中国东部燕山期埃达克岩的特征及其构造-成矿意义

The characteristics and tectonic-metallogenic significances of the adakites in Yanshan period from eastern China.

埃达克岩是一套中酸性的火成岩 ,以亏损 HREE和无负铕异常为特征 ,表明其形成深度很大 ,源区有石榴石残留。中国东部燕山期有许多中酸性岩浆岩类似埃达克岩的地球化学特征 ,但其形成环境却与消减作用无关。因此 ,本文将埃达克岩分为 O型和 C型两类 :O型埃达克岩富 Na,其成因与板块的消减作用有关 ;C型埃达克岩富 K (大部分仍然是钠质的 ,少数为钾质的 ) ,可能是玄武岩浆底侵到加厚的陆壳 (>5 0 km )底部导致的下地壳麻粒岩部分熔融的产物。 C型埃达克岩对解释中国东部燕山期许多地质现象是有启发的。由于 C型埃达克岩保存了下地壳的许多印记 ,因此 ,还可以利用 C型埃达克岩来反演下地壳的组成 ,探讨与下地壳及壳

Adakite is a suite of intermediate-acid igneous rocks characterized by HREE depletion and no obvious negative Eu anomaly, indicating the derivation from very deep source with garnet in the residue. A lot of Yanshanian intermediate-acid magmatic recks in eastern China have similar geochemical characteristics to the adakite, their formation environment however is unrelated to subduction process. In this paper, adakite is divided into two types: one is O-type adakite, which is characterized by Na enrichment and is related to subduction process; another is C-type adakite, which is enriched in II (most of them are still enriched in Na, a few K-enriched), is probably a product of partial melting of the lower-crust granulite in the thickened crust (> 50km) resulted from underplating of basaltic magma. The occurrence of C-type adakites in eastern China is indicative to the explanation of the geological phenomenon of Yanshanian magmatism. Because C-type adakite can preserve same imprints of the lower crust, it in turn can trace the composition of the lower crust and discuss metallogenesis related to the lower crust and crust-mantle process.