Paleomagnetism of the Paleocene Ghost Rocks Formation, Prince William Terrane, Alaska

Abstract

The mean paleomagnetic inclination of Paleocene volcanics from two regions on Kodiak Island in the Ghost Rocks Formation suggests that the Prince William terrane originated at mid latitudes, about 25° south of its ‘expected’ Alaskan latitude in Paleocene time. The remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age. The mean declinations of the two regions, however, differ by approximately 120°, suggesting they have rotated with respect to each other, perhaps during emplacement. We suggest that, despite the lack of evidence for a major Tertiary suture zone between the Prince William terrane and central Alaska, the Prince William and perhaps adjacent terranes may have lain substantially south of their present position in the Early Tertiary.

Dextral-slip reactivation of an arc-forearc boundary during Late Cretaceous-early Eocene oblique convergence in the northern Cordillera

“…Thus, the results from this study, which indicate that the record of ridge interaction with the trench was moving with respect to North America, help resolve the contradictions between the plate models and geologic data sets. Paleomagnetic data from igneous rocks within the Chugach accretionary complex provide the only direct estimate of the paleolatitude of ridge-trench interaction, and they also locate the triple junction substantially south of the paleolatitude expected if the accretionary complex had not moved with respect to North America (Plumley et al, 1983;Bol et al, 1992). Despite large error bars on the data sets, they show northward displacement of 25° since 62 Ma (Plumley et al, 1983) and 13° since 59 Ma (Bol et al, 1992).…”

“…Paleomagnetic data from igneous rocks within the Chugach accretionary complex provide the only direct estimate of the paleolatitude of ridge-trench interaction, and they also locate the triple junction substantially south of the paleolatitude expected if the accretionary complex had not moved with respect to North America (Plumley et al, 1983;Bol et al, 1992). Despite large error bars on the data sets, they show northward displacement of 25° since 62 Ma (Plumley et al, 1983) and 13° since 59 Ma (Bol et al, 1992). Paleomagnetic data from Paleocene volcanics immediately north of the Border Ranges fault system indicate no northward displacement (Hillhouse and Grommé, 1982).…”

Constrictional flow within the Eocene forearc of Southern Alaska: An effect of dextral shear during ridge subduction

“…Nonetheless, the net slip on these structures estimated from displaced geologic markers continues to be far lower than estimates based on paleomagnetic discordance. This discrepancy is particularly acute for the outermost part of the accretionary complex (Prince William terrane) where several paleomagnetic studies suggest northward displacements of >1500 km since the Paleocene (e.g., Plumley et al, 1983;Bol et al, 1992). This problem is related to the Baja British Columbia problem of the central Cordillera.…”

Flysch deposition and preservation of coherent bedding in an accretionary complex: Detrital zircon ages from the Upper Cretaceous Valdez Group, Chugach terrane, Alaska

“…Zircons of this age are coeval with plu tonism in the Alaska Range, Talkeetna Mountains, and the Coast Mountains Batholith (Nokleberg et al, 1985;Trop et al, 2002Trop et al, , 2005Ridgway et al, 2002;Gehrels et al, 2009). However, structural reconstructions of strikeslip motion along the Border Ranges fault (e.g., Pavlis and Roeske, 2007) and paleomagnetic data (e.g., Plumley et al, 1983;Cowan, 2003) indicate that the Valdez Group (and the entire Chugach terrane) was originally deposited between ~200 km and ~2000 km south of its modern location. Regardless of the magnitude of displacement, the Valdez Group was situated south of its present location.…”