[SCG66-07] MOWALL – Moho Observation along long transform fault WALLs
Keywords:transform fault, oceanic crust, mantle heterogeneity, mid-ocean ridge process
Marie Celeste TF: The Central Indian Ridge spreads at rate of 37-40mm/yr. and a 215km long transform exposes the oceanic crust from 0 to 12 Ma. Pre-existed bathymetry data just south of transform indicate large temporal variation of melt supply. On-axis sheet lava flow and recent off-axis volcanoes suggest vigorous melt supply since ca. 3Ma, whereas a couple of OCCs were developed just before then. We plan to do 25km interval dredge hauls along the fault wall in coming R/V Hakuho-maru cruise in October 2020. Along axis gravity/magnetic mapping is also planned to estimate the crustal thickness variation and precise age dating.
Shikoku-Parece Vela TFs: In the Shikoku -Parece Vela backarc basins in the Philippine Sea, remnant backarc rift is closely segmented by many transforms. Several OCCs including the world-largest Godzilla Mullion and smooth seafloors are discovered along the rift, indicating large fluctuation of melt supply. The transforms are generally short and not suitable for long-term variation analysis; however, existing peridotite samples show clear fluctuation of degree of melting from different parts of the OCC. Our recent cruises in 2018 and 2019 and many previous cruises reveal the detailed history of melt supply in the final stage of backarc basin formation.
Vulcan TF: The Vulcan transform is located unexplored Southern Ocean, 59°S, 17°W. The South American-Antarctic Ridge spreads at rate of 14 mm/yr. and the ridge axis is offset about 55km by this transform exposing 8 Myr age transect. During R/V Hakuho-maru cruise KH-19-4, we conducted five dredge hauls along the transform at 15-20km interval.
We present the preliminary results of survey in the Shikoku-Parece Vela and the Vulcan TFs and introduce the pre-cruise studies on Marie Celeste TF.