Transition of Ridge Axis Gravity with Spreading Rate: The Effect of a Weak Lower Crust

首席调查员对地球卫星测高观测的初步分析表明，大洋中脊轴线重力的突然变化，其扩展速度比地形变化更明显。在60-70 mm/年的扩展速率下，脊轴重力信号具有高幅度并且是可变的，而在该速率以上，重力信号的突然变化取决于地形和补偿机制，重力信号的突变必然标志着均衡补偿机制的突变，地形中没有突变。首席调查员的解释是，海底扩张有两种动态不同的模式。这项工作将从模拟和观测的角度讨论脊轴形态及其随扩张速度、地壳厚度和地幔温度的变化问题。其目的是开发一种脊轴动力学的定量模型，它结合了现实的非线性流动规律以及流变学上不同的地壳和地幔，以扩散率、地壳厚度和推断的地幔温度来描述脊线存在/侧面重力和脊轴/侧面地形，并通过将模型重力/地形与观测进行比较，确定较弱的下地壳层在扩张类型之间的转换中的作用。

The principal investigator's preliminary analysis of Geosat altimetry observations reveal an abrupt change in mid-ocean ridge axis gravity with spreading rate that is more pronouced than the topographic variations. below a spreading rate of 60-70 mm/yr the ridge-axis gravity signature has high amplitudes and is variable where as above this rate the gravity depends upon both the topography and the compensation mechanism, the abrupt change in the gravity signature must signify an abrupt change in the isostatic compensation mechanism, there being no abrupt change in the topography. The principal investigator's interpretation is that there are two dynamically distinct modes of seafloor spreading. This work will address the problem of ridge-axis morphology and its variation with spreading rate, crustal thinckness, and mantle temperature from both a modeling and observational stand point. The objectives are to develop a quantitative model of ridge-axis dynamics which in corporates a realistic non-linear flowlaw as well as a rheologically distinct crust and mantle to characterize ridge exis/flank gravity and ridge axis/flanktopography in terms of spreading rate, crustal thickness and inferred mantle temperature, and, by comparing model gravity/topography with observations, to establish the role of the weak lower crustal layer in the transition between spreading types.