Garnet compositions as recorders of P-T-t history of metamorphic rocks
Garnet compositions as recorders of P-T-t history of metamorphic rocks
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石榴石成分作为变质岩 P-T-t 历史的记录者
DOI：
10.1016/j.gr.2009.12.010
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发表时间：
2010
影响因子：
6.1
通讯作者：
J. Ganguly
中科院分区：
文献类型：
--
作者：
M. Tirone;J. Ganguly
在最近研究的基础上，我们得出的结论是，石榴石-黑云母Fe-Mg交换和Grs=Plag+Aluminosilicate+Qtz（GASP）反应的平衡条件的同时解决方案，制定的基础上选择的实验数据和良好的约束热力学混合性质的石榴石和斜长石，提供了可靠的估计的P-T条件的变质组合，包括上述矿物。另外的计算显示的兼容性检索的P-T条件的天然组合与铝硅酸盐相图。我们还计算了石榴石的最小晶粒尺寸，应用于计算峰变质P-T（Pp，Tp）条件，使用合理的初始猜测值的最小冷却速率和最大Tp。检索的热历史的变岩，我们已经开发了一个有限差分方案，模拟多组分的扩散分布在石榴石，纳入规定连续成核和生长。这已经与遗传算法，允许检索的温度与时间的路径的变岩通过建模的石榴石分区配置文件，保持几个模型参数作为浮动变量。数值代码已被应用到检索的T-T历史的低压高温Royke变质带，日本，通过模拟的浓度剖面的Fe，Mn，Mg和Ca的不同尺寸的石榴石，已推断已开发的连续成核和生长的过程。
On the basis of tests made in recent studies, we conclude that the simultaneous solutions of the equilibrium conditions of garnet–biotite Fe–Mg exchange and Grs=Plag+Aluminosilicate+Qtz (GASP) reactions, as formulated on the basis selected experimental data and well constrained thermodynamic mixing properties of garnet and plagioclase, offer robust estimates of P–T conditions of metapelitic assemblages that consist of the above minerals. Additional calculations are presented to show the compatibility of the retrieved P–T conditions of natural assemblages with the aluminosilicate phase diagram. We also calculate the minimum grain sizes of garnets that should be used for the calculation of the peak metamorphic P–T (Pp, Tp) conditions, using reasonable initial guessed values of minimum cooling rate and maximum Tp. To retrieve the thermal history of metapelites, we have developed a finite difference scheme for modeling multicomponent diffusion profiles in garnet, incorporating provisions for continuous nucleation and growth. This has been interlinked with a genetic algorithm that permits retrieval of the temperature vs. time path of metapelites through modeling of the zoning profiles in garnets, keeping several model parameters as floating variables. The numerical code has been applied to retrieve the T–t history of the low pressure–high temperature Royke metamorphic belt, Japan, by modeling the concentration profiles of Fe, Mn, Mg and Ca of garnets of different sizes that have been inferred to have developed by a process of continuous nucleation and growth.