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 提议对阿拉斯加东南部的兰格尔 - 彼得堡 - 威尔士亲王岛地区（= 兰格尔横断面）的东西横断面沿线的白垩纪和第三纪岩石进行多学科研究。 先前的研究表明，将古地磁研究与年代学、热年代学、气压学和构造地质观测相结合，可以对BC省西部和阿拉斯加东南部的岛屿超级地体和海岸山脉造山带的构造演化产生重要的见解。 PI 最近在鲁珀特王子港附近的研究结果表明，古地磁学是调查挖掘出的浅层和中地壳部分的多学科工作的关键组成部分。 当与精心协调的多学科研究计划所产生的地质观测相结合时，侵入火成岩的古地磁数据可以提供有关变形区域构造发展的关键信息，而这些信息是无法通过其他方式获得的。 例如，PI 已记录，在始新世伸展期间，包含海岸剪切带以东的 Palcocene Quottoon 火成岩杂岩的地壳板经历了东侧向上倾斜，范围达到 40 英尺。 此外，他们的年代学、古地磁、气压和构造地质数据表明，白垩纪中期的 Ecstall 岩体在向西的逆冲过程中发生了褶皱。 这些发现对于了解科迪勒拉山脉北部大陆边缘的地壳结构和构造发展至关重要。由于火成岩在白垩纪、整个古近纪和中新世都侵位到这部分岩浆弧中，因此兰格尔横断面提供了在空间和时间上追踪走滑板块边缘不断演化的变形的机会。 除古地磁分析外，方法还包括锆石和榍石的 U/Pb 地质年代学、Al-in-homblende 气压测定、40 Ar/39 Ar 热年代学、锆石 (U-Th)/He 定年、变质岩石学和构造地质调查以及古地磁分析。 对样线东部部分的初步调查表明，自 20 Ma 以来，该地区围绕方位角为 22' 的轴经历了 1 7' ESE 侧向倾斜。 横断面的观测表明，白垩纪岩体的古地磁方向是可变的，既有一致的倾向，也有不一致的倾向。 对兰格尔横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/折叠和/或大规模迁移是否可以解释白垩纪岩体不一致的古地磁方向。 结合鲁珀特王子港地区的研究成果，该研究的成功完成可以为过去 10 年来海岸山脉和岛屿超地层的构造和古地理演化提供综合模型。