The age of IODP Site 1473, Atlantis Bank; constraints from initial zircon U-Pb dating and geochemistry by SIMS

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Author(s): Cheadle, Michael J.; John, Barbara E.; Coble, Matthew A.; Koepke, Jürgen; Rioux, Matthew E.; Liu, Chuan Z.
International Ocean Discovery Program, Expedition 360 Scientists
Author Affiliation(s): Primary:
University of Wyoming, Laramie, WY, United States
Stanford University, United States
Leibniz University of Hannover, Germany
University of California at Santa Barbara, United States
Chinese Academy of Sciences, Institute of Geology and Geophysics, China
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, sited at the top of the Atlantis Bank oceanic core complex (OCC) on the southwest Indian Ridge, extends 809m into gabbroic lower ocean crust. The recovered core consists dominantly of olivine gabbro, with subordinate gabbro, Fe-Ti oxide gabbro and felsic veins. Geochemical data define three magmatic series in the core. Ninety samples of evolved gabbro and felsic veins were collected to carry out a comprehensive geochronologic study of the core. When combined with high-precision data from nearby ODP Holes 735B and 1105A (Rioux et al., 2016), the new data will ultimately provide a 4-D view of the lateral continuity and evolution of the lower crust, and the process of magmatic accretion in space and time. Initial zircon U-Pb dating using the Stanford-USGS SHRIMP-RG ion-microprobe yielded a near solidus (∼ 850°C), weighted mean 206Pb/238U, age of 11.86±0.09 Ma (MSWD =1.01; n=28) for 4 samples of felsic veins and Fe-Ti gabbro from the lower two magmatic series of Hole U1473A. The difference between this age and the high precision TIMS age for ODP Hole 1105A is consistent with an asymmetric spreading rate of 14.1 mm/yr for the OCC. Dates for felsic veins from magmatic series II and felsic veins and oxide gabbro from magmatic series III overlap within uncertainty, however a felsic vein from the ∼50m thick uppermost series I has a date of 12.12+/-0.18 Ma, and thus could indicate that magmatic series I predates the underlying series, as observed in core from ODP Hole 735B. The presence of any age differences will be subsequently explored by high-precision ID-TIMS dating. The zircon compositions are similar to those from ODP Hole 735B; Hf and U concentrations range from 7,600-33,200 and 2-5,700 ppm, respectively, and Ti-in-zircon temperatures range from 974-718°C. They are typical ocean zircons as defined by the trace element discrimination plots of Grimes et al. (2015). However, the zircons from Hole U1473A show more evidence for hydrothermal alteration than those from ODP Hole 735B, with some grains showing partial resorption and others total recrystallization. One set of hydrothermal zircons from the top of magmatic series III yielded a weighted mean 206Pb/238U date of 11.28±0.33 Ma, potentially reflecting hydrothermal flow for ≥0.6±0.3 Ma after intrusion.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 02 Geochemistry; Atlantis Bank; Expedition 360; Geochemistry; IODP Site U1473; Indian Ocean; International Ocean Discovery Program; Ion probe data; Mass spectra; SloMo; Southwest Indian Ridge; Spectra
Coordinates: S324222 S324222 E0571641 E0571641
Record ID: 2017068225
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States