Silurian Granitoid Magmatism of the Rassokha Terrane (North-East Russia)
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Silurian Granitoid Magmatism of the Rassokha Terrane (North-East Russia) S. N. Sycheva,b,c, A. K. Khudoleya,b,*, O. Yu. Lebedevaa,b, A. V. Rogovb, Corresponding Member of the RAS S. D. Sokolovc, K. R. Chamberlaind,e, V. S. Maklashinb, and P. A. Lvovb Received June 1, 2020; revised July 2, 2020; accepted August 7, 2020
Abstract—U–Pb dating of zircons from granitoids located within the Rassokha terrane show a Silurian age of their formation. Younger dates from one of the samples are related to radiogenic lead loss during secondary alteration of the rocks. Based on REE distributions as well as well-defined positive anomalies of K and Pb and negative anomalies of Ba, Sr, Nb, Ta, and Ti, the granitoids are comparable to rocks from supra-subduction environments. Combined with intrusive ages from adjacent areas, Silurian granitoid magmatism of the Rassokha terrane supports the existence of a back-arc basin and a long island arc in Ordovician-Silurian time. Keywords: Granitoid, U–Pb dating of zircons, Silurian, Rassokha Terrane DOI: 10.1134/S1028334X20100104
The Rassokha terrane consists of Cambrian-Ordovician and Devonian–Early Jurassic volcanic and sedimentary rocks and is located in the inner part of the Verkhoyansk-Kolyma Fold Belt. On the southeast, it is bounded by the Omulevka passive margin terrane and on the northeast—by the Argatass oceanic terrane [1–3]. The Rassokha terrane rocks are unconformably overlapped by the Uyandina-Yasachnaya Middle–Late Jurassic volcanic belt (Fig. 1). Although an island–arc affinity of the Rassokha terrane has been proposed in papers many times [3–5], the occurrence of synchronous granite intrusions and their possible correlation are still under debate. Our study addresses this gap. The main subjects of this study are two granitoid stocks located in the Tryulinya – Bulkut interfluve. They are Tryulinya (3 × 2.5 km) and Levobulkut (1.5 × 1 km) stocks, which along with a few other granite intrusions of the Omulevka uplift, have been previously interpreted to be Late Jurassic–Late Cretaceous in age [6, 7]. They cut Lower Ordovician, predomaSt. Petersburg State University, St. Petersburg, 199034 Russia bKarpinsky
Russian Geological Research Institute, St. Petersburg, 199106 Russia cGeological Institute of the Russian Academy of Sciences, Moscow, 119017 Russia dDepartment of Geology and Geophysics, University of Wyoming, Laramie, United States of America eNational Research Tomsk State University, 634050 Tomsk, Russia *e-mail: [email protected]
inantly coarse-grained, terrigenous rocks (Ichensk Formation [7]) and are separated by faults from Lower Devonian carbonate rocks. Intrusions have similar compositions and were formed in two phases. The first phase produced small volumes and consists of monzodiorite porphyry, whereas the second phase consists of granosyenite- and granodiorite-porphyry. Contacts between rocks of the first and second phases are of intrusive origin. U–Pb zircon dating was done by SHRIMP-II in the Center of Isotopic Research VSEGEI. Method of dating is the same
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