A message from the mantle
Mount Süphan is a 4,058-meter-tall stratovolcano located just north of Lake Van in eastern Turkey. As the second-highest volcano in the country, its snow-capped peak is a feature of the landscape. Geological studies show the volcano was active during the Quaternary period, with eruptions occurring between 0.76 and 0.06 million years ago. The last major eruption is dated to around 10,000 years ago. Over its active life, Süphan has produced a wide variety of volcanic rocks, from dark, fluid basalt to light, viscous rhyolite, covering an area of approximately 2,000 square kilometers.
The ascending magma that fueled these eruptions is a messenger from deep within the Earth. While solid fragments of the mantle called xenoliths are not found at Süphan, the chemical makeup of the lavas themselves provides a detailed fingerprint of their origin. By analyzing the geochemistry of these volcanic rocks, scientists can reconstruct the composition of the mantle source from which the magma was generated. This process helps study the Earth's interior, providing information that would otherwise require impossibly deep drilling operations. The volcano's diverse eruptive products point to a complex subterranean plumbing system involving magma mixing and interaction with the Earth's crust.
Decoding the deep earth
Scientific analysis of Mount Süphan's lavas involves precise measurements of trace elements and isotope ratios of elements like strontium, neodymium, and lead. The results of these studies allow geologists to model the conditions of magma formation. Geochemical modeling indicates that the parent magmas of Süphan originated from the partial melting of the upper mantle. More specifically, the data points to a source region containing spinel lherzolite and garnet lherzolite. Lherzolite is a type of peridotite rock, the primary component of the Earth's upper mantle.
Further analysis shows that these mantle-derived magmas did not travel directly to the surface. They stalled in magma chambers within the crust at pressures around 500 megapascals (MPa). In these chambers, different batches of magma mixed, and the hot liquid melted and assimilated some of the surrounding crustal rock. This process, known as energy-constrained assimilation and fractional crystallization (EC-AFC), accounts for the wide spectrum of lava compositions found on the volcano today, from basaltic trachyandesite to rhyolite. The chemistry of the rocks at Mount Süphan records deep mantle melting followed by complex crustal processing.