Preliminary integrated geologic map databases for the United States: Digital data for the geology of Wrangell-Saint Elias National Park and Preserve, Alaska

[1] We use air gun shots recorded by ocean-bottom and land seismometers to constrain a 3-D velocity structure and a Moho interface depth for the Yakutat terrane in southern Alaska. We use a tomographic inversion of ~61,000 first-arrival picks from 64 receivers to create a 3-D velocity model. The average velocity-depth function north of the coastline has velocities at the surface of ~4-5 km/s, increasing to velocities of >6 km/s at ~12-13 km below the surface. Average velocities at the surface are slower near the coast (3.8 km/s) than under the highest topography (4.7 km/s). We carry out an interface inversion of ~19,000 PmP reflection picks from 50 receivers to constrain a 2-D Moho interface model. The average Moho depth of the Yakutat terrane in the marine portion of our study area is ~30 km, but depth rapidly increases onshore to 40-45 km beneath the high topography of the Chugach-St. Elias Mountains. Moho depths are consistent with Airy isostasy beneath the orogen. Our data set supports a continuous Moho at the base of the Yakutat terrane, with no evidence for Pacific oceanic crust underthrusting the Yakutat terrane. We present several geologic models for crustal thickening beneath the Chugach-St. Elias orogen that are consistent with the seismic observations and surface geology and compare these models with geologic mapping in the region. We argue that crustal thickening and topography at the Chugach-St. Elias Mountains is obtained via a duplex system that produces a vertically growing antiformal stack of sedimentary and metasedimentary material.

show abstract

“…Geologic map of the study area modified from Wilson et al . [] and Witmer []. Red dashed line marks the profile location displayed in Figure .…”

Section: Discussionmentioning

confidence: 99%

Moho interface beneath Yakutat terrane, southern Alaska

et al. 2013

View full text Add to dashboard Cite

show abstract

“…Simplified map of south‐central Alaska showing the distribution of the Nikolai Formation (black), derived from the GIS‐based digital map compilations of Wilson et al [1998, 2005] and J. M. Schmidt (personal communication, 2006). The three main areas that were studied are outlined with boxes and indicated in the legend.…”

Section: Geologic Settingmentioning

confidence: 99%

“…(a) Stratigraphic column depicts late Paleozoic to Jurassic units on the south side of the Wrangell Mountains, derived from Smith and MacKevett [1970] and MacKevett [1978]. (b) Simplified map showing the distribution of the Nikolai Formation (green) in the Wrangell Mountains, derived from the GIS‐based digital map compilation of Wilson et al [2005]. The four areas of field study are outlined with labeled boxes.…”

Section: Geologic Settingmentioning

confidence: 99%

Wrangellia flood basalts in Alaska: A record of plume‐lithosphere interaction in a Late Triassic accreted oceanic plateau

Greene

Scoates

Weis

2008

Geochem Geophys Geosyst

View full text Add to dashboard Cite

[1] The Wrangellia flood basalts are part of one of the best exposed accreted oceanic plateaus on Earth. They provide important constraints on the construction of these vast submarine edifices and the source and temporal evolution of magmas for a plume head impinging beneath oceanic lithosphere. Wrangellia flood basalts ($231-225 Ma) extend $450 km across southern Alaska (Wrangell Mountains and Alaska Range) where $3.5 km of mostly subaerial flows are bounded by late Paleozoic arc volcanics and Late Triassic limestone. The vast majority of the flood basalts are light rare earth element (LREE) -enriched high-Ti basalt (1.6-2.4 wt % TiO 2 ) with uniform ocean island basalt (OIB) -type Pacific mantle isotopic compositions (e Hf (t) = +9.7 to +10.7; e Nd (t) = +6.0 to +8.1; t = 230 Ma). However, the lowest $400 m of stratigraphy in the Alaska Range is LREE-depleted low-Ti basalt (0.4-1.2 wt % TiO 2 ) with pronounced negative high field strength element (HFSE) anomalies and Hf isotopic compositions (e Hf (t) = +13.7 to +18.4) that are decoupled from Nd (e Nd (t) = +4.6 to +5.4) and displaced well above the OIB mantle array (De Hf = +4 to +8). The radiogenic Hf of the low-Ti basalts indicates involvement of a component that evolved with high Lu/Hf over time but not with a correspondingly high Sm/Nd. The radiogenic Hf and HFSE-depleted signature of the low-Ti basalts suggest pre-existing arc lithosphere was involved in the formation of flood basalts that erupted early in construction of part of the Wrangellia plateau in Alaska. Thermal and mechanical erosion of the base of the lithosphere by the impinging plume head may have led to melting of arc lithosphere or interaction of plume-derived melts and subduction-modified mantle. The high-Ti lavas dominate the main phase of construction of the plateau and were derived from a depleted mantle source distinct from the source of MORB and with compositional similarities to that of ocean islands (e.g., Hawaii) and plateaus (e.g., Ontong Java) in the Pacific Ocean.

