摘要
太古宙登封绿岩带中变基性火山岩(2.5Ga)的ε_(Nd)~i=+2.16,经计算表明,具此值的岩石遭受了ε_(Nd)=-5的大陆地壳的混染,混染量约为16％,而正常的、无混染的幔源岩浆在2.5Ga前的ε_(Nd)~i值应为+3.7。据此推断,登封绿岩带是在有陆壳基底存在的裂谷盆地中发育起来的,同时,前登封绿岩基底是以长英质为主而且下部经历了麻粒岩相变质作用的陆壳,这一陆壳的年龄在2.9Ga以上(据锆石pb-pb年龄)。由于古老地壳麻粒岩相变质作用的影响,造成混染的绿岩带基性火山岩过低的^(87)Sr/^(86)Sr初始值以及该值与ε_(Nd)~i值相关性的破坏。
ε_(Nd)~i value of basic vocanics in the Dengfeng greenstone belt is +2.16. By calculation, it is indicated that the rocks were contaminated by continental crust whose ε_(Nd)~1 equals-5,2.5Ga ago, contamination volume is 16%, while normal ε_(Nd)~1 value of the mantle-derived magmas should be+3.7. According to the evidence above mentioned, It is infered that the Dengfeng greenstone belt developed in a rift on an old thinned basement and no oceanic crust occurred. In addition,the lower part of the greenstone belt basement is composed of felsic rocks and underwent granulite facies metamorphism, because the metamorphism of the old crust, caused too low initial ^(87)Sr/^(86)Sr ratios and destoration of correlation between ε_(Sr)~i and ε_(Nd)~i of contaminated rocks.
出处
《西北大学学报（自然科学版）》
CAS
CSCD
1989年第1期97-102,共6页
Journal of Northwest University（Natural Science Edition）
基金
国家科学基金
关键词
登封绿岩带
陆壳混染
陆壳基底
Dengfeng greenstone belt
Continental crust contamination
Continental crust basement
