Abstract:

Using least squares regression procedure, a best regression equation (t _Zr=1.0005×t _Rb+0.493041) with high correlation
coefficient (R =0.997) is fitted for 723 pairs of zircon U-Pb ages (t _Zr) and whole rock Rb-Sr ages (t _Rb) of granite plutons. The
frequency analysis of 723 individual values of differences between t _Zr and t _Rb (Δt _Zr-Rb) for granites shows symmetrical normal
distribution (skewness C _SK=0.193; kutrocess C _KU=6.722) with the Mean of 0.624 Ma and the Mode of 1.0 Ma. These statistical
characteristics indicate that for the granites as a whole, both the zircon U-Pb dating ages and the whole-rock Rb-Sr isochron ages
are consistent within permissible errors. However, because of a time difference between emplacement age and crystallizationsolidification
age, this isotope thermochronological method can be applicable only for the stage after their crystallizationsolidification.
Based on the differences between zircon U-Pb ages and whole-rock Rb-Sr isochron ages and the closure temperatures
of corresponding isotopic systems, previous researchers studied the cooling rates (CR _Zr-Rb) and thermal evolution history of 10
granite plutons, but these cooling rates are incorrelate to the volume change of granite plutons and contrary to the basic law of
thermophysics, i.e., the cooling rate of a larger hot body should be slower compared with a smaller one. In this paper, based on the
theory of thermal conductivity and using the concept of time difference between emplacement age and crystallization-consolidation
age, developed by present authors (2010), we come to a conclusion that, at the same thermo-physical conditions, the volume scale is the most important parameter that controls cooling rate of the granite plutons. On the example of existing 10 granites, and for
the high temperature thermal stage from magma emplacement to magma crystallization-consolidation, we derived a power function
regression equation to describe the relationship of cooling rate with volume parameter D: CR _ECTD=7544.7×D -2.1686. The calculated
results are obviously more reasonable and evidently conformable to the basic law of thermophysics.

Key words: high temperature thermochronology of granite plutons, zircon U-Pb age, whole-rock Rb-Sr isochron age, time difference between granite emplacement and crystallization-solidification, cooling rate of granite plutons