Theory of a methodology for initial lead determination, and a procedure to resolve it to some of its stages

A method for determining the initial Pb of a terrain, on the basis of the measured isotopic compositions of its rocks, is put forward in this report. The method was inspired by the premise that the initial Pb inherited by the rocks from a reservoir from which they were extracted, is immutable and inerasable, irrespective ofthe multitude of disturbances that may have subsequently been superimposed on the terrain. This is because while these disturbances may have altered the isotopic composition of some or all the rocks, they lacked the vehemence to re-melt the entire terrain or at least a very large portion of it, which is a pre-requisite for altering the isotopic composition of initial Pb. If this rational is valid, then a large Pb isotope database (including data on mineral separates with low affinities for U and Th) that is representative of a terrain, when plotted on any Pb isotope correlation diagram (e.g., the conventional Pb/Pb plot), may define a dispersion field that tapers toward a single spot. That single spot (once unambiguously determined) is the initial Pb isotopic composition.