Persistent influence of Proterozoic accretionary boundaries in the tectonic evolution of southwestern North America: Interaction of cratonic grain and mantle modification events

Abstract

Northeast-striking tectonic provinces and boundaries were established during 1.8-1.6-Ga assembly of juvenile continental lithosphere in the southwestern United States. This continental grain repeatedly has influenced subsequent intracratonic tectonism and magmatism. After 200 m.y. of stability, cratonic lithosphere was affected by regional, ~1.4-Ga, dominantly granitic magmatism and associated tectonism that reactivated older northeast-striking shear zones in the Proterozoic accreted terranes, but not the Archean lithosphere. In contrast, 1.1-Ga, dominantly mafic magmatism and rifting did not reactivate northeast-striking zones, but occurred along new north-south fracture zones (e.g., Rocky Mountain trend) that reflect cracking of Laurentian lithosphere at a high angle to the Grenville collision. By 500 Ma, rifting had thinned the crust and mantle in the western United States creating the north-south Cordilleran miogeocline. East of the Cordilleran hingeline, isopachs in Lower Paleozoic sedimentary rocks follow northeast-trending structures (Cheyenne belt, Transcontinental arch, and YavapaiMazatzal province boundary), suggesting that older boundaries influenced isostatic response of the craton during thermal subsidence of the margin. Ancestral Rockies and Laramide uplifts and basins did not strongly reactivate northeast-striking boundaries. However, Ancestral Rockies structures end at the Archean-Proterozoic boundary, and Laramide magmatism (Colorado mineral belt) and metallogenic provinces follow northeast-striking Proterozoic boundaries, both suggesting deep-seated lithospheric influences on tectonism.Present mantle structure and topography in the Rocky Mountain region continue to record an interaction between older crustal structures and younger mantle reorganization. Zones of partially molten mantle underlie northeast-striking Proterozoic boundaries (e.g., Snake River Plain, Saint George lineament, and Jemez lineament) and the north-striking Rio Grande rift, and are inferred to record replacement of lithosphere by asthenosphere preferentially along Archean-Proterozoic, Mojave-Yavapai, Yavapai-Mazatzal, and 1.1-Ga lithospheric anisotropies. Highest topography coincides with areas of low-velocity mantle, suggesting an importance of mantle buoyancy in the isostatic balance. Changes in topographic character across ancient crustal boundaries suggests a continued influence of crustal structures in differential uplift and denudation.Inheritance of the Proterozoic northeast grain involves two basic factors: (1) "volumetric" inheritance, in which density and fertility of lithospheric blocks of differing compositions influence isostatic and magmatic response to tectonism; and (2) "interface" inheritance, in which mechanical boundaries are zones of weakness and mass transport. "Volumetric" inheritance is suggested by the distinctive isotopic signatures of different provinces and by the observation that Archean lithosphere has been consistently less fertile for magmas than Proterozoic lithosphere, due to thicker, colder ...

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

“…Notable is the close correlation between this structure and the boundary between the 2.0-1.8 Ga and 1.8-1.7 Ga crustal provinces inferred from, albeit sparse, neodymium isotopic data [Bennett and DePaolo, 1987] and the good agreement between the westward continuation of this lineament and the location of this boundary in the Colorado Plateau determined from receiver function analysis [Gilbert et al, 2007]. These findings indicate that present Moho depths record the Proterozoic accretional assembly of this region and emphasize the importance of foundational inherited structures in lithospheric architecture [Dueker et al, 2001;Gilbert et al, 2007;Karlstrom et al, 2005;Karlstrom and Humphreys, 1998]. …”

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

“…Juvenile crust assembly in volcanic arcs between 1.8-1.7 Ga were subsequently accreted along the southeastern margin of Laurentia forming the Yavapai Province, which currently extends from Arizona to the mid-continent (Karlstrom & Humphreys, 1998;Van Schmus et al, 2007;Whitmeyer & Karlstrom, 2007). Whole-rock Nd model ages for the Yavapai Province range between 2.0-1.8 Ga (DePaolo, 1981).…”

Tectonic Evolution of the Adirondack Mountains and Grenville Orogen Inliers within the USA

“…In our summary, we have relied heavily on detailed studies by Karlstrom and Humphreys (1998), Karlstrom et al (2001), and an extensive review by Whitmeyer and Karlstrom (2007), as well as references given therein. We have excluded the Mojave Province, or Mojavia, situated west of the Yavapai Province from our discussion, because it has recently been interpreted by Nelson et al (2011) to be underlain by Yavapai crust overlain by a thick layer of Archean metasedimentary debris derived from the Wyoming Craton (Fig.…”