摘要
通常认为暗色麻粒岩是基性火山岩层遭受高级变质的产物。文章根据内蒙集宁和山西阳高地区的高级变质区的岩石组合、结构构造、矿物共生、地质温度计等9方面资料,论证了工作区暗色麻粒岩不是基性火山岩的进变,而是原始苏长辉长岩的逆变(degeneration,指由原始岩浆岩的高温矿物组合变为变质矿物组合),根据麻粒岩的矿物组合和组构变化,结合其它地质和物理化学特征,将工作区的暗色麻粒岩分成了A、B、C三种类型,大体相应于苏长辉长岩变为暗色麻粒岩的逆变序列。文章最后提出了麻粒岩和麻粒岩相的修订意见,并指出高级区麻粒岩并非一定属于太古代产物。
It is generally accepted that melanogranulites (plagioclase-two-pyroxene granulite, hornblende-two-pyroxene granulite etc.)were metamorphosed from basic volcanic basalt at prograde granulite facies conditions. The view that the original rocks of the melanogranulite are basic volcanics is mainly based on its layered structure and chemical composition corresponding to that of basalt. According to the data concerning 9 aspects, such as the rock association, textures and structures, mineral assemblages and geothermometry, of the high-grade metamorphic terrane in the work area, it has been demonstrated that the protoliths of the melanogranulite is igneous norite-gabbro, not volcanics.
In the light of mafic minerals and textures of the melanogranulite, three types of melanogranulite have been distinguished (Table 2):
Type A——original norite-gabbro, hypersthene + diopside + plagioclase (An>60), without brown hornblende;
Type B——metanorite-gabbro, hypersthene+ diopside+ (brown hornblende) + plagioclase (An50 ±), bracketed minerals showing paraequilibrium or metasomatic relationship;
Type C——hornblende-two-pyroxene granulite, hypersthene + diopside+brown hornblende+plagioclase (An35—50) + sillimanite, the last mineral being derived from peralumina of decalcification of basic plagio clase.
The alteration from Type A (original norite-gbbbro) with an original hightemperature igneous assemblage to Type C (hornblende-two-pyroxene granulite) with a high-grade metamorphic assemblage is here named 'degeneration', which is different from retrogressive metamorphism or diaphthoresis that means that the protolith changes progressively to a high-grade metamorphic assemblage which again converts to an assemblage (usually more hydrous) stable at lower temperature.
Since brown hornblende-bearing melanogranulite in derived from high-grade metamorphism of norite-gabbro, it is suggested that brown hornblende is used as the diagnostic mineral of granulite facies, not hypersthene.
出处
《地质论评》
CAS
CSCD
北大核心
1989年第1期1-12,共12页
Geological Review
