Zircon age dating
illuminates progress in studies of sedimentary provenance, which have evolved dramatically during the past fifty years.During my dissertation research at Virginia Tech, Professor Wally Lowry advised me to think of “sandstones as microconglomerates” in which some sand grains are small rock fragments, characterizing the lithology of the source of the sediment.
Scientists can use monazite, titanite, baddeleyite and zirconolite for uranium dating. Zircon is commonly found as the primary mineral in igneous rocks.structure allows a small amount of tetravalent uranium to substitute for zirconium but excludes with great efficiency the incorporation of lead.(It might be said that one begins with an empty box.) Second, zircon, once formed, is highly resistant to change and has the highest blocking temperature ever observed.If left at low surface temperatures for a geologically long time, the radioactivity within the crystal can destroy the crystal lattice structure, whereas at higher temperatures this process is self-annealing.In fact, when examined by X-ray methods, some zircons have no detectable structure, indicating that at least 25 percent of the initial atoms have been displaced by ) in biotite can cause lead to be lost in some grains.Of course, such a high blocking temperature can have its disadvantages.Inherited cores may give a mixed false age when the age of crystallization is sought. Scientists use this method to date rocks that formed from between 1 million to 4.5 billion years ago, and they estimate the Earth is 4.543 billion years old. The oldest and most reliable method they use is called Uranium-lead (U-Pb) dating.For this reason, three or more grain types or parts of a grain are analyzed to establish that material of only one age is present.Experience with the results of the uranium–lead method for zircons has demonstrated an interesting paradox.