Paleomagnetic constraints on the evolution of Atlantis Bank; results from IODP Expedition 360 "SW Indian Ridge lower crust and Moho"

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Author(s): Morris, Antony; Bowles, Julie A.; Tivey, Maurice
International Ocean Discovery Program, Expedition 360 Scientists
Author Affiliation(s): Primary:
Plymouth University, United Kingdom
University of Wisconsin at Milwaukee, United States
Woods Hole Oceanographic Institute, 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 Expedition 360 was the first step in a multiphase drilling program designed to better understand the nature of lower oceanic crust and the Moho at slower spreading ridges. Hole U1473A was drilled to 790 meters below seafloor on the summit of Atlantis Bank, an oceanic core complex, where the lower crust has been exposed by detachment faulting. Paleomagnetic data on the gabbroic cores allow us to constrain tectonic rotations, investigate magmatic and sub-solidus deformation of the rocks, and better understand the nature of lower crustal contributions to marine magnetic anomalies. The average paleomagnetic inclination at U1473A is consistent with results found at other ODP Atlantis Bank Holes 735B and 1105A and suggests a minimum platform-wide rotation of ∼20° subsequent to cooling through magnetic blocking temperature(s). However, in detail, inclination data from U1473A reveal down-core variations consistent with relative tectonic rotation of up to 12° across at least one major fault zones. Anisotropy of magnetic susceptibility results show magnetic fabrics that on average are slightly more foliated than lineated, with a foliation that dips at ∼40°, with considerable down-hole variation and with a reasonable correlation with observed macroscopic crystal-plastic fabric dips. While the majority of Hole U1473A carries a reversed polarity magnetization, consistent with formation in geomagnetic polarity chron C5r.3r, some narrow zones of altered gabbro carry an apparent normal polarity. These zones were likely remagnetized during a subsequent normal polarity period, and although the timing of the alteration cannot be uniquely determined, this suggests that the boundary between reverse chron C5r.3r and normal chron C5r.2n may occur near the current bottom of the hole.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Atlantis Bank; Crust; Expedition 360; IODP Site U1473; Indian Ocean; International Ocean Discovery Program; Lower crust; Paleomagnetism; SloMo; Southwest Indian Ridge
Coordinates: S324222 S324222 E0571641 E0571641
S324225 S324220 E0571645 E0571635
Record ID: 2017068232
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