Dating sr

Petrochemically, the volcanic rocks are dominantly medium-K calc-alkaline in composition and show enrichment of large ion lithophile elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magmas derived from an enriched mantle source.Chondrite-normalized rare-earth element patterns of the volcanic rocks are concave upwards with low- to-medium enrichment (La) of 0.68 to 1.02 Ga, suggesting an enriched lithospheric mantle source of Proterozoic age.The possibility of isotopic fractionation as an explanation for differences in Sr has been proposed to both authors on many occasions.It therefore seems worthwhile to point out that isotopic fractionation does occur during the mass spectrometric ratio measurement. When diffusive isotope fractionation of Sr isotopes is repeated a sufficient number of times by within-mantle processes on isotopically-anomalous mantle xenoliths (each of which originally had low Sr ratios.When mixed with variable amounts of terrestrial nonradiogenic strontium, these remnants generate mixing lines indistinguishable from age-indicative Rb-Sr isochrons.Trace element and isotopic data, as well as the modelling results, show that fractional crystallization and minor assimilation played an important role in the evolution of the volcanic rocks studied.The Eocene to Miocene volcanism in the region has resulted from lithospheric delamination and the associated convective thinning of the mantle, which led to the partial melting of the subduction-metasomatized lithospheric mantle.

To provide access without cookies would require the site to create a new session for every page you visit, which slows the system down to an unacceptable level.For example, the site cannot determine your email name unless you choose to type it.Allowing a website to create a cookie does not give that or any other site access to the rest of your computer, and only the site that created the cookie can read it.Previous attempts at dating these rocks using zircon concentrates have not succeeded.Using zircon U-Pb ion microprobe we found these granitoids have a crystallization age of 482 ± 2 Ma, and they are therefore coeval with the spatially related peraluminous magmas.Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium-87 compared with the stable isotopes.

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