SWIRheat: proof of asthenospehere topography at ultra slow midocean ridges by heat flow determinations on the Southwest Indian Ridge

西南印度洋脊（SWIR）是一个超低扩展的洋中脊（< 20mm /a）。岩石学调查表明，岩浆活动中心与岩浆平静带相互交换。本地产生的少量熔体需要从较深的地方进行横向输送，并需要岩浆集中在活动中心。这就产生了岩石圈-软流圈边界沿脊轴变化明显的假设。在超低速扩张的尼波维奇海脊（北极）的地震观测显示出明显的震源分布。较深地震的深度在8至25公里之间画出一条正弦曲线。较浅的震源深度与活动中心有关，较深的震源深度与脊的岩浆剖面有关。最大震源深度很可能遵循LAB，而LAB又可视为等温线（~800°C）。因此，测得的海底热流应反映出LAB的显著深度变化。根据SWIR的地震学研究，我们可以推断，那里的拉布拉多也显示出明显的地形，就像在尼波维奇岭看到的那样。热流测量与AWI的新地震观测相结合，将为强变化LAB的概念提供重要的约束。

The Southwest-Indian Ridge (SWIR) is an ultraslow spreading midocean ridge (< 20 mm/a full rate). Petrological investigations revealed that centers of magmatic activity and magmatic quiet zones interchange. The poor amount of locally generated melt requires a lateral transport from greater depths and a concentration of magma at the active centers. This led to the hypothesis that the lithosphere-asthenosphere boundary (LAB) varies significantly along the ridge axis. Seis-mo¬logical observations at the ultraslow spreading Knipovich Ridge (Arctic) showed a distinct distribution of hypocenters. The depth of the deeper earthquakes draw a sinoidal contour between 8 and 25 km. Shallower hypocenter depths correlate with active centers, greater depths with an amagmatic section of the ridge. The maximum hypocenter depths follow most likely the LAB which in turn can be regarded as isotherm (~800°C). A significant depth change of LAB should therefore be reflected in the measured seafloor heat flow. Based on seismological studies from SWIR we can infer that there the LAB also shows a pronounced topography as seen at the Knipovich-Ridge. Heat flow measurements in conjunction with new seismological observations of AWI will provide important constraints of the concept of a strongly varying LAB.