The Nature of Crustal Seismic Heterogeneity: A Case Study From the Grenville Province
Over the range of scales for which most seismic reflection data contain information, lithologic variation is one of the major sources of heterogeneity in the crystalline crust. This is particularly true at depths greater than ~10 to 15 km where most of the fractures and microfractures that contribute to upper crustal heterogeneity are closed. The spatial distribution of lithologic heterogeneity is a function of the range of magmatic and tectonic processes that progressively distribute and redistribute the various lithologic components of the crust (the “tectonic roulette” of Fountain and Salisbury, 1981). Although the seismic reflection wavefield responds indirectly to lithologic variation, it is directly responsive to fluctuations of acoustic impedance that are more closely coupled to mineralogy than lithology. Accordingly, pressure and temperature variations that modify mineralogy, but not bulk chemistry, combine with lithologic variation to play both static and dynamic roles in defining the heterogeneity of the Earth’s crust.
KeywordsShear Zone Reflection Coefficient Seismic Data Seismic Reflection Acoustic Impedance
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