Late Ordovician Mafic Magmatic Event, Southeast Siberia: Tectonic Implications, LIP Interpretation, and Potential Link with a Mass Extinction

Abstract

A geochronological, isotopic, and geochemical study of the Suordakh event of mafic magmatic intrusions on the southeast Siberian margin was undertaken. U-Pb baddeleyite dating of a mafic sill intruding lower Cambrian rocks, yielded a 458 ± 13 Ma emplacement age. The chemical composition and stratigraphic setting of this dated sill differed from that previously attributed to the Suordakh event, implying that additional intrusions, previously mapped as Devonian, potentially belonged to the Suordakh event. No correlation between L.O.I. and concentration of highly mobile major and trace elements was documented, showing small or no influence of hydrothermal alteration on the chemical composition of the intrusions. A new tectonic reconstruction located an island arc and active margin relatively close to the study area. However, all samples had chemical compositions close to that of OIB and did not display Ta-Nb and Ti-negative anomalies, nor other features typical for subduction-related magmatism. The major and trace element distribution was most characteristic of within-plate basalts with the mantle source composition being transitional from spinel to garnet lherzolite. Combining four U-Pb baddeleyite dates of mafic sills and dykes from southeast Siberia, the age of the Suordakh event was estimated at 454 ± 10 Ma. The area of the Suordakh event was at least 35,000–40,000 km2 (an estimate including sills previously interpreted as Devonian), and could be increased with additional dating in Southeastern Siberia. Similar ages for within-plate intrusions were reported from South Korea, West Mongolia, South Argentina, North Iran and Northwest Canada, and these ca. 450 Ma ages were collectively close in timing with the latest Ordovician (Hirnantian) mass extinction. More high-precision dating is necessary to fully test a link between the Suordakh event (and the other age-correlative events) and the end-Ordovician mass extinction.

Global Implication of Mesoproterozoic (1.4 Ga) Magmatism Within Sette-Daban Range (Southeast Siberia)

“…Geological setting of the central part and eastern limb of the Gornostakh Anticline (Belaya River area) and location of sampled dolerite dyke in this study (geology after 27,28 modified and simplified). 450 Ma sills (Suordakh event) from 25,26 . Grey field denotes to a typical range of apatite REE compositions from mafic host rocks 32 .…”

“…Two major mafic magmatic events are recognized in the Sette-Daban: 1000-950 Ma Sette-Daban event, and 370-360 Ma Yakutsk-Vilyui LIP which are associated with rift-extensional tectonics in the area 12,19,23,24 . Other mafic intrusions (mainly sills) with the age of 440-450 Ma are widespread on the eastern limb of the Gornostakh Anticline cutting Mesoproterozoic to Cambrian rocks and they are termed the Suordakh magmatic event 25,26 . The analyzed in this study Gornostakh dyke according to the geological maps crosscuts only the sediments of the Uchur Group in the core of the Gornostakh Anticline (Figure 2).…”

Detrital Zircon U-Pb Data for Jurassic–Cretaceous Strata from the South-Eastern Verkhoyansk-Kolyma Orogen—Correlations to Magmatic Arcs of the North-East Asia Active Margin

“…Early to Middle Silurian syenite and granite intrusions are associated with slab-window related asthenospheric upwelling across the Omolon-Taigonos area, with zircon U-Pb crystallization ages of 433-425 Ma [34]. In the South Verkhoyansk region, Ordovician Mafic dikes and sills with baddeleyite U-Pb ages of 445-458 Ma have been reported [35][36][37], while Ordovician arc-related volcanic and volcaniclastic rocks occur in the Omulevka Terrane [38][39][40]. SHRIMP zircon U-Pb dating of small island arc-type granitic plutons within the Rassokha block of the Omulevka Terrane yielded a crystallization age of 440 ± 2 Ma [31] (Figure 1).…”

Geochemical variations in the composition of LIPs of the south-east of the Siberian platform

“…The southeastern margin of the Siberian Craton is commonly known as a passive margin with well-recognized early Neoproterozoic (ca. 1000-950 Ma, Sette-Daban LIP) and Middle-Late Devonian rifting events (380-360 Ма, Yakutsk-Vilyui LIP) associated with mafic magmatism, normal faulting, and deposition of clastic rocks and evaporites [1]. Ordovician sills were later discovered in this area and are now identified as the Suordakh complex (490-480 Ma), although most of the Ordovician and Silurian is reported as a period of tectonic quiescence, with deposition of thick units of carbonates with numerous reef-like build-ups [1].…”