山东诸诚地区胶南群榴辉岩围岩高压变质作用特征

大别－苏北－胶南－荣成含榴辉岩带长达１３００ｋｍ，胶南合榴辉岩地体位于这一变质带中段。本文通过对胶南地体西北缘的诸城地区榴辉岩围岩的岩石学、矿物学及热力学等方面的研究，首次在该区发现了一些高压的特征矿物：（石榴）镁钠门石暗硬玉片麻岩中暗硬玉具有较高的硬玉分子含量，最高达２２．５ｍｏｌ％，并具明显的成份环带；石榴多硅白云母二长片麻岩及石榴多硅白云母变粒岩中，多硅白云母略具粉红色多色性，其中Ｓｉ＝３．４４～３．５５，ｂ０＝９．０６。同时探讨了胶南群变质作用特征及Ｐ—Ｔ—ｔ演化趋势。

HIGH-PRESSURE METAMORPHISM OF ECLOGITIC COUNTRY ROCKS,JIAONAN GROUP,ZHUCHENG DISTRICT,SHANDONG PROVINCE

Jiaonan terrane at the tectonic boundary between the Sino-Korean and Yangtze Cratons in East China. Zhucheng district is situated at the northwest of Jiaonan terrane. Rocks in Jiaonan Group is the oldest in this area, in which eclogite distributes. Two periodical high-pressure metamorphism are recognized according to petrological features and mineral paragenesis: Calcite garnet pyroxenolite, relic of the first metamorphism, consists of fassaite (34% ), garnet (40% ), calcite (5% ), rutile (1 % ). It occurs as a lenticular body in garnet biotite phengite granulite; In chloromelanite gneiss, there is a compositional zone in chloromelanite, the core of which is composed of Jd22. 5 Ac58. 8 Hd7.8 Di10.9, the rim, Jd9. 9Ac70.3 Hd5.9 Di13.9; In biotite garnet granulite, garnet shows degrade zoning, with Mn2+ increasing and Mg2+,Ca2+ decreasing from the core to rim. That the grossular content of core garnet is 50 percent shows that the first high-pressure metamorphism exists. The condition of the first metamorphism is: T= 550￣650℃, P= 11￣ 16kb, and the second is: T≈458. 4℃, P≈7. 3 kb, PTt paths in eclogitic country rocks is clockwise.The authors suggest that the thickening crust caused by the collision between the Sino-Korean and Yangtze Cratons produce a high-pressure environment on a regional scale. Basaltic rocks turned into eclogite in such conditions. With the uplift of crust,regional rocks underwent the second Deriodical metamorphism.China university of Geosciences, Beijing, 100083 1 Peking University, Beijing, 100871