Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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136 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 'Oo0 ' + Pillow and massive basalt 0 Sheeted dike Gabbro A Diorite K20+Na20, IN WEIGHT PERCENT Figure 6. Alteration test based on Na20 and K20 variation (after Miyashiro, 1975). On several major-oxide variation diagrams, the samples generally plot in a tight cluster sometimes overlapping different tectonic settings. Figure 9 (CaO and A1203 vs Ti02) shows a MORB-like pattern that contrasts with arc rocks and several classic ophiolites, such as those at Betts Cove and Troodos (Sun and Nesbitt, 1978), that are now thought to have formed in a suprasubduction zone setting. FeO* (total iron as FeO)/MgO vs Ti02 (fig. 10) also shows a strong cluster of the samples in the MORB field. In a plot of Ti02 vs FeO*/FeO* + MgO (fig. ll), the samples plot in the field of high-Ti ophiolites, which Sem (1981) considered typical of several tectonic settings including back-arc basins, ensialic back-arc basins, or major ocean basins, as well as spreading centers along transcurrent plate boundaries. Other alternatives are suggested by the Ti02-MnO-P 0 discrimination diagram 2. 5 (fig. 12) of Mullen (1983), which shows that these samples plot in three fields: mid-ocean ridge basalt (MORB), ocean-island tholeiite (OIT), and island-arc tholeiite (IAT). Ce (307) Sm (. 195) Gd (est) Dy (.325) Yb (.203) Figure 7. Chondrite-normalized rare-earth element abundances of samples from Knight Island. Normalization constants shown for each element; Gd values are estimates (G.A. Wandless, 1991, written commun.). A, Pillow and massive basalts. B, Symbols same as on figure 6.
GEOCHEMISTRY OF OPHIOLITIC ROCKS FROM KNIGHT ISLAND, PRINCE WILLIAM SOUND Figure 8. AMF diagram for samples from Knight Island. Tholeiitic (TH) and calc-alkaline (CA) trends after Wilson (1989). Same symbols as on figure 6. Circled values are "unaltered" samples from figure 6. :--. , . . . . ; '. \. Arc '\ '. . , ' .._... --. -. --. -. ---...A+@ *.--&..p MORB + MORE --a%.@+ -..._. TiO, IN WEIGHT PERCENT Figure 9. CaO/Ti02 and AI2O3/TiO2 vs Ti02 for samples from Knight Island. Based on Sun and Nesbitt (1978). Same symbols as on figure 6. Circled values are "unaltered" samples from figure 6. MORB, mid-ocean ridge basalt; arc, arc rocks. 137 Figure 10. FeO*/MgO vs Ti02 for samples from Knight Island (after Glassley, 1974). Symbols same as on figure 6. Circled values are "unaltered samples from figure 6. MORB, mid-ocean ridge basalt; 01, ocean island rocks; IAT, island-arc tholeiite. 3 ___--- High Ti A Low Ti 0 0 % .I .2 .3 .4 .5 .6 .7 FeO*/FeO*+MgO Figure 11. High-titanium vs low-titanium classification of samples from Knight Island (after Sem, 1981). Symbols same as on figure 6. Ti02 Figure 12. Ti02-MnO-P205 (weight percent) ternary diagram for samples from Knight Island. Fields based on Mullen (1983). OIT, ocean-island tholeiite; MORB, mid-ocean ridge basalt; IAT, island-arc tholeiite; OIA, ocean-island alkaline basalt; CAB, calc-alkaline basalt. Same symbols as on figure 6. Circled values are "unaltered" samples from figure 6.
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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U-Pb AGES OF ZIRCON, MONAZITE, AND
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APPEAL FOR NONPROLIFERATION OF ESCA
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FAVORABLE AREAS FOR METALLIC MINERA
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Page 91 and 92: FAVORABLE AREAS FOR METALLIC MINERA
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Page 107 and 108: EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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Page 125 and 126: RESERVOIR FRAMEWORK ARCHITECTURE, C
Page 137: GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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Page 180 and 181: Table 1. Isotopic ages of intrusive
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Page 184 and 185: GEOCHEMICAL EVALUATION OF STREAM-SE
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186 GEOLOGIC STUDIES IN ALASKA BY T
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20 GEOLOGIC STUDIES IN ALASKA BY TH
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Table 3. Summary of geochemical sig
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GEOCHEMICAL CHARACTER OF UPPER PALE
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RECONNAISSANCE GEOCHEMISTRY OF BASA
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OSTRACODE ASSEMBLAGES FROM MODERN B
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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US. GEOLOGICAL SURVEY REPORTS ON AL
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U.S. GEOLOGICAL SURVEY REPORTS ON A
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U.S. GEOLOGICAL SURVEY REPOR TS ON
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REPORTS ABOUT ALASKA IN NON-USGS PU
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REPORTS ABOUT ALASKA IN NON-USGS PU
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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