AN ISOTOPIC VIEW OF AN ANCIENT CONTINENTAL ARC SYSTEM: PAIRED ZIRCON U-PB-HF ANALYSIS OF THE YAVAPAI-MAZATZAL BOUNDARY, NEW MEXICO, USA

Growth of continental lithosphere along the Paleoproterozoic margin of Laurentia has been the subject of debate for over 35 years. Prior models interpreted this as a long-lived continental margin composed of two temporally separate suites of juvenile arcs—the 1.80-1.76 Ga Yavapai Province and the 1.68-1.60 Ga Mazatzal Province—that were sutured at the Jemez Lineament. This lineament has long been proposed as the southernmost extent of >1.7 Ga crust in the southwestern USA. However, Paired U-Pb-Hf analysis of zircon from 17 metasedimentary and igneous units from throughout northern and central New Mexico demonstrate mixing of older and juvenile lithosphere with periodic addition of distinctly juvenile crust. In northern New Mexico, igneous zircon ages indicate a dominant peak at 1.75-1.70 Ga with 1.9-1.8 Ga inherited zircons. eHf(t) values for these samples range from +2.9 to +11.6, which supports the recycling of 1.85 Ga lower crust throughout the end of the Yavapai orogeny. Detrital zircon ages from northern New Mexico produce unimodal age peaks at 1.72 Ga and contain juvenile eHf(t) signatures that support derivation from local arcs. Igneous zircon from the Mazatzal Province yield eHf(t) values ranging from +6 to +12 at 1.65 Ga. These values are interpreted as heterogeneous lower crust derived from juvenile material mixed with reworked Yavapai crust. Mazatzal Group metasedimentary units are dominated by 1.65 Ga age peaks with minor pre-Mazatzal influence. The 1.65 Ga zircon population produced juvenile eHf(t) values ranging from +3 to +10, whereas the xenocrystic zircons yield ­eHf(t) signatures that correlate with pre-Yavapai Laurentia. Lastly, a suite of 1.45 Ga plutons have eHf(t) values that range from +1.9 to +11.8 and have no local supracrustal equivalents. These values represent recycling of both Yavapai and Mazatzal crust without the addition of isotopically juvenile crust. The consistent inclusion of >Yavapai age Hf isotope signatures, inherited zircon, and detrital zircon across the study area disputes the interpretation of the Yavapai and Mazatzal as two distinct domains with a finite suture zone. The isotopic character of these provinces is consistent with a long-lived cordilleran margin where juvenile arc terranes were accreted to and imbricated with chemically evolved continental lithosphere.