show abstract

“…Here, we increase the scope of that effort through improved control on surface geology that was made possible through acquisition of new 0.5-and 1-m-resolution satellite images, and expand the geologic mapping westward into the upper Yahtse Glacier (Plate 2). The geology of the upper Yahtse Glacier is based on satellite image interpretation guided by the reconnaissance mapping of Richter et al (2006) and Wilson et al (2005) and 1:63,360scale fi eld maps from G. Plafker (1999, written commun.). The fi nal result is a geologic map with an accompanying detailed cross section along the Tyndall Glacier (Plate 2).…”

Section: Icy Bay Transectmentioning

confidence: 99%

“…Here moderately folded Kulthieth Formation structurally overlies the Poul Creek Formation along the ridge crest, but the Poul Creek-Kulthieth contact shows a footwall cutoff downslope, and there is complex detachment folding in the underlying upper Kulthieth Formation (Plate 2). To the west, however, across Tyndall Glacier, we were not able to directly examine rock exposures during our fi eld work, and rock unit identifi cations are based solely on reconnaissance mapping by Plafker (cited in Richter et al, 2006;Wilson et al, 2005;G. Plafker, 1999, written commun.…”

Section: Coal Glacier Thrust Sheetmentioning

confidence: 99%

Untitled

et al. 2012

View full text Add to dashboard Cite

Previous studies in the Yakataga foldthrust belt of the St. Elias orogen in southernAlaska have demonstrated high exhumation rates associated with alpine glaciation; however, these studies were conducted with only a rudimentary treatment of the actual structures responsible for the deformation that produced long-term uplift. We present results of detailed geologic mapping in two corridors across the onshore fold-thrust system: the Duktoth River transect just west of Cape Yakataga and the Icy Bay transect in the Mount St. Elias region. In the Duktoth transect, we recognize older, approximately eastwest-trending structures that are overprinted by open, northwest-trending fold systems, which we correlate to a system of northeasttrending, out-of-sequence, probably active thrusts. These younger structures overprint a fold-thrust stack that is characterized by variable structural complexity related to detachment folding along coal-bearing horizons and duplexing within Eocene strata. In the Icy Bay transect, we recognize a similar structural style, but a different kinematic history that is constrained by an angular unconformity at the base of the syntectonic Yakataga Formation. At high structural levels, near the suture, structures show a consistent northwest trend, but fold-thrust systems rotate to east-west For permission to copy, contact editing@geosociety.org

show abstract

Preliminary integrated geologic map databases for the United States: Digital data for the geology of Wrangell-Saint Elias National Park and Preserve, Alaska

Cited by 7 publications

References 0 publications

Moho interface beneath Yakutat terrane, southern Alaska

Moho interface beneath Yakutat terrane, southern Alaska

Wrangellia flood basalts in Alaska: A record of plume‐lithosphere interaction in a Late Triassic accreted oceanic plateau

Untitled

Contact Info

Product

Resources

About