The temporal and spatial distribution of magmatism during lower crustal accretion at an ultraslow-spreading ridge; high-precision U-Pb zircon dating of ODP Holes 735B and 1105A, Atlantis Bank, Southwest Indian Ridge

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doi: 10.1016/j.epsl.2016.05.047
Author(s): Rioux, Matthew; Cheadle, Michael J.; John, Barbara E.; Bowring, Samuel A.
Author Affiliation(s): Primary:
University of California at Santa Barbara, Earth Research Institute, Santa Barbara, CA, United States
Massachusetts Institute of Technology, United States
University of Wyoming, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.449, p.395-406. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendices. 51 refs.; illus., incl. 1 table, sketch map
Summary: Ocean Drilling Program Hole 735B at Atlantis Bank on the Southwest Indian Ridge sampled 1508 m of plutonic oceanic crust, hosted in the footwall of an oceanic detachment fault. We present new high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon dates from samples spanning the length of Hole 735B, and from the shallower adjacent Hole 1105A (158 m). The new dates provide the most complete and precise record of both the spatial and temporal distribution of magmatism during accretion of the lower oceanic crust to date. Whole rock and mineral geochemistry from Hole 735B define three main igneous series. Weighted mean 206Pb/238U dates suggest each igneous series intruded beneath the preceding series. Weighted mean 206Pb/238U dates range from 12.175 to 11.986 Ma in Series 1; 11.974 to 11.926 Ma in Series 2; and 11.936 to 11.902 Ma in Series 3 (±0.015 to 0.069 Ma). Weighted mean 206Pb/238U dates from Hole 1105A range from 11.9745 to 11.9573 Ma (±0.0082 to 0.0086 Ma). The Hole 1105A dates are coeval with Series 2 in Hole 735B, consistent with previous correlations of Fe-Ti oxide-rich layers between the two holes, suggesting individual magmatic series formed sheet-like bodies that were ≥250 m thick and extended ≥1.1 km parallel to the ridge axis (E-W) and ≥0.48 km in the spreading direction (N-S). The data suggest a total duration of magmatism in Hole 735B of ≥0.214 ± 0.032 Ma, corresponding to accretion over a horizontal distance of ≥2.6 ± 0.4 km. The crust at Atlantis Bank was formed during active detachment faulting, and the successive underplating of each magmatic unit may have been favored in this environment. The combined U-Pb dates, and reported Ti-in-zircon temperatures, are consistent with magmatic cooling rates of 103-104 °C/Ma over the temperature interval of 900-700 °C.
Year of Publication: 2016
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 05 Petrology, Igneous and Metamorphic; Absolute age; Accretion; Active faults; Atlantis Bank; Atlantis II fracture zone; Cenozoic; Cores; Crust; Dates; Detachment faults; Faults; Indian Ocean; Leg 179; Lower crust; Magmatism; Mass spectra; Mid-ocean ridges; Miocene; Neogene; Nesosilicates; ODP Site 1105; ODP Site 735; Ocean Drilling Program; Oceanic crust; Orthosilicates; Rates; Silicates; Southwest Indian Ridge; Spatial distribution; Spectra; Temporal distribution; Tertiary; Thermal ionization mass spectra; U/Pb; Underplating; Zircon; Zircon group
Coordinates: S324327 S324318 E0571618 E0571557
S324308 S324308 E0571639 E0571639
Record ID: 2016079075
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands