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The Palmer Gneiss * by Carl A BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 46, PP. 1137-1162, PL. 93. 8 FIGS. JULY 31, 1938 THE PALMER GNEISS * BY CARL A. LAMEY (Accepted by the Committee on Publications, 1985) CONTENTS Page Introduction........................................................................................................... 1137 The Palmer area................................................................................................... 1140 The Palmer gneiss problem................................................................................... 1142 The Middle Huronian series................................................................................ 1143 General statement.......................................................................................... 1143 Ajibik quartzite.............................................................................................. 1144 The Lower Huronian series................................................................................... 1146 General statement.......................................................................................... 1146 Kona dolomite................................................................................................ 1147 Kona-Mesnard contact.................................................................................. 1150 Mesnard quartzite.......................................................................................... 1151 Remaining Palmer gneiss belt............................................................................... 1155 Region south of the Palmer gneiss belt................................................................ 1157 Structure................................................................................................................. 1158 Conclusions........................................................................................................... 1160 INTRODUCTION The Palmer gneiss was originally described as a part of the Base­ ment Complex of the Marquette district in northern Michigan.1 This gneiss was thought to consist of Archean rocks intruded by Laurentian granite. More detailed work later disclosed that some of the rocks designated Palmer gneiss are Middle Huronian sediments.2 Also, since these Huronian sediments were found to be extensively intruded by granite, it became evident that this granite must be as late as Middle Huronian and that its intrusion probably gave rise to some of the metamorphism which caused the Huronian sediments to be * Manuscript received by the Secretary of the Society, December 21, 1934. 1C. R. Van His«, W. S. Bayley, and H. L. Smyth: The Marquette iron-bearing district of Michigan, U. S. Geol. Surv., Mon. 28 (1897) p. 149-160, 190-192, 194, 211-220. 2 C. R. Van Hise and C. K. Leith: The geology of the Lake Superior region, U. S. Geol. Surv., Mon. 52 (1911) p. 255-256. (1137) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1138 C. A. LAMEY— THE PALMER GNEISS described as Palmer gneiss.3 During the course of a field study of the relations of this younger granite (the Republic granite) to the Huronian formations, the writer observed outcrops of dolomite, quartz- ite, and graywacke in the rocks still designated Palmer gneiss. The presence of these sediments, especially the dolomite, and their strati- graphic position below the conglomeratic base of the Middle Huronian series, suggested that at least a part of the remaining Palmer gneiss might well be Lower Huronian formations intruded and metamor­ phosed by the Republic granite.4 Consequently, a study of the com­ position and origin of the Palmer gneiss was undertaken, the results of which are presented in this paper. The field work was conducted during the summers of 1930, 1931, and 1932, in connection with the problem of the Republic granite, and completed in the summer of 1934 under a Penrose research grant from the Geological Society of America. It consisted of an examina­ tion of the rocks previously designated Palmer gneiss, and the making of a geological map, showing the different formations comprising this gneiss. Mapping was done by means of a dial compass, because of magnetic attraction, and by counting paces, care being taken to check on section comers and other known locations as frequently as possible. An airplane map of the region was a valuable aid. As a rule, the Ajibik quartzite, the lowest formation of the Middle Huronian series, was the horizon from which traverses were started, as the base of this formation generally furnished one boundary of the Palmer gneiss. From this established horizon the gneiss belt was subdivided as far as possible—until granite intrusions rendered recognition of its com­ ponent formations uncertain. Many rock specimens were collected, both from the Palmer gneiss area and from the Huronian areas near Marquette and Negaunee. Thin sections were obtained of those not readily identified by means of a hand lens, and the slides were studied from time to time in the field with a petrographic microscope, put at the writer’s disposal through the courtesy of the Michigan College of Mining and Technology. In this manner it was possible to investi­ gate more thoroughly any doubtful areas and to obtain additional specimens for more detailed petrographic study wherever necessary. 3 C. A. Lamey: Granite intrusions in the Huronian formations of northern Michigan, Jour. Geol., vol. 39 (1931) p. 291; The intrusive relations of the Republic granite, Jour. Geol., vol. 41 (1933) p. 493-494; Some metamorphic effects of the Republic granite, Jour. Geol., vol. 42 (1934) p. 261-262. 4 C. A. Lamey: What is the Palmer gneiss? Geol. Soc. Am., Pr., 1933 (1934) p. 92. The presence of outcrops of this character, and their probable significance, had been known by A. E. Seaman for some years. Oral communication. See, also, A. C. Lane: Sixth Ann. Report of the State Geologist of Michigan, 1904 (1905) p. 146. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 INTRODUCTION 1139 For laboratory study, 194 thin sections were selected from the many specimens collected. Preliminary pétrographie work was conducted during 1933 and 1934 from specimens previously collected, and final study of all thin sections was completed in the fall of 1934. The final 89* 88* 87* Figtjbe 1.—Index map showing location of the area described and its position with respect to the Marquette synclinorium pétrographie study was made near field headquarters, in order that any doubtful areas could be re-examined before the close of the field season. The writer is greatly indebted to the Geological Society of America for a Penrose bequest research grant which made possible the comple­ tion of the Palmer gneiss investigation. Also, acknowledgment is due to the Geology Department of Northwestern University for many courtesies extended during the course of this study; to the Michigan College of Mining and Technology for the use of equipment and laboratories; and to Professor A. E. Seaman for much valuable advice and for the use of field equipment. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 1140 C. A. LAMEY— THE PALMER GNEISS THE PALMER AREA Geologically, the Palmer area is a part of the Marquette district, which in turn is part of the Lake Superior pre-Cambrian region (Fig. 1). The most recent rock succession for the Marquette district is given by Leith.5 Not all the formations in this succession are repre­ sented in the Palmer area, due in part to structural conditions. Post Keweenawan Upper Cambrian sandstone Algonkian ---------- Unconformity------ Killamey Granite Acidic intrusives Basic intrusives Keweenawan Huronian Upper Upper Michigamme slates Bijiki iron formation Lower Michigamme slates Clarksburg volcanics Greenwood iron formation Goodrich quartzite ---------- Unconformity----- Middle Negaunee iron formation Siamo slates Ajibik quartzite ---------- Unconformity- - - Lower Wewe slate Kona dolomite Mesnard quartzite Algoman Granite Knife Lake (may be Lower Huronian) Archban ---------- Unconformity--------- Laurentian Granite Granite, syenite, peridotite Palmer gneiss Keewatin Kitchi schist and Mona schist The rocks in the immediate vicinity of Palmer form a part of the southern limb of the Marquette synclinorium, but a fault of consider­ able magnitude, north of Palmer, causes the area to appear as a pro­ jection along the southern side of the synclinorium. This fault, com­ bined with other features of the local structure, gives the Palmer area the aspect of an independent syncline (Fig. 2B). A fairly consistent relation of topography to structure exists within the area, and gives rise to its basin-like aspect. Northward, a fault 8 C. K. Leith: The pre-Cambrian, Geol. Soc. Am., Pr., 1933 (1934) opposite p. 176, Correlation Chart—Lake Superior Region. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/46/7/1137/3415306/BUL46_7-1137.pdf by guest on 26 September 2021 THE PALMER AREA 1141 scarp forms the wall of the basin; eastward, quartzite ridges tend to establish another boundary; granite masses partially block the western end; and ridges of northward-dipping iron formation and quartzite, together with other ridges of dolomite, granite, and gneiss, form the F ig ure 2.— Geologic map of the Palmer area A,
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