The Indian Ocean is more than just a vast body of water; it hides a geological marvel—the Ninetyeast Ridge. Stretching an impressive 5,000 kilometers (3,107 miles), this underwater mountain range surpasses the length of the North American Rockies yet remains concealed beneath the ocean’s surface. Recent scientific investigations have revealed intriguing insights about the formation and evolution of this submerged feature, challenging long-standing assumptions about volcanic activity associated with hotspots in Earth’s mantle.
To fully comprehend the Ninetyeast Ridge, we must first explore the phenomenon of seamounts. These underwater volcanoes are ubiquitous across the planet’s oceans and arise from ‘hotspots’—areas of focused thermal activity beneath the Earth’s crust. Initially, it was believed that these hotspots were stationary, causing tectonic plates to glide over them and resulting in sequential volcanic formations. This understanding can be visualized as a sewing machine with its needle fixed in one place and fabric (the tectonic plate) moving above. However, this simplified view has been overturned by recent studies focusing on the Indian Ocean.
Geoscientists have now highlighted that the Ninetyeast Ridge was not formed by a stationary hotspot. Instead, it appears that the hotspot responsible for this ridge, known as the Kerguelen hotspot, exhibited lateral movement over time. According to Hugo Olierook, a geoscientist from Curtin University, this hotspot functions more like a fountain pen, with its tip moving and depositing molten material in various locations. This revelation underscores the complexity of geothermal processes and how they contribute to the geological features we see today.
A comprehensive study involving researchers from Australia, Sweden, China, and the US has provided substantial evidence supporting the idea of a mobile hotspot. By analyzing basalt samples from the Ninetyeast Ridge, these scientists have traced the Kerguelen hotspot’s journey as the Indian Plate migrated northward, leading to the formation of the Indian Ocean. Their findings indicate that rather than remaining fixed while the tectonic plate drifted above it, the Kerguelen hotspot showed movement that matched neither the plate’s speed nor direction, prompting a reevaluation of geological models related to seafloor spreading.
Radioisotopic dating has been a crucial tool in understanding the timeline of the Ninetyeast Ridge’s formation. The data suggests that between 83 and 66 million years ago, the peaks of this underwater mountain range formed at approximately half the rate of the surrounding seafloor spreading. This unexpected finding indicates that the Kerguelen hotspot was not stationary beneath the tectonic activity as previously posited. Instead, the movement of this mantle plume was likely influenced by the Indian-Antarctic spreading ridge and its dynamics.
Around 66 million years ago, a significant shift occurred when the Kerguelen plume became disconnected from the spreading ridge, likely due to the ridge’s lateral movement away from the hotspot. This disconnection marked a pivotal moment in the geological history of the Indian Ocean, as the plume subsequently reattached itself to another spreading ridge, continuing to exert its influence on the region’s geological activity. By around 42 million years ago, the hotspot had delineated a vertical barrier that now serves as a natural division between the eastern and western segments of the Indian Ocean.
Fred Jourdan, an earth scientist at Curtin, emphasizes that these findings significantly alter our understanding of tectonic processes and the history of Earth’s lithosphere. For years, estimations of the Ninetyeast Ridge’s age have informed models regarding the relative motions of tectonic plates. Now, with the revelation of a moving hotspot, scientists are compelled to reconsider previous assumptions and refine their models, allowing for a more nuanced understanding of the dynamic forces shaping our planet.
The Ninetyeast Ridge offers a fascinating glimpse into the complex interplay of geological forces beneath the Indian Ocean. As research continues, it promises to shed light on how such monumental features are formed and how understanding them can refine our comprehension of tectonic activity globally. The discovery of a mobile hotspot adds depth to the narrative of Earth’s geological history and invites further exploration of the oceanic mysteries that lie beneath.
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