Ancient recycled crust beneath the ontong Java plateau: Isotopic evidence from the garnet clinopyroxenite xenoliths, Malaita, Solomon Islands
Ancient recycled crust beneath the ontong Java plateau: Isotopic evidence from the garnet clinopyroxenite xenoliths, Malaita, Solomon Islands
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DOI：
10.1016/j.epsl.2007.04.034
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发表时间：
2007-07-15
影响因子：
5.3
通讯作者：
Nakamura, Eizo
中科院分区：
文献类型：
--
作者：
Ishikawa, Akira;Kuritani, Takeshi;Nakamura, Eizo
本文报道了所罗门群岛马莱塔地区一套石榴单斜辉石岩捕虏体的Sr、Nd、Hf和Pb同位素研究结果，以探讨太平洋地幔的地壳再循环作用。地质、温压和岩石化学证据强烈支持橄榄岩是一系列高压（> 3GPa）玄武岩熔融残留物的来源，橄榄岩来自与翁东爪哇高原岩浆活动有关的太平洋对流地幔。本研究揭示了辉石的同位素变化，最好的解释是不同程度的化学反应与环境橄榄岩的背景下，熔融的复合源地幔。受环境橄榄岩影响的双矿物配子单斜辉石的同位素组成落在大洋玄武岩阵列，类似于Ontong爪哇高原熔岩。与此相反，石英-玛瑙单斜辉石岩，其主要元素组成保持完整，具有较低的Pb-206/（204）Pb-Nd-143/（144）Nd和较高的（87）Sr/Sr-86-Pb-207/（204）Pb比值比大多数大洋玄武岩。这些同位素特征显示出与所提出的回收来源（例如所谓的EM-1或DUPAL类型）的一些亲和力。石英-石榴单斜辉石岩的主量和微量元素特征、Hf-Nd同位素的大幅度退耦以及Ph同位素与Stacey-Kramers曲线的良好吻合，都表明南太平洋地幔的污染是由新元古代麻粒岩下地壳（0.5- 1Ga）的俯冲或拆沉作用造成的。这种地壳再循环可能发生在Rodinia超大陆的缝合线周围，其中一部分在地幔上涌期间重新出现，造成了白垩纪Ontong Java高原。(c)2007 Elsevier B. V.保留所有权利。
We present a Sr, Nd, Hf and Pb isotope investigation of a set of garnet clinopyroxenite xenoliths from Malaita, Solomon Islands in order to constrain crustal recycling in the Pacific mantle. Geological, thermobarometric and petrochemical evidence from previous studies strongly support an origin as a series of high-pressure (> 3 GPa) melting residues of basaltic material incorporated in peridotite, which was derived from Pacific convective mantle related to the Ontong Java Plateau magmatism. The present study reveals isotopic variations in the pyroxenites that are best explained by different extents of chemical reaction with ambient peridotite in the context of a melting of composite source mantle. Isotopic compositions of bimineralic gamet clinopyroxenites affected by ambient peridotite fall within the oceanic basalt array, similar to those of Ontong Java Plateau lavas. In contrast, a quartz-gaenet clinopyroxenite, whose major element compositions remain intact, has lower Pb-206/(204) Pb-Nd-143/(144) Nd and higher (87)sr/Sr-86-Pb-207/(204) Pb ratios than most oceanic basalts. These isotopic signatures show some affinity with proposed recycled sources such as the so-called EM-1 or DUPAL types. Constraints from major and trace element characteristics of the quartz-garnet clinopyroxenite, the large extent of Hf-Nd isotopic decoupling and the good coincidence of Ph isotopes to the Stacey-Kramers curve, all indicate that pollution of southern Pacific mantle occurred by the subduction or delamination of Neoproterozoic granulitic lower crust (0.5-1 Ga). This crustal recycling could have taken place around the suture of Rodinia supercontinent, a part of which resurfaced during mantle upwelling responsible for creating the Cretaceous Ontong Java Plateau. (c) 2007 Elsevier B.V. All rights reserved.