屏東恆春半島地區螢光碳氫化合物液包體水晶之特徵研究

本篇主要探究屏東恆春半島地區新發現，一類在紫外線照射下內部液包體會顯現出螢光現象的水晶，即相似於商業上所稱「油膽水晶」者。為臺灣首次發現此類標本。它的產狀為數毫米大小的自形短六方雙錐水晶，與薄層的方解石及少量的重晶石伴生，一同發育在硬頁岩層內之薄層砂岩的節理裂隙中。這種具有螢光的液包體主要在水晶及方解石中發現，在重晶石中則未見其存在。經由對這種液包體均化溫度的測量，其封存溫度達167℃以上，如以30℃/km之平均地溫梯度來估算，結晶發育約在地下5公里處。液包體是結晶發育過程中周圍流體被結晶捕捉封存於內部所致的特徵，成分一般由常見的地質流體所組成，例如水、二氧化碳或甲烷等物質，然而這些物質在紫外線照射下並不具有螢光。在過往的研究中所示，紫外線下具有螢光特徵的液包體多在油氣探採的岩芯樣本中發現，其成分主要是芳香烴族的碳氫化合物。這類液包體在自然光下呈無、淡黃或棕色，經由紫外線的照射會根據成分的差異激發出橙色、黃色、綠色及藍白色的螢光。在石油地質研究中，原油螢光的波長差異也被用於評估油氣的品質或是儲油層的環境，是重要的油質指標項目之一。本研究發現樣本的兩個地點，主要位在晚中新世牡丹層的獅子頭砂岩及里龍山砂岩中，而過往在其下年代更老且深埋程度更高的潮州層中發現的其他水晶類型，其液包體之成分則以含水及二氧化碳為主，這種現象可能隱示此區域晚中新世地層的上部過往可能有少量的油氣物質存在，並受到成岩作用的溫度影響而發生分異。

關鍵字

恆春半島；油膽水晶；螢光液包體；碳氫化合物液包體；石油氣

並列摘要

This study probe a type of fluid inclusion in quartz, which appeared fluorescence emission under the UV light. The characteristic of this quartz is very similar as ＂petroleum quartz＂ on the mineral trading market. This is the first time to discover and record this type of specimen in Taiwan. The occurrences of specimen are mostly euhedral crystals with doubly terminated forms and grow within in few millimeter lengths. The quartz sometimes associates with crystalline calcite and barite within the joint of thin sandstone layer in argillite formation. The fluorescence fluid inclusions are majorly found inside of quartz and calcite crystals, but never been found it being trapped into the later stages barite. Through the measurement of the homogenization temperature of the fluid inclusions, the homogenization temperature is above 167℃. If estimated by the average geothermal gradient of 30℃/km, the crystals grow about 5km deep. The fluid inclusions are a feature that indicates geological fluid trapping inside the mineral crystals. In the common cases, the compositions of fluid inclusion generally include water, carbon dioxide or methane etc.; however, most of these materials have no fluorescence emission under the UV light exposure. In the most cases of researches, fluorescent fluid inclusions were usually found inside drilling core specimens in the oil and gas exploration. The main cause of fluorescent composition in fluid inclusions are aromatic hydrocarbons. The original colors of hydrocarbons under the sun light are color less, pale yellow or brown, but it might display difference emission color of fluorescence, for example white, pale blue, yellow or orange when they expose to the UV light. According to the fluorescence wavelength of fluid inclusions that provides a key to assess grade of oil maturity or formation temperature. This is one of a very important index using for the petroleum geology. In this study, the specimens have been found in two localities. One is Shizitou sandstone and the other is Lilongshan sandstone in the Mudan formation of Late Miocene. The compositions of fluid inclusions within quartz mainly included water and carbon dioxide are usually found in the older and buried in Chaozhou formation. This might imply a little amount oil-gas contain inside the upper part of formations after the stage of Late Middle Miocene, however the oil may be decomposed as the temperature increasing under the diagenesis process.

並列關鍵字

Hengchun Peninsula ； petroleum quartz ； fluorescent fluid inclusions ； hydrocarbon-bearing fluid inclusions ； oil gas

參考文獻

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