冲绳海槽地壳结构的研究
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摘要
根据1990年以来对冲绳海槽地质地球物理调查的最新实测资料，包括多道和单道反射地震、海底地震仪折射地震、重磁测量、水深测量、海底岩石拖网，结合国内外学者对冲绳海槽的调查研究成果，对冲绳海槽地壳结构进行了探讨，得出如下初步结论：（1）冲绳海槽是一个典型的发育在大陆地壳边缘、由陆壳张裂而成、处于裂谷作用最高演化阶段、洋壳即将产生、海底扩张即将出现的弧后活动裂谷。（2）根据火成岩发育、沉积层分布和地壳结构分析，冲绳海槽尚缺少已经开始“扩张”的证据，还不能确定海槽中央已经发育了大洋地壳。冲绳海槽目前仍属于拉薄的大陆地壳。（3）冲绳海槽作为一个浅海槽状地貌单元，形成于距今6Ma。作为一个弧后裂谷，自距今2Ma以来开始强烈的张裂活动。海槽中央张裂地堑（槽中槽）距今2Ma以来开始形成并逐渐发展。中央张裂地堑内的火成岩年龄不大于1Ma。因此，冲绳海槽是一个年青的、正在活动的弧后裂谷盆地。
The Okinawa Trough which lies at the southastem margin of the East China Sea,is an astive back-are rift and a part of the Ryukyu T-A-BA system. Many geological and geophysical studies have shown that the Okinawa Trough is associated with an extremely high heat flow,strong submarine hydrothermal activities,frequent earthquaks,strong volcanic eruptions, well-developed central grabens and active faults,and a thin crust and lithosphere. Up to now, the crustal nature of the Trough is still a key debating question.Based on the new geological and geophysical data collected since 1990,includ ing, single and multiple channel seismic reflections, ocean bottom seismometer (OBS) refractions, gravity and geomagnetic measurements,water depth sounding,submarine sampling and sea bottom dragging,the authors have undraken analyses of the crustal structure of the Okinawa Trough. The conclusions obtained in this study are listed below.1. Except the Andaman Sea with a complex oblique opening,the Okinawa Trough is the ouly example in the world of an active marginal back-arc rift opening along a continental boundary; it is formed by continental crustal extension,at a special high evoluting stage of a back-are rift,near the end of a rifting period and the beginning of a spread. Hence the Okinawa Trough is tectonicly a modern active rift valley.2. Analyses of igneous rock distribution patterns,sediment thickness and crustal structures,show that there is no oceanic crust in the central graben of the Trough and the Okinawa Trough has not begun to "spread" till now. The crust of the Trough is still continental in character because of the continental extension.3. Based on an seismic profile interpretation,the K-Ar dating for igneous rock sampes and heat flow calculations,as a submarine "Trough",the Okinawa Trough was formed 6 Ma B. P.; however,as a back-arc rift 4. The Okinawa Trough is a typical astive zone in the marginal area of the westem Pacific. The study on its crust nature and tectonic astivity is of great significance for many key questions about continental marginal tectonics such as back-arc rifting processes,influence from the subducted slab,mechanisms of the back-arc hydrothermal ctivity,mantle-crust interaction in the astive back-arc basin,relationships between the volcanic activity and back-arc rifting, differences in crustal fluid ectivities between mid-ocean ridges and back-arc basins,the tectonic evolution and geodynamics of active back are rifts. Therefore, it is required to carry out an ODP driling more accurate and more detailed geological and geophysical investigations for the Okinawa Trough.
