Joined: Aug. 2007
More claims on "faulty" radiometric dating in New Zealand from Snelling:
Has any scientist investigated these claims yet ?:
|The Rb-Sr, Sm-Nd, and Pb-Pb radioisotopic ratios in these samples of the recent (1949–1975) andesite lava flows at Mt. Ngauruhoe, New Zealand, as anticipated, do not yield any meaningful “age” information, even with selective manipulation of the data. Instead, these data provide evidence of the mantle source of the lavas, of magma genesis, and of crustal contamination of the parental basalt magmas. Subduction of the Pacific Plate beneath the Taupo Volcanic Arc has carried trench sediments with it—sediments identical in composition to the Torlesse metasediment basement underlying, and outcropping adjacent to, these volcanoes. Scraped off the subducting slab, the sediments have contaminated the basalt magmas generated by partial melting of the peridotitic mantle wedge at the mantle-slab interface. The resultant andesite magmas rose in the melt column through the mantle wedge, and then ascended through fracture conduits in the overlying crust into magma chambers below the volcanoes that erupted when full. |
The Sr-Nd-Pb radioisotopic systematics are thus characteristic of the depleted mantle source, modified by mixing with the crustal contaminant. Variations in the depleted mantle Nd “model ages”, which range from 724.5 to 1453.3 Ma, and which are meaningless in this recent (even in conventional terms) tectonic and petrogenetic framework, and the Pb isotopic linear arrays, indicate geochemical heterogeneity in the mantle wedge. Thus the radioisotopic ratios in these recent Ngauruhoe andesite lava flows were inherited from both the peridotitic mantle wedge and the subducted trench sediments, and are fundamental characteristics of their geochemistry. They therefore only reflect the origin and history of the mantle and crustal sources from which the magma was generated, and therefore have no age significance.
By implication, the radioisotopic ratios in ancient lavas found throughout the geologic record are likely fundamental characteristics of their geochemistry. They therefore probably only reflect the magmatic origin of the lavas from mantle and crustal sources, and any history of mixing or contamination in their petrogenesis, rather than any valid age information. Even though radioisotopic decay has undoubtedly occurred during the earth’s history, conventional radioisotopic dating of these rocks therefore does not necessarily provide valid absolute “ages” for them. This is especially so if accelerated nuclear decay accompanied the catastrophic operation of those geologic and tectonic processes responsible for the mixing of the radioisotopic decay products during magma genesis.
A job for someone then, especially as it's puporting to be peer reviewed science.