Isotope-geochemical (Sm–Nd, Rb–Sr, REE, HFSE) composition of the University foidolite-gabbro pluton, Kuznetsk Alatau ridge, Siberia

Abstract

The University foidolite-gabbro pluton is located among the Cambrian carbonate-volcanogenic deposits. Its composition is dominated by moderately-alkaline and alkaline mafic rocks, broken by dikes of ijolite-urtites, nepheline and alkaline syenites. The chemical composition of igneous rocks is characterized by low silica contents (SiO2 = 41–49 wt. %), wide variations of alkalinity (Na2O + K2O = 3–19 wt. %; Na2O / K2O = 1.2–7.2 wt. %), low titanium content (TiO2 = 0.07 1.59 wt. %) and high alumina content (Al2O3 = 15–28 wt. %), which corresponds to the K-Na derivatives of the basic alkaline formation. By the content of rare earth elements, alkaline rocks (104–246 ppm; La/Yb(n) = 5.79–12.73) are more differentiated derivatives than gabbro (94–111 ppm; La/Yb(n) = 6.87‑6.95). All varieties are characterized by low concentrations of most highly charged elements (Nb, Ta, Zr, Hf + Y), which in terms of accumulation are located between the basalts of oceanic islands and basalts of island arcs. The presence of negative Nb–Ta anomaly and the relative enrichment of Rb, Ba, Sr, and U indicate the probable interaction of plume material with previously formed accretionary complexes of subduction zones. The primary isotope 87Sr/86Sr ratio (~ 0.705 – 0.706) and a wide range of εNd (T) from +3.2 to +8.7 in the rocks also indicate a mantle-crustal nature and a complex geodynamic setting of the Paleozoic alkaline magmatism of the Kuznetsk Alatau. The obtained results of Sm‑Nd dating suggest the formation of moderately-alkaline gabbroids in the Early Paleozoic (494–491 ± 36 Ma), with the intrusion of dikes of alkaline rocks of the Middle Paleozoic age (394 ± 16 and 389 ± 37 Ma).

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

“…Drilling of the University pluton (the maximum borehole depth was 160 m) did not yield the expected nepheline ore deposits, but urtite xenoliths were found in trenches to the west of the bodies of subalkaline gabbroids, and in drill-hole number C-46, an urtite-porphyry dike N-trending was found breaking through the Berikul formation (see note in Figure 4 sample C-46 from drill-hole and Figure 6) [33,56]. We interpreted that the distinct linear anomaly in the western part of the pluton was caused by bodies of urtites, which we discovered for the first time (Boloto intrusion).…”

“…Consequently, it will be possible to compare the magmatic events that took place at the University pluton with the events of other alkaline-basic intrusions KA, which will help to reveal the conditions of the formation of the University pluton. Accordingly, as a result of the data from isotope-geochronological studies (Sm-Nd, Rb-Sr, U-Pb and Ar-Ar), alkaline intrusions can be divided into three age groups, corresponding to the Cambrian and Early Ordovician (510-480 Ma), Early and Middle Devonian (410-390 Ma) and Late Permian (265 Ma) [8][9][10][11][12]18,21,27,28,[31][32][33]45,46,48,72].…”

Evolution of Syenite Magmas: Insights from the Geology, Geochemistry and O-Nd Isotopic Characteristics of the Ordovician Saibar Intrusion, Altai-Sayan Area, Russia

“…Within the Saibar intrusion, there are no mafic rocks with a SiO2 content of 52 wt.% that preceded or accompanied the formation of syenites. This limits the po of reconstructing the composition of magmas that was parental for the syenitic r the same time, the other syenite-bearing intrusions of the Altai-Sayan fold belt mafic rocks formed synchronously with examined syenites, which indicates the spondence to the composition of parent magmas [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Accordingly, the geolo finity of the Saibar intrusion to other similar intrusions suggests a genetic conne tween its rocks and the mafic magmas, which occurred at levels of the magmati inaccessible to observation.…”

“…This part of the CAOB covers the sizable Altay-Sayan fold belt, where alkaline magmatism produced the syenites typical of Kuznetsk Alatau and southeast of Tuva in the Eastern Sayan Mountains and Sangilen Highland, as well as in the Minusinsk Trough subdividing these territories. Alkaline magmatism proceeded several times throughout the Paleozoic epoch in the Early Paleozoic (510-450 Ma), Devonian (410-390 Ma), and Late Carboniferous and Early Permian (305-280 Ma) [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. [47,48].…”

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

“…1000-950 Ma Neoproterozoic mafic intrusions from the same area, ca. 490-480 Ma post-orogenic intrusions from the southwest margin of the Siberian craton and 183 Ma flood basalts of the Karoo LIP (of South Africa), all of which show some influence of inherited subduction material or crustal contamination (Figure 15a) [30,51,74]. On a Zr/Nb-Nb/Th diagram (Figure 15b), the studied intrusions occupy the field of oceanic plateau basalts close to the margin of OIB and out of the field of island arc basalts.…”