TABLE OF CONTENTS Historical background The Portage Lake Volcanics on the Keweenaw Peninsula The Portage Lake Volcanics on Isle Royale General description Correlation between Isle Royale and the Keweenaw Peninsula Origin of the Portage Lake Volcanics ILLUSTRATIONS FIGURE 1. Sketch map showing generalized distribution of Keweenawan rocks in the Lake Superior region 2. Chart showing nomenclature for middle and upper Keweenawan rocks of northern Michigan and adjacent parts of Wisconsin 3. Longitudinal stratigraphic section of the Portage Lake Volcanics on the Keweenaw Peninsula 4. Photographs showing characteristic textures of volcanic rocks on Isle Royale 5. Photograph showing coarse ophite with knobby weathered surface 6. Chart showing nomenclature for named volcanic flows within the Portage Lake Volcanics on Isle Royale 7. Plot showing tholeiitic affinities of analyzed specimens of rocks from the Portage Lake Volcanics on Isle Royale 8. Plot illustrating the predominantly basaltic nature of analyzed specimens of rocks from the Portage Lake Volcanics on Isle Royale 9. Shaded-relief map of Isle Royale National Park 10. Schematic columnar section of the Portage Lake Volcanics on Isle Royale 11. Simplified map of bedrock geology of Isle Royale 1216. Photographs showing: 12. Porphyrite from Huginnin Flow 13. Beach cobble of porphyrite from Grace Island Flow 14. Columnar jointing in Edwards Island Flow 15. Specimen of Amygdaloid Island Flow with characteristic agate amygdules 16. Specimen of ophite from Washington Island Flow 17. Columnar section of upper part of Portage Lake Volcanics showing distribution of sedimentary units in the Chippewa Harbor area 1821. Photographs showing: 18. Scour-and-fill structure in pebbly sandstone near the west end of Chippewa Harbor 19. Breccia occurring above the Amygdaloid Island Flow 20. Tuff-breccia overlying the Greenstone Flow 21. Agates typical of those occurring in the tuff-breccia overlying the Greenstone Flow 22. Geologic section of Isle Royale in the vicinity of Lake Desor and Houghton Ridge 23. Longitudinal stratigraphic section showing variations in thickness of the Portage Lake Volcanics on Isle Royale 24. Stratigraphic diagram illustrating correlation of sedimentary horizons in the Portage Lake Volcanics between Isle Royale and the Keweenaw Peninsula TABLES TABLES 1. Analyses of volcanic rocks of the Portage Lake Volcanics, Isle Royale 2. Correlation of clastic units in the Portage Lake Volcanics between the Keweenaw Peninsula and Isle Royale
pp/754-C/contents.htm Last Updated: 22-Jan-2009 |