Rheology and Biostratigraphy of the Mariana Serpentine Muds Unravel Mud Volcano Evolution

Abstract

In late 2016, the IODP Expedition 366 drilled 21 holes on summits and flanks of three serpentinite mud volcanoes (SMVs) of the Mariana Forearc: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). The drilling reached the forearc sediments underneath the SMVs only at Site U1498 where, according to data from this study, the biostratigraphic age of Fantangisña appears to be well constrained, with a pelagic cover on top of the serpentine mud flows of 0.44 Ma and an age of the forearc sediments of 11.21 Ma. With an estimated age of at least 10.77 Myr this is, to our knowledge, the oldest mud volcano ever dated. To link the age of the edifice with its eruptive dynamics, we performed rheological tests of natural samples of serpentine mud from the Fantangisña SMV for the first time. These experiments not only confirm the highly viscous characteristic of the mud breccia but also identify different muds' mineralogical compositions (i.e., serpentine-rich vs. serpentine-poor sediments) and water contents as being responsible for the main rheological variations. The viscosity from the rheological data, together with the physical properties of the mud breccia and the clasts measured onboard IODP366, under several assumptions, allow us to estimate of flow velocities and a depth of the mud source at ∼8.4 km below seafloor. Moreover, comparison of erupted mud breccia volumes from bathymetry, seismic data, and calculations shows how the SMV evolution is linked to episodic events, highlighting that Fantangisña has actively been expelling sediments during 2.41% of its life span.

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

“…The large cluster in the north is below and downdip of Asùt Tesoru, Quaker, and several other smaller seamounts, and the southern cluster is downdip of Turquoise and Fantangisña Seamounts. These seamounts are thought to be long‐lived features, with Fantangisña estimated to be at least 10.77 Ma (Menapace et al, 2019). These serpentine seamounts are built over deep‐seated extensional faults that formed due to slab rollback and increased curvature of the arc (Fryer et al, 2006; Menapace et al, 2019).…”

“…These seamounts are thought to be long‐lived features, with Fantangisña estimated to be at least 10.77 Ma (Menapace et al, 2019). These serpentine seamounts are built over deep‐seated extensional faults that formed due to slab rollback and increased curvature of the arc (Fryer et al, 2006; Menapace et al, 2019). Vertical tectonism caused by the subduction of plate seamounts likely furthers the development of these faults that penetrate the forearc to allow serpentinite muds to travel to the seafloor (Fryer et al, 2000; Oakley et al, 2007; Stern & Smoot, 1998).…”

Rheology of Natural Sediments and Its Influence on the Settling of Dropstones in Hemipelagic Marine Sediment

“…where τ is shear stress, τ y is the yield stress, is strain rate, K is consistency, and n is the flow index. We adopt the Herschel‐Bulkley model, but note that models without a yield stress have also been used to model mud rheology especially for low strain rates and high viscosities (e.g., Menapace et al, ).…”

“…These idealized mixtures differ from naturally occurring submarine sediment in particle size and size distribution as well as composition. There are few studies of the rheology of natural submarine deposits (e.g., Imran et al, 2001;Jeong, 2013;Locat et al, 2004;Menapace et al, 2019).…”

Foraminifera assemblages from Fantangisña serpentinite mud seamount in the NW Pacific Ocean during the Pleistocene (IODP Expedition 366)

“…At the top of the edifice, normal faulting induced the formation of a 5 km long, 3.5 km wide, U-shaped depression (Oakley, 2007). Menapace et al (2019) attempted to assess the timing of the onset of Fantangisña serpentinite mud volcanic activity using combined planktonic foraminiferal and calcareous nannofossil biostratigraphy on samples collected during IODP Expedition 366. Their proposed age for the emplacement of the seamount was estimated at 10.77 Ma (Menapace et al, 2019).…”