南海北部大陸邊緣東沙-澎湖隆起構造演化之研究

Abstract

南海北部大陸邊緣於中生代屬於活動大陸邊緣。然而，由於新生代被動大陸構造演化的變動，導致中生代遺留構造研究困難，只有極少數文獻報導過此區域中生代的構造演化。本研究以南海北部大陸邊緣東沙-澎湖隆起地區之震測剖面資料進行解釋，佐以位於此地區之MZ-1-1井的古生物定年、碎屑鋯石鈾鉛定年、井壁岩心氬氬定年等年代控制，及地球化學分析等作為研究資料。根據震測剖面解釋，可以發現一系列由正斷層再活動而形成之高角度逆衝斷層與褶皺，顯示出構造反轉的證據。利用定年控制，本研究認為此構造反轉事件可能開始於早白堊紀，於晚白堊紀發展，並於新生代前結束；震測解釋可劃分出其影響範圍大約100公里寬，局限於東沙-澎湖隆起地區。藉由南海的古地理重建模式可知，此構造反轉可能源於晚白堊紀時期，海底火山(seamount)，主要為卡拉棉群島(Calamian Islands)─現在位於北巴拉望地塊(North Palawan block)，與南海北部大陸邊緣的碰撞所造成。The northern South China Sea (SCS) continental margin was proposed to be an active margin during the Mesozoic. However, only a few papers discussed the Mesozoic structural evolution in the Dongsha-Penghu Uplift area. Here, we provide information based on the seismic profile interpretations with age control from biostratigraphic studies and detrital zircon U-Pb dates of well MZ-1-1 in the western Dongsha-Penghu Uplift of the northern SCS continental margin. The industrial seismic profiles reveal evidence for structural inversion as represented by folds and high-angle reverse faults, formed by reactivation of pre-existing normal faults. The inversion event likely started after the Early Cretaceous, and developed in Late Cretaceous, but ceased before the Tertiary. The areal extent of the structural inversion was restricted in the western Dongsha-Penghu Uplift and was approximately 100 km in width. Based on the paleogeographic reconstruction of SCS, the structural inversion was likely formed by a collision between the seamount (volcanic islands) swarm of the current North Palawan block (mainly the Calamian Islands) and the northern SCS continental margin around Late Cretaceous.