U-Pb dating reveals rapid accretion of gabbroic crust at the ultraslow-spreading Southwest Indian Ridge

Author(s): Baines, G.; Cheadle, M. J.; John, B. E.; Grimes, C. B.; Wooden, J. L.
Author Affiliation(s): Primary:
University of Wyoming, Laramie, WY, United States
Other:
U. S. Geological Survey, United States
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English
Summary: Absolute dating of gabbroic rocks at mid-ocean ridges can provide important constraints on the processes of oceanic crustal accretion. We present 206Pb/238U ages of igneous zircon for nine samples from 53- 1430 mbsf in ODP Hole 735B, drilled through 1508 m of gabbroic crust at Atlantis Bank on the Southwest Indian Ridge (SWIR). The Pb/U zircon ages are the same, within error, showing no systematic variation of age with depth. Consequently, individual magmatic series and tectonic blocks recognized within Hole 735B all have the same Pb/U age of 11.97±0.06 Ma (93 analyses). This observation of constant age down hole suggests that >74% (at the 95% confidence level) of Hole 735B accreted in <0.12 Myr and thus within 1.7 km of the SWIR axis. The average Pb/U age is ≈0.2 Myr older than the estimated magnetic age of Hole 735B, and so implies that the magnetic remanence was acquired ≈3 km off-axis. The absence of a systematic pattern of age with depth in Hole 735B, is consistent with the accretion/growth of oceanic crust by intrusion at multiple depths (a many sill' model) below an active detachment fault. It is also consistent with the cupola' intrusion model of Natland & Dick (2002) provided the three intrusions accreted in <0.12 Myr. However, our data do not preclude accretion of Hole 735B from a single zone of intrusion, a model analogous to the glacier flow model' at fast-spreading ridges, provided that the rate at which gabbro moved away from this zone of intrusion was >12.5 km/Myr. This rate of motion is similar to the plate spreading rate at the Southwest Indian Ridge, and so could be accommodated by tectonic rotation and/or denudation of crust during detachment faulting at Atlantis Bank.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 18 Geophysics, Solid-Earth; Absolute age; Accretion; Atlantis Bank; Cenozoic; Crust; Dates; Gabbros; Igneous rocks; Indian Ocean; Low-velocity zones; Metals; Neogene; Nesosilicates; ODP Site 735; Ocean Drilling Program; Oceanic crust; Orthosilicates; Plate tectonics; Plutonic rocks; Rare earths; Sea-floor spreading; Silicates; Southwest Indian Ridge; Spreading centers; Tertiary; U/Pb; Velocity; Zircon; Zircon group
Coordinates: S324327 S324318 E0571618 E0571557
S413000 S223000 E0673000 E0440000
Record ID: 2008067361
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.