Tertiary cooling and tectonic history of the White River uplift, Gore Range, and western Front Range, central Colorado: Evidence from fission-track and ³⁹Ar/⁴⁰ Ar ages

Abstract

Apatite fission-track (AFT) data from Proterozoic and Paleozoic rocks in the mountains of north central Colorado (White RiverUplift, Gore Range, and western Front Range) record significant cooling that began with uplift and erosion related to the Laramide Orogeny and continued through the Tertiary to Pliocene time. The mountains immediately flanking the Blue River half graben (Williams Fork Mountains to the east and the Gore Range to the west) cooled significantly during the Neogene. The AFT ages along the flanks of the Blue River half graben are significantly younger than AFT ages farther to the east in the central and eastern Front Range and to the west in the White River uplift. In both of these areas, the apatite ages suggest Laramide cooling. The Williams Fork Mountains-Gore Range zone of young AFT ages extends southward adjacent to the axis of the Rio Grande rift through southern Colorado and New Mexico. These young ages result from a combination of elevated heat flow, uplift, and erosion along the axis of the Rio Grande rift during Neogene time.Zircons from Proterozoic rocks yield Proterozoic fission-track ages, indicating that this part of the Colorado basement has not been heated to temperatures Ͼ200 ЊC since Middle Proterozoic time.A sanidine 40 Ar/ 39 Ar age of 27 Ma from a rhyolite tuff just above a basal boulder conglomerate of the Troublesome Formation in a tilted fault block within the Blue River half graben shows that Tertiary deposition started there in middle Oligocene time. Xenocrystic sanidine from a basalt stratigraphically higher than the rhyolite tuff has an age of 24 Ma. Thus, the basalt is significantly younger than its postulated source, the 32 Ma laccolithic complex at Green Mountain.

Mantle-driven dynamic uplift of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified hypothesis

“…5A) is representative of many areas in the Rocky Mountains that cooled through AFT closure temperatures of ~110 °C during the Laramide, 70-40 Ma (see also Naeser et al, 2002;Kelley and Chapin, 2004). Apparent Laramide exhumation rates here were ~60 m/Ma.…”

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

“…70-40 Ma; Kelley , 2003), the Nacimiento uplift (81-33 Ma; Kelley , 2003), the Gunnison uplift (ca. 55 Ma; Bryant and Naeser, 1980), the Sawatch Range (51-52 Ma; Bryant and Naeser, 1980), the Montosa uplift (65-37 Ma; Kelley et al, 1992), the northern Sierra uplift (57-45 Ma, based on clasts derived from the uplift, which subsequently subsided into the Rio Grande rift; Kelley et al, 2009), parts of the Front Range (79-45 Ma; Bryant and Naeser, 1980;67-57 Ma;Kelley and Chapin, 2004), the Sangre de Cristo uplift (Santa Fe Range portion, 74-44 Ma; Kelley and Duncan, 1986;Kelley, 1990;Kelley and Chapin, 1995), the Laramie uplift (82-65 Ma; Kelley, 2005), the northern Medicine Bow uplift (79-60 Ma; Kelley, 2005), the Sierra Madre uplift (79-49 Ma; Kelley, 2005), the Park Range uplift (75-45 Ma; Kelley, 2005), the White River uplift (70-40 Ma;Naeser et al, 2002), the Wind River uplift (80-50 Ma; Cerveny and Steidtmann, 1993), and the Sierra Madre Oriental of northeastern Mexico (74-64 Ma; Gray et al, 2001).…”

History and causes of post-Laramide relief in the Rocky Mountain orogenic plateau

“…Normal faulting associated with the Rio Grande Rift can be traced along the crest of the Rocky Mountains into northern Colorado with decreasing influence as it approaches the Wyoming border (Tweto, 1979;Chapin and Gather, 1994;Naeser et al, 2002;Buffler, 2003). As noted earlier, the zones of most active faulting along the rift and its projection into Wyoming are associated with the regions of least incision and the rift flanks are associated with more incision.…”