14. PETROLOGY OF VOLCANIC ROCKS RECOVERED ON DSDP LEG 19 FROM THE NORTH PACIFIC OCEAN AND THE BERING SEA

• Main Authors: Richard J. Stewart, Bering Sea
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Bering Sea; Derickson Seamount; Gulf of Alaska; Meiji Guyot; Pacific; Kamchatka; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.6016; http://www.deepseadrilling.org/19/volume/dsdp19_14.pdf

On Leg 19 of the Deep Sea Drilling Project, basaltic volcanic rocks were recovered from Site 183 in the western Gulf of Alaska, Site 191 on the floor of Kamchatka Basin, and Site 192 atop Meiji Guyot, the northernmost of the Emperor Seamounts. At Site 183, alkali-olivine basalt was recovered underlying the thick sedimentary sequence of the Aleutian Abyssal Plain. The rocks strongly resemble Hawaiian alkali basalts, have high K, Sr, Zr, and Ba contents, and may be associated with the formation of nearby Derickson Seamount. They are inferred to postdate the basement age estimated from magnetic anomalies and to be extrusive onto oceanic crust. Tholeiitic basalt recovered at Site 191 beneath the sedimentary fill of Kamchatka Basin has low K2O, Ba, and Sr-87/Sr-86 values similar to midocean ridge tholeiites, but has higher Rb, Sr, and Zr values which follow patterns established for other inter-arc basin basalts. The basalt is probably part of a regionally developed basaltic basement which may have intruded and enveloped older basin deposits in middle Oligocene time. A series of at least five extrusive alkali basalt flows was recovered from near the crest of Meiji Guyot. The rocks are striking in having potassium feldspar cores in most Plagioclase phenocrysts, and in their coarse grain size, reaching sub-gabbroic textures in some flow interiors. Theoretical and experimental data indicate the almost pure potassium feldspar could not crystallize in equilibrium with associated labradorite. Origin as xenocrysts derived from late-stage plutonic differentiation and later inclusion in basaltic lavas is not possible as glassy rinds containing no potassium feldspar xenocrysts. The mineralogy probably results from secondary replacement of calcic Plagioclase cores by potassium-rich alkaline solutions produced during alteration of the basalts.