台灣主要的地熱潛能區除大屯山位於火成岩區以外，均位於變質泥岩區，複雜的地質構造與不易透水的岩層特性，使台灣地熱資源開發的困難度相當高。國外火成岩區地熱研究顯示，主要地熱儲集層上方常有熱水換質礦物所組成的蓋層，蓋層的電阻率極低(<10 Ω-m)是地熱資源調查的重要特徵。變質岩區地熱構造是否具有蓋層特徵?熱水儲集層與溫度在空間上的分布特性是否與火成岩區相似?對台灣地區的地熱資源熱開發而言，這些問題均有待釐清。 本研究以金崙地熱區為例，進行變質岩區地熱構造的特性研究，期透過本研究獲得變質岩區的地熱特性，做為後續地熱資源開發的參考。金崙地熱區位於中央山脈東南側，地表出露的地層為中新世廬山層，岩性以板岩及變質砂岩為主。本研究綜合使用音頻大地電磁探測、重力測勘及自然放射能探測等地球物理方法，獲得金崙地區地下可能的地質構造模型，並以前人在本研究區的各項地質、溫泉及地熱調查資料為輔助，建立金崙地區的地熱概念模式。本研究主要結論說明如下: 1.金崙地熱可能是板塊逆衝作用使深部高溫岩體向上快速抬昇所造成，地熱水來自西側的中央山脈天降水，冷水滲入地下深處受到高溫岩體加熱後，因熱對流或水頭壓力使熱水沿地層破碎帶向東流動，一部份熱水受到逆衝斷層RF2的影響向上湧出地表形成溫泉，一部份熱水與圍岩產生熱水換質作用形成極低電阻帶，主要地熱儲集層位於極低電阻層下方逆衝斷層RF1造成的破碎帶中。 2.在金崙地熱區及清水地熱區的電性剖面均出現與世界其它主要地熱區相同的極低電阻率層，顯示在台灣地區以變質岩為主的地熱區，極低電阻率層特徵仍為地熱構造調查的重要指標。 Geothermal resources exploitation is difficult at Taiwan area because of structure complexity and low permeability in metapelites. The low resistivity anomalies have generally been the main target for geophysical exploration of geothermal resources in many countries. It is worth further study that if there exists low resistivity anomaly in metamorphic geothermal area. Also, temperature and geothermal reservoir distribution are important information in future geothermal exploration in Taiwan area. This study aimed at the characterics study of Jinlun geothermal site which is located at southeast part of Taiwan. The lithology of Jinlun area is composed of slate and metasandstone. Incorporated with Audio frequency Magnetotellurics, gravity, nature gamma methods were conducted in this study to establish geothermal conceptual model. Two significant findings are proposed. 1.High temperature gradient at Jinlun area could be the result of rapid uplift caused by subduction and exhumation at convergent margin. Recharge to the Jinlun geothermal system appears to be from high-elevation meteoric waters originating in the Central Range. These waters circulate to considerable depth where they are heated within the metamorphic basement. Under hydraulic head or buoyancy, hot water flow along RF2 to surface as hot spring. Saline fluid and clay alteration together with the high temperatures associated with geothermal activity tend to result lower resistivity area. The geothermal reservoir may located at the fracture zone which is caused by RF1. 2.The low resistivity anomalies on geophysical exploration are important characteristics both on Jinlun and Chingshui geothermal area. This implies that low resistivity anomalies are also the main target for geothermal exploration at metamorphic area.
