Ji Fuwu

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Ji
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Fuwu
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  • Article
    Development and evolution of detachment faulting along 50 km of the Mid-Atlantic Ridge near 16.5°N
    (John Wiley & Sons, 2014-12-05) Smith, Deborah K. ; Schouten, Hans A. ; Dick, Henry J. B. ; Cann, Johnson R. ; Salters, Vincent J. M. ; Marschall, Horst R. ; Ji, Fuwu ; Yoerger, Dana R. ; Sanfilippo, Alessio ; Parnell-Turner, Ross ; Palmiotto, Camilla ; Zheleznov, Alexei ; Bai, Hailong ; Junkin, Will ; Urann, Ben ; Dick, Spencer ; Sulanowska, Margaret ; Lemmond, Peter ; Curry, Scott
    A multifaceted study of the slow spreading Mid-Atlantic Ridge (MAR) at 16.5°N provides new insights into detachment faulting and its evolution through time. The survey included regional multibeam bathymetry mapping, high-resolution mapping using AUV Sentry, seafloor imaging using the TowCam system, and an extensive rock-dredging program. At different times, detachment faulting was active along ∼50 km of the western flank of the study area, and may have dominated spreading on that flank for the last 5 Ma. Detachment morphologies vary and include a classic corrugated massif, noncorrugated massifs, and back-tilted ridges marking detachment breakaways. High-resolution Sentry data reveal a new detachment morphology; a low-angle, irregular surface in the regional bathymetry is shown to be a finely corrugated detachment surface (corrugation wavelength of only tens of meters and relief of just a few meters). Multiscale corrugations are observed 2–3 km from the detachment breakaway suggesting that they formed in the brittle layer, perhaps by anastomosing faults. The thin wedge of hanging wall lavas that covers a low-angle (6°) detachment footwall near its termination are intensely faulted and fissured; this deformation may be enhanced by the low angle of the emerging footwall. Active detachment faulting currently is limited to the western side of the rift valley. Nonetheless, detachment fault morphologies also are present over a large portion of the eastern flank on crust >2 Ma, indicating that within the last 5 Ma parts of the ridge axis have experienced periods of two-sided detachment faulting.
  • Article
    Jurassic zircons from the Southwest Indian Ridge
    (Nature Publishing Group, 2016-05-17) Cheng, Hao ; Zhou, Huaiyang ; Yang, Qunhui ; Zhang, Lingmin ; Ji, Fuwu ; Dick, Henry J. B.
    The existence of ancient rocks in present mid-ocean ridges have long been observed but received less attention. Here we report the discovery of zircons with both reasonably young ages of about 5 Ma and abnormally old ages of approximate 180 Ma from two evolved gabbroic rocks that were dredged from the Southwest Indian Ridge (SWIR) in the Gallieni fracture zone. U–Pb and Lu–Hf isotope analyses of zircons were made using ion probe and conventional laser abrasion directly in petrographic thin sections. Young zircons and their host oxide gabbro have positive Hf isotope compositions (εHf = +15.7–+12.4), suggesting a highly depleted mantle beneath the SWIR. The spread εHf values (from−2.3 to−4.5) of abnormally old zircons, together with the unradiogenic Nd-Hf isotope of the host quartz diorite, appears to suggest an ancient juvenile magmatism along the rifting margin of the southern Gondwana prior to the opening of the Indian Ocean. A convincing explanation for the origin of the unusually old zircons is yet to surface, however, an update of the theory of plate tectonics would be expected with continuing discovery of ancient rocks in the mid-oceanic ridges and abyssal ocean basins.