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

由微大陆块体增生形成的大陆生长是一个重要的造山过程，但人们对其了解甚少。弗兰格里亚-亚历山大超地体是西科迪勒拉地区记录最完整的微大陆之一，但在其白垩纪增生之前，人们对其构造和沉积历史知之甚少。本项目详细研究了格拉维纳带西摩运河组的物源和沉积学，以及弗兰格利亚-亚历山大微大陆最终闭合前沉积在内侧斜坡上的侏罗-白垩纪复理石和火山岩序列，以限制这次碰撞的性质。该项目将重点研究重力带的少量变质部分，开展砂岩和砾岩碎屑岩相学研究，并对砂岩和火成岩中的斜长石和斜辉石进行矿物化学研究，以确定物源和构造背景。将浊积岩岩相分析与古流相研究相结合，重建盆地历史，并将新的微化石生物地层学与火山、碎屑黑云母和角闪石颗粒的氩40/39辐射定年相结合，完善沉积的时间框架。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，并可能作为对科迪勒兰其他更神秘的侏罗-白垩纪复理石盆地的初步研究。

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.