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 increased 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.
Highlights
The genesis of Early Paleozoic volcanic and intrusive complexes in Gorny Altai is a controversial issue
The Ust’-Sema Formation volcanics are enriched in clinopyroxene phenocrysts and are classified into two groups: ankaramites and diopside porphyry basalts (Di-basalts) [10]. These rocks are spatially associated with ultramafic–mafic intrusions of the Barangol Complex considered to be comagmatic to volcanic rocks of the Ust’-Sema Formation [4,5,6]
The mineral composition, petrography, and chemistry of the volcanic rocks from the Biyka volcanic edifice were studied in detail in previous work [10]
Summary
The genesis of Early Paleozoic volcanic and intrusive complexes in Gorny Altai (in the western part of the Altai–Sayan Fold Belt) is a controversial issue. Previous researchers attributed them to either the magmatism of back-arc basins and island arcs or continental margin rifting, or a mid-ocean ridge subduction and suprasubduction setting combination [1,2,3,4,5,6,7,8,9,10]. These magmatic associations include Middle Cambrian volcanic rocks of the Ust’-Sema Formation and intrusions of the Barangol Complex. The origin of magmatic protoliths of the Barangol Complex intrusions is still poorly understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
