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.
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Ltd, 3. Presentation information Print Tweet. Hence, in-situ measurements are highly desired for geochronology. Moens et al.
Lu-Hf method utilizing the age of asteroids in a mesosiderite asuka Pdf the radioactive. In the document focuses mainly with canonical. These minerals.
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.
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Brouwer , M. Groen, O. Nebel, J. Wijbrans , H. Qiu, Q.
Hf–Zr anomalies in clinopyroxene from mantle xenoliths from France and Poland: implications for Lu–Hf dating of spinel peridotite lithospheric.
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.
Rare-Earth Clocks, Sm-Nd and Lu-Hf Dating Models: Radioactive Dating, Part 5
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.
ABSTRACT. Lu–Hf isotope system and Sr–Nd–Hf–Os isotope systematics of mantle rocks is capable to unravel the early processes in collision.
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Rare-Earth Clocks, Sm-Nd and Lu-Hf Dating Models 2: Radioactive Dating, Part 6
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This had strong impact on the isotopic dating results and led to “decoupling” of the Sm-Nd and Lu-Hf clocks, which recorded timing of the two.
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Downes, Hilary and de Vries, C. International Journal of Earth Sciences 1 , pp. ISSN Clinopyroxenes in some fresh anhydrous spinel peridotite mantle xenoliths from the northern Massif Central France and Lower Silesia Poland , analysed for a range of incompatible trace elements by laser ablation inductively coupled plasma mass spectrometry, show unusually strong negative anomalies in Hf and Zr relative to adjacent elements Sm and Nd, on primitive mantle-normalised diagrams.
Similar Zr—Hf anomalies have only rarely been reported from clinopyroxene in spinel peridotite mantle xenoliths worldwide, and most are not as strong as the examples reported here.
Palavras-chave: Morro do Polvilho; Metatraquidacito; Magma de alta temperatura; Condições redutoras; Grupo São Roque. U-Pb dating, Lu-Hf isotope.
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