent mixtures. The replicates of Sesia-Lanzo whole rocks represent different powder aliquots. The numbers in parentheses are twice the standard error. The Nd and Hf isotopic compositions of the Monviso whole rock sample plots in the field of mid-ocean-ridge basalts, whereas those of the Dora Maira massif and the Sesia-Lanzo zone plot in the field of continental rocks. This eclogite was eclogite exhumation have so far been dated using only two methods.

The Monviso sample U—Pb dating of zircons gives, in principle, reliable crystallization is a mafic garnet—omphacite—glaucophate eclogite equilibrated at ages, although zircon is not a mineral specific to high-pressure , 8C and 15 kbar ref.

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The Sesia-Lanzo sample is a felsic assemblages. In addition, as best shown in the case of Dora Maira6,14, eclogite equilibrated at 8C and. In each case, linear arrays defining concordia lower intercepts indicate the the decompression took place with no noticeable reheating. Ion-probe dating can recognize old discordant garnets which reaches 3 for felsic rocks and 8 for the mafic eclogite areas in zircons, but the youngest part of the concordia is linear, of Monviso. Because the samples were not dissolved in pressurized making mixing between young populations difficult to identify.

The bombs, the reproducibility of Lu—Hf replicate analyses of felsic second method, which is that of Sm—Nd internal isochrons in garnet-bearing rocks, often fails when isotopic equilibration between clinopyroxene and garnet has not been achieved In Helvetic units Pennine units Austro- Alpine units Tertiary plutons addition, the small spread of Sm—Nd ratios severely limits the Cover Cover Cover precision of this method of dating.

The closure temperature of Sm— Basement Basement Basement Eclogite facies rocks Nd in garnet is still debated but is supposed20—22 to be higher than Ophiolitic units South-Alpine domain 8C, which should provide valuable information on the timing of eclogite exhumation. An advantage of the Lu—Hf method of dating is therefore a relatively fast radiogenic ingrowth of Hf which in particular is three times faster than that of Nd. The uncertainty on the decay constant affects Lu—Hf ages by no more than 1.

The Plasma 54 in Lyon can determine the isotopic composition of Hf on small quantities 20 ng with an excellent external reproducibility 40 p. Separation of Lu and Hf, blanks, standard values, and mass spectrometry are described elsewhere Internal precision on Sesia-Lanzo Hf isotope compositions is usually in the range of 20—40 p. Dora Maira High-pressure rocks are found in three internal units of the Alps massif known, from bottom to top, as Pennine, ophiolitic and Austro- Alpine25 Fig.

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The Helvetic minerals, notably garnet, phengite and clinopyroxene. The Dora units represent the European mainland, the Pennine units the European margin Maira coesite—pyrope—quartzite assemblage described by Chopin1 and the Tethyan oceanic crust, and the Austro-Alpine units the Apulian margin. Phengite, clinopyroxene and whole 0. Error bars are significantly smaller than the symbols.

The rather garnet Monviso The ages, however, are well Dora Maira massif constrained by the garnet fractions. This problem, however, eclogites of Monviso and Sesia-Lanzo. Because of the high The exhumation of eclogites seems to be very rapid. The coesite-pyrope quartzites Similar arguments also support fast ellenbergerite13, The whole-rock garnet age of the Monviso exhumation for the Sesia-Lanzo zone and Monviso.

The phengite-garnet age of method on the same type of mineral is older when the structural A less-purified fraction of the Early Oligocene collision between the European and Apulian plates, same garnet gives a slightly older age of This shows within errors with the collision and is found in the Pennine unit that, owing to the high Hf content of garnets with respect to other at Dora Maira and Alpe Arami in the central Alps It predates by eclogitic minerals, Lu—Hf dating is far less sensitive to the quality of less than a few Myr the intense Myr-old magmatic activity mineral separation than Sm—Nd.

The Monviso sample was inad- represented by the emplacement of the granitic pluton at Bergell35 vertently underspiked. The 63 6 7 Myr Sm—Nd age obtained from and other localities36, and by the eruption of the widespread the clinopyroxene-phengite pair from the Sesia-Lanzo sample and andesites found as clasts in the Taveyannaz and Champsaur the crude 40 6 10 Myr clinopyroxene-garnet Sm—Nd age acquired formations U—Pb ages of concordant zircons duration of the high-pressure conditions.

Lutetium–hafnium dating

Some eclogites are already date the crystallization of this mineral. By contrast, K—Ar ages brought to the surface well before the protolith of others even generally date closure at low temperature. Because little is known become buried. The exhumation of the Sesia-Lanzo zone was about diffusion of Hf in common minerals, it is not clear whether complete ,35 Myr before the Dora Maira massif was metamor- Lu—Hf ages of eclogitic garnets reflect a closure temperature or phosed in the eclogite facies. Some eclogites therefore rise through a the time of crystallization. Hafnium in granitic liquids diffuses near steady-state mechanism apparently unrelated to the collision, more slowly than neodymium The ionic radius31 of six-fold- possibly through prism flow40 in a subduction environment.

Comparison with the closure temperature of 1. The crust formation process is supposedly chemically depleting the mantle, as crust forms from partial melts originating from the mantle. Hf ages determined from detrital zircon can help to identify major event of crustal growth. Hf ages from detrital zircon also help tracing sediment source.

From Wikipedia, the free encyclopedia. The Lu-Hf Isotope System". Encyclopedia of Scientific Dating Methods: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets". Earth and Planetary Science Letters. Applied Radiation and Isotopes.

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Retrieved 15 November Geochemistry - Earth's System Processes. Contributions to Mineralogy and Petrology.

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  7. Geological Society, London, Special Publications. Journal of Metamorphic Geology. Chronometric closure and implications for dating petrological processes". New constraints on garnet growth rates and duration of metamorphism during continental collision Menderes Massif, Turkey ". A new geochronometer for subduction zone processes". Retrieved from " https: Radiometric dating Lutetium Hafnium.

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