全球三大洋底高原重力异常与地壳厚度特征及对比研究*

翁通爪哇高原、凯尔盖朗高原与沙茨基海隆是全球三大洋底高原, 是大量岩浆喷发到地表的结果, 火山面积分别达1.90×10⁶、1.25×10⁶、0.53×10⁶km²。本文详细分析了该三大洋底高原的地形、剩余地幔布格重力异常(residual mantle Bouguer anomaly, RMBA)与重力反演的相对地壳厚度, 并结合地质与地球化学特征约束进行对比研究。结果显示, 翁通爪哇高原、凯尔盖朗高原与沙茨基海隆分别高出周围海底约4.3、5、4km, 相应的地幔布格重力异常最大变化值分别为250、330、200mGal, 以及相应的相对地壳厚度变化分别为11、13、9km, 表明形成三大洋底高原的岩浆量远远大于正常洋中脊的岩浆量。此外, 三大洋底高原皆形成于洋中脊附近。Nd、Pb、Hf同位素比值分析表明, 翁通爪哇高原的玄武岩组分为洋岛玄武岩; 凯尔盖朗高原大部分类似于洋岛玄武岩, 并含有洋中脊玄武岩组分; 沙茨基海隆的玄武岩组分主要为东太平洋海隆正常洋中脊玄武岩, 却又存在少量位于全球洋岛玄武岩范围内。这些特征揭示了三大洋底高原可能形成于“地幔柱-洋中脊相互作用”。对此本文提出了两种模式: 一为洋中脊被地幔柱拖拽至其上方; 二为洋中脊之下的软流圈受到地幔柱影响, 从而产生超常熔融与超厚地壳。

Characteristics of gravity anomaly and crustal thickness of three largest oceanic plateaus

The Ontong Java Plateau, Kerguelen Plateau, and Shatsky Rise are the three largest oceanic plateaus on Earth, exhibiting voluminous magmatism with areas of 1.90×10⁶, 1.25×10⁶, and 0.53×10⁶ km², respectively. In this study, we conducted a detailed comparative analysis of bathymetry, residual mantle Bouguer anomaly (RMBA), and gravity-derived relative crustal thickness of the three plateaus, correlating results with geological and geochemical constraints. Relative to adjacent normal seafloors, the Ontong Java Plateau is elevated by 4.3 km; the Kerguelen Plateau, by 5 km; and the Shatsky Rise, by 4 km. The corresponding peak-to-trough amplitudes in RMBA are about 250, 330, and 200 mGal, while the relative crustal thickness variations are of 11, 13, and 9 km, respectively, implying that the magma output forming these three oceanic plateaus is far more than that generated by a normal mid-ocean ridge. Moreover, all three plateaus were formed near mid-ocean ridge or ridge triple junction settings. Isotopic analyses of Nd, Pb, and Hf reveal that the Ontong Java Plateau is characterized by ocean island basalts (OIB); most of the Kerguelen Plateau is predominantly OIB, but is mixed with some mid-ocean ridge basalts (MORB); and most of the Shatsky Rise volcanism shows East Pacific Rise-type MORB, with a few exceptions of OIB-like components. These features imply that these oceanic plateaus were probably formed by “plume-ridge interaction”. Two models are proposed herein: (1) the peripheral mid-ocean ridge is dragged onto the top of the mantle plume, and/or (2) the asthenosphere is fed by plume material nearby, resulting in melting anomalies and the resultant thickened crust along the mid-ocean ridge.