Inferring magmatic sources in gabbroic rocks from hole 735B of the Ocean Drilling Program and EBSD analysis of YBCO thin films.

摘要

This thesis contains work on two different studies. Chapters 1 through 7 are concerned with the geochemistry of Leg 118 gabbros and Chapter 8 is concerned with a electron backscattered diffraction study of YBCO thin films.; The structure and composition of the lower oceanic crust have largely been inferred from deep marine studies and comparison to ophiolites. Site 735B lies on the edge of the Atlantis II Fracture Zone at 32°43'S, 57°7'E, 95 km south of axis of the Southwest Indian Ridge. 500 meters of gabbroic rock were drilled with a total recovery of 87%. The material recovered is composed mainly of gabbroic rock with minor felsic veins and a diabase dike.; Electron microprobe analysis has been carried out on the minerals present in thin sections. From these samples, Leg 118 olivines cover a range in composition from Fo₈₃ to Fo₃₀. Plagioclase compositions range from An₇₂ to An₃₃. Clinopyroxene compositions range in Mg-numbers from 89 to 49.; Clinopyroxenes have been analyzed for trace elements by ion microprobe. Clinopyroxene cores exhibit the following ranges in trace elements: Ti ranges from 2340 to 5590 ppm; Zr ranges from 12 to 65 ppm; and Hf ranges from 0.78 to 3.9 ppm. The rims are approximately 1 to 7 times the core abundances. The clinopyroxenes have the following ranges in REE contents: La ranges from 0.31 to 1.26 ppm; Sm ranges from 1.4 to 4.8 ppm; and Yb ranges from 1.6 to 6.9 ppm.; The variation in major elements present in minerals of the Leg 118 gabbros indicate that they were formed by the fractional crystallization of a basaltic liquid. Minor elements, particularly Ni in olivine and Cr in chnopyroxene, are also consistent with a simple fractional crystallization history. At first glance, the REE patterns exhibited by the clinopyroxenes also appear to follow a simple fractional crystallization pathway.; However, some geochemical indications require more complex processes than implied in simple crystallization models. The range in the REE patterns exhibited by the Leg 118 clinopyroxenes requires extensive crystallization, beyond the ranges produced by simple crystallization processes. Simple magma chamber evolution models, however, cannot explain the presence of intimately intermixed evolved samples with comparatively primitive samples.; In situ fractional crystallization produces mineral phases with very primitive compositions similar to those found at Site 735B. In situ fractional crystallization is also capable of producing the complete range in REE patterns and similar trace elements (e.g. Ti) exhibited by clinopyroxenes, while maintaining the limited range in Mg-number. However, in situ fractional crystallization cannot produce the complete range in major elements. Therefore, it is suggested that the Leg 118 gabbros formed by a mixture of at least two processes, namely simple fractional crystallization and in situ fractional crystallization.; In addition, YBa₂Cu₃O_7−δ thin films grown on various substrates, SrTiO₃, LaAlO₃, yttria-stabilized zirconia, and CeO₂, have been studied by electron backscattered diffraction. Thin films grown on CeO₂ exhibit the highest quality thin film based on the crystal alignment of YBCO grains and those grown on yittria-stabilized zirconia exhibit the lowest quality. The differences in the alignments of grains, and thus the quality of the thin film produced, have been ascribed to the different film/substrate mismatch.