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Petrography of the Island of Hawaii

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Petrography of the Island of Hawaii Petrography of the Island of Hawaii GEOLOGICAL SURVEY PROFESSIONAL PAPER 214-D Petrography of the Island of Hawaii By GORDON A. MACDONALD GEOLOGICAL SURVEY PROFESSIONAL PAPER 214-D A study of representative samples of rock types from every volcano on Hawaii by thin sections, mineral grains, and hand specimens. UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1949 UNITED STATES DEPARTMENT OF THE INTERIOR J. A. Krug, Secretary GEOLOGICAL SURVEY W. E: Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 35 cents (paper cover) CONTENTS Page Page Abstract.. __J1_____________________________________ 51 HualalaL ____---__-__-__-__--_---___-___- 75 Introduction. -_-------___-_-_______-_-_____________ 51 General geology._____________________ 75 Previous investigations._____________________________ 51 Hualalai volcanic series..____----_-_--_ 75 Principal rock types_______________________________ 53 Lavas-__________________________ 75 Basaltic rocks.-________________________________ 54 Gabbroic and ultrabasie" xenoliths— 76 Andesites._____________________________________ 54 Phreatic explosion debris._________ 76 Trachytes. _----------_______--_-_________-____. 56 Trachyte of Puu Waawaa.—______ 76 Mauna Loa________________________________________ 56 Chemical analyses.___________________ 77 General geology._______________________________ 56 Mauna Kea__--__-_________-_-_-_--__-_-- 78 Lavas of the Ninole volcanic series..._____________ 57 General geology._____________________ 78 Lavas of the Kahuku volcanic series_____________ 58 Hamakua volcanic series--------------- 79 Pahala ash on Mauna Loa and Kilauea____________ 58 Lavas--__-__-_____-_-_______----. 79 Kau volcanic series____________________________ 59 Inclusions in lavas._______________ 80 Lavas of prehistoric age.____________________ 59 Lavas of the Laupahoehoe volcanic series. 80 Lavas of historic age________________________ 61 Pyroclastic rocks.___________________. 80 Inclusions in lavas.________----_-_-_-_______ 62 Intrusive rocks _____________________________ 62 Ash beds._______________________ 80 Ejected blocks near Mokuaweoweo__________ 62 Cinder cones______________________ 81 Chemical analyses______________________________ 62 Plutonic ejecta.________-___-_-___. 82 Kilauea______•____-__.____________________________ 63 Chemical analyses._______-_---_______. 82 General geology._______________________________ 63 Kohala __-___________-__-..---_-_-_____--. 84 Hilina volcanic series____'______-_______. _________ 64 General geology.____________--_--_--_. 84 Puna volcanic series.._____-_-__--_--_-__________ 64 Pololu volcanic series______.--_-_____. 84 Lavas of prehistoric age.____________________ 64 Hawi volcanic series__________________ 85 Ejected blocks from Halemaumau____________ 65 Lavas-___________________________ 85 Lavas of historic age_______-_----___________ 66 Inclusions in lavas__-_-_-_____-___. 86 Intrusive rocks _____________________________ 67 Uwekahuna ash,___________________________ 67 Intrusive rocks____________________ 87 Surficial pyroclastic deposits surrounding Kilauea Chemical analyses_____________________ 87 caldera-_________________-------____-____ 69 Magmatic differentiation__________________ 88 Littoral cone deposits.______________________ 72 Literature cited.___________________________ 92 Chemical analyses.____________--___-_---_-_____ 72 Index _____________________ — _____-_--_-_. 95 ILLUSTRATIONS Pa£e PLATE 11. Mauna Loa from the southeast, showing Mokuaweoweo caldera and the row of pit craters along the upper part of the southwest rift zone_______________________________________-_____________------------_--__----__ 54 12. Geologic*map of the Island of Hawaii___________________-_____-_-----____------_-----~7------_------___- 62 13. Surficial ash deposits at the south edge of Kilauea caldera___-____----------_--_------------------------ in pocket 14. A, Small lenticular sill and its dike feeder, cutting lavas of the Kau volcanic series in the west wall of Mokuaweoweo caldera; B, Cross section of a thick aa flow of andesite belonging to the Laupahoehoe volcanic series exposed in a quarry near Paauilo on the northeastern slope of Mauna Kea________________________________________ 63 FIGURE 1. Variation diagram of lavas of Mauna Kea_____--__--__--_-_----_-_-------------__----------------------- 83 811316—49———1 HI PETROGRAPHY OF THE ISLAND OF HAWAII By GORDON A. MACDONALD ABSTRACT Kohala, were collected by the writer during areal sur­ The lavas of Mauna Loa and Kilauea Volcanoes consist pre­ veys of those parts of the island in 1941, 1942, and 1943. dominantly of olivine basalt, with smaller proportions of basalt Most of the specimens from Hualalai