Ophiolitic Complex of the Matachingai River on Eastern Chukotka: Fragment of Lithosphere in Mesozoic Back-Arc Basin


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Abstract

The Matachingai River basin is known among the few ophiolitic complexes on eastern Chukotka as the southern boundary of the Chukotka Fold System (in terms of tectonics, the Chukotka microcontinent or a fragment of the Arctic Alaska–Chukotka microplate). This complex comprises tectonic blocks of residual spinel harzburgite with dunite bodies and pyroxenite, olivine gabbro, and leucogabbro veins; blocks of hornblende gabbro, diorite, and plagiogranite; and Upper Jurassic–Lower Cretaceous basaltic–cherty and cherty–carbonate rocks. The geological relationships of rocks within tectonic blocks, the compositions of primary minerals, the bulk geochemistry of rocks, as well as the strontium, neodymium, and lead isotopic compositions, make it possible to consider individual tectonic blocks of the complex as fragments of a disintegrated oceanic-type lithosphere that formed in a back-arc spreading center. The melts, crystallization products of which are represented by hornblende gabbro of blocks, olivine gabbro of veins, and basalts, separated from geochemically and isotopically heterogeneous mantle. Blocks composed of rocks with various modal composition are likely relicts of an oceanic lithosphere of different segments of a back-arc basin. The studied complex may be a lithosphere of one of the Middle–Late Jurassic back-arc basins. Fragments of these basins are retained in ophiolitic complexes on Great Lyakhovsky Island of the New Siberian Islands Archipelago, western Chukotka, and the Brooks Range in Alaska.

About the authors

G. V. Ledneva

Geological Institute

Author for correspondence.
Email: ledneva@ilran.ru
Russian Federation, Moscow, 119017

B. A. Bazylev

Vernadsky Institute of Geochemistry and Analytical Chemistry

Email: ledneva@ilran.ru
Russian Federation, Moscow, 119991

A. V. Moiseev

Geological Institute

Email: ledneva@ilran.ru
Russian Federation, Moscow, 119017

S. D. Sokolov

Geological Institute

Email: ledneva@ilran.ru
Russian Federation, Moscow, 119017

A. Ishiwatari

Nuclear Regulation Authority

Email: ledneva@ilran.ru
Japan, Minato-ku, Tokyo, 106-8450

D. V. Kuzmin

Sobolev Institute of Geology and Mineralogy, Siberian Branch

Email: ledneva@ilran.ru
Russian Federation, Novosibirsk, 630090

B. V. Belyatsky

Center for Isotope Research

Email: ledneva@ilran.ru
Russian Federation, St. Petersburg, 199106

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