Researchers at St Petersburg University, as part of an international team, have discovered in the Tien Shan mountains a specific complex of rocks that formed in the Cambrian ocean about 500 million years ago. The age of the rock assemblage was established thanks to adakites - a group of acid volcanic rocks, described from one of the islands in the Aleutian arc. The findings of the research, which will help to learn more about the geological history of the region, are published in the journal Geoscience Frontiers.

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Double rainbow over ancient island arc assemblages discovered in the Tien Shan mountains

The scientists from St Petersburg University began to study the geology of Central Asia in the middle of the 20th century. Multi-year research and rich field experience have made it possible to create the world's leading school of thought in the geology of the Tien Shan at the University. At present, work continues with active collaboration with scientists throughout the world. 

One of the recent discoveries of the international research team is the discovery of this specific rock assemblage that is characteristic of modern oceanic island arcs. The rocks of this complex, found in the Songkultau Mountains in Kyrgyzstan, were formed in the Cambrian ocean about 500 million years ago. This is confirmed by the find of adakites. These are the rocks first described from Adak Island, which is part of the Aleutian island arc in the North Pacific Ocean.

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(a) Tectonic units of the Tien Shan in Kyrgyzstan; (b) schematic geological map of the Songkultau area

‘Studying the conditions of formation of ancient rocks is necessary not only for a better understanding of the geological history of the region. It is important to know this for more practical purposes, especially given that large ore deposits are often associated with adakites, an example of which are the famous copper and gold deposits in Chile,’ said Dmitry Konopelko, Head of the research team, Associate Professor at St Petersburg University.

The unique composition of Songkultau granites captured the scientists’ attention during regional mapping work carried out in 2007. According to Professor Reimar Seltmann, Head of the Centre for Russian and Central Eurasian Mineral Studies (CERCAMS) at the Natural History Museum in London, this prompted additional research, which led to the discovery of previously unknown fragments of the island arc complex. Professor Johan De Grave from Ghent University in Belgium and Professor Stijn Glorie from the University of Adelaide in Australia were involved in field work in the Tien Shan mountains. Analytical measurements and processing of field data were carried out by: Inna Safonova, a research associate at Novosibirsk State University; and Alla Dolgopolova from the Natural History Museum London. They did it under the guidance of Professor Min Sun in the laboratories of the University of Hong Kong.

The discovery of previously unknown fragments of an ancient island arc in the Kyrgyz Tien Shan is only one of the recent discoveries made within the framework of current projects: IGCP 662 Project ‘Orogenic Architecture and Crustal Growth from Accretion to Collision’ and grant from the Ministry of Education and Science of the Russian Federation 4.Y26.31.0018. They are aimed at deciphering the structures of the Central Asian Orogenic Belt, which is one of the largest ancient mountain systems on Earth.

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St Petersburg University scientists are examining pillow basalts formed at the bottom of the ancient ocean