Crustal Structure beneath Yinggehai Basin and Adjacent Hainan Island, and Its Tectonic Implications  

作　　者：吴世敏 丘学林 周蒂 曾刚平 夏戡原 叶三余 

机构地区：[1]Key Laborotary of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences,Guangzhou 510301, China [2]Hainan Branch of State Seismological Bureau,Haikou 570203, China [3]NedreToppenhaug 100, N-1353, Brums Verk, Norway

出　　处：《Journal of China University of Geosciences》2009年第1期13-26,共14页中国地质大学学报（英文版）

基　　金：supported by the National Basic Research Program of China (No. 2007CB411706-05);the National Natural Science Foundation of China (No. 40576025)

摘　　要：Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai （莺歌海） basin （YGHB） with ocean bottom hydrophones （OBHs） and piggyback recorded by onshore stations located on the Hainan （海南） Island. Detailed velocity-depth models were obtained through traveltime modeling and partially constrained by amplitude calculations. More than 15 km Tertiary sedimentary infill within the YGHB can be divided in to three layers with distinct velocity-depth distribution. Overall, the upper layer has a high velocity gradient with 3.8--4.1 km/s at its bottom, consistent with progressive compaction and diagenesis. Its thickness increases gradually towards the basin center, reaching 4.5 km along the southern profile. The middle layer is characterized in its most part as a pronounced low velocity zone （LVZ） with average velocity as low as 3.0 km/s. Its thickness increases from 3.0 to over 4.5 km from NW towards SE. The primary causes of the velocity inversion are high accumulation rate and subsequent under-compaction of sediments. The velocity at the top of the lower layer is estimated at about 4.5 km/s. Despite strong energy source used （4 × 12L airgun array）, no reflections can be observed from deeper levels within the basin. Towards NE the basin is bounded sharply by a clear and deep basement fault （Fault No. 1）, which seems to cut through the entire crust. A typical continental crust with low-velocity middle crust is found beneath the coast of the western Hainan Island. Its thickness is determined to be 28 km and shows no sign of crustal thinning towards the basin. The sharp change in crustal structure across Fault No. 1 indicates that the fault is a strike-slip fault. The crustal structure obtained in this study clearly favors the hypothesis that the YGHB is a narrow pull-apart basin formed by strike-slip faulting of the Red River fault zone.Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai （莺歌海） basin （YGHB） with ocean bottom hydrophones （OBHs） and piggyback recorded by onshore stations located on the Hainan （海南） Island. Detailed velocity-depth models were obtained through traveltime modeling and partially constrained by amplitude calculations. More than 15 km Tertiary sedimentary infill within the YGHB can be divided in to three layers with distinct velocity-depth distribution. Overall, the upper layer has a high velocity gradient with 3.8--4.1 km/s at its bottom, consistent with progressive compaction and diagenesis. Its thickness increases gradually towards the basin center, reaching 4.5 km along the southern profile. The middle layer is characterized in its most part as a pronounced low velocity zone （LVZ） with average velocity as low as 3.0 km/s. Its thickness increases from 3.0 to over 4.5 km from NW towards SE. The primary causes of the velocity inversion are high accumulation rate and subsequent under-compaction of sediments. The velocity at the top of the lower layer is estimated at about 4.5 km/s. Despite strong energy source used （4 × 12L airgun array）, no reflections can be observed from deeper levels within the basin. Towards NE the basin is bounded sharply by a clear and deep basement fault （Fault No. 1）, which seems to cut through the entire crust. A typical continental crust with low-velocity middle crust is found beneath the coast of the western Hainan Island. Its thickness is determined to be 28 km and shows no sign of crustal thinning towards the basin. The sharp change in crustal structure across Fault No. 1 indicates that the fault is a strike-slip fault. The crustal structure obtained in this study clearly favors the hypothesis that the YGHB is a narrow pull-apart basin formed by strike-slip faulting of the Red River fault zone.

关 键 词：crustal structure strike-slip fault pull-apart basin Yinggehai South China Sea 

分 类 号：P736.15[天文地球—海洋地质]