摘要
本文在系统讨论白云母的化学成分与形成条件关系的基础上,研究了浙江绍兴——江山断裂带及其两侧两类不同成因的白云母的形成温压条件。韧性剪切变质成因的白云母,化学成分中 Na、A1Ⅳ和 A1Ⅵ含量较低,Si、Mg 和 Fe 含量较高,区域变质成因的白云母则相反。前者多为:205～400℃,400～600MPa;后者多为:310～520℃,200～400MPa。在低级变质作用中,除岩石化学成分在一定程度上的影响之外,白云母化学成分中的 Mg含量与其形成压力密切相关,高压变质作用形成的白云母 Mg 含最多较高。绍兴——江山断裂带内韧性剪切带中的白云母,b_o 值乡大于式近于9.040×10^(-10)m,本文认为这不能反映其形成于高压条件。因此,在运用 F·P·Sassi 等人的白云母 b_o 值压力指示剂时应该特别慎重。
Based on a systematic discussion of the relationship between che- mical compositions and formation conditions of muscovite,the for- mation P-T conditions of two different genetic types of muscovites from the rocks inside and near the Shaoxing—Jiangshan fault belt have been studied in this paper.Muscovites formed during ductile shear metamorphism are characterized by conta ining more Si,Mg and Fe and less Na,Al^(Ⅳ) and Al^(Ⅵ) in their chemical compositions,however, those formed during regional metamorphism are contrary.The forma- tion P-T conditions of the former are mainly 250～400℃,400～600 MPa,and of the latter are mainly 320～520℃,200~400 MPa.Except for some influence of whole rock chemical compositions,the content of Mg^(2+) in muscovites formed during lower grade metamorphism is closely related to the metamorphic pressure.Muscovites crystallized during high-pressure metamorphism contain more Mg^(2+).The b。va- lues of muscovites from the ductile shear zones inside the Shaoxing- Jiangshan Fault Belt are mostly greater than or approximate to 9.040×10^(-10)m.There is no evidence that the muscovites were formed at a high metamorphic pressure.So it must be cautious to use the b。value barometric indicator of muscovite given by F.P.Sassi, et al.
