Tectonic and magmatic contrasts across a two-province Proterozoic boundary in central Arizona

Abstract

One of the first major discoveries of the infant discipline of zircon geochronology was that the Early Proterozoic of Arizona comprised two age provinces with a boundary in the central part of the state (Silver, 1965, 1967, 1969). Rocks in the central to northwestern part of the state are about 1.70 to 1.78 Ga, whereas those in the central to southeastern part of the state are about 1.61 to 1.71 Ga. Since these results were first reported, the exact position and nature of the two-province boundary have been the subject of much debate and still elude geologists. It has become obvious that several iterations of field and geochronologic studies, each giving direction and raising questions for the next, are required for a understanding of the boundary and the Early Proterozoic history of Arizona in any detail. Because The two-province boundary in Arizona may extend northeastward into the mid-continent and perhaps farther and because the Transition Zone in Arizona offers superb outcrops across this boundary, Arizona may hold answers to questions regarding the Early Proterozoic crustal growth of the southern part of the North American craton. One of the major goals of this field trip is to examine the nature of the proposed boundary through stops and discussions of rocks in both provinces.