Multistage Magmatism in Ophiolites and Associated Metavolcanites of the Ulan-Sar’dag Mélange (East Sayan, Russia)

Olga N Kiseleva,Dmitriy K Belyanin,Sergey M Zhmodik,Semyon A Kovalev,Igor V Ashchepkov,Evgeniya V Airiyants

doi:10.3390/min10121077

Abstract

We present new whole-rock major and trace element, mineral chemistry, and U-Pb isotope data for the Ulan-Sar’dag mélange, including different lithostratigraphic units: Ophiolitic, mafic rocks and metavolcanites. The Ulan-Sar’dag mélange comprises of a seafloor and island-arc system of remnants of the Paleo-Asian Ocean. Detailed studies on the magmatic rocks led to the discovery of a rock association that possesses differing geochemical signatures within the studied area. The Ulan-Sar’dag mélange includes blocks of mantle peridotite, podiform chromitite, cumulate rocks, deep-water siliceous chert, and metavolcanic rocks of the Ilchir suite. The ophiolitic unit shows overturned pseudostratigraphy. The nappe of mantle tectonites is thrusted over the volcanic-sedimentary sequence of the Ilchir suite. The metavolcanic series consist of basic, intermediate, and alkaline rocks. The mantle peridotite and cumulate rocks formed in a supra-subduction zone environment. The mafic and metavolcanic rocks belong to the following geochemical types: (1) Ensimatic island-arc boninites; (2) island-arc calc-alkaline andesitic basalts, andesites, and dacites; (3) tholeiitic basalts of mid-ocean ridges; and (4) oceanic island basalts. U–Pb dating of zircons from the trachyandesite, belonging to the second geochemical type, yielded a date of 833 ± 4 Ma which is interpreted as the crystallization age during mature island-arc and intra-arc rifting stages. The possible influence of later plume magmatic-hydrothermal activities led to the appearance of moderately alkaline igneous rocks (monzogabbro, trachybasalt, trachyandesite, subalkaline gabbro, and metasomatized peridotites) with a significant subduction geochemical fingerprint.

Highlights

IntroductionThe studied area is located in the southeastern region of Eastern Sayan
The studied area is located in the southeastern region of Eastern Sayan. This region was tectonically juxtaposed during the Neoproterozoic accretionary orogeny of the Central Asian Orogenic Belt (CAOB), which consists of a complex amalgamation of geologic terranes comprised of rocks of Archaean to Mesozoic ages [1,2,3,4,5,6,7]
The earliest stages in the CAOB formation are associated with the development of the Paleo-Asian Ocean, which was opened during the Late Riphean split of the Laurasia supercontinent into the Siberian and Laurentian cratons and a number of microcontinents [2,5,8,9,10,11,12,13]

Summary

Introduction

The studied area is located in the southeastern region of Eastern Sayan. This region was tectonically juxtaposed during the Neoproterozoic accretionary orogeny of the Central Asian Orogenic Belt (CAOB), which consists of a complex amalgamation of geologic terranes comprised of rocks of Archaean to Mesozoic ages [1,2,3,4,5,6,7]. The earliest stages in the CAOB formation are associated with the development of the Paleo-Asian Ocean, which was opened during the Late Riphean split of the Laurasia supercontinent into the Siberian and Laurentian cratons and a number of microcontinents [2,5,8,9,10,11,12,13]. During the early Paleozoic to late Mesozoic periods, the island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateau, and microcontinents were joined to the Siberian craton (Figure 1a) [2,7,14,15,16]

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