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Geochemistry and mineralogy of sediments from southeast Explorer Rift (50 N, 130 W), northeast Pacific : in search of evidence of hydrothermal activity

University of British Columbia

The composition of sediments in a portion of Explorer Spreading Centre, Explorer Deep, is examined. Clay mineral, bulk mineral and chemical compositions (Al, Ba, Ca, CI, Co, Cu, Fe, K, Mg, Mn, Ni, P, Si, Na, Ti, Zn) of hemipelagic sediments on the floor of Explorer Deep are compared to those on adjacent flanks, and to Explorer Deep metalliferous sediment, to determine the extent of hydrothermal mineral formation. Explorer Deep hemipelagic sediments are composed of quartz, opal, feldspar, amphibole, carbonate, phyllosiIIcates, iron and manganese hydroxides,illmenlte, rutile and hematite. Individual phyllosiIlcates have distinct size-distributions; fine clay (<0.2 urn) is composed almost entirely of smectite. In contrast, illite and chlorite are most abundant in coarser clay and silt. Three types of smectite are present: very fine grained smectite, likely detrital montmorilIonIte; smectite In mixed-layer clays; and authigenic nontronlte. Smectite is more abundant in sediments from the floor of Explorer Deep than in flank sediments. The chemical composition of Explorer Deep hemipelagic sediments is between that of "average shale" and average "Pacific pelagic clay". Sediments from the floor are Al- and P-poor but have higher Ba, Ni, Zn, and non-terrigenous Fe and Si contents than sediments from the flanks. Detrital aI urnInosilicates are the principal source of Al, suggesting an abundance of detrital minerals in sediments from the flanks. The distribution of Ca reflects dissolution of carbonate with increased water depth. Ba, Fe, Ni, Si and Zn are associated with smectite in an AI-, Ca- and P-poor phase that is present in sediments from the floor. The tectonic setting in Explorer Deep is suitable for circulation of hydrothermal solutions, and recovery of a metalliferous crust Indicates that formation of mounds of hydrothermal minerals has occurred locally. Differences in mineral and chemical composition of sediments from the floor of Explorer Deep and those away from the Influence of hydrothermal activity, on the flanks, can be explained by the presence of hydrothermal minerals in sediments on the floor. Slow percolation of hydrothermal solutions through sediments on the floor results in in situ formation of authigenic iron oxides and nontronite similar to those in the metalliferous crust. The presence of a hydrothermal component in sediments from the floor of Explorer Deep is obscured by diagenetlc processes which modify element and mineral distributions, and by dilution due to high rates of hemipelagic sedimentation.

Text

2010-05-15

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http://hdl.handle.net/2429/24698

Geological Sciences

University of British Columbia

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