A Tectonically Active Region
The Nattaung Volcanic Field is caused by immense geological forces shaping Southeast Asia. It sits within a complex and active tectonic region dominated by the ongoing collision between the Indian and Eurasian plates. This collision produces major fault systems, including the nearby Sagaing Fault, a massive right-lateral strike-slip fault that runs for approximately 1,400 kilometers through central Myanmar. This fault accommodates a significant portion of the tectonic strain as the Indian Plate pushes northward.
The volcanism in this part of Myanmar is geologically very young, belonging to the Quaternary period, which began 2.6 million years ago. The activity is linked to a process known as slab tearing, where the subducting Indian oceanic plate is tearing away from the more buoyant Indian continental plate. This tear, or "slab window," allows hotter asthenospheric mantle material to rise, decompress, and melt, ultimately feeding magma to the surface. This mechanism explains the presence of small-scale, recent volcanic activity in areas like Nattaung, distinct from the larger volcanic arcs found elsewhere. The volcanic field itself consists of features like dolerite dykes, which are vertical sheets of solidified magma that intruded into existing rock layers.
Chemistry of a Young Volcano
The lavas erupted at the Nattaung field and other Quaternary volcanoes in central Myanmar are primarily basaltic. Geochemical analysis reveals they belong to a high-K to shoshonitic series, indicating they are enriched in potassium. Specifically, the rocks include compositions like trachybasalt and basaltic trachyandesite with relatively high titanium dioxide content, around 2% by weight.
These chemical signatures provide clues about their origin. The magma appears to be generated by small degrees of partial melting of the asthenospheric mantle, which was previously modified by subduction processes. Isotopic data, such as strontium and neodymium ratios, suggest a significant contribution from an enriched asthenosphere layer that may have flowed from beneath southeastern Tibet. The presence of certain trace elements and negative anomalies in tantalum, niobium, and titanium are characteristic fingerprints of magma formed in a subduction-related setting. While the surface cones and flows are dormant, the detection of gas emissions confirms that the magmatic system that created them is not extinct. The heat source remains, showing a dynamic and evolving geological environment deep beneath the surface.