东南印度洋中脊澳大利亚-南极洲不整合带地区岩浆供应与构造作用沿洋脊的变化

We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge(SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance(AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly(RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na_(8.0) being greater and Fe_(8.0) being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD.Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes(OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at ～124°–126°E, as well as at the eastern end of Zone C at ～115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments.The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs.

Large along-axis variations in magma supply and tectonism of the Southeast Indian Ridge near the Australian-Antarctic Discordance

We analyzed seafloor morphology and geophysical anomalies of the Southeast Indian Ridge (SEIR) to reveal the remarkable changes in magma supply along this intermediate fast-spreading ridge. We found systematic differences of the Australian-Antarctic Discordance (AAD) from adjacent ridge segments with the residual mantle Bouguer gravity anomaly (RMBA) being more positive, seafloor being deeper, morphology being more chaotic, M factors being smaller at the AAD. These systematic anomalies, as well as the observed Na_8.0 being greater and Fe_8.0 being smaller at AAD, suggest relatively starved magma supply and relatively thin crust within the AAD. Comparing to the adjacent ridges segments, the calculated average map-view M factors are relatively small for the AAD, where several Oceanic Core Complexes (OCCs) develop. Close to 30 OCCs were found to be distributed asymmetrically along the SEIR with 60% of OCCs at the northern flank. The OCCs are concentrated mainly in Segments B3 and B4 within the AAD at~124°-126°E, as well as at the eastern end of Zone C at~115°E. The relatively small map-view M factors within the AAD indicate stronger tectonism than the adjacent SEIR segments. The interaction between the westward migrating Pacific mantle and the relatively cold mantle beneath the AAD may have caused a reduction in magma supply, leading to the development of abundant OCCs.