Lateral variability of the lower ocean crust at Atlantis Bank, SW Indian Ridge, results of IODP Expedition 360

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Author(s): Dick, Henry J.; MacLeod, Christopher J.; Blum, Peter
International Ocean Discovery Program, Expedition 360 Scientists
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Woods Hole, MA, United States
Cardiff University, United Kingdom
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: IODP Hole U1473A drilled 809.4 m into a 700-m depth wave-cut platform at Atlantis Bank on the SW Indian Ridge. It is an oceanic core complex where massive gabbro was emplaced into the footwall of a single detachment fault for ≥2.7 Myr, with total slip ≥39 km. It was then uplifted to its present position flanking the 6,100 m deep 199-km Atlantis II Transform. The gabbros are back-tilted ∼20°S, while a sub-horizontal 15 km long mantle peridotite-gabbro contact lies along the transform wall at ∼4200 m depth ∼11.5 km west of Hole U1473A. Hole U1473A is 1.4 km north of 158-m deep Hole 1105A and 2.2 km NNE of 1508-m deep Hole 735B. Thus we examine the lateral continuity of the lower ocean crust at ultraslow rates (∼15-16 mm/yr.), and compare it to 1400-m Hole U1309D in the Atlantis Massif MAR core complex (24 mm/yr.) flanking the 63-km Atlantis Transform. The three Atlantis Bank holes are very similar, consisting of a complex series of oxide-rich gabbros and olivine gabbros. Several dikes crosscutting the gabbro sections show that they passed through the dike-gabbro transition after crystallizing and cooling deeper in the crust. They all show extensive high-temperature crystal-plastic deformation predating dike intrusion. A small amount of troctolite was recovered only in Hole 735B. By contrast, gabbro, rather than olivine gabbro was the dominant lithology in Hole U1309D, with intercalations of troctolite and mantle peridotite, and subordinate oxide gabbro. Oxide gabbro is often associated with crystal-plastic deformation. While these are concentrated in the upper 1/3 of Hole 735B, they are more uniformly distributed in Hole U1309D. While one section cannot be traced directly to the other at Atlantis Bank, it appears that they can be correlated based on chemical and structural similarities, with the 1105A and 1473A sections lying some hundreds of meters deeper structurally than Hole 735B, consistent with erosion on the platform. All these sections represent sequential emplacement of small gabbro bodies, with upward compaction of late melt, often fault controlled. The primary differences in the sections are due to variations in the melt supply, which was significantly lower at Hole U1309D, resulting in incorporation of mantle peridotite screens into the section as additional gabbro intrusions were added to the base of the section.
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; Oceanic crust; SloMo; Southwest Indian Ridge
Coordinates: S324222 S324222 E0571641 E0571641
Record ID: 2017068201
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