The most important latest Mesozoic and Cenozoic, postaccretionary geologic features of southeastern Alaska are those related to the magmatic activity that affected a large part of the region and to the resultant metamorphism and deformation. The metamorphic history is discussed elsewhere in this volume (Dusel-Bacon, this volume), and the magmatic activity is a continuation of the late Mesozoic activity discussed by Miller (this volume). Postaccretionary geologic history starts with the accumulation of the Gravina belt overlap assemblage of rocks in Late Jurassic and Early Cretaceous time (Berg and others, 1972). The locally voluminous volcanic rocks within that assemblage are probably the extrusive equivalents of island-arc intrusive rocks, which are preserved west of the Gravina belt over a large area in northern southeastern Alaska (Brew and Morrell, 1983). Neither the volcanics nor the granitoids are discussed in this chapter.
Previous syntheses concerned with the magmatic rocks of southeastern Alaska comprise a summary of post-Carboniferous volcanic activity (Brew, 1968), summaries of the distribution and general characteristics of the plutonic rocks (Brew and Morrell, 1980, 1983), a summary of the geochronologic data available (Wilson and Shew, 1982), and two reports concerned with the tectonic significance of major- and trace-element chemical data (Barker and Arth, 1984; Barker and others, 1986). Karl and Brew (1984) discussed migmatitic rocks associated with some of the intrusive rocks; that topic is not considered in this report.
In this chapter, the latest Mesozoic and Cenozoic magmatic rocks are grouped chronometrically (Table 1); the same time divisions are used elsewhere
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You get a comprehensive overview of the geology, tectonic evolution, and mineral resources of Alaska and adjacent areas of the continental margin. Plates include state-wide maps showing geology, physiography, lithotectonic terranes, metamorphic rocks, igneous rocks, sedimentary basins, isotopic age data, neotectonics, isostatic gravity, magnetics, and metallic mineral deposits. Summaries of bedrock geology and geologic history are given for eleven large regions of Alaska and adjacent offshore areas. Twenty topical chapters synthesize data on metamorphic and igneous rocks; major onshore and offshore sedimentary basins; the paleomagnetics evidence for latitudinal displacements and rotations, glacial history and periglacial phenomena; and the occurrence, evolution, and potential of Alaska's vast resources of petroleum, coal, and metallic minerals. A summary chapter provides an overview and presents a possible model for Alaska's Phanerozoic evolution. The Geology of Alaska is the largest publication produced in the Decade of North American Geology program, a fitting tribute to this magnificent area.