两种不同类型大陆边缘的初步研究

A PRELIMINARY STUDY ON THE TWO DIFFERENT TYPES OF CONTINENTAL MARGIN

1986年10月-1987年5月，中国第三次南极考察暨首次环球科学考察的实测重力资料表明，太平洋型活动陆缘重力异常面貌复杂，空间异常变化剧烈，处于极度不均衡状态。用sixx／x法反演了莫氏面深度，利用水层和地壳引起的垂直引力之和与实测的空间异常之差反演了软流层顶界的深度。结果显示，在海沟及其洋侧冷的软流层发生了大规模的沉降，而弧后热的软流层则强烈抬升。在弧沟间隙两侧，软流层这种大规模的差异运动是造成太平洋型活动陆缘强烈构造活动及不均衡状态的主要原因。而大西洋型被动陆缘，以单调的正、负不对称重力异常为主，“地壳的边界效应”在这里表现的较为明显；它缺少大规模的软流层升降运动和其它强烈的构造活动，且已达到均衡状态。

The third Chinese Antarctic Expedition and the First Global Scientific Investigation were successfully conducted in the period from October, 1986 to May,1987, during which a team from the First Institute of Oceanography, State Oceanic Administration, carried out the a gravity survey yielding about. 52780 kilometers of gravity profile across the Pacific, Indian and Atlantic Oceans. The above data were used for the Pacific active continental margin and Atlantic passive continental margin study. On the Pacific active continental margin gravity anomalies appear very complicated, and free-air anomalies change greatly, suggesting a state of non-equilibrium. The conversion result shows that the cold asthenosphere sinks in large scale along trenches and ocean-sides and hot asthenosphere rises greatly along the arc-back area. On both sides of are and trench, the large scale differential movement of asthenospheric materials scale contributes to the strong tectonic activities of the Pacific active continental margin, leading to a non-equilibrium state. Compared with the Pacific active continental margin the Atlantic passive margin is characterised by monotonous gravity anomalies with positive and negative unsymmetry resulting from the 'boundary effect of the earth's crust'. It lacks a massive lifting and sinking movement of asthenospheric materials and other tectonic activities suggeste an equilibium state there.