The Overmaraat-Gol Alkaline Pluton in Northern Mongolia: U–Pb Age and Preliminary Implications for Magma Sources and Tectonic Setting

Abstract

A new Wenlockian zircon U–Pb age (~426 Ma) of the Overmaraat-Gol nepheline syenite (foyaite, juvite) pluton in the SW Lake Hovsgol area (Northern Mongolia) prompts a long history of alkaline magmatism in the western Central Asian Orogenic Belt, exceeding the duration of the Devonian and Permian–Triassic events. The LILE and HFSE patterns of pluton samples analyzed by X-ray fluorescence (XRF) and inductively coupled plasma (ICP-MS) methods indicate intrusion in a complex tectonic setting during interaction of a mantle plume with accretionary-collisional complexes that previously formed on the active continental margin. As a result, the parent magma had a heterogeneous source with mixed mantle (PREMA and EM) and crustal components. This source composition is consistent with Nd–Sr isotope ratios of the Overmaraat-Gol alkaline rocks, from −0.1 to −1.2 εNd(t) and from ~0.706 to 0.707 87Sr/86Sr(t).

The Paleozoic-Aged University Foidolite-Gabbro Pluton of the Northeastern Part of the Kuznetsk Alatau Ridge, Siberia: Geochemical Characterization, Geochronology, Petrography and Geophysical Indication of Potential High-Grade Nepheline Ore

“…One of the possible mechanisms of selective crustal contamination during the emplacement of magmas is the thermal mobilization of Sr-rich brines conserved in the Cambrian sedimentary strata of the KA [74,75]. Due to the strong contamination of all igneous rocks by crustal strontium, we assumed that the primary source of the magmatic melt was the plume component of the primitive mantle (PREMA) and these data are consistent with a number of studies [8,9,20,27,74,76]. V.V.…”

“…These approximate ages suggest that the University pluton belongs ca. 500 Ma event, which is widespread in Mongolia (Figure 6 in [20,47]), while the crosscutting N-S dikes belong to the ca. 400 Ma Altay-Sayan Rift/LIP event [43,48].…”

“…This North-Asian superplume ca. 500 Ma affected the northern part of the KA; Gornaya Shoriya; Batenevskii range; Gorny Altai; Eastern and Southeastern Tuva; Eastern Sayan, Southern Pribaikal'e; Yenisei range; Priolkhon'e; Zabaikal'e, Prikhubsugul'e and Western Mongolia during the period from the Early Cambrian to the Middle Ordovician, producing large volumes of granites and various types of mantle magmatism [20,47,78]. The University pluton, with 494-491 Ma subalkaline gabbroids was part of this superplume event during the accretion of the KA terrane.…”

“…Subalkaline and alkaline plutonic rocks of the University pluton had within-plate character suggesting a plume source, but occurred in a region with an active continental margin (Figure 11a-d). These processes can be the interaction of plume material with more ancient accretion-collisional complexes on the active margin of the Paleo-Asian Ocean [8,10,20,22,27,31].…”