Cr-spinel assemblage from the Upper Triassic gritstones of the northeastern Siberian Platform

Abstract

An assemblage of Cr-spinels widespread in Carnian (Upper Triassic) diamondiferous deposits in the northeastern Siberian Platform is studied. Analysis of their morphology and chemical composition has revealed two dominant varieties of Cr-spinels and has demonstrated certain regularities in their distribution in the study area. Correlations have been established between the areal distribution of the recognized types of Cr-spinels and diamond varieties typical of kimberlite sources and between the distribution of Cr-spinels and rounded diamond dodecahedrons. The phase and chemical compositions of polyphase inclusions in the Cr-spinels are studied. The spatial arrangement of inclusions along the crystal growth zones indicates their primary genesis and trapping from the melt during crystallization. Compositional features of some minerals in the inclusions—SiO2 impurity in apatite and high CaO contents (0.2–0.8 wt.%) in olivines—point to a nonkimberlite source of these Cr-spinels. The presence of K- and Na-containing phases and calcite in the inclusions indicates saturation of the initial melt with alkalies, Ca, and CO2. The data obtained suggest that the numerous Late Vendian diatremes in K-rich alkaline basites of the Olenek Uplift area are the source of the dominant Cr-spinel variety.

The importance of trace element analyses in detrital Cr‐spinel provenance studies: An example from the Upper Triassic of the Barents Shelf

“…Further work on Cr-spinel-based provenance F I G U R E 8 Palaeogeographic reconstruction with outlines of the Siberian Traps LIP, the present-day Ural mountains, the Taimyr Orogen Ophiolite and sample locations from this study. The map is a modified version from Sømme et al (2018), with the Siberian Traps LIP from Ivanov et al (2018), the Urals from Garuti et al (2012), the Taimyr Orogen Ophiolite map from Priyatkina et al (2017) and Osipai Formation sample locations from Nikolenko et al (2018). The Osipai Formation detrital Cr-spinel chemistry is generally consistent with a provenance from a LIP, while detrital Cr-spinel of this study is consistent with a metamorphosed ophiolitic source.…”

“…(2017) and Osipai Formation sample locations from Nikolenko et al. (2018). The Osipai Formation detrital Cr‐spinel chemistry is generally consistent with a provenance from a LIP, while detrital Cr‐spinel of this study is consistent with a metamorphosed ophiolitic source.…”

“…Garuti, Pushkarev, Thalhammer, & Zaccarini, 2012). A comparison of our dataset to the Osipai Formation detrital Cr-spinel in F I G U R E 5 Distribution of the De Geerdalen and Snadd formations Cr-spinel grains in a Al 2 O 3 wt% versus TiO 2 wt% plot compared to the distributions of Kamenetsky et al, (2001), along with detital Cr-spinel from the Carnian Osipai Formation in the Lena Delta area (Nikolenko et al, 2018). Only a minor portion of individual grains from the Barents Shelf plot outside the compostional space expected for Supra-Subduction-Zone Peridotites.…”

“…The added information could help assess recycling histories and group different Cr-spinel grains, akin to cathodoluminescence imaging of zircon. Grouping based on rounding is, for example, essential in the study of Nikolenko et al (2018). Identification of primary and recycled material could help test the regional tectonic model hypothesised by Flowerdew et al (2019) who suggest a Snadd formation provenance from recycled Uralian Orogen foreland sediments.…”

“…The ~235 Ma age peak present in these data is associated with local volcanism (Letnikova et al., 2014). Detrital Cr‐spinel compositions from the same formation suggest that the Siberian Traps LIP is a major source (Nikolenko et al, 2018).…”