and the western and picrite-basalt. Andesites are unknown. Hypersthene- slope of Mauna Loa, and about half of those from Ko­ bearing lavas are moderately abundant on Mauna Loa but rare on Kilauea. The lavas of Mauna Loa show considerably greater hala, were collected by H. T. Stearns in 1940 and 1943. variation than those of Kilauea. One specimen from Kohala was collected by W. O. Hualalai Volcano is built largely of olivine basalt, with asso­ Clark. Several thin sections of pyroclastic rocks v^ere ciated smaller amounts of basalt, of rocks transitional between loaned by C. K. Wentworth. olivine basalt and picrite-basalt, and of rare andesite. The lava The investigation has involved the study of about flow of 1801 is olivine basalt. Xenoliths of gabbrb, dunite, and augite peridotite are present in the lavas. Soda trachyte forms 400 thin sections. In addition, many specimens lave a cinder cone and thick flow on the north flank of the mountain. been studied by means of mineral grains immersed in Only the earliest stages of magmatic differentiation are indicated, oils of known refractive index, and many others lave thus strengthening the conclusion reached at other Hawaiian been studied with a hand-lens. An effort has b^en volcanoes that appreciable differentiation commences near the made to obtain representative samples of every rock end of the caldera-fillmg stage. The lavas of Mauna Kea Volcano are divided into the older type, and from all parts of each volcano. The latter Hamakua volcanic series and the younger Laupahoehoe volcanic objective was not entirely fulfilled on Hualalai and series. The Hamakua volcanic series consists of two members. Kohala, but the entire surface area of the other vol­ The lavas of the lower member are very largely olivine basalt, canoes is fairly well represented in the collections. with less numerous flows of basalt, and primitive picrite-basalt The composition of the feldspar has been determined containing abundant phenocrysts of olivine. The lavas of the upper member include olivine basalt, basalt, andesine andesite, in some rocks by extinction-angle methods but in most and augite-rich picrite-basalt. The Laupahoehoe volcanic rocks by immersion of fragments of the rock in oih of series is preponderantly andesine andesite, with a smaller pro­ known refractive index. Optic-axial angles have t ^en portion of olivine basalt. Coarse-grained inclusions and ejecta estimated from the appearance of optic-axis or acute- comprise gabbro, dunite, and augite peridotite. bisectrix interference figures. The lavas of Kohala Volcano are divided into the earlier or Pololu volcanic series and the later or Hawi volcanic series. The The writer wishes to thank C. S. Ross and H. T. Pololu lavas are largely olivine basalt, and to a minor extent ba­ Stearns of the United States Geological Surrey, who salt and picrite-basalt. The Hawi lavas are predominantly have read and criticized the manuscript of this pape~. oligoclase andesite, with less abundant trachyte. Coarse­ grained inclusions of gabbro, dunite, and augite-hypersthene PREVIOUS INVESTIGATIONS peridotite are present. Differentiation was largely or entirely by crystal settling. The Mauna Loa.—Several previous investigators have parent magma was olivine basalt. Sinking of intratelluric examined and described specimens of lavas of Mauna olivine crystals during early magmatic phases produced olivine- rich picrite-basalt and a reciprocal phase of basalt poor in olivine. Loa from scattered localities, but none of the collections Later, the removal of crystals of calcic plagioclase, hypersthene, were sufficiently large or from localities widely enough and augite yielded rest-magmas equivalent to andesine andesite, dispersed to represent adequately the petrography of oligoclase andesite, and trachyte. the entire volcano. The earliest microscopic investigations of the lavas INTRODUCTION of Mauna Loa were those of Cohen (1880), who studied The study of the petrography of the island of Hawaii, several specimens collected by Hillebrand. However, the results of which are described in this paper, is a part many of the rocks were largely glassy, and Cohen's of the general investigation of the geology and ground- descriptions were for the most part generalized. He water resources of the island by the United States reports olivine-rich basalt from the Mokuaweo^eo Geological Survey in cooperation with the Territory of caldera and basaltic pumice from the eruption of If 68. Hawaii. Most of the rock specimens from Mauna Loa, Dana (1889) studied a large suite of specimens col­ Kilauea, and Mauna Kea, and part of those from lected b/ E. P. Baker, many of which came from 51 52 PETEOGRAPHY OF THE ISLAND OF, HAWAII Mokuaweoweo. Probably all of them were of the late each of the three main stratigraphic
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