An official website of the United States government
Abstract The modern topography within the Laramide region consists of high‐relief ranges and high‐elevation low‐relief (HELR) surfaces separated by intraforeland basins. However, the timing and development of this topography within the type‐locality of the Wyoming Laramide province is poorly understood. Previous models suggest that the modern topography is a young feature that was acquired after Laramide tectonism, post‐Laramide burial, and basin evacuation; however, evidence of such a progression is sparse. We present low‐temperature‐thermochronological data from two Laramide uplifts in Wyoming, the Wind River and Bighorn Ranges, which document an early record of Laramide exhumation, subsequent reheating, and significant cooling after 10 Ma. Our results indicate that the Laramide ranges were buried by post‐Laramide Cenozoic basin fill, creating a low‐relief topography by the early Miocene that was reduced due to late Miocene regional incision and basin evacuation. We suggest that HELR surfaces experienced further relief reduction from Pleistocene glaciation.
more »
« less
The Rise and Fall of Laramide Topography and the Sediment Evacuation From Wyoming
The modern topography within the Laramide region consists of high-relief ranges and high-elevation low-relief (HELR) surfaces separated by intraforeland basins. However, the timing and development of this topography within the type-locality of the Wyoming Laramide province is poorly understood. Previous models suggest that the modern topography is a young feature that was acquired after Laramide tectonism, post-Laramide burial, and basin evacuation; however, evidence of such a progression is sparse. We present low-temperature-thermochronological data from two Laramide uplifts in Wyoming, the Wind River and Bighorn Ranges, which document an early record of Laramide exhumation, subsequent reheating, and significant cooling after 10 Ma. Our results indicate that the Laramide ranges were buried by post-Laramide Cenozoic basin fill, creating a low-relief topography by the early Miocene that was reduced due to late Miocene regional incision and basin evacuation. We suggest that HELR surfaces experienced further relief reduction from Pleistocene glaciation.
more »
« less
- Award ID(s):
- 1919179
- PAR ID:
- 10508452
- Editor(s):
- NA
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Edition / Version:
- NA
- Volume:
- NA
- Issue:
- NA
- ISSN:
- GL103218
- Page Range / eLocation ID:
- NA
- Subject(s) / Keyword(s):
- NA
- Format(s):
- Medium: X Size: NA Other: NA
- Size(s):
- NA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Slim Buttes is a 30 km long by 10 km wide set of buttes containing Paleogene strata in northwest South Dakota. At Reva Gap in northern Slim Buttes, Eocene-Oligocene terrestrial strata of Chadron and Brule Formations of the White River Group unconformably overlie the Paleocene Fort Union Formation. An angular unconformity separates the White River Group from overlying Oligocene and Miocene strata of the Arikaree Group. Using detrital zircon U-Pb ages, we determine the provenance of these rocks as part of a broader synthesis of post-Laramide sedimentation in the Rocky Mountains and western Great Plains. The Chadron Formation age spectrum is dominated by Cretaceous and Proterozoic grains that are interpreted to be locally recycled from the underlying Cretaceous and Paleocene strata. The Brule Formation has a maximum depositional age of ~34 Ma; Paleogene zircons dominate the age spectrum, and a wide variety of older zircons are also present. The Oligocene zircons are interpreted to have been sourced from volcanic systems in the Great Basin to the southwest, while the subsequent proportions of the zircons were derived from a variety of source areas in the Nevadaplano and Rocky Mountain areas to the southwest. Sparse amounts of Archean zircons are thought to represent the burial of Laramide uplifts throughout Wyoming at the time of Brule deposition, making for a regional paleotopography with little relief across the western interior of the United States. The Miocene-age Arikaree Group sand has a maximum depositional age of ~26 Ma and a multimodal detrital zircon age spectrum. The Arikaree Group provenance likely represents continued sourcing in the Great Basin volcanic systems and Nevadaplano, the beginnings of the re-exhumation of Laramide basement uplifts, and subsequent sediment evacuation out of the western interior and into the Gulf of Mexico to the southeast. Our findings indicate that the transport process and detrital zircon provenance signatures of these strata are decoupled, and each have their own independent evolution. The volcanic signature is primarily transported via aeolian processes (i.e. volcanic ash), and the recycled detrital zircon signature is primarily transported via fluvial processes.more » « less
-
Abstract Low‐temperature thermochronometric data can reveal the long‐term evolution of erosion, uplift, and thrusting in fold‐thrust belts. We present results from central Idaho and southwestern Montana, where the close spatial overlap of the Sevier fold‐thrust belt and Laramide style, basement‐involved foreland uplifts signify a complex region with an unresolved, long‐term tectono‐thermal history. Inverse QTQt thermal history modeling of new zircon (U‐Th)/He (ZHe,n = 106), and apatite (U‐Th)/He dates (AHe,n = 43) collected from hanging walls of major thrusts systems along a central Idaho to southwestern Montana transect, and apatite fission track results from 6 basement samples, reveal regional thermal and spatial trends related to Sevier and Laramide orogenesis. Inverse modeling of foreland basement uplift samples suggest Phanerozoic exhumation initiated as early as ∼80 Ma and continued through the early Paleogene. Inverse modeling of interior Idaho fold‐thrust belt