How much gabbro is in ocean seismic layer 3?

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doi: 10.1029/92GL01452
Author(s): Swift, Stephen A.; Stephen, Ralph A.
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United States
Volume Title: Geophysical Research Letters
Source: Geophysical Research Letters, 19(18), p.1871-1874. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0094-8276 CODEN: GPRLAJ
Note: In English. 30 refs.; illus.
Summary: Ocean seismic layer 3 is distinguished from layer 2 by higher velocities, lower variability, and lower gradients in velocity with depth. Based on studies of rocks recovered from ophiolites and walls of fracture zones, most models of lower ocean crust correlate seismic layer 3 with sequences of gabbroic lithologies. The average velocity (6.5 km/s) for a vertical seismic profile in a gabbro sequence at Ocean Drilling Program (ODP) Hole 735B is consistent with refraction values for layer 3. However, the Q (inverse attenuation) obtained from these data, after correction to temperature and pressure conditions in lower crust, are too low to be consistent with amplitudes of signals observed in refraction experiments. Laboratory measurements of Q on gabbros from Hole 735B and ophiolites are also one to two orders of magnitude lower than seismic refraction Q. These results indicate that the gabbro sequence at Hole 735B cannot be typical of seismic layer 3. Based on Q, upper layer 3 may be metadolerite, and lower layer 3 may include interbedded gabbros and ultramafics. Serpentine is highly attenuating and is unlikely to be a major component. Copyright 1992 by the American Geophysical Union.
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 20 Geophysics, Applied; Atlantis II fracture zone; Gabbros; Geophysical methods; Geophysical profiles; Geophysical surveys; Igneous rocks; Indian Ocean; Leg 118; ODP Site 735; Occurrence; Ocean Drilling Program; Plutonic rocks; Q; Seismic methods; Seismic profiles; Surveys; Vertical seismic profiles
Coordinates: S330518 S320655 E0571618 E0565839
S324327 S324318 E0571618 E0571557
Record ID: 1992062473
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute.