The border connection; geological correlations and contrasts between Arizona and Sonora

Abstract

The same tectonostratigraphic evolution characterizes a broad belt of rocks centered along the border between Arizona and Sonora. Differences are evident in areas tens of kilometers north and south of the border region. No counterpart of the stable Colorado Plateau north of the border belt exists in Sonora. Terranes, south of the border belt, are separated by faults or less obvious discontinuities in structural, stratigraphic and isotopic patterns. Directions of movement on postulated faults are hotly debated. Locally, where terrane borders are strongly obscured by subsequent tectonism, volcanism, intrusion and/or sedimentation, they are almost mystical or mythical. Tests of the hypothesis that some of the terranes record hundreds of kilometers of left-lateral offset have been undertaken. Although the results are not probative, they are very supportive.