UNITED STATES DEPARTMENT OF INTERIOR GEOLOGICAL SURVEY Preliminary petrology of igneous and sedimentary rocks recovered from central Pacific seamounts by Walter B. Friesen Open File Report 87-640 This report is preliminary and has not been reviewed for conformity with the U. S. Geological Survey editorial standards and stratigraphic nomenclature Menlo Park, California 1987 Table of Contents Abstract...............................................1 Introduction...........................................1 Area A................................................. 5 Area B................................................. 7 Area C................................................. 8 Area D................................................. 9 Area E................................................ 10 Area F................................................ 12 Area G................................................13 Area H................................................ 14 Area I................................................17 Discussion............................................18 Acknowledgments.......................................19 References............................................20 List of figures 1. Area location map of Midpac 2.....................2 2. Location maps of Areas A through D...............6 3. Location maps of Areas E through G..............11 4. Location maps of Areas H and I..................15 List of tables 1. Location coordinates and seabed data, Midpac 2A..3 2. Location coordinates and seabed data, Midpac 2B..4 Abstract Nine submarine volcanic structures in the central Pacific were studied on the Federal Republic of Germany's Midpac 2 Program. This program was designed to examine and assess the cobalt-rich ferromanganese crust resources in the central Pacific. Great abundances of volcanogenic and biogenic rock samples with thin to thick encrustations of ferromanganese oxide, in places enriched with small amounts of cobalt, nickel, and plati­ num, were recovered during two cruises by the R. V. Sonne, a research ship from the Fede­ ral Republic of Germany. The study areas visited are located in the Hawaiian, Line, and Phoenix Archipelagoes, and in the Mid-Pacific Mountains. Samples were recovered prima­ rily between 1000m and 2000m water depth on the upper slopes and summits of the volcanic edifices. Rocks recovered are mainly breccias composed of alkalic basalt and its differ­ entiates, trachyte and syenite, basaltic and differentiated lava hyaloclastite and tuff, and phosphatized calcarenite and chalk, or loose clasts of these breccia components. Lithic distribution on the seamounts suggests the following general eruptive sequence for the upper 1000m of the volcanic edifices: (1) alkali olivine basalt, (2) trachyte and differentiated alkalic lavas, and (3) subsilicic alkalic lavas. Most of the submarine volcanic edifices are guyots. Subsidence has gradually brought about their submergence to various depths. The inferred igneous eruptive sequence observed in the Midpac 2 seamounts is similar to that of the Hawaiian Islands-Emperor Seamounts chain and to that of other central Pacific linear island and seamount chains. I. Introduction An interesting variety of igneous and sedimentary rocks was recovered from nine central Pacific submarine volcanic edifices. These rocks commonly bear thin to thick encrustations of ferromanganese oxides and thin deposits of biogenic phosphorite. The ferromanganese oxide deposits are in places strongly enriched in the strategic metals cobalt, nickel, and platinum. The phosphorite has an interest potential to agriculture because of its high phosphorus and calcium content. A cooperative program between the United States and the Federal Republic of Germany was designed to study and assess the resource potential of the ferromanganese oxides and other seabed mineral deposits. The German part of the program is called Midpac and has included five research cruises. Midpac 1 (1981) surveyed submarine volcanic edifices in the northern Line Islands Archi­ pelago and in the Mid-Pacific Mountains. Midpac 2A (1984) surveyed the same areas and also Cross Seamount south of Oahu Island. Midpac 2B (1985) surveyed submarine volcanic edifices south of Johnston Island in the Line Islands Archipelago and Titov Seamount southeast of Baker Island in the Phoenix Archipelago. Midpac 3/1 and Midpac 3/2 (1986) surveyed submarine volcanic edifices in the Marshall Islands Archipelago and in the John­ ston Seamount Group south of Johnston Island, respectively. Rocks from the Midpac 2 study areas are the subject of this report. The regions surveyed were designated Areas "A" through "I" (Fig. 1). The West German research ship Sonne, under the scientific direction of Professor Peter Halbach of the Technical University of Clausthal, served as the work support vessel on Midpac 2A and 2B. Bottom photographs and videos, bathymetric data, and rock, ferromanganese oxide crust, water, and biological samples were collected from the study areas. The preliminary petrology of the rock samples is presented in the following pages. Locations and water depths of operations on Midpac 2A and 2B are sum­ marized in Tables 1 and 2, respectively. 