Yavapai Series; a greenstone belt

Abstract

The Yavapai Series in the Prescott-Jerome area consists of two groups of volcanic and volcaniclastic rocks totalling about 40,000 feet in thickness. It is defined as a time-stratigraphic term, and Pb-U dating of zircons places the time interval from l,775 ± 10 m. y. to 1,820+ m. y. Several plutons intrude the Yavapai Series, and two have Pb-U dates of 1,760 ± 15 m. y. and the third pluton has an apparent age of 1 ,770 ± 15 m. y. The folded and low-grade metamorphosed volcanic rocks of the Yavapai Series resemble many of the older Precambrian greenstone belts, occurring characteristically as scattered remnants in silicic cratons. Some geologists suggest that the linear pattern of these belts indicates their formation at continental-oceanic boundaries (island arcs). Other geologists suggest that downwarping and spreading of thin (or thick) sialic crusts are responsible for the location and development of the belts. There is general agreement that the mafic volcanics are the accumulation of oceanic basalts.