Geochemistry of Kerguelen-Heard Plateau basalts

During Leg 120 basalts were recovered at four drill holes on the Kerguelen-Heard Plateau. This paper reports the trace element and Sr, Nd, Hf, and Pb isotopic characteristics of these basalts and compares these basalts with Indian Ocean basalts and Kerguelen and Heard island volcanics. Kerguelen-Heard Plateau basalts are extremely heterogeneous in character. Intersite variations are larger than intrasite variations. Part of the chemical variations of the plateau volcanics overlap with those characteristics of Kerguelen Island volcanics, which indicates tapping of the same mantle source during the two different periods of activity. The estimates of the degree of melting for the plateau basalts (smaller degree of melting than for mid-ocean ridge basalts) and the heterogeneous character of the plateau exclude an origin that requires large degrees of melting or more rigorous convection than at ocean ridges. However, all characteristics indicate an oceanic origin for the Kerguelen-Heard Plateau.在第120航次中，研究人员于凯尔盖朗-赫德高原（Kerguelen-Heard Plateau）的4个钻探站位获取了玄武岩样品。本文报道了这批玄武岩的微量元素以及Sr、Nd、Hf、Pb同位素组成特征，并将其与印度洋玄武岩及凯尔盖朗岛、赫德岛火山岩开展对比分析。凯尔盖朗-赫德高原玄武岩的地球化学特征极不均一，站位间差异显著大于站位内差异。该高原火山岩的部分化学组成变化特征与凯尔盖朗岛火山岩高度重合，这表明两次不同火山活动期均从同一地幔源区获取了岩浆物质。对该高原玄武岩熔融程度的估算结果显示，其熔融程度低于洋中脊玄武岩（mid-ocean ridge basalt, MORB），结合其不均一的地球化学特征，可排除其形成需要更高程度熔融或比洋脊更强烈对流的成因假说。但所有地球化学特征均表明，凯尔盖朗-赫德高原的成因属于大洋成因。