25' 20* Area F Johnston I \ PACIFIC Area I Area A *^^ Area E Area G 10' Area B Area C AreaD Kingman Reef Howltnd I . 0' Baker I Area H 10' 15' Fiji Islands OCEAN 20C 200 KM ,25* 170« 175' 180* 175' 170' 165' 160' 155' 150' Figure 1. Area location map of Midpac 2 displaying study areas, reference islands and archipelagoes, and lOOOfm con­ tour (modification of a portion of "Central Pacific islands, reefs, and shoals" by Chase, Seekins, and Lund, 1984). 2 Table i. Location coordinates and seabed data from Midpac 2A. Area Station Average Average Average water Length of Average slope latitude Longitude depth (m) dredge (km)* angle Cdegrees)* "W A 1 DK 180 41'40"N 158° 22 '54 4112 4 .0 17 "W A 2 DK 18° 39' 07 "N 158° 17 '59 2021 3 .2 5 "W A 3 DK 18° 38 '03"N 158° 18 '56 2140 3 .1 22 A 6 DK 18° 40 '59"N 158° 18'46 "W 870 1 .0 51 B 8 DK 9 -42 1 06"N 162° 10'58 "W 2262 4 .4 13 B 9 DK 9° 42 '31"N 162° 10 '40 "W 1793 5 .2 4 11 W B 15 DK 9M3 '43"N 162° 09'53 1487 3 .8 6 "W B 17 DK 9°41 1 36"N 162° 10 '41 2448 4 .6 11 '06"N "W B 18 DK 9° 42 162° 10 '57 1755 1 .4 23 '47"N "W C 24 DS 6° 30 162° 24'18 2154 4 .2 10 "W C 25 DS 6° 30 '15"N 162° 22 '08 2619 2 .5 13 "W C 29 DK 6° 16 '35"N 162° 52'23 2788 3 .6 14 "W C 30 DK 6° 16 '19"N 162° 52'57 2045 3 .4 23 '54"N "W C 31 DK 6° 16 162° 52 '36 1418 1 .1 12 "W C 33 DS 6° 16 02"N 162° 57 '35 2714 3 .2 12 '43"N "W C 34 DS 6° 17 162° 57'26 2021 4 .3 16 '57"N "W D 37 DK 9° 09 164° 50'43 2366 2 .1 2 "W D 38 DK 9° 10 '43"N 164° 49 '22 1637 2 .1 15 "W D 39 DK 9° 11 '28"N 164° 50 '05 1217 3 .9 2 "W D 40 DK 9° 11 31"N 164° 48 '59 1267 8 .5 2 "W D 41 DK 9° 08 '41"N 164° 47'22 2348 4 .0 13 "W D 42 DK 9° 10 '28"N 164° 46'52 1721 2 .9 16 D 43 DK 9° 11 '50"N 164° 46 '12 W 1502 1 .3 16 "W D 44 DK 9° 13 '32"N 164° 46 '45 1464 1 .6 1 D 47 DK 9° 10 '02"N 164° 53'46 "W 1388 5 .2 8 D 48 DK 9° 15 '04"N 164° 50'37 "W 1324 3 .0 3 D 49 DK 9° 12 '01"N 164° 55*73 "W 1350 - E 55 DK 15° 35 '12"N 169° 12 '26 "W 1477 1 .5 13 E 56 DK 15° 35 55"N 169" 12 '03 11 W 1387 3 .0 4 E 57 DK 15° 35 '22"N 169° 12 '30 "W 1209 2 .4 7 E 58 DK 15° 35 '30"N 169° 12 '24 "W 1332 2 .2 3 E 62 DK 15° 32 38"N 169° 12 '13 "W 1728 3 .3 5 E 63 DK 15° 30 '00"N 169° 15 '09 "W 2905 3 .7 6 E 64 DK 15*30 '23"N 169° 13'26 "W 2161 2 .7 22 E 66 DK 15° 35 '41"N 169° 12 '52 "W 1432 0 .6 31 F 69 DK 20° 07 '54"N 170° 41'27 "W 1496 0 .8 5 F 71 DK 20° 13 '25"N 170° 36 '00 "W 1997 2 .1 55 F 72 DK 20° 13 '06"N 170° 35' 30 "W 1548 1 .2 15 + Length of dredge determined from ship position when dredge on bottom and off bottom, * Slope determined from bathymetric data. Table 2. Location coordinates and seabed data from Midpac 2B. Area Station Average Average Average water Length of Average slope latitude longitude depth (m) dredge (km)* angle (degrees)* H 5 DK 0°22' 24"S 176° 05' 10"W 1777 3 .4 13 H 6 DK 0°24' 10"S 176° 07' 30"W 1472 3 .0 4 G 9 DK 14°27' 75"N 169° 00' 65"W 1893 1 .7 12 G 10 DK 14° 27' 34"N 169° 59' 09"W 1640 1 .5 15 I 15 DS 15°41' 00"N 170° 21' 00"W 1895 2 .5 18 I 16 DS 15°40' 68"N 170° 21' 75"W 1552 1 .0 22 I 17 DS 15°40' 63"N 170° 22' 34"W 1408 2 .2 12 I 18 DS 15° 39' 22"N 170° 24' 52"W 2019 1 .5 17 I 19 DS 15°40' 66"N 170° 24' 26"W 1653 3 .2 7 I 20 DS 15°39' 92 "N 170° 23' 50"W 1310 1 .9 10 I 27 DS 15° 38' 44"N 170° 23' 62 "W 1771 2 .6 21 I 28 DS 15° 38' 67"N 170° 23' 71"W 1741 4 .3 1 I 29 DS 15°39' 70"N 170° 21' 80"W 1572 1 .3 13 I 30 DS 15° 39' 91"N 170" 22' 86"W 1179 2 .4 4 E 36 DS 15°36' 90"N 169° 13' 33"W 1535 3 .1 4 E 37 DS 15° 34' 00"N 169° 12' 52"W 1717 2 .5 3 E 39 DS 15° 37' 47"N 169° 06' 95 "W 2014 3 .4 4 E 40 DS 15° 38' 11"N 169° 05' 42"W 3050 4 .9 13 E 41 DS 15° 38' 05"N 169° 07' 00"W 2417 2 .6 17 E 43 DS 15° 32' 64"N 169° 13' 68"W 1592 2 .2 10 E 44 DS 15° 37' 28"N 169° 12' 64 "W 1451 3 .1 2 E 46 DS 15' 35' 60"N 169° 12' 64"W 1464 1 .5 13 E 47 DS 15° 38' 40"N 169° 15' 35"W 1497 2 .7 4 t Length of dredge determined from ship position when dredge on bottom and off bottom, * Slope determined from bathymetric data.