引文
李乃胜 1992.冲绳海槽海底热流研究.海洋学报,14(4):87-93
李乃胜主编1995.冲绳海槽地热.青岛:青岛出版社,138
喻普之 李乃胜, 1989.琉球沟弧盆系及邻近海区的重力场和深部构造特征海洋学报, 11(3): 325-330
木村政昭, 1990.冲绳先生形成.地质学论集, 34: 77—88
桂忠彦 大岛章一 获野卓司等,1986.冲绳南西部海域地质、地球物理的诸性质.水路研究报告,21:21-47
Hirata N, Kinoshita H,Kato H et al, 1991 Report on DELP 1988 Cruise in the Okinawa Trough,Part 3:Crustal structuer of the southem Okinawa Trough Bull Eri Univ Toky66(1):37-70
Ishikawa M ,Sato H,Furokawa M et al, 1991.Report on DELP 1988 Cruise in the Okinawa Trough,Part 6:Petrology of Volcanic Rocki. Bull Eri Univ Tokoy,66(1): 151- 178
Kimare M,1985.Formation of Active Ocean Margins Tokyo:Terra pub、567-591
Kimura M,Kaneoka I,Kato I et al,1986.Report on DELP 1984 cruise in the middle Okinawa Trough,part 5Topography and geology of the central grabens and their Vicinity Bull Eri Univ Tokyo, 61(2):269—310
Kimura M,Frukawa M, Ixawa E et al,1991.Report on DELP 1988 Cruise in the Okinawa Trough,Part 7Geologic investigation of the central fift in the middle to southem Okinawa Trough,Bull Eri Univ Tokyo,66(1):179-210
Lee C- S Shor G G Jr,Bibee L D et al ,1980 Okinawa Trough: Origin of a back-arc basin Mar Geol,35(1-3):219-241
Letouzey J.Kimura M 1985Okinawa Trough genesis:Structure and evolution of a backarc basin developedin acontinent.Mar Petroleum Geol,2:111-130
Nagumo S,Kinoshita H,Kasahara J et al 1986Report on DELP 1984 cruise in the Middle Okinawa Trough,Part II:Seismic structural studies. Bull Eri Uniy Tokyo,61(2): 167-202
Nash D F,1979The Geological development of the morthem Okinawa Trough area from Neogene time torecent.J Jap Assoc Pet Technol,44:341—351
Parsons B,Scalter J G, 1977. An analysis of the variation of ocean floor bathmentry and heat flow with age.JGR, 82:803-827
Shibata K,Uchiumi S,Uto K et al,1984、K-Ar age results-2 new data from the Geological Survey of Japan.Bull Geol Surv Japan,35:331-340
Sibuet J-C,Letouzey J,Barbier F et al, 1987. Back-are extension in the Okinawa Trongh, JGR, 92: 14 014-14063
李乃胜主编1995.冲绳海槽地热.青岛:青岛出版社,138
喻普之 李乃胜, 1989.琉球沟弧盆系及邻近海区的重力场和深部构造特征海洋学报, 11(3): 325-330
木村政昭, 1990.冲绳先生形成.地质学论集, 34: 77—88
桂忠彦 大岛章一 获野卓司等,1986.冲绳南西部海域地质、地球物理的诸性质.水路研究报告,21:21-47
Hirata N, Kinoshita H,Kato H et al, 1991 Report on DELP 1988 Cruise in the Okinawa Trough,Part 3:Crustal structuer of the southem Okinawa Trough Bull Eri Univ Toky66(1):37-70
Ishikawa M ,Sato H,Furokawa M et al, 1991.Report on DELP 1988 Cruise in the Okinawa Trough,Part 6:Petrology of Volcanic Rocki. Bull Eri Univ Tokoy,66(1): 151- 178
Kimare M,1985.Formation of Active Ocean Margins Tokyo:Terra pub、567-591
Kimura M,Kaneoka I,Kato I et al,1986.Report on DELP 1984 cruise in the middle Okinawa Trough,part 5Topography and geology of the central grabens and their Vicinity Bull Eri Univ Tokyo, 61(2):269—310
Kimura M,Frukawa M, Ixawa E et al,1991.Report on DELP 1988 Cruise in the Okinawa Trough,Part 7Geologic investigation of the central fift in the middle to southem Okinawa Trough,Bull Eri Univ Tokyo,66(1):179-210
Lee C- S Shor G G Jr,Bibee L D et al ,1980 Okinawa Trough: Origin of a back-arc basin Mar Geol,35(1-3):219-241
Letouzey J.Kimura M 1985Okinawa Trough genesis:Structure and evolution of a backarc basin developedin acontinent.Mar Petroleum Geol,2:111-130
Nagumo S,Kinoshita H,Kasahara J et al 1986Report on DELP 1984 cruise in the Middle Okinawa Trough,Part II:Seismic structural studies. Bull Eri Uniy Tokyo,61(2): 167-202
Nash D F,1979The Geological development of the morthem Okinawa Trough area from Neogene time torecent.J Jap Assoc Pet Technol,44:341—351
Parsons B,Scalter J G, 1977. An analysis of the variation of ocean floor bathmentry and heat flow with age.JGR, 82:803-827
Shibata K,Uchiumi S,Uto K et al,1984、K-Ar age results-2 new data from the Geological Survey of Japan.Bull Geol Surv Japan,35:331-340
Sibuet J-C,Letouzey J,Barbier F et al, 1987. Back-are extension in the Okinawa Trongh, JGR, 92: 14 014-14063
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