纳米比亚达马拉造山带新元古界朝斯组条带状铁建造的特征及成因

Characteristics and genesis of banded iron formation in the Neoproterozoic Chuos Formation in Damara belt of Namibia

以纳米比亚北部台地区的新元古代成冰期朝斯(Chuos)组沉积变质型条带状铁建造为研究对象,通过研究该区的大地构造背景、矿物学、岩石学、地球化学等特征,针对该区域朝斯组地层特征、构造历史、结构构造、矿物组成、形成环境及成因等方面进行研究,结合"雪球地球"假说,认为研究区含铁建造与成冰期的一定条件下的裂谷作用形成海盆和热液组分有直接成因联系,在雪球期内的氧化还原环境多变的裂谷大洋、海底热液流体、大陆风化作用、海洋生物圈变化、大气与海水的物质组分交换等多重因素的作用下,最终导致了含铁条带建造的沉积层序的形成。

This work analyzed the stratigraphic features, tectonic history, textures and structures, mineral composition, formation en- vironment and mineral genesis of the Chuos Formation sedimentary metamorphic type Banded Iron Formation （BIF） formed during gla- cial period of Neoproterozoic in the northern platform of Namibi, by studying the geotectonic setting, mineralogical, lithological and ge- ochemical characteristics. Integrated with the evidence of ＂snowball＂ hypothesis, it is suggested the NIF in this region was closely relat- ed to the formation of sea basin caused by rifting during the glacial period and the composition of hydrothermal fluids. The combination of the changeable oxidation-reduction environment of ocean, seabed hydrothermal fluids, weathering of continent, changes of marine biosphere, material-exchanges between atmosphere and ocean, and other factors accounted for the formation of NIF.