- 作者: 余樹楨
- 作者服務機構: 國立成功大學地球科學系
- 中文摘要: 本文以鑽石高壓砧將超基性擄獲岩中橄欖石晶體加壓並分別在一大氣壓、4.3、12.5及26千粑下,收集X光繞射資料及分析其高壓下之晶體結構。 受壓時,本橄欖石之晶室參數及鎂鐵配位八面體皆出現差異收縮的現象。在4.3~12.5千粑時,b軸壓縮遠大於a及c軸;而M1配位八面體收縮又明顯大於M2八面體。當壓力從12.5到26千粑時,差異收縮的趨勢反轉過來,即a及c軸壓縮大於b軸,M2八面體壓縮大於M1八面體。 晶室參數及M1、M2多面體之壓縮,主要導源於M1-0與M2-0鍵距因受壓而收縮的結果。在26千粑下,四面體配位的Si-O鍵長幾乎不變。同時由鍵結角的少有變異可以看出矽氧四面體及M1、M2八面體在高壓下其多面體幾何形狀幾乎未受影響。本分析顯示受壓時橄欖石的結構會由扭曲的、較疏鬆的結構轉化為理想化的六方緊密排列。
- 英文摘要: An olivine crystal from the harzburgite xenolith in Penghu basalt has been studied as a functionof pressure using a diamond anvil cell. Crystal structures were refined from the X-ray intensity datacollected at pressures up to 26 Kbar and under ambient temperature conditions. Differential contractions in the unit cell parameters and cation octahedra were observed under thestudied pressure range. Between 4.3 and 12.5 Kbar, the b axis compressed more profoundly than didthe a and c axes, and the M1-octahedra contracted more significantly than did the M2-polyhedra. From12.5 to 26 Kbar, the variation trends in the cell dimensions and cation octahedra with pressure were reversed.Meanwhile, the silicon tetrahedra contracted insignificantly to 26 Kbar pressure. The decreases in the M1-O and M2-O bond distances with increasing pressure were responsiblefor reduction in the cell constants and contraction in the M1 and M2 polyhedra. However, the silicontetrahedra, M1 and M2 octahedra remained almost unaltered in the polyhedral geometry at pressures upto 26 Kbar as indicated by the limited bond angle variations. Transformation from a less compact anddistorted HCP structure to a more compact ideal HCP array for olivine crystal under pressure is suggestedby the results of the present investigation.
- 中文關鍵字: olivine; crystal structure; high pressure; X-ray diffraction
- 英文關鍵字: --