Whole-Rock K-Ar Model and Isochron, and Rb-Sr, Sm-Nd, and Pb-Pb Isochron, "Dating" of the Somerset Dam Layered Mafic Intrusion, Australia

Download PDFDownload Whole-Rock K-Ar Model and Isochron, and Rb-Sr, Sm-Nd, and Pb-Pb Isochron, "Dating" of the Somerset Dam Layered Mafic Intrusion, Australia PDF

Presented at the Fifth International Conference on Creationism, Pittsburgh, Pennsylvania, August 4–9, 2003. Published in: Proceedings of the Fifth International Conference on Creationism, R. L. Ivey (Eds.), pp. 305–324, 2003.

© 2003 Creation Science Fellowship, Inc., Pittsburgh, PA, USA. Published with permission. All rights reserved.

Abstract

The Somerset Dam layered mafic intrusion in southeast Queensland, Australia, has been conventionally dated as Late Triassic by the apparently successful application of radioisotopic dating techniques. Mineralogical, geochemical, and isotopic evidence indicates that all of this gabbro intrusion’s cyclic units were derived coevally from the same parental basaltic magma, with an initial homogeneous
isotopic mixture ideal for yielding concordant isochron ages. However, newly obtained K-Ar, Rb-Sr, Sm-Nd, and Pb-Pb radioisotopic data from 15 whole-rock samples (representing all gabbro macrolayers in four of the intrusion’s cyclic units) yield discordant isochron “ages,” although the excellent-fitting 15-point K-Ar isochron suggests the resultant 174±8 Ma “age” (Middle Jurassic) should be regarded as the revised conventional age of the layered intrusion. Nevertheless, it is concluded that these discordances between the radioisotope systems are likely due to changes in their decay rates in the past, with the longer half-life β-emitter 87Rb being accelerated more and thus yielding an older “age.” Furthermore, the Sr, Nd, and Pb isotopes indicate the parental basaltic magma was derived from a depleted mantle source, while the large spread of Nd TDM “ages” suggests accelerated radioisotopic decay rates during the partial melting and magma ascent. It is concluded that the Somerset Dam layered mafic intrusion has inherited the radioisotopic signature of its mantle source, and so the conventional radioisotopic dating techniques do not provide its true age.

Keywords

Gabbro, Layered Intrusion, Australia, Potassium-Argon, Rubidium-Strontium, Samarium-Neodymium, Lead-Lead, Radioisotopic Dating, Whole-Rock Model “Ages,” Whole-Rock Isochron “Ages,” Discordances, Decay “Constants,” Accelerated Decay, Mantle Source Inheritance

For Full Text

Please see the Download PDF link above for the entire article.

The Latest
NEWS
Delicate Spider Fossil Discovered
Discovering fossil spiders has become fairly common.1 Each time they have been 100% spiders, not vague evolutionary ancestors with partial or transitional...

NEWS
A T. rex Swimming with Sharks?
The last time I checked, sharks didn’t swim on land. Most shark species inhabit saltwater oceans. Maybe tyrannosaurs swam some, but they didn’t...

NEWS
"Ancient" Fossil Still Has Hagfish Slime Residue
Hagfish look creepy. They can act creepy, too. Having no bones, they tie themselves into sliding figure eight knots that help them tear mouthfuls of...

CREATION PODCAST
What Do We Do With Darwin Day?
Many secularist and humanist organizations celebrate February 12 as Darwin Day, a day set aside to honor Charles Darwin and his legacy. But is Darwinism...

NEWS
Meteorite Impact Observed During Lunar Eclipse
On January 21, 2019, during a total lunar eclipse, astronomers and amateur stargazers alike saw a small meteorite strike the lunar surface.1 The collision...