ZHe samples documents Early Cretaceous cooling at ∼125 Ma in the Lost River Range (western transect), and a younger cooling episode in the Lemhi Arch region (mid‐transect) at ∼90–80 Ma through the late Paleogene. This cooling in the Lemhi Arch temporally overlaps with cooling in southwestern Montana's basement‐cored uplifts, which we interpret as roughly synchronous exhumation related to contractional tectonics and post‐orogenic collapse. These data and models, integrated with independent timing constraints from foreland basin strata and previously published thermochronometric results, suggests that middle Cretaceous deformation of southwestern Montana's basement‐cored uplifts was low magnitude and preceded tectonism along the classic Arizona‐Wyoming Laramide “corridor.” In contrast, Late Cretaceous and Paleogene thrust‐related exhumation was more significant and largely complete by the Eocene. The basement‐involved deformation was contemporaneous with and younger than along‐strike Sevier belt thrusting in central Idaho.more » « less
-
Western North America is the archetypical Cordilleran orogenic system that preserves a Mesozoic to Cenozoic record of oceanic Farallon plate subduction-related processes. After prolonged Late Jurassic through mid-Cretaceous normal-angle Farallon plate subduction that produced the western North American batholith belt and retroarc fold-thrust belt, a period of low-angle, flat-slab subduction during Late Cretaceous−Paleogene time caused upper plate deformation to migrate eastward in the form of the Laramide basement-involved uplifts, which partitioned the original regional foreland basin. Major questions persist about the mechanism and timing of flat-slab subduction, the trajectory of the flat-slab, inter-plate coupling mechanism(s), and the upper-plate deformational response to such processes. Critical for testing various flat-slab hypotheses are the timing, rate, and distribution of exhumation experienced by the Laramide uplifts as recorded by low-temperature thermochronology. In this contribution, we address the timing of regional exhumation of the Laramide uplifts by combining apatite fission-track (AFT) and (U-Th-Sm)/He (AHe) data from 29 new samples with 564 previously published AFT, AHe, and zircon (U-Th)/He ages from Laramide structures in Arizona, Utah, Wyoming, Colorado, Montana, and South Dakota, USA. We integrate our results with existing geological constraints and with new regional cross sections to reconstruct the spatial and temporal history of exhumation driven by Laramide deformation from the mid-Cretaceous to Paleogene. Our analysis suggests a two-stage exhumation of the Laramide province, with an early phase of localized exhumation occurring at ca. 100−80 Ma in Wyoming and Montana, followed by a more regional period of exhumation at ca. 70−50 Ma. Generally, the onset of enhanced exhumation occurs earlier in the northern Laramide province (ca. 90 Ma) and later in the southern Laramide province (ca. 80 Ma). Thermal history models of selected samples along regional cross sections through Utah−Arizona−New Mexico and Wyoming−South Dakota show that exhumation occurred contemporaneously with deformation, implying that Laramide basement block exhumation is coupled with regional deformation. These results have implications for testing proposed migration pathway models of Farallon flat-slab and for how upper-plate deformation is expressed in flat-slab subduction zones in general.more » « less
-
The Himalaya is known for dramatically rugged landscapes including the highest mountains in the world. However, there is a limited understanding of the timing of attainment of high elevation and relief formation, especially in the Nepalese Himalaya. Anomalous high-elevation low-relief (HELR) surfaces, which exhibit geomorphic antiquity and are possibly remnants of formerly widespread high-elevation paleosurfaces, provide a unique opportunity to assess the attainment of regional high elevation in the Himalaya. The Bhumichula plateau is one such HELR surface (4300−4800 m) in the western Nepalese Himalayan fold-thrust belt. The Bhumichula plateau is situated in the Dadeldhura klippe (also called the Karnali klippe), an outlier of Greater Himalayan Sequence high-grade metasedimentary/igneous rocks surrounded by structurally underlying Lesser Himalayan Sequence low-grade metasedimentary rocks. We assess the origin of the Bhumichula plateau by combining regional geological relationships and zircon and apatite (U-Th-Sm)/He and apatite fission track thermochronologic ages. The HELR surface truncates pervasive west-southwestward dipping foliations, indicating that it post-dates tilting of rocks in the hanging wall of the Main Central thrust above the Lesser Himalayan duplex. This suggests that the surface originated at high elevation by erosional beveling of thickened, uplifted crust. Exhumation through the ∼180−60 °C thermal window occurred during middle Miocene for samples on the plateau and between middle and late Miocene for rocks along the Tila River, which bounds the north flank of the Bhumichula plateau. Cooling ages along the Tila River are consistent with erosional exhumation generated by early Miocene emplacement of the Main Central (Dadeldhura) thrust sheet, middle Miocene Ramgarh thrust emplacement, and late Miocene growth of the Lesser Himalayan duplex. The most recent middle-late Miocene exhumation took place as the Tila River and its northward flowing tributaries incised upstream, such that the Bhumichula plateau is a remnant of a more extensive HELR paleolandscape. Alpine glaciation lowered relief on the Bhumichula surface, and surface preservation may owe to its relatively durable lithology, gentle structural relief, and elevation range that is above the rainier Lesser Himalaya.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- The DOI is not currently available.
