Siberian scientists have completed a field expedition to the Eastern Pamirs, where they examined rocks that have passed through extreme depths and preserved traces of high pressures. These rare materials help us understand what happens to the Earth’s crust as it sinks into the mantle and then rises back to the surface.
Group of Institute specialists geology and Mineralogy SB RAS worked in the highlands, where pipe-shaped channels are located – the remains of ancient explosive eruptions. It is precisely such structures that are capable of “throwing” to the surface fragments of crustal rocks that rose from great depths practically unchanged. The goal of the expedition was to collect samples with a minimal degree of processing and obtain data on melt inclusions that arise during partial melting of crustal material.
Modern research shows that part of the earth’s crust can go to depths of over one hundred kilometers. In this case, the main volume of the descended material is irreversibly dissolved in the mantle, and individual fragments return back as part of xenoliths. Such rocks are rare, so each find is important for understanding the processes of high-pressure mineral formation.
During the uplift, the rocks have time to undergo changes, but in some cases the melt is “hardened” so quickly that it retains its primary structural features. In the collected samples, researchers expect to find just such inclusions – they make it possible to assess the composition of the melts from which rocks are formed at great depths, and to clarify the mechanisms of migration of matter within the earth’s crust.
One of the questions raised by the expedition was the assumption of the possible presence of metamorphogenic diamonds. Diamond serves as an indicator of ultra-high pressures, however, preliminary analysis showed that the depths from which the studied samples rose could be insufficient for its natural formation. In addition, the researchers take into account the possibility of artificial introduction of diamond particles into the samples due to the use of diamond tools.
The scientists’ route covered about a thousand kilometers through difficult areas of the Pamirs. The base camp was located at an altitude of more than four thousand meters, from where daily trips were made to the areas where explosion tubes appeared. During the work, we managed to collect about six hundred kilograms of material, which was delivered to Novosibirsk for comprehensive analysis.
Now the samples are being prepared for laboratory study: they are sawed, thin sections are made and analyzed under a microscope. The main goal of the project is to reconstruct the picture of partial melting of crustal matter at mantle depths and to establish what processes determine the formation of rocks and minerals in high-pressure zones.
The data obtained will help refine models of the evolution of the earth’s crust and understand what conditions are necessary for the formation of rare minerals and deep-seated rocks.
The material was prepared with the support of the Russian Ministry of Education and Science as part of the Decade of Science and Technology.
Source: www.sbras.info
