Phosphate Lu–Hf geochronology

Barfod, Gry H.; Otero, Olga; Albarède, Francis

doi:10.1016/s0009-2541(03)00202-x

Cited by 58 publications

(44 citation statements)

References 47 publications

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“…The mean value of the 176 Lu decay constant obtained from the analysis of these terrestrial samples (1.867 · 10 À11 a À1 ) is $4% lower than the meteorite value, and, when applied to meteorites, makes their Lu-Hf ages unacceptably old ($4.75 Ga). In contrast, the 'terrestrial' decay constant, when applied to 3.7 Ga supracrustal rocks from Isua, to 2.1 Ga old rocks from West Africa (Blichert-Toft et al, 1999), and to apatites from the Eocene Gardiner intrusion (Barfod et al, 2003), yields Lu-Hf ages that agree with ages from other isotope systems, whereas, the meteorite value results in ages that are conspicuously too young. The alternatives therefore are that either all the terrestrial values are consistently wrong or the 176 Hf isochrons defined by chondrites and eucrites are biased by an early process that acted exclusively before Earth's accretion.…”

Section: Introductionmentioning

confidence: 79%

γ-ray irradiation in the early Solar System and the conundrum of the 176Lu decay constant

Albarède

Scherer²,

Blichert‐Toft

et al. 2006

Geochimica et Cosmochimica Acta

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118

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Section: Introductionmentioning

confidence: 79%

γ-ray irradiation in the early Solar System and the conundrum of the 176Lu decay constant

Albarède

Scherer²,

Blichert‐Toft

et al. 2006

Geochimica et Cosmochimica Acta

Self Cite

118

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“…1.3). The intercept of the iso- Barfod et al 2003). Abbreviations: PLAG plagioclase; WR whole rock; CPX clinopyroxene; OPX orthopyroxene; AP apatite (AP1, AP2, AP3 indicate different analyses of apatite) chron is equal to the initial ratio, which is useful for fingerprinting magma sources and contamination.…”

Section: Mineral-whole Rock Isochronsmentioning

confidence: 99%

“…Apatite preferentially incorporates rare earth elements (REE) and contains little Hf (typically ≪1 ppm) (e.g., Fujimaki 1986). Barfod et al (2003) presented a method for the separation of Lu and Hf from apatite that allows for rapid sample processing prior to analysis by multiple collectorinductively coupled plasma-mass spectrometry (MC-ICP-MS). When applied to a sample from Upper Zone b of the Skaergaard intrusion, isotopic data from three apatite fractions and the whole rock yield an isochron with a precise Lu-Hf age of 58.28 ± 0.44 Ma (Barfod et al 2003 (Fig.…”

Section: Mineral-whole Rock Isochronsmentioning

confidence: 99%

Geochronology of Layered Intrusions

Scoates

Wall

2015

Springer Geology

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Layered intrusions crystallize mainly from basaltic magma to form large bodies of igneous rocks that exhibit prominent layering and they preserve stunning rock records of the processes by which magma evolves in crustal magma chambers. These intrusions contain world-class deposits of chromium, platinum group elements (PGE), and vanadium, metals that are vital to industry and society in general. Despite their scientific and practical importance, precise age constraints are lacking for many layered intrusions, and geochronological frameworks linking crystallization and cooling ages for the most part do not exist. This has resulted in critical knowledge gaps related to their origin and formation. This chapter provides an overview of dating methods (U-Th-Pb, 40 Ar/ 39 Ar) and mineral chronometers (e.g., zircon, baddeleyite, rutile, apatite, titanite) potentially present in layered intrusions that is coupled with field, textural, and petrographic criteria for targeting sample selection to allow for the successful implementation of geochronologic studies of layered mafic-ultramafic rocks of any age. As an application, we demonstrate how the thermal history of the Bushveld Complex is documented by mineral ages from samples of the PGE-rich Merensky Reef. High-precision U-Pb zircon ages, involving pretreatment of zircon by the chemical abrasion (annealing and leaching) or CA-TIMS technique, for two samples separated by > 300 km are indistinguishable from each other (2056.88 ± 0.41 Ma, Eastern Limb; 2057.04 ± 0.55 Ma, Western Limb; uncertainty reported as 2s) confirming synchronous crystallization of this horizon at near-solidus conditions across the intrusion. Rapid cooling (~ 125 °C/Ma) down to temperatures of ~ 400-450 °C is defined by U-Pb rutile ages from the same samples (2052( .96 ± 0.61 Ma, 2053.0 ± 2.7 Ma) and a regional hydrothermal event is signaled in 40 Ar/ 39 Ar biotite ages (1999 ± 10 Ma, 2002 ± 10 Ma). The geochronology of layered intrusions, where magma differentiation processes are captured in a wide range of rock textures and structures, represents an essential tool for assessing the evolution of mafic magmatism in the Earth's crust.

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“…The long-lived 176 Hf chronometer benefits from a large range in P/D among different minerals and a high closure temperature in silicates (e.g., Scherer et al, 2000) and apatite (Barfod et al, 2003); therefore, it is potentially precise and robust against post-crystallisation heating and shock. Unsupported 176 Hf has been observed in many meteorites however, resulting in Lu-Hf dates that are up to 300 Myr older than the Pb-Pb age of the Solar System (e.g., Blichert-Toft et al, 2002;Bizzarro et al, 2012).…”

confidence: 99%