Origin of deep crustal reflections: Implications of coincident seismic refraction and reflection data in Nevada

Journal Article · Fri Feb 01 04:00:00 EST 1991 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1991)019<0175:OODCRI>2.3.CO;2· OSTI ID:5572691

Holbrook, W S ^[1]; Catchings, R D ^[2]; Jarchow, C M ^[3]

---

1. Woods Hole Oceanographic Institution, MA (USA)
2. U.S. Geological Survey, Menlo Park, CA (USA)
3. Stanford Univ., CA (USA)

The authors compare seismic refraction and reflection results along the PASSCAL/COCORP 40{degree}N transect in the northern Basin and Range of Nevada in order to determine the origin of the prominent reflections from the deep crystalline crust. Reflection data along the transect show a thick zone of discontinuous, subhorizontal reflections, beginning at 4-6 s two-way traveltime (10-20 km depth) and ending at 9-11 s (27-35 km). Two independently derived velocity models, based on refraction data, are largely similar and agree on many important aspects of the reflectivity-velocity relation. Both models show that the top of the reflective zone lies 3-8 km above a prominent mid-crustal velocity discontinuity, which is interpreted to separate bulk silicic from bulk dioritic-gabbroic crust; in most places, the silicic mid-crust is more strongly reflective than the mafic lower crust. This pattern is expected in areas where ductile shearing is the mechanism responsible for the reflectivity. One of the velocity models, however, suggests that, in places, the strongest reflectivity spans both the middle (6.1-6.3 km/s) and lower (6.6 km/s) crust; this pattern suggests that the combined influence of ductile strain fabrics and mafic intrusions gives rise to crustal reflections. Both models show that the lowermost crust and crust/mantle transition are highly reflective, also suggesting the presence of mafic and/or ultramafic intrusions. Thus the observed reflection patterns suggest that ductile shearing and the intrusion of mantle-derived magma - both of which are likely to have accompanied the extreme Cenozoic extension - are important factors in generating deep crustal reflections.

• OSTI ID: 5572691
• Journal Information: Geology; (USA), Journal Name: Geology; (USA) Vol. 19:2; ISSN GLGYB; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BOUNDARY LAYERS
CENOZOIC ERA
COMPARATIVE EVALUATIONS
CONTINENTAL CRUST
DEPTH
DIMENSIONS
EARTH CRUST
EARTH MANTLE
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
IGNEOUS ROCKS
LAYERS
MAGMATISM
NEVADA
NORTH AMERICA
OPTICAL PROPERTIES
ORIGIN
PHYSICAL PROPERTIES
PLUTONIC ROCKS
REFLECTIVITY
REFRACTIVITY
ROCKS
SEISMIC SURVEYS
SEISMIC WAVES
SURFACE PROPERTIES
SURVEYS
USA
WAVE PROPAGATION