弓长岭太古代条带状硅铁建造中长英质变质岩的原岩恢复及地层学意义

THE RECOGNITION OF ORIGINAL ROCKS OF FELSIC METAMORPHIC ROCKS IN GUANGCHANGLING ARCHEAN BANDED IRON FORMATION AND STRATIGRAPHIC IMPLICATION

弓长岭太古代条带状硅铁建造中的长英质变质岩为该地层的标志层(K和K_S层)。原岩恢复表明二矿区黑云母石英钠长变粒岩(K层)为含火山灰的中酸性火山熔岩;而岭东区的石榴云母石英片岩(K_S层)为含火山灰的泥砂质沉积岩,二者不能对比。据此,本文补充和完善了该区地层剖面。它表明弓长岭硅铁建造生成于大陆边缘的陆棚浅海环境,其铁矿层赋存于一海进层序的中上部。该建造的沉积岩组合特征与绿岩带不同,而与典型的高级区表壳岩组合类似。

This study recognized that original rocks of the felsic metamorphic rocks from a key horizon (termed K and K_S) in Guangchangling Archean Banded Iron Formation are tuffaceous intermediate acidic volcanic lava for biotite-quartz-albite gneiss (K) and tuffaceous sedimentary rock for garnet-mica-quartz schist (K_S) respectively.Therefore, K and K_S can not be the same horizon. According to this and some new stratigraphic sections, the stratigraphic section for Guangchangling Archean Banded Iron Formation was renewed. It suggests that this banded iron formation was developed in a shallow sea environment on a continental shelf and the iron ore beds are in mid-upper part of the transgressive series. The characteristics of sedimentary rock association of Guangchangling Banded Iron Formation are different from that of greenstone belt and similar to that of typical supracrustal rocks in high-grade terranes.