变质作用中的地质温压计

THE GEOTHERMOBAROMETRY IN METAMORPHISM

作为测定变质作用的温度和压力的地质温压计近代取得了重要的进展。大量地质温压计的数据应用于变质地带中的温度和压力的变化以及它们与相继出现的构造事件的联系,从而得出它的P—T—t轨迹。地质温压计的发展取决于:1.变质矿物和矿物对的电子探针分析和X光晶体分析数据;2.岩石学的热力学;3.相平衡变质反应实验,其中热力学是它的理论基础,相平衡反应实验是热力学的应用,而分析数据则是在这一范围内的必要的鉴定温度和压力的数据. 近代认为地质温压计的划分应以变质反应的特性及其控制为前提。一般分为:Ⅰ.固体溶液参与的反应,其中又分为1.变换反应(包括晶内和晶间交换),2.非交换反应;Ⅱ.固定组分参与的反应,其中又分为1.固溶分解反应,2.固体—固体反应。地质温压计的研究切记不要照搬照套。工作中主要应注意:1.不同原岩组分对矿物组合的影响,注意其再现性和差异性;2.审慎选择时行的温压计;3.应结合变质地区中等变质级及其它数据并与其区内的其它温压计对比。

The study of the geologic thermometry and barometry, estimates of metamorphic temperatures and pressures, has been in, progress. Voluminous geothermobarometric data have made available to demonstrate the context of the temperature pressure variation with the successive structural events within an metamorphic belt, as shown by its P-T-t path. The development of the geothermobarometry relies on: 1)the electron microbe analysis and X-ray crystallographic measurements of the metamorphic mineral and mineral pairs; 2) application of thermodynamics to petrology; and 3) laboratory phase equilibrium experiments involving metamorphic reactions, among which the thermodynamics acts as the foundation, the phase equilibrium experiments are regarded as the applications of the thermodynamic process, and the microtechnic analysis the necessary requisites for the evaluation of the temperature and pressure within such framework in the geothermobarometry. Current opinion on the classification of the types of geothermobarometry largely follows the nature and the constraints of the metamorphic reactions. They are: Ⅰ. metamorphic reactions involving solid solution, which may be subdivided into 1) exchange reactions consisting of the intra-and inter-crystalline dxchanges; and 2) non-exchange reactions; Ⅱ. metamorphic reactions involving fixed composition, which may be divided as 1)solvi reactions; and 2)solid-solid reactions. Careful works must be done much more than plug in the number or read off the graphs. One should test the individual geothermobarometers by:l) making repeated measurements on the same assemblage in variable bulk compositions to ensure the reproducibility and the effects of variable compositions; 2) choosing cautiously the current fashionable geothermobarometers; 3) running calibrations against other thermobarometers and comparing with the informations on the isograde or other data collected from the metamorphic terrains.