摘要
延边地区晚古生代–早白垩世花岗岩的Nd同位素研究显示,该区可以富尔河–古洞河断裂为界划分为南北两个岩区。北区显示亏损、年轻的源区特征(εNd(t)=?0.7^+3.8,tDM2=691~976 Ma),南区可能继承了古老富集端元组分(εNd(t)=–13.6~–0.6,tDM2=1004~2166 Ma)。从二叠纪到白垩纪,北区花岗岩的εNd(t)值随着年龄变新递减,南区的εNd(t)值则随着年龄变新递增,并在早白垩世时两区花岗岩的εNd(t)值达到基本相同。这种Nd同位素组成的变化趋势,说明南北两区深部地壳物质组成随时间变新而趋于均一化,反映了北区和南区先前存在的古亚洲洋型增生地壳和华北克拉通古老再循环地壳,在中生代期间遭受了古太平洋板块俯冲形成的新增生弧地壳的强烈改造和置换,使得两区深部地壳组成在白垩纪时基本一致。该研究结果为深入理解中生代古太平洋俯冲作用对东北地区深部地壳的改造过程提供了可靠的同位素地球化学制约。
A detailed Nd isotopic study on the Late Paleozoic-Early Cretaceous granitoids from the Yanbian area, NE China, is presented in this paper. The new results show that there are two granite zones in the area, i.e., the North and South Granite Zones separated by the Fu＇erhe-Gudonghe Fault. Most of the granitoids in the Northern Zone are characterized by positive εNd（t） values（？0.7–＋3.8） and younger tDM2 model ages（691–976 Ma）, suggesting a significant contribution of juvenile crustal material. In contrasting, the granitoids in the South Zone show negative εNd（t） values, ranging from –13.6 to –0.6, and older tDM2 ages of 1004–2166 Ma, implying that the Precambrian old recycled crust of North China Craton played a significant role in the generation of these rocks. Following the youthening of the emplacement age, the εNd（t） value of the granitoids in the North Zone decreases gradually, whereas it increases in the South Zone. During the Early Cretaceous, the εNd（t） value of the granitoids in both zones tends to be identical. Such a Nd isotopic variation trend reflects that the compositions of the deep crust beneath the two granite zones were the same in the Early Cretaceous. Our results indicate that the pre-existing deep crustal materials, which had been inherited from the North China Craton and the Central Asian Accretion Orogen respectively, were strongly replaced by the newly accreted crust formed by Mesozoic subduction of the Paleo-Pacific Ocean. Our conclusions provide new insight into the deep crustal replacement beneath NE China superimposed by the subduction of Paleo-Pacific Ocean.
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2015年第3期446-459,共14页
Geotectonica et Metallogenia
基金
国家重点基础研究发展计划(973项目)(2013CB429804)资助
