马尼拉海沟增生楔北部海域天然气水合物成藏机制及其潜在地质灾害风险  

Mechanism of gas hydrate accumulation and its potential geological hazard risk in the northern accretionary wedge of Manila Trench

作　　者：鞠东 高红芳 李学杰 Ju Dong;Gao Hongfang;Li Xuejie(Guangzhou Marine Geological Survey,China Geological Survey,Guangzhou 511458,China;Southern Marine Science and Engineer-ing Guangdong Laboratory(Guangzhou),Guangzhou 511458,China)

机构地区：[1]中国地质调查局广州海洋地质调查局,广东广州511458 [2]南方海洋科学与工程广东省实验室(广州),广东广州511458

出　　处：《海洋学报》2024年第3期22-32,共11页

基　　金：NSFC-广东省联合基金重点项目(U1901214);海南省自然科学基金青年基金项目(420QN376);中国地质调查局地质调查项目(DD20221712,DD20221696)。

摘　　要：天然气水合物由于其巨大的资源潜力而受到广泛关注,但以往研究多集中在南海北部海域被动陆缘,对南海东部主动陆缘的天然气水合物关注相对较少。本文基于南海东北部马尼拉海沟主动陆缘区多道地震剖面分析,识别出似海底反射、振幅空白带、极性反转等典型天然气水合物识别标志以及逆断层、泥底辟等流体运移通道。台湾西南部造山带是马尼拉海沟增生楔的延伸,其泥火山伴生气以CH_(4)为主,少部分表现出高氮异常;其地球化学特征表明,该区天然气主要为热解成因的成熟烃类气,且主要是新近纪巨厚海相沉积烃源岩的贡献。分析认为,其成因是板块俯冲运动将深部烃类物质带入增生楔内,并形成高压环境,热成因烃类气体沿着泥底辟和逆断层等通道向上运移,在运移过程中部分天然气被微生物逐步改造,并混合原位生物气。热成因和生物成因甲烷最终在合适的稳定带内混合;形成以热成因为主,部分具有生物成因特征的逆冲推覆控藏混合气源天然气水合物藏。另外,随着外界环境的变化及俯冲运动的持续活动,天然气水合物的稳定条件遭到破坏而发生分解渗漏,可能引起滑坡,在对本区天然气水合物资源进一步的勘探开发过程中必须注意其潜在地质灾害风险。Natural gas hydrates have received widespread attention due to their enormous resource potential,but previous researches have focused mostly on the passive continental margin in the northern South China Sea,while rarely on the active continental margin in the eastern South China Sea.Based on the analysis of multi-channel seis-mic profiles in the active continental margin area of the Manila Trench in northeast of the South China Sea,this pa-per identified typical gas hydrate indicators such as bottom simulating reflector,blanking zone,polarity-reversal,and fluid migration channels,such as reverse fault and mud diapir are identified in this paper.The Orogenic Belt in southwestern Taiwan is an extension of the accretionary wedge of the Manila Trench.The associated gas of mud volcano is mainly CH4 and minorly showing high nitrogen anomaly.The geochemical characteristics of the associ-ated gas show that natural gas in this area is mainly mature hydrocarbon gas of pyrolysis origin,and is mainly the contribution of Neogene thick marine sedimentary source rock.According to the analysis,the cause is that the plate subduction brought deep hydrocarbon into the accretionary wedge and formed a high-pressure environment.The thermally generated hydrocarbon gas migrated upward along mud diapir and reverse fault.During the migration,some natural gas was gradually transformed by decomposition of microorganisms and mixed with in-situ microbial gas.The thermogenic and biogenic methane eventually mixed in the suitable stable zone to form a mixed gas hy-drate reservoir dominated by thermogenic and partly biogenic.In addition,with the change of external environment and the continuous activities of subduction movement,the stability of natural gas hydrate is damaged and decom-position leakage occurs,which may cause landslide.In the further exploration and development of natural gas hy-drate resources in this area,we must pay attention to the potential geological disaster risk.

关 键 词：天然气水合物 成藏机制 马尼拉海沟增生楔 主动陆缘 南海 

分 类 号：P744.4[天文地球—海洋科学]