Provenance and Sedimentologic Constraints on a Microconti- nent-Continent Collision, Gravina Belt, Southeast Alaska

微大陆地体的增长是一种重要的造山过程，但人们对此知之甚少。兰格利亚-亚历山大上地体是科迪勒拉西部记录最充分的微大陆之一，但在白垩纪吸积之前，人们对其构造和沉积历史知之甚少。该项目详细研究了格拉维纳带Seymour运河建造的物源和沉积学，以及最终闭合前在Wrangellia-Alexander微大陆内侧斜坡沉积的侏罗纪-白垩纪复理石和火山岩序列，以限制这次碰撞的性质。该项目将重点放在格拉维纳带较少变质的部分，并对砂岩和砾岩碎屑进行岩石学研究，同时对砂岩和火成岩中的斜长石和单斜辉石进行矿物化学研究，以确定物源和构造环境。它将结合浊积岩岩相分析、遗迹相和古流研究，以重建盆地历史，并通过新的微体化石生物地层学与火山和碎屑黑云母、角闪石颗粒的放射性测年相结合，利用Argon 40/39方法精炼沉积的时间框架。这些研究将有助于记录在这次微大陆碰撞中起作用的沉积学和构造过程，并可能作为科迪勒兰其他更神秘的侏罗纪-白垩纪复理石盆地的先导研究。

Continental growth by the accretion of microcontinental terranes is an important but poorly understood orogenic process. The Wrangellia-Alexander superterrane is one of the best documented microcontinents in the western Cordillera, yet little is known of its tectonic and depositional history immediately prior to its Cretaceous accretion. This project is a detailed study of the provenance and sedimentology of the Seymour Canal Formation of the Gravina belt, and Jura-Cretaceous sequence of flysch and volcanic rocks deposited on the inboard slope of the Wrangellia-Alexander microcontinent prior to final closure, in order to constrain the nature of this collision. The project will focus on little-metamorphosed portions of the Gravina belt, and carry out petrographic studies of sandstones and conglomerate clasts, coupled with mineral chemistry studies of plagioclase and clinopyroxene in sandstones and igneous rocks to establish provenance and tectonic setting. It will integrate turbidite lithofacies analysis and ichnofacies and paleo- current studies in order to reconstruct basin history, and refine the temporal framework of deposition by combining new microfossil biostratigraphy with radiometric dating of volcanic and detrital biotite and hornblende grains using Argon 40/39 methods. These studies will help document sedimentologic and tectonic processes operative in this microcontinent collision, and may serve as a pilot study for other, more enigmatic Jura-Cretaceous flysch basins of the Cordilleran.