Kurnosov, Victor (2008): Alteration of igneous rocks from seamounts and oceanic intraplate rises


Kurnosov, Victor
Geological Institute, Russian Federation

Alteration of igneous rocks from seamounts and oceanic intraplate rises
In: Anonymous, 33rd international geological congress; abstracts
[International Geological Congress], [location varies], International
Volcanic rocks recovered during DSDP/ODP Legs on the Emperor Seamount Chain, West Pacific Guyots, Hess Rise, and Kerguelen-Ninetyeast lineament are hawaiites, alkaline basalts, trachy-andesites, olivine basalts, tholeiitic picrites, ankaramites, and tholeiitic basalts. All studied volcanic rocks have been affected by alteration under the smectite facies in relatively cold parts of the volcanic edifices remote from zones of ascending hot solutions. In the rock series tholeiite - alkaline basalt - hawaiite - olivine tholeiite - tholeiitic picriteite, the following secondary minerals are formed: smectites; smectites + mixed-layer smectite-swelling chlorite minerals in trace amounts; smectites + mixed-layer smectite-swelling chlorite minerals in trace amounts + illite in trace amounts (illite occurs at the flow top and bottom only); smectites + mixed-layer chlorite-swelling chlorite and smectite-chlorite minerals; and smectites + mixed-layer chlorite-swelling chlorite and smectite-chlorite minerals (sometimes with serpentine in trace amount) + chlorite, or only chlorite, respectively. Smectites dominate among secondary minerals that replace groundmass and phenocrysts in basalts of both alkaline and tholeiite series. They also fill vesicles and fissures in the lava flows. Chlorite phases and serpentine wide spread in basalts with high content of MgO. In trachy-andesite with very high K (sub 2) O content, secondary K-feldspar is formed. Tholeiite, alkaline basalt, and hawaiite are replaced by Fe-Mg smectites with MgO content of approximately 9 wt%. Smectites replacing olivine tholeiite and tholeiitic picrite are higher in magnesium, with MgO contents as much as 15-21 wt%. Smectites replacing hawaiite and alkaline basalt contain more K (sub 2) O (1.32 and 1.18 wt%, respectively) than smectites from tholeiite (K (sub 2) O = 0.36 wt%) and olivine tholeiite, which contains 0.25-0.52 wt% K2O. In the oxidized parts of the flows, smectites are higher in iron than smectites from internal nonoxidized parts of the flows. Dioctahedral Al-smectite of montmorillonite type with high K (sub 2) O content (2.06 wt%) is detected in the oxidized zone. Low-temperature alteration of studied volcanic rocks at sea water-rock interaction result in redistribution of some elements. The vesicular and/or brecciated extremely altered and strongly oxidized basalts from the flow tops are enriched in H (sub 2) O (super +) , Fe total, Fe (sub 2) O (sub 3) /FeO ratio, K, Mn and depleted in Ca, Si, Mg, Sr, and Zn and often in Na, Rb, and Ba. On the contrary, strongly altered nonoxidized basalts commonly contain less K and more Mg compared to fresh rocks. Ca content decreases, as in oxidized basalts. Redistribution of elements at water-rock interaction in open hydrothermal systems of volcanic edifices influences the chemical composition of solutions circulating within the edifices and ultimately discharging into the ocean.
Coverage:Geographic coordinates:
West:20.0000East: 147.0000

Igneous and metamorphic petrology; Geochemistry of rocks, soils, and sediments; alteration; basalts; chemical reactions; Deep Sea Drilling Project; Emperor Seamounts; geochemistry; Hess Rise; igneous rocks; Indian Ocean; Kerguelen Plateau; North Pacific; Northwest Pacific; Ocean Drilling Program; ocean floors; Pacific Ocean; seamounts; secondary minerals; volcanic rocks; water-rock interaction; West Pacific;