35. Elastic Properties of Selected Ophiolitic Rocks from Papua New Guinea: Nature and Composition of Oceanic Lower Crust and Upper Mantle

  1. George H. Sutton,
  2. Murli H. Manghnani,
  3. Ralph Moberly and
  4. Ethel U. Mcafee
  1. L. W. Kroenke,
  2. Murli H. Manghnani,
  3. C. S. Rai,
  4. P. Fryer and
  5. Ralph Ramananantoandro

Published Online: 17 MAR 2013

DOI: 10.1029/GM019p0407

The Geophysics of the Pacific Ocean Basin and Its Margin

The Geophysics of the Pacific Ocean Basin and Its Margin

How to Cite

Kroenke, L. W., Manghnani, M. H., Rai, C. S., Fryer, P. and Ramananantoandro, R. (1976) Elastic Properties of Selected Ophiolitic Rocks from Papua New Guinea: Nature and Composition of Oceanic Lower Crust and Upper Mantle, in The Geophysics of the Pacific Ocean Basin and Its Margin (eds G. H. Sutton, M. H. Manghnani, R. Moberly and E. U. Mcafee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM019p0407

Author Information

  1. Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822

Publication History

  1. Published Online: 17 MAR 2013
  2. Published Print: 1 JAN 1976

ISBN Information

Print ISBN: 9780875900193

Online ISBN: 9781118663592

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Keywords:

  • Geophysics—Pacific area—Congresses;
  • Woollard, George Prior, 1908

Summary

Results of compressional (Vp ) and shear wave (Vs ) velocity measurements to 10 kbar and 350°C on a selected suite of ultramafic and mafic rocks from the Papua New Guinea ophiolite complex fit well on Birch velocity-density (∼21) plots. The rocks investigated include cumulate and non-cumulate ultramafics, ranging in composition from peridotite (harzburgite) to pyroxenite (clinopyroxenite and orthopyroxenite), and mafic rocks of gabbroic composition. Some of the cumulate ultramafics (harzburgites) are highly anisotropic (ΔVp ∼ 6–16%) and have a wide range of Vp as a result of varying degrees of serpentinization. A clinopyroxenite, also a cumulate (?) ultramafic rock, containing appreciable CaO (present as diopsidic augite) gave Vp values significantly higher (8.03 to 8.48 km/sec) than those for single-crystal bronzite and bronzitite reported previously, corresponding more closely to upper mantle seismic velocities. The mean lO-kbar values of Vp and of density for gabbroic rocks fall in narrow ranges, 7.56 to 7.59 km/sec and 3.02 to 3.06 g/cm3, respectively, which, after correction for pressure and temperature assumed in the lower crust (3 kbar, 125°–200°C), yield the values of 7.2 to 7.3 km/sec, and 2.95 to 2.98 g/cm3. These values when compared with the seismic data suggest that the basal oceanic crustal layer (layer 3) in this region is gabbroic. The velocity-density systematics of the Papuan rocks and the previously studied tholeiitic basalts are used to derive an oceanic crustal model based on H. L. Davies' ‘overthrust' concept. On the basis of Bouguer anomaly profiles, this model is found to be more acceptable than the model proposed by E. Rod.