Revised location for the Yavapai-Mazatzal crustal province boundary in New Mexico: Hf isotopic data from Proterozoic rocks of the Nacimiento Mountains

Lithospheric growth of southwestern Laurentia during the Paleoproterozoic has been hypothesized to have involved addition of two dominantly juvenile crustal provinces: the 1.8–1.7 Ga Yavapai province and the 1.7–1.6 Ga Mazatzal province. Timing of assembly of these two crustal provinces has been stated to have occurred during the 1.72–1.68 Ga Yavapai orogeny and 1.65–1.60 Ga Mazatzal orogeny, with both provinces undergoing high temperature deformation and metamorphism at middle crustal depths accompanying Mesoproterozoic intrusions from 1.45–1.35 Ga. The boundary between provinces remains poorly understood, but has been inferred to lie along the northern edge of the Jemez volcanic lineament and through the Nacimiento uplift in northern New Mexico. This basement-cored Laramide uplift exposes a 53-km-long north-south transect dominated by Paleoproterozoic and Mesoproterozoic granite, providing an ideal locality to examine age and origin of continental lithosphere across this proposed boundary on a local scale. A quartzite metasedimentary unit from the northern Nacimiento that is intruded by ca. 1696 Ma granite was analyzed with U-Pb and Hf isotopic analyses of zircons. The detrital zircon data show a narrow unimodal age peak at 1720 Ma and a maximum depositional age of ~1.7 Ga. Detrital zircons from this sample yield initial epsilon Hf (ɛHf(t)) values ranging from +6.4 to +14.2 suggesting an isotopically juvenile ca. 1.7–1.8 Ga source region for the quartzites. Detrital zircon ages suggest a correlation with the greater Hondo Group and equivalents of northern New Mexico. A 1449 ±12 Ma granite from the southern Nacimiento Mountains has initial epsilon Hf (ɛHf(t)) values of +2.6 to +10.5 suggesting that the lower crustal melt source region contained 1.7–1.8 Ga (Yavapai) crust that was partially melted by and may have mixed with juvenile 1.4 Ga melt. Together these data suggest that >1.7 Ga (Yavapai) crustal province rocks extend in the subsurface south of the southern Nacimiento Mountains. (Karlstrom and Humphreys, 1998; Shaw and Karlstrom., 1999; Karlstrom and Williams, 2006). 2) Some models suggest the provinces are made up of dominantly juvenile additions to the lithosphere (1.7–1.8 for Yavapai and 1.7–1.6 Ga for Mazatzal; Bowring and Karlstrom, 1990), while others have proposed there is significant older crust in the subsurface, i.e. pre-1.8 Ga for the Yavapai (Bickford and Hill, 2007; Karlstrom et al., 2007) and pre-1.7 Ga for the Mazatzal province (Amato, 2008). 3) The timing of accretionary deformation(s) and location of any accretionary sutures is debated. Some models envision suturing of terranes to have accompanied and closely followed lithospheric growth during the 1.72–1.68 Ga Yavapai and 1.65–1.60 Ga Mazatzal orogenies (Whitmeyer and Karlstrom, 2007); others question the arc accretion model as the mechanism for crustal growth (Bickford and Hill, 2007; c.f. Karlstrom et al., 2007); and some suggest final suturing of the Mazatzal terrane in northern New Mexico may have taken place later, during the 1.45 Ga Picuris orogeny (Daniel et al., 2013). Northern New Mexico is an important locality to continue to refine and test models of crustal growth throughout the Proterozoic. Various datasets that need improving include the delineation and definition of surface and subsurface crustal age provinces, timing and nature of magmatic events, and more precise geochronologic constraints on timing of basin formation, deformation, and metamorphism. The purpose of this paper is to evaluate INTRODUCTION Growth of continental crust along the southwestern margin of Laurentia by accretion and stabilization of arc terranes throughout the Proterozoic has been postulated for over 30 years (e.g. Condie, 1982; Karlstrom et al., 1987; Karlstrom et al., 2001). In New Mexico, two crustal age provinces have been proposed based largely on geophysical lineaments, U-Pb ages, and isotopic character of surface outcrops: Yavapai (1.8–1.7 Ga) and Mazatzal (1.7–1.6 Ga). A northeast-trending boundary between the age provinces has been defined as the north edge of a zone of positive aeromagnetic anomalies associated with the Jemez lineament (Karlstrom and Daniel, 1993) and the southern extent of pre-1.7 Ga basement rock exposures (Karlstrom and Humphreys, 1998). This boundary has been drawn through the Nacimiento Mountains in the northern part of New Mexico (Karlstrom and Daniel, 1993; Karlstrom et al., 2004). A plate scale model for progressive southwards growth of Proterozoic lithosphere was presented by Whitmeyer and Karlstrom (2007). Several aspects of this model are debated: 1) The boundary between the age provinces has been variably defined as a relatively discrete suture between age provinces (Fig. 1; Magnani et al., 2004; 2005; Karlstrom et al., 2005) and/or as part of a wide distributed transitional zone of terrane imbrication that extends north into southern Colorado New Mexico Geological Society Guidebook, 66th Field Conference, Geology of the Meadowlands, Las Vegas Region, 2015, p. 175–184 Appendix data for this paper can be accessed at: http://nmgs.nmt. edu/repository/index.cfm? rid=2015001 176 GRAMBLING, HOLLAND, KARLSTROM, GEHRELS, and PECHA the previously defined crustal boundary posited to pass through the Nacimiento uplift using paired U-Pb-Hf isotopic data from igneous and detrital zircon. We use the Hf isotopic composition of zircons separated from 1.4 Ga granites in the Nacimiento Mountains to probe lower crustal composition and help delineate lower crustal age provinces (e.g. Cecil et al., 2011; Foster et al., 2012). U-Pb and Hf isotopic data from detrital zircon in quartzites in the Nacimiento uplift are also examined to help test regional stratigraphic correlations. Our new data are the first published Hf isotopic data obtained from Proterozoic rocks of northern New Mexico.