The Bell Island Pluton, S.E. Alaska: Paleomagnetic Analysis of a Tilted Pluton

点击翻译按钮获取中文摘要

Discordant Cretaceous paleomagnetic directions observed in plutons of the North Cascades and the Coast Mountains Batholith indicate major tectonic disturbance subsequent to magnetization. Several lines of geological evidence suggest that consistent and large-scale tilting has affected intrusive rocks of this Mesozoic plutonic welt along the western margin of North America from the North Cascades to southeast Alaska. This may be a fundamental tectonic process the scope of which has not been previously appreciated. The Bell Island pluton is a 90 Ma pluton on the western flank of the Coast Mountain Batholith north of Ketchikan in southeast Alaska. Extensive structural, petrologic, and isotopic data indicate that the Bell Island pluton experienced 25o of northeast-side-up tilting in the 90 Ma to 50 Ma interval. This pluton provides an excellent opportunity to study the paleomagnetic and geologic record resulting from tilting of a large panel of crust and the tectonic processes involved in regional-scale tilting. This study is a combined geologic and paleomagnetic investigation along a southwest to northeast transect across the Bell Island pluton. The research could provide crucial information towards: (1) resolution of the northwards transport - versus - crustal tilting debate regarding discordant Cretaceous paleomagnetic directions (and therefore determination of a Cretaceous paleogeography for North America); and (2) determination of the importance of tilting of crustal panels in the tectonic evolution of North America.