冲绳海槽超临界二氧化碳热液的形成

The formation of supercritical carbon dioxide hydrothermal vents in the Okinawa Trough

冲绳海槽超临界二氧化碳热液喷口位于俯冲的加瓜海岭之上.菲律宾海盆水深通常超过5000 m,在碳酸盐补偿深度之下,因此洋壳上碳酸盐不稳定.而加瓜海岭的水深在碳酸盐补偿深度之上,碳酸盐稳定.加瓜海岭俯冲携带的碳酸盐被俯冲板片释放的流体所溶解,向上运移、聚焦,高浓度的二氧化碳在冲绳海槽形成超临界二氧化碳喷口.结合高温高压实验结果,我们推断携带富碳酸盐沉积物的俯冲板片可以直接释放大量二氧化碳.被动陆缘是富碳酸盐沉积物形成和存储的最主要的构造背景,其俯冲可能对气候变化起了重要作用.鉴于此,我们认为新生代大气二氧化碳的长期增加是由于新特提斯洋关闭期间,被动大陆边缘富碳酸盐沉积物俯冲造成的.

Supercritical carbon dioxide(scCO2)has been observed in hydrothermal vents in the Okinawa Trough[1].This is the first natural scCO2 so far reported.Pure carbon dioxide becomes supercritical under pressures higher than 7.38 MPa and temperatures higher than 31.1 C.The occurrence of scCO2 in the Okinawa Trough indicates high flux of subducted carbon returning back to the atmosphere.It,however,remains obscure how scCO2 vents formed,why they appear in the Okinawa Trough and what’s the implication of such geologic process.Here we show that these scCO2 hydrothermal vents are closely associated with the subduction of the Gagua Ridge.