[B-PT23_30PO1] Decoding the history of Earth: From Hadean to Modern

[BPT23-P01] Reconstruction of tectonic history of the Cleaverville area in Coastal Pilbara Terrane ,western Australia

*Yuhei AIHARA¹, Shoichi KIYOKAWA¹, Ryoji TANAKA², Eizo NAKAMURA², Chie SAKAGUCHI² (1.Earth and Planetary Science, Kyushu Universiy, 2.Pheasant Memorial Laboratory, Institute for the Study of the Earth's Interior at Misasa)

The Dixon Island - Cleaverville formations of the Coastal Pilbara Terrane, Western Australia, is one of the most complete sections of a volcano-hydrothermal sequence of the immature island arc (Kiyokawa &Taira, 1998). These formations composed of the Dixon Island (DX) Formation, Dixon pillow basalt and the Cleaverville (CL) Formation. The CL Formation is uncomformably overlain by the Lizard Hills Formation. The Lizard Hills Formation was formed in syncline basin (66 Hill Member) during collisional D1 deformation and pull-apart basin (44 Hill Member) during sinistral slip D2 deformation (Kiyokawa et al., 2002). In this study, depositional ages of the CL Formation and the Lizard Hills Formation (44 Hill Member and 66 Hill Member) were examined by the analysis of U-Pb zircon dating. Zircons were measured using SHRIMP2 at National Institute of Polar Research. Metamorphic age of the DX Formation was obtained by the whole-rock 87Rb-86Sr isochronusing TIMS (Thermo TRITON and MAT253) at the Pheasant Memorial Laboratory, Institute for the Study of the Earth's Interior at Misasa. As a result, U-Pb zircon age of felsic tuff in the CL Formation is 3108(+14/-7) Ma. Detrital zircon ages of the 44 Hill Member showed main peaks at 3280-3200Ma and 3030-3020Ma. Detrital zircon ages of the 66 Hill Member also showed peaks at 3300-3200Ma, 3100-3050Ma, and miner group of 3700Ma. The Rb-Sr data define clear correlation line in the 87Rb-87Sr evolution diagram which corresponds to an age of 2210+/-60 Ma. In conclusion, sedimentation age of the DX formation is 3195+/-12Ma (Kiyokawa et al.,2002) and the CL Formation is 3108(+14/-7) Ma. The average of sedimentation rate in DX-CL formations is 2~3mm/ky as total thickness between these ages is 250m. After the sedimentation of the CL Formation, syncline basin (the Sity-Six Hill Member) was formed by D1 during 3088~3020 Ma. D2 faulting with pull-apart basin (44 Hill Member) was formed after the quartz porphyry (3020Ma) and the massive tonalite became to expose on land surface. The Rb-Sr age in the DX Formation as 2210+/-60 Ma corresponds to the timing of Ophthalmian orogeny (2145~2215Ma) in the southern margin of the Pilbara Craton (Rasmussen & Sheppard, 2005). The DX-CL formations probably had been affected by wide scale metamorphism at this timing.