Abstract The Quadrilatero Ferrifero (QF) is an important, polydeformed mineral province, located in the southernmost portion of Sao Francisco Craton. The Rio das Velhas greenstone belt (RVGB) is an Archean meta-volcano-sedimentary succession from the QF, the Corrego do Sitio unit (CdS) being its most widely distributed sedimentary sequence. Detailed sedimentology study allied to x-ray diffraction-XRD and geochronological (LA-ICP-MS in detrital zircon) analyses provide evidence for a new interpretation of the CdS. The identified sedimentary structures of the CdS (e.g. flaser and lenticular bedding, sharp and erosional base, normal grading, mud drapes, quartz granules, syndepositional deformation, and ball & pillow) led the interpretation of these couplets as turbidity currents deposits corresponding to TA and TE facies of the classic Bouma Sequence. The CdS sequence was deposited on distal portions of an ancient submarine fan environment by turbidity current mechanisms, then it was partially reworked by tidal bottom currents. Geochronological data pointed out the main influence of the Rio das Velhas II magmatic event in the deposition of the eastern QF metasedimentary sequence, as evidenced by the maximum depositional age at 2818 ± 31 Ma. The surrounding metamorphic complexes terrains may have acted as source areas during the deposition of the sedimentary sequences, probably in a convergent to a collisional marginal tectonic setting (subduction stage).

中文翻译：

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巴西 Quadrilátero Ferrífero Rio das Velhas 绿岩带东部太古代变沉积层序的特征和年代学

摘要 Quadrilatero Ferrifero (QF) 是一个重要的多变形矿区，位于圣弗朗西斯科克拉通最南端。Rio das Velhas 绿岩带 (RVGB) 是来自 QF 的太古代变质火山沉积序列，Corrego do Sitio 单元 (CdS) 是其分布最广泛的沉积层序。详细的沉积学研究与 X 射线衍射-XRD 和地质年代学（碎屑锆石中的 LA-ICP-MS）分析相结合，为 CdS 的新解释提供了证据。已识别的 CdS 的沉积结构（例如，flaser 和透镜状层理、尖锐和侵蚀基底、正常级配、泥帘布、石英颗粒、同沉积变形和球状和 Pillow) 将这些对联解释为对应于经典 Bouma 层序的 TA 和 TE 相的浊流沉积物。CdS 序列通过浊流机制沉积在古代海底扇环境的远端部分，然后被潮汐底流部分改造。年代学资料指出Rio das Velhas II岩浆事件对东QF变沉积序列沉积的主要影响，最大沉积年龄为2818±31 Ma。周围的变质杂岩地形可能在沉积层序的沉积过程中充当了源区，可能会聚到碰撞边缘构造环境（俯冲阶段）。CdS 序列通过浊流机制沉积在古代海底扇环境的远端部分，然后被潮汐底流部分改造。年代学资料指出Rio das Velhas II岩浆事件对东QF变沉积序列沉积的主要影响，最大沉积年龄为2818±31 Ma。周围的变质杂岩地形可能在沉积层序的沉积过程中充当了源区，可能会聚到碰撞边缘构造环境（俯冲阶段）。CdS 序列通过浊流机制沉积在古代海底扇环境的远端部分，然后被潮汐底流部分改造。年代学资料指出Rio das Velhas II岩浆事件对东QF变沉积序列沉积的主要影响，最大沉积年龄为2818±31 Ma。周围的变质杂岩地形可能在沉积层序的沉积过程中充当了源区，可能会聚到碰撞边缘构造环境（俯冲阶段）。最大沉积年龄为 2818 ± 31 Ma。周围的变质杂岩地形可能在沉积层序的沉积过程中充当了源区，可能会聚到碰撞边缘构造环境（俯冲阶段）。最大沉积年龄为 2818 ± 31 Ma。周围的变质杂岩地形可能在沉积层序的沉积过程中充当了源区，可能会聚到碰撞边缘构造环境（俯冲阶段）。