摘要
南极拉斯曼丘陵及其邻区的(含)夕线片麻岩类的原岩可以是杂砂岩、亚杂砂岩、石英砂岩、泥质岩或页岩等。粘土岩或页岩之类的富铝沉积岩与富夕线片麻岩并没有直接对应关系。没有一种泥质岩的化学组成可以与富夕线片麻岩相对应。研究区内夕线石片麻岩的形成主要与黑云斜长片麻岩有关,影响夕线石出现的决定性因素是特定温压条件下的变形变质改造过程,而不是原岩成分。夕线石片麻岩在很大程度上是黑云斜长片麻岩经长英质组分迁移之后的滞留-残留体。夕线石化过程中岩石组分发生了改造,相关变质作用已经明显偏离等化学过程,基本上属于开放体系。原岩中Al2O3的含量也不能控制夕线石的出现与否,含夕线石的岩石未必富铝,反之亦然,岩石富铝也可以不出现夕线石;但是夕线石化过程往往是Al2O3相对增加的过程,这些认识对于夕线石片麻岩成岩环境的确定和原岩建造的重建都具有重要意义。
The protoliths of the sillimanite gneisses from the Larsemann Hills, east Antarctica, and their adjacent area may be greywacke, sub-greywacke, quartz sandstone, pelite or shale. The aluminum rich sediments such as clays or shale need not correspond to sillimanite-rich gneisses. No known argillaceous rock equals to sillirnanite-rich gneiss in chemical composition. The source rock from which the sillimanite gneisses derive is probably biotite plagioclase gneiss in the study area. It is the deformation-metamorphism process under pressure and temperature condition, not the original rock composition, that controls the presence of sillimanite. We suggest that the sillimanite gneiss is a mixture of materials from the migrating felsic melt, the biotite-plagioclase gneiss undergoing partial melting and the restites after the melt is removed. During metamorphism and sillirnanite formation the original rock changes its chemical composition and, the process is an open system, which deviates from being isochemical. In addition, the Al2O3 contents of the original rock is an important, but not critical factor for the formation of sillimanite, i. e. , the sillimanite-hearing rock need not be aluminum rich in composition, and vise versa, an aluminum-rich rock does not necessarily produce sillimanite. Therefore we postulate that the source rock from which the aluminum rich rocks derive need not be enriched in this ele- ment, but we point out that the formation of sillimanite generally involves a Alz03 increasing process. If correct, this conclusion is of significant implication for the determination of the sillimanite gneiss formation process and the reconstruction of the protolith setting.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2007年第1期75-84,共10页
Earth Science Frontiers
基金
国家自然科学基金资助项目(40172065
40572041)
中国地质调查局项目(200413000023)
国土资源部百名优秀青年科技人才项目
