Insights into oceanic core complex formation from structural studies of IODP Hole U1473A, Expedition 360 Atlantis Bank, Southwest Indian Ridge

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http://abstractsearch.agu.org/meetings/2016/FM/OS23F-03.html
Author(s): Deans, Jeremy R.; Cheadle, Michael J.; Ferrando, Carlotta; Plümper, Oliver; Viegas, Gustavo
Author Affiliation(s): Primary:
University of Southern Mississippi, Department of Geography and Geology, Stennis Space Center, MS, United States
Other:
University of Wyoming, United States
Géosciences Montpellier, France
Utrecht University, Netherlands
Plymouth 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: Atlantis Bank formed as an oceanic core complex by exhumation along a detachment shear zone (DSZ). IODP Hole U1473A is sited on the wave-cut platform of Atlantis Bank and was cored to 809 m consisting of lower crustal gabbro, partly through this DSZ. The uppermost 600 m of the hole is a zone of intense, locally pervasive, granulite to amphibolite grade, crystal-plastic deformation. Numerous intervals of porphyroclastic to ultramylonitic gabbro, often Fe-Ti oxide-rich, reveal a protracted history of deformation. This deformation overprints primary magmatic features including igneous contacts, layering, and fabrics. From 600 mbsf to 809 mbsf, crystal-plastic deformation becomes less pervasive, but meter- to cm-scale shear zones extend to the bottom of the hole. Individual shear zones throughout the hole predominately dip between 10-50° and below 50 mbsf notably exhibit a reverse sense of shear. Amphibole veins occur mostly in the upper 300 m of the hole and crosscut the crystal-plastic foliations at high angle. These veins may both transpose and fault older crystal-plastic fabrics indicating that vein injection occurred at temperatures close to the brittle-plastic transition. Additionally, the uppermost 500 m of Hole U1473A is cut by a series of brittle faults ranging from discrete 5 cm thick cataclasites at the top to a major fault zone at 411-469 mbsf. Carbonate veins and oxidative reddish clay replacement of olivine are conspicuous in these fault zones. The distribution of deformation, and importantly the dominant reverse sense of shear recorded in Hole U1473A, is very similar to that from 400-1100 mbsf in ODP Hole 735B. Given that Hole U1473A is in the north-central part of the platform and Hole 735B is in the western margin of the platform, we suggest that preferential erosion of the central platform may have removed the upper part of the DSZ from the site of Hole U1473. If this is the case, then Hole U1473A records the crystal-plastic deformation from the lower part of the DSZ and we speculate that the conspicuous reverse sense of shear developed as a response to flexure during exhumation.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Atlantis Bank; Decollement; Exhumation; Expedition 360; Faults; IODP Site U1473; Indian Ocean; International Ocean Discovery Program; Shear zones; SloMo; Southwest Indian Ridge; Tectonics
Coordinates: S324222 S324222 E0571641 E0571641
Record ID: 2017068202
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