The Yavapai-Mazatzal crustal boundary in the Southern Rocky Mountains

Abstract

A major geologic boundary has been proposed in the Southern Rocky Mountains separating Proterozoic crustal provinces with different ages and tectonic histories. These provinces probably correlate with the Yavapai (1.8-1.7 Ga) and Mazatzal (1.7-1.6 Ga) provinces of Arizona. Geologic, geochemical, geochronologic, and xenolith data suggest that the boundary lies within a ~3 0 0 km-wide zone that trends northeastward through southern Colorado and northern New Mexico. This zone also seems to have focused later tectonic and thermal effects. However, no major shear zone that might represent a discrete tectonic suture has been identified in the area, and there is no agreement on precisely where the boundary is or what tectonic significance it may have.We present a review of evidence supporting extrapolation of the Yavapai-Mazatzal boundary through the Southern Rocky Mountains. Limitations in the precision, quantity, and interpretation of available data probably contribute to disagreement over the location of the boundary. However, the disparity in boundaries defined by different data sets may partly reflect a complex or gradational transition between crustal domains. We propose a speculative model for the boundary based on a preliminary structural analysis. lkctonic fabrics appear to be consistent with the initial juxtaposition of arc terranes of the Yavapai and Mazatzal provinces on a lowangle thrust system with later modification and steepening of the boundary during continued crustal shortening. This model explains the diffuse isotopic boundary as a manifestation of a vertically heterogeneous crustal column that might promote isotopic mixing. The cryptic structural expression of the suture may result from a layer-parallel style of suturing and complex post-accretionary tectonic overprinting.

Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA

“…The 1.7-1.6 Ga Mazatzal Province contains juvenile crust that formed in continental arcs and backarcs (Shaw & Karlstrom, 1999) and whole-rock Nd isotopic data yield depleted mantle model ages of 1.8-1.7 Ga (Bennett & DePaolo, 1987;Wooden & DeWitt, 1991;Aleinikoff et al, 1993). The Mazatzal Province is adjacent to the Yavapai Province and extends from the southwestern U.S.A. through the mid-continent to the related Labradorian orogen in Canada (Whitmeyer & Karlstrom, 2007).…”

A rootless rockies—Support and lithospheric structure of the Colorado Rocky Mountains inferred from CREST and TA seismic data

“…The location of the exact suture is uncertain [see Shaw and Karlstrom, 1999], and other workers have suggested the main suturing occurred further south along the Jemez lineament in New Mexico [Magnani et al, 2004]. Nevertheless, most convergent zones are characterized by wide zones of imbrication and bivergent thrusting associated with the suturing, and the imaged crustal welt in southern Colorado is interpreted to be part of this collision.…”

Cripple Creek and other alkaline-related gold deposits in the southern Rocky Mountains, USA: influence of regional tectonics

“…9). Shaw and Karlstrom (1999) demonstrated a similar in¯uence of the YavapaiMazatzal boundary on the isotopic composition of young igneous rocks in Arizona.…”

“…Major blocks include the: (1) Archean craton, with protoliths and deformation dated between 2.5±3.5 Ga; (2) a 1.76±1.72-Ga juvenile arc terrane that constitutes the Yavapai Province (termed the Colorado Province in Colorado; Sims et al 2001); and (3) Mazatzal province, 1.7±1.6-Ga supracrustal rocks on unknown basement (Karlstrom and Bowring 1988). No major shear zone that might represent a discrete suture between the Yavapai and Mazatzal provinces has been identi®ed (Karlstrom and Humphreys 1998;Shaw and Karlstrom 1999). Instead, the boundary between the Yavapai and Mazatzal province is a wide zone, de®ned at its northern edge by the northern extent of 1.65-Ga deformation, and its southern edge by the southernmost extent of Yavapai (pre-1.7-Ga) crust (Karlstrom and Humphreys 1998).…”