MATERIAL SOURCE OF SEDIMENTS FROM WEST CLARION–CLIPPERTON ZONE (PACIFIC): EVIDENCE FROM RARE EARTH ELEMENT GEOCHEMISTRY AND CLAY MINERALS COMPOSITIONS

Abstract

THE GEOCHEMISTRY AND MINERALOGY OF SEDIMENTS PROVIDE RELEVANT INFORMATION FOR THE UNDERSTANDING OF THE ORIGIN AND METALLOGENIC MECHANISM OF FERROMANGANESE NODULES AND CRUSTS. AT PRESENT, THERE ARE STILL FEW STUDIES ON THE SEDIMENT ORIGIN OF THE CLARION–CLIPPERTON ZONE (CCZ) OF THE EAST PACIFIC, PARTICULARLY ON THE SYSTEMATIC ORIGIN OF SEDIMENTS WITH A LONGER HISTORY/LENGTH. HERE, BULK SEDIMENT GEOCHEMISTRY AND CLAY MINERAL COMPOSITIONS WERE ANALYZED ON A 5.7 M GRAVITY CORE (GC04) OBTAINED AT THE CCZ, AN AREA RICH IN POLYMETALLIC NODULES. THE RESULTS INDICATE THAT THE AVERAGE TOTAL CONTENT OF RARE EARTH ELEMENTS (REE), INCLUDING YTTRIUM (REY), IN SEDIMENTS IS 454.7 PPM AND THE REES DISTRIBUTION PATTERNS NORMALIZED BY THE NORTH AMERICAN SHALE COMPOSITE OF SAMPLES ARE HIGHLY CONSISTENT, WITH ALL SHOWING NEGATIVE CE ANOMALIES AND MORE OBVIOUS ENRICHMENT IN HEAVY REE (HREE) THAN THAT OF LIGHT REE (LREE). MONTMORILLONITE/ILLITE RATIO, DISCRIMINANT FUNCTIONS AND SMEAR SLIDE IDENTIFICATION INDICATE MULTIPLE ORIGINS FOR THE MATERIAL, AND ARE STRONGLY INFLUENCED BY CONTRIBUTIONS FROM MARINE BIOMASS, WHILE TERRESTRIAL MATERIALS, SEAMOUNT BASALTS AND THEIR ALTERATION PRODUCTS AND AUTHIGENIC SOURCE ALSO MAKE CERTAIN CONTRIBUTIONS. THE REY CHARACTERISTICS OF THE SEDIMENTS IN THE STUDY AREA ARE DIFFERENT FROM THOSE OF MARGINAL OCEANIC AND BACK-ARC BASINS, AND MORE SIMILAR TO PELAGIC DEEP-SEA SEDIMENTS. BASED ON LREE/HREE-1/ΔCE AND LREE/HREE-Y/HO DIAGRAMS, WE CONCLUDE THAT SAMPLES FROM THE STUDY AREA HAD PELAGIC SEDIMENTARY PROPERTIES WHICH SUFFERED FROM A STRONG “SEAWATER EFFECT”.