[B-CG04] 地球史解読：冥王代から現代まで

[BCG04-07] エジプト、中央東砂漠地域の新原生代エルダバー層の層序と縞状鉄鉱層について

*清川 昌一¹、鈴木 大志¹、堀江 憲路²、竹原 真美²、 Maher Dawoud³ (1.九州大学大学院理学研究院地球惑星部門、2.国立極地研究所、3.メノフィーヤ大学)

キーワード：新原生代、中央東砂漠、縞状鉄鉱層

The El-Dabbah Group records a history of oceanic island arc accretion, collision, and collapse within the northern East African Orogeny during 770-570 Ma in Neoproterozoic.The El-Dabbah Group is an iron formation containing metavolcanic rocks in the Nubian Shield, Central Eastern Desert, Egypt. It preserves a sequence of relatively undeformed lower greenschist-facies rocks, overlain by subaerial sedimentary strata deposited in strike-slip basins (the Atsham Formation and the Hammamat Group). This formation includes a metavolcanics succession (>5500 m thick) containing three members, including coarse massive metavolcanic rock, pillow lavas, volcaniclastics with banded iron formation, and bedded volcaniclastic rock.At least 14 iron formations successions have been identified stratigraphically middle unit within 5500m thick volcaniclastic sequence at which are interbedded with greenish and black shales. Iron oxide beds most likely originated from dissolved Fe²⁺ sourced from oceanic arc volcanism, with repeated iron precipitation occurring during successive volcanically active periods. Four faulting were distinguished within the El-Dabbah area: (1) top-to-the-S low-angle thrusting; (2) NNE side down normal faulting; (3) sinistral displacement on north–south faults; and (4) WNE trend N-side-down normal faulting with the Hammamat Group. We obtained the crystallization ages of a granite (638.1 ± 2.9 Ma) and a quartz porphyry (659.6 ± 3.0 Ma). The detrital zircon age of the Hammamat Group show peaks at 650, 680, and 790 Ma. The El Dabbar Group formed several iron formations within relative proximal basin with hydrothermal section, which may be not related glacial condition.