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京都大学0048新制・課程博士博士(理学)甲第9337号理博第2472号新制||理||1268(附属図書館)UT51-2002-G95京都大学大学院理学研究科地球惑星科学専攻(主査)教授 北村 雅夫, 教授 小畑 正明, 助教授 下林 典正学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

U-Pb age and origin of gem zircon from the New England sapphire fields, New South Wales, Australia

Chemical compositions and geochronological data utilising the laser ablation ICP-MS technique are presented for zircon megacrysts found in alluvial gem corundum deposits associated with Upper Cretaceous-Cenozoic alkali basalts in the Inverell district-New England field, New South Wales, eastern Australia. Three localities, Kings Plains, Swan Brook and Mary Anne Gully, produce gem-quality transparent dark brown and yellow zircon megacrysts, mostly under 10 mm in size. Although brown zircon shows relative enrichment in Hf and REE, there are no differences in relative transition metal concentrations between the colours. Chemical homogeneity within a single crystal indicates stable crystallisation conditions. The 206Pb/ 238U age of zircon megacrysts from these three localities define older and younger groups of 216-174 Ma and 45-37.7 Ma, respectively. The ε{lunate} Hf values of zircon megacrysts from Kings Plains show +7.51±0.34 in the older group and +10.72±0.31 in the younger group. Swan Brook zircons give +11.54±0.47 and +8.32±0.58, and Mary Anne Gully zircons are +13.67±0.63 and +8.50±0.48, respectively. These zircons from New England alluvial gem deposits have two main formational events around Upper Triassic-Lower Jurassic and Eocene episodes. Most originated from lithospheric mantle and all were brought-up by later host basaltic magmas

Structural Changes From Heating Amber and Copal as Observed by Nuclear Magnetic Resonance Spectroscopy

Structural changes caused by heating of fossilized (amber) and semifossilized (copal) resins have been examined by nuclear magnetic resonance spectroscopy. A set of 28 samples was constituted to include different geographical sources, degrees of maturation, colors, and structural groupings. The onset of structural alterations was determined by observation of the lowest temperature at which spectral changes occurred. Both proton spectra in solution and carbon‐13? spectra in the solid state then were recorded of cooled samples after heating for 12 hr at temperature increments, until liquification of the sample began. The spectra of both nuclides exhibit loss of a few peaks, broadening of most peaks, and enhancement of the unsaturated or aromatic region at the expense of saturated resonances. Such changes are irreversible and lead to a harder and less soluble material on cooling. The changes parallel those that occur with maturation of fossil resins or materials that lead to coal