The Investigator Ridge, located along the prominent Investigator Fracture Zone in the Wharton Basin, northeast Indian Ocean, was chosen to investigate the temporal and geochemical evolution of the Indian upper mantle. We present new Ar/Ar age, as well as major and trace element and Sr-Nd-Pb-Hf isotope data, from a large part of this so far scarcely sampled ridge. The Ar/Ar ages range from 100.0 Ma to 64.1 Ma, and except for the two youngest samples (65.5 and 64.1 Ma) of likely Christmas Island Seamount Province (CHRISP) origin, display decreasing ages along the ridge from south to north. This pattern is consistent with the ages derived from paleomagnetic anomalies on the local oceanic crust that also decrease in age northwards and suggests an origin of the studied rocks at or near the now extinct Wharton spreading center. These ages also provide information about the displacements along the multiple Investigator Fracture Zones indicating large left-lateral as well as right-lateral offsets of the paleo spreading axis. The fracture zone also shows signs of recent tectonic reactivation. The Investigator Ridge samples are derived from a DUPAL-like mantle source similar to present-day Indian MORB. This source contains a depleted mantle type component, an enriched, moderately HIMU-like, component such as common “C” or “FOZO”, and an additional enriched component of recycled subcontinental lithospheric mantle material. In both the Investigator Ridge and CHRISP samples, the trace element and isotope compositions systematically change with age implying a temporal geochemical evolution of the Indian Mantle Domain in this region. It contained higher proportions of subcontinental lithospheric material delaminated during breakup of Gondwana and mixed with depleted upper mantle material in its early phase. With time, the source evolved in the direction of “C” or “FOZO”, which then became the dominant enriched component and is observed in the youngest samples.

中文翻译：

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印度洋东北部调查者海岭揭示的印度 MORB 地幔的地球化学和时间演化


调查者海岭位于印度洋东北部沃顿盆地著名的调查者断裂带沿线，被选来研究印度上地幔的时间和地球化学演化。我们提供了新的 Ar/Ar 年龄，以及主量元素和微量元素以及 Sr-Nd-Pb-Hf 同位素数据，这些数据来自迄今为止几乎没有采样的山脊的大部分。 Ar/Ar 年龄范围从 100.0 Ma 到 64.1 Ma，除了可能起源于圣诞岛海山省 (CHRISP) 的两个最年轻的样本（65.5 和 64.1 Ma）外，显示出年龄沿着海脊从南到北递减。这种模式与当地洋壳古地磁异常得出的年龄一致，该年龄也向北减少，表明所研究的岩石起源于现已灭绝的沃顿扩张中心或附近。这些年龄还提供了有关沿多个调查断裂带的位移的信息，表明古扩张轴存在较大的左侧和右侧偏移。断裂带还显示出近期构造重新激活的迹象。 Investigator Ridge 样本源自类似于当今印度 MORB 的 DUPAL 类地幔源。该源包含贫化地幔类型成分、富集的、中等 HIMU 类成分，例如常见的“C”或“FOZO”成分，以及再循环的次大陆岩石圈地幔物质的额外富集成分。在 Investigator Ridge 和 CHRISP 样本中，微量元素和同位素组成随着年龄而系统地变化，这意味着该地区印度地幔域的时间地球化学演化。 它含有较高比例的冈瓦纳大陆分裂期间分层的次大陆岩石圈物质，并与早期阶段耗尽的上地幔物质混合。随着时间的推移，来源朝着“C”或“FOZO”的方向演化，然后成为主要的富集成分，并在最年轻的样本中观察到。