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

在北喀斯喀斯特和海岸山脉岩基中观察到的白垩纪古地磁方向不协调，表明磁化后发生了重大的构造扰动。几条地质证据表明，持续的大规模倾斜作用影响了北美西部边缘从北喀斯喀特到阿拉斯加东南部的这一中生代深成岩带的侵入岩。这可能是一个基本的构造过程，其范围以前从未被认识到。贝尔岛岩体是一个90 Ma的岩体，位于阿拉斯加东南部凯奇坎以北的海岸山脉岩基的西侧。广泛的构造、岩石学和同位素数据表明，贝尔岛岩体在90 Ma至50 Ma之间经历了25o的东北侧向上倾斜。该岩体为研究一大片地壳倾斜产生的古地磁和地质记录以及区域尺度倾斜所涉及的构造过程提供了极好的机会。这项研究是一项地质和古地磁联合调查，沿着一条西南向东北的横跨贝尔岛岩体的断面进行。这项研究可为以下方面提供关键信息：(1)解决关于白垩纪古地磁方向不一致的向北输送与地壳倾斜的争论(从而确定北美白垩纪的古地理)；(2)确定地壳板块倾斜在北美构造演化中的重要性。

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.