Collaborative Research: A Multidisciplinary Study of an Exhumed Active Continental Margin: The Wrangell Transect, SE Alaska

合作研究：对挖出的活动大陆边缘的多学科研究：阿拉斯加东南部的兰格尔断面

• 批准号: 0207586
• 负责人: Maria Crawford
• 金额: $ 7.31万
• 依托单位: Bryn Mawr College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-06-01 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0207586&HistoricalAwards=false
• 关键词: Collaborative; Research; Multidisciplinary; Study; Exhumed

The PI's propose a multidisciplinary study of Cretaceous and Tertiary rocks along an east-west transect in the Wrangell - Petersburg - Prince of Wales Island area of SE Alaska (= Wrangell transect). Previous research demonstrates that integration of paleomagnetic studies with geochronologic, thennochronologic, barometric, and structural geologic observations can produce important insights into the tectonic evolution of the Insular superterrane and Coast Mountains orogen in western BC and SE Alaska. The PI's recent results from near Prince Rupert show that paleomagnetism is a key component of multidisciplinary efforts investigating exhumed shallow and mid-crustal sections. When accompanied by geologic observations resulting from a carefully coordinated multidisciplinary research program, paleomagnetic data on intrusive igneous rocks yield critical infon-nation on the tectonic development of defon-ned regions that cannot otherwise be obtained. For example, the PI's have documented that panels of crust containing the Palcocene Quottoon igneous complex east of the Coast shear zone have experienced east-side-up tilts ranging to 40' during Eocene extension. In addition, their geochronologic, paleomagnetic, barometric, and structural geologic data suggest that the midCretaceous Ecstall pluton was folded during west-directed thrusting. These discoveries are fundamental to understanding the crustal architecture and tectonic development of the continental margin in the northern Cordillera.Because igneous rocks were emplaced into this part of the magmatic arc during the Cretaceous, throughout the Paleogene, and into the Miocene, the Wrangell transect provides the opportunity to track deformation of an evolving convergent to strike-slip plate margin in space and time. Methods will include U/Pb geochronology of zircon and sphene, Al-in-homblende barometry, 40 Ar/39 Ar thennochronology, (U-Th)/He dating of zircon, metamorphic petrology, and structural geologic investigations in addition to paleomagnetic analysis. Preliminary investigations on the eastern portion of the transect indicate that this area experienced - 1 7' ESEside-up tilt about an axis with azimuth 22' since 20 Ma. Observations from across the transect indicate that paleomagnetic directions from Cretaceous plutons are variable, with both concordant and discordant inclinations. Paleomagnetic study of the Cretaceous and Tertiary igneous rocks of the Wrangell transect, coupled with the geochronologic, thermochronologic, and barometric analyses, can determine: (1) when and where Cenozoic deformation occurred; and (2) whether regionally consistent tilting/folding and/or large-scale transport can account for discordant paleomagnetic directions from Cretaceous plutons. Combined with results from the Prince Rupert area, successful completion of the proposed research can provide a comprehensive model for the tectonic and paleogeographic evolution of the Coast Mountains and Insular superterrane for the past I 00 m.y.

PI建议对阿拉斯加东南部兰格尔-彼得堡-威尔士王子岛地区沿着东西向断面（=兰格尔断面）的白垩纪和第三纪岩石进行多学科研究。 以往的研究表明，整合古地磁研究与地质年代学，热年代学，气压，和结构地质观测可以产生重要的见解的构造演化的岛屿上和海岸山脉造山带在公元前西部和阿拉斯加东南部。 PI最近在鲁珀特王子岛附近的研究结果表明，古地磁学是多学科研究的一个关键组成部分。 当伴随着一个精心协调的多学科研究计划产生的地质观测时，侵入火成岩的古地磁数据产生了无法通过其他方式获得的关于变形区域构造发展的关键信息。 例如，PI已经证明，在始新世伸展期间，包含海岸剪切带东部的古新世Quottoon火成岩复合体的地壳板块经历了东侧向上的倾斜，范围为40'。 此外，他们的地质年代学，古地磁，气压，和结构地质数据表明，白垩纪中期埃克斯托尔岩体在西向逆冲过程中折叠。 这些发现是了解地壳结构和构造发展的大陆边缘在北方科迪勒拉山脉。因为火成岩侵位到这部分的岩浆弧在白垩纪，整个古近纪，并进入中新世，兰格尔断面提供了机会，跟踪变形的演变收敛到走滑板块边缘的空间和时间。 方法包括锆石和辉石的U/Pb年代学、铝同位素压力法、40 Ar/39 Ar热年代学、锆石的（U-Th）/He定年、变质岩石学、构造地质调查以及古地磁分析。 对样带东部的初步调查表明，20 Ma以来，该地区经历了一次以方位角22'为轴的-17' ESE侧倾。 从整个断面的观测表明，白垩纪岩体的古地磁方向是可变的，既有一致的和不一致的倾角。 对兰格尔断面白垩纪和第三纪火成岩的古地磁研究，结合地质年代学、热年代学和气压分析，可以确定：（1）新生代变形发生的时间和地点;（2）区域一致的倾斜/褶皱和/或大规模搬运是否可以解释白垩纪侵入岩的不一致古地磁方向。 结合鲁珀特王子岛地区的研究成果，成功完成上述研究，可为近1亿年来海岸山脉和岛屿表层的构造和古地理演化提供一个全面的模式。