The nature of the intrusive crust and Moho at slower spreading ridges; SloMo Leg 1 (IODP Expedition 360)

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Author(s): MacLeod, Christopher J.; Dick, Henry J.; Blum, Peter
International Ocean Discovery Program, Expedition 360 Scientists
Author Affiliation(s): Primary:
Cardiff University, United Kingdom
Woods Hole Oceanographic Institution, United States
Texas A&M University, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: International Ocean Discovery Program (IODP) Expedition 360 formed the first leg of Phase I of the 'SloMo' project, a multiphase drilling programme that seeks to investigate the nature of the intrusive crust and Moho at slower spreading ridges by ultimately drilling through the Moho for the first time. In December 2015-January 2016 IODP Expedition 360 commenced drilling Hole U1473A on the summit of Atlantis Bank, an oceanic core complex adjacent to the Atlantis II transform on the SW Indian Ridge at 57degE. On the basis of the discovery of partially serpentinised peridotite on its flanks and summit it has been recognised that Atlantis Bank is the optimum place to investigate the hypothesis that the Moho, which sparse seismic data suggest is at approximately 5km below the exposed surface of the core complex here, may represent a hydration front in the lithospheric mantle rather than the boundary between igneous crust and mantle peridotite. A gabbro-serpentinite boundary is believed to lie some way above the Moho in this location. The goal of SloMo is to drill an ultra-deep hole that ultimately penetrates the Moho beneath Atlantis Bank and determines the nature of this fundamental seismic discontinuity. On its way to this goal SloMo will test the possibility that methanogenesis associated with widespread serpentinisation at depth within the mantle lithosphere may support a substantial deep biosphere, and assess the attendant consequences for global element cycling. Further scientific objectives include determining the mechanisms and spatio-temporal scales of accretion of igneous crust in the footwalls of active detachment faults, and nature of marine magnetic anomalies in such environments. Hole U1473A is located 1-2 km from previous ODP drill Holes 735B and 1105A and, like them, is sited in gabbroic rocks that were emplaced and variably deformed upon incorporation into the footwall of the active Atlantis Bank detachment fault. During Expedition 360 Hole U1473A was drilled to 789.7 m below seafloor, and subsequently deepened to 809.4 mbsf in the course of a brief return to the hole in July 2016 during transit Expedition 362T. In this contribution we will outline the principal findings of Expedition 360 and how initial results are already providing significant insights into the first-order questions outlined here.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Crust; Expedition 360; IODP Site U1473; Indian Ocean; International Ocean Discovery Program; Mohorovicic discontinuity; Oceanic crust; Plate tectonics; Sea-floor spreading; SloMo; Southwest Indian Ridge; Spreading centers
Coordinates: S324222 S324222 E0571641 E0571641
Record ID: 2017068200
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