AV俱乐部

An intact core from IODP (Integrated Ocean Drilling Program) Site 1256, located in the eastern equatorial pacific (Cocos Plate), was collected on three different legs (legs 206, 309, and 312). This is the fourth deepest hole that IODP has drilled since 1968, and is the first hole to reach the uppermost portion of in situ gabbroic oceanic layer 3. The purpose of this study is to examine down-hole petrological and textural trends, including variations in hydrothermal alteration products.

Fifty-three thin sections were cut at specific depths down-core and point counts of primary and secondary minerals were done on all samples. Some systematic trends can be inferred from the modal analyses concerning the dominant minerals and alteration products. Trends include a change from possible smectites to chlorite at 1050 mbsf, concentrations of quartz at varying depths, and changes in opaque oxides at 1230 mbsf. Electron microprobe analysis was done on six representative thin sections to identify some unknown minerals, including amphiboles, opaque oxides, and possible clay minerals, suggested by previous work that showed clays to be present in the upper part of the core. Results show the presence of minimal sulphides, orthopyroxene and olivine, an abundance of clays, and amphiboles were determined to be hornblende and actinolite. Point-counts and electron microprobe analyses from a core collected from the Kane Fracture Zone on the Mid-Atlantic Ridge were used to supplement data obtained from the Site 1256 core, in particular observing variations in texture and alteration minerals. Results from both cores will assist in understanding spatial variations in igneous and hydrothermal processes at mid-ocean ridges.

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Pages: 213
Supervisors: Matt Salisbury / Rebecca Jamieson