Geologic and geochronologic reconnaissance of a northwest- trending zone of metamorphic core complexes in southern and western Arizona.

Reconnaissance mapping indicates that parts of nine mountain ranges previously considered to be Precambrian basement are instead variations of Tertiary metamorphic core complexes. Of 19 radiometric ages of rocks reported, 17 range from 16.2 + or - 0.4 - 70.3 + or - 2.6 m.y., whereas one is 140.4 + or - 3.2 and one 875 + or - 20 m.y. Two of these are based on whole-rock analyses, one on muscovite, two on hornblende and biotite analyses, one on hornblende only, and thirteen on biotite.A.P.