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ABSTRACT: Distribution of Hydrothermal Deposits in Relation to Tectonic Setting in the Lau Basin, S.W. Pacific

Richard Hodkinson, David Cronan

Geochemical variations in surface sediments in the Lau Basin have been investigated in relation to the tectonic evolution of its eastern and central spreading centers (ELSC, CLSC). Highest concentrations of hydrothermally associated Fe, Cu, and Zn all occur in sediments from the CLSC, while highest Mn and Ni occur to the west of the spreading centers. Factor analysis of the geochemical data indicates that the hydrothermal component is distributed between two factors, Mn and Ni being loaded on Factor 2 and Fe, Zn and Cu on Factor 3. Factor 1 represents the detrital volcaniclastic input of elements to the sediments and exhibits low loadings of normally hydrothermally associated elements. Maximum factor scores for Factor 2 are associated with the CLSC and the area to the wes of it, while maximum scores for Factor 3 occur in sediments from both the CLSC and the ELSC. Such a pattern is considered to reflect the expected localized nature of the hydrothermal activity giving sulfide mineralization on the spreading centers, as opposed to the more widely dispersed pattern of hydrothermally derived oxides reflected in the more evenly distributed scores for Factor 2. Along the CLSC and ELSC axes, nondetrital P, Mn, and Ni all increase towards the propagating tips where maximum values occur. This could be explained by a hydrothermal supply of Mn and P, with Ni being scavenged from seawater by the Mn. These trends can be used to pinpoint the location of the richest hydrothermal deposits in the Lau Basin.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990