Mathematics – Logic
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.118...75j&link_type=abstract
Earth and Planetary Science Letters, Volume 118, Issue 1-4, p. 75-89.
Mathematics
Logic
3
Scientific paper
Crust formation rates and mass-age distributions calculated for the southwestern United States, including California, Nevada, Utah, Colorado, New Mexico, and Arizona, indicate significant crust formation in the Mesozoic and Cenozoic, and possibly at 1.4 Ga. These periods have been previously thought to be associated with only minor formation of new crust, particularly in regions underlain by Precambrian crust. New isotopic data require revision of this conclusion, based on the large mantle component in Mesozoic and Cenozoic plutonic and volcanic rocks, and recognition of the major role the lithospheric mantle has in influencing the isotopic composition of continental basaltic magmas. Recognition of the importance of the lithospheric mantle in determining the isotopic compositions of continental magmatism also suggests that 1.4 Ga anorogenic granites may have a larger mantle component than previously thought. Crust formation rates calculated here are best constrained for Cenozoic magmatism, and these rates are probably similar to true growth rates. While relatively short-lived, these formation rates exceeded early Proterozoic formation rates by a factor of 2 to 3, particularly in regions that underwent large-scale Cenozoic extension and volcanism, and are similar to growth rates associated with accretionary processes in the Canadian Cordillera. Although volcanism is often poorly preserved in the geologic record, the results presented here suggest that crustal growth models which do not consider the significant mantle input that may be common in large-volume volcanic fields may significantly underestimate mantle contributions; crustal growth rates calculated using relatively small, crust-dominated plutonic systems that are not associated with large volcanic systems will be strongly biased toward conclusions that little recent crustal growth has occurred.
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