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‘s建议对阿拉斯加东南部兰格尔-彼得堡-威尔士亲王岛地区东西走向的白垩纪和第三系岩石进行多学科研究。以前的研究表明，将古地磁研究与地质年代学、非年代学、气压和构造地质观察相结合，可以对不列颠哥伦比亚省西部和阿拉斯加东南部的岛状超地体和海岸山脉造山带的构造演化产生重要的见解。国际和平研究所最近在鲁珀特王子附近的研究结果表明，古地磁是调查出土的浅层和中地壳部分的多学科努力的关键组成部分。当伴随着由仔细协调的多学科研究计划产生的地质观察时，侵入火成岩的古地磁数据提供了关于防御工区构造发展的关键信息，否则无法获得这些信息。例如，PI记录了在始新世伸展期间，海岸剪切带以东的含有帕尔科新世Quottoon火成岩杂岩的地壳板块经历了从东到上的倾角，范围从东到40‘。此外，它们的地质年代学、古地磁、气压和构造地质数据表明，中白垩世榴辉岩体是在西向逆冲期间褶皱的。这些发现是了解科迪勒拉北部大陆边缘地壳结构和构造发展的基础。由于火成岩在白垩纪、整个古近纪和中新世侵位到这部分岩浆弧中，兰格尔断面提供了在空间和时间上追踪汇聚到走滑板块边缘的演化变形的机会。方法除古地磁分析外，还将包括锆石和辉石的U/Pb年代学、铝均闪石压力法、40Ar/39Ar年代学、锆石(U-Th)/He测年、变质岩石学和构造地质调查。对样带东段的初步研究表明，该地区自20 Ma以来经历了-17‘ESE向上倾斜，方位角为22’。横穿断面的观测表明，白垩纪深成岩体的古地磁方向是不同的，既有一致的倾向，也有不一致的倾向。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/或大规模运移是否可以解释白垩纪深成岩体不协调的古地磁方向。结合鲁珀特王子地区的研究结果，这项拟议研究的成功完成将为100多年来海岸山脉和岛屿上地体的构造和古地理演化提供一个全面的模式。