台灣北部觀音山地區兩輝安山岩之初步實驗岩石學研究

A Preliminary Report on the Experimental Study of the Two-pyroxene Andesite from Kuanyinshan, Northern Taiwan

本校地球科學系新成立實驗岩石實驗室擁有一台高溫爐（溫度可高達1500℃）和活塞鋼筒高溫高壓儀一部（溫度可高達2200℃，壓力可達25千巴）。高溫爐爐內恆溫區大於10公分，本實驗室之一號R型熱電偶，其校正值為-21.2℃。高溫高壓儀用途很廣，可用來合成高溫環境下的礦物或材料，也可供研究材料在高溫高壓下的物理化學性質；在岩石學方面，由於它可提供地底下深至75公里、溫度高達2200℃的環境；很適合做岩漿成因的模擬試驗。臺灣北部觀音山下牛寮之兩輝安山岩初步研究顯示：其在一大氣壓、10千巴和20千巴下之液相溫度分別為1210℃、1250℃和1290℃，液相溫度在壓力每增加10千巴上升約40℃。近液相礦物在低壓範圍為鐵鈦氧化物和斜長石；及至高壓區域，則為斜長石。

The high temperature furnace and the high pressure high temperature piston-cylinder apparatus were set up in the experimental petrological laboratory of Department of Earth Sciences, National Tai-wan Normal University. The thermal gradient in the high temperature furnace is smaller than 1 °C per 10 cm in the uniform zone. The precisions for the pressure and temperature measurements of the pis-ton-cylinder apparatus are 0.3 kb and 5 °C , respectively. The thermocouple used in the present experi-ments was calibrated and the temperature correction is -21.2 °C . The liquidus temperatures of the Kuanyinshan andesite were determined to be 1210 °C , 1250 °C , and 1290 °C at the atmospheric pressure, 10 kbar and 20 kbar, respectively. Near-liquidus minerals at atmospheric pressure are iron-titanium ox-ides and plagioclase. Plagioclase, however, is the near-liquidus mineral at 10 kbar and 20 kbar. The slope of the liquidus curve of the andesitic melt is about 40 °C per 10 kbar.