New Thinking, Method and Calculated Examples of High Temperature Thermochronology of Granite Plutons
详细信息
- 责任者：Zhang Bangtong (State Key Laboratory for Mineral Deposits Research ; School of Earth Sciences ; Nanjing University ; Nanjing 210093 ; China) ; Ling Hongfei
- 刊名：Geological Journal of China Universities
- 出版年：2013
- 卷期：19(3)
- 关键词：花岗岩 ; granite ; 热年代学 ; thermochronology
- 页码：p.385-402
- 图表：6 illus., 7 tables, 31 refs.
- 分类号：0801
- issnNo：ISSN1006-7493
- isbnNo：CN32-1440/P
摘要
Using least squares regression procedure,a best regression equation(tZr =1.0005×tRb +0.493041) with high correlation coefficient(R=0.997) is fitted for 723 pairs of zircon U-Pb ages(tZr) and whole rock Rb-Sr ages(tRb) of granite plutons.The frequency analysis of 723 individual values of differences between tZr and tRb(ΔtZr-Rb) for granites shows symmetrical normal distribution(skewness CSK =0.193;kutrocess CKU =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(CRZr-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 parameterD: CRECTD =7544.7×D-2.1686.The calculated results are obviously more reasonable and evidently conformable to the basic law of thermophysics.
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