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Contribution of crystallographic preferred orientation to seismic anisotropy across a surface analog of the continental Moho at Cabo Ortegal, Spain

2012; Geological Society of America; Volume: 124; Issue: 9-10 Linguagem: Inglês

10.1130/b30568.1

1943-2674

Sergio Llana‐Fúnez, Dennis Brown,

Geological and Geophysical Studies Worldwide

Research Article| September 01, 2012 Contribution of crystallographic preferred orientation to seismic anisotropy across a surface analog of the continental Moho at Cabo Ortegal, Spain Sergio Llana-Fúnez; Sergio Llana-Fúnez † 1Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, L69 3GP Liverpool, UK2Departamento de Geología, Universidad de Oviedo, c/Arias de Velasco s/n, 33005, Oviedo, Spain †E-mail: slf@geol.uniovi.es Search for other works by this author on: GSW Google Scholar Dennis Brown Dennis Brown 3Instituto de Ciencias de la Tierra "Jaume Almera," Consejo Superior de Investigaciones Científicas (CSIC), c/Lluís Sole i Sabaris s/n, 08028, Barcelona, Spain Search for other works by this author on: GSW Google Scholar Author and Article Information Sergio Llana-Fúnez † 1Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, L69 3GP Liverpool, UK2Departamento de Geología, Universidad de Oviedo, c/Arias de Velasco s/n, 33005, Oviedo, Spain Dennis Brown 3Instituto de Ciencias de la Tierra "Jaume Almera," Consejo Superior de Investigaciones Científicas (CSIC), c/Lluís Sole i Sabaris s/n, 08028, Barcelona, Spain †E-mail: slf@geol.uniovi.es Publisher: Geological Society of America Received: 28 Jun 2011 Revision Received: 11 Apr 2012 Accepted: 14 Apr 2012 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2012 Geological Society of America GSA Bulletin (2012) 124 (9-10): 1495–1513. https://doi.org/10.1130/B30568.1 Article history Received: 28 Jun 2011 Revision Received: 11 Apr 2012 Accepted: 14 Apr 2012 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Sergio Llana-Fúnez, Dennis Brown; Contribution of crystallographic preferred orientation to seismic anisotropy across a surface analog of the continental Moho at Cabo Ortegal, Spain. GSA Bulletin 2012;; 124 (9-10): 1495–1513. doi: https://doi.org/10.1130/B30568.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The lithostratigraphic sequence of the Upper Allochthon of the Cabo Ortegal complex in northwestern Spain provides an excellent analog for the direct study of petrophysical properties of the continental Moho transition. The various lithologies present were sampled for velocity measurements on minicores and determination of seismic velocities through microstructural analyses, with emphasis on the crustal part of the sequence. Here, we present data from electron backscatter diffraction (EBSD) to determine the crystallographic preferred orientation of all major rock-forming minerals. The orientation data are then combined with the elastic properties, densities, and modal fractions of the mineral phases to calculate P-wave and S-wave velocities. Calculated velocities coincide very well with direct measurements made on minicores of the same samples in the high-pressure laboratory. The three-dimensional velocity patterns show the significant contribution of the crystallographic preferred orientation of certain constituent minerals on the bulk properties of the rock. The bulk anisotropic signal is dominated by highly anisotropic phases that are susceptible to both shape and crystal preferred orientation. Factors of particular importance are small modal fractions of micas in gneisses, and amphiboles and clinopyroxenes in eclogites and high-pressure granulites. In the lower-crustal rocks, the direction of maximum P-wave velocities, although contained in the foliation plane, does not coincide with the orientation of the mineral and stretching lineation and therefore cannot be used as an indicator of the main strain direction in rocks. The maximum seismic birefringence is often contained within the foliation plane but very rarely coincides with the lineation. Our data set also illustrates the strong effect of the breakdown reactions of clinopyroxene and the appearance of plagioclase on the petrophysical properties of mafic lower-crustal rocks. While it does not enhance anisotropy, it does produce a drop in velocity and as a consequence enhances the reflectivity of the contact between lower-crustal rocks and ultramafics from the mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.