磷灰石中氦扩散参数的确定方法及求解过程  

Detailed Procedure for Determining the Helium Diffusion Parameter in Apatite

作　　者：张彦[1] 陈文[1] 刘新宇[1] 

机构地区：[1]中国地质科学院地质研究所氩-氩年代学实验室,北京100037

出　　处：《高校地质学报》2010年第2期213-217,共5页Geological Journal of China Universities

基　　金：国家自然科学基金(编号40773043);基本科研业务费项目(J0711;JB0708);国土资源大调查项目(1212010761401)联合资助

摘　　要：基于Arrhenius关系图解,详细介绍了磷灰石中氦扩散参数及其封闭温度的确定方法及求解过程,并以Wolfetal(1996)的阶段升温数据为例进行了演示性和验证性计算。主要求解步骤如下:(1)对磷灰石做阶段升温试验,得到每一阶段的氦累积丢失分数;(2)根据球形颗粒的扩散模型公式计算出每一阶段的lnD/a2;(3)以lnD/a2作为纵坐标,1/T作为横坐标作图(T为阶段升温试验每一阶段的温度),如果在某一温度范围内得到的是一条直线,说明在这一温度范围内磷灰石中氦的扩散遵从Arrhenius关系式,那么在Arrhenius关系图解上,扩散参数E和lnD0/a2可通过直线的斜率和截距得到;(4)把E和lnD0/a2代入封闭温度的计算公式,通过迭代计算就可得到磷灰石的封闭温度。求解过程中需要注意两个关键问题:(1)由于1/T为小数,对于磷灰石的氦扩散数据来说,需乘以104将其化为整数,与纵坐标的数值为同一数量级;(2)计算封闭温度时,需把冷却速率的单位从"℃/Ma"转化为"K/s",转化时需注意1℃/Ma=1K/Ma。In this paper we present the detailed procedure to calculate the helium diffusion parameter and its closure temperature in apatite.We use the step-heating data of Wolf（1996）to show this procedure and its correction.This method is based on the Arrhenius relationship which describes the diffusivity variation with temperature.This procedure is as follows：（1）Do step-heating experiment to get the cumulative gas release fraction.（2）Calculate the lnD/a 2 of every step using spherical diffusion equation.（3） Make Arrhenius plot,taking the lnD/a 2 as y-axis and the 1/T（T is the temperature of every step）as x-axis.In this plot,if the points defined by lnD/a 2 values and the 1/T values within some temperature range show linearity,it indicates that within this temperature range the apatite diffusion obeys the Arrhenius relationship and thus we can get the diffusion parameter E from the slope and the LnD0/a 2 from the intercept in the Arrhenius plot.（4）Insert the value of E and LnD0/a 2 into the closure temperature equation to calculate the closure temperature using iterative method.In addition,when we use the above method to calculate the helium diffusion parameter,we should pay attention to the following aspects：（1）Because 1/T is decimal fraction,for apatite diffusion data,1/T should be multiplied by 104,making it the same order with lnD/a 2.（2）When calculating the closure temperature,the unit of the cooling rate℃/Ma should be converted to K/s.For the cooling rate,1℃/Ma equals to 1 K/Ma.

关 键 词：磷灰石 氦扩散参数 封闭温度 

分 类 号：P578.923[天文地球—矿物学]