U pb dating minerals
Next, the slope k of the tangent line at point A on the general curve of Equation (5) was determined.The partial derivative of (Equation (3)) with respect to t is isotope concentrations determine the mathematical expressions for the general graph in Figure 2.The slope and slope year were calculated using Equations (24) and (10), respectively, and found to be k.Present slope years (with 1σ error) for (a) Qinghu granite, (b) a Zimbabwe uranium deposit, (c) Yingxian amphibolites and (d) Hebi amphibolites.According to conventional theories, this age indicates that the samples will experience a metamorphic process in a distant age. (2012), all zircons in HBxa from Hebi basalt are also discordant, but yield no upper intercept age.
This Discordia and Concordia intercept at A and B, for which the meanings in conventional theories are shown in the lower-right corner.
Slope k and Slope Year Tslope In mathematics, the variance on the ordinate is a function of the variance on the abscissa  .
Therefore, n(The theoretical expressions for this function under different conditions are given in Section 2.4.
Two counter-examples to traditional theories are also shown: HBxa (hexagon points and red Discordia, Zheng et al. isotope concentrations in host minerals can be precisely measured using mass spectrometry (MS).
(2012)) and YX1 (right triangle points and green Discordia, Zheng et al. Such MS instruments include sensitive high mass-resolution ion microprobe (SHRIMP)   , Laser Probe-inductively coupled plasma mass spectrometry (LP-ICPMS)  and Cameca IMS-series   , etc.2.2.