Basalt analyses from different DSDP Holes in the Mozambique Basin and Ridge and from the Southwest Indian Ridge

Basalts from DSDP Sites 248, 249, 250 and 251 in the southwestern Indian Ocean formed in a complex tectonic region affected by the separation of Africa and South America. The different ages and variable geochemical features of these DSDP basalts probably reflect this tectonic complexity. For example, Site 251 on the flanks of the Southwest Indian Ridge is represented by normal MORB which probably originated at the Southwest Indian Ridge. Site 250 in the Mozambique Basin includes an older incompatible- element enriched unit which may represent basalt associated with the Prince Edward Fracture Zone; the upper unit is normal MORB. Basalts at Site 248 also in the Mozambique Basin are geochemically very unlike MORB and have strong continental affinities; they are also comparable in age to some of the continental Karroo basalts. They appear to be related to a subcontinental mantle source or to contamination by continental basement associated with the tectonic elevation of the Mozambique Ridge. Basalts from Site 249 on the Mozambique Ridge are relatively weathered but appear to be normal MORB. Their age, location, and composition are consistent with their origin at an early Cretaceous rift which has been postulated to have separated the Falkland Plateau from the Mozambique Ridge.

印度洋西南部深海钻探计划（Deep Sea Drilling Project, DSDP）248、249、250及251站位的玄武岩，形成于受非洲与南美分离作用影响的复杂构造区域。该批DSDP玄武岩的形成时代各异且地球化学特征多变，这大概率反映了该区域的构造复杂性。例如，位于西南印度洋中脊（Southwest Indian Ridge）侧翼的251站位玄武岩以正常洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）为代表，其成因可能与西南印度洋中脊相关。位于莫桑比克盆地（Mozambique Basin）的250站位玄武岩包含一套古老的不相容元素富集单元，该单元可能代表与爱德华王子断裂带（Prince Edward Fracture Zone）相关的玄武岩；其上覆单元则为正常洋中脊玄武岩。同样位于莫桑比克盆地的248站位玄武岩，其地球化学特征与洋中脊玄武岩差异显著，且表现出强烈的大陆亲缘性，其形成时代与部分卡鲁玄武岩（Karroo basalts）相当。该类玄武岩似乎与大陆下伏地幔源区相关，或是受与莫桑比克海岭（Mozambique Ridge）构造抬升相关的大陆基底物质混染所致。位于莫桑比克海岭的249站位玄武岩风化程度相对较强，但整体仍属于正常洋中脊玄武岩。其形成时代、产出位置与地球化学组成均与早白垩世裂谷的成因机制相符——该裂谷曾被认为将福克兰高原（Falkland Plateau）与莫桑比克海岭分隔开来。