摘要
最近在承德市北部地区发现了许多呈透镜状包体产于花岗片麻岩中的高压基性麻粒岩。运用全岩Ｓｍ －Ｎｄ、Ｒｂ－Ｓｒ、单颗粒锆石Ｕ－Ｐｂ 等多种同位素方法对这些高压麻粒岩进行了年代测定，得出了７个可供研究的年龄数据，即全岩Ｓｍ －Ｎｄ 等时线年龄２５５０±２１Ｍａ和３０６０±２．３Ｍａ，全岩Ｒｂ－Ｓｒ等时线年龄１５５０±３３Ｍａ 和１５６８Ｍａ，和单颗粒锆石Ｕ－Ｐｂ 同位素不一致线的上、下交点年龄分别为３４３２±５５６Ｍａ 和１８１７±１７Ｍａ， 颗粒锆石的谐和年龄１８３１±４ Ｍａ。在详细分析这些年代学数据可能的地质解释的基础上，认为该区的高压麻粒岩经历了复杂的地质演化过程，推测其原岩最早可能形成于新太古代早期至中太古代，并经受了太古宙末期花岗质岩浆侵入和变质作用改造。但其高压麻粒岩相变质很可能是古元古代末一次碰撞造山作用的产物， 最终进入上地壳可能在中元古代早期才完成，
A lot of high pressure basic granulites have recently been identified in the north region to Chengde, northern Hebei province, China. They occur as enclaves like lenses in granitic gneiss. Although the isotope composition of seven whole rock samples from these granulites can not define unique Sm Nd isochron and Rb Sr isochron on the corresponding isochron diagrams, they can yield two comparatively precise lines respectively. The two referable Sm Nd isochron ages are 3060±2.3 Ma with I Nd =0 508827, ε Nd ( t )=+3 3, and 2550±21 Ma with I Nd =0 50955, ε Nd ( t )=+4 5, and the two alike Rb Sr isochron ages are 1550±33 Ma with I Sr =0 702860, and 1568 Ma with I Sr =0 700942 The zircons from one of seven samples are dated using the single zircon U Pb method, and yield a low intercept age of 1817±17 Ma and subconcordant ages of ca. 1800 Ma. The likely explanation of these ages is that: the 3060±2 3 Ma is the time of protolith emplacement or crystallization through underplating; the 2550±21 Ma reflects a widespread thermal event, and most likely represents magmatic activity related to formation and intrusion of the country rock granitic gneiss; the 1817±17 Ma may date a stage when the ganulites exhumed to certain medium pressure level; the 1550±33 Ma may indicate a late large scale thermal event, and imply the granulites lastly reached to the upper crust or supracrust till the initiation of nearby middle Proterozoic aulacogen. It is noted to say although the zircon U Pb ages don't reflect the age of peak pressure temperature of metamorphism, the geologic relationships provide an upper age limit of 1900 2000 Ma. Based on these studies, it can be deduced that the high pressure granulites may indicate a collision at the end of Early Proterozoic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1999年第4期524-531,共8页
Acta Petrologica Sinica
基金
原地质矿产部 "九五"资源与环境科技攻关项目
关键词
同位素年龄
高压基性麻粒岩
地质演化
麻粒岩
Isotope age, High-pressure basic granulites, Geologic evolution, Chengde
