Open AccessReflection characteristics of a mylonite zone based on compressional wave velocities of rock samples
Author(s) -
McDonough Daniel T.,
Fountain David M.
Publication year - 1988
Publication title -
geophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0952-4592
DOI - 10.1111/j.1365-246x.1988.tb03880.x
Subject(s) - mylonite , geology , lithology , anisotropy , metamorphic rock , reflection (computer programming) , mafic , mineralogy , petrology , seismology , shear zone , physics , computer science , tectonics , programming language , quantum mechanics
SUMMARY A combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the Kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites. Because of its structural and petrologic characteristics, this mylonite zone can be regarded as a model for mid‐ to deep‐crustal mylonite zones. CDP reflection profiling revealed that the mylonite zone is reflective. Laboratory measurements of compressional wave velocities ( V p ) at high confining pressures in samples collected directly up‐dip from the CDP reflection line revealed a wide variation of V p in common mid‐crustal lithologies. Mafic and carbonate rock mean V p values range from 6.67 to 7.31 km s −1 at 600 MPa, and quartzite and quartzo‐feldspathic values range from 6.16 to 6.52 km s −1 . Seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation, whereas the latter effect controls anisotropy at high pressures. The laboratory data provide the basis for a seismic model which indicates that the Kettle dome mylonite zone can generate reflections from zones where high‐ and low‐velocity lithologies are interlayered. These reflections correlate with those observed on the CDP data, thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature. In this case, it is not necessary to explain the reflections by the effects of anisotropy, retrogression, high pore pressure, or constructive interference.