Dating basaltic


10-Nov-2014 02:22

About 3% of the witnessed falls of all meteorite types are the achondrites known as eucrites, which makes them the fourth-most-common meteorite to fall. Ar age of Ibitira: Dating the time of chemical equilibration of eucritic pyroxenes?

Eucrites are similar to basalts and are believed to be space debris from the crust of main belt asteroid 4-Vesta.

There is also scatter of the U-Pb, Pb-Pb, Th-Pb, Rb-Sr, K-Ar, and Ar-Ar model ages, in most cases likely due to thermal disturbances resulting from metamorphism or impact cratering of the parent asteroid.

They appear to consistently yield 4.55–4.57 Ga radioisotope ages, adding to the uniformitarians’ confidence in the radioisotope dating methods.

Achondrites, meteorites not containing chondrules, account for about 8% of meteorites overall.

(rarely) as the dominant mafic minerals; basalts without olivine are also well represented.

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They strongly cluster in many of these eucrites at 4.55–4.57 Ga, dominated by Pb-Pb and U-Pb isochron and model ages, testimony to that technique’s supremacy as the uniformitarians’ ultimate dating tool, which they consider very reliable. These ages are confirmed by Rb-Sr, Lu-Hf, and Sm-Nd isochron ages, but agreement could be due to calibration with the Pb-Pb system. They predominate among the lavas of mountain belts; their flows may build enormous plateaus, as in the northwestern United States, the Deccan of , the rock is known as nepheline-basalt; if the replacement is only partial, the term nepheline-basanite is used.Similarly, there are analcime- and leucite-basalts and leucite-basanites.

Most nepheline-basalts are fine-grained, very dark-coloured rocks and date to the early Cenozoic Era (65.5 million years ago to the present).

Meteorites date the earth with a 4.55 ± 0.07 Ga Pb-Pb isochron called the geochron.



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