Fission track thermochronology of the Wind River Range, Wyoming: Evidence for timing and magnitude of Laramide exhumation

Abstract

Fission track analysis of Wind River Range basement rocks provides information about the timing, magnitude, and cooling that occurred in response to Laramide uplift. Eighty samples were collected from Precambrian rock along six traverses in the northern, central, and southern parts of the range over 5 km of elevation. Apatite fission track ages and track length data suggest that the range did not have a uniform thermal history during late Mesozoic and Cenozoic time. Zircon fission track ages are Precambrian, implying that these rocks have not been at temperatures higher than ~ 200øC (9-10 km burial depth) since Precambrian time. Apatite ages from the northeastern and southwestern flanks of the range suggesst that cooling may have initiated in the Wind River Range by about 85 Ma but was definitely occurring by 75 Ma. Data from the Green River Lakes area and Fremont Peak in the northern part of the range indicate that cooling was occurring by 62 Ma and was most rapid between 60 and 57 Ma. Apparent rates of exhumation vary from 94 m/m.y. to 246 m/m.y. in this part of the range. The central part of the range records this same period of rapid cooling, but structural and topographic relief are not as great. Ages from the southern part of the range suggest that uplift and erosion may have been initiated earlier there but continued at much slower rates (34 m/m.y.) over a longer period of time than in the north. Samples from a drill hole in the central Wind River Range have apatite ages ranging from 37 Ma to 86 Ma and suggest a significant cooling event at approximately 42 Ma involving nearly 2 km of the rock column. Timing, magnitudes, and apparent rates of exhumation have varied spatially in the Wind River Range. INTRODUCTION The Wind River Range is a basement-cored uplift in central western Wyoming, exposing Precambrian crystalline rocks over an area of about 6000 km 2. The purpose of this study is to determine the low-temperature thermal history of the Wind 1Now at Arco Exploration and Production Technology, Plano, Texas. River Range using fission track dating of apatite and zircon, and fission track length data from apatite. The data set was derived from surface samples of basement rocks of the Wind River Range and from core and cuttings from the Air Force "A" drill hole. Isotopic systems of low closure temperature, such as fission track dating of apatite and zircon, are sensitive to cooling events because they record the thermal history at shallow crustal depths. Where topographic relief is sufficient, the fission track ages will vary with elevation. If it is possible to collect a suite of samples over a range of elevations, an apparent rate of exhumation (cooling) may be determined [Wagner et al., 1977; Parrish, 1983; Gleadow and Fitzgerald, 1987]. Only a few fission track uplift/cooling studies have been completed in the ranges of the Cordilleran Foreland. These include the Beartooth Range [Giegengack et al., 1986; Omar et a1.,1989], the Front Range of Colorado [Bryant and Naeser, 1980; Lindsey et al., 1986], and ...

Mountain Building Triggered Late Cretaceous North American Megaherbivore Dinosaur Radiation

“…More specifically, the Wind River Mountains of southern Wyoming started cooling between 85–75 Ma [23], and the Big Horn Mountains began cooling as early as 70 Ma [24]. The Rock Springs and Douglas Creek uplift initiated simultaneously in the Campanian [72].…”

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

“…The depth of erosion in the basins is not well constrained, although AFT data from a well on the northern margin of the greater Green River Basin indicate ~2 km of erosion ca. 42 Ma (Cerveny and Steidtmann, 1993). Stable isotope data from mammalian teeth suggest that kilometer-scale relief was present in southcentral Wyoming during the Chadronian ( Barton and Fricke, 2006).…”

“…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).…”

Changes in Depositional Processes--An Ingredient in a New Generation of Sequence-Stratigraphic Models

“…The exact timing for the initiation of the Laramide Orogeny varies from one place to another, but by the Santonian the bathymetry of parts of the deeper, central part of the Western Interior Seaway was likely to have become broken and more complex (e.g., Gustason et al 1988;Cerveny and Steidtmann 1993;Martinsen 2003) (Fig. 3B).…”