The recent study by an Indian researcher traced the tectonic evolution and nature of the Greater Maldive Ridge. This significant geodynamic feature in the western Indian Ocean’s origin has sparked many scientific debates. The research undertaken by the Indian Institute of Geomagnetism, Mumbai, offers new clarity on continental and oceanic lithosphere, earthquakes, volcanoes, and plate tectonics.
Decoding Tectonic Plates
Tectonic plates or lithospheric plates are massive, irregularly-shaped slabs of solid rock, generally comprising both continental and oceanic lithosphere. The lithosphere includes the crust and top mantle, varying between 5-100km in thickness in oceanic parts and about 200km in the continental areas. A tectonic plate might be a continental plate or an oceanic plate, depending on which of the two occupies the larger portion of the plate. Crucially, these plates are not static but move horizontally over the Asthenosphere as rigid units. This movement leads to phenomena like earthquakes and volcanic eruptions.
Understanding Mid-Ocean Ridges
A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range formed by plate tectonics. These ridges spread apart as new seafloor is created by magma pushing up from the mantle, the layer beneath the crust.
The Mohorovičić Discontinuity (Moho)
Named after Croatian seismologist Andrija Mohorovicic, who discovered it in 1909, the Mohorovicic Discontinuity or “Moho” represents the boundary between the crust and mantle. It’s a seismic discontinuity surface where seismic waves change velocity and accelerate. This surface lies at an average depth of 8 kilometres beneath the ocean basin and at an average depth of 32 kilometres beneath the continents.
The Greater Maldive Ridge: An Overview
The Maldive Ridge is an aseismic ridge unassociated with earthquake activities. Found in the western Indian Ocean, southwest of India, it is imperative to understand its structure and geodynamics for understanding the evolution of ocean basins.
Insights from the Study
By analysing satellite-derived high-resolution gravity data, the researchers discerned the geological cross-sections along the Greater Maldive Ridge (GMR). This data helped provide a three-dimensional picture of Moho variation along the Greater Maldive Ridge and the adjoining ocean basins. Assumptions are that GMR may be underlain by an oceanic crust, providing a layout of the crustal architecture and the state of gravitational equilibrium or “isostasy” between Earth’s crust and mantle.
Effective Elastic Thickness
The study found that Moho is deeper over the MR region and shallows southwards in the Deep Sea Channel region (DSC). However, the effective elastic thickness values (a measure of lithosphere strength) were lower over the MR compared to the DSC region.
Understanding Hotspots
Hotspots refer to areas where volcanic activities occur within plates rather than along or adjacent to plate boundaries. There are approximately 40 to 50 hotspots worldwide. The research suggests that the MR might have formed close to a Mid-Oceanic Ridge, while the DSC region was under a long transform fault, which hindered melt production.
Transform Faults Explained
A transform fault is a type of fault where two tectonic plates slide past one another. This geological feature doesn’t create or destroy lithosphere, but offsets between spreading centres.
Why is this Study Important?
This research can help reconstruct the original Gondwanaland break up and dispersal, leading to the present-day configuration of continents and formation of ocean basins in the Indian Ocean. The study will assist in understanding the plate-tectonic evolution of the Indian Ocean better. Understanding these processes can lead to more accurate predictions concerning earthquakes and volcanoes, proving beneficial for disaster management efforts and public safety.