Mineral Chemistry and Trace Element Composition of Clinopyroxenes from the Middle Cambrian Ust’-Sema Formation Ankaramites and Diopside Porphyry Basalts and the Related Barangol Complex Intrusions, Gorny Altai, Russia

Nezar Khlif, Andrey Vishnevskiy, Andrey Izokh, Maria Chervyakovskaya

Research output: Contribution to journalArticlepeer-review

Abstract

The origin and geodynamic settings of the Ust’-Sema Formation and the Barangol Complex are some of the most controversial issues in the Early Paleozoic history of the Altai–Sayan Fold Belt. The Ust’-Sema Formation volcanic rocks are enriched in high-Ca clinopyroxene phenocrysts and were classified as ankaramites and diopside porphyry basalts. In this work, we first present LA- ICP-MS analyses of the clinopyroxenes, along with studies of the petrography, mineral composition, and whole-rock chemistry of the Ust’-Sema Formation and related Barangol Complex rocks. An LA- ICP-MS clinopyroxene study showed a slight depletion of light rare-earth elements (La/Yb)N = 0.1– 1.0 (on average 0.4); and strong depletion of the high-field-strength elements (Zr, Hf, and Nb) and large-ion lithophile (Rb) elements. An Sr anomaly showed a positive correlation with Mg#. Major-and trace-element composition of the clinopyroxene cores show that these clinopyroxene grains were not captured from the mantle rocks as previously assumed and that the Ust’-Sema Formation and the Barangol Complex rocks were formed from magma with island arc characteristics. The in-creased titanium and light rare-earth element contents in the phenocryst rims from Biyka volcano suggest an active interaction of the ankaramitic magma with rocks or melts of OIB type.

Original languageEnglish
Article number113
JournalMinerals
Volume12
Issue number2
DOIs
Publication statusPublished - Feb 2022

Keywords

  • Ankaramites
  • Clinopyroxene phenocrysts
  • Diopside-rich rocks
  • LA-ICP-MS
  • Ural-Alaskan-type intrusions

OECD FOS+WOS

  • 1.05 EARTH AND RELATED ENVIRONMENTAL SCIENCES
  • 1.05.GC GEOCHEMISTRY & GEOPHYSICS
  • 1.05.RE MINERALOGY

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