Physical properties and logging of the lower oceanic crust; Hole 735B

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doi: 10.1029/GM070p0041
Author(s): von Herzen, R. P.; Goldberg, D.; Manghnani, M.
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Woods Hole, United States
University of Michigan, United States
University of Wales College of Cardiff, United Kingdom
Bundesanstalt für Geowissenschaften und Rohstoffe, Federal Republic of Germany
Lamont-Doherty Geological Observatory of Columbia University, United States
Lamont-Doherty Geological Observatory, United States
University of Hawaii, Honolulu, United States
Volume Title: Synthesis of results from scientific drilling in the Indian Ocean
Volume Author(s): Duncan, Robert A., editor; Rea, David K.; Kidd, Robert B.; von Rad, Ulrich; Weissel, Jeffrey K.
Source: Synthesis of results from scientific drilling in the Indian Ocean, edited by Robert A. Duncan, David K. Rea, Robert B. Kidd, Ulrich von Rad and Jeffrey K. Weissel. Geophysical Monograph, Vol.70, p.41-56. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0065-8448. ISBN: 978-1-118-66803-0 CODEN: GPMGAD
Note: In English with English summary. 38 refs.; illus., incl. 1 table, sketch map
Summary: Results from downhole logging instrumentation and physical properties measurements on samples recovered from a 500-m-thick section of gabbros at Site 735 on the SW Indian Ridge are compared. Here we emphasize particularly the seismic, electrical, and nuclear logging measurements to deduce the physical state and evolution of this crustal section over the 11-12 m.y. since its formation. Various seismic methods give compressional velocities ranging from 6.5 to >7 km/s, typical of lower oceanic crustal velocities determined from marine refraction measurements. Except for the unusually low intrinsic electrical resistivity (<10 ohm-m) of some Fe-Ti-oxide gabbros, the relatively high range of resistivities (∼3×102 - 2×104 ohm-m) for most of the section deeper than 150 meters below seafloor is consistent with low porosities (few percent) derived from the neutron log. The decrease with depth of thin, relatively high porosity (20-25%) zones, low temperature (sea water) rock alteration, and fluid permeability suggests that overburden stress is an important factor maintaining closed fractures in young ocean crust.
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Alkaline earth metals; Atlantis II fracture zone; Basalts; Chemical ratios; Crust; Flood basalts; Hot spots; Igneous rocks; Indian Ocean; Indian Ocean Islands; Intraplate processes; Isotopes; Kerguelen Islands; Lead; Lower crust; Magmas; Major elements; Mantle; Mantle plumes; Mascarene Islands; Metals; Nd-144/Nd-143; Neodymium; ODP Site 735; Ocean Drilling Program; Oceanic crust; Pb-206/Pb-204; Pb-207/Pb-204; Pb-208/Pb-204; Physical properties; Plate tectonics; Radioactive isotopes; Rare earths; Reunion; Southwest Indian Ridge; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Volcanic rocks; Volcanism; Well-logging
Coordinates: S324327 S324318 E0571618 E0571557
Record ID: 2007093154
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