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Reconnaissance Survey of the Roberts Mountains, Nevada

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Reconnaissance Survey of the Roberts Mountains, Nevada BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 53. PP. 1675-1728, 4 PLS., 3 FIGS. DECEMBER 1, 1942 RECONNAISSANCE SURVEY OF THE ROBERTS MOUNTAINS, NEVADA BY C. W. MERRIAM AND C. A. ANDERSON CONTENTS Page Abstract....................................................................................................................................... 1676 Introduction.............................................................................................................................. 1677 Acknowledgments..................................................................................................................... 1677 Topography................................................................................................................................ 1679 General stratigraphy................................................................................................................ 1680 Normal sequence of Paleozoic strata.................................................................................. 1680 General statement........................................................................................................... 1680 Pogonip group.................................................................................................................. 1683 Eureka quartzite.............................................................................................................. 1684 Hanson Creek formation............................................................................................... 1685 Roberts Mountains formation...................................................................................... 1686 Lone Mountain formation (restricted)....................................................................... 1688 Nevada formation (restricted)..................................................................................... 1688 Devils Gate formation................................................................................................... 1690 Diamond Peak beds........................................................................................................ 1690 Undifferentiated Carboniferous and Permian.......................................................... 1691 Dolomites of Cooper Peak............................................................................................ 1692 Undifferentiated Paleozoic rocks................................................................................. 1693 Rocks of Roberts Mountains thrust plate......................................................................... 1693 General statement........................................................................................................... 1693 Lower Vinini..................................................................................................................... 1694 General statement.................................................................................................. 1694 Lava flows and tuffs............................................................................................... 1694 Age of lower Vinini................................................................................................. 1695 Upper Vinini...................................................................................................................... 1695 General statement................................................................................................... 1695 Upper Vinini cherts................................................................................................ 1696 Age of upper Vinini................................................................................................ 1697 Garden Pass (Summit) graptolite zone............................................................. 1697 Facies change in Lower and Middle Ordovician.............................................................. 1699 General statement............................................................................................................ 1699 Eastern facies.................................................................................................................... 1699 Western facies................................................................................................................... 1699 Roberts Mountains thrust..................................................................................................... 1701 General statement........................................................................................................... 1701 Evidence of major thrusting......................................................................................... 1702 Direction of movement................................................................................................... 1703 Structural history............................................................................................................. 1704 (1675) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/53/12_1/1675/3431011/BUL53_12A-1675.pdf by guest on 30 September 2021 1676 MERRIAM AND ANDERSON— SURVEY OF ROBERTS MOUNTAINS, NEVADA Page Post-thrusting igneous rocks................................................................................................. 1707 General statement............................................................................................................ 1707 Alaskite stock and alaskite porphyry sills................................................................ 1707 Rhyolite porphyry plugs and dikes............................................................................ 1708 Tuffs and breccias............................................................................................................ 1709 Andesite flows and dikes................................................................................................ 1711 Quartz latite flows............................................................................................................ 1712 Post-quartz latite volcanic activity............................................................................ 1713 Other volcanic rocks....................................................................................................... 1713 Age of igneous rocks....................................................................................................... 1713 Postvolcanic faulting............................................................................................................... 1714 Outline of Roberts Mountains block................................................................................ 1714 Petrography of igneous rocks................................................................................................ 1716 General statement........................................................................................................... 1716 Alaskite and alaskite porphyry.................................................................................... 1717 Rhyolite porphyry........................................................................................................... 1718 Quartz latite...................................................................................................................... 1719 Andesite.............................................................................................................................. 1721 Olivine basalt.................................................................................................................... 1723 Chemical characters of igneous rocks................................................................................ 1723 Summary of conclusions......................................................................................................... 1725 References cited........................................................................................................................ 1725 ILLUSTRATIONS Figure Page 1. Index map of Nevada.................................................................................................... 1678 2. Correlation chart of the Ordovician........................................................................... 1682 3. Diagram of the k ratio plotted against Si02 content.............................................. 1724 Plate Facing Page 1. Roberts Mountains......................................................................................................... 1680 2. Undifferentiated Carboniferous, Vinini cherts and Mount Hope plug............... 1681 3. Roberts Mountains thrust plate................................................................................. 1696 4. Reconnaissance geologic map of Roberts Mountains with cross sections........ 1728 ABSTRACT The Roberts Mountains region, central Nevada, provides an excellent section of Paleozoic rocks ranging from Upper Cambrian to Permian. Major low-angle thrust­ ing is indicated by deformed Ordovician strata resting on Paleozoics of varying age. Overlying a thick breccia zone, the upper thrust plate consists of sandstones, andesitic flows and tuffs, black shales, and bedded cherts (Vinini formation). Ordovician age of the Vinini is established on the basis of graptolite faunules. A belt of Lower to Middle Ordovician graptolitic facies similar to the Vinini formation crosses the Great Basin west of Roberts Mountains. Deposits of roughly the same age in the Roberts Mountains meridian and eastward
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