【摘要】 <正> 一、南图瓦卢礁群区重力、水深测量概况 1976年3月至1978年10月,国家海洋局“向阳红05”号海洋调查船(14,000吨)对太平洋中部海域先后进行了四次远洋综合科学调查,为研究该海域的自然环境提供了大量的地质-地球物理、水文、气象、生物、化学资料,并在南纬11°41′.2,西经178°20′.5处新发现了一个水深仅32米的珊瑚礁滩——“向阳礁”.四次远洋调查共完成的重力、更多还原

【Abstract】 From March 1976 to October 1978, comprehensive scientific investigations to the Central Pacific region were carried out four times by the R/V Xiangyanghong No.5. The total profiling line for the gravity and water depth is 57,492 km long. A beach of coral reef (32 m deep) is found at 11° 41′.2S, 178° 20.′5W. The first two cruises have been made in the South Tuvalu reef group area, covering the range within 10°-14° S and 177° 40′E -177° W.Various kinds of reliefs are concentrated in this area, with the northeast portion belonging to the Central Pacific Basin, northwest segment to Melanesina Basin and the south section being part of the Fiji tableland. In the middle of this area there is a typical coral island reef group, which is the. product of gradual sinking of submarine volcanic cluster under tropical oceanic’condition. In the area studied,the average water depth is 2,829 m, the maximum depth is 4,828m, and the mean slop is about 5*.The spread of free-air gravity anomaly is identical with the submarine relief. The anomaly on the island reef amounts to + 230 mgal, and the anomaly in the trough returns to - 139 mgal. The positive and negative anomaly zones are arrayed alternately in the reef group area.The horizontal variation of the anomaly is great and the greatest gradient is 15 mgal/km .The Bouguer anomaly is high (310 mgal) in the north and low(110 mgal) in the middle. In the whole area, the average of free-air anomaly is 5.6 mgal and the average of Bouguer anomaly is 199 mgal, showing that the observed area, as a whole is still close to isostatic state.The isostatic compensation is mainly realized by slow sinking of the seafloor. Judging from island reef morphology, guyot depth and gravity field isostatic adjustment, we are aware of the fact that the seafloor of this area sank 800-1,000 m since the Tertiary.According to the analysis of correlation between gravity anomaly and water depth in this area, the isostasies of various parts can be inferred and the areal crustal thickness can further be estimated. The boundary of the northern basin determined is mainly along 220 mgal Bouguer anomaly contour ( 3,800-4,500 m water depth) ,and the area south of 180 mgal contour is a typical seamount zone.更多还原